Research Of Graphene Encapsulated Metal Nanoparticles

As a lithium-ion battery anode material,nature graphite is very appropriate for its flat charge/discharge plateau,high theoretical lithium intercalating capacity and structural stability.Itswide source and low price make it more popular and now its commercialization is almost mature.However,its interlayer bonding energy is small and the layers are easy to exfoliate in the process of charge-discharge cycles,leading to poor cycle performance and short service life of the battery,the charge-discharge performances at large current is also not satisfied.The defects of natural graphite have affected the further application of it as an anode material for lithium ion batteries.In this case,the appropriate expansion of the graphite layers is helpful.Graphene encapsulated metal nano-particles（GEMNPs）is a composite material formed by embedding the nano scale metal particles into the graphite carbon network.Its appearance is flaky or scaly with a two-dimensional structure and the particles of metal are in shape of two or quasi-two dimension.Dozens of synthetic methods for its precursor,graphite intercalation compounds（GICs）,have been developed from 1841,but these methods are criticized for long reaction time,imperfect product structure,high cost and low production cost.The expanded graphite,spherical graphite and copper chloride were used to prepare CuCl₂-GICs and the quantities of synthesized samples could reach 100 grams.Circumfluence liquid-phase reduction was used and the pure sample of graphene encapsulated copper nano-particles（GECNPs）could be prepared under a facile reaction condition.The component,morphology structure and stability of the CuCl₂-GICs and GECNPs were characterized via XRD,SEM,TEM,and Raman spectrum measurements.The results showed that the structures of CuCl₂-GICs and GEMNPs are both different under graphite and copper chloride molar ratio and firing temperature.The shape of GECNP was little lamina and the particles of copper was two or quasi-two dimension with a size of about 25 nm.Under nitrogen atmosphere,GECNPs had evident steady calorific.Conductivity test results showed that conductivities of CuCl₂-GICs were higher than that of its corresponding raw graphite;conductivities of GECNPs were lower than the corresponding precursor CuCl₂-GICs;conductivities of SGECNPs were higher than that of EGECNPs.The first charge-discharge efficiency of lithium-ion batteries which with SGECNPs sample Q1-Q3 as anode material was respectively 78.6%,70.92% and 70.17% and the first charge capacity was 284.8mAh/g,314.7mAh/g and 235.9mAh/g.After 100 cycles,the specific capacity of batteries Q1-Q3 was reduced by 0.37%,1.14%,0.69%.The capacity and cycle performance were satisfied at the charge and discharge rate of 0.5C,1C and 5C.These results indicated that the structure of EGECNPs was very stable during the cycle charge-discharge,which can improve the stability of the lithium-ion battery and prolong its service life;lithium ion fast diffused between the GECNPs layer and its charge-discharge performance was also good even under a large current.