Design Of Three-Dimensional Electrocatalytic Networks For High-Performance Lithium–Sulfur Batteries

Global energy requirements gradually increase and the reserves of traditional energy sources such as oil,coal,gas,etc.decrease,which leads to a large energy depletion and are unfavorable for the economic development.It’s urgently desired to attain renewable and clean energy sources,and exploit advanced energy storage accordingly.Li–S battery（LSB）is recognized as one of the most promising advanced energy storage systems due to its high energy density(2600 Wh kg^–1),low raw material consumption and long lifespan.Therefore,the research of LSB has attracted the ever-increasing attention of the industry and academia.However,some mechanism problems of LSB limit its commercialization process,mainly pertaining to nonconductive features of sulfur and lithium sulfide（Li₂S）,volume variation effect due to the density difference of sulfur and Li₂S,sluggish sulfur conversion reaction kinetics,the shuttle phenomenon of polysulfides（PS）occurring between cathode to anode.The afore-mentioned issues comprehensively cause to the low sulfur utilization efficiency,low discharge capacity as well as inferior cycling stability of LSB.In view of the existing problems,this dissertation aims at designing active cathodes and interlayers with the three-dimensional（3D）electrocatalytic networks.The active cathodes can make full use of their advantages in networks,free-standing and binder-free structures to elevate the electrochemical performance of LSB.And the functional interlayers can also realize the uniform distribution of electrocatalysts into the carbon architecture for effectively optimizing the LSB systems.The detailed investigation contents are summarized as follows:（i）The self-supporting carbon electrode with controllable defect density is used for LSB performance optimization.Combined with the wet chemical method,the density of carbon vacancy defects on the carbon electrode is adjusted to form the synchronization of the vacancy defect network and the conductive network,which not only reduces the shuttle effect of PS,but also accelerates the redox reaction kinetics of the nucleation and decomposition process of Li₂S,thus giving the battery a favorable electrochemical performance.Therein,the cell can still demonstrate a surface capacity of 8.5 m Ah cm^-2 under a high sulfur loaded of 11.1 mg cm^-2.The electrode has the following structural and performance advantages:realizing the regulation of vacancy defect density;the effective construction of a highly active three-dimensional electrocatalytic network was achieved;at the same time,the reasonable design of self-supporting and binder-free electrodes is realized.（ii）Successful growth of V₈C₇ active center on polyimide carbon aerogel functional interlayer by hydrothermal reaction and high temperature annealing V₈C₇active centers was designed by metal organic framework MIL–47（V）derivatization strategy.In this structure,the V₈C₇coating layer anchors PS through physical confinement and chemical adsorption,giving the carbon aerogel functional barrier a stronger ability to inhibit polysulfide shuttle and a higher electrocatalytic activity for sulfur conversion.At the same time,the unique three–dimensional network structure of the V₈C₇–coated polyimide carbon aerogel functional interlayer gives it excellent conductivity,which can accelerate the transport of ion electrons and thus accelerate the electrochemical reaction.The first discharge specific capacity was 1072.6 m Ah g^–1 at a current density of 0.2 C.The capacity was maintained at 90.7%with 100 cycles.