Summary In this paper, a systematic method has been developed to produce highly flexible and robust graphene/LiMn2O4 (G/LMO) and graphene/LiCr0.05Mn1.95O4 (G/LCMO) free‐standing composite cathode electrodes with increased specific capacity and improved electrochemical capability. Spinel LMO nanorods are synthesized by calcination method followed by a hydrothermal reaction technique. As‐synthesized nanorods were then embedded in a graphene layer which will in turn serve as a self‐standing binder‐free cathode electrode. Spinel LMO and LCMO nanorods with a length of 600 nm and width of 50 nm were then homogenously entrapped and distributed within the layers of conductive graphene structure. This hybrid structure will help to eliminate the use of heavy metal current collectors and electrically resistant binders or even conductive additives. A discharge capacity of 114.5 mAh g−1 is obtained after first cycle and %72 capacity retention is obtained after 250 cycles from G/LCMO freestanding samples. The enhancement in the electrochemical properties is due to the unique freestanding structure of the cathode electrodes.

Summary In this paper, nanosized Ni3Sn4 nanoparticles were synthesized by chemical reduction technique. A facile strategy is also developed to synthesize the yolk‐shell Ni3Sn4 nanoparticles decorated between the layers of multilayer graphene to obtain high‐capacity, long service life with comparable cost Li‐ion batteries. Ni3Sn4 nanoparticles in the form of yolk‐shell morphology were synthesized between 30 and 130 nm in size and homogeneously anchored on graphene layers as spacers preventing the layers merging after vacuum filtration. The characterization of the as‐synthesized composite electrodes was performed by scanning electron microscopy and X‐ray diffraction methods. As an anode electrode, yolk‐shell Ni3Sn4/graphene composite electrodes revealed a stable capacity of 324.5 mAh g−1 after 250 cycles, indicating that the composites might have a promising future application in Li‐ion batteries. The results have shown that unique yolk‐shell Ni3Sn4/graphene hybrid composite structure shows extraordinary electrochemical performance with superior reversible capacity and improved cyclic performance, indicating that the stacking of the active electrode nanoparticles between the graphene layers is a good method for maximum specific capacity outputs.

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The transition from ‘fossil ‘economy to a greener and sustainable economy cannot be achieved without efficient energy storage systems. The recovery of energy from renewable sources such as solar or wind power has enormous potential to meet current and future energy needs and to lead to a better preservation of nature and the environment. In the United States for example, the combustion of fossil fuel results in more than 90% of the greenhouse gas emissions, which is also the main cause of global warming. This noticeable climate changes have urged major vehicles producers to develop zero-emission vehicles (electric or hybrid vehicles). To achieve the aim to develop a suitable energetic solutions for mobile and stationary applications, an efficient and low cost energy storage system is needed. The lithium-ion batteries with high energy density have long been effective solution to meet these demands. Nano structured electrode materials have shown improved electrochemical performance due to the large surface area which facilitates the electrode-electrolyte contact. Tailoring the electrode morphology in the forms of nanowires and nanorods are particularly attractive since they provide large surface area and efficient one-dimensional electron transport pathways and facile strain relaxation during battery charge and discharge. Spinel LiMn2O4 based cathode electrode materials are one of the most promising alternative cathode materials for Li-ion power batteries, which is due to the advantages such as low cost, good environmental compatibility, and good thermal stability. It has been reported that the charged LiMn2O4 material shows obviously higher thermal stability in the electrolyte at high temperature than LiCoO2 and LiNiO2. The good thermal stability of spinel LiMn2O4 is beneficial for its use in high power batteries. Although many reports revealed that the LiMn2O4 based electrodes offer a potentially attractive alternative to the presently commercialized LiCoO2, there are still some issues prohibiting LiMn2O4 from commercialization is its severe capacity and cycling performance fading during cycling. It is reported that both the particle size and its size distribution play important roles in the electrochemical performance. To overcome this problem, many researchers are focused on nanocomposite electrodes. Mats or so-called freestanding electrode that contains high concentrations of graphene nanosheets have the potential to form strong and light weight composite materials. The formation of intense surface films may increase the electrode impedance and even electrically isolate part of the active mass. In this study, LiMn2O4 nanorods were produced via cost effective and facile method by chemically converting a-MnO2 structure. a-MnO2 nanorods were produced via microwave hydrothermal synthesis method KMnO4 and manganese sulfate MnSO4.H2O as the starting precursors. LiMn2O4 nanorods were then chemically obtained by using a-MnO2 nanorods by a simple solid-state reaction. As-synthesized LiMn2O4 nanorods were then decorated between graphene nanosheets through a vacuum filtration process and freestanding cathode electrodes were obtained. Graphene/LiMn2O4 cathode electrode exhibited higher rate capability, specific capacity and cycle performance when compared with pristine LiMn2O4 electrode. This is due high surface area of LiMn2O4 nanoparticles and good electronic conductivity of graphene. The improved electrochemical performance of the graphene coated LiMn2O4 electrode was attributed to decreasing Mn dissolution into electrolyte. The improved electrochemical performance of the LiMn2O4/graphene nanocomposite makes it the promising cathode material for high-performance lithium-ion batteries. Keywords: LiM2O4 nanorods, graphene, freestanding electrodes, Li ion batteries.

To globally solve the problem of an environmentally clean and secure distribution of energy is a major task for scientist worldwide. The use of clean energy will have a direct positive influence on, for example, the emission of greenhouse gases and our future climate. Today the rechargeable battery with the highest energy density is the Li-ion or Li-polymer battery. Commercially this battery is used for mobile phones, laptops and camcorders. The development of new batteries of this type has to go towards larger batteries for hybrid vehicles or towards further miniaturisation for smaller electronic devices. Both these routes will, however, require basic materials research within chemistry and physics; new materials must be synthesized (some materials used today are too expensive for up-scaling) and the complex chemistry occurring both in bulk electrode materials and at the interface between electrolyte and electrode most be better understood. Among different electrode materials, layered transition metal oxides (LMO) are the most successful cathode material in application at present time, but its further development is severely hindered due to the intrinsic safety limitation and the cost. Seeking for some other cost-effective cathode materials with better performance is a significant task. And therefore, olivine-structured phosphate LiMPO4 (M = Fe, Mn, Co, etc.) materials have attracted great attention due to many advantages, such as lower toxicity, lower cost, better thermal, chemical stability. Unfortunately, phosphate based cathode material possesses low intrinsic electronic and ionic conductivity. So, that it is difficult to prepare LiMPO4 (M: Fe, Mn, Co, etc) with a high performance, and many groups have explored various solutions to solve the problems, including enhancing the electronic conductivity among particles. In order to overcome these issues, studies are mostly focused on synthesis methods with a coating of an electronically conductive phase such as carbon. Another route to solve these problems could be done by using graphene. It has been reported that the two-dimensional graphene has unique properties such as excellent electrical and mechanical properties, unique physical properties such as high specific surface area (2630 m2/g), high electrical conductivity, a broad electrochemical window and good flexibility. Graphene oxide paper and graphene paper have been produced by vacuum filtration of graphene sheets. As a result, graphene free standing electrodes have been used directly as electrode materials for flexible energy storage devices without binder, conductive additives and current collectors. As compared with conventional electrodes, free-standing electrodes can increase the electrical conductivity of electrode materials meanwhile achieve higher active material-to-substrate mass ratios. In this study, a microwave hydrothermal synthesis process is used to produce novel, and facile strategy for the preparation of LiMPO4 (M=Mn, Fe, and Co) microstructures at a low temperature, using ethanol as the solvent, LiI as the lithium source, transitional metal salt as the M sources, H3PO4 as the phosphorous source, and poly(vinyl pyrrolidone) as the carbon source and template. As-synthesized LiMPO4 were then subjected to vacuum filtration techniques with graphene in order to obtain freestanding cathode electrodes for high capacity Li-ion batteries. Keywords: LiMPO4, graphene, freestanding electrode, cathode electrode, Li ion.