Rational Design of MXene-Based Heterostructures for Potassium-Ion and Aluminum-Ion Batteries: From Structure Engineering to Charge-Storage Mechanisms.

Potassium-ion batteries (PIBs) and aluminum-ion batteries (AIBs) have attracted considerable attention as promising substitutes for lithium-ion batteries (LIBs) because potassium (K) and aluminum (Al) are naturally abundant, inexpensive, and environmentally sustainable. However, progress in anode development remains slower than that of cathode materials. Traditional carbonaceous and metal-based composite anodes generally suffer from limited electrochemical performance and severe volume expansion during cycling. In this work, MXene-derived materials are investigated as prospective anodes for PIBs and AIBs. Particular emphasis is placed on synthesis approaches for obtaining high-quality MXenes with tunable surface terminations and controllable layer thickness, which strongly affect electrical conductivity, ion interaction, and interlayer spacing. Furthermore, the ion-storage mechanisms and diffusion kinetics of K+ and Al3+ ions within MXene interlayers are examined and compared with those of conventional anode systems. This review also establishes a benchmark for evaluating MXene electrodes against advanced anode materials based on electrochemical and structural characteristics. Overall, the article provides comprehensive insights into the synthesis, surface engineering, and energy storage properties of MXene anodes for next-generation PIBs and AIBs.