CN114207903A

CN114207903A - Electrolytes, electrochemical devices, and electronic devices

Info

Publication number: CN114207903A
Application number: CN202180004733.0A
Authority: CN
Inventors: 王翔; 刘奥; 唐超; 崔辉
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-03-31
Filing date: 2021-03-31
Publication date: 2022-03-18
Also published as: WO2022205172A1

Abstract

本申请提供了一种电解液、电化学装置以及电子装置。所述电解液包括式(I)表示的化合物；在式(I)中，X选自经取代或未经取代基的酸酐；经取代时，取代基包括烷基、芳基、酰氧基、醛基、氰基或卤素中的至少一种。所述电解液可以显著改善所述电化学装置在4.4至4.8V高电压下的高温循环性能。

The present application provides an electrolyte, an electrochemical device, and an electronic device. The electrolyte includes a compound represented by formula (I); in formula (I), X is selected from substituted or unsubstituted acid anhydrides; when substituted, the substituents include alkyl, aryl, acyloxy, At least one of aldehyde group, cyano group or halogen. The electrolyte can significantly improve the high temperature cycling performance of the electrochemical device at a high voltage of 4.4 to 4.8V.

Description

Electrolyte solution, electrochemical device, and electronic device

Technical Field

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

Background

With the recent weight reduction and size reduction of electrical products, increasing the energy density of electrochemical devices (for example, lithium ion batteries) has become an important development direction of lithium ion batteries, and increasing the design use upper limit voltage is an important way to increase the energy density thereof. The rated voltage of the lithium ion battery of the lithium cobaltate system can reach 4.45V to 4.5V at present, which means that the battery needs to realize storage and charge and discharge under high voltage, so the damage to the positive electrode structure and the negative electrode structure is increasingly serious, and higher requirements are provided for the oxidation resistance and the film forming stability of the electrolyte.

Therefore, how to develop an electrolyte additive capable of improving the cycle performance of a battery 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), X is selected from substituted or unsubstituted anhydrides; when substituted, the substituent includes at least one of alkyl, aryl, acyloxy, aldehyde, cyano, or halogen.

In some embodiments, the anhydride is selected from at least one of succinic anhydride, maleic anhydride, benzomaleic anhydride, glutaric anhydride, benzoglutaric anhydride, crotonic anhydride, chlamydia anhydride, itaconic anhydride, phthalic anhydride, benzoic anhydride, methyl acetic anhydride, propionic anhydride, butyric anhydride, or hydrogenated nadic anhydride.

In some embodiments, the compound represented by formula (I) includes at least one of compounds represented by formulae (I-1) to (I-8);

in some embodiments, the compound represented by formula (I) is present in an amount of n%, 0.05. ltoreq. n.ltoreq.5, based on the weight of the electrolyte.

In some embodiments, the compound represented by formula (I) is contained in an amount of 0.1% to 3% 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%, the content of vinylene carbonate is m%, 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 meet the condition that k + m + n is more than or equal to 1 and less than or equal to 15; in some embodiments, 3 ≦ k + m + n ≦ 15.

In some embodiments, 0 < k + m ≦ 14.

In some embodiments, the electrolyte further comprises a carboxylic acid ester; 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 60, 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, the content of the carboxylic acid ester is 50% or less based on the weight of the electrolyte, and the ratio of the content of the compound of formula (I) to the content of the carboxylic acid ester is 0.02 to 0.2.

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

In some embodiments, the electrolyte further includes 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, methyl ethyl sulfone.

In some embodiments, the sum of the contents of the sulfonate-based compound and the nitrile-based compound is 0.1% to 15% based on the weight of the electrolyte.

In some embodiments, the sum of the contents of the sulfonate-based compound and the nitrile-based compound is 3% to 10% based on the weight of the electrolyte.

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) through formula (v);

wherein R is₂₁Selected from substituted or unsubstituted C₁-C₁₂Alkylene, substituted or unsubstituted C₁-C₁₂An alkyleneoxy group; r₃₁、R₃₂Each independently selected from the group consisting of a single bond, substituted or unsubstituted C₁-C₁₂An alkylene group; r₄₁、R₄₂、R₄₃Each independently selected from the group consisting of a single bond, substituted or unsubstituted C₁-C₁₂Alkylene, substituted or unsubstituted C₁-C₁₂An alkyleneoxy group; r₅₁Selected from substituted or unsubstituted C₁-C₁₂Alkylene, substituted or unsubstituted C₂-C₁₂Alkenylene, substituted or unsubstituted C₆-C₁₂Arylene, substituted or unsubstituted C₃-C₁₂A cyclic idene group; 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 the electrolyte in an amount of b% by weight, 0.1. ltoreq. b.ltoreq.10, based on the weight of the electrolyte.

In some embodiments, the nitrile compound is present in the electrolyte in an amount of 0.5% to 7% by weight, based on the weight of the electrolyte.

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

In some embodiments, the end-of-charge voltage of the electrochemical device is 4.4V to 4.8V

Further, the present application also provides an electronic device comprising the electrochemical device described herein.

The electrolyte provided by the application can remarkably improve the high-temperature cycle performance of an electrochemical device using the electrolyte under the high voltage of 4.4-4.8V.

Detailed Description

It is to be understood that the disclosed embodiments are merely exemplary of the application that may be embodied in various forms and that 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 groups in the compounds may be substituted or unsubstituted.

In the description of the present application, alkyleneoxy is a divalent group formed by an ether that has two hydrogen atoms removed, which ether may contain one or more ether linkages.

In the description of the present application, terms, substitutions in structural formulae, and the like, which are not explicitly described, should be understood in accordance with conventional, customary means or manners known to those of ordinary skill in the art.

The electrolyte solution, electrochemical device and electronic device according to the present invention will be described in detail below.

[ electrolyte ]

< additive A >

In some embodiments, the electrolyte contains an additive A, wherein the additive A is a compound represented by formula (I), and in the formula (I), X is selected from substituted or unsubstituted acid anhydride; when substituted, the substituent includes at least one of alkyl, aryl, acyloxy, aldehyde, cyano, or halogen.

In the electrolyte, the additive A is a bridging substance of phthalimide and anhydride, wherein the anhydride can form an SEI film after being reduced, the protection effect on graphite or silicon negative electrodes is obvious, and the phthalimide has a positive electrode complexing transition metal oxide and can inhibit the contact of a solvent and a positive electrode active substance. When two monomer groups are bridged at the molecular level, compared with a monomer, the high-temperature long-cycle electrochemical device has smaller impedance and stronger high-temperature stability, and can realize stable high-temperature long-cycle performance of the electrochemical device under the high voltage of more than 4.4V.

In some embodiments, the compound represented by formula (I) includes at least one of the compounds represented by formulas (I-1) to (I-8):

in some embodiments, the content of the compound represented by formula (I) is n%, 0.05. ltoreq. n.ltoreq.5, based on the weight of the electrolyte, and when the content of the compound represented by formula (I) is too low, the formed protective film is insufficient and the improvement of the performance of the electrochemical device is insignificant; when the content of the compound represented by formula (I) is too high, the resistance of the formed film is large, which may affect the cycle performance of the electrochemical device. In some embodiments, the compound represented by formula (I) is contained in an amount of 0.1% to 3% based on the weight of the electrolyte.

< additive B >

In some embodiments, the electrolyte may further include an additive B, and the additive B is at least one of fluoroethylene carbonate (FEC) and Vinylene Carbonate (VC).

The additive B and the additive A can form a good solid interface dielectric layer (SEI) on the negative electrode, and the composite use of the additive B and the additive A is favorable for the composite generation of an organic layer and an inorganic layer, and the stability of the SEI is enhanced.

In some embodiments, based on the weight of the electrolyte, the content of fluoroethylene carbonate is k% and the content of vinylene carbonate is m%, 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 satisfy 1 is more than or equal to k + m + n and is less than or equal to 15, in some embodiments, 3 is more than or equal to k + m + n and is less than or equal to 15, when the total content of additive B and additive A is too low, the two can not be compounded to form an effective electrolyte interface protective film, and the performance of the lithium ion battery is not obviously improved; when the total content of the additive B and the additive A is too high, on one hand, the formed film has large resistance and can affect the cycle performance of an electrochemical device, and on the other hand, the fluoroethylene carbonate and/or vinylene carbonate can be decomposed and generate gas at the positive electrode, thereby affecting the cycle thickness expansion rate. In some embodiments, 0 < k + m ≦ 14.

< additive C >

In some embodiments, the electrolyte may further include an additive C, and the additive C is at least one of a sulfonate compound or a nitrile compound.

In some embodiments, the sum of the contents of the sulfonate-based compound and the nitrile-based compound is 0.1% to 15% based on the weight of the electrolyte. On the basis of adding a proper amount of the compound shown in the formula I, when the sum of the contents of the sulfonate compound and the nitrile compound is 3-10%, the film forming stability of the anode and the cathode of the lithium ion battery can be effectively improved, so that the high-temperature performance of the battery is improved. If the value of c is too small, no effective synergistic effect with the compound of formula I can be achieved, and if the value of c is too large, the cycle performance of the battery is affected to some extent.

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

< organic solvent >

In some embodiments, the electrolyte further comprises an organic solvent. The organic solvent is an organic solvent known in the art to be suitable for an electrochemical device, and for example, a nonaqueous organic solvent is generally used. In some embodiments, the non-aqueous organic solvent comprises at least one of a carbonate-based solvent, a carboxylate-based solvent. In some embodiments, the organic solvent content is 20% to 90% by weight of the electrolyte.

In some embodiments, the carbonate-based solvent comprises a cyclic ester and a chain ester. In some embodiments, the cyclic ester-based solvent comprises at least one of Ethylene Carbonate (EC), Propylene Carbonate (PC), γ -Butyrolactone (BL), butylene carbonate. In some embodiments, the chain ester solvent comprises at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), propyl ethyl carbonate, fluoro ethyl methyl carbonate, fluoro dimethyl carbonate, fluoro diethyl carbonate, and the like. In some embodiments, the atoms on the carbonate may be substituted, the substituents comprising halogen atoms.

In some embodiments, the carboxylate-based solvent comprises at least one of Ethyl Acetate (EA), Propyl Acetate (PA), Butyl Acetate (BA), Ethyl Propionate (EP), Propyl Propionate (PP), or Butyl Propionate (BP).

In some embodiments, the content of the carboxylic acid ester is a%, 5. ltoreq. a.ltoreq.60, based on the weight of the electrolyte, and a and n satisfy the relationship when the compound represented by formula (I) is contained in the electrolyte in a mass content of n%: n/a is more than or equal to 0.0005 and less than or equal to 0.7, if the n/a ratio is lower, the protection of the positive electrode of the electrolyte is insufficient, and the solvent is easy to decompose to generate gas; if the n/a ratio is too high, the resistance of the formed films of the anode and the cathode is large, a smooth lithium ion transmission channel cannot be provided, and the charge and discharge performance is influenced. In some embodiments, the content of the carboxylic acid ester is 50% or less based on the weight of the electrolyte, and the ratio of the content of the compound of formula (I) to the content of the carboxylic acid ester is 0.02 to 0.2.

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

< electrolyte salt >

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

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

In some embodiments, the lithium salt comprises LiPF₆、LiBF₄、LiB(C₆H₅)₄、LiCH₃SO₃、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiC(SO₂CF₃)₃、LiSiF₆At least one of LiBOB and LiDFOB, preferably LiPF₆。

In the present application, the content of the electrolyte is not particularly limited, and may be reasonably added according to actual needs. In the present application, the preparation method of the electrolyte is not limited, and can be prepared according to a conventional preparation method of the 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 and sodium ion batteries. In particular, the electrochemical device is a lithium secondary battery.

In some embodiments, the electrochemical device comprises a positive electrode tab, a negative electrode tab, a separator, and an electrolyte as described herein before.

< Positive electrode sheet >

The positive electrode tab is a positive electrode tab known in the art that can be used in an electrochemical device. 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.

The positive electrode active material comprises at least one lithiated intercalation compound capable of reversibly intercalating and deintercalating lithium ions. In some embodiments, the positive electrode active material comprises a composite oxide. In some embodiments, the composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

In some embodiments, the positive active material is selected from lithium cobaltate (LiCoO)₂) Lithium Nickel Cobalt Manganese (NCM) ternary material, lithium iron phosphate (LiFePO)₄) Lithium manganate (LiMn)₂O₄) Or any combination thereof.

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 a chemical change. In some embodiments, the positive electrode conductive agent includes 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 powder or metal fiber 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 binding properties between the positive electrode active material particles and 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, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon.

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

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

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

< negative electrode sheet >

The negative electrode tab is a negative electrode tab known in the art that may be used in an electrochemical device. 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 active material includes at least one of lithium metal, lithium metal alloy, transition metal oxide, carbon material, and silicon-based material.

In some embodiments, the negative electrode binder may comprise various polymeric binders. In some embodiments, the negative electrode binder comprises at least one of 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, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon.

In some embodiments, the negative electrode active material layer further includes a negative electrode 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 negative electrode conductive agent is a conductive material known in the art that can be used as a negative electrode active material layer. The negative electrode conductive agent may be selected from any conductive material as long as it does not cause a chemical change.

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

< isolation film >

In some embodiments, the electrochemical devices of the present application comprise a separator. The separator is a separator known in the art that can be used for an electrochemical device, such as, but not limited to, polyolefin porous films. In some embodiments, the polyolefin porous film substrate comprises a single layer or multiple layers of one or more of Polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methyl methacrylate copolymer.

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

The method of preparing the separator is a method of preparing a separator that can be used in 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 dimple coating method, and subjected to a drying process to obtain a desired separator.

In some embodiments, an electrochemical device comprises an electrolyte as described herein.

In some embodiments, the electrochemical device comprises an electrolyte as described herein and the electrochemical device has an end-of-charge voltage of 4.4V to 4.8V.

In some embodiments, when the electrochemical device comprises the electrolyte described herein, the positive active material comprises at least one of LCO and NCM, and the negative electrode employs a Gr, Si system, further electrochemical performance can be obtained.

[ 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-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium ion capacitor. Note that the electrochemical device of the present application is applicable to an energy storage power station, a marine vehicle, and an air vehicle, in addition to the above-listed electronic devices. The air transport carrier device comprises an air transport carrier device in the atmosphere and an air transport carrier device outside the atmosphere.

In some embodiments, an electronic device comprises an electrochemical device described herein.

The present application is further illustrated below with reference to examples. It should be understood that these examples are for illustrative purposes only 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 prepared as follows.

1) Preparation of positive plate

The positive electrode active material lithium cobaltate (LiCoO)₂) Conductive agent Super P, adhesive polyvinylidene fluorideMixing vinyl fluoride according to the weight ratio of 98:0.4:1.6, adding N-methyl pyrrolidone (NMP), and uniformly stirring under the action of a vacuum stirrer to obtain anode slurry; uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil; and drying the aluminum foil, then carrying out cold pressing, cutting and slitting, and drying under a vacuum condition to obtain the positive plate.

2) Preparation of negative plate

Mixing the negative active material artificial graphite, the thickener sodium carboxymethyl cellulose (CMC) and the binder Styrene Butadiene Rubber (SBR) according to the 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 copper foil of a negative electrode current collector; and drying the copper foil, then carrying out cold pressing, cutting and slitting, and drying under a vacuum condition to obtain the negative plate.

3) Preparation of the separator

Boehmite was mixed with polyacrylate and dissolved into deionized water to form a coating slurry. And then uniformly coating the coating slurry on two surfaces of the polyethylene porous substrate by using a micro-gravure coating method, and drying to obtain the required separation film.

4) Preparation of the electrolyte

In a dry argon atmosphere glove box, the components were added using EC (ethylene carbonate): PC (propylene carbonate): DEC (diethyl carbonate) ═ 2:2:6 as the base solvent, with the contents of tables 1 to 4 being referred to, dissolved and fully stirred, and then the lithium salt LiPF was added₆Mixing uniformly to obtain LiPF₆The content of (b) is 1 mol/L. Specific kinds and contents of the solvents and additives used in the electrolyte are shown in tables 1 to 4, wherein the contents of the components in the tables are mass percentages calculated based on the mass of the electrolyte.

It should be noted that: wherein the examples in Table 3 are set based on examples 2-11, the differences from examples 2-11 are listed in Table 3; the examples in Table 4 are set based on examples 3-17, and the differences from examples 3-17 are listed in Table 4.

5) Preparation of lithium ion battery

Stacking the positive plate, the isolating film and the negative plate in sequence to enable the isolating film to be positioned between the positive plate and the negative plate to play an isolating role, and then winding to obtain a bare cell; and (3) after welding a tab, placing the naked electric core into an outer packaging foil aluminum-plastic film, injecting the prepared electrolyte into the dried naked electric core, and performing vacuum packaging, standing, formation, shaping, capacity test and other processes to obtain the soft package lithium ion battery.

The following describes the high-voltage, high-temperature cycle performance testing process of the lithium ion battery.

And (3) placing the lithium ion battery in a constant temperature box at 45 ℃ and standing for 30min to keep the temperature of the lithium ion battery constant. Charging the lithium ion battery reaching the constant temperature to 4.5V at a constant current of 0.7C, then charging the lithium ion battery to 0.025C at a constant voltage of 4.5V, testing the battery by a micrometer, and recording the thickness of the battery as D₀Then, the mixture was discharged at a constant current of 1C to a voltage of 3.0V, which was 1 charge-discharge cycle. Taking the first discharge capacity as 100%, repeating the charge-discharge cycle for 300 circles, stopping the test, and recording the thickness D of the battery when fully charged_nAnd the cycle capacity retention rate is used as an index for evaluating the cycle performance of the lithium ion battery.

Wherein, (1) the cycle capacity retention ratio is the capacity at the time of cycle to a certain round/the capacity at the time of first discharge × 100%; (2) thickness expansion ratio ═ D_n-D₀)/D₀×100％。

Relevant parameters of the lithium ion batteries of the examples and comparative examples and performance test results of the lithium ion batteries are shown in tables 1 to 4.

Wherein, table 1 shows the effect of the compound represented by formula (I) in the electrolyte on the high-voltage and high-temperature cycle performance of the lithium ion battery.

Table 2 shows the effect of the content relationship between the compound represented by formula (I) in the electrolyte and the carbonate additive on the high-pressure and high-temperature cycle performance of the lithium ion battery.

Table 3 shows the effect of the content relationship between the compound represented by formula (I) in the electrolyte and the carboxylate solvent on the high-voltage and high-temperature cycle performance of the lithium ion battery.

Table 4 shows the effect of the content relationship between the compound represented by formula (I) and the nitrile compound on the high-voltage and high-temperature cycle performance of the lithium ion battery.

TABLE 1

Note: "\\" indicates a substance to which the component was not added.

Referring to table 1, it can be seen from comparative examples 1 to 1 that when the compound of formula I is not added to the electrolyte, the high-temperature cycle capacity retention rate of the lithium ion battery is poor, the thickness growth rate is high, and the high-temperature cycle performance of the lithium ion battery at high voltage is poor. From comparative examples 1-1 to 1-3 and examples 1-4, it can be seen that the compound of formula I provided herein has more excellent high-temperature cycle capacity retention and thickness growth inhibition than the low-voltage system additives phthalimide and glutaric anhydride for lithium ion batteries. The two monomer groups are bridged at the molecular level, so that when the electrolyte is used as an additive in an electrolyte, a protective layer formed on a positive electrode and a negative electrode is more stable, the generation of byproducts is effectively inhibited, the structural stability of a positive electrode active substance is protected, and high-temperature long circulation is realized at high voltage of more than 4.4V.

By comparing examples 1-1 to examples 1-25 with comparative example 1-1, it can be seen that, when the compound of formula I is added to the electrolyte, the capacity retention rate of the lithium ion battery after cycling for 300 cycles at high temperature and high voltage is increased, and the thickness growth rate is reduced significantly, that is, the high-temperature cycle performance of the lithium ion battery at high voltage can be improved by adding the compound of formula I to the electrolyte. The multi-group in the compound shown in the formula I participates in the film formation of the electrode interface of the lithium ion battery, so that the failure of the anode and cathode solid electrolyte interface film can be effectively delayed in high-temperature storage, the decomposition and gas generation of electrolyte can be inhibited, and the high-temperature cycle performance of the lithium ion battery is improved.

From the performance test results of examples 1-1 to 1-7, it can be seen that the mass percentage of the compound represented by formula I in the electrolyte of example 1-1 is only 0.05%, the mass content of the compound represented by formula I is too small, the stability of the positive and negative electrode protective films is insufficient, the retention rate of the cycle capacity of the lithium ion battery at high temperature and high cut-off voltage is not significantly improved compared with that of comparative example 1-1, and the performance is poor compared with that of examples 1-2 to 1-6. The mass percentage of the compound represented by formula I in the electrolytes of examples 1 to 7 was 6%, and the mass content of the compound represented by formula I was too large, which resulted in a large film resistance, and irreversible lithium deposition, which in turn possibly hindered the ion transport channel of the electrolyte and accelerated capacity fade.

According to the performance test results of the examples 1-1 to 1-7, when the mass content of the compound shown in the formula I in the electrolyte is 0.05% to 5%, the comprehensive performance of the lithium ion battery under high temperature and high cut-off voltage is remarkably improved. The reason is that the compound shown in the formula I with proper content participates in film formation of the positive electrode and the negative electrode, so that the stability of the SEI film is improved, and the accumulation of reaction byproducts at high voltage and high temperature is favorably inhibited. Therefore, in some embodiments of the present application, the amount percentage content of the compound represented by formula I in the electrolyte is 0.05% to 5%, and further preferably, the mass percentage content of the compound represented by formula I in the electrolyte is 0.5% to 3%.

As can be seen from the performance test results of examples 1-1 to 1-25, when the compound shown in formula I is specifically the compound shown in formula I-1 or I-3, I-6, the performance improvement effect on the lithium ion battery is better.

TABLE 2

Note: "\\" indicates a substance to which the component was not added.

Referring to table 2, it can be seen from comparative analysis of the data of examples 1 to 4 and 2 to 1 to 2 to 13 that when 0.5% to 14% of fluoroethylene carbonate (FEC) and Vinylene Carbonate (VC) are added to the electrolyte, the retention ratio of the cycle capacity of the lithium ion battery at high temperature and high charge cut-off voltage is increased. In comparison with comparative example 2-1, it is found that FEC, VC and the compound represented by formula I act synergistically to further suppress the increase in thickness, indicating the retention rate of the circulating capacity.

From the analysis of the data of comparative example 1-1, example 2-1 to example 2-13, it can be seen that when the total amount of the carbonate additive and the compound of formula I is 1% to 15%, the cycle performance of the lithium ion battery at high voltage is improved to a different extent than when the two types of materials are not used, and when the content of the carbonate additive and the compound of formula I in the electrolyte is controlled to be 3% to 15% by mass, the performance improvement effect on the lithium ion battery is the best.

TABLE 3

Note: "/" indicates that the component was not added.

Referring to Table 3, by analyzing the data of comparative example 3-1, example 2-9, and examples 3-1 to 3-19: in cooperation with the compound additive shown in the formula I, a certain content of carboxylic ester has an effect of improving the high-temperature cycle capacity and thickness increase of the lithium ion battery, wherein the improvement effect of ethyl propionate and propyl propionate is better than that of ethyl acetate.

By analyzing comparative examples 3-11 to comparative examples 3-16: by adjusting the type and the content of the carboxylic ester, when the total amount of the carboxylic ester is less than 50%, the compound additive I is combined according to a certain proportion, so that the capacity retention ratio and gas generation of the lithium ion battery after high-voltage high-temperature circulation can be further improved.

TABLE 4

Note: "/" indicates that the component was not added.

Referring to table 4, it can be seen from the analysis of the data of comparative example 3-1, comparative example 4-2, example 3-17, and example 4-1 to example 4-20 that when a nitrile compound and a sulfonate compound are added to an electrolyte, the high-temperature cycle capacity retention ratio of a lithium ion battery is increased and the thickness growth ratio is decreased under the synergistic effect of the nitrile compound and the sulfonate compound shown in formula I, so that the cycle performance of the lithium ion battery under high voltage is significantly improved. The nitrile compound effectively inhibits the oxidation reaction of the anode surface of the charged lithium ion battery to the electrolyte, and the sulfonate compound is oxidized on the surface of the anode active material in preference to the compound shown in the formula I and is cooperated with the compound shown in the formula I to form a stable SEI film, so that the side reaction of the electrolyte and the surface of the anode active material is reduced, and the high-temperature cycle performance and gas generation of the lithium ion battery are synergistically improved.

When the mass percentage content of the nitrile compound added into the electrolyte is too high, the high-temperature cycle capacity retention rate of the lithium ion battery is reduced, and the thickness increase is increased. This is probably because excessive nitrile compounds cause the increase of the by-product coating on the surface of the positive electrode, which hinders the passage of lithium ions to be extracted and inserted, and rather deteriorates the high-temperature cycle performance of the lithium ion battery.

In the aspects of gas production inhibition and circulation capacity retention rate, the 1,3, 6-hexanetricarbonitrile is combined with two dinitriles for use and has advantages compared with the single dinitrile, wherein the sum of the contents is 3-7%, and the circulation performance of the lithium ion battery can be improved to a great extent. This is probably because, when other nitrile compounds are used simultaneously, chain molecules having a smaller steric hindrance than the trinitrile can act synergistically with the trinitrile compound to form effective separation between the easily oxidizable component in the electrolyte and the surface of the positive electrode.

Although the present disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

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

2. The electrolyte of claim 1, wherein the anhydride comprises at least one of succinic anhydride, maleic anhydride, benzomaleic anhydride, glutaric anhydride, benzoglutaric anhydride, crotonic anhydride, chlamydia anhydride, itaconic anhydride, phthalic anhydride, benzoic anhydride, methyl acetic anhydride, propionic anhydride, butyric anhydride, or hydrogenated nadic anhydride.

3. The electrolyte of claim 1, wherein the compound represented by formula (I) includes at least one of compounds represented by formulae (I-1) to (I-8);

4. the electrolyte according to claim 1, wherein the compound represented by formula (I) is contained in an amount of n%, 0.05. ltoreq. n.ltoreq.5, based on the weight of the electrolyte.

5. The electrolyte of claim 4, 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%, the content of vinylene carbonate is m%, 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 meet the condition that k + m + n is more than or equal to 1 and less than or equal to 15.

6. The electrolyte of claim 4, wherein the electrolyte further comprises a carboxylic acid ester; 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 60, 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.

7. The electrolyte of claim 6, wherein the carboxylic acid ester comprises at least one of ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, or butyl propionate.

8. The electrolyte of any of claims 1-7, wherein the electrolyte further comprises at least one of 1, 3-propane sultone, 2, 4-butane sultone, methyl ethyl sulfone, or a nitrile compound.

9. The electrolyte solution according to claim 8, wherein the nitrile compound includes at least one of compounds represented by formulae (ii) to (v);

N≡C-R₂₁-C ≡ N formula (II)

Wherein R is₂₁Selected from substituted or unsubstituted C₁-C₁₂Alkylene, substituted or unsubstituted C₁-C₁₂An alkyleneoxy group;

R₃₁、R₃₂each independently selected from the group consisting of a single bond, substituted or unsubstituted C₁-C₁₂An alkylene group;

R₄₁、R₄₂、R₄₃each independentlySelected from single bond, substituted or unsubstituted C₁-C₁₂Alkylene, substituted or unsubstituted C₁-C₁₂An alkyleneoxy group;

R₅₁selected from substituted or unsubstituted C₁-C₁₂Alkylene, substituted or unsubstituted C₂-C₁₂Alkenylene, substituted or unsubstituted C₆-C₁₂Arylene, substituted or unsubstituted C₃-C₁₂A cyclic idene group;

wherein when substituted, the substituent is halogen.

10. The electrolyte of claim 9, wherein the nitrile compound includes at least one of:

11. the electrolyte according to claim 9, wherein the nitrile compound is present in the electrolyte in an amount of b%, 0.1. ltoreq. b.ltoreq.10, based on the weight of the electrolyte.

12. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte according to any one of claims 1 to 11.

13. The electrochemical device according to claim 12, wherein a charge termination voltage of the electrochemical device is 4.4V to 4.8V.

14. An electronic device comprising the electrochemical device according to claims 12-13.