A local high-concentration aqueous electrolyte, a preparation method thereof, and a sodium ion battery

Abstract

The present invention provides a local high-concentration aqueous electrolyte, a preparation method thereof, and a sodium ion battery, belonging to the field of electrolyte materials. The local high-concentration aqueous electrolyte provided by the present invention uses an organic solvent as a bridge, and by adjusting the amount of water, organic solvent, and TTE, TTE and water can be miscible to form a local high-concentration electrolyte, thereby reducing the concentration of sodium salt in the salt-in-water electrolyte, thereby reducing the viscosity of the salt-in-water electrolyte, improving the wettability of the electrolyte, and then improving the conductivity of the electrolyte, thereby improving the electrochemical performance of the battery. The local high-concentration aqueous electrolyte provided by the present invention has a high conductivity at 0.1mV·S ‑1 At a scan rate of , the voltage window reaches a width of about 3.4V, which can adapt to the stable operation of carbon-coated sodium vanadium phosphate as anode and cathode. The sodium ion battery prepared using a local high-concentration aqueous electrolyte has a capacity retention rate of nearly 100% after 100 cycles, which can improve the electrochemical performance of the battery.

Description

Technical Field

[0001] The present invention relates to the field of electrolyte materials, and in particular to a local high-concentration aqueous electrolyte, a preparation method thereof, and a sodium ion battery. Background Art

[0002] Salt-in-water electrolyte is an innovative technology that has attracted much research attention in the field of sodium-ion batteries in recent years. In traditional electrolytes, water molecules pose a challenge to the stability of the battery because water molecules can react with active substances in the battery, leading to the decomposition of the electrolyte and the decline of battery performance. In order to solve this problem, researchers proposed a strategy of using high-concentration salts to "encapsulate" water molecules to form a salt-in-water electrolyte.

[0003] The core idea of ​​this design is to effectively fix water molecules through high concentrations of salts to form a special solvent sheath, thereby limiting the direct reaction of water molecules with the active substances in the battery. This method of "wrapping" water molecules helps to broaden the electrochemical stability window of the battery and improve the energy density and output power of the battery.

[0004] The introduction of water-in-salt electrolyte technology provides a new approach to solving the problem of water in sodium-ion batteries and creates better conditions for the development of sodium-ion batteries. However, high-concentration water-in-salt sodium-ion battery electrolytes face a series of challenges. For example, although highly soluble imide salts can be used to broaden the electrochemical window, this also brings disadvantages such as high electrolyte cost, high viscosity, and poor wettability. In the prior art, researchers have introduced diluents into high-concentration electrolytes to maintain local high-concentration electrolytes and reduce the disadvantages of high viscosity and poor wettability of high-concentration electrolytes. Summary of the invention

[0005] The object of the present invention is to provide a local high-concentration aqueous electrolyte and a preparation method thereof. The local high-concentration aqueous electrolyte provided by the present invention has low viscosity, good wettability, high conductivity, and a wide electrochemical stability window, and can improve the electrochemical performance of the battery.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a local high-concentration aqueous electrolyte, comprising sodium salt, water, an organic solvent and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0008] The volume ratio of water to organic solvent is 1:(5-7);

[0009] The amount of substance of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is not greater than the amount of substance of the organic solvent.

[0010] Preferably, the ratio of the amount of the sodium salt to the total mass of water and the organic solvent is (4-5) mol:1 kg.

[0011] Preferably, the sodium salt comprises sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide or sodium trifluoromethanesulfonate.

[0012] Preferably, the molar ratio of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether to the organic solvent is (0.3-1):1.

[0013] Preferably, the organic solvent includes N,N-dimethylformamide, sulfolane, dimethyl sulfoxide or ethylene glycol dimethyl ether.

[0014] The present invention provides a method for preparing the local high-concentration aqueous electrolyte described in the above technical solution, comprising the following steps:

[0015] After the sodium salt, water and organic solvent are mixed, they are mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether for a second time to obtain a local high-concentration aqueous electrolyte.

[0016] The present invention also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte is the local high-concentration aqueous electrolyte described in the above technical solution or the local high-concentration aqueous electrolyte prepared by the preparation method described in the above technical solution.

[0017] Preferably, the positive / negative electrode sheets in the sodium ion battery include a current collector and a positive / negative electrode coating coated on the current collector; the positive / negative electrode coating includes a positive / negative electrode active material, a conductive agent and a binder.

[0018] Preferably, the mass ratios of the positive / negative electrode active material, the conductive agent and the binder are independently (6.8-7.2):(1.8-2.2):(0.8-1.2).

[0019] Preferably, the positive electrode active material and the negative electrode active material are both carbon-coated sodium vanadium phosphate.

[0020] The present invention provides a local high-concentration aqueous electrolyte, comprising sodium salt, water, an organic solvent and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; the volume ratio of the water to the organic solvent is 1:(5-7); the amount of the substance of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is not greater than the amount of the substance of the organic solvent. The present invention uses an organic solvent as a bridge, and by adjusting the amount of water, the organic solvent and TTE, TTE and water can be miscible to form a local high-concentration electrolyte, thereby reducing the concentration of sodium salt in the salt-in-water electrolyte, thereby reducing the viscosity of the salt-in-water electrolyte, improving the wettability of the electrolyte, and then improving the conductivity of the electrolyte, thereby improving the electrochemical performance of the battery. The results of the embodiment show that the local high-concentration aqueous electrolyte provided by the present invention has a high conductivity at 0.1mV·S -1 At a scan rate of , the voltage window reaches a width of about 3.4V, which can adapt to the stable operation of carbon-coated sodium vanadium phosphate as anode and cathode. The sodium ion battery prepared using a local high-concentration aqueous electrolyte has a capacity retention rate of nearly 100% after 100 cycles, which can improve the electrochemical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The local high concentration aqueous electrolyte of Example 1 of the present invention is 0.1V·S -1 Linear voltammetry curve at scan rate;

[0022] Figure 2 The Raman spectra of the local high-concentration aqueous electrolyte of Example 1 of the present invention and the electrolyte prepared in Comparative Example 1;

[0023] Figure 3 This is a sodium ion battery cycle performance diagram obtained in Application Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The present invention provides a local high-concentration aqueous electrolyte, comprising sodium salt, water, an organic solvent and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0025] The volume ratio of water to organic solvent is 1:(5-7);

[0026] The amount of substance of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is not greater than the amount of substance of the organic solvent.

[0027] In the present invention, the sodium salt preferably includes sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide or sodium trifluoromethanesulfonate, more preferably sodium bis(trifluoromethylsulfonyl)imide. The present invention limits the type of sodium salt to the above range to promote the miscibility of the diluent and the solution, thereby further improving the conductivity of the electrolyte.

[0028] In the present invention, the volume ratio of water to organic solvent is 1: (5-7), preferably 1: 6. The present invention limits the type of mixed solvent and the volume ratio of water to organic solvent in the mixed solution to the above range to ensure subsequent miscibility with the diluent.

[0029] In the present invention, the organic solvent preferably includes N,N-dimethylformamide, sulfolane, dimethyl sulfoxide or ethylene glycol dimethyl ether, and more preferably N,N-dimethylformamide. The present invention limits the type of organic solvent to the above range to reduce the cost of the electrolyte.

[0030] In the present invention, the ratio of the amount of the sodium salt to the total mass of water and the organic solvent is preferably (4-5) mol:1 kg, more preferably 4.5 mol:1 kg. The present invention limits the ratio of the amount of the sodium salt to the total mass of water and the organic solvent to the above range to ensure that the electrolyte has good conductivity.

[0031] In the present invention, the amount of the substance of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is not greater than the amount of the substance of the organic solvent; the amount ratio of the substance of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether to the organic solvent is preferably (0.3-1):1, more preferably (0.3-0.8):1, and further preferably 0.5:1. In the present invention, if the amount of the substance of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether exceeds the organic solvent, the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is incompatible with water. In the present invention, the molar ratio of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether to the organic solvent is limited to the above range so that 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and the mixed solution can be miscible.

[0032] The present invention uses an organic solvent as a bridge, and by adjusting the amount of water, the organic solvent and TTE, TTE and water can be miscible to form a local high-concentration electrolyte, thereby reducing the concentration of sodium salt in the water-in-salt electrolyte, thereby reducing the viscosity of the water-in-salt electrolyte, improving the wettability of the electrolyte, and further improving the conductivity of the electrolyte, thereby improving the electrochemical performance of the battery.

[0033] The present invention also provides a method for preparing the local high-concentration aqueous electrolyte described in the above technical solution, comprising the following steps:

[0034] After the sodium salt, water and organic solvent are mixed, they are mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether for a second time to obtain a local high-concentration aqueous electrolyte.

[0035] The present invention has no special requirements for the mixing operation, and the sodium salt, water and organic solvent can be uniformly mixed using a technical solution for preparing a solution well known to those skilled in the art.

[0036] The present invention has no special requirements for the secondary mixing operation, and the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and the solution system can be uniformly mixed using a material mixing technical scheme well known to those skilled in the art.

[0037] The present invention also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte is the local high-concentration aqueous electrolyte described in the above technical solution or the local high-concentration aqueous electrolyte prepared by the preparation method described in the above technical solution.

[0038] In the present invention, the positive / negative electrode sheets in the sodium ion battery preferably include a current collector and a positive / negative electrode coating coated on the current collector; the positive / negative electrode coating includes a positive / negative electrode active material, a conductive agent and a binder.

[0039] In the present invention, the current collector is preferably titanium foil.

[0040] In the present invention, the loading amount of the positive / negative active material in the positive / negative electrode sheet is preferably 1 to 1.5 mg / mm 2 .

[0041] In the present invention, the mass ratio of the positive / negative active material, the conductive agent and the binder is preferably independently (6.8-7.2): (1.8-2.2): (0.8-1.2), and more preferably 7: 2: 1. The present invention limits the mass ratio of the positive / negative active material, the conductive agent and the binder to the above range to ensure that the positive / negative electrode slurry has good performance, thereby ensuring the performance of the battery.

[0042] In the present invention, the positive electrode active material and the negative electrode active material are preferably both carbon-coated sodium vanadium phosphate. The present invention limits the positive / negative electrode active materials to the above types to ensure that the battery has good performance.

[0043] In the present invention, the method for preparing the positive / negative electrode sheet in the sodium ion battery preferably includes:

[0044] (1) mixing the positive / negative electrode active material, the conductive agent, the binder and the solvent, grinding and ultrasonicating the mixture to obtain the positive / negative electrode slurry;

[0045] (2) The positive / negative electrode slurry obtained in step (1) is coated on a current collector, dried, and then punched to obtain a positive / negative electrode sheet.

[0046] In the present invention, the positive / negative electrode active material, the conductive agent, the binder and the solvent are preferably mixed and then ground and ultrasonicated to obtain the positive / negative electrode slurry.

[0047] The present invention has no special restrictions on the types of the conductive agent, binder and solvent, and any conductive agent, binder and solvent known to those skilled in the art can be used. In a specific embodiment of the present invention, the conductive agent is conductive carbon black; the binder is polyvinylidene fluoride (PVDF); and the solvent is N-methylpyrrolidone (NMP).

[0048] In the present invention, the mass ratio of the positive / negative electrode active material to the volume of the solvent is preferably independently 1 g: (4-6) mL, more preferably 1 g: 5 mL. The present invention limits the mass ratio of the positive / negative electrode active material to the volume of the solvent to the above range to obtain a positive / negative electrode slurry with good performance for subsequent coating.

[0049] The present invention has no particular limitation on the mixing operation, and any mixing operation desired by those skilled in the art may be used.

[0050] The present invention has no special limitation on the grinding operation, and the grinding operation commonly used by those skilled in the art can be used. In a specific embodiment of the present invention, the grinding is performed manually for 30 minutes.

[0051] In the present invention, the ultrasonic time is preferably 30 minutes. The present invention has no special limitation on the ultrasonic frequency, and any frequency commonly used by those skilled in the art can be used.

[0052] After obtaining the positive / negative electrode slurry, the present invention coats the positive / negative electrode slurry on a current collector, dries the slurry, and then performs stamping to obtain a positive / negative electrode sheet.

[0053] In the present invention, the drying is preferably carried out in a blast drying oven and a vacuum drying oven in sequence; when drying in a blast drying oven, the drying temperature is preferably 60°C and the drying time is preferably 6 hours; when drying in a vacuum drying oven, the drying temperature is preferably 90°C and the drying time is preferably 12 hours. The present invention sets the drying method and parameters within the above range to ensure that the slurry on the current collector is fully dried.

[0054] The present invention has no special limitation on the stamping operation, as long as a pole piece of a desired size can be obtained.

[0055] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Example 1

[0057] A local high-concentration aqueous electrolyte, consisting of sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), water, N,N-dimethylformamide (DMF) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0058] The volume ratio of water to N,N-dimethylformamide (DMF) is 1:6;

[0059] The molar ratio of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether to N,N-dimethylformamide (DMF) is 0.5:1;

[0060] The ratio of the amount of substance of the sodium salt to the total mass of water and the organic solvent is 4.5 mol:1 kg.

[0061] The method for preparing the local high-concentration aqueous electrolyte comprises the following steps:

[0062] Sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) is mixed with water and an organic solvent, and then mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether for a second time to obtain a locally high-concentration aqueous electrolyte.

[0063] The local high-concentration aqueous electrolyte obtained in Example 1 was subjected to electrochemical testing. Before the test, the electrolyte was passed through an inert gas for 2 h to remove dissolved oxygen in the water. Then, a titanium foil was used as a working electrode, an Ag / AgCl electrode was used as a reference electrode, and a platinum electrode was used as an auxiliary electrode to form a traditional three-electrode system. The scan rate was 0.1 mV·S -1 , and determine its electrochemical window.

[0064] The conductivity of the local high-concentration aqueous electrolyte obtained in Example 1 was tested using a DDS-11A instrument, and its conductivity was 14.8 mS·cm at room temperature. -1 .

[0065] The local high concentration aqueous electrolyte of Example 1 is 0.1V·S -1 The linear voltammetric curve at the scan rate is shown in Figure 1 As shown, from Figure 1 It can be seen that at 0.1mV·S-1 At a scan rate of , after adding TTE, the electrolyte voltage window reached a width of about 3.4 V, which can adapt to the stable operation of carbon-coated sodium vanadium phosphate as anode and cathode.

[0066] Comparative Example 1

[0067] The difference between Comparative Example 1 and Example 1 is that 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is not added, and the other parts are the same as Example 1.

[0068] The Raman spectra of the local high concentration aqueous electrolyte of Example 1 and the electrolyte of Comparative Example 1 are as follows: Figure 2 As shown, from Figure 2 It can be seen that the addition of TTE did not change the solvation structure in the solution.

[0069] The conductivity of the electrolyte obtained in Comparative Example 1 was tested using a DDS-11A instrument, and its conductivity was 6 mS·cm at room temperature. -1 .

[0070] Comparative Example 2

[0071] The difference between Comparative Example 2 and Example 1 is that the volume ratio of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether to N,N-dimethylformamide (DMF) is 1.5:1, and the rest is the same as Example 1.

[0072] After adding 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, the electrolyte in Comparative Example 1 was stratified and the electrolyte was immiscible.

[0073] Application Example 1

[0074] A sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte is the local high-concentration aqueous electrolyte of Example 1;

[0075] The positive / negative electrode sheets in the sodium ion battery are titanium foil and positive / negative electrode coatings coated on the titanium foil; the positive / negative electrode coatings include positive / negative electrode active materials, conductive carbon black and polyvinylidene fluoride (PVDF); the mass ratio of the positive / negative electrode active materials, conductive carbon black and polyvinylidene fluoride (PVDF) is 7:2:1; the positive electrode active materials and negative electrode active materials are both carbon-coated sodium vanadium phosphate; the diameter of the positive / negative electrode sheets is 16 mm, and the loading amount of the carbon-coated sodium vanadium phosphate on the positive electrode sheets is 1.2 mg / mm 2 The loading amount of carbon-coated sodium vanadium phosphate on the negative electrode sheet is 1.1 mg / mm 2 .

[0076] The preparation method of the positive / negative electrode sheet in the sodium ion battery is as follows:

[0077] (1) mixing carbon-coated sodium vanadium phosphate, conductive carbon black, polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP), manually grinding for 30 minutes, and ultrasonicating for 30 minutes to obtain positive / negative electrode slurry; the volume ratio of the carbon-coated sodium vanadium phosphate to N-methylpyrrolidone (NMP) is 1 g: 5 mL;

[0078] (2) The positive / negative electrode slurry obtained in step (1) is coated on a titanium foil, and then placed in a forced air drying oven and dried at 60° C. for 6 h, and then placed in a vacuum drying oven and dried at 90° C. for 12 h, and finally the current collector is punched into a positive / negative electrode sheet; the diameter of the electrode sheet is 16 mm.

[0079] The sodium ion battery in Application Example 1 was placed in a 25°C constant temperature box for charge and discharge tests, with the voltage set to 0-2V and the current density set to 1C.

[0080] The sodium ion battery cycle performance obtained in Application Example 1 is as follows Figure 3 As shown, from Figure 3 It can be seen that the capacity retention rate of the full battery prepared with locally high-concentration aqueous electrolyte is nearly 100% after 100 cycles.

[0081] The local high concentration aqueous electrolyte provided by the present invention has a -1 At a scan rate of , the voltage window reaches a width of about 3.4V, which can adapt to the stable operation of carbon-coated sodium vanadium phosphate as anode and cathode. The sodium ion battery prepared using a local high-concentration aqueous electrolyte has a capacity retention rate of nearly 100% after 100 cycles, which can improve the electrochemical performance of the battery.

[0082] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A local high concentration aqueous electrolyte comprising sodium salt, water, an organic solvent and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; The volume ratio of water to organic solvent is 1:(5-7); The molar ratio of the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether to the organic solvent is (0.5-0.8):1; The ratio of the amount of the sodium salt to the total mass of water and the organic solvent is (4-4.5) mol: 1 kg; The method for preparing the local high-concentration aqueous electrolyte comprises the following steps: After the sodium salt, water and organic solvent are mixed, they are mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether for a second time to obtain a local high-concentration aqueous electrolyte.

2. The local high concentration aqueous electrolyte according to claim 1, characterized in that: The sodium salt includes sodium perchlorate, sodium bis(trifluoromethylsulfonyl)imide or sodium trifluoromethanesulfonate.

3. The local high concentration aqueous electrolyte according to claim 1, characterized in that: The organic solvent includes N,N-dimethylformamide, sulfolane, dimethyl sulfoxide or ethylene glycol dimethyl ether.

4. The method for preparing the local high-concentration aqueous electrolyte according to any one of claims 1 to 3, comprising the following steps: After the sodium salt, water and organic solvent are mixed, they are mixed with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether for a second time to obtain a local high-concentration aqueous electrolyte.

5. A sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, characterized in that: The electrolyte is the locally high-concentration aqueous electrolyte described in any one of claims 1 to 3 or the locally high-concentration aqueous electrolyte prepared by the preparation method described in claim 4.

6. The sodium ion battery according to claim 5, characterized in that: The positive / negative electrode sheet in the sodium ion battery includes a current collector and a positive / negative electrode coating coated on the current collector; The positive / negative electrode coating comprises positive / negative electrode active materials, a conductive agent and a binder.

7. The sodium ion battery according to claim 6, characterized in that: The mass ratios of the positive / negative electrode active material, the conductive agent and the binder are independently (6.8-7.2):(1.8-2.2):(0.8-1.2).

8. The sodium ion battery according to claim 6 or 7, characterized in that: The positive electrode active material and the negative electrode active material are both carbon-coated sodium vanadium phosphate.

Images