Electrolyte, battery, battery pack and electric equipment

Abstract

The invention provides an electrolyte, a battery, a battery pack and electric equipment. The electrolyte comprises a sulfur-containing cyano compound; the structural formula of the thiocyano-containing compound is R-SCN; wherein R comprises at least one of alkyl, heteroatom group substituted alkyl, halogenated heteroatom group substituted alkyl, aryl, heteroatom group substituted aryl and halogenated heteroatom group substituted aryl. The ionic conductivity of an electrode-electrolyte interface can be improved, and the interface impedance of the battery is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrolyte battery, a battery pack and electrical equipment containing a thiocyanate compound. Background Art

[0002] In existing technologies, sulfate / sulfonate additives are often added to electrolytes. These additives decompose into a series of inorganic / organic lithium sulfate or lithium sulfite salts on the negative electrode surface, improving the solid electrolyte interface and effectively passivating graphite. Commonly used sulfate / sulfonate additives include propylene sulfite, vinyl sulfate, and methylene methanedisulfonate.

[0003] However, the lithium sulfate or lithium sulfite salts generated by sulfate / sulfonate additives on the negative electrode surface have low ionic conductivity, which can easily lead to slow ion transport, reduce the ionic conductivity of the electrode-electrolyte interface, and increase the interfacial impedance of the battery.

[0004] Therefore, there is an urgent need for an electrolyte to improve the interfacial impedance of the battery. Summary of the Invention

[0005] In order to solve the above problems, an embodiment of the present invention provides an electrolyte, which includes a thiocyanate-containing compound, wherein the structural formula of the thiocyanate-containing compound is R-SCN, wherein R includes at least one of an alkyl group, an alkyl group substituted with a heteroatom group, an alkyl group substituted with a halogenated heteroatom group, an aromatic group, an aromatic group substituted with a heteroatom group, and an aromatic group substituted with a halogenated heteroatom group.

[0006] Optionally, the thiocyanate-containing compound includes at least one of methyl thiocyanate, ethyl thiocyanate, n-propyl thiocyanate, isopropyl thiocyanate, butyl thiocyanate, (4,4,4-trifluorobutyl) thiocyanate, 1,1-nitrothiocyanatocyclohexane, and benzyl thiocyanate, preferably at least one of methyl thiocyanate, (4,4,4-trifluorobutyl) thiocyanate, and 1,1-nitrothiocyanatocyclohexane.

[0007] Optionally, the mass percentage of the thiocyanate-containing compound to the total mass of the electrolyte is 0.2 wt% to 5 wt%, preferably 0.2 wt% to 2 wt%.

[0008] Optionally, the electrolyte further includes an organic solvent, and the organic solvent includes at least one of ethylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, and vinylene carbonate.

[0009] Optionally, the organic solvent includes ethylene carbonate, dimethyl carbonate and diethyl carbonate, wherein the ethylene carbonate accounts for 20 vol% to 50 vol% of the total volume of the organic solvent, the dimethyl carbonate accounts for 30 vol% to 60 vol% of the total volume of the organic solvent, and the diethyl carbonate accounts for 20 vol% to 50 vol% of the total volume of the organic solvent.

[0010] Optionally, the organic solvent includes ethylene carbonate, dimethyl carbonate and ethyl acetate; wherein the ethylene carbonate accounts for 20 vol% to 30 vol% of the total volume of the organic solvent, the dimethyl carbonate accounts for 40 vol% to 60 vol% of the total volume of the organic solvent, and the ethyl acetate accounts for 10 vol% to 40 vol% of the total volume of the organic solvent.

[0011] Optionally, the electrolyte further includes a lithium salt; wherein the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorooxalatoborate, and lithium tetrafluoroborate.

[0012] Optionally, the molar concentration of the lithium salt is 0.5 to 3 mol / L.

[0013] Optionally, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the molar ratio between the lithium hexafluorophosphate and the lithium bis(fluorosulfonyl)imide is (0.1-3):1.

[0014] Optionally, the lithium salt includes lithium tetrafluoroborate and lithium bis(oxalatoborate), and the molar ratio between the lithium tetrafluoroborate and the lithium bis(oxalatoborate) is (0.1-3):1.

[0015] An embodiment of the present invention further provides a battery, which includes the electrolyte as described in the embodiment of the present invention.

[0016] An embodiment of the present invention further provides a battery pack, comprising the battery as described above.

[0017] An embodiment of the present invention further provides an electrical device, which includes the battery or the battery pack as described above.

[0018] The thiocyanate-containing electrolyte provided by the embodiment of the present invention, wherein the thiocyanate group (-SCN) in the thiocyanate-containing compound has a lower lowest unoccupied molecular orbital energy level and a higher highest occupied molecular orbital energy level, can form a positive electrode electrolyte interface film and a negative electrode electrolyte interface film at the positive electrode and the negative electrode, respectively, thereby improving the electronic conductivity of the electrode-electrolyte interface and reducing the interfacial impedance of the battery. DETAILED DESCRIPTION

[0019] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with specific embodiments.

[0020] Sulfate / sulfonate additives are commonly added to electrolytes to improve the solid electrolyte interface and effectively passivate graphite. However, the lithium sulfate or lithium sulfite salts generated by these commonly used sulfate / sulfonate additives on the negative electrode surface have low ionic conductivity, which can easily slow ion transport, reduce the ionic conductivity at the electrode-electrolyte interface, and increase the interfacial impedance of the battery.

[0021] Existing technologies usually use technical means such as introducing highly electronegative groups (such as fluorine atoms) into sulfate molecules and grafting lithium sulfonate functional groups to improve the above problems, but there are still disadvantages such as the negative electrode electrolyte interface film is too thick, resulting in unstable positive electrode electrolyte interface film.

[0022] The present invention provides an electrolyte, which includes a thiocyanate-containing compound; the structural formula of the thiocyanate-containing compound is R-SCN, wherein R includes at least one of an alkyl group, an alkyl group substituted by a heteroatom group, an alkyl group substituted by a halogenated heteroatom group, an aromatic group, an aromatic group substituted by a heteroatom group, and an aromatic group substituted by a halogenated heteroatom group.

[0023] Among them, heteroatoms refer to atoms other than carbon (C) and hydrogen (H) in organic molecules, including oxygen (O), nitrogen (N), sulfur (S), phosphorus (P), halogens (F, Cl, Br, I), boron (B), silicon (Si), etc.

[0024] Here, the heteroatom group refers to a functional group containing heteroatoms.

[0025] In one embodiment of the present invention, the heteroatom group is selected from at least one of hydroxyl, carbonyl, amino, carboxyl, nitro, cyano, thiol, sulfonic acid, phosphoric acid, boric acid, and halogen.

[0026] Among them, the halogenated heteroatom group is a functional group containing a heteroatom (O, N, S, P, Si, etc.), the hydrocarbon group to which it is connected is substituted by a halogen (Cl, Br, I, F), or the heteroatom itself is substituted by a halogen.

[0027] In one embodiment of the present invention, the halogenated heteroatom group is selected from at least one of a halogenated alkoxy group, a halogenated carbonyl group, a halogenated alkylamine group, an N-halogenated amide group, a sulfonyl halide group, a sulfonyl halide group, a halogenated sulfide group, a phosphoryl halide group, a phosphoryl halide group, a halogenated borane group, and a halogenated silane group.

[0028] In the present invention, the electrolyte may include a thiocyanate-containing compound, which may serve as an additive to improve battery performance.

[0029] The inventors have found through long-term research that the nitrogen atom in the cyano group carries a lone pair of electrons and has good nucleophilicity. It can form a coordination bond with the electron-deficient metal site present on the positive electrode surface of the battery, or bind to the positive electrode surface of the battery through electrostatic interaction. Compared with the solvent in the electrolyte or the anion of the lithium salt, it is preferentially adsorbed on the positive electrode surface of the battery, so that the charge distribution layer formed at the electrode and the electrolyte interface, i.e., the double electric layer, can be regulated. However, the highest occupied molecular orbital (HOMO) energy level of the nitrile compound formed by the cyano group directly connected to the R group is low, and it is difficult to participate in the cathode electrolyte interphase (CEI, Cathode Electrolyte Interphase) formation process, and it is impossible to achieve the regulation of the cathode electrolyte interphase, and it is difficult to play the nucleophilicity of the cyano group itself. When the cyano group is connected to the highly electronegative sulfur atom, it can simultaneously have a lower lowest unoccupied molecular orbital (LUMO) energy level and a lower HOMO energy level, and can form a positive electrode electrolyte interface film and a negative electrode electrolyte interface film at the positive electrode and the negative electrode respectively, thereby improving the electronic conductivity of the electrode-electrolyte interface and reducing the interfacial impedance of the battery.

[0030] Thus, the electrolyte provided by the present invention includes a thiocyanate-containing compound and has a lower LUMO energy level and a higher HOMO energy level. Wherein, LUMO refers to the molecular orbital with the lowest energy in a molecule that is not occupied by electrons. It usually represents the molecular orbital in the molecule that is most likely to accept electrons. The energy released by the molecular orbital to obtain an electron is the LUMO energy level. In the case of a lower LUMO energy level, it means that it is easier to accept electrons and can exhibit higher reduction resistance. HOMO refers to the molecular orbital with the highest energy in a molecule that is occupied by electrons. It usually represents the molecular orbital in the molecule that is most likely to lose electrons. The energy required for the molecular orbital to lose an electron is the HOMO energy level. In the case of a higher HOMO energy level, it means that it is easier to lose electrons and can exhibit higher antioxidant properties.

[0031] Therefore, the thiocyanate-containing compound can react preferentially on the surface of the battery's negative electrode, ahead of the solvent in the electrolyte. This forms a negative electrode electrolyte interface (SEI) film containing more sulfur- and / or nitrogen-containing lithium compounds, thereby improving the battery's negative electrode's ion transport capacity. Similarly, the thiocyanate-containing compound can react preferentially on the surface of the battery's positive electrode, ahead of solvents in the electrolyte, such as vinylene carbonate, ethylene carbonate, and dimethyl carbonate, to form a CEI film. Compared to the thinner SEI and CEI films formed by existing solvents, the SEI and CEI films formed by the electrolyte of the present invention can reduce the battery's interfacial impedance, thereby improving the battery's overall performance.

[0032] Furthermore, thiocyanate compounds can react with water to form amides, which can remove trace amounts of water that may remain in the electrolyte, inhibit the formation of hydrogen fluoride, and reduce the risk of transition metal dissolution. Furthermore, because amides are relatively stable, they help improve the stability of the battery's positive and negative electrode interfaces.

[0033] In one embodiment of the present invention, the thiocyanate-containing compound includes at least one of methyl thiocyanate (CH3SCN), ethyl thiocyanate (CH3CH2SCN), n-propyl thiocyanate (CH3CH2CH2SCN), isopropyl thiocyanate (CH3CH3CHSCN), butyl thiocyanate (CH3CH2CH2CH2SCN), (4,4,4-trifluorobutyl) thiocyanate (CF3CH2CH2CH2SCN), 1,1-nitrothiocyanatocyclohexane, and benzyl thiocyanate.

[0034] Among them, the structural formula of 1,1-nitrothiocyanatocyclohexane is:

[0035]

[0036] The structural formula of benzyl thiocyanate is:

[0037]

[0038] In the embodiment of the present invention, when the thiocyanate-containing compound is at least one of methyl thiocyanate (CH3SCN), ethyl thiocyanate (CH3CH2SCN), n-propyl thiocyanate (CH3CH2CH2SCN), isopropyl thiocyanate (CH3CH3CHSCN), butyl thiocyanate (CH3CH2CH2CH2SCN), (4,4,4-trifluorobutyl) thiocyanate (CF3CH2CH2CH2SCN), 1,1-nitrothiocyanatocyclohexane, and benzyl thiocyanate, its LUM The O energy level is not only lower than that of the electrolyte solvent, but also close to that of existing conventional additives. The SEI film formed on the surface of the battery negative electrode contains more sulfur- and / or nitrogen-containing lithium compounds, thereby improving the ion transport capacity of the battery negative electrode. At the same time, its HOMO energy level is higher than that of the electrolyte solvent and existing conventional additives, and can preferentially react to form a CEI film on the surface of the battery positive electrode. Compared with existing solvents and additives, a thinner SEI film is formed, and the CEI film is thinner, which can reduce the interfacial impedance of the battery, thereby improving the overall performance of the battery.

[0039] The HOMO energy levels and LUMO energy levels of the thiocyanate-containing compounds in the embodiments of the present invention are shown in Table 1; the HOMO energy levels and LUMO energy levels of conventional solvents are shown in Table 2; and the HOMO energy levels and LUMO energy levels of conventional additives are shown in Table 3.

[0040] The present invention uses first principles and density functional theory (DFT) to calculate the HOMO and LUMO energy levels of the thiocyanate-containing compound, solvent, and additive. The specific steps are as follows:

[0041] Step 1: Structural Modeling

[0042] (1) Operation: Use visualization software (such as GaussView, Avogadro) to construct the initial molecular structure:

[0043] Ⅰ. Bond length / bond angle refer to experimental crystal data (CCDC database) or standard compound parameters.

[0044] II. Molecules containing flexible chains require conformational search (molecular mechanics pre-optimization, such as the UFF force field, is recommended).

[0045] (2) Output:

[0046] Save as a coordinate file (such as .gjf or .xyz).

[0047] Step 2: Geometry Optimization

[0048] (1) Input file settings:

[0049] Ⅰ. Functional selection: Hybrid functionals B3LYP or PBE0 (balancing efficiency and accuracy) are recommended.

[0050] II. Basis set selection: medium basis set such as 6-31G(d) or def2-SVP (double ζ plus polarization).

[0051] III. Keywords:

[0052] Opt: Start geometry optimization

[0053] Freq: Subsequent frequency calculation (required)

[0054] Opt=Tight:Raise the convergence standard (force <0.0005 )

[0055] (2) Perform calculations:

[0056] Run the optimization task and output the optimized structure and energy.

[0057] Step 3: Frequency Analysis Verification

[0058] (1) Purpose: To confirm that the optimized structure is the minimum point of the potential energy surface (not a saddle point).

[0059] (2) Check the output:

[0060] Ⅰ. Search for "Imaginary frequencies" in the log file.

[0061] II. Qualification standard: The number of imaginary frequencies is 0 (if there is imaginary frequency, the structure needs to be perturbed along the direction of the imaginary frequency and then re-optimized).

[0062] (3) Additional information:

[0063] Obtain infrared / Raman vibration frequencies (for comparison with experimental spectra).

[0064] Step 4: High-precision single-point energy calculation

[0065] (1) Input file settings:

[0066] Ⅰ. Functional upgrade: Switch to the long-range correction functional CAM-B3LYP or ωB97XD (significantly improves LUMO accuracy).

[0067] II. Basis set upgrade: Large basis sets such as 6-311+G(d,p) or def2-TZVP (triple ζ plus diffusion / polarization function).

[0068] III. Solvent effect: Add implicit solvent model (such as SCRF = (Solvent = Ethanol, Method = SMD)).

[0069] IV. Key parameters:

[0070] Geom=Check: Read the optimized structure from the previous step

[0071] Integral = UltraFineGrid: Avoid numerical errors

[0072] Guess = Read: Initial guess of the wave function following the optimization step

[0073] (2) Perform calculations: run single-point energy tasks and output orbital energy.

[0074] Step 5: Extract HOMO / LUMO energy levels

[0075] (1) Locate in the output log file:

[0076] Search for the keyword "Alpha occ.eigenvalues" → the last value is the HOMO energy level (unit: Hartree).

[0077] Search for the keyword "Alpha virt.eigenvalues" → the first value is the LUMO energy level (unit: Hartree).

[0078] (2)Unit conversion:

[0079] Convert Hartree to eV: multiply by 27.211 (Example: HOMO = -0.2 Hartree → -5.44 eV).

[0080] Step 6: Energy Level Calibration (Critical Step)

[0081] The LUMO calculated by DFT is often underestimated and needs to be calibrated:

[0082] (1) Experimental value fitting method (if there is experimental data):

[0083] Calculate the offset: Δ = ε_HOMO_exp - ε_HOMO_DFT

[0084] Calibrate LUMO: ε_LUMO_corr=ε_LUMO_DFT+Δ

[0085] (2) Functional empirical calibration (no experimental data):

[0086] Functional LUMO correction value (eV) B3LYP +1.0～+1.5 PBE +1.5～+2.0 CAM-B3LYP +0.3～+0.6

[0087] 3. Error Control and Verification

[0088] (1) Basis set convergence test:

[0089] Gradually increase the basis set (e.g., 6-31G(d)→6-311++G(2df,2pd)), requiring the HOMO / LUMO change to be <0.1eV.

[0090] (2) Functional sensitivity test:

[0091] Compare the B3LYP, CAM-B3LYP, and PBE0 results and select the functional that best matches the experiment.

[0092] (3) Verification of solvent effect:

[0093] The HOMO energy level in polar solvents is usually shifted up by 0.1–0.5 eV (needs to be compared with experimental data of solutions).

[0094] Table 1

[0095]

[0096] Table 2

[0097]

[0098] Table 3

[0099]

[0100]

[0101] As can be seen from Tables 1, 2, and 3, the LUMO energy levels of the thiocyanate-containing compounds provided by the embodiments of the present invention are lower than those of commonly used solvents, such as vinylene carbonate (-0.1 eV), ethylene carbonate (0.07 eV), and diethyl carbonate (0.20 eV). The LUMO energy levels of methyl thiocyanate, butyl thiocyanate, (4,4,4-trifluorobutyl)thiocyanate, 1,1-nitrothiocyanatocyclohexane, and benzyl thiocyanate are even lower than those of dimethyl carbonate (0.15 eV) and ethyl methyl carbonate (0.18 eV), which are commonly used as solvent components in electrolytes. The LUMO energy level of 1,1-nitrothiocyanatocyclohexane is even lower than the 0.1 eV of ethyl acetate, a common solvent component in electrolytes. Furthermore, the LUMO energy level of the thiocyanate-containing compound is close to the -0.19 eV of propylene sulfite, -0.3 eV of vinyl sulfate, and -0.48 eV of methylene methanedisulfonate, commonly used electrolyte additives. Therefore, the thiocyanate-containing compound provided by the embodiments of the present invention can preferentially react on the surface of the battery's negative electrode over solvents in the electrolyte, such as vinylene carbonate, ethylene carbonate, and diethyl carbonate, to form sulfur- and / or nitrogen-containing lithium compounds, thereby improving the ion transport capacity of the battery's negative electrode interface.

[0102] Furthermore, the HOMO energy levels of the thiocyanate-containing compounds provided by the embodiments of the present invention are all greater than -7.04 eV, which is higher than those of commonly used solvents such as ethylene carbonate (-8.41 eV), diethyl carbonate (-8.07 eV), vinylene carbonate (-7.10 eV), dimethyl carbonate (-8.12 eV), ethyl methyl carbonate (-8.10 eV), and ethyl acetate (-9.03 eV). They are also higher than those of commonly used electrolyte additives such as propylene sulfite (-7.92 eV), vinyl sulfate (-7.47 eV), and methylene methanedisulfonate (-9.24 eV). Therefore, these thiocyanate-containing compounds are more easily oxidized and react preferentially on the battery's positive electrode surface over electrolyte additives such as vinylene carbonate, thereby reducing the thickness of the resulting positive electrode electrolyte interface film. In contrast, the HOMO energy levels of commonly used sulfate / sulfonate additives such as propylene sulfite and vinyl sulfate are only higher than those of some solvents such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl acetate, but still lower than those of vinylene carbonate. Vinylene carbonate preferentially decomposes to form a positive electrode electrolyte interface film rich in organic phase, making it thicker.

[0103] In one embodiment of the present invention, the thiocyanate-containing compound includes at least one of methyl thiocyanate, (4,4,4-trifluorobutyl)thiocyanate, and 1,1-nitrothiocyanatocyclohexane.

[0104] Specifically, methyl thiocyanate is readily available, has a lower cost than other thiocyanate-containing compounds, and is more readily applicable in practical production. (4,4,4-Trifluorobutyl)thiocyanate, in addition to containing a thiocyanate group, also contains a fluorine group, which can form lithium fluoride (LiF) on the electrode surface, which has excellent ion conductivity and further improves interfacial ion conduction efficiency. 1,1-Nitrothiocyanatocyclohexane, in addition to containing a thiocyanate group, also contains a nitro group, which can form lithium nitride on the electrode surface, which also has excellent ion conductivity and further improves interfacial ion conduction efficiency.

[0105] In one embodiment of the present invention, the thiocyanate-containing compound accounts for 0.2 wt% to 5 wt% of the total mass of the electrolyte.

[0106] For example, the mass percentage of the thiocyanate-containing compound in the total mass of the electrolyte can be 0.2 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or any range therebetween. When the mass percentage of the thiocyanate-containing compound in the electrolyte is within the range of 0.2 wt% to 5 wt%, both high electrode-electrolyte interface ionic conductivity and low interface impedance can be effectively achieved.

[0107] Preferably, the thiocyanate-containing compound accounts for 0.2 wt% to 2 wt% of the total mass of the electrolyte.

[0108] For example, the content of the thiocyanate-containing compound is 0.2 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, 1.5 wt%, 2 wt% or any range therebetween, based on the total mass of the electrolyte. When the mass percentage of the thiocyanate-containing compound in the electrolyte is between 0.2 wt% and 2 wt%, the ion conduction efficiency and interfacial impedance at the electrode-electrolyte interface can be improved.

[0109] In one embodiment of the present invention, the electrolyte further includes an organic solvent, and the organic solvent includes at least one of ethylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, and vinylene carbonate.

[0110] Specifically, the LUMO energy level of the above-mentioned organic solvent is higher than the LUMO energy level of the thiocyanate-containing compound, and the thiocyanate-containing compound can preferentially react at the negative electrode of the battery; at the same time, the HOMO energy level of the above-mentioned organic solvent is lower than the HOMO energy level of the thiocyanate-containing compound, and the thiocyanate-containing compound can preferentially react at the positive electrode of the battery to form a positive electrode electrolyte interface film.

[0111] In one embodiment of the present invention, the organic solvent includes ethylene carbonate, dimethyl carbonate, and diethyl carbonate; wherein ethylene carbonate accounts for 20 vol% to 50 vol% of the total volume of the organic solvent, dimethyl carbonate accounts for 30 vol% to 60 vol% of the total volume of the organic solvent, and diethyl carbonate accounts for 20 vol% to 50 vol% of the total volume of the organic solvent.

[0112] For example, ethylene carbonate accounts for 20 vol%, 22 vol%, 25 vol%, 30 vol%, 40 vol%, 50 vol%, or any range therebetween of the total volume of the organic solvent; dimethyl carbonate accounts for 30 vol%, 32 vol%, 35 vol%, 40 vol%, 50 vol%, 60 vol%, or any range therebetween of the total volume of the organic solvent; and diethyl carbonate accounts for 20 vol%, 22 vol%, 25 vol%, 30 vol%, 40 vol%, 50 vol%, or any range therebetween of the total volume of the organic solvent. Under the above ratios, the electrode-electrolyte interface has good ionic conductivity and good high-temperature stability.

[0113] For example, the volume ratio of ethylene carbonate, dimethyl carbonate, and diethyl carbonate can be 1:1:1. The electrolyte of this composition can better balance the electrode-electrolyte interface ionic conductivity and high-temperature stability.

[0114] In one embodiment of the present invention, the organic solvent includes ethylene carbonate, dimethyl carbonate, and ethyl acetate; wherein ethylene carbonate accounts for 20 vol% to 30 vol% of the total volume of the organic solvent, dimethyl carbonate accounts for 40 vol% to 60 vol% of the total volume of the organic solvent, and ethyl acetate accounts for 10 vol% to 40 vol% of the total volume of the organic solvent.

[0115] For example, ethylene carbonate accounts for 20 vol%, 21 vol%, 22 vol%, 25 vol%, 28 vol%, 30 vol%, or any range therebetween, of the total volume of the organic solvent; dimethyl carbonate accounts for 40 vol%, 42 vol%, 45 vol%, 50 vol%, 60 vol%, or any range therebetween, of the total volume of the organic solvent; and ethyl acetate accounts for 10 vol%, 12 vol%, 15 vol%, 30 vol%, 40 vol%, or any range therebetween, of the total volume of the organic solvent. Under the above ratios, the electrode-electrolyte interface has good ionic conductivity and good low-temperature fluidity.

[0116] For example, the volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl acetate can be 1:2:1. The electrode-electrolyte interface under this composition has good ionic conductivity and good low-temperature performance, and the cost can be relatively low, which is easier to use.

[0117] In one embodiment of the present invention, the electrolyte further comprises a lithium salt, and the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorooxalatoborate, and lithium tetrafluoroborate.

[0118] Specifically, lithium hexafluorophosphate (LiPF6) can have good ionic conductivity; lithium bis(fluorosulfonyl)imide (LiFSI) can have good thermal stability, can be compatible with high temperature environments, and can inhibit the formation of lithium dendrites to a certain extent; lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) can have good stability and a wider electrochemical window; lithium difluorooxalatoborate can participate in the formation of the positive electrode electrolyte interface film to generate lithium fluoride (LiF) and lithium metaborate (LiBO2); lithium tetrafluoroborate (LiBF4) has good low-temperature performance and good hydrolysis stability.

[0119] In one embodiment of the present invention, the concentration of the lithium salt is 0.5 to 3 mol / L.

[0120] For example, the concentration of lithium salt is 0.5 mol / L, 0.6 mol / L, 1 mol / L, 2 mol / L, 3 mol / L or any range between two of them. The lithium salt at the above concentration can provide more carriers (Li + ), has good ionic conductivity, and can avoid the electrolyte viscosity being too high to affect the carrier mobility and reduce the ionic conductivity.

[0121] In one embodiment of the present invention, the lithium salt includes lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, and the molar ratio between the lithium hexafluorophosphate and the lithium bisfluorosulfonyl imide is (0.1-3):1.

[0122] For example, the molar ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide can be 0.1:1, 0.2:1, 0.5:1, 0.8:1, 1:1, 2:1, 3:1, or any range therebetween. By compounding lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the above molar ratio, good high-temperature stability and ionic conductivity can be achieved.

[0123] For example, the lithium salt includes lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, and the molar ratio between lithium hexafluorophosphate and lithium bisfluorosulfonyl imide can be 1.5:1. At this molar ratio, better thermal stability and ionic conductivity can be obtained at a lower cost; the molar ratio between lithium hexafluorophosphate and lithium bisfluorosulfonyl imide can be 0.25:1. By increasing the proportion of lithium bisfluorosulfonyl imide, the lithium salt as a whole has better thermal stability and is suitable for high voltage or high temperature scenarios.

[0124] In one embodiment of the present invention, the lithium salt includes lithium tetrafluoroborate and lithium bis(oxalatoborate), and the molar ratio between lithium tetrafluoroborate and lithium bis(oxalatoborate) is (0.1-3):1.

[0125] For example, the molar ratio of lithium tetrafluoroborate to lithium bis(oxalatoborate) can be 0.1:1, 0.2:1, 0.5:1, 0.8:1, 1:1, 2:1, 3:1, or any range therebetween. By compounding lithium tetrafluoroborate and lithium bis(oxalatoborate) in the above molar ratio, good low-temperature performance and high-pressure stability can be achieved.

[0126] For example, the lithium salt includes lithium tetrafluoroborate and lithium bis(oxalatoborate), and the molar ratio between lithium tetrafluoroborate and lithium bis(oxalatoborate) can be 1:1. At this molar ratio, the low-temperature performance of lithium tetrafluoroborate can be effectively utilized to improve the ionic conductivity, and the thermal stability of lithium bis(oxalatoborate) can be utilized to obtain a lithium salt suitable for a wider temperature range, so that the battery has better low-temperature performance and high-voltage stability.

[0127] For example, the lithium salt includes lithium tetrafluoroborate and lithium bis(oxalatoborate), and the molar ratio between lithium tetrafluoroborate and lithium bis(oxalatoborate) may be 3:1. Under this molar ratio, the lithium salt may be more suitable for use in a low-temperature environment.

[0128] An embodiment of the present invention further provides a battery, which includes the electrolyte as described above.

[0129] Optionally, in one embodiment, the battery further includes a pole piece and a separator.

[0130] Among them, the electrode pieces may include positive electrode pieces and negative electrode pieces, the separator may be a diaphragm, etc., and the electrolyte plays the role of conducting ions between the electrode pieces.

[0131] Alternatively, in one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium ion transition metal oxide. The lithium ion transition metal oxide includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate.

[0132] Optionally, in one embodiment, the positive electrode plate further includes a positive electrode conductive agent, and the positive electrode conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, hard carbon, carbon fiber, and carbon microspheres.

[0133] In some embodiments of the present invention, the positive electrode plate further includes a positive electrode adhesive, and the positive electrode adhesive includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic resin.

[0134] In some embodiments, the positive electrode sheet is prepared as follows: the components for preparing the positive electrode sheet, such as the positive electrode active material, positive electrode binder and positive electrode conductive agent including the above-mentioned positive electrode material, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector such as aluminum foil; and after drying, rolling, die-cutting and other processes, the positive electrode sheet can be obtained.

[0135] In other embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The above-mentioned negative electrode active material layer can adopt negative electrode active materials used for batteries, and the negative electrode active materials include any one of hard carbon, soft carbon, graphite, silicon carbon, silicon oxide, and silicon, or a combination of at least two of them.

[0136] In other embodiments, the negative electrode plate further includes a negative electrode conductive agent and a negative electrode binder; optionally, the negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the negative electrode binder includes a carboxymethyl cellulose-based binder and a resin binder.

[0137] In the case where the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode sheet is prepared as follows: the components for preparing the negative electrode sheet, such as the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as copper foil; and after processes such as baking, rolling, cutting, and slitting, the negative electrode sheet can be obtained.

[0138] In practical applications, the negative electrode sheet, separator and positive electrode sheet are stacked in order and wound to obtain a core, which is then packaged to obtain a bare cell. The bare cell is baked and then injected with the above-mentioned electrolyte, formed, sealed and sorted to obtain the above-mentioned secondary battery.

[0139] The present application also provides a battery pack, which may be composed of at least one or more batteries. The batteries in the battery pack contain the electrolyte of the present invention.

[0140] The battery pack may include two or more of the above-mentioned batteries, or may include one or more batteries and at least one common battery.

[0141] An embodiment of the present invention further provides an electrical device, which includes the battery according to the embodiment of the present invention.

[0142] The electrical equipment in the embodiments of the present application can be conventional electrical equipment in this field, such as power equipment (such as electric vehicles, electric cars), electronic equipment (such as mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without special restrictions.

[0143] For the above-mentioned battery embodiments, battery pack embodiments and electrical equipment embodiments, they include the above-mentioned electrolyte and can achieve the same technical effects. To avoid repetition, they will not be described here. For relevant details, please refer to the partial description of the electrolyte embodiment.

[0144] The following describes some of the advantages of the embodiments of the present invention compared to the prior art through specific experimental data.

[0145] Example 1

[0146] (1) In a glove box filled with high-purity argon, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are dissolved in an organic solvent to obtain a basic electrolyte for a lithium-ion battery; wherein the organic solvent is a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1, and the concentration of lithium hexafluorophosphate in the electrolyte is 0.6 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.4 mol / L;

[0147] (2) Adding 0.5 wt% of a thiocyanate-containing compound, methyl thiocyanate (CH3SCN), to a basic electrolyte to obtain an electrolyte.

[0148] (3) A commercial NCM811 positive electrode sheet, a separator, and a graphite negative electrode sheet were Z-stacked to form a core, 24 g of the above electrolyte was added, and a soft-pack battery with a capacity of 5 Ah was assembled.

[0149] Examples 2 to 4

[0150] The difference from Example 1 is that in step (2), methyl thiocyanate is adjusted to butyl thiocyanate, (4,4,4-trifluorobutyl)thiocyanate, and 1,1-nitrothiocyanatocyclohexane, respectively.

[0151] Example 5

[0152] The difference from Example 1 is that in step (2), methyl thiocyanate is adjusted to 1,1-nitrothiocyanatocyclohexane and benzyl thiocyanate, and the mass fractions are 0.3 wt % and 0.2 wt %, respectively.

[0153] Example 6

[0154] The difference from Example 1 is that in step (2), methyl thiocyanate is adjusted to ethyl thiocyanate, n-propyl thiocyanate, and isopropyl thiocyanate, and the mass fractions are 0.2 wt%, 0.2 wt%, and 0.1 wt%, respectively.

[0155] Examples 7 to 9

[0156] The difference from Example 4 is that in step (2), the mass fractions of 1,1-nitrothiocyanatocyclohexane are adjusted to 0.2 wt%, 2 wt%, and 5 wt%, respectively.

[0157] Examples 10 to 12

[0158] The difference from Example 4 is that in step (1), the organic solvent is adjusted to be a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in volume ratios of 2:3:5, 5:3:2, and 2:6:2, respectively.

[0159] Examples 13 to 15

[0160] The difference from Example 4 is that in step (1), the organic solvent is adjusted to be a mixture of ethylene carbonate, dimethyl carbonate, and ethyl acetate in volume ratios of 1:2:1, 2:4:4, and 3:6:1.

[0161] Example 16

[0162] The difference from Example 4 is that in step (1), the lithium salt is adjusted to lithium tetrafluoroborate and lithium difluorooxalatoborate; wherein the concentration of lithium tetrafluoroborate in the electrolyte is 0.6 mol / L, and the concentration of lithium difluorooxalatoborate in the electrolyte is 0.6 mol / L.

[0163] Examples 17-18

[0164] The difference from Example 16 is that in step (1), the concentration of lithium tetrafluoroborate in the electrolyte is adjusted to 0.06 mol / L and the concentration of lithium difluorooxalatoborate in the electrolyte is adjusted to 0.6 mol / L, the concentration of lithium tetrafluoroborate in the electrolyte is adjusted to 1.8 mol / L and the concentration of lithium difluorooxalatoborate in the electrolyte is adjusted to 0.6 mol / L.

[0165] Example 19

[0166] The difference from Example 4 is that in step (1), the lithium salt is adjusted to lithium bis(trifluoromethylsulfonyl)imide; wherein the concentration of lithium bis(trifluoromethylsulfonyl)imide in the electrolyte is 1 mol / L.

[0167] Examples 20 to 23

[0168] The difference from Example 4 is that in step (1), the concentration of lithium hexafluorophosphate in the electrolyte is adjusted to 0.3 mol / L and the concentration of lithium bisfluorosulfonyl imide in the electrolyte is 0.2 mol / L, the concentration of lithium hexafluorophosphate in the electrolyte is 1.8 mol / L and the concentration of lithium bisfluorosulfonyl imide in the electrolyte is 1.2 mol / L, the concentration of lithium hexafluorophosphate in the electrolyte is 0.04 mol / L and the concentration of lithium bisfluorosulfonyl imide in the electrolyte is 0.4 mol / L, and the concentration of lithium hexafluorophosphate in the electrolyte is 1.2 mol / L and the concentration of lithium bisfluorosulfonyl imide in the electrolyte is 0.4 mol / L.

[0169] Comparative Example 1

[0170] The difference from Example 4 is that step (2) is omitted and the basic electrolyte is injected in step (3).

[0171] Comparative Example 2

[0172] The difference from Example 13 is that step (2) is omitted and the basic electrolyte is injected in step (3).

[0173] Comparative Example 3

[0174] The difference from Example 16 is that step (2) is omitted and the basic electrolyte is injected in step (3).

[0175] Comparative Example 4

[0176] The difference from Example 7 is that in step (2), methyl thiocyanate is adjusted to vinyl sulfate.

[0177] Comparative Example 5

[0178] The difference from Example 7 is that in step (2), methyl thiocyanate is adjusted to methylene methanedisulfonate.

[0179] Test Case

[0180] Physical property tests and electrochemical tests were performed on the batteries in each embodiment and comparative example:

[0181] (1) Physical property test methods

[0182] 1. Group test:

[0183] Using infrared spectroscopy detection, the operation is as follows:

[0184] Take 5 μL of electrolyte and press it into a potassium bromide (KBr) salt film (thickness ≤ 20 μm) with a 4 cm -1 Scan at a resolution of 4000-500 cm-, and observe at 2120-2170 cm- after subtracting the solvent background. -1 interval sharp peaks (full width at half maximum <15 cm-);

[0185] Interference elimination: The cyano (-CN) peak is located at 2200-2260 cm -1 , isocyanate (-NCO) is 2260-2275cm -1 Wide double peak.

[0186] Among them, all thiocyanates (R-SCN) are in the range of 2120-2170 cm -1 Sharp CN stretching vibration characteristic peaks appear in all intervals (transmittance <20%). The characteristic peaks of each specific compound are as follows:

[0187] Methyl thiocyanate: 2152 cm -1 (typical fatty chain ester peak);

[0188] Ethyl thiocyanate: 2150 cm -1 (peak shape is symmetrical);

[0189] Thiocyanate-n-lactone: 2148 cm -1 (The peak position coincides with that of isopropyl ester);

[0190] Isopropyl thiocyanate: 2148 cm -1 (Full width at half height increased to 12 cm);

[0191] Butyl thiocyanate: 2145 cm -1 (slight red shift as the carbon chain grows);

[0192] (4,4,4-Difluorobutyl)thiocyanate: 2138 cm -1 (blue shift + peak width increased to 25cm -1 , due to the strong electron pulling effect of the CF bond);

[0193] 1,1-Nitrothiocyanatocyclohexane: 2155 cm -1 (need to confirm 1530cm simultaneously -1 nitro peak);

[0194] Benzyl thiocyanate: 2125 cm -1 (Significant red shift, the benzene ring weakens the C=N bond order).

[0195] 2. Mass percentage test:

[0196] The samples were analyzed using an Agilent 7890B gas chromatograph coupled to a 5977B mass spectrometer. Chromatographic separation was performed using a DB-5MS capillary column (30 m x 0.25 mm x 0.25 μm). The ammonia carrier gas flow rate was constant at 1.0 mL / min. The temperature program was set as follows: initially at 50°C for 1 minute, then ramped to 280°C in two steps and held for 5 minutes. The injection port temperature was 250°C, and injection was performed in pulsed splitless mode.

[0197] Before analysis, 100 μL of electrolyte sample was extracted with 900 μL of n-hexane, cleaned up with a Florisi solid-phase extraction column, and concentrated to an appropriate volume under nitrogen purge. Nitro compounds were silanized using BSTFATMCS (20 L, derivatized at 70°C for 30 minutes).

[0198] During the analysis, the mass spectrometer used an electron impact source (EI, 70 eV) and selected ion monitoring (SIM) mode. The ion source and quadrupole temperatures were set to 230°C and 150°C, respectively, and the mass percentage of each target compound in the sample was output. The characteristic ions and retention time windows of each target compound are detailed in Table 4.

[0199] The system was quantified using an internal standard method (2-bromoanisole) to establish a standard curve, and method validation showed a recovery rate of 85-110% (RSD < 5%).

[0200] Table 4

[0201] Compound Time window (min) Quantitative ion (m / z) Auxiliary ion (m / z) Dwell time Methyl thiocyanate 6.5-7.1 73 58,45 100 Ethyl thiocyanate 8.0-8.5 87 60 100 n-Propyl thiocyanate 9.9-10.3 57 41,76 50 Isopropyl thiocyanate 9.5-9 9 41 43,76 50 Butyl thiocyanate 12.3-12 7 56 71 80 (4,4,4-Trifluorobutyl)thiocyanate 14.0-14.6 126 69,97 150 1.1-Nitrothiocyanatocyclohexane 16.7-17.1 72 82,132 150 Benzyl thiocyanate 18.5-18.9 91 65.39 100

[0202] 3. Solvent volume ratio test:

[0203] The determination was performed using a 400 MHz nuclear magnetic resonance spectrometer, and the steps included:

[0204] (1) Take 100 μL of electrolyte sample and dissolve it in 500 μL of tritiated chloroform (CDCl3), add 0.03 vol% tetramethylsilane (TMS) as an internal standard, obtain the characteristic peak integral curve of the solvent, integrate the characteristic peak interval of each solvent according to Table 5, and then calculate the molar percentage Cx (mol%) of each solvent according to the following formula: Cx (mol%) = [Ax / Nx] / Σ(Ai / Ni) × 100; where Ax is the integrated area of ​​the characteristic peak of the target solvent, and Nx is the corresponding proton number;

[0205] (2) The molar percentage of each solvent is combined with the molecular weight and density of each solvent to obtain the volume percentage of each solvent.

[0206] Table 5

[0207]

[0208]

[0209] 4. Lithium salt concentration test:

[0210] Determined by ion chromatography using an ion chromatography system equipped with an electrolytic self-regenerating suppressor and a conductivity detector, the steps include:

[0211] Take 50 μL electrolyte sample and dilute it 200 times with ultrapure water, filter it through 0.22 μm polyvinylidene fluoride (PVDF) membrane and inject it. Separate it using hydroxide selective anion exchange column (250*4 mm), elute it with potassium hydroxide (KOH) solution gradient (0-15min: 10-45mM, 15-25min: 45mM), flow rate 1.2mL / min, column temperature 30℃, suppressor current 50mA, injection volume 20μL; then use anion (PF6 - / FSI - / BF4 - / DFOB - The external standard method was used for quantification, and the concentration range of the standard curve was 0.1~50mg / L (r 2 >0.995) and the detection limit of the method was 0.05 mg / L.

[0212] The relevant parameter designs in the electrolyte of each embodiment and comparative example are shown in Table 6.

[0213] Table 6

[0214]

[0215]

[0216]

[0217] (2) Performance test

[0218] (1) Impedance test: Under the condition of charge and discharge rate of 0.3C, the charge and discharge state of the battery cell at the 50th cycle was subjected to the alternating current impedance test (EIS) to obtain the ion transfer impedance (R SEI ) and charge transfer resistance (R ct ).

[0219] (2) Rate performance test: The charge and discharge voltage range is 2.8V to 4.3V, and the capacity of the battery cell is tested at 0.1C and 1C discharge rates.

[0220] (3) Moisture test: Detect the water content W0 ppm in the initial state of the battery and the water content W1 ppm after 30 days of storage, and calculate the water growth value (W1-W0) ppm.

[0221] The performance test results are shown in Table 7

[0222] Table 7

[0223]

[0224]

[0225] From the test results, it can be seen that compared with comparative examples 1 to 5, the ion transfer impedance (R SEI ), charge transfer impedance (R ct ) as well as the 0.1C discharge specific capacity and the 1C discharge specific capacity are better than those of Comparative Examples 1 to 5, indicating that Examples 1 to 23 can effectively improve the electrode-electrolyte interface ionic conductivity and reduce the interface impedance by adding the thiocyanate-containing compound as an additive.

[0226] In summary, the electrolyte provided by the embodiments of the present invention can improve the ionic conductivity of the battery electrode-electrolyte interface and reduce the overall interfacial impedance of the battery.

[0227] The above is a detailed introduction to an electrolyte, a battery, a battery pack and an electrical device provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a thiocyanate-containing compound, the structural formula of the thiocyanate-containing compound is R-SCN, wherein R includes at least one of an alkyl group, an alkyl group substituted with a heteroatom group, an alkyl group substituted with a halogenated heteroatom group, an aromatic group, an aromatic group substituted with a heteroatom group, and an aromatic group substituted with a halogenated heteroatom group.

2. The electrolyte according to claim 1, characterized in that The thiocyanate-containing compound includes at least one of methyl thiocyanate, ethyl thiocyanate, n-propyl thiocyanate, isopropyl thiocyanate, butyl thiocyanate, (4,4,4-trifluorobutyl) thiocyanate, 1,1-nitrothiocyanatocyclohexane, and benzyl thiocyanate, preferably at least one of methyl thiocyanate, (4,4,4-trifluorobutyl) thiocyanate, and 1,1-nitrothiocyanatocyclohexane.

3. The electrolyte according to claim 1, characterized in that The mass percentage of the thiocyanate-containing compound to the total mass of the electrolyte is 0.2 wt% to 5 wt%, preferably 0.2 wt% to 2 wt%.

4. The electrolyte according to claim 1, characterized in that The electrolyte further includes an organic solvent, and the organic solvent includes at least one of ethylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, propyl propionate, ethyl n-butyrate, and vinylene carbonate.

5. The electrolyte according to claim 4, characterized in that The organic solvent includes ethylene carbonate, dimethyl carbonate and diethyl carbonate, wherein the ethylene carbonate accounts for 20 vol% to 50 vol% of the total volume of the organic solvent, the dimethyl carbonate accounts for 30 vol% to 60 vol% of the total volume of the organic solvent, and the diethyl carbonate accounts for 20 vol% to 50 vol% of the total volume of the organic solvent.

6. The electrolyte according to claim 4, characterized in that The organic solvent includes ethylene carbonate, dimethyl carbonate and ethyl acetate; wherein the ethylene carbonate accounts for 20 vol% to 30 vol% of the total volume of the organic solvent, the dimethyl carbonate accounts for 40 vol% to 60 vol% of the total volume of the organic solvent, and the ethyl acetate accounts for 10 vol% to 40 vol% of the total volume of the organic solvent.

7. The electrolyte according to claim 1, characterized in that The electrolyte further includes a lithium salt; wherein the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorooxalatoborate, and lithium tetrafluoroborate.

8. The electrolyte according to claim 7, characterized in that The molar concentration of the lithium salt is 0.5 to 3 mol / L.

9. The electrolyte according to claim 7 or 8, characterized in that The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the molar ratio between the lithium hexafluorophosphate and the lithium bis(fluorosulfonyl)imide is (0.1-3):

1.

10. The electrolyte according to claim 7 or 8, characterized in that The lithium salt includes lithium tetrafluoroborate and lithium bis(oxalatoborate), and the molar ratio between the lithium tetrafluoroborate and the lithium bis(oxalatoborate) is (0.1-3):

1.

11. A battery, characterized in that: The battery comprises the electrolyte according to any one of claims 1 to 10.

12. A battery pack, characterized in that: The battery pack includes the battery according to claim 11.

13. An electrical device, characterized in that: The electric device comprises the battery according to claim 11 or the battery pack according to claim 12.

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