Comparative Study on Chitosans as Green Binder Materials for LiMn2O4 Positive Electrodes in Lithium Ion Batteries

Abstract The increasing demand for lithium ion batteries consequently involves research on environmentally benign materials and processing routes. Environmentally friendly cobalt‐free, and fluorine‐free electrodes processed without organic solvents were targeted as this approach combines high work safety and sustainability with good electrochemical performance. In this study, chitosan‐based biopolymers were synthesized and systematically investigated for the first time as “green” binders for positive electrodes utilizing LiMn 2 O 4 (LMO). In particular, chitosans with different specifically designed low and high degrees of polymerization (DP), each with comparable degree of acetylation (DA), revealed insights into the impact on the mechanical and electrochemical performance of LMO positive electrodes. Herein, low DP chitosan provided twice the adhesion strength compared to the state‐of‐the‐art binder polyvinylidene difluoride (PVdF) in LMO electrodes, thus, showing the opportunity to reduce the binder content and increase the specific energy. Electrodes with DA<16 % chitosan‐based binder could deliver higher discharge capacities than cathodes using PVdF or chitosans with DA>16 % in LMO||Li metal cells. Cross‐linking of chitosans with citric acid (CA) was demonstrated to significantly increase the discharge capacity up to 80 mAh g −1 at 10 C charge/discharge rate.