High-voltage-resistant wide-temperature-range electrolyte, preparation method thereof, sodium ion total battery and sodium ion half battery

Abstract

The invention is applicable to the technical field of materials, and provides a high-voltage-resistant wide-temperature-range electrolyte, a preparation method thereof, a sodium ion total battery and a sodium ion half battery, the electrolyte contains sodium salt, an organic solvent (carbonic esters or phosphate esters) and a fluorinated diluent, and the volume ratio of the organic solvent to the diluent is 1: 1-1: 4. A local high-concentration system is constructed through the ester solvent and the fluorine-containing diluent, an anion-rich solvation structure is formed, and the defects of electrode structure damage, capacity reduction, poor cycle stability and high and low temperature performance of an existing electrolyte under high voltage are overcome; compared with a common high-concentration electrolyte, the sodium salt consumption is reduced while high coulombic efficiency and other performance are guaranteed, the cost is reduced, and the wettability and the conductivity are improved; compared with an ether system, the ester solvent improves the oxidation resistance and is more economical, the inorganic-rich passivation layer formed by anion decomposition is more stable, the wide-temperature-range cycle performance is optimized, and a foundation is laid for the extreme environment and large-scale energy storage application of the sodium-ion battery.

Description

Technical Field

[0001] The present application belongs to the field of material technology, and in particular relates to a high-voltage, wide-temperature range electrolyte and a preparation method thereof, and a sodium ion full battery and half battery. Background Art

[0002] Lithium-ion batteries, with their high power density and long cycle life, dominate energy storage systems, electric vehicles, and portable electronic devices. However, the uneven distribution and scarcity of lithium resources on which they rely severely restrict their application in large-scale power storage. In contrast, sodium resources are abundant, widely distributed, and inexpensive. Furthermore, sodium and lithium are both alkali metals with similar chemical and electrochemical properties, making sodium-ion batteries a highly promising alternative or complementary technology for large-scale energy storage, showing significant application prospects in areas such as grid energy storage and low-speed electric vehicles.

[0003] However, the practical application of sodium-ion batteries still faces the dual challenges of extreme temperatures and high-voltage conditions. The optimal operating temperature range of conventional batteries is narrow (-5°C to 35°C), but in cold areas such as high altitudes and high latitudes, batteries need to operate for a long time below -15°C; in high-temperature environments such as deserts and tropical regions, they need to withstand continuous high temperatures of 50°C and above. Currently, most commercial electrolytes are based on ethylene carbonate (EC), but its high melting point of 36.4°C causes the electrolyte to easily solidify or crystallize at low temperatures, significantly reducing ionic conductivity, resulting in a sudden drop in battery capacity and insufficient power output; at the same time, EC is easily oxidized and decomposed with the positive electrode material under high-voltage conditions, generating gas and consuming electrolyte, aggravating the damage to the electrode structure, resulting in rapid battery capacity decay and deterioration of cycle stability.

[0004] As the core medium for ion transport in sodium-ion batteries, the performance of the electrolyte directly affects the energy density, safety and cycle life of the battery. Although the electrode material determines the theoretical specific capacity of the battery, the physical and chemical properties of the electrolyte (such as ionic conductivity, electrochemical window, high and low temperature stability, etc.) will significantly affect the reversible capacity and interface stability of the electrode active material. Existing sodium-ion battery electrolytes have another key problem under high voltage: as the voltage increases, the interfacial reaction between the electrolyte and the positive electrode intensifies, forming an unstable solid electrolyte interface (SEI) film, which may also cause the structural collapse of the positive electrode material (such as phase change of layered oxides and dissolution of transition metals), resulting in a rapid decrease in battery capacity and a shortened cycle life. These defects make it difficult for existing electrolytes to meet the application requirements of harsh working conditions such as high voltage and wide temperature range, greatly limiting the promotion and application of sodium-ion batteries in extreme environments. Therefore, the development of new electrolytes with both high-voltage tolerance and wide temperature adaptability has become a core breakthrough in promoting the practical application of sodium-ion batteries. Summary of the Invention

[0005] The purpose of the embodiments of the present application is to provide an electrolyte that is resistant to high voltage and wide temperature range, aiming to solve the problem that existing electrolytes are difficult to meet the application requirements of harsh working conditions such as high voltage and wide temperature range, which greatly limits the promotion and application of sodium ion batteries in extreme environments.

[0006] The embodiment of the present application is implemented as follows: a high-voltage and wide-temperature range electrolyte includes a sodium salt, an organic solvent and a diluent; wherein the organic solvent is a carbonate solvent or a phosphate solvent; the diluent is a fluorinated diluent; and the volume ratio of the organic solvent to the diluent is 1:1 to 1:4.

[0007] Another object of the embodiments of the present application is a method for preparing the above-mentioned high-voltage and wide-temperature range electrolyte, comprising:

[0008] Under argon atmosphere, the sodium salt is fully dissolved in an organic solvent to obtain a sodium salt mixed solution;

[0009] A diluent is added to the sodium salt mixture and mixed evenly to obtain a high-voltage and wide-temperature range electrolyte.

[0010] Another object of an embodiment of the present application is a sodium ion full battery or half battery, which includes the above-mentioned high-voltage and wide-temperature range electrolyte.

[0011] The high-voltage and wide-temperature-range electrolyte provided in the embodiments of the present application constructs a local high-concentration system through an ester solvent and a fluorine-containing diluent to form an anion-rich solvation structure, which not only solves the problems of electrode structure destruction, capacity reduction and poor cycle stability caused by existing electrolytes under high pressure, but also overcomes the defects of easy decomposition at high temperature, easy freezing at low temperature, and insufficient compatibility with electrodes; compared with ordinary high-concentration electrolytes, while ensuring high coulombic efficiency, low self-discharge rate and long cycle life, the cost is reduced by reducing the amount of sodium salt used, and the wettability and conductivity are improved; compared with the traditional system of ether solvents, ester solvents have improved oxidation resistance and are more economical, and the inorganic-rich passivation layer formed by the decomposition of anions is more stable, which significantly optimizes the wide-temperature-range cycle performance, laying the foundation for the application of sodium-ion batteries in extreme environments and large-scale energy storage fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a comparison chart of the cycle capacity curves of sodium ion half-cells prepared using the electrolytes of Example 1 and Comparative Examples 1 and 5 of the present application;

[0013] Figure 2 A comparison of the cycle capacity curves of sodium ion half-cells prepared using the electrolytes of Example 4 and Comparative Examples 2 and 6 of the present application;

[0014] Figure 3This is a comparison chart of the cycle capacity curves of sodium ion half-cells prepared with the electrolytes of Example 9 and Comparative Example 3 of the present application;

[0015] Figure 4 1. A comparison of the cycle capacity curves of sodium ion half-cells prepared using the electrolytes of Example 10 and Comparative Example 4 of the present application;

[0016] Figure 5 This is a comparison chart of the cycle capacity curves of sodium ion full batteries prepared with the electrolytes of Example 17 of the present application and Comparative Example 10. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0018] In order to solve the problem that existing electrolytes are difficult to meet the requirements of harsh working conditions such as high voltage and wide temperature range, thereby limiting the promotion and application of sodium ion batteries in extreme environments, the embodiments of the present application propose a high-voltage and wide-temperature-range resistant local high-concentration electrolyte. Compared with ordinary high-concentration sodium salt electrolytes, this local high-concentration electrolyte not only ensures the high coulombic efficiency, low self-discharge rate and long cycle life of the battery, but also greatly reduces the cost by reducing the amount of conductive sodium salt used, while improving the wettability and conductivity of the electrolyte. Compared with the solution of using ether solvents as the main solvent for traditional local high-concentration electrolytes, the present application uses ester solvents, which not only improves the antioxidant properties of the electrolyte, but also further reduces the cost. In addition, the combination of high-dielectric-constant ester solvents and low-viscosity fluorinated ether diluents produces dipole-dipole interactions, constructing a typical anion-rich solvation structure dominated by contact ion pairs (CIPs) and aggregates (AGGs), which gives the electrolyte greater electrochemical stability. This structure also increases the probability of anion decomposition, and after anion decomposition, the main form is inorganic-rich passivation products, which are more stable than the rich organic products produced by the decomposition of solvent molecules in traditional low-concentration electrolytes. At the same time, the overall performance of the electrolyte in coping with extreme temperatures is improved, and the cycling performance in both high and low temperature environments is improved.

[0019] Specifically, the high-voltage and wide-temperature-range electrolyte of the embodiment of the present application includes a sodium salt, an organic solvent and a diluent; wherein the organic solvent is a carbonate solvent or a phosphate solvent; the diluent is a fluorinated diluent; the volume ratio of the organic solvent to the diluent is 1:1 to 1:4, preferably 2:3.

[0020] Preferably, the organic solvent is at least one of ethylene carbonate (EC), propylene carbonate (PC), trimethyl phosphate (TMP), and triethyl phosphate (TEP).

[0021] Preferably, the diluent is at least one of bis(2,2,2-trifluoroethyl) ether (NTFE), 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether (HFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE).

[0022] Preferably, the sodium salt comprises at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bis(fluorosulfonyl)imide, and may optionally comprise sodium difluorooxalatoborate.

[0023] Preferably, the molar concentrations of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bis(fluorosulfonyl)imide in the electrolyte are all 0.5-1.5 mol / L; if sodium difluorooxalatoborate is included, its molar concentration is 0.01-0.3 mol / L.

[0024] More preferably, the molar concentrations of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bis(fluorosulfonyl)imide in the electrolyte are all 0.8-1 mol / L; if sodium difluorooxalatoborate is included, its molar concentration is 0.1-0.2 mol / L.

[0025] More preferably, the sodium salt in the high-voltage, wide-temperature-range electrolyte is selected from any one of the following: (1) sodium bis(trifluoromethylsulfonyl)imide (optionally containing sodium difluorooxalatoborate); (2) sodium hexafluorophosphate (optionally containing sodium difluorooxalatoborate); the organic solvent is trimethyl phosphate; and the diluent is 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether. When the sodium salt is sodium bis(trifluoromethylsulfonyl)imide, its molar concentration is 0.5-1.5 mol / L; if it contains sodium difluorooxalatoborate, its molar concentration is 0.01-0.3 mol / L; when the sodium salt is sodium hexafluorophosphate, its molar concentration is 0.5-1.5 mol / L; if it contains sodium difluorooxalatoborate, its molar concentration is 0.01-0.3 mol / L; preferably, the molar concentration of sodium bis(trifluoromethylsulfonyl)imide is 0.8-1 mol / L; if it contains sodium difluorooxalatoborate, its molar concentration is 0.1-0.2 mol / L. The molar concentration of sodium hexafluorophosphate is 0.8-1 mol / L; if it contains sodium difluorooxalatoborate, its molar concentration is 0.1-0.2 mol / L.

[0026] More preferably, the sodium salt is selected from any one of the following: (1) sodium bis(trifluoromethylsulfonyl)imide; (2) a mixture of sodium hexafluorophosphate and sodium difluorooxalatoborate.

[0027] It should be noted that the high-voltage and wide-temperature-range electrolyte can be composed of the above-mentioned sodium salt, organic solvent and diluent, and may also contain conventional electrolyte additives (such as film-forming additives, flame retardants) not exceeding 5% of the total mass. Since the amount of such conventional additives added is extremely small, they only play an auxiliary role and will not have a substantial impact on the core performance of the battery.

[0028] An embodiment of the present application also provides a method for preparing the above-mentioned high-voltage and wide-temperature-range electrolyte, comprising: fully dissolving a sodium salt in an organic solvent under an argon atmosphere to obtain a sodium salt mixture; adding a diluent to the sodium salt mixture, stirring and mixing the mixture evenly, to obtain a high-voltage and wide-temperature-range electrolyte.

[0029] The present application also provides a sodium ion battery comprising the above-mentioned high-voltage wide-temperature range electrolyte. The sodium ion battery is divided into a half-cell and a full-cell, both of which are assembled in an argon-filled glove box: the half-cell is assembled in the order of a negative electrode shell, a sodium sheet, a diaphragm, the high-voltage wide-temperature range electrolyte, a positive electrode sheet, and a positive electrode shell; the full-cell is assembled in the order of a negative electrode shell, a negative electrode sheet, a diaphragm, the high-voltage wide-temperature range electrolyte, a positive electrode sheet, and a positive electrode shell, wherein the positive electrode sheet can be a layered oxide positive electrode sheet (such as NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, namely NFM) or polyanion positive electrode sheet (such as Na4Fe3(PO4)2P2O7, namely NFPP).

[0030] The following will be combined with preferred embodiments to provide a more comprehensive and detailed description of the high-voltage wide-temperature electrolyte and its preparation method, and the sodium-ion battery provided by the present application, but the scope of protection of the present application is not limited to the following specific embodiments. Unless otherwise defined, all professional terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application. Unless otherwise specified, the various reagents and raw materials used in this application are all commodities that can be purchased from the market or products that can be prepared by known methods.

[0031] Example 1

[0032] The electrolyte composition of this embodiment is composed of 1 mol / L sodium bis(trifluoromethylsulfonyl)imide, 40% by volume of trimethyl phosphate (TMP), and 60% by volume of 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether (HFE).

[0033] The preparation method of the high-voltage and wide-temperature-range electrolyte is as follows:

[0034] In an argon-filled glove box, the sodium salt was first dissolved in the above-mentioned volume fraction of trimethyl phosphate solvent, and then the above-mentioned volume fraction of 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether was added thereto to a final concentration of 1 mol / L. A magnetic stirrer was added for 12 hours to ensure uniform mixing.

[0035] The sodium-ion half-cell is assembled as follows:

[0036] In a glove box filled with argon, the negative electrode shell, sodium sheet, diaphragm, high-voltage wide-temperature electrolyte, positive electrode sheet, and positive electrode shell are assembled in the order of the negative electrode shell, and the battery is sealed by a sealing machine and left at room temperature for 12 hours before the corresponding electrochemical performance test (the test temperature of the electrochemical test is 30°C and the voltage range is 2-4V). Among them, the positive electrode sheet is a layered oxide positive electrode sheet, and its preparation method is as follows: the positive electrode material layered oxide NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, binder PVDF, and conductive agent Kb are dispersed in the organic solvent NMP in a ratio of 8:1:1, stirred for 8 hours in a dry environment, and then evenly coated on the aluminum current collector. It is placed in a vacuum oven at 100°C for 12 hours and then cut into 12mm diameter positive electrode sheets for use.

[0037] Example 2

[0038] The electrolyte composition of this embodiment differs from that of Example 1 in that it comprises 1 mol / L sodium bis(trifluoromethylsulfonyl)imide, 30% by volume of trimethyl phosphate (TMP), and 70% by volume of 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether (HFE). All other conditions are consistent with those of Example 1.

[0039] Example 3

[0040] The electrolyte composition of this embodiment differs from that of Example 1 in that it comprises 1 mol / L sodium bis(trifluoromethylsulfonyl)imide, 50% by volume of trimethyl phosphate (TMP), and 50% by volume of 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether (HFE). All other conditions are consistent with those of Example 1.

[0041] Example 4

[0042] The electrolyte composition of this embodiment differs from that of Example 1 in that it comprises 1 mol / L sodium hexafluorophosphate, 40% by volume of trimethyl phosphate (TMP), and 60% by volume of 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether (HFE). All other conditions are consistent with those of Example 1.

[0043] Example 5

[0044] The difference from Example 1 is that the voltage range of the electrochemical test is 2-4.2 V. The other conditions are the same as those in Example 1.

[0045] Example 6

[0046] The difference from Example 4 is that the voltage range of the electrochemical test is 2-4.2V; the other conditions are the same as those of Example 4.

[0047] Example 7

[0048] The electrolyte composition of this embodiment is different from that of Example 6 in that the electrolyte composition of this embodiment is composed of 1 mol / L sodium hexafluorophosphate, 40% triethyl phosphate (TEP) by volume, and 60% 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether (HFE) by volume; the other conditions are the same as those of Example 6.

[0049] Example 8

[0050] The electrolyte composition of this embodiment is different from that of Example 6 in that the electrolyte composition of this embodiment is composed of 1 mol / L sodium hexafluorophosphate, 40% by volume of trimethyl phosphate (TMP), and 60% by volume of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE); the other conditions are the same as those of Example 6.

[0051] Example 9

[0052] The difference between this embodiment and embodiment 1 is that the test temperature of the electrochemical test is 50° C. The other conditions are the same as those of embodiment 1.

[0053] Example 10

[0054] The difference between this embodiment and embodiment 1 is that the test temperature of the electrochemical test is -15° C. The other conditions are the same as those in embodiment 1.

[0055] Example 11

[0056] The difference between this embodiment and Example 1 is that the positive electrode sheet is a polyanion positive electrode, and its preparation method is as follows: the positive electrode material layered oxide Na4Fe3(PO4)2P2O7, the binder PVDF, and the conductive agent superP are dispersed in the organic solvent NMP in a ratio of 8:1:1, stirred for 8 hours in a dry environment, and then evenly coated on the aluminum current collector, placed in a vacuum oven at 100°C for 12 hours, and then cut into positive electrode sheets with a diameter of 12 mm for standby use.

[0057] The voltage range of the electrochemical performance test is 1.5-4V, and the test cycle current density is 645mAg -1 Constant current charge and discharge 1000 times.

[0058] Example 12

[0059] The electrolyte composition of this embodiment differs from that of embodiment 11 in that the sodium salt is 0.8 mol / L sodium hexafluorophosphate and 0.1 mol / L sodium difluorooxalatoborate. The other conditions are the same as those of embodiment 11.

[0060] Example 13

[0061] The electrolyte composition of this embodiment is different from that of Example 6 in that the electrolyte composition of this embodiment is composed of 1 mol / L sodium hexafluorophosphate, 40% by volume of trimethyl phosphate (TMP), and 60% by volume of bis(2,2,2-trifluoroethyl) ether (BTTE); the other conditions are the same as those of Example 6.

[0062] Example 14

[0063] The electrolyte composition of this embodiment is different from that of Example 6 in that: the electrolyte composition of this embodiment is composed of 1 mol / L sodium hexafluorophosphate, 40% by volume of trimethyl phosphate (TMP), and 60% by volume of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE); the other conditions are the same as those of Example 6.

[0064] Example 15

[0065] The electrolyte composition of this embodiment is different from that of Example 6 in that: the electrolyte composition of this embodiment is composed of 1 mol / L sodium hexafluorophosphate, 40% by volume of ethylene carbonate (EC), and 60% by volume of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE); the other conditions are the same as those of Example 6.

[0066] Example 16

[0067] The difference between this embodiment and Example 6 is that the electrolyte composition of this embodiment is composed of 1 mol / L sodium hexafluorophosphate, 40% by volume of propylene carbonate (PC), and 60% by volume of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE); the other conditions are the same as those of Example 6.

[0068] Example 17

[0069] The electrolyte composition of this embodiment is composed of 1 mol / L sodium bis(trifluoromethylsulfonyl)imide, 40% by volume of trimethyl phosphate (TMP), and 60% by volume of 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether.

[0070] The preparation method of the high-voltage and wide-temperature-range electrolyte is as follows:

[0071] In an argon-filled glove box, the sodium salt was first dissolved in the above-mentioned volume fraction of trimethyl phosphate solvent, and then the above-mentioned volume fraction of 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether was added thereto to a final concentration of 1 mol / L. A magnetic stirrer was added for 12 hours to ensure uniform mixing.

[0072] The preparation method of sodium ion full battery is as follows:

[0073] In a glove box filled with argon, the negative electrode shell, negative electrode sheet, diaphragm, electrolyte, positive electrode sheet, and positive electrode shell are assembled in the order of the negative electrode shell, and the battery is sealed by a sealing machine and left at room temperature for 12 hours before the corresponding electrochemical performance test. The preparation method of the positive electrode sheet is as follows: the positive electrode material layered oxide NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, binder PVDF, and conductive agent Kb are dispersed in the organic solvent NMP in a ratio of 8:1:1, stirred in a dry environment for 8 hours, and then evenly coated on the aluminum current collector. The mixture is placed in a vacuum oven at 100°C for 12 hours and then cut into 12mm diameter positive electrode sheets for use. The negative electrode sheet is prepared by dispersing the negative electrode material hard carbon HC, binder PVDF, and conductive agent SuperP in the organic solvent NMP in a ratio of 8:1:1. The mixture is stirred in a dry environment for 8 hours, and then evenly coated on the copper current collector. The mixture is placed in a vacuum oven at 100°C for 12 hours and then cut into 14mm diameter negative electrode sheets for use.

[0074] Comparative Example 1

[0075] The electrolyte composition of this comparative example is different from that of Example 1 in that the electrolyte composition of this example is composed of 1 mol / L sodium hexafluorophosphate (NaPF6), 50% by volume of ethylene carbonate (EC), 50% by volume of diethyl carbonate (DMC), and 5% by volume of fluoroethylene carbonate (FEC); the other conditions are the same as those of Example 1.

[0076] Comparative Example 2

[0077] The electrolyte composition of this comparative example is different from that of Example 1 in that: the electrolyte composition of this example is composed of 1 mol / L sodium hexafluorophosphate (NaPF6), 50% by volume of ethylene carbonate (EC), 50% by volume of diethyl carbonate (DMC), and 5% by volume of fluoroethylene carbonate (FEC); the voltage range of the electrochemical test is 2-4.2 V; and the other conditions are the same as those of Example 1.

[0078] Comparative Example 3

[0079] The difference between this comparative example and comparative example 1 is that the test temperature of the electrochemical test is 50° C.; the other conditions are the same as those of comparative example 1.

[0080] Comparative Example 4

[0081] The difference between this comparative example and comparative example 1 is that the test temperature of the electrochemical test is -15°C; the other conditions are the same as those of comparative example 1.

[0082] Comparative Example 5

[0083] The electrolyte composition of this comparative example is different from that of Example 1 in that the electrolyte composition of this example is composed of 1 mol / L sodium hexafluorophosphate and the solvent is trimethyl phosphate (TMP); the other conditions are the same as those of Example 1.

[0084] Comparative Example 6

[0085] The electrolyte composition of this comparative example is different from that of Example 3 in that the electrolyte composition of this example is composed of 1 mol / L sodium hexafluorophosphate and the solvent is trimethyl phosphate (TMP); the other conditions are the same as those of Example 3.

[0086] Comparative Example 7

[0087] The electrolyte composition of this comparative example is different from that of Example 9 in that the electrolyte composition of this example is composed of 1 mol / L sodium perchlorate (NaClO4), 50% by volume of ethylene carbonate (EC), 50% by volume of propylene carbonate (PC), and 5% by volume of fluoroethylene carbonate (FEC); the other conditions are the same as those of Example 9.

[0088] Comparative Example 8

[0089] The electrolyte composition of this comparative example is different from that of Example 5 in that the electrolyte composition of this embodiment is composed of 1 mol / L sodium bis(trifluoromethylsulfonyl)imide, 40% dimethyl ether (DME) by volume, and 60% 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether (HFE) by volume; the other conditions are the same as those in Example 5.

[0090] Comparative Example 9

[0091] The electrolyte composition of this embodiment is different from that of Example 1 in that: the electrolyte composition of this embodiment is composed of 1 mol / L sodium bis(trifluoromethylsulfonyl)imide, 10% by volume of trimethyl phosphate (TMP), and 90% by volume of 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether (HFE); the other conditions are the same as those of Example 1.

[0092] Comparative Example 10

[0093] The difference between the electrolyte composition of this embodiment and that of Example 17 is that the electrolyte composition of this embodiment is composed of 1 mol / L sodium bis(trifluoromethylsulfonyl)imide and the solvent is trimethyl phosphate (TMP); the other conditions are the same as those of Example 17.

[0094] The sodium ion batteries prepared in Examples 1 to 17 and Comparative Examples 1 to 9 were subjected to cycle performance tests. For the layered oxide positive electrode material: the sodium ion battery was subjected to a cycle performance test at 150 mA g / min within a specific voltage range. -1 For polyanion cathode materials: charge and discharge the sodium ion battery at a current density of 645 mA g in a specific voltage range. -1 The battery was charged and discharged 1000 times at a constant current density of , and its capacity retention rate was calculated.

[0095] The test selected 9 comparative examples and 16 batteries of the embodiment for comparison and testing. The test results are shown in Table 1 and Figure 1-5 As shown, Table 1 shows the concentration and type of electrolyte salt, the selection and ratio of the solvent and the type of the tested positive electrode, the test temperature and voltage, and the capacity retention rate after a specific number of cycles.

[0096] Table 1

[0097]

[0098]

[0099] Depend on Figure 1 、 Figure 2As can be seen from Table 1, by adding a fluorinated ether diluent to the phosphate ester organic solvent, the cycle retention rate of the battery at normal pressure and high pressure can be significantly improved. This shows that the addition of the diluent plays an indispensable role in improving the antioxidant capacity of the electrolyte. Due to the dipole-dipole interaction, the fluorine-containing functional groups on the diluent interact with the organic solvent, which reduces the content of the organic solvent in the first solvation shell of the electrolyte and forms a solvation shell dominated by anions. This forms a local high-concentration electrolyte with a better electrochemical platform and a smaller degree of polarization, further proving that the modified electrolyte is effective in protecting the structure of electrode materials and inhibiting side reactions. When the remaining components of the local high-concentration electrolyte were adjusted, the performance of the battery deteriorated slightly. This may be due to the increased steric hindrance of other solvents, which hinders the migration of sodium ions, and the slightly poor antioxidant properties of conventional sodium hexafluorophosphate.

[0100] Figure 3 and Figure 4 The discharge specific capacity-cycle number diagrams of local high-concentration electrolytes and conventional commercial electrolytes at high and low temperatures are shown respectively. It can be seen that the local high-concentration electrolyte combines the high boiling point of ester solvents and the low freezing point of ether solvents, so that the electrolyte exhibits a better capacity retention rate than conventional electrolytes at both high and low temperatures. In the long cycle performance test process of sodium ion batteries with polyanion materials as positive electrodes, it can be found that after 1000 cycles, the local high-concentration electrolyte still maintains a high cycle retention rate, and there is no capacity collapse like conventional commercial electrolytes, which proves that the electrolyte has a universal optimization effect on different positive electrodes. Therefore, it can be found that the present application must be a local high-concentration electrolyte composed of the synergistic effect of ester solvents and diluents to achieve the best electrochemical performance under comprehensive conditions.

[0101] Figure 5 This is a graph showing the cyclic discharge capacity of a local high-concentration electrolyte compared to an ordinary phosphate electrolyte in an assembled full-battery environment. Due to the poor compatibility of ester solvents with hard carbon negative electrodes, the performance of the assembled full-battery decays sharply. The electrolyte with the addition of fluorinated ethers is obviously stable and compatible with the full-battery, and the retention rate is still 92.4% after 200 cycles, showing excellent cycle stability.

[0102] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0103] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A high-voltage and wide-temperature electrolyte, characterized in that: The invention comprises sodium salt, organic solvent and diluent; wherein the organic solvent is a carbonate solvent or a phosphate solvent; the diluent is a fluorinated diluent; and the volume ratio of the organic solvent to the diluent is 1:1 to 1:

4.

2. The high-voltage and wide-temperature-range electrolyte according to claim 1, characterized in that: The organic solvent is at least one of ethylene carbonate, propylene carbonate, trimethyl phosphate, and triethyl phosphate.

3. The high-voltage and wide-temperature-range electrolyte according to claim 1, characterized in that: The diluent is at least one of bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

4. The high-voltage and wide-temperature range electrolyte according to claim 1, characterized in that The sodium salt comprises at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide, and sodium bis(fluorosulfonyl)imide, and may optionally comprise sodium difluorooxalatoborate.

5. The high-voltage and wide-temperature-range electrolyte according to claim 4, characterized in that: The molar concentrations of the sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide and sodium bis(fluorosulfonyl)imide in the electrolyte are all 0.5-1.5 mol / L; if sodium difluorooxalatoborate is included, its molar concentration is 0.01-0.3 mol / L.

6. The high-voltage and wide-temperature-range electrolyte according to claim 5, characterized in that: The molar concentrations of the sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(trifluoromethylsulfonyl)imide and sodium bis(fluorosulfonyl)imide in the electrolyte are all 0.8-1 mol / L; if sodium difluorooxalatoborate is included, its molar concentration is 0.1-0.2 mol / L.

7. The high-voltage and wide-temperature-range electrolyte according to claim 4, characterized in that: The sodium salt is selected from any one of the following: (1) sodium bis(trifluoromethylsulfonyl)imide; (2) a mixture of sodium hexafluorophosphate and sodium difluorooxalatoborate; The organic solvent is trimethyl phosphate; The diluent is 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroether.

8. The high-voltage and wide-temperature range electrolyte according to claim 1, characterized in that: The volume ratio of the organic solvent to the diluent is 2:

3.

9. A method for preparing the high-voltage and wide-temperature-range electrolyte according to any one of claims 1 to 8, characterized in that: include: Under argon atmosphere, the sodium salt is fully dissolved in an organic solvent to obtain a sodium salt mixed solution; A diluent is added to the sodium salt mixture and mixed evenly to obtain a high-voltage and wide-temperature range electrolyte.

10. A sodium ion full battery or half battery, characterized in that: The sodium ion full battery or half battery comprises the high-voltage and wide-temperature range electrolyte according to any one of claims 1 to 8.

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