A lithium-ion secondary battery, a battery module, a battery pack, and an electric device

Abstract

This invention relates to a lithium-ion secondary battery, comprising (1) a negative electrode sheet, which includes a negative electrode current collector and a negative electrode film disposed on the surface of the negative electrode current collector and containing a negative electrode active material; (2) a positive electrode sheet, which includes a positive electrode current collector and a positive electrode film disposed on the surface of the positive electrode current collector and containing a positive electrode active material; and (3) an electrolyte, which includes lithium iodide, lithium salt, solvent and additives; wherein the positive electrode film has a unit area (1540.25 mm²) 2 The coating weight CW1 and the weight percentage m of lithium iodide in the electrolyte satisfy the following formula (1): CW1=(CW2╳b╳C2 / CB-m╳X╳199╳S0 / S) / (C1╳a)(1) where, a is the weight percentage of the positive electrode active material of the positive electrode film, based on the total weight of the positive electrode film; C1 is the specific capacity of the positive electrode active material, mAh / g; CW2 is the unit area of ​​the negative electrode film (1540.25mm²). 2 The coating weight is ( ) in g; b is the weight percentage of the negative electrode active material in the negative electrode film, based on the total weight of the negative electrode film; C2 is the specific capacity of the negative electrode active material, mAh / g; m is the weight percentage of lithium iodide in the electrolyte, based on the total weight of the electrolyte; X is the total weight of the electrolyte, g; S0 is the coating weight at 1540.25 mm. 2 The unit area is calculated; S is the positive electrode area, mm². 2 CB is the ratio of the capacity of a negative electrode per unit area to the capacity that a positive electrode per unit area can provide; and it relates to related battery modules, battery packs, and electrical devices.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a long-life lithium-ion secondary battery, battery module, battery pack, and power supply device. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on their lifespan.

[0003] The main methods for improving the lifespan of lithium-ion rechargeable batteries in existing technologies include: selecting positive electrode active materials and graphite types with good cycle and storage performance; optimizing electrolyte formulations (changing organic solvents and additives); optimizing positive and negative electrode film formulations; and optimizing the formation conditions of the solid electrolyte interphase (SEI) film. These methods all focus on suppressing negative electrode side reactions and delay the reduction of active lithium ions through throttling, thus their effectiveness is limited. Currently, the highest cycle life of lithium-ion rechargeable batteries can be achieved at around 5000-6000 cycles, which is still significantly lower than the target cycle life of over 10,000 cycles for long-life electric buses and large-scale energy storage systems. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a long-life lithium-ion secondary battery with good cycle performance and high-temperature storage performance.

[0005] To achieve the above objectives, a first aspect of this application provides a lithium-ion secondary battery comprising (1) a negative electrode sheet including a negative current collector and a negative electrode film disposed on the surface of the negative current collector and containing a negative electrode active material; (2) a positive electrode sheet including a positive current collector and a positive electrode film disposed on the surface of the positive current collector and containing a positive electrode active material; and (3) an electrolyte comprising lithium iodide, lithium salt, solvent, and additives; wherein the positive electrode film has a unit area (1540.25 mm²) 2 The coating weight CW1 and the weight percentage m of lithium iodide in the electrolyte satisfy the following formula (1):

[0006] CW1=(CW2×b×C2 / CB-m×X×199×S0 / S) / (C1×a)(1)

[0007] in,

[0008] a represents the weight percentage of the positive electrode active material in the positive electrode membrane, based on the total weight of the positive electrode membrane;

[0009] C1 is the specific capacity of the positive electrode active material, mAh / g;

[0010] CW2 represents the negative electrode film with a unit area of ​​1540.25 mm². 2 The coating weight, in grams;

[0011] b represents the weight percentage of the negative electrode active material in the negative electrode membrane, based on the total weight of the negative electrode membrane;

[0012] C2 represents the specific capacity of the negative electrode active material, in mAh / g;

[0013] m is the weight percentage of lithium iodide in the electrolyte, based on the total weight of the electrolyte;

[0014] X is the total weight of the electrolyte, in grams;

[0015] S0 is 1540.25mm 2 The unit area is calculated;

[0016] S is the area of ​​the positive electrode, in mm² 2 ;

[0017] CB is the ratio of the capacity per unit area of ​​negative electrode to the capacity per unit area of ​​positive electrode.

[0018] Therefore, by adding a specific amount of lithium iodide to the electrolyte, the present invention determines the coating weight per unit area of ​​the positive electrode film, thereby ensuring the total amount of active lithium in the battery system from the source, thus improving the cycle life and high-temperature storage performance of the battery.

[0019] In any embodiment, the weight percentage m of lithium iodide in the electrolyte is 1-10% by weight, based on the total weight of the electrolyte. Therefore, by controlling the amount of lithium iodide added to the system, the coating weight per unit area of ​​the secondary battery's positive electrode film can be adjusted, thereby improving the battery's cycle life and high-temperature storage performance.

[0020] In any embodiment, the weight percentage 'a' of the positive electrode active material in the positive electrode film of the secondary battery is 92-97%, preferably 94-96%, based on the total weight of the positive electrode film. This allows for control over the coating weight per unit area of ​​the positive electrode film, thereby improving the battery's cycle life and high-temperature storage performance.

[0021] In any embodiment, the coating weight CW2 per unit area of ​​the negative electrode film is 0.140-0.170 g, preferably 0.150-0.160 g; the weight percentage b of the negative electrode active material in the negative electrode film is 92-96%, preferably 93-95%, based on the total weight of the negative electrode film. Therefore, the coating weight per unit area of ​​the positive electrode film in the secondary battery can be controlled, thereby improving the battery's cycle life and high-temperature storage performance.

[0022] In any embodiment, the lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium tetrafluorooxalate phosphate, lithium bis(oxaloyl)borate, lithium trifluoromethanesulfonate, and lithium bis-(trifluoromethanesulfonyl)imide; optionally, the content of the lithium salt is 1-15% by weight, based on the weight of the electrolyte. Thus, the specific type and content of lithium salt ensures the conductivity of the electrolyte, thereby improving the cycle life and high-temperature storage performance of the battery.

[0023] In any embodiment, the additive is selected from one or more of vinylene carbonate (VC), vinylene sulfate (DTD), fluoroethylene carbonate (FEC), 1,3-propanecyclolactone (PS), and succinic anhydride (SA); optionally, the content of the additive is 0-9% by weight, based on the weight of the electrolyte. Thus, specific types of additives can promote the formation of a dense SEI film, preventing the electrolyte from being redox-decomposed during charge and discharge, thereby improving the battery's cycle life and high-temperature storage performance.

[0024] A second aspect of this application provides a battery module, including the secondary battery of the first aspect of this application.

[0025] A third aspect of this application provides a battery pack that includes the battery module of the second aspect of this application.

[0026] A fourth aspect of this application provides an electrical device comprising at least one selected from the secondary battery of the first aspect of this application, the battery module of the second aspect of this application, or the battery pack of the third aspect of this application.

[0027] This application improves the cycle life and high-temperature storage performance of the battery by adding lithium iodide to the electrolyte and precisely controlling the coating weight per unit area of ​​the positive electrode film based on the amount of lithium iodide. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0029] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0030] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0031] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0032] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0033] Figure 6 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.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0036] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the lithium-ion secondary battery, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0037] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is 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 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 "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0038] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0040] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0041] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0042] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0043] Unless otherwise specified, in this application, the term "unit area" refers to a dimension of 1540.25 mm². 2 The area is denoted as S0. The coating weight, capacity, and corresponding amount of lithium iodide for the positive and negative electrode films are all based on a 1540.25 mm² area. 2 Calculation of unit area.

[0044] Currently, lithium-ion rechargeable batteries are widely used in various fields, with huge usage volumes and increasingly stringent requirements for their lifespan. Existing technologies primarily improve the lifespan of lithium-ion rechargeable batteries by: selecting positive electrode active materials and graphite types with good cycle and storage performance; optimizing electrolyte formulations (changing organic solvents and additives); optimizing positive and negative electrode film formulations; and optimizing the solid electrolyte interphase (SEI) film formation conditions. These methods all focus on suppressing negative electrode side reactions, delaying the reduction of active lithium ions through throttling, thus their effectiveness is limited. Currently, the cycle life of lithium-ion rechargeable batteries still lags significantly behind the target cycle life of long-life electric buses and large-scale energy storage systems. Through extensive research, the inventors have discovered that the lithium-ion rechargeable battery of the first aspect of this invention can effectively improve the cycle performance and high-temperature storage performance of the rechargeable battery by precisely controlling the amount of lithium iodide added to the electrolyte and the corresponding coating weight per unit area of ​​the positive electrode film.

[0045] Lithium-ion secondary batteries

[0046] In one embodiment of this application, a first aspect of this application provides a lithium-ion secondary battery comprising (1) a negative electrode sheet, which includes a negative electrode current collector and a negative electrode film disposed on the surface of the negative electrode current collector and containing a negative electrode active material; (2) a positive electrode sheet, which includes a positive electrode current collector and a positive electrode film disposed on the surface of the positive electrode current collector and containing a positive electrode active material; and (3) an electrolyte comprising lithium iodide, lithium salt, solvent, and additives; wherein the positive electrode film has a unit area (1540.25 mm²) 2 The coating weight CW1 and the weight percentage m of lithium iodide in the electrolyte satisfy the following formula (1):

[0047] CW1=(CW2╳b╳C2 / CB-m╳X╳199╳S0 / S) / (C1╳a)(1)

[0048] in,

[0049] a represents the weight percentage of the positive electrode active material in the positive electrode membrane, based on the total weight of the positive electrode membrane;

[0050] C1 is the specific capacity of the positive electrode active material, mAh / g;

[0051] CW2 represents the negative electrode film with a unit area of ​​1540.25 mm². 2 The coating weight, in grams;

[0052] b represents the weight percentage of the negative electrode active material in the negative electrode membrane, based on the total weight of the negative electrode membrane;

[0053] C2 represents the specific capacity of the negative electrode active material, in mAh / g;

[0054] m is the weight percentage of lithium iodide in the electrolyte, based on the total weight of the electrolyte;

[0055] X is the total weight of the electrolyte, in grams;

[0056] S0 is 1540.25mm 2 The unit area is calculated;

[0057] S is the area of ​​the positive electrode, in mm² 2 ;

[0058] CB is the ratio of the capacity per unit area of ​​negative electrode to the capacity per unit area of ​​positive electrode.

[0059] Although the mechanism is not yet clear, the applicant has unexpectedly discovered that by adding a specific amount of lithium iodide to the electrolyte, the coating weight per unit area of ​​the positive electrode film can be determined, thereby ensuring the total amount of active lithium in the battery system from the source, thus improving the cycle life and high-temperature storage performance of the battery.

[0060] Typically, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes.

[0061] Electrolyte

[0062] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0063] In some embodiments, the electrolyte is liquid. The electrolyte includes lithium iodide, lithium salt, solvent, and additives.

[0064] In some embodiments, the weight percentage m of lithium iodide in the electrolyte is 1-10% by weight, preferably 3-7% by weight, based on the total weight of the electrolyte. Therefore, by controlling the amount of lithium iodide added to the system, the coating weight per unit area of ​​the secondary battery's positive electrode film can be adjusted, thereby improving the battery's cycle life and high-temperature storage performance.

[0065] In some embodiments, the lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium tetrafluorooxalate phosphate, lithium bis(oxaloyl)borate, lithium trifluoromethanesulfonate, and lithium bis-(trifluoromethanesulfonyl)imide; optionally, the content of the lithium salt is 1-15% by weight, preferably 9-13% by weight, based on the weight of the electrolyte. Thus, the specific type and content of lithium salt ensures the conductivity of the electrolyte, thereby improving the cycle life and high-temperature storage performance of the battery.

[0066] In some embodiments, the additive is selected from one or more of vinylene carbonate (VC), vinylene sulfate (DTD), fluoroethylene carbonate (FEC), 1,3-propanecyclolactone (PS), and succinic anhydride (SA); optionally, the additive content is 0-9% by weight, preferably 3-5% by weight, based on the weight of the electrolyte. Thus, certain types of additives can promote the formation of a dense SEI film, preventing the electrolyte from being redox-decomposed during charge and discharge, thereby improving the battery's cycle life and high-temperature storage performance.

[0067] In some embodiments, the solvent may be selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate (DMC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0068] [Positive electrode tablets]

[0069] The positive electrode includes a positive current collector and a positive electrode membrane disposed on at least one surface of the positive current collector. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode membrane is disposed on either or both of the two opposite surfaces of the positive current collector.

[0070] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0071] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one 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 battery positive electrode active materials 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, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 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 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0072] In some preferred embodiments, the positive electrode active material in the positive electrode film is selected from one or more of lithium iron phosphate, ternary materials, lithium manganese oxide, and lithium cobalt oxide. Optionally, the ternary material is selected from one or two of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. Thus, the secondary battery of the present invention can be constructed, thereby improving the battery's cycle life and high-temperature storage performance.

[0073] In some embodiments, the weight percentage 'a' of the positive electrode active material in the positive electrode film of the secondary battery is 92-97%, preferably 94-96%, based on the total weight of the positive electrode film. This allows for control over the coating weight per unit area of ​​the positive electrode film, thereby improving the battery's cycle life and high-temperature storage performance.

[0074] In some embodiments, the positive electrode membrane may optionally include an adhesive. As an example, the adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0075] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0076] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0077] [Negative electrode plate]

[0078] The negative electrode includes a negative current collector and a negative electrode film disposed on at least one surface of the negative current collector, the negative electrode film including a negative electrode active material.

[0079] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode diaphragm is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0080] 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0081] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one 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.

[0082] In some embodiments, the coating weight per unit area of ​​the negative electrode film, CW2, is 0.140-0.170 g, preferably 0.150-0.160 g; the weight percentage b of the negative electrode active material in the negative electrode film is 92-96%, preferably 93%-95%, based on the total weight of the negative electrode film. This allows for control over the coating weight per unit area of ​​the positive electrode film in the secondary battery, thereby improving the battery's cycle life and high-temperature storage performance.

[0083] In some embodiments, the negative electrode membrane may optionally include an adhesive. The adhesive may be selected from at least one 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).

[0084] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, the negative electrode membrane may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0086] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0087] [Isolation membrane]

[0088] In some embodiments, the secondary battery further includes a separator membrane disposed between the positive and negative electrode plates. The separator membrane primarily serves to prevent short circuits between the positive and negative electrodes while allowing ions to pass through. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0089] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven 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.

[0090] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0091] 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.

[0092] 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. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0093] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example is a secondary battery with a square-shaped box structure.

[0094] In some implementations, refer to Figure 2 The housing may include a shell 51 and a cover 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0095] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0096] Figure 3This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0097] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0098] 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.

[0099] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0100] 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.

[0101] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0102] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0103] 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.

[0104] Example

[0105] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0106] Example 1

[0107] (1) Electrolyte preparation

[0108] In an argon-atmospheric glove box with a water content of <10ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC = 3:3:3 to obtain a mixed organic solvent. Then, lithium iodide, lithium bisfluorosulfonylimide (LiFSI), and VC were added to the mixed organic solvent and stirred until homogeneous to obtain an electrolyte. The concentration of LiFSI was 1 mol / L, the weight percentage of VC was 5 wt%, and the weight percentage of lithium iodide was 1 wt%. All weight percentages are based on the total weight of the electrolyte.

[0109] (2) Preparation of negative electrode

[0110] Artificial graphite (specific capacity C2 of 372 mAh / g), acetylene black (conductive agent), and SBR+CMC (binder) were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain a uniform negative electrode slurry. This slurry was then coated onto both surfaces of the copper foil used as the negative electrode current collector. The coating weight per unit area (CW2) of the negative electrode film was 0.140 g / 1540.25 mm². 2 (Based on weight excluding solvent), the negative electrode sheet is obtained after drying and cold pressing.

[0111] (3) Preparation of positive electrode

[0112] Lithium iron phosphate (specific capacity C1 of 160 mAh / g) was used as the positive electrode active material, and the weight percentage a of the positive electrode active material in the positive electrode film was set to 95% by weight, based on the total weight of the positive electrode film; the total mass X of the electrolyte added to the battery was 0.5g; and the positive electrode area S was set to 2079mm². 2 ;CB is 1.2; then according to

[0113] CW1=(CW2╳b╳C2 / CB-m╳X╳199╳S0 / S) / (C1╳a)

[0114] The calculated unit area of ​​the positive electrode film is 1540.25 mm². 2The coating weight CW1 is 0.266g / 1540.25mm. 2

[0115] The positive electrode active material lithium iron phosphate (specific capacity C1 is 160mAh / g), conductive agent acetylene black, and binder PVDF are mixed in a weight ratio of 95:4:1. N-methylpyrrolidone solvent is added and the mixture is stirred and mixed thoroughly to obtain a positive electrode slurry. Then, the slurry is coated on the two surfaces of the positive electrode current collector aluminum foil according to the coating weight calculated above. After drying and cold pressing, the positive electrode sheet is obtained.

[0116] (4) Preparation of the separating membrane

[0117] Polyethylene porous membrane is used as the separation membrane.

[0118] (5) Preparation of lithium-ion secondary batteries

[0119] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound to obtain a bare cell. The bare cell is placed in an outer package, electrolyte is injected, and it is sealed to obtain a lithium-ion secondary battery.

[0120] Examples 2-8

[0121] The procedure was the same as in Example 1, except that the concentration of lithium iodide in the electrolyte, the type and content of additives in the electrolyte, the type and weight percentage of the positive electrode active material, the type and weight percentage of the negative electrode active material, and the coating weight per unit area of ​​the negative electrode film were changed. Specific parameters are summarized in Table 1.

[0122] Comparative Example 1

[0123] The same steps as in Example 1 were followed, except that the electrolyte did not contain lithium iodide.

[0124] The relevant parameters of Comparative Example 1 are summarized in Table 1.

[0125] Table 1: Parameter results of Examples 1-12 and Comparative Examples 1-2

[0126]

[0127] Performance testing

[0128] The secondary batteries obtained in Examples 1-23 and Comparative Examples 1-2 were subjected to performance tests. The test results are shown in Table 2 below.

[0129] (1) Cyclic performance test of secondary battery at 60℃

[0130] The battery cells were placed in a constant temperature chamber at 60℃ and cycled using a test rate of 1C / 1C. The ratio of the capacity after 500 cycles to the capacity after the first cycle was used to calculate the cycle capacity retention rate.

[0131] (2) Storage capacity retention test of secondary batteries at 60°C

[0132] First, test the cell's capacity before storage. Then, adjust the cell to 100% SOC and place it in a constant temperature 60℃ chamber for 90 days. After storage, remove the cell from the chamber and test its capacity after storage in a normal temperature environment. Calculate the ratio of the capacity after storage to the capacity before storage, which is the storage capacity retention rate.

[0133] Table 2: Performance tests of the secondary batteries in Examples 1-23 and Comparative Examples 1-2

[0134]

[0135] Based on the above results, it can be seen that in Examples 1-23, by adding lithium iodide to the electrolyte, the cycle retention rate of the secondary battery was maintained at over 91.9%, and the storage capacity retention rate was maintained at over 94%.

[0136] In contrast, Comparative Example 1, which does not add lithium iodide, has a lower cycle retention rate and storage capacity retention rate for its secondary battery compared to the embodiments of the present invention.

[0137] 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 lithium-ion secondary battery, comprising (1) a negative electrode sheet including a negative current collector and a negative electrode film disposed on the surface of the negative current collector and containing a negative electrode active material; (2) a positive electrode sheet including a positive current collector and a positive electrode film disposed on the surface of the positive current collector and containing a positive electrode active material; and (3) an electrolyte comprising lithium iodide, lithium salt, solvent and additives; wherein the coating weight CW1 per unit area of ​​the positive electrode film and the weight percentage m of lithium iodide in the electrolyte satisfy the following formula (1): CW1=(CW2╳b╳C2 / CB-m╳X╳199╳S0 / S) / (C1╳a) (1) in, a represents the weight percentage of the positive electrode active material in the positive electrode membrane, based on the total weight of the positive electrode membrane; C1 is the specific capacity of the positive electrode active material, mAh / g; CW2 is the coating weight per unit area of ​​the negative electrode film, in grams; the unit area represents a size of 1540.25 mm². 2 The area; b represents the weight percentage of the negative electrode active material in the negative electrode membrane, based on the total weight of the negative electrode membrane; C2 represents the specific capacity of the negative electrode active material, in mAh / g; m is the weight percentage of lithium iodide in the electrolyte, based on the total weight of the electrolyte; X is the total weight of the electrolyte, in grams; S0 is 1540.25mm 2 The unit area is calculated; S is the area of ​​the positive electrode plate, in mm² 2 ; CB is the ratio of the capacity per unit area of ​​negative electrode to the capacity per unit area of ​​positive electrode.

2. The secondary battery according to claim 1, characterized in that, The weight percentage m of lithium iodide in the electrolyte is 1-10% by weight, based on the total weight of the electrolyte.

3. The secondary battery according to claim 1 or 2, characterized in that, The positive electrode active material of the positive electrode membrane of the secondary battery has a weight percentage (a) of 92-97%, based on the total weight of the positive electrode membrane.

4. The secondary battery according to claim 3, characterized in that, The weight percentage (a) of the positive electrode active material in the positive electrode membrane of the secondary battery is 94-96%.

5. The secondary battery according to any one of claims 1-2 or claim 4, characterized in that, The coating weight per unit area of ​​the negative electrode film, CW2, is 0.140-0.170 g; the weight percentage b of the negative electrode active material in the negative electrode film is 92-96%, based on the total weight of the negative electrode film.

6. The secondary battery according to claim 5, characterized in that, The coating weight per unit area of ​​the negative electrode film, CW2, is 0.150-0.160g.

7. The secondary battery according to claim 5, characterized in that, The weight percentage (b) of the negative electrode active material in the negative electrode membrane is 93-95%.

8. The secondary battery according to any one of claims 1-2 or claim 4 or any one of claims 6-7, characterized in that, The lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium tetrafluorooxalate phosphate, lithium bis(oxaloyl)borate, lithium trifluoromethanesulfonate, and lithium bis-(trifluoromethanesulfonyl)imide.

9. The secondary battery according to claim 1, characterized in that, The lithium salt content is 1-15% by weight, based on the weight of the electrolyte.

10. The secondary battery according to any one of claims 1-2, or claim 4, or any one of claims 6-7, or claim 9, characterized in that, The additive is selected from one or more of vinylene carbonate, vinylene sulfate, fluorovinyl carbonate, 1,3-propane cyclolactone, and succinic anhydride.

11. The secondary battery according to claim 10, characterized in that, The additive content is 0-9% by weight, based on the weight of the electrolyte.

12. A battery module, characterized in that, The secondary battery includes any one of claims 1-11.

13. A battery pack, characterized in that, Includes the battery module as described in claim 12.

14. An electrical appliance, characterized in that, It includes at least one selected from the secondary battery of any one of claims 1-11, the battery module of claim 12, or the battery pack of claim 13.

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