Deciphering the degradation mechanisms of nano-Si and micro-SiO anodes in lithium-ion battery full-cells using distribution relaxation times analysis

Silicon (Si) and silicon monoxide (SiO) have attracted great interest as next-generation anode materials for lithium-ion batteries (LiBs) due to their high energy density. However, their commercialization has been hindered by rapid capacity fading, which stems from mechanical degradation (e.g., cracking and delamination) and the aggressive formation of solid electrolyte interphase (SEI) layer. While understanding these degradation mechanisms in batteries necessitates in-operando measurement techniques, very few non-destructive analytical methods have been documented in literature. This paper highlights the effectiveness of combined electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) techniques in performing systematic characterization of LiNi0.6Mn0.2Co0.2O2 (NMC)/nano-Si and NMC/micro-SiO full-cells. The systematic design of experiments enabled the separate deconvolution of anode and cathode aging using symmetrical cells. This approach offered a clear understanding of the overall degradation mechanisms in the full-cells. The major impedance sources in the NMC/nano-Si full-cell were anode contact impedance, resulting from mechanical degradation of Si, and cathode charge transfer impedance, due to significant lithium loss and consequently deeper extraction of lithium ions in NMC. In contrast, micro-SiO anodes exhibited less electrode-level degradation, as evidenced by SEM images and relatively stable impedance behaviors during extended cycling, which strongly corroborate its superior capacity retention (66 % at 300th cycle) compared to that of nano-Si anode in full-cells (26.5 % at 300th cycle).