Low-temperature-resistant electrolyte, battery and energy storage equipment

Abstract

The low-temperature-resistant electrolyte provided by the invention comprises electrolyte salt, a non-aqueous organic solvent and a low-temperature-resistant additive, and the low-temperature-resistant additive comprises one or more of fluorocarboxylate with a structure shown in a formula I and oxazolidinone compounds with a structure shown in a formula II, the structure of the formula I is # imgabs 0 #, and the structure of the formula II is # imgabs 1 #. The low-temperature-resistant electrolyte provided by the invention solves the problems of high electrolyte viscosity and unstable interface in a battery low-temperature environment, especially the problem that an interface film NaF in a sodium ion battery is easy to decompose, and the low-temperature cycle performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a low-temperature resistant electrolyte, a battery and an energy storage device. Background Art

[0002] With the rapid development of science and technology, the application scope of battery technology continues to expand. From consumer electronics to electric vehicles to energy storage systems, batteries play an increasingly important role in our daily lives. However, the performance of batteries under extreme temperature conditions, especially the stability in low temperature environments, remains a key technical challenge.

[0003] Under low temperature conditions, the physical and chemical properties of battery electrolytes will change significantly. Specifically, the viscosity of the electrolyte will increase significantly, while the conductivity will decrease significantly. This change directly affects the discharge performance of the battery, which is manifested as a decrease in battery capacity and a decrease in output power. Therefore, improving the performance of batteries under low temperature conditions has become an important topic of concern for researchers.

[0004] A widely studied solution is to improve the properties of the electrolyte by using fluorinated solvents. Fluorinated solvents can effectively reduce the viscosity of the electrolyte, thereby increasing the ionic conductivity of the electrolyte. This modification shows certain prospects in improving the low-temperature performance of batteries. However, this method also brings new problems: fluorinated solvents may cause the interface film formed on the electrode surface to be rich in sodium fluoride (NaF) during battery operation. These NaF components may dissolve and regenerate during the battery cycle, resulting in a decrease in the stability of the interface film, thereby accelerating the battery's cycle life decay. How to improve the low-temperature performance of the battery while avoiding the decomposition of the interface film has become a complex and important challenge facing the current field of battery technology. Summary of the invention

[0005] In order to solve the problems of the prior art, the present invention provides a low-temperature resistant electrolyte, which solves the problem that the viscosity of the electrolyte increases and the interface film NaF is easily decomposed in a low-temperature environment, thereby improving the cycle performance of the battery in a low-temperature environment.

[0006] In a first aspect, the present invention provides a low-temperature resistant electrolyte, comprising an electrolyte salt, a non-aqueous organic solvent, and a low-temperature resistant additive, wherein the low-temperature resistant additive comprises one or more of a fluorocarboxylic acid ester having a structure of formula I and an oxazolidinone compound having a structure of formula II;

[0007]

[0008] Wherein, R1 is selected from any one of cyano, substituted or unsubstituted alkyl, substituted or unsubstituted silane and aryl, the alkyl has 1 to 8 carbon atoms, the aryl has 6 to 8 carbon atoms, and when substituted, the substituent is selected from any one of halogen and cyano; R2 is selected from any one of H, halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted silane and aryl, the alkyl has 1 to 8 carbon atoms, the aryl has 6 to 8 carbon atoms, and when substituted, the substituent is selected from any one of halogen and cyano, and alkenyl; R3 is selected from any one of H, halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted silane and aryl, the alkyl has 1 to 8 carbon atoms, the aryl has 6 to 8 carbon atoms, and when substituted, the substituent is selected from any one of halogen and cyano.

[0009] As some preferred schemes, R1 is selected from any one of substituted or unsubstituted alkyl and silyl groups, the alkyl group has 1 to 6 carbon atoms, and the substituent is selected from F; R2 is selected from F, a substituted alkyl group having 1 to 6 carbon atoms, and the substituent is selected from any one of F and cyano; R3 is selected from H, an alkyl group having 1 to 6 carbon atoms substituted by F, and the substituent is selected from any one of F, cyano, and a substituted or unsubstituted alkyl group.

[0010] As some exemplary schemes, the fluorocarboxylate having the structure of formula I can be Any one or more of them.

[0011] As some exemplary schemes, the oxazolidinone compound having the structure of formula II can be Any one or more of them.

[0012] As a further solution, the fluorinated carboxylic acid ester accounts for 0.3-3 wt % of the total mass of the low-temperature resistant electrolyte.

[0013] As a further solution, the fluorinated carboxylic acid ester accounts for 0.3-2 wt % of the total mass of the low-temperature resistant electrolyte.

[0014] As a further solution, the oxazolidinone compound accounts for 0.2 to 5 wt % of the total mass of the low-temperature resistant electrolyte.

[0015] As a further solution, the oxazolidinone compound accounts for 0.4-3wt% of the total mass of the low-temperature resistant electrolyte.

[0016] As a further solution, the total mass of the fluorocarboxylic acid ester and the oxazolidinone compound accounts for 0.5-5wt% of the total mass of the low-temperature resistant electrolyte.

[0017] As a further solution, the fluorocarboxylic acid ester and oxazolidinone compounds account for 0.8-2.5 wt % of the total mass of the low-temperature resistant electrolyte.

[0018] As a further solution, the concentration of the electrolyte salt in the electrolyte is selected from 0.5 to 2 mol / L.

[0019] The electrolyte salt is selected from any one of lithium salt and sodium salt;

[0020] The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, and lithium difluorobis(oxalatophosphate).

[0021] As a further embodiment, the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(trifluoromethylsulfonyl)imide, sodium dioxalatoborate, sodium difluorooxalatoborate, sodium difluorophosphate, and sodium difluorobis(oxalatophosphate).

[0022] As a further solution, the non-aqueous organic solvent is selected from any one or more of carbonate solvents and carboxylate solvents.

[0023] As a further solution, the carboxylate solvent accounts for 20-80 wt % of the total mass of the low-temperature resistant electrolyte, and the carbonate solvent accounts for 10-75 wt % of the total mass of the low-temperature resistant electrolyte.

[0024] As a further solution, the carboxylate solvent accounts for 30-70 wt % of the total mass of the low-temperature resistant electrolyte, and the carbonate solvent accounts for 30-75 wt % of the total mass of the electrolyte.

[0025] As a further solution, the carbonate solvent is selected from a mixture of one or more of cyclic carbonates and linear carbonates.

[0026] As a further solution, the carboxylate solvent is selected from one or a mixture of acetate solvents, propionate solvents, and butyrate solvents.

[0027] As a further solution, the low-temperature resistant electrolyte may further include a second additive.

[0028] As a further solution, the second additive is selected from any one of sulfite additives, sulfonate additives, carbonate additives, and sulfate additives, or a mixture of several of them.

[0029] As a further solution, the total mass content of the second additive in the low-temperature resistant electrolyte is selected from 0.2 to 10 wt %.

[0030] In a second aspect, the present invention provides a battery comprising the low-temperature resistant electrolyte proposed in the present invention.

[0031] As a further solution, the battery further includes a positive electrode;

[0032] As a further solution, the positive electrode includes a positive electrode material layer and a positive electrode current collector.

[0033] As a further solution, the positive electrode current collector is not limited in principle. As some exemplary solutions, the positive electrode current collector can be selected from any one of aluminum foil and stainless steel.

[0034] As a further solution, the positive electrode material layer includes a positive electrode active material, a positive electrode binder and a positive electrode conductor.

[0035] As a further solution, the positive electrode active material is selected from one or more of sodium copper iron manganate, sodium nickel iron manganate, sodium vanadium phosphate, sodium fluorovanadium phosphate, sodium iron pyrophosphate, sodium iron sulfate, and modified sodium ferrocyanide.

[0036] As a further solution, the positive electrode binder is selected from at least one of thermoplastic resin and acrylic resin.

[0037] As a further solution, the battery also includes a negative electrode.

[0038] As a further solution, the negative electrode includes a negative electrode material layer and a negative electrode current collector.

[0039] As a further solution, the negative electrode current collector is not limited in principle. As some exemplary solutions, the negative electrode current collector can be selected from any one of aluminum foil, copper foil, and stainless steel.

[0040] As a further embodiment, the negative electrode includes a negative electrode active material, a negative electrode binder and a negative electrode conductor.

[0041] As a further solution, the negative electrode active material is selected from at least one of soft carbon, hard carbon, sodium titanate, metallic sodium, carbon nanotubes, carbon black, carbon aerogel, graphite, and graphene.

[0042] As a further solution, the type of the negative electrode binder is not limited, and technicians can choose it according to actual needs, including at least one of styrene butadiene rubber (SBR), styrene-butadiene rubber, water-based acrylic resin and carboxymethyl cellulose (CMC).

[0043] As a further solution, the negative electrode conductive agent is selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, conductive carbon black and carbon nanofibers.

[0044] As a further solution, the battery further includes a separator.

[0045] Compared with the prior art, the present invention has at least the following beneficial effects:

[0046] This solution successfully solves the problems of excessive viscosity and insufficient conductivity of battery electrolyte in low temperature environment by introducing fluorocarboxylic acid ester with formula I structure and oxazolidinone compound with formula II structure. Specifically, this solution firstly significantly improves the ion migration ability of electrolyte in low temperature environment by compounding fluorocarboxylic acid ester with formula I structure and oxazolidinone compound with formula II structure, thereby improving the conductivity of battery and ensuring the efficient operation of battery under low temperature conditions; secondly, fluorocarboxylic acid ester with formula I structure can make electrolyte have lower viscosity, thereby improving the cycle performance of battery; thirdly, the presence of sulfonyl group in fluorocarboxylic acid ester with formula I structure helps to form an interface film with high ionic conductivity on the surface of positive electrode, inhibits the dissolution of transition metal ions and gas generation during the cycle, thereby improving the cycle performance of battery, and by introducing oxazolidinone compound with formula II structure, it helps to utilize the characteristic that Si-N bond is easy to break during cycle, provides additional interface protection, and introduces nitrogen and silicon components with high ionic conductivity into the film, protects the stability of sodium fluoride and further improves the ionic conductivity of interface film. DETAILED DESCRIPTION

[0047] For ease of understanding, the present invention will be described in more detail below and examples of the present invention are given, but the scope of the present invention is not limited thereby.

[0048] In a first aspect, the present invention provides a low-temperature resistant electrolyte, comprising an electrolyte salt, a non-aqueous organic solvent, and a low-temperature resistant additive, wherein the low-temperature resistant additive comprises one or more of a fluorocarboxylic acid ester having a structure of formula I and an oxazolidinone compound having a structure of formula II;

[0049] in,

[0050]

[0051] Wherein, R1 is selected from any one of cyano, substituted or unsubstituted alkyl, substituted or unsubstituted silane and aryl, the alkyl has 1 to 8 carbon atoms, the aryl has 6 to 8 carbon atoms, and when substituted, the substituent is selected from any one of halogen and cyano; R2 is selected from any one of H, halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted silane and aryl, the alkyl has 1 to 8 carbon atoms, the aryl has 6 to 8 carbon atoms, and when substituted, the substituent is selected from any one of halogen and cyano, and alkenyl; R3 is selected from any one of H, halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted silane and aryl, the alkyl has 1 to 8 carbon atoms, the aryl has 6 to 8 carbon atoms, and when substituted, the substituent is selected from any one of halogen and cyano.

[0052] In this scheme, we introduce a fluorocarboxylic acid ester of formula I and an oxazolidinone compound of formula II, and utilize the combined effect of the two to optimize the viscosity of the electrolyte in a low-temperature environment, while improving the conductivity in a low-temperature environment, thereby optimizing the cycle performance of the battery. First, we introduce fluorocarboxylates containing ester groups, sulfonyl groups, and fluorine elements, and use the polar ester groups to form coordination bonds with lithium ions or sodium ions. At the same time, through the induction effect, fluorine atoms are used to further reduce the electron density of the ester group, reduce the mutual attraction with lithium ions or sodium ions, thereby reducing the binding energy with lithium ions or sodium ions and improving the migration ability of lithium ions or sodium ions. At the same time, the presence of sulfonyl groups in fluorocarboxylates with the formula I structure also helps to form an interface film with high ionic conductivity on the surface of the positive electrode, while inhibiting the dissolution of transition metal ions at the positive electrode and the gas generation phenomenon during high-temperature circulation during the cycle. Secondly, for compounds with the formula I structure, the Si-N bond is prone to breakage during the battery cycle and forms a film on the positive and negative electrode surfaces to protect the sodium fluoride generated during the cycle and inhibit the decomposition of sodium fluoride, thereby improving the cycle performance. At the same time, nitrogen- and silicon-containing components can be introduced into the surface films of the positive and negative electrodes to improve the ionic conductivity of the interface film. In addition, the presence of trimethylsilyl can react with active protons in water and acid, thereby achieving the purpose of removing water and acid and improving interface stability; under the joint action of fluorocarboxylic acid esters with structure I and oxazolidinone compounds with structure II, we improved the low-temperature ionic conductivity of the electrolyte and reduced the viscosity of the electrolyte in a low-temperature environment, ultimately improving the low-temperature performance of the battery.

[0053] As some preferred schemes, R1 is selected from any one of substituted or unsubstituted alkyl and silyl groups, the alkyl group has 1 to 6 carbon atoms, and the substituent is selected from F; R2 is selected from F, a substituted alkyl group having 1 to 6 carbon atoms, and the substituent is selected from any one of F and cyano; R3 is selected from H, an alkyl group having 1 to 6 carbon atoms substituted by F, and the substituent is selected from any one of F, cyano, and a substituted or unsubstituted alkyl group.

[0054] As some exemplary schemes, the fluorocarboxylate having the structure of formula I can be Any one or more of them.

[0055] As some exemplary schemes, the oxazolidinone compound having the structure of formula II can be Any one or more of them.

[0056] As a further solution, the fluorinated carboxylic acid ester accounts for 0.3-3 wt % of the total mass of the low-temperature resistant electrolyte.

[0057] As a further solution, the fluorinated carboxylic acid ester accounts for 0.3-2 wt % of the total mass of the low-temperature resistant electrolyte.

[0058] As a further solution, the oxazolidinone compound accounts for 0.2 to 5 wt % of the total mass of the low-temperature resistant electrolyte.

[0059] As a further solution, the oxazolidinone compound accounts for 0.4-3wt% of the total mass of the low-temperature resistant electrolyte.

[0060] As a further solution, the fluorocarboxylic acid ester and oxazolidinone compounds account for 0.5-5wt% of the total mass of the low-temperature resistant electrolyte.

[0061] As a further solution, the fluorocarboxylic acid ester and oxazolidinone compounds account for 0.8-2.5 wt % of the total mass of the low-temperature resistant electrolyte.

[0062] As a further solution, the concentration of the electrolyte salt in the low-temperature resistant electrolyte is selected from 0.5 to 2 mol / L.

[0063] As a further solution, the electrolyte salt is selected from any one of lithium salt and sodium salt.

[0064] The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, and lithium difluorobis(oxalatophosphate).

[0065] The sodium salt is selected from one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(oxalato)borate, sodium difluorooxalatoborate, sodium difluorophosphate, and sodium difluorobis(oxalato)phosphate.

[0066] As a further solution, the non-aqueous organic solvent is selected from any one or more of carbonate solvents and carboxylate solvents, the carboxylate solvent accounts for 20-80wt% of the total mass of the low-temperature resistant electrolyte, and the carbonate solvent accounts for 10-75wt% of the total mass of the low-temperature resistant electrolyte.

[0067] As a further solution, the carboxylate solvent accounts for 30-70 wt % of the total mass of the low-temperature resistant electrolyte, and the carbonate solvent accounts for 30-75 wt % of the total mass of the electrolyte.

[0068] As a further solution, the carbonate solvent is selected from a mixture of one or more of cyclic carbonates and linear carbonates.

[0069] As a further embodiment, the cyclic carbonate solvent is selected from the group consisting of vinylene carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl vinyl carbonate, methyl propylene carbonate, fluoroethylene carbonate, fluoropropylene carbonate, bis(fluoromethyl) carbonate, difluoroethylene carbonate, vinyl carbonate, fluoroethylene carbonate, γ-butyrolactone, or a mixture of one or more thereof.

[0070] As a further embodiment, the linear carbonate solvent is selected from one or a mixture of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, methyl isobutyl carbonate, dipropyl carbonate, methyl propyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and methyl tert-butyl carbonate.

[0071] As a further solution, the carboxylate solvent is selected from one or a mixture of acetate solvents, propionate solvents, and butyrate solvents.

[0072] As a further embodiment, the acetate solvent is selected from one or a mixture of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, hexyl acetate, benzyl acetate, cyclohexyl acetate, and n-propyl acetate.

[0073] As a further solution, the propionate solvent is selected from one or a mixture of isopropyl isobutyrate, butyl propionate, isobutyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0074] As a further solution, the butyrate solvent is selected from one or a mixture of methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, isobutyl butyrate, and ethyl n-butyrate.

[0075] As a further solution, the low-temperature resistant electrolyte may further include a second additive, wherein the second additive is selected from any one of sulfite additives, sulfonate additives, carbonate additives, and sulfate additives, or a mixture of several of them.

[0076] As a further solution, the sulfite additive is selected from any one of ethylene sulfite and propylene sulfite or a mixture of several of them.

[0077] As a further solution, the sulfonate additive is selected from any one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone, or a mixture of several of them.

[0078] As a further solution, the carbonate additive is selected from any one or more of vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and diphenyl carbonate.

[0079] As a further embodiment, the sulfate ester additive is selected from vinyl sulfate.

[0080] As a further solution, the total mass content of the second additive in the low-temperature resistant electrolyte is selected from 0.2 to 10 wt %.

[0081] In a second aspect, the present solution also provides a battery comprising the low-temperature resistant electrolyte proposed in the present solution.

[0082] As a further solution, the battery further includes a positive electrode, and the positive electrode includes a positive electrode material layer and a positive electrode current collector.

[0083] As a further solution, the positive electrode material layer includes a positive electrode active material, a positive electrode binder and a positive electrode conductor.

[0084] As a further solution, the positive electrode active material is selected from one or more of sodium copper iron manganate, sodium nickel iron manganate, sodium vanadium phosphate, sodium fluorovanadium phosphate, sodium iron pyrophosphate, sodium iron sulfate, and modified sodium ferrocyanide.

[0085] As a further solution, the positive electrode binder is selected from at least one of thermoplastic resin and acrylic resin.

[0086] As a further embodiment, the thermoplastic resin includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-chlorotrifluoroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a thermoplastic polyimide, polyethylene and polypropylene.

[0087] As a further solution, the acrylic resin includes at least one of vinyl acrylate resin, methyl acrylate resin, butyl acrylate resin, acrylic styrene resin, acrylate resin, acrylate copolymer resin, acrylic resin, and acrylic emulsion resin.

[0088] As a further solution, the positive electrode conductive agent includes at least one of conductive graphite, carbon nanotubes, graphene, reduced graphene oxide, conductive carbon black, conductive carbon balls, and conductive carbon fibers.

[0089] As a further solution, the battery also includes a negative electrode.

[0090] As a further embodiment, the negative electrode includes a negative electrode active material, a negative electrode binder and a negative electrode conductor.

[0091] As a further solution, the negative electrode active material is selected from at least one of soft carbon, hard carbon, sodium titanate, metallic sodium, carbon nanotubes, carbon black, carbon aerogel, graphite, and graphene.

[0092] As a further solution, the type of the negative electrode binder is not limited, and technicians can choose it according to actual needs, including at least one of styrene butadiene rubber (SBR), styrene-butadiene rubber, water-based acrylic resin and carboxymethyl cellulose (CMC).

[0093] As a further solution, the negative electrode conductive agent is selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, conductive carbon black and carbon nanofibers.

[0094] As a further solution, the battery further includes a separator.

[0095] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application and do not represent all possible embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0096] The chemical raw materials involved in the following examples and comparative examples are all prior art and are commercially available. The experimental devices, test devices, etc. involved in the following examples and comparative examples are all conventional devices in the art, without special requirements and limitations.

[0097] Take sodium-ion batteries as an example:

[0098] Example 1

[0099] The electrolyte was prepared in an inert atmosphere glove box with H2O and O2 contents less than 0.1 ppm. Ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and ethyl acetate were mixed in a ratio of 4:2:1:3 by mass. Then 0.8 mol / L sodium hexafluorophosphate and 0.2 mol / L sodium bis(fluorosulfonyl)imide were added, mixed evenly, and 0.3 wt% of fluorocarboxylic acid ester I-1 was added. and 0.5wt% oxazolidinone compound II-1

[0100] Preparation of batteries

[0101] The battery is prepared using sodium copper iron manganese oxide as the positive electrode material, hard carbon as the negative electrode material, and a polyethylene-based separator.

[0102] Example 2

[0103] The preparation method is the same as that of Example 1, except that the mass proportion of the oxazolidinone compound II-1 in the electrolyte is 1 wt %.

[0104] Example 3

[0105] The preparation method is the same as that of Example 1, except that the mass proportion of the oxazolidinone compound II-1 in the electrolyte is 2 wt %.

[0106] Example 4

[0107] The preparation method is the same as that of Example 1, except that the mass proportion of the fluorocarboxylate I-1 in the electrolyte is 0.5 wt %, and the mass proportion of the oxazolidinone compound II-1 in the electrolyte is 0.5 wt %.

[0108] Example 5

[0109] The preparation method is the same as that of Example 1, except that the mass proportion of the fluorocarboxylate I-1 in the electrolyte is 1 wt %.

[0110] Example 6

[0111] The preparation method is the same as in Example 1, except that the oxazolidinone compound II-2 is used. Replace the oxazolidinone compound II-1.

[0112] Example 7

[0113] The preparation method is the same as in Example 1, except that the oxazolidinone compound II-3 is used. Replace the oxazolidinone compound II-1.

[0114] Example 8

[0115] The preparation method is the same as that of Example 1, except that the fluorocarboxylate I-3 is used. Replacement of fluorocarboxylate I-1.

[0116] Example 9

[0117] The preparation method is the same as in Example 1, except that the fluorocarboxylate I-4 is used. Replacement of fluorocarboxylate I-1.

[0118] Comparative Example 1

[0119] The preparation method is the same as that of Example 1, except that the fluorocarboxylic acid ester I-1 and the oxazolidinone compound II-1 are not added.

[0120] Comparative Example 2

[0121] The preparation method is the same as that of Example 1, except that the oxazolidinone compound II-1 is not added.

[0122] Comparative Example 3

[0123] The preparation method is the same as that of Example 1, except that no fluorocarboxylate I-1 is added.

[0124] Comparative Example 4

[0125] The preparation method is the same as that of Example 1, except that 3-methyl-2-oxazolidinone is used to replace the oxazolidinone compound II-1.

[0126] Comparative Example 5

[0127] The preparation method is the same as that of Example 1, except that methyl trifluoroacetate is used to replace the fluorocarboxylate I-1.

[0128] Comparative Example 6

[0129] The preparation method is the same as that of Example 1, except that the mass proportion of the oxazolidinone compound II-1 in the electrolyte is 10 wt %.

[0130] Comparative Example 7

[0131] The preparation method is the same as that of Example 1, except that the mass proportion of the fluorocarboxylate I-1 in the electrolyte is 10 wt %.

[0132] The specific parameters of Examples 1-9 and Comparative Examples 1-7 are shown in Table 1.

[0133] Test Method

[0134] Normal temperature cycle test: Place the battery in a 25°C environment, charge it to 4.0V at 1C constant current and constant voltage, then discharge it to 1.5V at 1C constant current, and calculate the capacity retention rate based on the discharge capacity of the first cycle.

[0135] Capacity retention rate after 500 cycles at room temperature = (discharge capacity at the 500th cycle at room temperature / discharge capacity at the 1st cycle at room temperature)*100%.

[0136] -50℃ discharge capacity test: Place the battery in a 25℃ environment, charge it to 4.0V at 1C constant current and constant voltage, discharge it to 1.5V at 1C constant current, and then charge it to 4.0V at 1C constant current and constant voltage. Transfer the fully charged battery to a -50℃ environment for more than 4 hours, and discharge it to 1.5V at 0.2C constant current.

[0137] -50℃ discharge capacity retention rate % = (low temperature discharge capacity / normal temperature discharge capacity)*100%.

[0138] The test results are shown in Table 2.

[0139] Table 1

[0140]

[0141]

[0142] Table 2

[0143]

[0144]

[0145] It can be observed from Examples 1-9 and Comparative Examples 1-7 that the examples as a whole exhibit better room temperature cycle capacity retention rate and -50°C discharge retention rate than the comparative examples, indicating that the addition of low temperature resistant additives can effectively alleviate the problem of increased electrolyte viscosity in a low temperature environment, optimize the discharge capacity of the battery in a low temperature environment, and improve its cycle capacity in a normal temperature environment.

[0146] From Example 1 and Comparative Example 1, it can be observed that when no low-temperature resistant additive is added, the capacity retention rate of Comparative Example 1 after 500 cycles at room temperature is 35.97%, and the discharge capacity retention rate after 500 cycles at -50°C is 43.04%, which are much lower than those in Example 1. This indicates that the addition of low-temperature resistant additives can effectively improve the capacity retention rate of the battery during normal temperature cycles while optimizing the performance of the battery in a low-temperature environment.

[0147] Among the low-temperature resistant additives, the combination of the fluorocarboxylic acid ester having the structure of Formula I and the oxazolidinone compound having the structure of Formula II is crucial to improving the battery cycle capacity and optimizing the battery performance. It can be observed from Example 1 and Comparative Examples 2-3 that, regardless of the lack of the fluorocarboxylic acid ester having the structure of Formula I or the lack of the oxazolidinone compound having the structure of Formula II, Comparative Examples 2-3 all exhibited weaker room temperature cycle capacity retention capacity and low temperature discharge capacity retention rate than Example 1. On the one hand, this may be because the fluorocarboxylic acid ester having an ester group, a sulfonyl group, and a fluorine element can effectively reduce the viscosity of the electrolyte in a low temperature environment. At the same time, since the fluorocarboxylic acid ester having the structure of Formula I has a lower binding energy with lithium ions or sodium ions, it can effectively optimize the ionic conductivity and improve the battery performance in a low temperature environment. The presence of trimethylsilyl and sulfonic acid groups can form an interface film containing multiple components such as sodium fluoride and sulfonic acid ester on the surface of the positive and negative electrodes, which has high ionic conductivity and is beneficial to improving the room temperature cycle and low temperature performance. On the other hand, in the oxazolidinone compounds with the structure of formula I, since the Si-N bond is easily broken during the battery cycle and forms a film on the surface of the positive and negative electrodes, high ionic conductivity components containing nitrogen and silicon are introduced into the surface films of the positive and negative electrodes. At the same time, the presence of trimethylsilyl can react with active protons in water and acid, thereby achieving water and acid removal. After the fluorocarboxylic acid ester with the structure of formula I and the oxazolidinone compounds with the structure of formula II generate an interface film, the oxazolidinone compounds with the structure of formula II can effectively maintain the stability of the interface, thereby improving the conductivity and optimizing the room temperature and low temperature cycle performance of the battery.

[0148] Example 1 and Comparative Example 4 show that when 3-methyl-2-oxazolidinone is used to replace the oxazolidinone compound II-1, the room temperature cycle capacity retention rate and the -50°C discharge capacity retention rate of Comparative Example 4 are lower than those of Example 1, indicating that 3-methyl-2-oxazolidinone cannot cooperate with the fluorocarboxylic acid ester having the structure of Formula I to play the effect of protecting the positive and negative electrodes. In addition, since there is no Si-N bond in 3-methyl-2-oxazolidinone, the protection effect on the positive and negative electrodes is poor. Therefore, Comparative Example 4 exhibits lower room temperature cycle ability and low temperature performance than Comparative Example 1.

[0149] Example 1 and Comparative Example 5 discuss the results when methyl trifluoroacetate is used to replace the fluorocarboxylate I-1. It can be observed that in Example 5, the cycle capacity retention rate after 500 cycles at room temperature is 70.94%, and the -50°C discharge capacity retention rate is 69.35%, which is still far lower than the effect of Example 1, indicating that the use of methyl trifluoroacetate cannot replace the effect of the fluorocarboxylate I-1.

[0150] Example 1, Comparative Examples 6 and 7 further discuss the influence of the content of the fluorocarboxylic acid ester having the structure of formula I and the oxazolidinone compound having the structure of formula II in the low-temperature resistant additive on the normal temperature cycle performance of the battery and the discharge performance in a low temperature environment. It can be observed that when the mass proportion of the oxazolidinone compound II-1 in the electrolyte is 10wt% (Comparative Example 6), the cycle capacity of the battery is severely affected whether it is at room temperature or in a low temperature environment. This may be because when the mass proportion of the oxazolidinone compound II-1 in the electrolyte reaches 10wt%, the excess oxazolidinone compound II-1 may react with sodium hexafluorophosphate to produce a serious side reaction, which reduces the sodium salt concentration and is accompanied by the risk of gas production, thereby affecting the cycle performance of the battery. When the mass proportion of the fluorocarboxylic acid ester I-1 in the electrolyte reaches 10wt%, the cycle capacity in Comparative Example 7 is also affected. This may be because the sodium salt concentration is relatively reduced relative to the fluorocarboxylic acid ester I-1 with a mass proportion of 10wt%, thereby affecting the cycle performance.

[0151] Examples 1-3 further discuss the effect of the mass proportion of the oxazolidinone compound II-1 in the electrolyte on the battery performance. It can be observed that Examples 1 and 2 exhibit higher room temperature cycle capacity retention and -50°C discharge capacity retention than Example 3. This may be because compared with Example 3 in which the mass proportion in the electrolyte reaches 2wt%, the oxazolidinone compound II-1 in Examples 1 and 2 can cooperate with the fluorocarboxylic acid ester I-1 to generate a more stable and uniform interface film and avoid side reactions with sodium hexafluorophosphate, thereby improving the battery cycle capacity.

[0152] Examples 1, 4, and 5 discuss the effect of the mass proportion of fluorocarboxylate I-1 in the electrolyte on the battery performance. It can be observed that, on the basis that fluorocarboxylate I-1 accounts for 0.3 to 3 wt% of the total mass of the low-temperature resistant electrolyte, as the content of fluorocarboxylate I-1 gradually increases, the room temperature cycle capacity retention rate and -50°C discharge capacity retention rate of Examples 1, 4, and 5 are optimized. This may be because when the content of fluorocarboxylate I-1 accounts for 0.3 to 3 wt% of the total mass of the low-temperature resistant electrolyte, the increase in the content of fluorocarboxylate I-1 does not affect the relative content of sodium salt. On the contrary, it can better exert the effect of fluorocarboxylate I-1, and cooperate with oxazolidinone compound II-1, thereby improving the battery's cycle capacity in room and low temperature environments.

[0153] Examples 1, 6, and 7 demonstrate the effects of different substituents in oxazolidinone compounds having the structure of Formula II on the performance of the battery in a low-temperature environment. Compared with Examples 1 and 7, Example 6 exhibits a better low-temperature cycle capacity retention rate of -50°C. This may be due to the high electronegativity and low van der Waals radius of the fluorine element. Replacing alkyl and aryl groups helps to further improve the solubility of the electrolyte at low temperatures and construct a more stable sodium fluoride interface film, thereby improving the low-temperature performance of the battery.

[0154] Different substituent groups in the fluorocarboxylic acid ester having the structure of formula I are also one of the factors affecting the room temperature and low temperature cycle performance of the battery. It can be observed from Examples 1, 8, and 9 that Example 8 exhibits better room temperature cycle capacity retention and -50°C discharge capacity retention than Examples 1 and 9, Example 9 exhibits a better room temperature cycle capacity retention than Example 1, and Example 1 exhibits a better -50°C discharge capacity retention than Example 9. This may be because compared to H, F substitution can give the fluorocarboxylic acid ester having the structure of formula I a stronger polarity and promote the formation of the positive and negative electrode interface film; therefore, Example 8 exhibits better room temperature cycle ability and low temperature discharge capacity retention than Examples 1 and 9; in addition, the double bond is easily polymerized on the negative electrode surface, so Example 9 exhibits a better room temperature cycle capacity retention than Example 1, while Example 1 exhibits a better -50°C discharge capacity retention.

[0155] The technical features of the above-described embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. Although the embodiments of the present invention have been shown and described above, it can be understood that the above-described embodiments are exemplary and cannot be understood as limitations of the present invention. Those of ordinary skill in the art can change, modify, replace and deform the above-described embodiments within the scope of the present invention. In addition, those of ordinary skill in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples without contradiction.

Claims

1. A low temperature resistant electrolyte, characterized in that: It includes an electrolyte salt, a non-aqueous organic solvent, and a low-temperature resistant additive, wherein the low-temperature resistant additive includes one or more of a fluorocarboxylic acid ester having a structure of formula I and an oxazolidinone compound having a structure of formula II; Wherein, R1 is selected from any one of cyano, substituted or unsubstituted alkyl, substituted or unsubstituted silane and aryl, the alkyl has 1 to 8 carbon atoms, the aryl has 6 to 8 carbon atoms, and when substituted, the substituent is selected from any one of halogen and cyano; R2 is selected from any one of H, halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted silane and aryl, the alkyl has 1 to 8 carbon atoms, the aryl has 6 to 8 carbon atoms, and when substituted, the substituent is selected from any one of halogen and cyano, and alkenyl; R3 is selected from any one of H, halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted silane and aryl, the alkyl has 1 to 8 carbon atoms, the aryl has 6 to 8 carbon atoms, and when substituted, the substituent is selected from any one of halogen and cyano.

2. The low temperature resistant electrolyte according to claim 1, characterized in that: The R1 is selected from any one of a substituted or unsubstituted alkyl group and a silyl group, the alkyl group has 1 to 6 carbon atoms, and the substituent is selected from F; R2 is selected from F, a substituted alkyl group with 1 to 6 carbon atoms, and the substituent is selected from any one of F and a cyano group; R3 is selected from H, an alkyl group with 1 to 6 carbon atoms substituted by F, and the substituent is selected from any one of F, a cyano group, and a substituted or unsubstituted alkyl group.

3. The low temperature resistant electrolyte according to claim 1, characterized in that: The fluorinated carboxylic acid ester having the structure of formula I is selected from Any one or more of the following; The oxazolidinone compound having the structure of formula II is selected from Any one or more of them.

4. The low temperature resistant electrolyte according to claim 1, characterized in that: The fluorinated carboxylic acid ester accounts for 0.3-3wt% of the total mass of the low-temperature resistant electrolyte; Preferably, the fluorinated carboxylic acid ester accounts for 0.3-2 wt% of the total mass of the low-temperature resistant electrolyte; The oxazolidinone compound accounts for 0.2 to 5 wt% of the total mass of the low-temperature resistant electrolyte; Preferably, the oxazolidinone compound accounts for 0.4-3wt% of the total mass of the low-temperature resistant electrolyte; The fluorocarboxylic acid ester and oxazolidinone compound account for 0.5 to 5 wt% of the total mass of the low-temperature resistant electrolyte; Preferably, the fluorocarboxylic acid ester and oxazolidinone compound account for 0.8-2.5 wt % of the total mass of the low-temperature resistant electrolyte.

5. The low temperature resistant electrolyte according to claim 1, characterized in that: The concentration of the electrolyte salt in the electrolyte is selected from 0.5 to 2 mol / L; The electrolyte salt is selected from any one of lithium salt and sodium salt; The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, and lithium difluorobis(oxalatophosphate); The sodium salt is selected from one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(oxalato)borate, sodium difluorooxalatoborate, sodium difluorophosphate, and sodium difluorobis(oxalato)phosphate.

6. The low temperature resistant electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent is selected from any one or more of carbonate solvents and carboxylate solvents; The carbonate solvent is selected from a mixture of one or more of cyclic carbonate and chain carbonate; Preferably, the carboxylate solvent is selected from one or a mixture of acetate solvents, propionate solvents, butyrate solvents; The carboxylate solvent accounts for 20-80wt% of the total mass of the low-temperature resistant electrolyte, and the carbonate solvent accounts for 10-75wt% of the total mass of the electrolyte; Preferably, the carboxylate solvent accounts for 30-70 wt % of the total mass of the low-temperature resistant electrolyte, and the carbonate solvent accounts for 30-75 wt % of the total mass of the electrolyte.

7. The low-temperature electrolyte according to claim 1, characterized in that: The low temperature resistant electrolyte further includes a second additive; The second additive is selected from any one of sulfite additives, sulfonate additives, carbonate additives, and sulfate additives, or a mixture of several thereof; The total mass content of the second additive in the low-temperature resistant electrolyte is selected from 0.2 to 10 wt %.

8. A battery, characterized in that: The invention comprises the low temperature resistant electrolyte according to any one of claims 1 to 7, wherein the battery is selected from a lithium ion battery and a sodium ion battery.

9. The sodium ion battery according to claim 8, characterized in that: The sodium ion battery also includes a positive electrode, a negative electrode, and a separator; The positive electrode comprises a positive electrode material layer and a positive electrode current collector; The positive electrode material layer includes a positive electrode active material, a positive electrode binder and a positive electrode conductor; The positive electrode active material is selected from one or more of sodium copper iron manganate, sodium nickel iron manganate, sodium vanadium phosphate, sodium fluorovanadium phosphate, sodium iron pyrophosphate, sodium iron sulfate, and modified sodium ferrocyanide; The positive electrode binder is selected from at least one of a thermoplastic resin and an acrylic resin; The negative electrode comprises a negative electrode material layer and a negative electrode current collector; The negative electrode material layer includes a negative electrode active material, a negative electrode binder and a negative electrode conductor. The negative electrode active material is selected from at least one of soft carbon, hard carbon, sodium titanate, metallic sodium, carbon nanotubes, carbon black, carbon aerogel, graphite, and graphene.

10. An energy storage device, characterized in that: It comprises the low-temperature electrolyte according to any one of claims 1 to 7, the battery according to claim 8, or the sodium ion battery according to claim 9.

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