Development of design strategies for conjugated polymer binders in lithium-ion batteries

Lithium-ion batteries (LIBs) are complex electrochemical systems whose performance is determined by the proper design and optimization of its individual components, such as active materials, separators, polymer binders, electrolytes and conductive additives. In the quest for high-energy and high-power density batteries and next-generation ultrahigh-capacity battery electrodes, industry and academia have worked hand-in-hand over the last few decades, developing strategies for improving the performance of each component in an LIB. However, only recently has the development of multifunctional polymer binders become a focus, with the goal of providing additional functionality beyond simple mechanical adhesion. Polymer binders, exemplified by poly(vinylidene fluoride) (PVDF), are typically an inactive component in a composite electrode that does not contribute to capacity. Moreover, limited binding strength, poor mechanical properties and the absence of electronic and ionic conductivity make PVDF inadequate for application in emerging high-capacity and high-power density batteries. In this regard, conjugated polymers have gained attention as conductive polymer binders and/or coatings for the cathodes and anodes in LIBs. The ability of conjugated polymers to transport both electronic and ionic charge carriers endows them with mixed electron and Li+ ion transporting properties in an LIB. Based on the enormous potential of conjugated polymer binders to enhance the performance of LIBs, in this review, we present an overview of conducting polymer binders/coatings and their chemical design strategies, developed in the last decade, for use in LIBs. Chemical design strategies developed in the last decade for conjugated polymer binders in lithium-ion batteries (LIBs) are reviewed here. The first part of this review discusses the mechanism of operation and role of binders in LIBs, and the importance of conductivity in advanced binder systems. The second part of this review gives an account of various conducting polymer binders developed for cathodes and anodes of LIBs. The review concludes with an emphasis on sustainable synthetic design strategies for next-generation conducting polymer binders for greener electrochemical energy storage systems.