| Supercapacitors are energy storage devices with broad application prospects,which feature high power density,fast charging and discharging speed,and long cycle life.However,in addition to the above characteristics,higher energy density and excellent flexibility are also important for applications in wearable electronic devices,photovoltaic energy storage devices,etc.Among them,the emerging 2D material MXene is an excellent energy storage material with high conductivity and high capacity,so it is essential to study it deeply for developing high-performance energy storage products.In this paper,we mainly use nanocellulose（CNF）as a modified material to combine with MXene and other energy storage materials to regulate the electrode structure in different ways and assemble them into supercapacitors,and conduct systematic tests and studies on their electrochemical properties,and then explore the effect and mechanism of CNF in the electrode structure.The main studies are as follows:（1）Flexible MCNF composite film electrodes were prepared by simple ultrasonic dispersion and vacuum filtration self-assembly using nanocellulose（CNF）and monolayer Ti3C2Tx MXene as raw materials.By varying the mass fraction of nanocellulose in the composite electrode,the structure,morphology,chemical bonding,physical properties and electrochemical properties of the electrode materials were characterized,and it was found that the MCNF flexible film electrode exhibited ultra-high mechanical properties（Young’s modulus of 3.2 MPa,tensile strength of 30.6 MPa）,superior flexibility and ultrathin thickness（6-13μm）.Based on the redox reaction of H+on MXene surface,it exhibits excellent specific capacity at a voltage window of 0.6 V:89 F?g-1 at 5 m V?s-1(160m F?cm-2)and a capacitance retention rate of 50.6%at 100 m V?s-1.Furthermore,the MCNF flexible device still has 88.7%capacity retention after 5000 cycles.The balance between electrochemical and physical properties of flexible thin film electrodes is demonstrated to meet the practical application requirements of energy storage devices.（2）The fully pseudocapacitive MCNF//CP asymmetric supercapacitor was assembled by using the MCNF flexible electrode as the negative electrode and the CP as the positive electrode which was fabricated by polymerizing polyaniline directly on carbon cloth.By utilizing the complementary positive and negative potential windows,the assembled devices exhibit a wide operating voltage window of 1.5 V and a mass energy density of up to 30.6 Wh?Kg-1(power density up to 8023 W?Kg-1).A good specific capacitance(97 F?g-1(281 m F?cm-2))is ensured by the charge storage mechanism of highly reversible protonation/deprotonation pseudo-capacitance of the surface functional groups.Moreover,the asymmetric device shows excellent electrochemical stability by maintaining a high capacitance retention of 86%at a high current density of 20 A?g-1.In addition,the bendability of the asymmetric device is quite outstanding due to the good flexibility of both positive and negative electrode materials,and no significant degradation of the capacitance performance is found in the bending test.（3）Combining hydrothermal and freeze-drying methods,three-dimensionally interconnected macroporous composite aerogels were prepared by employing highly conductive two-dimensional nanosheets of MXene and r GO as the main capacitance-contributing and charge-conducting materials,respectively,with CNF as the"bridge"between the two nanolayers and VC as both an antioxidant for MXene and a reducing agent for GO.When the MCG aerogel materials were used as electrodes for supercapacitors,excellent areal specific capacitance was obtained(671 m F?cm-2 at 5 m V?s-1 and 352 m F?cm-2 at 100 m V?s-1 with a capacitance retention rate of52.5%).The assembled devices exhibit a power density of 1.0 m W?cm-2 and a high energy density of 60.9μWh?cm-2 at a voltage window of 1.0 V.In addition,the symmetrical device maintains a superior capacitance retention of 79.4%at a high current density of 20 m A?cm-2,showing good electrochemical stability. |
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