Sodium ion battery and electrolyte thereof

Abstract

The application discloses a sodium ion battery and an electrolyte thereof. The electrolyte comprises a sodium salt, an organic solvent and a combined additive. The combined additive comprises an additive A and an additive B. The additive A is sodium silane borate and / or sodium silane phosphite. The additive B is a sulfur-containing compound. When the sodium ion battery containing the electrolyte is used, a stable and anti-swelling and anti-shrinking interface film can be preferentially formed at the interface between the positive and negative electrodes of the battery. In addition, the propylene carbonate solvent in the electrolyte can effectively improve the oxidation resistance of the electrolyte, thereby improving the initial efficiency of the sodium ion battery, improving the cycle life of the lithium ion battery, improving the high-temperature storage capacity recovery rate of the sodium ion battery, and inhibiting the gas production in the high-temperature storage process to a certain extent.

Description

Technical Field

[0001] This invention relates to a sodium-ion battery and its electrolyte, belonging to the field of sodium-ion battery technology. Background Technology

[0002] With the rapid development of society and the economy, energy and the environment have become increasingly important concerns. Lithium-ion batteries, as green and environmentally friendly energy storage devices, have been widely used in consumer electronics, energy storage, and electric vehicles due to their advantages such as high energy density, long cycle life, and low pollution. However, the shortage and rising price of lithium resources have severely constrained their development. Sodium, with similar physicochemical properties to lithium, is the sixth most abundant element in the Earth's crust, with evenly distributed resources and low prices, making it a promising candidate for widespread application in energy storage and low-speed electric vehicles. In the past decade, research on sodium-ion batteries, which have similar working mechanisms and battery structures to lithium-ion batteries, has made rapid progress.

[0003] Sodium-ion batteries, similar to lithium-ion batteries, mainly consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a current collector. During charging and discharging, energy is stored and released through the extraction and insertion of sodium ions between the positive and negative electrodes. Sodium-ion batteries have many advantages over lithium-ion batteries: ① Sodium is more abundant on Earth than lithium, resulting in lower costs; ② Sodium ions have a smaller Stokes diameter than lithium ions, leading to higher ionic conductivity in electrolytes of the same concentration and better fast-charging performance; ③ Better low-temperature performance, maintaining over 80% discharge retention even in sub-zero temperatures; ④ Better safety performance. However, due to the similar physicochemical properties of sodium ions to lithium ions, the similar working principle of sodium-ion batteries, and the seamless switching between the two battery manufacturing processes, sodium-ion batteries hold promise as a new type of battery for large-scale energy storage or power applications. With the industry's increasing focus on sodium-ion batteries, both the technology and applications of sodium-ion batteries have developed rapidly. They can also replace lead-acid batteries and are expected to develop rapidly in multiple fields such as low-speed electric vehicles, electric boats, home / industrial energy storage, 5G communication base stations, data centers, large-scale access to renewable energy, and smart grids. This will promote the development of clean energy technology applications in my country and enhance my country's competitiveness and influence in the field of energy storage technology.

[0004] Layered oxide materials are ideal cathode materials for sodium-ion batteries due to their high compaction density, high specific capacity, and high plateau voltage, and are currently the most widely researched and applied cathode materials in the industry. However, layered oxide materials are prone to phase transitions under high voltage and high temperature, resulting in particle breakage, oxygen release, and metal ion dissolution. At the same time, the cathode materials exhibit strong oxidizing properties, further aggravating side reactions with the electrolyte and the positive and negative electrode interfaces, thus deteriorating the initial efficiency, cycle life, and high-temperature storage life of sodium-ion batteries.

[0005] In view of the above problems, it is necessary to develop a sodium-ion battery and its electrolyte to improve the initial efficiency, cycle life and high-temperature storage life of sodium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a sodium-ion battery and its electrolyte to improve the first-efficiency, cycle life and high-temperature storage life of sodium-ion batteries.

[0007] In a first aspect, the present invention provides a sodium-ion battery electrolyte, comprising a sodium salt, an organic solvent, and a combination of additives, wherein the combination of additives includes additive A and additive B; additive A is sodium silaneborate and / or sodium silane phosphite, and additive B is a sulfur-containing compound; the structural formula of additive A is shown in Formula I or Formula II.

[0008]

[0009] Wherein, X and Y are phosphorus or boron, and R1 to R9 are each independently an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms substituted with halogen atoms, wherein the halogen atom is one of F, Cl, Br and I.

[0010] In conjunction with the first aspect, further, the additive B is any one or more combinations of the compounds represented by Formula III:

[0011]

[0012] Among them, R 10 ~R 13 Independently, it is any one of hydrogen atoms, halogen atoms, or alkyl groups having 1 to 4 carbon atoms, where A is an oxygen atom or a carbon atom, and R... 14 It is an alkyl or sulfonic acid group with 1 to 3 carbon atoms substituted by alkyl or halogen atoms, where a and b are independently 0 or 1.

[0013] In conjunction with the first aspect, the additive A is further comprising one or more of sodium bis(trimethylsilyl)phosphite, sodium bis(trimethylsilyl)borate, disodium trimethylsilyl phosphite, and disodium trimethylsilylborate.

[0014] In conjunction with the first aspect, further, the additive B is any one or more of 1,3-propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, fluorovinyl sulfate, vinyl sulfite, methylene disulfonate, and propylene sulfate.

[0015] In conjunction with the first aspect, further, the mass fraction of additive A in the electrolyte is 0.05% to 2%, and the mass fraction of additive B in the electrolyte is 0.1% to 3%.

[0016] In conjunction with the first aspect, the organic solvent is further defined as at least one of carbonate solvents, fluorocarbonate solvents, carboxylic acid ester solvents, fluorocarboxylic acid ester solvents, ether solvents, and fluoroether solvents, and the sodium salt is any one or more of NaPF6, NaFSI, NaTFSI, NaBF4, NaClO4, NaAsF6, and NaSbF6.

[0017] In conjunction with the first aspect, the organic solvent further comprises propylene carbonate, wherein the mass fraction of propylene carbonate in the organic solvent is 5% to 30%.

[0018] In a second aspect, the present invention also provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and a sodium-ion battery electrolyte as described in any one of claims 1 to 7;

[0019] The positive electrode and the negative electrode are immersed in the sodium-ion battery electrolyte and separated by a separator.

[0020] In conjunction with the second aspect, furthermore, the positive electrode is a layered oxide with the structural formula NaM. x O y M is one or more of iron, copper, nickel, cobalt and manganese, 0.8≤x≤1.5, 1.5≤y≤2.5.

[0021] In conjunction with the second aspect, the negative electrode is one or more of hard carbon, soft carbon, expanded graphite, titanium-based materials, alloy materials, and organic materials.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0023] First, additive A of this invention is sodium silaneborate and / or sodium silane phosphite, which preferentially reacts at the interface of the positive and negative electrode materials of the battery to form a stable interface film with low impedance. This can suppress the oxidation of the electrolyte solvent by the positive electrode material under high voltage and suppress the reduction of the electrolyte solvent at the negative electrode interface. At the same time, additive A is a sodium salt, which can act as a sodium replenisher, reducing the consumption of active sodium ions and improving the initial efficiency and lifespan of sodium-ion batteries. The boron in sodium silaneborate of additive A has an electron-deficient structure and can combine with oxygen on the positive electrode surface. The phosphorus in sodium silane phosphite of additive A contains lone pairs of electrons and can combine with metal ions on the positive electrode surface. Both can stabilize the positive electrode interface and suppress the phase transition and decomposition of the positive electrode material. At the same time, the trimethylsilyl group on additive A can capture substances such as HF in the battery and cut off the path of HF corrosion to the positive electrode material. In addition, when additive A forms an interface film, it is also more conducive to the formation of sodium salts with good thermal stability such as phosphite, phosphate, and borate, thereby improving the high-temperature tolerance of sodium-ion batteries.

[0024] Although additive A has many advantages as an electrolyte additive for sodium-ion batteries, the inventors discovered that the interfacial film formed by additive A at the electrode material interface is an inorganic film, which is prone to breakage during the expansion and contraction of the positive and negative electrode materials during long-term charge-discharge cycles. The inventors found that introducing additive B into the electrolyte can react at the positive and negative electrode interface to form a tough polymer film, which has better resistance to expansion and contraction than the inorganic interfacial film formed by additive A alone. The use of combined additives in the electrolyte can improve both the thermal stability and the resistance to contraction of the interfacial film. At the same time, additive B can combine with oxygen release to suppress battery gas production. Furthermore, the combined use of both additives can better improve the initial efficiency, long cycle life, and high-temperature storage performance of sodium-ion batteries.

[0025] In addition, by introducing a certain amount of propylene carbonate solvent on the basis of additives A and B, the oxidation resistance of the electrolyte can be significantly improved, and the overall performance of sodium ions can be further improved. Detailed Implementation

[0026] The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0027] Unless otherwise specified, all reagents, materials and instruments used in the following examples and comparative examples are commercially available.

[0028] This invention provides a sodium-ion battery electrolyte, comprising a lithium salt, an organic solvent, and a combination of additives, wherein the combination of additives includes additive A and additive B; additive A is sodium silaneborate and / or sodium silane phosphite, and additive B is a sulfur-containing compound; the structural formula of additive A is shown in Formula I and Formula II.

[0029]

[0030] Wherein, X and Y are phosphorus or boron, and R1 to R9 are each independently an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms substituted with halogen atoms, wherein the halogen atom is one of F, Cl, Br and I.

[0031] Additive B is any one or more combinations of the compounds represented by Formula III:

[0032]

[0033] Implementably, in Formula III, R 10 ~R 13 Independently, it is any one of hydrogen atoms, halogen atoms, or alkyl groups having 1 to 4 carbon atoms, where A is an oxygen atom or a carbon atom, and R... 14 It is an alkyl or sulfonic acid group with 1 to 3 carbon atoms substituted by alkyl or halogen atoms, where a and b are independently 0 or 1.

[0034] In practice, additive A is one or more of sodium bis(trimethylsilyl)phosphite, sodium bis(trimethylsilyl)borate, disodium trimethylsilyl phosphite, and disodium trimethylsilylborate.

[0035] Implementably, the additive combination may also include sodium silane phosphate, such as sodium bis(trimethylsilyl)phosphate and disodium trimethylsilyl phosphate.

[0036] In practice, additive B is any one or more of 1,3-propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, fluorovinyl sulfate, vinyl sulfite, methylene disulfonate, and propylene sulfate.

[0037] In addition to sulfur-containing compounds as shown in Formula III, additive B may also include bicyclic sulfur-containing compounds, such as Compound 1, Compound 2, and Compound 3 as described below.

[0038]

[0039] In practice, the mass fraction of additive A in the electrolyte is 0.05% to 2%, and the mass fraction of additive B in the electrolyte is 0.1% to 3%. If the content of additive A is too low, the improvement effect will be limited; if the content is too high, it may not be able to dissolve fully in the electrolyte. If the content of additive B is too low or too high, it will cause the film-forming impedance to be too high, thus degrading the overall performance of the battery.

[0040] Optionally, the organic solvent is at least one of carbonate solvents, fluorocarbonate solvents, carboxylic acid ester solvents, fluorocarboxylic acid ester solvents, ether solvents, and fluoroether solvents.

[0041] Preferably, the organic solvent contains propylene carbonate (PC), and the mass fraction of PC in the electrolyte organic solvent ranges from 5% to 30%. Too low a PC content has limited effect on inhibiting gas production, while too high a content may deteriorate the negative electrode interface and significantly increase the viscosity of the electrolyte.

[0042] Implementably, the carbonate solvent includes ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0043] In practice, fluorocarbonate solvents include fluoroethylene carbonate, difluoroethylene carbonate, methyltrifluoromethyl carbonate, methyltrifluoroethyl carbonate, and di(2,2,2-trifluoroethyl) carbonate.

[0044] Practically, the carboxylic acid ester solvent includes methyl formate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, and ethyl butyrate.

[0045] In practice, fluorocarboxylic acid ester solvents include ethyl fluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, 2,2,2-trifluoroethyl difluoroacetate, methyl pentafluoropropionate, and 2,2-difluoroethyl acetate.

[0046] In practice, ether solvents include tetrahydrofuran, 1,3-dioxapentane, diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0047] In practice, fluorinated ether solvents include bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0048] Alternatively, the sodium salt may be any one or more of NaPF6, NaFSI, NaTFSI, NaBF4, NaClO4, NaAsF6, and NaSbF6.

[0049] Using the sodium-ion battery electrolyte described above, this invention produces a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and the sodium-ion battery electrolyte described above.

[0050] In practice, the positive electrode is a layered oxide with the structural formula NaM x O y M includes one or more selected from iron, copper, nickel, cobalt, and manganese, 0.8≤x≤1.5, 1.5≤y≤2.5, and the values ​​of x and y satisfy the charge balance of the chemical formula.

[0051] In practice, the cathode material is NaFe. 0.5 Mn 0.5 O2, NaNi 0.3 Fe 0.4 Mn 0.3 O2, NaNi 0.33 Fe 0.34 Mn 0.33 O2, NaNi 0.25 Fe 0.5 Mn 0.25 O2, NaNi 0.2 Cu 0.1 Fe 0.4 Mn 0.3 O2, NaNi 0.25 Fe 0.4 Co 0.1 Mn 0.25 O2, NaNi 0.5 Fe 0.4 Mn 0.4 O 2.4 and NaNi 0.4 Fe 0.2 Mn 0.3 O 1.8 Any one or more of the following.

[0052] Alternatively, the positive electrode may also include a conductive agent, which may be any one or more of carbon black, carbon nanotubes, and graphene.

[0053] In practice, the negative electrode can be one or more of hard carbon, soft carbon, expanded graphite, titanium-based materials, alloy materials, and organic materials.

[0054] Preferably, the negative electrode comprises hard carbon, soft carbon, and a composite material of hard and soft carbon.

[0055] Alternatively, the negative electrode sheet may also include a negative current collector, which may be an aluminum foil or copper foil, an aluminum foil or copper foil doped with other elements, or an aluminum foil or copper foil with a coating layer on its surface.

[0056] In the embodiments and comparative examples of this invention, the additives used to prepare the sodium-ion battery electrolyte are as follows:

[0057] Additive A: Sodium bis(trimethylsilyl)phosphite (A1), sodium bis(trimethylsilyl)borate (A2), disodium trimethylsilyl phosphite (A3), disodium trimethylsilylborate (A4);

[0058] Additive B: 1,3-propanesulfonate lactone (PS), 3-fluoro-1,3-propanesulfonate lactone (FPS), vinyl sulfate (DTD), methylene disulfonate (MMDS);

[0059] Organic solvents: propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC);

[0060] Sodium salt: NaPF6.

[0061] Electrolytes in Examples 1-11 of this invention were prepared sequentially according to the following preparation method:

[0062] First, in a glove box, sodium salt is slowly added to a mixture of PC, EC, DMC, and EMC. After the container temperature drops to room temperature, additives A and B are added. After thorough mixing, the electrolyte is prepared. The mass ratios of EC, DMC, and EMC in the electrolyte solvent, as well as the mass fractions (contents) of additives A and B in the electrolyte, are shown in Table 1 below. The molar concentration of sodium salt in the electrolyte is 1 mol / L.

[0063] Table 1: Names and proportions of components in the electrolytes of Examples 1-11

[0064]

[0065] Comparative Examples 1 to 9 of this invention all prepared electrolytes sequentially according to the following preparation method:

[0066] First, in a glove box, sodium salt is slowly added to a mixture of PC, EC, DMC, and EMC. After the container temperature drops to room temperature, additives A and B are added. After thorough mixing, the electrolyte is prepared. The mass ratios of EC, DMC, and EMC in the electrolyte solvent, as well as the mass fractions (contents) of additives A and B in the electrolyte, are shown in Table 2 below. The molar concentration of sodium salt in the electrolyte is 1 mol / L.

[0067] Table 2: Names and proportions of components in the electrolytes of Comparative Examples 1–9

[0068]

[0069] Preparation of sodium-ion batteries:

[0070] The electrolytes obtained in the examples and comparative examples were applied to lithium-ion batteries for performance testing. The sodium-ion battery was prepared using the following steps:

[0071] (1) Preparation of positive electrode

[0072] Positive electrode material: Sodium nickel iron manganese oxide (NaNi) 0.3 Fe 0.4 Mn 0.3The mass ratio of O2, binder (polyvinylidene fluoride), and conductive agent (conductive carbon black) is fixed at 96:2:2. The positive electrode material sodium nickel iron manganese oxide, binder, conductive agent, additive A, and additive B are mixed according to their respective proportions. After adding N-methylpyrrolidone (NMP), the mixture is stirred to prepare the positive electrode slurry. A portion of the positive electrode slurry needs to be reserved for viscosity testing.

[0073] The positive electrode slurry is uniformly coated onto aluminum foil. After the coated aluminum foil is dried at room temperature, it is transferred to a 120°C oven to dry for 1 hour. Then it is dried at 85°C, cold-pressed, trimmed, cut into pieces, and slit. Finally, it is dried under vacuum at 85°C for 4 hours and the tabs are welded to produce the positive electrode of a sodium-ion secondary battery that meets the requirements.

[0074] (2) Anode preparation

[0075] Hard carbon, thickener sodium carboxymethyl cellulose (CMC), binder styrene-butadiene rubber latex (SBR), and conductive agent (conductive carbon black) are dissolved in deionized water at a mass ratio of 94:1:2:3 and mixed evenly to prepare a negative electrode slurry.

[0076] The negative electrode slurry is evenly coated on the current collector copper foil, then dried at 85°C, cold pressed, trimmed, cut into pieces, and slit. After drying under vacuum at 110°C for 4 hours, the tabs are welded to produce the negative electrode of a sodium-ion secondary battery that meets the requirements.

[0077] (3) Preparation of sodium-ion batteries

[0078] The corresponding positive electrode, negative electrode and separator (PE film + 3um ceramic coating) are wound into a bare cell and then placed into an aluminum-plastic film. After baking at 90°C to remove water, electrolyte is injected and then sealed. After standing, hot and cold pressing, formation, degassing and capacity testing, a sodium-ion battery is obtained.

[0079] The electrolyte and sodium-ion battery obtained above were tested, including the following performance tests:

[0080] (1) First-time efficiency (first charge and discharge efficiency) test

[0081] The initial efficiency test procedure is included in the formation and capacity testing processes. At 25°C, the sodium-ion battery is left to stand for 30 minutes, then charged at a constant current rate of 0.5C to 4.05V, and then charged at a constant voltage rate of 4.05V to 0.05C. The total capacity at this point is recorded as C0. After that, it is left to stand for 30 minutes, then discharged at a constant current rate of 0.5C to 1.5V. The total capacity at this point is recorded as D0.

[0082] The initial efficiency (%) of a sodium-ion battery = D0 / C0.

[0083] (2) High-temperature cycle performance test of sodium-ion battery at 25℃

[0084] At 25°C, the sodium-ion battery was left to stand for 30 minutes, then charged at a constant current rate of 1C to 4.05V, followed by constant voltage charging at 4.05V to 0.05C, and left to stand for 5 minutes. It was then discharged at a constant current rate of 1C to 1.5V, completing one charge-discharge cycle. The resulting discharge capacity is the initial discharge capacity C1 of the sodium-ion battery. This was followed by 300 charge-discharge cycles, with the discharge capacity of the 300th cycle recorded as C00. 300 .

[0085] The capacity retention rate (%) of a sodium-ion battery after 300 cycles = C 300 / C1.

[0086] (4) High-temperature storage test of sodium-ion battery at 60℃

[0087] First, the sodium-ion battery was left to stand at 25°C for 30 minutes. It was then charged to 4.05V at a constant current of 0.5C, and further charged at a constant voltage of 4.05V until the current reached 0.5C. Next, the sodium-ion battery was discharged to 1.5V at a constant current of 0.5C; this discharge capacity is recorded as C0s. It was then charged again to 4.05V at a constant current of 0.5C, and further charged at a constant voltage of 4.05V until the current reached 0.5C. Finally, the battery volume was measured using the water displacement method; this is the volume V0 before storage. Afterward, the sodium-ion battery was stored at 60°C for 30 days. After storage, the sodium-ion rechargeable battery was placed at 25°C, and the battery volume was measured using the water displacement method; this is the volume V after storage. 30 Then, the sodium-ion battery is discharged to 1.5V at a constant current of 0.5C; then, the sodium-ion secondary battery is charged to 4.05V at a constant current of 0.5C, and further charged to a current of 0.5C at a constant voltage of 4.05V; then, the sodium-ion secondary battery is discharged to 1.5V at a constant current of 0.5C. The discharge capacity at this point is denoted as C. 30s .

[0088] Sodium ion storage capacity recovery rate (%) after 30 days of storage = C 30S / C0S ;

[0089] Volume expansion rate (%) of sodium-ion batteries after 30 days of storage = (V 30 -V0) / V0.

[0090] The performance test data of the sodium-ion batteries in the embodiments and comparative examples of this invention are shown in Table 3.

[0091] Table 3: Test Results of Sodium-ion Batteries

[0092]

[0093] As can be seen from Comparative Examples 1-3 and Example 2 in Table 3, compared with the electrolyte without any additives, the addition of additive A alone to the sodium-ion battery electrolyte significantly improves the initial efficiency, cycle life, high-temperature storage capacity, and battery volume expansion. The addition of additive B alone improves all performance aspects, mainly with better volume expansion than additive A. It is speculated that additive B can combine with oxygen released from the positive electrode, which can better suppress electrolyte oxidation and gas production, thereby improving battery volume expansion. Other aspects are worse than additive A. When additive A and additive B are added at the same time, the initial efficiency, cycle life, high-temperature storage capacity, and battery volume expansion of the sodium-ion battery are further improved. It is speculated that the two form a film together at the positive and negative electrode interfaces, forming both an inorganic interface film with good thermal stability and an organic interface film resistant to expansion and contraction. They complement each other, allowing the sodium-ion battery to better balance cycle life and high-temperature storage performance.

[0094] As can be seen from Comparative Examples 3-5 and Examples 1-3 in Table 3, when the content of additive A in the electrolyte is less than 0.05%, it has little effect on the performance of sodium-ion batteries. With the increase of additive A content, the first-time efficiency, cycle life, high-temperature storage capacity, and battery volume expansion of sodium-ion batteries are significantly improved. However, when the content of additive A reaches 2%, the improvement in 25°C 1C / 1C cycle performance is not obvious. When the content of additive A is further increased to 3%, the 25°C cycle performance deteriorates. It is speculated that, on the one hand, excessive additive A content will deteriorate the conductivity of the sodium-ion battery electrolyte and affect the transport of sodium ions. On the other hand, excessive additive A content will thicken the interfacial film formed at the positive and negative electrode interfaces, affecting the insertion and extraction of sodium ions at the positive and negative electrode interfaces.

[0095] As can be seen from Comparative Examples 6-7 and Examples 4-6 in Table 3, initially, with the increase of additive B content, the first-efficiency, cycle life, high-temperature storage capacity, and battery volume expansion of sodium-ion batteries were all improved. However, after a certain amount of additive B PS (1,3-propanesulfonate lactone) was added, it increased the interfacial impedance and thickened the interface, thus affecting the insertion and extraction of sodium ions at the positive and negative electrode interfaces. In addition, sulfur-based additives are acidic, and if there is too much, they will decompose and produce acidic substances, thereby damaging the positive and negative electrode interfaces and deteriorating the life of sodium-ion batteries. However, as the additive B content continued to increase, the volume expansion at 60°C continued to improve. It is speculated that the more additive B there is, the higher the efficiency of binding oxygen released from the positive electrode, and the better the effect of suppressing gas generation and battery expansion, but the improvement in volume expansion will decrease.

[0096] As can be seen from Examples 1 to 9 in Table 3, different types and amounts of additive A and additive B can be combined to achieve different improvements in the first-time efficiency, cycle life, high-temperature storage capacity, and battery volume expansion of sodium-ion batteries. Different types and amounts of additive A and B can be selected according to different cell designs and performance requirements.

[0097] As can be seen from Comparative Examples 8-9 and Examples 9-11 in Table 3, adding PC (propylene carbonate) to the electrolyte in addition to additives A and B can further improve the overall performance of sodium-ion batteries. However, when the content is too high, the 25°C cycle life deteriorates. PC has good oxidation stability and a high dielectric constant, which can improve the conductivity of the electrolyte, thereby improving the initial efficiency, 25°C cycle life, and high-temperature volume expansion. However, when its content is too high, the viscosity of the electrolyte increases. In addition, its compatibility with the negative electrode is poor, thus deteriorating the cycle life of the sodium-ion battery. Therefore, it is necessary to design an appropriate dosage according to the requirements.

[0098] In summary, by combining additives A and B in the positive electrode of a sodium-ion battery, this invention can significantly improve the initial efficiency, cycle life, and high-temperature storage performance of sodium-ion batteries. Furthermore, the addition of a certain amount of PC solvent can further enhance the overall performance of sodium-ion batteries.

[0099] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A sodium-ion battery electrolyte, characterized in that, The mixture includes sodium salts, organic solvents, and a combination of additives, wherein the combination of additives includes additive A and additive B; additive A is sodium silaneborate and / or sodium silane phosphite, and additive B is a sulfur-containing compound; the structural formula of additive A is shown in Formula I or Formula II. ； Wherein, X is phosphorus, Y is phosphorus or boron, and R1 to R9 are each independently an alkyl group having 1 to 4 carbon atoms or an alkyl group having 1 to 4 carbon atoms substituted with halogen atoms, wherein the halogen atom is one of F, Cl, Br and I. The additive B is any one or more combinations of the compounds shown in Formula III: ； Among them, R 10 ~R 13 Independently, it is any one of hydrogen atoms, halogen atoms, or alkyl groups having 1 to 4 carbon atoms, where A is an oxygen atom or a carbon atom, and R... 14 It is an alkyl or sulfonic acid group with 1 to 3 carbon atoms substituted by alkyl or halogen atoms, where a and b are independently 0 or 1; The mass fraction of additive A in the electrolyte is 0.05%~2%, and the mass fraction of additive B in the electrolyte is 0.1%~3%. The organic solvent contains propylene carbonate, and the mass fraction of propylene carbonate in the organic solvent is 5% to 30%.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, Additive A is one or more of sodium bis(trimethylsilyl)phosphite, disodium trimethylsilyl phosphite, and disodium trimethylsiloxane.

3. The sodium-ion battery electrolyte according to claim 1, characterized in that, The additive B is any one or more of 1,3-propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, fluorovinyl sulfate, vinyl sulfite, methylene disulfonate, and propylene sulfate.

4. The sodium-ion battery electrolyte according to claim 1, characterized in that, The organic solvent is at least one of carbonate solvents, fluorocarbonate solvents, carboxylic acid ester solvents, fluorocarboxylic acid ester solvents, ether solvents, and fluoroether solvents, and the sodium salt is any one or more of NaPF6, NaFSI, NaTFSI, NaBF4, NaClO4, NaAsF6, and NaSbF6.

5. A sodium-ion battery, characterized in that, Includes a positive electrode, a negative electrode, a separator, and the sodium-ion battery electrolyte according to any one of claims 1 to 4; The positive electrode and the negative electrode are immersed in the sodium-ion battery electrolyte and separated by a separator.

6. The sodium-ion battery according to claim 5, characterized in that, The positive electrode is a layered oxide with the structural formula NaM. x O y M is one or more of iron, copper, nickel, cobalt and manganese, 0.8≤x≤1.5, 1.5≤y≤2.

5.

7. The sodium-ion battery according to claim 5, characterized in that, The negative electrode is one or more of hard carbon, soft carbon, expanded graphite, titanium-based materials, alloy materials, and organic materials.

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