Braithwaite, JS; (2000) A theoretical study of lithium intercalation in transition metal oxides. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The physical and electronic structural changes that occur during lithium intercalation into two vanadium oxides. V205 and V6013, and the mixed metal spinel materials, Li,CoyMn4,08, where y = 0.1,2, 4 and x = 0,1,2, have been studied using a combination of theoretical methods. These transition metal oxides are of great interest as are possible cathode materials in solid-state lithium-ion batteries. Both interatomic potential based static lattice or `atomistic' modelling, and electronic structure calculations based on Density Functional Theory have been used in this study. An interatomic potential model for V6013 has been derived using empirical fitting methods. We use Mott-Littleton methods to find the lowest energy sites occupied by intercalated lithium ions in both V,05 and V6013. Electronic structure methods have been used to investigate the relative stability of a series of Li,V,05 phases, where 0 x 2, and Li,V6013 phases. where 0 x 4, which has allowed us to predict average discharge voltages for both materials that are in good agreement with experiment. Calculated electron density distributions show that the lithium insertion reaction is accompanied by the localised reduction of vanadium metal atoms in both Li,V,05 and LixV6013. Li+ has been shown to be mobile along the [0/01 direction in Vi05. Calculated average voltages for the spinel family. Li,CoyMn4_y08, are in good agreement with experiment. and clearly show that the presence of cobalt is fundamental to the generation of voltages over 5V. The oxygen atoms are also shown to accept electron density during lithium intercalation and may play a role in the generation of such high voltages.

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