Ultra-High Capacity and Cyclability of β-phase Ca_(0.14)V_2O_5 as a Promising Cathode in Calcium-Ion Batteries

摘要

Crystalline water-free β-phase Ca_(0.14)V_2O_5 is reported for the first time as aviable cathode material for calcium-ion batteries (CIBs). In contrast to layeredα-V_2O_5 and δ-CaxV_2O_5·nH_2O, which have limited capacity, the β-phasedelivers a reversible capacity of ≈247 mAh g?1, which corresponds to theinsertion/extraction of Ca~(2+) between Ca_(0.14)V_2O_5 and Ca1.0V_2O_5. The processof Ca~（2+） insertion process and the accompanying structural relaxation aretheoretically and experimentally verified. The initial insertion of Ca~(2+) intoCa_(0.14)V_2O_5 causes a slight shift of oxygen atoms surrounding hepta-coordinationsites, creating penta-coordinated sites that are then partially filled up toCa_(0.33)V_2O_5. Further insertion occurs through the stepwise occupation of upto 50% of neighboring hexa- and tetra-coordination sites to form Ca0.67V_2O_5and Ca1.0V_2O_5, respectively. The rearrangement of oxygen atoms in Ca_(0.14)V_2O_5also minimizes dimensional changes, leading to high cyclic stability duringrepeated charge/discharge cycles. The remarkable electrochemical performanceof full cells containing a Ca_(0.14)VV_2O_5 cathode and a K metal anode inCa~(2+)/K~+ hybrid electrolytes, is also demonstrated, thanks to the inertness ofK~+ insertion into Ca_(0.14)V_2O_5 and the absence of calcium plating/stripping. Thecyclic stability and high capacity of Ca_(0.14)V_2O_5 is not compromised in hybridelectrolytes, making it a viable CIB cathode.