The richness of V2O5 polymorphs as superior cathode materials for sodium insertion

In this paper, a special emphasis is given to the newly obtained electrochemical properties at room temperature of the two-dimensional ε′- and γ′-V2O5 polymorphs as sodium intercalation compounds. The structural peculiarities and electrochemical properties of each phase are presented. A full electrochemical and structural reversibility is demonstrated for both compounds upon sodium insertion at high voltage of 2.8 V. This noticeable voltage enhancement (+1 V) compared to α-V2O5 cathode is ascribed to the specific layers organization consisting of bilayered and puckered sheets in ε′-V2O5 and γ′-V2O5, respectively. Promising data, with large capacities (from 120 to 200 mAh g−1) and an excellent cycle life allow to identify new high performance V2O5- forms as positive electrode materials for sodium-ion batteries.