Synthesis And Performance Research Of Graphite Oxide,Graphene Oxide/S Composite As Cathode Materials For Lithium-ion Batteries

Among the various energy-storage device,such as batteries,supercapacitors and so on,lithium ion batteries(LIBs)wereone of the mostpromising candidate,especially as the power source for pluginhybrid and electrical vehicles.Because the oxygen-containing functional groups of graphite oxide-based materials,such as graphite oxide,graphene oxide,reduced graphene oxide,can react with lithium ion at higher potentials,these materials were graduallyused as cathode of LIBs in recent years.In this paper,the graphite oxide cathode materials with different degrees of oxidation were synthesized by modified Hummer's method,to investigatethe optimum conditions.Then,the relationship between the time of low temperature and electrochemical performance was explored.Subsequently,we also synthesized graphene oxide/S composite to enhance the capacity.Through XRD,FTIR,TGA,XPS,SEM,CV,EIS,charge/discharge test,the composition,morphology and electrochemical properties of the synthesized materials were analyzed.Orthogonal design for synthesis of graphite oxides.Through the orthogonal experiment design,different kinds/numbers of oxygen-containing functional groups of graphite oxides were synthesized by modified Hummer's method.Subsequently,graphite oxides with rationally designed functional groups have been utilized as cathode materials for LIBs.Combining with electrochemical test,we have chosen the optimumreaction conduction as followed: i.e.medium temperature time(t2),high temperature(T2),low temperature time(t1)and medium temperature(T1).During nine groups of orthogonal experiments,the optimum synthesis conditions,t1=60 min,T2=100?,t1=120 min,T1=48 ?,have been obtained.The materials exhibited a remarkableelectrochemical performance:initial charge/discharge capacity of 212 and 163 mAh g-1 at a current density is 100 mA g-1,respectively.Specific capacity of the material can reach145 mAh g-1after 43 cycles and decay rate per lap was only0.21%.Influence of low temperature reaction time on electrochemical performance of graphite oxide.When reaction time at low temperature was prolonged,the initial capacity of releavantmaterial could be greatly enhanced and the reversible capacity maintained stabled.The initial charge/discharge capacity is 168 and 332 mAh g-1 at a current density of 100 m A g-1.Meanwhile,the sample showed an excellent long-term electrochemical performance.After 800 cycles,the capacity is also maintained at around 135 mAh g-1with a decay rate ofonly 0.03%/cycle.It was found that the reaction time of low temperature reaction only affected the irreversible capacity of the material.Trying to increase the capacity of graphene oxide-based cathode material.After ultrasonic,graphene oxide suspension with sulfur(GO/S)was synthesized through hydrothermal methods.It was found thatgraphite oxide has been partially reduced.Compared with the raw materials,graphene oxide/S(GO/S)composites exhibited the initial capacity of105 mAh g-1 at a current density of 100 mA g-1,lessthan 332 mAh g-1 of the graphite oxide material.After the 250 cycles,the capacity of GO/S composite can maintain at around 120 m Ah g-1,which is lower than the raw materials.It also shows that adding of sulfur would reduce some irreversible oxygen-containing functional group of graphene oxide.