Addressing the Instability of High Capacity Lithium Battery Cathodes

Layered lithium- and manganese-rich mixed metal oxides are receiving worldwide attention as cathode materials for lithium-ion batteries because, once activated above 4.5 V, they can provide the theoretical capacity of a typical LiMO₂ (M=Mn, Ni, Co) electrode (250-260 mAh/g) [1-3].  These Li- and Mn-rich materials can be represented in their initial state by the two-component formula xLi₂MnO₃·(1-x)LiMO₂ or, in normalized layered notation, Li_1+xM_1-xO₂.

Although xLi₂MnO₃·(1-x)LiMO₂ electrodes maintain their capacity when repeatedly charged to high potetials (>4.5 V), structural changes result in voltage decay and hysteresis during repeated charge/discharge cycles, repressing their use in commercial battery products.   The structural decay has been attributed to the irreversible migration of transition metal ions (predominantly Mn) into the lithium-depleted layers.  This disadvantage is being addressed by slightly reducing the lithium content in parent xLi₂MnO₃·(1-x)LiMO₂materials to introduce ‘pillaring’ transition metal ions in the lithium layers of the composite structure.

This presentation will discuss the background and versatility of composite electrode structures and highlight the opportunity that these materials present for overcoming voltage fade, with a specific focus on composite ‘layered-spinel’ electrode structures.

References

1. Z. Lu and J. R. Dahn, J. Electrochem. Soc., 149, A778 (2002).
2. J-S. Kim, C. S. Johnson, J. T. Vaughey, M. M. Thackeray, S. A. Hackney, W. Yoon and C. P. Grey, Chem Mater. 16, 1996 (2004).
3. M. M. Thackeray, C. S. Johnson, J. T. Vaughey, N. Li and S. A. Hackney, J. Mater. Chem. 15, 2257 (2005).