Valence-Tuned Lithium Titanate Nanopowder for High-Rate Electrochemical Energy Storage

Abstract

In recent years, numerous studies have explored ways to overcome the low intrinsic electrical conductivity of lithium titanate (Li4Ti5O12, LTO) for energy storage with lithium‐ion batteries. These approaches almost exclusively considered element doping and elaborate LTO‐carbon nanocomposites, whereas simple adjustment of the defect concentration remains largely unexplored. In our study, we tune the Ti3+/Ti4+ concentration of a commercial LTO nanopowder through oxygen vacancy formation during thermal annealing in hydrogen atmosphere. We investigate the impact of the treatment on material properties like energy band structure, electrical conductivity, crystallinity, phase distribution, surface chemistry, and particle morphology, and correlate these parameters to the electrochemical performance. At optimum treatment conditions, the intrinsic electrical conductivity can be greatly improved, while circumventing LTO phase transformations or amorphization. This enables the reduction of the carbon concentration to 5 mass%, while yielding a high electrode capacity of about 70 mAh/g (82 mAh/g based on active mass) at ultrahigh C‐rates of 100C. When combined with an activated carbon/lithium manganese oxide composite cathode, an excellent energy and power performance of 70 Wh/kg and 47 kW/kg were obtained (82 Wh/kg and 55 kW/kg based on active mass), while maintaining 83 % of its energy ratings after 5000 cycles at 10C (78 % after 15000 cycles at 100C).