Application Of Spatially Separated Dual Carbon Materials In Metallic Lithium Anodes

Lithium-ion batteries(LIBs)have been widely used as energy storage devices, such as electric vehicles,drones,and portable electronic devices since the first commercialization in the early 1990s.However,conventional lithium ion batteries,fabricated from metal oxide positive electrodes and graphite negative electrodes,are unable to meet the current stringent requirements for the above applications due to their inherent limitations in theoretical capacity.Recently,emerging next-generation batteries such as lithium metal batteries(LMBs),all-solid lithium secondary batteries,and lithium-sulfur batteries have solved the above challenges by using Li metal as anodes.However,the problems limiting the development of lithium metal anodes are as follows:the growth of lithium dendrites;the low coulombic efficiency.This thesis mainly studies and constructs two three-dimensional(3D)frame protection structures:surface lithiophilic N-doped carbon spheres(NCS)and conductive acetylene black(AB);coral reef-like conductive polypyrrole and high mechanical oxidation zinc(PPy/ZnO)composite.The main contents are as follows:(1)Synergistic effect of spatially separated NCS and AB.AB has the lithiophobic surface,but the good electron conductivity.NCS has the lithiophilic surface,but the relatively poor conductivity.In this case,NCS provides a large number of nitrogenous and oxygenous functional groups,thereby adsorbing lithium ions,making the local electric field distribution uniform and inhibiting the formation of lithium dendrites;on the other hand,AB constructs a 3D conductive framework throughout the electrodes,promoting the reaction kinetics.The synergistic collabration of these effects improves the electrochemical performance so much that NCS+AB is able to display an average coulombic efificiency of 98.4%over 800 cycle at 1 mA cm-2 for 1 mA h cm-2.Even for 3.5 mA h cm-2,the coulombic efficiency is kept for 400 cycles,much better than those of NCS and AB alone.Substituting NCS and AB with alternatives with similar key features,such as OCS+AB(oxygen-doped carbon spheres and acetylene black),NCS+SP(nitrogen-doped carbon spheres and conductive carbon black),yields similar conclusions,indicating that it is the general strategy of Li anode.(2)By constructing an organic-inorganic composite material,that is,a polypyrrole zinc oxide composite material(PPy/ZnO)frame structure,the functional deficiency of a single material is compensated,and the electrochemical performance of the lithium metal negative electrode is improved.Here,the polypyrrole has favourable electrical conductivity,and the zinc oxide has good mechanical properties,effectively suppresses volume expansion,and collectively inhibits the formation of lithium dendrites.The PPy/ZnO composite is cycled for 150 times at the current density of 0.5 mA cm-2 with a capacity of 1 mA h cm-2.Therefore,the average coulombic efficiency is 97.3%before 150 cycles,which is much higher than the performance of copper foils.