Non-aqueous electrolyte and lithium-ion battery

Abstract

To provide a non-aqueous electrolyte and a lithium ion battery for improving a gas generation problem of a lithium ion battery under high temperatures.SOLUTION: The non-aqueous electrolyte includes a non-aqueous organic solvent, lithium salt, and an additive. The additive includes chloroethylene carbonate and lithium difluoro(bis(oxalato))phosphate. By combining additives, a double-layer structure consisting of LiCl-LiF inorganic salt and vinylene carbonate oligomer can be formed on the surface of the negative electrode, and this provides an excellent coating effect at the interface with the negative electrode. The rigidity of LiF and the low solubility of LiCl in the inorganic salt ensure the stability of a negative electrode protective layer after mixing, thereby improving the performance of the battery at high temperatures.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and more particularly to non-aqueous electrolytes and lithium-ion batteries.

Background Art

[0002] In recent years, with the popularization of cameras, mobile phones, watches, laptops, electric vehicles, etc., the requirements for the applications of lithium-ion batteries have been increasing. Therefore, miniaturization, weight reduction, increase in energy density, extension of service life, etc. have become the development trends in the battery product industry.

[0003] The electrolyte is an important component of a lithium-ion battery. The electrolyte functions to transport lithium ions between the positive electrode and the negative electrode. The safety, charge-discharge cycle performance, rate performance, and charge-discharge capacity of the battery are all closely related to the electrochemical properties of the electrolyte. Currently, the electrolyte widely used in lithium-ion batteries is generally an electrolyte using lithium hexafluorophosphate (LiPF6) as the electrolyte salt and a mixture of cyclic carbonate and chain carbonate as the organic solvent. However, such electrolytes have many defects. In particular, the negative electrode interface protection layer (SEI film) of a lithium-ion battery is prone to breakage and repair under high voltage, and the electrochemical reaction between the electrolyte solvent and other additive components cannot be avoided, resulting in the problem of gas generation.

[0004] In view of the above, it is urgent to develop a new lithium-ion battery electrolyte to solve the above problems.

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of the above drawbacks of the prior art, the present invention provides a non-aqueous electrolyte and a lithium-ion battery for improving the gas generation problem of a lithium-ion battery at high temperatures.

Means for Solving the Problems

[0006] To achieve the above object and other related objects, the present invention provides a non-aqueous electrolyte containing a non-aqueous organic solvent, a lithium salt, and an additive. The additive includes chloroethylene carbonate and lithium difluorobis(oxalato)phosphate, and chloroethylene carbonate includes a compound represented by the following structural formula.

Chemical formula

[0007] In the formula, the R group is selected from a Cl group or a CCl3 group.

[0008] In one embodiment of the present invention, the content of chloroethylene carbonate in the non-aqueous electrolyte is 0.5% to 5% by mass percentage.

[0009] In one embodiment of the present invention, the content of chloroethylene carbonate in the non-aqueous electrolyte is 1% to 2.5% by mass percentage.

[0010] In one embodiment of the present invention, the content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte is 0.5% to 2% by mass percentage.

[0011] In one embodiment of the present invention, the content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte is 0.5% to 1% by mass percentage.

[0012] In one embodiment of the present invention, the conductivity of the non-aqueous electrolyte is 7.0 mS / cm to 12.5 mS / cm.

[0013] In one embodiment of the present invention, the structural formula of chloroethylene carbonate is as follows.

Chemical formula

[0014] In one embodiment of the present invention, the lithium salt includes lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide.

[0015] In one embodiment of the present invention, the content of the lithium salt in the non-aqueous electrolyte is 8 to 20% by mass percentage.

[0016] In one embodiment of the present invention, the non-aqueous organic solvent includes cyclic carbonate and chain carbonate. The cyclic carbonate includes one or both of ethylene carbonate and propylene carbonate. The chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0017] Another aspect of the present invention provides a lithium-ion battery including a positive electrode sheet, a negative electrode sheet, a separator, and the above non-aqueous electrolyte.

Advantages of the Invention

[0018] The present invention introduces a chlorine-containing organic additive, which is chloroethylene carbonate (ClEC) and lithium difluoro(bis(oxalato))phosphate (LiODFP), into the non-aqueous electrolyte. During the introduction process, chloroethylene carbonate and lithium difluoro(bis(oxalato))phosphate can form a double-layer structure having LiCl-LiF inorganic salt and vinylene carbonate oligomer on the surface of the negative electrode. Since a part of the vinylene carbonate oligomer is an organic compound, it has high flexibility and a more preferable coating effect at the interface with the negative electrode. Due to the rigidity of LiF and the low solubility of LiCl in the inorganic salt, the stability of the negative electrode protection layer (SEI film) after blending is ensured, thereby improving the performance of the battery at high temperatures.

Modes for Carrying Out the Invention

[0019] Hereinafter, the implementation of the present invention will be described with specific examples. A person skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementations. Various details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. Note that as long as there is no contradiction between each embodiment, the following embodiments and the characteristic parts in each embodiment may be combined. It should also be understood that the terms used in the embodiments of the present invention are for explaining specific embodiments and are not for limiting the scope of the present invention. For test methods that do not specify specific conditions in the following examples, usually, conventional conditions or conditions recommended by each manufacturer are adopted.

[0020] For simplicity, the present invention only explicitly discloses several numerical ranges, and all points or individual values between the endpoints of the range are included within that range. Therefore, each point or single value can function as its own lower or upper limit in combination with other points or single values, or in combination with other lower or upper limits, to form ranges that are not explicitly described.

[0021] The present invention provides a non-aqueous electrolyte and a lithium-ion battery. The lithium-ion battery contains the non-aqueous electrolyte of the present invention. Since chloroethylene carbonate and lithium difluorobis(oxalato)phosphate are introduced into the non-aqueous electrolyte, a double-layer structure having LiCl-LiF inorganic salt and vinylene carbonate oligomer can be formed on the surface of the negative electrode, thereby improving the coating effect and stability of the negative electrode interface film, and improving the performance of the lithium-ion battery at high temperatures.

[0022] The above non-aqueous electrolyte contains a non-aqueous organic solvent, a lithium salt, and an additive. The lithium salt and the additive are dissolved in the non-aqueous organic solvent. The additive contains a chlorine-containing organic additive and lithium difluorobis(oxalato)phosphate. The chlorine-containing organic additive contains chloroethylene carbonate, and the structural formula of chloroethylene carbonate is as follows.

Chem.

[0023] In the formula, the R group is selected from a Cl group or a CCl3 group. That is, chloroethylene carbonate may be a compound represented by the structural formula (1), may be a compound represented by the structural formula (2), or may be a composition in which the compounds represented by the structural formula (1) and the structural formula (2) are mixed at an arbitrary ratio.

Chem.

[0024] Since both the structural formula (1) and the structural formula (2) contain a vinylene carbonate group and a chlorine-containing group, during the operation of the battery, by mixing the structural formula (1) and the structural formula (2) with lithium difluorobis(oxalato)phosphate, a double-layer structure having LiCl-LiF inorganic salt and vinylene carbonate oligomer can be formed on the surface of the negative electrode. Here, the vinylene carbonate oligomer layer is an organic compound layer with high flexibility and good coating effect at the interface with the negative electrode. Due to the rigidity of LiF and the low solubility of LiCl, the stability of the negative electrode protective layer (SEI film) after blending can be ensured.

[0025] Chloroethylene carbonate is preferably a compound represented by the structural formula (1).

Chem.

[0026] As a result of the research, it was found that the combination of the compound represented by the structural formula (1) and lithium difluorobis(oxalato)phosphate has a higher production efficiency of LiCl-LiF composite inorganic salt and vinylene carbonate oligomer than the combination of the compound represented by the structural formula (2) and lithium difluorobis(oxalato)phosphate. Therefore, chloroethylene carbonate is preferably a compound represented by the structural formula (1).

[0027] In some embodiments, the content of chloroethylene carbonate in the non-aqueous electrolyte accounts for 0.5% to 5% by mass percentage, such as 0.5%, 1%, 3%, 5%, etc. The content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte accounts for 0.5% to 2% by mass percentage, such as 0.5%, 1.5%, 2%, etc. Further, the content of chloroethylene carbonate in the non-aqueous electrolyte accounts for 1% to 2.5% by mass percentage, such as 1.5%, 2%, 2.5%, etc. The content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte accounts for 0.5% to 1% by mass percentage, such as 0.5%, 0.8%, 1.0%, etc. By adjusting the ratio of chloroethylene carbonate and lithium difluorobis(oxalato)phosphate, the conductivity of the electrolyte can be adjusted to 7.0 mS / cm to 12.5 mS / cm. Here, the conductivity of the electrolyte is not limited and can be adjusted within the above range, such as 7.0 mS / cm, 10 mS / cm, 12 mS / cm, etc.

[0028] It should be noted that both chloroethylene carbonate and lithium difluorobis(oxalato)phosphate of the present invention can be purchased through general commercial routes or can be prepared using conventional preparation methods in this field.

[0029] The lithium salt in the non-aqueous electrolyte functions as an electrolyte salt. When the lithium salt dissolves in the non-aqueous solvent, a large amount of active lithium ions are released, improving the conductivity of the electrolyte. To obtain a better electrolyte, substances with the characteristics of low dissociation energy and high solubility are usually adopted for the lithium salt. Due to the low dissociation energy, the electrolyte formed after the lithium salt dissolves has high conductivity, thereby achieving a high battery rate. Due to the high solubility, sufficient lithium ions required for transportation are present in the electrolyte, improving stability. Therefore, when the battery operates at high voltage and high temperature, the lithium salt does not react with other components. Due to the excellent SEI film formation performance, the electrolyte is not continuously consumed during subsequent cycles. It also has an excellent passivation effect on the aluminum current collector, preventing the corrosion of the aluminum foil under high voltage. Such an electrolyte is cost-effective and has no toxicity or pollution.

[0030] In one example, the lithium salt may be selected from lithium hexafluorophosphate (LiPF6) and / or lithium bis(fluorosulfonyl)imide (LiFSI). That is, the lithium salt may be selected from lithium hexafluorophosphate alone, may be selected from lithium bis(fluorosulfonyl)imide alone, or may be selected from a composition of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. In other examples, the lithium salt may be selected from lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(trifluoromethane)sulfonimide (LiTFSI), or lithium difluorophosphate (LiPF2O2). The lithium salt is preferably selected from lithium hexafluorophosphate having better overall performance, or lithium hexafluorophosphate functions as a main component and is combined with other lithium salts added in an appropriate amount, and the combination is used to improve the performance of the electrolyte through the composition. The concentration of the lithium salt can be set according to conventional selections in this field. In one example, the content of the lithium salt in the non-aqueous electrolyte occupies 8% - 20% by mass percentage, such as 8%, 12.5%, 15%, or 20%, etc.

[0031] The non-aqueous organic solvent can be selected from the conventional combinations of solvents in this field. In the present invention, the non-aqueous organic solvents include cyclic carbonates and chain carbonates. The cyclic carbonate includes one or both of ethylene carbonate (EC) and propylene carbonate (PC). For example, the cyclic carbonate may be ethylene carbonate, propylene carbonate, or a mixture of ethylene carbonate and propylene carbonate mixed in any ratio. The chain carbonate includes one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). That is, the chain carbonate may be any of those listed above, such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate. The chain carbonate may be a combination of any two or three of those listed above, such as a combination of dimethyl carbonate and diethyl carbonate, a combination of diethyl carbonate and ethyl methyl carbonate, or a combination of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. When the chain carbonate is a composition, the ratio of each component in the composition is not particularly limited and may be mixed in any ratio.

[0032] The non-aqueous electrolyte of the present invention can be produced according to a conventional production method. For example, first, the non-aqueous organic solvent is mixed and stirred in a glove box, then a lithium salt is added, and stirring is continued until the lithium salt is completely dissolved. Finally, chloroethylene carbonate and lithium difluoro(bis(oxalato))phosphate are added and stirred well. The nitrogen content in the glove box is 99.999%, the actual oxygen content in the glove box is 0.1 ppm, and the water content is 0.1 ppm.

[0033] A second aspect of the present invention provides a lithium-ion battery. The battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charge and discharge process of the battery, lithium ions are intercalated and deintercalated between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet and has a separating function. The electrolyte has a function of propagating ions between the positive electrode sheet and the negative electrode sheet. The electrolyte is the non-aqueous electrolyte described above in the present invention. Since the non-aqueous electrolyte contains chloroethylene carbonate and lithium difluorobis(oxalato)phosphate, the mixture of the two can form a double-layer structure having LiCl-LiF inorganic salt and vinylene carbonate oligomer on the surface of the negative electrode, thereby ensuring the stability of the negative electrode protective layer (SEI film), and thus having performance at high and low temperatures.

[0034] Specifically, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector may be made of a material having good conductivity and mechanical strength, such as aluminum foil. The positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on one or both of the two opposing surfaces of the positive electrode current collector. The positive electrode active material layer includes a positive electrode material, a positive electrode conductive agent, and a positive electrode binder. The specific types of the positive electrode material, the positive electrode conductive agent, and the positive electrode binder are not particularly limited and can be selected by those skilled in the art according to actual needs.

[0035] As an example, the positive electrode material can be selected from ternary materials and lithium-containing phosphates. Specifically, the ternary materials include, but are not limited to, lithium nickel cobalt manganese oxide and lithium nickel cobalt manganese oxide doped with metal ions. The doping element is, for example, any one or more selected from Zr, Ti, Mo, Al, Sr, W, Y, Ta, Nb, Mg, and Ba. The lithium-containing phosphates include, but are not limited to, lithium iron manganese phosphate, lithium iron phosphate, lithium manganese phosphate, etc. The positive electrode binder is selected from, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc. The positive electrode conductive agent is, for example, one selected from carbon black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, etc., or a mixture of two or more of them in any ratio.

[0036] The positive electrode sheet can be manufactured according to methods known in the art. As an example, the positive electrode material, the positive electrode conductive agent, and the positive electrode binder are dispersed in a solvent (for example, N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry. The positive electrode slurry is applied onto the positive electrode current collector and subjected to processes such as drying and cold pressing to obtain the positive electrode sheet. The ratio of each component in the positive electrode slurry can be set with reference to conventional ratios, and the present invention is not limited thereto.

[0037] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be made of a material having good electrical conductivity and mechanical strength such as copper foil. The negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on one or both of the two opposing surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode material, a negative electrode conductive agent, a negative electrode binder, and a thickener. The specific types of the negative electrode material, the negative electrode conductive agent, and the negative electrode binder are not particularly limited. Materials known in the art that can be used in lithium-ion batteries can be employed and can be selected by those skilled in the art according to actual needs.

[0038] Preferably, the negative electrode material is a silicon-containing negative electrode material such as elemental silicon, silicon oxygen compound, silicon carbon compound, etc. Chloroethylene carbonate (ClEC) and lithium difluorobis(oxalato)phosphate can form a bilayer structure having LiCl-LiF composite inorganic salt and vinylene carbonate oligomer on the surface of the silicon negative electrode, so that a better coating effect can be obtained at the interface with the silicon negative electrode. Due to the rigidity of LiF and the low solubility of LiCl, the stability of the silicon negative electrode protection layer after blending can be ensured. The negative electrode conductive agent is selected from one or a combination of two or more selected from carbon black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, etc. in any ratio. The negative electrode binder is selected from any one of polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), or a mixture of a plurality of compositions in any ratio. The thickener is selected from carboxymethyl cellulose (CMC).

[0039] The negative electrode sheet can be manufactured according to a method known in the art. For example, the negative electrode material, negative electrode binder, thickener and negative electrode conductive agent are dispersed in deionized water to form a uniform negative electrode slurry. The negative electrode slurry is applied on the negative electrode current collector, and through processes such as drying, cold pressing and others, a negative electrode sheet is obtained. The ratio of each component in the negative electrode slurry can be set with reference to the conventional ratio, and the present invention is not limited thereto.

[0040] As the separator, a conventional one adopted in the field such as a porous PE film is selected. The thickness of the separator is 9 μm to 18 μm, the air permeability is 180 s / 100 mL to 380 s / 100 mL, and the porosity is 30% to 50%.

[0041] The battery assembly is carried out according to the conventional method. After the preparation is completed, the negative electrode sheet, separator, and positive electrode sheet are laminated in sequence, and this is placed in an aluminum-laminated film to form a shell cell. The shell cell is baked at 80 °C to remove moisture. The prepared electrolyte is injected into the shell cell and sealed to obtain a lithium-ion battery product.

[0042] The technical solution of the present invention will be described in detail below through several specific examples and comparative examples. The raw materials and reagents used in the following examples are, unless otherwise specified, commercially available products or can be prepared by conventional methods in the art. All the equipment used in the examples is commercially available.

[0043] Example 1

[0044] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were uniformly mixed at a mass ratio of 3:5:2 to prepare a non-aqueous organic solvent. Dried lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvent and uniformly mixed. Next, the compound represented by structural formula (1) and lithium difluoro(bis(oxalato))phosphate (LiODFP) were added and uniformly mixed to prepare a non-aqueous electrolyte. The content of lithium hexafluorophosphate in the non-aqueous electrolyte was 12.5% by mass, the content of the compound represented by structural formula (1) in the non-aqueous electrolyte was 1% by mass, and the content of lithium difluoro(bis(oxalato))phosphate in the non-aqueous electrolyte was 0.7% by mass.

[0045] Example 2

[0046] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were uniformly mixed at a mass ratio of 3:5:2 to prepare a non-aqueous organic solvent. Dried lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvent and uniformly mixed. Next, the compound represented by structural formula (2) and lithium difluorobis(oxalato)phosphate (LiODFP) were added and uniformly mixed to prepare a non-aqueous electrolyte. The content of lithium hexafluorophosphate in the non-aqueous electrolyte was 12.5% by mass, the content of the compound represented by structural formula (2) in the non-aqueous electrolyte was 1.5% by mass, and the content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte was 2% by mass.

[0047] Example 3

[0048] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were uniformly mixed at a mass ratio of 3:5:2 to prepare a non-aqueous organic solvent. Dried lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvent and uniformly mixed. Next, the compound represented by structural formula (1) and lithium difluorobis(oxalato)phosphate (LiODFP) were added and uniformly mixed to prepare a non-aqueous electrolyte. The content of lithium hexafluorophosphate in the non-aqueous electrolyte was 12.5% by mass, the content of the compound represented by structural formula (1) in the non-aqueous electrolyte was 0.5% by mass, and the content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte was 0.7% by mass.

[0049] Example 4

[0050] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were uniformly mixed at a mass ratio of 3:5:2 to prepare a non-aqueous organic solvent. Dried lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvent and uniformly mixed. Next, the compound represented by structural formula (1) and lithium difluorobis(oxalato)phosphate (LiODFP) were added and uniformly mixed to prepare a non-aqueous electrolyte. The content of lithium hexafluorophosphate in the non-aqueous electrolyte was 12.5% by mass, the content of the compound represented by structural formula (1) in the non-aqueous electrolyte was 2.5% by mass, and the content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte was 0.7% by mass.

[0051] Example 5

[0052] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were uniformly mixed at a mass ratio of 3:5:2 to prepare a non-aqueous organic solvent. Dried lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvent and uniformly mixed. Next, the compound represented by structural formula (1) and lithium difluorobis(oxalato)phosphate (LiODFP) were added and uniformly mixed to prepare a non-aqueous electrolyte. The content of lithium hexafluorophosphate in the non-aqueous electrolyte was 12.5% by mass, the content of the compound represented by structural formula (1) in the non-aqueous electrolyte was 5% by mass, and the content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte was 0.7% by mass.

[0053] Example 6

[0054] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were uniformly mixed at a mass ratio of 3:5:2 to prepare a non-aqueous organic solvent. Dried lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvent and uniformly mixed. Next, the compound represented by structural formula (1) and lithium difluorobis(oxalato)phosphate (LiODFP) were added and uniformly mixed to prepare a non-aqueous electrolyte. The content of lithium hexafluorophosphate in the non-aqueous electrolyte was 12.5% by mass, the content of the compound represented by structural formula (1) in the non-aqueous electrolyte was 1% by mass, and the content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte was 0.5% by mass.

[0055] Example 7

[0056] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were uniformly mixed at a mass ratio of 3:5:2 to prepare a non-aqueous organic solvent. Dried lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvent and uniformly mixed. Next, the compound represented by structural formula (1) and lithium difluorobis(oxalato)phosphate (LiODFP) were added and uniformly mixed to prepare a non-aqueous electrolyte. The content of lithium hexafluorophosphate in the non-aqueous electrolyte was 12.5% by mass, the content of the compound represented by structural formula (1) in the non-aqueous electrolyte was 1% by mass, and the content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte was 1.2% by mass.

[0057] Example 8

[0058] Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) were uniformly mixed at a mass ratio of 3:5:2 to prepare a non-aqueous organic solvent. Dried lithium hexafluorophosphate (LiPF6) was added to the non-aqueous organic solvent and uniformly mixed. Next, the compound represented by structural formula (1) and lithium difluorobis(oxalato)phosphate (LiODFP) were added and uniformly mixed to prepare a non-aqueous electrolyte. The content of lithium hexafluorophosphate in the non-aqueous electrolyte was 12.5% by mass, the content of the compound represented by structural formula (1) in the non-aqueous electrolyte was 1% by mass, and the content of lithium difluorobis(oxalato)phosphate in the non-aqueous electrolyte was 2% by mass.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that in this comparative example, lithium difluorobis(oxalato)phosphate (LiODFP) is not added.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that in this comparative example, the compound represented by structural formula (1) is not added.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 1 is that in this comparative example, the compound represented by structural formula (1) and lithium difluorobis(oxalato)phosphate (LiODFP) are not added.

[0065] Comparative Example 4

[0066] The difference between this comparative example and Example 1 is that in this comparative example, the addition amount of the compound represented by structural formula (1) is 7% and the addition amount of lithium difluorobis(oxalato)phosphate (LiODFP) is 5%.

[0067] Comparative Example 5

[0068] The difference between this comparative example and Example 1 is that in this comparative example, the amount of the compound represented by structural formula (1) added is 7%, and lithium difluorobis(oxalato)phosphate (LiODFP) is not added.

[0069] Comparative Example 6

[0070] The difference between this comparative example and Example 1 is that in this comparative example, the compound represented by structural formula (1) was not added, and the amount of lithium difluorobis(oxalato)phosphate (LiODFP) added in this comparative example was 5%.

[0071] The electrolyte solutions prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were each used in a lithium ion battery to verify the effectiveness of chloroethylene carbonate and lithium difluorobis(oxalato)phosphate. The process for manufacturing a lithium-ion battery is as follows.

[0072] (1) Positive electrode sheet: LiNi 0.9 Co 0.05 Mn 0.05 A positive electrode active material selected from O2, a conductive agent selected from acetylene black, and a binder selected from polyvinylidene fluoride were dissolved in N-methylpyrrolidone (NMP) in a mass ratio of 95:3:2, and the resulting uniformly mixed slurry was applied onto an aluminum foil, dried, rolled, and cut to obtain a positive electrode sheet.

[0073] (2) Negative electrode sheet: A negative electrode active material selected from a silicone compound, a conductive agent selected from acetylene black, a thickener selected from CMC-Li, and a binder selected from SBR were mixed in a mass ratio of 96.4:1:1.2:1.4, and then deionized water was added and mixed uniformly and thoroughly to obtain a negative electrode slurry. Next, deionized water was added to the negative electrode slurry and mixed uniformly, and the mixture was applied to a copper foil, dried, rolled, and cut to obtain a negative electrode sheet.

[0074] (3) Separator: A porous PE film with a thickness of 11 μm was selected as the separator.

[0075] (4) Battery Assembly: The separator was placed between the positive electrode sheet and the negative electrode sheet, and the prepared positive electrode sheet, separator, and negative electrode sheet were laminated in sequence to perform an insulation function. The laminated materials were placed in an aluminum plastic film to obtain a dry battery cell. The dry battery cell was baked at 80 °C to remove moisture. The prepared electrolyte was injected into the dry battery cell and sealed to obtain a lithium-ion battery.

[0076] Performance tests were conducted on the lithium-ion batteries assembled using the electrolytes of Examples 1 to 8 and Comparative Examples 1 to 6. The test results are shown in Table 1. The test method is as follows.

[0077] (1) Initial Impedance DCR at 25 °C:

[0078] The temperature of the thermostat was set to 25 °C and left standing for 10 minutes. It was charged to 4.25 V at a constant current of 0.33C, then charged to 0.05 V at a constant voltage of 4.25 V and left standing for 30 minutes. Next, it was discharged to 2.5 V at a constant current of 0.33C. Charging and discharging were performed for 2 cycles at 0.33C, and the last discharge capacity was recorded as C0. After standing for 30 minutes, it was discharged to 50% C0 at 0.33C to adjust the SOC of the battery cell to 50%. After standing for 1 hour, the standing terminal voltage was recorded as V1. It was discharged for 30 minutes at a constant current of 4C0, the terminal voltage was recorded as V2, and the current was recorded as I, and DCR = (V1 - V2) / I was calculated.

[0079] (2) Volume Expansion Rate after Storage at 60 °C for 30 Days:

[0080] At 25 °C, the lithium-ion battery was charged to 4.25 V at a constant current of 1C, and then charged to a current of 0.05C at a constant voltage. The volume of the lithium-ion battery was tested and recorded as X0. Next, the fully charged battery was stored in an oven at 60 °C for 30 days. The volume after storage was tested and recorded as X1. The volume expansion rate with respect to the lithium-ion battery before storage was calculated by the following formula.

[0081] Volume expansion rate (%) = (X1 - X0) / X0 × 100%.

[0082] [Table 1]

[0083] Comparing Example 1 and Example 2, it can be seen that the combination of the compound represented by structural formula (1) and LiODFP can achieve a significantly better effect in terms of initial impedance and gas storage performance than the combination of the compound represented by structural formula (2) and LiODFP. This indicates that the compound represented by structural formula (1) is superior in the formation efficiency of the LiCl - LiF composite inorganic salt and vinylene carbonate oligomer.

[0084] Comparing Example 1, Examples 3 - 5, when a certain amount of LiODFP is added, as the addition amount of the compound represented by structural formula (1) increases, the initial impedance first decreases and then increases, and the gas storage amount at high temperature decreases and then increases. It can be seen that the optimal addition amount of the compound represented by structural formula (1) is about 1%. In this way, the uniformity and appropriate thickness of the formed SEI can be ensured. If the amount of the compound represented by structural formula (1) is too small, the amount of the formed SEI film will be small and the negative electrode interface cannot be completely covered. Referring to Comparative Examples 4 and 5 together, if the addition amount of the compound represented by structural formula (1) is too large, the formed SEI film will be thick, which is not favorable for lithium ion transport and stability at high temperature.

[0085] Comparing Examples 1, 6 to 8, when the addition amount of the compound represented by Structural Formula (1) is fixed, as the addition amount of LiODFP increases, the initial impedance first decreases and then increases in the same manner, and the gas storage amount at high temperature first decreases and then increases. This indicates that the optimal amount of LiODFP is about 0.7%. If the addition amount of LiODFP is too high (see Comparative Examples 4 and 6) or too low, the stability of the SEI film decreases, which has an adverse effect on the performance of the battery cell.

[0086] Comparing Example 1, Comparative Example 1, and Comparative Example 2, when the compound represented by Structural Formula (1) and LiODFP are simultaneously added to the electrolyte, both the initial impedance and the gas storage amount at high temperature are lower compared to the case where only one additive is added. This indicates that only when two additives coexist, the negative electrode surface can be coated with a double-layer structure having an inorganic salt of LiCl-LiF and vinylene carbonate oligomer, and a single additive alone cannot form the corresponding structure, resulting in poor effects.

[0087] The present invention introduces chloroethylene carbonate and lithium difluoro(bis(oxalato))phosphate into a non-aqueous electrolyte to form a double-layer structure having an inorganic salt of LiCl-LiF and vinylene carbonate oligomer on the negative electrode surface, thereby improving the coating effect and stability of the negative electrode interface film and improving the performance of the lithium-ion battery at high temperature. Therefore, the present invention effectively overcomes some practical problems in the prior art, has high utilization value, and great significance in use.

Industrial Applicability

[0088] Furthermore, the non-aqueous electrolyte provided by the present invention and the lithium-ion battery containing the same can be used in the field of electronics engineering and have high industrial applicability.

[0089] The above embodiments illustrate the principles and effects of the present invention and do not limit the present invention. Anyone skilled in this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed in the present invention shall also be included in the scope of the claims of the present invention.

Claims

**Claim 1**: A non-aqueous electrolyte for a lithium-ion battery, comprising: a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive includes chloroethylene carbonate and lithium difluoro(bis(oxalato))phosphate, and the chloroethylene carbonate is a compound represented by the following structural formula: The content of the chloroethylene carbonate in the non-aqueous electrolyte is 1% to 2.5% by mass percentage, and the content of the lithium difluoro(bis(oxalato))phosphate in the non-aqueous electrolyte is 0.5% to 2% by mass percentage. A non-aqueous electrolyte. 【Chemical 1】 In the formula, the R group is selected from a Cl group or a CCl ３ group. **Claim 2**: The content of the lithium difluoro(bis(oxalato))phosphate in the non-aqueous electrolyte is 0.5% to 1% by mass percentage. The non-aqueous electrolyte according to Claim 1. **Claim 3**: The conductivity of the non-aqueous electrolyte is 7.0 mS / cm to 12.5 mS / cm. The non-aqueous electrolyte according to Claim 1. **Claim 4**: The structural formula of the chloroethylene carbonate is as follows: The non-aqueous electrolyte according to Claim 1. 【Chemical Formula 2】 **Claim 5**: The lithium salt includes lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide, and the content of the lithium salt in the non-aqueous electrolyte is 8% to 20% by mass percentage. The non-aqueous electrolyte according to Claim 1. **Claim 6**: The non-aqueous organic solvent includes a cyclic carbonate and a chain carbonate. The cyclic carbonate includes one or both of ethylene carbonate and propylene carbonate, and the chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The non-aqueous electrolyte according to Claim 1. **Claim 7**: A lithium-ion battery including a positive electrode sheet, a negative electrode sheet, a separator, and the non-aqueous electrolyte according to any one of Claims 1 to 6.