阅读说明：本技术 锂离子二次电池用正极活性物质 (Positive electrode active material for lithium ion secondary battery ) 是由 李于利 吕吉先 于 2018-06-27 设计创作，主要内容包括：本发明提供一种锂离子二次电池用正极活性物质,其由LiCo<Sub>(1－α－β)</Sub>A<Sub>(α)</Sub>B<Sub>(β)</Sub>O<Sub>2</Sub>表示,其高充电电压下循环特性和热稳定性均良好、且可抑制二次电池的膨胀。本发明还提供使用上述锂离子二次电池用正极活性物质的正极和二次电池。(The invention provides a positive electrode active material for lithium ion secondary battery, which is made of LiCo (1－α－β) A (α) B (β) O 2 It was shown that the cycle characteristics and thermal stability were good at high charging voltage, and the swelling of the secondary battery was suppressed. The present invention also provides a positive electrode and a secondary battery using the positive electrode active material for a lithium ion secondary battery.)

1. A positive electrode active material for lithium ion secondary battery is prepared from LiCo_{(1－α－β)}A_(α)B_(β)O₂The substance represented is characterized in that,

the element A is one or more elements selected from Mg, Sc, Ti, Fe, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ru, Rh, Pd, In, Sn, Hf, Ta, W, Re, Cr, Y, Sb, Lu, Au, Pb, Er, the element B is one or more elements selected from Na, Al, Si, Ge, Mn, Ca, Te, Hg, Bi, La, Ce, Pr, Nd, Sm, V,

the difference between the ionic radius of the element A and the ionic radius of the lithium is less than 20 percent, the difference between the ionic radius of the element B and the ionic radius of the lithium is more than 25 percent,

the total doping amount alpha + beta of the element A and the element B is more than or equal to 0.1 mol% and less than or equal to alpha + beta and less than or equal to 8 mol%, the doping amount alpha of the element A is more than or equal to 0.05 mol% and less than or equal to alpha and less than or equal to 5 mol%, the doping amount beta of the element B is more than or equal to 0.05 mol% and less than or equal to beta and less than or equal to 5 mol%,

the average valence of the element A is 1.5-3.5, the average valence of the element B is 2.0-4.0,

the element a is uniformly distributed in the particles of the positive electrode active material,

the concentration of element B on the surface of the particles is higher than the concentration of element B inside the particles.

2. A positive electrode for a lithium ion secondary battery, characterized in that the positive electrode active material for a lithium ion secondary battery according to claim 1 is used as the positive electrode active material.

3. The positive electrode for a lithium ion secondary battery according to claim 2, characterized in that its bulk density is more than 3.8 g/cc.

4. A lithium ion secondary battery, characterized in that the positive electrode active material for a lithium ion secondary battery according to claim 1 is used as the positive electrode active material.

5. The lithium ion secondary battery according to claim 4, wherein the amount of the nitrile compound added to the electrolyte is 0.2% to 10%.

6. The lithium ion secondary battery according to claim 5, wherein a full battery charging voltage thereof is greater than or equal to 4.40V.

7. The lithium ion secondary battery according to claim 6, wherein the charging voltage is relative to Li/Li⁺The redox electron pair is greater than or equal to 4.45V.

Technical Field

The present invention relates to a positive electrode active material for a lithium ion secondary battery, and a positive electrode sheet and a lithium ion secondary battery using the positive electrode active material. More particularly, the present invention relates to a positive electrode active material for a lithium ion secondary battery, which has excellent cycle characteristics and thermal stability at a high charging voltage and can suppress the swelling of the secondary battery, and a positive electrode sheet and a lithium ion secondary battery using the same.

Background

Currently, lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones, notebook computers, digital cameras, and electric vehicles due to their advantages of high energy density, high operating voltage, many cycle times, no memory effect, and relative environmental friendliness. Compared with the negative electrode material, the current positive electrode material has small specific capacity, and the development of a new positive electrode material becomes urgent. In a common lithium ion batteryElectrode material (e.g. lithium cobaltate LiCo0₂Lithium nickel oxide LiNi0₂Lithium manganate LiMn₂0₄And lithium iron phosphate LiFeP0₄) In the prior art, only lithium cobaltate realizes real large-scale industrial production by a simple and feasible synthesis method, high specific capacity and good cycle performance.

The parameter characterizing the amount of energy stored in a lithium ion secondary battery is the energy density, which is approximately equal in value to the product of the voltage and the battery capacity. In order to effectively increase the power storage capacity of a lithium battery, people generally use a method for increasing the battery capacity to achieve the purpose. However, in order to further miniaturize a device using a battery, it is difficult to increase the stored electricity amount of the battery by capacity increase, and therefore, increasing the charging voltage is another effective means for further increasing the energy density of the lithium ion secondary battery. The charge cut-off voltage of the existing lithium ion secondary battery is mostly between 3.0 and 4.3V, and the discharge specific capacity of the existing lithium ion secondary battery is about 140m Ah/g; the specific discharge capacity of a lithium ion secondary battery using lithium cobaltate as a positive electrode material can be significantly improved by about 20% at a charging voltage of about 4.5V.

However, in the current situation, simply increasing the charging voltage of the battery causes lithium cobaltate to be over-delithiated, which results in that the lithium-poor hexagonal phase structure is unstable and easily destroyed, and lithium ions are changed from order to disorder, and then the unit cell is changed from hexagonal phase to monoclinic phase. The generation of monoclinic phase causes a drastic decay of the battery capacity. LiCoO on the other hand₂Co in the structure³⁺Is oxidized into strongly oxidizing Co⁴⁺The reaction of the Co ions with the electrolyte is accelerated, i.e. the dissolution of Co results. As a result of the above-described phenomenon, the cycle performance of the battery is greatly reduced, and thermal stability is not good, thereby causing swelling of the battery and causing a problem in safety.

Therefore, a positive electrode active material for a lithium ion secondary battery, which has good cycle characteristics and thermal stability at a high charge voltage and can suppress the swelling of the secondary battery, is urgently required.

The bulk doping of the positive electrode active material particles can be generally improved to improve the performance of the positive electrode active material.

The Chinese patent document CN102751481A proposes the introduction of structurally stable Li₂MnO₃With LiCoO₂Forming a composite material to inhibit the phase change of lithium cobaltate in the charge and discharge process; but not to the matrix LiCoO₂The material is modified, so that the cycle performance of the material under high voltage is poor; in addition, the preparation method adopted by the patent document is a solid-phase mixed raw material and is subjected to three-stage high-temperature sintering, so that the uniform distribution of trace elements in the composite material cannot be ensured, and the synthesis steps are complex and the energy consumption is high.

Chinese patent document CN107799733A discloses a lithium cobaltate-based positive electrode active material that does not decrease even at high voltage and can ensure surface stability by including Co, which is generated at a low ratio and has higher reactivity with an electrolyte solution, in a surface (i.e., shell) thereof at high voltage⁴⁺Lithium cobaltate poor in ion prevents the surface stability of the positive electrode active material and the cycle characteristics of the secondary battery from being degraded at high voltage, but this patent document has a problem that the energy density is degraded because the lithium ion concentration on the surface is reduced.

Non-patent literature "Ni-Mn co-doped high voltage lithium cobalt oxide lithium ion battery positive electrode material" (huo rong et al, journal of inorganic chemistry, 2015, 1 month, vol.31no.1, page 159-165) reports a lithium cobalt oxide positive electrode material doped with two elements of Ni and Mn, which can be charged at high voltage, has improved cycle performance compared with pure lithium cobalt oxide. However, this document does not relate to the thermal stability of the secondary battery, nor does it show the expansion of the battery that can be avoided.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a positive electrode active material for a lithium ion secondary battery, which has good cycle characteristics and thermal stability at a high charge voltage and can suppress the swelling of the secondary battery.

Another object of the present invention is to provide a positive electrode sheet and a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery.

One aspect of the present invention relates to a lithium ionA positive electrode active material for a secondary battery, which is composed of LiCo_{(1－α－β)}A_(α)B_(β)O₂The substances represented, wherein,

the element A is one or more elements selected from Mg, Sc, Ti, Fe, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ru, Rh, Pd, In, Sn, Hf, Ta, W, Re, Cr, Y, Sb, Lu, Au, Pb, Er, the element B is one or more elements selected from Na, Al, Si, Ge, Mn, Ca, Te, Hg, Bi, La, Ce, Pr, Nd, Sm, V,

the difference between the ionic radius of the element A and the ionic radius of the lithium is less than 20 percent, the difference between the ionic radius of the element B and the ionic radius of the lithium is more than 25 percent,

the total doping amount (alpha + beta) of the element A and the element B is more than or equal to 0.1 mol% and less than or equal to alpha + beta and less than or equal to 8 mol%, the doping amount alpha of the element A is more than or equal to 0.05 mol% and less than or equal to alpha and less than or equal to 5 mol%, the doping amount beta of the element B is more than or equal to 0.05 mol% and less than or equal to beta and less than or equal to 5 mol%,

the average valence of the element A is 1.5-3.5, the average valence of the element B is 2.0-4.0,

the element a is uniformly distributed in the particles of the positive electrode active material,

the concentration of element B on the surface of the particles is higher than the concentration of element B inside the particles.

Another aspect of the present invention relates to a positive electrode using the above positive electrode active material for a lithium ion secondary battery.

Still another aspect of the present invention relates to a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery, wherein the positive electrode active material for a lithium ion secondary battery is used as the positive electrode active material.

Still another aspect of the present invention relates to a method for manufacturing a positive electrode active material for a lithium ion secondary battery, including the steps of:

reacting a cobalt source and an element B source with a precipitant solution to obtain a precursor of the positive active substance, wherein the distribution of the concentration of the element B is adjusted by changing the adding speed of the element B source;

and mixing the precursor with lithium carbonate and an element A source, calcining, and sieving to obtain the positive active material lithium cobaltate.

The present invention provides a positive electrode active material for a lithium ion secondary battery, which has excellent cycle characteristics and thermal stability at a high charge voltage and can suppress the swelling of the secondary battery, and a positive electrode sheet and a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery.

Detailed Description

Positive electrode active material

The positive electrode active material of the present invention is LiCo_{(1－α－β)}A_(α)B_(β)O₂By selecting the kind, ionic radius, valence state, and doping method of the element A, B doped in the substance, a positive electrode active material for a lithium ion secondary battery, which has excellent cycle characteristics and thermal stability at a high charge voltage and can suppress the expansion of the secondary battery, can be obtained.

The charging and discharging process of a lithium ion secondary battery is essentially a process of lithium electron deintercalation and intercalation. Currently, layered LiCoO is often used as a positive electrode active material for lithium ion secondary batteries mainly composed of lithium cobaltate₂The structure is relatively stable. The theoretical capacity is 274mAh/g, but the actual capacity is only 145mAh/g at present, so that the method has larger development potential. In the ideal layered LiCoO₂In, Li⁺And Co³⁺Located in alternating octahedral sites in a cubic close-packed oxygen layer. But in practice, due to Li⁺And Co³⁺Unlike the force of the atomic layer of oxygen, the distribution of the atomic oxygen does not present an ideal close-packed structure, but deviates somewhat, presenting a three-dimensional symmetry. During charging and discharging, Li⁺Reversible deintercalation/intercalation from the plane in which it is located, lithium ion migration in the positive electrode active material can be represented by the following formula:

charging: LiCoO₂→xLi⁺+Li_1-xCoO₂+xe^－

Discharging: li_1-xCoO₂+yLi⁺+xe^－→Li_1-x+yCoO₂(0＜x≤1，0＜y≤x)

During charging, lithium ions are deintercalated from octahedral sites to release an electron, Co³⁺Oxidation to Co⁴⁺(ii) a During discharge, lithium ions are inserted into octahedral sites to obtain an electron, Co⁴⁺Reduction to Co³⁺。

The actual specific capacity of lithium cobaltate is lower than the theoretical specific capacity, and after multiple charge-discharge cycles, the phase structure of the positive active material changes after multiple contractions and expansions, resulting in LiCoO₂Loosening and falling off, increasing internal resistance and reducing capacity. The reason for this is LiCoO₂Is an intercalation compound for lithium ions, if more than half of the lithium ions are derived from LiCoO during charging₂In case of medium emergence, LiCoO₂Modification of crystal form of LiCoO₂No longer having the function of deintercalating/intercalating lithium ions.

Although attempts have been made to improve the characteristics of lithium ion secondary batteries by bulk phase doping, the prior art has insufficient understanding of the action of each additive element at higher charging voltages (≥ 4.40V), and cannot achieve a balance between the performances such as cycling, thermal stability and swelling.

The present inventors have found that by doping two different types of elements into lithium cobaltate, it is possible to achieve both cycle characteristics, thermal stability, and suppression of swelling while avoiding collapse of the phase structure and while minimizing the influence on normal deintercalation and intercalation of Li.

In the present invention, the element a moves to the position of Li during charge and discharge, thereby preventing structural collapse and improving thermal stability. However, the element a affects the deintercalation of lithium, and thus deteriorates the cycle characteristics. The element B does not move to the position of Li during charge and discharge, and plays a role in stabilizing the crystal structure. Meanwhile, element B improves cycle characteristics and can suppress battery swelling. But the effect of improving the thermal stability is not large. Further, in the present invention, by controlling the doping amount and valence state of the elements a and B, the balance among thermal stability, expansion and cycle performance is achieved, so that lithium cobaltate can work at a higher charging voltage.

[ element A ]

The element A is one or more elements selected from Mg, Sc, Ti, Fe, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ru, Rh, Pd, In, Sn, Hf, Ta, W, Re, Cr, Y, Sb, Lu, Au, Pb, Er.

Specifically, in order to allow the element a to move to the position of Li during charge and discharge, and to prevent structural collapse and improve thermal stability, the element a having an ionic radius close to that of lithium is selected. "close" as used herein means that the ionic radii differ by 20% or less, more preferably by 18% or less, even more preferably by 16% or less, and most preferably by 14% or less. Since the ionic radius differs depending on the valence state, coordination number, and the like, the ionic radius referred to herein refers to the ionic radius of the element a and the lithium ion after the element A, B and its valence state are selected.

Element A in LiCo_{(1－α－β)}A_(α)B_(β)O₂The average valence of (B) is 1.5 to 3.5, preferably 2.0 to 3.0. If the average valence of the element A is in the range, the layered structure of the lithium cobaltate is more stable in the circulation process, so that the cathode material shows excellent cyclic charge-discharge stability; if the average valence of the element a in the positive electrode material is outside this range, the cycle performance becomes poor.

[ element B ]

The element B is one or more elements selected from Na, Al, Si, Ge, Mn, Ca, Te, Hg, Bi, La, Ce, Pr, Nd, Sm, and V.

Specifically, in order to prevent the element B from moving to the position of Li, stabilize the crystal structure, and improve the cycle characteristics and suppress the battery expansion, the element B having a large difference in ionic radius from that of lithium is selected. The phrase "greatly different" as used herein means that the difference in ionic radii is 25% or more, more preferably 27% or more, still more preferably 29% or more, and most preferably 31% or more. The ionic radius referred to herein means the ionic radius of the selected element A, B and the element B and lithium ion after the valence thereof, since the ionic radius differs in different valences, different coordination numbers, and the like.

Element B in LiCo_{(1－α－β)}A_(α)B_(β)O₂The average valence of (B) is 2.0 to 4.0, preferably 2.5 to 3.5. If the average valence of the element B is in the range, the layered structure of the lithium cobaltate is more stable in the circulation process, so that the cathode material shows excellent cyclic charge-discharge stability; if the average valence of the element B in the positive electrode material is outside this range, the cycle performance is deteriorated.

[ doping amount ]

In LiCo_{(1－α－β)}A_(α)B_(β)O₂In the above-mentioned method, the total doping amount (α + β) of the element A and the element B is 0.1 mol% or more and 8 mol% or less, preferably 0.2 mol% or more and 7 mol% or less, more preferably 0.5 mol% or more and 6 mol% or less, still more preferably 1 mol% or more and 5 mol% or less, based on the total mol amount of the element A, the element B and the cobalt element.

Wherein the doping amount alpha of the element A is more than or equal to 0.05 mol% and less than or equal to 5 mol%. If the doping amount α of the element a is higher than 5 mol%, the phase structure of lithium cobaltate may be affected due to the presence of too much element a; if the doping amount α of the element a is less than 0.05 mol%, the element a is too small to be able to move to the position of Li during charge and discharge, thereby preventing the structure from collapsing and improving the thermal stability. The doping amount α of the element A is preferably 0.2 mol% or more and 3 mol% or less, more preferably 0.4 mol% or more and 2.5 mol% or less, and further preferably 0.6 mol% or more and 2 mol% or less.

The doping amount beta of the element B is more than or equal to 0.05 mol% and less than or equal to 5 mol%. If the doping amount β of the element B is higher than 5 mol%, the phase structure of lithium cobaltate may be affected due to the presence of too much element B; if the doping amount β of the element B is less than 0.05 mol%, the effect of stabilizing the crystal structure cannot be exerted because the element B is present too little. The doping amount β of the element B is preferably 0.2 mol% or more and not more than 3 mol% or less, more preferably 0.4 mol% or more and not more than 2.5 mol% or less, and further preferably 0.6 mol% or more and not more than 2 mol% or less.

[ doping profiles ]

In the positive electrode active material particle of the present invention, the element a and the element B may have different distribution patterns.

In charge and discharge, it is required that the element a can move to the position of Li during charge and discharge, and therefore the element a can be uniformly distributed in the positive electrode active material particle to move uniformly during charge and discharge, thereby preventing structural collapse and improving thermal stability.

The element B does not need to move to the position of Li during charge and discharge, and the effect of stabilizing the crystal structure of the element B can be achieved as long as the concentration of the element B in the particle surface reaches a certain concentration, and therefore the concentration of the element B in the particle surface can be larger than that in the inside of the particle.

[ production of Positive electrode active Material ]

Adding a cobalt source solution and an element B source solution into a precipitator solution at certain speeds respectively according to a certain proportion, washing, filtering, drying and calcining after reaction to obtain a precursor of the positive active substance, wherein the concentration of the element B on the surface of the particles is higher than that in the interior of the particles by more than 20 percent by controlling the adding speed of the element B source solution;

mixing the precursor and lithium carbonate according to a certain molar ratio, adding a source A according to a certain proportion, uniformly mixing the mixture by using a mixer, placing the mixture into a roasting furnace for calcination after mixing, and crushing and sieving the mixture to obtain the anode active substance

The positive electrode active material thus produced is granular on a microscopic scale, and therefore, the positive electrode active material is also referred to herein as positive electrode active material particles. The positive electrode active material particles may be surface-coated, if necessary.

Positive electrode active material particles

[ surface coating ]

In order to allow the positive electrode active material to exhibit good performance during charge and discharge, the surface of the positive electrode active material particles may be coated in addition to bulk phase doping to suppress structural phase change during charge and discharge. The ideal coating substance should have a certain stability, i.e. not be dissolved in the electrolyte system and not be destroyed at higher potentials; and simultaneously, the lithium ion battery also has good electronic and lithium ion conductivity so as to be beneficial to the conduction of electrons in the electrode and the diffusion of lithium ions.

In the present invention, materials generally used for surface coating of particles of positive electrode active material, such as carbon, elemental silver, Al, can be used₂O₃、MgO、TiO₂、ZnO、ZrO₂、SiO₂、CeO₂、La₂O₃、RuO₂Isometal oxides, Li₄Ti₅O₁₂、LoMn₅O₁₂、Li₂O-2B₂O₃、La₂O₃/Li₂O/TiO₂、Li₂ZrO₃、LiAlO₂Isolithium-containing composite oxide, Y₃Al₅O₁₂、3LaAlO₃:Al₂O₃、ZrTiO₄、MgAlO₄8% mole fraction Y₂O₃-92% mole fraction ZrO₂Etc. do not contain lithium composite oxide, AlF₃Isofluorides, Al (OH)₃Isohydroxide, AlPO₄、Co₃(PO₄)₂Iso-phosphates, MnSiO₄And silicates, polymers such as conductive polymer polypyrrole (PPy), and the like.

As a method for coating the surface of the positive electrode active material particles, a method generally used for coating the surface of the positive electrode active material particles can be used, and there is no particular limitation as long as the surface coating of the positive electrode active material particles can be achieved. Such as vapor deposition, organic pyrolysis, precipitation, sol-gel, electroless plating, and the like.

[ particle diameter ]

The average particle diameter (D) of the positive electrode active material particles of the present invention₅₀) It may be 5 to 30 μm, preferably 8 to 25 μm, and more preferably 10 to 22 μm. Specifically, when the average particle diameter (D) is₅₀) Less than 5 μm, the cathode active material particles are minute, resulting in an increase in specific surface area, and thus the content of the binder is increased, resulting in a decrease in battery capacity per the same volume. When the average particle diameter (D) is₅₀) Above 30 μm, the cell efficiency with respect to weight may be lowered due to the excessively large size of the particles.

The average particle diameter (D)₅₀) In the particle size distributionThe particle diameter of (b) is defined based on 50%, and can be measured by a method generally used for measuring particle diameters, such as a laser diffraction method.

In the case where the positive electrode active material particles of the present invention are surface-coated, the surface-coating layer is also included in the particle diameter of the positive electrode active material particles. The thickness of the surface cladding layer can be determined by those skilled in the art according to the actual circumstances, and may be, for example, 50nm to 100 nm.

Lithium ion secondary battery positive electrode

The positive electrode for a lithium ion secondary battery of the present invention is a positive electrode for a lithium ion secondary battery produced by coating a slurry containing the positive electrode active material particles of the present invention, a conductive material, and a binder on a positive electrode current collector. Specifically, for example, the positive electrode for a lithium ion secondary battery may be prepared by coating a positive electrode current collector with a positive electrode slurry obtained by mixing a positive electrode active material composed of positive electrode active material particles, a conductive material, a binder, and, if necessary, a filler. By the above and following limitations, the lithium ion secondary battery positive electrode of the present invention has a bulk density of greater than 3.8 g/cc.

The positive electrode for a lithium ion secondary battery of the present invention can be produced by a method generally used for producing a positive electrode for a lithium ion secondary battery, which is well known to those skilled in the art and can be appropriately adjusted according to actual needs, in addition to using the positive electrode active material particles including the present invention.

[ Positive electrode Current collector ]

The thickness of the positive electrode current collector is generally 3 μm to 201 μm. The positive electrode current collector is not particularly limited, and a positive electrode current collector generally used for a lithium ion secondary battery may be used as long as it does not cause chemical changes in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, and aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver can be used. The surface of the positive electrode current collector may also be formed with minute concave-convex portions to improve the adhesion of the positive electrode active material, and a film, a sheet, a foil, a net, a porous structure, a foam, a non-woven fabric, or the like may be used.

[ Positive electrode active Material ]

The positive electrode active material of the present invention may include only the positive electrode active material particles of the present invention, but may also include other positive electrode active material particles. Specifically, lithium nickelate (LiNiO) may be mentioned₂) Isolamellar compounds or compounds substituted with one or more transition metals; chemical formula Li_1+xMn_2-xO₄(wherein x is 0 to 0.33) and LiMnO₃、LiMn₂O₃、LiMnO₂Lithium manganate and the like; lithium cuprate (Li)₂CuO₂)；LiV₃O₈、LiV₃O₄、V₂O₅、Cu₂V₂O₇Vanadium oxide, etc.; from the formula LiNi_1-xM_xO₂(wherein M is Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x is 0.01 to 0.3); represented by the chemical formula LiMn_2-xM_xO₂(wherein M is Co, Ni, Fe, Cr, Zn or Ta, and x is 0.01 to 0.1) or Li₂Mn₃MO₈(wherein M ═ Fe, Co, Ni, Cu, or Zn); LiMn of formula in which part of Li is substituted by alkaline earth metal ion₂O₄(ii) a A disulfide compound; fe₂(MoO₄)₃Etc., but are not limited thereto.

[ conductive Material ]

As the conductive material used in the positive electrode of the present invention, a conductive material generally used in a positive electrode of a lithium ion secondary battery can be used. The kind of the conductive material is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. For example, graphite such as natural or artificial graphite, carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride powder, aluminum powder, and nickel powder, conductive whiskers such as zinc oxide whisker and potassium titanate whisker, conductive metal oxides such as titanium oxide, polyphenylene derivatives, and the like can be used.

In the present invention, the conductive material is generally added in a proportion of 0.1 to 30 wt% with respect to the total weight of the cathode slurry including the cathode active material.

[ Binders ]

The binder included in the positive electrode may use a binder generally used in a positive electrode of a lithium ion secondary battery, and is not particularly limited as long as it contributes to adhesion between an active material and a conductive material and adhesion of the active material to a current collector. For example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, and the like can be used.

In the present invention, the binder is generally added in a proportion of 0.1 to 30% by weight, relative to the total weight of the cathode slurry including the cathode active material.

Lithium ion secondary battery

The lithium ion secondary battery of the present invention is composed of a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode of the present invention as described above is used as the positive electrode. By using the positive electrode of the present invention, a lithium ion secondary battery having good cycle characteristics and thermal stability at a high charge voltage and capable of suppressing the swelling of the secondary battery can be obtained. Specifically, by using the positive electrode of the present invention as described above in the positive electrode, the lithium ion secondary battery of the present invention can achieve a full battery charging voltage of 4.40V or more or a positive electrode with respect to Li/Li in a balance of cycle characteristics, thermal stability, and suppression of swelling⁺The charge potential of the redox couple is 4.45V or more.

The lithium ion secondary battery of the present invention can be produced by a method generally used for producing lithium ion secondary batteries, which is well known to those skilled in the art and can be appropriately adjusted according to actual needs, in addition to using a positive electrode including the positive electrode active material of the present invention.

The following is a description of the components of the lithium ion secondary battery other than the positive electrode.

[ negative electrode ]

The negative electrode is obtained by coating a negative electrode active material on a negative electrode current collector and then drying, and may optionally contain the components contained in the positive electrode as described above.

The thickness of the anode current collector is generally 3 μm to 500 μm. The anode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like can be used. In addition, as in the positive electrode current collector, a film, a sheet, a foil, a net, a porous structure, a foam, a non-woven fabric, or the like may be used, with a minute concave-convex portion on the surface to enhance the adhesion of the negative electrode active material.

As the negative electrode active material, for example, carbon such as non-graphitized carbon or graphitized carbon, Li_xFe₂O₃(0≤x≤1)、Li_xWO₂(0≤x≤1)、Sn_xMe_1-xMe’_yO_z(Me: Mn, Fe, Pb, Ge; Me' is Al, B, P, Si, an element of group I, group III or group III of the periodic Table, halogen; x is more than 0 and less than or equal to 1; y is more than or equal to 1 and less than or equal to 3; z is more than or equal to 1 and less than or equal to 8), lithium metal, lithium alloy, silicon-based alloy, tin-based alloy, SnO₂、PbO、PbO₂、Pb₂O₃、Pb₃O₄、Sb₂O₃、Sb₂O₄、Sb₂O₅、GeO、GeO₂、Bi₂O₃、Bi₂O₄And Bi₂O₅And the like, conductive polymers such as polyacetylene, Li-Co-Ni based materials, and the like.

[ electrolyte ]

The electrolyte of the lithium ion secondary battery is lithium salt non-aqueous electrolyte and consists of non-aqueous electrolyte, lithium salt and additive.

As the nonaqueous electrolytic solution, a nonaqueous electrolytic solution generally used for a lithium ion secondary battery, such as a nonaqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like, can be used, but not limited thereto. In particular toExamples of the organic solvent include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ -butyrolactone, 1, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, dioxolane, nitromethane, methyl formate, methyl acetate, phosphotriester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1, 3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, and other non-aqueous organic solvents, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyethylene oxide derivatives, polypropylene oxide derivatives, polyethylene oxide, polyethylene, Organic solid electrolytes such as poly agitation lysine (poly agitation lysine), polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation group, and Li as lithium nitride, halide, sulfate, and the like₃N、LiI、Li₅NI₂、Li₃N-LiI-LiOH、LiSiO₄、LiSiO₄-LiI-LiOH、Li₂SiS₃、Li₄SiO₄、Li₄SiO₄-LiI-LiOH、Li₃PO₄-Li₂S-SiS₂And the like inorganic solid electrolytes. These nonaqueous electrolytic solutions may be used singly or in combination of two or more.

As the lithium salt, a lithium salt generally used for an electrolyte of a lithium ion secondary battery, such as LiClO, may be used₄、LiAsF₆、LiBF₄、LiCF₃SO₃、LiPF₆、LiCl、LiI、LiBr、LiB₁₀Cl₁₀、LiCF₃CO₂、LiSbF₆、LiAlCl₄、CH₃SO₃Li、CF₃SO₃Li、(CF₃SO₂)₂NLi, etc. The concentration of the lithium salt in the nonaqueous electrolytic solution may be 0.5 to 2 mol/L. These lithium salts may be used singly or in combination of two or more.

As an additive, an additive may be added to the electrolyte. In general, different additives are added depending on the other materials used and the actual needs.

Specifically, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-glyme (N-glyme), hexaphosphoric triamide (hexaphosphoric triamide), nitrobenzene derivatives, sulfur, quinonimine dyes, N-substituted oxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, and the like may be added for the purpose of improving charge-discharge characteristics, flame retardancy, and the like. To impart incombustibility, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be added. In order to improve high-temperature storage characteristics, carbon dioxide gas, fluoroethylene carbonate (FEC), propylene sultone (PRS), and the like may be added. To improve the conductivity, acetamide, acetylamino, acetylamine, etc. may be added. These additives may be used singly or in combination of two or more.

Among them, in order to form a relatively effective protective film on the surface of the positive electrode, cover the active site thereof, and reduce the reactivity of the positive electrode with respect to the electrolyte solution, it is preferable to add a nitrile additive to the electrolyte solution of the present invention, and examples thereof include butyronitrile, valeronitrile, n-heptanitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, 1,2, 3-propanetricitrile, 1,3, 5-pentanedinitrile, and hexanetrinitrile. These nitrile additives may be used singly or in combination of two or more. The nitrile additives may also include phosphazene additives, and specifically, hexamethylphosphazene, hexachlorocyclotriphosphazene, and ethoxypentafluorocyclotriphosphazene may be mentioned. These phosphazene additives may be used singly or in combination. The nitrile additive is added in a proportion of 0.2 to 10 wt% with respect to the total weight of the electrolyte including the lithium salt, more preferably 1 to 9 wt%, further 2 to 8 wt%, most preferably 3 to 7 wt%.

Further, the combination of the nitrile additive and the lithium salt in the electrolytic salt provides a further improved effect. For example, the lithium salt in the electrolyte is LiPF₆In the case of (2), the use of additives of the dinitrile type will give better results.

[ separator ]

The separator is provided between the positive electrode and the negative electrode, and an insulating thin film having high ion permeability and high mechanical strength is used as the separator. The diameter of the pores of the separator is generally 0.01 μm to 10 μm, and the thickness thereof is generally 5 μm to 300. mu.m. As such a separator, for example, a sheet or nonwoven fabric made of an olefin-based polymer such as polypropylene, glass fiber, or polyethylene, which is chemically resistant and hydrophobic, is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium ion secondary battery described above is excellent in both cycle characteristics and thermal stability at a high charging voltage, and can suppress the expansion of the secondary battery, so that the energy density of the lithium ion secondary battery can be effectively increased, and a larger amount of stored electricity can be provided.

The lithium ion secondary battery of the present invention can be further fabricated into a battery pack and a device including the battery pack. Since such a battery pack and a device using the same are well known in the art, the structure, the manufacturing method, and the use thereof will be known to those skilled in the art, and thus a detailed description thereof will be omitted herein.

The device may be a notebook, a netbook, a tablet, a mobile phone, an MP3, a wearable electronic device, an Electric tool (power tool), an Electric Vehicle (EV), a Hybrid Electric Vehicle (HEV), a Plug-in Hybrid Electric Vehicle (PHEV), an Electric bicycle (E-bike), an Electric scooter (E-scooter), an Electric balance car, an Electric golf cart (Electric golf cart), or a system for storing Electric power, but is not limited thereto.