Hard carbons: potential anode materials for potassium ion batteries and their current bottleneck

Owing to the desire for fulfilled energy density and competitively low production costs of lithium-ion battery supplements, potassium ion batteries with the advantages of abundant raw material sources, high safety and excellent electrochemical performance have been a strong contender. In practical applications, hard carbon materials are considered promising anodes owing to their wide range of sources, remarkable economic benefits, environmental friendliness and excellent performance. At present, researchers focus on the study of structure-activity relationship and energy storage mechanism, aiming to obtain universal rules and guide the real commercialization of hard carbon anodes. For this purpose, we herein summarize the current mainstream research views on the K+ storage mechanism, list the common hard carbon anodes and discuss the effects of various modification techniques. In addition, we notice the bottleneck of hard carbon anode development and propose the future direction for technical improvement. In this review, we summarize the current mainstream research views on K+ storage mechanisms, obstacles and solutions.