CN114287079B

CN114287079B - Electrolyte, electrochemical device, and electronic device

Info

Publication number: CN114287079B
Application number: CN202180004883.1A
Authority: CN
Inventors: 王蕊; 王翔; 唐超
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-03-31
Filing date: 2021-03-31
Publication date: 2023-08-29
Anticipated expiration: 2041-03-31
Also published as: CN114287079A; WO2022205065A1

Abstract

The application provides an electrolyte, an electrochemical device and an electronic device. The electrolyte comprises a compound represented by the formula (I), wherein R ₁₁ Selected from covalent bond, oxygen, sulfur, C ₁ ‑C ₁₀ Hydrocarbylene, C ₁ ‑C ₅ Alkyleneoxy or C ₁ ‑C ₅ An alkylene group including alkylene, alkenylene, arylene; r is R ₁₂ Selected from covalent bonds, C ₁ ‑C ₁₀ Alkylene or C ₁ ‑C ₁₀ Hydrocarbylsulfonyl, the hydrocarbylene group includes alkylene, alkenylene, arylene; x is selected from substituted or unsubstituted C ₁ ‑C ₁₀ A heterocyclic group containing at least one of an oxygen, nitrogen or sulfur atom; when substituted, the substituents include hydrocarbyl groups, including alkyl groups, alkenyl groups, alkynyl groups, cyano groups, halogen atoms; the heterocyclic ring comprises cyclic ether, morpholine, pyridine, triazole, furan, pyran, piperidine, pyrrole, pyrazole, pyrazine, pyridazine and imidazole. The electrolyte can remarkably improve the high-temperature cycle performance of the electrochemical device at a high voltage of 4.4V to 4.8V, and reduce the cycle resistance increase.

Description

Electrolyte, electrochemical device, and electronic device

Technical Field

The application relates to the field of electrochemistry, in particular to electrolyte, an electrochemistry device and an electronic device.

Background

With the recent reduction in weight and size of electric products, there is an increasing demand for an electrochemical device (e.g., lithium ion battery) that is lightweight and slim. The development of lithium ion secondary batteries with high energy density is gradually advancing, the upper limit voltage of the design is also improved along with the development, and the rated voltage of the lithium ion batteries of the lithium cobaltate system can reach 4.45V to 4.5V at present, which means that the high voltage storage and charge and discharge are carried out, and the damage to the positive electrode structure and the negative electrode structure is more serious, so that higher demands are put forward on the oxidation resistance and the film forming stability of the electrolyte.

The method for improving the oxidation resistance of the electrolyte generally comprises the following steps: inert solvents with higher oxidation potential such as fluoroesters, fluoroethers and the like are used; the content of the additives such as nitrile or propane sultone is increased. However, the fluorinated solvent has high viscosity and weak ion transmission capability, and is difficult to realize rapid charging under high voltage; and increasing the amount of the additive further deteriorates the conductivity of the electrolyte and the battery resistance.

Therefore, how to develop an electrolyte additive capable of improving the battery cycle performance at high voltage has become an important issue for improving the battery performance.

Disclosure of Invention

In some embodiments, the present application provides an electrolyte comprising a compound represented by formula (I),

in formula (I), R ₁₁ Selected from covalent bond, oxygen, sulfur, C ₁ -C ₁₀ Hydrocarbylene, C ₁ -C ₅ Alkyleneoxy or C ₁ -C ₅ An alkylene group, including an alkylene group, an alkenylene group, or an arylene group;

R ₁₂ selected from covalent bonds, C ₁ -C ₁₀ Alkylene or C ₁ -C ₁₀ Hydrocarbylsulfonyl, the hydrocarbylene group comprising an alkylene, alkenylene, or arylene group;

x is selected from substituted or unsubstituted C ₁ -C ₁₀ A heterocyclic group containing at least one of an oxygen, nitrogen or sulfur atom; when substituted, the substituents include hydrocarbyl, cyano, or halogen, including alkyl, alkenyl, or alkynyl; the heterocycle includes at least one of cyclic ether, morpholine, pyridine, triazole, furan, pyran, piperidine, pyrrole, pyrazole, pyrazine, pyridazine, or imidazole.

In some embodiments, the compound represented by formula (I) includes at least one of compounds represented by formulas (I-1) to (I-7);

in some embodiments, the compound represented by formula (I) is present in an amount of n.ltoreq.n.ltoreq.7 based on the weight of the electrolyte.

In some embodiments, the electrolyte further comprises at least one of fluoroethylene carbonate, vinylene carbonate; based on the weight of the electrolyte, the content of fluoroethylene carbonate is k percent, the content of vinylene carbonate is m percent, wherein k is more than or equal to 0, m is more than or equal to 0, k+m is more than 0, and k, m and n are more than or equal to-1 and less than or equal to k+m-n and less than or equal to 12.

In some embodiments, 0 < k+m.ltoreq.14.

In some embodiments, the electrolyte further comprises a carboxylate; based on the weight of the electrolyte, the content of the carboxylic ester is a%, a is more than or equal to 5 and less than or equal to 30, and a and n satisfy the relation: n/a is more than or equal to 0.0005 and less than or equal to 0.7. In some embodiments, 0.05.ltoreq.n/a.ltoreq.0.1.

In some embodiments, the carboxylic acid ester comprises at least one of ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate.

In some embodiments, the electrolyte further comprises at least one of a sulfonate compound or a nitrile compound.

In some embodiments, the sulfonate compound includes at least one of 1, 3-propane sultone, 2, 4-butane sultone.

In some embodiments, the sulfonate compound is present in an amount of 0.1 to 5% based on the weight of the electrolyte.

In some embodiments, the nitrile compound includes at least one of the compounds represented by formula (ii) to formula (v);

wherein R is ₂₁ Selected from substituted or unsubstituted C ₁ -C ₁₂ Alkylene, substituted or unsubstituted C ₁ -C ₁₂ An alkyleneoxy group; r is R ₃₁ 、R ₃₂ Each independently selected from the group consisting of covalent bonds, substituted or unsubstituted C ₁ -C ₁₂ An alkylene group; r is R ₄₁ 、R ₄₂ 、R ₄₃ Each independently selected from the group consisting of covalent bonds, substituted or unsubstituted C ₁ -C ₁₂ Alkylene, substituted or unsubstituted C ₁ -C ₁₂ An alkyleneoxy group; r is R ₅₁ Selected from substituted or unsubstituted C ₁ -C ₁₂ Alkylene, substituted or unsubstituted C ₂ -C ₁₂ Alkenylene, substituted or unsubstituted C ₆ -C ₁₂ Arylene, substituted or unsubstituted C ₃ -C ₁₂ A cyclic subunit; wherein when substituted, the substituent is halogen.

In some embodiments, the nitrile compound includes at least one of the following compounds;

in some embodiments, the nitrile compound is present in an amount of 0.05 to 10% based on the weight of the electrolyte.

In some embodiments, the present application also provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte according to the present application.

In some embodiments, the electrochemical device has a charge cutoff voltage of 4.4 to 4.8V.

Further, the application also provides an electronic device, which comprises the electrochemical device.

The electrolyte provided by the application can obviously improve the high-temperature cycle performance of an electrochemical device under the high voltage of 4.4V to 4.8V, and reduce the cycle impedance increase.

Detailed Description

It is to be understood that the disclosed embodiments are merely exemplary of the application, which may be embodied in various forms and that the specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present application.

In the description of the present application, unless otherwise indicated, all of the groups of a compound may be substituted or unsubstituted.

In the description of the present application, the term "heteroatom" means an atom other than C, H. In some embodiments, the heteroatom includes at least one of B, N, O, si, P, S. In the description of the present application, the term "heterocyclyl" refers to a cyclic group comprising at least one heteroatom. In some embodiments, the heterocyclyl comprises a heterocyclyl containing at least one of an oxygen, nitrogen, or sulfur atom. In some embodiments, the heterocycle comprises cyclic ethers, morpholines, pyridines, triazoles, furans, pyrans, piperidines, pyrroles, pyrazoles, pyrazines, pyridazines, imidazoles.

In the description of the present application, an alkylene group is a divalent group formed by the loss of one hydrogen atom from a hydrocarbon group. Alkylene is a divalent radical formed by the loss of one hydrogen atom from an alkyl group, alkenylene is a divalent radical formed by the loss of one hydrogen atom from an alkenyl group, and arylene is a divalent radical formed by the loss of one hydrogen atom from an aryl group. In the description of the present application, subunit structures not explicitly specified are all read in accordance with the description of this paragraph.

In the context of the present application, an alkyleneoxy group is a divalent radical formed by the loss of two hydrogen atoms from an ether, which may contain one or more ether linkages.

In the description of the application, the cyclic ether may contain one or more ether linkages.

In the description of the present application, terms not explicitly described, substitutions in structural formulae, etc., should be understood in accordance with well known, conventional, customary means or modes of operation by those skilled in the art.

The electrolyte, the electrochemical device and the electronic device according to the present application are described in detail below.

[ electrolyte ]

< additive A >

In some embodiments, the electrolyte contains an additive A, wherein the additive A is at least one of compounds represented by the formula (I);

in formula (I), R ₁₁ Selected from covalent bond, oxygen, sulfur, C ₁ -C ₁₀ Hydrocarbylene, C ₁ -C ₅ Alkyleneoxy or C ₁ -C ₅ An alkylene group, including an alkylene group, an alkenylene group, or an arylene group; r is R ₁₂ Selected from covalent bonds, C ₁ -C ₁₀ Alkylene or C ₁ -C ₁₀ Hydrocarbylsulfonyl, the hydrocarbylene group comprising an alkylene, alkenylene, or arylene group; x is selected from substituted or unsubstituted C ₁ -C ₁₀ A heterocyclic group containing at least one of an oxygen, nitrogen or sulfur atom; when substituted, the substituents include hydrocarbyl, cyano, or halogen, including alkyl, alkenyl, or alkynyl; the heterocycle includes at least one of cyclic ether, morpholine, pyridine, triazole, furan, pyran, piperidine, pyrrole, pyrazole, pyrazine, pyridazine, or imidazole.

In the electrolyte, the additive A is a heterocyclic ring substituted furfural derivative, wherein aldehyde groups can strengthen SEI (Solid Electrolyte Interphase, solid electrolyte interface) stability, dislocation substituent groups containing hetero atoms and heterocycles have film forming effects, particularly nitrogen and sulfur, so that the material can have the dual functions of protecting positive and negative electrodes, realize remarkable improvement of high-temperature cycle performance of an electrochemical device under the high voltage of 4.4V to 4.8V, and reduce the cycle impedance growth of the electrochemical device under the chemical system.

In some embodiments, the compound represented by formula (I) comprises at least one of the compounds represented by formulas (I-1) to (I-7);

< additive B >

In some embodiments, the electrolyte may further include an additive B, where the additive B is at least one of fluoroethylene carbonate and vinylene carbonate.

In some embodiments, the fluoroethylene carbonate is present in an amount of k% and the vinylene carbonate is present in an amount of m% based on the weight of the electrolyte, wherein k.gtoreq.0, m.gtoreq.0, 0 < k+m.ltoreq.14, and k, m and n satisfy-1.ltoreq.k+m-n.ltoreq.12.

< additive C >

In some embodiments, the electrolyte may further include at least one of a sulfonate compound or a nitrile compound.

In some embodiments, the sulfonate compound is present in an amount of 0.1% to 5% based on the weight of the electrolyte.

In some embodiments, the nitrile compound comprises at least one of the compounds represented by formulas (ii) to (v);

wherein R is ₂₁ Selected from substituted or unsubstituted C ₁ -C ₁₂ Alkylene, substituted or unsubstituted C ₁ -C ₁₂ An alkyleneoxy group; r is R ₃₁ 、R ₃₂ Each independently selected from the group consisting of covalent bonds, substituted or unsubstituted C ₁ -C ₁₂ An alkylene group; r is R ₄₁ 、R ₄₂ 、R ₄₃ Each independently selected from covalent bonds, warpSubstituted or unsubstituted C ₁ -C ₁₂ Alkylene, substituted or unsubstituted C ₁ -C ₁₂ An alkyleneoxy group; r is R ₅₁ Selected from substituted or unsubstituted C ₁ -C ₁₂ Alkylene, substituted or unsubstituted C ₂ -C ₁₂ Alkenylene, substituted or unsubstituted C ₆ -C ₁₂ Arylene, substituted or unsubstituted C ₃ -C ₁₂ A cyclic subunit; wherein when substituted, the substituent is halogen.

In some embodiments, the nitrile compound comprises at least one of the following compounds:

In some embodiments, the nitrile compound is present in an amount of 0.1 to 10% based on the weight of the electrolyte.

< organic solvent >

In some embodiments, the electrolyte further comprises an organic solvent. The organic solvent is an organic solvent well known in the art to be suitable for an electrochemical device, for example, a nonaqueous organic solvent is generally used. In some embodiments, the nonaqueous organic solvent comprises at least one of a carbonate solvent, a carboxylate solvent.

In some embodiments, the carbonate-based solvent comprises at least one of dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate.

In some embodiments, the carboxylate solvent comprises at least one of ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate.

In some embodiments, the carboxylate is present in an amount of a% based on the weight of the electrolyte, and when the electrolyte contains a compound of formula (I) in an amount of n%, 5.ltoreq.a.ltoreq.30, and a and n satisfy the relationship: n/a is less than or equal to 0.0005 and less than or equal to 0.7, if the ratio of n/a is lower, the electrolyte cannot form an effective protective layer on the anode, and the solvent is easy to decompose and produce gas; if the n/a ratio is too high, the negative electrode film forming resistance is large, and a clear lithium ion transport channel cannot be provided. In some embodiments, 0.05.ltoreq.n/a.ltoreq.0.1.

In the present application, the organic solvent in the electrolyte may be one non-aqueous organic solvent or a mixture of a plurality of non-aqueous organic solvents, and when a mixed solvent is used, electrochemical devices of different properties can be obtained by controlling the mixing ratio.

< electrolyte salt >

In some embodiments, the electrolyte further comprises an electrolyte salt. The electrolyte salt is an electrolyte salt suitable for an electrochemical device, which is well known in the art. Suitable electrolyte salts may be selected for different electrochemical devices. For example, for lithium ion batteries, lithium salts are typically used as electrolyte salts.

In some embodiments, the lithium salt comprises at least one of an organolithium salt or an inorganic lithium salt.

In some embodiments, the lithium salt comprises LiPF ₆ 、LiBF ₄ 、LiB(C ₆ H ₅ ) ₄ 、LiCH ₃ SO ₃ 、LiCF ₃ SO ₃ 、LiN(SO ₂ CF ₃ ) ₂ 、LiC(SO ₂ CF ₃ ) ₃ 、LiSiF ₆ At least one of LiBOB or LiDFOB, preferably LiPF ₆ 。

In the application, the content of the electrolyte is not particularly limited, and can be reasonably added according to actual needs. In the present application, the preparation method of the electrolyte is not limited, and may be prepared according to a conventional preparation method of an electrolyte known to those skilled in the art.

[ electrochemical device ]

Next, the electrochemical device of the present application will be described.

The electrochemical device of the present application may be any one selected from the following devices: lithium secondary batteries or sodium ion batteries. In particular, the electrochemical device is a lithium secondary battery.

In some embodiments, the electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator, and the aforementioned electrolyte of the present application.

< positive electrode sheet >

The positive electrode sheet is a positive electrode sheet that can be used in an electrochemical device, as known in the art. In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

In some embodiments, the positive electrode active material includes at least one of Lithium Cobalt Oxide (LCO), lithium nickel manganese cobalt ternary material (NCM), lithium iron phosphate, lithium manganese iron phosphate, lithium manganate. In some embodiments, when the electrochemical device employs an LCO, NCM system, further electrochemical performance can be achieved using the electrolyte additives provided by the present application.

The positive electrode conductive agent is used for providing conductivity for the positive electrode, and can improve the conductivity of the positive electrode. The positive electrode conductive agent is a conductive material known in the art that can be used as a positive electrode active material layer. The positive electrode conductive agent may be selected from any conductive material as long as it does not cause chemical change. In some embodiments, the positive electrode conductive agent comprises at least one of a carbon-based material (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber), a metal-based material (e.g., metal powders or metal fibers including copper, nickel, aluminum, silver, etc.), a conductive polymer (e.g., a polyphenylene derivative).

The positive electrode binder is a binder known in the art that can be used as a positive electrode active material layer. The positive electrode binder may improve the binding property of the positive electrode active material particles to each other and to the positive electrode current collector. In some embodiments, the positive electrode binder comprises at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethyleneoxy-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon.

The positive electrode current collector is a metal, such as, but not limited to, aluminum foil in some embodiments.

In some embodiments, the structure of the positive electrode sheet is a structure of a positive electrode sheet that can be used in an electrochemical device as known in the art.

In some embodiments, the method of preparing the positive electrode sheet is a method of preparing a positive electrode sheet that can be used in an electrochemical device, as known in the art. In some embodiments, in the preparation of the positive electrode slurry, a positive electrode active material, a binder, and a conductive material and a thickener are added as needed, and then dissolved or dispersed in a solvent to prepare the positive electrode slurry. The solvent is volatilized during the drying process. The solvent is a solvent known in the art that can be used as the positive electrode active material layer, such as, but not limited to, N-methylpyrrolidone (NMP).

< negative plate >

The negative electrode sheet is a negative electrode sheet that can be used in an electrochemical device, as known in the art. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. In some embodiments, the anode active material layer may include an anode active material, an anode conductive agent, and an anode binder.

In some embodiments, the negative electrode active material comprises at least one of lithium metal, lithium metal alloy, transition metal oxide, carbon material, silicon-based material.

In some embodiments, the anode binder may include various polymer binders. In some embodiments, the negative electrode binder comprises at least one of a vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethyleneoxy-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon.

In some embodiments, the anode active material layer further comprises an anode conductive agent. The negative electrode conductive agent is used for providing conductivity to the negative electrode, and can improve the conductivity of the negative electrode. The anode conductive agent is a conductive material known in the art that can be used as an anode active material layer. The negative electrode conductive agent may be selected from any conductive material as long as it does not cause chemical change.

In some embodiments, the structure of the negative electrode sheet is a structure of a negative electrode sheet that can be used in an electrochemical device, as known in the art.

In some embodiments, the method of preparing the negative electrode sheet is a method of preparing a negative electrode sheet that can be used in an electrochemical device, as known in the art. In some embodiments, in the preparation of the anode slurry, the anode active material, the binder, and the conductive material and the thickener are added as needed, and then dissolved or dispersed in a solvent to prepare the anode slurry. The solvent is volatilized during the drying process. The solvent is a solvent known in the art that can be used as the anode active material layer, and is, for example, but not limited to, water. The thickener is a thickener known in the art that can be used as the anode active material layer, such as, but not limited to, sodium carboxymethyl cellulose.

< separation Membrane >

In some embodiments, the electrochemical device of the present application comprises a separator. The separator is a separator known in the art that can be used in electrochemical devices, such as, but not limited to, polyolefin-based porous membranes. In some embodiments, the substrate of the polyolefin-based porous membrane comprises a monolayer or multilayer of one or more of Polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-methyl methacrylate copolymer.

The form and thickness of the separator are not particularly limited in the present application.

The preparation method of the separator is a preparation method of a separator which can be used for an electrochemical device, which is well known in the art, for example: boehmite is mixed with polyacrylate and dissolved in deionized water to form a coating slurry, which is then uniformly coated on both surfaces of a porous substrate by a micro-gravure coating method, and dried to obtain a desired release film.

In some embodiments, the electrochemical device of the present application has a charge cutoff voltage of 4.4 to 4.8V.

[ electronic device ]

The electronic device of the present application may be any electronic device such as, but not limited to, a notebook computer, a pen-type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD, a mini-compact disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable audio recorder, a radio, a standby power supply, a motor, an automobile, a motorcycle, a power assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flash lamp, a camera, a household large-sized battery, a lithium ion capacitor. It is noted that the electrochemical device of the present application is applicable to energy storage power stations, marine vehicles, and air vehicles in addition to the above-listed electronic devices. The air carrier comprises an air carrier within the atmosphere and an air carrier outside the atmosphere.

In some embodiments, an electronic device comprises an electrochemical device according to the present application.

The application is further illustrated by the following examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. In the following specific embodiments of the present application, only an embodiment in which the battery is a lithium ion battery is shown, but the present application is not limited thereto. In the following examples and comparative examples, reagents, materials and the like used were commercially available or synthetically obtained unless otherwise specified.

The lithium ion batteries of examples and comparative examples were each prepared as follows.

1) Preparation of positive plate

Lithium cobalt oxide (LiCoO) as a positive electrode active material ₂ ) Mixing a conductive agent Super P and a binder polyvinylidene fluoride according to a weight ratio of 97.9:0.4:1.7, adding N-methylpyrrolidone (NMP), and uniformly stirring under the action of a vacuum stirrer to obtain positive electrode slurry; uniformly coating the anode slurry on an anode current collector aluminum foil; and drying the aluminum foil, cold pressing, cutting and slitting, and drying under vacuum conditions to obtain the positive plate.

2) Preparation of negative electrode sheet

Mixing negative active material artificial graphite, thickener sodium carboxymethylcellulose (CMC) and binder styrene-butadiene rubber (SBR) according to a weight ratio of 97:1:2, adding deionized water, and obtaining negative slurry under the action of a vacuum stirrer; uniformly coating the negative electrode slurry on a negative electrode current collector copper foil; and drying the copper foil, and then carrying out cold pressing, cutting and slitting, and drying under a vacuum condition to obtain the negative plate.

3) Preparation of a separator film

Boehmite was mixed with polyacrylate and dissolved in deionized water to form a coating slurry. The coating slurry is then uniformly coated on both surfaces of a polyethylene porous substrate by a gravure coating method, and dried to obtain a desired release film.

4) Preparation of electrolyte

In a dry argon atmosphere glove box, EC (ethylene carbonate): PC (propylene carbonate): DEC (diethyl carbonate) =2:2:6 by weight was used as a base solvent, and the components were added at the contents according to tables 1 to 5, dissolved and stirred well, and then lithium salt LiPF was added ₆ Evenly mixing to obtain LiPF ₆ The content of (3) is 1 mol/L. Wherein, the contents of all components in the table are weight percentages calculated based on the weight of the electrolyte.

5) Preparation of lithium ion batteries

Sequentially stacking the positive plate, the isolating film and the negative plate, enabling the isolating film to be positioned between the positive plate and the negative plate to play a role of isolation, and then winding to obtain a bare cell; and (3) placing the bare cell in an aluminum plastic film of an outer packaging foil after welding the tab, injecting the prepared electrolyte into the dried bare cell, and performing procedures such as vacuum packaging, standing, formation, shaping, capacity testing and the like to obtain the soft-package lithium ion battery.

Next, a performance test process of the lithium ion battery will be described.

(1) High temperature cycle performance test of lithium ion battery

And placing the lithium ion battery in a 45 ℃ incubator, and standing for 30min to keep the lithium ion battery at a constant temperature. Charging the constant temperature-reached lithium ion battery to a voltage of 4.45V at a constant current of 1C, then charging to a current of 0.025C at a constant voltage of 4.45V, and then discharging to a voltage of 3.0V at a constant current of 1C, which is a charge-discharge cycle, recording the first discharge capacity Q ₁ . The test was stopped after 400 charge and discharge cycles in the above manner, and the discharge capacity Q after the cycle was recorded ₂ . The capacity retention after high temperature cycling can be obtained by: high-temperature cycle capacity retention = post-cycle discharge capacity Q ₂ First discharge capacity Q ₁ ×100％。

(2) Cyclic impedance growth rate test for lithium ion batteries

The lithium ion battery is placed in a constant temperature box at 25 ℃ and kept stand for 1 hour. The lithium ion battery was charged to 4.45V at a constant current of 1C, charged to a current of 0.025C at a constant voltage, left for 120min, then charged for 10 seconds at 0.1C and charged for 360 seconds at 1C, and then the direct current impedance of the lithium ion battery at 80% state of charge (SOC) was recorded. And (3) carrying out charge and discharge circulation for 400 times according to the standard in the high-temperature circulation performance test of the lithium ion battery (1), and then measuring and recording the direct current impedance of the lithium ion battery at the state of charge (SOC) of 80% by using the measuring method. The direct current impedance of the lithium ion battery is calculated by the following steps: dc impedance= (0.1C discharge end voltage-1C discharge end voltage)/(0.1C discharge end current-1C discharge end current). The cyclic impedance growth rate of the lithium ion battery was calculated by the following formula: cycle impedance increase rate= (direct current impedance of lithium ion battery after cycle-direct current impedance of lithium ion battery before cycle)/direct current impedance of lithium ion battery before cycle x 100%.

The relevant parameters of the lithium ion batteries of examples and comparative examples and the performance test results of the lithium ion batteries are shown in tables 1 to 5.

Among them, table 1 shows the effect of the compound represented by formula (I) on the high temperature cycle performance and cycle resistance increase rate of the lithium ion battery.

Table 2 shows the effect of the content of the compound represented by formula (I) in the electrolyte on the high-temperature cycle performance and the cycle resistance increase rate of the lithium ion battery.

Table 3 shows the effect of the content relationship of the additive B with the compound represented by formula (I) on the high temperature cycle performance and the cycle resistance increase rate of the lithium ion battery.

Table 4 shows the effect of the content relationship of the carboxylate solvent to the compound represented by formula (I) on the high-temperature cycle performance and the cycle resistance increase rate of the lithium ion battery.

Table 5 shows the effect of the combination of additive C and the compound represented by formula (I) on the high temperature cycle performance and cycle resistance increase rate of the lithium ion battery.

TABLE 1

Note that: "/" indicates a substance to which the component is not added.

The performance test results of table 1 show that the addition of the compound represented by formula (I) to the electrolyte can significantly improve the high temperature cycle performance of the lithium ion battery and significantly reduce the cycle resistance increase thereof. Compared with comparative examples 1-2, the compound represented by formula (I) has more obvious high-temperature cycle improving effect than the single furfural compound, because the heterocycle containing nitrogen, sulfur and oxygen atoms, which is branched on the furfural, can enrich LiN and Li of SEI _x S and Li _x SO _y And the like, so that the compound formed by combining the heterocycle and the furfural has better high-voltage stability than the lithium alkoxide organic component generated by single furfural. As is clear from examples 1-1 to 1-9, the formula (I-4) has relatively good effects on the improvement of the high temperature cycle capacity retention rate and the reduction of the impedance increase, and then the formula (I-2) and the formula (II)I-3) this is probably due to the branched heterocyclic groups which are not preferred to be too large, otherwise the steric hindrance is large, which affects the compact stability of the film formation.

TABLE 2

Note that: "/" indicates a substance to which the component is not added.

The performance test results of table 2 show that when the content of the compound represented by formula (I) in the electrolyte is in the range of 0.02% to 7%, it contributes to further improving the high-temperature cycle performance of the lithium ion battery and reducing the cycle resistance increase rate thereof. When the content of the compound represented by the formula (I) in the electrolyte is in the range of 0.5% to 3%, the improvement of the high-temperature cycle performance and the cycle resistance increase rate of the lithium ion battery is particularly remarkable. When the content of the compound shown in the formula (I) is lower than 0.02%, the improvement of the high-temperature cycle performance of the lithium battery under high voltage is not obvious; when the content of the compound represented by the formula (I) is higher than 7%, the compound in the electrolyte is excessive, which results in a large interfacial film resistance, causing irreversible lithium precipitation, obstructing the ion transport path of the electrolyte, and accelerating the decay of the battery capacity.

TABLE 3 Table 3

Note that: "/" indicates a substance to which the component is not added.

The results of the performance test in Table 3 show that when the electrolyte contains additive B (at least one of fluoroethylene carbonate (FEC), vinylene Carbonate (VC)) and the content m% of the first additive satisfies-1.ltoreq.k+m-n.ltoreq.12 with the content n% of the compound represented by formula (I), the lithium ion battery has significantly improved high temperature cycle performance and significantly reduced cycle resistance increase rate. And a proper amount of FEC and VC, which are matched with the compound of the formula (I), can further enrich the LiF composition in the SEI film. Therefore, the combination of FEC and VC with the compound of formula (I) at a proper content has a significant improvement effect on the stability of the negative electrode in the high-temperature cycle of the lithium ion battery, but when the relative content of FEC and VC is high, the high-temperature cycle performance of the lithium ion battery is adversely affected, probably due to the fact that FEC and VC are easily oxidized and decomposed to generate gas at a high voltage, and the excessively high relative addition amount thereof makes the additive composition unable to form a combined electrolyte interface with good protection effect on the electrode sheet and good electrolyte ion channel. The combined use of FEC, VC and the compound represented by formula (I) can further enhance the film forming stability of the electrochemical device at a negative electrode under high voltage, inhibit the increase of impedance through synergistic effect and improve the cycle performance of the lithium ion battery under high voltage.

TABLE 4 Table 4

Note that: "/" indicates a substance to which the component is not added.

The results of the performance test of table 4 show that when the electrolyte contains a carboxylate, it helps to further improve the high temperature cycle performance of the lithium ion battery and reduce the cycle resistance increase rate thereof. When the content a% of the carboxylic ester and the content n% of the compound represented by the formula (I) are 0.05-0.1, the improvement on the high-temperature cycle performance and the cycle impedance growth rate of the lithium ion battery is particularly obvious. The carboxylic ester is introduced, so that the viscosity of the electrolyte can be effectively reduced, the lithium ion transmission is facilitated, the film forming impedance is reduced, but the excessive carboxylic ester is easily oxidized and decomposed under high voltage, and is not beneficial to maintaining the lithium ion transmission in the circulation. By combining the compound shown in the formula (I) in a certain content ratio, the impedance increase can be further inhibited through synergistic effect, and the cycle performance of the lithium ion battery under high voltage is improved.

TABLE 5

Note that: "/" indicates a substance to which the component is not added.

The performance test results of table 5 show that when the electrolyte contains the nitrile compound, the high-temperature cycle performance of the lithium ion battery is further improved and the cycle resistance increase rate of the lithium ion battery is reduced, because the nitrile compound can form an organic protective layer on the surface of the positive electrode, and organic molecules on the surface of the positive electrode can well separate easily-oxidized components in the electrolyte from the surface of the positive electrode, so that on one hand, the oxidation effect of the surface of the positive electrode on the electrolyte under high voltage is reduced, and on the other hand, the structural damage caused by excessive oxygen release of the transition metal oxide of the positive electrode is reduced. The improvement of the high-temperature cycle performance and the cycle resistance increase rate of the lithium ion battery is particularly obvious when the nitrile content is 0.5 to 5 percent.

As can be seen from examples 5 to 20, examples 5 to 24, comparative examples 2 to 4 and examples 5 to 22, when a proper amount of sulfonate compound is further added to the electrolyte, the electrolyte has a remarkable improvement effect on the high-temperature cycle performance and the resistance increase rate of the lithium ion battery.

By comparing examples 5-20 to 5-24 with examples 2-4, examples 3-13, examples 3-14 and examples 5-18, it is known that the stability of the positive and negative electrolyte interfaces of lithium ion batteries in a high voltage system can be improved by using one or more of fluoroethylene carbonate, vinylene carbonate, carboxylate, nitrile compound or thiooxidative double bond compound in a suitable range on the basis of including the compound of formula (I) in the electrolyte, thereby improving the high temperature cycle performance of lithium ion batteries and inhibiting the increase of impedance.

While the application has been described in terms of preferred embodiments, it will be understood by those skilled in the art that various changes and modifications can be made without departing from the scope of the application, and it is intended to cover the principles of the application as defined in the appended claims.

Claims

1. An electrolyte, which comprises a compound represented by the formula (I),

in formula (I), R ₁₁ Selected from covalent bonds, sulfur, C ₁ -C ₅ An alkyleneoxy group;

R ₁₂ selected from covalent bonds, C ₁ -C ₁₀ Alkylene or C ₁ -C ₁₀ Hydrocarbylsulfonyl, said hydrocarbylene comprising arylene;

x is selected from substituted or unsubstituted C ₁ -C ₁₀ A heterocyclic group containing at least one of oxygen and nitrogen atoms; when substituted, the substituents include hydrocarbyl groups, including alkyl groups; the heterocycle comprises at least one of cyclic ether, morpholine, pyridine and triazole;

wherein the content of the compound represented by the formula (I) is n%, based on the weight of the electrolyte, and n is more than or equal to 0.02 and less than or equal to 7.

2. The electrolyte according to claim 1, wherein the compound represented by formula (I) includes at least one of compounds represented by formulas (I-1) to (I-7);

3. the electrolyte of claim 1, wherein the electrolyte further comprises at least one of fluoroethylene carbonate, vinylene carbonate;

based on the weight of the electrolyte, the content of fluoroethylene carbonate is k percent, the content of vinylene carbonate is m percent, wherein k is more than or equal to 0, m is more than or equal to 0, k+m is more than 0, and k, m and n are more than or equal to-1 and less than or equal to k+m-n and less than or equal to 12.

4. The electrolyte of claim 1, wherein the electrolyte further comprises a carboxylate; based on the weight of the electrolyte, the content of the carboxylic ester is a%, a is more than or equal to 5 and less than or equal to 30, and a and n satisfy the relation: n/a is more than or equal to 0.0005 and less than or equal to 0.7.

5. The electrolyte of claim 4, wherein the carboxylic acid ester comprises at least one of ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, butyl propionate.

6. The electrolyte of any one of claims 1-5, wherein the electrolyte further comprises at least one of 1, 3-propane sultone, 2, 4-butane sultone, or nitrile compound.

7. The electrolyte according to claim 6, wherein the nitrile compound includes at least one of compounds represented by formulas (ii) to (v);

N≡C-R ₂₁ -C≡N type (II)

Wherein R is ₂₁ Selected from substituted or unsubstituted C ₁ -C ₁₂ Alkylene, substituted or unsubstituted C ₁ -C ₁₂ An alkyleneoxy group;

R ₃₁ 、R ₃₂ each independently selected from the group consisting of covalent bonds, substituted or unsubstituted C ₁ -C ₁₂ An alkylene group;

R ₄₁ 、R ₄₂ 、R ₄₃ each independently selected from the group consisting of covalent bonds, substituted or unsubstituted C ₁ -C ₁₂ Alkylene, substituted or unsubstituted C ₁ -C ₁₂ Alkyloxy group；

R ₅₁ Selected from substituted or unsubstituted C ₁ -C ₁₂ Alkylene, substituted or unsubstituted C ₂ -C ₁₂ Alkenylene, substituted or unsubstituted C ₆ -C ₁₂ Arylene, substituted or unsubstituted C ₃ -C ₁₂ A cyclic subunit;

wherein when substituted, the substituent is halogen.

8. The electrolyte of claim 7, wherein the nitrile compound comprises at least one of the following compounds;

9. an electrochemical device comprising a positive electrode, a negative electrode, a separator, and the electrolyte according to any one of claims 1 to 8.

10. The electrochemical device according to claim 9, wherein a charge cutoff voltage of the electrochemical device is 4.4 to 4.8V.

11. An electronic device comprising the electrochemical device according to any one of claims 9-10.