Positive electrode sheet and single battery

Abstract

The application discloses a positive plate and a single battery, and belongs to the technical field of batteries. The positive plate comprises a positive current collector, only a first positive active layer is arranged on one side of the positive current collector, and only a second positive active layer is arranged on the other side of the positive current collector, the material of the first positive active layer comprises a first positive active material, the material of the second positive active layer comprises a second positive active material, and the first positive active material is different from the second positive active material. According to the technical scheme, the expansion forces generated by the first positive active material and the second positive active material in the charging and discharging process are no longer concentrated in the active layer on the same side of the current collector or the interlayer interface, but are evenly distributed in the whole single battery level, so that the problems of delamination and peeling of the active layer of the positive plate caused by the different expansion rates of the two materials can be fundamentally solved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode and a single cell battery. Background Technology

[0002] Currently, the core development direction of lithium batteries is high safety, high energy density, long lifespan, good low-temperature performance, and high rate performance. The main lithium battery chemistry systems popular in the market include ternary lithium batteries, lithium cobalt oxide batteries, lithium iron phosphate batteries, and the emerging lithium manganese iron phosphate batteries. With the rapid development of materials technology, the battery lifespan of various chemistry systems has been significantly improved, leading to a gradual shift in market focus towards high safety, high energy density, and good low-temperature performance.

[0003] Traditional single-chemical systems are no longer sufficient to meet the current market's demands for high safety, high energy density, and extreme low-temperature performance. To overcome the performance bottlenecks of single-chemical systems, the industry has begun to explore hybrid lithium-ion batteries, which integrate the advantages of different cathode materials through synergistic complementarity to fill the performance gaps of single-chemical systems.

[0004] Currently, multiple different cathode materials are usually mixed on one side of the current collector. Due to the differences in crystal structure and electrochemical properties of the two materials, the volume expansion rate of the materials is different during charge and discharge cycles, which can easily cause problems such as delamination and shedding of the active layer of the electrode, resulting in a significant decline in battery electrical performance (such as cycle life and capacity retention). Utility Model Content

[0005] This application provides a positive electrode and a single-cell battery to at least partially solve the above-mentioned technical problems.

[0006] To achieve the above objectives, this application provides a positive electrode sheet, comprising: a positive current collector, wherein only a first positive active layer is provided on one side of the positive current collector, and only a second positive active layer is provided on the other side of the positive current collector, wherein the material of the first positive active layer includes a first positive active material, and the material of the second positive active layer includes a second positive active material, wherein the first positive active material and the second positive active material are different.

[0007] In some embodiments, the ratio of the mass of the second positive electrode active material to the mass of the first positive electrode active material ranges from 10% to 90%.

[0008] In some embodiments, the areal density of a single first positive electrode active layer is 180 g / m². 2 -220g / m 2 . In some embodiments, the areal density of a single second positive electrode active layer is 20 g / m². 2 -150g / m 2 .

[0009] In some embodiments, the first positive electrode active material includes one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium manganese oxide.

[0010] In some embodiments, the second positive electrode active material includes one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0011] In some embodiments, lithium nickel cobalt manganese oxide includes one of NCM111, NCM523, NCM613, NCM622, NCM811, Ni90, Ni95, and Ni98.

[0012] To achieve the above objectives, this application also provides a single-cell battery, which includes a positive electrode, a negative electrode, and a separator, wherein the separator is disposed between the positive electrode and the negative electrode.

[0013] In some embodiments, the negative electrode sheet includes a negative current collector, a first negative active layer, and a second negative active layer, wherein the first negative active layer is disposed on one side of the negative current collector and the second negative active layer is disposed on the other side of the negative current collector.

[0014] In some embodiments, the material of the first negative electrode active layer includes a first negative electrode active material, the material of the second negative electrode active layer includes a second negative electrode active material, and both the first negative electrode active material and the second negative electrode active material are graphite.

[0015] This application embodiment disposes a first positive electrode active layer, including a first positive electrode active material, and a second positive electrode active layer, including a second positive electrode active material different from the first positive electrode active material, on both sides of the positive electrode current collector. This ensures that the expansion forces generated by the first and second positive electrode active materials during charge and discharge are no longer concentrated within the active layer or interlayer interface on the same side of the current collector, but are evenly distributed throughout the entire single-cell battery layer. This fundamentally solves the problem of active layer delamination and detachment caused by the different expansion rates of the two materials. Consequently, the positive electrode maintains its complete structural morphology and stable electrode reaction interface during long-term charge-discharge cycles, preventing problems such as active material loss and increased electrode impedance due to structural damage. This significantly improves the cycle capacity retention rate of the positive electrode and greatly slows down the cycle decay rate, effectively extending the lifespan of the positive electrode and providing a crucial guarantee for the long-term stable operation of the single-cell battery. It also reduces safety hazards such as internal short circuits and thermal runaway caused by structural damage, significantly improving the safety of the single-cell battery.

[0016] The positive electrode sheet in this embodiment includes a positive current collector, a first positive electrode active layer, and a second positive electrode active layer. The first positive electrode active material of the first positive electrode active layer is different from the second positive electrode active material of the second positive electrode active layer. By combining the first positive electrode active material and the second positive electrode active material, the advantages of different chemical systems can be taken into account, achieving the effect of complementing each other's strengths and weaknesses. This can effectively reduce the risk of thermal runaway, improve the stability of the battery under extreme conditions, and meet the market's demand for high safety. It enables a single battery cell to store more energy per unit volume or mass, meeting the market's demand for high energy density. It can effectively improve the conductivity and ion transport capability of the single battery cell at low temperatures, thereby ensuring the normal operation of the single battery cell under low temperature conditions and meeting the market's demand for extreme low-temperature performance. It achieves comprehensive optimization of electrical performance and also improves rate performance, meeting the market's demand for rate performance. This enables the single battery cell to maintain excellent performance in a variety of application scenarios.

[0017] Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0019] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet provided in an exemplary embodiment of this disclosure; Figure 2 This is a schematic diagram of the structure of a single battery provided in an exemplary embodiment of this disclosure. Figure 1 ; Figure 3 This is a schematic diagram of the structure of the negative electrode sheet provided in an exemplary embodiment of this disclosure; Figure 4 This is a schematic diagram of the structure of a single battery provided in an exemplary embodiment of this disclosure. Figure 2 ; Figure 5 This is a schematic diagram of the structure of a single battery provided in an exemplary embodiment of this disclosure. Figure 3 ; Figure 6This is a charge-discharge curve of a single battery provided in an exemplary embodiment of this disclosure, mainly showing the charge-discharge curve of a single battery when the mass ratio of the second positive electrode active material to the mass of the first positive electrode active material is 10%, 30%, 50%, 70%, and 90%, respectively.

[0020] Explanation of reference numerals in the attached figures: 100. Single cell battery; 1. Positive electrode plate; 2. Negative electrode plate; 3. Separator; 11. Positive current collector; 12. First positive active layer; 13. Second positive active layer; 21. Negative electrode current collector; 22. First negative electrode active layer; 23. Second negative electrode active layer. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0022] Currently, the core development direction of lithium batteries is high safety, high energy density, long lifespan, good low-temperature performance, and high rate performance. The main lithium battery chemistry systems popular in the market include ternary lithium batteries, lithium cobalt oxide batteries, lithium iron phosphate batteries, and the emerging lithium manganese iron phosphate batteries. With the rapid development of materials technology, the battery lifespan of various chemistry systems has been significantly improved, leading to a gradual shift in market focus towards high safety, high energy density, and good low-temperature performance.

[0023] Traditional single-chemical systems are no longer sufficient to meet the current market demands for high safety, high energy density, and extreme low-temperature performance. To overcome the performance bottlenecks of single-chemical systems, the industry has begun exploring hybrid lithium-ion battery systems. This involves integrating the advantages of different cathode materials through synergistic complementarity, thereby filling the performance gaps of single-chemical systems. Specifically, lithium manganese iron phosphate (LFP) batteries can fill the niche market between LFP and ternary lithium batteries, while composite systems of LFP and ternary materials can further bridge the performance gap between them. In particular, the composite system of LFP and ternary materials, with their complementary characteristics in safety and energy density, is expected to gain a competitive advantage in the intermediate market between LFP and ternary lithium batteries.

[0024] In related technologies, multiple different cathode materials are typically mixed on one side of the current collector. Due to differences in the crystal structure and electrochemical properties of the two materials, their volume expansion rates differ during charge-discharge cycles, easily leading to problems such as delamination and detachment of the active layer of the electrode, resulting in a significant decrease in battery performance (such as cycle life and capacity retention). For example, the drawbacks of using a dual-coating process to uniformly coat one material onto another for mixing include: complex equipment modifications are required during electrode preparation, resulting in high equipment investment costs and a cumbersome production process, leading to a significant increase in production costs; due to differences in the crystal structure and electrochemical properties of the two materials, their volume expansion rates differ during charge-discharge cycles, easily leading to problems such as delamination and detachment of the active layer of the electrode, resulting in a significant decrease in battery performance (such as cycle life and capacity retention). While using a composite process to separately composite the cathode materials and then prepare a slurry, or directly mixing and dispersing the two cathode materials uniformly during slurry preparation, can alleviate the volume expansion problem during cycling of a single material to some extent, and the electrode manufacturing method is compatible with existing mass production processes, requiring no modification to the production equipment, and exhibiting high equipment adaptability. However, this process still has insurmountable drawbacks: First, the composite ratio of the two materials directly affects the volume expansion ratio of the electrode structure. Although homogenization can alleviate the material expansion problem, it cannot fundamentally eliminate the inconsistency in expansion caused by differences in material properties. Second, different composite ratios correspond to different electrode volume expansion characteristics. For each composite ratio, the electrode structure and preparation process parameters need to be redeveloped, which not only leads to a significant increase in R&D investment but also generates high hidden costs (such as extended R&D cycles and increased process debugging costs), severely restricting the large-scale promotion and performance optimization of hybrid lithium batteries. Therefore, neither the double-layer coating process nor the material composite process can fundamentally eliminate the inconsistency in expansion caused by differences in material properties. Different volume expansion rates of materials during charge-discharge cycles can easily lead to problems such as electrode delamination and active material detachment.

[0025] For example, when lithium iron phosphate (LFP) is blended with lithium nickel cobalt manganese oxide (NCM) (e.g., NCM811), the crystal expansion rate of LFP is 6%-7%, while that of NCM811 is 13%-16%. The peak cell expansion force of LFP (the "volume expansion" of the cell during a single charge-discharge cycle (usually the first charge-discharge or under specific operating conditions) is due to chemical reactions and structural changes in the internal active materials. The corresponding maximum mechanical pressure value is 4kN-6kN, and the peak expansion force of NCM811 is 8kN-12kN; the cyclic expansion increment of LFP (referring to the cumulative increase of the cell's "volume / expansion force" relative to the "initial state (or the previous cycle stage)" after a certain number of cycles during multiple charge-discharge cycles (or from the start of the cycle to a specific number of cycles)) is ≤0.3mm / 100 cycles, and the cyclic expansion increment of NCM811 is ≥0.8mm / 100 cycles; Please see Figure 1 This application provides a positive electrode sheet 1. The positive electrode sheet 1 includes: a positive current collector 11, a first positive active layer 12, and a second positive active layer 13. Only the first positive active layer 12 is provided on one side of the positive current collector 11, and only the second positive active layer 13 is provided on the other side. In this embodiment, only one layer of the first positive active layer 12 is provided on one side of the positive current collector 11, that is, the first positive active layer 12 is formed by a single-layer coating method; only one layer of the second positive active layer 13 is provided on the other side of the positive current collector 11, that is, the second positive active layer 13 is formed by a single-layer coating method. The first positive active layer 12 and the second positive active layer 13 are respectively disposed on opposite sides of the positive current collector 11.

[0026] The first positive electrode active layer 12 comprises a first positive electrode active material, a first conductive agent, and a first binder. The first positive electrode active material includes one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium manganese oxide. In this embodiment, the first positive electrode active material is lithium iron phosphate (LFP). The first conductive agent includes at least one of carbon-based conductive agents, such as conductive carbon black, conductive graphite, acetylene black, vapor-grown carbon fibers, graphene, and carbon nanotubes. The first binder includes at least one of polyvinylidene fluoride, polyethylene oxide, styrene-butadiene rubber, polyacrylic acid, polymethyl acrylate, polyurethane, polyacrylonitrile, polytetrafluoroethylene, sodium alginate, gelatin, β-cyclodextrin, sodium carboxymethyl cellulose, sodium hydroxypropyl methylcellulose, and sodium carboxymethyl cellulose.

[0027] The second positive electrode active layer 13 comprises a second positive electrode active material, a second conductive agent, and a second binder. The second positive electrode active material differs from the first positive electrode active material. The second positive electrode active material includes one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. Specifically, lithium nickel cobalt manganese oxide includes one of NCM111, NCM523, NCM613, NCM622, NCM811, Ni90, Ni95, and Ni98. In this embodiment, the second positive electrode active material is NCM811. The second conductive agent includes at least one of carbon-based conductive agents, such as conductive carbon black, conductive graphite, acetylene black, vapor-grown carbon fibers, graphene, and carbon nanotubes. The second binder includes at least one of polyvinylidene fluoride, polyethylene oxide, styrene-butadiene rubber, polyacrylic acid, polymethyl acrylate, polyurethane, polyacrylonitrile, polytetrafluoroethylene, sodium alginate, gelatin, β-cyclodextrin, sodium carboxymethyl cellulose, sodium hydroxypropyl methyl cellulose, and sodium hydroxymethyl cellulose.

[0028] The mass ratio of the second positive electrode active material to the first positive electrode active material ranges from 10% to 90%. In this embodiment, the mass ratio of the second positive electrode active material to the first positive electrode active material is 70%. In other embodiments, the mass ratio of the second positive electrode active material to the first positive electrode active material is any one or any two of the following values: 10%, 20%, 30%, 40%, 50%, 60%, 80%, and 90%.

[0029] The areal density of a single first positive electrode active layer 12 is 180 g / m². 2 -220g / m 2 The areal density of a single first positive electrode active layer 12 refers to the total mass of the material coated on a unit area of ​​the first positive electrode active layer 12 (including the first positive electrode active material, the first conductive agent, and the first binder). In this embodiment, the areal density of a single first positive electrode active layer 12 is 200 g / m². 2 In other embodiments, the areal density of a single first positive electrode active layer 12 is 180 g / m². 2 185g / m 2 190g / m 2 195g / m 2 205g / m 2 210g / m 2 215g / m 2 220g / m 2 The range between any one or any two values ​​in the range.

[0030] The areal density of a single second positive electrode active layer 13 is 20 g / m². 2 -150g / m 2The areal density of a single second positive electrode active layer 13 refers to the total mass of the material coated on a unit area of ​​the second positive electrode active layer 13 (including the second positive electrode active material, the second conductive agent, and the second binder). In this embodiment, the areal density of a single second positive electrode active layer 13 is 120 g / m². 2 In other embodiments, the areal density of a single second positive electrode active layer 13 is 20 g / m². 2 30g / m 2 40g / m 2 50g / m 2 60g / m 2 70g / m 2 80g / m 2 90g / m 2 100g / m 2 110g / m 2 130g / m 2 140g / m 2 150g / m 2 The range between any one or any two values ​​in the range.

[0031] The preparation method of the positive electrode sheet 1 of this application includes: 1. Dispersing a first positive electrode active material (LFP), a first conductive agent and a first binder in N-methylpyrrolidone (NMP), stirring evenly to obtain a first slurry, and coating it on one side surface of the positive electrode current collector 11, wherein the mass ratio of the first positive electrode active material, the first conductive agent and the first binder is 96%~97.5%: 0.5%~1.5%: 1%~2%; 2. Dispersing a second positive electrode active material (NCM911), a second conductive agent and a second binder in N-methylpyrrolidone (NMP), stirring evenly to obtain a second slurry, and coating it on the other side surface of the positive electrode current collector 11, wherein the mass ratio of the second positive electrode active material, the second conductive agent and the second binder is 96%~97.5%: 0.5%~1.5%: 1%~2%; 3. Obtaining the positive electrode sheet 1 through drying, cold pressing and other processes.

[0032] This application, by distributing a first positive electrode active layer 12, comprising a first positive electrode active material, and a second positive electrode active layer 13, comprising a second positive electrode active material different from the first positive electrode active material, on both sides of the positive electrode current collector 11, ensures that the expansion forces generated by the first and second positive electrode active materials during charge and discharge are no longer concentrated within the active layer or interlayer interface on the same side of the current collector, but are evenly distributed throughout the entire cell 100. This fundamentally solves the problem of active layer delamination and shedding of the electrode sheet caused by the different expansion rates of the two materials. Consequently, the positive electrode sheet 1 can maintain its complete structural morphology and stable electrode reaction interface during long-term charge and discharge cycles, preventing problems such as loss of active material and increased electrode impedance due to structural damage. This significantly improves the cycle capacity retention rate of the positive electrode sheet 1 and greatly slows down the cycle decay rate, thereby effectively extending the service life of the positive electrode sheet 1 and providing a key guarantee for the long-term stable operation of the cell 100. This application can also reduce safety hazards such as internal short circuits and thermal runaway in the cell 100 caused by structural damage, significantly improving the safety of the cell 100 in use.

[0033] Please see Figure 2 This application also provides a single-cell battery 100. The single-cell battery 100 includes a positive electrode 1, a negative electrode 2 and a separator 3 as described in this application, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2.

[0034] Please see Figure 3 The negative electrode 2 includes a negative electrode current collector 21, a first negative electrode active layer 22, and a second negative electrode active layer 23. The first negative electrode active layer 22 is disposed on one side of the negative electrode current collector 21, and the second negative electrode active layer 23 is disposed on the other side of the negative electrode current collector 21.

[0035] The first negative electrode active layer 22 comprises a first negative electrode active material, a third conductive agent, and a third binder. In this embodiment, the first negative electrode active material is graphite. The third conductive agent includes at least one carbon-based conductive agent, such as conductive carbon black, conductive graphite, acetylene black, vapor-grown carbon fiber, graphene, and carbon nanotubes. The third binder includes at least one of polyvinylidene fluoride, polyethylene oxide, styrene-butadiene rubber, polyacrylic acid, polymethyl acrylate, polyurethane, polyacrylonitrile, polytetrafluoroethylene, sodium alginate, gelatin, β-cyclodextrin, sodium carboxymethyl cellulose, sodium hydroxypropyl methyl cellulose, and sodium hydroxymethyl cellulose.

[0036] The second negative electrode active layer 23 comprises a second negative electrode active material, a fourth conductive agent, and a fourth binder. In this embodiment, the second negative electrode active material is graphite. The fourth conductive agent includes at least one carbon-based conductive agent, such as conductive carbon black, conductive graphite, acetylene black, vapor-grown carbon fiber, graphene, and carbon nanotubes. The fourth binder includes at least one of polyvinylidene fluoride, polyethylene oxide, styrene-butadiene rubber, polyacrylic acid, polymethyl acrylate, polyurethane, polyacrylonitrile, polytetrafluoroethylene, sodium alginate, gelatin, β-cyclodextrin, sodium carboxymethyl cellulose, sodium hydroxypropyl methyl cellulose, and sodium hydroxymethyl cellulose.

[0037] The preparation method of the negative electrode 2 of this application includes: 1. dispersing (graphite), a third conductive agent and a third binder in N-methylpyrrolidone (NMP), stirring evenly to obtain a third slurry, and coating it on both sides of the negative electrode current collector 21; 2. obtaining the negative electrode 2 through drying, cold pressing and other processes.

[0038] Please see Figure 2 In this embodiment, the layer arrangement of the single cell 100 can end with the negative electrode surrounding the positive electrode. In other embodiments, the layer arrangement of the single cell 100 can also end with the positive electrode surrounding the negative electrode (e.g., Figure 4 and Figure 5 ).

[0039] The method for preparing the single-cell battery 100 of this application includes: cutting, die-cutting, and slitting the vacuum-dried positive electrode sheet 1, negative electrode sheet 2, and separator 3; then injecting electrolyte under high temperature and negative pressure to assemble them into a pouch battery with a pouch capacity of 2.0-2.5 Ah. It is worth noting that the single-cell battery 100 of this application can be used in pouch batteries, as well as in prismatic and cylindrical batteries. The structure of the single-cell battery 100 of this application can be used in stacked batteries or wound batteries.

[0040] Table 1

[0041] Table 1 shows the discharge capacity at 25°C, discharge capacity at -20°C, and discharge capacity retention rate when the mass ratio of the second positive electrode active material to the first positive electrode active material is 0%, 10%, 30%, 50%, 70%, and 90%, respectively.

[0042] As shown in Table 1, the capacity retention rate is 67.5% for pure LFP; when the NCM content in LFP is 90%, the capacity retention rate increases to 82.4%. With the increase in the proportion of ternary materials (NCM), the discharge capacity retention rate gradually improves. This indicates that the addition of ternary materials (NCM) can improve the low-temperature discharge performance of the battery, enhance its capacity retention capability in low-temperature environments, and enable the battery to release more electricity at low temperatures, making it more suitable for low-temperature operating scenarios.

[0043] Combination Figure 6 It can be seen that the higher the proportion of NCM, the closer the battery is to the high-voltage discharge characteristics of ternary lithium batteries; the higher the proportion of LFP, the closer the battery is to the low-voltage and long-life (cycle stability) characteristics of lithium iron phosphate batteries.

[0044] This application, through the composite of a first positive electrode active material and a second positive electrode active material, can take into account the advantages of different chemical systems, achieving a complementary effect. This effectively reduces the risk of thermal runaway, improves battery stability under extreme conditions, and meets market demands for high safety. It also enables the single-cell battery 100 to store more energy per unit volume or mass, meeting market demands for high energy density. Furthermore, it effectively improves the conductivity and ion transport capability of the single-cell battery 100 at low temperatures, ensuring normal operation under these conditions and meeting market demands for extreme low-temperature performance. Finally, it achieves comprehensive optimization of electrical performance and improves rate performance, meeting market demands for rate performance. This allows the single-cell battery 100 to maintain excellent performance in various application scenarios.

[0045] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0046] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not described in detail in a particular embodiment can be referred to in the relevant descriptions of other embodiments. The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0047] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A positive electrode (1), characterized in that, include: A positive current collector (11) is provided on one side only with a first positive active layer (12) and on the other side only with a second positive active layer (13). The material of the first positive active layer (12) includes a first positive active material and the material of the second positive active layer (13) includes a second positive active material. The first positive active material and the second positive active material are different.

2. The positive electrode (1) according to claim 1, characterized in that, The ratio of the mass of the second positive electrode active material to the mass of the first positive electrode active material is in the range of 10%-90%.

3. The positive electrode (1) according to claim 1, characterized in that, The areal density of a single first positive electrode active layer (12) is 180 g / m². 2 -220g / m 2 .

4. The positive electrode (1) according to claim 1, characterized in that, The areal density of a single second positive electrode active layer (13) is 20 g / m². 2 -150g / m 2 .

5. The positive electrode (1) according to claim 1, characterized in that, The first positive electrode active material includes one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, and lithium manganese oxide.

6. The positive electrode (1) according to claim 1, characterized in that, The second positive electrode active material includes one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

7. The positive electrode (1) according to claim 6, characterized in that, The lithium nickel cobalt manganese oxide includes one of NCM111, NCM523, NCM613, NCM622, NCM811, Ni90, Ni95 and Ni98.

8. A single-cell battery (100), characterized in that, The invention comprises a positive electrode (1), a negative electrode (2), and a separator (3) as described in any one of claims 1-7, wherein the separator (3) is disposed between the positive electrode (1) and the negative electrode (2).

9. The single-cell battery (100) according to claim 8, characterized in that, The negative electrode sheet (2) includes a negative electrode current collector (21), a first negative electrode active layer (22) and a second negative electrode active layer (23). The first negative electrode active layer (22) is disposed on one side of the negative electrode current collector (21), and the second negative electrode active layer (23) is disposed on the other side of the negative electrode current collector (21).

10. The single-cell battery (100) according to claim 9, characterized in that, The material of the first negative electrode active layer (22) includes a first negative electrode active material, and the material of the second negative electrode active layer (23) includes a second negative electrode active material. Both the first negative electrode active material and the second negative electrode active material are graphite.

Images