Si/Graphite@C Composite Fabricated by Electrostatic Self-Assembly and Following Thermal Treatment as an Anode Material for Lithium-Ion Battery.

Commercial graphite anode has advantages such as low potential platform, high electronic conductivity, and abundant reserves. However, its theoretical capacity is only 372 mA h g-1. High-energy lithium-ion batteries have been a research hotspot. The Si anode has an extremely high specific capacity, but its application is hindered by defects such as large volume changes, poor electronic conductivity, and a small lithium-ion diffusion coefficient. Here, the Si/thermally reduced graphite oxide@carbon (Si/RGtO@C) composite was fabricated by electrostatic self-assembly followed by thermal treatment. The RGtO synergistic carbon coating layer can effectively compensate for the low electronic conductivity and buffer the volume expansion effect of the Si nanoparticles during charge/discharge cycles. The Si/RGtO@C anode demonstrated a significantly increased capacity compared to the RGtO. After 300 cycles, Si/RGtO@C kept a discharged capacity of 367.6 mA h g-1 at a high current density of 1.0 A g-1. The Si/RGtO@C anode shows an application potential for commercial high-energy lithium-ion batteries.

Fe2O3nanoparticles anchored on thermally oxidized MWCNTs as anode material for lithium-ion battery.

Thermally oxidized MWCNTs (OMWCNTs) are fabricated by a thermal treatment of MWCNTs at 500 °C for 3 h in an oxygen-containing atmosphere. The oxygen content of OMWCNTs increases from 1.9 wt% for MWCNTs to 8.3 wt%. And the BET specific surface area of OMWCNTs enhances from 254.2 m2g-1for MWCNTs to 496.1 m2g-1. The Fe2O3/OMWCNTs nanocomposite is prepared by a hydrothermal method. Electrochemical measurements show that Fe2O3/OMWCNTs still keeps a highly reversible specific capacity of 653.6 mA h g-1after 200 cycles at 0.5 A g-1, which shows an obviously higher capacity than the sum of that of single Fe2O3and OMWCNTs. The OMWCNTs not only buffer the volume changes of Fe2O3nanoparticles but also provide high-speed electronic transmission channels in the charge-discharge process. The thermal oxidation method of OMWCNTs avoids using strong corrosive acids such as nitric acid and sulfuric acid, which has the advantages of safety, environmental protection, macroscopic preparation, etc.

Enhanced lithium storage performance of graphene nanoribbons doped with high content of nitrogen atoms.

Nitrogen doping can provide a large number of active sites for lithium-ion storage, thus can yield a higher capacity for lithium-ion batteries. However, most of the reported N-doped graphene-based materials have low nitrogen content (<10 wt%) as the introduction of nitrogen atoms prefer to be produced at edges and defects in the graphene lattices. Owing to the formation of edges and defects, the doped states or active sites can easily be located and nitrogen contents can be determined precisely. Here we present the preparation of N-doped graphene nanoribbons with high nitrogen contents (11.8 wt%) and a facile tunable configuration of doped states. The material can be used as an anode for lithium-ion batteries and shows a higher capacity (the electrode has a reversible capacity of 1100.34 mA h g-1 at a charge/discharge rate of 100 mA g-1, corresponds to a discharge time of about 9 h), better rate performance (the electrode has a reversible capacity of 471 mA h g-1 at the current density of 2 A g-1, corresponds to a discharge time of about 11.6 min) and improved cycling stability (87.37% of the initial capacity after 200 cycles). The experimental results and first-principle calculations suggest that the residual oxygen-containing functional groups of N-doped graphene nanoribbons promote the formation of pyrrolic nitrogen at edges and substantially increase the room for nitrogen doping. This work opens new strategies for designing and developing N-doped graphene anodes for high performance lithium-ion batteries.

Performance-Enhanced Activated Carbon Electrodes for Supercapacitors Combining Both Graphene-Modified Current Collectors and Graphene Conductive Additive.

Graphene has been widely used in the active material, conductive agent, binder or current collector for supercapacitors, due to its large specific surface area, high conductivity, and electron mobility. However, works simultaneously employing graphene as conductive agent and current collector were rarely reported. Here, we report improved activated carbon (AC) electrodes (AC@G@NiF/G) simultaneously combining chemical vapor deposition (CVD) graphene-modified nickel foams (NiF/Gs) current collectors and high quality few-layer graphene conductive additive instead of carbon black (CB). The synergistic effect of NiF/Gs and graphene additive makes the performances of AC@G@NiF/G electrodes superior to those of electrodes with CB or with nickel foam current collectors. The performances of AC@G@NiF/G electrodes show that for the few-layer graphene addition exists an optimum value around 5 wt %, rather than a larger addition of graphene, works out better. A symmetric supercapacitor assembled by AC@G@NiF/G electrodes exhibits excellent cycling stability. We attribute improved performances to graphene-enhanced conductivity of electrode materials and NiF/Gs with 3D graphene conductive network and lower oxidation, largely improving the electrical contact between active materials and current collectors.