Poly(3,4-ethylenedioxythiophene) encapsulation/intercalation boosting stability and zinc ion storage properties of vanadyl phosphates

The electrochemical properties of vanadyl phosphates as cathode materials for Zn-ion batteries have been severely hindered by their inherent poor electronic conductivity, unavoidable dissolution in aqueous solutions, and sluggish reaction kinetics. In this study, poly(3,4-ethylenedioxythiophene) (PEDOT) is introduced in vanadyl phosphates (PEDOT-VOP) through the in situ polymerization as interlayer guest species and surface coating layer, along with the generation of oxygen vacancies. The intercalated PEDOT develops strong interaction with the host layer, which can maintain its structural integrity. In addition, the PEDOT coating shell can enhance electronic conductivity together with oxygen vacancies to promote efficient electron transfer and prevent dissolution of active materials to stabilize the vanadyl phosphate core. As a result, the PEDOT-VOP electrode demonstrates a high discharge capacity of 180 mA h g−1 at 0.1 A/g with good rate performance (128 mA h g−1 at 2 A/g) and enhanced cycling stability (a capacity retention of 88.6 % after 2000 cycles at 1 A/g). The reversible Zn2+ insertion/extraction mechanism is further validated by diverse ex situ tests.