High-voltage electrolyte and sodium ion secondary battery

Abstract

The invention discloses a high-voltage electrolyte and a sodium ion secondary battery, the high-voltage electrolyte comprises a first additive a and a second additive b, the first additive a is one or more of chain-like sulfonyl oxygen structure compounds, the second additive b is one or more of compounds containing-O-P-F and-O = P-F groups, and the first additive a is one or more of chain-like sulfonyl oxygen structure compounds, and the second additive b is one or more of chain-like sulfonyl oxygen structure compounds. The dosage of the first additive a and the dosage of the second additive b in the electrolyte meet the conditions that 0.01% < = A < = 3% and 0.1% < = B < = 2.5%, A is the mass percentage content of the first additive a in the electrolyte, and B is the mass percentage content of the second additive b in the electrolyte. The problems that the capacity of the sodium-ion battery is rapidly attenuated, the cycle performance is poor, the cycle DCR is greatly increased, and gas production of a battery cell is serious are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery electrolyte additives, and in particular to a high-voltage electrolyte and a sodium ion secondary battery. Background Art

[0002] With the rapid development of the new energy industry, the requirements for battery energy density are getting higher and higher. Sodium-ion batteries are being used more and more widely in the fields of energy storage and power. Sodium is abundant and evenly distributed in the earth's crust, which has the advantages of abundant resources and low cost for the development of new sodium-ion battery energy storage systems. From the perspective of raw material costs, the cost of sodium-ion batteries can be reduced by 30% to 40%; lithium and sodium belong to the same main group elements, sodium-ion batteries and lithium-ion batteries have similar working principles, and the battery production processes are highly similar; therefore, the development of high-performance sodium-ion battery electrochemical energy storage technology with cost and resource advantages is expected to replace some application scenarios of lead-acid batteries and lithium-ion batteries in the future, and realize the sustainable development of low-cost large-scale energy storage technology.

[0003] Increasing the operating voltage of sodium-ion batteries (SIBs) is an important approach to increasing their energy density. However, conventional SIB electrolytes, primarily based on ethylene carbonate (EVC), accelerate oxidative decomposition of the electrolyte on the cathode material during charge and discharge at high cutoff voltages, triggering a series of side reactions that lead to rapid performance degradation and the production of large amounts of CO₂, CO gas, and H₂O. The production of CO₂ poses a potential threat to the safety of the battery cell, while the production of H₂O promotes the decomposition of NaPF₆ to produce HF, which further leads to the dissolution of more transition metals, causing structural collapse of the cathode material and catalytic electrolyte decomposition. At high voltages, especially above 4.0 V, the structural stability of the cathode material deteriorates. Furthermore, at high voltages and temperatures, the electrochemical stability of the binder also faces significant challenges. Reduced adhesion and increased cracking of the cathode material particles can lead to delamination of the active material. These factors inevitably lead to rapid capacity decay, excessively increased cycle-to-load (DCR), and severe cell gassing, significantly limiting the widespread application of SIBs. Therefore, the development of new additives and high-voltage electrolytes is crucial. Summary of the Invention

[0004] In response to the problems of rapid capacity decay, poor cycle performance, large cycle DCR growth, and severe gas production in sodium ion batteries in the prior art, the present invention discloses a high-voltage electrolyte and a sodium ion secondary battery. By optimizing the composition and content of sodium ion battery electrolyte additives, the formation of a stable interface film to protect electrode materials is promoted, the dissolution of transition metals is inhibited, the occurrence of side reactions is slowed down, the high-voltage stability of the battery cell is improved, gas production is inhibited, and the internal resistance growth is further reduced, thereby improving the overall cycle performance and enabling the electrolyte system to have both high energy density and low impedance long cycle performance.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention first provides a high-voltage electrolyte, comprising a first additive a and a second additive b;

[0007] The first additive a is selected from one or more compounds having a chain sulfonyloxy structure and has the following structure:

[0008]

[0009] Wherein, R1 is selected from an alkali metal atom, a C1-C6 halogenated or non-halogenated hydrocarbon group;

[0010] R2 is selected from a halogen atom, a C1-C6 halogenated or non-halogenated hydrocarbon group, a C1-C6 halogenated or non-halogenated hydrocarbonoxy group, a C1-C6 halogenated or non-halogenated ester group or acyloxy group, a C1-C6 halogenated or non-halogenated sulfonyloxy group;

[0011] The second additive b is selected from one or more compounds containing -OPF and -O=PF groups, and has the following structure:

[0012]

[0013] wherein X is an alkali metal atom, a C1-C3 halogenated or non-halogenated hydrocarbon group,

[0014] Y is a halogen atom, a C1-C3 halogenated or non-halogenated hydrocarbonoxy group,

[0015] When X is a halogenated or non-halogenated hydrocarbon group and Y is a halogenated or non-halogenated hydrocarbonoxy group, the second additive b may be a chain or a cyclic compound connected by CC bonds.

[0016] In the figure, X---Y represents a chain compound in which X and Y are not connected, or a cyclic compound formed by C-C bonds.

[0017] The amounts of the first additive a and the second additive b in the electrolyte satisfy: 0.01%≤A≤3%, 0.1%≤B≤2.5%, wherein A is the mass percentage of the first additive a in the electrolyte, and B is the mass percentage of the second additive b in the electrolyte.

[0018] The above-mentioned design of the present invention, by selecting chain sulfonyloxy structure compounds and fluorine-containing phosphorus oxide compounds containing -OPF or -O=PF groups as electrolyte additives, and synergistically optimizing their types and amounts, effectively solves key problems such as rapid battery capacity attenuation, cycle performance degradation, excessive growth of cyclic DC internal resistance (DCR), and severe gas production of battery cells. By combining specific types of additives and precisely controlling their content, the additives are preferentially decomposed to form a low-solubility cathode electrolyte interface (CEI) film. This design successfully constructs a dense, complete, and sulfur-rich interface protective layer, significantly improving the cycle performance of the battery. The sulfur-rich CEI film enhances the stability of the battery cell at high voltage, effectively inhibits complex side reactions, especially gas production reactions, and avoids the peeling of active electrode particles at high voltage, thereby optimizing the cycle performance as a whole and significantly inhibiting the growth of cyclic DCR and battery gas production. Fluorophosphorus compounds containing -OPF and -O=PF groups remove acidic substances produced by side reactions in the electrolyte, providing an environment with fewer by-products for chain sulfonyloxy structure compounds, enabling them to decompose more effectively to form stable, low-solubility sulfur-rich organic-inorganic hybrid membranes. At the same time, inorganic substances (NaF, Na x PO y F z ) can fill the gaps in the sulfur-rich organic network, forming a denser, more complete, flexible and rigid composite CEI membrane. This synergistic effect is the key to achieving a "dense, complete and sulfur-rich interfacial protective layer."

[0019] As a further solution, we preferably select a single amount of each component to satisfy at least one of the following: 0.05%≤A≤1.5%, 0.5%≤B≤2%.

[0020] As a further embodiment, R2 in the first additive a is one of a halogen atom, a C1-C6 halogenated hydrocarbon group, a C1-C6 halogenated hydrocarbonoxy group, a C1-C6 halogenated ester group or acyloxy group, and a C1-C6 halogenated sulfonyloxy group.

[0021] Preferably, the first additive a preferably has R2 as a halogen atom.

[0022] As a further embodiment, the second additive b is a compound having the following structure:

[0023] As a further preferred embodiment, X is one of C1-C3 halogenated or non-halogenated hydrocarbon groups, and Y is one of a halogen atom and a C1-C3 halogenated or non-halogenated hydrocarbonoxy group.

[0024] As a further preferred embodiment, X is one of C1-C3 halogenated or non-halogenated hydrocarbon groups, and Y is one of C1-C3 halogenated or non-halogenated hydrocarbonoxy groups, and the second additive b is a chain compound.

[0025] As a further preferred embodiment, at least one of X and Y is a halogenated group.

[0026] As a further solution, a high-voltage resistant sodium ion battery electrolyte also includes sodium salt and an organic solvent.

[0027] As a further embodiment, the sodium salt is one or more of sodium hexafluorophosphate, sodium difluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium difluorooxalatoborate, sodium bis(oxalatoborate), sodium nitrate, sodium hexafluoroantimonate, sodium hexafluoroarsenate, sodium difluorobis(oxalatophosphate), sodium tetrafluorooxalatophosphate, and sodium tetrafluoroborate.

[0028] As a further embodiment, the sodium salt is sodium hexafluorophosphate.

[0029] As a further solution, the organic solvent is one or more of an ether solvent, an ester solvent, and an ionic liquid.

[0030] As a further embodiment, the ether solvent is selected from one or more of ether solvents containing hydroxyl groups, ether solvents containing a single ether bond, and ether solvents containing complex functional groups.

[0031] As a further embodiment, the complex functional group is selected from one or more of C1-C10 alkoxy, alkenyl, and alkynyl groups.

[0032] As a further solution, the hydroxyl-containing ether solvent is selected from one or more of dipropylene glycol butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol monomethyl ether, triethylene glycol monomethyl ether, and tetraethylene glycol dimethyl ether.

[0033] As a further solution, the ether solvent containing a single ether bond is selected from one or more of cyclopentyl methyl ether, ethyl ether, and propyl ether.

[0034] As a further solution, the ether solvent containing complex functional groups is selected from one or more of butynediol dipropoxy ether, propargyl ether, and propargyl ether.

[0035] As a further solution, the ester solvent is selected from one or more of linear ester solvents and cyclic carbonate solvents.

[0036] As a further embodiment, the linear ester is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl vinyl carbonate, methyl acetate, and propyl acetate.

[0037] As a further embodiment, the cyclic carbonate is selected from one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, and 1,2 - propylene glycol carbonate.

[0038] As a further embodiment, the source of nickel element in the positive electrode material is not limited, and nickel element can be introduced into the positive electrode material in any feasible manner according to needs. As some optional ways, nickel element can be directly used as one of the structural components of the positive electrode active material, or can be introduced into the positive electrode material as a nickel - containing additive in the form of a nickel - containing additive, such as NiO, etc.

[0039] As a further embodiment, the positive electrode active material is a metal layered oxide, and the general formula of the metal layered oxide is Na x Mn y M z O2, where 0.95 < x ≤ 1.05, 0.01 ≤ y ≤ 0.6, y + z = 1, and M represents a transition metal element with an unfilled d - electron orbital, specifically including one or more of scandium (Sc), yttrium (Y), lanthanide elements (from lanthanum (La) to lutetium (Lu)), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), copper (Cu), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), and mercury (Hg).

[0040] As a further embodiment, M in the positive electrode active material includes Ni.

[0041] As a further preferred embodiment, the molar percentage content of Ni element in the positive electrode active material among all transition metal elements is 10% - 50%.

[0042] As a further embodiment, an oil - based binder is used, and the binder includes at least one of a thermoplastic resin, an acrylic resin, sodium carboxymethyl cellulose, and styrene - butadiene rubber.

[0043] As a further embodiment, the thermoplastic resin includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride - hexafluoropropylene, a copolymer of tetrafluoroethylene - hexafluoropropylene, a copolymer of tetrafluoroethylene - perfluoroalkyl vinyl ether, a copolymer of ethylene - tetrafluoroethylene, a copolymer of vinylidene fluoride - tetrafluoroethylene, a copolymer of vinylidene fluoride - trifluoroethylene, a copolymer of vinylidene fluoride - trichloroethylene, a copolymer of vinylidene fluoride - fluoroethylene, a copolymer of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene.

[0044] As a further solution, the acrylic resin includes at least one of vinyl acrylate resin, methyl acrylate resin, butyl acrylate resin, acrylic styrene resin, acrylate resin, acrylate copolymer resin, acrylic resin, and acrylic emulsion resin.

[0045] As a further solution, the binder is polyvinylidene fluoride (PVDF).

[0046] Preferably, the binder accounts for 1% to 3% by mass of the positive electrode slurry.

[0047] The present invention also provides a sodium ion battery, comprising the electrolyte, a positive electrode sheet containing the positive electrode material, a negative electrode sheet containing the negative electrode material, and a separator.

[0048] As a further solution, the sodium ion battery is manufactured by forming the positive electrode sheet, the negative electrode sheet, and the isolation membrane into an electrode assembly through a winding process or a lamination process, and the preferred solution is the winding process.

[0049] As a further solution, the positive electrode material includes a positive electrode active material NaCu 1 / 10 Ni 3 / 10 Fe 2 / 10 Mn 4 / 10 O2, the binder polyvinylidene fluoride (PVDF), and also includes conductive carbon black Super-P, conductive agent CNT, solvent and positive electrode current collector aluminum foil.

[0050] As a further solution, the negative electrode material includes one or more of hard carbon, conductive agent Super P, thickener CMC, binder SBR and negative electrode current collector aluminum foil.

[0051] As a further solution, the outer packaging of the sodium ion battery is a bag-type soft package or an aluminum shell or a steel shell.

[0052] As a further solution, the shape of the sodium ion battery is not limited and can be cylindrical, square or any other shape. A preferred solution is a cylindrical aluminum shell.

[0053] The characteristics and beneficial effects of the present invention are:

[0054] The present invention provides a high-voltage electrolyte and a sodium-ion secondary battery. This technical solution significantly improves the stability of the sodium-ion battery under high voltage, helps to build a stable interface film, and enhances the interaction between the overall active particles and the binder. Together, they effectively prevent the occurrence of problems such as structural collapse of the positive electrode material, active particle fragmentation, transition metal dissolution, excessive side reactions, and battery gas expansion under high voltage and high temperature, thereby improving the battery's cycle performance under high temperature and high voltage.

[0055] By regulating the content of the first additive a and the second additive b to 0.01%≤A≤3%, 0.1%≤B≤2.5%, additive a, as a salt additive, produces a more compact and dense CEI interface film with its anion, which preferentially protects the positive electrode, forms a dense passivation film on the surface of the positive electrode that is resistant to high temperature and corrosion, and inhibits the dissolution of transition metals; additive b decomposes to produce organic phosphate compounds, ring-opening products of cyclic phosphates, and inorganic Na x PO y F z 、NaF and other dense CEI interface films, filling the gaps in the sulfur-rich interface film, enhancing the stability and integrity of the interface film, and helping to improve the stability under high voltage, reduce the occurrence of complex side reactions, and significantly inhibit gas production. The first additive a and the second additive b are in Ni 2+ The inorganic components in the passivation layer are anchored to the surface of the positive electrode material in the form of chemical bonds, and the cross-linked organic polymer at the other end is anchored to the conductive bonding network formed by the binder and the conductive agent in the form of mechanical interlocking, thereby avoiding the serious shedding of positive electrode particles under high voltage; the stability of the battery cell under high voltage can be optimized, and the performance of the battery cell can be further improved; the passivation layer has lower solubility and lower impedance, which to a certain extent alleviates the rapid growth of the cycle DCR, inhibits the dissolution of transition metals, inhibits the gas production of the battery, and improves the cycle performance of the battery under high temperature and high voltage; in addition, the present invention further optimizes the specific types of the first additive a and the second additive b, and conducts in-depth optimization for the different chemical properties, film-forming properties, antioxidant capacity and side reaction inhibition capacity brought by different substituents, thereby further improving the cycle performance of the battery under high temperature and high voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The capacity retention rate of Example 1 and Comparative Example 1 of the present invention at 45°C, 2-4.2V, and 1C / 1C charge-discharge cycle;

[0057] Figure 2 It is the DCR growth of Example 1 and Comparative Example 1 in the present invention under 45°C cycling. DETAILED DESCRIPTION

[0058] To facilitate understanding of the present invention, a high-voltage electrolyte and a sodium-ion secondary battery will be described more comprehensively below in combination with specific details and embodiments of the present invention, but the scope of the present invention is not limited thereby.

[0059] The present invention first provides a high-voltage electrolyte, including a first additive a and a second additive b;

[0060] The first additive a is selected from one or more compounds having a chain sulfonyloxy structure and has the following structure:

[0061]

[0062] Wherein, R1 is selected from an alkali metal atom, a C1-C6 halogenated or non-halogenated hydrocarbon group;

[0063] R2 is selected from a halogen atom, a C1-C6 halogenated or non-halogenated hydrocarbon group, a C1-C6 halogenated or non-halogenated hydrocarbonoxy group, a C1-C6 halogenated or non-halogenated ester group or acyloxy group, a C1-C6 halogenated or non-halogenated sulfonyloxy group;

[0064] The second additive b is selected from one or more compounds containing -OPF and -O=PF groups, and has the following structure:

[0065]

[0066] wherein X is an alkali metal atom, a C1-C3 halogenated or non-halogenated hydrocarbon group,

[0067] Y is a halogen atom, a C1-C3 halogenated or non-halogenated hydrocarbonoxy group,

[0068] When X is a halogenated or non-halogenated hydrocarbon group and Y is a halogenated or non-halogenated hydrocarbonoxy group, the second additive b may be a chain or a cyclic compound connected by CC bonds.

[0069] In the figure, X---Y represents a chain compound in which X and Y are not connected, or a cyclic compound formed by connecting them with a C-C bond.

[0070] The amounts of the first additive a and the second additive b in the electrolyte satisfy: 0.01%≤A≤3%, 0.1%≤B≤2.5%, wherein A is the mass percentage of the first additive a in the electrolyte, and B is the mass percentage of the second additive b in the electrolyte.

[0071] By selecting chain sulfonyloxy structure compounds and fluorine-containing phosphorus oxide compounds containing -OPF or -O=PF groups as electrolyte additives, and synergistically optimizing their types and dosages, key problems such as rapid battery capacity attenuation, cycle performance degradation, excessive growth of cyclic DC internal resistance (DCR), and severe gas production in the battery cells have been effectively solved. By combining specific types of additives and precisely controlling their content, the additives are preferentially decomposed to form a low-solubility cathode electrolyte interface (CEI) film. This design successfully constructs a dense, complete, and sulfur-rich interface protective layer, significantly improving the battery's cycle performance at high voltage. The sulfur-rich CEI film enhances the stability of the battery cell at high voltage, effectively inhibits complex side reactions, especially gas production reactions, and avoids the peeling of active electrode particles at high voltage, thereby optimizing the cycle performance as a whole and significantly inhibiting the growth of cyclic DCR and battery gas production. Fluorophosphorus compounds containing -OPF and -O=PF groups remove acidic substances produced by side reactions in the electrolyte, providing an environment with fewer by-products for chain sulfonyloxy structure compounds, enabling them to decompose more effectively to form stable, low-solubility sulfur-rich organic-inorganic hybrid membranes. At the same time, inorganic substances (NaF, Na x PO y F z ) can fill the gaps in the sulfur-rich organic network, forming a denser, more complete, flexible, and rigid composite CEI film. This synergistic effect is the key to achieving a dense, complete, and sulfur-rich interfacial protective layer and high voltage performance.

[0072] As a further preferred example, we prefer that the single amount of each component satisfies at least one of the following: 0.05%≤A≤1.5%, 0.5%≤B≤2%.

[0073] Preferably, 0.05%≤A≤1.5%, and the mass content of the first electrolyte additive a is controlled within an appropriate range, which is more inclined to decompose and form more CEI films with lower solubility, construct a dense and complete S-rich interface film, and improve the cycle performance.

[0074] Preferably, 0.5%≤B≤2%. Controlling the mass content of the second additive b in the electrolyte within an appropriate range is more conducive to improving stability under high voltage, reducing the occurrence of complex side reactions, and significantly inhibiting gas production.

[0075] When the above range is met, the high voltage stability of the obtained battery cell is significantly improved. This is mainly because the synergistic relationship between the content of the first additive a and the content of the second additive b has a very significant impact on the interface stability and the stability between the positive electrode active particles. When the above dosage is not met, under high voltage and high temperature conditions, due to the poor interface stability and the stability between the positive electrode active particles, the dissolution of the transition metal and the decomposition of the electrolyte will be accelerated, and the cycle performance of the battery cell will be deteriorated, especially the cycle performance under high temperature and high voltage cycles. The gas production level will increase, and even some safety problems may arise.

[0076] As a further preferred example, R1 in the first additive a provided by the present invention is preferably a sodium atom.

[0077] Sodium sulfonate salt as an electrolyte additive can effectively reduce the viscosity of the electrolyte, thereby reducing internal resistance, improving the charge and discharge efficiency of the battery, improving the ionic conductivity of the electrolyte, and thus improving the overall performance of the battery.

[0078] As a further preferred example, R2 in the first additive a is one of a halogen atom, a C1-C6 halogenated hydrocarbon group, a C1-C6 halogenated hydrocarbonoxy group, a C1-C6 halogenated ester group or acyloxy group, and a C1-C6 halogenated sulfonyloxy group.

[0079] Preferably, the first additive a preferably has R2 as a halogen atom.

[0080] When halogen-containing additives are reduced on the negative electrode surface, inorganic components are preferentially generated. These substances have high electrical conductivity, promote rapid sodium ion transmission, reduce interfacial impedance, and the halogen-containing interfacial film has high mechanical strength, resisting further decomposition of the electrolyte and stabilizing the SEI film.

[0081] As a preferred example, the second additive b is a compound having the following structure:

[0082] Preferably, X is one of C1-C3 halogenated or non-halogenated hydrocarbon groups, and Y is one of a halogen atom and a C1-C3 halogenated or non-halogenated hydrocarbonoxy group;

[0083] Preferably, X is one of C1-C3 halogenated or non-halogenated hydrocarbon groups, Y is one of C1-C3 halogenated or non-halogenated hydrocarbonoxy groups, and the second additive b is a chain compound.

[0084] As a further preferred embodiment, at least one of X and Y is a halogenated group.

[0085] As a further preferred example, the first additive a provided by the present invention is selected from: a-1

[0086] a-2 a-3 a-4 a-5 a-6 a-7 a-8 a-9 a-10 a-11 a-12 a-13 One or more of .

[0087] As a further preferred example, the present invention also provides a second additive b selected from b-1 b-2 b-3 b-4 b-5 b-6 b-7 b-8 b-9 b-10 B-11 b-12 B-13 b-14 b-15 B-16 B-17 B-18 B-19 B-20 One or more of .

[0088] As an example, a high-voltage resistant sodium ion battery electrolyte also includes sodium salt and an organic solvent.

[0089] Illustratively, the sodium salt is one or more of sodium hexafluorophosphate, sodium difluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorooxalatoborate), sodium bis(oxalatoborate), sodium nitrate, sodium hexafluoroantimonate, sodium hexafluoroarsenate, sodium difluorobis(oxalatophosphate), sodium tetrafluorooxalatophosphate, and sodium tetrafluoroborate.

[0090] As a preferred example, the sodium salt is sodium hexafluorophosphate (NaPF6).

[0091] Illustratively, the organic solvent is one or more of an ether solvent, an ester solvent, and an ionic liquid.

[0092] As an example, the ether solvent is selected from one or more of an ether solvent containing a hydroxyl group, an ether solvent containing a single ether bond, and an ether solvent containing a complex functional group;

[0093] The complex functional group is selected from one or more of C1-C10 alkoxy, alkenyl, and alkynyl groups;

[0094] The hydroxyl-containing ether solvent is selected from one or more of dipropylene glycol butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol monomethyl ether, triethylene glycol monomethyl ether, and tetraethylene glycol dimethyl ether.

[0095] The ether solvent containing a single ether bond is selected from one or more of cyclopentyl methyl ether, ethyl ether, and propyl ether.

[0096] The ether solvent containing complex functional groups is selected from one or more of butynediol dipropoxy ether, propargyl ether, and propargyl ether;

[0097] As an example, the ester solvent is selected from one or more of linear ester solvents and cyclic carbonate solvents.

[0098] The linear ester solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl vinyl ester, methyl acetate, and propyl acetate.

[0099] The cyclic carbonate solvent is selected from one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, and 1,2-propylene glycol carbonate.

[0100] The source of the nickel element in the positive electrode material is not limited, and the nickel element can be introduced into the positive electrode material in any feasible manner as needed. As some optional methods, the nickel element can be directly used as one of the structural components of the positive electrode active material, or can be introduced into the positive electrode material in the form of a nickel-containing additive as a positive electrode additive, such as NiO.

[0101] As an example, the positive electrode active material is a metal layered oxide, and the metal layered oxide has the general formula of Na x Mn y M zO2, where 0.95 < x ≤ 1.05, 0.01 ≤ y ≤ 0.6, y + z = 1, and M represents a transition metal element with unfilled d electron orbitals, specifically including scandium (Sc), yttrium (Y), lanthanide elements (from lanthanum (La) to lutetium (Lu)), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), copper (Cu), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), or one or more of them.

[0102] Exemplarily, M in the positive electrode active material includes Ni.

[0103] The molar percentage content of Ni element in all transition metal elements in the positive electrode active material is from 10% to 50%.

[0104] Controlling the molar percentage content of Ni element in the positive electrode material within a suitable range neither affects the role of Ni element in stabilizing the positive electrode material structure nor jointly acts with the first additive a and the second additive b to enhance the stability of the positive electrode active particles and the conductive binder network, avoiding the exfoliation of the positive electrode particles at higher voltages. Because the first additive a and the second additive b will decompose under the 2+ catalytic action of Ni to generate a passivation layer of a cross-linked polymer rich in inorganic components, and this passivation layer interacts with the binder to avoid the exfoliation of the positive electrode active material.

[0105] Exemplarily, the binder uses an oil-based binder, and the binder includes at least one of thermoplastic resin, acrylic resin, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0106] Exemplarily, the thermoplastic resin includes at least one of polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene.

[0107] As an example, the acrylic resin includes at least one of vinyl acrylate resin, methyl acrylate resin, butyl acrylate resin, acrylic styrene resin, acrylate resin, acrylate copolymer resin, acrylic resin, and acrylic emulsion resin.

[0108] As a preferred example, the binder is polyvinylidene fluoride (PVDF).

[0109] Preferably, the binder accounts for 1% to 3% by mass of the positive electrode slurry.

[0110] Controlling the binder content within an appropriate range can not only ensure that the components of the electrode are evenly dispersed and give full play to the role of bonding active materials, conductive agents and current collectors, but also avoid affecting the overall energy density of the battery cell due to excessive content. At the same time, it will strengthen the interaction between the inorganic / cross-linked organic mixed passivation layer and the conductive bonding network.

[0111] The present invention also provides a sodium ion battery, comprising the electrolyte, a positive electrode sheet containing the positive electrode material, a negative electrode sheet containing the negative electrode material, and a separator.

[0112] The sodium ion battery is manufactured by forming the positive electrode sheet, the negative electrode sheet, and the separator into an electrode assembly through a winding process or a lamination process, and the preferred solution is the winding process.

[0113] The positive electrode sheet includes a positive electrode active material NaCu 1 / 10 Ni 3 / 10 Fe 2 / 10 Mn 4 / 10 O 22 , the binder polyvinylidene fluoride (PVDF), and also includes conductive carbon black Super-P, conductive agent CNT, solvent and positive electrode current collector aluminum foil.

[0114] The negative electrode sheet includes one or more of hard carbon, a conductive agent Super P, a thickener CMC, a binder SBR, and a negative electrode current collector aluminum foil.

[0115] The outer packaging of the sodium ion battery is a bag-type soft package or an aluminum shell or a steel shell.

[0116] The shape of the sodium ion battery is not limited and can be cylindrical, square or any other shape. The preferred embodiment is a cylindrical aluminum shell.

[0117] As a specific embodiment of the present invention, the following detailed cases are provided:

[0118] Example 1:

[0119] This embodiment provides a sodium ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0120] The positive electrode sheet includes a positive electrode active material NaCu 1 / 20 Ni 6 / 20 Fe 6 / 20 Mn 7 / 20 O2, conductive carbon black Super-P, binder polyvinylidene fluoride (PVDF) and positive electrode current collector aluminum foil, the average pore radius distribution range of the positive electrode sheet is 6 μm;

[0121] The negative electrode sheet includes a negative electrode material layer and a negative electrode current collector aluminum foil, wherein the negative electrode material layer includes negative electrode active material hard carbon, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC), and the average pore radius distribution range of the negative electrode sheet is 50 μm;

[0122] Preparation of the electrolyte: In an argon atmosphere, the environmental indicators of the glove box are H2O≤0.5ppm, O2≤0.5ppm, first, the solvents propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 30:50:20, and then 1M sodium salt NaPF6 is dissolved in the mixed solvent, and then the first additive a-1 and the second additive b-1 are added and stirred evenly to obtain an electrolyte; based on the total mass of the electrolyte, the mass content of the first additive a-1 is 0.5%, and the mass content of the second additive b-1 is 1%.

[0123] Preparation of the positive electrode sheet: the positive electrode active material NaCu 1 / 10 Ni 3 / 10 Fe 2 / 10 Mn 4 / 10 O2, conductive agent SuperP, conductive agent CNT, and binder PVDF are dissolved in solvent N-methyl-2-pyrrolidone (NMP) in a mass ratio of 96.5:1.5:0.5:1.5, and stirred evenly to obtain a positive electrode slurry with a slurry viscosity of 5000±1000mPa·s and a solid content of 65±0.5wt%. The obtained positive electrode slurry is then evenly coated on aluminum foil, and then dried, cold pressed, and cut to obtain positive electrode sheets.

[0124] Preparation of the negative electrode sheet: The negative electrode active material hard carbon, the conductive agent Super P, the thickener CMC, and the binder SBR are mixed in a mass ratio of 94:2:1.5:2.5, and deionized water is added and stirred uniformly to obtain a negative electrode slurry. The slurry viscosity is adjusted to 4500±500mPa·s and the solid content is 50±0.5wt%; the slurry is then coated on the negative electrode current collector aluminum foil, and then dried, cold pressed, and slit to obtain the negative electrode sheet.

[0125] Preparation of the sodium ion battery: The positive electrode sheet, the negative electrode sheet, and the separator are formed into an electrode assembly through a winding process or a lamination process. This embodiment adopts the winding process.

[0126] The outer packaging of the sodium ion battery can be a bag-type soft bag or an aluminum shell, a steel shell, etc. The shape of the sodium ion battery is not limited and can be cylindrical, square or any other shape. This embodiment uses a bag-type soft bag.

[0127] Under the above conditions, the following tests were performed:

[0128] Battery gas production test: The water displacement method is used to test the gas production of soft-pack batteries. The water displacement method is a soft-pack battery gas production test method based on the Archimedean principle. The gas production is calculated by measuring the volume change of the liquid displaced by the battery when immersed in the liquid. At room temperature, a glass container is filled with a sufficient amount of ultrapure water, with the liquid height higher than the battery height. The battery cell at the beginning of the cycle is fixed on a suspension device so that it is completely immersed in the liquid, and the initial weighing reading M1 is recorded. After the high-temperature cycle is completed, the battery cell is immersed in the liquid again, and the weighing reading M2 is recorded at this time. The gas production is calculated according to the formula V = (M2-M1) / ρ, where ρ is the density of ultrapure water.

[0129] High temperature cycle test: At a high temperature of 45±2℃, charge and discharge cycles are performed at 1C / 1C with a voltage range of 2 to 4.2V, and the number of cycles until the capacity decays to 80% is recorded;

[0130] Cycling DCR growth test: record the DCR at the beginning of the cycle at 45℃ and the DCR when the capacity decays to 80% at 45℃;

[0131] Examples 2 to 30, Comparative Examples 1 to 11:

[0132] A sodium ion battery was prepared and tested in the same manner as in Example 1, with some parameters modified. The parameter modifications and results are listed in Table 1.

[0133] The test results obtained in Examples 1 to 30 and Comparative Examples 1 to 11 are shown in Table 1:

[0134] Table 1

[0135]

[0136]

[0137] From Examples 1 to 33 and Comparative Examples 1 to 5, it can be observed that:

[0138] When 0.01%≤A≤3% and 0.1%≤B≤2.5% are met at the same time, the battery gas production is ≤4.78mL / Ah, the number of cycles at which the capacity decays to 80% at high temperature is ≥639, and the DCR increase at which the capacity decays to 80% is ≤29.34%. The above parameters can ensure the most basic performance of the sodium-ion battery. Compared with the comparative example, the battery gas production is reduced, the cycle performance and capacity retention rate at high temperature are improved, and the increase of DCR is reduced.

[0139] Comparative Examples 1 to 5 show the relevant performance when 0.01%≤A≤3% and 0.1%≤B≤2.5% are not satisfied. Under these parameters, the most basic performance of the sodium ion battery cannot be guaranteed.

[0140] Specifically, such as Figure 1 and Figure 2 The data shown shows the number of cycles required for the capacity to decay to 80% and the DCR growth rate at 1C for Example 1 and Comparative Example 1 at 45°C. Under high temperature and high voltage conditions, the number of cycles required for the capacity to decay to 80% was 803 for Example 1, while the number of cycles required for Comparative Example 1 to decay to 80% was 295. The DCR growth rate was 22.10% when the capacity decayed to 80% for Example 1, while the DCR growth rate was 36.30% when the capacity decayed to 80% for Comparative Example 1. The relevant performance of Comparative Example 1 is far inferior to that of Example 1.

[0141] Comparative Examples 1 to 2 and Comparative Example 3 are the cases where only the first additive a, only the second additive b, and no additive are added, respectively; at this time, the battery gas production is high, all greater than 12.6 mL / Ah, and the cycle performance is also poor. The number of cycles at which the capacity decays to 80% at high temperature is ≤295, and the DCR increase at which the capacity decays to 80% is ≥36.3%.

[0142] This shows that the first additive and the second additive have a synergistic effect in the formation and stabilization of the inorganic component-rich cross-linked polymer passivation layer and in the suppression of battery gas production. The lack of either additive will lead to the instability of the SEI film, which is not conducive to the construction of a dense and complete S-rich interface film and reduces the cycle life at high temperatures. The first additive preferentially forms a sulfur-rich inorganic skeleton Na2SO4 on the electrode surface, providing a mechanical barrier to inhibit the dissolution of transition metals. The second additive b decomposes on the positive electrode surface to produce organic phosphate compounds, ring-opening products of cyclic phosphates, and inorganic Na x PO y F z , NaF and other dense CEI interface films, which inhibit the side reactions on the positive electrode side, effectively suppress serious gas production of the battery cell, and further improve the cycle stability and high temperature performance of the battery.

[0143] Comparative Examples 4 and 5 are cases where the first additive a or the second additive b is excessive. In this case, the battery gas production is high and the cycle life at high temperature and the number of cycles at which the capacity is retained at 80% are also low. This is because the electrolyte additive decomposes under high pressure or high temperature, generating gas; or reacts with the electrolyte solvent or sodium salt to generate gas products. Excessive additives will also promote excessive growth of the SEI film, increase the diffusion resistance of sodium ions, and lead to increased polarization.

[0144] As a further preferred example, according to Examples 1 to 5 and 10 to 13, under the same other conditions, 0.05% ≤ A ≤ 1.5% is preferably used as the mass percentage of the first additive a, and 0.5% ≤ B ≤ 2% is preferably used as the mass percentage of the second additive b. Optimizing the content range of each component further improves the performance of the sodium ion battery.

[0145] According to Examples 1, 18-21, and 30-31, the binder content of the positive electrode slurry was optimized to be 1% to 3% by mass. Binders are typically used to fix active materials, conductive agents, and current collectors, and simultaneously form a stable cross-linked network structure with the interfacial film to promote ion transport. Therefore, insufficient binder may affect structural stability and cause active material shedding, which directly reduces battery capacity. Furthermore, high internal resistance can lead to more severe battery heating, reduced charge and discharge efficiency, and potentially affected rate performance. Excessive electrolyte penetration can form an excessively thick SEI film, consuming sodium sources, further increasing internal resistance, and shortening battery life.

[0146] According to Examples 1, 22 to 25, and 32 to 33, the molar percentage of Ni in all transition metal elements is optimized to be 10% to 50%, and the molar percentage of Ni in all transition metal elements in the positive electrode material is controlled within an appropriate range, which does not affect the role of Ni in stabilizing the structure of the positive electrode material, and works together with the first additive a and the second additive b to enhance the stability of the positive electrode active particles and the conductive bonding network, thereby avoiding the peeling of the positive electrode particles at higher voltages. 2+ Under catalytic action, it will decompose to produce a passivation layer of a cross-linked polymer rich in inorganic components, and this passivation layer interacts with the binder to prevent the peeling of the positive electrode active material.

[0147] According to the comparison of Examples 1, 6, 7, 8, and 9, when R2 in the first additive a is a halogen, a halogenated hydrocarbon group of C1 to C6, a halogenated hydrocarbonoxy group of C1 to C6, a halogenated ester group or acyloxy group of C1 to C6, or a halogenated sulfonyloxy group of C1 to C6, the performance is better than that of a non-halogenated group, and when R2 in the first additive a is F, the performance is even better.

[0148] This may be because the highly electronegative halogen reduces the electron cloud density of oxygen atoms through a strong electron-withdrawing effect, making the molecules more likely to participate in the reaction on the electrode surface and promoting the formation of a stable SEI film.

[0149] As a further solution, according to Examples 1, 14, 15, 16, and 17, the second additive b has a structure of a compound having -OPF, which has better performance than -O=PF. Further, when X is one of C1-C3 halogenated or non-halogenated hydrocarbon groups, and Y is one of halogen, C1-C3 halogenated or non-halogenated hydrocarbonoxy, it is better. When X is a C1-C3 halogenated or non-halogenated hydrocarbon group, and Y is a halogenated or non-halogenated hydrocarbonoxy group, and the second additive b is a chain compound, it is better. When at least one of X and Y is a halogenated group, the performance is better.

[0150] This may be because the OPF structure may have stronger coordination ability than O=PF, can form more stable complexes with sodium ions, and reduce side reactions; the introduction of hydrocarbon and hydrocarbon oxygen groups may adjust the polarity and solubility of the molecule, making it more evenly dispersed in the electrolyte, and the halogenated group may enhance the molecule's antioxidant and thermal stability, especially under high voltage or high temperature conditions; the chain structure may have lower viscosity than the ring structure, which is conducive to ion transport and provides more binding sites.

[0151] The organic electrolyte provided by the present invention comprises a first additive a and a second additive b in the additive, and at a high potential, the first additive a and the second additive b are Ni in the positive electrode material. 2+ Under the catalytic action of Ni, a passivation layer of a cross-linked organic polymer rich in inorganic components is produced. 2+ The valence electrons are concentrated in the 3d orbital, and the valence electrons 3d8 and the presence of unpaired single electrons give it a unique electron transfer ability. In addition, the content of Ni in high-capacity positive electrode materials is relatively high, which makes it easier to catalyze the decomposition of the first additive a and the second additive b. The inorganic components in the decomposed passivation layer are anchored on the surface of the positive electrode material through chemical bonds, and the other end of the cross-linked organic polymer is anchored on the conductive bonding network formed by the binder and the conductive agent in the form of mechanical interlocking. Among them, the first additive a is a salt additive, and the CEI interface film produced by its anions is more compact and dense. After the film is formed on the surface of the positive electrode material, the main inorganic components produced, such as sulfates Na2SO4 and Na2S x O y , sodium sulfonate salt ROSO2Na and other inorganic cross-linked S-containing organic polymers, which give priority to protecting the positive electrode, inhibiting the dissolution of transition metals, stabilizing the CEI interface film, and reducing the impedance of the CEI film; the second additive b will decompose to produce important organic phosphate compounds, ring-opening products of cyclic phosphates and inorganic products Na x PO yF z , NaF, etc., which inhibit the side reactions on the positive electrode side and effectively suppress the serious gas production of the battery cell. The inorganic component structure in the passivation film is anchored to the surface of the positive electrode material through chemical bonds, and the cross-linked polymer organic component is anchored to the conductive bonding network formed by the binder and the conductive agent in the form of mechanical interlocking, which significantly improves the stability of the positive electrode active material and the conductive bonding network and avoids the peeling and shedding of the positive electrode active material. The synergistic effect of the above factors constructs a more stable interface film, improves the stability of the positive electrode active material and the conductive network, so that the sodium ion battery exhibits excellent high-voltage cycle stability and suppresses battery gas production.

[0152] This technical solution significantly improves the stability of sodium-ion batteries at high voltages, helps build a stable interface film, and enhances the interaction between the overall active particles and the binder. Together, they effectively prevent the structural collapse, active particle fragmentation, transition metal dissolution, and excessive side reactions of the positive electrode material under high voltage and high temperature, reducing the rapid growth of the cycle DCR and improving the high-temperature cycle performance of the battery. This avoids the rapid decay of the battery cell capacity, while reducing the growth of the cycle DCR, improving the battery's charge and discharge cycle performance, and inhibiting gas production. The electrolyte additive prepared by this method improves the electrochemical performance and safety of sodium-ion batteries.

[0153] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high voltage electrolyte, characterized in that: comprising a first additive a and a second additive b; The first additive a is selected from one or more compounds having a chain sulfonyloxy structure and has the following structure: wherein R1 is selected from an alkali metal atom, a C1-C6 halogenated or non-halogenated hydrocarbon group; R2 is selected from a halogen atom, a C1-C6 halogenated or non-halogenated hydrocarbon group, a C1-C6 halogenated or non-halogenated hydrocarbonoxy group, a C1-C6 halogenated or non-halogenated ester group or acyloxy group, and a C1-C6 halogenated or non-halogenated sulfonyloxy group; The second additive b is selected from one or more compounds containing -OPF and -O=PF groups, and has the following structure: wherein X is an alkali metal atom, a C1-C3 halogenated or non-halogenated hydrocarbon group, Y is a halogen atom, a C1-C3 halogenated or non-halogenated hydrocarbonoxy group, When X is a halogenated or non-halogenated hydrocarbon group and Y is a halogenated or non-halogenated hydrocarbonoxy group, the second additive b may be a chain or a cyclic compound connected by CC bonds. The amounts of the first additive a and the second additive b in the electrolyte satisfy 0.01%≤A≤3%, 0.1%≤B≤2.5%, wherein A is the mass percentage of the first additive a in the electrolyte, and B is the mass percentage of the second additive b in the electrolyte.

2. A high voltage electrolyte according to claim 1, characterized in that: A and B satisfy at least one of the following: 0.05%≤A≤1.5%, 0.5%≤B≤2%.

3. The high voltage electrolyte according to claim 1, characterized in that: In the first additive a, R2 is one of a halogen atom, a C1-C6 halogenated hydrocarbon group, a C1-C6 halogenated hydrocarbonoxy group, a C1-C6 halogenated ester group or acyloxy group, and a C1-C6 halogenated sulfonyloxy group; Preferably, the first additive a preferably has R2 as a halogen atom.

4. The high voltage electrolyte according to claim 1, characterized in that: The second additive b is a compound having the following structure: Preferably, X is one of C1-C3 halogenated or non-halogenated hydrocarbon groups, and Y is one of a halogen atom and a C1-C3 halogenated or non-halogenated hydrocarbonoxy group; Preferably, X is one of C1-C3 halogenated or non-halogenated hydrocarbon groups, Y is one of C1-C3 halogenated or non-halogenated hydrocarbonoxy groups, and the second additive b is a chain compound; Preferably, at least one of X and Y is a halogenated group.

5. The high voltage electrolyte according to claim 1, characterized in that: The first additive a is selected from One or more of; The second additive b is selected from One or more of .

6. The high voltage electrolyte according to claim 1, characterized in that: Also includes sodium salts and organic solvents.

7. A high voltage electrolyte according to claim 6, characterized in that: The sodium salt is one or more of sodium hexafluorophosphate, sodium difluorophosphate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium difluorooxalatoborate, sodium bis(oxalatoborate), sodium nitrate, sodium hexafluoroantimonate, sodium hexafluoroarsenate, sodium difluorobis(oxalatophosphate), sodium tetrafluorooxalatophosphate, and sodium tetrafluoroborate; Preferably, the sodium salt is sodium hexafluorophosphate.

8. The high voltage electrolyte according to claim 6, characterized in that: The organic solvent is one or more of an ether solvent, an ester solvent, and an ionic liquid; Preferably, the ether solvent is selected from one or more of ether solvents containing hydroxyl groups, ether solvents containing a single ether bond, and ether solvents containing complex functional groups; Preferably, the complex functional group is selected from one or more of C1-C10 alkoxy, alkenyl, and alkynyl groups; Preferably, the hydroxyl-containing ether solvent is selected from one or more of dipropylene glycol butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol monomethyl ether, triethylene glycol monomethyl ether, and tetraethylene glycol dimethyl ether; Preferably, the ether solvent containing a single ether bond is selected from one or more of cyclopentyl methyl ether, ethyl ether, and propyl ether; Preferably, the ether solvent containing complex functional groups is selected from one or more of butynediol dipropoxy ether, propargyl ether, and propargyl ether; Preferably, the ester solvent is selected from one or more of linear ester solvents and cyclic carbonate solvents; Preferably, the linear ester is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl vinyl carbonate, methyl acetate, and propyl acetate; Preferably, the cyclic carbonate is selected from one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, and 1,2-propylene glycol carbonate.

9. The high voltage electrolyte according to claim 1, characterized in that: The source of nickel in the positive electrode material includes directly being one of the structural components of the positive electrode active material and / or being introduced into the positive electrode material as a positive electrode additive in the form of a nickel-containing additive; Preferably, the nickel-containing additive is NiO; Preferably, the positive electrode active material is a metal layered oxide, and the general formula of the metal layered oxide is Na x Mn y M z O2, where 0.95 < x ≤ 1.05, 0.01 ≤ y ≤ 0.6, y + z = 1, and M represents a transition metal element with an unfilled d electron orbital, specifically including scandium (Sc), yttrium (Y), lanthanide elements (from lanthanum (La) to lutetium (Lu)), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), copper (Cu), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), or one or more of them; Preferably, M in the positive electrode active material comprises Ni; The molar percentage of Ni element in the positive electrode active material to all transition metal elements is 10% to 50%; Preferably, the binder uses an oil-based binder, and the binder includes at least one of a thermoplastic resin, an acrylic resin, sodium carboxymethyl cellulose, and styrene butadiene rubber; Preferably, the thermoplastic resin includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene and polypropylene; Preferably, the acrylic resin includes at least one of vinyl acrylate resin, methyl acrylate resin, butyl acrylate resin, acrylic styrene resin, acrylate resin, acrylate copolymer resin, acrylic resin, and acrylic emulsion resin; Preferably, the binder is polyvinylidene fluoride (PVDF); Preferably, the binder accounts for 1% to 3% by mass of the positive electrode slurry.

10. A sodium ion secondary battery, characterized in that: The high-voltage electrolyte comprises the high-voltage electrolyte according to any one of claims 1 to 9, and further comprises a positive electrode sheet, a negative electrode sheet and a separator.

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