CN115579518A

CN115579518A - Electrolyte and lithium ion battery

Info

Publication number: CN115579518A
Application number: CN202211287369.6A
Authority: CN
Inventors: 余乐; 林双双
Original assignee: Envision Power Technology Jiangsu Co Ltd; Envision Ruitai Power Technology Shanghai Co Ltd
Current assignee: Envision Power Technology Jiangsu Co Ltd; Envision Ruitai Power Technology Shanghai Co Ltd
Priority date: 2022-10-20
Filing date: 2022-10-20
Publication date: 2023-01-06

Abstract

The invention provides an electrolyte. The electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises a first additive, the first additive comprises a fluorosulfonyl fluorocarboxylic acid ester additive shown as a formula 1, wherein at least one of R1 and R2 is a fluorine atom or a fluorine-substituted hydrocarbon group containing 1 to 6 carbon atoms, and the number of fluorine atoms in the fluorosulfonyl fluorocarboxylic acid ester additive is 1 to 3. The electrolyte is applied to the lithium ion battery, so that the normal-high temperature cycle life and the high-temperature storage performance of the battery are improved.

Description

Electrolyte and lithium ion battery

Technical Field

The invention relates to the field of lithium ion batteries, in particular to an electrolyte and a lithium ion battery.

Background

Lithium ion batteries are widely used in daily life, work and production, but people have higher and higher requirements on the lithium ion batteries, such as higher energy density. The development of a high-energy-density lithium ion battery can improve the voltage of a positive electrode material or adopt a high-nickel ternary positive electrode material and the like, but the existing scheme can generate adverse effects on the electrolyte. If the content of the nickel element is too high, the stability of the cathode material is reduced, and trivalent unstable nickel ions can cause the electrolyte to be subjected to oxidative decomposition in the cathode; the electrolyte is more easily oxidized and decomposed by increasing the charging voltage of the battery, and the situation can cause a series of problems of battery flatulence, interface impedance increase and the like. In view of the above, there is a need to develop an electrolyte formulation with improved battery capacity and dynamic performance, and long cycle life, good rate capability and high temperature storage capability.

The existing commercial carbonate-based electrolyte mainly has two problems under high voltage: 1) The electrolyte is easy to oxidize and decompose on the surface of the anode of the high-voltage lithium ion battery, so that the internal resistance of the lithium ion battery is increased; 2) The lithium ion positive electrode transition metal is easily dissolved out and reduced under high voltage, so that the impedance of the lithium ion battery is increased, and the performance of the battery is deteriorated. The commonly used method for improving the high voltage performance of the electrolyte comprises the following steps: and (1) increasing the concentration of the electrolyte. The oxidation resistance of the electrolyte can be improved by increasing the concentration of the carbonate electrolyte. The lithium salt concentration in the high-concentration electrolyte is high, and the oxidation resistance of solvent molecules under high voltage is enhanced, so that the stability and the flame retardance of the high-concentration electrolyte are enhanced, and the performance and the safety of the battery are improved compared with those of the traditional electrolyte. And (2) adding a specific additive. The addition of additives is one of the ways to address the chemistry of many materials, and can also be used with high voltage electrolytes. The high-voltage electrolyte additive can form a positive electrode protective film on the surface of a positive electrode, reduce the contact between the positive electrode and the electrolyte and inhibit the oxidation reaction of the electrolyte. At present, organic additives mainly comprising vinylene carbonate, novel organic additives and the like are mostly adopted as high-voltage electrolyte additives, and the main mechanism of the high-voltage electrolyte is that organic matters are preferentially polymerized or decomposed in the charging and discharging processes to form an electrode protective film.

The high-voltage working environment of the battery is a normal state, and with the arrival of an ultrahigh-voltage super-charging energy-supplementing technology, the requirement on the working performance of the battery in the high-voltage environment is an important development direction, and the high-voltage electrolyte is a popular research field. However, at present, since problems such as technical problems and cost problems remain to be solved, development efforts still need to be increased.

Disclosure of Invention

In view of the defects in the prior art, the invention aims to provide a high-voltage resistant electrolyte with long sequential life, high rate capability and high-temperature storage performance and a lithium ion battery containing the same, wherein the electrolyte comprises a lithium salt, a non-aqueous organic solvent and additives, the additives comprise a first additive, the first additive comprises a fluorosulfonyl fluorocarboxylic acid ester additive shown in a formula 1,

wherein at least one of R1 and R2 is a fluorine atom or a fluorine-substituted hydrocarbon group having 1 to 6 carbon atoms, and the number of fluorine atoms in the fluorosulfonyl fluorocarboxylic acid ester additive is 1 to 3.

The second purpose of the invention is to provide a lithium ion battery, which comprises the electrolyte according to the first purpose, and also comprises a positive electrode and a negative electrode.

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

the medium electrolyte is applied to the lithium ion battery, so that the normal-high temperature cycle life and the high-temperature storage performance of the battery are improved. The normal temperature cycle life of the battery can reach more than 950 times, the high temperature cycle life can reach more than 790 times, the high temperature storage impedance growth rate in 60 days can be lower than 16%, and the high temperature storage gas production rate in 60 days can be lower than 10%.

Detailed Description

The invention provides an electrolyte, which comprises a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises a first additive, the first additive comprises a fluorosulfonyl fluorocarboxylic acid ester additive shown as a formula 1,

wherein, at least one of R1 and R2 is fluorine atom or fluorine substituted hydrocarbyl containing 1 to 6 carbon atoms, and the fluorine atom number in the fluorosulfonyl fluorocarboxylic acid ester additive is 1 to 3.

The number of carbon atoms may be 1, 2, 3, 4, 5 or 6, the number of fluorine atoms may be 1, 2 or 3, the degree of unsaturation may be 0 to 4, 0, 1, 2, 3 or 4, but the present invention is not limited to the recited values, and other values not recited in the above numerical ranges are also applicable.

The fluorosulfonyl fluorocarboxylic acid ester additive shown in the formula 1 contains fluorine-containing substituent groups, so that a passivation film rich in inorganic components such as LiF can be generated, and the internal resistance of the battery can be effectively reduced. The trimethylsilyl and the trimethylsiloxy on the molecular structure can also generate a stable anode passivation film and can eliminate trace HF in the electrolyte, thereby improving the stability of the anode material and the electrolyte at high temperature, inhibiting gas generation and improving the high-temperature cycle and storage performance of the battery. Thus, the problems of low high-temperature storage performance, short high-temperature cycle life, serious gas generation and the like of the lithium ion battery under high voltage are solved.

As a preferred embodiment of the present invention, the fluorosulfonyl fluorocarboxylic acid ester additive includes any one of compounds represented by formulas 2 to 7 or a combination of at least two thereof, wherein the combination is typically, but not limited to, a combination of formulas 2 and 3, a combination of formulas 3 and 4, a combination of formulas 4 and 5, a combination of formulas 5 and 6, or a combination of formulas 6 and 7, and the like.

Preferably, the fluorosulfonyl fluorocarboxylic acid ester additive includes a combination of at least two of the compounds represented by formula 2 to formula 7. In a preferred embodiment of the present invention, the mass fraction of the fluorosulfonyl fluorocarboxylic acid ester additive in the electrolyte is 0.1% to 10% based on 100% by mass of the electrolyte, wherein the mass fraction may be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned value range are also applicable, and preferably 0.1% to 5%.

If the content of the fluorosulfonyl fluorocarboxylic acid ester additive is too low, the improvement effect of the additive on inhibiting gas generation is not obvious, and if the content of the additive is too high, a thicker passivation film is formed by the addition of the additive, so that the internal impedance of the battery is increased, and the capacity of the battery is reduced. The mass of the additive accounts for 0.1-10% of the mass of the electrolyte, so that the battery can obtain better high-temperature performance and has higher capacity exertion.

As a preferred embodiment of the present invention, the additive further comprises a second additive.

Preferably, the second additive comprises a cyclic carbonate, a cyclic sultone, a cyclic sulfate, and a lithium-containing additive.

Preferably, the cyclic carbonate includes any one of vinylene carbonate, fluoroethylene carbonate or ethylene carbonate or a combination of at least two thereof, wherein typical but non-limiting examples thereof are: a combination of vinylene carbonate and fluoroethylene carbonate, a combination of fluoroethylene carbonate and ethylene carbonate, or a combination of vinylene carbonate and ethylene carbonate, and the like.

Preferably, the cyclic sultone comprises 1, 3-propane sultone and/or 1, 3-propene sultone.

Preferably, the cyclic sulfate includes vinyl sulfate.

Preferably, the lithium-containing additive comprises any one of lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaoxalato borate, lithium tetrafluoroborate or lithium difluorooxalato phosphate, or a combination of at least two thereof, wherein typical but non-limiting examples of such combinations are: a combination of lithium difluorophosphate and lithium difluorooxalato borate, a combination of lithium difluorooxalato borate and lithium dioxaoxalato borate, a combination of lithium dioxaoxalato borate and lithium tetrafluoroborate, a combination of lithium tetrafluoroborate and lithium difluorooxalato phosphate, and the like.

In a preferred embodiment of the present invention, the second additive accounts for 0.5 to 20% of the electrolyte solution by mass based on 100% of the electrolyte solution, wherein the mass fraction may be 0.5%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or the like, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned value range are also applicable. Preferably 0.5% to 5%.

As a preferred embodiment of the present invention, the non-aqueous organic solvent includes any one of vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate or diethyl carbonate, or a combination of at least two thereof, wherein the combination is exemplified by, but not limited to: a combination of vinylene carbonate and dimethyl carbonate, a combination of dimethyl carbonate and ethyl methyl carbonate, a combination of ethyl methyl carbonate and propylene carbonate, a combination of propylene carbonate and diethyl carbonate, or the like.

As a preferable technical scheme of the invention, the lithium salt comprises LiFSI, liTFSI and LiPF ₆ 、LiBF ₄ 、LiClO ₄ Or LiAsF ₆ Any one or a combination of at least two of the following, typical but non-limiting examples of which are: combination of LiFSI and LiTFSI, liTFSI and LiPF ₆ Combination of (2), liPF ₆ And LiBF ₄ Combination of (1), liBF ₄ And LiClO ₄ Or LiClO ₄ And LiAsF ₆ Combinations of (a) and (b), and the like.

Preferably, the concentration of the lithium salt in the electrolyte is 0.5M to 2M, wherein the concentration may be 0.5M, 0.8M, 1.0M, 1.2M, 1.4M, 1.6M, 1.8M, 2M, or the like, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.

Preferably, the mass fraction of the lithium salt in the electrolyte is 12% to 15% based on 100% of the mass of the electrolyte, wherein the mass fraction may be 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, or the like, but is not limited to the recited values, and other values not recited in this range are also applicable.

The invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode and an electrolyte solution according to one purpose.

As a preferred embodiment of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material.

Preferably, the positive active material includes any one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide or a combination of at least two thereof, wherein the combination is typically but not limited to: a combination of lithium cobalt oxide and lithium nickel oxide, a combination of lithium manganese oxide and lithium nickel manganese oxide, a combination of lithium nickel manganese oxide and lithium nickel cobalt manganese oxide, or a combination of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, and the like.

As a preferred embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material.

Preferably, the negative active material comprises any one of soft carbon, hard carbon, artificial graphite, natural graphite, silicon oxy-compound, silicon carbon compound, or lithium titanate, or a combination of at least two thereof, wherein the combination is typically but not limited to: a combination of soft carbon and hard carbon, a combination of hard carbon and artificial graphite, a combination of artificial graphite and natural graphite, a combination of natural graphite and silicon, a combination of silicon and silicon oxy compound, a combination of silicon oxy compound and silicon carbon compound, or a combination of silicon carbon compound and lithium titanate, and the like.

The numerical ranges set forth herein include not only the recited values but also any values between the recited numerical ranges not enumerated herein, and are not intended to be exhaustive or otherwise clear from the intended disclosure of the invention in view of brevity and clarity.

The technical solution of the present invention is further explained by the following embodiments.

Example 1

The embodiment provides a lithium ion battery electrolyte:

the lithium ion battery electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive.

Non-aqueous organic solvent: ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate; based on 100% of the electrolyte, the ethylene carbonate accounts for 13% of the electrolyte, the ethyl methyl carbonate accounts for 45% of the electrolyte, and the diethyl carbonate accounts for 24% of the electrolyte.

Lithium salt: lithium hexafluorophosphate; the mass fraction of the lithium hexafluorophosphate in the electrolyte is 13.5% based on 100% by mass of the electrolyte.

Additive: a compound of formula 2

Lithium difluorophosphate, vinylene carbonate, 1, 3-propylene sultone and vinyl sulfate; based on 100% of the mass of the electrolyte, the compound shown in the formula 2 accounts for 1% of the mass of the electrolyte, the lithium difluorophosphate accounts for 0.5% of the mass of the electrolyte, the vinylene carbonate accounts for 2% of the mass of the electrolyte, the 1, 3-propylene sultone accounts for 0.2% of the mass of the electrolyte, and the vinyl sulfate accounts for 0.8% of the mass of the electrolyte.

Example 2

The embodiment provides a lithium ion battery electrolyte:

Non-aqueous organic solvent: vinylene carbonate, propylene carbonate, and diethyl carbonate; the electrolyte is characterized in that the electrolyte is 100% in mass, the vinylene carbonate accounts for 10% of the electrolyte, the propylene carbonate accounts for 45% of the electrolyte, and the diethyl carbonate accounts for 29.4% of the electrolyte.

Lithium salt: liFSI; and based on 100% of the mass of the electrolyte, the mass fraction of the LiFSI in the electrolyte is 12%.

Additive: a compound represented by the formula 2

Lithium difluorooxalato borate, fluoroethylene carbonate, 1, 3-propane sultone and vinyl sulfate;based on 100% of the electrolyte, the compound shown in the formula 2 accounts for 0.1% of the electrolyte, the lithium difluoro-oxalato-borate accounts for 0.5% of the electrolyte, the fluoroethylene carbonate accounts for 2% of the electrolyte, the 1, 3-propane sultone accounts for 0.2% of the electrolyte, and the vinyl sulfate accounts for 0.8% of the electrolyte.

Example 3

The embodiment provides a lithium ion battery electrolyte:

Non-aqueous organic solvent: ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate; based on 100% of the electrolyte, the ethylene carbonate accounts for 13% of the electrolyte, the ethyl methyl carbonate accounts for 39.5% of the electrolyte, and the diethyl carbonate accounts for 24% of the electrolyte.

Lithium salt: liClO ₄ (ii) a The LiClO is calculated by taking the mass of the electrolyte as 100 percent ₄ Accounting for 15 percent of the mass fraction of the electrolyte.

Additive: a compound represented by the formula 2

Lithium tetrafluoroborate, ethylene carbonate, 1, 3-propylene sultone, and vinyl sulfate; based on 100% of the electrolyte, the compound shown in the formula 2 accounts for 5% of the electrolyte, the lithium tetrafluoroborate accounts for 0.5% of the electrolyte, the ethylene carbonate accounts for 2% of the electrolyte, the 1, 3-propylene sultone accounts for 0.2% of the electrolyte, and the vinyl sulfate accounts for 0.8% of the electrolyte.

Example 4

This example is prepared by adding a compound of formula 2 to the additive

Substitution is made to a compound represented by formula 3

Otherwise, the conditions were the same as in example 1.

Example 5

This example excludes the compound of formula 2 as an additive

Substitution is made to a compound represented by formula 4

Otherwise, the conditions were the same as in example 1.

Example 6

This example excludes the compound of formula 2 as an additive

Substitution is made to a compound represented by the formula 5

Otherwise, the conditions were the same as in example 1.

Example 7

This example excludes the compound of formula 2 as an additive

Instead, as shown in equation 6Of (a) a compound

Otherwise, the conditions were the same as in example 1.

Example 8

This example excludes the compound of formula 2 as an additive

Substitution is made to a compound represented by formula 7

Otherwise, the conditions were the same as in example 1.

Example 9

In this example, the conditions were the same as in example 1 except that the mass fraction of the compound represented by formula 2 in the electrolyte was changed from 1% to 10%, and the mass fraction of ethyl methyl carbonate in the electrolyte was changed from 45% to 36%.

Example 10

This example was carried out under the same conditions as example 1 except that lithium difluorophosphate was not added and the mass fraction of lithium hexafluorophosphate in the electrolyte was changed to 13.5% to 14%.

Example 11

The conditions of this example were the same as those of example 1, except that vinylene carbonate was not added, and the mass fraction of ethyl methyl carbonate in the electrolyte was changed from 45% to 47%.

Example 12

The conditions of this example were the same as those of example 1 except that 1, 3-propylene sultone was not added, and 45.2% was replaced with 45% of ethyl methyl carbonate in the mass fraction of the electrolyte.

Example 13

The present example was carried out under the same conditions as in example 1 except that no ethylene sulfate was added and 45.8% was replaced with 45% of ethyl methyl carbonate based on 45% of the electrolyte.

Example 14

This example was carried out under the same conditions as in example 1 except that lithium difluorophosphate, vinylene carbonate, 1, 3-propylene sultone and vinyl sulfate were not added and 49.5% was substituted instead of 45% by ethyl methyl carbonate based on the mass fraction of the electrolyte.

Example 15

In the embodiment, a compound which accounts for 1 percent of the mass fraction of the electrolyte and is shown as a formula 5 is added

Namely, the electrolyte is added with the compounds shown in the formulas 2 and 5 at the same time, and the mass fraction of the ethyl methyl carbonate in the electrolyte is 45% and is replaced by 44%, and the other conditions are the same as the embodiment 1.

Example 16

In the embodiment, a compound which accounts for 1 percent of the mass fraction of the electrolyte and is shown as a formula 7 is added

Namely, the electrolyte is added with the compounds shown in the formulas 2 and 7 at the same time, and the mass fraction of the ethyl methyl carbonate in the electrolyte is 45% and is replaced with 44%, and other conditions are the same as those in the embodiment 1.

Comparative example 1

The comparative example was carried out under the same conditions as in example 1 except that the compound represented by formula 2 was not added and the mass fraction of ethyl methyl carbonate in the electrolyte was changed from 45% to 46%.

Comparative example 2

This comparative example is a compound represented by the formula 8 except that the compound represented by the formula 2 is replaced with a compound represented by the formula 8 containing no fluorine substituent

Otherwise, the conditions were the same as in example 1.

Comparative example 3

This comparative example is shown in formula 2The compound is replaced by a compound which does not contain trimethylsilyl and is shown as a formula 9

Otherwise, the conditions were the same as in example 1.

Comparative example 4

This comparative example is prepared by replacing the compound represented by the formula 2 with a compound represented by the formula 10 which does not contain trimethylsiloxy groups

Otherwise, the conditions were the same as in example 1.

The electrolytes of examples 1 to 16 and comparative examples 1 to 4 were assembled into a lithium ion battery by the following method:

LiNi as positive electrode active material _0.8 Co _0.1 Mn _0.1 O ₂ (LNCM), acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 95:3:2, fully stirring and uniformly mixing the mixture in an N-methylpyrrolidone solvent system, coating the mixture on an aluminum foil, drying and cold-pressing the mixture to obtain the positive pole piece, wherein the compaction density of the positive pole piece is 3.5g/cm ³ 。

Preparing a negative electrode active material graphite, a conductive agent acetylene black, a binder Styrene Butadiene Rubber (SBR), and a thickening agent sodium carboxymethyl cellulose (CMC) according to a mass ratio of 96:2:1:1, fully stirring and uniformly mixing in a deionized water solvent system, coating the mixture on a Cu foil, drying and cold-pressing to obtain a negative pole piece, wherein the compaction density of the negative pole piece is 1.65g/cm ³ 。

Polyethylene (PE) with the thickness of 9 mu m is used as a base film, and a nano aluminum oxide layer with the thickness of 3 mu m is coated on the base film to obtain the diaphragm.

And stacking the positive pole piece, the diaphragm and the negative pole piece in sequence, so that the diaphragm is positioned between the positive pole piece and the negative pole piece to play a role in isolation, and stacking the pieces to obtain the bare cell.

And (3) placing the bare cell into an aluminum plastic film, baking at 80 ℃ to remove water, injecting corresponding electrolyte, sealing, standing, hot-cold pressing, forming, clamping, capacity grading and other procedures to obtain the finished product of the flexibly-packaged lithium ion secondary battery.

The lithium ion batteries in examples 1 to 16 and comparative examples 1 to 4 were subjected to normal-temperature sequential, high-temperature sequential and high-temperature storage performance tests, the test methods were as follows:

(1) Normal temperature cycle life test

The full-state battery after capacity separation was discharged at 25 ℃ to 2.8V at 1C, and the initial discharge capacity was designated as DC (1-R). Then charging to 4.2V at 25 deg.C with constant current and constant voltage of 1C, stopping current at 0.05C, standing for 5min, discharging to 2.8V with 1C, and recording discharge capacity DC (2-R). This is repeated until DC (N-R) <80% DC (1-R). And recording the discharge times N, wherein N is the normal-temperature cycle life.

(2) High temperature cycle life test

The fully charged battery after capacity division was placed in a 45 ℃ incubator and discharged at 1C to 2.8V, and the initial discharge capacity was recorded as DC (1-H). Charging to 4.2V at constant current and constant voltage of 1C, stopping current at 0.05C, standing for 5min, discharging to 2.8V at 1C, and recording discharge capacity DC (2-H). This is cycled until DC (N-H) <80% DC (1-H). And recording the discharge times N, wherein N is the high-temperature cycle life.

(3) High temperature storage gassing and DCR growth

After standing the fully charged battery for 30min after capacity grading at normal temperature, discharging for 30S to 2.8V by 4C, recording initial fully charged discharging DCR (0-S), measuring initial cell volume Vol (0-S), storing in a 60 ℃ incubator for N days, taking out the battery at room temperature, charging to 4.2V by constant current and constant voltage of 1C, stopping current of 0.05C, after standing for 30min, discharging for 30S by 4C, recording fully charged discharging DCR (N-S) after storing for N days, wherein the increase rate of DCR =100% [ DCR (N-S) -DCR (0-S) ]/DCR (0-S), measuring cell volume Vol (N-S), and storing gas production rate =100% [ Vol (N-S) -Vol (0-S) ]/Vol (0-S).

The lithium ion batteries of examples 1 to 16 and comparative examples 1 to 4 of the present invention were subjected to normal temperature sequential, high temperature sequential and high temperature storage performance tests, and the test results are shown in the following tables.

TABLE 1

From table 1 it can be obtained: examples 1 to 3 the nonaqueous electrolytic solutions containing the first additive fluorosulfonyl fluorocarboxylic acid ester additive in different amounts can improve the normal and high temperature cycle performance of the lithium ion battery.

TABLE 2

From table 2 it can be obtained: when the different first additives in the formulas 2 to 8 are applied to the electrolyte, the normal temperature and high temperature performance of the lithium ion battery can be improved to different degrees.

TABLE 3

From table 3 it can be obtained: the content of the first additive is excessive, resulting in a decrease in the normal and high temperature cycle performance of the battery and a decrease in the storage performance.

TABLE 4

As can be seen from the comparison between example 1 and examples 10 to 14 in Table 4, the first additive and the other additives advantageously form a mixture rich in LiF and Li, which contains F or N substituent groups ₃ The passivation film of inorganic components such as N and the like can effectively reduce the internal resistance of the battery; and the trimethylsilyl and the trimethylsiloxy on the molecular structure of the first additive can also generate a stable anode passivation film and eliminate trace HF in the electrolyte, so that the stability of the anode material and the electrolyte at high temperature is improved, gas generation is inhibited, and the high-temperature cycle and storage performance of the battery are improved. When the cyclic carbonate additive is absent,the cycle performance is degraded to a certain degree but the increase of the stored DCR can be slightly improved, and the gas generation has no obvious influence; the cycle performance is significantly degraded but the storage performance is not significantly affected in the absence of the cyclic sultone additive; in the absence of cyclic sulfate additives, the cycle performance is somewhat degraded but storage gassing and DCR growth are significantly improved; in the absence of lithium-containing additives, both cycling performance and storage performance are significantly degraded.

TABLE 5

From table 5 it can be obtained: it can be seen from comparative examples 1, 6 and 15 or comparative examples 1, 8 and 16 that the combination of the two first additives can improve the high-temperature cycle performance and the storage performance of the lithium ion battery more effectively, and the content of the fluorine-containing or trimethylsilyl-containing active group of the first additive is increased or complemented by the combination, so that the effect is better than that obtained by using only the first additive.

TABLE 6

As can be seen from table 6, as can be seen from comparison between example 1 and comparative example 1, when the electrolyte containing no first additive is applied to the lithium ion battery, both the normal and high temperature cycle performance and the storage performance of the battery are deteriorated, and as can be seen from comparison between example 1 and comparative examples 2 to 3, when the additive contains no fluorine substituent, trimethylsilyl group or trimethylsiloxy group, both the normal and high temperature cycle performance and the storage performance of the battery are deteriorated. The main reasons are considered as follows: because the comparative example does not contain the first additive or related active groups, the passive film rich in inorganic components such as LiF and the like is difficult to generate, the internal resistance of the battery is effectively reduced, and meanwhile, trimethylsilyl and trimethylsiloxy do not generate a stable anode passive film and trace HF in the electrolyte is eliminated, so that the performances such as circulation, storage and the like are poor.

The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that the electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises a first additive, the first additive comprises a fluorosulfonyl fluorocarboxylic acid ester additive shown in formula 1,

2. The electrolyte of claim 1, wherein the fluorosulfonyl fluorocarboxylic acid ester additive comprises any one of compounds represented by formulas 2 to 7 or a combination of at least two of the compounds,

3. the electrolyte of claim 1, wherein the mass fraction of the fluorosulfonyl fluorocarboxylic acid ester additive in the electrolyte is 0.1% to 10%.

4. The electrolyte of any one of claims 1-3, wherein the additives further comprise a second additive, the second additive comprising a cyclic carbonate comprising any one or a combination of at least two of vinylene carbonate, fluoroethylene carbonate, or ethylene carbonate, a cyclic sultone comprising 1, 3-propane sultone and/or 1, 3-propene sultone, a cyclic sultone comprising vinyl sulfate, a cyclic sulfate comprising a lithium difluorophosphate, a lithium difluorooxalato borate, a lithium dioxalate borate, a lithium tetrafluoroborate, or a lithium difluorooxalato phosphate, or a combination of at least two thereof.

5. The electrolyte of claim 4, wherein the second additive is present in an amount of 0.5 to 20% by weight of the electrolyte.

6. The electrolyte of any one of claims 1-3, wherein the non-aqueous organic solvent comprises any one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, or diethyl carbonate, or a combination of at least two thereof.

7. The electrolyte of any one of claims 1-3, wherein the lithium salt comprises LiFSI, liTFSI, liPF ₆ 、LiBF ₄ 、LiClO ₄ Or LiAsF ₆ The concentration of the lithium salt in the electrolyte is 0.5M to 2M, and the mass fraction of the lithium salt in the electrolyte is 12% to 15%.

8. A lithium ion battery comprising a positive electrode, a negative electrode and the electrolyte of any one of claims 1-7.

9. The lithium ion battery of claim 8, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material, wherein the positive electrode active material comprises any one of or a combination of at least two of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

10. The lithium ion battery of claim 8, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material, wherein the negative electrode active material comprises any one of or a combination of at least two of soft carbon, hard carbon, artificial graphite, natural graphite, silicon oxy-compound, or lithium titanate.