A lithium battery negative electrode sheet, a battery cell and a lithium battery

Abstract

The application provides a lithium battery negative plate, a battery cell and a lithium battery. The lithium battery negative plate according to the application comprises a negative current collector, an active layer and a safety coating. The active layer comprises a first active layer, a second active layer and a third active layer arranged in sequence, thereby forming a multilayer active layer structure, which can improve the rapid penetration of lithium ions on the surface of the negative plate, reduce the risk of lithium precipitation on the surface of the negative plate, and effectively improve the charging rate of the lithium ion battery when used in the lithium battery. The setting of the safety coating can significantly improve the mechanical strength of the negative plate. When the negative plate according to the application is used in the battery cell, the mechanical strength of the battery cell can be improved, the efficient heat transfer in the battery cell can be promoted, the safety and reliability of the battery cell can be enhanced, and the risk of fire and explosion of the battery cell under extreme use conditions such as thermal abuse or mechanical abuse can be greatly reduced. The application further provides a battery cell and a lithium battery containing the above-mentioned negative plate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a lithium battery negative plate, a battery cell and a lithium battery. BACKGROUND

[0002] With the rapid development of lithium ion battery technology, the energy density of the battery has been greatly improved. The demand for shortening the charging time in the consumer electronics market and the power battery market is increasing, and the fast charging technology has become an important trend in the development of lithium ion battery technology in recent years. Fast charging mainly ensures that lithium ions can be quickly extracted from the positive electrode and quickly inserted into the negative electrode, and cannot cause deposition of lithium ions (to ensure safety performance).

[0003] Graphite negative electrodes are still the most commonly used negative electrode material in the current lithium ion battery market due to their high theoretical specific capacity (372 mAh / g), low operating potential (~0.1 V vs. Li / Li + ) and good structural stability (volume change <10%) and other advantages. However, the layered structure of graphite material determines that lithium ions must be inserted from the end face of the material and then diffuse to the inside of the particle, resulting in a long transport path and a large irreversible capacity. The slow lithium insertion process hinders the fast charging application of lithium ion batteries. Furthermore, the lithium insertion potential of graphite is too small and the kinetic conditions are poor. In the case of too fast charging speed, the lithium insertion potential of graphite will be reduced to below 0 V due to the large polarization on the graphite negative electrode side, which will cause the deposition of metal lithium on the negative electrode surface, easily causing loss of limited lithium source, increase of battery internal resistance, capacity decay, etc., thereby aggravating the instability of the interface, leading to a rapid increase in cycle performance degradation rate, and seriously affecting the service life of the power battery. In addition, the deposited lithium metal will grow in the form of dendrites, which will pierce the separator and cause internal short circuit of the battery, causing serious safety problems, etc.

[0004] In related technologies, the commonly used lithium battery fast charging negative electrode material is lithium titanate (Li4Ti5O 12), which is a composite oxide with a spinel structure, has three-dimensional lithium ion diffusion channels, is conducive to the rapid migration of lithium ions therein, has an ion diffusion coefficient one order of magnitude higher than that of graphite, has a fast electrochemical reaction speed, and greatly shortens the charging time. Lithium titanate is an ideal negative electrode material that simultaneously has fast charging, long cycle life, and high safety. When used as an anode material, lithium titanate has a potential platform as high as 1.55 V, which is more than 1 V higher than that of traditional graphite anode materials, can prevent the negative electrode voltage from being zero, prevents the generation and deposition of metallic lithium during charging, is not prone to lithium dendrite, and has a stable discharge voltage, thereby improving the safety performance of lithium batteries. However, due to the high potential platform, the platform of the battery cell is significantly reduced, which greatly affects the energy density of the battery cell, and lithium titanate is not suitable for being applied alone to the power battery market (mainly referring to the electric car market) which has an increasingly high requirement for the energy density of battery cells.

[0005] Therefore, there is still a need to develop a lithium battery negative plate that can balance fast charging and safety performance. SUMMARY

[0006] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the present application provides a lithium battery negative plate, which comprises a negative current collector, an active layer and a safety coating, and balances the fast charging and safety performance of the lithium battery negative plate.

[0007] The present application also provides a preparation method of a lithium battery negative plate.

[0008] The present application also provides a lithium battery cell.

[0009] The present application also provides a lithium battery.

[0010] The first aspect of the present application provides a lithium battery negative plate, comprising:

[0011] a negative current collector;

[0012] an active layer, the active layer being arranged on the surface of the negative current collector, the active layer comprising a first active layer, a second active layer and a third active layer arranged in sequence;

[0013] a safety coating, the safety coating being arranged on the surface of the third active layer;

[0014] The preparation raw material of the active layer comprises fast-charging artificial graphite, the material specific capacity of the fast-charging artificial graphite is ≤352 mAh / g, and the compaction density is 1.6 g / cm 3 ~ 1.75 g / cm 3 .

[0015] The present application relates to a technical solution in a lithium battery negative plate, which has at least the following beneficial effects:

[0016] The lithium battery negative pole piece of the present application comprises a negative pole current collector, an active layer and a safety coating. The active layer comprises a first active layer, a second active layer and a third active layer arranged in sequence, thereby forming a multi-layer active layer structure, which can improve the rapid penetration of lithium ions on the surface of the negative pole piece, reduce the risk of lithium precipitation on the surface of the negative pole piece, and effectively improve the charging rate of the lithium ion battery when used in a lithium battery. The setting of the safety coating can significantly improve the mechanical strength of the negative pole piece. When the negative pole piece of the present application is used in a battery cell, the mechanical strength of the battery cell can be improved, the efficient heat transfer in the battery cell can be promoted, the safety and reliability of the battery cell can be enhanced, and the risk of fire and explosion of the battery cell under extreme use conditions such as thermal abuse or mechanical abuse can be greatly reduced.

[0017] According to some embodiments of the present application, the raw materials for preparing the first active layer include the fast-charging artificial graphite, a thickening agent and a first negative pole binder.

[0018] According to some embodiments of the present application, the D50 particle size range of the fast-charging artificial graphite in the first active layer is 2-15 mu m.

[0019] The D50 particle size range of the fast-charging artificial graphite in the first active layer is 2-15 mu m, which is beneficial to improve the fast-charging capacity of the battery cell while taking into account the high compaction characteristics of the anode pole piece. Less than 2 mu m may result in a significant decrease in the compaction of the pole piece, which reduces the energy density of the battery cell. Greater than 15 mu m may result in an increase in the diffusion path of lithium ions in the pole piece, which reduces the fast-charging capacity of the battery cell.

[0020] The D90 particle size range of the fast-charging artificial graphite in the second active layer is 4-25 mu m, which is beneficial to improve the fast-charging capacity of the battery cell while taking into account the high compaction characteristics of the anode pole piece. Less than 4 mu m may result in a significant decrease in the compaction of the pole piece, which reduces the energy density of the battery cell. Greater than 25 mu m may result in an increase in the diffusion path of lithium ions in the pole piece, which reduces the fast-charging capacity of the battery cell.

[0021] According to some embodiments of the present application, the thickness of the first active layer is 40-150 mu m.

[0022] According to some embodiments of the present application, the thickening agent in the first active layer comprises CMC-Li.

[0023] According to some embodiments of the present application, the content of the thickening agent in the first active layer is 1-1.5 wt%.

[0024] According to some embodiments of the present application, the first negative pole binder comprises SBR.

[0025] According to some embodiments of the present application, the content of the first negative pole binder in the first active layer is 1-2 wt%.

[0026] According to some embodiments of the present application, the preparation raw material of the second active layer comprises the fast-charging artificial graphite, hard carbon and second negative electrode binder.

[0027] Using hard carbon and soft carbon as fast-charging materials, the voltage platform is more conducive to the rapid embedding of lithium ions, and is less likely to cause lithium precipitation, and has better safety performance. However, the hard carbon and soft carbon materials have problems such as small compaction density and low first coulomb efficiency, which will seriously affect the improvement of the energy density of lithium ion batteries, and have high cost. In the lithium battery negative plate of the present application, the preparation raw material of the second active layer adds fast-charging artificial graphite, which can significantly improve the overall charging rate of the lithium ion battery, reduce the risk of lithium precipitation on the surface of the negative plate, and also reduce the cost.

[0028] According to some embodiments of the present application, the D50 particle size of the preparation raw material of the second active layer is in the range of 0.5-2 μm, which is conducive to improving the fast-charging capacity of the battery cell while keeping the film of the layer compacted at a high level. If the D50 particle size is less than 0.5 μm, the compaction of the pole piece will be greatly reduced, resulting in a decrease in the energy density of the battery cell. If the D50 particle size is greater than 2 μm, the fast-charging capacity of the battery cell will be reduced.

[0029] According to some embodiments of the present application, the D90 particle size of the preparation raw material of the second active layer is in the range of 3-5 μm, which is conducive to improving the fast-charging capacity of the battery cell while keeping the film of the layer compacted at a high level. If the D90 particle size is less than 3 μm, the compaction of the pole piece will be greatly reduced, resulting in a decrease in the energy density of the battery cell. If the D90 particle size is greater than 5 μm, the fast-charging capacity of the battery cell will be reduced.

[0030] According to some embodiments of the present application, in the preparation raw material of the second active layer, the mass ratio of artificial graphite to hard carbon is 1-9:1.

[0031] According to some embodiments of the present application, in the preparation raw material of the second active layer, the mass ratio of artificial graphite to hard carbon is 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 or 9:1.

[0032] According to some embodiments of the present application, in the preparation raw material of the second active layer, the mass ratio of artificial graphite to hard carbon is 4:6, 5:5 or 6:4.

[0033] According to some embodiments of the present application, in the preparation raw material of the second active layer, the second negative electrode binder comprises SBR and PAA-Li.

[0034] According to some embodiments of the present application, in the preparation raw material of the second active layer, the content of the second negative electrode binder in the second active layer is 1-5 wt%.

[0035] According to some embodiments of the present application, the preparation raw material of the second active layer further comprises a thickening agent.

[0036] According to some embodiments of the present application, the content of the thickening agent in the second active layer is 1wt%-5wt%.

[0037] According to some embodiments of the present application, the content of the thickening agent in the second active layer is 1wt%-1.5wt%.

[0038] According to some embodiments of the present application, the thickening agent in the second active layer can be the same as that in the first active layer.

[0039] According to some embodiments of the present application, the raw material for preparing the second active layer further comprises at least one conductive additive selected from Super P Li and carbon nanotubes.

[0040] According to some embodiments of the present application, the content of the conductive additive in the second active layer is 0.2wt%-10wt%.

[0041] According to some embodiments of the present application, the content of the conductive additive in the second active layer is 1wt%-2wt%.

[0042] According to some embodiments of the present application, the thickness of the second active layer is 5μm-40μm.

[0043] According to some embodiments of the present application, the raw material for preparing the third active layer comprises Li 3+x at least one of V2O5 and intercalation transition metal oxide.

[0044] According to some embodiments of the present application, the intercalation transition metal oxide comprises at least one of lithium titanate and niobium-based oxide.

[0045] Li 3+x V2O5 and intercalation transition metal oxide have a potential of 0.6V-1.6V relative to lithium, lithium metal is not easy to be deposited on the surface thereof, and lithium ions have a high diffusion coefficient in the material thereof.

[0046] According to some embodiments of the present application, Li 3+x V2O5 is Li3V2O5, has a potential of 0.6V relative to lithium, and has a disordered rock layer structure.

[0047] According to some embodiments of the present application, the D50 particle size range in the raw material for preparing the third active layer is 0.2μm-1μm, which is beneficial to improve the fast charging capacity of the battery cell while keeping the film sheet of the layer compacted at a high level, less than 0.2μm, which may cause the compaction of the electrode sheet to greatly decrease and the energy density of the battery cell to decrease; and greater than 1μm, which may cause the fast charging capacity of the battery cell to decrease.

[0048] According to some embodiments of the present invention, in the raw materials for preparing the third active layer, the D90 particle size range is 1.2μm to 2μm, which is beneficial to improve the fast charging capability of the battery cell while maintaining a high compaction of the film layer. If the particle size is less than 1.2μm, it may cause a significant decrease in electrode compaction, resulting in a decrease in the energy density of the battery cell; if the particle size is greater than 2μm, it may cause a decrease in the fast charging capability of the battery cell.

[0049] According to some embodiments of the present invention, the raw materials for preparing the third active layer also include a binder.

[0050] According to some embodiments of the present invention, the binder in the raw materials for preparing the third active layer includes PVDF.

[0051] According to some embodiments of the present invention, the content of the adhesive in the third active layer is 1 wt% to 10 wt%.

[0052] According to some embodiments of the present invention, the thickness of the third active layer is 3 μm to 10 μm.

[0053] According to some embodiments of the present invention, the raw materials for preparing the safety coating include at least one selected from hexagonal boron nitride, titanium nitride, titanium diboride, titanium carbide, aluminum nitride, aluminum oxide, and silicon dioxide.

[0054] The raw materials used to prepare the aforementioned safety coating are characterized by high temperature resistance, excellent thermal conductivity, and high hardness, which can significantly improve the mechanical strength of the electrode.

[0055] According to some embodiments of the present invention, in the raw materials for preparing the safety coating, the D50 particle size range is 0.1μm to 0.8μm, which is beneficial to improving the mechanical strength of the electrode. At the same time, the proportion of the non-active layer in the electrode is kept at an appropriate level to keep the cell at a high energy density. If the particle size is less than 0.1μm, it may increase the difficulty of pulping and be detrimental to mass production; if the particle size is greater than 0.8μm, it may lead to a large proportion of the non-active layer in the electrode, which may sacrifice the energy density of the cell.

[0056] According to some embodiments of the present invention, in the raw materials for preparing the safety coating, the D90 particle size range is 1μm to 2μm, which is beneficial to improving the mechanical strength of the electrode. At the same time, the proportion of the non-active layer in the electrode is kept at an appropriate level to keep the cell at a high energy density. If the particle size is less than 1μm, it may increase the difficulty of pulping and be detrimental to mass production; if the particle size is greater than 2μm, it may lead to a large proportion of the non-active layer in the electrode, which may sacrifice the energy density of the cell.

[0057] According to some embodiments of the present invention, the thickness of the safety coating is 2 μm to 5 μm.

[0058] According to some embodiments of the present invention, in the lithium battery negative electrode sheet, the total thickness of the negative electrode current collector, the active layer and the safety coating is 50 μm to 200 μm.

[0059] The second aspect of the present application provides a method for preparing the lithium battery negative electrode sheet, the method comprising: preparing a first active layer slurry, a second active layer slurry, a third active layer slurry and a safety coating slurry respectively, and coating the first active layer slurry, the second active layer slurry, the third active layer slurry and the safety coating slurry on the surface of the negative electrode current collector in sequence to obtain the lithium battery negative electrode sheet.

[0060] The present application relates to a technical solution in the preparation method of the lithium battery negative electrode sheet, which has at least the following beneficial effects:

[0061] The preparation method of the lithium battery negative electrode sheet of the present application only needs to prepare a first active layer slurry, a second active layer slurry, a third active layer slurry and a safety coating slurry respectively, and then coat the first active layer slurry, the second active layer slurry, the third active layer slurry and the safety coating slurry on the surface of the negative electrode current collector in sequence to obtain the lithium battery negative electrode sheet. The process is simple, the equipment requirement is low, and the industrial production is facilitated.

[0062] The third aspect of the present application provides a lithium battery cell comprising the lithium battery negative electrode sheet.

[0063] The present application relates to a technical solution in the lithium battery cell, which has at least the following beneficial effects:

[0064] The lithium battery cell of the present application comprises the lithium battery negative electrode sheet of the present application, thereby having all the beneficial effects of the lithium battery negative electrode sheet and taking into account safety and performance. Specifically:

[0065] The lithium battery cell of the present application comprises a negative electrode current collector, an active layer and a safety coating. The active layer comprises a first active layer, a second active layer and a third active layer arranged in sequence, thereby forming a multi-layer active layer structure, which can improve the rapid penetration of lithium ions on the surface of the negative electrode sheet and reduce the risk of lithium precipitation on the surface of the negative electrode sheet. When used in a lithium battery, the lithium ion battery can effectively improve the charging rate. The safety coating can significantly improve the mechanical strength of the negative electrode sheet. When the negative electrode sheet of the present application is used in a cell, the mechanical strength of the cell can be improved, the efficient heat transfer in the cell can be promoted, the safety and reliability of the cell can be enhanced, and the risk of fire and explosion of the cell under extreme use conditions such as thermal abuse or mechanical abuse can be greatly reduced.

[0066] According to some embodiments of the present application, a separator film is further included, and the raw material for preparing the separator film comprises a base film and a 3D network structure composite coating layer arranged on the surface of the base film.

[0067] The thermal stability of the separator film, as one of the key materials of lithium batteries, is closely related to the thermal safety performance of lithium batteries. A high-safety separator film requires good thermal dimensional stability, no obvious deformation under certain high-temperature environment, good thermal closing performance and good mechanical strength to avoid internal short circuit of the battery, so as to inhibit the combustion and explosion of the battery. Among various separator films, ceramic separator films with excellent heat resistance have become the first choice for lithium batteries in recent years. The introduction of ceramic coating can effectively improve the thermal shrinkage temperature of the separator film, block the heat diffusion in the battery, inhibit the expansion of some thermal runaway points to form overall thermal runaway, and thus improve the safety performance of the battery. The preparation process of such separator film is relatively simple, and it is easy to mass produce and use. The ceramic material used in the traditional ceramic separator film is inert inorganic nanoparticles, such as Al2O3, AlOOH, MgOH, SiO2, BaSO4, etc. Although the ceramic coating can effectively improve the thermal stability of the separator film and improve the safety of the battery, it has little contribution to the electrochemical performance of the lithium battery, and the thermal conductivity of the traditional ceramic separator film coating is poor, which is not conducive to the conduction of heat in the battery cell.

[0068] In the production process of lithium ion battery cell, the positive and negative electrode rolls are usually cut and tabbed by cutting knife or die cutting technology. However, when cutting knife or die cutting metal current collector, burr will inevitably be generated on the cutting end face. The metal burr can pierce or even pierce the separator film, causing micro-short circuit or even short circuit of the battery. In order to improve the resistance of the separator to the burr, a composite separator film is developed, that is, a coating with higher strength, such as inorganic oxide (hydroxide) coating or aramid coating, is added on the porous polymer. However, since the coating must have the ability to penetrate the electrolyte, the coating is also porous, and the burr that occurs in the actual production process can still pierce the coating. Especially with the progress of lithium battery technology, in order to improve the energy density of the battery, the positive and negative electrode compaction density is increased, and in order to ensure that the current collector does not break during the manufacturing process, the current collector often uses higher strength aluminum foil or copper foil. In this case, the burr is more likely to pierce the battery and cause short circuit. When the battery cell is pressed by a heavy object or a sharp object, or even pierced, a large amount of metal debris or burr will be generated, which will pierce the separator film and cause the battery cell to short circuit in a large area, generating a large amount of heat and causing the battery cell to catch fire and explode. Research shows that the contact between the aluminum foil and the graphite-coated negative electrode sheet area generates the most heat, and this short circuit mode is the most dangerous.

[0069] The separator film in the battery cell of the present application is prepared from a base film and a 3D network structure composite coating on the surface of the base film. The 3D network structure composite coating has fire-resistant and flame-retardant functions, and has high thermal conductivity and high mechanical strength.

[0070] According to some embodiments of the present application, the base film of the separator film in the battery cell of the present application can be a polyolefin commercial separator film.

[0071] According to some embodiments of the present application, the preparation raw material of the 3D network structure composite coating includes micro-nano sheet material, nanowire and isolation film binder.

[0072] According to some embodiments of the present application, the micro-nano sheet material refers to micro sheet material and nano sheet material.

[0073] According to some embodiments of the present application, the micro-nano sheet material includes at least one of boron nitride micro-nano sheet and aluminum nitride micro-nano sheet.

[0074] According to some embodiments of the present application, the nanowire includes hydroxyapatite nanowire.

[0075] According to some embodiments of the present application, the isolation film binder includes at least one of PVDF, PMMA, PCN and CMC.

[0076] According to some embodiments of the present application, in the micro-nano sheet material, the D50 particle size range in the micrometer range can be 0.1 μm to 0.8 μm, which is beneficial to improve the mechanical strength of the isolation film, and meanwhile, the appropriate thickness of the finished isolation film is beneficial to keep the battery with high energy density, less than 0.1 μm, which may cause difficulty in slurry preparation and is not conducive to mass production; greater than 0.8 μm, which may cause the finished isolation film to be too thick and sacrifice the energy density of the battery.

[0077] According to some embodiments of the present application, in the micro-nano sheet material, the D90 particle size range in the micrometer range can be 1 μm to 2 μm, which is beneficial to improve the mechanical strength of the isolation film, and meanwhile, the appropriate thickness of the finished isolation film is beneficial to keep the battery with high energy density, less than 1 μm, which may cause difficulty in slurry preparation and is not conducive to mass production; greater than 2 μm, which may cause the finished isolation film to be too thick and sacrifice the energy density of the battery.

[0078] According to some embodiments of the present application, in the preparation raw material of the 3D network structure composite coating, the diameter of the nanowire is 10 nm to 200 nm, and the length is 10 μm to 200 μm.

[0079] According to some embodiments of the present application, the isolation film binder can be a commonly used polymer binder.

[0080] The fourth aspect of the present application provides a lithium battery including the lithium battery cell of the claim.

[0081] One of the technical solutions of the present application related to the lithium battery has at least the following beneficial effects:

[0082] Because the lithium battery of the present invention contains the negative electrode sheet and the battery cell of the present invention, it possesses all the beneficial effects of the negative electrode sheet and the battery cell. Specifically, the negative electrode sheet in the battery cell of the lithium battery includes a negative electrode current collector, an active layer, and a safety coating. The active layer includes a first active layer, a second active layer, and a third active layer arranged sequentially, thereby forming a multi-layer active layer structure. This structure can improve the rapid penetration of lithium ions onto the surface of the negative electrode sheet, reduce the risk of lithium plating on the surface of the negative electrode sheet, and effectively improve the charging rate of the lithium-ion battery when used in a lithium battery. The safety coating can significantly improve the mechanical strength of the negative electrode sheet. When the negative electrode sheet of the present invention is used in a battery cell, it can improve the mechanical strength of the battery cell, promote efficient heat transfer within the battery cell, enhance the safety and reliability of the battery cell, and significantly reduce the risk of fire and explosion of the battery cell under extreme usage conditions such as thermal abuse or mechanical abuse.

[0083] According to some embodiments of the present invention, the lithium battery of the present invention further includes a positive electrode, an electrolyte, a packaging shell, and tabs. Attached Figure Description

[0084] Figure 1 This is a schematic diagram of the structure of the lithium battery negative electrode sheet of the present invention.

[0085] Figure 2 This is a schematic diagram of the isolation membrane structure of the present invention.

[0086] Figure label:

[0087] 1: Negative electrode current collector.

[0088] 2: First active layer.

[0089] 3: Second active layer.

[0090] 4: Third active layer.

[0091] 5: Safety coating.

[0092] 6: Base membrane.

[0093] 7: 3D network structure composite coating. Detailed Implementation

[0094] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0095] refer to Figure 1 As shown, in some embodiments of the present invention, the present invention provides a lithium battery negative electrode sheet, comprising:

[0096] Negative electrode current collector 1;

[0097] The active layer is arranged on the surface of the negative current collector 1, and comprises a first active layer 2, a second active layer 3 and a third active layer 4 arranged in sequence.

[0098] The safety coating layer 5 is arranged on the surface of the third active layer 4.

[0099] The raw material of the active layer comprises fast-charging artificial graphite, the material specific capacity of the fast-charging artificial graphite is less than or equal to 352 mAh / g, and the compacted density is 1.6 g / cm 3 ~ 1.75 g / cm 3 .

[0100] It can be understood that the lithium battery negative electrode sheet of the present application comprises a negative current collector, an active layer and a safety coating layer. The active layer comprises a first active layer, a second active layer and a third active layer arranged in sequence, thereby forming a multi-layer active layer structure, which can improve the rapid penetration of lithium ions on the surface of the negative electrode sheet and reduce the risk of lithium precipitation on the surface of the negative electrode sheet. When used in a lithium battery, the charging rate of the lithium ion battery can be effectively improved. The setting of the safety coating layer can significantly improve the mechanical strength of the negative electrode sheet. When the negative electrode sheet of the present application is used in a battery cell, the mechanical strength of the battery cell can be improved, the efficient heat transfer in the battery cell can be promoted, the safety and reliability of the battery cell can be enhanced, and the risk of fire and explosion of the battery cell under extreme use conditions such as thermal abuse or mechanical abuse can be greatly reduced.

[0101] It should be noted that, unlike conventional artificial graphite, the fast-charging artificial graphite mainly differs in raw materials.

[0102] In some embodiments of the present application, the raw material of the first active layer comprises fast-charging artificial graphite, thickening agent and first negative electrode binder.

[0103] In some embodiments of the present application, the D50 particle size range of the fast-charging artificial graphite in the first active layer is 2-15 mu m.

[0104] Specifically, the D50 particle size range of the fast-charging artificial graphite in the first active layer is 2-15 mu m, which is beneficial to improve the fast-charging capacity of the battery cell while taking into account the high compaction characteristics of the anode sheet. Less than 2 mu m may result in a significant decrease in the compaction of the electrode sheet, which reduces the energy density of the battery cell. Greater than 15 mu m may result in an increase in the diffusion path of lithium ions in the electrode sheet and a decrease in the fast-charging capacity of the battery cell.

[0105] The D90 particle size range of the fast-charging artificial graphite in the second active layer is 4-25 mu m, which is beneficial to improve the fast-charging capacity of the battery cell while taking into account the high compaction characteristics of the anode sheet. Less than 4 mu m may result in a significant decrease in the compaction of the electrode sheet, which reduces the energy density of the battery cell. Greater than 25 mu m may result in an increase in the diffusion path of lithium ions in the electrode sheet and a decrease in the fast-charging capacity of the battery cell.

[0106] According to some embodiments of the present application, the thickness of the first active layer is 40-150 μm.

[0107] In some embodiments of the present application, the thickening agent in the first active layer comprises CMC-Li.

[0108] In some embodiments of the present application, the content of the thickening agent in the first active layer is 1-1.5 wt%.

[0109] In some embodiments of the present application, the first negative electrode binder comprises SBR.

[0110] In some embodiments of the present application, the content of the first negative electrode binder in the first active layer is 1-2 wt%.

[0111] In some embodiments of the present application, the raw material for preparing the second active layer comprises fast-charging artificial graphite, hard carbon and a second negative electrode binder.

[0112] It should be noted that using hard carbon and soft carbon as fast-charging materials, the voltage platform is more conducive to the rapid embedding of lithium ions, and is less likely to cause lithium precipitation, thus being safer. However, hard carbon and soft carbon materials have problems such as small compaction density and low first coulomb efficiency, which will seriously affect the improvement of the energy density of lithium ion batteries, and are high in cost. In the lithium battery negative electrode sheet of the present application, fast-charging artificial graphite is added to the raw material for preparing the second active layer, which can significantly improve the overall charging rate of the lithium ion battery, reduce the risk of lithium precipitation on the surface of the negative electrode sheet, and also reduce the cost.

[0113] According to some embodiments of the present application, the D50 particle size of the raw material for preparing the second active layer is 0.5-2 μm, which is conducive to improving the fast-charging capacity of the battery cell while keeping the film of the layer compacted to a high degree. Less than 0.5 μm may cause the compaction of the electrode sheet to decrease greatly, thus reducing the energy density of the battery cell; and greater than 2 μm may cause the fast-charging capacity of the battery cell to decrease.

[0114] According to some embodiments of the present application, the D90 particle size of the raw material for preparing the second active layer is 3-5 μm, which is conducive to improving the fast-charging capacity of the battery cell while keeping the film of the layer compacted to a high degree. Less than 3 μm may cause the compaction of the electrode sheet to decrease greatly, thus reducing the energy density of the battery cell; and greater than 5 μm may cause the fast-charging capacity of the battery cell to decrease.

[0115] In some embodiments of the present application, the mass ratio of artificial graphite to hard carbon in the raw material for preparing the second active layer is 1-9:1.

[0116] In some embodiments of the present application, the mass ratio of artificial graphite to hard carbon in the raw material for preparing the second active layer is 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 or 9:1.

[0117] In some embodiments of the application, the mass ratio of artificial graphite and hard carbon in the raw material for preparing the second active layer is 4:6, 5:5 or 6:4.

[0118] In some embodiments of the application, the content of hard carbon in the raw material for preparing the second active layer can be 0.05wt% to 0.5wt%.

[0119] In some embodiments of the application, the second negative electrode binder in the raw material for preparing the second active layer includes SBR and PAA-Li.

[0120] In some embodiments of the application, the content of the second negative electrode binder in the second active layer in the raw material for preparing the second active layer is 1wt% to 5wt%.

[0121] In some embodiments of the application, the raw material for preparing the second active layer further includes a thickening agent.

[0122] In some embodiments of the application, the content of the thickening agent in the second active layer is 1wt% to 5wt%.

[0123] In some embodiments of the application, the content of the thickening agent in the second active layer is 1wt% to 1.5wt%.

[0124] In some embodiments of the application, the thickening agent in the raw material for preparing the second active layer can be the same as the thickening agent in the first active layer.

[0125] In some embodiments of the application, the raw material for preparing the second active layer further includes at least one conductive additive of Super P Li and carbon nanotubes.

[0126] In some embodiments of the application, the content of the conductive additive in the second active layer is 0.2wt% to 10wt%.

[0127] In some embodiments of the application, the content of the conductive additive in the second active layer is 1wt% to 2wt%.

[0128] In some embodiments of the application, the thickness of the second active layer is 5μm to 40μm.

[0129] In some embodiments of the application, the raw material for preparing the third active layer includes Li 3+x at least one of V2O5 and intercalation transition metal oxide.

[0130] In some embodiments of the application, the intercalation transition metal oxide includes at least one of lithium titanate and niobium-based oxide.

[0131] Li 3+xThe potential of V2O5 and intercalation transition metal oxide relative to lithium is 0.6V-1.6V, lithium metal is not easy to be deposited on the surface of the same, and the diffusion coefficient of lithium ion in the material is higher.

[0132] In some embodiments of the present application, Li 3+x V2O5 is Li3V2O5, and the potential relative to lithium is 0.6V, having a disordered rock structure.

[0133] In some embodiments of the present application, the D50 particle size range of the preparation raw material of the third active layer is 0.2μm-1μm, which is beneficial to improve the fast charging capacity of the battery cell while keeping the film of the layer compacted at a higher level, less than 0.2μm, which may cause the electrode sheet to be greatly compacted, resulting in a decrease in the energy density of the battery cell; greater than 1μm, which may cause the fast charging capacity of the battery cell to decrease.

[0134] According to some embodiments of the present application, the D90 particle size range of the preparation raw material of the third active layer is 1.2μm-2μm, which is beneficial to improve the fast charging capacity of the battery cell while keeping the film of the layer compacted at a higher level, less than 1.2μm, which may cause the electrode sheet to be greatly compacted, resulting in a decrease in the energy density of the battery cell; greater than 2μm, which may cause the fast charging capacity of the battery cell to decrease.

[0135] In some embodiments of the present application, the preparation raw material of the third active layer further comprises a binder.

[0136] In some embodiments of the present application, the binder comprises PVDF.

[0137] In some embodiments of the present application, the content of the binder in the third active layer is 1wt%-10wt%.

[0138] In some embodiments of the present application, the thickness of the third active layer is 3μm-10μm.

[0139] In some embodiments of the present application, the preparation raw material of the safety coating layer comprises at least one of hexagonal boron nitride, titanium nitride, titanium diboride, titanium carbide, aluminum nitride, aluminum oxide and silicon dioxide.

[0140] It should be noted that the preparation raw material of the safety coating layer has the characteristics of high temperature resistance, excellent heat conduction performance, and high hardness, which can significantly improve the mechanical strength of the electrode sheet.

[0141] In some embodiments of the present application, the D50 particle size range of the preparation raw material of the safety coating layer is 0.1μm-0.8μm, which is beneficial to improve the mechanical strength of the electrode sheet, while the proportion of the non-active layer in the electrode sheet keeps a suitable proportion to keep the battery cell at a higher energy density, less than 0.1μm, which may cause the difficulty of pulping to increase, which is not conducive to mass production; greater than 0.8μm, which may cause the proportion of the non-active layer of the electrode sheet to be large, sacrificing the energy density of the battery cell.

[0142] According to some embodiments of the present application, the D90 particle size range of the raw material for preparing the safety coating is 1-2 μm, which is conducive to improving the mechanical strength of the pole piece, while the proportion of the inactive layer in the pole piece remains a suitable proportion to maintain a high energy density of the battery cell. Less than 1 μm may increase the difficulty of pulping and is not conducive to mass production; greater than 2 μm may result in a large proportion of the inactive layer of the pole piece, sacrificing the energy density of the battery cell.

[0143] In some other embodiments of the present application, the present application provides a method for preparing the lithium battery negative pole piece of the present application, which comprises: preparing first active layer slurry, second active layer slurry, third active layer slurry and safety coating slurry respectively, and coating the first active layer slurry, the second active layer slurry, the third active layer slurry and the safety coating slurry on the surface of the negative current collector in sequence to obtain the lithium battery negative pole piece.

[0144] It can be understood that the method for preparing the lithium battery negative pole piece of the present application only needs to prepare the first active layer slurry, the second active layer slurry, the third active layer slurry and the safety coating slurry in sequence, and then coat the first active layer slurry, the second active layer slurry, the third active layer slurry and the safety coating slurry on the surface of the negative current collector in sequence to obtain the lithium battery negative pole piece. Without complex process control, the process is simple, the equipment requirement is low, and it is conducive to industrial production.

[0145] In some other embodiments of the present application, the present application provides a lithium battery cell comprising the lithium battery negative pole piece of the present application.

[0146] It can also be understood that the lithium battery cell of the present application comprises the lithium battery negative pole piece of the present application, thereby having all the beneficial effects of the lithium battery negative pole piece and taking into account safety and performance. Specifically:

[0147] The lithium battery cell of the present application, wherein the negative pole piece comprises a negative current collector, an active layer and a safety coating. The active layer comprises a first active layer, a second active layer and a third active layer arranged in sequence, thereby forming a multi-layer active layer structure, which can improve the rapid penetration of lithium ions on the surface of the negative pole piece, reduce the risk of lithium precipitation on the surface of the negative pole piece, and effectively improve the charging rate of the lithium ion battery when used in a lithium battery. The setting of the safety coating can significantly improve the mechanical strength of the negative pole piece, thereby improving the mechanical strength of the battery cell when the negative pole piece of the present application is used in the battery cell, and also promoting the efficient transfer of heat inside the battery cell, enhancing the safety and reliability of the battery cell, and greatly reducing the risk of fire and explosion of the battery cell under extreme use conditions such as thermal abuse or mechanical abuse.

[0148] In some embodiments of the present application, reference is made to Figure 2As shown, the battery cell further comprises a separator film, and the separator film is prepared from a raw material comprising a base film 6 and a 3D network structure composite coating layer 7 arranged on the surface of the base film 6.

[0149] The separator film is one of the key materials of lithium batteries, and its thermal stability is closely related to the thermal safety performance of the lithium battery. A high-safety separator film requires good thermal dimensional stability, no obvious deformation under certain high-temperature environment, good thermal closing performance and good mechanical strength to avoid internal short circuit of the battery, thereby inhibiting the combustion and explosion of the battery. Among various separator films, ceramic separator films with excellent heat resistance have become the first choice for lithium batteries in recent years. The introduction of ceramic coating can effectively improve the thermal shrinkage temperature of the separator film, block the heat diffusion inside the battery, inhibit the expansion of some thermal runaway points to form overall thermal runaway, and thus improve the safety performance of the battery. The preparation process of such separator film is relatively simple and easy to mass produce and use. The ceramic material used in the traditional ceramic separator film is inert inorganic nanoparticles, such as Al2O3, AlOOH, MgOH, SiO2, BaSO4, etc. Although the ceramic coating can effectively improve the thermal stability of the separator film and improve the safety of the battery, it contributes little to the electrochemical performance of the lithium battery, and the thermal conductivity of the coating of the traditional ceramic separator film is poor, which is not conducive to the conduction of heat inside the battery.

[0150] In the production process of lithium ion battery cell, the positive and negative electrode rolls are usually cut and tabbed by cutting knife or die cutting technology. However, when cutting knife or die cutting metal current collector, burrs will inevitably be generated on the cutting end face. The metal burr can pierce or even pierce the separator film, causing micro-short circuit or even short circuit of the battery. In order to improve the resistance of the separator to the burr, a composite separator film is developed, that is, a coating with higher strength, such as an inorganic oxide (hydroxide) coating of alumina or an aramid coating, is added on the porous polymer. However, since the coating must have the ability to permeate the electrolyte, the coating is also porous, and the burrs that occur in actual production can still pierce the coating. In particular, with the advancement of lithium battery technology, in order to improve the energy density of the battery, the positive and negative electrode compaction density is increased, and in order to ensure that the current collector does not break during the manufacturing process, the current collector often uses higher strength aluminum foil or copper foil. In this case, the burr becomes more likely to pierce the battery and cause short circuit. When the battery cell is pressed by a heavy object or a sharp object, or even pierced, a large amount of metal debris or burrs will be generated, which will pierce the separator film and cause the battery cell to short circuit in a large area, generating a large amount of heat and causing the battery cell to catch fire and explode. Research shows that the contact between the aluminum foil and the graphite-coated negative electrode sheet area generates the most heat, and this short circuit mode is the most dangerous.

[0151] The separator film in the battery cell of the present application is prepared from a raw material comprising a base film and a 3D network structure composite coating layer arranged on the surface of the base film. The 3D network structure composite coating layer has fire-resistant and flame-retardant functions, and has high thermal conductivity and high mechanical strength.

[0152] In some embodiments of the present application, the separator film in the battery cell of the present application can be a polyolefin-based commercial separator film.

[0153] In some embodiments of the present application, the preparation raw materials of the 3D network structure composite coating include micro-nano sheet materials, nanowires and separator film adhesives.

[0154] In some embodiments of the present application, the micro-nano sheet material refers to micro-sheet material and nano-sheet material.

[0155] In some embodiments of the present application, the micro-nano sheet material includes at least one of boron nitride micro-nano sheet and aluminum nitride micro-nano sheet.

[0156] In some embodiments of the present application, the nanowire includes hydroxyapatite nanowire.

[0157] In some embodiments of the present application, the separator film adhesive includes at least one of PVDF, PMMA, PCN and CMC.

[0158] In some embodiments of the present application, in the micro-nano sheet material, the D50 particle size range in the micrometer range can be 0.1 μm to 0.8 μm, which is beneficial to improve the mechanical strength of the separator film, and at the same time, the appropriate thickness of the finished separator film is beneficial to the battery cell to maintain a high energy density. Less than 0.1 μm, it may cause the difficulty of pulp making to increase and is not conducive to mass production; greater than 0.8 μm, it may cause the finished separator film to be too thick and sacrifice the energy density of the battery cell.

[0159] According to some embodiments of the present application, in the micro-nano sheet material, the D90 particle size range in the micrometer range can be 1 μm to 2 μm, which is beneficial to improve the mechanical strength of the separator film, and at the same time, the appropriate thickness of the finished separator film is beneficial to the battery cell to maintain a high energy density. Less than 1 μm, it may cause the difficulty of pulp making to increase and is not conducive to mass production; greater than 2 μm, it may cause the finished separator film to be too thick and sacrifice the energy density of the battery cell.

[0160] In some embodiments of the present application, in the preparation raw materials of the 3D network structure composite coating, the diameter of the nanowire is 10 nm to 200 nm, and the length is 10 μm to 200 μm.

[0161] In some embodiments of the present application, the separator film adhesive can be a commonly used polymer adhesive.

[0162] In some other embodiments of the present application, the present application provides a lithium battery including the lithium battery cell of the present application.

[0163] It can be understood that, due to the lithium battery of the present application, containing the negative electrode sheet and the battery cell of the present application, thereby, all the beneficial effects of the negative electrode sheet and the battery cell are possessed. Specifically, the negative electrode sheet in the battery cell in the lithium battery comprises a negative electrode current collector, an active layer and a safety coating layer. Among them, the active layer comprises a first active layer, a second active layer and a third active layer arranged in sequence, thereby forming a multi-layer active layer structure, which can improve the rapid penetration of lithium ions on the surface of the negative electrode sheet, reduce the risk of lithium precipitation on the surface of the negative electrode sheet, and when used in lithium batteries, the charging rate of lithium ion batteries can be effectively improved. The setting of the safety coating layer can significantly improve the mechanical strength of the negative electrode sheet, when the negative electrode sheet of the present application is used in the battery cell, thereby the mechanical strength of the battery cell can be improved, and the efficient heat transfer in the battery cell can be promoted, the safety and reliability of the battery cell can be enhanced, and the risk of fire and explosion of the battery cell under extreme use conditions such as thermal abuse or mechanical abuse can be greatly reduced.

[0164] In some embodiments of the present application, the lithium battery of the present application further comprises a positive electrode sheet, an electrolyte, a packaging shell and a tab.

[0165] The technical solutions of the present application will be better understood in combination with the specific embodiments below.

[0166] Embodiment 1

[0167] In this embodiment, first active layer slurry, second active layer slurry, third active layer slurry and safety coating slurry are prepared respectively.

[0168] The raw materials used in this embodiment are:

[0169] The fast-charging artificial graphite is directly purchased from the market, which can be the fast-charging artificial graphite of Zichen RE31 / AGT / A-T or the QCG-X fast-charging artificial graphite of Sansheng Technology.

[0170] The thickening agent can be CMC-Na, CMC-Li or PVA, and in this embodiment, it is PVA.

[0171] The first negative electrode binder can be a high molecular polymer such as SBR, PAN, PAA, etc., and specifically can be purchased from Japan Zeon 451B, 430B, or JSR 104A, 105A, or A&L 307N, or Showa LB300, or Daowin GD1564, GD1332, or Haodian AWG101. In this embodiment, the first negative electrode binder is Japan Zeon 451B.

[0172] The second / third negative electrode binder can also be a high molecular polymer such as SBR, PAN, PAA, etc., and in this embodiment, Japan Zeon 451B is also used.

[0173] The hard carbon is purchased from Betrue, BHC-400.

[0174] The conductive additive was purchased from Showa Denko, Japan (specifically, VGCF-H).

[0175] The nanosheet boron nitride was purchased from Beijing Keda Gold (specification <100 nm, 99.9%).

[0176] The nanoporous alumina was purchased from Anhui Keliun Nanometer Technology, high-purity 99.9% nanometer alumina.

[0177] The binder used for the safety coating was purchased from Japan Zhiwon 451B.

[0178] The coupling agent was a Japanese Shin-Etsu silane coupling agent.

[0179] The dispersant was purchased from Guangzhou Yuantai New Material YY-502A.

[0180] The solvent was NMP, purchased from Zhonglun Chemical, purity ≥ 99.9%

[0181] 1) Preparation of the first active layer slurry:

[0182] 97.7 g of fast-charging artificial graphite, 0.9 g of thickening agent, 1.4 g of the first negative electrode binder, 66 g of deionized water were mixed to prepare the first active layer slurry.

[0183] 2) Preparation of the second active layer slurry:

[0184] 48 g of fast-charging artificial graphite, 48 g of hard carbon, 1 g of thickening agent, 1.2 g of the first negative electrode binder, 0.8 g of the second negative electrode binder, 1 g of conductive additive, 75 g of deionized water were stirred under the action of a vacuum stirrer until the mixture formed a second active layer slurry with uniform fluidity.

[0185] 3) Preparation of the third active layer slurry:

[0186] 90 g of lithium titanate, 5 g of the third negative electrode binder, 5 g of conductive additive, 80 g of N-methyl pyrrolidone were stirred under the action of a vacuum stirrer until the mixture formed a third active layer slurry with uniform fluidity.

[0187] 4) Preparation of the safety coating slurry:

[0188] The nanosheet boron nitride, nanoporous alumina, binder, coupling agent, dispersant were added to the stirring tank in a certain mass ratio (solid content ratio 55%) and in a certain order, and stirred under the action of a vacuum stirrer until the mixture formed a safety coating slurry with uniform fluidity.

[0189] In every 100 g of the slurry, there were 14 g of nanosheet boron nitride, 10 g of nanoporous alumina, 30 g of binder PVDF, 0.5 g of coupling agent, 0.5 g of dispersant, and 45 g of solvent NMP.

[0190] Example 2

[0191] A negative electrode sheet A was prepared in this example, specifically as follows.

[0192] The first active layer slurry prepared in Example 1 was coated on the negative electrode current collector, and after drying, the first active layer slurry formed a first active layer. The electrode sheet was rolled and cut to obtain the negative electrode sheet A.

[0193] Example 3

[0194] A negative electrode sheet B was prepared in this example, specifically as follows.

[0195] The second active layer slurry prepared in Example 1 was coated on the first active layer of the negative electrode sheet A, and after baking, a second active layer was formed. Then, the third active layer slurry was coated on the second active layer, and after baking, a third active layer was formed. The electrode sheet was rolled and cut to obtain the negative electrode sheet B.

[0196] Example 4

[0197] A negative electrode sheet C was prepared in this example, specifically as follows.

[0198] The safety coating slurry prepared in Example 1 was coated on the negative electrode sheet B, and after baking, the electrode sheet was rolled and cut to obtain the negative electrode sheet C.

[0199] Example 5

[0200] A separator film A was prepared in this example, specifically as follows.

[0201] Nanosheet boron nitride, hydroxyapatite nanowires, a binder, a coupling agent, a flame-retardant additive, and a dispersant were sequentially added to a stirring tank in a mass ratio (solid content ratio 50%) and stirred under the action of a vacuum stirrer until the mixture formed a uniform and flowable separator film composite coating slurry. The coating slurry was coated on the separator film base film, dried, and cut into a finished product separator film A in a certain width for winding for use.

[0202] In 100 g of the slurry, there were 10 g of nanosheet boron nitride, 5 g of hydroxyapatite nanowires, 33 g of a binder PVDF, 0.5 g of a coupling agent, 1 g of a flame-retardant additive, 0.5 g of a dispersant, and 50 g of a solvent NMP.

[0203] Example 6

[0204] A separator film B was prepared in this example, specifically as follows.

[0205] A conventional separator film coating slurry composed of aluminum oxide ceramic + PVDF binder was coated on the separator film base film, dried, and cut into a finished product separator film B in a certain width for winding for use.

[0206] Each 100g of slurry contains: 15g of alumina ceramic, 35g of binder, and 50g of NMP solvent.

[0207] In Examples 5 and 6:

[0208] The base membrane of the separator is a 5μm PP separator membrane from SK.

[0209] The nanosheet boron nitride was purchased from Beijing Kedaojin (specification <100nm, ≥99.9%).

[0210] The hydroxyapatite nanowires were purchased from Xi'an Entaiyuan Biotechnology Co., Ltd. as high-purity hydroxyapatite nanowires.

[0211] The adhesive was purchased from Haodian Technology SWA610 adhesive.

[0212] The coupling agent was purchased from Shin-Etsu Chemical Co., Ltd. in Japan (silane-based coupling agent).

[0213] The flame retardant additive was purchased from Suzhou Yake Technology Co., Ltd. (GC≥99.9% high purity ethoxy(pentafluoro)cyclotriphosphazene).

[0214] The dispersant was purchased from Guangzhou Yuantai New Materials YY-502A.

[0215] The alumina ceramics were purchased from Anhui Kerun Nanotechnology Co., Ltd., and were 99.9% pure nano-grade alumina. The PVDF binder was purchased from Sinochem Lantian.

[0216] Example 7

[0217] This embodiment prepares a positive electrode sheet, specifically as follows:

[0218] 97.7g of positive electrode active material (lithium cobalt oxide), 1.3g of conductive agent (conductive carbon black), and 1g of positive electrode binder were mixed together, and 45g of N-methylpyrrolidone was added. The mixture was stirred under vacuum until a uniform and fluid positive electrode slurry was formed. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 9μm. After baking, the electrode was rolled and cut to obtain positive electrode sheets.

[0219] The conductive carbon black was purchased from DENKALI 400 high-purity conductive carbon black from Nippon Denko Corporation.

[0220] The positive electrode binder was purchased from Arkema HSV900.

[0221] Example 8

[0222] This embodiment uses the negative electrode, separator, and positive electrode prepared in Examples 1 to 7 to prepare five types of battery cells, all with a model number of 98×25×33 (corresponding to the following cell dimensions: maximum thickness 9.8mm, maximum width 25.3mm, and maximum length 33mm). Specifically:

[0223] The negative electrode A, positive electrode, and separator B are wound together, packaged in aluminum-plastic film, baked to remove moisture, and then injected with electrolyte. The hot-pressing process is used to form the battery cell A.

[0224] The negative electrode A, positive electrode A, and separator A are wound together, packaged in aluminum-plastic film, baked to remove moisture, and then injected with electrolyte. The hot-pressing process is used to form the battery cell B.

[0225] The negative electrode B, positive electrode, and separator A are wound together, packaged in aluminum-plastic film, baked to remove moisture, and then injected with electrolyte. The hot-pressing process is used to form the battery cell C.

[0226] The negative electrode C, positive electrode, and separator A are wound together, packaged in aluminum-plastic film, baked to remove moisture, and then injected with electrolyte. The hot-pressing process is used to form the battery cell D.

[0227] The negative electrode C, positive electrode, and separator B are wound together, packaged in aluminum-plastic film, baked to remove moisture, and then injected with electrolyte. The hot-pressing process is used to form the battery cell E.

[0228] Performance testing

[0229] The performance of cells A through E was tested, and the specific test items and results are shown in Table 1.

[0230] Table 1

[0231]

[0232]

[0233] As can be seen from the test results in Table 1, all performance parameters of cell D are qualified, indicating that the cell prepared by the negative electrode sheet of the present invention has the best performance in terms of cell safety.

[0234] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A lithium battery negative electrode sheet, characterized in that, include: Negative electrode current collector; An active layer is disposed on the surface of the negative electrode current collector. The active layer is composed of a first active layer, a second active layer and a third active layer arranged sequentially. The raw material for preparing the active layer includes fast-charging artificial graphite. The raw materials for preparing the first active layer include the fast-charging artificial graphite, thickener, and first negative electrode binder; The raw materials for preparing the second active layer include the fast-charging artificial graphite, hard carbon, and the second negative electrode binder; The raw materials for preparing the third active layer include intercalated transition metal oxides, and the intercalated transition metal oxides include at least one of lithium titanate and niobium-based oxides; A safety coating is provided on the surface of the third active layer; The raw materials for preparing the safety coating include at least one of hexagonal boron nitride, titanium nitride, titanium diboride, titanium carbide, aluminum nitride, aluminum oxide, and silicon dioxide. The fast-charging artificial graphite has a specific capacity of ≤352mAh / g and a compaction density of 1.6g / cm³. 3 ~1.75g / cm 3 .

2. A method for preparing the lithium battery negative electrode sheet as described in claim 1, characterized in that, The method is as follows: a first active layer slurry, a second active layer slurry, a third active layer slurry, and a safety coating slurry are prepared respectively, and the first active layer slurry, the second active layer slurry, the third active layer slurry, and the safety coating slurry are sequentially coated on the surface of the negative electrode current collector to obtain the lithium battery negative electrode sheet.

3. A lithium battery cell, characterized in that, Includes the lithium battery negative electrode sheet as described in claim 1.

4. The lithium battery cell according to claim 3, characterized in that, It also includes an isolation membrane, the raw materials for which the isolation membrane is prepared include a base membrane and a 3D network structure composite coating disposed on the surface of the base membrane.

5. The lithium battery cell according to claim 4, characterized in that, The raw materials for preparing the 3D network structure composite coating include micro / nanosheet materials, nanowires, and a separator adhesive.

6. A lithium battery, characterized in that, Includes the lithium battery cell as described in any one of claims 3 to 5.

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