Graphite is a promising candidate for the anode material in lithium-ion batteries. To enhance its electrochemical performance, graphite can be rolled into spheres by impact milling and then coated with carbon by thermal vapor decomposition (TVD). The obtained spherical graphite samples show excellent performance in terms of high rate capacity, high reversible capacity, high coulombic efficiency and low irreversible capacity. The improvements in performance have been mainly correlated with the morphologies of carbon-coated spherical graphite.
A model of changes from mesophase to graphite during heat treatment
Capacitors and SuperCapacitors
Capacitors are devices that store electric charge on two conducting surfaces separated by an insulating gap – the larger the surface area of the capacitor, the greater its capacity to hold charge. Charging a capacitor requires electrical energy, which is recovered when the device is discharged. Supercapacitors, also known as electric double-layer capacitors or electrochemical capacitors, store more charge thanks to the double layer formed at an electrolyte–electrode interface when a voltage is applied. Although already used in applications such as mobile phones, these devices are currently limited by their relatively low energy storage density compared with batteries.
Researchers have discovered a new form of carbon produced by "activating" expanded graphite oxide. The material is full of tiny nanometre-sized pores and contains highly curved atom-thick walls throughout its 3D structure. The team has also found that the material performs exceptionally well as an electrode material for supercapacitors, allowing such energy-storage devices to be used in a wider range of applications.