Multi‐Phase Synergy Enhances Lithium‐Ion Storage Performance of Transition Metal Oxalates

ABSTRACT Transition metal oxalates have been proven to be a promising electrode material for lithium‐ion batteries. Here, we have designed a series of multi‐phase transition metal oxalates with different structures and compositions by simply adjusting the proportions of five transition metal elements. Among them, the multi‐phase mixture ( M C 2 O 4 ·2H 2 O ‐ CuC 2 O 4 ‐ M C 2 O 4 ·2H 2 O, M = Mn, Fe, Co, Ni, Cu) provides a more stable framework for the material during lithiation and delithiation, effectively alleviating the structural collapse during the cycling process. In addition, the electron transport and fast charge compensation processes of multiple electrochemically active metal pairs also contribute to the improvement of performance. Therefore, the multi‐phase transition metal oxalate TMOx‐2 electrode with an additional CuC 2 O 4 phase exhibits high reversible capacity and long‐term cycling stability. After 400 cycles at 100 and 500 mA/g, the specific discharge capacities are 827 mAh/g and 498 mAh/g, respectively. Constructing multi‐metal, multi‐phase systems by combining different transition metals enables control over potential, reaction pathways, and stability of high‐performance electrodes.