| Summary: | Lithium manganite, Li<sub>2</sub>MnO<sub>3</sub>, is an attractive cathode material for rechargeable lithium ion batteries due to its large capacity, low cost and low toxicity. We employed well-established atomistic simulation techniques to examine defect processes, favourable dopants on the Mn site and lithium ion diffusion pathways in Li<sub>2</sub>MnO<sub>3</sub>. The Li Frenkel, which is necessary for the formation of Li vacancies in vacancy-assisted Li ion diffusion, is calculated to be the most favourable intrinsic defect (1.21 eV/defect). The cation intermixing is calculated to be the second most favourable defect process. High lithium ionic conductivity with a low activation energy of 0.44 eV indicates that a Li ion can be extracted easily in this material. To increase the capacity, trivalent dopants (Al<sup>3+</sup>, Co<sup>3+</sup>, Ga<sup>3+</sup>, Sc<sup>3+</sup>, In<sup>3+</sup>, Y<sup>3+</sup>, Gd<sup>3+</sup> and La<sup>3+</sup>) were considered to create extra Li in Li<sub>2</sub>MnO<sub>3</sub>. The present calculations show that Al<sup>3+</sup> is an ideal dopant for this strategy and that this is in agreement with the experiential study of Al-doped Li<sub>2</sub>MnO<sub>3</sub>. The favourable isovalent dopants are found to be the Si<sup>4+</sup> and the Ge<sup>4+</sup> on the Mn site.
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