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 1 only on the stoichiometry of Li, Fe, P, and O [13] , but also on the melting and cooling process as well as the partial pressure of oxygen. Figure 11 presents qualitative x-ray diffraction (XRD) anal- ysis results showing the presence of LFP and some of a P-rich secondary phase (Li 4 P 2 O 7 ), but without other impurities such as Fe 2 P, Fe 2 O 3 , or oxidation prod- ucts. During process development, it was found that an insufficient reac- tion time and inadequate argon cover gas during melting and casting steps could lead to the presence of residual Fe 3+ in the synthesized product. These Fe 3+ contaminants are typically pres- ent in the form of Fe 2 O 3 and Li 3 Fe 2 (PO 4 ) 3 as reported previously [5] . Insufficient melt protection, despite a long reac- tion time, could result in the final syn- thesized product having between 5% to 10% of the total iron in the Fe 3+ state. When operating with adequate melt protection, minor contaminants such as Li 4 P 2 O 7 and LiPO 3 were observed as a result of excess precipitation from stoi- chiometric imbalances. Based on 40-kg melt synthe- sis trials, energy consumption was 3 kWh/kg. This value was achieved for heating the cold batch of precursors from room temperature to a 1400 o C peak temperature in a pilot-scale fur- nace without any energy recovery, in- sulation, or process intensification, as could be the case in a semi-batch operation. SUMMARY An induction melting process was evaluated to produce LFP ingots as well as granules from low-cost precur- sors. The melt casting process can pro- vide the benefits of utilizing various precursors, rapid reaction kinetics, ho- mogeneous liquid composition, and scale-up readiness. More important- ly, this process also offers the possibil- ity of lower-cost battery materials at a similar or better performance level as compared to solid state methods. Fur- ther experiments are required to opti- mize the melting and casting process with regard to LFP purity, melt tem- perature and holding time, protective atmosphere, and crucible materials. If successful, melt synthesis of battery cathode material could offer a novel application of the conventional casting process. ~AM&P Fig. 11 — X-ray diffraction results of a cast LFP sample showing the LFP phase and some P-rich secondary phase. No other impurities such as Fe 2 P or Fe 2 O 3 were detected. Fig. 10 — SEMmicrograph in secondary electron mode (SE) of a fractured surface of a cast LFP specimen. (1) LFP crystals, (2) dispersed impurities such as FeO visible at the crystal surface as identified by Gauthier et al. [5] .