No abstract

Si is regarded as one of the most promising anode materials for next generation Li-ion batteries, but it usually exhibits poor cycling stability due to the low intrinsic electrical conductivity and huge volume change induced by the alloying reaction with Li. In this study, we present a double protection strategy by fabricating graphene/carbon-coated Si nanoparticle hybrids to improve the electrochemical performance of Si in Li storage. The Si nanoparticles are wrapped between the graphene and the amorphous carbon coating layers in the hybrids. The graphene and the amorphous carbon coating layers work together to effectively suppress the aggregation and destruction of Si nanoparticles, keeping the overall electrode highly conductive and active in Li storage. As a result, the produced graphene/carbon-coated Si nanoparticle hybrids exhibit outstanding reversible capacity for Li storage (902 mAh g(-1) after 100 cycles at 300 mA g(-1)). This work suggests a strategy to improve the electrochemical performance of Li-ion batteries by using graphene as supporting sheets for loading of active materials and carbon as the covering layers.

Improving the Li storage properties of a Si negative electrode is of great significance for Li-ion batteries. A major challenge is to fabricate Si-based active materials with good electronic conduction and structural integrity in the process of discharging and charging. In this study, novel Si nanoparticles-graphene composites have been synthesized by hybrid electrostatic assembly between positively charged aminopropyltriethoxysilane modified Si nanoparticles and negatively charged graphene oxide, followed by thermal reduction. Commercially available Si nanoparticles are well embedded and uniformly dispersed into the graphene sheets, and the typically wrinkled graphene sheets form a network and cover the highly dispersed Si nanoparticles well. No any obvious aggregation of the Si nanoparticles can be found and many nanospaces exist around the Si nanoparticles, which provide buffering spaces needed for volume changes of Si nanoparticles during insertion/extraction of Li. High capacity and long cycle life (822 mA h g(-1) after 100 cycles at a current density of 0.1 A g(-1)) have been realized in the novel Si nanoparticles-graphene composites for Li-ion batteries. The excellent electrochemical performance is ascribed to the uniform distribution of Si nanoparticles and graphene, which effectively prevents aggregation and pulverization of Si nanoparticles, keeps the overall electrode highly conductive, and maintains the stability of the structure.

Direct sampling mass spectrometry enables high-performance clinical analysis, such as imaging, drug monitoring and point-of-care testing.