Abstract
Polyanion phosphate based Li3V2(PO4)3 material has attracted considerable attention as a novel cathode material for potential use in rechargeable lithium ion batteries. The defect chemistry and dopant properties of this material are studied using well-established atomistic scale simulation techniques. The most favourable intrinsic defect process is the Li Frenkel (0.45 eV/defect) ensuring the formation of Li vacancies required for Li diffusion via the vacancy mechanism. Long range lithium paths via the vacancy mechanism were constructed and it is confirmed that the lowest activation energy of migration (0.60 eV) path is three dimensional with curved trajectory. The second most stable defect energy process is calculated to be the anti-site defect, in which Li and V ions exchange their positions (0.91 eV/defect). Tetravalent dopants were considered on both V and P sites in order to form Li vacancies needed for Li diffusion and the Li interstitials to increase the capacity respectively. Doping by Zr on the V site and Si on the P site are calculated to be energetically favourable.
Highlights
Atomistic modelling based on the classical pair potentials is a poweful method and can provide useful information about the defect processes, cation doping behavior and ion migration mechanism
As the intrinsic lithium ion diffusion of Li3V2(PO4)[3] material is of crucial importance when assessing its use as a possible high-rate cathode material in lithium batteries, we used the present static atomistic simulation to examine various possible diffusion paths responsible for Li ion conduction, which are often difficult to explore on the atomic scale by experiment alone
Solution energies of CeO2 and GeO2 are 2.31 eV and 2.35 eV respectively meaning that Ce and Ge are promising candidate dopants. As these solution energies are higher compared to the Li Frenkel process, the solution of ZrO2, GeO2 and CeO2 during synthesis should be examined experimentally as they can increase the Li vacancy concentration (via relation (9))
Summary
The second most stable defect energy process is calculated to be the anti-site defect, in which Li and V ions exchange their positions (0.91 eV/defect). Atomistic modelling based on the classical pair potentials is a poweful method and can provide useful information about the defect processes, cation doping behavior and ion migration mechanism. We employ established atomistic modeling techniques to investigate the intrinsic defect chemistry, the impact of doping on the formation of lithium interstitials and lithium ion diffusion pathways in Li3V2(PO4)[3].
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