Analysis of limiting Processes within Li-ion Batteries

Abstract

International audienceLi-ion battery is a mature technology widely applied as a power source for consumer electronic devices, and nowadays, their use is expanded towards electric vehicles and stationary applications. However, improvement of current battery systems is needed to meet the requirements of the transport sector in terms of energy density, safety, cycle life, and costs. Among the different strategies to increase battery autonomy, one is focusing on electrode loading to increase the ratio of active materials (negative and positive electrode thickness) to inactive components (separator, current collector…) . However, by doing so, the output power density becomes strongly limited by the charge transport within the composite electrodes. Thus, our objective is to optimize the battery design to find the best compromise between energy and power density in Li metal-based batteries. In this work, we studied Li-battery capacity as a function of the current density with respect to electrode loading, formulation, porosity, and aging. For this purpose, (LiFePO4) LFP based electrodes were formulated at different loadings (from 0.4 to 3.2 mAh.cm-2), compositions (LFP%, Carbon%, PVDF %), and calendered to reach different porosities (from 20 to 60 %). The microstructure of electrodes is investigated using SEM and BET to determine their specific area. Subsequently, the power performance is fully captured and analyzed using a time-saving methodology. The limiting C-rate (resp. current density, Jlim) is obtained through capacity vs. discharge current curves, which allows us to determine an effective diffusion coefficient of the limiting transport process (Deff) via the Sand equation.Finally, Deff is compared to the diffusion coefficient obtained using the conventional alvanostatic Intermittent Titration Technique (GITT) to assess the nature of the limiting phenomena such as Li+ diffusion within the solid phase and/or Li+diffusion in liquid phase through electrode porosity. The coupling of the various processes according to the studied parameters is discusse