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High iodine loading and high‐temperature adaptability of the iodine cathode are prerequisites to achieving high energy density at full battery level and promoting the practical application for the zinc‐iodine (Zn‐I2) battery. However, it would aggravate the polyiodide shuttle effect when employing high iodine loading and working temperature. Here, a sustainable cationic cellulose nanofiber (cCNF) was employed to confine the active iodine species through strong physiochemical adsorption to enlarge the iodine loading and stabilize it even at high temperatures. The cCNF could accommodate dual‐functionality by enlarging the iodine loading and suppressing the polyiodide shuttle effect, owing to the unique framework structure with abundant surface positive charges. As a result, the iodine cathode based on the cCNF could deliver high iodine mass loading of 14.1 mg cm−2 with a specific capacity of 182.7 mAh g−1, high areal capacity of 2.6 mAh cm−2, and stable cycling over 3000 cycles at 2 A g−1, thus enabling a high energy density of 34.8 Wh kg−1 and the maximum power density of 521.2 W kg−1 at a full Zn‐I2 battery level. In addition, even at a high temperature of 60 °C, the Zn‐I2 battery could still deliver a stable cycling. [ABSTRACT FROM AUTHOR]

Herein, non‐carbonized wood‐based electrodes and separators with well‐aligned channels and excellent mechanical properties are developed for supercapacitors. To enhance the conductivity and boost the capacitance, Ti3C2 (MXene) nanosheets with high electrical conductivity and excellent electrochemical activity are loaded into the wood cells via self‐assembly triggered by fast evaporating water in Ti3C2 suspension. By the assistance of positive charged polydopamine microspheres with large surface area, the self‐restacking of Ti3C2 nanosheets can be avoided and the high mass loading (50 wt%) can be achieved due to the extra driving force for Ti3C2 absorption. Benefiting from the conductive Ti3C2 nanosheets with massive active sites and the multiple well‐aligned channels in wood with efficient transportation pathways for charge carriers, the as‐designed free‐standing electrode shows a large areal capacitance of 1060 mF cm−2 at 0.5 mA cm−2 and high capacitance retention of 67% at 10 mA cm−2. Also, this electrode is highly size‐customizable, showing a good ability to be industrially processed into various shapes and dimensions. Furthermore, an all‐wood based supercapacitor with Ti3C2/wood composites as two layers of electrodes and a wood slice as the separator is fabricated, presenting a high energy density of 10.5 μW h cm−2 at 389.9 μW cm−2. [ABSTRACT FROM AUTHOR]

The search for wearable electronics has been attracted great efforts, and there is an ever-growing demand for all-solid-state flexible energy storage devices. However, it is a challenge to obtain both positive and negative electrodes with excellent mechanical strength and match positive and negative charges to achieve high energy densities and operate voltages to satisfy practical application requirements. Here, flexible MXene (Ti3C2Tx)/cellulose nanofiber (CNF) composite film negative electrodes (MCNF) were fabricated with a vacuum filtration method, as well as positive electrodes (CP) by combining polyaniline (PANI) with carbon cloth (CC) using an in-situ polymerization method. Both positive and negative free-standing electrodes exhibited excellent electrochemical behavior and bendable/foldable flexibility. As a result, the all-pseudocapacitance asymmetric device of MCNF//CP assembled with charge-matched between anode and cathode achieves an extended voltage window of 1.5 V, high energy density of 30.6 Wh·kg−1 (1211 W·kg−1), and 86% capacitance retention after 5000 cycles, and the device maintains excellent bendability, simultaneously. This work will pave the way for the development of all-pseudocapacitive asymmetric supercapacitors (ASC) with simultaneously preeminent mechanical properties, high energy density, and wide operating voltage window. [ABSTRACT FROM AUTHOR]

Direct ink writing technology is capable of using 2D MXene to construct 3D architectures for electrochemical energy storage (EES) devices that are normally difficult to achieve using conventional techniques. However, to meet specific rheological requirements for 3D printing, a large amount of MXene is needed in the ink, resulting in a severe self‐restacking structure after drying. Herein, a series of cellulose nanofibers (CNFs) with different morphologies and surface chemistries are applied to enhance the rheology of the MXene‐based inks with exceptional 3D printability. Various 3D architectures with superior shape fidelity and geometric accuracy are successfully printed using the optimized hybrid ink at a low solid content, generating self‐standing, hierarchically porous structures after being freeze‐dried, which improves surface area accessibility, ion transport efficiency, and ultimately, capacitive performance. A solid‐state interdigitated symmetrical supercapacitor is further 3D printed, which delivers an areal capacitance of 2.02 F cm−2 and an energy density of 101 μWh cm−2 at a power density of 0.299 mW cm−2, and maintains a capacitance retention rate of 85% after 5000 cycles. This work demonstrates the integration of 1D CNFs and 2D MXene in 3D printing technology to prepare customized, multiscale, and multidimensional architectures for the next generation of EES devices. [ABSTRACT FROM AUTHOR]

Conventional self‐charging systems are generally complicated and highly reliant on the availability of energy sources. Herein, a chemically self‐charging, flexible solid‐state zinc ion battery (ssZIB) based on a vanadium dioxide (VO2) cathode and a polyacrylamide‐chitin nanofiber (PAM‐ChNF) hydrogel electrolyte is developed. With a power density of 139.0 W kg‐1, the ssZIBs can deliver a high energy density of 231.9 Wh kg‐1. The superior electrochemical performance of the ssZIBs is attributed to the robust tunnel structure of the VO2 cathode and the entangled network of PAM‐ChNF electrolyte, which provide efficient pathways for ion diffusion. Impressively, the designed ssZIBs can be chemically self‐charged by the redox reaction between the cathode and oxygen in ambient conditions. After oxidation for 6 h in air, the ssZIBs manifest a high discharging capacity of 263.9 mAh g‐1 at 0.2 A g‐1, showing excellent self‐rechargeability. With the assistance of a small amount of acetic acid added to the hydrogel electrolyte, the galvanostatic discharging and chemical self‐charging cycles can reach 20. More importantly, such ssZIBs are able to operate well at chemical or/and galvanostatic charging hybrid modes, demonstrating superior reusability. This work brings a new prospect for designing flexible chemically self‐charging ssZIBs for portable self‐powered systems. [ABSTRACT FROM AUTHOR]

The synthesis of biomass-derived porous carbons (PCs) for supercapacitors by conventional two-steps method (chemical activation after carbonization) is complicated and time-consuming. In this study, we present a one-step microwave activation strategy to prepare hierarchically PCs from waste palm boosted by activated carbons (ACs). ACs with various specific surface areas (14, 642, and 1344 m2·g−1) were used for the first time to fast absorb microwave energy for converting waste palm into hierarchically PCs, that is, PC1, PC2, and PC3, respectively. The morphological and structural characterizations of PCs were studied. Also, the electrochemical performances of supercapacitors based on PCs as electrodes were further investigated. The results showed that the PC (PC1) boosted by AC with the lowest specific surface area possessed a porous structure (containing micro-, meso-, and macro- pores) with the largest specific surface area (1573 m2·g−1) and the highest micropore volume (0.573 cm3·g−1), as well as the suitable mesoporosity (29.69%). The as-prepared PC1 supercapacitor even in a gel electrolyte (PVA/LiCl) exhibited a high specific capacitance of 226.0 F·g−1 at 0.5 A·g−1 and presented excellent charge-discharge performance with an energy density of 72.3 Wh·kg−1 at a power density of 1.4 kW·kg−1 and 50.0 Wh·kg−1 at 28.8 kW·kg−1. Moreover, this promising method exhibited a simple, rapid, and cost-effective preparation of carbon materials from renewable biomass for energy storage applications. [ABSTRACT FROM AUTHOR]

• The single-step synthesis from wheat straw to a porous carbon only required 5 min. • The wheat straw-derived char acted as a good microwave absorber. • The obtained porous carbon possessed a balanced pore distribution. • A high specific capacitance and an excellent rate capability were both achieved. Single-step synthesis of porous carbon (PC) from biomass is a challenge via microwave heating, because biomass rarely absorbs the microwave energy. Herein, wheat-straw-derived char, as a good microwave absorber, was used to achieve rapidly single-step synthesis of PC from an agricultural waste (wheat straw). KOH was used to generate abundant micropores in the PCs. High heating rate caused by microwave heating combined with the pyrolysis gases resulted in the formation of meso-/macropores. A series of post-oxidation reactions between active sites in the PCs and oxygen in the air led to the doping of oxygen-containing chemical groups. Consequently, the obtained PC possessed a high specific surface area of 1905 m2 g−1, a balanced pore distribution with abundant micropores (0.62 cm3 g−1), considerable content of meso-/macropores (0.53 cm3 g−1), and an oxygen-enriched structure (oxygen content up to 21.6%). These characteristics not only contributed to the achievement of a high specific capacitance of 268.5 F g−1 at 0.5 A g−1 for the resultant supercapacitor, but also resulted in an excellent rate capability with a high capacitance retention of 81.2% at 10 A g−1 in a gel electrolyte (polyvinyl alcohol/LiCl). This supercapacitor can extract a high energy density of 21.5 W h kg−1 at 0.5 A g−1 and a high power density of 7.2 kW kg−1 at 10 A g−1. [ABSTRACT FROM AUTHOR]

The demerits of the carbonized eggshell membrane (EM), such as high cost, high brittleness, immutable shape and size, greatly limit its application in demanding supercapacitors as free-standing electrode. Herein, the reconstituted EM (REM) with good flexibility and excellent size-customizability is developed, which is due to their fibrous structure and abundant surface polar groups. Ti 3 C 2 nanosheet (a typical MXene) with ultra-high electrical conductivity and good electrochemical activity is then coated on REM surface, and undergoes a low-temperature carbonization (350 °C) to prepare CREM/T. Multi-functions of Ti 3 C 2 are exhibited: (1) constructing a conductive network on REM surface by randomly stacking to yield a high electrical conductivity of 78.1 S cm−1, (2) being as a protective mold to remain the inherent flexibility and porosity of REM during carbonization, (3) creating nanopores by inducing self-activation, and (4) yielding a large capacitance of 1729 mF cm−2 at 0.5 mA cm−2 and a high rate capability of 82 % after increasing the current density by 50 folds. Furthermore, an all-EM-based supercapacitor is fabricated with REM as the separator and CREM/T as the electrode. It delivers a high energy density of 16.1 μW h cm−2 at 1301 μW cm−2, and shows stable capacitive behaviors during bending. • The reconstitution strategy endows good size-customizability to eggshell membrane. • MXene remains the inherent structure of eggshell membrane during carbonization. • MXene induces a self-activation on eggshell membrane during carbonization. • An all eggshell-membrane-based supercapacitor is fabricated. [ABSTRACT FROM AUTHOR]

Cellulose nanofiber (CNF) has been widely used in MXene film electrodes to improve its mechanical properties and rate capability for supercapacitors. However, all the above enhancements are obtained with inevitably sacrificing the capacitance, because of the non-electrochemically-active characteristic of CNF. Herein, to address this issue, lignin-containing cellulose fibers (LCNF) is innovatively used to substitute CNF. Specifically, LCNF play a role as a bridge to significantly reinforce mechanical strength of LCNF/MXene film electrode (LM) by binding the adjacent MXene nanosheets, reaching a tensile strength of 34.2 MPa. Lignin in LCNF contributes to pseudocapacitance through the reversible conversion of its quinone/hydro-quinone (Q/QH 2), thus yielding an excellent capacitance of 364.4 F g−1 at 1 A g−1. Meanwhile, LCNF has different diameters in which microfibers form a loose structure for LM, nanofibers enlarge d -spacing between adjacent MXene nanosheets, and fibers self-crosslinking creates abundant pores, thus constructing graded channels to achieve an outstanding rate capability of 87 % at 15 A g−1. The fabricated supercapacitor demonstrates a large energy density of 1.8 Wh g−1 at 71.3 W g−1. This work provides a promising approach to decouple the trade-off between electrochemical performance and mechanical properties of MXene film electrodes caused by using CNF, thus obtaining high-performance supercapacitors. • LCNF decouples the trade-off between capacitance and tensile strength for MXene film. • Multiscale cellulose fibers in LCNF construct graded channels for fast ion diffusion. • Lignin in LCNF avoids sacrificing the capacitance of MXene film. [ABSTRACT FROM AUTHOR]

• Integrating carbonization, activation, and in-situ growth of Cu x O y in one step. • Regulating the morphology and valence state of Cu x O y by constant potential method. • The specific capacitance of electrode is boosted by 98.6% after regulating Cu x O y. Using bottom-top methodology to load metal oxides with high pseudocapacitive activity onto carbonized wood (CW) is an efficient strategy to fabricate electrodes with large capacitance, while the morphology and metal valence in metal oxides are as important as their content but have received little attention. Herein, a heating treatment integrating carbonization and activation processes is used on Cu2+ loaded natural wood to prepare CW/Cu x O y electrodes in which Cu x O y with pseudocapacitive activity and CW with a high specific surface area (SSA) of 832 m2/g and good electric conductivity of 1.25 S cm−1 are collaboratively achieving a capacitance of 430.5F/g at 150 mA g−1. Then, a constant potential method is utilized not only to regulate the valence state of Cu and Cu2+ in Cu x O y to Cu+ with much higher pseudocapacitive activity, but also to convert the morphology of Cu x O y from sphericity to urchin-like and cluster structure with more available active sites. Therefore, the optimized electrode achieves a greatly improved capacitance of 855F/g, and the fabricated supercapacitor delivers an energy density of 75.93 Wh kg−1 at 138 W kg−1. This work provides an approach to enhance the specific capacitance of metal oxides-based electrodes from a fresh perspective. [ABSTRACT FROM AUTHOR]

Lignocellulose including cellulose, lignin, and hemicellulose could be extracted from wood, and has been used to prepare carbon electrode. However, complicated extraction greatly increases preparation cost. To achieve maximum utilization of lignocellulose and avoid complicated extraction, wood with porous structure and good mechanical strength is used as carbon precursor. Additionally, chemical activation is commonly used to create micropores to provide high capacitance, but it brings in natural structure destruction, and generation of wastewater during pickling. Moreover, to achieve desirable energy density, multi-step strategy with long duration is required for loading active materials on carbonized lignocellulose (CL). Herein, a one-step method is developed to prepare a free-standing hybrid CL electrode (CLE) by using Lewis acid in three aspects: (1) as structure protection agent, (2) as activating agent, (3) as active materials donor, which bypasses pickling and further avoids the generation of wastewater. Additionally, natural vessels in wood can not only provide large space for active materials loading, but also act as rapid ions diffusion way, simultaneously confining active materials detachment. Benefiting from the synergistic effect of porous structure and Lewis acid, this work not only makes full utilization of lignocellulose, but also makes CLE exhibit excellent performance in hybrid oxide supercapacitor. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hydrogel electrolyte shows advantages of dual-network structure and good water-retaining property. • The activity of water molecule in the hydrogel electrolyte is limited during charging/discharging. • Such this hydrogel electrolyte suppresses the dendrite growth and widens the voltage window of the solid-state battery. Undesirable side reactions and uncontrollable dendrite growth on zinc anode surface severely restrict the practical applications of the rechargeable zinc-ion batteries (RZIBs). In this work, a lignin-containing cellulose nanofibers (LCNF)-polyacrylamide hydrogel (LPH) electrolyte with a unique dual-network structure and excellent water-retaining property is developed for high-energy and dendrite-free solid-state zinc-ion batteries. Benefiting from these advantages, the activity of water molecule in LPH is limited and the water-induced side reactions are restricted, leading to a significantly widen voltage window. Assembled with LPH electrolyte, the Zn/Zn symmetric cells can maintain a long cycling lifespan of 4000 h at the current density of 0.5 mA cm−2 under 1 mAh cm−2. With LPH electrolyte, Zn/MgVO full batteries delivered a high capacity of 149.2 mAh/g with the capacity retention of 91.9 % after 4000 cycles at 5 A/g. Moreover, with a widened voltage window of 0.2 V to 1.9 V, the full batteries with LPH can deliver a high energy density of 255.4 Wh kg−1 at the power density of 341.7 W kg−1 for over 5000 cycles. This design of LPH electrolyte provides a new insight to stabilize the zinc anode and achieve high energy density for the further development of RZIBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • This facile strategy boosts the volumetric capacitance of the electrode by 9 times. • This strategy endows the electrode with stable capacitive behaviors during bending. • This strategy is more advanced as a substitute for designing thick electrodes. Wood-based thick electrodes (>400 μm) always exhibit low volumetric loading of active material and poor flexibility. Herein, a "thick to thin" strategy including densification and low-temperature heating treatment is innovatively proposed and then applied in a MXene (Ti 3 C 2 T x)/wood thick electrode (500 μm) to simultaneously realize large volumetric loading and excellent flexibility. It is found that the densification can significantly increase the volumetric mass loading of Ti 3 C 2 T x by 10 times owing to the great reduction of the electrode thickness (50 μm), and endow the electrode with excellent flexibility by changing porous microstructure to compact microstructure. Furthermore, the low-temperature heating treatment greatly improves the electrochemical performances of the electrode by generating meso -/macropores for ion transport and exposing more active sites to the electrolyte. After conducting our proposed strategy, the optimized electrode exhibits 9 times higher volumetric capacitance (reaching 187F cm−3) than the control electrode, and still has a high rate capability of 77 % when the current density increases by 100 folds. Additionally, the optimized free-standing electrode is used to fabricate a quasi-solid-state supercapacitor which demonstrates stable capacitive behaviors during bending and a large volumetric energy density of 3 mWh cm−3 at 30.6 mW cm−3. [ABSTRACT FROM AUTHOR]

• A highly conductive net is constructed in MXene/PC film by introducing CNT. • The flexibility of MXene/PC film is improved without sacrificing its conductivity. • The flexible supercapacitor can withstand an ultrahigh san rate of 1 V s−1. Porous carbon (PC) can effectively alleviate the typical self-stacking phenomenon of 2D MXene-based films as a spacer, and can easily customize their porous structure. Nevertheless, the contact between 3D PC and 2D MXene flakes is generally presented at a point-to-point form owing to the irregular shape of PC, leading to a low efficiency on electron delivery and stress concentration with a fragile characteristic in the resulting films. Herein, 1D carbon nanotube (CNT) was introduced to construct a highly conductive net structure, tightly anchoring PC on MXene flakes, thus ensuring fast electron delivery by increasing the contact area between MXene and PC. Additionally, the interwoven CNTs bridge the horizontal MXene flakes, making internal structure more integral, thereby enhancing the flexibility. Consequently, the Ti 3 C 2 T x (a typical MXene)/CNT/PC (TCP) film has an ability to bear a large scan rate of 1 V s−1 and shows a high areal specific capacitance of 364.8 mF cm−2 at 0.5 mA cm−2 which remains above 80% even at a high current density of 50 mA cm−2. Furthermore, the fabricated flexible quasi-solid-state supercapacitor (SC) demonstrates a large areal energy density of 10.5 μ Wh cm−2 at 29.8 μ W cm−2. This study provides a promising approach to overcome the poor flexibility of MXene/PC film without sacrificing the conductivity, meanwhile paving a way for the development of flexible SCs with large charge storage capacity and high rate capability. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel coating method with quickness and high uniformity is developed. • A high MXene loading capacity of 6.1 mg cm−2 is achieved in the composite. • A supercapacitor consisting of all clean wipers is fabricated. • The prepared all-solid-state supercapacitor is flexible and stretchable. MXene-loaded textiles can be used as free-standing electrodes for multi-functional supercapacitors (SCs), due to their good conductivity, high electrochemical activity, excellent flexibility, and stretchability. However, the typically self-restacking phenomenon would emerge with the increase in MXene amount, resulting in a significant reduction of the ion-accessible surface areas and active sites of MXene. Herein, a dot-matrix drop-casting method with the advantages of quickness and high uniformity is developed to load high amount (6.1 mg cm−2) of Ti 3 C 2 (a typical MXene) on a clean wiper (CW, a typical textile), and simultaneously to alleviate the resultantly self-restacking phenomenon of Ti 3 C 2. The results show that the obtained composite (CWM) has a high conductivity of 2.3 S cm−1 and large specific capacitance of 282 mF cm−2 at 1 mA cm−2, whereas it remains a high tensile strength of 20.1 MPa and developed porous structure (33.4 m2 g−1). These attractive properties make CWM an ideal free-standing electrode. Further, CW is used as a separator to fabricate an all-CW-derived SC (CWM//CW//CWM), because its porous structure provides abundant routes for facile ion transport. Such a SC has an excellent rate capability with a high capacitance retention of 78.2% from 1 to 20 mA cm−2, large specific capacitance of 118 mF cm−2 at 1 mA cm−2, and high energy density of 10.1 μWh cm−2 at 389.9 μW cm−2. Moreover, an all-solid-state SC (CWM//CWM) is fabricated, and shows an excellent stability on capacitive behaviors during bending (0–120°) or stretching (10–40% strains), manifesting its great potential on wearable and portable electronics. [ABSTRACT FROM AUTHOR]

Ti 3 C 2 T x (a typical MXene) films can be used as free-standing electrodes due to their ultrahigh electrical conductivity, well flexibility and high electrochemical activity. However, inevitable self-restacking issue of Ti 3 C 2 T x nanosheets largely decreases exposed area and impedes the ion transport in Ti 3 C 2 T x film. Herein, hierarchically porous carbon (HPC) introduced into Ti 3 C 2 T x film can not only act as the pillar for adjacent Ti 3 C 2 T x nanosheets to prevent their typical self-restacking and further accelerate rapid ion transport in the transverse direction, but also ensure rapid ion transport in the longitudinal direction by introducing abundant macro/mesopores. By easily changing the amount of HPC (0–60%), the porosity of the film is well controlled, with adjustable specific surface area (SSA) from 8 m2 g−1 to 755 m2 g−1. The prepared quasi-solid-state supercapacitor fabricated by 60% HPC shows a good stability after different bending angles, high capacitance of 211 mF cm−2, energy density of 4.68 μW h cm−2 at 19.91 μW cm−2, and high capacitance retention of 86% after 10,000 charging-discharging cycles. This work will pave a facile route to alleviate the self-restacking phenomenon of Ti 3 C 2 T x film by constructing transverse and longitudinal channels for rapid ion transport. [Display omitted] • The porous structure can be easily adjusted in the MXene film. • Both transverse and longitudinal channels are constructed in the MXene film. • The supercapacitor has a good flexibility and a high areal specific capacitance. [ABSTRACT FROM AUTHOR]