A New Class of Solid Electrolytes Discovered
Compositionally complex ceramics (CCCs), including high-entropy ceramics, provide a vast compositional space for new materials discovery beyond the classical doping strategy in stoichiometric compounds.
Recently, researchers from UC San Diego and UC Irvine in the Center for Complex and Active Materials (CCAM) discovered a new class of compositionally complex perovskite oxides (CCPOs) as Li-ion solid electrolytes. This work was published in Matter on June 21, 2023with open access (https://doi.org/10.1016/j.matt.2023.05.035). The research team demonstrated interface-enabled ionic conductivity improvements in CCPOs. For example, a quenched (Li0.375Sr0.4375)(Ta0.375Nb0.375Zr0.125Hf0.125)O3-d shows >270% improvement in total ionic conductivity from the (Li0.375Sr0.4375)(Ta0.75Zr0.25)O3-d (LSTZ) baseline, with similar electrochemical stability (1.75-4.0 V).
“This collaborative study realized conductivity improvements via both exploiting non-equimolar complex compositional designs and controlling interfaces and microstructures,” said the lead corresponding author Jian Luo, UC San Diego Professor of NanoEngineering and Professor of Materials Science and Engineering.
Notably, the team showed that the specific grain boundary ionic conductivity could be improved by 77% after air quenching. “We were curious about how cooling rates affect grain boundary structures and subsequently ionic conductivity. Therefore, it is essential to use advanced electron microscopy and atomistic simulation techniques to investigate underly the mechanisms”, said the lead first-author Shu-Ting Ko, a Ph.D. student from Professor Luo’s group at UC San Diego.
Empowered by Irvine Materials Research Institute facilities, the aberration-corrected scanning transmission electron microscopy (STEM) experiments were led by Professor Xiaoqing Pan’s group at UC Irvine. The results revealed the compositional and structural changes in the grain boundaries in air-quenched LSTNZH specimens. In parallel, Professor Shyue Ping Ong’s group at UC San Diego used active learning moment tensor potential to accelerate studies of Li-ion transport and grain boundaries characteristics of complex CCPOs. The findings suggest that Nb segregation with increased vacancies at grain boundaries induces interfacial disordering at high temperatures captured by quenching, thereby promoting grain growth. Furthermore, grain boundary Li depletion is less of a problem for these CCPOs to constrain the total ionic conductivities.
High-performance solid electrolytes are promising for making solid-state batteries for electric vehicles with improved energy density and safety. “More generally, this work suggests new strategies to discover, design, and tailor a broader range of compositionally complex and high-entropy ceramics for a broad range of applications,” said Prof. Luo.
This research showcases the capability of studying complex scientific problems through collaborations among Prof. Jian Luo and Prof. Shyue Ping Ong at UCSD, Prof. Xiaoqing Pan and Prof. William J. Bowman at UCI, junior researchers Shu-Ting Ko, Tom Lee, Ji Qi Dawei Zhang, Wei-Tao Peng, Xin Wang, and Wei-Che Tsai, Shikai Sun, and Zhaokun Wang. This research was supported by the National Science Foundation Materials Research Science and Engineering Center (MRSEC) program through the UC Irvine CCAM (Grant No. DMR-2011967).