Polaronic Influences on the Charge Transport Properties of Battery Anodes

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Batteries, especially those based on the transfer of lithium ions, are ubiquitous in modern society and, with the advent of electro-mobility, are becomming even more important. Given this degree of pervasiveness, it is quite astonishing that elementary processes occurring in common battery anode materials such as lithium titanium oxide (LTO) are not at all well understood. Our recent discovery of polarons, electrons localized through the polarisation of the surrounding material, in reduced LTO for the first time explained how the generation of oxygen vacancies leads to an, experimentally observed, much improved electronic conductivity of the material. Similar improvements upon reduction have been found for the ionic conductivity, raising the important question if also there polarons play a role. Therefore, we propose to test the hypothesis that many of the (also in operando) experimentally observed properties of LTO and lanthanum lithium titanium oxide, another proposed battery anode material, can be explained considering the occurrence of polarons. To this end, we will employ an efficient solid state embedding technique developed by us together with Hubbard-corrected density functional theory to explore different localization patterns of polarons in both materials and their influence on electronic and ionic conductivity. Thereby, we will estimate kinetic diffusion barriers which will serve as the basis of a to be developed dynamical model. This will allow us to examine the possibly correlated motion of either charge carrier at different degrees of lithiation of the material (i.e. charging of the battery), different defect concentrations, and different defect distributions. All in all, besides yielding a detailed understanding of the transport mechanisms in LTO and, potentially, LLTO, this project will also point the way towards rational design criteria for improved battery anodes, e.g. in the form certain defect patterns.