Advanced anode materials for potassium batteries: Sorting out opportunities and challenges by potassium storage mechanisms

The development of lithium-ion batteries for the integration of renewable energy generation and the widespread use of electric vehicles has been greatly hampered by the scarcity of Li-ions as a natural resource as well as the limitation of an energy density that almost reaches the threshold. Potassium-ion batteries (PIBs), working on the same rocking-chair principle, have gained increasing attention as a "beyond-Li-ion" battery technology due to the reduced economic cost and the promising potential for large-scale energy storage. Pursuing suitable electrode materials with low cost, good conductivity, high capacity, and high chemical and structural stabilities is always at the heart of rechargeable battery studies. In this review, we comprehensively review five types of anode electrodes for PIBs, including K-metal, intercalation, conversion, alloying, and conversion-alloying in terms of materials synthesis, electrochemical characters, and functional mechanisms. The most recent progress is summarized with a focus on specific challenges (the K dendrite issue, electrode structural instability, sluggish transfer kinetics, etc.) as well as the fundamental science behind related improvement strategies (host constructing, nanoarchitecture tailoring, composite constructing, built-in electric field introducing, etc.). Several possible topics for future research are suggested for going beyond existing technological bottlenecks and achieving desirable PIB anode functionality.