Synthesis Of New Two-dimensional Material Mxene And Its Application In Lithium Batteries

Lithium-ion batteries?LIBs?are the most widely used in energy storage devices due to their advantages such as high energy density,good charge and discharge stability,and no memory effect.However,with the development of society,conventional LIBs are more and more difficult to meet people's requirements.Thus,LIBs with higher performance have become one of the most important research topics.Li Ni_0.8Co_0.1Mn_0.1?NCM811?,with higher energy density,has become a candidate for the LIBs with the development of new energy vehicles.However,the poor cycle stability and unsafety of NCM811 limits its further application.In order to improve these properties of based on NCM811 LIBs,a great deal of methods has been proposed,such as separator modification.MXene,as a new type of two-dimensional material,has a high specific surface area,good electrical conductivity,excellent mechanical properties and electrochemical performance,which is similar to graphene.Since found in 2011,it has received great attention because of its wide application prospects,especially for Ti₃C₂T_X,one of MXene materials.Although the preparation methods of Ti₃C₂T_Xare various,the systematic research on the optimal conditions for the preparation of Ti₃C₂T_Xhas not found.Moreover,most papers focus on the application of Ti₃C₂T_Xin electrode materials,but rarely pay attention to its application in the fields of modified separator,conductive agents,and so on.Therefore,its use should be further expanded.The Ti₃C₂T_Xmentioned above with hydrophilic properties make it possible for the modification of separator,thereby improving the performance of based on NCM811 LIBs.Herein,this work mainly studied the application of Ti₃C₂T_Xin modified separator.In briefly,the experimental conditions of currently popular Li F/HCl etching method for the preparation of Ti₃C₂T_Xwere optimized.Then,prepare the composited separators with single layer/few layers Ti₃C₂T_Xand study their electrochemical performance.The details of this work are as follows:Firstly,the effect of Li F/HCl etching method at different temperature?30?,40?,50?,60?,70??on morphology and properties of Ti₃C₂T_Xwere studied.The results of SEM and XRD show that the optimum temperature for etching is 40?.Based on this experimental condition,Ti₃C₂T_Xsample has the largest layer spacing of 1.497nm with an accordion-like structure.Then,the soft,partially folded Ti₃C₂T_Xsamples with single layer/few layers and curled border were successfully obtained via ultrasonic method,which can be made into self-supporting films.Secondly,the Ti₃C₂T_X@PP separators were prepared by spraying Ti₃C₂T_Xprepared above into the PP separator.The study found that Ti₃C₂T_X@PP separator have better electrolyte wettability compared to pristine PP separator.Then,the overall performance test of LIBs assembled with Ti₃C₂T_X@PP separator and Li Ni_0.8Co_0.1Mn_0.1?NCM811?cathode materials is conducted.LIBs with Ti₃C₂T_X@PP separator has higher capacity,better cycle stability and rate performance.At first 80 cycles,its discharge capacity decreases with a rate of 0.11%per cycle,and maintains 166m Ah/g even after 100 laps at 0.5C?1C=200m Ah/g?,which is better than LIBs with a common PP separator.Thirdly,polyamic acid?PAA?was synthesized from pyromellitic dianhydride and 4-4'diaminodiphenyl ether,and then PI film was made by electrospinning method and thermal imidization of PAA.Finally,Ti₃C₂T_X@PI separator was obtained successfully via the spraying method mentioned above.The test results show that PI fibers with uniform shape are interconnected,and Ti₃C₂T_Xslightly penetrates into PI film without any effect on its structure.LIBs assembled with Ti₃C₂T_X@PI separator and Li Ni_0.8Co_0.1Mn_0.1?NCM811?cathode materials has excellent rate performance,which maintains a capacity of 157m Ah/g at 4C rate and still has a capacity of 128m Ah/g at 8C rate.