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The coupling of metal oxide nanoparticles and electrochemically active polymers has been considered as an effective way to improve the lithium storage performance of individual electrode materials. This work reports an electrospinning process followed by thermal annealing to produce composite nanofibers of cyclized-polyacrylonitrile (cPAN) containing Co3O4 nanoparticles (cPAN/Co3O4). The as-prepared cPAN/Co3O4 nanofiber exhibits a porous nanostructure with an average diameter of 85 nm. When used for lithium-ion battery, the cPAN/Co3O4 anode delivers a reversible specific capacity as high as 997.6 mA h g−1 at 0.1 A g−1, and still maintains 396.5 mA h g−1 at 1.0 A g−1. Meanwhile, the cPAN/Co3O4 anode shows good cycling stability with a retention of 81% capacity after running 50 cycles at 0.1 A g−1. The electrochemical performance of cPAN/Co3O4 significantly outperforms its individual counterparts of cPAN and Co3O4.

Boosting high-rate lithium storage performance by core–shell heteroarchitectured cathodes consisting of conductive carbon nanotubes and redox-active azo-linked hyperbranched polymers.

Yarn-based strain sensor is an emerging candidate for the fabrication of wearable electronic devices. The intrinsic properties of yarn, such as excellent lightweight, flexibility, stitchability, and especially its highly stretchable performance, stand out the yarn-based strain sensor from conventional rigid sensors in detection of human body motions. Recent advances in conductive materials and fabrication methods of yarn-based strain sensors are well reviewed and discussed in this work. Coating techniques including dip-coating, layer by layer assemble, and chemical deposition for deposition of conductive layer on elastic filament were first introduced, and fabrication technology to incorporate conductive components into elastic matrix via melt extrusion or wet spinning was reviewed afterwards. Especially, the recent advances of core–sheath/wrapping yarn strain sensor as-fabricated by traditional spinning technique were well summarized. Finally, promising perspectives and challenges together with key points in the development of yarn strain sensors were presented for future endeavor.

A pairwise coupling of 0D Super-P (SP), 1D carbon nanotubes (CNTs), and 2D graphene nanosheets (GNs) into binary carbon-based conductive additives was used here for the LiFePO4 cathode in lithium-ion batteries. For comparison, the LiFePO4 cathode with SP, CNT, or GN unitary conductive agent was also examined. Electrochemical test results suggest that the cathodes with binary conducting additives present greatly improved electrochemical performance than the traditional cathode system (only SP used). Especially, the LiFePO4 cathode containing 3% CNT component exhibits the highest specific capacity and the best cycling stability among all the cathodes with binary conducting additives, indicating that an appropriate amount of CNTs is critical in enhancing the conductivity and practical capacity output. However, an excess of CNTs leads to entangling with each other, hampering the uniform distribution of active materials and resulting in poor electrode performance. Furthermore, the combination of CNT and GN can effectively improve the capacity and cycling stability of the LiFePO4 cathodes due to the synergistic effect of 3D conductive networks constructed by the two.

Heteroatom-doped porous carbons with hierarchical structures have been regarded as promising electrode materials for high-performance supercapacitors. Herein N, S co-doped hierarchically porous carbon (NSHPC) was synthesized by a molten-salt templated method using eutectic KCl/LiCl as the template, chitosan as the carbon/nitrogen source, and K2SO4 as the sulfur source, respectively. The as-prepared NSHPC exhibits a large specific surface area of 994.2 m2 g−1 with hierarchical pores of 1.6, 2.5, and 3.7 nm in diameter, as well as high heteroatom content with 4.5% of N and 10.2% of S elements. Consequently, the NSHPC electrode delivers high specific capacitances of 277 F g−1 at a scan rate of 25 mV s−1, and 195 F g−1 at a current density of 10 A g−1, and also retains a 48.9% retention when the current density is increased to 50 A g−1. Moreover, the electrode also remains 87.4% of initial capacitance after submitting 5000 charge/discharge cycles at 10 A g−1.

Vertically aligned 2D few-layered VS2 nanosheets onto a 2D graphene substrate were, for the first time, crafted by scalable solvothermal and post-annealing processes. The resulting 3D heterostructured VS2-on-graphene (denoted as VS2@Gr) is composed of interconnected nanosheet networks with an efficient exposure of electrochemically active surfaces, nanosheet edges, and abundant porous channels. Such robust hierarchical architectures possess significant advantages over individual building blocks, inhibiting intersheet aggregation, facilitating electrolyte percolation/active-material utilization, promoting ion diffusion/electron conduction, and retaining structural integrity/mechanical stability. Surprisingly, these synergetic characteristics endow VS2@Gr with very favorable capacitive kinetics in the Li-storage behavior. When employed as an anode, the VS2@Gr exhibits remarkable electrochemical performance with large reversible capacity (989 mA h g−1 at 0.1 A g−1), high initial coulombic efficiency (64%), a larger ion diffusion coefficient, superior rate capability (675 mA h g−1 at 1 A g−1), and long cycling stability (77% retention at 10 A g−1 after 10 000 cycles), outperforming its VS2 counterpart with a dominant diffusion-controlled behavior. This work may provide new insights into the architectural engineering of 3D heterostructured nanomaterials comprising two dissimilar 2D constituents for advanced energy storage.

Graphene/polyaniline composites have attracted considerable attention as high-performance supercapacitor electrode materials; however, there are still numerous challenges for their practical applications, such as the complex preparation process, high cost, and disequilibrium between energy density and power density. Herein, we report an efficient method to produce graphene/polyaniline composites via a one-pot ball-milling process, in which aniline molecules act as both the intercalator for the exfoliation of graphite and the monomer for mechanochemical polymerization into polyaniline clusters on the in situ exfoliated graphene sheets. The graphene/polyaniline composite electrode delivered a large specific capacitance of 886 F g−1 at 5 mV s−1 with a high retention of 73.4% at 100 mV s−1. The high capacitance and rate capability of the graphene/polyaniline composite can contribute to the fast electron/ion transfer and dominantly capacitive contribution because of the synergistic effects between the conductive graphene and pseudocapacitive polyaniline. In addition, a high energy density of 40.9 W h kg−1 was achieved by the graphene/polyaniline-based symmetric supercapacitor at a power density of 0.25 kW kg−1, and the supercapacitor also maintained 89.1% of the initial capacitance over 10 000 cycles.

Binary composites comprised of metal oxides and graphene with novel microstructure prepared via a simple, rapid and high-efficiency strategy is of key significance for the development of high-performance supercapacitor. In this work, Co3O4 nanoparticles with average size of 10 nm were in situ grown on reduced graphene oxide (RGO) nanosheets via a time-saving sonochemical treatment, to yield Co3O4/RGO composites with a unique sandwich structure. The RGO skeleton supported the uniform growth of Co3O4 nanoparticles onto it, inhibiting the restacking of graphene nanosheets and affording a large surface area for more effective ion accessibility. Moreover, the excellent electrical conductivity of RGO network ensured the fast electron transfer at Co3O4/RGO interfaces to facilitate the pseudo-capacitive reaction of Co3O4. As a supercapacitor electrode, Co3O4/graphene composite exhibited a high-specific capacitance of 276.6 F g−1 at current density of 0.5 A g−1 and retained 210 F g−1 at 10 A g−1, indicating an excellent rate capability. Furthermore, the composite electrode demonstrated a good cycling stability with 92.4% capacitance retention after 5000 cycles at 5 A g−1. The superior capacitance performance of the composite electrode was attributed to the pseudo-capacitance effect of Co3O4 nanoparticles combined with the electrical double-layer capacitor contribution of RGO nanosheets.

Carbon aerogels are suffering from moderate specific capacitance and inferior energy density for the as-fabricated electric double-layer capacitors. Meanwhile, such aerogels are limited by mechanical brittleness and traditional process of high-cost templates and unsustainable precursors. Herein mechanically-robust and compressible carbon aerogels were readily fabricated by low-temperature lyophilization of the frozen aqueous suspension of bamboo cellulose nanofibers in liquid nitrogen followed by high-temperature pyrolysis. Free-standing carbon aerogels were further coated through in-situ oxidative polymerization of pyrrole, producing homogeneous core-sheath carbon aerogel/polypyrrole (PPy@CA) composites. The symmetrical supercapacitor using the PPy@CA electrodes delivers a specific capacitance of 268.5 F g−1 at 0.5 A g−1 and an energy density of 23.8 Wh Kg−1 at the power density of 450.4 W kg−1. At an elevated current density of 10 A g−1, the energy density remains as high as 19.6 Wh kg−1 at the highest power density of 8018.2 W kg−1. Moreover, the supercapacitor retains 88% of its initial capacitance after running 10,000 cycles at 10 A g−1. These excellent performances for PPy@CA are attributable to their electrically-conductive 3D carbon frameworks and interconnective porous channels capable of efficient diffusion of electrolyte ions, fast transport of electrons, and preserving structural stability. Such active nanocomposites are currently pursued as supercapacitor electrodes due to the synergistic effect between high power density of CAs and high energy density of pseudo-capacitive PPy.

The past decade has witnessed substantial achievements on electrochemical energy storage in employing graphene-based composites; however, of which have been usually produced on a laboratory scale with a limited compatibility with future industrialization. Herein a facile, cheap, and scalable sonochemical method was developed to prepare MnO2/graphene composite electrodes for supercapacitors. Petal-like MnO2 arrays were densely grown on the surface of graphene oxide followed by annealing at 220 °C under an air atmosphere. The as-fabricated MnO2/graphene hierarchical composite electrodes deliver 292.9 and 156.1 F/g at 5 and 100 mV/s, respectively, showing higher specific capacitance and better rate capability compared to the MnO2 electrode. An excellent cyclability with a capacitance retention as high as 91.5% was also achieved for the composite electrodes after running 1000 cycles. Such excellent electrochemical performances are ascribed to the robust composite structure and synergetic contribution from petal-like MnO2 arrays and conductive graphene sheets.

Co3O4 polyhedra were well encapsulated in reduced graphene oxide (rGO) sheets by in situ growth of Co-based zeolitic imidazolate framework (ZIF-67) polyhedra in the presence of graphene oxide followed by thermal annealing. The resultant rGO/Co3O4 composites consist of a continuously-conductive double-network constructed from graphene sheets and the derived N-doped carbons from ZIF-67, showing a large specific surface area of 523 m2 g−1. The as-fabricated symmetrical supercapacitor based on rGO/Co3O4 exhibits a high specific capacitance of 277.5 F g−1 at 25 A g−1 and an energy density of 24.7 W h kg−1 at a power density of up to 40 kW kg−1. The supercapacitor also retains 87.5% of the initial capacitance over 5000 cycles at 5 A g−1. Such large capacitance, high energy density, and excellent cycling stability for rGO/Co3O4 are attributable to the 3D double conductive network from 2D graphene sheets and porous channels of pseudo-capacitive Co3O4 polyhedra.

The combination of activity-enriched heteroatoms and highly-conductive networks is a powerful strategy to craft carbon-based electrodes for high-efficiency electrochemical energy storage. Herein, N-doped carbon (N-C) coated carbon nanotubes (N-CNTs) were fabricated via a facile in situ synthesis of polyimide in the presence of carbon nanotubes (CNTs), followed by carbonization. The polyimide-divided N-C layers were uniformly covered on the surface of CNTs with a tailored layer thickness. The as-fabricated N-CNTs were further used as electrode active materials for energy storage. When employed as the electrodes for supercapacitors, the N-CNTs exhibited a specific capacitance of 63 F g−1 at 0.1 A g−1 (an energy density of 1.4 W h kg−1 at a power density of 20 W kg−1), which was much higher than that of pure N-C (5 F g−1) and CNTs (13 F g−1). The supercapacitor also retained 66.7% of its initial capacitance (42 F g−1 at 10 A g−1) after a 100-fold increase in the current density and nearly 100% of its initial capacitance after running 10 000 cycles. Furthermore, functioning as an anode material for a Li-ion battery, the N-CNTs also delivered a larger reversible capacity (432 mA h g−1 at 50 mA g−1), higher rate capability, and better cycling stability compared to pure CNTs. The electrochemical performances of the N-CNTs were improved overall due to the synergistic effects of interconnected 3D networks and core–shell structures capable of facilitating electrolyte percolation and charge transportation, enhancing conductivity and surface/interface wettability, and contributing additional pseudocapacitance.

Metal compound/graphene composites have been dominantly fabricated by in-situ intercalation of metal-containing precursors into graphene or graphene oxide (GO) followed by chemical and/or thermal treatment. This process usually leads to the formation of 0D oxide nanoparticles/2D graphene composites with the limited improvements in the supercapacitor performance. Herein a facile two-step method was reported to fabricate 3D porous Ni(OH)2/graphene composite hydrogels (NiGH) by incorporating the pre-synthesized 1D Ni(OH)2 nanobelts into a GO suspension followed by the hydrothermal process. The resulted hydrogels show large specific surface area (370.6 m2/g) and can be directly used as the self-supported electrodes. The NiGH electrode exhibits the specific capacitance up to 1738.3 F/g at 10 mV/s and 1701.5 F/g at 1 A/g, retains 1385.0 F/g at 100 mV/s and 1152.0 F/g at 8 A/g, respectively. The capacitance and rate performance of NiGH are far superior to those of Ni(OH)2 (841.2 F/g at 10 mV/s; 592.5 F/g at 1.0 A/g), graphene hydrogel (207.5 F/g at 10 mV/s), and the control Ni(OH)2 nanoparticle/graphene composite powder (NiGP: 1045.8 F/g at 10 mV/s; 950.8 F/g at 1.0 A/g) prepared by the one-pot hydrothermal processing of Ni salt and GO. Meanwhile, the NiGH electrode also shows lower resistance and higher cycling stability (retaining 100.8% of initial capacitance over 5000 cycles at 5 A/g) as compared to Ni(OH)2, graphene hydrogel, and NiGP due to the efficient combination of pseudo-capacitive 1D Ni(OH)2 nanobelts and conductive 2D graphene sheets to create 3D architectures. Such a facile two-step protocol enables the superiority of ultrathin oxide nanobelts to fabricate 3D graphene-based composite hydrogels for high-performance supercapacitor electrodes.

Graphene/polyaniline composites have attracted considerable attention as high-performance supercapacitor electrode materials; however, there are still numerous challenges for their practical applications, such as the complex preparation process, high cost, and disequilibrium between energy density and power density. Herein, we report an efficient method to produce graphene/polyaniline composites

Advanced phase change materials (PCMs) with three-dimensional (3D) thermal conductive skeletons reveal the promising prospect in the thermal management of lithium battery. However, the high filler-to-filler interfacial thermal resistance (ITR) arising from the weak interfacial contact connection in 3D skeleton is still challenging. Herein, we demonstrate a “carbon welding” strategy for reducing the filler-to-filler ITR in 3D graphene skeleton by achieving the lattice connection between contact graphene. Typically, the ordered 3D graphene skeleton was constructed by unidirectionally ice template assembling graphene nanoplates (GNP) with the assistance of poly (amic acid) (PAA). Imidization and carbonization treatments were employed to weld the adjacent GNP in 3D skeleton. The similar lattice structure of carbonized polyimide (PI) and graphene can result in the significant reduction of phonon scattering and ITR at these contact areas. After impregnation with polyvinyl alcohol (PEG), the high-performance PCMs with high-efficient phonon transmission expressway were obtained. As expected, the prepared composites reveal the high thermal conductivities with a maximum value of 7.032 W m−1 K−1 at ~11.6 vol% GNP, which is more than two-fold than that of the composite with uncarbonized skeleton. Finite element simulation and nonlinear model analyses confirm that the reduced filler-to-filler ITR in skeleton is the main reason for the improving thermal conductivity. In addition, the presence of 3D graphene skeleton can effectively avoid the leakage during solid–liquid phase change, and significantly improve the shape stability of the PCMs. At the same time, the graphene skeleton can endow the PCM with an excellent solar-to-heat conversion performance, which ensure a wide range of application in actual environment.

Flexible and ultrathin electromagnetic interference (EMI) shielding films are urgently required to manage increasingly serious radiation pollution. In this work, the EMI shielding performance and flexibility of conductive polymer films were addressed by assembling magnetic graphene-based hybrid and cellulose nanofiber (CNF). Briefly, magnetic graphene hybrid anchored by Ni nanoparticles (TRGO@Ni) was synthesized by in situ thermal reduction. Then, highly flexible and ultrathin CNF/TRGO@Ni film with “brick-mortar” layered structure was assembled via a facile vacuum filtration method. As expected, CNF/TRGO@Ni film with 50 wt% filler loading exhibits an enhanced electrical conductivity (262.7 S/m) and EMI shielding effectiveness (32.2 dB) comparing to CNF/TRGO film. Moreover, the excellent mechanical flexibility of CNF/TRGO@Ni film results in that the electrical conductivity and EMI SE only declines by 7.5% after bending 1000 cycles. The EMI shielding mechanism is attributed to the combination of enhancing impedance mismatch, multireflection in “brick-mortar” lamellar structure and endowing synergetic loss by graphene and Ni nanoparticles.

Interfacial tailoring is always the key to preparing high-performance polymer-based thermal conductive composites (PTCs). Herein, we reported a multi-functional interface tailoring approach to simultaneously improve the thermal conductivity, flame retardancy, thermal and mechanical properties of PTCs, by forming a core-shell structured graphene oxide coating Al2O3 hybrid (Al2O3@HGO). Simultaneously a flame retardant bridging agent was introduced to improve the coating amount and flame retardant efficiency of the hybrid. The morphology analysis revealed the significant reinforcement of interfacial interaction of Al2O3 in epoxy (EP) by HGO coating. As a result, such the interfacial tailoring induced both the significant decrease in interfacial thermal resistance and the formation of additional thermal conductive paths by the graphene coating layer, resulting in the significant improvement in thermal conductivity of EP/Al2O3@HGO composites. The flame retardant parameters, peak heat release rate, total heat release and total smoke production, showed a 49.3%, 40.9% and 71.2% reduction, respectively, comparing to neat EP, which was ascribed to the strong interface with GO coating layer and the flame retardant bridging agent catalyzed charring to form an intact and compact char protective layer with Al2O3. Moreover, the strong interfacial interaction also restricted the segment movement, increasing the storage modulus and Tg.

Phosphorus and/or nitrogen doping is an effective method of improving the physical and chemical properties of reduced graphene oxide (rGO). In this work, phosphorus and nitrogen co-doped rGO (PN-rGO), synthesized using a scalable hydrothermal and microwave process, was used as an additive to improve the flame retardancy of epoxy resin (EP) for the first time. Chemical structure and morphology characterization confirmed that the nitrogen and phosphorus atoms were doped into the graphite lattice adopting pyrrolic-N, pyridinic-N, quaternary-N and pyrophosphate and metaphosphate forms. Doping increased the oxidization resistance of rGO and the thermal-oxidative stability of its composites’ char, while also improving the catalytic charring ability of polymer. Both effects resulted in the formation of a stable char protective layer during burning and to a significant improvement in flame retardation and smoke suppression in the final composites. The peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) for the EP-based composite (containing 5 wt% PN-rGO) decreased by 30.9%, 29.3% and 51.3%, respectively, compared to neat EP. Our work has produced a promising graphene-based flame retardant additive for the mass production of high-performance composites, also expended the application of heteroatom-doped graphene.

As alternative flame-retardant additive for polymers, reduced graphene oxide (RGO) is often limited by its poor interfacial compatibility with matrix. In this work, a new flame retardant, containing phosphorous, nitrogen and silicon elements was used to functionalize RGO. The wrapped flame retardant chains induced the improvement in the dispersion and compatibility of RGO in epoxy (EP) matrix. As a result, the mechanical, thermal and flame retardant properties of EP-based composites were significantly improved by adding flame retardant-functionalized RGO. The peak heat release rate, total heat release and total smoke production reduced by 34%, 14% and 30%, respectively, compared to neat resin. Based the char analyses, the enhancement in flame retardancy is attributed to the outstanding char layers with high strength and thermal stability resulting from the template effect of graphene, the charring effect of phosphorus and nitrogen elements and the enhancing effect of silicon element in grafted flame retardant chains.

The durability and large-scale production of Ti3C2Tx MXene-based composites are the main obstacles in industrialized application. Herein, a scalable blade coating method is demonstrated for fabricating the flexible and durable polyvinylidene fluoride (PVDF)/Ti3C2Tx MXene layered films with compact hierarchical brick-and-mortar structure. The highly aligned MXene nanosheets make the obtained PVDF/MXene films with high electrical conductivity from 21.1 to 214.6 S cm−1. In combination to the multiple wave reflection in hierarchical layered structure and the interfacial polarization between dielectric matrix and MXene, PVDF/MXene films reveal excellent electromagnetic interference (EMI) performance with an optimal specific EMI shielding effectiveness (SSE/t) of 19504.8 dB cm2 g−1 at only 17 μm thickness. More importantly, the PVDF/MXene film can withstand the damages from mechanical deformation, hot/cold attack and chemical corrosion, meanwhile maintain a stable EMI shielding performance within floating of 5%. Besides, arising from the surface plasmon resonance effect and high electrical conductivity, the PVDF/MXene film reveals photo/electro-thermal heating abilities with rapid response time, high stability and controllability, which ensure their reliable EMI shielding performance under extremely cold conditions.

A bioinspired Co 3 O 4 /graphene composite film was fabricated by an electrostatic self-assembly of poly(diallyldimethylammonium chloride)-stabilized porous Co 3 O 4 flakes and graphene oxide nanosheets under vacuum filtration-induced directional flow in combination with subsequent thermal annealing. The resulting composite film was then empolyed as a self-supported electrode for supercapacitors. The narce-like layered architecture allows for an intimate interface contact and strong interactions between the two. This ensures a large ion-accessible surface and high structural integrality of the electrode during charging-discharging cycles. The high porosity of Co 3 O 4 is capable of affording short diffusion paths of charges and high electrochemical utilization of the electrode. Graphene sheets also construct a highly-conductive platform for fast charge transport and electrochemical reactions. Such unique bioinspired morphology and synergistic effects between porous Co 3 O 4 flakes and graphene sheets promise excellent electrochemical performance. As expected, the free-standing electrode exhibits a specific capacitance of 623.8 F/g at a scan rate of 5 mV/s, and retains 83% of initial capacitance in the current density increasing from 1.0 to 8.0 A/g, suggesting large energy storage and high rate capabilities. The retention of initial capacitance remains 87% after 1000 cycles at 20 mV/s, indicating excellent cycling stability and reversibility.

Fire hazards related to polymer-based thermally conductive composites (PTCs) used in electronic equipment are a significant, but often neglected, risk. Here, we offer a solution by incorporating flame retardant-functionalized graphene (PFR-fRGO) into PTCs using a procedure that improves both their flame resistance and thermal conductivity. Briefly, PFR-fRGO was prepared by covalently grafting a polyphosphoramide oligomer (PDMPD) onto the surface of graphene, which was then introduced in situ into epoxy resin/Al2O3 (EP/Al2O3) composites. As expected, the incorporation of PFR-fRGO not only increased the thermal conduction paths by weakening the settlement of microparticles, but also reduced the interfacial thermal resistance by enhancing interfacial interactions, both of which resulted in an enhancement of the thermal conductivity of the ternary composites. The resultant EP/Al2O3/PFR-fRGO composite exhibited a superior flame retarding ability with dramatic decreases being seen in the high peak heat release rate (PHRR), the total heat release (THR) and the total smoke production (TSP), i.e. 53%, 37% and 57%, respectively, when compared to pure epoxy resin. Additionally, a synergistic flame retarding effect was found in the ternary composite compared to the EP/PFR-fRGO and EP/Al2O3 composites. The remarkable enhancement in flame retardancy was mainly attributed to the catalytic charring effect of PFR-fRGO and the template effect of Al2O3, both of which resulted in the formation of a high strength, thermally stable protective layer in the condensed phase that is able to retard the permeation of heat and volatile degradation products during combustion, slow down the heat release rate and protect the underlying polymer.

Although various types of nanoparticle have been ubiquitously employed as additives to promote the practical performances of composite polymer electrolytes (CPEs) in lithium-ion batteries, the influence of the type of chemical bond between the core and canopy of the modified nanoparticle on the properties of CPEs has rarely been investigated. Herein, two types of nanoparticle additive, namely, ionic bond modified nanoparticles (IBNs) and covalent bond modified nanoparticles (CBNs), were prepared conveniently based on nanosilica with different particle sizes in order to optimize the overall performance of the electrolyte. Furthermore, the CPEs were fabricated by doping IBNs or CBNs as well as lithium salts within a poly(ethylene oxide) matrix and their electrochemical properties were investigated. The dramatic enhancement of the ionic conductivity of the CPEs resulted from the addition of fillers into the system, and the improvement became more significant when the fillers were IBNs that used the smaller silica nanoparticle as the core segment, due to the increased chain mobility, as estimated by the smaller Tg value. Moreover, a broad electrochemical stability window was obtained in the presence of IBNs, and the lithium-ion transference number of the system containing lithium bis(trifluoromethanesulfonimide), which has large anions in the structure, was almost two times higher than the CPEs using lithium perchlorate as the lithium source. Therefore, the synergistic effects of the filler structures and the electrolyte compositions are the key factors to improve the electrochemical performances of CPEs.

A cationic polymerization of 2-thiophenemethanol (ThM) and a sol–gel polycondensation of tetraethylorthosilicate (TEOS) were simultaneously catalyzed by trifluoroacetic acid in a single process step to produce poly(2-thiophenemethanol)/silica (PThM/SiO2) composites. S-Doped mesoporous carbon (S-MC) materials were then achieved by high-temperature carbonization of PThM/SiO2 under an inert atmosphere and subsequent etching off SiO2 in hydrofluoric acid. This in situ crafting process allows us to tailor the porosity of S-MC in the range of 6 to 30 nm. The specific surface area (278–650 m2 g−1) and pore volume (0.15–0.67 cm3 g−1) increase with increasing the feed ratio of TEOS to ThM. Both the specific surface area and pore volume of S-MC are also higher than those of the un-doped mesoporous carbon (MC) materials using furfuryl alcohol as the starting monomer. The S-MC electrodes thus show larger specific capacitance (Cs) values (252 F g−1 at 25 mV s−1 and 125 F g−1 at 0.5 A g−1) compared to the un-doped MC electrode (203 F g−1 at 25 mV s−1 and 110 F g−1 at 0.5 A g−1). The retention of initial Cs for S-MC is 66%, higher than 53% for MC after a 20-fold increase in the scan rate. After 1000 charge/discharge cycles, the Cs retention for S-MC is 97%, also higher than that of MC (93%). As expected, the S-MC electrodes exhibit larger Cs, higher rate performance, and better cycling stability, compared to the MC counterparts and those fabricated in the absence of TEOS by identical experimental processes. Excellent performance can be contributed to the mesoporous morphology in combination with active doping of rich S heteroatoms.

Direct reduction of graphene oxide (GO) to graphene often results in an irreversible agglomeration and hence suppressing its effective surface available for energy storage. In this work, GO was solvothermally reduced in the presence of imidazolium-based poly(ionic liquid) (PIL) of poly(1-butyl-3-vinylimidazolium hexafluorophosphate) to produce a PIL-modified reduced GO (PIL-rGO) composite. The integration of PILs with rGO is capable of preventing the restacking of rGO sheets, and hence, providing a large electrolyte ion-accessible surface and an abundant interior space for charge storage by enlarging the interlayer spacing in PIL-rGO. The PIL-rGO composite was then used as the supercapacitor electrode associated with a compatible IL of 1-butyl-3-methylimidazolium hexafluorophosphate as the electrolyte. The PIL herein improves the interface wettability between the electrode and electrolyte, and the IL electrolyte enables a wide potential window as well. Specific capacitances correspond to 196 F/g at a current density of 1 A/g, 160 F/g at 2 A/g, and 144.8 F/g at a scan rate of 60 mV/s, which are much higher than those (104 F/g at 2 A/g, and 48.1 F/g at 60 mV/s) of pure rGO. The capacitance retention is as high as 80.7% after 1000 charge-discharge cycles at a discharge current density of 2 A/g. The interfacial charge-transfer resistance of the PIL-rGO electrode (4.6 Ω) is also much lower than that of the rGO electrode (18.7 Ω). Such graphene-base electrodes may promise a candidate for high performance supercapacitors.

Silver-doped graphene/MnO2 (SGM) hierarchical composites were readily fabricated by silver-ion-assisted room-temperature catalytic growth of urchin-like MnO2 spheres from the surface of graphene oxide (GO) followed by chemical reduction. This in-situ crafting strategy allows us to control the size of MnO2 spheres by tuning the concentration of silver ions in the reaction mixture. Graphene herein functions as a separator to prevent the agglomeration of MnO2 and a wrapper around MnO2 to avoid the electrochemical dissolution during charging/discharging cycles. MnO2 spheres grown from the surface of GO sheets ensure an intimate interface contact and large interface area between the two, and also prevent the stacking of graphene, thus affording open channels, high accessible surface, short diffusion paths of charges and high electrochemical utilization of the electrode. Furthermore, graphene sheets bridge a robust conductive network which facilitates fast transport of electrolyte ions and electrons throughout the electrode. As expected, an optimized SGM composite electrode delivers a much higher specific capacitance (∼273.1 F g−1 at 5 mV s−1, and ∼260 F g−1 at 0.2 A g−1) compared to the reduced GO (119.4 F g−1) and MnO2 (140.9 F g−1) counterparts. The retention of initial capacitance reaches 77.8% after a 20-fold increase in the scan rate, and remains 83.5% after 1200 cycles, indicating high rate capability and excellent cyclability.

Co3O4 polyhedra were well encapsulated in reduced graphene oxide (rGO) sheets by in situ growth of Co-based zeolitic imidazolate framework (ZIF-67) polyhedra in the presence of graphene oxide followed by thermal annealing. The resultant rGO/Co3O4 composites consist of a continuously-conductive double-network constructed from graphene sheets and the derived N-doped carbons from ZIF-67, showing a large specific surface area of 523 m2 g-1. The as-fabricated symmetrical supercapacitor based on rGO/Co3O4 exhibits a high specific capacitance of 277.5 F g-1 at 25 A g-1 and an energy density of 24.7 W h kg-1 at a power density of up to 40 kW kg-1. The supercapacitor also retains 87.5% of the initial capacitance over 5000 cycles at 5 A g-1. Such large capacitance, high energy density, and excellent cycling stability for rGO/Co3O4 are attributable to the 3D double conductive network from 2D graphene sheets and porous channels of pseudo-capacitive Co3O4 polyhedra.

Developing multifunctional transparent shielding films (TSFs) are highly desirable for the advanced visualization electronic devices. Herein, based on the excellent electrical conductivity of two-dimensional Ti3C2Tx (MXene), flexible hydrophobic MXene-based transparent conducting films are applied in the field of shielding electromagnetic wave and electrical heating. Typically, a spraying coupled with spinning technique is demonstrated to orderly deposit MXene and hydrophobic fumed silica (Hf-SiO2) on transparent polycarbonate (PC) for developing the multifunctional TSFs. The obtained sandwich structural PC/MXene/Hf-SiO2 film exhibits the balanced optical and electrical properties with a low electrical resistance of 35.1 Ω/sq and corresponding transmittance of 33.4%, showing an effective electromagnetic interference shielding effectiveness (EMI SE > 20 dB) combined with a rapid steady joule heating performance at safe voltages (~100 °C at 13 V), simultaneously. Meanwhile, the superhydrophobic Hf-SiO2 coating layer not only endows the film with excellent self-cleaning ability, but also prevents MXene from oxidation. As a result, the hydrophobicity, conductivity and shielding performance of this film can steadily maintain in outdoor conditions for 100 days. Besides, outstanding flexibility gives the film with superior mechanical fatigue resistance (

Inspired by sedimentary rock structure, we demonstrate a flexible heterogeneous multilayered film with high thermal conductivity (TC) and excellent electromagnetic interference (EMI) shielding performance by stacking and concentrating graphene nanosheets (GNS) into alternating conductive layers. Typically, the multilayered film with alternating cellulose nanofiber (CNF) layers and conductive CNF/GNS layers was fabricated by alternating vacuum filtration. Arising from the unique nacre-like oriented structure and highly concentrated conductive filler, high-efficiency phonon and electron transmission paths can be formed in the obtained multilayered CNF@GNS film. As a result, the optimal film with only 25 wt% GNS reveal a high in-plane TC of 33.55 W/(m·K), which increases by 144.6% comparing to the homogeneous CNF/GNS film. Simultaneously, the multilayered films exhibit the effective EMI shielding performance with the highest shielding effectiveness (SE) of 27.4 dB, which is mainly attributed to the enhancing impedance matching and multiple microwave reflections induced by the unique alternating multilayer structure.

Boosting the energy density of supercapacitors without sacrificing power density and lifespan, requires ingenious electrode materials outfitting both sufficient assessable surface area and fast electrochemical reaction kinetics. Herein, hierarchically porous core-sheath nanoarchitecture was elaborately designed, via a robust support-coating strategy using a cellulose-derived porous carbon aerogel as the conductive 3D skeleton to support a uniform coating of conjugated polyimide. The inner carbon aerogel skeleton ensures a fast electron transfer and the outer conjugated polyimide layer affords abundant micropores and sufficient active sites, hence enriching the charge storage in such a porous core-sheath nanoarchitecture. The as-designed electrode was then applied to a redox electrolyte-assisted supercapacitor (RESC) with the KI-doped H2SO4 redox electrolyte. Due to the redox electrolyte further expediting the electrochemical reaction kinetics, the as-fabricated RESC delivers an ultrahigh electrode specific capacitance of 1139 F g−1 at 5 A g−1, high energy density of 94 Wh kg−1 at a well-maintained power density, and long-term capability with 90% capacitance retention after 10,000 cycles at 100 A g−1. The successful construction of high-performance electrode materials and RESC in this work opens a new insight into the development of the state-of-the-art energy storage systems.

Graphene/Co3O4 composites have been considered as promising electrode materials for high-performance supercapacitors; however, their practical applications have been limited by the complex synthesis technologies and narrow potential window of around 0.5 V. Herein we report a facile and economical approach to the massive production of graphene/Co3O4 composites through the one-pot ball-milling of graphite, (NH4)2CO3, and Co(CH3COO)2. During the process, graphite was intercalated by (NH4)2CO3 and synchronously exfoliated into few-layer graphene sheets containing functional groups. Co3O4 nanocrystals were then in-situ grown on the surface of graphene sheets via mechanochemical reactions between (NH4)2CO3 and Co(CH3COO)2. The as-prepared graphene/Co3O4 composites exhibit a high specific capacitance of 570 F g−1 at 1 A g−1, and retain 93% of initial capacitance when the current density is increased by 20 times. The excellent electrochemical performance can be attributed to the synergistic effect between the highly-conductive graphene and nanostructured Co3O4 capable of accelerating the electron conduction and ion transport for increasing the capacitive contribution. Asymmetric supercapacitors were also assembled using graphene and graphene/Co3O4 as negative and positive electrodes, respectively. The asymmetric devices demonstrate a wide operating potential window up to 1.6 V, thus achieving a high specific capacitance of 190 F g−1 at 1 A g−1. Accordingly, the energy density is as high as 67.5 W h kg−1 at the power density of 0.8 kW kg−1. This work provides an affordable and scalable approach to prepare graphene-based composites with metal oxides for high-performance electrode materials for electrochemical energy storage.

Understanding the influence of interface on interfacial thermal resistance (Rb) is important in preparing polymer-based thermal conductive composites. In this work, we demonstrated the competitive relation of the interfacial hydrogen bonding interaction and the thermal insulating effect produced by polydopamine (PDA) modification on Rb in nacre-like cellulose nanofiber/graphene nanosheet (CNF/GNS) film. By increasing PDA grafting amount on GNS, both the interfacial hydrogen bonding interaction, positive role in reducing Rb, and the thermal insulating effect, negative role in reducing Rb, were reinforced simultaneously. For the CNF/GNS film with low filler loading (10 wt%), appropriate PDA grafting amount can maximize its hydrogen bonding effect and simultaneously minimize its thermal insulation effect, thus reducing Rb to 8.61 × 10−9 m2 K/W from 1.11 × 10−8 m2 K/W and improving thermal conductivity to 13.47 W/mK from 10.91 W/mK comparing to unmodified film. However, for the films with high GNS loading (50 wt%), PDA modification failed to improve the thermal conductivity since the dominant face-to-face direct contact between overlapping GNS (contact thermal resistance) was separated by PDA layer. The new understanding on Rb affected by interfacial modification would act as guiding function in preparing high thermal conductive nacre-like layered structural films.

Polyaniline (PANI) has been used as a popular pseudo-capacitive material for supercapacitors due to its higher capacitance compared to carbon-based electric double-layer capacitors. However, PAN I exhibits relatively low conductivity, poor cycle stability, and hence limited usage in high power capability due to its large volumetric change. The integration of PANI with carbonaceous nanomaterials has been highly efficient in improving the above disadvantages. This chapter reports recent developments of carbon-based PANI composites for supercapacitors. Various methods, including chemical oxidative polymerization, electrochemical polymerization, interfacial polymerization, Pickering emulsion polymerization, electrodeposition, electrospinning, solution mixing, self-assembly, and chemical grafting are demonstrated, respectively. The relationship between the device performance and nanostructures of PANI and its composites is then discussed. General guidelines for rational design and optimal fabrication of carbon-based PANI composites for supercapacitors are further provided. Critical challenges and potential perspectives regarding the composites for supercapacitors are finally presented.

Covalently-functionalised graphene (FG) was successfully obtained by grafting m-isopropenyl-α, α′-dimethyl benzyl isocyanate (m-TMI) to graphene oxide (GO) followed by the chemical and solvothermal reduction of GO. The FG sheets were hydrophobic and stable in polar solvents such as N,N-dimethylformamide. The reactive vinyl-benzyl groups of m-TMI attached to FG copolymerised with methyl methacrylate to produce graphene/poly(methyl methacrylate) (PMMA) composites. The FG sheets were well dispersed in PMMA and formed strong interfacial bonds with the matrix, contributing to large increases in elastic modulus (+72.9%) and indentation hardness (+51.2%) at 1% loading by weight. The incorporation of FG into PMMA changed its elastic-plastic behaviour; hence, a decrease in the plasticity index and an increase in recovery resistance were observed for the resulting composites due to the increased portion related to the elastic work. The onset decomposition temperature and glass transition temperature of neat PMMA increased by 100 °C and 12.7 °C, respectively, by the addition of 1 wt% FG. Herein, in situ copolymerisation of monomers and well-suspended FG promotes the exfoliation of graphene associated with strong chemical bonding with the polymer matrix. This report provides a promising and facile method for fabricating high-performance polymeric composites.

Here the oxidative polymerization of 3, 4-ethylenedioxythiophene and hydrothermal reduction of graphene oxide were proceeded simultaneously, which enables the in-situ coating of the bridged poly(3, 4-ethylenedioxythiophene) (PEDOT) nanodendrites onto the highly-conductive graphene skeletons. The as-produced homogeneous graphene/PEDOT composites possess open channels, large accessible surface, fast charge transport, and high electrochemical utilization. The as-fabricated supercapacitor based such nanocomposites therefore exhibits larger specific capacitance (364 F g−1 at 10 mV s−1; 174 F g−1 at 1.0 A g−1), better rate capability (154 F g−1 at 20.0 A g−1), lower interface resistance, and higher cycling stability (retaining 91.4% over 10,000 cycles at 10 A g−1) compared to the PEDOT counterpart (328 F g−1 at 10 mV s−1; 147 F g−1 at 1.0 A g−1; 87% retention after 10,000 cycles). Moreover, its energy density is as high as 24.2 Wh kg−1 at the power density of 1 kW kg−1, and can remain 21.4 Wh kg−1 at the high power density of 20 kW kg−1. The proposed method is facile, novel, and scalable in developing high-performance supercapacitors by combining graphene and pseudocapacitive PEDOT nanodendrites.