High-Capacity O2-Type Layered Oxide Cathode Materials for Lithium-Ion Batteries: Ion-Exchange Synthesis and Electrochemistry
Zhaoshun Wang, Yong Wang, Dechao Meng, Qinfeng Zheng, Yixiao Zhang, Feipeng Cai, Di Zhu, Jiabing Liu, Yu‐Shi He, Liwei Chen, Zi‐Feng Ma, Linsen Li
Abstract
The O2-type layered oxide cathode materials have attracted strong research interest recently because of their high specific capacity and their unique lattice structure that may help suppress the detrimental layer-to-spinel phase transition. These materials are metastable and commonly prepared through Li-Na exchange methods from the Na-containing P2-type oxides. Here we investigated the structural, chemical, and morphological changes during the ion-exchange processes in both the LiBr/hexanol solution and the LiNO 3 /LiCl molten salts. The solution method was more favorable in preparing high-capacity O2-type cathode materials, even though the structural reorganization was slower compared with the molten-salt method. The as-made O2-type cathode materials, contrary to the previous belief, were actually Li-deficient at their pristine states, but could accept more Li ions than that it was extracted during the first charge/discharge cycle. The O2-type cathode materials exhibited high capacities (up to 266 mAh g −1 ) but the cycle performance requires further improvements. XRD and Raman spectroscopy studies indicated that the structural changes in the bulk were quite reversible. Using a fluorinated electrolyte to address the interface instability improved the cycle performance. Our results provide a more complete understanding of the O2-type cathode materials and useful guidance in the design of low-cost, high-energy cathode materials for LIBs.