Positive electrode slurry, positive electrode tab, preparation method thereof, secondary battery, and electric device

Abstract

This application provides a positive electrode slurry, a positive electrode sheet, a method for preparing the same, a secondary battery, and an electrical device. The positive electrode slurry comprises a positive electrode active material and a chlorinated polymer additive, and the surface of the positive electrode active material has residual lithium. By adding a chlorinated polymer to the positive electrode slurry, during the heating and curing process of the positive electrode slurry in the preparation of the positive electrode sheet, the chlorinated polymer decomposes to produce hydrogen chloride. The hydrogen chloride reacts with the residual lithium on the surface of the positive electrode active material to form lithium chloride, which acts as a lithium replenishing agent. Using the above-mentioned positive electrode slurry not only effectively forms a lithium replenishing agent on the surface of the positive electrode active material but also removes residual lithium from the surface of the positive electrode active material, thereby improving the specific capacity of the positive electrode. The positive electrode sheet prepared using this positive electrode slurry can improve the energy density of the battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a positive electrode slurry, a positive electrode sheet and its preparation method, a secondary battery and an electrical device. Background Technology

[0002] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0003] In recent years, as the application scope of secondary batteries has become increasingly wide, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles and electric vehicles.

[0004] Due to the significant advancements in secondary batteries, higher demands have been placed on their energy density. Batteries with higher energy density place stringent requirements on the positive electrode. For example, high-energy-density batteries typically require the positive electrode to have a large specific capacity.

[0005] Therefore, seeking positive electrode sheets with larger specific capacity to improve the energy density of batteries is one of the key areas of focus for those skilled in the art. Summary of the Invention

[0006] This application is made in view of the above-mentioned issues, and one of its objectives is to provide a positive electrode slurry, wherein the positive electrode sheet prepared using the positive electrode slurry has a large positive electrode specific capacity.

[0007] To achieve the above objectives, a first aspect of this application provides a positive electrode slurry comprising a positive electrode active material and a chlorine-containing polymer additive, wherein the surface of the positive electrode active material has residual lithium.

[0008] This application introduces a chlorinated polymer into the positive electrode slurry. During the heating and solidification process of the positive electrode slurry in the preparation of the positive electrode sheet, the chlorinated polymer decomposes to produce hydrogen chloride. The hydrogen chloride reacts with residual lithium on the surface of the positive electrode active material to form lithium chloride. Since the theoretical decomposition potential of lithium chloride is relatively low, it can act as a lithium replenishing agent during normal battery charging, decomposing to form metallic lithium, thereby achieving the lithium replenishment function. Using the above-mentioned positive electrode slurry not only effectively forms a lithium replenishing agent on the surface of the positive electrode active material but also removes residual lithium from the surface of the positive electrode active material, thus improving the specific capacity of the positive electrode and consequently increasing the energy density.

[0009] In any embodiment, the chlorinated polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-butadiene copolymer, and vinyl chloride-vinyl ether copolymer. Thus, the aforementioned chlorinated polymer can decompose at the normal heating and curing temperature of the positive electrode slurry to produce hydrogen chloride, thereby effectively reacting with residual lithium on the surface of the positive electrode active material to generate lithium chloride, achieving a good lithium replenishment effect.

[0010] In any embodiment, the chlorinated polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, and vinyl chloride-acrylonitrile copolymer. Thus, using these chlorinated polymers not only achieves good lithium replenishment but also improves the adhesion of the positive electrode sheet.

[0011] In any embodiment, the mass fraction of the chlorinated polymer additive is 0.1% to 1.5% based on the total mass of the solute in the cathode slurry. This effectively increases the specific capacity of the cathode while avoiding a decrease in the proportion of active cathode material and thus a reduction in battery energy density due to excessive addition of chlorinated polymer.

[0012] In any embodiment, the mass fraction of the chlorinated polymer additive is 0.5% to 1.0% based on the total mass of the solute in the positive electrode slurry. This allows for a more effective increase in the specific capacity of the positive electrode and facilitates an increase in the content of the positive electrode active material in the positive electrode film.

[0013] In any embodiment, based on the total mass of the positive electrode active material, the mass fraction of the residual lithium is 0.005% to 2.0%. Thus, this residual lithium can react with hydrogen chloride produced by the decomposition of chlorine-containing polymers to generate an appropriate amount of lithium chloride on the surface of the positive electrode active material as a lithium replenishing agent, achieving a good lithium replenishment effect.

[0014] In any embodiment, the mass fraction of residual lithium is 0.5% to 2.0% based on the total mass of the positive electrode active material. This further improves the charge / discharge specific capacity of the positive electrode and enhances the lithium replenishment effect.

[0015] A second aspect of this application provides a method for preparing a positive electrode sheet, comprising the following steps:

[0016] The positive electrode slurry of the first aspect of this application is attached to the positive electrode current collector; and

[0017] Heating solidifies the positive electrode slurry to form a positive electrode film layer on the positive electrode current collector and converts the residual lithium into lithium chloride.

[0018] By adding a chlorinated polymer to the positive electrode slurry, the polymer decomposes to produce hydrogen chloride during the heating and curing process. This hydrogen chloride reacts with residual lithium on the surface of the positive electrode active material to form lithium chloride. Since lithium chloride has a relatively low theoretical decomposition potential, it can act as a lithium replenishing agent during normal battery charging, decomposing to form metallic lithium, thus achieving lithium replenishment. This preparation method not only effectively forms a lithium replenishing agent on the surface of the positive electrode active material but also removes residual lithium, thereby improving the specific capacity of the positive electrode. Positive electrode sheets prepared using this method can increase the energy density of the battery.

[0019] In any embodiment, the heating temperature is 80°C to 120°C, and the heating time is 4 hours to 24 hours. This allows the chlorine-containing polymer in the positive electrode slurry to fully decompose and generate hydrogen chloride, which further reacts with residual lithium on the surface of the positive electrode active material to generate lithium chloride.

[0020] In any embodiment, the heating temperature is 90℃~100℃, and the heating time is 8h~15h. This not only allows the residual lithium on the surface of the positive electrode active material to fully react and generate lithium chloride, but also appropriately improves the curing efficiency.

[0021] A third aspect of this application provides a positive electrode sheet, which is prepared by the method for preparing a positive electrode sheet according to the second aspect of this application. Thus, the positive electrode sheet has a large specific capacity.

[0022] A fourth aspect of this application provides a secondary battery comprising a positive electrode sheet as described in the third aspect of this application. Thus, the secondary battery has a high energy density.

[0023] The fifth aspect of this application provides an electrical device comprising a secondary battery according to the fourth aspect of this application.

[0024] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0025] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0026] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0027] Figure 2 for Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0028] Figure 3 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0029] Explanation of reference numerals in the attached figures:

[0030] 5. Battery cell; 51. Casing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0031] The following describes in detail, with appropriate reference to the accompanying drawings, embodiments of the positive electrode slurry, positive electrode sheet, preparation method thereof, secondary battery, and power device of this application. However, some unnecessary details 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.

[0032] The "range" disclosed in this application can be defined in the form of 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 the specific range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently, and they can be combined arbitrarily; 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 expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also 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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0033] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0036] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can 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.

[0037] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0038] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0039] The weights described in the embodiments of this application may be weight units known in the chemical industry, such as μg, mg, g, and kg.

[0040] Currently, due to the significant development of rechargeable batteries, higher demands are being placed on their energy density. Batteries with higher energy density place high requirements on the positive electrode sheet. For example, high-energy-density batteries typically require the positive electrode sheet to have a large specific capacity. Therefore, seeking positive electrode sheets with larger specific capacity to improve battery energy density is one of the key areas of focus for those skilled in the art. In this regard, this application provides a positive electrode slurry that, by adding a chlorinated polymer additive, can react with residual lithium on the surface of the positive electrode active material to generate lithium chloride, which acts as a lithium replenishing agent, effectively improving the specific capacity of the positive electrode.

[0041] In some embodiments, the first aspect of this application provides a positive electrode slurry comprising a positive electrode active material and a chlorinated polymer additive, wherein the surface of the positive electrode active material has residual lithium.

[0042] This application introduces a chlorinated polymer additive into the positive electrode slurry. During the heating and solidification process of the positive electrode slurry in the preparation of the positive electrode sheet, the chlorinated polymer decomposes to produce hydrogen chloride. The generated hydrogen chloride can further react with residual lithium on the surface of the positive electrode active material to form lithium chloride. Lithium chloride has a relatively low theoretical decomposition potential (approximately 3.68V). This lithium chloride, acting as a lithium replenishing agent, can undergo a redox reaction to generate metallic lithium during normal charging at the battery's normal charging voltage, thus achieving a lithium replenishment function. Using the aforementioned positive electrode slurry not only effectively forms a lithium replenishing agent on the surface of the positive electrode active material but also removes residual lithium from the surface, thereby improving the specific capacity of the positive electrode. Using the positive electrode sheet prepared using this positive electrode slurry in a secondary battery can increase the battery's energy density.

[0043] It should be noted that, compared to directly adding small-molecule lithium compounds (such as lithium chloride) as lithium replenishing agents to the positive electrode film, this application adds a chlorinated polymer as an additive to the positive electrode slurry. During the heating and curing process of the positive electrode slurry, the chlorinated polymer can react with residual lithium on the surface of the positive electrode active material, generating lithium chloride in situ on the surface of the positive electrode active material. This forms highly nano-sized and uniformly dispersed lithium chloride particles on the surface of the positive electrode active material, achieving a better lithium replenishment effect and removing residual lithium on the surface of the positive electrode active material. If the chlorinated polymer is replaced with a fluorinated polymer or a bromine polymer, the fluorinated polymer and bromine polymer have better thermal stability, with a general decomposition temperature of around 300℃. They will not decompose to produce hydrogen fluoride or hydrogen bromide at the normal heating and curing temperature of the positive electrode slurry, and therefore cannot react with residual lithium on the surface of the positive electrode active material to generate lithium fluoride, lithium bromide, etc., as lithium replenishing agents, thus failing to achieve the lithium replenishment effect.

[0044] It is understandable that residual lithium on the surface of the positive electrode active material refers to residual lithium compounds such as Li₂CO₃, LiHCO₃, and LiOH present on the surface of the positive electrode active material. The presence of these residual lithium compounds not only increases the instability of the positive electrode active material and leads to the degradation of its electrochemical performance, but also causes battery safety issues.

[0045] In some embodiments, the chlorinated polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-butadiene copolymer, and vinyl chloride-vinyl ether copolymer. Using the above-mentioned chlorinated polymers as additives allows for decomposition at the normal heating and curing temperature of the positive electrode slurry to generate hydrogen chloride, which can then effectively react with residual lithium on the surface of the positive electrode active material to generate lithium chloride, achieving a good lithium replenishment effect.

[0046] In some embodiments, the chlorinated polymer additive includes one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, and vinyl chloride-acrylonitrile copolymer. Thus, using one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, and vinyl chloride-acrylonitrile copolymer as the chlorinated polymer additive not only achieves good lithium replenishment, but also enhances the adhesion between particles and between particles and the substrate through strong intermolecular forces or hydrogen bonding, thereby improving the adhesion between the positive electrode film layer and the positive electrode current collector in the positive electrode sheet.

[0047] In some embodiments, the mass fraction of the chlorinated polymer additive is 0.1% to 1.5% based on the total mass of the solute in the cathode slurry. Controlling the mass fraction of the chlorinated polymer additive in the cathode slurry within the range of 0.1% to 1.5% can effectively improve the specific capacity of the cathode while avoiding a decrease in the proportion of the cathode active material and thus the battery energy density due to excessive chlorinated polymer addition. It is understood that the solute in the cathode slurry refers to all components other than the solvent. In this application, the solute in the cathode slurry includes the cathode active material, conductive agent, binder, and chlorinated polymer additive.

[0048] It is understood that the mass fraction of chlorinated polymer additives in the solute of the positive electrode slurry can be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, and 1.5%.

[0049] In some embodiments, the mass fraction of the chlorinated polymer additive is 0.5% to 1.0% based on the total mass of the solute in the cathode slurry. Controlling the mass fraction of the chlorinated polymer additive in the solute of the cathode slurry within the range of 0.5% to 1.0% can more effectively improve the specific capacity of the cathode and better avoid the situation where excessive chlorinated polymer reduces the proportion of cathode active material and the energy density of the battery.

[0050] In some embodiments, the mass fraction of residual lithium on the surface of the positive electrode active material is 0.005% to 2.0% based on the total mass of the positive electrode active material. The residual lithium on the surface of the positive electrode active material can react with hydrogen chloride produced after the decomposition of the chlorinated polymer additive to generate lithium chloride on the surface of the positive electrode active material as a lithium replenishing agent. It is understood that the amount of chlorinated polymer additive added to the positive electrode slurry can be adjusted accordingly based on the amount of residual lithium on the surface of the positive electrode active material. If the amount of residual lithium on the surface of the positive electrode active material is low, the amount of chlorinated polymer additive added to the positive electrode slurry can be reduced accordingly; if the amount of residual lithium on the surface of the positive electrode active material is high, the amount of chlorinated polymer additive added to the positive electrode slurry can be increased accordingly.

[0051] Understandably, the mass fraction of residual lithium on the surface of the positive electrode active material can be, but is not limited to, 0.005%, 0.008%, 0.01%, 0.015%, 0.02%, 0.03%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%.

[0052] In some embodiments, the mass fraction of residual lithium on the surface of the positive electrode active material is 0.5% to 2.0% based on the total mass of the positive electrode active material. Controlling the mass fraction of residual lithium on the surface of the positive electrode active material within the above range can further improve the charge-discharge specific capacity of the positive electrode and further improve the lithium replenishment effect.

[0053] In some embodiments, the positive electrode slurry may further include a binder. The binder may be one or more of, but not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0054] In some embodiments, the positive electrode slurry may further include a conductive agent. The conductive agent may be one or more of, but not limited to, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0055] In some embodiments, the second aspect of this application also provides a method for preparing a positive electrode sheet, comprising the following steps:

[0056] The first aspect of this application provides a positive electrode slurry comprising a positive electrode active material and a chlorine-containing polymer additive, wherein the surface of the positive electrode active material has residual lithium.

[0057] The positive electrode slurry is attached to the positive electrode current collector; and

[0058] Heating solidifies the positive electrode slurry on the positive electrode current collector to form a positive electrode film layer on the positive electrode current collector, and converts the residual lithium on the surface of the positive electrode active material into lithium chloride.

[0059] By adding a chlorinated polymer to the positive electrode slurry, the polymer decomposes to produce hydrogen chloride during the heating and curing process. This hydrogen chloride reacts with residual lithium on the surface of the positive electrode active material to form lithium chloride. Since lithium chloride has a relatively low theoretical decomposition potential, it can act as a lithium replenishing agent during normal battery charging, decomposing to form metallic lithium, thus achieving lithium replenishment. This preparation method not only effectively forms a lithium replenishing agent on the surface of the positive electrode active material but also removes residual lithium, thereby improving the specific capacity of the positive electrode. Positive electrode sheets prepared using this method can increase the energy density of the battery.

[0060] In some embodiments, the heating temperature for solidifying the positive electrode slurry on the positive electrode current collector and converting residual lithium on the surface of the positive electrode active material into lithium chloride is 80°C to 120°C, and the heating time is 4h to 24h. Under these heating temperature and time conditions, the positive electrode slurry can be solidified on the positive electrode current collector to form a positive electrode film layer, and the chlorine-containing polymer in the positive electrode slurry can decompose to generate hydrogen chloride. The hydrogen chloride reacts with the residual lithium on the surface of the positive electrode active material to generate lithium chloride.

[0061] It is understood that the heating temperature can be, but is not limited to, 80℃, 82℃, 85℃, 88℃, 90℃, 92℃, 95℃, 98℃, 100℃, 102℃, 105℃, 108℃, 110℃, 112℃, 115℃, 118℃, and 120℃; and the heating time can be, but is not limited to, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, and 24h.

[0062] In some embodiments, the heating temperature for curing the positive electrode slurry is 90°C to 100°C, and the heating time is 8 hours to 15 hours. By controlling the heating temperature and heating time of the positive electrode slurry on the positive electrode current collector within the above range, the positive electrode slurry can be well cured to form a positive electrode film layer, and the residual lithium on the surface of the positive electrode active material can be fully reacted to generate lithium chloride, and the curing efficiency is high.

[0063] In some embodiments, the third aspect of this application also provides a positive electrode sheet, which is prepared by the method for preparing a positive electrode sheet according to the second aspect of this application. Therefore, the positive electrode sheet has a high specific capacity.

[0064] In some embodiments, the fourth aspect of this application also provides a secondary battery comprising the positive electrode of the third aspect of this application. Therefore, the secondary battery has a high energy density.

[0065] In some embodiments, the fifth aspect of this application also provides an electrical device that includes a secondary battery according to the fourth aspect of this application.

[0066] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0067] Unless otherwise specified, the battery components, material types or contents mentioned apply to both lithium-ion and sodium-ion secondary batteries.

[0068] In one embodiment of this application, a secondary battery is provided.

[0069] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. 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 between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0070] Positive electrode sheet

[0071] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0072] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0073] In some embodiments, the positive electrode 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 material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0074] In some embodiments, the positive electrode active material may comprise a positive electrode active material known in the art for use in batteries.

[0075] As a non-limiting example, the positive electrode active material of a lithium-ion secondary battery may include one or more of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials of batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and their modified compounds. Non-limiting examples of lithium phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium manganese iron phosphate and carbon composites. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al 0.05 O2.

[0076] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. Unless otherwise specified, the Li content in the examples of positive electrode materials listed in this application refers to the initial state of the material. When a positive electrode material is applied to a positive electrode in a battery system, the Li content in the positive electrode material typically changes after charge-discharge cycles. The Li content can be measured using molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for the positive electrode material; non-limiting examples include coating modification.

[0077] In the examples of cathode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in molar content, but is not limited to this.

[0078] As a non-limiting example, the positive electrode active material of a sodium-ion secondary battery may include one or more of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0079] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be one or more selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0080] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si; n represents (YO4). n- The price state.

[0081] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n-A class of compounds containing anionic units and halide anions. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si, and n represents (YO4). n- The valence state; halogens can be one or more of F, Cl and Br.

[0082] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be one or more of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; halogens can be one or more of F, Cl and Br.

[0083] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (where M' is one or more of V, Fe, Mn and Ni), and Na3(VO4) y )2(PO4)2F 3-2y One or more of (0≤y≤1).

[0084] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. Transition metals can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds include, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently one or more of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0085] In some embodiments, the positive electrode film layer may optionally include a binder. As a non-limiting 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. The binder constitutes 0% to 20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0086] In some embodiments, the positive electrode film may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent comprises 0% to 20% by weight in the positive electrode film, based on the total weight of the positive electrode film.

[0087] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40wt% to 80wt%, and the viscosity at room temperature is adjusted to 5000 mPa·s to 25000 mPa·s. The positive electrode slurry is then coated onto the surface of the positive current collector, dried, and cold-pressed using a cold rolling mill to form the positive electrode sheet; the positive electrode powder coating has a unit areal density of 150 mg / m². 2 ~350mg / m 2 The compaction density of the positive electrode sheet is 3.0 g / cm³. 3 ~3.6g / cm 3 3.3g / cm³ is an option. 3 ~3.5g / cm 3 .

[0088] The formula for calculating the compaction density is:

[0089] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0090] The mass M of the positive electrode active material per unit area of ​​the positive electrode membrane can be obtained by weighing using a standard balance.

[0091] The thickness T of the positive electrode film can be measured using a micrometer, such as a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm. It should be noted that the thickness of the positive electrode film mentioned in this application refers to the thickness of the positive electrode film in the positive electrode sheet used for battery assembly after cold pressing and compaction.

[0092] Negative electrode sheet

[0093] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0094] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0095] 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 polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0096] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries.

[0097] As a non-limiting example, the negative electrode active material of a lithium-ion secondary battery may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include 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 for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0098] As a non-limiting example, the negative electrode active material of a sodium-ion secondary battery is typically a hard carbon material, a two-dimensional metal carbide, or a nitride. Preferably, the negative electrode active material of a sodium-ion secondary battery is typically a hard carbon material.

[0099] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may include 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).

[0100] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0102] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing, and other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, minus solvent) can be 75 g / m². 2 ~220g / m 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 ~1.8g / cm 3 .

[0103] electrolytes

[0104] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0105] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0106] In some embodiments, the electrolyte salt of the lithium-ion secondary battery may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0107] In some embodiments, the solvent may include one or more of the following: fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0108] 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.

[0109] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0110] Separating membrane

[0111] In some embodiments, the secondary battery also includes a separator. 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.

[0112] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0113] In some embodiments, the thickness of the isolation membrane is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0114] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0115] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0116] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0117] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0118] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0119] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0120] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover plate 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 plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0121] In some embodiments, the battery cells 5 can be assembled into a battery module, and the number of battery cells 5 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.

[0122] In the battery module, multiple battery cells 5 can be arranged sequentially along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be secured with fasteners.

[0123] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0124] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack 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 pack.

[0125] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0126] 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.

[0127] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0128] Figure 3 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0129] 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.

[0130] The following are some examples.

[0131] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0132] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0133] I. Implementation Examples

[0134] Example 1:

[0135] 1) Preparation of positive electrode sheet

[0136] NCM positive electrode active material 811 The residual lithium content is 1.2%, conductive carbon black, carbon nanotubes, 5130 binder, and chlorinated polymer additive polyvinyl chloride (PVC) are mixed evenly in a mass ratio of 97:1.0:0.5:1.0:0.5. Then, N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry with a solid content of 75wt%.

[0137] The positive electrode slurry was uniformly coated onto the surface of a 13 μm thick aluminum foil for the positive electrode current collector, resulting in a single-sided membrane weighing 300 mg / 1540.25 mm. 2 The double-sided electrode sheet (excluding the substrate) is dried at 105℃ for 24 hours, and then cold-pressed and processed through processes such as tab forming and slitting to obtain the positive electrode sheet.

[0138] 2) Preparation of negative electrode sheet

[0139] Artificial graphite (anode active material), conductive carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and carboxymethyl cellulose (CMC) (thickener) were mixed in a mass ratio of 96:0.9:1.6:1.5. Deionized water was added as a solvent, and the mixture was stirred under vacuum until the system was homogeneous, resulting in a cathode slurry with a solid content of 54 wt%.

[0140] The negative electrode slurry is uniformly coated onto the surface of an 8μm thick copper foil for the negative electrode current collector, dried at 110℃, and then cold-pressed. After processes such as tab forming and slitting, the negative electrode sheet is obtained. The thickness of the negative electrode film layer in the negative electrode sheet is 110μm.

[0141] 3) Preparation of electrolyte

[0142] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), non-aqueous organic solvents ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain an electrolyte solvent. Subsequently, lithium salt LiPF6 was dissolved in the above mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0143] 4) Separating membrane

[0144] Polypropylene film is used as the separator.

[0145] 5) Preparation of lithium-ion batteries

[0146] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion secondary battery is obtained.

[0147] Example 2:

[0148] This embodiment is basically the same as Embodiment 1, except that the mass ratio of positive electrode active material, conductive agent carbon black, carbon nanotubes, 5130 binder, and chlorinated polymer additive PVC in the positive electrode slurry is 97.4:1.0:0.5:1.0:0.1.

[0149] Example 3:

[0150] This embodiment is basically the same as Embodiment 1, except that the mass ratio of positive electrode active material, conductive agent carbon black, carbon nanotubes, 5130 binder, and chlorinated polymer additive PVC in the positive electrode slurry is 96.5:1.0:0.5:1.0:1.0.

[0151] Example 4:

[0152] This embodiment is basically the same as Embodiment 1, except that the mass ratio of positive electrode active material, conductive carbon black, carbon nanotubes, 5130 binder, and chlorinated polymer additive PVC in the positive electrode slurry is 96:1.0:0.5:1.0:1.5.

[0153] Example 5:

[0154] This embodiment is basically the same as Embodiment 1, except that: vinyl chloride-acrylate copolymer is used as a chlorine-containing polymer additive in the positive electrode slurry.

[0155] Example 6:

[0156] This embodiment is basically the same as Embodiment 1, except that: vinyl chloride-acrylonitrile copolymer is used as a chlorine-containing polymer additive in the positive electrode slurry.

[0157] Example 7:

[0158] This embodiment is basically the same as Embodiment 1, except that: vinyl chloride-butadiene copolymer is used as a chlorine-containing polymer additive in the positive electrode slurry.

[0159] Example 8:

[0160] This embodiment is basically the same as Embodiment 1, except that: vinyl chloride-vinyl ether copolymer is used as a chlorine-containing polymer additive in the positive electrode slurry.

[0161] Example 9:

[0162] This embodiment is basically the same as Embodiment 1, except that the electrode coated with positive electrode slurry is dried at 80°C for 24 hours.

[0163] Example 10:

[0164] This embodiment is basically the same as Embodiment 1, except that the electrode coated with positive electrode slurry is dried at 120°C for 4 hours.

[0165] Example 11:

[0166] This embodiment is basically the same as Embodiment 1, except that the electrode coated with positive electrode paste is dried at 90°C for 15 hours.

[0167] Example 12:

[0168] This embodiment is basically the same as Embodiment 1, except that the electrode coated with positive electrode slurry is dried at 100°C for 8 hours.

[0169] Example 13:

[0170] This embodiment is basically the same as Embodiment 1, except that the positive electrode active material in the positive electrode slurry is NCM. 811 The mass fraction of residual lithium on the surface of the positive electrode active material is 0.005%.

[0171] Example 14:

[0172] This embodiment is basically the same as Embodiment 1, except that the positive electrode active material in the positive electrode slurry is NCM. 811 The mass fraction of residual lithium on the surface of the positive electrode active material is 0.5%.

[0173] Example 15:

[0174] This embodiment is basically the same as Embodiment 1, except that the positive electrode active material in the positive electrode slurry is NCM. 811 The mass fraction of residual lithium on the surface of the positive electrode active material is 2.0%.

[0175] II. Comparative Example

[0176] Comparative Example 1:

[0177] This comparative example is basically the same as Example 1, except that: no PVC is added to the positive electrode slurry; the mass ratio of positive electrode active material, conductive carbon black, carbon nanotubes and 5130 binder in the positive electrode slurry is 97.0:1.0:0.5:1.5.

[0178] Comparative Example 2:

[0179] This comparative example is basically the same as Example 1, except that: no PVC is added to the positive electrode slurry, and polyvinyl fluoride (PVF) is added to the positive electrode slurry as an additive; the mass ratio of positive electrode active material, conductive agent carbon black, carbon nanotubes, 5130 binder and PVF in the positive electrode slurry is 97:1.0:0.5:1.0:0.5.

[0180] Comparative Example 3:

[0181] This comparative example is basically the same as Example 1, except that: no PVC is added to the positive electrode slurry, and lithium chloride is added to the positive electrode slurry as a lithium supplement agent; the mass ratio of positive electrode active material, conductive carbon black, carbon nanotubes, 5130 binder and lithium chloride in the positive electrode slurry is 97:1.0:0.5:1.0:0.5.

[0182] III. Performance Testing

[0183] 1) Positive electrode adhesion test

[0184] A tensile testing machine was used to perform a 90° peel test on the positive electrode sheet;

[0185] Sample preparation: The cold-pressed positive electrode sheet is attached to the substrate with double-sided tape;

[0186] Test: Place the pasted positive electrode sample on a tensile testing machine and use the 90° peel test method to test the adhesion between the positive electrode film and the positive current collector. Record the tensile force (N / m) of the tensile testing machine when the positive electrode film is peeled off from the positive current collector.

[0187] 2) Positive electrode specific capacity test

[0188] At 25℃, the lithium-ion battery was charged at a constant current of 1 / 3C to a voltage of 4.35V, and then charged at a constant voltage of 4.35V to a current of 0.05C. The charging capacity C0 was recorded. After standing for 5 minutes, the lithium-ion battery was discharged at a constant current of 1 / 3C to 2.8V. The discharge capacity D0 was recorded.

[0189] Charging capacity = C0 / m1;

[0190] Discharge capacity = D0 / m1;

[0191] Where m1 = m0 * a; m1 represents the mass of positive electrode active material per unit area in the positive electrode film, m0 represents the total solid weight per unit area in the positive electrode film, and a represents the mass percentage of positive electrode active material in the positive electrode film.

[0192] 3) Initial coulombic efficiency calculation of the battery

[0193] The initial coulombic efficiency of a battery = discharge capacity / charge capacity = D0 / C0.

[0194] 4) Residual lithium test on the surface of positive electrode active material

[0195] Reference standard: Chemical reagents: General rules for potentiometric titration (GB / T 9725-2007);

[0196] The specific testing method is as follows:

[0197] 4.1) Power on: Turn on the device power and software, and allow it to stabilize for 20 to 30 minutes;

[0198] 4.2) Sample weighing: Weigh 30.0000±0.5000g of sample into a 250mL iodine flask using a balance;

[0199] 4.3) Stirring: Add 100 mL of pure water to the iodine flask and stir on a magnetic stirrer for 30 min;

[0200] 4.4) Settling: Seal and let stand for 10 minutes;

[0201] 4.5) Vacuum filtration: Vacuum filtration using a 0.45μm microporous membrane;

[0202] 4.6) Plugging: According to the sample type, transfer quantitative filtrate V3 into a clean 100 mL beaker;

[0203] 4.7) Drainage: In the "Manual Control" interface of the testing software, select "Liquid Adder 2" to drain the liquid;

[0204] 4.8) Electrode: Completely immerse the composite pH electrode and the liquid addition tube in the solution;

[0205] 4.9) Titration: Use potentiometric titration. Click "Working Platform" in the software to switch to the working interface. Enter the sample name and number in the "ID1" field and the sample mass in the "Sample size" field. Click "Start" to begin the test.

[0206] 4.10) Cleaning: Clean the glassware after the test is completed.

[0207] Data processing:

[0208] Li2CO3%=(V2-V1)×C×73.886×n×100 / 1000m

[0209] LiOH%=[V2-2×(V2-V1)]×C×23.946×n×100 / 1000m

[0210] Li + % = V² × C × 6.94 × n × 100 / (m × 1000)

[0211] In the above formula:

[0212] C represents the concentration of the hydrochloric acid standard solution, in mol / L.

[0213] n is the ratio of the volume transferred to the total volume, i.e., n = V³ / 100;

[0214] m is the mass of the sample, which is 30g here, in grams;

[0215] 73.886 is the molecular weight of lithium carbonate;

[0216] 23.946 is the molecular weight of lithium hydroxide;

[0217] 6.94 is the molecular weight of lithium;

[0218] V1 is the volume corresponding to the first titration endpoint, in mL;

[0219] V2 is the volume corresponding to the second titration endpoint, in mL;

[0220] V2-V1 represents the volume of hydrochloric acid consumed by LiHCO3 (i.e., the second step of the Li2CO3 reaction);

[0221] 2×(V2-V1) represents the volume of hydrochloric acid consumed by Li2CO3;

[0222] V2-2×(V2-V1) is the volume of hydrochloric acid consumed by LiOH.

[0223] The parameters and performance test data of the lithium-ion secondary batteries in the above embodiments and comparative examples are shown in Table 1.

[0224] Table 1

[0225]

[0226]

[0227]

[0228] As shown in Table 1:

[0229] In various embodiments of this application, adding chlorinated polymers such as polyvinyl chloride, vinyl chloride-acrylate copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-butadiene copolymer, or vinyl chloride-vinyl ether copolymer to the positive electrode slurry can achieve good lithium replenishment and improve the charge and discharge capacity of the positive electrode sheet.

[0230] Comparing Examples 1-4, it can be seen that controlling the content of chlorinated polymer additives in the solute of the positive electrode slurry to 0.5%-1.0% can make the positive electrode sheet have higher charge and discharge specific capacity and higher initial coulombic efficiency, and can achieve better lithium replenishment effect.

[0231] By comparing Examples 1 and 13-15, it can be seen that controlling the mass fraction of residual lithium on the surface of the positive electrode active material within the range of 0.5% to 2.0% can further improve the charge and discharge specific capacity of the positive electrode sheet and further improve the lithium replenishment effect.

[0232] Comparative Example 1 did not add any chlorine-containing polymer additives to the positive electrode slurry, and its charge-discharge specific capacity of the positive electrode sheet was significantly lower than that of Example 1. Comparative Example 2 added an equal amount of PVF to the positive electrode slurry to replace the chlorine-containing polymer additives. Due to the good thermal stability of polyvinyl fluoride, it is difficult to decompose and produce hydrogen fluoride at the normal heating and curing temperature of the positive electrode slurry, resulting in poor lithium replenishment effect. Its charge-discharge specific capacity of the positive electrode sheet was significantly lower than that of Example 1. In Comparative Example 3, an equal amount of lithium chloride was used to replace the chlorine-containing polymer additives, but it also failed to achieve a good lithium replenishment effect.

[0233] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0234] 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 slurry, characterized in that, It includes a positive electrode active material and a chlorine-containing polymer additive, wherein the surface of the positive electrode active material has residual lithium.

2. The positive electrode slurry according to claim 1, characterized in that, The chlorine-containing polymer additives include one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-butadiene copolymer, and vinyl chloride-vinyl ether copolymer.

3. The positive electrode slurry according to claim 2, characterized in that, The chlorine-containing polymer additives include one or more of polyvinyl chloride, vinyl chloride-acrylate copolymer, and vinyl chloride-acrylonitrile copolymer.

4. The positive electrode slurry according to any one of claims 1 to 3, characterized in that, Based on the total mass of the solute in the cathode slurry, the mass fraction of the chlorine-containing polymer additive is 0.1% to 1.5%.

5. The positive electrode slurry according to any one of claims 1 to 3, characterized in that, Based on the total mass of the solute in the cathode slurry, the mass fraction of the chlorine-containing polymer additive is 0.5% to 1.0%.

6. The positive electrode slurry according to any one of claims 1 to 3, characterized in that, Based on the total mass of the positive electrode active material, the mass fraction of the residual lithium is 0.005% to 2.0%.

7. The positive electrode slurry according to any one of claims 1 to 3, characterized in that, Based on the total mass of the positive electrode active material, the mass fraction of the residual lithium is 0.5% to 2.0%.

8. A method for preparing a positive electrode sheet, characterized in that, include: The positive electrode slurry according to any one of claims 1 to 7 is attached to the positive electrode current collector; as well as Heating solidifies the positive electrode slurry to form a positive electrode film layer on the positive electrode current collector and converts the residual lithium into lithium chloride.

9. The method for preparing the positive electrode sheet according to claim 8, characterized in that, The heating temperature is 80℃~120℃, and the heating time is 4h~24h.

10. The method for preparing the positive electrode sheet according to claim 8 or 9, characterized in that, The heating temperature is 90℃~100℃, and the heating time is 8h~15h.

11. A positive electrode plate, characterized in that, The positive electrode sheet is prepared by the method for preparing a positive electrode sheet according to any one of claims 8 to 10.

12. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 11.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 12.

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