CN113659205A - Lithium ion battery non-aqueous electrolyte and lithium ion battery - Google Patents

Abstract

The invention provides a lithium ion battery non-aqueous electrolyte and a lithium ion battery. According to the invention, through the matching of the film forming additive, the low impedance additive and the anti-gas-expansion water removal additive, the internal resistance of the lithium battery can be effectively reduced, the capacity attenuation of the battery cell caused by the increase of the impedance is reduced, the residual moisture in the electrolyte can be effectively removed, meanwhile, gases such as oxygen, hydrofluoric acid and the like generated in the battery cell circulation process can be absorbed, and the risk of gas expansion of the soft package battery cell is reduced.

Description

Lithium ion battery non-aqueous electrolyte and lithium ion battery

Technical Field

The invention belongs to the technical field of lithium ion batteries, and relates to a lithium ion battery non-aqueous electrolyte and a lithium ion battery.

Background

In recent years, the development of 5G technology and the widespread use of 5G base stations have directly pulled the demand for lithium ion batteries. Meanwhile, the lead-acid battery of the traditional electric vehicle is gradually replaced by the lithium ion battery, which further increases the demand of the lithium battery. The lithium iron phosphate soft package battery technology is an important development direction of the lithium ion battery technology, has the characteristics of high safety, long cycle stability, environmental friendliness and the like, is widely applied to the fields of energy storage and electric vehicles, and is more and more favored by people.

However, the lithium iron phosphate soft package battery also has certain disadvantages: (1) the conductivity of the lithium iron phosphate material is poor, and the impedance increase at the later stage of long circulation is serious; (2) the lithium iron phosphate material has a small particle diameter ratio and is coated with carbon, so that residual moisture cannot be effectively removed; (3) residual moisture can take place the side reaction in electric core, produces gas, and then can make laminate polymer battery performance decay rapidly, the development of lithium iron phosphate laminate polymer battery that these problems are also very big hindrance.

Therefore, in the art, it is desired to develop a battery material capable of reducing impedance, improving conductivity, and effectively removing moisture to prevent side reactions from occurring.

Disclosure of Invention

In view of the defects of the prior art, the invention aims to provide a lithium ion battery nonaqueous electrolyte and a lithium ion battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

in one aspect, the invention provides a lithium ion battery nonaqueous electrolyte comprising lithium hexafluorophosphate, a nonaqueous solvent and additives, the additives comprising a film forming additive, a low impedance additive and an anti-gassing water removal additive.

In the invention, through the matching of the film forming additive, the low impedance additive and the anti-swelling and water removing additive, the internal resistance of the lithium battery can be effectively reduced, the capacity attenuation of the battery cell caused by the increase of the impedance is reduced, the residual moisture in the electrolyte can be effectively removed, meanwhile, the gases such as oxygen, hydrofluoric acid and the like generated in the battery cell circulation process can be absorbed, and the risk of swelling generated in the soft package battery cell is reduced. And the low-impedance additive can effectively reduce the consumption of the film-forming additive in the formation stage of the battery, so that the film-forming additive can continuously repair an SEI film in the circulation process, and the stability of the electric core system in the circulation process is further ensured. The anti-ballooning water-removing additive can consume acidic substances such as hydrofluoric acid and the like, inhibit the breakage of the hydrofluoric acid to an SEI film, and reduce the loss of the film-forming additive in the circulating process, thereby prolonging the circulating life of the battery cell.

Preferably, the film-forming additive comprises a combination of vinylene carbonate and fluoroethylene carbonate.

Preferably, the content of the vinylene carbonate in the lithium ion battery nonaqueous electrolyte solution is 0.5 to 3% by mass (e.g., 0.5%, 0.8%, 1%, 1.5%, 1.8%, 2%, 2.5%, 2.8% or 3%) and the content of the fluoroethylene carbonate in the lithium ion battery nonaqueous electrolyte solution is 0.2 to 2% by mass (e.g., 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8% or 2%).

Preferably, the film-forming additive is present in the nonaqueous electrolyte solution of the lithium ion battery in an amount of 2 to 5% by mass (e.g., 2%, 2.2%, 2.5%, 2.8%, 3%, 3.5%, 3.8%, 4%, 4.5%, 4.8%, or 5%).

Preferably, the low impedance additive comprises a combination of lithium difluorophosphate and lithium difluorooxalate phosphate.

Preferably, the lithium difluorophosphate is contained in the lithium ion battery non-aqueous electrolyte in an amount of 0.2% to 1% (e.g., 0.2%, 0.5%, 0.8%, or 1%) by mass, and the lithium difluorooxalate phosphate is contained in the lithium ion battery non-aqueous electrolyte in an amount of 0.1% to 0.5% (e.g., 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%) by mass.

Preferably, the low impedance additive is present in the lithium ion battery nonaqueous electrolyte in an amount of 0.3 to 2% by mass, for example 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8% or 2%.

Preferably, the anti-ballooning water-removal additive comprises a combination of triphenyl phosphite and dicyclohexylcarbodiimide.

Preferably, the triphenyl phosphite is contained in the lithium ion battery nonaqueous electrolyte in an amount of 0.005% to 0.1% by mass (e.g., 0.005%, 0.008%, 0.01%, 0.03%, 0.05%, 0.08%, 0.1%) and the dicyclohexylcarbodiimide is contained in the lithium ion battery nonaqueous electrolyte in an amount of 0.001% to 0.02% by mass (e.g., 0.001%, 0.003%, 0.005%, 0.008%, 0.01%, 0.015%, 0.018%, or 0.02%).

Preferably, the content of the anti-ballooning water-removing additive in the lithium ion battery nonaqueous electrolyte solution is 0.01 to 0.1% by mass, for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.1%.

Preferably, the lithium hexafluorophosphate is present in the lithium ion battery nonaqueous electrolyte in an amount of 13 to 17% by mass, for example, 13%, 14%, 15%, 16% or 17%.

Preferably, the nonaqueous solvent comprises the following components in percentage by mass of the nonaqueous electrolyte of the lithium ion battery: 5% to 20% (e.g. 5%, 7%, 9%, 10%, 13%, 15%, 18% or 20%) dimethyl carbonate, 15% to 30% (e.g. 15%, 18%, 20%, 22%, 25%, 28% or 30%) ethylene carbonate, 30% to 60% (e.g. 30%, 35%, 40%, 45%, 50%, 55% or 605) ethyl methyl carbonate, 2% to 7% (e.g. 2%, 3%, 4%, 5%, 6% or 7%) propylene carbonate.

Preferably, the nonaqueous solvent accounts for 75 to 90 mass percent of the nonaqueous electrolyte of the lithium ion battery, for example, 75%, 78%, 80%, 83%, 85%, 88% or 90%.

In another aspect, the invention provides a lithium ion battery, which comprises the lithium ion battery nonaqueous electrolyte.

Preferably, the lithium ion battery is a soft-package lithium iron phosphate lithium ion battery.

Compared with the prior art, the invention has the following beneficial effects:

the electrolyte can ensure high lithium salt concentration, and ensures that the consumption of the lithium salt in the circulation process does not influence the conductivity of the electrolyte; the internal resistance of the lithium battery can be effectively reduced, and the capacity attenuation of the battery cell caused by the increase of the impedance is reduced; residual moisture in the electrolyte is effectively removed, and meanwhile, gases such as oxygen and hydrofluoric acid generated in the battery cell circulating process can be absorbed, so that the risk of flatulence generated by a soft package battery cell is reduced.

Drawings

Fig. 1 is a graph of cycle performance test results of the lithium iron phosphate soft-package cells of example 1 and comparative example 1 of the present invention.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

The preparation method of the electrolyte comprises the following steps:

weighing different solvents in proportion by using an electronic balance in a glove box under argon atmosphere (the oxygen content is less than or equal to 1ppm, the water content is less than or equal to 1ppm), adding the weighed solvents into a clean aluminum bottle, and shaking up to fully and uniformly mix the solvents; then weighing lithium hexafluorophosphate according to a proportion, slowly adding the lithium hexafluorophosphate into the mixed solvent, controlling the salt adding speed and preventing the temperature of the solution from rising too high; after the solution is cooled to room temperature, adding the required additives in proportion; finally, the solution is stirred sufficiently to dissolve all the substances sufficiently to form a uniform and stable solution. Each electrolyte was prepared in a mass of 1 kg.

Comparative example 1

The comparative example was prepared according to the electrolyte preparation method, and the contents of the components were as follows: 27% of ethylene carbonate, 40.5% of ethyl methyl carbonate, 12% of dimethyl carbonate, 5% of propylene carbonate, 1.5% of vinylene carbonate, 1% of fluoroethylene carbonate and 13% of lithium hexafluorophosphate.

Comparative example 2

The comparative example was prepared according to the electrolyte preparation method, and the contents of the components were as follows: 26.72% of ethylene carbonate, 40.08% of ethyl methyl carbonate, 12% of dimethyl carbonate, 5% of propylene carbonate, 1.5% of vinylene carbonate, 1% of fluoroethylene carbonate, 0.5% of lithium difluorophosphate, 0.2% of lithium difluorooxalato phosphate and 13% of lithium hexafluorophosphate.

Comparative example 3

The comparative example was prepared according to the electrolyte preparation method, and the contents of the components were as follows: 26.71 percent of ethylene carbonate, 40.06 percent of ethyl methyl carbonate, 12 percent of dimethyl carbonate, 5 percent of propylene carbonate, 2.5 percent of vinylene carbonate, 0.5 percent of lithium difluorophosphate, 0.2 percent of lithium difluorooxalate phosphate, 0.02 percent of dicyclohexylcarbodiimide, 0.01 percent of triphenyl phosphite and 13 percent of lithium hexafluorophosphate.

Comparative example 4

The comparative example was prepared according to the electrolyte preparation method, and the contents of the components were as follows: 26.71 percent of ethylene carbonate, 40.06 percent of ethyl methyl carbonate, 12 percent of dimethyl carbonate, 5 percent of propylene carbonate, 2.5 percent of fluoroethylene carbonate, 0.5 percent of lithium difluorophosphate, 0.2 percent of lithium difluorooxalate phosphate, 0.02 percent of dicyclohexylcarbodiimide, 0.01 percent of triphenyl phosphite and 13 percent of lithium hexafluorophosphate.

Comparative example 5

The comparative example was prepared according to the electrolyte preparation method, and the contents of the components were as follows: 26.71 percent of ethylene carbonate, 40.06 percent of ethyl methyl carbonate, 12 percent of dimethyl carbonate, 5 percent of propylene carbonate, 1.5 percent of vinylene carbonate, 1 percent of fluoroethylene carbonate, 0.7 percent of lithium difluorooxalate phosphate, 0.02 percent of dicyclohexylcarbodiimide, 0.01 percent of triphenyl phosphite and 13 percent of lithium hexafluorophosphate.

Comparative example 6

The comparative example was prepared according to the electrolyte preparation method, and the contents of the components were as follows: 26.71 percent of ethylene carbonate, 40.06 percent of ethyl methyl carbonate, 12 percent of dimethyl carbonate, 5 percent of propylene carbonate, 1.5 percent of vinylene carbonate, 1 percent of fluoroethylene carbonate, 0.7 percent of lithium difluorophosphate, 0.02 percent of dicyclohexylcarbodiimide, 0.01 percent of triphenyl phosphite and 13 percent of lithium hexafluorophosphate.

Comparative example 7

The comparative example was prepared according to the electrolyte preparation method, and the contents of the components were as follows: 26.71 percent of ethylene carbonate, 40.06 percent of ethyl methyl carbonate, 12 percent of dimethyl carbonate, 5 percent of propylene carbonate, 1.5 percent of vinylene carbonate, 1 percent of fluoroethylene carbonate, 0.5 percent of lithium difluorophosphate, 0.2 percent of lithium difluorooxalato phosphate, 0.03 percent of dicyclohexylcarbodiimide and 13 percent of lithium hexafluorophosphate.

Comparative example 8

The comparative example was prepared according to the electrolyte preparation method, and the contents of the components were as follows: 26.71 percent of ethylene carbonate, 40.06 percent of ethyl methyl carbonate, 12 percent of dimethyl carbonate, 5 percent of propylene carbonate, 1.5 percent of vinylene carbonate, 1 percent of fluoroethylene carbonate, 0.5 percent of lithium difluorophosphate, 0.2 percent of lithium difluorooxalato phosphate, 0.03 percent of triphenyl phosphite and 13 percent of lithium hexafluorophosphate.

Example 1

In this example, the electrolyte is prepared according to the electrolyte preparation method, and the contents of the components are as follows: 26.71 percent of ethylene carbonate, 40.06 percent of ethyl methyl carbonate, 12 percent of dimethyl carbonate, 5 percent of propylene carbonate, 1.5 percent of vinylene carbonate, 1 percent of fluoroethylene carbonate, 0.5 percent of lithium difluorophosphate, 0.2 percent of lithium difluorooxalato phosphate, 0.02 percent of dicyclohexylcarbodiimide, 0.01 percent of triphenyl phosphite and 13 percent of lithium hexafluorophosphate.

Example 2

In this example, the electrolyte is prepared according to the electrolyte preparation method, and the contents of the components are as follows: 22% of ethylene carbonate, 51.67% of ethyl methyl carbonate, 5% of dimethyl carbonate, 5% of propylene carbonate, 2% of vinylene carbonate, 0.5% of fluoroethylene carbonate, 0.5% of lithium difluorophosphate, 0.3% of lithium difluorooxalato phosphate, 0.02% of dicyclohexylcarbodiimide, 0.01% of triphenyl phosphite and 13% of lithium hexafluorophosphate.

Example 3

In this example, the electrolyte is prepared according to the electrolyte preparation method, and the contents of the components are as follows: 27% of ethylene carbonate, 38.77% of ethyl methyl carbonate, 10% of dimethyl carbonate, 7% of propylene carbonate, 1.5% of vinylene carbonate, 1% of fluoroethylene carbonate, 0.5% of lithium difluorophosphate, 0.2% of lithium difluorooxalato phosphate, 0.02% of dicyclohexylcarbodiimide, 0.01% of triphenyl phosphite and 14% of lithium hexafluorophosphate.

Example 4

In this example, the electrolyte is prepared according to the electrolyte preparation method, and the contents of the components are as follows: 27% of ethylene carbonate, 38.24% of ethyl methyl carbonate, 10% of dimethyl carbonate, 7% of propylene carbonate, 1.5% of vinylene carbonate, 1% of fluoroethylene carbonate, 0.5% of lithium difluorophosphate, 0.2% of lithium difluorooxalato phosphate, 0.01% of dicyclohexylcarbodiimide, 0.005% of triphenyl phosphite and 14.5% of lithium hexafluorophosphate.

Example 5

In this example, the electrolyte is prepared according to the electrolyte preparation method, and the contents of the components are as follows: 24% of ethylene carbonate, 39.44% of ethyl methyl carbonate, 15% of dimethyl carbonate, 2% of propylene carbonate, 1.5% of vinylene carbonate, 2% of fluoroethylene carbonate, 1% of lithium difluorophosphate, 0.5% of lithium difluorooxalate, 0.01% of dicyclohexylcarbodiimide, 0.005% of triphenyl phosphite and 14.5% of lithium hexafluorophosphate.

Example 6

26% of ethylene carbonate, 35.98% of ethyl methyl carbonate, 15% of dimethyl carbonate, 5% of propylene carbonate, 0.5% of vinylene carbonate, 2% of fluoroethylene carbonate, 1% of lithium difluorophosphate, 0.5% of lithium difluorooxalate phosphate, 0.01% of dicyclohexylcarbodiimide, 0.01% of tris (trimethylsilyl) phosphite and 14% of lithium hexafluorophosphate.

Example 7

26% of ethylene carbonate, 35.98% of ethyl methyl carbonate, 15% of dimethyl carbonate, 5% of propylene carbonate, 3% of vinylene carbonate, 0.2% of fluoroethylene carbonate, 0.2% of lithium difluorophosphate, 0.1% of lithium difluorooxalato phosphate, 0.01% of dicyclohexylcarbodiimide, 0.01% of tris (trimethylsilyl) phosphite and 14.5% of lithium hexafluorophosphate.

Example 8

26% of ethylene carbonate, 35.899% of methyl ethyl carbonate, 15% of dimethyl carbonate, 5% of propylene carbonate, 2% of vinylene carbonate, 1% of fluoroethylene carbonate, 0.5% of lithium difluorophosphate, 0.5% of lithium difluorooxalate phosphate, 0.01% of dicyclohexylcarbodiimide, 0.001% of tris (trimethylsilyl) phosphite and 14% of lithium hexafluorophosphate.

And respectively injecting the prepared lithium ion battery electrolyte into a soft package lithium ion battery with a positive electrode material of lithium iron phosphate and an artificial graphite negative electrode, and carrying out processes of packaging, shelving, formation, aging, secondary packaging, capacity grading and the like on the battery after liquid injection to obtain the lithium iron phosphate soft package lithium ion battery. The nominal capacity of a single cell is 5Ah, the lower limit voltage is 2.5V, and the upper limit voltage is 3.65V.

The batteries prepared in the examples and comparative examples were subjected to 25 ℃ cycle performance test and high temperature 70 ℃ 7-day storage test, and the test results are shown in table 1.

TABLE 1.25 ℃ cycling Performance and high temperature 70 ℃ storage Performance

Comparing comparative example 1, comparative example 2 and example 1, it can be seen that: the low-impedance additive provided by the embodiment of the invention can effectively reduce impedance, and particularly, the internal resistance is only increased by 7.8% after 1000 cycles (fig. 1 shows the cycle performance test results of the lithium iron phosphate soft-package battery cells of the embodiment 1 and the comparative example 1), which shows that lithium difluorophosphate and lithium difluorooxalato phosphate can effectively inhibit the increase of cycle during the cycle process; simultaneously, the anti-flatulence and dewatering additive can well solve the flatulence problem of the soft package battery cell, and after dicyclohexylcarbodiimide and triphenyl phosphite are added, the storage volume of the battery cell is expanded by only about 2% and the phenomenon of gas generation is not seen.

Comparing comparative example 3, comparative example 4 and example 1, the capacity retention rate of comparative example 3 at 1000 weeks is 91.3%, which is 4 percentage points lower than that of example 1, while the capacity retention rate of comparative example 4 is only 71.2%, which indicates that the single use of vinylene carbonate or fluoroethylene carbonate cannot effectively improve the cycle performance, and the common use of vinylene carbonate and fluoroethylene carbonate can effectively inhibit the side reaction of the electrode and electrolyte interface, reduce the consumption rate of the film-forming additive, and prolong the service life of the battery cell.

Comparing comparative example 5, comparative example 6 and example 1, the increase in impedance of comparative examples 4 and 5 was significantly higher than that of example 1, which also demonstrates that the use of lithium difluorophosphate and lithium difluorooxalate in combination can better suppress the increase in impedance. Comparing comparative example 7, comparative example 8 and example 1, the volume expansion of comparative examples 7 and 8 is more pronounced, which also demonstrates that the use of triphenyl phosphite together with dicyclohexylcarbodiimide better suppresses the side reactions caused by the acid and water, thereby reducing the rate of volume expansion. At the same time, the suppression of the impedance and the reduction of the volume expansion can further improve the cycle performance of the battery.

In addition, examples 4 and 5 also showed good cycle performance and high-temperature storage performance, which indicates that dicyclohexylcarbodiimide and triphenyl phosphite can also play a role in suppressing gas evolution and removing water with a small amount of addition.

The applicant states that the present invention is illustrated by the above examples of the process of the present invention, but the present invention is not limited to the above process steps, i.e. it is not meant that the present invention must rely on the above process steps to be carried out. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.

Claims (10)

1. The non-aqueous electrolyte of the lithium ion battery is characterized by comprising lithium hexafluorophosphate, a non-aqueous solvent and additives, wherein the additives comprise a film forming additive, a low impedance additive and an anti-ballooning water removal additive.

2. The nonaqueous electrolyte solution for lithium ion batteries according to claim 1, wherein the film-forming additive comprises a combination of vinylene carbonate and fluoroethylene carbonate.

3. The nonaqueous electrolyte solution for lithium ion batteries according to claim 2, wherein the vinylene carbonate is contained in the nonaqueous electrolyte solution for lithium ion batteries in an amount of 0.5 to 3% by mass, and the fluoroethylene carbonate is contained in the nonaqueous electrolyte solution for lithium ion batteries in an amount of 0.2 to 2% by mass.

4. The lithium-ion battery nonaqueous electrolyte solution of any one of claims 1 to 3, wherein the film-forming additive is contained in the lithium-ion battery nonaqueous electrolyte solution in an amount of 2 to 5% by mass.

5. The nonaqueous electrolyte solution for lithium-ion batteries according to any one of claims 1 to 4, wherein the low impedance additive comprises a combination of lithium difluorophosphate and lithium difluorooxalate phosphate;

preferably, the mass percentage of the lithium difluorophosphate in the lithium ion battery non-aqueous electrolyte is 0.2-1%, and the mass percentage of the lithium difluorooxalate phosphate in the lithium ion battery non-aqueous electrolyte is 0.1-0.5%.

6. The nonaqueous electrolyte solution for lithium ion batteries according to any one of claims 1 to 5, wherein the low impedance additive is contained in the nonaqueous electrolyte solution for lithium ion batteries in an amount of 0.3 to 2% by mass.

7. The nonaqueous electrolyte solution for a lithium-ion battery according to any one of claims 1 to 6, wherein the anti-ballooning water-removing additive comprises a combination of triphenyl phosphite and dicyclohexylcarbodiimide;

preferably, the mass percentage content of the triphenyl phosphite in the lithium ion battery non-aqueous electrolyte is 0.005-0.1%, and the mass percentage content of the dicyclohexylcarbodiimide in the lithium ion battery non-aqueous electrolyte is 0.001-0.02%;

preferably, the mass percentage of the anti-ballooning water-removing additive in the lithium ion battery non-aqueous electrolyte is 0.01-0.1%.

8. The nonaqueous electrolyte solution for lithium ion batteries according to any one of claims 1 to 7, wherein the lithium hexafluorophosphate is contained in the nonaqueous electrolyte solution for lithium ion batteries in an amount of 13 to 17% by mass.

9. The nonaqueous electrolyte solution for lithium ion batteries according to any one of claims 1 to 8, wherein the nonaqueous solvent comprises the following components in percentage by mass of the nonaqueous electrolyte solution for lithium ion batteries: 5-20% of dimethyl carbonate, 15-30% of ethylene carbonate, 30-60% of ethyl methyl carbonate and 2-7% of propylene carbonate;

preferably, the nonaqueous solvent accounts for 75-90% of the nonaqueous electrolyte of the lithium ion battery by mass.

10. A lithium ion battery comprising the lithium ion battery nonaqueous electrolyte solution according to any one of claims 1 to 9;

preferably, the lithium ion battery is a soft-package lithium iron phosphate lithium ion battery.

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