CN115295876A

CN115295876A - Electrolyte and battery

Info

Publication number: CN115295876A
Application number: CN202211008436.6A
Authority: CN
Inventors: 王海; 李素丽; 李俊义
Original assignee: Zhuhai Cosmx Battery Co Ltd
Current assignee: Zhuhai Cosmx Battery Co Ltd
Priority date: 2022-08-22
Filing date: 2022-08-22
Publication date: 2022-11-04

Abstract

The invention relates to the technical field of batteries, in particular to electrolyte and a battery comprising the electrolyte. The electrolyte contains a first fluorine-containing organic substance, the content of fluorine element in the first fluorine-containing organic substance is not less than 33 wt%, and the solubility of the first fluorine-containing organic substance to lithium salt is not more than 1.5g/100g. The electrolyte has higher oxidation resistance, and can realize better stability under high pressure; the obtained battery of the electrolyte can bear the voltage of more than 4.55V, thereby having larger energy density and more stable cycle performance.

Description

Electrolyte and battery

Technical Field

The invention relates to the technical field of batteries, in particular to electrolyte and a battery comprising the electrolyte.

Background

With the progress of science and technology and the development of society, people increasingly depend on electric tools such as consumer electronics and electric vehicles in modern society. As mobile devices, they require lithium ion batteries to provide a source of energy for them. Compared with other types of batteries, the lithium ion battery has the advantages of higher specific energy density, long cycle life and the like.

With the further development of technology, the energy density of batteries is increasing. It has been found that the energy density of the battery can be further increased by using higher voltages. At present, the voltage of a cobalt acid lithium battery is below 4.5V, and the energy density of the lithium ion battery can be further greatly improved by adopting a positive electrode material capable of resisting above 4.55V, but the problems of fast electrolyte consumption and fast cycle attenuation exist. For example, the electrolyte solution of a conventional carbonate solvent is difficult to withstand a voltage of 4.55V or more, and even by adding a large amount of additives such as nitriles, boron and the like, the requirement for long cycle time cannot be satisfied.

Therefore, it is very important to invent a battery that can withstand a voltage of 4.55V or more, has a higher energy density, and has more stable cycle performance.

Disclosure of Invention

The present invention is directed to overcoming the above problems of the prior art and to providing an electrolyte and a battery including the same. The electrolyte has higher oxidation resistance, and can realize better stability under high pressure; the battery obtained by the electrolyte can bear the voltage of more than 4.55V, so that the battery has higher energy density and more stable cycle performance.

The inventors of the present invention have found that the energy density of the battery can be increased by improving the high-voltage resistance of the electrolyte.

The inventors of the present invention have further studied intensively and found that, in order to improve the high pressure resistance of the electrolyte, a specific compound may be added to the electrolyte to form an SEI film and a CEI film having a high content of LiF, thereby improving the mechanical strength and oxidation resistance of the interface film, and further providing the electrolyte with better oxidation resistance. The inventors of the present invention have intensively studied and screened out a specific compound capable of achieving an effect of improving the oxidation resistance of an electrolyte.

In order to achieve the above object, a first aspect of the present invention provides an electrolyte, which contains a first fluorine-containing organic substance, wherein the content of fluorine in the first fluorine-containing organic substance is not less than 33 wt%, and the solubility of the first fluorine-containing organic substance in lithium salt is not more than 1.5g/100g.

In a second aspect, the invention provides a battery, wherein the electrolyte of the battery is the electrolyte of the first aspect of the invention.

Through the technical scheme, compared with the prior art, the invention at least has the following advantages:

(1) The electrolyte disclosed by the invention has good oxidation resistance;

(2) The electrolyte has good stability under high pressure;

(3) The battery can bear the voltage of more than 4.55V;

(4) The battery of the invention has high energy density;

(5) The battery of the present invention has improved attenuation slope of the cycle capacity, and thus has stable cycle performance.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

The first aspect of the invention provides an electrolyte, wherein the electrolyte contains a first fluorine-containing organic substance, the content of fluorine element in the first fluorine-containing organic substance is not less than 33 wt%, and the solubility of the first fluorine-containing organic substance to lithium salt is not more than 1.5g/100g.

In the present invention, by adding the above-described first fluorine-containing organic substance to the electrolytic solution, it has been possible to achieve higher oxidation resistance and stronger high-pressure resistance of the electrolytic solution than in the prior art. To further enhance the effect, one or more of the technical features may be further preferred.

The content of the fluorine element in the first fluorine-containing organic substance is not less than 33% by weight, and means a content of the fluorine element in the first fluorine-containing organic substance is not less than 33% by weight, for example, in a range of 33% by weight, 35% by weight, 40% by weight, 45% by weight, 50% by weight, 55% by weight, 60% by weight, 65% by weight, 70% by weight, 75% by weight, 80% by weight, or any combination thereof, based on the total weight of the first fluorine-containing organic substance.

Preferably, the content of fluorine element in the first fluorine-containing organic substance is not less than 42 wt%.

The solubility of the first fluorine-containing organic substance to lithium salt is not more than 1.5g/100g, which means that 100g of the first fluorine-containing organic substance can dissolve lithium salt which is not more than 1.5g.

In the present invention, the term "lithium salt" particularly refers to a lithium salt for providing lithium ions in the electrolyte.

Preferably, the first fluorine-containing organic substance is incapable of dissolving a lithium salt. In the present invention, the terms "not less than" and "not more than" are used in a meaning including a boundary. Specifically, the content of the fluorine element in the first fluorine-containing organic substance is not less than 33 wt%, and when the content of the fluorine element in the first fluorine-containing organic substance is equal to 33 wt%, the protection range of the first fluorine-containing organic substance is also included; the solubility of the first fluorine-containing organic substance to the lithium salt is not more than 1.5g/100g, and when the solubility of the first fluorine-containing organic substance to the lithium salt is equal to 1.5g/100g, the protection range of the first fluorine-containing organic substance is also included.

According to a specific embodiment, the first fluorinated organic compound is present in an amount of 15 to 50wt% (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%) based on the total weight of the electrolyte.

When the weight of the first fluorine-containing organic substance accounts for less than 15% of the total weight of the electrolyte, the fluorine content in the electrolyte is relatively low, a high-content LiF component is difficult to form under high voltage, and other organic solvents are difficult to maintain the low viscosity of the electrolyte while being in a high-salt solvation state with high pressure resistance.

When the weight of the first fluorine-containing organic matter accounts for more than 50% of the total weight of the electrolyte, the dissociation of lithium salt is limited or the viscosity of the electrolyte is too high, so that the conductivity of the electrolyte is low, and normal charge and discharge are difficult to meet.

In one example, the first fluoroorganic is present in an amount of 20-40 wt.%.

According to a specific embodiment, the first fluorine-containing organic substance is at least one selected from the group consisting of polyfluorobenzene, polyfluoroether and polyfluoroether.

In one embodiment, the first fluorine-containing organic may be selected from polyfluorobenzenes.

According to a specific embodiment, the polyfluorobenzene has the chemical formula C ₆ H _n F _6-n 。

Wherein n represents the number of hydrogen atoms, and n may be an integer of 0 to 4 (e.g., 0,1,2,3,4), preferably 0,1 or 2. When n is 0, it means that all H on benzene are substituted by F.

According to a specific embodiment, the polyfluorobenzene is selected from one or more of o-difluorobenzene, p-difluorobenzene, m-difluorobenzene, trifluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, and 1,2,3,4,5-pentafluorobenzene.

In one embodiment, the first fluorine-containing organic may be selected from polyfluoroethers.

According to one embodiment, the polyfluoroether has the general chemical formula C _x H _(2x-y+2) O _z F _y 。

Wherein x represents the number of carbon atoms, and x may be an integer of 2 to 8 (e.g., 2,3,4,5,6,7,8), preferably an integer of 4 to 7.

Wherein y represents the number of fluorine atoms, and y may be an integer of 3 to 14 (e.g., 3,4,5,6,7,8,9,10,11,12,13,14), preferably an integer of 7 to 11.

Wherein z represents the number of oxygen atoms, and z can be an integer of 1 to 4 (e.g., 1,2,3,4).

In one embodiment, the polyfluoroether is selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,3,3-tetrafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, tris (trifluoroethoxy) methane (TFEO).

In one example, the first fluoroorganic compound comprises both polyfluorobenzene and polyfluoroether.

In one embodiment, the weight ratio of the polyfluorobenzene to the polyfluoroether may be from 1: (0.5-5), for example 1.

In one example, the first fluoro-organic may be selected from polyfluoro esters.

According to one embodiment, the polyfluoro ester has the general chemical formula C _a+1 H _(2a-b+2) O ₃ F _b 。

Wherein a represents the number of carbon atoms, and a can be an integer of 2 to 8 (e.g., 2,3,4,5,6,7,8).

Wherein b represents the number of fluorine atoms, and b may be an integer of 4 to 12 (e.g., 4,5,6,7,8,9,10,11,12).

According to a specific embodiment, the polyfluoro ester is selected from one or more of bis (2,2,2-trifluoroethyl) carbonate, 2,2,3,3-tetrafluoropropyl methyl carbonate, 2,2,3,3-tetrafluoropropyl ethyl carbonate, 2,2,3,3,3-pentafluoropropyl ethyl carbonate, bis hexafluoroisopropyl carbonate and hexafluoroisopropyl 2,2,2-trifluoroethyl carbonate.

In one example, the polyfluoro ester is present in an amount from 0 to 50wt% (e.g., 5wt%,10wt%,15wt%,20wt%,25wt%,30wt%,35wt%,40wt%,45wt%,50 wt%) based on the total weight of the first fluorochemical.

When the content of the polyfluorinated ester is 0wt%, the first fluorine-containing organic substance does not contain polyfluorinated ester.

According to a specific embodiment, the electrolyte further comprises a second fluorine-containing organic compound. The second fluorine-containing organic compound selected by the invention has the effect of improving the oxidation resistance of the electrolyte, has better using effect by being matched with the first fluorine-containing organic compound which improves the mechanical strength of the interface film and the oxidation resistance of the electrolyte, and can further improve the oxidation resistance of the electrolyte.

The second fluorine-containing organic substance is distinguished from the first at least in that the second fluorine-containing organic substance has a solubility for the lithium salt that is greater than a solubility of the first fluorine-containing organic substance for the lithium salt.

In one embodiment, the second fluoroorganic compound has a formula in which the number of fluorine atoms is 1 or more.

In one embodiment, the second fluoroorganic has a solubility for lithium salts of greater than 12.5g/100g.

According to a specific embodiment, the second fluorinated organic compound is present in an amount of 35 to 70 wt% (e.g., 35%, 40%, 45%, 50%, 55%, 60%, 65%) based on the total weight of the electrolyte.

In one example, the second fluoro-organic material is present in an amount of 50 to 70 wt% based on the total weight of the electrolyte.

According to a preferred embodiment, the electrolyte solution contains both the first fluorine-containing organic substance and the second fluorine-containing organic substance.

In one embodiment, the second fluorine-containing organic compound is selected from one or more of fluoro carbonate, fluoro carboxylate, fluoro nitrile.

In one example, the fluoro carbonate is selected from one or more of fluoroethylene carbonate (FEC), bis (2,2,2-trifluoroethyl) carbonate (FDEC), and methyl trifluoroethyl carbonate (FEMC).

In one example, the fluorocarboxylic acid ester is selected from 2,2-difluoroethyl acetate (DFEA) and/or 2,2,2-trifluoroethyl acetate (TFEA).

In one example, the fluoronitrile is selected from one or more of fluoroacetonitrile, fluoropropionitrile, and fluorobutyronitrile.

According to a specific embodiment, the electrolyte further comprises an additive of the boron lithium salt type. The boron lithium salt-based additive may also provide lithium ions.

In one embodiment, the boron lithium salt additive is selected from the group consisting of lithium difluorooxalato borate (LiDFOB), lithium tetrafluoroborate (LiBF) ₄ ) And lithium bis (oxalato) borate (LiBOB). The boron-lithium salt additive selected by the invention has the effect of inhibiting the dissolution of transition metal, and can be used in combination with the first fluorine-containing organic matter to further improve the cycle performance of the battery under high voltage.

According to a specific embodiment, the electrolyte contains both the first fluorine-containing organic substance and the additive of the boron-lithium salt type.

According to a specific embodiment, the content of the boron-lithium salt additive is 0.5-2 wt% based on the total weight of the electrolyte.

In one embodiment, the electrolyte further comprises a lithium salt.

In one example, the lithium salt is selected from lithium hexafluorophosphate (LiPF) ₆ ) Lithium bis (fluorosulfonyl) imide (LiFSI), lithium difluorophosphate (LiPO) ₂ F ₂ ) One or more of lithium bistrifluoromethylsulfonyl imide (LiTFSI), lithium difluorobis oxalate phosphate, lithium bis oxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (pentafluoroethylsulfonyl) imide, lithium tris (trifluoromethylsulfonyl) methide or lithium bis (trifluoromethylsulfonyl) imide.

According to a specific embodiment, the lithium salt is present in an amount of 10 to 18 wt% (e.g., 10%, 12%, 12.5%, 13.5%, 14%, 15%, 16%, 18%) based on the total weight of the electrolyte.

In one embodiment, the electrolyte further comprises additives conventionally used in the art for electrolytes.

In one example, the additive is selected from one or more of 1,3-propane sultone (1,3-PS), 1,3-propene sultone, succinonitrile, adiponitrile (ADN), glycerol trinitrile, and 1,3,6-Hexane Trinitrile (HTCN).

In one example, the additive is present in an amount of 0 to 10wt% (e.g., 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%) based on the total weight of the electrolyte. When the content of the additive is 0%, it means that the additive is not contained in the electrolyte.

In one embodiment, the electrolyte is suitable for use in high voltage batteries above 4.55V.

The materials of the battery except the battery electrolyte can be processed according to the mode in the field, and the effects of bearing the voltage of more than 4.55V, having higher energy density and more stable cycle performance can be realized.

The battery is preferably a lithium ion battery.

The charge cutoff voltage of the battery is 4.55V or more.

The battery also comprises a positive plate containing a positive active material, a negative plate containing a negative active material, and a separation film.

The positive electrode sheet may be a conventional one in the art, and for example, includes a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector.

The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

In one example, the positive electrode active material is contained in an amount of 80 to 99.8 wt%, the conductive agent is contained in an amount of 0.1 to 10wt%, and the binder is contained in an amount of 0.1 to 10wt%, based on the total weight of the positive electrode active material layer.

Preferably, the content of the positive electrode active material is 90 to 99.6 wt%, the content of the conductive agent is 0.2 to 5wt%, and the content of the binder is 0.2 to 5wt%, based on the total weight of the positive electrode active material layer.

In a preferred embodiment, the positive active material is selected from the group consisting of transition metal lithium oxides and/or lithium-rich manganese-based positive electrode materials in order to cooperate with the first fluorine-containing compound of the present invention.

The chemical formula of the transition metal lithium oxide is Li _1+x Ni _y Co _z M _(1-y-z) O ₂ Wherein x is more than or equal to-0.1 and less than or equal to 1; y is more than or equal to 0 and less than or equal to 1,0 and less than or equal to 1, and y + z is more than or equal to 0 and less than or equal to 1; wherein M is one or more of Mg, zn, ga, ba, al, fe, cr, sn, V, mn, sc, ti, nb, mo and Zr.

In one example, the lithium metal oxide is lithium cobaltate.

In one example, the lithium-rich manganese-based cathode material has a chemical formula of xLiMO ₂ ·(1-x)Li ₂ MnO ₃ Wherein x is more than 0 and less than 1,M is Ni, co, mg, zn,Ga. One or more of Ba, al, fe, cr, sn, V, mn, sc, ti, nb, mo and Zr. The first fluorine-containing organic matter and the lithium-rich manganese-based positive electrode material are matched for use, so that the effect is better.

The negative electrode sheet may be a conventional one in the art, and for example, includes a negative electrode collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode collector.

The anode active material layer includes an anode active material, a conductive agent, and a binder.

In one example, the negative electrode active material is contained in an amount of 80 to 99.8 wt%, the conductive agent is contained in an amount of 0.1 to 10wt%, and the binder is contained in an amount of 0.1 to 10wt%, based on the total weight of the negative electrode active material layer.

Preferably, the negative electrode active material is contained in an amount of 90 to 99.6 wt%, the conductive agent is contained in an amount of 0.2 to 5wt%, and the binder is contained in an amount of 0.2 to 5wt%, based on the total weight of the negative electrode active material layer.

In one example, the anode active material includes a carbon-based anode material and/or a silicon-based anode material.

The carbon-based negative electrode material comprises one or more of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon and soft carbon.

The silicon-based negative electrode material is selected from nano silicon (Si) and silicon-oxygen negative electrode material (SiO) _x (0<x<2) And silicon carbon anode material.

In one example, the conductive agent is selected from one or more of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.

In one example, the binder is selected from one or more of sodium carboxymethylcellulose, styrene-butadiene latex, polytetrafluoroethylene, polyethylene oxide.

The battery can bear the voltage of more than 4.55V due to the electrolyte contained in the battery, so that the energy density of the battery is increased, the attenuation slope of the cycle capacity of the battery is improved, and the cycle stability of the battery is improved.

The present invention will be described in detail below by way of examples. The described embodiments of the invention are only some, but not all embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.

It is understood that the lithium ion battery of the present invention includes a negative electrode tab, an electrolyte, a positive electrode tab, a separator, and an exterior package. The lithium ion battery can be obtained by stacking the positive plate, the isolating membrane and the negative plate to obtain the battery cell or stacking the positive plate, the isolating membrane and the negative plate, then winding to obtain the battery cell, placing the battery cell in an outer package, and injecting electrolyte into the outer package.

The following examples are provided to illustrate the electrolytes of the present invention.

Example 1

(1) Ingredient preparation

First fluorine-containing organic matter: 30 parts by weight of TTE,10 parts by weight of 1,3,5-trifluorobenzene;

a second fluoroorganic, totaling 57 parts by weight, wherein 25 parts by weight of FEC,32 parts by weight of FEMC;

boron lithium salt additive: 0.5 parts by weight in total, 0.25 parts by weight of LiDFOB and 0.25 parts by weight of LiBF ₄ ；

Lithium salt: 12.5 pbw of lithium hexafluorophosphate.

(2) Preparing an electrolyte:

in a glove box filled with argon (H) ₂ O<0.1ppm，O ₂ <0.1 ppm), uniformly mixing the first fluorine-containing organic matter and the second fluorine-containing organic matter, quickly adding fully dried lithium salt into the mixture, dissolving the mixture, adding a boron-lithium salt additive, uniformly stirring the mixture, and carrying outAnd obtaining the required electrolyte after the moisture and the free acid are detected to be qualified.

Example 2

(1) Ingredient preparation

A first fluorine-containing organic compound: a total of 30 parts by weight of TFEO, 18 parts by weight of 1,2,4,5-tetrafluorobenzene;

a second fluorine-containing organic substance, wherein the total amount is 57 parts by weight, 25 parts by weight of FEC, and 32 parts by weight of DFEA;

boron lithium salt additive: 0.5 parts by weight in total, of which 0.25 part by weight of LiDFOB,0.25 part by weight of LiBOB;

lithium salt: 12.5 parts by weight of lithium hexafluorophosphate.

(2) An electrolyte was prepared according to the method of example 1.

Example 3

(1) Ingredient preparation

A first fluorine-containing organic compound: 30 parts by weight in total, wherein 22 parts by weight of 1,1,2,3,3,3-hexafluoropropyl-2,2,3,3-tetrafluoropropyl ether and 8 parts by weight of 1,2,3,4,5-pentafluorobenzene;

a second fluorine-containing organic substance, in a total of 57 parts by weight, of 25 parts by weight of fluoroacetonitrile, 32 parts by weight of FEMC;

Lithium salt: 12.5 pbw of lithium hexafluorophosphate.

(2) An electrolyte was prepared according to the method of example 1.

EXAMPLE 4 group

This set of examples is presented to illustrate the effect that occurs when the first fluoroorganic is changed.

This set of examples was carried out with reference to example 1, except that the choice and/or content of the first fluoro-organic substance was varied, in particular:

example 4a, the content of the first fluorine-containing organic substance was changed to 15 parts by weight while keeping the internal ratio constant;

example 4b, the content of the first fluorine-containing organic substance was changed to 50 parts by weight while keeping the internal ratio constant;

example 4c, the first fluoroorganic was changed to 30 parts by weight TTE;

example 4d, the selection of the first fluoroorganic was changed to 30 parts by weight of 1,3,5-trifluorobenzene;

example 4e, the selection of the first fluoro-organic compound was changed to 30 parts by weight in total, wherein 20 parts by weight of TTE and 10 parts by weight of fluorobenezene;

example 4f varying the selection of the first fluoroorganic, for a total of 30 parts by weight, 24 parts by weight TTE,6 parts by weight bis (2,2,2-trifluoroethyl) carbonate.

EXAMPLE 5 group

This set of examples is presented to illustrate the effect that occurs when the second fluoroorganic is changed.

This set of examples was carried out with reference to example 1, with the difference that the choice and/or the weight ratio of the second fluorine-containing organic substance to the first fluorine-containing organic substance was varied, in particular:

example 5a, the second fluoroorganic content was changed to 70 parts by weight (internal ratio was not changed), and the first fluoroorganic content was changed to 17 parts by weight (internal ratio was not changed);

example 5b, the second fluorine containing organic was replaced with the same weight parts of a non-fluorine modified organic, specifically 25 weight parts of Ethylene Carbonate (EC), 32 weight parts of Ethyl Methyl Carbonate (EMC);

example 6

Reference is made to example 1, except that the choice of the additive of the lithium borate salt type is varied, in particular 0.5 parts by weight of 1,3,6-Hexanetricarbonitrile (HTCN).

Comparative example 1

The procedure of example 1 was followed, except that the first fluorine-containing organic compound was replaced with the same weight part of the second fluorine-containing organic compound (the internal ratio was not changed), that is, the electrolyte solution did not contain the first fluorine-containing organic compound.

Comparative example 2

The procedure of comparative example 1 was followed except that the second fluorine-containing organic material was replaced with the same weight parts of the non-fluorine-containing modified organic material, specifically 38 weight parts of Ethylene Carbonate (EC), 49 weight parts of Ethyl Methyl Carbonate (EMC), for a total of 87 weight parts.

Preparation example

The electrolytes obtained in the examples and the comparative examples were used to prepare lithium ion batteries in the following manners, respectively:

(1) Preparation of positive plate

Mixing lithium cobaltate (LiCoO) ₂ ) Mixing polyvinylidene fluoride (PVDF), SP (super P) and Carbon Nano Tubes (CNT) according to a mass ratio of 96; uniformly coating the positive active slurry on two surfaces of the aluminum foil; and drying the coated aluminum foil, and then rolling and slitting to obtain the required positive plate.

(2) Preparation of negative plate

Mixing artificial graphite, silicon monoxide, sodium carboxymethylcellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) according to a mass ratio of 39.5; uniformly coating the negative active slurry on two surfaces of a copper foil; and airing the coated copper foil at room temperature, transferring the copper foil to an oven at 80 ℃ for drying for 10 hours, and then carrying out cold pressing and slitting to obtain the negative plate.

(3) Lithium ion battery preparation

Stacking the positive plate in the step 1), the negative plate in the step 2) and the isolation film in the order of the positive plate, the isolation film and the negative plate, and then winding to obtain a battery cell; and (3) placing the battery cell in an aluminum foil package, injecting the electrolyte obtained in the embodiment into the package, and performing the processes of vacuum packaging, standing, formation, shaping, sorting and the like to obtain the lithium ion battery.

Test example

The lithium ion batteries obtained in the examples and comparative examples were subjected to a 25 ℃ cycle performance test and a 45 ℃ cycle performance test, respectively.

(1) 25 ℃ cycle performance test

The batteries in Table 1 were charged and discharged at 25 ℃ at a rate of 1CCharging and discharging cycle is carried out for 1000 weeks in the voltage stopping range, and the discharge capacity at the 1 st week is measured and is x ₁ mAh, discharge capacity at week N, as y ₁ mAh; dividing the Nth week capacity by the 1 st week capacity to obtain the Nth week cycle capacity retention ratio R ₁ ＝y ₁ /x ₁ 。

(2) 45 ℃ cycle performance test

The batteries of Table 1 were subjected to charge-discharge cycles at 45 ℃ at a rate of 1C within the charge-discharge cutoff range for 1000 weeks, and the discharge capacity at 1 st week was measured and found to be x ₂ mAh, discharge capacity at week N, as y ₂ mAh; dividing the capacity at the Nth week by the capacity at the 1 st week to obtain the circulation capacity retention rate R at the Nth week ₂ ＝y ₂ /x ₂ 。

The results are shown in Table 1.

TABLE 1

As can be seen from table 1, the capacity retention rate of the battery prepared from the electrolyte of the example is obviously improved as seen from the comparative example and the example, which shows that the introduction of the first fluorine-containing organic substance improves the oxidation resistance of the electrolyte, increases the energy density of the battery, improves the attenuation slope of the cycle capacity of the battery, and improves the cycle stability of the battery.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including various technical features being combined in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. The electrolyte is characterized by comprising a first fluorine-containing organic substance, wherein the content of fluorine in the first fluorine-containing organic substance is not less than 33 wt%, and the solubility of the first fluorine-containing organic substance to lithium salt is not more than 1.5g/100g.

2. The electrolyte of claim 1, wherein the first fluoro-organic material is present in an amount of 15 to 50wt%, based on the total weight of the electrolyte; and/or the first fluorine-containing organic matter is at least one selected from polyfluorobenzene, polyfluoroether and polyfluoroether.

3. The electrolyte of claim 2, wherein the polyfluorobenzene has a chemical formula of C ₆ H _n F _6-n N is an integer of 0 to 4; and/or the presence of a gas in the atmosphere,

the polyfluorobenzene is selected from one or more of o-difluorobenzene, p-difluorobenzene, m-difluorobenzene, trifluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene and 1,2,3,4,5-pentafluorobenzene.

4. The electrolyte of claim 2, wherein the polyfluoroether has the general chemical formula C _x H _(2x-y+2) O _z F _y X is an integer of 2 to 8, y is an integer of 3 to 14, and z is an integer of 1 to 4; and/or the presence of a gas in the gas,

the polyfluoroether is selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,3,3-tetrafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, and tris (trifluoroethoxy) methane.

5. The electrolyte as claimed in any one of claims 2 to 4, wherein the electrolyte contains both the polyfluorobenzene and the polyfluoroether in a weight ratio of polyfluorobenzene to polyfluoroether of 1: (0.5-5).

6. The electrolyte of claim 2, wherein the polyfluoro ester has the formula C _(a+1) H _(2a-b+2) O ₃ F _b A is an integer of 2-8, b is an integer of 4-12; and/or the presence of a gas in the gas,

the polyfluoro ester is selected from one or more of bis (2,2,2-trifluoroethyl) carbonate, 2,2,3,3-tetrafluoropropyl methyl carbonate, 2,2,3,3, -tetrafluoropropyl ethyl carbonate, 2,2,3,3,3-pentafluoropropyl ethyl carbonate, bis hexafluoroisopropyl carbonate and hexafluoroisopropyl 2,2,2-trifluoroethyl carbonate.

7. The electrolyte of claim 1, wherein the electrolyte further comprises a second fluorine-containing organic substance, the second fluorine-containing organic substance is selected from one or more of fluoro-carbonate, fluoro-carboxylate and fluoro-nitrile, and the second fluorine-containing organic substance has a molecular formula in which the number of fluorine atoms is greater than or equal to 1 and the solubility to lithium salt is greater than 12.5g/100g.

8. The electrolyte of claim 7, wherein the second fluoroorganic is present in an amount ranging from 35 to 70 wt.%, based on the total weight of the electrolyte.

9. The electrolyte of claim 1, wherein the electrolyte further comprises a boron lithium salt additive selected from one or more of lithium difluorooxalato borate, lithium tetrafluoroborate, and lithium dioxaoxalato borate; and/or the presence of a gas in the gas,

based on the total weight of the electrolyte, the content of the boron lithium salt additive is 0.5-2 wt%.

10. A battery comprising an electrolyte as claimed in any one of claims 1 to 9.