Correlating structural changes of the improved cyclability upon Nd-substitution in LiNi0.5Co0.2Mn0.3O2 cathode materials

Spherical LiNi0.5Co0.2Mn0.3O2 (NCM523), cycling to voltages greater than 4.3 V, often suffers from structure instability and the resultant inferior cyclability. Here, Nd is used as dopant into NCM523 to address this long-standing issue. The mechanism of Nd substitution effect on the structural evolution of NCM523 is also investigated. In-situ X-ray diffraction reveals that volume variation of the cathode could be alleviated due to the Nd doping effect. The larger-diameter Nd3+, integrating into the crystal lattice of NCM523 as a positively charged center, is beneficial to the diffusion of Li ion, stability of crystal phase and physical structure upon cycling. In-situ Raman spectroscopic measurements verify that partial Nd substitution can lead sustainable structure evolution during the first cycle. More importantly, the stable cut-off voltage could be enhanced to as high as 4.6 V.