Positive electrode sheet, secondary battery and method for manufacturing the same, and battery module, battery pack, and electric device including the secondary battery

Abstract

The application provides a positive electrode sheet, a secondary battery and a preparation method thereof, and a battery module, a battery pack and a power utilization device comprising the secondary battery. The positive electrode sheet comprises a positive current collector, a positive active material layer arranged on at least one surface of the positive current collector, and a lithium supplement layer arranged on the surface of the positive active material layer opposite to the positive current collector, wherein the lithium supplement layer comprises a positive lithium supplement material, a conductive agent and a binder A, the positive lithium supplement material comprises a lithium-rich metal oxide, and the binder A is selected from a polymer comprising a first monomer unit represented by Formula I and a second monomer unit represented by Formula II, wherein R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are independently selected from hydrogen or substituted or unsubstituted C1-C8 alkyl, and R is selected from substituted or unsubstituted C1-C8 alkyl.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a positive electrode sheet, a secondary battery and its preparation method, as well as a battery module, battery pack and power device containing the secondary battery. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and various electronic products. As the application scope of rechargeable batteries becomes increasingly broad, higher requirements are being placed on their capacity performance and cycle performance.

[0003] However, during the first charge of a secondary battery, an SEI (solid electrolyte interface) film inevitably forms on the negative electrode, causing the consumption of active ions. The resulting irreversible capacity loss is difficult to eliminate, thereby reducing the first discharge capacity and posing a challenge to improving the cycle life of the secondary battery. Summary of the Invention

[0004] This application was made in view of the aforementioned problems, and its object is to provide a positive electrode sheet that enables a secondary battery to achieve a high initial discharge capacity and a long cycle life. Another object of this application is to provide a secondary battery with a high initial discharge capacity and a long cycle life, and a method for preparing the same. Yet another object of this application is to provide a battery module, battery pack, and power-consuming device incorporating the secondary battery of this application.

[0005] To achieve the above objectives, a first aspect of this application provides a positive electrode sheet, comprising a positive current collector, a positive active material layer disposed on at least one surface of the positive current collector, and a lithium replenishment layer disposed on the surface of the positive active material layer opposite to the positive current collector. The lithium replenishment layer comprises a positive lithium replenishment material, a conductive agent, and a binder A. The positive lithium replenishment material comprises a lithium-rich metal oxide, and the binder A is selected from polymers comprising a first monomer unit represented by Formula I and a second monomer unit represented by Formula II.

[0006]

[0007] R 1 R 2 R 3 R 4 R 5 and R 6 Each is independently selected from hydrogen or substituted or unsubstituted C1 to C8 alkyl groups, and R is selected from substituted or unsubstituted C1 to C8 alkyl groups.

[0008] This application, by placing the lithium replenishment layer on the surface of the positive electrode active material layer opposite to the positive electrode current collector, facilitates the release of more lithium ions from the positive electrode lithium replenishment material and promotes the migration of extracted active lithium to the negative electrode for lithium replenishment. The lithium replenishment layer uses a polymer comprising a first monomer unit and a second monomer unit as a binder, which consumes free lithium compounds such as LiOH and Li2CO3 on the surface of lithium-rich metal oxides. This effectively improves the gelation problem of the slurry and ensures a tight bond between the lithium replenishment layer and the positive electrode active material layer. Simultaneously, it effectively avoids reactions between excessive carboxyl groups in the binder and active lithium ions, thereby helping the positive electrode lithium replenishment material release more lithium ions during charging and ensuring that more lithium ions are used for lithium replenishment. Therefore, the positive electrode lithium replenishment material in this application achieves a high utilization rate of active lithium, thereby improving the battery's initial charge / discharge capacity and energy density, and enabling the battery to achieve a longer cycle life. Furthermore, the positive electrode of this application can have good electronic conductivity and lithium-ion transport performance after the lithium replenishment layer is delithiated, thus further improving the cycle life of the secondary battery using it.

[0009] In any embodiment of this application, the content of the first monomer unit is 30% to 70%, optionally 40% to 60%, based on the total weight of the first and second monomer units. The binder A contains an appropriate amount of the first and second monomer units, which can further improve the initial charge-discharge capacity and cycle life of the battery.

[0010] In any embodiment of this application, the weight-average molecular weight of binder A is 30,000 to 600,000, optionally 50,000 to 500,000, and even more preferably 100,000 to 300,000. When the molecular weight of binder A is within an appropriate range, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0011] In any embodiment of this application, the first monomer unit satisfies: R 1 R 2 and R 3 Each is independently selected from hydrogen or substituted or unsubstituted C1-C4 alkyl groups. Optionally, R 1 R 2 and R 3 Each is independently selected from hydrogen or methyl.

[0012] In any embodiment of this application, the first monomer unit includes one or more of the monomer units shown in Formula S1 and Formula S2.

[0013]

[0014] In any embodiment of this application, the second monomer unit satisfies the following condition: R is selected from substituted or unsubstituted C1 to C4 alkyl groups.

[0015] In any embodiment of this application, the second monomer unit satisfies R 4 R 5 and R 6 Each is independently selected from hydrogen or substituted or unsubstituted C1-C4 alkyl groups. Optionally, R 4 R 5 and R 6 Each is independently selected from hydrogen or methyl. Alternatively, R 4 R represents hydrogen or methyl. 5 and R 6 Both represent hydrogen.

[0016] In any embodiment of this application, the second monomer unit includes one or more of the monomer units shown in formulas S3 to S8.

[0017]

[0018]

[0019] In any embodiment of this application, binder A is selected from one or more of the following: polymers comprising monomer units S1 and S5, polymers comprising monomer units S1 and S8, polymers comprising monomer units S1, S5 and S8, polymers comprising monomer units S1, S3, S5 and S8, polymers comprising monomer units S2 and S8, polymers comprising monomer units S2 and S7, polymers comprising monomer units S2 and S5, and polymers comprising monomer units S2 and S6. In some embodiments, binder A is selected from one or more of the following: polymers comprising monomer units S1 and S5, polymers comprising monomer units S1 and S8, polymers comprising monomer units S1, S5 and S8, polymers comprising monomer units S1, S3, S5 and S8, polymers comprising monomer units S2 and S8, polymers comprising monomer units S2 and S7, polymers comprising monomer units S2 and S5, and polymers comprising monomer units S2 and S6. Selecting a suitable binder A can further improve the initial charge-discharge capacity and cycle life of the battery.

[0020] In any embodiment of this application, the pH of the positive electrode lithium replenishment material, measured by titration, is ≤13. Optionally, pH is ≤12.5. Further optionally, pH is ≤11 ≤ pH ≤ 12.5. A pH within the above range is beneficial for further improving the lithium replenishment effect, thereby increasing the battery's initial charge / discharge capacity and cycle life.

[0021] In any embodiment of this application, the specific capacity of the positive electrode lithium replenishment material is ≥400mAh / g, and optionally ≥500mAh / g. The positive electrode lithium replenishment material has a high specific capacity, which can further improve the initial charge-discharge capacity and cycle life of the battery.

[0022] In any embodiment of this application, the lithium-rich metal oxide is selected from Li3M 1 O4, Li5M 2 O4, Li6M 3 One or more of O4, of which M 1 Including one or more of V, Nb, Cr, and Mo, M 2 Including one or more of Fe, Cr, V, Mo, and Al, M 3 The lithium-rich metal oxide contains one or more of the following elements: Co, V, Cr, and Mo. In this lithium-rich metal oxide, the valence state of each metal element except Li is lower than its highest oxidation state. Optionally, the lithium-rich metal oxide is selected from one or more of Li3VO4, Li3NbO4, Li5FeO4, and Li6CoO4.

[0023] In any embodiment of this application, the lithium-rich metal oxide comprises single-crystal particles, and the number of single-crystal particles in the lithium-rich metal oxide accounts for 60% to 100%, optionally 80% to 100%. The lithium-rich metal oxide is mainly composed of single-crystal particles, which enables the battery to achieve extended cycle life and is beneficial to improving the energy density of the battery.

[0024] In any embodiment of this application, the volume average particle size D of the lithium-rich metal oxide v The thickness of 50 is 5μm to 25μm, optionally 6μm to 20μm, and also optionally 10μm to 15μm. Lithium-rich metal oxides also satisfy D... v Within an appropriate range, 50 can further improve the cycle life and energy density of the battery.

[0025] In any embodiment of this application, the positive electrode lithium replenishment material accounts for 90% to 97% of the weight of the lithium replenishment layer, and optionally 92.5% to 95%.

[0026] In any embodiment of this application, the binder A accounts for 2% to 7% of the weight of the lithium replenishment layer, optionally 3.5% to 5%.

[0027] In any embodiment of this application, the conductive agent accounts for 1% to 3% by weight in the lithium replenishment layer, optionally 1.5% to 2.5%.

[0028] In any embodiment of this application, the positive electrode active material layer includes binder B and binder C, wherein binder B includes one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), and binder C is selected from one or more polymers comprising the group consisting of the third monomer unit represented by Formula III and the fourth monomer unit represented by Formula IV. In some embodiments, the content of binder C is 5% to 20% based on the total weight of binder B and binder C. The presence of an appropriate amount of binder C in the positive electrode active material layer can further improve the cycle life of the battery while ensuring a high initial charge-discharge capacity.

[0029]

[0030] R a R b R c R d R e and R f Each monomer unit is independently selected from hydrogen or substituted or unsubstituted C1 to C8 alkyl groups, and R' is selected from substituted or unsubstituted C1 to C8 alkyl groups; optionally, the third monomer unit includes one or more of the monomer units shown in Formula S1 and Formula S2, and the fourth monomer unit includes one or more of the monomer units shown in Formula S3 to Formula S8.

[0031] In any embodiment of this application, the weight-average molecular weight of binder C is 50 to 5000, optionally 100 to 4000. A suitable weight-average molecular weight of binder C is beneficial for the battery to simultaneously achieve high initial charge / discharge capacity and cycle life.

[0032] In some embodiments of this application, the positive electrode active material layer comprises a layered lithium transition metal oxide, wherein the content of binder C is 10% to 20% based on the total weight of binder B and binder C. Optionally, the layered lithium transition metal oxide comprises one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified materials of the above substances. If the positive electrode active material comprises a layered lithium transition metal oxide, and the positive electrode active material layer contains an appropriate proportion of binder C, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0033] In some embodiments, the weight-average molecular weight of binder C is 500 to 4000, optionally 1000 to 3000. If the positive electrode active material comprises layered lithium transition metal oxide, and the weight-average molecular weight of binder C is within the given range, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0034] In some embodiments, binder C is selected from polymers comprising one or more of the third monomer units. Optionally, binder C is selected from polymers comprising monomer unit S1. Further optionally, binder C is selected from polymers comprising monomer unit S1. If the positive electrode active material comprises layered lithium transition metal oxide, and binder C is selected from the above-mentioned polymers, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0035] In some embodiments, the compaction density of the positive electrode active material layer is 3.5 g / cm³. 3 ~3.8g / cm 3 The optional value is 3.55 g / cm³. 3 ~3.65g / cm 3 Among them, the volume average particle size D of the positive electrode active material v The thickness of the 50 layer ranges from 2μm to 10μm, and optionally from 4μm to 8μm. A higher compaction density in the positive electrode active material layer further improves the energy density of the battery.

[0036] In some other embodiments of this application, the positive electrode active material layer comprises a polyanionic positive electrode material, wherein the content of binder C is 5% to 10% based on the total weight of binder B and binder C. Optionally, the polyanionic positive electrode material comprises a lithium phosphate with an olivine structure, and may also optionally comprise one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and modified materials of the above substances. If the positive electrode active material comprises a polyanionic positive electrode material, and the positive electrode active material layer contains an appropriate proportion of binder C, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0037] In some embodiments, the weight-average molecular weight of binder C is 100–3000, optionally 500–1500. If the positive electrode active material includes a polyanionic positive electrode material, and the weight-average molecular weight of binder C is within the given range, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0038] In some embodiments, the binder C is selected from polymers that simultaneously include a third monomer unit and a fourth monomer unit; alternatively, the binder C is selected from one or more polymers that include one or more monomer units selected from S1 to S2 and one or more polymers selected from S2 to S8. If the positive electrode active material includes a polyanionic positive electrode material, and the binder C is selected from the above-mentioned polymers, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0039] In some embodiments, the compaction density of the positive electrode active material layer is 2.4 g / cm³. 3 ~2.7g / cm 3 Optionally, it can be 2.45 g / cm³.3 ~2.55g / cm 3 Among them, the volume average particle size D of the positive electrode active material v The thickness of the positive electrode active material layer ranges from 0.2 μm to 1.5 μm, and optionally from 0.5 μm to 1.2 μm. A higher compaction density is achieved, which can further improve the energy density of the battery.

[0040] In any embodiment of this application, based on the total thickness of the positive electrode active material layer and the lithium replenishment layer, the thickness ratio of the lithium replenishment layer is 3% to 22%, optionally 5% to 20%, and even more optionally 8% to 15%. A lithium replenishment layer thickness ratio within an appropriate range enables the battery to achieve higher energy density and cycle life.

[0041] A second aspect of this application provides a secondary battery including a positive electrode, wherein the positive electrode includes the positive electrode according to this application. Because the secondary battery of this application uses the positive electrode of this application, it can simultaneously achieve higher initial charge / discharge capacity, higher energy density, and longer cycle life.

[0042] In any embodiment of this application, the secondary battery includes an electrolyte. The electrolyte contains an electrolyte lithium salt, which includes a fluorinated electrolyte lithium salt. Optionally, the fluorinated electrolyte lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)methyl lithium, and tri(trifluoromethanesulfonyl)methyl lithium. In this application, a lithium replenishment layer is disposed on the surface of the positive electrode active material layer opposite to the positive electrode current collector. The lithium-rich metal oxides therein, after delithiation, can preferentially react with HF in the fluorinated electrolyte, thereby reducing the loss of positive electrode active material and enabling the battery to achieve a longer cycle life. In particular, the metal fluoride formed by the reaction can also improve the lithium-ion migration performance of the lithium replenishment layer.

[0043] A third aspect of this application provides a battery module that includes a secondary battery according to this application.

[0044] A fourth aspect of this application provides a battery pack that includes at least one of a secondary battery or a battery module according to this application.

[0045] The fifth aspect of this application provides an electrical device that includes at least one of a secondary battery, a battery module, or a battery pack according to this application.

[0046] The battery module, battery pack, and power device of this application include the secondary battery described in this application, and therefore have at least the same or similar technical effects as the secondary battery.

[0047] The sixth aspect of this application provides a method for manufacturing a secondary battery, comprising the steps of preparing a positive electrode sheet by: forming a positive electrode active material layer on at least one surface of a positive electrode current collector; forming a lithium replenishment layer on the surface of the positive electrode active material layer opposite to the positive electrode current collector, the lithium replenishment layer comprising a positive electrode lithium replenishment material, a conductive agent, and a binder A, wherein the positive electrode lithium replenishment material comprises a lithium-rich metal oxide, and the binder A is selected from a polymer comprising a first monomer unit and a second monomer unit.

[0048]

[0049] Wherein, the R 1 R 2 R 3 R 4 R 5 and R 6 Each R is independently selected from hydrogen or substituted or unsubstituted C1 to C8 alkyl groups, wherein R is selected from substituted or unsubstituted C1 to C8 alkyl groups.

[0050] According to the manufacturing method of this application, by disposing the lithium replenishment layer on the surface of the positive electrode active material layer opposite to the positive electrode current collector, and using a polymer comprising a first monomer unit and a second monomer unit as a binder in the lithium replenishment layer, it is helpful to achieve a higher active lithium utilization rate in the positive electrode lithium replenishment material in the positive electrode sheet, thereby improving the initial charge-discharge capacity and energy density of the battery, and enabling the battery to achieve a longer cycle life. Furthermore, according to the manufacturing method of this application, the positive electrode sheet exhibits good electronic conductivity and lithium-ion transport performance after lithium removal from the lithium replenishment layer, thus further improving the cycle life of the secondary battery using it. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the structure of a positive electrode sheet provided in one embodiment of this application.

[0052] Figure 2 This is a schematic diagram of the structure of the positive electrode sheet provided in another embodiment of this application.

[0053] Figure 3 This is a schematic diagram of one embodiment of a secondary battery.

[0054] Figure 4 yes Figure 3 The exploded diagram.

[0055] Figure 5 This is a schematic diagram of one embodiment of the battery module.

[0056] Figure 6 This is a schematic diagram of one embodiment of the battery pack.

[0057] Figure 7 yes Figure 6 The exploded diagram.

[0058] Figure 8 This is a schematic diagram of one embodiment of a device that uses a secondary battery as a power source. Detailed Implementation

[0059] The following detailed description, with appropriate reference to the accompanying drawings, discloses the positive electrode sheet, secondary battery, and methods for preparing the same, as well as embodiments of the battery module, battery pack, and power-consuming device comprising the secondary battery. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0060] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0062] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0063] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0064] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0065] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0066] Unless otherwise specified, the terms "above" and "below" in this application include the stated number, and "several types" means two or more types.

[0067] To meet the high energy density requirements of secondary batteries, a lithium-rich composite positive electrode can be prepared by incorporating a lithium replenishment layer containing a positive electrode lithium replenishment material. During the first charge of the secondary battery, the positive electrode lithium replenishment material releases active lithium, which can be used to compensate for the irreversible loss of active lithium caused by the formation of an SEI film on the negative electrode.

[0068] Cathode lithium replenishment materials can contain lithium-rich metal oxides. However, to increase their lithium content, existing lithium-rich metal oxides often incorporate excess lithium sources during synthesis. The residual lithium source on the surface of these oxides reacts with CO2 and H2O from the environment to form free lithium compounds such as LiOH and Li2CO3. The presence of these free lithium compounds not only reduces the battery's energy density but also leads to a higher pH value (e.g., pH ≥ 11) in the cathode lithium replenishment material. During the preparation of the lithium replenishment layer slurry, the high pH value of the cathode lithium replenishment material reacts with commonly used cathode binders (e.g., polyvinylidene fluoride, PVDF), causing the slurry to gel. This not only makes the lithium replenishment layer difficult to process but also affects the adhesion between the lithium replenishment layer and adjacent active material layers, thus reducing the lithium replenishment effect.

[0069] Further research by the inventors revealed that by optimizing the design of the lithium replenishment layer, including the combination design of the positive electrode lithium replenishment material and the binder, the above problems can be solved and the lithium replenishment effect can be improved.

[0070] Based on this, one embodiment of this application provides a positive electrode sheet. The positive electrode sheet includes a positive current collector, a positive active material layer disposed on at least one surface of the positive current collector, and a lithium replenishment layer disposed on the surface of the positive active material layer opposite to the positive current collector. The lithium replenishment layer comprises a positive lithium replenishment material, a conductive agent, and a binder A. The positive lithium replenishment material comprises a lithium-rich metal oxide, and the binder A is selected from polymers comprising a first monomer unit represented by Formula I and a second monomer unit represented by Formula II.

[0071]

[0072] R 1 R 2 R 3 R 4 R 5 and R 6 Each is independently selected from hydrogen or substituted or unsubstituted C1 to C8 alkyl groups; R is selected from substituted or unsubstituted C1 to C8 alkyl groups.

[0073] The term "C1-C8 alkyl" refers to an alkyl group containing 1 to 8 carbon atoms. Examples of C1-C8 alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, n-hexyl, n-heptyl, n-octyl, etc. In "substituted C1-C8 alkyl," one or more hydrogen atoms may be substituted by other elements or groups. Other elements may include, but are not limited to, F, Cl, O, etc. Other groups may include, but are not limited to, hydroxyl, amino, phenyl, methoxy, etc.

[0074] The positive electrode is the electrode with the highest potential in the battery. The positive electrode sheet is the electrode plate placed on the positive electrode. Positive electrode lithium replenishment material is typically placed on the positive electrode and provides additional active lithium during the first charge or initial charging of the battery. The active lithium provided by the positive electrode lithium replenishment material can be used to compensate for the irreversible loss of active lithium caused by the formation of the SEI film on the negative electrode, thereby increasing the amount of active lithium in the battery and its lifespan.

[0075] The positive electrode lithium replenishment material contains lithium-rich metal oxide, and the lithium replenishment layer uses a polymer (i.e., binder A) comprising a first monomer unit and a second monomer unit as a binder. The first monomer unit in binder A has a carboxyl group, which can undergo an acid-base neutralization reaction with free lithium compounds such as LiOH and Li₂CO₃ on the surface of the lithium-rich metal oxide, thereby lowering the pH value of the positive electrode lithium replenishment material containing lithium-rich metal oxide and effectively improving the gelation problem of the slurry. Simultaneously, the structure of binder A also includes a second monomer unit, which effectively prevents reactions between excessive carboxyl groups in binder A and active lithium ions, thereby reducing active lithium loss and ensuring that more active lithium is used for lithium replenishment. As can be seen, in this application, the binder in the lithium replenishment layer is a polymer comprising a first monomer unit and a second monomer unit, which can improve the stability of the slurry containing lithium-rich metal oxide cathode lithium replenishment material and the slurry has good fluidity. Therefore, the processability of the lithium replenishment layer on the surface of the cathode active material layer is effectively improved, and a tight bond is formed between the lithium replenishment layer and the cathode active material layer. At the same time, it also helps the cathode lithium replenishment material release more lithium ions during charging.

[0076] Therefore, the positive electrode lithium replenishment material in the positive electrode sheet of this application can achieve a high utilization rate of active lithium. The active lithium provided by the positive electrode lithium replenishment material can more effectively compensate for the active lithium loss caused by the formation of the SEI film, thereby improving the initial discharge capacity of the battery and thus enabling the battery to achieve a higher energy density. A portion of the active lithium from the positive electrode lithium replenishment material can also be intercalated into the negative electrode active material, placing the negative electrode active material in a certain lithium-intercalated state, which can alleviate the volume change of the negative electrode active material to a certain extent. Therefore, the risk of negative electrode active material cracking or powder shedding is reduced, while maintaining good electrolyte wettability and liquid retention. This portion of active lithium stored in the negative electrode can also be used to compensate for the active lithium loss during battery cycling in the middle and later stages of cycling. Therefore, the battery can also have a longer cycle life.

[0077] Furthermore, the carboxyl lithium (-COOLi) formed by the reaction of the carboxyl groups in binder A with free lithium compounds can reversibly undergo lithium-ion dissociation and recombination, thus serving as a lithium-ion transport channel and improving the lithium-ion transport performance of the replenishment layer. This not only helps improve the replenishment efficiency but also enables the delithiated replenishment layer to have good ion transport performance, thereby contributing to improved initial charge-discharge capacity and cycle life of the battery.

[0078] Placing the lithium replenishment layer on the surface of the positive electrode active material layer, opposite to the positive electrode current collector, facilitates the release of more lithium ions from the positive electrode lithium replenishment material. Furthermore, the proximity of the lithium replenishment layer to the negative electrode promotes the migration of active lithium extracted from the positive electrode lithium replenishment material to the negative electrode for lithium replenishment. Therefore, the positive electrode lithium replenishment material exhibits high active lithium utilization, resulting in a high active lithium reserve in the battery, which helps improve the battery's initial charge / discharge capacity, energy density, and cycle life.

[0079] After delithiation, the cathode material often undergoes volume shrinkage. Placing the lithium replenishment layer on the surface of the cathode active material layer opposite to the cathode current collector can avoid adversely affecting the electronic conductivity of the cathode active material layer and its relationship with the cathode current collector. In particular, the voids created by particle volume shrinkage can promote electrolyte diffusion into the cathode active material layer inside the electrode, thus enhancing lithium-ion transport. Therefore, the cycle life of the battery can be further improved.

[0080] In some embodiments, the first single-unit satisfies: R 1 R 2 and R 3 Each is independently selected from hydrogen or substituted or unsubstituted C1-C8 alkyl groups. Optionally, R 1 R 2 and R 3 Each alkyl group is independently selected from hydrogen or from substituted or unsubstituted C1-C4 alkyl groups. Alternatively, R... 1 R 2 and R 3 Each is independently selected from hydrogen or methyl. As an example, R 2 and R 3 R represents hydrogen, respectively. 1 It indicates hydrogen or methyl.

[0081] Optionally, the first monomer unit includes one or more of the monomer units shown in Formula S1 and Formula S2.

[0082]

[0083]

[0084] In some embodiments, the second monomer unit satisfies: R 4 R 5 and R 6 Each is independently selected from hydrogen or substituted or unsubstituted C1-C8 alkyl groups. Optionally, R 4 R 5 and R 6 Each alkyl group is independently selected from hydrogen or from substituted or unsubstituted C1-C4 alkyl groups. Alternatively, R... 4 R 5 and R 6Each is independently selected from hydrogen or methyl. As an example, R 4 R represents hydrogen or methyl. 5 and R 6 They represent hydrogen.

[0085] In some embodiments, the second monomer unit satisfies that R is selected from substituted or unsubstituted C1-C8 alkyl groups. Optionally, R is selected from substituted or unsubstituted C1-C4 alkyl groups. As an example, R is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, sec-butyl, or isobutyl. Optionally, R is selected from methyl, ethyl, n-propyl, or n-butyl.

[0086] Optionally, the second monomer unit includes one or more of the monomer units shown in formulas S3 to S8.

[0087] Adhesive A may be selected from polymers comprising any one or more first monomer units and any one or more second monomer units. In some embodiments, adhesive A is selected from polymers comprising monomer units S1 and S5, polymers comprising monomer units S1 and S8, polymers comprising monomer units S1, S5 and S8, polymers comprising monomer units S1, S3, S5 and S8, polymers comprising monomer units S2 and S8, polymers comprising monomer units S2 and S7, polymers comprising monomer units S2 and S5, and polymers comprising monomer units S2 and S6.

[0088] In some embodiments, adhesive A is selected from one or more of the following: polymers of monomer units S1 and S5, polymers of monomer units S1 and S8, polymers of monomer units S1, S5 and S8, polymers of monomer units S1, S3, S5 and S8, polymers of monomer units S2 and S8, polymers of monomer units S2 and S7, polymers of monomer units S2 and S5, and polymers of monomer units S2 and S6. Optionally, adhesive A is selected from one or more of the following: polymers of monomer units S1 and S5, polymers of monomer units S1 and S8, polymers of monomer units S2 and S8, polymers of monomer units S2 and S7, polymers of monomer units S2 and S5, and polymers of monomer units S2 and S6. Further optionally, adhesive A is selected from one or more of the following: polymers of monomer units S1 and S5, polymers of monomer units S1 and S8, polymers of monomer units S2 and S7, and polymers of monomer units S2 and S5. In some examples, adhesive A comprises polymers of monomer units S1 and S5.

[0089] In some embodiments, based on the total weight of the first and second monomer units, the content of the first monomer unit in binder A is 30% to 70%, optionally 40% to 60%. Binder A containing an appropriate amount of the first monomer unit can more fully consume free lithium compounds on the surface of lithium-rich metal oxides, further alleviating the slurry gelation problem. Furthermore, binder A can react with free lithium compounds to form an appropriate amount of carboxylated lithium, thereby improving the lithium-ion transport performance of the lithium replenishment layer. Therefore, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0090] In some embodiments, based on the total weight of the first and second monomer units, the content of the second monomer unit in binder A can be selected as 70% to 30%, and optionally 60% to 40%. The binder A containing an appropriate amount of the second monomer unit can further reduce active lithium loss and improve the utilization rate of active lithium for lithium replenishment. Furthermore, an appropriate content of the second monomer unit helps to give binder A a suitable molecular chain segment length, thereby enabling binder A to perform better cross-linking and bonding, improving the adhesion between particles in the lithium replenishment layer and between the lithium replenishment layer and the positive electrode active material layer. Simultaneously, the compressive strength of the positive electrode sheet can be improved.

[0091] In some embodiments, the weight-average molecular weight of binder A is 30,000 to 600,000, optionally 50,000 to 600,000, 50,000 to 500,000, 100,000 to 400,000, 100,000 to 300,000, 150,000 to 350,000, 180,000 to 300,000, or 150,000 to 250,000. When the molecular weight of binder A is within an appropriate range, it can provide sufficient carboxyl groups to alleviate slurry gelation problems, reduce active lithium loss to improve the capacity utilization rate of the positive electrode lithium replenishment material, and simultaneously provide good cross-linking and entanglement for the positive electrode lithium replenishment material, thereby enhancing the adhesion of binder A.

[0092] In some embodiments, the binder A accounts for 2% to 7% of the weight of the lithium replenishment layer, optionally 3% to 6%, 3% to 4.5%, or 3.5% to 5%. The lithium replenishment layer containing an appropriate amount of binder A effectively alleviates the slurry gelation problem and fosters strong adhesion between the particles of the lithium replenishment layer and between the lithium replenishment layer and the positive electrode active material layer. Simultaneously, the lithium replenishment layer can also have a high proportion of positive electrode lithium replenishment material. Therefore, both the energy density and cycle life of the battery can be improved.

[0093] In some embodiments, the specific capacity of the positive electrode lithium replenishment material is ≥400 mAh / g, optionally ≥450 mAh / g, ≥500 mAh / g, ≥600 mAh / g, ≥700 mAh / g, or ≥900 mAh / g. The specific capacity of the positive electrode lithium replenishment material is the ratio of the capacity released by the positive electrode lithium replenishment material to its mass. A higher specific capacity of the positive electrode lithium replenishment material allows for the use of a thinner lithium replenishment layer to provide more active lithium for lithium replenishment, thereby increasing the amount of active lithium in the negative electrode while ensuring that the positive electrode has high ion transport performance, thus further improving the battery's initial charge-discharge capacity and cycle life.

[0094] In some embodiments, the lithium-rich metal oxide may be selected from Li3M. 1 O4, Li5M 2 O4, Li6M 3 One or more of O4. M 1 It may include one or more of V, Nb, Cr, and Mo. Optionally, M 1 It includes one or more of V, Nb, and Mo. As an example, Li3M 1 O4 may include one or more of Li3VO4, Li3NbO4, and Li3MoO4. Optionally, Li3M 1 O4 includes one or more of Li3VO4 and Li3NbO4. M 2 It may include one or more of Fe, Cr, V, Mo, and Al. Optionally, M 2 This includes one or more of Fe, Cr, and V. As an example, Li5M 2 O4 may include one or more of Li5FeO4, Li5CrO4, and Li5VO4. Optionally, Li5M 2 O4 includes Li5FeO4. M 3 It may include one or more of Co, V, Cr, and Mo. Optionally, M 3 This includes one or more of Co, V, and Cr. As an example, Li6M... 3 O4 may include one or more of Li6CoO4, Li6VO4, and Li6CrO4. Optionally, Li6M 3 O4 includes Li6CoO4. In lithium-rich metal oxides, the valence state of each metal element except Li is lower than its highest oxidation state.

[0095] The aforementioned lithium-rich metal oxides can have high specific capacity. Optionally, the lithium-rich metal oxides are selected from one or more of Li3VO4, Li3NbO4, Li5FeO4, and Li6CoO4.

[0096] In some embodiments, the lithium-rich metal oxide may also be optionally selected from other lithium-rich metal oxides that can be used as cathode lithium replenishment materials. For example, Li₂M 4 O2, Li2M 5 One or more of O3. M 4 It may include one or more of Ni, Co, Fe, Mn, Zn, Mg, Ca, and Cu. As an example, Li₂M 4 O2 may include Li2NiO2, Li2MnO2, Li2CuO2, Li2Ni 0.6 Cu 0.4 O2, Li2Co 0.6 Mn 0.4 One or more of O2, etc. M 5 It can include one or more of Mn, Sn, Mo, Ru, and Ir. As an example, Li₂M 5 O3 can include one or more of Li2MnO3 and Li2MoO3. In lithium-rich metal oxides, the valence state of each metal element except Li is lower than its highest oxidation state.

[0097] In some embodiments, the lithium-rich metal oxide comprises single-crystal particles. The percentage of single-crystal particles in the lithium-rich metal oxide can be selected as 60%–100%, and optionally 80%–100%, 90%–100%, or 95%–100%. The lithium-rich metal oxide, predominantly composed of single-crystal particles, improves the compressive strength of the lithium replenishment layer and the positive electrode active material layer, thereby reducing particle cracking under pressure (e.g., electrode rolling pressure and battery cycle expansion force), thus improving particle structure stability. Therefore, the battery achieves extended cycle life. Furthermore, the positive electrode active material layer can achieve a higher compaction density, which is beneficial for improving the battery's energy density.

[0098] Optionally, the volume average particle size D of lithium-rich metal oxides v The thickness of 50 is 5μm to 25μm, optionally 6μm to 20μm, 8μm to 16μm, 10μm to 15μm, or 11μm to 13μm. The lithium-rich metal oxide contains a large number of single-crystal particles while also satisfying D... v Within an appropriate range, 50 can further improve the compressive strength of the lithium replenishment layer and the positive electrode active material layer, thereby further improving the cycle life and energy density of the battery.

[0099] In some embodiments, the pH of the positive electrode lithium replenishment material is ≤13, and optionally, pH is ≤12.5. The pH of the positive electrode lithium replenishment material is determined by titration. The reagent solution used for titration is, for example, a standard hydrochloric acid solution. An exemplary test method is as follows: 30g of the positive electrode lithium replenishment material is added to 100mL of deionized water and stirred at 200 rpm for 30min to obtain the sample to be tested; the free lithium compounds in the sample to be tested are titrated with a standard hydrochloric acid solution, using a composite pH electrode as the indicator electrode, and the titration endpoint is determined by the abrupt change in potential, thus testing the pH of the positive electrode lithium replenishment material.

[0100] Having a pH within the aforementioned range for the positive electrode lithium replenishment material helps to further reduce the risk of gelation in the lithium replenishment layer slurry. Optionally, the pH of the positive electrode lithium replenishment material is 11–13, preferably 11–12.5, or 12–12.5. This positive electrode lithium replenishment material can have a high specific capacity.

[0101] In some embodiments, the positive electrode lithium replenishment material accounts for 90% to 97% of the weight of the lithium replenishment layer, optionally 92% to 96%, 92.5% to 95%, or 93% to 95%. An appropriate proportion of positive electrode lithium replenishment material provides more active lithium, achieving a good lithium replenishment effect, thereby improving the battery's initial charge-discharge capacity and cycle life.

[0102] In some embodiments, the conductive agent accounts for 1% to 3% of the weight of the lithium replenishment layer, optionally 1.5% to 2.5%. The lithium replenishment layer contains an appropriate amount of conductive agent, which can improve the electronic conductivity of the lithium replenishment layer, thus helping the positive electrode lithium replenishment material to release more lithium ions, thereby improving the battery's first charge-discharge capacity and cycle life.

[0103] The conductive agent in the lithium replenishment layer can be any conductive agent known in the art for use in secondary batteries. For example, the conductive agent in the lithium replenishment layer can be selected from one or more of superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, based on the total thickness of the positive electrode active material layer and the lithium replenishment layer, the thickness ratio of the lithium replenishment layer is 3% to 22%, optionally 5% to 20%, 8% to 15%, 10% to 14%, 11% to 13%, 8% to 20%, 10% to 18%, or 12% to 16%. A suitable thickness ratio of the lithium replenishment layer ensures both an appropriate proportion of positive electrode lithium replenishment material for effective lithium replenishment and an appropriate proportion of positive electrode active material to provide high reversible capacity, thus enabling the battery to achieve high energy density and cycle life. Furthermore, an appropriate thickness ratio of the lithium replenishment layer facilitates process control and reduces fabrication difficulty.

[0105] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material refers to the material in the positive electrode sheet that participates in the insertion and extraction of active ions during the battery charging and discharging process. In the positive electrode sheet of this application, the positive electrode active material can be an active material known in the art for use in secondary battery positive electrodes. As an example, the positive electrode active material may include one or more of the following: polyanionic positive electrode materials, lithium transition metal oxides, and modified materials of the above substances. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). x1 Co y1 Mn z1 O2, where 0 < x1 < 1, 0 < y1 < 1, 0 < z1 < 1, x1 + y1 + z1 = 1. A specific example is LiNi. 1 / 3Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2), lithium nickel cobalt aluminum oxide (such as LiNi) x2 Co y2 Al z2 O2, where 0 < x2 < 1, 0 < y2 < 1, 0 < z2 < 1, x2 + y2 + z2 = 1. Specific examples include LiNi. 0.85 Co 0.15 Al 0.05 O2) and one or more of the above-mentioned modified materials. Examples of polyanionic cathode materials include, but are not limited to, lithium iron phosphate (such as LiFePO4), lithium manganese phosphate (such as LiMnPO4), lithium vanadium phosphate (such as Li3V2(PO4)3), and lithium manganese iron phosphate (such as LiFe x3 Mn 1-y3 The active material is selected from PO4 (where 0 < y3 < 1) and one or more of the modified materials mentioned above. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries can also be used. A single positive electrode active material can be used alone, or two or more materials can be used in combination.

[0106] In this application, the modified material for lithium transition metal oxide or polyanion cathode material can be a coating modified material, a doping modified material, or a combination of doping and coating modified material.

[0107] In some embodiments, the positive electrode active material accounts for 95% to 98% of the weight of the positive electrode active material layer.

[0108] In some embodiments, the positive electrode active material layer may optionally include a binder. The binder may be one or more binders known in the art for positive electrode active material layers. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0109] In some embodiments, the binder accounts for 1% to 3% of the weight of the positive electrode active material layer, optionally 1% to 2%, or 1.5% to 2.5%.

[0110] Further research by the inventors revealed that by designing a combination of the binder for the positive electrode active material layer and the binder for the lithium replenishment layer, the performance of the positive electrode sheet can be further improved.

[0111] In some embodiments, the positive electrode active material layer includes binder B and binder C, wherein binder B includes one or more of PVDF and PTFE, and binder C is selected from one or more polymers comprising the group consisting of the third monomer unit represented by Formula III and the fourth monomer unit represented by Formula IV.

[0112]

[0113] In Equation III, R a R b and R c Each is independently selected from hydrogen or substituted or unsubstituted C1-C8 alkyl groups. Optionally, R a R b and R c Each alkyl group is independently selected from hydrogen or from substituted or unsubstituted C1-C4 alkyl groups. Alternatively, R... a R b and R c Each is independently selected from hydrogen or methyl. In some embodiments, R a Selected from hydrogen or methyl, R b and R c Each represents hydrogen. As an example, the third monomer unit includes one or more of the monomer units shown in Formula S1 and Formula S2.

[0114] In equation IV, Rd R e and R f Each is independently selected from hydrogen or substituted or unsubstituted C1-C8 alkyl groups. Optionally, R d R e and R f Each alkyl group is independently selected from hydrogen or from substituted or unsubstituted C1-C4 alkyl groups. Alternatively, R... d R e and R f Each is independently selected from hydrogen or methyl. In some embodiments, R d Selected from hydrogen or methyl, R e and R f They represent hydrogen.

[0115] In Formula IV, R' is selected from substituted or unsubstituted C1-C8 alkyl groups. Optionally, R' is selected from substituted or unsubstituted C1-C4 alkyl groups. As an example, R' is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, sec-butyl, or isobutyl. Optionally, R' is selected from methyl, ethyl, n-propyl, or n-butyl.

[0116] As an example, the fourth monomer unit includes one or more of the monomer units shown in Equations S3 to S8.

[0117] In some embodiments, the adhesive C may be selected from one or more of the following: polymer C-1 comprising any one or more third monomer units, polymer C-2 comprising any one or more fourth monomer units, and polymer C-3 comprising any one or more third monomer units and any one or more fourth monomer units. Examples of polymer C-1 may be polymers comprising monomer unit S1, polymers comprising monomer unit S2, and polymers comprising monomer units S1 and S2; further examples may be polymers comprising monomer unit S1, polymers comprising monomer unit S2, and polymers comprising monomer units S1 and S2. Examples of polymer C-2 may be polymers comprising monomer unit S3, polymers comprising monomer unit S4, polymers comprising monomer unit S5, polymers comprising monomer units S5 and S8, polymers comprising monomer units S3, S5, and S8, etc.; further examples may be polymers comprising monomer unit S3, polymers comprising monomer unit S4, polymers comprising monomer unit S5, polymers comprising monomer units S5 and S8, and polymers comprising monomer units S3, S5, and S8. Examples of polymer C-3 may be selected from polymers including monomer units S1 and S5, polymers including monomer units S1 and S8, polymers including monomer units S1, S5 and S8, polymers including monomer units S1, S3, S5 and S8, polymers including monomer units S2 and S8, polymers including monomer units S2 and S7, polymers including monomer units S2 and S5, polymers including monomer units S2 and S6, etc.; further selected from polymers including monomer units S1 and S5, polymers including monomer units S1 and S8, polymers including monomer units S1, S5 and S8, polymers including monomer units S1, S3, S5 and S8, polymers including monomer units S2 and S8, polymers including monomer units S2 and S7, polymers including monomer units S2 and S5, polymers including monomer units S2 and S6. Optionally, adhesive C may be selected from one or more of polymers C-1 and C-3.

[0118] In some embodiments, the content of binder C is 5% to 20% based on the total weight of binder B and binder C. The presence of binder C in the positive electrode active material layer improves the bonding strength at the interface between the positive electrode active material layer and the lithium replenishment layer, enabling the formation of a good conductive network at the interface, thereby further improving the cycle performance of the battery. Simultaneously, the positive electrode active material layer also contains an appropriate amount of binder B, which reduces active lithium loss and ensures that more active lithium ions are used during the battery charging / discharging process. Therefore, the initial charge / discharge capacity and cycle life of the battery can be further improved.

[0119] In some embodiments, the weight-average molecular weight of binder C is 50 to 5000, optionally 100 to 4000. When the weight-average molecular weight of binder C is within an appropriate range, it can improve the interfacial bonding strength between the positive electrode active material layer and the lithium replenishment layer, while also consuming free lithium compounds on the surface of the positive electrode active material and ensuring minimal loss of active lithium due to reaction with binder C. Therefore, it can further improve the battery's initial charge-discharge capacity and cycle life.

[0120] In some embodiments, the positive electrode active material in the positive electrode active material layer comprises a layered lithium transition metal oxide, wherein the content of binder C is 5% to 20%, optionally 10% to 20%, further optionally 12% to 18%, or 13% to 17%, based on the total weight of binder B and binder C. The layered lithium transition metal oxide can be any lithium transition metal oxide known in the art as a positive electrode active material and having a layered structure, such as those described herein. In some embodiments, the layered lithium transition metal oxide comprises one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified materials thereof. The inventors have found that if the positive electrode active material comprises a layered lithium transition metal oxide, and the positive electrode active material layer contains an appropriate proportion of binder C, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0121] In these embodiments, the weight-average molecular weight of binder C is optionally 500–4000, optionally 1000–3000, or 1500–2800. If the positive electrode active material comprises layered lithium transition metal oxide, and the weight-average molecular weight of binder C is within the given range, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0122] Optionally, the binder C is selected from polymer C-1, which includes any one or more third monomer units. Further optionally, the binder C is selected from polymers including monomer units S1. Further optionally, the binder C is selected from polymers including monomer units S1. If the positive electrode active material includes layered lithium transition metal oxides, and the binder C is selected from polymer C-1, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0123] Optionally, the compaction density of the positive electrode active material layer is 3.5 g / cm³. 3 ~3.8g / cm 3 Optionally, it can be 3.5g / cm³. 3 ~3.65g / cm 3 3.55g / cm 3 ~3.65g / cm 3 3.5g / cm 3 ~3.6g / cm 3 , or 3.55g / cm3 ~3.6g / cm 3 Among them, the volume average particle size D of the positive electrode active material v The thickness of the positive electrode active material layer is 2μm to 10μm, and optionally 4μm to 8μm. A higher compaction density is achieved in this layer, which improves the energy density of the battery. Optionally, the positive electrode active material is a secondary particle formed by the polymerization of multiple primary particles.

[0124] In some embodiments, the positive electrode active material in the positive electrode active material layer comprises a polyanionic positive electrode material, wherein the content of binder C is 5% to 15% based on the total weight of binder B and binder C, optionally 5% to 12%, 5% to 10%, 6% to 10%, or 7% to 9%. The polyanionic positive electrode material can be any polyanionic positive electrode material known in the art as a positive electrode active material, such as those described herein. In some embodiments, examples of polyanionic positive electrode materials may include olivine-structured lithium-containing phosphates. Olivine-structured lithium-containing phosphates are selected, for example, from one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and modified materials of the above substances. The inventors have found that if the positive electrode active material comprises a polyanionic positive electrode material, and the positive electrode active material layer contains an appropriate proportion of binder C, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0125] In these embodiments, the weight-average molecular weight of the binder C is optionally 100–3000, optionally 500–3000, 500–1500, 800–1500, or 800–1200. If the positive electrode active material includes a polyanionic positive electrode material, and the weight-average molecular weight of the binder C is within the given range, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0126] Optionally, the binder C is selected from one or more polymers C-3 that include any one or more third monomer units and any one or more fourth monomer units. If the positive electrode active material includes a polyanionic positive electrode material, and the binder C is selected from polymer C-3, the initial charge-discharge capacity and cycle life of the battery can be further improved.

[0127] Optionally, the adhesive C is selected from one or more polymers including one or more of monomer units S1 to S2 and one or more of S3 to S8. As an example, the adhesive C may be selected from one or more of the following polymers: polymers including monomer units S1 and S2, polymers including monomer units S1 and S3, polymers including monomer units S1 and S4, polymers including monomer units S1 and S5, polymers including monomer units S1 and S6, polymers including monomer units S1 and S7, polymers including monomer units S1 and S8, polymers including monomer units S1, S5 and S8, polymers including monomer units S1, S3, S5 and S8, polymers including monomer units S2 and S8, polymers including monomer units S2 and S7, polymers including monomer units S2 and S3, polymers including monomer units S2 and S4, polymers including monomer units S2 and S5, and polymers including monomer units S2 and S6. Further optionally, the adhesive C may be selected from one or more of the following polymers: polymers of monomer units S1 and S2, polymers of monomer units S1 and S3, polymers of monomer units S1 and S4, polymers of monomer units S1 and S5, polymers of monomer units S1 and S6, polymers of monomer units S1 and S7, polymers of monomer units S1 and S8, polymers of monomer units S1, S5 and S8, polymers of monomer units S1, S3, S5 and S8, polymers of monomer units S2 and S8, polymers of monomer units S2 and S7, polymers of monomer units S2 and S3, polymers of monomer units S2 and S4, polymers of monomer units S2 and S5, and polymers of monomer units S2 and S6. Also optionally, the adhesive C may be selected from one or more of the following polymers: polymers of monomer units S1 and S7, polymers of monomer units S1 and S6, and polymers of monomer units S2 and S7.

[0128] Optionally, the compaction density of the positive electrode active material layer is 2.4 g / cm³. 3 ~2.7g / cm 3 Optionally, it can be 2.4 g / cm³. 3 ~2.55g / cm 3 2.45g / cm 3 ~2.55g / cm 3 2.4g / cm 3 ~2.5g / cm 3 , or 2.45g / cm 3 ~2.5g / cm 3 Among them, the volume average particle size D of the positive electrode active material vThe particle size of 50 is 0.2 μm to 1.5 μm, optionally 0.5 μm to 1.2 μm, or 0.6 μm to 1.0 μm. A higher compaction density in the positive electrode active material layer improves the energy density of the battery. Optionally, the polyanionic positive electrode material is a non-aggregated primary particle.

[0129] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE, etc.).

[0130] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] In some embodiments, the conductive agent accounts for 1% to 2% of the weight of the positive electrode active material layer.

[0132] In the positive electrode of this application, the positive active material layer can be disposed on one side of the positive current collector, or it can be disposed on both sides of the positive current collector. A lithium replenishment layer is provided on the positive active material layer on at least one side of the positive current collector.

[0133] Figure 1 This is an example of a positive electrode sheet. The positive electrode sheet consists of a positive current collector 11, positive active material layers 12 respectively disposed on both sides of the positive current collector 11, and a lithium replenishment layer 13 disposed on the positive active material layer 12.

[0134] Figure 2 This is another example of a positive electrode. The positive electrode consists of a positive current collector 11, a positive active material layer 12 disposed on one side of the positive current collector 11, and a lithium replenishment layer 13 disposed on the positive active material layer 12.

[0135] It should be noted that the film parameters (such as film thickness, compaction density, etc.) given in this application refer to the parameter range of the film layer on one side of the positive electrode current collector. When a positive electrode active material layer and a lithium replenishment layer are provided on both sides of the positive electrode current collector, the film parameters on either side that meet the requirements of this application are considered to fall within the protection scope of this application. Furthermore, the film thickness, compaction density, and other ranges mentioned in this application refer to the film parameters after cold pressing and compaction and used for battery assembly.

[0136] In this application, the thickness of the lithium replenishment layer has a meaning known in the art and can be measured using methods and instruments known in the art. For example, it can be measured using a scanning electron microscope (SEM). An exemplary test method is as follows: fabricate a cross-section of the positive electrode sheet in the thickness direction; use a scanning electron microscope (e.g., ZEISS Sigma 300) to measure the thickness of the lithium replenishment layer. The cross-section of the positive electrode sheet can be obtained using an ion polisher (e.g., an argon ion cross-section polisher, such as IB-19500CP). Using a scanning electron microscope, a clear interface between the lithium replenishment layer and the positive electrode active material layer can be observed in the cross-section, thus facilitating thickness measurement.

[0137] In this application, the volume average particle size D of the positive electrode active material is... v 50 has a well-known meaning in the art and can be determined using methods and instruments known in the art. For example, it can be determined using a laser particle size analyzer (e.g., Malvern Mastersizer 2000E) according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. Wherein, D v 50 indicates the particle size corresponding to a cumulative volume distribution percentage of 50%.

[0138] In this application, the percentage of single-crystal particles in lithium-rich metal oxide has a meaning known in the art and can be determined using methods and instruments known in the art. For example, scanning electron microscopy (SEM) can be used. An exemplary testing method includes: laying and adhering lithium-rich metal oxide onto conductive adhesive to form a sample to be tested, measuring 6 cm in length and 1.1 cm in width; and testing the particle morphology using a scanning electron microscope (e.g., ZEISS Sigma 300). The test can be referenced in JY / T010-1996. To ensure the accuracy of the test results, multiple (e.g., 5) different regions can be randomly selected from the sample to be tested for scanning, and at a certain magnification (e.g., 1000x), the percentage of single-crystal particles in each region relative to the total number of particles can be calculated, which is the percentage of single-crystal particles in that region. The average of the test results from multiple test regions is taken as the test result. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be used to repeat the above test, and the average of each test sample is taken as the final test result.

[0139] In this application, the compaction density of the positive electrode active material layer has a meaning known in the art and can be measured using methods and instruments known in the art. The compaction density of the positive electrode active material layer = weight of the positive electrode active material layer / (thickness of the positive electrode active material layer × area of ​​the positive electrode active material layer).

[0140] Next, the secondary battery, battery module, battery pack, and power supply device of this application will be described with appropriate reference to the accompanying drawings.

[0141] In one embodiment of this application, a secondary battery is provided.

[0142] Typically, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes.

[0143] [Positive electrode plate]

[0144] In the secondary battery of this application, the positive electrode can be one or more of the positive electrode types described in this application. Therefore, the secondary battery can achieve higher initial charge-discharge capacity and energy density, as well as a longer cycle life.

[0145] [Negative electrode plate]

[0146] In the secondary battery of this application, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material. As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0147] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE, etc.).

[0148] In some embodiments, the negative electrode active material may be an active material known in the art for use as a negative electrode in secondary batteries. For example, the negative electrode active material may include one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in secondary batteries may also be used. A single negative electrode active material may be used, or two or more may be used in combination.

[0149] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0150] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from one or more of superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0151] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose, CMC-Na).

[0152] [Electrolytes]

[0153] This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0154] In some embodiments, the electrolyte may be an electrolyte solution. The electrolyte solution includes an electrolyte lithium salt and a solvent.

[0155] In some embodiments, the electrolyte lithium salt may be selected from electrolyte lithium salts known in the art that can be used in secondary battery electrolytes. For example, one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)methyl lithium, tri(trifluoromethanesulfonyl)methyl lithium, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0156] In some embodiments, the electrolyte lithium salt may include a fluorinated electrolyte lithium salt. Optionally, the fluorinated electrolyte lithium salt may be selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorodiooxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)methyllithium, and tri(trifluoromethanesulfonyl)methyllithium. Electrolytes using fluorinated electrolyte salts often contain trace amounts of HF. In this application, a lithium replenishment layer is disposed on the surface of the positive electrode active material layer opposite to the positive electrode current collector. The lithium-rich metal oxides therein, after delithiation, can preferentially react with HF in the electrolyte, thereby protecting the internal positive electrode active material layer and reducing the loss of positive electrode active material. Therefore, the battery can achieve a longer cycle life. In particular, the metal fluoride formed by the reaction can also improve the lithium-ion migration performance of the lithium replenishment layer.

[0157] In some embodiments, the solvent may be selected from one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0158] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0159] [Isolation membrane]

[0160] In some embodiments, the secondary battery further includes a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. As an example, the separator material can be selected from one or more of the following: glass fiber film, non-woven fabric, polyethylene film, polypropylene film, and polyvinylidene fluoride film, or a composite film of two or more of the above films.

[0161] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0162] In some embodiments, the secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above. The outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0163] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0164] In some embodiments, refer to Figure 4The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0165] In some embodiments, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0166] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0167] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0168] In some embodiments, the secondary batteries or battery modules can also be assembled into a battery pack. The number of secondary batteries or battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0169] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0170] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0171] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0172] Figure 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0173] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0174] This application also provides a method for preparing a secondary battery. The method includes preparing the positive electrode sheet of the secondary battery through the following steps: forming a positive electrode active material layer on at least one surface of a positive electrode current collector; forming a lithium replenishment layer on the surface of the positive electrode active material layer opposite to the positive electrode current collector, wherein the lithium replenishment layer comprises a positive electrode lithium replenishment material, a conductive agent, and a binder A, wherein the positive electrode lithium replenishment material comprises a lithium-rich metal oxide, and the binder A is selected from a polymer comprising a first monomer unit and a second monomer unit.

[0175]

[0176] Wherein, the R 1 R 2 R 3 R 4 R 5 and R 6 Each R is independently selected from hydrogen or substituted or unsubstituted C1 to C8 alkyl groups, wherein R is selected from substituted or unsubstituted C1 to C8 alkyl groups.

[0177] The positive electrode active material layer can be prepared by dispersing the positive electrode active material, optional conductive agent, optional binder and any other optional components in a solvent (e.g., N-methylpyrrolidone NMP) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector to form a positive electrode coating; and drying and cold pressing the positive electrode coating to form the positive electrode active material layer.

[0178] The lithium replenishment layer can be prepared by the following method: dispersing the positive electrode lithium replenishment material, conductive agent, binder A and any other optional components in a solvent (e.g., NMP) to form a lithium replenishment layer slurry; coating the lithium replenishment layer slurry onto the positive electrode active material layer or positive electrode coating to form a lithium replenishment coating; and drying and cold pressing the lithium replenishment coating to form a lithium replenishment layer.

[0179] In some embodiments, a positive electrode coating may first be formed on the surface of the positive electrode current collector; after the positive electrode coating is dried and cold-pressed, a positive electrode active material layer is formed; then a lithium replenishment coating is coated on the positive electrode active material layer; after the lithium replenishment coating is dried and cold-pressed, a lithium replenishment layer is formed.

[0180] In some embodiments, a positive electrode coating may first be formed on the surface of the positive electrode current collector; after the positive electrode coating is dried, a lithium replenishment coating is applied; after the lithium replenishment coating is dried, the positive electrode coating and the lithium replenishment coating are cold-pressed to form a positive electrode active material layer and a lithium replenishment layer.

[0181] In some embodiments, a positive electrode coating can be formed on the surface of the positive electrode current collector, and a lithium replenishment coating can be formed on the positive electrode coating; then, after drying and cold pressing, a positive electrode active material layer and a lithium replenishment layer are formed. In these embodiments, the positive electrode slurry and the lithium replenishment layer slurry can be coated simultaneously in one step or coated in two steps. Optionally, the positive electrode slurry and the lithium replenishment layer slurry can be coated simultaneously in one step. Simultaneous coating in one step can improve the adhesion between the positive electrode active material layer and the lithium replenishment layer.

[0182] Besides the method for preparing the positive electrode sheet of this application, other structures and preparation methods of the secondary battery of this application are known. For example, the negative electrode sheet of this application can be prepared by the following method: dispersing the negative electrode active material, as well as optional conductive agent, optional binder and any other optional components in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0183] In some embodiments, a negative electrode, a positive electrode, a separator, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process; the electrode assembly is placed in an outer package, an electrolyte is injected, and the secondary battery is obtained through processes such as vacuum sealing, settling, formation, and shaping.

[0184] In this application, binder A and binder C can each be a random copolymer. The term "random" means that the comonomers of the random copolymer are randomly distributed within the copolymer in this application. Binder A and binder C are commercially available or can be prepared using conventional polymerization methods in the art. Binder A and binder C can be prepared using similar methods. Taking an exemplary preparation method of binder A as an example, a monomer mixture including a first monomer and a second monomer can be polymerized in the presence of an initiator to obtain binder A.

[0185] First monomer: Second monomer:

[0186] R 1 R 2 R 3 R 4 R 5 R 6 R and R are defined as in this paper.

[0187] As a specific example, the monomer units shown in S1 to S8 can be derived from the monomers shown in m1 to m8 below, respectively.

[0188]

[0189]

[0190] There are no particular limitations on the type of initiator; any conventional choice in the field can be used. For example, the initiator can be one or more of azobisisobutyronitrile, azobisisobutyramidine hydrochloride, azobisisobutyramidazole hydrochloride, azobisisobutyramidazole, azobisisopropylimidazoline, etc. There are no particular limitations on the polymerization reaction conditions and the amount of initiator used; they can be selected according to the specific types of monomers and initiators. For example, if the monomer mixture contains a first monomer m1 and a second monomer m5, and the initiator is azobisisobutyronitrile, the amount of initiator used is 0.05–0.15 parts by weight relative to 100 parts by weight of the monomer mixture. The polymerization temperature is 25°C–45°C, the polymerization is carried out at atmospheric pressure, and the polymerization time is 2–8 hours.

[0191] In the adhesive A described in this application, the first monomer unit is derived from the first monomer; the second monomer unit is derived from the second monomer. The content ratio of the first monomer unit and the second monomer unit can be calculated according to the content ratio of the first monomer and the second monomer, that is, the content ratio of the first monomer unit and the second monomer unit can be considered to be approximately equal to the feeding ratio of the first monomer and the second monomer.

[0192] Similarly, in the adhesive C described in this application, the third monomer unit is derived from the third monomer; the fourth monomer unit is derived from the fourth monomer.

[0193] Third monomer: Fourth monomer:

[0194] R a R b R c R d R e R f R and R' are defined as in this paper.

[0195] The optional technical features of the secondary battery in this application are also applicable to the preparation method of this application, and the corresponding technical effects are obtained.

[0196] Example

[0197] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0198] The adhesive A used in the following embodiments is selected from A1 to A16, as specifically listed in Table 1. The first monomer unit content in Table 1 refers to the content of the first monomer unit based on the total weight of the first and second monomer units.

[0199] Table 1

[0200]

[0201] The adhesive C used in the following embodiments is selected from C1 to C11, as specifically listed in Table 2. The third monomer unit content in Table 2 refers to the content of the third monomer unit based on the total weight of the third and fourth monomer units.

[0202] Table 2

[0203]

[0204] The binder used for the lithium replenishment layers in the following comparative examples is selected from:

[0205] Adhesive D1: Polyvinylidene fluoride (PVDF); weight-average molecular weight is 20,000;

[0206] Adhesive D2: Polyacrylic acid (PAA); weight average molecular weight is 20,000;

[0207] Adhesive D3: A mixture of PAA and ethyl polyacrylate; both PAA and ethyl polyacrylate have a weight-average molecular weight of 20,000; based on the total weight of PAA and ethyl polyacrylate, the content of PAA is 50%;

[0208] Adhesive D4: PVDF; weight-average molecular weight is 200,000;

[0209] Adhesive D5: PAA; weight-average molecular weight is 200,000;

[0210] Adhesive D6: A mixture of PAA and ethyl polyacrylate; both PAA and ethyl polyacrylate have a weight-average molecular weight of 200,000; based on the total weight of PAA and ethyl polyacrylate, the content of PAA is 50%.

[0211] The lithium-rich metal oxides used in the following embodiments and comparative examples are all single-crystal particles.

[0212] Example 1

[0213] Preparation of positive electrode sheet

[0214] The positive electrode active material LiFePO4 (abbreviated as LFP), conductive agent Super P, and binder PVDF (weight average molecular weight approximately 1 million) were dispersed in the solvent NMP at a weight ratio of 97:2:1 and stirred until homogeneous to obtain the positive electrode slurry. The positive electrode active material D... v 50 is 0.8μm.

[0215] Lithium-replenishing cathode material Li5FeO4 (LFO), conductive agent Super P, and binder A3 were dispersed in NMP solvent at a weight ratio of 94:2:4 and stirred until homogeneous to obtain a lithium-replenishing layer slurry. The specific capacity of the LFO cathode material is 690 mAh / g. The D of the lithium-replenishing cathode material... v 50 is 12μm.

[0216] A positive electrode slurry is coated onto two opposite surfaces of a positive electrode current collector aluminum foil to form a positive electrode coating. Simultaneously, a lithium replenishment layer slurry is coated onto the surface of the positive electrode coating opposite to the positive electrode current collector. After drying and cold pressing, a positive electrode sheet is obtained. The positive electrode sheet includes a positive active material layer and a lithium replenishment layer disposed on the surface of the positive active material layer opposite to the positive electrode current collector. The compaction density of the positive active material layer is 2.5 g / cm³. 3 The thickness of the positive electrode active material layer is 82.8 μm. The thickness of the lithium replenishment layer is 4.35 μm.

[0217] Preparation of negative electrode sheet

[0218] Artificial graphite (anode active material), Super P (conductive agent), SBR (binder), and CMC-Na (thickener) were dispersed in deionized water at a weight ratio of 96:1.5:1.5:1.0 and stirred until homogeneous to obtain a cathode slurry. The cathode slurry was then coated onto the two opposite surfaces of a copper foil current collector. After drying and cold pressing, a cathode electrode sheet was obtained. The compaction density of the cathode active material layer was 1.65 g / cm³. 3 The thickness is 200μm.

[0219] Preparation of electrolyte

[0220] Ethyl carbonate (EC) and ethyl methyl carbonate (EMC) are mixed evenly at a weight ratio of 30:70 to obtain an organic solvent; lithium salt LiPF6 is then dissolved in the above organic solvent and mixed evenly to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0221] Preparation of secondary batteries

[0222] The positive electrode sheet, the porous polyethylene (PE) separator, and the negative electrode sheet are stacked in sequence and then wound to obtain an electrode assembly. The electrode assembly is then placed in an outer package, injected with electrolyte, and sealed to obtain a secondary battery.

[0223] Examples 2-16 and Comparative Examples 1-3: The preparation of the secondary battery was similar to that of Example 1, except that the relevant parameters in the preparation of the positive electrode were adjusted, as detailed in Table 3.

[0224] Example 17 and Comparative Examples 4-6: The preparation of the secondary battery was similar to that in Example 1, except that the positive electrode active material was LiNi. 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as NCM811); D of the positive electrode active material v The thickness of the 50 layer is 6 μm; the weight-average molecular weight of the PVDF binder is approximately 1.1 million; the compaction density of the positive electrode active material layer is 3.6 g / cm³. 3 The thickness of the lithium replenishment layer is 14.61 μm; the compaction density of the negative electrode active material layer is 2.35 g / cm³. 3 The thickness is 250μm; other differences are detailed in Table 3.

[0225] Examples 18-20: The preparation of the secondary batteries was similar to that in Example 3, except that the relevant parameters in the preparation of the positive electrode were adjusted, as detailed in Table 4. The specific capacity of the positive electrode lithium replenishment material Li3VO4 was 590 mAh / g; the specific capacity of the positive electrode lithium replenishment material Li3NbO4 was 450 mAh / g; and the specific capacity of the positive electrode lithium replenishment material Li6CoO4 was 970 mAh / g.

[0226] Examples 21-27: The preparation of the secondary battery is similar to that of Example 3, except that the relevant parameters in the preparation of the positive electrode are adjusted, as detailed in Table 5.

[0227] Examples 28-36: The preparation of the secondary battery is similar to that of Example 3, except that the binder in the positive electrode slurry is a combination of PVDF and binder C; other differences are detailed in Table 6.

[0228] Examples 37-45: The preparation of the secondary battery is similar to that in Example 17, except that the binder in the positive electrode slurry is a combination of PVDF and binder C; other differences are detailed in Table 6.

[0229] In the table, the lithium replenishment layer thickness percentage is based on the total thickness of the positive electrode active material layer and the lithium replenishment layer. The binder C content refers to the binder C content based on the total weight of binder B and binder C.

[0230] Test section

[0231] (1) Initial discharge capacity and cycle life test of secondary battery

[0232] At 25℃, the secondary battery is charged at a constant current rate of 1C to the upper limit cutoff voltage, and then charged at a constant voltage until the current reaches 0.05C. The charging capacity at this point is recorded as the first charge capacity. Next, it is discharged at a constant current rate of 1C to the lower limit cutoff voltage, and then allowed to stand for 5 minutes. This completes one charge-discharge cycle, and the discharge capacity at this point is recorded as the first discharge capacity. The battery is then subjected to charge-discharge tests using the above method, and the discharge capacity of each cycle is recorded until the battery's capacity retention rate decreases to 80%. The number of cycles at this point is the cycle life.

[0233] Initial discharge capacity (mAh / g) = First discharge capacity / Mass of positive electrode active material contained in the battery

[0234] During testing, when the positive electrode active material was LFP, the charge / discharge voltage range of the secondary battery was 2.5V to 3.65V; when the positive electrode active material was NCM811, the charge / discharge voltage range of the secondary battery was 2.8V to 4.25V.

[0235] (2) Bonding strength test of positive electrode sheet

[0236] Take the electrode to be tested (single-sided coating; if double-sided coating, remove the film layer on one side first), and cut a sample with a width of 0.02m and a length of 0.1m. Attach a 0.02m wide and 0.09m long double-sided adhesive tape to a 0.02m wide and 0.2m long steel plate, with one end of the tape flush with one end of the steel plate. Place the electrode sample onto the double-sided tape, ensuring the lithium-supplementing layer adheres to the tape. Use corrugated adhesive to fix a 0.02m wide and 0.15m long paper strip to the current collector surface of the electrode sample. Secure the end of the steel plate without the electrode attached using the lower clamp of a tensile testing machine. Fold the paper strip upwards and secure it with the upper clamp. Turn on the tensile testing machine and perform continuous 180° peeling at a peeling speed of 0.05m / min. Record the maximum tensile force F displayed by the tensile testing machine when the electrode film layer is peeled from the current collector. The bonding strength of the electrode (N / m) = F / width of the electrode sample.

[0237] In the positive electrode bonding strength test of this invention, no peeling occurred between the lithium replenishment layer and the positive electrode active material layer, indicating that the interlayer bonding strength between the lithium replenishment layer and the positive electrode active material layer is high. However, in the peeling test, the lithium replenishment layer using PVDF binder (such as Comparative Example 1 and Comparative Example 4) peeled off between the lithium replenishment layer and the positive electrode active material layer.

[0238] Table 3: Preparation parameters and test results of Examples 1-17 and Comparative Examples 1-6

[0239]

[0240] Based on the above results, it can be seen that in Examples 1 to 17, since a lithium replenishment layer is provided on the surface of the positive electrode active material layer opposite to the positive electrode current collector, the lithium replenishment layer includes a lithium-rich metal oxide lithium replenishment material and a binder A. The binder A is selected from a polymer including a first monomer unit and a second monomer unit. Therefore, the secondary batteries all obtained higher initial discharge capacity and cycle life.

[0241] In contrast, Comparative Examples 1 to 6, due to their failure to meet the requirements of this application, did not achieve an effective improvement in the initial discharge capacity and cycle life of the secondary batteries.

[0242] Table 4: Preparation parameters and test results of Examples 18-20

[0243]

[0244] The results above indicate that using appropriate cathode lithium replenishment materials can further improve the initial discharge capacity and cycle life of the battery.

[0245] Table 5: Preparation parameters and test results of Examples 21-27

[0246]

[0247] Based on the above results, it can be seen that using polymer binder A comprising a first monomer unit and a second monomer unit in the lithium replenishment layer, while using single-crystal particles with an appropriate particle size as the positive electrode lithium replenishment material, helps to improve the compaction density of the positive electrode active material layer, thereby increasing the energy density of the battery. Furthermore, the positive electrode sheet can also achieve higher bonding strength, resulting in higher conductivity and thus improving the battery's cycle life.

[0248] Table 6: Preparation parameters and test results of Examples 28-45

[0249]

[0250] Based on the above results, it can be seen that by using binder A in the lithium replenishment layer and adding an appropriate proportion of binder C to the positive electrode active material layer, the cycle life of the secondary battery can be further improved.

[0251] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode sheet, comprising a positive current collector, a positive active material layer disposed on at least one surface of the positive current collector, and a lithium supplement layer disposed on a surface of the positive active material layer opposite to the positive current collector. in, The lithium replenishment layer comprises a positive electrode lithium replenishment material, a conductive agent, and a binder A. The positive electrode lithium replenishment material includes lithium-rich metal oxides. The adhesive A is selected from polymers comprising a first monomer unit represented by Formula I and a second monomer unit represented by Formula II. Wherein, the R 1 R 2 R 3 R 4 R 5 and R 6 Each R is independently selected from hydrogen or substituted or unsubstituted C1 to C8 alkyl groups, wherein R is selected from substituted or unsubstituted C1 to C8 alkyl groups; The positive electrode active material layer includes a positive electrode active material, binder B, and binder C, wherein... The binder B includes one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); The adhesive C is selected from one or more polymers comprising the group consisting of the third monomer unit shown in Formula III and the fourth monomer unit shown in Formula IV. Wherein, the R a R b R c R d R e and R f Each monomer unit is independently selected from hydrogen or substituted or unsubstituted C1-C8 alkyl groups, wherein R' is selected from substituted or unsubstituted C1-C8 alkyl groups; the third monomer unit includes one or more monomer units shown in formulas S1 and S2, and the fourth monomer unit includes one or more monomer units shown in formulas S3 to S8. Based on the total weight of adhesive B and adhesive C, the content of adhesive C is 5% to 20%; The weight-average molecular weight of the adhesive C is 50 to 5000.

2. The positive electrode sheet according to claim 1, wherein, Based on the total weight of the first monomer unit and the second monomer unit, the content of the first monomer unit is 30% to 70%.

3. The positive electrode sheet according to claim 1, wherein, Based on the total weight of the first monomer unit and the second monomer unit, the content of the first monomer unit is 40% to 60%.

4. The positive electrode sheet according to claim 1, wherein, The weight-average molecular weight of the adhesive A is 30,000 to 600,000.

5. The positive electrode sheet according to claim 1, wherein, The weight-average molecular weight of the adhesive A is 50,000 to 500,000.

6. The positive electrode sheet according to claim 1, wherein, The weight-average molecular weight of the binder A is 100,000 to 300,000.

7. The positive electrode sheet according to any one of claims 1-6, wherein, The first single-unit satisfies: the R 1 R 2 and R 3 Each is independently selected from hydrogen or substituted or unsubstituted C1 to C4 alkyl groups.

8. The positive electrode sheet according to claim 7, wherein, The first single-unit satisfies: the R 1 R 2 and R 3 Each is independently selected from hydrogen or methyl.

9. The positive electrode sheet according to claim 7, wherein, The first monomer unit includes one or more of the monomer units shown in formula S1 and formula S2. And / or, The second monomer unit satisfies the following: R is selected from substituted or unsubstituted C1-C4 alkyl groups; and / or, R 4 R 5 and R 6 Each is independently selected from hydrogen or substituted or unsubstituted C1 to C4 alkyl groups.

10. The positive electrode sheet according to claim 9, wherein, The R 4 R 5 and R 6 Each is independently selected from hydrogen or methyl.

11. The positive electrode sheet according to claim 9, wherein, The R 4 Representing hydrogen or methyl, the R 5 and R 6 Both represent hydrogen.

12. The positive electrode sheet according to claim 9, wherein, The second monomer unit includes one or more of the monomer units shown in formulas S3 to S8.

13. The positive electrode sheet according to claim 1, wherein, The adhesive A is selected from one or more of the following polymers: polymers including monomer units S1 and S5, polymers including monomer units S1 and S8, polymers including monomer units S1, S5 and S8, polymers including monomer units S1, S3, S5 and S8, polymers including monomer units S2 and S8, polymers including monomer units S2 and S7, polymers including monomer units S2 and S5, and polymers including monomer units S2 and S6.

14. The positive electrode sheet according to claim 1, wherein, The adhesive A is selected from one or more of the following: polymers of monomer units S1 and S5, polymers of monomer units S1 and S8, polymers of monomer units S1, S5 and S8, polymers of monomer units S1, S3, S5 and S8, polymers of monomer units S2 and S8, polymers of monomer units S2 and S7, polymers of monomer units S2 and S5, and polymers of monomer units S2 and S6.

15. The positive electrode sheet according to claim 1, wherein, The pH of the positive electrode lithium replenishment material, as determined by titration, is ≤13.

16. The positive electrode sheet according to claim 1, wherein, The pH of the positive electrode lithium replenishment material, as determined by titration, is ≤12.

5.

17. The positive electrode sheet according to claim 1, wherein, The pH value of the positive electrode lithium replenishment material, as determined by titration, is 11 ≤ pH ≤ 12.

5.

18. The positive electrode sheet according to claim 1, wherein, The specific capacity of the positive electrode lithium replenishment material is ≥400mAh / g.

19. The positive electrode sheet according to claim 1, wherein, The specific capacity of the positive electrode lithium replenishment material is ≥500mAh / g.

20. The positive electrode sheet according to claim 1, wherein, The lithium-rich metal oxide is selected from Li3M. 1 O4, Li5M 2 O4, Li6M 3 One or more of O4, of which M 1 Including one or more of V, Nb, Cr, and Mo, M 2 Including one or more of Fe, Cr, V, Mo, and Al, M 3 It includes one or more of Co, V, Cr, and Mo, wherein the valence state of each metal element except Li in the lithium-rich metal oxide is lower than its highest oxidation state.

21. The positive electrode sheet according to claim 1, wherein, The lithium-rich metal oxide is selected from one or more of Li3VO4, Li3NbO4, Li5FeO4, and Li6CoO4.

22. The positive electrode sheet according to claim 1, wherein, The lithium-rich metal oxide comprises single-crystal particles, and the number of single-crystal particles in the lithium-rich metal oxide accounts for 60% to 100%.

23. The positive electrode sheet according to claim 1, wherein, The lithium-rich metal oxide comprises single-crystal particles, and the number of single-crystal particles in the lithium-rich metal oxide accounts for 80% to 100%.

24. The positive electrode sheet according to claim 1, wherein, The volume average particle size D of the lithium-rich metal oxide v 50 is 5μm to 25μm.

25. The positive electrode sheet according to claim 1, wherein, The volume average particle size D of the lithium-rich metal oxide v 50 is 6μm to 20μm.

26. The positive electrode sheet according to claim 1, wherein, The volume average particle size D of the lithium-rich metal oxide v 50 represents 10μm to 15μm.

27. The positive electrode sheet according to claim 1, wherein, The positive electrode lithium replenishment material accounts for 90% to 97% of the weight of the lithium replenishment layer.

28. The positive electrode sheet according to claim 1, wherein, The positive electrode lithium replenishment material accounts for 92.5% to 95% of the weight of the lithium replenishment layer; and / or, The binder A accounts for 2% to 7% of the weight of the lithium replenishment layer.

29. The positive electrode sheet according to claim 1, wherein, The binder A comprises 3.5% to 5% by weight in the lithium replenishment layer; and / or, The conductive agent accounts for 1% to 3% of the weight of the lithium replenishment layer.

30. The positive electrode sheet according to claim 1, wherein, The conductive agent accounts for 1.5% to 2.5% of the weight of the lithium replenishment layer.

31. The positive electrode sheet according to claim 1, wherein, The weight-average molecular weight of the binder C is 100 to 4000.

32. The positive electrode sheet according to claim 1, wherein, The positive electrode active material layer includes a layered lithium transition metal oxide.

33. The positive electrode sheet according to claim 32, wherein, The layered lithium transition metal oxide includes one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified materials of the above substances. Wherein, based on the total weight of adhesive B and adhesive C, the content of adhesive C is 10% to 20%.

34. The positive electrode sheet according to claim 1, wherein, The weight-average molecular weight of the binder C is 500 to 4000.

35. The positive electrode sheet according to claim 1, wherein, The weight-average molecular weight of the adhesive C is 1000-3000.

36. The positive electrode sheet according to claim 1, wherein, The adhesive C is selected from polymers including one or more of the third monomer units.

37. The positive electrode sheet according to claim 1, wherein, The adhesive C is selected from polymers including monomer units S1.

38. The positive electrode sheet according to claim 1, wherein, The adhesive C is selected from polymers of monomer unit S1.

39. The positive electrode sheet according to claim 32, wherein, The compaction density of the positive electrode active material layer is 3.5 g / cm³. 3 ~3.8g / cm 3 .

40. The positive electrode sheet according to claim 39, wherein, The compaction density of the positive electrode active material layer is 3.55 g / cm³. 3 ~3.65g / cm 3 ; Wherein, the volume average particle size D of the positive electrode active material v 50 is 2μm to 10μm.

41. The positive electrode sheet according to claim 40, wherein, The volume average particle size D of the positive electrode active material v 50 is 4μm to 8μm.

42. The positive electrode sheet according to claim 1, wherein, The positive electrode active material layer includes polyanionic positive electrode materials.

43. The positive electrode sheet according to claim 42, wherein, The polyanionic cathode material includes lithium phosphate with an olivine structure.

44. The positive electrode sheet according to claim 42, wherein, The polyanionic cathode material includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and modified materials of the above substances. Wherein, based on the total weight of adhesive B and adhesive C, the content of adhesive C is 5% to 10%.

45. The positive electrode sheet according to claim 44, wherein, The weight-average molecular weight of the binder C is 100 to 3000.

46. ​​The positive electrode sheet according to claim 44, wherein, The weight-average molecular weight of the binder C is 500 to 1500.

47. The positive electrode according to any one of claims 44-46, wherein, The adhesive C is selected from polymers that simultaneously include a third monomer unit and a fourth monomer unit.

48. The positive electrode sheet according to claim 47, wherein, The adhesive C is selected from one or more polymers including one or more monomer units S1 to S2 and one or more polymers selected from S2 to S8.

49. The positive electrode sheet according to claim 42, wherein, The compaction density of the positive electrode active material layer is 2.4 g / cm³. 3 ~2.7g / cm 3 .

50. The positive electrode sheet according to claim 49, wherein, The compaction density of the positive electrode active material layer is 2.45 g / cm³. 3 ~2.55g / cm 3 ; Wherein, the volume average particle size D of the positive electrode active material v 50 ranges from 0.2μm to 1.5μm.

51. The positive electrode sheet according to claim 50, wherein, The volume average particle size D of the positive electrode active material v 50 is 0.5μm to 1.2μm.

52. The positive electrode sheet according to claim 1, wherein, Based on the total thickness of the positive electrode active material layer and the lithium replenishment layer, the thickness of the lithium replenishment layer accounts for 3% to 22%.

53. The positive electrode sheet according to claim 52, wherein, Based on the total thickness of the positive electrode active material layer and the lithium replenishment layer, the thickness of the lithium replenishment layer accounts for 5% to 20%.

54. The positive electrode sheet according to claim 52, wherein, Based on the total thickness of the positive electrode active material layer and the lithium replenishment layer, the thickness of the lithium replenishment layer accounts for 8% to 15%.

55. A secondary battery comprising the positive electrode sheet as described in any one of claims 1-54.

56. The secondary battery according to claim 55, wherein, It includes an electrolyte, the electrolyte containing an electrolyte lithium salt, the electrolyte lithium salt including a fluorinated electrolyte lithium salt.

57. The secondary battery according to claim 56, wherein, The fluorinated electrolyte lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, lithium difluorosulfonylimide, lithium difluoromethanesulfonylimide, lithium trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)methyl lithium, and tri(trifluoromethanesulfonyl)methyl lithium.

58. A battery module comprising a secondary battery according to claim 55 or 56.

59. A battery pack comprising at least one of a secondary battery according to claim 55 or 56, or a battery module according to claim 58.

60. An electrical device comprising at least one of the following: a secondary battery according to claim 55 or 56, a battery module according to claim 58, or a battery pack according to claim 59.

61. A method for manufacturing a secondary battery, comprising the step of preparing a positive electrode sheet using the following method: A positive electrode active material layer is formed on at least one surface of the positive electrode current collector; A lithium replenishment layer is formed on the surface of the positive electrode active material layer opposite to the positive electrode current collector. The lithium replenishment layer comprises a positive electrode lithium replenishment material, a conductive agent, and a binder A. The positive electrode lithium replenishment material comprises a lithium-rich metal oxide, and the binder A is selected from polymers comprising a first monomer unit shown in Formula I and a second monomer unit shown in Formula II. in, The R 1 R 2 R 3 R 4 R 5 and R 6 Each R is independently selected from hydrogen or substituted or unsubstituted C1 to C8 alkyl groups, wherein R is selected from substituted or unsubstituted C1 to C8 alkyl groups; The positive electrode active material layer includes a positive electrode active material, binder B, and binder C, wherein... The binder B includes one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); The adhesive C is selected from one or more polymers comprising the group consisting of the third monomer unit shown in Formula III and the fourth monomer unit shown in Formula IV. Wherein, the R a R b R c R d R e and R f Each monomer unit is independently selected from hydrogen or substituted or unsubstituted C1-C8 alkyl groups, wherein R' is selected from substituted or unsubstituted C1-C8 alkyl groups; the third monomer unit includes one or more monomer units shown in formulas S1 and S2, and the fourth monomer unit includes one or more monomer units shown in formulas S3 to S8. Based on the total weight of adhesive B and adhesive C, the content of adhesive C is 5% to 20%; The weight-average molecular weight of the adhesive C is 50 to 5000.

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