Electrolyte solution, sodium-ion battery, and electronic device

Abstract

The present invention relates to the technical field of batteries, and disclosed are an electrolyte solution, a sodium-ion battery, and an electronic device. The electrolyte solution comprises an electrolyte salt, an organic solvent, and an electrolyte solution additive, wherein the organic solvent includes a cyclic carbonate solvent, a linear carbonate solvent, and a carboxylate solvent; and the electrolyte solution additive includes an organic additive and a sodium salt additive, the organic additive including a sulfur-containing ester compound. By regulating and controlling the content of the components of the organic solvent and the content of the components of the organic solvent and the additive in the electrolyte solution, the electrolyte solution has a relatively high electrical conductivity, thereby facilitating the de-solvation of sodium ions on the electrode-electrolyte solution interface.

Description

Electrolyte, sodium ion battery and electronic device

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on November 14, 2023, with application number 202311519730.8 and application name “A kind of electrolyte, sodium ion battery and electronic device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to an electrolyte, a sodium ion battery and an electronic device. Background Art

[0003] With the development of the economy and technology, most electronic devices (such as portable electronic devices, drones, and electric vehicles) urgently need energy storage devices such as batteries that have higher energy density, higher power density, longer cycle life, and greater safety. Sodium-ion batteries, for example, are considered a promising candidate for energy storage due to their abundant sodium resources and low cost. However, their widespread application is currently hampered by shortcomings such as poor low-temperature cycling performance and sodium precipitation during low-temperature charging.

[0004] The electrolyte is an important component of sodium-ion batteries. Its physical and chemical properties and chemical composition not only determine the kinetic performance of sodium ions in the electrolyte, but also determine the composition and structure of the solid electrolyte interphase (SEI) film on the electrode surface, which has a significant impact on the rate performance, electrode structure stability and cycle life of sodium-ion batteries. Typically, the electrolyte of a sodium-ion battery uses esters as solvents and sodium salts as solutes. When the solvent has a high melting point and high viscosity, it will have a strong interaction with the sodium ions in the solute, which to a certain extent limits the diffusion of sodium ions in the solution and is not conducive to the desolvation of sodium ions at the electrode-electrolyte interface. This, in turn, affects the life and stability of the sodium-ion battery.

[0005] Summary of the Invention

[0006] The embodiments of the present application provide an electrolyte, a sodium ion battery, and an electronic device. By regulating the content of the organic solvent and the components of the additive in the electrolyte, the electrolyte has a higher conductivity and is conducive to the desolvation of sodium ions at the electrode-electrolyte interface.

[0007] To achieve the above objectives, the embodiments of the present application adopt the following technical solutions:

[0008] In a first aspect, an embodiment of the present application provides an electrolyte, which includes an electrolyte salt, an organic solvent and an electrolyte additive, wherein the organic solvent includes a cyclic carbonate solvent, a linear carbonate solvent and a carboxylate solvent; the electrolyte additive includes an organic additive and a sodium salt additive, and the organic additive includes a sulfur-containing ester compound.

[0009] The mass ratio of the carboxylic acid ester solvent to the sulfur-containing ester compound is 1.2:1 to 40:1, and the mass ratio of the cyclic carbonate solvent to the sodium salt additive is 5:1 to 80:1.

[0010] The embodiments of the present application adjust the content and mass ratio between carboxylate solvents and sulfur-containing ester compounds, cyclic carbonate solvents and sodium salt additives, so that the content of cyclic carbonate and carboxylate solvents in the organic solvent is appropriate, thereby preventing the electrolyte viscosity from being too high and the electrolyte conductivity from being low. At the same time, the content of sulfur-containing ester compounds and sodium salt additives in the additives is also appropriate, thereby preventing the cyclic carbonate solvents and carboxylate solvents from being oxidized and decomposed at the positive electrode of the battery under high temperature scenarios to produce a large amount of gas, thereby improving the high-temperature cycle performance and safety of the battery. Avoiding too high or too low content of sulfur-containing ester compounds causes the sulfur-containing ester compounds to form a high-impedance interface film or an unstable interface film with low ion conductivity on the surface of the positive and negative electrode materials. Furthermore, it is not conducive to the low or high temperature performance of the battery.

[0011] In an implementation of the first aspect, the mass ratio of the cyclic carbonate solvent to the linear carbonate solvent is 0.3:1 to 1.5:1, the mass ratio of the cyclic carbonate solvent to the carboxylate solvent is 0.7:1 to 7:1; and the mass ratio of the linear carbonate solvent to the carboxylate solvent is 1.2:1 to 9:1.

[0012] The present invention controls the mass ratio of cyclic carbonate solvents, linear carbonate solvents, and carboxylate solvents to prevent excessive electrolyte viscosity and low electrolyte conductivity. Furthermore, the invention suppresses the oxidative decomposition of cyclic carbonate solvents and carboxylate solvents at the battery's positive electrode in high-temperature environments, thereby improving the battery's high-temperature cycling performance, low-temperature performance, and safety.

[0013] In an implementation of the first aspect, the organic additive further includes a fluorinated carbonate compound, and the mass ratio of the carboxylate solvent to the fluorinated carbonate compound is 1.2:1 to 40:1.

[0014] The present invention's embodiments can control the mass ratio of carboxylate solvents to fluorocarbonate compounds, which not only inhibits battery gassing and reduces electrolyte viscosity, but also facilitates the formation of a film of the fluorocarbonate compound on the electrode surface, improving film quality. This improves the sodium-ion battery's low-temperature characteristics while also ensuring high-temperature cycling performance.

[0015] In an implementation of the first aspect, the organic additive further includes an acid anhydride compound, and the mass ratio of the cyclic carbonate solvent to the acid anhydride compound is 15:1 to 400:1.

[0016] The present invention can control the mass ratio of the cyclic carbonate solvent to the anhydride compound, which not only inhibits battery gassing and reduces electrolyte viscosity, but also facilitates the formation of anhydride films on the electrode surface, improving film quality. This improves the low-temperature characteristics of sodium-ion batteries while also taking into account high-temperature cycling performance.

[0017] In one implementation of the first aspect, the organic additive further comprises a nitrile compound. The mass percentage of the sulfur-containing ester compound in the electrolyte is 0.5%-5%, the mass percentage of the fluorocarbonate compound in the electrolyte is 0.5%-5%, the mass percentage of the nitrile compound in the electrolyte is 0.5%-5%, and the mass percentage of the acid anhydride compound in the electrolyte is 0.05%-1%. Controlling the various additives to appropriate levels allows them to exert their beneficial effects without degrading other battery properties.

[0018] In one implementation of the first aspect, the nitrile compound includes a mononitrile compound and / or a polynitrile compound; the mononitrile compound includes at least one of acetonitrile and p-methylbenzonitrile; and the polynitrile compound includes one or more of succinonitrile, glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetrinitrile. The nitrile compound can complex transition metal ions in the positive electrode material, reducing the catalytic activity of the transition metal ions, reducing the dissolution of the transition metal ions, and improving the oxidation resistance of the electrolyte.

[0019] In one implementation of the first aspect, the acid anhydride compound includes one or more of succinic anhydride, glutaric anhydride, adipic anhydride, maleic anhydride, and cyclic phosphoric anhydride. The acid anhydride compound can form a film on the surface of the positive and negative electrode materials, thereby reducing the problem caused by the high alkalinity of the positive electrode material.

[0020] In one implementation of the first aspect, the fluorinated carbonate compound includes one or more of fluoroethylene carbonate and bisfluoroethylene carbonate. The fluorinated ester compound can form a high-quality interfacial film on the surface of the negative electrode material, thereby improving the cycling performance of the sodium-ion battery.

[0021] In one implementation of the first aspect, the sulfur-containing ester compound includes one or more of dimethyl sulfite, diethyl sulfite, vinyl sulfite, vinyl sulfate, propylene sulfate, methylene methanedisulfonate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate, and 4-methylethylene sulfate. The sulfur-containing ester compound can form a high-quality interfacial film on the surface of the positive and negative electrode materials, improving the high-temperature performance of the sodium-ion battery and suppressing gas production.

[0022] In one implementation of the first aspect, the sodium salt additive comprises 0.05% to 3% by weight of the electrolyte, and the organic additive comprises 0.1% to 15% by weight of the electrolyte. Adding an appropriate amount of the sodium salt additive provides an additional sodium ion source for the sodium ion battery, facilitating film formation on the electrode surface and improving film quality. Furthermore, this improves the battery's high-temperature cycling performance.

[0023] In one implementation of the first aspect, the organic solvent further comprises an ether solvent; the mass percentage of the ether solvent in the electrolyte is 0% to 20%. The ether solvent includes at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether.

[0024] In an implementation of the first aspect, the mass percentage of the cyclic carbonate solvent in the electrolyte is 10%-40%, the mass percentage of the linear carbonate solvent in the electrolyte is 20%-50%, and the mass percentage of the carboxylate solvent in the electrolyte is 5%-25%.

[0025] By regulating the content of cyclic carbonate solvents, linear carbonate solvents, and carboxylate solvents, the electrolyte viscosity is prevented from being too high and the electrolyte conductivity is prevented from being too low. At the same time, the oxidation and decomposition of cyclic carbonate solvents and carboxylate solvents at the battery positive electrode under high temperature conditions is suppressed, thereby improving the battery's high-temperature cycle performance, low-temperature performance, and safety performance.

[0026] In one implementation of the first aspect, the cyclic carbonate solvent includes at least one of ethylene carbonate and propylene carbonate; the weight percentage of ethylene carbonate in the electrolyte is 0%-20%, and the weight percentage of propylene carbonate in the electrolyte is 10%-40%. Ethylene carbonate has a higher dielectric constant than propylene carbonate, and its addition can improve the corresponding conductivity of the electrolyte. Similarly, the lower weight percentage of ethylene carbonate compared to propylene carbonate can suppress gas generation, thereby improving the high-temperature cycling performance of the battery.

[0027] In one implementation of the first aspect, the linear carbonate solvent includes at least one of diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; the weight percentage of diethyl carbonate in the electrolyte is 0%-40%, the weight percentage of ethyl methyl carbonate in the electrolyte is 0%-40%, and the weight percentage of dimethyl carbonate in the electrolyte is 0%-20%. The addition of dimethyl carbonate can reduce the viscosity of the electrolyte. Similarly, compared to the weight percentages of diethyl carbonate and ethyl methyl carbonate, the lower weight percentage of dimethyl carbonate can prevent rapid volatilization and the generation of large amounts of gas in high-temperature environments.

[0028] In an implementation of the first aspect, the carboxylate solvent includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, methyl difluoroacetate, and methyl trifluoroacetate.

[0029] In an implementation of the first aspect, the sodium salt additive includes at least one of sodium bis(oxalatoborate), sodium difluorooxalatoborate, sodium difluorobis(oxalatophosphate), and sodium difluorophosphate.

[0030] In one implementation of the first aspect, the molar concentration of the electrolyte salt is 0.05 mol / L-5.0 mol / L, and the electrolyte salt includes NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, NaTDI, Na[(CF3SO2)2N], Na[(FSO2)2N] and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N]; wherein m and n are natural numbers.

[0031] In a second aspect, an embodiment of the present application further provides a sodium ion battery comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and the electrolyte of any one of the first aspects, wherein the electrolyte is filled between the positive electrode and the negative electrode.

[0032] In a third aspect, an embodiment of the present application further provides an electronic device, which includes a housing, and electronic components and a battery housed in the housing. The battery supplies power to the electronic components, and the battery includes the sodium ion battery described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a schematic structural diagram of a sodium ion battery provided in an embodiment of the present application;

[0034] FIG2 is a schematic diagram of test results of a sodium ion battery provided in an embodiment of the present application;

[0035] FIG3 is a schematic structural diagram of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Among them, in the description of the present application, unless otherwise specified, " / " indicates that the objects associated before and after are in an "or" relationship. For example, A / B can represent A or B; "and / or" in the present application is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. In addition, in the description of the present application, unless otherwise specified, "multiple" refers to two or more than two. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, c can be single or multiple. In addition, in order to facilitate a clear description of the technical solutions of the embodiments of the present application, in the embodiments of the present application, words such as "first" and "second" are used to distinguish identical or similar items with basically the same functions and effects.

[0037] Those skilled in the art will understand that words such as "first" and "second" do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit differences. At the same time, in some embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or design. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a concrete way for easy understanding.

[0038] For ease of understanding, some examples of concepts related to the embodiments of this application are provided for reference as follows:

[0039] Cathode: In a primary cell, the electrode from which current flows has a higher potential and is the positive electrode, gaining electrons to perform a reduction process. In an electrolytic cell, the positive electrode is the electrode connected to the positive terminal of the power supply and loses electrons to perform an oxidation process.

[0040] Anode: In a primary cell, the electrode into which current flows has a lower potential and is the negative electrode, losing electrons and causing oxidation. In an electrolytic cell, the anode is the electrode connected to the negative terminal of the power supply and receives electrons and causes reduction.

[0041] Electrolyte: A medium that provides ion exchange between the positive and negative electrodes of a battery.

[0042] Separator: The main function of the separator is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and short-circuiting. In addition, it also has the function of allowing electrolyte ions to pass through.

[0043] Film-forming additives: A type of substance that decomposes on the surface of materials before organic solvents to form an interfacial film, which can significantly improve battery performance.

[0044] Solid Electrolyte Interphase (SEI): During the first charge and discharge process of the battery, the electrode material and the electrolyte react at the solid-liquid interface to form a passivation layer covering the surface of the electrode material. Taking sodium-ion batteries as an example, this passivation layer is an interface layer that has the characteristics of a solid electrolyte. It is an electronic insulator but a Na + Excellent conductor, Na + Free insertion and extraction are possible through this passivation layer.

[0045] Cathode Electrolyte Interphase (CEI) film: also known as an interface protective film, refers to a passivation film layer with solid electrolyte properties.

[0046] Related art discloses a lithium secondary battery electrolyte comprising a lithium salt, a non-aqueous organic solvent, and functional additives. The functional additives include the following components in the following mass percentages in the lithium secondary battery electrolyte: 3%-12% cyclotriphosphazene compound, 3%-9% fluorocarbonate, 2%-6% sulfur-containing ester compound, and 1%-6% nitrile compound. It can be seen that the related art improves the stability of interfacial film formation by simply controlling the ratios between the various additives. Non-aqueous organic solvents, such as carbonate solvents, have a higher melting point and interact strongly with lithium ions in the solute, resulting in poor low-temperature performance.

[0047] To address the above technical issues, the present invention provides an electrolyte, a sodium-ion battery, and an electronic device. The electrolyte, as the name suggests, is used to prepare a sodium-ion battery. On the one hand, the electrolyte has a low viscosity and high conductivity, which to a certain extent promotes the diffusion of sodium ions in the solution and facilitates the desolvation of sodium ions at the electrode-electrolyte interface, thereby improving the low-temperature performance of the sodium-ion battery.

[0048] Furthermore, the electrolyte can react between the positive and negative electrodes to form a stable, high-quality interfacial film, thereby inhibiting the dissolution of metal ions from the positive electrode material and reducing side reactions between them and the electrolyte. Furthermore, the electrolyte is not easily oxidized and decomposed at high temperatures, reducing gas generation and thus improving the high-temperature and cycle performance of sodium-ion batteries.

[0049] FIG1 is a schematic diagram of the structure of a sodium-ion battery provided in an embodiment of the present application. As shown in FIG1 , the sodium-ion battery includes a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte 40, wherein the separator 30 is disposed between the positive electrode 10 and the negative electrode 20, and the electrolyte 40 is filled between the positive electrode 10 and the negative electrode 20 and infiltrates the separator 30. During charging, sodium ions are released from the positive electrode active material 102 of the positive electrode 10, and after passing through the electrolyte 40, they are embedded in the negative electrode active material 202 of the negative electrode 20; during discharging, sodium ions are released from the negative electrode active material 202, and after passing through the electrolyte 40, they are inserted into the positive electrode active material 102.

[0050] As shown in FIG1 , the positive electrode 10 includes a positive electrode current collector 101 and a positive electrode material layer coated on the surface of the positive electrode current collector 101 . The positive electrode material layer may include not only the positive electrode active material 102 but also a certain amount of binder, conductive agent and other components.

[0051] The positive electrode current collector 101 can be a metal foil, such as aluminum foil, gold foil, or platinum foil. The positive electrode active material 102 can reversibly intercalate and deintercalate sodium ions. The positive electrode active material 102 includes, but is not limited to, at least one of a layered sodium transition metal oxide, a Prussian white compound, a Prussian blue compound, and a sodium polyanionic compound.

[0052] Sodium transition metal oxides such as sodium nickel iron manganese (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, NFM111), Prussian white compounds such as (Na2Mn[Fe(CN)6], PBA), Prussian blue compounds such as (NaMn[Fe(CN)6], PBA), sodium polyanionic compounds such as sodium iron phosphate (NaFePO4, NFP), sodium iron sulfate (Na2Fe2(SO4)3, NFS). The binder may be, for example, polyvinylidene fluoride (poly 1,1-difluoroethylene, PVDF), and the conductive agent may be, for example, conductive carbon black (super P), graphite, amorphous carbon, carbon nanotubes, carbon fiber, graphene, etc. The above-mentioned positive electrode current collector 101, positive electrode active material 102, binder and conductive agent for preparing the positive electrode 10 are only exemplary illustrations, and the embodiments of the present application are not limited thereto. Taking the positive electrode active material 102 as an example, in theory, it can be a compound that can reversibly embed / de-embed sodium ions.

[0053] Continuing to refer to FIG1 , in the sodium ion battery provided in the embodiment of the present application, the negative electrode 20 includes a negative electrode current collector 201 and a negative electrode material layer coated on the surface of the negative electrode current collector. In addition to including the negative electrode active material 202, the negative electrode material layer may also include a certain amount of binder, conductive agent and other components.

[0054] The negative electrode current collector 201 may be a metal foil, such as copper foil, aluminum foil, gold foil, platinum foil, etc. The negative electrode active material 202 may include at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, and porous carbon materials. The negative electrode active material 202 may be a carbon-based material, tin-based material, phosphorus-based material, or sodium material capable of intercalating and deintercalating sodium ions. Carbon-based materials include, but are not limited to, one or more of graphite, hard carbon, soft carbon, and graphene. Tin-based materials include, but are not limited to, one or more of tin, tin-carbon, tin oxide, and tin metal compounds; phosphorus-based materials include, but are not limited to, one or more of red phosphorus, black phosphorus, and phosphorus compounds; and sodium materials include, but are not limited to, metallic sodium or sodium alloys. The binder may, for example, be sodium carboxymethyl cellulose (CMC) and / or styrene-butadiene rubber (SBR). The conductive agent may, for example, be acetylene black, graphite, or amorphous carbon. The negative electrode current collector 201 , the negative electrode active material 202 , the binder, and the conductive agent used to prepare the negative electrode 20 are merely exemplary and are not limited in this embodiment of the present application.

[0055] Continuing with FIG1 , in the sodium-ion battery provided in the embodiment of the present application, separator 30 blocks electrons while allowing ions to pass through. Separator 30 includes, but is not limited to, single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, and ceramic-coated PE.

[0056] As shown in Figure 1, in a sodium ion battery, the electrolyte 40 is the transmission medium when sodium ions are transmitted between the positive electrode 10 and the negative electrode 20. In one embodiment of the present application, the electrolyte 40 includes an organic solvent, an electrolyte salt, and an electrolyte additive. Among them, the electrolyte salt and the electrolyte additive are both dissolved in the organic solvent. The organic solvent provided in the embodiment of the present application includes a cyclic carbonate solvent, a linear carbonate solvent, and a carboxylate solvent; the electrolyte additive includes an organic additive and a sodium salt additive, and the organic additive includes a sulfur-containing ester compound.

[0057] The mass ratio of the carboxylic acid ester solvent to the sulfur-containing ester compound is 1.2:1 to 40:1, and the mass ratio of the cyclic carbonate solvent to the sodium salt additive is 5:1 to 80:1.

[0058] Specifically, the mass ratio of cyclic carbonate solvents to linear carbonate solvents is 0.3:1 to 1.5:1, the mass ratio of cyclic carbonate solvents to carboxylate solvents is 0.7:1 to 7:1; and the mass ratio of linear carbonate solvents to carboxylate solvents is 1.2:1 to 9:1.

[0059] It should be noted that the mass ratio of the carboxylic acid ester solvent to the sulfur-containing ester compound is 1.2:1 to 40:1. The value of this numerical ratio can be typically but not limited to 1.2:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, and numbers between any two of the above values, all of which are acceptable ranges. For example, the numerical ratio can be taken from a value between 1.2:1-10:1, a value between 5:1-20:1, a value between 15:1-30:1, a value between 25:1-40:1, and a value between any two other values.

[0060] The mass ratio of the cyclic carbonate solvent to the sodium salt additive is 5: 1 to 80: 1. The value of the numerical ratio can be typically but not limited to 5: 1, 10: 1, 20: 1, 30: 1, 40: 1, 50: 1, 60: 1, 70: 1, 80: 1 and numbers between any two of the above values, all of which are possible ranges. For example, the numerical ratio can be taken from a value between 5: 1-20: 1, a value between 10: 1-40: 1, a value between 30: 1-60: 1, a value between 50: 1-80: 1, or a value between any two other values.

[0061] The mass ratio of the cyclic carbonate solvent to the linear carbonate solvent is 0.3:1 to 1.5:1. The value of this numerical ratio can be typically but not limited to 0.3:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1 and numbers between any two of the above values, all of which are possible ranges. For example, the numerical ratio can be taken from a value between 0.3:1-0.8:1, a value between 0.5:1-1:1, a value between 0.8:1-1.2:1, a value between 1:1-1.5:1, and a value between any two other values.

[0062] The mass ratio of the cyclic carbonate solvent to the carboxylate solvent is 0.7:1 to 7:1. The value of this numerical ratio can be typically but not limited to 0.7:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1 and numbers between any two of the above values, all of which are possible ranges. For example, the numerical ratio can be a value between 0.7:1-2:1, a value between 1:1-4:1, a value between 2:1-5:1, a value between 3:1-7:1, or a value between any two other values.

[0063] The mass ratio of the linear carbonate solvent to the carboxylate solvent is 1.2:1 to 9:1. Typical but non-limiting examples of this ratio include 1.2:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and numbers between any two of the above values, all of which are acceptable ranges. For example, the ratio can be 1.2:1-3:1, 2:1-5:1, 4:1-7:1, 5:1-9:1, or any other number between any two values.

[0064] As can be seen from the above, the embodiments of the present application can regulate the content of each component in the organic solvent, specifically the mass ratio of each component in the organic solvent. The mass ratio of each component in the organic solvent includes the mass ratio between cyclic carbonate solvents and linear carbonate solvents, cyclic carbonate solvents and carboxylate solvents, and linear carbonate solvents and carboxylate solvents.

[0065] The present invention regulates the mass ratio of cyclic carbonate solvents, linear carbonate solvents, and carboxylate solvents to achieve an appropriate content of cyclic carbonate, linear carbonate solvents, and carboxylate solvents in the organic solvent, thereby preventing excessive viscosity and low electrolyte conductivity. Furthermore, in high-temperature scenarios, the cyclic carbonate solvents and carboxylate solvents are inhibited from oxidatively decomposing and producing large amounts of gas at the battery's positive electrode, thereby improving the battery's high-temperature cycling performance, low-temperature performance, and safety performance.

[0066] In this way, the embodiment of the present application can reduce the viscosity of the electrolyte and increase the conductivity of the electrolyte by regulating the mass ratios between cyclic carbonate solvents and linear carbonate solvents, cyclic carbonate solvents and carboxylate solvents, and linear carbonate solvents and carboxylate solvents, thereby promoting the diffusion of sodium ions in the solution to a certain extent, facilitating the desolvation of sodium ions at the electrode-electrolyte interface, and improving the low-temperature performance corresponding to the sodium ion battery.

[0067] The embodiments of the present application can also adjust the mass ratio between the organic solvent and the electrolyte additive, specifically the mass ratio between the carboxylic acid ester solvent and the sulfur-containing ester compound, and the mass ratio between the cyclic carbonate solvent and the sodium salt additive.

[0068] By regulating the content and mass ratio between carboxylic acid ester solvents and sulfur-containing ester compounds, and cyclic carbonate solvents and sodium salt additives, the content of cyclic carbonate and carboxylic acid ester solvents in the organic solvent is made appropriate, as well as the content of sulfur-containing ester compounds and sodium salt additives in the additives is made appropriate, thereby preventing the cyclic carbonate solvents and carboxylic acid ester solvents from oxidatively decomposing and producing a large amount of gas at the positive electrode of the battery under high-temperature scenarios, thereby improving the high-temperature cycle performance and safety of the battery. At the same time, it is also necessary to avoid the sulfur-containing ester compound content being too high or too low, so that the sulfur-containing ester compound forms a high-impedance interface film or an unstable and low-ion-conducting interface film on the surface of the positive and negative electrode materials. In turn, this is not conducive to the low or high-temperature performance of the battery.

[0069] By controlling the mass ratio of the carboxylic acid ester solvent to the sulfur-containing ester compound, the sulfur-containing ester compound can form a stable, high-quality interfacial film during the reaction between the positive and negative electrodes, thereby inhibiting the dissolution of metal ions from the positive electrode material and reducing side reactions with the electrolyte. Simultaneously, the oxidative decomposition reaction of the carboxylic acid ester solvent at high temperatures is suppressed, reducing gas generation.

[0070] The present invention controls the mass ratio of the cyclic carbonate solvent to the sodium salt additive, adjusting the content of the cyclic carbonate solvent to reduce electrolyte viscosity and inhibit battery gassing. The addition of the sodium salt additive also provides an additional sodium ion source for the sodium-ion battery, facilitating film formation on the electrode surface and improving film quality. This, in turn, enhances the high-temperature cycling performance of the sodium-ion battery.

[0071] In some embodiments of the present application, the mass percentage of the cyclic carbonate solvent in the electrolyte is 10%-40%. As an example, the mass percentage of the cyclic carbonate solvent can be 10%, 20%, 30%, 40%, and any number between any two of the above values, which are all acceptable ranges.

[0072] The mass percentage of the linear carbonate solvent in the electrolyte is 20%-50%. As an example, the linear carbonate solvent can be 20%, 30%, 40%, 50% or any number between the above two values, which are all acceptable ranges.

[0073] The mass percentage of the carboxylate solvent in the electrolyte is 5%-25%. As an example, the value of the carboxylate solvent can be 5%, 10%, 15%, 20%, 25% and numbers between any two of the above values, all of which are acceptable range values.

[0074] In some embodiments of the present application, the sulfur-containing ester compound includes one or more of dimethyl sulfite, diethyl sulfite, vinyl sulfite, 1,3,2-Dioxathiolane 2,2-dioxide (DTD), propylene sulfate (TS), methylene methanedisulfonate (MMDS), 1,3-propane sulfonate (PS), 1,3-propene sultone (PST), 1,4-butane sultone (BS), dimethyl sulfate, diethyl sulfate, and 4-methylethylene sulfate. Sulfur-containing ester compounds can form high-quality interface films on the surfaces of positive and negative electrode materials, improve the high-temperature performance of sodium-ion batteries, and inhibit gas production.

[0075] In some embodiments of the present application, the organic additive may further include a fluorinated carbonate compound; the mass ratio of the carboxylic acid ester solvent to the fluorinated carbonate compound is 1.2:1 to 40:1. As an example, the value of the numerical ratio may be typically but not limited to 1.2:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, and numbers between any two of the above values, all of which are acceptable ranges. For example, the numerical ratio may be a value between 1.2:1-10:1, a value between 5:1-20:1, a value between 15:1-30:1, a value between 25:1-40:1, or a value between any two other values.

[0076] The present invention's embodiments can control the mass ratio of carboxylate solvents to fluorocarbonate compounds, which not only inhibits battery gassing and reduces electrolyte viscosity, but also facilitates the formation of a film of the fluorocarbonate compound on the electrode surface, improving film quality. This improves the sodium-ion battery's low-temperature characteristics while also ensuring high-temperature cycling performance.

[0077] Fluorinated carbonate compounds include one or more of fluoroethylene carbonate (FEC) and bis(fluoroethylene carbonate). Fluorinated ester compounds can form a high-quality interfacial film on the surface of negative electrode materials, improving the cycling performance of sodium-ion batteries.

[0078] In some embodiments of the present application, the organic additive may further include an anhydride compound; the mass ratio of the cyclic carbonate solvent to the anhydride compound is 15:1 to 400:1. As an example, the value of the numerical ratio may be typically but not limited to 15:1, 30:1, 50:1, 80:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1, and numbers between any two of the above values, all of which are acceptable ranges. For example, the numerical ratio may be a value between 15:1-80:1, a value between 50:1-150:1, a value between 100:1-250:1, a value between 150:1-400:1, or a value between any two other values.

[0079] The present invention can control the mass ratio of the cyclic carbonate solvent to the anhydride compound, which not only inhibits battery gassing and reduces electrolyte viscosity, but also facilitates the formation of anhydride films on the electrode surface, improving film quality. This improves the low-temperature characteristics of sodium-ion batteries while also taking into account high-temperature cycling performance.

[0080] Acid anhydride compounds include one or more of succinic anhydride (SA), glutaric anhydride (GA), adipic anhydride, maleic anhydride, and cyclic phosphoric anhydride. Acid anhydride compounds can form films on the surfaces of positive and negative electrode materials, reducing the problems caused by the high alkalinity of the positive electrode material.

[0081] In some embodiments of the present application, the organic additive may further include a nitrile compound; the nitrile compound includes a mononitrile compound and / or a polynitrile compound; the mononitrile compound includes at least one of acetonitrile and p-methylbenzonitrile; and the polynitrile compound includes one or more of succinonitrile (SN), glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetrinitrile. Nitrile compounds can complex transition metal ions in the positive electrode material, reduce the catalytic activity of the transition metal ions, reduce the dissolution of the transition metal ions, and improve the oxidation resistance of the electrolyte.

[0082] In some embodiments of the present application, the mass percentage of the sulfur-containing ester compound in the electrolyte is 0.5%-5%. As an exemplary illustration, the value of the sulfur-containing ester compound can be, for example, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0% and numbers between any two of the above values, all of which are acceptable range values.

[0083] The mass percentage of the fluorocarbonate compound in the electrolyte is 0.5%-5%. As an example, the value of the fluorocarbonate can be, for example, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0% and numbers between any two of the above values, all of which are acceptable ranges.

[0084] The mass percentage of nitrile compounds in the electrolyte is 0.5%-5%. As an example, the values ​​of nitrile compounds can be, for example, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0% and numbers between any two of the above values, all of which are acceptable range values.

[0085] The mass percentage of the acid anhydride compound in the electrolyte is 0.05%-1%. As an example, the value of the acid anhydride compound can be, for example, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0% and numbers between any two of the above values, all of which are acceptable range values.

[0086] Controlling the above-mentioned different additives to appropriate contents is beneficial for not degrading other battery properties while allowing them to exert their beneficial effects.

[0087] In some embodiments of the present application, the organic additive may include one or more of sulfur-containing ester compounds, fluorocarbonate compounds, nitrile compounds and acid anhydride compounds. It should be noted that the organic additive in the embodiments of the present application may include the above-mentioned sulfur-containing ester compounds, or sulfur-containing ester compounds and fluorocarbonate compounds, or sulfur-containing ester compounds and nitrile compounds, or sulfur-containing ester compounds and acid anhydride compounds, or sulfur-containing ester compounds, fluorocarbonate compounds and nitrile compounds, or sulfur-containing ester compounds, fluorocarbonate compounds and acid anhydride compounds, or sulfur-containing ester compounds, fluorocarbonate compounds and acid anhydride compounds, or sulfur-containing ester compounds, fluorocarbonate compounds, nitrile compounds and acid anhydride compounds.

[0088] The organic additives in the embodiments of the present application may also include nitrile compounds, or nitrile compounds and acid anhydride compounds. The embodiments of the present application do not specifically limit the types of the organic additives.

[0089] In some embodiments of the present application, the mass percentage of the sodium salt additive in the electrolyte is 0.05%-3%, and the mass percentage of the organic additive in the electrolyte is 0.1%-15%. Among them, the sodium salt additive includes at least one of sodium bis(oxalatoborate) (NaBOB), sodium difluorooxalatoborate (NaDFOB), sodium difluorobis(oxalatophosphate) (NaDFOP), and sodium difluorophosphate (NaPO2F2). Adding an appropriate amount of sodium salt additive can supplement an additional sodium ion source for the sodium ion battery, which is beneficial to participate in film formation on the electrode surface and improve the film quality. In addition, the high-temperature cycle performance of the battery is improved.

[0090] In some embodiments of the present application, the organic solvent provided in the embodiments of the present application includes but is not limited to one or more of cyclic carbonate solvents, linear carbonate solvents, carboxylate solvents and ether solvents.

[0091] That is, the organic solvent provided in the embodiments of the present application may also include an ether solvent; the weight percentage of the ether solvent in the electrolyte is 0%-20%. As an example, the value of the ether solvent can be 0%, 5%, 10%, 15%, 20%, and any number between the above two values, all of which are acceptable ranges.

[0092] The ether solvent includes at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.

[0093] In some embodiments of the present application, the cyclic carbonate solvent includes at least one of ethylene carbonate (EC) and propylene carbonate (PC);

[0094] The mass percentage of ethylene carbonate in the electrolyte is 0%-20%. As an example, the value of ethylene carbonate can be, for example, 0%, 5%, 10%, 15%, 20% and numbers between any two of the above values, all of which are acceptable range values.

[0095] The mass percentage of propylene carbonate in the electrolyte is 10%-40%. As an example, the value of propylene carbonate can be 10%, 20%, 30%, 40% and any number between the above two values, which are all acceptable ranges.

[0096] Ethylene carbonate has a higher dielectric constant than propylene carbonate. Adding ethylene carbonate can improve the conductivity of the electrolyte. Similarly, compared to the weight percentage of propylene carbonate, the lower weight percentage of ethylene carbonate can inhibit gas generation, thereby improving the battery's high-temperature cycling performance.

[0097] It should be noted that, of course, the cyclic carbonate solvents in the embodiments of the present application may only include ethylene carbonate, and the present application does not limit the specific solvent types in the cyclic carbonate solvents.

[0098] In some embodiments of the present application, the linear carbonate solvent includes at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC);

[0099] The mass percentage of diethyl carbonate in the electrolyte is 0%-40%. As an example, the value of diethyl carbonate can be, for example, 0%, 10%, 20%, 30%, 40% and numbers between any two of the above values, all of which are acceptable range values.

[0100] The mass percentage of ethyl methyl carbonate in the electrolyte is 0%-40%. As an example, the value of ethyl methyl carbonate can be, for example, 0%, 10%, 20%, 30%, 40% and numbers between any two of the above values, all of which are acceptable range values.

[0101] The mass percentage of dimethyl carbonate in the electrolyte is 0%-20%. As an example, the value of dimethyl carbonate can be, for example, 0%, 5%, 10%, 15%, 20% and numbers between any two of the above values, all of which are acceptable range values.

[0102] Adding dimethyl carbonate can reduce the corresponding viscosity of the electrolyte. Similarly, compared with the mass percentage of diethyl carbonate and ethyl methyl carbonate, the mass percentage of dimethyl carbonate is lower, which can prevent it from volatilizing faster in high temperature scenarios and generating a large amount of gas.

[0103] The carboxylate solvent includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate (EP), propyl propionate, methyl difluoroacetate, and methyl trifluoroacetate.

[0104] In some embodiments of the present application, the molar concentration of the electrolyte salt is 0.05 mol / L-5.0 mol / L, and the electrolyte salt may include a sodium salt, and the sodium salt includes NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, NaTDI, Na[(CF3SO2)2N], Na[(FSO2)2N] and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N]; wherein m and n are natural numbers. It should be understood that the concentration range of the sodium salt in the electrolyte may allow for certain measurement and testing system errors in practical applications, and the values ​​within the system error range are all within the range defined in the embodiments of this application.

[0105] In addition, as an exemplary illustration, the concentration of the sodium salt in the electrolyte can be 0.05 mol / L, 5.0 mol / L, and any value between 0.05 mol / L and 5.0 mol / L, which are not listed here one by one.

[0106] It can be understood that the mass ratio of the above-mentioned organic solvent and electrolyte additive will have a certain impact on the mass ratio test of the electrolyte solvent and the additive due to the formation of the interface film after actual battery formation, fractionation or circulation, and a certain measurement test error can be allowed. The values ​​within the error range can be understood as the range defined in the embodiments of the present application, or the numerical range of the mass ratio of the electrolyte solvent and the additive tested after formation, fractionation or circulation is still within the above range and can be understood as the range defined in the embodiments of the present application.

[0107] It can be understood that the calculated values ​​of the above numerical ratios may allow for certain measurement test system errors during actual test operations, and the values ​​within the system error range may be understood as the range defined by the embodiments of the present application.

[0108] The electrolyte and sodium ion batteries containing the electrolyte are introduced below through specific examples. Sodium ion batteries are prepared using the electrolytes prepared in the examples, and the performance of various sodium ion batteries is tested.

[0109] Example 1

[0110] In Example 1, the electrolyte was prepared according to the following steps.

[0111] 15% cyclic carbonate (PC), 50% linear carbonate (10% DEC and 40% EMC) and 20% carboxylate (EP) accounting for the mass percentage of the electrolyte are mixed to obtain a mixture, and sodium hexafluorophosphate (NaPF6) is added to the obtained mixture to a molar concentration of 1 mol / L, and then solvents and electrolyte additives of different types and amounts as shown in Table 1 below are added.

[0112] In some embodiments of the present application, the positive electrode material includes NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (NFM), Na2Mn[Fe(CN)6] (PBA), NaFePO4 (NFP), and Na2Fe2(SO4)3 (NFS). Anode materials include hard carbon and soft carbon materials.

[0113] Sodium ion batteries are made using the following preparation methods:

[0114] Step S100: Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent Super P, and 96% positive electrode active material (NFM, PBA, NFP, or NFS) by weight, add them to N-methylpyrrolidone (NMP) in sequence, stir and mix them thoroughly, apply the slurry on an aluminum foil current collector, dry, cold press, and cut to obtain positive electrode sheets.

[0115] Step S101: Weigh 1.5% CMC, 2.5% SBR, 1% Super P, and 95% negative electrode active material (hard carbon or soft carbon) by weight, add them to deionized water in sequence, stir and mix thoroughly, apply the slurry on a copper foil current collector, dry, cold press, and cut to obtain a negative electrode sheet.

[0116] Step S102: The positive electrode sheet, negative electrode sheet and PE separator prepared above are made into a battery cell, which is packaged with a polymer, and the electrolyte prepared above is poured into the battery cell. After chemical formation and other processes, a 2Ah soft-pack sodium ion battery is produced.

[0117] Examples 2-28 and Comparative Examples 1-10 were prepared according to the preparation steps of Example 1, which will not be repeated here.

[0118] The difference is that the types of materials and median particle size values ​​in the positive electrode active materials and negative electrode active materials of the sodium ion battery are different, and the types and contents of organic solvents and electrolyte additives in the electrolyte are different. The specific contents are shown in Table 1 above and will not be repeated here.

[0119] Table 1 Parameter details of Examples 1-28 and Comparative Examples 1-10

[0120] The sodium ion batteries prepared in Examples 1-28 and Comparative Examples 1-10 were tested for performance. See the following test methods:

[0121] 1. High temperature cycle performance test:

[0122] The sodium ion batteries prepared in Examples 1-28 and Comparative Examples 1-10 were placed in an oven at a constant temperature of 45±3°C, charged to 3.95V at a constant current of 0.5C, then charged at a constant voltage until the current dropped to 0.05C, left to rest for 10 minutes, and then discharged to 2.0V at a constant current of 0.5C. This cycle was repeated 300 times, and the discharge capacities of the first and 300th cycles were recorded. The capacity retention rate of the cycle was calculated according to the following formula:

[0123] Capacity retention rate (%)=discharge capacity at the 300th cycle / discharge capacity at the 1st cycle×100%.

[0124] 2.-40℃ low temperature performance test:

[0125] At an ambient temperature of 25±3°C, charge the battery to 3.95V at a constant current of 0.2C, then charge it at a constant voltage until the current drops to 0.05C, let it rest for 10 minutes, and then discharge it to 2.0V at a constant current of 0.2C. The capacity at this time is the initial capacity. The battery is placed at a temperature of -40°C for 4 hours, then charge it to 3.95V at a constant current of 0.2C, then charge it at a constant voltage until the current drops to 0.05C, let it rest for 10 minutes, and then discharge it to 2.0V at a constant current of 0.2C. This is recorded as the residual capacity, and the residual capacity retention rate is recorded (remaining capacity / initial capacity×100%). The test results are shown in Table 2 and Figure 2.

[0126] Table 2 Test results of Examples 1-28 and Comparative Examples 1-10

[0127] Referring to Table 2 and Figure 2, comparing the sodium ion batteries prepared in Examples 1-15 of the present application and Comparative Examples 1-4, the capacity retention rate of the sodium ion batteries prepared in Examples 1-15 after 300 cycles at 45°C was 95.2%-96.3%, and the capacity retention rate of the sodium ion batteries prepared in Comparative Examples 1-4 after 300 cycles at 45°C was 88.6%-93.9%. The capacity retention rate of the sodium ion batteries prepared in Examples 1-15 of the present application after 300 cycles at 45°C was significantly higher than that of the sodium ion batteries prepared in Comparative Examples 1-4.

[0128] That is, in Examples 1-15, the mass ratio of the carboxylate solvent to the sulfur-containing ester compound is 1.2:1 to 40:1, the mass ratio of the cyclic carbonate solvent to the sodium salt additive is 5:1 to 80:1, the mass ratio of the cyclic carbonate solvent to the linear carbonate solvent is 0.3:1 to 1.5:1, the mass ratio of the cyclic carbonate solvent to the carboxylate solvent is 0.7:1 to 7:1; and the mass ratio of the linear carbonate solvent to the carboxylate solvent is 1.2:1 to 9:1. Comparative Examples 1-4 do not meet these numerical ratios.

[0129] Specifically, in Example 7, the mass ratio of the carboxylate solvent (EP) to the sulfur-containing ester compound (TS) is 5:1, the mass ratio of the cyclic carbonate solvent (PC) to the sodium salt additive (NaDFOB) is 70:1, the mass ratio of the cyclic carbonate solvent (PC) to the linear carbonate solvent (DEC+EMC) is 0.78:1, the mass ratio of the cyclic carbonate solvent (PC) to the carboxylate solvent (EP) is 7:1, and the mass ratio of the linear carbonate solvent (DEC+EMC) to the carboxylate solvent (EP) is 9:1.

[0130] In Comparative Example 2, the mass ratio of cyclic carbonate solvent (PC) to carboxylate solvent (EP) is 8:1, and greater than 7:1. The mass percentage of cyclic carbonate in the electrolyte is too high, resulting in too high electrolyte viscosity and limited sodium ion transport. Furthermore, the diffusion of sodium ions in the solution is restricted, and it is not conducive to the desolvation of sodium ions at the electrode-electrolyte interface, that is, the low-temperature performance of the battery is poor. Then, in Comparative Example 3, no sodium salt additive was added. In this way, the electrolyte additive cannot supplement an additional sodium ion source for the sodium ion battery, is not conducive to participating in film formation on the electrode surface, and results in low film quality. Furthermore, the high-temperature cycle performance of the battery is affected.

[0131] Continuing to refer to Table 2, comparing the sodium ion batteries prepared in Examples 16-20 of the present application and Comparative Examples 5-6, the sodium ion batteries prepared in Examples 16-20 have a -40°C low-temperature capacity retention rate of 48.0%-48.6%, and a 45°C cycle 300-cycle capacity retention rate of 96.2%-96.4%. The sodium ion batteries prepared in Comparative Examples 5-6 have a -40°C low-temperature capacity retention rate of 33.1%-45.3%, and a 45°C cycle 300-cycle capacity retention rate of 92.8%-93.6%. The -40°C low-temperature capacity retention rate and the 45°C cycle 300-cycle capacity retention rate of the sodium ion batteries prepared in Examples 16-20 of the present application are significantly higher than those of the sodium ion batteries prepared in Comparative Examples 5-6.

[0132] That is, in Examples 16-20, the mass ratio of the carboxylate solvent to the sulfur-containing ester compound is 1.2:1 to 40:1, the mass ratio of the cyclic carbonate solvent to the sodium salt additive is 5:1 to 80:1; the mass ratio of the cyclic carbonate solvent to the linear carbonate solvent is 0.3:1 to 1.5:1, the mass ratio of the cyclic carbonate solvent to the carboxylate solvent is 0.7:1 to 7:1; and the mass ratio of the linear carbonate solvent to the carboxylate solvent is 1.2:1 to 9:1. Comparative Examples 5-6 do not meet these numerical ratios.

[0133] Specifically, in Example 20, the mass ratio of EP to TS was 15:1, the mass ratio of PC to NaDFOB was 60:1, the mass ratio of PC to DEC and EMC was 0.75:1, the mass ratio of PC to EP was 2:1, and the mass ratio of DEC, EMC to EP was 2.67:1. In Comparative Example 5, the mass ratio of PC to NaDFOB was 150:1, exceeding 80:1. This indicates that the high cyclic carbonate content leads to excessive electrolyte viscosity, limiting sodium ion transport. This, in turn, restricts sodium ion diffusion in the solution, resulting in poor low-temperature battery performance.

[0134] At the same time, the low NaDFOB content also fails to provide an additional sodium ion source for sodium-ion batteries, hindering their ability to form a film on the electrode surface and a stable interfacial film. Consequently, the carbonate decomposes severely at high temperatures, generating large amounts of gas and leading to reduced high-temperature cycling performance.

[0135] In Comparative Example 6, the mass ratio of EP to TS is 1:1 and less than 1.2:1. The low EP content and high TS content will cause TS to form a high-impedance interface film on the surface of the positive and negative electrode materials, reducing the high-temperature performance of the sodium-ion battery.

[0136] Continuing to refer to Table 2, comparing the sodium ion batteries prepared in Examples 21-24 of the present application and Comparative Examples 7-8, the -40°C low-temperature capacity retention rate of the sodium ion batteries prepared in Examples 21-24 is 46.0%-46.4%, and the capacity retention rate after 300 cycles at 45°C is 96.4%-96.7%. The -40°C low-temperature capacity retention rate of the sodium ion battery prepared in Comparative Example 7 is 31.5%, and the capacity retention rate after 300 cycles at 45°C is 93.6%. The capacity retention rate of the sodium ion battery prepared in Comparative Example 8 is 90.5%. The -40°C low-temperature capacity retention rate and the 45°C 300-cycle capacity retention rate of the sodium ion batteries prepared in Examples 21-24 of the present application are significantly higher than those in Comparative Example 7, and the capacity retention rate of the sodium ion batteries prepared in Examples 21-24 of the present application are significantly higher than those in Comparative Example 7, and the capacity retention rate of the sodium ion batteries prepared in Comparative Example 7 is 96.4%-96.7%.

[0137] The capacity retention rates of the sodium ion batteries prepared in Examples 21-24 after 300 cycles at 45°C were significantly higher than that of Comparative Example 8.

[0138] That is, in Examples 21-24, the mass ratio of the carboxylate solvent to the sulfur-containing ester compound is 1.2:1 to 40:1, the mass ratio of the cyclic carbonate solvent to the sodium salt additive is 5:1 to 80:1, the mass ratio of the cyclic carbonate solvent to the linear carbonate solvent is 0.3:1 to 1.5:1, the mass ratio of the cyclic carbonate solvent to the carboxylate solvent is 0.7:1 to 7:1, and the mass ratio of the linear carbonate solvent to the carboxylate solvent is 1.2:1 to 9:1. However, the above numerical ratios are not met in Comparative Examples 7-8.

[0139] Specifically, in Example 22, the mass ratio of EP to TS was 15:1, the mass ratio of PC to NaDFOB was 60:1, the mass ratio of PC to DEC and EMC was 0.75:1, the mass ratio of PC to EP was 2:1, and the mass ratio of DEC, EMC, and EP was 2.67:1. In Comparative Example 7, the mass ratio of DEC, EMC, and EP was 10:1, which was greater than 7:1.

[0140] Too high a linear carbonate content affects the electrolyte's conductivity, limiting sodium ion transport and resulting in poor low-temperature battery performance. Furthermore, linear carbonates are not heat-resistant, causing them to decompose severely at high temperatures, producing large amounts of gas and leading to poor high-temperature performance.

[0141] In Comparative Example 8, the mass ratio of EP to TS is 50:1, and greater than 40:1. The high EP content, low TS content, and low S content can lead to unstable interfacial films formed by TS on the positive and negative electrode surfaces, resulting in low ion conductivity and poor high-temperature performance of the battery.

[0142] Continuing to refer to Table 2, comparing the sodium ion batteries prepared in Examples 25-28 of the present application and Comparative Examples 9-10, the sodium ion batteries prepared in Examples 25-28 have a -40°C low-temperature capacity retention rate of 45.3%-45.9%, and a 45°C cycle 300-cycle capacity retention rate of 96.1%-96.5%. The sodium ion battery prepared in Comparative Example 9 has a -40°C low-temperature capacity retention rate of 30.9%, and a 45°C cycle 300-cycle capacity retention rate of 93.2%. The sodium ion battery prepared in Comparative Example 10 has a 45°C cycle 300-cycle capacity retention rate of 90.2%. This application

[0143] The -40°C low-temperature capacity retention rate and the 45°C cycle 300-cycle capacity retention rate of the sodium ion batteries prepared in Examples 25-28 are significantly higher than those in Comparative Example 9, and the 45°C cycle 300-cycle capacity retention rate of the sodium ion batteries prepared in Examples 25-28 of the present application are significantly higher than those in Comparative Example 10.

[0144] That is, in Examples 25-28, the mass ratio of the carboxylate solvent to the sulfur-containing ester compound was 1.2:1 to 40:1, the mass ratio of the cyclic carbonate solvent to the sodium salt additive was 5:1 to 80:1, the mass ratio of the cyclic carbonate solvent to the linear carbonate solvent was 0.3:1 to 1.5:1, the mass ratio of the cyclic carbonate solvent to the carboxylate solvent was 0.7:1 to 7:1, and the mass ratio of the linear carbonate solvent to the carboxylate solvent was 1.2:1 to 9:1. Comparative Examples 9-10, however, did not meet these numerical ratios.

[0145] Specifically, in Example 25, the mass ratio of EP to TS is 15:1, the mass ratio of PC to NaDFOB is 60:1, the mass ratio of PC to DEC and EMC is 0.75:1, the mass ratio of PC to EP is 2:1, and the mass ratio of DEC, EMC to EP is 2.67:1. In Comparative Example 9, the mass ratio of DEC, EMC to EP is 10:1, which is greater than 7:1. Excessively high linear carbonate content affects the conductivity of the electrolyte, limiting sodium ion transport and resulting in poor low-temperature performance of the battery. At the same time, linear carbonates are not resistant to high temperatures, causing severe decomposition of linear carbonates at high temperatures, producing large amounts of gas, and resulting in poor high-temperature performance. In Comparative Example 10, the mass ratio of EP to TS is 50:1, which is greater than 40:1. The high EP content, low TS content, and low S content will make the interfacial film formed by TS on the positive and negative electrode surfaces unstable, resulting in low ion conductivity, which is not conducive to the high-temperature performance of the battery.

[0146] An embodiment of the present application also provides a sodium ion battery, comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and the above-mentioned electrolyte, wherein the electrolyte is filled between the positive electrode and the negative electrode.

[0147] The present application also provides an electronic device, comprising a housing, and electronic components and a battery housed within the housing, the battery powering the electronic components, the battery comprising the aforementioned sodium-ion battery. Referring to FIG3 , the electronic device may be, for example, a mobile phone 1100, and may also include a smart screen, a tablet computer, a personal computer (PC), a personal digital assistant (PDA), a smartwatch, a power bank, a netbook, a wearable device, an augmented reality (AR) device, a virtual reality (VR) device, an in-vehicle device, an energy storage device, a base station, and a car, etc. The present application does not impose any particular restrictions on the specific form of the electronic device.

[0148] In some embodiments, multiple embodiments of the present application may be combined and the combined embodiments may be implemented. Optionally, some operations in the processes of the various method embodiments may be optionally combined, and / or the order of some operations may be optionally changed. Furthermore, the execution order between the steps of each process is merely exemplary and does not constitute a limitation on the execution order between the steps. Other execution orders may also be used between the steps. This is not intended to indicate that the execution order is the only order in which these operations may be performed.

[0149] A person of ordinary skill in the art will think of many ways to reorder the operations described in the embodiments of the present application. In addition, it should be noted that the process details involved in a certain embodiment of the present application are also applicable to other embodiments in a similar manner, or different embodiments can be used in combination. In addition, some steps in the method embodiment can be equivalently replaced with other possible steps. Alternatively, some steps in the method embodiment can be optional and can be deleted in certain usage scenarios. Alternatively, other possible steps can be added in the method embodiment. Moreover, each method embodiment can be implemented separately or in combination. The above content is only a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises an electrolyte salt, an organic solvent and an electrolyte additive, wherein the organic solvent comprises a cyclic carbonate solvent, a linear carbonate solvent and a carboxylic acid ester solvent; the electrolyte additive comprises an organic additive and a sodium salt additive, and the organic additive comprises a sulfur-containing ester compound; The mass ratio of the carboxylate solvent to the sulfur-containing ester compound is 1.2:1 to 40:1, and the mass ratio of the cyclic carbonate solvent to the sodium salt additive is 5:1 to 80:

1.

2. The electrolyte according to claim 1, characterized in that The mass ratio of the cyclic carbonate solvent to the linear carbonate solvent is 0.3:1 to 1.5:1, the mass ratio of the cyclic carbonate solvent to the carboxylate solvent is 0.7:1 to 7:1; the mass ratio of the linear carbonate solvent to the carboxylate solvent is 1.2:1 to 9:

1.

3. The electrolyte according to claim 1 or 2, characterized in that The organic additives also include fluorinated carbonate compounds; The mass ratio of the carboxylate solvent to the fluorocarbonate compound is 1.2:1 to 40:

1.

4. The electrolyte according to claim 3, characterized in that The organic additives also include anhydride compounds; The mass ratio of the cyclic carbonate solvent to the acid anhydride compound is 15:1 to 400:

1.

5. The electrolyte according to claim 4, characterized in that The organic additives also include nitrile compounds; The mass percentage of the sulfur-containing ester compound in the electrolyte is 0.5%-5%, the mass percentage of the fluorocarbonate compound in the electrolyte is 0.5%-5%, the mass percentage of the nitrile compound in the electrolyte is 0.5%-5%, and the mass percentage of the acid anhydride compound in the electrolyte is 0.05%-1%.

6. The electrolyte according to claim 5, characterized in that The nitrile compounds include mononitrile compounds and / or polynitrile compounds; the mononitrile compounds include at least one of acetonitrile and p-methylbenzonitrile; the polynitrile compounds include one or more of succinonitrile, glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane and 1,3,6-hexanetrinitrile.

7. The electrolyte according to any one of claims 4 to 6, characterized in that: The acid anhydride compound includes one or more of succinic anhydride, glutaric anhydride, adipic anhydride, maleic anhydride and cyclic phosphoric anhydride.

8. The electrolyte according to any one of claims 3 to 7, characterized in that: The fluorinated carbonate compound includes one or more of fluoroethylene carbonate and bisfluoroethylene carbonate.

9. The electrolyte according to any one of claims 1 to 8, characterized in that: The sulfur-containing ester compound includes one or more of dimethyl sulfite, diethyl sulfite, vinyl sulfite, vinyl sulfate, propylene sulfate, methylene methanedisulfonate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate and 4-methylethylene sulfate.

10. The electrolyte according to any one of claims 1 to 9, characterized in that: The mass percentage of the sodium salt additive in the electrolyte is 0.05%-3%, and the mass percentage of the organic additive in the electrolyte is 0.1%-15%.

11. The electrolyte according to any one of claims 1 to 10, characterized in that: The organic solvent also includes an ether solvent; the mass percentage of the ether solvent in the electrolyte is 0%-20%.

12. The electrolyte according to claim 11, characterized in that The ether solvent includes at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and bis(2,2,2-trifluoroethyl) ether.

13. The electrolyte according to any one of claims 1 to 12, characterized in that: The mass percentage of the cyclic carbonate solvent in the electrolyte is 10%-40%, the mass percentage of the linear carbonate solvent in the electrolyte is 20%-50%, and the mass percentage of the carboxylate solvent in the electrolyte is 5%-25%.

14. The electrolyte according to claim 13, characterized in that The cyclic carbonate solvent includes at least one of ethylene carbonate and propylene carbonate; The mass percentage of the ethylene carbonate in the electrolyte is 0%-20%, and the mass percentage of the propylene carbonate in the electrolyte is 10%-40%.

15. The electrolyte according to claim 13 or 14, characterized in that: The linear carbonate solvent includes at least one of diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate; The mass percentage of the diethyl carbonate in the electrolyte is 0%-40%, the mass percentage of the ethyl methyl carbonate in the electrolyte is 0%-40%, and the mass percentage of the dimethyl carbonate in the electrolyte is 0%-20%.

16. The electrolyte according to any one of claims 1 to 15, characterized in that: The carboxylate solvent includes at least one of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, methyl difluoroacetate and methyl trifluoroacetate.

17. The electrolyte according to any one of claims 1 to 16, characterized in that: The sodium salt additive includes at least one of sodium bis(oxalatoborate), sodium difluorooxalatoborate, sodium difluorobis(oxalatophosphate) and sodium difluorophosphate.

18. The electrolyte according to any one of claims 1 to 17, characterized in that: The molar concentration of the electrolyte salt is 0.05 mol / L-5.0 mol / L, and the electrolyte salt includes NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, NaTDI, Na[(CF3SO2)2N], Na[(FSO2)2N] and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N]; wherein m and n are natural numbers.

19. A sodium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and the electrolyte according to any one of claims 1 to 18, wherein the electrolyte is filled between the positive electrode and the negative electrode.

20. An electronic device, characterized in that: The electronic device comprises a shell, and electronic components and a battery housed in the shell, wherein the battery supplies power to the electronic components, and the battery comprises the sodium ion battery according to claim 19.

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