Electrolyte and secondary battery, battery module, battery pack, and power device using the same

Abstract

This application provides an electrolyte that prevents the corrosion of the positive electrode material and the dissolution of the transition metal, as well as a secondary battery using the same. The electrolyte contains an organic solvent and one or more compounds (A) represented by general formula (I) or general formula (II), wherein the content of compound (A) in the electrolyte is 0.01 wt%–5 wt%, and the content of ethylene carbonate in the organic solvent is less than or equal to 3 wt%. The secondary battery of this application exhibits excellent cycle life and storage performance under high-voltage operating conditions.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to an electrolyte for secondary batteries, a secondary battery using the same, a battery module, a battery pack, and an electrical device. Background Technology

[0002] In recent years, with the increasingly wide application of secondary batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Secondary batteries generally consist of a positive electrode, a negative electrode, and an electrolyte. For example, in lithium-ion secondary batteries, charge transfer is typically achieved through the intercalation and deintercalation of lithium ions between the positive and negative electrodes, and the transfer of charge via the electrolyte in the electrolyte, thus converting chemical energy into electrical energy.

[0003] However, in existing technologies, the corrosion of the positive electrode material by solvents in the electrolyte leads to structural collapse of the positive electrode material and dissolution of transition metals, resulting in capacity decay and reduced cycle life of the secondary battery cells. This is especially true in high-voltage secondary batteries, where the corrosion of the positive electrode surface intensifies the oxidizing power of the active material when the battery is charged to high voltage, causing continuous oxidation reactions on the positive electrode surface and further accelerating capacity decay. Summary of the Invention

[0004] This application is made in view of the above-mentioned technical problems, and its purpose is to provide an electrolyte for a secondary battery that prevents the positive electrode material from being corroded and the transition metal from being dissolved, as well as a secondary battery using the same, thereby improving the cycle life and storage performance of the secondary battery, especially in the case of a secondary battery operating at high voltage (≥4.35V).

[0005] The first aspect of this application provides an electrolyte comprising an organic solvent and one or more compounds (A) represented by general formula (I) or general formula (II) below.

[0006]

[0007] In the general formula (I) or general formula (II),

[0008] X includes any one of the elements O, S, and N.

[0009] When X includes O, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, straight-chain alkyl or branched-chain alkyl group with 2-4 carbon atoms, straight-chain alkyl group with 1-4 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not; when X includes S or N, R includes one or more of the following: hydrogen atom, cyano or isocyanate group, trimethylsilyl group, straight-chain alkyl or branched-chain alkyl group with 1-4 carbon atoms, straight-chain alkyl group with 1-4 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not.

[0010] The content of compound (A) in the electrolyte is 0.01 wt%-5 wt%.

[0011] The content of ethylene carbonate in the organic solvent is less than or equal to 3 wt%.

[0012] Therefore, compound (A) can capture transition metal ions dissolved in the electrolyte and form a film on the positive electrode to protect the positive electrode material. Furthermore, by controlling the content of ethylene carbonate, the penetration and erosion of the positive electrode material by the solvent can be reduced, and the dissolution of transition metals in the positive electrode material can be reduced, thereby improving the cycle life and storage performance of the secondary battery. In particular, the secondary battery can still maintain its cycle life and storage performance when operating at high voltage (≥4.35V).

[0013] In any embodiment, in general formula (I) or general formula (II), when X includes O, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, straight-chain alkyl group with 2-4 carbon atoms, straight-chain alkyl group with 1-4 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not; when X includes S or N, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, hydrogen atom, straight-chain alkyl group with 2-4 carbon atoms, straight-chain alkyl group with 1-4 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not.

[0014] Optionally, when X includes O, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, straight-chain alkyl group with 2-3 carbon atoms, straight-chain alkyl group with 1-3 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not; when X includes S or N, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, hydrogen atom, straight-chain alkyl group with 2-3 carbon atoms, straight-chain alkyl group with 1-3 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not.

[0015] Therefore, the protective effect of compound (A) on the cathode material can be further improved, and the cycle life and storage performance of the secondary battery can be further enhanced.

[0016] In any embodiment, the compound (A) is one or more of the following compounds (A1)-(A12):

[0017]

[0018]

[0019] Optionally, the compound (A) includes one or more of the compounds (A1), (A2), (A4)-(A6), (A8), (A9), and (A11).

[0020] Therefore, the ability of compound (A) to capture transition metal ions can be further improved, and the ability of compound (A) to form a film on the positive electrode surface can be improved, thereby further enhancing the protective effect of compound (A) on the positive electrode material and further improving the cycle life and storage performance of the secondary battery.

[0021] In any embodiment, the content of compound (A) in the electrolyte is 1wt%-5wt%, optionally 2wt%-3wt%. This balances the protective effect of compound (A) on the positive electrode material with the ion conductivity of the electrolyte, thereby improving the cycle life and storage performance of the secondary battery without increasing the internal resistance of the battery.

[0022] In any embodiment, the organic solvent does not contain ethylene carbonate (EC). This further reduces the penetration and erosion of the cathode material by the solvent in the electrolyte, and further prevents the structural collapse of the cathode material caused by the dissolution of transition metal ions in the electrolyte, thereby further improving the cycle life and storage performance of the battery.

[0023] In any embodiment, the organic solvent contains one or more of the following: cyclic carbonates other than chain carbonates and ethylene carbonates, carboxylic acid esters, and ether solvents. This ensures that the electrolyte maintains sufficient ionic conductivity even with a reduced ethylene carbonate content, thereby reliably improving the battery's cycle life and storage performance.

[0024] In any embodiment, the content of the aforementioned chain carbonate in the electrolyte is 40wt%-90wt%. This balances the protective effect of the electrolyte on the positive electrode material with the electrolyte's ion conductivity, thereby reliably improving the battery's cycle life and storage performance.

[0025] In any embodiment, the aforementioned chain carbonates include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and trifluoroethylmethyl carbonate; the aforementioned cyclic carbonates other than ethylene carbonates include fluoroethylene carbonates; the aforementioned carboxylic acid esters include ethyl acetate, methyl acetate, and propyl acetate; and the aforementioned ether solvents include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, desflurane, and 2,2,2-trifluoroethyl-30,30,30,20,20-pentafluoropropyl ether. Therefore, the electrolyte can possess excellent ion conductivity, thereby reliably improving the battery's cycle life and storage performance.

[0026] A second aspect of this application provides a secondary battery comprising the electrolyte of the first aspect of this application.

[0027] A third aspect of this application provides a battery module that includes the secondary battery of the second aspect of this application.

[0028] A fourth aspect of this application provides a battery pack that includes the battery module of the third aspect of this application.

[0029] The fifth aspect of this application provides an electrical device comprising at least one selected from the second aspect of this application, the third aspect of this application, or the fourth aspect of this application.

[0030] This enables the provision of secondary batteries with improved cycle life and storage performance, particularly improved cycle life and storage performance when operating at high voltage (≥4.35V), as well as battery modules, battery packs, and electrical devices including such secondary batteries. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0032] Figure 2 yes Figure 1The diagram shown is an exploded view of a secondary battery according to one embodiment of this application.

[0033] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0034] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0035] Figure 5 yes Figure 4 The diagram shown is an exploded view of a battery pack according to one embodiment of this application.

[0036] Figure 6 This is a schematic diagram of an electrical device according to one embodiment of this application.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0039] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the electrolyte, secondary battery, battery module, battery pack, and electrical 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.

[0040] 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.

[0041] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0042] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0043] 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.

[0044] 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.

[0045] 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).

[0046] In existing technologies, the reaction between lithium salts and trace amounts of water in the electrolyte can produce impurities such as hydrofluoric acid. These acidic impurities can corrode the cathode material, dissolving transition metals and other active substances within it. This can lead to the collapse of the cathode material structure, directly resulting in reduced battery storage performance and cycle life. Furthermore, when the battery operates at high voltage, redox reactions are more likely to occur on the surface of the cathode material. The transition metal ions in the cathode material dissolve more rapidly under the influence of the electrolyte, severely restricting the electrochemical performance of the cathode material and potentially causing battery safety issues such as explosions.

[0047] This application studies the problem from the perspective of electrolytes. On the one hand, by adding specific additives to the electrolyte, these additives can form a film on the electrode surface to protect the positive electrode material. On the other hand, by adjusting the composition of the electrolyte, the content of components in the electrolyte that would corrode the positive electrode material is reduced. This synergistically protects the positive electrode material from being corroded and dissolved by the electrolyte, thereby improving the cycle life and storage performance of the battery. Especially when the battery is operating at high voltage, it can also protect the positive electrode material, stabilize the storage performance of the secondary battery, and improve the cycle life of the secondary battery.

[0048] Electrolyte

[0049] One embodiment of this application provides an electrolyte comprising an organic solvent and one or more compounds (A) represented by general formula (I) or general formula (II) below, wherein the content of the compound (A) in the electrolyte is 0.01wt%-5wt%, and the content of ethylene carbonate in the organic solvent is less than or equal to 3wt%.

[0050]

[0051] (In general formula (I) or general formula (II), X includes any one of the elements O, S, and N. When X includes O, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, straight-chain alkyl or branched alkyl group with 2-4 carbon atoms, straight-chain alkyl group with 1-4 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not; when X includes S or N, R includes one or more of the following: hydrogen atom, cyano or isocyanate group, trimethylsilyl group, straight-chain alkyl or branched alkyl group with 1-4 carbon atoms, straight-chain alkyl group with 1-4 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not.)

[0052] This application contains the specific compound (A) in the electrolyte within the aforementioned specific range and reduces the content of ethylene carbonate, a commonly used organic solvent. This not only reduces the corrosive force of the electrolyte on the positive electrode material but also forms a protective film on the surface of the positive electrode material. This effectively protects the positive electrode material from the corrosion and dissolution of the electrolyte and improves the cycle life and storage performance of the secondary battery.

[0053] Although the mechanism is not yet clear, the specific compound (A) has the ability to complex transition metals, thus it can capture transition metal ions dissolved in the electrolyte and prevent the transition metals from being dissolved by the electrolyte. In addition, the specific compound (A) has a certain adsorption effect on the positive electrode material and can form a film on the surface of the positive electrode material to protect the positive electrode material from the corrosion of the electrolyte.

[0054] Furthermore, existing technologies have consistently used organic solvents containing high levels of ethylene carbonate (EC) in electrolytes to improve conductivity. However, during battery cycling or storage, the ethylene carbonate solvent continuously diffuses and penetrates the SEI film on the surface of the positive electrode material, directly contacting the surface of the positive electrode active material particles and undergoing oxidative decomposition. Moreover, this oxidative decomposition process is often accompanied by side reactions such as gas production, oxygen release, and the formation of acidic substances. The resulting acidic substances further corrode the positive electrode material, leading to further dissolution of transition metals and accelerating cell capacity decay. Therefore, reducing the ethylene carbonate content in the electrolyte can reduce the corrosion of the positive electrode material by the solvent in the electrolyte, further enhancing the protective effect of the electrolyte on the positive electrode material.

[0055] In some embodiments, in the above general formula (I) or general formula (II), when X includes O, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, straight-chain alkyl group with 2-4 carbon atoms, straight-chain alkyl group with 1-4 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not; when X includes S or N, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, hydrogen atom, straight-chain alkyl group with 2-4 carbon atoms, straight-chain alkyl group with 1-4 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not. Optionally, when X includes O, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, straight-chain alkyl group with 2-3 carbon atoms, straight-chain alkyl group with 1-3 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not; when X includes S or N, R includes one or more of the following: cyano or isocyanate group, trimethylsilyl group, hydrogen atom, straight-chain alkyl group with 2-3 carbon atoms, straight-chain alkyl group with 1-3 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not.

[0056] By selecting appropriate X and R, the complexation ability of compound (A) for transition metal ions can be enhanced, and the adsorption of compound (A) on the surface of the cathode material can be improved, thereby further enhancing the capture ability of compound (A) for transition metal ions and improving the film-forming property of compound (A) on the cathode surface. This effectively prevents transition metal ions from dissolving in the electrolyte and protects the cathode material from electrolyte corrosion.

[0057] In some embodiments, the compound (A) comprises one or more of compounds (A1)-(A12). Optionally, compound (A) comprises one or more of compounds (A1), (A2), (A4)-(A6), (A8), (A9), and (A11).

[0058]

[0059]

[0060] Therefore, compound (A) can efficiently capture the transition metal ions dissolved in the cathode material and easily form a film on the surface of the cathode material, thereby effectively protecting the cathode material from electrolyte corrosion.

[0061] In some embodiments, the content of compound (A) in the electrolyte is 1wt%-5wt%, optionally 2wt%-3wt%. If the content of compound (A) in the electrolyte is too low, a good interfacial film cannot be formed on the positive electrode surface, making it difficult to prevent solvent decomposition and transition metal dissolution under high voltage. If the content of compound (A) in the electrolyte is too high, it will increase the viscosity of the electrolyte, increase the resistance to lithium ion migration, and result in an excessively thick interfacial film on the positive electrode surface, leading to excessively high film impedance and charge transfer impedance of the secondary battery.

[0062] In some embodiments, the organic solvent is substantially free of ethylene carbonate. This completely eliminates the effect of ethylene carbonate on the cathode material, preventing the leaching and corrosion of transition metals.

[0063] In some embodiments, the organic solvent contains one or more of the following: cyclic carbonates other than chain carbonates and ethylene carbonates, carboxylic acid esters, and ether solvents. This can replace the role of ethylene carbonate commonly used in the prior art, thereby reducing the corrosion of the positive electrode material by the electrolyte while maintaining the conductivity of the electrolyte and ensuring the normal charging and discharging of the secondary battery. This effectively improves the battery's cycle life and storage performance.

[0064] In some embodiments, the content of chain carbonates in the electrolyte is 40wt%-90wt%. This balances the protective effect of the electrolyte on the cathode material with the electrolyte's ion conductivity, thereby effectively improving the battery's cycle life and storage performance.

[0065] In some embodiments, the aforementioned chain carbonates include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and trifluoroethylmethyl carbonate; cyclic carbonates other than ethylene carbonates include fluoroethylene carbonates; carboxylic acid esters include ethyl acetate, methyl acetate, and propyl acetate; and ether solvents include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, desflurane, and 2,2,2-trifluoroethyl-30,30,30,20,20-pentafluoropropyl ether. This allows the electrolyte to possess excellent ion conductivity, thereby reliably improving the battery's cycle life and storage performance.

[0066] In some embodiments, the organic solvent content in the electrolyte is 60wt%-98wt%.

[0067] In some embodiments, the organic solvent may also include any one of 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl sulfone, and diethyl sulfone.

[0068] In some embodiments, the electrolyte further comprises an electrolyte salt, wherein the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0069] In some embodiments, the electrolyte may optionally include other additives such as negative electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0070] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0071] [Rechargeable Battery]

[0072] In one embodiment of this application, a secondary battery is provided.

[0073] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0074] The electrolyte in the secondary battery of this embodiment is the electrolyte provided in the above embodiment.

[0075] [Positive electrode plate]

[0076] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0077] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0078] 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.).

[0079] 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) 0.8 Co 0.15 Al 0.05At 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.

[0080] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0081] 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.

[0082] 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 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.

[0083] [Negative electrode plate]

[0084] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0085] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0086] 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.).

[0087] 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.

[0088] In some embodiments, the negative electrode film layer may optionally include a binder. The binder 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).

[0089] 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.

[0090] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0091] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0092] [Isolation membrane]

[0093] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0094] 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.

[0095] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0096] 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.

[0097] 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.

[0098] 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 This is an example of a square-structured secondary battery 5.

[0099] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0100] 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.

[0101] Figure 3 This 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.

[0102] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0107] 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.

[0108] 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.

[0109] Example

[0110] 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 shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, may be conventional products obtained commercially.

[0111] Examples 1-19, Comparative Examples 1-8

[0112] (1) Preparation of electrolyte

[0113] The electrolytes of Examples 1-19 and Comparative Examples 1-8 were prepared according to the following method.

[0114] In an argon-atmospheric glove box with a water content of <10 ppm, ethyl methyl carbonate (EMC), a chain carbonate, was used as the main solvent. The EMC and various auxiliary solvents were mixed according to the weight ratio of auxiliary solvent to main solvent shown in Table 1 (auxiliary solvent: main solvent (EMC)) to obtain a mixed solvent. Compound (A) shown in Table 1 and fully dried lithium salt LiPF6 with a concentration of 1 mol / L were then dissolved in the above mixed solvent and stirred until homogeneous to obtain the electrolyte. In Table 1, the weight percentage (wt%) of compound (A) is relative to the weight percentage (wt%) of the electrolyte.

[0115] (2) Preparation of secondary batteries

[0116] The secondary batteries of Examples 1-19 and Comparative Examples 1-8 were prepared according to the following method.

[0117] [Preparation of negative electrode sheet]

[0118] The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are mixed in a weight ratio of graphite:acetylene black:styrene-butadiene rubber:sodium carboxymethyl cellulose = 95:2:2:1. After adding deionized water, the mixture is stirred thoroughly to form a uniform negative electrode slurry. This slurry is coated onto the negative electrode current collector copper foil, then dried and cold-pressed to obtain the negative electrode sheet.

[0119] [Preparation of positive electrode sheet]

[0120] The positive electrode active material NCM211(LiNi) 0.5 Co 0.25 Mn 0.25 O2), conductive agent acetylene black, and binder polyvinylidene fluoride are mixed in a weight ratio of 97:2:1. N-methylpyrrolidone solvent is added and the mixture is stirred thoroughly to form a uniform positive electrode slurry. This slurry is coated onto the positive electrode current collector aluminum foil, then dried and cold-pressed to obtain the positive electrode sheet.

[0121] [Battery manufacturing]

[0122] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging foil, and the electrolyte prepared in step (1) is injected into the dried bare cell. The cells are then subjected to vacuum sealing, settling, formation, and shaping processes to obtain a secondary battery.

[0123] Table 1

[0124]

[0125] Note: In Table 1, " / " indicates that no compound of any kind (A) was added. "-" indicates that no auxiliary solvent was added and only EMC was used as the solvent. EC content is expressed as a weight percentage (wt%) relative to the organic solvent.

[0126] The secondary batteries obtained in Examples 1-19 and Comparative Examples 1-8 were tested for their high-temperature cycling performance and high-temperature storage performance under high-voltage operating conditions according to the following method, and the results are shown in Table 2.

[0127] (1) High-temperature cycle performance test of secondary batteries

[0128] After preparing the secondary battery, it was first charged to 4.5V at a constant current of 0.5C at 45℃, then further charged to 0.025C at a constant voltage of 4.5V, and finally discharged to 3.0V at a constant current of 0.5C. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is taken as the discharge capacity of the first cycle. The secondary battery was subjected to cyclic charge-discharge tests in the above manner, and the discharge capacity of the 100th cycle was measured. The capacity retention rate (%) of the secondary battery after high-temperature cycling was calculated according to the following formula, and the results are shown in Table 2.

[0129] The capacity retention rate (%) of a secondary battery after high-temperature cycling = [discharge capacity of the 100th cycle / discharge capacity of the 1st cycle] × 100%.

[0130] (2) High-temperature storage performance test of secondary batteries

[0131] After the secondary battery was prepared, it was first charged to 4.5V at a constant current of 0.5C at 25℃, and then charged to 0.025C at a constant voltage of 4.5V. The volume of the secondary battery was then measured in deionized water by the water displacement method as the initial volume of the secondary battery (i.e., the volume of the secondary battery before high-temperature storage). After the surface of the secondary battery was dried, it was stored at 60℃ for 30 days. After the storage was completed, the volume of the secondary battery was measured as the volume of the secondary battery after high-temperature storage, and the volume expansion rate (%) of the secondary battery after high-temperature storage was calculated according to the following formula. The results are shown in Table 2.

[0132] The volume expansion rate (%) of a secondary battery after high-temperature storage = [(volume of the secondary battery after high-temperature storage - initial volume of the secondary battery) / initial volume of the secondary battery] × 100%.

[0133] Table 2

[0134]

[0135] The comparison between Examples 1-5 and Comparative Examples 1-3 shows that, when using a solvent without EC (ethylene carbonate), the secondary batteries of Examples 1-5, with an appropriate amount of compound (A4), exhibit better high-temperature cycling and high-temperature storage performance under high-voltage (4.5V) operating conditions than the secondary battery of Comparative Example 1, which did not contain any compound (A4). Specifically, they achieve higher capacity retention after high-temperature cycling and lower volume expansion after high-temperature storage. This is because compound (A4) possesses the function of positive electrode film protection and capturing transition metal ions dissolved in the electrolyte. However, when the content of compound (A4) exceeds 5 wt% (Comparative Example 3), the capacity retention after high-temperature cycling deteriorates. This may be because compound 1 occupies an excessive proportion of the organic solvent, increasing the viscosity of the electrolyte and leading to increased lithium-ion migration resistance. Simultaneously, the interfacial film formed on the positive electrode surface is too thick, resulting in excessively high film impedance and charge transfer impedance of the secondary battery, thus affecting its cycling performance. However, when the weight percentage of compound (A4) in the electrolyte is as low as 0.005 wt% (Comparative Example 2), the content of compound (A4) is too low to effectively form a good interfacial film on the positive electrode surface, thus making it difficult to prevent the dissolution of transition metals in the positive electrode, and the improvement on the performance of the secondary battery is not obvious.

[0136] Furthermore, a comparison between Examples 6-12 and Comparative Example 1 shows that using one or more compounds (A) conforming to general formula (I) or (II) as additives can improve the high-temperature cycling performance and high-temperature storage performance of secondary batteries. The resulting secondary batteries can achieve high capacity retention after high-temperature cycling and low volume expansion rate after high-temperature storage under high-voltage (4.5V) operating conditions. This is because these compounds (A) have relatively strong complexing ability for transition metal elements, and the F, trimethylsilyl, and other substituent groups in some compounds (A) also have a certain adsorption effect on the cathode material. Therefore, they can all perform the functions required by this application of forming a film on the cathode surface and capturing transition metal elements dissolved in the electrolyte.

[0137] Furthermore, comparing Examples 3, 15-19 with Comparative Examples 7, 8, it was found that, with the addition of an equal amount of compound (A), the high-temperature cycle performance and high-temperature storage performance of the secondary battery obtained using an electrolyte containing more than 5 wt% ethylene carbonate (EC) were significantly worse. This trend can also be observed in the comparison between Comparative Example 1 and Comparative Examples 4-6 without the addition of compound (A). This is because when the organic solvent contains a large amount of EC, EC continuously diffuses and penetrates the SEI film on the surface of the positive electrode material, directly contacting the surface of the positive electrode active material particles, thereby causing oxidative decomposition. Moreover, during this oxidative decomposition process, side reactions such as gas production, oxygen release, and the formation of acidic substances are also present. The acidic substances produced further corrode the positive electrode material, leading to further dissolution of transition metals and further accelerating the capacity decay of the cell. Therefore, by reducing the EC content in the electrolyte, the erosion of the positive electrode material by the electrolyte can be reduced, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery. Further comparison of Examples 3 and 19 shows that by controlling the EC content in the organic solvent to below 3 wt%, the corrosive effect of EC and its gas-generating side effects can be essentially eliminated. Therefore, by further controlling the content of ethylene carbonate in the organic solvent of the electrolyte, the protective effect of the electrolyte on the positive electrode material can be further enhanced, thereby reliably improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0138] 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 secondary battery, characterized in that, Including electrolyte, The electrolyte contains an organic solvent and one or more compounds (A) represented by general formula (I) or general formula (II) below. (AND) (II) In the general formula (I) or general formula (II), X includes any one of the elements S and N. R includes one or more of the following: hydrogen atom, cyano or isocyanate group, trimethylsilyl group, straight-chain alkyl or branched alkyl with 1-4 carbon atoms, straight-chain alkyl with 1-4 carbon atoms in which some or all hydrogen atoms are substituted by halogen, phenyl or benzyl group in which some or all hydrogen atoms are substituted by halogen or not, and sulfonyl or sulfonic acid group in which some or all hydrogen atoms are substituted by halogen or not. The content of compound (A) in the electrolyte is 1 wt% - 5 wt%. The content of ethylene carbonate in the organic solvent is less than or equal to 3 wt%.

2. The secondary battery according to claim 1, characterized in that, In the general formula (I) or general formula (II), R includes straight-chain alkyl groups having 2-4 carbon atoms.

3. The secondary battery according to claim 1, characterized in that, R includes one or more of the following: straight-chain alkyl groups having 2-3 carbon atoms, and straight-chain alkyl groups having 1-3 carbon atoms in which some or all of the hydrogen atoms are replaced by halogens.

4. The secondary battery according to claim 1 or 2, characterized in that, The compound (A) includes one or more of the following compounds (A1)-(A3): (A1) (A2) （A3）。 5. The secondary battery according to any one of claims 1-3, characterized in that, The content of compound (A) in the electrolyte is 2wt%-3wt%.

6. The secondary battery according to any one of claims 1-3, characterized in that, The organic solvent does not contain ethylene carbonate.

7. The secondary battery according to any one of claims 1-3, characterized in that, The organic solvent contains one or more of the following: cyclic carbonates other than chain carbonates and ethylene carbonates, carboxylic acid esters, and ether solvents.

8. The secondary battery according to claim 7, characterized in that, The content of the chain carbonate in the electrolyte is 40wt%-90wt%.

9. The secondary battery according to claim 7, characterized in that, The chain carbonates include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and trifluoroethylmethyl carbonate; the cyclic carbonates other than ethylene carbonate include fluoroethylene carbonate; the carboxylic acid esters include ethyl acetate, methyl acetate, and propyl acetate; and the ether solvents include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, desflurane, and 2,2,2-trifluoroethyl-30,30,30,20,20-pentafluoropropyl ether.

10. The secondary battery according to any one of claims 1-3, characterized in that, The organic solvent in the electrolyte contains 60wt%-98wt%.

11. A battery module, characterized in that, Includes the secondary battery as described in any one of claims 1-10.

12. A battery pack, characterized in that, Includes the battery module as described in claim 11.

13. An electrical appliance, characterized in that, It includes at least one selected from the secondary battery of any one of claims 1-10, the battery module of claim 11, or the battery pack of claim 12.

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