A review of flexible potassium-ion based energy storage devices

The development of flexible potassium ion-based energy storage devices (PESDs) carries tremendous potential, primarily due to the high energy density they offer and the abundant availability of potassium resources. However, realizing PESDs that combine excellent stability, safety, and high electrochemical performance continues to be a significant challenge. The construction of flexible electrodes and solid-state electrolytes with robust mechanical stability and rapid ion/electron diffusion capabilities can effectively address these issues. In this review, we spotlight significant advancements and accomplishments in the realm of flexible components for PESDs. Initially, we provide a succinct introduction to the ion storage mechanisms and prevailing challenges of typical PESDs. Following this, we explore the progress in flexible electrodes, with a special emphasis on the development and application of flexible electrode materials, including carbon, metal, and MXene-based materials. Additionally, we suggest overarching design principles for crafting advanced flexible electrode materials. Moreover, we delve into notable advancements in solid electrolytes — encompassing polymer electrolytes and inorganic solid electrolytes — as these are pivotal components in crafting flexible PESDs. Finally, we foresee specific challenges and suggest directions for realizing high-performance flexible PESDs, aspiring to steer further research and development in this dynamic and swiftly progressing field.