Mechanisms for Improved Anode Performance in Titanium Niobate via Neodymium Doping

High-powered Li-ion battery anodes are a rapidly developing class of materials, being essential to the success of various applications, such as medical devices and heavy machinery. One material of significant recent interest is TiNb2O7, which is attractive due to its high theoretical capacity of 388 mA h g–1. This capacity is not typically achieved, but our recent efforts to improve the performance of TiNb2O7 by substitutional doping with Nd have increased the capacity by 19% over the undoped material to 321 mA h g–1 with only a 1.2% substitution. In this work, experimental investigations of lithium and electron transport properties revealed that the enhanced performance of Nd-doped TiNb2O7 is primarily due to an increased number of lithium storage sites and improved accessibility through more efficient diffusion pathways. X-ray absorbance spectroscopy and computational modeling were used to understand the mechanism behind these improvements. The two methods suggest that Nd in the TiNb2O7 lattice increases the size of certain channels for lithium diffusion while decreasing the size of others. The fact that this results in faster diffusion and increased lithium storage capacity demonstrates that those paths that increased in size act as bottlenecks in the undoped TiNb2O7. This complement of experiment and computation guides the further design of these materials by identifying the key structural limitations in the material.