Effects of cation and anion substitution in KVPO4F for K-ion batteries
Young‐Woon Byeon, Minjeong Gong, Zijian Cai, Yingzhi Sun, Nathan J. Szymanski, Jianming Bai, Dong‐Hwa Seo, Haegyeom Kim
Abstract
The effects of cation (Ti 4+ ) and anion (O 2− ) substitution on the electrochemical properties of KVPO 4 F cathodes are investigated in this work. Both forms of substitution lead to smoothing of the associated voltage profile as well as reduced charging time at high voltage (>4.8 V vs. K/ K + ). These changes effectively suppress electrolyte decomposition, thereby enhancing the capacity retention in the ion-substituted KV (1 − x ) Ti x PO 4+ y F 1− y materials. Ionic substitution also enables the intercalation of excess K ions at a reasonably high voltage (∼1.8 V vs. K/ K + ) relative to that required in pure KVPO 4 F (<1.0 V vs. K/ K + ). Finally, this study reveals that detours in the synthesis reaction pathways can be created by using a pre-reacted precursor, VPO 4 , rather than the conventional precursors V 2 O 3 and NH 4 H 2 PO 4 to form stoichiometric (or non-substituted) KVPO 4 F. These results highlight several design criteria that can be used to optimize KVPO 4 F and related compositions to prepare K-ion batteries with high capacity, good cyclability, and fast rate capability.