Fast Li-Ion Conduction in Spinel-Structured Solids

Spinel-structured solids were studied to understand if fast Li(+) ion conduction can be achieved with Li occupying multiple crystallographic sites of the structure to form a “Li-stuffed” spinel, and if the concept is applicable to prepare a high mixed electronic-ionic conductive, electrochemically active solid solution of the Li(+) stuffed spinel with spinel-structured Li-ion battery electrodes. This could enable a single-phase fully solid electrode eliminating multi-phase interface incompatibility and impedance commonly observed in multi-phase solid electrolyte–cathode composites. Materials of composition Li(1.25)M(III)(0.25)TiO(4), M(III) = Cr or Al were prepared through solid-state methods. The room-temperature bulk Li(+)-ion conductivity is 1.63 × 10(−4) S cm(−1) for the composition Li(1.25)Cr(0.25)Ti(1.5)O(4). Addition of Li(3)BO(3) (LBO) increases ionic and electronic conductivity reaching a bulk Li(+) ion conductivity averaging 6.8 × 10(−4) S cm(−1), a total Li-ion conductivity averaging 4.2 × 10(−4) S cm(−1), and electronic conductivity averaging 3.8 × 10(−4) S cm(−1) for the composition Li(1.25)Cr(0.25)Ti(1.5)O(4) with 1 wt. % LBO. An electrochemically active solid solution of Li(1.25)Cr(0.25)Mn(1.5)O(4) and LiNi(0.5)Mn(1.5)O(4) was prepared. This work proves that Li-stuffed spinels can achieve fast Li-ion conduction and that the concept is potentially useful to enable a single-phase fully solid electrode without interphase impedance.