WO2022141215A1

WO2022141215A1 - Electrolyte, electrochemical device comprising same, and electronic device

Info

Publication number: WO2022141215A1
Application number: PCT/CN2020/141474
Authority: WO
Inventors: 熊亚丽; 王翔; 唐超
Original assignee: 东莞新能源科技有限公司
Priority date: 2020-12-30
Filing date: 2020-12-30
Publication date: 2022-07-07
Also published as: CN114616711A

Abstract

Provided is an electrolyte. The electrolyte comprises a compound shown in formula I: in formula I, R11 and R12 are each independently selected from a substituted or unsubstituted C1-C4 alkyl, a substituted or unsubstituted C2-C6 alkenyl , a substituted or unsubstituted C2-C6 alkynyl and sulfonyl, a substituted or unsubstituted C1-C4 alkoxylate, a substituted or unsubstituted C6-C8 aryl, a substituted or unsubstituted C2-C8 cycloalkylene oxide, a substituted or unsubstituted C3-C8 cycloalkyl, an N heterocyclic group, or a fluorine atom. M+ is selected from a piperidine cation, a tetrahydropyrrole cation, an imidazole cation, a piperazine cation, a pyridine cation, a morpholine cation, or a quaternary ammonium salt cation. Also provided in the present application are an electrochemical device comprising said electrolyte, and an electronic device comprising said electrochemical device.

Description

Electrolyte, electrochemical device and electronic device containing the same

technical field

The invention belongs to the technical field of batteries, in particular to the technical field of lithium ion batteries, and in particular to an electrolyte, an electrochemical device and an electronic device containing the electrolyte.

Background technique

With the development of society, people have higher and higher requirements for electrochemical devices such as lithium-ion batteries, such as high energy density and fast charging, which have become the main research directions of many scientific research institutions and battery companies.

Since the power and energy that the electrochemical device can provide is proportional to the working voltage, in order to solve the above problems, increasing the voltage of the electrochemical device is the simplest and most direct method. However, the problem of improving the working voltage of electrochemical devices is that the commercial organic carbonate electrolytes in the electrolyte are easily oxidatively decomposed at high voltages, resulting in the rapid decline of their electrical conductivity. Therefore, research and preparation of electrochemical device electrolytes that can withstand high voltages is of great significance for the development of high-energy-density electrochemical devices.

In recent years, based on the advantages of ionic liquids, the use of ionic liquids as electrolytes has received extensive attention from researchers. It is a feasible idea to prepare ionic liquids with appropriate solvents and additives as electrolytes for high-voltage electrochemical devices. However, for many ionic liquids, their physicochemical properties largely depend on the structure of the anion. However, existing ionic liquid anions are increasingly unable to meet the needs of modern society for higher-performance electrolytes for electrochemical devices. Therefore, there is an urgent need for a new type of ionic liquid with better electrochemical stability, thermal stability, better cycle and high temperature storage performance under electrochemical system, and lower cost.

SUMMARY OF THE INVENTION

In view of the current state of the art, one of the objects of the present application is to provide an ionic liquid, the anion of the ionic liquid contains an asymmetric imino group, and one side of the asymmetric imino group is a methyl-substituted sulfonyl group, The other side is a carbonate group. After many experiments, the inventor found that when the ionic liquid containing asymmetric imine group is used in the electrolyte, it can preferentially form a film on the surface of the positive and negative electrodes of the battery, and can widen the electrochemical window of the electrolyte and inhibit the electrolyte in the electrolyte. Side reactions on the surface of the positive and negative electrodes of the battery; in addition, due to the weak electron withdrawing effect of the carbonate group in the asymmetric imine group, the delocalization of the negative charge is reduced, which in turn leads to an increase in the electrostatic interaction between the anion and the cation. , which can improve the conductivity of the electrolyte. In addition, ionic liquids containing asymmetric imine groups have good electrochemical, chemical and thermal stability, and at the same time have the advantages of wide liquid range, low viscosity, high conductivity, high solubility and low cost, which can effectively improve the battery. excellent cycle life characteristics and high temperature storage performance.

Another object of the present application is to provide an electrolyte solution, a negative electrode plate including the above electrolyte solution, and an electrochemical device and an electronic device including the negative electrode plate.

To this end, the application provides an ionic liquid for electrolyte, and the ionic liquid comprises a compound shown in formula I:

In formula I, R ₁₁ and R ₁₂ are each independently selected from substituted or unsubstituted C ₁ -C ₄ alkyl, substituted or unsubstituted C ₂ -C ₆ alkenyl, substituted or unsubstituted C ₂ ~ _C6 alkynyl, sulfonyl, substituted or unsubstituted _C1 ~ _C4 alkoxy, substituted or unsubstituted _C6 ~ _C8 aryl, substituted or unsubstituted _C2 ~ _C8 Epoxy alkyl group, substituted or unsubstituted C ₃ -C ₈ cycloalkyl group, nitrogen-containing heterocyclic group or fluorine atom; wherein, when substituted, the substituent is selected from at least one of halogen atom or cyano group;

M ⁺ is selected from substituted or unsubstituted piperidinium cation, substituted or unsubstituted tetrahydropyrrole cation, substituted or unsubstituted imidazolium cation, substituted or unsubstituted piperazine cation, substituted or unsubstituted pyridinium cation, substituted or unsubstituted pyridinium cation, substituted or unsubstituted Unsubstituted morpholine cation, substituted or unsubstituted quaternary ammonium salt cation; wherein, when substituted, the substituent is selected from C ₁ -C ₆ alkyl, C ₂ -C ₆ alkenyl, C ₃ -C ₁₀ alkyl At least one of a phosphono ester group, a C ₂ -C ₆ sulfonyl group, a cyano group or a halogen atom.

In the ionic liquid described in the present application, it is preferred that the anion of the compound represented by the formula I comprises at least one of the anions represented by the formula I-1-1 to the formula I-1-16,

In the ionic liquid described in the present application, it is preferred that the cation of the compound represented by the formula I comprises at least one of the cations represented by the formula I-2-1 to the formula I-2-12,

In the ionic liquid described in this application, preferably, the compound represented by the formula I comprises at least one of the compounds represented by the formula I-1 to the formula I-12,

To this end, the present application also provides an electrolyte solution, comprising the above-mentioned ionic liquid, and the content of the ionic liquid is 0.01%-5%, preferably 0.1%-3%, based on the weight of the electrolyte solution. When the content of the ionic liquid in the electrolyte is less than 0.01%, the protective film formed by it is insufficient and has little effect on the battery performance; when the content is higher than 5%, the formed protective film has a large impedance and affects the battery performance.

In the electrolyte solution described in the present application, preferably, the electrolyte solution further contains additives, lithium salts and organic solvents.

In the electrolyte solution described in the present application, preferably, the organic solvent contains at least one of cyclic carbonate, chain carbonate and chain carboxylate;

It is further preferred that the cyclic carbonate comprises ethylene carbonate and propylene carbonate, further preferably, based on the weight of the electrolyte, the content of the ethylene carbonate is 5%-30%, the propylene carbonate is The content of ester is below 30%;

It is further preferred that the chain carbonate comprises at least one of diethyl carbonate and ethyl methyl carbonate;

It is further preferred that the chain carboxylate contains at least one of ethyl propionate and propyl propionate.

In the electrolyte described in this application, preferably, the lithium salt is selected from one or more of inorganic lithium salts and organic lithium salts, and further preferably, the lithium salt is selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium One or more of lithium fluorosulfonimide and lithium bistrifluoromethanesulfonimide, more preferably, the lithium salt is lithium hexafluorophosphate.

In the electrolyte solution described in the present application, preferably, the concentration of the lithium salt in the electrolyte solution is 0.6 mol/kg-2 mol/kg, more preferably 0.7 mol/kg-1.25 mol/kg.

Preferably, the electrolyte solution described in the present application further comprises a polynitrile compound, and the polynitrile compound comprises at least one of the compounds represented by formula II to formula V,

Wherein, R ₂₁ is selected from substituted or unsubstituted C1-12 alkylene, substituted or unsubstituted C1-12 alkyleneoxy; R ₃₁ and R ₃₂ are each independently selected from single bond, substituted or unsubstituted C1 ~12 alkylene, substituted or unsubstituted C1-12 alkyleneoxy; R ₄₁ , R ₄₂ , R ₄₃ are each independently selected from single bond, substituted or unsubstituted C1-12 alkylene, substituted or unsubstituted Substituted C1-12 alkyleneoxy; R ₅₁ is selected from substituted or unsubstituted C1-12 alkylene, substituted or unsubstituted C2-12 alkenylene, substituted or unsubstituted C6-26 arylene, Substituted or unsubstituted C2-12 heterocyclic groups; wherein when the above groups are substituted, the substituents are halogen atoms;

Further preferably, based on the weight of the electrolyte, the content of the polynitrile compound is 0.1% to 12%, more preferably 0.5% to 5%.

In the electrolyte solution described in the present application, preferably, the polynitrile compound comprises the compound represented by formula II and at least one other polynitrile compound selected from the compounds represented by formula III to formula V; further Preferably, the amount of the compound represented by the formula II is greater than that of the other polynitrile compounds.

In the electrolyte solution described in the present application, preferably, the polynitrile compound contains at least one of the compounds represented by formula II-1 to formula V-2,

In the electrolyte solution described in the present application, preferably, the additive further comprises a boron-containing lithium compound, and the boron-containing lithium compound comprises one or more of the compounds represented by formulas VI-1 to VI-12; further Preferably, based on the weight of the electrolyte, the amount of the boron-containing lithium compound is 0.1%-5%;

In the electrolyte described in this application, preferably, the additive further comprises a fluorine-containing pyridine compound, and the fluorine-containing pyridine compound comprises one or more of the compounds represented by formula VII; further preferably, based on The weight of the electrolyte, the amount of the fluorine-containing pyridine compound is 0.01%-5%;

Wherein, R ₇₁ , R ₇₂ , R ₇₃ , R ₇₄ , R ₇₅ are each independently selected from hydrogen, halogen, substituted or unsubstituted C1-12 alkyl, substituted or unsubstituted C2-12 alkenyl, substituted or unsubstituted C1-12 alkynyl, substituted or unsubstituted C2-12 alkoxy, and at least one of R ₇₁ , R ₇₂ , R ₇₃ , R ₇₄ , R ₇₅ is fluorine or at least one has fluorine substitution base.

In the electrolyte solution described in the present application, it is preferred that the fluorine-containing pyridine compound comprises one or more of the compounds represented by formula VII-1 to formula VII-10,

To this end, the present application also provides an electrochemical device comprising a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte.

In the electrochemical device described in the present application, preferably, the positive electrode includes a current collector and a positive electrode active material layer provided on the current collector. The current collector may be Al, but is not limited thereto. The positive electrode active material layer is formed of a positive electrode active material including a compound that reversibly intercalates and deintercalates lithium ions (ie, a lithiated intercalation compound). The positive electrode active material may further include a composite oxide containing lithium and at least one of cobalt, manganese, and nickel.

In the electrochemical device described in the present application, preferably, the composite oxide includes LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _c )O ₂ (0<a< 1, 0<b<1, 0<c<1, a+b+c=1), LiMn ₂ O ₄ , LiNi _1-y Co _y O ₂ , LiCo _ly Mn _y O ₂ , LiNi _ly Mn _y O ₂ (0<y<1), Li(Ni _a Mn _b Co _c )O ₄ (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn _2- _z Ni _z O ₄ , LiMn _2-z Co _z O ₄ (0<z<2), Li(Ni _a Co _b Al _c )O ₂ (0<a<1, 0<b<1, 0<c< 1, at least one of a+b+c=1), LiCoPO ₄ and LiFePO ₄ . In addition to the above-mentioned composite oxides, sulfides, selenides, halides, and the like can be used as the positive electrode active material.

In the electrochemical device described in the present application, it is preferable that the above-mentioned compounds such as complex oxides, sulfides, selenides and halides may have a coating layer on the surface, or may be mixed with a compound having a coating layer. The coating layer can be selected from oxides of the coating elements, hydroxides of the coating elements, oxyhydroxides of the coating elements, oxycarbonates of the coating elements, and hydroxycarbonates of the coating elements. (hydroxyl carbonate), the compound used to form the coating layer may be amorphous or crystalline. The coating element may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr or a mixture thereof. The coating layer in the present application may be formed by any method as long as the properties of the positive electrode active material are not negatively affected by the coating element. For example, the method may include any coating method known to those skilled in the art, such as spraying, dipping, and the like.

In the electrochemical device described in the present application, preferably, the positive electrode active material may further include a binder and a conductive material. The binder improves the binding properties of the positive electrode active material particles to each other and the positive electrode active material particles to the current collector. Non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-containing Oxygen polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin, nylon, etc. The conductive material is used to provide electrical conductivity to the electrodes. The conductive material may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of the conductive material include at least one of the following conductive materials: natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, metal fiber, etc.; copper, nickel , aluminum, silver, etc.; or polyphenylene derivatives, etc.

In the electrochemical device described in the present application, preferably, the negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, the negative electrode active material layer is formed of a negative electrode active material, and the negative electrode active material may be These include materials that reversibly intercalate/deintercalate lithium ions, lithium metal, lithium metal alloys, materials capable of doping/dedoping lithium, or transition metal oxides. The material for reversibly intercalating/deintercalating lithium ions may be a carbon material. The carbon material may be any carbon-based negative active material commonly used in lithium-ion rechargeable electrochemical devices. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and combinations thereof. The crystalline carbon may be amorphous, plate-shaped, platelet-shaped, spherical or fiber-shaped natural graphite, and may also be amorphous, plate-shaped, platelet-shaped, spherical or fiber-shaped artificial graphite. The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization product, fired coke, and the like. Both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. As the low-crystalline carbon material, soft carbon and hard carbon can be generally included. As the highly crystalline carbon material, natural graphite, crystalline graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microbeads, mesophase pitch, and high temperature calcined carbon (such as petroleum or coke derived from coal tar pitch can be generally included) ).

In the electrochemical device described in the present application, preferably, the negative electrode active material layer further comprises a binder, and the binder may include various binder polymers, such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polymer Vinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin , nylon, etc., but not limited thereto.

In the electrochemical device described in the present application, preferably, the negative electrode active material layer further contains a conductive material that can improve the conductivity of the electrode. Any conductive material can be used as the conductive material as long as it does not cause chemical change. Non-limiting examples of conductive materials include: carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.; metal-based materials, such as metal powders including copper, nickel, aluminum, silver, etc. Or metal fibers; conductive polymers, such as polyphenylene derivatives, etc.; or their mixtures.

In the electrochemical device described in the present application, preferably, the current collector of the negative electrode can be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, foamed copper, polymer substrate coated with conductive metal, or their combination.

For the electrochemical device described in the present application, the material and shape of the separator are not particularly limited, and it can be any technology disclosed in the prior art. For example, the separator may include a substrate layer and a surface treatment layer provided on at least one surface of the substrate layer. The base material layer is a non-woven fabric, film or composite film with a porous structure, and the material of the base material layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected. The surface treatment layer may be a polymer layer or an inorganic substance layer, or may be a layer formed by mixing a polymer and an inorganic substance. Wherein, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, oxide One or more of zirconium, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxy , one or more of polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. Wherein, the polymer layer contains a polymer, and the material of the polymer is selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxy, polyvinylidene fluoride At least one of ethylene and poly(vinylidene fluoride-hexafluoropropylene).

In the electrochemical device described in the present application, preferably, the separator includes a polyolefin-based microporous membrane and a coating, and the coating includes an organic coating and an inorganic coating, wherein the organic coating is selected from the group consisting of polyolefins. Vinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyimide, acrylonitrile-butadiene copolymer, acrylonitrile-styrene-butadiene copolymer, polymethyl methacrylate , at least one of polymethyl acrylate, polyethyl acrylate, acrylic acid-styrene copolymer, polydimethylsiloxane, sodium polyacrylate and sodium carboxymethyl cellulose, and the inorganic coating is selected from SiO ₂ , One or more of Al ₂ O ₃ , CaO, TiO ₂ , ZnO ₂ , MgO, ZrO ₂ and SnO ₂ ; the polymer binder in the separator is selected from polyvinylidene fluoride.

In the electrochemical device described in the present application, preferably, the separator is made of polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer A single-layer or multi-layer polyolefin-based microporous membrane composed of one or more of ethylene-methyl methacrylate copolymers.

To this end, the present application also provides an electronic device including the above electrochemical device.

The beneficial effects of this application are:

The ionic liquid provided by this application contains asymmetric imine groups, half of the asymmetric imine groups are methyl-substituted sulfonyl groups, and the other half are carbonate groups, which can preferentially form films on the surfaces of positive and negative electrodes, and can Widen the electrochemical window of the electrolyte and inhibit the side reaction of the electrolyte on the surface of the positive and negative electrodes; in addition, due to the weak electron withdrawing effect of the carbonate group in the asymmetric imine group, the delocalization of the negative charge is reduced, which leads to The electrostatic interaction between anions and cations increases, and when used in an electrolyte, the conductivity of the electrolyte can be improved.

The electrolyte provided by the present application can improve the high-temperature cycle and high-temperature storage performance of electrochemical devices, especially lithium-ion batteries, and reduce the internal resistance of electrochemical devices and lithium-ion batteries, and can be used to solve the problems of cycling and high-temperature storage of high-voltage lithium-ion batteries.

The electrochemical device provided by the present application has excellent high temperature storage, high temperature cycling and low impedance performance.

Detailed ways

The embodiments of the present application are described in detail below: the present embodiment is implemented on the premise of the technical solution of the present invention, and provides detailed implementation methods and processes, but the protection scope of the present invention is not limited to the following embodiments, the following The experimental methods that do not specify specific conditions in the examples are usually in accordance with conventional conditions.

1. Battery performance test method:

(1) Test 1: Storage expansion rate 12H at 85°C

Discharge the battery to 3.0V at 0.5C at 25°C, charge it to 4.5V at 0.5C, charge it to 0.05C under constant voltage at 4.5V, test and record the thickness of the battery with a micrometer and record it as H ₁₁ , and place it at 85°C In the oven, 4.5V constant voltage for 12 hours, after 12 hours, use a micrometer to test and record the thickness of the battery, denoted as H ₁₂ ,

Thickness expansion ratio=(H ₁₂ -H ₁₁ )/H ₁₁ *100%.

(2) Test 2: 60℃ storage expansion rate 70D

Discharge the battery to 3.0V at 0.5C at 25°C, charge it to 4.5V at 1C, and charge it to 0.05C at 4.5V with constant voltage. Test and record the thickness of the battery with a micrometer as W ₁₁ , and place it in a 60°C oven. Among them, 4.5V constant voltage for 70 days, after 70 days, use a micrometer to test and record the thickness of the battery, recorded as W ₁₂ ,

Thickness expansion ratio=(W ₁₂ -W ₁₁ )/W ₁₁ *100%.

3) Test 3: 45 ℃ cycle capacity retention rate (300 times)

Place the battery in a 45°C incubator for 30 minutes to allow the battery to reach a constant temperature. The battery that has reached a constant temperature is charged to 4.5V at a constant current of 0.2C at 45°C, charged to a constant voltage of 0.05C at 4.5V, left for 5 minutes, and then discharged to a constant current of 0.2C to 3.0V, and left for 5 minutes; then Then charge at 1.3C constant current to 4.15V, then charge at 4.15V constant voltage until the current is 1C; then charge at 1C constant current to 4.25V, then charge at 4.25V constant voltage until the current is 0.8C; then at 0.8C Charge with constant current to 4.5V, then charge with 4.5V constant voltage until the current is 0.05C; leave it for 5 minutes; then discharge with 1C constant current until the voltage is 3.0V, let it stand for 3 minutes; this is a charge-discharge cycle. Thus charged/discharged, the capacity retention rate of the battery after 300 cycles was calculated.

The capacity retention rate (%) of the battery after N cycles = discharge capacity at the Nth cycle/discharge capacity at the first cycle×100%.

In this way, the high temperature cycle performance of the battery was evaluated.

4) Test 4. DC Impedance DCR (0℃)

Let the battery stand for 1 hour in a high and low temperature box at 0 °C to make the battery reach a constant temperature; charge it with a constant current of 0.5C to 4.2V, then charge it with a constant current of 0.3C to 4.5V, and charge it with a constant voltage of 4.5V until the current is 0.02C , let stand for 30 minutes; then discharge to 3.4V with 0.1C constant current, let stand for 30 minutes, the capacity of this step is used as the benchmark. Under the condition of 0 ℃, charge to 4.2V with 0.5C constant current, then charge with 0.3C constant current to 4.5V, 4.5V constant voltage charge until the current is 0.02C, let stand for 30 minutes; discharge with 0.1C constant current for 60min (with Calculate the actual capacity obtained in the previous step), record the voltage at this time as V ₁ ; then discharge it at a constant current of 1C for 1s (the capacity is calculated based on the battery’s marked capacity), record the voltage at this time as V ₂ , and calculate the corresponding 20% SOC state of the battery DC impedance.

20% SOC DC impedance = (V ₁ -V ₂ )/1C.

5) Test five, 45℃ float test expansion rate 1000H

Charge the battery with 1.3C constant current to 4.15V at 25°C, then charge with 4.15V constant voltage until the current is 1C; charge with 1C constant current to 4.25V, then charge with 4.25V constant voltage until the current is 0.8C; Charge to 4.5V with 0.8C constant current, and then charge with 4.5V constant voltage until the current is 0.05C; test and record the thickness of the battery with a micrometer and record it as D11; stand at 45°C for ₁ hour, charge with 0.4C constant current to 0.05C; 4.55V, then charge with 4.55V constant voltage for 1000h, test with a micrometer and record the thickness of the battery as D ₁₂ ;

Thickness expansion ratio=(D ₁₂ -D ₁₁ )/D ₁₁ *100%.

2. Specific Examples and Comparative Examples

Example 1

1. Battery preparation

1) Preparation of electrolyte: In an argon atmosphere glove box with water content <10ppm, ethylene carbonate, namely ethylene carbonate (abbreviated as EC), propylene carbonate, namely propylene carbonate (abbreviated as PC), carbonic acid Diethyl ester (abbreviated as DEC) and propyl propionate (abbreviated as PP) were mixed uniformly according to the weight ratio of 3:6: ₆ :5, and then fully dried lithium salt LiPF6 (1mol/kg) was dissolved in the above In the non-aqueous solvent, an asymmetric imide-based ionic liquid was added at the end, the type and content of which were shown in Table 1, and the electrolyte was made up.

2) Preparation of positive pole piece: the positive active material LCO (molecular formula is LiCoO ₂ ), conductive carbon black, conductive paste, and binder polyvinylidene fluoride (abbreviated as PVDF) are in a weight ratio of 97.1:1.0:0.3: 1.6 Fully stir and mix in an appropriate amount of N-methylpyrrolidone (abbreviated as NMP) solvent to form a uniform positive electrode slurry; coat the slurry on the positive electrode current collector Al foil, dry and cold-press to obtain For the positive pole piece, the compaction density of the positive pole piece is 4.15 g/cm ³ .

3) Preparation of negative pole piece: The negative electrode active material graphite, binder styrene-butadiene rubber (abbreviated as SBR), and thickener sodium carboxymethyl cellulose (abbreviated as CMC) are mixed in an appropriate amount according to the weight ratio of 97.7:1.3:1.0. Fully stirred and mixed in the deionized water solvent of the prepared negative electrode to form a uniform negative electrode slurry; this slurry was coated on the negative electrode current collector Cu foil, dried and cold pressed to obtain a negative electrode pole piece, and the compaction of the negative pole piece The density was 1.75 g/cm ³ .

4) Preparation of diaphragm:

Use 7μm thick polyethylene isolation film.

5) Preparation of the battery: stack the positive pole piece, the separator, and the negative pole piece in order, so that the separator is placed between the positive pole piece and the negative pole piece to play a role of isolation, and then roll to obtain a bare cell; The battery is placed in the outer packaging foil, and the electrolyte prepared above is injected, and then a full battery is obtained through the processes of vacuum packaging, standing, forming, and shaping.

2. Performance test

The battery was tested for performance, and the test results are shown in Table 1. Table 1 shows the effect of compounds of formula I on battery performance.

Example 2-18

Except that some solvent compositions and the types of asymmetric imine-containing ionic liquids are different from those in Example 1, the rest of the preparation methods are the same as those in Example 1. Wherein embodiment 14 solvent is composed of ethylene carbonate, propylene carbonate, i.e. propylene carbonate, diethyl carbonate, propyl propionate are mixed in a weight ratio of 1:3:3:3, and embodiment 15 solvent is composed of ethylene carbonate , propylene carbonate is propylene carbonate, diethyl carbonate, propyl propionate is mixed with weight ratio 5:3:6:6, embodiment 16 solvent is composed of ethylene carbonate, propylene carbonate, propylene carbonate, Diethyl carbonate and propyl propionate were mixed in a weight ratio of 3:1:3:3, other differences from Example 1 were shown in Table 1, and the results of the battery performance test were shown in Table 1.

Comparative Examples 1-3

Except that the ionic liquid containing asymmetric imine group is not added, and the solvent composition is different from that of Example 1, the rest of the preparation method is the same as that of Example 1, wherein the solvent composition of Comparative Example 2 is ethylene carbonate, propylene carbonate That is, propylene carbonate, diethyl carbonate and propyl propionate are mixed in a weight ratio of 3:1:3:3, and the ionic liquid structural formula I-13 that Comparative Example 3 adds is as follows:

Other differences from Example 1 are shown in Table 1, and the results of the battery performance test are shown in Table 1.

Table 1

Referring to Table 1, it can be seen from the comparison between Example 1 and Comparative Example 1, Example 16 and Comparative Example 2 that after adding the ionic liquid containing an asymmetric imine group shown in Formula I to the electrolyte of the battery, the high temperature of the battery Storage and DCR performance are significantly improved. Referring to Examples 1-18, it can be seen that when the content of the asymmetric imine group-containing ionic liquid represented by formula I satisfies 0.01%-5%, the high-temperature storage and DCR performance of the battery are comprehensively relatively good. Further, when the content of the asymmetric imine group-containing ionic liquid represented by formula I satisfies 0.1%-3%, the high-temperature storage and DCR performance of the battery are comprehensively relatively better.

Examples 19-28

The difference from Example 1 is that in the preparation process of the electrolyte, a polynitrile compound is also added after the ionic liquid is added. The specific type and content of the polynitrile compound and the results of the battery performance test are shown in Table 2. Table 2 shows the effect of the compound of formula I, ethylene carbonate and nitrile compound additives on battery performance.

Comparative Example 4

The difference from Comparative Example 1 is that in the preparation process of the electrolyte, a polynitrile compound is also added, and the specific type and content of the polynitrile compound and the results of the battery performance test are shown in Table 2.

Table 2

Referring to Table 2, it can be seen from the comparison of Examples 19-24 with Comparative Examples 1 and 4 that after adding the asymmetric imine group-containing ionic liquid and polynitrile compound shown in Formula I to the electrolyte of the battery, the high temperature of the battery Cycling and high temperature storage performance are significantly improved. Moreover, it can be seen from the comparison between Example 19 and Example 1 that the high temperature storage performance of the battery can be further improved by using the asymmetric imine group-containing ionic liquid represented by Formula I in combination with a polynitrile compound. This may be due to the fact that the energy level of the lone pair electron in the nitrile functional group is similar to the energy level of the outermost vacant orbital of the transition metal atom in the cathode active material of the battery, so that the organic molecule containing the nitrile functional group can be complexed on the cathode surface. adsorption. The organic molecules adsorbed on the surface of the cathode can well separate the easily oxidizable components in the electrolyte from the surface of the cathode, which greatly reduces the oxidation of the electrolyte on the cathode surface of the battery in the charged state, thereby improving the cycle performance and high temperature of the battery. storage performance.

Referring to Table 2, it can be seen from the comparison of Examples 19-24 and 25-28 that when the content of the ionic liquid containing asymmetric imino groups is constant, the dinitrile compounds are used in combination with other polynitriles, and the dinitrile compounds are controlled. The content of nitrile compounds is greater than that of polynitrile compounds, which can improve the performance of the battery better; this may be because the size of the organic molecules containing nitrile functional groups has an optimal value, and the molecules are too small, forming an isolated space Limited, it cannot effectively separate the easily oxidizable components in the electrolyte from the surface of the cathode, and the molecules are too large, and the easily oxidizable components in the electrolyte can contact the surface of the cathode through the gap of organic molecules containing nitrile functional groups, but still cannot Play a good isolation effect.

Examples 29-33

The difference from Example 19 is that during the preparation of the electrolyte, a boron-containing lithium compound was added after the ionic liquid and the polynitrile compound were added. The specific type and content of the boron-containing lithium compound and the results of the battery performance test are shown in Table 3. Table 3 shows the effects of compounds of formula I, polynitriles and boron-containing lithium compounds on battery performance.

table 3

Referring to Table 3, it can be seen from the comparison between Example 19 and Examples 29-33 that adding boron-containing lithium salt on the basis of the electrolyte of Example 19 can significantly improve the cycle and float performance of the battery. This is mainly due to the higher film-forming potential of boron-containing lithium salts than that of polynitrile compounds, which can preferentially form films and inhibit the consumption of polynitrile compounds, thereby improving the floating charge performance of the battery.

Examples 34-42

The difference from Example 19 is that in the preparation process of the electrolyte, fluorine-containing pyridine compounds were also added after adding the ionic liquid and the polynitrile compound. The specific type and content of the fluorine-containing pyridine compounds and the results of the battery performance test are shown in the table. 4. Table 4 shows the effect of fluorine-containing pyridine compounds on battery performance.

Table 4

Referring to Table 4, it can be seen from the comparison between Example 19 and Examples 34-42 that when the fluorine-containing pyridine compound meets the above content range, the combination of high temperature storage performance and thermal cycle performance of the battery is relatively good. Further, when the fluorine-containing pyridine compound meets the content range of 0.3% to 2%, the combination of high temperature storage performance and high temperature cycle performance of the battery is relatively better.

Of course, the present invention can also have other various embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformation should belong to the protection scope of the present invention.

Claims

A kind of electrolyte, it is characterized in that, comprise compound shown in formula I:

In formula I, R 11 and R 12 are each independently selected from substituted or unsubstituted C 1 -C 4 alkyl, substituted or unsubstituted C 2 -C 6 alkenyl, substituted or unsubstituted C 2 ~ C6 alkynyl, sulfonyl, substituted or unsubstituted C1 ~ C4 alkoxy, substituted or unsubstituted C6 ~ C8 aryl, substituted or unsubstituted C2 ~ C8 Epoxy alkyl group, substituted or unsubstituted C 3 -C 8 cycloalkyl group, nitrogen-containing heterocyclic group or fluorine atom; wherein, when substituted, the substituent is selected from at least one of halogen atom or cyano group;

M + is selected from substituted or unsubstituted piperidinium cation, substituted or unsubstituted tetrahydropyrrole cation, substituted or unsubstituted imidazolium cation, substituted or unsubstituted piperazine cation, substituted or unsubstituted pyridinium cation, substituted or unsubstituted pyridinium cation, substituted or unsubstituted Unsubstituted morpholine cation, substituted or unsubstituted quaternary ammonium salt cation; wherein, when substituted, the substituent is selected from C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 3 -C 10 alkyl At least one of a phosphono ester group, a C 2 -C 6 sulfonyl group, a cyano group or a halogen atom.
The electrolyte according to claim 1, wherein the anion of the compound represented by the formula I comprises at least one of the anions represented by the formula I-1-1 to the formula I-1-16:
The electrolyte according to claim 1, wherein the cation of the compound shown in the formula I comprises at least one of the cations shown in the formula I-2-1 to the formula I-2-12:
The electrolyte according to claim 1, wherein the compound shown in the formula I comprises at least one of the compounds shown in the formula I-1 to the formula I-12:
The electrolyte according to any one of claims 1 to 4, characterized in that, based on the weight of the electrolyte, the content of the compound represented by the formula I is 0.01% to 5%, preferably 0.1% to 3%.
The electrolyte solution according to claim 5, wherein at least one of the following conditions (a)-(d) is satisfied:

(a) further comprising ethylene carbonate and/or propylene carbonate, based on the weight of the electrolyte, the content of the ethylene carbonate is 5%-30%, and the content of the propylene carbonate is 30% the following;

(b) further comprising diethyl carbonate and/or ethyl methyl carbonate;

(c) further comprising ethyl propionate and/or propyl propionate;

(d) further includes a polynitrile compound, and the content of the polynitrile compound is 0.1% to 12%.
The electrolyte solution according to claim 6, further comprising a polynitrile compound, the polynitrile compound comprising at least one of the compounds represented by formula II to formula V,

Wherein, R 21 is selected from substituted or unsubstituted C1-12 alkylene, substituted or unsubstituted C1-12 alkyleneoxy; R 31 and R 32 are each independently selected from single bond, substituted or unsubstituted C1 ~12 alkylene, substituted or unsubstituted C1-12 alkyleneoxy; R 41 , R 42 , R 43 are each independently selected from single bond, substituted or unsubstituted C1-12 alkylene, substituted or unsubstituted Substituted C1-12 alkyleneoxy; R 51 is selected from substituted or unsubstituted C1-12 alkylene, substituted or unsubstituted C2-12 alkenylene, substituted or unsubstituted C6-26 arylene, A substituted or unsubstituted C2-12 heterocyclic group; when the above group is substituted, the substituent is a halogen atom.
The electrolyte according to claim 6, wherein the polynitrile compound comprises at least one of the compounds represented by formula II-1 to formula V-2,
An electrochemical device, characterized by comprising a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1-8.
An electronic device comprising the electrochemical device of claim 9 .