a Noble Aqueous Lithium-Metal Chloride Rechargeable Battery �
Authors: Morita Yoshinori , Zhang Peng , Wang Hui , Takeda Yasuo , Yamamoto Osamu , Imanishi Nobuyuki 
Published: February 2020

Recently, a demand for rechargeable batteries with a high specific energy density for electric vehicles (EVs) has increased, because the driving range of EVs with conventional rechargeable batteries is limited. In this report, a new type of the high specific energy density rechargeable battery is proposed. Here we report a demonstration of the feasibility of an aqueous lithium rechargeable battery with a water soluble cathode of MCl2 (M = Co, Ni, and Zn) and lithium metal anode, where the catholyte and lithium metal anode were separated by a water stable high lithium ion conductivity solid electrolyte ofthe NASICON-type Li1.4Al0.4Ge0.2Ti1.4(PO4)3 (LAGTP) film. The electrode reactions in this battery are as follows; anode: Li(s) = Li+(aq) + e
and
cathode: M2+(aq) + 2e = M(s)
The calculated mass and volume specific energy densities of the Li/CoCl2, Li/NiCl2 and Li/ZnCl2 couples are 1032, 1041, and 815 Wh kg-1and 2295, 3019, and 1681 Wh L-1, respectively. These calculated　mass specific energy densities are more than two times higher than those of the lithium-ion battery with the carbon anode and LiCoO3 cathode. The liquid cathode could be expected no degradation of the cell performance with increasing the cathode capacity, because of no binder and conductive additive, and a rapid diffusion of M2+ and Li+ to the reaction sites though the cathode, compared with the composite cathode with solid active materials like LiCoO2, a binder like PdFE and a conductive additive lile carbon.
The cell performance of the Li/[Li(FSO2)2N(LiFSI)-2 tetraethylene glycol dimethyl ether (G4)]-50 vol.% 1,3 dioxylane (DOL)/LAGTP/saturated MCl2 (M = Co, Ni, and Zn) and LiCl aqueous solution/M cell was examined at room temperature. The LAGTP film was prepared using a tap casting method1. An epoxy resin (about 3 wt%) was added to protect a water permeation through the film. The electrical conductivity of the film was around 5x10-4 S cm-1 at 25 oC. The LAGTP film was stable in the saturated MCl2 (M=Co, Ni, and Zn) and LiCl aqueous solution. The interlayer of (LiFSI-2G4)-50 vol% DOL2 was used to avoid the direct contact of lithium metal and LAGTP, because LAGTP is unstable in contact with lithium. The interlayer was reported that the lithium dendrite formation was not observed at room temperature and 1.0 mA cm-2. The OCVs of the Li/MCl2 (M=Co, Ni, and Zn)/M cells were comparable with the calculated cell voltages from the standard electrode potential differences of Li/Li+ and M/M2+. The Li/saturated MCl2 and LiCl aqueous solution (M=Co, Ni, and Zn)/M cells showed a successful charge and discharge performant at 25 ℃ and 1.0 mA cm-2. The Li/MCl2 (M=Fe and Cu)/M cells with a low concentration of MCl2 were discharged to the theoretical capacity of MCl2 and charged, but the cells with saturated MCl2 (M=Fe and Cu) and LiCl aqueous solution could not be operated, because gel-type materials were formed in the saturated LiCl and MCl2 (M=Fe and Cu).aqueous solution.
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