Investigation of the electrochemical performance and structural stability of O6-type lithium-rich layered oxide as a positive electrode active material for improved lithium battery performance

Abstract

A cobalt-free manganese-based lithium-rich layered oxide with an unusual O6-type structure has been successfully synthesized by solid-state ion-exchange reaction from the intermediate P2-type sodium-based layered oxide precursor Na_5/6[Li_1/6Ni_1/6Mn_4/6]O₂ using lithium chloride at moderate temperature. The synchrotron and neutron diffraction of the as-prepared O6-LiNi_1/6Mn_4/6O₂ phase revealed an in-plane transition metal cation ordering in the (Li, Ni, Mn)O₂ layers and only a moderate number of stacking faults along the c-axis direction in the oxygen stacking sequence. During the lithium electrochemical deintercalation and intercalation, both the in-plane metal transition ordering and the O6-type stacking are preserved and the lithium metal battery cells with the O6-LiNi_1/6Mn_4/6O₂ phase as active material at the positive electrode show high (230 mA h g⁻¹ for the first discharge) and relatively stable capacity with almost no voltage decay. This could be attributed to the environment surrounding the transition metal ions, which is more favorable for reversible migration of transition metal cations compared to the conventional O3-type lithium-rich layered oxides. All this indicates that O6-type lithium-rich layered oxides could be promising active materials for lithium-ion batteries.