Electrolyte and method for repairing aged battery
By using a specific electrolyte composition and repair method, the SEI film is dissolved and reconstructed, and the lithium source is replenished, thus solving the problem of poor repair effect of aged lithium-ion batteries and improving battery capacity and stability.
Patent Information
- Application Number
- CN202511079904.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-01
- Publication Date
- 2025-11-11
AI Technical Summary
Existing technologies have poor repair effects on aged lithium-ion batteries and cannot effectively solve the battery degradation problem caused by loss of active lithium and electrolyte decomposition.
An electrolyte with a specific composition, including lithium salt, a first additive, and a second additive, is used to dissolve the aged SEI film and form a new SEI film by reacting with the inorganic components in the SEI film. This replenishes the lithium source, reduces HF corrosion, optimizes the electrolyte composition ratio, and improves the repair process, which includes static and charge-discharge activation steps.
It improves the charge/discharge capacity and cycle stability of aged batteries, extends battery life, and solves the problems of interface impedance and active lithium loss in aged batteries.
Smart Images
Figure BDA0005531392170000161 
Figure BDA0005531392170000171
Abstract
Description
Technical Field
[0001] This application relates to the field of lithium-ion batteries, and more specifically, to a method for repairing electrolytes and aged batteries. Background Technology
[0002] Lithium-ion batteries are widely used in 3C consumer batteries, power batteries and energy storage batteries due to their advantages such as high operating voltage, high energy density and environmental friendliness, and they also have broad application prospects in aerospace, defense and military industries.
[0003] However, lithium-ion battery aging negatively impacts its economic value. Capacity degradation is inevitable during equipment transportation and use due to the loss of active lithium and electrolyte decomposition. Current research indicates that battery aging is primarily caused by the loss of active lithium and the decomposition of the electrolyte.
[0004] Currently, most solutions to battery aging involve introducing negative voltage and low current to suppress SEI film formation, or "lithium replenishment." However, the SEI film has a complex composition, and both methods may produce complex electrochemical reactions, affecting the repair effect. Summary of the Invention
[0005] The main objective of this application is to provide a method for repairing electrolytes and aged batteries, in order to solve the problem that the repair effect of existing methods for repairing aged batteries is poor.
[0006] To achieve the above objectives, a first aspect of this application provides an electrolyte comprising: a lithium salt, an additive, and an organic solvent; wherein the concentration of the lithium salt in the electrolyte is 0.5–1.5 mol / L, and the mass content of the additive in the electrolyte is 0.5–1.2%; the additive comprises a first additive and a second additive; the first additive is selected from MX. a Y b Compounds and / or MX c • L complex; wherein each M is independently selected from Group IIIA and / or Group IVA elements, and each X is independently selected from halogens and / or C1 to C2. 10 Alkyl group, where Y is C1 to C2. 10 Alkoxy group, L is an organic ligand, a is 1, 2 or 3, b is 1, 2 or 3, c is 3 or 4; the second additive is a difluorophosphorus compound.
[0007] Furthermore, the mass ratio of the first additive to the second additive is 1:(0.1 to 0.8).
[0008] Furthermore, each M is independently selected from any one or more of B, Al, and Si; and / or each X is independently selected from any one or more of F, Cl, Br, and C1-C6 alkyl; and / or Y is a C1-C6 alkoxy group; and / or L is selected from any one or more of dimethyl carbonate, diethyl ether, and tetrahydrofuran.
[0009] Furthermore, each X is independently selected from any one or more of F, methyl, ethyl and propyl; and / or, Y is selected from any one or more of methoxy, ethoxy and propoxy.
[0010] Furthermore, the first additive is selected from any one or more of BF(OCH3)2, AlF(OCH3)2, AlCl3·tetrahydrofuran, AlF(OC2H5)2, SiCH3(OC2H5)3 and BF3·tetrahydrofuran.
[0011] Furthermore, the first additive is a combination of BF(OCH3)2 and AlCl3·tetrahydrofuran, and the mass ratio of BF(OCH3)2 to AlCl3·tetrahydrofuran is 1:2 to 2:1.
[0012] Furthermore, the difluorophosphorus compound is a difluorophosphate compound; preferably, the difluorophosphate compound is selected from lithium difluorophosphate and / or lithium difluorodioxarate phosphate.
[0013] Furthermore, the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium methanesulfonate; and / or, the organic solvent is selected from any one or more of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.
[0014] The second aspect of this application provides a method for repairing an aged battery, the method comprising: step S1, fully discharging an aged battery with a capacity decay of not less than 20% and then subjecting it to a first settling period to obtain a first settling aged battery; step S2, injecting the aforementioned electrolyte into the first settling aged battery and subjecting it to a second settling period to obtain a second settling aged battery; and step S3, activating the second settling aged battery by charging and discharging to complete the repair.
[0015] Further, the first settling time is 12-15 hours; and / or, the second settling time is 12-15 hours; and / or, the charge-discharge activation conditions are: charging at a constant current of 0.1-0.2C to 3.6-3.7V at 25℃±2℃, settling for 10-15 minutes, heating to 50℃±5℃, and then discharging at a constant current of 0.05-0.06C to 2.5-2.6V. This is counted as one charge-discharge cycle, and the charge-discharge cycle is repeated 2-5 times; and / or, the ratio of the injected electrolyte mass to the original electrolyte mass in the aged battery is (5-15):100.
[0016] By applying the technical solution of this application, the first additive reacts with inorganic components in the SEI film, such as LiF and LiCO3, to effectively dissolve these components, thereby reducing the interfacial impedance of the SEI film. Subsequently, a new SEI film is formed through an electrochemical process, which helps to improve the cycle stability and safety of the battery. The Group IIIA and / or Group IVA elements in the first additive can react with Li during charging. + They combine to form a complex, and release Li during the discharge process. + This provides the battery with an additional reversible lithium source, helping to compensate for the loss of active lithium caused by aging, thereby improving the battery's capacity retention. The second additive works synergistically with the first additive to further reduce the corrosion of battery components by HF, forming a protective film and extending battery life. Controlling the mass content of the additive in the electrolyte within the above-mentioned range helps the additive to dissolve the SEI film and provide a lithium source without causing excessive deposition or interface instability due to excessive concentration, thus avoiding the rapid capacity decay problem caused by excessive M element deposition. Applying the electrolyte of this application to repair aging batteries helps to improve the charge-discharge capacity and cycle stability of aging batteries, thereby helping to extend the service life of aging batteries. 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 application will now be described in detail with reference to the embodiments.
[0018] As described in the background section, existing methods for repairing aged batteries suffer from poor repair effectiveness. To address this problem, a first aspect of this application provides an electrolyte comprising, by mass percentage: a lithium salt, an additive, and an organic solvent; wherein the concentration of the lithium salt in the electrolyte is 0.5–1.5 mol / L, and the mass content of the additive in the electrolyte is 0.5–1.2%; the additive includes a first additive and a second additive; the first additive is selected from MX... a Y b Compounds and / or MX c• L complex; wherein each M is independently selected from Group IIIA and / or Group IVA elements, and each X is independently selected from halogens and / or C1 to C2. 10 Alkyl group, where Y is C1 to C2. 10 Alkoxy group, L is an organic ligand, a is 1, 2 or 3, b is 1, 2 or 3, c is 3 or 4; the second additive is a difluorophosphorus compound.
[0019] The first additive in this application reacts with inorganic components in the SEI film, such as LiF and LiCO3, to effectively dissolve these components, thereby reducing the interfacial impedance of the SEI film. Subsequently, a new SEI film is formed through an electrochemical process, which helps to improve the cycle stability and safety of the battery. The Group IIIA and / or Group IVA elements in the first additive can react with Li during charging. + They combine to form a complex, and release Li during the discharge process. + This provides the battery with an additional reversible lithium source, helping to compensate for the loss of active lithium caused by aging, thereby improving the battery's capacity retention. The second additive works synergistically with the first additive to further reduce the corrosion of battery components by HF, forming a protective film and extending battery life. Controlling the mass content of the additive in the electrolyte within the above-mentioned range helps the additive to dissolve the SEI film and provide a lithium source without causing excessive deposition or interface instability due to excessive concentration, thus avoiding the rapid capacity decay problem caused by excessive M element deposition. Applying the electrolyte of this application to repair aging batteries helps to improve the charge-discharge capacity and cycle stability of aging batteries, thereby helping to extend the service life of aging batteries.
[0020] Furthermore, the mass ratio of the first additive and the second additive is 1:(0.1 to 0.8), which can be selected as 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, or any range between two ratios.
[0021] Controlling the mass ratio of the first additive and the second additive within the above range helps to enhance their synergistic effect, thereby helping to further reduce the corrosion of battery components by HF, form a protective film, and extend battery life.
[0022] Furthermore, each M is independently selected from any one or more of B, Al, and Si; and / or each X is independently selected from any one or more of F, Cl, Br, and C1-C6 alkyl; and / or Y is a C1-C6 alkoxy group; and / or L is selected from any one or more of dimethyl carbonate, diethyl ether, and tetrahydrofuran.
[0023] Different combinations of M and X can form SEI film precursors with different properties. Due to its electronic structure, B can form a relatively stable but moderately reactive SEI film; Al and Si can provide lithium-ion storage sites to some extent, while the resulting SEI film has better mechanical strength and lithium-ion conductivity. Controlling the type of Y within the above range helps to regulate the stability and reactivity of the first additive in the electrolyte, allowing the additive to participate in SEI film reconstruction at an appropriate potential, and also enhancing the storage stability of the additive. Controlling the type of L within the above range helps to promote lithium-ion migration in the electrolyte, accelerate the electrochemical reaction rate, and facilitate efficient SEI film reconstruction, while also helping to reduce excessive lithium-ion deposition on the electrode surface.
[0024] Furthermore, each X is independently selected from one or more of F, methyl, ethyl, and propyl; and / or Y is selected from one or more of methoxy, ethoxy, and propoxy.
[0025] F can form stronger chemical bonds with inorganic components in the SEI membrane. Therefore, the first additive containing F has higher solubility and can more effectively remove components such as LiF and LiCO3 from the SEI membrane, promoting the regeneration of new SEI membranes. The presence of methyl, ethyl, and propyl groups helps to further reduce the damage that may be caused by over-reaction. The presence of methoxy, ethoxy, and propoxy groups helps to form an SEI membrane with elasticity and stability.
[0026] To further improve the charge-discharge capacity and cycle stability of the repaired aged battery, the first additive is further selected from any one or more of BF(OCH3)2, AlF(OCH3)2, AlCl3·tetrahydrofuran, AlF(OC2H5)2, SiCH3(OC2H5)3 and BF3·tetrahydrofuran.
[0027] Furthermore, the first additive is a combination of BF(OCH3)2 and AlCl3·tetrahydrofuran, and the mass ratio of BF(OCH3)2 to AlCl3·tetrahydrofuran is 1:2 to 2:1.
[0028] The synergistic effect of BF(OCH3)2 and AlCl3·tetrahydrofuran stems from the difference in their reduction potentials. High reduction potentials preferentially form films, while low reduction potentials enhance the mechanical strength of the SEI film and broaden ion channels by filling pores and buffering stress. Together, they form a more stable SEI film.
[0029] Furthermore, the aforementioned difluorophosphorus compound is a difluorophosphate compound; furthermore, the difluorophosphate compound is selected from lithium difluorophosphate and / or lithium difluorodioxarate phosphate.
[0030] Lithium difluorophosphate and lithium difluorodioxarate phosphate can react with HF to form relatively stable complexes, thereby reducing the corrosion of the battery by HF, maintaining the integrity of the battery's internal structure, and promoting the formation of a more stable SEI film.
[0031] Furthermore, the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium methanesulfonate; and / or, the organic solvent is selected from any one or more of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.
[0032] Controlling the types of lithium salts within the above-mentioned range helps improve electrolyte stability. Controlling the types of organic solvents within the above-mentioned range helps optimize lithium-ion dissociation and improve electrolyte stability.
[0033] Furthermore, the mass ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate is (25-35):(15-25):(35-45).
[0034] Ethylene carbonate, due to its high dielectric constant and viscosity, helps form a stable SEI film; however, the high viscosity of pure ethylene carbonate solvent limits the migration rate of lithium ions. Ethyl methyl carbonate, with its lower viscosity and better flowability, can significantly improve the migration rate of lithium ions, but using ethyl methyl carbonate alone may lead to SEI film instability. Dimethyl carbonate possesses a moderate dielectric constant and viscosity, playing a balancing role between lithium ion transport and SEI film stability. Controlling the mass ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate within the aforementioned range helps accelerate SEI film formation and also allows for the regulation of SEI film thickness and composition, resulting in a more uniform and dense protective layer.
[0035] The repair mechanism of BF3 in BF3·tetrahydrofuran is as follows:
[0036] SEI membrane dissolution reaction
[0037] Dissolution of LiF: LiF + BF3 → LiBF4
[0038] Li₂CO₃ dissolution: Li₂CO₃ + 2BF₃ → 2LiBF₄ + CO₂↑
[0039] SEI membrane regeneration reaction
[0040] EC (ethylene carbonate) + 2e - +2Li + →Li2CO3+C2H4↑
[0041] DEC (diethyl carbonate) + e - +Li+ →ROCO2Li+C2H5OHDEC+e - +Li + →ROCO2Li+C2H5OH
[0042] The reaction provides lithium salt
[0043] LiBF 4 →Li + +BF 4-
[0044] BF 4- +e - +Li + →LiF+BF 3
[0045] Reduce reaction with HF corrosion
[0046] BF3+HF→HBF4
[0047] The second aspect of this application provides a method for repairing an aged battery, the method comprising: step S1, fully discharging an aged battery with a capacity decay of not less than 20% and then subjecting it to a first settling period to obtain a first settling aged battery; step S2, injecting the aforementioned electrolyte into the first settling aged battery and subjecting it to a second settling period to obtain a second settling aged battery; and step S3, activating the second settling aged battery by charging and discharging to complete the repair.
[0048] Completely discharging the aged battery helps eliminate residual charge inside the battery. The first settling process allows the internal chemical substances of the battery to reach a state of equilibrium, which is beneficial for the uniform wetting and deep penetration of the electrolyte in the subsequent process, ensuring that the repair components can fully contact the electrode surface and begin the repair process. Injecting the electrolyte into the aged battery after the first settling period allows the electrolyte to penetrate deep into the battery electrodes and begin to dissolve the inorganic components of the old SEI film, alleviating its interfacial impedance and laying the foundation for the formation of a new, more stable SEI film. The second settling process provides sufficient time for the electrolyte to distribute evenly inside the battery, promoting full contact between the electrolyte and the electrodes and ensuring the uniformity and effectiveness of the repair process. By performing charge-discharge activation—that is, charging and discharging the aged battery after the second settling period under specific voltage and current conditions—SEI film reconstruction and active lithium replenishment are promoted, interfacial impedance is reduced, and charge transfer capability is improved. Because the aged battery is repaired using the electrolyte of this application, the repaired aged battery exhibits excellent charge-discharge capacity and cycle stability.
[0049] Further, the first settling time is 12-15 hours; and / or, the second settling time is 12-15 hours; and / or, the charge-discharge activation conditions are: charging at a constant current of 0.1-0.2C to 3.6-3.7V at 25℃±2℃, settling for 10-15 minutes, heating to 50℃±5℃, and then discharging at a constant current of 0.05-0.06C to 2.5-2.6V. This is counted as one charge-discharge cycle, and the charge-discharge cycle is repeated 2-5 times; and / or, the ratio of the injected electrolyte mass to the original electrolyte mass in the aged battery is (5-15):100.
[0050] Controlling the first settling time within the aforementioned range helps eliminate residual charge and stress inside the battery; controlling the second settling time within the aforementioned range helps improve the electrolyte's wettability inside the battery; by controlling the charge-discharge activation conditions within the aforementioned range, high temperature accelerates the dissolution of inorganic components by additives, while low temperature stabilizes the newly formed SEI film, thereby further improving the charge-discharge capacity and cycle stability of the repaired aged battery. Controlling the ratio of the injected electrolyte mass to the original electrolyte mass in the aged battery within the aforementioned range further helps improve the charge-discharge capacity and cycle stability of the repaired aged battery.
[0051] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.
[0052] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of this application.
[0053] Example 1
[0054] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were prepared as an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, BF(OCH3)2 and lithium difluorophosphate were added to the solution in sequence to obtain an electrolyte. The total mass content of BF(OCH3)2 and lithium difluorophosphate in the electrolyte was 0.8%, and the mass ratio of BF(OCH3)2 to lithium difluorophosphate was 1:0.5. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0055] Example 2
[0056] The difference from Example 1 is that AlCl3·tetrahydrofuran is used instead of BF(OCH3)2;
[0057] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were prepared as an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, AlCl3·tetrahydrofuran and lithium difluorophosphate were added to the solution in sequence to obtain an electrolyte. The total mass content of AlCl3·tetrahydrofuran and lithium difluorophosphate in the electrolyte was 0.8%, and the mass ratio of AlCl3·tetrahydrofuran to lithium difluorophosphate was 1:0.5. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0058] Example 3
[0059] The difference from Example 1 is that AlF(OC2H5)2 is used instead of BF(OCH3)2;
[0060] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate were prepared as an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, AlF(OC2H5)2 and lithium difluorophosphate were added to the solution in sequence to obtain an electrolyte. The total mass content of AlF(OC2H5)2 and lithium difluorophosphate in the electrolyte was 0.8%, and the mass ratio of AlF(OC2H5)2 to lithium difluorophosphate was 1:0.5. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0061] Example 4
[0062] The difference from Example 1 is that SiCH3(OC2H5)3 is used instead of BF(OCH3)2;
[0063] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were prepared as an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, SiCH3(OC2H5)3 and lithium difluorophosphate were added to the solution in sequence to obtain an electrolyte. The total mass content of SiCH3(OC2H5)3 and lithium difluorophosphate in the electrolyte was 0.8%, and the mass ratio of SiCH3(OC2H5)3 to lithium difluorophosphate was 1:0.5. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0064] Example 5
[0065] The difference from Example 1 is that BF3·tetrahydrofuran is used instead of BF(OCH3)2;
[0066] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were prepared as an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, BF3·tetrahydrofuran and lithium difluorophosphate were added to the solution in sequence to obtain an electrolyte. The total mass content of BF3·tetrahydrofuran and lithium difluorophosphate in the electrolyte was 0.8%, and the mass ratio of BF3·tetrahydrofuran to lithium difluorophosphate was 1:0.5. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0067] Example 6
[0068] The difference from Example 3 is that the total mass content of AlF(OC2H5)2 and lithium difluorophosphate in the electrolyte is 1.2%;
[0069] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate were prepared as an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, AlF(OC2H5)2 and lithium difluorophosphate were added to the solution in sequence to obtain an electrolyte. The total mass content of AlF(OC2H5)2 and lithium difluorophosphate in the electrolyte was 1.2%, and the mass ratio of AlF(OC2H5)2 to lithium difluorophosphate was 1:0.5. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0070] Example 7
[0071] The difference from Example 3 is that the total mass content of AlF(OC2H5)2 and lithium difluorophosphate in the electrolyte is 0.5%;
[0072] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate were prepared as an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, AlF(OC2H5)2 and lithium difluorophosphate were added to the solution in sequence to obtain an electrolyte. The total mass content of AlF(OC2H5)2 and lithium difluorophosphate in the electrolyte was 0.5%, and the mass ratio of AlF(OC2H5)2 to lithium difluorophosphate was 1:0.5. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0073] Example 8
[0074] The difference from Example 1 is that BF(OCH3)2 is replaced by a combination of BF(OCH3)2 and AlCl3·tetrahydrofuran, and the mass ratio of BF(OCH3)2 to AlCl3·tetrahydrofuran in the combination of BF(OCH3)2 and AlCl3·tetrahydrofuran is 2:1.
[0075] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate were prepared as an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, a combination of BF(OCH3)2 and AlCl3·tetrahydrofuran, lithium difluorophosphate, and other components were added sequentially to the solution to obtain an electrolyte. The total mass content of the combination of BF(OCH3)2 and AlCl3·tetrahydrofuran and lithium difluorophosphate in the electrolyte was 0.8%, and the mass ratio of the combination of BF(OCH3)2 and AlCl3·tetrahydrofuran to lithium difluorophosphate was 1:0.5. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0076] Example 9
[0077] The difference from Example 1 is that BF(OCH3)2 is replaced by a combination of BF(OCH3)2 and AlCl3·tetrahydrofuran, and the mass ratio of BF(OCH3)2 to AlCl3·tetrahydrofuran in the combination of BF(OCH3)2 and AlCl3·tetrahydrofuran is 1:2.
[0078] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were prepared as an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, a combination of BF(OCH3)2 and AlCl3·tetrahydrofuran, and lithium difluorophosphate were added sequentially to the solution to obtain an electrolyte. The total mass content of the combination of BF(OCH3)2 and AlCl3·tetrahydrofuran and lithium difluorophosphate in the electrolyte was 0.8%, and the mass ratio of the combination of BF(OCH3)2 and AlCl3·tetrahydrofuran to lithium difluorophosphate was 1:0.5. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0079] Example 10
[0080] The difference from Example 1 is that the mass ratio of BF(OCH3)2 to lithium difluorophosphate is 1:0.1.
[0081] Example 11
[0082] The difference from Example 1 is that the mass ratio of BF(OCH3)2 to lithium difluorophosphate is 1:0.8.
[0083] Example 12
[0084] The difference from Example 1 is that the mass ratio of BF(OCH3)2 to lithium difluorophosphate is 1:1.
[0085] Comparative Example 1
[0086] The difference from Example 1 is that the addition of BF(OCH3)2 is omitted;
[0087] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were prepared into an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain a solution. Then, lithium difluorophosphate was added to the solution in sequence to obtain an electrolyte. The mass content of lithium difluorophosphate in the electrolyte was 0.8%, and the concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0088] Comparative Example 2
[0089] The difference from Example 1 is that lithium difluorophosphate is omitted;
[0090] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were prepared into an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and dissolved completely to obtain a solution. Then, BF(OCH3)2 and lithium hexafluorophosphate were added to the solution in sequence to obtain an electrolyte. The mass content of BF(OCH3)2 in the electrolyte was 0.8%, and the concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0091] Comparative Example 3
[0092] The difference from Example 1 is that the addition of BF(OCH3)2 and lithium difluorophosphate is omitted;
[0093] In a glove box filled with argon at 25°C, with a water oxygen content of <0.1ppm, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were prepared into an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate was added to the organic solvent and fully dissolved to obtain an electrolyte. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L.
[0094] Aging battery preparation
[0095] Preparation method of positive electrode sheet: Lithium iron phosphate positive electrode material, super conductive carbon black, polyvinylidene fluoride, and polypyrrolidone are mixed in a mass ratio of 9.6:0.2:0.17:0.03 with N-methylpyrrolidone solvent and stirred evenly to obtain a positive electrode slurry. The obtained positive electrode slurry is uniformly coated onto a 12μm aluminum foil, and after drying, a positive electrode sheet is obtained.
[0096] Preparation method of negative electrode sheet: Negative electrode material (graphite to silicon carbon mass ratio of 95:5), super conductive carbon black, carboxymethyl cellulose, polyvinylidene fluoride, and deionized water are mixed in a mass ratio of 96:0.5:0.5:0.8 and stirred evenly to obtain a negative electrode slurry. The obtained negative electrode slurry is uniformly coated on a 5μm thick copper foil, and after drying, a negative electrode sheet is obtained.
[0097] The diaphragm adopts a 7+2+2 coated diaphragm, which has a three-layer structure. The middle layer is a 7μm thick polyethylene base membrane, and the top and bottom layers are 2μm thick coating layers. The coating layers are made of boehmite and polyvinylidene fluoride adhesive.
[0098] Electrolyte preparation method: In a glove box filled with argon at 25℃, with water oxygen content <0.1ppm, ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are prepared into an organic solvent in a mass ratio of 30:20:40. Lithium hexafluorophosphate is added to the organic solvent and fully dissolved to obtain a solution. The concentration of lithium hexafluorophosphate in the electrolyte is 1mol / L.
[0099] The positive electrode sheet, negative electrode sheet, and separator prepared above are cut, stacked, shelled, vacuum baked, injected with electrolyte, left to stand, and subjected to capacity testing to obtain a fresh battery. The fresh battery is then subjected to cycle aging until its capacity decreases to 80%, resulting in an aged battery.
[0100] Repair methods for aged batteries
[0101] (1) Test the discharge capacity Q0 of the fresh battery. Charging steps: starting current 1 / 3C, cutoff voltage 3.65V, cutoff current 0.05C; Discharging steps: constant current 1 / 3C to 2.5V, cycle three times, and record the discharge capacity Q0 of the last cycle.
[0102] (2) The aged soft-pack battery (capacity decayed to 80% SOC) was completely discharged in a battery cabinet and left to stand for 12 hours. In a glove box filled with argon gas at a temperature of 25°C and a water oxygen content of <0.1ppm, a hole was made at the gap between the positive and negative electrodes at the bottom of the soft-pack battery with a syringe needle. Then, the electrolyte prepared in the examples and comparative examples was slowly injected into the aged soft-pack battery through the syringe needle. The ratio of the mass of the injected electrolyte to the mass of the original electrolyte in the aged battery was 10:100.
[0103] (3) Seal the hole with adhesive to prevent electrolyte leakage and contact with air, and let it stand for 12 hours to allow the electrolyte to fully soak in;
[0104] (4) Charge the battery at 0.1C constant current to 3.65V at 25℃ and let it stand for 10 minutes; raise the temperature to 50℃ and discharge it at 0.05C constant current to 2.5V as one cycle. Repeat the cycle 3 times to obtain the repaired aged battery, and record the discharge capacity Q1 of the last cycle. The capacity recovery rate C1=(Q1 / Q0)×100%.
[0105] 25℃ Cyclic Performance Test
[0106] The repaired aged battery was charged and discharged at 25°C, 1C / 1C, 0-100% SOC for 100 cycles, and the discharge capacity Q2 of the last cycle was recorded. The capacity recovery rate C2 = (Q2 / Q0) × 100%.
[0107] The battery was tested in the example and comparative examples after repair. The discharge capacity Q0, discharge capacity Q1 and discharge capacity Q2 were recorded, and the capacity recovery rate C1 and capacity recovery rate C2 were calculated. The results are shown in Table 1.
[0108] Table 1
[0109]
[0110]
[0111] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:
[0112] The first additive in this application reacts with inorganic components in the SEI film, such as LiF and LiCO3, to effectively dissolve these components, thereby reducing the interfacial impedance of the SEI film. Subsequently, a new SEI film is formed through an electrochemical process, which helps to improve the cycle stability and safety of the battery. The Group IIIA and / or Group IVA elements in the first additive can react with Li during charging. + They combine to form a complex, and release Li during the discharge process. +This provides the battery with an additional reversible lithium source, helping to compensate for the loss of active lithium caused by aging, thereby improving the battery's capacity retention. The second additive works synergistically with the first additive to further reduce the corrosion of battery components by HF, forming a protective film and extending battery life. Controlling the mass content of the additive in the electrolyte within the above-mentioned range helps the additive to dissolve the SEI film and provide a lithium source without causing excessive deposition or interface instability due to excessive concentration, thus avoiding the rapid capacity decay problem caused by excessive M element deposition. Applying the electrolyte of this application to repair aging batteries helps to improve the charge-discharge capacity and cycle stability of aging batteries, thereby helping to extend the service life of aging batteries.
[0113] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.
[0114] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. An electrolyte, characterized in that, The electrolyte comprises: lithium salt, additives, and organic solvent; wherein the concentration of the lithium salt in the electrolyte is 0.5–1.5 mol / L, and the mass content of the additives in the electrolyte is 0.5–1.2%. The additive includes a first additive and a second additive; the first additive is selected from MX. a Y b Compounds and / or MX c • L complex; wherein each M is independently selected from Group IIIA and / or Group IVA elements, and each X is independently selected from halogens and / or C1 to C2. 10 Alkyl group, where Y is C1 to C2. 10 Alkoxy group, L is an organic ligand, a is 1, 2 or 3, b is 1, 2 or 3, c is 3 or 4; the second additive is a difluorophosphorus compound.
2. The electrolyte according to claim 1, characterized in that, The mass ratio of the first additive to the second additive is 1:(0.1 to 0.8).
3. The electrolyte according to claim 1 or 2, characterized in that, Each of the M is independently selected from any one or more of B, Al, and Si; And / or, each of the X's is independently selected from any one or more of F, Cl, Br, and C1-C6 alkyl groups; And / or, the Y is a C1-C6 alkoxy group; And / or, the L is selected from any one or more of dimethyl carbonate, diethyl ether, and tetrahydrofuran.
4. The electrolyte according to claim 3, characterized in that, Each of the X's is independently selected from any one or more of F, methyl, ethyl, and propyl; And / or, the Y is selected from any one or more of methoxy, ethoxy, and propoxy.
5. The electrolyte according to claim 4, characterized in that, The first additive is selected from any one or more of BF(OCH3)2, AlF(OCH3)2, AlCl3·tetrahydrofuran, AlF(OC2H5)2, SiCH3(OC2H5)3 and BF3·tetrahydrofuran.
6. The electrolyte according to claim 5, characterized in that, The first additive is a combination of BF(OCH3)2 and AlCl3·tetrahydrofuran, and the mass ratio of BF(OCH3)2 to AlCl3·tetrahydrofuran is 1:2 to 2:
1.
7. The electrolyte according to any one of claims 1 to 6, characterized in that, The difluorophosphorus compound is a difluorophosphate compound; preferably, the difluorophosphate compound is selected from lithium difluorophosphate and / or lithium difluorooxalate phosphate.
8. The electrolyte according to any one of claims 1 to 7, characterized in that, The lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium methanesulfonate. And / or, the organic solvent is selected from any one or more of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.
9. A method for repairing an aged battery, characterized in that, The repair method includes: Step S1: After fully discharging the aged battery with a capacity decay of not less than 20%, perform a first static setting to obtain the first static aged battery. Step S2: Inject the electrolyte of any one of claims 1 to 8 into the first static aging battery for a second static aging process to obtain the second static aging battery; Step S3: The second statically aged battery is activated by charging and discharging to complete the repair.
10. The repair method according to claim 9, characterized in that, The first settling time is 12-15 hours; and / or, the second settling time is 12-15 hours; And / or, the conditions for charge-discharge activation are as follows: charge at a constant current of 0.1 to 0.2C to 3.6 to 3.7V at 25℃±2℃, let stand for 10 to 15 minutes, raise the temperature to 50℃±5℃, and then discharge at a constant current of 0.05 to 0.06C to 2.5 to 2.6V. This is counted as one charge-discharge cycle, and the charge-discharge cycle is repeated 2 to 5 times. And / or, the ratio of the injected electrolyte mass to the original electrolyte mass in the aged battery is (5-15):100.