Design of manganese sulfate mixed electrolyte and application of manganese sulfate mixed electrolyte in aqueous manganese metal battery

Abstract

The invention provides a design of a manganese sulfate mixed electrolyte and an application of the manganese sulfate mixed electrolyte in an aqueous manganese metal battery, and belongs to the field of aqueous manganese ion batteries. The mixed electrolyte takes manganese sulfate (MnSO4) as a solute and a mixture of ethylene glycol (EG) and water as a solvent. The electrolyte obviously widens an electrochemical stability window (ESW) and effectively inhibits a hydrogen evolution reaction and an oxygen evolution reaction. In the charging and discharging process, a karst cave-shaped structure is formed on the surface of the anode material, so that the specific surface area of the anode material is increased, and more nucleation sites are provided for manganese deposition. Meanwhile, the anode material is protected by the structure, and corrosion caused by direct contact between the anode material and electrolyte is reduced.

Description

Technical Field

[0001] The present invention relates to the field of aqueous manganese ion batteries, and specifically explores the design of a manganese sulfate mixed electrolyte and its application in aqueous manganese metal batteries. Background Art

[0002] For hundreds of years, fossil energy has been the main energy source for humanity. However, with the rapid development of the economy, non-renewable fossil energy is facing the problem of overconsumption. Against this background, the market share of renewable energy has been continuously increasing, and electrochemical energy storage systems have thus been widely developed. Electrochemical energy storage systems, especially batteries, have attracted extensive attention from researchers due to their flexibility, rapid response, environmental friendliness, and low maintenance costs. Since the 1990s, lithium-ion batteries (LiBs) have been rapidly commercialized and have taken a leading position in the fields of electric vehicles and portable devices. However, the high cost of lithium-ion batteries, the scarcity of lithium resources, and safety issues limit their application in large-scale energy storage.

[0003] Aqueous metal ion batteries, as potential alternatives to lithium-ion batteries, have attracted the attention of researchers. Currently, aqueous metal ion batteries mainly focus on magnesium (Mg), manganese (Mn), zinc (Zn), aluminum (Al), and calcium (Ca) ion batteries. Among them, aqueous manganese ion batteries have received extensive attention due to their relatively high theoretical specific capacity (7250 mAh cm -3 , 976 mAh g -1 ). In addition, manganese can be produced on a large scale by electrodeposition in an aqueous solution, and the industrial current efficiency exceeds 70%. These characteristics indicate that manganese metal is attractive as an anode material in electrochemical energy storage systems. However, the current problems faced by aqueous manganese ion batteries include the narrow theoretical electrochemical stability window (ESW) of water, and the easy generation of dendrites and corrosion when the aqueous electrolyte contacts the anode material.

[0004] Based on the above analysis, this patent proposes a method for preparing a MnSO4 mixed electrolyte. The MnSO4 mixed electrolyte consists of MnSO4 as the solute and a mixture of ethylene glycol (EG) and water as the solvent. During the charge and discharge process, a cave-like structure is formed on the surface of the anode material, increasing the specific surface area of the anode material, providing more nucleation sites for manganese deposition, protecting the anode material, and inhibiting the corrosion caused by the direct contact between the anode material and the electrolyte. With the introduction of EG, the hydrogen bond (HB) formed between H2O and EG weakens the inherent hydrogen bond between H2O molecules, inhibiting the activity of free water. In addition, MnSO4 does not break the intramolecular bond of EG and forms a new coordination bond with EG. Therefore, while maintaining the structural stability of EG, the MnSO4 mixed electrolyte effectively inhibits the activity of free water, improves the electrochemical performance of the electrolyte, inhibits the corrosion of the negative electrode material and the generation of dendrites, and expands the electrochemical stability window (ESW) of the electrolyte. The protection of this mixed electrolyte for the electrode material provides the possibility for preparing a manganese ion battery electrolyte with long-term stable cycling. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a MnSO4 mixed electrolyte, which consists of ethylene glycol (EG) and deionized water as the solvent and manganese sulfate (MnSO4) as the solute. The specific preparation steps are as follows: (1) First, dissolve MnSO4·H2O in a certain volume of deionized water to prepare an aqueous MnSO4 solution.

[0006] (2) Then, add an equal volume of ethylene glycol (EG) to the solution obtained in step (1) to obtain a MnSO4 mixed electrolyte.

[0007] In this preparation method, the preferred conditions are that the concentration of the electrolyte in step (2) is 1.8 mol / L, and the volume ratio of the solvent is ethylene glycol (EG) to water 1:1.

[0008] This preparation method is simple and low-cost, providing a design idea for a new type of mixed electrolyte for aqueous manganese ion batteries. The MnSO4 mixed electrolyte provided by the present invention forms a cave-like structure on the electrode surface during the charge and discharge process of the battery, providing a large number of nucleation sites for manganese deposition. This not only broadens the electrochemical stability window (ESW) of the electrolyte but also increases the specific surface area of the negative electrode material. In addition, this electrolyte can effectively prevent the direct contact between the negative electrode material and the electrolyte, thereby inhibiting passivation and corrosion. Compared with traditional pure aqueous electrolytes, the MnSO4 mixed electrolyte of the present invention shows more excellent electrochemical performance when used to prepare symmetric batteries and aqueous manganese ion full batteries. Description of the Drawings

[0009] Figure 1, XRD pattern of the electrode surface of the symmetric cell assembled with the MnSO4 mixed electrolyte after cycling.

[0010] Figure 2 , SEM images of the electrode surface of the symmetric cell assembled with the MnSO4 mixed electrolyte after cycling.

[0011] Figure 3 , Energy-dispersive X-ray spectroscopy (EDX) elemental mapping of the electrode surface of the symmetric cell assembled with the MnSO4 mixed electrolyte after cycling.

[0012] Figure 4 , Fourier transform infrared spectroscopy (FTIR) diagram of the MnSO4 mixed electrolyte.

[0013] Figure 5 , Raman spectroscopy (Raman) diagram of the MnSO4 mixed electrolyte.

[0014] Figure 6 , Long-term cycling performance diagram of the symmetric cell assembled with the MnSO4 mixed electrolyte at a current density of 0.1 mA cm −2 when.

[0015] Figure 7 , Tafel curve (Tafel) of the three-electrode system using the MnSO4 mixed electrolyte with a stainless steel working electrode, a carbon rod counter electrode, and an Ag / AgCl reference electrode.

[0016] Figure 8 , Linear sweep voltammetry (LSV) test of the three-electrode system using the MnSO4 mixed electrolyte with a stainless steel working electrode, a carbon rod counter electrode, and an Ag / AgCl reference electrode.

[0017] Figure 9 , Cyclic charge-discharge test of the all-solid-state battery assembled with the MnSO4 mixed electrolyte, nickel-based Prussian blue analogue, and zinc foil at a current density of 0.2 A g -1 . Specific implementation mode

[0018] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Embodiment

[0019] In this embodiment, the preparation steps of the MnSO4 mixed electrolyte are as follows: A. First, dissolve MnSO4·H2O in a certain volume of deionized water to prepare an aqueous MnSO4 solution.

[0020] B. Next, add an ethylene glycol (EG) solution to the prepared aqueous MnSO4 solution, ensuring that the volume ratio of deionized water to ethylene glycol is 1:1, and at the same time making the concentration of MnSO4 reach 1.8 mol / L. Example

[0021] In this example, the preparation steps of the MnSO4 aqueous electrolyte are as follows: Dissolve MnSO4·H2O in a certain volume of deionized water to prepare an aqueous MnSO4 solution with a concentration of 1.8 mol / L.

[0022] Morphology and structure characterization of materials Figure 2 The XRD pattern of the electrode surface after cycling of the symmetric cell assembled using the MnSO4 mixed electrolyte of the present invention is shown. It can be observed from the figure that Mn3SO4(OH)2·H2O is formed on the electrode surface.

[0023] Figure 3 The SEM image of the electrode surface of the symmetric cell assembled using the MnSO4 mixed electrolyte after cycling is shown, indicating that Mn3SO4(OH)2·H2O exhibits a loose and porous deposition morphology, similar to a karst cave. This structure not only provides abundant nucleation sites for manganese deposition but also effectively inhibits the corrosion and side reactions caused by the direct contact between the electrode and the electrolyte.

[0024] Figure 3 The energy-dispersive X-ray spectroscopy (EDX) elemental mapping further confirms the presence of Mn3SO4(OH)2·H2O.

[0025] Figure 4 The Fourier transform infrared spectrum (FTIR) of the MnSO4 mixed electrolyte of the present invention is shown, confirming that the hydrogen bond formed between ethylene glycol and water weakens the inherent hydrogen bond between water molecules.

[0026] Figure 5 The Raman spectrum of the MnSO4 mixed electrolyte of the present invention is provided, indicating that the electrolyte does not damage the molecular structure of ethylene glycol.

[0027] Test results of the electrochemical performance of materials: First, use the MnSO4 mixed electrolyte prepared in Example 1 to assemble a symmetric cell and perform a cyclic stability test at a current density of 0.1 mA cm−2. In addition, the mixed electrolyte was tested by Tafel curve (Tafel) and linear voltammetry in a three-electrode system. The specific configuration was that the working electrode was stainless steel, the counter electrode was a carbon rod, and the reference electrode was Ag / AgCl. Furthermore, the electrolyte is also used in an aqueous manganese-ion full battery composed of a nickel-based Prussian blue analogue cathode and a zinc foil anode, and cyclic charge-discharge tests are carried out at a current density of 0.2 A g-1.

[0028] From Figure 6 the results of the galvanostatic charge-discharge tests, it can be seen that for the symmetric battery using the MnSO4 mixed electrolyte, at a current density of 0.1 mA cm-2, after 250 hours of galvanostatic charge-discharge cycling, the overpotential is only 160.6 mV. While the symmetric battery using the aqueous MnSO4 electrolyte shows instability after 20 hours of cycling, which may be due to side reactions or dendrite formation in the battery. Thus, the MnSO4 mixed electrolyte significantly improves the cycling performance of the battery.

[0029] Figure 7 shows the results of the Tafel curve test, indicating that the corrosion current of the mixed electrolyte is 4.733×10-2 mA cm-2, while the corrosion current of the aqueous MnSO4 electrolyte is 9.708×10-2 mA cm-2. This shows that the MnSO4 mixed electrolyte effectively reduces the corrosion rate of the electrode. Ethylene glycol (EG) effectively inhibits the activity of free water through its interaction with water molecules, thereby reducing the corrosion rate of the electrolyte on the electrode.

[0030] Figure 8 is the test result of linear sweep voltammetry (LSV), showing that the MnSO4 mixed electrolyte significantly broadens the electrochemical stability window (ESW). When the voltage exceeds 1.5 V and is lower than -0.75 V, the curve of the aqueous MnSO4 electrolyte shows severe fluctuations, while the MnSO4 mixed electrolyte effectively inhibits the hydrogen evolution and oxygen evolution reactions by suppressing the activity of free water.

[0031] From Figure 9 it can be seen that at a current density of 0.2 A g-1, the battery using the nickel-based Prussian blue analogue as the cathode material exhibits an initial specific capacity of 200 mAh g-1. The MnSO4 mixed electrolyte has good application prospects in the field of aqueous manganese-ion batteries, and the method of the present invention has wide applicability and can be extended to other energy storage battery systems, providing new ways and concepts for improving the cycling stability of batteries and inhibiting negative electrode corrosion.

[0032] The above description is only the preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention all belong to the scope of the technical solution of the present invention.

Claims

1. Design of manganese sulfate mixed electrolyte, characterized by the following steps: (1) Dissolve MnSO4·H2O in a certain volume of deionized water to prepare an aqueous MnSO4 solution; (2) Add the same volume of ethylene glycol (EG) as in step (1) to the solution obtained in step (1) to obtain a MnSO4 mixed electrolyte.

2. The preparation method according to claim 1, characterized in that, The concentration of the aqueous MnSO4 solution prepared in step (1) is 3.6 mol / L.

3. The preparation method according to claim 1, characterized in that, The electrolyte obtained in step (2) is a 1.8 mol / L MnSO4 mixed electrolyte, in which the volume ratio of ethylene glycol (EG) to water is 5:

5.

4. Application of the MnSO4 mixed electrolyte according to claim 1 in the electrolyte of an aqueous aluminum-ion battery.

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