Systematic Approach to Constructing Safe and High-Performance Supercapacitors with Nonflammable Electrolytes.

The successful implementation of supercapacitors in large-scale applications necessitates careful consideration of safety aspects, along with factors such as energy density, power density, working voltage, and cycling performance. One effective method for ensuring safety is the utilization of nonflammable trimethyl phosphate (TMP) electrolyte in supercapacitors. However, this approach suffers from the drawback of low power density due to its low ionic conductivity. To overcome this limitation, we propose the addition of co-solvents, namely propylene carbonate, acetonitrile, and propionitrile (PN), to enhance limited electrochemical properties of TMP-based electrolytes. We systematically investigate the impact of incorporating TMP into various organic solvents on physical and electrochemical properties. Binary electrolytes show improved ionic conductivity, capacitance, power density, energy density, and working voltage compared to the single TMP-based electrolyte. Notably, our result highlights that the carbon-based supercapacitors using TMP-PN with 70 : 30 volume ratio electrolyte provide the best compromise between ionic conductivity (13.5 mS cm-1 ), capacitance (24.0 F g-1 ), energy density (13.2 Wh kg-1 ), power density (2.3 kW kg-1 ), working voltage (3.5 V), and safety. By combining the nonflammable properties of TMP with co-solvents, we can overcome the trade-off between safety and electrochemical performances, presenting advancement in the development of supercapacitors for energy storage applications.

Advances in high-voltage supercapacitors for energy storage systems: materials and electrolyte tailoring to implementation.

To achieve a zero-carbon-emission society, it is essential to increase the use of clean and renewable energy. Yet, renewable energy resources present constraints in terms of geographical locations and limited time intervals for energy generation. Therefore, there is a surging demand for developing high-performance energy storage systems (ESSs) to effectively store the energy during the peak time and use the energy during the trough period. To this end, supercapacitors hold great promise as short-term ESSs for rapid power recovery or frequency regulation to improve the quality and reliability of power supply. In particular, the electrical double layer capacitor (EDLC) which offers long and stable cycle retention, high power densities, and fast charge/discharge characteristics with a moderate operating voltage window, is a suitable candidate. Yet, for implementation of the EDLC in ESSs, further research effort is required in terms of increasing the operating voltage and energy densities while maintaining the long-term cycle stability and power densities which are desirable aspects for ESS operation. Here, we examine the advances in EDLC research to achieve a high operating voltage window along with high energy densities, covering from materials and electrolytes to long-term device perspectives for next-generation supercapacitor-based ESSs.