Structure stability, electronic property and voltage profile of LiFe1−nNnP1−mMmO4 olivine cathode material

• Published in: Rare metals 2021-12, Vol.40 (12), p.3512-3519
• Main Authors: Cui, Zhi-Hong, Lu, Xue-Feng, Luo, Jian-Hua, Guo, Xin, Xue, Hong-Tao, Tang, Fu-Ling
• Format: Article
• Language: English
• Subjects: Biomaterials; Charge density; Chemistry and Materials Science; Density functional theory; Doping; Electric potential; Electrode materials; Energy; Energy gap; First principles; Intercalation; Lithium; Materials Engineering; Materials Science; Metallic Materials; N-type semiconductors; Nanoscale Science and Technology; Olivine; Original Article; P-type semiconductors; Physical Chemistry; Structural stability; Voltage
• ISSN: 1001-0521; 1867-7185
• DOI: 10.1007/s12598-020-01689-7

First-principles computational studies under density functional theory (DFT) framework were used to investigate the structural stability, conductivity and voltage profile of LiFe 1− n N n P 1− m M m O 4 (N, M = Si or S) electrode materials. It is found that the LiFeP 7/8 Si 1/8 O 4 system has the most stable structure. After doping, the band gap values of the systems decrease gradually, and LiFe 7/8 S 1/8 PO 4 system has a minimum band gap of 1.553 eV, attributed to the hybridization of the Fe-d and S-p orbital electrons. The LiFeP 7/8 S 1/8 O 4 system demonstrates the characteristic of n-type semiconductor, and other doping systems have the feature of p-type semiconductor. Charge density difference maps show that the covalent property of Si–O bond is enhanced in the LiFeP 7/8 Si 1/8 O 4 system. The average distance of Li and O atoms in the S doping systems increases from 0.21026 to 0.21486 and 0.21129 nm, respectively, indicating that doping broadens significantly the channel of Li ion de-intercalation in LiFe 7/8 S 1/8 PO 4 and LiFeP 7/8 S 1/8 O 4 . Additionally, the results of lithium intercalation potential imply that the voltages of the doping systems fall into the range of 2.23–2.86 V. Graphic abstract