High-voltage-resistant sodium-ion battery electrolyte and application thereof

Abstract

The invention discloses a high-voltage-resistant sodium-ion battery electrolyte which 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 halogenated or / and cyclic carbonate structure compounds containing unsaturated double bonds, and the first additive a is one or more of chain sulfonyloxy structure compounds, the second additive b is one or more of halogenated or / and cyclic carbonate structure compounds containing unsaturated double bonds, and the second additive b is one or more of halogenated or / and cyclic carbonate structure compounds containing unsaturated double bonds. The formula relation is as follows: 2.6 < = (AB + 100) C / (C + D) < = 14.3, 0.2% < = A < = 3%, 0.3% < = B < = 3%, 1% < = C < = 3% and 10% < = D < = 50%, A is the mass percentage content of the first additive a in the electrolyte, B is the mass percentage content of the second additive b in the electrolyte, C is the mass percentage content of the binder in the positive electrode powder, and D is the molar percentage content of Mn in all transition metal elements; the problems that the capacity of the sodium-ion battery is rapidly attenuated, the cycle performance is poor, and the cycle DCR is greatly increased 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 resistant sodium ion battery electrolyte and its application 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] With technological advancements and the continuous development of the market, improving the energy density of sodium-ion batteries is becoming increasingly important and urgent. In addition to developing higher-capacity cathode materials, developing compatible and stable electrolytes to form a stable solid electrolyte interface (SEI) film is also essential. This is because at high potentials, the oxidative decomposition of the electrolyte on the cathode material surface is significantly aggravated, triggering a series of side reactions that lead to increased internal resistance and transition metal dissolution in sodium-ion batteries. Furthermore, transition metal dissolution in the cathode material not only deteriorates the structural stability of the cathode material but also catalyzes further electrolyte decomposition. Furthermore, reduced deposition at the anode can damage the SEI film. Furthermore, at high voltages and temperatures, the electrochemical stability of the binder also faces significant challenges. Reduced adhesion leads to the delamination of the active material. These factors inevitably lead to rapid capacity decay, poor cycling performance, and significant increases in the cycle-dependent charge / discharge ratio (DCR), severely restricting the application of sodium-ion batteries. Therefore, it is necessary to develop a high-voltage-resistant electrolyte that facilitates the formation and stabilization of the SEI film, minimizes transition metal dissolution, enhances the structural stability of the cathode material, and improves battery cycling performance. Summary of the Invention

[0004] The present invention addresses the problems of rapid capacity decay, poor cycle performance, and large cycle DCR growth in sodium ion batteries in the prior art. The present invention discloses a high-voltage-resistant sodium ion battery electrolyte. By optimizing the composition and content ratio of the binder in the battery positive electrode powder and the Mn element in the positive electrode active material, the electrolyte promotes the formation of a stable interface film to protect the electrode material, inhibits the dissolution of transition metals, slows down the occurrence of side reactions, and improves the high-voltage stability of the battery cell. At the same time, the interaction between the active particles and the binder is enhanced to avoid the peeling of the active particles under high voltage, thereby improving the overall cycle performance and reducing the DCR growth under battery cycling. This enables 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 resistant sodium ion battery 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 one of alkali metal atoms;

[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 cyclic carbonate compounds having halogenation and / or containing unsaturated double bonds, and the specific structure is as follows:

[0012]

[0013] Wherein, R3 is selected from one of C1-C3 halogenated or non-halogenated alkylene, C2-C3 halogenated or non-halogenated alkenylene;

[0014] R4 is selected from one of a hydrogen atom, a halogen atom, a C1-C6 halogenated or non-halogenated alkyl group, and a C2-C3 halogenated or non-halogenated alkenyl group;

[0015] represents one of a single bond or an unsaturated double bond;

[0016] Furthermore, at least one of R3 and R4 contains a halogenated group, and / or the second additive b contains an unsaturated double bond.

[0017] Specifically, when the second additive b is a halogenated cyclic carbonate structure compound, at least one of R3 and R4 may contain a halogenated group, and It can represent either a single bond or an unsaturated double bond;

[0018] When the second additive b is a cyclic carbonate structure compound containing an unsaturated double bond, the following two situations may be included:

[0019] i) R3 is a C2-C3 halogenated or non-halogenated alkenylene group, or R4 is a C2-C3 halogenated or non-halogenated alkenyl group, and represents a single bond;

[0020] ii) R3 is selected from C1-C3 halogenated or non-halogenated alkylene, R4 is selected from one of hydrogen atom, halogen atom, C1-C6 halogenated or non-halogenated alkyl, and Indicates an unsaturated double bond.

[0021] The amounts of the first additive a and the second additive b in the electrolyte satisfy the following formula: 2.6≤(AB+100)C / (C+D)≤14.3, and 0.2%≤A≤3%, 0.3%≤B≤3%, 1%≤C≤3%, 10%≤D≤50%, 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 Mn element in the positive electrode material of the battery to all transition metal elements.

[0022] The above design of the present invention solves the problems of rapid battery capacity decay, poor cycle performance, and large cycle DCR growth by optimizing the first additive a, the second additive b, the percentage of the binder in the positive electrode powder, and the molar percentage of the Mn element in all transition metal elements; by matching different types of electrolyte additives and optimizing and adjusting the additive content, the electrolyte additives are decomposed to form a low-solubility SEI film; a dense and complete S-rich electrolyte interface film is constructed, 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 cycle stability and high temperature performance of the battery are improved, and the stability under high voltage is improved. The presence of Mn element regulates the electrolyte additive in Mn 2+ The degree of decomposition under catalysis to produce a passivation layer of a cross-linked polymer rich in inorganic components is achieved by combining regulation to control the molar ratio of the Mn element in the transition metal to balance the structural stability and energy density. At the same time, the passivation layer interacts with the relatively regulated binder to construct a suitable network cross-linking structure, avoid the peeling of the positive electrode active material, and improve the cycle stability of the passivation film; the binder ensures the uniform dispersion of the various components of the electrode, fully plays the role of binding the active material, conductive agent and current collector, and does not affect the overall energy density of the battery cell due to excessive content ratio; through the above design, the high voltage stability of the battery cell is improved, and at the same time, the interaction between the active particles and the binder is improved to avoid the peeling of the active particles under high voltage, thereby improving the overall cycle performance and reducing the DCR growth under battery cycling.

[0023] As a further solution, we prefer that the single amount of each component satisfies at least one of the following: 0.5%≤A≤1.5%, 0.5%≤B≤2%, 1.2%≤C≤2%, and / or 30%≤D≤40%.

[0024] As a further solution, each component satisfies the formula relationship of 3.7≤(AB+100)C / (C+D)≤5.5.

[0025] As a further solution, when the above-mentioned conditions of 0.5%≤A≤1.5%, 0.5%≤B≤2%, 1.2%≤C≤2%, and 30%≤D≤40% are met, preferably 3.7≤(AB+100)C / (C+D)≤5.5, and the performance is better when 1.5≤(A+B) / C≤2 and 1≤B / A≤2 are met.

[0026] 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.

[0027] As a further solution, R2 in the first additive a provided by the present invention is preferably a halogen atom.

[0028] As a further embodiment, R2 in the first additive a provided by the present invention is preferably a fluorine atom.

[0029] As a further solution, the second additive b provided by the present invention is preferably one of the halogenated cyclic carbonate structural compounds;

[0030] Wherein, R3 is one of C1 to C3 haloalkyl groups, or / and, R4 is one of halogen atoms and C1 to C6 haloalkyl groups.

[0031] As a further embodiment, R3 in the second additive b is a C1-C3 non-halogenated alkyl group, and R4 is a C1-C6 halogenated alkyl group.

[0032] In a further preferred embodiment, R4 in the second additive b is a C1 halogenated alkyl group.

[0033] As a further solution, a high-voltage resistant sodium ion battery electrolyte also includes sodium salt and an organic solvent.

[0034] 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.

[0035] As a further embodiment, the sodium salt is sodium hexafluorophosphate.

[0036] As a further solution, the organic solvent is one or more of an ether solvent, an ester solvent, and an ionic liquid.

[0037] 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.

[0038] As a further embodiment, the complex functional group is selected from one or more of C1-C10 alkoxy, alkenyl, and alkynyl groups.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] As a further solution, the ester solvent is selected from one or more of linear ester solvents and cyclic carbonate solvents.

[0043] 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.

[0044] 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.

[0045] As a further solution, the source of the manganese element in the positive electrode material is not limited, and the manganese element can be introduced into the positive electrode material in any feasible manner as needed. As some optional methods, the manganese 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 manganese-containing additive as a positive electrode additive, such as MnO2.

[0046] As a further solution, the positive electrode active material containing manganese is a metal layered oxide containing manganese, and the metal layered oxide containing manganese 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), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), and mercury (Hg).

[0047] As a further solution, M in the manganese-containing cathode active material includes at least one of Ni, Fe, and Cu.

[0048] As a further solution, 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.

[0049] 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.

[0050] 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

[0051] [[ID=~15]]As an even further solution, the binder is polyvinylidene fluoride (PVDF).

[0052] The present invention also provides a sodium-ion battery, which includes the electrolyte, a positive electrode sheet containing the positive electrode material, and further includes a negative electrode sheet containing a negative electrode material and a separator.

[0053] As a further solution, in the fabrication of the sodium-ion battery, the positive electrode sheet, the negative electrode sheet, and the separator are made into an electrode assembly through a winding process or a stacking process, and the preferred solution is the winding process.

[0054] As a further solution, the positive electrode material includes a positive electrode active material NaCu 1 / 20 Ni 6 / 20 Fe 6 / 20 Mn 7 / 20 O2, the binder polyvinylidene fluoride (PVDF), and also include conductive carbon black Super-P, solvent and positive electrode current collector aluminum foil.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] The characteristics and beneficial effects of the present invention are:

[0059] (1) The present invention provides a high-voltage resistant sodium ion battery electrolyte. 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 positive electrode material from undergoing structural collapse, active particle breakage, transition metal dissolution, and excessive side reactions under high voltage and high temperature, reduce the rapid growth of the cycle DCR, and improve the battery's high temperature and high voltage cycle performance.

[0060] On the one hand, by regulating the contents of additive a, additive b, binder and Mn in the positive electrode material to 0.2%≤A≤3%, 0.3%≤B≤3%, 1%≤C≤3%, 10%≤D≤50%, 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 high-temperature and corrosion-resistant dense passivation film on the positive electrode surface, and inhibits the dissolution of transition metals; additive b decomposes to produce important inorganic products, enhances the stability of the interface film, further improves the cycle stability and high-temperature performance of the battery, solves the problem that organic electrolyte salts cannot form SEI and CEI in sodium batteries, and improves the battery cycle life. Additive a and additive b have a strong influence on the Mn 2+ The inorganic components in the 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, thus avoiding the serious shedding of positive electrode particles under high voltage;

[0061] On the other hand, under the condition of satisfying the formula of 2.6≤(AB+100)C / (C+D)≤14.3, the relationship between the mass percentage of additives, binders and Mn ions in the positive electrode powder is balanced, and the energy density and structural stability are balanced. + The migration rate can significantly reduce the growth of interfacial resistance (DCR) during the cycle, which can optimize the stability of the battery cell at high voltage, slow down the growth of cycle DCR, and further improve the cycle performance at high temperature and high voltage.

[0062] (2) The present invention provides a high-voltage sodium ion battery electrolyte, which improves the stability of the battery under high voltage by optimizing the ratio between the binder and the electrolyte additive. Although a higher binder ratio can enhance the stability of the electrode structure, reduce the shedding of active materials, extend the cycle life, and improve the electrode processing performance, it will also increase the electrode internal resistance, reduce the energy density and rate performance, and may cause the electrolyte wettability to deteriorate; a lower binder ratio improves the electrode conductivity and ion transmission efficiency, improves the rate performance, but the electrode is prone to cracking or pulverization, the cycle life is reduced, and the processing difficulty increases. Therefore, it is crucial to balance the ratio between the binder and the electrolyte additive. When 1.5≤(A+B) / C≤2 is satisfied, the performance is relatively good. When the mass percentage of the second additive b in the electrolyte is 1 to 2 times that of the first additive a, the impedance growth rate is effectively reduced by synergistically optimizing the ion transmission efficiency and the dense passivation film performance, further enhancing the overall performance of the sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 The capacity retention rate of Example 1 and Comparative Example 1 of the present invention at 45°C, 2-4.25V, 1C / 1C charge-discharge cycle

[0064] Figure 2 The DCR growth of Example 1 and Comparative Example 1 under 45°C cycle DETAILED DESCRIPTION

[0065] To facilitate understanding of the present invention, the following will provide a more comprehensive description of a high-voltage sodium ion battery electrolyte 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.

[0066] The present invention first provides a high-voltage resistant sodium ion battery electrolyte, comprising a first additive a and a second additive b;

[0067] The first additive a is selected from one or more compounds having a chain sulfonyloxy structure and has the following structure:

[0068]

[0069] 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;

[0070] The second additive b is selected from one or more cyclic carbonate compounds having halogenation and / or containing unsaturated double bonds, and the specific structure is as follows:

[0071]

[0072] Wherein, R3 is selected from one of C1-C3 halogenated or non-halogenated alkylene, C2-C3 halogenated or non-halogenated alkenylene;

[0073] R4 is selected from one of a hydrogen atom, a halogen atom, a C1-C6 halogenated or non-halogenated alkyl group, and a C2-C3 halogenated or non-halogenated alkenyl group;

[0074] represents one of a single bond or an unsaturated double bond;

[0075] Furthermore, at least one of R3 and R4 contains a halogenated group, and / or the second additive b contains an unsaturated double bond.

[0076] Specifically, when the second additive b is a halogenated cyclic carbonate structure compound, at least one of R3 and R4 may contain a halogenated group, and It can represent either a single bond or an unsaturated double bond.

[0077] When the second additive b is a cyclic carbonate structure compound containing an unsaturated double bond, the following two situations may be included:

[0078] i) R3 is a C2-C3 halogenated or non-halogenated alkenylene group, or R4 is a C2-C3 halogenated or non-halogenated alkenyl group, and both represent a single bond;

[0079] ii) R3 is selected from C1-C3 halogenated or non-halogenated alkylene, R4 is selected from one of hydrogen atom, halogen atom, C1-C6 halogenated or non-halogenated alkyl, and Indicates an unsaturated double bond.

[0080] The amounts of the first additive a and the second additive b in the electrolyte satisfy the following formula: 2.6≤(AB+100)C / (C+D)≤14.3, and 0.2%≤A≤3%, 0.3%≤B≤3%, 1%≤C≤3%, 10%≤D≤50%, 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 Mn element in the positive electrode material of the battery to all transition metal elements.

[0081] The above design of the present invention solves the problems of rapid battery capacity decay, poor cycle performance, and large cycle DCR growth by optimizing the first additive a, the second additive b, the percentage of the binder in the positive electrode powder, and the molar percentage of the Mn element in all transition metal elements; by matching different types of electrolyte additives and optimizing and adjusting the additive content, the electrolyte additives are decomposed to form a low-solubility SEI film; a dense and complete S-rich electrolyte interface film is constructed, 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 cycle stability and high temperature performance of the battery are improved, and the stability under high voltage is improved. The presence of Mn element regulates the electrolyte additive in Mn 2+ The degree of decomposition of the passivation layer of the cross-linked polymer rich in inorganic components under catalytic action is balanced with the structural stability and energy density by combining and regulating the molar ratio of the Mn element in the transition metal. At the same time, the passivation layer interacts with the relatively regulated binder to construct a suitable network cross-linking structure, avoid the peeling of the positive electrode active material, and improve the cycle stability of the passivation film; the binder ensures the uniform dispersion of the various components of the electrode, fully plays the role of binding the active material, conductive agent and current collector, and does not affect the overall energy density of the battery cell due to excessive content ratio; through the above design, the high voltage stability of the battery cell is improved, and the interaction between the active particles and the binder is improved, avoiding the peeling of the active particles under high voltage, thereby improving the overall cycle performance and reducing the cycle DCR growth.

[0082] As a further preferred example, we prefer that the single amount of each component satisfies at least one of the following: 0.5%≤A≤1.5%, 0.5%≤B≤2%, 1.2%≤C≤2%, and / or 30%≤D≤40%.

[0083] Preferably, 0.5%≤A≤1.5%, controlling the mass content of the first electrolyte additive a within a suitable range, is more inclined to decompose and form more SEI films with lower solubility, constructing a dense and complete S-rich interface film, and is beneficial to the Na in the CEI layer. + conductivity.

[0084] Preferably, 0.5%≤B≤2%, controlling the mass content of the second electrolyte additive b within an appropriate range, effectively reducing the thickness of the CEI interface film, improving the cycle stability and high temperature performance of the battery, and further contributing to improving stability at high voltage.

[0085] Preferably, 1.2%≤C≤2%, and the content of the binder is controlled within an appropriate range, which can 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, while not affecting the overall energy density of the battery cell due to excessive content.

[0086] Preferably, 30%≤D≤40%, and the mass percentage of the Mn element in the positive electrode material is controlled within an appropriate range, which does not affect the role of the Mn element in stabilizing the structure of the positive electrode material, ensuring that the Mn element inhibits structural phase change and lattice distortion, 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.

[0087] In a further preferred example, each component satisfies the relationship of 3.7≤(AB+100)C / (C+D)≤5.5.

[0088] 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, the content of the second additive b, the content of Mn and the content of the binder has a very significant impact on the interface stability and the stability between the positive electrode active particles. When the above relationship 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, the cycle performance of the battery cell, especially the cycle performance under high temperature cycles, will deteriorate, and even cause some safety problems.

[0089] As a further example, when the above conditions of 0.5% ≤ A ≤ 1.5%, 0.5% ≤ B ≤ 2%, 1.2% ≤ C ≤ 2%, and 30% ≤ D ≤ 40% are met, preferably 3.7 ≤ (AB + 100) C / (C + D) ≤ 5.5, and 1.5 ≤ (A + B) / C ≤ 2 and 1 ≤ B / A ≤ 2 are met, the performance is even better. In this case, the transition metal dissolution Mn content in the battery is ≤ 18 ppm, the number of cycles at 45°C to 80% capacity decay is ≥ 727, and the DCR increase at 45°C to 80% capacity decay is ≤ 23.1%.

[0090] As a further preferred example, R1 in the first additive a provided by the present invention is preferably a sodium atom.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] As a further preferred example, R2 in the first additive a provided by the present invention is preferably a halogen atom.

[0095] As a further preferred example, R2 in the first additive a provided by the present invention is preferably a fluorine atom.

[0096] As a further preferred example, the first additive a provided by the present invention is selected from a-1 a-2 a-3 a-4 a-5 a-6 a-7 a-8 a-9 One or more of .

[0097] As a further preferred example, the second additive b is preferably one of the halogenated cyclic carbonate structural compounds;

[0098] wherein R3 is one of C1 to C3 haloalkyl groups, or / and R4 is one of halogen atoms and C1 to C6 haloalkyl groups;

[0099] As a preferred example, R3 in the second additive b is a C1-C3 non-halogenated alkyl group, and R4 is a C1-C6 halogenated alkyl group;

[0100] As a further preference, R4 in the second additive b is a C1 halogenated alkyl group.

[0101] 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 One or more of .

[0102] As an example, a high-voltage resistant sodium ion battery electrolyte also includes sodium salt and an organic solvent.

[0103] 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.

[0104] As a preferred example, the sodium salt is sodium hexafluorophosphate (NaPF6).

[0105] Illustratively, the organic solvent is one or more of an ether solvent, an ester solvent, and an ionic liquid.

[0106] 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;

[0107] The complex functional group is selected from one or more of C1-C10 alkoxy, alkenyl, and alkynyl groups;

[0108] 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.

[0109] The ether solvent containing a single ether bond is selected from one or more of cyclopentyl methyl ether, ethyl ether, and propyl ether.

[0110] The ether solvent containing complex functional groups is selected from one or more of butynediol dipropoxy ether, propargyl ether, and propargyl ether;

[0111] As an example, the ester solvent is selected from one or more of linear ester solvents and cyclic carbonate solvents.

[0112] 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.

[0113] The cyclic carbonate solvent is selected from one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, and 1,2-propylene glycol carbonate.

[0114] The source of manganese element in the positive electrode material is not limited, and manganese element can be introduced into the positive electrode material in any feasible manner according to needs. As some optional ways, manganese 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 positive electrode additive in the form of a manganese-containing additive, such as MnO2 and the like.

[0115] Exemplarily, the positive electrode active material containing manganese element is a metal layered oxide containing manganese element, and the general formula of the metal layered oxide containing manganese element is Na x Mn y M z O2, where 0.95 < x ≤ 1.05, 0.01 ≤ y ≤ 0.6, y + z = 1, 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), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg).

[0116] Exemplarily, M in the positive electrode active material containing manganese element includes at least one of Ni, Fe, and Cu.

[0117] Exemplarily, 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.

[0118] 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.

[0119] Exemplarily, the acrylic resin includes at least one of acrylic vinyl ester resin, acrylic methyl ester resin, acrylic butyl ester resin, acrylic styrene resin, acrylate resin, acrylate copolymer resin, acrylic resin, and acrylic emulsion resin.

[0120] As a preferred example, the binder is polyvinylidene fluoride (PVDF).

[0121] 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.

[0122] 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.

[0123] The positive electrode sheet includes a positive electrode active material NaCu 1 / 20 Ni 6 / 20 Fe 6 / 20 Mn 7 / 20 O2, the binder polyvinylidene fluoride (PVDF), and also include conductive carbon black Super-P, solvent and positive electrode current collector aluminum foil.

[0124] The negative electrode sheet includes one or more of hard carbon, a conductive agent SuperP, a thickener CMC, a binder SBR, and a negative electrode current collector aluminum foil.

[0125] The outer packaging of the sodium ion battery is a bag-type soft package or an aluminum shell or a steel shell.

[0126] 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.

[0127] As a specific embodiment of the present invention, the following detailed cases are provided:

[0128] Example 1:

[0129] This embodiment provides a sodium ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0130] 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, 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;

[0131] 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;

[0132] 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 1%, and the mass content of the second additive b-1 is 1.5%.

[0133] Preparation of the positive electrode sheet: the positive electrode active material NaCu 1 / 20 Ni 6 / 20 Fe 6 / 20 Mn 7 / 20 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 (that is, the binder PVDF accounts for 1.5% of the mass of the positive electrode powder), 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 the surface of manganese-containing aluminum foil prepared by mechanical alloying, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0134] The negative electrode sheet is prepared by mixing the negative electrode active material hard carbon, the conductive agent Super P, the thickener CMC, and the binder SBR in a mass ratio of 94:2:1.5:2.5, adding deionized water and stirring evenly to obtain a negative electrode slurry, wherein the slurry viscosity is adjusted to 4500±500mPa·s and the solid content is 50±0.5wt%; then, the slurry is coated on the negative electrode current collector aluminum foil, and then dried, cold pressed, and slit to obtain the negative electrode sheet.

[0135] 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.

[0136] 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.

[0137] Under the above conditions, the following tests were performed:

[0138] Test for the dissolution of transition metal Mn 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°C until it is completely dissolved, cool it to room temperature, and dilute it to the mark. Transfer it to a volumetric flask and adjust the volume to 50ml. After calibrating the instrument with a standard solution, introduce the prepared sample solution into the ICP instrument for measurement. Calculate the transition metal Mn content in the sample based on the data output by the instrument.

[0139] High temperature cycle test: At 45°C, charge and discharge cycles are performed at 1C / 1C with a voltage range of 2 to 4.25V. The number of cycles required for the capacity to decay to 80% is recorded.

[0140] Cycling DCR growth test: records the DCR at the beginning of the cycle at a high temperature of 45°C, and the DCR when the cycling capacity decays to 80% at a high temperature of 45°C;

[0141] Examples 2 to 29, Comparative Examples 1 to 11:

[0142] 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.

[0143] The test results obtained in Examples 1 to 29 and Comparative Examples 1 to 11 are shown in Table 1:

[0144] Table 1

[0145]

[0146]

[0147] From Examples 1 to 29 and Comparative Examples 1 to 11, it can be observed that:

[0148] When 0.2%≤A≤3%, 0.3%≤B≤3%, 1%≤C≤3%, 10%≤D≤50% are satisfied at the same time, and the formula relationship of 2.6≤(AB+100)C / (C+D)≤14.3 is satisfied, the transition metal dissolution Mn content in the battery is ≤27ppm, the number of cycles when the capacity decays to 80% is ≥645, and the DCR increase when the capacity decays to 80% is ≤26.54%. The above parameters can ensure the most basic performance of the sodium ion battery. Compared with the comparative example, to a certain extent, the dissolution of transition metals is inhibited and the capacity retention rate of the cycle is improved.

[0149] Comparative Examples 1 to 9 show the relevant performance when 0.2%≤A≤3%, 0.3%≤B≤3%, 1%≤C≤3%, and 10%≤D≤50% are not satisfied. Under these parameters, the most basic performance of the sodium ion battery cannot be guaranteed.

[0150] Specifically, such as Figure 1 and Figure 2 The data shown shows the capacity retention and cyclic DCR growth rate of Example 1 and Comparative Example 1 from 0 to 400 cycles at 45°C. Under high temperature and high voltage conditions, the number of cycles until the capacity decayed to 80% was 735 for Example 1, while the number of cycles until the capacity decayed to 80% was 299 for Comparative Example 1. The DCR growth rate when the capacity decayed to 80% was 21.90% for Example 1, while the DCR growth rate when the capacity decayed to 80% was 25.31% for Comparative Example 1. The relevant performance of Comparative Example 1 is far inferior to that of Example 1.

[0151] Comparative Examples 1 to 2 and Comparative Example 3 are the cases where only the first additive a is added, only the second additive b is added, and no additive is added, respectively; at this time, the transition metal eluted Mn content is relatively high, both greater than 60 ppm. Comparing the comparative examples lacking the first additive a or the second additive b with Example 1, the Mn elution content of Comparative Example 1 is approximately 3.9 times that of Example 1, and the Mn elution content of Comparative Example 2 is 4 times that of Example 1.

[0152] 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 inhibiting the dissolution of transition metals. 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, and the second additive directional adsorbs free Mn through polar groups. 2+ , while continuously repairing SEI film defects during cycling, decomposing to produce important inorganic products such as NaF and Na2CO3, as well as alkyl carbonates, enhancing the stability of the interfacial film and further improving the battery's cycling stability and high-temperature performance. In the absence of the first additive, the SEI film may exhibit a porous amorphous structure. In the absence of the second additive, the dynamic stability of the interfacial film deteriorates, and the recrystallization of the sulfur component at high temperatures may cause crack propagation, reducing performance.

[0153] Comparative Examples 4 and 5 illustrate the cases where the first additive a or the second additive b is insufficient or excessive. When the electrolyte additive content is insufficient, the transition metal Mn content is high, and the cycle life at high temperatures and the number of cycles required to retain 80% of the capacity are also low. This is likely due to a lack of stable conditions for SEI film formation, leading to excessive metal dissolution and reduced battery cycle performance. When the electrolyte additive content is excessive, the interfacial film becomes too thick, resulting in poor membrane stability, increased interfacial impedance, and increased polarization, which in turn reduces cycle performance.

[0154] Comparative Examples 6 and 7 show the situations when the binder is insufficient or excessive. The binder 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 transport. Therefore, if the binder is insufficient, it may affect the structural stability and the active material will fall 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 and forms an overly thick SEI film, which consumes the sodium source, further increases the internal resistance, and affects the life. When the binder is excessive, the active material and the conductive agent are over-wrapped, which hinders their effective contact and significantly increases the electronic impedance of the electrode. The dense binder network will block the electrode pores, seriously hindering the electrolyte infiltration and ion transfer dynamics.

[0155] Comparative Examples 8 and 9 show the situation when there is no Mn or when Mn is excessive. Mn, as an important catalyst for electrolyte additives, can generate a composite passivation layer rich in inorganic components and cross-linked polymers. Not adding Mn 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. When Mn is excessive, the strength of the electrode structure increases, but the addition of Mn 2+ Dissolution risk: a passivation layer that is too thick or too rigid will seriously hinder the transmission of sodium ions at the interface, resulting in a significant increase in interfacial impedance.

[0156] In particular, in Comparative Examples 10 and 11, the single parameters all satisfy 0.2%≤A≤3%, 0.3%≤B≤3%, 1%≤C≤3%, and 10%≤D≤50%, but do not satisfy the formula relationship of 2.6≤(AB+100)C / (C+D)≤14.3. The results are also poor, the transition metal dissolution Mn content in the battery is greater than 40 ppm, the number of cycles at which the capacity remains 80% is less than 400, and the DCR increases by more than 30% when the capacity decays to 80%. This shows that even if the respective conditions are met individually, if 2.6≤(AB+100)C / (C+D)≤14.3 is not satisfied, the performance requirements cannot be met.

[0157] Under this formula, the additive plays a role in inhibiting the dissolution of transition metals in the electrolyte, oxidizing to form a sulfur-containing CEI film on the surface of the positive electrode, inhibiting the dissolution of transition metals. The first additive a decomposes to form more SEI films with lower solubility, constructing a dense and complete S-rich interface film, and is beneficial to the Na in the CEI layer. + The conductivity of the battery is improved, and the content of the second additive b is within a suitable range, which effectively reduces the thickness of the CEI interface film, improves the cycle stability and high-temperature performance of the battery, and is more conducive to improving the stability under high voltage; the product relationship between the first additive A and the second additive B shows that the addition of too low an amount of any one additive will greatly reduce the synergistic effect of the two additives.

[0158] The mass percentage C of the binder in the positive electrode powder is an important coefficient. It plays a core role in bonding the active material particles, conductive agent (such as carbon black) and current collector (aluminum foil) to form a stable electrode structure. Insufficient bonding force will lead to the separation of active material particles and current collector, increase electrode brittleness, and easy cracking during coating. Excessive binder covers the surface of the active material and hinders electron / ion transmission. The binder is an electrochemically inert substance. If the percentage is too high, the proportion of active material will be diluted. At the same time, the positive electrode powder with too high a binder content will also make the pole piece too hard and prone to breakage during winding or stacking. The right amount of binder can ensure that the various components of the electrode are evenly dispersed and give full play to the role of bonding active material, conductive agent and current collector, without affecting the overall energy density of the battery cell due to excessive content.

[0159] The binder and Mn ions both play a role in mechanical support and structural stability. At the same time, the Mn dissolved 2+ It can catalyze the decomposition of electrolyte additives to generate a composite passivation layer rich in inorganic components and cross-linked polymers. This formula shows that a high Mn ratio can improve structural stability, but increasing Mn 2+ Dissolution risk requires more electrolyte additives and binders to inhibit dissolution and enhance electrode adhesion; low Mn content reduces the dissolution risk but sacrifices energy density, requiring a lower binder content to optimize conductivity.

[0160] Therefore, when the formula relationship of 2.6≤(AB+100)C / (C+D)≤14.3 is satisfied, the relationship between the mass percentages of additives, Mn ions, and binders in the positive electrode powder is balanced, and the energy density and structural stability performance are balanced.

[0161] As a further preferred example, according to Examples 1 to 5, 0.5%≤A≤1.5% is preferably selected as the mass percentage of the first additive a; according to Example 1, Examples 9 to 12, 0.5%≤B≤2% is preferably selected as the mass percentage of the second additive b; according to Example 1, Examples 15 to 18, 1.2%≤C≤2% is preferably selected as the mass percentage of the binder in the positive electrode powder in the battery; according to Example 1, Examples 19 to 22, 30%≤D≤40% is preferably selected as the molar percentage of the Mn element in the positive electrode material of the battery to all transition metal elements.

[0162] When 0.5%≤A≤1.5%, 0.5%≤B≤2%, 1.2%≤C≤2%, and 30%≤D≤40%, the content range of each component is optimized to further improve the performance of the sodium ion battery.

[0163] As a further preferred example, when 0.5%≤A≤1.5%, 0.5%≤B≤2%, 1.2%≤C≤2%, and 30%≤D≤40% are satisfied, 3.7≤(AB+100)C / (C+D)≤5.5 is preferably satisfied; the embodiments under this condition all meet the following conditions: the transition metal dissolution Mn content in the battery is ≤20ppm, the number of cycles for capacity decay to 80% is ≥711, and the DCR increase for capacity decay to 80% is ≤24.58%.

[0164] Therefore, while satisfying the mass percentage of different electrolyte additives and binders in the positive electrode powder and the molar percentage of Mn elements in all transition metal elements within a certain range, calculating and further optimizing the (AB+100)C / (C+D) range has important practical significance for improving and optimizing the performance of sodium-ion batteries.

[0165] As a further example, when the above-mentioned conditions of 0.5%≤A≤1.5%, 0.5%≤B≤2%, 1.2%≤C≤2%, and 30%≤D≤40% are satisfied, preferably 3.7≤(AB+100)C / (C+D)≤5.5, the performance is better when 1.5≤(A+B) / C≤2 and 1≤B / A≤2 are satisfied.

[0166] At this time, the transition metal dissolution Mn content in the battery is ≤18ppm, the number of cycles at 45°C for capacity decay to 80% is ≥727, and the DCR increase at capacity decay to 80% is ≤23.1%.

[0167] Examples 1, 4, 11, and 20, shown in the table, are significantly superior to Examples 3, 10, 17, and 25. This may be due to the ratio between the binder and electrolyte additives. While a higher binder ratio can enhance electrode structural stability, reduce active material shedding, extend cycle life, and improve electrode processing performance, it also increases electrode internal resistance, reduces energy density and rate performance, and may lead to poor electrolyte wettability. A lower binder ratio improves electrode conductivity and ion transport efficiency, improving rate performance, but it also increases electrode cracking or pulverization, reduces cycle life, and increases processing difficulty. Balancing the ratio between the binder and electrolyte additives is crucial. When the amount of the second additive b is 1 to 2 times that of the first additive a, the impedance increase is effectively reduced by synergistically optimizing ion transport efficiency and dense passivation film performance, further enhancing the overall performance of the sodium-ion battery. Therefore, when the conditions 1.5 ≤ (A + B) / C ≤ 2 and 1 ≤ B / A ≤ 2 are met, relatively good performance is achieved.

[0168] According to Example 28 compared with Examples 1, 6, 7, and 8, when the R2 group in the structure of the first additive a is one of halogen, C1 halogenated hydrocarbon group or hydrocarbonoxy group, and C1 halogenated sulfonyloxy group, it is better than non-halogenated hydrocarbon group.

[0169] According to the comparison between Examples 1, 6, 7, and 8, when the R2 group in the structure of the first additive a is a halogen, it is better than when C1 is a halogenated hydrocarbon group, better than when C1 is a halogenated hydrocarbonoxy group, and better than when C1 is a halogenated sulfonyloxy group;

[0170] 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. The electronic effect of C1's non-halogenated or halogenated hydrocarbon oxygen groups, non-halogenated ester groups or acyloxy groups is weaker, which may also be related to the fact that the steric hindrance of halogen atoms is smaller, which promotes the dispersion of additives and their rapid migration to the electrode surface.

[0171] As a further solution, according to Examples 1, 13, 14, and 29, it is shown that when the second additive b is a halogenated cyclic carbonate compound, it is superior to a cyclic carbonate compound containing an unsaturated double bond.

[0172] As a further solution, according to Examples 1, 13, and 14, the performance is better when the structure R3 of the second additive b is preferably a non-halogenated hydrocarbon group and R4 is preferably a halogenated alkyl group of C1;

[0173] This may be because the multiple fluorine atoms in the fluoroalkyl group significantly reduce the HOMO (highest occupied molecular orbital) energy level of the cyclic carboxylate through a strong electron-withdrawing effect, making it more difficult to be oxidized; this is especially important under high voltage, which can inhibit the premature decomposition of the additive at high potential.

[0174] 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 Mn in the positive electrode material. 2+ Under the catalytic action of Mn, a cross-linked polymer passivation layer rich in inorganic components is produced. 2+ The outer d orbital of the first additive a has many unpaired electrons, which makes it have unique electron transfer ability and can easily 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 anion 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 Na2SO4, Na2S x O yThe S-containing organic cross-linked polymer preferentially protects the positive electrode and inhibits the dissolution of transition metals. Additive b decomposes to produce important inorganic products such as NaF and Na2CO3, as well as alkyl carbonates, enhancing the stability of the interfacial film and further improving the battery's cycling stability and high-temperature performance. The synergistic effect of these three essential factors creates a more stable interfacial film, inhibiting the dissolution of transition metals. Furthermore, it enhances the stability of the positive electrode active material and the conductive network, resulting in the excellent high-voltage cycling stability of sodium-ion batteries.

[0175] This technical solution significantly improves the stability of sodium-ion batteries at high voltages, helps build a stable interfacial film, and enhances the interaction between the active particles and the binder. Together, they effectively prevent structural collapse, active particle fragmentation, transition metal dissolution, and excessive side reactions in the cathode material under high voltage and high temperature, reducing the rapid increase in cycle DCR and improving the battery's high-temperature cycling performance. The electrolyte additive prepared by this method improves the electrochemical performance and safety of sodium-ion batteries.

[0176] 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 sodium ion battery 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 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 cyclic carbonate compounds having halogenation and / or containing unsaturated double bonds, and the specific structure is as follows: wherein R3 is selected from one of C1-C3 halogenated or non-halogenated alkylene, C2-C3 halogenated or non-halogenated alkenylene; and R4 is selected from one of hydrogen atom, halogen atom, C1-C6 halogenated or non-halogenated alkyl, C2-C3 halogenated or non-halogenated alkenyl; represents one of a single bond or an unsaturated double bond; and at least one of R3 and R4 contains a halogenated group, and / or the second additive b contains at least one unsaturated double bond; The amounts of the first additive a and the second additive b in the electrolyte satisfy the following formula: 2.6≤(AB+100)C / (C+D)≤14.3, and 0.2%≤A≤3%, 0.3%≤B≤3%, 1%≤C≤3%, 10%≤D≤50%, 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 Mn element in the positive electrode material of the battery to all transition metal elements.

2. The high-voltage sodium ion battery electrolyte according to claim 1, characterized in that: A, B, C, and D also satisfy at least one of the following: 0.5%≤A≤1.5%, 0.5%≤B≤2%, 1.2%≤C≤2%, and 30%≤D≤40%; Further preferably, the sodium ion battery electrolyte further satisfies 3.7≤(AB+100)C / (C+D)≤5.5; More preferably, the sodium ion battery electrolyte also satisfies 1.5≤(A+B) / C≤2 and 1≤B / A≤2.

3. The high-voltage sodium ion battery electrolyte 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 high-voltage sodium ion battery electrolyte according to claim 1, characterized in that: The second additive b is one of the halogenated cyclic carbonate structural compounds, wherein R3 is one of C1 to C3 haloalkyl groups, or / and R4 is one of halogen atoms and C1 to C6 haloalkyl groups; Preferably, R3 in the second additive b is a C1-C3 non-halogenated alkyl group, and R4 is a C1-C6 halogenated alkyl group; More preferably, R4 in the second additive b is a C1 halogenated alkyl group.

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

7. The high-voltage sodium ion battery 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 sodium ion battery 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 sodium ion battery electrolyte according to claim 1, characterized in that: The source of manganese in the positive electrode material includes directly using it as one of the structural components of the positive electrode active material and / or introducing it into the positive electrode material as a positive electrode additive in the form of a manganese-containing additive; Preferably, the manganese-containing additive is MnO2; Preferably, the manganese-containing positive electrode active material is a manganese-containing metal layered oxide, and the general formula of the manganese-containing 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, 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 manganese-containing positive electrode active material includes at least one of Ni, Fe, and 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 high-voltage-resistant sodium ion battery 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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