  The kinetic performance of graphite particles is difficult to deconvolute
from half-cell experiments, where the influences of the working electrode
porosity and the counter electrode contribute nonlinearly to the
electrochemical re-sponse. Therefore, thin-layer electrodes of circa 1 {\mu}m
thickness were prepared with standard, highly crystalline graphite particles to
evaluate their rate capability. The performance was evaluated based on the
different stage transitions. We found that the tran-sitions towards the dense
stages 1 and 2 with LiC6 in-plane densi-ty are one of the main rate limitations
for charge and discharge. But surprisingly, the transitions towards the dilute
stages 2L, 3L, 4L, and 1L progress very fast and can even compensate for the
initial diffusion limitations of the dense stage transitions during discharge.
We show the existence of a substantial difference between the diffusion
coefficients of the liquid-like stages and the dense stages. We also
demonstrate that graphite can be charged at a rate of ~6C (10 min) and
discharged at 600C (6 s) while maintaining 80 % of the total specific charge
for particles of 3.3 {\mu}m median diameter. Based on these findings, we
propose a shrinking annuli mechanism which describes the propagation of the
different stages in the particle at medium and high rates. Besides the limited
applicable overpotential during charge, this mechanism can explain the
long-known but as yet unexplained asymmetry between the charge and discharge
rate performance of lithium intercalation in graphite.
