In situ TEM observation of the (De)potassiation process of α-MnO2 nanowires

Abstract

Based on lithium-ion batteries (LIBs), a new type of electrochemical device known as potassium-ion batteries was developed. Potassium-ion batteries potentially offer several key benefits over LIBs in Non-aqueous and several electrode materials, including steady discharge, high rate performance, cheap cost and lower charge density. Therefore, Potassium-ion batteries (PIBs) are highly likely to become the best candidate for low-cost, long-life batteries in the future, and are expected to extensively be employed in a variety of industries, including mobile devices and new energy vehicles. In recent years, research on the electrochemistry of potassium-ion batteries is still in its initial stage. Here, we use in situ transmission electron microscopy to observe the irreversible volume expansion of α-MnO2 nanowire during potassiation and depotassiation. During the first potassiation, the single crystalline α-MnO2 nanowire transformed to K1.33Mn8O16, causing a volume expansion of 35.6 %, which was unable to recover during the depotasiation process. The irreversible volume expansion suggests that most potassium ions inserted into the α-MnO2 nanowire cannot be extracted during the depotassiation process, which leads to low Coulombic efficiency in the first cycle. The cycle performance and Coulombic efficiency of α-MnO2 maybe still limited by insufficient electronic conductivity. Composite Au on the surface of α-MnO2 maybe improves its electronic conductivity. The α-MnO2 on Au (α-MnO2/Au) nanowires’ irreversible and cycle performance was better than pristine materials by the first principle calculations. Traditionally the first cycle capacity loss is attributed to the formation of the solid electrolyte interface (SEI). This research provides a new approach of the first cycle capacity loss mechanism in potassiation of α-MnO2 cathode. Also, the α-MnO2/Au improves the cycle performance and Coulombic efficiency of the K-(α-MnO2) nanobattery.