γ'-V2O5 polymorph as a promising host structure for potassium storage: an electrochemical and structural study

International audienceK-ion batteries (KIBs) are receiving increasing interest because of the low K + /K redox potential and their reduced cost. This emerging alternative is however strongly dependent on the development of cathode materials with suitable structure for accommodating K + ions. We show here the promising properties of the puckered layered γ'-V2O5 polymorph that inserts up to 0.9 K + mol-1 at 3.3 V vs K + /K at C/60. An initial depotassiation capacity of 72 mAh g-1 corresponding to the exchange of 0.5 K + ions is still delivered at C/10 and a reversible capacity of 48 mAh g-1 , stable over 100 cycles, is achieved in the 4.4 V − 2.4 V voltage window. The reaction mechanism, investigated by XRD and Raman spectroscopy, involves the formation on first discharge of a new layered KxV2O5 host structure. The K0.78V2O5 bronze obtained at 2.4 V exhibits unfolded V2O5 sheets and an unexpected moderate expansion of the interlayer spacing compared to γ'-V2O5. Depotassiation-potassiation reversibly occurs within KxV2O5 (0.3 ≤ x ≤ 0.78) with less than 2% breathing. Such findings demonstrate the remarkable structural flexibility of γ'-V2O5 to accommodate the large-sized K + ions and illustrates the richness of V2O5 polymorphs as positive electrode materials for KIBs