Molecular Engineering on Solvation Structure of Carbonate Electrolyte toward Durable Sodium Metal Battery at −40 °C

Abstract

Carbonate electrolytes have excellent chemical stability and high salt solubility, which are ideally practical choice for achieving high-energy-density sodium (Na) metal battery at room temperature. However, their application at ultra-low temperature (À 40 °C) is adversely affected by the instability of solid electrolyte interphase (SEI) formed by electrolyte decomposition and the difficulty of desolvation. Here, we designed a novel low-temperature carbonate electrolyte by molecular engineering on solvation structure. The calculations and experimental results demonstrate that ethylene sulfate (ES) reduces the sodium ion desolvation energy and promotes the forming of more inorganic substances on the Na surface, which promote ion migration and inhibit dendrite growth. At À 40 °C, the Na j j Na symmetric battery exhibits a stable cycle of 1500 hours, and the Na j j Na 3 V 2 (PO 4 ) 3 (NVP) battery achieves 88.2 % capacity retention after 200 cycles.

Wide-temperature-range sodium-metal batteries: from fundamentals and obstacles to optimization

“…115 A creative carbonate electrolyte was designed by using a 1 M sodium bis(fluorosulfonyl)imide (NaFSI) in ethylene carbonate/ propylene carbonate/diethyl carbonate (EC/PC/DEC) at a volume ratio of 1 : 1 : 4, which was employed to operate at À40 1C for SMB. 85 Fig. 6a shows the frontier orbital energies of FSI À , ES, PC, EC and DEC, respectively.…”

“…85,213 Calculation of the frontier molecular orbital energy can aid assessment of the reduction stability of each electrolyte component and the contribution of additives in an SEI membrane. 85,213 ES has a LUMO energy of B0.14 eV, which indicates that foreign electrons end to occupy their lower electron orbitals, making ES easier to reduce and participate in the generation of a SEI at higher voltages. 85,213 Conversely, FSI À , with a high LUMO energy of 3.78 eV, has relatively high reduction stability.…”

“…85,213 ES has a LUMO energy of B0.14 eV, which indicates that foreign electrons end to occupy their lower electron orbitals, making ES easier to reduce and participate in the generation of a SEI at higher voltages. 85,213 Conversely, FSI À , with a high LUMO energy of 3.78 eV, has relatively high reduction stability. 85,213 However, FSI À remains thermodynamically unstable on the highly reactive Na metal surface.…”

“…85,213 Conversely, FSI À , with a high LUMO energy of 3.78 eV, has relatively high reduction stability. 85,213 However, FSI À remains thermodynamically unstable on the highly reactive Na metal surface. As a strategy, adding ES (6 vol%) to 1 M NaFSI-(EC/PC/DEC) can effectively enhance the interfacial charge-transfer dynamics and passivation performance of the SEI, and this LT electrolyte is denoted as ''ES6-BLTE''.…”

“…1 shows the development timeline of SMBs in recent years, with some important breakthroughs recorded. [73][74][75][76][77][78][79][80][81][82][83][84][85] For example, a simple liquid electrolyte, sodium hexafluorophosphate in glymes, was first reported in 2015. 73 An ultra-stable SMB with an energy density 4200 W h kg À1 was first reported by Zheng and colleagues in 2021.…”