Associating Mechano-electrochemical Phenomena to Stochastic Current Events in Micro-Electrochemical Cells Containing TiNb2O7 Particles

Abstract

While searching for ultra-safe high-power anodes for Li-ion batteries, TiNb₂O₇ (TNO) emerged as a promising material for higher energy density compared to the current state-of-the-art Li₄Ti₅O₁₂ (LTO). Here, the electrochemistry of isolated carbon coated particles of both anode materials were for the first time studied using scanning electrochemical cell microscopy (SECCM). Interestingly, stochastic current event observations were made possible because of the small electrochemical cell created by SECCM and were designated as potential-driven stochastic events (PDSEs). The PDSEs were especially prominent in TNO compared to LTO. Metrics for judging the frequency and intensity of PDSEs were developed to compare the impact of different C-rates, particle masses and sizes of SECCM landings. The frequency and/or intensity of PDSEs increases with higher C-rates and larger overpotentials. Possible theories for the PDSEs were explored, including droplet electrowetting/spreading, gas evolution, (de)lithiation mechanisms, mass transfer limitations and inter-/intra- particle cracking. We speculate that the propensity of TNO to undergo PDSEs as compared to LTO is mainly related to the fact that TNO is known to crack extensively during cycling.