CN115133125A - Method for improving solubility of lithium salt additive and electrolyte containing lithium salt additive - Google Patents
Method for improving solubility of lithium salt additive and electrolyte containing lithium salt additive Download PDFInfo
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- H—ELECTRICITY
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
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Abstract
The invention discloses a method for improving the solubility of a lithium salt additive in an electrolyte and the electrolyte containing the lithium salt additive, wherein the method comprises the following steps: adding a boron trifluoride complex as a dissolution accelerator for accelerating the dissolution of the lithium salt additive into the electrolyte, wherein the boron trifluoride complex is selected from at least one of the structures shown in the following formulas (IA) and (IB):
substituent R 11 And R 12 See the description. The electrolyte provided by the invention can improve the solubility of a lithium salt additive, reduce the turbidity of the electrolyte and contribute to improving the low-temperature discharge of the electrolytePerformance and normal temperature cycle performance.
Description
Technical Field
The invention relates to the field of lithium ion battery electrolyte, in particular to a method for improving the solubility of a lithium salt additive and electrolyte containing the lithium salt additive.
Background
The lithium ion battery is widely applied to the fields of digital codes, energy storage, electric vehicles and the like due to the advantages of long cycle life, high safety performance, no memory effect and the like. With the continuous development of new energy markets, the requirements of people on the energy density of lithium ion batteries are continuously improved. Accordingly, ternary lithium ion batteries are receiving increasing attention. In order to improve the comprehensive performance of the ternary lithium ion battery, some lithium salt additives (such as lithium difluorophosphate and lithium bis (oxalato) borate) with excellent performance are widely used. However, some of these additives have low solubility in the electrolyte and are limited in the amount of addition, so that their excellent properties cannot be fully exerted. In addition, among such lithium salt additives, when the amount of the dissolved lithium salt additive is relatively high, a small amount of the additive is liable to be dissolved to cause a large turbidity, resulting in defective quality of the electrolytic solution, and quality risks due to the presence of insoluble solids, such as clogging of separator pores to cause non-uniformity in the inside of the battery to cause deterioration in performance.
In order to increase the solubility of such lithium salt additives and eliminate the turbidity caused by dissolution at higher concentrations, a solution is sought.
Patent CN109524716A discloses a method of adding boron-containing anion and cation acceptor compounds to the electrolyte to improve the solubility of lithium salt, and proposes additives such as tripropyl borate and tris (pentafluorophenyl) borane to promote the dissolution. However, tris (pentafluorophenyl) boron is expensive and difficult to apply to industrial applications, and the present inventors have found that boric acid ester compounds such as tripropyl borate and tris (hexafluoroisopropyl) borate can lower the internal resistance of the system, but their high-temperature performance is significantly deteriorated and their cycle life is also reduced, resulting in a large disadvantage in application.
Disclosure of Invention
In order to solve the above technical problems, the present invention proposes a method of significantly improving the solubility of a lithium salt additive in an electrolyte.
The purpose of the invention is realized by the following technical scheme:
a method of increasing the solubility of a lithium salt additive in an electrolyte, the method comprising: adding a boron trifluoride complex as a dissolution accelerator for accelerating the dissolution of the lithium salt additive into the electrolyte, wherein the boron trifluoride complex is selected from at least one of the structures shown in the following formulas (IA) and (IB):
wherein R is 11 、R 12 Is independently selected from C 1-12 Alkyl radical, C 1-12 Alkoxy radical, C 2-12 Alkenyl radical, C 6-16 Aryl radical, C 6-16 Aryloxy group, and C substituted by halogen, sulfonic acid group or sulfonyl group 1-12 Alkyl radical, C 1-12 Alkoxy radical, C 2-12 Alkenyl radical, C 6-16 Aryl or C 6-16 An aryloxy group; r 13 Is selected from C 1-5 Alkylene radical, C 1-5 Haloalkylene, C 2-5 Alkenylene radical, C 2-5 A haloalkenylene group.
Preferably, R 11 、R 12 Is independently selected from C 1-6 Alkyl radical, C 1-6 Alkoxy radical, C 2-6 Alkenyl, phenyl, phenoxy, and halo C 1-6 Alkyl radical, C 1-6 Alkoxy radical, C 2-6 Alkenyl, halophenyl or halophenoxy; r 13 Is selected from C 2-3 Alkylene radical, C 2-3 Haloalkylene, C 2-3 Alkenylene radical, C 2-3 A haloalkenylene group.
More preferably, R 11 、R 12 Independently selected from methyl, ethyl, fluoromethyl, fluoroethyl; r 13 Selected from ethylene or propylene.
Most preferably, the boron trifluoride complex is at least one selected from the group consisting of dimethyl carbonate boron trifluoride complex, diethyl carbonate boron trifluoride complex, and vinyl carbonate boron trifluoride complex.
The lithium salt additive is at least one selected from lithium difluorophosphate, lithium bis (oxalato) borate, lithium difluoro (oxalato) phosphate, lithium tetrafluoro (oxalato) phosphate, lithium tri (oxalato) phosphate, lithium fluoride and lithium oxalate. The amount of the boron trifluoride complex compound used depends on the lithium salt additive and the organic solvent in the electrolyte. Generally, the boron trifluoride complex is used in an amount of 0.1 to 10.0 wt%, preferably 0.3 to 5.0 wt%, and more preferably 0.5 to 3.0 wt% based on the mass of the organic solvent.
The present inventors speculate that the boron atom in the boron trifluoride complex contains a 2p vacancy, which is a typical lewis acid, and may interact or react with a negative ion group (lewis base) dissociated in the electrolyte solution to promote the dissolution of the lithium salt additive, thereby improving the solubility of the lithium salt additive. Further, boron trifluoride can react with lithium fluoride (impurities or decomposition products) or the like which is hardly soluble in the electrolyte to form a salt having a higher solubility such as lithium tetrafluoroborate, and the turbidity of the electrolyte can be reduced.
Based on the dissolution assisting effect of the boron trifluoride complex, the content of the lithium salt additive in the electrolyte is greatly improved, and generally, the solubility of the lithium salt additive in the electrolyte can be improved by more than 60%. For example, the content of the lithium difluorophosphate in the electrolyte can be increased from 1.0-1.3 wt% to more than 2.1 wt%. In addition, the dissolution rate of the lithium salt additive in the electrolyte is also greatly improved.
The present invention also provides an electrolyte containing a lithium salt additive, the electrolyte further comprising: a primary lithium salt, an organic solvent and a lithium salt additive, and a boron trifluoride complex as described in any of the above.
The lithium salt additive comprises at least one of lithium difluorophosphate, lithium bis (oxalato) borate, lithium difluorooxalato phosphate, lithium tetrafluorooxalato phosphate, lithium tris (oxalato) phosphate, lithium fluoride and lithium oxalate, and accounts for 0.5-5.0 wt% of the total amount of the electrolyte.
The amount of the boron trifluoride complex is 0.1-10.0 wt%, preferably 0.3-5.0 wt%, and more preferably 0.5-3.0 wt% based on the mass of the organic solvent.
In a specific embodiment, the lithium salt additive comprises lithium difluorophosphate, which accounts for 2.1 wt% of the total electrolyte, and the boron trifluoride complex accounts for 0.8 wt% of the mass of the organic solvent.
In another specific embodiment, the lithium salt additive includes lithium bis (oxalato) borate in an amount of 3.5 wt% based on the total amount of the electrolyte, and the boron trifluoride complex is used in an amount of 0.8 wt% based on the mass of the organic solvent.
The main lithium salt of the present invention is selected from lithium hexafluorophosphate (LiPF) 6 ) Lithium tetrafluoroborate (LiBF) 4 ) Lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), and lithium tetrafluoroborate (LiBF) 4 ) At least one of them, in an amount of 5 to 20 wt%.
The organic solvent is selected from at least one of carbonate or carboxylate. Preferably, the organic solvent is selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), Ethylene Carbonate (EC), Propylene Carbonate (PC), methyl acetate, ethyl propionate, propyl acetate, propyl propionate, methyl butyrate, ethyl butyrate, γ -butyrolactone, and the like. The commonly used organic solvents are 2-4 kinds of mixture of cyclic carbonate (such as EC and PC) and linear carbonate (such as DMC, EMC or DEC), wherein the proportion of cyclic carbonate in the organic solvent is 10-50%, and the rest is linear carbonate or carboxylic ester, and the combination can achieve better dielectric constant and dissolving capacity, and is beneficial to the dissolution of lithium salt and the conductivity of the electrolyte.
In order to improve the performance of the electrolyte, the electrolyte also comprises a basic additive, wherein the basic additive is at least one selected from a sulfonic acid ester compound, a sulfuric acid ester compound, a fluoro carbonate compound and an unsaturated carbonate compound, and the dosage of the basic additive accounts for 0.1-5.0% of the total mass of the electrolyte. Preferably:
the sulfonate compound is at least one selected from 1, 3-propane sultone, 1, 3-propylene sultone, 1, 4-butane sultone and methylene methanedisulfonate;
the sulfate ester compound is at least one selected from vinyl sulfate, 4-methyl vinyl sulfate, 4-fluoro vinyl sulfate and 4,4' -divinyl disulfate;
the fluoro carbonate compound is at least one selected from fluoro ethylene carbonate, difluoro ethylene carbonate and trifluoromethyl ethylene carbonate;
the unsaturated carbonate compound is selected from vinylene carbonate and/or vinyl ethylene carbonate.
The electrolyte containing the lithium salt additive can be prepared by adding a boron trifluoride complex compound into a lithium salt solution or adding a lithium salt into a boron trifluoride complex compound solution.
In order to improve the dissolution efficiency of the lithium salt additive, the electrolyte of the present invention is preferably prepared by the following steps:
A1. dissolving boron trifluoride complex in an organic solvent;
A2. adding main lithium salt for dissolving;
A3. adding lithium salt additive to dissolve.
More preferably, the a2 step further includes dissolution of the base additive.
The invention also provides a lithium ion battery which comprises a positive electrode, a negative electrode and a diaphragm, and the lithium ion battery also comprises any electrolyte containing the lithium salt additive.
Compared with the prior art, the invention has the following beneficial effects:
the boron trifluoride complex provided by the invention can obviously improve the solubility of lithium salt additives such as lithium difluorophosphate and the like in the electrolyte, increases the addition amount of the lithium salt additives in the electrolyte and is beneficial to improving the electrochemical performance of the electrolyte.
Detailed Description
The present invention is further illustrated by the following examples, which are not intended to limit the invention to these embodiments. It will be appreciated by those skilled in the art that the present invention encompasses all alternatives, modifications and equivalents as may be included within the scope of the claims.
Firstly, preparing electrolyte
Example 1
This embodiment provides an electrolyte containing a lithium salt additive, the electrolyte including:
main lithium salt: lithium hexafluorophosphate with a concentration of 1 mol/L;
organic solvent: the mixed solvent of Ethylene Carbonate (EC) and diethyl carbonate (DEC) is prepared from the following components in percentage by mass: DEC ═ 3: 7;
lithium salt additive: lithium difluorophosphate (LiPO) 2 F 2 ) The using amount accounts for 2.1 wt% of the total mass of the electrolyte;
and (3) dissolution promoter: dimethyl carbonate boron trifluoride complex (the molar ratio of boron trifluoride to dimethyl carbonate is 1:1), and the using amount of the boron trifluoride complex is 0.8 wt% of the mass of the electrolyte;
additive: vinylene Carbonate (VC) in an amount of 2.0 wt% based on the total mass of the electrolyte.
The preparation process of the electrolyte is as follows:
s1, preparing a mixed solution of a dimethyl carbonate boron trifluoride complex and an organic solvent in a glove box filled with argon atmosphere;
s2, adding lithium hexafluorophosphate solid into the mixed solution, and stirring; then Vinylene Carbonate (VC) is added and mixed evenly;
and S3, continuously adding lithium difluorophosphate powder into the mixed solution to obtain the electrolyte.
The stirring time and the dissolution of the lithium salt additive in the electrolyte solution in the step S3 were recorded, and the results are shown in table 1.
Example 2
The operation of this example is the same as example 1 except that: the cosolvent adopts diethyl carbonate boron trifluoride complex instead of dimethyl carbonate boron trifluoride complex.
Example 3
The operation of this example is the same as example 1 except that: the cosolvent adopts ethylene carbonate boron trifluoride complex instead of dimethyl carbonate boron trifluoride complex.
Example 4
The operation of this example is the same as example 1 except that: lithium difluorophosphate (LiPO) 2 F 2 ) The amount of (B) was 1.6 wt% based on the total mass of the electrolyte.
Example 5
The operation of this example is the same as example 1 except that: lithium difluorophosphate (LiPO) 2 F 2 ) The amount of the electrolyte is 1.3 wt% of the total mass of the electrolyte.
Example 6
The operation of this example is the same as example 1 except that: lithium difluorophosphate (LiPO) 2 F 2 ) The amount of (B) was 2.6 wt% based on the total mass of the electrolyte.
Example 7
The operation of this example is the same as example 1 except that: the lithium salt additive adopts lithium bis (oxalato) borate (LiBOB), and the dosage of the lithium salt additive accounts for 3.5 wt% of the total mass of the electrolyte.
Example 8
The operation of this example is the same as example 1 except that: lithium difluorophosphate (LiPO) is adopted as lithium salt additive 2 F 2 ) And the mixture of the electrolyte and lithium bis (oxalato) borate (LiBOB) accounts for 1.5 wt% and 2.0% of the total mass of the electrolyte respectively.
Example 9
The operation of this example is the same as example 1 except that: the usage of the cosolvent dimethyl carbonate boron trifluoride complex is changed to be 0.4 wt% of the total mass of the electrolyte;
example 10
The operation of this example is the same as example 1 except that: the usage of the cosolvent dimethyl carbonate boron trifluoride complex is changed to be 1.6 wt% of the total mass of the electrolyte;
example 11
The formulation of the electrolyte containing lithium salt additive provided in this example is the same as example 1, except that: the preparation process of the electrolyte is adjusted as follows:
s1, preparing a mixed solvent of Ethylene Carbonate (EC) and diethyl carbonate (DEC) in a glove box filled with argon atmosphere, adding lithium hexafluorophosphate solid into the mixed solvent, and stirring; then Vinylene Carbonate (VC) is added and mixed evenly;
s2, continuously adding lithium difluorophosphate powder into the mixed solution, and stirring;
and S3, continuously adding the boron trifluoride complex and stirring.
The stirring time and the dissolution of the lithium salt additive in the electrolyte solution in the step S3 were recorded, and the results are shown in table 1.
Comparative example 1
The operation of this example is the same as example 1 except that: no cosolvent is used.
Comparative example 2
The operation of this example is the same as example 5 except that: no cosolvent is used.
TABLE 1 lithium salt additive dissolution Table
As can be seen from table 1 above, the boron trifluoride complex can improve the solubility of the lithium salt additive and accelerate the dissolution rate of the lithium salt additive in the organic solvent. Comparing example 1, example 9 and example 10, it is seen that the solubility of the lithium salt additive is increased and the dissolution rate is also increased as the amount of boron trifluoride complex added is increased.
Secondly, manufacturing and testing the battery
The electrolytes prepared in the above examples and comparative examples were injected into lithium ion batteries, respectively, and performance tests were performed. The lithium ion battery comprises a positive pole piece and a negative pole pieceA diaphragm, electrolyte and battery auxiliary materials, wherein the positive active material is LiNi 0.73 Co 0.07 Mn 0.2 O 2 The negative active material is graphite.
The preparation process of the battery is as follows:
preparing a lithium nickel manganese cobalt ternary material from a positive active material nickel cobalt lithium manganate ternary material, a conductive agent and a binder polyvinylidene fluoride according to the weight ratio: conductive agent: polyvinylidene fluoride 97.3: 1.5: 1.2, mixing, adding solvent N-methyl pyrrolidone, and fully stirring and mixing to form uniform anode slurry; and coating the slurry on an aluminum foil of the positive current collector, drying, rolling, slitting and die cutting to obtain the positive plate.
The negative active material graphite, the conductive agent, the binder styrene butadiene rubber and the thickener sodium carboxymethyl cellulose are mixed according to the weight ratio of graphite: conductive agent: styrene-butadiene rubber: sodium carboxymethylcellulose (96.4): 0.6: 1.8: 1.2, mixing, adding deionized water, and fully stirring to obtain uniform cathode slurry; and coating the slurry on a copper foil of a negative current collector, drying, rolling, slitting and die cutting to obtain a negative plate.
And sequentially stacking the negative plate, the diaphragm and the positive plate according to a rule, placing the diaphragm between the positive plate and the negative plate to play an isolation role, obtaining a bare cell through one layer of lamination, injecting the electrolyte into the bare cell after the bare cell is assembled and baked, and then obtaining the battery through the procedures of infiltration, formation, packaging, capacity grading and the like.
And (3) performance testing:
(1) -20 ℃ low temperature discharge: and discharging the capacity-divided battery cell to 2.8V at a constant current of 1C in an environment of 25 ℃, standing for 10min, then charging to 4.2V at a constant current of 1C and a constant voltage, stopping current at 0.05C, and recording the charging capacity. And then, standing the full-electric cell in an environment of-20 ℃ for 6h, discharging to 2.8V at a constant current of 1C in the environment of-20 ℃, recording the discharge capacity at-20 ℃, and calculating the low-temperature discharge efficiency at-20 ℃.
(2) -30 ℃ low temperature discharge: and discharging the capacity-divided battery cell to 2.8V at a constant current of 1C in an environment of 25 ℃, standing for 10min, then charging to 4.2V at a constant current of 1C and a constant voltage, stopping current at 0.05C, and recording the charging capacity. And then, standing the full-electric-state battery cell for 6 hours in an environment of minus 30 ℃, discharging to 2.8V at a constant current of 1C in the environment of minus 30 ℃, recording the discharge capacity at minus 30 ℃, and calculating the low-temperature discharge efficiency at minus 30 ℃.
Low-temperature discharge efficiency (%) — low-temperature discharge capacity/low-temperature discharge coin full charge capacity × 100%.
(3) And (3) testing the normal-temperature cycle performance at 25 ℃: charging the batteries after capacity grading to 4.35V at constant current and constant voltage of 1C in a constant temperature box at 25 ℃, stopping current for 0.05C, standing for 10min, and discharging the 1C to 2.8V; and calculating the capacity retention rate after 800 th circulation according to the process steps and 800 circles.
The 800 th cycle capacity retention (%) (800 th cycle discharge capacity/first cycle discharge capacity) was 100%.
(4) And (3) testing the normal-temperature cycle performance at 45 ℃: charging the batteries after capacity grading to 4.35V at constant current and constant voltage of 1C in a constant temperature box at 45 ℃, stopping current at 0.05C, standing for 10min, and discharging the batteries at 1C to 2.8V; and (5) calculating the capacity retention rate after 500 cycles according to the above steps and cycles for 500 circles.
The 500 th cycle capacity retention ratio (%) (500 th cycle discharge capacity/first cycle discharge capacity) × 100%.
The electrical property test results are shown in table 2 below:
TABLE 2 test results of low-temperature discharge properties
According to the above 2 example and comparative example, when boron trifluoride complex is added as a dissolution promoter to the electrolyte, the obtained electrolyte can improve the low-temperature discharge performance of the battery, especially the low-temperature discharge performance under the condition of-30 ℃ is obviously improved, and the addition of boron trifluoride complex can improve the normal-temperature cycle without deteriorating the high-temperature cycle performance.
Claims (15)
1. A method of increasing the solubility of a lithium salt additive in an electrolyte, comprising: the method comprises the following steps: adding a boron trifluoride complex as a dissolution accelerator for accelerating the dissolution of the lithium salt additive into the electrolyte, wherein the boron trifluoride complex is selected from at least one of the structures shown in the following formulas (IA) and (IB):
wherein R is 11 、R 12 Independently selected from C 1-12 Alkyl radical, C 1-12 Alkoxy radical, C 2-12 Alkenyl radical, C 6-16 Aryl radical, C 6-16 Aryloxy group, and C substituted by halogen, sulfonic acid group or sulfonyl group 1-12 Alkyl radical, C 1-12 Alkoxy radical, C 2-12 Alkenyl radical, C 6-16 Aryl or C 6-16 An aryloxy group; r 13 Is selected from C 1-5 Alkylene radical, C 1-5 Haloalkylene, C 2-5 Alkenylene radical, C 2-5 A haloalkenylene group.
2. The method of claim 1, wherein the step of increasing the solubility of the lithium salt additive in the electrolyte comprises: r 11 、R 12 Independently selected from C 1-6 Alkyl radical, C 1-6 Alkoxy radical, C 2-6 Alkenyl, phenyl, phenoxy, and halo C 1-6 Alkyl radical, C 1-6 Alkoxy radical, C 2-6 Alkenyl, halophenyl, or halophenoxy; r 13 Is selected from C 2-3 Alkylene radical, C 2-3 Haloalkylene, C 2-3 Alkenylene radical, C 2-3 A haloalkenylene group.
3. The method of claim 2, wherein the step of increasing the solubility of the lithium salt additive in the electrolyte comprises: r 11 、R 12 Independently selected from methyl, ethyl, fluoromethyl, fluoroethyl; r 13 Selected from ethylene or propylene.
4. The method of claim 3, wherein the step of increasing the solubility of the lithium salt additive in the electrolyte comprises: the boron trifluoride complex is at least one selected from dimethyl carbonate boron trifluoride complex, diethyl carbonate boron trifluoride complex and ethylene carbonate boron trifluoride complex.
5. The method of any of claims 1 to 4, wherein the step of increasing the solubility of the lithium salt additive in the electrolyte comprises: the lithium salt additive comprises at least one of lithium difluorophosphate, lithium bis (oxalato) borate, lithium difluorooxalato phosphate, lithium tetrafluorooxalato phosphate, lithium tris (oxalato) phosphate, lithium fluoride and lithium oxalate.
6. An electrolyte containing a lithium salt additive, characterized in that: the electrolyte further includes: a primary lithium salt, an organic solvent, a lithium salt additive, and a boron trifluoride complex as claimed in any one of claims 1 to 5.
7. The lithium salt additive-containing electrolyte of claim 6, wherein: the lithium salt additive comprises at least one of lithium difluorophosphate, lithium bis (oxalato) borate, lithium difluorooxalato phosphate, lithium tetrafluorooxalato phosphate, lithium tris (oxalato) phosphate, lithium fluoride and lithium oxalate, and accounts for 0.5-5.0% of the total mass of the electrolyte.
8. The lithium salt additive-containing electrolyte of claim 7, wherein: the lithium salt additive comprises lithium difluorophosphate, and accounts for 0.7-3.0% of the total mass of the electrolyte.
9. The lithium salt additive-containing electrolyte of any one of claims 6 to 8, wherein: the dosage of the boron trifluoride complex compound accounts for 0.1-10.0% of the total mass of the electrolyte.
10. The lithium salt additive-containing electrolyte of claim 6, wherein: the main lithium salt is at least one selected from lithium hexafluorophosphate, lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethanesulfonyl) imide.
11. The lithium salt additive-containing electrolyte of claim 6, wherein: the organic solvent is at least one selected from chain or cyclic organic carbonates.
12. The electrolyte solution containing a lithium salt additive according to any one of claims 6 to 11, wherein: the electrolyte also comprises a basic additive, wherein the basic additive is at least one of a sulfonate compound, a sulfate compound, a fluoro carbonate compound and an unsaturated carbonate compound, and the using amount of the basic additive accounts for 0.1-5.0% of the total mass of the electrolyte.
13. The method of preparing the electrolyte containing a lithium salt additive according to any one of claims 6 to 12, wherein: the preparation method comprises the following steps:
A1. dissolving boron trifluoride complex in an organic solvent;
A2. adding main lithium salt for dissolution;
A3. adding lithium salt additive to dissolve.
14. The method of claim 13, wherein the electrolyte solution containing a lithium salt additive is prepared by: the a2 step also includes dissolution of the base additive.
15. A lithium ion battery comprises a positive electrode, a negative electrode and a diaphragm, and is characterized in that: the lithium ion battery further comprising an electrolyte containing a lithium salt additive according to any one of claims 6 to 12.
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