Ball milling is a widely used method to produce graphene and other two-dimensional (2D) materials for both industry and research. Conventional ball milling generates strong impact forces, producing small and thick nanosheets that limit their applications. In this study, a viscous solvent-assisted planetary ball milling method has been developed to produce large thin 2D nanosheets. The viscous solvent simultaneously increases the exfoliation energy (E e) and lowers the impact energy (E i). Simulations show a giant ratio of η = E e/E i, for the viscous solvent, 2 orders of magnitude larger than that of water. The method provides both a high exfoliation yield of 74%, a high aspect ratio of the generated nanosheets of 571, and a high quality for a representative 2D material of boron nitride nanosheets (BNNSs). The large thin BNNSs can be assembled into high-performance functional films, such as separation membranes and thermally conductive flexible films with some performance parameters better than those 2D nanosheets produced by chemical exfoliation methods.

High theoretical capacitance of MnO2 nanoparticles were successfully electrodeposited on the conductive graphene/activated carbon (GN/AC) composite film, and the urchin type MnO2 microspheres were controlled by adjusting the electro-deposition reaction times. The GN/AC/MnO2-1200s composite electrodes exhibited a maximum specific capacitance of 1231 mF/cm2 (MnO2 loading mass of 7.65 mg/cm2 and the mass specific capacitance of 123 F/g) at a current density of 0.5 mA/cm2. The assembled flexible solid-state symmetric supercapacitor had a good mechanical flexibility (about 88.6% of its original capacitance after 500 bending times) and prominent cycling stability (about 82.8% retention in capacitance over 10000 cycles). More importantly, the device could possess a maximum energy density of 0.27 mW h/cm3 and a maximum power density of 0.02 W/cm3. These results well demonstrate a great potential for applications of GN/AC/MnO2 composite electrodes in flexible energy storage devices.

A ternary composite of graphene/activated carbon/polypyrrole (GN/AC/PPy) used as an electrode active material for supercapacitors has been synthesized via vacuum filtration and anodic constant current deposition methods. The ACs sandwiched between GN sheets can be used as flexible substrates for PPy nanoparticles, and the microscopic morphologies and electrochemical performances of GN/AC/PPy electrodes were synthesized and designed through regulating different deposition current densities and deposition times. The GN/AC/PPy 15 -200 s electrode exhibits a maximum areal specific capacitance of 906 mF cm À2 with a PPy loading mass of 2.75 mg cm À2 (specific capacitance of 178 F g À1 ) at a current density of 0.5 mA cm À2 . Its capacitance retention still remained at 64.4% after 5000 charge-discharge cycles and 83.6% after 500 stretching-bending cycles at a current density of 3 mA cm À2 . The flexible, free-standing and binder-free GN/AC/PPy electrodes have a broad prospect in flexible energy storage devices. Fig. 4 (a) GCD curves of all samples at the current density of 1 mA cm À2 ; (b) CV curves of samples at the scan rate of 10 mV s À1 ; (c) areal specific capacitances of all samples at different current densities; (d) Nyquist plot of all samples.This journal is

In this paper, litchi-like microspheres structures of NiCo 2 Se 4 @carbon microspheres (NCSC) hybrids were successfully synthesized via a simple two-step hydrothermal method. The effects of the content of NiCo 2 Se 4 on the structure of NCSC composites are investigated. The morphology and nanostructure of the as-obtained NCSC hybrids were examined by XRD, XPS, FESEM and TEM. The results indicate that the carbon microspheres (CM) were uniformly covered with NiCo 2 Se 4 and with the increase of NiCo 2 Se 4 content, the superficies of NCSC also exhibits homogeneous rough nanoparticles and regular spheres connect with each other. Meanwhile, the electrochemical tests indicate a suitable mass ratio of NiCo 2 Se 4 and carbon microspheres (2:3) showed the highest specific capacitance value (1394 F g −1 at the current density of 0.5 A g −1 , 766 F g −1 even at the current density of 50 A g −1 ), excellent rate property and outstanding cycling stability (80.093% of the initial value after 10000 cycles at the current density of 5 A g −1 ). Benefiting from the above integrated advantages, asymmetric supercapacitors (ASC) fabricated with NCSC composites as the positive electrode and porous activated carbon as negative electrode operating at the voltage window of 0-2 V deliver a high energy density of 101 Wh kg −1 at a power density of 0.749 kW kg −1 , with the specific capacitance retention of 81.095% after 10000 cycles at the current density of 10 A g −1 , superior to most of reported supercapacitors.