Electrochemical aspects of Li[Ni0.6Co0.2Mn0.2]O2 cathode materials doped by various ionic radius cations

The capacity of Li[Ni0.6Co0.2Mn0.2]O-2 cathode materials decreases rapidly due to layer structure degradation, grain cracking, and electrolyte side reaction during cycling. In this paper, metal ions with different ionic radius (W6+= 0.62 & Aring;, Mg2+= 0.72 & Aring;, Y3+= 0.90 & Aring;) were doped into single crystal Li[Ni0.6Co0.2Mn0.2]O-2, which were synthesized by high-temperature solid-phase technology. X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM) were employed to characterize various samples doped with different ionic radius. The results reveal that the radius of the doped ions plays a crucial role in improving the stability of material structure. It is attributed to the incorporation of metal ions into the Li+ or Ni2+ site, thus maintaining the integrity of the layer and reducing cation mixing. However, it is also detrimental to the performance of single crystal Li[Ni0.6Co0.2Mn0.2]O-2 because of lattice distortion caused by the ionic radius of the doped metal being much greater than that of the doped site. These results show superior capability and reveal the performance trend of Li[Ni0.6Co0.2Mn0.2]O-2 with metal ions of different radius. The initial discharge capacity at 0.1 C for the undoped sample was 183.8 mAh/g, compared with 189.9, 192.3 and 199.8 mAh/g for NCM622-W, NCM622-Mg, and NCM622-Y, respectively. After 100 cycles, NCM, NCM-W, NCM-Mg, and NCM-Y delivered retentions of 90.88 %, 98.16 %, 97.13 %, 94.37 %, respectively. The defect model is mainly responsible for the improvement in electrochemical performance.