Recently, Prof. Chen Renjie, School of Materials, BIT, with his research group members has made research progress in new aqueous lithium-ion battery electrolytes and published an article titled An “Ether-In-Water” Electrolyte Boosts Stable Interfacial Chemistry for Aqueous Lithium-Ion Batteries in Advanced Materials, one of the top international journal in the field of materials, whose first author is Dr. Shang Yanxin and co-corresponding authors are Associate Researcher Chen Nan, Associate Professor Li Yuejiao and Prof. Chen Renjie.

　　With the rapid development of economy and society, the demand for lithium-ion batteries with high efficiency and reversible energy storage is increasing. Nevertheless, most commercial lithium batteries use organic liquid electrolyte, which has problems of leakage, volatilization, oxidative decomposition and thermal runaway. Electrolytes used in aqueous lithium-ion batteries have become a hot topic in the field of new battery systems and key materials due to their high ionic conductivity, environmental friendliness and low cost. However, the inherently narrow electrochemical stability window (1.23V) of water itself limits the working voltage and energy density of the aqueous battery. Although the SEI film can broaden the electrochemical window of electrolyte, the decomposition products of the traditional aqueous battery electrolyte are H2 and O2, which cannot be deposited on the electrode surface in a solid state. In recent years, some pioneering works have provided new ideas for the design and research of high-concentration brine electrolyte materials by reducing water activity and constructing stable SEI film on the electrode surface.

　　Generally, the ideal aqueous SEI film should have uniform thickness, low solubility, good flexibility and the ability to effectively separate active materials and electrolytes. Ether solvents, especially TEGDME, have a high dielectric constant, which can effectively separate the cation and anion pairs of the electrolyte lithium salt and increase the concentration of the lithium salt in the electrolyte, so as to obtain a higher conductivity. Besides, the SEI film formed by ether solvent has the advantages of thinness, compactness and uniform structure, etc., so it can be used as an effective solvent component of aqueous electrolyte to improve the stability of battery.

　　A new type of “ether−in−water” electrolyte (EIWE) aqueous mixed electrolyte is proposed by the research group of Prof. Chen, of which, the electrochemical stability window was extended to 4.2V, the phase interaction of TEGDME/H2O/LiTFSI in the new solvated structure is analyzed by infrared/Raman spectroscopy, and the mechanism of film formation is studied by DFT and AIMD simulation. The results show that when LiTFSI:TEGDME:H2O=4:1:7, the reduction potentials of Li+2(TFSI−) and Li+4(TEGDME) are higher than the hydrogen evolution potential of water, and both of them will preferentially reduce to form SEI films which are double-layer interfaces composed of an inorganic substance LiF obtained by the reduction of Li+2(TFSI−) and an organic carbonaceous substance obtained by the reduction of Li+4(TEGDME). Through the comparative experiments of different concentrations, the best inhibition effect of EIWE at 15m (mol/kg) on water decomposition and hydrogen evolution is verified. TEM characterization has also further studied the protective mechanism of interfacial film on electrodes. Both CEI and SEI films show good uniformity and stability in 15mEIWE. The amount of H2 and O2 produced by the decomposition of H2O with different concentrations was quantitatively analyzed by DEMS. In addition, H2 releases obviously at 2.6V in 9mEIWE, while the amount released in 15mEIWE can be ignored, indicating that 15mEIWE can significantly inhibit the decomposition of H2 and O2, which plays a key role in electrolyte stability. This unique electrolyte structure provides a new design idea for establishing stable interface in aqueous battery. Related research work was published in the Advanced Materials of Wiley Publishing House, and was reported on both the Materials Views China website (https://www.materialsviewschina.com/2020/09/49231/) and the its official WeChat account. What’s more, it was also reported on the website of the Cailiaoren.com.

Structure of EIWE-based aqueous lithium-ion batteries

Formation mechanism of SEI film

　　Link to the article: An “Ether-In-Water” Electrolyte Boosts Stable Interfacial Chemistry for Aqueous Lithium-Ion Batteries. Adv. Mater., 2020, DOI:10.1002/adma.202004017.

　　Under the guidance of Academician Wu Feng, the research group of Prof. Chen has been engaged in the research of new functional electrolyte materials such as ionic liquids, multi-component solvents, functional additives and composite solid electrolytes for a long time. Some recent related work is as follows:
1. Angew. Chem. Int. Ed., 2020, DOI:10.1002/anie.201903459. (IF=“12.959”, the first author: Lai Jingning, doctoral student)
2. J. Mater. Chem. A, 2020, DOI:10.1039/D0TA02098B. (IF=“11.301”, the first author: Wen Ziyue, doctoral student)
3. ACS Appl. Mater. Interfaces, 2020, DOI:10.1021/acsami.0c00621. (IF=“8.758”, the first author: Yan Mingxia, postgraduate)
4. J. Power Sources, 2020, DOI:10.1016/j.jpowsour.2020.228161. (IF=“8.274”, the first author: Wen Ziyue, doctoral student)
5. ACS Appl. Mater. Interfaces, 2019, DOI:10.1021/acsami.9b01417. (IF=“8.758”, the first author: Chen Nan, Associate Researcher)
6. J. Mater. Chem. A, 2019, DOI:10.1039/C8TA12539B. (IF=“11.301”, the first author: Chen Nan, Associate Researcher)
7. Adv. Mater. 2019, DOI:10.1002/adma.201808393. (IF=“27.398”, the first author: Huang Yongxin, Associate Researcher)
8. Adv. Funct. Mater. 2018, DOI:10.1002/adfm.201800919. (IF=“16.836”, the first author: Wang Lili, doctoral student)
9. Mater. Horizons, 2016, DOI:10.1039/C6MH00218H. (IF=“12.319”, the first author: Qu Wenjie, doctoral student)
10. Advanced Battery Functional Electrolyte Materials, Chen Renjie, Science Press, 2020, ISBN 978-7-03-060719-5
The above-mentioned research results have been supported by the National Key R&D Program of China, the National Natural Science Foundation of China, the Outstanding Young Scientist Program of Beijing Higher Education Institutions, and the Innovative Talent Support Program of BIT, etc..

Brief introduction of the authors:

　　Shang Yanxin, born in May 1994, is a doctoral student major in Materials science and Engineering of BIT, whose supervisor is Prof. Chen Shi. Her main research direction is New Secondary Battery Systems, focusing on the exploration and development of new aqueous lithium-ion battery electrolyte systems. She first proposed a new type of Li4(TEGDME)(H2O)7 aqueous mixed electrolyte with stable interfacial chemistry, which improved the electrochemical stability window of aqueous electrolyte from less than 2.0V to 4.2V. Besides, she has participated in research projects such as the National Natural Science Foundation of China and the National Key R&D Program of China and has taken part in many domestic academic conferences and exchanges.

　　Chen Nan, Associate Researcher, is mainly engaged in the research of new energy materials, including solid electrolyte, flame retardant electrolyte, lithium metal electrode and other key materials for secondary batteries. As the project leader, she is responsible for some major projects, which are supported by the Youth Science Fund of National Natural Science Foundation of China, Beijing Youth Fund, and General and Specific China Postdoctoral fund. As the research backbone, she also participates the projects of National Key R&D Program of China and National Key Basic R&D Program (973 Program). So far, Chen has published more than 30 research papers in international famous journals, such as Advanced Materials, Energy&Environmental Science, Advanced Energy Materials, Chemistry of Materials, Nano Energy, Advanced Science and Journal of Materials Chemistry A, and has applied over 10 invention patents, among which, 4 has already been authorized.

　　Li Yuejiao, Associate Professor, is mainly engaged in teaching and scientific research on the development and application of new electrolyte materials and lithium-ion high-safety cathode materials. As the project leader, she is responsible for the co-construction project of Basic Research Fund of BIT and Beijing Municipal Education Commission. As the research backbone, she also participates the “research on common technology and evaluation system of power battery and key materials” of National High-tech R&D Program (863 Program), “basic research on new secondary batteries and related energy materials” of 973 Program, the New Energy Special Project of the National Key R&D Program of China and projects related to Sino-US international science and technology cooperation, etc.. In addition, Li has published over 30 SCI papers, and has applied and authorized about 10 patents.

　　Prof. Chen Renjie, doctoral supervisor of School of Material, BIT, the member of professional group of national ministries and commissions, the member of Chinese Materials Research Society, C-MRS (Secretary General of Energy Conversion and Storage Materials Branch), the member of Chinese Solid State Ion Society, the member of International Academy of Electrochemical Energy Science (IAOEES), the member of New Chemical Materials Committee of the Chemical Industry and Engineering Society of China, (CIESC), the industry expert of national battery of China Battery Industry Association (CBIA), is mainly engaged in teaching and scientific research on the new system and key materials of multi-electron high specific energy secondary batteries, new ionic liquids and functional composite electrolyte materials, new thin film materials and structural devices for special power sources, and resource regeneration of green secondary batteries. He has presided over the projects of the National Natural Science Foundation of China, the National Key R&D Program of China, 863 Program, transformation of major achievements of universities in Beijing, and Beijing Science and Technology Program, etc.. Chen has also published more than 200 SCI papers (including over 80 paper with IF>10), has applied 82 invention patents in which 35 are authorized, and has been approved 7 software copyrights and 2 academic monographs. As the leading person, he has won 1 national second prize of technological invention and 3 ministerial first prizes of science and technology. Moreover, Prof. Chen has been successively elected to be the member of/as Supported by Program for New Century Excellent Talents in University, Beijing Municipal Excellent Talents Training Funding Program, Beijing Science and Technology Rising Star, Outstanding Young Scientist Program of Beijing Higher Education Institutions, Outstanding Young Scholar in Frontiers of Chinese Engineering and Royal Society of Chemistry (RSC).