Addressing the Limitations of Layered LiMO2 Electrodes: Structural, Compositional and Electrochemical Control of Integrated ‘Layered-Layered-Spinel’ Cathode Structures

Lithium- and manganese rich xLi₂MnO₃•(1-x)LiMO₂ composite structures  (M=Mn, Ni, Co) are currently one of the most promising classes of cathode materials for advanced Li-ion batteries.  When charged below 4.3 V, and when used in low concentration (typically 0.03<x<0.1), the electrochemically inactive Li₂MnO₃ component acts as a structural stabilizer to enable modest improvements in electrochemical properties.  When higher concentrations of Li₂MnO₃ are embedded in the matrix (typically 0.3<x<0.5), and when the cells are electrochemically-activated above 4.5 V, significantly higher capacities (250 mAh/g or more) can be achieved.  Unfortunately, these high capacity electrode structures are unstable when charged repeatedly to such a high cell voltage. On cycling, the transition metals (M) migrate into the lithium layers; this migration leads to hysteresis, voltage fade, rate impairment and energy inefficiency - despite the retention of electrode capacity.  We have addressed these limitations by strategically introducing a small amount of LiM₂O₄ spinel (M=Mn, Ni, Co) to form ‘layered-layered-spinel’ composite structures.  The advantage of this approach is that the M cations of the spinel component occupy alternate layers of an oxygen array, which is structurally compatible with the LiMO₂ component, in a 3:1 ratio, thereby imparting stability to the parent ‘layered-layered’ structure. This presentation will provide our recent results in tailoring and improving the structural, compositional and electrochemical properties of structurally-integrated electrode materials that mitigate the voltage fade phenomenon and energy decay of lithium cells.