Electrolyte additive, preparation method therefor, and use thereof

Abstract

An electrolyte additive, a preparation method therefor, and an application thereof. The electrolyte additive comprises a halogen-substituted tris(oxalato)diborate, the halogen-substituted tris(oxalato)diborate having a structure as shown in formula I, where R1 and R2 are each independently selected from one of the halogens, and M+ are selected from one of the alkali metal ions. The halogen-substituted tris(oxalato)diborate has relatively good chemical stability and electrochemical stability, is used in an electrolyte of a secondary battery, and improves the thermal stability effect of a product. In addition, since the halogen-substituted tris(oxalato)diborate has more oxalate functional groups, the ion concentration in the electrolyte can be well adjusted, which can effectively improve the conductivity of an electrolyte, such that the voltage of a battery can be more easily maintained within a suitable range.

Description

An electrolyte additive, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202411521802.7, filed on October 9, 2024, entitled "An Electrolyte Additive and Its Preparation Method and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of secondary battery technology, and in particular to an electrolyte additive, its preparation method, and its application. Background Technology

[0003] Lithium difluorooxalate borate (LiODFB) and sodium difluorooxalate borate are compounds with significant application value in the field of secondary batteries such as lithium-ion batteries and sodium-ion batteries. They have a wide operating temperature range, high conductivity, good film-forming properties, and excellent cycle performance. Against the backdrop of the booming development of the new energy vehicle industry, the continuous growth in the market shipments of lithium-ion batteries, sodium-ion batteries, and electrolytes has brought broad development prospects to the market for lithium difluorooxalate borate and sodium difluorooxalate borate.

[0004] However, the inventors found that the chemical stability, electrochemical stability, and thermal stability of compounds such as lithium difluorooxalate borate and sodium difluorooxalate borate in electrolytes still need to be improved. Therefore, it is urgent to find a substitute compound for lithium difluorooxalate borate and sodium difluorooxalate borate that has excellent chemical stability, electrochemical stability, and thermal stability in electrolytes to meet potential market demand. Summary of the Invention

[0005] In view of this, one objective of this application is to provide an electrolyte additive comprising a halosubstituted trioxalatobisborate, which exhibits good chemical and electrochemical stability and is used in the electrolyte of secondary batteries to improve the thermal stability of the product. Simultaneously, because the halosubstituted trioxalatobisborate contains more oxalate functional groups, it can effectively regulate the ion concentration in the electrolyte, thereby effectively improving the electrolyte conductivity and making it easier to maintain the battery voltage within a suitable range.

[0006] Another objective of this application is to provide a method for preparing an electrolyte additive.

[0007] Another object of this application is to provide a secondary battery electrolyte.

[0008] To achieve the above objectives, a first aspect of this application provides an electrolyte additive comprising a halosubstituted trioxalic acid diborate having the structure shown in Formula I:

[0009] Wherein, R1 and R2 are each independently selected from one of the halogens, and M + It is selected from one of the alkali metal ions.

[0010] In some embodiments, R1 and R2 are each independently selected from one of F, Cl, Br, and I.

[0011] In some implementations, the M + It is selected from one of lithium ions, sodium ions, and potassium ions.

[0012] In some embodiments, the halosubstituted trioxalatobisborate is selected from at least one of compound 1 and compound 2:

[0013] A second aspect of this application provides a method for preparing an electrolyte additive, comprising:

[0014] The halogen-containing alkali metal borate is reacted with an oxalate silicate compound in a solvent, followed by purification, to obtain the halogenated trioxalate diborate.

[0015] In some embodiments, the halogen-containing alkali metal borate includes at least one of alkali metal borates containing four halogen atoms and alkali metal borates containing two halogen atoms.

[0016] In some embodiments, the oxalate silicate compound includes at least one of bis(trimethylsilyl)oxalate and bis(triethylsilyl)oxalate.

[0017] In some embodiments, the molar ratio of the halogen-containing alkali metal borate to the oxalate silicate compound is 1:a, where 1 < a < 2.

[0018] In some embodiments, the solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0019] In some embodiments, the reaction temperature is 10-100°C and the reaction time is 1-24 hours.

[0020] A third aspect of this application provides a secondary battery electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and the electrolyte additives described in this application.

[0021] In some embodiments, the content of halogenated trioxamate diborate in the electrolyte additive is 0.05-10% based on the total mass of the electrolyte (100%).

[0022] In some embodiments, the electrolyte salt includes at least one selected from lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt.

[0023] In some embodiments, the electrolyte salt is a lithium salt, and the concentration of the lithium salt in the electrolyte is 0.1-8 mol / L.

[0024] In other embodiments, the electrolyte salt is a sodium salt, and the concentration of the sodium salt in the electrolyte is 0.1-2 mol / L.

[0025] In some embodiments, the non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents.

[0026] In some embodiments, the electrolyte further includes auxiliary additives, which include at least one of cyclic carbonate compounds, cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, borate compounds, and nitrile compounds.

[0027] In some embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and the compound shown in structural formula 2.

[0028] In structural formula 2, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group.

[0029] In some embodiments, the cyclic sulfate compounds include vinyl sulfate, 4-methylvinyl sulfate, propylene sulfate, etc. At least one of them.

[0030] In some embodiments, the sulfonyl lactone compounds include 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, etc. At least one of them.

[0031] In some embodiments, the phosphate ester compounds include saturated phosphate ester compounds and unsaturated phosphate ester compounds, wherein the saturated phosphate ester compounds include tris(trimethylsilane) phosphate esters, and the unsaturated phosphate ester compounds include compounds shown in structural formula 3.

[0032] In structural formula 3, R 31 R 32 R 32 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, -Si(CH3)3, -Si(C2H5)3, or -Si(C3H7)3, and R 31 R 32 R 33 At least one of them is a C1-C5 unsaturated hydrocarbon group.

[0033] In some embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0034] In some embodiments, the nitrile compound includes at least one selected from succinic anhydride, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitil.

[0035] A fourth aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the electrolyte described in this application.

[0036] The electrolyte additives described in this application can bring at least the following beneficial effects:

[0037] This electrolyte additive is a halosubstituted trioxalatobisborate, which exhibits good chemical and electrochemical stability. Used in secondary battery electrolytes, it improves the product's thermal stability. Furthermore, because halosubstituted trioxalatobisborate contains more oxalate functional groups, it can effectively regulate the ion concentration in the electrolyte, thereby significantly improving the electrolyte's conductivity and making it easier to maintain the battery voltage within a suitable range.

[0038] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0039] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0040] in:

[0041] Figure 1 shows the NMR B spectrum of the product prepared in Example 1.

[0042] Figure 2 shows the NMR B spectrum of the product prepared in Example 2.

[0043] Figure 3 shows the NMR B spectrum of the product prepared in Comparative Example 1.

[0044] Figure 4 shows the NMR B spectrum of the product prepared in Comparative Example 2. Detailed Implementation

[0045] The embodiments of this application are described in detail below. These embodiments are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0046] In this application, the disclosure of numerical ranges includes all values ​​throughout the range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0047] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0048] <Electrolyte Additives>

[0049] The electrolyte additive in this application includes a halosubstituted trioxalic acid diborate, which has the structure shown in Formula I:

[0050] Among them, R1 and R2 are each independently selected from one of the halogens, and M + It is selected from one of the alkali metal ions.

[0051] For example, halogens include, but are not limited to, F, Cl, Br, I, etc.

[0052] As a preferred approach, R1 and R2 are each independently selected from one of F, Cl, Br, and I.

[0053] For example, M + It is selected from one of lithium ions, sodium ions, and potassium ions.

[0054] As a more preferred embodiment, the halogenated trioxalatobisborate is selected from at least one of compound 1 and compound 2:

[0055] The electrolyte additives in this application embodiment can bring at least the following beneficial effects:

[0056] This electrolyte additive is a halosubstituted trioxalatobisborate, which exhibits good chemical and electrochemical stability. When used in secondary battery electrolytes, it effectively improves the electrolyte's conductivity and enhances the product's thermal stability. Furthermore, because this halosubstituted trioxalatobisborate contains more oxalate functional groups, it can effectively regulate the ion concentration in the electrolyte, making it easier to maintain the battery voltage within a suitable range.

[0057] <Preparation Method of Electrolyte Additives>

[0058] The method for preparing the electrolyte additive in this application embodiment can be used to prepare the electrolyte additive in this application embodiment.

[0059] The method for preparing the electrolyte additive according to the embodiments of this application includes the following steps:

[0060] Halogen-containing alkali metal borates are reacted with oxalate silicate compounds in a solvent, followed by purification, to obtain halosubstituted trioxalate diborate.

[0061] In some embodiments, halogen-containing alkali metal borates include, but are not limited to, at least one of alkali metal borates containing four halogen atoms and alkali metal borates containing two halogen atoms.

[0062] For example, alkali metal borates containing four halogen atoms include, but are not limited to, lithium tetrafluoroborate, sodium tetrafluoroborate, potassium tetrafluoroborate, etc.

[0063] For example, alkali metal borates containing two halogen atoms include, but are not limited to, lithium difluoroborate, sodium difluoroborate, potassium difluoroborate, etc.

[0064] As an alternative example, halogenated alkali metal borates are alkali metal borates containing four halogen atoms.

[0065] In some embodiments, the oxalate silicate compound includes, but is not limited to, at least one of bis(trimethylsilyl)oxalate, bis(triethylsilyl)oxalate, etc.

[0066] As an alternative example, the oxalate silicate compound is bis(trimethylsilyl)oxalate.

[0067] In some embodiments, the molar ratio of the halogenated alkali metal borate to the oxalate silicate compound is 1:a, where 1 < a < 2. In the embodiments of this application, when the molar ratio of the halogenated alkali metal borate to the oxalate silicate compound is within the above range, a halosubstituted trioxalate diborate having the structure shown in Formula I can be synthesized; outside the above range, a halosubstituted trioxalate diborate having the structure shown in Formula I cannot be synthesized. For example, when the molar ratio of the halogenated alkali metal borate to the oxalate silicate compound is greater than or equal to 1:1, the synthesized product is lithium difluorooxalate borate (LiODFB); when the molar ratio of the halogenated alkali metal borate to the oxalate silicate compound is less than or equal to 1:2, the synthesized product is lithium dioxalate borate (LiBOB).

[0068] For example, the molar ratio of halogenated alkali metal borate to oxalate silicate compounds includes, but is not limited to, 1:1.02, 1:1.05, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, or 1:1.9.

[0069] In some embodiments, the solvent includes, but is not limited to, at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0070] In some embodiments, the reaction temperature is 10-100°C, including but not limited to 10°C, 25°C, 50°C, 80°C or 100°C.

[0071] In some implementations, the reaction time is 1-24 hours, including but not limited to 1 hour, 2 hours, 4 hours, 10 hours, 15 hours, 20 hours, or 24 hours.

[0072] Alkali metal borates containing halogens, where R1 and R2 are both F in the aforementioned Formula I structure, are alkali metal borates containing four F atoms (MBF). 4) Taking the case where the oxalate silicate compound is bis(trimethylsilyl)oxalate as an example, the synthetic route of the halosubstituted trioxalate diborate (where R1 and R2 are both F in the aforementioned Formula I structure of this application) is as follows:

[0073] In some implementations, purification methods include recrystallization, etc.

[0074] The preparation method of the electrolyte additive in this application embodiment has the beneficial effects of the electrolyte additive in this application embodiment, and at least the following beneficial effects: the preparation conditions of this preparation method are relatively mild, and no by-products are generated in the process route.

[0075] Electrolyte

[0076] The electrolyte of this application includes a non-aqueous organic solvent, an electrolyte salt, and an electrolyte additive of this application.

[0077] In some embodiments, based on the total mass of the electrolyte as 100%, the content of halosubstituted trioxalatobisborate in the electrolyte additive of this application embodiment is 0.05-10%, including but not limited to 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0078] In the embodiments of this application, when the content of the compound shown in Formula I (halogenated trioxarate diborate) is within the above range, the stability of the film formed on the electrode surface can be effectively maintained and the battery performance can be improved. If the content of the compound shown in Formula I is too low, it is difficult to significantly improve the performance of the battery. If the content of the compound shown in Formula I is too high, it may affect the function of other substances in the electrolyte due to the excessive decomposition products.

[0079] As a preferred example, based on the total mass of the electrolyte, the content of halogenated trioxamate diborate in the electrolyte additive of this application embodiment is 0.1-5%.

[0080] In some embodiments, the electrolyte salt includes, but is not limited to, at least one selected from lithium salts, sodium salts, potassium salts, magnesium salts, zinc salts, and aluminum salts. In a preferred embodiment, the electrolyte salt is selected from lithium salts or sodium salts.

[0081] Alkali metal ions, formed by the dissociation of electrolyte salts in the electrolyte, intercalate and deintercalate between the positive and negative electrodes to complete the charge-discharge cycle. The concentration of the electrolyte salt directly affects the transfer rate of alkali metal ions, which in turn affects the potential change of the negative electrode. During fast charging, it is necessary to maximize the movement speed of alkali metal ions to prevent the negative electrode potential from dropping too quickly, which could lead to the formation of lithium dendrites and pose a safety hazard to the battery. This also helps prevent the battery's cycle capacity from decaying too rapidly. If the electrolyte salt content is too low, the intercalation and deintercalation efficiency of alkali metal ions between the positive and negative electrodes will be reduced, failing to meet the requirements of fast charging. Conversely, if the electrolyte salt content is too high, the viscosity of the non-aqueous electrolyte will increase, which is also detrimental to improving the intercalation and deintercalation efficiency of alkali metal ions and increases the battery's internal resistance.

[0082] In some embodiments, the electrolyte salt is a lithium salt, and the concentration of the lithium salt in the electrolyte is 0.1-8 mol / L, including but not limited to 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, or 8 mol / L. In a preferred embodiment, the concentration of the lithium salt is 0.5-2.5 mol / L.

[0083] In some embodiments, the lithium salt includes, but is not limited to, LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, and Li2B. 10 Cl 10 At least one of the following: lithium salts of lower aliphatic carboxylic acids.

[0084] In other embodiments, the electrolyte salt is a sodium salt, and the concentration of the sodium salt in the electrolyte is 0.1-2 mol / L, including but not limited to 0.1 mol / L, 0.4 mol / L, 0.5 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, or 2 mol / L. In a preferred embodiment, the concentration of the sodium salt is 0.4-1.5 mol / L.

[0085] In some embodiments, the sodium salt includes, but is not limited to, at least one of sodium perchlorate (NaClO4), sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethanesulfonate (NaOTf), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0086] In some embodiments, the electrolyte also includes auxiliary additives.

[0087] In some embodiments, the auxiliary additives include, but are not limited to, at least one of cyclic carbonate compounds, cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, borate compounds, and nitrile compounds.

[0088] In some embodiments, the cyclic carbonate compound includes, but is not limited to, at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and the compound shown in structural formula 2.

[0089] In structural formula 2, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group.

[0090] By way of a non-limiting example, C1-C5 groups include, but are not limited to, methyl, trifluoromethyl, ethyl, vinyl, propyl, or allyl groups.

[0091] As a preferred example, the compounds shown in structural formula 2 include, but are not limited to, at least one of the compounds shown in compounds 2-1 to 2-6 below:

[0092] In some embodiments, cyclic sulfate compounds include, but are not limited to, vinyl sulfate, 4-methylvinyl sulfate, At least one of propylene sulfate, etc.

[0093] In some embodiments, sulfonyl lactone compounds include, but are not limited to, 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone. At least one of the following.

[0094] In some embodiments, the phosphate ester compounds include saturated phosphate ester compounds and unsaturated phosphate ester compounds.

[0095] In some embodiments, saturated phosphate compounds include, but are not limited to, tris(trimethylsilane) phosphates.

[0096] In some embodiments, the unsaturated phosphate ester compound includes the compound shown in structural formula 3:

[0097] In structural formula 3, R 31 R 32 R 32 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, -Si(CH3)3, -Si(C2H5)3, or -Si(C3H7)3, and R 31 R 32 R 33 At least one of them is a C1-C5 unsaturated hydrocarbon group.

[0098] In the embodiments of this application, the term "saturated hydrocarbon group," also known as alkyl, refers to a straight-chain or branched alkyl radical containing 1 to 5 carbon atoms. Examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, etc.

[0099] In the embodiments of this application, the term "unsaturated hydrocarbon group" refers to a hydrocarbon compound whose molecule contains carbon-carbon double or triple bonds.

[0100] By way of non-limiting example, the C1-C5 unsaturated hydrocarbon groups and C1-C5 haloalkanes have 1, 2, 3, 4, or 5 carbon atoms. For example, C1-C5 unsaturated hydrocarbon groups include, but are not limited to, vinyl, ethynyl, allyl, 2-methylpropene, 1,4-butadienyl, propargyl, etc. C1-C5 haloalkanes include, but are not limited to, trifluoromethyl, 2,2,2-trifluoroethyl, 3,3,3-trifluoropropyl, hexafluoroisopropyl, etc.

[0101] As a preferred example, the compounds shown in structural formula 3 include, but are not limited to, at least one of the following: triargyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0102] In some embodiments, the borate ester compounds include, but are not limited to, at least one of tris(trimethylsilane)borate, tris(triethylsilane)borate, etc.

[0103] In some embodiments, the nitrile compound includes, but is not limited to, at least one of succinic acid, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, sebaconitol, etc.

[0104] In the embodiments of this application, with the total mass of the electrolyte as 100%, the mass content of the auxiliary additives in the electrolyte varies depending on the type of auxiliary additive chosen. Specifically, in some embodiments, when the auxiliary additive is selected from at least one of the following substances other than fluoroethylene carbonate: cyclic carbonates, cyclic sulfates, sulfonyl lactones, phosphates, borates, and nitriles, the content of any one of these optional substances in the non-aqueous electrolyte is less than 10%, including but not limited to 0.05%, 0.08%, 0.1%, 0.5%, and 0.8%. The content of any one of the above optional substances in the non-aqueous electrolyte is 0.1-5%, more preferably 0.1-3%. In other embodiments, when fluoroethylene carbonate is selected as the auxiliary additive, the content of fluoroethylene carbonate is 0.05-30% based on the total mass of the electrolyte (100%), including but not limited to 0.05%, 1%, 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, or 30%.

[0105] In the electrolyte of the embodiments of this application, compared with single addition or combination of other existing additives, the compound shown in Formula I (i.e., halogenated trioxalatobisborate) and the above-mentioned auxiliary additives together exhibit a significant synergistic effect in improving battery performance. This shows that the compound shown in Formula I and the auxiliary additives can form a film together on the electrode surface to compensate for the film formation defects of single addition and obtain a more stable passivation film.

[0106] In some embodiments, the non-aqueous organic solvent includes, but is not limited to, at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents.

[0107] In some embodiments, the ether solvent includes cyclic ethers or chain ethers.

[0108] By way of non-limiting example, cyclic ethers may specifically include, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), 2-trifluoromethyltetrahydrofuran (2-CF3-THF), etc.

[0109] By way of non-limiting example, the chain ether may specifically include, but is not limited to, at least one of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (TEGDME), etc.

[0110] By way of a non-limiting example, nitrile solvents may specifically include, but are not limited to, at least one of acetonitrile, glutaronitrile, malononitrile, etc.

[0111] In some embodiments, carbonate solvents include, but are not limited to, cyclic carbonates or chain carbonates.

[0112] By way of non-limiting example, cyclic carbonates may specifically include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), butylene carbonate (BC), etc.

[0113] By way of non-limiting example, chain carbonates may specifically include, but are not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), etc.

[0114] By way of non-limiting example, carboxylic acid ester solvents may specifically include, but are not limited to, at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), butyl propionate, etc.

[0115] By way of non-limiting example, sulfone solvents include, but are not limited to, at least one of sulfolane, ethyl vinyl sulfone, ethyl isopropyl sulfone, etc.

[0116] Secondary batteries

[0117] The secondary battery of this application embodiment includes a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte is the electrolyte of this application embodiment.

[0118] In the embodiments of this application, the secondary battery uses the electrolyte of the embodiments of this application, which can form a high-performance passivation film on the positive and negative electrodes, thereby effectively improving the high-temperature storage performance and high-temperature cycle performance of the battery and enhancing the battery power characteristics.

[0119] In some implementations, the secondary battery includes, but is not limited to, lithium metal batteries, lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, magnesium-ion batteries, potassium-ion batteries, zinc-ion batteries, or lithium aluminum ions.

[0120] In some embodiments, the positive electrode includes a positive electrode material layer, which includes a positive electrode active material. There are no particular restrictions on the type and content of the positive electrode active material, which can be selected according to actual needs. It can be any positive electrode active material or conversion type positive electrode material that can reversibly insert / deintercalate metal ions (lithium ions, sodium ions, potassium ions, magnesium ions, zinc ions, aluminum ions, etc.).

[0121] As a preferred example, the secondary battery is a lithium-ion battery, and the positive electrode active material of the secondary battery includes, but is not limited to, lithium-containing sulfides, lithium-containing selenides, lithium-containing halides, and LiFe. 1-x’ M' x’ PO4, LiMn 2-y’ M y’ O4 and LiNi x Co y Mn z M 1-x-y-z At least one of O2, etc., wherein M' includes, but is not limited to, at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, etc., and M includes, but is not limited to, at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, etc., and 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

[0122] As a non-restrictive enumeration, the values ​​of x', y', y, x, z, and x+y+z include, but are not limited to, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0123] As a more preferred example, when the secondary battery is a lithium-ion battery, the positive electrode active material of the secondary battery can be selected from LiCoO2, LiFePO4, LiFe 0.8 Mn 0.2 PO4, LiMn2O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2, LiNi 0.5 Co 0.2 Al 0.3At least one of O2.

[0124] As another preferred example, the secondary battery is a sodium-ion battery, and the positive electrode active material includes, but is not limited to, at least one of sodium-containing transition metal oxides, sodium-containing Prussian materials, sodium-containing phosphates, sodium-containing sulfates, sodium-containing titanates, etc.

[0125] In some embodiments, the sodium-containing transition metal oxide may be Na. a T b O c T includes, but is not limited to, at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V, etc., where 1≤a≤4, 3≤b≤6, and 7≤c≤13.

[0126] More preferably, the sodium-containing transition metal oxide is NaNi. m Fe n Mn p O2 (m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1) or NaNi m Co n Mn p O2(m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1).

[0127] As a non-restrictive enumeration, the values ​​of m, n, and p include, but are not limited to, 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0128] In some embodiments, the molecular formula of the sodium-containing Prussian-like material is Na. d Q[Q′(CN)6] e ·fH₂O, where Q is a transition metal, Q′ is a transition metal, and 0 <d≤2,0.8≤e<1,0<f≤20。

[0129] By way of non-limiting enumeration, Q and Q′ include, but are not limited to, at least one of Cr, Fe, Co, Ni, Cu, Mn, Mo, V, Ti, Zr, etc.

[0130] As a non-restrictive enumeration, the values ​​of d include, but are not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.3, 1.5, 1.8, or 2.

[0131] As a non-restrictive enumeration, the values ​​of e include, but are not limited to, 0.8, 0.85, 0.9, or 0.95.

[0132] As a non-restrictive enumeration, the values ​​of f include, but are not limited to, 0.1, 0.5, 1, 5, 10, 15, or 20.

[0133] More preferably, the sodium-containing Prussian material is Na h Mn[Fe(CN)6] i ·jH2O (0<h≤2,0<i≤1,0<j≤10) or Na h Fe[Fe(CN)6] i ·jH2O (0<h≤2, 0<i≤1, 0<j≤10).

[0134] As a non-restrictive enumeration, the values ​​of h include, but are not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.3, 1.5, 1.8, or 2.

[0135] As a non-restrictive enumeration, the values ​​of i include, but are not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0136] As a non-restrictive enumeration, the values ​​of j include, but are not limited to, 0.1, 0.5, 1, 3, 5, 8, or 10.

[0137] In some embodiments, the sodium-containing phosphate has the chemical formula Na3(GO). 1-k PO4)2F 1+2k 0≤k≤1, G is selected from at least one of Al, V, Ge, Fe, Ga, and more preferably, the sodium-containing phosphate is Na3(VPO4)2F3 or Na3(VOPO4)2F.

[0138] As a non-restrictive list, the values ​​of k include, but are not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.

[0139] In other embodiments, the sodium-containing phosphate has the chemical formula Na2JPO4F, where J is selected from at least one of Fe and Mn. More preferably, the sodium-containing phosphate is Na2FePO4F or Na2MnPO4F.

[0140] In some embodiments, sodium-containing titanate materials include, but are not limited to, Na2Ti3O7 and Na2Ti6O7. 13 Na4Ti5O 12 At least one of NaTi2(PO4)3, etc.

[0141] In some embodiments, the sodium-containing sulfate has the chemical formula Na2Z(SO4)2·2H2O, where Z can be selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0142] In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is disposed on the surface of the positive electrode current collector.

[0143] In some embodiments, the positive current collector is selected from a metallic material that can conduct electrons. Preferably, the positive current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0144] In some embodiments, the above-mentioned positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0145] In some embodiments, the positive electrode binder includes, but is not limited to, at least one of the following: polyvinylidene fluoride, copolymers of polyvinylidene fluoride, polytetrafluoroethylene, copolymers of polyvinylidene fluoride and hexafluoropropylene, copolymers of tetrafluoroethylene and hexafluoropropylene, copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ethers, copolymers of ethylene and tetrafluoroethylene, copolymers of polyvinylidene fluoride and tetrafluoroethylene, copolymers of polyvinylidene fluoride and trifluoroethylene, copolymers of polyvinylidene fluoride and trichloroethylene, copolymers of polyvinylidene fluoride and fluorinated vinylides, copolymers of polyvinylidene fluoride and hexafluoropropylene and tetrafluoroethylene, thermoplastic polyimide, thermoplastic resins such as polyethylene and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0146] In some embodiments, the positive electrode conductive agent includes, but is not limited to, at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0147] In some embodiments, the negative electrode includes a negative electrode material layer, which includes a negative electrode active material. The type and content of the negative electrode active material are not particularly limited and can be selected according to actual needs.

[0148] In some preferred embodiments, the secondary battery is a lithium-ion battery, and its negative electrode active material includes, but is not limited to, at least one of carbon-based negative electrodes, silicon-based negative electrodes, tin-based negative electrodes, and lithium negative electrodes. Specifically, carbon-based negative electrodes may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; silicon-based negative electrodes may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials; tin-based negative electrodes may include tin, tin-carbon, tin-oxygen, and tin metal compounds; and lithium negative electrodes may include metallic lithium or lithium alloys. The lithium alloy may specifically be at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys.

[0149] In some preferred embodiments, the secondary battery is a sodium-ion battery, and its negative electrode active material includes, but is not limited to, at least one of metallic sodium, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with sodium. The alloy material may also be selected from at least one of Si, Ge, Sn, Pb, and Sb combined with C; the graphite may be selected from at least one of artificial graphite, natural graphite, and modified graphite; the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0150] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer is disposed on the surface of the negative electrode current collector. The material of the negative electrode current collector can be the same as that of the positive electrode current collector, and will not be described again here.

[0151] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, negative electrode binder, and negative electrode conductive agent are blended to obtain the negative electrode material layer. The negative electrode binder and negative electrode conductive agent can be the same as the positive electrode binder and positive electrode conductive agent, respectively, and will not be described in detail here.

[0152] In some embodiments, the secondary battery also includes a separator located between the positive and negative electrodes.

[0153] In some embodiments, the diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a nonwoven fabric, an inorganic-organic composite diaphragm, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0154] The following non-limiting embodiments further illustrate certain features of the present technology.

[0155] I. Performance Testing

[0156] 1. Lithium-ion batteries

[0157] (1) High-temperature storage performance test

[0158] The test method is as follows: After formation, the lithium-ion battery is charged at room temperature with a constant current of 1C to 4.2V, then charged with constant current and constant voltage until the current drops to 0.05C. It is then discharged at a constant current of 1C to 3.0V. The initial discharge capacity D1, initial battery volume V1, and initial impedance F1 are measured. After being fully charged, the battery is stored at 60℃ for 30 days, then discharged at 1C to 3V. The retention capacity D2, recovery capacity D3, impedance after storage F2, and battery volume V2 after storage are measured. The calculation formula is as follows:

[0159] Battery capacity retention rate (%) = Retained capacity D2 / Initial capacity D1 × 100%;

[0160] Battery capacity recovery rate (%) = Recovered capacity D3 / Initial capacity D1 × 100%;

[0161] Volume expansion rate (%) = (Battery volume after storage V2 - Initial battery volume V1) / Initial battery volume V1 × 100%;

[0162] Internal resistance growth rate (%) = Impedance after storage F2 / Initial impedance F1 × 100%.

[0163] 2. Sodium-ion battery

[0164] (1) High-temperature storage performance test

[0165] The test method is as follows: After formation, the sodium-ion battery is charged at room temperature with a constant current of 0.5C to 4.0V, then charged at a constant voltage until the current drops to 0.03C. It is then discharged at a constant current of 1C to 1.5V. The initial discharge capacity D1, initial battery volume V1, and initial impedance F1 are measured. After being fully charged, the battery is stored at 60℃ for 30 days, then discharged at 1C to 3V. The remaining capacity D2, recovered capacity D3, impedance F2 after storage, and battery volume V2 after storage are measured. The calculation formula is as follows:

[0166] Battery capacity retention rate (%) = Retained capacity D2 / Initial capacity D1 × 100%;

[0167] Battery capacity recovery rate (%) = Recovered capacity D3 / Initial capacity D1 × 100%;

[0168] Volume expansion rate (%) = (Battery volume after storage V2 - Initial battery volume V1) / Initial battery volume V1 × 100%;

[0169] Internal resistance growth rate (%) = Impedance after storage F2 / Initial impedance F1 × 100%.

[0170] (2) High-temperature cycling performance

[0171] The test method is as follows: after formation, the battery is left to stand at 45°C for 2 hours, charged at a constant current rate of 0.5C to 4.0V, then charged at a constant voltage to a current of 0.03C, and then discharged at a constant current rate of 1C to 1.5V, and cycled for 200 times.

[0172] Measure the initial discharge capacity D1, the discharge capacity D2 after 200 cycles, and the battery coulombic efficiency E.

[0173] Battery capacity retention rate (%) = Capacity D2 / Initial capacity D1 × 100%.

[0174] II. Examples and Comparative Examples

[0175] 1. Electrolyte additives

[0176] The electrolyte additives involved in each preparation example are halosubstituted trioxalic acid diborates having the structure shown in Formula I, as detailed in Table 1:

[0177] Table 1 shows the structure of halosubstituted trioxalanoate diborate according to Formula I.

[0178] Preparation Example 1

[0179] The electrolyte additive prepared in this example is compound 1, and its preparation method includes:

[0180] Lithium tetrafluoroborate (LiBF4) and bis(trimethylsilyl)oxalate were reacted in dimethyl carbonate solvent at a molar ratio of 1:1.7 at 40°C for 20 h, followed by recrystallization to obtain the product.

[0181] The products prepared in this example were subjected to NMR analysis, and the results are shown in Figure 1. As can be seen from Figure 1, the products containing compound 1 mainly consist of LiBOB (lithium dioxolane-borate), compound 1, and LiODFB (lithium difluorooxolane-borate). Specifically, the product at the 3 ppm shift is LiODFB, the product at the 3.75 ppm shift is compound 1, and the product at the 7.5 ppm shift is LiBOB. The yield of compound 1 was 70%.

[0182] Preparation Example 2

[0183] The electrolyte additive prepared in this example is compound 1, and its preparation method includes:

[0184] Lithium tetrafluoroborate (LiBF4) and bis(trimethylsilyl)oxalate were reacted in dimethyl carbonate solvent at a molar ratio of 1:1.5 at 40°C for 20 h, followed by recrystallization to obtain the product.

[0185] The NMR spectrometry results of this preparation example are shown in Figure 2. As can be seen from Figure 2, the products containing compound 1 are mainly LiBOB (lithium dioxolane-borate), compound 1, and LiODFB (lithium difluorooxolane-borate). Specifically, the product at the 3 ppm shift is LiODFB, the product at the 3.75 ppm shift is compound 1, and the product at the 7.5 ppm shift is LiBOB. The yield of compound 1 is 88%.

[0186] Preparation Example 3

[0187] The electrolyte additive prepared in this example is compound 2, and its preparation method includes:

[0188] Lithium tetrafluoroborate (NaBF4) and bis(trimethylsilyl)oxalate were reacted in dimethyl carbonate solvent at a molar ratio of 1:1.5 at 40°C for 20 h, followed by recrystallization to obtain the product.

[0189] Nuclear magnetic resonance (NMR) analysis of the prepared product confirmed that the product contained compound 2, with a yield of 80%.

[0190] Comparative Example 1 (Lithium tetrafluoroborate:silyl oxalate = 1:0.7) was prepared.

[0191] The preparation comparison example is basically the same as that in preparation example 1, except that:

[0192] The molar ratio of lithium tetrafluoroborate (LiBF4) to bis(trimethylsilyl)oxalate is 1:0.7.

[0193] The products of the comparative preparation were subjected to NMR analysis, and the results are shown in Figure 3. As can be seen from Figure 3, there are no peaks at the 3.75 ppm and 7.5 ppm shifts, and only a peak representing LiODFB (lithium difluorooxalate borate) is present at the 3 ppm shift, proving that the synthesized products are all LiODFB (lithium difluorooxalate borate).

[0194] Comparative Example 2 (Lithium tetrafluoroborate:silyl oxalate = 1:2.5) was prepared.

[0195] The preparation comparison example is basically the same as that in preparation example 1, except that:

[0196] The molar ratio of lithium tetrafluoroborate (LiBF4) to bis(trimethylsilyl)oxalate is 1:2.5.

[0197] The products of the comparative preparation were subjected to NMR analysis, and the results are shown in Figure 4. As can be seen from Figure 4, there are no peaks at the 3.75 ppm and 3 ppm shifts, and only a peak representing LiBOB (lithium dicoxalate borate) is present at the 7.5 ppm shift, proving that the synthesized products are all LiBOB (lithium dicoxalate borate).

[0198] 2. Lithium-ion batteries

[0199] In each embodiment corresponding to the lithium-ion battery, the compound 1 involved is the compound 1 prepared in the aforementioned preparation example 2.

[0200] Example 1

[0201] <Methods for preparing electrolyte>

[0202] The electrolyte preparation method of this embodiment is as follows: ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC = 1:1:0.9, and then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L. Based on the total weight of the electrolyte being 100%, 0.05% of an electrolyte additive, namely compound 1, is added.

[0203] 1) Preparation of the positive electrode: Lithium nickel cobalt manganese oxide (LiNiO) was mixed with the positive electrode active material in a mass ratio of 93:4:3. 0.5 Co 0.2 Mn 0.3 O2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) were dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry with a viscosity of 8000 mPa·s. The slurry was uniformly coated on opposite surfaces of an 18 μm thick aluminum foil, dried, rolled, and vacuum dried, and then aluminum leads were welded on using an ultrasonic welder to obtain a positive electrode sheet with a thickness of 120 μm.

[0204] 2) Preparation of the negative electrode:

[0205] Artificial graphite, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5, and then dispersed in deionized water to obtain a negative electrode slurry with a viscosity of approximately 4000 mPa·s. The slurry was coated onto the opposite surfaces of an 8 μm thick copper foil, and after drying, calendering, and vacuum drying, nickel leads were welded on using an ultrasonic welder to obtain a negative electrode plate with a thickness of 120 μm.

[0206] 3) Cell fabrication:

[0207] A three-layer PP / PE / PP separator with a thickness of 20μm is placed between the positive and negative electrodes. Then, the sandwich structure composed of the positive electrode, negative electrode and separator is wound up, and the wound body is flattened and placed in an aluminum foil packaging bag. It is then vacuum baked at 75℃ for 48h to obtain the battery cell to be injected with electrolyte.

[0208] 4) Electrolyte injection and formation of the battery cell:

[0209] In a glove box with the dew point controlled below -40°C, the electrolyte prepared in this embodiment was injected into the battery cell, vacuum sealed, and left to stand for 24 hours.

[0210] The initial formation was then performed as follows: constant current charging at 0.05C for 180 minutes, constant current charging at 0.2C to 3.95V, followed by a second vacuum sealing. Then, it was further charged at a constant current of 0.2C to 4.2V, left to stand at room temperature for 24 hours, and finally discharged at a constant current of 0.2C to 3.0V to obtain a LiNi alloy. 0.5 Co 0.2 Mn 0.3 O2 / artificial graphite lithium-ion battery.

[0211] Examples 2-15 and Comparative Examples 1-8 are basically the same as Example 1, except that the selection and dosage of some additives are different, as shown in Table 2.

[0212] It should be noted that when the electrolyte contains auxiliary additives in addition to electrolyte additives, lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the electrolyte additives and auxiliary additives are added based on 100% of the total weight of the electrolyte; when the electrolyte contains only auxiliary additives, lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and the auxiliary additives are added based on 100% of the total weight of the electrolyte.

[0213] Table 2. Selection of some substances and parameters, and high-temperature storage performance in Examples 1-15 and Comparative Examples 1-8.

[0214] Note: In Table 2, VC is vinylene carbonate, DTD is vinyl sulfate, PS is 1,3-propanesulfonyl lactone, LiODFB is lithium difluorooxalate borate, and LiBOB is lithium dioxalate borate; the structural formula of compound 2-2 is:

[0215] According to Table 2:

[0216] The test results of Examples 1-8, 12, 13 and Comparative Example 1 show that, compared with the electrolyte without the addition of the halogenated trioxalate diborate of Formula 1, adding the halogenated trioxalate diborate of Formula 1 as an electrolyte additive can effectively improve the high-temperature performance of lithium-ion batteries. The test results of Examples 1-8 and Examples 12-13 show that, with the increase of the content of the halogenated trioxalate diborate of Formula 1, the high-temperature storage performance of the lithium-ion battery first increases and then decreases. In particular, when the content of the compound is 0.5%-5.0%, the lithium-ion battery exhibits the best overall performance. When the content of halogenated trioxarate diborate in the structure shown in Formula 1 is too low, it is difficult to form a complete passivation film on the positive and negative electrode surfaces, resulting in no significant improvement in the performance of the secondary battery. When the content of halogenated trioxarate diborate in the structure shown in Formula 1 is higher than 6%, the high-temperature storage performance of the battery decreases, the rate of increase in internal resistance increases, the rate of volume expansion increases, and the high-temperature cycle performance is poor. It is speculated that the SEI film formed by excessively high content of halogenated trioxarate diborate in the structure shown in Formula 1 is thicker, which increases the cross-sectional impedance of the positive and negative electrodes and degrades the high-temperature performance of the battery.

[0217] A comparison of Examples 4 and Comparative Examples 2-8 shows that, compared to traditional vinylene carbonate (VC), vinyl sulfate (DTD), 3-propanesulfonate lactone (PS), lithium difluorooxalate borate (LiODFB), lithium dicoxalate borate (LiBOB), and compounds 2-2 and triallyl phosphate involved in this application, using the halogenated trioxalate diborate with the structure shown in Formula 1 provided in this application as an additive can significantly improve the storage performance of lithium-ion batteries at high temperatures. This indicates that the passivation film formed by the halogenated trioxalate diborate with the structure shown in Formula 1 has superior high-temperature stability and is not easily damaged under high-temperature conditions. A comparison of Examples 4 and 10 shows that the auxiliary additive and the halogenated trioxalate diborate with the structure shown in Formula 1 have a synergistic effect in improving the high-temperature storage performance of the battery.

[0218] The test results of Examples 4, 9-11, and 14-15 show that the combination of vinylene carbonate (VC), vinyl sulfate (DTD), 1,3-propanesulfonate lactone (PS), compound 2-2, and triallyl phosphate with the halosubstituted trioxamate diborate of Formula 1 can significantly improve the high-temperature storage performance of lithium-ion batteries. It is speculated that this is because VC, DTD, PS, compound 2-2, and triallyl phosphate, together with the halosubstituted trioxamate diborate of Formula 1, participate in the formation of the passivation film on the positive and negative electrode surfaces, which is beneficial to improving the quality of the passivation film.

[0219] 1. Sodium-ion battery

[0220] In each embodiment corresponding to the sodium-ion battery, compound 1 is compound 2 prepared in the aforementioned preparation example 3.

[0221] Example 16

[0222] <Methods for preparing electrolyte>

[0223] The electrolyte preparation method of this embodiment is as follows: ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC = 1:1:1, and then sodium hexafluorophosphate (NaPF6) is added to a molar concentration of 1 mol / L. Based on the total weight of the electrolyte being 100%, 0.05% of an electrolyte additive, namely compound 2, is added.

[0224] <Preparation Methods of Sodium-ion Batteries>

[0225] The electrolyte preparation method of this embodiment is as follows: ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC = 1:1:1, and then sodium hexafluorophosphate (NaPF6) is added to a molar concentration of 1 mol / L. Based on the total weight of the electrolyte being 100%, 0.05% of an additive, namely compound 1, is added.

[0226] <Preparation Methods of Sodium-ion Batteries>

[0227] The method for preparing the sodium-ion battery in this embodiment includes the following steps:

[0228] 1) Preparation of the positive electrode:

[0229] The positive electrode active material Na3V2(PO4)3, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 94:3:3, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry with a viscosity of approximately 8000 mPa·s. The slurry was uniformly coated on both sides of a 15 μm aluminum foil, and after drying, calendering, and vacuum drying, aluminum leads were welded on using an ultrasonic welder to obtain a positive electrode sheet with a thickness of 150 μm.

[0230] 2) Preparation of the negative electrode:

[0231] The negative electrode active materials, spherical hard carbon, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 97:1:1:1, and then dispersed in deionized water to obtain a negative electrode slurry with a viscosity of approximately 5000 mPa·s. The slurry was coated on both sides of a 15 μm aluminum foil, dried, calendered, and vacuum dried, and then nickel leads were welded on using an ultrasonic welder to obtain a negative electrode sheet with a thickness of 150 μm.

[0232] 3) The positive electrode, separator (20μm three-layer PP / PE / PP separator), and negative electrode are stacked in sequence, and then packaged with aluminum-plastic film, baked, injected with electrolyte, left to stand, formed, shaped with fixture, resealed, and capacity tested to complete the preparation of sodium-ion battery.

[0233] Examples 16-27 and Comparative Examples 10-15 are basically the same as Example 16, except that the selection and dosage of some additives are different. It should be noted that the additives here include the compound shown in structural formula 1 (electrolyte additive) and / or auxiliary additives. See Table 3 for details.

[0234] It should be noted that when the electrolyte contains auxiliary additives in addition to electrolyte additives, sodium hexafluorophosphate (NaPF6) is added to a molar concentration of 1 mol / L, based on 100% of the total weight of the electrolyte, along with the electrolyte additives and auxiliary additives; when the electrolyte contains only auxiliary additives, sodium hexafluorophosphate (NaPF6) is added to a molar concentration of 1 mol / L, based on 100% of the total weight of the electrolyte, along with the auxiliary additives.

[0235] Table 3. Selection of some substances and parameters, high-temperature cycling performance, and high-temperature storage performance in Examples 16-27 and Comparative Examples 10-15.

[0236] Note: In Table 3, VC is vinylene carbonate, DTD is vinyl sulfate, PS is 1,3-propanesulfonyl lactone, LiODFB is lithium difluorooxalate borate, and LiBOB is lithium dioxalate borate.

[0237] According to Table 3:

[0238] Comparing the test results of Examples 16-27 and Comparative Examples 10-15, it can be seen that, similar to the role of halogenated trioxalate diborate with the structure shown in Formula 1 in lithium-ion batteries, adding halogenated trioxalate diborate with the structure shown in Formula 1 to the electrolyte of sodium-ion batteries can also improve the high-temperature storage performance of sodium-ion batteries. This indicates that the passivation film formed by the decomposition of halogenated trioxalate diborate with the structure shown in Formula 1 on the positive and negative electrode surfaces has high high-temperature stability, improves the performance stability of positive and negative electrode materials in long-term cycling, and improves the cycle performance and storage performance of sodium-ion batteries at high temperatures. The test results from Examples 16-27 show that as the content of halogenated trioxarate diborate of the structure shown in Formula 1 increases, the high-temperature storage performance and high-temperature cycling performance of sodium-ion batteries first increase and then decrease. In particular, when the content of the compound is 0.5-5%, the sodium-ion battery has the best overall performance. This indicates that during the charge-discharge cycle of sodium-ion batteries, when the content of halogenated trioxarate diborate of the structure shown in Formula 1 in the electrolyte is 0.5-5%, the formed SEI film can be guaranteed to be regular and of moderate thickness, with better stability.

[0239] As can be seen from the test results of Examples 19 and Comparative Examples 10-15, compared with conventional film-forming additives such as vinylene carbonate (VC), vinyl sulfate (DTD) or fluoroethylene carbonate (FEC), lithium difluorooxalate borate (LiODFB) or lithium dioxalate borate (LiBOB), using halogenated trioxalate diborate with the structure shown in Formula 1 provided in this application as an additive can significantly improve the storage performance of sodium-ion batteries at high temperatures. The passivation film formed by halogenated trioxalate diborate with the structure shown in Formula 1 has better high-temperature stability.

[0240] As can be seen from the test results of Examples 19 and 24-26, the combination of vinylene carbonate (VC), vinyl sulfate (DTD), or fluorovinyl carbonate (FEC) with the halosubstituted trioxarate diborate of Formula 1 can significantly improve the high-temperature cycle performance of sodium-ion batteries. It is speculated that this is because VC, DTD, or FEC and the halosubstituted trioxarate diborate of Formula 1 jointly participate in the formation of the passivation film on the positive and negative electrode surfaces, which is beneficial to improving the quality of the passivation film.

[0241] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0242] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

An electrolyte additive, characterized in that, This includes halosubstituted trioxalic acid diborate, which has the structure shown in Formula I: Wherein, R1 and R2 are each independently selected from one of the halogens, and M + It is selected from one of the alkali metal ions. According to claim 1, the electrolyte additive, R1 and R2 are each independently selected from one of F, Cl, Br, and I; The M + It is selected from one of lithium ions, sodium ions, and potassium ions. The electrolyte additive according to claim 2 is characterized in that, The halosubstituted trioxalic acid diborate is selected from at least one of compound 1 and compound 2: A method for preparing an electrolyte additive as described in any one of claims 1 to 3, characterized in that, include: The halogen-containing alkali metal borate is reacted with an oxalate silicate compound in a solvent, followed by purification, to obtain the halogenated trioxalate diborate. The preparation method according to claim 4 is characterized in that, The halogen-containing alkali metal borates include at least one of alkali metal borates containing four halogen atoms and alkali metal borates containing two halogen atoms; and / or, The oxalate silicate compounds include at least one of bis(trimethylsilyl)oxalate and bis(triethylsilyl)oxalate. The preparation method according to claim 4 is characterized in that, The molar ratio of the halogen-containing alkali metal borate to the oxalate silicate compound is 1:a, where 1 < a < 2. The preparation method according to claim 4 is characterized in that, The solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; The preparation method according to claim 4 is characterized in that, The reaction temperature is 10-100℃, and the reaction time is 1-24h. An electrolyte, characterized in that, It includes non-aqueous organic solvents, electrolyte salts, and electrolyte additives as described in any one of claims 1 to 3. The electrolyte according to claim 9 is characterized in that, Based on the total mass of the electrolyte as 100%, the content of halogenated trioxamate diborate in the electrolyte additive is 0.05-10%; And / or, the electrolyte salt includes at least one of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt; And / or, the non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents; And / or, the electrolyte further includes auxiliary additives, which include at least one of cyclic carbonate compounds, cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, borate compounds, and nitrile compounds. The electrolyte according to claim 10 is characterized in that, The electrolyte salt is a lithium salt, and the concentration of the lithium salt in the electrolyte is 0.1-8 mol / L; or, the electrolyte salt is a sodium salt, and the concentration of the sodium salt in the electrolyte is 0.1-2 mol / L; and / or, The cyclic carbonate compounds include at least one of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and the compound shown in structural formula 2: In structural formula 2, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group; And / or, the cyclic sulfate compounds include vinyl sulfate, 4-methylvinyl sulfate, propylene sulfate, etc. At least one of them; And / or, the sulfonyl lactone compounds include 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, At least one of them; And / or, the phosphate ester compounds include saturated phosphate ester compounds and unsaturated phosphate ester compounds, the saturated phosphate ester compounds including tris(trimethylsilane) phosphate esters, and the unsaturated phosphate ester compounds including compounds shown in structural formula 3: In structural formula 3, R 31 R 32 R 32 Each is independently selected from C1-C5 saturated hydrocarbon groups, C1-C5 unsaturated hydrocarbon groups, C1-C5 halohydrocarbon groups, -Si(CH3)3, -Si(C2H5)3, or -Si(C3H7)3, and R 31 R 32 R 33 It contains at least one unsaturated hydrocarbon group that is C1-C5; And / or, the borate esters include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; And / or, the nitrile compounds include at least one of succinic anionyl nitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebacate. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The electrolyte is the electrolyte as described in any one of claims 9 to 11.

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