A negative electrode active material and use thereof

Abstract

The application discloses a kind of negative active material and its application.A kind of negative active material, including carbon material and silicon-based material;The carbon material includes artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microsphere, at least one in graphene;The chemical formula of the silicon-based material is X a Si b Y c Wherein, X includes at least one of P, As, Se, B, Ga, Mg, Al, Zn, Li, Y includes at least one of O, C, a, b, c satisfy 0≤a≤8, 0≤c≤10, 1≤(a+b)≤10, 2≤(b+c)≤10.The application has the advantages of improving the energy density, rate performance and cycle performance of lithium battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a negative electrode active material and its application. Background Technology

[0002] Lithium-ion batteries, due to their advantages such as high specific energy, long cycle life, and environmental safety, are now widely used in electric vehicles, hybrid electric vehicles, and plug-in hybrid electric vehicles. With the rapid development of electric vehicles, the demand for longer driving range from lithium-ion batteries is increasing. Therefore, improving the capacity of lithium-ion batteries has gradually become a top priority in their development.

[0003] Currently, the industry primarily uses graphite (artificial graphite and natural graphite) in lithium-ion batteries. Graphite's theoretical specific capacity is 372 mAh / g, and the specific capacity of mass-produced graphite is already close to this theoretical capacity, reaching the limit for further improving battery energy density. To further increase the capacity of lithium-ion batteries, the main focus is on developing new anode active materials with high capacity characteristics, such as silicon or tin. Their theoretical capacity is at least 10 times that of graphite, and they are expected to replace graphite anode materials to improve the energy density of lithium-ion batteries. However, when silicon-based materials are used as anode active materials, they undergo significant volume expansion during the charging and discharging process of lithium-ion batteries. This reduces the density of the anode active material layer, and in severe cases, can even lead to peeling and breakage, significantly degrading the performance of the lithium-ion battery.

[0004] Various attempts have been made to improve the properties of silicon-based materials, such as Si / carbon composites. However, their complex manufacturing processes and low yields have hindered their commercialization. Therefore, there is an urgent need to develop a lithium-ion battery that utilizes silicon-based materials as the negative electrode active material to achieve comprehensive performance. Summary of the Invention

[0005] In order to improve the energy density of lithium batteries while ensuring excellent rate performance and cycle performance, this invention provides a negative electrode active material and its application.

[0006] In a first aspect, the present invention provides a negative electrode active material, which adopts the following technical solution:

[0007] A negative electrode active material, comprising carbon materials and silicon-based materials;

[0008] The carbon material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, and graphene.

[0009] The chemical formula of the silicon-based material is X. a Si b Y cX includes at least one of P, As, Se, B, Ga, Mg, Al, Zn, and Li, Y includes at least one of O and C, and a, b, and c satisfy 0≤a≤8, 0≤c≤10, 1≤(a+b)≤10, and 2≤(b+c)≤10.

[0010] First, the silicon-based material doped with the aforementioned elements forms more lithium intercalation sites, which helps to improve the energy density of lithium batteries. The silicon-based material in this invention, when mixed with carbon materials, can significantly improve the energy density of lithium batteries, with the highest energy density reaching 400Wh / kg. While the volume change of silicon-based materials is large during lithium intercalation, the negative electrode active material in this invention can remain within a reasonable volume expansion range. This is because, on the one hand, by doping the silicon-based material with the aforementioned elements and controlling the numerical range of a, b, and c while satisfying the aforementioned inequalities, the silicon-based material can have a stable lattice, significantly reducing the lattice expansion of the silicon-based material caused by lithium ion intercalation, thereby improving the charge-discharge stability of lithium batteries and helping to improve the cycle performance of lithium batteries. On the other hand, the negative electrode active material in this invention is also combined with carbon materials, which have small expansion. When mixed with silicon-based materials, the overall expansion of the negative electrode active material can be reduced. Second, the doping elements introduce shallow donor or acceptor levels into silicon, which can be intuitively understood as adding a springboard between the valence band and conduction band, facilitating the transition of electrons or holes from the valence band to the conduction band, thereby reducing the resistivity of silicon-based materials. This helps to further improve the cycle performance of lithium batteries using silicon-containing anodes. Third, due to the atomic orbital hybridization of the doping elements, the conductivity of the anode active material is also improved, reducing the impact of silicon-based materials on the overall conductivity of the anode active material, which helps to improve the rate performance of lithium batteries. Fourth, when Y in the silicon-based material is O, the volume change of silicon can be restricted by the framework of silicon oxide, thereby further improving the cycle stability of silicon-based materials; while when Y in the silicon-based material is C, since carbon expansion is less than silicon expansion, the volume change of silicon-based materials during charge and discharge can be mitigated, thereby improving the cycle stability of silicon-based materials. At the same time, since carbon materials have good conductivity, the conductivity of silicon-based materials can also be further improved. In summary, the silicon-containing anode active material of this invention can achieve both high energy density and excellent rate performance.

[0011] Preferably, a and c satisfy 0.1≤a≤8 and 0.1≤c≤8.

[0012] Preferably, when X includes at least one of As, Se, B, Ga, a, b, and c satisfy 1≤a≤4, 1≤c≤3, 1≤(a+b)≤7, and 2≤(b+c)≤8.

[0013] By further limiting the types of X to include As, Se, B, and Ga, it is helpful to improve the structural stability of silicon-based anode materials and improve the rate performance of lithium batteries.

[0014] Preferably, when X includes at least one of P, Mg, Al, Zn, and Li, a, b, and c satisfy 2≤a≤6, 1≤c≤5, 1≤(a+b)≤9, and 2≤(b+c)≤6.

[0015] By further limiting the types of X to include P, Mg, Al, Zn, and Li, it is helpful to form more lithium intercalation potentials in silicon-based materials, which is more conducive to improving the energy density of lithium batteries. More lithium intercalation sites are formed, and the energy density of the material is improved. At the same time, due to the orbital hybridization of the atoms of the doping elements, the conductivity of the material is improved, and the rate performance is further improved.

[0016] Preferably, when Y is O in the silicon-based material, the silicon-based material is prepared by a method including the following steps: mechanically ball-milling silicon oxide to obtain silicon particles with a particle size of 50-500 nm, mixing dopant element powder with high-purity silicon by high-speed ball milling, and calcining at 900-1200°C to obtain the silicon-based material;

[0017] When Y is C in the silicon-based material, the silicon-based material is prepared by a method including the following steps: high-purity silicon is mechanically ball-milled to obtain silicon particles with a particle size of 50-500 nm; dopant element powder is mixed with high-purity silicon by high-speed ball milling and calcined at 900-1200 °C to obtain doped silicon material; then the doped silicon material is dispersed and mixed with carbon coating agent by high-speed dispersion using a fusion machine and calcined at 1000-1500 °C to obtain the silicon-based material; wherein, the carbon coating agent includes at least one of asphalt, heavy oil, and phenolic resin.

[0018] Preferably, when the carbon material includes at least one of artificial graphite and natural graphite, Y is 0 or C.

[0019] Since graphite is an ordered layered material, it has a high initial coulombic efficiency. However, its interlayer expansion is large during the charge and discharge process. By controlling Y to be O or C, silicon-based materials can be combined with graphite materials to reduce the initial efficiency loss to a certain extent.

[0020] Preferably, when the carbon material includes at least one of soft carbon, hard carbon, mesophase carbon microspheres, and graphene, Y is C.

[0021] Because soft carbon, hard carbon, mesophase carbon microspheres, and graphene have good disordered or porous structures, they have excellent rate performance, but the energy density of the above carbon materials is low. When Y is C, the above carbon materials are used in combination with SiC materials, which can effectively improve the energy density of lithium batteries.

[0022] Preferably, when the carbon material includes at least one of artificial graphite and natural graphite, the carbon material has a D50 of 5-18 μm, (D90-D10) / D50 ≤ 3, and a specific surface area of ​​0.5-3.0 m². 2 / g.

[0023] Preferably, when the carbon material includes at least one of soft carbon, hard carbon, mesophase carbon microspheres, and graphene, the carbon material has a D50 of 0.5-20 μm, 1 ≤ (D90-D10) / D50 ≤ 5, and a specific surface area of ​​1.5-5.0 m². 2 / g.

[0024] By selecting carbon materials with appropriate particle sizes based on their expansion degree and pairing them with silicon-based anode materials, materials with low expansion degrees, such as soft carbon, hard carbon, mesophase carbon microspheres, and graphene, exhibit a wide particle size distribution. Larger carbon particles can form more stable containment spaces, providing a buffer zone for the expansion of silicon-based materials and reducing the expansion deformation of the anode active material layer. Smaller carbon particles can be distributed among silicon-based material particles, forming a good conductive network and improving the conductivity of the anode active material layer. Therefore, by controlling the particle size (D50), particle size concentration, and specific surface area of ​​different types of carbon materials, the compatibility between carbon and silicon-based materials can be improved, forming an anode active material layer with suitable tortuosity. This significantly increases the lithium-ion transport speed at the anode, avoids lithium dendrite formation at the anode, and improves both the rate performance and cycle stability of the lithium battery.

[0025] Preferably, the D50 of the silicon-based material is 0.05-5 μm.

[0026] By selecting silicon-based materials with appropriate particle sizes, the particle size of silicon-based materials can be controlled within a small range, resulting in shorter ion diffusion paths, which helps to improve the rate performance of lithium batteries.

[0027] Preferably, the mass ratio of the carbon material to the silicon-based material is 20-98:0.5-30.

[0028] Secondly, the present invention provides a negative electrode sheet, which adopts the following technical solution:

[0029] A negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer comprising the negative electrode active material as described in any one of claims 1-9.

[0030] Preferably, the negative electrode active material layer further includes a conductive agent and a binder; the conductive agent includes at least one of Ketjen black, acetylene black, carbon fiber VGCF, and carbon nanotubes CNT; the binder includes at least one of polyvinylidene fluoride PVDF, carboxymethyl cellulose CMC, and polyacrylic acid PAA.

[0031] Preferably, when the carbon material includes at least one of artificial graphite and natural graphite, the mass ratio of the carbon material, the silicon-based material, the conductive agent, and the binder is 70-98:0.5-25:0.1-5:0.1-6.0.

[0032] Preferably, when the carbon material includes at least one of soft carbon, hard carbon, mesophase carbon microspheres, and graphene, the mass ratio of the carbon material, the silicon-based material, the conductive agent, and the binder is 30-90:0.5-30:0.1-5:0.1-6.0.

[0033] Preferably, the porosity of the negative electrode active material layer is 10%-70%.

[0034] Preferably, the ratio of the D50 of the silicon-based material to the thickness of the negative electrode active material layer in the negative electrode sheet is 0.0002-0.8:1.

[0035] By controlling the ratio of the D50 of the silicon-based material to the thickness of the negative electrode active material layer, the expansion effect generated by the silicon-based active material during cycling not only does not negatively affect the structural stability of the negative electrode active material layer, but also generates a porous structure in the negative electrode active material layer that facilitates ion transport, thereby improving the ion transport performance between the positive and negative electrodes and thus improving the rate performance and cycle performance of the lithium battery.

[0036] Preferably, the areal density of the negative electrode sheet is 180-500 g / m³. 2 .

[0037] Thirdly, the present invention provides a lithium battery, which adopts the following technical solution:

[0038] A lithium battery includes a positive electrode, a separator, an electrolyte, and a negative electrode as described above. Detailed Implementation

[0039] To better understand and implement this invention, the technical solution of the present invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0041] Unless otherwise stated, all numerical values ​​for the amounts of expressed components, reaction conditions, etc., used in the specification and claims are to be understood as being modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values ​​that can be varied to obtain the desired performance.

[0042] The word “and / or” as used in this article refers to one or all of the elements mentioned.

[0043] The terms "include" and "contain" as used in this article cover both cases where only the mentioned elements exist and cases where there are other unmentioned elements in addition to the mentioned elements.

[0044] All percentages in this invention are weight percentages, unless otherwise stated.

[0045] Unless otherwise stated, the terms “a,” “an,” “an,” and “the” as used in this specification are intended to include “at least one” or “one or more.” For example, “a component” refers to one or more components, and therefore more than one component may be considered and may be employed or used in the implementation of the described embodiments.

[0046] Example 1

[0047] 1. Preparation of negative electrode active materials

[0048] The negative electrode active materials include carbon materials and silicon-based materials in a mass ratio of 70:5;

[0049] The carbon material is artificial graphite, with a particle size D50 of 6 μm, (D90-D10) / D50 = 2.2, and a specific surface area of ​​2.8 m². 2 / g;

[0050] The chemical formula of silicon-based materials is X a Si b Y c X is As, Y is O, a = 0.1, c = 0.1, (a+b) = 9, (b+c) = 9; the D50 of the silicon-based material is 0.2 μm.

[0051] 2. Preparation of negative electrode sheet

[0052] The negative electrode slurry was prepared as follows: The above-mentioned negative electrode active material (the mass ratio of carbon material and silicon-based material is 70:5), conductive agent acetylene black, thickener CMC, and binder SBR were added to a vacuum mixer in a mass ratio of 70:5:0.2:0.2 and mixed. Then, deionized water was added to the resulting mixture, and the mixture was stirred under vacuum until it became homogeneous, thereby obtaining the negative electrode slurry of this embodiment.

[0053] The above-mentioned negative electrode slurry is uniformly coated on both surfaces of the negative electrode current collector copper foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a negative electrode semi-finished product is obtained. Then, the negative electrode semi-finished product is cold-pressed and cut to obtain the negative electrode sheet to be assembled.

[0054] 3. Preparation of positive electrode sheet

[0055] The positive electrode slurry was prepared as follows: the positive electrode active material (lithium iron phosphate), the conductive agent acetylene black, and the binder PVDF were added to a vacuum mixer at a mass ratio of 97.9:0.9:1.2 and mixed. Then, the solvent NMP was added to the mixed slurry, and the mixed slurry was stirred until it was homogeneous under the action of the vacuum mixer, thereby obtaining the positive electrode slurry of this embodiment.

[0056] The above-mentioned positive electrode slurry is uniformly coated on both surfaces of the positive electrode current collector aluminum foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a positive electrode semi-finished product is obtained. Then, the positive electrode semi-finished product is cold-pressed and cut to obtain the positive electrode sheet to be assembled.

[0057] 4. Lithium-ion battery assembly

[0058] Commercially available polyethylene film is used as the separator for the lithium-ion battery, and a commercially available electrolyte suitable for 3.65V (upper charging voltage limit) battery system is used as the electrolyte. The above-mentioned positive electrode sheet, negative electrode sheet and separator are wound together to obtain bare cell. The bare cell is then packaged, injected with electrolyte, left to stand, formed and tested for capacity to obtain the finished battery.

[0059] Example 2

[0060] 1. Preparation of negative electrode active materials

[0061] The negative electrode active materials include carbon materials and silicon-based materials in a mass ratio of 95:20;

[0062] The carbon material is natural graphite, with a particle size D50 of 16 μm, (D90-D10) / D50 = 2.8, and a specific surface area of ​​0.8 m². 2 / g;

[0063] The chemical formula of silicon-based materials is X a Si b Yc X is P, Y is C, a = 8, c = 8, (a+b) = 10, (b+c) = 10; the D50 of silicon-based materials is 0.05-5μm.

[0064] 2. Preparation of negative electrode sheet

[0065] The negative electrode slurry was prepared as follows: The above-mentioned negative electrode active material (the mass ratio of carbon material to silicon-based material is 95:20), conductive agent acetylene black, thickener CMC, and binder SBR were added to a vacuum mixer at a mass ratio of 95:20:4.5:5.8 and mixed. Then, deionized water was added to the resulting mixture, and the mixture was stirred under vacuum until it became homogeneous, thereby obtaining the negative electrode slurry of this embodiment.

[0066] The above-mentioned negative electrode slurry is uniformly coated on both surfaces of the negative electrode current collector copper foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a negative electrode semi-finished product is obtained. Then, the negative electrode semi-finished product is cold-pressed and cut to obtain the negative electrode sheet to be assembled.

[0067] 3. Preparation of positive electrode sheet

[0068] The positive electrode slurry was prepared as follows: the positive electrode active material (lithium iron phosphate), the conductive agent acetylene black, and the binder PVDF were added to a vacuum mixer at a mass ratio of 97.9:0.9:1.2 and mixed. Then, the solvent NMP was added to the mixed slurry, and the mixed slurry was stirred until it was homogeneous under the action of the vacuum mixer, thereby obtaining the positive electrode slurry of this embodiment.

[0069] The above-mentioned positive electrode slurry is uniformly coated on both surfaces of the positive electrode current collector aluminum foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a positive electrode semi-finished product is obtained. Then, the positive electrode semi-finished product is cold-pressed and cut to obtain the positive electrode sheet to be assembled.

[0070] 4. Lithium-ion battery assembly

[0071] Commercially available polyethylene film is used as the separator for the lithium-ion battery, and a commercially available electrolyte suitable for 3.65V (upper charging voltage limit) battery system is used as the electrolyte. The above-mentioned positive electrode sheet, negative electrode sheet and separator are wound together to obtain bare cell. The bare cell is then packaged, injected with electrolyte, left to stand, formed and tested for capacity to obtain the finished battery.

[0072] Example 3

[0073] 1. Preparation of negative electrode active materials

[0074] The negative electrode active materials include carbon materials and silicon-based materials in a mass ratio of 90:30;

[0075] The carbon material is hard carbon, with a particle size D50 of 17 μm, (D90-D10) / D50 = 3, and a specific surface area of ​​1.5 m². 2 / g;

[0076] The chemical formula of silicon-based materials is X a Si b Y c X is Mg, Y is C, a = 0.5, c = 1.5, (a+b) = 1, (b+c) = 2; the D50 of the silicon-based material is 5 μm.

[0077] 2. Preparation of negative electrode sheet

[0078] The negative electrode slurry was prepared as follows: The above-mentioned negative electrode active material (the mass ratio of carbon material and silicon-based material is 90:30), conductive agent acetylene black, thickener CMC, and binder SBR were added to a vacuum mixer in a mass ratio of 90:30:5:6 and mixed. Then, deionized water was added to the resulting mixture, and the mixture was stirred until homogeneous under the action of a vacuum mixer to obtain the negative electrode slurry of this embodiment.

[0079] The above-mentioned negative electrode slurry is uniformly coated on both surfaces of the negative electrode current collector copper foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a negative electrode semi-finished product is obtained. Then, the negative electrode semi-finished product is cold-pressed and cut to obtain the negative electrode sheet to be assembled.

[0080] 3. Preparation of positive electrode sheet

[0081] The positive electrode slurry was prepared as follows: the positive electrode active material (lithium iron phosphate), the conductive agent acetylene black, and the binder PVDF were added to a vacuum mixer at a mass ratio of 97.9:0.9:1.2 and mixed. Then, the solvent NMP was added to the mixed slurry, and the mixed slurry was stirred until it was homogeneous under the action of the vacuum mixer, thereby obtaining the positive electrode slurry of this embodiment.

[0082] The above-mentioned positive electrode slurry is uniformly coated on both surfaces of the positive electrode current collector aluminum foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a positive electrode semi-finished product is obtained. Then, the positive electrode semi-finished product is cold-pressed and cut to obtain the positive electrode sheet to be assembled.

[0083] 4. Lithium-ion battery assembly

[0084] Commercially available polyethylene film is used as the separator for the lithium-ion battery, and a commercially available electrolyte suitable for 3.65V (upper charging voltage limit) battery system is used as the electrolyte. The above-mentioned positive electrode sheet, negative electrode sheet and separator are wound together to obtain bare cell. The bare cell is then packaged, injected with electrolyte, left to stand, formed and tested for capacity to obtain the finished battery.

[0085] Example 4

[0086] 1. Preparation of negative electrode active materials

[0087] The negative electrode active materials include carbon materials and silicon-based materials in a mass ratio of 30:1;

[0088] The carbon material is soft carbon, with a particle size D50 of 1.5 μm, (D90-D10) / D50 = 1, and a specific surface area of ​​5 m². 2 / g;

[0089] The chemical formula of silicon-based materials is X a Si b Y c X is Se, Y is C, a = 1, c = 1, (a+b) = 2, (b+c) = 2; the D50 of the silicon-based material is 0.1 μm.

[0090] 2. Preparation of negative electrode sheet

[0091] The negative electrode slurry was prepared as follows: The above-mentioned negative electrode active material (the mass ratio of carbon material and silicon-based material is 30:1), conductive agent acetylene black, thickener CMC, and binder SBR were added to a vacuum mixer in a mass ratio of 30:1:0.1:0.1 and mixed. Then, deionized water was added to the resulting mixture, and the mixture was stirred under vacuum until it became homogeneous, thereby obtaining the negative electrode slurry of this embodiment.

[0092] The above-mentioned negative electrode slurry is uniformly coated on both surfaces of the negative electrode current collector copper foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a negative electrode semi-finished product is obtained. Then, the negative electrode semi-finished product is cold-pressed and cut to obtain the negative electrode sheet to be assembled.

[0093] 3. Preparation of positive electrode sheet

[0094] The positive electrode slurry was prepared as follows: the positive electrode active material (lithium iron phosphate), the conductive agent acetylene black, and the binder PVDF were added to a vacuum mixer at a mass ratio of 97.9:0.9:1.2 and mixed. Then, the solvent NMP was added to the mixed slurry, and the mixed slurry was stirred until it was homogeneous under the action of the vacuum mixer, thereby obtaining the positive electrode slurry of this embodiment.

[0095] The above-mentioned positive electrode slurry is uniformly coated on both surfaces of the positive electrode current collector aluminum foil. After drying at room temperature, it is transferred to an oven for further drying. After drying in the oven, a positive electrode semi-finished product is obtained. Then, the positive electrode semi-finished product is cold-pressed and cut to obtain the positive electrode sheet to be assembled.

[0096] 4. Lithium-ion battery assembly

[0097] Commercially available polyethylene film is used as the separator for the lithium-ion battery, and a commercially available electrolyte suitable for batteries with a charging upper limit of 3.651SeV is used as the electrolyte. The above-mentioned positive electrode, negative electrode and separator are wound together to obtain bare cells. The bare cells are then packaged, injected with electrolyte, left to stand, formed and tested for capacity to obtain the finished battery.

[0098] Example 5

[0099] The difference between this embodiment and Example 1 lies in the preparation of the negative electrode active material, specifically:

[0100] The negative electrode active materials include carbon materials and silicon-based materials in a mass ratio of 70:5;

[0101] The carbon material is artificial graphite, with a particle size D50 of 6 μm, (D90-D10) / D50 = 2.2, and a specific surface area of ​​2.8 m². 2 / g;

[0102] The chemical formula of silicon-based materials is X a Si b Y c X is As, Y is O, a = 1, c = 3, (a+b) = 6, (b+c) = 8; the D50 of the silicon-based material is 0.2 μm.

[0103] All other steps and parameter settings are consistent with those in Example 1.

[0104] Example 6

[0105] The difference between this embodiment and Example 1 lies in the preparation of the negative electrode active material, specifically:

[0106] The negative electrode active materials include carbon materials and silicon-based materials in a mass ratio of 70:5;

[0107] The carbon material is artificial graphite, with a particle size D50 of 6 μm, (D90-D10) / D50 = 2.2, and a specific surface area of ​​2.8 m². 2 / g;

[0108] The chemical formula of silicon-based materials is X a Si b Y c X is As, Y is O, a = 1, c = 2, (a+b) = 7, (b+c) = 8; the D50 of the silicon-based material is 0.2 μm.

[0109] All other steps and parameter settings are consistent with those in Example 1.

[0110] Example 7

[0111] The difference between this embodiment and Embodiment 3 lies in the preparation of the negative electrode active material, specifically:

[0112] The negative electrode active materials include carbon materials and silicon-based materials in a mass ratio of 90:30;

[0113] The carbon material is soft carbon, with a particle size D50 of 1.5 μm, (D90-D10) / D50 = 1, and a specific surface area of ​​5 m². 2 / g;

[0114] The chemical formula of silicon-based materials is X a Si b Y c X is Mg, Y is C, a = 5, c = 2, (a+b) = 9, (b+c) = 6; the D50 of the silicon-based material is 0.1 μm.

[0115] All other steps and parameter settings are consistent with those in Example 3.

[0116] Example 8

[0117] The difference between this embodiment and Embodiment 3 lies in the preparation of the negative electrode active material, specifically:

[0118] The negative electrode active materials include carbon materials and silicon-based materials in a mass ratio of 90:30;

[0119] The carbon material is soft carbon, with a particle size D50 of 1.5 μm, (D90-D10) / D50 = 1, and a specific surface area of ​​5 m². 2 / g;

[0120] The chemical formula of silicon-based materials is X a Si b Y c X is Mg, Y is C, a = 2, c = 1, (a+b) = 3, (b+c) = 2; the D50 of the silicon-based material is 0.1 μm.

[0121] All other steps and parameter settings are consistent with those in Example 3.

[0122] Example 9

[0123] The difference between this embodiment and Embodiment 1 is that D50 is 1.5 μm, (D90-D10) / D50 = 1, and the specific surface area is 5 m². 2 / g. All other steps and parameter settings are consistent with those in Example 1.

[0124] Example 10

[0125] The difference between this embodiment and Embodiment 3 is that Y in the silicon-based material is O. All other steps and parameter settings remain the same as in Embodiment 3.

[0126] Example 11

[0127] The difference between this embodiment and Embodiment 3 is that the particle size D50 of the carbon material is 6 μm, (D90-D10) / D50 = 0.5, and the specific surface area is 1.2 m². 2 / g. All other steps and parameter settings are consistent with those in Example 3.

[0128] Example 12

[0129] The difference between this embodiment and Embodiment 1 is that the ratio of the D50 of the silicon-based material to the total thickness of the negative electrode active material layer in the negative electrode sheet is 0.9:1. All other steps and parameter settings remain the same as in Embodiment 1.

[0130] Example 13

[0131] The difference between this embodiment and Embodiment 1 is that the ratio of the D50 of the silicon-based material to the total thickness of the negative electrode active material layer in the negative electrode sheet is 0.0001:1. All other steps and parameter settings remain the same as in Embodiment 1.

[0132] Comparative Example 1

[0133] The difference between this comparative example and Example 1 is that X is not doped into the silicon-based material. All other steps and parameter settings remain the same as in Example 1.

[0134] Comparative Example 2

[0135] The difference between this comparative example and Example 1 is that in the silicon-based material, a = 4, c = 5, (a+b) = 11, and (b+c) = 12. All other steps and parameter settings are consistent with Example 1.

[0136] Test methods

[0137] I. Electrode Areal Density Test

[0138] The areal density of the negative electrode in the above embodiments and comparative examples was tested. The specific test method was as follows: take an anode with a standard area (S), dry it, and weigh it by an electronic balance to obtain a weight of m, and its areal density is m / S.

[0139] II. Coating Porosity Test

[0140] The porosity of the negative electrode active material layer on the negative electrode sheet in the above embodiments and comparative examples was tested. The specific test method was as follows: a certain amount of electrode sheet was taken and baked in a vacuum drying oven for 8 hours at a baking temperature of 70°C. The baked electrode sheet was placed in a mercury porosimeter and the pressure was set to 200 MPa. The porosity was calculated by measuring the pore volume under different external pressures.

[0141] III. Electrode Expansion Rate Test

[0142] The initial full-charge expansion rate of the negative electrode active material layer on the negative electrode sheet in the above embodiments and comparative examples was tested. The specific test method was as follows: the initial thickness of the negative electrode sheet was recorded as d0; the lithium battery was placed in an environment of 25°C, and after being fully charged with a current of 0.5C, the battery was disassembled and the anode thickness was tested and recorded as d1; the initial full-charge expansion rate of the negative electrode sheet = (d1-d0) / d0×100%.

[0143] IV. Energy Density Test

[0144] The energy density of the lithium batteries in the above embodiments and comparative examples was tested. The specific test method was as follows: the weight of the test battery was weighed and recorded as m; the battery was placed in a fixture and a force of 3000N was applied. The single battery was charged to 3.65V with a constant current of 0.5C, and then left to rest for 30 minutes. It was then discharged to 2.5V with a constant current of 0.5C and left to rest for 30 minutes. This cycle was repeated 3 times. The energy E (average value of the three cycles) was calculated. The discharge energy density = E / m (in Wh / kg).

[0145] V. Cyclic Performance Testing

[0146] The lithium batteries in the above embodiments and comparative examples were subjected to cycle performance tests. The specific test method was as follows: at 25°C and with the voltage range set to 2.5-3.65V, the prepared batteries were subjected to charge-discharge cycle tests at a current of 1C for 1000 cycles, and the cycle capacity retention rate was recorded.

[0147] VI. Ratio Performance Test

[0148] The lithium batteries in the above embodiments and comparative examples were subjected to rate performance testing. The specific testing method was as follows: at 25°C and with the voltage range set to 2.5-3.65V, the prepared batteries were charged with constant current and constant voltage at a 3C current. The cutoff voltage was 3.65V. The constant current charging capacity was recorded as C0, the total charging capacity as C1, and the 3C charging constant current ratio = C0 / C1 × 100%.

[0149] Table 1

[0150]

[0151] Based on Examples 1-4, Comparative Examples 1-2, and Table 1, it can be seen that the carbon material and silicon-based material of the present invention are combined. Appropriate particle sizes of carbon materials are selected to combine with silicon-based materials according to different types of carbon materials. Furthermore, suitable elements are doped into the silicon-based material. The silicon-based material doped with these elements forms more lithium intercalation sites, which helps to improve the energy density of the lithium battery, with the highest energy density reaching 400Wh / kg. Moreover, the silicon-based material doped with these elements has a more stable crystal structure. Combined with the carbon material, which has weak self-expansion properties, this allows the negative electrode active material in the present invention to be controlled within a reasonable volume expansion range. At the same time, the doped elements can reduce the resistivity of the silicon-based material, all of which contribute to improving the cycle performance and rate performance of the lithium battery.

[0152] Combining Examples 1, 5-6, 3, 7-8 and Table 1, it can be seen that by further adjusting the values ​​of a, b, and c in the silicon-based material according to the different doping elements, the rate performance and cycle performance of the lithium battery can be further improved.

[0153] Based on Examples 1 and 9 and Table 1, it can be seen that when the doping elements in the silicon-based material do not match the values ​​of a, b, and c, it will affect the structural stability of the silicon-based material to a certain extent, and will be detrimental to the improvement of the conductivity of the silicon-based material, which will affect the cycle performance and rate performance of the lithium battery to a certain extent.

[0154] Based on Examples 3, 10-11 and Table 1, it can be seen that when the carbon material is artificial graphite but its particle size parameters do not meet the specified range, or when the carbon material is hard carbon but its particle size parameters do not meet the specified range, the cycle performance of the lithium battery decreases. This is because the silicon-based material cannot form a good matching effect with the carbon material, which is not conducive to forming a negative electrode active material layer with a suitable pore structure, and will be detrimental to improving the cycle performance of the lithium battery.

[0155] Based on Examples 3, 12-13, and Table 1, it can be seen that when the ratio of D50 of the silicon-based material to the total thickness of the negative electrode active material layer is too large, the expansion of the silicon negative electrode active material will affect the structural stability of the pore structure in the negative electrode active material layer. In severe cases, it may even cause deformation and cracks in the negative electrode active material layer, which will affect the cycle performance of the lithium battery. When the ratio of D50 of the silicon-based material to the total thickness of the negative electrode active material layer is too small, it is not conducive to the formation of a pore structure in the negative electrode active material layer that facilitates the transport of lithium ions and electrons, affecting the ion transport performance between the positive and negative electrodes, and thus hindering the improvement of the rate performance and cycle performance of the lithium battery.

[0156] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A negative electrode active material, characterized in that: Including carbon-based materials and silicon-based materials; When the carbon material includes at least one of soft carbon, hard carbon, mesophase carbon microspheres, and graphene, the carbon material has a D50 of 0.5-20 μm, 1 ≤ (D90-D10) / D50 ≤ 5, and a specific surface area of ​​1.5-5.0 m². 2 / g; The chemical formula of the silicon-based material is X. a Si b Y c X includes at least one of P, Mg, Al, Zn, and Li, Y is C, and a, b, and c satisfy 2≤a≤6, 1≤c≤5, 1≤(a+b)≤9, and 2≤(b+c)≤6. The D50 of the silicon-based material is 0.05-5μm. The mass ratio of the carbon material to the silicon-based material is 30-90:5-30.

2. A negative electrode sheet, characterized in that: The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material as described in claim 1.

3. The negative electrode sheet according to claim 2, characterized in that: The porosity of the negative electrode active material layer is 10%-70%.

4. The negative electrode sheet according to claim 2, characterized in that: The ratio of the D50 of the silicon-based material to the thickness of the negative electrode active material layer in the negative electrode sheet is 0.0002-0.8:

1.

5. The negative electrode sheet according to claim 2, characterized in that: The areal density of the negative electrode is 180-500 g / m³. 2 .

6. A lithium battery, characterized in that: It includes a positive electrode, a separator, an electrolyte, and a negative electrode as described in any one of claims 2-5.

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