While rechargeable magnesium batteries (RMBs) promise high energy density, their room‐temperature operation is still limited; strong Mg 2+ –O 2− interactions suppress ion diffusion and complicate positive electrode evaluation. This concept review outlines a practical pathway coupling cell design with nanoparticle strategies. First, weakly coordinating‐anion electrolytes—especially Mg Z (hfip) 4 2 ( Z = B, Al) with high oxidative stability—provide a fair baseline for rigorously verifying genuine Mg intercalation. On this foundation, the extreme downsizing strategy is summarized. Nanosized MgMn 2 O 4 operates when particle dimensions approach the Mg penetration depth, and composition control further reduces resistance and overpotential, as electronically conductive CuMn 2 O 4 nanospinels deliver higher capacities and rates. For rigid tunnel frameworks, ultrasmall, low‐aspect‐ratio α ‐MnO 2 shortens 1D diffusion paths, increases discharge capacity, and improves retention. Beyond size effects, geometry‐guided design motivates the exploration for host tunnels with the preferred Mg 2+ site; romanechite with asymmetric 3 × 2 channels enables reversible intercalation without phase transition or tunnel collapse. Looking ahead, nanoparticulation remains essential for realizing stable, high‐energy RMB positive electrodes operating at room temperature.
Yabu et al. (Tue,) studied this question.