Electrolyte material of sodium ion battery and preparation method and application thereof

Abstract

The application belongs to the technical field of electrolyte materials, and particularly relates to an electrolyte material of a sodium ion battery and a preparation method and application thereof. The electrolyte material comprises a sodium salt and a film-forming additive; the film-forming additive comprises A and B; the structural formulae of A and B are respectively: A and B with specific structures are used as the film-forming additive to be added into the electrolyte material, and the two are used in combination, so that a stable SEI film can be formed, and the film can be formed on the surface of the positive electrode material, thereby being beneficial to the migration of sodium ions at the positive electrode interface, effectively reducing the oxidation activity of the positive electrode material to the electrolyte material, inhibiting the reduction reaction of transition metals, thereby inhibiting the dissolution of metal ions and the deposition of the metal ions at the negative electrode, improving the high-temperature cycle performance and high-temperature storage performance of the sodium ion battery, and improving the first-cycle coulomb efficiency and the room-temperature cycle performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrolyte materials, and particularly relates to an electrolyte material for a sodium ion battery and a preparation method and application thereof. BACKGROUND

[0002] With the advent of the electric era, lithium batteries are widely used in many fields such as 3C, but as the demand for lithium batteries grows rapidly, the supply of lithium resources has become increasingly tight. Therefore, sodium ion batteries with similar working principles as lithium ion batteries have attracted much attention.

[0003] Sodium is abundant, accounting for about 2.64% of the earth's element reserves, widely distributed, and has a significant price advantage, so sodium ion batteries have the potential for large-scale application. Sodium ion batteries usually use a positive electrode (such as sodium transition metal oxide) and a negative electrode (such as hard carbon), and a non-aqueous organic electrolyte material is used to transport sodium ions between the positive and negative electrodes to charge and discharge. Sodium ion monomers based on sodium ion conduction have high energy density, are non-toxic and recyclable, and have greater competitive advantage than lithium ion batteries.

[0004] In addition, with the deepening of the subject of energy storage, sodium ion batteries have become an important part of energy storage systems. Although they have high energy density and low cost, they have problems such as capacity decay and cycle efficiency decline in long-term cycling, which is due to the difficulty of traditional non-aqueous liquid electrolytes and solid-state electrolytes to build a good SEI or CEI film. In order to obtain an electrolyte material with good performance such as high stability, high ionic conductivity and good wettability, the use of electrolyte additives is considered to be the most feasible, economical and effective method to improve the comprehensive performance of electrolytes. Among the three components of sodium battery electrolyte materials: sodium salt and solvent formula change less, but the composition and content of additives are the key to the performance of electrolyte materials, and additives have the characteristics of small amount and outstanding performance improvement. After injection into the battery, it is easily affected by the environment temperature, and the existing additives have poor high-temperature performance and cycle performance in sodium batteries.

[0005] Therefore, it is urgent to provide an electrolyte material which can form a stable SEI film, inhibit the precipitation of transition metal elements, thereby inhibiting the dissolution of metal ions and the deposition of the negative electrode, so that the prepared sodium ion battery has good high-temperature cycle performance, high-temperature storage performance, room-temperature cycle performance and first-cycle coulombic efficiency. SUMMARY

[0006] The present application aims to solve one or more technical problems existing in the prior art described above, and at least provide a beneficial alternative or create conditions. Specifically, the present application provides an electrolyte material of a sodium ion battery, which can form a stable SEI film, inhibit the precipitation of transition metal elements, so that the prepared sodium ion battery has good high-temperature cycle performance, high-temperature storage performance, room-temperature cycle performance and first-cycle coulombic efficiency.

[0007] The inventive concept of the present application: the electrolyte material of the present application comprises a sodium salt and a film-forming additive; the film-forming additive comprises A and B, and A and B have specific structural formulas. The film-forming additive with the specific structure of the present application has more active double bonds, triple bonds and halogen atoms, so that it is preferentially oxidized and reduced to form a film on the surface of the material compared with the solvent, which ensures the stability of the negative electrode SEI film while also having the effect of reducing the internal resistance of the battery. At the same time, the film-forming additive composed of nitrile compounds can form a film on the surface of the positive electrode material of the battery, which is conducive to the migration of sodium ions at the positive electrode interface, can effectively reduce the oxidation activity of the positive electrode material to the electrolyte material, inhibit the reduction reaction of transition metals and the dissolution and deposition at the negative electrode, thereby greatly improving the high-temperature performance of the sodium ion battery. The battery containing the additive has good capacity retention rate and capacity recovery rate under high-temperature conditions, and can greatly inhibit gas production, so that the prepared sodium ion battery has good high-temperature cycle performance, high-temperature storage performance, room-temperature cycle performance and first-cycle coulombic efficiency.

[0008] Therefore, the first aspect of the present application provides an electrolyte material of a sodium ion battery.

[0009] Specifically, the electrolyte material of the sodium ion battery comprises a sodium salt and a film-forming additive; the film-forming additive comprises A and B; the structural formulas of A and B are respectively:

[0010]

[0011] Preferably, the molar ratio of A to B is (0.9-3.3):(0.9-3.3).

[0012] Further preferably, the molar ratio of A to B is (1-3):(1-3).

[0013] Preferably, the electrolyte material further comprises a solvent, and the electrolyte material comprises 10-14% of the sodium salt, 0.1-4.5% of the film-forming additive, and 81.5-89.9% of the solvent by mass percentage.

[0014] Further preferably, the electrolyte material comprises 11-13.5% of the sodium salt, 0.1-4.0% of the film-forming additive, and 82.5-88.9% of the solvent by mass percentage.

[0015] Further preferably, the mass percentage of the sodium salt in the electrolyte material is 12.5%.

[0016] Further preferably, the mass percentage of the solvent in the electrolyte material is 75-85%.

[0017] Preferably, the sodium salt comprises at least one of NaPF6, NaClO4, NaAlCl4, NaSO3CF3, NaBF4, NaBCl4, NaNO3, NaPOF4, NaSCN, NaCN, NaAsF6, NaCF3CO2, NaSbF6, NaC6H5CO2, Na(CH3)C6H4SO3, NaHSO4, and NaB(C6H5)4.

[0018] Preferably, the sodium salt comprises NaPF6.

[0019] Preferably, the solvent comprises at least one of vinyl carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE).

[0020] Further preferably, the solvent comprises vinyl carbonate, ethyl methyl carbonate, and diethyl carbonate, or the solvent comprises fluoroethylene carbonate, vinyl carbonate, and dimethyl carbonate.

[0021] Preferably, when the solvent comprises vinyl carbonate, ethyl methyl carbonate, and diethyl carbonate, the mass ratio of the vinyl carbonate, ethyl methyl carbonate, and diethyl carbonate is 1:(0.9-3.3):(0.9-3.3); further preferably, the mass ratio of the vinyl carbonate, ethyl methyl carbonate, and diethyl carbonate is 1:(1-3):(1-3); further preferably, the mass ratio of the vinyl carbonate, ethyl methyl carbonate, and diethyl carbonate is 1:1:1.

[0022] Preferably, when the solvent comprises fluoroethylene carbonate, vinyl carbonate and dimethyl carbonate, the mass ratio of the fluoroethylene carbonate, vinyl carbonate and dimethyl carbonate is 1 : (0.9-3.3) : (0.9-3.3); further preferably, the mass ratio of the fluoroethylene carbonate, vinyl carbonate and dimethyl carbonate is 1 : (1-3) : (1-3); more further preferably, the mass ratio of the fluoroethylene carbonate, vinyl carbonate and dimethyl carbonate is 1 : 1 : 1.

[0023] Specifically, the solvent is a non-aqueous solvent.

[0024] Preferably, the electrolyte material further comprises an auxiliary additive.

[0025] Preferably, the auxiliary additive comprises at least one of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, sodium bisfluorosulfonylimide (NaFSI).

[0026] Preferably, the electrolyte material comprises, by mass percentage, sodium salt 10-14%, film-forming additive 0.1-4.5%, solvent greater than or equal to 70.5% and less than 89.9%, auxiliary additive greater than 0% and less than or equal to 11%.

[0027] Further preferably, the electrolyte material comprises, by mass percentage, sodium salt 11-13.5%, film-forming additive 0.1-4.0%, solvent greater than or equal to 72.5% and less than 88.9%, auxiliary additive greater than 0% and less than or equal to 10%.

[0028] Preferably, when the auxiliary additive comprises vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone and NaFSI, the mass fraction of the vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone in the electrolyte material is greater than 0% and less than or equal to 2.2%, and the mass fraction of the NaFSI is greater than 0% and less than or equal to 4.4%.

[0029] Further preferably, when the auxiliary additive comprises vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone and NaFSI, the mass fraction of the vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone in the electrolyte material is greater than 0% and less than or equal to 2%, and the mass fraction of the NaFSI is greater than 0% and less than or equal to 4%.

[0030] More further preferably, when the auxiliary additive comprises vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone and NaFSI, the mass fraction of the vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone and NaFSI in the electrolyte material is 0.5%, 1%, 1% and 1.5%, respectively.

[0031] The second aspect of the present application provides a preparation method of the electrolyte material of the sodium-ion battery according to the first aspect of the present application.

[0032] Specifically, the preparation method of the electrolyte material of the sodium-ion battery comprises the following steps:

[0033] The raw material components are mixed to obtain the electrolyte material of the sodium-ion battery.

[0034] The third aspect of the present application provides a battery.

[0035] Specifically, the battery comprises a positive electrode, a negative electrode, a separator and the electrolyte material of the sodium-ion battery according to the first aspect of the present application.

[0036] Preferably, the battery is a sodium-ion battery.

[0037] Specifically, the active ions (sodium ions) are reversibly intercalated and deintercalated between the positive electrode and the negative electrode; the electrolyte material plays a role of ion conduction between the positive electrode and the negative electrode; the separator is arranged between the positive electrode and the negative electrode, mainly playing a role of preventing the short circuit of the positive electrode and the negative electrode, and at the same time allowing the ions to pass through.

[0038] Preferably, the molar concentration of the sodium ions in the electrolyte material in the sodium-ion battery is 0.45-2.2 mol / L.

[0039] Further preferably, the molar concentration of the sodium ions in the electrolyte material in the sodium-ion battery is 0.5-2 mol / L.

[0040] More preferably, the molar concentration of the sodium ions in the electrolyte material in the sodium-ion battery is 1 mol / L.

[0041] Preferably, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector.

[0042] Preferably, the positive electrode current collector comprises any one of a metal foil and a composite current collector; further preferably, the positive electrode current collector comprises a metal foil; more preferably, the positive electrode current collector is an aluminum foil.

[0043] Preferably, the composition of the positive electrode active material layer comprises an active material, a binder and a conductive agent.

[0044] Preferably, the active material comprises at least one of a layered metal oxide, a polyanion compound and Prussian blue; further preferably, the active material comprises a sodium transition metal oxide.

[0045] Preferably, the transition metal in the sodium transition metal oxide comprises at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, Ce.

[0046] Preferably, the sodium transition metal oxide comprises Na m M x (PO4) y .

[0047] Preferably, the M comprises at least one of Ti, V, Mn, Co, Ni, Fe, Cr, Cu.

[0048] Preferably, the m, x and y are respectively 0

[0049] Preferably, the active material comprises at least one of NaFePO4, NaCoPO4, Na3V2(PO4)3.

[0050] Preferably, the binder comprises at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylate resin.

[0051] Preferably, the conductive agent comprises at least one of superconducting carbon, acetylene black, carbon black, carbon dots, carbon nanotubes, graphene, carbon nanofibers.

[0052] Preferably, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector.

[0053] Preferably, the composition of the negative electrode active material layer comprises an active material, a conductive agent, a thickening agent, a binder.

[0054] Preferably, the active material comprises at least one of graphite, soft carbon, hard carbon, sodium titanate, and a metal that can form an alloy with sodium; further preferably, the active material comprises hard carbon.

[0055] Preferably, the negative electrode current collector comprises a copper foil.

[0056] Specifically, the material, shape of the separator is not particularly limited, as long as it does not significantly impair the effects of the present application, and a known separator can be arbitrarily used. Among them, a resin, glass fiber, inorganic matter, etc. formed of a stable material, a porous sheet or non-woven fabric-like material having excellent liquid retention, etc. can be used.

[0057] Preferably, the material of the diaphragm is selected from any one of polyethylene, polypropylene and other polyolefins, polytetrafluoroethylene, polyethersulfone, and glass filter; further preferably, the material of the diaphragm is selected from any one of polyolefins and glass filter; more preferably, the material of the diaphragm is polyolefin.

[0058] Specifically, in some embodiments of the present application, the material of the diaphragm is polyethylene.

[0059] Preferably, the thickness of the diaphragm is 1-45 μm; further preferably, the thickness of the diaphragm is 11-40 μm; more preferably, the thickness of the diaphragm is 10-30 μm; for example, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, and the like.

[0060] Specifically, the present application does not have special restrictions on the thickness of the diaphragm, which can be adjusted according to the actual situation.

[0061] Compared with the prior art, the technical scheme provided by the present application has the following beneficial effects:

[0062] (1) The electrolyte material of the present application includes sodium salt and film-forming additive; the film-forming additive includes A and B, and A and B have specific structural formula. The film-forming additive with specific structure of the present application has more active double bond, triple bond and halogen atom, so that it is preferentially oxidized and reduced on the surface of the material to form a film, which not only ensures the stability of the negative electrode SEI film, but also has the effect of reducing the internal resistance of the battery. At the same time, the film-forming additive composed of nitrile compounds can form a film on the surface of the positive electrode material, which is conducive to the migration of sodium ions at the positive electrode interface, can effectively reduce the oxidation activity of the positive electrode material to the electrolyte material, inhibit the reduction reaction of transition metal and the deposition at the negative electrode, thereby greatly improving the high-temperature performance of the sodium ion battery. The secondary battery containing the additive has good capacity retention rate and capacity recovery rate under high temperature conditions, and can greatly inhibit gas production.

[0063] (2) The auxiliary additive of the present application contains carbonate, which has high dielectric constant and low viscosity, and can further improve the rate performance of the sodium ion battery; or contains fluorine, because the fluorine atom has strong electronegativity, which can improve the oxidation resistance of the electrolyte and thus raise the upper limit of the electrochemical window of the electrolyte, and improve the high and low temperature performance.

[0064] (3) The preparation process of the present application is simple and easy for industrial application. DETAILED DESCRIPTION

[0065] In order to make the skilled in the art more clearly understand the technical scheme of the present application, the following examples are given for illustration. It should be pointed out that the following examples do not constitute a limitation on the scope of protection required by the present application.

[0066] The raw materials, reagents or devices used in the following examples, unless otherwise specified, can be obtained by conventional commercial channels, or can be obtained by existing known methods.

[0067] Example 1

[0068] A sodium ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte material; the electrolyte material comprises sodium hexafluorophosphate 12.5% (1 mol / L), a film-forming additive 0.1% (the mass ratio of A and B is 1:1), a solvent 83.4% (EC, DEC and EMC are mixed in a weight ratio of 1:1:1), and an auxiliary additive 4% (0.5% VC, 1% FEC, 1% PS, 1.5% NaSIF); the structural formulas of A and B in the film-forming additive are as follows, respectively:

[0069]

[0070] A preparation method of a sodium ion battery, comprising the following steps:

[0071] Preparation of the positive electrode: Na3V2(PO4)2F3, acetylene black, adhesive PVDF and carbon nanotube (CNT) are mixed in a mass ratio of 95:2.2:2:0.8, N-methyl pyrrolidone (NMP) is added, and the mixture is stirred uniformly under the action of a vacuum stirrer to obtain a positive electrode slurry of the sodium ion battery. The positive electrode slurry is uniformly coated on an aluminum foil, dried in a blast oven at 120°C, and then cold-pressed and die-cut to obtain the positive electrode.

[0072] Preparation of the negative electrode: the negative electrode material active hard carbon, conductive agent SuperP, thickening agent sodium carboxymethyl cellulose, and adhesive styrene-butadiene rubber emulsion (SBR) are mixed in a mass ratio of 95.8:1.4:1.2:1.6, deionized water is added, and the mixture is mixed uniformly under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on a copper foil, dried in a blast oven at 120°C for 1 h, and then cold-pressed and die-cut to obtain the negative electrode.

[0073] Preparation of the electrolyte material: in an argon-filled glove box with a water content of <10 ppm, sodium hexafluorophosphate, a film-forming additive, a solvent, and an auxiliary additive are mixed uniformly to obtain the electrolyte material.

[0074] Preparation of sodium ion battery: the positive electrode sheet, polyethylene isolation film, negative electrode sheet are stacked in order, the isolation film is between the positive and negative electrodes to play the role of isolation, then the cell is wound, the pole lug is connected, and it is put into the aluminum plastic film shell, dried at 100°C, then the electrolyte material is injected and sealed, and the uncharged battery is obtained. The uncharged battery is sequentially subjected to standing for 5h, hot and cold pressing, and formation for 2h under the conditions of negative pressure 0.05MPa and temperature 45°C, vacuumizing, double sealing, and capacity distribution processes, and the sodium ion laminated battery is obtained.

[0075] Example 2

[0076] The difference between Example 2 and Example 1 is only that the mass fraction of the film-forming additive in the electrolyte material of Example 2 is 0.2%, and the mass fraction of the solvent is 83.3%, and the others are the same as Example 1.

[0077] Example 3

[0078] The difference between Example 3 and Example 1 is only that the mass fraction of the film-forming additive in the electrolyte material of Example 3 is 0.3%, and the mass fraction of the solvent is 83.2%, and the others are the same as Example 1.

[0079] Example 4

[0080] The difference between Example 4 and Example 1 is only that the mass fraction of the film-forming additive in the electrolyte material of Example 4 is 0.5%, and the mass fraction of the solvent is 83.0%, and the others are the same as Example 1.

[0081] Example 5

[0082] The difference between Example 5 and Example 1 is only that the mass fraction of the film-forming additive in the electrolyte material of Example 5 is 0.7%, and the mass fraction of the solvent is 82.8%, and the others are the same as Example 1.

[0083] Example 6

[0084] The difference between Example 6 and Example 1 is only that the mass fraction of the film-forming additive in the electrolyte material of Example 6 is 0.9%, and the mass fraction of the solvent is 82.6%, and the others are the same as Example 1.

[0085] Example 7

[0086] The difference between Example 7 and Example 1 is only that the mass fraction of the film-forming additive in the electrolyte material of Example 7 is 1.2%, and the mass fraction of the solvent is 82.3%, and the others are the same as Example 1.

[0087] Example 8

[0088] Example 8 and Example 1 differ only in that the mass fraction of the film-forming additive in the electrolyte material of Example 8 is 1.5%, and the mass fraction of the solvent is 82%, and the rest is the same as Example 1.

[0089] Example 9

[0090] Example 9 and Example 1 differ only in that the mass fraction of the film-forming additive in the electrolyte material of Example 9 is 2.0%, and the mass fraction of the solvent is 81.5%, and the rest is the same as Example 1.

[0091] Example 10

[0092] Example 10 and Example 1 differ only in that the mass fraction of the film-forming additive in the electrolyte material of Example 10 is 3.0%, and the mass fraction of the solvent is 80.5%, and the rest is the same as Example 1.

[0093] Example 11

[0094] Example 11 and Example 1 differ only in that the mass fraction of the film-forming additive in the electrolyte material of Example 11 is 1.0%, and the mass fraction of the solvent is 82.5%, and the mass ratio of the A substance and the B substance of the film-forming additive is 1:2, and the rest is the same as Example 1.

[0095] Example 12

[0096] Example 12 and Example 11 differ only in that the mass ratio of the A substance and the B substance of the film-forming additive in the electrolyte material of Example 12 is 1:3, and the rest is the same as Example 11.

[0097] Example 13

[0098] Example 13 and Example 11 differ only in that the mass ratio of the A substance and the B substance of the film-forming additive in the electrolyte material of Example 13 is 2:1, and the rest is the same as Example 11.

[0099] Example 14

[0100] Example 14 and Example 11 differ only in that the mass ratio of the A substance and the B substance of the film-forming additive in the electrolyte material of Example 14 is 3:1, and the rest is the same as Example 11.

[0101] Comparative Example 1

[0102] Comparative Example 1 and Example 11 differ only in that the same amount of A is used to replace B in the film-forming additive of the electrolyte material of Comparative Example 1, i.e. no B substance is contained, and the mass percentage of the A substance is 1%, and the rest is the same as Example 11.

[0103] Comparative Example 2

[0104] The difference between Comparative Example 2 and Example 11 is only that the film-forming additive of the electrolyte material of Comparative Example 2 is replaced by an equal amount of B instead of A, i.e. no A substance, and the mass percentage of B substance is 1%, and the rest is the same as Example 11.

[0105] Comparative Example 3

[0106] The difference between Comparative Example 3 and Example 11 is only that the electrolyte material of Comparative Example 3 does not contain a film-forming additive, and the mass percentage of the solvent is 83.5%, and the rest is the same as Example 11.

[0107] Performance test

[0108] The sodium ion batteries prepared in Examples 1-14 and Comparative Examples 1-3 are subjected to first cycle coulombic efficiency test, cycle capacity retention rate test, high temperature cycle performance test, and high temperature storage performance test, and the test methods of each test item are as follows:

[0109] First cycle coulombic efficiency test: the sodium ion batteries prepared in Examples 1-14 and Comparative Examples 1-3 are allowed to stand at 25°C for 12h to allow the electrolyte material to fully soak the positive and negative electrodes and the separator; then in a normal pressure environment, the sodium ion battery is charged at a rate of 0.1C to a voltage of 4.2V, and the record is C2; then discharged at 0.1C to 2V, and the discharge capacity is recorded as Cdischarge, and the charge capacity during formation is C1, C1+C2=Ccharge, and the first cycle coulombic efficiency=Ccharge / Cdischarge x 100%. 放电 充电

[0110] Among them, the charge capacity during formation is: in the formation process, the uncharged battery is charged at a rate of 0.05C to 30% state of charge (SOC), and the charge capacity at this time is recorded as the charge capacity during formation C1.

[0111] Cycle capacity retention rate test: at 25°C and normal pressure, the sodium ion batteries prepared in Examples 1-14 and Comparative Examples 1-3 are charged at a rate of 0.2C to 4.2V, further charged at a constant voltage of 4.1V to a cutoff current of 0.05C, and then discharged at a rate of 1C to 2.5V, and the obtained capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery, and the discharge capacity of the battery after the nth cycle is recorded as Cn. Then the capacity retention rate P of the battery after each cycle is calculated as follows: n n n = Cn / C0 x 100%, and in this test process, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and the 500th cycle corresponds to n=500.

[0112] ​​​​High temperature cycle performance test: the sodium ion battery prepared in examples 1-14, comparative examples 1-3 is charged at 45℃ with 1C constant current to 4.2V, further charged with 4.1V constant voltage to the cutoff current is 0.05C, then discharged with 1C constant current to 2.5V, this is a charge-discharge cycle, the discharge capacity of the first cycle, then according to the above conditions for 500 cycles, the capacity retention rate of sodium ion battery after 500 cycles (%) = (500th cycle discharge capacity / first discharge capacity) x 100%.

[0113] High temperature storage performance test: the sodium ion battery prepared in examples 1-14, comparative examples 1-3 is charged at room temperature with 1C constant current constant voltage to 4.2V, 0.05C cutoff, then 1C constant current discharge, 3.0V cutoff, the discharge capacity of this time is the initial capacity Co, then put into the high temperature test cabinet 60℃ storage for 21 days; the above sodium battery is placed at room temperature for 4h, then discharged with 1C constant current to 2.5V, record the discharge capacity C1, charge percentage = C1 / C0, capacity retention rate (%) = (C1 / C0) x 100%; the above sodium battery (battery after 60℃ storage for 21 days) is charged at room temperature with 1C constant current constant voltage to 4.2V, 0.05C cutoff, then 1C constant current discharge, 2.5V cutoff, record the recovery capacity C2; recovery percentage = C2 / C0, capacity recovery rate (%) = (C2 / C0) x 100%.

[0114] Each of the above test items is tested in parallel with 3 batteries and the average value is taken as the test result, the absolute deviation of the sodium battery test is within ±1%.

[0115] The performance test results of the sodium ion battery prepared in examples 1-14, comparative examples 1-3 are shown in table 1.

[0116] Table 1: performance test results of sodium ion battery of examples 1-14, comparative examples 1-3

[0117]

[0118] From table 1, it can be seen that the sodium ion battery prepared by the application has good first circle coulomb efficiency, room temperature cycle performance, high temperature cycle performance and high temperature storage performance.

[0119] From examples 1-10, it can be seen that: with the increase of the addition amount of film forming additives A and B, the 45℃ / 1C cycle capacity retention rate, 60℃ high temperature storage capacity retention rate and 60℃ high temperature storage capacity retention rate under 4.2V charge cutoff voltage show a trend of first increase and then decrease, and when the addition amount of A and B film forming additives is about 1.0%, the performance is best.

[0120] Compared with Example 11, Comparative Example 1 does not contain film-forming additive B, which results in lower first-cycle coulombic efficiency, room-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance. Compared with Example 11, Comparative Example 2 does not contain film-forming additive A, which results in lower first-cycle coulombic efficiency, room-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance. Compared with Example 11, Comparative Example 3 does not contain film-forming additives A and B, which results in significantly lower first-cycle coulombic efficiency, room-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance. It is shown that the sodium-ion battery can have significantly improved first-cycle coulombic efficiency, room-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance only when both A and B are used as film-forming additives.

[0121] In summary, the sodium-ion battery can have improved first-cycle coulombic efficiency, room-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance when A and B with specific structures are used as film-forming additives in the electrolyte material. This is attributed to the fact that film-forming additives A and B have more active double bonds, triple bonds and halogen atoms, which result in their preferential oxidation-reduction film formation on the material surface, ensuring the stability of the negative electrode SEI film and reducing the internal resistance of the battery. In addition, the nitrile compound-based additive can form a film on the surface of the positive electrode material, which is conducive to the migration of sodium ions at the positive electrode interface, effectively reducing the oxidation activity of the positive electrode material to the electrolyte material, inhibiting the reduction reaction of transition metals, and thus inhibiting the dissolution of metal ions and the deposition of metal ions at the negative electrode, greatly improving the high-temperature performance of the sodium-ion battery, and having good capacity retention rate and capacity recovery rate under high-temperature conditions, and can greatly inhibit gas production.

[0122] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application.

Claims

1. An electrolyte material, characterized by, The sodium salt, a film-forming additive; the film-forming additive comprises A and B; the structural formula of A and B is as follows respectively:

2. The electrolyte material of claim 1, wherein, The molar ratio of A and B is (0.9-3.3):(0.9-3.3).

3. The electrolyte material of claim 1, wherein, The electrolyte material further comprises a solvent, and the electrolyte material comprises the sodium salt 10-14%, the film-forming additive 0.1-4.5%, and the solvent 81.5-89.9% by mass percentage.

4. The electrolyte material of claim 1, wherein, The sodium salt comprises at least one of NaPF6, NaClO4, NaAlCl4, NaSO3CF3, NaBF4, NaBCl4, NaNO3, NaPOF4, NaSCN, NaCN, NaAsF6, NaCF3CO2, NaSbF6, NaC6H5CO2, Na(CH3)C6H4SO3, NaHSO4, and NaB(C6H5)4.

5. The electrolyte material of claim 3, wherein, The solvent comprises at least one of vinyl carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butanedisulfone, methyl ethyl sulfone, and diethyl sulfone.

6. The electrolyte material of claim 1, wherein, The electrolyte material further comprises an auxiliary additive.

7. The electrolyte material of claim 6, wherein, The auxiliary additive comprises at least one of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, and sodium bisfluorosulfonylimide.

8. Process for the production of the electrolyte material according to any one of claims 1 to 7, characterized in that The method comprises the following steps: Mixing each raw material component to prepare the electrolyte material.

9. A battery, characterized by The battery comprises a positive electrode, a negative electrode, a separator, and the electrolyte material according to any one of claims 1-7.

10. The battery of claim 9, wherein, The battery comprises a sodium ion battery.

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