Fast Charging of All-Active-Material Architected Electrodes through Nonequilibrium Multiphase Lithiation.

Abstract

Ion transport across solid and liquid phases in alkali-ion battery electrodes dictates the rate at which they can be charged and discharged. As such, nanosized Lithium titanate (LTO) particles are commonly used as an anode material deployed in thin electrode layers for high-power applications. While safe and effective, these anodes are limited in energy density due to low tap density. Sintering nanosized particles decreases porosity, thereby increasing the anode energy density, while introducing longer solid-state diffusion distances. However, recent studies have suggested that solid transport of lithium ions is promoted at the interface of sintered LTO particles due to lattice hopping. Here, we report an all-active-material sintered LTO anode with aligned electrolyte-filled channels for fast ion transport and percolating grain boundaries for electron transport. In these architected and sintered LTO electrodes, we find that expanding the voltage window of operation promotes rate-dependent formation of three phases, including a highly lithiated γ phase (Li7+xTi5O12) that under fast lithiating (charging) conditions exists out of equilibrium with the nonlithiated α phase (Li4Ti5O12). The coupling of transport-enhancing architectural features with out-of-equilibrium multiphase lithiation allows for up to 92% capacity retention at 2 C in an application-relevant electrode with a capacity of 4.9 mAh cm-2 and a total porosity of 0.32.