Synthesis and Electrochemical Reaction of Tin Oxalate-Reduced Graphene Oxide Composite Anode for Rechargeable Lithium Batteries

Unlike for SnO₂, few studies have reported on the use of SnC₂O₄ as an anode material for rechargeable lithium batteries. Here, we first introduce a SnC₂O₄-reduced graphene oxide composite produced via hydrothermal reactions followed by a layer-by-layer self-assembly process. The addition of rGO increased the electric conductivity up to ∼10^-3 S cm^-1. As a result, the SnC₂O₄-reduced graphene oxide electrode exhibited a high charge (oxidation) capacity of ∼1166 mAh g^-1 at a current of 100 mA g^-1 (0.1 C-rate) with a good retention delivering approximately 620 mAh g^-1 at the 200th cycle. Even at a rate of 10 C (10 A g^-1), the composite electrode was able to obtain a charge capacity of 467 mAh g^-1. In contrast, the bare SnC₂O₄ had inferior electrochemical properties relative to those of the SnC₂O₄-reduced graphene oxide composite: ∼643 mAh g^-1 at the first charge, retaining 192 mAh g^-1 at the 200th cycle and 289 mAh g^-1 at 10 C. This improvement in electrochemical properties is most likely due to the improvement in electric conductivity, which enables facile electron transfer via simultaneous conversion above 0.75 V and de/alloy reactions below 0.75 V: SnC₂O₄ + 2Li⁺ + 2e^- → Sn + Li₂C₂O₄ + xLi⁺ + xe^- → Li_xSn on discharge (reduction) and vice versa on charge. This was confirmed by systematic studies of ex situ X-ray diffraction, transmission electron microscopy, and time-of-flight secondary-ion mass spectroscopy.

Mesoporous SnO2 Nanostructures of Ultrahigh Surface Areas by Novel Anodization

Here we report a novel type of hierarchical mesoporous SnO₂ nanostructures fabricated by a facile anodization method in a novel electrolyte system (an ethylene glycol solution of H₂C₂O₄/NH₄F) followed by thermal annealing at a low temperature. The SnO₂ nanostructures thus obtained feature highly porous nanosheets with mesoporous pores well below 10 nm, enabling a remarkably high surface area of 202.8 m²/g which represents one of the highest values reported to date on SnO₂ nanostructures. The formation of this novel type of SnO₂ nanostructures is ascribed to an interesting self-assembly mechanism of the anodic tin oxalate, which was found to be heavily impacted by the anodization voltage and water content in the electrolyte. The electrochemical measurements of the mesoporous SnO₂ nanostructures indicate their promising applications as lithium-ion battery and supercapacitor electrode materials.