CN115714204A - Electrolyte and lithium ion battery - Google Patents

Abstract

R1‑R4各自独立为烷基、氟代烷基；R1和R2、R3和R4各自独立或相连成环；所述第一添加剂含有异氰酸酯基团、饱和或不饱和的环烷基。该电解液采用含有异氰酸酯基团、饱和或不饱和的环烷基的第一添加剂和含硼的第二添加剂复配；此类第一添加剂具有抑制产气的功效，但是在高温电化学性能、常温电化学性能方面并无明显的优势，通过与含硼的第二添加剂复配，可强化第二添加剂的高温电化学性能。同时，本发明还公开了一种锂离子电池。The invention belongs to the technical field of lithium-ion batteries, and specifically relates to an electrolyte, including lithium salts, non-aqueous organic solvents, and additives; second additive;

Each of R1‑R4 is independently an alkyl group or a fluoroalkyl group; R1 and R2, R3 and R4 are each independently or connected to form a ring; the first additive contains an isocyanate group and a saturated or unsaturated cycloalkyl group. The electrolyte is compounded with a first additive containing isocyanate groups, a saturated or unsaturated cycloalkyl group, and a second additive containing boron; this type of first additive has the effect of inhibiting gas production, but in high temperature electrochemical performance, There is no obvious advantage in the electrochemical performance at room temperature, and the high-temperature electrochemical performance of the second additive can be enhanced by compounding with the second additive containing boron. At the same time, the invention also discloses a lithium ion battery.

Description

A kind of electrolyte and lithium ion battery

technical field

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

Background technique

CNCN111416153A discloses a high-voltage lithium-ion battery and its electrolyte and electrolyte additive. The high-voltage lithium-ion battery silicon cyanide electrolyte additive provided by the invention is a silicon cyanide compound, with silicon as a stable group, through the anchor It has a stabilizing effect, inhibits the complete oxidation of the cyano functional group and the cross-reduction reaction with the negative electrode under high voltage, and avoids the deterioration of the battery. In addition, the silicon element can also increase the wettability of the electrolyte. The cyano functional group in the silyl cyano compound can eliminate free hydrogen in the electrolyte, reduce the moisture in the electrolyte and eliminate HF, reduce the hydrolysis of LiPF ₆ and the damage of HF to the positive electrode material, and inhibit the interface of the positive electrode material under high voltage Side reaction with electrolyte. In addition, the silico functional group can also form an organic and inorganic interfacial film containing N at the interface of the positive and negative electrodes. Through the immobilization of silicon elements, the interfacial film can be effectively stabilized and the electrochemical performance of the high-voltage lithium-ion battery can be further improved.

In comparative example 4 of this patent, cyclopentyl isocyanate was used to replace the silanyl cyanide compound used, and it was found that the performance of cyclopentyl isocyanate was inferior to that of silyl cyano compound; its 100-week cycle retention rate was 75%;

The main purpose of this case is: how to realize the effective utilization of cyclopentyl isocyanate in the electrolyte and improve the high temperature performance of the electrolyte.

Contents of the invention

The object of the present invention is to provide a kind of electrolytic solution, and this electrolytic solution adopts the first additive that contains isocyanate group, saturated or unsaturated cycloalkyl group and the second additive that contains boron; However, it has no obvious advantages in terms of high-temperature electrochemical performance and room-temperature electrochemical performance. By compounding with the second additive containing boron, the high-temperature electrochemical performance of the second additive can be strengthened.

At the same time, the invention also discloses a lithium ion battery.

Technical scheme of the present invention is:

A kind of electrolytic solution, comprises lithium salt, non-aqueous organic solvent, additive; Said additive comprises the first additive for suppressing gas production and the boron-containing second additive shown in following formula 1;

Formula 1

R1-R4 are each independently an alkyl group or a fluoroalkyl group; R1 and R2, R3 and R4 are each independently or connected to form a ring;

The first additive contains isocyanate groups, saturated or unsaturated cycloalkyl groups;

The weight ratio of the first additive to the second additive is 0.1-5:0.1-5;

Preferably, the weight ratio of the first additive to the second additive is 1-4:1-4;

More preferably, the weight ratio of the first additive to the second additive is 1-3:1-3.

Preferably, the isocyanate group, saturated or unsaturated cycloalkyl group in the first additive can be directly connected, and an alkyl group can also be added between the two; the alkyl group is preferably a C1-C3 alkyl group group; the saturated cycloalkyl is cyclopentane, cyclohexane; the unsaturated cycloalkyl is generally a benzene ring;

Preferably, R1-R4 are each independently methane, ethane, monofluoromethyl, difluoromethyl, perfluoromethyl, monofluoroethyl or difluoroethyl;

R1-R4 can also be connected to form a ring; specifically, R1, R2, two oxygen atoms, and one boron atom can form a five-membered ring or a six-membered ring;

A substituent group can also be connected to the formed five-membered ring or six-membered ring; the substituent group can be C1-C3 alkyl, C1-C3 fluoroalkyl or F; the optional substituent group is methyl radical, ethyl, propyl, perfluoromethyl, perfluoroethyl, monofluoromethyl, difluoromethyl, monofluoroethyl, difluoroethyl or F. There may be one or two substituents on a single five-membered ring or six-membered ring.

Preferably, the first additive is cyclopentyl isocyanate or phenyl isocyanate.

Preferably, the R1-R4 are each independently methyl, ethyl, perfluoromethyl;

Preferably, the second additive is one of the following compounds:

Tetramethoxydiborane, tetraethoxydiborane, tetraperfluoromethoxydiborane, 2-(1,3,2-dioxaborin-2yl)1,3 ,2-dioxaborinane, difluoro-2-(1,3,2-dioxaborin-2yl)1,3,2-dioxaborinane or diboronic acid Neopentyl glycol esters.

Preferably, the first additive is equivalent to 0.1-5 wt% of the total weight of the electrolyte; the second additive is equivalent to 0.1-5 wt% of the total weight of the electrolyte.

As a preference of the present invention, the first additive is equivalent to 0.1wt%, 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3wt% of the total weight of the solution , 5wt%;

Preferably, its dosage is 0.2wt%-4wt%;

More preferably, its usage is 0.5wt%-3wt%.

The second additive is equivalent to 0.1wt%, 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3wt%, 5wt% of the total weight of the solution;

Preferably, its dosage is 0.2wt%-4wt%;

More preferably, its usage is 0.5wt%-3wt%.

In the above electrolytic solution, the lithium salt is lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluorophosphate, lithium difluorooxalatephosphate, lithium tetrafluorooxalatephosphate, lithium difluorobisoxalatephosphate, and difluorophosphate lithium At least one of the lithium sulfonylimides, the concentration of the lithium salt is 0.5-2M. Generally speaking, the concentration of the more commonly used lithium salt is 1-1.5M; however, high or low lithium salt concentration is also acceptable.

In the above electrolytic solution, the non-aqueous organic solvent is a cyclic organic solvent and/or a chain organic solvent;

The cyclic organic solvent is one or more combinations of propylene carbonate (PC), ethylene carbonate (EC) and butylene carbonate (BC);

Described chain organic solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl formate (MF), ethyl formate ( EF), methyl acetate (MA), ethyl acetate (EA) in one or more combinations.

As a preferred embodiment of the present invention, the present invention can also add additional additives as described below, and the amount of additional additives generally does not exceed 10wt% equivalent to the weight of the electrolyte; preferably 0.01-5wt%; more preferably 0.1-3wt%; more preferably 0.2-2wt%, more preferably 0.3-1wt%;

Described additional additive can optionally following specific chemical formula:

In order to further improve the electrochemical characteristics in a wide temperature range, it is preferable to further add other additives to the non-aqueous electrolytic solution.

Specific examples of other additives include the following compounds (a) to (j) suitably.

(a) Nitrile

One or two or more nitriles selected from acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile and sebaconitrile.

Among them, one or more kinds selected from succinonitrile, glutaronitrile, adiponitrile and pimelonitrile are more preferred.

(b) Aromatic compounds

Cyclohexylbenzene, fluorocyclohexylbenzene compounds (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), tert-butylbenzene, tert-amyl Benzene, 1-fluoro-4-tert-butylbenzene and other aromatic compounds with branched chain alkyl, biphenyl, terphenyl (ortho, meta, para), diphenyl ether, fluorobenzene, Difluorobenzene (ortho-position, meta-position, para-position), anisole, 2,4-difluoroanisole, partial hydrogenation of terphenyl (1,2-dicyclohexylbenzene, 2-phenylbicyclo Hexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl) and other aromatic compounds.

(c) Isocyanate compounds with other acyclic substituents

Selected from methyl isocyanate, ethyl isocyanate, butyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, acrylic 2-isocyanate One or more isocyanate compounds selected from ethyl acetate and 2-isocyanatoethyl methacrylate.

(d) Compounds containing triple bonds

Selected from 2-propynyl methyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate propynyl ester, 2-(methanesulfonyloxy)propionate 2-propynyl ester, bis(2-propynyl) oxalate, 2-propynyl oxalate methyl ester, 2-propynyl oxalate ethyl base ester, bis(2-propynyl glutarate), 2-butyne-1,4-diyl dimesylate, 2-butyne-1,4-diyl dicarboxylate, and 2 , 4-hexadiyne-1,6-diyl dimesylate, one or two or more triple bond-containing compounds.

(e) Compounds containing S=O groups

Selected from 1,3-propane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-propene sultone, 2,2-dioxide-1,2-oxathiolane-4-yl acetate, 5,5-dimethyl-1,2-oxathiolane-4-one 2,2 - Dioxide and other sultones, ethylene sulfite, hexahydrobenzo[1,3,2]dioxathiolane-2-oxide (also known as 1,2-cyclohexanedi Alcohol cyclic sulfite), 5-vinyl-hexahydro-1,3,2-benzodioxylthiol-2-oxide and other cyclic sulfites, butane-2,3-diyl di Mesylate, butane-1,4-diyl dimesylate, methylene methane disulfonate and other sulfonates, divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane One or more kinds of S=O group-containing compounds among vinyl sulfone compounds such as alkane and bis(2-vinylsulfonylethyl) ether.

As the above-mentioned cyclic S=O group-containing compound, suitably exemplified are selected from 1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, 2, 4-butane sultone, 1,3-propene sultone, 2,2-dioxide-1,2-oxathiolan-4-yl acetate, 5,5-dimethyl- 1,2-oxathiolan-4-one 2,2-dioxide, methylene methane disulfonate, ethylene sulfite, and 4-(methylsulfonylmethyl)-1 , one or more of 3,2-dioxathiolane 2-oxides.

In addition, as the chain-like S=O group-containing compound, preferably, a compound selected from butane-2,3-diyl dimethanesulfonate, butane-1,4-diyl dimethanesulfonate, One or more of dimethylmethane disulfonate, pentafluorophenyl methanesulfonate, divinyl sulfone, and bis(2-vinylsulfonylethyl) ether.

Among the above-mentioned cyclic or chain S=O group-containing compounds, more preferably selected from 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 2 , 2-dioxide-1,2-oxathiolane-4-yl acetate, 5,5-dimethyl-1,2-oxathiolane-4-one 2,2- One or more of dioxide, butane-2,3-diyl dimesylate, pentafluorophenyl mesylate, and divinyl sulfone.

(f) Cyclic acetal compounds

Cyclic acetal compounds such as 1,3-dioxolane, 1,3-dioxane, and 1,3,5-trioxane. Among them, 1,3-dioxolane and 1,3-dioxane are preferable, and 1,3-dioxane is more preferable.

(g) Phosphorous compounds

Preferable examples include trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) phosphate base) methyl ester, bis(2,2,2-trifluoroethyl)ethyl phosphate, bis(2,2,2-trifluoroethyl)2,2-difluoroethyl phosphate, bis(2,2-trifluoroethyl)phosphate 2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl ester, bis(2,2-difluoroethyl) 2,2,2-trifluoroethyl phosphate, bis(2, 2,3,3-tetrafluoropropyl) 2,2,2-trifluoroethyl ester, phosphoric acid (2,2,2-trifluoroethyl) (2,2,3,3-tetrafluoropropyl) methyl ester, tris(1,1,1,3,3,3-hexafluoropropane-2-yl) phosphate, methyl methylene bisphosphonate, ethyl methylene bisphosphonate, ethylene bisphosphine Methyl ethylene diphosphonate, ethyl ethylene bisphosphonate, methyl butylene bisphosphonate, ethyl butylene bisphosphonate, methyl 2-(dimethylphosphoryl)acetate, 2-(dimethylphosphoryl ) ethyl acetate, 2-(diethylphosphoryl) methyl acetate, 2-(diethylphosphoryl) ethyl acetate, 2-(dimethylphosphoryl) acetate 2-propynyl ester, 2-( 2-propynyl diethylphosphoryl) acetate, 2-(dimethoxyphosphoryl) methyl acetate, 2-(dimethoxyphosphoryl) ethyl acetate, 2-(diethoxyphosphoryl) ) methyl acetate, 2-(diethoxyphosphoryl) ethyl acetate, 2-(dimethoxyphosphoryl) acetate 2-propynyl ester, 2-(diethoxyphosphoryl) acetate 2-propane Phosphorus-containing compounds of one or more of alkyne esters, methyl pyrophosphate, and ethyl pyrophosphate.

Among them, tris(2,2,2-trifluoroethyl) phosphate, tris(1,1,1,3,3,3-hexafluoropropan-2-yl) phosphate, 2-(dimethyl Phosphoryl) methyl acetate, 2-(dimethylphosphoryl) ethyl acetate, 2-(diethylphosphoryl) methyl acetate, 2-(diethylphosphoryl) ethyl acetate, 2-(two Methylphosphoryl) acetate 2-propynyl ester, 2-(diethylphosphoryl) acetate 2-propynyl ester, 2-(dimethoxyphosphoryl) methyl acetate, 2-(dimethoxyphosphoryl) Acyl)ethyl acetate, 2-(diethoxyphosphoryl)acetate methyl ester, 2-(diethoxyphosphoryl)acetate ethyl ester, 2-(dimethoxyphosphoryl)acetate 2-propynyl ester , or 2-(diethoxyphosphoryl) acetate 2-propynyl ester, more preferably tris(2,2,2-trifluoroethyl) phosphate, tris(1,1,1,3,3, 3-hexafluoropropane-2-yl) ester, 2-(diethylphosphoryl) ethyl acetate, 2-(dimethylphosphoryl) acetate 2-propynyl ester, 2-(diethylphosphoryl) 2-propynyl acetate, ethyl 2-(diethoxyphosphoryl)acetate, 2-propynyl acetate 2-(dimethoxyphosphoryl) or 2-(diethoxyphosphoryl)acetic acid 2 - propargyl esters.

(h) Cyclic anhydrides

Suitable examples include chain carboxylic anhydrides such as acetic anhydride and propionic anhydride, or cyclic anhydrides such as succinic anhydride, maleic anhydride, 2-allylsuccinic anhydride, glutaric anhydride, itaconic anhydride, and 3-sulfo-propionic anhydride. acid anhydride.

(i) Cyclic phosphazene compound

Preferable examples include cyclic phosphazene compounds such as methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotriphosphazene. .

(j) fluorinated compounds;

Preferable examples include ethyl methyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, fluoroacetic acid Ethyl, methyl fluoroacetate or propyl fluoroacetate.

At the same time, the invention also discloses a lithium-ion battery, the electrolyte used is as described above.

In the above lithium ion battery, the positive electrode of the lithium ion battery is selected from transition metal oxides of lithium, wherein the transition metal oxides of lithium are LiCoO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , Li ₂ MnO ₄ , LiFePO ₄ , Li _1+a Mn _1-x MxO ₂ , LiCo _1-x M _x O ₂ , LiFe _1-x M _x PO ₄ , Li ₂ Mn _1-x O ₄ , wherein M is selected from Ni, One or more of Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, 0≤a<0.2, 0≤x<1, the negative electrode is selected from graphite, silicon-carbon composite materials , at least one of lithium titanate.

In the present invention, the well-known lithium ion battery should include separator and negative pole;

The negative electrode is selected from at least one of graphite, silicon-carbon composite material, and lithium titanate.

The negative electrode active material in the negative electrode includes at least one of carbonaceous material, silicon carbon material, alloy material, lithium-containing metal composite oxide material, but not limited thereto, the negative electrode active material can be selected from various known in the art can be Traditionally known materials capable of electrochemically intercalating and deintercalating active ions used as negative electrode active materials for electrochemical devices;

The preparation method of the negative electrode sheet is a preparation method of the negative electrode sheet that can be used in electrochemical devices known in the art; the negative electrode active material layer also includes a binder and a solvent. Add binder and solvent to the negative electrode active material and add thickener, conductive agent, filler material, etc. as needed to make negative electrode slurry, then coat the negative electrode slurry on the negative electrode current collector, dry and press to prepare the negative electrode sheet, the negative electrode slurry is dried and cold-pressed to form a negative electrode active material layer. Likewise, in the preparation of the negative electrode slurry, a solvent is usually added. The solvent is removed during drying. The binder is known in the art and can be used as the negative electrode active material layer, such as but not limited to styrene-butadiene rubber. The solvent is known in the art and can be used as a negative electrode active material layer, such as but not limited to water. The thickener is known in the art and can be used as a thickener for the negative electrode active material layer, such as but not limited to carboxymethylcellulose. In some embodiments, when the negative electrode active material includes an alloy material, methods such as evaporation, sputtering, and plating can be used to form the negative electrode active material layer;

The separator is known in the art and can be used in electrochemical devices and is stable to the electrolyte used, such as but not limited to, resin, glass fiber, inorganic material.

For example, the separator contains at least one of polyolefin, aramid, polytetrafluoroethylene, and polyethersulfone. Preferably, the polyolefin comprises at least one of polyethylene and polypropylene. Preferably, the polyolefin comprises polypropylene. Preferably, the isolation film is formed by laminating multiple layers of materials, for example, the isolation film is a three-layer isolation film formed by laminating polypropylene, polyethylene, and polypropylene in sequence.

The beneficial effects of the present invention are as follows:

The present invention adopts the compounding of the first additive containing isocyanate group, saturated or unsaturated cycloalkyl group and the second additive containing boron; this kind of first additive has the effect of suppressing gas production, but in high temperature electrochemical performance, normal temperature There is no obvious advantage in electrochemical performance, and the high-temperature electrochemical performance of the second additive can be enhanced by compounding with the second additive containing boron.

Under high voltage, the first additive represented by cyclopentyl isocyanate will open the ring to form free radicals, polymerize and generate polymers; the first additive represented by phenyl isocyanate has excellent film-forming properties; and due to The nitrogen of the first additive contains a lone pair of electrons, which will form a coordination bond with the transition metal on the surface of the positive electrode. Therefore, the polymer film formed by the first additive will adhere to the positive electrode surface to play a protective role. The boron in the second additive represented by neopentyl glycol biborate contains a lone pair of electrons, which can combine with fluoride ions in hydrofluoric acid to eliminate hydrofluoric acid and protect the material.

The two are compounded with each other to achieve excellent high-temperature performance improvement results.

Detailed ways

The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments, but this does not constitute any limitation to the present invention.

Example 1

1. Electrolyte preparation: use EC and DEC as solvents, add lithium salt LiPF ₆ after mixing, adjust the concentration of lithium salt in the system to 1.0M; add the first additive: cyclopentyl isocyanate and the second additive: biboronic acid new Pentylene glycol ester; the first additive is equivalent to 0.2% of the total weight of the electrolyte; the second additive is equivalent to 0.2% of the total weight of the electrolyte.

2. Preparation of the positive electrode sheet: the positive electrode material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ), the conductive agent SuperP, the binder PVDF and the carbon nanotube (CNT) are uniformly mixed at a mass ratio of 95:2.3:2:0.7. Lithium-ion battery cathode slurry with a certain viscosity is coated on the aluminum foil for the current collector, and the coating amount is 35g/m ² , dried at 85°C and then cold-pressed; then trimmed, cut into pieces, and divided into strips , after slitting, dry at 85°C for 4 hours under vacuum conditions, weld the tabs, and make a positive electrode sheet of lithium-ion batteries that meets the requirements.

3. Preparation of negative electrode sheet: make slurry with graphite, conductive agent SuperP, thickener CMC, and adhesive SBR (styrene-butadiene rubber emulsion) in a mass ratio of 95:1.5:1.0:2.5, mix evenly, and use After the mixed slurry is coated on both sides of the copper foil, the negative electrode sheet is obtained after drying and rolling, and the lithium ion battery negative electrode sheet meeting the requirements is manufactured.

4. Preparation of lithium-ion battery: The positive electrode sheet, negative electrode sheet and diaphragm prepared according to the above process are laminated into a lithium-ion battery with a thickness of 4.7mm, a width of 55mm, and a length of 60mm, and vacuum-dry at 75°C Bake for 10 hours and inject the above electrolyte. After standing still for 24 hours, put the battery in an environment of 45°C, apply a pressure of 3kg, charge it at 0.1C (160mA) to 4.0V, let it stand for 2 days to fully activate the battery, and then conduct a performance test.

Example 2

It is substantially the same as in Example 1, except that: cyclopentyl isocyanate is equivalent to 0.5% of the total weight of the electrolyte; neopentyl glycol diborate is equivalent to 0.5% of the total weight of the electrolyte.

Example 3

It is substantially the same as in Example 1, except that cyclopentyl isocyanate is equivalent to 1% of the total weight of the electrolyte; neopentyl glycol diboronate is equivalent to 1% of the total weight of the electrolyte.

Example 4

It is substantially the same as in Example 1, except that cyclopentyl isocyanate is equivalent to 2% of the total weight of the electrolyte; neopentyl glycol diboronate is equivalent to 2% of the total weight of the electrolyte.

Example 5

It is substantially the same as in Example 1, except that cyclopentyl isocyanate is equivalent to 3% of the total weight of the electrolyte; neopentyl glycol diboronate is equivalent to 3% of the total weight of the electrolyte.

Example 6

It is substantially the same as in Example 1, except that cyclopentyl isocyanate is equivalent to 0.1% of the total weight of the electrolyte; neopentyl glycol diborate is equivalent to 0.9% of the total weight of the electrolyte.

Example 7

It is substantially the same as in Example 1, except that: cyclopentyl isocyanate is equivalent to 0.3% of the total weight of the electrolyte; neopentyl glycol diborate is equivalent to 0.7% of the total weight of the electrolyte.

Example 8

It is substantially the same as in Example 2, except that cyclopentyl isocyanate is equivalent to 0.9% of the total weight of the electrolyte; neopentyl glycol diborate is equivalent to 0.1% of the total weight of the electrolyte.

Example 9

It is substantially the same as in Example 2, except that: cyclopentyl isocyanate is equivalent to 0.7% of the total weight of the electrolyte; neopentyl glycol diborate is equivalent to 0.3% of the total weight of the electrolyte.

Example 10

It is substantially the same as in Example 2, except that the first additive is phenyl isocyanate.

Example 11

It is substantially the same as in Example 2, except that the second additive is tetramethoxydiborane.

Example 12

It is substantially the same as in Example 2, except that the second additive is tetraperfluoromethoxydiborane.

Example 13

It is roughly the same as in Example 2, except that the solvent is adjusted to PC and DEC; the weight ratio of PC and DEC is 1:1; the total amount of the two is the same as in Example 2.

Example 14

It is generally the same as that of Embodiment 2, except that the positive electrode material is adjusted to be LiCoO ₂ .

Comparative example 1

It is substantially the same as in Example 2, except that the second additive is not included, the first additive is cyclopentyl isocyanate, and cyclopentyl isocyanate is equivalent to 1% of the total weight of the electrolyte.

Comparative example 2

It is substantially the same as in Example 2, except that the first additive is not included, the second additive is neopentyl glycol diborate, and neopentyl glycol diborate is equivalent to 1% of the total weight of the electrolyte.

Comparative example 3

It is substantially the same as Example 2, except that no additives are added.

Comparative example 4

It is substantially the same as Example 13, except that no additives are added.

Comparative example 5

It is substantially the same as Example 14, except that no additives are added.

Performance Testing

Test item 1: High temperature performance test

The lithium-ion batteries in Examples 1-14 and Comparative Examples 1-5 were tested for high-temperature cycle performance and high-temperature storage performance, and the test method was as follows;

High-temperature cycle performance: At 45°C, the lithium-ion battery is first charged with a constant current of 1.0C to a voltage of 4.4V, and then discharged to 3.0V with a constant current of 1.0C, and the charge-discharge test is performed for 200 cycles, and the discharge of the 200th cycle is detected capacity.

Capacity retention rate = (200th discharge capacity / 1st discharge capacity) × 100%

High-temperature storage performance: At room temperature, charge the lithium-ion battery with a constant current of 1C to a voltage of 4.4V, and charge it with a constant voltage of 4.4V to a current of 0.05C. At this time, the thickness of the lithium-ion battery is recorded as H ₀ ; After being stored in an oven at 60°C for 14 days, take it out and test the thickness first, and record it as H ₁ ; take out the lithium-ion battery and cool it to room temperature, and first discharge it to 3.0V at 1C, and record the discharge capacity; then discharge the lithium-ion battery at 1C constant Current charging to a voltage of 4.4V, charging at a constant voltage of 4.4V to a current of 0.05C, and discharging at 1C to 3.0V. After 10 cycles, record the capacity at the 10th week as the recovery capacity.

High temperature storage capacity retention rate = (discharge capacity after storage / discharge capacity before storage) × 100%;

High temperature storage capacity recovery rate = (recovery capacity after storage / discharge capacity before storage) × 100%;

High temperature storage expansion ratio = (H ₁ /H ₀ )×100%.

Test item 2: normal temperature performance test

The lithium-ion batteries in Examples 1-14 and Comparative Examples 1-5 were tested for cycle performance at normal temperature, and the test method was as follows;

At 25°C, the lithium-ion battery was first charged at a constant current of 1.0C to a voltage of 4.4V, and then discharged at a constant current of 1.0C to 3.0V. The charge and discharge test was carried out for 200 cycles, and the discharge capacity of the 200th cycle was detected.

Capacity retention=(200th discharge capacity/1st discharge capacity)×100%.

The test results are shown in Table 1 below:

Table 1 Li-ion battery test results

Under high voltage, the first additive represented by cyclopentyl isocyanate will open the ring to form free radicals, polymerize and generate polymers; the first additive represented by phenyl isocyanate has excellent film-forming properties; and due to The nitrogen of the first additive contains a lone pair of electrons, which will form a coordination bond with the transition metal on the surface of the positive electrode. Therefore, the polymer film formed by the first additive will adhere to the positive electrode surface to play a protective role. The boron in the second additive represented by neopentyl glycol biborate contains a lone pair of electrons, which can combine with fluoride ions in hydrofluoric acid to eliminate hydrofluoric acid and protect the material.

By way of embodiment 1-9, for comparison, it is found that embodiment 2 has the best effect, at this moment, cyclopentyl isocyanate is 0.5%, and neopentyl glycol diboronic acid ester is 0.5%. When the contents of cyclopentyl isocyanate and neopentyl glycol diborate are simultaneously reduced to 0.2% or increased by more than 0.5%, the overall performance of the battery becomes poor. When the overall additive content was 1%, it was found that the performance was best when the ratio of the two was 1:1. Below 0.5% cyclopentyl isocyanate, the interfacial film is too sparse at this time to have no protective effect. If it is lower than 0.5% neopentyl glycol diborate, the elimination effect on hydrofluoric acid is not enough at this time. Above 0.5% cyclopentyl isocyanate, the interfacial film is too dense at this time, resulting in increased impedance. Higher than 0.5% neopentyl glycol diborate, although it can eliminate hydrofluoric acid, it will adhere to the positive electrode after excessive, resulting in too dense interfacial film.

By comparing Example 2 with Examples 10, 11, and 12, it is found that the performance of cyclopentyl isocyanate is better than that of phenyl isocyanate, which may be due to the more stable interfacial film formed by it; The performance of diol is better than that of tetramethoxydiborane and tetraperfluoromethoxydiborane, which should be due to its better effect on eliminating hydrofluoric acid.

By comparing Example 2 with Comparative Examples 1, 2, and 3, it is found that using cyclopentyl isocyanate and neopentyl glycol diboronate alone can improve battery performance, but the focus is different, and the former focuses more on reducing swelling. , the latter is more focused on improving cycle performance and high temperature retention and recovery rate. After the two are used together, a better synergistic effect will be produced.

By comparing Examples 13 and 14 with Comparative Examples 4 and 5, it is found that even if the solvent and positive electrode material are changed, the combination of cyclopentyl isocyanate and neopentyl glycol diboronate can play a role.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (9)

1. An electrolytic solution is characterized in that, comprises lithium salt, non-aqueous organic solvent, additive; Said additive comprises the first additive for suppressing gas production and the boron-containing second additive shown in following formula 1;

R1-R4 are each independently an alkyl group or a fluoroalkyl group; R1 and R2, R3 and R4 are each independently or connected to form a ring; The first additive contains isocyanate groups, saturated or unsaturated cycloalkyl groups; The weight ratio of the first additive to the second additive is 0.1-5:0.1-5. 2. The electrolytic solution according to claim 1, wherein the first additive is cyclopentyl isocyanate or phenyl isocyanate. 3. The electrolyte solution according to claim 1, wherein said R1-R4 are each independently methyl, ethyl, or perfluoromethyl. 4. The electrolyte solution according to claim 2, wherein the second additive is one of the following compounds: Tetramethoxydiborane, tetraethoxydiborane, tetraperfluoromethoxydiborane, 2-(1,3,2-dioxaborin-2yl)1,3 ,2-dioxaborinane, difluoro-2-(1,3,2-dioxaborin-2yl)1,3,2-dioxaborinane or diboronic acid Neopentyl glycol esters. 5. The electrolyte according to claim 1, wherein the first additive is equivalent to 0.1-5 wt% of the total weight of the electrolyte; the second additive is equivalent to 0.1-5 wt% of the total weight of the electrolyte. 6. The electrolytic solution according to claim 1, wherein the lithium salt is lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorophosphate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, At least one of lithium difluorobisoxalate phosphate and lithium bisfluorosulfonimide, the concentration of the lithium salt is 0.5-2M. 7. The electrolytic solution according to claim 1, wherein the non-aqueous organic solvent is a cyclic organic solvent and/or a chain organic solvent; The cyclic organic solvent is one or more combinations of propylene carbonate, ethylene carbonate and butylene carbonate; The chain organic solvent is one or more combinations of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate . 8. A lithium ion battery, characterized in that the electrolyte used is as described in any one of claims 1-7. 9. The lithium-ion battery according to claim 8, wherein the positive electrode of the lithium-ion battery is selected from transition metal oxides containing lithium, wherein the transition metal oxides of lithium are LiCoO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , Li ₂ MnO ₄ , LiFePO ₄ , Li _1+a Mn _1-x MxO ₂ , LiCo _1-x M _x O ₂ , LiFe _1-x M _x PO ₄ , Li ₂ Mn _1-x O ₄ , wherein, M is one or more selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, 0≤a<0.2, 0≤x<1 ; The negative electrode is selected from at least one of graphite, silicon-carbon composite material, and lithium titanate.