Abstract
Silicon–graphite (SiGr) blended negative electrodes have reached the Li-ion battery (LIB) market and outperform pure graphite in specific capacity. However, commercial implementations still rely on low Si contents, whereas industry targets ≈30 wt% Si and higher, where accelerated degradation and complex Si–Gr coupling limit the usable Si fraction and hinder the transition to Si-rich electrodes. This study resolves the dynamic interplay between Si and Gr (de)lithiation reactions in a 30:70 Si:Gr blended electrode over the first five
cycles by combining operando synchrotron X-ray diffraction with TEM observations. Crystalline silicon (c-Si) undergoes ≈95% amorphization in the first cycle, leaving minor crystalline remnants in core–shell domains. A broad first-cycle reduction feature in the voltage–capacity profile at 0.35–0.70 V vs Li/Li+ accompanies this structural transition and the substantial irreversible capacity loss. From the second cycle onward, Gr lithiation degree (x in LixC6) declines from 0.84 to 0.33, evidencing a shifting in Si–Gr utilization balance. A benchmark
under identical conditions against a partially amorphized Si-rich electrode retaining ≈25 % c-Si after cycling and exhibiting a more stable Gr lithiation degree demonstrates that the extent of early Si amorphization governs both the Si–Gr balance and overall electrode behavior. By quantitatively tracking amorphization with high temporal resolution and comparing extensive versus partial transformation pathways, this work establishes a time-resolved structural framework for Si-rich blended anodes, underscoring early-cycle amorphization control as a practical design lever.
Highlights
• Operando XRD shows ≈ 95% Si amorphization in the first cycle of 30:70 SiGr anodes.
• Extensive Si amorphization progressively limits graphite utilization.
• Early-cycle Si transformation reshapes the Si–Gr utilization balance.