Prior vacuuming for supercritical fluid synthesis of SnO2/graphene nanocomposites with superior electrochemical Li+ storage performance

• Published in: Electrochimica acta 2018-12, Vol.292, p.951-959
• Main Authors: Xie, Jian-De, Li, Hui-Ying, Umesh, Bharath, Lee, Tai-Chou, Chang, Jeng-Kuei, Gandomi, Yasser Ashraf
• Format: Article
• Language: English
• Subjects: Anode; Composites; Li-ion battery; SnO2 nanoparticles; Supercritical CO2
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2018.09.084

Supercritical CO2 (SCCO2) fluid, exhibiting gas-like diffusivity, extremely low viscosity, and near-zero surface tension, is used to synthesize uniformly dispersed and tightly anchored SnO2 nanoparticles (a 3-nm diameter was achieved) on graphene nanosheets (GNSs). Usually, the conventional synthesis processes (in the absence of SCCO2) results in aggregated SnO2 clusters; whereas the technique described in this work eliminates this limitation. This study reveals the significance of two crucial factors (the SCCO2 pressure (i.e., fluid density) and the degassing step (i.e., vacuuming stage) in autoclave before injecting CO2) on the uniform distribution of the synthesized SnO2 nanoparticles on GNSs. Increasing the pressure leads to an increase in SCCO2 density (and viscosity), suppressing the transport of SnO2 precursors throughout the sample. On the other hand, vacuuming the autoclave before injecting CO2 improves the uniformity of SnO2 particle distributions. To assess the electrochemical performance of the synthesized nanoparticles, the specific capacity, rate capability, and cyclic stability were determined for various samples. A capacity of ∼787 mAh g−1 at 100 mA g−1 was achieved for an optimal configuration of the SnO2/GNS electrodes. The capacity retention was 60% when the charge‒discharge rate increased to 6000 mA g−1. Supercritical CO2 fluid with gas-like diffusivity, extremely low viscosity, and near-zero surface tension is used to synthesize uniformly dispersed and tightly anchored SnO2 nanoparticles (a 3-nm diameter is achievable) on graphene nanosheets, which is a potential anode for lithium-ion batteries. [Display omitted] •Supercritical CO2 fluid is used to synthesize uniform SnO2 particles on graphene.•This study reveals two key factors: pressure and degassing before injecting CO2.•The SnO2 nanoparticle with 3-nm diameter is achievable under an optimal condition.•The optimal SnO2/GNS electrode shows a capacity of ∼787 mAh g−1 at 100 mA g−1.•The battery retains 60% of this capacity when the rate increases to 6000 mA g−1.