Non-aqueous electrolyte, sodium-ion battery containing same and electric device

Abstract

The invention provides a non-aqueous electrolyte which comprises a first sodium salt, a second sodium salt and a third sodium salt, the first sodium salt comprises at least one of sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium perchlorate and sodium trifluoroacetate; the second sodium salt comprises one, two or more of sodium salt with sulfonate radical, sodium salt with oxalate radical, sodium salt with phosphate radical and sodium salt with borate radical. The non-aqueous electrolyte provided by the invention is suitable for the sodium-ion battery, can improve the normal-temperature and high-temperature cycle performance of the sodium-ion battery and the capacity retention rate after high-temperature storage, and can significantly reduce the volume expansion rate of the sodium-ion battery after high-temperature storage.

Description

Non-aqueous electrolyte, sodium ion battery containing the same, and electrical device Technical Field

[0001] The present application relates to a non-aqueous electrolyte comprising at least two sodium salts, wherein the first sodium salt comprises at least one of sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium perchlorate, and sodium trifluoroacetate, and the second sodium salt comprises one, two, or more of a sodium salt having a sulfonate group, a sodium salt having an oxalate group, a sodium salt having a phosphate group, and a sodium salt having a borate group. Furthermore, the present application relates to a sodium ion battery and an electrical device comprising the non-aqueous electrolyte. Background Art

[0002] In order to achieve the national "dual carbon" strategic goals, the utilization of new energy resources has become particularly important. Lithium-ion batteries have shown good development prospects in the fields of mobile phones, computers, electric vehicles, portable electronic devices, etc. due to their high energy density. However, due to the limited and uneven distribution of lithium resources around the world, and the rapid increase in the price of lithium resources (such as lithium carbonate) in recent years, resource and cost issues will limit the large-scale and long-term use of lithium-ion batteries. Therefore, the further development of new battery systems with high performance and low cost is of great research significance.

[0003] Compared to lithium, sodium is more abundant in the Earth's crust, ranking sixth in abundance. Furthermore, sodium resources are relatively evenly distributed throughout the Earth's crust, existing globally. Therefore, their utilization is not severely limited by reserves or geographic location. More importantly, sodium resources are relatively inexpensive, making them suitable for large-scale, long-term use. Therefore, sodium-ion batteries offer significant advantages over lithium-ion batteries in terms of both resources and cost. Furthermore, metallic sodium shares similar physical and chemical properties with lithium, allowing sodium-ion batteries to draw upon the development experience and production processes of lithium-ion batteries.

[0004] Sodium-ion batteries show good development prospects in the field of electrochemical energy storage, and the industrial development of sodium-ion batteries has great strategic significance and economic value.

[0005] Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its purpose is to provide a non-aqueous electrolyte suitable for sodium ion batteries, which can improve the high-temperature cycle performance and capacity retention rate of sodium ion batteries after high-temperature storage, and can reduce the battery volume expansion rate of sodium ion batteries after high-temperature storage, as well as a sodium ion battery and an electrical device including the non-aqueous electrolyte.

[0007] In order to achieve the above-mentioned objectives, the present application provides a first aspect of a non-aqueous electrolyte solution comprising:

[0008] a first sodium salt comprising at least one of sodium hexafluorophosphate (NaPF6), sodium hexafluoroarsenate (NaAsF6), sodium perchlorate (NaClO4) and sodium trifluoroacetate (CF3COONa); optionally, the first sodium salt is sodium hexafluorophosphate;

[0009] The second sodium salt includes one, two or more of a sodium salt having a sulfonate group, a sodium salt having an oxalate group, a sodium salt having a phosphate group and a sodium salt having a borate group; optionally, the second sodium salt includes a sodium salt having a sulfonate group, a sodium salt having an oxalate group, a sodium salt having a phosphate group and a sodium salt having a borate group.

[0010] The non-aqueous electrolyte is obtained by dissolving a sodium salt electrolyte containing electron-rich anions in a non-aqueous solvent. As described above, by selectively adding the first and second sodium salts, the solvation structure of the sodium ions in the electrolyte and the chemical environment of the solvent molecules can be regulated, thereby resolving the gassing problem caused by the continuous decomposition of the solvent in sodium-ion batteries.

[0011] In any embodiment, in the non-aqueous electrolyte, the molar concentration ratio of the first sodium salt to the second sodium salt is greater than 1 / 1, and can be selected to be greater than 3 / 1, and less than 40 / 1, and more preferably less than 15 / 1.

[0012] In the entire electrolyte, the molar concentration ratio of the first sodium salt to the second sodium salt is within the above range, which can reduce the risk of excessive film formation on the electrode surface and reduce the resistance to sodium ion transmission at the electrode / electrolyte interface, thereby having less impact on the kinetic process of the sodium ion battery.

[0013] In any embodiment, the sodium salt having a sulfonate group includes sodium fluorosulfonate (FSO3Na), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]), sodium bis(trifluoromethylsulfonyl)imide (Na[(CF3SO2)2N]), sodium methanesulfonate (CH3SO3Na), sodium vinylsulfonate (C2H3NaO3S), sodium methylsulfate (CH3OSO3Na), sodium methylthiosulfonate (C2H3NaO3S), sodium methylsulfon ... H3NaO2S2), sodium 1,2-ethanedisulfonate (NaO3SCH2CH2SO3Na), sodium ethyl sulfate (C2H5NaO4S), sodium propanesulfonate (C3H7NaO3S), sodium ethanethiosulfonate (C2H5NaO2S2), sodium 2-iodobenzenesulfonate (C6H4INaO3S), sodium 4-nitrobenzene methanesulfonate (C7H6NNaO5S), sodium styrenesulfonate (C8H7NaO3S), sodium 4-isopropylbenzenesulfonate (C9H 11 NaO3S), sodium phenolsulfonate (C6H5NaO4S), sodium β-styrenesulfonate (C8H7NaO3S), sodium cyclohexanesulfonate (C6H 11NaO3S), sodium 2-cyclohexylaminoethanesulfonate (C8H 16 NNaO3S), 4-amino-N-methylbenzenesulfonamide (C7H 10 N2O2S), sodium polydisulfide dipropane sulfonate (C6H 12 Na2O6S4), sodium pyridine-3-sulfinate (C5H4NNaO2S), piperazine-1,4-diethanesulfonic acid monosodium salt (C8H 17 N2NaO6S2) one or more, optionally including one or more of sodium fluorosulfonate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium methanesulfonate, and sodium methyl sulfate.

[0014] In any embodiment, the concentration of the sodium salt having sulfonate groups in the non-aqueous electrolyte is in the range of 0.0005-1 mol / L, optionally in the range of 0.01-0.3 mol / L.

[0015] In the second sodium salt, the concentration of the sodium salt containing sulfonate in the electrolyte is above 0.0005 mol / L, which can have the effect of improving the stability of the first sodium salt in the electrolyte. Moreover, it enables the sodium ion battery to form a stable solid electrolyte interface film on the electrode surface during the electrochemical reaction, effectively inhibiting the decomposition and gas production of the solvent in the electrolyte on the electrode surface, and improving the electrochemical performance of the sodium ion battery (especially at high temperatures). Optionally, the concentration of the sodium salt containing sulfonate in the electrolyte may be above 0.01 mol / L. In addition, the concentration of the sodium salt with sulfonate in the electrolyte is below 0.3 mol / L, which can more effectively reduce the risk of excessive film formation on the electrode, and thus will not have a significant impact on the electrochemical performance of the sodium ion battery at high temperatures. Optionally, the concentration may be below 0.15 mol / L.

[0016] In any embodiment, the sodium salt having oxalate includes one or more of sodium oxalate (Na2C2O4), sodium bis(oxalato)borate (C4BNaO8), sodium difluoro(oxalato)borate (C2BF2NaO4), sodium tetrafluoro(oxalato)phosphate (C2F4NaO4P), and sodium difluorobis(oxalato)phosphate (C4F2NaO8P).

[0017] In any embodiment, the concentration of the sodium salt having oxalate in the non-aqueous electrolyte is in the range of 0.0005-0.1 mol / L, optionally in the range of 0.006-0.08 mol / L, further optionally in the range of 0.01-0.02 mol / L.

[0018] In the second sodium salt, the concentration of the sodium salt containing oxalate in the electrolyte is above 0.0005 mol / L, which can significantly improve the stability of the first sodium salt in the electrolyte, and has an improvement effect on the cycle performance of the sodium ion battery at high temperature and the improvement of the capacity retention rate after storage. Optionally, the concentration can be above 0.006 mol / L, and further can be above 0.01 mol / L. In addition, the concentration is preferably below 0.08 mol / L, which can more effectively reduce the possibility of excessive film formation of the sodium salt with oxalate on the electrode, thereby not having a significant impact on the kinetic process during the charge and discharge process of the sodium ion battery.

[0019] In any embodiment, the sodium salt having phosphate group includes sodium difluorophosphate (NaPO2F2), sodium monofluorophosphate (Na2PO3F), sodium trimetaphosphate (Na3P3O9), sodium hexametaphosphate (Na6P6O 18 ), sodium hydroxyethylidene diphosphonate (C2H7NaO7P2), clodronate disodium (CH2Cl2Na2O6P2), olpadronate sodium (C5H 15 NO7P2), diethylenetriamine penta methylenephosphonate sodium (C9H 18 N3Na 10 O 15 P5), sodium tripolyphosphate (Na5P3O 10 ) and disodium phenyl phosphate (C6H5Na2O4P) and one or more thereof, optionally including one or more thereof: sodium difluorophosphate (NaPO2F2) and sodium fluorophosphate (Na2PO3F).

[0020] In any embodiment, the concentration of the sodium salt having phosphate in the non-aqueous electrolyte is in the range of 0.0005-0.12 mol / L, optionally in the range of 0.01-0.05 mol / L, and more optionally in the range of 0.01-0.03 mol / L.

[0021] In the second sodium salt, the molar concentration of the sodium salt containing phosphate in the non-aqueous electrolyte is above 0.0005 mol / L, which can improve the stability of the first sodium salt in the electrolyte and enable the sodium ion battery to form a thin and solid solid electrolyte film mainly composed of inorganic components on the electrode surface during the formation process, which can significantly suppress the gas production problem in the sodium ion battery. Optionally, the concentration is above 0.01 mol / L. In addition, the concentration is below 0.12 mol / L, which can effectively reduce the possibility of excessive film formation of the sodium salt containing phosphate on the electrode surface, and thus will not have a significant impact on the kinetic process during the charge and discharge process of the sodium ion battery.

[0022] In any embodiment, the sodium salt having a borate group includes sodium tetrafluoroborate (NaBF4), sodium metaborate (BNaO2), sodium tetraphenylborate ((C6H5)4BNa), sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (C 32 H 12 BF 24 Na), optionally including one or more of sodium tetrafluoroborate, sodium metaborate and sodium tetraphenylborate, and further optionally including one or more of sodium tetrafluoroborate and sodium metaborate.

[0023] In any embodiment, the concentration of the sodium salt having a borate group in the non-aqueous electrolyte is in the range of 0.0005-0.05 mol / L, optionally in the range of 0.01-0.04 mol / L.

[0024] In the second sodium salt, the molar concentration of the sodium salt containing borate in the non-aqueous electrolyte is above 0.0005 mol / L, which can have a certain effect on improving the stability of the first sodium salt in the electrolyte, and enable the sodium ion battery to form a thin and dense solid electrolyte interface film on the electrode surface, thereby inhibiting the continuous decomposition of the solvent in the electrolyte at the electrode / electrolyte interface, thereby significantly inhibiting the gas production problem in the sodium ion battery, and also improving the capacity retention rate after the cycle and high temperature storage of the sodium ion battery (especially at high temperature). In addition, the concentration is below 0.05 mol / L, which can effectively reduce the possibility of excessive film formation of the sodium salt containing borate on the electrode surface, and thus will not have a significant impact on the kinetic process during the charge and discharge process of the sodium ion battery.

[0025] In any embodiment, among the first sodium salts, when sodium hexafluorophosphate is used in combination with at least one of sodium hexafluoroarsenate, sodium perchlorate and sodium trifluoroacetate, the concentration of the other sodium salts except sodium hexafluorophosphate in the non-aqueous electrolyte is 0.001 mol / L or more, optionally 0.01 mol / L or more, further optionally 0.03 mol / L or more, and 1 mol / L or less, optionally 0.5 mol / L or less.

[0026] Among the first sodium salts, if the concentration of other sodium salts other than sodium hexafluorophosphate (NaPF6) in the non-aqueous solvent is above 0.001 mol / L, the electrochemical performance of the sodium ion battery at high temperature is improved. If the concentration of other sodium salts in the non-aqueous solvent is below 1 mol / L, the solvation structure of the sodium ions in the electrolyte and the chemical environment of the non-aqueous solvent molecules can be regulated to a certain extent, thereby inhibiting the decomposition and gas production of the electrolyte under high temperature conditions, and promoting the improvement of the electrochemical performance of the sodium ion battery at high temperature.

[0027] In any embodiment, the second sodium salt includes a sodium salt having a sulfonate group, and further includes one or more of a sodium salt having an oxalate group, a sodium salt having a phosphate group, and a sodium salt having a borate group.

[0028] Among the second sodium salts, the combination of a sodium salt having a sulfonate group and a sodium salt having one or more of oxalate, phosphate and borate groups will produce a synergistic effect, synergistically participating in the solvation process of sodium ions in the electrolyte, providing partial electrons for the sodium ions, and effectively inhibiting the strong electron-withdrawing property of sodium ions to non-aqueous solvent molecules, and significantly inhibiting the continuous decomposition and gas production of the electrolyte; in addition, the combination of a sodium salt having a sulfonate group and a sodium salt having one or more of oxalate, phosphate and borate groups can form a thinner and dense solid electrolyte interface film rich in inorganic components at the electrode / electrolyte interface, which has a significant improvement effect on the electrochemical performance of sodium ion batteries (especially at high temperatures).

[0029] In any embodiment, the second sodium salt includes a sodium salt having a sulfonate group and a sodium salt having an oxalate group. Optionally, the molar ratio of the sodium salt having a sulfonate group to the sodium salt having an oxalate group is 0.03 / 1 to 70 / 1, and optionally 0.5 / 1 to 20 / 1.

[0030] The combination of sodium salts with oxalate groups, sodium salts with phosphate groups, and sodium salts with borate groups improves the inhibition of electrolyte decomposition and gas production. When the molar ratio of sodium salts with sulfonate groups to sodium salts with oxalate groups is between 1 / 1 and 10 / 1, a thin solid electrolyte interface film composed primarily of inorganic components is more likely to form on the electrode surface during charge and discharge of sodium-ion batteries.

[0031] In any embodiment, the non-aqueous electrolyte contains cyclic carbonate, and the mass concentration of the cyclic carbonate in the non-aqueous electrolyte is greater than 10%, optionally greater than 15%, and less than 60%.

[0032] When the mass concentration of the cyclic carbonate in the non-aqueous electrolyte is within the above range, the stability of the electrode / electrolyte interface film of the sodium ion battery under high temperature conditions can be improved to a certain extent without substantially affecting the sodium ion migration rate.

[0033] In any embodiment, the non-aqueous electrolyte contains linear carbonates and linear carboxylates, and the mass percentage of the sum of the linear carbonates and linear carboxylates in the non-aqueous electrolyte is above 40%, optionally above 50%, more optionally above 60%, and below 90%, optionally below 85%, and further optionally below 80%.

[0034] The mass percentage of the linear carbonate and the linear carboxylic acid ester in the electrolyte is above 40%, optionally above 50%, and more optionally above 60%, so that the viscosity of the electrolyte will not be too high; the upper limit of the content is below 90%, optionally below 85%, and further optionally below 80%, so that the ionic conductivity does not decrease much, and the impact on the electrochemical performance of the sodium ion battery is small.

[0035] In any embodiment, the non-aqueous electrolyte includes at least one cyclic carbonate and at least one chain ester, and the mass percentage of the at least one cyclic carbonate to the at least one chain ester is greater than 0.1:1 and less than 1.5:1, optionally less than 1:1, and more optionally, between 0.2:1 and 1:1.

[0036] When the mass percentage of cyclic carbonate and chain ester in the non-aqueous electrolyte described in the present application is within the above range, it will have a certain inhibitory effect on the decomposition and gas production of the electrolyte at high temperature of the sodium ion battery, and have a certain promoting effect on the improvement of the electrochemical performance of the sodium ion battery.

[0037] In any embodiment, the non-aqueous electrolyte contains one or more of the following combinations of substances: cyclic carbonate and chain carbonate; cyclic carbonate and chain carboxylate; cyclic carbonate and ether; chain carbonate and chain carboxylate; chain carbonate and ether; chain carboxylate and ether; cyclic carbonate, chain carbonate and chain carboxylate; cyclic carbonate, chain carbonate and ether; cyclic carbonate, chain carboxylate and ether; chain carbonate, chain carboxylate and ether.

[0038] The cyclic carbonates, chain carbonates, chain carboxylates, ethers, etc. included in the non-aqueous electrolyte described in this application exist as non-aqueous solvents. These specific combinations of non-aqueous solvents can not only improve the solubility and dispersion of the electrolyte sodium salt therein, but also participate in the formation of certain specific sodium ion solvation configurations, thereby effectively suppressing the decomposition of the solvent in the electrolyte and the accompanying gas production problem, further improving the electrochemical performance of the sodium ion battery (especially under high temperature conditions).

[0039] In any embodiment, the non-aqueous solvent in the non-aqueous electrolyte includes one or more of propylene carbonate, ethyl methyl carbonate, ethyl acetate, diethyl carbonate, methyl propionate, ethyl propionate, diethylene glycol dimethyl ether, and fluoroethylene carbonate.

[0040] In any embodiment, the non-aqueous electrolyte includes one or more of anhydride additives, fluorine-containing organic additives, nitrile additives, silicone additives, aldehyde additives, sulfur-containing additives, lithium salt additives, and potassium salt additives. Optionally, the total mass percentage of these additives in the non-aqueous electrolyte is greater than 0.001%, optionally greater than 0.2%, and less than 5%, optionally less than 4%.

[0041] To further optimize the stability of the film formed on the electrode surface during the charge and discharge process of sodium-ion batteries and to obtain a thin, dense electrode / electrolyte interface film primarily composed of inorganic components, the aforementioned additive can be optionally added to the electrolyte. A mass percentage of the additive in the non-aqueous electrolyte of 0.001% or greater, preferably 0.2% or greater, improves the stability of the film formed on the electrode surface; an upper limit of 5% or less, preferably 4% or less, reduces the likelihood of excessive film formation on the electrode surface.

[0042] A second aspect of the present application provides a sodium ion battery, which includes a positive electrode sheet, a negative electrode sheet and the non-aqueous electrolyte described in the first aspect of the present application.

[0043] The third aspect of the present application provides an electrical device, which includes the non-aqueous electrolyte described in the first aspect of the present application or the sodium ion battery described in the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0045] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

[0046] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0047] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0048] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0049] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0050] Description of reference numerals:

[0051] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0052] Below, embodiments of the non-aqueous electrolyte and sodium ion battery are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0053] " range " disclosed in the application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-6. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0055] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0056] Unless otherwise specified, all steps of the present application may be performed sequentially, randomly, or optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0057] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0058] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0059] Sodium-ion batteries are mainly composed of positive and negative electrode materials that can embed / extract sodium ions, and electrolytes containing sodium salts and non-aqueous solvents. Among them, the electrolyte plays an important role in the development of sodium-ion batteries. As a bridge for the transmission of sodium ions between the positive and negative electrodes, the electrolyte determines the capacity of the positive and negative electrode materials, thereby affecting the electrochemical performance of the sodium-ion battery. However, the electrolyte is also affected by factors such as the positive and negative electrode materials, the environment (such as temperature), and test conditions (such as voltage).

[0060] Generally, the electrolyte of sodium-ion batteries is greatly affected by the negative electrode materials. The negative electrode materials of sodium-ion batteries include metallic sodium, carbon materials (such as hard carbon, graphite, etc.), metal compounds (such as metal oxides, alloys, etc.), etc. The sodium insertion potential of these materials is often relatively low, which may cause the electrolyte to undergo reductive decomposition. Especially at high temperatures, the problem of reductive decomposition of the solvent in the electrolyte on the surface of the negative electrode is more serious. The continuous decomposition of the solvent will cause the sodium-ion battery to face serious gas production problems. The large amount of gases produced (such as carbon dioxide, carbon monoxide, hydrogen, propylene, etc.) will accumulate in the sodium-ion battery, which will increase the risk of safe use of the sodium-ion battery. In addition, the continuous decomposition of the solvent often forms a large amount of organic decomposition products. These organic substances are deposited on the surface of the negative electrode to form a thick and uneven organic solid electrolyte (SEI) film, which will significantly slow down the transport dynamics of sodium ions at the negative electrode / electrolyte interface, and ultimately deteriorate the electrochemical performance (such as cycle and rate performance, etc.) of the sodium-ion battery (especially at high temperatures); moreover, the continuous deposition of the organic SEI film will also cause the electrode to expand. The expansion of the electrode and the large amount of gas production cause the sodium-ion battery to expand in volume, which will cause certain safety hazards in the use of the sodium-ion battery.

[0061] The electrolyte of sodium-ion batteries is also affected by factors such as the operating voltage and chemical composition of the positive electrode material. Currently, the main positive electrode materials for sodium-ion batteries include transition metal oxides, polyanionic compounds, and Prussian blue analogs. These positive electrode materials often undergo sodium ion insertion / extraction reactions in the high voltage range. Under high voltage conditions, the electrolyte will undergo oxidative decomposition at the positive electrode, accompanied by a large amount of gas precipitation. In addition, the transition metals (such as iron, cobalt, nickel, etc.) in some metal oxide positive electrode materials have strong catalytic properties and may catalyze the decomposition of solvents and electrolyte / positive electrode interface films. This will require sodium-ion batteries to continuously consume electrolyte film during use, thereby losing a large amount of reversibly active sodium and solvent, ultimately resulting in a significant reduction in the service life of sodium-ion batteries. Under high temperature conditions, the decomposition rate of the electrolyte tends to accelerate significantly, and the gas production problem becomes more serious. Moreover, continuous solvent decomposition will produce a large amount of organic decomposition products deposited on the positive electrode surface, forming a thick and uneven electrolyte / positive electrode interface film, which seriously increases the transmission resistance of sodium ions at the electrolyte / positive electrode interface, and ultimately affects the electrochemical performance of sodium ion batteries.

[0062] During the actual use of sodium-ion batteries, the battery continuously releases heat and heats up as the electrochemical reaction proceeds. At high temperatures, the problem of gassing caused by electrolyte decomposition becomes more serious, which will affect the industrial development of sodium-ion batteries. Therefore, it is of great research significance to rationally design electrolytes to meet the requirements of sodium-ion battery use at high temperatures and improve their safety and electrochemical performance.

[0063] Our research has found that the gassing problem in sodium-ion batteries primarily stems from the continuous decomposition of the solvent at the electrode / electrolyte interface, which is closely related to the chemical environment of the solvent in the electrolyte. Typically, in sodium-ion battery electrolytes, due to the difference in electrostatic potential between sodium ions and solvent molecules, sodium ions attract solvent molecules through electrostatic interactions, forming a solvated sodium ion shell structure around them. However, due to the strong electron-withdrawing property of sodium ions, some electrons from the solvent molecules are transferred to the sodium ions, weakening the chemical bonds within the solvent molecules in the shell structure and leading to reduced chemical stability of these solvent molecules. Furthermore, compared to pure solvent molecules, the energy of the lowest unoccupied molecular orbital (LUMO) of the solvated sodium ions is further reduced. This makes the solvent molecules in the sodium ion solvated shell structure more likely to receive electrons at the anode surface and undergo reductive decomposition, making the electrolyte more susceptible to reductive decomposition than pure solvent. Therefore, regulating the chemical environment of solvent molecules in sodium-ion battery electrolytes is key to suppressing gassing from solvent decomposition.

[0064] Based on existing reports and our own systematic research, the composition of metal salts (especially the anions in the metal salts) plays a crucial role in the chemical and electrochemical stability of batteries. Within the same solvent, the type of metal salt determines the electrolyte's solvation structure and thermodynamic stability, thereby influencing the electrolyte's decomposition behavior and, in turn, regulating the electrode / electrolyte interface and the electrode's electrochemical performance. Introducing electron-rich anions into sodium-ion battery electrolyte systems can significantly suppress solvent decomposition and gassing. Electron-rich anions participate in the sodium ion solvation structure, donating some electrons to the sodium ions, weakening the strong electron-withdrawing properties of the sodium ions from the solvent molecules and reducing the weakening of chemical bonds and molecular instability caused by local electron loss. Furthermore, our research has found that the choice of anion type and radius can further regulate the sodium ion solvation structure and the chemical environment of the solvent molecules in the electrolyte. Importantly, some different anion types exhibit synergistic effects in the electrolyte. These anions act as electron "sponges," providing electrons to the sodium ion solvation shell, synergistically improving the chemical, electrochemical, and thermal stability of the electrolyte. Furthermore, our research has found that the partial electron transfer from some fluorinated anions to sodium ions weakens the local chemical bonds in their ionic structure. During the electrochemical reaction of sodium-ion batteries, these anions preferentially decompose to form a thin, dense electrode / electrolyte interface film rich in inorganic components. This significantly inhibits the continued decomposition and gas production of the solvent in the electrolyte, effectively improving the electrochemical performance of sodium-ion batteries (especially at high temperatures).

[0065] Therefore, the purpose of the present application is to provide a sodium ion battery electrolyte and a sodium ion battery containing electron-rich anions by regulating the solvation structure of sodium ions in the electrolyte and the chemical environment of the solvent molecules, so as to solve the gas production problem caused by the continuous decomposition of the solvent in the sodium ion battery.

[0066] Based on the above content, the first aspect of the present application provides a non-aqueous electrolyte, comprising:

[0067] a first sodium salt comprising at least one of sodium hexafluorophosphate (NaPF6), sodium hexafluoroarsenate (NaAsF6), sodium perchlorate (NaClO4) and sodium trifluoroacetate (CF3COONa); optionally, the first sodium salt is sodium hexafluorophosphate;

[0068] The second sodium salt includes one, two or more of a sodium salt with a sulfonate group, a sodium salt with an oxalate group, a sodium salt with a phosphate group and a sodium salt with a borate group; optionally, the second sodium salt includes a sodium salt with a sulfonate group, a sodium salt with an oxalate group, a sodium salt with a phosphate group and a sodium salt with a borate group.

[0069] In this application, the sulfonate group in the sodium salt having a sulfonate group includes, but is not limited to, for example SO3 2-、(SO3CF3) - 、[N(FSO2)2] - etc.; the oxalate in the sodium salt having oxalate includes, but is not limited to, for example C2O4 2- 、(C2O4BF2) - 、[(C2O4)2B] - etc.; the borate radical in the sodium salt having a borate radical includes, but is not limited to, for example BF4 - , BO2 - etc.; the phosphate group in the sodium salt having a phosphate group includes, but is not limited to, for example PO4 3- 、(PO3F) 2- 、(PO2F2) - wait.

[0070] The non-aqueous electrolyte is obtained by dissolving a sodium salt electrolyte containing electron-rich anions in a non-aqueous solvent. As described above, by selectively adding the first and second sodium salts, the solvation structure of the sodium ions in the electrolyte and the chemical environment of the solvent molecules can be regulated, thereby resolving the gassing problem caused by the continuous decomposition of the solvent in sodium-ion batteries.

[0071] In some optional embodiments, in the non-aqueous electrolyte, the molar concentration ratio of the first sodium salt to the second sodium salt is above 1 / 1, can be optionally above 2 / 1, more can be optionally above 5 / 1, further can be optionally above 10 / 1, and is below 1000 / 1, can be optionally below 40 / 1, and more can be optionally below 20 / 1.

[0072] In some embodiments, in the non-aqueous electrolyte, the molar concentration ratio of the first sodium salt to the second sodium salt is greater than 1 / 1, and can be selected as greater than 3 / 1, and less than 40 / 1, and more preferably less than 15 / 1.

[0073] In the entire electrolyte, the molar concentration ratio of the first sodium salt to the second sodium salt is within the above range, which can reduce the risk of excessive film formation on the electrode surface and reduce the resistance to sodium ion transmission at the electrode / electrolyte interface, thereby having less impact on the kinetic process of the sodium ion battery.

[0074] In some embodiments, the sodium salt having a sulfonate group includes sodium fluorosulfonate (FSO3Na), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]), sodium bis(trifluoromethylsulfonyl)imide (Na[(CF3SO2)2N]), sodium methanesulfonate (CH3SO3Na), sodium vinylsulfonate (C2H3NaO3S), sodium methylsulfate (CH3OSO3Na), sodium methylthiosulfonate (C2H3NaO3S), sodium methylsulfon ...sulfonate (C2H3NaO3S), sodium methylsulfonate (CH3OSO3Na), sodium methylsulfonate (C2H3NaO3S), sodium methylsulfonate (CH3OSO3Na H3NaO2S2), sodium 1,2-ethanedisulfonate (NaO3SCH2CH2SO3Na), sodium ethyl sulfate (C2H5NaO4S), sodium propanesulfonate (C3H7NaO3S), sodium ethanethiosulfonate (C2H5NaO2S2), sodium 2-iodobenzenesulfonate (C6H4INaO3S), sodium 4-nitrobenzene methanesulfonate (C7H6NNaO5S), sodium styrenesulfonate (C8H7NaO3S), sodium 4-isopropylbenzenesulfonate (C9H 11 NaO3S), sodium phenolsulfonate (C6H5NaO4S), sodium β-styrenesulfonate (C8H7NaO3S), sodium cyclohexanesulfonate (C6H 11 NaO3S), sodium 2-cyclohexylaminoethanesulfonate (C8H 16 NNaO3S), 4-amino-N-methylbenzenesulfonamide (C7H 10 N2O2S), sodium polydisulfide dipropane sulfonate (C6H 12 Na2O6S4), sodium pyridine-3-sulfinate (C5H4NNaO2S), piperazine-1,4-diethanesulfonic acid monosodium salt (C8H 17 N2NaO6S2) one or more, optionally including one or more of sodium fluorosulfonate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium methanesulfonate, and sodium methyl sulfate.

[0075] In some embodiments, the concentration of the sodium salt having a sulfonate group in the non-aqueous electrolyte is in the range of 0.0005-1 mol / L, optionally in the range of 0.01-0.3 mol / L.

[0076] In some optional embodiments, the concentration of the sodium salt having sulfonate groups in the non-aqueous electrolyte is 0.001 mol / L or more, optionally 0.01 mol / L or more, and 0.3 mol / L or less, optionally 0.15 mol / L or less.

[0077] In the second sodium salt, the concentration of the sodium salt containing sulfonate in the electrolyte is above 0.0005 mol / L, which can have the effect of improving the stability of the first sodium salt in the electrolyte. Moreover, it enables the sodium ion battery to form a stable solid electrolyte interface film on the electrode surface during the electrochemical reaction, effectively inhibiting the decomposition and gas production of the solvent in the electrolyte on the electrode surface, and improving the electrochemical performance of the sodium ion battery (especially at high temperatures). Optionally, the concentration of the sodium salt containing sulfonate in the electrolyte can be above 0.01 mol / L. In addition, the concentration of the sodium salt with sulfonate in the electrolyte is below 1 mol / L, which can more effectively reduce the risk of excessive film formation on the electrode, and thus will not have a significant impact on the electrochemical performance of the sodium ion battery at high temperatures. Optionally, the concentration can be below 0.15 mol / L.

[0078] In some embodiments, the sodium salt having oxalate includes one or more of sodium oxalate (Na2C2O4), sodium bis(oxalato)borate (C4BNaO8), sodium difluoro(oxalato)borate (C2BF2NaO4), sodium tetrafluoro(oxalato)phosphate (C2F4NaO4P), and sodium difluorobis(oxalato)phosphate (C4F2NaO8P).

[0079] Sodium bis(oxalato)borate and sodium difluoro(oxalato)borate contain both oxalate and borate, and can be classified as sodium salts with oxalate or sodium salts with borate, and are here classified as sodium salts with oxalate. Similarly, sodium tetrafluoro(oxalato)phosphate and sodium difluorobis(oxalato)phosphate can also be classified as sodium salts with phosphate, and are here classified as sodium salts with oxalate.

[0080] In some optional embodiments, the concentration of the sodium salt having oxalate in the non-aqueous electrolyte is above 0.001 mol / L, optionally above 0.006 mol / L, further optionally above 0.01 mol / L and below 0.08 mol / L.

[0081] In some embodiments, the concentration of the sodium salt having oxalate in the non-aqueous electrolyte is in the range of 0.0005-0.1 mol / L, optionally in the range of 0.006-0.08 mol / L, and further optionally in the range of 0.01-0.02 mol / L.

[0082] In the second sodium salt, the concentration of the sodium salt containing oxalate in the electrolyte is above 0.0005 mol / L, which can significantly improve the stability of the first sodium salt in the electrolyte, and has an improvement effect on the cycle performance of the sodium ion battery at high temperature and the improvement of the capacity retention rate after storage. Optionally, the concentration can be above 0.006 mol / L, and further can be above 0.01 mol / L. In addition, the concentration is preferably below 0.08 mol / L, which can more effectively reduce the possibility of excessive film formation of the sodium salt with oxalate on the electrode, thereby not having a significant impact on the kinetic process during the charge and discharge process of the sodium ion battery.

[0083] In some embodiments, the sodium salt having a phosphate group includes sodium difluorophosphate (NaPO2F2), sodium monofluorophosphate (Na2PO3F), sodium trimetaphosphate (Na3P3O9), sodium hexametaphosphate (Na6P6O 18 ), sodium hydroxyethylidene diphosphonate (C2H7NaO7P2), clodronate disodium (CH2Cl2Na2O6P2), olpadronate sodium (C5H 15 NO7P2), diethylenetriamine penta methylenephosphonate sodium (C9H 18 N3Na 10 O 15 P5), sodium tripolyphosphate (Na5P3O 10 ) and disodium phenyl phosphate (C6H5Na2O4P) and one or more thereof, optionally including one or more thereof: sodium difluorophosphate (NaPO2F2) and sodium fluorophosphate (Na2PO3F).

[0084] In some optional embodiments, the concentration of the sodium salt having phosphate in the non-aqueous electrolyte is above 0.001 mol / L, optionally above 0.01 mol / L, and below 0.12 mol / L.

[0085] In some embodiments, the concentration of the sodium salt having phosphate in the non-aqueous electrolyte is in the range of 0.0005-0.12, optionally in the range of 0.01-0.05 mol / L, and more optionally in the range of 0.01-0.03 mol / L.

[0086] In the second sodium salt, the molar concentration of the sodium salt containing phosphate in the non-aqueous electrolyte is above 0.0005 mol / L, which can improve the stability of the first sodium salt in the electrolyte and enable the sodium ion battery to form a thin and solid solid electrolyte film mainly composed of inorganic components on the electrode surface during the formation process, which can significantly suppress the gas production problem in the sodium ion battery. Optionally, the concentration is above 0.01 mol / L. In addition, the concentration is below 0.12 mol / L, which can effectively reduce the possibility of excessive film formation of the sodium salt containing phosphate on the electrode surface, and thus will not have a significant impact on the kinetic process during the charge and discharge process of the sodium ion battery.

[0087] In some embodiments, the sodium salt having a borate group includes sodium tetrafluoroborate (NaBF4), sodium metaborate (BNaO2), sodium tetraphenylborate ((C6H5)4BNa), sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (C 32 H 12 BF 24 Na), optionally including one or more of sodium tetrafluoroborate, sodium metaborate and sodium tetraphenylborate, and further optionally including one or more of sodium tetrafluoroborate and sodium metaborate.

[0088] In some optional embodiments, the concentration of the sodium salt having a borate group in the non-aqueous electrolyte is greater than 0.001 mol / L, optionally greater than 0.008 mol / L, and less than 0.03 mol / L.

[0089] In some embodiments, the concentration of the sodium salt having a borate group in the non-aqueous electrolyte is in the range of 0.0005-0.05 mol / L, optionally in the range of 0.01-0.04 mol / L.

[0090] In the second sodium salt, the molar concentration of the sodium salt containing borate in the non-aqueous electrolyte is above 0.0005mol / L, which can have a certain effect on improving the stability of the first sodium salt in the electrolyte, and enables the sodium ion battery to form a thin and dense solid electrolyte interface film on the electrode surface during the electrochemical reaction, thereby suppressing the continuous decomposition of the solvent in the electrolyte at the electrode / electrolyte interface, thereby significantly inhibiting the gas production problem in the sodium ion battery, and also improving the capacity retention rate after the circulation and high temperature storage of the sodium ion battery (especially at high temperatures). In addition, the concentration is below 0.05mol / L, which can effectively reduce the possibility of excessive film formation of the sodium salt containing borate on the electrode surface, and thus will not have a greater impact on the kinetic process during the charge and discharge process of the sodium ion battery. Alternatively, the concentration of the sodium salt with borate in the non-aqueous electrolyte is within the range of 0.01-0.02mol / L.

[0091] In some embodiments, among the first sodium salts, when sodium hexafluorophosphate is used in combination with at least one of sodium hexafluoroarsenate, sodium perchlorate and sodium trifluoroacetate, the concentration of the other sodium salts except sodium hexafluorophosphate in the non-aqueous electrolyte is 0.001 mol / L or more, optionally 0.01 mol / L or more, further optionally 0.03 mol / L or more, and 1 mol / L or less, optionally 0.5 mol / L or less.

[0092] Optionally, among the first sodium salts, the concentration of other sodium salts except sodium hexafluorophosphate (NaPF6) in the non-aqueous solvent is preferably above 0.005 mol / L, more preferably above 0.01 mol / L, and further preferably above 0.02 mol / L, and the upper limit of the concentration is preferably below 0.7 mol / L, and further preferably below 0.6 mol / L.

[0093] The concentration of sodium hexafluorophosphate in the non-aqueous electrolyte described in this application can be any concentration or conventional concentration. Optionally, the concentration of sodium hexafluorophosphate in the non-aqueous electrolyte described in this application is 0.4-1.6 mol / L.

[0094] Among the first sodium salts, if the concentration of other sodium salts other than sodium hexafluorophosphate (NaPF6) in the non-aqueous solvent is above 0.001 mol / L, the electrochemical performance of the sodium ion battery at high temperature is improved. If the concentration of other sodium salts in the non-aqueous solvent is below 1 mol / L, the solvation structure of the sodium ions in the electrolyte and the chemical environment of the non-aqueous solvent molecules can be regulated to a certain extent, thereby inhibiting the decomposition and gas production of the electrolyte under high temperature conditions, and promoting the improvement of the electrochemical performance of the sodium ion battery at high temperature.

[0095] In some embodiments, the second sodium salt includes a sodium salt having a sulfonate group, and further includes one or more of a sodium salt having an oxalate group, a sodium salt having a phosphate group, and a sodium salt having a borate group.

[0096] Among the second sodium salts, the combination of a sodium salt having a sulfonate group and a sodium salt having one or more of oxalate, phosphate and borate groups will produce a synergistic effect, synergistically participating in the solvation process of sodium ions in the electrolyte, providing partial electrons for the sodium ions, and effectively inhibiting the strong electron-withdrawing property of sodium ions to non-aqueous solvent molecules, and significantly inhibiting the continuous decomposition and gas production of the electrolyte; in addition, the combination of a sodium salt having a sulfonate group and a sodium salt having one or more of oxalate, phosphate and borate groups can form a thinner and dense solid electrolyte interface film rich in inorganic components at the electrode / electrolyte interface, which has a significant improvement effect on the electrochemical performance of sodium ion batteries (especially at high temperatures).

[0097] In some embodiments, the second sodium salt comprises a sodium salt having a sulfonate group and a sodium salt having an oxalate group, and optionally, the molar ratio of the sodium salt having a sulfonate group to the sodium salt having an oxalate group is 0.03 / 1 to 70 / 1, optionally 0.5 / 1 to 20 / 1. Also optionally, the molar ratio of the sodium salt having a sulfonate group to the sodium salt having an oxalate group is 1 / 1 to 10 / 1.

[0098] The combination of sodium salts with oxalate groups, sodium salts with phosphate groups, and sodium salts with borate groups improves the inhibition of electrolyte decomposition and gas production. When the molar ratio of sodium salts with sulfonate groups to sodium salts with oxalate groups is between 1 / 1 and 10 / 1, a thin solid electrolyte interface film composed primarily of inorganic components is more likely to form on the electrode surface during charge and discharge of sodium-ion batteries.

[0099] The non-aqueous solvent in the non-aqueous electrolyte may include cyclic carbonates, linear esters and / or ethers. Optionally, the non-aqueous solvent includes one or more of cyclic carbonates, chain carbonates, chain carboxylates and ethers.

[0100] In some embodiments, the non-aqueous electrolyte contains cyclic carbonate, and the mass concentration of the cyclic carbonate in the non-aqueous electrolyte is greater than 10%, optionally greater than 15%, and less than 60%.

[0101] The cyclic carbonates are those commonly used as solvents in batteries, including, but not limited to, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfite (ES), propylene sulfite (PS), vinylethylene carbonate (VEC), 4-ethynyl-1,3-dioxolane-2-one (EEC), cis-4,5-difluoro-1,3-dioxolane-2-one and trans-4,5-difluoro-1,3-dioxolane-2-one. One or more of them may be selected, and more optionally, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC).

[0102] When the mass concentration of the cyclic carbonate in the non-aqueous electrolyte is within the above range, the stability of the electrode / electrolyte interface film of the sodium ion battery under high temperature conditions can be improved to a certain extent without substantially affecting the sodium ion migration rate.

[0103] Among cyclic carbonates, the use of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC) has a certain improvement effect on the kinetic process of sodium ion batteries at high temperatures.

[0104] In some embodiments, the non-aqueous electrolyte contains linear carbonates and linear carboxylates, and the mass percentage of the sum of the linear carbonates and linear carboxylates in the non-aqueous electrolyte is above 40%, optionally above 50%, more optionally above 60%, and below 90%, optionally below 85%, and further optionally below 80%.

[0105] The chain carbonates are those that can be used as solvents in batteries, and optionally include the following substances: one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate and dibutyl carbonate; among the chain carbonates, one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and methyl propyl carbonate (MPC) can be selected.

[0106] The chain carboxylic acid esters are those that can be used as solvents in batteries, and optionally include the following substances: one or more of methyl formate (MF), ethyl formate (EF), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), ethyl butyrate (EB), methyl acetate (MA), ethyl acetate (EA) and propyl acetate (PA); optionally one or more of methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl acetate (MA), ethyl acetate (EA) and propyl acetate (PA).

[0107] The mass percentage of the linear carbonate and the linear carboxylic acid ester in the electrolyte is above 40%, optionally above 50%, and more optionally above 60%, so that the viscosity of the electrolyte will not be too high; the upper limit of the content is below 90%, optionally below 85%, and further optionally below 80%, so that the ionic conductivity does not decrease much, and the impact on the electrochemical performance of the sodium ion battery is small.

[0108] In some embodiments, the non-aqueous electrolyte includes at least one cyclic carbonate and at least one chain ester, and the mass percentage of the at least one cyclic carbonate to the at least one chain ester is greater than 0.1:1 and less than 1.5:1, optionally less than 1:1, and more optionally, between 0.2:1 and 1:1.

[0109] The cyclic carbonate is as described above. The chain ester includes the chain carbonate and chain carboxylic acid ester as described above.

[0110] Optionally, the total number of types of cyclic carbonates and chain esters in the non-aqueous electrolyte described in the present application is two or more.

[0111] When the mass percentage of cyclic carbonate and chain ester in the non-aqueous electrolyte described in the present application is within the above range, it will have a certain inhibitory effect on the decomposition and gas production of the electrolyte at high temperature of the sodium ion battery, and have a certain promoting effect on the improvement of the electrochemical performance of the sodium ion battery.

[0112] In some embodiments, the non-aqueous electrolyte contains one or more of the following combinations of substances: cyclic carbonate and chain carbonate; cyclic carbonate and chain carboxylate; cyclic carbonate and ether; chain carbonate and chain carboxylate; chain carbonate and ether; chain carboxylate and ether; cyclic carbonate, chain carbonate and chain carboxylate; cyclic carbonate, chain carbonate and ether; cyclic carbonate, chain carboxylate and ether; chain carbonate, chain carboxylate and ether.

[0113] The cyclic carbonate, chain carbonate, and chain carboxylate are as described above. The ether is one that can be used as a solvent in a battery, and may optionally include one or more of dioxolane (DOL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), tetrahydropyran (THP), 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (DG), 1,2-diethoxyethane, and 1,2-dibutoxyethane.

[0114] The cyclic carbonates, chain carbonates, chain carboxylates, ethers, etc. included in the non-aqueous electrolyte described in this application exist as non-aqueous solvents. These specific combinations of non-aqueous solvents can not only improve the solubility and dispersion of the electrolyte sodium salt therein, but also participate in the formation of certain specific sodium ion solvation configurations, thereby effectively suppressing the decomposition of the solvent in the electrolyte and the accompanying gas production problem, further improving the electrochemical performance of the sodium ion battery (especially under high temperature conditions).

[0115] In some embodiments, the non-aqueous solvent in the non-aqueous electrolyte includes one or more of propylene carbonate, ethyl methyl carbonate, ethyl acetate, diethyl carbonate, methyl propionate, ethyl propionate, diethylene glycol dimethyl ether, and fluoroethylene carbonate.

[0116] In some embodiments, the non-aqueous electrolyte includes one or more of anhydride additives, fluorine-containing organic additives, nitrile additives, silicone additives, aldehyde additives, sulfur-containing additives, lithium salt additives, and potassium salt additives. Optionally, the total mass percentage of these additives in the non-aqueous electrolyte is greater than 0.001%, optionally greater than 0.2%, and less than 5%, optionally less than 4%.

[0117] In order to further optimize the stability of the film formed on the electrode surface during the charge and discharge process of the sodium ion battery and obtain a thin and dense electrode / electrolyte interface film mainly composed of inorganic components, some additives can be optionally added to the electrolyte. For example, some additives can be added, which are specifically introduced as follows:

[0118] Anhydride additives are those that can be used in the electrolyte and may include, but are not limited to, for example, one or more of succinic anhydride, maleic anhydride, caproic anhydride, maleic anhydride, succinic anhydride, butyric anhydride, crotonic anhydride, phthalic anhydride, pyromellitic dianhydride, allylsuccinic anhydride or 3-allylsuccinic anhydride;

[0119] Fluorine-containing organic additives may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), bisfluoroethylene carbonate (DFEC), tris(2,2,2-trifluoroethyl) borate, tris(hexafluoroisopropyl) phosphate, and tris(2,2,2-trifluoroethyl) phosphite;

[0120] Nitrile additives are those that can be used in the electrolyte, and may include, but are not limited to, for example, one or more of succinonitrile, malononitrile, isophthalonitrile, glutaronitrile, methoxypentafluorocyclotriphosphazene, acrylonitrile, cyclobutanenitrile, dimethylaminopropionitrile, ethoxypentafluorocyclotriphosphazene, dicyandiamide, phenoxypentafluorocyclotriphosphazene, ethyl cyanoacrylate, p-chlorophenylacetonitrile, 2-chloro-5-nitrobenzonitrile, p-toluenesulfonylmethyl isocyanide, adiponitrile, and pimelonitrile;

[0121] The organosilicon additives are those that can be used in the electrolyte and may include, but are not limited to, for example, one or more of silane, trimethylsilanol, trimethylchlorosilane, hexamethyldisiloxane, bis(diethylamino)silane, chloromethylsilane, octamethylcyclotetrasiloxane, N-methyl-N-trimethylsilanetrifluoroacetamide, diphenylsilanediol, phenyltrichlorosilane, chlorophenylsilane, tris(trimethylsilyl)phosphate, bromodifluoro(trimethylsilyl)methane or methyldichlorosilane;

[0122] Aldehyde additives may include, but are not limited to, for example, one or more of 2-imidazolecarboxaldehyde, 3-indolecarboxaldehyde, 2-pyrrolecarboxaldehyde, p-chlorobenzaldehyde, 6-chloronicotinaldehyde, 1-methylindole-3-carboxaldehyde, 2-formylthiazole, 5-chloro-2-furfural, or oxazole-2-carboxaldehyde;

[0123] Sulfur-containing additives are those that can be used in the electrolyte, and may include, but are not limited to, for example, one or more of thiourea, sultone, 1,5-naphthalene disulfonic acid, dimethyl sulfone, cyclopentane, methylsulfonic anhydride, dimethyl sulfoxide, 2-mercapto-5-methyl-1,3,4-thiadiazole, dithiooxalamide, tert-butyldimethylsilyl trifluoromethanesulfonate, sodium 2,7-dihydroxynaphthalene-3,6-disulfonate, vinyl sulfate, propylene sulfate, butylene sulfate or vinyl sulfone;

[0124] Lithium salt additives are those that can be used in the electrolyte, and may include, but are not limited to, for example, one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoroacetate, lithium fluorosulfonate, lithium trifluoromethylsulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium methanesulfonate, or lithium ethyl sulfate;

[0125] Potassium salt additives are those that can be used in the electrolyte, and may include, but are not limited to, for example, one or more of potassium hexafluorophosphate, potassium perchlorate, potassium tetrafluoroborate, potassium trifluoroacetate, potassium fluorosulfonate, potassium trifluoromethylsulfonate, potassium bis(fluorosulfonyl)imide, and potassium bis(trifluoromethylsulfonyl)imide;

[0126] The mass percentage of the additive in the non-aqueous electrolyte is above 0.001%, optionally above 0.2%, which has an effect of improving the stability of the film formed on the electrode surface; the upper limit is below 5%, optionally below 4%, which reduces the possibility of excessive film formation on the electrode surface.

[0127] The composition of the sodium ion battery electrolyte in this application can be detected with reference to the sodium salt detection standard in the electrolyte: General Rules for Ion Chromatography Analysis Methods in the General Rules for Analytical Methods of Modern Analytical Instruments (JY / T 020-1996, issued on January 23, 1997, and implemented on April 1, 1997). The sodium salt and anion in the electrolyte are tested and analyzed using the ion chromatography analysis method.

[0128] A second aspect of the present application provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, and the non-aqueous electrolyte described in the first aspect of the present application.

[0129] All the above descriptions of the non-aqueous electrolyte also apply to the sodium ion battery described in the second aspect of this application and the electrical device described in the third aspect of this application.

[0130] In the sodium ion battery, the use of components such as the positive electrode sheet, the negative electrode sheet, and the separator other than the above-mentioned nonaqueous electrolyte is not particularly limited.

[0131] The positive electrode material used for the positive electrode sheet of the sodium ion battery in the present application is an electroactive material that can reversibly insert / extract sodium ions, which may include, but is not limited to, for example, any one of transition metal oxides, Prussian blue analogs, polyanion compounds and organic positive electrode materials, but the present application is not limited to these materials.

[0132] The negative electrode material used for the negative electrode sheet of the sodium ion battery in this application is an electroactive material that can reversibly embed / de-insert sodium ions, and can be appropriately selected from any one of metallic sodium, hard carbon, graphite, metal oxide, metal sulfide, metal phosphide, and alloy negative electrode, but this application is not limited to these materials.

[0133] In the sodium ion battery described in the present application, the positive electrode sheet and the negative electrode sheet may further include a conductive agent and a binder, the types and contents of which are not specifically limited and can be selected and optimized according to actual needs.

[0134] In the sodium ion battery described in the present application, the isolation membrane is often arranged between the positive electrode sheet and the negative electrode sheet to isolate the positive and negative electrode sheets. The type and thickness of the isolation membrane are not subject to specific restrictions and can be any isolation membrane material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride or its multilayer composite film, but the present application is not limited to these materials.

[0135] In some optional embodiments, the sodium ion battery includes a positive electrode sheet and a negative electrode sheet, and the capacity ratio of the positive electrode sheet to the negative electrode sheet is 1:(1-1.3).

[0136] In the sodium ion battery of the present application, when the capacity ratio of the positive electrode sheet to the negative electrode sheet is within the above range, the possibility of excessive film formation of the electrolyte on the electrode surface is reduced, and the continuous decomposition of the electrolyte and the accompanying gas production rate can be appropriately slowed down, thereby promoting the improvement of the electrochemical performance of the sodium ion battery (especially at high temperatures).

[0137] For example, the test method for the capacity ratio of the positive electrode sheet to the negative electrode sheet is as follows:

[0138] Positive electrode capacity test: The positive electrode sheet was punched into small discs with a diameter of 14 mm. A sodium metal sheet was used as the negative electrode and a polypropylene film was used as the separator to assemble a button cell. The positive electrode charge specific capacity Q1 was obtained by constant current charge and discharge tests at a voltage range of 1.5-4.2 V and a rate of 0.1C.

[0139] Negative electrode capacity test: The negative electrode sheet was punched into small discs with a diameter of 14 mm. A sodium metal sheet was used as the negative electrode and a polypropylene film was used as the separator to assemble a button cell. Constant current charge and discharge tests were performed in the voltage range of 0.005-2V. The discharge process was carried out at a constant current rate of 0.05C, 40μA and 10μA to 0.005V. The charge process was carried out at a constant current rate of 0.05C to 2V. The charge specific capacity was recorded as Q2.

[0140] Positive and negative electrode capacity ratio = Q1 / Q2.

[0141] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0142] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0143] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0144] The present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery with a square structure as an example.

[0145] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0146] Secondary batteries come in the form of battery cells, battery modules, and battery packs. In some embodiments, battery cells can be assembled into a battery module, which can contain one or more battery cells. The specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0147] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0148] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0149] In some embodiments, the battery cells can be assembled into a battery pack. In some embodiments, the battery modules can also be assembled into a battery pack, which can contain one or more battery modules. The specific number can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0150] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0151] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the second aspect of the present application. The secondary battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0152] As the electrical device, a secondary battery can be selected according to its usage requirements.

[0153] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0154] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0155] Example

[0156] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0157] The present application is further described below with reference to the following examples. These examples are only used to illustrate the present application and are not used to limit the scope of the present application.

[0158] The secondary batteries of each embodiment and comparative example were prepared according to the following method:

[0159] (1) Preparation of electrolyte

[0160] Example 1: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), a non-aqueous organic solvent (see Table 1 below) was mixed uniformly according to the mass ratio in Table 1, and the following sodium salts were slowly added thereto: the first sodium salt, the second sodium salt and the additive in Table 1, and stirred uniformly to obtain the corresponding electrolyte;

[0161] The other examples and comparative examples were similar to Example 1, using the respective non-aqueous solvents, first sodium salts, second sodium salts and additives in Table 1 to prepare corresponding non-aqueous electrolytes;

[0162] (2) Preparation of positive electrode

[0163] The positive electrode active material NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2, conductive agent acetylene black, and binder polyvinylidene fluoride are dissolved in solvent N-methylpyrrolidone in a mass ratio of 94:3:3, and the mixture is thoroughly stirred and mixed to obtain a positive electrode slurry; the positive electrode slurry is then evenly coated on the positive electrode current collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet;

[0164] (3) Preparation of negative electrode sheet

[0165] The active material hard carbon, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose were dissolved in deionized water at a weight ratio of 95:2:2:1, and the mixture was uniformly mixed with the deionized water to prepare a negative electrode slurry; the negative electrode slurry was then uniformly coated on the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet;

[0166] (4) Preparation of isolation membrane

[0167] The isolation film uses polypropylene film;

[0168] (5) Preparation of sodium ion batteries (cells)

[0169] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role. Then they are wound and packaged to obtain a soft-pack battery. After vacuum drying, the electrolyte is injected, and then a sodium ion soft-pack battery with a capacity of 2Ah is obtained through processes such as formation and standing.

[0170] The meanings of the abbreviations in Table 1 are as follows:

[0171] The solvent abbreviations are: PC: propylene carbonate, EMC: ethyl methyl carbonate, DEC: diethyl carbonate, EP: ethyl propionate, DG: diethylene glycol dimethyl ether;

[0172] Sodium salt abbreviations are: NaPF6: sodium hexafluorophosphate, NaAsF6: sodium hexafluoroarsenate, NaClO4: sodium perchlorate, C2F3NaO2: sodium trifluoroacetate, Na(FSO2)2N: sodium bis(fluorosulfonyl)imide, CF3NaO3S: sodium trifluoromethanesulfonate, C2BF2NaO4: sodium difluoro(oxalato)borate, C4BNaO8: sodium bis(oxalato)borate, NaPO2F2: sodium difluorophosphate, Na2PO3F: sodium monofluorophosphate, NaBF4: sodium tetrafluoroborate, BNaO2: sodium metaborate;

[0173] Additive abbreviations are: FEC: Fluoroethylene carbonate.

[0174] All substances mentioned in the table are chemically pure and commercially available.

[0175] The following is the test process of relevant parameters:

[0176] 1. Sodium ion battery internal resistance mΩ test

[0177] At 25°C, charge the sodium-ion battery at a constant current of 1C to 4.2V, then charge at a constant voltage of 4.2V until the current is less than 0.05C. Discharge the battery at 1C for 30 minutes, adjusting the battery's capacity to 50% SOC. Then, touch the positive and negative test leads of a TH2523A AC internal resistance tester to the positive and negative terminals of the battery, respectively, and read the battery's internal resistance using the tester.

[0178] 2.25℃ cycle 500 times capacity retention test

[0179] At 25°C, the sodium ion battery is charged at a constant current rate of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current is less than 0.05C, then discharged at a constant current rate of 1C to 1.5V, and then discharged at a constant current of 0.04C to 1.5V. This is a charge and discharge process. Repeat the charge and discharge process in this way to calculate the capacity retention rate of the sodium ion battery after 500 cycles. The specific calculation formula is as follows:

[0180] Capacity retention rate (%) of the sodium ion battery after 500 cycles at 25° C. = (discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0181] 3.45℃ cycle 500 times capacity retention test

[0182] At 45°C, the sodium ion battery is charged at a constant current rate of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current is less than 0.05C, then discharged at a constant current rate of 1C to 1.5V, and then discharged at a constant current of 0.04C to 1.5V. This is a charge and discharge process. Repeat the charge and discharge process in this way to calculate the capacity retention rate of the sodium ion battery after 500 cycles. The specific calculation formula is as follows:

[0183] Capacity retention rate (%) of the sodium ion battery after 500 cycles at 45° C. = (discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0184] 4. Capacity retention test after high temperature storage

[0185] At 25°C, the sodium ion battery was discharged at a constant current of 1 / 3C to 1.5V, then charged at a constant current rate of 1 / 3C to 4.2V, and charged at a constant voltage of 4.2V until the current was less than 0.05C. It was then stored at 60°C in a constant temperature box for 2 months. After that, the sodium ion battery after high temperature storage was cooled to 25°C and discharged at a constant current of 1 / 3C to 1.5V. The capacity retention rate of the sodium ion battery after storage at 4.2V at 60°C was calculated as follows:

[0186] Capacity retention rate (%) of sodium ion battery after 60°C high-temperature storage = (discharge capacity at 25°C after high-temperature storage / first discharge capacity at 25°C) × 100%.

[0187] 5. Volume expansion test after high temperature storage

[0188] At 25°C, charge at a constant current of 1C to a voltage of 4.2V, and then charge at a constant voltage of 4.2V to a current of 0.05C. At this time, the volume of the sodium ion battery is tested and recorded as V1; then the fully charged sodium ion battery is placed in a constant temperature box at 60°C and stored for 2 months. The volume is tested using the drainage method and recorded as V2.

[0189] The volume expansion ratio (%) of the sodium ion battery after storage at 60°C for 2 months = (V2-V1) / V1×100%.

[0190] The test results of each embodiment and comparative example are as follows.

[0191] Table 2 Performance of sodium ion batteries of Examples and Comparative Examples

[0192] It can be seen from the data in Table 1-2 that compared with Comparative Examples 1-6, Example 1-43 significantly reduces the volume expansion rate of the battery after high-temperature storage while ensuring that the internal resistance of the battery is equivalent, and improves the capacity retention rate after room temperature, high-temperature cycling and high-temperature storage.

[0193] According to the experimental results of Comparative Example 1, it can be seen that even in the presence of the film-forming additive FEC, the cycle performance of the sodium-ion battery based on the ester electrolyte at 25°C is still relatively poor. When the temperature rises to 45°C, the capacity retention rate of the sodium-ion battery after 500 cycles is significantly reduced. More seriously, the volume expansion rate of the sodium-ion battery is relatively high after 2 months of high-temperature storage. This is because during the charge and discharge process of the sodium-ion battery, the electrolyte faces serious decomposition and is accompanied by a large amount of gas generation, which will lead to serious safety hazards during the use of the sodium-ion battery.

[0194] From Comparative Examples 2-5, it can be seen that after adding a second sodium salt containing an electron-rich anion (having sulfonate / oxalate / phosphate / borate) to the electrolyte of Comparative Example 1, the capacity retention rate of the sodium ion battery after 500 cycles at 25°C and 45°C, and the capacity retention rate after high temperature (60°C) storage will be improved and the volume expansion rate of the battery will be reduced. This shows that the addition of a second sodium salt containing an electron-rich anion can inhibit the decomposition of the electrolyte and the accompanying gas production problem to a certain extent. This is because the electron-rich anion participates in the solvation structure of the sodium ion and provides some electrons to the sodium ion, thereby weakening the strong electron-withdrawing effect of the sodium ion on the solvent molecules in the electrolyte, reducing the magnitude of the reduction in the chemical bond strength in the solvent molecules, thereby inhibiting the decomposition of the solvent molecules and the accompanying gas production problem. However, the addition of a single sodium salt containing an electron-rich anion cannot have a significant inhibitory effect, which may be related to the number, size, electron-donating ability and film formation of the anion.

[0195] As can be seen from Comparative Example 6, when the first sodium salt (NaPF6) is removed from the electrolyte, the sodium ion battery's cycle performance at 25°C and 45°C and the capacity retention rate after high-temperature storage at 60°C are significantly deteriorated. This shows that the first sodium salt plays an indispensable role in the overall electrochemical performance of the sodium ion battery. The combined use of the first sodium salt and the second sodium salt can synergistically improve the electrochemical performance of the sodium ion battery. In addition, the content of the second sodium salt also has a certain influence on the electrochemical performance of the sodium ion battery.

[0196] It can be seen from Examples 1-5 that when 0.0005M and 0.001M of the second sodium salt (Na(FSO2)2N) having a sulfonate group is added to the electrolyte (Example 1-2), the 25°C and 45°C cycle performance of the battery is improved, the capacity retention rate after high-temperature storage at 60°C is significantly improved, and the volume expansion rate of the battery after high-temperature storage is significantly reduced, but such a low content of the second sodium salt (Na(FSO2)2N) has a poor regulating effect on the electrolyte. It is worth noting that when 0.01M and 0.03M of the second sodium salt (Na(FSO2)2N) are added (Examples 3-4), the electrochemical performance of the sodium ion battery is further improved, and the various performance improvements are obvious compared with Comparative Examples 1-6. It can be concluded from Example 5 that when the addition amount of the second sodium salt (Na(FSO2)2N) is 1M, the resistance of the sodium ion battery is improved. This is because the addition of an excessive amount of the second sodium salt will cause excessive film formation and worsen the interface resistance, thereby affecting the kinetic process of the sodium ion battery.

[0197] In addition to the second sodium salt with a sulfonate group, the second sodium salt with an oxalate group also has a certain impact on the electrochemical performance of the sodium ion battery. From Examples 6-11, it can be concluded that after adding 0.0005M of the second sodium salt with an oxalate group (C2BF2NaO4), the electrochemical performance of the sodium ion battery can be improved to a certain extent. When the addition amount exceeds 0.015M, the electrochemical performance of the corresponding battery deteriorates, indicating that excessive addition may affect the interfacial impedance and kinetic process of the sodium ion battery.

[0198] In addition, it can be seen from Examples 12-23 that the addition of a second sodium salt containing an electron-rich anion (having phosphate / borate) also improves the electrochemical performance of the sodium ion battery.

[0199] In addition, it can be concluded from Examples 24-29 that the combination of the second sodium salt having sulfonate, oxalate, phosphate and borate will have a certain improvement effect on the sodium ion battery's cycle performance at 25°C / 45°C, high temperature storage performance and volume expansion rate at high temperature.

[0200] It can be concluded from Examples 30-33 that changing the type of the second sodium salt having sulfonate, oxalate, phosphate and borate also has a similar effect on improving the electrochemical performance of sodium ion batteries.

[0201] As can be seen from Examples 34-39, in addition to carbonate solvents, after adding a second sodium salt containing electron-rich anions (having sulfonate, oxalate, phosphate and borate) to an electrolyte containing carboxylate and ether solvents, the decomposition and gas production of the sodium ion battery electrolyte also have a similar inhibitory effect, and the improvement of the electrochemical performance of the sodium ion battery (especially at high temperatures) has a promoting effect. This shows that the addition of the second sodium salt can play a better regulatory role in the solvation process of sodium ions in the electrolyte and the chemical environment of the solvent molecules in the electrolyte, and it is easy to form a thin and dense solid electrolyte interface film mainly composed of inorganic components, thereby effectively suppressing the decomposition of the solvent in the electrolyte and the accompanying gas production problem, and improving the electrochemical performance of the sodium ion battery. In addition, even after adding four second sodium salts containing electron-rich anions (having sulfonate, oxalate, phosphate and borate) to the electrolyte at the same time, the impedance value of the sodium ion battery does not change much, indicating that the possibility of using a sodium salt containing electron-rich anions while affecting the impedance of the sodium ion battery is relatively small.

[0202] As can be seen from Examples 40-42, the combination of the second sodium salt and other types of first sodium salts can also have a certain improvement effect on the electrochemical performance of the sodium ion battery. At the same time, we found that the electrochemical performance of the sodium ion battery varies when different types of first sodium salts are used in the electrolyte.

[0203] In addition, it can be seen from Example 43 that after removing the additive FEC from the electrolyte, the electrochemical performance of the sodium ion battery deteriorates, indicating that the additive in the electrolyte will participate in the formation of the electrode / electrolyte interface film in the sodium ion battery, and also plays an important role in improving the electrochemical performance of the sodium ion battery.

[0204] The sodium ion battery non-aqueous electrolyte and sodium ion battery of the present application are targeted at solving the problems of electrolyte decomposition and gas production in the actual application of sodium ion batteries, and have good applicability in the industrialization process.

[0205] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A non-aqueous electrolyte, comprising: a first sodium salt, which includes at least one of sodium hexafluorophosphate, sodium hexafluoroarsenate, sodium perchlorate and sodium trifluoroacetate, optionally, the first sodium salt is sodium hexafluorophosphate; a second sodium salt, which includes one, two or more of a sodium salt having a sulfonate group, a sodium salt having an oxalate group, a sodium salt having a phosphate group and a sodium salt having a borate group; optionally, the second sodium salt includes a sodium salt having a sulfonate group, a sodium salt having an oxalate group, a sodium salt having a phosphate group and a sodium salt having a borate group.

2. The non-aqueous electrolyte according to claim 1, characterized in that In the non-aqueous electrolyte, the molar concentration ratio of the first sodium salt to the second sodium salt is greater than 1 / 1, and can be selected as greater than 3 / 1, and is less than 40 / 1, and can be further selected as less than 15 / 1.

3. The non-aqueous electrolyte according to claim 1 or 2, characterized in that The sodium salt having a sulfonate group includes sodium fluorosulfonate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium methanesulfonate, sodium vinylsulfonate, sodium methyl sulfate, sodium methylthiosulfonate, sodium 1,2-ethanedisulfonate, sodium ethyl sulfate, sodium propane sulfonate, sodium ethylthiosulfonate, sodium 2-iodobenzenesulfonate, sodium 4-nitrobenzenesulfonate, sodium styrenesulfonate, sodium 4-isopropylbenzenesulfonate, phenolsulfonic acid One or more of sodium, sodium β-styrene sulfonate, sodium cyclohexane sulfonate, sodium 2-cyclohexylaminoethane sulfonate, 4-amino-N-methylbenzenesulfonamide, sodium polydisulfide dipropane sulfonate, sodium pyridine-3-sulfinic acid, and monosodium piperazine-1,4-diethanesulfonic acid salt, and optionally one or more of sodium fluorosulfonate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium methane sulfonate, and sodium methyl sulfate.

4. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that The concentration of the sodium salt having sulfonate groups in the non-aqueous electrolyte is in the range of 0.0005-1 mol / L, and optionally in the range of 0.01-0.3 mol / L.

5. The non-aqueous electrolyte according to any one of claims 1 to 4, characterized in that The sodium salt having oxalate includes one or more of sodium oxalate, sodium bis(oxalate)borate, sodium difluoro(oxalate)borate, sodium tetrafluoro(oxalate)phosphate, and difluorobis(oxalate)sodium phosphate, and may optionally include one or more of sodium oxalate, sodium bis(oxalate)borate, sodium difluoro(oxalate)borate, sodium tetrafluoro(oxalate)phosphate, and difluorobis(oxalate)sodium phosphate.

6. The non-aqueous electrolyte according to any one of claims 1 to 5, characterized in that The concentration of the sodium salt having oxalate in the non-aqueous electrolyte is in the range of 0.0005-0.1 mol / L, optionally in the range of 0.006-0.08 mol / L, further optionally in the range of 0.01-0.02 mol / L.

7. The non-aqueous electrolyte according to any one of claims 1 to 6, characterized in that: The sodium salt having a phosphate group includes one or more of sodium difluorophosphate, sodium monofluorophosphate, sodium trimetaphosphate, sodium hexametaphosphate, sodium hydroxyethylidene diphosphonate, disodium clodronate, sodium olpadronate, sodium diethylenetriamine penta methylenephosphonate, sodium tripolyphosphate and disodium phenyl phosphate, and may optionally include one or more of sodium difluorophosphate and sodium fluorophosphate.

8. The non-aqueous electrolyte according to any one of claims 1 to 7, characterized in that: The concentration of the sodium salt having phosphate in the non-aqueous electrolyte is in the range of 0.0005-0.12, optionally in the range of 0.01-0.05 mol / L, and more preferably in the range of 0.01-0.03 mol / L.

9. The non-aqueous electrolyte according to any one of claims 1 to 8, characterized in that The sodium salt having a borate group includes one or more of sodium tetrafluoroborate, sodium metaborate, sodium tetraphenylborate, and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, and may optionally include one or more of sodium tetrafluoroborate, sodium metaborate, and sodium tetraphenylborate, and may further optionally be one or more of sodium tetrafluoroborate and sodium metaborate.

10. The non-aqueous electrolyte according to any one of claims 1 to 9, characterized in that: The concentration of the sodium salt having borate in the non-aqueous electrolyte is in the range of 0.0005-0.05 mol / L, and optionally in the range of 0.01-0.04 mol / L.

11. The non-aqueous electrolyte according to any one of claims 1 to 10, characterized in that: Among the first sodium salts, when sodium hexafluorophosphate is used in combination with at least one of sodium hexafluoroarsenate, sodium perchlorate and sodium trifluoroacetate, the concentration of other sodium salts except sodium hexafluorophosphate in the non-aqueous electrolyte is 0.001 mol / L or more, can be optionally 0.01 mol / L or more, further can be optionally 0.03 mol / L or more, and is 1 mol / L or less, can be optionally 0.5 mol / L or less.

12. The non-aqueous electrolyte according to any one of claims 1 to 11, characterized in that The second sodium salt includes a sodium salt having a sulfonate group, and also includes one or more of a sodium salt having an oxalate group, a sodium salt having a phosphate group, and a sodium salt having a borate group.

13. The non-aqueous electrolyte according to any one of claims 1 to 12, characterized in that: The second sodium salt includes a sodium salt having a sulfonate group and a sodium salt having an oxalate group. Optionally, a molar ratio of the sodium salt having a sulfonate group to the sodium salt having an oxalate group is 0.03 / 1 to 70 / 1, and optionally 0.5 / 1 to 20 / 1.

14. The non-aqueous electrolyte according to any one of claims 1 to 13, characterized in that The non-aqueous electrolyte contains cyclic carbonate, and the mass concentration of the cyclic carbonate in the non-aqueous electrolyte is greater than 10%, and can be greater than 15%, and less than 60%.

15. The non-aqueous electrolyte according to any one of claims 1 to 14, characterized in that: The non-aqueous electrolyte contains chain carbonates and chain carboxylates, and the mass percentage of the sum of the chain carbonates and chain carboxylates in the non-aqueous electrolyte is above 40%, optionally above 50%, more optionally above 60%, and below 90%, optionally below 85%, and further optionally below 80%.

16. The non-aqueous electrolyte according to any one of claims 1 to 15, characterized in that: The non-aqueous electrolyte includes at least one cyclic carbonate and at least one chain ester, and the mass percentage of the at least one cyclic carbonate to the at least one chain ester is greater than 0.1:1 and less than 1.5:1, optionally less than 1:1, and more optionally, between 0.2:1 and 1:

1.

17. The non-aqueous electrolyte according to any one of claims 1 to 16, characterized in that: The non-aqueous electrolyte comprises one or more of the following combinations of substances: cyclic carbonate and chain carbonate; cyclic carbonate and chain carboxylic acid ester; cyclic carbonate and ether; chain carbonate and chain carboxylic acid ester; chain carbonate and ether; chain carboxylic acid ester and ether; cyclic carbonate, chain carbonate and chain carboxylic acid ester; cyclic carbonate, chain carbonate and ether; Cyclic carbonates, chain carboxylates and ethers; chain carbonates, chain carboxylates and ethers.

18. The non-aqueous electrolyte according to any one of claims 1 to 17, characterized in that: The non-aqueous solvent in the non-aqueous electrolyte includes one or more of propylene carbonate, ethyl methyl carbonate, ethyl acetate, diethyl carbonate, methyl propionate, ethyl propionate, diethylene glycol dimethyl ether, and fluoroethylene carbonate.

19. The non-aqueous electrolyte according to any one of claims 1 to 18, characterized in that The non-aqueous electrolyte includes one or more of anhydride additives, fluorine-containing organic additives, nitrile additives, silicone additives, aldehyde additives, sulfur-containing additives, lithium salt additives, and potassium salt additives. Optionally, the total mass percentage of these additives in the non-aqueous electrolyte is greater than 0.001%, optionally greater than 0.2%, and less than 5%, optionally less than 4%.

20. A sodium ion battery comprising a positive electrode sheet, a negative electrode sheet and the non-aqueous electrolyte according to any one of claims 1 to 19.

21. An electrical device comprising the non-aqueous electrolyte according to any one of claims 1 to 19 or the sodium ion battery according to claim 20.

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