Recent progress and perspective on electrolytes for sodium/potassium-based devices

As the incremental deficiency of Li resources, it is significant and instant to supersede Li with other earth-abundant elements for electrochemical energy storage (EES) devices. Accordingly, Na/K-ion energy storage devices, including rechargeable batteries and ionic capacitors with similar energy storage mechanisms to Li-ion devices, have attracted widespread concerns due to the abundant reserves of Na/K and low cost. Meanwhile, electrolytes are one of the significant hotspots to promote the comprehensive electrochemical performances of these devices. However, compared to electrode materials, insights into electrolytes in these devices are still in its infancy, leading to an inherent restriction on their performance enhancement. In this review, a brief introduction of advanced analysis and characterization technologies for electrolytes is discussed, and recent applications of various electrolytes including organic, aqueous, ionic liquid, and solid-state electrolytes for rechargeable batteries and ionic capacitors based Na/K-ion devices are also summarized. Finally, the remaining challenges and future research orientations are identified and proposed. It is hoped that this report will promote the commercial application of EES devices based on Na/K in the post lithium era.