Conducting Polymer Composites As Multifunctional Electrode Matrices for Lithium-Ion Batteries

Abstract

The rising number of lithium-ion battery cells fabricated to power electric vehicles has raised concerns about the environmental impacts of battery electrode fabrication process. Typically, N-Methyl-2-pyrrolidone (NMP) solvent is used to blend active materials and electrode matrices, which are normally polyvinylidene fluoride/carbon-black (PVDF/C) mixtures. The use of NMP solvent, however, requires extensive energy for electrode drying and toxic solvent recovery. In addition, the PVDF/C electrode matrix offers weak interactions with active materials, which results in poor morphological integrity and rapid capacity fading, especially for high-volume-change electrode materials. Using water-processable binders such as carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) has been proven to enable a greener electrode-casting process as well as improve electrode performance. However, the electrical conductivity of these electrodes relies mainly on carbon additives, which are subjected to agglomeration and volumetric-capacity reduction. In this study, new electrode matrices are developed from in situ polymerized polypyrrole:carboxymethyl-cellulose (PPy:CMC) composites with water-processable and electrical-conductive features. By forming a composite structure in which CMC acts as an anionic dopant for PPy conducting polymer, the PPy:CMC composites show good electrical conductivity, allowing them to be used as mono-component electrode matrices. As a result, carbon-additive-free LiCoO2/PPy:CMC electrodes can cycle at different C-rate. More importantly, the PPy:CMC composites enable aqueous slurry electrode casting, addressing the environmental pollution associated with NMP solvent utilization. The study introduces another potential application of conducting polymer composites in Li-ion batteries.Keywords: aqueous electrode casting, conducting polymers, polypyrrole.