Reaction mechanisms of tridymite iron phosphate with lithium ions in the low-voltage range

• Published in: Electrochimica acta 2007-12, Vol.53 (4), p.1843-1849
• Main Authors: Kim, Tae-Gon, Lee, Joon-Gon, Son, Dongyeon, Jin, Seonghyun, Kim, Min Gyu, Park, Byungwoo
• Format: Article
• Language: English
• Subjects: Applied sciences; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrode; Exact sciences and technology; Iron oxide; Iron phosphate; Li-ion battery; Lithium oxide
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2007.08.037

The electrochemical reaction mechanisms of tridymite FePO 4 with Li ions were studied in the voltage range of 2.4–0 V. The lithiation/delithiation of FePO 4 was found to be similar to that of binary 3d-metal oxides, which involve the formation and decomposition of Li 2O along with the reduction and oxidation of nanoscale 3d-metal nanoparticles. In the first discharge, FePO 4 was reduced to metallic Fe nanoparticles dispersed in a lithium compound matrix consisting of Li 3PO 4 and Li 2O. In the subsequent charge, these metallic Fe nanoparticles were partially oxidized to FeO by the decomposition of Li 2O. The Li 3PO 4 matrix was inactive during the change of potential from 0 to 2.4 V. It is notable that the re-oxidation of metallic Fe occurred only in the case of small nanoparticles, and the large Fe particles remained electrochemically inert during the reversible reaction.