Sub-10 nm SnO2/Fe3O4/graphene nanosheets: Nanocatalysis to improve initial coulombic efficiency for lithium storage

Abstract

SnO2 is considered as an ideal substitute for graphite anode in lithium ion batteries since it has a four-fold theoretical capacity and low discharge potential. However, the poor transformation from Sn/Li2O to SnO2 due to sluggish kinetic results in a low initial Coulombic efficiency (ICE) of only 52.4%. At the same time, the intrinsically low ionic/electronic conductivity and high volume swings during charge/discharge processes seriously limit its long-term stability and high-rate performance. Different from traditional strategies, nanotechnology and composite, this work prepares sub-10 nm SnO2/Fe3O4/graphene nanosheets with controllable Fe/Sn atomic ratios through a hydrothermal method to study the nanocatalytic effect of Fe on improving the ICE. The component, structure and lithium storage performance of the samples, with varied Sn/Fe ratios, are systematically investigated. The sample with Sn/Fe of 1.31 shows a high ICE of 70.9% (considering the negative effect of huge solid/electrolyte interface films, this value is quite high) and an outstanding reversible capacity of 1048 mA h g−1 after 800 cycles at the current density of 200 mA g−1. The valence states of Sn and Fe before and after cycling are analyzed by X-ray photoelectron spectroscopy. Our findings offer new evidence for electrochemical catalytic conversion mechanism for lithium storage and highlight opportunities to boost the energy storage capability of the fourth main group compounds.