Revealing the Li Nucleation and Growth Mechanism by In-situ and Operando Multimodal Characterizations

Rechargeable lithium-metal batteries (LMBs) with lithium metal anodes are the most promising alternatives of lithium-ion batteries (LIBs), as they have the potential to double the energy density of the LIBs. Despite their high energy density, LMBs still face obstacles, notably rapid performance degradation and severe safety concerns, stemming from issues like uneven metal deposition, pulverization, and interfacial side reactions. To address these obstacles, it is imperative to gain a microscopic-level understanding of the intrinsic mechanisms governing the lithium metal deposition and growth. This project aims to developing the state-of-the-art in-situ and operando multimodal characterization technologies to reveal the intrinsic mechanisms of the lithium metal deposition and growth during charge and discharge cycles of LMBs. Specifically, we will develop a cutting-edge in-situ liquid phase transmission electron microscopy (TEM) technology, which enables the integration of fluid and electric fields along with other external factors, and thereby allows to observe the lithium nucleation and growth process in real time with high resolution. To achieve this, we will construct an electrochemical liquid cell within the TEM, employing a titanium metal as the electrode material and various liquid electrolytes for investigation, including LiClO4, LiPF6, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), in combination with solvents like propylene carbonate (PC), ethylene carbonate/diethyl carbonate (EC/DEC), ethylene carbonate/dimethyl carbonate/methyl ethyl carbonate (EC/DMC/EMC), or triethylene glycol dimethyl ether (TEGDME). Additionally, we will introduce additives such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), and LiNO3for further investigation. Through this in-situ setup, we can dynamically monitor the electrochemical reaction process of the lithium anodes. Leveraging the TEM's high-resolution in-situ manipulation capabilities, we will elucidate the microstructural evolution of lithium during charge and discharge cycles. This includes investigating the formation mechanism of the solid electrolyte interface (SEI) at the nanoscale, thereby offering a comprehensive understanding of the electrochemical reaction mechanism and operational principles of lithium - an essential step in addressing fundamental scientific challenges in LMBs. Our research approach will also encompass a range of in-situ/ex-situ characterizations (in-situ XRD/Raman/XAS, ex-situ HAADF-STEM, EDS mapping, 4D-STEM, SAED, SEM, XPS, FTIR, NMR etc.), molecular dynamics simulations, and first-principles calculations. These will be instrumental in studying the morphological characteristics of initial metal nucleation in Li metal batteries, uncovering the evolution of lithium's microstructure, and proposing theoretical models for lithium metal deposition and dissolution. To end, building on this research, our objectives include optimizing the uniform deposition and dissolution of metals, developing surface-protected lithium metal anodes, and formulating interface-stabilizing electrolytes.