Carbothermic reduction of nickel oxide: Effect of catalysis on kinetics

Investigation of the Inorganic Compounds NaMV2(PO4)3 (M = Fe, Co, Ni) as Anode Materials for Sodium-Ion Batteries

The new compounds NaMV₂(PO₄)₃ (M = Fe, Co, Ni) were synthesized via a sol-gel synthesis route, and their crystal structures were refined using the Rietveld method from X-ray powder diffraction data. NaCoV₂(PO₄)₃ was also characterized by TGA, cyclic voltammetry, and galvanostatic cycling. The three phases crystallize with the orthorhombic symmetry and the space group Imma. The structures are isotypic to the stuffed α-CrPO₄-type structure and contain two vacant sites in which two sodium atoms can be intercalated. When NaCoV₂(PO₄)₃ is cycled at a 1C rate in the voltage ranges of 0.1-3 and 0.7-3 V vs Na⁺/Na, it delivers specific capacities of 190 and 75 mA h/g, respectively, with an average operation potential of ∼1.4 V. This attests to the electrochemical activity of this compound and indicates that the α-CrPO₄-type compounds could be suitable for hosting other guest ions.