Sodium-ion battery non-aqueous electrolyte, sodium-ion battery, battery module, battery pack and electric device

Abstract

The invention relates to the technical field of sodium-ion batteries, in particular to a sodium-ion battery non-aqueous electrolyte, a sodium-ion battery, a battery module, a battery pack and a power utilization device.The sodium-ion battery non-aqueous electrolyte comprises sodium salt, an organic solvent and a functional additive, the sodium salt comprises sodium bis (fluorosulfonyl) imide and sodium hexafluorophosphate, and the organic solvent comprises sodium bis (fluorosulfonyl) imide and sodium hexafluorophosphate. The molar ratio of the sodium bis (fluorosulfonyl) imide to the sodium hexafluorophosphate is (8: 2)-(7: 3); the organic solvent is prepared from chain carbonate and cyclic carbonate, and the functional additive is prepared from 2-trifluoromethyl-1, 3-propene sultone and 1-fluoro-2-methyl-ethylene carbonate. According to the invention, the ionic conductivity and thermal stability of the sodium-ion battery electrolyte can be improved through reasonable proportioning and use of the double-ion sodium salt, and meanwhile, corrosion of sodium bis (fluorosulfonyl) imide to an aluminum structural part can also be avoided. The sodium salt and the functional additive cooperate with each other to form an effective interface film on the surface of the electrode, so that the high-temperature storage performance and the high-temperature cycle performance of the sodium ion battery can be remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, in particular to a sodium ion battery non-aqueous electrolyte, a sodium ion battery, a battery module, a battery pack and a power utilization device. BACKGROUND

[0002] As a new type of secondary battery, sodium ion batteries have potential advantages such as abundant resources and low cost, and have broad application prospects in power batteries and energy storage. The working principle of sodium ion batteries is the same as that of lithium ion batteries, and the commonly used electrolyte solvent is also a carbonate solvent. In high-temperature and high-pressure application scenarios, there is also a risk of thermal runaway, and the activity of sodium is stronger than that of lithium, and the reaction is more violent, so there are higher requirements for the thermal stability of the electrolyte of sodium ion batteries. Sodium salt, as an important component of the electrolyte, can determine the performance of the electrolyte and the battery to some extent. At present, the commonly used sodium salt of sodium ion battery is sodium hexafluorophosphate (NaPF6), which is similar to lithium hexafluorophosphate (LiPF6). NaPF6 is sensitive to water and is easy to hydrolyze to generate HF, which will greatly harm the performance of the battery, and is not conducive to the high-temperature performance and cycle performance of the sodium ion battery. Sodium bisfluorosulfonylimide (NaFSI) is not sensitive to water and is not easy to hydrolyze to generate HF, and has higher thermal stability and chemical stability. However, the bisfluorosulfonylimide anion can corrode the aluminum structural parts (aluminum tab and aluminum current collector) in the battery, which limits the further development of NaFSI to some extent. At present, the main methods to inhibit the corrosion of bisfluorosulfonylimide anion to aluminum structural parts are to add corrosion-resistant additives (see CN117438653A) and high-concentration electrolyte (see CN116995302A), but they will all cause the reduction of ionic conductivity, cycle life and increase of cost, which is not conducive to the improvement of the comprehensive performance of the battery.

[0003] Based on the above situation, an electrolyte is needed to solve the problem of corrosion of NaFSI to aluminum structural parts, and also to effectively improve the cycle performance and high-temperature storage performance of the battery. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a sodium ion battery non-aqueous electrolyte, a sodium ion battery, a battery module, a battery pack and a power utilization device. It is found in many experiments that NaPF6 can form a passivation layer on the surface of the aluminum structural part, which can inhibit the occurrence of corrosion. Therefore, by adjusting the proportion of sodium salt in the electrolyte of the sodium ion battery, NaFSI can effectively exert high thermal stability and film-forming performance, and NaPF6 can react with the aluminum structural part to generate a large amount of AlF3 attached to the surface of the structural part, thereby inhibiting the occurrence of corrosion and improving the cycle performance. The sodium salt can also have a synergistic effect with the functional additive to form an interface film with excellent performance on the surface of the electrode, thereby improving the high-temperature performance.

[0005] The technical scheme of the present application is: The first aspect of the present application provides a sodium ion battery non-aqueous electrolyte, the sodium ion battery non-aqueous electrolyte comprises a sodium salt, an organic solvent and a functional additive, the sodium salt comprises sodium bisfluorosulfonylimide and sodium hexafluorophosphate, the molar ratio of sodium bisfluorosulfonylimide and sodium hexafluorophosphate is 8:2~7:3; the organic solvent comprises a chain carbonate and a cyclic carbonate, and the functional additive comprises 2-trifluoromethyl-1,3-propylene sulfite and 1-fluoro-2-methyl-vinyl carbonate.

[0006] The second aspect of the present application provides a sodium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and the sodium ion battery non-aqueous electrolyte of the first aspect of the present application.

[0007] The third aspect of the present application provides a battery module, comprising the sodium ion battery of the second aspect of the present application.

[0008] The fourth aspect of the present application provides a battery pack, comprising the battery module of the third aspect of the present application.

[0009] The fifth aspect of the present application provides an electric device, comprising the sodium ion battery of the second aspect of the present application, the sodium ion battery is used as the power supply of the electric device, and the electric device comprises a mobile device, an electric vehicle, an electric train, a satellite, a ship and an energy storage system.

[0010] By adopting the foregoing technical scheme, the present application has the following beneficial effects: (1) By adjusting the ratio of sodium bisfluorosulfonylimide (NaFSI) and sodium hexafluorophosphate (NaPF6) in the electrolyte of the sodium ion battery, the improvement of the thermal stability of the electrolyte and the inhibition of the corrosion of NaFSI to aluminum structural parts can be realized, and the safety performance of the sodium ion battery can be effectively improved.

[0011] (2) 1-fluoro-2-methyl-ethylene carbonate (FMPC) has a high reduction potential, and can form a NaF-rich SEI film base preferentially to solvents and other additives. 2-trifluoromethyl-1,3-propene sulfite (TFMPS) can decompose to form inorganic sulfates, sulfites and oligomers, in which the inorganic salts can be combined with NaF to form a stable and high ionic conductivity SEI film base. FMPC can also form an elastic organic interface film by polymerizing itself and the oligomers generated by the decomposition of TFMPS, and these organic components will be deposited on the inorganic base. In addition, the methyl group in FMPC has strong reducing properties, which can make it film-forming at the positive electrode and protect the electrolyte from oxidation. Therefore, the interaction of FMPC and TFMPS can form a high-quality interface film on the electrode surface, which has both high ionic conductivity and high toughness, and will not easily break down, which can effectively improve the high-temperature storage performance and high-temperature cycle performance of the battery.

[0012] (3) TFMPS has a strong coordination effect with sodium ions, which can change the solvation structure of sodium ions, promote anions (FSI - ) to participate in the solvation structure, and reduce the solvation energy barrier of sodium ions. In addition, TFMPS and NaFSI both have the same sulfur-containing group, and the combined action of the two promotes the formation of a sulfur-rich SEI film and improves the ionic conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 CV test results of electrolyte showing 1M NaPF6 as a sodium salt; Figure 2 CV test results of electrolyte showing 1M NaFSI as a sodium salt; Figure 3 CV test results of electrolyte showing 0.7M NaFSI+0.3M NaPF6 as a sodium salt; Figure 4 CV test results of electrolyte showing 0.8M NaFSI+0.2M NaPF6 as a sodium salt; Figure 5 CV test results of electrolyte showing 0.9M NaFSI+0.1M NaPF6 as a sodium salt; Figure 6 SEM images of each group of aluminum foils after CV test. DETAILED DESCRIPTION

[0014] Hereinafter, embodiments of a sodium ion battery non-aqueous electrolyte, a sodium ion battery, a battery module, a battery pack, and a power consumption device provided by the present application will be described in detail.

[0015] "RANGES" disclosed herein are defined, for each range by a combination of an upper and a lower limit, the upper and lower limits defining the boundaries in the specified range. Ranges defined by the combination of an upper and a lower limit can be inclusive or exclusive of the stated limits, and are arbitrarily combinable, i.e., any upper limit can be combined with any lower limit to define a range. For example, if a range of 60-120 and 80-110 is listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" indicates a range of any integers between a and b, in which a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, "0-5" is merely a shorthand for listing all of these numerical combinations. Also, when a parameter is stated to be an integer > 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0016] The inventors of the present application have made a large number of exploratory studies, and provide a sodium ion battery non-aqueous electrolyte, a sodium ion battery, a battery module, a battery pack, and an electric device, which can inhibit corrosion of an aluminum structural member (the aluminum structural member is an aluminum current collector and an aluminum tab) of a sodium ion battery, improve the safety performance of the battery, and also take into account high-temperature performance. NaFSI is not sensitive to moisture and has high thermal stability, but can corrode the aluminum structural member. NaPF6 can effectively passivate the aluminum structural member to inhibit corrosion, but has poor thermal stability and is prone to hydrolysis to generate HF. In the present application, a large number of experiments have verified that by adjusting the content of NaFSI and NaPF6, the defects of the two can be mutually compensated for, the advantages of each can be exerted, and by further adding a functional additive, the high-temperature performance of the sodium ion battery is effectively improved. On this basis, the present application is completed.

[0017]

Sodium ion battery non-aqueous electrolyte

[0018] In the non-aqueous electrolyte of the sodium ion battery, the molar ratio of the sodium bisfluorosulfonylimide (NaFSI) and the sodium hexafluorophosphate (NaPF6) is 8:2-7:3. By adjusting the ratio of NaFSI and NaPF6 in the electrolyte of the sodium ion battery, the ionic conductivity and thermal stability of the electrolyte can be effectively improved, and the corrosion of NaFSI to aluminum structural parts can be avoided. Further, by matching with functional additives, the high-temperature storage performance and high-temperature cycle performance of the sodium ion battery can be significantly improved. In some embodiments, the molar ratio of the sodium bisfluorosulfonylimide (NaFSI) and the sodium hexafluorophosphate (NaPF6) in the sodium salt is 7:3-7.5:2.5, 8:2-7.5:2.5, etc. Too large a proportion of NaFSI will result in an insignificant passivation effect of NaPF6, which cannot effectively inhibit corrosion. Too small a proportion of NaFSI is not conducive to the improvement of the thermal stability and high-pressure resistance of the electrolyte, and the high-temperature cycle performance of the battery cannot be effectively improved.

[0019] In the non-aqueous electrolyte of the sodium ion battery provided by the application, the concentration of the sodium salt in the non-aqueous electrolyte is 0.5 mol / L-2 mol / L. In some embodiments, the concentration of the sodium salt in the non-aqueous electrolyte can also be 1 mol / L-1.2 mol / L or 1.2 mol / L-2 mol / L, etc. Preferably, the concentration of the sodium salt in the non-aqueous electrolyte is 1 mol / L-1.2 mol / L. The sodium salt is the main source of sodium ions in the electrolyte, and has a great influence on the energy density, power density, wide electrochemical window, cycle life, safety performance, etc. of the sodium battery. Too much sodium salt will cause the viscosity of the electrolyte to increase, and too little sodium salt will not provide enough sodium ions, both of which will reduce the ionic conductivity.

[0020] In the non-aqueous electrolyte of the sodium ion battery provided by the application, the organic solvent includes cyclic carbonate and chain carbonate. Further, the organic solvent is selected from one or more combinations of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0021] In the non-aqueous electrolyte of the sodium ion battery provided by the application, the mass proportion of the organic solvent in the non-aqueous electrolyte is 68wt%-75wt%. In some embodiments, the mass proportion of the organic solvent in the non-aqueous electrolyte can also be 68wt%-70wt%, or 70wt%-75wt%, etc. The electrolyte solvent is mainly mixed by cyclic carbonate solvent and chain carbonate solvent in a certain proportion. The cyclic carbonate solvent has a high dielectric constant, which is conducive to the dissociation of sodium ions, but too much cyclic carbonate solvent will increase the viscosity of the electrolyte and hinder ion conduction. The chain carbonate solvent has a low viscosity and better electrochemical stability, but too much chain carbonate solvent will cause poor dissociation of sodium ions.

[0022] The volume ratio of the chain carbonate and the cyclic carbonate in the non-aqueous electrolyte of the sodium ion battery provided by the application is 5:5-9:1, which can be 5:5-7:3, 7:3-9:1, 5:5-6:4, 6:4-7:3, 7:3-8:2, 8:2-9:1.

[0023] Optionally, the organic solvent is diethyl carbonate (DEC), propylene carbonate (PC) and ethyl methyl carbonate (EMC), and further optionally, the volume ratio of diethyl carbonate (DEC), propylene carbonate (PC) and ethyl methyl carbonate (EMC) is 5:3:2.

[0024] The mass ratio of the 2-trifluoromethyl-1,3-propylene sulfite (TFMPS) in the non-aqueous electrolyte is 1wt%-2.5wt%. In some embodiments, the mass ratio of the 2-trifluoromethyl-1,3-propylene sulfite (TFMPS) in the non-aqueous electrolyte can also be 1wt%-2.5wt%, 1wt%-2wt%, 1wt%-1.5wt%, 1.5wt%-2.5wt%, 1.5wt%-2wt%, 2wt%-2.5wt% and the like. The sulfur atom at the center of the TFMPS molecule and the trifluoromethoxy group both have strong electronegativity, and the reduction property of the negative electrode is stronger than that of the carbonate solvent, and the reduction potential is higher, which can preferentially form a stable SEI film on the electrode surface by ring-opening polymerization, inhibit the reaction of the carbonate solvent, and the SEI film is rich in sulfur elements, which can effectively improve the ion conductivity of the SEI film, reduce the internal resistance of the battery, and has obvious effects on improving the high-temperature performance, cycle performance and low-temperature performance. Too little TFMPS (less than 1wt%) has little effect on the optimization of the SEI film of the sodium ion battery; too much TFMPS (more than 2.5wt%) will make the SEI film thicker, the viscosity of the electrolyte increases, and the ion conductivity becomes poor.

[0025] In the non-aqueous electrolyte of the sodium ion battery provided by the application, the mass percentage of the 1-fluoro-2-methyl-vinylene carbonate (FMPC) in the non-aqueous electrolyte is 0.5wt%-2wt%. In some embodiments, the mass percentage of the 1-fluoro-2-methyl-vinylene carbonate (FMPC) in the non-aqueous electrolyte can also be 0.5wt%-1wt%, 0.5wt%-1.5wt%, 1wt%-2wt%, 1.5wt%-2wt%, 1wt%-1.5wt%, 1.5wt%-2wt%, etc. FMPC has a higher reduction potential and can form a SEI film base rich in NaF on the negative electrode surface in preference to the solvent, insulate electrons, and protect the electrode. In addition, the methyl group has strong reducing properties, so that FEMC can form a film on the positive electrode in preference, protecting the electrolyte from oxidation by the positive electrode. Too little FMPC (less than 0.5wt%) is not very good for optimizing the SEI film of the sodium ion battery; too much FMPC (more than 2wt%) will increase the internal resistance of the battery and increase the gas production of the battery.

[0026] In summary, by using a reasonable proportion of double-ion sodium salt, the application can improve the ionic conductivity and thermal stability of the electrolyte of the sodium ion battery, and also avoid the corrosion of double-fluorosulfonyl imide sodium to aluminum structural parts. The sodium salt and the functional additive synergize with each other to form an effective interface film on the electrode surface, which can significantly improve the high-temperature storage performance and high-temperature cycle performance of the sodium ion battery.

[0027]

Sodium ion battery

[0028] The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used as an aluminum current collector. 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 positive electrode active material layer includes a positive electrode active material, and can further include a conductive agent and a binder. The positive electrode active material can be selected from one or more of a transition metal layered oxide, a polyanion-based material, or a Prussian blue-based material. Preferably, the positive electrode active material is a transition metal layered oxide. A person skilled in the art can select a conductive agent and a binder suitable for a sodium ion battery in the art. Among others, the conductive agent can include at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, for example. The binder can include at least one 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, for example.

[0029] In some embodiments, the positive electrode can be prepared by dispersing the components described above for preparing the positive electrode, such as the positive electrode material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector; and drying, cold-pressing, or the like to obtain the positive electrode.

[0030] The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used as an aluminum current collector. 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 negative electrode active material layer includes a negative electrode active material, and can further include a plasticizer, a conductive agent, and a binder. The negative electrode active material can be selected from one or more of a carbon-based material, a titanium-based oxide material, and an alloy-based material, and preferably, the negative electrode active material can be selected from a hard carbon material. A person skilled in the art can select a plasticizer, a conductive agent, and a binder suitable for a sodium ion battery in the art. Among others, the conductive agent can be selected from at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, for example. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS), carboxymethyl cellulose sodium (CMC-Na), for example.

[0031] In some embodiments, the negative electrode can be prepared by dispersing the above-mentioned components for preparing the negative electrode, such as the negative electrode material, the conductive agent, the binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode can be obtained.

[0032] The sodium-ion battery provided in the second aspect of the present application can be prepared by using a method known in the art. For example, the positive electrode, the separator and the negative electrode are stacked in order, with the separator between the positive electrode and the negative electrode to play a separating role, and then the stack is obtained to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried, and then a non-aqueous electrolyte is injected into the soft package battery, and after vacuum packaging, standing, formation, and other processes, a sodium-ion battery is obtained.

[0033]

Battery module

[0034]

Battery pack

[0035] The number of battery modules in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0036]

Electric device

[0037] The beneficial effects of the present application are further illustrated in the following examples.

[0038] In order to make the invention objectives, technical solutions and beneficial technical effects of the present invention clearer, the present invention is further described in detail below with reference to the examples. However, it should be understood that the examples of the present invention are only for the purpose of explaining the present invention and are not intended to limit the present invention, and the examples of the present invention are not limited to the examples given in the specification. In the examples, where no specific experimental conditions or operating conditions are specified, the products were prepared under conventional conditions or under the conditions recommended by the material supplier.

[0039] Furthermore, it should be understood that the one or more method steps mentioned in the present invention do not exclude the presence of other method steps before or after the combination step, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified. It should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the presence of other devices / apparatuses before or after the combination device / apparatus, or the insertion of other devices / apparatuses between two explicitly mentioned devices / apparatuses, unless otherwise specified. Furthermore, unless otherwise specified, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be considered within the scope of the present invention.

[0040] In the following examples, unless otherwise specified, various raw materials of the present invention can be purchased commercially or prepared according to conventional methods in the art.

[0041] The positive electrode material of the sodium ion battery used in the embodiment and comparative example of the present invention is sodium nickel iron manganese oxide, the negative electrode is hard carbon, and the electrolyte injection amount of each battery is 4g.

[0042] The preparation process of the sodium ion battery electrolytes of Examples 1 to 8 and Comparative Examples 1 to 16 is as follows: Electrolyte solutions (water and oxygen content <0.01 ppm) were prepared in a glove box. Diethyl carbonate (DEC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 5:3:2 as an organic solvent. Sodium salts and additives in varying proportions, as shown in Table 1, were then added to the solvent and mixed thoroughly to produce the electrolyte solutions of Examples 1-8 and Comparative Examples 1-16. The prepared electrolyte solutions were injected into soft-pack batteries. After standing, formation, and volume separation, sodium-ion batteries were obtained.

[0043] Table 1: Formulas of sodium ion battery electrolytes for Examples 1 to 8 and Comparative Examples 1 to 16

[0044] The following experiments were conducted on the sodium ion batteries of Examples 1 to 8 and Comparative Examples 1 to 16. The test results are shown in Table 2.

[0045] (1) High temperature cycle performance test: the batteries obtained in Examples 1-8 and Comparative Examples 1-16 were subjected to formation and capacity distribution, and then subjected to 1C constant current constant voltage charging to a voltage of 4V and a current of 0.05C at 45°C, and then left for 10 minutes, and then subjected to 1C constant current discharging to 1.5V, and the above was one cycle of charging and discharging. The obtained batteries were subjected to formation and capacity distribution, and then subjected to 300 cycles of charging and discharging at 45°C.

[0046] (2) High temperature storage performance test: the batteries obtained in Examples 1-8 and Comparative Examples 1-16 were subjected to formation and capacity distribution, and then subjected to 1C constant current constant voltage charging to a voltage of 4V and a current of 0.05C at 25°C, and then the 1C capacity Q and the thickness H of the battery were recorded, respectively; the batteries in a full state were stored at 60°C for 30 days, and then the 1C discharge capacity Q1 and the thickness H1 of the battery were recorded at 25°C, and then the batteries were subjected to 1C constant current constant voltage charging to a voltage of 4V and a current of 0.05C, and then subjected to 1C constant current discharging to 1.5V, and then the 1C discharge capacity Q2 was recorded, and the capacity retention rate, the capacity recovery rate and the battery expansion rate of the battery after storage were calculated.

[0047] The calculation formulas are as follows: Capacity retention rate = Q1 / Q x 100%; capacity recovery rate = Q2 / Q x 100%; battery expansion rate = (H1-H) / H x 100%.

[0048] Table 2: Test results of the batteries obtained in Examples 1-8 and Comparative Examples 1-16

[0049] As can be seen from Table 2, the sodium ion batteries of the examples of the present application and the sodium ion batteries of the comparative examples, the sodium ion batteries with a molar mass ratio of NaFSI and NaPF6 in the electrolyte between 8:2 and 7:3 and simultaneously adding 1wt%-2.5wt% TFMPS and 0.5wt%-2wt% FMPC showed more excellent high temperature cycle performance and high temperature storage performance, and among them, the sodium ion battery with the electrolyte formula of 0.7mol / L NaFSI+0.3mol / L NaPF6+2wt% TFMPS+1wt% FMPC had the most excellent comprehensive performance. This is mainly due to: the reasonable mass ratio of NaFSI and NaPF6 ensures the high thermal stability and ionic conductivity of the electrolyte, and also avoids the corrosion of NaFSI to the aluminum tab; both TFMPS and FMPC have excellent positive and negative electrode film forming effect, forming a stable interface film, which not only ensures a high ion pass rate but also has high toughness, and will not easily break down in the long-term cycle process, playing a stable protection role for the battery.

[0050] In order to study the inhibition of NaPF6 on NaFSI corrosion current collector, the present application prepares electrolyte with different sodium salt ratio (test example 1-2, control example 1-3), takes aluminum structural parts as working electrode, metal sodium as reference electrode, and metal platinum as counter electrode, tests the corrosion current of aluminum structural parts of each group by cyclic voltammetry (CV), and then tests the surface of the tested aluminum structural parts by SEM to observe the corrosion condition.

[0051] CV test: voltage range: 2V-5V; Current sweep speed: 0.1mV / s; SEM magnification: 100 times and 500 times; Control example 1 Electrolyte: 1M NaPF6; Control example 2 Electrolyte: 1M NaFSI; Test example 1 Electrolyte: 0.7M NaFSI+0.3M NaPF6; Test example 2 Electrolyte: 0.8M NaFSI+0.2M NaPF6; Control example 3 Electrolyte: 0.9M NaFSI+0.1M NaPF6.

[0052] Figure 1 CV test result of 1M NaPF6 as sodium salt electrolyte; Figure 2 CV test result of 1M NaFSI as sodium salt electrolyte; Figure 3 CV test result of 0.7M NaFSI+0.3M NaPF6 as sodium salt electrolyte; Figure 4 CV test result of 0.8M NaFSI+0.2M NaPF6 as sodium salt electrolyte; Figure 5 CV test result of 0.9M NaFSI+0.1M NaPF6 as sodium salt electrolyte; Figure 6 SEM diagram of aluminum foil after CV test: from left to right, it is the SEM diagram of aluminum foil in control example 1, test example 1, control example 2, test example 2 and control example 3 respectively. Figures 1-5 From the CV test result of 1M NaPF6 as sodium salt electrolyte, the current in the CV curve of the electrolyte with pure NaFSI as sodium salt increases with the increase of cycle number, which presents a typical corrosion characteristic, and the electrolyte with pure NaPF6 as sodium salt has no obvious corrosion on aluminum foil. NaPF6 in the group of 0.7M NaFSI+0.3M NaPF6 and the group of 0.8M NaFSI+0.2M NaPF6 also has obvious passivation effect on aluminum foil, but the corrosion inhibition effect is not good in the group of 0.9M NaFSI+0.1M NaPF6 due to the small amount of NaPF6. From the SEM diagram of aluminum foil after CV test, Figure 6It can also be seen from the SEM images that after the CV test, the pure NaFSI group and the 0.9M NaFSI+0.1M NaPF6 group have more traces of spot corrosion on the aluminum foil, while the 0.7M NaFSI+0.3M NaPF6 group and the 0.8M NaFSI+0.2M NaPF6 group have passivation of NaPF6, and the aluminum foil surface has no obvious spot corrosion.

[0053] In summary, the present application effectively overcomes the shortcomings of the prior art and has a high industrial utilization value.

[0054] The above description is only the preferred embodiment of the present application, and is not any form and substantial limitation of the present application. It should be pointed out that for ordinary skilled in the art, without departing from the method of the present application, a number of improvements and supplements can be made, and these improvements and supplements should be considered as the protection scope of the present application. For those skilled in the art, without departing from the spirit and scope of the present application, some changes, modifications and equivalent changes of the above disclosed technical content can be made, which are equivalent embodiments of the present application; at the same time, any equivalent changes, modifications and evolution of the above-mentioned embodiments according to the essential technology of the present application are still within the scope of the technical solutions of the present application.

Claims

1. A non-aqueous electrolyte for sodium ion batteries, characterized in that: The sodium ion battery non-aqueous electrolyte includes a sodium salt, an organic solvent, and a functional additive. The sodium salt includes sodium bis(fluorosulfonyl)imide and sodium hexafluorophosphate, and the molar ratio of the sodium bis(fluorosulfonyl)imide to sodium hexafluorophosphate is 8:2 to 7:

3. The organic solvent includes a chain carbonate and a cyclic carbonate. The functional additive includes 2-trifluoromethyl-1,3-propene sultone and 1-fluoro-2-methyl-ethylene carbonate.

2. The non-aqueous electrolyte for sodium ion batteries according to claim 1, wherein The concentration of the sodium salt in the non-aqueous electrolyte is 0.5 to 2 mol / L.

3. The non-aqueous electrolyte for sodium ion batteries according to claim 1, wherein The organic solvent is selected from a combination of one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate; And / or, the mass proportion of the organic solvent in the non-aqueous electrolyte is 68wt% to 75wt%; And / or, the volume ratio of the linear carbonate to the cyclic carbonate is 5:5 to 9:

1.

4. The non-aqueous electrolyte for sodium ion batteries according to claim 1, wherein The mass proportion of the 2-trifluoromethyl-1,3-propene sultone in the sodium ion battery non-aqueous electrolyte is 1 wt % to 2.5 wt %.

5. The non-aqueous electrolyte for sodium ion batteries according to claim 1, wherein The mass proportion of the 1-fluoro-2-methyl-ethylene carbonate in the sodium ion battery non-aqueous electrolyte is 0.5 wt % to 2 wt %.

6. A sodium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and a non-aqueous electrolyte for a sodium ion battery, wherein the non-aqueous electrolyte is the non-aqueous electrolyte for a sodium ion battery according to any one of claims 1 to 5.

7. The sodium ion battery according to claim 6, characterized in that The negative electrode comprises a negative electrode active material, and the negative electrode active material is selected from a combination of one or more of carbon-based materials, titanium-based oxide materials and alloy materials; And / or, the positive electrode comprises a positive electrode active material, and the positive electrode active material is selected from a combination of one or more transition metal layered oxides, polyanionic materials, or Prussian blue materials.

8. A battery module, characterized in that: Comprising the sodium ion battery according to claim 6 or 7.

9. A battery pack, characterized in that: Comprising the battery module according to claim 8.

10. An electrical device, characterized in that: The sodium ion battery according to claim 6 or 7 is used as a power source for the device, and the power-consuming device includes a mobile device, an electric vehicle, an electric train, a satellite, a ship, and an energy storage system.

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