Research group of Professor Zhang Huigang of Nanjing University: Design of sulfur positive electrode in micro nano reactor with ni2co4p3 catalyst

Lead lithium sulfur battery has attracted more and more attention because of its high theoretical energy density (2600 wh kg − 1), environmental friendliness, low price and abundant sulfur reserves However, the shuttle effect of the intermediate product polysulfide (Li 2S n, 4 ≤ n ≤ 8), the insulation property of the charge and discharge products and the slow dynamic transformation seriously hinder the further commercial application of lithium sulfur batteries, which needs to be solved urgently How to speed up the conversion of polysulfides to improve the utilization rate and rate performance of active materials while limiting the diffusion of polysulfides is a challenging problem Recently, Professor Zhang Huigang's research group of Nanjing University has made a new breakthrough in this field (adv funct Mater 2019, DOI: 10.1002/adfm.201906661) Brief introduction of Professor Zhang Huigang Professor Zhang Huigang was engaged in postdoctoral research in UIUC Department of materials science and Engineering in 2007 The research content mainly focuses on "thermal photovoltaic", "electrocatalysis" and "Application of three-dimensional structured electrodes in lithium-ion batteries" In 2012, he obtained commercial investment and established xerion advanced battery Corp based on his patented technology, and held the position of senior scientist in the company He developed lithium-ion rechargeable batteries with high energy density and high power density Dr Zhang Huigang published many articles in Nature journal, nano letters and other journals, and applied for three patents in the United States and the world In 2013, he was selected into the fifth group of young thousand talents program of the Organization Department of the Central Committee, and in 2014, he joined the Department of energy science and engineering of the College of modern engineering and applied sciences His research direction is mainly chemical energy storage and electrocatalysis Cutting edge scientific research achievements: in the early work of the design of sulfur positive electrode of micro nano reactor supported with Ni 2CO 4P 3 catalyst, Professor Zhang Huigang's research team developed a kind of polar co 3S 4 nanotubes (nano energy 2017, 37, 7-14) with a network structure for the adsorption of polar polysulfides and the inhibition of their diffusion On this basis, considering the polarity difference between sulfur and polysulfide, the research team first used Staphylococcus aureus as the initial structure and proposed a "bionic" bipolar anode (adv energy mater 2018, 1702373) On the one hand, the biological carbon sphere containing nitrogen element has a multilayer structure inside, which can fix sulfur in it; on the other hand, the external TiO2 acts as a polar adsorbent and catalyst, which can adsorb polysulfide, reduce its dissolution and "shuttle" Figure 1 Schematic diagram of the mechanism of the catalytic process of cation doping regulating d-band (source: adv funct Mater.) however, lithium sulfur catalyst Most of the studies are focused on the macro level of polar adsorption The common characterization means of catalytic performance is to observe the changes of current response and cyclic voltammetry voltage characteristics in soluble polysulfide electrolyte, which lacks the understanding of the relationship between electronic structure characteristics and catalytic performance from the molecular level On the basis of previous work, the author designed transition metal doped catalyst by theoretical calculation and experimental method, regulated the interaction between metal d-band and sulfur 3P, studied the mechanism of catalytic process, and prepared high activity polysulfide conversion catalyst (Figure 1) Figure 2 Characterization of catalytic performance after cation doping (source: adv funct Mater.) the author took Ni 2p as the research object, doped transition metal co element, and studied the catalytic performance before and after doping (Figure 2) Through the cyclic voltammetry (CV) test of symmetrical cell, it is found that cobalt doping has a higher current response, which indicates that cobalt doping catalyzes the conversion process of polysulfide This characterization can be relatively simple to judge the catalytic performance, but no specific kinetic parameters are given On this basis, the activation energy barrier of the reaction process can be calculated by CV test The author also studied the nucleation process before and after CO doping, and found that after CO doping, the surface of Li 2S nucleated more, so it had better catalytic effect Figure 3 Study on the catalytic mechanism after cation doping (source: adv funct Mater.) in order to understand the difference in catalytic performance caused by CO doping at the molecular level, the author analyzed the partial wave density of state (PDOS), d-band center, charge difference density and overlapping orbit distribution before and after doping through the first principle calculation Distribution (coop) (Figure 3) The results show that cobalt doping makes the d-band center move up, strengthens the 3P orbital interaction with sulfur, enhances the adsorption, and weakens the S-S bond in polysulfide, thus catalyzing the conversion process of polysulfide Figure 4 Construction and characterization of sulfur positive electrode in micro / nano reactor supported with Ni 2CO 4P 3 catalyst (source: adv funct Mater.) efficient catalyst is very important to improve the performance of lithium sulfur battery Meanwhile, in order to build better lithium sulfur battery to adapt to the high load sulfur positive electrode, the author designed a kind of Ni 2CO 4P 3 Nanowire is used as a micro nano reactor of catalyst (Fig 4) to maximize the effectiveness of catalyst The composite structure of Ni 2CO 4P 3 nanowire is rooted on the metal conductive framework, which is conducive to unfolding the metal structure, maximizing the electronic conduction and charge transfer, while the nanowire has high catalytic activity, thus greatly improving the polysulfide conversion reaction Figure 5 Electrochemical performance test of sulfur positive electrode in micro nano reactor (source: adv funct Mater.) the author tested the electrochemical performance of sulfur positive electrode in micro nano reactor (Figure 5) It was found that when the sulfur loading amount was 5 mg cm − 2, the specific capacity was 1223 Mah G − 1 at 0.1 C ratio, and could still be kept at 1110 MAH g − 1 after cycling 100 。 When the load reaches 25 mg cm − 2, the specific discharge capacity of 413 MAH g − 1 can still be obtained after 150 cycles, which shows excellent electrochemical performance Figure 6 Visualization of polysulfide diffusion and surface analysis of lithium anode after cycling (source: adv funct Mater.) finally, the author carried out visualization experiments on polysulfide diffusion during the discharge process, and the sulfur positive pole of micro nano reactor can effectively block the dissolution and diffusion of polysulfide At the same time, the surface analysis of lithium metal after circulation shows that the application of micro nano reactor avoids the reaction of polysulfide diffusion to lithium anode and lithium metal Conclusion: the interaction between metal d-band and sulfur 3P was regulated by doping transition metal cations The mechanism of the catalytic process was studied and a high activity polysulfide conversion catalyst was prepared Furthermore, in order to realize the application of sulfur with high load, the sulfur positive electrode of micro nano reactor is constructed, which can still charge and discharge effectively under the condition of ultra-high load In this work, the reaction mechanism of lithium sulfur catalyst was studied theoretically from the molecular level, and the relationship between the electronic structure and catalytic properties of the catalyst was constructed, which is conducive to the design of catalyst materials for lithium sulfur battery.