| 1. |
- Li, G. H., et al.
(författare)
-
Surface element segregation and electrical conductivity of lithium layered transition-metal oxide cathode materials
- 2018
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 427, s. 226-232
-
Tidskriftsartikel (refereegranskat)abstract
- Surface element segregation and electric conductivity are critical in determining lithium storage ability of given cathode materials, which are poorly understood and not correlated with the structure and overall performance. Here, layered lithium transition-metal oxides, one of the state-of-the-art cathode materials for lithium ion batteries are chosen to study. A serial of LiNixCo1-2xMnxO2 samples were prepared via a solid state reaction and subsequently characterized by XRD in conjunction with structural refinement, XPS depth profiling, and AC impedance spectroscopy. Slightly different expansion rates are observed for lattice parameters (a and c/3) with varying of Ni content, which is attributed to the increase of average metalion radius and an increase of e(g) electron that enhances the columbic repulsion between transition metal and oxygen atoms. XPS depth profiling results show that surface composition is significantly deviated from bulk, in which Ni and Mn atoms tend to enrich in the surface region, while Co element is relatively deficient. Further, surface element segregation is alleviated by the increase of Ni/Mn content. Moreover, increasing the Ni/Mn content also raises the activation energy of bulk conduction.
|
|
| 2. |
- Chen, Shaoqing, et al.
(författare)
-
Anchoring High-Concentration Oxygen Vacancies at Interfaces of CeO2–x/Cu toward Enhanced Activity for Preferential CO Oxidation
- 2015
-
Ingår i: ACS Applied Materials & Interfaces. - 1944-8252 .- 1944-8244. ; 7:41, s. 22999-23007
-
Tidskriftsartikel (refereegranskat)abstract
- Catalysts are urgently needed to remove the residual CO in hydrogen feeds through selective oxidation for large-scale applications of hydrogen proton exchange membrane fuel cells. We herein propose a new methodology that anchors high concentration oxygen vacancies at interface by designing a CeO2–x/Cu hybrid catalyst with enhanced preferential CO oxidation activity. This hybrid catalyst, with more than 6.1% oxygen vacancies fixed at the favorable interfacial sites, displays nearly 100% CO conversion efficiency in H2-rich streams over a broad temperature window from 120 to 210 °C, strikingly 5-fold wider than that of conventional CeO2/Cu (i.e., CeO2 supported on Cu) catalyst. Moreover, the catalyst exhibits a highest cycling stability ever reported, showing no deterioration after five cycling tests, and a super long-time stability beyond 100 h in the simulated operation environment that involves CO2 and H2O. On the basis of an arsenal of characterization techniques, we clearly show that the anchored oxygen vacancies are generated as a consequence of electron donation from metal copper atoms to CeO2 acceptor and the subsequent reverse spillover of oxygen induced by electron transfer in well controlled nanoheterojunction. The anchored oxygen vacancies play a bridging role in electron capture or transfer and drive molecule oxygen into active oxygen species to interact with the CO molecules adsorbed at interfaces, thus leading to an excellent preferential CO oxidation performance. This study opens a window to design a vast number of high-performance metal-oxide hybrid catalysts via the concept of anchoring oxygen vacancies at interfaces.
|
|
| 3. |
- Fan, Jianming, et al.
(författare)
-
Hydrothermal-assisted synthesis of Li-rich layered oxide microspheres with high capacity and superior rate-capability as a cathode for lithium-ion batteries
- 2015
-
Ingår i: Electrochimica Acta. - 0013-4686. ; 173, s. 7-16
-
Tidskriftsartikel (refereegranskat)abstract
- Li-rich layered oxide materials possess high voltage and high specific capacity, which makes them attractive cathode candidates for lithium-ion batteries. However, they still suffer from a poor rate capability, which seriously blocks their widespread practical applications. In this work, Li(Li0.167Mn0.5Co0.167Ni0.167)O2 microspheres were synthesized by a hydrothermal-assisted method, in which Ni-Co-Mn-based microspherical precursors obtained by a hydrothermal process with polyethylene glycol-600 (PEG-600) as a surfactant were mixed with lithium sources and then sintered to yield the final products. It is found that the as-prepared Li-rich layered oxide microspheres exhibit high discharge capacity and superior rate performance: delivering an initial discharge capacity of 292 mAh g−1 at a current density of 20 mA g−1, 189 mAh g−1 at a current density of 600 mA g−1 and 142 mAh g−1 at a current density of 2000 mA g−1 (10C), which are better than that of the sample as-prepared by co-precipitation method. The high discharge capacity and improved rate-capability were beneficial from the microspheres assembled by uniform primary particles around 250 nm, more reversible redox and better electrode kinetics comparing to that of the co-precipitation sample. The preparation strategy reported here may offer hints for achieving various advanced Li-rich layered composite materials that would be used in high-performance energy storage.
|
|
| 4. |
- Fu, Chaochao, et al.
(författare)
-
Nickel-Rich Layered Microspheres Cathodes: Lithium/Nickel Disordering and Electrochemical Performance
- 2014
-
Ingår i: ACS Applied Materials & Interfaces. - 1944-8252 .- 1944-8244. ; 6:18, s. 15822-15831
-
Tidskriftsartikel (refereegranskat)abstract
- Nickel-rich layered metal oxide materials are prospective cathode materials for lithium ion batteries due to the relatively higher capacity and lower cost than LiCoO2. Nevertheless, the disordered arrangement of Li+/Ni2+ in local regions of these materials and its impact on electrochemistry performance are not well understood, especially for LiNi1–x–yCoxMnyO2 (1–x–y > 0.5) cathodes, which challenge one’s ability in finding more superior cathode materials for advanced lithium-ion batteries. In this work, Ni–Co–Mn-based spherical precursors were first obtained by a solvothermal method through handily utilizing the redox reaction of nitrate and ethanol. Subsequent sintering of the precursors with given amount of lithium source (Li-excess of 5, 10, and 15 mol %) yields LiNi0.7Co0.15Mn0.15O2 microspheres with different extents of Li+/Ni2+ disordering. With the determination of the amounts of Li+ ions in transition metal layer and Ni2+ ions in Li layer using structural refinement, the impact of Li+/Ni2+ ions disordering on the crystal structure, valence state of nickel ions, and electrochemical performance were investigated in detailed. It is clearly demonstrated that with increasing the amount of lithium source, lattice parameters (a and c) and interslab space thickness of unit cell decrease, and more Li+ ions incorporated into the 3a site of transition metal layer which leads to an increase of Ni3+ content in LiNi0.7Co0.15Mn0.15O2 as confirmed by X-ray photoelectron spectroscopy and a redox titration. Moreover, the electrochemical performance for as-prepared LiNi0.7Co0.15Mn0.15O2 microspheres exhibited a trend of deterioration due to the changes of crystal structure from Li+/Ni2+ mixing. The preparation method and the impacts of Li+/Ni2+ ions disordering reported herein for the nickel-rich layered LiNi0.7Co0.15Mn0.15O2 microspheres may provide hints for obtaining a broad class of nickel-rich layered metal oxide microspheres with superior electrochemical performance.
|
|
| 5. |
- Li, Qi, 1990, et al.
(författare)
-
A Study on Storage Characteristics of Pristine Li-rich Layered Oxide Li1.20Mn0.54Co0.13Ni0.13O2: Effect of Storage Temperature and Duration
- 2015
-
Ingår i: Electrochimica Acta. - 0013-4686. ; 154, s. 249-158
-
Tidskriftsartikel (refereegranskat)abstract
- Lithium-ion batteries always suffer from serious capability decay, especially when stored at high temperature and/or for prolonged duration. In this work, electrochemical performance for Li-rich layered oxides Li1.20Mn0.54Co0.13Ni0.13O2 was systematically investigated as a function of temperature and duration. Plenty of techniques like SEM, EDS, EIS, ARC, Raman, XRD, and XPS were utilized to characterize the structures, valence states, compositions, particle sizes, and morphologies of the layered oxides with varying temperature and duration. The results reveal that room temperature storage may alter surface kinetics, but hardly influence the electrochemical performance. While in the case of high temperature storage in pristine state, cycling stability is highly dependent on the storage duration. The degradation mechanism at high temperature storage with prolonged duration is demonstrated to be the accumulation of surface species like LiF/LixPFyOz initiated by the strong reactions between LiPF6 electrolyte and electrode. The results reported here may shed light on predicting electrochemical performance by surface analysis and also provide vital hints on enhancing the high-temperature storage stability of Li-rich layered oxides.
|
|
| 6. |
- Li, Qi, 1990, et al.
(författare)
-
Balancing stability and specific energy in Li-rich cathodes for lithium ion batteries: a case study of a novel Li–Mn–Ni–Co oxide
- 2015
-
Ingår i: Journal of Materials Chemistry. - 1364-5501 .- 0959-9428. ; 3:19, s. 10592-10602
-
Tidskriftsartikel (refereegranskat)abstract
- Lithium batteries for UPS, portable electronics and electrical vehicles rely on high-energy cathodes. Li-rich manganese-rich oxide (xLi2MnO3·(1 − x)LiMO2, M = transition metals) is one of the few materials that might meet such a requirement, but it suffers from poor energy retention due to serious voltage and/or capacity fade, which challenges its applications. Here we show that this challenge can be addressed by optimizing the interactions between the components Li2MnO3 and LiMO2 in the Li-rich oxide (i.e. stabilizing the layered structure through Li2MnO3 and controlling Li2MnO3 activation through LiMO2). To realize this synergistic effect, a novel Li2MnO3-stabilized Li1.080Mn0.503Ni0.387Co0.030O2 was designed and prepared using a hierarchical carbonate precursor obtained by a solvo/hydro-thermal method. This layered oxide is demonstrated to have a high working voltage of 3.9 V and large specific energy of 805 W h kg−1 at 29 °C as well as impressive energy retention of 92% over 100 cycles. Even when exposed to 55 °C, energy retention is still as high as 85% at 200 mA g−1. The attractive performance is most likely the consequence of the balanced stability and specific energy in the present material, which is promisingly applicable to other Li-rich oxide systems. This work sheds light on harnessing Li2MnO3 activation and furthermore efficient battery design simply through compositional tuning and temperature regulation.
|
|
| 7. |
- Li, Qi, 1990, et al.
(författare)
-
K+-Doped Li1.2Mn0.54Co0.13Ni0.13O2: A Novel Cathode Material with an Enhanced Cycling Stability for Lithium-Ion Batteries
- 2014
-
Ingår i: ACS Applied Materials & Interfaces. - 1944-8252 .- 1944-8244. ; 6:13, s. 10330-10341
-
Tidskriftsartikel (refereegranskat)abstract
- Li-rich layered oxides have attracted much attention for their potential application as cathode materials in lithium ion batteries, but still suffer from inferior cycling stability and fast voltage decay during cycling. How to eliminate the detrimental spinel growth is highly challenging in this regard. Herein, in situ K+-doped Li1.20Mn0.54Co0.13Ni0.13O2 was successfully prepared using a potassium containing α-MnO2 as the starting material. A systematic investigation demonstrates for the first time, that the in situ potassium doping stabilizes the host layered structure by prohibiting the formation of spinel structure during cycling. This is likely due to the fact that potassium ions in the lithium layer could weaken the formation of trivacancies in lithium layer and Mn migration to form spinel structure, and that the large ionic radius of potassium could possibly aggravate steric hindrance for spinel growth. Consequently, the obtained oxides exhibited a superior cycling stability with 85% of initial capacity (315 mA h g–1) even after 110 cycles. The results reported in this work are fundamentally important, which could provide a vital hint for inhibiting the undesired layered-spinel intergrowth with alkali ion doping and might be extended to other classes of layered oxides for excellent cycling performance.
|
|
| 8. |
- Luo, Dong, et al.
(författare)
-
A New Spinel-Layered Li-Rich Microsphere as a High-Rate Cathode Material for Li-Ion Batteries
- 2014
-
Ingår i: Advanced Energy Materials. - 1614-6840 .- 1614-6832. ; 4:11
-
Tidskriftsartikel (refereegranskat)abstract
- Li-rich layered materials are considered to be the promising low-cost cathodes for lithium-ion batteries but they suffer from poor rate capability despite of efforts toward surface coating or foreign dopings. Here, spinel-layered Li-rich Li-Mn-Co-O microspheres are reported as a new high-rate cathode material for Li-ion batteries. The synthetic procedure is relatively simple, involving the formation of uniform carbonate precursor under solvothermal conditions and its subsequent transformation to an assembled microsphere that integrates a spinel-like component with a layered component by a heat treatment. When calcined at 700 °C, the amount of transition metal Mn and Co in the Li-Mn-Co-O microspheres maintained is similar to at 800 °C, while the structures of constituent particles partially transform from 2D to 3D channels. As a consequence, when tested as a cathode for lithium-ion batteries, the spinel-layered Li-rich Li-Mn-Co-O microspheres obtained at 700 °C show a maximum discharge capacity of 185.1 mA h g−1 at a very high current density of 1200 mA g−1 between 2.0 and 4.6 V. Such a capacity is among the highest reported to date at high charge-discharge rates. Therefore, the present spinel-layered Li-rich Li-Mn-Co-O microspheres represent an attractive alternative to high-rate electrode materials for lithium-ion batteries.
|
|
| 9. |
- Luo, Dong, et al.
(författare)
-
LiMO2 (M = Mn, Co, Ni) hexagonal sheets with (101) facets for ultrafast charging–discharging lithium ion batteries
- 2015
-
Ingår i: Journal of Power Sources. - 0378-7753. ; 276, s. 238-246
-
Tidskriftsartikel (refereegranskat)abstract
- Developing energy storage equipments that can work at very high charge–discharge rate is crucial, but highly challenging for more efficient use of energy. From the perspective of chemistry, high-rate property of Li-ion batteries can only be achieved by significantly improving the kinetics of lithium ions and electrons in electrode. Here, we for the first time report on a simple method to resolve kinetics problems of ultrafast charging–discharging Li-ion batteries by fabrication of layered LiMO2 (M = Mn, Co, Ni) hexagonal sheet exposing with facets {101}. The synthetic procedure of hexagonal sheets is proceeded via a simple PVP-assisted co-precipitation, which is followed by a heat treatment. All hexagonal sheets LiMnxCoyNizO2 were demonstrated to deliver a superior excellent rate capability and outstanding cycle stability at high current density of 3000 mA g−1 and under a high cutoff voltage of 4.4 V. The discharge capacity for the composition LiMn0.075Co0.775Ni0.15O2 at an ultrahigh charge–discharge rate of 10,000 mA g−1 is almost as large as that for LiMn2O4 and commercial LiFePO4 at low rate of 1C. The methodology reported here to resolve the kinetic problems of lithium ions and electrons in electrodes may have many implications that would help scientists to find more high-rate lithium-ion batteries for powering electric vehicles and other applications.
|
|
| 10. |
- Xie, Dongjiu, et al.
(författare)
-
Improved Cycling Stability of Cobalt-free Li-rich Oxides with a Stable Interface by Dual Doping
- 2016
-
Ingår i: Electrochimica Acta. - 0013-4686. ; 196, s. 505-516
-
Tidskriftsartikel (refereegranskat)abstract
- Li-rich cobalt-free oxides, popularly used as a cathode with high capacity in lithium ion battery, always suffer from poor cycling stability between 2.0 and 4.8 V vs Li+/Li, especially when cycled at high temperatures (>50 °C). To overcome this issue, Na+ and Al3+ dual-doped NaxLi1.2-xMn0.6-xAlxNi0.2O2 Li-rich cathode is prepared in this study. It is shown that the side reactions between cathode and electrolyte during cycling are suppressed. The improved cycling performance is observed for all of the doped samples, among which the sample with x = 0.03 exhibits the highest capacity retention of 86.1% after 200 cycles between 2.0 and 4.8 V at 2C (1C = 200 mA g−1) and shows a remarkable cycling stability, even at a high temperature of 55 °C (a capacity retention of 92.2% after 100 cycles). Moreover, the average voltage of the sample with x = 0.03 after 100 cycles at 0.5C remains at 3.11 V with a retention ratio of 86.6%. This work provides a new strategy to develop Li-rich cobalt-free cathodes with excellent cycling stability for lithium ion batteries at high temperatures.
|
|
| 11. |
- Zhang, Yuelan, et al.
(författare)
-
Smart Solution Chemistry to Sn-Containing Intermetallic Compounds through a Self-Disproportionation Process
- 2016
-
Ingår i: Chemistry - A European Journal. - 1521-3765 .- 0947-6539. ; 22:40, s. 14196-14204
-
Tidskriftsartikel (refereegranskat)abstract
- Developing new methods to synthesize intermetallics is one of the most critical issues for the discovery and application of multifunctional metal materials; however, the synthesis of Sn-containing intermetallics is challenging. In this work, we demonstrated for the first time that a self-disproportionation-induced in situ process produces cavernous Sn−Cu intermetallics (Cu3Sn and Cu6Sn5). The successful synthesis is realized by introducing inorganic metal salts (SnCl2⋅2 H2O) to NaOH aqueous solution to form an intermediate product of reductant (Na2SnO2) and by employing steam pressures that enhance the reduction ability. Distinct from the traditional in situ reduction, the current reduction process avoided the uncontrolled phase composition and excessive use of organic regents. An insight into the mechanism was revealed for the Sn−Cu case. Moreover, this method could be extended to other Sn-containing materials (Sn−Co, Sn−Ni). All these intermetallics were attempted in the catalytic effect on thermal decompositions of ammonium perchlorate. It is demonstrated that Cu3Sn showed an outstanding catalytic performance. The superior property might be primarily originated from the intrinsic chemical compositions and cavernous morphology as well. We supposed that this smart solution reduction methodology reported here would provide a new recognition for the reduction reaction, and its modified strategy may be applied to the synthesis of other metals, intermetallics as well as some unknown materials.
|
|
| 12. |
- Zhang, Yuelan, et al.
(författare)
-
Two-Step Grain-Growth Kinetics of Sub-7 nm SnO2 Nanocrystal under Hydrothermal Condition
- 2015
-
Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 119:33, s. 19505-19512
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, the grain growth kinetics of SnO2 quantum dots under hydrothermal conditions was investigated. By varying the reaction temperature and duration, SnO2 particle sizes were tuned from 2 to 7 nm. It is demonstrated that the growth behavior of subnanometer-sized SnO2 underwent two distinct processes: below the critical size of 5.5 nm, about double of Bohr radius, the grain growth kinetics obeys an Ostwald ripening mechanism, while above that, an oriented attachment process governs the particle growth. For the former cases, the activation energies were Ea1 = 61.94 kJ/mol at 200 °C and Ea1′ = 62.84 kJ/mol at 160 °C, which greatly differs from that of Ea2 = 131.32 kJ/mol for the latter case. High-resolution transmission electron microscope, X-ray diffraction as well as UV–vis diffuses reflectance, photoluminescence, Fourier transmission infrared, and Raman spectra were employed to reveal the size-dependent properties. As the particle size of SnO2 reduces, there occurred a lattice expansion, band gap broadening, and an abnormal blue shift. All these characteristics are closely related to the size changing in a narrow range from quantum dots to several nanometers. The findings reported here may shed light on further understanding the unique behaviors of quantum dots.
|
|
| 13. |
- Li, Feiran, 1993, et al.
(författare)
-
Improving recombinant protein production by yeast through genome-scale modeling using proteome constraints
- 2022
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 13:1
-
Tidskriftsartikel (refereegranskat)abstract
- Eukaryotic cells are used as cell factories to produce and secrete multitudes of recombinant pharmaceutical proteins, including several of the current top-selling drugs. Due to the essential role and complexity of the secretory pathway, improvement for recombinant protein production through metabolic engineering has traditionally been relatively ad-hoc; and a more systematic approach is required to generate novel design principles. Here, we present the proteome-constrained genome-scale protein secretory model of yeast Saccharomyces cerevisiae (pcSecYeast), which enables us to simulate and explain phenotypes caused by limited secretory capacity. We further apply the pcSecYeast model to predict overexpression targets for the production of several recombinant proteins. We experimentally validate many of the predicted targets for alpha-amylase production to demonstrate pcSecYeast application as a computational tool in guiding yeast engineering and improving recombinant protein production. Due to the complexity of the protein secretory pathway, strategy suitable for the production of a certain recombination protein cannot be generalized. Here, the authors construct a proteome-constrained genome-scale protein secretory model for yeast and show its application in the production of different misfolded or recombinant proteins.
|
|
| 14. |
- Wu, Jingnan, 1994, et al.
(författare)
-
Modulating the nanoscale morphology on carboxylate-pyrazine containing terpolymer toward 17.8% efficiency organic solar cells with enhanced thermal stability
- 2022
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 446
-
Tidskriftsartikel (refereegranskat)abstract
- It had been commonly accepted in the organic photovoltaic (OPV) community that subtle variations in the molecular structure of active layer materials would cause profound impacts on their aggregating structure and blend morphology and therefore the performance of such polymer solar cells (PSCs). Herein, we employed an electron-deficient building block 3,6-dithiophenyl-2-carboxylate pyrazine (DTCPz) for constructing one series of promising donor terpolymers of PMZ1, PMZ2, and PMZ3, respectively, gaining their relatively lower-lying highest occupied molecular orbital (HOMO) energy levels, more closed π-π stacking and enhanced crystallinity in thin films, and lower miscibility with acceptor Y6, in comparison with their parent polymer counterpart (namely PM6). Reaching DTCPz moieties up to 20% (mol/mol%) in its terpolymer composition, the resulting polymer (PMZ2) achieved more favorable phase separation with improved exciton dissociation, and charge transport and extraction. As a result, an outstanding fill factor of 77.2% and a promising power conversion efficiency of 17.8 % was achieved. Moreover, the corresponding device shows better thermal stability over the PM6-based one. This work suggests a facile method for significantly improving the thin film morphology of the active-layer materials via fine-tuning the chemical structure of electron-deficient units on the backbone of the wide bandgap donor polymer, therefore achieving enhanced photovoltaic performance and thermal stability for practical applications.
|
|
| 15. |
- Hansson, Josef, 1991, et al.
(författare)
-
Bipolar electrochemical capacitors using double-sided carbon nanotubes on graphite electrodes
- 2020
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 451
-
Tidskriftsartikel (refereegranskat)abstract
- The electrochemical capacitor (EC) is a key enabler for the miniaturized self-powered systems expected to become ubiquitous with the advent of the internet-of-things (IoT). Vertically aligned carbon nanotubes (VACNTs) on graphite holds promise as electrodes for compact and low-loss ECs. However, as with all ECs, the operating voltage is low, and miniaturization of higher voltage devices necessitates a bipolar design. In this paper, we demonstrate a bipolar EC using graphite/VACNTs electrodes fabricated using a joule heating chemical vapor deposition (CVD) setup. The constructed EC contains one layer of double-sided VACNTs on graphite as bipolar electrode. Compared to a series connection of two individual devices, the bipolar EC has 22% boost in volumetric energy density. More significant boost is envisaged for stacking more bipolar electrode layers. The energy enhancement is achieved without aggravating self-discharge (71.2% retention after 1 h), and at no sacrifice of cycling stability (96.7% over 50000 cycles) owing to uniform growth of VACNTs and thus eliminating cell imbalance problems.
|
|
| 16. |
- Haque, Mohammad Mazharul, 1984, et al.
(författare)
-
Exploiting low-grade waste heat to produce electricity through supercapacitor containing carbon electrodes and ionic liquid electrolytes
- 2022
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 403
-
Tidskriftsartikel (refereegranskat)abstract
- Low-grade thermal energy harvesting presents great challenges to traditional thermoelectric systems based on the Seebeck effect, the thermogalvanic effect, and the Soret effect due to fixed temperature gradient and low voltage output. In this study, we report an ionic thermoelectric system, essentially a supercapacitor (SC) containing an ionic liquid (IL) electrolyte and activated carbon electrodes, which works on the thermocapacitive effect and does not require any fixed temperature gradient, rather it works in a homogeneously changing temperature. A systematic investigation is carried out on SCs containing two different ILs, 1-Ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl), EMIm TFSI, and 1-Ethyl-3-methylimidazolium acetate, EMIm OAc. A high voltage output of 176 mV is achieved for EMIm TFSI containing SC by exposing just to 60 °C environment. Moreover, a large voltage of 502 mV is recovered from the SC upon subjecting to heat after one electrical charge/discharge cycle. A system containing two SCs in series demonstrates a significant voltage of 947 mV. The observed performance difference between the two ILs is rationalized in terms of the extent of asymmetry in the interfaces of the electrical double layer that essentially originates from different diffusivity of individual ions. The mechanism can be applied to a plethora of ILs to exploit low-grade heat to store electricity without a fixed temperature gradient, opening up the possibility to merge different scientific communities and enrich this rising research field.
|
|
| 17. |
- Haque, Mohammad Mazharul, 1984, et al.
(författare)
-
Identification of self-discharge mechanisms of ionic liquid electrolyte based supercapacitor under high-temperature operation
- 2021
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 485
-
Tidskriftsartikel (refereegranskat)abstract
- Ionic liquids (ILs) are promising electrolytes for supercapacitors (SCs) aimed for high-temperature applications, where increased ionic conductivity results in superior capacitive performance compared to room temperature (RT) performance. However, an increased temperature also accelerates the self-discharge rate that adversely affects energy retention and restricts the usage of SCs in standalone applications. In this study, a detailed electrochemical investigation on the self-discharge behaviour of carbon-based SCs containing an IL, 1-Ethyl-3-methylimidazolium acetate (EMIM Ac), has been carried out in the temperature range RT - 60 °C, and the underlying self-discharge mechanisms are identified. The results reveal that at a high voltage of 1.5 V, the self-discharge is characterized by a combination of charge redistribution and diffusion at both RT and 60 °C. At 60 °C, the diffusion-controlled mechanism dominates at lower voltages over the charge redistribution effect, while at RT both mechanisms contribute to a similar extent. The observed difference in the self-discharge mechanism between RT and 60 °C is explained in terms of a decreased RC time constant (τRC) at elevated temperature, and the same conclusions are potentially applicable to other IL-containing SCs as well.
|
|
| 18. |
- Haque, Mohammad Mazharul, 1984, et al.
(författare)
-
Ionic liquid electrolyte for supercapacitor with high temperature compatibility
- 2017
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 922:1
-
Konferensbidrag (refereegranskat)abstract
- This work describes the electrochemical investigation of two ionic liquids (ILs), 1-ethyl-3-methylimidazolium acetate (EMIM Ac) and 1-butyl-3-methylimidazolium chloride (BMIM Cl), as electrolytes in supercapacitors (SC). A comprehensive study on high temperature (HT) endurance that is required for system integration in microelectronics has also been carried out. It has been found that EMIM Ac containing SC performs better than a BMIM Cl containing SC, and HT treatment improves the capacitive performance.
|
|
| 19. |
- Haque, Mohammad Mazharul, 1984, et al.
(författare)
-
Self-discharge and leakage current mitigation of neutral aqueous-based supercapacitor by means of liquid crystal additive
- 2020
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 453
-
Tidskriftsartikel (refereegranskat)abstract
- Self-discharge is being recognized as one of the main obstacles to implementing the supercapacitor (SC) in standalone self-powered systems. Strategies for addressing this issue include the modification of electrodes, electrolytes, separators, and diverse device configurations. However, an improved self-discharge behavior is often achieved with a large compromise on other prominent figures of merit such as capacitance, energy density, or cycle life of the device. In this work, a thorough comparative electrochemical investigation of SCs containing a neutral aqueous electrolyte, 1 M Li2SO4, and with a liquid crystal (LC) additive, 2% 4-n-pentyl-4′-cyanobiphenyl (5CB) in 1 M Li2SO4, has been carried out at different states of charge. The results demonstrate that the device containing the LC additive 5CB exhibits a reduced self-discharge and leakage current without compromising the capacitive performance at different nominal voltages compared to the behavior of the device without 5CB. We suggest an explanation of the difference of the self-discharge behavior between the devices through tunability of the effective conductivity of the electrolyte composite upon applied voltages. As a result, in an open circuit condition, the device containing LC shows a slower diffusion of ions that facilitates a decreased self-discharge and leakage current.
|
|
| 20. |
- Haque, Mohammad Mazharul, 1984, et al.
(författare)
-
Thermal influence on the electrochemical behavior of a supercapacitor containing an ionic liquid electrolyte
- 2018
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 263, s. 249-260
-
Tidskriftsartikel (refereegranskat)abstract
- Emerging demands on heat-durable electronics have accelerated the need for high temperature supercapacitors as well as for understanding the influence of elevated temperatures on the capacitive behavior. In this work, we present a comprehensive study of the thermal influence on a supercapacitor containing 1-ethyl-3-methylimidazolium acetate (EMIM Ac) electrolyte and activated carbon (AC) electrodes. The performance variation as a function of temperature in a range from 21 °C to 150 °C reveals that a high specific capacitance of 142 F g−1 can be achieved at 150 °C at a current density of 2 A g−1 with a rate capability of 87% at 15 A g−1 (relative to 2 A g−1). At 150 °C, equivalent series resistance (ESR) is only 0.37 Ω cm2, which is a result of improved ionic conductivity of the electrolyte at elevated temperature. The ESR value of 2.5 Ω cm2 at room temperature reflects a good compatibility between EMIM Ac and AC. In addition, a capacitance retention of more than 95% (in the end of 1000 cycles) is maintained up to120 °C followed by 85% at 150 °C. These results confirm EMIM Ac as a suitable candidate for carbon-based high temperature supercapacitors, and the observations regarding the thermal influence on performance metrics e.g. usable operation voltage could be applicable to other energy storage devices.
|
|
| 21. |
- Huang, Qi, et al.
(författare)
-
A method for generating case-specific vehicle models from a single-view vehicle image for accurate pedestrian injury reconstructions
- 2024
-
Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575 .- 1879-2057. ; 200
-
Tidskriftsartikel (refereegranskat)abstract
- Developing vehicle finite element (FE) models that match real accident-involved vehicles is challenging. This is related to the intricate variety of geometric features and components. The current study proposes a novel method to efficiently and accurately generate case-specific buck models for car-to-pedestrian simulations. To achieve this, we implemented the vehicle side-view images to detect the horizontal position and roundness of two wheels to rectify distortions and deviations and then extracted the mid-section profiles for comparative calculations against baseline vehicle models to obtain the transformation matrices. Based on the generic buck model which consists of six key components and corresponding matrices, the case-specific buck model was generated semi-automatically based on the transformation metrics. Utilizing this image-based method, a total of 12 vehicle models representing four vehicle categories including family car (FCR), Roadster (RDS), small Sport Utility Vehicle (SUV), and large SUV were generated for car-to-pedestrian collision FE simulations in this study. The pedestrian head trajectories, total contact forces, head injury criterion (HIC), and brain injury criterion (BrIC) were analyzed comparatively. We found that, even within the same vehicle category and initial conditions, the variation in wrap around distance (WAD) spans 84–165 mm, in HIC ranges from 98 to 336, and in BrIC fluctuates between 1.25 and 1.46. These findings highlight the significant influence of vehicle frontal shape and underscore the necessity of using case-specific vehicle models in crash simulations. The proposed method provides a new approach for further vehicle structure optimization aiming at reducing pedestrian head injury and increasing traffic safety.
|
|
| 22. |
|
|
| 23. |
- Lennon, Matthew J., et al.
(författare)
-
Use of Antihypertensives, Blood Pressure, and Estimated Risk of Dementia in Late Life An Individual Participant Data Meta-Analysis
- 2023
-
Ingår i: JAMA NETWORK OPEN. - 2574-3805. ; 6:9
-
Tidskriftsartikel (refereegranskat)abstract
- IMPORTANCE The utility of antihypertensives and ideal blood pressure (BP) for dementia prevention in late life remains unclear and highly contested. OBJECTIVES To assess the associations of hypertension history, antihypertensive use, and baseline measured BP in late life (age >60 years) with dementia and the moderating factors of age, sex, and racial group. DATA SOURCE AND STUDY SELECTION Longitudinal, population-based studies of aging participating in the Cohort Studies of Memory in an International Consortium (COSMIC) group were included. Participants were individuals without dementia at baseline aged 60 to 110 years and were based in 15 different countries (US, Brazil, Australia, China, Korea, Singapore, Central African Republic, Republic of Congo, Nigeria, Germany, Spain, Italy, France, Sweden, and Greece). DATA EXTRACTION AND SYNTHESIS Participants were grouped in 3 categories based on previous diagnosis of hypertension and baseline antihypertensive use: healthy controls, treated hypertension, and untreated hypertension. Baseline systolic BP (SBP) and diastolic BP (DBP) were treated as continuous variables. Reporting followed the Preferred Reporting Items for Systematic Review and Meta-Analyses of Individual Participant Data reporting guidelines. MAIN OUTCOMES AND MEASURES The key outcome was all-cause dementia. Mixed-effects Cox proportional hazards models were used to assess the associations between the exposures and the key outcome variable. The association between dementia and baseline BP was modeled using nonlinear natural splines. The main analysis was a partially adjusted Cox proportional hazards model controlling for age, age squared, sex, education, racial group, and a random effect for study. Sensitivity analyses included a fully adjusted analysis, a restricted analysis of those individuals with more than 5 years of follow-up data, and models examining the moderating factors of age, sex, and racial group. RESULTS The analysis included 17 studies with 34 519 community dwelling older adults (20 160 [58.4%] female) with a mean (SD) age of 72.5 (7.5) years and a mean (SD) follow-up of 4.3 (4.3) years. In the main, partially adjusted analysis including 14 studies, individuals with untreated hypertension had a 42% increased risk of dementia compared with healthy controls (hazard ratio [HR], 1.42; 95% CI 1.15-1.76; P =.001) and 26% increased risk compared with individuals with treated hypertension (HR, 1.26; 95% CI, 1.03-1.53; P =.02). Individuals with treated hypertension had no significant increased dementia risk compared with healthy controls (HR, 1.13; 95% CI, 0.99-1.28; P =.07). The association of antihypertensive use or hypertension status with dementia did not vary with baseline BP. There was no significant association of baseline SBP or DBP with dementia risk in any of the analyses. There were no significant interactions with age, sex, or racial group for any of the analyses. CONCLUSIONS AND RELEVANCE This individual patient data meta-analysis of longitudinal cohort studies found that antihypertensive usewas associated with decreased dementia risk compared with individuals with untreated hypertension through all ages in late life. Individuals with treated hypertension had no increased risk of dementia compared with healthy controls.
|
|
| 24. |
|
|
| 25. |
- Li, Qi, 1990, et al.
(författare)
-
Compact and low loss electrochemical capacitors using a graphite / carbon nanotube hybrid material for miniaturized systems
- 2019
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 412, s. 374-383
-
Tidskriftsartikel (refereegranskat)abstract
- With the establishment of the internet of things (IoT) and the rapid development of advanced microsystems, there is a growing demand to develop electrochemical capacitors (ECs) to replace bulky electrolytic capacitors on circuit boards for AC line filtering, and as a storage unit in energy autonomous systems. For this purpose, ECs must be capable of handling sufficiently high signal frequencies, display minimum energy loss through self-discharge and leakage current as well as maintaining an adequate capacitance. Here, we demonstrate ECs based on mechanically flexible, covalently bonded graphite/vertically aligned carbon nanotubes (graphite/VACNTs) hybrid materials. The ECs employing a KOH electrolyte exhibit a phase angle of −84.8°, an areal capacitance of 1.38 mF cm−2 and a volumetric capacitance (device level) of 345 mF cm−3 at 120 Hz, which is among the highest values for carbon based high frequency ECs. Additionally, the performance as a storage EC for miniaturized systems is evaluated. We demonstrate capacitive charging/discharging at μA current with a gel electrolyte, and sub-μA leakage current reached within 50 s, and 100 nA level equilibrium leakage within 100 s at 2.0 V floating with an ionic liquid electrolyte.
|
|
| 26. |
- Li, Qi, 1990
(författare)
-
Electrochemical Capacitors for Miniaturized Self-powered Systems
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Miniaturized self-powered systems with harvest-store-use architectures have been recognized as a key enabler to the internet-of-things (IoT), and further the internet-of-everything (IoE), 5G communication and tactile internet. Electrochemical capacitors (ECs), also known as supercapacitors, are promoted to be the energy storage component in such systems, because of their advantages such as an almost limitless cycle life that is ideal for the vision of “fit-and-forget” maintenance-free networks. Moreover, ECs are able to undertake tasks beyond energy storage. For example, high-frequency ECs can potentially replace the bulky electrolytic capacitors as AC line filters, with benefits in sizing down the circuitry boards and thus constructing compact systems which are pursued by the IoT technology. Bringing the IoT high-level requirements down to the device-level specifications, challenges to ECs are identified in different aspects, including device electrochemical performance, and device encapsulation/integration. Regarding the performance, challenges exist in (1) improving the energy density, (2) maximizing the operating voltage limit, (3) widening the working temperature range, (4) minimizing the self-discharge and leakage current, and (5) enhancing the frequency response property. Regarding the encapsulation and integration aspect, challenges exist in device design and fabrication. Novel encapsulation and integration EC concepts are thus appreciated to be compatible with the surface mount technology, allow for convenient adaption in the form factor and arbitrary choice of the EC materials (electrodes, electrolytes and separators). Moreover, the EC materials should be durable under the ambient conditions that occur during the encapsulation and integration processes, such as high-temperature exposure for the reflow soldering technique. The thesis research work addresses the device performance challenges. Specifically, the use of redox electrolytes is promoted for improving the energy density of ECs towards a battery-level, and at the same time keeping the capacitor-level power capability and cycling stability. With a redox-active electrolyte KBr, hybrid devices combining the features of both batteries and ECs are constructed, and a 1.9 V maximum operating voltage is achieved in the aqueous system. Furthermore, voltage- and history-dependent behaviors are revealed, reminding the complexity of hybrid systems. To explore the extreme high-temperature performance, a special measurement setup is customized and an EMImAc (1-Ethyl-3-methylimidazolium acetate) ionic liquid (IL) electrolyte is employed to enable an operation at a maximum of 150 °C. It is observed that the energy and power densities at high temperatures may not be sacrificed when decreasing the operating voltage limit, therefore it is proposed that for neat IL-based ECs, a strategy of trading the voltage limit for gaining stability at extreme high-temperatures can be considered. With a graphite and carbon nanotubes hybrid material, it is demonstrated that the self-discharge and leakage current can be suppressed by employing a gel polymer electrolyte. Using the same electrode material, high-frequency ECs that are suitable for AC line filtering tasks are fabricated. The working frequency range is up to kHz with a state-of-art level areal (1.38 mF cm-2) and volumetric capacitances (345 mF cm-3), benefiting from a possible covalent bonding between graphite substrate and the CVD grown CNTs. Not limited to the above research findings, this thesis has critically reviewed and summarized the general strategies and methods to address all the identified challenges to ECs for their application in miniaturized self-powered systems.
|
|
| 27. |
- Li, Qi, 1990
(författare)
-
Electrochemical capacitors for miniaturized self-powered systems: challenges and solutions
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrochemical capacitors (ECs), also known as supercapacitors, are recognized as a key technology that will enable miniaturized self-powered systems, which will constitute the hardware base nodes of the internet of things (IoT), the internet of everything (IoE) and the tactile internet. Systems employing ECs can be designed to be maintenance-free thanks to the ultra-long cycling stability of ECs. Besides the function as a main or backup energy storage unit, advanced ECs can be used to support batteries at peak power load and they can be a substitute for conventional electrolytic capacitors used in a.c. line filtering, with clear advantages for system down-sizing due to their superior capacitance density. However, a number of challenges remain to be solved to advance the development of ECs for miniature systems. Regarding the performance as a competitor to e.g. batteries, the ECs suffer from inferior energy density, low working voltage, severe self-discharge and leakage current. For IoT systems embedded in a harsh environment, the ability to enduring extreme temperature is inadequate for most general-purpose ECs. The response at high frequency needs to be enhanced to enable functions such as a.c. line filtering. As for encapsulation and integration, novel concepts are appreciated for compatibility with surface mount technology and reflow soldering, allowing convenient adaption in the form factor and making possible an arbitrary choice of EC materials (electrodes, electrolytes and separators). To address the challenges, the thesis (1) explores the utilization of the redox electrolyte KBr to enhance the energy density of EDLCs; (2) adopts an ionic liquid electrolyte EMImAc to achieve working temperature beyond 120 °C; (3) uses an advanced graphite/VACNTs material for high-frequency ECs as a.c. line filters and low loss storage units in microsystems; (4) develops a bipolar EC prototype that doubles the working voltage limit; (5) mitigates the self-discharge and leakage current through the liquid crystal additive in an electrolyte; and (6) presents a cellulose-derived carbon nanofiber-based electrode material with enhanced capacitive performance. Generic strategies and methods to address each identified challenge are provided in the thesis, highlighting a step-by-step optimization route starting from the material properties, moving on to the electrode structures, and further to the device design.
|
|
| 28. |
- Li, Qi, 1990, et al.
(författare)
-
Explanation of anomalous rate capability enhancement by manganese oxide incorporation in carbon nanofiber electrodes for electrochemical capacitors
- 2020
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 340
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochemical capacitors (ECs) can provide ultra-long cycle life and ultra-fast energy delivery, characteristics which most battery technologies lack. Making composites out of carbon and pseudocapacitive materials is a popular strategy directed on narrowing the gap in energy density with regard to batteries. Usually, the incorporation of pseudocapacitive materials leads to a decrease in power performance compared to a pure carbon matrix, due to inferior electrical conductivity. This work, however, presents significant improvement in rate capability demonstrated by a composite electrode containing carbon nanofibers (NCNF) and manganese oxides (MnO2). The NCNF/MnO2 is prepared with a common method through the reaction with permanganate. The material has excellent performance metrics, especially a 78.2% rate capability (capacitance retention at 15 A g−1 relative to 0.5 A g−1), more than 10 times that for the NCNF carbon matrix. The exceptional enhancement can be explained by the development of micropores and surface area of NCNF, thus alleviating the “pore starvation” issue, and surface functional groups variation that enhances capacitive performance. This work highlights the importance of paying attention to the modification of carbon substrate when investigating carbon composite electrodes e.g. carbon/MnO2 networks.
|
|
| 29. |
- Li, Qi, 1990, et al.
(författare)
-
Finger Number and Device Performance: A Case Study of Reduced Graphene Oxide Microsupercapacitors
- 2021
-
Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2
-
Tidskriftsartikel (refereegranskat)abstract
- Microsupercapacitors (MSCs) are recognized as suitable energy storage devices for the internet of things (IoTs) applications. Herein is described the work conducted to assess the areal energy and power densities of MSCs with 2, 10, 20, and 40 interdigital finger electrodes on a fixed device footprint area (the finger interspacing is fixed at 40 μm, and the finger width and length are allowed to vary to fit the footprint area). The MSCs are based on reduced graphene oxide (rGO) materials and fabricated with a spin-coating and etch method. The performance evaluation indicates a strong dependency of areal capacitance and energy density on the number of fingers, and the maximum (impedance match) power density is also influenced to a relatively large extent, whereas the average power density is not sensitive to the configuration parameters in the present evaluation settings (scan rate 20–200 mV s−1 and current density of 100 μA cm−2). For the rGO-based devices, the equivalent distributed resistance may play an important role in determining the device resistance and power-related performance.
|
|
| 30. |
|
|
| 31. |
- Li, Qi, 1990, et al.
(författare)
-
Graphite paper / carbon nanotube composite: A potential supercapacitor electrode for powering microsystem technology
- 2017
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 922:1
-
Konferensbidrag (refereegranskat)abstract
- This work describes fabrication of a flexible supercapacitor electrode. The fabrication starts with graphite paper (GP). Carbon nanotubes (CNTs) are then grown directly to the carbon surface by chemical vapor deposition (CVD), forming a heterogeneous structure of GP/CNT. The integration of CNT enhances capacitive performance while maintaining the flexibility of GP, thus making GP/CNT a promising supercapacitor electrode material for potentially powering microsystem technology.
|
|
| 32. |
|
|
| 33. |
- Li, Qi, 1990, et al.
(författare)
-
Nanocomposite materials for miniaturized supercapacitors
- 2017
-
Ingår i: International Conference and Exhibition on Integration Issues of Miniaturized Systems 2017, SSI 2017, Cork, Ireland, 8-9 March 2017. ; , s. 199-205
-
Konferensbidrag (refereegranskat)
|
|
| 34. |
- Li, Qi, 1990, et al.
(författare)
-
Redox enhanced energy storage in an aqueous high-voltage electrochemical capacitor with a potassium bromide electrolyte
- 2017
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 348, s. 219-228
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports a detailed electrochemical investigation of a symmetric carbon-carbon electrochemical device with a potassium bromide (KBr) electrolyte. Below 1.6 V, KBr gives electrochemical double layer behavior. At higher voltages the Br-/Br-3 redox reaction comes into effect and enhances the energy storage. The redox-enhanced device has a high energy density, excellent stability, as well as high coulombic and energy efficiencies even at 1.9 V. More importantly, the redox contribution can be “triggered” by pre-cycling at 1.9 V, and remains beneficial after switching to 1.6 V. The triggering operation leads to a 22% increase in stored energy with negligible sacrifice of power. The intriguing behavior is accompanied by a series of complex variations including the shifts of electrode potential limits and the shift of potential of zero voltage. The electro-oxidation of the positive electrode and kinetics of the Br-/Br-3 electrode reactions are proposed to be the main causes for the triggering phenomenon. These findings provide means to improve the design and operation of devices that contain bromine, or other redox species with a comparably high electrode potential.
|
|
| 35. |
- Rajendra Babu Kalai Arasi, Azega, 1995, et al.
(författare)
-
Effect of plasma treatment on electrochemical performance of lignin-based carbon fibers
- 2023
-
Ingår i: Journal of Electroanalytical Chemistry. - 1572-6657. ; 946
-
Tidskriftsartikel (refereegranskat)abstract
- The abundant and renewable nature of lignin obtained from wood renders it as a sustainable carbon resource for energy storage applications. However, their environmentally unfavorable processing conditions and limited energy storage performance prohibit the use of lignin-based carbon materials' use as supercapacitor electrodes. The material's properties require advancement to overcome the limitation of low specific capacitances. In this study, we report on the impact on the electrochemical performance of inherently hydrophobic lignin-based carbon fibers (LCF) by subjecting them to a mild plasma treatment. The electrode’s capacitance was thus increased by 20%, with better rate capability and energy-power performance (11 Wh/kg and 0.8 kW/kg) in the KOH electrolyte. The quantified improvements were attributed to the capacitive functional groups, and enhanced surface wettability, which increased ion accessibility to active surface area improving charge-transfer ability to the surface with more additional functional groups. Remarkably, the selected plasma conditions introduced mostly desirable functional groups that limited any parasitic faradaic reactions prone to affect the device's long-term cycling stability and self-discharge characteristics. Furthermore, the impact of different inherent and introduced oxygen surface functional groups, including COO−, COH, CO, and CO, on the capacitive performance of these fibers at different device conditions (such as cycling and electrochemical activation) was investigated in different aqueous electrolytes. To ensure environmental favorability, the electrospinning of lignin fibers was conducted using a high molecular fraction of lignin without the inclusion of any fossil-based co-spinning polymers.
|
|
| 36. |
- Smith, Anderson David, 1985, et al.
(författare)
-
Carbon-Based Electrode Materials for Microsupercapacitors in Self-Powering Sensor Networks : Present and Future Development
- 2019
-
Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 19:19
-
Tidskriftsartikel (refereegranskat)abstract
- There is an urgent need to fulfill future energy demands for micro and nanoelectronics. This work outlines a number of important design features for carbon-based microsupercapacitors, which enhance both their performance and integration potential and are critical for complimentary metal oxide semiconductor (CMOS) compatibility. Based on these design features, we present CMOS-compatible, graphene-based microsupercapacitors that can be integrated at the back end of the line of the integrated circuit fabrication. Electrode materials and their interfaces play a crucial role for the device characteristics. As such, different carbon-based materials are discussed and the importance of careful design of current collector/electrode interfaces is emphasized. Electrode adhesion is an important factor to improve device performance and uniformity. Additionally, doping of the electrodes can greatly improve the energy density of the devices. As microsupercapacitors are engineered for targeted applications, device scaling is critically important, and we present the first steps toward general scaling trends. Last, we outline a potential future integration scheme for a complete microsystem on a chip, containing sensors, logic, power generation, power management, and power storage. Such a system would be self-powering.
|
|
| 37. |
- Smith, Anderson David, 1985, et al.
(författare)
-
Toward CMOS compatible wafer-scale fabrication of carbon-based microsupercapacitors for IoT
- 2018
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1052:1
-
Konferensbidrag (refereegranskat)abstract
- This work presents a wafer-scale method of microsupercapacitor (MSC) fabrication. Deposition of the electrode precursor, i.e. graphene oxide, is accomplished through spin-coating which allows for potential application in CMOS compatible processes for future integrated on-chip energy storage systems. Our MSCs have an areal capacitance of 0.4 mF/cm2at 10 μA, which is a very promising result. Further, the MSC has good rate capability as its capacitance decreases by only 0.03 mF/cm2when the current increases to 50 μA. The MSCs have a maximum energy density of 0.04 μWh/cm2and a maximum power density as high as 96 μW/cm2. Additionally, the wafer-scale process demonstrates industrial viability.
|
|
| 38. |
- Velasco, Andres, et al.
(författare)
-
Investigation of vertical carbon nanosheet growth and its potential for microsupercapacitors
- 2021
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1837:1
-
Konferensbidrag (refereegranskat)abstract
- One of the biggest applications that are coming with the Internet of Things (IoT) are miniaturized sensor networks that connect wirelessly to each other and the internet. Microsupercapacitors (MSCs) are ideal to power these devices, with large cyclability and lifetime. Porous carbons are the material of choice for these devices, but their morphology and manufacturing are far from optimized. Vertically oriented graphene MSCs have shown great promise due to their high specific surface areas and conductivity. In this work, the growth of vertically aligned carbon nanosheets (CNS) on 2-inch wafers has been studied, and it has been used as active material to manufacture MSC and transmission line model (TLM) wafers. The fabricated CNS MSC devices show a capacitance of 7.4 ?F (50.7 ?F/cm2, normalized to the area of the electrodes), a five-times increase from previous results obtained by the group.
|
|
| 39. |
- Vyas, Agin, 1992, et al.
(författare)
-
Comparison of Thermally Grown Carbon Nanofiber-Based and Reduced Graphene Oxide-Based CMOS-Compatible Microsupercapacitors
- 2021
-
Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2
-
Tidskriftsartikel (refereegranskat)abstract
- Microsupercapacitors as miniature energy storage devices require complementary metal-oxide-semiconductor (CMOS) compatible techniques for electrode deposition to be integrated in wireless sensor network sensor systems. Among several processing techniques, chemical vapor deposition (CVD) and spin coating, present in CMOS manufacturing facilities, are the two most viable processes for electrode growth and deposition, respectively. To make an argument for choosing either of these techniques to fabricate MSCs utilizable for an on-chip power supply, we need a comparative assessment of their electrochemical performance. Herein, the evaluation of MSCs with CVD-grown carbon nanofiber (CNF)-based and spin-coated reduced graphene oxide (rGO)-based electrodes is reported. The devices are compared for their capacitance, energy and power density, charge retention, characteristic frequencies, and ease of fabrication over a large sweep of scan rates, current densities, and frequencies. The rGO-based MSCs demonstrate 112 mu F cm(-2) at 100 mV s(-1) and a power density of 12.8 mW cm(-2). The CNF-based MSCs show 269.7 mu F cm(-2) and 30.8 mW cm(-2). CVD-grown CNF outperforms spin-coated rGO in capacitive storage at low frequencies, whereas the latter is better in terms of charge retention and high-frequency capacitance response.
|
|
| 40. |
- Vyas, Agin, 1992, et al.
(författare)
-
Enhanced Electrode Deposition for On-Chip Integrated Micro-Supercapacitors by Controlled Surface Roughening
- 2020
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:10, s. 5219-5228
-
Tidskriftsartikel (refereegranskat)abstract
- On-chip micro-supercapacitors (MSCs), integrated with energy harvesters, hold substantial promise for developing self-powered wireless sensor systems. However, MSCs have conventionally been manufactured through techniques incompatible with semiconductor fabrication technology, the most significant bottleneck being the electrode deposition technique. Utilization of spin-coating for electrode deposition has shown potential to deliver several complementary metal-oxide-semiconductor (CMOS)-compatible MSCs on a silicon substrate. Yet, their limited electrochemical performance and yield over the substrate have remained challenges obstructing their subsequent integration. We report a facile surface roughening technique for improving the wafer yield and the electrochemical performance of CMOS-compatible MSCs, specifically for reduced graphene oxide as an electrode material. A 4 nm iron layer is deposited and annealed on the wafer substrate to increase the roughness of the surface. In comparison to standard nonroughened MSCs, the increase in surface roughness leads to a 78% increased electrode thickness, 21% improvement in mass retention, 57% improvement in the uniformity of the spin-coated electrodes, and a high yield of 87% working devices on a 2″ silicon substrate. Furthermore, these improvements directly translate to higher capacitive performance with enhanced rate capability, energy, and power density. This technique brings us one step closer to fully integrable CMOS-compatible MSCs in self-powered systems for on-chip wireless sensor electronics. ©
|
|
| 41. |
- Vyas, Agin, 1992, et al.
(författare)
-
Impact of electrode geometry and thickness on planar on-chip microsupercapacitors
- 2020
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 10:52, s. 31435-31441
-
Tidskriftsartikel (refereegranskat)abstract
- We report an assessment of the influence of both finger geometry and vertically-oriented carbon nanofiber lengths in planar micro-supercapacitors. Increasing the finger number leads to an up-scaling in areal power densities, which increases with scan rate. Growing the nanofibers longer, however, does not lead to a proportional growth in capacitance, proposedly related to limited ion penetration of the electrode.
|
|
| 42. |
- Vyas, Agin, 1992, et al.
(författare)
-
Investigation of palladium current collectors for vertical graphene-based microsupercapacitors
- 2019
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1319:1
-
Konferensbidrag (refereegranskat)abstract
- As microsystems are reduced in size and become integrated in the Internet of Things (IoT), they require an adequate power supply which can be integrated at the same size scale. Microsupercapacitors (MSCs), if coupled with on-chip harvesters, can offer solutions for a self-sustaining, on-chip power supply. However, the implementation of reliable MSC wafer-scale production compatible with CMOS technology remains a challenge. Palladium (Pd) is known as a CMOS compatible metal and, in this paper, we investigate the use of Pd as a contact material for vertical graphene (VG) electrodes in wafer-scale MSC fabrication. We show that a Ti diffusion barrier is required to prevent short-circuiting for the successful employment of Pd contacts. The fabricated MSCs demonstrate a capacitance of 1.3 μF/cm2 with an energy density of 0.42 μJ/cm2. Thus, utilization of a Ti diffusion barrier with a CMOS compatible Pd metal electrode is a step towards integrating MSCs in semiconductor microsystems.
|
|
| 43. |
- Vyas, Agin, 1992, et al.
(författare)
-
Spin-Coated Heterogenous Stacked Electrodes for Performance Enhancement in CMOS-Compatible On-Chip Microsupercapacitors
- 2022
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:4, s. 4221-4231
-
Tidskriftsartikel (refereegranskat)abstract
- Integration of microsupercapacitors (MSCs) with on-chip sensors and actuators with nanoenergy harvesters can improve the lifetime of wireless sensor nodes in an Internet-of-Things (IoT) architecture. However, to be easy to integrate with such harvester technology, MSCs should be fabricated through a complementary-metal-oxide-semiconductor (CMOS) compatible technology, ubiquitous in electrode choice with the capability of heterogeneous stacking of electrodes for modulation in properties driven by application requirements. In this article, we address both these issues through fabrication of multielectrode modular, high energy density microsupercapacitors (MSC) containing reduced graphene oxide (GO), GO-heptadecane-9-amine (GO-HD9A), rGO-octadecylamine (rGO-ODA), and rGO-heptadecane-9-amine (rGO-HD9A) that stack through a scalable, CMOS compatible, high-wafer-yield spin-coating process. Furthermore, we compare the performance of the stack with individual electrode MSCs fabricated through the same process. The individual electrodes, in the presence of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI), demonstrate a capacitance of 38, 30, 36, and 105 μF/cm^2 at 20 mV/s^1 whereas the fabricated stack of electrodes demonstrates a high capacitance of 280 μF/cm^2 at 20 mV/s^1 while retaining and enhancing the material-dependent capacitance, charge retention, and power density.
|
|
| 44. |
- Vyas, Agin, 1992, et al.
(författare)
-
Surface Roughening with Iron Nanoparticles for Promoted Adhesion of Spin Coated Microsupercapacitor Electrodes
- 2019
-
Ingår i: MRS Advances. - : Springer Science and Business Media LLC. - 2059-8521. ; 4:23, s. 1335-1340
-
Konferensbidrag (refereegranskat)abstract
- Microsupercapacitors (MSCs) are miniaturized energy storage devices that can be integrated in an on-chip platform as a component of a power supply for Internet of things' sensors. Integration of these on-chip MSCs require them to be fabricated through CMOS compatible fabrication techniques such as spin coating. One of the biggest challenges in spin coated MSCs is the poor surface adhesion. In this work, we present a CMOS compatible electrode deposition process with enhanced adhesion and retention for reduced graphene oxide (rGO) using spin coating. In order to improve the adhesion and surface uniformity of the deposited electrode material, the surface of Si/SiO 2 wafers was subjected to roughening through Fe nanoparticle formation. A 4 nm thick Fe layer deposition substantially magnified the average mean surface roughness of the substrates. In comparison with substrates without the Fe deposition, the treated ones have more than 300% improvement in surface coverage and rGO mass retention after sonication testing. These results suggest that the surface roughening has a positive influence on electrode deposition via a spin-coating method.
|
|
| 45. |
- Vyas, Agin, 1992, et al.
(författare)
-
Towards Integrated Flexible Energy Harvester and Supercapacitor for Self-powered Wearable Sensors
- 2020
-
Ingår i: 2019 19TH INTERNATIONAL CONFERENCE ON MICRO AND NANOTECHNOLOGY FOR POWER GENERATION AND ENERGY CONVERSION APPLICATIONS (POWERMEMS).
-
Konferensbidrag (refereegranskat)abstract
- We present the first results of a flexible energy harvester and a foldable supercapacitor to power wearable and flexible sensors. The flexible energy harvester is fabricated by using 38 mu m piezoelectric polyvinylidene difluoride (PVDF) sandwiched between carbon electrodes. Both the design and process excel in simplicity and cost-effectiveness. The flexible harvester demonstrates a power output of 2.6 mu W cm(-3) at a resonant frequency of 50 Hz with a 3dB bandwidth of about 11 Hz, which is higher than devices previously reported and similar to a commercial PZT harvester film of same size. A flexible energy storage supercapacitor (GP-SC) was fabricated using a graphite/VACNTs (vertically aligned carbon nanotubes) material as electrodes. A prototype GP-SCs has an areal capacitance of about 1.2 mF cm(-2). Finally, an integrated scheme is proposed for future work.
|
|
