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The reasons for capacity fading of an LiNi 1/3 Mn 1/3 Co 1/3 O 2 /5 M LiNO 3 ͑pH 11͒/Li x V 2 O 5 lithium-ion cell based on structure and dissolution of transition metals were investigated. X-ray diffraction and inductively coupled plasma results showed that the properties of the anode have an impact on the cycle life of the cell. To stabilize the cycling capacity of the anode, and thus improve the cycle life of the cell, coating with a conductive polyaniline on the surface of the anode was proposed. Cycle tests revealed that the stability of the lithium-ion cell with surface coated anode was greatly improved.The lithium-ion battery with aqueous electrolyte proposed by Dahn has been of great interest not only for basic studies but also for applications. 1,2 Compared with a nonaqueous lithium-ion battery, the safety problem is essentially settled, server manufacture conditions are ignored, and the conductivities of inorganic electrolyte are typically two orders of magnitude larger than that of a nonaqueous system, which can satisfy the high rate capacity and specific power requirements. Although the energy density is lower than that of nonaqueous Li-ion battery, it can be compared to that of the Pb-acid and Ni-Cd batteries. On the other hand, the aqueous Li-ion battery does not need to use strong acid/alkaline and appears to be a more environmental friendly and safe device.Unfortunately, the poor cycle life of this battery is a major obstacle preventing wide investigation. Details of rapid capacity fading during cycling are still unclear. Some other research on aqueous lithium-ion batteries has also been conducted in compounds with respect to its fundamental performances and electrode material in aqueous cell. [3][4][5][6] Electronically conducting polymers such as polypyrrole, polyaniline ͑PAn͒, and polythiophene have been used to form composite cathodes such as V 2 O 5 -PAn 7 and LiMn 2 O 4 -PPy 8,9 to improve the conductivity of the electrode, the coulombic efficiency, rate capability, and the cycle life of the electrode material. For example, in the case of LiMn 2 O 4 -PPy composites, the addition of polypyrrole increases the capacity of the pure LiMn 2 O 4 from 110 to 125 mAh g −1 over 120 cycles.The conducting polymer coating on transition metal oxides may reduce the dissolving of transition metal ions and stabilize the capacity of the electrodes, enhancing the cycle life of an aqueous lithium-ion battery. With such an idea, we prepared composite Li x V 2 O 5 /PAn as an anode for an aqueous lithium-ion battery. LiNi 1/3 Mn 1/3 Co 1/3 O 2 was used as the cathode. A 5 M LiNO 3 at pH 11 was used as the electrolyte due to the cathode being sensitive to the pH values of electrolytes according to our previous investigation. The cycling performance of cells with bare and coated anodes was compared. Here we focus our attention on the cycle life of the aqueous lithium-ion cell. Hence we ignore the high capacity and high discharge plateau profiles of the batteries. To the best of our knowledge, there have been no repo...

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