Sealing porous carbon via surface-initiated polymerization achieves low-surface-area Si-C microparticles for Li-ion batteries

Porous Si-carbon composite architecture represents an effective design for lithium-ion batteries (LIBs) anodes. However, the high specific surface area (SSA) greatly negates cell initial Coulombic efficiency (ICE), and the function of porous carbon is challenged by practical conditions such as calendaring and high-mass-loading cycling. Here, we report a crosslinked conductive polymer layer as sealing layer for porous Si-C particles to enable high ICE and stable cycling of densified Si-anodes. A surface-initiated polymerization was adopted to form a conformal polymeric skin that can greatly lower the SSA and improve ICE of porous Si-C particles (94.8 vs. 5.7 m2/g, and 77.3% vs. 84.4%). The "sealed" Si-C particle maintains desirable intraparticle porosity to digest the volume changes during Li insertion, while the polymeric skin is key to shield off electrolyte penetration into the particles interior and to mechanically package the porous secondary particles throughout calendaring and cycling. The Si-C graphite mixtures anode (650 mAh/g) retains 70.8% capacity after 500 cycles. Adopting high-mass-loading NCM622, the full cell with stringent electrode metrics (anode at 1.2 g/cm3, NCM622 at 3.1 g/cm3, 3.4 mAh/cm2) demonstrates 65.9% capacity retention after 100 cycles. This study opens up a pathway to produce low-SSA porous anodes for practical LIBs.