Lithium ion battery, preparation method thereof and electric equipment

Abstract

The invention provides a lithium ion battery, a preparation method thereof and electric equipment, and relates to the field of secondary batteries. The positive electrode active layer of the lithium ion battery comprises a first bottom layer and a first surface layer, the particle size of a positive electrode active material in the first bottom layer is smaller than that of a positive electrode active material in the first surface layer, and the content of a positive electrode conductive agent in the first bottom layer is lower than that of a positive electrode conductive agent in the first surface layer; the content of the positive electrode binder in the first bottom layer is higher than that of the positive electrode binder in the first surface layer. The negative active layer comprises a second bottom layer and a second surface layer, the particle size of graphite in the second bottom layer is larger than that of graphite in the second surface layer, the content of the negative conductive agent in the second bottom layer is lower than that of the negative conductive agent in the second surface layer, and the content of the negative binder in the second bottom layer is higher than that of the positive binder in the second surface layer. The positive / negative plate provided by the invention is beneficial to improving the lithium ion migration rate and reducing concentration polarization; the lithium ion battery provided by the invention has high energy density and rapid charging capability at the same time.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of secondary batteries, in particular to a lithium ion battery, a preparation method thereof and an electric device. BACKGROUND

[0002] In recent years, with the rapid growth of the global electric vehicle (EV) market, the demand for long driving range (>500 km) and short charging time (<20 minutes) of electric vehicles has increased, which has promoted the development of lithium ion batteries (LIB) with high energy density and fast charging capability, and one of the most effective methods to improve energy density is to increase the mass loading of active materials, thereby reducing the proportion of non-active components such as current collectors, separators and electrolytes. This method increases the specific energy to some extent, but due to the limitations of mass and electron transport in the liquid electrolyte phase, high area capacity batteries cannot be output at high power. Therefore, how to balance the battery capacity, the internal electron and ion transport rate of the battery and the microstructure design of the battery to ensure high energy density while considering the rate performance and safety performance is the main challenge faced by the development of new lithium ion batteries. + mass and electron transport, high area capacity batteries cannot be output at high power. Therefore, how to balance the battery capacity, the internal electron and ion transport rate of the battery and the microstructure design of the battery to ensure high energy density while considering the rate performance and safety performance is the main challenge faced by the development of new lithium ion batteries. SUMMARY

[0003] The present application aims to provide a lithium ion battery with high energy density and fast charging, a preparation method thereof and an electric device, to solve the above problems.

[0004] To achieve the above purpose, the present application adopts the following technical solutions: A lithium ion battery, comprising a positive electrode sheet and a negative electrode sheet; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on at least one side of the positive electrode current collector, and the material forming the positive electrode active layer comprises a positive electrode conductive agent, a positive electrode binder and a positive electrode active material; the positive electrode active layer comprises a first bottom layer and a first surface layer stacked together, and the first bottom layer is located on the side close to the positive electrode current collector; The particle size of the positive electrode active material in the first bottom layer is smaller than that of the positive electrode active material in the first surface layer, the content of the positive electrode conductive agent in the first bottom layer is lower than that of the positive electrode conductive agent in the first surface layer, and the content of the positive electrode binder in the first bottom layer is higher than that of the positive electrode binder in the first surface layer; The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one side of the negative electrode current collector, and the material forming the negative electrode active layer comprises a negative electrode conductive agent, a negative electrode binder and a negative electrode active material, and the negative electrode active material comprises graphite and a silicon-based negative electrode material; the negative electrode active layer comprises a second bottom layer and a second surface layer stacked together, and the second bottom layer is located on the side close to the negative electrode current collector; The particle size of the graphite in the second bottom layer is larger than the particle size of the graphite in the second surface layer, the content of the silicon-based negative electrode material in the second bottom layer is lower than the content of the silicon-based negative electrode material in the second surface layer, the content of the negative electrode conductive agent in the second bottom layer is lower than the content of the negative electrode conductive agent in the second surface layer, and the content of the negative electrode binder in the second bottom layer is higher than the content of the negative electrode binder in the second surface layer.

[0005] According to an embodiment of the present application, the lithium ion battery satisfies at least one of the following conditions: (1) the D50 particle size of the positive electrode active material in the first bottom layer is 4-6 μm, and the D50 particle size of the positive electrode active material in the first surface layer is 8-12 μm; (2) the positive electrode conductive agent comprises at least one of conductive carbon black, carbon nanotubes, composite conductive paste, and graphene conductive paste; (3) the positive electrode binder comprises at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, and polyvinyl butyral; (4) the mass ratio of the positive electrode active material to the positive electrode conductive agent and the positive electrode binder in the first bottom layer is 100%:8.6-13.5%:1.4-1.8%; (5) the mass ratio of the positive electrode active material to the positive electrode conductive agent and the positive electrode binder in the first surface layer is 100%:14-17.4%:1-1.4%; (6) the ratio of the area density of the first bottom layer to the area density of the first surface layer is 1:1; (7) the single-sided area density of the positive electrode active layer is 200-260 g / m 2 ; (8) the positive electrode current collector is an aluminum foil with a thickness of 9-15 μm.

[0006] According to an embodiment of the present application, the lithium ion battery satisfies at least one of the following conditions: (9) when the positive electrode active layer is provided on one side of the positive electrode current collector, the area density of the positive electrode active layer is 200-260 g / m 2 ; (10) when the positive electrode active layer is provided on both sides of the positive electrode current collector, the area density of the positive electrode active layer is 400-520 g / m 2 .

[0007] According to an embodiment of the present application, the lithium ion battery satisfies at least one of the following conditions: a. the D50 particle size of the graphite in the second bottom layer is 12-15 μm, and the D50 particle size of the graphite in the second surface layer is 5-7 μm; b. the negative electrode conductive agent comprises at least one of conductive carbon black, carbon nanotube, composite conductive paste, and graphene conductive paste; c. the negative electrode binder comprises at least one of butadiene styrene rubber, sodium carboxymethyl cellulose, and polyacrylic acid; d. the mass ratio of graphite, silicon-based negative electrode material, negative electrode conductive agent, and negative electrode binder in the second bottom layer is 88-92%:8-12%:8.3-12.6%:3.8-4.8%; e. the mass ratio of graphite, silicon-based negative electrode material, negative electrode conductive agent, and negative electrode binder in the second surface layer is 84-88%:12-16%:12.5-16.8%:2.6-3.8%; f. the ratio of the area density of the second bottom layer to the area density of the second surface layer is 1:1; g. the silicon-based negative electrode material comprises at least one of silicon-oxygen material and silicon-carbon; h. the single-sided area density of the negative electrode active layer is 80-140 g / m 2 ; i. the negative electrode current collector is a copper foil with a thickness of 6-10 μm.

[0008] According to embodiments of the present application, the lithium ion battery satisfies at least one of the following conditions: g. when one side of the negative electrode current collector is provided with a negative electrode active layer, the area density of the negative electrode active layer is 80-140 g / m 2 ; k. when both sides of the negative electrode current collector are provided with a negative electrode active layer, the area density of the negative electrode active layer is 160-280 g / m 2 .

[0009] The present application also provides a preparation method of the lithium ion battery as described above, comprising: mixing a first solvent, a positive electrode conductive agent, a positive electrode binder, and a positive electrode active material to prepare a first bottom layer slurry and a first surface layer slurry, so that the proportion of the positive electrode conductive agent in the first bottom layer slurry is lower than the proportion of the positive electrode conductive agent in the first surface layer slurry, the proportion of the positive electrode binder in the first bottom layer slurry is higher than the proportion of the positive electrode binder in the first surface layer slurry, and the particle size of the positive electrode active material in the first bottom layer slurry is smaller than the particle size of the positive electrode active material in the first surface layer slurry; coating the first bottom layer slurry and the first surface layer slurry to at least one side surface of a positive electrode current collector, drying, and forming a positive electrode active layer on the positive electrode current collector to obtain a positive electrode sheet; wherein the drying causes the first bottom layer slurry to form a first bottom layer and the first surface layer slurry to form a first surface layer; The second solvent, the negative electrode conductive agent, the negative electrode binder and the negative electrode active material are mixed to prepare a second bottom layer slurry and a second surface layer slurry, the proportion of the negative electrode conductive agent in the second bottom layer slurry is lower than the proportion of the negative electrode conductive agent in the second surface layer slurry, the proportion of the negative electrode binder in the second bottom layer slurry is higher than the proportion of the negative electrode binder in the second surface layer slurry, the particle size of the graphite in the second bottom layer slurry is larger than the particle size of the graphite in the second surface layer slurry, and the content of the silicon-based negative electrode material in the second bottom layer is lower than the content of the silicon-based negative electrode material in the second surface layer. The second bottom layer slurry and the second surface layer slurry are coated on at least one side surface of the negative electrode current collector, dried, and a negative electrode active layer is formed on the negative electrode current collector to obtain a negative electrode sheet; wherein the drying causes the second bottom layer slurry to form a second bottom layer and the second surface layer slurry to form a second surface layer.

[0010] According to the embodiments of the present application, the solid content of the first bottom layer slurry and the first surface layer slurry is the same or different and is independently selected from 70-80%.

[0011] According to the embodiments of the present application, the solid content of the second bottom layer slurry and the second surface layer slurry is the same or different and is independently selected from 50-60%.

[0012] According to the embodiments of the present application, the first solvent comprises NMP and the second solvent comprises water.

[0013] The present application also provides a lithium ion battery comprising the lithium ion battery described above or the lithium ion battery prepared by the preparation method described above.

[0014] Compared with the prior art, the present application has the following advantages: In the lithium ion battery provided by the present application, the content of the bottom layer conductive agent near the positive electrode current collector is low, the content of the binder is high, and small particles of the positive electrode active material are mixed, which is beneficial to the Li + rapidly removed; the content of the surface layer conductive agent away from the positive electrode current collector is high, the content of the binder is low, and large particles of the positive electrode active material are mixed, the bottom layer active material reacts rapidly to lose electrons and remove Li + at the beginning of charging, the electrons are rapidly transferred, which can reduce the electrochemical polarization, the Li +Diffusion migration from high concentration to low concentration of the surface layer (lithium ions driven by the concentration gradient through the pores of the electrode material, to the interface between the electrolyte and the solid electrode), the surface layer of large particles reduces the tortuosity of lithium ion migration and thus improves the lithium ion migration rate, and reduces the concentration difference polarization. On the negative side, the surface layer of the negative electrode has high content of conductive agent and low content of binder, and is mixed with small particle fast charging graphite and high content of silicon carbon material, the surface layer of small particle graphite provides the best porosity, which is beneficial to Li + Fast insertion, reducing the concentration difference polarization of the negative electrode surface; the bottom layer close to the negative electrode current collector has low content of conductive agent and high content of binder, and is mixed with large particle fast charging graphite and low content of silicon carbon, during the charging process, Li + Migrate through the electrolyte to the negative electrode and react first on the surface layer of the negative electrode, the surface layer of graphite is small particles which can promote Li + Fast insertion, the rest of Li + Continue to diffuse to the bottom layer, the large particle graphite in the bottom layer reduces the tortuosity of Li + Migration, thereby reducing the internal Li + Concentration difference. In addition, the lithium intercalation potential platform of silicon is relatively high (0.3-0.5V vs. 0.1V of graphite), which is not easy to lithium precipitation during fast charging, reducing the safety hidden danger; and during the coating and drying process, the binder migrates to the surface, resulting in a decrease in the adhesion between the electrode and the current collector, both the positive and negative electrodes are designed to have a binder layer structure, which can compensate for the migration of the binder, enhance the structural integrity of the electrode, and enhance the cycle performance. The lithium ion battery of the present application has high energy density and fast charging capability. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope of the present application.

[0016] Figure 1 The structure of the positive electrode sheet in the present application is shown in the figure; Figure 2 The structure of the negative electrode sheet in the present application is shown in the figure; Figure 3 The cycle performance comparison curves of Example 1 and Comparative Examples 1-4 at room temperature are shown in the figure; Figure 4 The cycle performance comparison curves of Example 1 and Comparative Examples 1-4 at high temperature are shown in the figure.

[0017] Explanation of reference signs: 100-positive electrode current collector, 200-first bottom layer, 300-first surface layer, 400-negative electrode current collector, 500-second bottom layer, and 600-second surface layer. DETAILED DESCRIPTION

[0018] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0019] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0020] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0021] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0022] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0023] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0024] In order to better illustrate the technical solutions provided in the present application, before the embodiments, the technical solutions are stated as a whole, as follows: A lithium ion battery comprises a positive electrode sheet and a negative electrode sheet; Referring to Figure 1 , the positive electrode sheet comprises a positive electrode current collector 100 and a positive electrode active layer located on at least one side of the positive electrode current collector 100, the material forming the positive electrode active layer comprises a positive electrode conductive agent, a positive electrode binder and a positive electrode active material; the positive electrode active layer comprises a first bottom layer 200 and a first surface layer 300 stacked together, the first bottom layer 200 is located on the side close to the positive electrode current collector 100; The particle size of the positive electrode active material in the first bottom layer is smaller than that in the first surface layer, the content of the positive electrode conductive agent in the first bottom layer is lower than that in the first surface layer, and the content of the positive electrode binder in the first bottom layer is higher than that in the first surface layer; Referring to Figure 2 , the negative electrode sheet comprises a negative electrode current collector 400 and a negative electrode active layer located on at least one side of the negative electrode current collector 400, the material forming the negative electrode active layer comprises a negative electrode conductive agent, a negative electrode binder and a negative electrode active material, the negative electrode active material comprises graphite and a silicon-based negative electrode material; the negative electrode active layer comprises a second bottom layer 500 and a second surface layer 600 stacked together, the second bottom layer 500 is located on the side close to the negative electrode current collector 400; The particle size of the graphite in the second bottom layer is larger than that in the second surface layer, the content of the silicon-based negative electrode material in the second bottom layer is lower than that in the second surface layer, the content of the negative electrode conductive agent in the second bottom layer is lower than that in the second surface layer, and the content of the negative electrode binder in the second bottom layer is higher than that in the second surface layer.

[0025] In the positive electrode sheet of the present application, the bottom layer close to the positive electrode current collector has low content of conductive agent, high content of binder and mixed small particles of positive electrode active material, which is beneficial to the fast release of Li + ; the surface layer away from the positive electrode current collector has high content of conductive agent, low content of binder and mixed large particles of positive electrode active material, the active material in the bottom layer reacts quickly to lose electrons and release Li + + at the beginning of charging, the fast transfer of electrons in the bottom layer can reduce the electrochemical polarization, and the Li + + in the bottom layer diffuses and migrates from high concentration to low concentration of the surface layer (lithium ions pass through the pores of the electrode material under the driving of the concentration gradient to reach the interface between the electrolyte and the solid electrode), and the large particles in the surface layer reduce the tortuosity of lithium ion migration, thereby improving the lithium ion migration rate and reducing the concentration polarization.

[0026] In the negative electrode sheet of the present application, the surface layer conductive agent far from the negative electrode current collector has a high content of conductive agent and a low content of binder, and is mixed with small-particle graphite and a high content of silicon-carbon material. The small-particle graphite in the surface layer provides optimal porosity, which is conducive to the Li + rapid insertion, reduces the concentration polarization on the negative electrode surface, increases the stability of the electrode structure, and improves the fast-charging capability of the negative electrode; the bottom layer conductive agent close to the negative electrode current collector has a low content of conductive agent and a high content of binder, and is mixed with large-particle graphite and a low content of silicon-carbon. During the charging process, Li + reacts first on the surface layer of the negative electrode by migrating to the negative electrode. The small-particle graphite in the surface layer can promote the Li + rapid insertion, and the remaining Li + continues to diffuse to the bottom layer, and the large-particle graphite in the bottom layer reduces the Li + migration tortuosity, thereby reducing the internal concentration polarization. In addition, the lithium intercalation potential platform of silicon is relatively high (0.3-0.5V vs. 0.1V of graphite), which is not prone to lithium precipitation during fast charging, thereby reducing the safety hazard.

[0027] During the coating and drying process, the migration of the positive electrode / negative electrode binder to the surface leads to a decrease in the adhesion between the active layer and the current collector. Therefore, both the positive electrode and the negative electrode are designed to have a layered structure of the binder, which can compensate for the migration of the positive electrode / negative electrode binder, enhance the structural integrity of the positive electrode / negative electrode, and allow the electrode sheet to have a higher upper limit of thickness, thereby enhancing the cycle performance.

[0028] According to embodiments of the present application, the lithium ion battery satisfies at least one of the following conditions: (1) the D50 particle size of the positive electrode active material in the first bottom layer is 4-6μm, and the D50 particle size of the positive electrode active material in the first surface layer is 8-12μm; In some embodiments, the positive electrode active material includes a ternary positive electrode active material, which includes but is not limited to LiNi 0.925 Co 0.055 Mn 0.02 O2, LiNi 0.90 Co 0.05 Mn 0.05 O2.

[0029] (2) the positive electrode conductive agent includes at least one of conductive carbon black, carbon nanotubes, composite conductive paste, and graphene conductive paste; wherein the carbon nanotubes include at least one of multi-walled carbon nanotubes and single-walled carbon nanotubes.

[0030] (3) the positive electrode binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, and polyvinyl butyral; The content of the positive electrode binder in the first bottom layer is greater than the content of the positive electrode binder in the first surface layer, which can improve the adhesion between the active material and the positive electrode current collector in the bottom layer, thereby improving the mechanical integrity and cycle performance of the positive electrode sheet; (4) the mass ratio of the positive electrode active material to the positive electrode conductive agent and the positive electrode binder in the first bottom layer is 100%:8.6-13.5%:1.4-1.8%; For example, the mass ratio of the positive electrode active material to the positive electrode conductive agent and the positive electrode binder in the first bottom layer can be 100%:8.6%:1.4%, 100%:8.6%:1.8%, 100%:13.5%:1.4%, 100%:13.5%:1.8%, 100%:11%:1.6%, or any value between 100%:8.6-13.5%:1.4-1.8%.

[0031] In some embodiments, the positive electrode conductive agent in the first bottom layer is a combination of conductive carbon black and multi-walled carbon nanotubes, and the mass ratio of the positive electrode active material to the conductive carbon black, the multi-walled carbon nanotubes, and the positive electrode binder in the first bottom layer is 100%:0.6-1.0%:8-12.5%:1.4-1.8%.

[0032] (5) the mass ratio of the positive electrode active material to the positive electrode conductive agent and the positive electrode binder in the first surface layer is 100%:14-17.4%:1-1.4%; For example, the mass ratio of the positive electrode active material to the positive electrode conductive agent and the positive electrode binder in the first surface layer can be 100%:14%:1%, 100%:14%:1.4%, 100%:17.4%:1%, 100%:17.4%:1.4%, 100%:15.7%:1.2%, or any value between 100%:14-17.4%:1-1.4%; In some embodiments, the positive electrode conductive agent in the first surface layer is a combination of conductive carbon black and multi-walled carbon nanotubes, and the mass ratio of the positive electrode active material to the conductive carbon black, the multi-walled carbon nanotubes, and the positive electrode binder in the first surface layer is 100%:1.0-1.4%:13-16%:1-1.4%; (6) the ratio of the area density of the first bottom layer to the area density of the first surface layer is 1:1; (7) the single-sided area density of the positive electrode active layer is 200-260 g / m 2 ; For example, the single-sided area density of the positive electrode active layer can be 200 g / m 2 , 210 g / m 2 , 220 g / m 2 , 230 g / m 2 , 240 g / m 2 , 250 g / m2 260 g / m 2 or any value between 200 and 260 g / m 2 .

[0033] In some embodiments, the areal density of the first bottom layer is 100-130 g / m 2 , and the areal density of the first top layer is 100-130 g / m 2 .

[0034] (8) The positive electrode current collector is an aluminum foil having a thickness of 9-15 μm.

[0035] For example, the thickness of the aluminum foil can be 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any value between 9 and 15 μm.

[0036] According to embodiments of the present application, the lithium ion battery satisfies at least one of the following conditions: (9) When the positive electrode current collector has a positive electrode active layer on one side, the areal density of the positive electrode active layer is 200-260 g / m 2 . For example, the areal density of the positive electrode active layer can be 200 g / m 2 , 210 g / m 2 , 220 g / m 2 , 230 g / m 2 , 240 g / m 2 , 250 g / m 2 , 260 g / m 2 , or any value between 200 and 260 g / m 2 .

[0037] (10) When the positive electrode current collector has positive electrode active layers on both sides, the areal density of the positive electrode active layers is 400-520 g / m 2 .

[0038] For example, the areal density of the positive electrode active layer can be 400 g / m 2 , 410 g / m 2 , 420 g / m 2 , 430 g / m 2 , 440 g / m 2 , 450 g / m 2 , 460 g / m 2 , 470 g / m 2 , 480 g / m 2 , 490 g / m 2 , 500 g / m 2 , 510 g / m 2 , 520 g / m2 or any value between 400-520 g / m 2 or any value between 400-520 g / m

[0039] According to embodiments of the present application, the lithium ion battery satisfies at least one of the following conditions: a. the D50 particle size of the graphite in the second bottom layer is 12-15 pm, and the D50 particle size of the graphite in the second surface layer is 5-7 pm; In some embodiments, fast-charging graphite supporting 4-6 C rate with a D50 particle size of 12-15 pm is used in the second bottom layer, and fast-charging graphite supporting 5-10 C rate with a D50 particle size of 5-7 pm is used in the second surface layer.

[0040] b. the negative electrode conductive agent comprises at least one of conductive carbon black, carbon nanotube, composite conductive paste, and graphene conductive paste; the carbon nanotube comprises at least one of single-walled carbon nanotube and multi-walled carbon nanotube.

[0041] In some embodiments of the present application, the negative electrode conductive agent in the second bottom layer and the second surface layer is a combination of conductive carbon black and single-walled carbon nanotube, and the content of the conductive carbon black and the single-walled carbon nanotube in the second bottom layer is lower than that in the second surface layer, which is beneficial to improve the charging capacity of the negative electrode.

[0042] c. the negative electrode binder comprises at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid; In the present application, the binder in the second bottom layer and the second surface layer is a combination of styrene-butadiene rubber and sodium carboxymethyl cellulose, and the total content of the styrene-butadiene rubber and the sodium carboxymethyl cellulose in the second bottom layer is greater than that in the second surface layer, which can improve the adhesion between the active material in the bottom layer and the negative electrode current collector, thereby improving the mechanical integrity and cycle performance of the negative electrode sheet.

[0043] d. the mass ratio of the graphite, the silicon-based negative electrode material, the negative electrode conductive agent, and the negative electrode binder in the second bottom layer is 88-92%:8-12%:8.3-12.6%:3.8-4.8%; For example, the mass ratio of the graphite, the silicon-based negative electrode material, the negative electrode conductive agent, and the negative electrode binder in the second bottom layer can be 88%:8%:8.3%:3.8%, 92%:12%:12.6%:4.8%, 90%:10%:10.5%:4.3%, or any value between 88-92%:8-12%:8.3-12.6%:3.8-4.8%.

[0044] In some embodiments, the negative electrode conductive agent in the second bottom layer is a combination of conductive carbon black and carbon nanotubes, the binder in the second bottom layer is a combination of styrene-butadiene rubber and sodium carboxymethyl cellulose, and the mass ratio of graphite, silicon-based negative electrode material, conductive carbon black, carbon nanotubes, styrene-butadiene rubber, and sodium carboxymethyl cellulose in the second bottom layer is 88-92%:8-12%:0.3-0.6%:8-12%:1.2-1.6%:2.6-3.2%. e. The mass ratio of graphite to silicon-based negative electrode material, negative electrode conductive agent, and negative electrode binder in the second surface layer is 84-88%:12-16%:12.5-16.8%:2.6-3.8%. For example, the mass ratio of graphite to silicon-based negative electrode material, negative electrode conductive agent, and negative electrode binder in the second surface layer can be 84%:12%:12.5%:2.6%, 88%:16%:16.8%:3.8%, 85%:14%:14.7%:3.2%, or any value between 84-88%:12-16%:12.5-16.8%:2.6-3.8%. In some embodiments, the negative electrode conductive agent in the second surface layer is a combination of conductive carbon black and carbon nanotubes, the binder in the second surface layer is a combination of styrene-butadiene rubber and sodium carboxymethyl cellulose, and the mass ratio of graphite, silicon-based negative electrode material, conductive carbon black, carbon nanotubes, styrene-butadiene rubber, and sodium carboxymethyl cellulose in the second surface layer is 84-88%:12-16%:0.5-0.8%:12-16%:0.8-1.2%:1.8-2.6%.

[0045] f. The ratio of the area density of the second bottom layer to the area density of the second surface layer is 1:1. g. The silicon-based negative electrode material includes at least one of silicon-oxygen material and silicon-carbon. The content of the silicon-based negative electrode material in the second bottom layer of the present application is 8-12%, and the content of the silicon-based negative electrode material in the second surface layer is 12-16%. During the charging and discharging process, the relatively small content of silicon-carbon in the second bottom layer can slow down the shedding of active materials caused by the volume expansion of the silicon-based negative electrode.

[0046] In some embodiments, the D50 of the silicon-based negative electrode material is 3-13 μm.

[0047] In some embodiments, the silicon-carbon material is a silicon-carbon composite negative electrode material prepared by chemical vapor deposition. By depositing nano-silicon particles on a porous carbon skeleton, the energy density and fast charging performance of the battery can be significantly improved. Moreover, the lithium intercalation potential platform of silicon is relatively high (0.3-0.5V vs. 0.1V of graphite), which is not prone to lithium precipitation during fast charging, reducing the safety risk. Moreover, the wrinkle structure design on its surface increases the electrolyte contact area and improves the ion conduction efficiency.

[0048] h. the single-sided area density of the negative electrode active layer is 80-140 g / m 2 ; For example, the single-sided area density of the negative electrode active layer can be 80 g / m 2 , 90 g / m 2 , 100 g / m 2 , 110 g / m 2 , 120 g / m 2 , 130 g / m 2 , 140 g / m 2 , or any value between 80-140 g / m 2 .

[0049] In some embodiments, the area density of the second bottom layer is 40-70 g / m 2 ; and the area density of the second surface layer is 40-70 g / m 2 .

[0050] i. the negative electrode current collector is a copper foil with a thickness of 6-10 μm.

[0051] For example, the thickness of the copper foil can be 6 μm, 8 μm, 10 μm, or any value between 6-10 μm.

[0052] According to embodiments of the present application, the lithium ion battery satisfies at least one of the following conditions: g. when one side of the negative electrode current collector is provided with a negative electrode active layer, the area density of the negative electrode active layer is 80-140 g / m 2 ; For example, the area density of the negative electrode active layer can be 80 g / m 2 , 90 g / m 2 , 100 g / m 2 , 110 g / m 2 , 120 g / m 2 , 130 g / m 2 , 1400 g / m 2 , or any value between 80-140 g / m 2 .

[0053] k. when both sides of the negative electrode current collector are provided with a negative electrode active layer, the area density of the negative electrode active layer is 160-280 g / m 2 .

[0054] For example, the area density of the negative electrode active layer can be 160 g / m 2 , 180 g / m 2 , 200 g / m 2 , 220 g / m 2 , 240 g / m 2, 260 g / m 2 , 280 g / m 2 or 160-280 g / m 2 between any values.

[0055] The application also provides a preparation method of the lithium ion battery as described above, comprising: mixing the first solvent, the positive electrode conductive agent, the positive electrode binder and the positive electrode active material to prepare the first bottom layer slurry and the first surface layer slurry, respectively, so that the proportion of the positive electrode conductive agent in the first bottom layer slurry is lower than the proportion of the positive electrode conductive agent in the first surface layer slurry, the proportion of the positive electrode binder in the first bottom layer slurry is higher than the proportion of the positive electrode binder in the first surface layer slurry, and the particle size of the positive electrode active material in the first bottom layer slurry is smaller than the particle size of the positive electrode active material in the first surface layer slurry; coating the first bottom layer slurry and the first surface layer slurry to at least one side surface of the positive electrode current collector, drying, and forming a positive electrode active layer on the positive electrode current collector to obtain a positive electrode sheet; wherein the drying causes the first bottom layer slurry to form a first bottom layer and the first surface layer slurry to form a first surface layer.

[0056] According to the embodiments of the application, the solid content of the first bottom layer slurry and the first surface layer slurry is the same or different and is independently selected from 70-80%.

[0057] In some embodiments, the preparation of the first bottom layer slurry comprises: adding the positive electrode binder into the first solvent according to the proportions described above while stirring, adding the CNTs after uniform stirring to prepare a conductive glue solution by high-speed stirring; dry mixing the positive electrode active material and the conductive carbon black to uniform stirring, adding 70% of the conductive glue solution to the uniformly mixed powder, and then adding the remaining 30% of the glue solution after uniform stirring to form the first bottom layer slurry. In some embodiments, the preparation of the first surface layer slurry comprises: adding the positive electrode binder into the first solvent according to the proportions described above while high-speed stirring, adding the CNTs after uniform stirring to prepare a conductive glue solution by high-speed stirring; dry mixing the positive electrode active material and the conductive carbon black to uniform stirring, adding 70% of the glue solution to the uniformly mixed powder, and then adding the remaining 30% of the glue solution after uniform stirring to form the first surface layer slurry. In some embodiments, the first bottom layer slurry and the first surface layer slurry can be coated on one side surface of the positive electrode current collector by a slit extrusion type double-layer coating technology, and after drying, a single-sided positive electrode active layer is obtained; the first bottom layer slurry and the first surface layer slurry can also be coated on the other side surface of the positive electrode current collector by a slit extrusion type double-layer coating technology at the same time, and after drying, a double-sided positive electrode active layer is obtained. According to the embodiment of the present application, the preparation method further comprises: mixing the second solvent, the negative electrode conductive agent, the negative electrode binder and the negative electrode active material, respectively preparing the second bottom layer slurry and the second surface layer slurry, so that the proportion of the negative electrode conductive agent in the second bottom layer slurry is lower than the proportion of the negative electrode conductive agent in the second surface layer slurry, the proportion of the negative electrode binder in the second bottom layer slurry is higher than the proportion of the negative electrode binder in the second surface layer slurry, the particle size of the graphite in the second bottom layer slurry is larger than the particle size of the graphite in the second surface layer slurry, and the content of the silicon-based negative electrode material in the second bottom layer is lower than the content of the silicon-based negative electrode material in the second surface layer. The second bottom layer slurry and the second surface layer slurry are coated on at least one side surface of the negative electrode current collector, dried, and a negative electrode active layer is formed on the negative electrode current collector to obtain a negative electrode sheet; wherein the drying causes the second bottom layer slurry to form a second bottom layer and the second surface layer slurry to form a second surface layer.

[0058] According to the embodiment of the present application, the solid content of the second bottom layer slurry and the second surface layer slurry is the same or different and is independently selected from 50-60%.

[0059] In some embodiments, the preparation of the second bottom layer slurry comprises: adding sodium carboxymethyl cellulose into the second solvent according to the above-mentioned ratio, stirring while adding, uniformly mixing, adding single-walled carbon nanotubes, stirring uniformly to obtain a conductive glue solution; dry mixing graphite, silicon-based negative electrode material and conductive carbon black, stirring uniformly, adding dry powder, first adding conductive carbon black and then adding silicon-based negative electrode material, then adding the glue solution into the powder three times to disperse, uniformly dispersing, and finally adding styrene-butadiene rubber to form a bottom layer coating slurry. In some embodiments, the preparation of the second surface layer slurry comprises: adding sodium carboxymethyl cellulose into the second solvent according to the above-mentioned ratio, stirring while adding, uniformly mixing, adding single-walled carbon nanotubes, stirring uniformly to obtain a conductive glue solution; dry mixing graphite, silicon-based negative electrode material and conductive carbon black, stirring uniformly, adding dry powder, first adding conductive carbon black and then adding silicon-based negative electrode material, then adding the glue solution into the powder three times to disperse, uniformly dispersing, and finally adding styrene-butadiene rubber to form a surface layer coating slurry. In some embodiments, the second bottom layer slurry and the second surface layer slurry can be coated on one side surface of the negative electrode current collector by a slit extrusion type double-layer coating technology, and after drying, a single-sided negative electrode active layer is obtained; the second bottom layer slurry and the second surface layer slurry can also be simultaneously coated on the other side surface of the negative electrode current collector by a slit extrusion type double-layer coating technology, and after drying, a double-sided negative electrode active layer is obtained. According to the embodiment of the present application, the first solvent comprises NMP, and the second solvent comprises water.

[0060] The application also provides a power utilization device comprising the lithium ion battery described above or the lithium ion battery prepared by the preparation method described above.

[0061] The embodiments of the present application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be obtained by commercial purchase.

[0062] Example 1 The present example provides a lithium ion battery, and the preparation method thereof comprises the following steps: 1) Preparation of the slurry of the positive electrode bottom layer coating: according to the proportion, the binder PVDF with a content of 1.8% is added to the solvent NMP while stirring at high speed, and then the CNTs with a content of 10% are added to prepare the conductive glue solution after uniform stirring; the ternary material lithium nickel cobalt manganese oxide (LiNi 0.925 Co 0.055 Mn 0.02 O2) with a content of 0.8% is dry-mixed and stirred uniformly, 70% of the conductive glue solution is added to the uniformly mixed powder, and then the remaining 30% of the glue solution is added and stirred uniformly to form the slurry of the positive electrode bottom layer coating, and the solid content of the slurry is 74.17%; 2) Preparation of the slurry of the positive electrode surface layer coating: according to the proportion, the binder PVDF with a content of 1.0% is added to the solvent NMP while stirring at high speed, and then the CNTs with a content of 15% are added to prepare the conductive glue solution after uniform stirring; the ternary material lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2) with a content of 1.2% is dry-mixed and stirred uniformly, 70% of the glue solution is added to the uniformly mixed powder, and then the remaining 30% of the glue solution is added and stirred uniformly to form the slurry of the positive electrode surface layer coating, and the solid content of the slurry is 74.52%; 3) The slurry of the positive electrode bottom layer and the positive electrode surface layer coating obtained above is coated on the surface of the positive electrode current collector on one side by the slit extrusion type double-layer coating technology to form a single-sided double-layer coating structure, and the area density is 250 g / m 2, the positive current collector is an aluminum foil with a thickness of 15 pm; after drying the above-formed single-sided double-layer coating structure in an oven, the slurry of the above-obtained bottom layer and surface layer coating is repeatedly coated on the other side surface of the positive current collector by the slit extrusion double-layer coating technology to form a double-sided double-layer coating structure, and the areal density is 500 g / m 2 After the coating is completed, a lithium ion battery positive electrode sheet is obtained.

[0063] 4) Preparation of the slurry of the negative electrode bottom layer coating: according to the proportion, 1.3% of sodium carboxymethyl cellulose is added to the solvent H2O while stirring, and after being uniformly mixed, 10% of carbon nanotubes (O2HO17) is added and stirred uniformly to prepare a conductive glue solution; 90% of graphite (F50) with a particle size D50 of 12-14 pm, 10% of silicon-carbon material (SH-S02) with a particle size D50 of 3-13 pm, and 0.3% of conductive carbon SP are dry-mixed and stirred uniformly; when adding the dry powder, SP is added first, then the active material is added; then the glue solution is added into the powder three times for stirring and dispersion; after being uniformly dispersed, 3.0% of the binder SBR is added and stirred uniformly to form the slurry of the negative electrode bottom layer coating, and the solid content of the slurry is 51.24%; 5) Preparation of the slurry of the negative electrode surface layer coating: according to the proportion, 1.1% of sodium carboxymethyl cellulose is added to the solvent H2O while stirring, and after being uniformly mixed, 15% of carbon nanotubes (O2HO17) is added and stirred uniformly to prepare a glue solution; 86% of graphite (A61C) with a particle size D50 of 5-7 pm, 14% of silicon-carbon material (SH-S02) with a particle size D50 of 3-13 pm, and 0.5% of conductive carbon SP are dry-mixed and stirred uniformly; when adding the dry powder, SP is added first, then the active material is added; then the glue solution is added into the powder three times for stirring and dispersion; after being uniformly dispersed, 2.2% of the binder SBR is added and stirred uniformly to form the slurry of the negative electrode surface layer coating, and the solid content of the slurry is 51.68%; 6) The slurry of the above-obtained negative electrode bottom layer and negative electrode surface layer coating is simultaneously coated on the surface of one side of the negative current collector by the slit extrusion double-layer coating technology to form a single-sided double-layer coating structure, and the areal density is 109.8 g / m 2 The negative current collector is a copper foil with a thickness of 10 pm; after drying the above-formed single-sided double-layer coating structure in an oven, the slurry of the above-obtained bottom layer and surface layer coating is simultaneously coated on the other side surface of the negative current collector by the slit extrusion double-layer coating technology to form a double-sided double-layer coating structure, and the areal density is 219.7 g / m 2 After the coating is completed, a lithium ion battery negative electrode sheet is obtained.

[0064] Comparative Example 1 A lithium ion battery was prepared according to the method of Reference Example 1, and other steps and parameters were the same as those of Example 1, except that in step 1), the slurry for the positive electrode bottom coating layer was prepared using lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2) with a particle size D50 of 8-12 μm, and in step 2), the slurry for the positive electrode surface coating layer was prepared using lithium nickel cobalt manganese oxide (LiNi 0.925 Co 0.055 Mn 0.02 O2) with a particle size D50 of 4-6 μm.

[0065] Comparative Example 2 A lithium ion battery was prepared according to the method of Reference Example 1, and other steps and parameters were the same as those of Example 1, except that in step 1), the slurry for the positive electrode bottom coating layer was prepared using lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2) with a particle size D50 of 8-12 μm, and in step 2), the slurry for the positive electrode surface coating layer was prepared using lithium nickel cobalt manganese oxide (LiNi 0.925 Co 0.055 Mn 0.02 O2) with a particle size D50 of 4-6 μm; in step 4), the slurry for the negative electrode bottom coating layer was prepared using graphite (A61C) with a particle size D50 of 5-7 μm; and in step 5), the slurry for the negative electrode surface coating layer was prepared using graphite (F50) with a particle size D50 of 12-14 μm.

[0066] Comparative Example 3 A lithium ion battery was prepared according to the method of Reference Example 1, and other steps and parameters were the same as those of Example 1, except that in step 4), the slurry for the negative electrode bottom coating layer was prepared using graphite (A61C) with a particle size D50 of 5-7 μm; and in step 5), the slurry for the negative electrode surface coating layer was prepared using graphite (F50) with a particle size D50 of 12-14 μm.

[0067] Comparative Example 4 Comparative Example 4 provides a lithium ion battery, and a preparation method thereof includes the following steps: 1) Preparation of the slurry for the positive electrode coating layer: a binder PVDF with a content of 1.4% was added to a solvent NMP while stirring at high speed, and after uniform stirring, CNTs with a content of 12.5% were added to prepare a conductive glue solution; a first ternary material lithium nickel cobalt manganese oxide (LiNi 0.925 Co 0.055 Mn 0.02 O2) with a particle size D50 of 4-6 μm and a content of 50%, and a second ternary material lithium nickel cobalt manganese oxide (LiNi 0.90Co 0.05 Mn 0.05 O2) is dry-mixed with 1% conductive carbon SP until uniform. 70% conductive adhesive is added to the uniformly mixed powder and stirred until uniform. Then, the remaining 30% adhesive is added and stirred until uniform to form a slurry for the positive electrode coating. The solid content of the slurry is 74.32%. 2) The obtained positive electrode coating slurry is applied to the surfaces on both sides of the positive electrode current collector to form a single-layer coating structure; after the coating is completed, the lithium-ion battery positive electrode sheet can be obtained.

[0068] 3) Preparation of negative electrode coating slurry: Add 1.2% sodium carboxymethyl cellulose to solvent H2O while stirring, and mix evenly. Then add 12.5% ​​carbon nanotubes (O2HO17) and stir evenly to obtain conductive adhesive. Dry mix 50% graphite (F50) with a D50 particle size of 12-14μm, 50% graphite (A61C) with a D50 particle size of 5-7μm, 12% silicon carbide material (SH-SO2) with a D50 particle size of 3-13μm, and 0.4% conductive carbon SP. Stir evenly. When adding dry powder, add SP first and then add active material. Then add adhesive evenly to powder in three portions and stir to disperse. Finally, add 2.6% binder SBR and stir evenly to form negative electrode coating slurry. The solid content of slurry is 51.45%.

[0069] 4) Apply the slurry of the above-obtained negative electrode coating to the surfaces on both sides of the negative electrode current collector to form a single-layer coating structure; after the coating is completed, the lithium-ion battery negative electrode sheet can be obtained.

[0070] Performance testing: The positive and negative electrode sheets prepared in the above embodiments and comparative examples were assembled into pouch cells and then their cycle performance was tested. Cyclic performance test conditions: (1) Charging: 25±2℃, charge at 1C to 4.2V, then charge at 4.2V constant voltage until the current ≤0.01C, and let stand for 5min; Discharging: 1C to 2.75V cut-off, and let stand for 5min; (2) Charging: 45±2℃, charge at 1C to 4.2V, then charge at a constant voltage of 4.2V until the current is ≤0.05C, and let stand for 5 minutes; Discharge: 1C to 2.75V cutoff, let stand for 5 minutes.

[0071] The test results are shown in Table 1.

[0072] Table 1. Comparison of Cyclic Performance between Example 1 and Comparative Examples 1-4

[0073] In the table 1, the data means the cycle number at the capacity retention of 80%, 830+ means the cycle number is more than 830 times, and 820+ means the cycle number is more than 820 times.

[0074] From the table 1 and Figure 3 、 Figure 4 It can be seen that the cycle stability of the lithium ion battery of the embodiment 1 under the 1C / 1C charge-discharge condition is significantly better than that of the comparative examples 1-4.

[0075] The lithium ion battery of the present application has high positive and negative surface density, and the increase of the surface density reduces the amount of the current collector and thus improves the energy density of the battery. The energy density of the battery of the present application is as high as 250-300 Wh / kg. Moreover, the battery of the present application can be cycled for more than 800 times under the 1C / 1C charge-discharge condition, and the 1C / 1C charge-discharge cycle is faster than the conventional 0.5C / 0.5C test condition, which proves that the lithium ion battery of the present application has the feature of fast charging. In general, the lithium ion battery of the present application has the advantages of high energy density and fast charging. Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacement to some or all of the technical features thereof. Such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0076] In addition, those skilled in the art can understand that although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments means to be within the scope of the present application and form different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in the background section is only intended to deepen the understanding of the overall background of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes the prior art known to those skilled in the art.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on at least one side of the positive electrode current collector, and the material forming the positive electrode active layer comprises a positive electrode conductive agent, a positive electrode binder, and a positive electrode active material. The first bottom layer comprises a positive electrode active material with a particle size smaller than that of the positive electrode active material in the first surface layer, a positive electrode conductive agent with a content lower than that of the positive electrode conductive agent in the first surface layer, and a positive electrode binder with a content higher than that of the positive electrode binder in the first surface layer. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one side of the negative electrode current collector, and the material forming the negative electrode active layer comprises a negative electrode conductive agent, a negative electrode binder, and a negative electrode active material comprising graphite and a silicon-based negative electrode material. The second bottom layer comprises graphite with a particle size larger than that of the graphite in the second surface layer, a silicon-based negative electrode material with a content lower than that of the silicon-based negative electrode material in the second surface layer, a negative electrode conductive agent with a content lower than that of the negative electrode conductive agent in the second surface layer, and a negative electrode binder with a content higher than that of the negative electrode binder in the second surface layer.

2. The lithium-ion battery of claim 1, wherein, The lithium ion battery satisfies at least one of the following conditions: (1) The D50 particle size of the positive electrode active material in the first bottom layer is 4-6 μm, and the D50 particle size of the positive electrode active material in the first surface layer is 8-12 μm; (2) The positive electrode conductive agent comprises at least one of conductive carbon black, carbon nanotubes, composite conductive paste, and graphene conductive paste; (3) The positive electrode binder comprises at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, and polyvinyl butyral; (4) The mass ratio of the positive electrode active material to the positive electrode conductive agent and the positive electrode binder in the first bottom layer is 100%:8.6-13.5%:1.4-1.8%; (5) The mass ratio of the positive electrode active material to the positive electrode conductive agent and the positive electrode binder in the first surface layer is 100%:14-17.4%:1-1.4%; (6) The ratio of the area density of the first bottom layer to the area density of the first surface layer is 1:1; (7) the single surface area density of the positive electrode active layer is 200 to 260 g / m 2 ; (8) The positive electrode current collector is an aluminum foil with a thickness of 9-15 μm.

3. The lithium-ion battery of claim 2, wherein, The lithium ion battery satisfies at least one of the following conditions: (9) when the positive electrode current collector side is provided with a positive electrode active layer, the positive electrode active layer has a surface density of 200 to 260 g / m2 2 ; (10) when the opposite sides of the positive electrode current collector are each provided with a positive electrode active layer, the positive electrode active layer has a surface density of 400 to 520 g / m 2 .

4. The lithium-ion battery of claim 1, wherein, The lithium ion battery satisfies at least one of the following conditions: a. The D50 particle size of the graphite in the second bottom layer is 12-15 μm, and the D50 particle size of the graphite in the second surface layer is 5-7 μm; b. The negative electrode conductive agent comprises at least one of conductive carbon black, carbon nanotubes, composite conductive paste, and graphene conductive paste; c. The negative electrode binder comprises at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid; d. the mass ratio of graphite, silicon-based negative electrode material, negative electrode conductive agent, and negative electrode binder in the second bottom layer is 88-92%:8-12%:8.3-12.6%:3.8-4.8%; e. the mass ratio of graphite, silicon-based negative electrode material, negative electrode conductive agent, and negative electrode binder in the second surface layer is 84-88%:12-16%:12.5-16.8%:2.6-3.8%; f. the ratio of the area density of the second bottom layer to the area density of the second surface layer is 1:1; g. the silicon-based negative electrode material comprises at least one of silicon-oxygen material and silicon-carbon; h. The single-sided area density of the negative electrode active layer is 80-140 g / m 2 ; i. the negative electrode current collector is a copper foil with a thickness of 6-10 μm.

5. The lithium-ion battery of claim 4, wherein, The lithium ion battery satisfies at least one of the following conditions: g.The areal density of the negative electrode active layer is 80 to 140 g / m 2 when the negative electrode current collector side is provided with the negative electrode active layer. k.The face density of the negative electrode active layer is 160-280 g / m2 when the opposite sides of the negative electrode current collector are each provided with the negative electrode active layer. 2 .

6. A method of producing a lithium-ion battery as claimed in any one of claims 1 to 5, characterized in that, comprises: mixing the first solvent, the positive electrode conductive agent, the positive electrode binder, and the positive electrode active material to prepare a first bottom layer slurry and a first surface layer slurry, so that the proportion of the positive electrode conductive agent in the first bottom layer slurry is lower than the proportion of the positive electrode conductive agent in the first surface layer slurry, the proportion of the positive electrode binder in the first bottom layer slurry is higher than the proportion of the positive electrode binder in the first surface layer slurry, and the particle size of the positive electrode active material in the first bottom layer slurry is smaller than the particle size of the positive electrode active material in the first surface layer slurry; coating the first bottom layer slurry and the first surface layer slurry to at least one side surface of the positive electrode current collector, drying, and forming a positive electrode active layer on the positive electrode current collector to obtain a positive electrode sheet; wherein the drying causes the first bottom layer slurry to form a first bottom layer and the first surface layer slurry to form a first surface layer; mixing the second solvent, the negative electrode conductive agent, the negative electrode binder, and the negative electrode active material to prepare a second bottom layer slurry and a second surface layer slurry, so that the proportion of the negative electrode conductive agent in the second bottom layer slurry is lower than the proportion of the negative electrode conductive agent in the second surface layer slurry, the proportion of the negative electrode binder in the second bottom layer slurry is higher than the proportion of the negative electrode binder in the second surface layer slurry, the particle size of the graphite in the second bottom layer slurry is larger than the particle size of the graphite in the second surface layer slurry, and the content of the silicon-based negative electrode material in the second bottom layer is lower than the content of the silicon-based negative electrode material in the second surface layer; coating the second bottom layer slurry and the second surface layer slurry to at least one side surface of the negative electrode current collector, drying, and forming a negative electrode active layer on the negative electrode current collector to obtain a negative electrode sheet; wherein the drying causes the second bottom layer slurry to form a second bottom layer and the second surface layer slurry to form a second surface layer.

7. The method for preparing a lithium-ion battery according to claim 6, characterized in that, The solid content of the first bottom layer slurry and the first surface layer slurry is the same or different and is independently selected from 70-80%.

8. The method for preparing a lithium-ion battery according to claim 6, characterized in that, The solid content of the second bottom layer slurry and the second surface layer slurry is the same or different and is independently selected from 50-60%.

9. The method of claim 6, wherein the lithium ion battery is prepared by the steps of: The first solvent comprises NMP, and the second solvent comprises water. ​ 10. An electric device, characterized by The lithium ion battery prepared by the preparation method of the lithium ion battery according to any one of claims 6-9.

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