Résumé
The degradation of coated LiNi0.8Mn0.1Co0.1O2 (NMC811) cells with Silicon-Graphite (SiGr) composite anodes containing varying Si content is investigated using Differential Voltage Analysis (DVA), Incremental Capacity Analysis (ICA) and Distribution of Relaxation Times (DRT). ICA distinguishes Si from Gr specific degradation processes. It is observed an incomplete delithiation-related Si capacity loss in cells with 7 % and 11 % Si, which increases during early cycles and later stabilizes. Such behavior is not the reported permanent Si loss of active material, as the capacity of moderately and highly lithiated Si remains unchanged. Instead, a sudden rise in resistance at low states of charge is revealed. That is likely due to Si particle-particle contact loss during shrinkage, after particles are accommodated by a grown Solid Electrolyte Interphase (SEI) matrix and due to SEI cracks closure when particles contract. Data suggest a minimal threshold amount of Si may be necessary to trigger it, explained by Gr acting as electrical-contact keeper to Si particles. The proposed coupling of techniques made observable Si-driven effects in NMC811/SiGr cells, capacity fading primarily due to loss of lithium inventory and resistance increase dominated by the Si at lower voltages and by the NMC811 at medium and higher voltages.