Composite positive pole piece as well as preparation method and application thereof

Abstract

The invention provides a composite positive pole piece and a preparation method and application thereof.The composite positive pole piece comprises a positive current collector, a first active substance layer and a second active substance layer, the first active substance layer and the second active substance layer are sequentially arranged on the surface of at least one side of the positive current collector in a stacked mode, and the first active substance layer comprises lithium manganese iron phosphate and nickel cobalt lithium manganate; according to the lithium-rich manganese-based lithium ion battery disclosed by the invention, the double active material layers are adopted, the types of the active materials in the active material layers are reasonably matched, the advantages of various materials are coordinated, and the cycle performance of the pole piece is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and relates to a composite positive electrode sheet and a preparation method and application thereof. Background Art

[0002] Ternary cathode materials (NCM) have a higher theoretical gram capacity than other cathode materials. During the charge and discharge process, ternary materials mainly rely on the change of nickel element. Therefore, high-nickel ternary materials will become the mainstream development object in the future. However, their own cycle instability, thermal instability and air instability limit their development.

[0003] NCM can improve its own shortcomings by mixing LMFP, especially in terms of safety issues. At the same time, the introduction of LMFP can increase its voltage window. The voltage platform of NCM is generally 3.7V, while the voltage platform of LMFP is 4.1V, which is much higher than NCM. LMFP is low in price and its introduction into NCM can also reduce costs. However, LMFP has poor cycle stability and conductivity, and the dissolution of manganese ions affects the electrochemical performance of the battery.

[0004] CN115893363A discloses a MOF-coated LMFP and NCM composite positive electrode material as a lithium-ion battery positive electrode material. By carbonizing and coating the MOF on the surface of the composite material, the rate performance, high-temperature storage and high-temperature cycle performance of the battery are improved. However, the preparation process is more complicated than simple physical mixing and coating, and MOF as the outer layer in contact with the electrolyte may cause its structure to collapse in a high-rate charge and discharge environment, affecting the life of the battery.

[0005] CN115458707A discloses a secondary battery and electrical equipment, wherein the positive electrode material is prepared by coating a double layer of manganese iron lithium oxide, wherein the manganese content of the outer layer of manganese iron lithium oxide is less than that of the inner layer, so that the portion of the outer layer in contact with the electrolyte is in a manganese-poor state, thereby achieving the effect of inhibiting manganese dissolution. Since both layers are made of manganese iron lithium oxide material, there will also be problems such as poor cycle performance and low conductivity. Summary of the invention

[0006] The purpose of the present invention is to provide a composite positive electrode plate and its preparation method and application. The present invention adopts a double active material layer, reasonably matches the types of active materials in the active material layer, and synergizes the advantages of various materials to improve the cycle performance of the plate.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a composite positive electrode plate, comprising a positive electrode current collector and a first active material layer and a second active material layer stacked in sequence on at least one side surface of the positive electrode current collector, wherein the first active material layer comprises lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, and the second active material layer comprises a lithium-rich manganese-based material.

[0009] The present invention adopts the method of coating a first layer of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide composite positive electrode slurry on the current collector, and then coating a small amount of a second layer of lithium-rich manganese-based material on the surface of the first layer, thereby suppressing the dissolution of manganese while satisfying the high capacity and wide voltage window of lithium iron manganese phosphate / lithium nickel cobalt manganese oxide, and the preparation process is simple; the lithium-rich manganese-based material of the outer layer can make the material have a good high-voltage cycle and a high voltage platform, and the lithium-rich material can increase the Li + migration power, thereby achieving the purpose of improving low conductivity.

[0010] Preferably, the first active material layer and the second active material layer further include a conductive agent and a binder.

[0011] Preferably, the conductive agent includes any one of conductive carbon black, carbon nanotubes or graphene, or a combination of at least two of them.

[0012] Preferably, the binder comprises styrene-butadiene rubber and / or polyvinylidene fluoride.

[0013] Preferably, the mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide in the first active material layer is 1:(0.1-2), for example: 1:0.1, 1:0.5, 1:1, 1:1.5 or 1:2, etc., preferably 1:(0.3-1).

[0014] The present invention introduces lithium iron manganese phosphate into lithium nickel cobalt manganese oxide, and improves some defects of lithium nickel cobalt manganese oxide by adjusting different ratios of the two, thereby reducing the safety performance of NCM positive electrode materials and widening their voltage window. The price of lithium iron manganese phosphate is low, and the cost can also be reduced.

[0015] The mass ratio of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide in the composite positive electrode plate of the present invention will affect its performance. When the mass ratio of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide is controlled at 1: (0.3-1), the performance of the composite positive electrode plate is better. If the proportion of lithium iron manganese phosphate is too low, it is beneficial to the gram capacity and storage, but the cycle performance is poor. If the proportion of lithium iron manganese phosphate is too high, it is beneficial to the cycle, but the gram capacity is relatively poor.

[0016] Preferably, based on the total mass of active materials in the first active material layer and the second active material layer as 100%, the mass fraction of the lithium-rich manganese-based material in the second active material layer is 3% to 10%, for example: 3%, 6%, 7%, 8% or 10%, etc., preferably 5% to 8%.

[0017] The cycle stability and conductivity of lithium manganese iron phosphate / lithium nickel cobalt manganese oxide are relatively poor, and the dissolution of manganese ions affects the electrochemical performance of the battery. By coating the surface of the two with lithium-rich manganese-based materials, their electrochemical performance can be greatly improved, which is very helpful for the improvement of high-voltage cycles and voltage platforms. Since the lithium-rich manganese-based materials are in direct contact with the electrolyte, Li + motivation for migration.

[0018] The mass ratio of the lithium-rich manganese-based material in the composite positive electrode plate of the present invention will affect its performance. The proportion of the lithium-rich manganese-based material is controlled at 5-8% of the total active material. The performance of the composite positive electrode plate is better. If the proportion of the lithium-rich manganese-based material is too low, it is beneficial to the cyclability, but the gram capacity is relatively poor. If the proportion of the lithium-rich manganese-based material is too high, it is beneficial to the gram capacity, but the cycling performance is poor.

[0019] Preferably, the lithium nickel cobalt manganese oxide comprises NCM622.

[0020] Preferably, the chemical formula of the lithium-rich manganese-based material is Li2MnO3.

[0021] In a second aspect, the present invention provides a method for preparing the composite positive electrode sheet as described in the first aspect, the preparation method comprising the following steps:

[0022] (1) mixing lithium iron manganese phosphate, lithium nickel cobalt manganese oxide, a conductive agent, a binder and a solvent to obtain a first slurry, and mixing a lithium-rich manganese-based material, a conductive agent, a binder and a solvent to obtain a second slurry;

[0023] (2) The first slurry is coated on at least one side of the positive electrode current collector, and the second slurry is coated on the surface of the first slurry to obtain the composite positive electrode sheet.

[0024] In a third aspect, the present invention provides a lithium-ion battery, comprising the composite positive electrode sheet, negative electrode sheet, separator and electrolyte as described in the first aspect.

[0025] Preferably, the negative electrode sheet comprises a negative electrode active material, a conductive agent and a binder.

[0026] Preferably, the negative electrode active material includes any one of graphite, soft carbon or hard carbon, or a combination of at least two of them.

[0027] Preferably, the conductive agent comprises conductive carbon black and / or carbon nanotubes.

[0028] Preferably, the binder comprises styrene-butadiene rubber.

[0029] Preferably, the separator comprises a PE separator.

[0030] Preferably, the electrolyte comprises a solvent, an electrolyte and an additive.

[0031] Preferably, the solvent comprises ethylene carbonate and / or dimethyl carbonate.

[0032] Preferably, the electrolyte comprises lithium hexafluorophosphate.

[0033] Preferably, the additive comprises vinylene carbonate.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) In the positive electrode plate of the present invention, both the first layer and the second layer contain manganese-based active materials, which reduces the grain boundary impedance between different materials, makes the contact between the two layers of materials closer, and also inhibits manganese dissolution. Lithium iron manganese phosphate, lithium nickel cobalt manganese oxide and lithium-rich manganese-based materials complement each other in the composite positive electrode active material. The three materials not only retain their own advantages but also complement each other's shortcomings. This synergistic relationship makes it impossible to achieve the technical effect of the present invention without any of the materials.

[0036] (2) The capacity of the battery made of the composite positive electrode sheet of the present invention can reach more than 272.8 mAh / g, the capacity retention rate after 300 cycles at 25°C-1C / 1C can reach more than 93.5%, the voltage drop can reach less than 0.16V, and the capacity retention rate after 45 days of storage at 45°C can reach more than 93.2%. By adjusting the mass ratio of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide and the mass proportion of lithium-rich manganese-based positive electrode materials in the two layers of active materials, the capacity can reach more than 286.8 mAh / g, the capacity retention rate after 300 cycles at 25°C-1C / 1C can reach more than 97.9%, the voltage drop can reach less than 0.09V, and the capacity retention rate after 45 days of storage at 45°C can reach more than 95.8%. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0038] In the embodiment of the present invention, the mass proportion of active materials in the solid of the first slurry is 97%, and the mass proportion of lithium-rich manganese-based materials in the solid of the second slurry is 95%, but the proportion of each active material in the slurry is not limited thereto.

[0039] In the embodiment of the present invention, the lithium nickel cobalt manganese oxide is taken as NCM622, and the lithium-rich manganese-based positive electrode material is taken as Li2MnO3, but it is not limited thereto.

[0040] Example 1

[0041] This embodiment provides a composite positive electrode sheet, and the preparation method of the composite positive electrode sheet is as follows:

[0042] Lithium iron manganese phosphate, lithium nickel cobalt manganese oxide (NCM622), conductive carbon black and PVDF are mixed with NMP in a mass ratio of 64.7:32.3:2:1 to obtain a first slurry, and lithium-rich manganese-based material (Li2MnO3), conductive carbon black, styrene-butadiene rubber are mixed with NMP in a mass ratio of 95:2:3 to obtain a second slurry;

[0043] The first slurry is coated on both sides of the aluminum foil to obtain a first active material layer, and the second slurry is coated on the surface of the first active material layer to obtain a second active material layer. After coating, rolling-slitting-die-cutting and other processes are performed to obtain the composite positive electrode plate. In the composite positive electrode plate, the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 1:0.5. Taking the total mass of the lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and lithium-rich manganese-based material as 100%, the mass fraction of the lithium-rich manganese-based material is 5%.

[0044] Example 2

[0045] This embodiment provides a composite positive electrode sheet, and the preparation method of the composite positive electrode sheet is as follows:

[0046] Lithium iron manganese phosphate, lithium nickel cobalt manganese oxide (NCM622), conductive carbon black and PVDF are mixed with NMP in a mass ratio of 53.9:43.1:2:1 to obtain a first slurry, and lithium-rich manganese-based material (Li2MnO3), conductive carbon black, styrene-butadiene rubber are mixed with NMP in a mass ratio of 95:2:3 to obtain a second slurry;

[0047] The first slurry is coated on both sides of the aluminum foil to obtain a first active material layer, and the second slurry is coated on the surface of the first active material layer to obtain a second active material layer. After coating, rolling-slitting-die-cutting and other processes are performed to obtain the composite positive electrode plate. In the composite positive electrode plate, the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 1:0.8. Taking the total mass of the lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and lithium-rich manganese-based material as 100%, the mass fraction of the lithium-rich manganese-based material is 6%.

[0048] Example 3

[0049] This embodiment provides a composite positive electrode sheet, and the preparation method of the composite positive electrode sheet is as follows:

[0050] Lithium iron manganese phosphate, lithium nickel cobalt manganese oxide (NCM622), conductive carbon black and PVDF are mixed with NMP in a mass ratio of 88.2:8.8:2:1 to obtain a first slurry, and lithium-rich manganese-based material (Li2MnO3), conductive carbon black, styrene-butadiene rubber are mixed with NMP in a mass ratio of 95:2:3 to obtain a second slurry;

[0051] The first slurry is coated on both sides of the aluminum foil to obtain a first active material layer, and the second slurry is coated on the surface of the first active material layer to obtain a second active material layer. After coating, rolling-slitting-die-cutting and other processes are performed to obtain the composite positive electrode plate. In the composite positive electrode plate, the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 1:0.1. Taking the total mass of the lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and lithium-rich manganese-based material as 100%, the mass fraction of the lithium-rich manganese-based material is 5%.

[0052] Example 4

[0053] This embodiment provides a composite positive electrode sheet, and the preparation method of the composite positive electrode sheet is as follows:

[0054] Lithium iron manganese phosphate, lithium nickel cobalt manganese oxide (NCM622), conductive carbon black and PVDF are mixed with NMP in a mass ratio of 38.8:58.2:2:1 to obtain a first slurry, and lithium-rich manganese-based material (Li2MnO3), conductive carbon black, styrene-butadiene rubber are mixed with NMP in a mass ratio of 95:2:3 to obtain a second slurry;

[0055] The first slurry is coated on both sides of the aluminum foil to obtain a first active material layer, and the second slurry is coated on the surface of the first active material layer to obtain a second active material layer. After coating, rolling-slitting-die-cutting and other processes are performed to obtain the composite positive electrode plate. In the composite positive electrode plate, the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 1:1.5. Taking the total mass of the lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and lithium-rich manganese-based material as 100%, the mass fraction of the lithium-rich manganese-based material is 5%.

[0056] Example 5

[0057] This embodiment provides a composite positive electrode sheet, and the preparation method of the composite positive electrode sheet is as follows:

[0058] Lithium iron manganese phosphate, lithium nickel cobalt manganese oxide (NCM622), conductive carbon black and PVDF are mixed with NMP in a mass ratio of 64.7:32.3:2:1 to obtain a first slurry, and lithium-rich manganese-based material (Li2MnO3), conductive carbon black, styrene-butadiene rubber are mixed with NMP in a mass ratio of 95:2:3 to obtain a second slurry;

[0059] The first slurry is coated on both sides of the aluminum foil to obtain a first active material layer, and the second slurry is coated on the surface of the first active material layer to obtain a second active material layer. After coating, rolling-slitting-die-cutting and other processes are performed to obtain the composite positive electrode plate. In the composite positive electrode plate, the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 1:0.5. Taking the total mass of the lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and lithium-rich manganese-based material as 100%, the mass fraction of the lithium-rich manganese-based material is 3%.

[0060] Example 6

[0061] This embodiment provides a composite positive electrode sheet, and the preparation method of the composite positive electrode sheet is as follows:

[0062] Lithium iron manganese phosphate, lithium nickel cobalt manganese oxide (NCM622), conductive carbon black, PVDF and NMP are mixed in a mass ratio of 64.7:32.3:2:1 to obtain a first slurry, and lithium-rich manganese-based material (Li2MnO3), conductive carbon black, styrene-butadiene rubber are mixed in a mass ratio of 95:2:3 and NMP to obtain a second slurry;

[0063] The first slurry is coated on both sides of the aluminum foil to obtain a first active material layer, and the second slurry is coated on the surface of the first active material layer to obtain a second active material layer. After coating, rolling-slitting-die-cutting and other processes are performed to obtain the composite positive electrode plate. In the composite positive electrode plate, the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 1:0.5. Taking the total mass of the lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and lithium-rich manganese-based material as 100%, the mass fraction of the lithium-rich manganese-based material is 10%.

[0064] Comparative Example 1

[0065] The only difference between this comparative example and Example 1 is that the lithium nickel cobalt manganese oxide and the lithium-rich manganese-based material are all replaced by lithium iron manganese phosphate, and the other conditions and parameters are exactly the same as those in Example 1.

[0066] Comparative Example 2

[0067] The only difference between this comparative example and Example 1 is that the lithium iron manganese phosphate and the lithium-rich manganese-based material are all replaced by lithium nickel cobalt manganese oxide, and the other conditions and parameters are exactly the same as those in Example 1.

[0068] Comparative Example 3

[0069] The only difference between this comparative example and Example 1 is that lithium nickel cobalt manganese oxide and lithium iron manganese phosphate are all replaced by lithium-rich manganese-based materials, and other conditions and parameters are exactly the same as those in Example 1.

[0070] Comparative Example 4

[0071] The only difference between this comparative example and Example 1 is that lithium iron manganese phosphate is not added to the first slurry, and other conditions and parameters are exactly the same as those in Example 1.

[0072] Comparative Example 5

[0073] The only difference between this comparative example and Example 1 is that the second slurry is not applied, and the other conditions and parameters are exactly the same as those in Example 1.

[0074] Performance Test:

[0075] Using the positive electrode materials obtained in Examples 1-6 and Comparative Examples 1-5, graphite is used as the negative electrode material, and a PE separator is used. The sheets are assembled into a roll core, encapsulated in an aluminum-plastic film, and injected with 1M LiPF6 / EC+DMC lithium ion electrolyte to assemble into a soft-pack lithium ion battery. The prepared lithium ion battery is subjected to a charge and discharge test at 25±0.5°C using a charge and discharge test system to calculate the capacity. The charge and discharge conditions are: charge termination voltage 4.3V, discharge termination voltage 2.8V, and charge and discharge current density: 0.33C. At the same time, the prepared lithium ion battery is subjected to a charge and discharge cycle test at 25±0.5°C using a charge and discharge test system. The charge and discharge conditions are: charge termination voltage 4.3V; discharge termination voltage 2.8V; charge and discharge current density: 1C, and the cycle performance is the cycle performance of 300 cycles under 1C conditions. The test results are shown in Table 1:

[0076] Table 1

[0077]

[0078] As can be seen from Table 1, from Examples 1-6, the capacity of the battery made of the composite positive electrode sheet of the present invention can reach more than 272.8 mAh / g, the capacity retention rate of 300 cycles at 25 ° C -1C / 1C can reach more than 93.5%, the voltage drop can reach less than 0.16V, and the capacity retention rate of 45 ° C storage for 45 days can reach more than 93.2%. By adjusting the mass ratio of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide and the mass proportion of lithium-rich manganese-based positive electrode materials in the two-layer active material, the capacity can reach more than 286.8 mAh / g, the capacity retention rate of 300 cycles at 25 ° C -1C / 1C can reach more than 97.9%, the voltage drop can reach less than 0.09V, and the capacity retention rate of 45 ° C storage for 45 days can reach more than 95.8%.

[0079] By comparing Example 1 with Examples 3-4, it can be seen that the mass ratio of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide in the composite positive electrode plate of the present invention affects its performance. When the mass ratio of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide is controlled at 1:(0.3-1), the performance of the composite positive electrode plate is better. If the proportion of lithium iron manganese phosphate is too low, it is beneficial to the gram capacity and storage, but the cycle performance is poor. If the proportion of lithium iron manganese phosphate is too high, it is beneficial to the cycle, but the gram capacity is relatively poor.

[0080] By comparing Example 1 with Examples 5-6, it can be seen that the mass ratio of the lithium-rich manganese-based material in the composite positive electrode plate of the present invention will affect its performance. When the proportion of the lithium-rich manganese-based material is controlled at 5-8% of the total active material, the performance of the composite positive electrode plate is better. If the proportion of the lithium-rich manganese-based material is too low, it is beneficial to the cyclability, but the gram capacity is relatively poor. If the proportion of the lithium-rich manganese-based material is too high, it is beneficial to the gram capacity, but the cycling performance is poor.

[0081] By comparing Example 1 with Comparative Examples 1-3, it can be seen that the present invention adopts the method of coating a first layer of lithium manganese iron phosphate (LMFP) and lithium nickel cobalt manganese oxide (NCM) composite positive electrode slurry on the current collector, and then coating a small amount of a second layer of lithium-rich manganese-based material (Li2MnO3) on the surface of the first layer, while satisfying the high capacity and wide voltage window of LMFP / NCM, inhibiting the dissolution of manganese, and having a simple preparation process; the outer layer of Li2MnO3 can make the material have a good high-voltage cycle and a high voltage platform, and the lithium-rich material can Li + migration power, thereby achieving the purpose of improving low conductivity.

[0082] By comparing Example 1 and Comparative Example 4, it can be seen that the present invention introduces LMFP into NCM and improves some defects of NCM by adjusting different ratios of the two, thereby reducing the safety performance of high-nickel NCM (622) and widening its voltage window. LMFP is low in price and can also reduce costs.

[0083] By comparing Example 1 with Comparative Example 5, it can be seen that the cycle stability and conductivity of LMFP / NCM are relatively poor, and the dissolution of manganese ions affects the electrochemical performance of the battery. By coating the surface of the two with lithium-rich materials (Li2MnO3), the electrochemical performance can be greatly improved, which is of great help to the improvement of high-voltage cycle and voltage platform. Since the lithium-rich manganese-based materials are in direct contact with the electrolyte, Li can be increased. + motivation for migration.

[0084] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite positive electrode sheet, characterized in that: The composite positive electrode sheet includes a positive electrode current collector and a first active material layer and a second active material layer stacked in sequence on at least one side of the positive electrode current collector, wherein the first active material layer includes lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, and the second active material layer includes a lithium-rich manganese-based material.

2. The composite positive electrode sheet according to claim 1, characterized in that: The first active material layer and the second active material layer further include a conductive agent and a binder; Preferably, the conductive agent comprises any one of conductive carbon black, carbon nanotubes or graphene, or a combination of at least two thereof; Preferably, the binder comprises styrene-butadiene rubber and / or polyvinylidene fluoride.

3. The composite positive electrode sheet according to claim 1 or 2, characterized in that: The mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide in the first active material layer is 1:(0.1-2), preferably 1:(0.3-1).

4. The composite positive electrode sheet according to any one of claims 1 to 3, characterized in that: Taking the mass of the total active material of the first active material layer and the second active material layer as 100%, the mass fraction of the lithium-rich manganese-based material in the second active material layer is 3 to 10%, preferably 5 to 8%.

5. The composite positive electrode sheet according to any one of claims 1 to 4, characterized in that: The nickel cobalt manganese oxide includes NCM622; Preferably, the chemical formula of the lithium-rich manganese-based material is Li2MnO3.

6. A method for preparing a composite positive electrode sheet according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: (1) mixing lithium iron manganese phosphate, lithium nickel cobalt manganese oxide, a conductive agent, a binder and a solvent to obtain a first slurry, and mixing a lithium-rich manganese-based material, a conductive agent, a binder and a solvent to obtain a second slurry; (2) The first slurry is coated on at least one side of the positive electrode current collector, and the second slurry is coated on the surface of the first slurry to obtain the composite positive electrode sheet.

7. A lithium ion battery, characterized in that: The lithium-ion battery comprises the composite positive electrode sheet, negative electrode sheet, separator and electrolyte as described in any one of claims 1 to 5.

8. The lithium ion battery according to claim 7, characterized in that The negative electrode sheet comprises a negative electrode active material, a conductive agent and a binder; Preferably, the negative electrode active material includes any one of graphite, soft carbon or hard carbon, or a combination of at least two thereof; Preferably, the conductive agent comprises conductive carbon black and / or carbon nanotubes; Preferably, the binder comprises styrene-butadiene rubber.

9. The lithium ion battery according to claim 7 or 8, characterized in that: The separator includes a PE separator.

10. The lithium ion battery according to any one of claims 7 to 9, characterized in that: The electrolyte comprises a solvent, an electrolyte and an additive; Preferably, the solvent comprises ethylene carbonate and / or dimethyl carbonate; Preferably, the electrolyte comprises lithium hexafluorophosphate; Preferably, the additive comprises vinylene carbonate.

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