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Sodium super‐ionic conductor (NASICON)‐structured phosphates are emerging as rising stars as cathodes for sodium‐ion batteries. However, they usually suffer from a relatively low capacity due to the limited activated redox couples and low intrinsic electronic conductivity. Herein, a reduced graphene oxide supported NASICON Na3Cr0.5V1.5(PO4)3 cathode (VC/C‐G) is designed, which displays ultrafast (up to 50 C) and ultrastable (1 000 cycles at 20 C) Na+ storage properties. The VC/C‐G can reach a high energy density of ≈470 W h kg−1 at 0.2 C with a specific capacity of 176 mAh g−1 (equivalent to the theoretical value); this corresponds to a three‐electron transfer reaction based on fully activated V5+/V4+, V4+/V3+, V3+/V2+ couples. In situ X‐ray diffraction (XRD) results disclose a combination of solid‐solution reaction and biphasic reaction mechanisms upon cycling. Density functional theory calculations reveal a narrow forbidden‐band gap of 1.41 eV and a low Na+ diffusion energy barrier of 0.194 eV. Furthermore, VC/C‐G shows excellent fast‐charging performance by only taking ≈11 min to reach 80% state of charge. The work provides a widely applicable strategy for realizing multi‐electron cathode design for high‐performance SIBs. [ABSTRACT FROM AUTHOR]

Supercapacitors are increasingly used in short‐distance electric transportation due to their long lifetime (≈15 years) and fast charging capability (>10 A g−1). To improve their market penetration, while minimizing onboard weight and maximizing space‐efficiency, materials costs must be reduced (<10 $ kg−1) and the volumetric energy‐density increased (>8 Wh L−1). Carbon nanofibers display good gravimetric capacitance, yet their marketability is hindered by their low density (0.05–0.1 g cm−3). Here, the authors increase the packing density of low‐cost, free‐standing carbon nanofiber mats (from 0.1 to 0.6 g cm−3) through uniaxial compression. X‐ray computed tomography reveals that densification occurs by reducing the inter‐fiber pore size (from 1–5 µm to 0.2–0.5 µm), which are not involved in double‐layer capacitance. The improved packing density is directly proportional to the volumetric performances of the device, which reaches a volumetric capacitance of 130 F cm−3 and energy density of 6 Wh L−1 at 0.1 A g−1 using a loading of 3 mg cm−2. The results outperform most commercial and lab‐scale porous carbons synthesized from bioresources (50–100 F cm−3, 1–3 Wh L−1 using 10 mg cm−2) and contribute to the scalable design of sustainable electrodes with minimal 'dead volume' for efficient supercapacitors. [ABSTRACT FROM AUTHOR]

Polypyrrole (PPy) has high electrochemical activity and low cost, so it has great application prospects in wearable supercapacitors. Herein, we have successfully prepared polypyrrole/reduced graphene oxide (PPy/rGO) nanocomposite cotton fabric (NCF) by chemical polymerization, which exhibits splendid electrochemical performance compared with the individual. The addition of rGO can block the deformation of PPy caused by the expansion and contraction. The as-prepared PPy-0.5/rGO NCF electrode exhibits the brilliant specific capacitance (9300 mF cm−2 at 1 mA cm−2) and the capacitance retention with 94.47% after 10 000 cycles. At the same time, the superior capacitance stability under different bending conditions and reuse capability have been achieved. All-solid-state supercapacitor has high energy density of 167 μWh cm−2 with a power density of 1.20 mW cm−2. Therefore, the PPy-0.5/rGO NCF electrode has a broad application prospect in high-performance flexible supercapacitor fabric electrode. [ABSTRACT FROM AUTHOR]

Heteroatom-doped carbon materials with a high specific area, a well-defined porous structure is important to high-performance supercapacitors (SCs). Here, S and N co-doped three-dimensional porous graphene aerogel (NS-3DPGHs) have been synthesized in a facile and efficient self-assembly process with thiourea acting as the reducing and doping agent solution. Operating as a SC electrode, fabricated co-doping graphene, i.e. the sample of NS-3DPGH-150 exhibits the highest specific capacitance of 412.9 F g−1 under 0.5 A g−1 and prominent cycle stabilization with 96.4% capacitance retention in the back of 10 000 cycles. Furthermore, based on NS-3DPGH-150, the symmetrical supercapacitor as-prepared in 6 M KOH displays a superior energy density of 12.9 Wh kg−1 under the power density of 249 W kg−1. Hence, NS-3DPGHs could be considered as an excellent candidate for SCs. [ABSTRACT FROM AUTHOR]

Nanoporous carbons (NPCs) with engineered specific pore sizes and sufficiently high porosities (both specific surface area and pore volume) are necessary for storing energy in the form of electric charges and molecules. Herein, NPCs, derived from biomass pine‐cones, coffee‐grounds, graphene‐oxide and metal‐organic frameworks, with systematically increased pore width (<1.0 nm to a few nm), micropore volume (0.2–0.9 cm3 g−1) and specific surface area (800–2800 m2 g−1) are presented. Superior CO2, H2, and H2O uptakes of 35.0 wt% (≈7.9 mmol g−1 at 273 K), 3.0 wt% (at 77 K) and 85.0 wt% (at 298 K), respectively at 1 bar, are achieved. At controlled microporosity, supercapacitors deliver impressive performance with a capacity of 320 and 230 F g−1 at 500 mA g−1, in aqueous and organic electrolytes, respectively. Excellent areal capacitance and energy density (>50 Wh kg−1 at high power density, 1000 W kg−1) are achieved to form the highest reported values among the range of carbons in the literature. The noteworthy energy storage performance of the NPCs for all five cases (CO2, H2, H2O, and capacitance in aqueous and organic electrolytes) is highlighted by direct comparison to numerous existing porous solids. A further analysis on the specific pore type governed physisorption capacities is presented. [ABSTRACT FROM AUTHOR]

Hierarchical porous channels and a well-modulated interface are two main parameters for electrode materials that can promote their energy storage performance by accelerating the electrolyte diffusion and realizing their strong coupling with electrolyte ions. Inspired by the COMSOL Multiphysics simulations and density functional theory calculations, we design B, N dual-doped, hierarchical porous carbon (BN-HPC) by pyrolyzing hierarchical porous zeolitic imidazolate framework-8 with boric acid. The resulted BN-HPC electrode achieves a high specific capacitance of 236.9 F g−1 at a current density of 1 A g−1 in 1 M H 2 SO 4 electrolyte, which is further assembled into the BN-HPC//BN-HPC symmetric supercapacitor with a high energy density of 33.3 Wh kg−1 at a power density of 212.5 W kg−1. The excellent energy storage performance of the BN-HPC electrode is attributed to its hierarchical porous structure and bi-heteroatom (N and B) doped carbon surface with a low binding energy value of −2.77 eV. This work provides a general and fresh insight into the design of dodecahedral carbon by combining hierarchical porous structure and bi-heteroatom doping strategy that can be used for not only aqueous supercapacitors but also other energy storage devices. [Display omitted] • B, N co-doped, hierarchical porous carbon is obtained by pyrolyzing ZIF-8 with H 3 BO 3. • COMSOL Multiphysics and DFT jointly illustrate the improved storage performance. • B, N co-doped strategy shows a synergistic effect on improving the adsorption of H+. • A hierarchical porous structure facilitates the penetration of electrolytes. [ABSTRACT FROM AUTHOR]

Abstract: Thermal runaway is a major cause of failure in Li-ion batteries (LIBs), and of particular concern for high energy density transport applications, where safety concerns have hampered commercialisation. A clear understanding of electro-thermal properties and how these relate to structure and operation is vital to improving thermal management of LIBs. Here a combined thermal imaging, X-ray tomography and electrochemical impedance spectroscopy (EIS) approach was applied to commercially available 18650 cells to study their thermal characteristics. Thermal imaging was used to characterise heterogeneous temperature distributions during discharge above 0.75C; the complementary information provided by 3D X-ray tomography was utilised to evaluate the internal structure of the battery and identify the regions causing heating, specifically the components of the battery cap. [Copyright &y& Elsevier]

All-solid-state and flexible supercapacitors have attracted tremendous attention due to the rapid development of modern smart and wearable electronics. In this study, copper and nickel co-coated cotton textile was developed as the substrate, on which tremella-like Ni–Co–S nanoflakes were electrochemically deposited. The obtained electrode exhibits high specific capacity with good rate capability, flexibility and bendability. An asymmetric supercapacitor cell containing Ni–Co–S as cathode, active carbon as anode and PVA/KOH as the solid-state electrolyte, demonstrate superior electrochemical properties for wearable energy storage applications. The obtained supercapacitor cell delivers a high energy density of 48.9 Wh kg−1 at 390 W kg−1. When four cells were connected in series, the connected cells can be safely operated at a wide voltage window of 0.0–6.4 V due to the good electrochemical stability and consistency of the assembled cells. These results demonstrated the flexible textile electrode developed by this work hold great potential for practical application in wearable energy storage devices. Image 1 • Cu-sputtered textile with electroplated Ni layer was firstly used as collector fluid. • A flexible electrode was fabricated by electroplating Ni–Co–S onto conductive textile. • Obtained wearable supercapacitor delivers an energy density of 48.9 Wh kg−1 at 390 W kg−1. • A high voltage window of 0.0–6.4 V is safely achieved by connecting four cells in series. [ABSTRACT FROM AUTHOR]

A flexible cathode with highly electrochemical performance for bendable supercapacitors have been achieved by electrochemical depositing hierarchical nanostructured Ni 3 S 2 /Ni(OH) 2 compounds on the surface of commercial conductive textile. The morphology and physical properties of as-prepared electrode are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS). Based on its unique nanostructure, the obtained flexible Ni 3 S 2 /Ni(OH) 2 electrode exhibits a highly electrochemical capacitance of 1800 F g−1 at 3 mA cm−2 with good rate capability, excellent stability and bendability. Ni 3 S 2 /Ni(OH) 2 electrode as cathode is assembled with active carbon as anode and PVA/KOH as electrolyte into an asymmetric capacitor to evaluate its performance in a real supercapacitor. The obtained supercapacitor cell delivers a high energy density of 0.49 mWh cm−2 at 3.54 mW cm−2 and maintains the energy density at 0.38 Wh cm−2 when power density increases to 21.53 mW cm−2. When the assembled cells are connected in series, these connected cells can work safely and properly at a much higher voltage window due to their good stability and consistency. Considering its low-cost, facile fabrication and highly electrochemical performance, the obtained Ni 3 S 2 /Ni(OH) 2 electrode is a promising flexible material. Image 1 • Asymmetric flexible supercapacitor based on Ni 3 S 2 /Ni(OH) 2 can deliver high power density. • Ni 3 S 2 /Ni(OH) 2 directly grown on Ni foam is synthesized via a facile process. • Raw materials and experimental conditions enable large-scale production. [ABSTRACT FROM AUTHOR]