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

A series of different spherical Co-free Li1+x(Mn0.5Ni0.5)(1-x)O-2 powders with 0 <= x <= 0.16 was synthesized to investigate the effect of excess Li+ on the host structure of LiMn0.5Ni0.5O2. 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(Mn0.5Ni0.5)(0.93)O-2 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.