Study On Energy Storage Of Titanium-based Double Transition Metal MXene

Electrochemical energy storage devices have gained significant attention due to their high energy efficiency,convenient use,minor environmental impact,and unrestricted geographical application.Unlike traditional heat engines that rely on the Carnot cycle for energy conversion,electrochemical energy storage devices offer the potential for more sustainable and efficient energy storage solutions.MXene has shown excellent electrochemical performance in the field of supercapacitors and lithium-sulfur batteries owing to controlled surface chemistry,excellent conductivity and outstanding mechanical properties.The capacitance of MXene under acidic conditions mainly arises from the protonation and deprotonation processes of M-O.In this work,the surface-O functional group content of Ti₃C₂T_x is regulated in this work by doping Nb/V atoms at the M-site.Meanwhile,Additionally,MXene exhibits a unique physicochemical adsorption to polysulfides and a significant catalytic effect on the polysulfide conversion process,making it an attractive material for use as a sulfur host and as a septum modification in lithium-sulfur batteries.Therefore,its electrochemical performance is investigated through a comprehensive design in lithium-sulphur batteries.Details are as follows:The Ti-Nb double transition metal Ti_3-yNb_yAl C₂ MAX phases were successfully prepared by SHS,and the corresponding Ti_3-yNb_yC₂T_x MXenes were obtained by in situ acid etching.By introducing Nb atoms at the M-position,the functional groups of Ti_3-yNb_yC₂T_x MXenes can be tailored in a controlled manner,and the resulting Ti_3-yNb_yC₂T_x MXenes have a larger layer spacing and better electrochemical properties.Both exhibit excellent rate performance and excellent cycling stability when used as supercapacitor electrode materials.Among them,Ti_2.9Nb_0.1C₂T_x has a volumetric specific capacity of 1014 F cm^-3 at a scan rate of 2 m V s^-1,422 F cm^-3 at a scan rate of2000 m V s^-1 and a cycle life of 84,000 cycles at a current density of 10 A g^-1（75%of initial capacity retention）.The Ti-V double transition metal Ti_3-yV_yAl C₂ MAX phases were successfully prepared by SHS,and the corresponding Ti_3-yV_yC₂T_x MXenes were obtained by in situ acid etching.By introducing V atoms at the M-position,the functional groups of Ti_3-yV_yC₂T_x MXenes can be tailored in a controlled manner,and the resulting Ti_3-yV_yC₂T_x MXenes have a larger layer spacing and better electrochemical properties.Both exhibit excellent rate performance and excellent cycling stability when used as supercapacitor electrode materials.Among them,Ti_2.9V_0.1C₂T_x has a volume specific capacity of 951 F cm^-3 at a scan rate of 2 m V s^-1 and still shows a volume specific capacity of 506 F cm^-3 even at a scan rate of 2000 m V s^-1.At a current density of 10 A g^-1,Ti_2.9V_0.1C₂T_x still has a capacity retention rate of 89.6%after 20,000 cycles,while Ti₃C₂T_x has a capacity retention rate of 73.4%after 20,000 cycles.The Ti_3-yNb_yC₂T_x-Ti O₂ heterostructure(O-Ti_3-yNb_yC₂T_x)was obtained by in situ growth of Ti O₂ on the surface of Ti_3-yNb_yC₂T_x MXene by means of anhydrous ethanol solvent heat,which has excellent adsorption and catalytic properties for polysulfides.Then O-Ti_3-yNb_yC₂T_x was used for lithium-sulfur battery separators modification and modification of cathodes by a comprehensive design approach,which exhibited excellent rate performance and long cycle life.The cathode modified with O-Ti_2.7Nb_0.3C₂T_x has excellent rate performance,with an initial discharge capacity of1260 m Ah g^-1 at a current density of 0.1C and 640 m Ah g^-1 even at a current density of4C.It also has an initial specific capacity of 1014 m Ah g^-1 at a current density of 1 C,with an initial capacity retention rate of 42.09%after 2000 long cycles.