Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet contains lithium-containing transition metal phosphate; and the lithium-containing transition metal phosphate contains submicron-sized particles and micron-sized particles. In addition, the electrolyte in the secondary battery contains a lithium salt and a film-forming stabilizer; and the lithium salt comprises a first lithium salt and a second lithium salt, wherein the first lithium salt contains lithium hexafluorophosphate, and the second lithium salt contains one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide. The secondary battery designed in the present application is advantageous in taking into account the energy density, the rate performance and the cycle performance of the battery.

Description

Secondary batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 2024103385921, filed on March 22, 2024, entitled “Secondary Battery and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the field of batteries, and specifically relates to a secondary battery and an electrical device. Background Art

[0004] Secondary batteries are widely used in various consumer electronics and electric vehicles due to their outstanding features such as light weight, no pollution, and no memory effect. Among them, lithium-ion batteries are widely used in portable electronic devices, electric vehicles and other fields.

[0005] As the application scope of secondary batteries becomes wider and wider, the requirements for battery performance are also getting higher and higher. Summary of the Invention

[0006] The present application provides a secondary battery and an electrical device. The secondary battery designed in the present application is conducive to balancing the comprehensive performance of the battery. For example, to a certain extent, it takes into account energy density, fast charging performance and cyclability.

[0007] A first aspect of the present application is to provide a secondary battery, comprising:

[0008] Positive electrode sheet: comprising lithium-containing transition metal phosphate, wherein the lithium-containing transition metal phosphate comprises submicron and micron particles;

[0009] negative electrode;

[0010] Electrolyte: comprising a lithium salt and a film-forming stabilizer, wherein the lithium salt comprises a first lithium salt and a second lithium salt;

[0011] The first lithium salt comprises lithium hexafluorophosphate, and the second lithium salt comprises one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0012] The advantages of the lithium-containing transition metal phosphate provided by the present application include but are not limited to the following: (1) Submicron and micron particles have a small size effect, which facilitates uniform stacking of particles to improve the energy density of the electrode; (2) Submicron and micron particles have a higher specific surface area and more grain boundaries, further providing more and faster lithium ion diffusion channels on the basis of reducing the depth and stroke of lithium ion insertion and extraction, thereby reducing the impedance of the positive electrode and improving the battery's rate capability. However, submicron and micron particles of lithium-containing transition metal phosphates also have defects as active materials for positive electrode sheets, namely, lithium-containing transition metal phosphates have strong water absorption, and this part of the absorbed water is difficult to be discharged by conventional auxiliary means. For example, after baking for a period of time under certain conditions, trace amounts of water will still remain. This trace amount of water can easily increase the probability of side reactions between the active material and the electrolyte during subsequent battery recycling, affecting the battery's cyclability. The design concept of the present application is to select a suitable particle size of lithium-containing transition metal phosphate and combine it with an electrolyte to improve the energy density and rate capability of lithium-ion batteries and reduce the impact on cyclability.

[0013] The electrolyte selected for this application follows this design concept to mitigate the issues associated with the strong water absorption of lithium-containing transition metal phosphates. Specifically, the lithium salt in this electrolyte comprises a first lithium salt and a second lithium salt. The first lithium salt is essential for the proper functioning of the battery and includes, but is not limited to, lithium hexafluorophosphate. However, the first lithium salt readily reacts with trace amounts of water in the battery system, producing a strong acid that easily undergoes side reactions with the organic solvent in the electrolyte. Therefore, the first and second lithium salts are selected for use in combination. The second lithium salt has good hydrolysis stability, including but not limited to one or two of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). This type of lithium salt is less sensitive to water than the first lithium salt. Secondly, this type of lithium salt should have a higher ionic conductivity to improve the rate capability of the battery. However, the second lithium salt also has disadvantages compared to the first lithium salt, that is, the second lithium salt is more susceptible to corrosion of the current collector. Therefore, based on the advantages and disadvantages of the first and second lithium salts themselves, the present application selects the first lithium salt and the second lithium salt for use in combination with the lithium-containing transition metal phosphate. At the same time, the present application also selects to add a film-forming stabilizer as an additive to the electrolyte to improve the stability of the positive and negative electrode interface films and ultimately reduce the impact on the battery's cyclability. Therefore, the secondary battery designed in this application is beneficial for taking into account the battery's energy density, rate capability, and cyclability.

[0014] In some embodiments of the present application, the lithium-containing transition metal phosphate satisfies one or both of the following conditions:

[0015] (1.1) The volume particle size distribution of the lithium-containing transition metal phosphate satisfies the following requirements: Dv50 is 0.3 μm to 2.0 μm, 3.0 μm ≤ Dv90 ≤ 20 μm; 0.1 μm ≤ Dv10 ≤ 1 μm;

[0016] (1.2) The lithium-containing transition metal phosphate includes any one or two or more of lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate.

[0017] In some embodiments of the present application, the Dv50 of the lithium-containing transition metal phosphate is 0.35 μm to 1.8 μm.

[0018] In some embodiments of the present application, the positive electrode sheet satisfies one or more of the following conditions:

[0019] (1.1) The coating weight on one side of the positive electrode sheet is 0.25g~0.50g / 1540.25mm 2 ;

[0020] (1.2) The mass percentage of lithium-containing transition metal phosphate in the positive electrode is 90% to 98%;

[0021] (1.3) The compaction density of the positive electrode is 2.4g / cm 3 ~2.7g / cm 3 .

[0022] In some embodiments of the present application, the lithium salt satisfies one or more of the following:

[0023] (3.1) The mass percentage content of the first lithium salt is a, the mass percentage content of the second lithium salt is b, and: 0.2<a / b≤7;

[0024] (3.2) 2%≤a≤15%;

[0025] (3.3)0.2%≤b≤8%.

[0026] In some embodiments of the present application, the lithium salt satisfies the following conditions:

[0027] The mass percentage content of the first lithium salt is a, 4%≤a≤10%;

[0028] and / or;

[0029] The mass percentage content of the second lithium salt is b, 0.8%≤b≤6%.

[0030] In some embodiments of the present application, the film-forming stabilizer satisfies one or both of the following conditions:

[0031] (4.1) The film-forming stabilizer comprises one or both of lithium fluorosulfonate and lithium difluorophosphate;

[0032] (4.2) Based on the total mass of the electrolyte, the mass percentage content of the film-forming stabilizer is 0.02% to 2%.

[0033] In some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage content of the film-forming stabilizer is 0.1% to 1.5%.

[0034] In some embodiments of the present application, the film-forming stabilizer comprises lithium fluorosulfonate and lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage content of lithium difluorophosphate is ≤1%, and the mass percentage content of lithium fluorosulfonate is greater than or equal to 0.2% and less than 2%.

[0035] In some embodiments of the present application, the electrolyte comprises a solvent, the solvent comprises a carboxylate, and the carboxylate satisfies one or both of the following conditions:

[0036] (5.1) Carboxylic acid esters have the following structural formula:

[0037] R1-COO-R2;

[0038] wherein R1 and R2 each independently comprise a substituted and / or unsubstituted C1-C5 alkyl group;

[0039] (5.2) Based on the mass of the electrolyte, the mass percentage content of the carboxylic acid ester is 5% to 70%.

[0040] In some embodiments of the present application, the electrolyte comprises a solvent, the solvent comprises a carboxylate, and the carboxylate satisfies one or both of the following conditions:

[0041] (6.1) Carboxylic acid esters include one or more of ethyl acetate, methyl acetate, ethyl propionate, propyl acetate, methyl propionate, and methyl butyrate;

[0042] (6.2) Based on the mass of the electrolyte, the mass percentage content of the carboxylic acid ester is 10% to 60%.

[0043] In some embodiments of the present application, the electrolyte comprises a solvent, the solvent comprises a carboxylate and a carbonate, and the carbonate satisfies one or both of the following conditions:

[0044] (7.1) The mass percentage of carbonate is greater than or equal to 5% based on the mass of the electrolyte;

[0045] (7.2) The carbonate ester includes one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0046] In some embodiments of the present application, the negative electrode plate satisfies one or both of the following conditions:

[0047] (8.1) The coating weight on one side of the negative electrode sheet is 0.13g to 0.25g / 1540.25mm 2 ;

[0048] (8.2) The negative electrode plate comprises carbon material.

[0049] The second aspect of the present application is to provide an electrical device comprising the secondary battery described in the first aspect.

[0050] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0052] FIG1 is a schematic diagram of a battery structure according to some embodiments of the present application;

[0053] FIG2 is a schematic diagram of the exploded structure of batteries according to some embodiments of the present application;

[0054] FIG3 is a schematic diagram of a vehicle structure according to some embodiments of the present application;

[0055] FIG4 is a schematic diagram of the battery pack structure of some embodiments of the present application;

[0056] FIG5A is a schematic structural diagram of a positive electrode sheet according to some embodiments of the present application;

[0057] FIG5B is a schematic structural diagram of another positive electrode sheet according to some embodiments of the present application.

[0058] The figure numbers in the specific implementation manner are as follows: 10000, vehicle; 1000, battery; 2000, controller; 3000, motor; 100, battery cell; 200, casing; 210, first part; 220, second part; 10, secondary battery; 101, casing; 102, electrode assembly; 103, cover plate; 1, positive electrode sheet; 11. positive electrode current collector; 12, positive electrode film layer; Coordinate axis x direction: length or width direction of positive electrode sheet; Coordinate axis z direction: thickness direction of positive electrode sheet. DETAILED DESCRIPTION

[0059] Below, the embodiments of the secondary battery and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0060] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0062] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0063] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

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

[0065] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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, in this application, the terms "first", "second", etc. are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0067] Unless otherwise specified, in this application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0068] The term "alkyl" is intended to be a straight chain saturated hydrocarbon structure having 1 to 20 carbon atoms. "Alkyl" is also intended to be a branched or cyclic hydrocarbon structure having 3 to 20 carbon atoms. When specifying an alkyl group with a specific carbon number, it is intended to encompass all geometric isomers with that carbon number; therefore, for example, "butyl" means including n-butyl, sec-butyl, isobutyl, tert-butyl and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Alkyl examples include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, etc.

[0069] The term "substituted" includes the replacement of hydrogen atoms in the alkyl group by other groups, and the number of substitutions is determined by the number of hydrogen atoms.

[0070] Secondary batteries have been widely used in various products due to their advantages such as high energy density, long cycle life, safety and reliability. In recent years, with the significant increase in demand for secondary batteries as energy sources, higher requirements have been placed on the performance of secondary batteries, such as dynamic performance and cycle performance.

[0071] Lithium-containing transition metal phosphates are the most commonly used cathode active materials. They offer good thermal stability, low cost, and excellent cycling performance. However, their drawbacks are poor rate performance and low energy density in lithium-ion batteries.

[0072] One of the existing methods for improving the rate capability and energy density of lithium-containing transition metal phosphates as positive electrode active materials in lithium-ion batteries is to optimize the material particles. However, the optimized particles also bring technical defects: increased water absorption, which is difficult to discharge through conventional auxiliary means, and the resulting side reactions with the electrolyte increase, affecting the battery's cyclability.

[0073] If the rate capability and energy density of lithium-containing transition metal phosphates as positive electrode active materials in lithium-ion batteries can be improved while taking into account their cyclability, the performance of secondary batteries can be further improved.

[0074] Based on the above considerations, in order to solve the problem that lithium-containing transition metal phosphates as positive electrode active materials in lithium-ion batteries cannot simultaneously achieve rate performance, energy density and cyclability, a secondary battery and power-consuming device were obtained based on the above design concept and related experimental research.

[0075] A secondary battery provided in the present application includes: a positive electrode plate, a negative electrode plate and an electrolyte, the positive electrode plate contains a lithium-containing transition metal phosphate, and the lithium-containing transition metal phosphate contains submicron and micron particles; at the same time, the electrolyte in the secondary battery contains a lithium salt and a film-forming stabilizer, the lithium salt contains a first lithium salt and a second lithium salt, wherein the first lithium salt contains lithium hexafluorophosphate, and the second lithium salt contains one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0076] The lithium-containing transition metal phosphates used in this application as active materials in the positive electrode plates have a small size effect due to their submicron and micron-sized particles. This facilitates uniform particle stacking, thereby improving the energy density of the plates. Furthermore, the submicron and micron-sized particles have a higher specific surface area and more grain boundaries, further reducing the depth and distance of lithium ion insertion and extraction, providing more and faster lithium ion diffusion channels. This, in turn, reduces the impedance of the positive electrode plates and improves the battery's rate capability. However, lithium-containing transition metal phosphates inherently absorb water, such as from the environment. When formed into submicron and micron-sized particles, this water absorption becomes even stronger. This absorbed water is difficult to remove through conventional auxiliary means. For example, even after baking under certain conditions for a period of time, trace amounts of water may still remain. This trace amount of water can easily increase the probability of side reactions between the active material and the electrolyte during subsequent battery cycling, affecting the battery's cyclability. Furthermore, because lithium-containing transition metal phosphates form more lithium ion diffusion channels, which also ensure sufficient electrolyte wetting, side reactions are further enhanced. To minimize the problems associated with the high water absorption of lithium-containing transition metal phosphates, this application utilizes a second lithium salt with excellent hydrolytic stability and a film-forming stabilizer in the electrolyte. By appropriately reducing the amount of the first lithium salt, this balances the small size effect of the lithium-containing transition metal phosphate particles and reduces the impact on battery cyclability. Consequently, the secondary battery designed in this application achieves a balanced balance of energy density, rate capability, and cyclability.

[0077] The secondary battery provided by the present application alleviates the technical problems of low energy density and poor rate performance of lithium-containing transition metal phosphates as positive electrode active materials, and achieves the technical purpose of improving battery performance by taking into account the energy density, rate performance and cyclability of the battery. The battery may include an outer packaging. The outer packaging can be used to encapsulate the electrode assembly and the electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, which can be made by a winding process or a lamination process. The outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastics, polypropylene, polybutylene terephthalate and polybutylene succinate can be listed.

[0078] The present application has no particular limitation on the shape of the battery, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 10 with a square structure as an example.

[0079] According to some embodiments of the present application, referring to Figure 2, the outer packaging may include a shell 101 and a cover plate 103. Among them, the shell 101 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 101 has an opening connected to the receiving cavity, and the cover plate 103 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 102 through a winding process or a lamination process. The electrode assembly 102 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 102. The number of electrode assemblies 102 contained in the secondary battery 10 can be one or more, and those skilled in the art can select according to specific actual needs.

[0080] The electrode assembly provided in the present application is applied to batteries to improve battery performance. The battery can be used as a power source for an electrical device or as an energy storage unit for an electrical device. The electrical device is applied to the power field, such as mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but not limited to the above-mentioned fields.

[0081] For ease of explanation, some embodiments of this application are described using a vehicle as an example. The battery provided in this application has good rate capability, so the vehicle starts quickly. On the other hand, the battery has a high energy density, so it can provide a longer driving range for the vehicle within the available space.

[0082] Please refer to Figure 3, which is a structural schematic diagram of the vehicle 10000 provided in some embodiments of the present application. The vehicle 10000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 1000 is provided inside the vehicle 10000, and the battery 1000 can be provided at the bottom, head or tail of the vehicle 10000. The battery 1000 can be used to power the vehicle 10000. For example, the battery 1000 can serve as an operating power source for the vehicle 10000. The vehicle 10000 may also include a controller 2000 and a motor 3000. The controller 2000 is used to control the battery 1000 to power the motor 3000, for example, for starting, navigating and driving the vehicle 10000.

[0083] In some embodiments of the present application, the battery 1000 can serve not only as an operating power source for the vehicle 10000, but also as a driving power source for the vehicle 10000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 10000.

[0084] Please refer to Figure 4, which is an exploded view of a battery 1000 provided in some embodiments of the present application. Battery 1000 includes a housing 200 and a battery cell 100. Conventional battery cells include primary or secondary batteries, but this application specifically protects secondary batteries. Battery cell 100 is housed within housing 200. Housing 200 is used to accommodate battery cell 100 and can adopt a variety of structures.

[0085] In some embodiments, the housing 200 may include a first portion 210 and a second portion 220. The first portion 210 and the second portion 220 overlap each other, and together define a storage space for accommodating the secondary battery 100. The second portion 220 may be a hollow structure with one end open, and the first portion 210 may be a plate-like structure. The first portion 210 overlaps the open side of the second portion 220, so that the first portion 210 and the second portion 220 together define the storage space. The first portion 210 and the second portion 220 may also be hollow structures with one end open, with the open side of the first portion 210 overlapping the open side of the second portion 220. Of course, the housing 200 formed by the first portion 210 and the second portion 220 may have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0086] In the battery 1000, there may be multiple battery cells 100, and the multiple battery cells 100 may be connected in series, in parallel, or in a hybrid connection. A hybrid connection refers to a combination of series and parallel connections among the multiple battery cells 100. The multiple battery cells 100 may be directly connected in series, in parallel, or in a hybrid connection, and then the entire battery 100 structure may be housed within the housing 200. Of course, the battery 1000 may also be a battery module formed by first connecting multiple battery cells 100 in series, in parallel, or in a hybrid connection, and then the multiple battery modules 1000 are further connected in series, in parallel, or in a hybrid connection to form an entire battery 1000 structure, and then housed within the housing 200. The battery 1000 may also include other structures, for example, the battery 1000 may also include a busbar component for electrically connecting the multiple battery cells 100.

[0087] secondary batteries

[0088] The present application discloses, in some embodiments, a secondary battery, comprising: a positive electrode plate, a negative electrode plate, and an electrolyte, wherein the positive electrode plate comprises a lithium-containing transition metal phosphate, and the lithium-containing transition metal phosphate comprises submicron and micron particles; at the same time, the electrolyte in the secondary battery comprises a lithium salt and a film-forming stabilizer, and the lithium salt comprises a first lithium salt and a second lithium salt, wherein the first lithium salt comprises lithium hexafluorophosphate, and the second lithium salt comprises one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0089] The positive electrode plate of the present application includes a positive electrode film layer, which is formed on one or two surfaces of the positive electrode plate, and a lithium-containing transition metal phosphate serves as the active material of the positive electrode film layer. The preparation method of the lithium-containing transition metal phosphate includes preparing large-particle salts by conventional preparation methods in the art, and then grinding to obtain submicron and micron particles. The micron-sized particles in the present application include particles with a particle size of 1 μm or more and less than or equal to 50 μm, and the submicron-sized particles include particles with a particle size of less than 1 μm. The submicron-sized particles in the present application include particles with a particle size greater than or equal to 0.1 μm and less than 1 μm. If the particle size of the lithium-containing transition metal phosphate is reflected by the particle size distribution, it includes particles with a particle size less than 1 μm and particles greater than 1 μm. The average particle size of the submicron-sized particles needs to be calculated based on the specific number of different particle size intervals. The preparation method of the lithium-containing transition metal phosphate of the present application includes, but is not limited to, mixing various metal precursors and then reacting them via a solid-phase method or a liquid-phase method. The solid-phase method includes, but is not limited to, high-temperature solid-phase reaction, carbothermal reduction, microwave synthesis, and pulsed laser deposition. The liquid-phase method includes, but is not limited to, sol-gel method, hydrothermal synthesis, precipitation method, and solvothermal synthesis.

[0090] The advantages of the lithium-containing transition metal phosphate provided in this application include but are not limited to the following: (1) Submicron and micron-sized particles have a small size effect, which facilitates uniform stacking of particles to improve the energy density of the electrode; (2) Submicron and micron-sized particles have a higher specific surface area and more grain boundaries, further providing more and faster lithium ion diffusion channels on the basis of reducing the depth and stroke of lithium ion insertion and extraction, thereby reducing the impedance of the positive electrode and improving the battery's rate capability. However, lithium-containing transition metal phosphates also have disadvantages as active materials for the positive electrode film layer, namely, lithium-containing transition metal phosphates have strong water absorption. When they form submicron and micron-sized particles, the water absorption will be even stronger. This part of the absorbed water is difficult to discharge through conventional auxiliary means. For example, after baking for a period of time under certain conditions, trace amounts of water will still remain. This trace amount of water can easily increase the probability of side effects between the active material and the electrolyte during subsequent battery recycling, affecting the battery's cyclability. The design concept of this application is to improve the technical problems of poor energy density and rate capability of lithium-containing transition metal phosphates as active materials for the positive electrode film layer in lithium-ion batteries, and to reduce the impact on cyclability.

[0091] The electrolyte selected for this application follows this design concept to mitigate the issues associated with the strong water absorption of lithium-containing transition metal phosphates. Specifically, the lithium salt in this electrolyte comprises a first lithium salt and a second lithium salt. The first lithium salt is essential for the proper functioning of the battery and includes, but is not limited to, lithium hexafluorophosphate. However, the first lithium salt readily reacts with trace amounts of water in the battery system, producing a strong acid that easily undergoes side reactions with the organic solvent in the electrolyte. Therefore, the first and second lithium salts are selected for use in combination. The second lithium salt has good hydrolysis stability, including but not limited to one or two of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). This type of lithium salt is less sensitive to water than the first lithium salt. Secondly, this type of lithium salt should have a higher ionic conductivity to improve the rate capability of the battery. However, the second lithium salt also has disadvantages compared to the first lithium salt, that is, the second lithium salt is more susceptible to corrosion of the current collector. Therefore, the present application considers the advantages and disadvantages of the first and second lithium salts themselves, and selects the first lithium salt and the second lithium salt for use in combination in order to match the small size effect particles of the lithium transition metal phosphate. At the same time, the present application also chooses to add a film-forming stabilizer as an additive to the electrolyte to improve the stability of the positive and negative electrode interface films, and ultimately reduce the impact on the battery cyclability. Therefore, the secondary battery designed in the present application is conducive to taking into account the energy density, rate capability and cyclability of the battery.

[0092] In some embodiments of the present application, the lithium-containing transition metal phosphate satisfies one or both of the following conditions:

[0093] (1.1) The volume particle size distribution of the lithium-containing transition metal phosphate satisfies the following requirements: Dv50 is 0.3 μm to 2.0 μm, 3.0 μm ≤ Dv90 ≤ 20 μm; 0.1 μm ≤ Dv10 ≤ 0.3 μm;

[0094] (1.2) The lithium-containing transition metal phosphate includes any one or two or more of lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate.

[0095] The Dv50 of the lithium transition metal phosphate containing the present application includes particles with a particle size larger than it, accounting for 50% of the volume, and particles with a particle size smaller than it, accounting for 50% of the volume. It is also called the median diameter, which is usually used to represent the average particle size of the particles. Compared with the micron-sized particles conventionally used in the prior art, the particle size of the particles of the present application has decreased, but it has not decreased to the nanometer level. This is because the nanometer-sized particles have stronger water absorption and easily cause the particles to stick together. The Dv90 of the lithium transition metal phosphate containing the present application includes particles with a particle size smaller than it, accounting for 90% of the volume, and Dv10 includes particles with a particle size smaller than it, accounting for 10% of the volume. Whether it is Dv90 or Dv10, conventional measurement methods in the art can be used, such as using a particle size analyzer to measure the particle size distribution and then obtain it statistically. In these embodiments, the present application chooses to refer to the laser diffraction particle size analysis method for measurement, specifically referring to the standard GB / T19077-2016 to obtain the particle size distribution diagram, and then obtains it by calculation.

[0096] The median diameter Dv50 of this application affects the compaction density and specific surface area of ​​the lithium-containing transition metal phosphate. Generally speaking, under the same conditions, the larger the median diameter Dv50, the greater the compaction density and the smaller the specific surface area. In these embodiments, this application selects Dv50 as 0.3μm to 2.0μm, 3.0μm≤Dv90≤20μm; 0.1μm≤Dv10≤1μm; to improve the energy density and rate capability of the secondary battery, while at the same time being able to be used in conjunction with subsequent electrolytes. In these embodiments, this application discloses that Dv50 is any one of 0.3μm, 0.35μm, 0.5μm, 1.0μm, 1.5μm, 1.8μm, 2.0μm or any one of the values ​​in the above range. The present application discloses in these embodiments that Dv90 is any one of 20 μm, 15 μm, 10 μm, 8 μm, 6 μm, 5 μm, 4 μm, 3.8 μm, 3.5 μm, and 3 μm. The present application discloses in these embodiments that Dv10 is any one of 0.1 μm, 0.2 μm, 0.22 μm, 0.25 μm, 0.28 μm, 0.45 μm, 0.5 μm, 0.9 μm, and 1.0 μm.

[0097] The lithium-containing transition metal phosphate in this application includes any one or more of lithium iron phosphate, lithium manganese phosphate and lithium iron manganese phosphate. The chemical formula of lithium iron phosphate, lithium manganese phosphate and lithium iron manganese phosphate is Li 1-x Fe y Mn 1-yPO4, 0≤x<1, 0≤y≤1, the lithium-containing transition metal phosphate with this chemical formula has an olivine crystal structure, and the good stability of the crystal structure during the delithiation and insertion of lithium is conducive to ensuring the high cycle stability of the battery. At the same time, the battery assembled with the positive electrode active material having the above chemical formula in the present application will be accompanied by lithium deintercalation and consumption during the charging and discharging process. The molar content of lithium is different when the battery is discharged to different states. The above limitations include the lithium content of the battery in different charging and discharging states at a voltage of 2V to 5V.

[0098] In some embodiments of the present application, the Dv50 of the lithium-containing transition metal phosphate is 0.35 μm to 1.8 μm.

[0099] In these embodiments, the present application selects lithium-containing transition metal phosphate particles with a Dv50 of 0.35 μm to 1.8 μm. Lithium-containing transition metal phosphate particles with this median diameter can be used in combination with the electrolyte to further improve the energy density and rate capability of the secondary battery.

[0100] In some embodiments of the present application, the positive electrode plate satisfies one or more of the following conditions:

[0101] (1.1) The coating weight on one side of the positive electrode sheet is 0.25g~0.50g / 1540.25mm 2 ;

[0102] (1.2) The mass percentage of lithium-containing transition metal phosphate in the positive electrode is 90% to 98%;

[0103] (1.3) The compaction density of the positive electrode is 2.4g / cm 3 ~2.7g / cm 3 .

[0104] The positive electrode film layer of the present application can be formed on one or both surfaces of the positive electrode plate, as shown in Figure 5A or 5B. The positive electrode film layer is formed by a conventional coating method in the art: a positive electrode slurry containing a lithium transition metal phosphate is coated on one or both surfaces of the current collector, and the positive electrode film layer is obtained after drying and cold pressing. The single-sided coating weight of the positive electrode film layer can be calculated based on the actual coating situation. The single-sided coating weight of the positive electrode plate of the present application can be 0.25g / 1540.25mm 2 , 0.30g / 1540.25mm 2 , 0.35g / 1540.25mm 2 , 0.40g / 1540.25mm 2 , 0.45g / 1540.25mm 2 , 0.50g / 1540.25mm 2Any one of the above range values ​​or any one of the above range values. The present application selects the single-sided coating weight of the positive electrode sheet to be 0.25g~0.50g / 1540.25mm 2 This is achieved on the basis of the micron- and submicron-sized active materials selected in this application and in combination with certain coating conditions. The coating weight is increased compared to the conventional coating weight of lithium-containing transition metal phosphates in the field, and it can be clearly expected that the energy density of the battery will be greatly improved.

[0105] In addition to the lithium-containing transition metal phosphate, the positive electrode film layer of the present application also includes a positive electrode conductive agent, a positive electrode binder, etc., wherein the mass percentage of the lithium-containing transition metal phosphate is 90% to 98% based on the total content of each component in the positive electrode film layer. In these embodiments, the mass percentage of the lithium-containing transition metal phosphate can be any one of 90%, 92%, 94%, 95%, 96%, 98%, or any one of the above ranges. The positive electrode active material with this mass ratio is convenient for combining its particle size to ensure the above coating weight.

[0106] In the present application, the compacted density of the positive electrode sheet can be used to characterize the energy density of the positive electrode active material in the entire positive electrode sheet. The compacted density of the positive electrode sheet = the surface density of the positive electrode sheet / the thickness of the positive electrode sheet. The thickness of the positive electrode sheet includes the distance between one end face of the positive electrode sheet and the other end face opposite to it. The thickness of the positive electrode sheet can be detected using equipment and methods known in the art. The relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. The elements contained in the lithium-containing transition metal phosphate in the positive electrode sheet of the present application can be qualitatively or quantitatively determined using a single detection method, or by combining several detection methods. For example, it can be obtained according to GB / T 17359-2012 "Quantitative Analysis by Microbeam Energy Spectroscopy", or by taking an average value of multiple measurements using a measuring instrument such as a micrometer.

[0107] The present application discloses in these embodiments that the compacted density of the positive electrode sheet is 2.4 g / cm 3 , 2.46g / cm 3 , 2.48g / cm 3 , 2.55g / cm 3 , 2.6g / cm 3 , 2.62g / cm 3 , 2.68g / cm 3 , 2.69g / cm 3 , 2.7g / cm 3Any one of the above values ​​or any one of the above range values, the compaction density with this value is correlated with the type, content and coating weight of the positive electrode active material in the positive electrode film layer.

[0108] In some embodiments of the present application, in addition to containing a lithium-containing transition metal phosphate as a positive electrode active material, the positive electrode film layer also contains a positive electrode conductor and a positive electrode binder. In these embodiments, the present application discloses that the mass ratio satisfies the following: lithium-containing transition metal phosphate: positive electrode conductor: positive electrode binder is (90% to 98%): (0.5% to 5%): (0.5% to 5%). Among them, the positive electrode conductor includes but is not limited to one or a combination of two or more of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene and carbon nanofibers. The positive electrode binder includes but is not limited to polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc., or a combination of two or more.

[0109] In some embodiments of the present application, a method for preparing a positive electrode sheet comprises: mixing each component with a solvent in a certain mass ratio to obtain a positive electrode slurry, coating the positive electrode slurry on one or both surfaces of a positive electrode current collector, heating, drying, and cooling to obtain a positive electrode sheet comprising a positive electrode film layer. In these embodiments, the present application discloses that the heating and baking temperature is 90°C to 120°C, for example, it can be 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, etc. By regulating the baking temperature, the positive electrode active material and additives can be prevented from thermal decomposition due to overheating while promoting the volatilization of the solvent and solidification of the slurry. At the same time, the solvent used to prepare the positive electrode slurry includes one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), dimethyl sulfoxide (DMSO), pyridine, and tetrahydrofuran (THF). By selecting these solvents, the stability and uniformity of the positive electrode active material in the slurry can be improved. At the same time, the solubility of additives in the slurry can be increased, solving problems such as slurry instability, easy stratification, and sedimentation. The selected solvent is a non-aqueous system, which can solve the problem of additive hydrolysis caused by heat.

[0110] The present application also discloses in some embodiments that the positive electrode current collector can be a metal foil or a composite current collector, wherein the metal foil can be an aluminum foil, and the composite current collector can include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming a metal material such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0111] In some embodiments of the present application, the lithium salt satisfies one or more of the following conditions:

[0112] (3.1) The mass percentage content of the first lithium salt is a, the mass percentage content of the second lithium salt is b, and: 0.2<a / b≤7;

[0113] (3.2) 2%≤a≤15%;

[0114] (3.3)0.2%≤b≤8%.

[0115] As mentioned above, the first lithium salt is very easy to react with trace water in the battery system, and the second lithium salt is more likely to corrode the current collector. The present application chooses to use the first lithium salt and the second lithium salt in combination and control their content to improve the effect of the combination. To further provide the usage amount of the first lithium salt and the second lithium salt in the electrolyte, the present application provides a specific relationship between the two contents: 0.2<a / b≤7. In these embodiments, a / b can be any of 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0 or any value within the above range. The present application chooses to match the content of the first lithium salt and the second lithium salt. The lithium salt formed has the advantage of low sensitivity to water, organic solvents, etc., which is beneficial to reduce side reactions and reduce the impact on battery cycle stability. The specific components and contents in the electrolyte of the present application can be determined using methods known in the art. For example, it can be measured by gas chromatography, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), inductively coupled plasma optical emission spectrometry (ICP-OES), and the like.

[0116] Specifically, in some embodiments, the present application discloses that the mass percentage content a of the first lithium salt satisfies: 2%≤a≤15%. Compared with the content corresponding to the first lithium salt of lithium hexafluorophosphate in the prior art, the content of the first lithium salt selected in the present application is reduced. In these embodiments, the mass percentage content a of the first lithium salt can be any of 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, or any of the above ranges.

[0117] At the same time, the present application selects a second lithium salt with a certain content, and the mass percentage content of the second lithium salt can be any one of 0.2%, 0.5%, 0.8%, 1%, 1.4%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8% or any one of the above range values.

[0118] In some embodiments of the present application, the lithium salt satisfies the following conditions:

[0119] The mass percentage content of the first lithium salt is a, 4%≤a≤10%;

[0120] and / or;

[0121] The mass percentage content of the second lithium salt is b, 0.8%≤b≤6%.

[0122] In these embodiments, the present application selects the first lithium salt to satisfy the mass percentage content: 4%≤a≤10%; the second lithium salt to satisfy the mass percentage content: 0.8%≤b≤6%, so as to better match the content between the first lithium salt and the second lithium salt.

[0123] In some embodiments of the present application, the film-forming stabilizer satisfies one or both of the following conditions:

[0124] (4.1) The film-forming stabilizer comprises one or both of lithium fluorosulfonate and lithium difluorophosphate;

[0125] (4.2) Based on the total mass of the electrolyte, the mass percentage content of the film-forming stabilizer is 0.02% to 2%.

[0126] The film-forming stabilizer selected in the present application has the advantages of high stability, such as resistance to high voltage, high temperature or low temperature, etc. to improve the stability of the electrolyte, and can also promote the formation of a stable interface film between lithium ions and the electrolyte at the positive electrode interface and / or the negative electrode interface. The interface film includes an SEI film and a CEI film, wherein the SEI film is in situ coated on the surface of the negative electrode active material, and the CEI film is in situ coated on the surface of the positive electrode active material, thereby improving the cycle stability of the battery by reducing side reactions. Specifically, lithium fluorosulfonate and / or lithium difluorophosphate can enhance the film formation of the positive and negative electrodes, effectively reduce the catalytic oxidation reaction of the electrolyte on the surface of the positive and negative electrodes, and reduce the side reactions at the interface between the electrolyte and the positive and negative electrodes at high voltage and / or high temperature and / or low temperature, thereby effectively improving the cyclability of the battery. In these examples, the present application selected a film-forming stabilizer content of 0.02% to 2% by weight. This is affected by the solubility of each film-forming stabilizer. For example, the solubility of lithium difluorophosphate in organic solvents is not high. For example, the solubility in carbonate solvents is about 1%, and in carboxylic acid esters such as ethyl acetate, the content is about 3% to 4%. Further increasing its content causes the electrolyte to become turbid. On the other hand, the film-forming stabilizer content with this content is related to the total content of lithium salt in the electrolyte. Generally speaking, when the content of lithium salt is high, the content of film-forming stabilizer that matches it is also relatively high, and vice versa. The present application specifically discloses in these embodiments that the mass percentage content of the film-forming stabilizer can be 0.02%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9 %, 0.95%, 1.0%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, 1.5%, 1.55%, 1.6%, 1.65%, 1.7%, 1.75%, 1.8%, 1.85%, 1.9%, 1.95%, 2.0% or any one of the values ​​satisfying the above range.

[0127] In some embodiments of the present application, the weight percentage of the film-forming stabilizer is 0.1% to 1.5% based on the total weight of the electrolyte. In these embodiments, the present application selects a weight percentage of the film-forming stabilizer of 0.1% to 1.5% to better match a certain content of lithium salt and further take into account the energy density, rate capability, and cyclability of the battery.

[0128] In some embodiments of the present application, the film-forming stabilizer comprises lithium fluorosulfonate and lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage content of lithium difluorophosphate is ≤1%, and the mass percentage content of lithium fluorosulfonate is greater than or equal to 0.2% and less than 2%.

[0129] The present application selects lithium fluorosulfonate and lithium difluorophosphate as film-forming stabilizers and adds them to the electrolyte to better match the above-mentioned lithium salts. Wherein, due to the solubility of lithium difluorophosphate in the electrolyte, its mass percentage content is ≤1%, such as 0.9%, 0.8%, etc.; the mass percentage content of lithium difluorophosphate in the electrolyte can also be above 1%, such as 2%. The mass percentage content of lithium fluorosulfonate used in combination with lithium difluorophosphate is greater than or equal to 0.2% and less than 2%, for example, it can be any one of 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.95% or any one of the above-mentioned range values.

[0130] In some embodiments of the present application, the electrolyte comprises a solvent, the solvent comprises a carboxylate, and the carboxylate satisfies one or both of the following conditions:

[0131] (5.1) Carboxylic acid esters have the following structural formula:

[0132] R1-COO-R2;

[0133] wherein R1 and R2 each independently comprise a substituted and / or unsubstituted C1-C5 alkyl group;

[0134] (5.2) Based on the mass of the electrolyte, the mass percentage content of the carboxylic acid ester is 5 to 70%.

[0135] The solvents of this application include carboxylic acid esters, which are relatively stable, resistant to oxidation and reduction, and highly compatible with the aforementioned lithium salts and additives. Furthermore, the inclusion of carboxylic acid esters in the solvent can result in lower viscosity and surface tension in the electrolyte. When combined with lithium-containing transition metal phosphates, which possess relatively more lithium ion diffusion channels, these solvents facilitate effective contact between the lithium-containing transition metal phosphate and the electrolyte, thereby improving the battery's rate capability. The carboxylic acid esters selected in these embodiments are primarily linear carboxylic acid esters, as they have lower viscosity and are therefore better suited for use with lithium-containing transition metal phosphates. These embodiments also disclose a carboxylic acid ester content of 5% to 70% by weight, wherein the carboxylic acid ester content can be any of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%, or any value within the aforementioned ranges.

[0136] In some embodiments of the present application, the electrolyte comprises a solvent, the solvent comprises a carboxylate, and the carboxylate satisfies one or both of the following conditions:

[0137] (6.1) Carboxylic acid esters include one or more of ethyl acetate, methyl acetate, ethyl propionate, propyl acetate, methyl propionate, and methyl butyrate;

[0138] (6.2) Based on the mass of the electrolyte, the mass percentage content of the carboxylic acid ester is 10 to 60%.

[0139] Examples of carboxylic acid esters include one or more of ethyl acetate, methyl acetate, ethyl propionate, propyl acetate, methyl propionate, and methyl butyrate. Carboxylic acid ester solvents have relatively low viscosities, and when used in combination, multiple carboxylic acid ester solvents can result in an electrolyte having a lower surface tension.

[0140] In some embodiments of the present application, the electrolyte comprises a solvent, the solvent comprises a carboxylate and a carbonate, and the carbonate satisfies one or both of the following conditions:

[0141] (7.1) The mass percentage of carbonate is greater than or equal to 5% based on the mass of the electrolyte;

[0142] (7.2) The carbonate ester includes one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0143] The lithium salt selected in this application has better solubility in carbonates than in carboxylates. Therefore, this application chooses to use carboxylates and carbonates in combination to reduce the viscosity of the electrolyte without affecting the solubility of the lithium salt, thereby facilitating use with lithium-containing transition metal phosphates.

[0144] As examples of carbonates, carbonates include one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Selecting the carbonates exemplified is beneficial for better coordination with the carboxylate.

[0145] The electrolyte of the present application can be prepared according to conventional methods in the art. For example, a film-forming additive, a solvent, a lithium salt, etc. can be uniformly mixed to obtain an electrolyte. The order of adding the materials is not particularly limited. For example, the additive, lithium salt, etc. can be added to a non-aqueous solvent and mixed uniformly to obtain a non-aqueous electrolyte.

[0146] In the present application, the components and their contents in the electrolyte can be determined by methods known in the art. For example, they can be determined by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0147] It should be noted that when testing the electrolyte in this application, freshly prepared electrolyte can be directly taken, or electrolyte can be obtained from a secondary battery. An exemplary method for obtaining electrolyte from a secondary battery includes the following steps: discharging the secondary battery to the discharge cut-off voltage (for safety reasons, the battery is generally in a fully discharged state) and then centrifuging it, and then taking an appropriate amount of the liquid obtained by centrifugation is the non-aqueous electrolyte. The non-aqueous electrolyte can also be obtained directly from the injection port of the secondary battery.

[0148] In some embodiments of the present application, the negative electrode plate satisfies one or both of the following conditions:

[0149] (8.1) The coating weight on one side of the negative electrode sheet is 0.13g to 0.25g / 1540.25mm 2 ;

[0150] (8.2) The negative electrode plate comprises carbon material.

[0151] The negative electrode sheet of the present application includes a negative electrode film layer, wherein the negative electrode film layer can be formed on one or two surfaces of the negative electrode sheet, wherein the formation of the negative electrode sheet includes applying a negative electrode slurry containing a carbonaceous material to one or two surfaces of the current collector using a conventional coating method in the art, and obtaining the negative electrode sheet after drying and cold pressing. The single-sided coating weight of the positive electrode sheet can be calculated based on the actual coating situation. The single-sided coating weight of the negative electrode sheet of the present application can be 0.13g / 1540.25mm 2 , 0.15g / 1540.25mm 2 , 0.18g / 1540.25mm 2 , 0.20g / 1540.25mm 2 , 0.25g / 1540.25mm 2 Any one of the above range values ​​or any one of the above range values. The present application selects the negative electrode sheet with a single-sided coating weight of 0.13g to 0.25g / 1540.25mm 2 This is achieved on the basis of the carbon-containing material selected in this application and in combination with certain coating conditions. The negative electrode sheet with the coating amount is matched with the positive electrode sheet to improve the energy density of the battery.

[0152] The carbon material of the present application comprises graphitized carbon and amorphous carbon, wherein the graphitized carbon comprises one or more of natural graphite, artificial graphite, composite graphite, and mesophase carbon microspheres, and the amorphous carbon comprises any of hard carbon and soft carbon. The natural graphite, artificial graphite, composite graphite, or mesophase carbon microspheres in the present application comprise any conventional preparation method in the art. In some embodiments, the present application discloses that the graphitized carbon comprises artificial graphite.

[0153] In addition to the active material, the negative electrode film layer of the present application also includes a conductive agent, a thickener, a binder, etc., wherein the conductive agent includes but is not limited to one or a combination of two of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene and carbon nanofibers; the thickener includes cellulose and its sodium salt, and cellulose includes methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, etc.; the binder includes but is not limited to polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, polyethylene oxide, polyacrylic acid, polyacrylamide, sodium alginate, styrene-butadiene rubber (SBR), etc.

[0154] In some embodiments, the present application discloses a mass ratio of the carbon-containing material, the conductive agent, the thickener, and the binder: (90-97): (0.5-3): (0.5-3): (0.5-3).

[0155] In some embodiments, the present application discloses that the negative electrode current collector includes, but is not limited to, a metal foil or a composite current collector. The metal foil may be a copper foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material, such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, on a polymer material substrate, such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0156] The preparation method of the negative electrode film layer in these embodiments of the present application includes mixing the raw materials with a solvent in a certain mass ratio to form a negative electrode slurry, defoaming the negative electrode slurry, uniformly coating it on one or two surfaces of the negative electrode current collector, and drying it to obtain a negative electrode sheet containing the negative electrode film layer.

[0157] Isolation film

[0158] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0159] In some embodiments, the isolation membrane includes a base material layer and a coating provided on the surface of the base material layer; the base material of the base material layer includes one or more of polyethylene, polypropylene, poly(p-phenylene terephthalamide), polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide; the coating includes a ceramic coating and / or a polymer coating. The base material layer has a good permeability to lithium ions, which is conducive to the migration of lithium ions; the surface of the base material layer is provided with a coating, which can further improve the mechanical properties of the isolation membrane. Optionally, the ceramic particles in the ceramic coating include one or more of SiO2, Al2O3, AlOOH, CaO, TiO2, MgO, ZnO, ZrO2, Mg(OH)2, and BaSO4. Optionally, the polymer material of the polymer coating includes one or more of polyethylene (PE), polypropylene (PP), poly(p-phenylene terephthalamide) (PPTA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), and polyamide (PA). The polymer coating layer and the substrate layer may be made of the same or different materials, and the thickness of the polymer coating layer and the substrate layer may be different. Optionally, the thickness of the polymer coating layer is less than the thickness of the substrate layer.

[0160] In other embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can 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 can be the same or different, without particular limitation.

[0161] Example

[0162] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0163] Example 1

[0164] Select lithium manganese iron phosphate, the chemical formula of which is LiFe 0.5 Mn 0.5 PO4, the volume particle size distribution of the lithium manganese iron phosphate is shown in Table 1, and the lithium manganese iron phosphate raw material is baked in an oven at 110° C. for 12 hours.

[0165] 1. Preparation of positive electrode sheet:

[0166] Take the treated lithium iron manganese phosphate (Dv50 is 1 μm): positive electrode conductive agent carbon black: positive electrode binder polyvinylidene fluoride (PVDF) according to 98:0.9:1.1 and disperse them in an appropriate amount of solvent NMP and stir and mix them thoroughly to form a uniform positive electrode slurry; the positive electrode slurry is coated on both surfaces of the positive electrode current collector and heated and dried. Specifically, a multi-section oven is used with the temperature settings of 120℃ / 100℃ / 90℃ in sequence, and then a cold press is used for compaction to obtain a positive electrode sheet with a compaction density of 2.7g / cm 3 The positive electrode sheet has a single-sided coating weight of 0.40g / 1540.25mm 2 Among them, the particle size distribution of the positive electrode active material lithium iron manganese phosphate, the coating weight and compaction density of the positive electrode sheet and other related performance parameters are detailed in Table 1.

[0167] 2. Preparation of electrolyte:

[0168] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate and diethyl carbonate are mixed in a volume ratio of 1:1 to obtain a first solvent, ethyl acetate and propyl acetate are mixed in a volume ratio of 2:1 to obtain a second solvent, the first solvent and the second solvent are mixed in a certain amount to form a non-aqueous solvent, a first lithium salt of lithium hexafluorophosphate and a second lithium salt of lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethylsulfonyl)imide are added to the non-aqueous solvent, and then a film-forming stabilizer (lithium fluorosulfonate and / or lithium difluorophosphate) is added to form an electrolyte. The content of each component in the electrolyte is shown in Table 2.

[0169] 3. Preparation of negative electrode sheet:

[0170] The negative electrode active material artificial graphite, binder styrene butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na), and conductive agent carbon black (Super P) are mixed in an appropriate amount of deionized water as a solvent at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet. The single-sided coating weight of the negative electrode sheet is 0.18g / 1540.25mm 2 , among which, the coating weight of the negative electrode and other related performance parameters are detailed in Table 1.

[0171] 4. Isolation film;

[0172] A porous polyethylene (PE) film is used as the separator.

[0173] 5. Preparation of secondary batteries:

[0174] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0175] Example 2

[0176] A secondary battery is provided, wherein the particle size of the positive electrode active material and the parameters and performance of the electrolyte of the secondary battery are different from those of Example 1. Specifically, they are as shown in Examples 2-1 and 2-5, and the specific parameters and performance are different, as shown in Tables 1 and 2.

[0177] Example 3

[0178] A secondary battery is provided, wherein the coating weight and compaction density of the positive electrode sheet, the coating weight of the negative electrode sheet, and the related parameters and performance of the electrolyte of the secondary battery are different from those of Example 1. Specifically, as shown in Examples 3-1 to 3-3, see Tables 1 and 2 for details.

[0179] Example 4

[0180] A secondary battery is provided, wherein the positive electrode active material content, positive electrode plate coating weight and compaction density, negative electrode plate coating weight, and electrolyte-related parameters and performance of the secondary battery are different from those of Example 1. Specifically, as in Example 4-1 and Example 4-2, see Tables 1 and 2 for details.

[0181] Example 5

[0182] A secondary battery is provided, wherein the type of positive electrode active material, the coating weight of the positive electrode sheet, and the compaction density of the secondary battery are different from those in Example 1. Specifically, as in Example 5-1 and Example 5-2, the chemical formula of the lithium iron phosphate used in Example 5-1 is LiFePO4, and the chemical formula of the lithium manganese phosphate used in Example 5-2 is LiMnPO4, as shown in Tables 1 and 2.

[0183] Table 1 Parameters of positive and negative electrodes

[0184] Table 2 Parameters of electrolyte

[0185] Comparative Example 1

[0186] Differences from Example 1:

[0187] The positive electrode active material is selected from lithium iron phosphate particles of conventional particle size in the art, with a Dv50 of 5.0 μm and a Dv10 of 1.0 μm, and almost no submicron particles. The water content or hygroscopicity of particles of this size is significantly higher than that of the present application.

[0188] The electrolyte contains lithium hexafluorophosphate with a mass percentage of 16%, and the solvent is ethylene carbonate+diethyl carbonate.

[0189] Other details remain the same as in Example 1.

[0190] Comparative Example 2

[0191] Differences from Example 1:

[0192] The positive electrode active material is lithium iron phosphate particles with conventional particle sizes in the art, with a Dv50 of 5.0 μm and a Dv10 of 1.0 μm, and almost no submicron particles.

[0193] Other details remain the same as in Example 1.

[0194] Comparative Example 3

[0195] Differences from Example 1:

[0196] The electrolyte does not contain a film-forming stabilizer, and the amount of carbonate is increased to compensate for the absence of the film-forming stabilizer.

[0197] Comparative Example 4

[0198] Differences from Example 1:

[0199] The electrolyte does not contain the second lithium salt, and the amount of carbonate is increased to compensate for the lack of the second lithium salt.

[0200] The relevant parameters of Comparative Examples 1 to 4 are detailed in Tables 1 and 2, and the performance of the batteries is detailed in Table 3.

[0201] [Test of relevant parameters]

[0202] 1. Particle Size Test: Refer to standard GB / T19077-2016: Obtain the volume particle size distribution curve for lithium-containing transition metal phosphates. Take the particle size corresponding to 50% of the cumulative volume distribution percentage as the average particle size (Dv50), the particle size corresponding to 90% of the cumulative volume distribution percentage as the average particle size (Dv90), and the particle size corresponding to 10% of the cumulative volume distribution percentage as the average particle size (Dv10). The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0203] Volume average particle size Dv50 test:

[0204] Reference standard GB / T 19077-2016 / ISO 13320:2009 particle size distribution laser diffraction method. Use a laser particle size analyzer (Malvern 3000, MasterSizer 3000) for testing, and use a helium-neon red light source as the main light source. Take a clean small beaker and add 1g of the sample to be tested, add 20mL of deionized water (the sample concentration ensures that the shading is 8-12%), add a drop of surfactant to reduce the surface tension of the water to facilitate the wetting of the particles, and ultrasonicate at 53KHz / 120W for 5 minutes to ensure that the sample is completely dispersed. Turn on the laser particle size analyzer, clean the optical path system, and automatically test the background. Stir the ultrasonicated solution to be tested to make it evenly dispersed, put it into the sample cell as required, and start measuring the particle size. The measurement results can be read from the instrument.

[0205] 2. Test the compaction density of the positive electrode:

[0206] The compacted density of the positive electrode sheet can be measured by methods commonly used in the art. For example, the surface density can be measured first and then calculated using the equation: compacted density = surface density / thickness.

[0207] First, take the positive electrode sheet per unit area and weigh its mass m1, then weigh the mass m2 of the positive electrode foil per unit area, then subtract m2 from m1 to get the mass of the positive electrode film layer, and then divide it by the area of ​​the positive electrode film layer to get the surface density.

[0208] [Battery performance test]

[0209] 3. Energy density test:

[0210] At 25°C, the battery was charged at a constant current and constant voltage of 0.33C to the designed upper limit voltage of 3.75V, with a cut-off current of 0.05C. After standing for 30 minutes, it was discharged at 0.33C to the designed lower limit voltage of 2.5V. The discharge energy P (Wh) was recorded, and the weight of the battery cell was recorded as m (kg). The energy density (Wh / kg) = P / m.

[0211] 4. Fast charging capability test:

[0212] The batteries of the above embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, at 35°C, the batteries were charged at a constant current rate of 1C to a voltage of 4.4V, then charged at a constant voltage to a current of ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V. The actual capacity was recorded as C0. Then the battery is charged with a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 in sequence to the full battery charge cut-off voltage of 4.4V or the negative electrode cut-off potential of 0V (whichever is reached first). After each charge is completed, it is necessary to discharge with 1C0 to the full battery discharge cut-off voltage of 2.8V. Record the state of charge (SOC) at different charge rates to 10%, 20%, 30%, ..., 80%. Charge, state of charge, when "SOC = 0" means the battery is fully discharged, when "SOC = 100%" means the battery is fully charged) the corresponding negative electrode potential, draw the charge rate negative electrode potential curve under different SOC states, after linear fitting, the charge rate corresponding to the negative electrode potential of 0V under different SOC states is obtained, and the charge rate is the charging window under the SOC state, which is recorded as C10% SOC, C20% SOC, C30% SOC, C At 40% SOC, C50% SOC, C60% SOC, C70% SOC, and C80% SOC, the charging time T (in minutes) from 10% SOC to 80% SOC is calculated using the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%. The shorter this time, the better the battery's fast charging performance.

[0213] 5. Cycle performance test:

[0214] At 45°C, the secondary batteries prepared in the Examples and Comparative Examples were charged to 3.75V at a constant current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour). They were then charged at a constant voltage of 3.75V to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 2.5V, allowed to stand for 30 minutes. This constitutes one charge-discharge cycle, and the battery capacity at this point is recorded as C0. The battery was charged and discharged n times in this manner, and the battery capacity after n cycles was recorded as C1. The battery's cycle capacity retention at 25°C is then C1 / C0 × 100%. The number of cycles n corresponding to the measured cycle capacity retention of 80% was recorded.

[0215] Table 3 Battery performance list

[0216] Comparing the effect data of Examples 1 to 5 with Comparative Examples 1 to 4, it is found that the design method of the present application is conducive to taking into account the energy density, fast charging performance and cyclability of the battery. In Comparative Examples 1 and 2, the present application uses positive electrode active materials that do not contain submicron particles, and the energy density of the battery composed thereof is greatly reduced. Further combining Example 1 with Comparative Example 2, and Comparative Example 1 with Comparative Example 2, it can be seen that the particle size of the positive electrode active material has a greater influence on the energy density and fast charging performance of the battery. The larger the particle size, the lower the energy density and the longer the fast charging time.

[0217] Comparing Comparative Example 1 with Comparative Example 2, and Example 1 with Comparative Example 4, the presence of the second lithium salt can effectively improve the fast charging performance of the battery. Comparing Comparative Example 1 with Comparative Example 3, and Example 1 with Comparative Example 3, the film-forming stabilizer can effectively improve the cyclability of the battery.

[0218] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A secondary battery, characterized in that: include: Positive electrode sheet: comprising lithium-containing transition metal phosphate, wherein the lithium-containing transition metal phosphate comprises submicron and micron particles; negative electrode; An electrolyte comprising a lithium salt and a film-forming stabilizer, wherein the lithium salt comprises a first lithium salt and a second lithium salt; The first lithium salt comprises lithium hexafluorophosphate, and the second lithium salt comprises one or both of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

2. The secondary battery according to claim 1, wherein: The lithium-containing transition metal phosphate satisfies one or both of the following conditions: (1.1) The volume particle size distribution of the lithium-containing transition metal phosphate satisfies the following requirements: Dv50 is 0.3 μm to 2.0 μm, 3.0 μm ≤ Dv90 ≤ 20 μm; 0.1 μm ≤ Dv10 ≤ 1 μm; (1.2) The lithium-containing transition metal phosphate includes any one or more of lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate.

3. The secondary battery according to any one of claims 1 to 2, characterized in that: The Dv50 of the lithium-containing transition metal phosphate is 0.35 μm to 1.8 μm.

4. The secondary battery according to any one of claims 1 to 3, characterized in that: The positive electrode sheet satisfies one or more of the following conditions: (2.1) The coating weight of the positive electrode sheet on one side is 0.25g to 0.50g / 1540.25mm 2 ; (2.2) The mass percentage of the lithium-containing transition metal phosphate in the positive electrode plate is 90% to 98%; (2.3) The compaction density of the positive electrode sheet is 2.4 g / cm 3 ~2.7g / cm 3 .

5. The secondary battery according to any one of claims 1 to 4, characterized in that: The lithium salt satisfies one or more of the following conditions: (3.1) The mass percentage content of the first lithium salt is a, the mass percentage content of the second lithium salt is b, and: 0.2<a / b≤7; (3.2)2％≤a≤15％； (3.3)0.2％≤b≤8％。 6. The secondary battery according to any one of claims 1 to 5, characterized in that: The lithium salt meets the following conditions: The mass percentage content of the first lithium salt is a, 4%≤a≤10%; and / or; The mass percentage content of the second lithium salt is b, 0.8%≤b≤6%.

7. The secondary battery according to any one of claims 1 to 6, characterized in that: The film-forming stabilizer satisfies one or both of the following conditions: (4.1) The film-forming stabilizer comprises one or both of lithium fluorosulfonate and lithium difluorophosphate; (4.2) Based on the total mass of the electrolyte, the mass percentage content of the film-forming stabilizer is 0.02% to 2%.

8. The secondary battery according to any one of claims 1 to 7, characterized in that: Based on the total mass of the electrolyte, the mass percentage content of the film-forming stabilizer is 0.1% to 1.5%.

9. The secondary battery according to any one of claims 1 to 8, characterized in that: The film-forming stabilizer comprises lithium fluorosulfonate and lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage content of the lithium difluorophosphate is ≤1%, and the mass percentage content of the lithium fluorosulfonate is greater than or equal to 0.2% and less than 2%.

10. The secondary battery according to any one of claims 1 to 9, characterized in that: The electrolyte comprises a solvent, wherein the solvent comprises a carboxylate, and the carboxylate satisfies one or both of the following conditions: (5.1) The carboxylic acid ester has the following structural formula: R1-COO-R2; wherein R1 and R2 each independently comprise a substituted and / or unsubstituted C1-C5 alkyl group; (5.2) Based on the mass of the electrolyte, the mass percentage content of the carboxylate is 5% to 70%.

11. The secondary battery according to any one of claims 1 to 10, characterized in that: The electrolyte comprises a solvent, wherein the solvent comprises a carboxylate, and the carboxylate satisfies one or both of the following conditions: (6.1) The carboxylic acid ester comprises one or more of ethyl acetate, methyl acetate, ethyl propionate, propyl acetate, methyl propionate, and methyl butyrate; (6.2) Based on the mass of the electrolyte, the mass percentage content of the carboxylate is 10% to 60%.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The electrolyte comprises a solvent, wherein the solvent comprises a carboxylate and a carbonate, and the carbonate satisfies one or both of the following conditions: (7.1) The carbonate content is greater than or equal to 5% by mass based on the mass of the electrolyte; (7.2) The carbonate comprises one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

13. The secondary battery according to any one of claims 1 to 12, characterized in that: The negative electrode plate satisfies one or both of the following conditions: (8.1) The coating weight of the negative electrode sheet on one side is 0.13g to 0.25g / 1540.25mm 2 ; (8.2) The negative electrode plate comprises a carbon material.

14. An electrical device, characterized in that: A secondary battery according to any one of claims 1 to 13.

Images