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Fe 3+ reduction during melt‐synthesis of LiFePO 4
Author(s) -
Sauriol Pierre,
Li Delin,
Hadidi Lida,
Villazon Hernando,
Jin Liling,
Yari Bahman,
Gauthier Michel,
Dollé Mickaël,
Chartrand Patrice,
Kasprzak Wojciech,
Liang Guoxian,
Patience Gregory S.
Publication year - 2019
Publication title -
the canadian journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.404
H-Index - 67
eISSN - 1939-019X
pISSN - 0008-4034
DOI - 10.1002/cjce.23522
Subject(s) - graphite , crucible (geodemography) , reducing agent , agglomerate , materials science , eutectic system , metal , analytical chemistry (journal) , chemical engineering , metallurgy , chemistry , composite material , microstructure , chromatography , computational chemistry , engineering
LiFePO 4 (LFP) is a safe and low cost cathode material for Li‐ion batteries. Its solid‐state synthesis requires micron‐sized reactants yielding high production costs. Here, we melt‐synthesized up to 5 kg batches of LFP from low‐cost coarse Fe 2 O 3 (509 µm) in an induction furnace. Graphite from the crucible was an effective reducing agent. Adding metallic Fe or CO increased the Fe 2+ content and reaction kinetics. Metallic Fe improves the lifetime of the graphite crucible but requires a premixing step for it to be effective, otherwise the Fe powder agglomerates due to the presence of a eutectic in the LiPO 3 ‐Fe‐Fe 2 O 3 system. In a pushout furnace configuration, for an hour‐long holding period, injecting CO into the melt increased the Fe 2+ content from 0.301 to 0.315 g/g, which we attributed to melt protection. Likewise, graphite powder floating on top of the melt further improved the Fe 2+ content to 0.331 g/g. The Fe 2+ content reached 0.325 g/g when using fine Fe 3+ (142 µm) and CO as reducing agent at half the holding period at 1150 °C. We attribute the higher reaction rate to the improved contact between the suspended Fe 3+ and the CO reducing gas. When the graphite crucible is the unique reducing agent, the reaction rate was proportional to the crucible base surface area. A zero‐order kinetic model characterized the solids disappearance with time. A thermal model developed to compare lab‐scale data against small pilot‐scale demonstrated that the charge lagged the furnace temperature by as much as 22 min at 1000 °C.