Improved Cycle Life and Li-Ion Transport Parameters at Low Temperature in Doped Ni-Rich NMC Cathodes

The poor cycle life of Ni-rich NMC (LiNixMnyCo1-x-yO2 (x≥0.6)) cathodes remains a significant challenge for their widespread adoption in high-energy lithium-ion batteries. This study employed boron (B) and dual tin-boron (Sn-B) doping strategies to enhance the electrochemical performance and structural stability of NMC90-5-5 cathodes. Comprehensive characterisation techniques investigated structural, morphological, and surface composition changes. The doped materials retained the layered α-NaFeO2 structure and exhibited reduced cation mixing, lattice stabilisation, and suppression of detrimental phase transitions. Sn-B co-doped cathodes delivered superior rate performance and capacity retention, consistently outperforming both pristine and single-doped cathodes at room (25°C), elevated (45°C), and low (-5°C) temperatures. At 45°C, all doped materials maintained high discharge capacities and low charge-transfer resistance, with minimal CEI degradation. At -5°C, the dual Sn-B doped sample delivered significantly higher discharge capacities at faster rates due to enhanced lithium-ion diffusivity. Furthermore, post-mortem analyses confirmed that doping stabilised the oxidation states of transition metals and mitigated surface degradation caused by electrolyte decomposition. These findings highlight the synergistic role of Sn-B co-doping in improving the structural and electrochemical resilience of Ni-rich NMC cathodes at low and high temperatures, demonstrating the potential of tailored doping strategies for improving the performance of lithium-ion batteries under extreme conditions.