Water-Dispersible Conducting Polymer Composite:a Promising Binder for Cathode of Lithium Ion Batteries

Abstract Binders are a vital component in the electrode of Li-ion batteries that hold active materials and conductive additives in place. Most binder research focuses on anode binders after the introduction of ultrahigh capacity anode materials such as Si, Sn, Ti and its derivatives, which suffer from extreme volume expansion/contraction during charge/discharge cycles1. Cathode binders, on the other hand, attract less attention even though cathode materials such as layered transition-metal oxides, olivine LiFePO4, spinel LiMn2O4 are still experiencing mechanical deterioration (fracture, disintegration)2, poor electrical conductivity3, phase changes4 and side reactions that eventually lead to capacity fading over cycling. Cathode materials are currently also the most expensive material in commercial Li-ion batteries5 and contribute the highest weight. For these reasons, the development of better binders for cathodes is paramount important to reduce cost and increase specific energy of Li-ion batteries. Commercially prevalent is the PVDF/Carbon additives binder system at the cathode. This binder system offers limited adhesive forces between active materials. Besides that, the addition of electrochemically inert carbon additives to compensate the poor electrical conductivity also decreases the mass energy density of Li-ion batteries1. Moreover, volatile organic-solvents (most frequently N-methyl pyrrolidone) are involved in electrode fabrication with PVDF binder, posing a threat to the environment. In this research, a water-dispersible conducting polymer composite is introduced as a promising green binder for Li-ion intercalation cathodes. By carrying out in-situ polymerization of polypyrrole in the presence of carboxyl/hydroxyl containing polymers, the obtained polymers are electrically conductive and water-dispersible. The polypyrrole-based composite binder is designed to not only offer a continuous conductive matrix but also suppress capacity fading via intramolecular interactions. The presentation will describe our efforts in synthesizing these binders, characterizing their physical and chemical properties, and investigating their performance in Li-ion cathodes. Keywords: Conducting Polymers, Polypyrrole, Water-dispersive Binder, Li-ion batteries. References Chen, H. et al. Exploring Chemical, Mechanical, and Electrical Functionalities of Binders for Advanced Energy-Storage Devices. Chem. Rev. 118, 8936–8982 (2018). Wu, F. & Yushin, G. Conversion cathodes for rechargeable lithium and lithium-ion batteries. Energy Environ. Sci. 10, 435–459 (2017). Eliseeva, S. N., Levin, O. V, Tolstopyatova, E. G., Alekseeva, E. V & Kondratiev, V. V. Effect of addition of a conducting polymer on the properties of the LiFePO4-based cathode material for lithium-ion batteries. Russ. J. Appl. Chem. 88, 1146–1149 (2015). Zheng, J. et al. Corrosion/fragmentation of layered composite cathode and related capacity/voltage fading during cycling process. Nano Lett. 13, 3824–3830 (2013). Patry, G., Romagny, A., Martinet, S. & Froelich, D. Cost modeling of lithium-ion battery cells for automotive applications. Energy Sci. Eng. 3, 71–82 (2015).

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