Flexible Solid-State Supercapacitor with High Energy Density Enabled by N/B/O-Codoped Porous Carbon Nanoparticles and Imidazolium-Based Gel Polymer Electrolyte
Shiyu Yu, Bei Liu, Hongbiao Chen, Mei Yang, Yijiang Liu, Huaming Li
Abstract
Flexible solid-state supercapacitors (FSSCs) have great potentiality in powering flexible electronics, however, their low-energy densities, together with a bulky structure, hinder the practical applications. Here we report the synthesis of folic acid-derived N/B/O-codoped carbon nanoparticles (NBC-850) as well as imidazolium-based gel polymer electrolyte (MPEI-TF-IL) for high energy density FSSCs. Specifically, NBC-850 is prepared by carbonization of premixed precursors consisting of ammonia-treated folic acid, boric acid, and ammonium phosphate at 850 °C. MPEI-TF-IL is fabricated by a Debus–Radziszewski reaction of poly(ethylene imine) with glyoxal and formaldehyde, followed by an anion exchange and then mixing with 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIMTFSI). Owing to the large specific surface area (1400 m2 g–1), optimal porosity distribution, and high heteroatom contents (N, 9.62 at%; B, 1.47 at%; and O, 14.12 at%), the NBC-850 electrode shows a high capacitance of 447.3 F g–1 at 0.5 A g–1 in alkaline electrolyte. Symmetrical supercapacitors assembled with NBC-850 electrodes deliver energy densities of 13.67 and 32.61 Wh kg–1, respectively, in KOH and Na2SO4 electrolytes. More importantly, FSSC fabricated with NBC-850 electrodes and a MPEI-TF-IL electrolyte can deliver a large energy density of 57.5 Wh kg–1 at 357.7 W kg–1, showing its promising potential in powering flexible and wearable electronics.