From China:Lithium sulfur battery practical multifunctional diaphragm: back from the dead

Lithium-sulfur batteries with high specific energy characteristics are expected, but the “shuttle effect” caused by polysulfide dissolution reduces the cycle performance of the battery, especially when the positive electrode has a high sulfur load. Through increasing modification on the diaphragm can limit the effects of polysulfide shuttle to a certain extent, but only if the introduction of modified materials have adsorption function, is more and more sulfur will be gathered in the so-called “death of sulfur” is formed on the diaphragm, which reduces the electrochemical capacity directly outside and further hinder the lithium ion transport, the more obvious attenuation performance. On the other hand, membrane modification materials tend not to have electrochemical activity on their own, which also reduces the inherent mass and energy density of the battery. Therefore, the ideal membrane modification material should meet the following requirements :(1) effectively inhibit the polysulfide shuttle effect; (2) it has electrocatalytic activity and can promote the adsorption of polysulfide to continue to participate in the electrochemical conversion reaction; (3) It has high electrochemical activity and can contribute to the reaction; (4) The modified layer formed should ensure high lithium ion transmission efficiency.

[Job Description]
Recently, “A Sustainable Multipurpose Separator” was published on Advanced Energy Materials, an international top journal in the field of Energy Materials by Prof. Guoran Li of Nankai University, Prof. Kai Xi of Xi ‘an Jiaotong University, Prof. Huanglong Li of Tsinghua University and Dr. Bowen Li Directed Against the Shuttle Effect of Polysulfides for High-performance Lithium — Sulfur Batteries A new type of multifunctional diaphragm se0.06SPAN /MMT@PP (Selenium-doped sulfide polyacrylonitrile/montmorillonite/commercial polypropylene diaphragm) for the shuttle effect of lithium-sulfur batteries is reported. Commercial carbon material (BP2000) and sulfur compound are used as sulfur anode, and lithium metal is used as negative electrode. The stable cycle of high capacity lithium-sulfur battery was realized under practical test conditions. In the 1000 cycle, the average capacity decay rate is only 0.034%, and the ultra-high area capacity performance (33.07 mAh cm-2) can be achieved under high sulfur load (26.75 mg cm-2) and low electrolyte dosage (4.5µL mg-1). Moreover, the diaphragm is made of continuous coating by industrial coating machine, which has good mechanical strength, chemical stability and can be reused for many times, showing good practical potential. Dr. Wei Wang, PhD candidate from Nankai University, Dr. Kai Xi from Xi ‘an Jiaotong University and Dr. Bowen Li from Tsinghua University are the co-first authors of this paper, and Professor Guoran Li from Nankai University is the corresponding author.

The experimental and theoretical results of this study show that SE0.06span /MMT can effectively inhibit the polysulfide shuttle, and it has high catalytic activity and low lithium ion diffusion barrier, which can not only promote the transition of polysulfide to Li2S during the discharge process. It can also reduce the decomposition barrier of Li2S to Li2Sx conversion during charging process, and effectively promote the activation of “dead sulfur”. In addition, the lithium product (LixSE 0.06SPAN) can also catalyze the conversion of polysulfide. Unlike traditional diaphragm trims, SE0.06SPAN /MMT has both electrocatalytic and electrochemical activity, effectively improving battery performance. Under the conditions of 26.75 mg cm-2 high sulfur load, 4.5µL mg-1 poor electrolyte and 3.2 low N/P ratio, the ultra-high area capacity of 33.07 mAh cm-2 was achieved. In addition, the modified diaphragm shows excellent physical and electrochemical stability, and the assembled soft-pack battery can also continuously power under different bending states, showing a high practical prospect.

FIG. 1 Se0.06SPAN/MMT@PP diaphragm structure and working principle schematic diagram.

[Content Description]
PAN/MMT was prepared by in-situ polymerization of AN on the surface of MMT, followed by high-temperature selenium vulcanization to obtain SE0.06SPAN /MMT. SEM, TEM, XRD, IR and XPS tests all proved that se0.06SPAN /MMT composite was successfully synthesized and presented a two-dimensional layered stacked structure. Se0.06span was evenly coated between MMT layers, resulting in a larger spacing between MMT layers.
Figure 2. Synthesis and characterization of the materials.A) Synthesis process of SE0.06SPAN /MMT samples; B) SE0.06span, c) MMT and D) SE0.06span /MMT TEM images; E) MMT and F) SEM images with SE0.06span /MMT; G) XRD patterns of MMT, PAN/MMT and SE0.06SPAN /MMT; H) se0.06span /MMT (S 2p), and I) se0.06&Nbsp; SPAN/MMT (Se 3D) XPS analysis.

Se0.06span /MMT@PP membranes were prepared by scraper coating. SEM and EDS showed that se0.06span /MMT was uniformly coated on the membrane surface with a thickness of ~10 μm. Visual shuttle experiments, UV, XPS and theoretical calculations show that se0.06span /MMT can effectively adsorb polysulfide through synergistic action.
FIG. 3 Structure and properties of se0.06SPAN /MMT@PP diaphragm. a) Se  0.06SPAN/MMT@PP photo of coating process of diaphragm; B,c) SEM images of PP septum and SE0.06SPAN /MMT@PP septum (illustrations of (b) and (e) depict corresponding optical images); D) SEM image and EDS element distribution image of se0.06SPAN /MMT@PP diaphragm cross-section; E) Contact Angle of electrolyte droplet on se0.06SPAN /MMT@PP and exposed PP diaphragm surface; F) Diffusion tests of Li2S6 on PP, MMT@PP, Se0.06SPAN@PP and SE0.06SPAN /MMT@PP septum; G) UV-vis spectra of Li2S6 shuttled liquid; H) Density functional theory (DFT) calculates the absorption energy of Li2S6 at SE0.06span, MMT and SE0.06span /MMT.

A series of electrochemical tests showed that SE0.06SPAN /MMT could not only promote the conversion of Li2S8 to Li2S2 and Li2S during the discharge process, but also reduce the decomposition barrier of Li2Sx conversion during the charging process, activate the polysulfide anchored on the membrane, and promote the activation of “dead sulfur”. Theoretical calculation also assisted to verify the catalytic activity of SE0.06span /MMT. In addition, the electrochemical test results also showed that the lithium se0.06span /MMT was more favorable for promoting polysulfide conversion, which was more favorable for the whole electrochemical reaction process.
Figure 4. REDOX kinetics of polysulfide on se0.06SPAN /MMT@PP membrane. A) CV curves of symmetrical Li2S8 batteries with different diaphragms; B) The first cycle charging voltage curves of BP2000-Li2S, MMT-Li2s, SE0.06SPAN -Li2S and Se0.06span/MMT-Li2s electrodes; C) Energy distribution of Li2S cluster decomposition on MMT, SE0.06SPAN -Li2S and Se0.06span/mmT-Li2s; D) MMT, F) SE0.06span /MMT and e) SE0.06span top view diagram of corresponding decomposition paths. N, C, Li, S, Se, O, Si and Al atoms are represented by blue, gray, purple, yellow, orange, red, silver and beige spheres respectively. G) by Li | | Li symmetrical battery test Se0.06 SPAN/MMT @ the lithium ion transference number of PP membrane; H) CV diagram of se0.06SPAN /MMT@PP diaphragm at different scanning rates in a 1.7-2.8V window (relative to Li/Li+). I) Lithium migration energy barrier obtained by DFT.

The se0.06SPAN /MMT@PP membrane can be matched with ordinary sulfur carbon anode to show excellent electrochemical performance. After 1000 cycles at 1C, the capacity can be maintained at 784.2 mAh g — 1, and the capacity decay rate is only 0.034%. Under the harsh conditions of 26.75 mg cm-2 high sulfur load, 4.5µL mg-1 poor electrolyte and 3.2 low N/P ratio, the ultra-high area capacity of 33.07 mAh cm-2 is achieved, which is obviously better than the conventional PP diaphragm assembly battery.
Figure 5. Electrochemical performance of Li-S cell. A) Different septum at 0. Comparison of charge-discharge curves of Li-S batteries at 1 C rate; B) Cyclic stability of positive poles with different diaphragms at 0.1c; C) SE0.06SPAN /MMT@PP charge-discharge curves at different rates; D) Cyclic stability of different diaphragms at 1 C; E,f) se0.06SPAN /MMT@PP Positive electrode cycling performance of diaphragm under high sulfur load; G) se0.06SPAN /MMT@PP Septum in sulfur loading of 26.75mg cm&Nbsp; The first cycle charge-discharge curve at -2; H) Positive sulfur load of 16 mg cm&Nbsp; Initial charge-discharge curve of -2 PP diaphragm battery.

Se0.06span /MMT@PP membranes were prepared in batches using a coating machine to simulate a practical application scenario. Se0.06span /MMT@PP diaphragm has excellent mechanical stability through a series of bending, folding and puncture experiments. Moreover, the use of recycled SE0.06SPAN /MMT@PP separator to match the new sulfur anode and lithium anode still showed excellent electrochemical stability. In addition, se0.06SPAN /MMT@PP diaphragm was used to prepare 0.123Ah flexible battery, which can work continuously under different bending states, indicating that the diaphragm repair has great practical potential.
FIG. 6 Stability and practical application of se0.06SPAN /MMT@PP diaphragm. A) Photographs of large SE0.06SPAN /MMT@PP diaphragm preparation process; B) photos of wound se0.06SPAN /MMT@PP diaphragm; C) Photos and results of puncture tests; D) photos of various diaphragms after circulation; E) SE0.06span /MMT@PP SEM images after 100 cycles of septum at 0.2c; SEM images of lithium anode of f) PP diaphragm and G) SE0.06SPAN /MMT@PP diaphragm after 100 cycles at 0.2c were used. H) Electrochemical performance of se0.06SPAN /MMT@PP membrane matched with positive sulfur electrode; I) corresponding charge-discharge curve of the first cycle after matching with the positive sulfur electrode; J) the cycling performance of the flexible battery and the photos of the flexible battery; K) Flexibility test of flexible battery.

【 conclusion 】
In this study, the multifunctional membrane SE0.06SPAN /MMT@PP was prepared, in which SE0.06SPAN has both electrocatalytic activity and high electrochemical activity, which can contribute to the capacity of lithium sulfur battery. At the same time, the layered structure of MMT enables the diaphragm to have rapid lithium ion transport capability. Using commercial carbon material (BP2000) and sulfur compound as sulfur anode and metal lithium as negative electrode, the lithium sulfur battery with se0.06SPAN /MMT@PP separator can statically cycle 1000 cycles at 1 C, and the capacity decay rate of each cycle is only 0.034%. Even under harsh conditions of 26.75 mg cm-2 high sulfur load, 4.5µL mg-1 poor electrolyte, and 3.2 low N/P ratio, the ultra-high area capacity of 33.07 Mahcm-2 can be achieved. In addition, the se0.06SPAN /MMT@PP diaphragm can be reused many times, with excellent mechanical strength and electrochemical stability, as well as high flexibility, which has outstanding practical potential.

Wei Wang, Kai Xi, Bowen Li, Haojie Li, Sheng Liu, Jianan Wang, Hongyang Zhao, Huanglong Li, AmorM. Abdelkader, Xueping Gao, and Guoran Li. A Sustainable Multipurpose Separator Directed Against the Shuttle Effect of Polysulfides for High – Performance Lithium – Sulfur Batteries. & have spent The Advanced Energy Materials. 2022,

About the author:
Guoran Li is a professor at the School of Materials Science and Engineering, Nankai University. His research interests include the electrochemical conversion and storage of energy, including secondary batteries and novel solar cells. He has published more than 120 Sci papers in Adv Mater, Adv Energy Mater, Energy Environ Sci., Angew Chem Int Ed, and has been cited more than 10000 times, h-Index 55.

As the corresponding author, his recent papers are as follows:
1.Advanced Energy Materials, 2022, 2200160.
2.Advanced Materials, 2022, 2107888.
3.ACS Energy Letters, 2022, 7, 42-52.
4.Energy Storage Materials, 2022, 45, 1229-1237.
5.Advanced Energy Materials, 2022, 12(4): 2003885.
6.Green Energy & Environment, 2022.
7.ACS Appl. Mater. Interfaces 2022, 14, 14, 16348 — 16356.
8.ACS Appl. Mater. Interfaces 2022, 14, 4, 5247 — 5256.

Xi Kai, winner of the National Science Foundation for Outstanding Young Scholars, professor, doctoral supervisor of Xi ‘an Jiaotong University, First-class Young Talents CLASS A.Ph.D. in materials Science and Metallurgy from Cambridge University, M.S. in Applied Chemistry from Nankai University, B.S. in mechanical Engineering and automation from Xi ‘an Jiaotong University. The main research direction is the construction of high specific energy secondary battery based on multi-electron reaction, dedicated to energy efficient storage and utilization. He has published 42 SCI papers as the first/corresponding author (31 papers in the first area of Chinese Academy of Sciences, 26 papers with impact factors above 10, 13 papers with high citation ESI) in high-impact journals in the field of energy storage, with more than 6000 SCI citations and H factor 42 (Google Scholar as of April 2022). He was awarded the top prize in the Cambridge Entrepreneur Association entrepreneurship Competition and the champion of the UK Entrepreneurship Competition. He was interviewed by CCTV news 30 in London. And won the Dow Chemical Sustainable Development Innovation Award (ranked first, won the only grand award), “Chunhui Cup” Chinese Overseas Students Innovation and Entrepreneurship Competition award and other honors.

Professor Xi Kai has carried out systematic work in the field of lithium-sulfur batteries, and relevant results have been published in:
1.Energy Storage Materials, 2022, 45, 1229-1237.
2.Journal of Physics: Energy, 2021, 3 (3), 031501. (ESI)
3.Science CHINA-Materials, 2020, 63, 2443-2455
4.ACS nano, 2020, 14 (8), 9819. (ESI)
5.Advanced Energy Materials., 2019, 9, 1902001.
6.Advanced Energy Materials, 2019, 9, 1900953. (ESI)
7.Energy Storage Materials, 2019, 16, 228. (ESI)
8.Advanced Science, 2019, 6, 1800815. (ESI)
9.Journal of the American Chemical Society, 2018, 140 (50), 17515.
10.Advanced Functional Materials, 2016, 26 (46), 8418. (ESI)
11.Nano Energy, 2015, 12, 538.
12.Nanoscale, 2014, 6, 5746. (ESI)
13.Chemical Communications. 2013, 49, 2192. (ESI)

Job Posting:
There are tall buildings in the northwest, with floating clouds.
Willing to fly high with many swans.
Due to the needs of energy storage discipline construction in Xi ‘an Jiaotong University, the new Energy Materials Chemistry and Energy Storage Engineering team is looking for long-term positions of Distinguished Researcher (Top Young Talents Program of XI ‘an Jiaotong University), Assistant Professor (Youth Show Program of Xi ‘an Jiaotong University), postdoctoral fellow in West China, discipline postdoctoral fellow and research assistant. Background in situ electrochemical analysis, theoretical calculation, functional electrolyte, solid electrolyte, liquid flow battery, alkaline metal anode, metal air battery, battery thermal management is preferred.

Position salary:
Professor/Distinguished Researcher (QINGba Program A/B) : annual salary of 300,000 to 500,000 yuan + performance bonus, research start-up fee of 1,000,000 to 2,000,000 yuan, business establishment, selected candidates will be qualified as master and doctoral tutor, and the corresponding exclusive quota of graduate enrollment. Their children will enjoy the education conditions of primary and secondary school affiliated to JIAOTONG University.

Assistant Professor (Qingxiu Program A) : Annual salary RMB 300,000 + performance bonus; The nature of teachers shall be clearly defined and managed by the school according to the positions of teachers. The university will pay social insurance and housing fund, and provide benefits such as apartment housing and children’s education.

Assistant Professor (postdoctoral fellow in western China, discipline postdoctoral fellow) : annual salary of about 200,000 yuan + performance bonus; If the employment period requirements are met, the subsequent professional title applications (associate professor, professor) are normal promotion, and the conditions are open and transparent. The university pays social insurance and housing fund, and provides benefits such as apartment housing and children’s education.

The research Group also welcomes research assistants, joint training, visiting scholars and other talents with relevant research experience to join in the research group. The research group can ensure that the research results during the period of school belong to the actual completion of the project as the first author to sign the results. You are welcome to contact at any time.

Contact Information:
Please send your resume (including study and work experience, summary of scientific research content and list of achievements, etc.) and electronic documents of published papers or technical development and awards reflecting your scientific research level to with the subject of “applicant’s name + position applied”. Those who pass the interview will be hired.

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