Study of Alternative Binders for Battery Electrode in Aqueous System

Abstract

Materials used to prepare energy storage devices need to be affordable, durable, and safe for environment. PVDF, which is the most popular polymer used as a binder in battery electrodes, requires the use of and toxic solvents for processing, such as N-methyl-pyrrolidone (NMP).1 Water insoluble organic polymers could replace PVDF as the binder in aqueous batteries or redox flow batteries with solid boosters.2 For example, ethyl cellulose is a biodegradable and water-insoluble polymer. Ethyl cellulose-based slurry can be prepared using ethanol as solvent, which makes the process cheaper and more sustainable. Also cross-linked gluten could be used as a binder. In that case water-based slurry could be used to prepare the electrode. Replacing PVDF with more environmentally friendly binder would be beneficial in many ways. It would shorten the assembly procedure due to high speed of solvent evaporation, there are no strict requirements for humidity control and the recycling procedure is easier as there are no fluorinated compounds.3 Therefore, this replacement would enable to produce safer and cheaper energy storage devices.In this work positive electrodes with different composition have been described using galvanostatic charging-discharging and cyclic voltammetry. Various cell setups have been tested. LiMn2O4 (LMO) has been used as active material for cathode and carbon black Super P as conductive additive. PDVF has been compared with various organic biodegradable polymers as the binder. Using ethyl cellulose as a binder, discharge capacity 100 mAhg−1 was achieved at 0.2C rate for LMO cathode which is comparable to the results obtained with PVDF as a binder. 500 cycles at the rate of 1C showed somewhat better capacity retention for electrodes prepared using PVDF. Also rotating disk electrode experiments were conducted to study the effect of binder to the kinetics of the reaction. The results show that some biodegradable and cheaper binders could be promising option to replace PVDF as binder in aqueous systems. This is highly important in aqueous redox flow battery with solid boosters, where large amount of solid charge storage material is used in tanks to increase the capacity of the system.2 Acknowledgements: The research was supported by the Estonian Research Council grant MOBTP1023, Archimedes Foundation project SLTKT16432T and by the EU through the European Regional Development Fund under project TK141 (2014–2020.4.01.15–0011).