Aqueous electrolyte and use thereof

Abstract

The application relates to the technical field of water-based secondary batteries, and discloses a water-based electrolyte which comprises an electrolyte, water and an organic compound; the organic compound is an alcohol ether small-molecule compound. The application further discloses an application of the water-based electrolyte in a water-based secondary battery, and the negative electrode material of the water-based secondary battery comprises TiO2, and the positive electrode material comprises V2O5. The application solves the technical problem that the existing water-based electrolyte has a narrow electrochemical stability window.

Description

Technical Field

[0001] This invention relates to the field of aqueous secondary battery technology, specifically to an aqueous electrolyte and its application. 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, which avoids the use of flammable organic electrolytes, thus offering high safety and good ionic conductivity. However, the narrow electrochemical stability window of water molecules, theoretically only 1.23V, limits the overall electrochemical stability of aqueous electrolytes. While the addition of an electrolyte can broaden this window to around 1.8V, it is still far from the 4V of current lithium-ion batteries. This narrow electrochemical stability window of aqueous electrolytes has become a significant factor limiting the energy density of aqueous metal-ion batteries.

[0004] The narrow electrochemical stability window of aqueous electrolytes not only limits the energy density of aqueous ion batteries but also restricts the selection of electrode materials. Within the 1.8V electrochemical stability window, most electrode materials fail to function properly, instead exhibiting severe hydrogen and oxygen evolution side reactions. Therefore, developing an aqueous electrolyte that can be stably used within the 1.8V electrochemical stability window is of paramount importance. Summary of the Invention

[0005] The present invention aims to provide an aqueous electrolyte and its application to solve the technical problem that existing aqueous electrolytes have a narrow electrochemical stability window.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: an aqueous electrolyte comprising an electrolyte, water, and an organic compound; wherein the organic compound is a small molecule compound of alcohol ethers.

[0007] The present invention also provides an application of an aqueous electrolyte in an aqueous secondary battery, the aqueous secondary battery comprising a positive electrode, a negative electrode and the above-mentioned aqueous electrolyte.

[0008] The principle and advantages of this solution are as follows: As described in the background technology, existing aqueous secondary batteries have a narrow electrochemical stability window. The limiting electrochemical stability window after adding an electrolyte is around 1.8V. However, within this electrochemical stability window, most electrode materials and electrolytes cannot be adapted to work normally, which limits their practical application scenarios.

[0009] To address the aforementioned problems, the inventors of this application have creatively used alcohol ether small molecule compounds as organic additives in this electrolyte. Because these compounds possess hydrophilic groups, they can form a homogeneous miscible electrolyte with water, ensuring sufficient miscibility between the electrolyte and the electrolyte. Simultaneously, the O atoms in the alcohol ether small molecule compounds bind with the H atoms in the free water of the electrolyte, limiting the activity of free water and thus reducing the contact between free water and the electrode surface, thereby reducing the dissolution of the electrode material. Furthermore, similar to general organic additives, alcohol ether small molecule compounds can inhibit the occurrence of hydrogen evolution and oxygen evolution side reactions, broadening the electrochemical stability window of the aqueous electrolyte and increasing the range of electrode material selection. The addition of organic compounds disrupts the hydrogen bond network of water molecules in the aqueous electrolyte, reducing the activity of water molecules and decreasing the dissolution of the electrode material. At the same time, the organic compounds form coordination with magnesium or zinc ions, reducing the number of water molecules in the solvation sheath structure of magnesium or zinc ions, lowering the water molecule content at the electrode / electrolyte interface, and improving the voltage stability and cycle life stability of the battery.

[0010] Preferably, as an improvement, the organic compound includes one or more of diethylene glycol, triethylene glycol, and tripropylene glycol, and the mass percentage of the organic compound to water is 1% to 99.5%.

[0011] In this application, diethylene glycol, triethylene glycol, and tripropylene glycol are all small molecule compounds of alcohol ethers. The electrolyte composed of them has a high desolvation energy. During the magnesium intercalation process, desolvation is not performed. The magnesium intercalation / deintercalation process is completed by solvent co-intercalation / deintercalation mechanism. Therefore, the influence of the slow desolvation process on the magnesium intercalation kinetics can be reduced, and the stability of the secondary battery can be improved.

[0012] Preferably, as an improvement, the electrolyte may be a magnesium salt, which includes one or more of magnesium sulfate, magnesium chloride, magnesium perchlorate, magnesium acetate, magnesium chlorate, magnesium trifluoromethanesulfonate, and magnesium bis(trifluoromethanesulfonyl)imide.

[0013] In this application, most magnesium salts used in secondary batteries can be used as electrolytes in this scheme, among which magnesium chloride and magnesium bis(trifluoromethanesulfonyl)imide are preferred.

[0014] Preferably, as an improvement, the electrolyte may be a zinc salt, which includes one or more of zinc sulfate, zinc nitrate, zinc chloride, zinc perchlorate, zinc acetate, zinc chlorate, zinc trifluoromethanesulfonate, and zinc bis(trifluoromethanesulfonyl)imide.

[0015] In this application, most zinc salts used in secondary batteries can be used as electrolytes in this scheme, among which zinc chloride and zinc bis(trifluoromethanesulfonyl)imide are preferred.

[0016] Preferably, as an improvement, the concentration of the zinc salt or magnesium salt is 0.01–10 mol·kg⁻¹. -1 .

[0017] In this application, a high concentration of zinc or magnesium salts will increase the resistance in the electrolyte, causing the electrolyte to malfunction.

[0018] Preferably, as an improvement, the electrolyte further includes one or more of potassium salt, sodium salt, lithium salt, calcium salt, and aluminum salt.

[0019] In this application, most zinc salts used in secondary batteries can be used as electrolytes in this scheme.

[0020] Preferably, as an improvement, the concentration of the potassium salt, sodium salt, lithium salt, calcium salt, or aluminum salt is 0.01–12 mol·kg⁻¹. -1 .

[0021] In this application, it is necessary to ensure that the concentration of the electrolyte is within a suitable operating range, and the above range is the preferred applicable range in actual use of this application.

[0022] Preferably, as an improvement, the negative electrode material includes TiO2, and the positive electrode material includes V2O5.

[0023] In this application, when TiO2 is used as the negative electrode material, its charge and discharge voltage plateau in magnesium-ion batteries is relatively low, and its requirements for electrolyte are extremely high. Therefore, the use of TiO2 as the negative electrode material means that the electrolyte in this solution can meet the requirements of most negative electrode materials. Attached Figure Description

[0024] Figure 1 This is a constant current charge-discharge curve of the secondary battery in Embodiment 1 of the present invention;

[0025] Figure 2 This is a cycle curve diagram of the secondary battery in Embodiment 1 of the present invention;

[0026] Figure 3 This is the cyclic voltammogram of the secondary battery in Embodiment 1 of the present invention;

[0027] Figure 4 This is the cyclic voltammetry diagram of the secondary battery in Embodiment 2 of the present invention;

[0028] Figure 5 This is a linear scan voltammetry diagram of the secondary battery in Comparative Example 1 of the present invention;

[0029] Figure 6 This is the linear scan voltammogram in Experimental Example 1 of this invention;

[0030] Figure 7 The figures show the constant current intermittent titration curve and the change in magnesium ion diffusion rate in Experiment Example 2 of this invention. Detailed Implementation

[0031] The following detailed description illustrates the specific implementation method:

[0032] Example 1

[0033] An aqueous electrolyte comprises an electrolyte, water, and an organic compound. In this embodiment, the electrolyte is selected as 2 mol / kg. -1 Magnesium chloride was used, and the organic compound selected was triethylene glycol, with a weight percentage of 90% triethylene glycol to water. Specifically, 0.2 mol of magnesium chloride hexahydrate was added to a mixed solvent consisting of 10 g of water and 90 g of triethylene glycol, and stirred for 8 hours to prepare the electrolyte.

[0034] This embodiment also discloses the application of an aqueous electrolyte in a secondary battery. The negative electrode material of the secondary battery is TiO2, 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. Figure 1-4 As shown.

[0035] From the appendix Figure 1 It can be seen that there are multiple voltage plateaus during the charging and discharging process, and the voltage value at the plateau is related to... Figure 3 The redox peaks in the samples are in the same position, corresponding to the insertion and extraction of magnesium ions in the electrode material.

[0036] From the appendix Figure 2 As can be seen, the upper curve represents the coulombic efficiency change of the secondary battery. After 100 cycles, the coulombic efficiency remains close to 100%, showing almost no degradation. The lower curve represents the specific capacity change of the secondary battery. After 100 cycles, the specific capacity remains close to 60 mAh g. -1 This demonstrates that the specific capacity and coulombic efficiency of the secondary battery remained almost unchanged after 100 cycles, thus enhancing its practical application value.

[0037] From the appendix Figure 3 As can be seen, the cyclic voltammetry curves show 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.

[0038] Example 2

[0039] The difference between this embodiment and Example 1 is that the organic compound in the electrolyte is tripropylene glycol; all other aspects are the same as in the example. Experimental results are attached. Figure 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.

[0040] Comparative Example 1

[0041] The difference between this comparative example and Example 1 is that the organic compound in the electrolyte is ethylene glycol, and the weight percentage of ethylene glycol to water is 83%. All other aspects are the same as in the example.

[0042] Comparative Example 2

[0043] The difference between this comparative example and Example 1 is that the organic compound in the electrolyte is glycerol, while all other aspects are the same as in the example.

[0044] Comparative Example 3

[0045] The difference between this comparative example and Example 1 is that the organic compound in the electrolyte is diethylene glycol monomethyl ether, while all other aspects are the same as in the example.

[0046] Comparative Example 4

[0047] The difference between this comparative example and Example 1 is that the organic compound in the electrolyte is propylene glycol, while everything else is the same as in the example.

[0048] The electrochemical stability windows of the above examples and comparative examples were tested, and the results are recorded in the table below.

[0049] serial number Organic compound name Electrochemical stability window / V Example 1 Triethylene glycol 3.6 Example 2 Tripropylene glycol 3.6 Comparative Example 1 Ethylene glycol 2.6 Comparative Example 2 Glycerol 2 Comparative Example 3 Diethylene glycol monomethyl ether 2.2 Comparative Example 4 Propylene glycol 2

[0050] Test Results Summary: The test results show that using alcohol ether small molecule compounds can effectively broaden the chemical stability window of the electrolyte. The hydrophilic groups and O atoms in the structure of alcohol ether small molecule compounds play a key role, which not only increases the solubility of organic compounds in water, but also reduces the activity of free water in the electrolyte, reduces the dissolution of electrode materials and the occurrence of side reactions, thus broadening the electrochemical stability window of the electrolyte.

[0051] Experimental Example 1: The effect of the weight percentage of organic compounds and water on the battery stability window

[0052] Experimental Method: Electrolytes with triethylene glycol and water weight percentages of 83%, 90%, and 99% were prepared, 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 6 As shown. In this scheme, the weight percentages of organic compounds and water can form a relatively wide electrochemical stability window (3.6 v) within the specified range.

[0053] Experimental Example 2: Measurement of the diffusion coefficient of magnesium ions

[0054] Test method: Constant current intermittent titration technique

[0055] Calculation formula: The diffusion coefficient of magnesium ions in the electrode material can be calculated based on the curve obtained from the constant current intermittent titration technique. The calculation formula is as follows:

[0056]

[0057] Where τ, m B V M M B S and S represent the constant current pulse duration, the mass, molar volume, molar mass of the active material in the electrode material, and the electrode-electrolyte interface area, respectively; ΔEs is the static voltage difference; ΔEτ is the total change in battery voltage during the constant current pulse, neglecting the decrease in resistance. Experimental results are attached. Figure 7 As shown. The average diffusion coefficient of magnesium ions in this scheme is ~2.97×10⁻⁶. -11 cm 2 s -1 This is greater than the values ​​reported in existing literature.

[0058] 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. An aqueous electrolyte, characterized in that: The mixture includes an electrolyte, water, and an organic compound; the organic compound is triethylene glycol; the electrolyte is a magnesium salt, which includes one or more of magnesium sulfate, magnesium chloride, magnesium perchlorate, magnesium acetate, magnesium chlorate, magnesium trifluoromethanesulfonate, and magnesium bis(trifluoromethanesulfonyl)imide.

2. The aqueous electrolyte according to claim 1, characterized in that: The mass percentage of the organic compound to water ranges from 1% to 99.5%.

3. The aqueous electrolyte according to claim 2, characterized in that: The concentration of the magnesium salt is 0.01~10 mol·kg⁻¹. -1 .

4. The aqueous electrolyte according to claim 1, characterized in that: The electrolytes also include one or more of potassium salts, sodium salts, lithium salts, calcium salts, and aluminum salts.

5. The aqueous electrolyte according to claim 4, characterized in that: The concentration of the potassium, sodium, lithium, calcium, or aluminum salt is 0.01–12 mol·kg⁻¹. -1 .

6. The application of an aqueous electrolyte according to any one of claims 1 to 5, characterized in that: A secondary battery is prepared using an aqueous electrolyte, and the secondary battery further includes a positive electrode and a negative electrode.

7. The application of an aqueous electrolyte according to claim 6, characterized in that: The negative electrode material includes TiO2, and the positive electrode material includes V2O5.

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