A P3-Type K<sub>1/2</sub>Mn<sub>5/6</sub>Mg<sub>1/12</sub>Ni<sub>1/12</sub>O<sub>2</sub> Cathode Material for Potassium-Ion Batteries with High Structural Reversibility Secured by the Mg–Ni Pinning Effect
Liying Liu, Jinji Liang, Wanlin Wang, Chao Han, Qingbing Xia, Xi Ke, Jun Liu, Qinfen Gu, Zhicong Shi, Shulei Chou, Shi Xue Dou, Weijie Li
Abstract
Mn-based layered oxides are very attractive as cathodes for potassium-ion batteries (PIBs) due to their low-cost and environmentally friendly precursors. Their transfer to practical application, however, is inhibited by some issues including consecutive phase transitions, sluggish K+ deintercalation/intercalation, and serious capacity loss. Herein, Mg–Ni co-substituted K1/2Mn5/6Mg1/12Ni1/12O2 is designed as a promising cathode material for PIBs, with suppressed phase transitions that occurred in K1/2MnO2 and improved K+ storage performance. Part of Mg2+ and Ni2+ occupies the K+ layer, playing the role of a “nailed pillar”, which restrains metal oxide layer gliding during the K+ (de)intercalation. The “Mg–Ni pinning effect” not only suppresses the phase transitions but also reduces the cell volume variation, leading to the improved cycle performance. Moreover, K1/2Mn5/6Mg1/12Ni1/12O2 has low activation barrier energy for K+ diffusion and high electron conductivity as demonstrated by first-principles calculations, resulting in better rate capability. In addition, K1/2Mn5/6Mg1/12Ni1/12O2 also delivers a higher reversible capacity owing to the participation of the Ni element in electrochemical reactions and the pseudocapacitive contribution. This study provides a basic understanding of structural evolution in layered Mn-based oxides and broadens the strategic design of cathode materials for PIBs.