Preparation Of Three-Dimensional Lithium-Ion Battery Composite Electrodes And Their Electrochemical Properties

Li-ion batteries have been broadly applied in the electric vehicles and portable electronics because of their advantages including high energy conversion efficiency,high working voltage,low self-charging efficiency,and non-memory effect,etc.Currently,the poor performance of electrodes including the low capacity and energy density,and poor stability,greatly restricts the further development of Li-ion batteries,and thereby limits the development of electronics and new-energy vehicles.Since that,fabricating high-performance electrode materials has become a significant research direction,and it is also a hot research topic currently.In this thesis,high capacity and energy density three-dimensional composite electrodes including both anode and cathode were investigated.The preparation methods and lithium storage properties of the composites have been investigated comprehensively.Some high-capacity and stable anodes and cathodes have been prepared,which provide some promising materials and technologies for the development of high-performance Li-ion batteries.The main research contents and novelties are as follows:?1?A Li₃V₂?PO₄?₃/reduced graphene oxide?rGO?composite cathode was prepared using a route combining with the ball-milling process and hydrogel assisted hydrothermal synthesis.The Li₃V₂?PO₄?₃/rGO exhibits high energy density and stability at both potential windows of 4.3–3.0 V and 4.8–3.0 V.The Li₃V₂?PO₄?₃/rGO cathodes show capacities of¹01 mAh g^–1after 500 cycles over the range of 4.3–3.0V,and 79 mAh g^–11 after 100 cycles over the range of 4.8–3.0 V,which exhibit energy densities of 374 and 286 Wh kg^–1,respectively.The composite cathodes show much improved capacity retention at a temperature of–5°C,compared to the pristine Li₃V₂?PO₄?₃.The enhanced electrochemical performance is attributed to the improved electron transfer by rGO coating.This mechanism is also supported by the I-V curve test calculations.?2?A novel three-dimensional?3D?particle-embedded Li₂MnSiO₄/C cathode composite was synthesized by the template method,which greatly increased the loading of the active materials.The Li₂MnSiO₄/C composite exhibits a capacity of about 181 mAh g^–1for the first cycle at a rate of 0.1C over the voltage range of4.8–1.5 V,and the energy density is 688 Wh L^–1.After 50 cycles,the capacity of the composite still reaches 98 mAh g^–1.In addition,Li₂MnSiO₄/C composite cathode also shows good cycling capacity at–5°C and 50°C,respectively.?3?A TiO₂/Ge composite anode was prepared by using a nickel foam as the substrate and pre-fabricated ZnO nanowire arrays as sacrificial templates.The TiO₂/Ge anode exhibited a stable capacity of 1071 mAh g^–1at 0.1C after 130 cycles.In addition,the composite exhibits good electrochemical performance at the low temperature of–5°C.It was found that TiO₂ tube array provided buffer space for the volume expansion of supported Ge nanoparticles during charge-discharge.In Situ TEM analysis also showed that the structure of the electrode remained stable after cycles.