Influence of Acetylation and Polymerization Degree of Chitosan As Green Binder Material for LiMn2O4 Positive Electrodes in Lithium Ion Batteries

Abstract

The increasing market of lithium ion batteries within the climate crisis consequently leads to a need of environmentally friendly battery materials and production. Organic solvents, fluorinated binders and toxic transition metals are common components in state-of-the-art batteries. Aqueously processed ecofriendly electrodes are reported showing high electrical performance combined with high work safety and sustainability. In this study, the biopolymer chitosan is investigated electrochemically and mechanically as green binder for positive electrodes utilizing lithium manganese oxide (LiMn2O4; LMO) for the first time. Therefore, chitosans were tailored to a high and low degree of polymerization (DP) and three comparable degrees of acetylation (DA). The systematical comparison of these binder materials reveals insights into the impact of polymer binder properties on the electrochemical performance of positive electrodes. Low DP chitosan show a higher adhesive strength than high DP chitosans or PVdF, while chitosan-based electrodes with DA<16% deliver higher discharge capacities and Coulombic efficiencies in T-type cells than with DA>16% or even with the state-of-the-art binder polyvinylidene difluoride (PVdF). Crosslinking of chitosans with citric acid (CA) further increases discharge capacities up to 80 mAh g-1 at 10C and shows again a superior electrochemical performance with sustainable battery materials. Figure 1