Influence of copolymer chain sequence on electrode latex binder for lithium-ion batteries

Electrode binders have significant influences on lithium-ion battery performance. Good binders should be able to absorb electrolyte to accelerate lithium-ion transport while simultaneously maintaining adequate adhesion and mechanical strength after swelling. Currently, most polymer binders are based on homo or random copolymers so they may only meet one of these requirements, as an improvement in electrolyte swelling ability is detrimental to mechanical strength, and vice versa. This work investigates whether the design of chain sequence can resolve this contradiction. Reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization is employed to synthesize copolymer latex with different chain sequences as electrode binders, which are examined in both LiFePO4 cathode and silicon anodes. The results show a triblock copolymer chain sequence gives the best performance. The microphase separation in triblock copolymer distributes functionalities of electrolyte affinity and strength maintenance into disparate blocks and therefore satisfies both requirements simultaneously. The advantages of triblock chain sequence are demonstrated by superior ionic conductivity, mechanical strength after electrolyte absorption, and lithium-ion diffusion coefficient and then lead to better battery performance compared with random counterpart and commercial aqueous binders.