Constructing MXene/Si@C Core-shell Nanofibers Via Coaxing Electrospinning For High Performance Li-ion Batteries

In recent years,with the development of the new energy vehicles industry,the demand for high-performance,high-safety,long-life,and environmentally friendly lithium-ion batteries has continued to grow.Silicon is one of the most potential anode materials for LIB due to their ultra-high theoretical specific capacity(4200 mAh g-1),low lithium intercalation potential,low cost and abundant resourses.But the practical application of silicon materials is limited due to volume expansion and low conductivity,and it is an effective way to combine silicon with carbon materials.Carbon materials can not only serve as a conductive matrix,but also play an important role in alleviating the volume expansion of Si.The new two-dimensional material MXene has excellent electronic conductivity and ion conductivity,as well as good mechanical properties and large interlayer spacing,which makes it a very promising candidate for silicon-based composite materials.This paper uses coaxial electrospinning technology to introduce MXene into the Si/C composite system to prepare a multi-component nanofiber.Through structural design and composition adjustment,the structural stability and electrochemical dynamics of the electrode material are improved,and achieved an optimized electrochemical performance.First,the preparation process of MXene was explored.The MXene nanosheets were prepared by HF etching method and HCI/LiF etching method respectively.The MXene synthesised by HF etching method has accordion-like structure,which can be deliminated to nanosheets by TMAOH.MXene can be obtained directly by HCI/LiF etching method.There are abundant functional groups such as-O,-F and-OH on the surface of the MXene,giving it good dispersibility in water.The MXene prepared by the HCI/LiF etching method has a large interlayer space of 1.3nm and extremely high conductivity,1000-3000S cm-1,which is beneficial for the charge transfer and the migration of lithium ions.MXene has good thermal stability and can maintain structure stability at 700℃.When MXene is used in lithium-ion batteries,it has low specific capacity but with good cycle stability and rate performance.MXene,Si and C materials were compounded by coaxial electrospinning to prepare MXene/Si@C composite nanofibers.In this unique structure,MXene nanosheets and Si paticles are wrapped by carbon shell.The MXene nanosheets as conductive substrate can effectively bridge the Si particles and carbon shell by stable chemical bond to form a conductive network in MXene/Si@C nanofiber.The robust carbon shell and MXene nanosheets offer a double accommodation for the huge Si volume expansion during charge/discharge,which maintain the structural stability of the electrodes.MXene/Si@C achieves the optimal performance under 1%MXene content and 700℃ carbonization temperature,showing good rate performance and cycle stability,which shows 1083.1 mAh g-1,948.3 mAh g-1,731.8 mAh g-1,463.1 mAh g-1 and 301.1 mAh g-1 at 0.1 A g-1,0.2 A g-1,0.5 A g-1,1 A g-1 and 2 A g-1,respectively.And it also keeps 540 mAh g-1(0.1A g-1)after 100 cycles.In addition,the construction of the conductive network improves the Si utilization efficiency significantly to 86%.The rich functional groups and ultra-high conductivity of MXene also greatly increase the contribution ratio of the pseudocapacitance of the material,which reaches 88.4%at a sweep speed of 1mV s-1.