%0 Journal Article %A Daniil A Kitchaev %A Zhengyan Lun %A William D Richards %A Huiwen Ji %A Raphaële J Clément %A Mahalingam Balasubramanian %A Deok-Hwang Kwon %A Kehua Dai %A Joseph K Papp %A Teng Lei %A Bryan D McCloskey %A Wanli Yang %A Jinhyuk Lee %A Gerbrand Ceder %B Energy & Environmental Science %D 2018 %G eng %N 8 %P 2159 - 2171 %R 10.1039/c8ee00816g %T Design principles for high transition metal capacity in disordered rocksalt Li-ion cathodes %V 11 %8 05/2018 %! Energy Environ. Sci. %X

The discovery of facile Li transport in disordered, Li-excess rocksalt materials has opened a vast new chemical space for the development of high energy density, low cost Li-ion cathodes. We develop a strategy for obtaining optimized compositions within this class of materials, exhibiting high capacity and energy density as well as good reversibility, by using a combination of low-valence transition metal redox and a high-valence redox active charge compensator, as well as fluorine substitution for oxygen. Furthermore, we identify a new constraint on high-performance compositions by demonstrating the necessity of excess Li capacity as a means of counteracting high-voltage tetrahedral Li formation, Li-binding by fluorine and the associated irreversibility. Specifically, we demonstrate that 10–12% of Li capacity is lost due to tetrahedral Li formation, and 0.4–0.8 Li per F dopant is made inaccessible at moderate voltages due to Li–F binding. We demonstrate the success of this strategy by realizing a series of high-performance disordered oxyfluoride cathode materials based on Mn2+/4+ and V4+/5+ redox.