Wide potential water system magnesium ion electrolyte and application thereof

Abstract

The application relates to the technical field of aqueous secondary batteries, and discloses a wide-potential aqueous magnesium ion electrolyte and application thereof, wherein the electrolyte comprises magnesium chloride, water and polyethylene glycol, and the mass percentage of the polyethylene glycol and the water is 1% to 99.5%. The application further discloses an aqueous magnesium ion battery prepared by using the electrolyte, and low-potential materials such as TiO2(B) can be selected as negative electrode materials. The application solves the technical problem that the secondary battery with the existing negative electrode of TiO2(B) and other materials has a low potential and cannot adapt to the working electrolyte.

Description

Technical Field

[0001] This invention relates to the field of aqueous secondary battery technology, specifically to a wide-potential aqueous magnesium ion electrolyte and its applications. Background Technology

[0002] Secondary batteries, such as rechargeable lithium-ion batteries and aqueous magnesium-ion batteries, have become a research and application hotspot due to their high energy density, long cycle life, and high voltage. Among them, rechargeable lithium-ion batteries have been commercialized and occupy a significant share of the market for rechargeable energy storage devices. However, in recent years, the flammability of the organic electrolyte in lithium-ion batteries has led to frequent safety accidents caused by lithium-ion batteries, and the high requirements for their production environment (such as water oxygen content below 0.1 ppm) have limited the application of lithium-ion batteries in large-scale energy storage devices.

[0003] Aqueous magnesium-ion batteries use aqueous electrolytes, avoiding the use of flammable organic electrolytes, thus offering high safety and good ionic conductivity. Existing technology, such as CN113078373A, discloses an aqueous metal-ion secondary battery and its aqueous electrolyte. The aqueous metal-ion secondary battery includes a positive electrode, a negative electrode, and an aqueous electrolyte. The aqueous electrolyte comprises an electrolyte, water, and an organic compound. The electrolyte includes magnesium or aluminum salts. The organic compound includes one or more of ether compounds and alcohol compounds. The mass percentage of the organic compound to water ranges from 5% to 99.5%. This electrolyte is suitable for magnesium or aluminum metal negative electrodes, and various salts can meet the requirements, thus its application is relatively wide.

[0004] However, the existing technologies have the following problems: when the negative electrode is made of a material with a low potential, such as Bronze phase TiO2(B), the existing electrolyte cannot meet the requirements of the negative electrode for the electrode potential. Therefore, it is particularly important to develop a new aqueous rechargeable magnesium ion battery electrolyte with a wide potential range. Summary of the Invention

[0005] The present invention aims to provide a wide-potential aqueous magnesium ion electrolyte and its application, in order to solve the technical problem that existing secondary batteries with TiO2(B) and other materials as negative electrodes do not have suitable working electrolytes due to their low potential.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a wide potential aqueous magnesium ion electrolyte, comprising magnesium chloride, water and polyethylene glycol, wherein the mass percentage of polyethylene glycol to water is 1% to 99.5%.

[0007] The present invention also discloses the application of a wide-potential aqueous magnesium ion electrolyte in an aqueous magnesium ion battery, wherein the aqueous magnesium ion battery includes a positive electrode, a negative electrode and an electrolyte.

[0008] The principles and advantages of this scheme are:

[0009] The narrow electrochemical stability window of aqueous electrolytes not only limits the energy density of aqueous magnesium-ion batteries but also restricts the selection of electrode materials. At 1.8V (1.8V~3.6V vs. Mg...), 2+ Within the electrochemical stability window of Mg, most electrode materials cannot function properly, especially anode materials. TiO2 anode materials have advantages such as not forming dendrites, making them very promising anode materials for secondary batteries. In particular, bronze phase TiO2(B) has shown good electrochemical performance in aqueous rechargeable metal-ion batteries. However, TiO2(B) has high requirements for electrolytes due to its low potential, which means that existing conventional electrolytes cannot meet the electrode potential requirements of the anode.

[0010] To address the aforementioned problems, the inventors of this application selected magnesium chloride as the electrolyte. Compared to other magnesium salts such as magnesium nitrate and magnesium perchlorate, chloride ions exhibit greater stability, further broadening the electrochemical stability window of the electrolyte. The adsorption of magnesium ions by chloride ions also reduces the interfacial resistance to magnesium ion diffusion. In contrast, nitrate and perchlorate ions are highly oxidizing and decompose at low potentials, forming a solid electrolyte film on the electrode surface, preventing magnesium ions from intercalating.

[0011] Polyethylene glycol (PEG) was selected as an organic additive to suppress the side reactions of hydrogen evolution and oxygen evolution, thus broadening the electrochemical stability window of the aqueous electrolyte. Simultaneously, PEG disrupts the hydrogen bond network of water molecules in the aqueous electrolyte, reducing the activity of water molecules and decreasing the dissolution of electrode materials. Furthermore, PEG can coordinate with magnesium ions, reducing the number of water molecules in the solvation sheath structure of magnesium ions and lowering the desolvation energy of magnesium ions. This reduces the energy at the electrode / electrolyte interface in magnesium-ion batteries, improving voltage stability and cycle life stability, and also mitigating the slow desolvation process at the interface.

[0012] Preferably, as an improvement, the polyethylene glycol includes any one of polyethylene glycol 400, polyethylene glycol 300, and polyethylene glycol 200.

[0013] In this application, using polyethylene glycol with a lower molecular weight can improve ionic conductivity and ion diffusion coefficient. Higher molecular weight, on the other hand, leads to increased electrolyte viscosity, resulting in decreased ionic conductivity and diffusion coefficient.

[0014] Preferably, as an improvement, the concentration of magnesium chloride is 0.01–5 mol·kg⁻¹. -1 .

[0015] In this application, magnesium chloride is used as the electrolyte, and its concentration range maintains a wide electrochemical stability window for the battery. If the magnesium chloride concentration is too low, the battery electrolyte cannot function; if the magnesium chloride concentration is too high, its relative battery capacity decreases.

[0016] Preferably, as an improvement, the mass percentage of polyethylene glycol to water is 1%, 33%, 50%, 75%, 83%, or 90%.

[0017] In this application, the mass percentage of polyethylene glycol to water can be adjusted according to the electrolyte concentration, and the above are the optimal values ​​found in the experiment.

[0018] Preferably, as an improvement, the material of the positive electrode of the aqueous magnesium ion battery includes V2O5 or manganese magnesium oxide.

[0019] In this application, most of the positive electrode materials for secondary batteries can be used, and the positive electrode made of the above two materials is the preferred embodiment.

[0020] Preferably, as an improvement, the material of the anode of an aqueous magnesium-ion battery includes TiO2(B) or VO2.

[0021] In this application, both TiO2(B) and VO2 are electrode materials with low potentials. In particular, when TiO2(B) is used as the negative electrode material, its charge-discharge voltage plateau in a magnesium-ion battery is approximately 0.6V (vs. Mg). 2+ At such a potential ( / Mg), the requirements for the electrolyte are extremely high, and its successful application has broadened the selection range of existing secondary battery anode materials. Attached Figure Description

[0022] Figure 1 In Example 1 of this invention, TiO2(B) at 50 mAg -1 The constant current charge-discharge curves for the first three cycles at the current density;

[0023] Figure 2 In Example 1 of this invention, TiO2(B) at 100 mA g -1 Cyclic curve at current density;

[0024] Figure 3 This is a test graph of the cycling stability of TiO2(B) in Example 1 of the present invention;

[0025] Figure 4 This is a CV (cyclic voltammetry) curve of the aqueous magnesium-ion battery in Example 1 of the present invention;

[0026] Figure 5 The CV curve of the aqueous magnesium-ion battery in Comparative Example 1 of this invention is shown.

[0027] Figure 6 This is a CV curve of the aqueous magnesium-ion battery in Comparative Example 2 of the present invention;

[0028] Figure 7 The CV curve of the aqueous magnesium-ion battery in Comparative Example 3 of this invention is shown.

[0029] Figure 8 This is the CV curve of the aqueous magnesium-ion battery in Comparative Example 4 of the present invention.

[0030] Figure 9 This is a linear sweep voltammetry curve of the electrolyte in Experimental Example 1 of this invention;

[0031] Figure 10 This is a test graph of the cycling stability of TiO2(B) in Example 2 of the present invention. Detailed Implementation

[0032] The following detailed description illustrates the specific implementation method:

[0033] Example 1

[0034] A wide-potential aqueous magnesium ion electrolyte comprises water containing magnesium chloride and polyethylene glycol, wherein the concentration of magnesium chloride is 2 mol·kg⁻¹. -1 The weight percentage of polyethylene glycol to water is 75%. Specifically, 0.2 mol of magnesium chloride hexahydrate is added to a mixed solvent consisting of 25 g of water and 75 g of polyethylene glycol 400, and the mixture is stirred for 8 hours to prepare the electrolyte. In this embodiment, polyethylene glycol 400 is used. Choosing a polyethylene glycol with a smaller molecular weight can improve the ionic conductivity and the ion diffusion coefficient.

[0035] This embodiment also provides an application of a wide-potential aqueous magnesium-ion electrolyte in an aqueous magnesium-ion battery. The negative electrode material of the aqueous magnesium-ion battery is TiO2(B), the positive electrode material is V2O5, and the electrolyte is the aforementioned electrolyte. Carbon cloth is used as the current collector for both the positive and negative electrodes. The positive electrode, electrolyte, and negative electrode are assembled into a secondary battery in a stacked configuration, and performance testing is then performed. The test results are attached. Figures 1-4 As shown.

[0036] Example 2

[0037] The difference between this embodiment and Example 1 is that the concentration of magnesium chloride in the electrolyte is 4 mol·kg⁻¹. -1 Everything else was the same as in Example 1. See the appendix for detailed experimental results. Figure 10 .

[0038] Comparative Example 1

[0039] The difference between this comparative example and Example 1 is that magnesium nitrate is used instead of magnesium chloride as the electrolyte. All other aspects are the same as in Example 1. Detailed experimental results are shown in the appendix.Figure 5 .

[0040] Comparative Example 2

[0041] The difference between this comparative example and Example 1 is that magnesium perchlorate is used instead of magnesium chloride as the electrolyte. Everything else is the same as in Example 1. Detailed experimental results are shown in the appendix. Figure 6 .

[0042] Comparative Example 3

[0043] The difference between this comparative example and Example 1 is that a mixed solution of magnesium nitrate and magnesium chloride is used instead of magnesium chloride as the electrolyte, and the magnesium ion concentration in the mixed solution is 2 mol·kg⁻¹. -1 Everything else was the same as in Example 1. See the appendix for detailed experimental results. Figure 7 .

[0044] Comparative Example 4

[0045] The difference between this comparative example and Example 1 is that a mixed solution of magnesium perchlorate and magnesium chloride is used instead of magnesium chloride as the electrolyte, and the magnesium ion concentration in the mixed solution is 2 mol·kg⁻¹. -1 Everything else was the same as in Example 1. See the appendix for detailed experimental results. Figure 8 .

[0046] Experimental Example 1: The effect of the weight percentage of polyethylene glycol and water in the electrolyte on the electrochemical stability window

[0047] Experimental Methods: Electrolytes were prepared with weight percentages of 0%, 33%, 50%, 75%, 83%, and 90% of polyethylene glycol 400 and water, respectively. Other components of the electrolytes were the same as in Example 1. Linear sweep voltammetry curves of the electrolytes were measured, and the experimental results are attached. Figure 9 As shown.

[0048] Analysis of experimental results:

[0049] The aqueous magnesium-ion battery prepared in Example 1 of this application is shown in the attached figure. Figure 1 and 4 As shown, the cyclic voltammetry curve contains multiple pairs of redox peaks, corresponding to the insertion and extraction of magnesium ions in the electrode material. Meanwhile, no hydrogen or oxygen evolution side reactions occurred throughout the entire charge-discharge process.

[0050] As attached Figure 2 As shown, there are multiple voltage plateaus during the charging and discharging process, and the voltage value at the plateau is related to... Figure 1 The redox peaks in the samples are in the same position, corresponding to the insertion and extraction of magnesium ions in the electrode material.

[0051] As attached Figure 3The aqueous magnesium-ion battery prepared in Example 1 showed a coulombic efficiency close to 100% after 100 cycles, with almost no degradation. The curve at the bottom of the figure represents the specific capacity change of this secondary battery; after 100 cycles, the specific capacity of this secondary battery is still close to 60 mAh g⁻¹. -1 Therefore, it can be seen that after 100 cycles, the specific capacity and coulombic efficiency of this secondary battery have hardly decreased.

[0052] Appendix Figures 5-8 For the CV plots of Comparative Examples 1-4, it can be seen that when the electrolyte in the electrolyte is replaced with other magnesium salts and mixed magnesium salts, no redox peaks appear, which means there is no magnesium ion insertion and extraction process, and it cannot serve as a battery electrolyte.

[0053] Appendix Figure 9 The results show that when the weight ratio of organic additives to water in the electrolyte changes, a wider potential range can be formed, and the working requirements can be met when a negative electrode material with a lower potential is selected.

[0054] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. The application of a wide-potential aqueous magnesium ion electrolyte in the preparation of aqueous magnesium ion batteries, characterized in that: The electrolyte comprises magnesium chloride, water, and polyethylene glycol, with magnesium chloride being the only electrolyte; the mass percentage of polyethylene glycol to water is 1% to 99.5%; the polyethylene glycol includes any one of polyethylene glycol 400, polyethylene glycol 300, and polyethylene glycol 200; the concentration of magnesium chloride is 0.01 to 5 mol·kg⁻¹. -1 ; The aqueous magnesium-ion battery also includes a positive electrode and a negative electrode. The negative electrode material includes TiO2(B) or VO2, and the positive electrode material includes V2O5 or manganese magnesium oxide.

2. The application according to claim 1, characterized in that: The mass percentages of the polyethylene glycol and water are 1%, 33%, 50%, 75%, 83%, and 90%.

3. An aqueous magnesium-ion battery, characterized in that: Includes the electrolyte, positive electrode, and negative electrode as described in claim 1 or 2.

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