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A first‐principles study of bulk and surface Sn‐doped LiFePO 4 : The role of intermediate valence component in the multivalent doping
Author(s) -
Hou Lianxi,
Tao Guohua
Publication year - 2017
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201700041
Subject(s) - doping , dopant , materials science , density functional theory , valence (chemistry) , chemical physics , electrochemistry , band gap , vacancy defect , conductivity , ab initio , nanotechnology , computational chemistry , chemistry , optoelectronics , crystallography , electrode , organic chemistry
Doping can be employed to enhance the electrical conductivity and electrochemical performance of LiFePO 4 , a promising material for Li‐ion batteries. However, the microscopic mechanism of doping is not fully understood. In this study, ab initio density functional theory (DFT) with the generalized gradient approximation (GGA) + U calculations was performed on both bulk and surface Sn‐doped LiFePO 4 . Our results indicate that surface doping is preferred over bulk or subsurface doping because it shows a lower doping energy and surface energy. The doping effect appears to be local, and the effect of the Li vacancy (V Li ) distribution was examined. The multivalent Sn doping may facilitate the formation of an Fe 2+ /Fe 3+ complex with the involvement of an effective intermediate Sn 3+ component, which complements the existing charge transfer model for LiFePO 4 . The effective Sn 3+ –Fe 3+ /2V Li complex may exist on the LiFePO 4 surfaces, providing possible surface design schemes to control charge transfer. The results suggest that the Sn dopant could modulate band gap and local charge transfer, and improve the electrochemical performance at the last stage of the charging process with no capacity loss. However, an optimized doping concentration may exist for electrochemically inactive doping with an unfavorable doping energy.