Abstract
Supercritical CO2 (scCO2) is often used to prepare graphene/metal oxide nanocomposite anodes for high performance lithium-ion batteries (LIBs) by the assisted solvothermal method due to its low viscosity, high diffusion, zero surface tension and good surface wettability. However, the formation mechanism of metal oxides and the combination mechanism between metal oxides and graphene in this system are superficial. In this work, a cobalt monoxide/graphene (CoO/G) nanocomposite is fabricated via the scCO2 assisted solvothermal method followed by thermal treatment. We elucidate the mechanism that amorphous intermediates obtain by the scCO2 assisted solvothermal method, and then ultrafine CoO nanoparticles are crystallized during the heat treatment. In addition, scCO2 can promote CoO to be tightly fixed on the surface of graphene nanosheets by interfacial chemical bonds, which can effectively improve its cycle stability and rate performance. As expected, the CoO/G composites exhibit higher specific capacity (961 mAh g−1 at 100 mA g−1), excellent cyclic stability and rate capability (617 mAh g−1 after 500 cycles at 1000 mA g−1) when applied as an anode of LIB.
Highlights
With the increasing demand for recyclable energy, electrochemical energy storage devices that can effectively store the renewable energy sources of unstable output are in great demand, where lithium-ion batteries (LIBs) have been recognized as one of the most promising electrochemical energy storage devices [1,2]
While for the one prepared with Supercritical CO2 (scCO2), no crystalline diffraction peaks are found, suggesting an amorphous nature, which may be related with amorphous coordination complex containing CO3 2−
Average crystalline grain sizes are calculated as 8.5 and 11.5 nm for cobalt monoxide/graphene (CoO/G)-sc and Cobalt monoxide (CoO)/G-a by applying Scherrer equation, suggesting that sample prepared with scCO2 has smaller grain size and crystallinity
Summary
With the increasing demand for recyclable energy, electrochemical energy storage devices that can effectively store the renewable energy sources of unstable output are in great demand, where lithium-ion batteries (LIBs) have been recognized as one of the most promising electrochemical energy storage devices [1,2]. Cobalt monoxide (CoO) has attracted increasing attention due to its high theoretical capacity (715 mAh g−1 ), highly reversible electrochemical reaction, low cost and high thermal stability [9]. The application of the CoO anode in LIBs is hampered by its poor cycling stability caused by large volume variation during the Li+ insertion/extraction, leading to electrode pulverization and electrical detachment from the current collector [10]. The mostly used paradigms to solve the above-mentioned problems are nano-sizing electrode particles combined with highly conductive buffer fillers [11,12]. Nano-sizing will lead to re-aggregation during cycling, which calls for tightly anchoring on the conductive substrate [13,14,15,16,17]. For the later strategy, hybridizing CoO with graphene facilitate electron transfer, and inhibit the volume expansion of CoO during charge/discharge
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