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The titanium carbide nanosheets (MXene) hold great potential for fabricating high‐performance electronics due to their two‐dimensional layered structure, high electrical conductivity, and versatile surface chemistry. However, assembling the small MXene nanosheets into flexible macroscopic films for wearable electronics still remains a challenge. Herein, we report the hierarchical assembling of MXene nanosheets and cellulose nanofibers into high‐performance composite films via an electrostatic self‐assembly strategy induced by polyethyleneimine. Benefited from the nacre‐like microstructure of MXene "bricks" and cellulose nanofibers "mortars" interlocked by polyethyleneimine via hydrogen bonding and electrostatic interaction, composite films possess integrated superior flexibility, high tensile strength, and stable electrical conductivity, which are advantageous for wearable electronic applications. To provide a proof‐of‐concept design, a symmetric quasi‐solid‐state supercapacitor with the as‐prepared composite film as electrode is fabricated, which exhibits a specific capacitance of 93.9 mF cm−2 at a current density of 0.1 mA cm−2 and almost constant capacitive behavior under different bending states. In addition, the composite film possesses capacities of electrothermal conversion and complete degradation in a hydrogen peroxide solution. These results demonstrate that the electrostatically self‐assembled composite films hold great promise in the development of highly flexible, mechanically robust, and environmentally friendly energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

Uncontrollable zinc dendrite growth and parasitic reactions have greatly hindered the development of high energy and long life rechargeable aqueous zinc‐ion batteries. Herein, the synergic effect of a bifunctional lignin‐containing cellulose nanofiber (LCNF)‐MXene (LM) layer to stabilize the interface of zinc anode is reported. On one hand, the LCNF provides enough strength (43.7 MPa) at relative low porosity (52.2%) to enable the diffusion limited dendrite suppression, while, on the other hand, the MXene serves as a zinc gating layer, facilitating the zinc ion mobility, restricting the active water/anions from degradation in the electrode/electrolyte interface, and epitaxially guiding zinc deposition along (002) plane. Benefiting from the synergic effect of diffusion limited dendrite suppression and zinc gate, the LM layer enabled a high coulombic efficiency (CE) of 98.9% with a low overpotential of 43.1 mV at 1 mA cm−2 in Zn//Cu asymmetric cells. More importantly, Zn//MnO2 full cells with the LM layer achieve a high‐capacity retention of 90.0% for over 1000 cycles at 1 A g−1, much higher than the full cell without the protective layer (73.9% over 500 cycles). The work provides a new insight in designing a dendrite‐free zinc anode for long‐cycle‐life batteries. [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]

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]

• 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]