Latent dissolution behavior of electrolytes: high voltage, high stability batteries | NSR

Potassium-ion batteries are low-cost, abundant in resources, and have a potential high voltage window, showing great potential in the field of large-scale energy storage. The electrolyte has a significant impact on the performance of the battery. Ether-based electrolytes have attracted much attention because they can effectively dissolve potassium salts and provide high ionic conductivity. However, this type of electrolyte also has obvious shortcomings: weak antioxidant ability and poor compatibility with graphite negative electrode materials . This greatly limits its application in battery systems.

To address this problem, this paper proposes a latent electrolyte design strategy that breaks the solubility limitation of salts through ion-dipole interactions, significantly increases the size of anion-rich solvated clusters, effectively forms a stable electrode-electrolyte interface, and improves the compatibility of electrolytes with high-voltage electrodes . The related research was published in National Science Review ( NSR ), with Shen Mengkang from Hunan University and Dr. Dai Zhongqin from ShanghaiTech University as co-first authors, and Professor Lu Bing'an , Associate Professor Fan Ling from Hunan University and Associate Researcher Sun Fanfei from Shanghai Advanced Research Institute of the Chinese Academy of Sciences as co-corresponding authors.

Starting from the latent solubility phenomenon commonly used in pharmacy, the research team selected mixed solvents and precisely adjusted the proportion of each solvent to enhance the solubility of salts. According to analysis, the increase in salt solubility can promote more anions to enter the primary solvation shell and increase the number of solvation clusters (AGGs) . This process is directly related to the optimization and reconstruction of the electrolyte microstructure and is one of the key factors in designing electrolytes suitable for high-voltage batteries.

Latent electrolyte design strategy

In situ synchrotron radiation wide-angle X-ray scattering experiments 

show that as KFSI dissolution gradually increases, the peak at 0.81 Å ^-1 in the spectrum gradually moves to a lower Q value, indicating that the cluster size increases, which is consistent with previous analysis. In addition, at a constant concentration, increasing the DBE content, the clusters become larger; at a constant ratio, increasing the concentration, the clusters become larger. Larger solvated clusters are conducive to the formation of an effective electrode-electrolyte interface and enhance high-voltage stability.

(a) Schematic diagram of the in situ synchrotron wide-angle X-ray scattering (WAXS) experimental setup; (b) WAXS curve as the salt gradually dissolves; (c) Changes in the WAXS curve when the DBE content is increased at a constant concentration; (d) Changes in the WAXS curve when the concentration is increased at a constant ratio.

Linear sweep voltammetry tests and 4.5 V constant voltage corrosion experiments show that the latent electrolyte exhibits excellent oxidation stability. Under high voltage, it can effectively inhibit the corrosion of aluminum foil and keep the surface smooth and flat. In the voltage range of 2-4.5 V, the K||PB battery can be stably cycled for more than 700 times, with a capacity retention rate of up to 91.9% and an average coulombic efficiency of 99.2%.

(a) Linear sweep voltammograms of three electrolytes; (b) Corrosion of aluminum foil in three electrolytes; (c) Cycling performance of K||PB battery in CHVE and LHCE and (d) charge and discharge curves.

As an effective means of regulating the solvation structure, the latent dissolution phenomenon shows great potential in the design of high-performance electrolytes. This strategy can be extended to a variety of common ether-based solvents , such as 1,2-diethoxyethane (DEE) and 1,2-dimethoxyethane (DME), which themselves have limited stability under high pressure conditions. After being regulated by the latent dissolution phenomenon, the antioxidant properties of both are greatly improved. These results demonstrate the wide applicability and effectiveness of the latent electrolyte design strategy in different solvent systems.

(a) Optical photograph of latent dissolution in DEE/DME and DBE mixed electrolytes. (b) Linear sweep voltammetry curves of CHVE-1 and CHVE-2.

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