Tetramethylthiuram Monosulfide For Fast And Ultra-Long Cycle Lithium Batteries

With the development of society and the advancement of the technology,energy storage technology is becoming more and more important to human daily life.Lithium-ion batteries(LIBs)have captured a considerable share in the portable electronic devices and electric vehicle markets due to its high energy density,good cycle stability,and environmental friendliness.However,traditional metal-based lithium-ion batteries are limited by resources and energy density,making it difficult to develop in the field of large-scale energy storage.Organosulfur is a kind of derivatives of sulfur that widely exists in nature,which is environmentally friendly and green,and can be regenerated with low energy consumption.Organosulfur molecules contain electrochemically active S-S bonds,which can be paired with lithium anodes to form an electrochemical energy storage system,with the potential of low cost and high theoretical specific capacity.In addition,organosulfur has abundant resources and functional group diversity,which gives it a great advantage in the future energy storage field.Therefore,it is necessary to develop some organosulfur cathode materials with novel structures.In this paper,a monothiothiuramorganosulfur compound(tetramethylthiuram monosulfide,TMTM)was used as the starting material,and activated to make it an active material for energy storage.Since it has no S-S bond,it is generally believed that it cannot perform charge and discharge in past research.This paper innovatively proposes two strategies.Therefore,two methods are proposed to activate TMTM as cathode active materials in rechargeable lithium batteries.The main research contents are as follows:1)Activation of TMTM using electrochemical methods.After high-voltage electrochemical activation of TMTM,the nitrogen atoms on the molecule lose electrons,and a class of organosulfur molecules with electron-deficient structure are obtained.This structure stretches the electron cloud on the C-S bond,causing the C-S bond to break,generating sulfur radicals with nitrogen cations.The radicals recombine to form a class of organosulfur structures with electron defects.The unique electron-deficient structure can stretch the electrons cloud of adjacent S,and then abate the energy barrier of S-S bond.Thus,the S-S bond is easier to break and could accommodate lithium ion with ultrafast reaction kinetics.A lithium electron-deficient structure organosulfur cell demonstrates an ultralong cyclability over 8000 cycles with a low capacity fade rate of 0.0038%per cycle at a high rate of 10C.Up to 20 C,the capacity retention is still 92%of 0.5 C.At-50 ℃,it also achieves a high capacity retention of 75%over 300 cycles.This work provides a unique structure of organosulfur,enabling the use of organosulfur-based LIBs for practical energy applications.2)Activation of TMTM using chemical methods.The small molecule organic thiol is mixed with TMTM as the positive electrode of the battery,so that it can generate asymmetric organic disulfide in the battery,so as to achieve the effect of activating TMTM.P-methylthiophenol(CH3PhSH),p-fluorothiophenol(FPhSH),and 2-mercaptopyridine(PySH)were mixed in the electrolyte at a molar ratio of 2:1,respectively,as the battery cathode material.During the first cycle of discharge,after the small molecule thiol loses hydrogen,it attacks the TMTM molecule to break its C-S bond,and combines with the free radical generated by the small molecule thiol to form asymmetric disulfide,and then,through the cleavage and recombination of the S-S bond in the disulfides during charge and discharge,and the structure of the disulfide compounds was confirmed by some characterization methods.During battery cycling,the mixed compound exhibits good cycling performance with long cycle life and high capacity retention,stable cycling for thousands of hours at a rate of 2 C,and high Coulombic efficiency.This is another feasible and simple method for activating TMTM,so that TMTM molecules without redox activity themselves can be chemically reacted to generate a good energy storage material.