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An amorphous MnO(2)·nH(2)O/microporous carbon spheres (α-MnO(2)·nH(2)O/MCS) composite electrode material is prepared by a chemical co-precipitation method. It is observed that the amorphous MnO(2) particles are deposited on the surface of the MCS, which form a network with a uniquely developed three-dimensional open porous system containing macropores, mesopores and micropores. The electrochemical measurements reveal that the composite electrode material presents a much more stable and reversible capacitance behavior compared to the pure α-MnO(2)·nH(2)O in 1 M of Na(2)SO(4) electrolyte. The composite containing 25 wt% MCS exhibits optimal specific capacitance of 218.2 F g(-1) at 2 mV s(-1), and is still as high as 112.4 F g(-1) at 100 mV s(-1), while a drastic reduction from 197.0 F g(-1) at 2 mV s(-1) to only 40.7 F g(-1) at 100 mV s(-1) occurs for the pure α-MnO(2)·nH(2)O. The composite also shows a rather high electrode-specific capacitance of 3.13 F cm(-2) and a long cycle life. The remarkable enhancement in the electrochemical performance is mainly attributed to the microporous structure of the MCS contributing to the deposition of MnO(2) particles on the surface of the MCS, and the uniquely developed porous network of the composite facilitating the rapid transport of the electrolyte. These factors result in the high electrochemical utilization of MnO(2), a great reduction of the equivalent series resistance, and hence the relatively high and stable electrochemical behavior.

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The spherical pyrite FeS 2 was synthesized through a green and simple method with the addition of the polyvinylpyrrolidone (PVP) dispersant. The as-prepared FeS 2 displays a good electrochemical performance with an initial specific capacity over 80% of the theoretical value and a very low decay rate of 0.33% per cycle (calculated from 2 nd to 50 th at 0.1C). Rate capability testing exhibits a discharge capacities of around 371.6 mAh/g (0.1C), 343 mAh/g (0.2C), 294.9 mAh/g (0.5C), 239 mAh/g (1C) and 161.8 mAh/g (2C) respectively. Besides, coulombic efficiency close to 100% at various rates can also be obtained. We calculate Li + diffusion coefficient and multi-electron feature of the pyrite FeS 2 during charge/discharge process. It shows that smaller potential window is beneficial for cyclability, which was in good agreement with experimental results.