Sieving pores: stable,fast alloying chemistry of Si -electrodes in Li-ion batt

Summary

Synthesis and characterization of the SSC materialsThe SSC materials were prepared through a two-step chemical vapor deposition (CVD) process. First, Si was synthesized by the thermal decomposition of silane (SiH4) gas at 450 °C on porous carbons (PCs). This process led to the embedding of amorphous Si along the micropore walls of the PCs, resulting in the formation of a Si/C (SC) negative electrode with an open-pore structure38,39. Subsequently, acetylene (C2H2) gas was thermally decomposed at 600 °C to deposit sieving carbon onto the SC, effectively narrowing the pore entrances and forming the sieving-pore structure40 (Fig. 2a). Additionally, since the pyrolysis of C2H2 is a diffusion-controlled process, the deposition of C2H2 involves gradual gas diffusion from the pore entrance to the pore body. As a result, the rapid pyrolysis of C2H2 at 600 °C tends to occur at the pore entrances rather than the pore body, ultimately forming sieving-pore structures. Notably, the pore size distribution of PCs is crucial for the pyrolysis behavior of SiH4 and C2H2. CVD technology faces challenges in tightening the entrance size of mesopores and macropores to a sieving-pore structure due to the small molecular kinetic diameters of SiH4 and C2H2, while ultra-micropores (<1 nm) are easily fully occupied by the pyrolyzed Si or sealed by the deposited carbon, rendering them incapability of buffering or sieving (Fig. 2a). Therefore, the used PCs in this work were customized by pre-coating them with a layer of carbon to adjust the pore size distribution for better compatibility with Si and carbon deposition40. This SSC material can be fabricated on a large scale with an abundant source material supply and simple CVD technology (Supplementary Note 1). Supplementary Fig. 1 shows the 20 kg product of SSC materials per batch, demonstrating the potential for fabrication scalability and reproducibility in terms of material properties to electrochemical performance (Supplementary Note 2).Fig....