Breaking the Limits of Ionic Liquid‐Based Supercapacitors: Mesoporous Carbon Electrodes Functionalized with Manganese Oxide Nanosplotches for Dense, Stable, and Wide‐Temperature Energy Storage

Abstract

AbstractManganese oxide (MnO2) nanosplotches (NSs) are deposited on N‐ and S‐doped ordered mesoporous carbon (N,S‐CMK‐3) essentially blocking microporosity. The obtained N,S‐CMK‐3/MnO2 composite materials are assembled into ionic liquid (IL)‐based symmetric supercapacitors, which exhibit a high specific capacitance of 200 F g−1 (0–3.5 V) at a scan rate of 2 mV s−1, and good rate stability with 55.5% capacitance retention at a scan rate of 100 mV s−1. The device can operate in a wide temperature range (−20 to 60 °C), and high cycling stability of N,S‐CMK‐3/MnO2 composite electrode is demonstrated. Lower energy of −3.56 eV can be achieved for the adsorption of 1‐ethyl‐3‐methylimidazolium+ (EMIM+) cation on the edge between MnO2 NSs and N,S‐CMK‐3 than on the plane of MnO2 NS (−3.04 eV), both being more preferred than the surface of pristine N,S‐CMK‐3 (−1.52 eV). This strengthening of the ion adsorption at the three‐phase boundary between N,S‐CMK‐3, MnO2, and IL leads to enhancement of the specific capacity as compared to nondoped or MnO2‐free reference materials. Supercapacitors based on such composite electrodes show significantly enhanced areal capacity pointing to energy storage in the mesopores rather than in the electrochemical surface layer, demonstrating a new energy storage mechanism in ILs.