Diffusion-limited C-rate: A criterion of rate performance for lithium-ion batteries

Rate performance is one of the important indexes of lithium-ion batteries. However, the discharge capacity would sometimes collapse after a critical C-rate, which is related to a classic concept termed the diffusion-limited C-rate (DLC). In this work, DLC is revisited using the Pseudo-Two-Dimensional model. The DLC analytical model is improved by incorporating the concentration-dependent liquid diffusion coefficient and shows good effectiveness compared with the simulation results. Subsequently, the impact of rate-limiting factors on the rate performance is examined to determine the effective scope of the proposed DLC model. Based on the adjustment of resistance ratios and time constant ratios of different kinetic processes, we find that the rate performance below DLC is hardly limited by electronic transports and charge transfer processes while the discharge capacity below DLC may be severely decayed if the solid-state diffusion in the electroactive particles is too slow. DLC helps identify the ‘knee’ on discharge capacity curves with discharge C-rate, which is a criterion of rate performance in some scenarios. • The DLC analytical model is improved by incorporating the concentration-dependent liquid diffusion coefficient. • The rate performance below DLC is hardly limited by electronic transports and charge transfer processes. • The discharge capacity below DLC may be severely decayed if the solid-state diffusion is too slow. • A new transition phase below DLC is observed and its mechanism is investigated by the decomposed overpotential method.