To increase the energy density of lithium batteries, the development of high-capacity positive electrode materials is essential. Herein, we propose the use of a three-electron redox reaction of Mo3+/Mo6+ for a new series of high-capacity lithium insertion materials. In this study, a binary system of LiMoO2–Li3NbO4 is targeted, and nanosize and metastable Li9/7Nb2/7Mo3/7O2 is successfully prepared by a mechanical milling process. The sample delivers a large reversible capacity of ∼280 mAh g–1 in a Li cell with good capacity retention. On the basis of these results, the future possibility of high-capacity electrode materials with a three-electron Mo3+/Mo6+ redox reaction is discussed.

The binary system, xLi3NbO4-(1 - x)LiVO2, was first examined as an electrode material for rechargeable lithium batteries. The sample (x = 0.43) crystallizes into a cation-disordered rocksalt structure and delivers a reversible capacity of ca. 230 mA h g(-1), which originates from V(3+)/V(5+) redox with electrochemically inactive niobium ions.

We investigated the open-circuit potentials (OCPs) and structure of CoV3normalO8 in the first discharge and charge processes. The OCPs in the discharge and charge processes traced different routes. In the discharge process, the OCPs declined slowly at ∼2.4V and reduced more slowly at ∼2.2V . From the change in the cell parameters, lithium was found to be intercalated in the tunnel space of CoV3normalO8 at low lithium contents. Further lithium insertion induced an amorphous material and a crystalline one. The generation reaction of these substances containing lithium ions resulted in an irreversible capacity in the first cycle. Considering that the observed OCPs were distributed over a wide range of potentials in the charge process, it was probable that lithium was extracted dominantly from the newly generated amorphous substance. We concluded that the amorphous substance exhibited a reversible discharge-charge cycle performance after the second cycle.

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The lithium intercalation property of cobalt vanadium oxide ConormalV3normalO8 having tunnel space along the c -axis of the crystal structure was investigated. Lithiated samples, normalLixConormalV3normalO8 , were structurally analyzed by the Rietveld analysis. From the linear variation in the lattice parameters during lithiation, it was found that lithium was intercalated in the host compound ConormalV3normalO8 for 0.125