Tailoring Li-rich NMC cathodes through Sn and Al doping: a comparison of the Pechini method and supercritical CO₂-assisted synthesis

Lithium-rich layered oxide materials (Li-NMC) are widely regarded as promising cathode candidates for next-generation lithium-ion batteries owing to their high theoretical specific capacity. In this study, Sn-doped (Li_1.2Mn_0.515Sn_0.005Ni_0.2Co_0.08O₂) and Al-doped (Li_1.2Mn_0.48Al_0.04Ni_0.2Co_0.08O₂) Li-rich NMC cathodes were synthesized via the Pechini method and the Supercritical CO₂-assisted method, and their electrochemical performances were systematically compared. The Sn-doped cathode prepared by the Supercritical CO₂-assisted route delivered a discharge capacity of ∼ 250.2 mAh/g at C/20, outperforming its Pechini-derived counterpart (∼238.6 mAh/g). In contrast, Al-doped cathodes synthesized by both methods exhibited comparable discharge capacities of ∼ 244 mAh/g at the same rate. Across a wide current density range (C/20–3C), the reversible discharge capacities of undoped, Sn-doped, and Al-doped samples prepared by the Pechini method were consistently lower than those of their Supercritical CO₂ synthesized analogs. Furthermore, Sn- and Al-doped cathodes obtained through the Supercritical CO₂-assisted method demonstrated excellent cycling stability, retaining 93.17% and 92.79% of their initial capacity, respectively, after 120 cycles at C/3—significantly higher than the 84.29% retention observed for the Pechini-synthesized Sn-doped sample. These findings highlight the critical role of the supercritical CO₂-assisted synthesis approach in improving the electrochemical properties of Li-rich layered oxides.