Electrolyte, sodium ion battery and electronic equipment

Abstract

The embodiment of the invention provides an electrolyte, a sodium ion battery and electronic equipment, and relates to the technical field of batteries. The electrolyte provided by the embodiment of the invention 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 ester solvent; the electrolyte additive comprises an organic additive and a sodium salt additive, and the organic additive comprises a sulfur-containing ester compound. By regulating and controlling the contents of the components in the organic solvent in the electrolyte and the contents of the components in the organic solvent and the additive, the electrolyte has relatively high conductivity and is beneficial to desolvation of sodium ions on an electrode-electrolyte interface.

Description

Technical Field

[0001] 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

[0002] With the development of economy and technology, most electronic devices (such as portable electronic devices, drones, electric vehicles, etc.) are in urgent need of energy storage devices such as batteries with higher energy density, higher power density, longer cycle life and safer. Taking sodium-ion batteries as an example, sodium-ion batteries are considered to be very promising candidates in energy storage scenarios because of their advantages such as abundant sodium resources and low cost. However, sodium-ion batteries currently have disadvantages such as poor low-temperature cycle performance and sodium precipitation during low-temperature charging, which restricts their widespread application.

[0003] The electrolyte is an important component of sodium-ion batteries. Its physical and chemical properties and chemical composition not only determine the kinetic properties of sodium ions in the electrolyte, but also determine the composition and structure of the solid electrolyte interphase film (SEI film) on the electrode surface, which has an important influence on the rate performance, electrode structure stability and cycle life of sodium-ion batteries. Usually, the electrolyte of sodium-ion batteries 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 will limit the diffusion of sodium ions in the solution to a certain extent, and is not conducive to the desolvation of sodium ions at the electrode-electrolyte interface. In turn, it affects the life and stability of sodium-ion batteries. Summary of the invention

[0004] The embodiments of the present application provide an electrolyte, a sodium ion battery and an electronic device. By regulating the content of each component in the organic solvent and 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.

[0005] To achieve the above objectives, the embodiments of the present application adopt the following technical solutions:

[0006] In a first aspect, an embodiment of the present application provides an electrolyte, the electrolyte comprising an electrolyte salt, an organic solvent and an electrolyte additive, the organic solvent comprising a cyclic carbonate solvent, a linear carbonate solvent and a carboxylate solvent; the electrolyte additive comprising an organic additive and a sodium salt additive, the organic additive comprising a sulfur-containing ester compound.

[0007] 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.

[0008] 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, which prevents 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, which prevents the cyclic carbonate solvents and carboxylate solvents from being oxidized and decomposed at the positive electrode of the battery to produce a large amount of gas under high temperature scenarios, 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 sulfur-containing ester compounds to form high-impedance interface films or unstable and low-ion conductivity interface films on the surface of positive and negative electrode materials. Furthermore, it is not conducive to the low or high temperature performance of the battery.

[0009] In an implementable manner 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.

[0010] The embodiment of the present application prevents the electrolyte viscosity from being too high and the electrolyte conductivity from being low by regulating the mass ratio between the cyclic carbonate solvent, the linear carbonate solvent and the carboxylate solvent. At the same time, in high temperature scenarios, the cyclic carbonate solvent and the carboxylate solvent are inhibited from being oxidized and decomposed at the positive electrode of the battery to produce a large amount of gas, thereby improving the high temperature cycle performance, low temperature performance and safety performance of the battery.

[0011] In an implementation of the first aspect, the organic additive further includes a fluorocarbonate compound, and the mass ratio of the carboxylate solvent to the fluorocarbonate compound is 1.2:1 to 40:1.

[0012] The embodiment of the present application can control the mass ratio between the carboxylic acid ester solvent and the fluorocarbonate compound, which can not only inhibit the gas production of the battery and reduce the viscosity of the electrolyte, but also facilitate the fluorocarbonate compound to participate in the film formation on the electrode surface and improve the film quality. In this way, the high temperature cycle performance is taken into account while improving the low temperature characteristics of the sodium ion battery.

[0013] 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.

[0014] The embodiment of the present application can control the mass ratio between the cyclic carbonate solvent and the anhydride compound, which can not only inhibit the gas production of the battery and reduce the viscosity of the electrolyte, but also facilitate the anhydride compound to participate in the film formation on the electrode surface and improve the film quality. In this way, the high-temperature cycle performance is taken into account while improving the low-temperature characteristics of the sodium-ion battery.

[0015] In an 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 anhydride compound in the electrolyte is 0.05%-1%. Controlling the above-mentioned different additives to a suitable content is conducive to not reducing other performances of the battery when they exert their beneficial effects.

[0016] In an achievable manner 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; 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 the 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.

[0017] In one implementation of the first aspect, the anhydride compound includes one or more of succinic anhydride, glutaric anhydride, adipic anhydride, maleic anhydride and cyclic phosphoric anhydride. The anhydride compound can form a film on the surface of the positive and negative electrode materials to reduce the problem caused by the high alkalinity of the positive electrode material.

[0018] In one implementation of the first aspect, the fluorinated carbonate compound includes one or more of fluorinated ethylene carbonate and difluoroethylene carbonate. The fluorinated ester compound can form a high-quality interface film on the surface of the negative electrode material to improve the cycle performance of the sodium ion battery.

[0019] In an 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 disulfonate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate and 4-methylethylene sulfate. The sulfur-containing ester compound can form a high-quality interface film on the surface of the positive and negative electrode materials, improve the high temperature performance of the sodium ion battery and inhibit gas production.

[0020] In one implementation of the first aspect, 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%. Adding an appropriate amount of the 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 turn, the high temperature cycle performance of the battery is improved.

[0021] In an 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%-20%. The ether solvent comprises 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.

[0022] 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%.

[0023] By regulating the content of cyclic carbonate solvents, linear carbonate solvents and carboxylic acid ester solvents, the electrolyte viscosity is prevented from being too high and the electrolyte conductivity is prevented from being low. At the same time, in high-temperature scenarios, the cyclic carbonate solvents and carboxylic acid ester solvents are inhibited from oxidatively decomposing and producing a large amount of gas at the positive electrode of the battery, thereby improving the high-temperature cycle performance, low-temperature performance and safety performance of the battery.

[0024] In one possible implementation of the first aspect, the cyclic carbonate solvent includes at least one of ethylene carbonate and propylene carbonate; the mass percentage of ethylene carbonate in the electrolyte is 0%-20%, and the mass percentage of propylene carbonate in the electrolyte is 10%-40%. The dielectric constant of ethylene carbonate is higher than that of propylene carbonate. Adding ethylene carbonate can improve the corresponding conductivity of the electrolyte. Similarly, compared with the mass percentage of propylene carbonate, the mass percentage of ethylene carbonate is lower, which can inhibit gas generation. Thereby, the high temperature cycle performance of the battery is improved.

[0025] In an implementation of the first aspect, the linear carbonate solvent includes at least one of diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate; the mass percentage of diethyl carbonate in the electrolyte is 0%-40%, the mass percentage of ethyl methyl carbonate in the electrolyte is 0%-40%, and the mass percentage of dimethyl carbonate in the electrolyte is 0%-20%. 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 scenes and generating a large amount of gas.

[0026] 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.

[0027] 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.

[0028] In an 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.

[0029] 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.

[0030] 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, wherein 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

[0031] Figure 1 A schematic diagram of the structure of a sodium ion battery provided in an embodiment of the present application;

[0032] Figure 2 A schematic diagram of test results of a sodium ion battery provided in an embodiment of the present application;

[0033] Figure 3 A schematic diagram of the structure of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] 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 kind of association relationship describing 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. And, 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 its similar expressions refers to any combination of these items, including any combination of single items 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 clearly describe 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 the same or similar items with basically the same functions and effects.

[0035] Those skilled in the art will appreciate 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 the difference. 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 descriptions. 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 designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a concrete way for easy understanding.

[0036] For ease of understanding, some examples of concepts related to the embodiments of the present application are provided for reference, as shown below:

[0037] Cathode: In a primary cell, the electrode from which the current flows has a higher potential and is the positive electrode, which receives electrons for reduction. In an electrolytic cell, the cathode is the electrode connected to the positive pole of the power source and loses electrons for oxidation.

[0038] Anode: In a primary cell, the electrode into which the current flows has a lower potential and is the negative electrode, which loses electrons and causes oxidation. In an electrolytic cell, the negative electrode is the electrode connected to the negative pole of the power source and gains electrons and causes reduction.

[0039] Electrolyte: A medium that provides ion exchange between the positive and negative electrodes of a battery.

[0040] 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.

[0041] Film-forming additives: A type of substance that decomposes on the surface of materials before organic solvents to form an interface film, which can significantly improve battery performance.

[0042] 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 with the characteristics of a solid electrolyte. It is an electronic insulator but a Na + Excellent conductor, Na + Insertion and extraction are possible freely through the passivation layer.

[0043] Cathode Electrolyte Interphase (CEI) film: can also be expressed as an interface protection film, which refers to a passivation film layer with solid electrolyte properties.

[0044] The related art discloses a lithium secondary battery electrolyte, including lithium salt, non-aqueous organic solvent and functional additives, wherein the functional additives include the following components having the following mass percentages in the lithium secondary battery electrolyte: 3%-12% of cyclotriphosphazene compound, 3%-9% of fluorocarbonate, 2%-6% of sulfur-containing ester compound, and 1%-6% of nitrile compound. It can be seen that the related art only improves the stability of the interfacial film formation by controlling the ratio between the various additives. The non-aqueous organic solvent includes a carbonate solvent, and the solvent has a higher melting point and will have a stronger interaction with the lithium ions in the solute, and has poor low temperature performance.

[0045] In order to solve the above technical problems, the embodiments of the present application provide an electrolyte, a sodium ion battery and an electronic device. Among them, the electrolyte, as the name implies, is an electrolyte used to prepare a sodium ion battery. On the one hand, the electrolyte has a low viscosity and a high conductivity, which to a certain extent promotes the diffusion of sodium ions in the solution, facilitates the desolvation of sodium ions at the electrode-electrolyte interface, and improves the corresponding low-temperature performance of the sodium ion battery.

[0046] On the other hand, the electrolyte can also react at the positive electrode and the negative electrode to form a stable and high-quality interface film, thereby inhibiting the dissolution of metal ions in the positive electrode material and reducing the side reactions between the positive electrode material and the electrolyte. At the same time, the electrolyte is not easily oxidized and decomposed at high temperatures, reducing gas generation, thereby improving the high temperature and cycle performance of the sodium ion battery.

[0047] Figure 1 This is a schematic diagram of the structure of the sodium ion battery provided in the embodiment of the present application. Figure 1 As shown, 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 are embedded in the negative electrode active material 202 of the negative electrode 20 after passing through the electrolyte 40; during discharging, sodium ions are released from the negative electrode active material 202, and are inserted into the positive electrode active material 102 after passing through the electrolyte 40.

[0048] like Figure 1 As shown, 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.

[0049] The positive electrode current collector 101 may be a metal foil, such as aluminum foil, gold foil, platinum foil, etc. The positive electrode active material 102 can reversibly embed / de-embed sodium ions. The positive electrode active material 102 includes but is not limited to at least one of layered sodium transition metal oxides, Prussian white compounds, Prussian blue compounds, and sodium polyanionic compounds.

[0050] Sodium transition metal oxides such as sodium nickel iron manganese (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2, NFM111), Prussian white compounds such as (Na2Mn[Fe(CN)6], PBA), Prussian blue compounds such as (NaMn[Fe(CN)6], PBA), sodium polyanion compounds such as sodium iron phosphate (NaFePO4, NFP), sodium iron sulfate (Na2Fe2(SO4)3, NFS). The binder may be, for example, polyvinylidene fluoride (poly1,1-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 used to prepare the positive electrode 10 are only exemplary illustrations, and the embodiments of the present application are not limited to this. 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.

[0051] Continue reading Figure 1 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 the negative electrode active material 202, the negative electrode material layer may also include a certain amount of binder, conductive agent and other components.

[0052] Among them, 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, a tin-based material, a phosphorus-based material, or a sodium material capable of embedding and extracting 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; sodium materials include, but are not limited to, metallic sodium or sodium alloys. The binder may be, for example, sodium carboxymethyl cellulose (CMC) and / or styrene-butadiene rubber (SBR), etc. The conductive agent may be, for example, acetylene black, graphite, amorphous carbon, etc. 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 illustrative, and are not limited in this embodiment of the present application.

[0053] Continue reading Figure 1 In the sodium ion battery provided in the embodiment of the present application, the separator 30 blocks the passage of electrons and allows the passage of ions. The separator 30 includes but is not limited to single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, three-layer PP / PE / PP and ceramic-coated PE.

[0054] like Figure 1 As shown, in a sodium ion battery, the electrolyte 40 is a 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.

[0055] 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.

[0056] 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; the mass ratio of linear carbonate solvents to carboxylate solvents is 1.2:1 to 9:1.

[0057] 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 the numerical ratio can be typically but not limitatively, for example, 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 range values, 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.

[0058] 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 the number between any two of the above values, which are all possible range values, for example, the numerical ratio can be taken from the value between 5: 1-20: 1, can also be taken from the value between 10: 1-40: 1, can also be taken from the value between 30: 1-60: 1, can also be taken from the value between 50: 1-80: 1, can also be taken from the number between any two other values.

[0059] The mass ratio of the cyclic carbonate solvent to the linear carbonate solvent is 0.3: 1 to 1.5: 1. The value of the numerical ratio can be typically but not limitedly, for example, 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 acceptable range values, 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 number between any two other values.

[0060] The mass ratio of the cyclic carbonate solvent to the carboxylate solvent is 0.7: 1 to 7: 1. The value of the 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 acceptable range values, for example, the numerical ratio can be taken from 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, and a value between any two other values.

[0061] The mass ratio of the linear carbonate solvent to the carboxylate solvent is 1.2: 1 to 9: 1. The value of the numerical ratio can be typically but not limited to 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 range values, for example, the numerical ratio can be taken from a value between 1.2: 1-3: 1, a value between 2: 1-5: 1, a value between 4: 1-7: 1, a value between 5: 1-9: 1, and a number between any two other values.

[0062] 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.

[0063] The embodiment of the present application adjusts the mass ratio of cyclic carbonate solvents, linear carbonate solvents and carboxylate solvents to make the content of cyclic carbonate, linear carbonate solvents and carboxylate solvents in the organic solvent appropriate, thereby preventing the electrolyte viscosity from being too high and preventing the electrolyte conductivity from being low. At the same time, in high temperature scenarios, the cyclic carbonate solvents and carboxylate solvents are inhibited from oxidatively decomposing at the positive electrode of the battery to produce a large amount of gas, thereby improving the high temperature cycle performance, low temperature performance and safety performance of the battery.

[0064] In this way, the embodiments of the present application can reduce the viscosity of the electrolyte and improve the conductivity of the electrolyte by regulating the mass ratios between the cyclic carbonate solvent and the linear carbonate solvent, the cyclic carbonate solvent and the carboxylate solvent, and the linear carbonate solvent and the carboxylate solvent, 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 corresponding low-temperature performance of the sodium ion battery.

[0065] The embodiment 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.

[0066] By regulating the content and mass ratio between carboxylic acid ester solvents and sulfur-containing ester compounds, cyclic carbonate solvents and sodium salt additives, the content of cyclic carbonate and carboxylic acid ester solvents in organic solvents is appropriate, and the content of sulfur-containing ester compounds and sodium salt additives in additives is appropriate, so as to prevent cyclic carbonate solvents and carboxylic acid ester solvents from being oxidized and decomposed at the positive electrode of the battery to produce a large amount of gas under high temperature scenarios, thereby improving the high-temperature cycle performance and safety of the battery. At the same time, avoid too high or too low content of sulfur-containing ester compounds, so that the sulfur-containing ester compounds form high-impedance interface films or unstable and low-ion conductivity interface films on the surface of positive and negative electrode materials. In turn, it is not conducive to the low or high temperature performance of the battery.

[0067] In this way, by controlling the mass ratio between the carboxylic acid ester solvent and the sulfur-containing ester compound, the sulfur-containing ester compound can form a stable and high-quality interface film when the positive electrode and the negative electrode react, thereby inhibiting the dissolution of metal ions in the positive electrode material and reducing the side reaction between the positive electrode material and the electrolyte. At the same time, the oxidative decomposition reaction degree of the carboxylic acid ester solvent at high temperature is inhibited to reduce gas generation.

[0068] The embodiment of the present application controls the mass ratio between the cyclic carbonate solvent and the sodium salt additive, and sets the content of the cyclic carbonate solvent to reduce the viscosity of the electrolyte and inhibit the gas production of the battery. By adding the sodium salt additive, an additional sodium ion source can be added to the sodium ion battery, which is beneficial to participate in film formation on the electrode surface and improve the film quality. Thereby improving the high temperature cycle performance of the sodium ion battery.

[0069] In some embodiments of the present application, the mass percentage of the cyclic carbonate solvent in the electrolyte is 10%-40%. As an exemplary illustration, the value of the cyclic carbonate solvent can be, for example, 10%, 20%, 30%, 40% and a number between any two of the above values, all of which are acceptable range values.

[0070] The mass percentage of the linear carbonate solvent in the electrolyte is 20%-50%. As an example, the value of the linear carbonate solvent can be, for example, 20%, 30%, 40%, 50% and any number between the above two values, which are all acceptable ranges.

[0071] The mass percentage of carboxylate solvent in the electrolyte is 5%-25%. As an example, the value of carboxylate solvent can be 5%, 10%, 15%, 20%, 25% and numbers between any two of the above values, which are all acceptable ranges.

[0072] In some embodiments of the present application, the sulfur-containing ester compound includes one or more of dimethyl sulfite, diethyl sulfite, vinyl sulfite, vinyl sulfate (1,3,2-Dioxathiolane 2,2-dioxide, DTD), propylene sulfate (TS), methylene methanedisulfonate (MMDS), 1,3-propanesulfonate (PS), 1,3-propenesulfonate (PST), 1,4-butanesulfonate (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.

[0073] 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 limitedly 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 range values, 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.

[0074] The embodiment of the present application can control the mass ratio between the carboxylic acid ester solvent and the fluorocarbonate compound, which can not only inhibit the gas production of the battery and reduce the viscosity of the electrolyte, but also facilitate the fluorocarbonate compound to participate in the film formation on the electrode surface and improve the film quality. In this way, the high temperature cycle performance is taken into account while improving the low temperature characteristics of the sodium ion battery.

[0075] Fluorinated carbonate compounds include one or more of fluoroethylene carbonate (Fluoroethylene carbonate, FEC) and difluoroethylene carbonate. Fluorinated ester compounds can form a high-quality interface film on the surface of the negative electrode material, thereby improving the cycle performance of sodium ion batteries.

[0076] In some embodiments of the present application, the organic additive may further include anhydride compounds; 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 limitedly 15:1, 30:1, 50:1, 80:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1 and any number between any two of the above values, all of which are acceptable range values, 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.

[0077] The embodiment of the present application can control the mass ratio between the cyclic carbonate solvent and the anhydride compound, which can not only inhibit the gas production of the battery and reduce the viscosity of the electrolyte, but also facilitate the anhydride compound to participate in the film formation on the electrode surface and improve the film quality. In this way, the high-temperature cycle performance is taken into account while improving the low-temperature characteristics of the sodium-ion battery.

[0078] 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 to reduce the problems caused by the high alkalinity of the positive electrode materials.

[0079] In some embodiments of the present application, the organic additive may further include nitrile compounds; nitrile compounds include mononitrile compounds and / or polynitrile compounds; mononitrile compounds include at least one of acetonitrile and p-methylbenzonitrile; polynitrile compounds include 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 positive electrode materials, reduce the catalytic activity of transition metal ions, reduce the dissolution of transition metal ions and improve the oxidation resistance of electrolyte.

[0080] 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.

[0081] 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.

[0082] The mass percentage of nitrile compounds in the electrolyte is 0.5%-5%. As an example, the value 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 ranges.

[0083] 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 ranges.

[0084] Controlling the above-mentioned different additives to appropriate contents is beneficial in that other properties of the battery will not be reduced while the additives are exerting their beneficial effects.

[0085] 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 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 anhydride compounds, or sulfur-containing ester compounds, fluorocarbonate compounds and nitrile compounds, or sulfur-containing ester compounds, fluorocarbonate compounds and anhydride compounds, or sulfur-containing ester compounds, fluorocarbonate compounds and anhydride compounds, or sulfur-containing ester compounds, fluorocarbonate compounds, nitrile compounds and anhydride compounds.

[0086] 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.

[0087] 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(oxalyl)borate (NaBOB), sodium difluorooxalyl borate (NaDFOB), sodium difluorobis(oxalyl)phosphate (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.

[0088] 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.

[0089] That is to say, the organic solvent provided in the embodiment of the present application may also include an ether solvent; the mass percentage of the ether solvent in the electrolyte is 0%-20%. As an example, the value of the ether solvent may be, for example, 0%, 5%, 10%, 15%, 20% and a number between any two of the above values, which are all acceptable range values.

[0090] 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.

[0091] In some embodiments of the present application, the cyclic carbonate solvent includes at least one of ethylene carbonate (EC) and propylene carbonate (PC);

[0092] 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 ranges.

[0093] The mass percentage of propylene carbonate in the electrolyte is 10%-40%. As an example, the value of propylene carbonate can be, for example, 10%, 20%, 30%, 40% and numbers between any two of the above values, which are all acceptable ranges.

[0094] The dielectric constant of ethylene carbonate is higher than that of propylene carbonate. Adding ethylene carbonate can improve the corresponding conductivity of the electrolyte. Compared with the mass percentage of propylene carbonate, the mass percentage of ethylene carbonate is lower, which can inhibit gas generation. Thus, the high-temperature cycle performance of the battery is improved.

[0095] 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.

[0096] 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);

[0097] The mass percentage of diethyl carbonate in the electrolyte is 0%-40%. As an exemplary illustration, 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 ranges.

[0098] The mass percentage of ethyl methyl carbonate in the electrolyte is 0%-40%. As an exemplary illustration, 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.

[0099] 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 ranges.

[0100] 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.

[0101] The carboxylic acid ester 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.

[0102] 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 a certain measurement test system error in practical applications, and the values ​​within the system error range are all within the range defined in the embodiments of the present application.

[0103] In addition, as an exemplary illustration, the concentration of the sodium salt in the electrolyte may 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.

[0104] It can be understood that the mass ratio of the above-mentioned organic solvent and electrolyte additive may have a certain influence on the mass ratio test of the electrolyte solvent and the additive due to the formation of the interface film after the actual battery formation, capacity separation or cycle, and a certain measurement test error may 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, capacity separation or cycle is still within the above range and can be understood as the range defined in the embodiments of the present application.

[0105] It can be understood that, in actual test operations, the calculated values ​​of the above numerical ratios may allow for certain measurement test system errors, and the values ​​within the system error range may be understood as the range defined in the embodiments of the present application.

[0106] The above electrolyte and the sodium ion battery containing the electrolyte are introduced below through specific examples, and the sodium ion battery is prepared with the electrolyte prepared in the examples, and the performance of various sodium ion batteries is tested.

[0107] Example 1

[0108] In Example 1, the electrolyte was prepared according to the following steps.

[0109] 15% cyclic carbonate (PC), 50% linear carbonate (10% DEC and 40% EMC) and 20% carboxylate (EP) accounting for 15% by mass 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 contents as shown in the following Table 1 are added.

[0110] In some embodiments of the present application, the positive electrode material includes NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (NFM for short), Na2Mn[Fe(CN)6] (PBA for short), NaFePO4 (NFP for short), Na2Fe2(SO4)3 (NFS for short) materials. Negative electrode materials include hard carbon and soft carbon materials.

[0111] Sodium ion batteries are made using the following preparation methods:

[0112] Step S100, weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent Super P and 96% positive electrode active material (NFM or PBA or NFP or NFS) by weight, add them into N-methylpyrrolidone (NMP) in sequence, stir and mix them evenly, apply the slurry on the aluminum foil current collector, dry, cold press and cut to obtain positive electrode sheets.

[0113] 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 into deionized water in sequence, stir and mix them evenly, apply the slurry on the copper foil current collector, dry, cold press and cut to obtain negative electrode sheets.

[0114] 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 prepared electrolyte is poured into the battery cell, and a 2Ah soft-pack sodium ion battery is manufactured after a chemical formation process.

[0115] Examples 2-28 and Comparative Examples 1-10 were prepared according to the preparation steps of Example 1, which will not be repeated here.

[0116] 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.

[0117] Table 1 Parameter details of Examples 1-28 and Comparative Examples 1-10

[0118]

[0119]

[0120]

[0121]

[0122] The sodium ion batteries prepared in the above Examples 1-28 and Comparative Examples 1-10 were tested for performance. See the following test method:

[0123] 1. High temperature cycle performance test:

[0124] 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:

[0125] Capacity retention rate (%)=discharge capacity at the 300th cycle / discharge capacity at the 1st cycle×100%.

[0126] 2.-40℃ low temperature performance test:

[0127] At an ambient temperature of 25±3℃, charge to 3.95V at a constant current of 0.2C, then charge at a constant voltage until the current drops to 0.05C, let it rest for 10 minutes, then discharge to 2.0V at a constant current of 0.2C. The capacity at this time is the initial capacity. The battery is placed at -40℃ for 4 hours, then charged to 3.95V at a constant current of 0.2C, then charged at a constant voltage until the current drops to 0.05C, let it rest for 10 minutes, then discharged to 2.0V at a constant current of 0.2C, record it as the residual capacity, and record the residual capacity retention rate (remaining capacity / initial capacity×100%). The test results are shown in Table 2 and Figure 2 .

[0128] Table 2 Test results of Examples 1-28 and Comparative Examples 1-10

[0129]

[0130]

[0131] See 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 is 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 is 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 is significantly higher than that of the sodium ion batteries prepared in Comparative Examples 1-4.

[0132] That is, in Examples 1-15, the mass ratio of carboxylic acid ester solvent to sulfur-containing ester compound is 1.2:1 to 40:1, the mass ratio of cyclic carbonate solvent to sodium salt additive is 5:1 to 80:1, the mass ratio of cyclic carbonate solvent to linear carbonate solvent is 0.3:1 to 1.5:1, the mass ratio of cyclic carbonate solvent to carboxylic acid ester solvent is 0.7:1 to 7:1; the mass ratio of linear carbonate solvent to carboxylic acid ester solvent is 1.2:1 to 9:1. However, the above numerical ratios are not satisfied in Comparative Examples 1-4.

[0133] 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.

[0134] 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 viscosity of the electrolyte and limited sodium ion transport. In turn, 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.

[0135] Next, in Comparative Example 3, no sodium salt additive was added. Thus, the electrolyte additive cannot provide an additional sodium ion source for the sodium ion battery, and is not conducive to participating in film formation on the electrode surface, resulting in low film quality. Further, the high temperature cycle performance of the battery is affected.

[0136] 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 -40°C low temperature capacity retention rate of the sodium ion batteries prepared in Examples 16-20 is 48.0%-48.6%, and the capacity retention rate after 300 cycles at 45°C is 96.2%-96.4%. The -40°C low temperature capacity retention rate of the sodium ion batteries prepared in Comparative Examples 5-6 is 33.1%-45.3%, and the capacity retention rate after 300 cycles at 45°C is 92.8%-93.6%. 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 16-20 of the present application are significantly higher than those of the sodium ion batteries prepared in Comparative Examples 5-6.

[0137] That is, in Examples 16-20, the mass ratio of carboxylic acid ester solvent to sulfur-containing ester compound is 1.2:1 to 40:1, the mass ratio of cyclic carbonate solvent to sodium salt additive is 5:1 to 80:1; the mass ratio of cyclic carbonate solvent to linear carbonate solvent is 0.3:1 to 1.5:1, the mass ratio of cyclic carbonate solvent to carboxylic acid ester solvent is 0.7:1 to 7:1; the mass ratio of linear carbonate solvent to carboxylic acid ester solvent is 1.2:1 to 9:1. However, the above numerical ratios are not met in Comparative Examples 5-6.

[0138] Specifically, in Example 20, 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; the mass ratio of DEC, EMC to EP is 2.67:1. In Comparative Example 5, the mass ratio of PC to NaDFOB is 150:1, and greater than 80:1. It can be seen that the high content of cyclic carbonate leads to excessive viscosity of the electrolyte and limited sodium ion transport. In turn, the diffusion of sodium ions in the solution is restricted, and the low temperature performance of the battery is poor.

[0139] At the same time, the low content of NaDFOB also cannot provide additional sodium ion sources for sodium ion batteries, is not conducive to film formation on the electrode surface, and cannot form a stable interface film. As a result, carbonate esters decompose severely at high temperatures, produce a large amount of gas, and reduce high-temperature cycle performance.

[0140] 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.

[0141] 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 of 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 of 300 cycles at 45°C is 93.6%. The capacity retention rate of 300 cycles at 45°C 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 cycle 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 45°C cycle 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 8.

[0142] 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 satisfied in Comparative Examples 7-8.

[0143] Specifically, in Example 22, 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 and EP is 2.67:1. In Comparative Example 7, the mass ratio of DEC, EMC and EP is 10:1, which is greater than 7:1.

[0144] If the linear carbonate content is too high, it will affect the conductivity of the electrolyte, resulting in limited sodium ion transmission and poor low-temperature performance of the battery. At the same time, linear carbonate is not resistant to high temperatures, causing it to decompose severely at high temperatures, producing a large amount of gas, resulting in poor high-temperature performance.

[0145] 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 will make the interface film formed by TS on the positive and negative electrode surfaces unstable, and the interface film has low ion conductivity, which is not conducive to the high temperature performance of the battery.

[0146] 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 -40°C low temperature capacity retention rate of the sodium ion batteries prepared in Examples 25-28 is 45.3%-45.9%, and the capacity retention rate of 300 cycles at 45°C is 96.1%-96.5%. The -40°C low temperature capacity retention rate of the sodium ion battery prepared in Comparative Example 9 is 30.9%, and the capacity retention rate of 300 cycles at 45°C is 93.2%. The capacity retention rate of 300 cycles at 45°C of the sodium ion battery prepared in Comparative Example 10 is 90.2%. 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 of the present application 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.

[0147] That is, in Examples 25-28, the mass ratio of carboxylic acid ester solvent to sulfur-containing ester compound is 1.2:1 to 40:1, the mass ratio of cyclic carbonate solvent to sodium salt additive is 5:1 to 80:1, the mass ratio of cyclic carbonate solvent to linear carbonate solvent is 0.3:1 to 1.5:1, the mass ratio of cyclic carbonate solvent to carboxylic acid ester solvent is 0.7:1 to 7:1; the mass ratio of linear carbonate solvent to carboxylic acid ester solvent is 1.2:1 to 9:1. However, the above numerical ratios are not satisfied in Comparative Examples 9-10.

[0148] 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; 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, and greater than 7:1. The linear carbonate content is too high, which affects the conductivity of the electrolyte, and the sodium ion transmission is limited, 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 a large amount of gas, and resulting in poor high-temperature performance. In Comparative Example 10, the mass ratio of EP to TS is 50:1, and greater than 40:1. The high EP content, the low TS content, and the low S content will make the interface film formed by TS on the positive and negative electrode surfaces unstable, and the interface film has low ion conductivity, which is not conducive to the high-temperature performance of the battery.

[0149] The embodiment of the present application also provides a sodium ion battery, including 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.

[0150] An embodiment of the present application also 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 above-mentioned sodium ion battery.

[0151] See also Figure 3 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 smart watch, a mobile power supply, a netbook, a wearable device, an augmented reality (AR) device, a virtual reality (VR) device, a vehicle-mounted device, an energy storage device, a base station, and a car, etc. The embodiment of the present application does not impose any special restrictions on the specific form of the electronic device.

[0152] In some schemes, multiple embodiments of the present application may be combined, and the combined scheme may be implemented. Optionally, some operations in the process of each method embodiment 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 only exemplary and does not constitute a limitation on the execution order between the steps, and other execution orders may be used between the steps. It is not intended to indicate that the execution order is the only order in which these operations can be performed.

[0153] A person skilled in the art will be able to 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.

[0154] In addition, some steps in the method embodiment may be equivalently replaced with other possible steps. Alternatively, some steps in the method embodiment may be optional and may be deleted in certain usage scenarios. Alternatively, other possible steps may be added to the method embodiment. Moreover, each method embodiment may be implemented separately or in combination. The above content is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto, and any changes or replacements within the technical scope disclosed in the present application shall be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope 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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