Understanding the Impact of K-Doping on the Structure and Performance of LiFePO4/C Cathode Materials
The K-doped Li1−x K x FePO4 (x = 0, 0.005, 0.01, and 0.02) samples were synthesized successfully via a solid-state method, and the electronic structures of the samples were calculated by the first-principles based on density functional theory. Theoretical calculations show that the bandwidth of Li1−x K x FePO4 decreases with the increase in K+ doping, which is consistent with the experimental results. It was demonstrated that Li0.995K0.005FePO4 delivers higher capacity retention with 92.7% after 100 cycles compared with LiFePO4 (86.3%) at 1 C and shows better high-rate performance with capacities of 151.9, 151.8, 149.2, 128.3, and 84.6 mAh·g−1 at current densities of 0.1 C, 0.2 C, 0.5 C, 1 C, and 3 C; the corresponding values for LiFePO4 were 153.2, 136.5, 125.9, 111.5, and 66.0 mAh·g−1. Owing to the expanded Li ion diffusion pathway, EIS analysis showed that the lithium ion diffusion coefficient of LiFePO4 doped with K ion was significantly improved compared to LiFePO4; the values were 1.934×10−13 and 1.658×10−12 cm2·s−1, respectively. Additionally, Li0.995K0.005FePO4 showed a lower charge transfer resistance (300.2 Ω compared to 407.1 Ω of LiFePO4).
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Document Type: Research Article
Affiliations: School of Materials Science and Engineering, Changsha University of Science and Technology, Changsha 410114, China
Publication date: January 1, 2019
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