| 1. |
- Calcagno, Giulio, 1990, et al.
(author)
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Fast charging negative electrodes based on anatase titanium dioxide beads for highly stable Li-ion capacitors
- 2020
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In: Materials Today Energy. - : Elsevier BV. - 2468-6069. ; 16
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Journal article (peer-reviewed)abstract
- Hybrid energy storage systems aim to achieve both high power and energy densities by combining supercapacitor-type and battery-type electrodes in tandem. The challenge is to find sustainable materials as fast charging negative electrodes, which are characterized by high capacity retention. In this study, mesoporous anatase beads are synthetized with tailored morphology to exploit fast surface redox reactions. The TiO2-based electrodes are properly paired with a commercial activated carbon cathode to form a Li-ion capacitor. The titania electrode exhibits high capacity and rate performance. The device shows extremely stable performance with an energy density of 27 mWh g-1 at a specific current of 2.5 A g−1 for 10,000 cycles. The remarkable stability is associated with a gradual shift of the potential during cycling as result of the formation of cubic LiTiO2 on the surface of the beads. This phenomenon renews the interest in using TiO2 as negative electrode for Li-ion capacitors.
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| 2. |
- Lindberg, Simon, 1987, et al.
(author)
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Charge storage mechanism of α-MnO2 in protic and aprotic ionic liquid electrolytes
- 2020
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 460
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Journal article (peer-reviewed)abstract
- In this work we have investigated the charge storage mechanism of MnO2 electrodes in ionic liquid electrolytes. We show that by using an ionic liquid with a cation that has the ability to form hydrogen bonds with the active material (MnO2) on the surface of the electrode, a clear faradaic contribution is obtained. This situation is found for ionic liquids with cations that have a low pKa, i.e. protic ionic liquids. For a protic ionic liquid, the specific capacity at low scan rate rates can be explained by a densely packed layer of cations that are in a standing geometry, with a proton directly interacting through a hydrogen bond with the surface of the active material in the electrode. In contrast, for aprotic ionic liquids there is no interaction and only a double layer contribution to the charge storage is observed. However, by adding an alkali salt to the aprotic ionic liquid, a faradaic contribution is obtained from the insertion of Li+ into the surface of the MnO2 electrode. No effect can be observed when Li+ is added to the protic IL, suggesting that a densely packed cation layer in this case prevent Li-ions from reaching the active material surface.
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| 3. |
- Momodu, Damilola, et al.
(author)
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Stable ionic-liquid-based symmetric supercapacitors from Capsicum seed-porous carbons
- 2019
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In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 838, s. 119-128
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Journal article (peer-reviewed)abstract
- In this study, a symmetric ionic-liquid based supercapacitor was assembled with porous carbon derived from Capsicum (bell pepper) seeds. The “peppered”-activated carbon (ppAC) was synthesized using varying amounts of KHCO 3 activating agent (AA) at 850 °C carbonization temperature. The best device performance reported was recorded with optimum amounts of AA to raw material. The need for less amount of AA is crucial if the entire activation/carbonization process is to be scaled-up with the cost and final product yield also being important for a viable synthesis. A mechanism of saturation of pores with unreacted AA which leads to lower porosity metrics in the samples with increasing the amount of AA during carbonization/activation was also proposed. Using an ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bistrifluorosulfonylimide (EMIM-TFSI), the ppAC-based supercapacitor operated up to a maximum cell voltage of 3.20 V. A specific energy of 37 Wh kg −1 was obtainable with a corresponding practical power density of 0.6 kW kg −1 at 0.5 A g −1 . A specific energy of ∼26 Wh kg −1 was still achievable when the applied current was doubled to 1.0 A g −1 and a high cyclic stability (approx. 99% coulombic efficiency) was proven over 25,000 cycles. Further ageing test performed on the device revealed a remarkable improvement in the electrochemical performance after a 180 h (ca. 1 week) floating time. The obtained results also confirmed a uniquely distributed porous carbon in which the complete utilization of the entire less-corrosive KHCO 3 AA for optimal pore activation at elevated carbonization temperatures. Thus, the efficient design combinations for stable, high-energy and power ionic liquid-based supercapacitors with cheaper biomass-based materials are demonstrated.
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| 4. |
- Oyedotun, Kabir O., et al.
(author)
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Comparison of ionic liquid electrolyte to aqueous electrolytes on carbon nanofibres supercapacitor electrode derived from oxygen-functionalized graphene
- 2019
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In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 375
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Journal article (peer-reviewed)abstract
- A facial force-driven reflux technique was used to develop fibre-like carbon material from freeze-dried reduced graphene oxide (RGO) firstly prepared by using a modified Hummers method. The carbon nanofibres displayed a high specific surface area of ∼1317.8 m2 g−1, with good pore size distributions which could be beneficial for energy storage applications. Electrochemical measurements of the carbon nanofibre electrodes in a symmetric configuration with aqueous (1 M Na2SO4, 6 M KOH), and protic ionic liquid (1-ethylimidazolium bis(trifluoromethanesulfonly)imide) electrolytes (ILE) displayed excellent electrochemical performance with the dominant electric double layer capacitor (EDLC) behaviour. The fabricated device shows higher electrochemical performance in the ILE due to its larger cell operating potential (3.0 V) as compared with the aqueous electrolytes (0.8 V). The optimized electrochemical properties especially in terms of higher specific energy and superior stability, suggest the material's potential applications as electrode for supercapacitors.
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