Nafe(HPO4)2: A New Polyanionic Cathode Material for Lithium and Sodium-Ion Batteries

Thursday, 1 June 2017: 14:54
Grand Salon C - Section 13 (Hilton New Orleans Riverside)
P. Sandineni (Missouri University of Science & Technology) and A. Choudhury (Missouri University of Science and Technology)
There is a continuous quest for a low-cost, efficient and environmentally benign cathode materials for Li ion batteries. Several polyanionic compounds in the family of phosphates and sulfates have already been touted as excellent cathode materials, for example, olivine-type LiFePO4 and Triplite-LiFeFSO4. Herein, we are reporting a new phosphate compound, NaFe(HPO4)2, synthesized through a low-temperature hydrothermal route. The structure has been solved using single-crystal X-ray diffraction, showing a 3D structure built up of corner sharing FeO6 octahedra and PO4 tetarhedra yielding channels along C-axis. The Na ions occupy half of those channels leaving other half empty. Hence, further reductive insertion of alkali ions into the structure was hypothesized. The theoretical capacity of the compound based on one Li insertion is 98.97 mAhg-1, of which 60% of the capacity can be practically achieved in both Li- and Na-ion batteries with an average voltage of 3.0 and 2.80 V, respectively. Further ion-exchange of sodium with lithium was successfully carried out and the ion-exchanged compound, presumably LiFe(HPO4)2, showed better achievable capacity, up to 70% of theoretical capacity in a Li-ion battery with an average voltage of 3.0 V. The presentation will cover synthesis, structure, thermal and spectroscopic analysis of the samples and their detail electrochemical properties.