Electrolyte for improving high-voltage stability of sodium-ion battery and application of electrolyte

Abstract

The electrolyte comprises a first additive a and a second additive b, the first additive a is one or more of chain sulfonyloxy structure compounds, the second additive b is one or more of sulfur-containing ring structure compounds, and the dosage of the electrolyte meets the formula relation that 100 (A + B) / (5C + D) is larger than or equal to 2.18 and smaller than or equal to 52.94, 0.01% < = A < = 3%, 0.05% < = B < = 3%, 1% < = C < = 3%, 0.5% < = D < = 20%, A being the mass percentage of the first additive a in the electrolyte, B being the mass percentage of the second additive b in the electrolyte, C being the mass percentage of the binder in the positive electrode powder, and D being the molar percentage of the Cu element in all transition metal elements; and the battery stability problems of rapid capacity attenuation, cyclic diving, serious transition metal dissolution and the like of the sodium-ion battery under high voltage are solved.

Description

Technical Field

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

[0002] 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] In order to meet the demand for higher energy density in secondary batteries, the continuous development of higher capacity cathode materials or the improvement of battery cutoff voltage is driven to achieve the goal. Currently, the electrolyte of conventional sodium ion batteries is mainly non-aqueous organic electrolyte, and it is difficult to adapt to the challenges brought by higher potentials. Under high potential, the oxidative decomposition of the electrolyte on the surface of the cathode material will be accelerated, and a series of side reactions will occur; and under high voltage, especially >4.0V, the structural stability of the cathode material is poor, the cracks in the material particles increase, and the interface film is damaged; in addition, under high voltage and high temperature conditions, the electrochemical stability of the binder also faces huge challenges. The reduced adhesion leads to the peeling and shedding of the active material, which will inevitably lead to rapid capacity decay, cycle drop, severe transition metal dissolution and other battery failure problems. Therefore, there is an urgent need to develop an adaptive and stable high-voltage electrolyte, build a low-impedance and stable interface film, inhibit transition metal dissolution, and further improve the performance at high voltage, rate performance and cycle performance. Summary of the Invention

[0004] The present invention addresses the problems of rapid capacity decay, poor cycle performance, and severe transition metal dissolution in sodium ion batteries at high potentials in the prior art. The present invention discloses an electrolyte for improving the high-voltage stability of sodium ion batteries. By optimizing the composition and content ratio of the sodium ion battery electrolyte additives, the binder in the battery positive electrode powder, and the Cu element in the positive electrode active material, a more stable interface film is constructed, side reactions between the electrolyte and the positive electrode are suppressed, and severe transition metal dissolution is alleviated. At the same time, by adjusting parameters, the interaction between the active particles and the binder is enhanced, and the peeling of the active particles at high voltage is avoided. This further improves the stability of the entire system at high voltage and optimizes the cycle performance.

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

[0006] The present invention first provides an electrolyte for improving the high-voltage stability of a sodium ion battery, 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 one of alkali metal atoms; R2 is selected from one of halogen atoms, C1-C6 halogenated or non-halogenated hydrocarbon groups, C1-C6 halogenated or non-halogenated hydrocarbonoxy groups, C1-C6 halogenated or non-halogenated ester groups or acyloxy groups, and C1-C6 halogenated or non-halogenated sulfonyloxy groups;

[0010] The second additive b is selected from one or more compounds having a sulfur-containing cyclic structure and has the following structure:

[0011]

[0012] R3 is selected from one of an oxygen atom, a C1-C3 alkylene group, and a C2-C3 alkenylene group; R4 is selected from one of a C1-C3 halogenated or non-halogenated alkylene group; R5 is selected from one of a hydrogen atom, a fluorine atom, a C1-C3 halogenated or non-halogenated alkyl group, and a C2-C3 alkenyl group; and the second additive is a nine-membered ring at most;

[0013] Preferably, the second additive structure is a five-membered ring to a seven-membered ring;

[0014] Specifically, when the second additive is a five-membered ring, the total number of carbon atoms of R3 and R4 in the five-membered ring is 2;

[0015] When the second additive is a six-membered ring, the total number of carbon atoms of R3 and R4 in the six-membered ring is 3;

[0016] When the second additive is a seven-membered ring, the total number of carbon atoms of R3 and R4 in the seven-membered ring is 4;

[0017] The amounts of the first additive a and the second additive b in the electrolyte satisfy the following formula: 2.18≤100(A+B) / (5C+D)≤52.94, and 0.01%≤A≤3%; 0.05%≤B≤3%; 1%≤C≤3%; 0.5%≤D≤20%, wherein A is the mass percentage of the first additive a in the electrolyte, B is the mass percentage of the second additive b in the electrolyte, C is the mass percentage of the binder in the positive electrode powder in the battery, and D is the molar percentage of the Cu element in the positive electrode material of the battery to all transition metal elements.

[0018] The above design of the present invention solves the problems of rapid battery capacity decay, poor cycle performance, and transition metal dissolution by optimizing the mass percentage of the first additive a, the second additive b, the binder in the positive electrode powder, and the molar percentage of the Cu element in all transition metal elements. The electrolyte additive decomposes to form a low-solubility SEI film, constructing a dense and complete S-rich interface film, which is beneficial to the Na in the CEI layer. + The conductivity of the electrolyte is improved, the thickness of the CEI interface film is reduced, the stability under high voltage is improved, the cycle stability and high temperature performance of the battery are improved, and the molar ratio of the Cu element in the transition metal is controlled to balance the structural stability and energy density. 2+ Under the catalytic action, it will decompose to produce a passivation layer of a cross-linked polymer rich in inorganic components, and the passivation layer interacts with the binder to avoid the peeling of the positive electrode active material, thereby improving the cycle stability of the passivation film. The appropriate binder ensures that the components of the electrode are evenly dispersed, fully exerting the role of binding active substances, conductive agents and current collectors, without affecting the overall energy density of the battery cell due to excessive content. Through the above design, the content of each component is controlled within a certain range, and when a certain formula relationship is satisfied, the high voltage stability of the battery can be stably improved, while the interaction between the active particles and the binder is enhanced, the peeling of the active particles under high voltage is avoided, and the overall cycle performance is improved.

[0019] As a further solution, we prefer that the single dosage of each component satisfies at least one of the following: 0.1%≤A≤2%, 0.5%≤B≤2.5%, 1.5%≤C≤2.5%, 1%≤D≤12%.

[0020] As a further solution, each component satisfies the formula relationship of 7.6≤100(A+B) / (5C+D)≤28.

[0021] As a further solution, when the above conditions of 0.1%≤A≤2%, 0.5%≤B≤2.5%, 1.5%≤C≤2.5%, and 1%≤D≤12% are met, preferably 7.6≤100(A+B) / (5C+D)≤28, the performance is better when 1≤B / A≤2 and 3≤D / (A+B)≤9 are met.

[0022] As a further solution, R1 in the first additive a provided by the present invention is preferably a sodium atom.

[0023] As a further embodiment, R2 in the first additive a provided by the present invention is preferably 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.

[0024] As a further solution, R2 in the first additive a provided by the present invention is preferably a halogen atom.

[0025] As a further embodiment, R2 in the first additive a provided by the present invention is preferably a fluorine atom.

[0026] As a further solution, the present invention also provides a first additive a selected from a-1 a-2 a-3 a-4 a-5 a-6 a-7 a-8 a-9 One or more of .

[0027] As a further solution, R5 in the second additive b provided by the present invention is preferably a hydrogen atom.

[0028] As a further solution, R4 in the second additive b provided by the present invention is preferably a C1-C3 non-halogenated alkylene group.

[0029] As a further solution, R3 in the second additive b provided by the present invention is preferably a C1 alkylene group.

[0030] As a further solution, 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 One or more of .

[0031] As a further solution, an electrolyte for improving the high-voltage stability of a sodium ion battery also includes a non-aqueous organic solvent and a sodium salt.

[0032] 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 bis(fluorooxalato)borate, sodium bis(oxalato)borate, sodium nitrate, sodium hexafluoroantimonate, sodium hexafluoroarsenate, sodium difluorobis(oxalato)phosphate, sodium tetrafluorooxalatophosphate, and sodium tetrafluoroborate;

[0033] As a further embodiment, the sodium salt is sodium hexafluorophosphate (NaPF6).

[0034] As a further solution, the non-aqueous organic solvent is one or more of an ether solvent, an ester solvent, and an ionic liquid.

[0035] 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.

[0036] As a further embodiment, the complex functional group is selected from one or more of C1-C10 alkoxy, alkenyl, and alkynyl groups.

[0037] As a further solution, the hydroxyl-containing ether solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol butyl ether, triethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, and propylene glycol monomethyl ether.

[0038] 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.

[0039] As a further solution, the ether solvent containing complex functional groups is selected from one or more of butynediol dipropoxy ether and propargyl ether.

[0040] As a further solution, the ester solvent is selected from one or more of linear ester solvents and cyclic carbonate solvents.

[0041] As a further embodiment, the linear ester is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, trimethyl phosphate, triethyl phosphate, ethyl vinyl ester, methyl acetate, and propyl acetate.

[0042] 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.

[0043] As a further solution, the source of the copper element in the positive electrode material is not limited, and the copper element can be introduced into the positive electrode material in any feasible manner as needed. As some optional methods, the copper 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 copper-containing additive as a positive electrode additive, such as CuO.

[0044] As a further solution, 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 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), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg).

[0045] As a further solution, M in the positive electrode active material includes Cu.

[0046] As a further solution, an oil-based binder is used for the binder, and the binder includes at least one of a thermoplastic resin, an acrylic resin, sodium carboxymethyl cellulose, and styrene-butadiene rubber.<000016xx0>

[0047] As a further solution, 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.

[0048] As a further solution, the acrylic resin includes at least one of an acrylic vinyl ester resin, an acrylic methyl ester resin, an acrylic butyl ester resin, an acrylic styrene resin, an acrylate resin, an acrylate copolymer resin, an acrylic resin, and an acrylic emulsion resin.

[0049] [[ID=xx5]]As a further preferred solution, the binder is polyvinylidene fluoride (PVDF).

[0050] The present invention also provides a sodium-ion battery, including the electrolyte, a positive electrode sheet containing the positive electrode material, and further including a negative electrode sheet containing a negative electrode material and a separator membrane.

[0051] As a further solution, for the fabrication of the sodium-ion battery, the positive electrode sheet, the negative electrode sheet, and the separator membrane are made into an electrode assembly by a winding process or a stacking process, and the preferred process is the winding process.

[0052] It should be noted that in the original text, there seems to be an incorrect tag in line 9, which should probably be instead of <000016xx0>. Also, in line 15, it should be "As a further preferred solution" instead of "As a更进一步方案" for better English expression. The above translation has made corresponding corrections and translations according to the corrected content.As a further solution, the positive electrode material includes a positive electrode active material NaCu 1 / 20 Ni 7 / 20 Fe 3 / 10 Mn 3 / 10 O2, the binder polyvinylidene fluoride (PVDF), and also include conductive carbon black Super-P, solvent and positive electrode current collector aluminum foil.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The characteristics and beneficial effects of the present invention are:

[0057] The present invention provides an electrolyte for improving the high-voltage stability of sodium-ion batteries. This technical solution significantly improves the stability of sodium-ion batteries under high voltage, helps to build a stable interface film, enhances the interaction between the overall active particles and the binder, and works together to effectively prevent the positive electrode material from structural collapse, active particle fragmentation, transition metal dissolution, and excessive side reactions under high voltage and temperature, thereby improving the battery's cycle performance under high voltage.

[0058] On the one hand, by regulating the contents of additives a, additive b, binder and Cu in the positive electrode material at 0.01% ≤ A ≤ 3%; 0.05% ≤ B ≤ 3%; 1% ≤ C ≤ 3%; 0.5% ≤ D ≤ 20%, the first additive a is a salt additive, which mainly produces inorganic components such as Na2S, Na2SO4, etc. after film formation. The CEI interface film produced is more compact and dense, which preferentially protects the positive electrode, forms a dense passivation film that is resistant to high temperature and corrosion on the positive electrode surface, and inhibits the dissolution of transition metals; the second additive b is a ring structure, and the lonely electrons on O are more exposed and easily react with Cu at the positive electrode interface. 2+ The first additive a and the second additive b are added to the CuO2 battery to form a passivation film. The passivation film component contains a sulfur-containing organic cross-linked structure, which has good toughness and can inhibit the dissolution of positive transition metal ions and the decomposition of non-aqueous electrolytes. It solves the problem that organic electrolyte salts cannot form SEI and CEI in sodium batteries and improves the battery cycle life. 2+The inorganic components in the passivation layer are chemically anchored to the surface of the cathode material, while the cross-linked organic polymer at the other end is mechanically interlocked with the conductive bonding network formed by the binder and conductive agent. This prevents severe cathode particle shedding under high voltage, inhibits the dissolution of transition metals, and improves rate and cycle performance. Because both additives contain sulfur and the decomposition products have overlapping -ROSO2 groups, the passivation layer is more tightly bonded to the cathode material and the conductive bonding network.

[0059] On the other hand, under the condition of satisfying the formula of 2.18≤100(A+B) / (5C+D)≤52.94, the thickness of the interface film is reduced while the Na + The migration rate can optimize the stability of the battery at high voltage, improve the cycle performance at high voltage, and balance the electrolyte additives and Cu 2+ The relationship between the catalysis and the binder effect, the binder content and the Cu content can stabilize the Cu under a certain ratio relationship. 2+ The catalytic and chelating ability of the present invention further improves the battery cycle life; the present invention further prefers the range of 3≤D / (A+B)≤9 and 1≤B / A≤2, and also considers the ratio relationship between Cu and electrolyte additives. When the proportion of Cu is relatively excessive, although it can enhance the stability of the electrode structure, it may cause Cu 2+ Dissolution is out of control. When the additives are relatively excessive, it may lead to excessively thick interfacial films and a surge in impedance. Only when a certain balance is reached between the amounts of Cu and the first electrolyte additive a and the second electrolyte additive b can the relevant performance be stabilized. At the same time, when the first additive a and the second electrolyte additive b meet a certain weight ratio, the capacity retention rate under high-voltage charge and discharge cycles is further improved, the dissolution of transition metals is reduced, and the cycle life at high temperatures is further extended, further improving the battery's high-voltage cycle performance and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 The capacity retention rate of Example 3 and Comparative Example 4 of the present invention at 45°C, 2-4.25V, and 1C / 1C charge-discharge cycle;

[0061] Figure 2 The figure is a comparison of the percentage content of Ni element dissolved in Example 3 and Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0062] To facilitate understanding of the present invention, the following will provide a more comprehensive description of an electrolyte for improving the high-voltage stability of sodium ion batteries and its applications in combination with the specific details and embodiments of the present invention, but this does not limit the scope of the present invention.

[0063] The present invention first provides an electrolyte for improving the high-voltage stability of a sodium ion battery, comprising a first additive a and a second additive b.

[0064] The first additive a is selected from one or more compounds having a chain sulfonyloxy structure and has the following structure:

[0065]

[0066] wherein R1 is selected from one of alkali metal atoms; R2 is selected from one of halogen atoms, C1-C6 halogenated or non-halogenated hydrocarbon groups, C1-C6 halogenated or non-halogenated hydrocarbonoxy groups, C1-C6 halogenated or non-halogenated ester groups or acyloxy groups, and C1-C6 halogenated or non-halogenated sulfonyloxy groups;

[0067] The second additive b is selected from one or more compounds having a sulfur-containing cyclic structure and has the following structure:

[0068]

[0069] R3 is selected from one of an oxygen atom, a C1-C3 alkylene group, and a C2-C3 alkenylene group; R4 is selected from one of a C1-C3 halogenated or non-halogenated alkylene group; R5 is selected from one of a hydrogen atom, a fluorine atom, a C1-C3 halogenated or non-halogenated alkyl group, and a C2-C3 alkenyl group; and the second additive is a nine-membered ring at most;

[0070] As a preferred example, the second additive has a structure of a five-membered ring to a seven-membered ring, which is the most stable structure;

[0071] Specifically, when the second additive is a five-membered ring, the total number of carbon atoms of R3 and R4 in the five-membered ring is 2;

[0072] When the second additive is a six-membered ring, the total number of carbon atoms of R3 and R4 in the six-membered ring is 3;

[0073] When the second additive is a seven-membered ring, the total number of carbon atoms of R3 and R4 in the seven-membered ring is 4;

[0074] The amounts of the first additive a and the second additive b in the electrolyte satisfy the following formula: 2.18≤100(A+B) / (5C+D)≤52.94, and 0.01%≤A≤3%; 0.05%≤B≤3%; 1%≤C≤3%; 0.5%≤D≤20%, wherein A is the mass percentage of the first additive a in the electrolyte, B is the mass percentage of the second additive b in the electrolyte, C is the mass percentage of the binder in the positive electrode powder in the battery, and D is the molar percentage of the Cu element in the positive electrode material of the battery to all transition metal elements.

[0075] The above design of the present invention solves the problems of rapid battery capacity decay, poor cycle performance, and transition metal dissolution by optimizing the mass percentage of the first additive a, the second additive b, the binder in the positive electrode powder, and the molar percentage of the Cu element in all transition metal elements. The electrolyte additive decomposes to form a low-solubility SEI film, constructing a dense and complete S-rich interface film, which is beneficial to the Na in the CEI layer. + The conductivity of the electrolyte is improved, the thickness of the CEI interface film is reduced, the stability under high voltage is improved, the cycle stability and high temperature performance of the battery are improved, and the molar ratio of the Cu element in the transition metal is controlled to balance the structural stability and energy density. 2+ Under the catalytic action, it will decompose to produce a passivation layer of a cross-linked polymer rich in inorganic components, and the passivation layer interacts with the binder to avoid the peeling of the positive electrode active material, thereby improving the cycle stability of the passivation film. The appropriate binder ensures that the components of the electrode are evenly dispersed, fully exerting the role of binding active substances, conductive agents and current collectors, without affecting the overall energy density of the battery cell due to excessive content. Through the above design, the content of each component is controlled within a certain range, and when a certain formula relationship is satisfied, the high-voltage stability of the battery cell can be stably improved, while the interaction between the active particles and the binder is enhanced, the peeling of the active particles under high voltage is avoided, and the overall cycle performance is improved.

[0076] As a further preferred example, we prefer that the single dosage of each component satisfies at least one of the following: 0.1%≤A≤2%, 0.5%≤B≤2.5%, 1.5%≤C≤2.5%, 1%≤D≤12%.

[0077] It is further preferred that 0.1%≤A≤2%, and the mass content of the electrolyte additive a is controlled within an appropriate range. Through the potential-dependent decomposition mechanism, the electrolyte additive a selectively decomposes on the surface of the sodium ion battery electrode, and can be in situ decomposed on the electrode surface to generate low-solubility inorganic components, promote the formation of a dense and low-impedance SEI film, reduce the sodium ion diffusion energy barrier, inhibit electrolyte oxidation consumption, disordered sodium metal deposition and sodium dendrite formation, thereby synergistically improving the rate characteristics and cycle stability of the sodium ion battery.

[0078] Further preferably, 0.5%≤B≤2.5%, and the mass content of the electrolyte additive b is controlled within an appropriate range. Such components construct an S-doped gradient SEI film at the negative electrode interface through self-assembly characteristics, and simultaneously form a sulfur-based CEI layer on the positive electrode surface. The synergistic effect of the dual interfaces can reduce the dissolution rate of transition metals and fix the dissolved metal ions through the chemical chelation effect, thereby avoiding the problem of rapid capacity decay and further improving the cycle performance.

[0079] Further optimizing the binder content to be 1.5% ≤ C ≤ 2.5%, and controlling the binder mass content within an appropriate range, can construct a three-dimensional continuous conductive-adhesive network and enhance the interaction between the passivation layer and the conductive adhesive network. This ensures uniform dispersion of the electrode components, achieves uniform dispersion of the active material and the conductive agent, increases the electrode surface density, and fully utilizes the bonding of the active material, conductive agent, and current collector, without compromising the overall energy density of the battery due to excessive content. This optimization strategy reduces the electrode / electrolyte interface impedance and improves the stability of the electrode structure, increasing ion permeability, electronic conductivity, and mechanical toughness, thereby improving the battery's energy density and capacity retention.

[0080] It is further preferred that 1%≤D≤12%, and the mass percentage of Cu element in the positive electrode material is controlled within an appropriate range, which does not affect the role of Cu element in stabilizing the structure of the positive electrode material, and enhances the interaction with the first additive a and the second additive b to improve the stability of the positive electrode active particles and the conductive bonding network, and avoids 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.

[0081] As a further preferred example, each component satisfies the formula relationship of 7.6≤100(A+B) / (5C+D)≤28.

[0082] When 0.1%≤A≤2%, 0.5%≤B≤2.5%, 1.5%≤C≤2.5%, 1%≤D≤12% are satisfied, and the relationship of 7.6≤100(A+B) / (5C+D)≤28 is satisfied, the stability of the obtained battery at high voltage is significantly improved. This is mainly because the content of additives, the content of Cu and the content of binder have a very significant impact on enhancing the interface stability, enhancing the stability between the positive active particles, and enhancing the interaction between the passivation layer and the bonding network. At the same time, the formula relationship characterizes the relationship between the electrolyte additives and Cu 2+ The matching degree between the catalytic and binder effects, controlling the binder content and the Cu content in a certain relationship can stabilize Cu at a certain binder content. 2+ When the above relationship is not satisfied, the content of electrolyte additives and the binder and Cu 2+ The content of Cu2+ cannot be balanced. Under high voltage and high temperature conditions, the interface stability and the stability between the positive active particles are poor, which will accelerate the dissolution of transition metals and the decomposition of the electrolyte, deteriorate the cycle performance of the battery, and even cause some safety problems. For example, excessive additives will cause Cu2+ to 2+Excessive catalysis leads to excessive thickness of the CEI layer, decreased sodium ion migration, reduced ionic conductivity, insufficient binder reduces the interfacial binding energy, and accelerates the stripping of active particles under high pressure. Excessive Cu may induce lattice distortion and other problems.

[0083] As a further example, when the above conditions of 0.1% ≤ A ≤ 2%, 0.5% ≤ B ≤ 2.5%, 1.5% ≤ C ≤ 2.5%, and 1% ≤ D ≤ 12% are met, preferably 7.6 ≤ 100 (A + B) / (5C + D) ≤ 28, and 1 ≤ B / A ≤ 2, and 3 ≤ D / (A + B) ≤ 9 are met, the performance is even better. In this case, the transition metal dissolved Ni content in the battery is ≤ 12 ppm, the room temperature 2C cycle capacity retention rate is ≥ 99%, and the number of cycles at which the capacity is retained at 80% at 45°C is ≥ 835.

[0084] This may be due to the ratio between Cu and electrolyte additives. When Cu accounts for a relatively excessive proportion, although it can enhance the stability of the electrode structure, it may cause Cu 2+ Dissolution is out of control. When the additive is relatively excessive, it may lead to excessively thick interfacial films and a surge in impedance. When a certain balance is reached between Cu and the electrolyte additive, the relevant performance can be stabilized. At the same time, when the second additive b and the first additive a meet a certain mass ratio, the relevant performance is further improved. This may be because this ratio can better synergistically optimize ion transmission efficiency and form a dense passivation film, effectively reducing the increase in impedance and further enhancing the overall performance of the sodium-ion battery.

[0085] As a further preferred example, R1 in the first additive a provided by the present invention is preferably a sodium atom.

[0086] Sodium sulfonate salt as an electrolyte additive can effectively reduce the viscosity of the electrolyte, thereby reducing the internal resistance of the battery, improving the battery's charge and discharge efficiency, improving the ionic conductivity of the electrolyte, achieving a synergistic improvement in energy density and power density, and thereby improving the overall performance of the battery.

[0087] As a further preferred example, R2 in the first additive a provided by the present invention is preferably one of a halogen atom, a C1-C6 halogenated hydrocarbon group or hydrocarbonoxy group, a C1-C6 halogenated ester group or acyloxy group, and a C1-C6 halogenated sulfonyloxy group.

[0088] 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.

[0089] As a further preferred example, R2 in the first additive a provided by the present invention is preferably a halogen atom.

[0090] As a further preferred example, R2 in the first additive a provided by the present invention is preferably a fluorine atom.

[0091] As some examples, the present invention also provides a first additive a selected from a-1 a-2 a-3 a-4 a-5 a-6 a-7 a-8 a-9 One or more of .

[0092] As a further preferred example, R5 in the second additive b provided by the present invention is preferably a hydrogen atom.

[0093] As a further preferred example, R4 in the second additive b provided by the present invention is preferably a C1-C3 non-halogenated alkylene group.

[0094] As a further preferred example, R3 in the second additive b provided by the present invention is preferably a C1 alkylene group.

[0095] As some examples, 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 One or more of .

[0096] As an example, an electrolyte for improving the high-voltage stability of a sodium ion battery also includes a non-aqueous organic solvent and a sodium salt.

[0097] Illustratively, 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;

[0098] As a preferred example, the sodium salt is sodium hexafluorophosphate (NaPF6).

[0099] Sodium hexafluorophosphate has the characteristics of high ionic conductivity and high solubility in carbonate solvents.

[0100] As an example, the non-aqueous organic solvent is one or more of an ether solvent, an ester solvent, and an ionic liquid.

[0101] Illustratively, 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.

[0102] The complex functional group is selected from one or more of C1-C10 alkoxy, alkenyl, and alkynyl groups.

[0103] The hydroxyl-containing ether solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol butyl ether, triethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, and propylene glycol monomethyl ether.

[0104] The ether solvent containing a single ether bond is selected from one or more of cyclopentyl methyl ether, ethyl ether, and propyl ether.

[0105] The ether solvent containing complex functional groups is selected from one or more of butynediol dipropoxy ether and propargyl ether.

[0106] As an example, the ester solvent is selected from one or more of linear ester solvents and cyclic carbonate solvents.

[0107] The linear ester is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, trimethyl phosphate, triethyl phosphate, ethyl vinyl ester, methyl acetate, and propyl acetate.

[0108] The cyclic carbonate is selected from one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, and 1,2-propylene glycol carbonate.

[0109] As an example, the source of the copper element in the positive electrode material is not limited, and the copper element can be introduced into the positive electrode material in any feasible manner as needed. As some optional methods, the copper 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 copper-containing additive as a positive electrode additive, such as CuO.

[0110] 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 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), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg).

[0111] Exemplarily, M in the positive electrode active material includes Cu.

[0112] Exemplarily, an oil-based binder is used as the binder, and the binder includes at least one of a thermoplastic resin, an acrylic resin, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0113] Exemplarily, 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.

[0114] Exemplarily, the acrylic resin includes at least one of an acrylic vinyl ester resin, an acrylic methyl ester resin, an acrylic butyl ester resin, an acrylic styrene resin, an acrylate resin, an acrylate copolymer resin, an acrylic resin, and an acrylic emulsion resin.

[0115] As a preferred example, the binder is polyvinylidene fluoride (PVDF).

[0116] The present invention also provides a sodium ion battery, including the electrolyte, a positive electrode sheet containing the positive electrode material, and further including a negative electrode sheet containing a negative electrode material and a separator.

[0117] For the fabrication of the sodium ion battery, the positive electrode sheet, the negative electrode sheet, and the separator are made into an electrode assembly by a winding process or a stacking process, and the preferred solution is the winding process. [[ID=X]] [[ID=Y]]

[0118] The positive electrode sheet includes the positive electrode active material NaCu1 / 20 Ni 7 / 20 Fe 3 / 10 Mn 3 / 10 O2, the binder polyvinylidene fluoride (PVDF), also includes conductive carbon black Super-P, conductive agent CNT, solvent and positive electrode current collector aluminum foil.

[0119] 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.

[0120] The outer packaging of the sodium ion battery is a bag-type soft package or an aluminum shell or a steel shell.

[0121] 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.

[0122] As a specific example of the implementation of the present invention, a detailed case is provided as follows:

[0123] Example 1:

[0124] This embodiment provides a sodium ion battery, which includes a positive electrode, a negative electrode, a separator and an electrolyte.

[0125] The positive electrode comprises a positive electrode material layer and a positive electrode current collector aluminum foil, wherein the positive electrode material layer comprises a positive electrode active material NaCu 1 / 20 Ni 7 / 20 Fe 3 / 10 Mn 3 / 10 O2, conductive carbon black Super-P, conductive agent CNT, 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;

[0126] The negative electrode 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;

[0127] 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 0.01%, and the mass content of the second additive b-1 is 1%.

[0128] Preparation of the positive electrode: NaCu 1 / 20 Ni 7 / 20 Fe 3 / 10 Mn 3 / 10 The O2 positive electrode material, conductive agent SuperP, conductive agent CNT, and binder PVDF are dissolved in the solvent N-methyl-2-pyrrolidone (NMP) in a mass ratio of 96.5:1.5:0.5:1.5 (that is, the mass proportion of the binder PVDF in the positive electrode powder is 1.5%). After stirring evenly, the positive electrode slurry is obtained. The slurry viscosity is 5000±1000mPa·s and the solid content is 65±0.5wt%. The obtained positive electrode slurry is then evenly coated on aluminum foil, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0129] 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.

[0130] 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.

[0131] The outer packaging of the sodium ion battery can be a bag-type soft package or an aluminum shell, 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 cylindrical aluminum shell.

[0132] Under the above conditions, the following tests were performed:

[0133] Test for the dissolution of transition metal Ni in the battery: Disassemble the battery cell after high-temperature cycling, remove the negative electrode, clean it with DMC, dry it, and scrape about 0.2g of powder; weigh 0.2g of negative electrode powder and add it to aqua regia, heat it at 140℃ until it is completely dissolved, cool it to room temperature, and dilute it to the scale; transfer it to a volumetric flask, make it up to 50mL, calibrate the instrument with a standard solution, and then introduce the prepared sample solution into the ICP instrument for measurement; calculate the transition metal Ni content in the sample based on the data output by the instrument;

[0134] 2C cycle test: At room temperature (25±2°C), charge and discharge cycles are performed at 2C / 2C with a voltage range of 2 to 4.25V. The capacity retention rate is recorded after 300 cycles.

[0135] 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 4.25V, and the number of cycles until the capacity decays to 80% is recorded;

[0136] Examples 2 to 31, Comparative Examples 1 to 11:

[0137] 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.

[0138] The test results obtained in Examples 1 to 31 and Comparative Examples 1 to 11 are shown in the table:

[0139] Table 1 Performance test results

[0140]

[0141]

[0142] From Examples 1 to 31 and Comparative Examples 1 to 11, it can be observed that:

[0143] When the battery simultaneously satisfies 0.01%≤A≤3%; 0.05%≤B≤3%; 1%≤C≤3%; 0.5%≤D≤20%, and 2.18≤100(A+B) / (5C+D)≤52.94, the amount of transition metal Ni dissolved in the battery is ≤22ppm, the 2C cycle capacity retention rate is ≥93.02%, and the number of cycles in which the high-temperature cycle capacity decays to 80% is ≥750. The above parameters can ensure the most basic performance of the sodium ion battery. Compared with comparative examples 1 to 11, there is a certain improvement in the relevant performance, which inhibits the dissolution of transition metals, slows down the occurrence of electrode side reactions, meets the stability requirements of the battery under high voltage, and improves the rate performance.

[0144] Comparative Examples 1 to 9 show the relevant performance when 0.01%≤A≤3%; 0.05%≤B≤3%; 1%≤C≤3%; and 0.5%≤D≤20% are not satisfied. The most basic performance of the sodium ion battery cannot be guaranteed under these parameters.

[0145] Comparative Examples 1 to 3 represent the cases where no additive is added, the first additive a is not added, and the second additive b is not added, respectively. At this time, the transition metal dissolution Ni content is high, all greater than 70 ppm. Compared with Example 3, the Ni dissolution content of Comparative Examples 1 to 3 is 7 times higher than that of Example 3, the 2C cycle capacity retention rate is <75%, and the number of cycles for the high-temperature cycle capacity to decay to 80% is <400. The performance is far inferior to Example 3, which shows that in the present invention, the first additive a and the second additive b are indispensable.

[0146] Comparative Examples 4 to 5 are cases where the content of the first additive a or the second additive b exceeds the range of 0.01% ≤ A ≤ 3%, 0.05% ≤ B ≤ 3%. The transition metal dissolution Ni content is high and the cycle life at 2C and the number of cut-off cycles at which the capacity is maintained at 80% are also low. This may be related to the excessive decomposition of the electrolyte additive on the electrode surface, the formation of an excessively thick SEI film, the increase in the sodium ion migration resistance, the generation of a large amount of inactive products, and the acceleration of the transition metal dissolution. Figure 1 As shown, at room temperature 25±2°C, 2C / 2C charge and discharge cycles were performed with a voltage range of 2 to 4.25V, and the capacity retention rate after 300 cycles was recorded. The capacity retention rate of Comparative Example 4 after 300 cycles was 74.35%, and the capacity retention rate of Example 3 after 300 cycles was 99.65%. Figure 2 The transition metal eluted Ni content in Comparative Example 4 of the present invention is 63 ppm, while the transition metal eluted Ni content in Example 3 is 10 ppm. The relevant performance is inferior to that of Example 3. Therefore, it is crucial to meet the requirements of 0.01% ≤ A ≤ 3% and 0.05% ≤ B ≤ 3%.

[0147] Comparative Examples 6 and 7 show the situations when the adhesive is insufficient or excessive. At this time, the relevant performance is poor and still does not meet the basic performance requirements of the battery. The adhesive is usually used to fix the active material, conductive agent and current collector, and at the same time form a stable cross-linked network structure with the interface film to promote ion transmission. Therefore, if the adhesive is insufficient, it may affect the structural stability, the active particles are loosely combined with the current collector, and the active material falls off, which will directly reduce the battery capacity. At the same time, if the internal resistance is high, the battery heating will be more serious, the charge and discharge efficiency will be reduced, and the rate performance may also be affected. The electrolyte over-penetrates, forming an overly thick SEI film, consuming the sodium source, further increasing the internal resistance, and affecting the life. When the adhesive is excessive, the excess adhesive covers the surface of the active particles, the effective reaction area is reduced, and the surface capacity density decreases. Therefore, it is necessary to balance mechanical strength and transmission performance. Insufficient leads to collapse of the electrode structure, and excessive leads to transmission blockage. Both will significantly reduce the cycle life and energy density of the battery.

[0148] Comparative Examples 8 and 9 show the cases where Cu is not included or Cu is excessive. Cu, as an important catalyst for electrolyte additives, can catalyze the electrolyte additives to form a composite passivation layer rich in inorganic components and cross-linked polymers. Not adding Cu is not conducive to the formation of the passivation layer, which may cause the peeling of the positive electrode active material and reduce the stability of the passivation layer structure. Excessive addition of Cu will lead to Na + The decrease in diffusion coefficient increases transition metal dissolution and interface deterioration.

[0149] In particular, in Comparative Examples 10 and 11, the individual parameters all met the following conditions: 0.01% ≤ A ≤ 3%; 0.05% ≤ B ≤ 3%; 1% ≤ C ≤ 3%; and 0.5% ≤ D ≤ 20%. However, when the relationship 2.18 ≤ 100 (A + B) / (5C + D) ≤ 52.94 was not met, the performance was also poor. The transition metal Ni content in the battery was greater than 50 ppm, the number of cycles required for 80% capacity retention was less than 460, and the 2C cycle capacity retention rate was less than 80%. This indicates that even when each condition is met individually, performance requirements cannot be met if 2.18 ≤ 100 (A + B) / (5C + D) ≤ 52.94 is not met. Therefore, satisfying 2.18 ≤ 100 (A + B) / (5C + D) ≤ 52.94 is of great significance.

[0150] When the formula relationship of 2.18≤100(A+B) / (5C+D)≤52.94 is satisfied, the relationship between the mass percentage of additives, binders and Cu in the positive electrode powder is balanced, and the energy density and structural stability performance are balanced.

[0151] Under this formula, the first additive a and the second additive b play a role in inhibiting the dissolution of transition metals in the electrolyte, and oxidize on the surface of the positive electrode to form a sulfur-containing CEI film, which inhibits the dissolution of transition metals; the sum of the mass percentages of the first additive a and the second additive b in the formula shows the synergistic effect of the two, and the two additives work together to form and stabilize the SEI film with low solubility. Both additives are S-containing additives, and the decomposition products have overlapping -ROSO2 groups, which makes the passivation layer and the positive electrode material and the bonding conductive network closer. The synergistic effect of the above factors reduces the interfacial impedance while improving the stability of the positive electrode active material and the conductive network, so that the sodium ion battery exhibits excellent high-voltage cycle stability; at the same time, the ratio relationship of 100(A+B) / (5C+D) shows that the electrolyte additives and Cu 2+ The matching degree between the catalytic and binder effects, the relationship between 5C and D emphasizes that the binder content and the Cu content can stabilize Cu under a certain ratio. 2+ catalytic and chelating abilities.

[0152] As a further preferred example, when 0.1%≤A≤2%, 0.5%≤B≤2.5%, 1.5%≤C≤2.5%, and 1%≤D≤12% are satisfied, the performance is further improved.

[0153] As a further preferred example, when 0.1% ≤ A ≤ 2%, 0.5% ≤ B ≤ 2.5%, 1.5% ≤ C ≤ 2.5%, and 1% ≤ D ≤ 12%, preferably 7.6 ≤ 100 (A + B) / (5C + D) ≤ 28. All preferred embodiments satisfy the following conditions: the transition metal dissolved Ni content in the battery is ≤ 16 ppm, the 2C cycle capacity retention rate is ≥ 97.10%, and the number of cycles required for 80% capacity retention is ≥ 788.

[0154] Therefore, while satisfying the mass percentage of different electrolyte additives and binders in the positive electrode powder and the molar percentage of Cu element in all transition metal elements within a certain range, calculating and further optimizing the 100(A+B) / (5C+D) range has important practical significance for improving and optimizing the performance of sodium-ion batteries.

[0155] As a further example, when the above-mentioned conditions of 0.1%≤A≤2%, 0.05%≤B≤3%, 1.5%≤C≤2.5%, and 5%≤D≤12% are satisfied, preferably 7.6≤100(A+B) / (5C+D)≤28, the performance is better when 3≤D / (A+B)≤9 and 1≤B / A≤2 are satisfied.

[0156] The examples 3, 11, 19, and 24 shown in the table are significantly better than the examples 2, 4, 12, 22, 28, and 29 when they meet the above conditions of 0.1% ≤ A ≤ 2%, 0.05% ≤ B ≤ 3%, 1.5% ≤ C ≤ 2.5%, 5% ≤ D ≤ 12%, 7.6 ≤ 100 (A + B) / (5C + D) ≤ 28, and 3 ≤ D / (A + B) ≤ 9, 1 ≤ B / A ≤ 2. This may be due to the ratio between Cu and electrolyte additives. Although a relatively excessive amount of Cu can enhance the stability of the electrode structure, it may lead to Cu 2+ Dissolution is out of control. When the additive is relatively excessive, it may cause the interface film to be too thick and the impedance to surge. When a certain balance is reached between Cu and the electrolyte additive, the relevant performance can be stable. At the same time, when the second additive b and the first additive a meet a certain mass ratio relationship, the relevant performance is further improved. This may be because under this ratio, the ion transmission efficiency can be better synergistically optimized and a dense passivation film can be formed, which effectively reduces the increase in impedance and further enhances the overall performance of the sodium ion battery. Therefore, when 1≤B / A≤2 and 3≤D / (A+B)≤9 are met, the performance is relatively good.

[0157] As a further solution, according to the comparison of Examples 3, 6, 7, 8, and 9 with Example 33, when R2 in the structure of the first additive a is one of halogen, C1-C6 halogenated hydrocarbon group, C1-C6 halogenated hydrocarbonoxy group, C1-C6 halogenated ester group or acyloxy group, or C1-C6 halogenated sulfonyloxy group, it is more preferred. According to the comparison of Examples 3, 6, 7, 8, and 9, when the R2 group is a halogen atom, it is better than halogenated sulfonyloxy group, better than halogenated hydrocarbonoxy group or hydrocarbon group, and better than halogenated ester group or acyloxy group. This may be because the highly electronegative halogen reduces the electron cloud density of the oxygen atom through a strong electron-withdrawing effect, making the molecule more likely to participate in the reaction on the electrode surface and promoting the formation of a stable SEI film. The electronic effect of halogenated hydrocarbonoxy group or hydrocarbon group, halogenated ester group or acyloxy group is weaker, and it is also possible that the steric hindrance with the halogen atom is smaller, which promotes the dispersion of the additive and its rapid migration to the electrode surface.

[0158] As a further embodiment, according to Examples 3, 14, 15, 16, and 32, in the structure of the second additive b, R5 is preferably hydrogen. According to Examples 3, 14, 15, and 16, R4 is further preferably a C1-C3 non-halogenated alkyl group. According to Examples 3, 14, and 15, R3 is further preferably a C1 alkyl group. When R5 is hydrogen, the substituent has the smallest volume, which can significantly reduce intramolecular steric hindrance and enhance the conformational stability of the cyclic sulfur-containing compound backbone. The five-membered cyclic sulfur-containing compound structure, preferably free of alkenyl groups, synergistically optimizes ring strain, inhibits side reactions, and achieves a more stable structure.

[0159] In summary, according to the non-aqueous electrolyte provided by the present invention, the first additive a and the second additive b are added, and the Cu 2+ The cross-linked polymer passivation layer rich in inorganic components is decomposed under the catalytic action of Cu. 2+ Due to the presence of unfilled valence layer d orbitals, it is a relatively special d9 configuration, which gives it a unique electron transfer ability. Under high potential, it catalyzes the first additive a and the second additive b to produce a cross-linked polymer passivation layer rich in inorganic components. The inorganic component in the passivation layer is Cu at one end. 2+ The first additive a is a salt-type additive that mainly produces inorganic components after film formation, such as Na2SO4, NaRSO3, etc., which can improve the conductivity of the passivation film, reduce the interface impedance, and enhance the rate performance of the battery; the second additive b is a ring structure, and the lonely electrons on O are more exposed and easily interact with Cu at the positive electrode interface. 2+The passivation film components formed by coordination and complexation are sulfur-containing organic cross-linked structures, which have good toughness and can inhibit the dissolution of positive transition metal ions and the decomposition of non-aqueous electrolytes. Since both additives are S-containing additives and the decomposition products have overlapping -ROSO2 groups, the passivation layer is more closely connected to the positive electrode material and the bonding conductive network. The synergistic effect of the above factors reduces the interfacial impedance while improving the stability of the positive electrode active material and the conductive network, thereby making the sodium ion battery exhibit excellent high-voltage cycle stability.

[0160] This technical solution significantly improves the stability of sodium-ion batteries 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 positive electrode material from undergoing structural collapse, active particle breakage, and transition metal dissolution under high voltage and high temperature, thereby avoiding the rapid attenuation of the battery cell capacity and improving the battery's cycle performance.

[0161] 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. An electrolyte for improving the high voltage stability of a sodium ion battery, 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 one of alkali metal atoms; R2 is selected from one of halogen atoms, C1-C6 halogenated or non-halogenated hydrocarbon groups, C1-C6 halogenated or non-halogenated hydrocarbonoxy groups, C1-C6 halogenated or non-halogenated ester groups or acyloxy groups, and C1-C6 halogenated or non-halogenated sulfonyloxy groups; The second additive b is selected from one or more compounds having a sulfur-containing cyclic structure, specifically the following structure: R3 is selected from one of an oxygen atom, a C1-C3 alkylene group, and a C2-C3 alkenylene group, R4 is selected from one of a C1-C3 halogenated or non-halogenated alkylene group, R5 is selected from one of a hydrogen atom, a fluorine atom, a C1-C3 halogenated or non-halogenated alkyl group, and a C2-C3 alkenyl group, and the second additive b is at most a nine-membered ring; Preferably, the second additive b is a five-membered ring to a seven-membered ring; The amounts of the first additive a and the second additive b in the electrolyte satisfy the following formula: 2.18≤100(A+B) / (5C+D)≤52.94, and 0.01%≤A≤3%, 0.05%≤B≤3%, 1%≤C≤3%, 0.5%≤D≤20%, wherein A is the mass percentage of the first additive a in the electrolyte, B is the mass percentage of the second additive b in the electrolyte, C is the mass percentage of the binder in the positive electrode powder in the battery, and D is the molar percentage of the Cu element in the positive electrode material of the battery to all transition metal elements.

2. The electrolyte for improving the high voltage stability of a sodium ion battery according to claim 1, characterized in that: A, B, C, and D also satisfy at least one of the following: 0.1%≤A≤2%, 0.5%≤B≤2.5%, 1.5%≤C≤2.5%, and 1%≤D≤12%; More preferably, A, B, C, and D also satisfy 7.6≤100(A+B) / (5C+D)≤28; More preferably, A, B, C, and D also satisfy 1≤B / A≤2 and 3≤D / (A+B)≤9.

3. The electrolyte for improving the high voltage stability of a sodium ion battery according to claim 1, characterized in that: 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; Preferably, R2 in the first additive a is a halogen atom; Preferably, R2 in the first additive a is a fluorine atom.

4. The electrolyte for improving the high voltage stability of a sodium ion battery according to claim 1, characterized in that: R5 in the second additive b is a hydrogen atom; Preferably, R4 in the second additive b is a C1-C3 non-halogenated alkylene group; More preferably, R3 in the second additive b is a C1 alkylene group.

5. The electrolyte for improving the high voltage stability of a sodium ion battery 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 electrolyte for improving the high voltage stability of a sodium ion battery according to claim 1, characterized in that: Also includes sodium salts and non-aqueous organic solvents.

7. The electrolyte for improving the high voltage stability of a sodium ion battery 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 electrolyte for improving the high voltage stability of a sodium ion battery according to claim 6, characterized in that: The non-aqueous 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 alkenyl, alkoxy, and alkynyl groups; Preferably, the hydroxyl-containing ether solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol butyl ether, triethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, and propylene glycol monomethyl 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 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, ethylene carbonate, trimethyl phosphate, triethyl phosphate, ethyl vinyl ester, 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 electrolyte for improving the high voltage stability of a sodium ion battery according to claim 1, characterized in that: The source of the copper element 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 copper-containing additive; 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), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), 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 Cu; 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).

10. A sodium ion battery, characterized in that: The invention comprises the electrolyte for improving the high voltage stability of a sodium ion battery 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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