Nov_Dec_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 7 2 0 induction. However, when using electri- cally conductive crucibles (susceptor)— such as graphite, silicon carbide (SiC), or metal—rapid and efficient melting of the inorganic precursors is possible. Selection of the crucible affects prod- uct build-up resulting from the affini- ty of molten lithium oxide with metal and oxide species. The melt tempera- ture was controlled in a range of 1000 ° to 1400 ° C during the melt hold time using a contactless infrared pyrome- ter. This method was used instead of thermocouples to avoid their dissolu- tion and subsequent melt contamina- tion. A protective atmosphere, such as argon, is required during melting in the furnace as well as during casting and solidification in molds. Figure 7 shows crucible lip pouring of LFP melt into an ingot mold. Thermal analysis cooling curves of the LFP solidification process show liquidus (beginning of solidifica- tion) as well as solidus (end of solid- ification process) at 970 ° and 950 ° C respectively (Fig. 8). The recorded cool- ing curves could be used as an in-situ quality check to detect LFP and impu- rities during the process. The final LFP product is shown in Fig. 9 in the form of a 5-kg cast ingot as well granules of LFP ranging between 2 to 5 mm achieved by Fig. 5 — Precursors (1) loaded in the cruci- ble (2) inside the induction furnace. Fig. 6 — Vacuum induction furnace setup in a pilot-scale casting laboratory at Canmet- Materials. Fig. 7 — Pouring LFPmelt at approximately 1000 o C into 5-kg ingot molds. Fig. 8 — Thermal analysis curves of the LFPmaterial recorded during solidification; temperature vs. time (blue) and first derivative (cooling rate) vs. time (red). quenching liquidmaterial in water. Syn- thesized LFP needs to have minimum contamination including over-reduced species such as Fe, Fe 2 P, and Fe 3 C, and oxidized species including Fe 2 O 3 and Li 3 Fe 2 (PO 4 ) 3 in order to achieve the de- sired battery electrochemical perfor- mance and cycle life. Following the melt synthesis, LFP specimens undergo subsequent pro- cessing including crushing, grinding (dry and/or wet), drying, and carbon coating as needed for testing battery assemblies in coin cells. An SEM micro- graph of a cast ingot’s fractured surface clearly shows large LFP crystals. In ad- dition, secondary crystal phases are seen at the crystal boundary, indicating a different purity or concentration be- tween the two regions (Fig. 10). Phase purity in the final product depends not Fig. 9 — LFP specimens produced via a melting and casting synthesis process. (a) As-cast surface morphology of the 5-kg cast ingot, (b) water-quenched granules with diameters ranging between 2 and 5 mm.