Negative electrode sheet and lithium ion battery

Abstract

The application relates to the technical field of batteries, in particular to a negative plate and a lithium ion battery. The negative plate comprises a current collector, a graphite layer, a hard carbon layer and a ceramic layer. The graphite layer is arranged on at least one surface of the current collector, the hard carbon layer is arranged on the surface of the graphite layer away from the current collector, and the ceramic layer is arranged on the surface of the hard carbon layer away from the current collector. The application utilizes three kinds of materials with different layer spacings, porosities and compaction densities, designs a multilayer gradient negative electrode, constructs a high-flux ion migration path and realizes the super-fast charging target.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries have been popularized in daily life, including mobile phone type electronic products, electric vehicles and power grid energy storage, etc. At present, various high specific energy lithium ion batteries can meet the demand of electric vehicle range to a certain extent, but compared with traditional fuel vehicles, the charging time is still one of the bottlenecks of popularization and use. Although the electrolyte is the most significant factor affecting the essential fast charging capacity of the battery cell, under the condition of large current charging, a large number of lithium ions will be quickly and simultaneously stripped from the positive electrode and inserted into the negative electrode, causing polarization of the negative electrode. If the negative electrode potential drops below 0V, it will cause the lithium ions to be unable to insert into the negative electrode and be precipitated on the surface of the negative electrode, resulting in an increase in irreversible capacity decay and even causing safety problems. Therefore, optimizing the negative electrode structure and material system is crucial to improve the diffusion capacity of lithium ions.

[0003] The patent with publication number CN117352959A discloses a separator film. The technology sets a composite coating on the surface of the separator film, which includes ceramic material and polyacrylate. The composite coating forms an active ion bridge high-speed channel, which can improve the transportation efficiency of ions and improve the fast charging performance. However, there are differences in ion transportation paths between the coating on the surface of the separator film and the coating on the surface of the electrode, and the coating cannot improve the pore infiltration of the electrode, which is insufficient in performance during long cycle and high rate fast charging. SUMMARY

[0004] Therefore, the present application provides a negative electrode sheet and a lithium ion battery. The multi-layer gradient negative electrode design of the negative electrode sheet can improve the fast charging performance of the battery.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] In a first aspect, the present application provides a negative electrode sheet, which comprises:

[0007] a) a current collector 10;

[0008] b) a graphite layer 20, which is arranged on at least one surface of the current collector 10;

[0009] c) a hard carbon layer 30, which is arranged on the surface of the graphite layer 20 away from the current collector 10;

[0010] d) a ceramic layer 40, which is arranged on the surface of the hard carbon layer 30 away from the current collector 10.

[0011] In the embodiment of the present application, the interlayer spacing of the graphite of the graphite layer is denoted as Al, the interlayer spacing of the hard carbon of the hard carbon layer is denoted as A2, and the interlayer spacing of the ceramic of the ceramic layer is denoted as A3, and Al, A2, A3 satisfy Al < A2 < A3.

[0012] In the embodiment of the present application, the porosity of the graphite layer is denoted as Bl, the porosity of the hard carbon layer is denoted as B2, and the porosity of the ceramic layer is denoted as B3, and Bl, B2, B3 satisfy Bl < B2 < B3.

[0013] In the embodiment of the present application, the compact density of the graphite layer is denoted as Cl, the compact density of the hard carbon layer is denoted as C2, and the compact density of the ceramic layer is denoted as C3, and Cl, C2, C3 satisfy C2 < Cl < C3.

[0014] Preferably, the interlayer spacing of the graphite of the graphite layer is 0.3354-0.3366 nm.

[0015] Preferably, the interlayer spacing of the hard carbon of the hard carbon layer is 0.37-0.42 nm.

[0016] Preferably, the interlayer spacing of the ceramic of the ceramic layer is 0.44-0.47 nm.

[0017] Preferably, the porosity of the graphite layer is 10%-16%.

[0018] Preferably, the porosity of the hard carbon layer is 30%-40%.

[0019] Preferably, the porosity of the ceramic layer is 60%-90%.

[0020] Preferably, the compact density of the graphite layer is 1.4-1.6 g / cm 3 .

[0021] Preferably, the compact density of the hard carbon layer is 0.95-1.05 g / cm 3 .

[0022] Preferably, the compact density of the ceramic layer is 3.8-4.1 g / cm 3 .

[0023] In the embodiment of the present application, the graphite layer comprises composite graphite, and the composite graphite comprises first graphite and second graphite.

[0024] Preferably, the particle size D 50 of the first graphite is 12-15 μm.

[0025] Preferably, the particle size D 50 of the second graphite is 4-7 μm.

[0026] Preferably, the specific surface area of the first graphite is ≤1.4 m 2 / g.

[0027] As preferred, the specific surface area of the second graphite is ≤2.6m 2 / g.

[0028] As preferred, the compaction density of the first graphite is ≤1.6g / cm 3 .

[0029] As preferred, the compaction density of the second graphite is ≤1.4g / cm 3 .

[0030] As preferred, the gram capacity of the first graphite is ≥350mAh / g.

[0031] As preferred, the gram capacity of the second graphite is ≥330mAh / g.

[0032] As preferred, the mass ratio of the first graphite in the composite graphite is 80%~90%.

[0033] As preferred, the mass ratio of the second graphite in the composite graphite is 10%~20%.

[0034] In the embodiment of the present application, the hard carbon layer comprises at least one of biomass-based hard carbon, resin-based hard carbon and pitch-based hard carbon.

[0035] In the embodiment of the present application, the ceramic layer comprises at least one of Al2O3, SiO2, ZrO2, TiO2, MgO, MnO and Cr2O3.

[0036] In a preferred embodiment of the present application, the surface of the current collector comprises a main area 100 and an edge area 200, and the edge area 200 is located on both sides of the main area 100.

[0037] The hard carbon layer 30 is arranged on the surface of the main area 100 and the edge area 200.

[0038] In the main area 100, the graphite layer 20 is arranged on the surface of the current collector 10 and directly contacts the surface of the current collector; the hard carbon layer 30 is arranged on the surface of the graphite layer 20 and directly contacts the surface of the graphite layer.

[0039] In the edge area 200, the hard carbon layer 30 is arranged on the surface of the current collector and directly contacts the surface of the current collector.

[0040] In another preferred embodiment of the present application, the edge area 200 comprises a first edge area 210 and a second edge area 220, and the first edge area 210 is arranged between the main area 100 and the second edge area 220.

[0041] The ceramic layer 40 is arranged on the surface of the main area 100 and the edge area 200.

[0042] In the main body region 100, the ceramic layer 40 is disposed on the surface of the hard carbon layer 30 and directly contacts the surface of the hard carbon layer;

[0043] In the first edge region 210, the hard carbon layer 30 is disposed on the surface of the current collector and directly contacts the surface of the current collector;

[0044] In the second edge region 220, the ceramic layer 40 is disposed on the surface of the current collector and directly contacts the surface of the current collector.

[0045] Preferably, the width of the first edge region 210 is 10-40 μm.

[0046] Preferably, the width of the second edge region 220 is 2-5 μm.

[0047] Preferably, the thickness ratio of the graphite layer to the hard carbon layer is (1.5-2.5):1.

[0048] Preferably, the thickness ratio of the hard carbon layer to the ceramic layer is (6-20):1.

[0049] Preferably, the thickness of the graphite layer 20 is 60-80 μm.

[0050] Preferably, the thickness of the hard carbon layer 30 is 30-40 μm.

[0051] Preferably, the thickness of the ceramic layer 40 is 2-5 μm.

[0052] In a second aspect, the present application provides a lithium ion battery comprising the above negative electrode sheet.

[0053] Compared with the prior art, the present application has the beneficial effects of:

[0054] (1) Multilayer gradient negative electrode: The present application uses three kinds of materials with different layer spacing, porosity and compaction density to design a multilayer gradient negative electrode, which constructs a high-flux ion migration path and realizes the goal of super-fast charging. The multilayer gradient electrode design can ensure high-concentration lithium ion diffusion and embedding into graphite. During high-rate charging, a large number of lithium ions are released from the positive electrode, first entering the ceramic layer, which can store ions and accelerate ion migration. The layer spacing of the hard carbon layer is larger than that of the graphite layer, which can ensure rapid embedding of more ions and prevent lithium precipitation caused by the negative electrode being unable to quickly provide enough lithium-embedding sites during high-current charging, thereby improving the fast-charging performance of the battery.

[0055] (2) Ceramic layer: The ceramic layer has a high pore structure, can quickly absorb and store electrolyte, has excellent liquid absorption and liquid retention, and improves the electrolyte wetting effect of the negative electrode. After the battery is injected with electrolyte, the electrolyte will quickly wet the ceramic layer, and then enter the hard carbon layer and the graphite layer. Even if the graphite is in a high compaction density (compaction density > 1.5 g / cm 3 ), it can also be well wetted by the electrolyte. During the cycle process, the stored electrolyte in the ceramic layer can ensure the liquid-rich state of the electrode, prolonging the cycle life of the lithium ion battery.

[0056] Moreover, the ceramic layer is an oxide ceramic layer, which can improve the SEI film decomposition temperature and delay the thermal runaway time of the battery.

[0057] (3) Hard carbon layer: Li + The storage mechanism in the hard carbon mainly includes: 1) adsorption of Li + by nanopores, 2) adsorption of Li + by defect sites; 3) Li + intercalation reaction into the hard carbon layer. For hard carbon, the electrochemical intercalation of Li + begins at about 0.8 V, and the entire voltage curve does not have a clear platform, showing a gradual downward trend. This means that in the entire hard carbon layer, more Li + is stored by physical reaction rather than electrochemical reaction, which is more conducive to prolonging the service life of the material and ultimately improving the cycle performance of the battery. In addition, the high disorder of hard carbon provides more active sites for the storage of alkali metal ions, and the surface ceramic layer is a non-active coating that can delay the reaction between the liquid electrolyte and the electrode, reducing the additional active lithium consumption caused by the high specific surface area of the hard carbon.

[0058] (4) Graphite layer: The graphite in the bottommost graphite layer is selected from two kinds of graphite with different particle sizes, compaction densities and gram capacities. While ensuring the high gram capacity of the graphite negative electrode, it can also consider the fast charging kinetics of the negative electrode to ensure that Li + embedded in the graphite and extracted smoothly through the hard carbon layer. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 is a schematic diagram of the negative electrode sheet structure of Example 1.

[0060] Figure 2 is a schematic diagram of the negative electrode sheet structure of Example 7.

[0061] Figure 3 is a schematic diagram of the negative electrode sheet structure of Example 8.

[0062] The reference signs are as follows:

[0063] 10: current collector;

[0064] 20: Graphite layer

[0065] 30: Hard carbon layer;

[0066] 40: Ceramic layer;

[0067] 100: Main area;

[0068] 200: Edge region; 210: First edge region; 220: Second edge region. Detailed Implementation

[0069] This invention discloses a negative electrode sheet and a lithium-ion battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0070] In the description of this invention, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0071] In the description of this invention, the list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0072] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0073] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0074] If there is no special indication, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0075] If there is no special indication, the "includes" and "contains" mentioned in the present application represent open type, and can also be closed type. For example, the "includes" and "contains" can represent that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0076] Specifically, the present application adopts the following technical solutions:

[0077] In a first aspect, the present application provides a negative electrode sheet, which comprises:

[0078] a) a current collector 10;

[0079] b) a graphite layer 20, the graphite layer 20 being arranged on at least one surface of the current collector 10;

[0080] c) a hard carbon layer 30, the hard carbon layer 30 being arranged on a surface of the graphite layer 20 away from the current collector 10;

[0081] d) a ceramic layer 40, the ceramic layer 40 being arranged on a surface of the hard carbon layer 30 away from the current collector 10.

[0082] The graphite layer, the hard carbon layer and the ceramic layer in the present application have different material layer spacings, porosities and compaction densities. The present application utilizes three materials with different layer spacings, porosities and compaction densities to design a multi-layer gradient negative electrode, construct a high-flux ion migration path, and achieve the goal of super-fast charging. The multi-layer gradient electrode design can ensure high-concentration lithium ion diffusion and embedding into graphite. When high-rate charging, a large number of lithium ions are first introduced into the ceramic layer from the positive electrode. The ceramic layer can store ions and accelerate ion migration. The layer spacing of the hard carbon layer is greater than that of the graphite layer, which can ensure that more ions are quickly embedded and cannot cause lithium precipitation due to the negative electrode being unable to quickly provide sufficient lithium-embedding sites when high-current charging, thereby improving the fast-charging performance of the battery.

[0083] The ceramic layer has a high-pore structure, can quickly absorb and store electrolyte, has excellent liquid absorption and liquid retention, and improves the electrolyte wetting effect of the negative electrode. After the battery is injected with electrolyte, the electrolyte will quickly wet the ceramic layer, and then enter the hard carbon layer and the graphite layer. Even if the graphite is in a state of high compaction density (compaction density > 1.5 g / cm 3 ), it can also be well wetted by the electrolyte. During the cycle process, the electrolyte stored in the ceramic layer can ensure the liquid-rich state of the electrode, prolonging the cycle life of the lithium ion battery. Moreover, the ceramic layer is an oxide ceramic layer, which can improve the SEI film decomposition temperature and delay the thermal runaway time of the battery cell.

[0084] The hard carbon layer stores Li by physical reaction + rather than electrochemical reaction, which is more conducive to prolonging the service life of the material and ultimately improving the cycle performance of the battery cell. In addition, the high disorder of the hard carbon provides more active sites for the storage of alkali metal ions, and the surface ceramic layer acts as an inactive coating, which can delay the reaction between the liquid electrolyte and the electrode and reduce the additional active lithium consumption caused by the high specific surface area of the hard carbon.

[0085] In an embodiment of the present application, the interlayer spacing of the graphite of the graphite layer is denoted as A1, the interlayer spacing of the hard carbon of the hard carbon layer is denoted as A2, and the interlayer spacing of the ceramic of the ceramic layer is denoted as A3, and A1, A2, and A3 satisfy A1

[0086] In an embodiment of the present application, the porosity of the graphite layer is denoted as B1, the porosity of the hard carbon layer is denoted as B2, and the porosity of the ceramic layer is denoted as B3, and B1, B2, and B3 satisfy B1

[0087] In an embodiment of the present application, the compacted density of the graphite layer is denoted as C1, the compacted density of the hard carbon layer is denoted as C2, and the compacted density of the ceramic layer is denoted as C3, and C1, C2, and C3 satisfy C2

[0088] Preferably, the interlayer spacing of the graphite of the graphite layer is 0.3354-0.3366 nm. For example, the interlayer spacing of the graphite of the graphite layer is any one of 0.3354 nm, 0.3356 nm, 0.3358 nm, 0.336 nm, 0.3362 nm, 0.3364 nm, 0.3366 nm or any value within the range formed by any two of the above values.

[0089] As a preference, the interlayer spacing of the hard carbon of the hard carbon layer is 0.37-0.42 nm. Illustratively, the interlayer spacing of the hard carbon of the hard carbon layer is any of 0.37 nm, 0.38 nm, 0.39 nm, 0.40 nm, 0.41 nm, 0.42 nm or any value within a range defined by any two of the above values.

[0090] As a preference, the interlayer spacing of the ceramic of the ceramic layer is 0.44-0.47 nm. Illustratively, the interlayer spacing of the ceramic of the ceramic layer is any of 0.44 nm, 0.45 nm, 0.46 nm, 0.47 nm or any value within a range defined by any two of the above values.

[0091] As a preference, the porosity of the graphite layer is 10%-16%. Illustratively, the porosity of the graphite layer is any of 10%, 11%, 12%, 13%, 14%, 15%, 16% or any value within a range defined by any two of the above values.

[0092] As a preference, the porosity of the hard carbon layer is 30%-40%. Illustratively, the porosity of the hard carbon layer is any of 30%, 32%, 34%, 36%, 38%, 40% or any value within a range defined by any two of the above values.

[0093] As a preference, the porosity of the ceramic layer is 60%-90%. Illustratively, the porosity of the ceramic layer is any of 60%, 65%, 70%, 75%, 80%, 85%, 90% or any value within a range defined by any two of the above values.

[0094] As a preference, the compacted density of the graphite layer is 1.4-1.6 g / cm 3 . Illustratively, the compacted density of the graphite layer is any of 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 or any value within a range defined by any two of the above values.

[0095] As a preference, the compacted density of the hard carbon layer is 0.95-1.05 g / cm 3 . Illustratively, the compacted density of the hard carbon layer is any of 0.95 g / cm 3 , 0.97 g / cm 3 , 0.99 g / cm 3 , 1 g / cm 3 , 1.01 g / cm 3 , 1.03 g / cm 3, 1.05 g / cm 3 , or any value within a range bounded by any of the above values.

[0096] Preferably, the compacted density of the ceramic layer is 3.8-4.1 g / cm 3 . For example, the compacted density of the ceramic layer is any value within a range bounded by any of 3.8 g / cm 3 , 3.9 g / cm 3 , 4 g / cm 3 , 4.1 g / cm 3 , or any value within a range bounded by any of the above values.

[0097] In embodiments of the application, the graphite layer comprises composite graphite, the composite graphite comprising first graphite and second graphite.

[0098] Preferably, the particle size D 50 of the first graphite is 12-15 μm. For example, the particle size D 50 of the first graphite is any value within a range bounded by any of 12 μm, 13 μm, 14 μm, 15 μm, or any value within a range bounded by any of the above values.

[0099] Preferably, the particle size D 50 of the second graphite is 4-7 μm. For example, the particle size D 50 of the second graphite is any value within a range bounded by any of 4 μm, 5 μm, 6 μm, 7 μm, or any value within a range bounded by any of the above values.

[0100] Preferably, the specific surface area of the first graphite is ≤ 1.4 m 2 / g. For example, the specific surface area of the first graphite is any value within a range bounded by any of 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.4 m 2 / g, or any value within a range bounded by any of the above values.

[0101] Preferably, the specific surface area of the second graphite is ≤ 2.6 m 2 / g. For example, the specific surface area of the second graphite is any value within a range bounded by any of 2.0 m 2 / g, 2.1 m 2 / g, 2.2 m 2 / g, 2.3 m 2 / g, 2.4 m 2 / g, 2.5 m 2 / g, 2.6 m 2any value within a range formed by any two of the above values.

[0102] Preferably, the first graphite has a tap density of ≤ 1.6 g / cm 3 For example, the first graphite has a tap density of 1.0 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 , 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 any value within a range formed by any two of the above values.

[0103] Preferably, the second graphite has a tap density of ≤ 1.4 g / cm 3 For example, the second graphite has a tap density of 1.0 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 , 1.3 g / cm 3 , 1.4 g / cm 3 any value within a range formed by any two of the above values.

[0104] Preferably, the first graphite has a gravimetric capacity of ≥ 350 mAh / g. For example, the first graphite has a gravimetric capacity of 350 mAh / g, 360 mAh / g, 370 mAh / g, 380 mAh / g, 390 mAh / g, 400 mAh / g, or any value within a range formed by any two of the above values.

[0105] Preferably, the second graphite has a gravimetric capacity of ≥ 330 mAh / g. For example, the second graphite has a gravimetric capacity of 330 mAh / g, 340 mAh / g, 350 mAh / g, 360 mAh / g, 370 mAh / g, 380 mAh / g, or any value within a range formed by any two of the above values.

[0106] The graphite in the graphite layer is selected from the above two types of graphite with different particle sizes, different specific surface areas, different tap densities, and different gravimetric capacities. This can ensure high gravimetric capacity of the graphite negative electrode while taking into account the fast charging kinetics of the negative electrode, ensuring that the Li + inserted into and extracted from the graphite through the hard carbon layer smoothly.

[0107] As preferred, the mass ratio of the first graphite in the composite graphite is 80% to 90%. Exemplarily, the mass ratio of the first graphite in the composite graphite is any one of 80%, 82%, 84%, 86%, 88%, 90% or any value within the range formed by any two of the above values. Within the range, the first graphite with a high mass ratio is highly graphitized and high-capacity graphite, which can ensure the overall energy density of the battery cell.

[0108] As preferred, the mass ratio of the second graphite in the composite graphite is 10% to 20%. Exemplarily, the mass ratio of the second graphite in the composite graphite is any one of 10%, 12%, 14%, 16%, 18%, 20% or any value within the range formed by any two of the above values. Within the range, the second graphite with a smaller particle size, a larger interlayer spacing and a relatively lower graphitization degree can better match the high porosity and high interlayer spacing of the hard carbon layer and the ceramic layer after being mixed with the first graphite, thereby ensuring the power of lithium ions embedded in the graphite.

[0109] As preferred, the graphite includes artificial graphite and / or natural graphite. Preferably, the graphite is artificial graphite. Natural graphite has a high specific capacity, but has a small interlayer spacing and is prone to volume expansion during lithium extraction, which affects the cycle performance. Artificial graphite has a large interlayer spacing and is not prone to volume expansion. Therefore, the negative electrode is mostly made of artificial graphite with good comprehensive performance.

[0110] Hard carbon refers to difficultly graphitized carbon, which is a pyrolytic carbon obtained by pyrolyzing high molecular polymers, petrochemical products, biomass, etc. Curved graphene-like sheets are stacked into short-range ordered graphite-like crystalline fragments, and the twisted and short-range ordered graphite-like crystalline fragments are randomly stacked into an amorphous structure. At the same time, a large number of nano-pore structures are formed when the short-range ordered graphite sheets are randomly and disorderly stacked, and various morphologies are presented, including linear, spherical and porous.

[0111] In the embodiments of the present application, the hard carbon layer includes at least one of biomass-based hard carbon, resin-based hard carbon and pitch-based hard carbon. Preferably, the hard carbon layer is a biomass-based hard carbon material. The specific capacity of the biomass-based hard carbon material is generally distributed in 200 to 493 mAh / g, and the specific capacity of the resin-based hard carbon material and the pitch-based hard carbon material is about 300 mAh / g. The biomass-based hard carbon material with a specific capacity greater than 300 mAh / g is better than the resin-based hard carbon material and the pitch-based hard carbon material, and the high-capacity is more conducive to improving the overall energy density of the battery cell. In addition, the biomass-based hard carbon material has a wide range of precursor raw materials, low cost, including regenerated cotton, walnut shells, oak, lignin, coconut shells, etc.

[0112] In embodiments of the present invention, the ceramic layer includes at least one of Al2O3, SiO2, ZrO2, TiO2, MgO, MnO, and Cr2O3. Preferably, the ceramic layer includes Al2O3. Compared to other ceramic types, Al2O3 has relatively high ionic conductivity and density, and will not have too much negative impact on the energy density of the battery cell.

[0113] Preferably, Al₂O₃ includes α-Al₂O₃, β-Al₂O₃, γ-Al₂O₃, θ-Al₂O₃, δ-Al₂O₃, or x-Al₂O₃. In β-Al₂O₃, a portion of Li₂O₃ is present. + and Li + Coulomb repulsion occurs between them, preferentially occupying diffusion vacancies, resulting in a lower diffusion barrier for Li. + Increased concentration does not affect its structural stability; its structure itself is favorable for Li. + Diffusion. β-Al₂O₃ is preferred in this invention.

[0114] In embodiments of the present invention, the negative electrode sheet of the present invention includes the following three structures:

[0115] (1) First structure:

[0116] like Figure 1 As shown, the negative electrode includes a current collector 10, a graphite layer 20, a hard carbon layer 30, and a ceramic layer 40. The graphite layer 20 is disposed on at least one surface of the current collector 10, the hard carbon layer 30 is disposed on the surface of the graphite layer 20 away from the current collector 10, and the ceramic layer 40 is disposed on the surface of the hard carbon layer 30 away from the current collector 10.

[0117] (2) Second structure:

[0118] like Figure 2 As shown, the negative electrode includes a current collector 10, a graphite layer 20, a hard carbon layer 30, and a ceramic layer 40;

[0119] The current collector surface includes a main region 100 and an edge region 200, with the edge region 200 located on both sides of the main region 100;

[0120] A hard carbon layer 30 is disposed in the main body region 100 and the edge region 200;

[0121] In the main body region 100, the graphite layer 20 is disposed on the surface of the current collector 10 and is in direct contact with the surface of the current collector; the hard carbon layer 30 is disposed on the surface of the graphite layer 20 and is in direct contact with the surface of the graphite layer.

[0122] In the edge region 200, a hard carbon layer 30 is disposed on the surface of the current collector and is in direct contact with the surface of the current collector.

[0123] In an embodiment of the present application, the edge region 200 is located on both sides of the main body region 100 along the width direction of the current collector.

[0124] In another embodiment of the present application, the edge region 200 is located on both sides of the main body region 100 along the width direction of the current collector, and on both sides of the main body region 100 along the length direction of the current collector.

[0125] (3) The third structure:

[0126] As shown in FIG. 1, the negative electrode sheet includes a current collector 10, a graphite layer 20, a hard carbon layer 30, and a ceramic layer 40. Figure 3

[0127] The surface of the current collector includes a main body region 100 and an edge region 200, and the edge region 200 is located on both sides of the main body region 100.

[0128] The edge region 200 includes a first edge region 210 and a second edge region 220, and the first edge region 210 is arranged between the main body region 100 and the second edge region 220.

[0129] The ceramic layer 40 is arranged on the surface of the main body region 100 and the edge region 200.

[0130] In the main body region 100, the ceramic layer 40 is arranged on the surface of the hard carbon layer 30 and directly contacts the surface of the hard carbon layer.

[0131] In the first edge region 210, the hard carbon layer 30 is arranged on the surface of the current collector and directly contacts the surface of the current collector.

[0132] In the second edge region 220, the ceramic layer 40 is arranged on the surface of the current collector and directly contacts the surface of the current collector.

[0133] For the above-mentioned second structure and third structure of the coating method, the same gradient negative electrode performance can be ensured for the side edges of the negative electrode sheet.

[0134] In an embodiment of the present application, for the above-mentioned second structure, the width of the edge region 200 is 10-40 μm. For example, the width of the edge region 200 is any one of 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or any value within the range formed by any two of the above-mentioned values.

[0135] In an embodiment of the present application, for the above-mentioned third structure, the width of the edge region 200 is 12-45 μm. For example, the width of the edge region 200 is any one of 12 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or any value within the range formed by any two of the above-mentioned values. ​

[0136] Preferably, the width of the first edge region 210 is 10 to 40 μm. For example, the width of the first edge region 210 is any value among 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, and 40 μm, or any value within the range of any two of the above values.

[0137] Preferably, the width of the second edge region 220 is 2 to 5 μm. For example, the width of the second edge region 220 is any value selected from 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, and 5 μm, or any value within the range formed by any two of the above values.

[0138] Preferably, in the main region, the thickness ratio of the graphite layer to the hard carbon layer is (1.5 to 2.5):1. For example, the thickness ratio of the graphite layer to the hard carbon layer is any value from 1.5:1, 2:1, 2.5:1, or any value within the range formed by any two of the above values. Since the thickness of the hard carbon layer in the edge region is the sum of the thicknesses of the graphite layer and the hard carbon layer in the main region, the thickness of the hard carbon layer in the edge region is compatible with the thicknesses of the graphite layer and the hard carbon layer in the main region. For example, the second structure (the negative electrode sheet of Embodiment 7, its structural schematic diagram is shown below) Figure 2 As shown in the figure, the thicknesses of the graphite layer and the hard carbon layer in the main region are 60 μm and 30 μm, respectively, while the thickness of the hard carbon layer in the edge region is 90 μm. Therefore, the thickness ratio of the graphite layer to the hard carbon layer in the edge region is not limited.

[0139] Preferably, in the main region, the thickness ratio of the hard carbon layer to the ceramic layer is (6-20):1. For example, the thickness ratio of the hard carbon layer to the ceramic layer is any value from 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, or any value within the range of any two of the above values. Since the thickness of the hard carbon layer in the edge region is the sum of the thicknesses of the graphite layer and the hard carbon layer in the main region, and the thickness of the ceramic layer in the edge region is the sum of the thicknesses of the graphite layer, the hard carbon layer, and the ceramic layer in the main region, the thickness of the hard carbon layer in the edge region is compatible with the thicknesses of the graphite layer and the hard carbon layer in the main region, and the thickness of the ceramic layer in the edge region is compatible with the thicknesses of the graphite layer, the hard carbon layer, and the ceramic layer in the main region. For example, the third structure (the negative electrode sheet of Example 8, its structural schematic diagram is shown below) Figure 3As shown in the structural schematic diagram of the negative electrode sheet of the second structure (Example 7), in the main body region, the thicknesses of the graphite layer and the hard carbon layer are 60 μm and 30 μm, respectively, and the thickness of the hard carbon layer in the edge region is 90 μm.

[0140] Preferably, the thickness of the graphite layer 20 is 60-80 μm. For example, the thickness of the graphite layer is any one of 60 μm, 65 μm, 70 μm, 75 μm, 80 μm or any value within the range formed by any two of the above values.

[0141] Preferably, the thickness of the hard carbon layer 30 in the main body region is 30-40 μm. For example, the thickness of the hard carbon layer in the main body region is any one of 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm or any value within the range formed by any two of the above values. The thickness of the hard carbon layer in the edge region is the sum of the thicknesses of the graphite layer in the main body region and the hard carbon layer in the main body region, and the thickness of the hard carbon layer in the edge region is adapted to the thicknesses of the graphite layer and the hard carbon layer in the main body region. For example, the structural schematic diagram of the negative electrode sheet of the second structure (Example 7) shows that in the main body region, the thicknesses of the graphite layer and the hard carbon layer are 60 μm and 30 μm, respectively, and the thickness of the hard carbon layer in the edge region is 90 μm. Figure 2

[0142] Preferably, the thickness of the ceramic layer 40 in the main body region is 2-5 μm. For example, the thickness of the ceramic layer 40 in the main body region is any one of 2 μm, 3 μm, 4 μm, 5 μm or any value within the range formed by any two of the above values. The thickness of the ceramic layer in the edge region is the sum of the thicknesses of the graphite layer in the main body region, the hard carbon layer in the main body region and the ceramic layer in the main body region, and the thickness of the ceramic layer in the edge region is adapted to the thicknesses of the graphite layer, the hard carbon layer and the ceramic layer in the main body region. For example, the structural schematic diagram of the negative electrode sheet of the third structure (Example 8) shows that in the main body region, the thicknesses of the graphite layer, the hard carbon layer and the ceramic layer are 60 μm, 30 μm and 5 μm, respectively, and the thickness of the ceramic layer in the edge region is 95 μm. Figure 3

[0143] In the above thickness ranges of the graphite layer, the hard carbon layer and the ceramic layer, a large amount of Li + (ion radius 0.07 nm) is released from the positive electrode, enters the negative electrode after passing through the separator, and is embedded in the negative electrode, Li + is sequentially and smoothly embedded in the ceramic layer, the hard carbon layer and the graphite layer, thereby improving the fast-charging performance of the battery.

[0144] ​​In an embodiment of the present application, the graphite layer comprises graphite, a first conductive agent and a first binder, wherein the mass percentage of graphite is 90-99%, the mass percentage of the first conductive agent is 0.5-5%, and the mass percentage of the first binder is 0.5-5%.

[0145] In an embodiment of the present application, the hard carbon layer comprises hard carbon, a second conductive agent and a second binder, wherein the mass percentage of hard carbon is 90-99%, the mass percentage of the second conductive agent is 0.5-5%, and the mass percentage of the second binder is 0.5-5%.

[0146] In an embodiment of the present application, the ceramic layer comprises ceramic and a third binder, wherein the mass percentage of ceramic is 90-99%, and the mass percentage of the third binder is 1-10%.

[0147] In an embodiment of the present application, the first conductive agent and the second conductive agent independently comprise at least one of conductive carbon black (SP), vapor-grown carbon fiber (VGCF), graphene, and carbon nanotube (CNTs).

[0148] In an embodiment of the present application, the first binder and the second binder independently comprise at least one of water-based binder carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), and styrene butadiene rubber (SBR), or comprise oil-based binder polyvinylidene fluoride (PVDF).

[0149] In an embodiment of the present application, the third binder comprises oil-based binder PVDF or water-based binder polyacrylic acid (PAA).

[0150] In a second aspect, the present application provides a lithium ion battery, which comprises the negative electrode sheet described above.

[0151] In an embodiment of the present application, the lithium ion battery further comprises a positive electrode sheet, a separator and an electrolyte.

[0152] In an embodiment of the present application, the positive electrode active material in the positive electrode sheet comprises at least one of ternary nickel-cobalt-manganese, ternary nickel-cobalt-aluminum, lithium iron phosphate, lithium cobaltate, lithium-rich manganese-based and lithium manganate.

[0153] In an embodiment of the present application, the separator comprises a base film, and the base film comprises polypropylene (PP), polyethylene (PE), polyimide (PI) or PP / PE.

[0154] In an embodiment of the present application, the separator further comprises a coating layer arranged on at least one side surface of the base film, and the coating layer comprises at least one of aluminum oxide, boehmite and solid-state electrolyte.

[0155] In embodiments of the present invention, the lithium salt in the electrolyte is exemplary lithium hexafluorophosphate (LiPF6), and the solvent exemplary includes cyclic carbonates and / or chain carbonates. Cyclic carbonates are, for example, ethylene carbonate (EC), and chain carbonates are, for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). However, the types of lithium salts and solvents are not limited to these, and any type recognized by those skilled in the art is within the scope of protection of the present invention.

[0156] The reagents, instruments, and materials used in this invention can all be obtained through commercial channels.

[0157] The present invention will be further illustrated below with reference to the embodiments:

[0158] Example 1:

[0159] 1. Preparation of the negative electrode:

[0160] (1) Preparation of graphite layer slurry:

[0161] Preparation of composite graphite: Particle size D of the first type of graphite 50 It has a diameter of 13 μm and a specific surface area of ​​1.4 m². 2 / g, compacted density 1.6g / cm³ 3 The capacity is 350mAh / g; the particle size of the second type of graphite is D. 50 It has a thickness of 5 μm and a specific surface area of ​​2.6 m². 2 / g, compacted density 1.4g / cm³ 3 The specific capacity is 330 mAh / g. The interlayer spacing of the first and second graphite is 0.336 nm. The graphite is mixed with the first type comprising 80% and the second type comprising 20%.

[0162] Raw materials were selected according to the mass ratio of composite graphite, conductive agent (SP), CMC and SBR of 95:1.5:1.7:1.8. First, a CMC water-soluble adhesive with a solid content of 1.5% was prepared. Then, the conductive agent, composite graphite and SBR were added in sequence and stirred and dispersed to obtain a graphite layer slurry.

[0163] (2) Preparation of hard carbon layer slurry:

[0164] The raw materials were selected in a mass ratio of hard carbon (hard carbon interlayer spacing of 0.4 nm), conductive agent (SP), CMC and SBR of 95.3:1.2:1.7:1.8. The method for preparing hard carbon layer slurry is similar to the method for preparing graphite layer slurry described above.

[0165] (3) Coating of graphite layer and hard carbon layer:

[0166] The graphite layer slurry and the hard carbon layer slurry are simultaneously coated on the surface of the current collector by using a double-layer coating machine, and the graphite layer and the hard carbon layer are obtained after drying.

[0167] (4) Coating of the ceramic layer:

[0168] The raw materials are selected according to the mass ratio of aluminum oxide (the spacing of the aluminum oxide ceramic layer is 0.45 nm) to PVDF of 95:5, the aluminum oxide slurry is obtained after being dispersed in an NMP solution, and then the ceramic layer is formed by coating on the surface of the hard carbon layer.

[0169] (5) Preparation of the negative electrode sheet:

[0170] After coating, the graphite layer, the hard carbon layer and the ceramic layer with different thicknesses are obtained by rolling, the thicknesses are 60 μm, 30 μm and 2 μm respectively, the porosities are 15%, 35% and 75% respectively, and the compacted densities are 1.53 g / cm 3 , 0.98 g / cm 3 , 3.92 g / cm 3 respectively. The schematic diagram of the negative electrode sheet structure is shown in Figure 1 .

[0171] 2. Preparation of the positive electrode sheet:

[0172] The lithium iron phosphate, carbon nanotubes (CNT), conductive carbon black (SP) and polyvinylidene fluoride (PVDF) are mixed according to the mass ratio of 96.5:1:0.5:2, and then added to the solvent NMP to prepare a slurry, which is coated on the current collector to obtain the positive electrode sheet.

[0173] 3. Separator:

[0174] The separator is a polyethylene separator.

[0175] 4. Electrolyte:

[0176] The lithium salt of the electrolyte is 1 mol / L of LiPF6, and the solvent is a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1.

[0177] 5. Assembly of the battery:

[0178] The positive electrode sheet, the separator, the negative electrode sheet and the electrolyte are assembled into a lithium ion battery.

[0179] Example 2:

[0180] The difference between this example and Example 1 is that only the thickness of the ceramic layer is increased to 5 μm.

[0181] Example 3:

[0182] The difference between this example and Example 1 is that the thickness of the graphite layer is increased to 70 μm and the thickness of the hard carbon layer is increased to 35 μm.

[0183] Example 4:

[0184] The difference between this example and Example 1 is that the thickness of the graphite layer is increased to 70 μm, the thickness of the hard carbon layer is increased to 35 μm, and the thickness of the ceramic layer is increased to 5 μm.

[0185] Example 5:

[0186] The difference between this example and Example 1 is that the thickness of the graphite layer is increased to 80 μm, and the thickness of the hard carbon layer is increased to 40 μm.

[0187] Example 6:

[0188] The difference between this example and Example 1 is that the thickness of the graphite layer is increased to 80 μm, the thickness of the hard carbon layer is increased to 40 μm, and the thickness of the ceramic layer is increased to 5 μm.

[0189] Example 7:

[0190] The difference between this example and Example 2 is that the hard carbon layer further comprises a hard carbon layer of an edge region, the hard carbon layer of the edge region having a width of 10 mm and a thickness of 90 μm. The structure of the negative electrode sheet is shown in FIG. 2. Figure 2 .

[0191] Example 8:

[0192] The difference between this example and Example 2 is that the hard carbon layer further comprises a hard carbon layer of a first edge region, the hard carbon layer of the first edge region having a width of 10 mm and a thickness of 90 μm; and the ceramic layer further comprises a ceramic layer of a second edge region, the ceramic layer of the second edge region having a width of 5 mm and a thickness of 95 μm. The structure of the negative electrode sheet is shown in FIG. 3. Figure 3 .

[0193] Comparative Example 1:

[0194] The difference between this comparative example and Example 1 is that no ceramic layer is provided.

[0195] Comparative Example 2

[0196] The difference between this comparative example and Example 1 is that the thickness of the ceramic layer is 10 μm.

[0197] Comparative Example 3

[0198] The difference between this comparative example and Example 1 is that no hard carbon layer is provided.

[0199] Comparative Example 4

[0200] The difference between this comparative example and Example 1 is that no hard carbon layer and no ceramic layer are provided.

[0201] Battery performance test

[0202] The performance of the negative electrode sheets and batteries prepared in the examples and comparative examples was tested, and the test items included:

[0203] The electrolyte infiltration rate test method was as follows: in a protective gas atmosphere, the electrolyte container was placed on a heatable lifting platform, the lifting of the platform was driven by a motor, and the displacement could be accurately controlled. The electrode sample was hung on an electronic balance, and the lifting platform was controlled to immerse the electrode sample in the electrolyte by 5 mm. The data collector recorded the weight increase data of the sample in real time, and the electrolyte infiltration rate of the electrode was analyzed through the mass m-time t data. After the electrode was immersed in the electrolyte, the surface absorbed the electrolyte, and the mass increased rapidly. Then, the electrolyte infiltrated in the electrode pores, and the mass increased slowly. The electrolyte infiltration rate was mainly analyzed from the curve (m-t curve) of this process. After the electrolyte dropped off the electrode, the mass decreased rapidly, and then the mass of the electrolyte droplet on the surface of the electrode decreased slowly. The curve in the electrolyte infiltration stage was analyzed, and according to the formula:

[0204]

[0205] In the m-t curve, Δm represents the mass of the electrolyte, t represents time, ρ represents the density of the solution, A e represents the cross-sectional area of the electrode sample, and K represents the infiltration rate of the electrolyte in the porous electrode. The abscissa is the square root of time, and the ordinate is mass / (sample cross-sectional area·electrolyte density). The curve was linearly fitted, and the slope of the straight line was the electrolyte infiltration rate K.

[0206] The 8C charging 100% SOC negative electrode interface lithium precipitation test method was as follows: after the battery was cycled for 30 cycles, it was charged to 100% SOC state for battery disassembly, and the negative electrode interface state was observed. If the interface was all golden yellow, it was judged as no lithium precipitation. If black spots and white particle precipitates appeared on the surface of the negative electrode, it was considered that lithium precipitation occurred.

[0207] The 8C charging constant current ratio test method was as follows: after the battery was assembled and activated, it was first charged and discharged at 1C, the capacity of the battery was calibrated, and the battery was charged at 8C constant current and constant voltage to 4.25V according to the capacity, and the 8C charging constant current ratio was obtained.

[0208] The 5C charge and discharge 300 cycle retention rate test method was as follows: after the battery was assembled and activated, it was first charged and discharged at 0.5C, the capacity of the battery was calibrated, and the battery was charged at 5C constant current and constant voltage to 4.25V according to the calibrated capacity, and then the battery was left for 30 min, and discharged at 5C to 2.8V. This cycle was repeated for 300 cycles.

[0209] Table 1

[0210]

[0211] From the test results of the above table, it can be seen that examples 1-8 all have high electrolyte infiltration rate and good fast charging performance. Among them, when the thickness of the graphite layer, hard carbon layer and ceramic layer in example 2 is 60 μm, 30 μm and 5 μm respectively, the comprehensive performance of the battery is optimal, and the three layers synergize with each other. Examples 7 and 8 are more conducive to the rapid embedding of lithium ions, improving the fast charging performance, but the non-active substance is too high, and the electronic conductivity is low, which will weaken the cycle performance.

[0212] Comparative example 1 does not set the ceramic layer, which will reduce the electrolyte infiltration rate and affect the fast charging performance.

[0213] The ceramic layer in comparative example 2 is too thick, which will affect the fast charging performance. This is because the electronic migration rate is reduced.

[0214] Comparative example 3 does not set the hard carbon layer. Since there is no buffering effect of the hard carbon layer, the graphite layer cannot meet the rapid embedding of a large number of ions into the graphite during large current charging, and lithium precipitation will occur.

[0215] Comparative example 4 does not set the hard carbon layer and the ceramic layer. The constant current ratio is very low, which cannot meet the large current charging, and the cycle life will decay. A large amount of active lithium is consumed and precipitated, and lithium precipitation occurs.

[0216] The above only describes the preferred embodiments of the present application. It should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which should also be considered within the scope of protection of the present application.

Claims

1. A negative electrode sheet characterized by comprising: The negative electrode sheet comprises: a current collector (10); a graphite layer (20) disposed on at least one surface of the current collector (10); a hard carbon layer (30) disposed on a surface of the graphite layer (20) away from the current collector (10); a ceramic layer (40) disposed on a surface of the hard carbon layer (30) away from the current collector (10); the ceramic layer comprises at least one of Al2O3, SiO2, ZrO2, TiO2, MgO, MnO, and Cr2O3; an interlayer spacing of graphite in the graphite layer is denoted as A1, an interlayer spacing of hard carbon in the hard carbon layer is denoted as A2, and an interlayer spacing of ceramic in the ceramic layer is denoted as A3, and A1, A2, and A3 satisfy A1 and / or, a porosity of the graphite layer is denoted as B1, a porosity of the hard carbon layer is denoted as B2, and a porosity of the ceramic layer is denoted as B3, and B1, B2, and B3 satisfy B1 and / or, a compacted density of the graphite layer is denoted as C1, a compacted density of the hard carbon layer is denoted as C2, and a compacted density of the ceramic layer is denoted as C3, and C1, C2, and C3 satisfy C2 the surface of the current collector comprises a main body region (100) and an edge region (200), and the edge region (200) is located on both sides of the main body region (100); the hard carbon layer (30) is disposed on the main body region (100) and the edge region (200); in the main body region (100), the graphite layer (20) is disposed on the surface of the current collector (10) and directly contacts the surface of the current collector; and the hard carbon layer (30) is disposed on the surface of the graphite layer (20) and directly contacts the surface of the graphite layer; in the edge region (200), the hard carbon layer (30) is disposed on the surface of the current collector and directly contacts the surface of the current collector.

2. The negative electrode sheet according to claim 1, characterized by the interlayer spacing of graphite in the graphite layer is 0.3354-0.3366 nm, the interlayer spacing of hard carbon in the hard carbon layer is 0.37-0.42 nm, and the interlayer spacing of ceramic in the ceramic layer is 0.44-0.47 nm; and / or, the porosity of the graphite layer is 10%-16%, the porosity of the hard carbon layer is 30%-40%, and the porosity of the ceramic layer is 60%-90%; and / or the compaction density of the graphite layer is 1.4 to 1.6 g / cm 3 , the compaction density of the hard carbon layer is 0.95 to 1.05 g / cm 3 , the compaction density of the ceramic layer is 3.8 to 4.1 g / cm 3 .

3. The negative electrode sheet according to claim 1, characterized by the graphite layer comprises composite graphite, and the composite graphite comprises first graphite and second graphite; The particle size D of the first graphite is 12 to 15 μm 50 The particle size D of the second graphite is 4 to 7 μm 50 The particle size D of the first graphite is 12 to 15 μm and / or the specific surface area of the first graphite is < 1.4 m 2 / g, the specific surface area of the second graphite is < 2.6 m 2 / g; and / or the first graphite has a compacted density of < 1.6 g / cm 3 and / or the second graphite has a compacted density of < 1.4 g / cm 3 ; and / or, the gram capacity of the first graphite is greater than or equal to 350 mAh / g, and the gram capacity of the second graphite is greater than or equal to 330 mAh / g; and / or, the mass ratio of the first graphite in the composite graphite is 80%-90%, and the mass ratio of the second graphite in the composite graphite is 10%-20%.

4. The negative electrode sheet according to claim 1, characterized by the hard carbon layer comprises at least one of biomass-based hard carbon, resin-based hard carbon, and pitch-based hard carbon.

5. The negative electrode sheet according to claim 1, characterized by The edge region (200) comprises a first edge region (210) and a second edge region (220), the first edge region (210) is arranged between the main body region (100) and the second edge region (220); The ceramic layer (40) is arranged on the main body region (100) and the edge region (200); In the main body region (100), the ceramic layer (40) is arranged on the surface of the hard carbon layer (30) and directly contacts the surface of the hard carbon layer; In the first edge region (210), the hard carbon layer (30) is arranged on the surface of the current collector and directly contacts the surface of the current collector; In the second edge region (220), the ceramic layer (40) is arranged on the surface of the current collector and directly contacts the surface of the current collector.

6. The negative electrode sheet according to claim 5, characterized by The width of the first edge region (210) is 10-40 μm; The width of the second edge region (220) is 2-5 μm.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein The thickness ratio of the graphite layer to the hard carbon layer is (1.5-2.5):1; And / or, the thickness ratio of the hard carbon layer to the ceramic layer is (6-20):1; The thickness of the graphite layer (20) is 60-80 μm; The thickness of the hard carbon layer (30) is 30-40 μm; The thickness of the ceramic layer (40) is 2-5 μm.

8. A lithium-ion battery, characterized by The lithium ion battery comprises the negative electrode sheet according to any one of claims 1-7.

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