Research progress in anode materials based on multiple potassium storage mechanisms

Potassium-ion batteries (PIBs) are expected to develop into the next-generation large-scale energy storage technology because they inherit the advantages of both lithium-ion batteries and sodium-ion batteries, including high energy density, rich potassium reserves in the earth's crust, low cost, and excellent K-ion (K+) transport kinetics in the electrolyte. However, due to the large ion radius of K+, heavy mass of K element, and high activity of K metal, the commonly employed graphite anodes have suffered from apparent volume expansion during the K+ storage process, resulting in low coulomb efficiency, rapid capacity decay, and poor rate performance. Thus, developing suitable anode materials is one of the most effective ways to improve the K+ storage performance of PIBs. This review provides a summary of the current advances in the research of anode materials for PIBs based on several K+ storage mechanisms, namely intercalation/deintercalation, conversion, and alloying/dealloying mechanisms. The reported successful regulation techniques are also outlined, including the enhancement of electrolytes and binders, the boost of metal-containing material conductivity, the expansion of carbon material layer spacing, the construction of composite anodes, etc. Finally, PIBs' development efforts and application outlook are both highly promising.