阅读说明：本技术 正极活性材料、其制备方法、正极极片及锂离子二次电池 (Positive active material, preparation method thereof, positive pole piece and lithium ion secondary battery ) 是由 钭舒适 胡春华 蒋耀 吴奇 何金华 邓斌 于 2019-09-02 设计创作，主要内容包括：本发明公开一种正极活性材料、其制备方法、正极极片及锂离子二次电池。正极活性材料包括本体颗粒和包覆在本体颗粒外表面的包覆层,本体颗粒包括含镍元素及掺杂元素M~1的锂复合氧化物,包覆层包括M~2元素的氧化物；正极活性材料在11％脱锂态时,M~1元素的平均化合价为α~1,M~2元素的平均化合价为β~1；正极活性材料在78％脱锂态时,M~1元素的平均化合价为α~2,M~2元素的平均化合价为β~2；α~2＞α~1且β~1＝β~2；M~1元素包括Si、Ti、Cr、Mo、V、Se、Nb、Ru、Rh、Pd、Sb、Te、Ce及W中的一种或多种,M~2元素选自Mg、Al、Ca、Zr、Zn、Y及B中的一种或多种。采用本发明的正极活性材料及正极极片,能使锂离子二次电池兼具较高的能量密度及高温循环性能。(The invention discloses a positive active material, a preparation method thereof, a positive pole piece and a lithium ion secondary battery. The positive active material comprises body particles and a coating layer coated on the outer surface of the body particles, wherein the body particles comprise nickel-containing elements and doping elements M 1 The coating layer comprises M 2 An oxide of the element; m in the 11% delithiated state of the positive electrode active material 1 The average valence of the elements being alpha 1 ，M 2 The average valence of the elements being beta 1 (ii) a M in 78% delithiated state of the positive electrode active material 1 The average valence of the elements being alpha 2 ，M 2 The average valence of the elements being beta 2 ；α 2 ＞α 1 And beta is 1 ＝β 2 ；M 1 The element includes one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce and W, M 2 The element is selected from one or more of Mg, Al, Ca, Zr, Zn, Y and B. The positive active material and the positive pole piece can enable the lithium ion secondary battery to have higher energy density and high-temperature cycle performance.)

1. A kind ofThe positive active material is characterized by comprising body particles and a coating layer coated on the outer surface of the body particles, wherein the body particles comprise a nickel-containing element and a doping element M¹The coating layer comprises M²An oxide of the element;

when the positive active material is in 11% delithiated state, M¹The average valence of the elements being alpha¹Said M is²The average valence of the elements being beta¹；

When the positive active material is in 78% delithiated state, M¹The average valence of the elements being alpha²Said M is²The average valence of the elements being beta²；

A is said¹And alpha²Satisfies alpha²＞α¹And said beta¹And beta²Satisfies beta¹＝β²；

The M is¹The elements include one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce and W, and M²The element is selected from one or more of Mg, Al, Ca, Zr, Zn, Y and B.

2. The positive electrode active material according to claim 1, wherein α is¹And alpha²Satisfies alpha²＞α¹≥+3。

3. The positive electrode active material according to claim 1, wherein the M is¹The elements are uniformly doped in the bulk particles;

preferably, the bulk particles are secondary particles formed by aggregating two or more primary particles, and M at any point in the bulk particles¹The variation in the element mass concentration is 32% or less, preferably 20% or less.

4. The positive electrode active material according to claim 1, wherein the M is contained in the positive electrode active material¹Element and said M²The mole ratio of elements is 0.09:1 ℃4:1, preferably 0.1:1 to 3: 1.

5. The positive electrode active material according to any one of claims 1 to 4,

said M in said positive electrode active material¹The actual doping concentration of the element is 2300 mu g/cm³～49000μg/cm³Preferably 3000. mu.g/cm³～30000μg/cm³(ii) a And/or the presence of a gas in the gas,

said M in said positive electrode active material²The content of the element is 500ppm to 5000 ppm.

6. The positive electrode active material according to any one of claims 1 to 5,

the volume average particle diameter D of the positive electrode active material_v50 is 8-20 μm;

and/or the thickness T of the coating layer is 0.001-0.5 μm, and preferably, the thickness T of the coating layer and the average particle diameter D of the positive electrode active material satisfy: 0.003. ltoreq.T/D. ltoreq.0.025, preferably 0.005. ltoreq.T/D. ltoreq.0.02.

7. The positive electrode active material according to any one of claims 1 to 6, wherein the lithium composite oxide is a compound represented by chemical formula 1,

Li_1+a[Ni_xCo_yMn_zM¹ _b]O_2-pX_pchemical formula 1

In the chemical formula 1, X is selected from one or more of F, N, P and S, 0.5 ≦ X <1, 0 ≦ y <0.3, 0 ≦ z <0.3, -0.2< a <0.2, 0< b <0.2, 0 ≦ p <0.2, and X + y + z + b ≦ 1.

8. The positive electrode active material according to any one of claims 1 to 7,

the surface of the positive electrode active material is rough, and the specific surface area of the positive electrode active material is preferably 0.2m²/g～1.5m²A,/g, more preferably 0.3m²/g～1m²(ii)/g; and/or the presence of a gas in the gas,

the positive electrode active material has a true density of 4.6g/cm³～4.9g/cm³(ii) a And/or the presence of a gas in the gas,

the tap density of the positive electrode active material is 2.3g/cm³～2.8g/cm³。

9. A positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 8.

10. A lithium-ion secondary battery characterized by comprising the positive electrode sheet according to claim 9.

11. A method for preparing a positive electrode active material, comprising:

providing a transition metal source comprising nickel, a lithium source and M¹The precursor of the element is mixed, and the mixture is sintered to obtain the M-doped mixture¹Bulk particles of the element;

contacting said bulk particles with M²Mixing precursors of elements, and sintering to form M-containing particles on the outer surface of the bulk particles²A coating layer of an element oxide to obtain a positive electrode active material; wherein the content of the first and second substances,

when the positive active material is in 11% delithiated state, M¹The average valence of the elements being alpha¹Said M is²The average valence of the elements being beta¹；

When the positive active material is in 78% delithiated state, M¹The average valence of the elements being alpha²Said M is²The average valence of the elements being beta²；

A is said¹And alpha²Satisfies alpha²＞α¹And said beta¹And beta²Satisfies beta¹＝β²；

The M is¹The elements include one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce and W, and M²The element is selected from one or more of Mg, Al, Ca, Zr, Zn, Y and B.

12. The production method according to claim 11,

the mixture also comprises a precursor of an X element, and the obtained body particles are also doped with the X element, wherein the X element is selected from one or more of F, N, P and S; alternatively, the first and second electrodes may be,

after the bulk particles are mixed with M²Before the precursor of the element is mixed, the method also comprises the following steps:

and mixing the bulk particles with a precursor of an X element, and sintering to dope the X element into the bulk particles, wherein the X element is selected from F, N, P and one or more of S.

Technical Field

The invention belongs to the technical field of secondary batteries, and particularly relates to a positive active material, a preparation method thereof, a positive pole piece and a lithium ion secondary battery.

Background

A lithium ion secondary battery is a rechargeable battery that mainly operates by movement of lithium ions between a positive electrode and a negative electrode, and is a clean energy source that is currently widely used. The positive electrode active material is used as an important component of the lithium ion secondary battery and provides lithium ions which move in a reciprocating manner between the positive electrode and the negative electrode in the charging and discharging process of the battery, so that the positive electrode active material is very important for the performance of the battery.

As lithium ion secondary batteries are increasingly used in consumer electronics, electric vehicles, and other devices, higher requirements for energy density and high temperature cycle performance of lithium ion secondary batteries are also being made. Based on this, the present application is proposed.

Disclosure of Invention

The embodiment of the invention provides a positive active material, a preparation method thereof, a positive pole piece and a lithium ion secondary battery, and aims to improve the energy density and the high-temperature cycle performance of the lithium ion secondary battery.

In a first aspect, embodiments of the present invention provide a positive electrode active material, where the positive electrode active material includes a bulk particle and a coating layer coated on an outer surface of the bulk particle, the bulk particle includes a nickel-containing element and a doping element M¹The coating layer comprises M²An oxide of the element;

m in the 11% delithiated state of the positive electrode active material¹The average valence of the elements being alpha¹，M²The average valence of the elements being beta¹(ii) a M in 78% delithiated state of the positive electrode active material¹The average valence of the elements being alpha²，M²The average valence of the elements being beta²；α¹And alpha²Satisfies alpha²＞α¹And β¹And beta²Satisfies beta¹＝β²；

M¹The element includes one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce and W, M²The element is selected from one or more of Mg, Al, Ca, Zr, Zn, Y and B.

A second aspect of embodiments of the present invention provides a positive electrode sheet, including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, where the positive electrode active material layer includes the positive electrode active material according to the first aspect of the present invention.

A third aspect of embodiments of the present invention provides a lithium ion secondary battery comprising a positive electrode sheet according to the second aspect of the present invention.

A fourth aspect of an embodiment of the present invention provides a method for preparing a positive electrode active material, including:

providing a transition metal source comprising nickel, a lithium source and M¹The mixture of element precursor is sintered to obtain M doped with the element¹Bulk particles of the element;

mixing the bulk particles with M²Precursor of element is mixed and sintered to form M-containing particles on the outer surface of the bulk particles²A coating layer of an element oxide to obtain a positive electrode active material; wherein the content of the first and second substances,

m in the 11% delithiated state of the positive electrode active material¹The average valence of the elements being alpha¹，M²The average valence of the elements being beta¹(ii) a M in 78% delithiated state of the positive electrode active material¹The average valence of the elements being alpha²，M²Of elementsAverage valence of beta²；α¹And alpha²Satisfies alpha²＞α¹And β¹And beta²Satisfies beta¹＝β²；

M¹The element includes one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce and W, M²The element is selected from one or more of Mg, Al, Ca, Zr, Zn, Y and B.

Compared with the prior art, the embodiment of the invention at least has the following beneficial effects:

the positive active material provided by the embodiment of the invention comprises nickel-containing element and doping element M¹The lithium composite oxide bulk particle of (2) having M on the outer surface of the bulk particle²An oxide coating of the element. And with delithiation of the positive electrode active material, M¹Average valence of element is increased, M²The average valence of the element is constant. The capacity exertion of the positive active material is greatly improved, and the energy density of the lithium ion secondary battery adopting the positive active material is obviously improved. Meanwhile, the structural stability of the positive active material in the high-temperature circulation and high-temperature storage processes is greatly improved, the oxidation activity of the electrolyte on the surface of the positive active material is greatly reduced, and the decomposition gas production rate of the electrolyte in the high-temperature circulation and high-temperature storage processes of the battery can be reduced. Therefore, the high-temperature cycle performance and the high-temperature storage performance of the battery are also significantly improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic view illustrating doping and cladding of a positive active material according to an embodiment of the present invention.

FIG. 2 is a graph showing the results of mass grains of the positive electrode active materials of examples 1 to 28 and comparative examples 1 to 8M¹And (3) a point-taking position schematic diagram of the element mass concentration deviation test.

Detailed Description

In order to make the objects, technical solutions and advantageous technical effects of the present invention more clear, the present invention is further described in detail with reference to the following embodiments. It should be understood that the embodiments described in this specification are only for the purpose of explaining the present invention and are not intended to limit the present invention.

For the sake of brevity, only some numerical ranges are explicitly disclosed herein. However, any lower limit may be combined with any upper limit to form ranges not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and similarly any upper limit may be combined with any other upper limit to form a range not explicitly recited. Also, although not explicitly recited, each point or individual value between endpoints of a range is encompassed within the range. Thus, each point or individual value can form a range not explicitly recited as its own lower or upper limit in combination with any other point or individual value or in combination with other lower or upper limits.

In the description herein, it is to be noted that, unless otherwise specified, "above" and "below" are inclusive, and "a plurality" of "one or more" means two or more, "and" a plurality "of" one or more "means two or more.

The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The following description more particularly exemplifies illustrative embodiments. At various points throughout this application, guidance is provided through a list of embodiments that can be used in various combinations. In each instance, the list is merely a representative group and should not be construed as exhaustive.

Positive electrode active material

Referring to fig. 1, the positive active material includes a bulk particle and a coating layer coated on an outer surface of the bulk particle. The bulk particles comprise nickel-containing elements and doping elementsM¹The coating layer comprises M²An oxide of the element.

M in the 11% delithiated state of the positive electrode active material¹The average valence of the elements being alpha¹(ii) a M in 78% delithiated state of the positive electrode active material¹The average valence of the elements being alpha²；α¹And alpha²Satisfies alpha²＞α¹。

And the positive electrode active material is in 11% delithiated state, M²The average valence of the elements being beta¹(ii) a M in 78% delithiated state of the positive electrode active material²The average valence of the elements being beta²；β¹And beta²Satisfies beta¹＝β²。

M¹The elements comprise one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce and W; m²The element is selected from one or more of Mg, Al, Ca, Zr, Zn, Y and B.

In the positive active material provided by the embodiment of the invention, the bulk particles adopt nickel-based lithium composite oxide, and M is doped in the bulk particles¹And (4) elements. With delithiation of the positive electrode active material, M¹The average valence of the elements being increased, i.e. M¹The element can participate in redox reaction and release electrons during the delithiation of the positive electrode active material. Thus, the positive electrode active material can release more lithium ions, thereby exhibiting higher capacity exertion. The energy density of the lithium ion secondary battery can be obviously improved by adopting the anode active material.

In the positive electrode active material, M¹The element itself is capable of effectively binding oxygen atoms. At the same time, M¹The electrons contributed by the elements can compensate charges in the material, and further inhibit oxygen release of the material. Therefore, the structural stability of the positive active material in the high-temperature circulation and high-temperature storage process is greatly improved. Further, the outer surface of the bulk particle has M²Oxide coating layer of element, and M is removed with lithium of positive electrode active material²The average valence of the element is constant. The coating layer can form strong protection for the body particles continuously and stablyThe corrosion of the electrolyte to the body particles is effectively isolated, and the structural stability of the positive active material is further improved. Therefore, the high-temperature cycle performance and the high-temperature storage performance of the battery can be obviously improved by adopting the positive active material.

M¹Charge compensation of elements in positive active materials also reduces strongly oxidizing Ni in the materials⁴⁺And the surface oxygen defect of the material is reduced, so that the oxidation activity of the electrolyte on the surface of the material is effectively reduced, and the decomposition gas production of the electrolyte in the high-temperature circulation and high-temperature storage processes of the battery is greatly reduced. Meanwhile, the protective effect of the coating layer on the body particles can further reduce the decomposition and gas production of the electrolyte on the surface of the material. Therefore, the high-temperature cycle performance and the high-temperature storage performance of the battery are further improved.

Herein, the "78% delithiated state" refers to a state in which the molar content of lithium extracted from the positive electrode active material during charging of the battery is 78% of the theoretical lithium content. Similarly, "11% delithiated state" refers to a state in which the molar content of lithium extracted from the positive electrode active material during charging of the battery accounts for 11% of the theoretical lithium content. In the actual use process of the lithium ion secondary battery, a full discharge state and a full charge state are generally set, and a discharge cut-off voltage and a charge cut-off voltage are set corresponding to the battery so as to ensure the safe use of the battery. The "discharge cut-off voltage" and the "charge cut-off voltage" may have a certain difference depending on the difference in the positive electrode active material or the difference in the safety requirement. For a secondary battery prepared by the nickel-containing lithium composite oxide positive electrode active material, the delithiation state of the positive electrode active material is about 11% delithiation state generally when the secondary battery is in a fully discharge state, the delithiation state of the positive electrode active material is about 78% delithiation state generally when the secondary battery is in a fully charge state, and the secondary battery works between 11% delithiation state and 78% delithiation state corresponding to the positive electrode active material when the secondary battery is charged and discharged for use so as to ensure normal use.

In this context, the correspondence between "delithiated state" and "voltage" is combined to obtain a positive electrode active material in "11% delithiated state" and "78% delithiated state" for the study. Specifically, a series of standard button half cells are prepared by using the positive active material, and the cells are charged to 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V, …, 4.0V, 4.1V, 4.2V, 4.3V, 4.4V, and 4.5V (i.e., the charging voltage interval is 0.1V) at a rate of 0.1C, then a positive electrode piece of the cell is removed, the electrolyte is removed by washing, the positive active material is digested, the mass concentration of Li element of the positive active material is tested by using an inductively coupled plasma-Emission spectrometer (ICP-OES), so as to calculate the "delithiated state", and obtain the corresponding relationship between the charging voltage and the "delithiated state", and further obtain the charging voltage corresponding to the "11% delithiated state" and the "78% delithiated state".

Then, the half-cell containing the positive electrode active material was charged to a voltage U corresponding to the "11% delithiation state₁And then the anode active material in 11% delithiation state can be obtained by disassembling. Likewise, a half-cell containing the positive active material was charged to a voltage U corresponding to the "78% delithiated state"₂And then the anode active material in 78% delithiation state can be obtained by disassembling.

M in "11% delithiated" positive electrode active material and "78% delithiated" positive electrode active material¹Element and M²The valence of the element can be obtained by X-ray photoelectron spectroscopy (XPS) test. More precisely, it can be obtained by Synchrotron radiation photoelectron spectroscopy (SRPES) test.

In some preferred embodiments, M in the "11% delithiated" positive electrode active material¹Average valence a of the elements¹And M in "78% delithiated" positive electrode active material¹Average valence a of the elements²Satisfy alpha²＞α¹Not less than + 3. During charging and discharging of the positive electrode active material, M¹The average valence of the elements is kept above + 3. M in a higher valence state¹The element has stronger constraint capacity on oxygen atoms in the material, can improve the structural stability of the anode active material, and prevents the anode active material from generating lattice cracking in the high-temperature cycle process and the high-temperature storage process. Thus, it is possible to provideThe battery can have better high-temperature cycle performance and high-temperature storage performance.

M in a higher valence state¹The element can contribute more electrons in the positive active material, so that the oxidation activity of the electrolyte on the surface of the material is further reduced, and the high-temperature cycle performance and the high-temperature storage performance of the battery are further improved.

M in a higher valence state¹The element contributes more electrons in the positive active material, and can support the positive active material to release more lithium ions, so that the energy density of the battery is further improved.

Preferably, alpha¹Is one or more of +3, +4, +5 and + 6.

In some preferred embodiments, M¹The elements are uniformly doped in the bulk particles. M¹The uniform doping of the elements can keep the properties of all the parts in the body particles consistent, the structural stability of all the positions of the body particles is improved, and the problem of oxygen release of all the positions of the body particles is solved, so that the structural stability of the positive active material in the high-temperature storage and high-temperature circulation processes is improved, and the performance of the battery is improved better.

M¹The elements are uniformly doped in the body particles, the migration diffusion capacity of lithium ions in different areas in the body particles is in the same level, and the structural stability and the anti-deformation capacity of the body particles are close to each other, so that the stress distribution in the positive active material particles is uniform, the positive active material particles are not easy to break, the side reaction and the performance deterioration caused by the fresh surface exposed by the breakage are prevented, and the energy density, the high-temperature cycle performance and the high-temperature storage performance of the battery are further improved.

Preferably, the bulk particles are secondary particles formed by aggregating two or more primary particles, and M at any point in the bulk particles¹The variation in the element mass concentration is 32% or less, further 30% or less, preferably 20% or less, and more preferably 15% or less. The smaller the deviation of mass concentration at each site in the bulk particle, the smaller M in the bulk particle¹The more uniform the distribution of the elements, the better the overall performance of the cell.

In bookHere, M is present at any point in the bulk particle¹The mass concentration of the element being in the one point minimum volume, M¹The mass concentration of the elements in all the elements can be obtained by EDX (Energy Dispersive X-Ray Spectroscopy) or EDS (EDS) elemental analysis in combination with TEM (Transmission Electron Microscope) or SEM (Scanning Electron Microscope) single-point Scanning to measure the element concentration distribution or the like. Wherein the M in μ g/g at different sites in the bulk particles when measured by EDX or EDS elemental analysis in combination with TEM or SEM single point scan¹The mass concentrations of the elements are respectively denoted as eta₁、η₂、η₃、…、η_nAnd n is a positive integer of 15 or more.

In bulk particles M¹The average mass concentration of the elements being M within the individual bulk particles¹The mass concentration of the elements in all elements can be obtained by EDX or EDS element analysis combined with TEM or SEM surface scanning to test the element concentration distribution or other similar modes. Wherein the test surface includes all points in the single point test described above when tested in a manner that EDX or EDS elemental analysis combined with TEM or SEM surface scanning test element concentration distribution. In bulk particles M¹The mean mass concentration of the elements is recorded asThe unit is μ g/g.

M at any point in the bulk particle¹The mass concentration deviation σ of the element is calculated according to the following formula (1):

in some embodiments, M in the positive electrode active material¹Element and M²The molar ratio of the elements may be 0.09:1 to 4:1, preferably 0.1:1 to 3:1, further 0.2: 1 to 2.5: 1, and further O.5: 1 to 2: 1.

M in the positive electrode active material¹Element and M²Mole of elementsProper molar ratio can better exert M¹Modification by doping of elements and containing M²Synergistic effect of element oxide coating modification. Under the synergistic effect, the irreversible structural phase change of the positive active material can be effectively inhibited, the surface of the positive active material is effectively protected from being corroded by electrolyte, and the gas production of the battery is reduced, so that the high-temperature cycle performance and the high-temperature storage performance of the battery are further improved.

M in the positive electrode active material¹Element and M²The above molar ratio of the elements is also beneficial to improving the ion conducting performance of the positive active material, so that the energy density of the battery can be improved.

In some embodiments, M in the positive electrode active material¹The true doping concentration omega of the element may be 2000 mug/cm³～55000μg/cm³Preferably 2300. mu.g/cm³～49000μg/cm³More preferably 3000. mu.g/cm³～30000μg/cm³。

M in the positive electrode active material¹The true doping concentration omega of the element is 2000 mu g/cm³Above, preferably 2300. mu.g/cm³Above, more preferably 3000. mu.g/cm³By the method, the gram volume and the structural stability of the positive active material can be effectively improved, and the oxidation activity of the electrolyte on the surface of the material is reduced. M in the positive electrode active material¹The true doping concentration omega of the element is 55000 mu g/cm³Below, it is preferably 49000. mu. tg/cm³Hereinafter, more preferably 30000. mu.g/cm³The positive electrode active material can have a good layered crystal structure and can be prevented from M¹The elements enter the lithium layer to ensure that the positive active material provides a good carrier for the de-intercalation of lithium ions, so that the positive active material is beneficial to the intercalation and de-intercalation of the lithium ions, the irreversible consumption of the active lithium ions is effectively inhibited, and the positive active material has higher initial capacity and cycle capacity retention rate.

Thus, M in the positive electrode active material¹The real doping concentration omega of the element is in the range, so that the energy density, the high-temperature cycle performance and the high-temperature storage performance of the battery can be well improved.

Herein, M in the positive electrode active material¹The true doping concentration ω of the element is calculated by the formula (2):

in the formula (2), ω is M in the positive electrode active material¹True doping concentration of the element in units of μ g/cm³。

ρ_TrueIs the true density of the positive electrode active material and has the unit of g/cm³Which is equal to the ratio of the mass of the positive electrode active material to the true volume of the positive electrode active material, wherein the true volume is the actual volume of the solid substance, excluding the pores inside and among the positive electrode active material particles. Rho_TrueThe measurement can be carried out by an apparatus and a method known in the art, such as a gas volume method, and can be carried out by a powder true density tester.

M in units of μ g/g in the positive electrode active material¹Mass concentration of element, i.e., M contained in per gram of positive electrode active material¹The mass of the element. Wherein the content of the first and second substances,represents M in a macroscopic positive electrode active material¹Bulk content of elements, including M incorporated into bulk particles of positive electrode active material¹Element, M enriched in other phases on the surface of bulk particles of positive electrode active material¹Element, and M located between particles of positive electrode active material¹And (4) elements.Can be obtained by measurement of absorption spectrum of positive electrode active material solution, such as ICP (inductively Coupled Plasma Emission Spectrometer), XAFS (X-ray absorption fine structure spectrum), and the like.

In some embodiments, M in the positive electrode active material²The content of the element can be 300ppm to 6500 ppm. M in the positive electrode active material²The content of the elements can be more than or equal to 300ppm, more than or equal to 500ppm, more than or equal to 1000ppm, more than or equal to 1500ppm, more than or equal to 2000ppm, more than or equal to 2500 ppm; and can be less than or equal to 3000ppm, less than or equal to 3500ppm, less than or equal to 4000ppm, less than or equal to 4500ppm, less than or equal to 5000ppm and less than or equal to 6500 ppm. Preferably, M in the positive electrode active material²The content of the element is 500ppm to 5000 ppm. ppm (parts per million) is M in the positive electrode active material²The mass of the element accounts for a million parts of the mass of the positive electrode active material.

M in the positive electrode active material²The content of the elements is in the range, so that the coating layer and the body particles have higher bonding fastness, and the coating layer is prevented from falling off in the high-temperature circulation and high-temperature storage process of the battery, so that the protection effect of the coating layer on the body particles is effectively exerted, and the battery has higher high-temperature circulation performance and high-temperature storage performance. Meanwhile, the positive active material also keeps higher lithium ion diffusion and migration capacity, so that the battery has higher energy density.

M in the positive electrode active material²The content of the element can be obtained by measurement of an absorption spectrum of the positive electrode active material solution, such as ICP (inductively Coupled Plasma Emission Spectrometer), XAFS (X-ray absorption fine structure spectrum), and the like.

In some embodiments, the thickness T of the coating layer is preferably from 0.001 μm to 0.5 μm, such as from 0.01 μm to 0.4 μm, and further such as from 0.1 μm to 0.3 μm. The thickness T of the coating layer is in the range, the coating layer is not easy to fall off from the body particles in the process of repeatedly removing and inserting lithium of the positive active material, the protective effect on the body particles can be continuously exerted, and meanwhile, the positive active material is ensured to have higher lithium ion diffusion and migration capacity and gram capacity.

In some preferred embodiments, the thickness T of the coating layer and the average particle diameter of the positive electrode active materialSatisfies the following conditions:preference is given toSuch as Therefore, the protective effect of the coating layer on the body particles can be more effectively exerted, and the positive active material is ensured to have higher lithium ion diffusion migration capacity and gram capacity.

The thickness of the coating layer can be measured by methods known in the art. As an example, a cross-section of the positive electrode active material particles may be prepared using a cross-section polisher (such as an argon ion cross-section polisher type IB-09010CP of Japan Electronics (JEOL) corporation), the cross-section passing through the core of the positive electrode active material particles; then, an EDX or EDS elemental analysis is combined with a TEM or SEM (such as an EDS type X-Max of the Oxford instruments group in England is combined with a SEM type Sigma-02-33 of the ZEISS in Germany) to perform a surface scanning test to obtain an element distribution diagram in the cross section; the thickness of the coating layer is obtained according to the element distribution of the cross section. More precisely, the thickness of the cladding layer at a plurality (more than 3, such as 5, 8, 10, 12, etc.) of different positions on the cross section can be measured, and the average value is taken as the thickness of the cladding layer.

Average particle diameter of positive electrode active materialIs an average value of diameters of a plurality of different orientations of the positive electrode active material particles. For example, an element distribution diagram in a cross section of the positive electrode active material particles can be obtained from the above-described EDX or EDS elemental analysis in combination with TEM or SEM surface scanning test, and a plurality of (3 or more, such as 5, 8, 10, 12, etc.) diameters of different orientations can be obtained from the element distribution of the cross section, and the average is taken as the average particle diameter of the positive electrode active material

In some embodiments, the volume average particle diameter D of the positive electrode active material_v50 is preferably 8 to 20 μm, more preferably 9 to 18 μm, and still more preferably 9 to 16 μm. The volume average particle size of the positive active material is within the range, so that the transmission and diffusion performance of lithium ions and electrons in positive active material particles can be improved, the side reaction of electrolyte on the particle surfaces can be reduced, the agglomeration among particles can be inhibited, and the cycle performance and the rate performance of the battery can be improved. In addition, the average particle diameter of the positive electrode active material is within the range, so that the positive electrode active material has higher compaction density, and the energy density of the battery is improved.

The surface of the positive active material is preferably a rough surface, which is beneficial to improving the active specific surface area of the positive active material and improving the capacity exertion of the positive active material.

The specific surface area of the positive electrode active material may be 0.2m²/g～1.7m²A/g, preferably of 0.2m²/g～1.5m²A,/g, more preferably 0.3m²/g～1m²(ii) in terms of/g. The specific surface area of the anode active material is in the range, so that the anode active material is ensured to have higher active specific surface area, and the side reaction of the electrolyte on the surface of the anode active material is reduced, so that the capacity exertion and the cycle life of the anode active material are improved.

The tap density of the positive electrode active material is preferably 2.3g/cm³～2.8g/cm³And the battery has higher energy density.

The positive electrode active material may have a true density of 4.6g/cm³～5.2g/cm³Preferably 4.6g/cm³～4.9g/cm³The positive active material has higher specific capacity and energy density, thereby improving the capacity performance and energy density of the battery.

In some embodiments, the molar content of nickel in the lithium composite oxide is 50% to 95% of the total molar content of transition metal site elements, such as 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, and the like. The positive active material has higher specific capacity and can further improve the energy density of the battery.

The lithium composite oxide has a layered structure having lithium sites, transition metal sites, and oxygen sites. M¹The element is doped in the transition metal site. The transition metal site element refers to an element located at a transition metal site.

In some embodiments, the lithium composite oxide is a compound represented by chemical formula 1,

Li_1+a[Ni_xCo_yMn_zM¹ _b]O_2-pX_pchemical formula 1

In chemical formula 1, M¹Is doped and substituted on one or more of nickel site, cobalt site and manganese site of the bulk particles; x is oxygen substitution to the bulk particle, and X can be selected from one or more of F, N, P and S; and x is more than or equal to 0.5 and less than 1, y is more than or equal to 0 and less than 0.3, z is more than or equal to 0 and less than 0.3, a is more than 0.2 and less than 0.2, b is more than 0 and less than 0.2, p is more than or equal to 0 and less than 0.2, and x + y + z + b is 1. The battery adopting the high-nickel ternary material can better have higher energy density, high-temperature cycle performance and high-temperature storage performance.

Further, x is 0.6-0.9, such as 0.7-0.8.

In some embodiments, when the bulk particles are doped with the X element, the X element can be uniformly doped in the bulk particles, such as a doping element (containing M) at any point in the bulk particles¹Element and X element) may be 32% or less, for example 30% or less, further for example 20% or less. The uniformly doped positive active material has better structural stability as a whole.

The X element may also be a mass concentration gradient decreasing from the outer surface of the bulk particle to the core of the particle. For example, the X element is doped in the outer surface layer of the bulk particle. This can reduce the surface oxygen activity of the material, while enabling the material to have both higher kinetic performance and gram capacity.

Volume average particle diameter D of positive electrode active material_v50 is a term well known in the art, also referred to as median particle diameter, and represents a particle diameter corresponding to 50% of the volume distribution of particles of the positive electrode active material. Volume average particle diameter D of positive electrode active material_v50 can use the bookThe measurement may be carried out by apparatus and methods well known in the art, and may conveniently be carried out using, for example, a laser particle size analyser, such as the Mastersizer 3000 laser particle size analyser from malvern instruments ltd, uk.

The specific surface area of the positive electrode active material is a known meaning in the art and can be measured by an apparatus and a method known in the art, for example, by a nitrogen adsorption specific surface area analysis test by a NOVA2000e model specific surface area and pore size analyzer of corna, usa and can be calculated by a bet (brunauer Emmett teller) method. As a specific example, the test method is as follows: and taking 8.000-15.000G of the anode active material by using a weighed empty sample tube, uniformly stirring and weighing the anode active material, placing the sample tube into an NOVA2000e degassing station for degassing, weighing the total mass of the degassed anode active material and the sample tube, and subtracting the mass of the empty sample tube from the total mass to calculate the mass G of the degassed anode active material. Putting the sample tube into NOVA2000e, measuring the adsorption quantity of nitrogen on the surface of the positive active material under different relative pressures, obtaining the adsorption quantity of a monomolecular layer based on the Bronuore-Eltt-Taylor multilayer adsorption theory and the formula thereof, further calculating the total surface area A of the positive active material, and calculating the specific surface area of the positive active material through A/G.

The tap density of the positive electrode active material can be conveniently determined using instruments and methods known in the art, for example, using a tap density meter, such as a FZS4-4B tap density meter.

A method for preparing a positive electrode active material is schematically illustrated next. Any one of the above positive electrode active materials can be prepared according to the preparation method. The preparation method comprises a preparation step S10 of bulk particles and a preparation step S20 of a coating layer.

S10, providing a transition metal source containing nickel, a lithium source and M¹The mixture of element precursor is sintered to obtain M doped with the element¹Bulk particles of the element.

The transition metal source containing nickel is, for example, one or more of an oxide, a hydroxide and a carbonate containing Ni, for example, a hydroxide containing Ni, Co and Mn.

The hydroxide containing Ni, Co and Mn may be obtained by a method known in the art, for example, by a coprecipitation method, a gel method or a solid phase method.

As an example, a Ni source, a Co source, and a Mn source are dispersed in a solvent to obtain a mixed solution; simultaneously pumping the mixed solution, the strong base solution and the complexing agent solution into a reaction kettle with stirring by adopting a continuous parallel flow reaction mode, controlling the pH value of the reaction solution to be 10-13, controlling the temperature in the reaction kettle to be 25-90 ℃, and introducing inert gas for protection in the reaction process; after the reaction is finished, the hydroxide containing Ni, Co and Mn is obtained after aging, filtering, washing and vacuum drying.

The Ni source can be soluble nickel salt, such as one or more of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate and nickel acetate, further such as one or more of nickel sulfate and nickel nitrate, further such as nickel sulfate; the Co source can be soluble cobalt salt, such as one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate and cobalt acetate, further such as one or more of cobalt sulfate and cobalt nitrate, further such as cobalt sulfate; the Mn source may be a soluble manganese salt, such as one or more of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate and manganese acetate, further such as one or more of manganese sulfate and manganese nitrate, further such as manganese sulfate.

The strong base may be one or more of LiOH, NaOH, and KOH, for example NaOH. The complexing agent can be one or more of ammonia water, ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium citrate and disodium Ethylene Diamine Tetraacetate (EDTA), such as ammonia water.

The solvent of the mixed solution, the strong alkali solution and the complexing agent solution is not particularly limited, for example, the solvent of the mixed solution, the strong alkali solution and the complexing agent solution is one or more of deionized water, methanol, ethanol, acetone, isopropanol and n-hexanol, such as deionized water.

The inert gas introduced during the reaction is, for example, one or more of nitrogen, argon and helium.

The lithium source may be lithium oxide (Li)₂O), lithium phosphate (Li)₃PO₄) Lithium dihydrogen phosphate (LiH)₂PO₄) Lithium acetate (CH)₃COOLi), lithium hydroxide (LiOH), lithium carbonate (Li)₂CO₃) And lithium nitrate (LiNO)₃) One or more of (a). Further, the lithium source is one or more of lithium carbonate, lithium hydroxide and lithium nitrate; further, the lithium source is lithium carbonate.

M¹The precursor of the element may be M¹One or more of oxides, nitrates, carbonates, bicarbonates, sulfates, chlorides, hydroxides and acetates of the elements can be selected according to actual requirements. For example, M¹The precursor of the element is M¹Oxides of elements, e.g. silicon oxide (e.g. SiO)₂SiO, etc.), titanium oxide (e.g., TiO)₂TiO, etc.), chromium oxide (e.g., CrO)₃、Cr₂O₃Etc.), molybdenum oxide (e.g., MoO)₂、MoO₃Etc.), vanadium oxide (e.g. V)₂O₅、V₂O₄、V₂O₃Etc.), selenium oxide (e.g., SeO)₂Etc.), niobium oxide (e.g., Nb)₂O₅、NbO₂Etc.), ruthenium oxide (e.g., RuO)₂Etc.), palladium oxide (e.g., PdO, etc.), rhodium oxide (e.g., Rh)₂O₃Etc.), antimony oxide (e.g., Sb)₂O₅、Sb₂O₃Etc.), tellurium oxide (e.g., TeO)₂Etc.), cerium oxide (e.g., CeO)₂Etc.) and tungsten oxide (e.g., WO)₂、WO₃Etc.).

In step S10, a ball mill mixer or a high speed mixer may be used for material mixing. For example, a transition metal source containing nickel, a lithium source and M¹Adding element precursors into a high-speed mixer for mixing, wherein the mixing time can be 0.5-3 h.

In step S10, the mixed material may be added to an atmosphere sintering furnace for sintering. The sintering atmosphere is an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere. O of sintering atmosphere₂In a concentration of, for example70% to 100%, more preferably 80% or more, and still more preferably 85% or more. The sintering temperature is, for example, 500 ℃ to 1000 ℃, further for example 600 ℃ to 1000 ℃, further for example 700 ℃ to 900 ℃, such as 750 ℃ to 850 ℃. This is advantageous for M¹The elements being homogeneously doped in the bulk particles, in particular, such that M¹The element has higher doping uniformity in the bulk particles. The sintering time can be adjusted according to actual conditions, and is for example 5h to 25h, and further for example 5h to 15 h.

It should be noted that there are many theoretically feasible ways to regulate and control M in the lithium nickel composite oxide during the preparation of the positive electrode active material¹Distribution of elements and valence states in different delithiated states, e.g. M¹Valence state of element precursor itself, different M¹The dosage proportion of the element valence state precursor, the oxidizability of the sintering atmosphere during doping, the sintering times, the mixing uniformity, the sintering temperature, the sintering time and the like. In this document, a series of positive electrode active materials are obtained by controlling the doping precursor species, sintering time and temperature in the S10 step. The positive active material has the characteristics of high energy density, thermal stability and high-temperature cycle stability. Preferably, M is further controlled¹Element doping homogeneous phase M in different lithium removing states¹The positive active material with the element valence state characteristic has better effect.

In some embodiments, after the sintering process of step S10, the sintered product may be further subjected to a crushing process and a sieving process to obtain a cathode active material having an optimized particle size distribution and specific surface area. The crushing mode is not particularly limited, and may be selected according to actual requirements, for example, a particle crusher is used.

S20, mixing the bulk particles with M²Precursor of element is mixed and sintered to form M-containing particles on the outer surface of the bulk particles²And coating the element oxide to obtain the positive active material.

M²The precursor of the element may be M²Chlorides, sulfates, nitrates, oxides, hydroxides, fluorides of the elements,One or more of carbonate, bicarbonate, acetate, phosphate, dihydrogen phosphate and organic compound, but not limited thereto.

In step S20, a ball mill mixer or a high speed mixer may be used for material mixing. For example, the bulk particles are mixed with M²Adding element precursors into a high-speed mixer for mixing for 0.5-3 h.

In step S20, the mixed material may be added to an atmosphere sintering furnace for sintering. The sintering atmosphere is an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere. O of sintering atmosphere₂The concentration is, for example, 70% to 100%, more preferably 80% or more, and still more preferably 85% or more. The sintering temperature is, for example, 100 ℃ to 550 ℃, and further, for example, 200 ℃ to 500 ℃; the sintering time may be 3 to 25 hours, such as 5 to 10 hours. Due to the lower sintering temperature, M²The oxide of the element is not easy to diffuse into the bulk particles, but forms a coating layer coated on the outer surface of the bulk particles. M²The surface crystal lattices of the elements and the body particles are matched, so that the combination between the coating layer and the body particles is tight, the structure of the body particles cannot be damaged by the coating layer, and the coating layer can reliably protect the body particles.

In some optional embodiments, in step S10, the mixture further includes a precursor of an X element, and the obtained bulk particles are further doped with the X element, where the X element is selected from one or more of F, N, P and S.

The precursor of the element X may be selected from one or more of ammonium fluoride, lithium fluoride, hydrogen fluoride, elemental phosphorus, phosphorus oxide, ammonium dihydrogen phosphate, ammonium metaphosphate, ammonium dihydrogen phosphite, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium hydrogen carbonate, ammonium sulfate, ammonium hydrogen sulfite, ammonium hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur, for example, but is not limited thereto.

In other optional embodiments, before step S20, step S30 may be further included: and mixing the body particles with a precursor of the X element, and sintering to dope the X element into the body particles.

At step S30, a precursor of the X element as described previously may be employed.

In step S30, a ball mill mixer or a high speed mixer may be used for material mixing. For example, the bulk particles and the precursor of the element X are added to a high-speed mixer and mixed, and the mixing time can be 0.5h to 3 h.

In step S30, the mixed material may be added to an atmosphere sintering furnace for sintering. The sintering atmosphere is an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere. O of sintering atmosphere₂The concentration is, for example, 70% to 100%, and further 80% to 95%. The sintering temperature is, for example, 400 ℃ to 1000 ℃, such as 400 ℃ to 850 ℃, and further such as 400 ℃ to 750 ℃. The sintering time may be 3 to 25 hours, such as 5 to 10 hours.

By regulating and controlling the sintering temperature and the sintering time, the X element can be uniformly doped in the body particles, or the mass concentration gradient from the outer surface of the X element body particles to the core direction of the particles is reduced.

Positive pole piece

The embodiment of the invention also provides a positive pole piece, which comprises any one or more positive active materials.

Due to the adoption of the positive electrode active material provided by the embodiment of the invention, the positive electrode piece provided by the embodiment of the invention also has the beneficial effects. The positive pole piece can ensure that the lithium ion secondary battery has good high-temperature cycle performance, high-temperature storage performance and higher energy density at the same time.

As an example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector includes two opposite surfaces in a thickness direction thereof, and the positive electrode active material layer is stacked on either or both of the two surfaces of the positive electrode current collector.

The positive electrode active material layer includes any one or more of the positive electrode active materials described above in the embodiments of the present invention.

The positive electrode active material layer may further include a conductive agent and a binder. The types of the conductive agent and the binder in the positive electrode active material layer are not particularly limited, and can be selected according to actual requirements.

As an example, the conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may be one or more of Styrene Butadiene Rubber (SBR), water-based acrylic resin (water-based acrylic resin), sodium carboxymethylcellulose (CMC), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylic resin, and polyvinyl alcohol (PVA).

The positive electrode current collector may be a metal foil or a porous metal plate, such as an aluminum foil, having good electrical conductivity and mechanical properties.

The positive pole piece can be prepared according to the conventional method in the field. For example, the positive electrode active material, the conductive agent and the binder are dispersed in a solvent, wherein the solvent can be N-methyl pyrrolidone (NMP), so as to form uniform positive electrode slurry, the positive electrode slurry is coated on a positive electrode current collector, and the positive electrode pole piece is obtained after the procedures of drying, rolling and the like.

Lithium ion secondary battery

The embodiment of the invention also provides a lithium ion secondary battery, which comprises a positive pole piece, a negative pole piece, an isolating membrane and electrolyte, wherein the positive pole piece is the positive pole piece.

By adopting the positive active material and the positive pole piece of the embodiment of the invention, the lithium ion secondary battery can simultaneously give consideration to good normal temperature and high temperature cycle performance, higher high temperature storage performance and higher energy density.

The negative electrode plate can be a metal lithium plate.

The negative electrode plate can also comprise a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector. For example, the negative electrode current collector includes two opposite surfaces in a thickness direction thereof, and the negative electrode active material layer is stacked on either or both of the two surfaces of the negative electrode current collector.

The anode active material layer includes an anode active material. The kind of the negative electrode active material in the embodiment of the present invention is not particularly limited, and may be selected according to actual needs. As an example, the negative active material may be natural graphite, artificial graphite, mesophase micro carbon spheres (MCMB), hard carbon, soft carbon, silicon-carbon composite, SiO_m(0 < m < 2, e.g. m ═ 1), Li-Sn alloys, Li-Sn-O alloys, Sn, SnO₂Lithium titanate Li of spinel structure₄Ti₅O₁₂One or more of Li-A1 alloy and metallic lithium.

The anode active material layer may further include a conductive agent and a binder. The embodiment of the present invention does not specifically limit the types of the conductive agent and the binder in the negative electrode active material layer, and may be selected according to actual needs. As an example, the conductive agent is one or more of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder is one or more of Styrene Butadiene Rubber (SBR), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin (water-based acrylic resin) and sodium carboxymethylcellulose (CMC).

The negative electrode active material layer may further optionally include a thickener such as sodium carboxymethyl cellulose (CMC).

The negative electrode current collector may be a metal foil or a porous metal plate, such as a copper foil, having good electrical conductivity and mechanical properties.

The negative pole piece can be prepared according to the conventional method in the field. For example, the negative electrode active material, the conductive agent, the binder and the thickener are dispersed in a solvent, wherein the solvent can be N-methyl pyrrolidone (NMP) or deionized water, so as to form uniform negative electrode slurry, the negative electrode slurry is coated on a negative electrode current collector, and the negative electrode pole piece is obtained after the working procedures of drying, rolling and the like.

In the lithium ion secondary battery according to the embodiment of the present invention, the electrolyte may be a solid electrolyte, such as a polymer electrolyte, an inorganic solid electrolyte, or the like, but is not limited thereto. The electrolyte may be an electrolytic solution. The electrolyte solution includes a solvent and a lithium salt dissolved in the solvent.

The solvent may be a non-aqueous organic solvent, for example, one or more, preferably two or more, of Ethylene Carbonate (EC), Propylene Carbonate (PC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Formate (MF), Methyl Acetate (MA), Ethyl Acetate (EA), Propyl Acetate (PA), Methyl Propionate (MP), Ethyl Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB), and Ethyl Butyrate (EB).

The lithium salt may be LiPF₆(lithium hexafluorophosphate), LiBF₄Lithium tetrafluoroborate (LiClO), LiClO₄(lithium perchlorate) LiAsF₆(lithium hexafluoroarsenate), LiFSI (lithium bis (fluorosulfonylimide)), LiTFSI (lithium bis (trifluoromethanesulfonylimide)), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalato borate), LiBOB (lithium bis (oxalato borate)), LiPO₂F₂One or more of (lithium difluorophosphate), LiDFOP (lithium difluorooxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate), for example LiPF₆(lithium hexafluorophosphate), LiBF₄(lithium tetrafluoroborate), LiBOB (lithium bis (oxalato) borate), LiDFOB (lithium difluoro (oxalato) borate), LiTFSI (lithium bis (trifluoromethanesulfonyl) imide), and LiFSI (lithium bis (fluorosulfonyl) imide).

The electrolyte may optionally contain other additives such as Vinylene Carbonate (VC), ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), Succinonitrile (SN), Adiponitrile (ADN), Glutaronitrile (GLN), Hexanetricarbonitrile (HTN), 1, 3-propanesultone (1, 3-PS), vinyl sulfate (DTD), Methylene Methanedisulfonate (MMDS), 1-propene-1, 3-sultone (PST), 4-methyl-ethylene sulfate (PCS), 4-ethyl-ethylene sulfate (PES), 4-propyl-ethylene sulfate (PEGLST), propylene sulfate (TS), 1, 4-butane sultone (1, 4-BS), ethylene sulfite (DTO), dimethyl sulfite (DMS), One or more of Diethylsulfite (DES), cyclic quaternary ammonium sulfonate, tris (trimethylsilane) phosphate (TMSP), and tris (trimethylsilane) borate (TMSB), but is not limited thereto.

The lithium ion secondary battery according to the embodiment of the present invention is not particularly limited to the separator, and any known separator having a porous structure with electrochemical stability and mechanical stability, such as a single-layer or multi-layer film of one or more of glass fiber, non-woven fabric, Polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF), may be used.

The positive pole pieces and the negative pole pieces are alternately stacked, and the isolating film is arranged between the positive pole pieces and the negative pole pieces to play an isolating role, so that the battery cell is obtained, or the battery cell can be obtained after winding. And placing the battery cell in a shell, injecting electrolyte, and sealing to obtain the lithium ion secondary battery.

Examples

The present disclosure is more particularly described in the following examples that are intended as illustrations only, since various modifications and changes within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the equipment used in the examples is commercially available.

Example 1

Preparation of positive electrode active material

(1) Precursor of Ni-Co-Mn ternary material [ Ni ]_0.8Co_0.1Mn_0.1](OH)₂Lithium hydroxide LiOH and antimony trioxide Sb₂O₃Adding the mixture into a high-speed mixer to mix for 1h to obtain a mixture, wherein the molar ratio Li/Me of the nickel-cobalt-manganese ternary material precursor to lithium hydroxide is 1.05, and Me represents the total molar amount of Ni, Co and Mn in the nickel-cobalt-manganese ternary material precursor; sb₂O₃Is added in such an amount that the true doping concentration of Sb in the positive electrode active material is 25050. mu.g/cm³. Placing the mixture into an atmosphere sintering furnace for sintering, wherein the sintering temperature is 825 ℃, and the sintering atmosphere is O₂The preparation method comprises the steps of carrying out oxygen-containing atmosphere with the concentration of 90%, sintering for 15h, crushing and sieving to obtain body particles, wherein Sb is uniformly doped in the bulk phase structure of the body particles.

(2) Mixing the bulk particles with alumina Al₂O₃Adding into a high-speed mixer for mixing for 1h, wherein Al₂O₃Is added so that the content of Al in the clad layer is 3002ppm, which is the content in the positive electrode active material. Putting the mixed materials into an atmosphere sintering furnace for sintering, wherein the sintering temperature is 310 ℃, and the sintering atmosphere is O₂Oxygen-containing atmosphere with concentration of 90%, sintering time of 8h, and forming Al on the outer surface of the bulk particles₂O₃Coating layer to obtain positive electrode active material with average particle diameter D_v50 is 14 μm and the thickness T of the coating layer is 0.243. mu.m.

Preparation of the electrolyte

Mixing EC, DEC and DMC according to the volume ratio of 1:1 to obtain a solvent, and then adding lithium salt LiPF₆Dissolving in the above solvent to obtain an electrolyte solution, wherein LiPF₆The concentration of (2) is 1 mol/L.

Preparation of button cell

Dispersing the prepared positive electrode active material, conductive carbon black and binder PVDF into solvent N-methyl pyrrolidone (NMP) according to the weight ratio of 90: 5, and uniformly mixing to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on a positive current collector aluminum foil, and drying and cold pressing to obtain the positive electrode piece.

And in the button cell, sequentially stacking the positive pole piece, the isolating membrane and the metal lithium piece, injecting the electrolyte, and assembling to obtain the button cell.

Preparation of full cell

Dispersing the prepared positive electrode active material, conductive agent acetylene black and binder PVDF into solvent NMP according to the weight ratio of 94: 3, and uniformly mixing to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on a positive current collector aluminum foil, and drying and cold pressing to obtain the positive electrode piece.

Dispersing a negative active material artificial graphite, hard carbon, a conductive agent acetylene black, a binder Styrene Butadiene Rubber (SBR) and a thickening agent sodium carboxymethyl cellulose (CMC) into deionized water according to a weight ratio of 90: 5: 2: 1, and uniformly mixing to obtain negative slurry; and uniformly coating the negative electrode slurry on a negative current collector aluminum foil, and drying and cold pressing to obtain a negative electrode plate.

Polyethylene (PE) porous polymeric films were used as separators. And stacking the positive pole piece, the isolating membrane and the negative pole piece in sequence to obtain a bare cell, placing the bare cell in an external package, injecting the electrolyte, packaging, and performing procedures such as formation to obtain the full cell.

Examples 2 to 28 and comparative examples 1 to 8

In contrast to example 1, positive electrode active materials having predetermined parametric characteristics were obtained by changing relevant parameters in the steps of preparing the positive electrode active materials, as detailed in tables 1-1 to 1-2.

Wherein the precursors of the positive electrode active materials of examples 2 to 25 and comparative examples 1 to 5 are all [ Ni ]_0.8Co_0.1Mn_0.1](OH)₂(ii) a The precursors of the positive electrode active materials of examples 26 to 28 and comparative examples 6 to 8 were all [ Ni ]_0.5Co_0.2Mn_0.3(OH)₂。

M in example 2¹The precursor of the element is TiO; examples 3, 20, 21, 24 and 25 in which M¹The precursor of the element is NbO₂(ii) a M in example 4¹The precursor of the element is MoO₂(ii) a M in example 5¹The precursor of the element is RuO₂(ii) a M in example 6¹The precursor of the element is V₂O₃(ii) a M in examples 7, 22, 23 and 27¹The precursor of the element is WO₂(ii) a M in example 8¹The precursor of the element is Sb₂O₃And WO₂And the content of each precursor is basically the same; comparative example 4M¹The precursor of the element is Y₂O₃(ii) a Comparative example 5M¹The precursor of the element is MgO;

the rest of M's relating to differences from example 1²Precursors of elements selected from B₂O₃、ZrO₂、ZnO、Y₂O₃；

In the step (1) of example 20, the sintering temperature is 615 ℃, and the sintering time is 5 h; the sintering temperature in the step (2) is 305 ℃, and the sintering time is 8 h;

in the step (1) of example 21, the sintering temperature is 550 ℃ and the sintering time is 2 h; the sintering temperature in the step (2) is 290 ℃, and the sintering time is 9 h;

in the step (1) of example 22, the sintering temperature is 810 ℃, and the sintering time is 15 h; the sintering temperature in the step (2) is 110 ℃, and the sintering time is 3 h;

in the step (1) of example 23, the sintering temperature is 830 ℃, and the sintering time is 15 h; the sintering temperature in the step (2) is 550 ℃, and the sintering time is 20 hours;

in the step (1) of example 24, the sintering temperature is 770 ℃, and the sintering time is 16 h; in the step (2), the sintering temperature is 310 ℃, and the sintering time is 7 hours;

in the step (1) of example 25, the sintering temperature is 750 ℃, and the sintering time is 17 h; the sintering temperature in the step (2) is 260 ℃, and the sintering time is 9 h;

the sintering temperature in step (1) of examples 26 and 27 and comparative example 7 was 790 ℃, and the sintering time was 12 h; the sintering temperature in the step (2) is 280 ℃, and the sintering time is 7 hours;

in the step (1) of example 28, the sintering temperature was 500 ℃ and the sintering time was 2 hours; the sintering temperature in the step (2) is 240 ℃, and the sintering time is 6 h;

comparative examples 1 and 6 were not doped and coated and were both sintered once; the sintering temperature of comparative example 1 was 825 deg.C and the sintering time was 15 h; the sintering temperature of the comparative example 6 is 790 ℃, and the sintering time is 12 h;

comparative examples 2 and 7 were undoped M¹An element;

comparative examples 3 and 8 uncoated M²Elements, and all are sintered at one time; the sintering temperature of the comparative example 3 is 825 ℃ and the sintering time is 15 h; comparative example 8 firingThe junction temperature is 790 ℃, and the sintering time is 12 h.

The remaining parameters are shown in tables 1-1 and 1-2. In tables 1-1 and 1-2:

σ denotes M at any point in the bulk particle¹Deviation of mass concentration of elements;

M¹concentration of element M¹True doping concentration of the element in the positive active material;

M²the content of the element is M²The content of the element in the positive electrode active material;

the molar ratio represents M in the positive electrode active material¹Element and M²The molar ratio of the elements;

represents the thickness T of the coating layer and the average particle diameter of the positive electrode active materialThe ratio of.

Test section

1) M of positive active material in different delithiation states¹Element, M²Measurement of average valence of element at 25 ℃, 18 button cells are respectively charged to the upper limit of charge-discharge cut-off voltage at a constant current of 1C, then are charged at a constant voltage until the current is less than or equal to 0.05mA, and then are placed for 2 minutes, and then are discharged to the lower limit of charge-discharge cut-off voltage at a constant current of 1C.

Then, the 18 button cells after the charge and discharge were charged to 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V, …, 4.0V, 4.1V, 4.2V, 4.3V, 4.4V, and 4.5V, respectively, at a rate of 0.1C (i.e., the charging voltage interval was 0.1V). Taking each charged button cell, disassembling a positive pole piece in a drying room to be used as a sample, weighing and recording the mass of the sample, putting the sample into a digestion tank, slowly adding 10mL of aqua regia to be used as a digestion reagent, then putting the sample into a Mars5 microwave digestion instrument of the American CEM company, and digesting the sample at 2450Hz microwave emission frequency; transferring the digested sample solution into a volumetric flask, shaking up, sampling and putting into the American platinum ElmerA sample introduction system of 7000DV type inductively coupled plasma-emission spectrometer (ICP-OES) of (PE) company tests the mass concentration of Li, O, Ni, Co, Mn and doping elements on a positive active material at the argon pressure of 0.6MPa and the radio frequency power of 1300W, and converts the mass concentration of each element to obtain a chemical formula under each voltage so as to obtain a lithium removal state under each voltage. The chemical formula of the positive electrode active material converted under the voltage of 2.8V is Li_0.89Ni_0.8Co_0.1Mn_0.1O₂Then, the corresponding delithiated state is (1-0.89) × 100% ═ 11%, that is, the cell voltage corresponding to 11% delithiated state is 2.8V. Similarly, the chemical formula of the positive electrode active material obtained by conversion using the ICP-OES test is Li_0.22Ni_0.8Co_0.1Mn_0.1O₂The corresponding voltage is the voltage corresponding to the 78% delithiated state.

And obtaining voltages corresponding to the 11% lithium removal state and the 78% lithium removal state, taking a pole piece containing the anode active material to be detected, and manufacturing the button cell according to the method. The button cell is charged to voltages corresponding to 11% delithiation state and 78% delithiation state at a rate of 0.1C under 25 ℃, and then the following operations are respectively carried out:

firstly, a button type battery core is disassembled by scissors in a drying room, the whole positive pole piece is taken out and put into a beaker, a proper amount of high-purity anhydrous dimethyl carbonate (DMC) is poured, the DMC is replaced once every 8 hours, the continuous cleaning is carried out for 3 times, then the battery is put into a vacuum standing box of the drying room, the vacuumizing state is kept at-0.096 MPa, and the battery is dried for 12 hours; and scraping and grinding the dried positive pole piece in a drying room by using a blade, and weighing about 50mg of positive active material powder.

Wiping the surface of an aluminum foil of about 2cm multiplied by 2cm by acetone, cutting a double-sided adhesive tape of about 1cm multiplied by 1cm to be attached to the center of the aluminum foil, spreading a powder sample on the double-sided adhesive tape, and uniformly spreading the powder on the whole adhesive tape by using a clean stainless steel sampling spoon. And (3) taking another piece of aluminum foil which is wiped cleanly by acetone to cover the sample, integrally placing the aluminum foil between two flat stainless steel modules, and then tabletting by using a tabletting machine, wherein the pressure is about 10MPa, and keeping for 15 seconds.

③ use American Saimer Feishale (T)hermo) science and technology company escalab 250Xi type X-ray photoelectron spectrometer, a pressed sample is put into a sample cavity, a monochromatic Al K alpha (hv) 1486.6eV excitation source is arranged, the X-ray power is 150W, the focus spot is 500 mu M, and M is collected¹Element, M²The 2p or 3d spectra of the elements were processed by XPSpeak software for peak separation and M was determined¹Element, M²The valence state distribution of the elements, and calculating M respectively¹Element, M²Average valence of the element.

2) M at any point in the bulk particle¹Mass concentration deviation test of elements

Weighing 2g of positive active material powder sample, uniformly sprinkling the sample on a sample table adhered with conductive adhesive, slightly pressing to fix the powder, or cutting out a pole piece of 1cm multiplied by 1cm from a battery positive pole piece, and adhering the pole piece to the sample table to serve as a sample to be detected. Placing the sample stage in a vacuum sample chamber, fixing, and preparing the cross section of the positive electrode active material particles by using IB-09010CP type cross section polisher of JEOL (JEOL) to obtain the cross section of the bulk particles, as shown in FIG. 2; referring to the cross-section of the particle shown in FIG. 2, points were taken at 17 positions, each point having an area of 20nm by 20nm, and the 17 points M were tested using an X-Max type energy spectrometer (EDS) from Oxford instruments, England in combination with a Scanning Electron Microscope (SEM) from Sigma-02-33, ZEISS, Germany¹The mass concentration of the elements is measured by the following method: the detection elements are Li, O, Ni, Co, Mn and doping elements, SEM parameters are set as 20kV accelerating voltage, 60 mu M light bar, 8.5mm working distance and 2.335A current, when EDS test is carried out, the test is stopped when the spectrogram area reaches more than 250000cts (controlled by acquisition time and acquisition rate), and data is acquired to obtain M at each site¹The mass concentrations of the elements are respectively recorded as eta₁、η₂、η₃、…、η₁₇。

In bulk particles M¹Average mass concentration of elementsThe determination method comprises the following steps: by adopting the EDS-SEM test method, as shown by the dotted line box in FIG. 2, the test area covers the point scanning area of the bulk particlesA little bit, and not beyond the cross section of the bulk particle.

Then calculating any point M in the bulk particles according to the formula (1) above¹The mass concentration deviation σ of the element.

3) M in the positive electrode active material¹Element, M²Content of elements

Testing of M in positive active material by PE 7000DV type ICP-OES¹Element, M²The content of elements is tested by the following method: punching a pole piece containing the positive active material into a wafer with the total mass of more than 0.5g or taking at least 5g of a positive active material powder sample, weighing and recording the mass of the sample, putting the sample into a digestion tank, slowly adding 10mL of aqua regia as a digestion reagent, then putting the sample into a Mars5 microwave digestion instrument of the American CEM company, and digesting the sample at the microwave emission frequency of 2450 Hz; transferring the digested sample solution into a volumetric flask, shaking uniformly, sampling, putting into an ICP-OES sample injection system, and carrying out M in the positive active material at the argon pressure of 0.6MPa and the radio frequency power of 1300W¹Element, M²And (5) testing the element content.

Wherein the true density p of the positive electrode active material is measured by using a TD2400 type powder true density tester of Beijing Piaode electronic technology Limited_TrueThe test method is as follows: placing a certain mass of positive active material in a sample cup at 25 ℃, and recording the mass m of the positive active material; putting a sample cup filled with the positive active material into a test cavity of a true density instrument, sealing a test system, introducing inert gas with small molecular diameter such as helium or nitrogen, detecting the pressure of the gas in a sample chamber and an expansion chamber, measuring the true volume V of the tested material according to the Bohr's law PV-nRT, and calculating the true density rho of the secondary particles by m/V_True. Wherein n is the molar amount of gas in the sample cup; taking 8.314 as an ideal gas constant; t is ambient temperature and 298.15K. Then, M in the positive electrode active material is calculated according to the formula (2) described above¹The true doping concentration ω of the element.

4) Initial gram capacity test for button cell

And charging the battery to the upper limit of a charge-discharge cut-off voltage at a constant current of 0.1 ℃ at 25 ℃, then charging the battery to a constant voltage until the current is less than or equal to 0.05mA, standing for 2 minutes, and then discharging the battery to the lower limit of the charge-discharge cut-off voltage at a constant current of 0.1 ℃, wherein the discharge capacity at this time is the initial gram capacity of the button battery.

5) Initial gram capacity test of full cell

Charging the battery to the upper limit of a charge-discharge cut-off voltage at a constant current of 1/3 ℃ at 25 ℃, then charging the battery to a constant voltage until the current is less than or equal to 0.05mA, standing the battery for 5 minutes, and then discharging the battery to the lower limit of the charge-discharge cut-off voltage at a constant current of 1/3 ℃, wherein the discharge capacity at this time is the initial gram capacity of the whole battery.

6) High temperature cycle performance testing of full cells

Charging the battery at a constant current of 1C to the upper limit of the cut-off voltage of charge and discharge at 45 ℃, then charging the battery at a constant voltage until the current is less than or equal to 0.05mA, standing the battery for 5 minutes, and then discharging the battery at a constant current of 1C to the lower limit of the cut-off voltage of charge and discharge, which is a charge and discharge cycle, wherein the discharge capacity of the cycle is recorded as the discharge specific capacity D of the 1 st cycle₁. The battery is subjected to 400 times of cyclic charge and discharge tests according to the method, and the specific discharge capacity D of the 400 th cycle is recorded₄₀₀。

Capacity retention (%) of the full cell at 45 ℃ and 400 cycles of 1C/1C₄₀₀/D₁×100％

7) High temperature storage performance testing of full cells

Charging the battery at 25 deg.C with constant current of 1C rate to the upper limit of cut-off voltage, charging at constant voltage until the current is less than or equal to 0.05mA, and measuring the volume of the battery and recording as V₀(ii) a The cells were then placed in an 80 ℃ incubator and the volume of the cells after 10 days of storage was measured and recorded as V₁. In this test, the volume of the cell was tested using a drainage method.

Volume expansion rate Δ V (%) (V) after 10 days of storage at 80 ℃ of the full-cell₁-V₀)/V₀×100％

In tests 1), 4) to 7),

in examples 1 to 25 and comparative examples 1 to 5, the charge-discharge cut-off voltage of the button cell battery is 2.8V to 4.25V, and the charge-discharge cut-off voltage of the full cell battery is 2.8V to 4.2V;

in examples 26 to 28 and comparative examples 6 to 8, the charge-discharge cut-off voltage of the button cell battery was 2.8V to 4.35V, and the charge-discharge cut-off voltage of the full cell battery was 2.8V to 4.3V.

The test results of examples 1 to 28 and comparative examples 1 to 8 are shown in Table 2.

TABLE 2

As can be seen from comparison of examples 1 to 25 with comparative examples 1 to 5, and examples 26 to 28 with comparative examples 6 to 8, M was doped into the bulk particles of the nickel-containing lithium composite oxide¹Element, the outer surface of the body particle is also coated with M²A coating layer of an elemental oxide; and with delithiation of the positive electrode active material, M¹Average valence of element is increased, M²The average valence of the element is constant; and M¹Element and M²The elements are selected from specific element types, so that the lithium ion secondary battery has high initial gram capacity and high-temperature cycle performance and high-temperature storage performance.

As can be seen from the results of examples 1, 9 to 19, M in the positive electrode active material was added¹Element, M²The content of the elements and the molar ratio of the elements are in a proper range, so that the gram capacity, the high-temperature cycle performance and the high-temperature storage performance of the battery can be more effectively improved.

It can be seen from the results of examples 3, 20 and 21 and examples 26 and 28 that any point M in the bulk particles¹When the mass concentration variation of the element is 20% or less, M¹Better uniform doping property of elements and positive active material particlesThe properties of the particles in the particle are consistent, and the migration and diffusion capacities of lithium ions in different regions in the particle are at the same level; at the same time, M¹The anode active material with uniformly doped elements has better stability of the whole structure, uniform distribution of internal stress and difficult cracking. Therefore, the performance of the battery is improved remarkably. When the mass concentration deviation of any point of doping elements in the body particles is more than 20%, lithium ion diffusion channels and potential barriers at all positions in the positive active material particles are inconsistent, structural stability and deformation resistance of all regions are different, so that stress distribution in the material is uneven, the regions with large internal stress are easy to break, the positive active material is exposed out of a fresh surface, impedance is increased, and capacity performance, high-temperature cycle performance and high-temperature storage performance are further deteriorated.

From the results of examples 7, 22 and 23, it can be seen that the thickness of the coating layer and the average particle diameter of the positive electrode active materialThe proper ratio is beneficial to ensuring that the battery has higher gram capacity, high-temperature cycle performance and high-temperature storage performance at the same time.

As can be seen from the results of examples 3 and 24, the specific surface area of the positive active material is appropriate, which is advantageous for the battery to simultaneously achieve higher gram capacity, high-temperature cycle performance, and high-temperature storage performance.

It can be seen from the results of examples 3 and 25 that the true density of the positive active material is appropriate, which is advantageous for the battery to simultaneously achieve higher gram capacity, high-temperature cycle performance, and high-temperature storage performance.

While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications and substitutions can be easily made by those skilled in the art within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.