Silicon Microreactor as a Fast Charge, Long Cycle Life Anode with High Initial Coulombic Efficiency Synthesized via a Scalable Method

Applications of silicon as a high-performance anode material have been impeded by its low intrinsic conductivity and huge volume expansion (>300%) during lithiation. To address these problems, nano-Si particles along with conductive coatings and engineered voids are often employed, but this results in high-cost anodes. Here, we report a scalable synthesis method that can realize high specific capacity (∼800 mAh g–1), ultrafast charge/discharge (at 8 A g–1 Si), and high initial Coulombic efficiency (∼90%) with long cycle life (1000 cycles) at the same time. To achieve 1000 cycle stability, micron-sized Si particles are subjected to high-energy ball milling to create nanostructured Si building blocks with nano-channel-shaped voids encapsulated inside a nitrogen (N)-doped carbon shell (termed as Si microreactor). The nanochannel voids inside a Si microreactor not only offer the space to accommodate the volume expansion of Si but also provide fast pathways for Li-ion diffusion into the center of the nanostructured Si core and thus ultrafast charge/discharge capability. The porous N-doped carbon shell helps to improve the conductivity while allowing fast Li-ion transport and confining the volume expansion within the Si microreactor. Submicron-sized Si microreactors with a limited specific surface area (35 m2 g–1) afford sufficient electrode/electrolyte interfacial area for fast lithiation/delithiation, leading to the specific capacity ranging from ∼800 to 420 mAh g–1 under ultrafast charging conditions (8 A g–1), but not too much interfacial area for surface side reactions and thus high initial Coulombic efficiency (∼90%). Since Si microreactors with superior electrochemical properties are synthesized via an industrially scalable and eco-friendly method, they have the potential for practical applications in the future.