Non-aqueous electrolyte additive and application thereof

Abstract

This application discloses a non-aqueous electrolyte additive and its application. The non-aqueous electrolyte additive includes a compound represented by structural formula I, wherein M is selected from alkali metals, etc. The oxalate-phosphate additive of this application can reduce and form a stable SEI film at the negative electrode interface, and can also oxidize and decompose at the layered oxide positive electrode interface to form a protective layer. Electrolytes containing this additive can significantly improve the high and low temperature cycle performance of batteries, enhance the low-temperature discharge performance of batteries, suppress the increase of internal resistance of batteries during overcharge, and have a good effect on maintaining the durability and wide temperature range characteristics of batteries during use. Simultaneously, this type of oxalate-phosphate has good stability in the electrolyte and can effectively regulate the ion concentration in the electrolyte, making it easier to maintain the battery voltage within an appropriate range.

Description

Technical Field

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

[0002] Electrolyte, as one of the four key materials in secondary batteries, plays a crucial role in various battery performance characteristics. Additives also play a critical role in electrolytes; by adjusting the additives in the electrolyte, the physicochemical properties of the electrode interface can be significantly altered, such as impedance characteristics, oxidation resistance, reduction properties, interfacial film structure and stability, thereby affecting the battery's high and low temperature performance, storage performance, cycle performance, and power output performance.

[0003] For the reasons mentioned above, electrolyte formulations typically incorporate modular designs using negative electrode film-forming additives and positive electrode protectants. Traditional additives such as VC, FEC, and DTD primarily act on the negative electrode interface of the electrolyte, improving its structural stability and inhibiting solvent reduction and decomposition. Additives such as PST, MMDS, and TMSB often provide more significant protection to the positive electrode interface. Since traditional additives have different focuses, their effects, whether used alone or in combination, are not always satisfactory. Therefore, the industry has never ceased designing, developing, and utilizing novel additives. Summary of the Invention

[0004] In view of this, one objective of this application is to provide a non-aqueous electrolyte additive, which is an oxalate-phosphate additive. This additive can reduce and form a stable SEI film at the negative electrode interface, and can also oxidize and decompose at the layered oxide positive electrode interface to form a protective layer. Electrolytes containing this additive can significantly improve the high and low temperature cycle performance of batteries, enhance the low-temperature discharge performance of batteries, suppress the increase in internal resistance during overcharge, and effectively maintain the durability and wide-temperature characteristics of batteries during use. Simultaneously, this type of alkali metal salt exhibits good stability in the electrolyte and can effectively regulate the ion concentration in the electrolyte, making it easier to maintain the battery voltage within an appropriate range.

[0005] Another objective of this application is to provide a non-aqueous electrolyte.

[0006] Another object of this application is to provide a secondary battery.

[0007] To achieve the above objectives, the first aspect of this application provides a non-aqueous electrolyte additive comprising a compound represented by structural formula I:

[0008]

[0009] M is selected from one of the alkali metals.

[0010] In some embodiments, M is selected from lithium, sodium, and potassium.

[0011] In some embodiments, the compound with the structure shown in Formula I is selected from at least one of compound 1 and compound 2:

[0012]

[0013] A second aspect of this application provides a non-aqueous electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and an additive, wherein the additive comprises a first additive, which is the non-aqueous electrolyte additive described in this application.

[0014] In some embodiments, the content of the first additive is 0.05% to 10%, preferably 0.1% to 5%, based on 100% of the total mass of the non-aqueous electrolyte.

[0015] 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, preferably lithium salt or sodium salt.

[0016] In some embodiments, when the electrolyte salt is a lithium salt, the concentration of the lithium salt in the non-aqueous electrolyte is from 0.1 mol / L to 8 mol / L.

[0017] In some embodiments, when the electrolyte salt is a sodium salt, the concentration of the sodium salt in the non-aqueous electrolyte is from 0.1 mol / L to 2 mol / L.

[0018] 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.

[0019] In some embodiments, the additive further includes a second additive, which includes at least one of cyclic carbonate compounds, cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, borate compounds, and nitrile compounds.

[0020] 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 compounds represented by structural formula II.

[0021]

[0022] In structural formula II, R 21 R 22 R 23 R 24R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group.

[0023] In some embodiments, the cyclic sulfate compounds include vinyl sulfate, 4-methylvinyl sulfate, propylene sulfate, etc. At least one of them.

[0024] 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.

[0025] 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 represented by structural formula III:

[0026]

[0027] In structural formula III, R 31 R 32 R 32 Each is independently selected from one of the following: a C1-C5 saturated hydrocarbon group, a C1-C5 unsaturated hydrocarbon group, a C1-C5 halohydrocarbon group, -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.

[0028] In some embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0029] 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.

[0030] A third aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte described in this application.

[0031] The non-aqueous electrolyte additives described in this application can bring at least the following beneficial effects: The oxalate-phosphate additives of this application can reduce and form a stable SEI film at the negative electrode interface, and can also oxidize and decompose at the layered oxide positive electrode interface to form a protective layer. Electrolytes containing this additive can significantly improve the high and low temperature cycle performance of the battery, enhance the low temperature discharge performance of the battery, suppress the increase of internal resistance of the battery during overcharge, and have a good effect on maintaining the durability and wide temperature range of the battery during use. At the same time, this type of oxalate-phosphate has good stability in the electrolyte and can effectively regulate the ion concentration in the electrolyte, making it easier to maintain the battery voltage within an appropriate range.

[0032] 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

[0033] 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:

[0034] in, Figure 1 The nuclear magnetic resonance (F-spectrum) of lithium difluoropentaoxate phosphate in the product prepared by EMC as a solvent (i.e., compound 1) is shown. Detailed Implementation

[0035] 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.

[0036] 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.

[0037] 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.

[0038] <Non-aqueous electrolyte additives>

[0039] The non-aqueous electrolyte additives in this application include compounds represented by structural formula I:

[0040]

[0041] M is selected from one of the alkali metals.

[0042] For example, M is selected from lithium, sodium, potassium, etc.

[0043] As an optional example, the compound with the structure shown in Formula I is selected from at least one of Compound 1 and Compound 2:

[0044]

[0045] It should be noted that those skilled in the art, knowing the structural formula of the compound shown in structural formula I, can understand the preparation method of the above compound based on common knowledge in the field of chemical synthesis. For example, compound 1 can be prepared by the following method:

[0046] The substance was prepared by reacting a metal salt material with a silica oxalate compound in a solvent system under the action of an acidic catalyst and then purifying it by recrystallization.

[0047] For example, the acidic catalyst includes, but is not limited to, at least one of anhydrous hydrogen fluoride, oxalic acid, phosphoric acid, etc., with anhydrous hydrogen fluoride being preferred.

[0048] For example, the amount of acidic catalyst is 0.01% to 3.0% of the amount of oxalate silicate compound, including but not limited to 0.01%, 0.1%, 1.0% or 0.2%.

[0049] For example, the metal salt material includes, but is not limited to, at least one of lithium hexafluorophosphate, sodium hexafluorophosphate, potassium hexafluorophosphate, etc., preferably lithium hexafluorophosphate.

[0050] For example, oxalate silicate compounds include, but are not limited to, those mentioned above. At least one of the following, preferably

[0051] For example, the solvent includes, but is not limited to, at least one of methyl ethyl carbonate, dimethyl carbonate, ethylene carbonate, etc., preferably methyl ethyl carbonate.

[0052] For example, the molar ratio of the metal salt material to the oxalate silicate compound is 2:(4.9-5.5), including but not limited to 2:4.9, 2:5.0, 2:5.1, 2:5.2, 2:5.3, 2:5.4 or 2:5.5, preferably 2:5.2.

[0053] For example, during the heating reaction, the reaction temperature is 50-120℃, including but not limited to 50℃, 60℃, 70℃, 80℃, 90℃, 100℃ or 110℃, preferably 80℃.

[0054] For example, during the heating reaction, the reaction time is 16-21 hours, including but not limited to 16 hours, 17 hours, 18 hours, 19 hours or 20 hours, preferably 18 hours.

[0055] Taking the preparation of lithium difluoropentaoxalate phosphate (i.e., compound 1) using EMC as a solvent as an example, the specific preparation method includes the following steps:

[0056] 1. Preparation of Experimental Materials: Prepare a 2L three-necked round-bottom flask, two feeding funnels, a 500mL constant-pressure dropping funnel, and a 500mL single-necked flat-bottom flask. After drying, weigh all materials together in the glove box from the main storage area. First, add lithium hexafluorophosphate to the 500mL single-necked flat-bottom flask, then add EMC to prepare a 30wt% lithium hexafluorophosphate EMC solution. Transfer the 30wt% lithium hexafluorophosphate EMC solution into the constant-pressure dropping funnel and close all valves. Weigh the actual amount of 30wt% lithium hexafluorophosphate EMC solution used using the difference method, calculate the actual mass of lithium hexafluorophosphate, and then calculate the molar amount of silicate oxalate used (the solvent content of silicate oxalate needs to be known for the calculation). Based on the molar amount of silicate oxalate used, calculate the molar amount of acidic catalyst used. Add silicate oxalate to the 2L three-necked round-bottom flask. After adding the acidic catalyst anhydrous hydrogen fluoride, connect the 2L three-necked round-bottom flask and the constant-pressure dropping funnel. Apply negative pressure through the vacuum connector to tighten the connection of the device before removing it from the chamber.

[0057] 2. Synthesis: Place the reaction mixture in a ventilated oil pan equipped with a double-row pipe and a tail gas absorption device. Set the heating temperature to 50°C. Once the temperature reaches 50°C, begin dripping. Adjust the dripping rate according to the gas production, aiming for a gas production rate of 2 bubbles / s. Continue the reaction until gas production slows to one bubble every 3 seconds. Then, increase the temperature by 5°C or 10°C each time, depending on the gas production. The maximum temperature can be 120°C. Once gas production slows to one bubble every 3 seconds, rotate the stopcock of the vacuum pump connector to purge nitrogen gas and set the temperature to 60°C for cooling.

[0058] 3. Concentration: Remove the tail gas absorption pipe, connect the circulating water vacuum pump, connect the cold trap in the middle to collect the distillate, and start the concentration. During the process, observe the state inside the reaction flask and the amount of distillate in the cold trap. When the state inside the reaction flask and the amount of distillate in the cold trap no longer change significantly, remove the reaction apparatus from the oil pan, weigh the total weight, and subtract the weight of the reaction apparatus to know the actual weight of the sample.

[0059] 4. Purification: Operate in a glove box. Add twice the amount of crude acetonitrile to the reaction apparatus, heat and stir at 60°C until dissolved, and filter while hot using a vacuum funnel (note that the vacuum degree should not be too high, otherwise the solvent will evaporate and solids will precipitate and block the funnel filter holes). Rotate the filtrate to dryness.

[0060] 5. Enter the glove box and take samples.

[0061] The product prepared by the above method for preparing lithium difluoropentaoxate phosphate (i.e., compound 1) using EMC as a solvent was subjected to NMR testing under the conditions shown in Table A. The test results are as follows. Figure 1 As shown.

[0062] from Figure 1 It can be seen that lithium difluoropentaoxalate phosphate has appeared. Fluorine spectrum peaks ( 19 F NMR (376.5MHz, CD3CN) δ-41.05ppm, -43.21ppm).

[0063] Table A. NMR Testing Conditions

[0064] Solvent CD3CN (i.e., deuterated acetonitrile) \ Receiver gain 64 \ Dwell time 5.200 μsec DSP firmware filter sharp(standard) \ Digitizer type DRX \ Number of dummy scans 4 DS Number of scans 4 NS Loop count for‘td0’ 1 TD0 Spectral width 255.4050 SW[ppm] Spectral width 96153.846 SWH[Hz] Acquisition time 0.6815744 AQ[sec] Fid resolution 1.467191 FIDRES[Hz] Filter width 240000000.000 FW[Hz] Observe nucleus 19F NUC1 Transmitter frequency offset -22464.88 01[Hz] Transmitter frequency offset -59.668 01P[ppm] Transmitter frequency 376.4759013 SFO1[MHz] Basic transmitter frequency 376.4983662 BF1[MHz]

[0065] In the embodiments of this application, the preparation method of compound 2 is similar to that of compound 1, except that the metal salt material is replaced with the corresponding sodium metal salt.

[0066] The non-aqueous electrolyte additive of this application embodiment can bring at least the following beneficial effects:

[0067] The oxalate-phosphate additives of this application can reduce and form a stable SEI film at the negative electrode interface, and can also oxidize and decompose at the layered oxide positive electrode interface to form a protective layer. Electrolytes containing this additive can significantly improve the high and low temperature cycle performance of the battery, enhance its low-temperature discharge performance, suppress the increase in internal resistance during overcharge, and effectively maintain the battery's durability and wide-temperature characteristics. Simultaneously, this type of oxalate-phosphate exhibits good stability in the electrolyte, allowing for effective regulation of the ion concentration and making it easier to maintain the battery voltage within an appropriate range.

[0068] <Non-aqueous electrolyte>

[0069] The non-aqueous electrolyte of this application includes a non-aqueous organic solvent, an electrolyte salt, and an additive. The additive includes a first additive, which is the non-aqueous electrolyte additive of this application.

[0070] In some embodiments, the content of the first additive is 0.05% to 10% based on the total mass of the non-aqueous electrolyte, 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%. When the content of the first additive (i.e., the compound shown in structural formula I) is within the above range, it can effectively maintain the stability of the film formed on the electrode surface and improve battery performance. If the content of the first additive is too low (e.g., below 0.05%), it is difficult to produce a significant improvement effect on battery performance. If the content of the first additive is too high (e.g., above 10%), it may affect the function of other substances in the electrolyte due to the excessive decomposition products.

[0071] As a preferred example, the content of the first additive is 0.1% to 5% based on 100% of the total mass of the non-aqueous electrolyte.

[0072] In some embodiments, the electrolyte salt includes, but is not limited to, at least one of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt, and aluminum salt.

[0073] As a preferred example, the electrolyte salt is a lithium salt.

[0074] For example, lithium salts include, but are 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.

[0075] For example, lower aliphatic carboxylic acid lithium salts include, but are not limited to, at least one of lithium acetate, lithium formate, etc.

[0076] As another preferred example, the electrolyte salt is a sodium salt.

[0077] For example, the sodium salt includes 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), etc.

[0078] In non-aqueous electrolytes, alkali metal ions formed by the dissociation of electrolyte salts undergo intercalation and deintercalation between the positive and negative electrodes to complete charge-discharge cycles. The concentration of the electrolyte salt directly affects the transfer rate of alkali metal ions, which in turn affects the potential change at 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.

[0079] In some embodiments, when the electrolyte salt is a lithium salt, the concentration of the lithium salt in the non-aqueous electrolyte is from 0.1 mol / L to 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, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, 7 mol / L, 7.5 mol / L, or 8 mol / L.

[0080] As a preferred example, when the electrolyte salt is a lithium salt, the concentration of the lithium salt in the non-aqueous electrolyte is from 0.5 mol / L to 2.5 mol / L.

[0081] In some embodiments, when the electrolyte salt is a sodium salt, the concentration of the sodium salt in the non-aqueous electrolyte is from 0.1 mol / L to 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.

[0082] As a preferred example, when the electrolyte salt is a sodium salt, the concentration of the sodium salt in the non-aqueous electrolyte is from 0.4 mol / L to 1.5 mol / L.

[0083] 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.

[0084] In some embodiments, the ether solvent includes cyclic ethers or chain ethers.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] In some embodiments, carbonate solvents include, but are not limited to, cyclic carbonates or chain carbonates.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] In some embodiments, the additive further includes a second additive, which includes, but is not limited to, at least one of cyclic carbonate compounds, cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, borate ester compounds, and nitrile compounds.

[0094] 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 compounds represented by structural formula II.

[0095]

[0096] In structural formula II, 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.

[0097] By way of a non-limiting example, C1-C5 groups include, but are not limited to, methyl, trifluoromethyl, ethyl, vinyl, propyl, or allyl groups.

[0098] As a preferred example, the compounds represented by structural formula II include, but are not limited to, at least one of the compounds shown in compounds 2-1 to 2-6 below:

[0099]

[0100] In some embodiments, cyclic sulfate compounds include vinyl sulfate, 4-methylvinyl sulfate, propylene sulfate, etc. At least one of them.

[0101] In some embodiments, sulfonyl lactone compounds include 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, etc. At least one of them.

[0102] 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 represented by structural formula III:

[0103]

[0104] In structural formula III, R 31 R 32 R 32 Each is independently selected from one of the following: a C1-C5 saturated hydrocarbon group, a C1-C5 unsaturated hydrocarbon group, a C1-C5 halohydrocarbon group, -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.

[0105] 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.

[0106] 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.

[0107] 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, propenyl, 2-methylpropene, 1,4-butadienyl, propynyl, etc. C1-C5 haloalkanes include, but are not limited to, trifluoromethyl, 2,2,2-trifluoroethyl, 3,3,3-trifluoropropyl, hexafluoroisopropyl, etc.

[0108] As a preferred example, the compounds represented by structural formula III include, but are not limited to, at least one of the following: triargyl phosphate (TPP), diargylmethyl phosphate, diargylethyl phosphate, diargylpropyl phosphate, diargyltrifluoromethyl phosphate, diargyl-2,2,2-trifluoroethyl phosphate, diargyl-3,3,3-trifluoropropyl phosphate, diargylhexafluoroisopropyl 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.

[0109] In some embodiments, the borate ester compounds include, but are not limited to, at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0110] 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.

[0111] In the embodiments of this application, the aforementioned second additive can be understood as an auxiliary additive in the non-aqueous electrolyte. Taking the total mass of the electrolyte as 100%, the mass content of the second additive in the electrolyte will vary depending on the type of the second additive. Specifically, in some embodiments, when the second 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 0.1-6%, more preferably 0.1-3.5%. In other embodiments, when fluoroethylene carbonate is selected as the auxiliary additive, the content of fluoroethylene carbonate is 0.05-35% based on the total mass of the non-aqueous electrolyte as 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 35%.

[0112] In the non-aqueous electrolyte of the embodiments of this application, compared with single addition or combination of other existing additives, when the compound shown in structural formula I (i.e. the first additive) is added together with the second additive, it shows a significant synergistic effect in improving battery performance. This indicates that the compound shown in structural formula I and the second additive can form a film together on the electrode surface to compensate for the film formation defects of single addition, resulting in a dense, uniform and more stable passivation film, improving the transport efficiency of lithium ions, etc., and improving the high-temperature performance of the battery.

[0113] Secondary batteries

[0114] The secondary battery of this application embodiment includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte of this application embodiment.

[0115] In the embodiments of this application, the secondary battery, due to the use of the non-aqueous electrolyte of this application embodiment, 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.

[0116] 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.

[0117] 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.).

[0118] 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.

[0119] 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.

[0120] 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 Co0.2 Mn 0.2 Al 0.1 O2, LiNi 0.5 Co 0.2 Al 0.3 At least one of O2.

[0121] 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.

[0122] 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≤5, 2≤b≤6, and 6≤c≤15.

[0123] 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).

[0124] 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.

[0125] 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。

[0126] 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.

[0127] 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.

[0128] As a non-restrictive enumeration, the values ​​of e include, but are not limited to, 0.8, 0.85, 0.9, or 0.95.

[0129] 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.

[0130] 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).

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] For example, 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, polyethylene and polypropylene, etc.; acrylic resins; and styrene-butadiene rubber, etc.

[0143] For example, 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.

[0144] 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.

[0145] In a preferred embodiment, the aforementioned 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, the carbon-based negative electrode may include, but is not limited to, at least one of graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres; the silicon-based negative electrode may include, but is not limited to, at least one of silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials; the tin-based negative electrode may include, but is not limited to, at least one of tin, tin-carbon, tin oxide, and tin metal compounds; and the lithium negative electrode may include metallic lithium or lithium alloys. Specifically, the lithium alloy may be at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys.

[0146] In a preferred embodiment, 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.

[0147] 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.

[0148] 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, the negative electrode binder, and the negative electrode conductive agent are blended to obtain the negative electrode material layer. The negative electrode binder and the negative electrode conductive agent can be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described in detail here.

[0149] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0150] The aforementioned diaphragm can be any existing conventional diaphragm, such as a ceramic diaphragm, polymer diaphragm, non-woven fabric, 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.

[0151] The following non-limiting embodiments further illustrate certain features of the present technology.

[0152] I. Performance Testing

[0153] 1. Lithium-ion batteries

[0154] (1) High-temperature storage performance test

[0155] The test method is as follows: After formation, the lithium-ion battery is charged at room temperature (25℃) 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 battery's retention capacity D2, recovery capacity D3, impedance after storage F2, and battery volume V2 after storage are measured. The calculation formula is as follows:

[0156] Battery capacity retention rate (%) = Retained capacity D2 / Initial capacity D1 × 100%;

[0157] Battery capacity recovery rate (%) = Recovered capacity D3 / Initial capacity D1 × 100%;

[0158] Volume expansion rate (%) = (Battery volume after storage V2 - Initial battery volume V1) / Initial battery volume V1 × 100%;

[0159] Internal resistance growth rate (%) = Impedance after storage F2 / Initial impedance F1 × 100%.

[0160] 2. Sodium-ion battery

[0161] (1) High-temperature storage performance test

[0162] The test method is as follows: After formation, the sodium-ion battery is charged at room temperature (25℃) 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:

[0163] Battery capacity retention rate (%) = Retained capacity D2 / Initial capacity D1 × 100%;

[0164] Battery capacity recovery rate (%) = Recovered capacity D3 / Initial capacity D1 × 100%;

[0165] Volume expansion rate (%) = (Battery volume after storage V2 - Initial battery volume V1) / Initial battery volume V1 × 100%;

[0166] Internal resistance growth rate (%) = Impedance after storage F2 / Initial impedance F1 × 100%.

[0167] (2) High-temperature cycling performance

[0168] 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.

[0169] Measure the initial discharge capacity D1, the discharge capacity D2 after 200 cycles, and the battery coulombic efficiency E.

[0170] Battery capacity retention rate (%) = Capacity D2 / Initial capacity D1 × 100%.

[0171] II. Examples and Comparative Examples

[0172] The compounds used in the following examples are selected from Table 1:

[0173] Table 1 shows the compounds involved in each embodiment.

[0174]

[0175] 1. Lithium-ion batteries

[0176] <Preparation Methods of Non-Aqueous Electrolytes>

[0177] The preparation method of the non-aqueous electrolyte 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 lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L. Based on the total weight of the non-aqueous electrolyte being 100%, additives (i.e., the first additive and / or the second additive in Table 2) are added.

[0178] <Preparation Methods of Lithium-ion Batteries>

[0179] The method for preparing a lithium-ion battery includes the following steps:

[0180] 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 0.3O2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) were dispersed in 10 mL of N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry was uniformly coated on opposite sides of an aluminum foil with a thickness of 20 μm. After drying, rolling, and vacuum drying, aluminum leads were welded on using an ultrasonic welder to obtain a positive electrode sheet with a thickness of 126 μm.

[0181] 2) Preparation of the negative electrode:

[0182] 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 10 mL of deionized water to obtain a negative electrode slurry. The slurry was coated on opposite sides of a 10 μm thick copper foil, dried, calendered, and vacuum dried. Nickel leads were then welded on using an ultrasonic welder to obtain a negative electrode plate with a thickness of 130 μm.

[0183] 3) Cell fabrication:

[0184] 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.

[0185] 4) Electrolyte injection and formation of the battery cell:

[0186] In a glove box where the dew point is controlled below -40°C, the electrolyte prepared above is injected into the battery cell, vacuum sealed, and left to stand for 24 hours.

[0187] 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.

[0188] Non-aqueous electrolytes and lithium-ion batteries of Examples 1-15 and Comparative Examples 1-7 were prepared according to the above method. The types and contents of each additive in the preparation process of non-aqueous electrolytes of Examples 1-15 and Comparative Examples 1-7, as well as the electrochemical performance test results, are shown in Table 2.

[0189] Table 2. Types and contents of non-aqueous electrolyte additives in Examples 1-15 and Comparative Examples 1-7, and test results of battery electrochemical performance.

[0190]

[0191]

[0192] Note: In Table 2, VC is vinylene carbonate, DTD is vinyl sulfate, PS is 1,3-propanesulfonyl lactone, TPP is triargyl phosphate, LiODFP is lithium difluorodioxane, and the structural formulas of compounds 2-5 are as follows:

[0193] According to Table 2:

[0194] The test results from Examples 1-8, 12-13, and Comparative Example 1 show that, compared to non-aqueous electrolytes without the addition of the compound shown in Structural Formula I (i.e., the first additive), adding the compound shown in Structural Formula I as an additive to the non-aqueous electrolyte can effectively improve the high-temperature performance of lithium-ion batteries. The test results from Examples 1-8 and 12-13 show that, with the increase of the content of the compound shown in Structural Formula I, 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. This indicates that during the charging and discharging process of lithium-ion batteries, when the content of the compound shown in Structural Formula I in the electrolyte is 0.5%-5.0%, it can ensure that the formed SEI film is regular, of moderate thickness, and has better stability. When the content of the compound shown in Structural Formula I is too low (for example, the content of the compound shown in Structural Formula I in Comparative Example 1 is 0), it is difficult to form a complete passivation film on the surface of the positive and negative electrodes, and the performance improvement of the lithium-ion battery is not significant. When the content of the compound shown in Structural Formula I is higher than 6%, the high-temperature storage performance of the battery decreases, the rate of increase in battery internal resistance increases, and the thickness expansion rate increases. It is speculated that the SEI film formed by the excessively high content of the compound shown in Structural Formula I is thicker, which increases the cross-sectional impedance of the positive and negative electrodes and degrades the high-temperature performance of the battery.

[0195] A comparison of Example 4 and Comparative Examples 2-4 shows that, compared to traditional vinylene carbonate (VC), vinyl sulfate (DTD), and 1,3-propanesulfonate lactone (PS), using the compound shown in Structural Formula I 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 compound shown in Structural Formula I has superior high-temperature stability and is not easily damaged under high-temperature conditions. A comparison of Example 4 and Example 10 shows that the auxiliary additive (i.e., the second additive) and the compound shown in Structural Formula I have a synergistic effect in improving the high-temperature storage performance of the battery.

[0196] As can be seen from the test results of Examples 4 and 9-11, the combination of vinylene carbonate (VC), vinyl sulfate (DTD), or 1,3-propanesulfonate lactone (PS) with the compound shown in Structural Formula I can significantly improve the high-temperature storage performance of lithium-ion batteries. It is speculated that this is because VC, DTD, PS and the compound shown in Structural Formula I 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.

[0197] The test results of Example 4 and Comparative Example 7 show that, compared with the electrolyte containing lithium difluorodioxanone phosphate, adding lithium difluoropentaoxanone phosphate with the structure of compound 1 as an electrolyte additive can effectively improve the high-temperature performance of lithium-ion batteries, enhance the high-temperature storage performance of the batteries, reduce the increase rate of internal resistance and the decrease in volume expansion rate, indicating that the passivation film formed by lithium difluoropentaoxanone phosphate has better high-temperature stability.

[0198] 2. Sodium-ion battery

[0199] <Preparation Methods of Non-Aqueous Electrolytes>

[0200] The preparation method of the non-aqueous electrolyte 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 non-aqueous electrolyte being 100%, additives (i.e., the first additive and / or the second additive in Table 3) are added.

[0201] <Preparation Methods of Sodium-ion Batteries>

[0202] The preparation method of a sodium-ion battery includes the following steps:

[0203] 1) Preparation of the positive electrode sheet: 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 93:4:3, and then dispersed in 10 mL of N-methyl-2-pyrrolidone (NMP) to obtain the positive electrode slurry. The slurry was uniformly coated on the opposite surfaces of an aluminum foil with a thickness of 20 μm. After drying, rolling, and vacuum drying, aluminum leads were welded on using an ultrasonic welder to obtain the positive electrode sheet with a thickness of 160 μm.

[0204] 2) Preparation of the negative electrode:

[0205] 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 10 mL of deionized water to obtain a negative electrode slurry. The slurry was coated on opposite sides of an aluminum foil with a thickness of 20 μm, dried, calendered, and vacuum dried, and then aluminum leads were welded on using an ultrasonic welder to obtain a negative electrode sheet with a thickness between 80 and 300 μm.

[0206] 3) The positive electrode, separator (a three-layer PP / PE / PP separator with a thickness of 25μm) and negative electrode are stacked in sequence, and then packaged with aluminum-plastic film, baked, injected with electrolyte, left to stand, formed, shaped with fixtures, sealed again, and tested for capacity to complete the preparation of sodium-ion batteries.

[0207] Non-aqueous electrolytes and sodium-ion batteries for Examples 16-29 and Comparative Examples 8-14 were prepared according to the above method. The types and contents of each additive and the electrochemical performance test results during the preparation of non-aqueous electrolytes for Examples 16-29 and Comparative Examples 8-14 are shown in Table 3.

[0208] Table 3. Types and contents of non-aqueous electrolyte additives in Examples 16-29 and Comparative Examples 8-14, and test results of battery electrochemical performance.

[0209]

[0210] Note: In Table 3, VC is vinylene carbonate, DTD is vinyl sulfate, FEC is fluoroethylene carbonate, TPP is propargyl phosphate, NaODFP is sodium difluorodioxarate, and the structural formulas of compounds 2-5 are as follows:

[0211] According to Table 3:

[0212] Comparing the test results of Examples 15-29 and Comparative Examples 8-14, it can be seen that, similar to the role of the compound shown in Structural Formula I (i.e., the first additive) in lithium-ion batteries, adding the compound shown in Structural Formula I to the non-aqueous 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 the compound shown in Structural Formula I on the positive and negative electrode surfaces has high high-temperature stability, improving the performance stability of the positive and negative electrode materials during long-term cycling, and enhancing the cycle performance and storage performance of sodium-ion batteries at high temperatures. From the test results of Examples 15-23 and 27, it can be seen that as the content of the compound shown in Structural Formula I increases, the high-temperature storage performance and high-temperature cycle 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 exhibits the best overall performance. This indicates that during the charge-discharge cycle of sodium-ion batteries, when the content of the compound shown in Structural Formula I in the electrolyte is 0.5%-5%, it can ensure that the formed SEI film is regular and of moderate thickness, with better stability.

[0213] As can be seen from the test results of Example 19 and Comparative Examples 8-11, compared with conventional film-forming additives such as vinylene carbonate (VC), vinyl sulfate (DTD) or fluoroethylene carbonate (FEC), using the compound shown in Structural Formula I provided in this application as an additive can more significantly improve the storage performance of sodium-ion batteries at high temperatures, and the passivation film formed by the compound shown in Structural Formula I has better high-temperature stability.

[0214] The test results of Examples 19 and 24-26 show that using vinylene carbonate (VC), vinyl sulfate (DTD), or fluoroethylene carbonate (FEC) in combination with the compound shown in Structural Formula I can significantly improve the high-temperature cycle performance of sodium-ion batteries. It is speculated that this is because VC, DTD, or FEC, together with the compound shown in Structural Formula I, 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.

[0215] The test results of Example 19 and Comparative Example 14 show that, compared with the electrolyte containing sodium difluorodioxanoate phosphate, adding sodium difluoropentaoxanoate phosphate with the structure of Compound 2 as an electrolyte additive can effectively improve the high-temperature performance of lithium-ion batteries, enhance the high-temperature storage performance of the batteries, reduce the increase rate of internal resistance and the decrease in volume expansion rate. This indicates that the passivation film formed by sodium difluoropentaoxanoate phosphate with the structure shown in Compound 2 has superior high-temperature stability.

[0216] 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.

[0217] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0218] 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

1. A non-aqueous electrolyte additive, characterized in that, Including compounds represented by structural formula I: M is selected from one of the alkali metals.

2. The non-aqueous electrolyte additive according to claim 1, characterized in that, M is selected from lithium, sodium, and potassium.

3. The non-aqueous electrolyte additive according to claim 2, characterized in that, The compound with the structure shown in Formula I is selected from at least one of compound 1 and compound 2:

4. A non-aqueous electrolyte, characterized in that, It includes a non-aqueous organic solvent, an electrolyte salt, and an additive, wherein the additive includes a first additive, which is the non-aqueous electrolyte additive according to any one of claims 1 to 3.

5. The non-aqueous electrolyte according to claim 4, characterized in that, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the first additive is 0.05% to 10%; And / or, the electrolyte salt includes at least one selected from lithium, sodium, potassium, magnesium, zinc, and aluminum salts; 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.

6. The non-aqueous electrolyte according to claim 5, characterized in that, Based on the total mass of the non-aqueous electrolyte as 100%, the content of the first additive is 0.1% to 5%; And / or, the electrolyte salt is a lithium salt or a sodium salt.

7. The non-aqueous electrolyte according to claim 6, characterized in that, When the electrolyte salt is a lithium salt, the concentration of the lithium salt in the non-aqueous electrolyte is from 0.1 mol / L to 8 mol / L; And / or, when the electrolyte salt is a sodium salt, the concentration of the sodium salt in the non-aqueous electrolyte is from 0.1 mol / L to 2 mol / L.

8. The non-aqueous electrolyte according to claim 4, characterized in that, The additive further includes a second additive, which includes at least one of cyclic carbonate compounds, cyclic sulfate compounds, sulfonyl lactone compounds, phosphate compounds, borate compounds, and nitrile compounds.

9. The non-aqueous electrolyte according to claim 8, characterized in that, The cyclic carbonate compounds include at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and compounds represented by structural formula II. In structural formula II, 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, C1-C5 group; and / or, The cyclic sulfate compounds include vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate. At least one of them; and / or, The sulfonyl lactone compounds include 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 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, wherein the saturated phosphate ester compounds include tris(trimethylsilane) phosphate esters, and the unsaturated phosphate ester compounds include compounds represented by structural formula III: In structural formula III, R 31 R 32 R 32 Each is independently selected from one of the following: a C1-C5 saturated hydrocarbon group, a C1-C5 unsaturated hydrocarbon group, a C1-C5 halohydrocarbon group, -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.

10. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte is a non-aqueous electrolyte as described in any one of claims 4 to 9.

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