Preparation Of Lithium Battery Composite Electrode Materials With Microcapsule Structure And Their Electrochemical Energy Storage Properties

One of the urgently needed subject in battery field is high energy density lithium battery.At present,the high energy density lithium battery is limited by lithium ion battery anode materials because of its low capacity.However,the negative electrode materials with high theoretical capacity often have large volume changes in charge and discharge process,and the electrode is easy to pulverize and break,which leads to the rapid attenuation of battery capacity.Lithium-sulfur batteries with high theoretical energy density have attracted much attention due to the rapid development in recent years,but the problems such as large volume change of sulfur,low coulombic efficiency and"shuttle effect"during cycling have always restricted the industrialization development of lithium-sulfur batteries.At present,the market scale of various electronic consumer products and electric vehicles is expanding,and the development of high performance energy storage materials has become the hotspot of research.This paper designs a series of composite electrode materials with microcapsule structure based on the oil-in-water emulsion system,which effectively improves these problems existing in the electrode materials of lithium batteries.Related research work includes:?1?Micro-capsules filled with silicon?Si?nanoparticles were prepared by a oil-in-water emulsion system.The microcapsules leave enough space for Si volume changes when used as a negative electrode for lithium batteries during lithiation and delithiation;the active Si particles are protected by shell from reducing material losses and avoiding some side reactions;the conductive shells improve the conductivity of the composites effectively.It was found that the as-prepared silicon-filled carbon capsule-based anode exhibited excellent electrochemical performance including stable capacity and high rate performance.The battery capacity remained at 1100 m Ah g-1with coulombic efficiency?99.9%after 500 cycles at a current density of 1.9 A g^-1.At the same time,we also studied the mechanical stability of silicon in capsules by density functional theory simulation and in situ transmission electron microscopy.?2?A simple oil-in-water emulsion strategy was proposed to prepare tin?Sn?nano-flower-filled microcapsules.The stable carbon shell of capsule effectively reduces the crushing of the encapsulated Sn nanostructures.The voids inside the capsule provide an effective space for the volume change of tin during lithiation-delithiation,which is beneficial to improve the electrochemical performance of the capsule negative electrode.The kinetic and lithium-ion diffusion studies during charge/discharge processes suggest that carbon microcapsules provide a suitable environment for electron and lithium ion transport.Tin filled microcapsules exhibits a excellent capacity of 800 mAh g^-11 after 200 cycles at 0.38 A g^-1,and the electrochemical performance remains stable after three rounds of rate testing.?3?Co@CNTs@C/S composites with new microcapsule structure were prepared through a oil-in-water emulsion system.The 3D hollow structure encapsulated with CNTs can effectively accommodate and adsorb sulfur,reduce the shuttle dissolution of polysulfides during charge/discharge,and improve the loading and utilization of sulfur.In addition,the conductivity of the composites is also improved by the carbon layer and CNTs of microcapsule.Therefore,the cycling stability and rate performance of the battery are greatly improved.The sulfur content of the cathode material can reach 65.5 wt%,which shows a stable performance with a high capacity of 581 mAh g^-1 after 500 cycles at 0.1 C.