Synthesis, structure, and magnetic properties of [Li(H₂O)M(N₂H₃CO₂)₃]·0.5H₂O (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 P2₁ 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 μ_B 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.