期刊
CHEMICAL SCIENCE
卷 13, 期 3, 页码 726-736出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/d1sc05715d
关键词
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资金
- National Natural Science Foundation of China [51932011, 51972346]
- Hunan Natural Science Fund for Distinguished Young Scholar [2021JJ10064]
- Program of Youth Talent Support for Hunan Province [2020RC3011]
- Innovation-Driven Project of Central South University [2020CX024]
The study successfully doped magnesium and calcium ions into Na0.67Ni0.33Mn0.67O2 to improve cycling endurance by reducing O-type stacking in the high-voltage region, leading to a decrease in capacity. Density functional theory studies showed that the introduction of Mg2+ and Ca2+ made high-voltage reactions less accessible.
The conventional P2-type cathode material Na0.67Ni0.33Mn0.67O2 suffers from an irreversible P2-O2 phase transition and serious capacity fading during cycling. Here, we successfully carry out magnesium and calcium ion doping into the transition-metal layers (TM layers) and the alkali-metal layers (AM layers), respectively, of Na0.67Ni0.33Mn0.67O2. Both Mg and Ca doping can reduce O-type stacking in the high-voltage region, leading to enhanced cycling endurance, however, this is associated with a decrease in capacity. The results of density functional theory (DFT) studies reveal that the introduction of Mg2+ and Ca2+ make high-voltage reactions (oxygen redox and Ni4+/Ni3+ redox reactions) less accessible. Thanks to the synergetic effect of co-doping with Mg2+ and Ca2+ ions, the adverse effects on high-voltage reactions involving Ni-O bonding are limited, and the structural stability is further enhanced. The finally obtained P2-type Na0.62Ca0.025Ni0.28Mg0.05Mn0.67O2 exhibits a satisfactory initial energy density of 468.2 W h kg(-1) and good capacity retention of 83% after 100 cycles at 50 mA g(-1) within the voltage range of 2.2-4.35 V. This work deepens our understanding of the specific effects of Mg2+ and Ca2+ dopants and provides a stability-enhancing strategy utilizing abundant alkaline earth elements.
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