Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The invention discloses a sodium ion battery electrolyte and a sodium ion battery. The sodium-ion battery electrolyte comprises an organic solvent, a diluent and an additive, wherein the organic solvent comprises carboxylic ester; the diluent comprises an ether compound; the additive comprises unsaturated phosphorothioate; wherein the viscosity of the electrolyte at the temperature of minus 40 DEG C is 2.5 mPa.s-4. 5mPa.s, and the ionic conductivity of the electrolyte at the temperature of minus 40 DEG C is 1 mS / cm to 5 mS / cm. When the sodium-ion battery electrolyte provided by the invention is applied to the sodium-ion battery, the sodium-ion battery can have excellent low-temperature performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery technology, and in particular to a sodium ion battery electrolyte and a sodium ion battery. BACKGROUND

[0002] Sodium ion batteries have higher cost advantages compared to lithium ion batteries due to the higher abundance of sodium resources. However, the existing sodium battery system has significant performance degradation below-20℃. The generation of sodium dendrites on the negative electrode surface and the sharp drop in electrolyte ion conductivity under low temperature conditions result in rapid decay of sodium ion battery capacity retention and cycle life, limiting the application of sodium ion batteries in low temperature environments. Therefore, how to improve the low temperature performance of sodium ion batteries is one of the problems to be solved at present. SUMMARY

[0003] To solve the above technical problems, the present application provides a sodium ion battery electrolyte and a sodium ion battery.

[0004] In a first aspect, the present application provides a sodium ion battery electrolyte, which comprises an organic solvent, a diluent and an additive. The organic solvent comprises a carboxylic acid ester. The diluent comprises an ether compound. The additive comprises an unsaturated thiophosphate. The viscosity of the electrolyte at-40℃ is 2.5mPa·s-4.5mPa·s. The ion conductivity of the electrolyte at-40℃ is 1mS / cm-5mS / cm.

[0005] According to the present application, the carboxylic acid ester solvent itself has a low viscosity and a wide liquid temperature range, and exhibits a high ion conductivity in a low temperature environment. The addition of the ether compound diluent can effectively reduce the viscosity of the electrolyte in a low temperature environment, and the low viscosity characteristic of the unsaturated thiophosphate additive can further improve the ion conductivity of the electrolyte in a low temperature environment. Thus, by compounding the carboxylic acid ester solvent, the ether compound and the unsaturated thiophosphate, the electrolyte can have a low viscosity in normal temperature and low temperature environments, reduce the solidification of the electrolyte in a low temperature environment, and have a high ion conductivity in a low temperature environment, thereby improving the electrochemical performance of the sodium ion battery in a low temperature environment.

[0006] In some embodiments, the freezing point of the ether compound is less than or equal to-55℃. Thus, the electrolyte can be better diluted in a low temperature environment, reducing the solidification of the electrolyte in a low temperature environment, thereby reducing the viscosity of the electrolyte and improving the ion conductivity of the electrolyte.

[0007] In some embodiments, the ether compound has a viscosity of 0.45 mPa s-0.65 mPa s at -40℃. This is conducive to further reducing the viscosity of the electrolyte in a low-temperature environment, improving the transmission rate of sodium ions in the electrolyte, and improving the ionic conductivity of the electrolyte.

[0008] In some embodiments, the ether compound has a dielectric constant of 7-10. This can make the electrolyte have a higher ionic conductivity, which is conducive to further improving the electrochemical performance of the sodium ion battery in a low-temperature environment.

[0009] In some embodiments, the ether compound includes one or more of cyclopentyl methyl ether, hydrofluoroether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0010] In some embodiments, the volume percentage of the diluent in the electrolyte is 10%-30%. This can make the electrolyte have excellent normal temperature performance and low temperature performance, and the electrolyte has a lower viscosity and a higher ionic conductivity in normal temperature and low temperature environments, which is conducive to further improving the electrochemical performance of the sodium ion battery.

[0011] In some embodiments, the unsaturated thiophosphoric acid ester includes one or more of vinyl thiophosphoric acid ester, acryloyloxy thiophosphoric acid ester, and styryl thiophosphoric acid ester.

[0012] In some embodiments, the volume percentage of the additive in the electrolyte is 0.6%-6%. This can make the electrolyte have a higher ionic conductivity in a low-temperature environment, which is conducive to further improving the electrochemical performance of the sodium ion battery in a low-temperature environment.

[0013] In some embodiments, the organic solvent further includes a carbonate, and the volume ratio of the carboxylic acid ester to the carbonate is 1:1 to 1:2.

[0014] In some embodiments, the carboxylic acid ester includes one or more of methyl formate, methyl acetate, ethyl acetate, butyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, and butyl propionate.

[0015] In some embodiments, the carbonate includes one or more of vinyl carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, and fluorinated vinyl carbonate.

[0016] In some embodiments, the electrolyte further includes a sodium salt, and the molar concentration of the sodium salt in the electrolyte is 1 mol / L-3 mol / L.

[0017] In some embodiments, the sodium salt comprises one or more of sodium bisfluorosulfonimide, sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethylsulfonate, sodium difluorophosphate, sodium tetrafluoroborate, sodium difluoro oxalato borate, sodium di oxalato borate, sodium bistrifluoromethanesulfonimide.

[0018] In a second aspect, the embodiments of the present application provide a sodium ion battery comprising the sodium ion battery electrolyte of any of the embodiments of the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained according to the drawings without creative labor for those skilled in the art.

[0020] Figure 1 The cycle charge-discharge curve of the sodium ion battery provided in Example 1 of the present application.

[0021] Figure 2 The cycle charge-discharge curve of the sodium ion battery provided in Comparative Example 1 of the present application.

[0022] Figure 3 The cycle charge-discharge curve of the sodium ion battery provided in Comparative Example 2 of the present application.

[0023] Figure 4 The cycle charge-discharge curve of the sodium ion battery provided in Comparative Example 3 of the present application.

[0024] Figure 5 The cycle charge-discharge curve of the sodium ion battery provided in Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0025] Hereinafter, the sodium ion battery electrolyte and the sodium ion battery of the present application are specifically disclosed with appropriate reference to the drawings. However, there will be cases where unnecessary detailed descriptions are omitted. For example, there will be cases where detailed descriptions of matters known to those skilled in the art, repeated descriptions of substantially identical structures 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 in order for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0026] The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges are also intended to include any and all sub-ranges of the range, wherein each sub-range includes each integer within and adjacent to the range of from and including the lower limit to and including the upper limit. Furthermore, any lists of materials or agents are intended to include any and all sub-lists of the listed materials or agents, wherein each sub-list includes each member of the sub-list combined in any order with any member of the sub-list of any other sub-list of the stated range. For example, if a range is stated as 1-5, it is intended to include, individually and / or in combination, with any of the other ranges, 1, 2, 3, 4, 5, and 1-5, 1-4, 1-3, 1-2, 2-5, 2-4, 2-3, 3-5, 3-4, 4-5, and 4-5. It is also to be understood that all ranges and sub-ranges are inclusive of the endpoints.

[0027] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0028] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0029] Unless otherwise specified, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0030] Unless otherwise specified, in the present application, the terms "first", "second", etc. are used to distinguish different objects, and are not used to describe a specific order or primary and secondary relationship.

[0031] In the present application, the terms "a plurality of", "a plurality of" refer to two or more than two.

[0032] In the description of the embodiments of the present application, if no special description is made, the first feature is "on" or "under" the second feature, which can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature can be "above", "over" and "on" the second feature, which can be that the first feature is directly above or obliquely above the second feature, or only means that the horizontal height of the first feature is higher than that of the second feature. The first feature can be "below", "under" and "under" the second feature, which can be that the first feature is directly below or obliquely below the second feature, or only means that the horizontal height of the first feature is less than that of the second feature.

[0033] Unless otherwise specified, the terms used in the present application have the commonly known meanings understood by those skilled in the art.

[0034] Unless otherwise specified, the values of the parameters mentioned in the present application can be measured by various test methods commonly used in the art, for example, the test methods given in the embodiments of the present application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0035] The current technical route for improving the low-temperature performance of sodium ion batteries focuses on parallel modification of the material bulk phase and optimization of the electrolyte system. In the electrolyte dimension, existing technologies mainly achieve performance improvement through solvent molecular structure regulation (such as optimization of the molar ratio of linear carboxylate / cyclic carbonate) and functional additive screening (such as nitrate film-forming additives). However, with the emergence of new low-temperature scenarios such as polar exploration (-40°C working conditions) and high-cold energy storage (dynamic temperature range -30°C to 60°C), sodium ion batteries need to maintain ion transport stability at extremely low temperature conditions. This requires electrolyte design to meet the following requirements: 1) matching of low freezing point solvents with high ionic conductivity; 2) avoiding the use of excessively high concentrations of additives to exacerbate interface side reactions; 3) synergy of dynamic stability of SEI film and ion transport efficiency at extremely low temperature conditions. Therefore, how to construct an electrolyte system that adapts to the low-temperature working conditions of sodium ion batteries and break through the technical dilemma of the existing "low-temperature performance-cycle life-safety" has become a problem to be solved in the field.

[0036] In view of this, the embodiments of the present application provide a sodium ion battery electrolyte, which can maintain excellent conductivity of the sodium ion battery electrolyte in a low-temperature environment by optimizing the component design of the electrolyte, and can effectively improve the electrochemical performance of the sodium ion battery in a low-temperature environment.

[0037] Sodium ion battery electrolyte

[0038] In some embodiments, the viscosity of the electrolyte at -40℃ can be 2.5 mPa·s-4.5 mPa·s, for example, 2.5 mPa·s, 2.6 mPa·s, 2.7 mPa·s, 2.8 mPa·s, 2.9 mPa·s, 3.0 mPa·s, 3.1 mPa·s, 3.2 mPa·s, 3.3 mPa·s, 3.4 mPa·s, 3.5 mPa·s, 3.6 mPa·s, 3.7 mPa·s, 3.8 mPa·s, 3.9 mPa·s, 4.0 mPa·s, 4.1 mPa·s, 4.2 mPa·s, 4.3 mPa·s, 4.4 mPa·s, 4.5 mPa·s, or a range formed by any of the above values.

[0039] The carboxylic acid ester solvent itself has a relatively low viscosity and a relatively wide liquid temperature range, and exhibits a relatively high ionic conductivity in a low-temperature environment. The addition of the ether compound diluent can effectively reduce the viscosity of the electrolyte in a low-temperature environment, and the low-viscosity characteristic of the unsaturated thiophosphate additive can further improve the ionic conductivity of the electrolyte in a low-temperature environment. Thus, by compounding the carboxylic acid ester solvent, the ether compound, and the unsaturated thiophosphate, the electrolyte can have a relatively low viscosity in a normal-temperature and low-temperature environment, reduce the solidification of the electrolyte in a low-temperature environment, and have a relatively high ionic conductivity in a low-temperature environment, thereby improving the electrochemical performance of the sodium-ion battery in a low-temperature environment.

[0040] The viscosity of the electrolyte at -40℃ can be 2.5 mPa·s-4.5 mPa·s, for example, 2.5 mPa·s, 2.6 mPa·s, 2.7 mPa·s, 2.8 mPa·s, 2.9 mPa·s, 3.0 mPa·s, 3.1 mPa·s, 3.2 mPa·s, 3.3 mPa·s, 3.4 mPa·s, 3.5 mPa·s, 3.6 mPa·s, 3.7 mPa·s, 3.8 mPa·s, 3.9 mPa·s, 4.0 mPa·s, 4.1 mPa·s, 4.2 mPa·s, 4.3 mPa·s, 4.4 mPa·s, 4.5 mPa·s, or a range formed by any of the above values.

[0041] The ionic conductivity of the electrolyte at -40℃ can be 1 mS / cm-5 mS / cm, for example, 1.0 mS / cm, 1.5 mS / cm, 2.0 mS / cm, 2.5 mS / cm, 3.0 mS / cm, 3.5 mS / cm, 4.0 mS / cm, 4.5 mS / cm, 5.0 mS / cm, or a range formed by any of the above values.

[0042] In some embodiments, the freezing point of the ether compound can be less than or equal to -55℃.

[0043] By selecting an ether compound with a melting point meeting the above range as the diluent of the electrolyte, the electrolyte can be better diluted in a low-temperature environment, the solidification of the electrolyte in a low-temperature environment can be reduced, the viscosity of the electrolyte can be further reduced, and the ionic conductivity of the electrolyte can be improved.

[0044] In some embodiments, the viscosity of the ether compound at -40℃ can be 0.45 mPa s-0.65 mPa s, for example, can be 0.45 mPa s, 0.46 mPa s, 0.47 mPa s, 0.48 mPa s, 0.49 mPa s, 0.50 mPa s, 0.51 mPa s, 0.52 mPa s, 0.53 mPa s, 0.54 mPa s, 0.55 mPa s, 0.56 mPa s, 0.57 mPa s, 0.58 mPa s, 0.59 mPa s, 0.60 mPa s, 0.61 mPa s, 0.62 mPa s, 0.63 mPa s, 0.64 mPa s, 0.65 mPa s, or a range consisting of any of the above values.

[0045] By making the viscosity of the ether compound at -40℃ within the above range, it is beneficial to further reduce the viscosity of the electrolyte in a low temperature environment, improve the transmission rate of sodium ions in the electrolyte, and improve the ionic conductivity of the electrolyte.

[0046] In some embodiments, the dielectric constant of the ether compound can be 7-10.

[0047] By making the dielectric constant of the ether compound within the above range, the electrolyte can have a higher ionic conductivity, which is beneficial to further improve the electrochemical performance of the sodium ion battery in a low temperature environment.

[0048] In some embodiments, the ether compound can include one or more of cyclopentyl methyl ether (CPME), hydrofluoroether (HFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE-458).

[0049] According to the embodiments of the present application, by selecting the above ether compound as the diluent of the electrolyte, compared with the traditional ether solvent (such as ethylene glycol dimethyl ether DME, diethylene glycol dimethyl ether DEDM, etc.), the above ether compound has excellent ionic conductivity and low viscosity in a low temperature environment, which is beneficial to improve the low temperature performance of the electrolyte. At the same time, the above ether compound does not participate in the formation of the sodium ion solvation structure in the electrolyte, so when it is applied to the sodium ion battery electrolyte, it can improve the low temperature performance of the electrolyte while reducing the influence on the desolvation process of sodium ions, reducing dendrite formation, so that the sodium ion battery has good low temperature performance while having high capacity.

[0050] In some embodiments, the volume ratio of the diluent based on the total volume of the electrolyte can be 10%-30%, for example, can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or a range consisting of any of the above values.

[0051] According to the embodiment of the present application, by making the volume ratio of the diluent in the electrolyte in the above range, the electrolyte can have excellent room temperature performance and low temperature performance, and has low viscosity and high ionic conductivity in room temperature and low temperature environment, which is beneficial to further improve the electrochemical performance of the sodium ion battery. The diluent generally has low dielectric constant, and a high proportion will weaken the overall polarity of the electrolyte, leading to insufficient dissociation of sodium salt, and reducing the free Na + Concentration. Thus leading to a decrease in ionic conductivity. When the proportion of diluent is low, the flowability of sodium salt or high viscosity main solvent is poor at low temperature, and at the same time, the solubility of sodium salt decreases, which is easy to precipitate at low temperature.

[0052] In some embodiments, the unsaturated thiophosphates can include one or more of vinyl thiophosphates (VTP), acryloxy thiophosphates (ATP), styryl thiophosphates (SDTP).

[0053] According to the embodiment of the present application, by selecting the above unsaturated thiophosphates as additives of the electrolyte, the electrolyte can have low viscosity in low temperature environment, which is beneficial to further improve the sodium ion transmission rate of the electrolyte in low temperature environment, improve the ionic conductivity of the electrolyte, and further improve the electrochemical performance of the sodium ion battery in low temperature environment.

[0054] In some embodiments, the volume ratio of the additive can be 0.5%-5%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or a range consisting of any of the above values, based on the total volume of the electrolyte. Optionally, it can be 0.8%-4.0%.

[0055] According to the embodiment of the present application, by making the content of the additive in the electrolyte in the above range, the electrolyte can have high ionic conductivity in low temperature environment, which is beneficial to further improve the electrochemical performance of the sodium ion battery in low temperature environment. Excessive additives can participate in unintended redox reactions, in addition, excessive additives can also occupy the solvation shell, reducing the free Na + Concentration, reducing the ionic conductivity of the electrolyte.

[0056] In some embodiments, the organic solvent can also include carbonates; the molar ratio of carboxylic acid ester to carbonate can be 1:1 to 1:2.

[0057] By using carboxylic acid ester and carbonate as the solvent of electrolyte, the sodium ion battery electrolyte can have excellent low-temperature performance, and the film-forming performance of the electrolyte can be improved, which is beneficial to the formation of a uniform and stable solid electrolyte film (SEI) on the negative electrode of the sodium ion battery, and is beneficial to improving the cycle performance of the sodium ion battery.

[0058] As an example, the carboxylic acid ester can include one or more of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), butyl acetate (PA), butyl acetate (BA), isopropyl acetate (IA), methyl propionate (MP), ethyl propionate (EP), and butyl propionate (BP).

[0059] The carbonate can include one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), propylene carbonate (PC), and fluoroethylene carbonate (FEC).

[0060] In some embodiments, the electrolyte further includes a sodium salt. As an example, the sodium salt can include one or more of sodium bisfluorosulfonylimide, sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethylsulfonate, sodium difluorophosphate, sodium tetrafluoroborate, sodium difluoro oxalate borate, sodium dioxalate borate, and sodium bis-trifluoromethanesulfonimide, and can be sodium bisfluorosulfonylimide.

[0061] In some embodiments, the molar concentration of the sodium salt in the electrolyte can be 1 mol / L-3 mol / L, for example, can be 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3.0 mol / L, or a range formed by any of the above values, and can be 1.5 mol / L-2.8 mol / L, and can be 1.8 mol / L-2.5 mol / L.

[0062] According to the embodiments of the present application, by adding the above diluent and additive to the electrolyte, the diluent in the high-concentration sodium salt electrolyte is not simply diluted, and can maintain the high-salt-concentration characteristics by selective solvation and physical property optimization, for example, the affinity of ether diluent to sodium salt is weak, and will not destroy the Na +The sodium ion battery electrolyte has a coordination structure with anions and retains the solvation advantage of a high concentration of electrolyte. Thus, the sodium ion battery electrolyte has a high sodium salt concentration, which is conducive to further improving the electrochemical performance of the sodium ion battery electrolyte in a low-temperature environment.

[0063] Sodium ion battery

[0064] Embodiments of the second aspect of the present application provide a sodium ion battery, which can include the sodium ion battery electrolyte provided by any of the embodiments of the first aspect of the present application.

[0065] In some embodiments, the sodium ion battery further includes a positive electrode sheet, a negative electrode sheet, and a separator membrane, the separator membrane being located between the positive electrode sheet and the negative electrode sheet.

[0066] [Positive electrode sheet]

[0067] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0068] As an example, the positive electrode current collector has two opposite surfaces in the thickness direction of itself, and the positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

[0069] The positive electrode active material can be any known in the art, and the embodiments of the present application do not limit the same.

[0070] As an example, the positive electrode active material can include one or more of sodium nickel iron manganese acid, sodium nickel cobalt manganese acid, sodium vanadium phosphate, and sodium iron sulfate.

[0071] In some embodiments, the positive electrode film layer can further include a binder and a conductive agent, which can be any known in the art, and the embodiments of the present application do not limit the same.

[0072] As an example, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0073] As an example, the conductive agent can include one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0074] In some embodiments, the positive current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be made by forming a metal material, such as aluminum, aluminum alloy, copper, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc. on a polymer material base material, which can include a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc. base material.

[0075] [Anode electrode sheet]

[0076] In some embodiments, the anode electrode sheet can include an anode current collector and an anode film layer located on at least one side of the anode current collector, the anode film layer including an anode active material.

[0077] The anode active material can employ a material known in the art that can be suitable for a sodium-ion battery anode, which is not limited in the embodiments of the present application. As an example, the anode active material can include one or more of graphite, hard carbon, soft carbon, silicon, silicon-carbon composite material, etc.

[0078] In some embodiments, the anode film layer can further include a binder. As an example, the binder can include one or more of styrene butadiene rubber, polyacrylic acid, polymethacrylic acid, sodium polyacrylate, polyvinylamide, polyvinyl alcohol, etc.

[0079] In some embodiments, the anode film layer can further include a conductive agent. As an example, the conductive agent can include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon nanotube, graphene, carbon nanofiber, etc.

[0080] In some embodiments, the anode electrode sheet can be a metal anode.

[0081] In some embodiments, the anode current collector can employ a metal foil or a composite current collector. As an example, the metal foil can employ a copper foil, a copper alloy foil, an aluminum foil, an aluminum alloy foil. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one side of the polymer material base layer. As an example, the metal material can include, but is not limited to, one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0082] Separator film

[0083] The type of the separator film is not particularly limited, and a porous structure film having good chemical stability and mechanical stability known in the art can be selected.

[0084] As an example, the material of the separator film can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. An inorganic particle coating layer, an organic particle coating layer, or an organic / inorganic composite coating layer can be further applied to the surface of the separator film.

[0085] Examples

[0086] The disclosure is described more specifically by the following examples, which are merely illustrative and not restrictive, since various modifications and changes in the examples clearly will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further purification, and the instruments used in the examples are commercially available.

[0087] Example 1

[0088] Positive electrode sheet

[0089] The positive active material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, a conductive agent, conductive carbon black, and a binder, polyvinylidene fluoride (PVDF) were mixed in a solvent, N-methylpyrrolidone (NMP), in a mass ratio of 94:3:3, and stirred uniformly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of a positive electrode current collector, aluminum foil, and was subjected to drying, cold pressing, and slitting to obtain a positive electrode tab.

[0090] Negative electrode sheet

[0091] The negative active material, hard carbon, a conductive agent, conductive carbon black, a binder, sodium carboxymethyl cellulose, and butadiene styrene rubber were mixed and dispersed in deionized water in a mass ratio of 94.5:2:2.5:1 to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on the surface of a negative electrode current collector, aluminum foil, and was subjected to drying, cold pressing, and slitting to obtain a negative electrode tab.

[0092] Separator film

[0093] A polyethylene (PE) film having a thickness of 7 μm was selected, and both surfaces of the film were coated with an aluminum oxide ceramic coating layer having a thickness of 1.5 μm.

[0094] Preparation of electrolyte

[0095] Ethylene carbonate (EC) and methyl formate (MF) are mixed in a volume ratio of 1:1 to obtain an organic solvent, sodium bis(fluorosulfonyl)imide (NaFSI) is added to the organic solvent and mixed evenly, and then a diluent cyclopentyl methyl ether (CPME) is added and mixed evenly, and then an additive vinyl thiophosphate (VTP) is added and mixed evenly to obtain an electrolyte; the volume ratio of the organic solvent, diluent and additive in the electrolyte is controlled to be 77:20:3, and the lithium salt concentration is 1.5 mol / L.

[0096] Sodium-ion battery

[0097] The positive electrode sheet, negative electrode sheet and separator are stacked in order so that the separator is located on the positive electrode sheet and the negative electrode sheet, and then the electrolyte is injected into the shell to obtain a sodium ion battery.

[0098] Example 2-Example 16

[0099] The preparation method of the sodium ion battery is similar to that of Example 1, except that the composition parameters of the electrolyte are different. The specific parameter adjustments are detailed in Table 1.

[0100] Comparative Example 1-Comparative Example 4

[0101] The preparation method of the sodium ion battery is similar to that of Example 1, except that the composition parameters of the electrolyte are different. The specific parameter adjustments are detailed in Table 1.

[0102] Table 1

[0103]

[0104] In Table 1, “ / ” indicates that the parameter does not exist.

[0105] Test section

[0106] 1. The first coulombic efficiency of sodium-ion batteries

[0107] At -40°C, the sodium ion battery was charged to 3.95V at a constant current of 0.1C, and the charging capacity was recorded as D0; after standing for 30 minutes, it was discharged to 2.0V at a constant current of 0.1C, and the discharge capacity was recorded as C0. The first coulombic efficiency of the sodium ion battery = C0 / D0×100%.

[0108] 2. Low temperature cycle performance

[0109] At -40 ° C, the sodium ion battery was charged to 3.95V at a constant current of 0.3C; it was left to stand for 30 minutes, and then discharged to 2.0V at a constant current of 0.3C, and the discharge capacity was recorded as C0; the sodium ion battery was charged and discharged in the same manner as above, and the discharge capacity of the nth cycle was recorded as C0. n , cycle capacity retention rate = C nCo x 100%.

[0110] The test results are shown in Table 2.

[0111] Table 2

[0112] Item Initial coulombic efficiency / % -40 °C cycle capacity retention Example 1 82 200 cycles; 72% Example 2 78 200 cycles; 68% Example 3 78 200 cycles; 68% Example 4 77.5 200 cycles; 69% Example 5 64 200 cycles; 62% Example 6 66 200 cycles; 61% Example 7 67.2 200 cycles; 65% Example 8 67.6 200 cycles; 67% Example 9 75 200 cycles; 67% Example 10 66.5 200 cycles; 68% Example 11 64.2 200 cycles; 62.3% Example 12 64.8 200 cycles; 62.7% Example 13 79 200 cycles; 68.3% Example 14 79.5 200 cycles; 69.4% Example 15 78.7 200 cycles; 68.7% Example 16 61 200 cycles; 63.7% Comparative Example 1 53.1 80 cycles; 47% Comparative Example 2 55.7 80 cycles; 55.4% Comparative Example 3 57.2 80 cycles; 56.8% Comparative Example 4 58.6 80 cycles; 57.5%

[0113] In combination with the data in Table 2, the sodium ion battery electrolyte provided by the embodiments of the present application can make the sodium ion battery have high initial efficiency and high cycle capacity retention rate in a low temperature environment.

[0114] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art are applied to the embodiments, and other ways constructed by combining part of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A sodium ion battery electrolyte, characterized in that Including organic solvents, diluents and additives; The organic solvent includes a carboxylic acid ester; The diluent includes an ether compound; The additive includes an unsaturated thiophosphate; The viscosity of the electrolyte at -40°C is 2.5 mPa·s-4.5 mPa·s; and the ionic conductivity of the electrolyte at -40°C is 1 mS / cm-5 mS / cm.

2. The sodium ion battery electrolyte according to claim 1, characterized in that The ether compound satisfies at least one of the following conditions: (1) The freezing point of the ether compound is less than or equal to -55°C; (2) the viscosity of the ether compound at -40°C is 0.45 mPa·s to 0.65 mPa·s; (3) The dielectric constant of the ether compound is 7-10.

3. The sodium ion battery electrolyte according to claim 2, characterized in that The ether compound includes one or more of cyclopentyl methyl ether, hydrofluoroether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

4. The sodium ion battery electrolyte according to any one of claims 1 to 3, characterized in that Based on the total volume of the electrolyte, the volume proportion of the diluent is 10%-30%.

5. The sodium ion battery electrolyte according to claim 1, characterized in that The unsaturated thiophosphate includes one or more of vinyl thiophosphate, acryloxy thiophosphate, and styryl thiophosphate; Optionally, based on the total volume of the electrolyte, the volume percentage of the additive is 0.6%-6%.

6. The sodium ion battery electrolyte according to claim 1, characterized in that The organic solvent further comprises carbonate, and the volume ratio of the carboxylate to the carbonate is 1:1 to 1:

2.

7. The sodium ion battery electrolyte according to claim 6, characterized in that The carboxylic acid ester includes one or more of methyl formate, methyl acetate, ethyl acetate, butyl acetate, butyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, and butyl propionate; and / or The carbonate includes one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, and fluoroethylene carbonate.

8. The sodium ion battery electrolyte according to claim 1, characterized in that The electrolyte further includes sodium salt, and the molar concentration of the sodium salt in the electrolyte is 1 mol / L-3 mol / L.

9. The sodium ion battery electrolyte according to claim 8, characterized in that The sodium salt includes one or more of sodium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium tetrafluoroborate, sodium difluorooxalatoborate, sodium dioxalatoborate, and sodium bis(trifluoromethanesulfonyl)imide.

10. A sodium ion battery, characterized in that: The invention comprises the sodium ion battery electrolyte according to any one of claims 1 to 9.

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