Abstract
Graphene nanosheets (GNS) with attached MnOx nanoparticles are studied in regard to their structure and morphology. The relationship between the lithium storage performances and GNS contents as well as manganese valency was investigated. Experimental results showed that the specimen with 44 wt% GNS and high content of MnO delivered high reversible capacity (over twice of that in graphitic carbon anode), good cycling stability (0.8% fading per cycle), and high rate capability (67% at the 800 mA/g), which are dramatically better than pure Mn3O4. The improvement is attributed to the presence of GNS which provides continuous networks for fast electronic conduction and mechanical flexibility for accommodating the large volume change. The MnOx/GNS hybrid material has the added advantages over pure GNS, benefiting from its lithium storage potential of around 0.5 V which not only ensures high rate capability but also reduces the risk of metallic lithium formation with its safety hazard.
Highlights
Nanoparticles of transition metal oxides (MOx, where M is Co, Fe, Ni, or Cu) have recently received much attention as alternative anode materials for Li-ion batteries
The reverse reaction is thermodynamically unfavorable and the electrochemical kinetics is sensitive to the activity of Li2O [4,5,6], Tarascon et al has discovered that reducing the particle size of MOx to nanometer scale can enhance the electrochemical activities of Li2O and metal particles driving the reversible occurrence of the formation/decomposition reaction [1, 2]
Graphene nanosheets (GNS), known for their superior electrical conductivities and high surface areas, have been added to MO [12,13,14,15,16,17,18,19,20,21,22,23] forming 3D nanostructured MO-GNS hybrids which led to the improvement of lithium storage performances
Summary
Nanoparticles of transition metal oxides (MOx, where M is Co, Fe, Ni, or Cu) have recently received much attention as alternative anode materials for Li-ion batteries. The Co3O4-graphene hybrid material delivered a reversible capacity around 800 mAh/g at the 0.2 C rate with a columbic efficiency of 97% after 42 cycles. There are emerging reports on improving the reversible capacity, cycle life, and rate capability via dispersing MnOx nanoparticles in GNS [19,20,21,22,23]. We will report the lithium storage characteristics in GNS/nanoMnOx hybrid materials with similar morphologies but different contents of GNS and low-valent Mn component. The objective of this study is to experimentally clarify the impacts of the GNS content and manganese valency on the lithium storage characteristics in terms of Coulombic efficiency, capacity, cycle life, and rate capability
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