The development of super electrically conductive Si material with polymer brush acid and emeraldine base and its auto-switch design for high-safety and high-performance lithium-ion battery

Silicon is a promising anode material that can considerably increase the energy density of lithium-ion batteries (LIBs) owing to its high theoretical capacity and low cost. However, its huge volume changes and low electrical conductivity damage the structural stability of the material and reduce the reaction kinetics, thus resulting in poor electrochemical reversibility and rate performance. In this study, the super electrically conductive (SEC) Si material was developed by using a polymer brush and emeraldine base on the surface of each Si particles to improve the kinetics and maintain the stability of electrochemical properties. The results revealed that compared with the bare Si electrode, the Si-SEC electrode enhanced electrical conductivity by 104 times, reduced 75% of charge transfer resistance and the direct contact of electrolytes, prevented volume changes with high mechanical properties, and supported high diffusivity of the interfacial layer. The Si-SEC electrode delivered an initial capacity of 2650.0 mAh g−1 with a high columbic efficiency of 86.3%. After 300 cycles, the capacity remained at 1850.0 mAh g−1 with high cycle retention. The rate performance of the SEC-Si electrode was excellent for 577 mAh g−1 at 4C without requiring carbon/graphite composites and any electrolyte additives. Several techniques such as scanning electron microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, operando transmission X-ray microscopy, and operando X-ray diffraction were employed to investigate the effects of the SEC layer on Si. The SEC layer also provides auto-switch function by neutralizing the local pH of the electrode surface, which significantly increases the interfacial impedance to terminate current. This new designed Si material can be used to enhance the life, energy density, and safety issue of LIBs.