P2-Na0.61Ca0.03[Mg2/9Cu1/9Mn2/3]O2 as a High-Energy Oxygen Redox Cathode for Na-Ion Batteries: Investigation of Cu Substitution and Ca Doping to Enhance Cycling Stability, Advanced Functional Materals 35,39(2025)
Jin-Wei Kang, Hsu-Chen Cheng, Hsiang-Jung Chen, Shao-Chu Huang, Chih-Heng Lee, Chin-Lung Kuo, Sheng-Yu Yu, Heng-Liang Wu, Chia-Ching Lin, Chun-Han Kuo, Hao-Hsiang Chang, Chih-Wei Hu, Shu-Chih Haw*, Hsin-Yi Tiffany Chen*, and Han-Yi Chen*
2026/01/30
Oxygen redox-based cathode materials offer higher capacity than conventional Na-based layered transition metal oxides in Na-ion batteries (NIBs). Still, their performance is impeded by voltage hysteresis and structural instability. Herein, a novel P2-Na0.61Ca0.03[Mg2/9Cu1/9Mn2/3]O2 cathode material is developed with Li/Co-free composition for cost-effectiveness and environmental friendliness. Cu substitution in transition-metal layers stabilizes O ions during oxygen redox, while Ca doping in alkaline-metal layers acts as structural “pillars” to suppress phase transformation. The charge storage mechanism is analyzed via operando X-ray absorption spectroscopy, operando X-ray diffraction analysis, on-line gas chromatography, and density functional theory computation. Na0.61Ca0.03[Mg2/9Cu1/9Mn2/3]O2 exhibits a high specific capacity (205 mAh g−1 at 0.1 C), good cyclic stability, and impressive rate capability (142 mAh g−1 at 2.5 C). A Na0.61Ca0.03[Mg2/9Cu1/9Mn2/3]O2//hard carbon full cell with a high energy density (250.7 Wh kg−1) is achieved, demonstrating its potential for high-energy NIBs. This work provides new insights into oxygen-redox-dominated cathodes through a facile sol-gel synthesis and advanced characterization techniques.
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