Wang Chengliang research group of Huazhong University of science and technology: regulating π - system to realize high performance and quick charging organic sodium ion battery cathode material

Lead sodium ion battery is regarded as the most potential substitute for lithium ion battery because of its low cost and wide source of sodium element However, when inorganic materials or analogues in commercial lithium batteries are directly used in sodium batteries, the performance of the batteries will usually degrade or fail The main reason is that the large ion radius of sodium ions will make it difficult to embed / detach from the materials, and even cause the crushing damage of the material structure, which is particularly prominent when the batteries are charged quickly Therefore, the design of sodium ion battery cathode material with high specific capacity, good fast charging performance and excellent cycling performance has important scientific significance and application value for promoting the application of sodium ion battery in energy storage and other fields Recently, Professor Wang Chengliang's research group of Huazhong University of science and technology has designed and synthesized conjugated chain polymers, which have been successfully applied to sodium ion batteries, providing a new idea for the design of electrode materials for high-performance sodium ion batteries (CHEM, DOI: 10.1016 / j.champ 2018.08.014) Brief introduction to Professor Wang Chengliang's research group Professor Wang Chengliang's research group was founded in 2016, affiliated to the school of Optics and electronic information of Huazhong University of science and technology Relying on Wuhan National Research Center of Optoelectronics and sensitive ceramics engineering research center of the Ministry of education, the group now has 12 postdoctoral, doctoral and master's students A member The team is committed to making use of the characteristics of organic polymer materials to obtain high-performance organic semiconductors and organic energy storage materials and realize the flexibility of devices In the past two years, the team has made many breakthroughs in the field of energy storage, and published many papers in high-level magazines such as chem SOC Rev., chem, adv mater., J Phys Chem Lett Profile of Professor Wang Chengliang: Wang Chengliang, Professor, doctoral supervisor, School of Optics and electronic information, Huazhong University of Science and Technology, winner of the "youth thousand talents program" of the central organization department In 2005, he graduated from Nanjing University, and in 2010, he graduated from Institute of chemistry, Chinese Academy of Sciences, and then worked in Hong Kong and Germany successively He has been engaged in the application and basic research of organic electronics and organic energy storage So far, more than 40 SCI papers have been published in international academic journals such as chem Rev., chem SOC Rev., chem, adv mater., J am Chem SOC., adv funct Mater., and many of them have been rated as highly cited papers, with a total number of more than 3000 times cited He was invited to write important chapters in two monographs, including a Chinese version monograph molecular films and devices (published by chemical industry press in 2011) and an English version monograph Organic Optoelectronics (published by Wiley press in 2013) Since joining Huazhong University of science and technology in 2016 and establishing an independent research group, he has published many high-level papers, including chem SOC Rev (2018 impact factor: 40.182), chem (cell sister journal, 2018 first impact factor: 14.104), adv mater (2018 impact factor: 21.950), J Phys Chem Lett (2018 impact factor: 8.709 And so on The graduate students under the guidance have won the three good graduate students, national scholarship, knowledge and practice scholarship and other awards Postdoctoral, lecturer and associate professor positions are recruited by the research group all the year round Leading scientific research achievements: π - system is regulated to realize high-performance fast charging organic sodium ion battery cathode material conjugated organic polymer material is a kind of functional material with large conjugation system and charge can be delocalized, which can stabilize the gain and loss of electronic state, realize charge transmission, separation and combination, etc Based on these characteristics, conjugated organic polymer materials have attracted people's attention They have been used as semiconductor materials, which has led to the rapid development of organic electronics and flexible electronic equipment science and technology, such as field-effect transistors, light-emitting diodes and solar cells Wang Chengliang, Professor of Huazhong University of science and technology, has extended his previous experience in molecular design, single crystal, multi-functional micro nano structure and charge transfer in the field of organic electronics (chem SOC Rev 2018, 47, 422; chem Rev 2012, 112, 2208) to the field of energy storage, and has carried out a series of preliminary studies in the new field (j.am Chem SOC 2015, 137, 3124); Adv Funct.Mater 2016 , 26 , 1777; Adv Mater 2016 , 28 , 9182; Sci Bull 2017 , 62 , 1473; Chin Chem Lett 2018 , 29 , 232 ; J.Phys Chem Lett 2018 , 9 , 3205; J Phys Chem C 2018 , DOI: 10.1021/acs.jpcc.8b06170 ）。 Recently, the research group has further designed and synthesized the conjugated system (pentaphenyltetraketone, adv mater 2016, 28, 9182) and obtained the conjugated chain polymer (ppts, figure 1), which has greatly improved the capacity, fast charging performance and long-term cycling performance of organic sodium ion battery Specifically, the rigid π conjugated polymer material has the following advantages: 1) each structural unit has four carbonyls, providing theoretical specific capacity of up to 291 MAH / g; 2) large, linear conjugated system; 3) enhanced intermolecular π interaction; 4) better charge transfer performance; 5) stable charge and discharge state, thus increasing cycle stability; 6 ）Layered arrangement promotes ion transport; 7) insolubility improves long-range cycle life Figure 1 Molecular design of high-performance cathode material: expand the conjugation system to improve the performance of the battery (source: Chem) The author first confirmed that ppts polymer has good crystallinity through XRD, SEM, HRTEM and simulation calculation (Figure 2), significant π - π accumulation, realizing the layered arrangement of the polymer Based on this, the author believes that ppts is beneficial to ion transport, so that high-performance and fast charge discharge sodium ion batteries can be obtained Figure 2 Structure characterization of ppts (source: Chem) Subsequently, the author assembled ppts into traditional button cell (half cell) and tested its electrochemical performance (Figure 3) From the CV Curve of Fig 3 (a), we can see the obvious reversible redox peak of carbonyl group, and the three peaks show that it undergoes four electron process The theoretical calculation of this multi electron process is carried out and the calculated results are in good agreement with the experimental results Then, the ppts sodium ion battery can release a specific capacity of up to 290 MAH / g with a current density of 100 mA / g, which is very close to the theoretical capacity After 100 cycles, its performance is still maintained at 251 MAH / g, which shows that ppts has good cycle stability and high specific capacity Although pbqs with similar structure has higher theoretical specific capacity than ppts, its actual capacity and stability are obviously weaker than ppts under the same conditions It is suggested that this may be related to the smaller conjugated system of pbqs In addition, Non-in-situ XRD showed that the intercalation / detachment of sodium ions was mainly on the (011) plane, i.e the electrochemically active carbonyl site and the intercalation position of the layered arrangement, which proved that the layered arrangement was beneficial to ion transport Figure 3 Electrochemical performance analysis (source: Chem) based on the above series of analysis, the author believes that ppts may have good rate performance and fast charging performance Therefore, the author has carried out long-range stability, magnification performance and fast charging performance tests (Figure 4) Because ppts has a larger conjugated system than pbqs and PAQS, ppts has obvious advantages in both doubling performance and fast charging performance (Fig 4b) In terms of long-range stability, ppts can maintain a specific capacity of 230 MAH / g even after 2000 cycles with a current density of 1A / g, which is significantly better than pbqs and PAQS At the same time, PAQS has larger conjugated structure than pbqs, so it also shows better cycle stability Again, it is proved that the large conjugated system in sodium ion battery is conducive to improve the comprehensive electrochemical performance of materials In addition, ppts can maintain a specific capacity of 160 MAH / G after 5000 cycles at a current density of up to 10 A / g What's more, at a current density of 50 A / g, ppts can stably release nearly 100 MAH / g of capacity in tens of thousands of cycles, and it only takes 7 seconds to complete the process This property is very rare in the reported energy storage materials, which shows that π system plays an important role in obtaining high power organic sodium ion batteries Figure 4 Rate performance and long-range stability analysis (source: Chem) Finally, the author studied the reaction kinetics of ppts electrode based on CV and GITT (intermittent constant current potentiometric titration) The results show that the surface effect of ppts electrode is mainly in charge and discharge process, and the diffusion coefficient of sodium ion is as high as 10-9cm 2 s-1 The surface effect and high diffusion coefficient of ion can be attributed to its layered arrangement The interlayer provides a good channel for ion transport, which explains the internal cause of ppts outstanding rate performance Figure 5 Reaction kinetics analysis (source: Chem) Summary: Based on the design idea of regulating π system, Professor Wang Chengliang's team developed a kind of organic sodium ion battery positive material with large conjugate system and layered arrangement The π conjugation system enhanced the charge transfer, stability and ion transfer performance of the material, which showed high capacity, good cycle stability and fast charge performance This work has important scientific significance and application value for promoting the application of conjugated organic polymer materials in the field of energy storage and improving the performance of batteries through molecular design This work was published in the recent chem (DOI: 10.1016 / j.checker 2018.08.014) In this paper, the reasons of polymer's stacking structure and good electrochemical performance were analyzed Dr Tang MI is the first author of this paper, and Professor Wang Chengliang is the corresponding author The theoretical calculation of this work has been greatly assisted by Professor Ma Jing of Nanjing University, and vice professor Wang Erjing of Hubei University has also provided necessary assistance for this paper Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information, chembeangoapp, chembeango official microblog, CBG wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the domestic representative research group, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.