Preparation And Investigation Of Transition Metal Based Electrode Materials For Lithium Secondary Batteries

As one of the main energy storage devices,lithium-ion batteries have been widely used in kinds of portable electronic devices,electric cars,aerospace and other fields of high-density storage due to their high energy/capacity density,low self-discharge rate,no memory effect and toxic free properties.However,with the development of electronic industries and electric cars,how to exploit more efficient energy storage devices to satisfy the daily increasing storage needs is a challenging thing that we confront now.To achieve more efficient energy storage,on one hand,we can continue investigating the potential of lithium-ion batteries,for example,exploiting anode materials with higher lithium storage capability,on the other hand,we can also continuously develop new energy storage systems,such as lithium-sulfur batteries,lithium-air batteries,etc.,to achieve the essential breakthrough of energy storage.Herein,in view of the above two aspects,we synthesized the transition metal carbide anode material for lithium ion battery with excellent storage performance and the transition metal complex cathode material for Li-CO2 battery with highly catalytic activity,respectively.Through optimizing the morphology,structure,electronic conductivity and specific surface area of these transition metal materials thoroughly,the electrochemical performances of these materials in the battery have been largely improved.The main research contents of this thesis are listed as follows:1)We selected dopamine(PDA)as the carbon source,and synthesized Mo/PDA precursor by its chelation with MoO43-ions in a weak base environment.After calcining at high temperature,the molybdenum carbide microflower(?-MoCi-x on N-doped carbon microflowers,?-MoC1-x/NCF)with hierarchical self-supporting structure was finally obtained.This hybrid takes carbon microflower as the whole structure skeleton,while ?-MoC1-x nanoparticles are evenly dispersed on the carbon skeleton.Thanks to the synergy effect between ?-MoC1-x nanoparticles and 3D micro-carbon skeleton,?-MoC1-x/NCF hybrid exhibits excellent electronic conductivity,superior lithium storage activity and the ability to buffer volume change.Finally,the lithium-ion batteries exhibit good specific capacity(>1000 mAh/g),excellent cycling stability(over 300 cycles at 1 A/g)and rate capability(the specific capacity remains at 420 mAh/g when the current density is 10 A/g).2)To solve the problems of electrode-surface passivation and electrolyte decomposition caused by the irreversible decomposition of Li2CO3 in Li-CO2 batteries,a facile microwave method is developed to synthesize conjugated cobalt phthalocyanine(CoPPc)as the cathode catalyst of Li-CO2 batteries.The electrochemical test results suggest that the CoPPc polymer has highly catalytic performance to the reversible composition and decomposition of Li2CO3,thus the polarization has been effectively reduced and the coulombic efficiency in first several cycles has also been largely improved.Compared with previous reports about Li-CO2 batteries,the batteries here exhibit significantly increased areal specific capacity and enhanced cyclic stability.In addition,owing to the elastic and reprocessable property of the polymer,we fabricated flexible Li-CO2 batteries with excellent cycling performance and foldable properties.