Study of low temperature electrochemical performance of TiO₂ nanomaterials for Li-ion and Na-ion batteries anodes

Abstract

Owing to significant capacity loss at low temperatures, the applications of lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) are severely restricted. And the phase transitions of electrode materials at low temperatures remain poorly understood, due to difficulties of the direct monitoring. TiO2 shows promise as an intercalation-type electrode because of its low volume expansion during cycling, fast charging capability, and is an ideal model for this research. Our first work aims to examine the phase transition of anatase TiO2 upon Li+ ion intercalation across a range of temperatures. Operando Raman spectroscopy reveals that a decrease in temperature favors the formation of a supersaturated solid solution phase. Kinetic analyses illustrate that Li redistribution is facilitated at high temperature but limited at low temperature. Finally, we prove enhancing interfacial kinetics and creating an interconnected electrode architecture are effective ways to facilitate phase separation, and improve low-temperature performance of LIBs. In our second work, TiO2-B/anatase dual-phase nanowires are synthesized and applied as SIB anode. For the first time, we find the excellent Na-storage performance of the nanowire anode like rate-independent capacities and ultra-stable cycling stability at low temperature. Operando Raman spectroscopy reveals a different sodiation/desodiation mechanism at room and low temperatures. Finally, we confirm the synergy between structural transition and diffusion kinetics leads to rate-independent and ultra-stable Na-storage performance at low temperature. In the third work, we synthesize dual-phase TiO2 nanowires composed of anatase and TiO2-B phases with tunable phase ratios and study their electrochemical performance at extended potential range. It is found that the dual-phase nanowire with phase ratio of~1.0, named as TiO2-350, possesses the best rate and cycling performance. Cyclic voltammetry results demonstrate that the ultrahigh capacity of the TiO2 nanowire mainly attributes to the capacitive contribution below 1.0 V. Structural analyses show the solid solution reaction of the TiO2-350 nanowires with Li+ and excellent structure stability during cycling. Finally, we test the superb low temperature performance ot this anode at enlarged potential window. This thesis dedicates to addressing issues of low temperature performances of nanomaterials for LIBs and SIBs. Taking TiO2 as a model and utilizing in-situ Raman with other advanced technologies, we systematically investigate the effects of phase transition, reaction mechanism, as well as phase ratio on the low temperature performance. We believe our work can provide guideline for exploring the inner reaction mechanism and failure mechanism of next generation batteries at all-climate temperatures.