Preparation And Research Of Graphene Based Electrode Materials For Zinc Ions Energy Storage Performance

The rapid development of portable electronics and new energy industries has put forward higher requirements for the energy,power density and cycling life of electrochemical energy storage devices.Zinc ion capacitors（ZICs）have the characteristics of high theoretical capacity and safety,abundant zinc resources,being non-toxic and harmless,and are considered to be one of the most promising energy storage devices.To obtain the ideal ZICs with high energy,power density and long cycling life,it is important to select the right electrode materials and a reasonable material structural design.Graphene is one of the ideal electrode materials with high carrier mobility,large porous structured,excellent electrochemical and structural stability,and has attracted much attention in the ZICs research field in recent years.However,as a ZIC electrode material,graphene still has some drawbacks,such as easy stacking and agglomeration of sheets,low pore utilization,less effective specific surface area and a low specific capacity.Herein,to solve the problem of insufficient energy density and cycling life of ZIC,we have developed high-performance graphene-based electrode materials,employed flame reduced graphene oxide（FRGO）as the core material,and adopted strategies including material modification and structural designs.The structural characteristics of electrode materials,electrochemical reaction process,device performance and applications of the corresponding fabricated devices have been explored.The detailed research contents are as follows:（1）The 1,4,5,8-Naphthalenetetracarboxylic dianhydride（NTCDA）modified flame reduced graphene oxide（FRGO）film（N/FRGO）as a cathode with a high specific capacity,which is fabricated byπ-πnoncovalent interactions,and has abundant plicated nanosheets and fluffy pores to improve the interfacial contact performance,thus achieving sufficient ions storage areas.NTCDA molecules provide additional redox pseudocapacitance at the cathode,combined with Zn plating/stripping battery reaction,the N/FRGO based ZIC has achieved a high specific capacity of 217.0 m Ah g^-1 at 0.3 A g^-1.The maximum energy and power density were calculated to be 166.5 Wh kg^-1 and29.0 k W kg^-1,respectively.Moreover,the ZIC devices have realized the prominent capacity retention under different bending angles and presented high stability of 800bending cycles,and have promising applications in high energy density capacitors.（2）Combining the characteristics of the FRGO with fluffy structures,a compact freestanding graphene film with adjustable pore size was designed.By tuning the interlayer structure of FRGO using graphene oxides（GO）via a self-assembly strategy,a significantly improved volumetric energy density of ZICs was obtained.When the mass ratio of FRGO and GO is 75%:25%,the compact graphene film owns a bulk density of0.82 g cm^-3 and precisely regulated abundant mesoporous around 3.8 nm,which provides more active sites for ion storage.Profiting from the pseudocapacitance reaction between C=O and Zn²⁺,the compact graphene film with a thickness of 35μm as ZICs cathode has delivered a high volumetric energy density of 113.1 Wh L^-1 and outstanding gravimetric performance of 118.7 Wh kg^-1 with a bulk density of 0.95 g cm^-3,achieving the balanced gravimetric and volumetric characteristics.The ZIC electrodes have also presented a maximum volumetric power density of 21.2 k W L^-1 at 7.9 Wh L^-1 and 96.4%capacity retention after 8000 cycles,revealing an excellent compact energy storage effect.（3）FRGO@Zn anode was prepared on the surface of Zn foil by using porous FRGO as the ex-situ protective and regulated layer,which restricts the dendrite and side reactions,and significantly improves the cycling life and stability of ZIC.The FRGO possesses extensive nanoscale pores and zincophilic oxygen-containing functional groups,which can absorb Zn²⁺and preferentially nucleate on the surface of FRGO.The FRGO induces the growth of Zn parallel to the graphene sheet by matching the basal（002）plane of metallic Zn to minimize lattice strain.As a result,it has eliminated the tip effects and achieved a uniform and flat deposited Zn surface.The FRGO@Zn anode has significantly reduced the nucleation overpotential and improved the cycling life during the plating/stripping process.Notably,FRGO@Zn based ZIC has achieved 91.0%capacity retention after 20000 cycles at 5 A g^-1,and its capacity and maximum energy density were calculated to be 150.6 m Ah g^-1 and 118.8 Wh kg^-1,respectively.（4）The 3D porous Zn foam was used as the anode framework,and the FRGO@Zn foam anode was prepared by coating FRGO on the surface of Zn foam through a dipping strategy.The 3D porous structure of Zn foam can provide abundant Zn nucleation sites and reduce the overpotential of Zn nucleation.In addition,combined with the excellent adsorption and nucleation induction of Zn²⁺by FRGO,the grains can be refined to form a dense coating structure,which greatly improves the cycling life and stability of ZIC.The reversible regulation effect of FRGO on the formation/dissolution of basic zinc salt during the charge/discharge process was investigated,which inhibited hydrogen evolution and slowed down the growth rate of by-products.The symmetric cell based on the FRGO@Zn foam anode has a plating/stripping cycling life of more than 1800 h at 1m A cm^-2 and 1 m Ah cm^-2,while matching the compact graphene cathode achieved a high energy density of 118.4 Wh L^-1 and a capacity retention of 95.2%after 50000 cycles.This resulted in the long cycling life of ZIC with high energy and power density.