Novel Computational Approaches to Li Diffusion and Electron Transport for High Capacity Battery Materials
- PDF / 1,456,816 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 62 Downloads / 155 Views
Novel Computational Approaches to Li Diffusion and Electron Transport for High Capacity Battery Materials Stefano Leoni1*, Gotthard Seifert1, Luis Craco1 and Salah Eddine Boulfelfel2 1 Physical Chemistry Division, Dresden University of Technology, Dresden, Germany. 2 Department of Geosciences, Stony Brook University, Stony Brook, New Yory, U.S.A. *[email protected] ABSTRACT The intrinsic channel structure and low volume work makes olivines phosphates (LiMPO4) versatile for Li uptake and release. The understanding of Li cation diffusion/transport mechanisms inside olivines are crucial aspects, which we address using advanced molecular dynamics simulations. Activation energies calculated from DFT concluded 1D diffusion within channels as also indicated by neutron diffraction direct imaging techniques. On explicitly including temperature we find that - besides main conduction paths along the easy channels distinct, less frequent but relevant diffusion paths exist. We point out that capacity and diffusion/conduction issues must be understood in a much more detail-rich framework, under realistic simulation conditions within finite temperature simulations. For evaluating electrical conductivity, we use advanced DFT methods to correctly capture the insulating states of the charged and discharged olivine materials. Based on the Kubo formalism, reliable conductivity/resistivity curves can be calculated for comparison with experiments and for anticipating properties. INTRODUCTION Li based batteries are priority materials for a sustainable, clean energy economy [1]. Olivine phosphates LiMPO4 (M=Fe, Ni) have recently attracted considerable attention as novel cathode materials [2-5]. The olivine framework is built of PO43- tetrahedra, with divalent cations M2+ and Li+ inside corner-sharing and edge-sharing oxygen octahedra, respectively. In particular, LiFePO4 is indicated as viable alternative, in terms of costs and safety, to LiCoO2 based technologies. The intrinsic channel structure of the olivine structure type, as well as a moderate volume work makes this material versatile for reversible Li uptake and release. Additionally, the high voltage due to the Fe2+/Fe3+ couple, a high theoretical capacity (around 170 Ah/Kg) and good material stability in electrolyte environments grant olivine phosphates good battery properties. The relatively low bulk conductivity can be enhanced by particle size reduction and composite formation, but also by heterovalent cation substitution. Point defects, introduced at the atomistic level, have a decisive impact on physical properties, in driving n- into p-type semiconductors for example, and in affecting the ionic conducting properties of metal oxides. The understanding of Li cation diffusion mechanisms inside the olivine scaffolding, and the impact of point defects thereon, have accordingly moved into the focus of theoretical investigations [6]. Activation energies calculated from DFT and pair potentials [6, 7] concluded 1D diffusion within channels along [010] (b) as it is als
Data Loading...
