Electrolyte solution and battery

Abstract

The present application provides an electrolyte solution and a battery. The electrolyte solution comprises: an electrolyte sodium salt; and an organic solvent, the organic solvent being an isophthalate solvent and / or a terephthalate solvent, wherein the volume content of the organic solvent accounts for 50 vol% or above of the solvent in the electrolyte solution.

Description

Electrolyte and battery

[0001] The present disclosure claims priority to the Chinese patent application No. 202410637539.1, filed on May 21, 2024, and entitled "Electrolyte and battery", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] Embodiments of the present disclosure relate to the technical field of battery, and more particularly, to an electrolyte and a battery. BACKGROUND

[0003] The electrolyte of a sodium-ion battery, as one of the important components of the battery, is usually composed of a sodium salt, a solvent and an additive, which together determine the performance of the electrolyte of the sodium-ion battery.

[0004] The organic solvent of the electrolyte of a conventional sodium-ion battery is mainly a carbonate and an ether solvent, and the sodium-ion battery using the carbonate and the ether solvent as the organic solvent of the electrolyte mainly has the disadvantage of poor storage performance. In view of this, it is necessary to provide a new technical solution to solve the above technical problems. SUMMARY

[0005] The purpose of the present disclosure is to provide a new technical solution of an electrolyte and a battery.

[0006] In a first aspect, embodiments of the present disclosure provide an electrolyte. The electrolyte comprises:

[0007] an electrolyte sodium salt;

[0008] an organic solvent, the organic solvent being a m-phthalate solvent and / or a terephthalate solvent;

[0009] The volume content of the organic solvent in the electrolyte solvent is more than 50 vol%.

[0010] Optionally, the organic solvent in the electrolyte is a m-phthalate solvent and a terephthalate solvent.

[0011] The proportion of the m-phthalate solvent in the electrolyte solvent is greater than that of the terephthalate solvent.

[0012] Optionally, the electrolyte further comprises a co-solvent, and the volume content of the co-solvent in the electrolyte solvent is 0 vol% to 50 vol%.

[0013] Optionally, the electrolyte further comprises an additive, and the volume content of the additive in the electrolyte solvent is 0 vol% to 8 vol%.

[0014] Optionally, the chemical structural formula of the isophthalate solvent is chemical structural formula I:

[0015] wherein R1 and R2 are respectively selected from one of linear or branched alkyl, fluoroalkyl, alkenyl, alkynyl, silyl with carbon atom number being 1-6.

[0016] Optionally, the chemical structural formula of the terephthalate solvent is chemical structural formula II:

[0017] wherein R3 and R4 are respectively selected from one of linear or branched alkyl, fluoroalkyl, alkenyl, alkynyl, silyl with carbon atom number being 1-6.

[0018] Optionally, the organic solvent is diethyl isophthalate.

[0019] Optionally, the electrolyte sodium salt is one or a combination of multiple of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium methylsulfate, sodium perchlorate.

[0020] Optionally, the concentration of the electrolyte sodium salt ranges from 0.5 mol / L to 3 mol / L.

[0021] Optionally, the additive is one or a combination of multiple of vinyl carbonate, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilyl) phosphate, 1,3-propane sultone, methylene methane disulfonate, 1,3,6-hexane trinitrile, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, tris(hexafluoroisopropyl) phosphate.

[0022] In a second aspect, the present disclosure further provides a battery. The battery comprises the electrolyte as described in the first aspect.

[0023] According to the embodiments of the present disclosure, the organic solvent of the electrolyte is an isophthalate solvent and / or a terephthalate solvent, wherein the proportion of the organic solvent in the electrolyte solvent is above 50 vol%, so that the battery with the electrolyte has good storage performance.

[0024] Other features of the present disclosure, and the advantages thereof over other methods of solving the same problems will become apparent from the following detailed description of exemplary embodiments, when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings incorporated in and forming a part of the specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0026] Fig. 1 shows a comparison chart of AC impedance tests of Example 1 and Comparative Example 1 according to the embodiments of the present disclosure;

[0027] Fig. 2 shows a comparison chart of DC internal resistance tests of Example 1 and Comparative Example 1 according to the embodiments of the present disclosure;

[0028] Fig. 3 shows a comparison chart of cycle performance tests of Example 2 and Comparative Example 2 according to the embodiments of the present disclosure;

[0029] Fig. 4 shows a comparison chart of rate performance tests of Example 3 and Comparative Example 3 according to the embodiments of the present disclosure. DETAILED DESCRIPTION

[0030] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. Note that the relative arrangement, numerical expressions, and numerical values of components and steps set forth in these embodiments are not limiting to the scope of the present disclosure unless otherwise specifically stated.

[0031] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way limiting to the scope of the disclosure and its applications or uses.

[0032] Techniques and equipment known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered part of the specification where appropriate.

[0033] In all examples shown and discussed herein, any specific values should be interpreted as merely illustrative, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0034] Note that like reference numerals and letters indicate like items in the accompanying drawings, and thus, once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0035] At present, with the continuous development of new energy, sodium-ion batteries are expected to become the next generation of energy storage batteries. The power generated by new energy needs to be stored by energy storage batteries to achieve "peak clipping and valley filling", that is, the energy storage batteries are required to have good storage performance, cycle performance and rate performance.

[0036] The embodiments of the present disclosure provide an electrolyte, specifically, the electrolyte comprises: an electrolyte sodium salt; an organic solvent, the organic solvent is an isophthalate solvent and / or a terephthalate solvent; wherein the volume content of the organic solvent in the electrolyte solvent is more than 50 vol%.

[0037] In the battery electrolyte, the electrolyte sodium salt is one of the important components, and the electrolyte sodium salt plays a key role in the ionic conductivity and chemical stability of the electrolyte.

[0038] The organic solvent in the electrolyte is another important component of the electrolyte. Specifically, the organic solvent can dissolve the sodium salt, and the organic solvent affects the electrical conductivity and the ion movement speed.

[0039] In the sodium-ion electrolyte, common organic solvents are carbonate-based organic solvents and ether-based organic solvents. However, the carbonate-based organic solvents and the ether-based organic solvents have a high donor number, so that the components of the SEI and the CEI are more dissolved in the cycle and storage process, so that the storage performance and the cycle performance of the battery are reduced.

[0040] The organic solvent provided by the embodiments of the present disclosure is a phthalate-based solvent, specifically, the organic solvent is a m-phthalate-based solvent and / or a p-phthalate-based solvent. For example, the organic solvent in the electrolyte can be a m-phthalate-based solvent; or in one example, the organic solvent in the electrolyte can be a p-phthalate-based solvent; or in another example, the organic solvent in the electrolyte can be a m-phthalate-based solvent and a p-phthalate-based solvent.

[0041] The m-phthalate-based organic solvent and the p-phthalate-based solvent have a low donor number, a low ion desolvation energy, and a high dielectric constant, so that the organic solvent has good solubility for the sodium salt and good film-forming performance on the positive and negative electrode surfaces of the battery, so that the battery containing the electrolyte has better storage performance and cycle performance than the battery containing the electrolyte without the solvent.

[0042] Specifically, when the organic solvent has a high donor number, it means that the solvent has a strong electron-donating ability. The organic solvent with a high donor number interacts with the components of the SEI and the CEI, resulting in increased solubility. If the components of these interfaces are excessively dissolved in the cycle and storage process, the cycle performance and the storage performance of the battery can be negatively affected. For example, dissolution can cause the structure of the SEI and the CEI to be destroyed, thereby affecting the stability of the electrode and the ion transport efficiency, ultimately reducing the cycle life and the storage performance of the battery.

[0043] The m-phthalate-based solvent and / or the p-phthalate-based solvent used in the embodiments of the present disclosure have a low donor number, specifically, the m-phthalate-based solvent has a lower donor number than the carbonate-based organic solvent and the ether-based organic solvent, and the p-phthalate-based solvent has a lower donor number than the carbonate-based organic solvent and the ether-based organic solvent, so that the electrode surface can form a stable and protective SEI film and CEI film, which can inhibit the decomposition of the electrolyte and effectively prevent the graphite electrode from being damaged, ensuring the cycle performance and the storage performance of the battery.

[0044] The ion desolvation energy is the energy required to describe the ion dissociation from the solvent. When the ion enters the solution, it needs to overcome the attraction of the solvent molecules to migrate to another electrode, which is called the solvation energy barrier. In sodium ion batteries, the migration of sodium ions also needs to overcome the solvation energy barrier. If the sodium ion desolvation energy barrier can be reduced, the migration rate of sodium ions can be improved, thereby making the battery performance better and the cycle life longer. The isophthalate solvents and / or terephthalate solvents adopted in the embodiments of the present disclosure have smaller ion desolvation energy. Specifically, the isophthalate solvents have smaller ion desolvation energy than the carbonate organic solvents and the ether organic solvents, and the terephthalate solvents have smaller ion desolvation energy than the carbonate organic solvents and the ether organic solvents, so that the electrolyte generates stable SEI film and CEI film on the electrode side, which can well block the further reaction of the solvent and the electrode; in addition, the isophthalate solvents and / or terephthalate solvents have smaller ion desolvation energy, and the sodium ions have smaller desolvation energy in the embedding and de-embedding process, so that the sodium ion battery has higher rate performance.

[0045] The dielectric constant of the solvent is a physical quantity describing the response ability of the solvent to the electric field, which reflects the strength of the molecular interaction and the degree of polarity in the solvent. Specifically, the larger the dielectric constant, the stronger the interaction between the solvent molecules, and the interaction between the ions in the solution will also be enhanced, thereby affecting the solubility, reaction rate and reaction equilibrium of the chemical process. The isophthalate solvents and / or terephthalate solvents adopted in the embodiments of the present disclosure have higher dielectric constant. Specifically, the isophthalate solvents have higher dielectric constant than the carbonate organic solvents and the ether organic solvents, and the terephthalate solvents have higher dielectric constant than the carbonate organic solvents and the ether organic solvents, so that the organic solvent has good solubility for sodium salt.

[0046] In addition, in order to reduce the solubility of the electrolyte to the SEI film and the CEI film as a whole, and to ensure that there are enough organic solvents around the sodium ions in the electrolyte to reduce the desolvation energy, the volume content of the isophthalate solvents and / or terephthalate solvents in the electrolyte solvent is more than 50 vol%.

[0047] Therefore, in the embodiments of the present disclosure, the isophthalate solvents and the terephthalate solvents have lower donor number, higher dielectric constant and smaller ion desolvation energy, so that the battery has good positive and negative electrode surface film forming performance, the sodium ion battery has better storage performance, longer cycle life and better rate performance by using the isophthalate solvents and / or terephthalate solvents as the organic solvent of the electrolyte.

[0048] In addition, the isophthalic acid diester solvent and the p-terephthalic acid diester solvent have high flash points and wide electrochemical windows, so that the battery with the electrolyte has better safety.

[0049] The flash point of the solvent refers to the temperature at which the solvent starts to ignite and burn under specific conditions. It is an important indicator of the flammability of organic solvents. Generally speaking, the lower the flash point, the more flammable the solvent. The higher the flash point, the less flammable the solvent. The isophthalic acid diester solvent and / or the p-terephthalic acid diester solvent used in the embodiments of the present disclosure have a higher flash point, which ensures the safety of the electrolyte in use.

[0050] The electrode material of the sodium ion battery needs to withstand the corresponding voltage change during charging and discharging, and the electrochemical window determines the working voltage range of the battery. The isophthalic acid diester solvent and / or the p-terephthalic acid diester solvent used in the embodiments of the present disclosure can ensure a wide electrochemical window while achieving excellent rate performance and cycle stability.

[0051] Therefore, in the embodiments of the present disclosure, the isophthalic acid diester solvent or the p-terephthalic acid diester solvent has a low donor number, a small ion desolvation energy, a high flash point, a high dielectric constant, a wide electrochemical window, a good solubility for sodium salt, and a good film-forming performance on the positive and negative electrode surfaces. The battery containing the organic solvent has better storage performance, higher rate performance, better safety, longer cycle life, higher capacity retention rate, smaller alternating current impedance and direct current internal resistance than the battery without the organic solvent.

[0052] In an optional embodiment, when the organic solvent is an isophthalic acid diester solvent and a p-terephthalic acid diester solvent, the proportion of the isophthalic acid diester solvent is greater than that of the p-terephthalic acid diester solvent, so that the battery containing the electrolyte has good overall performance.

[0053] In an embodiment, the electrolyte further comprises a co-solvent, and the volume content of the co-solvent in the electrolyte solvent is 0vol% to 50vol%.

[0054] In this embodiment, the electrolyte further comprises a co-solvent, which can affect the conductivity of the electrolyte, the stability of the electrolyte, and the solubility of the electrolyte. Adding an appropriate amount of co-solvent to the electrolyte can improve the overall performance of the battery.

[0055] In a specific embodiment, the electrolyte can not contain a co-solvent, for example, the volume content of the isophthalic acid diester solvent and / or the p-terephthalic acid diester solvent in the electrolyte solvent is 100vol%.

[0056] In one embodiment, the electrolyte further comprises a co-solvent. In one embodiment, the co-solvent is present in the electrolyte in an amount of 10 vol% to 50 vol% based on the total volume of the electrolyte solvent.

[0057] For example, the co-solvent is present in the electrolyte in an amount of 10 vol% based on the total volume of the electrolyte solvent, and the isophthalic acid diester solvent and / or the terephthalic acid diester solvent is present in the electrolyte in an amount of 90 vol% based on the total volume of the electrolyte solvent.

[0058] For example, the co-solvent is present in the electrolyte in an amount of 30 vol% based on the total volume of the electrolyte solvent, and the isophthalic acid diester solvent and / or the terephthalic acid diester solvent is present in the electrolyte in an amount of 70 vol% based on the total volume of the electrolyte solvent.

[0059] For example, the co-solvent is present in the electrolyte in an amount of 50 vol% based on the total volume of the electrolyte solvent, and the isophthalic acid diester solvent and / or the terephthalic acid diester solvent is present in the electrolyte in an amount of 50 vol% based on the total volume of the electrolyte solvent.

[0060] Specifically, the co-solvent in the electrolyte is one or more of vinyl carbonate, fluorinated vinyl carbonate, vinylidene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl formate, methyl acetate, methyl butyrate, ethyl propionate, ethyl butyrate, butyl acetate, methyl propionate, propyl butyrate, trimethyl phosphate, triethyl phosphate, tetrahydrofuran, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethyl methanesulfonate, γ-butyrolactone, sulfolane, dimethyl sulfone, dimethyl sulfoxide, ethyl methyl sulfone, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl(2,2,2-trifluoroethyl) carbonate, methyl trifluoroacetate, acetonitrile, 1,3-dioxolane.

[0061] In one embodiment, the electrolyte further comprises an additive, and the additive is present in the electrolyte in an amount of 0 vol% to 8 vol% based on the total volume of the electrolyte solvent.

[0062] In this embodiment, the electrolyte further comprises an additive, and the additive can change the physical and chemical properties of the electrolyte. For example, some additives can change the solvation structure of sodium ions, affect the solubility of electrolyte salts, and thus change the ionic conductivity, viscosity, etc. of the electrolyte. This helps to improve the electrochemical stability of the solvent and sodium salt, widen the voltage window, improve the battery capacity, and improve the first coulomb efficiency, etc.

[0063] In one embodiment, the electrolyte comprises an appropriate amount of additive, for example, the volume content of the additive in the electrolyte solvent is 1 vol%, 3 vol%, 5 vol%, or 8 vol%.

[0064] Specifically, the additive is selected from one or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilyl) phosphate, 1,3-propane sultone, methylene methanedisulfonate, 1,3,6-hexanetricarbonitrile, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, and tris(hexafluoroisopropyl) phosphate.

[0065] In one embodiment, the electrolyte can not comprise a co-solvent and an additive, for example, the volume content of the m-benzenedicarboxylic acid diester solvent and / or the p-benzenedicarboxylic acid diester solvent in the electrolyte solvent is 100 vol%.

[0066] Alternatively, in one embodiment, the electrolyte can not comprise an additive, for example, the volume content of the co-solvent in the electrolyte solvent is Avol%, the volume content of the m-benzenedicarboxylic acid diester solvent and / or the p-benzenedicarboxylic acid diester solvent in the electrolyte solvent is Bvol%, and A+B=100, wherein B is greater than or equal to A, and preferably, B is greater than A. In this embodiment, the volume content of the organic solvent and the volume content of the co-solvent in the electrolyte are limited, and the volume content of the organic solvent is greater than the volume content of the co-solvent, thereby ensuring the overall performance of the sodium ion battery.

[0067] Alternatively, in one embodiment, the electrolyte can not comprise a co-solvent, for example, the volume content of the additive in the electrolyte solvent is Cvol%, the volume content of the m-benzenedicarboxylic acid diester solvent and / or the p-benzenedicarboxylic acid diester solvent in the electrolyte solvent is Bvol%, and C+B=100, wherein B is much greater than C. In this embodiment, the volume content of the organic solvent and the volume content of the co-solvent in the electrolyte are limited, and the volume content of the organic solvent is much greater than the volume content of the co-solvent, thereby ensuring the overall performance of the sodium ion battery.

[0068] Alternatively, in one embodiment, the electrolyte comprises a co-solvent and an additive, for example, the volume content of the co-solvent in the electrolyte solvent is Avol%, the volume content of the m-benzenedicarboxylic acid diester solvent and / or the p-benzenedicarboxylic acid diester solvent in the electrolyte solvent is Bvol%, and the volume content of the additive in the electrolyte solvent is Cvol%, wherein A+B+C=100, and B>A>C. In this embodiment, the volume content of the organic solvent, the volume content of the co-solvent, and the volume content of the additive in the electrolyte are limited, thereby ensuring the overall performance of the sodium ion battery.

[0069] In one embodiment, the chemical structure of the isophthalate-based solvent is Chemical Structure I:

[0070] wherein R1 and R2 are each selected from one of linear or branched alkyl, fluoroalkyl, alkenyl, alkynyl, silyl groups with carbon atom number 1-6.

[0071] In this embodiment, in the chemical structure of the isophthalate-based solvent, R1 and R2 as substituents have multiple possibilities, and R1 and R2 can be selected from one of linear or branched alkyl, fluoroalkyl, alkenyl, alkynyl, silyl groups with carbon atom number 1-6, respectively. Different choices of these substituents can significantly affect the physicochemical properties, solubility, and other properties of isophthalate.

[0072] For example, the substituents R1 and / or R2 are linear or branched alkyl (C1-C6). For linear or branched alkyl substituents, they can improve the solubility of the electrolyte, and help the uniform dispersion of sodium salts and other additives in the electrolyte. This helps to enhance the ionic conductivity and electrochemical performance of the electrolyte.

[0073] The substituents R1 and / or R2 are fluoroalkyl. The introduction of fluoroalkyl can increase the polarity of the electrolyte, which helps the transport and migration of sodium ions in the electrolyte. At the same time, the presence of fluorine atoms can also improve the chemical stability of the electrolyte and reduce the occurrence of side reactions.

[0074] The substituents R1 and / or R2 are alkenyl groups, which contain unsaturated bonds (double bonds). The alkenyl group increases the reactivity of the solvent, or affects the viscosity and flowability of the electrolyte, thereby affecting the migration rate of sodium ions and the ionic conductivity of the electrolyte.

[0075] The substituents R1 and / or R2 are alkynyl groups, which contain unsaturated bonds (triple bonds). The alkynyl group increases the reactivity of the solvent, or affects the viscosity and flowability of the electrolyte, thereby affecting the migration rate of sodium ions and the ionic conductivity of the electrolyte.

[0076] The substituents R1 and / or R2 are silyl groups. The introduction of silyl groups can change the interfacial properties of the electrolyte and affect the interaction between sodium ions and electrode materials. Silyl compounds generally have good thermal stability and chemical stability, which helps to improve the performance of the electrolyte under high temperature or high activity conditions.

[0077] It should be noted that different combinations of R1 and R2 can result in significant differences in the properties of isophthalate-based solvents. Therefore, when selecting and using such solvents, appropriate combinations of substituents need to be selected according to specific application scenarios and requirements.

[0078] In one embodiment, the chemical structure of the terephthalate-based solvent is Chemical Structure II:

[0079] wherein R3 and R4 are each selected from one of a linear or branched alkyl group having 1-6 carbon atoms, a fluoroalkyl group, an alkenyl group, an alkynyl group, and a silyl group.

[0080] In this embodiment, the application of terephthalate-based solvents in sodium-ion electrolytes, the selection of R3 and R4 in the chemical structure has a significant impact on the performance of the electrolyte. These substituents, including linear or branched alkyl groups with 1-6 carbon atoms, fluoroalkyl groups, alkenyl groups, alkynyl groups, and silyl groups, each bring different characteristics to the electrolyte.

[0081] For example, when the substituents R3 and / or R4 are linear or branched alkyl groups (C1-C6), the introduction of linear or branched alkyl groups can improve the solubility and wettability of the electrolyte, allowing sodium salts and other additives to better dissolve and disperse in the electrolyte. This helps to improve the ionic conductivity of the electrolyte, thereby enhancing the performance of the battery.

[0082] When the substituents R3 and / or R4 are fluoroalkyl groups, the introduction of fluoroalkyl groups can increase the polarity of the electrolyte, improve the solvation structure of sodium ions, and thus affect the ion transport performance of the electrolyte. At the same time, fluoroalkyl groups can also improve the chemical stability of the electrolyte, reducing the possibility of side reactions during battery operation.

[0083] When the substituents R3 and / or R4 are alkenyl groups, the introduction of alkenyl groups provides the electrolyte with special reactivity and physical properties. Unsaturated bonds (double bonds) participate in certain specific electrochemical reactions, or optimize the migration rate of sodium ions by affecting the viscosity and flowability of the electrolyte.

[0084] When the substituents R3 and / or R4 are alkynyl groups, the introduction of alkynyl groups provides the electrolyte with special reactivity and physical properties. Unsaturated bonds (triple bonds) participate in certain specific electrochemical reactions, or optimize the migration rate of sodium ions by affecting the viscosity and flowability of the electrolyte.

[0085] When the substituents R3 and / or R4 are silyl groups, the introduction of silyl groups can change the interfacial properties of the electrolyte, affecting the interaction between sodium ions and electrode materials, thereby improving the cycle stability and energy efficiency of the battery.

[0086] It should be noted that different combinations of R 3 and R 4 may result in significant differences in the performance of the electrolyte. Therefore, when selecting and designing terephthalate-based solvents as components of sodium-ion electrolytes, precise control is needed according to the specific battery type and performance requirements.

[0087] In one embodiment, the organic solvent is diethyl isophthalate.

[0088] In this embodiment, diethyl isophthalate is used as the only organic solvent. Diethyl isophthalate has an electron-withdrawing benzene ring and two C=O double bonds in its molecule, which have important influences on its chemical properties and applications.

[0089] Due to the presence of the benzene ring and C=O double bonds, this solvent has a low donor number, a high dielectric constant, a small ion desolvation energy, and good positive and negative electrode surface film-forming properties, so that the battery of this type of electrolyte has good storage performance and cycle performance.

[0090] In one embodiment, the electrolyte sodium salt is one or a combination of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium methylsulfate, and sodium perchlorate.

[0091] In this embodiment, the electrolyte sodium salt is one or a combination of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium methylsulfate, and sodium perchlorate. Preferably, the electrolyte sodium salt is sodium hexafluorophosphate, sodium perchlorate, or bisfluoromethylsulfonylimide.

[0092] In one embodiment, the concentration of the electrolyte sodium salt ranges from 0.5 mol / L to 3 mol / L.

[0093] In this embodiment, limiting the concentration of the sodium salt within this range can ensure that the electrolyte has sufficient ion concentration, thereby providing stable ion conduction performance. As the main ion source of the electrolyte, the concentration of the sodium salt directly affects the ion mobility and conductivity of the electrolyte. Within this concentration range, the electrolyte can maintain a high ion mobility and conductivity, which helps to improve the overall performance of the battery. In an alternative embodiment, the concentration of the electrolyte sodium salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 3 mol / L.

[0094] The present disclosure also provides a battery. The battery comprises the electrolyte as described above.

[0095] The present disclosure also provides a sodium-ion battery comprising the electrolyte containing isophthalate and / or terephthalate solvents as described above, for example, the sodium-ion battery is composed of a positive electrode sheet, a separator, an electrolyte comprising an electrolyte sodium salt, isophthalate and / or terephthalate solvents, and a negative electrode sheet.

[0096] The present disclosure will be further described in detail through specific embodiments below, which should not be considered as a limitation on the scope of protection of the present disclosure.

[0097] Example 1

[0098] In this example, the electrolyte only contains electrolyte sodium salt and organic solvent (the volume content of co-solvent and additive in electrolyte solvent is 0 vol%), so in this example, the volume content of organic solvent in electrolyte solvent is 100 vol%. Specifically, the organic solvent is diethyl isophthalate.

[0099] Specifically, the preparation of electrolyte: in the argon-filled glove box, sodium hexafluorophosphate (electrolyte sodium salt) is added to diethyl isophthalate and stirred uniformly to obtain a sodium ion battery electrolyte, wherein the molar concentration of NaPF6 is 1 mol / L.

[0100] Example 2

[0101] In this example, the electrolyte only contains electrolyte sodium salt, organic solvent and co-solvent (the volume content of additive in electrolyte solvent is 0 vol%), and in this example, the co-solvent is dimethyl carbonate and the organic solvent is diisobutyl phthalate.

[0102] Specifically, the preparation of electrolyte: in the argon-filled glove box, dimethyl carbonate (co-solvent) and diisobutyl terephthalate (organic solvent) are mixed in a volume ratio of 1:1, and sodium perchlorate (electrolyte sodium salt) is added and stirred uniformly to obtain a sodium ion battery electrolyte, wherein the concentration of sodium perchlorate is 2 mol / L.

[0103] Among them, dimethyl carbonate (co-solvent) and diisobutyl terephthalate (organic solvent) are mixed in a volume ratio of 1:1, so the volume content of dimethyl carbonate (co-solvent) in electrolyte solvent is 50 vol%, and the volume content of diisobutyl terephthalate (organic solvent) in electrolyte solvent is 50 vol%.

[0104] Example 3

[0105] In this example, the electrolyte only contains electrolyte sodium salt, organic solvent and co-solvent (the volume content of additive in electrolyte solvent is 0 vol%), and in this example, the co-solvent is ethylene glycol dimethyl ether and the organic solvent is diisobutyl terephthalate.

[0106] Specifically, the preparation of electrolyte: ethylene glycol dimethyl ether (co-solvent) and diisobutyl terephthalate (organic solvent) are mixed in a volume ratio of 1:2, and sodium difluoromethyl sulfonimide (electrolyte sodium salt) is added and stirred uniformly to obtain a sodium ion battery electrolyte, wherein the concentration of sodium difluoromethyl sulfonimide is 3 mol / L.

[0107] The ethylene glycol dimethyl ether (co-solvent) and the difluoromethyl phthalate (organic solvent) are mixed in a volume ratio of 1:2, the volume content of the ethylene glycol dimethyl ether (co-solvent) in the electrolyte solvent is 33.3 vol%, and the volume content of the difluoromethyl phthalate (organic solvent) in the electrolyte solvent is 66.7 vol%.

[0108] Example 4

[0109] In this example, the electrolyte only contains an electrolyte sodium salt, an organic solvent and an additive (the volume content of the co-solvent in the electrolyte solvent is 0 vol%), and in this example, the additive is fluoroethylene carbonate, and the organic solvent is diethyl phthalate.

[0110] Specifically, the preparation of the electrolyte: diethyl phthalate (organic solvent) and fluoroethylene carbonate (additive) are mixed in a volume ratio of 19:1, sodium hexafluorophosphate (electrolyte sodium salt) is added to the mixed solvent and stirred uniformly to obtain a sodium ion battery electrolyte, wherein the molar concentration of NaPF6 is 1 mol / L.

[0111] The diethyl phthalate (organic solvent) and the fluoroethylene carbonate (additive) are mixed in a volume ratio of 19:1, the volume content of the diethyl phthalate (organic solvent) in the electrolyte solvent is 95 vol%, and the volume content of the fluoroethylene carbonate (additive) in the electrolyte solvent is 5 vol%.

[0112] Example 5

[0113] In this example, the electrolyte contains an electrolyte sodium salt, an organic solvent, an additive and a co-solvent, and in this example, the co-solvent is dimethyl carbonate, the organic solvent is diisobutyl terephthalate, and the additive is fluoroethylene carbonate.

[0114] Specifically, the preparation of the electrolyte: dimethyl carbonate (co-solvent), diisobutyl terephthalate (organic solvent) and fluoroethylene carbonate (additive) are mixed in a volume ratio of 9:10:1, sodium perchlorate (electrolyte sodium salt) is added thereto and stirred uniformly to obtain a sodium ion battery electrolyte, wherein the concentration of sodium perchlorate is 2 mol / L.

[0115] The dimethyl carbonate (co-solvent), diisobutyl terephthalate (organic solvent) and fluoroethylene carbonate (additive) are mixed in a volume ratio of 9:10:1, the volume content of dimethyl carbonate (co-solvent) in the electrolyte solvent is 45 vol%, the volume content of diisobutyl terephthalate (organic solvent) in the electrolyte solvent is 50 vol%, and the volume content of fluoroethylene carbonate (additive) in the electrolyte solvent is 5 vol%.

[0116] Comparative Example 1

[0117] Preparation of electrolyte: sodium hexafluorophosphate was added to propylene carbonate and stirred uniformly to obtain a sodium ion battery electrolyte, wherein the molar concentration of sodium hexafluorophosphate was 1 mol / L.

[0118] Comparative Example 2

[0119] Dimethyl carbonate and ethylene carbonate were mixed in a volume ratio of 1:1, and sodium perchlorate was added to obtain a sodium ion battery electrolyte, wherein the concentration of sodium perchlorate was 2 mol / L.

[0120] Comparative Example 3

[0121] Sodium bisfluoromethylsulfonylimide was added to ethylene glycol dimethyl ether and stirred uniformly to obtain a sodium ion battery electrolyte, wherein the molar concentration of sodium bisfluoromethylsulfonylimide was 3 mol / L.

[0122] Comparative Example 4

[0123] Propylene carbonate and fluoroethylene carbonate were mixed in a volume ratio of 19:1, and sodium hexafluorophosphate was added to the mixed solvent and stirred uniformly to obtain a sodium ion battery electrolyte, wherein the molar concentration of NaPF6 was 1 mol / L.

[0124] Comparative Example 5

[0125] Dimethyl carbonate, ethylene carbonate and fluoroethylene carbonate were mixed in a volume ratio of 45:50:5, and sodium perchlorate was added and stirred uniformly to obtain a sodium ion battery electrolyte, wherein the concentration of sodium perchlorate was 2 mol / L.

[0126] The electrolytes prepared in Examples 1-5 and Comparative Examples 1-5 were respectively assembled to form Example 1 battery, Example 2 battery, Example 3 battery, Example 4 battery, Example 5 battery, Comparative Example 1 battery, Comparative Example 2 battery and Comparative Example 3 battery, Comparative Example 4 battery and Comparative Example 5 battery.

[0127] Performance test experiments were performed on Example 1 battery-Example 5 battery, and Comparative Example 1 battery-Comparative Example 5 battery.

[0128] Performance test experiment one - storage performance test

[0129] Storage performance test steps:

[0130] ① The battery to be tested is discharged to 2V in a 0.2C constant current discharge mode, and then charged to 3.4V in a constant current charging mode, and the initial capacity C1 is recorded;

[0131] ② Storage: the battery is placed in a constant temperature oven at a temperature of 60℃ for 7 days, 14 days, 21 days, 28 days, 56 days and 84 days;

[0132] ③ Residual capacity / recovery capacity: discharge to 2V in a 0.2C constant current discharge mode, and record the residual capacity C2, and then perform 3 times of charge-discharge cycles according to the standard charge-discharge mode, and take the maximum discharge capacity as the recovery capacity C3.

[0133] Residual capacity recovery rate = C3 (recovery capacity) / C1 (initial capacity) * 100%

[0134] Residual capacity recovery rate = C3 (recovery capacity) / C1 (initial capacity) * 100%

[0135] According to the above test steps, the storage performance test is performed on the battery of example 1 and the battery of comparative example 1, wherein the positive electrode material of the battery of example 1 and the battery of comparative example 1 is sodium vanadium phosphate, and the negative electrode material of the battery of example 1 and the battery of comparative example 1 is hard carbon.

[0136] Table 1 is the storage performance of the battery of example 1 and the battery of comparative example 1 at 60℃.

[0137] Table 1

[0138] As shown in Table 1, the battery of example 1 has a high residual capacity recovery rate and recovery rate relative to the battery of comparative example 1, and has better storage performance.

[0139] According to the above test steps, the storage performance test is performed on the battery of example 2 and the battery of comparative example 2, wherein the positive electrode material of the battery of example 2 and the battery of comparative example 2 is sodium electric layered oxide, and the negative electrode material of the battery of example 2 and the battery of comparative example 2 is hard carbon.

[0140] Table 2 is the storage performance of the battery of example 2 and the battery of comparative example 2 at 60℃.

[0141] Table 2

[0142] As shown in Table 2, the battery of example 2 has a high residual capacity recovery rate and recovery rate relative to the battery of comparative example 2, and has better storage performance.

[0143] The storage performance test was performed on the battery of Example 3 and the battery of Comparative Example 3 according to the above test procedure, wherein the positive electrode material of the battery of Example 3 and the battery of Comparative Example 3 was sodium electric layered oxide, and the negative electrode material of the battery of Example 3 and the battery of Comparative Example 3 was hard carbon.

[0144] Table 3 is the storage performance of the battery of Example 3 and the battery of Comparative Example 3 at 60°C.

[0145] Table 3

[0146] As shown in Table 3, the battery of Example 3 has high capacity remaining rate and recovery rate relative to the battery of Comparative Example 3, and has better storage performance.

[0147] The storage performance test was performed on the battery of Example 4 and the battery of Comparative Example 4 according to the above test procedure, wherein the positive electrode material of the battery of Example 4 and the battery of Comparative Example 4 was sodium electric layered oxide, and the negative electrode material of the battery of Example 4 and the battery of Comparative Example 4 was hard carbon.

[0148] Table 4 is the storage performance of the battery of Example 4 and the battery of Comparative Example 4 at 60°C.

[0149] Table 4

[0150] As shown in Table 4, the battery of Example 4 has high capacity remaining rate and recovery rate relative to the battery of Comparative Example 4, and has better storage performance.

[0151] The storage performance test was performed on the battery of Example 5 and the battery of Comparative Example 5 according to the above test procedure, wherein the positive electrode material of the battery of Example 5 and the battery of Comparative Example 5 was sodium electric layered oxide, and the negative electrode material of the battery of Example 5 and the battery of Comparative Example 5 was hard carbon.

[0152] Table 5 is the storage performance of the battery of Example 5 and the battery of Comparative Example 5 at 60°C.

[0153] Table 5

[0154] As shown in Table 5, the battery of Example 5 has high capacity remaining rate and recovery rate relative to the battery of Comparative Example 5, and has better storage performance.

[0155] Performance test experiment two - AC impedance test

[0156] AC impedance test method:

[0157] The battery to be tested was charged to 50% SOC after the capacity test was completed, and the AC impedance was tested.

[0158] The Example 1 cell and the Comparative Example 1 cell were tested for AC impedance according to the above method, and FIG. 1 is a comparison of the AC impedance of the Example 1 cell and the Comparative Example 1 cell at room temperature. As can be seen from FIG. 1, the Example 1 cell has a smaller AC impedance than the Comparative Example 1 cell.

[0159] Performance Test Experiment Three - DC Internal Resistance (DCIR) Test

[0160] DC Internal Resistance Test Method:

[0161] The sodium-ion battery was charged to 50% SOC after the capacity test was completed, and the DCIR was tested. The test conditions were to charge with a certain current density for 30 seconds, and DCIR = ΔV / I, where ΔV is the voltage rise of the battery during charging, and I is the charging current.

[0162] The Example 1 cell and the Comparative Example 1 cell were tested for DC internal resistance according to the above method, and FIG. 2 is the DC impedance of the Example 1 cell and the Comparative Example 1 cell at room temperature. As can be seen from FIG. 2, the Example 1 cell has a smaller DC internal resistance than the Comparative Example 1 cell.

[0163] Performance Test Experiment Four - Cycle Performance Test

[0164] The electrolyte prepared in Example 2 and Comparative Example 2 was respectively assembled into a full cell with a sodium battery layered oxide as the positive electrode material and hard carbon as the negative electrode material, forming an Example 2 cell and a Comparative Example 2 cell.

[0165] FIG. 3 is the cycle performance of the sodium battery layered oxide and hard carbon full cells assembled with the electrolyte of Example 2 and Comparative Example 2 at room temperature. As shown in FIG. 3, the sodium battery layered oxide and hard carbon full cell containing the electrolyte of Example 2 has a higher capacity retention rate and coulombic efficiency than the sodium battery layered oxide and hard carbon full cell containing the electrolyte of Comparative Example 2.

[0166] Performance Test Experiment Five - Rate Performance Test

[0167] The electrolyte prepared in Example 3 and Comparative Example 3 was respectively assembled into a full cell with a sodium battery layered oxide as the positive electrode material and hard carbon as the negative electrode material, forming an Example 3 cell and a Comparative Example 3 cell.

[0168] FIG. 4 is the cycle performance of the sodium battery layered oxide and hard carbon full cells assembled with the electrolyte of Example 3 and Comparative Example 3 at room temperature. As shown in FIG. 4, the sodium battery layered oxide and hard carbon full cell containing the electrolyte of Example 3 has a higher capacity at high rate than the sodium battery layered oxide and hard carbon full cell containing the electrolyte of Comparative Example 3.

[0169] The above embodiments mainly describe the differences between the various embodiments, and the optimization features different between the various embodiments can be combined to form a better embodiment without contradiction. For the sake of brevity, details are not repeated here.

[0170] Although some specific embodiments of the present disclosure have been described in detail by examples, those skilled in the art should understand that the above examples are only for illustration, not for limiting the scope of the present disclosure. Those skilled in the art should understand that the above embodiments can be modified without departing from the scope and spirit of the present disclosure. The scope of the present disclosure is defined by the appended claims.

Claims

1. An electrolyte, wherein, The electrolyte comprises: an electrolyte sodium salt; an organic solvent, which is an isophthalate solvent and / or a terephthalate solvent; The volume content of the organic solvent in the electrolyte solvent is more than 50 vol%.

2. The electrolyte of claim 1, wherein, The organic solvent in the electrolyte is an isophthalate solvent and a terephthalate solvent. The volume content of the isophthalate solvent in the electrolyte solvent is greater than that of the terephthalate solvent.

3. The electrolyte of claim 1 or 2, wherein, The electrolyte further comprises a co-solvent, and the volume content of the co-solvent in the electrolyte solvent is 0 vol% to 50 vol%.

4. The electrolyte according to any one of claims 1 to 3, wherein, The electrolyte further comprises an additive, and the volume content of the additive in the electrolyte solvent is 0 vol% to 8 vol%.

5. The electrolyte according to any one of claims 1 to 4, wherein, The chemical structural formula of the isophthalate solvent is chemical structural formula I: R1 and R2 are each selected from one of a linear or branched alkyl group with 1 to 6 carbon atoms, a fluorinated alkyl group, an olefinic group, an acetylenic group, and a silyl group.

6. The electrolyte of any one of claims 1-4, wherein, The chemical structural formula of the terephthalate solvent is chemical structural formula II: R3 and R4 are each selected from one of a linear or branched alkyl group with 1 to 6 carbon atoms, a fluorinated alkyl group, an olefinic group, an acetylenic group, and a silyl group.

7. The electrolyte of any one of claims 1-6, wherein, The organic solvent is diethyl isophthalate.

8. The electrolyte of any one of claims 1-7, wherein, The electrolyte sodium salt is one or a combination of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium methylsulfate, and sodium perchlorate.

9. The electrolyte of any one of claims 1-8, wherein, The concentration of the electrolyte sodium salt ranges from 0.5 mol / L to 3 mol / L.

10. The electrolyte of claim 4, wherein, The additive is one or a combination of vinyl carbonate, fluorinated vinyl carbonate, vinyl sulfate, tris(trimethylsilyl)phosphate, 1,3-propane sultone, methylene methane disulfonate, 1,3,6-hexane trinitrile, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, tris(hexafluoroisopropyl)phosphate.

11. A battery, wherein, The battery comprises the electrolyte according to any one of claims 1 to 10.

Images