Strategies to Optimize the Capacitive Behavior of Polypyrrole Electrodes

Polypyrrole (PPR) and composite PPR-multi-walled carbon nanotube (MCNT) electrodes for electrochemical supercapacitors were manufactured using new anionic additives for PPR polymerization. The analysis of the microstructure of PPR and PPR-MCNTs and electrochemical testing data provided information on the influence of the dopants on the mechanism of chemical polymerization and properties of nanostructured PPR and PPR-MCNT materials. The increase of the size and charge of the aromatic dopants resulted in decreasing PPR particle size, reducing agglomeration, and promoted the formation of PPR coatings on MCNTs. New additives allowed for the manufacturing of advanced electrodes with high active mass loading, excellent capacitance at high charging–discharging rates, and cyclic stability. A capacitance of 2.67 F cm^?2 at a potential variation rate of 100 mV s^?1 was achieved using composite PPR-MCNT electrodes. The electrodes were applied for the manufacturing of supercapacitor cells, which showed good electrochemical performance.     

3D Printing of Freestanding MXene Architectures for Current‐Collector‐Free Supercapacitors

Additive manufacturing (AM) technologies appear as a paradigm for scalable manufacture of electrochemical energy storage (EES) devices, where complex 3D architectures are typically required but are hard to achieve using conventional techniques. The combination of these technologies and innovative material formulations that maximize surface area accessibility and ion transport within electrodes while minimizing space are of growing interest. Herein, aqueous inks composed of atomically thin (1–3 nm) 2D Ti₃C₂T_x with large lateral size of about 8 µm possessing ideal viscoelastic properties are formulated for extrusion‐based 3D printing of freestanding, high specific surface area architectures to determine the viability of manufacturing energy storage devices. The 3D‐printed device achieves a high areal capacitance of 2.1 F cm^?2 at 1.7 mA cm^?2 and a gravimetric capacitance of 242.5 F g^?1 at 0.2 A g^?1 with a retention of above 90% capacitance for 10 000 cycles. It also exhibits a high energy density of 0.0244 mWh cm^?2 and a power density of 0.64 mW cm^?2 at 4.3 mA cm^?2. It is anticipated that the sustainable printing and design approach developed in this work can be applied to fabricate high‐performance bespoke multiscale and multidimensional architectures of functional and structural materials for integrated devices in various applications.     

A Solid‐State Fibriform Supercapacitor Boosted by Host–Guest Hybridization between the Carbon Nanotube Scaffold and MXene Nanosheets

Fiber‐shaped supercapacitors with improved specific capacitance and high rate capability are a promising candidate as power supply for smart textiles. However, the synergistic interaction between conductive filaments and active nanomaterials remains a crucial challenge, especially when hydrothermal or electrochemical deposition is used to produce a core (fiber)–shell (active materials) fibrous structure. On the other hand, although 2D pseudocapacitive materials, e.g., Ti₃C₂T _x (MXene), have demonstrated high volumetric capacitance, high electrical conductivity, and hydrophilic characteristics, MXene‐based electrodes normally suffer from poor rate capability owing to the sheet restacking especially when the loading level is high and solid‐state gel is used as electrolyte. Herein, by hosting MXene nanosheets (Ti₃C₂T _x ) in the corridor of a scrolled carbon nanotube (CNT) scaffold, a MXene/CNT fiber with helical structure is successfully fabricated. These features offer open spaces for rapid ion diffusion and guarantee fast electron transport. The solid‐state supercapacitor based on such hybrid fibers with gel electrolyte coating exhibits a volumetric capacitance of 22.7 F cm⁻³ at 0.1 A cm⁻³ with capacitance retention of 84% at current density of 1.0 A cm⁻³ (19.1 F cm⁻³), improved volumetric energy density of 2.55 mWh cm⁻³ at the power density of 45.9 mW cm⁻³, and excellent mechanical robustness.     

3D-Printed Structure Boosts the Kinetics and Intrinsic Capacitance of Pseudocapacitive Graphene Aerogels

The performance of pseudocapacitive electrodes at fast charging rates are typically limited by the slow kinetics of Faradaic reactions and sluggish ion diffusion in the bulk structure. This is particularly problematic for thick electrodes and electrodes highly loaded with active materials. Here, a surface-functionalized 3D-printed graphene aerogel (SF-3D GA) is presented that achieves not only a benchmark areal capacitance of 2195 mF cm⁻² at a high current density of 100 mA cm⁻² but also an ultrahigh intrinsic capacitance of 309.1 µF cm⁻² even at a high mass loading of 12.8 mg cm⁻². Importantly, the kinetic analysis reveals that the capacitance of SF-3D GA electrode is primarily (93.3%) contributed from fast kinetic processes. This is because the 3D-printed electrode has an open structure that ensures excellent coverage of functional groups on carbon surface and facilitates the ion accessibility of these surface functional groups even at high current densities and large mass loading/electrode thickness. An asymmetric device assembled with SF-3D GA as anode and 3D-printed GA decorated with MnO₂ as cathode achieves a remarkable energy density of 0.65 mWh cm⁻² at an ultrahigh power density of 164.5 mW cm⁻², outperforming carbon-based supercapacitors operated at the same power density.     

Tungsten Oxide@Polypyrrole Core–Shell Nanowire Arrays as Novel Negative Electrodes for Asymmetric Supercapacitors

Among active pseudocapacitive materials, polypyrrole (PPy) is a promising electrode material in electrochemical capacitors. PPy‐based materials research has thus far focused on its electrochemical performance as a positive electrode rather than as a negative electrode for asymmetric supercapacitors (ASCs). Here high‐performance electrochemical supercapacitors are designed with tungsten oxide@PPy (WO₃@PPy) core–shell nanowire arrays and Co(OH)₂ nanowires grown on carbon fibers. The WO₃@PPy core–shell nanowire electrode exhibits a high capacitance (253 mF/cm²) in negative potentials (–1.0–0.0 V). The ASCs packaged with CF‐Co(OH)₂ as a positive electrode and CF‐WO₃@PPy as a negative electrode display a high volumetric capacitance up to 2.865 F/cm³ based on volume of the device, an energy density of 1.02 mWh/cm³, and very good stability performance. These findings promote the application of PPy‐based nanostructures as advanced negative electrodes for ASCs.     

An Ultrafast Conducting Polymer@MXene Positive Electrode with High Volumetric Capacitance for Advanced Asymmetric Supercapacitors

Pseudocapacitors or redox capacitors that synergize the merits of batteries and double‐layer capacitors are among the most promising candidates for high‐energy and high‐power energy storage applications. 2D transition metal carbides (MXenes), an emerging family of pseudocapacitive materials with ultrahigh rate capability and volumetric capacitance, have attracted much interest in recent years. However, MXenes have only been used as negative electrodes as they are easily oxidized at positive (anodic) potential. To construct a high‐performance MXene‐based asymmetric device, a positive electrode with a compatible performance is highly desired. Herein, an ultrafast polyaniline@MXene cathode prepared by casting a homogenous polyaniline layer onto a 3D porous Ti₃C₂T_x MXene is reported, which enables the stable operation of MXene at positive potentials because of the enlarged work function after compositing with polyaniline, according to the first‐principle calculations. The resulting flexible polyaniline@MXene positive electrode demonstrates a high volumetric capacitance of 1632 F cm^?3 and an ultrahigh rate capability with 827 F cm^?3 at 5000 mV s^?1, surpassing all reported positive electrodes. An asymmetric device is further fabricated with MXene as the anode and polyaniline@MXene as the cathode, which delivers a high energy density of 50.6 Wh L^?1 and an ultrahigh power density of 127 kW L^?1.     

Highly Conductive Ti3C2Tx MXene Hybrid Fibers for Flexible and Elastic Fiber‐Shaped Supercapacitors

Fiber‐shaped supercapacitors (FSCs) are promising energy storage solutions for powering miniaturized or wearable electronics. However, the scalable fabrication of fiber electrodes with high electrical conductivity and excellent energy storage performance for use in FSCs remains a challenge. Here, an easily scalable one‐step wet‐spinning approach is reported to fabricate highly conductive fibers using hybrid formulations of Ti₃C₂T_x MXene nanosheets and poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate. This approach produces fibers with a record conductivity of ≈1489 S cm^?1, which is about five times higher than other reported Ti₃C₂T_x MXene‐based fibers (up to ≈290 S cm^?1). The hybrid fiber at ≈70 wt% MXene shows a high volumetric capacitance (≈614.5 F cm^?3 at 5 mV s^?1) and an excellent rate performance (≈375.2 F cm^?3 at 1000 mV s^?1). When assembled into a free‐standing FSC, the energy and power densities of the device reach ≈7.13 Wh cm^?3 and ≈8249 mW cm^?3, respectively. The excellent strength and flexibility of the hybrid fibers allow them to be wrapped on a silicone elastomer fiber to achieve an elastic FSC with 96% capacitance retention when cyclically stretched to 100% strain. This work demonstrates the potential of MXene‐based fiber electrodes and their scalable production for fiber‐based energy storage applications.     

Achieving High Capacitance of Paper‐Like Graphene Films by Adsorbing Molecules from Hydrolyzed Polyimide

To date, graphene‐based electric double layer supercapacitors have not shown the remarkable specific capacitance as theoretically predicted. An efficient strategy toward boosting the overall capacitance is to endow graphene with pseudocapacitance. Herein, molecules of hydrolyzed polyimide (HPI) are used to functionalize N‐doped graphene (NG) via π–π interaction and the resulting enhanced electrochemical energy storage is reported. These aromatic molecules in monolayer form on graphene contribute strong pseudocapacitance. Paper‐like NG films with different areal mass loadings ranging from 0.5 to 4.8 mg cm^?2 are prepared for supercapacitor electrodes. It is shown that the gravimetric capacitance can be increased by 50–60% after the surface functionalization by HPI molecules. A high specific capacitance of 553 F g^?1 at 5 mV s^?1 is achieved by the HPI‐NG film with a graphene mass loading of 0.5 mg cm^?2 in H₂SO₄ aqueous electrolyte. For the HPI‐NG film with highest mass loading, the gravimetric specific capacitance drops to 340 F g^?1 while the areal specific capacitance reaches a high value of 1.7 F cm^?2. HPI‐NG films are also tested in Li₂SO₄ aqueous electrolyte, over an extended voltage window of 1.6 V. High specific energy densities up to 40 Wh kg^?1 are achieved with the Li₂SO₄ electrolyte.     

Transparent,Flexible, and Conductive 2D Titanium Carbide (MXene) Films with High Volumetric Capacitance

2D transition‐metal carbides and nitrides, known as MXenes, have displayed promising properties in numerous applications, such as energy storage, electromagnetic interference shielding, and catalysis. Titanium carbide MXene (Ti₃C₂T_x ), in particular, has shown significant energy‐storage capability. However, previously, only micrometer‐thick, nontransparent films were studied. Here, highly transparent and conductive Ti₃C₂T_x films and their application as transparent, solid‐state supercapacitors are reported. Transparent films are fabricated via spin‐casting of Ti₃C₂T_x nanosheet colloidal solutions, followed by vacuum annealing at 200 °C. Films with transmittance of 93% (≈4 nm) and 29% (≈88 nm) demonstrate DC conductivity of ≈5736 and ≈9880 S cm^?1, respectively. Such highly transparent, conductive Ti₃C₂T_x films display impressive volumetric capacitance (676 F cm^?3) combined with fast response. Transparent solid‐state, asymmetric supercapacitors (72% transmittance) based on Ti₃C₂T_x and single‐walled carbon nanotube (SWCNT) films are also fabricated. These electrodes exhibit high capacitance (1.6 mF cm^?2) and energy density (0.05 µW h cm^?2), and long lifetime (no capacitance decay over 20 000 cycles), exceeding that of graphene or SWCNT‐based transparent supercapacitor devices. Collectively, the Ti₃C₂T_x films are among the state‐of‐the‐art for future transparent, conductive, capacitive electrodes, and translate into technologically viable devices for next‐generation wearable, portable electronics.     

Bath Electrospinning of Continuous and Scalable Multifunctional MXene‐Infiltrated Nanoyarns

Electroactive yarns that are stretchable are desired for many electronic textile applications, including energy storage, soft robotics, and sensing. However, using current methods to produce these yarns, achieving high loadings of electroactive materials and simultaneously demonstrating stretchability is a critical challenge. Here, a one‐step bath electrospinning technique is developed to effectively capture Ti₃C₂T_x MXene flakes throughout continuous nylon and polyurethane (PU) nanofiber yarns (nanoyarns). With up to ≈90 wt% MXene loading, the resulting MXene/nylon nanoyarns demonstrate high electrical conductivity (up to 1195 S cm^?1). By varying the flake size and MXene concentration, nanoyarns achieve stretchability of up to 43% (MXene/nylon) and 263% (MXene/PU). MXene/nylon nanoyarn electrodes offer high specific capacitance in saturated LiClO₄ electrolyte (440 F cm^?3 at 5 mV s^?1), with a wide voltage window of 1.25 V and high rate capability (72% between 5 and 500 mV s^?1). As strain sensors, MXene/PU yarns demonstrate a wide sensing range (60% under cyclic stretching), high sensitivity (gauge factor of ≈17 in the range of 20–50% strain), and low drift. Utilizing the stretchability of polymer nanofibers and the electrical and electrochemical properties of MXene, MXene‐based nanoyarns demonstrate potential in a wide range of applications, including stretchable electronics and body movement monitoring.     

High Volumetric Energy Density Asymmetric Supercapacitors Based on Well‐Balanced Graphene and Graphene‐MnO2 Electrodes with Densely Stacked Architectures

The well‐matched electrochemical parameters of positive and negative electrodes, such as specific capacitance, rate performance, and cycling stability, are important for obtaining high‐performance asymmetric supercapacitors. Herein, a facile and cost‐effective strategy is demonstrated for the fabrication of 3D densely stacked graphene (DSG) and graphene‐MnO₂ (G‐MnO₂) architectures as the electrode materials for asymmetric supercapacitors (ASCs) by using MnO₂‐intercalated graphite oxide (GO‐MnO₂) as the precursor. DSG has a stacked graphene structure with continuous ion transport network in‐between the sheets, resulting in a high volumetric capacitance of 366 F cm^–3, almost 2.5 times than that of reduced graphene oxide, as well as long cycle life (93% capacitance retention after 10 000 cycles). More importantly, almost similar electrochemical properties, such as specific capacitance, rate performance, and cycling stability, are obtained for DSG as the negative electrode and G‐MnO₂ as the positive electrode. As a result, the assembled ASC delivers both ultrahigh gravimetric and volumetric energy densities of 62.4 Wh kg^–1 and 54.4 Wh L^–1 (based on total volume of two electrodes) in 1 m Na₂SO₄ aqueous electrolyte, respectively, much higher than most of previously reported ASCs in aqueous electrolytes.     

Design of Novel Wearable,Stretchable, and Waterproof Cable‐Type Supercapacitors Based on High‐Performance Nickel Cobalt Sulfide‐Coated Etching‐Annealed Yarn Electrodes

Rapid advances in functional electronics bring tremendous demands on innovation toward effective designs of device structures. Yarn supercapacitors (SCs) show advantages of flexibility, knittability, and small size, and can be integrated into various electronic devices with low cost and high efficiency for energy storage. In this work, functionalized stainless steel yarns are developed to support active materials of positive and negative electrodes, which not only enhance capacitance of both electrodes but can also be designed into stretchable configurations. The as‐made asymmetric yarn SCs show a high energy density of 0.0487 mWh cm^?2 (10.19 mWh cm^?3) at a power density of 0.553 mW cm^?2 (129.1 mW cm^?3) and a specific capacitance of 127.2 mF cm^?2 under an operating voltage window of 1.7 V. The fabricated SC is then made into a stretchable configuration by a prestraining‐then‐releasing approach using polydimethylsiloxane (PDMS) tube, and its electrochemical performance can be well maintained when stretching up to a high strain of 100%. Moreover, the stretchable cable‐type SCs are stably workable under water‐immersed condition. The method opens up new ways for fabricating flexible, stretchable, and waterproof devices.     

A High‐Energy‐Density Hybrid Supercapacitor with P‐Ni(OH)2@Co(OH)2 Core–Shell Heterostructure and Fe2O3 Nanoneedle Arrays as Advanced Integrated Electrodes

Transition metal hydro/oxides (TMH/Os) are treated as the most promising alternative supercapacitor electrodes thanks to their high theoretical capacitance due to the various oxidation states and abundant cheap resources of TMH/Os. However, the poor conductivity and logy reaction kinetics of TMH/Os severely restrict their practical application. Herein, hierarchical core–shell P‐Ni(OH)₂@Co(OH)₂ micro/nanostructures are in situ grown on conductive Ni foam (P‐Ni(OH)₂@Co(OH)₂/NF) through a facile stepwise hydrothermal process. The unique heterostructure composed of P‐Ni(OH)₂ rods and Co(OH)₂ nanoflakes boost the charge transportation and provide abundant active sites when used as the intergrated cathode for supercapacitors. It delivers an ultrahigh areal specific capacitance of 4.4 C cm^?2 at 1 mA cm^?2 and the capacitance can maintain 91% after 10 000 cycles, showing an ultralong cycle life. Additionally, a hybrid supercapacitor composed with P‐Ni(OH)₂@Co(OH)₂/NF cathode and Fe₂O₃/CC anode shows a wider voltage window of 1.6 V, a remarkable energy density of 0.21 mWh cm^?2 at the power density of 0.8 mW cm^?2, and outstanding cycling stability with about 81% capacitance retention after 5000 cycles. This innovative study not only supplies a newfashioned electronic apparatus with high‐energy density and cycling stability but offers a fresh reference and enlightenment for synthesizing advanced integrated electrodes for high‐performance hybrid supercapacitors.     

Influence of Additives on Performance of Polypyrrole–Carbon Nanotube Supercapacitors

Polypyrrole (PP) and composite PP–multiwalled carbon nanotube (MWNT) materials were prepared for supercapacitors (SC) using new dopants for PP. The MWNT dispersion was achieved using advanced dispersants. The 36 mg cm^?2 PP electrochemical electrodes showed a capacitance of 6.3 F cm^?2 at 2 mV s^?1 scan rate. PP–MWNT composites showed enhanced capacitance for high charge–discharge rates and large electrode mass with enhanced cyclic stability. The mechanisms of MWNT dispersion and composite microstructure formation were discussed. Capacitance measurements provided new insight into the effect of additives on the characteristics of electrodes and cells. The SC cells have been manufactured, which showed promising performance for application in energy storage systems.     

Facile synthesis of graphene@NiMoO<Subscript>4</Subscript> nanosheet arrays on Ni foam for a high-performance asymmetric supercapacitor

Honeycomb-like NiMoO₄ with nanosheet arrays is grown on reduced graphene oxide, which is supported on Ni foam having successfully fabricated by a simple hydrothermal treatment followed by a calcined process. In the as-synthesized Ni foam@reduced graphene oxide@NiMoO₄, Ni foam served as “skeleton” to support reduced graphene oxide and reduced graphene oxide directly grown on Ni foam served as the “skin” to provide high passway of electrons and ions, which simultaneously accommodated the volume change during the process of charge–discharge and NiMoO₄ acted as active substance to provide high areal capacitance. It shows a high areal capacitance of 2165.9 mF cm^?2 at a current density of 1 mA cm^?2 and long cycle stability with 93.8% capacitance retained over 1000 charge–discharge cycles. Moreover, an asymmetric supercapacitor has been constructed by using Ni foam@reduced graphene oxide and Ni foam@reduced graphene oxide@NiMoO₄ as negative and positive electrodes. The energy density of this asymmetric supercapacitor is 0.579 mWh cm^?2, and it retains 93.1% capacitance over charge–discharge 5000 cycles. Therefore, it reveals great promise for practical applications in energy storage devices.     

Direct Laser‐Patterned Micro‐Supercapacitors from Paintable MoS2 Films

Micrometer‐sized electrochemical capacitors have recently attracted attention due to their possible applications in micro‐electronic devices. Here, a new approach to large‐scale fabrication of high‐capacitance, two‐dimensional MoS₂ film‐based micro‐supercapacitors is demonstrated via simple and low‐cost spray painting of MoS₂ nanosheets on Si/SiO₂ chip and subsequent laser patterning. The obtained micro‐supercapacitors are well defined by ten interdigitated electrodes (five electrodes per polarity) with 4.5 mm length, 820 μm wide for each electrode, 200 μm spacing between two electrodes and the thickness of electrode is ～0.45 μm. The optimum MoS₂‐based micro‐supercapacitor exhibits excellent electrochemical performance for energy storage with aqueous electrolytes, with a high area capacitance of 8 mF cm^?2 (volumetric capacitance of 178 F cm^?3) and excellent cyclic performance, superior to reported graphene‐based micro‐supercapacitors. This strategy could provide a good opportunity to develop various micro‐/nanosized energy storage devices to satisfy the requirements of portable, flexible, and transparent micro‐electronic devices.     

PWB compatible high value integral capacitors by MOCVD

The 1998 National Electronics Manufacturing Technology Roadmap indicates that a capacitance density of 50 nF cm^–2 will be required in 2001 for successful implementation of integral passive technology in the microelectronics packaging industries. Higher permittivity polymer/ceramic nanocomposites have been proven to be a viable option for integral capacitors on printed wiring boards (PWB). Although the nanocomposite materials are in their developmental stage, it is unlikely that this materials system could meet such high capacitance needs and still utilize a large area manufacturable process. In this study, an alternative metal organic chemical vapor deposition (MOCVD) technique has been implemented to deposit TiO₂ thin film dielectrics at temperatures below 180 °C with higher capacitance densities. Two different metal-dielectric-metal type parallel plate capacitor structures have been fabricated on silicon and PWB substrates for relatively high frequency (45 MHz–1 GHz) and low frequency (100 Hz–1 MHz) characterization. Copper was used as the ground and upper electrodes with a 10 nm Cr adhesion layer between the dielectric and the electrodes. Capacitance was measured using a Keithley LCZ meter and a HP4194 impedance gain-phase analzer at the lower frequency range. Specific capacitance as high as 200 nF cm^–2 was achieved at 1 MHz from devices built on silicon substrates and at 100 kHz from devices on PWB substrates. For the first time, thin film TiO₂ on PWB substrates is reported at temperatures below 180 °C using MOCVD.     

Sulfur‐Deficient Bismuth Sulfide/Nitrogen‐Doped Carbon Nanofibers as Advanced Free‐Standing Electrode for Asymmetric Supercapacitors

The use of free‐standing carbon‐based hybrids plays a crucial role to help fulfil ever‐increasing energy storage demands, but is greatly hindered by the limited number of active sites for fast charge adsorption/desorption processes. Herein, an efficient strategy is demonstrated for making defect‐rich bismuth sulfides in combination with surface nitrogen‐doped carbon nanofibers (dr‐Bi₂S₃/S‐NCNF) as flexible free‐standing electrodes for asymmetric supercapacitors. The dr‐Bi₂S₃/S‐NCNF composite exhibits superior electrochemical performances with an enhanced specific capacitance of 466 F g^?1 at a discharge current density of 1 A g^?1. The high performance of dr‐Bi₂S₃/S‐NCNF electrodes originates from its hierarchical structure of nitrogen‐doped carbon nanofibers with well‐anchored defect‐rich bismuth sulfides nanostructures. As modeled by density functional theory calculation, the dr‐Bi₂S₃/S‐NCNF electrodes exhibit a reduced OH^? adsorption energy of ‐3.15 eV, compared with that (–3.06 eV) of defect‐free bismuth sulfides/surface nitrogen‐doped carbon nanofiber (df‐Bi₂S₃/S‐NCNF). An asymmetric supercapacitor is further fabricated by utilizing dr‐Bi₂S₃/S‐NCNF hybrid as the negative electrode and S‐NCNF as the positive electrode. This composite exhibits a high energy density of 22.2 Wh kg^?1 at a power density of 677.3 W kg^?1. This work demonstrates a feasible strategy to construct advanced metal sulfide‐based free‐standing electrodes by incorporating defect‐rich structures using surface engineering principles.     

Vertically Aligned Niobium Nanowire Arrays for Fast‐Charging Micro‐Supercapacitors

Planar micro‐supercapacitors are attractive for system on chip technologies and surface mount devices due to their large areal capacitance and energy/power density compared to the traditional oxide‐based capacitors. In the present work, a novel material, niobium nanowires, in form of vertically aligned electrodes for application in high performance planar micro‐supercapacitors is introduced. Specific capacitance of up to 1 kF m^?2 (100 mF cm^?2) with peak energy and power density of 2 kJ m^?2 (6.2 MJ m^?3 or 1.7 mWh cm^?3) and 150 kW m^?2 (480 MW m^?3 or 480 W cm^?3), respectively, is achieved. This remarkable power density, originating from the extremely low equivalent series resistance value of 0.27 Ω (2.49 µΩ m² or 24.9 mΩ cm²) and large specific capacitance, is among the highest for planar micro‐supercapacitors electrodes made of nanomaterials.     

Conductive FeOOH as Multifunctional Interlayer for Superior Lithium–Sulfur Batteries

The commercial course of Li–S batteries (LSBs) is impeded by several severe problems, such as low electrical conductivity of S, Li₂S₂, and Li₂S, considerable volume variation up to 80% during multiphase transformation and severe intermediation lithium polysulfides (LiPSs) shuttle effect. To solve above problems, conductive FeOOH interlayer is designed as an effective trapper and catalyst to accelerate the conversion of LiPSs in LSBs. FeOOH nanorod is effectively affinitive to S that Fe atoms act as Lewis acid sites to capture LiPSs via strong chemical anchoring capability and dispersion interaction. The excellent electrocatalytic effect enables that reduced charging potential barrier and enhanced electron/ion transport is realized on the FeOOH interlayer to promote LiPSs conversion. Significantly, Li₂S oxidation process is improved on the FeOOH interlayer determined as a combination of reduced Li₂S decomposition energy barrier and enhanced Li‐ion transport. Therefore, the multifunctional FeOOH interlayer with conductive and catalytic features show strong chemisorption with LiPSs and accelerated LiPSs redox kinetics. As a result, LSBs with FeOOH interlayer displays high discharge capacity of 1449 mAh g^?1 at 0.05 C and low capacity decay of 0.05% per cycle at 1 C, as well as excellent rate capability (449 mAh g^?1 at 2 C).