(24) For this reason, polymers that can interact with Si through their functional groups including COOH and OH, such as polyacrylic acid (PAA), polyvinyl alcohol (PVA), and carboxymethyl cellulose (CMC), have been considered as potential binder materials for Si anodes.
A new type of polyamide imidazole (PAID) polymer with two functional groups for tight binding with silicon (Si) particles and carbon black is investigated as a binder for the Si anode in lithium-ion batteries (LIBs). PAID is synthesized via three reaction phases. The first phase is polyamide polymerization (p-PAID), the second phase is formation of imide and imidazole rings (i-PAID), and the last phase is ring cyclization for the PAID structure. Among these stages, i-PAID shows ambidextrous binding characteristics for LIBs. The planar π-conjugated backbone in the i-PAID provides a strong π–π stacking interaction with carbon black, thus sustaining the electrical conduction pathway in the Si electrode during cycling. The amine and carboxylic acid functional group in the i-PAID have a strong interaction with Si particles, which efficiently suppresses the volume expansion of the Si electrode, confirmed by in situ electrochemical dilatometry and ex situ SEM observation. The Si anode with the bifunctional i-PAID binder shows not only a higher reversible capacity but also a greatly enhanced cycle performance over 200 cycles in comparison to the Si anode with a simple polyimide binder. This ambidextrous polymer binder offers a new opportunity to positively impact the development of a mechanically robust Si anode for lithium-ion batteries.