Silicon-based negative electrode sheet, secondary battery and power-using device

Abstract

The present invention provides a silicon-based negative electrode plate, comprising a negative electrode current collector, a first active material layer and a second active material layer; the first negative electrode active material in the first active material layer comprises a first silicon-based material and a first carbon-based material; the second negative electrode active material in the second active material layer comprises a second silicon-based material and a second carbon-based material; wherein the ratio of the particle size D50 of the first silicon-based material to the particle size D50 of the second silicon-based material is 1.1 to 4, and the particle size D50 of the second carbon-based material is greater than the particle size D50 of the second silicon-based material; the ratio of the particle size D10 of the first silicon-based material to the particle size D10 of the second silicon-based material is 1.1 to 5; the ratio of the surface density of the first active material layer to the surface density of the second active material layer is 0.5 to 6. Compared with the prior art, the secondary battery containing the negative electrode plate of the present invention has high energy density and good fast charging performance and cycle performance.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and in particular to a silicon-based negative electrode plate, a secondary battery and an electrical device. Background Art

[0002] New energy vehicles are an industry that the automotive industry will vigorously develop in the future. Secondary batteries are widely used in the new energy vehicle industry because of their advantages such as high energy density, no memory effect, and long service life. However, as the requirements for the cruising range of new energy vehicles increase, the energy density allocated to the battery needs to be higher. Therefore, it is urgent to develop new positive and negative electrode materials for lithium-ion batteries. At present, the commonly used negative electrode materials on the market are graphite-based negative electrodes. The theoretical gram capacity of graphite is 372mAh / g. With the increasing maturity of industrial processes, high-end graphite can now reach 360-365mAh / g, which is very close to the theoretical capacity. However, due to the limitations of the material itself, the energy density of 280Wh / kg is almost the limit, and it is difficult to meet people's growing demand for higher energy density. The theoretical gram capacity of silicon materials is 4200mAh / g, and the advantages of relatively low delithiation potential (0.4V), environmental friendliness, and abundant resources are considered to be very potential for the next generation of high energy density lithium-ion battery negative electrode materials.

[0003] At present, many manufacturers have begun to use a mixed system of silicon dioxide (SiO) and graphite as a negative electrode material for high energy density lithium-ion batteries. However, there are many problems in the use of SiO. If SiO is used as a negative electrode active material, the volume expansion of SiO can reach 180% when the battery is fully charged. In order to improve the expansion problem of silicon-based materials, people have proposed various material-oriented solutions such as nano-silicon, carbon coating, metal doping, core-shell structure, etc., and at the same time, they have solved the system-oriented solutions such as conductive agents, electrolytes, and binders, and the expansion has been improved to a certain extent. However, under the premise of ensuring energy density, the fast charging performance is poor. The higher the energy density, the worse the fast charging performance. Some solutions use SiO materials with a small particle size D50, but although small particle size SiO can improve the fast charging capability, there are more particle expansion side reactions in the later charging and discharging process, and the cycle performance is seriously reduced, and it still cannot be used as a negative electrode.

[0004] In view of this, it is indeed necessary to provide a technical solution to the above problems. Summary of the invention

[0005] One of the purposes of the present invention is to provide a silicon-based negative electrode plate to address the deficiencies of the prior art. The use of the negative electrode plate can make the secondary battery have high energy density while having excellent fast charging performance and cycle performance.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A silicon-based negative electrode plate, comprising:

[0008] Anode current collector;

[0009] a first active material layer, coated on at least one surface of the negative electrode current collector, comprising a first negative electrode active material; the first negative electrode active material comprises a first silicon-based material and a first carbon-based material;

[0010] A second active material layer, coated on a surface of the first active material layer away from the negative electrode current collector, comprising a second negative electrode active material; the second negative electrode active material comprises a second silicon-based material and a second carbon-based material;

[0011] Among them, the ratio of the particle size D50 of the first silicon-based material to the particle size D50 of the second silicon-based material is 1.1-4, and the particle size D50 of the second carbon-based material is larger than the particle size D50 of the second silicon-based material; the ratio of the particle size D10 of the first silicon-based material to the particle size D10 of the second silicon-based material is 1.1-5; the ratio of the surface density of the first active material layer to the surface density of the second active material layer is 0.5-6.

[0012] Preferably, the ratio of the particle size D50 of the first silicon-based material to the particle size D50 of the second silicon-based material is 1.5-2.5; the ratio of the particle size D10 of the first silicon-based material to the particle size D10 of the second silicon-based material is 1.2-3; the ratio of the surface density of the first active material layer to the surface density of the second active material layer is 1-4.

[0013] Preferably, the particle size D50 of the first silicon-based material is 9 to 14 μm, the particle size D50 of the second silicon-based material is 4 to 8 μm, and the particle size D50 of the second carbon-based material is 8 to 14 μm.

[0014] Preferably, the particle size D10 of the first silicon-based material is 3-5 μm, the particle size D10 of the second silicon-based material is 1-4 μm, and the particle size D10 of the second carbon-based material is 2-4 μm.

[0015] Preferably, the surface density of the first active material layer is 0.007 to 0.025 g / cm 2 The surface density of the second active material layer is 0.007 to 0.025 g / cm 2 .

[0016] Preferably, the particle size concentration N of the first silicon-based material is 1 is 0 to 2, and the particle size concentration N of the second silicon-based material is 2 It is 0 to 2.

[0017] Preferably, the specific surface area of ​​the first silicon-based material is 0.8 to 2 m 2 / g, the specific surface area of ​​the second silicon-based material is 1.5 to 3.5 m 2 / g.

[0018] Preferably, the mass of the first silicon-based material is 3-80% of the mass of the first negative electrode active material; the mass of the second silicon-based material is 3-80% of the mass of the second negative electrode active material.

[0019] Preferably, the first silicon-based material and the second silicon-based material are each independently selected from SiO x , Li-containing SiO x 、SiO containing magnesium x At least one of 0<x≤2; wherein the lithium-containing SiO x The mass proportion of lithium in the SiO2 is 0-15%, and the mass proportion of magnesium in the SiO2 is 0-15%. x The mass proportion of magnesium in the carbon-based material is 0-15%; the first carbon-based material and the second carbon-based material are independently selected from at least one of artificial graphite, natural graphite, hard carbon, graphene, and soft carbon.

[0020] The second object of the present invention is to provide a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet is the silicon-based negative electrode sheet described in any one of the above items.

[0021] A third object of the present invention is to provide an electrical device comprising the secondary battery described above.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: the silicon-based negative electrode plate provided by the present invention adopts a double coating layer design, and both the first active material layer and the second active material layer contain silicon-based materials and carbon-based materials. On the one hand, the silicon-based material ensures the high energy density performance of the battery, and on the other hand, the silicon-based material and the carbon-based material with particle size that meets the requirements are selected as the negative electrode active material, and the surface density setting between the two coating layers is adjusted to ensure the fast charging performance and cycle performance of the battery. The second active material layer of the negative electrode plate designed in this way has a high porosity. During the charging and discharging process of the battery, ions can quickly pass through the second active material layer to the first active material layer to undergo lithium insertion reaction, and the silicon-based material in the second active material layer can take over the ions that have not completely reacted in the first active material layer under the condition of a higher rate of charging, avoiding the metal precipitation situation under a high rate current, and ensuring the fast charging performance of the battery; at the same time, the carbon-based material in the second active material layer can also play the purpose of inhibiting the expansion of the small-particle silicon-based material in this layer, ensuring the long cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1This is one of the structural schematic diagrams of the silicon-based negative electrode plate of the present invention.

[0024] Figure 2 This is the second structural schematic diagram of the silicon-based negative electrode plate of the present invention.

[0025] In the figure: 1 - negative electrode current collector; 2 - first active material layer; 3 - second active material layer. DETAILED DESCRIPTION

[0026] 1. Silicon-based negative electrode

[0027] The first aspect of the present invention is to provide a silicon-based negative electrode plate. Figures 1-2 As shown, it includes a negative electrode current collector 1, a first active material layer 2 coated on at least one surface of the negative electrode current collector 1, and a second active material layer 3 coated on a surface of the first active material layer 2 away from the negative electrode current collector 1.

[0028] One of the coating methods, such as Figure 1 As shown, the negative electrode sheet includes a three-layer coating structure of a negative electrode current collector 1, a first active material layer 2, and a second active material layer 3. The coating can be at least one of extrusion coating, transfer coating, and spray coating. Preferably, the coating is performed using a transfer coating machine.

[0029] The second coating method is Figure 2 As shown, the negative electrode sheet includes a five-layer coating structure of a second active material layer 3, a first active material layer 2, a negative current collector 1, a first active material layer 2, and a second active material layer 3. The coating can be at least one of extrusion coating, transfer coating, and spray coating. Preferably, a transfer coating machine is used for coating.

[0030] Among them, the first active material layer 2 includes a first negative electrode active material; the first negative electrode active material includes a first silicon-based material and a first carbon-based material; the mass of the first silicon-based material is 3-80% of the mass of the first negative electrode active material, specifically 3-5%, 5-10%, 10-15%, 15-20%, 20-25%, 25-30%, 30-35%, 35-40%, 40-45%, 45-50%, 50-55%, 55-60%, 60-65%, 65-70% or 70-80%, preferably, the content is 5-50%; the mass of the corresponding first carbon-based material is 20-97% of the mass of the first negative electrode active material, and the specific content of the two can be selected according to the actual required energy density, etc. In addition, the first active material layer 2 also includes a conductive agent and a binder, which are mixed with the first negative electrode active material in a solvent to form a slurry and then coated on the surface of the negative electrode current collector 1, and the first active material layer 2 is obtained after drying. The mass ratio of the first negative electrode active material to the conductive agent and the binder is (93-98):(1-4):(1-4).

[0031] The second active material layer 3 includes a second negative electrode active material; the second negative electrode active material includes a second silicon-based material and a second carbon-based material; the mass of the second silicon-based material is 3-80% of the mass of the second negative electrode active material, specifically 3-5%, 5-10%, 10-15%, 15-20%, 20-25%, 25-30%, 30-35%, 35-40%, 40-45%, 45-50%, 50-55%, 55-60%, 60-65%, 65-70% or 70-80%. Compared with the content of the first silicon-based material, the second silicon-based material is arranged in the second active material layer 3, located in the outer layer of the negative electrode plate, and its content can be set to be less than that of the first silicon-based material, that is, the content of the second carbon-based material is more, so that the expansion of the outer silicon-based material can be suppressed to a certain extent. The mass of the corresponding second carbon-based material is 20-97% of the mass of the second negative electrode active material, and the specific contents of the two can be selected according to the actual required energy density, etc. In addition, the second active material layer 3 also includes a conductive agent and a binder, which are mixed with the second negative electrode active material in a solvent to form a slurry, and then coated on the surface of the first active material layer 2, and dried to obtain the second active material layer 3. The mass ratio of the second negative electrode active material to the conductive agent and the binder in its layer is (93-98): (1-4): (1-4).

[0032] Specifically, the first silicon-based material and the second silicon-based material are each independently selected from SiO x , Li-containing SiO x 、SiO containing magnesium x At least one of 0<x≤2; wherein the lithium-containing SiO x The mass proportion of lithium in the SiO2 is 0-15%, and the mass proportion of magnesium in the SiO2 is 0-15%. x The mass percentage of magnesium in the carbon-based material is 0-15%; the first carbon-based material and the second carbon-based material are independently selected from at least one of artificial graphite, natural graphite, hard carbon, graphene, and soft carbon. x Can be SiO or SiO 2 .

[0033] The lithium-containing SiO x That is, pre-lithiation of silicon-based negative electrode materials. Since silicon-based materials consume a large amount of lithium to form SEI film during the first charging process, the first cycle efficiency of the battery is reduced and the lithium can be inserted and removed. By pre-lithiation of silicon-based materials, that is, replenishing lithium at the material end, the subsequent SEI film formation will consume this part of lithium, thereby improving the first efficiency of the battery. Similarly, in SiO x The presence of magnesium in the SiO2 can also improve the first cycle efficiency of silicon-based batteries and, to a certain extent, improve the expansion and conductivity of the battery. xThe mass proportion of lithium in the SiO2 is 0.1-8%. x The mass proportion of magnesium in the metal is 0.1 to 8%.

[0034] In addition, the silicon-based negative electrode plate should at least meet the following requirements: the ratio of the particle size D50 of the first silicon-based material to the particle size D50 of the second silicon-based material is 1.1-4, and the particle size D50 of the second carbon-based material is larger than the particle size D50 of the second silicon-based material; the ratio of the particle size D10 of the first silicon-based material to the particle size D10 of the second silicon-based material is 1.1-5; the ratio of the surface density of the first active material layer 2 to the surface density of the second active material layer 3 is 0.5-6.

[0035] The particle size D50 described herein refers to the particle size smaller than which 50% of the total particles are contained. The particle size D10 refers to the particle size smaller than which 10% of the total particles are contained. The particle size D90 refers to the particle size smaller than which 90% of the total particles are contained. D10, D50 and D90 of each material can be measured and screened by methods known in the art, for example, by using a laser particle size analyzer and screening with sieves of different mesh sizes.

[0036] Specifically, the ratio of the particle size D50 of the first silicon-based material to the particle size D50 of the second silicon-based material can be 1.1-1.5, 1.5-1.8, 1.8-2.0, 2.0-2.3, 2.3-2.5, 2.5-2.8, 2.8-3.0, 3.0-3.3, 3.3-3.5 or 3.5-4.0. At the same time, the second silicon-based material is selected so that its D50 is smaller than the particle size D50 of the second carbon-based material. In this way, the second carbon-based material can play a certain role in suppressing the expansion of the first silicon-based material on the one hand; on the other hand, when the second silicon-based material receives the unreacted ions of the first silicon-based material, it can also play a role in suppressing the expansion of the second silicon-based material; not only the fast charging performance of the battery is guaranteed, but also the subsequent long cycle performance is guaranteed. Compared with the negative electrode plate whose outer layer only covers the carbon-based material, the negative electrode plate of the present invention effectively guarantees the fast charging performance of the silicon-based battery, while avoiding the lithium plating problem of charging at a large rate. Compared with the single-layer coating system of silicon-based materials and carbon-based materials, the negative electrode plate of the present invention not only effectively guarantees the performance of fast charging, but also has better energy density and cycle life. Preferably, the ratio of the particle size D50 of the first silicon-based material to the particle size D50 of the second silicon-based material is 1.5 to 2.5. The ratio between the two is preferably avoided to be too large, which can also further ensure the connectivity of the first silicon-based material and the second silicon-based material for lithium insertion.

[0037] Further specifically, the particle size D50 of the first silicon-based material is 9-14 μm, specifically 9-10 μm, 10-11 μm, 11-12 μm, 12-13 μm or 13-14 μm; the particle size D50 of the second silicon-based material is 4-8 μm, specifically 4-5 μm, 5-6 μm, 6-7 μm or 7-8 μm; the particle size D50 of the second carbon-based material is 8-14 μm, specifically 8-9 μm, 9-10 μm, 10-11 μm, 11-12 μm, 12-13 μm or 13-14 μm. In addition, the particle size D50 of the first carbon-based material is also 8-14 μm, specifically 8-9 μm, 9-10 μm, 10-11 μm, 11-12 μm, 12-13 μm or 13-14 μm.

[0038] The ratio of the particle size D10 of the first silicon-based material to the particle size D10 of the second silicon-based material may be 1.1-1.5, 1.5-1.8, 1.8-2.0, 2.0-2.3, 2.3-2.5, 2.5-2.8, 2.8-3.0, 3.0-3.3, 3.3-3.5, 3.5-4.0 or 4.0-5.0. Similarly, the value of the second silicon-based material D10 remains smaller than the D10 of the first silicon-based material, which not only ensures that the first silicon-based material in the first active material layer 2 is a large particle material and the second silicon-based material in the second active material layer 3 is a small particle; and the uniformity of the distribution of each coating particle is better. Preferably, the ratio of the particle size D10 of the first silicon-based material to the particle size D10 of the second silicon-based material is 1.2-3.

[0039] More specifically, the particle size D10 of the first silicon-based material is 3-5 μm, specifically 3-4 μm or 4-5 μm; the particle size D10 of the second silicon-based material is 1-4 μm, specifically 1-2 μm, 2-3 μm or 3-4 μm; the particle size D10 of the second carbon-based material is 2-4 μm, specifically 2-3 μm or 3-4 μm. In addition, the particle size D10 of the first carbon-based material is also 2-4 μm, specifically 2-3 μm or 3-4 μm.

[0040] The second carbon-based material under the above-mentioned particle size is quite different from the second silicon-based material in overall particle size. It can be considered that the second carbon-based material is a large particle, while the second silicon-based material is a small particle. The two are mixed to form the second negative electrode active material, which has a higher porosity. It can not only keep ions passing through the second active material layer 3 quickly, but also its pores can alleviate the expansion of the first silicon-based material. When expanding, it will form an extrusion effect on the second active material layer 3, and the compaction density of the second active material layer 3 will increase accordingly. The capacity that can be stimulated by the second negative electrode active material in the future will be larger, further improving the energy density of the battery.

[0041] The first carbon-based material and the first silicon-based material under the above-mentioned particle size are similar in particle size, and the first negative electrode active material particles formed by mixing are more evenly distributed, and the embedding and extraction of ions will be more stable. In addition, as the number of charge and discharge times increases, although the first silicon-based material particles will expand, the particle size between them and the first carbon-based material will also increase, which still provides a certain gap for the embedding of ions, and to a certain extent alleviates the shortening of the cycle life caused by the expansion.

[0042] The ratio of the surface density of the first active material layer 2 to the surface density of the second active material layer 3 may be 0.5-0.8, 0.8-1.1, 1.1-1.5, 1.5-1.8, 1.8-2.0, 2.0-2.3, 2.3-2.5, 2.5-2.8, 2.8-3.0, 3.0-3.3, 3.3-3.5, 3.5-4.0, 4.0-5.0 or 5.0-6.0. Preferably, the ratio of the surface density of the first active material layer 2 to the surface density of the second active material layer 3 is 1-4. The surface density between the two layers is controlled synchronously. On the one hand, it is prevented that the surface density of the first active material is much larger than the surface density of the second active material layer 3, which results in the first active material layer 2 having too small a porosity, so that ions cannot be quickly embedded in the first active material layer 2, and the electrolyte is also difficult to enter the first active material layer 2, and the first cycle efficiency is too low; on the other hand, it is also prevented that the surface density of the first active material layer 2 is much smaller than the surface density of the second active material layer 3, which not only reduces the volume specific energy, but also affects the fast charging performance. The double-layer silicon-based negative electrode plate provided by the present invention synchronously controls the particle size of the silicon-based material and the carbon-based material of the two coatings, as well as the surface density of the two coatings, so that the secondary battery obtained has high energy density and excellent fast charging performance and cycle performance.

[0043] More preferably, the surface density of the first active material layer 2 is 0.007 to 0.025 g / cm 2 The surface density of the second active material layer 3 is 0.007 to 0.025 g / cm 2 Within the surface density range, the surface density ratio of the first active material layer 2 to the surface density of the second active material layer 3 only needs to satisfy the above range. Preferably, the surface densities of the two are similar to better ensure the cycle performance and rate performance of the battery.

[0044] More preferably, the porosity of the second active material layer 3 is 38-43%, and the porosity of the first active material layer 2 is 20-30%. To ensure that the porosity of the second active material layer 3 is greater than that of the first active material layer 2, ions can more quickly pass through the second active material layer 3 into the first active material layer 2 to undergo lithium insertion reaction, and the electrolyte can more easily infiltrate the interior of the electrode, thereby reducing the resistance of the battery, increasing the conductivity, and improving the first cycle efficiency.

[0045] In addition, in some embodiments, the particle size concentration N of the first silicon-based material is 1 is 0 to 2, and the particle size concentration N of the second silicon-based material is 2 The concentration referred to herein is (D90-D10)÷D50, which is the particle size concentration N of the first silicon-based material. 1 =(the particle size D90 of the first silicon-based material - the particle size D10 of the first silicon-based material)÷the particle size D50 of the first silicon-based material; similarly, the particle size concentration N of the second silicon-based material 2 =(D90 of the particle size of the second silicon-based material - D10 of the particle size of the second silicon-based material)÷D50 of the particle size of the second silicon-based material. Preferably, N 1 0.5~1.5, N 2 The present invention continues to regulate the particle size concentration of the silicon-based material, making the particle size more concentrated, avoiding the adverse effects caused by excessive fine powder contacting the electrolyte and causing side reactions, and further improving the long-term cycle life and rate performance of the battery. In addition, when the concentration is maintained at a certain level, the difference between D90 and D10 is small, the distribution of each particle size will be more uniform, and the coating consistency will be better. Preferably, the particle size concentration N of the first silicon-based material is 1 Greater than the particle size concentration N of the second silicon-based material 2 .

[0046] In some embodiments, the specific surface area of ​​the first silicon-based material is 0.8 to 2 m 2 / g, specifically 0.8~1.0m 2 / g, 1.0~1.2m 2 / g, 1.2~1.4m 2 / g, 1.4~1.6m 2 / g, 1.6~1.8m 2 / g or 1.8~2.0m 2 / g; the specific surface area of ​​the second silicon-based material is 1.5 to 3.5 m 2 / g, specifically 1.5~1.8m 2 / g, 1.8~2.0m 2 / g, 2.0~2.2m 2 / g, 2.2~2.4m 2 / g, 2.4~2.6m 2 / g, 2.6~2.8m 2 / g, 2.8~3.0m 2 / g, 3.0~3.2m 2 / g or 3.2~3.5m 2 / g. Preferably, the specific surface area of ​​the first silicon-based material is smaller than that of the second silicon-based material. With a suitable specific surface area, the silicon-based material has more contact with the electrolyte and higher conductivity. Keeping the specific surface area of ​​the second silicon-based material larger than that of the first silicon-based material can further ensure that the second silicon-based material is in a small particle state and the first silicon-based material is in a large particle state, thereby further ensuring the fast charging performance and cycle performance of the battery.

[0047] 2. Secondary battery

[0048] The second aspect of the present invention is to provide a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte separated between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet is the silicon-based negative electrode sheet described in any one of the above items.

[0049] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder, and the mass ratio of the positive electrode active material to the conductive agent and the binder is (93~98):(1~4):(1~4).

[0050] The positive electrode active material may be, but is not limited to, a chemical formula such as Li c Ni h Co y M z O 2-b N b (wherein 0.95≤c≤1.2, h>0, y≥0, z≥0, and h+y+z=1, 0≤b≤1, M is selected from a combination of one or more of Mn and Al, and N is selected from a combination of one or more of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO 2 、LiNiO 2 、LiVO 2 、LiCrO 2 、LiMn 2 O 4 、LiCoMnO 4 , Li 2 NiMn 3 O 8 、LiNi 0.5 Mn 1.5 O 4 、LiCoPO 4 、LiMnPO 4 、LiFePO 4 、LiNiPO 4 、LiCoFSO 4 , CuS 2, FeS 2 、MoS 2 、NiS、TiS 2 The positive electrode active material may also be subjected to a modification treatment. The method for modifying the positive electrode active material should be known to those skilled in the art. For example, the positive electrode active material may be modified by coating, doping, etc. The material used for the modification treatment may include but is not limited to a combination of one or more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive electrode current collector may be any material suitable for use as a positive electrode current collector for lithium-ion batteries in the art. For example, the positive electrode current collector may include but is not limited to metal foil, etc., and more specifically may include but is not limited to aluminum foil, etc.

[0051] The separator can be any material suitable for lithium-ion battery separators in the art, for example, it can be a combination of one or more materials including but not limited to polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fiber.

[0052] The secondary battery also includes an electrolyte, which includes an organic solvent, an electrolyte lithium salt and an additive. The electrolyte lithium salt can be LiPF used in high temperature electrolytes. 6 and / or LiBOB; it can also be LiBF used in low temperature electrolytes 4 、LiBOB、LiPF 6 It can also be LiBF used in the overcharge-proof electrolyte 4 、LiBOB、LiPF 6 , LiTFSI; it can also be LiClO 4 、LiAsF 6 、LiCF 3 SO 3 、LiN(CF 3 SO 2 ) 2 At least one of the above. The organic solvent may be a cyclic carbonate, including PC, EC; it may also be a chain carbonate, including DFC, DMC, or EMC; it may also be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include but are not limited to film-forming additives, conductive additives, flame retardant additives, overcharge prevention additives, and additives for controlling H in the electrolyte. 2 At least one of an additive for increasing the content of O and HF, an additive for improving low temperature performance, and a multifunctional additive.

[0053] 3. Electrical devices

[0054] A third aspect of the present invention is to provide an electrical device comprising the secondary battery described above.

[0055] The electrical device may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, etc. The vehicle may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc.; the spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, etc.; the electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy and an electric airplane toy, etc.; the electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator and an electric planer, etc.

[0056] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects will be described in further detail below in conjunction with specific implementation methods and accompanying drawings, but the implementation methods of the present invention are not limited thereto.

[0057] Example 1

[0058] A silicon-based negative electrode sheet comprises a negative electrode current collector 1, a first active material layer 2 (S1) coated on both surfaces of the negative electrode current collector 1, and a second active material layer 3 (S2) coated on the surface of the first active material layer 2. The first active material layer 2 comprises a first negative electrode active material, a conductive agent and a binder, wherein the first negative electrode active material comprises a first silicon-based material and a first carbon-based material; the second active material layer 3 comprises a second negative electrode active material; and the second negative electrode active material comprises a second silicon-based material and a second carbon-based material.

[0059] Among them, the first silicon-based material is SiO, the particle size D50 is 10.5 μm, and the particle size D10 is 3.2 μm; the second silicon-based material is SiO, the particle size D50 is 5.8 μm, and the particle size D10 is 1.6 μm; the first carbon-based material is graphite, the particle size D50 is 12 μm, and the particle size D10 is 3 μm; the second carbon-based material is graphite, the particle size D50 is 12 μm, and the particle size D10 is 3 μm; the surface density (CW) of the first active material layer 2 1 ) is 0.02g / cm 2 ; The surface density of the second active material layer 3 (CW 2 ) is 0.01g / cm 2 In the first active material layer 2, SiO accounts for 10% and graphite accounts for 90%; in the second active material layer 3, SiO accounts for 10% and graphite accounts for 90%.

[0060] The calculated ratio of the particle size D50 of the first silicon-based material to the particle size D50 of the second silicon-based material is 1.8; the ratio of the particle size D10 of the first silicon-based material to the particle size D10 of the second silicon-based material is 2; the particle size concentration N of the first silicon-based material 1 is 1, and the particle size concentration of the second silicon-based material N 2 is 1; and the ratio of the surface density of the first active material layer 2 to the surface density of the second active material layer 3 is 2.

[0061] The preparation method of the negative electrode plate is as follows: prepare a first active material slurry and a second active material slurry respectively, mix the negative electrode active material mixed with SiO and graphite with conductive carbon Super-P, conductive carbon tube CNT, binder sodium carboxymethyl cellulose CMC, and binder styrene-butadiene rubber SBR according to a mass ratio of 95:1.5:1.4:0.1:2, add deionized water and obtain a uniform slurry under vacuum stirring; firstly, evenly apply the first active material slurry on the copper foil, and obtain the first active material layer 2 after drying; then, apply the second active material slurry on the surface of the first active material layer 2, and obtain the silicon-based negative electrode plate after drying.

[0062] The obtained silicon-based negative electrode plate is applied to a secondary battery, and the preparation method is as follows:

[0063] 1) Preparation of positive electrode:

[0064] The positive electrode main material NCM811, conductive agent (Super P), binder (PVDF), etc. are mixed in a ratio of 97.5:1.4:1.2, and a solvent (NMP) is added. The mixture is stirred and mixed evenly under the action of a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then the positive electrode sheet is obtained after baking, cold pressing, and die-cutting.

[0065] 2) Preparation of electrolyte:

[0066] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then the fully dried lithium salt LiPF 6 It is dissolved in a mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0067] 3) Diaphragm preparation:

[0068] A 9μm polyethylene diaphragm is used with ceramic coated on one side.

[0069] 4) Battery assembly:

[0070] The positive electrode sheet, separator and negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging shell, and the prepared electrolyte is injected into the dried bare battery cell. After vacuum packaging, standing, forming, shaping and other processes, the secondary battery is obtained.

[0071] Comparative Example 1

[0072] The difference from Example 1 is the arrangement of the negative electrode plate.

[0073] The negative electrode sheet of this comparative example includes a negative electrode current collector 1, an active material layer coated on both surfaces of the negative electrode current collector 1, the active material layer includes a negative electrode active material, a conductive agent and a binder, the negative electrode active material includes SiO and graphite, SiO accounts for 10%, and graphite accounts for 90%. Among them, the particle size D50 of SiO is 12.4μm, the particle size D10 is 3.8μm, and the concentration N is 1; the particle size D50 of graphite is 12μm, and the particle size D10 is 3μm; the surface density of the active material layer is 0.015g / cm 2 .

[0074] The rest of the configuration is the same as that of Example 1 and will not be described in detail here.

[0075] Comparative Example 2

[0076] The difference from Example 1 is the arrangement of the negative electrode plate.

[0077] The negative electrode sheet of this comparative example includes a negative electrode current collector 1, an active material layer coated on both surfaces of the negative electrode current collector 1, the active material layer includes a negative electrode active material, a conductive agent and a binder, the negative electrode active material includes SiO and graphite, SiO accounts for 10%, and graphite accounts for 90%. Among them, the particle size D50 of SiO is 6.2μm, the particle size D10 is 1.5μm, and the concentration N is 1; the particle size D50 of graphite is 12μm, and the particle size D10 is 3μm; the surface density of the active material layer is 0.015g / cm 2 .

[0078] The rest of the configuration is the same as that of Example 1 and will not be described in detail here.

[0079] In addition, the negative electrode sheets and secondary batteries of Examples 2 to 21 were prepared referring to the configuration and preparation method of Example 1. The differences between the examples are described in Table 1 below.

[0080] Table 1

[0081]

[0082]

[0083] The performance of the lithium-ion batteries prepared in Examples 1 to 21 and Comparative Examples 1 to 2 was tested.

[0084] Performance Test:

[0085] 1) Dynamic performance test

[0086] At 25°C, the battery prepared in the embodiment and the comparative example is fully charged at x C and fully discharged at 1 C for 10 times, then the battery is fully charged at x C, and then the negative electrode plate is disassembled, and the lithium deposition on the surface of the negative electrode plate is observed. If there is no lithium deposition on the negative electrode surface, the charging rate x C is increased by 0.1C as a gradient and tested again until lithium deposition on the negative electrode surface, and the test is stopped. The charging rate (x-0.1) C at this time is the maximum charging rate of the battery. The value of x can be determined according to the actual system, surface density and other parameters.

[0087] 2) Cycle performance test

[0088] At 25° C., the lithium ion batteries prepared in the examples and comparative examples were charged at 1C and discharged at 1C rate, and a full charge and discharge cycle test was performed, and the capacity retention rate was recorded after 500 cycles.

[0089] The test results are shown in Table 2 below.

[0090] Table 2

[0091] Group Maximum charging rate Capacity retention rate / % Example 1 2.2C 92％ Example 2 2.1C 90％ Example 3 2.2C 91％ Example 4 2.3C 85％ Example 5 2.2C 88％ Example 6 2.2C 91％ Example 7 2.0C 81％ Example 8 2.3C 91％ Example 9 2.2C 91％ Example 10 2.2C 82％ Embodiment 11 2.2C 91％ Example 12 2.2C 81％ Embodiment 13 2.1C 80％ Embodiment 14 2.2C 88％ Embodiment 15 2.2C 94％ Example 16 2.1C 93％ Embodiment 17 2.2C 90％ Embodiment 18 2.1C 91％ Embodiment 19 2.2C 88％ Embodiment 20 2.3C 94％ Embodiment 21 2.2C 91％ Comparative Example 1 1.4C 90％ Comparative Example 2 2.3C 81％

[0092] It can also be seen from the comparison of Comparative Examples 1 to 2 that although small-particle silicon-based materials have better rate charging performance, the expansion and crushing of small-particle SiO2 in the long-term cycle process will consume a large amount of electrolyte and cannot maintain good long-cycle performance, such as Comparative Example 2. However, as in Comparative Example 1, the use of silicon-based particles with larger particle sizes can maintain a certain cycle performance, but the charge and discharge rate is low and cannot meet the needs of fast charging. As can be seen from the comparison of Examples 1 to 16, the silicon-based negative electrode plate of the present invention adopts double-layer coating, and simultaneously screens silicon-based materials and carbon-based materials of specific particle sizes, and limits the surface density of the two-layer coating during coating. Compared with conventional single-layer coating, it can effectively improve the maximum charging rate and cycle performance of the battery while ensuring energy density. It can be seen that the silicon-based negative electrode plate of the present invention has good fast charging performance.

[0093] Specifically, it can be seen from the comparison of Examples 1 to 13 that by adjusting D50 and D10 within the limited range, the secondary battery containing the silicon-based negative electrode plate has good rate performance and cycle performance. Although the rate performance is good beyond the above range, the cycle performance deteriorates. This is mainly because the silicon-based materials and carbon-based materials beyond the above range cannot withstand charging at high rates, the expansion of SiO is aggravated, and various side reactions are also aggravated. In particular, as in Examples 12 to 13, the particle size D50 of the second carbon-based material is ensured to be greater than the particle size D50 of the second silicon-based material, and the battery can maintain good cycle performance.

[0094] In addition, it can be seen from Examples 9 and Comparative Examples 14 to 16 that as the S1 layer CW 1 / S2 layer CW 2 As the ratio of CW increases, the rate performance of the battery is similar, but the cycle performance shows a trend of first increasing and then decreasing, indicating that with the consumption of electrolyte during the cycle, the influence of the surface density ratio on the performance gradually emerges. The experiment shows that CW 1 / CW 2 The performance is better when the ratio is close to .

[0095] In addition, it can be seen from the comparison between Examples 15 and 17 to 21 that the SiO particle size concentration N also affects the rate performance and cycle performance of the battery. 1 、N 2 The capacity retention rate of the battery can be further guaranteed, mainly because within this concentration range, the particle size can be more concentrated, thereby further reducing the impact of fine powder particles. 1 Greater than N 2 , it can better guarantee the battery's rate performance and cycle performance.

[0096] In summary, the silicon-based negative electrode plate and the secondary battery containing the negative electrode plate provided by the present invention have high energy density as well as good fast charging performance and cycle performance.

[0097] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can also change and modify the above embodiment. Therefore, the present invention is not limited to the above specific embodiment, and any obvious improvement, replacement or modification made by those skilled in the art on the basis of the present invention belongs to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A silicon-based negative electrode plate, characterized in that: include: Anode current collector; a first active material layer, coated on at least one surface of the negative electrode current collector, comprising a first negative electrode active material; The first negative electrode active material includes a first silicon-based material and a first carbon-based material; A second active material layer, coated on a surface of the first active material layer away from the negative electrode current collector, comprising a second negative electrode active material; the second negative electrode active material comprises a second silicon-based material and a second carbon-based material; The ratio of the particle size D50 of the first silicon-based material to the particle size D50 of the second silicon-based material is 1.1 to 4, and the particle size D50 of the second carbon-based material is larger than the particle size D50 of the second silicon-based material; the ratio of the particle size D10 of the first silicon-based material to the particle size D10 of the second silicon-based material is 1.1 to 5; The specific surface area of ​​the first silicon-based material is 0.8 to 2 m 2 / g, the specific surface area of ​​the second silicon-based material is 1.5 to 3.5 m 2 / g, the specific surface area of ​​the first silicon-based material is smaller than the specific surface area of ​​the second silicon-based material; The ratio of the surface density of the first active material layer to the surface density of the second active material layer is 0.5 to 6; the surface density of the first active material layer is 0.007 to 0.025 g / cm 2 The surface density of the second active material layer is 0.007 to 0.025 g / cm 2 ; The porosity of the second active material layer is 38-43%, and the porosity of the first active material layer is 20-30%.

2. The silicon-based negative electrode plate according to claim 1, characterized in that: The ratio of the particle size D50 of the first silicon-based material to the particle size D50 of the second silicon-based material is 1.5-2.5; the ratio of the particle size D10 of the first silicon-based material to the particle size D10 of the second silicon-based material is 1.2-3; the ratio of the surface density of the first active material layer to the surface density of the second active material layer is 1-4.

3. The silicon-based negative electrode plate according to claim 1 or 2, characterized in that: The particle size D50 of the first silicon-based material is 9 to 14 μm, the particle size D50 of the second silicon-based material is 4 to 8 μm, and the particle size D50 of the second carbon-based material is 8 to 14 μm.

4. The silicon-based negative electrode plate according to claim 1 or 2, characterized in that: The particle size D10 of the first silicon-based material is 3-5 μm, the particle size D10 of the second silicon-based material is 1-4 μm, and the particle size D10 of the second carbon-based material is 2-4 μm.

5. The silicon-based negative electrode plate according to claim 1 or 2, characterized in that: The particle size concentration N1 of the first silicon-based material is 0-2, and the particle size concentration N2 of the second silicon-based material is 0-2.

6. The silicon-based negative electrode plate according to claim 1 or 2, characterized in that: The mass of the first silicon-based material is 3-80% of the mass of the first negative electrode active material; the mass of the second silicon-based material is 3-80% of the mass of the second negative electrode active material.

7. The silicon-based negative electrode plate according to claim 6, characterized in that: The first silicon-based material and the second silicon-based material are each independently selected from SiO x , Li-containing SiO x 、SiO containing magnesium x At least one of 0<x≤2; wherein the lithium-containing SiO x The mass proportion of lithium in the SiO2 is 0-15%, and the mass proportion of magnesium in the SiO2 is 0-15%. x The mass proportion of magnesium in the carbon-based material is 0-15%; the first carbon-based material and the second carbon-based material are independently selected from at least one of artificial graphite, natural graphite, hard carbon, graphene, and soft carbon.

8. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet, characterized in that: The negative electrode plate is the silicon-based negative electrode plate according to any one of claims 1 to 7.

9. An electrical device, characterized in that: A secondary battery comprising the secondary battery as claimed in claim 8.

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