Enhanced Elastic Migration of Magnesium Cations in alpha‐Manganese Dioxide Tunnels Locally Tuned by Aluminium Substitution

The harsh conditions of large hydrated ion radius Mg2+ cations and the strong electrostatic interaction with host material put forward higher requirements for high-performance aqueous magnesium (Mg2+) energy storage devices. Herein, substituted aluminium ions (Al3+) doped α-MnO2 materials are prepared. introduction Al3+ adjust local chemical environment inside tunnel structure precisely regulates diffusion behavior inserted cations. shortened oxygens’ distance abundant oxygen defects result in a substantially enhanced elastic migration pattern driven by strengthened attraction, which brings lower barrier, improved reaction kinetics, adaptive volume expansion as evidenced Climbing Image-Nudged Elastic Band density function theory calculations coupled experimental confirmation X-ray photoelectron spectroscopy, electron paramagnetic resonance, galvanostatic intermittent titration technique. As result, this rationally designed cathode exhibits high reversible capacity 197.02 mAh g-1 at 0.1 A stable cycle performance 2500 cycles 82% retention. These parameters among best Mg-ion capacitors reported to date. This study offers detailed insight into tunning effect opens up new path modification tunnel-type structural materials.