Multifunctional conducting copolymer for high-capacity lithium-ion batteries

Abstract

As the requirement for ecofriendly zero-emission vehicles is becoming more significant, LiBs has attracted more attention. However, to facilitate LiBs in vehicles, much higher capacity is needed. Thus, various materials have been studied as a next-generation active material of LiBs. Among various number of candidates, Si is the most promising materials due to its superior capacity and richness. Even though Si has 10 times higher capacity (~4200 mAh/g) than that of conventional graphite anode, its critical problems hinders the commercialization of Si anode. The main challenge is rapid capacity fading resulting from extreme volume change of Si. The volume change induces significant contact loss and capacity fading. There have been many efforts to solve the problem. One promising approach is to develop advanced binders. We facilitated polyacrylamide (PAAM) which has superior mechanical properties as a new binder. Due to its mechanical strength and high adhesive force to other components, pulverization and induced capacity loss of Si anode were significantly lowered. With PAAM, PEDOT:PSS has been used together in Si anode. PEDOT:PSS is the most promising conducting polymer due to its higher electric conductivity, chemical, thermal stability, and processability. We tried to replace carbon black which is a universal conventional conducting material of cells to the PEDOT:PSS. To apply the two polymers in parallel, we adopted the strategy of chemically linking the polymers. First, PEDOT:PSS which has $N_3$ functional groups was synthesized with acid addition. And alkyne terminated PAAM was polymerized through reversible addition-fragmentation chain-transfer (RAFT) polymerization method. Finally, the polymers were combined using azide-alkyne Huisgen cycloaddtion (CuAAC) click reaction. The synthesized multifunctional binder showed significant improvement of cell performance in unit capacity and cyclability. This study of the new copolymer binder could be suggested as a solution for the critical issues of Si anode.