Modelling and experimental investigation of Nb2O5 as a high-rate battery anode material
Jie Lin, Siyu Zhao, Thomas G. Tranter, Zhenyu Zhang, Fei Peng, Dan J. L. Brett, Rhodri Jervis, Paul R. Shearing
Abstract
Modelling and understanding the battery electrochemical performance at high rates is a great challenge. Known for its fast rate and good cyclability, niobium pentoxide (Nb2O5) is a promising anode material for lithium-ion batteries and is specifically modelled and investigated in this work. Commercially sourced Nb2O5 was characterised using scanning electron microscopy, X-ray diffraction, and micro-computed tomography. The Nb2O5 material was found to contain large rod- and ball-like polycrystalline particles of tens of microns in size and have mixed T-Nb2O5 and H-Nb2O5 phases. The electrochemical performance of the material after ball milling was tested via cyclic voltammetry and constant-current cycling at different C-rates up to 50C (10,000 mA g−1). The material achieved a similar charge capacity (143 mAh g−1) to T-Nb2O5 at 0.5C and this capacity could be retained by more than 55% when C-rate was increased to 10C. The experimental results were used to support the development of the Doyle-Fuller-Newman electrochemical model for Nb2O5. By model parameterization, the reference exchange-current density and solid-state diffusivity of the present Nb2O5 were estimated to be 9.6 × 10−4 A m−2 and 6.2 × 10−14 m2 s−1, respectively. The model achieved accurate prediction of the battery performance up to currents of 5C with the obtained constant properties. However, the properties of Nb2O5 were found to be rate-dependent at higher C-rates when good agreements between the model and experiment were maintained. The decrease of the two properties at 10−50C revealed that there was a change of dominant charge storage mechanism from diffusion-controlled lithium insertion to capacitive effects, which was experimentally observed in the cyclic voltammetry.