Enhancing safety and performance of hybrid supercapacitors through material system optimization

Hybrid supercapacitors (HSCs) integrate battery-type materials and capacitive materials into the same electrode by means of internal parallel, which greatly improve the energy density while maintaining the power density and meet the needs of more applications. However, different material systems have varying effects on the electrical performance and safety characteristics of HSCs. This paper conducted theoretical research on the electrical and thermal properties of key materials for HSCs to achieve performance improvement. The cathode was composed of lithium nickel cobalt manganate oxide (LiNi_0.6Co_0.2Mn_0.2O₂, NCM622) and activated carbon (AC). It was found that adding an appropriate amount of AC can reduce the internal resistance. However, an excessively high proportion of AC leaded to a decrease in compact density and a decline in electrochemical performance. The optimal NCM/AC ratio was determined to be 9:1. Moreover, a comparative study of different separator materials revealed that the use of polyethylene terephthalate (PET)/ceramic composite separators significantly improves the safety of HSCs, reducing the maximum temperature during thermal runaway by 30 °C, and exhibiting a high self-discharge retention rate of 90% after 350 days at 55 °C. Furthermore, the investigation of different carbon materials for the anode found that hard carbon (HC) possesses larger interlayer spacing, more structural defects, and irregular edge spaces, resulting in superior rate capability, cycling performance, and high/low-temperature characteristics. Through material optimization, the constructed HSCs achieved an energy density of 122.8 Wh kg⁻¹, with 97.2% energy at 10 °C compared to 1 °C, a 99% energy retention rate after 5000 cycles, 76.24% energy at − 25 °C compared to 25 °C, and demonstrating exceptional safety properties.