CN114566711A

CN114566711A - Electrolyte, preparation method thereof and high-nickel lithium ion battery containing electrolyte

Info

Publication number: CN114566711A
Application number: CN202210201507.8A
Authority: CN
Inventors: 严成结; 邹志群; 曾汉民; 钟颖贤; 樊广恒; 刘顿; 徐秋红
Original assignee: Hubei Eve Power Co Ltd
Current assignee: Hubei Eve Power Co Ltd
Priority date: 2022-03-03
Filing date: 2022-03-03
Publication date: 2022-05-31

Abstract

The invention provides an electrolyte, a preparation method thereof and a high-nickel lithium ion battery containing the electrolyte. The electrolyte comprises a lithium salt, an organic solvent and an additive; the additive comprises a nitrile additive and the lithium salt comprises lithium difluorofluorosulfonylimide. According to the invention, the lithium bifluorosulfonyl imide is taken as a main electrolyte lithium salt, the lithium bifluorosulfonyl imide lithium difluorophosphate and the hydrocarbon nitrile additive are added simultaneously, and the corrosion of the lithium bifluorosulfonyl imide is effectively inhibited and the high-temperature storage characteristic and the rate capability are obviously improved by adjusting the mixing ratio of the lithium bifluorosulfonyl imide and the lithium bifluorosulfonyl fluoride phosphate and the content of the hydrocarbon nitrile additive.

Description

Electrolyte, preparation method thereof and high-nickel lithium ion battery containing electrolyte

Technical Field

The invention relates to the field of lithium ion batteries, in particular to an electrolyte, a preparation method thereof and a high-nickel lithium ion battery containing the electrolyte.

Background

Lithium hexafluorophosphate (LiPF) is mainly used as the electrolyte which is used as the main salt in the electrolyte of the current market₆) Mainly, but because lithium hexafluorophosphate is poor in thermal stability, decomposition occurs at 60 ℃ in high-temperature storage, so that capacity is attenuated. Meanwhile, HF is generated in the presence of trace water (more than 10ppm) so that the acidity of the electrolyte is increased, transition metal ions are dissolved out, the system is seriously deteriorated, and the high-temperature performance is poorer. The existing salt which can be used as the solute of the electrolyte is lithium tetrafluoroborate (LiBF)₄) Lithium bis (oxalato) borate (LiODFB), lithium difluoro (oxalato) borate (LiBOB), lithium difluoro (phosphorodiamidate) (LiPO)₂F₂) Etc., but there are cases where the conductivity is low, the solubility is low, the environment is polluted, and there is a safety risk.

CN112010894A discloses a phosphate ester compound, a nonaqueous lithium ion battery electrolyte containing the phosphate ester compound and a lithium ion battery, wherein the phosphate ester compound can improve the flame retardant capability of the battery, but side reactions are generated, and the rate capability of the battery is reduced.

CN112652816A discloses an electrolyte giving consideration to both low-temperature quick-charging performance and high-temperature performance, and a preparation method and application thereof, wherein a film-forming additive comprises fluoroethylene carbonate and/or vinylene carbonate, a functional additive comprises a sulfur-containing additive and a nitrile additive, but the selected nitrile additive cannot play a role in providing high rate performance for a battery, and the whole formula cannot play a beneficial effect in improving the rate performance and the electrochemical performance of the battery.

Therefore, how to prepare a lithium ion battery with low high-temperature storage gas generation, high capacity retention rate and high rate performance is an important research direction in the field.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide an electrolyte, a preparation method thereof and a high-nickel lithium ion battery containing the electrolyte.

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

an object of the present invention is to provide an electrolyte including a lithium salt, an organic solvent, and an additive.

The additive comprises a nitrile additive, and the structure of the nitrile additive is shown as formula 1:

n is equal to or more than one, wherein R is substituted or unsubstituted C1-C5 alkylene, the number of nitrile group substituent groups in the branched chain is equal to or less than 1, and the number of the nitrile group substituent groups can be 0 or 1.

The nitrile additive may be, for example, specifically 1,3, 6-hexanetrinitrile, adiponitrile or tert-butylmalononitrile.

The lithium salt comprises lithium difluorophosphate fluorosulfonyl imide and lithium difluorosulfonyl imide.

The invention adds a lithium salt into the electrolyte: the structure of the difluoro-phosphoric acid fluorine sulfonyl imide lithium is as shown in a formula 2:

and simultaneously adding a hydrocarbon nitrile additive, wherein R is a saturated or unsaturated alkane chain with 1-5 carbon atoms, and a branched chain can contain at most one nitrile functional group. The nitrile-group-containing functional group in the structure of the additive A can be oxidized and reduced to participate in positive and negative film formation, so that the high-temperature cycle and storage performance of a ternary high-voltage system are effectively improved.

As a preferable technical solution of the present invention, the lithium salt further includes lithium bis-fluorosulfonylimide.

Preferably, the concentration of the lithium bis (fluorosulfonyl) imide in the electrolyte is 0.9-1.2 mol/L, wherein the concentration can be 0.9mol/L, 1.0mol/L, 1.1mol/L, 1.2mol/L, etc., but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the concentration of the lithium difluorofluorosulfonylimide phosphate in the electrolyte is 0.1-0.3 mol/L, wherein the concentration can be 0.1mol/L, 0.2mol/L, 0.3mol/L, etc., but not limited to the recited values, and other values not recited in the numerical range are also applicable.

According to the invention, the corrosion of the lithium bis (fluorosulfonyl) imide is effectively inhibited by the mixing proportion of the lithium bis (fluorosulfonyl) imide and the lithium difluorophosphate fluorosulfonyl imide, and the high-temperature storage characteristic and rate capability are obviously improved.

In a preferred embodiment of the present invention, the nitrile additive is present in an amount of 0.2 to 1.0% by mass based on the electrolyte, wherein the amount of the nitrile additive may be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0% by mass, but the nitrile additive is not limited to the above-mentioned values, and other values not listed in the above-mentioned range of values are also applicable.

According to the invention, the lithium bifluorosulfonyl imide is taken as a main electrolyte lithium salt, a novel lithium salt difluorophosphoric acid fluorine sulfonyl imide lithium and a hydrocarbon nitrile additive are added at the same time, and by adjusting the mixing ratio of the lithium bifluorosulfonyl imide and the difluorophosphoric acid fluorine sulfonyl imide lithium and the content of the hydrocarbon nitrile additive, the corrosion of the lithium bifluorosulfonyl imide is effectively inhibited, and the high-temperature storage characteristic and the rate capability are obviously improved.

As a preferable technical scheme of the invention, the additive also comprises a carbonate additive and a sulfur-containing additive.

Preferably, the carbonate-based additive includes vinylene carbonate and/or fluoroethylene carbonate.

Preferably, the sulfur-containing additive comprises any one of Propane Sultone (PS), Propene Sultone (PST), or vinyl sulfate (DTD), or a combination of at least two thereof, wherein typical but non-limiting examples thereof are: a combination of PS and PST, a combination of PST and DTD, or a combination of PS and DTD, and the like.

Preferably, the lithium salt additive comprises any one of lithium difluorophosphate, lithium bis (oxalato) borate, or lithium difluorobis (oxalato) phosphate, or a combination of at least two of these, typical but non-limiting examples of such combinations being: a combination of lithium difluorophosphate and lithium bis (oxalato) borate, a combination of lithium bis (oxalato) borate and lithium bis (oxalato) phosphate, a combination of lithium difluorophosphate and lithium bis (oxalato) phosphate, or the like.

In a preferred embodiment of the present invention, the carbonate additive is present in an amount of 0.2 to 1.0% by mass based on the electrolyte, wherein the amount of the carbonate additive may be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0% by mass, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.

Preferably, the sulfur-containing additive accounts for 0.5-2.0% of the electrolyte by mass fraction, wherein the mass fraction may be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%, but is not limited to the recited values, and other non-recited values within the range of the values are also applicable.

Preferably, the lithium salt additive accounts for 0.5 to 1% of the electrolyte by mass, wherein the mass fraction may be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or the like, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

According to the invention, the carbonate additive forms a film on a negative electrode, but a compact SEI film cannot be formed when the addition amount is too small, and the impedance is larger and high-temperature gas generation is caused when the addition amount is too large; the sulfur-containing additive is used for assisting in forming a film on the positive electrode and the negative electrode, the thermal stability is high, a compact SEI film cannot be formed on the negative electrode when the addition amount is too small, and the cycle performance is reduced due to excessive film forming when the addition amount is too large.

As a preferred embodiment of the present invention, the organic solvent includes any two or any three of ethylene carbonate, dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate, wherein the combination is exemplified by typical but not limiting examples: a combination of ethylene carbonate and dimethyl carbonate, a combination of dimethyl carbonate and diethyl carbonate, a combination of diethyl carbonate and ethyl methyl carbonate, a combination of ethylene carbonate, dimethyl carbonate and diethyl carbonate, or the like.

Preferably, the volume ratio of the ethylene carbonate to the dimethyl carbonate to the diethyl carbonate to the ethyl methyl carbonate is (20-40): (0-20): (0-20): (30-50), wherein the volume ratio may be 20:0:20:30, 20:0:10:30, 20:0:0:30, 20:0:20:50, 20:0:10:50, 20:0: 50, 20:20:20:30, 20:20:10:30, 20:20:0:30, 20:10:20:30, 20:10:0:30, 30:0:20:30, 30:0:10:30, 30:0:0:30, 40:0:20:30, 40:0:10:30, or 40:0:0:30, but is not limited to the recited values, and other non-recited values within the range are also applicable.

Another object of the present invention is to provide a method for preparing the electrolyte according to the first object, the method comprising:

sequentially adding a carbonate additive, a sulfur-containing additive, a nitrile additive and a lithium salt additive into an organic solvent in an inert atmosphere, and finally adding a lithium salt for low-temperature mixing to obtain the electrolyte.

As a preferred technical scheme of the invention, the inert atmosphere comprises an argon atmosphere.

Preferably, the temperature of the low-temperature mixing is 8 to 12 ℃, wherein the temperature can be 8 ℃, 9 ℃, 10 ℃, 11 ℃ or 12 ℃, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.

The invention also aims to provide a high-nickel lithium ion battery, which comprises the electrolyte for one purpose;

the lithium ion battery also comprises a positive electrode, a negative electrode and a diaphragm.

In a preferred embodiment of the present invention, the active material of the positive electrode includes Li (Ni)_xCo_yMn_z)O₂Wherein x is more than or equal to 0.8<0.9，0<y≤0.1，0<z ≦ 0.1 and x + y + z ≦ 1, where x may have a value of 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, etc., y may have a value of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc., z may have a value of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc., but is not limited to the recited values, and other values not recited in this range of values are equally applicable.

Preferably, the active material of the negative electrode includes graphite.

The recitation of numerical ranges herein includes not only the above-recited numerical values, but also any numerical values between non-recited numerical ranges, and is not intended to be exhaustive or to limit the invention to the precise numerical values encompassed within the range for brevity and clarity.

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

the lithium ion battery prepared by the invention has low gas generation during high-temperature storage, the volume expansion rate can be reduced to below 10.2% under the condition of storing for 90 days at 60 ℃, the capacity retention rate can reach above 89.4%, the capacity recovery rate can reach above 91.5%, the capacity recovery rate can reach 100% at 25 ℃/1C/1C, the capacity recovery rate at 25 ℃/3C/1C can reach above 62.5%, and the capacity recovery rate at 25 ℃/5C/1C can reach above 51.6%. The HF content can be as low as 106.3ppm after 90 days of storage.

Detailed Description

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

Example 1

The embodiment provides an electrolyte and a preparation method thereof:

electrolyte solution: the electrolyte consists of an organic solvent, lithium salt and an additive, wherein the additive is a carbonate additive, a sulfur-containing additive, a nitrile additive and a lithium salt additive.

The carbonate additive is fluoroethylene carbonate, and the mass fraction of the fluoroethylene carbonate in the electrolyte is 0.3 percent;

the sulfur-containing additive is 1, 3-propane sultone, and the mass fraction of the sulfur-containing additive in the electrolyte is 1.0 percent;

the nitrile additive is 1,3, 6-hexanetricarbonitrile, and the mass fraction of the nitrile additive in the electrolyte is 1%;

the lithium salt additive is lithium difluorophosphate, and accounts for 0.7 percent of the mass of the electrolyte;

the lithium salt is a mixed salt of lithium bis (fluorosulfonyl) imide and lithium difluorophosphate fluorosulfonyl imide, the concentration of the mixed salt in the electrolyte is 1.2mol/L, and the contents of two electrolyte salts are 1mol/L and 0.2mol/L respectively;

the organic solvent consists of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, wherein the volume fraction of the ethylene carbonate is 30%, the volume fraction of the diethyl carbonate is 20% and the volume fraction of the ethyl methyl carbonate is 50% based on 100% of the total volume of the organic solvent.

The preparation method of the electrolyte comprises the following steps: adding a carbonate additive, a lithium salt additive, a sulfur-containing additive and a nitrile additive into an organic solvent according to the formula ratio in an argon atmosphere, then adding an electrolyte salt, and stirring and mixing at the temperature of 8 ℃ to obtain the electrolyte.

Example 2

The embodiment provides an electrolyte and a preparation method thereof:

electrolyte solution: the electrolyte consists of an organic solvent, electrolyte salt and an additive. The additive is carbonate additive, lithium salt additive, sulfur-containing additive and nitrile additive.

The carbonate additive is vinylene carbonate, and the mass fraction of the vinylene carbonate additive in the electrolyte is 0.2%;

the sulfur-containing additive accounts for 0.5 percent of the mass fraction of PST in the electrolyte;

the nitrile additive is adiponitrile, and the mass fraction of the nitrile additive in the electrolyte is 0.5%;

the lithium salt additive is lithium bis (oxalato) borate, and accounts for 0.5 percent of the mass of the electrolyte;

the lithium salt is a mixed salt of lithium bis (fluorosulfonyl) imide and lithium difluorophosphate fluorosulfonyl imide, the concentration of the lithium salt in the electrolyte is 1.0mol/L, and the contents of two electrolyte salts are 0.9mol/L and 0.1mol/L respectively;

the organic solvent consists of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, wherein the volume fraction of the ethylene carbonate is 40%, the volume fraction of the diethyl carbonate is 20% and the volume fraction of the ethyl methyl carbonate is 40% based on 100% of the total volume of the organic solvent.

The preparation method of the electrolyte comprises the following steps: adding a carbonate additive, a lithium salt additive, a sulfur-containing additive and a nitrile additive into an organic solvent according to the formula ratio in an argon atmosphere, then adding an electrolyte salt, and stirring and mixing at the temperature of 10 ℃ to obtain the electrolyte.

Example 3

The embodiment provides an electrolyte and a preparation method thereof:

The carbonate additive is fluoroethylene carbonate, and the mass fraction of the fluoroethylene carbonate in the electrolyte is 1.0 percent;

the sulfur-containing additive accounts for 2.0 percent of the mass fraction of DTD in the electrolyte;

the nitrile additive is tert-butyl malononitrile, and the mass fraction of the nitrile additive in the electrolyte is 0.2%;

lithium salt additive lithium difluorobis (oxalato) phosphate accounts for 1% of the mass fraction of the electrolyte;

the lithium salt is a mixed salt of lithium bis (fluorosulfonyl) imide and lithium difluorophosphate fluorosulfonyl imide, the concentration of the lithium salt in the electrolyte is 1.5mol/L, and the contents of two electrolyte salts are 1.2mol/L and 0.3mol/L respectively;

the organic solvent consists of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, wherein the volume fraction of the ethylene carbonate is 30%, the volume fraction of the dimethyl carbonate is 20% and the volume fraction of the ethyl methyl carbonate is 50% based on 100% of the total volume of the organic solvent.

The preparation method of the electrolyte comprises the following steps: adding a carbonate additive, a lithium salt additive, a sulfur-containing additive and a nitrile additive into an organic solvent according to the formula ratio in an argon atmosphere, then adding an electrolyte salt, and stirring and mixing at the temperature of 12 ℃ to obtain the electrolyte.

Example 4

This example was carried out under the same conditions as example 1 except that the mass fraction of fluoroethylene carbonate in the electrolyte solution was changed to 0.1% instead of 0.3%.

Example 5

This example was carried out under the same conditions as example 1 except that the mass fraction of fluoroethylene carbonate in the electrolyte solution was changed to 0.3% instead of 1.2%.

Example 6

In this example, the conditions were the same as in example 1 except that the mass fraction of 1, 3-propanesultone in the electrolyte was changed to 1.0% instead of 0.3%.

Example 7

In this example, the conditions were the same as in example 1 except that 1.0% by mass of 1, 3-propanesultone in the electrolyte was replaced with 2.2% by mass in the electrolyte.

Example 8

This example was carried out under the same conditions as example 1 except that the mass fraction of the nitrile additive in the electrolyte solution was changed to 1.0% instead of 0.1%.

Example 9

This example was carried out under the same conditions as example 1 except that the mass fraction of the nitrile additive in the electrolyte solution was changed to 1.0% instead of 1.2%.

Example 10

This example was conducted under the same conditions as example 1 except that the carbonate-based additive was not added and the remaining solution except for the lithium salt and the additive was filled with an organic solvent so that the total amount of the solution in this example was the same as in example 1.

Example 11

This example was conducted under the same conditions as example 1 except that the sulfur-containing additive was not added and the remaining solution except for the lithium salt and the additive was filled with an organic solvent so that the total amount of the solution in this example was the same as in example 1.

Example 12

This example was conducted under the same conditions as example 1 except that the lithium salt additive was not added and the remaining solution except for the lithium salt and the additive was filled with an organic solvent so that the total amount of the solution in this example was the same as in example 1.

Example 13

This example was carried out under the same conditions as in example 1 except that the concentration of lithium bis (fluorosulfonyl) imide in the electrolyte was changed to 0.8mol/L and the concentration of lithium difluorofluorosulfonyl imide in the electrolyte was changed to 0.4 mol/L.

Example 14

This example was carried out under the same conditions as in example 1 except that the concentration of lithium bis (fluorosulfonyl) imide in the electrolyte was changed to 1.15mol/L and the concentration of lithium difluorofluorosulfonyl imide in the electrolyte was changed to 0.05 mol/L.

Comparative example 1

This comparative example was conducted under the same conditions as in example 1 except that lithium difluorofluorosulfonylimide was not added and the concentration of lithium difluorosulfonimide was changed to 1.2 mol/L.

Comparative example 2

This comparative example was conducted under the same conditions as example 1 except that the nitrile additive was not added and the remaining solution except for the lithium salt and the additive was filled with an organic solvent so that the total amount of the solution of this comparative example was the same as example 1.

The electrolytes of examples 1 to 14 and comparative examples 1 to 2 were assembled into batteries, and performance tests were performed using lithium ion batteries, and the test results are shown in table 1:

the specific preparation method of the lithium ion battery for testing comprises the following steps: preparing a slurry of graphite serving as a negative electrode material, acetylene black serving as a conductive agent, a binder CMC and SBR according to the mass percent of 96:1:1:2, coating the slurry on a copper foil current collector, and drying in vacuum to obtain a negative electrode plate; preparing a positive electrode material NCM811, a conductive agent acetylene black and a binder PVDF into slurry according to a mass ratio of 98:1:1, coating the slurry on an aluminum foil current collector, and drying in vacuum to obtain a positive electrode plate. Assembling the positive pole piece, the negative pole piece, the Celgard2400 diaphragm and the electrolyte prepared in the embodiment or the comparative example into a soft package battery, performing electrochemical test by adopting a New Wei charge-discharge test cabinet, and determining the HF content of the electrolyte by adopting an ice water titration method.

(1) And (3) testing the HF content of the electrolyte:

storing the electrolyte at 60 ℃, and testing the HF content of 0d and 90d respectively by an ice water titration method, wherein the HF content is recorded as HF-0d and HF-90 d.

(2) And (3) testing the rate discharge performance of the lithium ion battery:

charging the lithium ion battery at a constant current of 1C (nominal capacity) to a voltage of 4.25V at 25 ℃, then charging at a constant voltage of 4.25V to a current of less than or equal to 0.05C, standing for 10min, and discharging at a constant current of 1C/3C/5C to a cut-off voltage of 2.8V.

Capacity retention (%) after different-rate discharge of the lithium ion battery is ═ x 100% (different-rate discharge capacity/1C discharge capacity).

(3) Testing the high-temperature storage performance of the lithium ion battery:

charging the lithium ion battery to a voltage of 4.25V at a constant current of 1C at 25 ℃, then charging to a current of 0.05C at a constant voltage of 4.25V, testing the volume of the lithium ion battery to be V0, and testing the initial capacity to be C0; and then putting the lithium ion battery into a constant temperature box at 60 ℃, storing for 90 days respectively, taking out the volume of the lithium ion battery to be tested and recording as V1, keeping the capacity to be C1, and recovering the capacity to be C2.

The lithium ion battery has a volume expansion ratio (%) of (V1-V0)/V0 × 100% after 90 days of storage at 60 ℃.

The capacity retention (%) of the lithium ion battery after 90 days of storage at 60 ℃ is (C1/C0) × 100%, and the capacity recovery (%) of the lithium ion battery after 90 days of storage at 60 ℃ is (C2/C0) × 100%.

TABLE 1

As can be seen from the above table, the additive of examples 1-3, the content of which is within the preferable range of the present invention, has excellent high temperature storage gas generation, high temperature volume expansion rate, high temperature capacity retention rate and high temperature capacity recovery rate, and the rate capability at normal temperature is good; in example 4, compared with example 1, the content of fluoroethylene carbonate is reduced, the high-temperature performance and the normal-temperature performance of the battery are reduced, the rate performance is reduced, and a compact SEI film cannot be formed when the addition amount is too small; example 5 the fluoroethylene carbonate content increased and the gas production increased on high temperature storage; example 6 the content of 1, 3-propane sultone, a sulfur-containing additive, is reduced, and the rate performance of the battery is reduced, because the sulfur-containing additive assists in forming a film on the positive electrode and the negative electrode, and the thermal stability is higher, and a dense SEI film cannot be formed on the negative electrode when the additive amount is too small; example 7 content of additive 1, 3-propane sultone increases, adding too much leads to excessive filming, the rate performance of the battery is reduced; example 8 the nitrile additive content was reduced, the nitrile additive content of example 9 was increased, and the electrochemical performance of the cell was reduced compared to example 1; in examples 10 to 12, the carbonate additive, the sulfur additive and the lithium salt additive were not added independently, and the rate performance and cycle performance of the battery were both reduced to some extent; examples 13 to 14 in which the amount of lithium difluorophosphate fluorosulfonylimide added was replaced outside the preferable range of the present invention, both the high-temperature storage performance and rate performance of the battery were reduced because the mixing ratio of lithium difluorosulfonyl imide and lithium difluorophosphate fluorosulfonylimide was effective in suppressing corrosion of lithium difluorosulfonyl imide.

Comparative example 1 was not added with lithium difluorofluorosulfonylimide phosphate, and comparative example 1 was greatly inferior in high-temperature storage performance and rate performance to example 1, comparative example 2 was not added with a nitrile additive, and comparative example 2 was also greatly inferior in high-temperature storage performance and rate performance to example 1.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit 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, an organic solvent and an additive;

n is equal to or more than 1, wherein R is substituted or unsubstituted C1-C5 alkylene, and the number of nitrile substituent groups in the branched chain is equal to or less than 1;

the lithium salt includes lithium difluorophosphate fluorosulfonylimide and lithium difluorosulfonimide.

2. The electrolyte according to claim 1, wherein the concentration of the lithium bis (fluorosulfonyl) imide in the electrolyte is 0.9 to 1.2 mol/L;

preferably, the concentration of the lithium difluorofluorosulfonylimide phosphate in the electrolyte is 0.1-0.3 mol/L.

3. The electrolyte solution according to claim 1 or 2, wherein the nitrile additive is present in an amount of 0.2 to 1.0% by mass based on the electrolyte solution.

4. The electrolyte of any one of claims 1-3, wherein the additives further comprise carbonate-based additives, sulfur-containing additives, and lithium salt additives;

preferably, the carbonate-based additive comprises vinylene carbonate and/or fluoroethylene carbonate;

preferably, the sulfur-containing additive comprises any one of propane sultone, propene sultone or vinyl sulfate or a combination of at least two of the same;

preferably, the lithium salt additive comprises any one of lithium difluorophosphate, lithium bis (oxalato) borate, or lithium difluorobis (oxalato) phosphate, or a combination of at least two thereof.

5. The electrolyte according to claim 4, wherein the carbonate additive accounts for 0.2-1.0% by mass of the electrolyte;

preferably, the sulfur-containing additive accounts for 0.5-2.0% of the electrolyte in terms of mass fraction;

preferably, the lithium salt additive accounts for 0.5-1% of the electrolyte by mass.

6. The electrolyte of any one of claims 1-5, wherein the organic solvent comprises a combination of any two or any three of ethylene carbonate, dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate;

preferably, the volume ratio of the ethylene carbonate to the dimethyl carbonate to the diethyl carbonate to the ethyl methyl carbonate is (20-40): (0-20): (0-20): (30-50).

7. A method of preparing the electrolyte of any of claims 1-6, comprising:

and sequentially adding a carbonate additive, a sulfur-containing additive, a nitrile additive and a lithium salt additive into an organic solvent in an inert atmosphere, and finally adding lithium salt for low-temperature mixing to obtain the electrolyte.

8. The production method according to claim 7, wherein the inert atmosphere includes an argon atmosphere;

preferably, the temperature of the low-temperature mixing is 8-12 ℃.

9. A high nickel lithium ion battery, characterized in that the lithium ion battery comprises the electrolyte of any one of claims 1 to 6;

10. The lithium ion battery of claim 9, wherein the active material of the positive electrode comprises Li (Ni)_xCo_yMn_z)O₂Wherein x is more than or equal to 0.8<0.9，0<y≤0.1，0<z ≦ 0.1 and x + y + z ═ 1;

preferably, the active material of the negative electrode includes graphite.