Long-term Cycle Life Research Articles

Semi-empirical long-term cycle life model coupled with an electrolyte depletion function for large-format graphite/LiFePO4 lithium-ion batteries

To overcome the limitation of simple empirical cycle life models based on only equivalent circuits, we attempt to couple a conventional empirical capacity loss model with Newman's porous composite electrode model, which contains both electrochemical reaction kinetics and material/charge balances. In addition, an electrolyte depletion function is newly introduced to simulate a sudden capacity drop at the end of cycling, which is frequently observed in real lithium-ion batteries (LIBs). When simulated electrochemical properties are compared with experimental data obtained with 20 Ah-level graphite/LiFePO4 LIB cells, our semi-empirical model is sufficiently accurate to predict a voltage profile having a low standard deviation of 0.0035 V, even at 5C. Additionally, our model can provide broad cycle life color maps under different c-rate and depth-of-discharge operating conditions. Thus, this semi-empirical model with an electrolyte depletion function will be a promising platform to predict long-term cycle lives of large-format LIB cells under various operating conditions.

(Invited) High Lithium Sulfide-Loading Electrode for Practical Li/S Cells

The development of the Li-ion battery (LIB) has led to a portable electronics revolution during last couple of decades, however, the traditional LIB seems to be insufficient for practical application in some emerging markets due to the limited specific energy of the cell. For mass market conversion to electric vehicles, high specific energy (> 300 Wh kg-1) rechargeable battery systems of low-cost for energy storage are required. Among all alternatives, the lithium/sulfur cell has been considered most promising due to its low cost, high abundance, ultrahigh theoretical specific energy (2,566 Wh kg-1) and theoretical energy density (4,260 Wh L-1) which far exceed those of conventional lithium-ion cells. Nevertheless, after extensive study of both sulfur cathodes and lithium sulfide cathodes, neither of these technologies has been commercialized due to poor long-term cycle life and low demonstrated specific energy of lithium/sulfur cells. Practical applications require high sulfur loading electrodes together with the lowest “dead weight” possible in the cell while maintaining good performance. This is quite challenging because commercial current collectors have mechanical limitations in electrode loading and sulfur utiliation. Due to the insulating nature of S and Li2S, the addition of a significant amount of a conductive additive into the high loading electrodes is required and introduces more surface area, and thus more electrolyte is needed which further leads to more dead weight. Recently, lithium sulfide was proposed to be a more desirable electrode material because it permits the cell to be assembled in discharged state and avoids problems associated with volume expansion of sulfur during discharge. Disadvantages of lithium sulfide include challenging issues due to its sensitivity toward moisture and solubility in many organic solvents. In order to achieve high specific energy, we have developed a novel Li2S/KB@Cf electrode (Li2S content: 74 %,) using a robust 3-dimensional (3-D) current collector with a high Li2S loading up to 11.29 mg cm-2 (S loading: 7.85 mg cm-2), which can deliver an areal capacity of 7 mAh cm-2 after 50 cycles with an Electrolyte/Sulfur ratio of 5.5 (see Fig. 1). We will present our recent progress in high S loading cells and more detailed information about active material development, electrode composition and modifications of the electrolyte and cell configuration. Figure 1

High-Energy/Power and Low-Temperature Cathode for Sodium-Ion Batteries: In Situ XRD Study and Superior Full-Cell Performance.

Sodium-ion batteries (SIBs) are still confronted with several major challenges, including low energy and power densities, short-term cycle life, and poor low-temperature performance, which severely hinder their practical applications. Here, a high-voltage cathode composed of Na3 V2 (PO4 )2 O2 F nano-tetraprisms (NVPF-NTP) is proposed to enhance the energy density of SIBs. The prepared NVPF-NTP exhibits two high working plateaux at about 4.01 and 3.60 V versus the Na+ /Na with a specific capacity of 127.8 mA h g-1 . The energy density of NVPF-NTP reaches up to 486 W h kg-1 , which is higher than the majority of other cathode materials previously reported for SIBs. Moreover, due to the low strain (≈2.56% volumetric variation) and superior Na transport kinetics in Na intercalation/extraction processes, as demonstrated by in situ X-ray diffraction, galvanostatic intermittent titration technique, and cyclic voltammetry at varied scan rates, the NVPF-NTP shows long-term cycle life, superior low-temperature performance, and outstanding high-rate capabilities. The comparison of Ragone plots further discloses that NVPF-NTP presents the best power performance among the state-of-the-art cathode materials for SIBs. More importantly, when coupled with an Sb-based anode, the fabricated sodium-ion full-cells also exhibit excellent rate and cycling performances, thus providing a preview of their practical application.

Mesoporous three dimension NiCo2O4/graphene composites fabricated by self-generated sacrificial template method for a greatly enhanced specific capacity

We reported a facile self-generated sacrificial template method for fabricating mesoporous three dimension NiCo2O4/graphene electrode material. Nickel, cobalt, and zinc ions dissolved in ethylene glycol reacted with potassium hydroxide solution to co-deposit onto graphene at 140 °C under atmospheric environment. With further addition of potassium hydroxide, zinc hydroxide as a self-generated sacrificial template was dissolved in situ, leading to the formation of mesoporous morphology. Structure and morphology characteristics were determined by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and N2 adsorption experiments. Electrochemical properties were analyzed by AC impedance spectroscopy, cycling voltammetry, and charge/discharge test in 2 M KOH. Results showed that the as—prepared NiCo2O4/graphene electrode possessed a large specific surface area of 281.4 m2 g−1, an ultrahigh specific capacity of 1024.99 and 662.12 C g−1 at current density of 1 and 50 A g−1 respectively, and a long-term cycling life of 10,000 charge/discharge tests.

Flexible P-Doped Carbon Cloth: Vacuum-Sealed Preparation and Enhanced Na-Storage Properties as Binder-Free Anode for Sodium Ion Batteries.

In this work, a flexible and self-supporting P-doped carbon cloth (FPCC), which is composed of interwoven mesh of hollow microtubules with porous carbon walls, is prepared via a vacuum-sealed doping technology by employing the commercially available cotton cloth as sustainable and scalable raw material. When directly used as binder-free anode for sodium-ion batteries, the as-prepared FPCC delivers superior Na-storage properties in terms of specific capacity up to 242.4 mA h g-1, high initial Coulombic efficiency of ∼72%, excellent rate capabilities (e.g., 123.1 mA h g-1 at a high current of 1 A g-1), and long-term cycle life (e.g., ∼88% capacity retention after even 600 cycles). All these electrochemical data are better than the undoped carbon cloth control, demonstrating the significance of P-doping to enhance the Na-storage properties of cotton-derived carbon anode. Furthermore, the technologies of electrochemical impedance spectroscopy and galvanostatic intermittent titration technique are implemented to disclose the decrease of charge transfer resistance and improvement of Na-migration kinetics, respectively.

Graphene-Scaffolded Na3V2(PO4)3 Microsphere Cathode with High Rate Capability and Cycling Stability for Sodium Ion Batteries.

High voltage, high rate, and cycling-stable cathodes are urgently needed for development of commercially viable sodium ion batteries (SIBs). Herein, we report a facile spray-drying method to synthesize graphene-scaffolded Na3V2(PO4)3 microspheres (NVP@rGO), in which nanocrystalline Na3V2(PO4)3 is embedded in graphene sheets to form porous microspheres. Benefiting from the highly conductive graphene framework and porous structure, the NVP@rGO material exhibits a high reversible capacity (115 mAh g-1 at 0.2 C), long-term cycle life (81% of capacity retention up to 3000 cycles at 5 C), and excellent rate performance (44 mAh g-1 at 50 C). The electrochemical properties of a full Na-ion cell with the NVP@rGO cathode and Sb/C anode are also investigated. The present results suggest promising applications of the NVP@rGO material as a high performance cathode for sodium ion batteries.

Delicate Structural Control of Si-SiOx-C Composite via High-Speed Spray Pyrolysis for Li-Ion Battery Anodes.

Despite the high theoretical capacity, silicon (Si) anodes in lithium-ion batteries have difficulty in meeting the commercial standards in various aspects. In particular, the huge volume change of Si makes it very challenging to simultaneously achieve high initial Coulombic efficiency (ICE) and long-term cycle life. Herein, we report spray pyrolysis to prepare Si-SiOx composite using an aqueous precursor solution containing Si nanoparticles, citric acid, and sodium hydroxide (NaOH). In the precursor solution, Si nanoparticles are etched by NaOH with the production of [SiO4]4-. During the dynamic course of spray pyrolysis, [SiO4]4- transforms to SiOx matrix and citric acid decomposes to carbon surface layer with the assistance of NaOH that serves as a decomposition catalyst. As a result, a Si-SiOx composite, in which Si nanodomains are homogeneously embedded in the SiOx matrix with carbon surface layer, is generated by a one-pot process with a residence time of only 3.5 s in a flow reactor. The optimal composite structure in terms of Si domain size and Si-to-O ratio exhibited excellent electrochemical performance, such as reversible capacity of 1561.9 mAh g-1 at 0.06C rate and ICE of 80.2% and 87.9% capacity retention after 100 cycles at 1C rate.

A long cycle life, high coulombic efficiency iron molten air battery

Despite the recent advancements in iron molten air batteries, great challenges still remain to realize cycling stability, high energy efficiency and a long-term cycling life.

Facile preparation of ultrafine manganese dioxide nanowires on activated carbon paper with enhanced capacitance for supercapacitors

In this paper, a structure with growing MnO2 nanowires (NWs) on activated carbon paper was designed and prepared using a simple hydrothermal method. Electrochemical measurements show that the specific capacitance of these MnO2 nanowires/ACP reached 390 F g−1 at a scan rate of 10 mV s−1 and 529 F g−1 at a current density of 2.0 A g−1. The long-term cycle life stability for MnO2 nanowires/ACP was examined and the results show that the capacitance decay was ~12% over 5000 cycles, indicating its long cycle life. Furthermore, they could also be used to assemble simple solid-state supercapacitors with high capacitance. These results show that the MnO2 nanowires/ACP could be a promising electrode material for energy storage.

Facile hydrothermal reduction synthesis of porous Co3O4 nanosheets@RGO nanocomposite and applied as a supercapacitor electrode with enhanced specific capacitance and excellent cycle stability

A facile hydrothermal reduction synthesis has been proposed to fabricate porous Co3O4 nanosheets anchored on reduced graphene oxide (Co3O4@RGO). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal that the Co3O4 nanosheets are porous and dispersed on RGO films. The supercapacitor based on Co3O4@RGO nanocomposite electrode reaches a higher specific capacitance of 894Fg−1 which is about three times higher than the pure Co3O4 electrode (300Fg−1) at the current density of 1Ag−1. In addition, both electrodes demonstrate remarkable long-term cycle life, especially for the Co3O4@RGO nanocomposite, which shows almost no obvious attenuation after 3000 cycles. The superior performance indicates that, due to the exceptional structure characteristics between Co3O4 nanosheets and RGO films, the composite possesses both higher specific capacitance and long-term cycle stability.

In Situ Study of Li Intercalation into Highly Crystalline Graphitic Flakes of Varying Thicknesses

An in situ Raman spectroelectrochemical study of Li intercalation into graphite flakes with different thicknesses ranging from 1.7 nm (3 graphene layers) to 61 nm (ca. 178 layers) is presented. The lithiation behavior of these flakes was compared to commercial microcrystalline graphite with a typical flake thickness of ∼100 nm. Li intercalation into the graphitic flakes was observed under potential control via in situ optical microscopy and Raman spectroscopy. As graphite flakes decreased in thickness, a Raman response indicative of increased tensile strain along the graphene sheet was observed during the early stages of intercalation. A progressively negative wavenumber shift of the interior and bounding modes of the split G band (E2g2(i) and E2g2(b)) is interpreted as a weakening of the C-C bonding. Raman spectra of Li intercalation into thin graphitic flakes are presented and discussed in the context of implications for Li ion battery applications, given that intercalation induced strain may accelerate carbon negative electrode aging and reduce long-term cycle life.

Applications of Novel Carbon/AlPO4 Hybrid-Coated H2Ti12O25 as a High-Performance Anode for Cylindrical Hybrid Supercapacitors.

The hybrid supercapacitor using carbon/AlPO4 hybrid-coated H2Ti12O25/activated carbon is fabricated as a cylindrical cell and investigated against electrochemical performances. The hybrid coating shows that the conductivity for the electron and Li ion is superior and it prevented active material from HF attack. Consequently, carbon/AlPO4 hybrid-coated H2Ti12O25 shows enhanced rate capability and long-term cycle life. Also, the hybrid coating inhibits swelling phenomenon caused by gas generated as decomposition reaction of electrolyte. Therefore, the hybrid supercapacitor using carbon/AlPO4 hybrid-coated H2Ti12O25/activated carbon can be applied to an energy storage system that requires a long-term life.

KOH etched graphite felt with improved wettability and activity for vanadium flow batteries

In this work, a simple and effective method to activate graphite felt (GF) electrode by using KOH as etching agent is studied for vanadium flow battery (VFB) application. The surface of GF is etched by KOH at 800°C to generate micropores and attain oxygen-containing functional groups, resulting in greatly improved electrolyte accessibility. Surface morphology, oxygen distribution and microstructure of the KOH etched graphite felts (eGFs) are characterized by SEM, EDX, XPS, XRD and Raman techniques. Due to the abundant exposed edge carbon sites and oxygen-containing functional groups introduced by KOH activation, electrochemical activity of eGFs towards both VO2+/VO2+ and V2+/V3+ redox couples are remarkably improved comparing with GF. In particular, eGF-2 (mass ratio of KOH/GF=1.25) exhibits the best electrochemical activity and VFB performance among all eGFs. Moreover, the VFB with eGF-2 electrode can run at current density up to 250mAcm−2 with the energy efficiency of 64%. Long-term cycle life test at higher current density of 150mAcm−2 confirms the outstanding stability of eGF-2 electrode.

Cobalt-Doped FeS2 Nanospheres with Complete Solid Solubility as a High-Performance Anode Material for Sodium-Ion Batteries.

Considering that the high capacity, long-term cycle life, and high-rate capability of anode materials for sodium-ion batteries (SIBs) is a bottleneck currently, a series of Co-doped FeS2 solid solutions with different Co contents were prepared by a facile solvothermal method, and for the first time their Na-storage properties were investigated. The optimized Co0.5 Fe0.5 S2 (Fe0.5) has discharge capacities of 0.220 Ah g(-1) after 5000 cycles at 2 A g(-1) and 0.172 Ah g(-1) even at 20 A g(-1) with compatible ether-based electrolyte in a voltage window of 0.8-2.9 V. The Fe0.5 sample transforms to layered Nax Co0.5 Fe0.5 S2 by initial activation, and the layered structure is maintained during following cycles. The redox reactions of Nax Co0.5 Fe0.5 S2 are dominated by pseudocapacitive behavior, leading to fast Na(+) insertion/extraction and durable cycle life. A Na3 V2 (PO4 )3 /Fe0.5 full cell was assembled, delivering an initial capacity of 0.340 Ah g(-1) .

Template-Engaged Synthesis of 1D Hierarchical Chainlike LiCoO2 Cathode Materials with Enhanced High-Voltage Lithium Storage Capabilities.

A novel 1D hierarchical chainlike LiCoO2 organized by flake-shaped primary particles is synthesized via a facile template-engaged strategy by using CoC2O4·2H2O as a self-sacrificial template obtained from a simple coprecipitation method. The resultant LiCoO2 has a well-built hierarchical structure, consisting of secondary micrometer-sized chains and sub-micrometer-sized primary flakes, while these primary LiCoO2 flakes have specifically exposed fast-Li(+)-diffused active {010} facets. Owing to this unique hierarchical structure, the chainlike LiCoO2 serves as a stable cathode material for lithium-ion batteries (LIBs) operated at a high cutoff voltage up to 4.5 V, enabling highly reversible capacity, remarkable rate performance, and long-term cycle life. Specifically, the chainlike LiCoO2 can deliver a reversible discharge capacity as high as 168, 156, 150, and 120 mAh g(-1) under the current density of 0.1, 0.5, 1, and 5 C, respectively, while about 85% retention of the initial capacity can be retained after 200 cycles under 1 C at room temperature. Moreover, the chainlike LiCoO2 also shows an excellent cycling stability at a wide operating temperature range, showing the capacity retention of ∼73% after 200 cycles at 55 °C and of ∼68% after 50 cycles at -10 °C, respectively. The work described here suggests the great potential of the hierarchical chainlike LiCoO2 as high-voltage cathode materials aimed toward developing advanced LIBs with high energy density and power density.

Surface Modification of Lithium Rich NMC for High Rate Lithium Ion Batteries

Recently, lithium manganese-rich layered oxides like Li1+xM1-xO2 (M = Ni, Mn, Co) have been extensively scrutinized as one of the most promising cathode materials for the next-generation lithium rechargeable batteries primarily due to their high reversible capacity over 250 mAh/g. These materials are targeted to be potentially utilized in such mid- and/or large- scale applications as electric vehicles (EV) and commercial electricity storage systems (ESS). However, recent studies show that they exhibit a poor electrochemical performance at high power rate and suffer from structural instability in long-term cycling. During the repeated charge and discharge, severe cation mixing and segregations are reported to occur, which causes a series of phase transitions from layered to a defect spinel, and eventually to a rock-salt structure. This phenomenon deteriorates the high-rate performance significantly because it tends to block the diffusion channels for Li+ ions. Herein, we developed a novel surface-modified lithium manganese-rich layered oxide, which shows a substantial improvement in the high-rate performance and long-term cycle life stability. A thin nano-scaled zirconium-doped surface layer was formed on Li1.2Ni0.13Co0.13Mn0.54O2 particle by using potassium nitrate as an additive to guide the crystal habit during the synthetic process. The addition of potassium nitrate is critical in promoting the preferential development of crystal facets open for the diffusion channel. By the low surface barrier driven by the facets growth, zirconium ions could easily enter the lithium octahedral sites within the structure. The Zr-doped surface layer is formed possibly having a cation-disordered rock-salt structure of a few nano-meter scales. This thin surface layer is believed to prevent the adverse phase transitions and cation segregations as well as to shorten the diffusion path for Li+ion within the particle. As a result, the high rate performances are significantly enhanced; a specific capacity at 30 C-rate is observed to be as high as 110 mAh/g and stable performance was obtained for 300 cycles. Figure. Zr-doped Li1.2Ni0.13Co0.13Mn0.54O2 nanoparticles (a) SEM image, (b) EDS mapping image of Zr-doped surface, (c) Z-contrast STEM-HADDF image taken along the [100] zone axis. This work is supported by the National Research Foundation of Korea (NRF-2011-0030539). Figure 1

A Novel Adhesion Map Correlating Adhesion Properties to the Electrode Design Parameters in Lithium-Ion Battery Electrode

Fabricating the electrodes satisfying the targeted energy density, power density, and loading level is not a simple task to achieve because there are interrelated electrode design parameters such as loading level, density, thickness, composition, etc., affecting on the electrode property. Thus far, the time-consuming repetitive trials have been an only answer to achieve this goal. To determine the optimized binder content and the electrode density have been also a difficult question because there has been few systematic research on adhesion properties for LIB electrodes. For instance, the conventional peel test with adhesive tape (3M Scotch tape) has been widely utilized to compare adhesion properties in electrode as a measuring tool. Our group have introduced the Surface and Interfacial Cutting and Analysis System (SAICAS), which are able to measure the shear stress as well as adhesion strength at the interfaces in the LIB electrodes [1-4]. Here in, we utilized the SAICAS to correlate the adhesion property and the typical electrode design parameters–the loading level and the density–by utilizing a SAICAS technique. First, we measured the adhesion properties of LiCoO2 electrodes, having four different electrode densities (2.0, 2.5, 3.0, and 3.5 g cm-3) and three different loading levels (5, 10, and 15 mg cm-2), at the interface between current collector and electrode coating layer and at the middle of the electrode coating layer. Second, from the obtained data, we draw an empirical equation to predict adhesion strength as a function of electrode density and loading level. Third, we verified our attempt was reasonable by predicting the adhesion strength of the LiCoO2electrode randomly chosen in a random loading level and a random density. Acknowledgements This work was supported by the Human Resource Training Program for Regional Innovation and Creativity through the Ministry of Education and National Research Foundation of Korea (NRF-2014H1C1A1066977).

High-Power Lithium Vanadate / Carbon Composite for Hybrid Supercapacitors

1. Introduction The next step in the improvement of the high-energy-density Li4Ti5O12(LTO) / activated carbon hybrid supercapacitor1 is to substitute the negative electrode (LTO) with other potential candidates with higher voltage and capacity. Here, we selected Li3VO4 (LVO) because of its low redox potential (1.0 V – 0.1 V vs. Li+/Li) and reversible insertion mechanism with high theoretical capacity (394 mAh g-1 in case of 2-electron reaction and 591 mAh g-1 in case of the 3-electron).2-4 To overcome the well-known drawbacks of LVO such as low electronic conductivity (<10-10 S m-1) and large voltage hysteresis (>500 mV) which prevent to achieve high rate performances5-7, we investigated the potentialities of a nanosized LVO (10-50 nm) hyper-dispersed within multi-walled carbon nanotube (MWCNT) matrix prepared by our original ultracentrifugation (UC) process. As expected, the rate performances are considerably enhanced for the uc-LVO/MWCNT, and in addition, the structural mechanism involved during the reversible insertion/extraction of Li is clarified thanks to a deep investigation using in operando XRD. The performances of the obtained composite show that it can be used as a LTO alternative for hybrid supercapacitors. 2. Experimental NH4VO3, citric acid, ethylene glycol and lithium hydroxide were dissolved into deionized water to form a clear orange solution. After the addition under stirring of MWCNT, the solution was subjected to the UC treatment at 80 ˚C for 5min. Then, the mixture was dried at 130˚C under vacuum for 12 h to accelerate the polymerization of ethylene glycol. A calcination stage at 300°C for 3h under air was applied to remove the polymer and a final sintering at 800˚C under N2 atmosphere allows obtaining the Li3VO4/MWCNT composite. Physicochemical characterizations were performed on the synthesized composites by XRD, XPS and TEM observation. Relation between electrochemical behavior and structure change were investigated by in operando XAFS and XRD measurements. 3. Results and discussion Successful synthesis of nanocrystalline LVO particles of ca. 10~50 nm on the surface of MWCNT was confirmed by the combination of HRTEM observation and XRD measurements. The LVO/MWCNT composite shows excellent electrochemical behavior such as high charge (delithiation) rate capability with 170 mAh g-1 per composite at a high rate of 20 A g-1, when charged and discharged down to 0.1 V vs. Li. In operando XRD patterns on the composites show the existence of irreversible structure changes acting as an activation process, where the reaction mechanism of LVO switches from a “two-phase” to a “solid-solution” reaction. The relationship between the hysteresis and Li insertion mechanism was further investigated by charge-discharge tests at different cut-off voltages. It was found that the “activated” LVO/MWCNT composites within the limited voltage window (0.76 -2.5 V vs. Li) can achieve higher reversibility and energy efficiency (low voltage hysteresis below 100mV) with ultrafast Li insertion kinetics and long-term cycle life for the needed hybrid supercapacitor applications. References 1) K. Naoi, W. Naoi, S. Aoyagi, J. Miyamoto and T. Kamino, Acc. Chem. Res., 46, 1075 (2013). 2) S. Ni, J. Zhang, J. Ma, X. Yang, L. Zhang and H. Zeng, Adv. Mater. Interfaces, 3, 1500340 (2016). 3) J. Zhang, S. Ni, J. Ma, X. Yang and L. Zhang, J. Power Sources, 301, 41 (2015). 4) Z. Liang, Y. Zhao, Y. Dong, Q. Kuang, X. Lin, X. Liu, D. Yan, J. Power Sources, 274, 345 (2015). 5) Y. Shi, J. Gao, H.-D. Abruna, H.-J. Li, H.-K. Liu, D. Wexler, J.-Z. Wang and Y. Wu, Chem. Eur. J., 20, 5608 (2014). 6) Y. Shi, J.-Z. Wang, S.-L. Chou, D. Wexler, H.-J. Li, K. Ozawa, H.-k. Liu and Y.-P. Wu, Nano lett., 13, 4715 (2013). 7) H. Li, X. Liu, T. Zhai, D. Li and H. Zhou, Adv. Energy Mater., 3, 428 (2012).

Graphene-Rich Wrapped Petal-Like Rutile TiO2 tuned by Carbon Dots for High-Performance Sodium Storage.

Carbon dots inducing petal-like rutile TiO2 wrapped by ultrathin graphene-rich layers are proposed to fabricate superior anodes for sodium-ion batteries, featuring high-rate capabilities and long-term cyclelife, benefiting from promoted electron transport and a shortened Na+ diffusion length. High capacities of 144.4 mA h g-1 (at 837.5 mA g-1 ) after 1100 cycles and 74.6 mA h g-1 (at 3350 mA g-1 ) after 4000 cycles are delivered outstandingly.

Facile fabrication of ultrathin hybrid membrane for highly flexible supercapacitors via in-situ phase separation of polyethersulfone

Abstract In this article, a facile method based on in-situ phase-separation was developed for the fabrication of ultrathin hybrid membranes for highly flexible supercapacitors. The structures and morphologies of the prepared electrodes were characterized by scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) measurements; and the electrochemical behaviors were examined in 2 M KOH solution. SEM and FTIR characterizations reveal that activated carbon was imbedded into the polymer membrane of polyethersulfone to form a uniform and flexible hybrid membrane. When the thin polymer-carbon membrane (PCM) was used as an electrode material for supercapacitor, a high specific capacitance of 169.4 Fg −1 was obtained at a current density of 0.5 Ag −1 along with good long-term cycle life of 94.6% capacity retention after 2000 charging-discharging cycles. Benefiting from these merits, the as-fabricated PCM//PCM cell shows an excellent electrochemical property. These results suggest a promising route towards the fabrication of highly flexible electrodes for high-performance supercapacitors.