Ruisheng Guo

Engineering the Electrochemical Capacitive Properties of Microsupercapacitors Based on Graphene Quantum Dots/MnO2 Using Ionic Liquid Gel Electrolytes

All-solid-state microsupercapacitors (MSCs) have been receiving intense interest due to their potential as micro/nanoscale energy storage devices, but their low energy density has limited practical applications. It has been reported that gel electrolytes based on ionic liquids (ionogels) with large potential windows can be used as solid electrolytes to enhance the energy density of MSCs, but a systematic study on how to select and evaluate such ionogels for MSCs is rare. In this study, we construct a series of all-solid-state asymmetric MSCs on the interdigital finger electrodes, using graphene quantum dots (GQDs) as the negative electrode, MnO2 nanosheets as the positive electrode, and different ionogels as the solid electrolytes. Among them, the MSC using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTF2]) with 4 wt % fumed SiO2 ionogel exhibited the best electrochemical performance, having excellent rate capability with the scan rate up to 2000 V s(-1), ultrafast frequency response (τ0 = 206.9 μs) and high energy density. The outstanding performance of this device mainly results from fast ion diffusion, high ion conductivity of the ionogel, and ionic liquid-matrix interactions. The results presented here provide guidance for picking out appropriate ionogels for use in high-performance all-solid-state MSCs to meet the growing requirement of micronanoscale energy storage devices. Additionally, the ultrafast frequency response of our MSCs suggests potential applications in ac line-filters.

A high-temperature flexible supercapacitor based on pseudocapacitive behavior of FeOOH in an ionic liquid electrolyte

Although flexible all-solid-state supercapacitors (f-SSCs) have been receiving much attention as promising flexible energy storage devices, most of them cannot operate at high temperatures due to the volatility or flammability of currently used aqueous and organic electrolytes. Here, we report an ionic liquid (IL) gel-based asymmetric supercapacitor having excellent heat-resistant performance and flexibility. To this end, low-cost γ-FeOOH is firstly electrodeposited on carbon cloth, and its pseudocapacitive behavior in a typical IL is investigated through an electrochemical quartz crystal microbalance (EQCM) for the first time. The results show that the pseudocapacitance mainly originates from a diffusion-controlled insertion process of the cations. By taking advantage of the prominent pseudocapacitance of γ-FeOOH, as well as excellent characteristics of IL gel electrolytes (thermostability, non-flammability, chemical inertness and wide potential), an advanced high-temperature f-SSC is fabricated by using γ-FeOOH as the anode and porous N-doped activated carbon as the cathode. The f-SSC exhibits outstanding electrochemical performance at elevated temperatures, and can achieve a maximum volumetric energy density of 1.44 mW h cm−3 (based on the whole device volume) at 200 °C. Moreover, it is able to maintain a stable energy-storage ability during the bending process even at 180 °C, providing the highest reported temperature for flexibility tests in f-SSCs to date.

Mesoporous Ni-doped MnCo2O4 hollow nanotubes as an anode material for sodium ion batteries with ultralong life and pseudocapacitive mechanism

Mesoporous Ni-doped MnCo2O4 hollow nanotubes (denoted as MCNO-HNTs) are successfully prepared through simple single-nozzle electrospinning combined with thermal treatment. MCNO-HNTs obviously exhibit a hollow structure and are assembled by a lot of small nanoparticles. When used as an anode material for sodium-ion batteries (SIBs), this electrode exhibits remarkable capacity retention of 81% at 1 A g−1 even after 11 000 cycles. The outstanding electrochemical performance can be attributed to the unique hollow mesoporous structure that alleviates stress caused by large volume changes, suppresses the agglomeration of the pulverized nanoparticles, and facilitates the transfer of electrons and electrolyte ions during prolonged cycling. Furthermore, the pseudocapacitive behavior of this material also effectively improves the electrochemical reaction kinetics. Therefore, due to the simple single-nozzle electrospinning technique and high electrochemical performance, mesoporous MCNO-HNTs have great potential as an anode material for rechargeable SIBs.

Carbon encapsulated RuO2 nano-dots anchoring on graphene as an electrode for asymmetric supercapacitors with ultralong cycle life in an ionic liquid electrolyte

Assembling asymmetric supercapacitors (SCs) combined with ionic liquid (IL) electrolytes is a very efficient strategy to enhance the energy density of SCs. However, the poor cycle stability of pseudocapacitive metal oxides in ILs seriously affects the performance of this class of asymmetric SCs. Improving the structural stability of metal oxides during the charge/discharge process is one of the greatest challenges at present. Herein, RuO2 nano-dots/reduced graphene oxide (RGO) composites are firstly prepared, and an IL-based asymmetric SC is built using the component-optimized composite (20 wt% RuO2/RGO) as the cathode and activated polyaniline-derived carbon nanorods (denoted as APDC) as the anode. It exhibits a high energy density of 108 W h kg−1, but shows poor cycling stability. In order to solve this problem, an ultrathin carbon layer originating from glucose is employed to encapsulate RuO2 nano-dots anchoring on RGO, forming a core/shell structure of RuO2@C. With the protection of the carbon shell, the as-made RuO2@C/RGO//APDC asymmetric SC exhibits superior long-term stability with 98.5% capacitance retention after 100 000 cycles in the IL electrolyte, as well as a high energy density of 103 W h kg−1 with a potential window of 3.8 V. Furthermore, this protection mechanism of the carbon layer is analyzed by electrochemical quartz crystal microbalance experiments.