4.6 V Moisture-Tolerant Electrolytes for Lithium-Ion Batteries

Commercial LiPF₆-based electrolytes face limitations in oxidation stability (4.2 V) and water tolerance (10 ppm). While replacing LiPF₆ with lithium bis(trifluoromethane)sulfonimide (LiTFSI) improves water tolerance, it induces Al current collector corrosion above 3.7 V vs. Li/Li⁺. To address this, lithium cyano(trifluoromethanesulfonyl)imide (LiCTFSI) is proposed here as a non-corrosive, moisture-tolerant alternative. The 2.0 M LiCTFSI/propylene carbonate (PC)-fluoroethylene carbonate (FEC) (7:3 by volume) electrolyte enables LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes to reach 210 mAh g⁻¹ (2.8-4.6 V) with a cycle life of 500. Full cells with NCM811||graphite (2.0 mAh cm⁻²) show 77.8% capacity retention after 500 cycles. Even with 2000 ppm moisture in the electrolyte, full cells maintain high cycling stability, reducing the need for costly dry rooms. The electrolyte’s low freezing point and high thermal stability enable the operation from -20 °C to 60 °C, delivering 168 mAh g⁻¹ at -20 °C and retaining 94% capacity after 100 cycles at 60 °C. In contrast, cells with commercial LiPF₆ electrolyte deliver 71 mAh g⁻¹ at -20°C and retain 52.7% after 100 cycles at 60 °C. This novel salt offers a cost-effective solution for developing robust, high-performance batteries suitable for extreme conditions. © 2024 Wiley-VCH GmbH.