School of Advanced Materials, Peking University, Shenzhen Graduate School, Shenzhen 518055, People's Republic of China.
Phys Chem Chem Phys. 2019 Feb 20;21(8):4578-4583. doi: 10.1039/c8cp06083e.
In order to understand and improve the conductivity of LiFePO4, lots of attempts have been made both experimentally and theoretically. Here we performed hybrid density functional theory calculations to systematically investigate the electronic structures with polaronic redox behavior of polyanionic intercalation compounds similar to LiFePO4, such as in XMPO4 (X = Li, Na; M = Mn, Fe, Co, Ni). It is proved that the replacement of Li ions does not eliminate the polaronic redox behavior of Fe ions during delithiation and hence does not lead to a significant improvement in electronic conductivity. By contrast, replacing Fe with Mn, Co or Ni can tune the polaronic redox behavior during delithiation by varying degrees. For Ni, the polaronic redox behavior has almost disappeared, and band gaps disappear during delithiation, indicating a better electronic conductivity. For Mn or Co, the polaronic redox behavior is still obvious with little improvement in the electronic conductivity. This study provides important clues to improve the electronic conductivity of LiFePO4-like cathode materials.
为了理解和提高 LiFePO4 的电导率，人们进行了大量的实验和理论尝试。在这里，我们进行了杂化密度泛函理论计算，系统地研究了具有类 LiFePO4 插层化合物的电子结构和极化子氧化还原行为，如 XMPO4（X = Li，Na；M = Mn，Fe，Co，Ni）。结果证明，Li 离子的取代并没有消除 Fe 离子在去锂化过程中的极化子氧化还原行为，因此不会导致电子电导率的显著提高。相比之下，用 Mn、Co 或 Ni 取代 Fe 可以通过不同程度来调节去锂化过程中的极化子氧化还原行为。对于 Ni，极化子氧化还原行为几乎消失，且在去锂化过程中带隙消失，表明具有更好的电子导电性。对于 Mn 或 Co，极化子氧化还原行为仍然很明显，电子电导率略有提高。这项研究为提高类 LiFePO4 阴极材料的电子电导率提供了重要线索。
