Synthesis of submicron-sized NiPS3 particles and electrochemical properties as active materials in all-solid-state lithium batteries

Abstract

Submicron-sized NiPS3 particles were synthesized by heating fine Ni powder (<100 nm), red phosphorus, and sulfur at 673 K for 48 h, and their electrochemical properties as cathodes in sulfide-based all-solid-state lithium batteries were investigated using discharge/charge measurements, X-ray diffraction (XRD) measurements, electrochemical impedance spectroscopy, and X-ray absorption near-edge structure spectroscopy (XANES). Batteries using submicron-sized NiPS3 as a cathode active material exhibited a 10th discharge capacity of 147 mAh g11, which was larger than that obtained with 10100 micron-sized NiPS3 (390 mAh g11). The XRD patterns of the composite cathode before and after discharge/charge suggested that Li4P2S6 was formed irreversibly (2NiPS3 + 4Li+ + 4e1 ¼ Li4P2S6 + 2Ni), and this irreversible reaction would reduce the capacity of the cathode. The XANES spectra suggested the oxidation/reduction of Ni during dischargecharge cycles, but the change in the spectra during the cycles was considerably small if one assumed the oxidation/reduction of Ni2+/Ni0