Preparation Of Graphene/metal Oxide Electrode Materials And Its Performance Of Lithium-ion Capacitors

As a new type of energy storage device,lithium-ion capacitors have attracted much attention due to the high power density of supercapacitors and the high energy density of lithium-ion batteries.Metal oxides are often used as lithium-ion capacitor anode materials due to their high theoretical specific capacity,but their dramatic volumetric changes during electrochemical reaction,which will cause the structural damage and greatly shorten the lifespan of capacitors,limits the application in lithium-ion capacitors.In this dissertation,with the aim of obtaining lithium-ion capacitors with high energy density,high power density and high cycle stability,the graphene/metal oxide anode materials are modified by hydrothermal or sol-gel method,while hydrothermal manganese oxide/graphene aerogels(HMnO/GA),sol-gel manganese oxide/graphene aerogels(SMnO/GA),tin oxide/expanded graphene(SnO2HG)anode materials are prepared and the electrochemical performance of half-cells and lithium-ion capacitors are researched.The specific research includes the following:(1)Hydrothermal manganese oxide/graphene aerogels(HMnO/GA)composites with three-dimensional porous structure were prepared by hydrothermal mthod and the optimal synthesis conditions were obtained by electrochemical characterization.As shown in results,the HMnO/GA8-3 prepared at the carbonization temperature of 800 0C and the Mn(NO3)2 content of 0.3 g exhibits the best half-cell electrochemical performance,the specific capacitor can reach 480 mAh·g-1 at the current density of 0.1 A g'1 after 100 cycles.The lithium-ion capacitor with LFP cathode and pre-lithiated HMnO/GA8-3 anode,which the pre-lithiation voltage was 0.15V,reaches the maximum energy density of 212.7 Wh·kg-1,and the maximum power density of 3000 W·kg-1.(2)The three-dimensional porous manganese oxide/graphene aerogels(SMnO/GA)composites were synthesized by one-step sol-gel method.It was found through the characterization that SMnO/GA has more ideal electrochemical performance that HMnO/GA with the same preparation conditionis.The SMnO/GA8-2 shows the highest electrochemical performance which the carbonization temperature is 800?and the mass ratio of Mn(NO3)2 and GO is 1:1,the specific capacity of such half-cell was 662.8 mAh·g-1 after 100 cycles at the current density of 0.1 A ·g-1.After that,the SMnO/GA8-2 was pre-lithiated and assembling LIC with LFP cathode.It shows that the SMnO/GA8-2P3//LFP with a pre-lithiation voltage of 0.15 V has the highest density of 194.1 Wh·kg-1 with the power density of 300 W·kg-1.(3)Layered tin oxide/expanded graphene(SnO2/HG)composites were synthesized by the hydrothermal method and the SnO2/HG-3 with 75 mL GO has the best half-cell performance.At the current density of 0.1C,the specific capacitor of SnO2/HG-3 can reach 1065 mAh·g-1 after 100 cycles.The LIC with pre-lithiated SnO2/HG-3 anode and LFP cathode were characterized,and SnO2/HG-3P3//LFP,which with a pre-lithiation voltage of 0.15 V,shows the best performance,the maximum power density and the maximum energy density is 3600 W·kg-1 and 202.2 Wh·kg-1,respectively.