Synthesis and characterization of LiCo0.3RhxNi0.7−xO2 (0≤ x ≤0.003) cathode materials for lithium ion batteries

LiCo0.3RhxNi0.7−xO2 (0≤ x ≤0.003) cathodes were synthesized by a sol–gel method. All samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance. The results show that Rh-doping not only increases the initial charge–discharge capacities of LiCo0.3Ni0.7O2 but also improves the capacity retention. The LiCo0.3Rh0.002Ni0.698O2 has the excellent electrochemical performance. After 50 cycles, the discharge capacity of LiCo0.3Rh0.002Ni0.698O2 is 185.3mAh g−1 at 0.15C in 3.0–4.5 V, which is 93.7% of the first discharge capacity. Meanwhile, the Rh-doping exhibits the effect of suppressing the impedance rise during cycling of Li/LiCo0.3Ni0.7O2 and promotes the diffusion of Li+ in LiCo0.3Ni0.7O2.Moreover, Rh-doping suppresses the phase transitions that usually occur in LiNiO2 during cycling and improves the charge–discharge reversibility of Li/LiCo0.3Ni0.7O2. Thermal stability of the charged cathodes is also improved by Rh-doping, which is possibly attributed to the lowered oxidation ability and the enhanced structure stability of those delithiated Rh-doped cathodes during cycling.