Rheological phase synthesis and electrochemical performances of LiVMoO6 as a high-capacity anode material for lithium ion batteries

Abstract

Research for new anode materials has been stimulated by the development of lithium ion batteries since the introduction of carbon as a negative material in 1990 by Sony Energetics Inc. Some metal oxides and metalbased composite oxides [1, 2], nitrides [3, 4] and intermetallics [5, 6], which capacities are comparable or superior to those of graphitized carbon (theoretical maximum capacity of 372 mA hr g−1 [7, 8]), were considered as possible candidates for next generation of anode materials. Recently, several vanadium composite oxides exhibited their high-capacity and high-rate performance as negative electrode materials due to their open structure and interesting characteristics from a standpoint of the variety of oxidation states [9–12]. LiMoVO6 crystallizes with the ThTi2O6 branneritetype structure [13] and its electrochemical properties as a positive electrode material for lithium secondary batteries have been investigated [14–16]. But the performance of LiMoVO6 as negative electrode material was seldom reported. In this work, brannerite-type LiMoVO6 powder was obtained by rheological phase reaction method [17]. The result of electrochemical tests showed that the obtained LiMoVO6 as a novel anode material was also feasible and demonstrated very high energy density. The precursor was prepared by rheological phase reaction method. Analytical reagent grade chemicals, LiOH·H2O, NH4VO3 and (NH4)6Mo7O24·4H2O, were used as the starting materials and fully mixed by grinding in a 1:1:1 molar ratio. A proper amount of water was added to get a rheological body and the mixture was sealed in a closed container for 8 hr at 80 ◦C. After drying under vacuum at 80 ◦C for several hours, the precursor was pyrolyzed at 550 ◦C for 10 hr in air, and soft yellow powder LiMoVO6 was obtained. Thermogravimetry and differential thermal analysis (TG/DTA) of the precursor were performed by the Netzsch STA 449 thermal analysis system at a heating rate of 10 ◦C/min in air. The X-ray diffraction (XRD) measurements of the sample were carried out by Shimadzu XRD-6000 diffractometer with CuKα1 radiation (λ = 1.54056 A). The particle sizes and morphological features were observed by a scanning electron microscope (Hitachi SEM X-650).