Electronic vs Ionic Limitations to Electrochemical Performance in Li4Ti5O12-Based Organic Suspensions for Lithium-Redox Flow Batteries

Here, we report the electrochemical response of the LTO/KB anolytes vs. lithium as function of the cycling rate in static mode (i.e. no flow) and using a home-made cell. The KB content was fixed at 3 wt% while the LTO content was varied between 15 and 25 wt%. The anolyte thickness in the cell was varied between 0.5 and 1.5 mm. Impedance spectroscopy allowed to quantify the extent of KB percolation in the anolyte. The active mass truly electrochemically reactive is critically dependent on the extent of percolation of the KB conductive additive. Rate limitations are influenced by both the ionic and the electronic wiring of the active mass. The electronic limitations are strongly dependent on the extent of percolation of KB which is influenced by the LTO/KB ratio and cell dimensions. Above a critical thickness in the 0.5-1 mm range, depending on the LTO content, the rate performance are significantly decreased. The better understanding of the rate limitations will allow a more efficient optimization of the suspension formulation as well as the design of RFB reactors. © 2014 The Electrochemical Society. All rights reserved.