Sodium-ion battery nonaqueous electrolyte, sodium-ion battery, battery module, battery pack, electric device

Abstract

The 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. 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, and the molar ratio of the sodium bisfluorosulfonylimide and the sodium hexafluorophosphate is 8:2-7:3. The organic solvent comprises a chain carbonate and a cyclic carbonate. The functional additive comprises 2-trifluoromethyl-1,3-propylene sulfite and 1-fluoro-2-methyl-vinyl carbonate. The sodium ion battery electrolyte ion conductivity and thermal stability can be improved by reasonably matching and using the dual-ion sodium salt, and the corrosion of sodium bisfluorosulfonylimide to aluminum structural parts can be avoided. The sodium salt and the functional additive are mutually synergistic, an effective interface film is formed on the electrode surface, and the high-temperature storage performance and the high-temperature cycle performance of the sodium ion battery can be remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to sodium-ion battery non-aqueous electrolyte, sodium-ion battery, battery module, battery pack, and electrical device. Background Technology

[0002] Sodium-ion batteries, as a novel type of rechargeable battery, possess potential advantages such as abundant resources and low cost, and have broad application prospects in power batteries and energy storage. Sodium-ion batteries operate on the same principle as lithium-ion batteries, and their commonly used electrolyte solvents are also carbonate-based. However, they also face the risk of thermal runaway under high-temperature and high-pressure applications. Furthermore, sodium is more reactive than lithium, resulting in more vigorous reactions, thus placing higher demands on the thermal stability of sodium-ion battery electrolytes. Sodium salts, as an important component of the electrolyte, can significantly determine the performance of both the electrolyte and the battery. Currently, the commonly used sodium salt for sodium-ion batteries is sodium hexafluorophosphate (NaPF6). Similar to lithium hexafluorophosphate (LiPF6), NaPF6 is sensitive to water and easily hydrolyzes to generate HF, which can significantly harm battery performance and negatively impact the high-temperature and cycle performance of sodium-ion batteries. In contrast, sodium bis(fluorosulfonyl)imide (NaFSI) is not sensitive to water, does not readily hydrolyze to generate HF, and exhibits higher thermal and chemical stability. However, bis(fluorosulfonyl)imide anions can corrode aluminum structural components in batteries (aluminum tabs and aluminum current collectors), which limits the further development of NaFSI to some extent. Currently, the main methods to inhibit the corrosion of aluminum structural components by bis(fluorosulfonyl)imide anions are adding corrosion inhibitors (see CN117438653A) and high-concentration electrolytes (see CN116995302A), but both of these methods lead to a decrease in ionic conductivity and cycle life, as well as an increase in cost, which is not conducive to improving the overall performance of the battery.

[0003] Based on the above, an electrolyte is needed to solve the problem of NaFSI corrosion of aluminum structural components, while also effectively improving the battery's cycle performance and high-temperature storage performance. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a non-aqueous electrolyte for sodium-ion batteries, a sodium-ion battery, a battery module, a battery pack, and an electrical device. Through multiple experiments, it was found that NaPF6 forms a passivation layer on the surface of aluminum structural components, which can inhibit corrosion. Therefore, by adjusting the proportion of sodium salts in the sodium-ion battery electrolyte, NaFSI can effectively exert its high thermal stability and film-forming properties. Simultaneously, NaPF6 can react with aluminum structural components to generate a large amount of AlF3, which adheres to the surface of the structural components, thereby inhibiting corrosion and improving cycle performance. Sodium salts can also synergistically interact with functional additives to form a high-performance interfacial film on the electrode surface, improving high-temperature performance.

[0005] The technical solution of this invention is:

[0006] A first aspect of the present invention provides a non-aqueous electrolyte for sodium-ion batteries, the non-aqueous electrolyte comprising a sodium salt, an organic solvent, and a functional additive, wherein the sodium salt comprises sodium difluorosulfonamide and sodium hexafluorophosphate, the molar ratio of sodium difluorosulfonamide and sodium hexafluorophosphate being 8:2 to 7:3; the organic solvent comprises chain carbonates and cyclic carbonates; and the functional additive comprises 2-trifluoromethyl-1,3-propenesulfonate lactone and 1-fluoro-2-methyl-ethylene carbonate.

[0007] A second aspect of the present invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte for sodium-ion batteries according to the first aspect of the present invention.

[0008] A third aspect of the present invention provides a battery module comprising the sodium-ion battery described in the second aspect of the present invention.

[0009] A fourth aspect of the present invention provides a battery pack including the battery module described in the third aspect of the present invention.

[0010] A fifth aspect of the present invention provides an electrical device comprising the sodium-ion battery described in the second aspect of the present invention, wherein the sodium-ion battery serves as a power source for the electrical device, and the electrical device includes mobile devices, electric vehicles, electric trains, satellites, ships, and energy storage systems.

[0011] By adopting the aforementioned technical solution, the beneficial effects of the present invention are:

[0012] (1) By adjusting the ratio of sodium difluorosulfonamide (NaFSI) and sodium hexafluorophosphate (NaPF6) in the electrolyte of sodium-ion batteries, the thermal stability of the electrolyte can be improved and the corrosion of aluminum structural parts by NaFSI can be inhibited, thereby effectively improving the safety performance of sodium-ion batteries.

[0013] (2) 1-Fluoro-2-methylethylene carbonate (FMPC) has a high reduction potential and can preferentially form a NaF-rich SEI film substrate compared to solvents and other additives. 2-Trifluoromethyl-1,3-propenesulfonate lactone (TFMPS) can decompose to form inorganic sulfates, sulfites, and oligomers. Among them, the inorganic salts can combine with NaF to form a stable SEI film substrate with high ionic conductivity. FMPC can also form an elastic organic interface film through its own polymerization and the oligomers generated by the decomposition of TFMPS. These organic components will be deposited on the inorganic substrate, and the methyl groups in FMPC have strong reducing properties, which can enable it to form a film on the positive electrode and protect the electrolyte from oxidation. Therefore, the interaction between FMPC and TFMPS will 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, thus effectively improving the high-temperature storage performance and high-temperature cycling performance of the battery.

[0014] (3) TFMPS has a strong coordination effect with sodium ions, which can change the solvation structure of sodium ions and promote the anion (FSI) - It participates in the solvation structure, lowering the solvation energy barrier of sodium ions. In addition, TFMPS and NaFSI both have the same sulfur-containing groups, and the two work together to promote the formation of sulfur-rich SEI films and improve ionic conductivity. Attached Figure Description

[0015] Figure 1 The results of the CV test for the electrolyte containing 1M NaPF6 sodium salt are shown.

[0016] Figure 2 The results of the CV test are shown for an electrolyte containing 1M NaFSI as the sodium salt.

[0017] Figure 3 The results of the CV test are shown for an electrolyte containing 0.7M NaFSI and 0.3M NaPF6 as sodium salts.

[0018] Figure 4 The results of the CV test are shown for an electrolyte containing 0.8M NaFSI and 0.2M NaPF6 as sodium salts.

[0019] Figure 5 The results of the CV test are shown for an electrolyte containing 0.9M NaFSI and 0.1M NaPF6 as sodium salts.

[0020] Figure 6 The images shown are SEM images of each group of aluminum foils after CV testing. Detailed Implementation

[0021] The following describes in detail the embodiments of the sodium-ion battery non-aqueous electrolyte, sodium-ion battery, battery module, battery pack, and electrical device provided by the present invention.

[0022] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] Through extensive research and exploration, the inventors of this invention provide a non-aqueous electrolyte for sodium-ion batteries, a sodium-ion battery, a battery module, a battery pack, and an electrical device. This invention can inhibit the corrosion of aluminum structural components (aluminum current collectors and aluminum tabs) in sodium-ion batteries, improving battery safety while maintaining high-temperature performance. NaFSI is insensitive to moisture and has high thermal stability, but it corrodes aluminum structural components. NaPF6 can effectively passivate aluminum structural components and inhibit corrosion, but it has poor thermal stability and is prone to hydrolysis to generate HF. In this application, extensive experiments have verified that by controlling the content of NaFSI and NaPF6, their respective shortcomings can be compensated for without affecting their respective advantages. Combined with functional additives, this effectively improves the high-temperature performance of sodium-ion batteries. Based on this, this application has been completed.

[0024] Sodium-ion batteries use non-aqueous electrolytes.

[0025] This invention provides a non-aqueous electrolyte for sodium-ion batteries, comprising sodium salts, organic solvents, and functional additives. The sodium salts include sodium difluorosulfonamide (NaFSI) and sodium hexafluorophosphate (NaPF6). The organic solvents include chain carbonates and cyclic carbonates. The functional additives include 2-trifluoromethyl-1,3-propenesulfonyl lactone (TFMPS) and 1-fluoro-2-methyl-ethylene carbonate (FMPC).

[0026] In the non-aqueous electrolyte for sodium-ion batteries provided by this invention, the molar ratio of sodium bis(fluorosulfonyl)imide (NaFSI) to sodium hexafluorophosphate (NaPF6) is 8:2 to 7:3. By adjusting the ratio of NaFSI to NaPF6 in the sodium-ion battery electrolyte, the ionic conductivity and thermal stability of the electrolyte can be effectively improved, while also preventing NaFSI from corroding aluminum structural components. Further, with the addition of functional additives, significant improvements in the high-temperature storage performance and high-temperature cycling performance of the sodium-ion battery can be achieved. In some embodiments, the molar ratio of sodium bis(fluorosulfonyl)imide (NaFSI) to sodium hexafluorophosphate (NaPF6) in the sodium salt is 7:3 to 7.5:2.5, 8:2 to 7.5:2.5, etc. A high NaFSI proportion leads to an insignificant passivation effect of NaPF6, failing to effectively inhibit corrosion. A low NaFSI proportion is detrimental to improving the thermal stability and high-voltage resistance of the electrolyte, and the high-temperature cycling performance of the battery cannot be effectively improved.

[0027] In the non-aqueous electrolyte for sodium-ion batteries provided by this invention, the concentration of the sodium salt in the non-aqueous electrolyte is 0.5 mol / L to 2 mol / L. In some embodiments, the concentration of the sodium salt in the non-aqueous electrolyte can also be 1 mol / L to 1.2 mol / L or 1.2 mol / L to 2 mol / L, etc. Preferably, the concentration of the sodium salt in the non-aqueous electrolyte is 1 mol / L to 1.2 mol / L. Sodium salt is the main source of sodium ions in the electrolyte and has a significant impact on the energy density, power density, wide electrochemical window, cycle life, and safety performance of sodium batteries. Too much sodium salt will increase the viscosity of the electrolyte, while too little sodium salt will fail to provide an adequate amount of sodium ions, both of which will lead to a decrease in ionic conductivity.

[0028] In the non-aqueous electrolyte for sodium-ion batteries provided by this invention, the organic solvent includes cyclic carbonates and chain carbonates. Further, the organic solvent is selected from one or more combinations of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0029] In the non-aqueous electrolyte for sodium-ion batteries provided by this invention, the organic solvent accounts for 68 wt% to 75 wt% of the electrolyte by mass. In some embodiments, the organic solvent may also account for 68 wt% to 70 wt%, or 70% to 75 wt%, etc. The electrolyte solvent is mainly composed of a mixture of cyclic carbonate solvents and chain carbonate solvents in a certain proportion. Cyclic carbonate solvents have a higher dielectric constant, which is beneficial to the dissociation of sodium ions, but a large amount will increase the viscosity of the electrolyte and hinder ion conduction. Chain carbonate solvents have a lower viscosity and better electrochemical stability, but a large amount will lead to poorer dissociation of sodium ions.

[0030] In the non-aqueous electrolyte for sodium-ion batteries provided by this invention, the volume ratio of the chain carbonate to the cyclic carbonate is 5:5 to 9:1, and can be selected as 5:5 to 7:3, 7:3 to 9:1, 5:5 to 6:4, 6:4 to 7:3, 7:3 to 8:2, or 8:2 to 9:1.

[0031] Optionally, the organic solvent is diethyl carbonate (DEC), propylene carbonate (PC), and methyl ethyl carbonate (EMC). More preferably, the volume ratio of diethyl carbonate (DEC), propylene carbonate (PC), and methyl ethyl carbonate (EMC) is 5:3:2.

[0032] In the non-aqueous electrolyte for sodium-ion batteries provided by this invention, the mass percentage of 2-trifluoromethyl-1,3-propenesulfonate lactone (TFMPS) in the non-aqueous electrolyte is 1 wt% to 2.5 wt%. In some embodiments, the mass percentage of 2-trifluoromethyl-1,3-propenesulfonate lactone (TFMPS) in the non-aqueous electrolyte may also be 1 wt% to 2.5 wt%, 1 wt% to 2 wt%, 1 wt% to 1.5 wt%, 1.5 wt% to 2.5 wt%, 1.5 wt% to 2 wt%, 2 wt% to 2.5 wt%, etc. Both the sulfur atom and trifluoromethoxy group at the center of the TFMPS molecule have strong electronegativity, resulting in stronger reducing power and a higher reduction potential at the negative electrode compared to carbonate solvents. This allows them to preferentially undergo ring-opening polymerization on the electrode surface to form a stable SEI film, inhibiting carbonate solvent reactions. Furthermore, the sulfur-rich SEI film effectively improves its ionic conductivity, significantly reducing the cell's internal resistance and enhancing high-temperature, cycle, and low-temperature performance. Insufficient TFMPS (less than 1 wt%) has little effect on optimizing the SEI film in sodium-ion batteries; excessive TFMPS (greater than 2.5 wt%) leads to a thicker SEI film, increased electrolyte viscosity, and consequently, decreased ionic conductivity.

[0033] In the non-aqueous electrolyte for sodium-ion batteries provided by this invention, the mass percentage of 1-fluoro-2-methyl-ethylene carbonate (FMPC) in the non-aqueous electrolyte is 0.5 wt% to 2 wt%. In some embodiments, the mass percentage of 1-fluoro-2-methyl-ethylene carbonate (FMPC) in the non-aqueous electrolyte can also be 0.5 wt% to 1 wt%, 0.5 wt% to 1.5 wt%, 1 wt% to 2 wt%, 1.5 wt% to 2 wt%, 1 wt% to 1.5 wt%, 1.5 wt% to 2 wt%, etc. FMPC has a higher reduction potential and can preferentially form a NaF-rich SEI film substrate on the negative electrode surface compared to the solvent, isolating electrons and protecting the electrode. In addition, the methyl group has strong reducing properties, allowing FMPC to preferentially form a film on the positive electrode, protecting the electrolyte from oxidation by the positive electrode. Too little FMPC (less than 0.5 wt%) will not significantly optimize the SEI film of sodium-ion batteries; too much FMPC (greater than 2 wt%) will increase the internal resistance of the battery and increase gas production.

[0034] In summary, this invention, through the rational use of dual-ion sodium salts, can improve the ionic conductivity and thermal stability of sodium-ion battery electrolytes, while also preventing the corrosion of aluminum structural components by sodium bis(fluorosulfonyl)imide. The synergistic effect of the sodium salts and functional additives forms an effective interfacial film on the electrode surface, significantly enhancing the high-temperature storage performance and high-temperature cycle performance of sodium-ion batteries.

[0035] Sodium-ion batteries

[0036] A second aspect of the present invention provides a sodium-ion battery, the sodium-ion battery further comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte for sodium-ion batteries, wherein the non-aqueous electrolyte for sodium-ion batteries is selected from the non-aqueous electrolyte for sodium-ion batteries of the first aspect of the present invention.

[0037] 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, aluminum foil can be used as an aluminum current collector. The composite current collector may 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 may also include a conductive agent and a binder. The positive electrode active material can be selected from one or more of transition metal layered oxides, polyanionic materials, or Prussian blue materials. Transition metal layered oxides are preferred. Those skilled in the art can select conductive agents and binders suitable for sodium-ion batteries. The conductive agent may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The adhesive may include, for example, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0038] In some embodiments, the positive electrode can be prepared by dispersing the above-mentioned components for preparing the positive electrode, such as the positive electrode material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode after drying, cold pressing and other processes.

[0039] 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, aluminum foil can be used as an aluminum current collector. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The negative electrode active material layer includes a negative electrode active material, and may further include a plasticizer, a conductive agent, and a binder. The negative electrode active material can be selected from one or more of carbon-based materials, titanium-based oxide materials, and alloy materials; preferably, the negative electrode active material can be selected from hard carbon materials. Those skilled in the art can select plasticizers, conductive agents, and binders suitable for sodium-ion batteries. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The adhesive may 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), carboxymethyl chitosan (CMCS), and sodium carboxymethyl cellulose (CMC-Na).

[0040] In some embodiments, the negative electrode can be prepared by dispersing the components used to prepare the negative electrode, such as the negative electrode material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode after drying, cold pressing and other processes.

[0041] The sodium-ion battery provided in the second aspect of this invention can be prepared using methods known in the art. For example, a positive electrode, a separator, and a negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes, and then the layers are stacked 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 a pouch cell; after vacuum sealing, settling, formation, and capacity testing, a sodium-ion battery is obtained.

[0042] Battery Module

[0043] A third aspect of the present invention provides a battery module comprising any one or more sodium-ion batteries described in the second aspect of the present invention. The number of sodium-ion batteries in the battery module can be adjusted according to the application and capacity of the battery module.

[0044] Battery Pack

[0045] A fourth aspect of the present invention provides a battery pack comprising any one or more battery modules described in the third aspect of the present invention. That is, the battery pack comprises any one or more sodium-ion batteries described in the second aspect of the present invention.

[0046] The number of battery modules in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0047] Electrical appliances

[0048] A fifth aspect of the present invention provides an electrical device comprising one or more sodium-ion batteries as described in the second aspect of the present invention. The sodium-ion batteries can be used as a power source for the electrical device. Preferably, the electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0049] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0050] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Unless otherwise specified, specific experimental or operational conditions in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0051] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0052] In the following embodiments, unless otherwise specified, all the raw materials of the present invention are commercially available or prepared according to conventional methods in the art.

[0053] In the embodiments and comparative examples of this invention, the positive electrode material of the sodium-ion battery is sodium nickel iron manganese oxide, the negative electrode is hard carbon, and the electrolyte injection amount of each battery is 4g.

[0054] The preparation processes of sodium-ion battery electrolytes in Examples 1-8 and Comparative Examples 1-16 are as follows:

[0055] Electrolytes (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 different proportions as shown in Table 1 were then added to the solvent, and after thorough mixing, the electrolytes of Examples 1-8 and Comparative Examples 1-16 were obtained. The prepared electrolytes were injected into pouch cells, and after standing, formation, and capacity testing, sodium-ion batteries were obtained.

[0056] Table 1: Electrolyte formulations for sodium-ion batteries in Examples 1-8 and Comparative Examples 1-16

[0057]

[0058] The sodium-ion batteries of Examples 1-8 and Comparative Examples 1-16 were subjected to the following experiments, and the test results are shown in Table 2.

[0059] (1) High-temperature cycle performance test: After formation and capacity testing, the batteries obtained in Examples 1-8 and Comparative Examples 1-16 were charged at 45°C with a constant current and constant voltage of 1C to a voltage of 4V and a current of 0.05C. After resting for 10 minutes, they were discharged at a constant current of 1C to a voltage of 1.5V. This constitutes one charge-discharge cycle. After formation and capacity testing, the obtained batteries were subjected to 300 charge-discharge cycles at 45°C.

[0060] (2) High-temperature storage performance test: After the batteries obtained in Examples 1 to 8 and Comparative Examples 1 to 16 were formed and capacity tested, they were charged at 25°C with 1C constant current and constant voltage to a voltage of 4V and a current of 0.05C. The 1C capacity Q and battery thickness H were recorded respectively. The fully charged batteries were stored at 60°C for 30 days. The 1C discharge capacity Q1 and battery thickness H1 were recorded at 25°C. The batteries were charged at 1C constant current and constant voltage to a voltage of 4V and a current of 0.05C and then discharged at 1C constant current to 1.5V. The 1C discharge capacity Q2 was recorded. The capacity retention rate, recovery rate and battery expansion rate of the batteries after storage were calculated.

[0061] The calculation formulas are as follows:

[0062] Capacity retention rate = Q1 / Q × 100%; Capacity recovery rate = Q2 / Q × 100%; Battery expansion rate = (H1-H) / H × 100%.

[0063] Table 2: Test results of batteries obtained in Examples 1-8 and Comparative Examples 1-16

[0064]

[0065] As shown in Table 2, compared with the sodium-ion batteries of the comparative examples, the sodium-ion batteries of the present invention with a NaFSI to NaPF6 molar ratio between 8:2 and 7:3 in the electrolyte, and the simultaneous addition of 1wt% to 2.5wt% TFMPS and 0.5wt% to 2wt% FMPC, exhibit superior high-temperature cycling and high-temperature storage performance. Among them, the sodium-ion battery with an electrolyte formulation of 0.7mol / L NaFSI + 0.3mol / L NaPF6 combined with 2wt% TFMPS + 1wt% FMPC shows the best overall performance. This is mainly due to: the reasonable mass ratio of NaFSI and NaPF6, which ensures high thermal stability and ionic conductivity of the electrolyte, and also avoids corrosion of the aluminum tabs by NaFSI; TFMPS and FMPC both have excellent positive and negative electrode film-forming effects, forming a stable interfacial film that ensures both high ion permeability and high toughness, and will not easily break down or decompose during long-term cycling, thus providing stable protection for the cell.

[0066] To investigate the inhibitory effect of NaPF6 on NaFSI corrosion current collectors, this invention prepared electrolytes with different sodium salt ratios (Experimental Examples 1-2, Control Examples 1-3). Using aluminum structural components as working electrodes, metallic sodium as reference electrodes, and metallic platinum as counter electrodes, the corrosion current of each group of aluminum structural components was tested by cyclic voltammetry (CV). Then, SEM tests were performed on the surface of the tested aluminum structural components to observe the corrosion.

[0067] CV test: Voltage range: 2V-5V;

[0068] Current sweep rate: 0.1 mV / s;

[0069] SEM magnification: 100x and 500x;

[0070] Compare with Example 1

[0071] Electrolyte: 1M NaPF6;

[0072] Compare with Example 2

[0073] Electrolyte: 1M NaFSI;

[0074] Experimental Example 1

[0075] Electrolyte: 0.7M NaFSI + 0.3M NaPF6;

[0076] Experimental Example 2

[0077] Electrolyte: 0.8M NaFSI + 0.2M NaPF6;

[0078] Compare with Example 3

[0079] Electrolyte: 0.9M NaFSI + 0.1M NaPF6.

[0080] Figure 1 The CV test results are for an electrolyte containing 1M NaPF6 as a sodium salt. Figure 2 The CV test results are for an electrolyte containing 1M NaFSI as sodium salt. Figure 3 CV test results for electrolytes containing 0.7M NaFSI + 0.3M NaPF6 (sodium salt); Figure 4 CV test results for an electrolyte containing 0.8M NaFSI + 0.2M NaPF6 as sodium salt; Figure 5 CV test results for an electrolyte containing 0.9M NaFSI + 0.1M NaPF6 as sodium salt; Figure 6 SEM images of each group of aluminum foils after CV testing. Figures 1-5 The CV test results show that the current in the CV curve of the electrolyte with pure NaFSI as the sodium salt increases continuously with the increase of the number of cycles, exhibiting typical corrosion characteristics. In contrast, the electrolyte with pure NaPF6 as the sodium salt shows no significant corrosion to the aluminum foil. The NaPF6 in the 0.7M NaFSI+0.3M NaPF6 and 0.8M NaFSI+0.2M NaPF6 groups also shows a significant passivation effect on the aluminum foil, but the corrosion inhibition effect of the 0.9M NaFSI+0.1M NaPF6 group is poor due to the low amount of NaPF6. Figure 6 The SEM images also show that after CV testing, the aluminum foils of the pure NaFSI group and the 0.9M NaFSI+0.1M NaPF6 group have more spot corrosion marks, while the 0.7M NaFSI+0.3M NaPF6 group and the 0.8M NaFSI+0.2M NaPF6 group have NaPF6 passivation and no obvious spot corrosion on the aluminum foil surface.

[0081] In summary, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A non-aqueous electrolyte for sodium-ion batteries, characterized in that, The sodium-ion battery non-aqueous electrolyte comprises sodium salt, organic solvent, and functional additives. The sodium salt includes sodium difluorosulfonylimide and sodium hexafluorophosphate, with a molar ratio of sodium difluorosulfonylimide to sodium hexafluorophosphate of 8:2 to 7:

3. The organic solvent includes chain carbonates and cyclic carbonates. The functional additives include 2-trifluoromethyl-1,3-propenesulfonate lactone and 1-fluoro-2-methyl-ethylene carbonate. The organic solvent accounts for 68 wt% to 75 wt% of the non-aqueous electrolyte. The 2-trifluoromethyl-1,3-propenesulfonate lactone accounts for 1 wt% to 2.5 wt% of the non-aqueous electrolyte. The 1-fluoro-2-methyl-ethylene carbonate accounts for 0.5 wt% to 2 wt% of the non-aqueous electrolyte.

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

3. The non-aqueous electrolyte for sodium-ion batteries according to claim 1, characterized in that, The organic solvent is selected from one or more combinations of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, and propylene carbonate; And / or, the volume ratio of the chain carbonate to the cyclic carbonate is 5:5 to 9:

1.

4. A sodium-ion battery, characterized in that, The invention includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte for a sodium-ion battery, characterized in that the non-aqueous electrolyte is the non-aqueous electrolyte for a sodium-ion battery as described in any one of claims 1 to 3.

5. The sodium-ion battery according to claim 4, characterized in that, The negative electrode includes a negative electrode active material, which is selected from one or more combinations of carbon-based materials, titanium-based oxide materials, and alloy materials. And / or, the positive electrode includes a positive electrode active material, which is selected from one or more combinations of transition metal layered oxides, polyanionic materials, or Prussian blue materials.

6. A battery module, characterized in that, Including the sodium-ion battery according to claim 4 or 5.

7. A battery pack, characterized in that, Includes the battery module according to claim 6.

8. An electrical device, characterized in that, Includes a sodium-ion battery according to claim 4 or 5, wherein the sodium-ion battery is used as a power source for the device, and the device includes mobile devices, electric vehicles, electric trains, satellites, ships, and energy storage systems.

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