Preparation And Lithium Storage Performances Of Graphene/Metal Selenides(Oxides)

Lithium-ion batteries have become an indispensable part of our daily lives,thus the research of battery anode materials has become a hot research topic.Chalcogenides are a kind of promising anode materials for lithium-ion batteries owing to their high conductivity,large capacity and fast ion transportation.In addition,they have abundant valence states which are favorable for charge storage.In this thesis,Ni Co₂O₄,Ni Se₂ and Co Se₂ based composites were designed and synthesized.Their electrochemical lithium-ion storage performances were also investigated in detail.The main contents of the thesis are as follows:Fe doped NiCo₂O₄(NiCoFeO)was synthesized through solvothermal approach and ion exchange,followed by high-temperature calcination.The content of doped iron element was optimized by changing the reaction time.In order to improve the conductivity of Ni Co Fe O,graphene nanosheets(RGO)were introduced to further improve the electrochemical performances.Electrochemical measurements demonstrate that the composite with graphene content of 5 wt.%exhibits excellent lithium storage performances compared with the other samples.The resultant composite achieves high specific capacity(1204 mAh·g^-1 at 0.1 A·g^-1)and excellent rate capability(978 mAh·g^-1 at 5 A·g^-1)as well as remarkable long-term cycling stability(1083 A·g^-1 after 100 cycles at 0.5 A·g^-1)with the capacity retention ratio of 99.5%.RGO/Ni_0.9Co_0.1Se₂-10 composite was synthesized by a solvothermal approach with hydrazine hydrate as the reducing agent and selenium powder as selenium source.The effect of the content of Co element and RGO on the electrochemical lithium-ion storage performances of the Ni Se₂ were investigated in detail.The RGO/Ni_0.9Co_0.1Se₂-10 composite with graphene content of 10%displays superior lithium-ion storage performances when serving as anode material for lithium-ion batteries.The composite exhibits high reversible capacity of996 mAh g^-1 at 0.1 A g^-1 and maintain 589 mAh g^-1 even at 0.5 A g^-1.Moreover,the RGO/Ni_0.9Co_0.1Se₂-10 shows high reversible capacity of 1120 mAh g^-1 after 200 cycles at0.2 A g^-1 with capacity retention ratio of 115.9%.RGO/Co_0.9Fe_0.1Se₂-10 composite was synthesized by solvothermal approach.The influence of doped Zn,Cu and Fe elements on the electrochemical performance of Co Se₂ was investigated.The as-obtained RGO/Co_0.9Fe_0.1Se₂-10 with RGO content of 10 wt.%displays high capacity of 882 and 629 mAh g^-1 at 0.1 and 0.5 A g^-1,respectively.Furthermore,the RGO/Co_0.9Fe_0.1Se₂-10 composite also exhibits outstanding long-term cycling stability with reversible capacity of 1936 mAh g^-1 after 100 cycles at 0.2 A g^-1.