Impact of Ti and Zn Dual-Substitution in P2 type Na 2/3 Ni 1/3 Mn 2/3 O 2 on Ni-Mn and Na-Vacancy Ordering and Electrochemical Properties.

High-entropy layered oxide materials containing various metals that exhibit smooth voltage curves and excellent electrochemical performances have attracted attention in the development of positive electrode materials for sodium-ion batteries. However, the smooth voltage curve can be obtained by suppression of the Na + -vacancy ordering, and therefore, Multi-elementalization of metals in the transition metal slab is not required. Here, the Na + -vacancy ordering is found to be disturbed by dual substitution of Ti IV for Mn IV and Zn II for Ni II in P2-Na 2/3 [Ni 1/3 Mn 2/3 ]O 2 . Dual-substituted Na 2/3 [Ni 1/4 Mn 1/2 Ti 1/6 Zn 1/12 ]O 2 demonstrates almost non-step voltage curves with a reversible capacity of 114 mAh g -1 and less structural changes with maintaining a high crystalline structure during charging and discharging. Synchrotron X-ray, neutron, and electron diffraction measurements reveal that dual-substitution with Ti IV and Zn II uniquely promotes in-plane Ni II -Mn IV ordering, which is quite different from the disordered mixing in conventional multiple metal substitution. This article is protected by copyright. All rights reserved.