WO2020135694A1 - Additive for battery electrolyte, and electrolyte and lithium ion battery using same - Google Patents

Abstract

Disclosed is an additive for a battery electrolyte, the structure of which additive is as shown in formula (I); and an electrolyte and a battery which use the additive. Also disclosed are a lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. The electrolyte comprises a lithium salt, a non-aqueous solvent and an additive, wherein the additive comprises an ethylene sulfate compound and an isocyanate compound; and the isocyanate compound contains 1 to 3 -N=C=O groups. The lithium ion battery electrolyte can also comprise the ethylene sulfate compound, the isocyanate compound and a compound of formula (I). The lithium ion battery electrolyte has the advantages of suppressing an increase in the acidity of the electrolyte, preventing the electrolyte from discoloring, improving the capacity retention ratio of the electrolyte, etc.

Description

Battery electrolyte additive, electrolyte and lithium ion battery using the additive Technical field

The invention belongs to the field of lithium-ion battery electrolytes, and relates to an additive for a lithium-ion battery electrolyte, an electrolyte using the additive and a lithium-ion battery.

Background technique

Lithium-ion batteries have the advantages of high energy density, long cycle life, high operating voltage, small self-discharge, and no memory effect. They are widely used in 3C, energy storage, and power batteries. Longer cycle life, higher energy density, faster rate performance, wider use temperature and lower price and cost are important directions for the development of lithium ion batteries.

The electrolyte is one of the key materials of lithium ion batteries. Its function is to conduct lithium ions between the positive electrode and the negative electrode, which will have an important impact on the rate performance, cycle life, and temperature window of the battery. Lithium ion electrolyte is mainly composed of three parts: solvent, lithium salt and additives. Among them, additives are divided into negative electrode film-forming additives, dewatering additives, positive electrode film-forming additives, conductivity-increasing additives, wettability-improving additives and Flame retardant additives, etc.

As for the negative electrode film-forming additive, when it is applied to a lithium ion battery, during the first charge of the lithium ion battery, the negative electrode film-forming additive undergoes reductive decomposition before the electrolyte solvent, and the resulting product is deposited on the surface of the negative electrode to form a passivation layer , Also known as SEI (Solid Electrochemical Interface) membrane. The SEI film only allows lithium ions to pass through, which not only effectively suppresses the insertion of solvated lithium ions between graphite layers, thereby preventing graphite peeling, but also effectively suppresses the side reaction between the negative electrode and the electrolyte, thereby improving the cycle stability of the lithium battery. . In addition, the SEI film also has an important effect on conductivity, temperature performance, etc.

In the prior art, typical negative electrode film-forming additives have been reported are vinylene carbonate (VC), ethylene ethylene carbonate (VEC), 1,3-propane sultone (PS) and fluoroethylene carbonate (FEC) etc. Although these negative electrode film-forming additives can improve the cycle performance of the negative electrode of the battery, there are still problems in improving the high temperature and rate performance.

Therefore, it is necessary to further study the negative electrode film-forming additives used in lithium ion batteries.

On the other hand, the electrolyte is the "blood" of the lithium-ion battery, which bears the heavy responsibility of transporting lithium ions and can directly affect the performance of the lithium-ion battery. The current commercial electrolyte lithium salt is mainly LiPF ₆ , which is prone to thermal decomposition reaction and hydrolysis reaction to generate PF ₅ and HF. PF ₅ and HF catalyze the polymerization of solvent molecules such as ethylene carbonate (EC) and ethyl methyl carbonate (EMC), producing polymers containing conjugated double bonds, which discolor the electrolyte.

Vinyl sulfate (abbreviated as DTD) has the advantage of significantly reducing the internal resistance of the battery. It has been widely used as an electrolyte additive, especially in high-nickel NCM batteries, which can effectively suppress the capacity decay during the battery cycle and reduce the battery after high temperature. Swell. However, the stability of the DTD is poor. After being configured as an electrolyte, the acidity and chromaticity of the electrolyte are easily exceeded, which has a greater impact on the battery performance. Therefore, the electrolyte containing DTD is not conducive to transportation and storage, which greatly limits its application prospect in the electrolyte.

At present, there are no reports about additives that can suppress the acidity and color of DTD-containing electrolytes. This application uses common types of electrolyte stabilizers for DTD-containing electrolytes. The study found the following defects:

(1) Silazane compounds, such as the hexamethylsilazane disclosed in patent CN105470563A, can react with HF, effectively reducing the HF content in the electrolyte. However, when silazane compounds are used in electrolytes containing DTD, white insoluble precipitates are easily produced.

(2) Phosphite compounds, such as the triphenyl phosphite disclosed in patent CN105895954A, have an antioxidant effect and can alleviate the increase in chromaticity during storage of the electrolyte at room temperature. However, phosphite compounds have very little inhibitory effect on the acidity of electrolytes containing DTD, and these compounds have a large pungent odor, which is harmful to health and is not suitable for industrial production.

(3) Carbodiimide compounds, such as the cyclohexylcarbodiimide disclosed in US6077628A, can slowly hydrolyze in the electrolyte, and its alkaline hydrolysate can slowly capture a small amount of HF in the electrolyte, but it is used for In the electrolyte containing DTD, it is also easy to produce white precipitate.

(4) Isocyanate compounds, which are rarely used as stabilizers and are usually used for other applications. For example, the hexamethylene diisocyanate disclosed in patent CN106025339A is used to improve the storage performance of lithium ion batteries at high temperatures; and the isocyanate compound disclosed in patent CN103380530A is used to suppress the capacity deterioration of non-aqueous electrolyte batteries when stored at high temperatures and Gas generation. Even if the prior art mentions the use of isocyanate compounds as stabilizers, it only involves a side-by-side summary with other stabilizers. There is no test data showing that it can inhibit the discoloration of the electrolyte when used as a stabilizer.

Summary of the invention

The first object of the present invention is to provide a battery electrolyte additive, which has the following structural formula (I):

among them:

R1, R2, R3 are independently selected from hydrogen, fluorine, C1-C20 alkyl, C1-C20 haloalkyl.

In the compound represented by the structural formula (I) provided by the present invention, the substituents R1, R2, and R3 are independently selected from hydrogen, fluorine, C1-C20 alkyl, and C1-C20 haloalkyl.

Preferably, the substituents R1, R2, R3 are independently selected from hydrogen, fluorine, C1-C12 alkyl, C1-C12 haloalkyl.

It is further preferred that the substituents R1, R2, R3 are independently selected from hydrogen, fluorine, C1-C5 alkyl, C1-C5 haloalkyl.

It is still further preferred that the substituents R1, R2, R3 are independently selected from hydrogen, fluorine, C1-C3 alkyl, C1-C3 haloalkyl.

Most preferably, the compound represented by the structural formula (I) is selected from lithium trifluoroethanol, lithium tetrafluoroethanol, lithium hexafluoroisopropoxide, lithium heptafluorobutoxide, lithium octafluoropentanol, and dodecafluoroheptanol At least one of lithium.

The battery electrolyte additive represented by the structural formula (I) provided by the present invention is suitable for use as a negative electrode film-forming additive in the battery electrolyte.

When the compound represented by the structural formula (I) of the present invention is used as a negative electrode film-forming additive, the negative electrode of the battery is preferably graphite and/or silicon carbon.

When the compound represented by the structural formula (I) of the present invention is used as a negative electrode film-forming additive, the negative electrode film-forming additive may further include other negative electrode film-forming additives.

As a preferred mode, the negative electrode film-forming additive includes a compound represented by structural formula (I) and is selected from vinylene carbonate, 1,3-propane sultone, and tris(trimethylsilyl)boronic acid At least one of ester, fluoroethylene carbonate, and ethylene ethylene carbonate.

As a further preferred mode, the negative electrode film-forming additive includes a compound represented by structural formula (I) and is selected from vinylene carbonate, 1,3-propane sultone, and tris(trimethylsilyl) borate At least one of them.

The present invention also provides a lithium ion battery electrolyte containing the compound represented by the above structural formula (I).

When the lithium ion battery electrolyte according to the present invention contains the compound represented by the above structural formula (I), the content of the compound represented by structural formula (I) in the lithium ion battery electrolyte is preferably 0.05% to 5%. It is further preferred that the content of the compound represented by structural formula (I) in the electrolyte of the lithium ion battery is 0.5% to 5%. Most preferably, the content of the compound represented by structural formula (I) in the electrolyte of the lithium ion battery is 1% to 2%.

The lithium ion battery electrolyte provided by the present invention may further contain a lithium salt, an organic solvent and additives in addition to the compound represented by the above structural formula (I), that is, the lithium ion battery electrolyte contains a lithium salt and an organic solvent , Additives and compounds represented by structural formula (I).

In the lithium ion battery electrolyte provided by the present invention, the lithium salt used may be a lithium salt commonly used in the art. Preferably, the lithium salt is selected from LiBF ₄ , LiPF ₆ , LiFSI, LiTFSI, LiAsF ₆ , LiClO ₄ , LiSO ₃ CF ₃ , LiC ₂ O ₄ BC ₂ O ₄ , LiF ₂ BC ₂ O ₄ , LiDTI and LiPO ₂ At least one of F ₂ .

The lithium ion battery electrolyte provided by the present invention may use an organic solvent commonly used in the art. Preferably, the organic solvent is selected from at least one of carbonate, phosphate, carboxylate, ether, nitrile, and sulfone solvents.

The additive for the lithium ion battery electrolyte provided by the present invention may be an additive that helps improve the performance of the electrolyte. Preferably, the additive is selected from at least one of negative electrode film-forming additives, water-removing additives, positive electrode film-forming additives, conductivity-increasing additives, wettability-improving additives, and flame retardant additives. It is further preferred that the additive is selected from biphenyl, vinylene carbonate (VC), fluoroethylene carbonate, ethylene ethylene carbonate, propylene sulfite, butylene sulfite, 1,3-propanesulfonate Acid lactone (PS), 1,4-butane sultone, 1,3-(1-propene) sultone, vinyl sulfite, vinyl sulfate, cyclohexylbenzene, tris(trimethylsilyl) At least one of borate (TMSB), tris(trimethylsilyl) phosphate, tert-butylbenzene, succinonitrile, ethylene glycol bis(propionitrile) ether, and succinic anhydride.

When the lithium ion battery electrolyte according to the present invention contains a lithium salt, an organic solvent, an additive, and a compound represented by structural formula (I), the lithium salt, an organic solvent, an additive, and the compound represented by structural formula (I) are in the electrolyte The content should improve battery performance. Preferably, in the lithium ion battery electrolyte, the lithium salt content is 5 to 15%, the organic solvent content is 72 to 95%, the additive content is 0.2 to 10%, and the content of the compound represented by structural formula (I) is 0.1%～5%.

The invention also provides a lithium ion battery containing the above electrolyte. In addition to containing the above electrolyte, the lithium ion battery according to the present invention also contains other commonly used components of the lithium ion battery described in the art.

The compound represented by the structural formula (I) provided by the present invention has the following advantages over the prior art when it is used in a battery electrolyte:

(1) The compound represented by structural formula (I) can effectively improve the interface wettability of the electrolyte to the electrode and reduce the interface contact resistance;

(2) The compound represented by structural formula (I) has a high reduction potential, which can be reduced and decomposed on the surface of graphite, silicon negative electrode, metal lithium and other negative electrodes before the common solvent of the electrolyte to generate a SEI film;

(3) The increased content of N and Li in the generated SEI film can not only make the SEI film more stable, but also effectively reduce the impedance of the SEI film;

(4) It can effectively reduce the interface resistance and charge transfer resistance between graphite and silicon carbon anode materials and the electrolyte, and then effectively improve the cycle stability and rate performance of these anode materials.

According to the second aspect of the present invention, the present invention proposes a lithium ion battery electrolyte that suppresses the increase in acidity of the electrolyte containing DTD, prevents discoloration of the electrolyte, improves the electrochemical performance of the battery, and particularly improves the battery capacity retention rate.

The purpose of the present invention is achieved by the following technical solutions:

An electrolyte for a lithium ion battery, including a lithium salt, a non-aqueous solvent, and an additive. The additive includes vinyl sulfate and a first type of additive. The first type of additive is selected from fluorine represented by the following general formula (I) Lithium alcohol compounds:

Wherein R ₁ , R ₂ and R _{3 are} independently selected from hydrogen, halogen, C ₁ -C ₂₀ alkyl, C ₁ -C ₂₀ haloalkyl, and the halogen is selected from fluorine, chlorine, bromine and iodine; preferably, R ₁ , R ₂ , and R _{3 are} independently selected from hydrogen, fluorine, C ₁ -C ₁₀ alkyl, and C ₁ -C ₁₀ fluoroalkyl; more preferably, R ₁ , R ₂ , and R _{3 are} independently selected From hydrogen, fluorine, methyl, ethyl, propyl, butyl, pentyl, trifluoromethyl, trifluoroethyl, pentafluoroethyl, hexafluoropropyl, octafluorobutyl, decafluoropentyl.

In order to further suppress the acidity of the electrolyte of the lithium ion battery, preferably, the additive further includes a second type of additive, the second type of additive is selected from isocyanate compounds, and the isocyanate compounds include 1 to 3 -N=C =O group; preferably, the isocyanate-based compound contains 2 -N=C=O groups.

According to the above lithium ion battery electrolyte, preferably, the second type of additive is selected from isocyanate compounds represented by the following general formula (II):

Wherein, R _{4 is} selected from C ₁ -C ₂₀ alkyl, C ₁ -C ₂₀ substituted alkyl, substituted phenyl, substituted biphenyl, the alkyl is a chain alkyl or cycloalkyl, and the substituent is Hydrogen, halogen, C ₁ -C ₂₀ alkyl, phosphate, sulfonyl, thio; the halogen is selected from fluorine, chlorine, bromine and iodine;

0≤x≤1, 0≤y≤1, 0≤z≤1.

Preferably, R _{4 is} selected from C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ substituted alkyl, the substituent is hydrogen, halogen, C ₁ -C ₁₀ alkyl.

According to the above-mentioned lithium ion battery electrolyte, optionally, the lithium fluoroalcohol compound is selected from lithium trifluoroethanol, lithium tetrafluoroethanol, lithium hexafluoroisopropoxide, lithium heptafluorobutoxide, octafluoropentanol At least one of lithium and lithium dodecafluoroheptanol. Preferably, the lithium fluoroalcohol compound is at least one selected from lithium trifluoroethoxide, lithium tetrafluoroethoxide, and lithium hexafluoroisopropoxide.

According to the above-mentioned lithium ion battery electrolyte, optionally, the isocyanate compound is selected from at least one of the following compounds shown in 1-12:

According to the above lithium ion battery electrolyte, optionally, the content of the vinyl sulfate accounts for 0.01% to 5% of the total mass of the lithium ion battery electrolyte. Preferably, the content of the vinyl sulfate accounts for 0.5%-3% of the total mass of the electrolyte of the lithium ion battery

According to the above-mentioned lithium ion battery electrolyte, optionally, the content of the isocyanate compound accounts for 0.005% to 5% of the total mass of the lithium ion battery electrolyte. Preferably, the content of the isocyanate compound accounts for 0.02%-1% of the total mass of the electrolyte of the lithium ion battery.

According to the above lithium ion battery electrolyte, optionally, the content of the lithium fluoroalcohol compound accounts for 0.005% to 5% of the total mass of the lithium ion battery electrolyte. Preferably, the content of the lithium fluoroalcohol compound accounts for 0.02%-1% of the total mass of the electrolyte of the lithium ion battery.

According to the foregoing lithium ion battery electrolyte, optionally, the non-aqueous solvent is selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, methyl propyl carbonate, and propionic acid At least two of ethyl acetate, ethyl acetate, ethyl formate, propyl butyrate and γ-butyrolactone, the content of the non-aqueous solvent accounts for 75.0%-88.0% of the total mass of the electrolyte of the lithium ion battery.

According to the foregoing lithium ion battery electrolyte, optionally, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bisoxalate borate, lithium difluorooxalate borate, and lithium bisfluorosulfonimide. The content accounts for 10.0%-18.0% of the total mass of the electrolyte of the lithium ion battery.

According to the above-mentioned lithium ion battery electrolyte, optionally, preferably, the additive further includes a third type of additive selected from the group consisting of vinylene carbonate, 1,3-propane sultone, and three At least one of (trimethylsilyl) borate, tri(trimethylsilyl) phosphate, fluoroethylene carbonate, and ethylene ethylene carbonate.

According to the above-mentioned lithium ion battery electrolyte, optionally, the content of the third type of additive accounts for 0.1%-5.0% of the total mass of the lithium ion battery electrolyte.

The present invention also provides a lithium ion battery, including a positive electrode, a negative electrode, and any of the above-mentioned lithium ion battery electrolytes.

Compared with the prior art, the beneficial effects of the present invention are:

1. The present invention uses lithium fluoroalcohol compounds as the first type of additives. A small amount of addition can reduce the acidity of the electrolyte, thereby effectively suppressing the increase in the chromaticity of the electrolyte containing DTD.

2. When the electrolyte of the present invention is used in a lithium-ion battery, the lithium fluoroalcohol compound can not only greatly improve the electrolyte wetting ability, but also have a negative electrode film-forming effect to reduce the battery impedance; at the same time, the isocyanate compound can further inhibit electrolysis The liquid discolors and preferentially decomposes on the surface of the negative electrode to form a stable solid electrolyte interface film to improve the cycle performance of the battery; the combination of the two types of compounds in the electrolyte containing DTD can improve the electrochemical performance of the lithium ion battery, especially the battery. Capacity retention rate.

3. In the present invention, lithium fluoroalcohol compounds and isocyanate compounds are added to the electrolyte containing DTD at the same time. Both products are soluble in most organic solvents, and no insoluble precipitates are produced.

According to a third aspect of the present invention, the present invention proposes a lithium ion battery electrolyte that suppresses the increase in acidity of an electrolyte containing DTD, prevents discoloration of the electrolyte, improves the electrochemical performance of the battery, and particularly improves the battery capacity retention rate.

The purpose of the present invention is achieved by the following technical solutions:

An electrolyte for a lithium ion battery, including a lithium salt, a non-aqueous solvent, and an additive, the additive includes vinyl sulfate and a second type of additive, the second type of additive is selected from isocyanate compounds, and the isocyanate compounds include 1 ~3 -N=C=O groups; preferably, the isocyanate-based compound contains 2 -N=C=O groups.

According to the foregoing lithium ion battery electrolyte, preferably, the second type of additive is selected from isocyanate compounds represented by the following general formula (I):

Wherein R _{1 is} selected from C ₁ -C ₂₀ alkyl, C ₁ -C ₂₀ substituted alkyl, substituted phenyl, substituted biphenyl, the alkyl is a chain alkyl or cycloalkyl, the substituent is Hydrogen, halogen, C ₁ -C ₂₀ alkyl, phosphate, sulfonyl, thio; the halogen is selected from fluorine, chlorine, bromine and iodine;

0≤x≤1, 0≤y≤1, 0≤z≤1.

Preferably, R _{1 is} selected from C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ substituted alkyl, the substituent is hydrogen, halogen, C ₁ -C ₁₀ alkyl.

In order to further suppress the acidity of the electrolyte of the lithium ion battery, preferably, the additive further includes a first type of additive selected from the lithium fluoroalcohol compounds represented by the following general formula (I):

Wherein R2, R3, R4 are independently selected from hydrogen, halogen, C ₁ -C ₂₀ alkyl, C ₁ -C ₂₀ haloalkyl, and the halogen is selected from fluorine, chlorine, bromine and iodine. Preferably, R ₂ , R ₃ , R _{4 are} independently selected from hydrogen, fluorine, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ fluoroalkyl.

According to the above-mentioned lithium ion battery electrolyte, optionally, the isocyanate compound is selected from at least one of the compounds shown in the foregoing 1-12.

According to the above-mentioned lithium ion battery electrolyte, optionally, the lithium fluoroalcohol compound is selected from lithium trifluoroethanol, lithium tetrafluoroethanol, lithium hexafluoroisopropoxide, lithium heptafluorobutoxide, octafluoropentanol At least one of lithium and lithium dodecafluoroheptanol. Preferably, the lithium fluoroalcohol compound is at least one selected from lithium trifluoroethoxide, lithium tetrafluoroethoxide, and lithium hexafluoroisopropoxide.

According to the above-mentioned lithium ion battery electrolyte, optionally, the content of the vinyl sulfate accounts for 0.01%-5% of the total mass of the lithium ion battery electrolyte. Preferably, the content of the vinyl sulfate accounts for 0.5%-3% of the total mass of the electrolyte of the lithium ion battery

According to the above-mentioned lithium ion battery electrolyte, optionally, the content of the isocyanate compound accounts for 0.005% to 5% of the total mass of the lithium ion battery electrolyte. Preferably, the content of the isocyanate compound accounts for 0.02%-1% of the total mass of the electrolyte of the lithium ion battery.

According to the above lithium ion battery electrolyte, optionally, the content of the lithium fluoroalcohol compound accounts for 0.005% to 5% of the total mass of the lithium ion battery electrolyte. Preferably, the content of the lithium fluoroalcohol compound accounts for 0.02%-1% of the total mass of the electrolyte of the lithium ion battery.

According to the foregoing lithium ion battery electrolyte, optionally, the non-aqueous solvent is selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, methyl propyl carbonate, and propionic acid At least two of ethyl acetate, ethyl acetate, ethyl formate, propyl butyrate and γ-butyrolactone, the content of the non-aqueous solvent accounts for 75.0%-88.0% of the total mass of the electrolyte of the lithium ion battery.

According to the above lithium ion battery electrolyte, optionally, the lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate, lithium bisoxalate borate, lithium difluorooxalate borate, and lithium bisfluorosulfonimide. The content accounts for 10.0%-18.0% of the total mass of the electrolyte of the lithium ion battery.

According to the above-mentioned lithium ion battery electrolyte, optionally, preferably, the additive further includes a third type of additive selected from the group consisting of vinylene carbonate, 1,3-propane sultone, and three At least one of (trimethylsilyl) borate, tri(trimethylsilyl) phosphate, fluoroethylene carbonate, and ethylene ethylene carbonate.

According to the foregoing lithium ion battery electrolyte, optionally, the content of the third type of additive accounts for 0.1%-5.0% of the total mass of the lithium ion battery electrolyte.

The present invention also provides a lithium ion battery, including a positive electrode, a negative electrode, and any of the above-mentioned lithium ion battery electrolytes.

The invention uses isocyanate compounds as additives, and the -N=C=O functional group contained in it can react with trace water in the electrolyte, inhibit the hydrolysis reaction of LiPF ₆ from the source, avoid PF ₅ and HF, and thus prevent electrolysis The liquid changes color.

When the electrolyte of the present invention is used in a lithium ion battery, the isocyanate compound can not only inhibit the discoloration of the electrolyte, but also preferentially decompose on the surface of the negative electrode, form a stable solid electrolyte interface film, and improve the cycle performance of the battery.

BRIEF DESCRIPTION

Figure 1 shows the LSV curves of the electrolytes prepared in Example 1, Example 4 and Comparative Example 1.

FIG. 2 is a perspective view of the electrolytes prepared in Example 1, Example 4 and Comparative Example 1 on the Ceglald 2400 separator.

FIG. 3 is an AC impedance spectrum before and after cycling of a metal lithium/graphite half-cell assembled with the electrolytes prepared according to Example 1, Example 4, and Comparative Example 1. FIG.

4 is a graph of rate performance of a metal lithium/graphite half-cell assembled with the electrolyte prepared according to Example 1, Example 4, and Comparative Example 1. FIG.

5 is an XPS diagram of the surface of the graphite negative electrode after the batteries assembled in Example 1 and Comparative Example 1 are cycled.

6 is a photo of a sample of color changes after storage for different times in Example 1, Example 4, and Comparative Example 1.

7 is a comparison diagram of the discharge capacity-cycle number of Comparative Example 16, Example 33, Comparative Example 21 and Example 46 of the present invention;

FIG. 8 is a comparison graph of 100-cycle impedances of Comparative Example 16, Example 33, Comparative Example 21 and Example 46 of the present invention.

detailed description

The present invention will be further described below in conjunction with specific examples, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

1. Electrolyte preparation and battery performance test

Example 1:

(1) Preparation of electrolyte

Mix ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of EC:DEC:EMC=3:2:5, and then add lithium hexafluorophosphate (LiPF ₆ ) to the mole The concentration is 1mol/L, and then 1% lithium hexafluoroisopropoxide based on the total mass of the electrolyte is added.

(2) Preparation of positive plate

Mix the positive electrode active material LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF) in a mass ratio of 93:4:3, and then disperse them In N-methyl-2-pyrrolidone (NMP), a positive electrode slurry was obtained. The positive electrode slurry is evenly coated on both sides of the aluminum foil, after drying, rolling and vacuum drying, and the aluminum lead wire is welded with an ultrasonic welding machine to obtain a positive electrode plate.

(3) Preparation of negative plate

Mix the negative electrode active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) at a mass ratio of 92:2:3:3, and then disperse them in deionized In water, a negative electrode slurry is obtained. The negative electrode slurry is coated on both sides of the copper foil, after drying, rolling and vacuum drying, and the lead wire made of nickel is welded with an ultrasonic welding machine to obtain a negative electrode plate.

(4) Preparation of batteries

A polyethylene microporous film with a thickness of 20 μm is placed between the positive electrode plate and the negative electrode plate as a separator, and then the sandwich structure composed of the positive electrode plate, the negative electrode plate and the separator is wound, and the electrode lugs are drawn out and encapsulated in an aluminum plastic film. Cell to be filled.

(5) Liquid injection and formation of batteries

In a glove box with a moisture content of less than 10 ppm, the prepared electrolyte is injected into the battery cell, and the amount of the electrolyte should ensure that the voids in the battery cell are filled. Then proceed to the following steps: 0.01C constant current charging for 30min, 0.02C constant current charging for 60min, 0.05C constant current charging for 90min, 0.1C constant current charging for 240min, and then set aside for 1hr after shaping and sealing, and then further with 0.2C current constant The battery is charged to 4.40V, and after being left at room temperature for 24hr, it is discharged to 3.0V with a constant current of 0.2C.

(6) Cycle performance test

Charge at a constant current of 1C to 4.40V and then charge at a constant voltage until the current drops to 0.1C, then discharge at a constant current of 1C to 3.0V, so cycle for 300 weeks, and record the discharge capacity of the first week and the 300th week Discharge capacity, calculate the capacity retention rate as follows:

Capacity retention rate = (discharge capacity at week 300/discharge capacity at week 1) * 100%

The data of the normal temperature cycle performance obtained from the test are shown in Table 1.

Example 2:

The 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 was replaced with 0.05% lithium hexafluoroisopropoxide, and the remaining electrolytes, positive plates, and negative plates were prepared according to the same operating conditions as in Example 1. , Batteries, and the battery injection and formation and battery cycle performance test. The obtained normal temperature cycle performance data is shown in Table 1.

Example 3:

The 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 was replaced with 0.1% lithium hexafluoroisopropoxide, and the remaining electrolytes, positive plates, and negative plates were prepared according to the same operating conditions as in Example 1. , Batteries, and the battery injection and formation and battery cycle performance test. The obtained normal temperature cycle performance data is shown in Table 1.

Example 4:

The 1% lithium hexafluoroisopropoxide in the prepared electrolyte in Example 1 was replaced with 0.5% lithium hexafluoroisopropoxide, and the remaining electrolytes, positive plates, and negative plates were prepared according to the same operating conditions as in Example 1. , Batteries, and the battery injection and formation and battery cycle performance test. The obtained normal temperature cycle performance data is shown in Table 1.

Example 5:

The 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 was replaced with 2% lithium hexafluoroisopropoxide, and the remaining electrolytes, positive plates, and negative plates were prepared according to the same operating conditions as in Example 1. , Batteries, and the battery injection and formation and battery cycle performance test. The obtained normal temperature cycle performance data is shown in Table 1.

Example 6:

The 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 was replaced with 5% lithium hexafluoroisopropoxide, and the remaining electrolytes, positive plates, and negative plates were prepared according to the same operating conditions as in Example 1. , Batteries, and the battery injection and formation and battery cycle performance test. The obtained normal temperature cycle performance data is shown in Table 1.

Example 7:

Replace the 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 with 1% lithium trifluoroethanolate, and prepare the electrolyte, positive electrode plate, negative electrode plate, and battery according to the same operating conditions as in Example 1. Core, and perform the injection and formation of the battery and the cycle performance test of the battery. The obtained normal temperature cycle performance data is shown in Table 1.

Example 8:

Replace the 1% lithium hexafluoroisopropoxide in the prepared electrolyte in Example 1 with 0.5% lithium trifluoroethanolate, and prepare the electrolyte, positive electrode plate, negative electrode plate, and battery according to the same operating conditions as in Example 1. Core, and perform the injection and formation of the battery and the cycle performance test of the battery. The obtained normal temperature cycle performance data is shown in Table 1.

Example 9:

Replace the 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 with 2% lithium trifluoroethanolate, and prepare the electrolyte, positive electrode plate, negative electrode plate, and battery according to the same operating conditions as in Example 1. Core, and perform the injection and formation of the battery and the cycle performance test of the battery. The obtained normal temperature cycle performance data is shown in Table 1.

Example 10:

The 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 was replaced with 1% lithium octafluoropentoxide, and the remaining electrolytes, positive plates, and negative plates were prepared according to the same operating conditions as in Example 1. Batteries, and perform the injection and formation of batteries and the cycle performance test of batteries. The obtained normal temperature cycle performance data is shown in Table 1.

Example 11:

Replace the 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 with 1% lithium tetrafluoroethanolate, and prepare the electrolyte, positive electrode plate, negative electrode plate, and battery according to the same operating conditions as in Example 1. Core, and perform the injection and formation of the battery and the cycle performance test of the battery. The obtained normal temperature cycle performance data is shown in Table 1.

Example 12:

The 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 was replaced with 1% lithium heptafluorobutoxide, and the remaining electrolytes, positive plates, and negative plates were prepared according to the same operating conditions as in Example 1. Batteries, and perform the injection and formation of batteries and the cycle performance test of batteries. The obtained normal temperature cycle performance data is shown in Table 1.

Example 13:

The 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 was replaced with 1% lithium dodecylfluoroheptanolate, and the remaining electrolytes, positive plates, and negative plates were prepared according to the same operating conditions as in Example 1. , Batteries, and the battery injection and formation and battery cycle performance test. The obtained normal temperature cycle performance data is shown in Table 1.

Example 14:

The 1% lithium hexafluoroisopropoxide in the electrolyte prepared in Example 1 was replaced with 1% lithium hexafluoroisopropoxide + 1% TMSB (tris(trimethylsilyl) borate), and the rest The electrolyte, the positive electrode plate, the negative electrode plate, and the battery cell were prepared according to the same operating conditions as in Example 1, and the injection and formation of the battery cell and the cycle performance test of the battery were performed. The obtained normal temperature cycle performance data is shown in Table 1.

Example 15:

The graphite in the preparation of the negative electrode plate of Example 1 was replaced with a silicon-carbon negative electrode (capacity of 450 mAh/g), and the remaining electrolytes, positive plates, negative plates, and batteries were prepared according to the same operating conditions as in Example 1, and the cells were processed. The liquid injection and formation and battery cycle performance test. The obtained normal temperature cycle performance data is shown in Table 1.

Example 16:

Replace LiNi _0.5 Co _0.2 Mn _0.3 O ₂ in the preparation of the positive electrode plate of Example 1 with LiCoO ₂ , and prepare the electrolyte, the positive electrode plate, the negative electrode plate and the battery cell according to the same operating conditions as in Example 1 Liquid injection and formation and battery cycle performance test. The obtained normal temperature cycle performance data is shown in Table 1.

Comparative Example 1:

The 1% lithium hexafluoroisopropoxide in the electrolyte preparation of Example 1 is removed, and the rest is prepared according to the same operating conditions as in Example 1 to prepare the electrolyte, the positive plate, the negative plate, and the batteries, and the batteries are filled And the formation and battery cycle performance test. The obtained normal temperature cycle performance data is shown in Table 1.

Comparative Example 2:

Replace the 1% lithium hexafluoroisopropoxide in the electrolyte preparation of Example 1 with 1% VC, and follow the same operating conditions as Example 1 to prepare the electrolyte, positive electrode plate, negative electrode plate, and battery cell, and proceed The injection and formation of batteries and the cycle performance test of batteries. The obtained normal temperature cycle performance data is shown in Table 1.

Comparative Example 3:

Replace the 1% lithium hexafluoroisopropoxide in the electrolyte preparation of Example 1 with 1% PS, and prepare the electrolyte, positive electrode plate, negative electrode plate, and battery cell under the same operating conditions as in Example 1 The injection and formation of batteries and the cycle performance test of batteries. The obtained normal temperature cycle performance data is shown in Table 1.

Comparative Example 4:

Replace the 1% lithium hexafluoroisopropoxide in the electrolyte preparation of Example 1 with 1% VC+1% PS, and prepare the electrolyte, positive plate, and negative plate according to the same operating conditions as in Example 1. Batteries, and perform the injection and formation of batteries and the cycle performance test of batteries. The obtained normal temperature cycle performance data is shown in Table 1.

Comparative Example 5:

Replace the 1% lithium hexafluoroisopropoxide in the electrolyte preparation of Example 1 with 0.5% VC + 0.5% PS, and prepare the electrolyte, positive plate, and negative plate according to the same operating conditions as in Example 1. Batteries, and perform the injection and formation of batteries and the cycle performance test of batteries. The obtained normal temperature cycle performance data is shown in Table 1.

Comparative Example 6:

The 1% lithium hexafluoroisopropoxide in the electrolyte preparation of Example 1 was replaced with 2% VC + 2% PS, and the remaining electrolytes, positive plates, and negative plates were prepared according to the same operating conditions as in Example 1. Batteries, and perform the injection and formation of batteries and the cycle performance test of batteries. The obtained normal temperature cycle performance data is shown in Table 1.

Comparative Example 7:

The 1% lithium hexafluoroisopropoxide in the electrolyte preparation of Example 1 was replaced with 1% VC+1% PS+1% TMSB, and the rest were prepared according to the same operating conditions as Example 1 Plate, negative plate, battery cell, and perform the injection and formation of battery cell and the cycle performance test of the battery. The obtained normal temperature cycle performance data is shown in Table 1.

Comparative Example 8:

Replace the 1% lithium hexafluoroisopropoxide in the electrolyte preparation of Example 1 with 1% VC+1% PS, and replace the graphite in the preparation of the negative plate with a silicon carbon negative electrode (capacity is 450mAh/g) In the rest, the electrolyte, the positive electrode plate, the negative electrode plate, and the battery cell were prepared according to the same operating conditions as in Example 1, and the injection and formation of the battery cell and the cycle performance test of the battery were performed. The obtained normal temperature cycle performance data is shown in Table 1.

Comparative Example 9:

Replace the 1% lithium hexafluoroisopropoxide in the electrolyte preparation of Example 1 with 1% VC+1% PS, and replace LiNi _0.5 Co _0.2 Mn _0.3 O ₂ with LiCoO during the preparation of the positive plate _{2. In the} rest, the electrolyte, the positive electrode plate, the negative electrode plate, and the battery cell were prepared according to the same operating conditions as in Example 1, and the injection and formation of the battery cell and the cycle performance test of the battery were performed. The obtained normal temperature cycle performance data is shown in Table 1.

Table 1

Second, the additive negative electrode film forming performance test

In order to verify the negative electrode film forming performance of the lithium ion battery electrolyte additive shown in formula (I) provided by the present invention, the present invention uses the electrolytes prepared in Example 1, Example 4 and Comparative Example 1 as samples for color change, LSV curve, the wettability of the separator and the AC impedance graph and rate performance test of graphite/Li half-cells.

1. Color change test

The electrolyte prepared in Comparative Example 1 was placed at room temperature, and after 7 days of storage, it was observed that the color of the electrolyte had started to yellow, and the color of the electrolyte gradually became darker with time. The color of the electrolyte changed significantly after storage for 35 days Yellow, the specific color changes are shown in Figure 6.

The electrolytes prepared in Example 1 and Example 4 were placed in the same environment. The electrolyte prepared in Example 4 began to turn yellow after 21 days of storage, and the color after 35 days of storage was better than that of the electrolyte prepared in Comparative Example 1. The color at 35 days was light, and the electrolyte prepared in Example 1 did not change color after 35 days of storage.

The color change of the electrolyte comes from the hydrolysis of LiPF ₆ , and it can be seen from the above color change of the electrolyte that the lithium fluoroalcohol provided by the present invention can suppress the hydrolysis of LiPF ₆ , thereby improving the cycle stability of the electrolyte.

2. LSV curve test

The LSV curve test method is as follows: the three-electrode method (the graphite electrode is the working electrode, and the metal lithium is the counter electrode and the reference electrode, respectively), the scanning rate is 0.05mV/s, and the lower scanning limit is 0.01V.

It can be seen from FIG. 1 that the electrolyte prepared in Comparative Example 1 lacks the additive provided by the present invention, and the electrolyte is reduced and decomposed from 0.8 V, and this potential corresponds to the film-forming potential of EC. While the electrolytes prepared in Example 1 and Example 4 were added with lithium hexafluoroisopropoxide and lithium trifluoroethanolate, respectively, the reduction potential of the electrolyte increased from 0.8V to 0.9V and 1.0V, respectively, indicating that hexafluoroisopropyl The reduction potential of lithium alkoxide and lithium trifluoroethanol is higher than that of EC.

Therefore, before the EC solvent is reduced, lithium hexafluoroisopropoxide and lithium trifluoroethanol are preferentially reduced, and the reduction product is deposited on the surface of the graphite anode to help form a more stable SEI film, which can effectively suppress the electrolyte and electrode during subsequent cycles The side reaction between them, in turn, significantly improves the battery cycle stability.

3. Wetting performance test

The test method for the wettability of the separator is: using the normal temperature wet viewing angle tester to test the wet viewing angle of the three electrolytes and the Celgard 2400 separator.

Figure 2 shows the angle of view of the electrolytes prepared by Example 1, Example 4 and Comparative Example 1 on the Ceglald 2400 separator.

It can be seen from FIG. 2 that the electrolytes prepared in Example 1 and Example 4 have an average viewing angle of 26.85° and 25.8° for the separator, respectively, while the electrolyte and the separator prepared in Comparative Example 1 have an average viewing angle of 41.0°. , Which shows that the addition of lithium hexafluoroisopropoxide and lithium trifluoroethanol can help to improve the wettability between the electrolyte and the separator, thereby reducing the contact resistance between the electrode and the electrolyte, and effectively improving the electrochemical performance of the battery .

4. Graphite/Li half-cell AC impedance spectrum and rate performance test

FIG. 3 is an AC impedance spectrum of a metal lithium/graphite half-cell assembled from the electrolytes prepared in Example 1, Example 4 and Comparative Example 1 before and after cycling. 4 is a graph of rate performance of a metal lithium/graphite half-cell assembled from the electrolytes prepared in Example 1, Example 4, and Comparative Example 1. FIG.

It can be seen from FIG. 3 and FIG. 4 that, compared with the metal lithium/graphite half-cell using the electrolyte prepared in Comparative Example 1, the metal lithium/graphite half-cell using the electrolyte prepared in Example 1 and Example 4 is Before and after the cycle, it has lower AC impedance and better rate performance, which shows that adding the compound shown by the structural formula (I) provided by the present invention can significantly improve the rate performance of the graphite half-cell.

5. X-ray photoelectron spectrum test

The electrolytes prepared in Comparative Example 1 and Example 1 were assembled into a metal lithium/graphite half-cell, and the graphite negative pole pieces after circulation were taken for X-ray photoelectron spectroscopy analysis. The results are shown in FIG. 5. It can be seen from FIG. 5 that the LiF content on the surface of the graphite negative electrode using the electrolyte prepared in Example 1 is significantly increased, and the increase in the LiF content can significantly improve the stability of the interface film.

3. Electrolyte preparation and battery performance test

Example 17:

In a glove box filled with argon gas (moisture <1 ppm, oxygen content <1 ppm), mix dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate in a 1:1:1 mass ratio, and slowly add to the mixed solution LiPF6 with a mass fraction of 12.0% (total mass proportion of electrolyte), stir until it is completely dissolved, add vinyl sulfate to the mixed solution with a mass fraction of 2.0% (total mass proportion of electrolyte), and finally add to the mixed solution A lithium fluoroalcohol compound is added to obtain an electrolyte for a lithium ion battery. The lithium fluoroalcohol compound is lithium trifluoroethanol with a mass fraction of 0.05% (total mass ratio of electrolyte).

Example 18:

The operation is the same as that in Example 17, except that the lithium fluoroalcohol compound finally added to the mixed solution is lithium hexafluoroisopropoxide with a mass fraction of 0.05%.

Example 19:

The operation is the same as that of Example 17, except that the lithium fluoroalcohol compound finally added to the mixed solution is lithium octafluoropentanol with a mass fraction of 0.05%.

Example 20:

The operation is the same as that in Example 17, except that the lithium fluoroalcohol compound finally added to the mixed solution is lithium trifluoroethanolate with a mass fraction of 0.1%.

Example 21:

The operation is the same as that in Example 17, except that the lithium fluoroalcohol compound finally added to the mixed solution is lithium hexafluoroisopropoxide with a mass fraction of 0.1%.

Example 22:

The operation is the same as that of Example 17, except that the lithium fluoroalcohol compound finally added to the mixed solution is lithium octafluoropentoxide with a mass fraction of 0.1%.

Example 23:

The operation is the same as that in Example 17, except that the lithium fluoroalcohol compound added to the mixed solution is lithium trifluoroethanolate with a mass fraction of 0.2%.

Example 24:

The operation is the same as that in Example 17, except that the lithium fluoroalcohol compound finally added to the mixed solution is lithium hexafluoroisopropoxide with a mass fraction of 0.2%.

Example 25:

The operation is the same as that in Example 17, except that the lithium fluoroalcohol compound finally added to the mixed solution is lithium octafluoropentoxide with a mass fraction of 0.2%.

Example 26:

In a glove box filled with argon gas (moisture <1 ppm, oxygen content <1 ppm), mix dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate in a 1:1:1 mass ratio, and slowly add to the mixed solution LiPF6 with a mass fraction of 12.0% (total mass proportion of electrolyte), stir until it is completely dissolved, add vinyl sulfate to the mixed solution with a mass fraction of 2.0% (total mass proportion of electrolyte), and finally add to the mixed solution A lithium fluoroalcohol compound and an isocyanate compound are added to obtain an electrolyte for a lithium ion battery. The lithium fluoroalcohol compound is lithium trifluoroethanol with a mass fraction of 0.05% (total mass ratio of electrolyte). The isocyanate The compound is hexamethylene diisocyanate with a mass fraction of 0.05% (total mass ratio of electrolyte).

Example 27:

The operation is the same as that in Example 26, except that the lithium fluoroalcohol compound added to the mixed solution is lithium trifluoroethanolate with a mass fraction of 0.1%, and the isocyanate compound is hexamethylene with a mass fraction of 0.05%. Diisocyanate.

Example 28:

The operation is the same as that in Example 26, except that the lithium fluoroalcohol compound added to the mixed solution is lithium hexafluoroisopropoxide with a mass fraction of 0.05%, and the isocyanate compound added is hexahedron with a mass fraction of 0.05%. Methyl diisocyanate.

Example 29:

The operation is the same as that in Example 26, except that the lithium fluoroalcohol compound added to the mixed solution is lithium hexafluoroisopropoxide with a mass fraction of 0.1%, and the isocyanate compound added is Liuya with a mass fraction of 0.05%. Methyl diisocyanate.

Example 30:

The operation is the same as that in Example 26, except that the lithium fluoroalcohol compound added to the mixed solution is lithium trifluoroethanolate with a mass fraction of 0.05%, and the isocyanate compound added is isophorone with a mass fraction of 0.05%. Diisocyanate.

Example 31:

The operation is the same as that of Example 26, except that the lithium fluoroalcohol compound added to the mixed solution is lithium hexafluoroisopropoxide with a mass fraction of 0.05%, and the isocyanate compound added is isophor with a mass fraction of 0.05%. Ketone diisocyanate. Comparative Example 10:

In a glove box filled with argon gas (moisture <1 ppm, oxygen content <1 ppm), mix dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate in a 1:1:1 mass ratio, and slowly add to the mixed solution LiPF6 with a mass fraction of 12.0% (total electrolyte mass ratio) is stirred until it is completely dissolved, and vinyl sulfate with a mass fraction of 2.0% (total electrolyte mass ratio) is added to the mixed solution to obtain a lithium ion battery electrolyte .

Comparative Example 11:

The operation is the same as that of Comparative Example 10. The difference is that on the basis of Comparative Example 10, hexamethyldisilazane with a mass fraction of 0.05% (total mass ratio of electrolyte) is added as an additive.

Comparative Example 12:

The operation is the same as that of Comparative Example 10. The difference is that on the basis of Comparative Example 10, triphenyl phosphite with a mass fraction of 0.05% (total mass of electrolyte) is added as an additive.

Comparative Example 13:

The operation is the same as that of Comparative Example 10. The difference is that cyclohexylcarbodiimide with a mass fraction of 0.05% (total mass ratio of electrolyte) is added as an additive on the basis of Comparative Example 10.

Comparative Example 14:

The operation is the same as that of Comparative Example 10, the difference is that hexamethylene diisocyanate with a mass fraction of 0.05% (total mass ratio of electrolyte) is added as an additive on the basis of Comparative Example 10.

Comparative Example 15:

The operation is the same as that of Comparative Example 10. The difference is that on the basis of Comparative Example 10, isophorone diisocyanate with a mass fraction of 0.05% (total mass ratio of electrolyte) is added as an additive.

Fourth, the electrolyte storage acidity and color test

Part of the electrolytes prepared in the above Examples 1-15 and Comparative Examples 1-6 were transferred to sealed aluminum bottles, placed in a 50°C constant temperature oven for storage, and stored in gloves before storage, 7 days storage, and 28 days storage respectively Sampling the box to check the acidity value and color value of the electrolyte. The acidity test method uses triethylamine titration, the acidity unit is ppm, the colority test method uses platinum-cobalt colorimetry, and the colority unit is Hazen. The test results are shown in Table 2 below:

Table 2 Electrolyte acidity and color test results table

It can be seen from Table 2 that the use of a single lithium fluoroalcohol compound additive or a mixture of lithium fluoroalcohol compound and isocyanate compound additives has a significant effect on reducing the acidity and chroma of the electrolyte, and the lower addition amount is used. It can achieve a very obvious inhibition effect, which is conducive to the storage and transportation of electrolyte containing DTD.

Comparing Comparative Examples 10-13 in Table 2, it can be seen that the use of conventional additives has a certain effect of reducing the acidity and color of the storage electrolyte at a high temperature of 50°C compared with no additives. However, white precipitation occurs in Comparative Example 11, and the Comparative Example 12 has a pungent odor, and a small amount of white precipitate appears in Comparative Example 13.

Comparing Comparative Example 10 and Examples 17-25 in Table 2, it can be seen that compared with no additives, the use of a single lithium fluoroalcohol compound additive has no adverse reactions or irritating odors, and has no effect on the acidity and color of the electrolyte. Degree has a more obvious reduction effect. With the increase of the added amount, the suppression of the acidity and chroma of the electrolyte is more obvious.

Comparing Examples 17-25, Comparative Examples 14-15, and Examples 26-31 in Table 2, it can be seen that the lithium fluoroalcohol-based compound is used compared to the use of a single lithium fluoroalcohol-based compound additive or a single isocyanate-based compound additive. 3. The mixed additives of isocyanate compounds have a very obvious inhibitory effect on the acidity and chroma of the electrolyte. To achieve the same suppression effect as the use of a single lithium fluoroalcohol compound additive or a single isocyanate compound additive, the amount of additive added can be greatly reduced.

5. Electrochemical performance test of electrolyte

The lithium ion battery electrolytes of Examples 17-31 and Comparative Examples 10-15 prepared above were injected into a fully dried 1Ah LiNi0.6Co0.2Mn0.2O2/graphite soft-pack battery, the injection volume was 4g, and the battery passed After 12 hours of shelving, hot-press forming, secondary sealing and conventional volume division, perform a 1C cycle performance test: at 25°C, charge the divided volume battery to 4.35V with a constant current and constant voltage of 1C, and a cut-off current of 0.05C. Then discharge at a constant current of 1C to 3.0V, and the calculation formula of the cycle capacity retention rate is as follows:

Cycle 500 cycle capacity retention rate (%) = (500th cycle discharge capacity/first cycle discharge capacity) × 100%;

The test results are shown in Table 3:

Table 3 Capacity retention rate test result table

It can be seen from Table 3 above that when a single lithium fluoroalcohol compound is used as an additive, as the amount of addition increases, there is no obvious change in the battery capacity retention rate, but the battery capacity is basically maintained or slightly higher than the case without additives . When a single isocyanate compound is used as an additive, as the amount of addition increases, the battery capacity retention rate gradually decreases, which is basically maintained or lower than that without the additive.

When lithium fluoroalcohol compounds and isocyanate compounds are used as mixed additives, the battery capacity retention rate is higher than when no additives are added (Comparative Example 10) and higher than when conventional additives are used (Comparative Examples 11-13), This is higher than the case of using a lithium fluoroalcohol-based compound alone (Examples 17-25) or the case of using an isocyanate-based compound alone (Comparative Examples 14-15).

Sixth, electrolyte preparation and battery performance test

Example 32:

In a glove box filled with argon gas (moisture <1 ppm, oxygen content <1 ppm), mix dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate in a 1:1:1 mass ratio, and slowly add to the mixed solution LiPF6 with a mass fraction of 12.0% (total mass proportion of electrolyte), stir until it is completely dissolved, add vinyl sulfate to the mixed solution with a mass fraction of 2.0% (total mass proportion of electrolyte), and finally add to the mixed solution An isocyanate compound is added to obtain an electrolyte for a lithium ion battery. The isocyanate compound is hexamethylene diisocyanate with a mass fraction of 0.05% (total mass ratio of electrolyte).

Example 33:

The operation is the same as that in Example 32, except that the isocyanate compound added to the mixed solution lastly is hexamethylene diisocyanate with a mass fraction of 0.1%.

Example 34:

The operation is the same as that in Example 32, except that the isocyanate compound added to the mixed solution lastly is hexamethylene diisocyanate with a mass fraction of 0.5%.

Example 35:

The operation is the same as that of Example 32, except that the isocyanate compound added to the mixed solution lastly is isophorone diisocyanate with a mass fraction of 0.05%.

Example 36:

The operation is the same as that of Example 32, except that the isocyanate compound added to the mixed solution lastly is isophorone diisocyanate with a mass fraction of 0.1%.

Example 37:

The operation is the same as that in Example 32, except that the isocyanate compound added to the mixed solution lastly is 0.5% by weight of isophorone diisocyanate.

Example 38:

The operation is the same as that in Example 32, except that the isocyanate compound added to the mixed solution lastly is phenyl isocyanate with a mass fraction of 0.1%.

Example 39:

In a glove box filled with argon gas (moisture <1 ppm, oxygen content <1 ppm), mix dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate in a 1:1:1 mass ratio, and slowly add to the mixed solution LiPF6 with a mass fraction of 12.0% (total mass proportion of electrolyte), stir until it is completely dissolved, add vinyl sulfate to the mixed solution with a mass fraction of 2.0% (total mass proportion of electrolyte), and finally add to the mixed solution An isocyanate compound and a lithium fluoroalcohol compound are added to obtain an electrolyte for a lithium ion battery. The isocyanate compound is hexamethylene diisocyanate with a mass fraction of 0.05% (total mass of electrolyte). The fluoroalcohol The lithium compound is lithium trifluoroethanol with a mass fraction of 0.01% (total mass ratio of electrolyte).

Example 40:

The operation is the same as that in Example 39, except that the isocyanate compound added to the mixed solution is hexamethylene diisocyanate with a mass fraction of 0.05%, and the lithium fluoroalcohol compound is trifluoro with a mass fraction of 0.05%. Lithium ethoxide.

Example 41:

The operation is the same as that in Example 39, except that the isocyanate compound added to the mixed solution is hexamethylene diisocyanate with a mass fraction of 0.05%, and the lithium fluoroalcohol compound is trifluoro with a mass fraction of 0.1%. Lithium ethoxide.

Example 42:

The operation is the same as that in Example 39, except that the isocyanate compound added to the mixed solution last is hexamethylene diisocyanate with a mass fraction of 0.05%, and the lithium fluoroalcohol compound added is hexafluoro with a mass fraction of 0.01% Lithium isopropoxide.

Example 43:

The operation is the same as that in Example 39, except that the isocyanate compound added to the mixed solution is hexamethylene diisocyanate with a mass fraction of 0.05%, and the lithium fluoroalcohol compound is hexafluoro with a mass fraction of 0.05%. Lithium isopropoxide.

Example 44:

The operation is the same as that in Example 39, except that the isocyanate compound added to the mixed solution last is hexamethylene diisocyanate with a mass fraction of 0.05%, and the lithium fluoroalcohol compound added is hexafluoro with a mass fraction of 0.1% Lithium isopropoxide.

Example 45:

The operation is the same as that in Example 39, except that the isocyanate compound added to the mixed solution is isophorone diisocyanate with a mass fraction of 0.05%, and the lithium fluoroalcohol compound added is trifluoro with a mass fraction of 0.05% Lithium ethoxide.

Example 46:

The operation is the same as that in Example 39, except that the isocyanate compound added to the mixed solution is isophorone diisocyanate with a mass fraction of 0.05%, and the lithium fluoroalcohol compound added is hexafluoro with a mass fraction of 0.05% Lithium isopropoxide.

Comparative Example 16:

In a glove box filled with argon gas (moisture <1 ppm, oxygen content <1 ppm), mix dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate in a 1:1:1 mass ratio, and slowly add to the mixed solution LiPF6 with a mass fraction of 12.0% (total electrolyte mass ratio) is stirred until it is completely dissolved, and vinyl sulfate with a mass fraction of 2.0% (total electrolyte mass ratio) is added to the mixed solution to obtain a lithium ion battery electrolyte .

Comparative Example 17:

The operation is the same as that of Comparative Example 16, except that, on the basis of Comparative Example 16, hexamethyldisilazane with a mass fraction of 0.05% (total mass ratio of electrolyte) is added as an additive.

Comparative Example 18:

The operation is the same as that of Comparative Example 16. The difference is that on the basis of Comparative Example 16, triphenyl phosphite with a mass fraction of 0.05% (total mass ratio of electrolyte) is added as an additive.

Comparative example 19:

The operation is the same as that of Comparative Example 16, except that, on the basis of Comparative Example 16, cyclohexylcarbodiimide with a mass fraction of 0.05% (total mass ratio of electrolyte) is added as an additive.

Comparative Example 20:

The operation is the same as that of Comparative Example 16, except that, on the basis of Comparative Example 16, lithium trifluoroethanolate with a mass fraction of 0.05% (total mass ratio of electrolyte) is added as an additive.

Comparative Example 21:

The operation is the same as that of Comparative Example 16, except that, on the basis of Comparative Example 16, lithium hexafluoroisopropoxide is added as an additive at a mass fraction of 0.05% (total mass ratio of electrolyte).

Comparative Example 22:

The operation is the same as that of Comparative Example 16, except that, on the basis of Comparative Example 16, lithium trifluoroethanolate with a mass fraction of 0.1% (total mass ratio of electrolyte) is added as an additive.

Comparative Example 23:

The operation is the same as that of Comparative Example 16. The difference is that: on the basis of Comparative Example 16, lithium hexafluoroisopropoxide with a mass fraction of 0.1% (total mass ratio of electrolyte) is added as an additive.

Comparative Example 24:

The operation is the same as that of Comparative Example 16, except that: on the basis of Comparative Example 16, triphenyl phosphite with a mass fraction of 0.05% (total electrolyte mass ratio) and a mass fraction of 0.05% (total electrolyte mass ratio) are added Of lithium trifluoroethanol as an additive.

Comparative example 25:

The operation is the same as that of Comparative Example 16, except that: on the basis of Comparative Example 16, triphenyl phosphite with a mass fraction of 0.05% (total electrolyte mass ratio) and a mass fraction of 0.05% (total electrolyte mass ratio) are added Lithium hexafluoroisopropoxide as an additive.

Seven, electrolyte storage acidity and color test

Part of the electrolyte solution prepared in Examples 32-46 and Comparative Examples 16-25 above was transferred to a sealed aluminum bottle, placed in a 50°C constant temperature oven for storage, and stored in gloves before storage, 7 days storage, and 28 days storage respectively Sampling the box to check the acidity value and color value of the electrolyte. The acidity test method uses triethylamine titration, the acidity unit is ppm, the colority test method uses platinum-cobalt colorimetry, and the colority unit is Hazen. The test results are shown in Table 4 below:

Table 4 Electrolyte acidity and color test results table

It can be seen from Table 4 that the use of a single isocyanate compound additive or a mixed additive of isocyanate compound and lithium fluoroalcohol compound has a significant effect on reducing the acidity and chroma of the electrolyte. The obvious inhibitory effect is conducive to the storage and transportation of electrolyte containing DTD.

Comparing Comparative Examples 16-19 in Table 4, it can be seen that the use of conventional additives has a certain effect of reducing the acidity and color of the storage electrolyte at a high temperature of 50°C compared with no additives. However, white precipitation occurs in Comparative Example 17, and the Comparative Example 18 had a pungent odor, and a small amount of white precipitate appeared in Comparative Example 19.

Comparing Comparative Example 16 and Examples 32-38 in Table 4, it can be seen that compared with no additives, the use of a single isocyanate compound additive has no adverse reactions or irritating odor generation, and has more Obvious reduction effect. With the increase of the added amount, the suppression of the acidity and chroma of the electrolyte is more obvious.

Comparing Comparative Example 16 and Comparative Examples 20-23 in Table 4 shows that the use of a single lithium fluoroalcohol compound additive also has a certain effect on the suppression of electrolyte acidity and chroma compared with no additives, but the effect ratio The use of a single isocyanate compound additive is slightly worse.

Comparing Example 38, Examples 33, and 36 in Table 4, it can be seen that the polyisocyanate compound additive is used as compared with the monoisocyanate compound additive, and the same additive usage amount has a more obvious inhibitory effect on the acidity and chromaticity of the electrolyte.

Comparing Examples 32-38, Comparative Examples 20-23 and Examples 39-46 in Table 4, it can be seen that the isocyanate-based compound and the fluorinated The lithium alcohol compound additive has a very obvious inhibitory effect on the acidity and color of the electrolyte. To achieve the same suppression effect as the use of a single isocyanate compound additive or a single lithium fluoroalcohol compound additive, the amount of additives added can be greatly reduced.

Comparing Examples 39-46 and Comparative Examples 24-25 in Table 4, using conventional additives and lithium fluoroalcohol compound additives, although it has a greater inhibitory effect on the acidity and color of the electrolyte, the inhibitory effect is not as good as the use Mixed additives of isocyanate compounds and lithium fluoroalcohol compounds.

8. Electrochemical performance test of electrolyte

The lithium ion battery electrolytes of Examples 32-46 and Comparative Examples 16-25 prepared above were injected into a fully dried 1Ah LiNi0.6Co0.2Mn0.2O2/graphite soft-pack battery, the injection volume was 4g, and the battery passed After 12 hours of shelving, hot-press forming, secondary sealing and conventional volume division, perform a 1C cycle performance test: at 25°C, charge the divided volume battery to 4.35V with a constant current and constant voltage of 1C, and a cut-off current of 0.05C. Then discharge at a constant current of 1C to 3.0V, and the calculation formula of the cycle capacity retention rate is as follows:

Cycle 500 cycle capacity retention rate (%) = (500th cycle discharge capacity/first cycle discharge capacity) × 100%;

The test results are shown in Table 5 below:

Table 5 Capacity retention rate test result table

As can be seen from Table 5 above, when a single isocyanate compound is used as an additive, as the amount of addition increases, the battery capacity retention rate gradually decreases, which is basically maintained or lower than that without the additive. When a single lithium fluoroalcohol compound is used as an additive, as the amount of addition increases, there is no obvious change in the battery capacity retention rate, but the battery capacity is basically maintained or slightly higher than the case without additives.

When isocyanate compounds and lithium fluoroalcohol compounds are used as mixed additives, the battery capacity retention rate is higher than when no additives are added (Comparative Example 16) and higher than when conventional additives are used (Comparative Examples 17-19), Higher than the case of using a single isocyanate compound or the case of using a lithium fluoroalcohol compound alone (Comparative Example 20-23), also higher than the case of a combination additive of conventional additives and lithium fluoroalcohol compounds (Comparative Example 24- 25).

The electrolyte solutions of Comparative Example 16, Example 33, Comparative Example 21, and Example 46 were used in lithium batteries to compare battery cycle performance. Fig. 7 is a comparison diagram of discharge capacity-cycle number, and Fig. 8 is a comparison diagram of impedance for 100 cycles.

As shown in FIG. 7, compared with the use of no additive (Comparative Example 16), or the use of a single isocyanate compound additive (Example 33), or the use of a single lithium fluoroalcohol compound additive (Comparative Example 21), the present invention is used When the isocyanate-based compound and the lithium fluoroalcohol-based compound described in Example 46 are mixed with additives, the battery cycle performance is more excellent. This shows that isocyanate compounds are used as one type of additives and lithium fluoroalcohol compounds are used as another type of additives. The two have a very good synergistic effect on the improvement of battery cycle performance.

As shown in FIG. 8, the present invention is used in comparison with no additives (Comparative Example 16), or a single isocyanate compound additive (Example 33), or a single lithium fluoroalcohol compound additive (Comparative Example 21). When the isocyanate-based compound and the lithium fluoroalcohol-based compound described in Example 46 are mixed with additives, the impedance value during the battery cycle is smaller. This indicates that the improvement in battery cycle performance is due to the smaller internal resistance of the battery.

Claims (38)

1. A battery electrolyte additive shown in structural formula (I),

   

   among them:

   R1, R2, R3 are independently selected from hydrogen, fluorine, C1-C20 alkyl, C1-C20 haloalkyl.
2. The battery electrolyte additive according to claim 1, wherein in the structural formula (I):

   R1, R2, R3 are independently selected from hydrogen, fluorine, C1-C12 alkyl, C1-C12 haloalkyl.
3. The battery electrolyte additive according to claim 2, wherein the structural formula (I):

   R1, R2, R3 are independently selected from hydrogen, fluorine, C1-C5 alkyl, C1-C5 haloalkyl.
4. The battery electrolyte additive according to claim 3, wherein in the structural formula (I):

   R1, R2, R3 are independently selected from hydrogen, fluorine, C1-C3 alkyl, C1-C3 haloalkyl.
5. The battery electrolyte additive according to claim 4, wherein the compound represented by the structural formula (I) is selected from lithium trifluoroethanol, lithium tetrafluoroethanol, lithium hexafluoroisopropoxide, lithium heptafluorobutoxide, octa At least one of lithium fluoropentanol and lithium dodecylfluoroheptanol.
6. The battery electrolyte additive according to claim 1, wherein the additive is used as a negative electrode film-forming additive.
7. The battery electrolyte additive according to claim 6, wherein the additive is used as a negative electrode film-forming additive, and the negative electrode of the battery is selected from graphite and/or silicon carbon.
8. The battery electrolyte additive according to claim 6, wherein the negative electrode film-forming additive includes a compound represented by structural formula (I) and is selected from vinylene carbonate, 1,3-propane sultone, and tri( At least one of trimethylsilyl) borate, fluoroethylene carbonate, and ethylene ethylene carbonate.
9. The battery electrolyte additive according to claim 8, wherein the negative electrode film-forming additive comprises a compound represented by the structural formula (I) and is selected from vinylene carbonate, 1,3-propane sultone and tri( At least one of trimethylsilyl) borate.
10. An electrolyte for a lithium ion battery, characterized in that the electrolyte for a lithium ion battery contains the compound represented by the structural formula (I) according to claim 1.
11. The electrolyte for a lithium ion battery according to claim 10, wherein the content of the compound represented by structural formula (I) in the electrolyte for the lithium ion battery is 0.05% to 5%.
12. The lithium ion battery electrolyte according to claim 11, wherein the content of the compound represented by structural formula (I) in the lithium ion battery electrolyte is 0.5% to 5%.
13. The lithium ion battery electrolyte according to claim 12, wherein the content of the compound represented by the structural formula (I) in the lithium ion battery electrolyte is 1% to 2%.
14. The electrolyte of a lithium ion battery according to claim 10, wherein the electrolyte of the lithium ion battery contains a lithium salt, an organic solvent, an additive, and a compound represented by structural formula (I).
15. The lithium ion battery electrolyte according to claim 14, wherein the lithium ion battery electrolyte has a lithium salt content of 5 to 15%, an organic solvent content of 72 to 95%, and an additive content of 0.2 to 10% The content of the compound represented by structural formula (I) is 0.1% to 5%.
16. A lithium ion battery, characterized in that the lithium ion battery contains the battery electrolyte according to claim 14.
17. An electrolyte for a lithium ion battery, including a lithium salt, a non-aqueous solvent, and an additive, characterized in that the additive includes vinyl sulfate and a first type of additive, and the first type of additive is selected from the following general formula (I) Lithium fluoroalcohol compounds shown:

    

    Wherein R ₁ , R ₂ and R _{3 are} independently selected from hydrogen, halogen, C ₁ -C ₂₀ alkyl, C ₁ -C ₂₀ haloalkyl, and the halogen is selected from fluorine, chlorine, bromine and iodine.
18. The electrolyte of a lithium ion battery according to claim 17, wherein R ₁ , R ₂ , and R _{3 are} independently selected from hydrogen, fluorine, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ fluoroalkyl .
19. The electrolyte of a lithium ion battery according to claim 18, wherein R ₁ , R ₂ and R _{3 are} independently selected from hydrogen, fluorine, methyl, ethyl, propyl, butyl, pentyl and trifluoro Methyl, trifluoroethyl, pentafluoroethyl, hexafluoropropyl, octafluorobutyl, decafluoropentyl.
20. The electrolyte of a lithium ion battery according to claim 17, wherein the lithium fluoroalcohol compound is selected from lithium trifluoroethanol, lithium tetrafluoroethanol, lithium hexafluoroisopropoxide, lithium heptafluorobutoxide, At least one of lithium octafluoropentanol and lithium dodecylfluoroheptanol.
21. The electrolyte for a lithium ion battery according to claim 17, wherein the additive further comprises a second type of additive, and the second type of additive is selected from the isocyanate compounds of the following general formula (II):

    

    Wherein, R _{4 is} selected from C ₁ -C ₂₀ alkyl, C ₁ -C ₂₀ substituted alkyl, substituted phenyl, substituted biphenyl, the alkyl is a chain alkyl or cycloalkyl, and the substituent is Hydrogen, halogen, C ₁ -C ₂₀ alkyl, phosphate, sulfonyl, thio; the halogen is selected from fluorine, chlorine, bromine and iodine;

    0≤x≤1, 0≤y≤1, 0≤z≤1.
22. The electrolyte for a lithium ion battery according to claim 21, wherein the isocyanate compound is selected from at least one of the following compounds shown in 1-12:

    

    
23. The electrolyte of a lithium ion battery according to claim 17, wherein the content of the vinyl sulfate accounts for 0.01% to 5% of the total mass of the electrolyte of the lithium ion battery.
24. The lithium ion battery electrolyte according to claim 23, wherein the content of the vinyl sulfate accounts for 0.5%-3% of the total mass of the lithium ion battery electrolyte.
25. The electrolyte for a lithium ion battery according to claim 17, wherein the content of the lithium fluoroalcohol compound accounts for 0.005% to 5% of the total mass of the electrolyte for the lithium ion battery.
26. The lithium ion battery electrolyte according to claim 25, wherein the content of the lithium fluoroalcohol compound accounts for 0.02% to 1% of the total mass of the lithium ion battery electrolyte.
27. The lithium ion battery electrolyte according to claim 21, wherein the content of the isocyanate compound accounts for 0.005% to 5% of the total mass of the lithium ion battery electrolyte.
28. The electrolyte for a lithium ion battery according to claim 21, wherein the additive further includes a third type of additive selected from the group consisting of vinylene carbonate and 1,3-propane sultone At least one of tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, fluoroethylene carbonate and ethylene ethylene carbonate.
29. The lithium ion battery electrolyte according to claim 28, characterized in that the content of the third type of additive accounts for 0.1%-5.0% of the total mass of the lithium ion battery electrolyte.
30. A lithium-ion battery, characterized in that the lithium-ion battery includes the lithium-ion battery electrolyte according to any one of claims 17-29.
31. An electrolyte for a lithium ion battery, including a lithium salt, a non-aqueous solvent and an additive, characterized in that the additive includes vinyl sulfate and a second type of additive, the second type of additive is selected from isocyanate compounds, and the isocyanate Such compounds contain 1 to 3 -N=C=O groups.
32. The lithium ion battery electrolyte according to claim 31, wherein the isocyanate compound contains two -N=C=O groups.
33. The lithium ion battery electrolyte according to claim 31, wherein the second type of additive is selected from the isocyanate compounds of the following general formula (II):

    

    Wherein R _{1 is} selected from C ₁ -C ₂₀ alkyl, C ₁ -C ₂₀ substituted alkyl, substituted phenyl, substituted biphenyl, the alkyl is a chain alkyl or cycloalkyl, the substituent is Hydrogen, halogen, C ₁ -C ₂₀ alkyl, phosphate, sulfonyl, thio; the halogen is selected from fluorine, chlorine, bromine and iodine;

    0≤x≤1, 0≤y≤1, 0≤z≤1.
34. The lithium ion battery electrolyte according to claim 31, wherein the content of the isocyanate compound accounts for 0.005% to 5% of the total mass of the lithium ion battery electrolyte.
35. The lithium ion battery electrolyte according to claim 34, wherein the content of the isocyanate compound accounts for 0.02% to 1% of the total mass of the lithium ion battery electrolyte.
36. The lithium ion battery electrolyte according to claim 31, wherein the additive further includes a third type of additive selected from the group consisting of vinylene carbonate and 1,3-propane sultone At least one of tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, fluoroethylene carbonate and ethylene ethylene carbonate.
37. The lithium ion battery electrolyte according to claim 36, wherein the content of the third type of additive accounts for 0.1%-5.0% of the total mass of the lithium ion battery electrolyte.
38. A lithium ion battery, characterized in that the lithium ion battery comprises the lithium ion battery electrolyte according to any one of claims 31-37.

Images