National Research Council of Canada. Energy, Mining and Environment
Next-generation anode materials for Li-ion batteries such as silicon can lead to ten times more capacity than the state-of-the-art graphite. However, novel binders are required to overcome the detrimental effects of volume changes during battery cycling of silicon because of the poor chemical interaction and electrical conductivity between silicon and the binder. Most studies focus on either ionic binders or electrically conductive binders, but herein it was demonstrated that a new family of polymers based on electrically conductive poly(thiophene) functionalized with an ionic alkyl carboxylate groups of various lengths can successfully work as multifunctional binders for silicon and commercial graphite anodes in Li-ion battery half-cells. It was determined that the polymer with shorter side chain (PT-3-LiA) gives the highest reversible capacity upon pairing with graphite or silicon, reaching 3000 mAh g−1 in the case of the latter, a capacity 500 mAh g−1 (≈22 %) higher than those obtained with the electrically, but non-ionically, conductive PEDOT:PSS binder and the ionically, but non-electrically, conductive sodium carboxymethyl cellulose (NaCMC) binder. It is demonstrated that the superior performance of this new type of multifunctional binders can be attributed to their ability to maintain their doping level and conductivity as well as due to good interaction with the silicon surface during cycling.