Almost two decades have passed since the emergence of lithium-ion batteries on the market. Despite steady improvements in performance, current technology is struggling to meet the demand for ever better energy density, power, safety, and environmental impact. A core problem lies in the intercalation materials used as electrodes in state-of-the-art lithium batteries. These materials have intrinsic limitations in terms of capacity and hence energy density and it is now widely recognized that new concepts are essential for future breakthroughs.
One promising avenue under intense investigation is electrode materials that function in a “conversion” rather than “intercalation” mode. In such systems, lithium undergoes a reversible electrochemical reaction with a binary transition metal oxide (or other suitable counteranion, such as sulfide or phosphide). Stable gravimetric capacities can thus be attained that are several times larger than for common intercalation materials such as graphite. Further advantages, for example, the potential to tune the operating voltage and choose low cost environmentally friendly materials, add to the attraction of this approach.
So what is hindering commercialization of Li-ion batteries based on these revolutionary conversion-reaction electrodes? Light is shed on the critical issues — namely, poor cyclability and large voltage hysteresis — by Rosa Palacin and co-workers in a progress report in the latest Advanced Energy Materials special section of Advanced Materials. The concepts behind conversion-reaction electrode materials and the characteristic performance of a wide range of transition metal binary phases are also discussed and strategies for overcoming major obstacles suggested. As the authors point out: “The promise of doubling the storage capacity of current electrode materials certainly justifies the attention of the materials science community to this fascinating reactivity”.
Esther Levy writes for MaterialsViews.