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Herein, we report an equivalent circuit model for electrochemical impedance spectroscopic (EIS) investigation of the Na + ion diffusion process in MnO 2 . We combine two constant phase elements (CPEs) active in the desired frequency ranges as the element associated with the diffusion reaction of ions in the solid active materials in a modified equivalent circuit model. Adoption of these CPEs instead of a finite-space Warburg impedance allows for the more precise analysis of measured impedance data for a cavity microelectrode (CME). The dependence of electrochemical properties of manganese oxide (MnO 2 )/multiwall carbon nanotube (MWCNT) composites on the MnO 2 content is then investigated using this EIS analysis. According to EIS analyzes, series resistance (R s ), electron-transfer resistance (R et ), degree of frequency dispersion in semi-infinite diffusion, and effective diffusion length is increased with an increase in MnO 2 loading amounts in the composites.

LiMn0.75Fe0.25PO4/C microspheres were synthesized using a microwave-assisted process with a complexing agent through the control of precursor pH. The LiMn0.75Fe0.25PO4/C microspheres exhibited a high tap density, high capacity, remarkable rate capability, and excellent cyclability.

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A phase-pure Li 4 Ti 5 O 12 /reduced graphene oxide nanocomposite was prepared using a simple one-pot synthesis of the Li-Ti-O precursor and subsequent heat treatment. The prepared nanocomposite delivers a reversible capacity of 168 mA h g À1 at 1 C-rate and a remarkable rate capability with 59% capacity retention at 50 C-rate.Spinel Li 4 Ti 5 O 12 has attracted much attention as an anode material for lithium-ion batteries because of its good Li-ion intercalation reversibility and extremely small structural changes during charge-discharge cycling. Despite these advantages, Li 4 Ti 5 O 12 is not quite ready for commercial use because of its low conductivity (10 À13 S cm À1 ), which in turn leads to poor rate capability. 1-3 Thus far, several effective ways to improve the rate capability of Li 4 Ti 5 O 12 have been proposed, including reduction of the particle size to the nanoscale, doping Li, Ti, or O sites with small amounts of metal or nonmetal ions, surface modication or carbon coating, and its incorporation into composites with carbonaceous materials. [4][5][6][7][8] Reduced graphene oxide (RGO) or graphene nanosheets, which are single layers of carbon atoms tightly packed into twodimensional (2D) honeycomb sp 2 carbon lattices, have rapidly emerged as potential electrode materials for electrochemical energy storage. RGO is characterized by its high conductivity, large surface area, and good mechanical properties, all of which are comparable to or better than the corresponding properties