Hierarchical strain-adaptive silicon-carbon microspheres for durable high-density lithium-ion anodes.

Micro-sized silicon (μSi) is a promising anode for next-generation high-energy-density lithium-ion batteries (LIBs) due to its high capacity and excellent tap density. However, its severe volume fluctuations induce mechanical degradation and rapid capacity fading. Here, we develop a strain-adaptive design to construct hierarchical Si/graphene composite microspheres (DSMG@C) via scalable spray-drying and chemical vapor deposition (CVD). The architecture integrates an internal graphene scaffold, dual-scale (micro/nano) silicon, and a conformal ∼10 nm graphitic carbon shell, enabling an internal compliant framework with distributed microvoids coupled with an external conformal carbon confinement layer. The graphene-based framework and distributed microvoids accommodate local deformation, while nano-Si serves as an adaptive interstitial filler to densify contacts and disperse stress. The nano-Si disperses stress and fills voids to enhance densification, while the carbon shell reinforces mechanical stability and interfacial robustness. As a result, the DSMG@C anode delivers a high reversible capacity of 1062.8 mAh g-1 after 500 cycles at 1 A g-1, an initial coulombic efficiency of 90.8%, and a superior volumetric capacity owing to its 1.22 g cm-3 compacted density. Kinetic and mechanical analyses confirm its fast ion/electron transport and durable structural integrity. Full cells paired with LiFePO4 exhibit a discharge capacity of 123.4 mAh g-1 at 1 C after 200 cycles with an initial coulombic efficiency (ICE) of 92.7%, demonstrating strong practical potential. This work offers an effective strategy for designing high-performance Si-based anodes through multiscale structural engineering.