Visualization of the Phase Propagation within Carbon-Free Li4Ti5O12 Battery Electrodes

Abstract

The electrochemical reactions occurring in batteries involve the transport of ions and electrons among the electrodes, the electrolyte, and the current collector. In Li-ion battery electrodes, this dual functionality is attained with porous composite electrode structures that contain electronically conductive additives. Recently, the ability to extensively cycle composite electrodes of Li4Ti5O12 without any conductive additives generated questions about how these structures operate, the answers to which could be used to design architectures with other materials that reduce the amount of additives that do not directly store energy. Here, the changes occurring in carbon-free Li4Ti5O12 electrodes during lithiation were studied by a combination of ex situ and operando optical microscopy and microbeam X-ray absorption spectroscopy (μ-XAS). The measurements provide visualizations of the percolation of lithiated domains through the thick (∼40-μm) structure after a depth of discharge of only 1%, followed by a sec...