Boron Trifluoride Anionic Side Groups in Polyphosphazene Based Polymer Electrolyte with Enhanced Interfacial...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Conventional polyphosphazene electrolytes (MEEP) suffer from low lithium-ion conductivity.
• Improving ionic conductivity and interfacial stability is key for advanced battery technologies.
• Immobilized anionic groups offer a strategy to enhance electrolyte performance.

Purpose of the Study:

• To synthesize a modified polyphosphazene with anionic trifluoroborate groups to boost lithium-ion conductivity.
• To investigate the impact of mixed side groups on mechanical and electrochemical properties.
• To evaluate the dendrite suppression capabilities and interfacial stability of the modified electrolyte.

Main Methods:

• Synthesis of modified polyphosphazene with 2-(2-methoxyethoxy)ethoxy and trifluoroborate groups.
• UV-induced radiation cross-linking for mechanical stabilization.
• Electrochemical characterization including conductivity measurements and cyclic voltammetry.
• Dendrite formation studies using visualization cells under constant current polarization.

Main Results:

• Modified polyphosphazene exhibited conductivities of 3.6 × 10⁻⁴ S·cm⁻¹ (total) and 1.8 × 10⁻⁵ S·cm⁻¹ (lithium-ion) at 60 °C.
• Enhanced dendrite suppression was observed, with onset at 21 h and short-circuit at 90 h.
• Gel polymer formation with EC/DMC significantly improved conductivity (σtotal = 1.05 mS·cm⁻¹, σLi⁺ = 0.22 mS·cm⁻¹) and lithium transference number (tLi⁺ = 0.18).
• Electrochemical stability window up to 4.5 V vs. Li/Li⁺ was maintained.

Conclusions:

• The modified polyphosphazene with immobilized anionic trifluoroborate groups effectively enhances lithium-ion conductivity and electrochemical stability.
• The improved interfacial stability and dendrite suppression are attributed to a more conductive solid electrolyte interphase (SEI) with fluoride components.
• The development of this modified polyphosphazene represents a promising advancement for solid-state lithium-ion battery electrolytes.