A flexible polyelectrolyte-based gel polymer electrolyte for high-performance all-solid-state supercapacitor application

A simple polymerization process assisted with UV light for preparing a novel flexible polyelectrolyte-based gel polymer electrolyte (PGPE) is reported. Due to the existence of charged groups in the polyelectrolyte matrix, the PGPE exhibits favorable mechanical strength and excellent ionic conductivity (66.8 mS cm⁻¹ at 25 °C). In addition, the all-solid-state supercapacitor fabricated with a PGPE membrane and activated carbon electrodes shows outstanding electrochemical performance. The specific capacitance of the PGPE supercapacitor is 64.92 F g⁻¹ at 1 A g⁻¹, and the device shows a maximum energy density of 13.26 W h kg⁻¹ and a maximum power density of 2.26 kW kg⁻¹. After 10 000 cycles at a current density of 2 A g⁻¹, the all-solid-state supercapacitor with PGPE reveals a capacitance retention of 94.63%. Furthermore, the specific capacitance and charge–discharge behaviors of the flexible PGPE device hardly change with the bending states.

A simple polymerization process assisted with UV light for preparing a novel flexible polyelectrolyte-based gel polymer electrolyte (PGPE) is reported.     

Oxygen functional groups improve the energy storage performances of graphene electrochemical supercapacitors

Graphene is a promising electrode material for supercapacitors due to its superior physical and chemical properties, but the influence of its oxygen functional groups on capacitive performance still remains somewhat uncertain. In this work, graphene sheets with different oxygen content have been prepared through thermal reduction in argon. Furthermore, oxidation and pore-forming treatment of graphene annealed at 800 °C are also performed to explore the important effect of oxygen functional groups. The effects of disorder degree, surface area and oxygen functional groups on the specific capacitance were explored systematically. The content and species of oxygen functional groups are found to be significant factors influencing the electrochemical supercapacitor performance of graphene electrodes. The specific capacitances of graphene annealed at 200, 400 and 800 °C are 201, 153 and 34 F g⁻¹, respectively. However, the specific capacitance of graphene reduced at 800 °C can be increased to 137 F g⁻¹ after nitric acid oxidation treatment, and is only 39 F g⁻¹ after pore forming on graphene surface, demonstrating that the oxygen functional groups can improve the capacitive performances of graphene electrochemical supercapacitors.

The content and species of oxygen functional groups are significant factors influencing the electrochemical supercapacitor performance of graphene electrodes.     

Low-temperature all-solid-state lithium-ion batteries based on a di-cross-linked starch solid electrolyte

The preparation of a low-temperature solid electrolyte is a challenge for the commercialization of the all-solid-state lithium-ion battery (ASSLIB). Here we report a starch-based solid electrolyte that displays phenomenal electrochemical properties below room temperature (RT). The starch host of the electrolyte is synthesized by two cross-linking reactions, which provide sufficient and orderly binding sites for the lithium salt to dissolve. At 25 °C, the solid electrolyte has exceptional ionic conductivity (σ, 3.10 × 10⁻⁴ S cm⁻¹), lithium-ion transfer number (t⁺, 0.82) and decomposition potential (dP, 4.91 V). At −20 °C, it still has outstanding σ (3.10 × 10⁻⁵ S cm⁻¹), t⁺ (0.72) and dP (5.50 V). The LiFePO₄ ASSLIB assembled with the electrolyte exhibits unique specific capacity and long cycling life below RT, and the LiNi_0.8Co_0.1Mn_0.1O₂ ASSLIB can operate at 4.3 V and 0 °C. This work provides a solution to solve the current challenges of ASSLIBs to widen their scope of applications.

The all-solid-state lithium battery based on di-cross-linked starch electrolyte is applicable at low temperature.     

Nanocellulose/polypyrrole aerogel electrodes with higher conductivity via adding vapor grown nano-carbon fibers as conducting networks for supercapacitor application

Nanocellulose-based conductive materials have been widely used as supercapacitor electrodes. Herein, electrode materials with higher conductivity were prepared by in situ polymerization of polypyrrole (PPy) on cellulose nanofibrils (CNF) and vapor grown carbon fiber (VGCF) hybrid aerogels. With increase in VGCF content, the conductivities of CNF/VGCF aerogel films and CNF/VGCF/PPy aerogel films increased. The CNF/VGCF₂/PPy aerogel films exhibited a maximum value of 11.25 S cm⁻¹, which is beneficial for electron transfer and to reduce interior resistance. In addition, the capacitance of the electrode materials was improved because of synergistic effects between the double-layer capacitance of VGCF and pseudocapacitance of PPy in the CNF/VGCF/PPy aerogels. Therefore, the CNF/VGCF/PPy aerogel electrode showed capacitances of 8.61 F cm⁻² at 1 mV s⁻¹ (specific area capacitance) and 678.66 F g⁻¹ at 1.875 mA cm⁻² (specific gravimetric capacitance) and retained 91.38% of its initial capacitance after 2000 cycles. Furthermore, an all-solid-state supercapacitor fabricated by the above electrode materials exhibited maximum energy and power densities of 15.08 W h Kg⁻¹, respectively. These electrochemical properties provide great potential for supercapacitors or other electronic devices with good electrochemical properties.

The electrochemical performances of nanocellulose-based electrode materials were improved via building nano-carbon conducting networks.     

Ice-interface assisted large-scale preparation of polypyrrole/graphene oxide films for all-solid-state supercapacitors

In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. The morphology, chemical structure and electrochemical property were characterized by field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS), respectively. The lamellar structure of GO and both strong interaction with ice and pyrrole could promote polymerization of pyrrole and improve the compactness of the film. With the aid of GO, the conjugation length of PPy increased, the resistance of the material decreased, and the electrochemical energy storage of the composite film was significantly enhanced. In the case of 2.5 wt% GO, the prepared PPy/GO nanocomposite supercapacitor exhibited a high area specific capacitance of 97.3 mF cm⁻² at 1 mA cm⁻². Furthermore, the PPy/GO film supercapacitor also showed excellent cycling stability and good flexibility.

A confirned polymerization method was employed to fabricate self-standing PPy/GO film for all-solid-state supercapacitor.     

A study on the preparation of polycation gel polymer electrolyte for supercapacitors

The polycation gel polymer electrolyte (PGPE) is a promising electrolyte material for supercapacitors due to its high ionic conductivity and great flexibility. Herein, we report a novel flexible PGPE film, which is prepared by thermal copolymerization. The superiority of PGPE is attributed to the existence of charged groups in the polymer skeleton. Consequently, the crystallinity of the polymer is effectively reduced, and the migration of the lithium ion is evidently promoted. Moreover, the liquid retention capacity of the film is improved, which enhances its ionic conductivity as well. The reported PGPE exhibits a high ionic conductivity of 57.6 mS cm⁻¹ at 25 °C and a potential window of 0–1.2 V. The symmetrical PGPE supercapacitor (AC/AC) shows 95.21% mass-specific capacitance retention after 5000 cycles at 2 A g⁻¹ with a maximum energy density of 12.8 W h kg⁻¹ and a maximum power density of 5.475 kW kg⁻¹. This study confirms the exciting potential of PGPE for high performance supercapacitors.

The polycation gel polymer electrolyte (PGPE) is a promising electrolyte material for supercapacitors due to its high ionic conductivity and great flexibility.     

Cu-MOF derived Cu–C nanocomposites towards high performance electrochemical supercapacitors

For the development of asymmetric supercapacitors with higher energy density, the study of new electrode materials with high capacitance is a priority. Herein, the electrochemical behavior of nano copper in alkaline electrolyte is first discovered. It is found that there are two obvious reversible redox symmetric peaks in the range of −0.8–0.2 V in the alkaline electrolyte, corresponding to the conversion of copper into cuprous ions, and then converting cuprous ions into copper ions, indicating that the nanocomposite electrode has the characteristics of a pseudocapacitive reaction. It has a specific capacitance of up to 318 F g⁻¹ at a current density of 1 A g⁻¹, which remains at nearly 100% after 10 000 cycles at the same current density. When assembled with a Ni(OH)₂-based electrode into an asymmetric supercapacitor, the device shows excellent capacitive behavior and good reaction reversibility. At 0.4 A g⁻¹, the supercapacitor delivers a reversible capacity of 8.33 F g⁻¹ with an energy density of 13.5 mW h g⁻¹. This study first discovers the electrochemical behavior of nano copper, which can provide a new research idea for further expanding the negative electrodes of supercapacitors with higher energy density.

A new Cu–C nanocomposite derived from Cu-based metal–organic framework exhibits greatly improved electrochemical performance.     

An ultrasonic-assisted synthesis of rice-straw-based porous carbon with high performance symmetric supercapacitors

Biomass porous carbon materials are ideal supercapacitor electrode materials due to their low price, rich source of raw materials and environmental friendliness. In this study, an ultrasonic-assisted method was applied to synthesize the rice-straw-based porous carbon (UPC). The obtained UPC exhibited a two-dimensional structure and high specific surface area. In addition, the electrochemical test results showed that the UPC with a 1 hour ultrasonic treatment and lower activation temperature of 600 °C (UPC-600) demonstrated optimal performance: high specific capacitances of 420 F g⁻¹ at 1.0 A g⁻¹ and 314 F g⁻¹ at a high current of 10 A g⁻¹. Significantly, the symmetric supercapacitors showed a high energy density of 11.1 W h kg⁻¹ and power density of 500 W kg⁻¹. After 10 000 cycles, 99.8% of the specific capacitance was retained at 20 A g⁻¹. These results indicate that UPC-600 is a promising candidate for supercapacitor electrode materials.

Rice-straw-based porous carbon was successfully prepared via an ultrasonic-assisted method to lower activation temperature and for ultra-stable electrode materials of symmetric supercapacitors.     

Rapid microwave activation of waste palm into hierarchical porous carbons for supercapacitors using biochars from different carbonization temperatures as catalysts

A rapid, simple and cost-effective approach to prepare hierarchical porous carbons (PCs) for supercapacitors is reported by microwave activation of abundant and low-cost waste palm, biochar (BC) and KOH. BCs from waste palm at different carbonization temperatures (300–700 °C), as catalysts and microwave receptors, were used here for the first time to facilitate the conversion of waste palm into hierarchical PCs. As a result, the high-graphitization PC obtained at a BC carbonization temperature of 300 °C (PC-300) possessed a high surface area (1755 m² g⁻¹), a high pore volume (0.942 cm³ g⁻¹) and a moderate mesoporosity (37.79%). Besides their high-graphitization and hierarchical porous structure, the oxygen doping in PC-300 can also promote the rapid transport of electrolyte ions. The symmetric supercapacitor based on the PC-300 even in PVA/LiCl gel electrolyte exhibited a high specific capacitance of 164.8 F g⁻¹ at a current density of 0.5 A g⁻¹ and retained a specific capacitance of 121.3 F g⁻¹ at 10 A g⁻¹, demonstrating a superior rate capacity of 73.6%. Additionally, the PC-300 supercapacitor delivered a high energy density of 14.6 W h kg⁻¹ at a power density of 398.9 W kg⁻¹ and maintained an energy density of 10.8 W h kg⁻¹ at a high power density of 8016.5 W kg⁻¹, as well as an excellent cycling stability after 2000 cycles with a capacitance retention of 92.06%.

A rapid, simple and cost-effective approach to prepare hierarchical porous carbons (PCs) for supercapacitors is reported by microwave activation of abundant and low-cost waste palm, biochar (BC) and KOH.     

All-solid-state flexible supercapacitor based on nanotube-reinforced polypyrrole hollowed structures

Supercapacitors are strong future candidates for energy storage devices owing to their high power density, fast charge–discharge rate, and long cycle stability. Here, a flexible supercapacitor with a large specific capacitance of 443 F g⁻¹ at a scan rate of 2 mV s⁻¹ is demonstrated using nanotube-reinforced polypyrrole nanowires with hollowed cavities grown vertically on a nanotube/graphene based film. Using these electrodes, we obtain improved capacitance, rate capability, and cycle stability for over 3000 cycles. The assembled all-solid-state supercapacitor exhibits excellent mechanical flexibility, with the capacity to endure a 180° bending angle along with a maximum specific and volumetric energy density of 7 W h kg⁻¹ (8.2 mW h cm⁻³) at a power density of 75 W kg⁻¹ (0.087 W cm⁻³), and it showed an energy density of 4.13 W h kg⁻¹ (4.82 mW h cm⁻³) even at a high power density of 3.8 kW kg⁻¹ (4.4 W cm⁻³). Also, it demonstrates a high cycling stability of 94.3% after 10 000 charge/discharge cycles at a current density of 10 A g⁻¹. Finally, a foldable all-solid-state supercapacitor is demonstrated, which confirms the applicability of the reported supercapacitor for use in energy storage devices for future portable, foldable, or wearable electronics.

Nanotube-reinforced polypyrrole nanowires with hollowed cavities allow the fabrication of a flexible supercapacitor with a large specific capacitance.     

Facile synthesis of bio-based nitrogen- and oxygen-doped porous carbon derived from cotton for supercapacitors

Biomass-derived O- and N-doped porous carbon has become the most competitive supercapacitor electrode material because of its renewability and sustainability. We herein presented a facile approach to prepare O/N-doped porous carbon with cotton as the starting material. Absorbent cotton immersed in diammonium hydrogen phosphate (DAP) was activated at 800 °C (CDAP800s) and then was oxidized in a temperature range of 300–400 °C. The electrochemical capacitance of the impregnated cotton was significantly improved by doping with O and N, and the yield was improved from 13% to 38%. The sample oxidation at 350 °C (CDAP800-350) demonstrated superior electrical properties. CDAP800-350 showed the highest BET surface area (1022 m² g⁻¹) and a relatively high pore volume (0.53 cm³ g⁻¹). In a three-electrode system, the CDAP800-350 electrodes had high specific capacitances of 292 F g⁻¹ in 6 M KOH electrolyte at a current density of 0.5 A g⁻¹. In the two-electrode system, CDAP800-350 electrode displayed a specific capacitance of 270 F g⁻¹ at 0.5 A g⁻¹ and 212 F g⁻¹ at 10 A in KOH electrolyte. In addition, the CDAP800-350-based symmetric supercapacitor achieved a high stability with 87% of capacitance retained after 5000 cycles at 5 A g⁻¹, as well as a high volumetric energy density (18 W h kg⁻¹ at 250 W kg⁻¹).

Biomass-derived O- and N-doped porous carbon has become one of the most competitive supercapacitor electrode material because of its renewability and sustainability.     

Quasi-solid-state highly stretchable circular knitted MnO2@CNT supercapacitor

Flexible and stretchable fiber supercapacitors have been progressively improved for wearable electronic devices. However, they should be further improved with respect to stretchable range and stable electrochemical performance during dynamic movement when considering the tensile range for wearable applications. Here, we report a quasi-solid-state circular knitted MnO₂@CNT supercapacitor with high tensile range. To fabricate this, CNT fibers were knitted into a circular shape using a knitting machine then subsequently electrochemically deposited by a pseudocapacitive material, MnO₂. Consequently, the knitted MnO₂@CNT fiber supercapacitors were structurally 100% stretchable, and their energy storage performance remained stable during knitted capacitor stretching of up to 100%. Maximum linear capacitance and area capacitance are considerably large (321.08 mF cm⁻¹, 511.28 mF cm⁻²). In addition, the supercapacitor showed negligible loss of capacitance after 10 000 repeated charge/discharge cycles and dynamic stretching cycle testing. Furthermore, we also provided double-walled knitted MnO₂@CNT supercapacitors by symmetrically inserting one knitted supercapacitor into another. The double-walled supercapacitor also exhibited a stable stretchability of up to 100% without loss of capacitance. Therefore, this highly stretchable fiber-type supercapacitor could be utilized for energy storage in wearable devices.

Flexible and stretchable double-walled circular knitted MnO₂@CNT supercapacitors shows high performance, electrochemical and mechanical stability and can be used for wearable electronics.     

N/O co-enriched graphene hydrogels as high-performance electrodes for aqueous symmetric supercapacitors

In this study, an easy one-pot hydrothermal strategy was used to prepare N/O co-enriched graphene hydrogels (NOGHs) using graphene oxide (GO) solution and n-propylamine as a reactant. The n-propylamine can be used not only as a reductant, nitrogen dopant and structure regulator, but also as a spacer to inhibit the agglomeration of graphene sheets. Benefiting from the synergistic effect between the heteroatoms (N, O), 3D porous structures and high specific surface area, the as-prepared NOGH samples present excellent electrochemical properties. Remarkably, the NOGH-140 based binder-free symmetric supercapacitor shows a high specific capacitance of 268.1 F g⁻¹ at the current density of 0.3 A g⁻¹ and retains 222.5 F g⁻¹ (82.9% of its initial value) at 10.0 A g⁻¹ in 6 M KOH electrolyte. Furthermore, the assembled device also displays a notable energy density (9.3 W h kg⁻¹) and outstanding cycling performance (1.8% increase of its initial specific capacitance after 10 000 cycles at 10 A g⁻¹). The simple preparation method and excellent electrochemical properties indicate that NOGHs can be used as electrode materials for commercial supercapacitors.

N/O co-enriched graphene hydrogel based supercapacitors were assembled. Owing to the synergistic effect between the heteroatoms (N, O), 3D porous structures and high specific surface area, they present excellent electrochemical properties.     

Preparation of a MoS2/carbon nanotube composite as an electrode material for high-performance supercapacitors

MoS₂ and MoS₂/carbon allotrope (MoS₂/C) composites for use as anodes in supercapacitors were prepared via a facile hydrothermal method. In this study, we report the effects of various carbon-based materials (2D graphene nanosheet (GNS), 1D carbon nanotube (CNT), and 0D nano carbon (NC)) on the electrochemical performances. Among all nanocomposites studied, MoS₂/CNT exhibited the best electrochemical performance. Specifically, the MoS₂/CNT composite exhibits remarkable performances with a high specific capacitance of 402 F g⁻¹ at a current density of 1 A g⁻¹ and an outstanding cycling stability with 81.9% capacitance retention after 10 000 continuous charge–discharge cycles at a high current density of 1 A g⁻¹, making it adaptive for high-performance supercapacitors. The superiority of MoS₂/CNT was investigated by field emission scanning electron microscopy and transmission electron microscopy, which showed that MoS₂ nanosheets were uniformly loaded into the three-dimensional interconnected network of nanotubes, providing an excellent three dimensional charge transfer network and electrolyte diffusion channels while effectively buffering the collapse and aggregation of active materials during charge–discharge processes. Overall, the MoS₂/CNT nanocomposite synthesized by a simple hydrothermal process presents a new and promising candidate for high-performance anodes for supercapacitors.

The effect of carbon supports on the electrochemical performance of MoS₂ nanosheets for supercapacitor applications was investigated.     

Hierarchical porous carbons from carboxylated coal-tar pitch functional poly(acrylic acid) hydrogel networks for supercapacitor electrodes

A gel carbonization strategy for the synthesis of hierarchical porous carbons (HPCs) from carboxylated coal-tar pitches (CCP) functional poly(acrylic acid) (PAA) hydrogel networks for advanced supercapacitor electrodes was reported. The amphiphilic CCP and PAA polymer could be easily self-assembled to gel by the major driving force of hydrogen bonding and π–π stacking. The HPCs containing interconnected macro-/meso-/micropores were fabricated by direct carbonization of the dried hydrogels. The resultant HPCs with a high specific surface area and total pore volume of 1294.6 m² g⁻¹ and 1.34 cm³ g⁻¹ respectively, as a supercapacitor electrode exhibit a high specific capacitance of 292 F g⁻¹ at 1.0 A g⁻¹ in two-electrode system. The electrode also exhibits ultra-long cycle life with a capacitance retention as high as 94.2% after 10 000 cycles, indicating the good electrochemical stability. Furthermore, the concept of such hierarchical architecture and synthesis strategy would expand to other materials for advanced energy storage systems, such as Na-ion batteries and metal oxides for supercapacitors.

As a supercapacitor electrode exhibit a high specific capacitance of 292 F g⁻¹ at 1.0 A g⁻¹.     

N/S co-doped coal-based porous carbon spheres as electrode materials for high performance supercapacitors

N/S co-doped porous carbon spheres (NSPCSs) were prepared by a simple ultrasonic spray pyrolysis (USP) using the mixed solution of coal oxide and l-cysteine, and without a subsequent activation process. The surface properties of carbon materials have been successfully modified by the concurrent incorporation of N and S. So the capacitive performance of NSPCSs was greatly enhanced. It is used as a supercapacitor electrode to achieve a high specific capacitance of 308 F g⁻¹ at a current density of 1 A g⁻¹ and 90.2% capacitance retention even after 10 000 cycles at 5 A g⁻¹. These numerical results show that the supercapacitors based on coal-based carbon materials have great potential in high performance electrochemical energy storage.

N/S co-doped porous carbon spheres were prepared using one step strategy for high performance supercapacitors.     

Facile preparation of flexible binder-free graphene electrodes for high-performance supercapacitors

A facile two-step strategy to prepare flexible graphene electrodes has been developed for supercapacitors using thermal reduction of graphene oxide (GO) and thermally reduced graphene oxide (TRGO) composite films. The tunable porous structure of the GO/TRGO film provided channels to release the high pressure generated by CO₂ gas. The graphene electrode obtained from reduced-GO/TRGO (1 : 1 in mass ratio) film showed great flexibility and high film density (0.52 g cm⁻³). Using the EMI-BF₄ electrolyte with a working voltage of 3.7 V, the as-fabricated free-standing reduced-GO/TRGO (1 : 1) film achieved a great gravimetric capacitance of 180 F g⁻¹ (delivering a gravimetric energy density of 85.6 W h kg⁻¹), a volumetric capacitance of 94 F cm⁻³ (delivering a volumetric energy density of 44.7 W h L⁻¹), and a 92% retention after 10 000 charge/discharge cycles. In addition, the solid state flexible supercapacitor with the free-standing reduced-GO/TRGO (1 : 1) film as the electrodes and the EMI-BF₄/poly (vinylidene fluoride hexafluopropylene) (PVDF-HFP) gel as the electrolyte also demonstrated a high gravimetric capacitance of 146 F g⁻¹ with excellent mechanical flexibility, bending stability, and electrochemical stability. The strategy developed in this study provides great potentials for the synthesis of flexible graphene electrodes for supercapacitors.

A supercapacitor electrode is developed with a free-standing graphene film by a facile two-step strategy. The graphene electrode achieved a gravimetric capacitance of 180 F g⁻¹ and a volumetric capacitance of 94 F cm⁻³.     

Nitrogen doped hierarchical activated carbons derived from polyacrylonitrile fibers for CO2 adsorption and supercapacitor electrodes

Nitrogen doped hierarchical activated carbons with high surface areas and different pore structures are prepared form polyacrylonitrile fibers through KOH activation by two steps. It is found that the specific surface area and porosity of the activated carbons depend strongly on the activation temperatures. The specific surface area increases from 607 m² g⁻¹ to 3797 m² g⁻¹ when the activation temperature increases from 600 °C to 800 °C, and then decreases to 3379 m² g⁻¹ at 900 °C. It shows that the hierarchical activated carbon prepared at a moderate activation temperature of 700 °C exhibits the largest CO₂ capture amount, i.e., 5.25 and 3.63 mmol g⁻¹ at 273 and 298 K, respectively, under the pressure of 1 bar. The excellent CO₂ capture properties are due to the high specific surface area of 2146 m² g⁻¹ and high nitrogen content (5.2 wt%) of the obtained sample. On the other hand, when used as supercapacitor electrodes, the sample with the activation temperature at 800 °C shows the largest specific capacitance of 302 F g⁻¹ at a current density of 1 A g⁻¹ in 6 M KOH aqueous electrolyte, with an excellent rate capability of 231 F g⁻¹ at 10 A g⁻¹. Furthermore, a nearly linear relationship between nitrogen content in the nitrogen doped activated carbons and specific CO₂ uptake as well as the specific capacitance were first established, indicating nitrogen doping was playing key roles in improving CO₂ adsorption and supercapacitor performance. The experimental results indicate that the thus obtained nitrogen doped hierarchical activated carbons are very promising for reducing CO₂ green house gas by adsorption as well as storing energy as utilized in supercapacitors.

Nitrogen doped activated carbons with high surface area up to 3797 m₂ g⁻¹ exhibit specific capacitance of 231 F g⁻¹ at a current density of 10 A g⁻¹.     

Rapid transformation of heterocyclic building blocks into nanoporous carbons for high-performance supercapacitors

The ever-increasing global energy consumption necessitates the development of efficient energy conversion and storage devices. Nitrogen-doped porous carbons as electrode materials for supercapacitors feature superior electrochemical performances compared to pristine activated carbons. Herein, a facile synthetic strategy including solid-state mixing of benzimidazole as an inexpensive single-source precursor of nitrogen and carbon and zinc chloride as a high temperature solvent/activator followed by pyrolysis of the mixture (T = 700–1000 °C under Ar) is introduced. The addition of ZnCl₂ prevents early sublimation of benzimidazole and promotes carbonization and pore generation. The sample obtained under the optimal carbonization temperature of 900 °C and ZnCl₂/benzimidazole weight ratio of 2/1 (ZBIDC-2-900) features a moderate specific surface area of 855 m² g⁻¹, high N-doping level (10 wt%), and a wide micropore size distribution (∼1 nm). ZBIDC-2-900 as a supercapacitor electrode exhibits a large gravimetric capacitance of 332 F g⁻¹ (at 1 A g⁻¹ in 1 M H₂SO₄) thanks to the cooperative advantages of the electrochemical activity of the nitrogen functional groups and the accessible porosity. The excellent capacitance performance coupled with robust cyclic stability, high yield and straightforward synthesis of the proposed carbons holds great potential for large-scale energy storage applications.

Zinc chloride activated benzimidazole derived carbons (ZBIDCs) with optimal textural and chemical properties exhibit remarkable and stable performance in supercapacitor applications.     

Novel poly(arylene ether ketone)/poly(ethylene glycol)-grafted poly(arylene ether ketone) composite microporous polymer electrolyte for electrical double-layer capacitors with efficient ionic transport

Polymer electrolytes have attracted considerable research interest due to their advantages of shape control, excellent safety, and flexibility. However, the limited use of traditional polymer electrolytes in electric double-layer capacitors due to their unsatisfactory ionic conductivities and poor mechanical properties makes them difficult to operate for long periods of time in large-scale energy storage. Therefore, we fabricated a high-performance microporous electrolyte based on poly(arylene ether ketone) (PAEK)/poly(ethylene glycol)-grafted poly(arylene ether ketone) (PAEK-g-PEG) using a certain amount of carboxylated chitosan with a high electrolyte uptake rate of 322 wt% and a high ionic conductivity of 2 × 10⁻² S cm⁻¹ at room temperature. A symmetric solid-state supercapacitor that uses activated carbon as electrodes and a composite microporous polymer film as the electrolyte shows a high specific capacitance of 134.38 F g⁻¹ at a current density of 0.2 A g⁻¹, while liquid electrolytes demonstrate a specific capacitance of 126.92 F g⁻¹. Energy density of the solid-state supercapacitor was 15.82% higher than that of the liquid supercapacitor at a current density of 5 A g⁻¹. In addition, the solid-state supercapacitor exhibited excellent cycling stability of over 5000 charge/discharge cycles at a current density of 1 A g⁻¹. Furthermore, solid-state supercapacitors display lower self-discharge behavior with an open-circuit potential drop of only 36% within 70 000 s, which is significantly better than that of conventional supercapacitors (52% @ 70 000 s), at a charging current density of 1 mA cm⁻². The satisfactory results indicated that the PAEK/PAEK-g-PEG composite microporous polymer film demonstrates high potential as an electrolyte material in practical applications of solid-state and portable energy storage devices.

Polymer electrolytes have attracted considerable research interest due to their advantages of shape control, excellent safety, and flexibility.