A "Liquid-In-Solid" Electrolyte for High-Voltage Anode-Free Rechargeable Sodium Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Anode-free batteries are crucial for high energy density and safety, especially for sodium (Na)-based systems facing challenges with low energy density and reactive Na metal anodes.
• Existing electrolytes struggle to balance high Na plating-stripping Coulombic efficiency (CE) with oxidative stability at high voltages, hindering stable anode-free Na battery development.

Purpose of the Study:

• To design a novel electrolyte integrating the benefits of both liquid and solid-state electrolytes for advanced anode-free sodium batteries.
• To achieve high Coulombic efficiency and excellent high-voltage stability simultaneously in sodium batteries.

Main Methods:

• A "liquid-in-solid" electrolyte strategy was employed, utilizing Na-containing zeolite molecular sieves modified via ion-exchange.
• Liquid ether electrolytes were confined within the nanopores and voids of the modified zeolites to create a composite electrolyte.

Main Results:

• The developed electrolyte demonstrated excellent high-voltage stability attributed to the solid-state zeolite component.
• It inherited ultra-high Coulombic efficiency (99.84%) from the liquid ether component.
• Anode-free Na batteries utilizing this electrolyte achieved an energy density of 412 W h kg⁻¹, comparable to state-of-the-art lithium-ion batteries, with 89.2% capacity retention after 370 cycles.

Conclusions:

• The "liquid-in-solid" electrolyte design successfully addresses the limitations of conventional electrolytes for anode-free Na batteries.
• This approach enables the development of safer, high-energy-density sodium batteries with enhanced cycling stability.