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In-plane microsupercapacitors (MSCs) hold great promise for microscale power source, due to the extremely high power density and ultra-long cycling life. However, the scalable fabrication of flexible MSCs with high energy density remains a major challenge. Here, we demonstrate the fabrication of vanadium carbide/reduced graphene oxide (V8C7/rGO) MSCs via laser scribing on ammonium metavanadate/graphene oxide (NH4VO3/GO) films, prepared by efficient continuous centrifugal casting method. More than 20 MSCs can be produced on a flexible substrate in 30 min, showing the potential for scalable fabrication. The laser-induced V8C7/rGO shows highly porous microstructure, where vanadium carbide nanoparticles are in-situ synthesized and uniformly decorated on graphene nanosheets. The well-defined architecture endows V8C7/rGO MSCs with excellent electrochemical performance. The areal capacitance of these devices can be as high as 49.5 mF cm−2, 11 times higher than that of rGO MSCs. The volumetric energy density and power density can be up to 3.4 mWh cm−3 and 401 mW cm−3, respectively, competitive with the commercially available energy storage devices and most reported MSCs. In addition, V8C7/rGO MSCs show excellent flexibility and integrability, as well as long cycling life, promising for practical applications.

Methanol crossover is still a significant barrier to the commercialization of direct methanol fuel cells with wide-used Nafion® membrane. Herein, molecular sieve is introduced into the design of polymer electrolyte membrane to alleviate methanol crossover. The UZM-9 zeolite with an intermediate window size of 0.42 nm can effectively separate hydrated methanol (ca. 1.10 nm) and hydrated proton (ca. 0.23 nm). The methanol diffusion rate through the membrane is effectively suppressed after modified with UZM-9, which is about four times lower than the origin Nafion® membrane. The resulted peak power density reached 80 mW cm−2 with 2 mol L−1 methanol solution feed, which is 2.5-fold higher than that of direct methanol fuel cell with commercial Nafion® membrane. These results open a promising route to alleviate methanol crossover in direct methanol fuel cells.

Extreme fast charging in a thick electrode film is critical for high rate lithium sulfur batteries. However, the high ion-path tortuosity of most carbon/sulfur cathodes dramatically hinder their mass transport, thus leading to poor rate performance. This situation goes worse with increasing the electrode thickness. Here, we report a binder-free vertically-aligned carbon nanotube/sulfur (VACNT/S) cathode with an excellent thickness-independent mass transport and high-rate performance. Compared with a conventional disordered carbon nanotube/sulfur electrode, the highly conductive VACNTs provide directional paths for the ultrafast transfer of both lithium ions and electrons, leading to improved kinetics and a stable redox activity. The VACNT/S electrode shows an extremely high initial specific capacity of 894 mA h g−1 at a 5 C rate, and very stable charge/discharge performance with a capacity of 486.1 mA h g−1 after 400 cycles and a low capacity decay rate of 0.1% per cycle. This work demonstrates an efficient pathway for the design of electrodes for high-rate lithium sulfur batteries.

Fabricating electrochemical power sources with both high specific energy and power is highly desirable but remains challenging. In this work, a kind of self-charging hybrid electric power device (HEPD) is created with an intrinsic combination of polymer electrolyte membrane fuel cells and supercapacitors on the electrode level. Because of the unique processes of electrocatalytic reactions boosted by the fast pseudocapacitive discharge, remarkably high specific energy (1550 Wh kg–1) and power (4080 W kg–1) can be delivered by the hybrid device. The working mechanism of HEPD is proposed and demonstrated by in situ characterization and extensive electrochemical investigations. The self-charging HEPD with its synergistic electrochemical processes will broaden the applications of electrochemical power sources.

Porous graphitic carbons are promising candidates for energy conversion and storage. At present, it is highly desired but remains challenging to construct high-surface-area hierarchical porous graphitic carbons. Herein, graphitic carbon nanosheets with hierarchical pores are easily fabricated from a multifunctional carbonaceous precursor (pentaerythritol melamine phosphate or PMP). The PMP carbonaceous precursor can be readily converted into a 3D macroporous scaffold enclosed by carbon nanosheets via chemical foaming without any sacrificial templates and special drying procedures. Then a subsequent potassium hydroxide chemical activation process dramatically increases the surface area (up to 3853 m2 g−1) and porosity (up to 2.79 cm3 g−1). Simultaneously, graphitization of the carbon nanosheets was promoted with increased aromaticity and size of the polyaromatic units via breaking the phosphate ester bonds with KOH etching at a temperature as low as 800 °C. The resulting porous graphitic carbon nanosheets are constructed with an interconnected continuous three-dimensional network surrounded by predominantly multilayer sp2-bonded carbon with a dense nanometer scale pore structure. Due to such synergistic features, the resulting porous graphitic carbon nanosheets deliver 188 F g−1 specific capacitance and excellent rate performance in nonaqueous electrolytes.

The microstructure of carbon materials in terms of its specific surface area and pore structure by its activation, are the key issues which determine the electrochemical performance of supercapacitors. In this work, we developed a particular chemical activation process assisted by nitrogen/sulfur co-doping for the preparation of hierarchical porous carbon materials with high specific surface area, aiming at improving the energy density of supercapacitors. The as-obtained hierarchical porous carbon materials exhibited both high Brunauer-Emmett-Teller surface area of up to 3652 m2 g−1 for more ions adsorption and high porosity (2.61 cm3 g−1) for rapid ion transport. Attributed to the synergistic effects of these two features, the porous carbon displays high gravimetric specific capacitance (324 F g−1) in KOH aqueous electrolyte with outstanding rate performance (73.3% capacitance retention at 100 A g−1). The symmetrical supercapacitor based on our hierarchical porous carbon displays a maximum specific energy of 9.76 Wh kg−1 and 94.5% retention over 10000 cycles at 15 A g−1. This synthesis strategy is facile, low-cost and industrialized, which provide a promising route to prepare the hierarchical porous carbon materials for energy storage and renewable delivery devices.

Fabrication of novel electrode architectures with tailored electrochemical interfaces (EI) is an effective strategy for enhancing charge and mass transport processes within electrochemical devices. Here, we design and fabricate a well-hybrid electrode based on the coupling of polyaniline (PANI) nanowires and Pt-based electrocatalysts to manufacture a hybrid electric power device (HEPD) combining the advantages of supercapacitors and fuel cells. Because of the boosted charge transfer between PANI nanowires and Pt-based materials via enhanced EIs, the HEPD assembled with hybrid electrodes shows remarkable performance with a peak power density of 222 mW cm-2, a specific power of 3810 W kg-1, and a specific energy of 2100 Wh kg-1, normalized to the mass of membrane electrode assemblies. The in situ Raman spectra and extended electrochemical studies demonstrate the intrinsic mechanism of charge transfer processes within hybrid electrodes, shedding light on the alternative progress of electrochemical energy conversion systems and storage devices.

Rechargeable batteries are considered promising replacements for environmentally hazardous fossil fuel-based energy technologies. High-energy lithium-metal batteries have received tremendous attention for use in portable electronic devices and electric vehicles. However, the low Coulombic efficiency, short life cycle, huge volume expansion, uncontrolled dendrite growth, and endless interfacial reactions of the metallic lithium anode are major obstacles in their commercialization. Extensive research efforts have been devoted to address these issues and significant progress has been made by tuning electrolyte chemistry, designing electrode frameworks, discovering nanotechnology-based solutions, etc. This Review aims to provide a conceptual understanding of the current issues involved in using a lithium metal anode and to unveil its electrochemistry. The most recent advancements in lithium metal battery technology are outlined and suggestions for future research to develop a safe and stable lithium anode are presented.

Sluggish evolution of lithium ions’ solvation sheath induces large charge-transfer barriers and high ion diffusion barriers through the passivation layer, resulting in undesirable lithium dendrite formation and capacity loss of lithium batteries, especially at low temperatures. Here, an ion-dipole strategy by regulating the fluorination degree of solvating agents is proposed to accelerate the evolution of the Li+ solvation sheath. Ethylene carbonate (EC)-based fluorinated derivatives, fluoroethylene carbonate (FEC) and di-fluoro ethylene carbonate (DFEC) are used as the solvating agents for a high dielectric constant. As the increase of the fluorination degree from EC to FEC and DFEC, the Li+-dipole interaction strength gradually decreases from 1.90 to 1.66 and 1.44 eV, respectively. Consequently, the DFEC-based electrolyte displays six times faster ion desolvation rate than that of a non-fluorinated EC-based electrolyte at −20 °C. Furthermore, LiNi0.8Co0.1Mn0.1O2||lithium cells in a DFEC-based electrolyte retain 91% original capacity after 300 cycles at 25 °C, and 51% room-temperature capacity at −30 °C. By bridging the gap between the ion-dipole interactions and the evolution of Li+ solvation sheath, this work provides a new technique toward rational design of electrolyte engineering for low-temperature lithium batteries.

Lithium-sulfur (Li-S) batteries, with high theoretical energy density, promise to be the optimal candidate of next-generation energy-storage. Rapid development in materials has made a major step forward in Li-S batteries. However, a big gap in cycle life and efficiency for practical applications still remains. Reasonable design of materials/electrodes a is significant aspect that must be addressed. The rising metal-organic frameworks (MOFs) are a new class of crystalline porous organic-inorganic hybrid materials. Abundant inorganic nodes and designable organic linkers allow tailored pore chemistry at a molecular-scale, which enables tunable interaction with electroactive components in Li-S batteries. In this review, the interaction between basic component/structure of MOFs and electroactive components in Li-S batteries is clarified to guide precise function-driven design of MOFs. First, the reaction mechanisms and issues in Li-S batteries are briefly summarized. Second, the structural advantages of MOFs in pore chemistry and morphology are highlighted. Based on the above two aspects of understanding, a bridge between issue-structure-function is proposed. The interaction between MOFs with transport and reaction of electroactive components are discussed. Finally, a perspective on the future development of MOFs based materials in Li-S batteries are given. It is believed that the tunable interaction will boost the frontier interdiscipline of MOFs based electrochemical systems.

High electrochemical surface area (ECSA) is the precondition for high performance of flexible supercapacitors, but remains a considerable obstacle. Because of the lower fluidity of hydrogel polymer electrolyte (HPE, generally utilized to fabricate flexible supercapacitors) than aqueous electrolyte (AE, used in traditional supercapacitors), it is difficult to infill a porous electrode with HPE completely, leading to a low ECSA between electrode materials and HPE. In this work, the structures of the polyaniline nanowires are designed to increase the ECSA. In comparison with nanowire network structure, the patulous structure of the polyaniline nanowire arrays is beneficial to increase the ECSA. The polyaniline nanowire arrays show a specific capacitance of 373.6 F g−1 at 0.1 A g−1 with the HPE, which is comparable to that with the AE at 0.1 A g−1 (376.6 F g−1). Flexible supercapacitors based on the polyaniline nanowire arrays exhibit similar performances under flat, folded, and twisted conditions, demonstrating their high potential application in flexible electrochemical energy storage devices.

High platinum requirements hinder the commercialization and wide adoption of polymer electrolyte membrane fuel cells (PEMFCs). Therefore, it is desirable to develop advanced electrode architectures that utilize Pt more effectively than the current designs. Herein, a novel electrode architecture based on Pt/graphene–Nafion® composite macroporous scaffold, prepared via facile freeze-drying approach, demonstrating ultra-high Pt utilization is presented. Within the electrode architecture, pores act as gas/liquid transport channels, whereas Nafion® ionomers act as proton carriers, and graphene sheets allow the conductance of electrons. By leveraging these tailored pathways for both mass and charges, a PEMFC prepared with this electrode architecture demonstrated superior performance, with a peak power density of 0.93 W cm−2 and cathode mass specific power density of 6.2 W mgPt−1. These values are 6-fold greater than those produced using a lamellar structure with the same mass loading of Pt/graphene–Nafion® and also 1.2-fold greater than the commercial Pt/C coated electrodes with the same Pt loading.

Notorious growth of dendritic lithium with low Coulombic efficiency causes safety and stability issues, which hinder practical applications. To control the lithium deposition so that one has a dendrite-free lithium metal anode with high Coulombic efficiency is highly desirable but challenging. Here, this work reports a copper substrate covered by a salt-derived solid electrolyte interphase that produced by electroreduction of a highly concentrated water-in-salt electrolyte to realize stable lithium deposition. Quite distinct from the resistive layer comprised principally of solvent-derived organic species (such as lithium alkyl carbonates) that produced in conventional dilute electrolyte, this salt-derived solid electrolyte interphase is rich in inorganic components (mainly Li2SxOy and LiF), which effectively reduce the overpotential and facilitate fast Li+ transport. In addition, a small number of reduced fluorine organic anions -CFx stabilize the space charge to give a uniform distribution of Li+. Such a solid electrolyte interphase on the copper substrate is able to modulate the lithium plating/stripping to produce uniform spherical lithium deposition with no dendrites, and a high Coulombic efficiency (≈98.2%) is achieved. This work provides a unique strategy to enlarge the functions of the lithium salt decompositions on the protection of lithium metal anodes.