Electrolyte and secondary battery

Abstract

The invention discloses an electrolyte and a secondary battery, relates to the technical field of batteries, and aims to solve the problem of poor ion conduction performance in the electrolyte in the charging and discharging process of the secondary battery. The electrolyte solution comprises an electrolyte salt and a trisiloxane solvent, the trisiloxane solvent and cations of the electrolyte salt are solvated to form solvated ions, and the trisiloxane solvent is at least configured to reduce the desolvation energy of the solvated ions; wherein the range of the ratio of the volume of the trisiloxane solvent to the volume of the electrolyte is 0.5-1.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrolyte and a secondary battery. Background Technology

[0002] Driven by the new energy market, rechargeable batteries have experienced unprecedented development. The ion conductivity of the electrolyte in a rechargeable battery directly affects the charge and discharge rate, thus impacting the battery's performance. Poor ion insertion and extraction rates during charge and discharge result in poor ion conductivity of the electrolyte, leading to suboptimal storage and cycle performance, as well as insufficient rate capability. Summary of the Invention

[0003] The purpose of this application is to provide an electrolyte and a secondary battery, which aims to solve the problem of poor ion conductivity in the electrolyte during the charging and discharging process of the secondary battery.

[0004] To achieve the above objectives, this application adopts the following technical solution:

[0005] In a first aspect, this application provides an electrolyte. The electrolyte comprises an electrolyte salt and a trisiloxane solvent. The trisiloxane solvent solvates the cations of the electrolyte salt to form solvated ions. The trisiloxane solvent is at least configured to reduce the desolvation energy of the solvated ions.

[0006] The ratio of the volume of the trisiloxane solvent to the volume of the electrolyte ranges from 0.5 to 1.

[0007] In the electrolyte provided in this application, the trisiloxane solvent molecules contain Si-O bonds, which can participate in the formation of solvated ions from the electrolyte salt cations. Because the d orbitals of silicon atoms and the p orbitals of oxygen atoms in the trisiloxane solvent molecules are pd-conjugated, the lone pair electrons on the oxygen atom are not easily lost, making them relatively stable and less likely to combine with other atoms. This results in fewer donors in the trisiloxane solvent molecules during solvation with the electrolyte salt cations, and a lower desolvation energy for the solvated ions. This allows for fewer solvent molecules to be removed when ions embed into the electrode materials on the positive and negative electrodes during charging and discharging, reducing the desolvation barrier and decreasing resistance during ion migration. This leads to faster ion conduction and improves the storage performance, cycle performance, and rate performance of the ion battery. Furthermore, the Si-O bonds in the trisiloxane solvents also have the ability to remove water and capture HF, giving the trisiloxane solvents a flame-retardant effect. Furthermore, trisiloxane solvents possess excellent liquid range, high flash point, and wide electrochemical window, enabling ion batteries to have a wider operating temperature range, better safety performance, and the ability to operate at higher voltages, further enhancing their cycle life. By setting the volume ratio of trisiloxane solvent to electrolyte within a suitable range, the ion conductivity in the electrolyte is improved.

[0008] In some embodiments, the trisiloxane solvent is selected from at least one of the structures shown in the following general formula (I);

[0009]

[0010] Among them, R1, R2, R3, R4, R5, R6, R7 and R8 may be the same or different, and are independently selected from any one of the following: straight-chain or branched alkyl groups with 1 to 6 carbon atoms, fluoroalkyl groups with 1 to 6 carbon atoms, olefinic groups with 1 to 6 carbon atoms, alkyneic groups with 1 to 6 carbon atoms, and alkoxy groups with 1 to 6 carbon atoms.

[0011] In some embodiments, any one of R1, R2, R3, R4, R5, R6, R7, and R8 is selected from at least one of methyl, ethyl, n-propyl, isopropyl, methoxy, and fluoromethyl.

[0012] In some embodiments, trisiloxane solvents include at least one of octamethyltrisiloxane, octaethyltrisiloxane, octa-n-propyltrisiloxane, octaisopropyltrisiloxane, octamethoxytrisiloxane, monomethoxyheptamethyltrisiloxane, and (1,7)difluoromethyltrisiloxane.

[0013] In some embodiments, trisiloxane solvents are the only solvents used for cationic solvation of electrolyte salts.

[0014] In some embodiments, the electrolyte further includes a diluent. The diluent does not undergo solvation with the cations of the electrolyte salt. The diluent is used at least to dilute trisiloxane solvents.

[0015] In some embodiments, the ratio of the volume of the diluent to the volume of the electrolyte ranges from 0 to 0.5.

[0016] In some embodiments, the diluent is a halogenated solvent.

[0017] In some embodiments, the diluent includes at least one of halolinear carbonates, halolinear carboxylic acids, halosulfonamides, and haloethers.

[0018] In some embodiments, the diluent includes at least one of fluorolinear carbonates, fluorolinear carboxylic acids, fluorosulfonamides, and fluoroethers.

[0019] In some embodiments, the diluent includes at least one selected from: ethyl difluoroacetate, ethyl dichloroacetate, methyl 2,3,3,3-tetrafluoropropionate, methyl difluoroacetate, methyl 2,2-difluoro-2-(fluorosulfonyl)acetate, 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0020] In some embodiments, the electrolyte further includes a film-forming aid. The film-forming aid is configured to promote the formation of a passivation film between the electrode and the electrolyte.

[0021] In some embodiments, the ratio of the mass of the film-forming aid to the mass of the electrolyte ranges from 0 to 0.08.

[0022] In some embodiments, the film-forming aid includes at least one selected from: vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) phosphate, 1,3-propane sulpholactone, methylene disulfonate, 1,3,6-hexanetrionitrile, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, and tris(hexafluoroisopropyl) phosphate.

[0023] In some embodiments, the electrolyte salt may be any one of sodium electrolyte salt, potassium electrolyte salt, or lithium electrolyte salt.

[0024] In some embodiments, the electrolyte sodium salt includes at least one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium methanesulfonate, and sodium perchlorate.

[0025] In some embodiments, the concentration range of the electrolyte salt is 0.5 mol·L⁻¹. -1 ~3mol·L -1 .

[0026] Secondly, this application provides a secondary battery. The secondary battery includes: a positive electrode, a separator, a negative electrode, and an electrolyte as described in any of the above embodiments. Detailed Implementation

[0027] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0028] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0029] In embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, article, or apparatus that includes that element.

[0030] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0031] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0032] Secondary batteries include ion batteries, such as lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries. They are all based on the migration of ions (such as lithium ions, sodium ions, and potassium ions) between positive and negative electrodes (such as positive and negative electrode plates) to achieve the charging and discharging process.

[0033] In some embodiments, a secondary battery is provided, comprising: a positive electrode, a separator, a negative electrode, and an electrolyte.

[0034] Specifically, when an ion battery is charged and discharged, the electrode material on the positive electrode plate will insert or extract ions, and the electrode material on the negative electrode plate will also extract or insert ions accordingly. The ions migrate between the positive and negative electrodes in the electrolyte through the dissociation and recombination of the electrolyte salt, thereby completing the charging and discharging process of the battery.

[0035] The diaphragm is positioned between the positive and negative electrodes, primarily to prevent short circuits between them while allowing ions to pass through. The electrolyte salt dissolves in the electrolyte solution, forming a solution capable of conducting ions.

[0036] In some embodiments, the electrolyte salt may be any one of sodium electrolyte salt, potassium electrolyte salt, or lithium electrolyte salt.

[0037] For example, the electrolyte salt in the electrolyte of a lithium-ion battery is an electrolyte lithium salt.

[0038] For example, the electrolyte salt in the electrolyte of a sodium-ion battery is a sodium electrolyte salt.

[0039] For example, the electrolyte salt in the electrolyte of a potassium-ion battery is a potassium electrolyte salt.

[0040] The electrolyte acts as a conductor between the positive and negative electrodes, serving as the medium for ion migration in a secondary battery and significantly influencing ion conduction. During the charging and discharging process, the migration of ions between the positive and negative electrodes—that is, the rate of insertion and extraction on the electrode materials—significantly affects the battery's charge and discharge performance. Faster ion conduction results in faster charging and discharging speeds, and vice versa. In other words, faster ion conduction in the electrolyte contributes to better battery storage, cycle life, and rate performance.

[0041] Based on this, this application provides an electrolyte. The electrolyte comprises an electrolyte salt and a trisiloxane solvent. The trisiloxane solvent solvates the cations of the electrolyte salt to form solvated ions. The trisiloxane solvent is configured to at least reduce the desolvation energy of the solvated ions.

[0042] It should be noted that electrolyte salt molecules in the electrolyte will dissociate into cations, and solvent molecules will surround the ions in the electrolyte through coordination bonds, hydrogen bonds and dipole interactions, forming solvated ions. During charging and discharging, when the ions approach the surface of the positive and negative electrode plates, they must remove the surrounding solvent molecules in order to embed into the electrode material on the positive and negative electrode plates. This process is called desolvation.

[0043] Trisiloxane solvent molecules contain Si-O bonds and are solvents that participate in the formation of solvated ionic liquids from electrolyte salt cations. Due to the pd conjugation between the d orbitals of silicon atoms and the p orbitals of oxygen atoms in trisiloxane solvent molecules, the lone pair electrons on the oxygen atom are not easily lost, making them relatively stable and less likely to combine with other atoms. This reduces the number of donors in the trisiloxane solvent molecule during the solvation process with electrolyte salt cations, resulting in a lower desolvation energy. This allows for a smaller desolvation barrier to be overcome when ions are embedded in the electrode materials of the positive and negative electrodes during the charging and discharging process of the ion battery. This reduces the resistance during ion migration, increases the ion conduction speed, and improves the storage performance, cycle performance, and rate performance of the ion battery.

[0044] Furthermore, the Si-O bonds in trisiloxane solvents also have the ability to remove water and capture HF, giving trisiloxane solvents flame-retardant properties. In addition, trisiloxane solvents also have excellent liquid range, high flash point and wide electrochemical window, which enables ion batteries to have a wider operating temperature range, better safety performance and the ability to operate at higher voltages. This allows ion batteries to have better storage performance, lower impedance, longer cycle life, better rate performance and better safety performance.

[0045] It should be noted that trisiloxane solvents are chosen over shorter or longer chains primarily because shorter-chain trisiloxane solvents are more toxic, easily vaporize at high temperatures, and have poor solubility for electrolyte salts due to insufficient oxygen content. Longer-chain trisiloxane solvents have higher viscosity, are prone to solidification at low temperatures, and their high oxygen content increases the desolvation energy between ions and the solvent.

[0046] In some embodiments, the ratio of the volume of the trisiloxane solvent to the volume of the electrolyte ranges from 0.5 to 1.

[0047] For example, the ratio of the volume of the trisiloxane solvent to the volume of the electrolyte can be 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc., and there is no limitation here.

[0048] By setting the ratio of the volume of the trisiloxane solvent to the volume of the electrolyte to be within the range of 0.5 to 1, the ratio can be kept within a suitable range, resulting in better ion conductivity in the electrolyte and further improving the storage performance, cycle performance, and rate performance of the ion battery.

[0049] In some embodiments, the trisiloxane solvent is selected from at least one of the structures shown in the following general formula (I);

[0050]

[0051] Among them, R1, R2, R3, R4, R5, R6, R7 and R8 may be the same or different, and are independently selected from any one of the following: straight-chain or branched alkyl groups with 1 to 6 carbon atoms, fluoroalkyl groups with 1 to 6 carbon atoms, olefinic groups with 1 to 6 carbon atoms, alkyneic groups with 1 to 6 carbon atoms, and alkoxy groups with 1 to 6 carbon atoms.

[0052] For example, the straight-chain alkyl group can be methyl, ethyl, propyl, butyl, pentyl, or hexyl, etc., and there is no limitation herein.

[0053] For example, the branched alkyl group can be isopropyl, sec-butyl, tert-butyl, or neopentyl, etc., and there is no limitation herein.

[0054] For example, the fluoroalkyl group can be fluoromethyl, difluoromethyl, trifluoromethyl, 1-fluoroethyl, 2-fluoroethyl, 1,1-difluoroethyl, 1,2-difluoroethyl or trifluoroethyl, etc., and there is no limitation herein.

[0055] For example, the olefin group can be vinyl, propenyl, 2-propenyl, 1-butenyl or 2-butenyl, etc., and there is no limitation herein.

[0056] For example, the alkyne group can be ethynyl, propynyl, 1-butynyl or 2-butynyl, etc., and there is no limitation here.

[0057] For example, the alkoxy group can be methoxy, ethoxy, propoxy, or butoxy, etc., and there is no limitation herein.

[0058] Here, the aforementioned straight-chain or branched alkyl, fluoroalkyl, olefinic, alkyneic, and alkoxy groups also include possible isomers.

[0059] In some embodiments, any one of R1, R2, R3, R4, R5, R6, R7, and R8 is selected from at least one of methyl, ethyl, n-propyl, isopropyl, methoxy, and fluoromethyl.

[0060] Among the R1 to R8 groups of the above-mentioned trisiloxane solvents, alkyl and fluoroalkyl groups have high chemical stability, which enables the electrolyte to maintain stability during the charging and discharging of ion batteries and reduces the occurrence of side reactions; alkoxy groups have good interfacial compatibility with the material surfaces on the positive and negative electrode plates, which helps the ion insertion and extraction process and improves the battery performance; olefin and alkyne groups are easy to polymerize, which is beneficial to the formation of passivation film.

[0061] Here, the passivation film refers to the layer formed on the surface of the electrode materials on the positive and negative electrodes during the initial charge and discharge process of an ion battery, where the electrode materials react with the electrolyte at the solid-liquid interface. The passivation film can be either a solid electrolyte interface (SEI) film on the negative electrode or a chemical-electrochemical interface (CEI) film on the positive electrode. The passivation film is an interface layer with characteristics of a solid electrolyte; it is an electronic insulator but an excellent conductor of ions. Ions can freely intercalate and deintercalate through the passivation film. It also prevents substances in the electrolyte from reacting with the electrode materials or dissolving the electrode materials in the electrolyte. This improves the ion transport speed between the materials on the positive and negative electrodes and the electrolyte, and protects the positive and negative electrodes.

[0062] Moreover, trisiloxane solvents have low polarity, resulting in less dissolution of the passivation film and thus contributing to its stability.

[0063] By setting the types and chain lengths of R1 to R8 groups, the physical properties of trisiloxane solvents, such as density, viscosity, dielectric constant, and melting point, can be adjusted, allowing the electrolyte to be optimized according to different ion battery requirements.

[0064] In some embodiments, the trisiloxane solvent includes at least one of octamethyltrisiloxane, octaethyltrisiloxane, octa-n-propyltrisiloxane, octaisopropyltrisiloxane, octamethoxytrisiloxane, monomethoxyheptamethyltrisiloxane, and (1,7)difluoromethyltrisiloxane.

[0065] The aforementioned trisiloxane solvents not only possess low desolvation energy, excellent liquid range, high flash point, and wide electrochemical window, but also exhibit good chemical stability, making them less prone to reacting with materials on the positive and negative electrode plates. This reduces side reactions during the charging and discharging process of ion batteries, further improving their storage performance, cycle performance, and rate performance.

[0066] In some embodiments, trisiloxane solvents are the only solvents used for cationic solvation of electrolyte salts.

[0067] This ensures that the potential barrier that the ions need to overcome during the charging and discharging process is relatively small, resulting in a faster ion conduction speed.

[0068] In some embodiments, the electrolyte further includes a diluent. The diluent does not undergo solvation with the cations of the electrolyte salt. The diluent is used at least to dilute trisiloxane solvents.

[0069] First, the addition of diluent allows it to form a stable solution that is miscible with trisiloxane solvents. Furthermore, when the diluent does not solvate the electrolyte salt cations, the proportion of trisiloxane solvents in the solvents that do solvate the electrolyte salt cations is relatively high. This ensures that the potential barrier that ions need to overcome during desolvation is smaller during the charging and discharging process, thus guaranteeing faster ion conduction. Simultaneously, the diluent reduces the viscosity of the trisiloxane solvent, making ion migration in the electrolyte easier and accelerating ion conduction. This further improves the storage performance, cycle performance, and rate performance of the ion battery.

[0070] In some embodiments, the ratio of the volume of the diluent to the volume of the electrolyte ranges from 0 to 0.5.

[0071] For example, the ratio of the volume of the diluent to the volume of the electrolyte can be 0, 0.1, 0.2, 0.3, 0.4 or 0.5, etc., and there is no limitation here.

[0072] By setting the above parameters, the ratio of the volume of the diluent to the volume of the electrolyte can be set within a suitable range, and the viscosity of the electrolyte can be within a suitable range, which can help the migration of ions in the electrolyte and thus improve the ion conduction rate.

[0073] In some embodiments, the diluent includes a halogenated solvent.

[0074] Understandably, on the one hand, the presence of halogen atoms (such as fluorine, chlorine, bromine, and iodine) gives the molecule a certain degree of polarity. Halogen atoms are highly electronegative, attracting electrons and resulting in an uneven charge distribution within the molecule, forming polar molecules. Trisiloxane solvents are mainly composed of nonpolar methyl groups and silicon-oxygen bonds. The oxygen atoms in the molecular structure are also electronegative, affecting the polarity of the molecule. Furthermore, the interactions between trisiloxane solvent molecules can also contribute to their polar characteristics through inductive effects and other mechanisms. Therefore, this "like dissolves like" principle gives halogenated solvents and trisiloxane solvents excellent compatibility. On the other hand, the high electronegativity of halogen atoms gives them a strong electron-withdrawing ability, allowing them to exist stably in compounds without easily losing electrons. When the diluent includes a halogenated solvent, the chemical bonds formed between halogen atoms and carbon or other elements (such as carbon-halogen bonds) have high bond energies, making the halogenated solvent relatively stable. Therefore, halogenated solvents are less likely to form solvated ions with the cations of electrolyte salts. Thus, compared to halogenated solvents, trisiloxane solvents are more likely to form solvated ions with the cations of electrolyte salts, and their low desolvation energy results in faster ion conduction in the electrolyte. This further improves the storage performance, cycle performance, and rate performance of ion batteries.

[0075] In some embodiments, the diluent includes at least one of halolinear carbonates, halolinear carboxylic acids, halosulfonamides, and haloethers.

[0076] Here, "linear" in halolinear carbonates and halolinear carboxylic esters refers to the fact that the atoms or groups of atoms in the molecule are connected in a straight line by covalent bonds, without branching or cyclic structures.

[0077] Understandably, the aforementioned halogenated linear carbonates, halogenated linear carboxylic esters, halogenated sulfonamides, and halogenated ethers possess high electrochemical stability, conductivity, low surface tension, low toxicity, and good compatibility, which can improve the stability of electrolytes and broaden their application range.

[0078] In some embodiments, the diluent includes at least one of fluorolinear carbonates, fluorolinear carboxylic acids, fluorosulfonamides, and fluoroethers.

[0079] Understandably, fluorine is a strong electron-withdrawing atom. Replacing hydrogen in carbonate, carboxylic acid esters, sulfonamide, and ether groups with fluorine can significantly improve the antioxidant capacity of the diluent, thereby enhancing the stability of the electrolyte.

[0080] In some embodiments, the diluent includes at least one selected from: ethyl difluoroacetate, ethyl dichloroacetate, methyl 2,3,3,3-tetrafluoropropionate, methyl difluoroacetate, methyl 2,2-difluoro-2-(fluorosulfonyl)acetate, 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0081] The aforementioned ethyl difluoroacetate, ethyl dichloroacetate, methyl 2,3,3,3-tetrafluoropropionate, methyl difluoroacetate, methyl 2,2-difluoro-2(fluorosulfonyl)acetate, 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether all exhibit excellent compatibility with trisiloxane solvents, further enhancing the stability of the electrolyte.

[0082] In some embodiments, the electrolyte further includes a film-forming aid. The film-forming aid is configured to promote the formation of a passivation film between the positive and negative electrode plates and the electrolyte.

[0083] As mentioned above, during the first charge and discharge of an ion battery, a passivation film will form on the surface of the electrode materials and electrolyte at the solid-liquid interface on the positive and negative electrode plates. Adding film-forming aids to the electrolyte can stabilize the structure and composition of the passivation film, reduce its decomposition and reconstruction during charge and discharge, promote the formation of the passivation film, and help improve the transport speed of ions between the materials and electrolyte on the positive and negative electrode plates, thereby improving the performance of the ion battery.

[0084] In some embodiments, the ratio of the mass of the film-forming aid to the mass of the electrolyte ranges from 0 to 0.08.

[0085] For example, the ratio of the mass of the film-forming aid to the mass of the electrolyte can be 0, 0.02, 0.04, 0.06 or 0.08, etc., and there is no limitation here.

[0086] When the ratio of the mass of the film-forming aid to the mass of the electrolyte is large, such as greater than 0.08, it may participate in the solvation structure of ions, increase the desolvation energy, increase the solubility of the passivation film in the electrolyte, and reduce the performance of the ion battery.

[0087] By setting the ratio of the mass of the film-forming aid to the mass of the electrolyte within a suitable range, the formation of the passivation film is promoted, and the passivation film has a certain degree of density. This helps to improve the transport speed of ions between the materials on the positive and negative electrode plates and the electrolyte, thereby improving the performance of the ion battery.

[0088] In some embodiments, the film-forming aid includes at least one selected from: vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) phosphate, 1,3-propane sulpholactone, methylene disulfonate, 1,3,6-hexanetrionitrile, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, and tris(hexafluoroisopropyl) phosphate.

[0089] The aforementioned film-forming aids help to form a tightly structured passivation film, which helps to improve the transport speed of ions between the materials and electrolyte on the positive and negative electrode plates, thereby improving the performance of the ion battery.

[0090] The electrolyte described in any of the above embodiments can be used in ion batteries, such as lithium-ion batteries, sodium-ion batteries, or potassium-ion batteries, and can achieve good storage performance, cycle performance, and rate performance.

[0091] In some embodiments, the electrolyte sodium salt includes at least one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium methanesulfonate, and sodium perchlorate.

[0092] In some embodiments, the concentration range of the electrolyte salt is 0.5 mol·L⁻¹. -1 ~3mol·L -1 .

[0093] For example, the concentration of the electrolyte salt can be 0.5 mol·L⁻¹. -1 1 mol·L -1 1.5 mol·L -1 2 mol·L -1 2.5 mol·L -1or 3 mol·L -1 There are no restrictions here.

[0094] When the concentration of electrolyte salt is high, for example greater than 3 mol·L⁻¹ -1 Enhanced interactions between sodium ions in the electrolyte (such as the formation of ion pairs) can lead to a decrease in sodium ion conduction velocity, thus affecting the performance of sodium-ion batteries.

[0095] When the concentration of electrolyte salt is low, for example less than 0.5 mol·L⁻¹ -1 This may cause the sodium ion concentration near the negative electrode to drop rapidly, while the sodium ion concentration near the positive electrode is relatively high. This concentration gradient will increase the internal resistance of the sodium battery and reduce the performance of the sodium-ion battery.

[0096] The concentration range of the electrolyte salt is 0.5 mol·L⁻¹. -1 ~3mol·L -1 The settings allow the concentration of electrolyte salts to be set within a suitable range, ensuring that the sodium ion concentration in the electrolyte remains relatively stable during charging and discharging, thereby increasing the sodium ion conduction speed and improving the performance of sodium-ion batteries.

[0097] The following is a detailed description of the application of electrolytes in ion batteries, taking sodium-ion batteries as an example.

[0098] Example 1

[0099] The electrolyte provided in Example 1 includes: octamethyltrisiloxane as the solvent; and sodium hexafluorophosphate as the electrolyte sodium salt at a concentration of 1 mol / L.

[0100] Example 2

[0101] The electrolyte provided in Example 2 includes: octamethyltrisiloxane as the solvent; 1 mol / L sodium bis(fluorosulfonyl)imide as the electrolyte sodium salt; and fluoroethylene carbonate as the film-forming aid, wherein the mass ratio of fluoroethylene carbonate to the mass of the electrolyte is 0.05.

[0102] Example 3

[0103] The electrolyte provided in Example 3 includes: a solvent consisting of a mixture of octamethyltrisiloxane and octaethyltrisiloxane in a volume ratio of 1:1; and a sodium electrolyte salt consisting of 2 mol / L sodium hexafluorophosphate.

[0104] Example 4

[0105] The electrolyte provided in Example 4 includes: a solvent consisting of a mixture of octamethyltrisiloxane and octaethyltrisiloxane in a volume ratio of 1:1; a sodium electrolyte salt consisting of 2 mol / L sodium bis(fluorosulfonyl)imide; and a film-forming aid consisting of fluoroethylene carbonate, wherein the mass ratio of fluoroethylene carbonate to the mass of the electrolyte is 0.05.

[0106] Example 5

[0107] The electrolyte provided in Example 5 comprises: octamethyltrisiloxane as solvent; methyl 2,3,3,3-tetrafluoropropionate as diluent; wherein the volume ratio of octamethyltrisiloxane to methyl 2,3,3,3-tetrafluoropropionate is 1:1; sodium electrolyte salt is 2 mol / L sodium difluorosulfonamide; and film-forming aid is fluoroethylene carbonate, wherein the mass ratio of fluoroethylene carbonate to electrolyte is 0.05.

[0108] Example 6

[0109] The electrolyte provided in Example 6 includes: octamethyltrisiloxane as the solvent; 1 mol / L sodium bis(fluorosulfonyl)imide as the electrolyte sodium salt; and fluoroethylene carbonate as the film-forming aid, wherein the mass ratio of fluoroethylene carbonate to the mass of the electrolyte is 0.1.

[0110] Comparative Example 1

[0111] The electrolyte provided in Comparative Example 1 includes: propylene carbonate as the solvent; and sodium hexafluorophosphate as the electrolyte sodium salt at a concentration of 1 mol / L.

[0112] Comparative Example 2

[0113] The electrolyte provided in Comparative Example 2 includes: propylene carbonate as solvent; sodium hexafluorophosphate as electrolyte sodium salt at 1 mol / L; fluoroethylene carbonate as film-forming aid; and the mass ratio of fluoroethylene carbonate to electrolyte mass is 0.05.

[0114] Comparative Example 3

[0115] The electrolyte provided in Comparative Example 3 includes: a solvent consisting of a mixture of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1; and a sodium electrolyte salt consisting of 2 mol / L sodium hexafluorophosphate.

[0116] Comparative Example 4

[0117] The electrolyte provided in Comparative Example 4 includes: a solvent consisting of a mixture of dimethyl carbonate and ethylene carbonate in a volume ratio of 1:1; a sodium electrolyte salt of 2 mol / L sodium bis(fluorosulfonyl)imide; and a film-forming aid of fluoroethylene carbonate, wherein the mass ratio of fluoroethylene carbonate to the mass of the electrolyte is 0.05.

[0118] Comparative Example 5

[0119] The electrolyte provided in Comparative Example 5 includes: a solvent consisting of a mixture of octamethyltrisiloxane and ethylene carbonate in a volume ratio of 1:1; and a sodium electrolyte salt consisting of 2 mol / L sodium hexafluorophosphate.

[0120] Performance testing

[0121] 1. Storage Performance Test: The sodium-ion battery packs of each embodiment and comparative example were converted into sodium-ion batteries with sodium vanadium phosphate as the electrode material on the positive electrode and hard carbon as the electrode material on the negative electrode. The sodium-ion batteries of each embodiment and comparative example were then subjected to the following tests, and the results are detailed in Table 1.

[0122] (1) The battery under test is discharged to 2V in 0.2C constant current discharge mode, and then charged to 3.4V in 0.2C constant current charging mode. This is recorded as the initial capacity C1.

[0123] (2) Storage: Store the batteries in a constant temperature chamber at 60°C for 7, 14, 21, 28, 56 and 84 days;

[0124] (3) Remaining capacity / recovery capacity: Discharge to 2V in 0.2C constant current discharge mode and record the remaining capacity C2. Then perform 3 charge and discharge cycles in standard charge and discharge mode and take the maximum discharge capacity as the recovery capacity C3.

[0125] Capacity remaining rate = C2 (remaining capacity) / C1 (initial capacity) * 100%;

[0126] Capacity recovery rate = C3 (recovered capacity) / C1 (initial capacity) * 100%.

[0127] Table 1. Storage performance results of sodium-ion batteries in the examples and comparative examples.

[0128]

[0129] As can be seen from Table 1 above, the remaining capacity and recovery rate of the sodium-ion batteries in Examples 1 to 6 are higher than those in Comparative Examples 1 to 5, indicating that the sodium-ion batteries in Examples 1 to 6 have better storage performance. This may be related to the use of trisiloxane solvents in the electrolyte of this application, which results in a lower desolvation energy of sodium ions during the charging and discharging process.

[0130] Comparing the data from Examples 2 and 1, and from Examples 4 and 3, it is evident that adding fluoroethylene carbonate (film-forming aid) to the electrolyte further improves battery storage performance. This is mainly because the film-forming aid forms a better passivation film during formation (the first charge of the sodium-ion battery) and capacity testing (charging and discharging the battery), while a small amount of the film-forming aid is consumed during capacity testing without affecting the solvation structure of sodium ions in the electrolyte. Comparing the data from Examples 2 and 6, the sodium-ion battery in Example 2 has a higher capacity retention rate and recovery rate, resulting in better storage performance. This indicates that excessive fluoroethylene carbonate (film-forming aid) content will participate in the solvation structure of sodium ions, increasing desolvation energy, increasing the solubility of the passivation film in the electrolyte, and reducing battery storage performance.

[0131] Comparing the data of Example 1 and Comparative Example 5, the sodium-ion battery of Example 1 has a high capacity remaining rate and recovery rate, and better storage performance. This indicates that when strong solvation such as carbonate is added to trisiloxane solvents, the battery performance will be degraded. This is mainly because the two solvents are not miscible. Strong solvation of carbonate leads to an increase in desolvation energy and an increase in the dissolution of the passivation film.

[0132] Comparing the data of Example 5 and Comparative Example 5, the sodium-ion battery of Example 5 has a high capacity remaining rate and recovery rate, and better storage performance, indicating that halogen-containing diluents are more suitable than carbonates as diluents for trisiloxane compounds.

[0133] 2. Cycle Performance Test: The sodium-ion battery packs of each embodiment and comparative example were converted into sodium-ion batteries with sodium-ion layered oxide as the electrode material on the positive electrode and hard carbon as the electrode material on the negative electrode. The sodium-ion batteries of each embodiment and comparative example were then tested as follows, and the results are detailed in Table 2.

[0134] (1) After the reaction is completed, the ratio of the capacity of the first cycle at -20℃ and 0.5C to the capacity of the first cycle at 25℃ and 0.5C is tested.

[0135] (2) Test the capacity retention rate after 500 cycles at 25°C and 0.5°C.

[0136] (3) Capacity retention rate after 250 cycles at 45°C and 1°C.

[0137] Table 2. Cyclic performance results of sodium-ion batteries in each embodiment and comparative example.

[0138]

[0139] As can be seen from Table 2 above, the capacity retention rates of sodium-ion batteries in Examples 1 to 6 after 500 cycles at 25°C and 0.5C, after 250 cycles at 45°C and 1C, and the ratio of the capacity of the first cycle at 20°C and 0.5C to the capacity of the first cycle at 25°C and 0.5C are all higher than those of sodium-ion batteries in Comparative Examples 1 to 5. This indicates that the sodium-ion batteries in Examples 1 to 6 have better cycle performance, with better room temperature cycle performance and high and low temperature performance. This may be related to the use of trisiloxane solvents in the electrolyte of this application, which results in a lower desolvation energy of sodium ions during the charging and discharging process.

[0140] Comparing the data from Examples 2 and 1, and Examples 4 and 3, it is evident that adding fluoroethylene carbonate (film-forming aid) to the electrolyte 50 containing trisiloxane solvents further improves battery cycle performance. This is mainly because the film-forming aid forms a better passivation film during the formation and capacity testing process. Comparing Examples 2 and 6, as the ratio of film-forming aid mass to electrolyte mass increases from 0.05 to 0.1, the cycle performance of the sodium-ion battery decreases. This is primarily because excessive film-forming aid dissolves the passivation film and participates in the sodium-ion solvation structure, increasing desolvation energy.

[0141] Comparing the data of Example 1 and Comparative Example 5, the sodium-ion battery of Example 1 has better cycle performance, indicating that the addition of strong solvation such as carbonate to trisiloxane solvents will degrade battery performance. This is mainly due to the poor miscibility of the two solvents. Strong solvation of carbonate leads to an increase in desolvation energy and an increase in the dissolution of the passivation film.

[0142] Comparing the data of Example 5 and Comparative Example 5, the sodium-ion battery of Example 5 has better cycle performance, indicating that halogen-containing diluents are more suitable than carbonates as diluents for trisiloxane compounds.

[0143] 3. Rate Performance Testing: The sodium-ion battery packs of each embodiment and comparative example were converted into sodium-ion batteries with sodium-ion layered oxide as the positive electrode material and hard carbon as the negative electrode material. The capacity retention rate of the sodium-ion batteries of each embodiment and comparative example was then tested at 0.2C, 0.5C, 1C, 2C, 3C, 4C, 5C, and 6C, respectively. The results are detailed in Table 3.

[0144] Table 3. Rate performance results of sodium-ion batteries in each embodiment and comparative example.

[0145]

[0146] As shown in Table 3, the retention rates of the sodium-ion batteries in Examples 1 to 6 at 0.2C, 0.5C, 1C, 2C, 3C, 4C, 5C, and 6C are all significantly higher than those of the sodium-ion batteries in Comparative Examples 1 to 5 at the same rates, indicating that the sodium-ion batteries in Examples 1 to 6 have better rate performance. This may be related to the use of trisiloxane solvents in the electrolyte of this application, which results in a lower desolvation energy of sodium ions during charging and discharging.

[0147] Comparing the data from Examples 2 and 1, and from Examples 4 and 3, it is evident that adding fluoroethylene carbonate (film-forming aid) to the electrolyte containing trisiloxane solvents further improves the battery rate performance. This is mainly because the film-forming aid forms a better passivation film during the formation and capacity testing process. Comparing the data from Examples 2 and 6, increasing the ratio of film-forming aid mass to electrolyte mass from 0.05 to 0.1 leads to a decrease in the rate performance of the sodium-ion battery. This is primarily because excessive film-forming aid dissolves the passivation film and participates in the sodium-ion solvation structure, increasing the desolvation energy.

[0148] Comparing the data of Example 1 and Comparative Example 5, the sodium-ion battery of Example 1 has better rate performance, indicating that the addition of strong solvation such as carbonate to trisiloxane solvents will degrade battery performance. This is mainly due to the poor miscibility of the two solvents. Strong solvation of carbonate leads to an increase in desolvation energy and an increase in the dissolution of the passivation film.

[0149] Comparing the data of Example 5 and Comparative Example 5, the sodium-ion battery of Example 5 has better rate performance, indicating that halogen-containing diluents are more suitable than carbonates as diluents for trisiloxane compounds.

[0150] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An electrolyte, characterized in that, include: Electrolyte salt and trisiloxane solvent; the trisiloxane solvent solvates the cation of the electrolyte salt to form a solvated ion, and the trisiloxane solvent is at least configured to: reduce the desolvation energy of the solvated ion; The ratio of the volume of the trisiloxane solvent to the volume of the electrolyte ranges from 0.5 to 1.

2. The electrolyte according to claim 1, characterized in that, The trisiloxane solvent is selected from at least one of the structures shown in the following general formula (I); Among them, R1, R2, R3, R4, R5, R6, R7 and R8 may be the same or different, and are independently selected from any one of the following: straight-chain or branched alkyl groups with 1 to 6 carbon atoms, fluoroalkyl groups with 1 to 6 carbon atoms, olefinic groups with 1 to 6 carbon atoms, alkyneic groups with 1 to 6 carbon atoms, and alkoxy groups with 1 to 6 carbon atoms.

3. The electrolyte according to claim 2, characterized in that, R1, R2, R3, R4, R5, R6, R7 and R8 are selected from at least one of methyl, ethyl, n-propyl, isopropyl, methoxy and fluoromethyl.

4. The electrolyte according to any one of claims 1 to 3, characterized in that, The trisiloxane solvents include at least one of the following: octamethyltrisiloxane, octaethyltrisiloxane, octa-n-propyltrisiloxane, octaisopropyltrisiloxane, octamethoxytrisiloxane, monomethoxyheptamethyltrisiloxane, and (1,7)difluoromethyltrisiloxane.

5. The electrolyte according to claim 1, characterized in that, The trisiloxane solvent is the only solvent that can be cationicly solvated with the electrolyte salt.

6. The electrolyte according to claim 1, characterized in that, Also includes: Diluent; The diluent does not undergo solvation with the cations of the electrolyte salt; the diluent is used at least to dilute the trisiloxane solvent.

7. The electrolyte according to claim 6, characterized in that, The ratio of the volume of the diluent to the volume of the electrolyte is in the range of 0 to 0.

5.

8. The electrolyte according to claim 6, characterized in that, The diluent includes a halogenated solvent.

9. The electrolyte according to claim 8, characterized in that, The diluent includes at least one of halogenated linear carbonates, halogenated linear carboxylic acids, halogenated sulfonamides, and halogenated ethers.

10. The electrolyte according to claim 9, characterized in that, The diluent includes at least one of fluorolinear carbonates, fluorolinear carboxylic acids, fluorosulfonamides, and fluoroethers.

11. The electrolyte according to claim 10, characterized in that, The diluent comprises at least one of the following: ethyl difluoroacetate, ethyl dichloroacetate, methyl 2,3,3,3-tetrafluoropropionate, methyl difluoroacetate, methyl 2,2-difluoro-2(fluorosulfonyl)acetate, 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

12. The electrolyte according to claim 1, characterized in that, Also includes: Film-forming aid; the film-forming aid is configured to promote the formation of a passivation film between the electrode sheet and the electrolyte.

13. The electrolyte according to claim 12, characterized in that, The ratio of the mass of the film-forming aid to the mass of the electrolyte is in the range of 0 to 0.

08.

14. The electrolyte according to claim 13, characterized in that, The film-forming aids include at least one of the following: vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilane) phosphate, 1,3-propane sulpholactone, methylene disulfonate, 1,3,6-hexanetrionitrile, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, and tris(hexafluoroisopropyl) phosphate.

15. The electrolyte according to claim 1, characterized in that, The electrolyte salt includes any one of sodium electrolyte salt, potassium electrolyte salt, and lithium electrolyte salt.

16. The electrolyte according to claim 15, characterized in that, The electrolyte sodium salt includes at least one of sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium methanesulfonate, and sodium perchlorate.

17. The electrolyte according to claim 16, characterized in that, In the electrolyte, the concentration range of the electrolyte salt is 0.5 mol·L⁻¹. -1 ~3mol·L -1 .

18. A secondary battery, characterized in that, include: Positive electrode, separator, negative electrode and electrolyte as described in any one of claims 1 to 17.

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