They published their work on Oct. 18 in Energy Material Advances.
"Constructing a good interface between cathode and electrolyte is crucial for the development of all-solid-state battery," said Chuang Yu, a professor at the State Key Laboratory of Advanced Electromagnetic Technology at Huazhong University of Science and Technology. "Currently, strategies such as coating protect layer on cathode surface and isolating cathode/sulfide electrolyte by halide electrolyte layer are typical solutions to solve the problems at the interface between the cathode and the sulfide electrolytes, but it is not yet clear who is more suitable for sulfide-based all-solid-state batteries."
Yu explained that sulfide electrolytes currently used will undergo oxidative decomposition during the operation, which deteriorates to cyclability, and strategies should be employed to suppress such decomposition.
"Halide electrolytes have wide electrochemical windows which can compensate for the shortage of sulfide electrolytes," Yu said. "The coating layer of the cathode surface can relieve the decomposition of sulfide electrolytes. Both strategies are favored to cycle performance."
But it's too simplistic to think that introducing halide electrolytes can significantly improve the cycling performance of batteries. According to Yu, the use of halides introduces a new interface that is the halide/sulfide interface. The compatibility is not fully understood yet between two electrolytes and efforts should be made to explore the answer.
"We take Li9.9SnP2S11.9Br0.1 sulfide electrolyte as an example, employing cathode surface coating and halide/sulfide bilayer electrolyte strategies to improve the electrochemical performance of batteries," Yu said. "The cycle performance of batteries with a coating layer is excellent. The initial discharge capacity of halide/sulfide bilayer electrolyte batteries is very high but the cyclability is undesirable."
"This provides us with an opportunity to explore the stability of halide/sulfide interface, as batteries with bilayer electrolyte have poor cycle performance. In fact, they are indeed unstable, and after a period of contact, the impedance of the two is significantly lower than when they contact at the beginning," Yu said.
"The products between halide and sulfide, such as In2S3, are the main culprit causing poor cycling performance," Yu added. "Strategies should be explored to enhance the interface stability between halide and sulfide. Otherwise, the only way to significantly enhance the cycling performance of batteries is to use the coating method on the cathode surface."
Other contributions include Qiyue Luo, Liang Ming, Chaochao Wei, Zhongkai Wu, Ziling Jiang, Chen Liu and Shijie Cheng, State Key Laboratory of Advanced Electromagnetic Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology; Shiyu Liu, Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology; Dong Zhang and Kecheng Cao, School of Physical Science and Technology & Shanghai Key Laboratory of High-resolution Electron Microscopy, Shanghai Tech University; Long Zhang, College of Physics and Energy, Fujian Normal University.
The National Key Research and Development Program (2021YFB2500200). This work is also supported by the National Natural Science Foundation of China (Nos. 52177214) and the National Key Research and Development Program (2021YFB2400300). This work uses resources of Analytical and Testing Center of Huazhong University of Science and Technology.
