Tailoring the electronic structure to enable rapid Li-ion diffusion and a stabilized LiF-LiCl rich...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• The solid electrolyte interphase (SEI) composition is crucial for lithium metal battery (LMB) performance.
• Current SEI engineering strategies require novel approaches to enhance stability and ion transport.
• Understanding interfacial chemistry is key to unlocking the potential of lithium metal anodes.

Purpose of the Study:

• To design a functional ionic salt (DG-Cl) for improved SEI formation in LMBs.
• To investigate the molecular-level mechanisms of SEI component regulation via DG-Cl.
• To evaluate the electrochemical performance enhancement in lithium metal batteries utilizing the engineered SEI.

Main Methods:

• Design and synthesis of a functional ionic salt (DG-Cl) with π-conjugated structure.
• Density functional theory (DFT) calculations to verify DG-Cl's interaction with Li+ and TFSI-.
• X-ray photoelectron spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) for SEI characterization.
• Electrochemical testing of lithium symmetric and Li/LiFePO4 full cells, including pouch cells.

Main Results:

• DG-Cl facilitates directional release of Cl- and anchors TFSI- via cation vacancies, promoting LiCl and LiF formation.
• DFT calculations show DG-Cl enhances C-F bond cleavage in TFSI-, leading to increased LiF generation.
• XPS and TOF-SIMS confirm uniform LiF-LiCl co-growth on the SEI, improving Li-ion transport and regulating Li deposition.
• Lithium symmetric batteries exhibit ultralong cycling stability (>4000 hours at 0.1 mA cm-2).
• Li/LiFePO4 full cells show 82.04% capacity retention after 800 cycles at 2C.
• Pouch cells demonstrate outstanding cycling performance with 96.6% retention after 150 cycles.

Conclusions:

• The functional ionic salt DG-Cl effectively regulates SEI composition and promotes the formation of LiF-LiCl.
• This molecular-level control over electron transfer leads to significantly enhanced cycling stability and performance in LMBs.
• The proposed strategy offers a promising pathway for developing high-performance and stable lithium metal batteries.