The Effect of Key Electronic States on Excess Lithium Intercalation in Li 2 Ru y Mn 1- y O 3 .

Excess reversible lithium storage is an alternative crucial strategy besides the expansion of redox centers to boost the capacity of layered cathodes. However, the mechanism of excess Li + intercalation is far from being comprehended, indisputably hindering the development of layered cathodes. Herein, the comparative study of Li 2 Ru y Mn 1- y O 3 and Li 2 Ru y Ti 1- y O 3 by X-ray absorption and photoemission spectroscopies attempts to illustrate the origin. The charge transfer from Ru to Mn through TM-O π bonding interaction with the formation of O holes has been revealed in Li 2 Ru y Mn 1- y O 3 , which originates from the inductive effect and the approaching energy level of Mn and Ru bands. The electronic state is thought to reduce the Coulomb repulsion of Li + with the matrix, promoting excess Li + intercalation. The results are instructive to the rational design of layered cathodes to achieve a larger reversible capacity in a wide voltage window.