First Principles Study of Small Hole Polaron Formation in Doped Olivine LiFe_1−xCo_xPO₄: Effects of Li Deficiency

การศึกษาการเกิดโฮลโพลารอนขนาดเล็กในสารโอลิวีนที่ถูกเจือ (LiFe_1−xCo_xPO₄) โดยมีผลมาจากการดึงลิเธียมออกด้วยวิธีคำนวณแบบเฟิสต์พรินซิเพิล

Chanaprom Cholsuk, Sujin Suwanna, Kritsanu Tivakornsasithorn*

Materials Today Communications, Volume 26, March 2021, 102043.

https://doi.org/10.1016/j.mtcomm.2021.102043

Understanding the localization of small polarons (p+) are important for improvement of electronic conductivity in cathode materials such as LiFePO₄ and LiCoPO₄ for Li-ion battery technology. In this study we calculate the formation energy (ΔF) due to Li vacancies in LiFe_1−xCo_xPO₄ by density functional theory with additional on-site Hubbard correction (DFT+U). We found that Li vacancies (V_Li−) can induce polaron formation preferentially at Fe rather than Co sites. Co also improves polaron binding to V_Li− to form a snall polaron complex (V_Li− - p+) and alters Li_1−yFePO₄ to the equilibrium phase (ΔF<0). Co doping can reduces the energy gap and increases the intercalation voltage. Overall, polaron localization plays key roles in electronic conductivity of LiFe_1−xCo_xPO₄ cathode materials.