Enhancement of the electrochemical performance of Sm-doped cobalt-free LiNi0.55Mn0.45O2 cathodes

Abstract

Co-free binary cathode materials (LiNi_xMn_1−xO₂, x ≥ 0.5) are promising candidates for lithium-ion batteries (LIBs) due to their high specific capacity and low cost. The degradation of the low-temperature electrochemical performance of these materials not only hinders their practical application but also emerges as a critical research focus in energy storage technologies. In this work, the effect of Sm doping on the structure and electrochemical performance of LiNi_0.55Mn_0.45O₂ (NM5545) cathode materials (x% Sm-NM5545, x = 0, 0.5, 1.0, 1.5) is systematically investigated over a wide temperature range (−10 to 45 °C). Sm doping significantly enhances the structural stability and enlarges interlayer spacing, which likely facilitates Li⁺ transport. Compared with undoped NM5545, the 1.0% Sm-NM5545 cathode materials exhibit remarkable improvements in capacity retention, which increases by 14.1%, 8.0%, and 9.4% after 100 cycles at temperatures of −10 °C, 25 °C, and 45 °C (1.0C, 3.0–4.45 V), respectively. Meanwhile, the discharge-specific capacity of 1.0% Sm-NM5545 cathode materials increases by 7.9 mA h g⁻¹, 9.1 mA h g⁻¹, and 12.9 mA h g⁻¹ at the above respective temperatures. Electrochemical impedance spectroscopy and galvanostatic intermittent titration technique analyses confirm that Sm doping has enhanced the lithium-ion migration rate while reducing the charge transfer resistance in the modified materials. Furthermore, post-cycling characterization via scanning electron microscopy and X-ray photoelectron spectroscopy reveals that Sm doping effectively reinforces the structural integrity, suppresses crack propagation during high voltage cycling, and inhibits detrimental cathode–electrolyte interfacial reactions.