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

Why It Matters

By solving Al corrosion and electrolyte instability, LiCTf2 paves the way for safer, longer‑lasting high‑voltage lithium‑ion batteries essential for next‑generation electric‑vehicle and grid storage applications.

Key Takeaways

• LiCTf2 replaces nitrogen with methine, reducing Al corrosion
• Forms low‑solubility Al³⁺ complexes, protecting current collector
• Enhances Li⁺ coordination, creating dense cathode‑electrolyte interphase
• Enables additive‑free stable cycling of NMC532 and NMC811
• Outperforms LiNTf2 and LiPF6 in capacity retention

Pulse Analysis

The relentless push for higher energy density has placed Ni‑rich layered oxides such as NMC532 and NMC811 at the forefront of lithium‑ion battery research. Yet their promise is hampered by rapid interfacial degradation when paired with conventional electrolytes. Lithium hexafluorophosphate (LiPF6), the industry standard, decomposes to hydrofluoric acid, eroding both active material and the aluminum current collector. Even more chemically stable lithium bis‑trifluoromethanesulfonyl‑imide (LiNTf2) suffers from severe Al corrosion above 3.7 V, limiting its practical voltage window. These degradation pathways also accelerate gas evolution, posing safety concerns.

The newly reported lithium bis‑trifluoromethanesulfonyl‑methide (LiCTf2) tackles these shortcomings through a simple yet powerful anion redesign. By swapping the central nitrogen atom of LiNTf2 for a methine (‑CH‑) group, the resulting CTf2⁻ anion exhibits a lower electron‑donating character, encouraging the formation of sparingly soluble Al³⁺ complexes that passivate the collector surface. Simultaneously, the altered charge distribution strengthens Li⁺ coordination, yielding a more compact solvation shell and promoting a hybrid inorganic‑organic cathode‑electrolyte interphase with well‑defined stratification. Molecular dynamics simulations corroborate the tighter Li⁺ solvation and reduced Al‑anion reactivity.

Electrochemical testing confirms that LiCTf2‑based electrolytes deliver markedly improved cycle life for both NMC532 and NMC811, retaining higher capacity over hundreds of charge‑discharge cycles without any film‑forming additives. Compared with LiNTf2 and LiPF6, the new salt reduces impedance growth and suppresses transition‑metal dissolution, translating into safer, longer‑lasting cells. For manufacturers, the additive‑free formulation simplifies electrolyte processing and lowers material costs, while the non‑corrosive nature expands design flexibility for high‑voltage packs. Continued optimization of methide‑based salts could therefore accelerate commercialization of next‑generation high‑energy lithium‑ion batteries. Future work will explore compatibility with silicon anodes and high‑voltage electrolytes.