Full-complexing manganese positive electrode electrolyte and application thereof

Abstract

The invention belongs to the technical field of new energy, and particularly relates to a full-complexing manganese positive electrode electrolyte and application thereof. In order to overcome the instability problem of Mn < 3 + > in the prior art and avoid the technical defects that the coulombic efficiency and the energy efficiency of a battery are reduced and the power performance is poor due to the fact that Mn < 3 + > is subjected to a disproportionation reaction in an aqueous solution to generate a solid-phase manganese dioxide product, the invention provides the fully-complexed manganese positive electrode electrolyte. Comprising an active substance, a solvent, a supporting electrolyte and a hydrolysis inhibitor, the supporting electrolyte is inorganic / organic salt containing halide ions; the active substance is manganese salt; halogen ions in the supporting electrolyte react with manganese ions in the manganese salt to form manganese (II) ions [MnXn] < 2 + > in a complexing state. The electrolyte provided by the invention is simple and easy to obtain, the used chemical substances are non-toxic and pollution-free, the electrolyte is clean and environment-friendly, the cost is low, and mass production is easy to realize.

Description

Technical Field

[0001] The present invention belongs to the field of new energy technology, and in particular relates to a fully complexed manganese positive electrode electrolyte and applications thereof. Background Art

[0002] The development of energy storage and conversion devices with high energy density, long cycle life, low cost and high safety is crucial for fully utilizing intermittent renewable energy sources such as solar, wind and hydropower. Lithium-ion batteries (LIBs) are currently the main power source for portable electronics and electric vehicles due to their good energy density and durability. However, limited lithium resources, high manufacturing costs, and safety issues caused by the toxic and flammable organic solvents used in lithium batteries (which make them difficult to recycle) are all obstacles to the widespread application of lithium batteries in large-scale energy storage. In contrast, aqueous redox flow batteries (RFBs) have become one of the most promising energy storage technology systems due to their decoupled energy / power capacity, ultra-long cycle life, low operation and maintenance costs, and good safety.

[0003] Among various RFB systems, all-vanadium redox flow batteries (RFBs) are considered one of the most promising commercial candidates due to their long cycle life, high efficiency, and excellent electrochemical reversibility. However, the mining and extraction of vanadium is expensive, has a limited operating temperature range, and is environmentally harmful, limiting the application prospects of vanadium flow.

[0004] Manganese-based materials have attracted much attention due to their low cost and rich valence states of manganese elements. 3+ / Mn 2+ Manganese salts have attracted widespread attention due to their high solubility and high standard redox potential (1.51 V vs. SHE). 3+ / Mn 2+ The cycling performance of Mn-based RFB is affected by Mn 3+ The instability limit in aqueous solution, Mn 3+ Easy to undergo disproportionation reaction to convert into Mn 2+ and solid MnO2, clogging the electrodes, pumps, and pipes of the RFB, resulting in a poor cycle life.

[0005] In order to solve the problem of stability, those skilled in the art have made some explorations. For example, the Chinese invention patent (CN113437340A) discloses the use of divalent manganese ion complex manganese disodium ethylenediaminetetraacetate as an active substance, which changes the hexahydrate coordination structure of manganese ions and the oxidation product Mn 3+ It also complexes with disodium EDTA to make Mn 3+The stability of the battery is improved, but the use of complexing agents significantly reduces the solubility of manganese salts and the working potential decreases significantly. For example, the Chinese invention patent (CN114400357A) discloses the introduction of sulfosalicylic acid additives to complex with manganese to avoid the production of manganese dioxide, but the cycle life of the battery is only 400 times, which needs to be further improved. Therefore, the development and research of technologies that can inhibit the formation of Mn 3+ The electrolyte of disproportionation reaction is of great significance to improve the stability of manganese-based batteries. Summary of the Invention

[0006] In order to overcome the existing technology of Mn 3+ To avoid the instability problem of Mn 3+ The disproportionation reaction in aqueous solution generates solid-phase manganese dioxide products, resulting in reduced coulombic efficiency and energy efficiency, and poor power performance. This invention optimizes the electrolyte components to provide a positive electrode electrolyte for manganese-based batteries, which can be used in stationary aqueous batteries or flow batteries.

[0007] On the one hand, the present invention provides a fully complexed manganese cathode electrolyte, comprising: an active substance, a solvent, a supporting electrolyte and a hydrolysis inhibitor; the supporting electrolyte is an inorganic / organic salt containing halogen ions; the active substance is a manganese salt; the halogen ions in the supporting electrolyte react with the manganese ions in the manganese salt to form a complexed manganese (II) ion [MnX n ] 2+ Preferably, during the charging process, the complexed manganese (II) ions [MnX n ] 2+ The complexed manganese (III) ion [MnX n ] 3+ .

[0008] In the present invention, the added halogen ions interact with the manganese ions in the electrolyte to change the Mn 2+ The solvation structure of [Mn(H2O)6] in conventional solution 2+ The structure changes to [MnX n ] 2+ Complex manganese ions, and the products generated are also complex manganese (Ⅲ) ions [MnX n ] 3+ exists in the form of a fully complexed state [MnX n ] 2+ / [MnX n ] 3+ The liquid-phase reaction process significantly inhibits the formation of solid-phase manganese dioxide and improves battery performance.

[0009] Preferably, the halogen ion X in the supporting electrolyte is selected from F -、Cl - Br - and I - At least one of .

[0010] Preferably, the manganese salt is selected from at least one of manganese chloride, manganese sulfate, manganese acetate, manganese perchlorate, manganese bromide and manganese nitrate, preferably manganese chloride and manganese bromide.

[0011] Preferably, the concentration of the manganese salt is 0.01 to 8 mol / kg.

[0012] Preferably, the supporting electrolyte is selected from at least one of sodium salts containing halogen ions, potassium salts containing halogen ions, lithium salts containing halogen ions, magnesium salts containing halogen ions, ammonium salts containing halogen ions, zinc salts containing halogen ions, cholines containing halogen ions, quaternary ammonium salts containing halogen ions, and imidazole salts containing halogen ions.

[0013] Preferably, the concentration of the supporting electrolyte is ≥4 mol / kg, preferably 4 to 60 mol / kg, more preferably 20 to 60 mol / kg.

[0014] Preferably, n represents the molar ratio of the halogen ion X to the manganese ion, preferably 4:1 to 60:1.

[0015] Preferably, the solvent is water.

[0016] Preferably, the hydrolysis inhibitor is a hydrohalic acid; the hydrohalic acid includes at least one of hydrofluoric acid, hydrochloric acid, hydrobromic acid and hydroiodic acid; and the concentration of the hydrohalic acid is in the range of 0.01 to 10 mol / kg.

[0017] On the other hand, the present invention provides a stationary aqueous battery, comprising: the above-mentioned fully complexed manganese positive electrode electrolyte.

[0018] In another aspect, the present invention provides a liquid flow battery, comprising: the above-mentioned fully complexed manganese positive electrode electrolyte.

[0019] Beneficial effects of the present invention: 1) The present invention provides a fully complexed manganese positive electrode electrolyte that can fully utilize the advantages of high solubility of manganese salts (the solubility of manganese chloride at room temperature is greater than 6M) and Mn 3+ / Mn 2+ The high reaction potential advantage (1.51V vs. SHE) improves the energy density of manganese-based battery systems; 2) By introducing high-solubility inorganic / organic salt supporting electrolytes containing halogen ions, on the one hand, the activity of free water molecules in the aqueous electrolyte is suppressed, and on the other hand, the introduced halogen ions react with Mn 2+ or oxidation product Mn 3+Formation of fully complexed manganese (II) / manganese (III) ions [MnX n ] 2+ / [MnX n ] 3+ , thereby avoiding the formation of solid-phase product manganese dioxide and improving the reversibility and stability of the positive electrode reaction; 3) The electrolyte provided by the present invention is simple and easy to obtain, and the chemical substances used are non-toxic, pollution-free, clean, environmentally friendly and low-cost, and can be easily produced in large quantities. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM image of the carbon felt electrode in a charged state in the three-electrode test of the electrolyte in Example 1; Figure 2 This is a SEM image of the carbon felt electrode in a charged state in the three-electrode test of the electrolyte in Comparative Example 1; Figure 3 1 is a cyclic voltammogram of the electrolyte in the three-electrode test in Example 1; Figure 4 The Raman images of the initial electrolyte and the electrolyte after charging in Example 1; Figure 5 The Raman images of the initial electrolytes of Comparative Example 1 and Comparative Example 4 are shown; Figure 6 This is a graph showing the cycle test performance of the electrolyte in Example 1 in a three-electrode test. DETAILED DESCRIPTION

[0021] In the present disclosure, the fully complexed manganese positive electrode electrolyte comprises: an active material, a solvent, a supporting electrolyte, and a hydrolysis inhibitor. The active material is a manganese salt, and the supporting electrolyte is an inorganic / organic salt containing halogen ions. The manganese ions in the manganese salt and the halogen ions in the supporting electrolyte form a fully complexed manganese (II) ion [MnX n ] 2+ X represents a complexing species, mainly one or more halogen ions (such as F - 、Cl - Br - and I - wherein n represents a molar ratio of halogen ion to manganese ion of 4:1 to 60:1, ensuring that the manganese ion remains fully complexed during the reaction. The solvent may be water.

[0022] In the present invention, the hydrolysis inhibitor, supporting electrolyte and active substance are dissolved in water according to the ratio to form a homogeneous solution.

[0023] In an optional embodiment, an inorganic or organic salt (high solubility) containing a halogen ion is used as the supporting electrolyte, preferably one or more of sodium salts, potassium salts, lithium salts, magnesium salts, ammonium salts, zinc salts, choline salts, and quaternary ammonium salts. The concentration of the supporting electrolyte ranges from 4 to 60 mol / kg, preferably ≥ 20 mol / kg.

[0024] In an optional embodiment, the water-soluble manganese salts include manganese chloride, manganese sulfate, manganese acetate, manganese perchlorate, manganese bromide, and manganese nitrate, preferably manganese chloride and manganese bromide containing halogen ions, wherein the manganese ion concentration can be 0.01 to 8 mol / kg.

[0025] In an optional embodiment, the hydrolysis inhibitor may be a hydrohalic acid. The hydrohalic acid may be one or more of hydrofluoric acid, hydrochloric acid, hydrobromic acid, and hydroiodic acid. The concentration of the hydrohalic acid may be in the range of 0.01 to 10 mol / kg.

[0026] The complex manganese cathode electrolyte provided in this invention effectively inhibits the disproportionation reaction of the oxidation product, manganese (III) ions, in aqueous solution, significantly improving the reversibility and stability of the cathode reaction. Furthermore, the chemical substances used are low-cost and easily mass-produced, showing excellent application prospects in stationary aqueous batteries or flow batteries.

[0027] Further cite embodiment below to describe the present invention in detail.Should be understood that following examples are only used for further illustrating the present invention, can not be construed as limiting the scope of protection of the present invention, some non-essential improvements and adjustments made by those skilled in the art according to the foregoing of the present invention all belong to protection scope of the present invention.The specific process parameters etc. of following example are also only an example in the appropriate range, and those skilled in the art can make selection in the appropriate range by the description of this article, and are not limited to the specific numerical value of hereinafter exemplified.Unindicated specific experimental steps or conditions in the following examples and comparative examples, can be carried out according to the operation or condition of the conventional experimental steps described in the document in this area.Reagents used or instrument are not indicated by manufacturer, and are all conventional reagent products that can be obtained by commercial purchase.

[0028] Example 1 The supporting electrolyte, choline chloride, the hydrolysis inhibitor, hydrochloric acid, and the active substance, manganese chloride, were dissolved in water to create a homogeneous cathode electrolyte. The choline chloride concentration in the electrolyte was 30 mol / kg, the hydrochloric acid concentration was 0.01 mol / kg, and the manganese chloride concentration was 1.0 mol / kg. A charge-discharge test was conducted using a three-electrode test system. After 50 cycles, the battery was again charged at a constant voltage of 1.2 V to 1.0 mAh, then cut off. The carbon felt electrode was removed, rinsed with anhydrous ethanol, and vacuum-dried. A SEM image was obtained.

[0029] Example 2 This Example 2 is basically the same as Example 1, except that the concentration of choline chloride is 20 mol / kg.

[0030] Example 3 This Example 3 is basically the same as Example 1, except that the concentration of choline chloride is 40 mol / kg.

[0031] Example 4 This Example 4 is basically the same as Example 1, except that the supporting electrolytes are magnesium chloride and choline chloride, wherein the concentration of magnesium chloride is 5 mol / kg and the concentration of choline chloride is 20 mol / kg.

[0032] Example 5 This Example 5 is basically the same as Example 1, except that the supporting electrolyte is 1-butyl-3-methylimidazolium chloride with a concentration of 30 mol / kg.

[0033] Example 6 This Example 6 is basically the same as Example 1, except that the manganese salt is manganese perchlorate with a concentration of 1.0 mol / kg.

[0034] Comparative Example 1 Comparative Example 1 is essentially the same as Example 1, except that the hydrolysis inhibitor, hydrochloric acid, and the active substance, manganese chloride, were dissolved in water to produce a homogeneous positive electrode electrolyte. The concentration of hydrochloric acid in the electrolyte was 0.01 mol / kg, and the concentration of manganese chloride was 1.0 mol / kg. A charge-discharge test was conducted using a three-electrode test system. After 50 cycles, the battery was again charged at a constant voltage of 1.2 V to 1.0 mAh, then the battery was cut off. The carbon felt electrode was removed, rinsed with anhydrous ethanol, and vacuum-dried. SEM images were then obtained.

[0035] Comparative Example 2 Comparative Example 2 is substantially the same as Example 1, except that the supporting electrolyte choline chloride and the active substance manganese chloride are dissolved in water to obtain a positive electrode homogeneous electrolyte, wherein the choline chloride solubility in the electrolyte is 30 mol / kg and the manganese chloride concentration is 1.0 mol / kg.

[0036] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that the active substance manganese chloride is dissolved in water to obtain a positive electrode homogeneous electrolyte, and the manganese chloride concentration is 1.0 mol / kg. However, hydroxide precipitates after standing.

[0037] Comparative Example 4 This comparative example 4 is basically the same as Example 1, except that the concentration of choline chloride is 10 mol / kg. When the concentration of chloride ions in the solution is too low, it is difficult to form a complex state of manganese (II) ions [MnX n ] 2+ .

[0038] Battery testing methods (1) The solutions prepared in Examples 1-3 and Comparative Example 1 were used as electrolytes, a carbon felt electrode was used as a working electrode, a graphite rod was used as a counter electrode, and a saturated calomel electrode was used as a reference electrode to assemble a three-electrode test system; (2) The three-electrode test system was subjected to a cycle test. The cycle performance test process was as follows: (the carbon felt electrode was used as the working electrode) the battery was charged to 1.0 mAh at a constant voltage of 1.2 V (the carbon felt area was 1.0 cm). 2 ), at 10.0 mA cm -2 Discharge at constant current to 0V and perform cycle test, with each step time interval of 5 minutes; (3) After the battery is cycled 50 times, calculate the average coulombic efficiency, voltage efficiency, energy efficiency and other performance data.

[0039] Table 1 shows the electrolyte performance data:

[0040] The positive electrode electrolyte can be prepared according to the formula of the above examples 1-3 and comparative example 1. It can be seen from example 1 and comparative example 1 that the efficiency of the positive electrode reaction can be significantly improved after adding a supporting electrolyte of a high solubility inorganic / organic salt containing halogen ions. Figure 1 (Example 1) and Figure 2 (Comparative Example 1) The SEM image of the carbon felt electrode in the charged state in the three-electrode test shows that the Mn generated by the electrolyte in Comparative Example 1 during charging 3+ A disproportionation reaction occurs to generate manganese oxides, some of which will fall off from the carbon felt electrode, resulting in reduced efficiency and poor stability. In Example 1, due to the formation of fully complexed manganese (II) / manganese (III) ions [MnX n ] 2+ / [MnX n ] 3+ The formation of almost no solid phase products on the carbon felt electrode indicates that the oxidation product manganese (III) ions exist stably in the electrolyte in a complex state.

[0041] It can be seen from Examples 1-6 that the reaction efficiency of the positive electrode is significantly improved with the adjustment of the supporting electrolyte component or content, but there are slight differences, which may be related to the effect of the introduction of different contents of additives on the conductivity.

[0042] Figure 3 The cyclic voltammogram of the electrolyte in Example 1 in the three-electrode test shows a pair of high-potential fully complexed manganese (II) / manganese (III) ions [MnX n ] 2+ / [MnX n ] 3+ Redox reactions; Figure 4 The Raman images of the initial electrolyte and the electrolyte after charging in Example 1 show that complex manganese (II) ions [MnX n ] 2+ After charging, complex manganese (Ⅲ) ions [MnX n ] 3+ , the ion strength of complexed manganese (Ⅱ) decreases; Figure 5 The Raman images of the initial electrolytes of Comparative Examples 1 and 4 show that it is difficult to form complexed manganese (II) ions [MnX n ] 2+ . Figure 6 The figure shows the cycling performance of the electrolyte in Example 1 in a three-electrode test. As can be seen from the figure, the formation of fully complexed manganese (II) / manganese (III) ions contributes to the reversibility of the positive electrode reaction, with almost no attenuation after 1000 cycles, further verifying the stability of the fully complexed manganese cathode electrolyte and demonstrating the huge application potential of the fully complexed manganese cathode electrolyte in static batteries or liquid flow systems.

[0043] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A fully complexed manganese cathode electrolyte, characterized in that include: Active material, solvent, supporting electrolyte and hydrolysis inhibitor; the supporting electrolyte is an inorganic / organic salt containing halogen ions; the active material is a manganese salt; the halogen ions in the supporting electrolyte react with the manganese ions in the manganese salt to form a complexed manganese (II) ion [MnX n ] 2+ .

2. The fully complexed manganese cathode electrolyte according to claim 1, characterized in that The halogen ion X in the supporting electrolyte is selected from F - 、Cl - Br - and I - At least one of .

3. The fully complexed manganese cathode electrolyte according to claim 1 or 2, characterized in that: The manganese salt is selected from at least one of manganese chloride, manganese sulfate, manganese acetate, manganese perchlorate, manganese bromide and manganese nitrate, preferably manganese chloride and / or manganese bromide; the concentration of the manganese salt is 0.01 to 8 mol / kg.

4. The fully complexed manganese cathode electrolyte according to any one of claims 1 to 3, characterized in that: The supporting electrolyte is selected from at least one of sodium salts containing halogen ions, potassium salts containing halogen ions, lithium salts containing halogen ions, magnesium salts containing halogen ions, ammonium salts containing halogen ions, zinc salts containing halogen ions, cholines containing halogen ions, quaternary ammonium salts containing halogen ions, and imidazole salts containing halogen ions; The concentration of the supporting electrolyte is ≥4 mol / kg, preferably 4 to 60 mol / kg, and more preferably 20 to 60 mol / kg.

5. The fully complexed manganese cathode electrolyte according to any one of claims 1 to 4, characterized in that: n represents the molar ratio of the halogen ion X to the manganese ion, and is preferably 4:1 to 60:

1.

6. The fully complex manganese cathode electrolyte according to any one of claims 1 to 5, characterized in that: The solvent is water.

7. The fully complexed manganese cathode electrolyte according to any one of claims 1 to 6, characterized in that: The hydrolysis inhibitor is a hydrohalic acid; the hydrohalic acid includes at least one of hydrofluoric acid, hydrochloric acid, hydrobromic acid and hydroiodic acid; The concentration of the hydrohalic acid ranges from 0.01 to 10 mol / kg.

8. The fully complex manganese cathode electrolyte according to any one of claims 1 to 7, characterized in that: During the charging process, the complexed manganese (II) ions [MnX n ] 2+ The complexed manganese (III) ion [MnX n ] 3+ .

9. A stationary aqueous battery, characterized in that: include: The fully complex manganese positive electrode electrolyte according to any one of claims 1 to 8.

10. A flow battery, characterized in that: include: The fully complex manganese positive electrode electrolyte according to any one of claims 1 to 8.

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