Recent advances in modulation engineering-enabled metal compounds for potassium-ion storage

Developing advanced energy storage technologies beyond lithium-ion batteries (LIBs) to meet the demand of large-scale energy storage with sustainability and low cost are urgent. The potassium-ion batteries (PIBs) and potassium-ion capacitors (PICs) by using the K⁺-ion as charge carriers have received more and more attention, due to the low standard redox potential of K/K⁺, high ionic conductivity in K-salt-containing electrolytes and cost effectiveness as well as earth abundance of potassium resources. However, the poor kinetics process and huge volume expansion caused by the large radius of K⁺-ion become the main challenges for PIBs and PICs anode materials. In recent years, ever-increasing investigations have been reported on metal compounds (MCs) with high theoretical capacity, low cost, moderate operation potential, environmental friendliness, abundant resources and redox reversibility as K⁺-ion storage anode materials. However, their potassium storage drawbacks such as intrinsic poor charge transfer kinetics process and weak structural stability become more important to adopt advanced structural engineering and thus enhance the potassium storage performance. Along this line, the recent research advances in performing modulation engineering on MCs for potassium storage are summarized in this review, including interface engineering with rich heterostructure and phase boundary, confine engineering with safe storage space and defect engineering with improved intrinsic physicochemical properties. Finally, the critical issues, challenges and perspectives for further developing MCs as high-performance potassium storage anode materials are also discussed.