Understanding the effects of different loadings on properties of a silicon/carbon anode for lithium batteries

Abstract

Battery cells based on different silicon/carbon (Si/C) loadings were assembled in this work. Their battery performance, in particular their capacity and cycling stability, was evaluated. The battery was assembled in a way that a pure Li metal counter electrode, LiPF₆ liquid electrolyte and pole piece with Si/C coatings were employed. Standardized differential capacity curves (dQ_m/dV curves) revealed a redox reaction resulting from the intercalation/deintercalation process of lithium ions. The first coulombic efficiencies and capacity retention were greatly affected by Si/C loading. Moderate rather than minimum or maximum Si/C loading for lithium batteries showed the best electrochemical performance. In addition, electrochemical impedance spectroscopy (EIS) quantified the resistances of organic electrolytes and the solid electrolyte interface (SEI). Mechanism analysis was conducted by drawing support from battery disassembly technology and material analysis methods. Notably, the phase and structure of Si/C anode materials undergoing charging and discharging were characterized. Raman spectra demonstrated that the charging and discharging processes significantly weaken the characteristics of Si owing to the formation of an Li_xSi alloy compound. The morphology and difference in electrode expansion of the anode with different Si/C loadings caused by long charge–discharge cycles were analyzed using scanning electron microscopy (SEM). Besides, elemental analysis results indicated that silicon lithium alloying is more prone to oxidation. It is proposed that this work could help provide a basis for the rational design of Si/C pole pieces for lithium batteries.