Material Preparation And Research Of Li-ion Hybrid Supercapacitors

Research on environmentally friendly energy storage devices with high performance and low cost has increased significantly as a result of the development of portable electronic devices in modern society,the demand for renewable energy products,and the growing demand for electric or hybrid electric vehicles.Supercapacitors and lithium-ion batteries are currently two of the most promising energy storage systems,and nowadays,lithium-ion battery?LIB?with its high energy density of and supercapacitor?SC?with its excellent power density are considered as two outstanding candidates for the latest energy storage devices with low-cost,excellent electrochemistry performance and environmentally friendly to meet the growing energy storage needs.LIBs typically can store up from 150 to 200 Wh·kg^-1 of energy,but their low power density(less than 100 W·kg^-1)and poor cycle life?often less than 1000cycles?limit their functional effects.Capacitors provide much higher power density(10 kW·kg^-1),longer cycle life?more than 1000 cycles?,and fast charge-discharge?less than a few seconds?,but lower energy density is still a big problem.In the pursuit of higher energy density without sacrificing power density,the supercapacitor-cell hybrid energy storage device-combined electrochemical double layer capacitor?EDLC?type cathode electrode and lithium ion battery type negative electrode is designed and manufactured.However,lithium-ion hybrid supercapacitors still have many problems to be solved,the performance also needs to be improved.The purpose of this work is to build a layer-by-layer lithium-ion hybrid supercapacitor with graphene paper as the cathode material.The first work is to design and preparation of graphene paper as a lithium-ion hybrid capacitor cathode material.Graphene paper was used as the positive electrode material to make full use of its high surface area(-800 m2·g^-1).In addition,making the graphene paper cathode material,is different from the traditional electrode material preparation,which need to join super-p,PVDF as conductive agent,binder into the material,the advantage of doing so is to reduce the quality of the electrode and reduce the cost of preparing the electrode material at the same time.In the second work,MnCO₃@FGS with high specific capacity were prepared by hydrothermal method as the negative electrode material of lithium ion hybrid capacitor.MnCO₃@FGS can gain a capacity of 1360 mAh·g^-1 at a current density of 100 mA·g^-1,and has little attenuation from the second cycle,retaining a capacity of 912 mAh·g^-1 after 100 cycles."We assembled a lithium-ion hybrid supercapacitor with MnCO₃@FGS as anode and graphene paper as cathode,when the energy density reaches 36.2 Wh·kg^-1,the power density can reach 250 W·kg^-1.We also prepared FeS₂@FGS with different carbon contents by a relatively simple chemical method,which can control the particle size and the distribution of the sulfide on the graphene surface,increasing the specific surface area of the bulk material and the contact area of electrode material and electrolyte,improving the efficiency of the use of materials and improving the conductivity of the material and energy density.FeS₂@FGS has a specific capacity of 882 mAh g'1 in the first cycle at a current density of 0.2 A·g^-1 and a capacity of 665 mAh g'1 retain after 100 cycles.The structure of the construction of quantum dots and graphene composite,greatly enhanced the electrochemical properties of materials.FeS₂@FGS and graphene paper were assembled into lithium-ion supercapacitors.The energy density reached 34.6 Wh·kg^-1 when the power density reached 250 W·kg^-1.All of these show the excellent performance of MnCO₃@FGS and FeS₂@FGS as lithium-ion hybrid supercapacitor anode material.