Adv. mater.: the team of Guo Shaohua, He Ping and Zhou Haoshen from Nanjing University made important progress in the study of reversible oxygen behavior of high specific energy lithium rich manganese based anode

Recently, the team of Guo Shaohua, He Ping and Zhou Haoshen from the school of modern engineering and Applied Sciences of Nanjing University combined in-situ Raman experiment and first principles calculation method to directly reveal the reversible behavior of oxygen activation and generation of peroxybond (O-O -) in lithium rich manganese based anode The related work was titled with direct visualization of reversible O 2 − / O − redox process in Li rich cathodematerials and published on adv material Online on February 20, 2018 Lithium ion batteries have been widely used in our life However, common commercial cathode materials such as LiCoO 2 and LiFePO 4 have specific capacity lower than 200 MAH g-1, which is easy to cause serious "mileage anxiety" in the field of electric vehicles Li 2 MnO 3 · (1-z) limo 2 (0 < Z < 1, M = Mn 0.5ni 0.5, Mn x Ni y CO (1-x-y) 0 < x, y < 1, 0 < x + y < 1) can provide a specific capacity greater than 250-300 MAH g-1, greatly improving the energy density of the electrode Matching with the silicon carbon negative electrode is expected to increase the energy density of the single battery to 400 wh kg-1, becoming one of the most promising materials for the future electric vehicle endurance The so-called lithium rich manganese based cathode materials can be generally considered to have evolved from layered materials Traditional layered anode materials (such as lithium cobaltite) are arranged longitudinally according to lithium layer, oxygen layer, transition metal layer, etc If a small part of lithium is used to replace the transition metal in the transition metal layer, the materials formed can be considered as lithium rich materials The large capacity behavior of lithium rich materials has always attracted researchers, because the traditional valence mechanism of transition metal can not explain its large capacity behavior, so in addition to the valence mechanism of transition metal, the mechanism of oxygen activation has been proposed in succession, and the activation of oxygen provides the possibility for high specific energy anode However, until now, it is not clear in the direct determination of oxygen activation behavior The specific behavior of oxygen can provide a more clear direction for the future design of materials Guo Shaohua, He Ping and Zhou Haoshen directly observed the reversible behavior of peroxy bond by surface enhanced in situ Raman technique Finally, the reversible behavior of O-O bond along the c-axis is verified by the first principle calculation of the material It is proposed that the reversible oxygen behavior is more easily obtained in the "linear like" lithium structure of the transition metal layer, indicating the direction for the design of high specific energy anode The charge density distribution (source: Adv Mater.) of Li 1.2-x Ni 0.2 Mn 0.6 O 2 system (x = 0.6,0.7, 0.8, 0.9, 1 and 1.1) can be used as the fingerprint spectrum to determine the covalent bond between substances In the Raman spectrum, the frequency band of peroxy bond is between 750cm-1 and 900cm-1, and the change of bond length corresponds to red shift or blue shift At the initial stage of charging, there is no peroxide bond When the charging potential is about 4.5V, the peroxide bond begins to appear and then blue shifts, indicating that the bond length is becoming shorter and the shortest at the end of charging Combined with in-situ X-ray diffraction observation, it shows that the bonding direction is along the c-axis In the subsequent discharge process and the second cycle, the oxygen behavior showed reversible changes The first principle calculation proves the experimental results theoretically, that is, in the initial stage of charging, the transition metal changes its valence to compensate for the charge, and there is no activation of oxygen in this stage When the potential reaches about 4.5V, the oxygen starts to activate, and the adjacent oxygen between the transition metal plates is close to each other, and finally the peroxide bond is formed This finding confirms that there is indeed a reversible transformation of O2 - and O - in lithium rich materials, accompanied by a significant increase in energy density, which is of great significance in the design of large capacity cathode materials in the future Li Xiang, a 2016 graduate student of the College of modern engineering and Applied Sciences, and Qiao Yu, a doctoral student of the Japan Institute of industrial technology, jointly wrote by Guo Shaohua, He Ping and Zhou Haoshen, associate professors, and Nanjing University as the first signing unit and communication unit of the work Thanks to Zhu Hong, associate professor of Shanghai Jiaotong University and his team members for their important contributions in computing The research has been greatly supported by platforms and projects such as the State Key Laboratory of solid microstructure physics and the collaborative innovation center of Artificial Microstructure science and technology, and also by the national key research and development plan, the National Natural Science Foundation and the Jiangsu Provincial Natural Science Foundation youth project Of the company Paper link: http://onlinelibrary.willey.com/doi/10.1002/adma.201705197/full correspondence Author: Guo Shaohua https://eng.nju.edu.cn/9d/4a/c5184a236874/page.htmhe Ping https://eng.nju.edu.cn/61/bd/c4935a156093/page.htmhzhou Haoshen https://eng.nju.edu.cn/24/41/c5016a140353/page.htmhe