Correlating structural changes of the improved cyclability upon Nd-substitution in LiNi_0.5Co_0.2Mn_0.3O₂ cathode materials

Spherical LiNi_0.5Co_0.2Mn_0.3O₂ (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.