Lithiation of Ag$_x$MnO$_2$: Insights from first principles

Stable electrode materials being able to capture high lithium concentrations are attracting considerable interest in science as well as industry. Recently hollandite $\alpha$-MnO$_2$ based structures are moving into the focus of electrochemists and are considered to be promising electrodes for increasing the capacity and efficiency of rechargeable lithium batteries. These favorable properties are mainly due to the tunnel structure consisting out of stacked 1$\times$1 and 2$\times$2 MnO$_2$ octahedra in the z-axis. It has been shown that large ions such as silver or potassium can stabilize and increase the cyclicity of pure hollandite $\alpha$-MnO$_2$ considerably. In this work we present new insights from first principles for lithiated silver hollandite Li$_y$Ag$_x$MnO$_2$ and demonstrate that the formation of oxygen vacancies play an important role for lithium diffusion.