Negative electrode sheet, method for manufacturing the same, and lithium battery

Abstract

The application relates to the technical field of lithium batteries, and discloses a negative electrode sheet, a preparation method thereof and a lithium battery. The negative electrode sheet comprises a current collector and an active layer arranged on the surface of the current collector; the composition of the active layer comprises a negative electrode active material, a conductive agent, a binder and an additive; and the additive is a metal oxide with an inverse opal structure. The active layer of the negative electrode sheet is added with the metal oxide with the inverse opal structure, the metal oxide can endow the negative electrode sheet with a special pore structure, improve the porosity of the negative electrode sheet, improve the wettability of electrolyte to the negative electrode sheet, and improve the liquid retention of the negative electrode sheet.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a negative electrode sheet, a preparation method thereof and a lithium battery. BACKGROUND

[0002] Lithium ion secondary battery technology is developing rapidly, and its application range is also becoming wider and wider. At present, the performance requirements for lithium ion batteries on the market are becoming higher and higher, and it is required that the lithium ion battery has high energy density and high rate performance at the same time. When the energy density of the lithium ion battery is improved by increasing the coating amount of the electrode sheet and the compaction density of the material, the conventional graphite and silicon negative electrode lithium ion battery will cause the tortuosity of the electrode sheet to increase significantly, the electrolyte infiltration degree to decrease, and the ion transmission rate to decrease, thereby causing the rate performance to decrease and the power performance of the battery to be lost. In order to realize high energy density and high rate performance of the lithium ion battery at the same time, it is necessary to improve the specific surface area of the negative electrode material, the porosity of the negative electrode sheet, and the micropore structure of the electrode sheet, so as to improve the energy density while ensuring the lithium ion transmission rate.

[0003] At present, the main ways to improve the porosity of the negative electrode sheet and the electrolyte infiltration include adding a pore-forming agent and laser drilling, etc. Among them, the method of adding a pore-forming agent will increase the impurity proportion due to the lack of lithium storage capacity of the pore-forming agent, which will affect the performance and energy density of the lithium battery, and the laser drilling method has high cost and increases the drilling process.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a negative electrode sheet, a preparation method thereof and a lithium battery.

[0006] The present application is implemented in the following manner:

[0007] In a first aspect, the present application provides a negative electrode sheet, comprising a current collector and an active layer arranged on the surface of the current collector.

[0008] The composition of the active layer comprises a negative electrode active material, a conductive agent, a binder and an additive.

[0009] The additive is a metal oxide with inverse opal structure.

[0010] In an optional embodiment, the active layer is a multilayer structure.

[0011] In the direction away from the current collector, the additive content of each layer of the multilayer structure of the active layer gradually increases.

[0012] In an optional embodiment, the additive content of each layer of the multilayer structure of the active layer satisfies the following formula: The active layer is defined as the layer closest to the current collector, where a1 represents the percentage of additives in the first layer relative to the total mass of the active layer. n The percentage of the additive in the nth layer relative to the total active mass, where n is the current layer number. 总 n is the total number of active layers. 总 ≥2, where p is the mass percentage of the additive in the entire active layer, 0.1% ≤ p ≤ 50%;

[0013] When n 总 ≥2, 0≤a1 <p / n 总 a n Starting from the current collector side, the layer gradually increases towards the outermost layer.

[0014] In an optional implementation, the metal oxide satisfies:

[0015] The D50 of the metal oxide is 1–40 μm; and / or the internal pore size of the metal oxide particles is 0.05–20 μm, and the internal pore volume accounts for 50–90% of the particle volume.

[0016] In an optional embodiment, the metal oxide is selected from at least one of titanium dioxide, tin dioxide, and germanium dioxide.

[0017] In an optional embodiment, the active layer comprises, by mass percentage, 43-97.9% negative electrode active material, 0.5-3% conductive agent, 1-2.5% binder, and 0.1-50% additives.

[0018] In an optional embodiment, the active layer further comprises 0.5 to 1.5% dispersant by mass percentage;

[0019] The dispersant is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and sodium carboxyethyl cellulose.

[0020] In an optional implementation, at least one of the following features (1)-(4) is also included:

[0021] (1) The conductive agent is selected from at least one of carbon black, graphite sheets, carbon nanotubes and graphene;

[0022] (2) The adhesive is selected from at least one of styrene-butadiene rubber, sodium polyacrylate, sodium alginate and polyacrylonitrile;

[0023] (3) The negative electrode active material is selected from at least one of graphite, hard carbon, soft carbon, lithium titanate and mesophase carbon microspheres;

[0024] (4) An active layer is provided on both opposite sides of the current collector.

[0025] In a second aspect, the application provides a method for preparing a negative electrode sheet, for preparing the negative electrode sheet according to any one of the preceding embodiments, comprising coating a negative electrode slurry containing various components of an active layer on the surface of a current collector, and then drying and cold-pressing.

[0026] In a third aspect, the application provides a lithium battery comprising the negative electrode sheet according to any one of the preceding embodiments.

[0027] The application has the following beneficial effects:

[0028] The negative electrode sheet provided by the embodiments of the application has the metal oxide with inverse opal structure added in the active layer of the negative electrode sheet, the metal oxide can endow the negative electrode sheet with special pore structure, improve the porosity of the negative electrode sheet, improve the wettability of the electrolyte to the negative electrode sheet, and improve the liquid retention amount of the negative electrode sheet. When the metal oxide with lithium storage function is selected as the additive, the lithium storage capacity of the negative electrode will not be reduced. Therefore, by adding the metal oxide with inverse opal structure in the negative electrode active layer, the rate capability of the negative electrode sheet can be increased, the internal resistance of the battery can be reduced, and the transmission rate of lithium ions can be ensured. The negative electrode sheet can solve the problems of reduced electrolyte wettability, reduced ion transmission rate, and further caused reduction of rate capability and loss of power performance of the battery when the coating amount and the compaction density of the material of the negative electrode sheet are increased to improve the energy density of the lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the 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 of the embodiments of the application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0030] Figure 1 The simulation structure schematic diagram of the active layer of the negative electrode sheet prepared for Example 2;

[0031] Figure 2 The simulation structure schematic diagram of the active layer of the negative electrode sheet prepared for Example 3.

[0032] Figure legend: 1-inverse opal porous layer; 2-graphite layer; 3-current collector; 4-inverse opal and graphite mixed porous layer. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the application more clear, the technical solutions in the embodiments of the application will be described clearly and completely. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be purchased on the market.

[0034] The features and performances of the present application are further described in detail below in combination with embodiments.

[0035] The negative electrode provided by the embodiments of the present application comprises a current collector and an active layer arranged on the surface of the current collector.

[0036] The components of the active layer comprise a negative electrode active material, a conductive agent, a binder and an additive.

[0037] The additive is a metal oxide with inverse opal structure.

[0038] The negative electrode provided by the embodiments of the present application has the metal oxide with inverse opal structure added in the active layer of the negative electrode. The metal oxide can endow the negative electrode with special pore structure, improve the porosity of the negative electrode, improve the wettability of the electrolyte to the negative electrode and improve the liquid retention of the negative electrode. Therefore, the addition of the metal oxide with inverse opal structure in the negative electrode active layer can increase the rate capability of the negative electrode, reduce the internal resistance of the battery and ensure the transmission rate of lithium ions. The negative electrode can solve the problems of reduced electrolyte wettability, reduced ion transmission rate and further caused decreased rate capability and lost power performance of the battery when the energy density of the lithium ion battery is improved by increasing the coating amount of the electrode and the compaction density of the material.

[0039] It should be noted that the preparation of the metal oxide with inverse opal structure is currently a prior art and thus is not described in detail in the present case.

[0040] Optionally, the active layer can be arranged on any one side or opposite sides of the current collector.

[0041] Optionally, to better improve the wettability and liquid retention of the negative electrode and other performances, the active layer has a multi-layer structure. The additive content of each layer of the multi-layer structure of the active layer gradually increases in the direction away from the current collector, and the additive is uniformly distributed in each layer of the active layer.

[0042] Further, to ensure that the negative electrode has better high-rate performance, the additive content of each layer of the multi-layer structure of the active layer satisfies the following formula: wherein the layer closest to the current collector in the active layer is the first layer, a1 is the percentage of the additive in the first layer in the mass of the entire active layer, a n a n is the percentage of the additive in the nth layer in the mass of the entire active layer, n is the current layer number, n 总 is the total number of layers of the active layer, n 总 ≥ 2, p is the mass percentage of the additive in the entire active layer, 0.1% ≤ p ≤ 50%;

[0043] when n 总≥ 2, 0 < a1 < p / n 总 , a n Gradually increase from the current collector side to the outermost layer.

[0044] Preferably, the metal oxide is a metal oxide with lithium storage capacity. When the added metal oxide is a metal oxide with lithium storage capacity, the negative electrode can have better lithium storage capacity, ensuring that the negative electrode has better energy density.

[0045] Optionally, to further ensure the electrochemical performance of the negative electrode sheet, the D50 of the metal oxide in the active layer is 1-40 μm. A D50 within this range can not only improve the porosity of the negative electrode sheet and improve the wettability of the electrolyte to the negative electrode sheet, but also enable the negative electrode sheet to have higher energy density. When the D50 is less than 1 μm, the particle size is too small to improve the porosity of the negative electrode sheet. When the D50 is greater than 40 μm, the compaction density of the negative electrode sheet will be reduced, thereby reducing the energy density of the lithium ion battery. Preferably, the D50 is 10 μm, 20 μm, or 30 μm.

[0046] Similarly, further, the internal pore size of the metal oxide particles is 0.05-20 μm. Within this range, not only can the porosity of the negative electrode sheet be improved, the wettability of the electrolyte to the negative electrode sheet can be improved, but also the negative electrode sheet can have higher energy density. Preferably, the internal pore size is 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, or 19 μm. When the internal pore size of the metal oxide particles is less than 0.05 μm, the particle pore size is too small to effectively improve the porosity of the negative electrode sheet. When the internal pore size of the metal oxide particles is greater than 20 μm, the compaction density of the negative electrode sheet will be reduced, thereby reducing the energy density of the lithium ion battery.

[0047] Similarly, further, the internal pore volume accounts for 50-90% of the particle volume. Within this range, not only can the porosity of the negative electrode sheet be improved, the wettability of the electrolyte to the negative electrode sheet can be improved, but also the negative electrode sheet can have higher energy density. Preferably, the internal pore volume accounts for 60%, 70%, or 80% of the particle volume. When the internal pore volume accounts for less than 50% of the particle volume, the porosity of the negative electrode sheet cannot be effectively improved. When the internal pore volume accounts for more than 90% of the particle volume, the compaction density of the negative electrode sheet will be reduced, thereby reducing the energy density of the lithium ion battery.

[0048] Optionally, the metal oxide is selected from at least one of titanium dioxide, tin dioxide, and germanium dioxide.

[0049] Optionally, the composition of the active layer includes, in terms of mass percentage, 43-97.9% of the negative electrode active material, 0.5-3% of the conductive agent, 1-2.5% of the binder, and 0.1-50% of the additive.

[0050] Optionally, to ensure that the negative electrode sheet has better performance, the coating surface density of the active layer is 40-400 g / m 2 .

[0051] Optionally, the negative active material is selected from at least one of graphite, hard carbon, soft carbon, lithium titanate and mesocarbon microbeads.

[0052] Optionally, the conductive agent is selected from at least one of carbon black, graphite sheet, carbon nanotube and graphene.

[0053] Optionally, the binder is selected from at least one of butadiene styrene rubber, sodium polyacrylate, sodium alginate and polyacrylonitrile.

[0054] Optionally, the active layer further includes 0.5-1.5% of a dispersant in terms of mass percentage.

[0055] Optionally, the dispersant is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose and sodium carboxyethyl cellulose.

[0056] The preparation method of the negative electrode sheet provided in the embodiments of the present application is used to prepare the negative electrode sheet provided in the embodiments of the present application, and includes coating negative electrode slurry containing various components of the active layer on the surface of the current collector, and then drying and cold pressing.

[0057] Specifically, if the active layer has a one-layer structure, the negative electrode slurry is coated in one layer, and then dried and cold pressed; if the active layer has a multi-layer structure, the negative electrode slurries corresponding to different layers are sequentially coated, and then dried and cold pressed.

[0058] The lithium battery provided in the embodiments of the present application includes the negative electrode sheet provided in the embodiments of the present application. Since the battery includes the negative electrode sheet provided in the embodiments of the present application, the battery has better electrochemical performance.

[0059] The present application will be further described below in combination with multiple embodiments and comparative examples.

[0060] Embodiment 1

[0061] A negative electrode sheet is prepared by the following method:

[0062] Graphite, titanium dioxide with inverse opal structure, conductive agent carbon black, binder butadiene styrene rubber and dispersant sodium carboxymethyl cellulose are mixed in a mass ratio of 47.5%:47.5%:2%:1.8%:1.2% with water to obtain negative electrode slurry, and the solid content of the negative electrode slurry is 45%. The particle size D50 of the titanium dioxide is 20 μm, the internal pore size is 1-5 μm, and the pore volume ratio is 70%.

[0063] The negative electrode slurry is coated on both sides of the current collector, dried, cold-pressed, and cut to obtain a negative electrode sheet, wherein the active layer coating surface density is 300 g / m 2 .

[0064] Example 2

[0065] A composite negative electrode sheet is prepared by the following method:

[0066] Graphite, conductive agent carbon black, adhesive styrene-butadiene rubber, and dispersant sodium carboxymethyl cellulose are mixed in a mass ratio of 95%:2%:1.8%:1.2% with water to obtain a negative electrode slurry a with a solid content of 45%.

[0067] Titanium dioxide with inverse opal structure, conductive agent carbon black, adhesive styrene-butadiene rubber, and dispersant sodium carboxymethyl cellulose are mixed in a mass ratio of 95%:2%:1.8%:1.2% with water to obtain a negative electrode slurry b with a solid content of 45%. The titanium dioxide has a particle size D50 of 20 μm, an internal pore size of 1-5 μm, and a pore volume ratio of 70%.

[0068] The slurry a is coated on both sides of the current collector, the slurry b is coated on the slurry a, dried, cold-pressed, and cut to obtain a negative electrode sheet, wherein the active layer coating surface density is 300 g / m 2 , the first layer is 150 g / m 2 , and the second layer is 150 g / m 2 .

[0069] In the prepared negative electrode sheet, the titanium dioxide with inverse opal structure is concentrated and dispersed on the side far from the current collector, and the graphite, titanium dioxide, conductive agent, adhesive, and dispersant are in a mass ratio of 47.5%:47.5%:2%:1.8%:1.2%.

[0070] The structure of the prepared negative electrode sheet is shown in Figure 1 , wherein the graphite layer 2 and the inverse opal porous layer 1 are sequentially formed on the opposite sides of the current collector 3.

[0071] Example 3

[0072] A composite negative electrode sheet is prepared by the following method:

[0073] Graphite, conductive agent carbon black, adhesive styrene-butadiene rubber, and dispersant sodium carboxymethyl cellulose are mixed in a mass ratio of 95%:2%:1.8%:1.2% with water to obtain a negative electrode slurry a with a solid content of 45%.

[0074] The graphite, the titanium dioxide with inverse opal structure, the conductive agent carbon black, the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose and water are mixed according to the mass ratio of 47.5%:47.5%:2%:1.8%:1.2% to obtain the negative electrode slurry b with a solid content of 45%. The titanium dioxide has a particle size D50 of 20 μm, an internal pore size of 1-5 μm, and a pore volume ratio of 70%.

[0075] The titanium dioxide with inverse opal structure, the conductive agent carbon black, the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose and water are mixed according to the mass ratio of 95%:2%:1.8%:1.2% to obtain the negative electrode slurry c with a solid content of 45%. The titanium dioxide has a particle size of 20 μm, an internal pore size of 1-5 μm, and a pore volume ratio of 70%.

[0076] The arrangement of each layer of the active layer satisfies the formula n 总 = 3, a1 = 0, and p = 47.5%; that is, the additive content of the first layer of the active layer is 0, the additive content of the second layer is 15.83%, and the additive content of the third layer is 31.67%. The slurry a is coated on both sides of the current collector, the slurry b is coated on the slurry a, the slurry c is coated on the slurry b, and then drying, cold pressing and cutting are performed to obtain the negative electrode sheet, wherein the surface density of the active layer is 300 g / m 2 , the surface density of the first layer is 100 g / m 2 , the surface density of the second layer is 100 g / m 2 , and the surface density of the third layer is 100 g / m 2 .

[0077] The prepared negative electrode sheet has the titanium dioxide with inverse opal structure gradiently dispersed on the side far from the current collector, and the graphite, the titanium dioxide, the conductive agent, the binder and the dispersant have a mass ratio of 47.5%:47.5%:2%:1.8%:1.2%.

[0078] The prepared negative electrode sheet has the structure as shown in Figure 2 , wherein the graphite layer 2 and the inverse opal and graphite mixed porous layer 4 are sequentially formed on the opposite sides of the current collector 3.

[0079] Example 4

[0080] The present example is basically the same as example 3, except that the present example does not satisfy the formula , the additive content of the first layer is 15.83%, the additive content of the second layer is 31.67%, and the additive content of the third layer is 0%.

[0081] The slurry a, the slurry b and the slurry c are prepared as in example 3, the slurry b is coated on both sides of the current collector, the slurry c is coated on the slurry b, and the slurry a is coated on the slurry c, and then drying, cold pressing and cutting are performed to obtain the negative electrode sheet.

[0082] The prepared negative electrode sheet has no reverse opal structure titanium dioxide distributed according to the formula, and the mass ratio of graphite, titanium dioxide, conductive agent, binder, dispersing agent in the negative electrode sheet is 47.5:47.5:2:1.8:1.2%.

[0083] Example 5

[0084] This example is basically the same as Example 2, except that the coating order of slurry a and slurry b is exchanged.

[0085] Example 6

[0086] This example is basically the same as Example 2, except that the components of slurry a are graphite: conductive agent carbon black: binder styrene butadiene rubber: dispersing agent sodium carboxymethyl cellulose = 95:2:1.8:1.2%;

[0087] The components of slurry b are graphite: opal structure titanium dioxide: conductive agent carbon black: binder styrene butadiene rubber: dispersing agent sodium carboxymethyl cellulose in the mass ratio of 94.8:0.2:2:1.8:1.2%.

[0088] The prepared negative electrode sheet has reverse opal structure titanium dioxide concentrated and dispersed away from the current collector side, and the mass ratio of graphite, titanium dioxide, conductive agent, binder, dispersing agent in the negative electrode sheet is 94.9:0.1:2:1.8:1.2%, wherein the first layer additive content is 0%, and the second layer content is 0.1%.

[0089] Similarly, the active layer coating surface density is 300 g / m 2 , the first layer is 150 g / m 2 , and the second layer is 150 g / m 2 .

[0090] Example 7

[0091] This example is basically the same as Example 2, except that the components of slurry a are graphite: conductive agent carbon black: binder styrene butadiene rubber: dispersing agent sodium carboxymethyl cellulose = 95:2:1.8:1.2%;

[0092] The components of slurry b are graphite: opal structure titanium dioxide: conductive agent carbon black: binder styrene butadiene rubber: dispersing agent sodium carboxymethyl cellulose in the mass ratio of 75:20:2:1.8:1.2%.

[0093] The prepared negative electrode sheet has the reverse opal structure titanium dioxide dispersed on the side far from the current collector, and the mass ratio of graphite, titanium dioxide, conductive agent, binder, and dispersant in the negative electrode sheet is 85%:10%:2%:1.8%:1.2%. The first layer contains 0% of the additive, and the second layer contains 10% of the additive.

[0094] Similarly, the active layer has a coating surface density of 300 g / m 2 , the first layer has a coating surface density of 150 g / m 2 , and the second layer has a coating surface density of 150 g / m 2 .

[0095] Example 8

[0096] This example is basically the same as Example 2, except that the components of slurry a are graphite: conductive agent carbon black: binder styrene-butadiene rubber: dispersant sodium carboxymethyl cellulose = 95%:2%:1.8%:1.2%.

[0097] The components of slurry b are graphite: opal structure titanium dioxide: conductive agent carbon black: binder styrene-butadiene rubber: dispersant sodium carboxymethyl cellulose in a mass ratio of 55%:40%:2%:1.8%:1.2%.

[0098] The prepared negative electrode sheet has the reverse opal structure titanium dioxide dispersed on the side far from the current collector, and the mass ratio of graphite, titanium dioxide, conductive agent, binder, and dispersant in the negative electrode sheet is 75%:20%:2%:1.8%:1.2%. The first layer contains 0% of the additive, and the second layer contains 20% of the additive.

[0099] Similarly, the active layer has a coating surface density of 300 g / m 2 , the first layer has a coating surface density of 150 g / m 2 , and the second layer has a coating surface density of 150 g / m 2 .

[0100] Comparative Example

[0101] A negative electrode sheet is prepared by the following method:

[0102] Graphite, conductive agent carbon black, binder styrene-butadiene rubber, dispersant sodium carboxymethyl cellulose, and water are mixed to obtain a negative electrode slurry with a solid content of 45%, which is coated on both sides of the current collector, dried, cold-pressed, and cut to obtain a negative electrode sheet.

[0103] Experimental Example

[0104] The above negative electrode sheets of each example and comparative example are assembled into soft-pack lithium ion batteries, and the positive electrode sheets, separators, and electrolytes involved are as follows:

[0105] Preparation of positive electrode sheet: lithium iron phosphate, conductive agent, and adhesive were mixed in a mass ratio of 95.5%:2.5%:2% with N-methyl pyrrolidone to obtain a positive electrode slurry with a solid content of 55%, which was coated on both sides of an aluminum foil current collector, dried, cold-pressed, and cut to obtain a positive electrode sheet.

[0106] Separator: a polypropylene separator with a thickness of 16 μm was used.

[0107] Preparation of electrolyte: dimethyl carbonate, ethylene carbonate, and diethyl carbonate were mixed in a ratio of 1:1:1, and lithium hexafluorophosphate was added, wherein the concentration of lithium hexafluorophosphate was 1.1 mol / L.

[0108] (1) Porosity test of electrode sheet: cut an electrode sheet of a certain size, calculate the apparent volume V1, use a true density tester to test the true volume V2 of the electrode sheet, and then calculate the porosity according to (V1-V2) / V1x100%.

[0109] (2) Rate discharge performance test: at 25°C, charge at 1C constant current and constant voltage to 3.65V, cut off at 0.05C current, stand for 30 min, discharge at nC constant current to 2.2V, record the discharge capacity retention rate, n=1, 3, 5, and the discharge capacity retention rate is nC discharge capacity / 1C discharge capacityx100%.

[0110] (3) Direct current resistance DCR test: at 25°C, adjust to 50% SOC state, stand for 1h, record OCV1, discharge at 3C for 10s, record OCV2, and then calculate DCR according to (OCV1-OCV2) / 3Cx1000. Record the test results in Table 1.

[0111] Table 1 Test results of each example and comparative example

[0112]

[0113] From the test data in Table 1, it can be seen that the negative electrode sheets prepared in each example of the application have better performance when assembled into batteries.

[0114] Comparing Examples 1-3 with the comparative example, the additive content is high, the porosity is significantly higher, the capacity retention rate is significantly higher, and the direct current resistance is significantly smaller.

[0115] Comparing Example 5 with Example 2, the performance of Example 2 is better, and comparing Example 1 with Example 2, the performance of Example 2 is better, which indicates that when the inverse opal structure titanium dioxide is concentrated on the outer side of the negative electrode sheet, it has better electrochemical performance.

[0116] Compared with example 6, example 7 and example 8, the electrochemical performance of example 2 is better, which indicates that when the titanium dioxide is distributed on the outside, the higher the content is, the better the rate performance is, and the smaller the direct current resistance is.

[0117] Compared with example 4, the performance of example 3 is better, which indicates that when the content is higher near the outside and meets the formula provided in the application, the electrochemical performance is better.

[0118] In summary, the negative electrode sheet provided in the embodiments of the application has the metal oxide with inverse opal structure added in the active layer of the negative electrode sheet, the metal oxide can give the negative electrode sheet special pore structure, improve the porosity of the negative electrode sheet, improve the wettability of the electrolyte to the negative electrode sheet, improve the liquid retention amount of the negative electrode sheet, and the metal oxide selected from the metal oxides with lithium storage function as the additive will not reduce the lithium storage capacity of the negative electrode, therefore, by adding the metal oxide with lithium storage function and inverse opal structure in the negative electrode active layer, the energy density and rate performance of the negative electrode sheet can be increased, and the transmission rate of lithium ions can also be ensured. The negative electrode sheet can improve the problem that when the energy density of the lithium ion battery is improved by increasing the coating amount of the electrode sheet and the compaction density of the material, the electrolyte wettability is reduced, the ion transmission rate is reduced, and then the rate performance is reduced, and the power performance of the battery is lost.

[0119] The above only describes the preferred embodiments of the application and is not used to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A negative electrode sheet, characterized in that, Includes a current collector and an active layer disposed on the surface of the current collector; The active layer comprises negative electrode active material, conductive agent, binder and additives; The additive is a metal oxide with an inverse opal structure; The active layer has a multi-layer structure; Along the direction away from the current collector, the additive content in each layer of the active layer of the multilayer structure gradually increases; The content of the additive in each layer of the multilayer structure of the active layer satisfies the following formula: The active layer, with the layer closest to the current collector being the first layer, is described as follows: The percentage of the additive in the first layer by the total mass of the active layer. This represents the percentage of the additive in the nth layer relative to the total active mass, where n is the current layer number. The total number of active layers. ≥2, where p is the mass percentage of the additive in the entire active layer, 0.1%≤p≤50%; when ≥2, / , Starting from the current collector side, the layer gradually increases towards the outermost layer.

2. The negative electrode sheet according to claim 1, characterized in that, The metal oxide satisfies: The D50 of the metal oxide is 1~40 μm; and / or, The internal pore size of the metal oxide particles is 0.05~20μm, and the internal pore volume accounts for 50~90% of the particle volume.

3. The negative electrode sheet according to claim 2, characterized in that, The metal oxide is selected from at least one of titanium dioxide, tin dioxide, and germanium dioxide.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that, The active layer comprises, by mass percentage, 43-97.9% of the negative electrode active material, 0.5-3% of the conductive agent, 1-2.5% of the binder, and 0.1-50% of the additives.

5. The negative electrode sheet according to claim 4, characterized in that, The active layer also includes 0.5-1.5% dispersant by mass percentage; The dispersant is selected from at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and sodium carboxyethyl cellulose.

6. The negative electrode sheet according to claim 1, characterized in that, It also includes at least one of the following features (1)-(4): (1) The conductive agent is selected from at least one of carbon black, graphite sheets, carbon nanotubes and graphene; (2) The adhesive is selected from at least one of styrene-butadiene rubber, sodium polyacrylate, sodium alginate and polyacrylonitrile; (3) The negative electrode active material is selected from at least one of graphite, hard carbon, soft carbon, lithium titanate and mesophase carbon microspheres; (4) The active layer is provided on both opposite sides of the current collector.

7. A method for preparing a negative electrode sheet, characterized in that, The method for preparing the negative electrode sheet as described in any one of claims 1 to 6 includes coating the surface of the current collector with a negative electrode slurry containing various components of the active layer, followed by drying and cold pressing.

8. A lithium battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 6.

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