High-Rate Lithium Deintercalation from Lithiated Graphite Single-Particle Electrode

The electrochemical behavior of a lithiated graphite single-particle electrode during high-rate Li deintercalation in an organic electrolyte was investigated using a microelectrode technique. A Ni-plated metal filament (diameter: 10 mu m) was attached to a mesocarbon microbead (MCMB) in the electrolyte under optical microscope observation, and galvanostatic charge-discharge tests were carried out. The discharge capacity of a lithiated MCMB particle (diameter: 18 mu m) was 2.02 nA h in the potential range of 0.005-2.5 V vs Li/Li+. The fully lithiated MCMB particle showed an extremely high rate capability and released more than 98% of the accommodated Li at a constant discharge current of 1000 nA within 10 s. At discharge currents lower than 200 nA, the charge transfer process at the interface controlled the reaction of the single-particle electrode, and the Li diffusion process in the MCMB particle did not significantly affect the Li deintercalation rate. The charge transfer resistance for Li intercalation/deintercalation was in the range of 20-50 Omega cm(2), and the apparent chemical diffusion coefficient of Li in the MCMB particle was estimated to be 8.3 x 10(-8) cm(2) s(-1).