Electrolyte additive, electrolyte and battery

Abstract

The application discloses an electrolyte additive, an electrolyte and a battery. The electrolyte additive comprises a diphosphate compound shown in structural formula I and a silicon isocyanate compound shown in structural formula II. The electrolyte additive can significantly improve the cycle life, high-temperature performance and safety performance of a lithium ion battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to an electrolyte additive, an electrolyte, and a battery. Background Technology

[0002] With the transformation of the global energy structure and the rapid development of electric vehicles, portable electronic devices and large-scale energy storage power stations, lithium-ion batteries, as core energy storage components, are facing increasingly higher requirements for comprehensive performance such as energy density, cycle life, safety performance and applicable ambient temperature.

[0003] Electrolyte, the "blood" of a lithium-ion battery, conducts lithium ions between the positive and negative electrodes and is a core component determining the battery's key performance characteristics. Currently, commercially available lithium-ion battery electrolytes mainly consist of high-purity organic carbonate solvents, lithium salts, and necessary functional additives. However, traditional electrolyte systems have several inherent defects, leading to instability at the electrolyte / electrode material interface and easily causing problems such as sudden capacity drops and a significantly increased risk of thermal runaway. To address these issues, adding small amounts of functional additives to the base electrolyte has become one of the most economical and effective methods for optimizing battery performance. Summary of the Invention The purpose of this invention is to provide an electrolyte additive, an electrolyte, and a battery, wherein the electrolyte additive can significantly improve the cycle life, high-temperature performance, and safety performance of lithium-ion batteries.

[0004] For the purposes of this invention, the following technical solution is adopted: On one hand, the present invention provides an electrolyte additive comprising a diphosphate ester compound represented by structural formula I and a silicon isocyanate-based compound represented by structural formula II.

[0005] Structural Formula I Structural Formula II R1 to R7 are each independently selected from one of the following: hydrogen group, halogen atom, cyano group, isocyanate group, isothiocyanate group, trimethylsilyl group, unsubstituted or substituted alkyl or alkoxy group of C1 to C10, unsubstituted or substituted alkenyl group of C2 to C10, unsubstituted or substituted alkynyl group of C2 to C10, and unsubstituted or substituted aryl group of C6 to C20; when a substituent is present on the alkyl, alkoxy, alkenyl, alkynyl, or aryl group, the substituent is selected from one of the following: halogen atom, trimethylsilyl group, and cyano group.

[0006] In embodiments of the present invention, R1 to R4 are each independently selected from unsubstituted or substituted alkyl groups of C1 to C4 or unsubstituted or substituted alkenyl groups of C2 to C4; when a substituent is present on the alkyl or alkenyl group, the substituent is a halogen atom.

[0007] In embodiments of the present invention, R5 to R7 are each independently selected from unsubstituted or substituted alkyl or isocyanate groups of C1 to C4; when a substituent is present on the alkyl group, the substituent is a halogen atom.

[0008] In embodiments of the present invention, R1 to R7 are each independently selected from fluorinated substituted alkyl groups.

[0009] Preferably, the fluorinated substituted alkyl group is trifluoromethyl and / or trifluoroethyl.

[0010] In embodiments of the present invention, structural formula I is selected from at least one of compounds having the following structures:

[0011] Compound 1-1

[0012] Compounds 1-2

[0013] Compounds 1-3.

[0014] Preferably, structural formula I is selected from compounds 1-2.

[0015] In embodiments of the present invention, structural formula II is selected from at least one of compounds having the following structures:

[0016] Compound 2-1

[0017] Compound 2-2

[0018] Compounds 2-3.

[0019] Preferably, the structural formula II is selected from compound 2-2 or compound 2-3.

[0020] On the other hand, the present invention also provides an electrolyte comprising the electrolyte additives described above.

[0021] In embodiments of the present invention, the mass percentages of the diphosphate ester compound and the isocyanate silicon-based compound are 0.1wt% to 5wt% and 0.1wt% to 3wt% of the total mass of the electrolyte, respectively.

[0022] Preferably, the mass percentages of the diphosphate ester compound and the silicon isocyanate-based compound are 0.5wt% to 3wt% and 0.5wt% to 2wt% of the total mass of the electrolyte, respectively.

[0023] In an embodiment of the present invention, the electrolyte further includes an organic solvent, a lithium salt, and conventional additives; the mass of the conventional additives accounts for 2wt% to 10wt% of the total mass of the electrolyte.

[0024] In embodiments of the present invention, the organic solvent accounts for 60% to 85% of the total mass of the electrolyte.

[0025] In an embodiment of the present invention, the lithium salt accounts for 10% to 20% of the total mass of the electrolyte.

[0026] In embodiments of the present invention, the conventional additives include at least one selected from fluoroethylene carbonate, 1,3-propanesulfonyl lactone, 1,3-sulfonyl lactone, 1,4-butanesulfonyl lactone, ethylene sulfate, vinylene carbonate, ethylene ethylene carbonate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, adiponitrile, succinic anhydride, ethylene glycol dipropionitrile ether, 1,3,6-hexanetrionitrile, succinic anhydride, maleic anhydride, citrate anhydride, and methanedisulfonate.

[0027] Preferably, the conventional additive is a combination of fluoroethylene carbonate and vinyl sulfate; wherein the weight ratio of the fluoroethylene carbonate and vinyl sulfate is 1~3:0.5~2.

[0028] In embodiments of the present invention, the organic solvent includes at least one selected from 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, γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Preferably, the organic solvent is at least three of the following: ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate. More preferably, the organic solvent is a combination of ethylene carbonate, propylene carbonate, diethyl carbonate and methyl ethyl carbonate, wherein the weight ratio of ethylene carbonate, propylene carbonate, diethyl carbonate and methyl ethyl carbonate is 10~30:5~10:10~20:40~75.

[0029] In embodiments of the present invention, the lithium salt includes lithium hexafluorophosphate.

[0030] Preferably, the lithium salt further includes at least one of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate. More preferably, the lithium salt includes at least two of lithium hexafluorophosphate, lithium difluorophosphate, and lithium difluorosulfonylimide; Most preferably, the lithium salt is a combination of lithium hexafluorophosphate, lithium difluorophosphate and lithium bis(fluorosulfonyl)imide, wherein the weight ratio of lithium hexafluorophosphate, lithium difluorophosphate and lithium bis(fluorosulfonyl)imide is 13~15:0.8~1:0.5~1.

[0031] In another aspect, the present invention also provides a battery comprising the electrolyte as described above.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: The electrolyte additives of this invention include diphosphate ester compounds and silicon isocyanate-based compounds. Both have higher HOMO values ​​and lower LUMO values ​​than the solvent, preferentially undergoing redox reactions in the solvent and participating in the formation of the interfacial passivation film. When used in combination, the derived SEI / CEI is rich in N, P, and silicate components, exhibiting better stability and ionic conductivity. Furthermore, the diphosphate ester compounds can generate P-containing free radicals, capturing and quenching free radicals that sustain combustion, thereby interrupting the chain reaction and effectively improving the safety performance of lithium batteries. Simultaneously, the -NCO groups in the silicon isocyanate-based compounds have excellent dehydration and deacidification effects, eliminating the adverse effects of HF. Therefore, the combined use of diphosphate ester and silicon isocyanate-based additives can significantly improve the cycle performance, high-temperature performance, and safety performance of lithium-ion batteries. Detailed Implementation

[0033] To better understand and implement this application, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only some of the embodiments of this application, and not all of them.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0035] Unless otherwise stated, all numerical values ​​for the amounts of expressed components, reaction conditions, etc., used in the specification and claims are to be understood as being modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values ​​that can be varied to obtain the desired performance.

[0036] For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range 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.

[0037] The word “and / or” as used in this article refers to one or all of the elements mentioned.

[0038] The terms "include" and "contain" as used in this article cover both cases where only the mentioned elements exist and cases where there are other unmentioned elements in addition to the mentioned elements.

[0039] Current electrolyte additive technologies mostly focus on solving single performance issues, and many novel additives have complex synthesis processes and high costs, making it difficult to meet the needs of commercial applications. Therefore, further development of novel and efficient electrolyte additives is needed to drive the development of next-generation high-performance and high-safety lithium-ion batteries.

[0040] The purpose of this invention is to provide an electrolyte additive that can significantly improve the cycle life, high-temperature performance, and safety performance of lithium-ion batteries. The following is a detailed description of this application.

[0041] Electrolyte additives On one hand, the present invention provides an electrolyte additive comprising a diphosphate ester compound represented by structural formula I and a silicon isocyanate-based compound represented by structural formula II.

[0042] Structural Formula I Structural Formula II R1 to R7 are each independently selected from one of the following: hydrogen group, halogen atom, cyano group, isocyanate group, isothiocyanate group, trimethylsilyl group, unsubstituted or substituted alkyl or alkoxy group of C1 to C10, unsubstituted or substituted alkenyl group of C2 to C10, unsubstituted or substituted alkynyl group of C2 to C10, and unsubstituted or substituted aryl group of C6 to C20; when a substituent is present on the alkyl, alkoxy, alkenyl, alkynyl, or aryl group, the substituent is selected from one of the following: halogen atom, trimethylsilyl group, and cyano group.

[0043] Among them, "electrolyte additive" can be used in electrolyte, and electrolyte containing the electrolyte additive can be used in battery, preferably in lithium metal battery.

[0044] "Substitution" can be mono- or poly-substitution; "R1~R7" can be the same or different.

[0045] In the above technical solution, the electrolyte additives of this invention include diphosphate ester compounds and silicon isocyanate-based compounds. Both have higher HOMO values ​​and lower LUMO values ​​than the solvent, preferentially undergoing redox reactions in the solvent and participating in the formation of the interfacial passivation film. When used in combination, the derived SEI / CEI is rich in N, P, and silicate components, exhibiting better stability and ionic conductivity.

[0046] Among them, diphosphate esters can generate phosphorus-containing free radicals, which can capture and quench free radicals that sustain combustion, thereby interrupting the chain reaction and effectively improving the safety performance of lithium batteries. Moreover, diphosphate esters not only have higher flame retardant efficiency, but also possess a dual-site synergistic effect due to the presence of two phosphorus atoms in the molecule (connected by a methylene group (-CH2-)). Specifically: 1) The two phosphorus centers can participate in interfacial reactions simultaneously or sequentially, resulting in more binding points with the electrode surface, forming a denser, more cross-linked, and mechanically stable interfacial film, thus providing stronger and longer-lasting protection under high voltage. 2) Because the molecular structure contains two phosphorus-oxygen double bonds (P=O), after one phosphorus center reacts, the other phosphorus center can act as an "anchor," chelating transition metal ions to prevent their dissolution and reduce side reactions.

[0047] Meanwhile, the -NCO groups in silicon isocyanate-based compounds have excellent dehydration and deacidification effects, thus eliminating the adverse effects of HF. Therefore, the combined use of diphosphate ester and silicon isocyanate-based additives can significantly improve the cycle performance, high-temperature performance, and safety performance of lithium-ion batteries.

[0048] In embodiments of the present invention, the halogen atom is selected from fluorine or chlorine atoms. Preferably, the halogen atom is a fluorine atom. In embodiments of the present invention, R1 to R4 are each independently selected from unsubstituted or substituted alkyl groups of C1 to C4 or unsubstituted or substituted alkenyl groups of C2 to C4; when a substituent is present on the alkyl or alkenyl group, the substituent is a halogen atom. The substituent can be monosubstituted or polysubstituted; R1 to R4 can be the same or different. Exemplarily, R1 to R4 are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, monofluoromethyl, difluoromethyl, trifluoromethyl, monochloroethyl, monobromopropyl, fluorinated vinyl, chlorosubstituted propenyl, and bromosubstituted butenyl. The halogen atom is selected from fluorine or chlorine atoms. Preferably, the halogen atom is a fluorine atom. When the substituent chain is too long, it will increase the viscosity of the electrolyte and reduce the conductivity. In addition, the bond energy of CH and CC bonds is relatively low, making them easy to break during battery operation, resulting in poor stability. At the same time, the interfacial film formed may lead to poor quality.

[0049] In embodiments of the present invention, R5 to R7 are each independently selected from unsubstituted or substituted alkyl or isocyanate groups of C1 to C4; when a substituent is present on the alkyl group, the substituent is a halogen atom. The substituent can be monosubstituted or polysubstituted; R5 to R7 can be the same or different. Exemplarily, R5 to R7 are each independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, monofluoromethyl, difluoromethyl, trifluoromethyl, monochloroethyl, isocyanate groups, etc. The halogen atom is selected from fluorine or chlorine atoms. Preferably, the halogen atom is a fluorine atom. When the substituent chain is too long, on the one hand, it increases the viscosity of the electrolyte and reduces the conductivity; on the other hand, the bond energies of the CH and CC bonds are relatively low, making them prone to breakage during battery operation, resulting in poor stability. Furthermore, the resulting interfacial film may lead to poor quality.

[0050] In embodiments of the present invention, R1 to R7 are each independently selected from fluorinated substituted alkyl groups. The fluorinated substitution form of the fluorinated substituted alkyl group can be monofluorinated, polyfluorinated, or perfluorinated; preferably, the fluorinated substituted alkyl group is a C1-C4 fluorinated substituted alkyl group. Exemplarily, R1 to R7 are each independently selected from monofluoromethyl, difluoromethyl, trifluoromethyl, monofluoroethyl, difluoroethyl, trifluoroethyl, pentafluoroethyl, fluorinated n-propyl, fluorinated isopropyl, fluorinated n-butyl, fluorinated isobutyl, etc. More preferably, the fluorinated substituted alkyl group is trifluoromethyl and / or trifluoroethyl. F-containing diphosphate compounds have a certain degree of non-flammability, and when combined with P, they can more effectively improve the safety performance of the electrolyte; moreover, isocyanate-based compounds contain F element, and the resulting interfacial film is rich in inorganic component LiF, which can further improve the stability of the interfacial film and help reduce interfacial impedance, promoting uniform transport of lithium ions.

[0051] In embodiments of the present invention, structural formula I is selected from at least one compound having the following structures:

[0052] Compound 1-1

[0053] Compounds 1-2

[0054] Compounds 1-3.

[0055] Preferably, structural formula I is selected from compounds 1-2. Compared with other diphosphate compounds, compounds 1-2 are more effective in improving the cycle performance, high-temperature performance, and safety performance of lithium-ion batteries. This is due to the role of trifluoromethyl groups: on the one hand, trifluoromethyl groups can promote film stability; on the other hand, trifluoromethyl groups can improve the oxidation resistance of the electrolyte, and substances containing fluorine (F) have a certain degree of non-flammability, which, when combined with phosphorus (P), can more effectively improve the safety performance of the electrolyte.

[0056] In embodiments of the present invention, structural formula II is selected from at least one of compounds having the following structures:

[0057] Compound 2-1

[0058] Compound 2-2

[0059] Compounds 2-3.

[0060] Preferably, structural formula II is selected from compound 2-2 or compound 2-3. Compared with other isocyanate-based compounds, the addition of compounds 2-2 and 2-3 to the electrolyte has a more significant effect on improving cycle performance, high-temperature performance, and safety performance. This is because compound 2-2 contains F element, and the resulting interfacial film is rich in inorganic component LiF, which can further improve the stability of the interfacial film and help reduce interfacial impedance, promoting uniform lithium ion transport. In addition to decomposing to form LiF, the F in compound 2-2 exists in the form of -CF3 groups, which has a strong electron-withdrawing inductive effect, which can significantly reduce the electron cloud density of adjacent atoms (silicon atoms) in the molecule, thereby changing the reactivity and preferential adsorption behavior of the molecule at the electrode / electrolyte interface, making it easier for it to participate in the reaction on the electrode surface. Compound 2-3 has three -NCO groups, which have better water and acid removal effects and eliminate the adverse effects of HF to a greater extent.

[0061] electrolyte On the other hand, the present invention also provides an electrolyte comprising the electrolyte additives described above.

[0062] Among them, "electrolyte" refers to the carrier that facilitates ion transport between the positive and negative electrodes of a battery.

[0063] In embodiments of the present invention, the mass percentages of diphosphate ester compounds and silicon isocyanate-based compounds are 0.1 wt% to 5 wt% and 0.1 wt% to 3 wt%, respectively, of the total electrolyte mass. For example, the mass percentages of diphosphate ester compounds and silicon isocyanate-based compounds are 0.1 wt% and 0.1 wt%, 1 wt% and 0.8 wt%, 2 wt% and 1.2 wt%, 2.8 wt% and 1.5 wt%, 3.5 wt% and 2 wt%, 4 wt% and 2.5 wt%, 5 wt% and 3 wt%, etc., of the total electrolyte mass. The addition amounts of diphosphate ester additives and silicon isocyanate-based additives, within the range of the present invention, can significantly improve the cycle life, high-temperature performance, and safety performance of the battery cell. When the amount added is too small, the SEI and CEI films formed by the additive are not uniform and dense enough, have poor stability, and generate fewer P-containing free radicals, so they cannot achieve the effect of capturing and quenching free radicals that sustain combustion. When the amount added is too large, on the one hand, it increases the viscosity of the electrolyte and the resulting interfacial film is too thick, leading to an increase in interfacial impedance, thereby degrading the performance of the battery cell. On the other hand, it increases the cost of the electrolyte.

[0064] Preferably, the mass percentages of the diphosphate ester compound and the silicon isocyanate-based compound are 0.5wt% to 3wt% and 0.5wt% to 2wt%, respectively, of the total mass of the electrolyte. For example, the mass percentages of the diphosphate ester compound and the silicon isocyanate-based compound are 0.5wt% and 0.5wt%, 1wt% and 0.8wt%, 2wt% and 1.2wt%, 2.8wt% and 1.5wt%, 3wt% and 2wt%, 1wt% and 2wt%, 2wt% and 0.8wt%, etc., of the total mass of the electrolyte. When the amounts of the diphosphate ester additive and the silicon isocyanate-based additive are within the above ranges, the effect on improving the cycle life, high-temperature performance, and safety performance of the battery cell is even better.

[0065] In embodiments of the present invention, the electrolyte further includes an organic solvent, a lithium salt, and conventional additives; the mass of the conventional additives accounts for 2 wt% to 10 wt% of the total mass of the electrolyte. For example, the mass of the conventional additives accounts for 2 wt%, 4 wt%, 5.5 wt%, 6 wt%, 7.5 wt%, 8 wt%, 9 wt%, 10 wt%, etc. of the total mass of the electrolyte.

[0066] In embodiments of the present invention, the organic solvent accounts for 60% to 85% of the total mass of the electrolyte. For example, the organic solvent accounts for 60%, 65%, 70%, 72%, 78%, 80%, 82%, 85% of the total mass of the electrolyte, etc.

[0067] In embodiments of the present invention, the lithium salt accounts for 10% to 20% of the total mass of the electrolyte. For example, the lithium salt accounts for 10%, 11%, 12.5%, 13%, 14%, 16%, 17%, 19%, 20% of the total mass of the electrolyte.

[0068] In embodiments of the present invention, conventional additives include at least one selected from the following: fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), 1,3-sulfonate lactone (PST), 1,4-butanesulfonate lactone (BS), vinyl sulfate (DTD), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), tris(trimethylsilane)borate (TMSB), tris(trimethylsilane)phosphate (TMSP), adiponitrile (ADN), succinic anhydride (SN), ethylene glycol dipropionitrile ether (DENE), 1,3,6-hexanetrionitrile (HTCN), succinic anhydride (SA), maleic anhydride (MA), citrate anhydride (CTA), and methanedisulfonate methylene (MMDS).

[0069] Preferably, the conventional additive is a combination of fluoroethylene carbonate (FEC) and vinyl sulfate (DTD); wherein the weight ratio of fluoroethylene carbonate (FEC) to vinyl sulfate (DTD) is 1~3:0.5~2. Exemplarily, the weight ratio of fluoroethylene carbonate (FEC) to vinyl sulfate (DTD) is 1:0.5, 1:1, 1.5:1, 2:1.5, 2.5:1.8, 3:2, etc.

[0070] In embodiments of the present invention, the organic solvent includes at least one of 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), γ-butyrolactone (GBL), γ-valerolactone (GVL), and δ-valerolactone (DVL).

[0071] Preferably, the organic solvent is at least three of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC).

[0072] More preferably, the organic solvent is a combination of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC), wherein the weight ratio of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) is 10~30:5~10:10~20:40~75. Exemplarily, the weight ratio of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) is 10:5:10:40, 20:10:20:50, 15:6:11:45, 20:7:15:58, 25:8:18:65, 30:10:20:75, etc.

[0073] In embodiments of the present invention, the lithium salt includes lithium hexafluorophosphate (LiPF6).

[0074] Preferably, the lithium salt further includes at least one of 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), and lithium tetrafluorooxalate phosphate (LiTFOP); More preferably, the lithium salt includes at least two of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), and lithium bis(fluorosulfonyl)imide (LiFSI); Most preferably, the lithium salt is a combination of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), and lithium bisfluorosulfonylimide (LiFSI), wherein the weight ratio of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), and lithium bisfluorosulfonylimide (LiFSI) is 13~15:0.8~1:0.5~1. Exemplarily, the weight ratios of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), and lithium bisfluorosulfonylimide (LiFSI) are 13:0.8:0.5, 13.5:0.85:0.55, 14:0.9:0.7, 14.3:0.92:0.75, 15:1:1, etc.

[0075] Battery In another aspect, the present invention also provides a battery comprising the electrolyte as described above.

[0076] In an embodiment of the present invention, the battery is a lithium-ion battery, which further includes a positive electrode, a negative electrode, and a separator. The separator is disposed between the positive and negative electrodes, and the electrolyte fills the pores of the separator and wets the positive and negative electrodes. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrodes; the electrolyte acts as a conductor between the positive and negative electrodes; the separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through. The present invention does not impose any particular limitations on the positive electrode, negative electrode, or separator, as long as the purpose of this application is achieved.

[0077] In embodiments of the present invention, the active material in the positive electrode sheet is LiCO2, LiMn2O4, LiFePO4, or LiNi. x Co y Mn z M 1-x-y-z O2 and LiNi x Co y Al z N 1-x-y-z At least one of O2; wherein M and N are independently selected from at least one of Mg, Al, Mo, Zn, B, Zr, La, Ga, Cr, V and Ti, 1≥x≥0.5, 0.5≥y≥0, 0.5≥z≥0, and x+y+z≤1; In an embodiment of the present invention, the active material in the negative electrode sheet is at least one of natural graphite, artificial graphite, and silicon-carbon composite material.

[0078] In an embodiment of the present invention, the operating voltage of the lithium-ion battery is ≥4.4V.

[0079] The present invention will be further illustrated below with reference to the embodiments: Example 1 1. Preparation of electrolyte Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a ratio of EC: PC: DEC: EMC = 2: 1: 2: 5. After thorough mixing, 13.5 wt% LiPF6, 1 wt% LiFSI, and 1 wt% LiPO2F2 were added sequentially. After complete dissolution, conventional and special additives were added. The conventional additives were 1 wt% FEC and 1 wt% DTD, and the special additives were 3 wt% diphosphate compound 1-1 and 2 wt% isocyanate silicon-based compound 2-1. After thorough mixing and dissolution, the mixture was ready for use.

[0080] 2. Preparation of the positive electrode The positive electrode active material NCM622, conductive carbon black (Super-P), carbon nanotubes (CNTs), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:1.4:0.7:0.9, and then dispersed in N-methyl-2-pyrrolidone (NMP). After thorough stirring, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated onto the positive electrode current collector Al foil, dried, and then rolled and die-cut to obtain a positive electrode sheet that meets the requirements.

[0081] 3. Preparation of the negative electrode Artificial graphite (anode active material), conductive carbon black (Super-P), styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose (CMC) thickener were mixed in a mass ratio of 96.2:1.2:1.6:1 and then dispersed in deionized water to obtain anode slurry. The anode slurry was uniformly coated onto Cu foil (anode current collector), dried, and then rolled and die-cut to obtain anode sheets that met the requirements.

[0082] 4. Preparation of lithium-ion batteries The positive and negative electrode sheets prepared by the above method are wound together with the separator and packaged to form a lithium-ion battery with a thickness of 4.0 mm, a length of 150 mm, and a width of 60 mm. The battery is then vacuum baked at 80°C for 24 h to obtain the cell to be injected with electrolyte. The prepared electrolyte is injected into the cell in a glove box with the dew point controlled below -40°C. After standing at high temperature and room temperature for 24 h respectively, the battery is formed, sealed again, and tested for capacity to complete the battery manufacturing.

[0083] Example 2 The difference from Example 1 is that the special additive added to the electrolyte is 3 wt% of diphosphate compounds 1-2, and the rest are the same.

[0084] Example 3 The difference from Example 1 is that the special additive added to the electrolyte is 3 wt% of diphosphate compounds 1-3, and the rest are the same.

[0085] Example 4 The difference from Example 1 is that the special additive added to the electrolyte is 2 wt% of silicon isocyanate-based compound 2-2, while the rest are the same.

[0086] Example 5 The difference from Example 1 is that the special additive added to the electrolyte is 2 wt% of silicon isocyanate-based compound 2-3, and the rest are the same.

[0087] Example 6 The difference from Example 1 is that the special additive added to the electrolyte is 0.1 wt% of a diphosphate compound 1-1, and the rest are the same.

[0088] Example 7 The difference from Example 1 is that the special additive added to the electrolyte is 5 wt% of a diphosphate compound 1-1, and the rest are the same.

[0089] Example 8 The difference from Example 1 is that the special additive added to the electrolyte is 0.1 wt% of silicon isocyanate-based compound 2-1, while the rest are the same.

[0090] Example 9 The difference from Example 1 is that the special additive added to the electrolyte is 3 wt% of silicon isocyanate-based compound 2-1, while the rest are the same. Example 10 The difference from Example 1 is that the special additive added to the electrolyte is 3 wt% of diphosphate compounds 1-4, in which R1~R4 are independently selected from neopentyl (-CH2C(CH3)3); the rest are the same.

[0091] Example 11 The difference from Example 1 is that the special additive added to the electrolyte is 2 wt% of isocyanate-based compound 2-4, in which R5~R7 are independently selected from tert-butyl groups. C (CH3)3); the rest are the same.

[0092] Example 12 The difference from Example 1 is that the special additive added to the electrolyte is 2 wt% of isocyanate-based compound 2-5, in which R5~R7 are independently selected from neopentyl (-CH2C(CH3)3); the rest are the same.

[0093] Comparative Example 1 The difference from Example 1 is that the electrolyte does not contain any special additives such as diphosphate esters, that is, it does not contain 3 wt% of compound 1-1, but all other aspects are the same. Comparative Example 2 The difference from Example 1 is that the electrolyte does not contain any special additives based on isocyanate, that is, it does not contain 2 wt% of compound 2-1, but all other aspects are the same. Comparative Example 3 The difference from Example 1 is that the electrolyte does not contain any special additives, namely, it does not contain 3 wt% of diphosphate compound 1-1 and 2 wt% of isocyanate silicon-based compound 2-1, but all other components are the same.

[0094] Comparative Example 4 The difference from Example 1 is that the electrolyte does not contain any special additives such as diphosphates, that is, it does not contain 3 wt% of compound 1-1, but it does contain 2 wt% of triisopropyl phosphate, and the rest are the same.

[0095] Comparative Example 5 The difference from Example 1 is that the electrolyte does not contain any special additives based on isocyanate, that is, it does not contain 2 wt% of compound 2-1, but it does contain 2 wt% of ethyl isocyanate, and the rest are the same.

[0096] Performance testing The lithium-ion batteries prepared in Comparative Examples 1-5 and Examples 1-11 were subjected to performance tests.

[0097] 1) Room temperature cycling performance test: At 25±2℃, charge to 4.4V with 1C constant current and constant voltage, cut off current 0.05C, and then discharge to 2.8V with 1C constant current. Record the initial discharge capacity as C0. Repeat the charge and discharge 600 times and record the discharge capacity on the 600th cycle as C1. Calculate the capacity retention rate of room temperature cycling according to the following formula: Capacity retention rate = C1 / C0*100%.

[0098] 2) High-temperature cycling performance test: In a constant temperature chamber at 45±2℃, charge at 1C constant current and constant voltage to 4.4V, cut off current 0.05C, and then discharge at 1C constant current to 2.8V. Record the initial discharge capacity as C0. Repeat the charge and discharge 600 times and record the discharge capacity on the 600th cycle as C1. Calculate the capacity retention rate of high-temperature cycling according to the following formula: Capacity retention rate = C1 / C0*100%.

[0099] 3) 14-Day Performance Test at 70℃: At 25±2℃, the battery was charged to 4.4V using a 1C constant current / constant voltage method, with a cutoff current of 0.05C. Then, it was discharged to 2.8V using a 1C constant current method, recording the initial discharge capacity as C0. The initial battery volume was then measured as V0. At 25±2℃, the battery was charged to 4.4V using a 1C constant current / constant voltage method, with a cutoff current of 0.05C. The fully charged battery was then transferred to 70±2℃ and stored for 14 days. After storage, the battery was left to rest at 25±2℃ for 2 hours, then discharged to 2.8V using a 1C constant current method, recording the discharge capacity as C1. The battery volume after storage (V1) was then measured. The volume change rate after 28 days of storage at 70℃ is calculated as (V1-V0) / V0 * 100%, and the capacity retention rate is calculated as C1 / C0 * 100%.

[0100] 4) Safety performance test: At 25±2℃, charge the battery to 4.4V with a constant current and constant voltage of 1C and a cutoff current of 0.05C. Then transfer the fully charged battery to the thermal abuse test chamber and heat it to 100℃ at a rate of 5℃ / min and hold it at that temperature for 30min. Then continue to heat it to 110℃ at a rate of 5℃ / min and hold it at that temperature for 30min. Then continue to heat it to 120℃ at a rate of 5℃ / min and hold it at that temperature for 30min. And so on. The test will end when the battery cell burns or explodes. Record the thermal runaway temperature of the battery cell.

[0101] The test data is shown in Table 1. Table 1. Lithium-ion battery performance test results

[0102] As shown in Comparative Examples 1-3 and Examples 1-11, the simultaneous addition of diphosphate ester compounds and silicon isocyanate-based compounds to the electrolyte is beneficial for improving the cycle life, high-temperature performance, and safety performance of lithium-ion batteries. This is because the SEI and CEI films formed when both are used together contain components such as Si, P, and N, resulting in more uniform and stable film formation and superior lithium-ion conductivity. This effectively mitigates the occurrence of side reactions at the electrolyte-electrode interface. In addition, the generated P-containing free radicals can capture and quench free radicals that sustain combustion, thereby interrupting the chain reaction and effectively improving the cycle performance and safety performance of lithium batteries.

[0103] Examples 1-11 show that, within the scope of this invention, the addition amounts of diphosphate ester compounds and isocyanate-based compounds can significantly improve the cycle life, high-temperature performance, and safety performance of the battery cell. When the addition amount is too small, the SEI and CEI films formed by the additives are not uniform and dense enough, have poor stability, and generate fewer P-containing free radicals, failing to achieve the effect of capturing and quenching free radicals that sustain combustion. When the addition amount is too large, on the one hand, it increases the viscosity of the electrolyte, and the resulting interfacial film is too thick, leading to an increase in interfacial impedance, thereby degrading the battery cell performance. On the other hand, it increases the cost of the electrolyte.

[0104] As shown in Comparative Example 1 and Examples 1-3, the addition of diphosphate compounds 1-1, 1-2, and 1-3 to the electrolyte can improve the cycle performance, high-temperature performance, and safety performance of lithium-ion batteries, with compound 1-2 showing a more significant improvement. This is due to the effect of trifluoromethyl groups, which promote film stability and enhance the electrolyte's antioxidant properties. Furthermore, the fluorine-containing substances possess a certain degree of non-flammability, and their combination with phosphorus (P) can more effectively improve the electrolyte's safety performance.

[0105] As shown in Comparative Examples 2, 1, 4, and 5, the addition of isocyanate-based compounds 2-2 and 2-3 to the electrolyte significantly improves cycle life, high-temperature performance, and safety. Compound 2-2 contains the -F element, resulting in an interfacial film rich in inorganic LiF, which further enhances the stability of the interfacial film and helps reduce interfacial impedance, promoting uniform lithium-ion transport. Compound 2-3 contains three -NCO groups, providing better dehydration and acid removal effects, and mitigating the adverse effects of HF to a greater extent.

[0106] As shown in Comparative Examples 1 and 4 and Example 1, adding triisopropyl phosphate to the electrolyte is also beneficial for improving the performance of ternary lithium-ion batteries, but the improvement effect is not as good as that of compound 1-1. This is because triisopropyl phosphate cannot participate in the formation of the SEI film and has poor compatibility with the negative electrode. As shown in Comparative Examples 2 and 5 and Example 1, ethyl isocyanate additives can also improve the performance of ternary lithium-ion batteries, but the effect is not as good as that of compound 2-1. The reason may be that compound 2-1 contains Si groups, and the derived interface film contains a certain amount of silicates, which have better lithium-ion conduction performance.

[0107] As can be seen from Examples 1-5 and 10-12, when there are more than 4 C cells in R1-R7, the cycle performance, high-temperature performance and safety performance of lithium-ion batteries can be improved, but the effect is slightly worse than when there are fewer C cells.

[0108] The technical means disclosed in this application are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. An electrolyte additive, characterized in that, This includes diphosphate ester compounds represented by structural formula I and isocyanate-based compounds represented by structural formula II. Structural Formula I Structural Formula II R1 to R7 are each independently selected from one of the following: hydrogen group, halogen atom, cyano group, isocyanate group, isothiocyanate group, trimethylsilyl group, unsubstituted or substituted alkyl or alkoxy group of C1 to C10, unsubstituted or substituted alkenyl group of C2 to C10, unsubstituted or substituted alkynyl group of C2 to C10, and unsubstituted or substituted aryl group of C6 to C20; when a substituent is present on the alkyl, alkoxy, alkenyl, alkynyl, or aryl group, the substituent is selected from one of the following: halogen atom, trimethylsilyl group, and cyano group.

2. The electrolyte additive as described in claim 1, characterized in that, R1 to R4 are each independently selected from unsubstituted or substituted alkyl groups of C1 to C4 or unsubstituted or substituted alkenyl groups of C2 to C4; when a substituent is present on the alkyl or alkenyl group, the substituent is a halogen atom; and / or, R5 to R7 are each independently selected from unsubstituted or substituted alkyl or isocyanate groups of C1 to C4; when a substituent is present on the alkyl group, the substituent is a halogen atom.

3. The electrolyte additive as described in claim 1, characterized in that, R1 to R7 are each independently selected from fluorinated substituted alkyl groups.

4. The electrolyte additive as described in claim 1, characterized in that, The structural formula I is selected from at least one of the following compounds: Compound 1-1 Compounds 1-2 Compounds 1-3.

5. The electrolyte additive as described in claim 1, characterized in that, The structural formula II is selected from at least one of the following compounds: Compound 2-1 Compound 2-2 Compounds 2-3.

6. An electrolyte, characterized in that, Includes the electrolyte additive as described in any one of claims 1 to 6.

7. The electrolyte as described in claim 6, characterized in that, The diphosphate ester compound and the isocyanate silicon-based compound account for 0.1wt% to 5wt% and 0.1wt% to 3wt% of the total mass of the electrolyte, respectively.

8. The electrolyte as described in claim 6, characterized in that, The electrolyte further includes an organic solvent, a lithium salt, and conventional additives; the conventional additives account for 2 wt% to 10 wt% of the total mass of the electrolyte; and / or, The organic solvent accounts for 60% to 85% of the total mass of the electrolyte; and / or, The lithium salt accounts for 10% to 20% of the total mass of the electrolyte.

9. The electrolyte as described in claim 8, characterized in that, The conventional additives include at least one selected from fluoroethylene carbonate, 1,3-propanesulfonyl lactone, 1,3-sulfonyl lactone, 1,4-butanesulfonyl lactone, ethylene sulfate, vinylene carbonate, ethylene ethylene carbonate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, adiponitrile, succinic acid, ethylene glycol dipropionitrile ether, 1,3,6-hexanetrionitrile, succinic anhydride, maleic anhydride, citrate anhydride, and methanedisulfonate.

10. A battery, characterized in that, The battery includes the electrolyte as described in any one of claims 6 to 9.

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