One‐Step Synthesis of Si–Graphene Heterostructures via in‐Flight Gas‐Phase Mixing for High‐Capacity Silicon‐Rich Anodes

The deliberate assembly of heterostructures has emerged as a powerful strategy for electrochemical energy storage, where integration of complementary components enables synergistic performance gains. Moving beyond serial production of individual components and their subsequent liquid-phase assembly, we report a one-step, continuous gas-phase synthesis of high-purity silicon/few-layer graphene heterostructures by coupling microwave-plasma and hot-wall reactors. This in-flight assembly yields exceptionally pure amorphous Si uniformly integrated within conductive few-layer graphene, eliminating liquid-phase processing. Electrochemical performance exhibits a non-monotonic dependence of performance on few-layer graphene content: capacity and cycle life maximize at an intermediate 15 wt.% few-layer graphene, attributed to a percolated, strain-buffering few-layer graphene network that preserves electrical contact while minimizing inactive mass. The optimized heterostructure delivers specific capacities of ~2800 mAh g⁻¹_Si+FLG (0.05 C) and ~1400 mAh g⁻¹_Si+FLG after 100 cycles at 1 C, outperforming other Si/graphene systems reported in the literature under similar conditions. These results highlight gas-phase self-assembly as a scalable route to integrate 0D/2D nanostructures into high-capacity, long-life Li-ion anodes and establish a new performance benchmark for low-carbon-fraction Si/graphene composites.