Aqueous Polypyrrole:Carboxymethyl Cellulose Conducting Binder for Graphite Electrodes in Lithium-Ion Batteries

Abstract

In lithium-ion batteries (LIBs), polymeric binders are utilized to ensure the mechanical integrity of composite electrodes and facilitate ion transport. Compared to conventional fluoropolymers, such as polyvinylidene fluoride (PVDF), water-processable polymers are advantageous from both ecological and economic standpoints. Aqueous sodium carboxymethyl cellulose (CMC-Na) and its composites with elastomers have been established as fluorine-free alternatives to conventional fluorinated binders in lithium intercalation anodes. Unlike the low polarity PVDF, CMC possesses functional groups (–COOH and –OH) that can strengthen interactions with other materials through hydrogen bonding and covalent bonding. CMC is also cost-effective, water-soluble, and biodegradable. To create a multifunctional binder with CMC and eliminate the need for conductive additives, our group previously synthesized conductive CMC composites by using CMC as a dopant in polypyrrole (PPy). As a conducting polymer in its oxidized form, it provides good conductivity and thermal and environmental stability. In this study, we report, for the first time, the application of PPy:CMC as a conducting binder in graphite anodes. Cycling stability, rate capability, and interfacial/charge transfer resistance were evaluated with galvanostatic cycling, cyclic voltammetry, and impedance spectroscopy, respectively. Degradation mechanisms and by-products were studied, and electrode morphology and homogeneity were characterized. It was found that although PPy:CMC is partially reduced under anode operating conditions, this does not adversely affect long-term battery cyclability. These findings establish PPy:CMC as a viable multifunctional binder for graphite anodes and provide new insight into the binder’s behavior, laying the groundwork for its application in next-generation high-energy-density LIBs.