In-Depth Study of Li4Ti5O12 Performing beyond Conventional Operating Conditions.

Abstract

Lithium-ion batteries (LIBs) are nowadays widely used in many energy storage devices, which have certain requirements on size, weight, and performance. State-of-the-art LIBs operate very reliably and with good performance under restricted and controlled conditions but lack in efficiency and safety when these conditions are exceeded. In this work, the influence of outranging conditions in terms of charging rate and operating temperature on electrochemical characteristics was studied on the example of lithium titanate (Li4Ti5O12, LTO) electrodes. Structural processes in the electrode, cycled with ultrafast charge and discharge, were evaluated by operando synchrotron powder diffraction and ex situ X-ray absorption spectroscopy. On the basis of the Rietveld refinement, it was shown that the electrochemical storage mechanism is based on the Li-intercalation process at least up to current rates of 5C, meaning full battery charge within 12 min. For applications at temperatures between -30 and 60 °C, four carbonate-based electrolyte systems with different additives were tested for cycling performance in half-cells with LTO and metallic lithium as electrodes. It was shown that the addition of 30 wt % [PYR14][PF6] to the conventional LP30 electrolyte, usually used in LIBs, significantly decreases its melting point, which enables the successful low-temperature application at least down to -30 °C, in contrast to LP30, which freezes below -10 °C, making battery operation impossible. Moreover, at elevated temperatures up to 60 °C, batteries with the LP30/[PYR14][PF6] electrolyte exhibit stable long-term cycling behavior very close to LP30. Our findings provide a guideline for the application of LTO in LIBs beyond conventional conditions and show how to overcome limitations by designing appropriate electrolytes.