image: This figure illustrates the solvation structures of three types of electrolytes: Traditional Electrolyte (TE), Localized High-Concentration Electrolyte (LHCE), and Cosolvent High-Voltage Electrolyte (CHVE). It also highlights the characteristics of each solvation structure.
Credit: ©Science China Press
Potassium-ion batteries are characterized by their low cost, abundant resources, and potential for high voltage windows, which make them highly promising for large-scale energy storage applications. The electrolyte plays a significant role in the performance of the battery, and ether-based electrolytes have garnered attention due to their ability to effectively dissolve potassium salts and provide high ionic conductivity. However, these electrolytes also have notable drawbacks: they exhibit weak antioxidant capacity and poor compatibility with graphite anode materials. These limitations significantly restrict their application in battery systems.
High-concentration electrolytes (HCE) significantly reduce the number of free solvent molecules, thereby promoting the formation of more contact ion pairs (CIPs) and aggregated clusters (AGGs). This approach effectively broadens the electrochemical stability window and facilitates the formation of a solid electrolyte interphase (SEI) dominated by anions, leading to substantial improvements in battery performance. However, the increased viscosity and higher cost of HCE have hindered its widespread practical application.
To address these challenges, localized high-concentration electrolytes (LHCE) were developed by introducing diluents into HCE, which lowers both the salt concentration and viscosity. The aim is to retain the beneficial CIPs and AGGs solvation structures and their characteristics from HCE. However, LHCE can suffer from salt precipitation when a large amount of diluent is added, particularly in potassium ion electrolytes. This precipitation decreases the salt concentration and reduces the proportion of AGGs, negatively impacting the electrochemical stability window.
Moreover, the use of fluorine-containing diluents in conventional LHCE systems is not only expensive but also poses potential environmental hazards, which contradicts the current emphasis on eco-friendly and sustainable battery technologies. Therefore, future research on LHCE should focus on exploring non-fluorinated diluents that do not significantly reduce salt solubility or the proportion of AGGs, while still enhancing the high-voltage properties of the electrolyte.
Scientists from Hunan University, the Shanghai Advanced Research Institute of the Chinese Academy of Sciences, and ShanghaiTech University have published a new research article in National Science Review, presenting an innovative electrolyte design strategy that effectively addresses the issues of stability under high voltage and compatibility with graphite anodes in ether-based electrolytes. By leveraging ion-dipole interactions, this newly designed cosolvency high-voltage electrolyte overcomes the limitations of salt solubility, significantly increasing the size of anion-rich solvation clusters. This results in the formation of a stable electrode-electrolyte interface and enhances the compatibility of the electrolyte with high-voltage electrodes.
Compared to traditional electrolytes and LHCE, this novel electrolyte achieves stable cycling performance at 4.5 V and enables the graphite anode to maintain stable cycling for over 17 months. Additionally, this strategy demonstrates broad applicability and effectiveness, as it can be extended to various common ether-based electrolytes and is compatible with different solvent systems. This research provides a new direction for the development of high-performance batteries and holds promise for advancing large-scale energy storage technologies.
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See the article:
Cosolvent electrolyte chemistries for high-voltage potassium-ion battery
https://doi.org/10.1093/nsr/nwae359
Journal
National Science Review