Negative plate and lithium ion battery

Abstract

The invention 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, away from the current collector, of the graphite layer, and the ceramic layer is arranged on the surface, away from the current collector, of the hard carbon layer. The multi-layer gradient negative electrode is designed by using three materials with different interlayer spacing, porosity and compaction density, a high-flux ion migration path is constructed, and the purpose of ultrafast charging is achieved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to negative electrode sheets and lithium-ion batteries. Background Art

[0002] Lithium-ion batteries have become popular in daily life, including electronic products such as mobile phones, electric vehicles, and grid energy storage. At present, various types of high-energy-density lithium-ion batteries can meet the needs of electric vehicle range to a certain extent, but compared with traditional fuel vehicles, charging time is still one of the bottlenecks for popular use. Although the electrolyte is the most significant factor affecting the intrinsic fast charging ability of the battery cell, under high-current charging conditions, a large number of lithium ions will quickly escape from the positive electrode and embed into the negative electrode, causing polarization of the negative electrode. If the negative electrode potential drops below 0V, the lithium ions cannot be embedded in the negative electrode and precipitate on the negative electrode surface, resulting in an increase in irreversible capacity decay, which can seriously cause safety problems. Therefore, optimizing the negative electrode structure and material system is crucial to improving the diffusion capacity of lithium ions.

[0003] The patent with publication number CN117352959A discloses a separator. The technology is to set a composite coating on the surface of the separator. The coating includes ceramic material and polyacrylate. The composite coating forms an active ion bridge high-speed path, which can improve the ion transport efficiency and improve the fast charging performance. However, there are differences in the ion transmission path between setting a coating on the surface of the separator and setting a coating on the surface of the electrode, and it cannot improve the pore infiltration of the electrode, and the performance is insufficient in the process of long cycle and high-rate fast charging. Summary of the invention

[0004] In view of this, the present invention 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 object of the invention, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising:

[0007] a) a current collector 10;

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

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

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

[0011] In the embodiment of the present invention, the interlayer spacing of graphite in the graphite layer is denoted as A1, the interlayer spacing of hard carbon in the hard carbon layer is denoted as A2, and the interlayer spacing of ceramic in the ceramic layer is denoted as A3, and A1, A2, and A3 satisfy A1<A2<A3.

[0012] In the embodiment of the present invention, the porosity of the graphite layer is recorded as B1, the porosity of the hard carbon layer is recorded as B2, and the porosity of the ceramic layer is recorded as B3. B1, B2, and B3 satisfy B1<B2<B3.

[0013] In the embodiment of the present invention, the compaction density of the graphite layer is recorded as C1, the compaction density of the hard carbon layer is recorded as C2, and the compaction density of the ceramic layer is recorded as C3. C1, C2, and C3 satisfy C2<C1<C3.

[0014] Preferably, the interlayer distance of graphite in the graphite layer is 0.3354 to 0.3366 nm.

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

[0016] Preferably, the ceramic layer has an interlayer spacing of 0.44 to 0.47 nm.

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

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

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

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

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

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

[0023] In an embodiment of the present invention, the graphite layer includes composite graphite, and the composite graphite includes first graphite and second graphite.

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

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

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

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

[0028] Preferably, the compacted density of the first graphite is ≤1.6 g / cm 3 .

[0029] Preferably, the compacted density of the second graphite is ≤1.4 g / cm 3 .

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

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

[0032] Preferably, the mass proportion of the first graphite in the composite graphite is 80% to 90%.

[0033] Preferably, the mass proportion of the second graphite in the composite graphite is 10% to 20%.

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

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

[0036] In a preferred embodiment of the present invention, the current collector surface includes a main region 100 and an edge region 200, and the edge region 200 is located on both sides of the main region 100;

[0037] The hard carbon layer 30 is disposed in the main region 100 and the edge region 200;

[0038] In the main 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;

[0039] In the edge region 200 , the 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.

[0040] In another preferred embodiment of the present invention, the edge region 200 includes a first edge region 210 and a second edge region 220, and the first edge region 210 is disposed between the main region 100 and the second edge region 220;

[0041] The ceramic layer 40 is disposed in the main region 100 and the edge region 200;

[0042] In the main body region 100 , the ceramic layer 40 is disposed on the surface of the hard carbon layer 30 and is in direct contact with 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 is in direct contact with 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 is in direct contact with 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 to 80 μm.

[0050] Preferably, the hard carbon layer 30 has a thickness of 30 to 40 μm.

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

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

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) Multilayer gradient negative electrode: The present invention utilizes three materials with different interlayer spacing, porosity and compaction density to design a multilayer gradient negative electrode, construct a high-throughput ion migration path, and achieve the goal of ultra-fast charging. The multilayer gradient electrode design can ensure the diffusion of high-concentration lithium ions and embedding in graphite. During high-rate charging, a large number of lithium ions escape from the positive electrode and first enter the ceramic layer. The ceramic layer can store ions and accelerate the migration of ions. The interlayer spacing of the hard carbon layer is larger than the interlayer spacing of the graphite layer, which can ensure the rapid embedding of more ions. When charging with a large current, the negative electrode cannot quickly provide enough lithium insertion sites to cause lithium precipitation, thereby improving the fast charging performance of the battery.

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

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

[0057] (3) Hard carbon layer: Li + The storage mechanisms in hard carbon mainly include: 1) nanopores for Li + 2) Defect sites for Li + Adsorption of Li + The intercalation reaction embeds the hard carbon layer. For hard carbon, Li + The electrochemical intercalation starts at about 0.8V, and the entire voltage curve has no obvious platform, showing a gradual downward trend. This means that in the entire hard carbon layer, more physical reactions are used to store Li + , rather than electrochemical reaction, which is more conducive to extending 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 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 ​​hard carbon.

[0058] (4) Graphite layer: The graphite in the bottom graphite layer is selected from two types of graphite with different compaction densities and gram capacities, namely large and small particles. While ensuring the high gram capacity of the graphite negative electrode, it can also take into account the fast charging dynamics of the negative electrode, ensuring that the Li + Smooth graphite embedding and ejection. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 Schematic diagram of the negative electrode structure of Example 1.

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

[0061] Figure 3 Schematic diagram of the negative electrode structure of Example 8.

[0062] The reference numerals 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 DESCRIPTION

[0069] The present invention discloses a negative electrode sheet and a lithium-ion battery. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the above. 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 the present invention. The method and application of the present invention have been described through preferred embodiments. It is obvious that relevant personnel can modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

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

[0071] In the description of the present invention, a 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, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, 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 include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0072] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0073] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0074] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0075] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

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

[0077] In a first aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising:

[0078] a) a current collector 10;

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

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

[0081] d) a ceramic layer 40 . The ceramic layer 40 is disposed on the surface of the hard carbon layer 30 away from the current collector 10 .

[0082] The graphite layer, hard carbon layer and ceramic layer in the present invention have different material interlayer spacing, porosity and compaction density. The present invention uses three materials with different interlayer spacing, porosity and compaction density to design a multi-layer gradient negative electrode, construct a high-throughput ion migration path, and achieve the goal of ultra-fast charging. The multi-layer gradient electrode design can ensure the diffusion of high-concentration lithium ions and embedding in the graphite. During high-rate charging, a large number of lithium ions escape from the positive electrode and first enter the ceramic layer. The ceramic layer can store ions and accelerate the migration of ions. The interlayer spacing of the hard carbon layer is larger than the interlayer spacing of the graphite layer, which can ensure the rapid embedding of more ions. When charging with a large current, the negative electrode cannot quickly provide enough lithium insertion sites to cause lithium precipitation, thereby improving the fast charging performance of the battery.

[0083] Among them, the ceramic layer has a high porosity structure, which can quickly absorb and store electrolyte, has excellent liquid absorption and liquid retention, and improves the electrolyte infiltration effect of the negative electrode. After the battery is filled with electrolyte, the electrolyte will quickly infiltrate the ceramic layer, and then enter the hard carbon layer and graphite layer, even if the graphite is at a high compaction density (compacted density> 1.5g / cm 3 ) state, it can also be well infiltrated by the electrolyte. During the cycle, the electrolyte stored in the ceramic layer can ensure the electrode is in a liquid-rich state and extend the cycle life of the lithium-ion battery. Moreover, the ceramic layer is an oxide ceramic layer, which can increase the decomposition temperature of the SEI film and delay the thermal runaway time of the battery cell.

[0084] The hard carbon layer stores Li by its physical reaction + , rather than electrochemical reaction, which is more conducive to extending 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 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 ​​hard carbon.

[0085] In the embodiment of the present invention, the interlayer spacing of graphite in the graphite layer is recorded as A1, the interlayer spacing of hard carbon in the hard carbon layer is recorded as A2, and the interlayer spacing of ceramic in the ceramic layer is recorded as A3, and A1, A2, and A3 satisfy A1<A2<A3. When the interlayer spacing of the materials meets this condition, the interlayer spacing of graphite, hard carbon, and ceramic gradually increases in the direction away from the current collector. Under this design, when fast charging, after lithium ions are released from the positive electrode, they will be quickly embedded in the negative electrode through the desolvation process. The relatively small interlayer spacing of graphite is difficult to meet the vacancy requirements for the instantaneous embedding of a large number of lithium ions, while the high interlayer spacing of ceramics ensures that lithium ions are embedded with lower impedance. The interlayer spacing of hard carbon is between the two. The interior of hard carbon is an amorphous structure, and lithium ions can also be quickly embedded, playing a buffering role before finally embedding into graphite.

[0086] In the embodiment of the present invention, the porosity of the graphite layer is recorded as B1, the porosity of the hard carbon layer is recorded as B2, and the porosity of the ceramic layer is recorded as B3, and B1, B2, and B3 satisfy B1<B2<B3. When the porosity meets this condition, the porosity of the graphite layer, the hard carbon layer, and the ceramic layer gradually increases in the direction away from the current collector. When a large amount of lithium ions escape from the positive electrode, the high porosity of the outermost ceramic layer can accommodate a large amount of lithium ions, and the porosity of the hard carbon layer is higher than that of graphite, which serves as a transition layer.

[0087] In the embodiment of the present invention, the compaction density of the graphite layer is recorded as C1, the compaction density of the hard carbon layer is recorded as C2, and the compaction density of the ceramic layer is recorded as C3. C1, C2, and C3 satisfy C2<C1<C3. When the compaction density meets this condition, the compaction density of the outer ceramic layer is the highest, the compaction density of the inner graphite layer is the second highest, and the compaction density of the middle hard carbon layer is the lowest. Under this design, after rolling, the electrode thickness variation range is small, and particles will not penetrate into other layers, which can maintain the stability between the particles of the three-layer structure.

[0088] Preferably, the interlayer spacing of the graphite in the graphite layer is 0.3354-0.3366 nm. Exemplarily, the interlayer spacing of the graphite in the graphite layer is any value among 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 consisting of any two of the above values.

[0089] Preferably, the interlayer spacing of the hard carbon layer is 0.37-0.42 nm. Exemplarily, the interlayer spacing of the hard carbon layer is any value among 0.37 nm, 0.38 nm, 0.39 nm, 0.40 nm, 0.41 nm, 0.42 nm, or any value within the range consisting of any two of the above values.

[0090] Preferably, the ceramic interlayer spacing of the ceramic layer is 0.44-0.47 nm. Exemplarily, the ceramic interlayer spacing of the ceramic layer is any value among 0.44 nm, 0.45 nm, 0.46 nm, 0.47 nm, or any value within the range consisting of any two of the above values.

[0091] Preferably, the porosity of the graphite layer is 10% to 16%. Exemplarily, the porosity of the graphite layer is any value among 10%, 11%, 12%, 13%, 14%, 15%, 16%, or any value within the range consisting of any two of the above values.

[0092] Preferably, the porosity of the hard carbon layer is 30% to 40%. Exemplarily, the porosity of the hard carbon layer is any value among 30%, 32%, 34%, 36%, 38%, 40%, or any value within the range consisting of any two of the above values.

[0093] Preferably, the porosity of the ceramic layer is 60% to 90%. Exemplarily, the porosity of the ceramic layer is any value among 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any value within the range of any two of the above values.

[0094] Preferably, the compacted density of the graphite layer is 1.4 to 1.6 g / cm 3 For example, the compacted density of the graphite layer is 1.4 g / cm 3 , 1.45g / cm 3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 Any value in or any value in the range consisting of any two of the above values.

[0095] Preferably, the compaction density of the hard carbon layer is 0.95 to 1.05 g / cm 3 For example, the compacted density of the hard carbon layer is 0.95 g / cm 3 , 0.97g / cm 3 , 0.99g / cm 3 , 1g / cm 3 , 1.01g / cm 3 , 1.03g / cm 3, 1.05g / cm 3 Any value in or any value in the range consisting of any two of the above values.

[0096] Preferably, the compaction density of the ceramic layer is 3.8 to 4.1 g / cm 3 For example, the compacted density of the ceramic layer is 3.8 g / cm 3 、3.9g / cm 3 , 4g / cm 3 , 4.1g / cm 3 Any value in or any value in the range consisting of any two of the above values.

[0097] In an embodiment of the present invention, the graphite layer includes composite graphite, and the composite graphite includes first graphite and second graphite.

[0098] Preferably, the particle size D of the first graphite 50 For example, the particle size D of the first graphite is 12 to 15 μm. 50 It is any value among 12μm, 13μm, 14μm, 15μm, or any value within the range consisting of any two of the above values.

[0099] Preferably, the particle size D of the second graphite 50 For example, the particle size D of the second graphite is 4 to 7 μm. 50 It is any value among 4μm, 5μm, 6μm, 7μm, or any value within the range consisting of any two of the above values.

[0100] Preferably, the specific surface area of ​​the first graphite is ≤1.4m 2 / g. Exemplarily, the specific surface area of ​​the first graphite is 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / any value in g or any value in the range consisting of any two of the above values.

[0101] Preferably, the specific surface area of ​​the second graphite is ≤2.6m 2 / g. Exemplarily, the specific surface area of ​​the second graphite is 2.0m 2 / g, 2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / any value in g or any value in the range consisting of any two of the above values.

[0102] Preferably, the compacted density of the first graphite is ≤1.6 g / cm 3 For example, the compacted density of the first graphite is 1.0 g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 Any value in or any value in the range consisting of any two of the above values.

[0103] Preferably, the compacted density of the second graphite is ≤1.4 g / cm 3 For example, the compacted density of the second graphite is 1.0 g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 Any value in or any value in the range consisting of any two of the above values.

[0104] Preferably, the gram capacity of the first graphite is ≥350 mAh / g. Exemplarily, the gram capacity of the first graphite is any value among 350 mAh / g, 360 mAh / g, 370 mAh / g, 380 mAh / g, 390 mAh / g, 400 mAh / g, or any value within the range consisting of any two of the above values.

[0105] Preferably, the gram capacity of the second graphite is ≥330 mAh / g. Exemplarily, the gram capacity of the second graphite is any value among 330 mAh / g, 340 mAh / g, 350 mAh / g, 360 mAh / g, 370 mAh / g, 380 mAh / g, or any value within the range consisting of any two of the above values.

[0106] The graphite in the graphite layer is selected from the above two graphites with different particle sizes, different specific surface areas, different compaction densities and different gram capacities. While ensuring the high gram capacity of the graphite negative electrode, it can also take into account the fast charging dynamics of the negative electrode and ensure that the Li + Smooth graphite embedding and ejection.

[0107] Preferably, the mass proportion of the first graphite in the composite graphite is 80% to 90%. Exemplarily, the mass proportion of the first graphite in the composite graphite is any value among 80%, 82%, 84%, 86%, 88%, 90%, or any value within the range of values ​​composed of any two of the above values. Within this range, the first graphite with a relatively high proportion is highly graphitized and high gram capacity graphite, which can ensure the overall energy density of the battery cell.

[0108] Preferably, the mass proportion of the second graphite in the composite graphite is 10% to 20%. Exemplarily, the mass proportion of the second graphite in the composite graphite is any value among 10%, 12%, 14%, 16%, 18%, 20%, or any value within the range of values ​​composed of any two of the above values. Within this range, the second graphite with a smaller particle size, a larger interlayer spacing, and a relatively low degree of graphitization can be better matched with the first graphite after being mixed with the high porosity and high layer spacing of the hard carbon layer and the ceramic layer, thereby ensuring the power of lithium ion embedding into the graphite.

[0109] Preferably, the graphite includes artificial graphite and / or natural graphite. Preferably, the graphite is artificial graphite. Natural graphite has a high specific capacity, but a small interlayer spacing, and is prone to volume expansion during lithium insertion and extraction, affecting the cycle performance, while artificial graphite has a large interlayer spacing and is not prone to volume expansion. Therefore, the negative electrode uses most artificial graphites with good comprehensive performance.

[0110] Hard carbon refers to carbon that is difficult to graphitize. It is a type of pyrolytic carbon obtained by pyrolysis of high molecular polymers, petrochemical products, biomass, etc. The curved graphene-like sheets are stacked into short-range ordered graphite-like microcrystalline fragments, and the twisted and short-range ordered graphite-like microcrystalline fragments are stacked in a disordered manner to form an amorphous structure. At the same time, when the short-range ordered graphite-like sheets are randomly and disorderly stacked, more nanopore structures will be formed, showing a variety of morphologies, including linear, spherical and porous shapes.

[0111] In an embodiment of the present invention, the hard carbon layer includes at least one of biomass-based hard carbon, resin-based hard carbon, and asphalt-based hard carbon. Preferably, the hard carbon layer is a biomass-based hard carbon material. The specific capacity of biomass-based hard carbon materials is generally distributed in the range of 200 to 493 mAh / g, and the specific capacity of resin-based hard carbon materials and asphalt-based hard carbon materials is around 300 mAh / g. Biomass-based hard carbon materials with a specific capacity greater than 300 mAh / g are superior to resin-based hard carbon materials and asphalt-based hard carbon materials. High gram capacity is more conducive to improving the overall energy density of the battery cell, and the raw materials of biomass-based hard carbon material precursors are widely available and low in cost, including recycled cotton, walnut shells, oak, lignin, coconut shells, etc.

[0112] In an embodiment 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 with other types of ceramics, Al2O3 has relatively high ionic conductivity and density, and will not cause 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, part of Li + and Li + Coulomb repulsion will occur between them, and Li will preferentially occupy the diffusion vacancies, and the diffusion energy barrier is low. + The increase in concentration will not affect its structural stability, and its structure is conducive to Li + Diffusion. In the present invention, β-Al2O3 is preferred.

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

[0115] (1) The first structure:

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

[0117] (2) The second structure:

[0118] like Figure 2 As shown, the negative electrode sheet 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, and the edge region 200 is located on both sides of the main region 100;

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

[0121] In the main 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 , the 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 one embodiment of the present invention, the edge region 200 is located on both sides of the main region 100 along the width direction of the current collector.

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

[0125] (3) The third structure:

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

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

[0128] The edge region 200 includes a first edge region 210 and a second edge region 220 , wherein the first edge region 210 is disposed between the main region 100 and the second edge region 220 ;

[0129] The ceramic layer 40 is disposed in the main region 100 and the edge region 200;

[0130] In the main body region 100 , the ceramic layer 40 is disposed on the surface of the hard carbon layer 30 and is in direct contact with the surface of the hard carbon layer;

[0131] In the first edge region 210 , the 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;

[0132] In the second edge region 220 , the ceramic layer 40 is disposed on the surface of the current collector and is in direct contact with the surface of the current collector.

[0133] For the coating methods of the second structure and the third structure mentioned above, it can be ensured that the side of the negative electrode sheet also has the same performance of the gradient negative electrode.

[0134] In the embodiment of the present invention, for the second structure, the width of the edge region 200 is 10-40 μm. Exemplarily, the width of the edge region 200 is any value among 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or any value within the range of any two of the above values.

[0135] In an embodiment of the present invention, for the third structure, the width of the edge region 200 is 12-45 μm. Exemplarily, the width of the edge region 200 is any value among 12 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or any value within a range consisting of any two of the above values.

[0136] Preferably, the width of the first edge region 210 is 10-40 μm. Exemplarily, the width of the first edge region 210 is any value among 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 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 2-5 μm. Exemplarily, the width of the second edge region 220 is any value among 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or any value within the range consisting of 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 (1.5-2.5):1. Exemplarily, the thickness ratio of the graphite layer to the hard carbon layer is any value among 1.5:1, 2:1, 2.5:1 or any value within the range of values ​​consisting of any two of the above values. Since the thickness of the hard carbon layer in the edge region is the sum of the thickness of the graphite layer in the main region and the hard carbon layer in the main region, the thickness of the hard carbon layer in the edge region is compatible with the thickness of the graphite layer and the hard carbon layer in the main region. For example, the second structure (the negative electrode sheet of Example 7, whose structural schematic diagram is shown in Figure 2 As shown in FIG. 1 , in the main region, the thickness 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. 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. Exemplarily, the thickness ratio of the hard carbon layer to the ceramic layer is any value among 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1 or any value within the range of values ​​consisting of any two of the above values. Since the thickness of the hard carbon layer in the edge region is the sum of the thickness of the graphite layer in the main region 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 thickness of the graphite layer in the main region, the hard carbon layer in the main region and the ceramic layer in the main region, the thickness of the hard carbon layer in the edge region is compatible with the thickness of the graphite layer in the main region and the hard carbon layer in the main region, and the thickness of the ceramic layer in the edge region is compatible with the thickness of the graphite layer in the main region, the hard carbon layer in the main region and the ceramic layer in the main region. For example, the third structure (the negative electrode sheet of Example 8, whose structural schematic diagram is shown in Figure 3As shown in the figure, in the main region, the thicknesses of the graphite layer and the hard carbon layer are 60 μm, 30 μm, and 5 μm, respectively, the thickness of the hard carbon layer in the edge region is 90 μm, and the thickness of the ceramic layer in the edge region is 95 μm. Therefore, the thickness ratio of the hard carbon layer in the edge region to the ceramic layer in the edge region, or the thickness ratio of the hard carbon layer in the main region to the ceramic layer in the edge region, or the thickness ratio of the hard carbon layer in the edge region to the ceramic layer in the main region is not limited.

[0140] Preferably, the thickness of the graphite layer 20 is 60-80 μm. Exemplarily, the thickness of the graphite layer is any value among 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 area is 30 to 40 μm. Exemplarily, the thickness of the hard carbon layer in the main area is any value among 30 μm, 32 μm, 34 μm, 36 μm, 38 μm, 40 μm or any value within the range of values ​​consisting of any two of the above values. The thickness of the hard carbon layer in the edge area is the sum of the thickness of the graphite layer in the main area and the hard carbon layer in the main area, and the thickness of the hard carbon layer in the edge area is compatible with the thickness of the graphite layer and the hard carbon layer in the main area. For example, the second structure (the negative electrode sheet of Example 7, whose structural schematic diagram is shown in Figure 2 As shown), in the main area, the thickness of the graphite layer and the hard carbon layer are 60μm and 30μm respectively, and the thickness of the hard carbon layer in the edge area is 90μm.

[0142] Preferably, the thickness of the ceramic layer 40 in the main region is 2 to 5 μm. Exemplarily, the thickness of the ceramic layer 40 in the main region is any value among 2 μm, 3 μm, 4 μm, 5 μm, or any value within the range of values ​​composed of any two of the above values. The thickness of the ceramic layer in the edge region is the sum of the thickness of the graphite layer in the main region, the hard carbon layer in the main region, and the ceramic layer in the main region, and the thickness of the ceramic layer in the edge region is compatible with the thickness of the graphite layer in the main region, the hard carbon layer in the main region, and the ceramic layer in the main region. For example, the third structure (the negative electrode sheet of Example 8, whose structural schematic diagram is shown in Figure 3 As shown), in the main area, the thickness of the graphite layer and the hard carbon layer are 60μm, 30μm, and 5μm respectively, and the thickness of the ceramic layer in the edge area is 95μm.

[0143] In the above-mentioned graphite layer, hard carbon layer and ceramic layer thickness range, a large amount of Li + (ion radius 0.07nm) escapes from the positive electrode, passes through the separator, and is embedded in the negative electrode. + The ceramic layer, hard carbon layer and graphite layer are smoothly embedded in sequence to improve the fast charging performance of the battery.

[0144] In an embodiment of the present invention, the graphite layer includes graphite, a first conductive agent and a first binder, wherein the graphite accounts for 90% to 99% by weight, the first conductive agent accounts for 0.5% to 5% by weight, and the first binder accounts for 0.5% to 5% by weight.

[0145] In an embodiment of the present invention, the hard carbon layer includes hard carbon, a second conductive agent and a second binder, wherein the hard carbon accounts for 90% to 99% by mass, the second conductive agent accounts for 0.5% to 5% by mass, and the second binder accounts for 0.5% to 5% by mass.

[0146] In an embodiment of the present invention, the ceramic layer includes ceramic and a third binder, wherein the ceramic accounts for 90% to 99% by weight and the third binder accounts for 1% to 10% by weight.

[0147] In an embodiment of the present invention, illustratively, the first conductive agent and the second conductive agent independently include at least one of conductive carbon black (SP), vapor-generated carbon fiber (VGCF), graphene, and carbon nanotubes (CNTs).

[0148] In an embodiment of the present invention, exemplarily, the first binder and the second binder independently include at least one of the aqueous binders carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), styrene-butadiene rubber (SBR), or include the oily binder polyvinylidene fluoride (PVDF).

[0149] In an embodiment of the present invention, exemplarily, the third binder includes an oily binder PVDF or a water-based binder polyacrylic acid (PAA).

[0150] In a second aspect, the present invention provides a lithium-ion battery comprising the above-mentioned negative electrode sheet.

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

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

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

[0154] In an embodiment of the present invention, the diaphragm further comprises a coating disposed on at least one surface of the base film, and the coating comprises at least one of aluminum oxide, boehmite, and a solid electrolyte.

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

[0156] The reagents, instruments or materials used in the present invention can be obtained through commercial channels.

[0157] The present invention will be further described below in conjunction with embodiments:

[0158] Embodiment 1:

[0159] 1. Preparation of negative electrode sheet:

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

[0161] Preparation of composite graphite: Particle size D of the first graphite 50 13μm, specific surface area 1.4m 2 / g, compacted density 1.6g / cm 3 , gram capacity 350mAh / g; the particle size of the second graphite is D 50 5μm, specific surface area 2.6m 2 / g, compacted density 1.4g / cm 3 , gram capacity 330mAh / g. The interlayer spacing of the first graphite and the second graphite is 0.336nm. The first graphite accounts for 80% and the second graphite accounts for 20% and is stirred and mixed.

[0162] The raw materials are 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 glue with a solid content of 1.5% is prepared, and then the conductive agent, composite graphite and SBR are added in sequence, stirred and dispersed to obtain a graphite layer slurry.

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

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

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

[0166] A double-layer coating machine is used to simultaneously coat the graphite layer slurry and the hard carbon layer slurry on the surface of the current collector, and the graphite layer and the hard carbon layer are obtained after being dried at the same time.

[0167] (4) Coating of ceramic layer:

[0168] The raw materials are selected according to a mass ratio of alumina (the spacing between alumina ceramic layers is 0.45 nm) to PVDF of 95:5, dispersed in an NMP solution to obtain an alumina slurry, which is then coated on the surface of the hard carbon layer to form a ceramic layer.

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

[0170] After coating, graphite layer, hard carbon layer and ceramic layer with different thicknesses were obtained by roller pressing. The thicknesses were 60 μm, 30 μm and 2 μm respectively, the porosities were 15%, 35% and 75% respectively, and the compaction density was 1.53 g / cm 3 、0.98g / cm 3 、3.92g / cm 3 The schematic diagram of the negative electrode structure is as follows: Figure 1 shown.

[0171] 2. Preparation of positive electrode:

[0172] Lithium iron phosphate, carbon nanotubes (CNT), conductive carbon black (SP), and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96.5:1:0.5:2, added into a solvent NMP to prepare a slurry, and coated onto a current collector to obtain a positive electrode sheet.

[0173] 3. Diaphragm:

[0174] The diaphragm is made of polyethylene.

[0175] 4. Electrolyte:

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

[0177] 5. Battery assembly:

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

[0179] Embodiment 2:

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

[0181] Embodiment 3:

[0182] The difference between this embodiment and embodiment 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] Embodiment 4:

[0184] The difference between this embodiment and embodiment 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] Embodiment 5:

[0186] The difference between this embodiment and embodiment 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] Embodiment 6:

[0188] The difference between this embodiment and embodiment 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] Embodiment 7:

[0190] The difference between this embodiment and embodiment 2 is that the hard carbon layer also includes a hard carbon layer in the edge region, and the hard carbon layer in the edge region has a width of 10 mm and a thickness of 90 μm. Figure 2 .

[0191] Embodiment 8:

[0192] The difference between this embodiment and embodiment 2 is that the hard carbon layer further includes a hard carbon layer in the first edge region, the width of the hard carbon layer in the first edge region is 10 mm, and the thickness is 90 μm; the ceramic layer further includes a ceramic layer in the second edge region, the width of the ceramic layer in the second edge region is 5 mm, and the thickness is 95 μm. Figure 3 .

[0193] Comparative Example 1:

[0194] This comparative example is different from Example 1 in 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] This comparative example is different from Example 1 in that no hard carbon layer is provided.

[0199] Comparative Example 4

[0200] This comparative example is different from Example 1 in that no hard carbon layer and no ceramic layer are provided.

[0201] Battery performance test

[0202] The negative electrode sheets and batteries prepared in the examples and comparative examples were subjected to performance tests, and the test items included:

[0203] Electrolyte infiltration rate test method: In a protective gas atmosphere, the electrolyte container is placed on a heated lifting platform. The platform is driven by a motor to precisely control the displacement. The pole piece sample is suspended on an electronic balance, and the lifting platform is controlled to immerse the pole piece sample in the electrolyte by 5mm. The data collector records the sample weight increase data in real time, and analyzes the electrolyte infiltration rate of the pole piece through the mass m-time t data. After the pole piece is immersed in the electrolyte, the surface absorbs the electrolyte and the mass increases rapidly. Afterwards, the electrolyte infiltrates into the pores of the electrode, and the mass slowly increases. The electrolyte infiltration rate is mainly obtained by analyzing the curve of this process (mt curve). The mass of the electrolyte decreases rapidly after it drops and leaves the pole piece, and then the mass of the electrolyte dripping on the electrode surface slowly decreases. The curve of the electrolyte infiltration stage is analyzed according to the formula:

[0204]

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

[0206] Test method for lithium deposition at the negative electrode interface of the battery cell when it is charged at 100% SOC at 8C: After the battery cell has been cycled for 30 times, charge it to 100% SOC and disassemble it to observe the interface state of the negative electrode sheet. If the interface is all golden yellow, it is judged that there is no lithium deposition; if black spots and white granular precipitates appear on the surface of the negative electrode, it is considered that lithium deposition has occurred.

[0207] 8C charging constant current ratio test method: After the battery cells are assembled and activated, first charge and discharge at 1C, calibrate the battery cell capacity, and then charge at 8C constant current and constant voltage according to the capacity to 4.25V, with a cutoff of 0.05C, to obtain the 8C charging constant current ratio.

[0208] 5C charge and discharge 300 cycles retention rate test method: After the battery cell is assembled and activated, first charge and discharge at 0.5C, calibrate the battery cell capacity, and charge at 5C constant current and constant voltage to 4.25V according to the calibrated capacity, cut off at 0.05C, leave for 30 minutes, and discharge at 5C to 2.8V, and repeat this cycle for 300 cycles.

[0209] Table 1

[0210]

[0211] It can be seen from the test results in the above table that Examples 1-8 all have a 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 are 60μm, 30μm and 5μm respectively, the comprehensive performance of the battery cell is optimal, and the three work synergistically with each other. Examples 7 and 8 are more conducive to the rapid embedding of lithium ions and improve the fast charging performance, but the inactive substances are too high and the electronic conductivity is low, which will weaken the electrical properties such as circulation.

[0212] In Comparative Example 1, no ceramic layer is provided, which will reduce the electrolyte infiltration rate and affect the fast charging performance.

[0213] In Comparative Example 2, the thickness of the ceramic layer is too large, which will affect the fast charging performance because the electron migration rate is reduced.

[0214] In Comparative Example 3, no hard carbon layer is provided. Due to the lack of buffering effect of the hard carbon layer, the graphite layer cannot meet the needs of a large number of ions to be quickly embedded in the graphite during high current charging, resulting in lithium deposition.

[0215] In Comparative Example 4, no hard carbon layer and ceramic layer are provided, and the constant current ratio is very low, which cannot meet the requirements of high current charging, and the cycle life will be attenuated, a large amount of active lithium will be consumed and precipitated, resulting in lithium precipitation.

[0216] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The negative electrode sheet comprises: current collector(10); a graphite layer (20), the graphite layer (20) being disposed on at least one surface of the current collector (10); a hard carbon layer (30), the hard carbon layer (30) being disposed on a surface of the graphite layer (20) away from the current collector (10); A ceramic layer (40) is disposed on a surface of the hard carbon layer (30) away from the current collector (10).

2. The negative electrode sheet according to claim 1, characterized in that: The interlayer spacing of graphite in the graphite layer is denoted as A1, the interlayer spacing of hard carbon in the hard carbon layer is denoted as A2, and the interlayer spacing of ceramic in the ceramic layer is denoted as A3, and A1, A2, and A3 satisfy A1<A2<A3; And / or, the porosity of the graphite layer is recorded as B1, the porosity of the hard carbon layer is recorded as B2, and the porosity of the ceramic layer is recorded as B3, and B1, B2, and B3 satisfy B1<B2<B3; And / or, the compaction density of the graphite layer is recorded as C1, the compaction density of the hard carbon layer is recorded as C2, and the compaction density of the ceramic layer is recorded as C3, and C1, C2, and C3 satisfy C2<C1<C3.

3. The negative electrode sheet according to claim 1, characterized in that: 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% to 16%, the porosity of the hard carbon layer is 30% to 40%, and the porosity of the ceramic layer is 60% to 90%; And / or, the compaction density of the graphite layer is 1.4-1.6 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 .

4. The negative electrode sheet according to claim 1, characterized in that: The graphite layer includes composite graphite, and the composite graphite includes first graphite and second graphite; The particle size D of the first graphite 50 is 12 to 15 μm, and the particle size D of the second graphite is 50 4~7μm; And / or, the specific surface area of ​​the first graphite is ≤1.4m 2 / g, the specific surface area of ​​the second graphite is ≤2.6m 2 / g; And / or, the compacted density of the first graphite is ≤1.6 g / cm 3 , the compaction density of the second graphite is ≤1.4g / cm 3 ; And / or, the gram capacity of the first graphite is ≥350 mAh / g, and the gram capacity of the second graphite is ≥330 mAh / g; And / or, the mass proportion of the first graphite in the composite graphite is 80% to 90%, and the mass proportion of the second graphite in the composite graphite is 10% to 20%.

5. The negative electrode sheet according to claim 1, characterized in that: The hard carbon layer includes at least one of biomass-based hard carbon, resin-based hard carbon, and asphalt-based hard carbon; And / or, the ceramic layer includes at least one of Al2O3, SiO2, ZrO2, TiO2, MgO, MnO, and Cr2O3.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The current collector surface comprises a main region (100) and an edge region (200), wherein the edge region (200) is located on both sides of the main region (100); The hard carbon layer (30) is disposed in the main 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 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; In the edge region (200), the 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.

7. The negative electrode sheet according to claim 6, characterized in that: The edge region (200) comprises a first edge region (210) and a second edge region (220), wherein 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 in the main body region (100) and the edge region (200); In the main body region (100), the ceramic layer (40) is disposed on the surface of the hard carbon layer (30) and is in direct contact with the surface of the hard carbon layer; In the first edge region (210), the 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; In the second edge region (220), the ceramic layer (40) is disposed on the surface of the current collector and is in direct contact with the surface of the current collector.

8. The negative electrode sheet according to claim 7, characterized in that: The width of the first edge region (210) is 10 to 40 μm; The width of the second edge region (220) is 2-5 μm.

9. The negative electrode sheet according to any one of claims 1 to 8, characterized in that: 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; Preferably, the thickness of the graphite layer (20) is 60 to 80 μm; Preferably, the thickness of the hard carbon layer (30) is 30-40 μm; Preferably, the thickness of the ceramic layer (40) is 2-5 μm.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to any one of claims 1 to 9.

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