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

Abstract

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.