Electrolyte, lithium ion battery, and electric device

Abstract

The present application relates to a lithium ion battery, and particularly relates to an electrolyte, a lithium ion battery and an electric device. The electrolyte provided by the present application contains dissolved oxygen, lithium salt and organic solvent; wherein the dissolved oxygen comprises oxygen. The electrolyte is injected into the lithium ion battery, and in the formation process of the lithium ion battery, the SEI structure of the negative electrode surface is optimized, the battery impedance is reduced, and the lithium ion battery has a higher low-temperature capacity retention rate and cycle capacity retention rate.

Description

TECHNICAL FIELD

[0001] The present application relates to a lithium ion battery, in particular to an electrolyte, a lithium ion battery containing the electrolyte, and an electric device containing the lithium ion battery. BACKGROUND

[0002] Lithium iron phosphate (LiFePO4) batteries are widely used in electric vehicles and energy storage systems. However, the discharge capacity of lithium iron phosphate batteries at low temperature is significantly reduced, i.e., the low-temperature discharge capacity is poor, which reduces the cruising range of electric vehicles under low-temperature conditions and affects user experience. There are many factors affecting the low-temperature performance of lithium iron phosphate batteries, such as the structure of the positive electrode material, the migration rate of lithium ions in the battery, the chemical composition of the SEI film, and the selection of lithium salts and solvents in the electrolyte. Among them, introducing functional additives into the electrolyte of the battery is considered to be one of the effective ways to improve the low-temperature performance of lithium iron phosphate batteries. However, there are many types of additives, and it is difficult to solve the problem with single-function additives; complex formula combinations of additives may cause system compatibility problems, resulting in insufficient performance of the battery and failing to achieve the use purpose.

[0003] Therefore, it is urgent to develop a new electrolyte that can effectively improve the low-temperature performance of lithium iron phosphate lithium ion batteries. SUMMARY

[0004] The present application aims to overcome the low-temperature discharge performance of existing lithium iron phosphate batteries, and provides an electrolyte, a lithium ion battery containing the electrolyte, and an electric device containing the lithium ion battery.

[0005] To achieve the above-mentioned purpose, the present application provides an electrolyte containing dissolved oxygen, lithium salt and organic solvent; wherein the dissolved oxygen includes oxygen.

[0006] Preferably, the concentration of the dissolved oxygen in the electrolyte is 0.001-0.1 mol / L, preferably 0.005-0.05 mol / L.

[0007] Preferably, the dissolved oxygen further includes ozone.

[0008] Preferably, the ozone in the dissolved oxygen is obtained by ultraviolet radiation of the dissolved oxygen.

[0009] Preferably, in the dissolved oxygen, the molar ratio of the oxygen and ozone is 1:0.001-1, preferably 1:0.005-0.1, and more preferably 1:0.01-0.1.

[0010] Preferably, the conditions of the ultraviolet radiation include: the wavelength of the ultraviolet light is 10-400 nm, preferably 100-400 nm; the power of the ultraviolet light generator is 10-3000 W, preferably 60-600 W; the ultraviolet radiation time is 0.1-1000 min, preferably 1-100 min.

[0011] The second aspect of the present application provides a lithium ion battery, which contains a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte provided by the first aspect.

[0012] Preferably, the lithium ion battery is subjected to formation to form a SEI film on the surface of the negative electrode sheet.

[0013] Preferably, the temperature of the formation is 20-40℃, preferably 20-30℃.

[0014] Preferably, the SEI film contains Li2O, and the content of Li2O is 10-40wt%, preferably 15-35wt%, based on the total weight of the SEI film.

[0015] Preferably, the SEI film further contains Li2CO3, and the content of Li2CO3 is 40-80wt%, preferably 50-70wt%, based on the total weight of the SEI film.

[0016] Preferably, the thickness of the SEI film is 2-200 nm, preferably 10-100 nm.

[0017] The fourth aspect of the present application provides an electric device, which comprises the lithium ion battery provided by the third aspect.

[0018] Through the above technical solution, the electrolyte provided by the present application contains dissolved oxygen, which can optimize the SEI structure and composition on the negative electrode side, thereby reducing the impedance of the battery, especially the impedance of the battery at low temperature; and further improving the low-temperature discharge capacity of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the X-ray photoelectron spectroscopy (XPS) spectrum of the SEI film of the finished lithium ion battery Q1 containing the electrolyte S1 of Example 1;

[0020] Figure 2 is the X-ray photoelectron spectroscopy (XPS) spectrum of the SEI film of the finished lithium ion battery DQ1 containing the electrolyte DS1 of Comparative Example 1. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not considered critical for the purposes of the application. Any numerical range recited herein is intended to include all sub-ranges of the same numbers (i.e., every subset of numbers within the indicated range). For ranges containing one or more endpoints, the endpoints are included in the range. For ranges excluding any endpoint, the endpoint is excluded from the range. If any numerical values are recited herein, they are intended to be approximations.

[0022] The first aspect of the present application provides an electrolyte, the electrolyte contains dissolved oxygen, lithium salt and organic solvent; wherein the dissolved oxygen includes oxygen.

[0023] The inventors of the present application have found that: by dissolving a certain proportion of oxygen in the electrolyte in advance, the proportion of oxygen in the electrolyte is much higher than that of the electrolyte without pre-dissolving oxygen, and the lithium ion battery prepared therefrom has lower impedance, especially under low temperature conditions, the proportion of impedance increase is reduced, and has better low temperature discharge capacity.

[0024] In some embodiments of the present application, preferably, the dissolved oxygen further includes ozone.

[0025] In the present application, unless otherwise specified, the ozone in the dissolved oxygen can be introduced separately or converted from the oxygen in the electrolyte. That is, the electrolyte provided by the present application is in an oxygen-rich environment, and the oxygen in the electrolyte is in a saturated state. When part of the oxygen is converted into ozone, a corresponding part of the oxygen will be dissolved, so that the oxygen and ozone in the dissolved oxygen are in a dynamic equilibrium state.

[0026] In the present application, unless otherwise specified, the dissolved oxygen includes oxygen and ozone means that the dissolved oxygen is a mixture of oxygen and ozone, and the oxygen and ozone are in a dynamic equilibrium state. Preferably, the dissolved oxygen is composed of oxygen and ozone.

[0027] In some embodiments of the present application, preferably, the concentration of the dissolved oxygen in the electrolyte is 0.001-0.1 mol / L, for example, 0.001 mol / L, 0.005 mol / L, 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, and any value in the range between any two of the above values, preferably 0.005-0.05 mol / L. When the dissolved oxygen is in the above range, the dissolved oxygen can be completely consumed during the formation of the battery, and will not affect the subsequent use of the battery.

[0028] In some embodiments of the present application, preferably, the ozone in the dissolved oxygen is obtained from the dissolved oxygen by ultraviolet radiation. In the present application, part of the dissolved oxygen is converted into ozone by ultraviolet irradiation, and the molar ratio of ozone to oxygen in the dissolved oxygen is adjusted, so that the proportion of oxygen or ozone in the electrolyte is much higher than that of the electrolyte without pre-dissolution.

[0029] In some embodiments of the present application, preferably, the molar ratio of oxygen to ozone in the dissolved oxygen is 1:0.001-1, for example, 1:0.001, 1:0.005, 1:0.01, 1:0.012, 1:0.015, 1:0.03, 1:0.05, 1:0.08, 1:0.1, 1:0.5, 1:1, and any value in the range between any two numerical values, preferably 1:0.005-0.1, and more preferably 1:0.01-0.1. When the molar ratio of oxygen to ozone in the dissolved oxygen is less than 1:0.001, the ozone concentration is too low, and the low-temperature impedance reduction effect of the battery is not obvious; when the molar ratio of oxygen to ozone in the dissolved oxygen is greater than 1:1, the ozone concentration is too high, the electrolyte side reaction increases, and the battery performance deteriorates.

[0030] In the present application, unless otherwise specified, the concentration of oxygen in the electrolyte is measured by the static phase equilibrium method, and the concentration of ozone is measured by CJ / T 3028.2-94; the test temperature is room temperature (i.e., 25-30℃).

[0031] In some embodiments of the present application, preferably, the conditions of the ultraviolet radiation include: the wavelength of the ultraviolet light is 10-400 nm; the power of the ultraviolet light generator is 10-3000 W; and the ultraviolet radiation time is 0.1-1000 min.

[0032] In some embodiments of the present application, further preferably, the conditions of the ultraviolet radiation include: the wavelength of the ultraviolet light is 100-400 nm; the power of the ultraviolet light generator is 60-600 W; and the ultraviolet radiation time is 1-100 min.

[0033] In some embodiments of the present application, preferably, the concentration of lithium salt in the electrolyte is 5-30 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, and any value in the range between any two numerical values, preferably 7-20 wt%.

[0034] In the present application, there is a wide selection range for the kind of the lithium salt. Preferably, the lithium salt is selected from at least one of LiPF6, LiAsF6, lithium bisfluorosulfonylimide and lithium bis(trifluoromethylsulfonyl)imide and derivatives thereof; further preferably, the lithium bis(trifluoromethylsulfonyl)imide derivative is selected from at least one of lithium bis(pentafluoroethylsulfonyl)imide, lithium trifluoromethylsulfonyl-pentafluoroethylsulfonylimide and lithium fluorosulfonyl-trifluoromethylsulfonylimide.

[0035] In some embodiments of the present application, preferably, the organic solvent is selected from at least one of an ether compound, an ester compound, an amide compound, a nitrile compound and an aromatic compound, preferably selected from an ether compound and / or an ester compound.

[0036] In some embodiments of the present application, preferably, the ether compound is selected from at least one of a cyclic ether, a linear ether and a fluorinated ether; further preferably, the cyclic ether is selected from at least one of 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, tetrahydropyran and propylene oxide; the linear ether is selected from at least one of dimethyloxymethane, dimethyloxyethane, ethyleneglycol dimethyl ether (DME), ethyleneglycol diethyl ether, ethyleneglycol methylethyl ether, t-butyl methyl ether, t-butyl ethyl ether, diethyleneglycol dimethyl ether, triethyleneglycol dimethyl ether, tetraethyleneglycol dimethyl ether and dipropylene glycol dimethyl ether; the fluorinated ether is selected from at least one of bis-2,2-trifluoroethyl ether (BTFE), 1,1,1,2,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, nonafluorobutyl methyl ether, nonafluorobutyl ethyl ether, nonafluorobutyl propyl ether, n-butyl-1,1,2,2-tetrafluoroethyl ether, 2,2,3,3,3-pentafluoropropyl methyl ether, 2,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether and trifluoroethyl dodecafluoroheptyl ether.

[0037] According to a preferred embodiment of the present application, the organic solvent is a linear ether and a cyclic ether, wherein the weight ratio of the linear ether to the cyclic ether is 10-50:50-90, preferably 25-50:50-75. The use of a mixture of a cyclic ether compound and a linear ether with a lower reduction potential in a preferred ratio can prepare an electrolyte with higher stability to lithium and prevent the reduction reaction of the electrolyte at the negative electrode.

[0038] In some embodiments of the present application, preferably, the ester compound is selected from an inorganic acid ester and / or an organic acid ester, the inorganic acid ester is preferably selected from a carbonate and / or a phosphate, the carbonate is selected from a cyclic carbonate and / or a linear carbonate.

[0039] In some embodiments of the present application, it is further preferred that the organic acid ester is at least one of methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, methyl propionate, γ-butyrolactone, γ-valerolactone, γ-hexalactone, δ-valerolactone and ε-hexalactone; more preferably, the organic acid ester is at least one of ethyl propionate, propyl propionate and methyl propionate. With the preferred conditions, it is more advantageous to reduce the viscosity of the electrolyte.

[0040] In some embodiments of the present application, it is further preferred that the cyclic carbonate is at least one of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate and vinylene carbonate, and halides thereof; and the linear carbonate is at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate and methyl propyl carbonate.

[0041] According to a preferred embodiment of the present application, the organic solvent is a cyclic carbonate and a linear carbonate, wherein the weight ratio of the cyclic carbonate to the linear carbonate is 10-50:50-90, preferably 25-50:50-75. With the preferred conditions, the cyclic carbonate with high dielectric constant and the linear carbonate with low viscosity are used in combination, which is more advantageous to improve the ionic conductivity of the electrolyte and prevent the reduction reaction of the electrolyte at the negative electrode.

[0042] In some embodiments of the present application, it is further preferred that the phosphate ester is at least one of trimethyl phosphine oxide, triethyl phosphine oxide, tripropyl phosphine oxide, triphenyl phosphine oxide, diethyl methyl phosphonate, dimethyl methyl phosphonate, diphenyl methyl phosphonate, bis(2,2,2-trifluoroethyl) methyl phosphonate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate and ethyl methyl phenyl phosphate.

[0043] In some embodiments of the present application, it is preferred that the nitrile compound is at least one of acetonitrile, propionitrile, butyronitrile, valeronitrile, hexanitrile, heptanitrile, cyclopentyl cyanide, cyclohexyl cyanide, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile and 4-fluorophenylacetonitrile.

[0044] In the present application, the amide compound and the aromatic compound have a wide range of selection, which are both specific compounds in the art, and the present application does not limit them.

[0045] In some embodiments of the present application, preferably, the electrolyte further comprises an additive; further preferably, the content of the additive in the electrolyte is 0.05-10wt%, for example, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 3wt%, 5wt%, 8wt%, 10wt%, and any value in the range between any two of the values, preferably 0.1-5wt%.

[0046] In the present application, the type of the additive has a wide range of selection. Preferably, the additive is selected from at least one of vinylene carbonate, vinyl carbonate, fluoroethylene carbonate, lithium difluorophosphate, lithium bisoxalato borate, lithium difluoro oxalato borate, 1,3-propane sultone, triallyl isocyanurate, methanediyl dimethanesulfonate, vinyl sulfate, triallyl phosphate and tripropargyl phosphate.

[0047] In the present application, the preparation method of the electrolyte has a wide range of selection, as long as the electrolyte contains dissolved oxygen, lithium salt and organic solvent. Preferably, the preparation method of the electrolyte comprises the following steps: (1) mixing lithium salt, additive and organic solvent to obtain a mixture; (2) contacting and dissolving the mixture and oxygen in a non-oxidizing atmosphere at a volume ratio of 1-100:1 to obtain an electrolyte precursor with an oxygen solubility of 0.001-0.09mol / L; (3) in a non-oxidizing atmosphere, ultraviolet radiation is applied to the electrolyte precursor to convert the dissolved oxygen into ozone to obtain an electrolyte with a dissolved oxygen of 0.001-0.1mol / L, wherein the dissolved oxygen comprises oxygen and ozone, and the molar ratio of oxygen to ozone is 1:0.001-1, preferably 1:0.005-0.1, and more preferably 1:0.01-0.1.

[0048] In the present application, without special circumstances, the types of lithium salt, additive and organic solvent, and the conditions of ultraviolet radiation are in accordance with the above-mentioned limitations, which will not be repeated here.

[0049] In some embodiments of the present application, preferably, in step (1), the weight ratio of the lithium salt, additive and organic solvent is 1-20:0.1-10:20-100.

[0050] In some embodiments of the present application, preferably, in step (2), the dissolving conditions include: temperature of 15-40℃, preferably 20-30℃; time of 10-40h, preferably 20-30h.

[0051] In the present application, in step (2), the oxygen solubility refers to the solubility of oxygen in the electrolyte precursor when the amount of dissolved oxygen reaches the saturation state.

[0052] The second aspect of the present application provides a lithium ion battery, which contains a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte provided by the first aspect.

[0053] In some embodiments of the present application, the lithium ion battery is preferably subjected to formation to form a SEI film on the surface of the negative electrode sheet. Meanwhile, during electrolyte formation, dissolved oxygen is completely consumed, which will not affect the subsequent use of the battery.

[0054] In some embodiments of the present application, the temperature of the formation is preferably 20-40℃, for example, 20℃, 25℃, 30℃, 35℃, 40℃, and any value in the range between any two of the values, preferably 20-30℃.

[0055] In some embodiments of the present application, the SEI film preferably contains Li2O, and the content of Li2O is 10-40wt%, for example, 10wt%, 15wt%, 25wt%, 35wt%, 40wt%, and any value in the range between any two of the values, preferably 15-35wt%, based on the total weight of the SEI film.

[0056] In some embodiments of the present application, the SEI film further contains Li2CO3, and the content of Li2CO3 is 40-80wt%, for example, 40wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 80wt%, and any value in the range between any two of the values, preferably 50-70wt%, based on the total weight of the SEI film.

[0057] In the SEI film, the content of Li2CO3 is 40-80wt%, preferably 50-70wt%, and the content of Li2O is 10-40wt%, preferably 15-35wt%.

[0058] In the present application, unless otherwise specified, the content of Li2CO3 and the content of Li2O in the SEI film are measured by peak fitting of XPS (X-ray photoelectron spectroscopy).

[0059] In the present application, unless otherwise specified, the SEI film further contains organic lithium salt in addition to Li2CO3 and Li2O.

[0060] In some embodiments of the present application, the thickness of the SEI film is preferably 2-200nm, for example, 2nm, 10nm, 30nm, 50nm, 80nm, 100nm, 150nm, 200nm, and any value in the range between any two of the values, preferably 10-100nm.

[0061] In the present application, the SEI film thickness parameter is obtained by TEM (Transmission Electron Microscope) test without special case.

[0062] In some embodiments of the present application, preferably, the working temperature of the lithium ion battery is -20℃ to 65℃, for example, -20℃, -10℃, 0℃, 10℃, 20℃, 25℃, 30℃, 50℃, 65℃, and any value in the range consisting of any two numerical values, preferably 20-30℃.

[0063] In some embodiments of the present application, preferably, the charge transfer impedance of the lithium ion battery at -20℃ is ≤1.2Ω·Ah, for example, 0.1Ω·Ah, 0.2Ω·Ah, 0.3Ω·Ah, 0.4Ω·Ah, 0.5Ω·Ah, 0.8Ω·Ah, 1Ω·Ah and 1.2Ω·Ah, and any value in the range consisting of any two numerical values, preferably 0.1-0.5Ω·Ah. In the present application, the charge transfer impedance of the lithium ion battery at -20℃ is tested by electrochemical workstation.

[0064] In some embodiments of the present application, preferably, the capacity retention rate of the lithium ion battery at -20℃ is ≥65%, preferably 65-80%; the capacity retention rate after 500 cycles at 25℃ is ≥91%, preferably 93.5-97.5%.

[0065] In the present application, the capacity retention rate is measured by lithium ion battery charge-discharge test cabinet without special case.

[0066] In the present application, the capacity retention rate test method at different temperatures is as follows: (1) at 25±5℃, charge to the upper limit voltage of the battery (0.05C current cutoff) at 1 / 3C (C is the rated capacity of the battery), stand for 10 min, then discharge to the lower limit voltage of the battery at 1 / 3C constant current, the obtained capacity is C0; (2) charge to the upper limit voltage of the battery (0.05C current cutoff) at 1 / 3C constant current, transfer the battery to the constant temperature oven, set the temperature of the constant temperature oven to the temperature to be tested, stand for 12h to make the temperature of the battery reach the temperature to be tested; (3) discharge to the lower limit voltage of the battery at 1 / 3C constant current, the obtained capacity is C1, C1 / C0 is the capacity retention rate at this temperature. Repeat steps (1)-(3) as above to test and obtain the capacity retention rate of the battery at different temperatures.

[0067] In the present application, the capacity retention rate test method after 500 cycles at 25℃ is as follows: (1) charge the battery to the upper limit voltage of the battery (cut off at 0.05C current) at 0.5C (C is the rated capacity of the battery) and constant current and constant voltage at 25±5℃, and stand for 10 min; (2) discharge the battery to the lower limit voltage of the battery at 0.5C constant current, and the capacity is C0, and stand for 10 min; repeat the above steps (1)-(2) for 500 times, and the discharge capacity of the 500th cycle is C500, and C500 / C0 is the capacity retention rate after 500 cycles at 25℃.

[0068] The fourth aspect of the present application provides a power consumption device, which comprises the lithium ion battery of the third aspect.

[0069] In the present application, the power consumption device includes but is not limited to mobile phones, cars, etc. without special circumstances.

[0070] According to a particularly preferred embodiment of the present application, an electrolyte comprises dissolved oxygen, a lithium salt, an additive and an organic solvent; wherein the dissolved oxygen comprises oxygen and ozone, and the ozone in the dissolved oxygen is obtained from the dissolved oxygen by ultraviolet radiation;

[0071] In the dissolved oxygen, the molar ratio of oxygen to ozone is 1:0.01-0.1.

[0072] In the electrolyte, the concentration of the dissolved oxygen is 0.005-0.05 mol / L.

[0073] The conditions of the ultraviolet radiation include: the wavelength of the ultraviolet light is 100-400 nm; the power of the ultraviolet light generator is 60-600 W; and the ultraviolet radiation time is 1-100 min.

[0074] The present application will be described in detail below through examples.

[0075] Preparation of the lithium ion battery P1: lithium iron phosphate: PVDF: carbon nanotube: graphene: NMP = 100:2.5:1:0.5:60 by weight, uniformly mixed to prepare a positive electrode slurry, coated on an aluminum foil current collector, and the single-sided area density of the positive electrode coating was controlled to be 200 g / m 2 After baking, a positive electrode sheet was obtained; at the same time, graphite: CMC: SBR: carbon black: H2O = 100:3:2:1:100 by weight, a negative electrode slurry was prepared, coated on a copper foil current collector, and the single-sided area density of the negative electrode was controlled to be 100 g / m 2 After baking, a negative electrode sheet was obtained; the above positive electrode sheet and negative electrode sheet were respectively rolled, cut, die-cut, laminated and assembled to prepare a lithium ion battery.

[0076] Example 1

[0077] (1) LiPF6, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, vinylene carbonate were mixed in a weight ratio of 13:30:11:12:34:5 to obtain a mixed solution;

[0078] (2) The above mixed solution was loaded into a stainless steel sealed container with a volume of 100 L, and the loading ratio was 90%. Then 10 L of oxygen was introduced into the stainless steel sealed container, and the mixed solution was allowed to stand at 25°C for 24 h to make the concentration of oxygen in the mixed solution tend to be saturated;

[0079] (3) A UV lamp was installed in the stainless steel sealed container, and the wavelength of the UV light was controlled to be 150 nm. The remaining dissolved oxygen was converted into ozone by external UV radiation under a power of 200 W for 1 h. The molar ratio of oxygen to ozone in the dissolved oxygen was controlled to be 1:0.012 to obtain electrolyte S1;

[0080] The concentration of dissolved oxygen in the above electrolyte S1 was 0.012 mol / L;

[0081] (4) The above electrolyte S1 was injected into the above lithium ion battery P1, and after sufficient soaking, the formed product lithium ion battery Q1 was sealed after being subjected to formation at 25±5°C, exhaust, liquid supplement, charging, aging, capacity distribution, self-discharge detection. The discharge capacity test at different temperatures was carried out, and the test results are shown in Table 1.

[0082] Example 2

[0083] According to the method of Example 1, except that,

[0084] In step (3), the wavelength of the UV light was controlled to be 200 nm, and the remaining dissolved oxygen was converted into ozone by external UV radiation under a power of 400 W for 1 h. The molar ratio of oxygen to ozone in the dissolved oxygen was controlled to be 1:0.015, and the remaining conditions were the same to obtain electrolyte S2;

[0085] The concentration of dissolved oxygen in the above electrolyte S2 was 0.018 mol / L;

[0086] In step (4), the above electrolyte S2 was injected into the above lithium ion battery P1, and after sufficient soaking, the formed product lithium ion battery Q2 was sealed after being subjected to formation at 25±5°C, exhaust, liquid supplement, charging, aging, capacity distribution, self-discharge detection. The discharge capacity test at different temperatures was carried out, and the test results are shown in Table 1.

[0087] Example 3

[0088] According to the method of Example 1, except that,

[0089] In step (3), the wavelength of the ultraviolet light is controlled to be 100 nm, and the electrolyte S3 is obtained by irradiating for 1 h at a power of 600 W, so that the remaining part of the dissolved oxygen is converted into ozone by external ultraviolet irradiation, and the molar ratio of oxygen to ozone in the dissolved oxygen is adjusted to be 1:0.03, and the other conditions are the same.

[0090] In the electrolyte S3, the concentration of the dissolved oxygen is 0.024 mol / L.

[0091] In step (4), the electrolyte S3 is injected into the lithium ion battery P1, and after being fully soaked, the electrolyte is subjected to formation at 25±5℃, and then subjected to exhaust, liquid supplement, charging, aging, capacity grading, self-discharge detection, and sealing. The finished lithium ion battery Q3 obtained is subjected to discharge capacity test at different temperatures, and the test results are shown in Table 1.

[0092] Example 4

[0093] According to the method of Example 1, except that

[0094] In step (3), the wavelength of the ultraviolet light is controlled to be 180 nm, and the electrolyte S4 is obtained by irradiating for 0.5 h at a power of 800 W, so that the remaining part of the dissolved oxygen is converted into ozone by external ultraviolet irradiation, and the molar ratio of oxygen to ozone in the dissolved oxygen is adjusted to be 1:0.05, and the other conditions are the same.

[0095] In the electrolyte S4, the concentration of the dissolved oxygen is 0.03 mol / L.

[0096] In step (4), the electrolyte S4 is injected into the lithium ion battery P1, and after being fully soaked, the electrolyte is subjected to formation at 25±5℃, and then subjected to exhaust, liquid supplement, charging, aging, capacity grading, self-discharge detection, and sealing. The finished lithium ion battery Q4 obtained is subjected to discharge capacity test at different temperatures, and the test results are shown in Table 1.

[0097] Example 5

[0098] According to the method of Example 1, except that

[0099] In step (3), the wavelength of the ultraviolet light is controlled to be 320 nm, and the electrolyte S5 is obtained by irradiating for 0.5 h at a power of 300 W, so that the remaining part of the dissolved oxygen is converted into ozone by external ultraviolet irradiation, and the molar ratio of oxygen to ozone in the dissolved oxygen is adjusted to be 1:0.008, and the other conditions are the same.

[0100] In the electrolyte S5, the concentration of the dissolved oxygen is 0.01 mol / L.

[0101] In step (4), the electrolyte S5 is injected into the lithium ion battery P1, and after being fully soaked, the lithium ion battery is sealed after being subjected to formation at 25±5℃, degassing, liquid supplementing, charging, aging, capacity grading, and self-discharge detection. The finished lithium ion battery Q5 obtained is subjected to discharge capacity test at different temperatures, and the test results are shown in Table 1.

[0102] Example 6

[0103] According to the method of Example 1, except that

[0104] In step (3), the wavelength of the ultraviolet light is controlled to be 160 nm, and the remaining part of the dissolved oxygen is converted into ozone by external ultraviolet radiation. The molar ratio of oxygen to ozone in the dissolved oxygen is controlled to be 1:0.8, and the remaining conditions are the same. The electrolyte S6 is obtained.

[0105] The concentration of the dissolved oxygen in the electrolyte S6 is 0.052 mol / L.

[0106] In step (4), the electrolyte S6 is injected into the lithium ion battery P1, and after being fully soaked, the lithium ion battery is sealed after being subjected to formation at 25±5℃, degassing, liquid supplementing, charging, aging, capacity grading, and self-discharge detection. The finished lithium ion battery Q6 obtained is subjected to discharge capacity test at different temperatures, and the test results are shown in Table 1.

[0107] Example 7

[0108] According to the method of Example 1, except that

[0109] In step (3), the wavelength of the ultraviolet light is controlled to be 160 nm, and the remaining part of the dissolved oxygen is converted into ozone by external ultraviolet radiation. The molar ratio of oxygen to ozone in the dissolved oxygen is controlled to be 1:2, and the remaining conditions are the same. The electrolyte S7 is obtained.

[0110] The concentration of the dissolved oxygen in the electrolyte S7 is 0.076 mol / L.

[0111] In step (4), the electrolyte S7 is injected into the lithium ion battery P1, and after being fully soaked, the lithium ion battery is sealed after being subjected to formation at 25±5℃, degassing, liquid supplementing, charging, aging, capacity grading, and self-discharge detection. The finished lithium ion battery Q7 obtained is subjected to discharge capacity test at different temperatures, and the test results are shown in Table 1.

[0112] Example 8

[0113] According to the method of Example 1, except that

[0114] There is no step (3), and the mixed solution obtained in step (2) is directly used as the electrolyte S8.

[0115] In step (4), the electrolyte S8 is injected into the lithium ion battery P1, and after sufficient soaking, formation is carried out at 25±5℃, and after degassing, liquid supplementing, charging, aging, capacity grading, self-discharge detection, and sealing, the finished lithium ion battery Q8 obtained is subjected to discharge capacity test at different temperatures, and the test results are shown in Table 1.

[0116] Comparative Example 1

[0117] According to the method of Example 1, except that,

[0118] Without steps (2)-(3), the mixed solution obtained in step (1) is directly used as the electrolyte DS1;

[0119] In step (4), the electrolyte DS1 is injected into the lithium ion battery P1, and after sufficient soaking, formation is carried out at 25±5℃, and after degassing, liquid supplementing, charging, aging, capacity grading, self-discharge detection, and sealing, the finished lithium ion battery DQ1 obtained is subjected to discharge capacity test at different temperatures, and the test results are shown in Table 1.

[0120] Table 1

[0121]

[0122] Continuation of Table 1

[0123]

[0124] From the data in Table 1, it can be seen that, compared with Comparative Example 1, the electrolyte prepared in Examples 1-8 is injected into the lithium ion battery, and the finished lithium ion battery obtained has higher capacity retention rate at low temperature and higher cycle capacity retention rate.

[0125] The photoelectron spectroscopy (XPS) spectrum of the SEI film of the finished lithium ion battery containing the electrolyte of Example 1 and Comparative Example 1 is shown in Figure 1 and Figure 2 It can be seen from Figures 1-2 that, compared with Comparative Example 1, the SEI structure of the finished lithium ion battery Q1 containing the electrolyte S1 of Example 1 has higher Li2O content.

[0126] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. An electrolyte, characterized by, The electrolyte contains dissolved oxygen, lithium salt and organic solvent; wherein the dissolved oxygen includes oxygen and ozone; The concentration of the dissolved oxygen in the electrolyte is 0.001-0.1 mol / L; and the molar ratio of the oxygen to the ozone in the dissolved oxygen is 1:0.001-1.

2. The electrolyte according to claim 1, characterized in that, The concentration of the dissolved oxygen in the electrolyte is 0.005-0.05 mol / L.

3. The electrolyte of claim 1, wherein, The ozone in the dissolved oxygen is obtained by ultraviolet radiation of the dissolved oxygen.

4. The electrolyte according to claim 3, characterized in that, The molar ratio of the oxygen to the ozone in the dissolved oxygen is 1:0.005-0.

1.

5. The electrolyte according to claim 4, characterized in that, The molar ratio of the oxygen to the ozone in the dissolved oxygen is 1:0.01-0.

1.

6. The electrolyte of claim 3, wherein, The conditions of the ultraviolet radiation include: the wavelength of the ultraviolet light is 10-400 nm; the power of the ultraviolet light generator is 10-3000 W; and the ultraviolet radiation time is 0.1-1000 min.

7. The electrolyte according to claim 6, characterized in that The conditions of the ultraviolet radiation include: the wavelength of the ultraviolet light is 100-400 nm; the power of the ultraviolet light generator is 60-600 W; and the ultraviolet radiation time is 1-100 min.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The concentration of the lithium salt in the electrolyte is 5-30 wt%; The lithium salt is at least one selected from LiPF6, LiAsF6, lithium bisfluorosulfonylimide and lithium bis(trifluoromethylsulfonyl)imide and derivatives thereof; The organic solvent is at least one selected from ether compound, ester compound, amide compound, nitrile compound and aromatic compound.

9. The electrolyte of claim 8, wherein, The concentration of the lithium salt in the electrolyte is 7-20 wt%; The organic solvent is at least one selected from ether compound and / or ester compound.

10. The electrolyte according to any one of claims 1 to 7, wherein The electrolyte further comprises an additive; The content of the additive in the electrolyte is 0.05-10 wt%.

11. The electrolyte according to claim 10, characterized in that The content of the additive in the electrolyte is 0.1-5 wt%; The additive is at least one selected from vinylene carbonate, fluoroethylene carbonate, lithium difluorophosphate, lithium bisoxalate borate, lithium difluoro oxalate borate, 1,3-propane sultone, triallyl isocyanurate, methanedisulfonate methylene, vinyl sulfate, triallyl phosphate and tripropargyl phosphate.

12. A lithium-ion battery, characterized by, The lithium ion battery comprises: a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1-11.

13. The lithium-ion battery of claim 12, wherein, The lithium ion battery is subjected to formation to form a SEI film on the surface of the negative electrode sheet; The temperature of the formation is 20-40℃.

14. The lithium-ion battery of claim 13, wherein, The temperature of the formation is 20-30℃.

15. The lithium-ion battery of claim 13, wherein, The SEI film contains Li2O; the content of Li2O is 10-40 wt% based on the total weight of the SEI film; The SEI film further contains Li2CO3; the content of Li2CO3 is 40-80 wt% based on the total weight of the SEI film; The thickness of the SEI film is 2-200 nm.

16. The lithium-ion battery of claim 15, wherein, The SEI film contains Li2O; the content of Li2O is 15-35 wt% based on the total weight of the SEI film; And / or, the SEI film further contains Li2CO3, and the content of Li2CO3 is 50-70 wt% based on the total weight of the SEI film; And / or, the thickness of the SEI film is 10-100 nm.

17. The lithium-ion battery of any of claims 12-16, wherein, The charge transfer impedance of the lithium ion battery at-20℃ is ≤1.2 Ω Ah; And / or, the capacity retention rate of the lithium ion battery at-20℃ is ≥65%, and the capacity retention rate after 500 cycles at 25℃ is ≥91%.

18. The lithium-ion battery of claim 17, wherein, The charge transfer impedance of the lithium ion battery at-20℃ is 0.1-0.5 Ω Ah; And / or, the capacity retention rate of the lithium ion battery at-20℃ is 65-80%, and the capacity retention rate after 500 cycles at 25℃ is 93.5-97.5%.

19. An electrical device, comprising: The electric device comprises the lithium ion battery according to any one of claims 12-18.

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