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2020-04-23 PHI CHINA Nanjing Laboratory Cooperation Achievements (2)

PHI CHINA Nanjing Laboratory Cooperation Achievements (2)

23-April-2020

 

With rapid development in science and technology in recent years, advanced surface analysis technology has become a necessary experimental technology for surface characteristics research in the fields of materials, energy, catalysis, microelectronics, and semiconductor industries. XPS is an important scientific instrument in surface analysis, which can provide surface composition and chemical state information.  It is widely used in scientific research and high-tech industries and take an important role to solve complex problems.

As a new type of solution-processable ionic semiconductor material, metal halide perovskite has become a hot material in the field of optoelectronic research in recent years due to its advantages of adjustable band gap, high defect tolerance and simple preparation. However, metal halide perovskites with a spatial structure similar to lithium ion conductor lanthanum lithium titanate (Li3xLa2 / 3-xTiO3) have little research on lithium ion doping characteristics and related applications.

 

Recently, the team of Professor Yao-Hongbin, School of Chemistry and Materials Science (SCMS) of University of Science and Technology of China (USTC), in collaboration with Associate Professor Zhang, Guozhen and Dr. Ju, Huanxin of PHI CHINA Nanjing Laboratory. They have made significant progress in the construction of metal halide perovskite lithium conducting layers and stabilizing lithium metal batteries. The team of Prof. Yao utilized the advantages of chlorine-based metal halide perovskite wide band gap, good film formation and simple preparation to develop a gradient lithium conductive layer based on the metal halide perovskite. Therefore, the isolation of the lithium metal anode and the electrolyte is achieved, which greatly improves the cycle stability of the lithium metal battery. The result was published in Nature's comprehensive journal Nature Communications under the title "Metal chloride perovskite thin film based interfacial layer for shielding lithium metal from liquid electrolyte" (DOI: 10.1038 / s41467-020-15643-9).

 

Fig. 1 Mechanism exploration of Li+ ion migration through the lattice of metal chloride perovskite.

a Schematic illustration of the mechanism of Li ions’ intercalation into perovskite lattice, the formation of perovskite-alloy gradient Li ion conductor and the deposition process. b hypothetical migration pathway of Li+ ion and corresponding potential energy. c, Cyclic voltammetry comparison of the cells spin coated with metal halide perovskite film.

 

The researchers found that chlorine perovskite (MASnCl3 and MAPbCl3) prepared by spin coating method has the characteristics of accommodating and transporting lithium ions (Fig. 1a). DFT and CI-NEB theoretical calculations show that the transport energy barrier of lithium ion in the lattice of metal halide perovskite MASnCl3 is 0.45eV in the direction of [001], which is equivalent to the know lithium-ion conductors such as Li4GeS4 (0.53eV) and γ-Li3PS4 (0.49 eV) (Fig. 1b). According to the result of the simulation, with the methylammonium [CH3NH3]- oriental adjustment, the shuttle behavior of lithium ion in perovskite lattice follows the hole between [SnCl6]4-octahedron and methylamine ion [CH3NH3]- . Through the cyclic voltammetry (Fig. 1c) and depth analysis of XPS, the researchers found that, lithium ion can be inserted into metal halide perovskite lattice, and can carry out alloying/dealloying reaction reversibly, forming a 300nm thick Li-Sn alloy layer at the bottom, constituting an unique perovskite –alloy gradient structure. The Li-Sn alloy layer has a higher lithium ion mobility coeffiecient (~~10-4 cm2 s-1), meanwhile, the byproduct LiCl has electrical insulation, protecting the upper layer of perovskite framework from collapse. This unique perovskite-alloy gradient structure is beneficial to the deposition/ desorption of lithium ions.

 

Fig. 2 a Schematic illustration of the mechanism of Li ions’ intercalation into perovskite lattice, the formation of perovskite-alloy gradient Li ion conductor and the deposition process. b hypothetical migration pathway of Li+ ion and corresponding potential energy. c, Cyclic voltammetry comparison of the cells spin coated with metal halide perovskite film.

 

Furthermore, the researchers have developed a convenient solid-phase transfer method to transfer the high-quality chlorine based perovskite (MASnCl3 and MAPbCl3)films prepared by spin coating method to the surface of lithium foil in situ, forming a lithium conducting layer with gradient structure (Fig. 2a). The metal halide perovskite lithium conducting layer can improve the interface between electrolyte and lithium metal, achieve dense lithium deposition and stripping, and avoid the growth of lithium dendrite and the pulverization of lithium metal electrode (Fig. 2b). The final electrochemical cycle test of lithium metal full cell shows that under the protection of metal halide perovskite conductive lithium layer, even under the strict conditions of poor lithium (50 μm) and limited electrolyte (20 μ L mah-1) and 2.8 mAh cm-2 surface capacity, the capacity of lithium cell without protective layer has been reduced to 40% after 50 cycles (Fig. 2 c).

 

In the process of XPS characterization of “perovskite-alloy-lithium metal” gradient interface structure, the partial reduction of B-site ions in ABX3 perovskite will be caused by depth profiling, which makes the depth XPS characterization based on Ar ion sputtering unable to truly and objectively reflect the change of the valance state of B-site elements at different depths (Fig. 3a,b). In this regards, using mechanical stripping method, the chemical composition of the interface layer at different depths are exposed. The researchers used Kapton tape for mechanical stripping under the protection of inert atmosphere in glove box (Fig. 4a). At the same time, the prepared samples are transferred from the glove box to the XPS experimental device of PHI China Nanjing Laboratory though the inert atmosphere transfer chamber. The environmental sensitive samples in the whole sample transfer process are always under the protection of inert atmosphere, ensuring the reliability of the experimental results (Fig. 4b).

 

Fig. 3 Partial reduction of B-site ions of ABX3 perovskite caused by Ar ion sputtering

 

Fig. 4 a, The perovskite-alloy interface at different depth exposed based on the mechanical stripping method. b Using inert atmospheric transfer vessel to transfer the prepared samples from the glove box to the XPS Instrument.

 

The researchers found that the “perovskite-alloy” interface made by solid phase transfer method in the initial state, the B-site elements on the surface show the same oxidation state (Sn2+ and Pb2+) as the original perovskite films. After the first mechanical stripping, the perovskite layer on the surface are removed, the alloy layer (Sn0+ and Pb0+ , from Li-Sn alloy and Li-Pb alloy) at the bottom of perovskite is exposed. Along with the times of mechanical stripping, the ratio of perovskite is decreasing gradually while the ratio of alloy is increasing gradually. The researchers used a depth profile XPS analysis to prove the “perovskite-alloy-lithium metal” gradient structure of the perovskite interface on the lithium metal surface (Fig. 5b,c). At the same time, the LiCl insulation layer formed at the bottom also proved by an XPS analysis (Fig. 6). LiCl insulation layer can effectively prevent the destruction of perovskite by electrons from the electrodes, only allow lithium ion passing through, this further promoted the stability of the perovskite interface layers during the circulation.

 

Fig. 5 The depth profile XPS analysis of the perovskite-alloy interface layer based on mechanical stripping method.

 

Fig. 6 The Li 1s binding energy of the perovskite interface at the bottom.

 

This work is the first attempt to apply metal halide perovskite material to a lithium metal halide perovskite material, and provides strong evidence of the high lithium ion conductivity of the metal halide perovskite material. At the same time, it provides new ideas for the design of new solid electrolytes and high-performance lithium metal batteries.

The first co-authors of the paper are Yin-Yichen, a doctoral student; Wang, Qian, a master student of SCMS and Yang-Jingtian, an undergraduate student in the Junior College.  Prof. Yao, Associate Prof. Zhang from SCMS and Dr. Ju from Nanjing Laboratory of PHI CHINA are co-corresponding authors of the paper. The research was supported by the National Natural Science Foundation of China, the Ministry of Science and Technology, Hefei National Laboratory for Physical Sciences at the Microscale and USTC Center for Micro Nano Research and Fabrication.

 

Article link: https://www.nature.com/articles/s41467-020-15643-9

 

Introduction of Research Group of Professor Yao, Hong bin

Professor Yao-Hongbin, professor and doctoral supervisor of the Department of Applied Chemistry, USTC. He graduated from Department of Chemistry, USTC in 2006.  In 2011, he obtained a Ph.D. in inorganic chemistry from Hefei National Laboratory for Physical Sciences at the Microscale while tutor was Professor Yu, Shuhong. From 2012 to 2015, he conducted postdoctoral research work at Stanford University and cooperated with Professor Cui, Yi. From August 2015 to present, he engaged in the research of new functional metal halides in energy storage and photoelectric conversion applications at Department of Applied Chemistry, USTC.

A multifunctional structure design system for functional metal halide crystals is established, and a method for adjusting the physical and chemical properties of metal halide crystals by effectively combining structural elements is proposed. The synthesis method of high-quality nanocrystals with metal halides of red, green and blue solid colors has been developed and applied to the construction of high-efficiency electroluminescent diodes. A highly linear metal halide luminescent material is designed to achieve complete polarization of fluorescence. Based on the metal halide frame structure, the construction of a new type of solid electrolyte is realized and successfully applied to the interface protection of metal lithium anodes.

In recent years, he has published more than 120 papers in high-impact academic journals in Chem. Soc. Rev., Angew. Chem., JACS, Nature Commun. Nano Lett., Adv. Mater., ACS Nano. Among them, 26 papers were rated as highly cited papers by ESI. The paper has been cited by SCI more than 11,000 times, and the H factor has reached 56 times. The original achievements have been featured reports and special reviews by professional media such as Nature, NPG Asia Materials, Materials Views China, Chemistry views, etc.

 

Research Group website: http://staff.ustc.edu.cn/~yhb/

 

Introduction of PHI CHINA Nanjing Laboratory

PHI CHINA Nanjing laboratory was established in December, 2018.  It is committed to provide technical support for PHI CHINA surface analysis equipment and promoting the application of advanced surface analysis technology in scientific research and high-tech industries through cooperation. At present, the XPS system in PHI CHINA laboratory integrates multiple surface analysis technologies (XPS-UPS-IPES-GCIB): the unique scanning-focus XPS can provide high surface sensitivity (<10nm) and high spatial resolution (<10um) chemical state analysis ability; By combining with UPS and IPES, it can realize the comprehensive detection of the electronic structure information of the core energy level, valence band and conduction band of semiconductor materials; By combining Argon Ion and cluster ion source, it can realize the depth profile analysis of inorganic / organic multilayer film structure materials.

 

 

 

During the epidemic, PHI CHINA Nanjing Laboratory held several the online surface analysis technology lectures, including XPS, AES and TOF-SIMS related analysis technology principles, sample preparation and data analysis. If you want to make better use of these surface analysis technologies to solve scientific problems in scientific research, please visit our WeChat account to watch the lectures playback.

 

Article link: https://www.nature.com/articles/s41467-020-15643-9