Preparation Of Ti₃C₂T_x Mxene-Based Composite Nanomaterials And Their Application In Energy Storage Devices

In the context of the country’s energy in deep transition,electrochemical energy storage technology is gradually becoming the mainstream energy storage technology.Among them,lithium-ion batteries（LIBs）are generally considered to be the optimal choice for electrochemical energy storage systems because of their advantages such as high energy density as well as energy conservation and environmental protection.In addition,supercapacitors（SCs）show potential for practical applications due to their high power density,but their further development is limited due to the failure of energy density to meet the requirements.Lithium-ion capacitors（LICs）,as a combination of LIBs and SCs,are emerging energy storage devices that combine higher energy density with greater power density.As the main storage carrier of ions,the anode materials directly affect the performance of the whole energy storage device.Ti₃C₂T_x MXene,as one of the newborn two-dimensional（2D）materials,has been widely used in LIBs/LICs because of its special layer morphology,exhibiting high electrical conductivity and adjustable terminal groups.However,there are also problems such as interlayer stacking and low actual capacity,which restrict its further development in the field of energy storage.To address these problems,this paper systematically investigates the energy storage mechanism as well as the reaction kinetics of Ti-based MXene composites,taking the optimization of Ti₃C₂T_x MXene structure and performance as the starting point.Through the assembly of LIBs/LICs,the great potential of Ti-based MXene composites in practical applications is demonstrated.The details of the study are as follows:（1）Ionic intercalation as well as surface functional group replacement of Ti₃C₂T_xMXene（KTi-400）was introduced into carbon nanofibers（CNFs）by electrospinning technique,resulting in a three-dimensional conductive network.In this KTi-400@CNFs composite,chemical bonding at the interface between KTi-400 and CNFs with Ti-O-C bonding establishes a bridge for rapid diffusion of charges in the longitudinal direction.Based on this,the composite at 10%KTi-400 addition ratio（10-KTi-400@CNFs）has the best electrochemical performance with a capacity of 594.1 m Ah g^-1 at a current density of 0.1 A g^-1 and still has a reversible capacity of 226.5 m Ah g^-1 at 5 A g^-1.More noteworthy is that the LICs assembled by using 10-KTi-400@CNFs as the anode electrode and choosing activated carbon（AC）as the cathode electrode achieves a high energy density(114.3 Wh kg^-1)while having high power density(12.8 k W kg^-1).（2）Pod-like SnS₂@f-Ti₃C₂T_x composites with heterogeneous structure were prepared by a facile hydrothermal synthesis method using graphene-like few-layer Ti₃C₂T_x MXene（f-Ti₃C₂T_x）nanosheets as the substrate material.SnS₂ was uniformly attached to the f-Ti₃C₂T_x nanosheets through interfacial interconnection to alleviate the interlayer stacking of f-Ti₃C₂T_x and buffer the volume expansion of SnS₂ during the reaction.When SnS₂@f-Ti₃C₂T_x was tested in LIBs,the reversible capacity was 1437.7m Ah g^-1 at 0.1 A g^-1.When the current density reaching to 1 A g^-1,a capacity of 570.3m Ah g^-1 was still achieved.In addition,the LICs assembled with SnS₂@f-Ti₃C₂T_x and AC achieves a capacity retention of 71.72%at a scan rate of 50 m V s^-1 for 5000 cycles.（3）In situ growth of NH₄V₄O₁₀ nanoparticles without changing the layered structure of Ti₃C₂T_x MXene will effectively alleviate the interlayer buildup problem of Ti₃C₂T_x MXene and act as an interlayer support.At the same time,the conductivity of the composite is improved,which facilitates the rapid charge transfer.Tested in LIBs,the capacity increased to 702.2 m Ah g^-1 after 170 cycles at 0.1 A g^-1.Meanwhile,the reversible capacity can still be maintained at 565.9 m Ah g^-1 when the current density of1 A g^-1 is applied,showing good rate performance as well as pseudocapacitive properties.When used as an anode material in LICs,it exhibits high energy density(151.15 Wh kg^-1)and power density(10 k W kg^-1).