The Preparation Of Germanium/reduced Graphene Oxide-based Composite Material And Its Lithium Storage Performance

Germanium(Ge)has attracted extensive attention as anode materials for Li-ion batteries(LIBs)because of its high theoretical capacity(1600 mA h g-1),high diffusivity(100 cm2 s-1),and high conductivity(2.17 s m-1).However,Ge undergoes large volume change vary during lithium getting off or in process,resulting in a rapid capacity fading and the difficulties in its research.Reduced graphene oxide owns high specific surface area and high electroconductivity,becoming a good substrate to manufacture nanocomposites.Regretfully,the reduced graphene oxide has low theoretical capacity when used for lithium ion batteries.While combined Ge nanoparticles with reduced graphene oxide-based,collaboration effect is able to occur and then the capacity is increased.The composites can both buffer the expansion of volume and the conductivity.Thus,they are desirable anode materials for high energy and power density lithium ion batteries.However,some researches have suggested that the production of well-dispersed Ge nanoparticles in a carbon network remains a challenge because of rapid grain growth during high-temperature thermal reduction.In my dissertation,we bring to facile strategies to synthesis Ge/Reduced graphene oxide-based composites with differ morphology and size.The composites are not only to solve the volumetric change,but improve its conductivity.Most importantly,it shows superior electrochemical performance.we report a PVP-assisted hydrolysis of wet chemistry approach for fabricating a Ge nanoparticles/reduced graphene oxide composite(called after Ge/RGO)made of?5 nm Ge nanoparticles that are uniformly distributed within a nitrogendoped RGO carbon matrix.The Ge/RGO composite exhibits an initial discharge capacity of 1475 mA h g-1 and a reversible capacity of 700 mA h g-1 after 200 cycles at a current density of 0.5 A g-1.Moreover,Ge/RGO shows a capacity of 210 mA h g-1 even at a high current density of 10 A g-1.The excellent performance of the Ge/RGO composite is attributed to its unique nanostructure,including Ge nanoparticles merely 5 nm,homogeneous particle distribution,and highly conductive RGO carbon matrix.we utilize freeze-drying technology and make polymer poly(vinylpyrrolidone)(PVP)as auxiliary reducer,leading the final product taking on germanium.PVP bounds germanium oxide growing into large size during freeze drying and achieves in situ N-hybrid in the course of thermal annealing process,resulting to hybridization of carbon with some nitrogen atoms(named as HC).Additionally,During freeze drying process,PVP can promote germanium oxide nanoparticles inserted uniformly into graphene oxide form a hierarchical nanostructure.In the process of thermal reduction,PVP decomposes to generate Nitrogen molecules,and graphene oxide(GO)is gradually reduced into graphene(RGO)simultaneously hybrid by N atom form N-hybrid carbon.Moreover,the germanium oxide turns into Ge completely,well encapsulated in as-formed HC buffers.The result is falling in line with expected,both the electronically conductivity and rate capability are greatly improved when being used as a negative material in LIBs.Or rather,in the preceding reports,none of researchers employ PVP as the auxiliary reducer in Ge-based anode materials,and this new strategy is quite feasible.It is skillful to use the azeotropic method fabricating porous germanium/reduced graphene oxide composite.The special technique of structure design avoids the precursors in phase separation when purified during the post-processing.Thus we are able to succeed to manufacture the porous germanium distributing uniformly into reduced graphene oxide.When it makes test the lithium storage performance,it can protect structural instability from causing properties attenuation too fast,guaranteeing the long circulating stably.