Graphite, as the most common anode for commercial Li-ion batteries, has been reported to have a very low capacity when used as a Na-ion battery anode. It is well known that electrochemical insertion of Na þ into graphite is significantly hindered by the insufficient interlayer spacing. Here we report expanded graphite as a Na-ion battery anode. Prepared through a process of oxidation and partial reduction on graphite, expanded graphite has an enlarged interlayer lattice distance of 4.3 Å yet retains an analogous long-range-ordered layered structure to graphite. In situ transmission electron microscopy has demonstrated that the Na-ion can be reversibly inserted into and extracted from expanded graphite. Galvanostatic studies show that expanded graphite can deliver a high reversible capacity of 284 mAh g À 1 at a current density of 20 mA g À 1 , maintain a capacity of 184 mAh g À 1 at 100 mA g À 1 , and retain 73.92% of its capacity after 2,000 cycles.

An improved recurrence algorithm to calculate the scattering field of a multilayered sphere is developed. The internal and external electromagnetic fields are expressed as a superposition of inward and outward waves. The alternative yet equivalent expansions of fields are proposed by use of the first kind of Bessel function and the first kind of Hankel function instead of the first and the second kinds of Bessel function. The final recursive expressions are similar in form to those of Mie theory for a homogeneous sphere and are proved to be more concise and convenient than earlier forms. The new algorithm avoids the numerical difficulties, which give rise to significant errors encountered in practice by previous methods, especially for large, highly absorbing thin shells. Various calculations and tests show that this algorithm is efficient, numerically stable, and accurate for a large range of size parameters andrefractive indices.

Silicon (Si) has been considered a very promising anode material for lithium ion batteries due to its high theoretical capacity. However, high-capacity Si nanoparticles usually suffer from low electronic conductivity, large volume change, and severe aggregation problems during lithiation and delithiation. In this paper, a unique nanostructured anode with Si nanoparticles bonded and wrapped by graphene is synthesized by a one-step aerosol spraying of surface-modified Si nanoparticles and graphene oxide suspension. The functional groups on the surface of Si nanoparticles (50-100 nm) not only react with graphene oxide and bind Si nanoparticles to the graphene oxide shell, but also prevent Si nanoparticles from aggregation, thus contributing to a uniform Si suspension. A homogeneous graphene-encapsulated Si nanoparticle morphology forms during the aerosol spraying process. The open-ended graphene shell with defects allows fast electrochemical lithiation/delithiation, and the void space inside the graphene shell accompanied by its strong mechanical strength can effectively accommodate the volume expansion of Si upon lithiation. The graphene shell provides good electronic conductivity for Si nanoparticles and prevents them from aggregating during charge/discharge cycles. The functionalized Si encapsulated by graphene sample exhibits a capacity of 2250 mAh g⁻¹ (based on the total mass of graphene and Si) at 0.1C and 1000 mAh g⁻¹ at 10C, and retains 85% of its initial capacity even after 120 charge/discharge cycles. The exceptional performance of graphene-encapsulated Si anodes combined with the scalable and one-step aerosol synthesis technique makes this material very promising for lithium ion batteries.

The integration of ultra-thin gate oxide, especially at sub-10 nm region, is one of the principle problems in MoS2 based transistors. In this work, we demonstrate sub-10 nm uniform deposition of Al2O3 on MoS2 basal plane by applying ultra-low energy remote oxygen plasma pretreatment prior to atomic layer deposition. It is demonstrated that oxygen species in ultra-low energy plasma are physically adsorbed on MoS2 surfaces without making the flakes oxidized, and is capable of benefiting the mobility of MoS2 flake. Based on this method, top-gated MoS2 transistor with ultrathin Al2O3 dielectric is fabricated. With 6.6 nm Al2O3 as gate dielectric, the device shows gate leakage about 0.1 pA/μm2 at 4.5 MV/cm which is much lower than previous reports. Besides, the top-gated device shows great on/off ratio of over 108, subthreshold swing (SS) of 101 mV/dec and a mobility of 28 cm2/Vs. With further investigations and careful optimizations, this method can play an important role in future nanoelectronics.

S and edge-opened graphite oxide, chemical reduction of graphene oxide and deposition of S. [23][24][25] Because the S in these graphene-S composites is not completely encapsulated by graphene, the polysulfi de intermediates still slowly dissolve into electrolyte resulting in progressive cycling decay. The ideal structure for the carbon-S composites is to intercalate S atoms or molecules into a graphite interlayer to form S intercalated graphite compounds, thus maximizing S loading and minimizing the dissolution of polysulfi des. However, only a small amount of S can be intercalated into graphite even under the conditions of high pressure and/or high temperature due to small layer spacing (planar distance ≈0.34 nm). [ 26 ] Because of the large interlayer distance, expanded graphite has been investigated as host to embed S. The expanded graphiteembedded sulfur nanocomposites were normally synthesized by two-step reactions: thermal reduction of graphite oxides in H 2 /Ar at a high temperature (450 °C) and fl owed by S meltdiffusion at a low temperature of ≈155 °C. [ 27,28 ] Since S vapor can reduce graphite oxide (GO) at a high temperature, in this work we report a novel one-step method to synthesize S intercalated graphite by S in situ reducing GO and intercalating into the reduced graphite oxide (RGO) under vacuum at 600 °C. Figure 1 schematically depicts the preparation process of the RGO/S composite. At room temperature, sulfur exists mainly in the form of cyclooctasulfur (S 8 ), as heating the mixture of graphite oxide and S 8 to 600 °C, the large molecule S 8 will be broken into smaller chain species S 2 . [ 29,30 ] Due to the large interplanar distance of GO, these S 2 molecules can intercalate into GO to deoxygenate GO and form SO 2 gas. [ 31 ] Further S 2 intercalation into RGO will form S intercalated graphite compounds. By manipulating the interlayer distance of graphite oxide through controlling the degree of oxidation of graphite, [ 32 ] the S intercalation level can be maximized. However, the S 2 molecules deposited on the external surface and the edges of RGO interlayer may recombine to form cyclo-S 8 when the temperature is cooling down from 600 °C to room temperature. Due to the high solubility of CS 2 to S 8 , the surface S 8 can be removed using CS 2 solvent at ease. Here, we demonstrate that the RGO/S composites with 52% S loading show high capacities and long cycling stabilities. The CS 2 -wash treatment can further enhance the cycling stability of RGO/S composites. Almost no capacity decline can be observed for CS 2 -washed RGO/S composites in 225 cycles. Figure 2 a shows the X-ray diffraction (XRD) patterns of pure S, pristine graphite, GO and RGO/S composite. The XRD pattern of S exhibits very sharp and strong peaks throughout the entire diffraction range, indicating a well-defi ned crystal S 8 structure. Graphite exhibits a sharp peak at 2 θ = 26.6° corresponding to the diffraction of (002) plane with interlayer distance of ≈0.34 nm. [ 33 ]