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.