Non-Corrosive Methide-Based Lithium Salt for Stabilizing Ni-Rich NMC Cathodes

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• High-nickel LiNi_xMn_yCo_1-x-yO₂ (NMC) cathodes offer high energy density for next-generation lithium-ion batteries (LIBs).
• Interfacial instability with conventional electrolytes, particularly lithium hexafluorophosphate (LiPF₆) and lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂), limits NMC cathode performance and battery lifespan.
• LiNTf₂ causes aluminum current collector corrosion above 3.7 V, necessitating the development of non-corrosive electrolyte alternatives.

Purpose of the Study:

• To introduce and evaluate a novel, non-corrosive methide-based lithium salt, lithium bis(trifluoromethanesulfonyl)methide (LiCTf₂), for stabilizing NMC cathodes.
• To investigate the mechanism by which LiCTf₂ suppresses aluminum corrosion and enhances interfacial stability.
• To demonstrate the improved electrochemical performance of NMC cathodes using LiCTf₂-based electrolytes.

Main Methods:

• Synthesis and characterization of the novel lithium bis(trifluoromethanesulfonyl)methide (LiCTf₂) salt.
• Electrochemical testing of LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532) and LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathodes in electrolytes containing LiCTf₂, LiNTf₂, and LiPF₆.
• Electrochemical and microscopic characterization to analyze interfacial stability and corrosion mechanisms.

Main Results:

• LiCTf₂ effectively suppresses aluminum current collector corrosion by forming low-solubility Al³⁺ complexes, unlike LiNTf₂.
• The LiCTf₂ anion enhances Li⁺ coordination, reinforcing solvation structures and promoting denser interphases.
• NMC532 and NMC811 cathodes cycled in LiCTf₂-based electrolytes exhibit significantly improved cycling stability compared to those using LiNTf₂ or LiPF₆, without needing film-forming additives.

Conclusions:

• Lithium bis(trifluoromethanesulfonyl)methide (LiCTf₂) is a promising non-corrosive lithium salt for advanced LIB electrolytes.
• LiCTf₂ offers intrinsic interfacial engineering capabilities, enhancing the electrochemical stability and cycling performance of high-nickel NMC cathodes.
• This work provides a new avenue for electrolyte optimization, crucial for developing safer and more durable next-generation lithium-ion batteries.