Design of an Amphiphilic Anion toward High Loading Solid-State Lithium Metal Battery

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• All-solid-state lithium metal batteries (ASSLMBs) require advanced lithium salt chemistries beyond LiTFSI.
• LiTFSI exhibits low lithium-ion transference numbers (T_Li⁺ ≈0.2) and poor solid-electrolyte interphase (SEI) formation.
• Improving ASSLMB performance necessitates salts with enhanced ion transport and interfacial stability.

Purpose of the Study:

• To design and synthesize a novel asymmetric lithium salt, LiC6,6TFSI, to overcome LiTFSI limitations.
• To enhance ASSLMB cyclability by tuning electrolyte transport properties and reducing anion mobility.
• To ensure cathode component compatibility through the development of an amphipathic lithium salt.

Main Methods:

• Synthesis of the asymmetric lithium salt: lithium (trifluoromethanesulfonyl)(N-N-dihexylsulfamoyl)imide (LiC_6,6TFSI).
• Fabrication of solid polymer electrolytes (SPEs) using LiC_6,6TFSI and poly(ethylene oxide) (PEO).
• Electrochemical characterization of SPEs, including T_Li⁺ measurements and battery performance testing (Li||LiFePO₄ cells).

Main Results:

• The LiC_6,6TFSI-based SPE demonstrated significantly reduced anion diffusivity and high T_Li⁺ values (≈0.52).
• The amphipathic nature of LiC_6,6TFSI improved compatibility between polar and non-polar cathode components.
• Li||LiFePO₄ cells utilizing the new SPE exhibited good capacity retention under demanding conditions (high areal loading and current rates).

Conclusions:

• The novel asymmetric lithium salt, LiC_6,6TFSI, effectively enhances ASSLMB performance.
• High T_Li⁺ and amphipathic properties contribute to improved cyclability and interfacial stability.
• LiC_6,6TFSI represents a promising alternative lithium salt for next-generation solid-state batteries.