Confined disproportionation of SiOx enabled by short-duration low-temperature carbonization and mechanical milling for high-performance silicon-based lithium-ion battery anodes

Silicon monoxide (SiO x , 0 < x  < 2) is a promising next-generation anode for lithium-ion batteries owing to its high theoretical capacity and the in situ formation of buffering Li 2 O and lithium silicate matrices that mitigate volume expansion. However, conventional high-temperature carbonization promotes excessive disproportionation of SiO x into electrochemically active Si and inert SiO 2 , which simultaneously coarsens nano-Si grains and consumes the active phase, leading to capacity loss and structural deterioration. Here, a confined-disproportionation strategy combining short-duration low-temperature carbonization (600 °C, 5 min) with subsequent high-energy ball milling is reported. The brief thermal step rapidly carbonizes the pitch coating while preserving an amorphous SiO x framework, and the milling step disperses the SiO@C particles into a graphite scaffold and triggers a localized, in situ disproportionation that introduces a controlled fraction of crystalline Si. The resulting SiO@C–graphite composite delivers a reversible capacity of 573 mAh g −1 after 500 cycles at 0.5C and 494 mAh g −1  at 1 C (capacity retentions of 95.5% and 94.8%, respectively) at 25 °C, and retains 748 and 786 mAh g −1 after 150 cycles at 45 and 60 °C. In situ XRD and quantitative kinetic analysis reveal that lithium storage proceeds through a reversible amorphous evolution of SiO x coupled with staged graphite intercalation, with surface-controlled pseudocapacitance contributing up to ∼90% of the capacity at 1.0 mV s −1 . This work demonstrates that decoupling thermal carbonization from disproportionation through a thermal–mechanical sequential design provides a generalizable route to balance amorphous robustness and crystalline activity in SiO x -based anodes.