In-depth structural characterization of the influence of Li+ excess on spherical, Co-free layered LiMn0.5Ni0.5O2 cathode material using correlative Raman–SEM microscopy

Abstract

A series of different spherical Co-free Li_1+x(Mn_0.5Ni_0.5)_1−xO₂ powders with 0 ≤ x ≤ 0.16 was synthesized to investigate the effect of excess Li⁺ on the host structure of LiMn_0.5Ni_0.5O₂. Structural investigation with XRD shows less Li⁺/Ni²⁺ disordering and strong broadening of the pattern indicating phase separation with increasing x. A deeper understanding of the structural changes was gained from a combined approach of SEM, EDX and Raman microscopy. A phase separation into Ni-rich and Li-/Mn-rich layered oxide domains could be proven. In the investigated series, the best electrochemical performance was obtained for Li_1.07(Mn_0.5Ni_0.5)_0.93O₂ with a stable specific discharge capacity of 173 mAh g⁻¹ (658 Wh kg⁻¹, 12 mA g⁻¹) after 40 cycles. The presented results strongly highlight the strength of correlating chemical (EDX), structural (Raman) and morphological (SEM) information with sub-micrometer lateral resolution for the development and understanding of future battery materials.