Weyl semimetal orthorhombic Td-WTe2 as an electrode material for sodium- and potassium-ion batteries

Alkali metals such as sodium and potassium have become promising candidates for the next generation of monovalent-ion batteries. However, a challenge for these battery technologies lies in the development of electrode materials that deliver high capacity and stable performance even at high cycling currents. Here we study orthorhombic tungsten ditelluride or Td-WTe2 as an electrode material for sodium- (SIB) and potassium-ion batteries (KIB) in propylene carbonate (PC) based electrolyte. Results show that despite larger Shannon's radius of potassium-ions and their sluggish diffusion in Td-WTe2 due to higher overpotential, at 100 mA.g−1 KIB-half cells showed higher cycling stability and low capacity decay of 4% versus 16% compared to SIB-half cells. Likewise, in a rate capability test at 61st cycle (at 50 mA.g−1), the KIB-half cells yielded charge capacity of 172 mAh.g−1 versus 137 mAh.g−1 of SIB-half cells. The superior electrochemical performance of Td-WTe2 electrode material in KIB-half cells is explained based on the concept of Stokes' radius—smaller desolvation activation energy resulted in higher mobility of potassium-ions in PC-based electrolyte. In addition, the likely mechanisms of electrochemical insertion and extraction of Na- and K-ions in Td-WTe2 are also discussed.