Structure Engineering and Structure-Property Study of TiNb2O7 Nanofibers As Anode for Safer Lithium Ion Batteries

Abstract

Lithium ion batteries (LIBs) have been the dominant energy storage technology for a wide range of applications including portable electronic, electrical vehicles, and grid-scale energy storage. Recently with safety and performance in mind, TiNb2O7 (TNO) has been studied as a promising anode material. It offers a theoretical capacity of 387.6 mA h g-1, which is comparable to that of graphite (372 mA h g-1) and two times that of Li4Ti5O12 (175 mA h g-1). TNO also exhibits an operational voltage larger than 1.0 V (vs Li+/Li0), which helps to avoid formation of dendritic lithium and ensure safe operation. TNO with various morphology and size has been studied intensely since its discovery by Goodenough et. al. in 2011 including mesoporous microspheres, solid or porous nanoparticles, and solid or hollow 1D fibers. However, no comprehensive study which studies the structure-property-aspect of TNO has been completed. Here, we are trying to prepare TNO with various morphology, size, and porosity as well as to study the correlation of TNO properties with electrochemical performance. Electrospinning technology is used to synthesize target materials, which are formulated from using poly(lactic acid) as a carrier polymer in various solvents (dimethylformamide, acetone, and dichloromethane) and adding titanium and niobium precursors. Parameters that affect the morphology of spun fibers are concentration, flow rate, applied voltage, collector plate distance, viscosity, and surface tension. Those parameters, especially solution chemistry, are carefully tuned to control the resulting fiber morphology and other properties. For example, solid, hollow, and porous (surface porous, inner porous, or highly porous) TNO fibers can be obtained by careful solvent selection as solvents have been proven to strongly affect evaporation and phase separation processes. All prepared TNO are further tested as anode materials in lithium ion battery and the property-performance correlation is carefully analyzed.