Study On The Preparation And Performance Of Metal Oxide Lithium Battery Anode Materials

Due to the characteristics of high energy density and operating voltage,low self-discharge rate,environmentally benign,the applications of Li-ion batteries(LIBs)have extended from the traditional portable electronics to novel electric vehicles and stationary energy storage.However,the low capacity of the widely used commercial graphit anode has nearly approached its theoretical level and is presently far from the ever-growing energy and power density demands of these new applications.Also,the flammable graphite is also a potential safety hazard of LIBs.Therefore,it is an urgent task to developing novel anode materials with higher energy density,longer cycling life and higher safety.Because of their high theoretical capacities,wide availability,and easy preparation,transition metal oxides(TMOs)are regarded as one of the most promising anode materials to replace graphite.But the TMOs anodes are limited in poor electrical conductivity and huge volume changes during lithiation-delithiation process that directed to poor cycling stability and rate capability.These drawbacks inhibit the commercial applications of TMOs.The documents indicate that the weak point of TMOs can be greatly improved by nanocrystallization,morphology control and hybrid-composites.This thesis fabricates a series hierarchical porous TMOs anode materials.These TMOs anode materials exhibit enhanced performances of electrochemical lithium storage due to the features of multi-component and the co-existance of micro-and nanostructure.(1)Microspheres that are assemblied by ZnO nanosheets are readily grown on nickel foam through simple hydrothermal reactions.The microspherical morphology sustains after heat treatment.The electroactive materials are tightly integrated by nickel foams.When used as anode materials of lithium-ion battery,the nickel networks bestow the materials greatly enhanced conductivity and abundant large pores.The problems of inhomogeneous non-conductive binder and conductive carbon black is facilely overcome by using the integrated materials as the electrode.These features render the batteries high specific capacity and improved rate performances.The materials exhibited a high initial specific capacity of 1118 mAh·g-1 at a current density of 100 mA·g-1.After 100 charge-discharge cycles,a capacity of 532 mAh·g-1 sustains with a Coulombic efficiency of 98%.(2)Microspherical assemblies of Ce modified ZnO nanosheets are easily grown on the surface of nickel foam by hydrothermal method.The spherical shape maintains after heat treatment.The presence of Ce element improves the cycling stability and rate properties when the materials are used as anode materials of LIBs.The Ce modified materials deliver a high initial specific capacity of 1234 mAh·g-1 at a current density of 100 mA·g-1.After 140 cycles,the capacity remained at 635 mAh·g-1 with a Coulombic efficiency of 98.4%.(3)Porous ZnCo2O4 microspheres were readily fabricated by calcining Prussian blue analogue(PBA)Zn3[Co(CN)6]2·xH2O at different temperatures.These ZnCo2O4 microspheres were assemblies of lots of nanoparticles of tens of nanometers in the size.The accumulation of the nanoparticles generated numerous interconnected mesopores and macropores.Elevating the heating temperature aroused an enhanced crystallinity and the grain growth of the nanoparticles that directed to the enlargement of the pore size.When used as anode material for Li-ion batteries,the porous ZnCo2O4 microspheres sintered at 550 ? exhibited a high initial specific capacity of 1737.1 mAh·g-1 at a current density of 100 mA·g-1.The sustained discharge capacity of 1051.6 mAh·9-1 after 100 charge-discharge cycles implied the excellent cycling stability at a current density of 100 mA·g-1.The present materials also exhibited a superior rate performance.Elevating the discharge rate had little effect on the cycling stability.The discharge capacity of 733.3 mAh·g-1 remained after 100 cycles at a current density of 500 mA·g-1.The improved battery performances originated from the porous structures.The abundant pores facilitated the diffusion of electrolytes and the migration of Li+ cations.The large pore volumes also contributed enough inner spaces to alleviate the stress that occurred by volumetric expansion and contraction during the charge-discharge process.(4)Two types of nickel-cobalt sulfides with Jellyfish shape and flower-like morphology are readily prepared with or without the addition of surfactant by simple hydrothermal process.Used as anode materials of LIBs,the electrochemical properties are investigated within the working voltage of 1.0-3.0 V by using ether electrolytes.Due to the co-contribution of Ni and Co cations with different valents and the good compatibility of sulfides and ether electrolytes,the synergetic effect of the bimetal sulfides exhibit good cycle stability and rate performance.After 200 charge-discharge cycles at a current density of 100 mA·g-1,the Jellyfish shaped Ni1.5Co1.5S4 anode still delivers a capacity of 390 mAh·g-1.A residual capacity of 405 mAh·g-1 sustains for the flower-like Ni1.5Co1.5S4 anode.