Evaluation of Polymeric Binders in Aqueous Electrolyte Environment

Abstract

Energy storage systems utilizing aqueous electrolytes are ever increasing in importance, as they are inherently cheap and safe when compared to their traditional lithium ion battery counter parts. To date, however, no thorough study on binder characteristics in the aqueous environment has been published. This work characterizes an acrylic based polymer, LA133, LA133+Carboxymethyl cellulose (CMC), Styrene-butadiene rubber (SBR), SBR+CMC, and Polytetrafluoroethylene (PTFE) in an LiMn2O4 cathode. Data presented includes cyclic voltammetry (CV), resistivity, and porosity. Future work will focus on characterizing binders for anode materials then galvanostatic cycling of full cells. Figure 1 shows half-cell (CV) data for LiMn2O4 cathodes cycled between 0-0.7 V at reference cycle rates of 3.33 mV/min and daily cycles rates of 30 mV/min. LA133 clearly degrades, while the other binders performed similarly. This is noteworthy, as it directly contradicts LA133’s behavior in organic electrolytes, as Wang, Rui et al. specifically selected it for its stability in the window of 0.1-3.0V [1]. Additionally, SBR appears to have poorer performance at faster scan rates, but the overall slow scan retention was on par with that of Acrylic and PTFE, indicating poor rate capability rather than electrode degradation. Overall slow scan retention is shown more clearly in Figure 2. This again contradicts findings from traditional Li-ion batteries, as Yingjin Wei et al. selected the SBR/CMC binder combination for its superior rate capability [2]. Figure 3 shows resistivity and porosity data for the LiMn2O4 cathodes. Measurements were taken at 10 MPa and 19 MPa of applied pressure, and the average values are presented here. The most noteworthy point is that the addition of CMC clearly reduces the resistivity in both LA133 and SBR. This motivates investigation into pairing CMC with the other binders, which is not traditionally done in Li-ion batteries. References Wang R, Feng L, Yang W, et al. Effect of Different Binders on the Electrochemical Performance of Metal Oxide Anode for Lithium-Ion Batteries. Nanoscale Res Lett. 2017;12(1):575. Published 2017 Oct 30. doi:10.1186/s11671-017-2348-6Yan X, Zhang Y, Zhu K, Gao Y, Zhang D, Chen G, Wang C, Wei Y (2014) Enhanced electrochemical properties of TiO2(B) nanoribbons using the styrene butadiene rubber and sodium carboxyl methyl cellulose water binder. J. Power Sources Figure 1