Electrolyte and sodium ion battery containing same

Abstract

The invention discloses an electrolyte and a sodium ion battery containing the electrolyte. The electrolyte comprises a sodium salt, an organic solvent and an additive, the organic solvent is an ether solvent; the additive is selected from non-sodium metal salts; the non-sodium metal salt is selected from at least one of a first additive, a second additive or a third additive; wherein the first additive is lithium metal salt; the second additive is magnesium metal salt; the third additive is aluminum metal salt. According to the electrolyte, the electrochemical window of the electrolyte can be improved, and the low-temperature capacity retention ratio and the cycle performance of the electrolyte can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a sodium ion battery electrolyte and a sodium ion battery containing the electrolyte. Background Art

[0002] Na + The desolvation energy of Li + About 25–30% smaller, which means that Na + The activation barrier for (de)embedding is low, which is expected to achieve faster charging and higher battery performance under low temperature conditions. Traditional carbonate electrolytes have poor compatibility with electrodes, and their stability and film-forming properties need to be improved. They have low ion conductivity under low temperature conditions, high ion desolvation energy barriers, and poor properties of the solid electrolyte interface (SEI) film formed on the surface of the hard carbon negative electrode, making it difficult to meet the requirements of the new generation of sodium ion battery cathode materials for electrolytes.

[0003] Ether electrolytes have good wettability and compatibility and can form stable solvation structures. In addition, ether solvents have low melting points and can achieve highly reversible solvent-co-intercalation reactions at low temperatures to form thin and stable SEI. However, their HOMO energy levels are high and their stability at high voltages is poor, which limits their applications. Therefore, improving the working voltage of ether electrolytes is of great significance for the development of high-voltage and low-temperature electrolytes. Summary of the invention

[0004] One of the purposes of the present invention is to provide a sodium ion battery electrolyte and a sodium ion battery comprising the electrolyte to address the deficiencies of the prior art. By adding a strongly complexed non-sodium metal salt as an additive, the electrochemical window of the electrolyte can be increased, and the low-temperature capacity retention rate and cycle performance of the electrolyte can be improved.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical scheme:

[0006] An electrolyte comprises a sodium salt, an organic solvent and an additive; the organic solvent is an ether solvent; and the additive is selected from non-sodium metal salts.

[0007] According to an embodiment of the present invention, the non-sodium metal salt is selected from at least one of the first additive, the second additive or the third additive, preferably the first additive; wherein the first additive is a lithium metal salt; the second additive is a magnesium metal salt; and the third additive is an aluminum metal salt.

[0008] According to an embodiment of the present invention, the sodium salt is NaPF 6 、NaClO 4 , NaBF 4 、NaAsF 6 、NaSiF6 、NaBOB、NaODFB、NaCF 3 SO 3 、Na(CF 3 SO 2 ) 3 、Na(CF 3 CO 2 ) 2 N、Na(CF 3 SO 2 ) 2 N, Na(SO 2 C 2 F 5 ) 2 N and Na(SO 3 CF 3 ) 2 At least one of N.

[0009] According to an embodiment of the present invention, in the electrolyte, the concentration of the sodium salt is 0.4-2 mol / L, for example, 0.5 mol / L, 1 mol / L, or 1.5 mol / L.

[0010] According to an embodiment of the present invention, the ether solvent is selected from at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, tetrahydrofuran, dioxolane, and γ-butyrolactone.

[0011] According to the embodiment of the present invention, the inventors found that the electrolyte containing the ether solvent of the present invention has a lower sodium ion desolvation barrier and better low-temperature performance.

[0012] According to an embodiment of the present invention, the content of the additive accounts for 0.01-3% of the total mass of the electrolyte, for example, 0.05%, 0.1%, 0.5%, 1%, or 2%.

[0013] According to an embodiment of the present invention, when the additive is selected from the first additive, the content of the first additive accounts for 0.01-3% of the total mass of the electrolyte, for example, 0.05%, 0.1%, 0.5%, 1%, 2%.

[0014] According to an embodiment of the present invention, when the additive is selected from the second additive, the content of the second additive is 0.01-3% by mass of the electrolyte, for example, 0.05%, 0.1%, 0.5%, 1%, or 2%.

[0015] According to an embodiment of the present invention, when the additive is selected from the third additive, the content of the third additive is 0.01-2% by mass of the electrolyte, for example, 0.05%, 0.1%, 0.5%, 1%, or 2%.

[0016] According to an embodiment of the present invention, the lithium metal salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide, preferably at least one of lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium difluorophosphate.

[0017] According to an embodiment of the present invention, the magnesium metal salt is selected from at least one of magnesium bis(trifluoromethylsulfonyl)imide, magnesium borohydride, magnesium perchlorate, magnesium trifluoromethanesulfonate, and magnesium chloride, preferably at least one of magnesium perchlorate and magnesium borohydride.

[0018] According to an embodiment of the present invention, the aluminum metal salt is selected from at least one of aluminum trifluoromethanesulfonate and aluminum chloride.

[0019] According to a preferred embodiment of the present invention, the additive is a first additive, and the first additive is selected from at least one of lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium difluorophosphate, and more preferably lithium difluorooxalate borate. Exemplarily, the additive is lithium difluorooxalate borate. Exemplarily, the additive is lithium hexafluorophosphate and lithium difluorooxalate borate, and the mass ratio thereof is 0.1 to 1:0.1 to 1, for example, 1:0.5. Exemplarily, the additive is lithium difluorophosphate and lithium difluorooxalate borate, and the mass ratio thereof is 0.1 to 1:0.1 to 1, for example, 1:0.5.

[0020] According to an embodiment of the present invention, the ether solvent can be complexed with the cation in the additive. The inventors found that after adding the additive, the cation in the additive participates in the solvation structure of the ether solvent, thereby reducing the proportion of free solvent.

[0021] According to an embodiment of the present invention, when the HOMO energy level of the anion in the additive is high, it can be passivated on the cathode surface, and the ether solvent can be prevented from being oxidized during the charge and discharge process, thereby making the electrochemical window of the electrolyte wider. Preferably, the HOMO energy level of the anion in the additive is selected from greater than -9eV. Exemplarily, the anion of the additive is, for example, difluorooxalatoborate, and its HOMO energy level is -7.6eV.

[0022] The present invention also provides application of the electrolyte in energy storage batteries.

[0023] The present invention also provides a sodium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a diaphragm; the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet; the electrolyte is selected from the above electrolytes.

[0024] According to an embodiment of the present invention, the positive electrode sheet includes a positive electrode material. Preferably, the positive electrode material is a ternary material of sodium nickel iron manganese oxide, sodium vanadium phosphate (such as Na 3 V 2 (PO 4 ) 3 ) or sodium ferric pyrophosphate (such as Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 ) at least one of the following. Further, the sodium nickel iron manganate ternary material is preferably Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O 2 .

[0025] According to an embodiment of the present invention, the negative electrode sheet comprises a negative electrode active material, a conductive agent and a binder. Preferably, the negative electrode active material is selected from at least one of hard carbon, nanocarbon materials, Sn, Si, In-based alloy anode materials and sodium titanate.

[0026] According to an embodiment of the present invention, the separator is selected from at least one of polyethylene (PE), polypropylene (PP), a composite separator of polyethylene and polypropylene, and a glass fiber separator.

[0027] Compared with the prior art solutions, the present invention has the following advantages:

[0028] The present invention provides a sodium ion battery electrolyte and a sodium ion battery comprising the electrolyte. By selecting the type of sodium salt, the type and proportion of ether solvents, the type of additives, etc., the electrochemical window of the electrolyte is improved, and the low-temperature capacity retention rate and cycle performance of the electrolyte are improved.

[0029] The sodium ion battery using the sodium ion battery electrolyte of the present invention has the following properties:

[0030] 1) The sodium ion battery of the present invention has excellent room temperature cycle performance: at a temperature of 25°C, 1C / 1C charge and discharge cycles of 600 cycles, using a ternary material of sodium nickel iron manganese oxide or a polyanion positive electrode material (Na 3 V 2 (PO 4 ) 3 Or Na 4 / 3 Fe 3 / 2 (PO4 ) 2 / 1 P 2 O 7 ), maintaining capacity retention rates of more than 80% and 95% respectively;

[0031] 2) The sodium ion battery of the present invention has excellent low temperature cycle performance: at temperatures of -20°C and -40°C, it maintains 90% and 60% of the room temperature capacity, respectively, and is charged and discharged for 600 cycles at 0.3C / 0.3C. The sodium ion battery using sodium nickel iron manganese oxide ternary material or polyanion positive electrode material (Na 3 V 2 (PO 4 ) 3 Or Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 ), maintaining capacity retention rates of over 80% and 95% respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Fourier transform infrared spectrum curves of different electrolytes;

[0033] Figure 2 LSV curves of different electrolytes;

[0034] Figure 3 The SEM images of the positive and negative electrodes of batteries with different electrolytes after 100 cycles at low temperature;

[0035] Figure 4 The conductivity and viscosity of the electrolyte change at different temperatures. DETAILED DESCRIPTION

[0036] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0037] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0038] Example 1

[0039] The present embodiment provides a sodium ion battery electrolyte, the electrolyte comprising a sodium salt, an organic ether solvent and an additive, the sodium salt being sodium tetrafluoroborate (with a concentration of 1 mol / L), the solvent being diethylene glycol dimethyl ether, and the additive being lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0040] The above electrolyte is used to prepare a sodium ion battery, wherein the positive electrode active material is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O 2 The negative electrode is hard carbon, the separator is a composite separator of polyethylene and polypropylene, and the preparation method of the battery is as follows:

[0041] (1) Preparation of positive electrode

[0042] Polyvinylidene fluoride (PVDF) was added to N-methyl-pyrrolidone (NMP) to prepare a solution with a mass fraction of 4 wt%. The positive electrode material was Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O 2 , conductive carbon black (SP), and polyvinylidene fluoride (PVDF) are fully stirred and mixed in a mass ratio of 90:5:5, coated on Al foil, dried, compacted and cut into pieces to obtain a positive electrode sheet.

[0043] (2) Negative electrode preparation

[0044] The negative electrode material is prepared by fully stirring and mixing hard carbon, conductive carbon black (SP) and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, coating the mixture on Al foil, drying, compacting and cutting the mixture into pieces to obtain a negative electrode sheet.

[0045] (3) Preparation of electrolyte

[0046] According to the above-mentioned electrolyte of this embodiment, sodium salt, organic ether solvent and additive are prepared. In an argon atmosphere glove box with a water content of <10ppm, the fully dried sodium salt is dissolved in the organic ether solvent, and then the additive is added to the organic ether solvent and mixed evenly to obtain an electrolyte.

[0047] (4) Preparation of batteries

[0048] The positive electrode sheet, the separator, the negative electrode sheet and the separator are placed in order, the separator is placed between the positive and negative electrode sheets to play a role of isolation, and they are wound to obtain a bare battery cell; the bare battery cell is packaged in an aluminum-plastic film packaging bag, the above-prepared electrolyte is injected into the battery after drying and dehydration, and the packaging, standing, formation, shaping and other processes are performed to obtain a battery.

[0049] Example 2

[0050] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.8 mol / L) and sodium hexafluorophosphate (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0051] The above electrolyte is used to prepare a sodium ion battery, wherein the positive electrode active material is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O 2 The preparation method of the battery is the same as that of Example 1.

[0052] Example 3

[0053] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.8 mol / L) and sodium bis(fluorosulfonyl)imide (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0054] The above electrolyte is used to prepare a sodium ion battery, wherein the positive electrode active material is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O 2 The preparation method of the battery is the same as that of Example 1.

[0055] Example 4

[0056] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.8 mol / L) and sodium bis(trifluoromethylsulfonyl)imide (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0057] The above electrolyte is used to prepare a sodium ion battery, wherein the positive electrode active material is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O 2 The preparation method of the battery is the same as that of Example 1.

[0058] Example 5

[0059] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.8 mol / L) and sodium trifluoromethanesulfonate (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0060] The above electrolyte is used to prepare a sodium ion battery, wherein the positive electrode active material is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O 2 The preparation method of the battery is the same as that of Example 1.

[0061] Example 6

[0062] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.8 mol / L) and sodium perchlorate (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0063] The above electrolyte is used to prepare a sodium ion battery, wherein the positive electrode active material is Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O 2 The preparation method of the battery is the same as that of Example 1.

[0064] Example 7

[0065] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.8 mol / L) and sodium hexafluorophosphate (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0066] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0067] Example 8

[0068] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium hexafluorophosphate (with a concentration of 0.8 mol / L) and sodium difluorooxalate borate (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0069] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0070] Example 9

[0071] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium bis(fluorosulfonyl)imide (with a concentration of 0.8 mol / L) and sodium difluorooxalate borate (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0072] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0073] Example 10

[0074] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium bis(trifluoromethylsulfonyl)imide (with a concentration of 0.8 mol / L) and sodium difluorooxalatoborate (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0075] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0076] Embodiment 11

[0077] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium trifluoromethanesulfonate (with a concentration of 0.8 mol / L) and sodium difluorooxalate borate (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0078] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0079] Example 12

[0080] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium trifluoromethanesulfonate (with a concentration of 0.8 mol / L) and sodium difluorooxalate borate (with a concentration of 0.2 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0081] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0082] Example 13

[0083] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.5 mol / L) and sodium hexafluorophosphate (with a concentration of 0.5 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 1:1), and the additive is lithium difluorooxalatoborate with a mass percentage of 1.5%.

[0084] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0085] Embodiment 14

[0086] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (concentration is 0.5 mol / L) and sodium hexafluorophosphate (concentration is 0.5 mol / L), the solvent is triethylene glycol dimethyl ether and tetrahydrofuran (volume ratio is 2:8), and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0087] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0088] Embodiment 15

[0089] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (concentration is 0.5 mol / L) and sodium hexafluorophosphate (concentration is 0.5 mol / L), the solvent is tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether and tetrahydrofuran (volume ratio is 1:1:8), and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0090] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0091] Example 16

[0092] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.3 mol / L) and sodium hexafluorophosphate (with a concentration of 0.7 mol / L), the solvent is diethylene glycol dimethyl ether and 1,3-dioxolane (with a volume ratio of 9:1), and the additive is lithium difluorooxalatoborate with a mass percentage of 1.5%.

[0093] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0094] Embodiment 17

[0095] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.5 mol / L) and sodium hexafluorophosphate (with a concentration of 0.5 mol / L), the solvent is diethylene glycol diethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0096] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0097] Embodiment 18

[0098] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.5 mol / L) and sodium hexafluorophosphate (with a concentration of 0.5 mol / L), the solvent is tetrahydrofuran, and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0099] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0100] Embodiment 19

[0101] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.5 mol / L) and sodium hexafluorophosphate (with a concentration of 0.5 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 1:1), and the additive is lithium difluorooxalatoborate with a mass percentage of 1.5%.

[0102] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0103] Embodiment 20

[0104] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (concentration is 0.5 mol / L) and sodium hexafluorophosphate (concentration is 0.5 mol / L), the solvent is ethylene glycol dimethyl ether and 1,3-dioxolane (volume ratio is 9:1), and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0105] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0106] Embodiment 21

[0107] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is ethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0108] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0109] Embodiment 22

[0110] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (concentration is 0.7 mol / L) and sodium hexafluorophosphate (concentration is 0.3 mol / L), the solvent is triethylene glycol dimethyl ether, diethanol dimethyl ether and tetrahydrofuran (volume ratio is 1:1:8), and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0111] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0112] Embodiment 23

[0113] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (concentration is 0.7 mol / L) and sodium hexafluorophosphate (concentration is 0.3 mol / L), the solvent is tetraethylene glycol dimethyl ether, diethanol dimethyl ether and tetrahydrofuran (volume ratio is 1:1:8), and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0114] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0115] Embodiment 24

[0116] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is 1,3-dioxolane, diethanol dimethyl ether and tetrahydrofuran (with a volume ratio of 1:1:8), and the additive is lithium difluorooxalatoborate with a mass percentage of 1.5%.

[0117] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0118] Embodiment 25

[0119] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is diethylene glycol diethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0120] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0121] Embodiment 26

[0122] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.3 mol / L) and sodium hexafluorophosphate (with a concentration of 0.7 mol / L), the solvent is tetrahydrofuran, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0123] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0124] Embodiment 27

[0125] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 2:8), and the additive is lithium difluorooxalatoborate with a mass percentage of 1.5%.

[0126] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0127] Embodiment 28

[0128] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 1 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalate borate, with a mass percentage of 1.5%.

[0129] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0130] Embodiment 29

[0131] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 2:8), and the additive is lithium hexafluorophosphate with a mass percentage of 1.5%.

[0132] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0133] Embodiment 30

[0134] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 2:8), and the additive is lithium tetrafluoroborate with a mass percentage of 1.5%.

[0135] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0136] Embodiment 31

[0137] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 2:8), and the additive is lithium bis(oxalatoborate) with a mass percentage of 1.5%.

[0138] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0139] Embodiment 32

[0140] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 2:8), and the additive is lithium difluorophosphate with a mass percentage of 1.5%.

[0141] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0142] Embodiment 33

[0143] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (concentration is 0.7 mol / L) and sodium hexafluorophosphate (concentration is 0.3 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (volume ratio is 2:8), and the additive is lithium difluorophosphate and lithium difluorooxalatoborate, with mass percentages of 1% and 0.5% respectively.

[0144] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0145] Embodiment 34

[0146] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 2:8), and the additive is lithium bis(trifluoromethylsulfonyl)imide with a mass percentage of 1.5%.

[0147] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0148] Embodiment 35

[0149] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 2:8), and the additive is lithium bis(fluorosulfonyl)imide with a mass percentage of 1.5%.

[0150] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0151] Embodiment 36

[0152] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.7 mol / L) and sodium hexafluorophosphate (with a concentration of 0.3 mol / L), the solvent is ethylene glycol dimethyl ether and tetrahydrofuran (with a volume ratio of 2:8), and the additive is lithium hexafluorophosphate and lithium difluorooxalatoborate, with a mass percentage of 1% and 0.5% respectively.

[0153] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0154] Embodiment 37

[0155] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.3 mol / L) and sodium hexafluorophosphate (with a concentration of 0.7 mol / L), the solvent is tetrahydrofuran, and the additive is aluminum trifluoromethanesulfonate, with a mass percentage of 1.5%.

[0156] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0157] Embodiment 38

[0158] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.3 mol / L) and sodium hexafluorophosphate (with a concentration of 0.7 mol / L), the solvent is tetrahydrofuran, and the additive is aluminum chloride with a mass percentage of 1.5%.

[0159] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0160] Embodiment 39

[0161] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.3 mol / L) and sodium hexafluorophosphate (with a concentration of 0.7 mol / L), the solvent is tetrahydrofuran, and the additive is magnesium chloride with a mass percentage of 1.0%.

[0162] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0163] Embodiment 40

[0164] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.3 mol / L) and sodium hexafluorophosphate (with a concentration of 0.7 mol / L), the solvent is tetrahydrofuran, and the additive is magnesium trifluoromethanesulfonate, with a mass percentage of 1.5%.

[0165] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0166] Embodiment 41

[0167] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.3 mol / L) and sodium hexafluorophosphate (with a concentration of 0.7 mol / L), the solvent is tetrahydrofuran, and the additive is magnesium perchlorate with a mass percentage of 1.5%.

[0168] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0169] Embodiment 42

[0170] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.3 mol / L) and sodium hexafluorophosphate (with a concentration of 0.7 mol / L), the solvent is tetrahydrofuran, and the additive is magnesium borohydride with a mass percentage of 1.5%.

[0171] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0172] Embodiment 43

[0173] The present embodiment provides a sodium ion battery electrolyte, comprising a sodium salt, an organic ether solvent and an additive, wherein the sodium salt is sodium tetrafluoroborate (with a concentration of 0.3 mol / L) and sodium hexafluorophosphate (with a concentration of 0.7 mol / L), the solvent is tetrahydrofuran, and the additive is magnesium bis(trifluoromethylsulfonyl)imide, with a mass percentage of 1.5%.

[0174] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that in Example 1. The positive electrode active material in the sodium ion battery provided in this example was Na 3 V 2 (PO 4 ) 3 .

[0175] Comparative Example 1

[0176] Preparation of electrolyte: the sodium salt is sodium hexafluorophosphate (concentration is 1 mol / L), the solvent is a PC (propylene carbonate) / EMC (ethyl methyl carbonate) mixed solvent (volume ratio is 1:1), and the mass fraction of the additive FEC (fluoroethylene carbonate) is 2 wt%.

[0177] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that of Example 1. The positive electrode active material in the sodium ion battery provided in this comparative example was Na 3 V 2 (PO 4 ) 3 .

[0178] Comparative Example 2

[0179] Preparation of electrolyte: the sodium salt is sodium hexafluorophosphate (concentration is 1 mol / L), the solvent is a PC (propylene carbonate) / DMC (dimethyl carbonate) mixed solvent (volume ratio is 1:1), and the mass fraction of the additive FEC (fluoroethylene carbonate) is 2 wt%.

[0180] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that of Example 1. The positive electrode active material in the sodium ion battery provided in this comparative example was Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O 2 .

[0181] Comparative Example 3

[0182] Preparation of electrolyte: the sodium salt is sodium hexafluorophosphate (concentration is 1 mol / L), the solvent is EC (ethylene carbonate) / EMC (ethyl methyl carbonate) mixed solvent (volume ratio is 1:1), and the mass fraction of the additive FEC (fluoroethylene carbonate) is 2 wt%.

[0183] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that of Example 1. The positive electrode active material in the sodium ion battery provided in this comparative example was Na 4 / 3 Fe 3 / 2 (PO 4 ) 2 / 1 P 2 O 7 .

[0184] Comparative Example 4

[0185] Preparation of electrolyte: The sodium salt is sodium tetrafluoroborate (concentration is 0.5 mol / L), and the solvent is diethylene glycol dimethyl ether.

[0186] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that of Example 1. The positive electrode active material in the sodium ion battery provided in this comparative example was Na 3 V 2 (PO4) 3 .

[0187] Comparative Example 5

[0188] Preparation of electrolyte: the sodium salt is sodium tetrafluoroborate (concentration is 0.5 mol / L), the solvent is diethylene glycol dimethyl ether, and the additive is lithium difluorooxalatoborate, with a mass percentage of 1.5%.

[0189] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that of Example 1. The positive electrode active material in the sodium ion battery provided in this comparative example was Na 3 V 2 (PO4) 3 .

[0190] Comparative Example 6

[0191] Preparation of electrolyte: The sodium salt is sodium tetrafluoroborate (concentration is 1 mol / L), and the solvent is diethylene glycol dimethyl ether.

[0192] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that of Example 1. The positive electrode active material in the sodium ion battery provided in this comparative example was Na 3 V 2 (PO4) 3 .

[0193] Comparative Example 7

[0194] Preparation of electrolyte: Sodium salts are sodium tetrafluoroborate (concentration is 0.3 mol / L) and sodium hexafluorophosphate (concentration is 0.7 mol / L), and the solvent is tetrahydrofuran, with a mass percentage of 1.5%.

[0195] The above electrolyte was used to prepare a sodium ion battery. The preparation method of the battery was the same as that of Example 1. The positive electrode active material in the sodium ion battery provided in this comparative example was Na 3 V 2 (PO 4 ) 3 .

[0196] Test Example 1

[0197] A. Electrolyte characterization and performance testing:

[0198] Take the electrolytes prepared in Example 1 and Comparative Examples 4-6, where the electrolytes of Comparative Examples 4, 5 and 6 are respectively recorded as 0.5M-BG2, 0.5M-BG2-LB and 1M-BG2, and the electrolyte in Example 1 is recorded as 1M-BG2-LB. The above four electrolytes are respectively tested as follows:

[0199] 1) Figure 1 The Fourier transform infrared spectra of the four electrolytes are shown in Figure 1. The infrared spectra show the COC peak (1050-1100 cm -1 ) has a significant blue shift, which proves that the complexing ability of non-sodium metal ions (such as lithium metal ions) in the additive with the solvent is stronger than that of sodium ions. The order of binding energy between different ions and solvents is: Al 3+ >Mg 2+ >Li + >Na +Therefore, when magnesium metal ion or aluminum metal ion salt is used, the coordination between non-sodium metal ion and solvent will be further strengthened.

[0200] 2) Figure 2 is the LSV curve of electrolyte 1M-BG2 and 1M-BG2-LB; Figure 2 It can be seen that non-sodium metal ions with strong binding energy (such as lithium, magnesium, and aluminum metal ions) coordinate with ether solvents, and the HOMO energy level of the ether solvents in the electrolyte is reduced. At the same time, since anions such as DFOB- are passivated on the cathode surface, the oxidation of ether solvents at the positive electrode can be avoided, thereby improving the electrochemical window of the ether electrolyte system.

[0201] B. Conductivity and viscosity test of electrolyte:

[0202] The electrolytes prepared in Example 1 and Comparative Examples 4-6 were tested for conductivity and viscosity at 25°C, 5°C and -20°C, respectively. The results were as follows: Figure 4 As shown in the left and right figures in Figure 4 As can be seen from the right figure, the ether solvent used has better low-temperature fluidity and good sodium removal / sodium insertion kinetics at low temperatures, thus achieving excellent low-temperature performance; Figure 4 As can be seen from the left figure, adding additives containing lithium, magnesium or aluminum metal ions can enhance the conductivity of the electrolyte system, reduce the initial charge transfer impedance and SEI impedance, and improve the kinetic characteristics of the interfacial reaction.

[0203] C. Battery performance test

[0204] The batteries prepared in Example 28 and Comparative Example 6 were subjected to 100 cycles of low-temperature cycling at -20°C and 0.3C, and then the positive and negative electrodes of the batteries were disassembled and low-temperature cycling performance tests were performed respectively. The specific results are as follows:

[0205] 1) Figure 3 The SEM images of the positive and negative electrodes of batteries with different electrolytes after 100 cycles at low temperature. Figure 3 It can be seen that the anions in the additive form a stable and dense solid electrolyte phase interface between the positive and negative electrodes, which can inhibit the dissolution of the positive electrode transition metal and prevent the structural damage of the positive electrode material.

[0206] 2) During the charging process, the non-sodium metal ions in the additives (such as lithium metal ions, magnesium metal ions, and aluminum metal ions) can form an electrostatic shielding effect on the surface of the negative electrode, thereby making the sodium ions deposit evenly and avoiding the formation of dendrites, such as Figure 3 shown.

[0207] The SEM images of the positive and negative electrodes of the batteries of other embodiments after 100 cycles of low-temperature cycling are basically the same as those of Example 28.

[0208] Test Example 2

[0209] The batteries prepared in Examples 1-43 and Comparative Examples 1-7 were tested as follows:

[0210] (1) Cycle performance test: At 25° C., the sodium ion batteries in Examples 1-43 and Comparative Examples 1-7 were charged to 4 V at a constant current of 0.1 C, then discharged to 2.0 V at a constant current of 0.1 C, and charged / discharged twice. Then, they were charged to 4 V at a constant current of 1 C, and then discharged to 2.0 V at a constant current of 1 C, and charged / discharged 600 times. The capacity retention rate was calculated.

[0211] The calculation formula of the capacity retention rate is as follows: capacity retention rate = discharge capacity of the corresponding cycle / discharge capacity of the first cycle×100%. The results are shown in Table 1.

[0212] (2) Low temperature cycle performance test: At 25°C, the sodium ion batteries in Examples 1-43 and Comparative Examples 1-7 were charged to 4V at a constant current of 0.1C, and then discharged to 2.0V at a constant current of 0.1C. After charging / discharging twice, they were left to stand at 0°C and -20°C for 12 hours, and then charged to 4V at a constant current of 0.3C, and then discharged to 2.0V at a constant current of 0.3C. This was repeated for 600 times. The capacity retention rate was calculated.

[0213] The calculation formula of the low-temperature discharge capacity retention rate is: low-temperature discharge capacity retention rate = discharge capacity of the corresponding cycle / 25°C discharge capacity × 100%. The results are shown in Table 1.

[0214] Table 1

[0215]

[0216]

[0217] According to the test results of Examples 1-7, when lithium salt is added to the electrolyte as an additive and different sodium salts and sodium tetrafluoroborate are used in combination as the sodium salt, the battery with NFM as the ternary positive electrode material has a capacity retention rate of greater than 85% at -20°C (compared with the capacity retention rate at room temperature), and a capacity retention rate of greater than 80% after 600 cycles at room temperature and -20°C. The capacity retention rate of the commonly used carbonate electrolyte (Comparative Example 2) is less than 80% at -20°C, 80.5% after 600 cycles at room temperature, and less than 20% after 600 cycles at -20°C, which is much lower than the capacity retention rate of the above-mentioned embodiments.

[0218] According to the test results of Examples 8-12, when lithium salt is added as an additive to the electrolyte and different sodium salts and sodium difluorooxalate borate are used as sodium salts, the capacity retention rate of the battery with NFPP as the positive electrode material at -20°C is about 90% (compared with the capacity retention rate at room temperature), and the capacity retention rate is greater than 98% after 600 cycles at room temperature and -20°C. The capacity retention rate of the commonly used carbonate electrolyte (Comparative Example 3) at -20°C is 70.8% (compared with the capacity retention rate at room temperature), and the capacity retention rate after 600 cycles at room temperature is 96.5%, which is close to the embodiment (98% to 99.2%), but the capacity retention rate after 600 cycles at -20°C is only 12.6%, which is much lower than the capacity retention rate of the above embodiment. .

[0219] According to the test results of Examples 13-28, when lithium salt is added as an additive to the electrolyte, and sodium tetrafluoroborate or a combination thereof with sodium hexafluorophosphate is used as the sodium salt, and different ether solvents or a combination of ether solvents are used as the solvent, the battery with NFPP or NVP as the positive electrode material has a capacity retention rate of about 90% at -20°C (compared with the capacity retention rate at room temperature), and the capacity retention rate is greater than 95% after 600 cycles at room temperature and -20°C. The capacity retention rate of the commonly used carbonate electrolyte (Comparative Example 1) at -20°C is 80.6% (compared with the capacity retention rate at room temperature), and the capacity retention rate after 600 cycles at -20°C is 21.5%, which is much lower than the capacity retention rate of the above examples. According to the test results of Comparative Examples 4 to 6, the cycle retention rates at room temperature and -20°C in the low-concentration sodium salt and LiDFOB-free electrolytes are lower than those in Example 28, which confirms that the LiDFOB additive can improve the battery cycle stability and enhance the low-temperature performance.

[0220] According to the test results of Examples 29-36, a combination of sodium tetrafluoroborate and sodium hexafluorophosphate is used as sodium salt in the electrolyte, and ethylene glycol dimethyl ether and tetrahydrofuran are used as solvents. When different lithium salts are used as additives, the battery with NVP as the positive electrode material has a capacity retention rate of about 90% at -20°C (compared with the capacity retention rate at room temperature), and the capacity retention rate is greater than 95% after 600 cycles at room temperature and -20°C, which verifies the effectiveness of different lithium salt additives.

[0221] According to the test results of Examples 37-43, a combination of sodium tetrafluoroborate and sodium hexafluorophosphate is used as the sodium salt in the electrolyte. When aluminum salt or magnesium salt is used as an additive, the capacity retention rate of the battery with NVP as the positive electrode material is about 90% at -20°C, and the capacity retention rate is greater than 95% after 600 cycles at room temperature and -20°C, which verifies the effectiveness of aluminum salt or magnesium salt as an additive.

[0222] In summary, the sodium ion electrolyte provided by the present invention can enable the sodium ion battery to have good capacity retention and cycle performance at room temperature and low temperature.

[0223] The above is a description of the exemplary embodiments of the present invention. However, the protection scope of the present application is not limited to the above embodiments. Any modification, equivalent substitution, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electrolyte, It is characterized in that The electrolyte comprises sodium salt, organic solvent and additive; the organic solvent is an ether solvent; the additive is selected from non-sodium metal salts; The non-sodium metal salt is selected from at least one of a first additive, a second additive or a third additive; wherein the first additive is a lithium metal salt; the second additive is a magnesium metal salt; and the third additive is an aluminum metal salt.

2. The electrolyte according to claim 1, It is characterized in that The sodium salt is NaPF 6 、NaClO 4 , NaBF 4 、NaAsF 6 、NaSiF 6 、NaBOB、NaODFB、NaCF 3 SO 3 、Na(CF 3 SO 2 ) 3 、Na(CF 3 CO 2 ) 2 N、Na(CF 3 SO 2 ) 2 N、Na(SO 2 C 2 F 5 ) 2 N and Na(SO 3 CF 3 ) 2 At least one of N. Preferably, in the electrolyte, the concentration of the sodium salt is 0.4-2 mol / L.

3. The electrolyte according to claim 1 or 2, It is characterized in that The ether solvent is selected from at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, tetrahydrofuran, dioxolane, and γ-butyrolactone.

4. The electrolyte according to any one of claims 1 to 3, It is characterized in that The content of the additive accounts for 0.01-3% of the total mass of the electrolyte.

5. The electrolyte according to any one of claims 1 to 4, It is characterized in that When the additive is selected from the first additive, the content of the first additive accounts for 0.01-3% of the total mass of the electrolyte. Preferably, when the additive is selected from the second additive, the content of the second additive is 0.01 to 3% of the mass of the electrolyte. Preferably, when the additive is selected from the third additive, the content of the third additive is 0.01-2% of the mass of the electrolyte.

6. The electrolyte according to any one of claims 1 to 5, It is characterized in that The lithium metal salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

7. The electrolyte according to any one of claims 1 to 6, It is characterized in that The magnesium metal salt is selected from at least one of magnesium bis(trifluoromethylsulfonyl)imide, magnesium borohydride, magnesium perchlorate, magnesium trifluoromethanesulfonate and magnesium chloride.

8. The electrolyte according to any one of claims 1 to 7, It is characterized in that The aluminum metal salt is selected from at least one of aluminum trifluoromethanesulfonate and aluminum chloride.

9. Use of the electrolyte according to any one of claims 1 to 8 in energy storage batteries.

10. A sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator; the separator is arranged between the positive electrode sheet and the negative electrode sheet; the electrolyte is selected from the electrolyte described in any one of claims 1 to 8.

Images