A Strongly Binding Lithium Salt with Stepwise Interphase Formation Mechanism Enables Stable High-Voltage Lithium...

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• Stabilizing high-voltage cathodes in lithium metal batteries (LMBs) is crucial but challenging due to interfacial degradation.
• Conventional anions are often chemically inert, limiting their ability to form protective cathode-electrolyte interphases (CEIs).
• Existing methods to improve anion reactivity involve compromises in battery performance or environmental safety.

Purpose of the Study:

• To design a novel multifunctional anion for enhanced CEI formation in high-voltage LMBs.
• To investigate a stepwise interphase formation mechanism involving both chemical and electrochemical decomposition.
• To demonstrate the efficacy of the designed anion with different high-voltage cathode chemistries.

Main Methods:

• Synthesis of a novel anion, 1,1,1-trifluoro-2,5,8-trioxa-1-borate (FTOB), incorporating a polyethylene glycol backbone and a -BF3 group.
• Investigation of the anion's decomposition pathways via chemical and electrochemical methods.
• Fabrication and cycling of LMBs utilizing high-nickel layered and cobalt-free spinel cathodes with FTOB-based electrolytes.

Main Results:

• The FTOB anion undergoes stepwise decomposition: chemical decomposition with PF6- at <4.5 V and direct electrochemical oxidation at higher potentials.
• This dual pathway facilitates the formation of stable LiF- and borate-rich CEIs.
• Stable cycling of LMBs was achieved using both 4.3-V high-nickel layered and 5-V cobalt-free spinel cathodes.

Conclusions:

• Rational anion design can integrate multiple interfacial formation mechanisms for improved battery performance.
• The FTOB anion offers a promising strategy for interphase engineering in high-voltage lithium metal batteries.
• This approach advances the development of next-generation energy storage devices.