Lithium-ion (de)intercalation mechanism in core-shell layered Li(Ni,Co,Mn)O₂ cathode materials

LiNi_xCo_yMn_1-x-yO₂ (NCM) intercalation compounds with core-shell architecture have been found to be promising cathode candidates for next-generation lithium-ion battery applications. The NCM cathodes' functional properties are dependent on the transition metal relative ratios, making it a challenge to control the real structure of core-shell NCM cathode materials and to understand the synergistic effect of core and shell during the electrochemical cycling. Herein, a universal and facile synthetic strategy is developed to synthesize the NCM material composed of an inner Ni-rich core and a Mn-rich shell on a secondary particle level. Both the Ni-rich particle core and the Mn-rich outer surface possess a layered α–NaFeO₂–type structure with the same space group (R3‾m). The in situ synchrotron-based X-ray diffraction and absorption spectroscopy results demonstrate that the two layered phases do not participate in the electrochemical reaction simultaneously during the first cycle between 2.7 and 4.3 V, while they exhibit a similar reversible (de)lithiation mechanism in the following cycles. These findings provide a new perspective for rational design of layered Ni-based cathode materials with high energy and long cycling life with particular two phase electrochemical characteristics.