Janus-Faced MgI₂ Interface Engineering Enables Stable High-Capacity Poly(ethylene oxide)-Based Lithium Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Poly(ethylene oxide) (PEO)-based polymer electrolytes face challenges in all-solid-state lithium-metal batteries (ASSLMBs), including low energy density and lithium dendrite growth.
• These limitations hinder the practical application of PEO in high-performance ASSLMBs.

Purpose of the Study:

• To introduce a dual-functional additive, magnesium iodide (MgI2), to simultaneously improve capacity and interfacial stability in PEO electrolytes.
• To address the limitations of PEO-based electrolytes for next-generation ASSLMBs.

Main Methods:

• Incorporation of a trace amount of MgI2 into PEO-based polymer electrolytes.
• Investigating the coordination behavior of Mg2+ with PEO chains and TFSI- anions.
• Analyzing the role of iodine species in cathode redox reactions and solid electrolyte interphase (SEI) formation.
• Electrochemical testing of Li||Li symmetric cells and Li||LiFePO4 full batteries.

Main Results:

• MgI2 addition weakened Li+-TFSI- interactions, promoting Li+ dissociation and enhancing interfacial lithium-ion transport.
• Iodine species facilitated robust, inorganic-rich SEI formation, effectively suppressing dendrite growth.
• Modified electrolytes achieved a critical current density of 1.7 mA/cm², and Li||Li symmetric cells cycled over 10,000 hours.
• Li||LiFePO4 full batteries showed 10x durability improvement and 93.28% capacity retention after 2000 cycles; pouch cells retained 95.80% capacity after 250 cycles.

Conclusions:

• MgI2 acts as a Janus additive, synergistically enhancing reversible capacity and interfacial chemistry in PEO electrolytes.
• This facile and economical strategy enables high-performance ASSLMBs with improved safety and energy density.