Dilute Aqueous/aprotic Electrolytes with Broad Electrochemical Windows for Zn-ion hybrid Supercapacitors

Description

With merits of high power output and long lifespan, supercapacitors well bridge the gap between traditional capacitors and rechargeable batteries, and therefore have been widely used for diverse commercial applications, such as hybrid electrical vehicles, grid power buffer, and energy harvesting systems. Compared with rechargeable batteries, supercapacitors can accept and deliver energy much more rapidly, and tolerate magnitude more charge-discharge cycles. However, the relatively low energy density ofthe supercapacitors is the bottleneck of their applications. Building a hybrid supercapacitor that consists of a battery-type anode and a capacitive-type cathode can improve the energy density of supercapacitors, and meanwhile maintain their power output. In the different configurations of hybrid supercapacitors, metallic Zn is an attractive anode material due to its high specific capacity, low redox potential, low cost, and natural abundance. However, the problems such as the low operation voltage of the hybrid supercapacitors and poor stability of metallic Zn anodes have impeded their practical applications. In this project, we will develop a dilute aqueous/aprotic electrolyte with a broad electrochemical window to improve the energy density and cycle stability of the Zn-ion hybrid supercapacitors. This project is based on the following concepts:1) the introduction of aprotic solvents in an aqueous solution is expected to regulate the solvation structure of electrolyte with enhanced interactions between water molecules and electrolyte ions, and broaden the electrochemical window of electrolyte; 2) a wide electrochemical window of electrolyte enables a higher operation voltage for the Zn-ion hybrid supercapacitors and increases their energy density; 3) the electrolyte with a wide electrochemical window is also favorable to prolong the lifetime of Zn-ion hybrid supercapacitors, because it can increase the Coulombic efficiency of repetitive Zn stripping/plating and slow down the galvanic corrosion of metallic Zn. In the project, a series of aprotic solvents (e.g., trimethyl phosphate, acetonitrile, propylene carbonate, and dimethyl sulfoxide) with distinct properties will be used to prepare electrolytes, and the impacts of aprotic solvent incorporation on the solvation structures and electrochemicalwindows of electrolytes will be studied. Moreover, the repetitive Zn stripping/plating behaviors and galvanic corrosion of Zn in the electrolytes will be systematically investigated, and the mechanism on how the solvation structures induced by aproticsolvents promote the stability of Zn anodes will be elucidated. The implementation of the proposed project will lead to further understanding, and insight into, the design and development of new electrolyte systems for high-performance Zn-ion hybridsupercapacitors.