Unveiling the Dilution-Shielding Effect as a Universal Strategy for Interfacial Regulation in Composite Polymer...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Composite polymer electrolytes (CPEs) combining PVDF-HFP and garnet fillers offer flexibility and conductivity.
• Parasitic interfacial reactions, like dehydrofluorination of PVDF-HFP, limit the stability of CPEs in solid-state lithium metal batteries (ssLMBs).
• Lanthanum sites on garnet fillers can coordinate with polar solvents, creating alkaline conditions that accelerate polymer degradation.

Purpose of the Study:

• To introduce a universal strategy, the dilution-shielding effect, for interfacial passivation of CPEs.
• To enhance the chemical and electrochemical stability of CPEs for improved Li+ transport.
• To enable uniform Li+ transport and long-term stable cycling in ssLMBs.

Main Methods:

• Incorporation of fluoroethylene carbonate (FEC) with a high dielectric constant into PVDF-HFP/garnet composite electrolytes.
• Utilizing the dilution-shielding effect to attenuate solvent activity and shield active sites.
• In situ characterizations to analyze interfacial passivation and Li+ transport.

Main Results:

• FEC incorporation effectively prevents alkaline microenvironment formation and dehydrofluorination of PVDF-HFP.
• A LiF-rich protective interphase is formed in situ, enhancing interfacial passivation.
• Li|Li symmetric cells demonstrated stable cycling over 700 hours, and LiFePO4|Li full cells achieved over 1200 cycles with 90.2% capacity retention.

Conclusions:

• The dilution-shielding effect is a transferable strategy for regulating interfaces in CPEs.
• FEC modification significantly improves the chemical and electrochemical stability of CPEs.
• This approach provides new insights for designing stable ssLMBs.