Synthesis and Electrode Performance of Li3NbO4 - LiVO2 Binary System for Li Batteries

Abstract

Rechargeable lithium batteries are used for electric vehicles, and the demand for high-energy and long-cycle-life positive electrodes is growing. Recently, Li1.3Nb0.3V0.4O2 with a cation-disordered rocksalt structure has been reported as a positive electrode material, which delivers high reversible capacity of >200 mAh g-1 with V3+/V5+ two-electron redox.[1] However, for Li1.3Nb0.3V0.4O2, 0.5 mole of Li+ remains in the crystal lattice after fully charge, and therefore further increase in the energy density is anticipated through the optimization of chemical compositions. In this study, we systematically examine crystal structure and electrochemical properties of x Li3NbO4 – (1 – x) LiVO2 binary system as positive electrode materials for rechargeable lithium batteries. Li-Nb-V-O samples were prepared by a solid-state reaction from stoichiometric amounts of Li2CO3, V2O3 and Nb2O5. The mixtures of precursors were calcined at 950 oC for 12 h in inert atmosphere. Thus prepared samples were mixed with acetylene black by mechanical ball-milling. The samples were characterized by XRD and SEM. Electrochemical properties as positive electrode materials were examined using two-electrode electrochemical cells. X-ray diffraction patterns of the binary system of x Li3NbO4 – (1 – x) LiVO2 with different compositions are shown in Figure 1 (a). Li1.3Nb0.3V0.4O2 (x = 0.43) crystallizes into cation-disordered rocksalt phase whereas partially cation-ordered rocksalt phase is found for Li1.25Nb0.25V0.5O2 (x = 0.33) and Li1.2Nb0.2V0.6O2 (x = 0.25). Electrochemical properties of the samples are also shown in Figure 1 (b). The cells were galvanostatically cycled at a rate of 10 mA g-1 in the voltage range of 1.5 – 4.8 V at room temperature. Among three samples (x = 0.25, 0.33, and 0.43), the highest reversible capacity of >250 mAh g-1 is obtained for Li1.25Nb0.25V0.5O2 (x = 0.33). Moreover, electrode performance is further increased by heat treatment of the samples. From these results, we will discuss the possibility of x Li3NbO4 – (1 – x) LiVO2 binary system with V3+/V5+ two-electron redox as high-capacity and long-cycle-life positive electrode materials for rechargeable lithium batteries. (1) N. Yabuuchi et al., Chem. Commun., 52, 2051 (2016). Figure 1