Faster and Deeper Mg ²⁺ Penetration Cathodes Unlock High Capacity in Low-Temperature Magnesium-Metal Batteries

Rechargeable magnesium-metal batteries (RMBs) have been regarded as promising candidates for energy storage systems owing to the high volumetric capacity, favorable safety profile, and high crustal abundance of Mg. However, the performance of RMBs is constrained by sluggish Mg²⁺ diffusivity in the cathode materials, leading to a substantial electrochemically inactive interior volume. Herein, we achieved the fast solid-state diffusion of Mg²⁺ by constructing an ordered shell-to-core built-in electric field (BEF) via orientated MoS₂/MoO₂ coaxial heterojunction nanotube arrays, giving rise to high capacity even at low temperatures. Benefiting from the easy transport and deep intercalation depth of Mg²⁺, the obtained cathode delivered an outstanding rate performance (312 mAh g^-1 at 0.05 A g^-1 and 115 mAh g^-1 at 5 A g^-1) and long-term durability with an average fade of 0.0025% per cycle over 4000 cycles. Impressively, a capacity of 150 mAh g^-1 was still retained at 0.05 A g^-1 even at -20 °C because of the maintained largely promoted Mg²⁺ diffusivity of 10^-10 cm² s^-1 at this low temperature, which is promising but rarely reported for RMBs.