Acrylic random copolymer and network binders for silicon anodes in lithium-ion batteries

The choice of a binder can greatly influence the electrochemical performance of lithium-ion batteries (LIBs), especially for silicon (Si) anodes. To systematically modulate the mechanical properties of binders and to investigate their impact on the electrochemical properties, we synthesize a series of random copolymers consisting of acrylic acid (AA) and n-butyl acrylate (n-BA) via reversible addition-fragmentation chain-transfer (RAFT) polymerization. The electrochemical properties of Si nanoparticle (SiNP) anodes prepared using copolymer binders exhibit a strong dependence on the relative composition of AA and n-BA. The incorporation of a moderate amount of n-BA (10–30 mol%) in the copolymer binder provides better cycling stability compared to a SiNP anode prepared using poly(acrylic acid) (PAA) binder. The binder containing 30 mol% of n-BA is further crosslinked by in-situ crosslinking using a variable amount of polyethylene glycol diglycidyl ether (PEGDE). The electrochemical properties (3050 mAh g−1 in the 1st cycle and 40% capacity retention in the 100th cycle at 0.5 A g−1) of a SiNP anode prepared using the crosslinked binder with 14 wt% of PEGDE show further improvement compared to those of a SiNP anode prepared using PAA binder (2310 mAh g−1 and 32% capacity retention in the 100th cycle at 0.5 A g−1).