Silicon/graphite composite anode with constrained swelling and a stable solid electrolyte interphase enabled by spent graphite

Abstract

Motivated by attributes including environmental hazards and resource value, the recycling of the spent graphite has aroused increasing attention. Meanwhile, a silicon/graphite composite has been considered as a promising high-capacity anode for lithium-ion batteries. However, uniform dispersion and outperformed stability of silicon (Si) particles in the graphite matrix still remain a great challenge. Current solutions mainly focus on the design of Si nanostructures and the overall architecture of the silicon/graphite composite, while little attention has been paid to the graphite matrix. Herein, the Si/spent graphite (Si/SG) composite was prepared based on the recycling of SG. The SG was in situ modified during the battery cycling process and formed unique physicochemical properties. By spontaneously tuning the zeta potential, the electrostatic force integrated the Si nanoparticles within the SG matrix to restrain the volume strain upon lithiation/delithiation. Besides, defect-enriched and exfoliated SG can effectively enhance the electric conductivity, facilitating the electrochemical kinetics in the electrodes. What is more, the oxygen-containing functional groups on the SG could adjust the solid electrolyte interphase (SEI) component by generating more organic components to improve the mechanical toughness of the SEI layer. Consequently, the Si/SG composite electrode delivers a high initial discharge capacity of 1321.8 mA h g⁻¹ at 0.05 A g⁻¹ and stable cycle life with a capacity retention of 69% at 1 A g⁻¹ after 400 cycles. The proposed composite may provide some guidelines for improving the interface stability of the Si/graphite anode and simultaneously the high-value application of spent graphite.