Oxidative Pyrolysis of Si/Polyacrylonitrile Composites As an Unconventional Approach to Fabricate High Performance Lithium Ion Battery Negative Electrodes

Abstract

High performance Si/polyacrylonitrile (PAN) composite negative electrodes are fabricated by a robust process of oxidative pyrolysis at a temperature between 250 and 400oC. Multiple techniques, including XRD, SEM, EDX, TGA, XPS, EIS, Raman, TEM, and nanoindentation, are employed to investigate the structural, chemical, and mechanical properties of the Si/PAN composite electrodes before and after oxidative pyrolysis. With increasing temperature, oxidation, dehydration, aromatization, and intermolecular crosslinking take place in PAN, resulting in a stable cyclized structure which functions as both a binder and a conductive agent in the Si/PAN composite electrodes. Meanwhile, PAN reacts with oxygen, forming volatile products and producing progressively porous Si/PAN composites with increasing temperature. With a Si mass loading of 1 mg/cm2, a discharge capacity of ~1600 mAh/g at the 100th cycle is observed from the 400oC treated Si/PAN composite electrode when cycled at a rate of C/3. This 400oC treated electrode also shows good rate capability. It exhibits a specific discharge capacity of ~500 mAh/g at 3C compared to the nearly zero capacity for those treated at lower temperatures. This facile method of synthesizing Si-based composite negative electrodes can potentially be applied to other Si/polymer systems for further increasing the power/energy density of lithium ion batteries.