Optimizing the Electron Density of PVDF-HFP-Based Solid Polymer Electrolyte by Donor-Acceptor COF Toward...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Solid-state lithium metal batteries (LMBs) offer enhanced safety and interfacial contact compared to liquid electrolyte counterparts.
• Key challenges for solid polymer electrolytes (SPEs) in LMBs include unstable solid electrolyte interphase (SEI) formation and slow Li+ transport kinetics.
• Existing SPEs often struggle to achieve the high ionic conductivity and stable cycling required for practical applications.

Purpose of the Study:

• To design and synthesize a bromine-modified covalent organic framework (Br-COF) to enhance the performance of PVDF-HFP-based SPEs.
• To investigate the effect of Br-COF on Li+ migration, SEI stability, and overall electrochemical performance in solid-state LMBs.
• To provide a strategy for regulating electron density in SPEs for improved lithium metal battery applications.

Main Methods:

• Incorporation of a donor-acceptor type Br-COF into a PVDF-HFP polymer matrix to create modified SPEs.
• Electrochemical characterization, including ionic conductivity measurements and Li+ transference number determination.
• Battery cycling tests using various cathode materials (Li, LFP, NCM90) to evaluate long-term stability and performance.

Main Results:

• The Br-COF@PVDF-HFP SPE achieved a high ionic conductivity of 9.2 × 10^-4 S cm^-1 and a Li+ transference number of 0.78.
• The material facilitated the formation of a stable, LiF-rich SEI layer, crucial for battery longevity.
• Demonstrated excellent cycling stability in Li|Br-COF@PVDF-HFP|Li cells (3000 h at 0.1 mA cm^-2) and LFP/NCM90 based cells (2000/250 cycles).

Conclusions:

• The developed Br-COF acts as an effective additive for PVDF-HFP-based SPEs, significantly improving Li+ transport and SEI stability.
• Regulating electron density within SPEs through functionalized COFs is a viable strategy for advancing solid-state LMB technology.
• The enhanced SPEs show great promise for the development of safer and more durable solid-state lithium metal batteries.