Electrolyte solution and sodium-ion battery

Abstract

An electrolyte solution and a sodium-ion battery. The electrolyte solution comprises a sodium salt, an additive, and an organic solvent, wherein the sodium salt comprises sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide, and the additive comprises pentaerythritol bicyclic sulfate; and the electrolyte solution comprises: in percentage by mass, 2-15 wt% of sodium hexafluorophosphate, 0.1-20 wt% of sodium bis(fluorosulfonyl)imide, 0.1-5 wt% of pentaerythritol bicyclic sulfate, and the balance being an organic solvent. The electrolyte solution has relatively strong stability in a room-temperature or high-temperature environment, so that stringent environmental requirements in stages of the preparation, transportation, and storage of electrolyte solutions are reduced to a certain extent, the production cost can be effectively controlled, and when the electrolyte solution is applied to a sodium-ion battery, the cycling stability of the battery can be improved.

Description

Electrolyte and sodium ion battery

[0001] This application requests the priority of the Chinese patent application filed with the China Patent Office on November 2, 2023, with application number 202311449268.9 and invention name “A kind of electrolyte and its application”, the entire contents of which are incorporated by reference into this application. Technical Field

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

[0003] Lithium-ion batteries are widely used in new energy vehicles, various portable electronic devices, and energy storage due to their high energy density, long cycle life, and compact size. However, due to the low lithium reserves and uneven resource distribution, the cost of lithium-ion batteries has been rising year by year, necessitating the development of a new battery system. Sodium, a member of the same family as lithium, has similar chemical properties and is more abundant, with reserves as high as 2.36%. It also offers lower costs and better safety. Furthermore, sodium-ion batteries offer the advantages of high energy density and cost-effectiveness, which can meet the needs of future sustainable energy development. However, sodium-ion batteries still face challenges in high-temperature cycling and storage.

[0004] As an important component of sodium-ion batteries, the electrolyte accounts for a large proportion of the battery, so the performance of the electrolyte will greatly affect the performance of the battery. At present, in order to effectively improve the service life and reliability of sodium-ion batteries in high-temperature storage environments, sodium difluorophosphate and vinyl sulfate are widely used as electrolyte additives. However, electrolytes including sodium difluorophosphate need to be stored at low temperatures to maintain their stability and avoid decomposition at room temperature or high temperature; and because there is trace water in the electrolyte itself, vinyl sulfate is easily hydrolyzed at room temperature or high temperature. The hydrolysis products include sulfuric acid and ethylene glycol monosulfate, which increases the overall acidity of the electrolyte. Moreover, this reaction will be aggravated in high-temperature storage environments, which undoubtedly limits the large-scale application of vinyl sulfate.

[0005] Therefore, electrolytes including vinyl sulfate and / or sodium difluorophosphate often require more stringent environmental control during preparation, transportation and storage, and the electrolyte storage shelf life is short, resulting in high costs.

[0006] Summary of the Invention

[0007] In response to the above-mentioned shortcomings, the present application provides an electrolyte that has strong stability at room temperature or high temperature, thereby reducing the stringent environmental requirements during the preparation, transportation, and storage of the electrolyte to a certain extent, extending the storage life of the electrolyte, and effectively controlling production costs. In a first aspect, the present application provides an electrolyte comprising a sodium salt, an additive, and an organic solvent, wherein the sodium salt comprises sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide, and the additive comprises pentaerythritol bicyclic sulfate;

[0008] The electrolyte comprises, by weight percentage, 2-15 wt% of sodium hexafluorophosphate, 0.1-20 wt% of sodium bis(fluorosulfonyl)imide, 0.1-5 wt% of pentaerythritol bicyclic sulfate, and the balance being an organic solvent.

[0009] Furthermore, the mass percentage of the sodium hexafluorophosphate in the electrolyte is 6 to 14 wt%.

[0010] Furthermore, the mass percentage of the pentaerythritol bicyclic sulfate in the electrolyte is 1-2 wt%.

[0011] Furthermore, the mass percentage of the sodium bis(fluorosulfonyl)imide in the electrolyte is 2-8 wt%.

[0012] Furthermore, the organic solvent includes at least one of carbonates, fluorinated carbonates, carboxylates, fluorinated carboxylates, ethers, and fluorinated ethers.

[0013] Furthermore, the electrolyte further includes a sodium salt additive, and the sodium salt additive includes at least one of sodium perchlorate, sodium bis(oxalatoborate), sodium difluorooxalatoborate, and sodium bis(trifluoromethylsulfonyl)imide.

[0014] Furthermore, the mass percentage of the sodium salt additive in the electrolyte is 0.01 to 1 wt%.

[0015] Furthermore, the electrolyte also includes an organic additive, and the organic additive includes at least one of vinyl ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, 1,6-hexamethylene diisocyanate, ethynyl ethylene carbonate, trans-difluoroethylene carbonate, 1,3-propane sultone, 1,4-propane sultone, 1,3-propylene sultone, 1,3,2-dioxathiolane-2,2-dioxide, 4-propyl-1,3,2-dioxathiolane-2,2-dioxide, methanedisulfonic acid methylene ester, 1,2-ethanedisulfonic anhydride, tris(trimethylsilyl)borate, succinonitrile, (ethoxy)pentafluorocyclotriphosphazene, tert-butylbenzene, tert-amylbenzene, fluorobenzene, and cyclohexylbenzene.

[0016] Furthermore, the mass percentage of the organic additive in the electrolyte is 0.1 to 20 wt%.

[0017] The second aspect of the present application provides a sodium ion battery, which includes the electrolyte provided by the first aspect of the present application. The sodium ion battery provided by the second aspect of the present application has good cycle performance.

[0018] The electrolyte of the present invention includes sodium hexafluorophosphate, sodium bisfluorosulfonyl imide and pentaerythritol bicyclic sulfate, wherein sodium hexafluorophosphate has high conductivity and ion transfer rate, which can improve the conductivity of the entire electrolyte system, but its stability is poor and its safety is not high. The present invention uses sodium hexafluorophosphate and sodium bisfluorosulfonyl imide as the main sodium salt, pentaerythritol bicyclic sulfate as an additive, and limits the mass percentage of sodium hexafluorophosphate, sodium bisfluorosulfonyl imide and pentaerythritol bicyclic sulfate in the electrolyte, so that the three cooperate with each other to finally obtain an electrolyte with strong storage stability. Therefore, the severity of the control of the ambient temperature can be reduced during preparation, storage and use, so that the electrolyte can be stored in harsh environments such as high temperature, thereby improving the storage life of the electrolyte and achieving the purpose of reducing storage and transportation costs. In addition, since the electrolyte has good high temperature stability, it can accelerate infiltration at high temperature, so that good wetting is formed between the electrolyte and the electrode and the diaphragm, improving the problem of poor wettability of the electrolyte in sodium ion batteries. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0020] In a first aspect, the present application provides an electrolyte comprising a sodium salt, an additive, and an organic solvent, wherein the sodium salt comprises sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide, and the additive comprises pentaerythritol bicyclic sulfate;

[0021] The electrolyte comprises, by weight percentage, 2-15 wt% of sodium hexafluorophosphate, 0.1-20 wt% of sodium bis(fluorosulfonyl)imide, 0.1-5 wt% of pentaerythritol bicyclic sulfate, and the balance being an organic solvent.

[0022] The present application does not limit the sources of the components, and any commercially available product or a product prepared by a conventional preparation method familiar to those skilled in the art may be used.

[0023] According to the technical solution provided in this application, by making the electrolyte include sodium hexafluorophosphate, sodium bisfluorosulfonyl imide and pentaerythritol bicyclic sulfate, sodium hexafluorophosphate and sodium bisfluorosulfonyl imide as the main salt of the composite sodium salt, pentaerythritol bicyclic sulfate as the electrolyte additive, and at the same time limiting the mass percentage of the three in the electrolyte, the storage stability of the electrolyte can be significantly increased, especially the storage stability under high temperature and harsh environment, the storage life of the electrolyte is improved, and the purpose of reducing storage and transportation costs is achieved. Based on this phenomenon, the inventor analyzed the raw materials with improved stability and believed that it may be that the combination of sodium hexafluorophosphate, sodium bisfluorosulfonyl imide and pentaerythritol bicyclic sulfate can change the solvation structure of the electrolyte system, forming a more stable solvation structure with sodium ions as the core, pentaerythritol bicyclic sulfate and organic solvent molecules as the middle layer, and hexafluorophosphate ions and bisfluorosulfonyl imide anions as the outer layer, thereby reducing the decomposition of sodium hexafluorophosphate at high temperature. Moreover, when the mass percentages of sodium hexafluorophosphate, sodium bis(fluorosulfonylimide) and pentaerythritol bicyclic sulfate in the electrolyte are within a limited range, the decomposition rate of the sodium salt in a high-temperature environment can be further reduced, so that the stability of the electrolyte in a normal temperature or high-temperature storage environment is significantly improved, thereby reducing the environmental requirements of the electrolyte during preparation, storage or use, thereby achieving the purpose of reducing costs.

[0024] In addition, the sodium ion battery including the above-mentioned electrolyte also has excellent ionic conductivity, electrical conductivity and wetting performance. The reason is that: the electrolyte of the present application limits the mass percentage of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide and pentaerythritol bicyclic sulfate in the electrolyte. The three cooperate with each other and influence each other, so that the electrolyte has good ionic conductivity and electrical conductivity, thereby reducing the internal resistance of the sodium ion battery and improving its first efficiency and rate performance; at the same time, because the electrolyte has good high temperature stability, it can accelerate the wetting at high temperature, so that good wetting is formed between the electrolyte and the electrode and the diaphragm, improving the problem of poor wettability of the electrolyte in the sodium ion battery.

[0025] In one embodiment, the mass percentage of sodium hexafluorophosphate in the electrolyte is 6 to 14 wt %. Within this range, sodium hexafluorophosphate can form a good synergistic effect with sodium bis(fluorosulfonyl)imide and pentaerythritol bicyclic sulfate, thereby making the electrolyte have good high-temperature stability and high ionic conductivity.

[0026] In one specific embodiment, the mass percentage of pentaerythritol bicyclic sulfate in the electrolyte is 1-2 wt %. Within this range, pentaerythritol bicyclic sulfate can better cooperate with sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide, further improving the high-temperature storage stability of the electrolyte. Furthermore, when applied to sodium-ion batteries, pentaerythritol bicyclic sulfate can form a stable and dense SEI film on the positive and negative electrode surfaces earlier during the charge and discharge process, thereby effectively reducing side reactions between the electrolyte and the positive and negative electrodes. This makes the pentaerythritol bicyclic sulfate's effect of improving electrolyte stability more significant, and improves the cycle life and safety performance of the sodium-ion battery.

[0027] In one embodiment, the mass percentage of sodium bis(fluorosulfonyl)imide in the electrolyte is 2-8 wt %. Within this range, sodium bis(fluorosulfonyl)imide can better cooperate with pentaerythritol bicyclic sulfate and sodium hexafluorophosphate, improving the high-temperature storage stability of the electrolyte and further reducing the electrolyte's temperature sensitivity, thereby reducing costs. Furthermore, sodium bis(fluorosulfonyl)imide and sodium hexafluorophosphate can synergize well, effectively inhibiting sodium bis(fluorosulfonyl)imide's corrosion of aluminum foil.

[0028] In a specific embodiment, organic solvent comprises at least a in carbonates, fluorocarbons, carboxylates, fluorocarboxylates, ethers, fluoroether organic solvent.For example, organic solvent can be at least a in propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, propylene carbonate, diethyl carbonate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, methyl trifluoroethyl carbonate, and the application is not too restricted.When organic solvent is the mixture of aforementioned multiple specific compounds, the application is not too restricted to the ratio between each specific compound.

[0029] In one specific embodiment, the electrolyte further includes a sodium salt additive, comprising at least one of sodium perchlorate, sodium bis(oxalatoborate), sodium difluorooxalatoborate, and sodium bis(trifluoromethylsulfonyl)imide. The addition of the sodium salt additive introduces anions that, along with the hexafluorophosphate ions and bis(trifluoromethylsulfonyl)imide anions, contribute to the formation of the outer layer of the solvation structure, thereby further stabilizing the electrolyte system and improving the stability of the electrolyte at room or elevated temperatures.

[0030] In addition, by further adding sodium salt additives to the electrolyte, the resulting sodium ion battery can further promote the formation of SEI film, thereby better avoiding side reactions between the electrolyte and the positive and negative electrodes, and improving the stability of the electrolyte system. At the same time, the anions in the sodium salt additives help to regulate the sodium ion solvation shell, improve the electrolyte ion conductivity, and reduce the migration resistance of sodium ions in the electrolyte, thereby making the sodium ion battery have higher first efficiency and rate performance.

[0031] In one embodiment, the sodium salt additive is present in the electrolyte in an amount of 0.01 to 1 wt %. Within this range, the stability of the electrolyte system at room temperature or high temperature can be further enhanced. Furthermore, the sodium salt additive can significantly enhance the ionic conductivity and electrical conductivity of the electrolyte, thereby improving the initial efficiency and rate performance of the sodium-ion battery.

[0032] In a specific embodiment, the electrolyte further includes an organic additive, and the organic additive includes at least one of vinyl ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, 1,6-hexamethylene diisocyanate, ethynyl ethylene carbonate, trans-difluoroethylene carbonate, 1,3-propane sultone, 1,4-propane sultone, 1,3-propylene sultone, 1,3,2-dioxathiolane-2,2-dioxide, 4-propyl-1,3,2-dioxathiolane-2,2-dioxide, methanedisulfonic acid methylene ester, 1,2-ethanedisulfonic anhydride, tris(trimethylsilyl)borate, succinonitrile, (ethoxy)pentafluorocyclotriphosphazene, tert-butylbenzene, tert-amylbenzene, fluorobenzene, and cyclohexylbenzene. The above-mentioned organic additive has good compatibility with pentaerythritol bicyclic sulfate and can participate in the construction of the intermediate layer in the solvation structure to obtain a more stable electrolyte, thereby further improving the stability of the electrolyte at room temperature or high temperature.

[0033] In addition, by adding organic additives, the SEI film can be generated earlier on the surface of the positive and negative electrodes, further reducing the side reactions between the electrolyte and the positive and negative electrodes, improving the stability of the electrolyte, and improving the wetting effect between the electrolyte and the positive and negative electrodes, solving the problem of poor wettability in sodium ion batteries, and at the same time improving the safety performance of sodium ion batteries.

[0034] In one embodiment, the organic additive comprises 0.1 to 20 wt% of the electrolyte. Within this range, the electrolyte exhibits improved stability while further enhancing wettability between the electrolyte and the positive and negative electrodes, shortening the sodium ion transport path and thereby improving the cycle life and rate performance of the sodium ion battery.

[0035] In a second aspect, the present application provides a sodium ion battery comprising the electrolyte of any one of the above items. Due to the synergistic effect and mutual influence between sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, and pentaerythritol bicyclic sulfate included in the electrolyte, the stability of the electrolyte at room temperature or high temperature is effectively improved, the cost is reduced, and the conductivity and ion transfer rate of the electrolyte are also improved. Therefore, the sodium ion battery not only has high cycle stability and low internal resistance at high temperature, but also has good infiltration effect, which can effectively reduce the production, storage, and transportation costs of the sodium ion battery.

[0036] Hereinafter, a sodium ion battery including the electrolyte of the present application will be described in detail through specific embodiments.

[0037] Example 1

[0038] In a glove box filled with argon, 40 wt% of organic solvents propylene carbonate, 20 wt% of ethyl methyl carbonate, and 20 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0039] Example 2

[0040] In a glove box filled with argon, 40.66 wt% of organic solvents propylene carbonate, 20.32 wt% of ethyl methyl carbonate, and 20.32 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 0.2 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 8.5 wt% of sodium hexafluorophosphate and 6.5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0041] Example 3

[0042] In a glove box filled with argon, 38.24 wt% of organic solvents propylene carbonate, 19.13 wt% of ethyl methyl carbonate, and 19.13 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 11.5 wt% of sodium hexafluorophosphate and 3.5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0043] Example 4

[0044] In a glove box filled with argon, 40 wt% of organic solvents propylene carbonate, 20 wt% of ethyl methyl carbonate, and 20 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 14.5 wt% of sodium hexafluorophosphate and 0.5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0045] Example 5

[0046] In a glove box filled with argon, 40 wt% of organic solvents propylene carbonate, 20 wt% of ethyl methyl carbonate, and 20 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 7 wt% of sodium hexafluorophosphate and 8 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0047] Example 6

[0048] In a glove box filled with argon, 35 wt% of organic solvents propylene carbonate, 17.5 wt% of ethyl methyl carbonate, and 17.5 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 15 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0049] Example 7

[0050] In a glove box filled with argon, 39.7 wt% of organic solvents propylene carbonate, 19.9 wt% of ethyl methyl carbonate, and 19.9 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate, 5 wt% of sodium bis(fluorosulfonyl)imide, and 0.5% of sodium perchlorate were added, and the mixture was stirred evenly to obtain the electrolyte of this embodiment.

[0051] Example 8

[0052] In an argon-filled glove box, 39.4 wt% of propylene carbonate, 19.7 wt% of ethyl methyl carbonate, and 19.7 wt% of diethyl carbonate were mixed as organic solvents, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate, 5 wt% of sodium bis(fluorosulfonyl)imide, and 1.2% of sodium perchlorate were added and stirred uniformly to obtain the electrolyte of this embodiment.

[0053] Example 9

[0054] In a glove box filled with argon, 30.5 wt% of organic solvents propylene carbonate, 15.5 wt% of ethyl methyl carbonate, and 15.5 wt% of diethyl carbonate were mixed, and then 6 wt% of fluoroethylene carbonate, 6 wt% of vinylene carbonate, 6 wt% of 1,3-propane sultone, 4 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0055] Example 10

[0056] In a glove box filled with argon, 41.5 wt% of organic solvents propylene carbonate, 21 wt% of ethyl methyl carbonate, and 21 wt% of diethyl carbonate were mixed, 1.5 wt% of pentaerythritol bicyclic sulfate was added, and finally 10 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0057] Example 11

[0058] In a glove box filled with argon, 43 wt% of organic solvents propylene carbonate, 22 wt% of ethyl methyl carbonate, and 22 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 3 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0059] Example 12

[0060] In a glove box filled with argon, 39.5 wt% of organic solvents propylene carbonate, 19.5 wt% of ethyl methyl carbonate, and 19.5 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 3 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0061] Example 13

[0062] In a glove box filled with argon, 40.7 wt% of organic solvents propylene carbonate, 20.35 wt% of ethyl methyl carbonate, and 20.35 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 0.1 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0063] Example 14

[0064] In an argon-filled glove box, 40.25 wt% of propylene carbonate, 20.125 wt% of ethyl methyl carbonate, and 20.125 wt% of diethyl carbonate were mixed as organic solvents, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred uniformly to obtain the electrolyte of this embodiment.

[0065] Example 15

[0066] In a glove box filled with argon, 39.75 wt% of organic solvents propylene carbonate, 19.875 wt% of ethyl methyl carbonate, and 19.875 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 2 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0067] Example 16

[0068] In a glove box filled with argon, 44 wt% of organic solvents propylene carbonate, 22 wt% of ethyl methyl carbonate, and 22 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 2 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0069] Example 17

[0070] In a glove box filled with argon, 42 wt% of organic solvents propylene carbonate, 21 wt% of ethyl methyl carbonate, and 21 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 6 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0071] Example 18

[0072] In a glove box filled with argon, 38 wt% of organic solvents propylene carbonate, 19 wt% of ethyl methyl carbonate, and 19 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 14 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0073] Example 19

[0074] In a glove box filled with argon, 37.5 wt% of organic solvents propylene carbonate, 18.75 wt% of ethyl methyl carbonate, and 18.75 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 15 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0075] Example 20

[0076] In a glove box filled with argon, 42.45 wt% of organic solvents propylene carbonate, 21.225 wt% of ethyl methyl carbonate, and 21.225 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 0.1 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0077] Example 21

[0078] In a glove box filled with argon, 41.5 wt% of organic solvents propylene carbonate, 20.75 wt% of ethyl methyl carbonate, and 20.75 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 2 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0079] Example 22

[0080] In a glove box filled with argon, 32.5 wt% of organic solvents propylene carbonate, 16.25 wt% of ethyl methyl carbonate, and 16.25 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 20 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0081] Example 23

[0082] In a glove box filled with argon, 41.7 wt% of organic solvents propylene carbonate, 20.85 wt% of ethyl methyl carbonate, and 20.85 wt% of diethyl carbonate were mixed, and then 0.1 wt% of fluoroethylene carbonate and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0083] Example 24

[0084] In a glove box filled with argon, 31.75 wt% of organic solvents propylene carbonate, 15.875 wt% of ethyl methyl carbonate, and 15.875 wt% of diethyl carbonate were mixed, and then 6 wt% of fluoroethylene carbonate, 6 wt% of vinylene carbonate, 6 wt% of 1,3-propane sultone, 2 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate and 5 wt% of sodium bis(fluorosulfonyl)imide were added and stirred evenly to obtain the electrolyte of this embodiment.

[0085] Example 25

[0086] In a glove box filled with argon, 39.994 wt% of organic solvents propylene carbonate, 19.998 wt% of ethyl methyl carbonate, and 19.998 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate, 5 wt% of sodium bis(fluorosulfonyl)imide, and 0.01% of sodium perchlorate were added and stirred evenly to obtain the electrolyte of this embodiment.

[0087] Example 26

[0088] In a glove box filled with argon, 39.5 wt% of organic solvents propylene carbonate, 19.75 wt% of ethyl methyl carbonate, and 19.75 wt% of diethyl carbonate were mixed, and then 1 wt% of fluoroethylene carbonate, 1 wt% of vinylene carbonate, 1 wt% of 1,3-propane sultone, 0.5 wt% of 1,3-propylene sultone, and 1.5 wt% of pentaerythritol bicyclic sulfate were added in sequence. Finally, 10 wt% of sodium hexafluorophosphate, 5 wt% of sodium bis(fluorosulfonyl)imide, and 1% of sodium perchlorate were added, and the mixture was stirred evenly to obtain the electrolyte of this embodiment.

[0089] Comparative Example 1

[0090] The preparation method of the electrolyte in this comparative example is basically the same as that in Example 1, except that vinyl sulfate is used instead of pentaerythritol bicyclic sulfate.

[0091] Comparative Example 2

[0092] The preparation method of the electrolyte in this comparative example is basically the same as that in Example 1, except that sodium difluorophosphate is used instead of pentaerythritol bicyclic sulfate.

[0093] Comparative Example 3

[0094] The preparation method of the electrolyte in this comparative example is basically the same as that in Example 1, except that a mixture of vinyl sulfate and sodium difluorophosphate is used instead of pentaerythritol bicyclic sulfate, wherein the mass percentage of sodium difluorophosphate in the electrolyte is 0.75wt%, the mass percentage of vinyl sulfate in the electrolyte is 0.75wt%, and the other components remain unchanged.

[0095] Comparative Example 4

[0096] The preparation method of the electrolyte of this comparative example is basically the same as that of Example 1, except that sodium perchlorate is used instead of sodium bis(fluorosulfonyl)imide.

[0097] Comparative Example 5

[0098] The preparation method of the electrolyte in this comparative example is basically the same as that in Example 1, except that the mass percentage of pentaerythritol bicyclic sulfate in the electrolyte is 6wt%. At this time, the mass percentage of the organic solvent propylene carbonate in the electrolyte is 37.76wt%, the mass percentage of ethyl methyl carbonate is 18.87wt%, and the mass percentage of diethyl carbonate is 18.87wt%. The other components remain unchanged.

[0099] Comparative Example 6

[0100] The preparation method of the electrolyte in this comparative example is basically the same as that in Example 1, except that lithium hexafluorophosphate is used instead of sodium hexafluorophosphate, and lithium bisfluorosulfonyl imide is used instead of sodium bisfluorosulfonyl imide, and the other parameters remain unchanged.

[0101] Comparative Example 7

[0102] The preparation method of the electrolyte in this comparative example is basically the same as that in Example 1, except that the mass percentage of sodium hexafluorophosphate in the electrolyte is adjusted to 17wt%. At this time, the mass percentage of propylene carbonate, the mass percentage of ethyl methyl carbonate, and the mass percentage of diethyl carbonate in the electrolyte is 37wt%, 18wt%, and 18wt%, respectively, and the other components remain unchanged.

[0103] Comparative Example 8

[0104] The preparation method of the electrolyte in this comparative example is basically the same as that in Example 1, except that the mass percentage of sodium bis(fluorosulfonyl)imide in the electrolyte is adjusted to 22wt%. At this time, the mass percentage of the organic solvent propylene carbonate in the electrolyte is 31wt%, the mass percentage of ethyl methyl carbonate is 16wt%, the mass percentage of diethyl carbonate is 16wt%, and the other components remain unchanged.

[0105] Test example

[0106] The electrolytes prepared in the above examples and comparative examples were divided into a first group of electrolytes, a second group of electrolytes, and a third group of electrolytes. The first group of electrolytes was freshly prepared, the second group of electrolytes was stored at 45° C. for 24 hours, and the third group of electrolytes was stored at room temperature of 25° C. for 180 days. The first group of electrolytes, the second group of electrolytes, and the third group of electrolytes were respectively made into sodium ion batteries. The steps for making the sodium ion batteries are as follows:

[0107] 90wt% NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3 O2 powder, 5wt% polyvinylidene fluoride, 5wt% acetylene black and solvent N-methylpyrrolidone were mixed to obtain a positive electrode active slurry. The slurry was coated on both surfaces of a 16μm thick aluminum foil and dried at 130°C for 12 hours. After drying, it was rolled, slit and welded to the tabs to obtain a positive electrode sheet. The thickness of the positive electrode material layer on one side was 58μm. After cutting, the positive electrode sheet was 558mm long and 55mm wide. 89wt% hard carbon, 1wt% conductive carbon black Super-P and 10wt% polyvinylidene fluoride were mixed to obtain a negative electrode active slurry. The slurry was coated on both surfaces of a 16μm thick aluminum foil and dried at 120°C for 12 hours. After drying, it was rolled, slit and welded to the tabs to obtain a negative electrode sheet. The thickness of the negative electrode material layer on one side was 67μm. After cutting, the negative electrode sheet was 708mm long and 59mm wide. The diaphragm uses a PE-coated ceramic diaphragm purchased from Xingyuan Materials. The model is PE ceramic 16+4, and the total thickness of the diaphragm is 20μm.

[0108] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive and negative electrode sheets to act as an insulator, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 85°C. The first, second, and third electrolytes prepared above are injected respectively, with an injection coefficient of 5g / Ah. After vacuum packaging, standing, forming, shaping, and sorting, a sodium ion battery is obtained. The standing time is 48 hours, and the formation step is 0.02C charging to 3.4V, then 0.2C charging to 3.8V, and then 0.5C charging to a formation upper limit voltage of 4V. The formation temperature is 45°C.

[0109] The sodium ion battery comprising the first group of electrolytes, the sodium ion battery comprising the second group of electrolytes, and the sodium ion battery comprising the third group of electrolytes prepared above were subjected to first efficiency, cycle performance, DCR direct current internal resistance, and wettability tests:

[0110] (1) 25℃ initial test

[0111] After the sodium ion battery is formed, the total charging capacity of the entire formation process is recorded, recorded as C1; after aging at 45°C for 24 hours, the first efficiency test is carried out at 25°C. The test steps are as follows: charge to 4.0V at a current of 0.2C, then switch to constant voltage charging with a cut-off current of 0.05C, and record the total charging capacity of the charging process, recorded as C2; after standing for 5 minutes, discharge to 1.5V at a current of 0.2C, and record the discharge capacity, recorded as C3. The first efficiency at 25°C is calculated as: first efficiency = C3 / (C1+C2)×100%

[0112] (2) Cycle performance

[0113] At 25°C and 45°C, respectively, the sodium ion battery prepared above was charged at a constant current of 0.2C to a voltage of 3.9V, then charged at a constant voltage of 3.9V with a cutoff current of 0.05C. After being left for 10 minutes, it was discharged at a constant current of 0.5C to 3.0V. This process step was repeated, and the number of cycles when the capacity decayed to 80% of the first cycle capacity was recorded. The test results are shown in Tables 1, 2 and 3.

[0114] (3) DCR DC internal resistance test

[0115] The sodium ion battery prepared above was subjected to a DC internal resistance test and calculation test at 0°C, 25°C and 45°C, respectively. The test steps were as follows: 0.2C constant current charging to a voltage of 4V, then 4V constant voltage charging with a cutoff current of 0.05C, after standing for 5 minutes, discharging at a current of 1C for 30 minutes, then placing it in a high and low temperature charge and discharge test cabinet, setting the corresponding test temperature, standing for 2 hours, and then discharging at a current of 2C for 10 seconds, recording the voltage values ​​of the first and last seconds of discharge, recorded as V1 and V2, respectively, and the DC internal resistance calculation: DCR = (V1-V2) / 2C; the test results are shown in Tables 1, 2 and 3.

[0116] (4) Wettability test

[0117] At 25°C, use a pipette with a range of 1 to 5 μL in a glove box to fill the electrolyte and drop it on the positive and negative electrodes respectively. The compaction density of the positive electrode material layer is 3.5 g / cm 3 The thickness of the positive electrode material layer on one side is 58μm. The size of the positive electrode sheet is a square with a side length of 55mm; the compaction density of the negative electrode material layer is 1.65g / cm 3 , the thickness of the single side of the negative electrode material layer is 67 μm, and the size of the negative electrode sheet is a square with a side length of 59 mm; the time required for one drop of the electrolyte prepared in the above embodiments and comparative examples to be completely absorbed by the electrode sheet is recorded. The test results are shown in Tables 1, 2 and 3. Table 1 is the test results of the sodium ion battery including the first group of electrolytes, Table 2 is the test results of the sodium ion battery including the second group of electrolytes, and Table 3 is the test results of the sodium ion battery including the third group of electrolytes.

[0118] Table 1

[0119] Table 2

[0120] Table 3

[0121] It can be seen from Table 1 and Table 2 that the electrolyte of Example 1-26 has high high temperature stability. After storage at high temperature for 24 hours, the cycle performance, wettability, first effect and DC internal resistance of the sodium ion battery including the electrolyte are all reduced by a small amount. As can be seen from Table 2, the number of cycles at 25 ° C can reach up to 1570 times, and the number of cycles at 45 ° C can reach up to 1152 times; while the electrolyte of Comparative Example 1-8, after high temperature storage, the cycle performance, wettability, first effect and DC internal resistance of the sodium ion battery including the electrolyte are greatly reduced, wherein the maximum number of cycles at 25 ° C is only 1128 times, and the maximum number of cycles at 45 ° C is only 633 times. It can be seen from this that the electrolyte of the present invention has high high temperature storage performance.

[0122] It can be seen from Tables 2 and 3 that the relevant performance of the sodium ion batteries prepared by the electrolytes of Examples 1-26 after being stored at 45°C for 24 hours and at 25°C for 180 days did not change much, but only slightly decreased. However, after the electrolytes of Comparative Examples 1-8 were stored under the same conditions, the relevant performance of the sodium ion batteries prepared decreased significantly. It can be seen that the electrolytes of the present application have excellent stability, can be stored in harsh environments such as high temperature, and have a long storage life.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises a sodium salt, an additive and an organic solvent, wherein the sodium salt comprises sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide, and the additive comprises pentaerythritol bicyclic sulfate; The electrolyte comprises, by weight percentage, 2-15 wt % of sodium hexafluorophosphate, 0.1-20 wt % of sodium bis(fluorosulfonyl)imide, 0.1-5 wt % of pentaerythritol bicyclic sulfate, and the remainder is an organic solvent.

2. The electrolyte according to claim 1, characterized in that The mass percentage of the sodium hexafluorophosphate in the electrolyte is 6-14wt%.

3. The electrolyte according to claim 1 or 2, characterized in that The mass percentage of the pentaerythritol bicyclic sulfate in the electrolyte is 1-2wt%.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The mass percentage of the sodium bis(fluorosulfonyl)imide in the electrolyte is 2-8wt%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The organic solvent includes at least one of carbonate, fluorinated carbonate, carboxylate, fluorinated carboxylate, ether, and fluorinated ether organic solvents.

6. The electrolyte according to any one of claims 1 to 5, characterized in that: The electrolyte also includes a sodium salt additive, and the sodium salt additive includes at least one of sodium perchlorate, sodium bis(oxalatoborate), sodium difluorooxalatoborate, and sodium bis(trifluoromethylsulfonyl)imide.

7. The electrolyte according to claim 6, characterized in that The mass percentage of the sodium salt additive in the electrolyte is 0.01-1 wt %.

8. The electrolyte according to any one of claims 1 to 7, characterized in that: The electrolyte also includes an organic additive, which includes at least one of vinyl ethylene carbonate, fluoroethylene carbonate, vinyl carbonate, 1,6-hexamethylene diisocyanate, ethynyl ethylene carbonate, trans-difluoroethylene carbonate, 1,3-propane sultone, 1,4-propane sultone, 1,3-propylene sultone, 1,3,2-dioxathiolane-2,2-dioxide, 4-propyl-1,3,2-dioxathiolane-2,2-dioxide, methanedisulfonic acid methylene ester, 1,2-ethanedisulfonic anhydride, tris(trimethylsilyl)borate, succinonitrile, (ethoxy)pentafluorocyclotriphosphazene, tert-butylbenzene, tert-amylbenzene, fluorobenzene, and cyclohexylbenzene.

9. The electrolyte according to claim 8, characterized in that The mass percentage of the organic additive in the electrolyte is 0.1-20wt%.

10. A sodium ion battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 1 to 9.

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