Ming Liu currently is an assistant professor at Tsinghua Shenzhen International Graduate School (SIGS) for fundamental battery research. He received his Ph.D. from both Tsinghua University and Hong Kong University of Science and Technology in 2017, and afterwards as a postdoc (2017−2021) in group of Prof. Marnix Wagemaker at Delft University of Technology. He has been engaged in the use of advanced characterization techniques such as solid-state nuclear magnetic resonance and neutron depth profiling to fundamentally understand the transport behavior of lithium-ion across solid-solid interface from the atomic scale to the mesoscale. He has published more than 70 SCI papers, which has been cited more than 5900 times (Web of Science) and H factor 37. The first author/corresponding author published in Nat. Nanotechnol.(2), Nat. Commun.（3）, Sci. Adv., Joule, Acc. Chem. Res., Adv. Mater., Energy Environ. Sci., ACS Energy Lett., Chem. Mater..

Driven by the intrinsic safety and potential to achieve higher energy densities, solid-state Li-metal batteries are intensively researched. The ideal solid electrolyte should possess a high conductivity, should have electrochemical stability both toward the Li-metal anode and to high voltage cathodes, should suppress dendrites, should provide flexibility to deal with the volumetric changes of the electrodes, and should be easy to process. This challenging combination is to date not fulfilled by any solid electrolyte, be it organic, inorganic, or even a hybrid of the two. Pushing the development of solid electrolytes toward reversible room temperature operation when used in tandem with Li-metal anodes demands an understanding of critical processes that determine the properties of the solid electrolyte. These include the complex Li-ion transport as well as the Li-metal plating processes. This already presents the first experimental hurdle as the ability to directly and noninvasively monitor the Li-ion kinetics, Li densities, and Li chemistries, under in/situ or operando, is not trivial.

The scope of this talk is the investigation and improvement of solid electrolytes, with the emphasis on the possibilities offered by solid-state NMR and neutron depth profiling as direct probes for the study of critical processes that involve Li ions and Li metal. Solid-state NMR allows us to unravel the complex interface chemical environment and the diffusion processes both in the bulk solid electrolyte and in the interface environment. These studies shed light on the role of interface composition, wetting and space-charge layers, on the macroscopic battery performance. Another technique that enables probing Li directly is operando neutron depth profiling, which allows us to determine the Li density as a function of depth. It provides a noninvasive and effectively nondestructive tool to examine delamination, irreversible reactions and dendrite formation during plating/stripping. Results demonstrate that it is very challenging to maintain the contact between Li metal and the SE during cycling, especially for the “anode-less” or “anode-free” configuration under low-pressure conditions. A perspective is provided on the potential improvement of the Li-ion transport, dendrite suppression, and preventing Li-metal-solid-electrolyte delamination as well as on the potential role of solid-state NMR and NDP techniques to guide these developments.