Scalable Synthesis of Pitch-Coated Nanoporous Si/Graphite Composite Anodes for Lithium-Ion Batteries

Si/graphite composites have long been considered as one of the promising anodes for Li-ion batteries with high energy densities. However, the poor interfacial contact between Si and graphite and the low intrinsic ionic conductivity of Si seriously deteriorate the battery performance and greatly hinder their practical applications. Herein, we report the preparation of pitch pyrolytic carbon-coated nanoporous Si/graphite (NP-Si@C/Gr) composites via a facile chemical dealloying and pitch coating process. Nanoporous silicon (NP-Si) is prepared by chemical dealloying of commercial microsized Al-Si alloy. The porous structure is achieved by selectively removing Al. The NP-Si@C/Gr composite is then prepared by pitch coating and grinding mixed graphite. The carbon layer firmly coated on NP-Si, which not only helps to maintain great interface contact between Si and graphite but also enhances the conductivity of the composite. As a result, the reversible capacity of NP-Si@C/Gr is 764.2 mAh g-1 after 100 cycles, which far exceeds that of NP-Si/Gr (328.1 mAh g-1). It delivers a discharge capacity of 1165.1 mAh g-1 at 100 mA g-1 and can still recover to 1138.4 mAh g-1 when it returns to the initial state after experiencing cycles at high current densities. In addition, a full cell coupled with a LiFePO4 cathode gives a high discharge capacity of 98.7 mAh g-1 after 80 cycles at 0.5 C. Our finding provides new insights into the rational design of Si/graphite composite anodes for next-generation LIBs with high energy densities.