New Barium Vanadate BaxV2O5 (x approximate to 0.16) for Fast Lithium Intercalation: Lower Symmetry for Higher Flexibility and Electrochemical Durability

Abstract

Na0.33V2O5-type metal vanadates generally show better cycling stability than alpha-V2O5 as a cathode in Li-ion batteries, because they contain enough crystallographic voids that allow for lithium intercalation without significant structural deformation, but metal leaching upon cycling deteriorates their capacity retention. Here a new barium vanadate Ba0.16(1)V2O5 is reported that does not undergo Ba leaching during cycling and shows a great promise for fast Li intercalation. Sr0.15(1)V2O5 is isostructural to Na0.33V2O5 (space group C2/m), while Ba0.16(1)V2O5 adopts a new structure (space group P2(1)/c), a derivative of Na0.33V2O5. The framework of Ba0.16(1)V2O5 consists of edge-shared VO6 octahedral layers and the VO5 pyramidal bridge, generating unidirectional tunnels. Unlike the in-plane arrangement of atoms in Sr0.15(1)V2O5, the nonplanar arrangement in Ba0.16(1)V2O5 makes the host framework more flexible and creates larger voids for Ba. Compared with the combination of displacement and intercalation mechanisms in the Sr0.15(1)V2O5 cathode, Li intercalation looks dominant in the Ba0.16(1)V2O5 cathode due to its increased flexibility. Hence, Ba0.16(1)V2O5 exhibits improved cycling stability compared to Sr0.15(1)V2O5, suggesting that lower symmetry leads to higher cyclic stability in the V2O5-related compounds. This study illustrates how guest cations can tune the structural symmetry to modulate the reaction mechanism of electrode materials toward superior performances.