An electrolyte and a lithium-ion battery

Abstract

This invention relates to the field of electrolyte technology, and more particularly to an electrolyte and a lithium-ion battery. The electrolyte comprises a lithium salt, additives, and an organic solvent; the additives include a first additive and a second additive; the first additive comprises a tetrathiofulvalene compound; and the second additive comprises a phosphite compound. To address the technical problems of easy decomposition, high interfacial impedance, and short cycle life in existing high-voltage lithium batteries, this invention introduces a tetrathiofulvalene compound with a specific structure into the electrolyte and combines it with a phosphite compound to construct a synergistic interfacial regulation system. This achieves dual optimization of interfacial stability and reaction kinetics, significantly improving the battery's cycle life and rate performance.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, and more particularly to an electrolyte and a lithium-ion battery. Background Technology

[0002] With the rapid development of new energy vehicles, large-scale energy storage systems, and high-end consumer electronics, the market demand for lithium-ion battery energy density continues to increase, making high-energy-density lithium-ion batteries a core research and development direction in the industry. Lithium-rich manganese-based cathode materials possess significant advantages such as reversible specific capacity exceeding 250 mAh / g and low cost, making them key candidate cathode materials for next-generation high-energy-density lithium-ion batteries.

[0003] However, lithium-rich manganese-based cathode materials still face several key technical challenges in practical applications: structural degradation easily occurs during material cycling, leading to poor cycle stability and continuous voltage decay; irreversible oxygen evolution occurs during the first charge activation, exacerbating electrolyte oxidation and decomposition, resulting in low initial coulombic efficiency and cell gas production and swelling; significant interfacial side reactions occur at high voltages, resulting in poor interfacial film stability and inability to suppress transition metal dissolution; dissolved transition metal ions migrate to the negative electrode, damaging the negative electrode interfacial film, causing loss of active lithium and further performance degradation.

[0004] Based on the above problems, there is an urgent need to develop a high-efficiency electrolyte additive suitable for high-voltage systems that can simultaneously improve interface stability and overall battery performance, so as to promote the practical application of lithium-rich manganese-based lithium-ion batteries. Summary of the Invention

[0005] To address the technical problems of easy electrolyte decomposition, high interfacial impedance, and short cycle life in existing high-voltage lithium batteries, this invention provides an electrolyte and a lithium-ion battery containing the electrolyte. By introducing a tetrathiofulvalene compound with a specific structure into the electrolyte and compounding it with a phosphite compound, a synergistic interface regulation system is constructed, achieving dual optimization of interface stability and reaction kinetics, and significantly improving the cycle life and rate performance of the battery.

[0006] The first aspect of the present invention provides an electrolyte comprising a lithium salt, an additive, and an organic solvent; The additives include a first additive and a second additive; The first additive includes tetrathiofulvalene compounds; The structural formula of the tetrathiofulvalene compound is: ; R1, R2, R3, and R4 are each independently selected from any one of hydrogen, halogen, cyano, isocyanate group, isothiocyanate group, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C1-C10 alkylthio, and substituted or unsubstituted C6-C10 aryl. The second additive includes phosphite compounds.

[0007] Optionally, in the structural formula of the tetrathiofulvalene compound, R1, R2, R3, and R4 are independently selected from any one of hydrogen, substituted or unsubstituted C2-C10 alkylthio groups, and substituted or unsubstituted C6-C10 aryl groups.

[0008] Optionally, the structural formula of the tetrathiofulvalene compound satisfies at least one of the following conditions: (1) R1 and R3 are the same, and R2 and R4 are the same; (2) R1, R2, R3, and R4 are all the same.

[0009] Further optionally, the tetrathiofulvalene compound includes , , , , or At least one of them.

[0010] Optionally, the phosphite compounds include one or more combinations of TMSPi, TEPi, TPPi, and TTFEPi; Further optionally, the phosphite compound includes TMSPi.

[0011] Optionally, the electrolyte satisfies at least one of the following conditions: (1) The amount of additive added to the electrolyte is 1-10 wt%; (2) The amount of the first additive added to the electrolyte is 0.2-2 wt%; (3) The amount of the second additive added to the electrolyte is 0.5-2 wt%; (4) The mass ratio of the first additive and the second additive in the electrolyte is (1-5):(1-2).

[0012] Optionally, the electrolyte satisfies at least one of the following conditions: (1) The amount of organic solvent added to the electrolyte is 70-90 wt%; (2) The organic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl trifluoroethyl carbonate, diethyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, ethyl butyrate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, γ-butyrolactone, γ-valerolactone, δ-valerolactone, fluoroethylene carbonate, 1,3-dioxolane, dimethoxyethane, methyl propyl carbonate, methyl acetate, or butyl acetate. (3) The organic solvent includes at least two of fluoroethylene carbonate, propylene carbonate, diethyl carbonate or methyl ethyl carbonate.

[0013] Optionally, the electrolyte satisfies at least one of the following conditions: (1) The amount of lithium salt added to the electrolyte is 10-20 wt%; (2) The lithium salt includes one or more of the following: LiPF6, LiPO2F2, LiODFB, LiBF4, LiFSI, LiTFSI, LiBOB, LiSbF6, LiAsF6, LiDFOP, LiTFOP, and LiCF3SO3. (3) The lithium salt includes at least two of LiPF6, LiPO2F2 or LiODFB.

[0014] A second aspect of the present invention provides a lithium-ion battery containing the electrolyte as described above.

[0015] Optionally, the lithium-ion battery satisfies at least one of the following conditions: (1) The positive electrode material of the lithium-ion battery includes lithium-rich manganese-based material, the chemical formula of which is xLi2MnO3·(1-x)LiMO2, where M is a transition metal and 0.1≤x≤0.7; (2) The charging cutoff voltage of the lithium-ion battery is above 4.5V.

[0016] Beneficial effects This invention provides an electrolyte and a lithium-ion battery, which have the following advantages: (1) This invention solves the core problems of easy decomposition of electrolyte, high interfacial impedance and easy consumption of additives during cycling in high-voltage lithium batteries by using a dual additive compound system of tetrathiofulvalene compounds and phosphite compounds. It achieves synergistic optimization of interfacial stability and reaction kinetics, and significantly improves the long cycle performance and rate performance of the battery. (2) The present invention preferably uses tetrathiofulvalene compounds with specific structures, which can undergo reversible redox reactions on the surface of the positive electrode, rapidly transfer electrons, homogenize the interfacial charge distribution, reduce the actual oxidation state of the positive electrode under high voltage, reduce electrolyte decomposition, and participate in the formation of a positive electrode interfacial film with excellent conductivity, thereby suppressing the occurrence of side reactions from the source. (3) The preferred phosphite compounds of the present invention (such as TMSPi) can rapidly form a low-resistance stable interface film rich in Si-OP and Li3PO4 on the positive and negative electrode surfaces through the preferential breaking of active bonds in the molecule. This effectively blocks the direct contact between the electrolyte and the electrode, inhibits the continuous decomposition of the electrolyte and the dissolution of transition metals, and at the same time reduces the unexpected consumption of tetrathiofulvalene additives. (4) By precisely controlling the mass ratio and amount of the two additives, this invention avoids the problem of excessively thick interfacial film or insufficient additive concentration caused by imbalance of ratio, and achieves the best balance between composite interfacial film structure and free additive concentration, ensuring that tetrathiofulvalene compounds can play a core role in interfacial charge regulation and high voltage side reaction inhibition in electrolyte for a long time, and ensuring the long-term effect of synergistic effect. (5) The electrolyte of the present invention can be adapted to the application scenarios of high-voltage lithium batteries. The formula is simple and easy to implement. It can be applied on a large scale without complex process adjustments. It has broad commercial prospects in the field of high-energy-density lithium-ion batteries. Detailed Implementation

[0017] To make the technical solution and beneficial effects of this application more apparent and understandable, a detailed description is provided below by listing specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this application are commercially available.

[0018] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0019] It should be noted that the relational terms (such as first and second) used in the description of this application are only used to distinguish one entity / operation from another entity / operation, and do not necessarily require or imply that there is an actual relationship or order between these entities / operations; in specific implementation, the principle of meeting actual use needs should be followed.

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0022] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0023] The first aspect of the present invention provides an electrolyte comprising a lithium salt, an additive, and an organic solvent; The additives include a first additive and a second additive; The first additive includes tetrathiofulvalene compounds; The structural formula of the tetrathiofulvalene compound is: ; R1, R2, R3, and R4 are each independently selected from any one of hydrogen, halogen, cyano, isocyanate group, isothiocyanate group, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C1-C10 alkylthio, and substituted or unsubstituted C6-C10 aryl. The second additive includes phosphite compounds.

[0024] The "tetrathiofulvalene compounds" involved in this invention refer to a class of conjugated organosulfur compounds with tetrathiofulvalene (TTF) as the core. Their general molecular structure is two 1,3-dithioheteropene rings connected by a central double bond. The four sites on the rings can be modified by substituents R1, R2, R3, and R4, respectively. Among them, R1, R2, R3, and R4 are independently selected from any one of hydrogen, halogen, cyano, isocyanate, isothiocyanate, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C1-C10 alkylthio, and substituted or unsubstituted C6-C10 aryl. The substituents can be the same or different, and the hydrogen atoms on the substituents can be further replaced by functional groups such as halogen, cyano, and aryl.

[0025] The "phosphite compounds" involved in this invention are derivatives formed by replacing one or more hydroxyl groups (-OH) in the phosphorous acid (H3PO3) molecule with organic groups (such as methyl, ethyl, phenyl, trimethylsiloxy, etc.).

[0026] The practical application of lithium-rich manganese-based cathode materials still faces a series of severe challenges, mainly including: 1) Poor cycle stability and voltage decay: During cycling, irreversible phase transitions occur on the material surface, leading to the dissolution, migration, and deposition of transition metal ions (especially Mn), resulting in crystal structure degradation and manifested as a continuous decrease in discharge voltage plateau and capacity decay; 2) Low initial efficiency and cell gas generation: During the first charge, under high voltage conditions greater than 4.5V relative to the lithium metal reference electrode, the activation of lithium-rich manganese materials will irreversibly release oxygen, accompanied by severe oxidative decomposition of the electrolyte. This not only results in low initial coulombic efficiency but also generates gases (such as O2 and CO2), leading to battery swelling and safety risks; 3) Severe interfacial side reactions: Conventional carbonate-based electrolytes have insufficient chemical / electrochemical stability under high voltage, resulting in continuous oxidative decomposition on the surface of lithium-rich manganese materials, forming a thick and unstable CEI film (Cathode Electrolyte). Interphase (positive electrode-electrolyte interface film): This film has high impedance and cannot suppress transition metal dissolution, further aggravating performance degradation; 4) Cross-influence with the negative electrode: Dissolved transition metal ions migrate to the negative electrode, damaging the SEI film of the negative electrode, accelerating electrolyte consumption and loss of active lithium. Introducing functional additives into the electrolyte can alleviate the above problems to some extent, but the high operating voltage of lithium-rich manganese materials places more stringent requirements on the oxidation potential, film-forming characteristics, and compatibility with positive and negative electrode materials of the additives. Existing electrolyte additives still cannot effectively solve the core problems such as interfacial side reactions, transition metal dissolution, and gas generation under the high voltage system of lithium-rich manganese-based positive electrodes, making it difficult to meet the needs of practical applications.

[0027] This invention provides an electrolyte whose core technology achieves dual optimization of lithium-ion battery interface stability and reaction kinetics through a dual-additive synergistic system. The electrolyte is designed to consist of a lithium salt, an organic solvent, and two types of additives. The first additive is a tetrathiofulvalene compound with a conjugated bis(1,3-dithiocyclopentene-2-yl) structure as its molecular core. The ring-substituted R1, R2, R3, and R4 can be selected from hydrogen, halogen, cyano, substituted / unsubstituted alkyl, alkoxy, alkylthio, or aryl groups, depending on requirements. This type of compound can undergo reversible oxidation / reduction reactions on the positive electrode surface, rapidly transferring electrons, homogenizing the interfacial charge distribution, and reducing the actual oxidation state of the positive electrode under high voltage, thereby inhibiting electrolyte decomposition. Simultaneously, it participates in the formation of a highly conductive positive electrode interfacial film. Further, the second additive is preferably a phosphite compound, taking TMSPi (tris(trimethylsilane)phosphite) as an example. It can preferentially react on the positive and negative electrode surfaces through the breaking of P=O bonds and Si-O bonds in the molecule, forming a low-impedance stable interface film rich in Si-OP and Li3PO4, which effectively inhibits electrolyte decomposition and transition metal dissolution.

[0028] This invention utilizes the preferential film-forming effect of phosphite compounds by combining two types of additives, thereby reducing the unexpected consumption of tetrathiofulvalene compounds during cycling. At the same time, by controlling the mass ratio of the two, the composition and structure of the composite interface film can be precisely controlled, ensuring that there is a sufficient amount of free tetrathiofulvalene compounds in the electrolyte to continuously perform the function of "redox mediator", ultimately significantly improving the cycle performance and rate performance of the battery.

[0029] Optionally, in the structural formula of the tetrathiofulvalene compound, R1, R2, R3, and R4 are independently selected from any one of hydrogen, substituted or unsubstituted C2-C10 alkylthio groups, and substituted or unsubstituted C6-C10 aryl groups.

[0030] Optionally, the structural formula of the tetrathiofulvalene compound satisfies at least one of the following conditions: (1) R1 and R3 are the same, and R2 and R4 are the same; (2) R1, R2, R3, and R4 are all the same.

[0031] The present invention further preferably uses a symmetrical structure for the tetrathiofulvalene compounds. Symmetrical structures offer a simpler molecular synthesis route, readily available raw materials, and fewer side reactions, significantly reducing preparation costs and making them more suitable for large-scale industrial applications. Simultaneously, the symmetrical structure endows the molecule with a more stable conjugated electron system, enabling it to exhibit both excellent electrochemical stability and reversible redox performance in electrolytes. This achieves a balance between cost control and performance optimization, providing a more feasible technical path for the commercialization of high-voltage, long-cycle lithium batteries.

[0032] Further optionally, the tetrathiofulvalene compound includes , , , , or At least one of them.

[0033] Further optionally, the tetrathiofulvalene compound includes , , At least one of them.

[0034] in, The CAS number is 31366-25-3, and the compound name is tetrathiofulvalene, abbreviated as TTF.

[0035] in, The CAS number is 5152-94-3, and the compound name is 4,4′-diphenyltetrathiafulvalene.

[0036] in, The CAS number is 132765-36-7, and the compound name is 2,3,6,7-tetra(2-cyanoethylthio)tetrathiofulvalene.

[0037] The tetrathiofulvalene compounds of this invention preferably possess the three structures described above, exhibiting optimal compatibility with phosphite additives (such as TMSPi) and the most significant synergistic effect. Specifically, unsubstituted tetrathiofulvalene molecules have a simple molecular structure and a regular conjugated system, forming a uniform and dense composite interfacial film with phosphite additives; phenyl-substituted tetrathiofulvalenes possess both good electrochemical stability and film-forming ability, effectively enhancing the mechanical strength of the interfacial film; and cyanoalkylthio-substituted tetrathiofulvalenes, through the strong polarity of the cyano group, can further optimize interfacial charge transfer efficiency. When used in combination with phosphite additives, these three tetrathiofulvalene compounds can comprehensively improve the interfacial stability, kinetic performance, and long cycle life of the electrolyte system, providing a reliable foundation for stable cycling of the electrolyte under high voltage.

[0038] Optionally, the phosphite compounds include one or more combinations of TMSPi (tris(trimethylsilane)phosphite), triethyl phosphite (TEPi), triphenyl phosphite (TPPi), and tri(trifluoroethyl) phosphite (TTFEPi); Further optionally, the phosphite compound includes TMSPi.

[0039] The preferred phosphite compound of this invention is TMSPi. Compared with other conventional additives, TMSPi contains both phosphorus-oxygen and silicon-oxygen active sites in its molecular structure, which can preferentially react on the positive and negative electrode surfaces to form a composite interface film that combines the Si-OP inorganic framework and the Li3PO4 phase. Its preferential film-forming effect can provide a stable interface environment for the tetrathiofulvalene additive, reduce its consumption due to unexpected side reactions during cycling, and maximize the function of the redox mediator. This provides a key guarantee for the long-cycle performance and rate performance of the electrolyte system of this invention.

[0040] Optionally, the electrolyte satisfies at least one of the following conditions: (1) The amount of additive added to the electrolyte is 1-10 wt%; examples include 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc. (2) The amount of the first additive in the electrolyte is 0.2-2 wt%; it can be listed as 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, etc. (3) The amount of the second additive in the electrolyte is 0.5-2wt%; examples include 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, etc. (4) The mass ratio of the first additive and the second additive in the electrolyte is (1-5):(1-2).

[0041] Further optionally, the amount of the second additive added to the electrolyte is 0.5-1.5 wt%.

[0042] Further optionally, the amount of the first additive added to the electrolyte is 0.5-1 wt%.

[0043] Further optionally, the mass ratio of the first additive and the second additive in the electrolyte is 1:(1-2); for example, 1:1, 1:1.5, 1:2, etc.

[0044] Further optionally, the amount of additive added to the electrolyte is 1-4 wt%; most preferably 2 wt%.

[0045] This invention reveals that the ratio and dosage of the two additives have a crucial impact on the interfacial stability and long-cycle performance of the electrolyte. If the dosage of the first additive is too low or the ratio is unbalanced, sufficient free "redox mediator" molecules cannot be formed, making it difficult to continuously homogenize the charge distribution at the positive electrode interface, leading to accelerated electrolyte decomposition under high voltage. If the dosage of the second additive is too high, it will excessively consume the first additive and form an excessively thick interfacial film, which will increase interfacial impedance and reduce battery rate performance. Therefore, this invention achieves a precise balance between the composite interfacial film structure and the concentration of free additives by controlling the mass ratio and dosage of the two additives within the aforementioned preferred range. This ensures both interfacial stability and continuous synergistic effects, ultimately significantly improving the battery's cycle life and rate performance.

[0046] Optionally, the electrolyte satisfies at least one of the following conditions: (1) The amount of organic solvent added in the electrolyte is 70-90 wt%; examples include 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, etc. (2) The organic solvent includes one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl trifluoroethyl carbonate (FEMC), diethyl carbonate (DEC), propyl propionate (PP), ethyl propionate (EP), methyl propionate (MP), propyl acetate (PA), ethyl acetate (EA), ethyl butyrate (EB), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), γ-butyrolactone (GBL), γ-valerolactone (GVL), δ-valerolactone (DVL), fluoroethylene carbonate (FEC), 1,3-dioxolane, dimethoxyethane, methyl propyl carbonate, methyl acetate, or butyl acetate; (3) The organic solvent includes at least two of fluoroethylene carbonate, propylene carbonate, diethyl carbonate or methyl ethyl carbonate.

[0047] Further optionally, the amount of organic solvent added to the electrolyte is 70-89 wt%.

[0048] Further optionally, the organic solvent includes one or more combinations of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl trifluoroethyl carbonate, diethyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, ethyl butyrate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

[0049] In some embodiments, the organic solvent includes FEC, PC, DEC and EMC; the mass ratio of FEC, PC, DEC and EMC is (1-5):(0.5-3):(1-3):(5-20).

[0050] This invention does not impose any particular limitation on the type of organic solvent used in the electrolyte, as long as it can achieve the purpose of dissolving and dissociating lithium salts and additives in the electrolyte.

[0051] Optionally, the electrolyte satisfies at least one of the following conditions: (1) The amount of lithium salt added in the electrolyte is 10-20 wt%; examples include 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, etc. (2) The lithium salt includes one or more of the following: lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalate borate) (LiBOB), lithium hexafluoroantimonyate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium difluorooxalate phosphate (LiDFOP), lithium tetrafluorooxalate phosphate (LiTFOP), and lithium trifluoromethanesulfonate (LiCF3SO3). (3) The lithium salt includes at least two of LiPF6, LiPO2F2 or LiODFB.

[0052] In some embodiments, the lithium salt includes LiPF6, LiPO2F2 and LiODFB; the mass ratio of LiPF6, LiPO2F2 or LiODFB is (5-20):(0.1-4):(0.1-4).

[0053] This invention does not impose any particular limitation on the type of lithium salt in the electrolyte, as long as it can achieve the purpose of lithium ion conduction in the electrolyte and charge balance during battery charging and discharging.

[0054] The present invention does not impose any particular limitation on the preparation method of the electrolyte, as long as an electrolyte with qualified performance and meeting the requirements of the present invention can be obtained; for example, lithium salt is added to an organic solvent, mixed and dissolved evenly, and then additives are added, mixed and dissolved evenly to obtain the electrolyte.

[0055] A second aspect of the present invention provides a lithium-ion battery containing the electrolyte as described above.

[0056] Optionally, the lithium-ion battery satisfies at least one of the following conditions: (1) The positive electrode material of the lithium-ion battery includes lithium-rich manganese-based material, the chemical formula of which is xLi2MnO3·(1-x)LiMO2, where M is a transition metal, 0.1≤x≤0.7; x can be listed as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, etc. (2) The charging cutoff voltage of the lithium-ion battery is above 4.5V.

[0057] The M may include Mn (manganese), nickel (Ni), Co (cobalt), Al (aluminum), Mg (magnesium), Fe (iron), Zr (zirconium), Ti (titanium), etc.; optionally, the M may include at least one of Mn, Ni, and Co.

[0058] In some embodiments, the lithium-rich manganese-based material may be exemplified as Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 (x=0.2), Li 1.2 Mn 0.6 Ni 0.2 O2 (x=0.2), Li1.2Mn0. 55 Ni0. 25 O2 (x=0.2), Li1.3Mn0. 54 Ni0. 13 Co0. 13 O2 (x=0.3), Li1.4Mn0.6Ni0.2O2 (x=0.4), Li1.5Mn0.5Ni0.5O2 (x=0.5), Li1.6Mn0.6Ni0.2O2 (x=0.6), Li1.7Mn0.7Ni0.3O2 (x=0.7), etc.

[0059] The "charging cut-off voltage" involved in this invention refers to the highest voltage value that a lithium-ion battery is allowed to reach during the charging process; for example, when the upper limit voltage is set to 4.5V when the battery is charging, the charging cut-off voltage is 4.5V.

[0060] Optionally, the lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, the electrolyte as described above, and a separator.

[0061] The present invention does not particularly limit the preparation method of the positive electrode sheet; for example: the positive electrode slurry is coated on the surface of the positive electrode current collector, and is successively dried, roll-pressed, and die-cut to obtain the positive electrode sheet.

[0062] In some embodiments, the preparation raw materials of the positive electrode slurry include a positive electrode material, a conductive agent, a binder, and a solvent; the mass ratio of the positive electrode material, the conductive agent, and the binder is (93-98):(0.5-3):(1-3).

[0063] Examples of the conductive agent in the positive electrode slurry include, but are not limited to, conductive carbon black (Super-P), carbon nanotubes (CNT), acetylene black, Ketjen black, graphene, carbon nanofibers, etc.; examples of the binder in the positive electrode slurry include, but are not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), etc.; examples of the solvent in the positive electrode slurry include, but are not limited to, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethylacetamide (DMAc), etc.; examples of the positive electrode current collector include, but are not limited to, aluminum foil, aluminum mesh, etc.

[0064] The present invention does not particularly limit the preparation method of the negative electrode sheet; for example: the negative electrode slurry is coated on the surface of the negative electrode current collector, and is successively dried, roll-pressed, and die-cut to obtain the negative electrode sheet.

[0065] In some embodiments, the preparation raw materials of the negative electrode slurry include a negative electrode material, a conductive agent, a binder, and a solvent; the mass ratio of the negative electrode material, the conductive agent, and the binder is (93-97):(0.5-3):(1-5).

[0066] In some embodiments, the negative electrode material of the lithium-ion battery includes a carbon-based negative electrode material, a silicon-based negative electrode material, or a carbon-based-silicon-based composite negative electrode material; examples of the carbon-based negative electrode material include, but are not limited to, natural graphite, artificial graphite, hard carbon, soft carbon, mesocarbon microbeads (MCMB), mesoporous carbon, carbon nanotubes, graphene, etc.; examples of the silicon-based negative electrode material include, but are not limited to, silicon monoxide (SiO x , 0<x<2), silicon nanowires, porous silicon, etc.

[0067] Examples of conductive agents in negative electrode slurries include, but are not limited to, conductive carbon black (Super-P), acetylene black, Ketjen black, carbon nanotubes (CNT), graphene, and conductive graphite; examples of binders in negative electrode slurries include, but are not limited to, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyimide (PI), and polyvinylidene fluoride (PVDF); examples of solvents in negative electrode slurries include, but are not limited to, deionized water and ethanol; and examples of negative electrode current collectors include, but are not limited to, copper foil and copper mesh.

[0068] In some embodiments, the preparation steps of the lithium-ion battery include: stacking and winding the positive electrode sheet, separator, and negative electrode sheet in sequence, sealing and vacuum baking to obtain the cell to be injected with electrolyte; injecting the electrolyte into the cell to be injected with electrolyte in a glove box, and after high temperature standing and room temperature standing, performing formation, secondary packaging and capacity testing processes to obtain the lithium-ion battery.

[0069] Optionally, the vacuum baking conditions are 70-85℃ vacuum baking for 15-48 hours; for example, 80℃ vacuum baking for 24 hours.

[0070] Optionally, when injecting the electrolyte into the battery cell to be injected, the dew point of the glove box should be controlled to be below -40°C.

[0071] Optionally, the high-temperature settling condition is settling at 40-50℃ for 12-36 hours; the room-temperature settling condition is settling at 5-35℃ for 12-36 hours.

[0072] Furthermore, the "dew point" involved in this invention refers to the temperature at which water vapor in the air reaches saturation and begins to condense into liquid water under isobaric conditions. It is a key indicator characterizing the degree of gas dryness. In this invention, controlling the dew point of the glove box below -40°C can prevent the electrolyte from undergoing hydrolysis when it comes into contact with water, thus ensuring battery performance and safety.

[0073] The "winding" involved in this invention refers to the conventional assembly process of stacking positive electrode sheets, separator membranes, and negative electrode sheets in sequence and then winding them into cylindrical or pouch cells using a winding device, so that the electrode sheets and separator membranes form a continuous alternating stacked structure.

[0074] The "formation" involved in this invention refers to the process of forming a stable SEI film on the electrode surface by controlling specific current, voltage and temperature conditions during the first charge of the battery, in order to improve the first charge and discharge efficiency and cycle stability of the battery.

[0075] The "capacity grading" involved in this invention refers to the process of conducting charge and discharge tests on the formed batteries and classifying and screening them according to their actual capacity to ensure the consistency of battery capacity and meet subsequent use requirements.

[0076] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0077] Example 1 This embodiment provides an electrolyte and a lithium-ion battery. By mass percentage, the electrolyte comprises 14.5% lithium salt, 2% additives, and the remainder is supplemented with organic solvent.

[0078] The lithium salt, based on the total mass of the electrolyte, consists of 13.5 wt% LiPF6, 0.5 wt% LiPO2F2 and 0.5 wt% LiODFB.

[0079] The additive consists of a first additive and a second additive in a mass ratio of 1:1; the first additive is tetrathiofulvalene, and its structural formula is [insert structural formula here]. The CAS number is 31366-25-3; the phosphite compound is TMSPi.

[0080] The organic solvent is composed of FEC, PC, DEC and EMC; the mass ratio of FEC, PC, DEC and EMC is 3:1:2:14.

[0081] The preparation steps of the electrolyte include: mixing FEC, PC, DEC and EMC evenly; then adding LiPF6, LiPO2F2 and LiODFB in sequence, mixing and dissolving evenly, then adding TMSPi and tetrathiofulvalene, mixing and dissolving evenly to obtain the electrolyte.

[0082] The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the electrolyte prepared above.

[0083] The preparation steps of the positive electrode sheet include: applying lithium-rich manganese-based positive electrode material ((Li... 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2), conductive carbon black (Super-P), carbon nanotubes (CNTs) and binder (PVDF) are mixed in a mass ratio of 96.2:1.4:0.7:1.7. The mixture is dispersed in NMP and stirred evenly to form a positive electrode slurry with a solid content of 70%. The positive electrode slurry is uniformly coated on the surface of a 13μm positive electrode current collector (aluminum foil), dried, rolled and die-cut to obtain the positive electrode sheet.

[0084] The isolation membrane has a thickness of 12 μm; it includes a base film made of PP (7 μm thick) and a double-sided ceramic coating disposed on the surface of the base film, with each side of the coating having a thickness of 2.5 μm.

[0085] The preparation steps of the negative electrode sheet include: mixing artificial graphite, silicon carbide, conductive carbon black (Super-P), SBR and PAA in a mass ratio of 73:21.3:1.5:1.4:2.8, dispersing the mixture in deionized water, and stirring evenly to form a negative electrode slurry with a solid content of 47%; uniformly coating the negative electrode slurry onto the surface of an 8μm negative electrode current collector (copper foil), drying it, and then rolling and die-cutting it to obtain the negative electrode sheet.

[0086] The preparation steps of the lithium-ion battery include: stacking and winding the positive electrode sheet, separator, and negative electrode sheet in sequence to obtain a bare cell with a thickness of 4.0 mm, a length of 150 mm, and a width of 60 mm; then vacuum baking at 80°C for 24 h to obtain a cell to be injected with electrolyte; injecting electrolyte into the cell to be injected with electrolyte in a glove box with a dew point below -40°C, and then subjecting it to high temperature (45°C) standing for 24 h and room temperature (25°C) standing for 24 h, followed by formation, secondary packaging, and capacity testing to obtain the lithium-ion battery.

[0087] Example 2 This embodiment provides an electrolyte and a lithium-ion battery, with the specific implementation method being the same as in Embodiment 1; the difference lies in that the first additive is 4,4′-diphenyltetrathiafulvalene, whose structural formula is [insert structural formula here]. The CAS number is 5152-94-3.

[0088] Example 3 This embodiment provides an electrolyte and a lithium-ion battery, with the specific implementation method being the same as in Embodiment 1; the difference lies in that the first additive is 2,3,6,7-tetra(2-cyanoethylthio)tetrathiofulvalene, whose structural formula is [insert structural formula here]. The CAS number is 132765-36-7.

[0089] Examples 4-12 and Comparative Examples 1-8 Examples 4-12 and Comparative Examples 1-8 respectively provide an electrolyte and a lithium-ion battery, with the specific implementation methods being the same as in Example 1; the difference lies in the selection of the type and amount of the first or second additive, as shown in Table 1.

[0090] In Table 1, compound 1 is tetrathiofulvalene, compound 2 is 4,4′-diphenyltetrathiofulvalene, and compound 3 is 2,3,6,7-tetra(2-cyanoethylthio)tetrathiofulvalene; the amount added represents the mass percentage of the first or second additive in the electrolyte.

[0091] Table 1

[0092] Performance testing The lithium-ion batteries prepared in the examples and comparative examples were tested as follows, and the test results are shown in Table 2.

[0093] 1. Room temperature cycling performance test At 25±2℃, the capacitor was charged to 4.5V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. Then, it was discharged to 2.0V at a constant current of 0.5C, and the initial discharge capacity was recorded as C0. The above charge-discharge cycle was repeated 500 times, and the discharge capacity of the 500th cycle was recorded as C1. The capacity retention rate at room temperature was calculated according to the following formula: Capacity retention rate = (C1 / C0) × 100%.

[0094] 2. Ratio Performance Test At 25℃, the capacitor was charged to 4.5V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. Subsequently, it was discharged to 2.0V at constant currents of 0.5C, 1C, 2C, and 3C, respectively, and the discharge capacities at each rate were recorded as C0, C1, C2, and C3. The rate retention was calculated using the following formula: 1C discharge ratio = (C1 / C0) × 100%; 2C discharge ratio = (C2 / C0) × 100%; 3C discharge ratio = (C3 / C0) × 100%.

[0095] Table 2

[0096] As shown in Table 2, the test results demonstrate that the introduction of tetrathiofulvalene compounds and phosphite compounds as compound additives into the electrolyte in this invention can effectively improve the cycle life and rate performance of lithium-ion batteries. Specific analysis follows.

[0097] Examples 1-3 respectively used three different tetrathiofulvalene compounds with TMSPi in a 1:1 mass ratio (1 wt% each). The battery's room temperature cycle capacity retention (87.30%~90.10%) and rate retention (93.90%~95.20% for 1C, 90.50%~92.00% for 2C, and 86.40%~89.70% for 3C) were significantly better than those of Comparative Example 1 without tetrathiofulvalene additives. This proves that the combination of tetrathiofulvalene additives with specific structures and TMSPi can effectively optimize the composition and structure of the electrode interface film, better protect the positive / negative electrode materials, and mitigate side reactions at the electrolyte-electrode interface, thereby improving cycle and rate performance.

[0098] Examples 4-12 verified the optimization effect of the dosage range and ratio of the present invention by adjusting the amount of tetrathiofulvalene additive and TMSPi and their mass ratio: when the mass ratio of the two is in the range of (1-5):(1-2), the battery performance is significantly improved, the room temperature cycle capacity retention rate can reach 77.60%~89.40%, and the rate retention rate is also maintained at a high level; this is because the composite interface film formed under this ratio is uniform, stable and highly protective, and at the same time, the electrolyte still retains an appropriate amount of free tetrathiofulvalene additive, which can continuously play its role as a "redox medium" and maximize the synergistic effect.

[0099] The test results of Comparative Examples 1, 4, and 5 show that the battery performance is significantly degraded when either of the two additives is added alone or not at all: when only TMSPi is added (Comparative Example 1), when only tetrathiofulvalene additives are added (Comparative Example 5), or when no additives are added at all (Comparative Example 4), the battery's room temperature cycle capacity retention and rate performance are significantly lower than those of the example with the two additives combined, proving that the synergistic effect of the two additives is the key to achieving performance improvement. The test results of Comparative Examples 2, 3, 6, and 7 show that when the dosage of tetrathiofulvalene additives or TMSPi deviates from the preferred range of the present invention, or when both are added in excess (Comparative Example 8), the interface film is prone to unevenness, excessive thickness, or functional imbalance, leading to increased cell internal resistance, decreased cycle stability and rate performance, and even increased electrolyte cost. This further confirms that only by controlling the dosage and ratio of tetrathiofulvalene additives and TMSPi within the preferred range of the present invention can a balance be achieved between interface protection and internal resistance control, significantly optimizing the cycle stability and rate performance of the battery, thereby meeting the requirements for high-voltage lithium-ion battery use, while also taking into account the cost of electrolyte use.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes lithium salts, additives, and organic solvents; The additives include a first additive and a second additive; The first additive includes tetrathiofulvalene compounds; The structural formula of the tetrathiofulvalene compound is: ； R1, R2, R3, and R4 are each independently selected from any one of hydrogen, halogen, cyano, isocyanate group, isothiocyanate group, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkoxy, substituted or unsubstituted C1-C10 alkylthio, and substituted or unsubstituted C6-C10 aryl. The second additive includes phosphite compounds.

2. The electrolyte according to claim 1, characterized in that, In the structural formula of the tetrathiofulvalene compound, R1, R2, R3, and R4 are independently selected from any one of hydrogen, substituted or unsubstituted C2-C10 alkylthio groups, and substituted or unsubstituted C6-C10 aryl groups.

3. The electrolyte according to claim 2, characterized in that, The structural formula of the tetrathiofulvalene compound satisfies at least one of the following conditions: (1) R1 and R3 are the same, and R2 and R4 are the same; (2) R1, R2, R3, and R4 are all the same.

4. The electrolyte according to claim 3, characterized in that, The tetrathiofulvalene compounds include , , , , or At least one of them.

5. The electrolyte according to claim 1, characterized in that, The phosphite compounds include one or more combinations of TMSPi, TEPi, TPPi, and TTFEPi; Preferably, the phosphite compound includes TMSPi.

6. The electrolyte according to claim 1, characterized in that, The electrolyte satisfies at least one of the following conditions: (1) The amount of additive added to the electrolyte is 1-10 wt%; (2) The amount of the first additive added to the electrolyte is 0.2-2 wt%; (3) The amount of the second additive added to the electrolyte is 0.5-2 wt%; (4) The mass ratio of the first additive and the second additive in the electrolyte is (1-5):(1-2).

7. The electrolyte according to claim 1, characterized in that, The electrolyte satisfies at least one of the following conditions: (1) The amount of organic solvent added to the electrolyte is 70-90 wt%; (2) The organic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl trifluoroethyl carbonate, diethyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, ethyl butyrate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, γ-butyrolactone, γ-valerolactone, δ-valerolactone, fluoroethylene carbonate, 1,3-dioxolane, dimethoxyethane, methyl propyl carbonate, methyl acetate, or butyl acetate. (3) The organic solvent includes at least two of fluoroethylene carbonate, propylene carbonate, diethyl carbonate or methyl ethyl carbonate.

8. The electrolyte according to claim 1, characterized in that, The electrolyte satisfies at least one of the following conditions: (1) The amount of lithium salt added to the electrolyte is 10-20 wt%; (2) The lithium salt includes one or more of the following: LiPF6, LiPO2F2, LiODFB, LiBF4, LiFSI, LiTFSI, LiBOB, LiSbF6, LiAsF6, LiDFOP, LiTFOP, and LiCF3SO3. (3) The lithium salt includes at least two of LiPF6, LiPO2F2 or LiODFB.

9. A lithium-ion battery, characterized in that, Contains the electrolyte according to any one of claims 1-8.

10. The lithium-ion battery according to claim 9, characterized in that, The lithium-ion battery satisfies at least one of the following conditions: (1) The positive electrode material of the lithium-ion battery includes lithium-rich manganese-based material, the chemical formula of which is xLi2MnO3·(1-x)LiMO2, where M is a transition metal and 0.1≤x≤0.7; (2) The charging cutoff voltage of the lithium-ion battery is above 4.5V.

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