Wei Hezhuan, Cheng Xiaolu, Fan Hongwei, Shan Qian, An Shengli, Qiu Xinping, Jia Guixiao
School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, Baotou, Inner Mongolia, 014010, P. R. China.
Key Laboratory of Organic Optoelectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing, 100084, P. R. China.
ChemSusChem. 2019 Jun 7;12(11):2471-2479. doi: 10.1002/cssc.201900241. Epub 2019 Apr 30.
High-energy-density and low-cost lithium-ion batteries are sought to meet increasing demand for portable electronics. In this study, a cobalt-free Li(Li Ni Fe Mn )O (LNFMO) cathode material is chosen, owing to the reversible anionic redox couple O /O . The aim is to elucidate the Fe-substitution function and oxygen redox mechanism of experimentally synthesized Li(Li Ni Fe Mn )O by DFT. The redox processes of cobalt-containing Li(Li Ni Co Mn )O (LNCMO) are compared with those of LNFMO. Redox couples including Ni /Ni /Ni , Fe /Fe or Co /Co , and O /O are found, confirmed by a X-ray photoelectron spectroscopy, and explained by redox competition between O and transition metals. In LNFMO and LNCMO, O ions with an Li-O-Li configuration readily participate in oxidation, and the most active O ions are coordinated to Mn and Li . Oxidation of O in LNCMO is triggered earlier, along with that of Co. Fe substitution activates O ions, contributes additional oxygen redox charge compensation of 0.44 e per formula unit, avoids concentrated accumulation of oxygen oxidation, and improves structural stability. This work provides new scope for designing cobalt-free, low-cost, and higher-energy-density cathode materials for Li-ion batteries.
人们一直在寻求高能量密度和低成本的锂离子电池，以满足便携式电子产品不断增长的需求。在本研究中，由于可逆的阴离子氧化还原对O²⁻/O²²⁻，选择了一种无钴的Li(Li₀.₂Ni₀.₂Fe₀.₂Mn₀.₄)O₂（LNFMO）阴极材料。目的是通过密度泛函理论（DFT）阐明实验合成的Li(Li₀.₂Ni₀.₂Fe₀.₂Mn₀.₄)O₂的铁取代功能和氧氧化还原机制。将含钴的Li(Li₀.₂Ni₀.₂Co₀.₂Mn₀.₄)O₂（LNCMO）的氧化还原过程与LNFMO的进行比较。通过X射线光电子能谱证实了包括Ni²⁺/Ni³⁺/Ni⁴⁺、Fe²⁺/Fe³⁺或Co²⁺/Co³⁺以及O²⁻/O²²⁻在内的氧化还原对，并通过O与过渡金属之间的氧化还原竞争进行了解释。在LNFMO和LNCMO中，具有Li-O-Li构型的O离子很容易参与氧化，最活跃的O离子与Mn和Li配位。LNCMO中O的氧化比Co的氧化更早触发。铁取代激活了O离子，每公式单位贡献了额外的0.44 e的氧氧化还原电荷补偿，避免了氧氧化的集中积累，并提高了结构稳定性。这项工作为设计用于锂离子电池的无钴、低成本和更高能量密度的阴极材料提供了新的思路。
