Iron(III) oxide-graphene sheet-on-sheet nanocomposite shows high performance as Li-ion battery anode material
|High-rate cycling performances of Fe2O3-graphene sheet-on-sheet composite. Kan and Wang. Click to enlarge.|
Researchers from Shanghai University have synthesized Fe2O3-graphene sheet-on-sheet sandwich-like nanocomposites that, when used as an anode for Li-ion battery, shows a high reversible capacity of 662.4 mAh g−1 after 100 cycles at 1000 mA g−1. An open access paper on their work is published in the journal Scientific Reports.
The Fe2O3-graphene sheet-on-sheet composite has a surface area of 173.9 m2 g-1—more than two times as large as that of Fe2O3-graphene particle-on-sheet composite (81.5 m2 g−1).
|Cycling performance of Fe2O3 based electrodes at 0.1 C. Kan and Wang. Click to enlarge.|
The team grew Fe2O3 nanosheets and nanoparticles on graphene by simply varying reaction solvents in a facile solvothermal/hydrothermal preparation. The Fe2O3 nanosheets were then uniformly dispersed among graphene nanosheets, forming a unique sheet-on-sheet nanostructure. Due to the structure affinity between two types of two-dimensional nanostructures, graphene nanosheets are separated better by Fe2O3 nanosheets compared to nanoparticles and their agglomeration is largely prevented.
The researchers attributed the substantially improved cycling performance to the unique structure affinity between Fe2O3 nanosheets and graphene nanosheets, which offers complementary property improvement.
Graphite has been widely used as an anode material for commercial Li-ion batteries with a low theoretical specific capacity (372 mAh g−1). In recent years, metal oxides such as Fe2O3, NiO, CuO and SnO2 have been the focus of anode materials for Li-ion battery due to the increasing demand for high energy storage. These metal oxides electrodes have shown much higher Li-ion storage capacities than that of commercial graphite anodes. Among these oxides, Fe2O3 is a promising anode material because of low cost, simple manufacturing process, wide range of sources, environmental friendliness and the most important factor, a large theoretical specific capacity (1007 mAh g−1). However, their cycling performances are not satisfactory because partial pulverization and electrode cracking may take place upon repetitive cycling reactions between Fe2O3 and Li ions.
Various carbon materials have been attempted to be composited with high-capacity metal oxides to improve their electrical contact and structure stability during cycling. Graphene nanosheet (GNS), a flat monolayer of sp2-bonded carbon atoms, has been one of the most popular research hotspots. Its high electrical conductivity, large specific surface area and highly flexible and stable structure are also desirable for Li-ion storage applications. Recently, various metal oxides-GNS nanocomposites have been reported as promising anode materials for Li-ion batteries with substantially improved electrochemical performances. It is known that the electrochemical properties of nanostructured anode materials are dependent on their morphology and size. Therefore Fe2O3-based anode materials have been synthesized with a variety of Fe2O3 morphologies such as nanoparticle, nanotube, nanoflake, nanorod, nanodendrite, nanodisk, nanorice, and nanospindle.
In this work, a new Fe2O3-graphene structure, namely sheet-on-sheet nanostructure, was prepared by a solvothermal method.… The specific capacities and cycling performances of Fe2O3-graphene sheet-on-sheet composite were found to be much better than pristine Fe2O3 nanosheets and Fe2O3-graphene particle-on-sheet composite, especially at high rates.—Kan and Wang
To explore the Li-ion storage properties of Fe2O3-graphene composites, the team mixed sheet-on-sheet and particle-on-sheet Fe2O3-graphene composites, carbon black, and polyvinyl difluoride (PVDF) at the weight ratio of 8:1:1 as working electrodes. The researchers found that the sheet-on-sheet composite has a better electrochemical activity due to larger surface area and shorter diffusion route for lithium insertion and extraction reactions.
Fe2O3-graphene sheet-on-sheet, Fe2O3-graphene particle-on-sheet, Fe2O3 nanosheet, Fe2O3 nanoparticle and bare graphene exhibited initial discharge capacities of 1652.8, 1421.7, 1140.8, 1279.3, 1413.3 mAh g−1 and charge capacities of 1074.9, 890.4, 812.2, 901.6, 863.4 mAh g−1 respectively.
Notably, the charge capacity (1074.9 mAh g−1) of Fe2O3-graphene sheet-on-sheet composite is slightly larger than the theoretical capacity (1007 mAh g−1) of Fe2O3. This may be attributed to additional storage of Li-ions in the defects or micro-pores of the sheet-on-sheet composite induced by partial insertion of Fe2O3 into graphene.—Kan and Wang
Jin Kan and Yong Wang (2013) “Large and fast reversible Li-ion storages in Fe2O3-graphene sheet-on-sheet sandwich-like nanocomposites,” Scientific Reports 3, Article number: 3502 doi: 10.1038/srep03502