Amorphous and Crystalline Vanadium Orthophosphate and Oxidized Multiwalled Carbon Nanotube Composites as Anode Materials in Sodium‐Ion Batteries

Abstract

AbstractVanadium orthophosphate and oxidized multiwalled carbon nanotube (ox‐MWCNT) composites were applied as anodic electroactive materials in a sodium‐ion battery. Carbon nanotubes reduce the resistance of anodic materials, prevent drastic volume expansion, and allow easy transport of electrolyte ions, leading to an improvement in the electrochemical performance of electroactive materials. Theoretical modeling of the VPO4 /ox‐CNT interphase indicates the conducting properties of the crystalline c‐VPO4 /ox‐MWCNT composite and the significant contribution of CNTs in the charge transfer process. As anodes in sodium‐ion batteries, crystalline VPO4 (c‐VPO4 ) and amorphous VPO4 (a‐VPO4 ) exhibited initial discharge capacities of 125 mAh g−1 and 110 mAh g−1, respectively. The incorporation of vanadium phosphate into the network of ox‐MWCNTs results in a large increase in the capacity performance of electroactive materials. Discharge capacities of 1642 mAh g−1 and 1680 mAh g−1 were obtained for the first cycle in the case of the c‐VPO4 /ox‐MWCNT 50 % w/w and a‐VPO4/ox‐MWCNT 50 % w/w anodes, respectively. The capacity of these composite materials significantly decreases in the second cycle, reaching a stable capacity performance. The limiting capacity was 328 mAh g−1 for composites containing 50 % w/w ox‐MWCNTs.