Electrolyte and secondary battery

Abstract

The invention provides an electrolyte and a secondary battery. The electrolyte comprises an organic solvent, a lithium salt, a film-forming additive and a metal corrosion inhibitor, the mass ratio of the metal corrosion inhibitor in the electrolyte is 0.001-2%; the metal corrosion inhibitor is a benzotriazole compound and / or a sulfonate compound; the chemical formula of the sulfonate compound is R-SO3M, R is C1-C16 straight-chain alkyl or phenyl-substituted C1-C12 straight-chain alkyl, and M is selected from any one of Li, Na and K. The invention further discloses a preparation method of the sulfonate compound. By adding the metal corrosion inhibitor according to the type and the mass ratio into the electrolyte, a protective layer can be formed on the surface of the steel shell of the cylindrical battery, so that the contact between acidic byproducts in the battery and the surface of the steel shell is isolated, the corrosion of the steel shell is inhibited, and the storage performance, the cycle life and the safety of the battery are further improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to an electrolyte and a secondary battery. Background Technology

[0002] With the development of emerging industries such as the low-altitude economy and humanoid robots, the demand for batteries with higher energy density is becoming increasingly urgent. Silicon anodes, with their high energy density, are being used more and more extensively in batteries. While increasing the amount of silicon anodes can significantly improve battery energy density, their high expansion characteristics result in substantial volumetric expansion stress in the battery. Pouch cells and prismatic cells cannot withstand this enormous volumetric expansion stress. Pouch cells and prismatic cells using high-silicon anodes are prone to deformation during cycling, affecting not only battery performance but also posing significant safety risks, thus limiting the application of high-silicon anodes in these types of batteries. Steel-cased cylindrical batteries, on the other hand, can withstand greater expansion forces without deformation, making them suitable for using high-silicon anodes.

[0003] However, the acidic byproducts such as hydrofluoric acid produced by the reaction of lithium salts in the electrolyte with trace amounts of water in the battery can corrode the steel. To improve the corrosion resistance of the steel shell, a metal protective layer is typically electroplated onto the surface of the cylindrical steel shell. Due to cost considerations, this protective layer is generally thin, and corrosion still occurs in some weakly protected areas under prolonged contact with the electrolyte. Furthermore, even with a thick plating layer protecting the steel shell surface, some plating damage can still occur in the weld area when the cover plate is welded to the shell. Therefore, the weld area also has a high probability of corrosion under prolonged contact with the electrolyte. The metal ions generated by corrosion enter the electrolyte and, during battery charging and discharging, deposit on the surfaces of the positive and negative electrodes as the potential changes, causing problems such as reduced capacity, voltage drop, and self-discharge in lithium-ion batteries, thus affecting the battery's electrical performance and even jeopardizing its safety.

[0004] Current solutions typically involve adding dehydrating agents to the electrolyte to reduce the formation of acidic byproducts, or adding deacidifying agents to react with these byproducts and reduce the acid content in the electrolyte. However, because acidic byproducts are continuously generated during battery cycling, deacidifying and dehydrating agents cannot completely eliminate them, and corrosion will still occur slowly after long-term battery use. Therefore, there is an urgent need to develop an electrolyte that can slow down the corrosion of the steel casing of cylindrical batteries. Summary of the Invention

[0005] The main objective of this invention is to provide an electrolyte and a secondary battery to solve the problem in the prior art where the reaction between lithium salts in the electrolyte and water in the battery produces acidic byproducts that corrode the steel of steel-cased batteries, leading to a decrease in the performance of lithium-ion batteries.

[0006] To achieve the above objectives, according to one aspect of the present invention, an electrolyte is provided, comprising an organic solvent, a lithium salt, and a film-forming additive, wherein the electrolyte further comprises a metal corrosion inhibitor; the mass percentage of the metal corrosion inhibitor in the electrolyte is 0.001~2%; the metal corrosion inhibitor is a benzotriazole compound and / or a sulfonate compound; the chemical formula of the sulfonate compound is R-SO3M, wherein R is C1~C2. 16 Straight-chain alkyl or phenyl-substituted C1~C 12 The straight-chain alkyl group, M is selected from any one of Li, Na, and K; the chemical structural formula of benzotriazole compounds is: (Formula I), wherein R1 is selected from any one of H, Li, Na, and K; and R2, R3, R4, and R5 are each independently selected from any one of H, halogens, C1-C6 straight-chain alkyl groups, and C3-C6 branched-chain alkyl groups.

[0007] Furthermore, in sulfonate compounds, R is C1~C2. 12 The sulfonate compound is a C1-C6 straight-chain alkyl group substituted with a straight-chain alkyl group or a C1-C3 straight-chain alkyl group substituted with a phenyl group; preferably, the sulfonate compound is selected from any one or more of lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, lithium butanesulfonate, lithium pentanesulfonate, lithium hexanesulfonate, lithium benzenesulfonate, sodium methanesulfonate, sodium ethanesulfonate, sodium propanesulfonate, sodium butanesulfonate, sodium pentanesulfonate, sodium hexanesulfonate, and sodium benzenesulfonate.

[0008] Further, in the benzotriazole compounds, R1 is selected from any one of H, Li, and Na; R2, R3, R4, and R5 are each independently selected from any one of H, -F, -Cl, -Br, -I, and C1~C3 straight-chain alkanes; preferably, the benzotriazole compounds are selected from any one or more of benzotriazole, 4-methylbenzotrithiazole, 5-methylbenzotriazole, sodium benzotriazole, sodium 4-methylbenzotrithiazole, sodium 5-methylbenzotriazole, lithium benzotriazole, lithium 4-methylbenzotrithiazole, lithium 5-methylbenzotriazole, 4-fluorophenyl-benzotrithiazole, and 5-fluorobenzotriazole.

[0009] Furthermore, when the metal corrosion inhibitor is a combination of benzotriazole compounds and sulfonate compounds, the molar ratio of benzotriazole compounds to sulfonate compounds is 1~99:1~99.

[0010] Furthermore, when the metal corrosion inhibitor is a combination of lithium methanesulfonate and benzotriazole, the molar ratio of lithium methanesulfonate to benzotriazole is 1~9:1~9; when the metal corrosion inhibitor is a combination of lithium methanesulfonate and 4-methylbenzotrithiazole, the molar ratio of lithium methanesulfonate to 4-methylbenzotrithiazole is 1~9:1~9; when the metal corrosion inhibitor is a combination of lithium methanesulfonate and sodium benzotriazole, the molar ratio of lithium methanesulfonate to sodium benzotriazole is 1~9:1~9; when the metal corrosion inhibitor is a combination of lithium methanesulfonate and lithium benzotriazole, the molar ratio of lithium methanesulfonate to lithium benzotriazole is 1~9:1~9; when the metal corrosion inhibitor is a combination of sodium hexanesulfonate and 4-fluorophenyl-benzotrithiazole, the molar ratio of sodium hexanesulfonate to 4-fluorophenyl-benzotrithiazole is 1~9:1~9.

[0011] Furthermore, the electrolyte contains 75-88% organic solvent by mass, and the organic solvent includes cyclic esters and chain esters, with a mass ratio of cyclic esters to chain esters of 1-3:7-9; and / or, the cyclic esters are selected from any one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; and / or, the chain esters are selected from any one or more of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0012] Furthermore, the lithium salt in the electrolyte accounts for 10-20% by mass; the lithium salt includes lithium hexafluorophosphate; preferably, the lithium salt also includes lithium bisfluorosulfonylimide; when the lithium salt is a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide, the lithium bisfluorosulfonylimide in the lithium salt accounts for ≤70% by mass, preferably 10-50%.

[0013] Further, the mass percentage of the film-forming additive in the electrolyte is 1-6%; and / or, the film-forming additive is selected from any one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, methylene disulfonate, vinyl sulfate, adiponitrile, hexanetrionitrile, triallyl phosphate, triargyl phosphate, tri(trimethylsilane)borate, tri(trimethylsilane) phosphate, hexamethylene diisocyanate, tetravinylsilane, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, hexafluorocyclotriphosphazene, and toluenesulfonyl isocyanate.

[0014] Furthermore, the mass ratio of organic solvent, lithium salt, film-forming additive and metal corrosion inhibitor is 78~86:12~18:2~4:0.01~0.2.

[0015] According to another aspect of the present invention, a secondary battery is provided, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0016] By applying the technical solution of this invention, a metal corrosion inhibitor is added to the electrolyte. This inhibitor can form a complex with the iron exposed on the steel shell surface of the battery, generating a protective layer. This prevents the contact between acidic byproducts in the electrolyte and active iron, thereby fundamentally solving the corrosion problem of the cylindrical battery's steel shell. Specifically, in the benzotriazole compounds of the above-mentioned structure, the triazole ring has electron-deficient characteristics, while the surface of the metal steel shell is electron-rich. Therefore, the benzotriazole compounds can chemically adsorb with the iron exposed on the steel shell surface to form a complex, thereby forming a stable protective layer. The sulfonate compounds of the above-mentioned structure can react with the iron exposed on the steel shell surface through the sulfonate group, thereby forming a stable protective layer with high mechanical strength. When benzotriazole compounds and sulfonate compounds are used in combination, their synergistic effect can be improved. On the one hand, sulfonates have dispersing and wetting effects, which can promote the dissolution of benzotriazole substances in the electrolyte solvent and promote the wetting of the steel shell surface by the electrolyte. On the other hand, sulfonate ions can remove the original adsorbates on the steel shell surface, cleaning the steel shell and promoting the adsorption and film formation of benzotriazole slow-release agents. This not only allows for the rapid formation of a protective layer on the steel shell surface but also maintains the durability and integrity of this protective layer, effectively inhibiting corrosion even under long-term battery cycling and complex operating conditions. In summary, the electrolyte of this application, with the aforementioned types and mass proportions of metal corrosion inhibitors, can form a protective layer on the surface of the cylindrical battery steel shell, thereby isolating acidic byproducts in the battery from contact with the steel shell surface, inhibiting steel shell corrosion, and thus improving the battery's cycle performance, lifespan, and safety. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0018] As analyzed in the background section of this application, the existing technology has a problem where the acidic byproducts produced by the reaction of lithium salts in the electrolyte with water in the battery cause corrosion of the steel in the steel-cased battery, leading to a reduction in the performance of the lithium-ion battery. In order to solve the above problems, this application provides an electrolyte and a secondary battery.

[0019] In a typical embodiment of this application, an electrolyte is provided, comprising an organic solvent, a lithium salt, and a film-forming additive. The electrolyte includes a metal corrosion inhibitor; the mass percentage of the metal corrosion inhibitor in the electrolyte is 0.001~2%; the metal corrosion inhibitor is a benzotriazole compound and / or a sulfonate compound; the chemical formula of the sulfonate compound is R-SO3M, where R is C1~C2. 16 Straight-chain alkyl or phenyl-substituted C1~C 12The straight-chain alkyl group, M is selected from any one of Li, Na, and K; the chemical structural formula of benzotriazole compounds is: (Formula I), wherein R1 is selected from any one of H, Li, Na, and K; and R2, R3, R4, and R5 are each independently selected from any one of H, halogens, C1-C6 straight-chain alkyl groups, and C3-C6 branched-chain alkyl groups.

[0020] This application adds a metal corrosion inhibitor to the electrolyte, which can form a complex with the exposed iron on the steel shell surface of the battery, generating a protective layer. This prevents acidic byproducts in the electrolyte from contacting the active iron, thus fundamentally solving the corrosion problem of the cylindrical battery's steel shell. Specifically, in the benzotriazole compounds of the aforementioned structure, the triazole ring has electron-deficient characteristics, while the surface of the metal steel shell is electron-rich. Therefore, the benzotriazole compounds can chemically adsorb with the exposed iron on the steel shell surface to form a complex, thereby forming a stable protective layer. The sulfonate compounds of the aforementioned structure can react with the exposed iron on the steel shell surface through the sulfonate group, thereby forming a stable protective layer with high mechanical strength. When benzotriazole compounds and sulfonate compounds are used in combination, their synergistic effect can be enhanced. On the one hand, sulfonates have dispersing and wetting effects, which can promote the dissolution of benzotriazole substances in the electrolyte solvent and promote the wetting of the steel shell surface by the electrolyte. On the other hand, sulfonate ions can remove the original adsorbates on the steel shell surface, cleaning the steel shell and promoting the adsorption and film formation of benzotriazole slow-release agents. This not only allows for the rapid formation of a protective layer on the steel shell surface but also maintains the durability and integrity of this protective layer, effectively inhibiting corrosion even under long-term battery cycling and complex operating conditions. In summary, the electrolyte of this application, with the aforementioned types and mass proportions of metal corrosion inhibitors, can form a protective layer on the surface of the cylindrical battery steel shell, thereby isolating acidic byproducts in the battery from contact with the steel shell surface, inhibiting steel shell corrosion, and thus improving the battery's cycle performance, lifespan, and safety.

[0021] In addition, the mass percentage of metal corrosion inhibitor in the electrolyte can be 0.001%, 0.01%, 0.05%, 0.1%, 0.12%, 0.15%, 0.17%, 0.2%, 0.5%, 1%, 1.2%, 1.5%, 1.8% or 2%. Of course, the mass percentage of metal corrosion inhibitor in the electrolyte can be any value within the above range.

[0022] To improve the protective effect of metal corrosion inhibitors and their compatibility with electrolytes, in one embodiment of this application, R in the above-mentioned sulfonate compound is C1~C1. 12The sulfonate compound is a C1-C6 straight-chain alkyl group substituted with a straight-chain alkyl group or a C1-C3 straight-chain alkyl group substituted with a phenyl group; preferably, the sulfonate compound is selected from any one or more of lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, lithium butanesulfonate, lithium pentanesulfonate, lithium hexanesulfonate, lithium benzenesulfonate, sodium methanesulfonate, sodium ethanesulfonate, sodium propanesulfonate, sodium butanesulfonate, sodium pentanesulfonate, sodium hexanesulfonate, and sodium benzenesulfonate.

[0023] The preferred sulfonate compounds are those within the above-mentioned range. On the one hand, the shorter alkyl chain or phenyl-substituted alkyl structure gives the sulfonate compounds better solubility in the electrolyte. On the other hand, due to their smaller molecular size, they diffuse faster in the electrolyte, which is more conducive to cleaning the original adsorbates on the steel shell surface, and thus better promotes the complexation reaction between benzotriazole compounds and active iron on the steel shell surface.

[0024] In one embodiment of this application, R1 in the benzotriazole compound is selected from any one of H, Li, and Na; R2, R3, R4, and R5 are each independently selected from any one of H, -F, -Cl, -Br, -I, and C1~C3 straight-chain alkanes; preferably, the benzotriazole compound is selected from any one or more of benzotriazole, 4-methylbenzotrithiazole, 5-methylbenzotriazole, sodium benzotriazole, sodium 4-methylbenzotrithiazole, sodium 5-methylbenzotriazole, lithium benzotriazole, lithium 4-methylbenzotrithiazole, lithium 5-methylbenzotriazole, 4-fluorophenyl-benzotrithiazole, and 5-fluorobenzotriazole.

[0025] The preferred benzotriazole compounds are within the above-mentioned range, which helps them to participate in the formation of more stable complexes that provide good protection for the steel shell, thereby better protecting the surface of the steel shell.

[0026] In one embodiment of this application, when the metal corrosion inhibitor is a combination of benzotriazole compounds and sulfonate compounds, the molar ratio of benzotriazole compounds to sulfonate compounds is 1~99:1~99.

[0027] Benzotriazole compounds form stable complexes with active iron sites on the steel shell surface, thereby preventing corrosion from media such as acidic byproducts. Sulfonate compounds remove pre-adsorbed dirt from the steel shell surface, clearing obstacles for a uniform and thorough complexation reaction between the benzotriazole compounds and the active iron sites. A combination of benzotriazole and sulfonate compounds is preferred as the metal corrosion inhibitor. Controlling the molar ratio of benzotriazole and sulfonate compounds within the aforementioned range helps enhance their synergistic effect, resulting in a more uniform and dense protective layer, while also strengthening the chemisorption, thus further improving the protective capability of the steel shell.

[0028] Furthermore, the molar ratio of benzotriazole compounds to sulfonate compounds can be 1:99, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, or 99:1. Of course, the molar ratio of benzotriazole compounds to sulfonate compounds can be any value within the above range.

[0029] To further improve the protective capability against steel shells, in one embodiment of this application, when the metal corrosion inhibitor is a combination of lithium methanesulfonate and benzotriazole, the molar ratio of lithium methanesulfonate to benzotriazole is 1~9:1~9, preferably 7~9:1~3; when the metal corrosion inhibitor is a combination of lithium methanesulfonate and 4-methylbenzotrithiazole, the molar ratio of lithium methanesulfonate to 4-methylbenzotrithiazole is 1~9:1~9, preferably 7~9:1~3; when the metal corrosion inhibitor is a combination of lithium methanesulfonate and benzotrithiazole... When the metal corrosion inhibitor is a combination of lithium methanesulfonate and benzotriazole sodium salt, the molar ratio of lithium methanesulfonate to benzotriazole sodium salt is 1~9:1~9, preferably 7~9:1~3; when the metal corrosion inhibitor is a combination of lithium methanesulfonate and benzotriazole lithium salt, the molar ratio of lithium methanesulfonate to benzotriazole lithium salt is 1~9:1~9, preferably 7~9:1~3; when the metal corrosion inhibitor is a combination of sodium hexanesulfonate and 4-fluorophenyl-benzotrithiazole, the molar ratio of sodium hexanesulfonate to 4-fluorophenyl-benzotrithiazole is 1~9:1~9.

[0030] The preferred metal corrosion inhibitor is the combination described above, which helps to form a uniform and stable adsorption layer on the surface of the cylindrical battery steel casing, thereby reducing the corrosion of the steel casing by acidic byproducts.

[0031] In one embodiment of this application, the electrolyte contains 75-88% organic solvent by mass, the organic solvent comprising cyclic esters and chain esters, the cyclic esters comprising 10%-30% by mass; the mass ratio of cyclic esters to chain esters is 1-3:7-9; and / or, the cyclic esters are selected from any one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; and / or, the chain esters are selected from any one or more of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0032] The preferred mass ratio of organic solvent in the electrolyte within the above-mentioned range helps to better dissolve lithium salts and film-forming additives, thereby improving lithium ion transport. Considering the difficulty of electrolyte wetting in cylindrical batteries, a low-viscosity electrolyte is beneficial to improving electrolyte wettability. The preferred mass ratio of cyclic esters to chain esters in the organic solvent within the above-mentioned range helps to improve electrolyte wettability. Cyclic esters have a higher dielectric constant, which is beneficial to the dissolution of lithium salts and the formation of a stable SEI film; while chain esters have lower viscosity, which helps to improve electrolyte flowability and promote better wetting performance. Therefore, controlling the mass ratio of cyclic esters to chain esters within the above-mentioned range in this application helps to achieve both high ionic conductivity and wettability in the electrolyte, thereby improving the electrochemical performance of the battery.

[0033] In addition, the mass percentage of organic solvent in the electrolyte can be 75%, 77%, 80%, 82%, 85% or 88%, and of course, the mass percentage of organic solvent in the electrolyte can be any value within the above range.

[0034] In one embodiment of this application, the mass percentage of lithium salt in the electrolyte is 10-20%; the lithium salt includes lithium hexafluorophosphate; preferably, the lithium salt also includes lithium bisfluorosulfonylimide; when the lithium salt is a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide, the mass percentage of lithium bisfluorosulfonylimide in the lithium salt is ≤70%, preferably 10%-50%.

[0035] The optimal mass percentage of lithium salt in the electrolyte within the aforementioned range not only helps improve the ion transport efficiency of the electrolyte but also promotes the formation of a more uniform and stable SEI film, thereby improving the cycle stability and lifespan of the battery. Lithium hexafluorophosphate has high conductivity, while lithium bis(fluorosulfonyl)imide has high thermal stability, electrochemical stability, and high conductivity. A combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide is preferred, and controlling the mass percentage of lithium bis(fluorosulfonyl)imide in the lithium salt within the aforementioned range helps the electrolyte maintain high conductivity while reducing the formation of corrosive products, thus protecting the battery's steel casing and reducing corrosion.

[0036] In addition, the mass percentage of lithium salt in the electrolyte can be 10%, 12%, 15%, 17% or 20%, and of course, the mass percentage of lithium salt in the electrolyte can be any value within the above range.

[0037] In one embodiment of this application, the mass percentage of the film-forming additive in the electrolyte is 1-6%; and / or, the film-forming additive is selected from any one or more of the following: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, methylene disulfonate, vinyl sulfate, adiponitrile, hexanetrionitrile, triallyl phosphate, triargyl phosphate, tri(trimethylsilane)borate, tri(trimethylsilane) phosphate, hexamethylene diisocyanate, tetravinylsilane, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium di(oxalate borate), lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, hexafluorocyclotriphosphazene, and toluenesulfonyl isocyanate.

[0038] The selection of film-forming additives within the above-mentioned range in terms of type and mass ratio helps to promote the formation of the SEI film, improve the stability of the SEI film, thereby reducing the side reactions of lithium ions during charging and discharging. It also helps to interact with metal corrosion inhibitors to build a multi-layer barrier, thereby improving the safety and electrochemical performance of the battery and extending the cycle life of the battery.

[0039] In addition, the mass percentage of film-forming additives in the electrolyte can be 1%, 2%, 3%, 4%, 5% or 6%. Of course, the mass percentage of film-forming additives in the electrolyte can be any value within the above range.

[0040] The preferred film-forming additive is a combination of vinylene carbonate, 1,3-propanesulfonate lactone, lithium difluorophosphate, and lithium difluorooxalate borate, wherein the mass ratio of vinylene carbonate, 1,3-propanesulfonate lactone, lithium difluorophosphate, and lithium difluorooxalate borate is 0.5~2:0.5~2:0.5~2:0.5~2.

[0041] In one embodiment of this application, the mass ratio of organic solvent, lithium salt, film-forming additive and metal corrosion inhibitor is 78~86:12~18:2~4:0.01~0.2.

[0042] Preferably, the mass ratio of organic solvent, lithium salt, film-forming additive, and metal corrosion inhibitor within the above range helps to improve the wettability, conductivity, and stability of the electrolyte. At the same time, the addition of metal corrosion inhibitor helps to further enhance its anti-corrosion ability, thereby improving battery safety and extending battery cycle life.

[0043] In another typical embodiment of this application, a secondary battery is provided, including a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0044] The electrolyte provided in this application is particularly suitable for secondary batteries with casings made of a single metal or a multi-metal alloy, including but not limited to lithium-ion secondary batteries. The secondary batteries of this application, including the aforementioned electrolyte that prevents corrosion of the steel casing, can significantly improve battery safety and lifespan, as well as enhance cycle stability and charge / discharge efficiency.

[0045] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0046] Example 1

[0047] By mass percentage, the electrolyte consists of 80% organic solvent, 15% lithium salt, 4% film-forming additives, and 1% metal corrosion inhibitor.

[0048] The organic solvent is a combination of cyclic ester ethylene carbonate (EC) and chain ester dimethyl carbonate (DMC) in a mass ratio of 2:8; the metal corrosion inhibitor is benzotriazole; the lithium salt is lithium hexafluorophosphate; and the film-forming additive is a combination of vinylene carbonate, 1,3-propanesulfonate lactone, lithium difluorophosphate, and lithium difluorooxalate borate in a mass ratio of 1:1:1:1.

[0049] Preparation method: An organic solvent was added to a container and stirred for 30 minutes at room temperature (25°C) using a magnetic stirrer. Lithium salt was then added to the organic solvent, and stirring continued until the lithium salt was completely dissolved, forming a clear and transparent solution. A film-forming additive was then added and stirred to mix. Finally, a metal corrosion inhibitor was added and stirring continued until the metal corrosion inhibitor was completely dissolved and uniformly distributed in the solution. The mixed solution was then filtered through a high-precision filter membrane to obtain the electrolyte.

[0050] Example 2

[0051] The difference from Example 1 is that the metal corrosion inhibitor is lithium methanesulfonate, and the mass ratio of the metal corrosion inhibitor in the electrolyte is 2%, resulting in the final electrolyte.

[0052] Example 3

[0053] The difference from Example 1 is that the metal corrosion inhibitor is a combination of lithium methanesulfonate and benzotrithiazole, with a molar ratio of lithium methanesulfonate to benzotrithiazole of 1:9, resulting in the final electrolyte.

[0054] Example 4

[0055] The difference from Example 1 is that the metal corrosion inhibitor is a combination of lithium methanesulfonate and benzotrithiazole, with a molar ratio of lithium methanesulfonate to benzotrithiazole of 0.5:99.5, resulting in the final electrolyte.

[0056] Example 5

[0057] The difference from Example 1 is that the metal corrosion inhibitor is a combination of lithium methanesulfonate and 4-methylbenzotrithiazole, with a molar ratio of lithium methanesulfonate to 4-methylbenzotrithiazole of 1:9, resulting in the final electrolyte.

[0058] Example 6

[0059] The difference from Example 1 is that the metal corrosion inhibitor is a combination of lithium methanesulfonate and 4-methylbenzotrithiazole, with a molar ratio of lithium methanesulfonate to 4-methylbenzotrithiazole of 0.5:99.5, resulting in the final electrolyte.

[0060] Example 7

[0061] The difference from Example 1 is that the metal corrosion inhibitor is a combination of lithium methanesulfonate and sodium benzotriazole, with a molar ratio of lithium methanesulfonate to sodium benzotriazole of 1:9, resulting in the final electrolyte.

[0062] Example 8

[0063] The difference from Example 1 is that the metal corrosion inhibitor is a combination of lithium methanesulfonate and lithium benzotriazole salt, with a molar ratio of lithium methanesulfonate to lithium benzotriazole salt of 2:8, resulting in the final electrolyte.

[0064] Example 9

[0065] The difference from Example 1 is that the metal corrosion inhibitor is a combination of lithium methanesulfonate and 4-fluorophenyl-benzotrithiazole, with a molar ratio of lithium methanesulfonate to 4-fluorophenyl-benzotrithiazole of 3:7, resulting in the final electrolyte.

[0066] Example 10

[0067] The difference from Example 3 is that the lithium salt is a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, with lithium bis(fluorosulfonyl)imide accounting for 50% by mass, ultimately yielding the electrolyte.

[0068] Example 11

[0069] The difference from Example 3 is that the lithium salt is a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, with lithium bis(fluorosulfonyl)imide accounting for 80% of the final electrolyte.

[0070] Example 12

[0071] The difference from Example 3 is that the mass ratio of organic solvent, lithium salt, film-forming additive and metal corrosion inhibitor is 80.8:15:4:0.2, and the final electrolyte is obtained.

[0072] Example 13

[0073] The difference from Example 3 is that the mass ratio of organic solvent, lithium salt, film-forming additive and metal corrosion inhibitor is 80.999:15:4:0.001, and the final electrolyte is obtained.

[0074] Comparative Example 1

[0075] The difference from Example 1 is that no metal corrosion inhibitor is added, and the final electrolyte is obtained.

[0076] Comparative Example 2

[0077] The difference from Example 1 is that the mass ratio of the metal corrosion inhibitor in the electrolyte is 3%, and the mass ratio of the organic solvent, lithium salt, film-forming additive and metal corrosion inhibitor is 78:15:4:3, thus obtaining the final electrolyte.

[0078] Comparative Example 3

[0079] The difference from Example 1 is that the metal corrosion inhibitor is replaced with the dehydrating agent DCC, and the final electrolyte is obtained.

[0080] Test method:

[0081] Electrolyte corrosion inhibition evaluation method: Fresh cylindrical battery steel casings were vacuum-baked at 80℃ for 24 hours. Then, 100g of fresh electrolyte was poured into the casing, and the casing was sealed with aluminum-plastic film and left at room temperature for 24 hours. The aluminum-plastic film was then cut open, and 0.1g of deionized water (water reacts with lithium hexafluorophosphate to produce hydrofluoric acid) was added to the casing. The aluminum-plastic film was then sealed again and placed in a 60℃ oven for 72 hours. After the resting period, the electrolyte was collected, and the iron ion content in the electrolyte was tested using the ICP method. A higher iron ion content indicates more severe corrosion, while a lower iron ion content indicates a more significant corrosion inhibition effect.

[0082] Battery electrical performance evaluation methods:

[0083] (1) Battery fabrication: The above electrolytes were injected into cylindrical batteries of the same batch according to the same battery fabrication process to produce batteries suitable for battery performance evaluation. The main material of the selected battery positive electrode was high-nickel ternary NCM811 material, the main material of the negative electrode was artificial graphite, and the separator was a 9+1μm single-sided ceramic-coated separator. The battery also contained commonly used auxiliary materials. After the battery was fabricated, capacity and cycle performance tests were conducted.

[0084] (2) Battery capacity and initial efficiency test: After the battery completes formation, it is aged at 45°C for 24 hours, and then charged to 4.25V at room temperature with a constant current and constant voltage of 0.333C. The cutoff current is 0.05C. After resting for 30 minutes, it is discharged to 2.75V with a constant current of 0.333C. The initial discharge capacity and initial efficiency are calculated.

[0085] (3) Battery DC internal resistance test: Adjust the battery power to 50% SOC state, use 2C discharge rate, constant current discharge for 10s, and test the battery discharge DCR.

[0086] (4) Room temperature cycling test: At 25℃, a current of 1C / 1C is used to conduct a room temperature cycling test in the voltage range of 2.75~4.25V. After 1000 cycles, the capacity retention rate is recorded.

[0087] (5) High-temperature storage retention rate: At room temperature, the battery was charged to 4.25V with a constant current and constant voltage of 0.333C, and the cutoff current was 0.05C. After resting for 30 minutes, it was discharged to 2.75V with a constant current of 0.333C. This cycle was repeated for 3 weeks, and then the battery was charged to 4.25V with a constant current and constant voltage of 0.333C, and the cutoff current was 0.05C. The average capacity after 3 weeks of discharge was the initial capacity. After the battery was fully charged and stored at 60℃ for 90 days, it was rested at room temperature for 24 hours, and then discharged to 2.75V with a constant current of 0.333C. The discharge capacity was the remaining capacity. High-temperature storage retention rate = remaining capacity / initial capacity × 100%

[0088] The test results are shown in Table 1.

[0089] Table 1

[0090]

[0091] As can be seen from the above, compared with Comparative Example 1, the addition of metal corrosion inhibitors in the embodiments of this application can inhibit steel shell corrosion. In particular, the combination of benzotriazole compounds and alkyl sulfonate compounds can exert a synergistic effect, which can not only significantly inhibit steel shell corrosion, but also have no significant adverse effect on battery performance.

[0092] Adding a high amount of benzotriazole to Comparative Example 2 can significantly reduce the iron ion content, but it will lead to a significant increase in the battery's DCR and a significant decrease in cycle performance.

[0093] In Comparative Example 3, the iron ion content decreased after adding a dehydrating agent, but remained high. This is because both the dehydrating agent and lithium hexafluorophosphate react with water. Although the dehydrating agent consumed some water, a large amount of water still reacted with lithium hexafluorophosphate to produce hydrofluoric acid, which caused corrosion of the steel casing. Furthermore, the excessive addition of the dehydrating agent led to a significant increase in the battery's DCR and a significant decrease in cycle performance.

[0094] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0095] This application adds a metal corrosion inhibitor to the electrolyte, which can form a complex with the exposed iron on the steel shell surface of the battery, generating a protective layer. This prevents acidic byproducts in the electrolyte from contacting the active iron, thus fundamentally solving the corrosion problem of the cylindrical battery's steel shell. Specifically, in the benzotriazole compounds of the aforementioned structure, the triazole ring has electron-deficient characteristics, while the surface of the metal steel shell is electron-rich. Therefore, the benzotriazole compounds can chemically adsorb with the exposed iron on the steel shell surface to form a complex, thereby forming a stable protective layer. The sulfonate compounds of the aforementioned structure can react with the exposed iron on the steel shell surface through the sulfonate group, thereby forming a stable protective layer with high mechanical strength. When benzotriazole compounds and sulfonate compounds are used in combination, their synergistic effect can be enhanced. On the one hand, sulfonates have dispersing and wetting effects, which can promote the dissolution of benzotriazole substances in the electrolyte solvent and promote the wetting of the steel shell surface by the electrolyte. On the other hand, sulfonate ions can remove the original adsorbates on the steel shell surface, cleaning the steel shell and promoting the adsorption and film formation of benzotriazole slow-release agents. This not only allows for the rapid formation of a protective layer on the steel shell surface but also maintains the durability and integrity of this protective layer, effectively inhibiting corrosion even under long-term battery cycling and complex operating conditions. In summary, the electrolyte of this application, with the aforementioned types and mass proportions of metal corrosion inhibitors, can form a protective layer on the surface of the cylindrical battery steel shell, thereby isolating acidic byproducts in the battery from contact with the steel shell surface, inhibiting steel shell corrosion, and thus improving the battery's cycle performance, lifespan, and safety.

[0096] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrolyte comprising an organic solvent, a lithium salt, and a film-forming additive, characterized in that, The electrolyte further includes a metal corrosion inhibitor; the mass percentage of the metal corrosion inhibitor in the electrolyte is 0.001~2%; the metal corrosion inhibitor is a benzotriazole compound and / or a sulfonate compound; the chemical formula of the sulfonate compound is R-SO3M, where R is C1~C2. 16 Straight-chain alkyl or phenyl-substituted C1~C 12 The straight-chain alkyl group, M is selected from any one of Li, Na, and K; The chemical structural formula of the benzotriazole compound is as follows: (Formula I) R1 is selected from any one of H, Li, Na, and K; R2, R3, R4, and R5 are each independently selected from any one of H, halogens, C1-C6 straight-chain alkyl groups, and C3-C6 branched-chain alkyl groups.

2. The electrolyte according to claim 1, characterized in that, In the sulfonate compound, R is C1~C1. 12 The sulfonate compound is a C1-C6 straight-chain alkyl group substituted with a straight-chain alkyl group or a C1-C3 straight-chain alkyl group substituted with a phenyl group; preferably, the sulfonate compound is selected from any one or more of lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, lithium butanesulfonate, lithium pentanesulfonate, lithium hexanesulfonate, lithium benzenesulfonate, sodium methanesulfonate, sodium ethanesulfonate, sodium propanesulfonate, sodium butanesulfonate, sodium pentanesulfonate, sodium hexanesulfonate, and sodium benzenesulfonate.

3. The electrolyte according to claim 1 or 2, characterized in that, In the benzotriazole compound, R1 is selected from any one of H, Li, and Na; R2, R3, R4, and R5 are each independently selected from any one of H, -F, -Cl, -Br, -I, and C1~C3 straight-chain alkanes; preferably, the benzotriazole compound is selected from any one or more of benzotriazole, 4-methylbenzotrithiazole, 5-methylbenzotriazole, sodium benzotriazole, sodium 4-methylbenzotrithiazole, sodium 5-methylbenzotriazole, lithium benzotriazole, lithium 4-methylbenzotrithiazole, lithium 5-methylbenzotriazole, 4-fluorophenyl-benzotrithiazole, and 5-fluorobenzotriazole.

4. The electrolyte according to any one of claims 1 to 3, characterized in that, When the metal corrosion inhibitor is a combination of the benzotriazole compound and the sulfonate compound, the molar ratio of the benzotriazole compound to the sulfonate compound is 1~99:1~99.

5. The electrolyte according to claim 4, characterized in that, When the metal corrosion inhibitor is a combination of lithium methanesulfonate and benzotriazole, the molar ratio of lithium methanesulfonate to benzotriazole is 1~9:1~9; When the metal corrosion inhibitor is a combination of lithium methanesulfonate and 4-methylbenzotrithiazole, the molar ratio of lithium methanesulfonate to 4-methylbenzotrithiazole is 1~9:1~9; When the metal corrosion inhibitor is a combination of lithium methanesulfonate and sodium benzotriazole, the molar ratio of lithium methanesulfonate to sodium benzotriazole is 1~9:1~9. When the metal corrosion inhibitor is a combination of lithium methanesulfonate and lithium benzotriazole, the molar ratio of lithium methanesulfonate to lithium benzotriazole is 1~9:1~9. When the metal corrosion inhibitor is a combination of sodium hexanesulfonate and 4-fluorophenyl-benzotrithiazole, the molar ratio of sodium hexanesulfonate to 4-fluorophenyl-benzotrithiazole is 1~9:1~9.

6. The electrolyte according to any one of claims 1 to 5, characterized in that, The organic solvent in the electrolyte accounts for 75-88% by mass, and the organic solvent includes cyclic esters and chain esters, with the mass ratio of the cyclic esters to the chain esters being 1-3:7-9. And / or, the cyclic ester is selected from any one or more of ethylene carbonate, propylene carbonate and fluoroethylene carbonate; And / or, the chain ester is selected from any one or more of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

7. The electrolyte according to any one of claims 1 to 6, characterized in that, The lithium salt in the electrolyte accounts for 10-20% by mass; the lithium salt includes lithium hexafluorophosphate. Preferably, the lithium salt further includes lithium bisfluorosulfonylimide; when the lithium salt is a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide, the mass percentage of lithium bisfluorosulfonylimide in the lithium salt is ≤70%, preferably 10~50%.

8. The electrolyte according to any one of claims 1 to 7, characterized in that, The mass percentage of the film-forming additive in the electrolyte is 1-6%; And / or, the film-forming additive is selected from any one or more of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, methylene disulfonate, vinyl sulfate, adiponitrile, hexanetrionitrile, triallyl phosphate, triargyl phosphate, tri(trimethylsilane)borate, tri(trimethylsilane) phosphate, hexamethylene diisocyanate, tetravinylsilane, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, hexafluorocyclotriphosphazene, and toluenesulfonyl isocyanate.

9. The electrolyte according to any one of claims 1 to 8, characterized in that, The mass ratio of the organic solvent, the lithium salt, the film-forming additive, and the metal corrosion inhibitor is 78~86:12~18:2~4:0.01~0.

2.

10. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The electrolyte is the electrolyte according to any one of claims 1 to 9.

Images