The galvanostatic
intermittent titration technique (GITT) is widely
used to evaluate solid-state diffusion coefficients in electrochemical
systems. However, the existing analysis methods for GITT data require
numerous assumptions, and the derived diffusion coefficients typically
are not independently validated. To investigate the validity of the
assumptions and derived diffusion coefficients, we employ a direct-pulse
fitting method for interpreting the GITT data that involves numerically
fitting an electrochemical pulse and subsequent relaxation to a one-dimensional,
single-particle, electrochemical model coupled with non-ideal transport
to directly evaluate diffusion coefficients. Our non-ideal diffusion
coefficients, which are extracted from GITT measurements of the intercalation
regime of FeS2 and independently verified through discharge
predictions, prove to be 2 orders of magnitude more accurate than
ideal diffusion coefficients extracted using conventional methods.
We further extend our model to a polydisperse set of particles to
show the validity of a single-particle approach when the modeled radius
is proportional to the total volume-to-surface-area ratio of the system.
Blood rheology shows viscoelastic, thixotropic (using a structural parameter λ) and viscoplastic characteristics shown in steady stress vs. shear-rate data.
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