Deep eutectic electrolyte and application thereof in aqueous sodium-ion battery

Abstract

The application discloses a deep eutectic electrolyte and application thereof in a water-based sodium ion battery, which is prepared by mixing sodium perchlorate monohydrate, water and urea and stirring into a transparent solution, so as to obtain the deep eutectic electrolyte. 0.44 The dissolution of Mn in the MnO2 (NMO) helps to maintain the structural integrity of the NMO, and further improves the cycle performance and coulombic efficiency of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of aqueous sodium ion battery electrolytes, and in particular to a deep eutectic electrolyte and application thereof in aqueous sodium ion batteries. Background Art

[0002] The growing demand for energy storage has driven the widespread application of lithium-ion batteries in portable electronic devices, electric vehicles, and smart grids. Although lithium-ion batteries have unique advantages in energy storage technology due to their high energy density and long cycle life, the safety of lithium and the continued rise in lithium prices due to limited lithium resources have hindered the large-scale application of lithium-ion batteries. Sodium has similar physical and chemical properties to lithium and is highly abundant, showing excellent sustainability and outstanding cost-effectiveness. Therefore, sodium-ion batteries are highly competitive in replacing lithium-ion batteries as a new energy storage technology. In particular, highly safe aqueous rechargeable sodium-ion batteries (ARSIBs) show more significant application prospects in large-scale energy storage.

[0003] Among the cathode materials, Prussian blue analogues, manganese oxide and NASICON-type Na3V2(PO4)3 have been tried to improve the electrochemical performance of ARSIBs. 0.44 MnO2 (NMO) boasts excellent cost-effectiveness and environmental friendliness, making it considered one of the most promising cathode materials for scalable synthesis. However, due to the close proximity of Na sites in NMO and the strong repulsive forces present, the NMO structure is unstable in aqueous electrolytes with high Na content. Furthermore, the dissolution of Mn during the redox process can also lead to structural collapse. This structural instability of NMO in aqueous electrolytes significantly limits its application in aqueous sodium-ion batteries. Summary of the Invention

[0004] In response to the above-mentioned problems currently existing in aqueous sodium-ion batteries, the present invention provides a deep eutectic electrolyte and its application in aqueous sodium-ion batteries. The deep eutectic electrolyte prepared by this method can effectively inhibit the dissolution of Mn in NMO, the positive electrode material of aqueous sodium-ion batteries, help maintain the structural integrity of NMO, and thus improve the cycle performance and coulombic efficiency.

[0005] To achieve the purpose, the present invention adopts the following technical solutions:

[0006] A deep eutectic electrolyte is obtained by mixing sodium perchlorate monohydrate NaClO4·H2O, water and urea CO(NH2)2 and stirring the mixture into a transparent solution.

[0007] Preferably, the usage ratio of sodium perchlorate monohydrate, water and urea is 1-3 mol: 1-3 mol: 1-3 mol.

[0008] Preferably, the stirring time is 12-18h.

[0009] The application also provides application of the deep eutectic electrolyte in a water-based sodium ion battery. 0.44 MnO2(NMO).

[0010] Compared with the prior art, the application has the following beneficial effects:

[0011] The application prepares a deep eutectic electrolyte with a low eutectic point through a simple scheme, the electrolyte has high ionic conductivity and suitable viscosity, most of the water molecules participate in the formation of the sodium ion solvation sheath structure, and the number of free water is greatly reduced. The preparation method is simple, and the prepared deep eutectic electrolyte effectively inhibits the dissolution of Mn in the NMO positive electrode material of the water-based sodium ion battery, helps to maintain the structural integrity of the NMO, and further improves the cycle performance and coulombic efficiency of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a differential scanning calorimetry data graph of the 1-4-2 electrolyte prepared in Example 1 of the application;

[0013] Figure 2 is a transmission electron microscope graph of the NMO positive electrode material prepared in Example 1 of the application;

[0014] Figure 3 is an X-ray diffraction spectrum of the NMO positive electrode material prepared in Example 1 of the application;

[0015] Figure 4 is a cyclic voltammetry curve graph of the NMO positive electrode in the 1-4-2 electrolyte prepared in Example 1 of the application, wherein a and b correspond to different voltage windows;

[0016] Figure 5 is a transmission electron microscope graph of the NMO positive electrode after 100 cycles in the 1-4-2 electrolyte prepared in Example 1 of the application;

[0017] Figure 6 is a cycle performance curve graph of the NMO positive electrode in the electrolyte prepared in Example 1 and Comparative Example 1 of the application;

[0018] Figure 7 is an X-ray diffraction spectrum of the NMO positive electrode after 100 cycles in the electrolyte prepared in Example 1 and Comparative Example 1 of the application;

[0019] Figure 8 is a transmission electron microscope graph of the NMO positive electrode after 100 cycles in the sodium sulfate electrolyte prepared in Example 1 of the application. DETAILED DESCRIPTION

[0020] In order to further illustrate the present application, a preparation method of a deep eutectic electrolyte and its application in a water-based sodium ion battery are described in detail below in combination with examples, and are described in combination with the accompanying drawings, but it cannot be understood as limiting the protection scope of the present application.

[0021] Example 1

[0022] The deep eutectic electrolyte was prepared according to the following steps:

[0023] The sodium perchlorate monohydrate, water and urea with a molar ratio of 1 mol: 3 mol: 2 mol were placed in a beaker, and the mixture was stirred into a transparent solution, thereby obtaining a deep eutectic electrolyte, which is recorded as 1-4-2 electrolyte.

[0024] The electrochemical performance of the 1-4-2 electrolyte prepared in this example was tested in a water-based sodium ion battery with NMO as the positive electrode material, and the preparation method of the NMO positive electrode material was as follows:

[0025] Step 1, 1.283 g of sodium carbonate was ground with 5.748 g of manganese carbonate for 1 h, and then the uniform mixture was pressed under a pressure of 10 MPa.

[0026] Step 2, the mixture obtained in step 1 was placed in a tube furnace with an argon atmosphere at 900℃ for 10 h, and the heating rate of the tube furnace was 5℃ / min -1 After natural cooling to room temperature, the NMO positive electrode material was obtained.

[0027] It can be seen from Figure 1 that the deep eutectic electrolyte mixed from sodium perchlorate monohydrate, water and urea in a ratio of 1:3:2 has a low eutectic temperature of -19℃. The concentration of sodium perchlorate in the electrolyte is moderate, so it has a suitable viscosity and at the same time has a relatively high ionic conductivity. Almost all water molecules participate in the formation of the sodium ion solvent sheath structure, which maximally reduces the number of free water, thereby effectively inhibiting the activity of water.

[0028] As can be seen from Figure 2 , the NMO positive electrode material prepared in this example has a micrometer-sized rod-like structure.

[0029] Figure 3 The X-ray diffraction pattern of the NMO positive electrode material, as shown in the figure, shows that the NMO has an orthorhombic structure, and no obvious impurity peak appears.

[0030] The three-electrode test system with the 1-4-2 electrolyte obtained in this example as the electrolyte, NMO as the working electrode, Pt as the counter electrode and Ag / AgCl as the reference electrode was used for electrochemical performance test on a CHI 600E electrochemical workstation.

[0031] From Figure 4 It can be seen that when the working voltage is 0-0.8V (vs. SHE), the cyclic voltammograms are well overlapped except the first cycle, indicating that NMO has excellent reversibility in 1-4-2 electrolyte. When the working voltage range is expanded to-0.3-0.8V (vs. SHE), the NMO electrode still has good reversibility.

[0032] Figure 5 The transmission electron microscopy image of NMO positive electrode after 100 cycles at a current density of 0.2C in 1-4-2 electrolyte can be seen that the cycled NMO still maintains good rod-like morphology, indicating that it has excellent structural stability in 1-4-2 electrolyte.

[0033] Comparative Example 1

[0034] The 1M sodium sulfate electrolyte was prepared according to the following steps:

[0035] 1.42g of sodium sulfate was added to a 10mL volumetric flask, deionized water was added to the volumetric flask to the calibration line, and the bottle cap was closed and shaken until the sodium sulfate was completely dissolved, thereby obtaining a 1M sodium sulfate electrolyte.

[0036] The electrochemical performance of the sodium sulfate electrolyte prepared in this example was tested in a water-based sodium ion battery with NMO as the positive electrode material, and the NMO positive electrode material was prepared according to the method described in Example 1.

[0037] The electrochemical performance test was carried out on a CHI 600E electrochemical workstation using a three-electrode test system with the 1M sodium sulfate solution obtained in this example as the electrolyte, NMO as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode.

[0038] Figure 6 The cycle performance curves of NMO positive electrode at a current density of 0.2C in Example 1 and Comparative Example 1 are shown, and from the figure, it can be seen that NMO has stronger cycle stability in 1-4-2 electrolyte, and the capacity retention rate after 100 cycles is as high as 95%; in contrast, the capacity retention rate in sodium sulfate electrolyte is only 65%, indicating that NMO may be damaged in sodium sulfate solution.

[0039] From Figure 7 It can be seen that after 100 cycles of NMO in 1-4-2 electrolyte, the X-ray diffraction peaks have little change, maintaining the original orthorhombic structure; on the contrary, in the sodium sulfate electrolyte prepared in Comparative Example 1, the intensity of NMO diffraction peaks is greatly reduced or even some peaks completely disappear, indicating that the crystal structure of NMO has changed, revealing the reason for the capacity decay.

[0040] Figure 8The transmission electron microscope image of NMO positive electrode after 100 cycles in 0.2C current density in sodium sulfate electrolyte, as can be seen from the figure, the rod structure of NMO is crushed.

[0041] Table 1 is the concentration of manganese element in the electrolyte of example 1 and comparative example 1 after 100 cycles. As can be seen from table 1, the detected Mn content in 1-4-2 electrolyte is much lower than that in 1M sodium sulfate electrolyte, indicating that 1-4-2 deep eutectic electrolyte can effectively inhibit the dissolution of Mn in NMO, which helps to maintain the structural integrity of NMO positive electrode material, and further improves the cycle performance and coulomb efficiency.

[0042] Table 1

[0043] Electrolyte Sodium sulfate 1-4-2 Mn concentration (mol L -1 ) 0.1 0.001

[0044] The above is only an exemplary embodiment of the present application, and is not intended to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A deep eutectic electrolyte, characterized in that: The deep eutectic electrolyte is obtained by mixing sodium perchlorate monohydrate, water and urea in a dosage ratio of 1 mol:3 mol:2 mol and stirring to form a transparent solution.

2. The deep eutectic electrolyte according to claim 1, wherein: The stirring time is 12 to 18 hours.

3. Use of the deep eutectic electrolyte according to any one of claims 1 to 2 in an aqueous sodium ion battery.

4. The use according to claim 3, characterized in that: The positive electrode material of the aqueous sodium ion battery is Na 0.44 MnO2.

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