Acidic “Water-in-Salt” Electrolyte Enables a High-Energy Symmetric Supercapacitor Based on Titanium Carbide MXene
Chengzhi Yuan (Shenzhen Technology University, Hubei University)
Chaofan Chen (TU Delft - RST/Storage of Electrochemical Energy)
Zhiwei Yang (Shenzhen Technology University)
Jiaji Cheng (Hubei University)
Ji Weng (Shenzhen Technology University)
Shuhui Tan (Shenzhen Technology University)
Renzhong Hou (Shenzhen Technology University)
Tao Cao (Shenzhen Technology University)
Zeguo Tang (Shenzhen Technology University)
Wei Chen (Shenzhen Technology University)
Baomin Xu (Southern University of Science and Technology )
Xuehang Wang (TU Delft - RST/Storage of Electrochemical Energy)
Jun Tang (Hubei University, Shenzhen Technology University)
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Abstract
Titanium carbide MXene, Ti3C2Tx, exhibits ultrahigh capacitance in acidic electrolytes at negative potentials yet poor stability at positive potentials, resulting in low-energy densities for Ti3C2Tx-based symmetric supercapacitors. Utilizing “water-in-salt” electrolytes has successfully expanded the stable operation potential window of MXenes. However, this advancement comes at the cost of sacrificing their high capacitance in acidic electrolytes. In this work, we report an acidic “water-in-salt” (AWIS) electrolyte composed of sulfuric acid and saturated lithium halide, which effectively doubled the energy density of the Ti3C2Tx-based symmetric supercapacitor compared to those with bare acidic electrolytes. Specifically, the AWIS electrolyte successfully expanded the voltage window of the symmetric device to 1.1 V. A high specific capacitance of 112.34 F g-1 (at 10 mV s-1) was obtained due to the presence of proton redox. As a result, the symmetric device achieved a high-energy density of 19.1 Wh kg-1 and a high capacitance retention of 96.3% after 10,000 cycles. This work demonstrates the importance of designing stable and redox-active electrolytes for high-energy MXene-based symmetric supercapacitors.