Preparation Of GaN Based Nanomaterials For Lithium Ion Batteries

Lithium-ion batteries have a wide range of applications in energy storage areas.In recent years,the application of metal nitrides in electrochemical energy storage has received increasing attention.As the third-generation semiconductor material,the application of gallium nitride is currently concentrated in light-emitting devices,laser detection,and extreme condition electronics.Although GaN has good physical and chemical stability,it is seldom used in energy storage areas,due to its relatively low specific discharge capacity.Therefore,how to increase the discharge capacity of GaN has become the research priority under the premise of ensuring the cycle stability.In this article,the lithium storage performance of GaN is improved through the introducing of defects,the compounding of carbon-based conductive materials,and the controlling of morphology.On this basis,the mechanism of the lithium storage and the pseudocapacitance characteristic of GaN are researched thoroughly.This will provide new ideas for the application of third-generation semiconductor materials represented by GaN in electrochemical lithium storage field.The specific research content is as follows:1.GaN nanoparticles were prepared by direct ammonia calcination,and defective GaN nanoparticles were obtained by extending the ammoniating time.Theoretical calculations showed that the presence of defect energy levels at the Fermi level of GaN,because of the introduction of defects.HRTEM directly observed that the outer layer of GaN lattice consists of a transition layer and amorphous layer.XAFS and Raman results directly indicated the presence of defects.UV-vis result revealed defective GaN nanoparticles had a narrower band gap comparing with conventional GaN nanoparticles.EIS result demonstrated that defects enhanced the conductivity of GaN nanoparticles.Electrochemical analysis showed that defective GaN nanoparticles exhibited good rate performance and cycling performance.2.Fully utilizing the adsorption property of reduced graphene oxide(rGO),GaN/rGO nanocomposites were prepared by hydrothermal and ammonia calcination methods.XRD and Raman results demonstrated the presence of graphene,and XPS measurements showed the bonding between graphene and GaN nanoparticles.At the same time,XAFS results showed that the as-obtained GaN nanoparticles had defects.As anode material for lithium ion batteries,GaN/rGO nanocomposites exhibited good discharge specific capacity and cycle stability.In addition,GaN/rGO nanocomposites also exhibited super full cell performance as negative electrode.3.To further increase the specific surface area of GaN,GaN nanowires were in situ prepared on the conductive graphite layer by chemical vapor deposition process.XRD and Raman results showed that GaN nanowires had good crystallinity,and conductivity test of single GaN nanowires showed the good conductivity.Electrochemical results showed that the synergistic effect between GaN nanowires and conductive graphite layer endowed the composite electrodes exhibited excellent electrochemical performances.The analysis based on electrochemical kinetics revealed the relationship between the capacitive capacity and the solid phase diffusion capacity of GaN nanowires,and the proportion of capacitive capacity was accurately calculated.Improved extrinsic pseudocapacitive contribution-was demonstrated as the origin of fast kinetics.The kinetics analysis and electrochemical reaction mechanism of GaN with Li+ was also revealed by ex situ XRD,HRTEM and XPS measurements.Ex situ results indicated the good electrochemical performance of GaN nanowires was derived from the reversible intercalation/deintercalation mechanism(GaN + xLi+ xe(?)LixGaN).4.In order to further enhance the electrochemical performance of GaN,a simple but efficient method was designed to prepare two dimensional GaN nanosheets using GO as a template.Because of the highly hydrophilic nature,and oxygen-containing functional groups with strong affinity to the inorganic ion,GO sheets can be used for superior 2D template to guide and stabilize the preparation of the 2D structure.AFM and TEM results showed the 2D characteristics of GaN nanosheets.XRD,Raman,and XAFS results revealed the structural differences between GaN nanosheets and conventional powder GaN.More importantly,this method is free from the dependence SiC substrate of the MEEG method,and avoiding the covalent bonding between the GaN nanosheets and the SiC substrate.Electrochemical results showed that GaN nanosheets exhibited good electrochemical performance,originating from the unique structural advantages.