Synthesis and characterization of novel lithium ion battery cathode materials produced via assisted soft chemistry

Lithium transition metal oxides, LiMO₂, are the most promising positive electrode material for lithium ion batteries because of their high charge capacity (>150 mAh/g) and facile lithium ion diffusion in their lattice. A new synthetic method for preparation of stabilized LiMO₂ has been developed as “Assisted Soft Chemistry.” Using this technique, the lithium in LiMO₂ can be exchanged partially for zinc or gallium. Powder X-ray diffraction studies verify that zinc or gallium doped Li_1−yZn_y/2MO₂ and Li _1−yGa_y/3MO₂, where ‘y’ equals 0.15 or 0.30 and ‘M’ is Co_0.7Ni_0.3, Co _0.3Ni_0.7, or Ni have the same lamellar structure as their respective non-doped precursors, LiCo_0.7Ni_0.3O ₂, LiCo_0.3Ni_0.7O₂, and LiNiO₂ . Observed electrical conductivities were determined by AC impedance spectroscopy and two point probe measurements and indicate marked electronic conductivity enhancement for the Zn substituted sample in the range of 1 to 2 orders of magnitude. Electrochemical charge/discharge profiles of the new cathode materials have shown reversible lithium insertion and extraction processes with charge capacity exceeding 150 mAh/g. The DSC analyses of the zinc-doped cathode materials show improved thermal stability of the new cathode materials when compared to non-doped commercial cathode materials.