阅读说明：本技术 一种电解液、电化学装置以及电子装置 (Electrolyte, electrochemical device and electronic device ) 是由 栗文强 郑建明 崔辉 郑湘岭 于 2020-03-03 设计创作，主要内容包括：本申请提供了一种电解液以及包含该电解液的电化学装置和电子装置。本申请的电解液包括二氟磷酸锂和含有二氟磷氧基的化合物。本申请提供的电解液能够在明显降低电化学装置的阻抗性能同时,提高高温存储容量保持性能。(An electrolyte, and an electrochemical device and an electronic device including the same are provided. The electrolyte of the present application includes lithium difluorophosphate and a compound containing a difluorophosphorus oxy group. The electrolyte provided by the application can obviously reduce the impedance performance of an electrochemical device and improve the high-temperature storage capacity retention performance.)

1. An electrolyte comprising lithium difluorophosphate and a compound containing difluorophosphorus oxy groups.

2. The electrolyte of claim 1, wherein the difluorophosphonooxy-containing compound is selected from compounds of formula I;

wherein R is¹Selected from substituted or unsubstituted C₁-C₁₀Alkyl, substituted or unsubstituted C₂-C₁₀Unsaturated alkyl, the substituent is selected from at least one of alkanoyl, nitrile group and halogen;

or, R¹Any one selected from the group represented by the following structures:

wherein R is²Selected from single bond, substituted or unsubstituted C₁-C₁₀Alkylene, substituted or unsubstitutedC of (A)₂-C₁₀Unsaturated alkyl, the substituent is halogen;

x is selected from a single bond or an oxygen atom;

denotes the connection position.

3. The electrolyte of claim 1, wherein the difluorophosphorus oxy-containing compound comprises at least one of:

4. the electrolyte according to claim 1, wherein the mass percentage of the compound containing difluorophosphorus oxy groups in the electrolyte is 0.001-5%, and the mass percentage of the lithium difluorophosphate in the electrolyte is 0.001-1%, based on the total mass of the electrolyte.

5. The electrolyte of any one of claims 1 to 4, wherein the electrolyte further comprises at least one of a polynitrile compound, a sultone compound, and a fluoroether compound.

6. The electrolyte of claim 5, wherein the polynitrile compound comprises at least one of:

the mass percentage of the polynitrile compound in the electrolyte is 0.01-10% of the total mass of the electrolyte.

7. The electrolyte of claim 5, wherein the sultone compound comprises a structure of formula III-A or formula III-B:

wherein R is³¹、R³²、R³³、R³⁴、R³⁵、R³⁶、R³⁷Each independently selected from H, F, Cl, Br, substituted or unsubstituted C₁～C₆Alkyl, substituted or unsubstituted C₂～C₆The substituent is selected from F, Cl and Br; the mass percentage of the sultone compound in the electrolyte is 0.01-10% of the total mass of the electrolyte.

8. The electrolyte of claim 7, wherein the sultone compound comprises the structure shown below:

9. the electrolyte of claim 5, wherein the fluoroether compound comprises at least one of the following compounds: desflurane, sevoflurane, fluoroethylene ether, 2,2, 2-trifluoroethyl ether, bis (fluoromethyl) ether, 2,2,3,3, 3-pentafluoropropyldifluoromethyl ether, 2, 2-difluoroethyltrifiuoromethyl ether, 1,2,3,3, 3-pentafluoropropyl2, 2, 2-trifluoroethyl ether, heptafluoropropyl1, 2,2, 2-tetrafluoroethyl ether, trifluoromethyl trifluorovinyl ether, 1,2,2, 2-tetrafluoroethyltrifiuoromethyl ether, 1,2,3,3, 3-pentafluoropropyldifluoromethyl ether, 1,2, 2-trifluoroethyl trifiuoromethyl ether, 2,2,3, 3-tetrafluoropropyldifluoromethyl ether, difluoromethyl-2, 2, 2-trifluoroethyl ether, 1-difluorodimethyl ether, trifluoromethyl methyl ether, 1,2, 2-tetrafluoroethylether, 1,2,3,3, 3-hexafluoropropyl methyl ether, 1,3, 3-tetrafluorodimethyl ether, bis (4-fluorobutyl) ether, ethyltrifluoromethyl ether, 2,2,3,3, 3-pentafluoropropyl methyl ether, methylnonafluorobutyl ether, 1,2,2, 2-tetrafluoroethyl methyl ether, pentafluorodimethyl ether, 1,2,3,3, 3-pentafluoropropyl ethyl ether, bis- (2, 2-difluoroethyl) ether, ethylperfluorobutyl ether, bis- (1,2,2, 2-tetrafluoroethyl) ether, 1,2, 2-tetrafluoroethyl methyl ether, 2-fluoroethyl (methyl) ether, perfluorobutyl methyl ether, ethylnonafluorobutyl ether, 2-perfluoropropoxy perfluoropropyl trifluorovinyl ether, 1,1,3,3, 3-hexafluoroisopropyl methyl ether, 1H,2H, 3H-decafluorodipropyl ether, perfluorodiethylene glycol dimethyl ether, 2, 2-difluoroethyl methyl ether, perfluoroethyl vinyl ether, perfluoro-n-propyl vinyl ether, perfluoroethyl vinyl ether, allyl 2,2,3, 3-tetrafluoropropyl ether, 2,2, 2-trifluoroethyl ether, perfluoro (3-butenyl vinyl ether); the mass percentage of the fluoroether compound in the electrolyte is 0.1-20% based on the total mass of the electrolyte.

10. An electrochemical device, comprising:

a positive electrode;

a negative electrode;

a separator provided between the positive electrode and the negative electrode; and

an electrolyte as claimed in any one of claims 1 to 9.

11. The electrochemical device according to claim 10, wherein the positive electrode comprises 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 comprises a positive electrode active material, the positive electrode active material comprises magnesium, and the magnesium content is m × 10 based on the total weight of the positive electrode active material layer³The value range of ppm and m is 0.5-2, the mass percent of lithium difluorophosphate in the electrolyte is recorded as a%, the mass percent of a compound containing difluorophosphorus oxy in the electrolyte is recorded as b%, and the mass percent of (a + b)/m is less than or equal to 1.

12. An electronic device comprising the electrochemical device of claim 10 or 11.

Technical Field

The present disclosure relates to the field of electrochemical technologies, and in particular, to an electrolyte, and an electrochemical device and an electronic device using the electrolyte.

Background

With the popularization and application of electronic products such as mobile phones, notebooks, cameras, and the like, electrochemical devices represented by lithium ion batteries also have wide applications. Lithium ion batteries are safe to use in severe environments, and are gradually the focus of attention of people. For example, whether normal use is possible under extremely low temperature conditions, whether safety risk is present in use at high temperature, whether high-rate discharge is possible during use, and the like. Therefore, it is highly desirable to develop a lithium ion battery that can simultaneously achieve both low-temperature performance and high-temperature performance.

Disclosure of Invention

In order to solve the problems in the prior art, the application provides an electrolyte.

One aspect of the present application provides an electrolyte comprising lithium difluorophosphate (L iPO)₂F₂) And a compound containing a difluorophosphonoxy group.

In some embodiments of the present application, the difluorophosphonoxy-containing compound is selected from compounds of formula I:

wherein R is¹Selected from substituted or unsubstituted C₁-C₁₀Alkyl, substituted or unsubstituted C₂-C₁₀Unsaturated alkyl, the substituent is selected from at least one of alkanoyl, nitrile group and halogen;

or, R¹Any one selected from the group represented by the following structures:

wherein R is²Selected from single bond, substituted or unsubstituted C₁-C₁₀Alkylene, substituted or unsubstituted C₂-C₁₀Unsaturated alkyl, wherein the substituent is selected from halogen;

x is selected from a single bond or an oxygen atom;

denotes the connection position.

In some embodiments of the present application, the difluorophosphonoxy-containing compound comprises at least one of the following compounds:

in some embodiments of the present application, the difluorophosphonoxy-containing compound comprises at least one of the following compounds:

in some embodiments of the present application, the compound containing difluorophosphorus oxy groups is present in the electrolyte in an amount of 0.001 to 5% by mass based on the total mass of the electrolyte.

In some embodiments of the present application, the compound containing difluorophosphorus oxy groups is present in the electrolyte in an amount of 0.1 to 1% by mass, based on the total mass of the electrolyte.

In some embodiments of the present application, the lithium difluorophosphate is present in the electrolyte in an amount of 0.001% to 1% by mass, based on the total mass of the electrolyte.

In some embodiments of the present application, the lithium difluorophosphate is present in the electrolyte in an amount of 0.001% to 0.49% by mass, based on the total mass of the electrolyte.

In some embodiments of the present application, the electrolyte further comprises a polynitrile compound comprising at least one of:

in some embodiments of the present application, the electrolyte further includes a sultone compound including a structure represented by formula III-a or formula III-B:

wherein R is³¹、R³²、R³³、R³⁴、R³⁵、R³⁶、R³⁷Each independently selected from H, F, Cl, Br, substituted or unsubstitutedC₁-C₆Alkyl, substituted or unsubstituted C₂-C₆The substituent is selected from F, Cl and Br.

In some embodiments of the present application, the sultone additive comprises at least one of the following compounds:

in some embodiments of the present application, the sultone compound is present in the electrolyte in an amount of 0.01% to 10% by mass based on the total mass of the electrolyte.

In some embodiments of the present application, the sultone compound is present in the electrolyte in an amount of 0.5% to 5% by mass based on the total mass of the electrolyte.

In some embodiments of the present application, the electrolyte further comprises a fluoroether compound comprising at least one of the following compounds: desflurane, sevoflurane, fluoroethylene ether, 2,2, 2-trifluoroethyl ether, bis (fluoromethyl) ether, 2,2,3,3, 3-pentafluoropropyldifluoromethyl ether, 2, 2-difluoroethyltrifiuoromethyl ether, 1,2,3,3, 3-pentafluoropropyl2, 2, 2-trifluoroethyl ether, heptafluoropropyl1, 2,2, 2-tetrafluoroethyl ether, trifluoromethyl trifluorovinyl ether, 1,2,2, 2-tetrafluoroethyltrifiuoromethyl ether, 1,2,3,3, 3-pentafluoropropyldifluoromethyl ether, 1,2, 2-trifluoroethyl trifiuoromethyl ether, 2,2,3, 3-tetrafluoropropyldifluoromethyl ether, difluoromethyl-2, 2, 2-trifluoroethyl ether, 1-difluorodimethyl ether, trifluoromethyl methyl ether, 1,2, 2-tetrafluoroethylether, 1,2,3,3, 3-hexafluoropropyl methyl ether, 1,3, 3-tetrafluorodimethyl ether, bis (4-fluorobutyl) ether, ethyltrifluoromethyl ether, 2,2,3,3, 3-pentafluoropropyl methyl ether, methylnonafluorobutyl ether, 1,2,2, 2-tetrafluoroethyl methyl ether, pentafluorodimethyl ether, 1,2,3,3, 3-pentafluoropropyl ethyl ether, bis- (2, 2-difluoroethyl) ether, ethylperfluorobutyl ether, bis- (1,2,2, 2-tetrafluoroethyl) ether, 1,2, 2-tetrafluoroethyl methyl ether, 2-fluoroethyl (methyl) ether, perfluorobutyl methyl ether, ethylnonafluorobutyl ether, 2-perfluoropropoxy perfluoropropyl trifluorovinyl ether, 1,1,3,3, 3-hexafluoroisopropyl methyl ether, 1H,1H,2H, 3H-decafluorodipropyl ether, perfluorodiethylene glycol dimethyl ether, 2, 2-difluoroethyl methyl ether, perfluoroethyl vinyl ether, perfluoro-n-propyl vinyl ether, perfluoroethyl vinyl ether, allyl 2,2,3, 3-tetrafluoropropyl ether, 2,2, 2-trifluoroethyl ether, perfluoro (3-butenyl vinyl ether).

In some embodiments of the present application, the fluoroether compound is present in the electrolyte in an amount of 0.1 to 20% by mass based on the total mass of the electrolyte.

In some embodiments of the present application, the fluoroether compound is present in the electrolyte in an amount of 0.5 to 10% by mass based on the total mass of the electrolyte.

Another aspect of the present invention provides an electrochemical device including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the electrolyte according to the present invention.

In some embodiments of the present application, the positive electrode 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 including a positive electrode active material, a binder, and a conductive agent.

In some embodiments of the present application, the positive electrode active material is optionally selected from the group consisting of lithium cobaltate L iCoO₂(L CO), ternary lithium nickel manganese cobalt (NCM), lithium iron phosphate, lithium manganate, these positive electrode active materials can be used alone, can also be used in any combination of 2 and more than 2.

In some embodiments of the present application, the cathode active material includes magnesium element in an amount of m × 10 based on the total weight of the cathode active material layer³ppm, m ranges from 0.5 to 2.

In some embodiments of the present application, the mass percent of the lithium difluorophosphate in the electrolyte is denoted as a%, and the mass percent of the compound containing difluorophosphorus oxy groups in the electrolyte is denoted as b%, wherein (a + b)/m is less than or equal to 1.

In some embodiments, (a + b)/m is 1, 0.8, 0.6, 0.4, 0.2, 0.1, 0.005, or a range consisting of any two of these values.

The technical scheme provided by the application can achieve the following beneficial effects:

compared with the prior art, the additive of the electrolyte comprises lithium difluorophosphate (L iPO)₂F₂) And a difluorophosphonoxy-containing compound, can significantly improve both the resistance and high-temperature storage capacity retention performance of a lithium ion battery, so that an electrochemical device comprising the electrolyte of the present application has excellent performance in both low-temperature and high-temperature usage scenarios.

Detailed Description

In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below with reference to the embodiments of the present application, and it should be apparent that the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those skilled in the art without any creative effort based on the technical solutions and the given embodiments provided in the present application belong to the protection scope of the present application.

One aspect of the present application provides an electrolyte including a lithium salt, an organic solvent, and an additive, wherein the additive includes lithium difluorophosphate (L iPO)₂F₂) And a compound containing a difluorophosphonoxy group.

In the electrolyte of the present application, a difluorophosphoryloxy group-containing compound and L iPO were used₂F₂The detailed action mechanism for obtaining the effect is not clear, but the combination of the two can promote the increase of L iF in the organic protective film, so that L iF has better stability and can reduce the further contact of other additives and active materials, and can play the effect of further enhancing the interface stability, reducing the film forming property of other additives and reducing the thickness of the organic protective filmL iF rich in the organic protective layer has good stability at high temperature, can effectively prevent the side reaction of the active material and the electrolyte at high temperature, and realizes the improvement of the retention performance of high-temperature storage capacity.

In some embodiments of the present application, the difluorophosphonoxy-containing compound is selected from compounds of formula I:

wherein R is¹Selected from substituted or unsubstituted C₁-C₁₀Alkyl, substituted or unsubstituted C₂-C₁₀Unsaturated alkyl, the substituent is selected from at least one of alkanoyl, nitrile group and halogen;

or, R¹Any one selected from the group represented by the following structures:

wherein R is²Selected from single bond, substituted or unsubstituted C₁-C₁₀Alkylene, substituted or unsubstituted C₂-C₁₀Unsaturated alkyl, the substituent is halogen;

x is selected from a single bond or an oxygen atom;

denotes the connection position.

In some embodiments of the present application, the difluorophosphonoxy-containing compound comprises at least one of the following compounds:

in some embodiments of the present application, the difluorophosphonoxy-containing compound comprises at least one of the following compounds:

in some embodiments of the present application, the compound containing difluorophosphorus oxy groups is present in the electrolyte in an amount of 0.001 to 5% by mass based on the total mass of the electrolyte. If the content of the compound containing the difluorophosphorus oxygroup in the electrolyte is too low, the compound cannot play a role in forming an effective composite protective film, and if the content is too high, the compound cannot be consumed in time, so that the difluorophosphorus oxygroup compound participating in film formation can be decomposed at high temperature, and the high-temperature storage performance of the electrochemical device is influenced. In some embodiments of the present application, the compound containing difluorophosphorus oxy groups is present in the electrolyte in an amount of 0.1 to 1% by mass, based on the total mass of the electrolyte. Within this range, the protective film formed from the fluorophosphoric oxy-group-containing compound is more excellent in performance. In the present application, the mass percentage of the difluorophosphorus oxy group-containing compound in the electrolyte solution is in a range selected from any of 4%, 3%, 2.5%, 2%, 1.5%, 1%, 0.8%, 0.5%, 0.3%, or any two of these values.

In some embodiments of the present application, the lithium difluorophosphate is present in the electrolyte in an amount of 0.001% to 1% by mass, based on the total mass of the electrolyte. In some embodiments of the present application, the lithium difluorophosphate is present in the electrolyte in an amount of 0.001% to 0.49% by mass, based on the total mass of the electrolyte. The lithium difluorophosphate with a small content is not beneficial to forming a protective film, the lithium difluorophosphate with a large content can only be partially formed into a film, and the residual lithium difluorophosphate can continuously react in the storage process and can deteriorate the high-temperature storage performance.

In some embodiments of the present application, the electrolyte further comprises a polynitrile compound.

In some embodiments of the present application, the polynitrile compound comprises at least one of:

in some embodiments of the present application, the polynitrile compound is present in the electrolyte in an amount of 0.01 to 10% by mass, based on the total mass of the electrolyte. The lithium difluorophosphate, the compound containing the difluorophosphorus oxy group and the polynitrile compound act together, so that the positive active material can be further protected, the contact between the electrolyte and the positive active material is reduced, and the impedance of the electrochemical device is further reduced. When the content of the polynitrile compound is within this range, the surface structure of the positive electrode can be effectively protected without affecting the lithium ion transport of the positive electrode, and the impedance property is deteriorated. The mass percentage of the polynitrile compound in the electrolyte solution in the present application may be in a range selected from any of 10%, 8%, 7%, 5%, 4%, 3%, 2%, 1% or any two of these values.

In some embodiments of the present application, the electrolyte further comprises a sultone compound.

In some embodiments of the present application, the sultone compound has a structure comprising at least one of a compound of formula III-a or formula III-B:

wherein R is³¹、R³²、R³³、R³⁴、R³⁵、R³⁶、R³⁷Are respectively and independently selected from H, F, Cl, Br, substituted or unsubstituted C1-C6 alkyl and substituted or unsubstituted C2-C6 unsaturated hydrocarbon groups, and the substituent is selected from F, Cl and Br.

In some embodiments of the present application, the sultone compound comprises the structure shown below:

in some embodiments of the present application, the sultone compound is present in the electrolyte in an amount of 0.01% to 10% by mass based on the total mass of the electrolyte. In some embodiments of the present application, the sultone compound is present in the electrolyte in an amount of 0.5% to 5% by mass based on the total mass of the electrolyte. Lithium difluorophosphate, a compound containing difluorophosphorus oxy and a sultone compound act together to further form a film on the positive electrode and the negative electrode, so that the high temperature resistance of the interface protective film of the positive electrode and the negative electrode is improved. When the content of the sultone compound is within the range, the film forming effect is better. In some embodiments of the present application, the sultone compound is present in the electrolyte in a mass percent range selected from 10%, 8%, 7%, 5%, 4%, 3%, 2%, 1%, 0.8%, or any two of these values.

In some embodiments of the present application, the electrolyte further includes a fluoroether compound. The lithium difluorophosphate, the compound containing the difluorophosphorus oxy group and the fluoroether compound act together to improve the voltage resistance of the electrolyte. In some embodiments of the present application, the fluoroether compound comprises at least one of the following compounds: desflurane, sevoflurane, fluoroethylene ether, 2,2, 2-trifluoroethyl ether, bis (fluoromethyl) ether, 2,2,3,3, 3-pentafluoropropyldifluoromethyl ether, 2, 2-difluoroethyltrifiuoromethyl ether, 1,2,3,3, 3-pentafluoropropyl2, 2, 2-trifluoroethyl ether, heptafluoropropyl1, 2,2, 2-tetrafluoroethyl ether, trifluoromethyl trifluorovinyl ether, 1,2,2, 2-tetrafluoroethyltrifiuoromethyl ether, 1,2,3,3, 3-pentafluoropropyldifluoromethyl ether, 1,2, 2-trifluoroethyl trifiuoromethyl ether, 2,2,3, 3-tetrafluoropropyldifluoromethyl ether, difluoromethyl-2, 2, 2-trifluoroethyl ether, 1-difluorodimethyl ether, trifluoromethyl methyl ether, 1,2, 2-tetrafluoroethylether, 1,2,3,3, 3-hexafluoropropyl methyl ether, 1,3, 3-tetrafluorodimethyl ether, bis (4-fluorobutyl) ether, ethyltrifluoromethyl ether, 2,2,3,3, 3-pentafluoropropyl methyl ether, methylnonafluorobutyl ether, 1,2,2, 2-tetrafluoroethyl methyl ether, pentafluorodimethyl ether, 1,2,3,3, 3-pentafluoropropyl ethyl ether, bis- (2, 2-difluoroethyl) ether, ethylperfluorobutyl ether, bis- (1,2,2, 2-tetrafluoroethyl) ether, 1,2, 2-tetrafluoroethyl methyl ether, 2-fluoroethyl (methyl) ether, perfluorobutyl methyl ether, ethylnonafluorobutyl ether, 2-perfluoropropoxy perfluoropropyl trifluorovinyl ether, 1,1,3,3, 3-hexafluoroisopropyl methyl ether, 1H,1H,2H, 3H-decafluorodipropyl ether, perfluorodiethylene glycol dimethyl ether, 2, 2-difluoroethyl methyl ether, perfluoroethyl vinyl ether, perfluoro-n-propyl vinyl ether, perfluoroethyl vinyl ether, allyl 2,2,3, 3-tetrafluoropropyl ether, 2,2, 2-trifluoroethyl ether, perfluoro (3-butenyl vinyl ether).

In some embodiments of the present application, the fluoroether compound is present in the electrolyte in an amount of 0.1 to 20% by mass based on the total mass of the electrolyte. In some embodiments of the present application, the fluoroether compound is present in the electrolyte in an amount of 0.5 to 10% by mass based on the total mass of the electrolyte. The fluorine ether compound contains more fluorine atoms, and the fluorine ether compound can play a role in blocking the transmission of lithium ions in the electrolyte along with the increase of the content of the fluorine atoms, so that the polarization of the electrolyte is increased. The increase in polarization further causes interfacial lithium precipitation during charging, thereby affecting the performance of the electrochemical device. In some embodiments of the present disclosure, the content of the fluoroether compound in the electrolyte solution is in a range selected from 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1% or a range consisting of any two of these values.

In the present application, the lithium salt may be selected from lithium salts commonly used in the art, and specifically, the lithium salt may be selected from L iPF₆Lithium bistrifluoromethanesulfonylimide (abbreviated to L iTFSI), lithium bis (fluorosulfonyl) imide (abbreviated to L iFSI), lithium dioxalate borate (abbreviated to L iBOB), lithium difluorooxalato borate (abbreviated to L iDFOB), lithium tetrafluorooxalate (abbreviated to L iPF iDFOB)₄C₂O₄) Lithium difluorooxalate (abbreviated as L iPF)₂(C₂O₄)₂) Lithium hexafluorocaesiate (abbreviated as L iCsF)₆) When the lithium salt contains L iPF₆And other lithium salts, L iPF₆The mass ratio of the lithium salt is more than 50 percent.

In the present application, the content of the lithium salt in the electrolyte is 0.5 mol/L-2 mol/L based on the total mass of the electrolyte.

In the present application, the organic solvent is a polar organic solvent. In some embodiments herein, the organic solvent comprises at least one of a cyclic carbonate, a chain carboxylate, or a cyclic carboxylate. Among them, examples of the carbonate may be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), and the like. Examples of the carboxylic acid ester may include methyl formate, ethyl formate, methyl acetate, ethyl acetate, n-propyl acetate, 1-dimethylethyl acetate, methyl propionate, ethyl propionate, methyl n-butyrate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonic lactone, caprolactone, and the like.

The electrolyte of the present application further includes an ether solvent, a phosphorus-containing organic solvent, an aromatic fluorine-containing solvent, a ketone solvent, an alcohol solvent or an aprotic solvent. A single organic solvent may be used, or a mixture of solvents may be used. When a mixture of organic solvents is used, the mixing ratio may be controlled according to desired electrochemical device properties.

In some embodiments, the ether solvent is a cyclic ether compound, wherein the cyclic ether includes, but is not limited to: tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 2-methyl-1, 3-dioxolane, 4-methyl-1, 3-dioxolane, 1, 3-dioxane, 1, 4-dioxane and dimethoxypropane. In some embodiments, the cyclic ether is present in the electrolyte in an amount of 0.1% by mass or more, based on the total mass of the electrolyte. In some embodiments, the cyclic ether is present in the electrolyte in an amount of 0.5% by mass or more, based on the total mass of the electrolyte. In some embodiments, the cyclic ether is present in the electrolyte in an amount of 2% by mass or more, based on the total mass of the electrolyte. In some embodiments, the cyclic ether is present in the electrolyte in an amount of 5% by mass or less, based on the total mass of the electrolyte.

In some embodiments, the ether solvent is a chain ether compound, wherein the chain ether compound includes, but is not limited to: dimethoxymethane, 1-dimethoxyethane, 1, 2-dimethoxyethane, diethoxymethane, 1-diethoxyethane, 1, 2-diethoxyethane, ethoxymethoxymethane, 1-ethoxymethoxyethane and 1, 2-ethoxymethoxyethane. In some embodiments, the chain ether compound is present in the electrolyte in an amount of 0.1% by mass or more, based on the total mass of the electrolyte. In some embodiments, the chain ether compound is present in the electrolyte in an amount of 0.5% by mass or more, based on the total mass of the electrolyte. In some embodiments, the chain ether compound is present in the electrolyte in an amount of 2% by mass or more, based on the total mass of the electrolyte. In some embodiments, the chain ether compound is present in the electrolyte in an amount of 3% by mass or more, based on the total mass of the electrolyte. In some embodiments, the chain ether compound is present in the electrolyte in an amount of 30% by mass or less, based on the total mass of the electrolyte.

In some embodiments, the phosphorus-containing organic solvent includes, but is not limited to, trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris (2,2, 2-trifluoroethyl) phosphate, and tris (2,2,3,3, 3-pentafluoropropyl) phosphate. In some embodiments, the phosphorus-containing organic solvent is present in the electrolyte in an amount of 0.1% by mass or more based on the total mass of the electrolyte. In some embodiments, the phosphorus-containing organic solvent is present in the electrolyte in an amount of 0.5% by mass or more based on the total mass of the electrolyte. In some embodiments, the phosphorus-containing organic solvent is present in the electrolyte in an amount of 2% by mass or more, based on the total mass of the electrolyte. In some embodiments, the phosphorus-containing organic solvent is present in the electrolyte in an amount of 3% by mass or more based on the total mass of the electrolyte. In some embodiments, the phosphorus-containing organic solvent is present in the electrolyte in an amount of 8% by mass or less, based on the total mass of the electrolyte.

In some embodiments, the aromatic fluorine-containing solvent includes, but is not limited to, fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene. In some embodiments, the aromatic fluorine-containing solvent is present in the electrolyte in an amount of 0.1 wt% or more based on the total mass of the electrolyte. In some embodiments, the aromatic fluorine-containing solvent is present in the electrolyte in an amount of 0.5% by mass or more based on the total mass of the electrolyte. In some embodiments, the aromatic fluorine-containing solvent is present in the electrolyte in an amount of 2% by mass or more based on the total mass of the electrolyte. In some embodiments, the aromatic fluorine-containing solvent is present in the electrolyte in an amount of 4% by mass or more based on the total mass of the electrolyte. In some embodiments, the aromatic fluorine-containing solvent is present in the electrolyte in an amount of 8% by mass or less based on the total mass of the electrolyte.

Examples of the ketone solvent include cyclohexanone and the like.

Examples of the alcohol solvent include ethanol, isopropanol, and the like. Examples of aprotic solvents include mononitriles such as R-CN (where R is C)₂-C₂₀Linear, branched, or cyclic hydrocarbon groups, which may include double bonds, aromatic rings, or ether linkages), amides (e.g., dimethylformamide), dioxolanes (e.g., 1, 3-dioxolane), sulfolane, and the like.

Another aspect of the present invention provides an electrochemical device comprising a cathode, a separator having an anode disposed between the cathode and the anode, and the electrolyte according to the present invention.

In the electrochemical device of the present application, the positive electrode 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 including a positive electrode active material, a binder, and a conductive agent. The positive active material includes a compound that reversibly intercalates and deintercalates lithium ions. The positive electrode active material may include a composite oxide containing lithium and at least one element selected from cobalt, manganese, and nickel. The specific kind of the positive electrode active material is not particularly limitedThe positive active material is optionally selected from the group consisting of L iCoO lithium cobaltate₂(L CO), ternary lithium nickel manganese cobalt (NCM), lithium iron phosphate, lithium manganate, these positive electrode active materials can be used alone, can also be used in any combination of 2 and more than 2.

In some embodiments, the cathode active material includes magnesium (Mg) element in an amount of m × 10 based on the total weight of the cathode active material layer³The value range of ppm and m is 0.5-2, the mass percent of lithium difluorophosphate in the electrolyte is recorded as a%, the mass percent of difluorophosphorus oxy-substances in the electrolyte is recorded as b%, and the mass percent of (a + b)/m is less than or equal to 1.

In some embodiments, m is 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, 2, or a range consisting of any two of these values.

In some embodiments, (a + b)/m is 1, 0.8, 0.6, 0.4, 0.2, 0.1, 0.005, or a range consisting of any two of these values.

The positive electrode active material may have a coating layer on the surface, or may be mixed with another compound having a coating layer. The coating may include at least one coating element compound selected from an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate (oxycarbonate) of the coating element, and an oxycarbonate (hydroxycarbonate) of the coating element. The compounds used for the coating may be amorphous or crystalline. The coating element contained in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer may be applied by any method as long as the method does not adversely affect the properties of the positive electrode active material. For example, the method may include any coating method well known to those of ordinary skill in the art, such as spraying, dipping, and the like.

The binder improves the binding of the positive electrode active material particles to each other, and also improves the binding of the positive electrode active material to the current collector. Non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like.

Including conductive materials to impart conductivity to the electrodes. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

The current collector may be aluminum (Al), but is not limited thereto.

Negative electrode

The negative electrode includes a current collector and a negative active material layer disposed on the current collector, the active material layer including a negative active material, specific kinds of the negative active material being not particularly limited and selected as required, and specifically, the negative active material is selected from natural graphite, artificial graphite, mesophase micro carbon spheres (abbreviated as MCMB), hard carbon, soft carbon, silicon-carbon composite, L i-Sn alloy, L i-Sn-O alloy, Sn, SnO, and₂spinel-structured lithiated TiO₂-Li4Ti₅O1₂Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, or mixtures thereof, the crystalline carbon may be natural or synthetic graphite that is amorphous or in the form of platelets, spheres, or fibers, the amorphous carbon may be mesophase pitch carbide, calcined coke, or the like.

The negative active material layer may include a binder and optionally further include a conductive material. The binder improves the binding of the negative active material particles to each other and the binding of the negative active material to the current collector. Non-limiting examples of adhesives include: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

Including conductive materials to impart conductivity to the electrodes. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, conductive metal coated polymeric substrates, and combinations thereof.

Isolation film

In some embodiments, the electrochemical device of the present application is provided with a separator between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separation film used in the electrochemical device of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.

For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

The inorganic layer comprises inorganic particles and a binder, wherein the inorganic particles are selected from one or more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from one or a combination of more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

The polymer layer comprises a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene)

The technical solution of the present application is exemplarily described below by specific embodiments:

1) preparing an electrolyte: at water content<In a 10ppm argon atmosphere glove box, Ethylene Carbonate (EC), diethyl carbonate (DEC) and Propylene Carbonate (PC) were mixed uniformly in a mass ratio of 2:6:2, and then a fully dried lithium salt L iPF was added₆Dissolved in the above solvent, L iPF₆Is 1 mol/L, and the electrolyte is called basic electrolyte.

As shown in Table 1, a compound containing formula I and L iPO were added to the base electrolyte₂F₂Or with SEI film forming additives.

Examples of compounds containing formula I are as follows:

examples of polynitrile compounds are as follows:

examples of sultone compounds are as follows:

examples of the fluoroether compounds are as follows:

1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether and 2, 2-difluoroethyl trifluoromethyl ether.

Preparing a lithium ion battery:

2) preparation of positive electrode active material:

taking the Mg element as 1000ppm as an example, CoCl is purchased commercially₂And MgCl₂Respectively preparing aqueous solution according to the molar ratio of active substances of 1: m (0-0.004027) and adding NH₃.HCO₃The solution adjusted the pH of the mixture to about 10.5 to obtain a precipitate. Calcining the obtained precipitate at 400 deg.C for 5h to obtain Mg-containing CO₃O₄. The obtained CO is₃O₄And L i₂CO₃After being uniformly mixed according to the molar ratio of 2: 3.15, the mixture is calcined at the temperature of 1000 ℃ for 8h to obtain L iCoO₂The L iCoO obtained₂Adding MgO according to the molar ratio of 1 (0.004027-m), mixing uniformly, sintering the mixed material at 800 ℃ for 8h to obtain the finished product of the positive active material lithium cobaltate (the molecular formula is L iCoO) containing Mg element₂) The obtained positive electrode active material lithium cobaltate (molecular formula L iCoO)₂) Fully stirring and mixing the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a proper amount of N-methyl pyrrolidone (NMP) solvent according to a weight ratio of 96:2:2 to form uniform anode slurry; coating the slurry on an Al foil of a positive current collector, drying, cold pressing to obtain a positive active material layer, and cutting and welding tabs to obtain the positive electrode. Wherein Mg element contained in lithium cobaltate, a positive electrode active material, unless otherwise specified, the following examples and comparative examplesWherein the content of Mg element is 1000ppm based on the total weight of the positive electrode active material layer.

3) Preparing positive electrode by mixing positive electrode active material lithium cobaltate (molecular formula is L iCoO)₂) Fully stirring and mixing acetylene black serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder in a proper amount of N-methylpyrrolidone (NMP) solvent according to a weight ratio of 96:2:2 to form uniform positive electrode slurry; coating the slurry on an Al foil of a positive current collector, drying, cold pressing to obtain a positive active material layer, and cutting and welding tabs to obtain the positive electrode.

4) Preparation of a negative electrode: fully stirring and mixing a negative electrode active material graphite, a conductive agent acetylene black, a binder Styrene Butadiene Rubber (SBR), and a thickener sodium carboxymethyl cellulose (CMC) in a proper amount of deionized water solvent according to a weight ratio of 95:2:2:1 to form uniform negative electrode slurry; coating the slurry on a Cu foil of a negative current collector, drying, cold pressing to obtain a negative active material layer, cutting and welding a tab to obtain a negative electrode.

5) And (3) isolation film: a PE porous polymer film is used as a separation film.

6) Preparing a lithium ion battery: and sequentially stacking the anode, the isolating membrane and the cathode to enable the isolating membrane to be positioned between the anode and the cathode to play an isolating role, then winding and placing the isolating membrane into an outer packaging foil, injecting the prepared electrolyte into the dried battery, and carrying out vacuum packaging, standing, formation, shaping and other procedures to complete the preparation of the lithium ion battery.

Test one, 50% SOC impedance test

The cell was discharged to 3.0V at 25 ℃ with a current of 0.5C, left for 5 minutes, and then charged to 4.45V with a current of 0.5C, with a constant voltage of 4.45V to 0.025C. After standing for 5 minutes, the discharge was carried out to 3.4V using a current of 0.1C, and the capacity discharged at this time was marked as C₁. Using 0.5C₁The capacity of the battery is charged to 4.45V, and the voltage is constant to 0.025C under the voltage of 4.45V₁Rest for 5min, use 0.1C₁Discharge current of 5h, the battery voltage at this time is denoted as V₁After that, the discharge was carried out for 1 second by applying a current of 1C, and the voltage at the final stage of the discharge was recorded asV₂. The 50% SOC impedance is calculated as: (V)₁-V₂)/(1C-0.1C₁)。

Test II, storage Capacity Retention ratio

The cell was discharged to 3.0V at 25 ℃ with a current of 0.5C and left to stand for 5 min. Charging to 4.45V at 0.5C, charging to 0.025C at 4.45V under constant voltage, standing for 5min, discharging to 3.0V with 0.5C current, and recording the discharged capacity as C₁. The charging is carried out by 0.5C to 4.45V, and the constant voltage charging is carried out at 4.45V to 0.025C. Placing the battery in a 70 deg.C oven, storing at 70 deg.C for 24 hr, testing for 24 hr, taking out, discharging at 25 deg.C with 0.5C current to 3.0V, and recording the discharged capacity as C₂. The calculation formula of the storage capacity retention rate at the temperature of 70 ℃ for 24h is as follows: (C)₂/C₁)×100％。

Test three, hot box test

The cell was discharged to 3.0V at 25 ℃ with a current of 0.5C and left to stand for 5 min. Then charging to 4.45V with 0.5C current, and charging to 0.05C with constant voltage at 4.45V. Then the battery is placed in a high temperature box, the temperature of the high temperature box is raised to 130 ℃ at the temperature raising speed of 5 plus or minus 2 ℃/min, and the battery is placed for 60 minutes at the constant temperature of 130 ℃. The battery did not ignite and explode and the pass was recorded. This experiment tested 10 lithium ion batteries, and the number of passed tests was recorded.

Test four, 45 ℃ cycle test

The cell was discharged to 3.0V at 45 ℃ with a current of 0.5C and left to stand for 5 min. Charging to 4.45V at 0.5C, charging to 0.05C at 4.45V under constant voltage, and discharging to 3.0V with 0.5C current after charging. According to the charging and discharging process, the circulation is carried out for 800 circles under the temperature condition of 45 ℃. The capacity of the first lap is denoted C₁The capacity discharged at the 500 th turn is denoted as C₅₀₀The formula for the capacity retention calculation is: (C)₁/C₅₀₀)×100％。

Test five, Mg element content test

Discharging the battery to 2.8V at 0.5C, resting for 5min, discharging to 2.8V at 0.05C, resting for 5min, discharging to 2.8V at 0.01C, and resting for 5minThe discharge was repeated three times with a 0.01C current. The battery is disassembled by wearing clean gloves, and the anode and the cathode are carefully separated and do not contact with each other. In a glove box, the anode is soaked in high-purity DMC (dimethyl carbonate, the purity is more than or equal to 99.99 percent) for 10 minutes, and then taken out and dried for 30 minutes. (DMC amount:>15mL/1540mm²area of the disc). In a dry environment, powder is scraped by using a ceramic scraper>0.4g, wrapping with weighing paper, weighing with an electronic balance to 0.0001g, recording the weight of the sample as d (d is less than or equal to 0.4) g, slowly adding 10m of aqua regia L with the mass ratio of concentrated nitric acid to concentrated hydrochloric acid being 1:1, flushing the sample on the inner wall into the bottom of the tank, gently shaking the digestion tank, wiping water drops outside the digestion tank with dust-free paper, assembling the digestion device, placing the digestion tank in a microwave digestion instrument for digestion, unloading the digestion tank, flushing the cover with ultrapure water for 2-3 times, pouring flushing fluid into the digestion tank, shaking the sample solution, slowly pouring the sample solution into a funnel, flushing the digestion tank for 3 times, fixing the volume to 100ml, shaking up, testing the sample by a plasma emission spectrometer (ICP) by using a standard curve method, and recording the concentration of the tested sample as rho₂g/ml. The calculation result of the content of the Mg element is as follows: (ρ)₂×100)/d。

The electrolytes and lithium ion batteries of examples 1.1 to 1.33 and comparative examples 1.1 to 1.3 were prepared according to the above preparation methods; the additives in the electrolyte and the respective amounts added are shown in table 1.

TABLE 1 EXAMPLES 1.1-1.33 AND COMPARATIVE EXAMPLES 1.1-1.3

It can be seen from examples 1.1-1.22 that the compounds I-1, I-7 and I-8 have significant improvement effects on the retention rate of impedance and storage capacity, and it can be seen from examples 1.22-1.33 that L iPO is accompanied with₂F₂The content is increased, the impedance (DCR) is obviously reduced, and the storage capacity retention rate is obviously improved. By way of examples 1.1 to 1.33 and comparative examples1.1-1.3 comparative analyses, Compounds of formula I and L iPO₂F₂The impedance of the battery can be reduced by adding the content at the same time, and the storage capacity retention rate is obviously improved.

The polynitrile compound has effect of enhancing the stability of positive electrode interface, and contains difluorophosphoryloxy compound and L iPO₂F₂The L iF component reduces the contact of the active material and the electrolyte, but has weak dissolution effect on the transition metal, the polynitrile compound stabilizes the transition metal of the anode through adsorption, and has obvious dissolution effect on the transition metal with high valence state, and the combination of the two can further reduce the side reaction under high temperature and high pressure, and further enhance the storage capacity retention rate of the battery, which can be illustrated by the examples in Table 2.

Table 2 examples 1.29, examples 2.1-2.24

By comparing example 1.29 with examples 2.1-2.24, it can be seen that the electrolyte solution is further improved by adding polynitrile compounds in the electrolyte, and the storage capacity retention rate is further improved.

Difluorophosphoxy group-containing compound, L iPO₂F₂Under the combined action of the sultone compound and the sultone compound, the sultone compound can form an organic protective film containing organic sulfuric acids in the battery through ring opening, the high-temperature resistance of the protective film iS outstanding, L iS and lithium sulfonate components in the organic protective film can be further converted and increased at a high temperature state, so that the effect of improving the performance of a battery hot box can be achieved while the storage capacity retention rate iS enhanced, and the effect iS illustrated through the embodiment in the table 3.

Table 3 examples 1.29 and 3.1-3.22

Through comparison between the embodiment 1.29 and the embodiments 31-3.22, the increase of the sultone compound can be found, the hot box passing rate is obviously improved, and the capacity retention rate is further enhanced after the sultone compound is added.

Difluorophosphoxy group-containing compound, L iPO₂F₂The oxidation resistance of the electrolyte can be improved by the combined action of the electrolyte and the fluoroether compound, the oxidative decomposition of the electrolyte can be reduced in the long-term high-temperature high-pressure cycle test process, HF and other byproducts generated by the decomposition of the electrolyte can be reduced, and the byproducts can be prevented from damaging active materials and organic protective films₂F₂The formed high L iF protective film can play a double protection role, and can improve the high-temperature cycle performance of the battery, which is specifically described by the examples in Table 4.

Table 4 examples 1.29 and examples 4.1-4.14

By adding the fluoroether compound in the examples 1.29 and 4.1-4.14, the cycle capacity retention rate at 45 ℃ of the battery is obviously improved.

Magnesium (Mg) element occupies crystal lattices of the anode material in the anode material and plays a better role in the stability of the anode material, particularly, when the anode is in a release state, the crystal lattices of lithium cobaltate can be changed, the stability is reduced, the crystal lattices cannot be stabilized like a fully-open state, the magnesium has the stability of the structure of the anode material, an organic protective film formed by lithium difluorophosphate and difluorophosphine oxide substances is added to reduce the contact between electrolyte and the anode material, and the acid resistance of the surface of the anode material is enhanced by the L iF-rich protective film, which is specifically illustrated by the examples in Table 5.

TABLE 5 examples 1.29 and examples 5.1-5.13