Preparation And Study Of Graphene-based Energy Storage Materials

Graphene has excellent thermal,electrical and high strength properties.The conductivity is 10 times as high as silicon,and the thermal conductivity is the best in carbon materials.As the anode of the lithium ion batteries,graphene has a lower theoretical specific capacity?740⁷80 mAh/g?,far lower than silicon?4200 mAh/g?,but the silicon has a severe volume expansion?>300%?during the delithiation/lithiation process,resulting in an increase in the resistance between the silicon and the gathering fluid,resulting in rapid decline of reversible capacity,which limits the large-scale commercial application of silicon,needs to be further studied by using silicon instead of traditional graphite as anode material.Therefore,combined with the characteristics of graphene and silicon,we prepared graphene and silicon composite materials to get high-performance anode materials in lithium ion batteries.The main work of this paper is as follows:?1?Graphene was prepared by oxidation-reduction method.The optimal experimental condition was analyzed by orthogonal experimental method.The proportion of the drug was selected as flaky graphite:NaNO₃:concentrated sulfuric acid?98%?:KMnO₄:Deionized water:H₂O₂?30%?=1 g:0.5 g:30 m L:3 g:50 mL:30m L.The experimental condition was as follows:the reaction was 2 h at low temperature?<5??,the reaction was 0.5 min at medium temperature?35??,and the reaction was 20min at high temperature?95??.The hydrochloric acid and deionized water were centrifuged for many times.The obtained graphite oxide was stripped by ultrasonic.Then the powder of graphene oxide was prepared by freezing vacuum drying to prepare the film.The diameter is 50⁸0 um graphene oxide.Graphene was obtained at 2 h at600?in nitrogen atmosphere.?2?Preparation of graphene by microwave method:oxidation of flake graphite by hydrogen peroxide?30%?.The mass ratio of medicine to scale graphite is concentrated sulfuric acid?98%?:H₂O₂?30%?=1 g:30 m L:10 mL.The experimental conditions were as follows:the reacting conditions were controlled at 25?for 1 h to get expandable graphite,centrifuged to neutral,drying at 12 h at 80?,then loaded into the quartz tube with argon atmosphere,and the worms were expanded by microwave heating for 1 min,and the tablets were obtained by ultrasonic centrifugation.?3?One step hydrothermal method is used to prepare graphene coated silicon and directly grow on foam nickel.The preparation method does not need conductive agent,no binder,and no need to abrade.The preparation process of graphene oxide:Deionized water:silicon=50 mg:50 m L:100 mg,adding graphene oxide to 1.5 h in deionized water and adding 30 min after adding silicon,then adding nickel foam to the above solution and stirring 5 min to react 14 h at 180?in the reactor,and then freeze vacuum drying and calcining the electrode.The specific capacity exceeds 2400 mAh/g after 50cycles at the current density of 0.2 A/g,and the specific capacity exceeds 1500 mAh/g after 2500 cycles at the current density of 2 A/g,and the specific capacity exceeds 600mAh/g after 2500 cycles at the 4 A/g current density;and in the ratio test,back to 0.2A/g from 0.5 A/g to 16 A/g has stable electricity.It still 500 mAh/g in the specific capacity of 16 A/g.?4?The graphene aerogels were synthesized by hydrothermal method.The weighed graphene oxide 50,100,150 mg were added into 3 beaker respectively,and each was added to the 50 mL deionized water.After 90 min ultrasonic stirring,the solution of graphene oxide was poured into the 100 m L reactor respectively.The graphene hydrogel was obtained at 180?for 14 h,and the hydrogel was soaked in ammonia water for 4 h,and the graphene aerogel was dried by freezing vacuum drying.The tubefurnace was heated at 10?/min in the nitrogen atmosphere and 2 h at 600?.The aerogels with high elasticity and excellent mechanical properties can be obtained by heating the aerogel into a quartz tube under argon atmosphere after 1 min microwave heating.?5?Via one-step hydrothermal method synthesis of graphene aerogel/silicon and directly slicing the negative electrode,no need fluid collection.The preparation material process found the graphene oxide:Deionized water:silicon=150 mg:50 m L:30 mg,after ultrasonic oxidation of graphene 1 h,adding silicon and then stirring 30 min into the reactor and reacting 14 h at 180?,drying the graphene aerogel/silicon in vacuum,and then slicing the electrode.The specific capacity is more than 748 m Ah/g after 50cycles of 0.2 A/g current density,and the specific capacity exceeds 500 mAh/g after1000 cycles of current density 1 A/g.In ratio test,back to 0.2 A/g from 0.2 A/g to 4 A/g,it has stable electrochemical multiplying performance and is still more than 100 mAh/g at 4 A/g in the rate tests.