Abstract:

With the widespread use of mobile electronic devices and increasing demand for electric energy storage in the transportation and energy sectors, lithium-ion batteries (LIBs) have become a major research and development focus in recent years. The current generation of LIBs use graphite as the anode material, which has a theoretical capacity of 372 mAh·g^-1. Tin-based materials are considered promising anode materials for next-generation LIBs because of their favorable working voltage and unsurpassed theoretical specific capacity. However, overcoming the rapid storage capacity degradation of tin caused by its large volumetric changes (>200%) during cycling remains a major challenge to the successful implementation of such materials. In this paper, SnO₂ nanoparticles with a diameter of 2-3 nm were used as active materials in LIB anodes and a threedimensional (3D) graphene hydrogel (GH) was used as a buffer to decrease the volumetric change. Typically, SnCl4 aqueous solution (18 mL, 6.4 mmol·L^-1) and graphene oxide (GO) suspension (0.5% (w, mass fraction), 2 mL) were mixed together via sonication. NaOH aqueous solution (11.4 mmol·L^-1, 40 mL) was slowly added and then the mixture was stirred for 2 h to obtain a stable suspension. Vitamin C (VC, 80 mg) was then added as a reductant. The mixture was kept at 80℃ for 24 h to reduce and self-assemble. The resulting black block was washed repeatedly with distilled deionized water and freeze-dried to obtain SnO₂-GH. In this composite, GH provides large specific surface area for efficient loading (54% (w)) and uniform distribution of nanoparticles. SnO₂-GH delivered a capacity of 500 mAh·g^-1 at 5000 mA·g^-1 and 865 mAh·g^-1 at 50 mA·g^-1 after rate cycling.This outstanding electrochemical performance is attributed to the 3D structure of GH, which provides large internal space to accommodate volumetric changes, an electrically conducting structural porous network, a large amount of lithium-ion diffusion channels, fast electron transport kinetics, and excellent penetration of electrolyte solution. This study demonstrates that 3D GH is a potential carbon matrix for LIBs.

Key words: Graphene hydrogel, SnO₂, Lithium-ion battery, Anode, Three-dimension