Poly (acrylic acid-co-N-methylol acrylamide-co-butyl acrylate) copolymer grafted carboxymethyl cellulose binder for silicon anode in lithium ion batteries

Abstract

A poly (acrylic acid-co-N-methylol acrylamide-co-butyl acrylate) copolymer grafted-carboxymethyl cellulose (PA-PN-PBA-g-CMC) binder is synthesized via a free radical copolymerization for Si-based anodes in lithium ion batteries. In this multifunctional polymer binder system, carboxyl-rich poly (acrylic acid) and carboxymethyl cellulose can bond with Si particles and copper current collectors. Additionally, a robust cross-linking network can be obtained through the condensation reaction between hydroxyl and hydroxymethyl groups which are present in carboxymethyl cellulose and N-methylol acrylamide segments, respectively. This network structure helps to keep the integrity of the Si electrode, and thereby significantly improves the cycling performance of the Si anodes (capacity retention rate after 200 cycles is above 90%). The butyl groups in poly (butyl acrylate) segments provide the nonpolar sections in the binder, which help the electrolytes easily wet the electrodes, allowing Li ions to diffuse rapidly in the Si anodes. With this multi-functional binder, the Si-based LIBs perform well in both cycle performance and rate performance.