The graphene nanosheet electrode with excellent high-rate performance and satisfactory cyclability is an ideal anode for sodium-ion batteries.

Pores and surface functional groups are endowed on graphene nanosheets (GNSs) to improve their electrochemical Na + storage properties. An optimal capacity of 220 mA g À1 is obtained (at a chargedischarge rate of 0.03 A g À1 ) in ethylene carbonate/diethyl carbonate mixed electrolyte containing 1 M NaClO 4 . Ex situ X-ray photoelectron spectroscopy and synchrotron X-ray diffraction techniques are employed to study the electrode charge storage mechanism. The results indicate that reversible surface redox reactions at the electrode surface are the predominant processes affecting charge storage in a potential range of 0.5-2.0 V (vs. Na/Na + ), whereas Na + intercalation/deintercalation between carbon layers occurs at lower potentials. When the charge-discharge rate was increased by >300 fold (to 10 A g À1 ), a capacity as high as 85 mA h g À1 is obtained, reflecting the excellent rate capability of the electrode. The physiochemical characteristics that affect the Na + storage performance are explored. A highly promising GNS anode for sodium-ion batteries is proposed.

Pores and surface functional groups are created on graphene nanosheets (GNSs) to improve supercapacitor properties in a butylmethylpyrrolidinium-dicyanamide (BMP-DCA) ionic liquid (IL) electrolyte. The GNS electrode exhibits an optimal capacitance of 330 F g(-1) and a satisfactory rate capability within a wide potential range of 3.3 V at 25 °C. Pseudocapacitive effects are confirmed using X-ray photoelectron spectroscopy. Under the same conditions, carbon nanotube and activated carbon electrodes show capacitances of 80 and 81 F g(-1) , respectively. Increasing the operation temperature increases the conductivity and decreases the viscosity of the IL electrolyte, further improving cell performance. At 60 °C, a symmetric-electrode GNS supercapacitor with the IL electrolyte is able to deliver maximum energy and power densities of 140 Wh kg(-1) and 52.5 kW kg(-1) (based on the active material on both electrodes), respectively, which are much higher than the 20 Wh kg(-1) and 17.8 kW kg(-1) obtained for a control cell with a conventional organic electrolyte.

Two-dimensional (2D) materials are promising anodes for Na-ion batteries owing to their unique architectures and tunable physiochemical properties. However, their high surface area requires sophisticated electrolyte/ electrode interface control to improve the charge−discharge efficiency and reversibility. This study uses microplasma-synthesized graphene nanosheets (MPGNSs) as a model 2D material. The effects of NaFSI concentration in an N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid (IL) electrolyte are systematically investigated. It is found that the chemical composition of the solid−electrolyte interphase depends on the electrolyte formulation, leading to distinct Coulombic efficiency, discharge capacity, rate capability, and cyclability of the MPGNS electrodes. The thermal reactivity of the sodiated MPGNSs (in terms of exothermic onset temperature and total heat released) upon heating is studied using differential scanning calorimetry. The IL electrolyte with a proper Na + fraction is superior to a conventional organic carbonate electrolyte for practical NIB applications.