Fe 2 O 3 for stable K-ion storage: mechanism insight into dimensional construction from stress distribution and micro-tomography.

Fe 2 O 3 is considered a potential electrode material owing to its high theoretical capacity, low cost, and non-toxic characteristics. However, the significant volume expansion and structural degradation during charging and discharging hinder its application in potassium ion batteries. The electrochemical properties of the electrode material are primarily influenced by the diffusion efficiency of ions and the mechanics of the object. From the construction of a one dimensional structure, a three-dimensional flower-like Fe 2 O 3 with a high specific surface and low-dimensional spherical Fe 2 O 3 were prepared. Considering the convenience and visualization of the research, micron-scale Fe 2 O 3 was prepared, although the larger particle size will lose part of the capacity. Notably, compared with the spherical structure, the specific capacity of the flower structure was increased by about 100%. The von Mises stress distribution on the two structures was simulated by the finite element method, revealing the mechanism of electrode failure induced by volume expansion and confirming the vital role of the multidimensional system in relieving stress concentration and improving electrochemical performance. Furthermore, synchrotron radiation soft X-ray absorption spectrum and X-ray micro-tomography revealed the phase transformation process and reaction mechanism of Fe 2 O 3 in potassium ion batteries. The dimensional structure construction strategy reported here can provide theoretical support for modifying transition metal oxides.