阅读说明：本技术 一种负极及包含该负极的锂二次电池 (Negative electrode and lithium secondary battery comprising same ) 是由 王俊姿 邓海福 李兴旺 李文文 于 2021-03-12 设计创作，主要内容包括：本发明提供了一种负极及包含该负极的锂二次电池,所述负极包括集流体、第一负极活性材料层、第二负极活性材料层,所述第一负极活性材料层形成在所述集流体的至少一个表面上,包括作为负极活性材料的天然石墨、人造石墨的混合物和第一粘合剂；所述第二负极活性材料层形成在所述第一负极活性材料层上,包括作为负极活性材料的磷碳复合物和第二粘合剂。本发明使用具有高能量密度、优异的Li～+传导性、表面含有有机物涂层的的磷碳化合物作为负极材料,并采用双层负极的结构的设计可以制备出高能量密度,快充特性和寿命优异的锂离子二次电池。(The invention provides a negative electrode and a lithium secondary battery comprising the same, wherein the negative electrode comprises a current collector, a first negative electrode active material layer and a second negative electrode active material layer, wherein the first negative electrode active material layer is formed on at least one surface of the current collector and comprises a mixture of natural graphite and artificial graphite serving as negative electrode active materials and a first binder; the second anode active material layer is formed on the first anode active material layer, and includes a phosphorus-carbon composite as an anode active material and a second binder. The present invention uses excellent Li having high energy density + The conductive phosphorus-carbon compound with the organic matter coating on the surface is used as a negative electrode material, and the design of a double-layer negative electrode structure is adopted, so that the lithium ion secondary battery with high energy density, quick charge characteristic and excellent service life can be prepared.)

1. A negative electrode, characterized by: the negative electrode includes a current collector, a first negative active material layer formed on at least one surface of the current collector, including a mixture of natural graphite, artificial graphite, and a first binder as a negative active material, and a second negative active material layer; the second anode active material layer is formed on the first anode active material layer, and includes a phosphorus-carbon composite as an anode active material and a second binder.

2. The anode of claim 1, wherein: in the first negative electrode active material layer, the weight ratio of the natural graphite to the artificial graphite is 1: 99-50: 50, and preferably 5: 95-30: 70.

3. The negative electrode according to claim 1 or 2, characterized in that: in the first negative electrode active material layer, the average diameter of natural graphite is 4-15 μm, and the average particle diameter D50 of artificial graphite is 20-30 μm.

4. The negative electrode according to claim 1 or 2, characterized in that: in the second anode active material layer, the surface of the phosphorus-carbon composite contains an organic coating, and the ratio of phosphorus: the carbon mass ratio is 9: 1-3: 2, preferably 4: 1.

5. The negative electrode according to claim 1 or 2, characterized in that: in the phosphorus-carbon composite, phosphorus is at least one of black phosphorus, red phosphorus and purple phosphorus, and black phosphorus is preferred; the carbon is at least one of graphite, hard carbon and soft carbon, and graphite is preferred.

6. The negative electrode according to claim 1 or 2, characterized in that: the organic matter coating on the surface of the phosphorus-carbon composite comprises at least one of phenolic resin, polyaniline, polyimide, polymer pyrolytic carbon, pitch carbon fiber and epoxy resin.

7. The negative electrode according to claim 1 or 2, characterized in that: the organic matter coating on the surface of the phosphorus-carbon composite accounts for 5-20% of the mass ratio of the phosphorus-carbon composite.

8. The negative electrode of any one of claims 1 to 7, wherein: the preparation method of the phosphorus-carbon composite comprises the following steps:

(1) ball-milling the mixture of the massive phosphorus and the carbon in a certain proportion by using a planetary ball mill, wherein the revolution rotating speed is 50-300/min, the rotation rotating speed is 100-500r/min, and the ball-milling time is 8-48h, so as to form a phosphorus-carbon compound;

(2) and (3) in a vacuum glove box, adding the organic matter for forming the organic matter coating into a ball milling tank containing the phosphorus-carbon compound, and carrying out ball milling again, wherein the revolution speed is 10-100r/min, the rotation speed is 50-200r/min, and the ball milling time is 2-6h, so as to form the phosphorus-carbon compound with the organic matter coating on the surface.

9. The negative electrode of claim 8, wherein: the mass ratio of the first negative electrode active material layer to the second negative electrode active material layer is less than or equal to 1: 1.

10. A lithium secondary battery comprising the anode according to any one of claims 1 to 9.

Technical Field

The invention belongs to the field of lithium ion batteries, and particularly relates to a negative electrode and a lithium secondary battery comprising the same.

Background

In general, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. In the secondary battery, energy transfer occurs while lithium ions reciprocate between opposite electrodes, so that lithium ions from a positive electrode active material are intercalated into a negative electrode active material, such as carbon particles, by first charging, and lithium ions are deintercalated during discharging, and in this way, the secondary battery can be charged and discharged.

With the wider application of lithium secondary batteries in the power automobile industry, the lithium secondary batteries have higher requirements on high energy density, long cycle life and high-rate charge and discharge performance. However, basic performance characteristics of the lithium secondary battery are greatly affected by the negative electrode material. In order to maximize the performance of the battery, the anode active material needs to satisfy the following conditions: the electrochemical reaction potential should be close to that of lithium metal, the reaction reversibility with lithium ions should be high, and the diffusion rate of lithium ions in the active material should be fast. Graphite has been widely used as a material to meet these requirements. In view of the excellent adhesion of natural graphite and the excellent output and life characteristics of artificial graphite, a mixture of natural graphite and artificial graphite has been used to improve the performance of various secondary batteries. However, when such a mixture is used, there is a problem in that the rapid charging performance is lowered due to natural graphite. Binary composite material consisting of an alloy element with high lithiation capacity (for example silicon) having a reversible capacity of 517mA · h/g (relative to the mass of the composite material) and greater than 3.3mA · h/cm²Area capacity of (c). However, this capacity is only achieved at a relatively low current density of 0.26A/g, with a charge time of about 2 hours. In order to solve this problem and ensure stability, a multilayer electrode has been proposed in which a portion close to the current collector, where adhesion is important, is composed of a mixture of natural graphite and artificial graphite, and a portion far from the current collector is composed of a mixture of Si and graphite. However, the above-mentioned multi-layered negative electrode cannot be charged with energy density quickly due to the characteristics of graphite and siliconThe electricity, stability and lifetime are improved to the desired level.

Layered phosphors exhibit a number of attractive functions in high rate, high volume lithium storage. By reaction with Li⁺Phosphorus theoretically provides a capacity density of 2596mA · h/g. The large capacity of phosphorus helps to counteract its relatively high voltage loss, thereby achieving a high specific energy density according to the formula E ═ v (q) x q (idis), where v (q) is the average cell voltage versus state of charge and q (idis) is the capacity density for a given discharge current. Furthermore, the conductivity of phosphorus is 300S/m, four orders of magnitude greater than that of silicon (6.7X 10-2S/m); li along the zigzag direction of layered phosphorus⁺The diffusion barrier property of only 0.08eV has caused the introduction of Li in phosphorus⁺Research on diffusion Rate, studies to date have shown that Li in bulk phosphorus⁺Has a higher diffusion rate than silicon or other conventional anode materials. However, atomic reconstruction near the zigzag diffusion channels of the phosphorus nanoflakes hinders Li⁺Kinetics of transfer over the entire surface. In addition, volume changes of phosphorus during charge and discharge cycles destabilize a solid-electrolyte interphase (SEI), resulting in poor cycle performance. And thus the use of phosphorus in lithium secondary batteries is limited.

Therefore, there is an urgent need to develop a high energy density lithium secondary battery having excellent thermal stability and improved rapid charge and discharge characteristics by solving the above problems.

Disclosure of Invention

In view of the above, the present invention is directed to a negative electrode and a lithium secondary battery comprising the same, so as to improve the fast charge and charge/discharge characteristics of a high-load lithium secondary battery in terms of a negative electrode material and solve the problem of fast charge of the lithium secondary battery.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a negative electrode comprising a current collector, a first negative electrode active material layer formed on at least one surface of the current collector, a second negative electrode active material layer comprising a mixture of natural graphite, artificial graphite, and a first binder as a negative electrode active material; the second anode active material layer is formed on the first anode active material layer, and includes a phosphorus-carbon composite as an anode active material and a second binder.

Preferably, in the first negative electrode active material layer, the weight ratio of the natural graphite to the artificial graphite is 1: 99-50: 50, and preferably 5: 95-30: 70.

Preferably, in the first negative electrode active material layer, the natural graphite has an average diameter of 4 to 15 μm, and the artificial graphite has an average particle diameter D50 of 20 to 30 μm.

Preferably, in the second anode active material layer, the surface of the phosphorus-carbon composite contains an organic coating layer, based on the weight of the phosphorus-carbon composite, the ratio of phosphorus: the carbon mass ratio is 9: 1-3: 2, preferably 4: 1.

Preferably, in the phosphorus-carbon composite, the phosphorus is at least one of black phosphorus, red phosphorus and purple phosphorus, and is preferably black phosphorus; the carbon is at least one of graphite, hard carbon and soft carbon, and graphite is preferred.

Preferably, the organic coating on the surface of the phosphorus-carbon composite comprises at least one of phenolic resin, polyaniline, polyimide, polymer pyrolytic carbon, pitch carbon fiber and epoxy resin.

Preferably, the organic coating on the surface of the phosphorus-carbon composite accounts for 5-20% of the mass of the phosphorus-carbon composite.

Preferably, the preparation method of the phosphorus-carbon composite pair comprises the following steps:

(1) ball-milling the mixture of the massive phosphorus and the carbon in a certain proportion by using a planetary ball mill, wherein the revolution rotating speed is 50-300/min, the rotation rotating speed is 100-500r/min, and the ball-milling time is 8-48h, so as to form a phosphorus-carbon compound;

(2) and (3) in a vacuum glove box, adding the organic matter for forming the organic matter coating into a ball milling tank containing the phosphorus-carbon compound, and carrying out ball milling again, wherein the revolution speed is 10-100r/min, the rotation speed is 50-200r/min, and the ball milling time is 2-6h, so as to form the phosphorus-carbon compound with the organic matter coating on the surface.

Preferably, the mass ratio of the first negative electrode active material layer to the second negative electrode active material layer is less than or equal to 1: 1.

Another object of the present invention is to provide a lithium secondary battery comprising the above negative electrode.

Compared with the prior art, the negative electrode and the lithium secondary battery comprising the same have the following beneficial effects:

the present invention is an electric double layer negative electrode design, and particularly, the second negative electrode active material layer includes a phosphorus carbon compound having high energy density, excellent Li + conductivity, and an organic coating layer on the surface thereof as a negative electrode material, so that a lithium secondary battery having high energy density, excellent quick charge characteristics, and a long life can be manufactured to meet the current market demand.

Specifically, in the present invention, the first negative electrode active material layer contains natural graphite and artificial graphite at a certain weight ratio, and the second negative electrode active material layer contains a phosphorus-carbon composite, wherein the surface of the phosphorus-carbon composite contains an organic coating. The mixture of natural graphite and artificial graphite close to the current collector may improve the adhesion of the active material layer to the current collector and may improve the compatibility between the second negative active material layer including the phosphorus-carbon composite and the first negative active material layer. The surface of the phosphorus-carbon composite contains the organic layer gel coating, so that the capacity and the quick charging characteristic can be improved, the oxidizability of phosphorus is inhibited, the direct contact of the phosphorus-carbon composite and an electrolyte is avoided, and the side reaction of the phosphorus-carbon composite and the electrolyte is prevented. The organic coating ensures a stable SEI and prevents the continued accumulation of poorly conducting substances, which is largely attributable to the protective and mediating effect of the organic gel layer swelling by the electrolyte. The swollen organic coating also fills the polymer matrix with Li + and protons and absorbs corrosive hydrogen fluoride after immersion in the electrolyte to facilitate charge transport throughout the electrode. Formation of lithium fluoride and lithium carbonate is suppressed, the conductivity of the swollen organic coating is increased, the transfer of charges at the electrode-electrolyte interface is promoted, and in addition, since the diffusion rate of Li + in phosphorus is higher than that of silicon or other conventional negative electrode materials and phosphorus has excellent capacity characteristics, a negative electrode for a lithium ion secondary battery having high energy density, fast charge characteristics and excellent life can be prepared.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is an SEM image of a black phosphorus-graphite composite of example 1;

FIG. 2 is an SEM image of a black phosphorus-graphite composite in which polyaniline is contained on the surface in example 1;

fig. 3 is SEM images of anodes having different thicknesses of the anode with the same capacity, in which a is SEM of the anode in example 1, and b is SEM image of the anode in comparative example 3.

Detailed Description

Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.

The present invention will be described in detail with reference to the following examples and accompanying drawings.

The positive electrode, the negative electrode and the diaphragm which form the lithium secondary battery of the invention can be manufactured and used in a conventional way, generally, the lithium secondary battery is prepared into an electrode assembly by a positive plate, a negative plate and the diaphragm which separates the positive plate and the negative plate in sequence through winding or stacking, the positive and negative electrode connection pieces of the electrode assembly are electrically connected with positive and negative electrode leads, then the electrode assembly is put into a shell with a certain shape, and encapsulation liquid injection formation and preparation of a single battery core are carried out.

(1) Negative electrode

An anode, comprising: a current collector, a first negative active material layer formed on at least one surface of the negative current collector and including a mixture of natural graphite and artificial graphite in a weight ratio of 1:99 to 50:50, preferably 5:95 to 30:70, as a negative active material, and a first binder; and a second anode active material layer formed on the first anode active material layer and including a phosphorus-carbon composite and a second binder as an anode active material. Wherein, the surface of the phosphorus-carbon composite contains an organic coating, based on the mass of the phosphorus-carbon composite, the organic composite coating accounts for 5-20%, based on the weight of the phosphorus-carbon composite, the weight ratio of phosphorus: the carbon mass ratio is 9: 1-3: 2, preferably 4: 1.

The negative electrode increases a contact force between a current collector and a negative active material by mixing natural graphite excellent in adhesiveness with artificial graphite in a first negative active material layer directly contacting the current collector, thereby ensuring stability and preventing deterioration of life characteristics. In addition, artificial graphite has excellent output and life characteristics, thereby improving thermal stability of the negative electrode.

Further, the second anode active material layer formed on the first anode active material layer is located on the surface of the anode and includes a phosphorus-carbon composite having a large capacity and a surface coated with an organic substance, and since the phosphorus-carbon composite participates in a reaction prior to graphite during charge and discharge, a rapid charge characteristic may be improved. Here, the mixture of natural graphite and artificial graphite may be in a range of 1:99 to 50:50, preferably 5:95 to 30:70, by weight. When the content of the natural graphite is excessively increased beyond the above range, the output characteristics may be deteriorated. If the content of the natural graphite is too small, the adhesion between the current collector and the active material layer may be reduced, so that an excessive amount of binder may be required, or a drastic reduction in lifespan characteristics may be caused due to the peeling of the active material layer during charge and discharge.

In the first negative electrode active material layer, a mixture in which the average particle diameter (D50) of the artificial graphite is 20 to 30 μm and the average diameter of the natural graphite is 4 to 15 μm, and the average particle diameter of the artificial graphite particles falls within the above range, is preferable in terms of achieving a battery excellent in rapid charging characteristics and high-temperature storage properties. In addition, the first anode active material particles preferably have a particle size of 20 to 25 μm in terms of further improving the above-described quick charge characteristics and high-temperature storage properties. The artificial graphite particles may have a spherical shape, which is preferable in terms of improving rolling performance, capacity characteristics, and rapid charging characteristics.

The natural graphite particles have a relatively small average particle diameter and are soft as compared with the artificial graphite particles, so when the artificial graphite particles and the natural graphite particles are blended, the natural graphite particles can be advantageously arranged between the artificial graphite particles and on the surface of the artificial graphite particles. Therefore, the variation in specific surface area of the anode mixture layer during the rolling process may be reduced, and thus high-temperature storage performance and high-temperature cycle characteristics may be improved.

In addition, phosphorus has excellent Li⁺Transport properties, and the phosphorus may specifically include: black phosphorus, red phosphorus, purple phosphorus, preferably black phosphorus; the carbon may specifically include: graphite, hard carbon, soft carbon, preferably graphite. The phosphorus-carbon composite can prevent edge reconstruction and ensure effective Li⁺Insertion and diffusion; and the surface contains an organic coating, based on the mass of the phosphorus-carbon composite, the organic composite coating accounts for 5-20%, and the organic coating comprises: at least one of phenolic resin, polyaniline, polyimide, polymer pyrolytic carbon, asphalt carbon fiber and epoxy resin can improve the capacity and the quick charging characteristic, inhibit the oxidization of phosphorus and avoid the direct contact of the phosphorus-carbon composite and the electrolyte so as to prevent the side reaction of the phosphorus-carbon composite and the electrolyte. The organic coating ensures a stable SEI and prevents the continued accumulation of poorly conducting substances, which is largely attributable to the protective and mediating effect of the organic gel layer swelling by the electrolyte. The swollen organic coating also allows the polymer matrix to be Li-filled after immersion in the electrolyte⁺And protons and absorb corrosive hydrogen fluoride to facilitate charge transport throughout the electrode. The formation of lithium fluoride and lithium carbonate is inhibited and the conductivity of the swollen organic coating is increased, facilitating the transfer of charge at the electrode-electrolyte interface.

Further, based on the weight of the phosphorus-carbon composite, phosphorus: the carbon mass ratio is 9: 1-3: 2, preferably 4: 1. When the content of phosphorus is too high to exceed the above range, the composite material is not good in conductivity and poor in structural stability during charge and discharge, causing a decrease in electrochemical properties. When the content of phosphorus is too small, the effect of improving thermal stability and quick charge characteristics, which is the desired effect of the present disclosure, cannot be obtained.

The preparation method of the phosphorus-carbon composite with the organic matter coating on the surface comprises the following steps: (1) ball-milling the mixture of the massive phosphorus and the carbon in a certain proportion by using a planetary ball mill, wherein the revolution speed is 50-300/min. The autorotation speed is 100-; (2) and (3) in a vacuum glove box, adding the organic matter forming the organic matter coating into a ball milling tank containing the phosphorus-carbon compound, and carrying out ball milling again, wherein the revolution speed is 10-100r/min, the revolution speed is 50-200r/min, and the ball milling time is 2-6h, so as to form the phosphorus-carbon compound with the organic matter coating on the surface.

Further, the mass ratio of the first negative electrode active material layer to the second negative electrode active material layer is 1:1 or less, that is, the second negative electrode active material layer surface density is higher than the first negative electrode surface density, and the first negative electrode active material layer containing natural graphite only needs to improve the adhesion of a specific portion between the current collector and the active material, and thus does not need to be formed too thick. When the content of natural graphite in the entire anode active material layer is increased, the overall performance of the secondary battery, such as output characteristics, capacity, and life characteristics, may be reduced. However, when the first anode active material layer is applied too thin, the effect of improving the adhesion to the current collector, which is expected to be achieved by including natural graphite, may not be obtained.

In addition, the second negative active material layer may be separately applied to at least one surface of the current collector, but this is not preferable.

Further, the first binder and the second binder may be the same kind of compound or different kinds of compounds. The content ratios of the first binder and the second binder may be the same as or different from each other on a per anode active material layer basis. Specifically, the first binder and the second binder are not limited as long as they are components contributing to the bonding between the active material and the conductive material, and the binder is generally added in 1 to 50 wt% based on the total weight of the mixture including the active material, and examples of the binder may include polyvinylidene fluoride (PVDF), 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 (SBR), fluororubber, various copolymers, and the like.

Meanwhile, the first and second anode active material layers may further include a conductive material, and in each anode active material layer, the conductive material may be included at 1 wt% to 10 wt% based on the total weight of the anode active material layer. The conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. Examples of the conductive material include: 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 and potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives; and the like. Specifically, the conductive material may be carbon black.

In addition, a thickener may be further included, and in each anode active material layer, the thickener may be included at 1 wt% to 5 wt% based on the total weight of the anode active material layer. The thickener may be, for example, a cellulose polymer, polyethylene glycol, polyacrylamide, poly (N-vinylamide) or poly (N-vinylpyrrolidone). The cellulose polymer may be at least one selected from the group consisting of carboxymethyl cellulose (CMC), Methyl Cellulose (MC), hydroxypropyl cellulose (HPC), methylhydroxypropyl cellulose (MHPC), ethyl hydroxyethyl cellulose (EHEC), methyl ethyl hydroxyethyl cellulose (MEHEC), and cellulose gum.

The negative electrode current collector used as a substrate for forming the active material layer is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, the negative current collector may be copper; stainless steel; aluminum; nickel; titanium; sintering carbon; copper or stainless steel surface-treated with carbon, nickel, titanium or silver; aluminum-cadmium alloy; or the like.

The thickness of the current collector is not particularly limited, but may be 3 to 500 μm, which is generally applied.

(2) Positive electrode

The positive electrode sheet has no particular requirement, and the positive electrode can be manufactured by forming a positive electrode mixture layer on a positive electrode current collector. The positive electrode mixture layer may be manufactured by the following process: a positive electrode current collector is coated with a positive electrode slurry including a positive electrode active material, a binder, a conductive material, and a solvent, and then the coated positive electrode current collector is dried and rolled.

The positive electrode current collector is not particularly limited, and has a thickness of 3 to 500 μm as long as it has conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used.

The positive electrode active material may be a compound capable of reversibly intercalating and deintercalating lithium ions, and specifically, the positive electrode active material may include: a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel or aluminum. More specifically, the lithium composite metal oxide may be: lithium-manganese oxides (e.g. LiMnO)₂、LiMn₂O₄Etc.), lithium-cobalt-based oxides (e.g., LiCoO)₂Etc.), lithium-nickel based oxides (e.g., LiNiO)₂Etc.), lithium-nickel-manganese-based oxides (e.g., LiNi)_1-YMn_YO₂(here, 0)<Y<1)、LiMn_2-ZNi_ZO₄(here, 0)<Z<2) Etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi)_1-Y1Co_Y1O₂(here, 0)<Y1<1) Etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo)_1-Y2Mn_Y2O₂(here, 0)<Y2<1)、LiMn_2-Z1Co_Z1O₄(here, 0)<Z1<2) Etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li (Ni)_pCo_qMn_r1)O₂(here, 0)<p<1，0<q<1，0<r1<1 and p + q + r1 ═ 1), Li (Ni)_p1Co_q1Mn_r2)O₄(here, 0)<p1<2，0<q1<2，0<r2<2 and p1+ q1+ r2 ═ 2, etc.) or a lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li (Ni)_p2Co_q2Mn_r3M_s2)O₂(Here, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 represent the atomic fraction of each individual element and satisfy 0<p2<1，0<q2<1，0<r3<1，0<s2<1 and p2+ q2+ r3+ s2 ═ 1, etc.), and these compounds may be used alone or in combination of two or more thereof. In particular, the lithium composite metal oxide may be LiCoO in that capacity characteristics and stability of the battery may be improved₂、LiMnO₂、LiNiO₂Oxides of the lithium-nickel-manganese-cobalt type (e.g. Li (Ni)_0.6Mn_0.2Co_0.2)O₂、Li(Ni_0.5Mn_0.3Co_0.2)O₂、Li(Ni_0.8Mn_0.1Co_0.1)O₂Etc.) or lithium-nickel-cobalt-aluminum-based oxides (e.g., Li (Ni)_0.8Co_0.15Al_0.05)O₂Etc.). The lithium composite metal oxide may be Li (Ni) in consideration of a significant improvement effect in adjusting the kind and content ratio of constituent elements forming the lithium composite metal oxide_0.6Mn_0.2Co_0.2)O₂、Li(Ni_0.5Mn_0.3Co_0.2)O₂、Li(Ni_0.7Mn_0.15Co_0.15)O₂、Li(Ni_0.8Mn_0.1Co_0.1)O₂And the like, and these compounds may be used alone or in combination of two or more thereof.

Examples of the binder, the conductive material, and the thickener are as described in the negative electrode.

(3) Diaphragm

The separator may be any separator used in a general secondary battery as long as it separates the anode from the cathode and provides a transfer path for lithium ions. In particular, a separator having low resistance to ion transfer in an electrolyte and excellent electrolyte-retaining ability may be used. For example, the separator may be a porous polymer film, for example, a porous polymer film formed of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, an ethylene/methacrylate copolymer, or the like, or a stacked structure having two or more layers formed of these materials. In addition, the separator may be a general porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, or the like. In addition, in order to secure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may also be used, and optionally, a structure having one or more layers of these materials may be used.

(4) Electrolyte solution

The electrolyte may be a non-aqueous electrolyte containing a lithium salt. The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt, and examples of the non-aqueous electrolyte include a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like, but are not limited thereto.

Example 1

A mixture of artificial graphite and natural graphite in a weight ratio of 80:20 as a negative electrode active material, SBR as a binder, CMC as a thickener, and carbon black as a conductive material were mixed in a weight ratio of 95.4: 2.3:1.3:1.0 by weight, and water was added thereto as a solvent to prepare a first negative electrode slurry. A mixture of artificial graphite and black phosphorus at a weight ratio of 20:80 as a negative electrode active material, SBR as a binder, CMC as a thickener, and carbon black as a conductive material, in which polyaniline was contained at a surface in an amount of 10% based on the weight of the phosphorus-carbon composite, were mixed at a weight ratio of 95.5:2.3:1.3:1.0 by weight, and water was added thereto as a solvent to prepare a second negative electrode slurry. The first negative electrode paste and the second negative electrode paste were applied to a copper foil having a thickness of 8 μm in a weight ratio of 1: 1. Drying to prepare the double-layer cathode.

The gram capacity of the selected negative active material is shown in table 1 below:

TABLE 1 gram capacity of negative active material

	Natural graphite	Artificial graphite	Black phosphorus	Red phosphorus
					Gram capacity (mAh/g)	362	355	1973	600

Example 2: changing the ratio of black phosphorus to graphite as the negative electrode active material in the second negative electrode active material layer

An anode was prepared in the same manner as in example 1 except that: the use weight ratio is 10: 90 of artificial graphite and dark phosphorus as a negative active material of the second negative electrode slurry.

Example 3: changing the content of the organic coating on the surface of the anode active material in the second anode active material layer

An anode was prepared in the same manner as in example 1 except that: the phosphorus-carbon composite as the second negative electrode active material contained 20% of an organic coating on the surface thereof, based on the weight of the phosphorus-carbon composite.

Example 4: changing black phosphorus as an anode active material in the second anode active material layer into red phosphorus

An anode was prepared in the same manner as in example 1 except that: the negative electrode active material in the second negative electrode active material layer is a red phosphorus graphite compound, and the others are unchanged.

Example 5: changing the ratio of natural graphite to artificial graphite as the negative electrode active material in the first negative electrode active material layer

An anode was prepared in the same manner as in example 1 except that: a mixture of artificial graphite and natural graphite in a weight ratio of 1:99 was used as a negative electrode active material of the first negative electrode slurry.

Example 6: changing the weight ratio of the first and second negative electrode active material layers

An anode was prepared in the same manner as in example 1 except that: the weight ratio of the first negative electrode active material layer to the second negative electrode active material layer was 1:2, and none of the others was changed.

Comparative example 1: not of a two-layer structure and not comprising a phosphorus-carbon composite

A mixture of artificial graphite and natural graphite in a weight ratio of 80:20 as a negative electrode active material, SBR as a binder, CMC as a thickener, and carbon black as a conductive material were mixed in a weight ratio of 95.4: 2.3:1.3:1.0 by weight, and water was added thereto as a solvent to prepare a negative electrode slurry. The negative electrode slurry was applied to a copper foil having a thickness of 8 μm, and dried to prepare a negative electrode sheet

Comparative example 2: not of two-layer structure but comprising a phosphorus-carbon composite

A mixture of artificial graphite and black phosphorus at a weight ratio of 20:80 as a negative electrode active material, SBR as a binder, CMC as a thickener, and carbon black as a conductive material were mixed in a weight ratio of 95.4: 2.3:1.3:1.0 by weight, and water was added thereto as a solvent to prepare a negative electrode slurry. The negative electrode slurry was applied to a copper foil having a thickness of 8 μm, and dried to prepare a double-layered negative electrode.

Comparative example 3: two-layer structure, but without phosphorus-carbon containing composite

An anode was prepared in the same manner as in example 1 except that: as a negative electrode active material of the second negative electrode slurry, only artificial graphite and a natural graphite composite were used in exactly the same ratio as in example 1.

Comparative example 4: two-layer structure, but the surface of the phosphorus-carbon composite does not contain organic matter coating

An anode was prepared in the same manner as in example 1 except that: the surface of the negative active material phosphorus-carbon composite in the second slurry does not contain a coating.

The negative electrode, the positive electrode, the polyethylene separator (thickness: 16 μ M) and the liquid electrolyte in which 1M LiPF6 was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and diethyl carbonate (ratio 1:2:1) prepared in the above examples and comparative examples were used to manufacture a secondary battery.

Test 1: areal density of negative electrode sheet

The battery cell capacity is designed to be 52Ah, N/P is 1.08, and the size of a pole piece is 271 mm-98 mm; the assembly mode is Z-shaped lamination, and the lamination layers comprise 22 positive electrodes and 23 negative electrodes; the design areal density for each example is shown in table 1 below.

And (3) testing 2: fast charge characteristic

The prepared secondary battery was measured for the time taken to be charged to 80% SOC by applying a 1.5C constant current 4.3V constant voltage to 0.1C. The results are shown in table 1 below.

Test 3

The secondary batteries prepared above were charged to 4.35V in steps of 2C, 1.8C, 1.2, 0.8C under constant current/constant voltage (CC/CV) conditions at 10 ℃, and then discharged to 2.75V under Constant Current (CC) conditions at 1C, and their discharge capacities were measured. The cycle number at a capacity retention rate of 80% is shown in table 2 below.

TABLE 2 data comparison table of examples and comparative examples

As can be seen from the test data in Table 2, the present invention uses excellent Li with high energy density⁺The conductive phosphorus-carbon compound with the organic matter coating on the surface is used as the cathode material, and the design of the double-layer cathode structure can be adopted to prepare the lithium ion secondary with high energy density, fast charge characteristic and excellent service lifeAnd a secondary battery.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.