High Capacity Lithium Ion Batteries Composed of Cobalt Oxide Nanoparticle Anodes and Raman Spectroscopic Analysis of Nanoparticle Strain Dynamics in Batteries

Cobalt nanoparticle thin films were electrophoretically deposited on copper current collectors and were annealed into thin films of hollow Co₃O₄ nanoparticles. These thin films were directly used as the anodes of lithium ion batteries without the addition of conducting carbons and bonding agents. Lithium ion batteries thus fabricated show high gravimetric capacities and long cycle lives. For »1.0 μm thick Co₃O₄ nanoparticle films the gravimetric capacities of the batteries were more than 800 mAh/g at a current rate of C/15 which is about 90% of the theoretical maximum. Additionally, the batteries were able to undergo 200 charge/discharge cycles at relatively fast rate of C/5 and maintain 50% of the initial capacitance. In order to understand the electrochemistry of lithiation in the context of nanoparticles, Raman spectra were collected at different stages of the electrode cycles to determine the chemical and structural changes in the nanomaterials. Our results indicate that initially the electrode nanoparticles are under significant strain and as the battery undergoes many cycles of charging/discharging the nanoparticles experience progressive strain relaxation.