Electrolyte Engineering with Tamed Electrode Interphases for High-Voltage Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) hold great promise for next-generation grid-scale energy storage. However, the highly instable electrolyte/electrode interphases threat long-term cycling of high-energy SIBs. In particular, the instable cathode electrolyte interphase (CEI) at high voltage causes persistent electrolyte decomposition, transition metal dissolution and fast capacity fade. Here we propose a balanced principle for molecular design of SIB electrolytes that enable an ultra-thin, homogeneous and robust CEI layer by coupling an intrinsically oxidation stable succinonitrile solvent with moderately solvating carbonates. The proposed electrolyte not only shows limited anodic decomposition thus leading to a thin CEI, but also suppresses dissolution of CEI components at high voltage. Consequently, the tamed electrolyte/electrode interphases enable extremely stable cycling of Na 3 V 2 O 2 (PO 4 ) 2 F (NVOPF) cathodes with outstanding capacity retention (> 90%) over 3000 cycles (eight months) at 1 C with a high charging voltage of 4.3 V. Further, the NVOPF||hard carbon full cell shows stable cycling over 500 cycles at 1 C with a high average Coulombic efficiency of 99.6%. The electrolyte also endows high-voltage operation of SIBs with great temperature adaptability from -25 o C to 60 °C, shedding light on the essence of fundamental electrolyte design for SIBs operating under harsh conditions. This article is protected by copyright. All rights reserved.