Electrolyte, preparation method thereof and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte, a preparation method thereof and a lithium ion battery. The electrolyte provided by the invention comprises a lithium salt electrolyte, an additive and an organic solvent, wherein the lithium salt electrolyte and the additive are dissolved in the organic solvent; the additives comprise fluoroethylene carbonate with the addition amount of 5 to 9 weight percent, 4-sulfonyl fluoride-triphenylamine benzonitrile with the addition amount of 0.5 to 1 weight percent, lithium difluorophosphate with the addition amount of 1 to 3 weight percent, 1, 3-propane sultone with the addition amount of 0.5 to 1 weight percent, triborate with the addition amount of 0.8 to 1.5 weight percent and propyl propionate with the addition amount of 2 to 4 weight percent, and the mass of the organic solvent is metered. According to the electrolyte provided by the invention, through the synergistic effect of the six-element additive, the problems of expansion capacity attenuation of a lithium ion battery cell and safety at high temperature and high pressure can be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to an electrolyte, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in fields such as digital, energy storage, power, military aerospace, and communication equipment due to their advantages of high energy density, high output power, and high charging efficiency. As a new type of cathode material, lithium iron manganese phosphate has advantages such as high energy density, low cost, and high safety, and is widely used in power batteries and energy storage fields. However, traditional electrolytes are prone to decomposition at high temperatures and gas generation under high pressure, resulting in a serious decline in battery performance, and even lithium dendrites and bulges are extremely likely to cause safety hazards.

[0003] In related technologies, the electrolyte applied to lithium iron manganese phosphate usually consists of a carbonate solvent and a lithium salt. However, at high temperatures, the electrolyte is prone to oxidative decomposition, resulting in a decrease in battery capacity and a shortening of the cycle life. Although using a high-concentration lithium salt or a fluorinated solvent can improve the high-voltage resistance, there are problems such as too high cost and poor low-temperature performance.

[0004] Therefore, developing an electrolyte with high temperature and high voltage resistance to match lithium iron manganese phosphate is an urgent problem to be solved in this field. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems in the related technologies to some extent. For this purpose, an embodiment of the present invention provides an electrolyte. Through the synergistic effect of a six-component additive in the electrolyte, problems such as the acceleration of the decomposition of the electrolyte solvent at high temperatures, the generation of gases and acidic substances leading to subsequent swelling and capacity attenuation of the battery cell, the destruction of the CEI film and structure of the lithium iron manganese phosphate cathode under high pressure, and the inhibition of the dissolution of manganese ions under high temperature and high pressure can be solved.

[0006] The electrolyte of the embodiment of the present invention includes a lithium salt electrolyte, an additive, and an organic solvent, and the lithium salt electrolyte and the additive are dissolved in the organic solvent; the additive includes 5-9 wt% of fluoroethylene carbonate, 0.5-1 wt% of 4-sulfonyl fluoride-triphenylamine benzonitrile, 1-3 wt% of lithium difluorophosphate, 0.5-1 wt% of 1,3-propane sultone, 0.8-1.5 wt% of triborate, and 2-4 wt% of propyl propionate, based on the mass of the organic solvent.

[0007] The advantages and technical effects brought by the electrolyte of the embodiments of the present invention are as follows: 1. In the embodiments of the present invention, in the additives used, fluoroethylene carbonate forms a fluorine-rich CEI film on the positive electrode. The sulfonyl fluoride group of 4-sulfonyl fluoride-triphenylamine benzonitrile captures free hydrogen ions, triphenylamine enhances antioxidant properties, and the nitrile group enhances the lithium ion migration rate. Lithium difluorophosphate and 1,3-propane sultone synergistically generate a dense LiF-POx-SOx composite CEI layer to block the side reaction between the electrolyte and the positive electrode. Triborate can form a stable SEI film containing B-O bonds on the surface of the negative electrode to inhibit the growth of lithium dendrites at high temperatures. Propyl propionate reduces viscosity and inhibits solvent volatilization; 2. In the embodiments of the present invention, through the synergistic effect of the six-component additive, it is possible to solve problems such as the acceleration of the decomposition of the electrolyte solvent at high temperatures, the generation of gases and acidic substances leading to subsequent swelling and capacity decay of the battery cells, the destruction of the CEI film and structure of the lithium iron phosphate manganese positive electrode under high voltage, and the inhibition of the dissolution of manganese ions under high temperature and high pressure.

[0008] In some embodiments, the additives include fluoroethylene carbonate with an addition amount of 6-7 wt%, 4-sulfonyl fluoride-triphenylamine benzonitrile with an addition amount of 0.6-0.8 wt%, lithium difluorophosphate with an addition amount of 1.5-2 wt%, 1,3-propane sultone with an addition amount of 0.6-0.8 wt%, triborate with an addition amount of 0.8-1 wt%, and propyl propionate with an addition amount of 2-3 wt%, based on the mass of the organic solvent.

[0009] In some embodiments, the lithium salt electrolyte includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0010] In some embodiments, the mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 50-70:30-50.

[0011] In some embodiments, the concentration of the lithium salt electrolyte in the electrolyte is 1.1-1.6 mol / L.

[0012] In some embodiments, the organic solvent includes ethylene carbonate and ethyl methyl carbonate.

[0013] In some embodiments, the volume ratio of ethylene carbonate to ethyl methyl carbonate is (1-3):(3-1).

[0014] The embodiments of the present invention also provide a preparation method of an electrolyte, including the following steps: mixing the organic solvents in proportion, adding the lithium salt and stirring evenly, and then adding the additives and stirring evenly.

[0015] In some embodiments, the preparation process is carried out in a glove box; the moisture and oxygen in the glove box are both less than 1 ppm.

[0016] An embodiment of the present invention also provides a lithium-ion battery, which includes the above-mentioned electrolyte or the electrolyte prepared by the above-mentioned preparation method, a positive electrode plate, a negative electrode plate and a separator. Detailed Embodiments

[0017] The embodiments of the present invention will be described in detail below. The embodiments are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0018] The electrolyte of the embodiment of the present invention includes a lithium salt electrolyte, an additive and an organic solvent. The lithium salt electrolyte and the additive are dissolved in the organic solvent; the additive includes fluoroethylene carbonate with an addition amount of 5-9 wt%, 4-sulfonyl fluoride-triphenylamine benzonitrile with an addition amount of 0.5-1 wt%, lithium difluorophosphate with an addition amount of 1-3 wt%, 1,3-propane sultone with an addition amount of 0.5-1 wt%, triborate with an addition amount of 0.8-1.5 wt% and propyl propionate with an addition amount of 2-4 wt%, based on the mass of the organic solvent.

[0019] In the electrolyte of the embodiment of the present invention, fluoroethylene carbonate in the used additive forms a fluorine-rich CEI film on the positive electrode. The sulfonyl fluoride group of 4-sulfonyl fluoride-triphenylamine benzonitrile captures free hydrogen ions, triphenylamine improves antioxidant properties, and the nitrile group enhances the lithium ion migration rate. Lithium difluorophosphate and 1,3-propane sultone cooperate to generate a dense LiF-POx-SOx composite CEI layer to block the side reaction between the electrolyte and the positive electrode. Triborate can form a stable SEI film containing B-O bonds on the surface of the negative electrode to inhibit the growth of lithium dendrites at high temperatures. Propyl propionate reduces viscosity and inhibits solvent volatilization. In the embodiment of the present invention, through the synergistic effect of the six-component additive, it is possible to solve problems such as the acceleration of the decomposition of the electrolyte solvent at high temperatures, the generation of gases and acidic substances leading to subsequent swelling and capacity decay of the battery cell, the destruction of the CEI film and structure of the lithium iron phosphate manganese oxide positive electrode under high voltage, and the inhibition of the dissolution of manganese ions under high temperature and high pressure.

[0020] In some embodiments, preferably, the additive includes fluoroethylene carbonate with an addition amount of 6-7 wt%, 4-sulfonyl fluoride-triphenylamine benzonitrile with an addition amount of 0.6-0.8 wt%, lithium difluorophosphate with an addition amount of 1.5-2 wt%, 1,3-propane sultone with an addition amount of 0.6-0.8 wt%, triborate with an addition amount of 0.8-1 wt% and propyl propionate with an addition amount of 2-3 wt%, based on the mass of the organic solvent.

[0021] In some embodiments, preferably, the lithium salt electrolyte includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Further preferably, the mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 50-70:30-50, such as 50:50, 55:45, 60:40, 65:35, 70:30, etc.

[0022] In the embodiments of the present invention, lithium bis(fluorosulfonyl)imide is used to improve the ionic conductivity and thermal stability of the lithium-ion battery, and lithium hexafluorophosphate is used to inhibit the corrosion of the aluminum foil current collector under high voltage, further improving the safety of the battery under high temperature and high pressure.

[0023] In some embodiments, preferably, the concentration of the lithium salt electrolyte in the electrolyte is 1.1 - 1.6 mol / L.

[0024] In some embodiments, preferably, the organic solvent includes ethylene carbonate and ethyl methyl carbonate. Further preferably, the volume ratio of ethylene carbonate to ethyl methyl carbonate is (1 - 3):(3 - 1), such as 1:3, 1:2, 1:1, 2:3, 2:1, 3:1 or 3:2, etc. Further preferably, the volume ratio of ethylene carbonate to ethyl methyl carbonate is 3:2.

[0025] In the embodiments of the present invention, ethylene carbonate and ethyl methyl carbonate are selected as solvents and the dosage ratio of the two is limited. Ethylene carbonate is suitable for high-temperature and high-pressure scenarios and can improve the cycle life and stability of the battery, while ethyl methyl carbonate is suitable for use at low temperatures. Although it is not resistant to high pressure, it can broaden the operating temperature range of the electrolyte.

[0026] The embodiments of the present invention also provide a method for preparing an electrolyte, including the following steps: mixing organic solvents in proportion, adding a lithium salt and stirring evenly, and then adding an additive and stirring evenly.

[0027] In some embodiments, preferably, the preparation process is carried out in a glove box; the moisture and oxygen in the glove box are both less than 1 ppm.

[0028] The embodiments of the present invention also provide a lithium-ion battery, including the above-mentioned electrolyte or the electrolyte prepared by the above-mentioned preparation method, a positive electrode sheet, a negative electrode sheet and a separator.

[0029] The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments.

[0030] Example 1

[0031] (1) Mix ethylene carbonate and ethyl methyl carbonate with a volume ratio of 3:2 evenly in a glove box;

[0032] (2) Add lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate with a mass ratio of 60:40 to the organic solvent obtained in step (1) and stir evenly; then add an additive and stir evenly.

[0033] In the electrolyte prepared in this example: the mass ratio of the lithium salt electrolytes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate is 60:40, where the concentration of lithium bis(fluorosulfonyl)imide is 1.3 mol / L and the concentration of lithium hexafluorophosphate is 0.3 mol / L; the organic solvent is ethylene carbonate and ethyl methyl carbonate with a volume ratio of 3:2; in the additives, the addition amount of fluoroethylene carbonate is 7 wt%, the addition amount of 4-sulfonyl fluoride-triphenylamine benzonitrile is 0.6 wt%, the addition amount of lithium difluorophosphate is 2 wt%, the addition amount of 1,3-propane sultone is 0.8 wt%, the addition amount of triborate is 1 wt%, and the addition amount of propyl propionate is 3 wt%, based on the mass of the organic solvent.

[0034] Example 2

[0035] The preparation method of this example is the same as that of Example 1, except that in the electrolyte prepared in this example: in the additives, the addition amount of fluoroethylene carbonate is 7 wt%, the addition amount of 4-sulfonyl fluoride-triphenylamine benzonitrile is 0.6 wt%, the addition amount of lithium difluorophosphate is 2 wt%, the addition amount of 1,3-propane sultone is 0.8 wt%, the addition amount of triborate is 0.8 wt%, and the addition amount of propyl propionate is 2 wt%, based on the mass of the organic solvent.

[0036] Example 3

[0037] The preparation method of this example is the same as that of Example 1, except that in the electrolyte prepared in this example: in the additives, the addition amount of fluoroethylene carbonate is 6 wt%, the addition amount of 4-sulfonyl fluoride-triphenylamine benzonitrile is 0.8 wt%, the addition amount of lithium difluorophosphate is 1.5 wt%, the addition amount of 1,3-propane sultone is 0.6 wt%, the addition amount of triborate is 0.8 wt%, and the addition amount of propyl propionate is 2 wt%, based on the mass of the organic solvent.

[0038] Comparative Example 1

[0039] The preparation method of this comparative example is the same as that of Example 1, except that in the electrolyte prepared in this comparative example: in the additives, the addition amount of fluoroethylene carbonate is 5 wt%, the addition amount of 4-sulfonyl fluoride-triphenylamine benzonitrile is 0.4 wt%, the addition amount of lithium difluorophosphate is 0.5 wt%, the addition amount of 1,3-propane sultone is 0.4 wt%, the addition amount of triborate is 0.7 wt%, and the addition amount of propyl propionate is 1.5 wt%, based on the mass of the organic solvent.

[0040] Comparative Example 2

[0041] The preparation method of this comparative example is the same as that of Example 1, except that in the electrolyte obtained in this comparative example: the addition amount of vinylene carbonate in the additive is 5 wt%, the addition amount of 4-sulfonyl fluoride-triphenylamine benzonitrile is 0.3 wt%, the addition amount of lithium difluorophosphate is 0.4 wt%, the addition amount of 1,3-propane sultone is 0.3 wt%, the addition amount of triborate is 0.6 wt%, and the addition amount of propyl propionate is 1 wt%, based on the mass of the organic solvent.

[0042] Comparative Example 3

[0043] The preparation method of this comparative example is the same as that of Example 1, except that in the electrolyte obtained in this comparative example: the addition amount of vinylene carbonate in the additive is 5 wt%, the addition amount of 4-sulfonyl fluoride-triphenylamine benzonitrile is 0.2 wt%, the addition amount of lithium difluorophosphate is 0.3 wt%, the addition amount of 1,3-propane sultone is 0.2 wt%, the addition amount of triborate is 0.5 wt%, and the addition amount of propyl propionate is 0.5 wt%, based on the mass of the organic solvent.

[0044] Comparative Example 4

[0045] The preparation method of this comparative example is the same as that of Example 1, except that in the electrolyte obtained in this comparative example: vinylene carbonate is not added.

[0046] Comparative Example 5

[0047] The preparation method of this comparative example is the same as that of Example 1, except that in the electrolyte obtained in this comparative example: 4-sulfonyl fluoride-triphenylamine benzonitrile is not added.

[0048] Comparative Example 6

[0049] The preparation method of this comparative example is the same as that of Example 1, except that in the electrolyte obtained in this comparative example: lithium difluorophosphate and 1,3-propane sultone are not added.

[0050] Comparative Example 7

[0051] The preparation method of this comparative example is the same as that of Example 1, except that in the electrolyte obtained in this comparative example: triborate is not added.

[0052] Comparative Example 8

[0053] The preparation method of this comparative example is the same as that of Example 1, except that in the electrolyte obtained in this comparative example: propyl propionate is not added.

[0054] The electrolytes, positive electrode sheets, negative electrode sheets, and separators prepared in Examples 1 to 3 and Comparative Examples 1 to 8 were assembled into lithium-ion batteries, and the performance of the lithium-ion batteries was tested. The test method was as follows: cycling 200 times at 1C, 2.5 - 4.4V at 60°C to measure the capacity retention rate; after being fully charged, storing at 70°C for 7 days to measure the capacity recovery rate; cycling 200 times at 1C, 2.5 - 4.4V at 60°C to record the gas generation degree of the battery. The results are shown in Table 1:

[0055] Table 1

[0056] Capacity retention rate Capacity recovery rate Gas generation degree Example 1 96.0％ 98.7％ No gas generation Example 2 95.5％ 98.5 No gas generation Example 3 95.3％ 98.2％ No gas generation Comparative example 1 93.2％ 97.1％ Slight gas generation Comparative example 2 92.8％ 96.7％ Slight gas generation Comparative example 3 92.0％ 96.2％ Slight gas generation Comparative example 4 91.5％ 95.6％ Slight gas generation Comparative example 5 87.3％ 94.2％ Slight gas generation Comparative example 6 85.2％ 93.1％ Substantial gas generation Comparative example 7 83.7％ 94.5％ Slight gas generation Comparative example 8 82.1％ 92.9％ Substantial gas generation

[0057] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0058] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, It includes a lithium salt electrolyte, an additive, and an organic solvent, and the lithium salt electrolyte and the additive are dissolved in the organic solvent; The additive includes fluoroethylene carbonate with an addition amount of 5-9 wt%, 4-sulfonyl fluoride-triphenylamine benzonitrile with an addition amount of 0.5-1 wt%, lithium difluorophosphate with an addition amount of 1-3 wt%, 1,3-propane sultone with an addition amount of 0.5-1 wt%, triborate with an addition amount of 0.8-1.5 wt%, and propyl propionate with an addition amount of 2-4 wt%, based on the mass of the organic solvent.

2. The electrolyte according to claim 1, characterized in that, The additive includes fluoroethylene carbonate with an addition amount of 6-7 wt%, 4-sulfonyl fluoride-triphenylamine benzonitrile with an addition amount of 0.6-0.8 wt%, lithium difluorophosphate with an addition amount of 1.5-2 wt%, 1,3-propane sultone with an addition amount of 0.6-0.8 wt%, triborate with an addition amount of 0.8-1 wt%, and propyl propionate with an addition amount of 2-3 wt%, based on the mass of the organic solvent.

3. The electrolyte according to claim 1, characterized in that, The lithium salt electrolyte includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

4. The electrolyte according to claim 3, characterized in that, The mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 50-70:30-50.

5. The electrolyte according to any one of claims 1, 3 or 4, characterized in that The concentration of the lithium salt electrolyte in the electrolyte is 1.1-1.6 mol / L.

6. The electrolyte according to claim 1, wherein The organic solvent includes ethylene carbonate and ethyl methyl carbonate.

7. The electrolyte according to claim 6, wherein The volume ratio of ethylene carbonate to ethyl methyl carbonate is (1-3):(3-1).

8. The preparation method of the electrolyte according to any one of claims 1 to 7, characterized in that, It includes the following steps: mixing the organic solvents in proportion, adding the lithium salt and stirring, and then adding the additive and stirring evenly.

9. The method for preparing the electrolyte according to claim 8, wherein, The preparation process is carried out in a glove box; the moisture and oxygen in the glove box are both less than 1 ppm.

10. A lithium-ion battery, characterized in that, It includes the electrolyte described in any one of claims 1-7 or the electrolyte prepared by the preparation method described in claim 8 or 9, a positive electrode plate, a negative electrode plate, and a separator.