Optimization of Von Mises Stress Distribution in Mesoporous α‐Fe2O3/C Hollow Bowls Synergistically Boosts Gravimetric/Volumetric Capacity and High‐Rate Stability in Alkali‐Ion Batteries.

Hollow structures are often used to relieve the intrinsic strain on metal oxide electrodes in alkali‐ion batteries. Nevertheless, one common drawback is that the large interior space leads to low volumetric energy density and inferior electric conductivity. Here, the von Mises stress distribution on a mesoporous hollow bowl (HB) is simulated via the finite element method, and the vital role of the porous HB structure on strain‐relaxation behavior is confirmed. Then, N‐doped‐C coated mesoporous α‐Fe2O3 HBs are designed and synthesized using a multistep soft/hard‐templating strategy. The material has several advantages: (i) there is space to accommodate strains without sacrificing volumetric energy density, unlike with hollow spheres; (ii) the mesoporous hollow structure shortens ion diffusion lengths and allows for high‐rate induced lithiation reactivation; and (iii) the N‐doped carbon nanolayer can enhance conductivity. As an anode in lithium‐ion batteries, the material exhibits a very high reversible capacity of 1452 mAh g−1 at 0.1 A g−1, excellent cycling stability of 1600 cycles (964 mAh g−1 at 2 A g−1), and outstanding rate performance (609 mAh g−1 at 8 A g−1). Notably, the volumetric specific capacity of composite electrode is 42% greater than that of hollow spheres. When used in potassium‐ion batteries, the material also shows high capacity and cycle stability. [ABSTRACT FROM AUTHOR]