Exploring Different Binders for a LiFePO4 Battery, Battery Testing, Modeling and Simulations

Abstract

This paper focuses on the LiFePO4 (LFP) battery, a classical and one of the safest Li-ion battery technologies. To facilitate and make the cathode manufacture more sustainable, two Kynar® binders (Arkema, France) are investigated which are soluble in solvents with lower boiling points than the usual solvent for the classical PVDF binder. Li-LFP and graphite-Li half cells and graphite-LFP full cells are fabricated and tested in electrochemical impedance spectroscopy, cyclic voltammetry (CV) and galvanostatic charge-discharge cycling. The diffusion coefficients are determined from the CV plots, employing the Rendles-Shevchik equation, for the LFP electrodes with the three investigated binders and the graphite anode, and used as input data in simulations based on the single-particle model. Microstructural and surface composition characterization is performed on the LFP cathodes, pre-cycling and after 25 cycles, revealing the aging effects of SEI formation, loss of active lithium, surface cracking and fragmentation. In simulations of battery cycling, the single particle model is compared with an equivalent circuit model, concluding that the latter is more accurate to predict “future” cycles and the lifetime of the LFP battery by easily adjusting some of the model parameters as a function of the number of cycles on the basis of historical data of cell cycling.