Aqueous Li4Ti5O12/LiMn2O4 Cell with a Li-Ion Conducive Solid Electrolyteseparator and an Electrodeposition of Zn to an Anode

Abstract

Li-ion batteries (LIBs) with non-aqueous electrolytes have high-energy density, highpower density, and long-cycle performance. However, generally LIBs have a risk due to their flammable organic electrolytes. Until now, a lot of attempt to reduce the risk of LIBs have been conducted such as all-solid-state battery. We have focused on Li-ion batteries with aqueous electrolytes with safer and low cost, but the electrochemical stability window of aqueous electrolytes is narrower than that of the organic electrolytes in LIBs. The stable operating voltage window of an aqueous electrolyte is approximately 1.23 V thermodynamically, beyond which the electrolysis of H2O occurs along with the evolution of H2 or O2 gas. To achieve an aqueous Li-ion battery with high discharge voltage, a suppression of H2 gas on the anode is needed.In this study, we report the widening of the overall electrochemical stability window with a Li-ion conductive solid electrolyte (SE) separator composed of NASICON-type Li-Al-Ti-P-O glass ceramic and an electrodeposition of Zn to an anode. We utilized a SE separator to suppress the H2 gas evolution on the anode electrode by preventing H+ migration from a cathode electrolyte. And we tried to electrodeposit Zn to the anode, since Zn shows a high hydrogen over voltage. A cathode, an anode, and an aqueous electrolyte was used as LiMn2O4, LiTi4O12, and 12 mol/L LiCl respectively. A Li-ion conductive solid electrolyte with a thickness of 150 μm and the conductivity of 10-4 S/cm at 25°C was used as the SE separator. We fabricated a LTO/LMO cell with the SE separator and a porous separator(1. Typical charge/discharge curves with SE separator and electrodeposition of Zn to LTO anode is shown in Fig. 1 (a). The aqueous LTO/LMO cell exhibited an average discharge voltage of over 2.4 V, a coulombic efficiency of over 94%, and good cycle perfromance. Compared to a cell with porus separator and no electrodeposition of Zn, the evolution of H2 gas on the LTO anode during charge in the LTO/LMO cell was kinetically suppressed and decreased to 1/6 as shown in Fig. 1 (b). Figure 1