Professor Huang Jianyu's team from the State Key Laboratory of Metastable Materials Science and Technology at Yanshan University developed a technology that combines cryogenic focused ion beam (cryo-FIB) and cryogenic transmission electron microscopy (cryo-TEM) to study the electrode/sulfide SSE interfaces in all-solid-state batteries (ASSBs), and characterized the micron silicon (μ-Si) negative electrode/sulfide SSE interface at the atomic scale, thus offering a comprehensive understanding of the μ-Si negative electrode/sulfide SSE interfaces from micron to atomic scale. In this study, the interface impedance has been found not to be a major issue in ASSBs. Instead, it is the sustainable interfacial reaction that depletes the active lithium source from the positive electrode, causing continuous capacity decay. This study provides the atomic-scale understanding of the complex interfaces in the μ-Si negative electrode and sulfide SSE based ASSBs via cryo-TEM, offering valuable scientific insights for the development of high-performance ASSBs. The findings were published in Nature Communications under the title: "Revealing interfacial failure mechanism of silicon-based all-solid-state batteries via cryogenic electron microscopy".
Lithium (Li) and silicon (Si) are both promising negative electrode candidates with high specific capacity. Understanding their stability with sulfide SSEs is critical for the development of high energy density ASSBs. However, due to the volume expansion during lithiation of the Si negative electrode, the continuous solid electrolyte interphase (SEI) growth between the organic liquid electrolyte and the Si negative electrode hinders the commercialization of Si negative electrodes in liquid electrolyte lithium-ion batteries. Previous studies predominantly employed conventional characterization methods to investigate Li/sulfide SSE interface failures, lacking systematic research on interfacial degradation mechanisms in silicon-based ASSBs. Moreover, atomic scale imaging the negative electrode/SSE interfaces in sulfide or halide-based ASSBs is very challenging due to both the air sensitivity of the sulfide and halide SSEs and the irradiation damage of electron/ion beam during the preparation and characterizations of interfaces.
Revealing Interfacial Reaction Mechanism of Si|SSE|NMC81 All-Solid-State Batteries via Cryogenic Electron Microscopy
The research team innovatively applied cryo-FIB-TEM (cryogenic focused ion beam-transmission electron microscopy) technology to reveal two distinct interfacial reaction mechanisms at the atomic scale for the first time. A mixed ionic-electronic conductor layer will be formed at the Si/LGPS interface with a thickness of 10–20 μm comprising of needle-shaped Li2S nanocrystals, electron-conductive Li-Ge, and Li₃P nanocrystals. The large-sized Li2S crystals originate from the semi-coherent relationship between Li₂S and Li-Ge. In contrast, a 100–200 nm-thick, uniform, and dense pure ionic conductor layer is formed at the Si/LSPSC interface, comprising nanocrystalline Li2S dispersed in an amorphous matrix. Although both interfacial layers comprise mainly Li2S, the Si/LGPS interface exhibits an electronic conductivity of 1.17x10-5 mS/cm - over 100 times higher than that of the Si/LSPSC interface - due to the embedded nanostructured Li-Ge and Li3P. This difference is the fundamental cause of sustained parasitic reactions and irreversible active lithium consumption in the former. This study challenges the traditional view by demonstrating that silicon and sulfide electrolytes exhibit good chemical compatibility. It is not the high interfacial impedance but the active lithium loss originated from the conductivity of sustainable interfacial reaction is the culprit for ASSB failure.
This work was supported by the National Natural Science Foundation of China, the Innovation Group funded by the Natural Science Foundation of Hebei Province, and the National Science Fund for Distinguished Young Scholars etc. Professors Huang Jianyu and Tang Yongfu from Yanshan University are the corresponding authors. PhD candidates Yao Jingming and Yu Zhixuan from Yanshan University are the first authors.
