Synthesis, structure, and magnetic properties of [Li(H2O) M(N2H3CO2)3]·0.5H 2O (M = Co,Ni) as single precursors to LiMO2 battery materials

Abstract

[Li(H2O)M(N2H3CO2) 3]·0.5H2O, M = Ni (1) and Co (2), has been synthesized in moderate yield from the corresponding metal salts and hydrazinecarboxylate anion, N2H3CO2 -, prepared by mixing N2H4, H2O and dry ice. Both the compounds crystallized in the chiral space group P2 1 and have interesting 2D bilayer network structures in the solid state comprising fused helical coordination polymers with extensive hydrogen bonding. Samples 1 and 2 exhibited paramagnetism, as shown by the variable temperature magnetic measurements. The calculated magnetic moments were 2.82 and 4.39 μB for 1 and 2, respectively. These two compounds have been investigated as single precursors for layered materials LiMO2, M = Ni and Co. Pyrolysis of 1 and 2 yields LiNiO2 and LiCoO2 at 700°C in an oxygen atmosphere and at T > 700°C in air, respectively. They were characterized by powder XRD, Rietveld refinement, and SEM. Cathodic properties of LiMO2 have been evaluated by cyclic voltammetry and galvanostatic charge-discharge cycling up to 20 cycles in the voltage ranges, 2.5-4.3 and 2.5-4.5 V vs Li metal. Results are in tune with those reported in the literature, thereby indicating that 1 and 2 are excellent single-source precursors for obtaining electrochemically active battery materials. © 2006 American Chemical Society.