Carbon/Polymer Bilayer-Coated Si-SiO x Electrodes with Enhanced Electrical Conductivity and Structural Stability.

Si-based electrodes offer exceptionally high capacity and energy density for lithium-ion batteries (LIBs), but suffer from poor structural stability and electrical conductivity that hamper their practical applications. To tackle these obstacles, we design a C/polymer bilayer coating deposited on Si-SiO micro-particles. The inner C coating is used to improve electrical conductivity. The outer C-nanoparticle-reinforced polypyrrole (CNP-PPy) is a polymer matrix composite that can minimize the volumetric expansion of Si-SiO and enhance its structural stability during battery operation. Electrodes made of such robust Si-SiO@C/CNP-PPy micro-particles exhibit excellent cycling performance: 83% capacity retention (794 mAh g) at 2 C rate after over 900 cycles for a coin-type half cell, and 80% capacity retention (with initial energy density of 308 Wh kg) after over 1100 cycles for a pouch-type full cell. By comparing the samples with different coatings, an in-depth understanding of the performance enhancement is achieved, i.e., the C/CNP-PPy with crosslink bondings formed in the bilayer coating plays a key role for the improved structural stability. Moreover, a full battery using the Si-SiO@C/CNP-PPy electrode successfully drives a car model, demonstrating a bright application prospect of the C/polymer bilayer coating strategy to make future commercial LIBs with high stability and energy density.