Average and local structure analysis of Na/Li ion-exchanged Lix(Mn,Ni,Ti)O2 using synchrotron X-ray and neutron sources

Mn-rich layered Li-x(Mn,Ni,Ti)O-2 was synthesized by Na/Li ion exchange of a P3-Na-0.7(Mn,Ni,Ti)O-2 precursor. The combined chemical analysis with the ICP-AES, titration technique, and XANES indicated that their electroneutralities were satisfied in some vacancies of the transition metals (TMs). Average structure analyzed using synchrotron X-ray and neutron powder diffraction patterns confirmed a significant amount of vacancies at TM sites and further revealed the existence of a minor tetrahedral Li in the layered rock-salt type Li-x(Mn,Ni,Ti)O-2. Electrochemical properties of Li0.6Na0.02Mn0.71Ni0.13Ti0.120.04O2 exhibited high first discharge capacity of ca. 250 mAh g(-1) and high cyclability of exceeding 200 mAh g(-1) at the 50th cycle. PDF analysis achieved good fittings for the both total scatterings of synchrotron X-ray and neutron with additional tetrahedral Li and some TM vacancies. Each (Mn,Ni,Co)O-6 octahedron in the refined local structure was calculated and expressed as 3D distributions, where the NiO6 and the host MnO6 octahedra were visually characterized as significantly less distorted and highly distorted octahedra, respectively. The co-substitution of Ni2+ ant Ti4+ played the role of stabilizing whole structure and preserving the transition metal vacancy to maintain the high capacity during cycles.

Automated summary

Synthesis of Mn-rich layered Li-x(Mn,Ni,Ti)O-2 was achieved through Na/Li ion exchange, where the presence of tetrahedral Li and TM vacancies were confirmed in the average structure analysis. The electrochemical properties of the compound showed high capacity and cyclability, with the co-substitution of Ni2+ and Ti4+ playing a crucial role in stabilizing the structure and maintaining high capacity during cycles.