Melt‐synthesis of LiFePO₄ over a metallic bath

Abstract

Compared with large-scale processes, the LiFePO 4 (LFP) melt-synthesis is a low-cost method with short dwell times and rapid reaction rates. However, secondary phases and impurities remaining in the olivine structure lower the cathode's electrochemical properties. Starting from a lowcost Fe 3þ precursor, we evaluated tin and silver charged metallic baths to purify the melt-synthesis of LiFePO 4 at laboratory scale. In the tin bath exploration, an x-ray diffraction (XRD) confirmed the olivine structure and a temperature-dependent generation of Li 3 PO 4 and Li 4 P 2 O 7 . An SEM image analysis identified tin-rich phases (Sn x P y O z ) segregated from the LFP structure and Fe x P phases on the internal walls of the crucible. A multielement analysis (ICP-AES) detected more than 0.03 g of Sn/g of LFP. The tin bath prepared samples delivered up to156 mAh/g of LFP in a carbonfree basis, 3 % lower than the capacity of the high purity Fe 2 O 3 -based material at 0.1 C. The silver bath-based LFP samples produced cleaner XRD patterns (less than 160 ppm of Ag in the LFP ingots), closer to the estimated molar ratios and neither silver compounds nor silver oxides. In this case, the sample delivered 161 mAh/g of LFP, the same capacity as the cathode prepared without a metallic bath. Starting from a commodity Fe 3þ source, future work should explore the silver bath roles as a reactive media, a heating source, a crucible insulator, and a potential contaminant trap for the melt-synthesis of LiFePO 4 .

LiFePO4 spray drying scale-up and carbon-cage for improved cyclability

“…An induction furnace at 1100 • C melted the precursors and synthesized LFP in a graphite crucible with a capacity of 50 kg The feed materials were: LiH 2 PO 4 , P 2 O 5 , Li 2 CO 3 and iron ore concentrate (>99 % Fe 2 O 3 with SiO 2 impurity) with a Li/Fe/P: 1.03/1/1.03 stoichiometry, [15,16,17] and we cast the melt into 200 mm ingots. [18] LFP is the dry solid fraction of our feed material, constisting of 97.8 % LiFePO 4 and 2.2 % γ-Li 3 PO 4 (±0.4 % CI 95 % n=6 , by AAS and XRD; 95 % confidence interval estimate, with a two-tail t-test for a sample number n).…”

Fe3+ reduction during melt‐synthesis of LiFePO4

“…Three reaction pathways are possible: 1) the reduction takes place in the solid phase (direct or electrochemical) followed by solubilization of the Fe 2+ and reaction in the liquid phase to form LFP; 2) the Fe 3+ is solubilized followed by the liquid phase reduction by contact with the reducing agent and reaction of the Fe 2+ species to form LFP; and 3) Villazon et al, considered a third pathway where a metal bath supported the Fe 3+ reduction using metallic iron as reducing agent to form a dissolved Fe 2+ within the metal bath. LFP was then formed by the reaction between the dissolved Fe 2+ with LiPO 3 in the supernatant layer.…”

Melt Synthesis of Lithium Manganese Iron Phosphate: Part I. Composition, Physical Properties, Structural Analysis, and Charge/Discharge Cycling

“…Besides low reactant cost, low purity requirements and process simplicity, melt synthesis is advantageous because it is fast (several minutes at 1000 °C required to melt LFP), produces no solid or liquid waste (all precursors are completely converted in the liquid phase), and produced a highly dense product (a solid LFP ingot). [14][15][16][17] Challenges are the need for grinding of the as-obtained ingot to submicron powder and a separate carbon coating step. The extra mechanical processing is probably preferable to a complex chemical synthesis and the calcination during carbon coating is beneficial to the crystallinity as we will show in this study.…”