Interface Material Design Of Lithium-sulfur Batteries And Three-phase Interface Simulation Study

The electrochemical performance of chemical power source is closely related to the electrode/electrolyte interface process,involving steps such as charge transfer,Gas diffusion,phase formation and transformation,and ion transport.Therefore,a deep understanding of the interface process is of great significance to device design and material optimization.In addition,the battery contains not only the interface between the electrode and the electrolyte but also other important interfaces,such as the three-phase interface in the catalytic layer of the fuel cell,the interface between the current collector and the electrode.Based on this,this paper explores the corresponding interface problems of the battery,and carried out the following two tasks:On the one hand,in order to solve the problem of the shuttle of polysulfides at the electrode/electrolyte interface in lithium sulfur batteries,tetraamino zinc phthalocyanine（Zn TAPc）was grafted onto modified carbon paper（CP）through amidation reaction to construct a"philic-polysulfide interface"as a carrier for lithium sulfur battery cathode materials to ease the shuttle of polysulfides.By means of XPS and FT-IR characterization,it was found that Zn TAPc and modified CP were linked by amide bond.The large conjugated system of Zn TAPc can provide a high electron cloud density environment,which was beneficial to improve the electron transport ability,and the central nitrogen atom can inhibit the shuttle of polysulfides through chemical adsorption.The good compatibility of the side chain Zn TAPc with the electrolyte can accelerate the wetting speed of the electrolyte to the matrix material,thereby accelerating the Li⁺transport at the solid-liquid interface and improving the battery dynamics.Electrochemical tests show that the lithium-sulfur battery based on Zn TAPc-CP/S positive electrode can establish an initial discharge specific capacity of 1018.5 m Ah g^-1at a current density of 0.5 C,and maintains a reversible capacity of 822.9 m Ah g^-1 after200 cycles;at a high current density of 2.0 C.After 500 cycles,the capacity retention rate was 65.5%,corresponding to a low capacity attenuation of 0.069%per cycle,showing good electrochemical performance.On the other hand,due to the complex internal structure of the catalytic layer and various influencing factors of physical and chemical changes,coarse-grained molecular dynamics（CG-MD）was used to simulate a set of research models for three-phase interfaces:CO₂,H₂O,polypropylene（D-PP）/Si O₂（Si O₂ with different wetting degrees:D-Si O₂ M-Si O₂ W-Si O₂）to simulate the transport and aggregation behavior of H₂O and the diffusion characteristics of gas.Meanwhile,the models were calculated based on Martini force field,which were in accordance with the experimental results Through the analysis of the diffusion coefficient and the number of bubbles,the diffusion coefficients of H₂O,CO₂ and H₂O at the interface in the system on D-PP were all greater than those of Si O₂ at different wettability levels,and the diffusion coefficient of H₂O at the interface of D-PP is the largest;The experiment of recording the number of bubbles showed that the larger the CO₂ diffusion coefficient,the more favorable the formation of more bubbles.On the other hand,the radial distribution function was used to analyze that the strength of H₂O at the interface and the interfacial force would affect the aggregation position of H₂O at the interface,and the interaction order of interface of D-PP,D-Si O₂,M-Si O₂,W-Si O₂ and H₂O was verified by the contact angle test.