Effect of Nb doping at Fe site on the cycling stability and rate capability of LiFePO4 for lithium-ion batteries. (September 2022)

• Record Type: Journal Article
• Authors: Teng, Tao; Xiao, Li; Shen, Li; Qiu, Guanzhou; Ran, Jianjun; Guo, Xiang; Zhu, Yirong; Chen, Han
• Is Part Of: Vacuum. Volume 203(2022)
• Publication Date: 2022-09
• Subjects: LiFePO4 -- First-principles calculation -- Nb5+ modification; Vacuum -- Periodicals; 621.55
• DOI: 10.1016/j.vacuum.2022.111306
• Languages: English
• ISSNs: 0042-207X

Abstract

Abstract: Olivine LiFePO4 structures with long cycle life, low cost, and environment friendly characteristics have widely been used as cathode effective constituents for lithium-ion batteries (LIBs) in China. However, their low electronic conductivity limits their wide applications in high-range electric vehicles. Here, Nb 5+ is doped at the Fe site of LiFePO4 on the basis of first-principles calculation, and Nb 5+ is doped into the crystal lattice of LiFePO4 to improve the electronic conductivity. The crystal cell parameter of the LFNbPO-0.75 sample (0.75% Nb2 O5 -doped LiFePO4 ) is smaller than that of the bare LiFePO4 sample, the micromorphology of LFNbPO-0.75 sample becomes fine and uniform in the process of Nb 5+ doping, and the Nb 5+ doped into LiFePO4 expands the crystal plane spacing, which is conducive to Li + diffusion. Amongst all the doped samples, the Li + diffusion coefficient of LFNbPO-0.75 is the largest, and the redox peak of LFNbPO-0.75 is more symmetrical, sharper and narrower, indicating that the proper amount of Nb 5+ -modified LiFePO4 can improve the charge and discharge specific capacity with better reversibility and capacity retention. The discharge capacity in LFNbPO-0.75 for LIBs is 169.87 mAh·g −1 in the first cycle at 1.0 C, which is approximately the same as the theoretical capacity of 169 mAh·g −1, and the corresponding capacity retention rate is 99.03% after 100 cycles. These results promote the wide applications of LiFePO4 batteries in high-range electric vehicles. Highlights: The DFT were used to determine changes in the conductive properties of LiFePO4 following doping with Nb. Nb 5+ doped at Fe-Site of LiFePO4 with a higher electronic conductivity effectively improved cycling performance. Nb 5+ doping into LiFePO4 expands the crystal plane spacing which is conducive to Li + diffusion.