Aqueous magnesium-ion batteries (AMIBs) have been regarded as one of the most promising battery systems among the post-lithium-ion batteries due to their inherent safety, low cost and environmental friendliness. Unfortunately, the sluggish cathode kinetics arising from the inherent high charge density and large ionic radius of Mg²⁺, alongside the structural constraints of cathode materials, remains a fundamental challenge hindering the broad deployment of AMIBs. Recent advances in cathode materials and their interfacial compatibility with electrolytes have yielded valuable insights for optimizing AMIBs systems. In this review, the energy storage mechanisms of AMIBs are systematically elucidated and discussed in detail. Besides, several optimization strategies for cathode materials are critically examined and thoroughly discussed, including but not limited to structural engineering, surface modification and electrolyte compatibility enhancement. Finally, we briefly address the outstanding challenges and potential future developments in this field. This review is poised to offer novel approaches and a significant impetus for material optimization, thereby enhancing the electrochemical performance of AMIBs and other emerging battery systems.

Potassium metal is regarded as a promising anode material for potassium-ion batteries due to its high theoretical capacity and low redox potential. However, its performance is hindered by rapid capacity fading, primarily caused by an unstable solid electrolyte interphase (SEI) and continuous dendrite growth. Herein, by coating liquid metal (LM) alloy (GaInSn) onto copper foil, we prepared a special LM@Cu substrate, significantly improving the deposition/stripping behavior of potassium metal and thus achieving long-cycling K metal battery. The excellent potassiophilicity and electrolyte wettability of LM@Cu effectively reduce the K nucleation overpotential, promote charge transfer kinetics, and enable self-diffusive planar growth mode. Moreover, ex situ scanning electron microscopy and in situ optical microscopy analyses show that the LM coating induces uniform potassium deposition, reduces volume expansion, and achieves a dendrite-free K anode. Additionally, when 3,4,9,10-perylene-tetracarboxylic diimide (PTCDI) is employed as the cathode and K-LM@Cu (LMK) as the anode, the potassium metal battery demonstrates an initial reversible capacity of 124.4 mAh·g⁻¹. Even after 4900 cycles at a current density of 500 mA·g⁻¹, it maintains a high reversible capacity of 78.2 mAh·g⁻¹. The self-diffusive planar growth mechanism enabled by liquid metal offers a promising approach for developing practical and durable potassium metal batteries.