Greatly enhanced energy density of all‐solid‐state rechargeable battery operating in high humidity environments

Abstract

Rubidium silver iodide (RbAg4I5) owing to its unprecedented ionic conductivity (>0.2 S cm−1 at room temperature) and high stability in a wide temperature range (0°C-100°C) is an ideal candidate for being used as an electrolyte material in solid-state batteries. Our previous study showed that the exchange current density at the Ag/RbAg4I5 anode and graphite/RbAg4I5 cathode interfaces increased by three orders of magnitude when the environmental relative humidity (RH) increased from 35% to 100%. This prompted us to develop an all-solid-state battery that can operate in a wide RH range with exceptional stability. Here, we presented a novel rechargeable all-solid-state battery employing RbAg4I5 solid electrolyte and Ag and graphite adhesive electrodes with the configuration of Ag, RbAg4I5/RbAg4I5/C, and RbAg4I5. Benefiting from the outstanding ionic conductivity of the solid electrolyte, the high electrochemical kinetics at high RH, a good interface between the RbAg4I5 solid electrolyte and Ag and graphite adhesive electrodes, the all-solid-state battery exhibited excellent performance with a high energy density (153 Wh L−1 at 0.5 C) when exposed to an ambient environment with RH of 82%. Galvanostatic charge/discharge measurements also showed that the discharge capacity of the all-solid-state battery obtained in dry nitrogen (RH ~10%) and oxygen environments (RH ~10%) could be increased by more than 10-folds in humid ambient air (RH ~80%), while the highest capacity was achieved under humidified argon environment (RH ~100%). The all-solid-state battery demonstrated excellent cyclic stability at 0.5 C with a capacity increase up to 2000 cycles due to the activation of the solid electrolyte and no capacity fade after 3500 cycles, whereas the capacity retention at 1.3 C was 36% after 1000 cycles. Our results unveiled that by the annealing process at 150°C for 12 hours, the charge/discharge capacity could be fully recovered. Electrochemical impedance spectroscopy and X-ray diffraction analyses suggested that the reduction of charge capacity upon cycling at 1.3 C was due to an incomplete reversing of the electrochemical reaction at the anode, leading to a phase change from RbAg4I5 to Rb2AgI3 and β-AgI. Nevertheless, annealing at 150°C converted Rb2AgI3 and β-AgI back into RbAg4I5. With the elimination of moisture-proof packaging and reduced complexity of fabrication as well as the opportunity of miniaturization, the all-solid-state battery holds great potentials for special applications such as reserve battery, power systems in space, and energy storage in electronics, which require high reliability, a high degree of safety, prolonged shelf-time, and ease of miniaturization.