Gel electrolyte, gel battery and preparation method and application thereof

Abstract

The invention provides a gel electrolyte, a gel battery and a preparation method and application thereof. The gel battery is prepared by the following steps: step 1, preparing a functional additive; 2, preparing a gel electrolyte precursor solution: mixing 1, 3-dioxolame, a (4-acetyl-2-fluorophenyl) boric acid / pyrrole polymer and the basic electrolyte, adding an initiator, and stirring to prepare the gel electrolyte precursor solution; and 3, preparing the gel battery. The prepared gel electrolyte has the conductivity of 3.04 * 10 <-3 > mS cm <-1 > at the temperature of-40 DEG C, and is only 7.1 * 10 <-3 > mS cm <-1 > lower than that of a corresponding electrolyte; and the capacity retention ratio of the prepared gel battery after 100 times of 0.1 C cycle test at-40 DEG C is 91%, the problem of rapid attenuation of the battery capacity can be effectively improved, and the cycle stability of the battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, and more particularly to a gel electrolyte, a gel battery and a preparation method and application thereof. BACKGROUND

[0002] Sodium-ion batteries (NIBs) have abundant raw material reserves (2.64wt%), are widely distributed in the earth's crust, and are economical, so sodium-ion batteries may be more suitable for large-scale energy storage applications and are expected to partially replace lithium-ion batteries (LIBs). In recent years, sodium-ion batteries (NIBs) have received unprecedented attention due to their certain advantages and greater potential in LT capacity and safety. Due to the needs of large-scale grid energy storage and space exploration applications, the rapid decline of the specific capacity and cycle stability of the battery at low temperatures has become an urgent problem to be solved. Large-scale energy storage stations in extremely cold regions are usually equipped with auxiliary temperature control systems. Metal foils used as heating elements are placed inside the battery and can be quickly heated by a program control system to ensure stable energy storage. This increases the cost of the energy storage system and reduces the energy density and reliability of the battery. Therefore, it is necessary to further develop batteries that can withstand low temperatures.

[0003] At the same time, the interface problem between the electrode and the electrolyte at low temperature is more severe, especially the desolvation energy barrier of sodium ions increases significantly during charging, which is more prone to form dendrites on the surface of the negative hard carbon, exacerbating the side reactions between the active material and the electrolyte, thereby causing serious safety hazards such as fire and explosion. Solving these safety problems is crucial for practical applications. In this case, solid-state batteries (SSBs) show great potential because they have a breakthrough potential in safety and energy density, can effectively make up for the shortcomings of organic electrolytes, prevent organic electrolyte leakage, prevent organic small molecule cathode materials from dissolving in organic electrolytes, and improve the stability of the battery system. The gel electrolyte can also resist dendrite penetration, thereby achieving higher energy density. In addition, solid-state electrolytes are not flammable, which significantly improves the safety of the battery. However, the contact area between the solid-state electrolyte and the electrode material of SSBs is small, resulting in a large contact resistance, which affects the transmission speed of ions, and research on the performance of SSBs in low-temperature environments is still limited.

[0004] Therefore, it is necessary to provide a gel electrolyte, a gel battery and a preparation method and application thereof to solve the problems in the prior art. SUMMARY

[0005] To achieve the object, the application provides a gel electrolyte, a gel battery and a preparation method and application thereof, so as to improve the poor interface compatibility between the electrode and the gel electrolyte, the poor conductivity of the gel battery and the reduction of the safety hazard of the battery in the prior art, and to improve the market application of the low-temperature battery.

[0006] To achieve the above object, the technical scheme of the application is as follows: In a first aspect, a preparation method of a gel battery is provided, comprising the following steps: Step 1: preparing a functional additive, (4-acetyl-2-fluorophenyl)boronic acid and pyrrole are reacted under the action of methanesulfonic acid to obtain a (4-acetyl-2-fluorophenyl)boronic acid / pyrrole polymer; Step 2: preparing a gel electrolyte precursor solution, 1,3-dioxolane, the (4-acetyl-2-fluorophenyl)boronic acid / pyrrole polymer and a basic electrolyte are mixed, and then an initiator is added to prepare the gel electrolyte precursor solution by stirring; Step 3: preparing a gel battery, the positive electrode, the negative electrode and the gel electrolyte precursor solution are assembled, and then the gel battery is prepared by baking.

[0007] In some embodiments, the basic electrolyte comprises sodium hexafluorophosphate, a solvent and an additive.

[0008] In some embodiments, the additive is at least one selected from sodium difluorophosphate, tris(trimethylsilyl)phosphite (TMSPi), bis(2,2,2-trifluoroethyl)carbonate (TFEC), 2,2,3,4,4,4-hexafluorobutyl acrylate (HFA) and 1,3,2-dioxazolothiophene-2,2-dioxide (DTD).

[0009] In some embodiments, the solvent is at least one selected from propylene carbonate (PC), ethylene carbonate (EC) and methyl ethyl carbonate (EMC).

[0010] In some embodiments, in the basic electrolyte, the sodium hexafluorophosphate accounts for 0.1%-25%, the ethylene carbonate accounts for 15%-40%, the propylene carbonate accounts for 15%-40% and the methyl ethyl carbonate accounts for 10%-35% by weight percentage.

[0011] In some embodiments, in the basic electrolyte, the sodium difluorophosphate accounts for 0.0001-0.1%, the tris(trimethylsilyl)phosphite accounts for 0.01-0.1%, the bis(2,2,2-trifluoroethyl)carbonate accounts for 0.01-0.5%, the 2,2,3,4,4,4-hexafluorobutyl acrylate accounts for 0.01-0.15% and the 1,3,2-dioxazolothiophene-2,2-dioxide accounts for 0.0001-0.1% by weight percentage.

[0012] In some embodiments, the basic electrolyte comprises sodium hexafluorophosphate in an amount of 0.1-25% by weight, preferably 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 5%, 10%, 15%, 20%, 25%, or any range formed by any two of the above values.

[0013] In some embodiments, the basic electrolyte comprises vinyl carbonate in an amount of 15-40% by weight, preferably 15%, 20%, 25%, 30%, 35%, 40%, or any range formed by any two of the above values.

[0014] In some embodiments, the basic electrolyte comprises propylene carbonate in an amount of 15-40% by weight, preferably 15%, 20%, 25%, 30%, 35%, 40%, or any range formed by any two of the above values.

[0015] In some embodiments, the basic electrolyte comprises methyl ethyl carbonate in an amount of 10-35% by weight, preferably 10%, 14%, 15%, 16%, 20%, 25%, 28%, 29%, 30%, 35%, or any range formed by any two of the above values.

[0016] In some embodiments, the basic electrolyte comprises sodium difluorophosphate in an amount of 0.0001-0.1% by weight, preferably 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, or any range formed by any two of the above values.

[0017] In some embodiments, the basic electrolyte comprises tris(trimethylsilyl)phosphite (TMSPi) in an amount of 0.01-0.1% by weight, preferably 0.01%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, or 0.1%, or any range formed by any two of the above values.

[0018] In some embodiments, the basic electrolyte comprises bis(2,2,2-trifluoroethyl) carbonate in an amount of 0.01-0.5% by weight, preferably 0.01%, 0.05%, 0.06%, 0.07%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, or any range formed by any two of the above values.

[0019] In some embodiments, the 2,2,3,4,4,4-hexafluorobutyl acrylate accounts for 0.01-0.15% by mass in the base electrolyte, preferably 0.01%, 0.05%, 0.06%, 0.07%, 0.08%, 0.1%, 0.12%, 0.15%, and any one component within the range formed by any two of the above values.

[0020] In some embodiments, the 1,3,2-dioxazolothiophene-2,2-dioxide DTD accounts for 0.0001-0.1% by mass in the base electrolyte, preferably 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, and any one component within the range formed by any two of the above values.

[0021] In some embodiments, the base electrolyte is prepared by mixing sodium hexafluorophosphate and the solvent, adding the additive, and mixing uniformly.

[0022] In some embodiments, the molar ratio of (4-acetyl-2-fluorophenyl)boronic acid to pyrrole is 1:(1-5), preferably 1:1, 1:2, 1:3, 1:4, 1:5, and any one component within the range formed by any two of the above values.

[0023] In some embodiments, the molar ratio of (4-acetyl-2-fluorophenyl)boronic acid to methanesulfonic acid is (1-5):1, preferably 1:1, 2:1, 3:1, 4:1, 5:1, and any one component within the range formed by any two of the above values.

[0024] In some embodiments, the mass ratio of 1,3-dioxolane monomer to functional additive is (60-750):1, preferably 60:1, 70:1, 75:1, 80:1, 90:1, 95:1, 100:1, 105:1, 110:1, 150:1, 170:1, 180:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1, 500:1, 650:1, 700:1, 720:1, 750:1, and any one component within the range formed by any two of the above values.

[0025] In some embodiments, the mass ratio of 1,3-dioxolane monomer to base electrolyte is (1-4):(5-60), preferably 1:5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:9, 1:10, 1:15, 1:20, 1:60, and any one component within the range formed by any two of the above values.

[0026] In some embodiments, the initiator is aluminum tris(triflate) (Al(OTf)3).

[0027] In some embodiments, the mass ratio of the 1,3-dioxolane monomer to the initiator is (1-40):1, preferably 1:1, 4:1, 4.5:1, 5:1, 8:1, 9:1, 10:1, 11:1, 12:1, 15:1, 17:1, 18:1, 20:1, 25:1, 30:1, 35:1, 36:1, 40:1, and any one component in the range constituted by any two of the above values.

[0028] In some embodiments, the temperature of the baking is 40-80°C, preferably 45-65°C, preferably 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, and any one component in the range constituted by any two of the above values.

[0029] In some embodiments, the baking time is 6-8h, preferably 6h, 7h, 8h, and any one component in the range constituted by any two of the above values.

[0030] In some embodiments, assembling the battery further comprises using a CR#2032 button cell shell and / or a GF / D glass fiber separator.

[0031] In some embodiments, the positive electrode slurry of the positive electrode comprises at least one of NFPP, PVDF5130, kappa100, and GO.

[0032] In some embodiments, in the positive electrode slurry, the mass ratio of NFPP:PVDF5130:kappa100:GO=90:5:4:1, and the solid content is 40-50%, preferably 40%, 45%, 50%, and any one component in the range constituted by any two of the above values.

[0033] In some embodiments, the positive electrode slurry is coated on the current collector, dried, and sheeted to obtain a positive electrode.

[0034] In some embodiments, the current collector is at least one of an aluminum foil, a composite aluminum foil, a copper foil, a steel mesh, and a foamed nickel.

[0035] In some embodiments, the temperature of the electrode drying is 95-105°C, preferably 95°C, 100°C, 105°C, and any one component in the range constituted by any two of the above values.

[0036] In some embodiments, the electrode is baked for 6-8 hours, preferably 6 hours, 7 hours or 8 hours, and any one of the ranges formed by any two of the above values.

[0037] In some embodiments, the negative electrode is a sodium sheet negative electrode.

[0038] In a second aspect, a gel battery prepared by the method of the present application is provided.

[0039] In a third aspect, a preparation method for preparing a gel electrolyte for a gel battery is provided, comprising the following steps: S1: preparing a base electrolyte: after mixing sodium hexafluorophosphate and a solvent, adding an additive and mixing uniformly to obtain; S2: functional additive: (4-acetyl-2-fluorophenyl) boronic acid and pyrrole are reacted under the action of methanesulfonic acid to obtain (4-acetyl-2-fluorophenyl) boronic acid / pyrrole polymer; S3: preparing a gel electrolyte precursor solution: after mixing 1,3-dioxolane monomer, functional additive and base electrolyte, adding an initiator and mixing uniformly to obtain a gel electrolyte precursor solution; S4: baking the gel electrolyte precursor solution to obtain a gel electrolyte.

[0040] In some embodiments, the base electrolyte comprises sodium hexafluorophosphate, a solvent and an additive.

[0041] In some embodiments, the additive is at least one selected from sodium difluorophosphate, tris(trimethylsilyl)phosphite (TMSPi), bis(2,2,2-trifluoroethyl) carbonate (TFEC), 2,2,3,4,4,4-hexafluorobutyl acrylate (HFA), 1,3,2-dioxazolthiophene-2,2-dioxide (DTD).

[0042] In some embodiments, the solvent is at least one selected from propylene carbonate (PC), ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0043] In some embodiments, in the base electrolyte, sodium hexafluorophosphate accounts for 0.1%-25%, ethylene carbonate accounts for 15%-40%, propylene carbonate accounts for 15%-40%, and ethyl methyl carbonate accounts for 10%-35% by weight percentage.

[0044] In some embodiments, the basic electrolyte comprises, by weight percentage, 0.0001-0.1% of sodium difluorophosphate, 0.01-0.1% of tris(trimethylsilyl)phosphite, 0.01-0.5% of bis(2,2,2-trifluoroethyl)carbonate, 0.01-0.15% of 2,2,3,4,4,4-hexafluorobutyl acrylate, and 0.0001-0.1% of 1,3,2-dioxazolothiophene-2,2-dioxide.

[0045] In some embodiments, the basic electrolyte comprises, by weight percentage, 0.1-25% of sodium hexafluorophosphate, preferably 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 5%, 10%, 15%, 20%, 25%, and any one component within a range defined by any two of the above values.

[0046] In some embodiments, the basic electrolyte comprises, by weight percentage, 15-40% of ethylene carbonate, preferably 15%, 20%, 25%, 30%, 35%, 40%, and any one component within a range defined by any two of the above values.

[0047] In some embodiments, the basic electrolyte comprises, by weight percentage, 15-40% of propylene carbonate, preferably 15%, 20%, 25%, 30%, 35%, 40%, and any one component within a range defined by any two of the above values.

[0048] In some embodiments, the basic electrolyte comprises, by weight percentage, 10-35% of methyl ethyl carbonate, preferably 10%, 14%, 15%, 16%, 20%, 25%, 28%, 29%, 30%, 35%, and any one component within a range defined by any two of the above values.

[0049] In some embodiments, the basic electrolyte comprises, by weight percentage, 0.0001-0.1% of sodium difluorophosphate, preferably 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, and any one component within a range defined by any two of the above values.

[0050] In some embodiments, the tris(trimethylsilyl)phosphite TMSPi accounts for 0.01-0.1% by mass percentage in the base electrolyte, preferably 0.01%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08% or 0.1%, and any one component within the range formed by any two of the above values.

[0051] In some embodiments, the bis(2,2,2-trifluoroethyl)carbonate accounts for 0.01-0.5% by mass percentage in the base electrolyte, preferably 0.01%, 0.05%, 0.06%, 0.07%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%, and any one component within the range formed by any two of the above values.

[0052] In some embodiments, the 2,2,3,4,4,4-hexafluorobutyl acrylate accounts for 0.01-0.15% by mass percentage in the base electrolyte, preferably 0.01%, 0.05%, 0.06%, 0.07%, 0.08%, 0.1%, 0.12%, 0.15%, and any one component within the range formed by any two of the above values.

[0053] In some embodiments, the 1,3,2-dioxazolothiophene-2,2-dioxide DTD accounts for 0.0001-0.1% by mass percentage in the base electrolyte, preferably 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, and any one component within the range formed by any two of the above values.

[0054] In some embodiments, the base electrolyte is prepared by mixing the sodium hexafluorophosphate and the solvent, adding the additive and mixing uniformly.

[0055] In some embodiments, the molar ratio of the (4-acetyl-2-fluorophenyl)boronic acid and the pyrrole is 1:(1-5), preferably 1:1, 1:2, 1:3, 1:4, 1:5, and any one component within the range formed by any two of the above values.

[0056] In some embodiments, the molar ratio of the (4-acetyl-2-fluorophenyl)boronic acid and the methanesulfonic acid is (1-5):1, preferably 1:1, 2:1, 3:1, 4:1, 5:1, and any one component within the range formed by any two of the above values.

[0057] In some embodiments, the mass ratio of the 1,3-dioxolane monomer to the functional additive is (60-750):1, preferably 60:1, 70:1, 75:1, 80:1, 90:1, 100:1, 150:1, 170:1, 180:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1, 500:1, 650:1, 700:1, 720:1, 750:1, and any one component in the range formed by any two of the above values.

[0058] In some embodiments, the mass ratio of the 1,3-dioxolane monomer to the base electrolyte is (1-4):(5-60), preferably 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:15, 1:20, 1:60, and any one component in the range formed by any two of the above values.

[0059] In some embodiments, the initiator is aluminum tris(trifluoromethanesulfonate) (Al(OTf)3).

[0060] In some embodiments, the mass ratio of the 1,3-dioxolane monomer to the initiator is (1-40):1, preferably 1:1, 4:1, 4.5:1, 5:1, 10:1, 15:1, 17:1, 18:1, 20:1, 25:1, 30:1, 35:1, 36:1, 40:1, and any one component in the range formed by any two of the above values.

[0061] In some embodiments, the baking temperature is 45-65℃, preferably 45℃, 50℃, 55℃, 60℃, 65℃, and any one component in the range formed by any two of the above values.

[0062] In some embodiments, the baking time is 6-8h, preferably 6h, 7h, or 8h, and any one component in the range formed by any two of the above values.

[0063] In a fourth aspect, the present application provides a use of the gel electrolyte prepared by the method of the present application, or the gel battery of the present application, or the gel battery prepared by the preparation method of the present application, in an energy storage device.

[0064] In the present application, "low temperature" refers to -40-0℃.

[0065] In the embodiments, "room temperature" refers to room temperature 10-40℃, preferably 20-30℃ or 25℃.

[0066] In this invention, both "gel" and "gel electrolyte" are prepared by baking a gel electrolyte precursor solution. In this invention, "gel" and "gel electrolyte" refer to the same type of substance; the names differ to distinguish them from different experiments.

[0067] In this invention, liquid electrolyte refers to basic electrolyte solution.

[0068] In this invention, the gel electrolyte precursor solution is prepared from a basic electrolyte.

[0069] Compared with the prior art, one of the above technical solutions has the following advantages or beneficial effects: This invention provides a gel electrolyte precursor solution or gel electrolyte, which is intended to be used in the preparation of gel batteries / low-temperature batteries to improve the poor compatibility between electrodes and gel electrolyte interfaces, poor conductivity and safety issues of existing low-temperature batteries, thereby enhancing the market application of low-temperature batteries.

[0070] The gel electrolyte of this invention is prepared by using a 1,3-dioxolane monomer, functional additives, and a basic electrolyte to form a gel electrolyte precursor solution, which is then assembled into a battery and baked. The solvent used in the preparation of the gel electrolyte of this invention is an organic solvent, resulting in a gel-state low-temperature electrolyte. Conventional electrolytes exhibit increased viscosity at low temperatures (-40°C), leading to crystallization. At -40°C, the activation energy of chemical reactions increases, and sodium ions in the electrolyte tend to remain only on the electrode interface film surface, easily causing sodium deposition. The gel electrolyte prepared in this invention is an organic low-temperature electrolyte, exhibiting a gel state, and does not crystallize at -40°C. Furthermore, the additives in the gel electrolyte contain S / P / F (sulfur, phosphorus, fluorine), which have strong electron delocalization properties. The resulting groups coordinate with sodium ions, easily separating from them, and can participate in the formation of the interface film at the electrode interface. This regulates the formation of the interface film containing S / P / F compounds, which are rich in anionic compounds and have strong ionic conductivity, facilitating the entry and exit of sodium ions and improving the interfacial resistance between the electrode and the electrolyte in the gel battery.

[0071] The flexible polymer chains in the gel electrolyte prepared by this invention adsorb charged ions (e.g., F, S, P) on the (-NH) groups. The polar groups (e.g., ether bonds) interact with the conductive ions to form dynamic bonds, thereby achieving charge conduction. The in-situ polymer-based gel electrolyte has good wettability on the electrode material surface. The flexibility of various functional groups (ether groups, boric acid, -NH) in the polymer matrix allows the electrolyte to better contact the electrode, thereby reducing the impedance of the electrolyte / electrode interface. Moreover, it can prevent the dissolution and shuttle of some small molecules, thus facilitating the obtaining of a battery system with long cycle life and high coulombic efficiency.

[0072] The gel electrolyte in the gel battery prepared by the present application has a conductivity of 3.04Х10 -3 mS cm -1 at low temperature of-40℃, which is only 7.1Х10 -3 mS cm -1 lower than that of the electrolyte in the corresponding liquid battery; the gel battery prepared by the present application using the gel electrolyte exhibits a charge transfer resistance similar to that of the liquid battery; the capacity retention rate of the gel battery is 91% after 0.1C cycle test at low temperature of-40℃ for 100 times, which can effectively improve the problem of rapid capacity decay of the battery and improve the cycle stability of the battery. More importantly, the gel battery and the gel electrolyte prepared by the present application have low production cost, and can be mass-produced using the existing liquid battery manufacturing technology. BRIEF DESCRIPTION OF DRAWINGS

[0073] Figure 1 It is the design schematic of the gel electrolyte of Example 1; reaction formula (a) is the synthesis of the functional additive; and reaction formula (b) is the ring-opening polymerization of the monomer.

[0074] Figure 2 It is the yield change graph of the gel electrolyte in Example 1.

[0075] Figure 3 It is the conductivity graph of the gel electrolyte and the electrolyte at different temperatures in Effect Example 1.

[0076] Figure 4 It is the electrochemical impedance (EIS) graph of the gel battery and the liquid battery in Effect Example 2.

[0077] Figure 5 It is the charge-discharge capacity-voltage curve graph of different gel batteries and liquid batteries in Effect Example 2.

[0078] Figure 6 It is the dQ / dV curve graph of the gel battery 4 and the liquid battery at different temperatures in Effect Example 2. Figure 6 a represents the dQ / dV curve graph of the battery at 25℃; Figure 6 b represents the dQ / dV curve graph of the battery at-20℃; Figure 6 c represents the dQ / dV curve graph of the battery at-30℃; Figure 6 d represents the dQ / dV curve graph of the battery at-40℃.

[0079] The present application will be further described below in combination with specific examples. These examples are only used to illustrate the present application and are not used to limit the scope of the present application. DETAILED DESCRIPTION

[0080] The application will be further described in connection with specific examples. These examples are only used to illustrate the application and not to limit the scope of the application.

[0081] I. Chemicals and instruments Sodium difluorophosphate NaPO2F2(99.7 wt%, water <100 ppm) powder was purchased from Multo Chemical Technology Co., Ltd. Tris(trimethylsilyl) phosphite TMSPi (97%), pyrrole (99%), bis(2,2,2-trifluoroethyl) carbonate (TFEC) and 2,2,3,4,4,4-hexafluorobutyl acrylate HFA were purchased from Shanghai Aldrin Biochemical Co., Ltd. Methanol standard solution (1 mol / L), dichloromethane standard solution (1 mol / L), propylene carbonate PC (99.7%) and ethylene carbonate EC (99%) were provided by Sinopharm Chemical Reagent Co., Ltd. 1,3,2-dioxazolothiophene-2,2-dioxide DTD (99.9%), 1,3-dioxolane DOL (99.5%) and tris(trifluoromethanesulfonate) aluminum Al(OTf)3 (98%) were purchased from Shanghai Lingn Science and Technology Development Co., Ltd. (4-acetyl-2-fluorophenyl)boronic acid (98%) was purchased from Shanghai Haohong Biological Medicine Technology Co., Ltd. The positive material polyanion NFPP (sodium iron phosphate NFPP-100) was provided by Shenzhen Zhitai Technology Co., Ltd. A rotary evaporator (R2100A) was provided by Wuxi Shenke Instrument Co., Ltd. An SZQ four-sided wet film coater 50-75-100-150 was purchased from Guangdong Huaguang Precision Detection Equipment Co., Ltd. A button cell hydraulic sealing machine PX-HS-20 was purchased from Shenzhen Pengxiang Yunda Co., Ltd. A pole piece punching machine JK20140311 and a vacuum drying box DZF-6050 were purchased from Hefei Kejing Material Technology Co., Ltd. A super-purification glove box Super (1220 / 750 / 900) was purchased from Shanghai Micronora Machinery Technology Co., Ltd. A constant temperature and humidity test box HT-S-50L was purchased from Dongguan Huitai Machinery Co., Ltd. A button cell tester CT-4008Tn was purchased from Shenzhen Xinweier Electronics Co., Ltd. An electrochemical workstation CHI 660E was purchased from Shanghai Chenhua Instrument Co., Ltd. A digital display table type conductivity meter DD50-3 was purchased from Zhejiang Lichen Science and Technology Instrument Co., Ltd.

[0082] II. The routine operations are as follows: (1) Preparation of basic electrolyte Preparation of NaPF6 low temperature electrolyte: The solvent used is propylene carbonate PC, ethylene carbonate EC and ethyl methyl carbonate EMC, NaPF6 accounts for 0.1%-25%, ethylene carbonate EC accounts for 15%-40%, propylene carbonate PC accounts for 15%-40%, ethyl methyl carbonate EMC accounts for 10%-35% by weight percentage of the total weight of the final prepared base electrolyte. EC, PC and EMC are weighed into a 100-250 mL beaker, the total volume of the liquid is 50-150 mL, 4A molecular sieve is added to 1 / 30-1 / 20 of the liquid volume, and the beaker is sealed to remove water for 24-48 h.

[0083] Take the supernatant, and add it to a 100-200 mL beaker together with NaPF6 to dissolve, and continue to add 0.0001-0.1% sodium difluorophosphate, 0.01-0.1% tris (trimethylsilyl) phosphite TMSPi, 0.01-0.5% di (2,2,2-trifluoroethyl) carbonate TFEC, 0.01-0.15% 2,2,3,4,4,4-hexafluorobutyl acrylate HFA, 0.0001-0.1% 1,3,2-dioxazolothiophene-2,2-dioxide DTD to the beaker to dissolve or mix evenly, and then transfer to a 50-150 mL volumetric flask to make up to volume. The solution is clear and transparent, and after making up to volume, it is transferred to an aluminum bottle, and the base electrolyte is stored at 0°C for standby. The above operations are all carried out in a glove box (water, oxygen value ≤ 0.1 ppm).

[0084] (2) Preparation of gel electrolyte precursor solution Preparation of functional additives: (4-acetyl-2-fluorophenyl) boronic acid (1.82 g, 0.1 mol), pyrrole (0.671 g, 0.1 mol) and catalyst methanesulfonic acid (0.961 g, 0.1 mol) are dissolved in 1 L of methanol, stirred at room temperature under nitrogen atmosphere for 6-12 h. Then the mixture is poured into a short silica gel column. Then the solvent is removed by rotary evaporation, and dichloromethane (DCM) and methanol (20:1) are used as eluent for silica gel chromatography purification. The crude product is recrystallized from acetic acid (50-100 ml) to obtain (4-acetyl-2-fluorophenyl) boronic acid / pyrrole polymer.

[0085] Preparation of gel electrolyte precursor solution: In a glove box (water, oxygen value ≤ 0.1 ppm), 1,3-dioxolane monomer (DOL, 1-3 mL), (4-acetyl-2-fluorophenyl)boronic acid / pyrrole polymer (0.005-0.1 g) and prepared base electrolyte 5-30 mL were continuously stirred in a 50 mL beaker for 60-90 min, and then the initiator tris (trifluoroaluminum sulfate) (Al(OTf)3, 0.01-0.5 g) was added to the above solution and stirred for 10 min. The obtained solution was transferred to an aluminum bottle and stored at 0°C for standby.

[0086] (3) Preparation of gel and method for obtaining chemical yield: The prepared gel electrolyte precursor solution was baked at 45°C for 8h to prepare the gel / gel electrolyte.

[0087] The prepared gel was washed 3 times in an EC, PC and EMC mixed solvent (mass ratio of 1:1:1) to wash away the unreacted monomers, initiators, small molecule byproducts and salts in the electrolyte, so as to remove the interference of the electrolyte. The obtained mass is the total mass of the added monomers, functional additives and initiators, and the yield is obtained.

[0088] (4) Preparation of gel battery Preparation of positive electrode: composite sodium iron phosphate (NFPP): polyvinylidene fluoride (PVDF5130): acetylene black (Kappa100): graphene oxide (GO) = 90:5:4:1, solid content is 40-50%; using 100-200µm doctor blade respectively coated on 14-16µm aluminum foil, vacuum drying at 95°C for 6h, and then the positive electrode was cut into a circular piece with a radius of 7mm.

[0089] Using 2032# button cell shell, GF / D glass fiber diaphragm, etc., in a glove box with water and oxygen values less than 0.1 ppm, the positive electrode, sodium sheet negative electrode and gel electrolyte precursor solution were assembled into a button cell. The button cell was placed in an oven at 45-65°C for 6-8 hours, and the gel battery was prepared. The battery surface was taken out and tested after the battery surface returned to room temperature.

[0090] (5) Test Low temperature conductivity test of electrolyte / electrolyte: The base electrolyte or gel electrolyte sealed in the bottle was pre-stored in a constant temperature and humidity box at 40°C, 30°C, 25°C, 10°C, 0°C, -10°C, -20°C, -30°C, -40°C for 1-2h, and then quickly placed in the constant temperature tank of the conductivity meter for testing.

[0091] The EIS test conditions were as follows: the electrochemical workstation used was a CHI 660E, and the frequency range was set to 10 Hz under the open-circuit voltage condition of the coin cell. -2 Hz to 10 6 Hz, AC amplitude is 10 mV.

[0092] Charge-discharge cycle test conditions: charge-discharge voltage window of 1.5-3.65V, theoretical specific capacity of 110 mAh g. -1 Step 1): Let stand at the test temperature for 4 hours; Step 2): Charge at 0.1C constant current and constant voltage to 3.65V, with a cutoff current of 0.05C; Step 3): Let stand for 10 minutes; Step 4): Discharge at 0.1C constant current to 1.5V; Step 5: Repeat steps 2) to 4) 100 times.

[0093] Example 1: Preparation of Gel Electrolytes Preparation of basic electrolyte Take 30 mL of ethylene carbonate PC, 30 mL of propylene carbonate EC and 30 mL of methyl ethyl carbonate EMC in a 250 mL beaker by mass percentage, add 4 Å molecular sieve to 1 / 25 of the liquid volume, seal the beaker to remove water for 28 h.

[0094] Take the supernatant of the dried solvent and dissolve it together with 95 mg of NaPF6 in a 200 mL beaker. Continue adding 1 mg of sodium difluorophosphate, 100 µL of tris(trimethylsilane)phosphite (TMSPi), 100 µL of bis(2,2,2-trifluoroethyl) carbonate (TFEC), 100 µL of 2,2,3,4,4,4-hexafluorobutyl acrylate (HFA), and 1 mg of 1,3,2-dioxazolthiophene-2,2-dioxide (DTD) to the beaker to dissolve or mix thoroughly. Then transfer to a 150 mL volumetric flask and bring to volume. The solution should be clear and transparent. After bringing to volume, transfer to an aluminum bottle, seal, and store at 0°C for later use to prepare the basic NaPF6 electrolyte. All operations were performed in a glove box (water and oxygen levels ≤ 0.1 ppm). The specific amounts of each component are shown in Table 1 below. Table 1. Components and dosage of basic electrolyte

[0095] Design principles and preparation of gel electrolytes 2.1 Design Principles The energy difference and symmetry characteristics of bonding and antibonding orbitals determine the stability of chemical bonds. Bonding orbitals, through in-phase superposition of atomic orbitals, significantly lower their energy, enhancing bonding. Figure 1In reaction formula a, pyrrole and (4-acetyl-2-fluorophenyl)boronic acid can be polymerized into conductive macrocycle under certain conditions. The nitrogen atom in the pyrrole molecule provides a pair of electrons to form a five-center six-electron conjugated π bond, while the π bond of the carbonyl group in (4-acetyl-2-fluorophenyl)boronic acid has a lower energy than the carbon-carbon double bond in the pyrrole molecule, and the electronegativity of O is greater than that of C, so when C and O form a double bond, the overlap of the electron cloud between them is more compact, thereby forming a more stable bonding orbital. For this reason, compared with the carbon-carbon double bond in the pyrrole molecule, the π bonding orbital of the carbonyl group of (4-acetyl-2-fluorophenyl)boronic acid is more difficult to release electrons, and is more prone to accept electrons. This characteristic makes the carbonyl group of (4-acetyl-2-fluorophenyl)boronic acid more inclined to act as an electrophile in chemical reactions, while pyrrole is an electron donor. Under certain conditions, the macrocycle formed by cross-linking can recognize various anions and neutral electron-rich substances through stable hydrogen bonding between NH to improve the conductivity of the electrolyte, and each macrocycle interacts with the nearest two adjacent rings through the OH hydrogen bonding of the phenylboronic acid to form a hydrogen-bonded organic framework to enhance the interaction between the polymer chains, thereby improving the mechanical properties and stability of the electrolyte.

[0096] Figure 1 In reaction formula b, Al(OTf)3 will be adsorbed on the oxygen atoms of 1,3-dioxolane monomer (DOL) to form oxonium ions, and then attack the oxygen atoms on the DOL monomer to achieve ring-opening polymerization, causing the solution to form a gel state (between solid and liquid states).

[0097] 2.2 Preparation of functional additives: (4-acetyl-2-fluorophenyl)boronic acid (1.82 g, 0.1 mol), pyrrole (0.671 g, 0.1 mol), and methanesulfonic acid (0.961 g, 0.1 mol) were dissolved in 1 L of methanol and stirred at room temperature under a nitrogen atmosphere for 6 h. Then the mixture was poured into a short silica gel column. Then the solvent was removed by rotary evaporation, and dichloromethane (DCM) and methanol (volume ratio 20:1) were used as eluent for silica gel chromatography purification. The crude product was recrystallized from acetic acid (50-100 ml) to obtain (4-acetyl-2-fluorophenyl)boronic acid / pyrrole polymer.

[0098] 2.3 Preparation of gels: The yield of the conductive gel obtained by in-situ polymerization is very important because it affects all the performances of the battery, and the excellent rheological properties (such as low viscosity, high wettability) of the gel electrolyte precursor solution are used to achieve close contact between the electrode material and the gel electrolyte interface. Due to the randomness of the crosslinking polymerization reaction, the three-dimensional crosslinked polymer product obtained may be challenging. The chemical properties of different nanogels obtained by high dilution in-situ polymerization are estimated by the chemical yield. The initiator content, monomer quality, crosslinker dosage and temperature will affect the chemical composition and morphology of the prepared polymer gel. In order to minimize the number of variables, the mass ratio of DOL monomer and functional additives is set to 100:1 at 45°C for 8h (the electrolyte can be decomposed at a temperature that can withstand the high temperature of the battery), and the prepared gel needs to maintain flexibility and does not require too much rigidity in order to be better compatible with the electrode. The mass of different initiators is explored to find the best gel electrolyte preparation method at low temperature, as shown in Table 2.

[0099] In the glove box (water, oxygen value ≤ 0.1 ppm), 1,3-dioxolane monomer (DOL), (4-acetyl-2-fluorophenyl) boronic acid / pyrrole polymer, and the prepared base electrolyte were poured into a 50ml beaker and continuously stirred for 70min. After adding tris (trifluoroaluminum sulfate) (Al(OTf)3) initiator to the above solution and stirring for 10min, the obtained solution was clear and transparent, and was transferred to an aluminum bottle to prepare a gel electrolyte precursor solution, which was sealed and stored at 0°C for standby. The above operations were all carried out in the glove box (water, oxygen value ≤ 0.1 ppm). (Stored at 0 degrees is to inhibit polymerization. In the subsequent preparation test of gel batteries, the gel electrolyte precursor solution is injected into the battery, which will be polymerized into a gel after baking.) The prepared gel electrolyte precursor solution was baked at 45°C for 8h to prepare a gel. The amount of each component is shown in Table 2, and the gel yield is shown in Table 2. Figure 2

[0100] Table 2 Gel yield table

[0101] From Table 2, it can be seen that without the presence of initiator Al(OTf)3, the DOL monomer cannot be polymerized at high temperature (45°C) to obtain a gel, and it can be seen that the initiator Al(OTf)3 is crucial for the preparation of the gel.

[0102] From Figure 2 ​It can be found that as the proportion of initiator Al(OTf)3 increases, the yield first increases and then decreases. It can be seen that the more the initiator, the more sufficient the polymerization of the compound, and the excess will cause side reactions and reduce the yield. The best polymerization yield of the gel polymerization reaction in this embodiment is 85.26% (as shown in the results of gel 5), but this result is only used as the best dose of the initiator, because in the process of obtaining the yield, the mixed solvents of EC, PC and EMC are used for washing, and the three-dimensional structure of the gel polymer is retained; Because organic reactions are multiple, linear monomer DOL has self-polymerization in the presence of Al(OTf)3, forming a linear block copolymer; Because the monomer DOL molecule is small, and the monomer DOL molecule also contains -C-O-C, it has strong electronic delocalization, and the mixed solvent is also an unsaturated carbonate, similar to the principle of similar solubility, the monomer DOL may be taken away in the mixed solvent washing.

[0103] 2.4 Preparation of gel electrolyte In the glove box (water, oxygen value ≤ 0.1 ppm), 1,3-dioxolane monomer (DOL), (4-acetyl-2-fluorophenyl) boronic acid / pyrrole polymer, and the prepared base electrolyte were poured into a 50 ml beaker and continuously stirred for 70 min. After adding tris(trifluorosulfonate aluminum) (Al(OTf)3) initiator to the above solution and stirring for 10 min, the obtained solution was clear and transparent, and was transferred to an aluminum bottle to prepare a gel electrolyte precursor solution, which was sealed and stored at 0°C for standby. The above operations were all carried out in the glove box (water, oxygen value ≤ 0.1 ppm). The prepared gel electrolyte precursor solution was baked at 45°C for 8h to prepare a gel electrolyte. After adjusting the amount of functional additives, the specific preparation is shown in Table 3: Table 3 Preparation of gel electrolyte prepared by different functional additives

[0104] Example 2 Preparation of gel battery 1. Preparation of positive electrode sheet S1: Pretreatment: NFPP, PVDF5130, kappa100 and GO were baked at 80°C for 5h respectively; PVDF5130 was prepared into a PVDF5130 solution with a mass fraction of 7% by using N-methyl pyrrolidone (NMP) (i.e. polyvinylidene fluoride PVDF 5130 binder); S2: Preparation of positive electrode slurry: weigh each component according to the weight ratio of NFPP: PVDF5130: kappa100: GO = 90: 5: 4: 1, mix these components, grind for 12 min, add the required PVDF5130 solution in the formula, get the mixture, add the appropriate amount of NMP to make the solid content of the mixture at 40%, stir until the slurry is uniform, and get the positive electrode slurry; S3: Preparation of positive electrode sheet: use a doctor blade to uniformly coat the slurry on the current collector aluminum foil, vacuum dry at 95°C for 6h, and then cut the positive electrode into a circular sheet with a radius of 7mm.

[0105] 2. Assembly of battery: 2.1 Preparation of low-temperature gel battery: Use 2032# button cell shell, GF / D glass fiber diaphragm, etc. in a glove box with water and oxygen values below 0.1 ppm, inject the prepared positive electrode sheet, sodium sheet negative electrode and gel electrolyte precursor solution into the button cell after assembly, and prepare the button cell. The remaining unrecorded content is a conventional technique, which will not be described here.

[0106] Place the button cell in an oven at 45°C for 8 hours, and the gel battery is ready. Take it out and test when the battery surface returns to room temperature.

[0107] Effect Example 1: conductivity test of basic electrolyte / gel electrolyte Test process: seal the basic electrolyte and gel electrolyte to be tested in a glass bottle, and pre-store them in a constant temperature and humidity box at 40°C, 30°C, 25°C, 10°C, 0°C, -10°C, -20°C, -30°C, -40°C for 1.5h respectively, and then quickly place them in the constant temperature tank of the conductivity meter for testing.

[0108] Comparison of physical properties of basic electrolyte and gel electrolyte In theory, the properties of gel electrolyte are between liquid electrolyte and all-solid-state electrolyte. While retaining the advantages of high room temperature ionic conductivity of liquid electrolyte, it also has the flexibility, safety and good processability of polymer electrolyte. Therefore, the conductivity difference between gel electrolyte with different functional additives and basic electrolyte was explored, and the results are shown in Table 4, and the conductivity graph of the gel electrolyte was obtained. Figure 3

[0109] Table 4: Conductivity difference between gel electrolyte and basic electrolyte

[0110] From Figure 3 ​It can be seen that the logarithm of conductivity and the reciprocal of absolute temperature show a stage linear change, which indicates that with the increase of temperature, the number of defects (interstitial ions and ion vacancies) of the electrolyte increases, and the conductivity increases. As shown in Table 4, the conductivity of the gel electrolyte 1 without adding a functional additive is 1.11Х10 -3 mS cm -1 With the increase of the functional additive, the conductivity of the gel electrolyte first gradually increases and then decreases, but the conductivity is higher than that of the gel electrolyte 1, which indicates that the appropriate addition of the functional additive is beneficial to the conductivity of the gel electrolyte. Among the gel electrolytes, the gel electrolyte 4 has the best conductivity. As shown in Table 4, the ionic conductivity of the gel electrolyte 4 at room temperature (25℃, i.e. 3.35 k -1 ) is 3.21Х10 -2 mS cm -1 , which is lower than the conductivity (9.89Х10 -2 mS cm -1 ) of the electrolyte at the same temperature. It is possible that the C-O-C, -NH, -OH and non-polar parts of the polymer in the gel electrolyte and the polar groups or atoms (F / S / P) in the liquid electrolyte form dynamic hydrophobic association, which reduces the free ion concentration. However, the conductivity of the gel electrolyte 4 at low temperature-40℃ is 3.04Х10 -3 mS cm -1 , and the conductivity of the base electrolyte is 1.0Х10 -2 mScm -1 , and the difference between the conductivity of the gel and the conductivity of the liquid is only 7.1Х10 -3 mS cm -1 , which indicates that the gel electrolyte prepared by the present application has good low-temperature performance.

[0111] Effect implementation example 2: comparison of the electrochemical performance of the base electrolyte and the gel electrolyte Gel electrolyte is composed of three phases, namely, organic electrolyte absorbed in dynamic cross-linked porous, gel phase formed by polymer matrix swelled by organic electrolyte and polymer matrix. All the three phases have the ability to conduct sodium ions, among which the continuous liquid phase and gel phase are beneficial to ion conduction at room temperature due to being in amorphous state, while the pure polymer matrix is not conducive to ion conduction due to being in ordered crystalline state at room temperature, which leads to the limitation of its movement. Therefore, researchers generally believe that the pure polymer matrix does not participate in ion conduction at room temperature, but only serves as a polymer framework support. In addition, the existence of the three-phase structure not only ensures high room temperature sodium ion conductivity and good mechanical properties, but also improves the liquid retention capacity of the system and inhibits the leakage of electrolyte, which has a potential and broad application prospect. Therefore, the gel electrolyte or the base electrolyte is assembled into a gel battery or a liquid battery, respectively, and the electrochemical impedance is explored.

[0112] (1) The research process of electrochemical impedance is as follows: Gel battery: using CR2032 button cell shell, GF / D glass fiber diaphragm, etc., the positive electrode sheet, negative sodium sheet and gel electrolyte precursor solution are injected and assembled in a glove box with water and oxygen values below 0.1 ppm, and then placed in an oven at 45°C for 6 hours to obtain a gel button cell, wherein the electrolyte is a gel electrolyte prepared by baking the gel electrolyte precursor solution, and the specific component ratio of the gel electrolyte is shown in Table 3.

[0113] Liquid battery: assembled in the same way as the above low-temperature gel battery, except that it is not heated at 45°C. The electrolyte is a base electrolyte.

[0114] The test conditions of EIS (electrochemical impedance spectroscopy) are as follows: the electrochemical workstation used is CHI 660E, the frequency interval is set to 10 -2 Hz to 10 6 Hz under the open circuit voltage condition of the button cell, and the alternating current amplitude is 10 mV.

[0115] Based on the research of electrode process kinetics and electrode interface structure, the electrochemical impedance (EIS) graph as shown in Figure 4 is obtained, in which the abscissa of the intersection of the curve and the horizontal axis is the bulk impedance (Rb), the intercept of the semicircle in the middle and the horizontal axis is the interface charge transfer impedance (Rct), and the last inclined straight line is the diffusion process impedance (Warburg impedance) in the electrode.

[0116] From Figure 4It can be seen that after 10 cycles at a rate of 0.1C within a voltage range of 1.5-3.65V at room temperature, the semicircle of the liquid battery is larger than that of the gel battery 4, indicating that the gel electrolyte 4 can effectively reduce the Rct of the battery. Although the Rb of the gel electrolyte 4 is larger than that of the basic electrolyte, this may be due to the presence of the polymer matrix in the three-phase structure, which increases the ohmic internal resistance. Moreover, it is obvious that the semicircle of the gel battery 1 is the largest, and the intercept of the horizontal axis is the largest, indicating that its Rct and Rb are the largest. In the gel battery, as the amount of functional additives increases, the Rct and Rb of the gel battery first decrease and then increase, indicating that the appropriate amount of functional additives can improve the internal resistance of the battery chemical reaction. In summary, gels can effectively reduce the battery Rct, reduce the impedance of the electrolyte / electrode interface, and prevent the dissolution and shuttle of some small molecules, effectively improving the problem of poor compatibility between the electrode and gel electrolyte interface in existing low-temperature batteries, thereby obtaining a battery system with long cycle life and high coulombic efficiency.

[0117] (2) Study on electrochemical charge-discharge performance To further investigate the differences in electrochemical charge-discharge performance between gel batteries and liquid batteries, the charge-discharge capacity and first-efficiency of different gel batteries were tested at room temperature. Figure 5 After selecting the optimal gel battery, charge-discharge cycle tests were conducted on the optimal gel battery and liquid battery at different temperatures. The charge-discharge voltage window was 1.5-3.65 V, and the theoretical specific capacity was 110 mAh g⁻¹. -1 The charge and discharge data are shown in Table 5.

[0118] Table 5. 0.1C charge / discharge of the entire battery at low temperatures.

[0119] The kinetic control of sodium-ion batteries is closely related to the sodium ion transport number in the electrolyte and the solid-electrolyte interfacial (SEI) film on the electrodes. The choice of electrolyte composition typically determines or influences the battery's energy density, safety, cycle life, storage performance, and operating conditions. Electrode materials determine the battery's specific capacity, while the reversible capacity of the active materials is affected by the electrolyte. A good interfacial state between the electrolyte and the electrodes will improve the performance of the electrode materials. When only the electrolyte composition is changed, the increase in reversible capacity and first-efficiency can be attributed to improved interfacial compatibility, and EIS testing also demonstrates that gel electrolytes effectively reduce the charge transfer resistance of the electrode surface.

[0120] Figure 5 This indicates that, in the charge / discharge capacity-voltage curves, the liquid battery exhibits the largest reversible capacity of 117.15 mAh g⁻¹. -1The initial efficiency is 94.14%, the charge curve is at the lowermost side, and the discharge curve is at the uppermost side, indicating that the oxidation of the substance in the liquid battery requires the minimum voltage when charging and has the maximum discharge voltage when discharging, and the electrochemical polarization is minimum. The reversible capacity of the gel battery 1 is the minimum 90.36 mA h g -1 The initial efficiency is 92.3%, the charge curve is at the lowermost side, and the discharge curve is at the uppermost side, indicating that the polarization voltage is maximum. In the gel battery, with the increase of the functional additive, the reversible capacity shows a trend of first increasing and then decreasing, and the reversible capacity of the gel battery 4 is the maximum, which is 115.87 mA h g -1 The initial efficiency is 95.47%. It is indicated that the functional additive can effectively improve the charge and discharge capacity and the initial efficiency of the gel battery. It is possible that the addition of the appropriate functional additive and the additive of the electrolyte form a good electrode-electrolyte interface SEI film in the process of battery charging and discharging, which is beneficial to improve the utilization rate of active substances, and then promote the rapid conduction of ions / electrons, and improve the polarization of the gel battery in the process of charging and discharging.

[0121] Then the preferred gel battery 4 and the liquid battery are tested at different temperatures, and table 5 is obtained. The initial discharge capacity of the gel battery 4 at room temperature reaches 115.87 mAh g -1 The capacity retention rate is 99.24% after 100 charge and discharge cycles at a current density of 0.1 C, and the initial coulombic efficiency (ICE) is 95.47%. The reversible capacity of the liquid battery is 117.15 mAh g -1 The initial efficiency (ICE) is 94.14%. Through comparison, it is analyzed that the gel electrolyte in the gel battery forms a uniform SEI film on the positive side during the first charge and discharge, which can maintain the stable embedding and stripping of sodium ions, and then the initial efficiency is high.

[0122] And in the liquid battery, due to the dissolution and consumption of transition metal ions in the positive material, the reversible capacity and the initial efficiency are slightly low. The capacity of the liquid battery decays to 97.51% of the capacity after 100 cycles. Although there are many factors affecting the electrical performance of sodium ion battery, the charge and discharge efficiency is also caused by the poor physical properties of the electrolyte, which also leads to the insufficient long cycle stability. The capacity retention of the liquid battery is only 81.52% when cycled to 100 times at-40℃.

[0123] And the capacity of the gel battery 4 can still be maintained at 91% when cycled to 100 times at-40℃. It can be seen that although the ionic conductivity of the organic electrolyte in the basic electrolyte is higher than that of the gel electrolyte, the transition metal ions in the positive electrode dissolve in the organic electrolyte. Therefore, the basic electrolyte in the liquid battery can easily lead to rapid capacity decay of the battery, and the gel battery can effectively weaken this phenomenon.

[0124] In summary, in the case of changing only the electrolyte component (from the base electrolyte to the gel electrolyte), the mass-to-charge transfer resistance at room temperature, the capacity of the battery at low temperature, and the initial efficiency are all improved, indicating that the electrochemical polarization of the battery during charging and discharging is reduced, and the effects of sodium precipitation and or electrolyte decomposition caused by polarization are reduced, and the joule heat generated by the polarization resistance is reduced, which can improve the safety of the battery operation. The gel electrolyte in the gel battery 4 can effectively improve the interfacial compatibility of the electrode-electrolyte, improve the poor conductivity and safety of the gel battery, and improve the cycle stability of the battery.

[0125] (3) Explore the electrochemical behavior of the battery at low temperature In order to explore the electrochemical behavior of the battery at low temperature, the present application analyzes the dQ / dV curve of the gel battery 4 and the liquid battery at different temperatures (25℃ / -20℃ / -30℃ / -40℃) during charging and discharging, and obtains Figure 6 The dQ / dV curve provides the differential relationship between voltage and charge during the charging and discharging process of the battery, so that the electrochemical reaction and physical process inside the battery can be analyzed, and the change rate of capacity is reflected. The place with large change rate is a characteristic peak displayed on the curve, which generally corresponds to an electrochemical reaction process. At the same time, because different chemical processes will produce different reaction rates in a specific voltage range, the dQ / dV curve can reflect the activation energy and reaction rate of different electrochemical reactions inside the battery. Figure 6 a shows that the diffraction peaks of the liquid battery and the gel battery 4 at room temperature 25℃ have good coincidence, indicating that the gel battery has good running stability at room temperature. Obviously, with the decrease of temperature, the intensity of each peak is decreasing, indicating that the activation energy of the electrochemical reaction is gradually increasing, and the chemical reaction rate is decreasing. Especially in Figure 6 d, which corresponds to the charging and discharging of the battery at-40℃, and the minimum reduction peak should appear at 3.05±0.2 V, indicating that among the tested temperatures, the polarization of the battery at-40℃ is the largest. In addition, Figure 6 b- Figure 6 d shows that at low temperature, the peak value of the gel battery 4 using the gel electrolyte 4 is slightly larger than that of the liquid battery using the base electrolyte, indicating that the gel battery 4 using the gel electrolyte 4 has a faster reaction rate, or perhaps the gel battery 4 using the gel electrolyte 4 has a smaller Rct.

[0126] The reaction rate is a physical quantity for quantitatively describing the speed of a chemical reaction, and is usually expressed by the change value of the concentration of a reactant or a product per unit time. In the case of only changing the composition of the electrolyte, the small charge transfer resistance Rct (rate-determining step of the chemical reaction kinetics on the electrode) of the gel electrolyte means that the electrode surface of the gel battery 4 has a faster chemical reaction rate in the same time, and ions can reach the electrode surface to participate in the reaction more quickly, thereby reducing the limitation of the "ion transfer lag" on the reaction rate, and improving the energy density, cycle life and other performances of the battery.

[0127] The above merely describes preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a gel battery, characterized in that, Includes the following steps: Step 1: Preparation of functional additives; (4-acetyl-2-fluorophenyl)boronic acid and pyrrole are reacted with methanesulfonic acid to obtain (4-acetyl-2-fluorophenyl)boronic acid / pyrrole polymer; Step 2: Preparation of gel electrolyte precursor solution: Mix 1,3-dioxolane, (4-acetyl-2-fluorophenyl)boric acid / pyrrole polymer and basic electrolyte, add initiator, and stir to obtain gel electrolyte precursor solution; Step 3: Preparation of gel battery: After assembling the positive electrode, negative electrode and gel electrolyte precursor solution, the gel battery is prepared by baking.

2. The preparation method according to claim 1, characterized in that, The basic electrolyte preparation process is as follows: sodium hexafluorophosphate and solvent are mixed and then additives are added and mixed evenly to obtain the electrolyte. The additives are sodium difluorophosphate, tris(trimethylsilane) phosphite, di(2,2,2-trifluoroethyl) carbonate, 2,2,3,4,4,4-hexafluorobutyl acrylate and 1,3,2-dioxazolthiophene-2,2-dioxide; The solvent is propylene carbonate, ethylene carbonate, and ethyl methyl carbonate.

3. The preparation method according to claim 2, characterized in that, The basic electrolyte comprises, by weight percentage, 0.1%-25% sodium hexafluorophosphate, 15%-40% ethylene carbonate, 15%-40% propylene carbonate, 10%-35% methyl ethyl carbonate, 0.0001-0.1% sodium difluorophosphate, 0.01-0.1% tris(trimethylsilane)phosphite, 0.01-0.5% di(2,2,2-trifluoroethyl) carbonate, 0.01-0.15% 2,2,3,4,4,4-hexafluorobutyl acrylate, and 0.0001-0.1% 1,3,2-dioxazolthiophene-2,2-dioxide.

4. The preparation method according to claim 1, characterized in that, The molar ratio of (4-acetyl-2-fluorophenyl)boronic acid to pyrrole is 1:(1-5). The molar ratio of (4-acetyl-2-fluorophenyl)boronic acid to methanesulfonic acid is (1-5):

1.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the 1,3-dioxolane monomer to the functional additive is (60-750):1; The mass ratio of the 1,3-dioxolane monomer to the basic electrolyte is (1-4):(5-60). The initiator is aluminum tri(trifluoromethanesulfonic acid); The mass ratio of the 1,3-dioxolane monomer to the initiator is (1-40):

1.

6. The preparation method according to claim 1, characterized in that, The baking temperature is 45-65℃; The baking time is 6-8 hours; The mass ratio of the 1,3-dioxolane monomer to the functional additive is (90-110):1; The mass ratio of the 1,3-dioxolane monomer to the basic electrolyte is 1:(6-8). The mass ratio of the 1,3-dioxolane monomer to the initiator is (8-12):

1.

7. The preparation method according to claim 1, characterized in that, The battery assembly also includes a button cell case using CR#2032 and / or a glass fiber separator using GF / D; The positive electrode slurry includes at least one of NFPP, PVDF5130, kappa100, and GO; The negative electrode is a sodium sheet negative electrode.

8. A gel battery, characterized in that, It is prepared by the method described in any one of claims 1-7.

9. A method for preparing the gel electrolyte in the gel battery of claim 8, characterized in that, Includes the following steps: S1: Preparation of basic electrolyte: Sodium hexafluorophosphate and solvent are mixed and then additives are added and mixed evenly to obtain the electrolyte. S2: Functional additive: (4-acetyl-2-fluorophenyl)boric acid and pyrrole are reacted with methanesulfonic acid to obtain (4-acetyl-2-fluorophenyl)boric acid / pyrrole polymer; S3: Gel preparation: Mix 1,3-dioxolane monomer, functional additives and basic electrolyte, add initiator and mix well to obtain gel electrolyte precursor solution; S4: The gel electrolyte is prepared by baking the gel electrolyte precursor solution.

10. Use of a gel battery prepared by the preparation method of any one of claims 1-7, or a gel electrolyte prepared by the method of claim 8, or a gel battery prepared by the method of claim 9, in an energy storage device.

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