PVD customized 2D porous amorphous silicon nanoflakes percolated with carbon nanotubes for high areal capacity lithium ion batteries†
Integrating nanostructured Si materials into a freestanding membrane with high mechanical strength and a continuous conductive network is a promising but challenging route to achieve high energy density lithium ion batteries (LIBs). Herein, we demonstrate that physical vapor deposition (PVD) customized two-dimensional (2D) porous amorphous Si nanoflakes, reinforced with ultralong multiwalled carbon nanotubes (MWCNTs), can be integrated into a freestanding film electrode with high volumetric/areal capacity and energy density. Owing to the special 1D/2D nanotube/nanoflake entangled architecture, the freestanding Si–MWCNT film is highly porous, electrically conductive, and mechanically robust. Moreover, the interconnected MWCNT network functions as a spacer to prevent adjacent Si nanoflakes from restacking, and the 2D porous Si nanoflakes provide a large electrode/electrolyte contact area, both of which enable fast Li+ transportation. Due to the existence of abundant pores in both amorphous Si nanoflakes (mesopores) and Si–MWCNT electrodes (macropores), the volume change is significantly suppressed, resulting in stable electrodes with tunable mass loadings from 1.7 to 5.4 mg cm−2. When directly used as an anode, the Si–MWCNT film with a mass loading of 2.9 mg cm−2 exhibits a high specific capacity of 1556 mA h g−1 and an areal capacity of 4.5 mA h cm−2. Remarkably, when this freestanding anode is coupled with a commercial LiNi1/3Co1/3Mn1/3O2 (NCM) cathode, the full battery delivers a high gravimetric energy density of ∼484.7 W h kg−1. This study offers a promising and general route to design freestanding electrodes by percolating CNTs with PVD generated 2D porous nanoflakes and provides significant insights for developing high energy battery systems.