Development of Rechargeable Lithium-Bromine Batteries with Lithium Ion Conducting Solid Electrolyte
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Development of Rechargeable Lithium-Bromine Batteries with Lithium Ion Conducting Solid Electrolyte Koshin Takemoto and Hirotoshi Yamada Graduate School of Engineering, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki, Japan ABSTRACT Electrochemical performances of a prototype Lithium-Bromine battery (LBB) employing a solid electrolyte was investigated. It showed the discharge capacity of c.a. 147 mAh/(g-LiBr) for the first cycle, which decreased with repeating charge/discharge cycles. The capacity fading was mainly due to increase of the interfacial resistance between an aqueous active material solution and a solid electrolyte. From the results of symmetric cells and structural analysis of the surface of the solid electrolyte immersed in Br2 solutions, it was suggested that a Li+-depletion layer was formed on the surface of the solid electrolyte by contact with bromine. INTRODUCTION Energy storage devices that exceed conventional lithium ion batteries have attracted much attention because of their potential application to electric vehicles and load leveling of renewable energy. New energy storage devices are required to exhibit much higher performance in terms of cyclic life, cost, and reliability as well as energy density and power density than current devices. When we think of new batteries, it should be noted that energy density is obtained on the basis not of active materials but of a cell or a whole battery system. ZincBromine (Zn-Br2) batteries, which are generally used as a flow battery, are known as one of batteries which have high energy density (433 Wh/kg-cell). However, Zn-Br2 batteries have suffered from some problems such as low working potential of 1.8 V, Br2 crossover and dendrite deposition on anode electrodes on charging that may cause short-circuit. To overcome these problems of Zn-Br2 batteries, we propose Lithium-Bromine Battery (LBB) employing Li-metal anode, a solid electrolyte (SE) and a Br2/Br－ redox couple in an aqueous active material solution (AAM). A solid electrolyte separates aqueous active material solution from Li metal and also hinders short-circuit. In addition, LBB is expected to exhibit high working voltage of ca. 4.1 V and higher energy density (> 650 Wh/kg and > 1,000 Wh/L) than current LIB (at most 200-300 Wh/kg) and Zn-Br2 battery, because Li metal is used as a negative electrode. Recently, superb performance of LBB has been successively reported by two groups.[1,2] The reversible capacity was more than 300 mAh/g-Br and their charge/discharge cycle was very stable. However, it should be mentioned that, in these reports, AAM cosists of at most 2 M “active” LiBr and 7 M “inactive” Br− to stabilize Br2 formed on charging through the reaction: Br2 + Br− Br3−. (1) Although the solubility of LiBr is as high as 160 g/100 g-H2O at 20°C (~10 M), that of Br2 is only 3.1 g/100 g-H2O at 20°C. Due to the large difference in the solubility between LiBr and Br2, when concentrated LiBr aqueous solution is used a LBB, a certain amount of free Br2 is produced on charging the LBB, which may ca
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