Tris(2-Carboxyethyl)Phosphine As an Additive for Cathodes in Li-S Batteries

Lithium-sulfur (Li-S) batteries are seen as a promising technology to satisfy the increasing demand for high energy density batteries for portable electronic devices and electric vehicles. However, they present different well-known drawbacks such as the solubility, deposition, and shuttle effect of lithium polysulfides that limit their practical applications. Additives or mediators can play a critical role to solve these problems. Tris (2-carboxyethyl) phosphine (TCEP) is mostly used in biological applications as a shear agent to cut higher-order polysulfides (Li2Sx , x>6) to low-order polysulfide (Li2Sx , x<4). Using this property, we incorporate TCEP in the cathode’s composition and test their electrochemical performance compared with cathodes without TCEP. When phosphine is present, not only a decrease in the energy barrier for the reduction reaction, but also a higher specific capacity is observed. The role of TCEP as a critical component is deeply studied by XPS and discussed herein.