Extensive applications of rechargeable lithium-ion batteries (LIBs) to various portable electronic devices and hybrid electric vehicles result in the increasing demand for the development of electrode materials with improved electrochemical performance including high energy, power density, and excellent cyclability, while maintaining low production cost. Here, we present a direct synthesis of ferrite/carbon hybrid nanosheets for high performance lithium-ion battery anodes. Uniform-sized ferrite nanocrystals and carbon materials were synthesized simultaneously through a single heating procedure using metal-oleate complex as the precursors for both ferrite and carbon. 2-D nanostructures were obtained by using sodium sulfate salt powder as a sacrificial template. The 2-D ferrite/carbon nanocomposites exhibited excellent cycling stability and rate performance derived from 2-D nanostructural characteristics. The synthetic procedure is simple, inexpensive, and scalable for mass production, and the highly ordered 2-D structure of these nanocomposites has great potential for many future applications.

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A composite of modified graphene and LiFePO4 has been developed to improve the speed of charging-discharging and the cycling stability of lithium ion batteries using LiFePO4 as a cathode material. Chemically activated graphene (CA-graphene) has been successfully synthesized via activation by KOH. The as-prepared CA-graphene was mixed with LiFePO4 to prepare the composite. Microscopic observation and nitrogen sorption analysis have revealed the surface morphologies of CA-graphene and the CA-graphene/LiFePO4 composite. Electrochemical properties have also been investigated after assembling coin cells with the CA-graphene/LiFePO4 composite as a cathode active material. Interestingly, the CA-graphene/LiFePO4 composite has exhibited better electrochemical properties than the conventional graphene/LiFePO4 composite as well as bare LiFePO4, including exceptional speed of charging-discharging and excellent cycle stability. That is because the CA-graphene in the composite provides abundant porous channels for the diffusion of lithium ions. Moreover, it acts as a conducting network for easy charge transfer and as a divider, preventing the aggregation of LiFePO4 particles. Owing to these properties of CA-graphene, LiFePO4 could demonstrate enhanced and stably long-lasting electrochemical performance.

In this manuscript, we introduce a facile hydrothermal method for the controlled growth of SnO 2 nanoparticles onto graphene oxide. Hydrazine plays a fundamental role in controlling the formation and crystallization of SnO 2 nanoparticles, and the reduction of graphene oxide to graphene. The SnO 2graphene composite consists of 3-4 nm monodisperse SnO 2 nanocrystals homogeneously dispersed at the surface of graphene. It is demonstrated that the composite can accommodate the large volume change of SnO 2 which occurs during lithiation-delithiation cycles. When used as an anode material for lithium ion batteries, it exhibits a first discharge capacity of 1662 mA h g À1 , which rapidly stabilizes and still remains at 626 mA h g À1 even after 50 cycles, when cycled at a current density of 100 mA g À1 . Even at the very high current density of 3200 mA g À1 , the composite displays a stable capacity of 383 mA h g À1 after 50 cycles.

It is still a challenging task to develop a facile and scalable process to synthesize porous hybrid materials with high electrochemical performance. Herein, a scalable strategy is developed for the synthesis of few-layer MoS2 incorporated into hierarchical porous carbon (MHPC) nanosheet composites as anode materials for both Li- (LIB) and Na-ion battery (SIB). An inexpensive oleylamine (OA) is introduced to not only serve as a hinder the stacking of MoS2 nanosheets but also to provide a conductive carbon, allowing large scale production. In addition, a SiO2 template is adopted to direct the growth of both carbon and MoS2 nanosheets, resulting in the formation of hierarchical porous structures with interconnected networks. Due to these unique features, the as-obtained MHPC shows substantial reversible capacity and very long cycling performance when used as an anode material for LIBs and SIBs, even at high current density. Indeed, this material delivers reversible capacities of 732 and 280 mA h g(-1) after 300 cycles at 1 A g(-1) in LIBs and SIBs, respectively. The results suggest that these MHPC composites also have tremendous potential for applications in other fields.

Abstract-High-frequency (HF) band wireless power transfer systems offer the promise of cutting the last cord, allowing users to seamlessly recharge mobile devices as easily as wireless communication. Yet there are still many technical issues that need to be overcome. Among them, one of the most difficult problems is maintaining impedance match over a short range, where the distance between a transmitter and receiver could vary. In this paper, the effect of impedance mismatch of a HFband wireless power transfer system is carefully investigated and two compensation methods are suggested to overcome this within a short range, where frequent impedance mismatch can occur. Each method has pros and cons. In order to verify the feasibility of the proposed methods, HF-band wireless power transfer systems, with a pair of rectangular loop resonators, were designed. The efficiency and input impedance variation were simulated and measured. From these results, proposed methods show enhanced efficiency performance than a typical wireless power transfer system without any compensation circuits.

There is a growing need to improve the electrical conductivity of the cathode and to suppress the rapid capacity decay during cycling in lithium-sulfur (Li-S) batteries. This can be achieved by developing facile methods for the synthesis of novel nanostructured carbon materials that can function as effective cathode hosts. In this Article, we report the scalable synthesis of ordered mesoporous carbon nanosheets (OMCNS) via the etching of self-assembled iron oxide/carbon hybrid nanosheets (IO-C NS), which serve as an advanced sulfur host for Li-S batteries. The obtained two-dimensional (2D) nanosheets have close-packed uniform cubic mesopores of ∼20 nm side length, and the gap between the pores is ∼4 nm, which resembles the honeycomb structure consisting of an ordered array of hexagonal pores. We loaded OMCNS with sulfur by a simple melting infusion process and evaluated the performance of the resulting OMCNS-sulfur composites as the cathode material. As a result, the sulfur-loaded OMCNS hybrid (OMCNS-S) electrode infiltrated with 70 wt % sulfur delivers a high and stable reversible capacity of 505.7 mA h g after 500 cycles at 0.5 C-rate with excellent capacity retention (a decay of 0.081% per cycle) and excellent rate capability (580.6 mA h g at a high current density of 2 C). The improved electrochemical properties could be attributed to the fact that the uniform cubic mesopores offer sufficient space for the volume expansion of sulfur inside them and therefore trap the polysulfides during the charging-discharging process. Therefore, these unique structured carbon nanosheets can be promising candidates for other energy-storage applications.