Nanostructured lithium-free oxyanion cathode, Li x Co 2(MoO4)3 [0∈x∈<3] for 3 v class lithium batteries

A new nanostructured framework-type polyanion material, Li x Co2(MoO4)3 [0∈x∈<3], was studied as a positive electrode for use in 3-Volt class lithium-ion cells for the first time. The new material was synthesized in a lithium-free composition and examined its structure, morphology, and electrochemical characteristics. Co 2(MoO4)3 was found to crystallize in a monoclinic structure with lattice parameters: a∈=∈14.280(9) Å, b∈=∈3.382(8) Å, c∈=∈10.557(1) Å, and β∈=∈117.9728° (space group P2/m). The redox behavior of this new material was demonstrated in lithium-containing test cells. The material offered a discharge capacity of approximately 110 mAh g-1 between 3.5 and 1.5 V during the first cycle and retained 50% capacity at the end of the 20th cycle. The poor capacity retention is obviously attributed to the poor electronic conductivity of Co2(MoO4)3 owing to its open framework structure. To overcome the intrinsic low electronic conductivity of polyanion materials, we have adapted a nanocomposite approach by way of adding nanoporous carbon matrix (particle size approximately 10 nm) together with the conventional conductive additive (acetylene black) and demonstrated that the overall electronic conductivity could be improved significantly, yielding an initial discharge capacity of 121 mAh g-1 using nanocomposite electrode in the potential range 3.5 V down to 2.0 V. © 2007 Springer-Verlag.