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 1 9 materials faster than solid state pro- cesses, which would reduce the overall cost of the cathode and accelerate EV adoption by consumers. Casting synthesis experiments to date have produced only small quan- tities (grams) at the laboratory scale, with resistance furnaces used as a heat- ing source. Processing cycles are slow in these facilities because their energy flux per unit of volume is insufficient to rapidly reach 1000 o C (e.g., above the melting point of LFP). Melting synthesis techniques for high capacity (>100 kg) require a high energy flux, along with excellent control of melt homogeneity and the solidification process. In 2013, a Canadian research con- sortium led by Polytechnique Montre- al initiated a battery of tests at larger scale (~40 kg) to generate basic data to scale-up the melt-casting synthesis of C-LFP cathode material to commercial- ly relevant quantities. The experimental design varied the operating parameters of the processing steps, raw materials, and melting and casting conditions. The objective was to achieve high-pu- rity LFP that meets the electrochemical performance standards at low cost [11] . This article shares insights on applying an induction melting and casting pro- cess as a synthesis method of LFP ma- terial for larger volumes. MELT CASTING SYNTHESIS OF LFP CATHODE MATERIAL Production of cathode material using the melt casting method includes mixing the precursors, melt synthe- sis, milling, drying, carbon coating, and pyrolysis. Melt synthesis is the key processing step because it affects all subsequent steps and consequently the battery performance. Various precur- sors can be used to synthesize the LFP compound as long as the precursors’ mixtures have the proper stoichiomet- ric ratios [5] (Table 1). Also, conditions during synthesis and casting need to be maintained as inert or slightly re- ducing to ensure high purity of the final product. An image showing precursors in the furnace is shown in Fig. 5. These compounds are in the form of powder, are nonconductive, and when they melt above approximately 1000 o C, the viscosity is similar to molten glass (called molten slag in the metal casting industry). Various melt synthesis methods were examined at a pilot-scale foundry at the CanmetMaterials laboratory (Fig. 6). Initially, an electric re- sistance furnace was tested to melt the precursors to synthe- size LFP. An induction furnace reduced the melting cycle time and improved temperature homogeneity compared to resistive heating. Typically, non-metal- lic charges cannot be directly heated by TABLE 1 — VARIOUS PRECURSORS USED FOR MELTING SYNTHESIS OF LFP [5,12] Li Fe P Li 2 CO 3 LiOH·H 2 O LiH 2 PO 4 Li 3 PO 4 Fe 2 O 3 Fe 3 O 4 FeO Fe 3 (PO 4 )2·8H 2 O FePO 4 ·2H 2 O Fe NH 4 H 2 PO 4 Fe 3 (PO 4 )2·8H 2 O P 2 O 5 LiH 2 PO 4 Li 3 PO 4