Sodium ion battery and electronic equipment

Abstract

The invention discloses a sodium-ion battery and electronic equipment, the sodium-ion battery comprises a positive pole piece, a negative pole piece and an electrolyte, the negative pole piece comprises a negative current collector and a negative active material coated on the negative current collector, the negative active material comprises a negative active material, and the negative active material comprises a positive electrode active material and a negative electrode active material. The negative electrode active material comprises at least one of a silicon-oxygen compound and a carbon-silicon composite material; the electrolyte comprises a sodium salt, a non-aqueous solvent and a zwitter-ion additive, the chemical formula of the zwitter-ion additive is # imgabs0 #, at least one R group is selected from any one of alkyl, alkenyl, alkynyl and aryl substituent groups with the carbon atom number of 1-6, 0-1 halogen atom, 0-1 carbonyl group and 0-1 ester group, and at least one R group is selected from any one of alkyl, alkenyl, alkynyl and aryl substituent groups with the carbon atom number of 1-6, 0-1 halogen atom, 0-1 carbonyl group and 0-1 ester group. At most two R groups are selected from substituent groups containing one cyclic alkyl group or cyclic alkenyl group, and n is greater than or equal to 1 and less than or equal to 3. The zwitterionic additive and the silicon-based composite material negative electrode system are matched for use, so that the high-temperature cycle performance and the gas production performance of the battery cell can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power batteries, and in particular to a sodium ion battery and an electronic device. Background Art

[0002] With the progress of the energy revolution, the application of traditional fossil energy has been greatly challenged due to its storage capacity and environmental friendliness. The development of new and environmentally friendly new energy is imminent. As a strategic industry of the country, my country's new energy vehicle industry has developed rapidly and is at the world's leading level. Among the power batteries of new energy vehicles, lithium-ion battery technology has been increasingly valued for its advantages such as high energy density, good cycle performance, no memory effect, low self-discharge rate, and no pollution. It has been widely used in new energy electric vehicles and occupies a core position in energy storage and power batteries. Since its commercialization, lithium-ion battery technology has become increasingly mature, but it has also faced many pain points. For example, lithium ore resources are becoming increasingly scarce and material prices are constantly soaring. These force us to develop more economical and efficient alternative technologies. Lithium and sodium belong to the same group I metals and have similar physical and chemical properties, but the reserves of sodium resources are far more abundant than lithium resources. After the system is developed and mature, the cost is also expected to be lower than lithium resources in the next five years. Therefore, the development of sodium-ion batteries has received widespread attention from the industry in recent years.

[0003] The research on sodium-ion batteries still faces many challenges. In order to obtain an energy density system close to that of lithium-ion batteries, the system of sodium-ion batteries is usually a high-voltage 4.0V layered ternary oxygen compound positive electrode material and a hard carbon negative electrode material. However, compared with traditional hard carbon negative electrode materials, silicon-based composite materials as negative electrode active materials have a very high theoretical gram capacity, which is several times that of graphite-based negative electrode active materials. Therefore, the industry expects to use silicon-based composite materials to improve the energy density of secondary batteries. However, the research on silicon-based composite negative electrode systems still faces many challenges. During the high-temperature cycling and storage of batteries, due to the activity and expansion characteristics of silicon-based composite materials, the negative electrode "solid electrolyte interface membrane" (SEI membrane) is easily damaged, which makes the life of silicon-based composite materials poor and the gas production more serious.

[0004] As an important component of the battery, the performance of the electrolyte is closely related to the battery performance. The electrolyte widely used in sodium-ion batteries is usually sodium hexafluorophosphate (NaPF 6) is used as the electrolyte salt, a mixture of cyclic carbonate and chain carbonate is used as the organic solvent, and a small amount of additives are added. The additives are mainly divided into film-forming additives, flame retardant additives, overcharge protection additives, etc. Electrolyte additives are becoming more and more important because of their small dosage and significant effect in improving battery cycle performance. Therefore, it is of great significance to develop an electrolyte based on additives that is suitable for use with a silicon-based composite negative electrode system and can effectively improve the electrochemical performance of sodium-ion batteries for the development of sodium-ion batteries. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a sodium ion battery and an electronic device to improve the electrochemical properties of the sodium ion battery, especially the high temperature cycle performance and gas production performance.

[0006] To achieve the above-mentioned object and other related objects, the present invention provides a sodium ion battery in a first aspect, comprising a positive electrode plate, a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector, wherein the negative electrode active material comprises a negative electrode active material, wherein the negative electrode active material comprises at least one of a silicon oxide compound and a carbon silicon composite material, wherein the chemical formula of the silicon oxide compound is SiO x , 0 <x≤2;

[0007] The electrolyte includes a sodium salt, a non-aqueous solvent and a zwitterionic additive, and the chemical structural formula of the zwitterionic additive is as follows:

[0008]

[0009] Among them, at least one R group is selected from any one of alkyl, alkenyl, alkynyl and aryl substituents having 1 to 6 carbon atoms, 0 to 1 halogen atoms, 0 to 1 carbonyl groups and 0 to 1 ester groups, and at most two R groups are selected from substituents containing 1 cyclic alkyl or cyclic alkenyl group, 1≤n≤3.

[0010] In one embodiment of the present invention, the zwitterionic additive is selected from at least one of the following compounds I to V:

[0011] Ⅰ: Ⅱ: III:

[0012] IV: V:

[0013] In one embodiment of the present invention, the negative electrode active material includes SiO.

[0014] In one embodiment of the present invention, the mass percentage of the zwitterionic additive in the electrolyte is 0.1% to 10%.

[0015] In one embodiment of the present invention, the mass percentage of the zwitterionic additive in the electrolyte is 0.5% to 3%.

[0016] In one embodiment of the present invention, the mass percentage of the sodium salt in the electrolyte is 6% to 12%.

[0017] In an embodiment of the present invention, the mass content of the non-aqueous solvent in the electrolyte is, for example, 70% to 95%.

[0018] In one embodiment of the present invention, the negative electrode active material further includes at least one of the metal elements Ti, Fe, Cu, Ni, Co, Mn, Ag, Au and Sn.

[0019] In one embodiment of the present invention, the mass content of the metal element in the negative electrode active material is 10 ppm to 500 ppm.

[0020] In one embodiment of the present invention, the charging cut-off voltage of the sodium ion battery is greater than or equal to 4.0V.

[0021] A second aspect of the present invention provides an electronic device comprising the sodium ion battery as described in the first aspect.

[0022] As described above, the sodium ion battery and electronic device of the present invention have the following beneficial effects:

[0023] In the sodium ion battery provided by the present invention, a zwitterionic additive is added to the electrolyte. In the case of a silicon-based composite material negative electrode system, the zwitterionic additive can form a structure similar to a monolayer on the negative electrode surface through Coulomb interaction. The monolayer structure can be uniformly adsorbed on the negative electrode interface, reducing the active reaction sites of the negative electrode interface, thereby ensuring stable high-temperature cycle performance; at the same time, as the silicon negative electrode material expands, a small amount of fresh interface is exposed to the outside, and less solvent or additive is consumed to form a negative electrode interface protective film SEI film, thereby improving high-temperature gas production performance. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] It should be understood that the present invention can be implemented in different forms and should not be interpreted as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0026] The technical scheme of the present invention is further described in detail below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The present invention proposes a sodium ion battery, including a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the electrolyte is filled between the positive electrode sheet, the negative electrode sheet and the separator. The present invention does not limit the type and shape of the sodium ion battery. In one embodiment of the present invention, the sodium ion battery is a primary battery or a secondary battery, and the secondary battery is, for example, a soft-pack battery, a square-shell battery or a cylindrical battery. In this embodiment, for example, a soft-pack secondary battery is used as an example for explanation.

[0028] In one embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material coated on at least one side of the positive current collector, and the positive active material includes a positive active material, a binder, and a conductive agent. Among them, the positive current collector can be, for example, a foil formed by surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel or carbon. In addition to the foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam and non-woven fabric. Among them, the thickness of the positive current collector is, for example, 8μm to 15μm. In this embodiment, the positive current collector is, for example, aluminum foil.

[0029] In one embodiment of the present invention, the positive electrode active material includes, for example, Na x [Ni y Fe z Mn t M (1-y-z-t) ]O 2-δ, wherein the M element is selected from at least one of Cr, Co, Ca, Mg, Cu, Ti, Al, Mo, W, and Zn, 0.7 < x < 1.1, 0 ≤ y < 0.5, 0 ≤ z < 0.5, 0 ≤ t < 0.5, 0 ≤ δ ≤ 0.1. The binder is, for example, selected from any one or more of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, and polymerized styrene butadiene rubber (SBR). The conductive agent is, for example, selected from any one or more of super P (SP), acetylene black, carbon nanotubes, and graphene. Sodium

[0030] In an embodiment of the present invention, the positive electrode active material is, for example, Na 0.95 Ni 0.5 Fe 0.25 Mn 0.25 O 2 , the binder is, for example, selected from polyvinylidene fluoride, and the conductive agent is, for example, selected from super P. After mixing the positive electrode active material, super P, and polyvinylidene fluoride in a mass ratio of 95:3:2, a non-aqueous solvent is added and stirred until the system becomes homogeneous to obtain a positive electrode slurry. Among them, the non-aqueous solvent is, for example, selected from N-methylpyrrolidone (NMP). After uniformly coating the positive electrode slurry on the aluminum foil, it is dried in the air and then dried under vacuum, and then the dried aluminum foil is cold-pressed and other processes are carried out to obtain a positive electrode plate.

[0031] In an embodiment of the present invention, the negative electrode plate includes a negative electrode current collector and at least a negative electrode active material coated on one side of the negative electrode current collector. The negative electrode active material includes a negative electrode active material, a binder, a conductive agent, a thickening agent, etc. Among them, the negative electrode current collector is, for example, selected from one of a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foam copper current collector, or a stainless steel current collector, and the thickness of the negative electrode current collector is, for example, 8 μm to 15 μm.

[0032] In an embodiment of the present invention, the negative electrode active material includes a silicon-based composite material, and for another example, it includes silicon oxide (SiO x, at least one of carbon and silicon composite materials, etc., where 0 < x < 2), and the negative electrode active material further includes at least one of metal elements such as Ti, Fe, Cu, Ni, Co, Mn, Ag, Au, and Sn. The content of the metal element in the negative electrode active material is, for example, 10 ppm to 500 ppm. Also, for example, it exists in the negative electrode active material by doping or coating, etc., to meet the requirements of high energy density and improve the cycle performance of the sodium-ion battery. In other embodiments, the negative electrode active material can be other silicon-based composite materials. The binder is, for example, selected from any one or more of polyvinylidene fluoride, polyamide, polypropylene, polyacrylate, polyethylene ether, polymethyl methacrylate, polyhexafluoropropylene, and styrene-butadiene rubber, etc. The conductive agent is, for example, selected from any one or more of conductive carbon black, acetylene black, carbon nanotubes, and graphene, etc. The thickening agent is, for example, selected from sodium carboxymethyl cellulose, etc.

[0033] In an embodiment of the present invention, the negative electrode current collector is, for example, selected from copper foil, the negative electrode active material is, for example, selected from silicon oxide compounds, the conductive agent is, for example, selected from conductive carbon black, the binder is, for example, selected from styrene-butadiene rubber, and the thickening agent is, for example, selected from sodium carboxymethyl cellulose. In an embodiment of the present invention, the silicon oxide compound, conductive carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose are mixed, for example, in a mass ratio of 96:2:1:1, deionized water is added, and the mixture is stirred充分 to obtain the negative electrode slurry. The negative electrode slurry is uniformly coated on the copper foil, then dried at room temperature and transferred to an oven for drying, and the negative electrode plate is obtained through processes such as drying and cold pressing.

[0034] In an embodiment of the present invention, the separator is, for example, a polyethylene film (Polyethylene, PE), a polypropylene film (Polypropylene, PP), a glass fiber film, a polyethylene film, or a composite film, etc. And the thickness of the separator is, for example, 9 μm to 15 μm. In an embodiment of the present invention, a polyethylene with a thickness of 8 μm to 10 μm is, for example, selected as the base film, and a nano-aluminum oxide coating with a thickness of 2 μm to 4 μm is coated on the base film to obtain the separator. In an embodiment of the present invention, the separator is, for example, a 12-μm polypropylene film, etc.

[0035] In an embodiment of the present invention, the electrolyte includes a non-aqueous solvent, a sodium salt, and an amphoteric ion additive, etc. Among them, the chemical structural formula of the amphoteric ion additive is shown as follows:

[0036]

[0037] Wherein, at least one R group is selected from any one of alkyl, alkenyl, alkynyl and aryl substituents having 1 to 6 carbon atoms, 0 to 1 halogen atoms, 0 to 1 carbonyl groups and 0 to 1 ester groups, and at most two R groups are selected from substituents containing 1 cyclic alkyl or cyclic alkenyl, and 1≤n≤3. In the high-voltage sodium cathode material system, the zwitterionic additive can form a monolayer-like structure with transition metal ions such as Fe and Mn on the cathode surface through Coulomb interaction. The monolayer structure can be uniformly adsorbed on the cathode interface to form a uniform and dense electrolyte membrane (Cathode Electrolyte Interface membrane, referred to as CEI membrane), avoiding the cathode interface from reacting with the solvent and sodium salt in the electrolyte, thereby ensuring stable high-temperature cycle performance.

[0038] In one embodiment of the present invention, the zwitterionic additive includes, for example, compound I: Compound II: Compound III: Compound IV:

[0039] And compound V: At least one of the above.

[0040] In one embodiment of the present invention, the mass content of the ionic liquid in the electrolyte is 0.1% to 10%, and for example 0.5% to 3%. Among them, when the mass content of the zwitterionic additive is too low, the fast charging performance and cycle performance of the sodium ion battery are not significantly improved. When the mass content of the zwitterionic additive is too high, the high-temperature cycle performance and gas production performance will be deteriorated. This may be due to excessive addition of the zwitterionic additive, and many unreacted components remain in the electrolyte. Excessive zwitterions themselves will form a built-in reverse electric field, which will deteriorate the battery performance.

[0041] In one embodiment of the present invention, the sodium salt includes sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium bis(oxalatoborate) (NaBOB), sodium difluorobis(oxalatophosphate) (NaF 2 C 2 PO 4 ), sodium difluorophosphate (NaDFP) and sodium trifluoromethanesulfonate (CF 3 SO 3 In this embodiment, the mass content of the sodium salt in the electrolyte is 6% to 12%.

[0042] In one embodiment of the present invention, the non-aqueous solvent includes at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC) and diethyl carbonate (DEC). In one embodiment of the present invention, the mass content of the non-aqueous solvent in the electrolyte is, for example, 70% to 95%. In this embodiment, the non-aqueous solvent includes, for example, battery-grade ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the mass ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 3:5:2. By controlling the content of the non-aqueous solvent, while exerting the performance of the electrolyte, it is prevented that the non-aqueous solvent content is too high, resulting in excessive viscosity of the electrolyte, thereby causing problems such as reduced ionic conductivity and wettability of the electrolyte.

[0043] In one embodiment of the present invention, when preparing the electrolyte, the content of a stable gas such as nitrogen or argon in the glove box is 99.999%, the actual oxygen content in the glove box is less than or equal to 0.1ppm, and the water content is less than or equal to 0.1ppm. After the non-aqueous solvent is mixed uniformly according to the mass ratio, the fully dried sodium salt is added to the non-aqueous solvent, and a zwitterionic additive is added to prepare the electrolyte of the sodium ion battery. Among them, the content of each component other than the non-aqueous solvent is the mass percentage calculated based on the total mass of the electrolyte.

[0044] In one embodiment of the present invention, the positive electrode sheet, the separator, and the negative electrode sheet are placed in sequence, so that the separator is located between the positive electrode sheet and the negative electrode sheet to play an isolating role, and a bare cell is obtained by winding or laminating. The bare cell is placed in an aluminum-plastic film, dried in a vacuum oven, injected with the prepared electrolyte, and sealed, and a soft-pack sodium-ion secondary battery is obtained after standing, hot and cold pressing, forming, clamping, and capacity division.

[0045] Another embodiment of the present invention further provides an electronic device, comprising at least one of the above-mentioned sodium ion batteries, and the sodium ion battery is used to provide electrical energy. Among them, the electronic device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and an electric tool, etc. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecrafts, etc., and electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the above-mentioned sodium ion battery, and therefore includes the advantages of the above-mentioned sodium ion battery, which will not be elaborated here.

[0046] Hereinafter, the present invention will be explained in more detail by citing examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, all of which fall within the technical scope of the present invention.

[0047] Example 1

[0048] Preparation of electrolyte: In a glove box filled with argon, when the nitrogen content in the glove box is 99.999%, the actual oxygen content in the glove box is less than 0.1ppm, and the moisture content is less than 0.1ppm, battery-grade ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of 3:5:2. Taking the total mass of the electrolyte as 100%, the sodium salt in the electrolyte is NaPF 6 and NaFSI, and NaPF 6 The mass content of NaFSI is 6%. The zwitterionic additive is compound I, and the mass content of compound I is 0.1%.

[0049] Preparation of positive electrode sheet: The positive electrode active material Na 0.95 [Ni 0.5 Fe 0.25 Mn 0.25 ]O 2 After mixing the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride, in a mass ratio of 95:3:2, NMP is added and stirred until the system becomes uniform to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on an aluminum foil, and then transferred to an oven for vacuum drying after drying at room temperature, and then the dried aluminum foil is subjected to a cold pressing process to obtain a positive electrode sheet.

[0050] Preparation of negative electrode sheet: negative electrode active material SiO, conductive agent conductive carbon black, binder styrene butadiene rubber and thickener sodium carboxymethyl cellulose are mixed in a mass ratio of 96:2:1:1, deionized water is added, and the mixture is stirred thoroughly to obtain negative electrode slurry. The negative electrode slurry is evenly coated on copper foil, and then dried at room temperature and transferred to an oven for drying, and the negative electrode sheet is obtained through drying and cold pressing processes.

[0051] Selection of diaphragm: Select 10μm polypropylene film as the diaphragm.

[0052] Preparation of battery: stack the positive electrode sheet, separator and negative electrode sheet in sequence, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and stack the sheets to obtain a bare battery cell. Then wrap it with aluminum plastic film, dry it in a vacuum oven, inject the above-prepared electrolyte and seal it, and perform electrolyte formation to obtain a soft-pack sodium ion secondary battery.

[0053] Example 2

[0054] The zwitterionic additive is compound I, and the mass content of compound I is 1%. Other operations are the same as those in Example 1.

[0055] Example 3

[0056] The zwitterionic additive is compound I, and the mass content of compound I is 5%. Other operations are the same as those in Example 1.

[0057] Example 4

[0058] The zwitterionic additive is compound I, and the mass content of compound I is 10%. Other operations are the same as those in Example 1.

[0059] Example 5

[0060] The zwitterionic additive is compound IV, and the mass content of compound IV is 0.1%. Other operations are the same as those in Example 1.

[0061] Example 6

[0062] The zwitterionic additive is compound IV, and the mass content of compound IV is 1%. Other operations are the same as those in Example 1.

[0063] Example 7

[0064] The zwitterionic additive is compound IV, and the mass content of compound IV is 5%. Other operations are the same as those in Example 1.

[0065] Example 8

[0066] The zwitterionic additive is compound IV, and the mass content of compound IV is 10%. Other operations are the same as those in Example 1.

[0067] Comparative Example 1

[0068] No zwitterionic additive compound I was added to the electrolyte, and other operations were the same as in Example 1.

[0069] Comparative Example 2

[0070] The zwitterionic additive is compound I, and the mass content of compound I is 20%. Other operations are the same as those in Example 1.

[0071] Comparative Example 3

[0072] The zwitterionic additive is compound I, and the mass content of compound I is 1%, and the positive electrode active material is Na 3 Fe 2 (P 2 O 7 )(PO 4 ), other operations are the same as those in Example 1.

[0073] Comparative Example 4

[0074] No zwitterionic additive compound IV was added to the electrolyte, and other operations were the same as in Example 1.

[0075] Comparative Example 5

[0076] The zwitterionic additive is compound IV, and the mass content of compound IV is 20%. Other operations are the same as those in Example 1.

[0077] Comparative Example 6

[0078] The zwitterionic additive is compound IV, and the mass content of compound IV is 1%. The negative electrode active material is graphite. Other operations are the same as those in Example 1.

[0079] The performance of the sodium ion batteries in Examples 1 to 4 and Comparative Examples 1 to 3 was tested using the following method. The test results are shown in Table 1.

[0080] The test method is as follows:

[0081] 1. Capacity retention rate of high temperature cycle at 45°C:

[0082] At 45°C, the sodium ion battery was charged to 4.0V at a constant current of 0.5C, then charged to a current of less than 0.05C at a constant voltage of 4.0V, and after standing for 30 minutes, it was discharged to 2.8V at a constant current of 1C. The discharge capacity of the sodium ion battery at this time was tested, which was the discharge capacity of the first cycle. The battery was cycled multiple times under the above conditions, and the capacity retention rate of the battery after 1000 cycles was calculated. The capacity retention rate after the cycle was calculated according to the following formula:

[0083] Capacity retention rate (%) = (discharge capacity corresponding to 1000 cycles / discharge capacity of the first cycle) × 100%.

[0084] 2. Volume expansion rate after 30 days of storage at 60℃:

[0085] At 25°C, the sodium ion battery was charged to 4.0V at a constant current of 0.5C, and then charged to a current of 0.05C at a constant voltage. The volume of the sodium ion battery was measured and recorded as V 0 ; Then place the fully charged battery in a 60℃ oven for 30 days, and measure the volume after storage and record it as V 1 , the volume expansion rate of the sodium ion battery before storage is calculated according to the following formula:

[0086] Volume expansion ratio (%) = (V 1 -V 0 ) / V 0 ×100%.

[0087] Table 1. Performance test results of sodium ion batteries in Examples 1 to 4 and Comparative Examples 1 to 3

[0088] Group Capacity retention rate after 1000 cycles at 45℃ (%) Volume expansion rate after storage at 60℃ for 30 days (%) Example 1 83.2 15.6 Example 2 87.5 12.1 Example 3 85.8 13.9 Example 4 82.7 18.2 Example 5 92.8 5.8 Example 6 94.2 4.3 Example 7 93.7 5.1 Example 8 90.1 7.9 Comparative Example 1 70.2 28.6 Comparative Example 2 78.5 20.7 Comparative Example 3 66.2 35.8 Comparative Example 4 70.2 28.6 Comparative Example 5 78.5 20.7 Comparative Example 6 66.2 35.8

[0089] Please refer to Table 1. Comparing Examples 1 to 4 and Examples 5 to 8, it can be found that the capacity retention of the sodium ion batteries of Examples 1 to 4 after 1000 cycles at 45°C first increases and then decreases, and the volume expansion of the batteries stored at 60°C for 30 days first decreases and then increases. The capacity retention rate of the sodium ion batteries of Examples 5 to 8 after 1000 cycles at 45°C also first increases and then decreases, and the volume expansion rate of the batteries stored at 60°C for 30 days also first decreases and then increases. This indicates that the optimal dosage of the zwitterionic additive is around 1%, and on the other hand, it indicates that in the high-voltage sodium positive electrode material system, the zwitterionic additive interacts with the positive electrode surface through Coulomb interaction, and forms a transition metal ion similar to Fe, Mn, etc. on its surface. The monolayer structure can be uniformly adsorbed on the positive electrode interface to form a uniform and dense CEI film, avoiding the reaction between the positive electrode interface and the solvent and sodium salt in the electrolyte, thereby ensuring stable high-temperature cycle performance; in the silicon-based composite negative electrode system, the zwitterionic additive can form a monolayer-like structure on the negative electrode surface through Coulomb interaction, and the monolayer structure can be uniformly adsorbed on the negative electrode interface to reduce the active reaction sites of the negative electrode interface, thereby ensuring stable high-temperature cycle performance; at the same time, with the expansion of the silicon negative electrode material, a small amount of fresh interface is exposed to the outside, which will consume less solvent or additive to form the negative electrode interface protective film SEI film, thereby improving the high-temperature gas production performance.

[0090] Please refer to Table 1. By comparing Example 2 with Comparative Example 1, it can be found that it is very necessary to add zwitterionic additive compound I to the electrolyte to form a CEI film at the positive electrode interface; by comparing Example 6 with Comparative Example 4, it can be found that it is very necessary to add zwitterionic additive compound IV to the electrolyte to form a SEI film at the negative electrode interface.

[0091] Please refer to Table 1, comparing Example 2 with Comparative Example 2, and Example 6 with Comparative Example 5, it can be found that excessive addition of zwitterionic additive Compound I or Compound IV will deteriorate the high temperature cycle performance. This may be due to excessive addition of zwitterionic additives. Excessive zwitterions themselves will form a built-in reverse electric field, deteriorating battery performance.

[0092] Please refer to Table 1. By comparing Example 2 and Comparative Example 3, it can be found that when the positive electrode active material is Na 3 Fe 2 (P 2 O 7 )(PO 4 ), the capacity retention rate of the sodium ion battery is greatly reduced after 1000 cycles at 45°C, and the volume expansion rate is greatly increased after 30 days of storage at 60°C. Compared with the sodium ion battery of Example 2, the high temperature cycle performance is poor and the gas generation is more serious. This is because the Na 3 Fe 2 (P 2 O 7 )(PO 4 ) This polyanion positive electrode active material is relatively inert and will not catalyze the decomposition of the zwitterionic additive compound I. The transition metal ions that are not dissolved in the positive electrode active material can interact with the zwitterionic additive through Coulomb interaction to form a uniform and dense CEI film, thereby deteriorating the high-temperature cycle performance. This shows that the zwitterionic additive needs to be used in combination with a system with high catalytic activity and high cell voltage to effectively improve the performance of sodium-ion batteries.

[0093] Please refer to Table 1. By comparing Example 6 and Comparative Example 6, it can be found that when graphite is selected as the negative electrode active material, the capacity retention rate of the sodium ion battery is greatly reduced after 1000 cycles at 45°C, while the volume expansion rate stored at 60°C for 30 days is greatly increased. Compared with Example 2, the high temperature cycle performance of the sodium ion battery is poor and the gas production is more serious. This is because graphite, a negative electrode active material, is relatively inert and will not catalyze the decomposition of the zwitterionic additive compound IV, thereby deteriorating the high temperature cycle performance. This shows that the zwitterionic additive needs to be used in combination with the silicon-based composite material negative electrode system to effectively improve the performance of the sodium ion battery.

[0094] In summary, the present invention adds a zwitterionic additive to the electrolyte and uses it in combination with a high-voltage sodium cathode material system and a silicon-based composite material anode system. On the one hand, the zwitterionic additive can form a structure similar to a monolayer with transition metal ions such as Fe and Mn on the surface of the cathode through Coulomb interaction. The monolayer structure can be uniformly adsorbed on the cathode interface to form a uniform and dense CEI film, thereby avoiding the cathode interface from reacting with the solvent and sodium salt in the electrolyte, thereby ensuring stable high-temperature cycle performance; on the other hand, in the silicon-based composite material anode system, the zwitterionic additive can form a structure similar to a monolayer on the cathode surface through Coulomb interaction. The monolayer structure can be uniformly adsorbed on the anode interface, reducing the active reaction sites on the anode interface, thereby ensuring stable high-temperature cycle performance; at the same time, as the silicon anode material expands, a small amount of fresh interface is exposed to the outside, and less solvent or additive is consumed to form the anode interface protection film SEI film, thereby improving the high-temperature gas production performance.

[0095] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector, wherein the negative electrode active material comprises a negative electrode active material, It is characterized in that The negative electrode active material comprises at least one of a silicon oxide compound and a carbon silicon composite material, wherein the chemical formula of the silicon oxide compound is SiO x , 0 <x≤2; The electrolyte includes a sodium salt, a non-aqueous solvent and a zwitterionic additive, and the chemical structural formula of the zwitterionic additive is as follows: Among them, at least one R group is selected from any one of alkyl, alkenyl, alkynyl and aryl substituents having 1 to 6 carbon atoms, 0 to 1 halogen atoms, 0 to 1 carbonyl groups and 0 to 1 ester groups, and at most two R groups are selected from substituents containing 1 cyclic alkyl or cyclic alkenyl group, 1≤n≤3.

2. The sodium ion battery according to claim 1, Features: The zwitterionic additive is selected from at least one of the following compounds I to V: Ⅰ： Ⅱ： Ⅲ： Ⅳ： Ⅴ： 3. The sodium ion battery according to claim 1, Features: The negative electrode active material includes SiO.

4. The sodium ion battery according to any one of claims 1 to 3, Features: The mass percentage of the zwitterionic additive in the electrolyte is 0.1% to 10%.

5. The sodium ion battery according to claim 4, Features: The mass percentage of the zwitterionic additive in the electrolyte is 0.5% to 3%.

6. The sodium ion battery according to claim 1 or 2, Features: The mass percentage of the sodium salt in the electrolyte is 6% to 12%.

7. The sodium ion battery according to claim 1 or 2, Features: The mass content of the non-aqueous solvent in the electrolyte is, for example, 70% to 95%.

8. The sodium ion battery according to claim 1, Features: The negative electrode active material further includes at least one of Ti, Fe, Cu, Ni, Co, Mn, Ag, Au and Sn metal elements.

9. The sodium ion battery according to claim 8, Features: The mass content of the metal element in the negative electrode active material is 10 ppm to 500 ppm.

10. An electronic device, Features: It comprises the sodium ion battery as claimed in any one of claims 1 to 9.

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