Largely Improved Battery Performance Using a Microsized Silicon Skeleton Caged by Polypyrrole as Anode.

Various architectures with nanostructured silicon have demonstrated promising battery performance while posing a challenge in industrial production. The current ratio of silicon in graphite as anode is less than 5 wt %, which greatly limits the battery energy density. In this article, we report a scalable synthesis of a large silicon cage composite (micrometers) that is composed of a silicon skeleton and an ultrathin (<5 nm) mesoporous polypyrrole (PPy) skin via a facile wet-chemical method. The industry available, microsized AlSi alloy was used as precursor. The hollow skeleton configuration provides sufficient space to accommodate the drastic volume expansion/shrinkage upon charging/discharging, while the conductive polymer serves as a protective layer and fast channel for Li+/e- transport. The battery with the microsilicon (μ-Si) cage as anode displays an excellent capacity retention upon long cycling at high charge/discharge rates and high material loadings. At 0.2 C, a specific capacity of ∼1660 mAh/g with a Coulombic efficiency (CE) of ∼99.8% and 99.4% was achieved after 500 cycles at 3 mg/cm2 loading and 400 cycles at 4.4 mg/cm2 loading, respectively. At 1.0 C, a capacity as high as 1149 mAh/g was retained after 500 cycles with such high silicon loading. The areal capacity of as high as 6.4 mAh/cm2 with 4.4 mg/cm2 loading was obtained, which ensures a high battery energy density in powering large devices such as electric vehicles.