Abstract

Sodium-based batteries have attracted considerable attention and are recognized as ideal candidates for large-scale and low-cost energy storage. Sodium (Na) metal anodes are considered as one of the most promising anodes for next-generation, high-energy, Na-based batteries owing to their high theoretical specific capacity (1166 mA h g-1 ) and low standard electrode potential. Herein, an overview of the recent developments in Na metal anodes for high-energy batteries is provided. The high reactivity and large volume expansion of Na metal anodes during charge and discharge make the electrode/electrolyte interphase unstable, leading to the formation of Na dendrites, short cycle life, and safety issues. Design strategies to enable the efficient use of Na metal anodes are elucidated, including liquid electrolyte engineering, electrode/electrolyte interface optimization, sophisticated electrode construction, and solid electrolyte engineering. Finally, the remaining challenges and future research directions are identified. It is hoped that this progress report will shape a consistent view of this field and provide inspiration for future research to improve Na metal anodes and enable the development of high-energy sodium batteries.

Highlights

  • Na anodes undergo severe volume expansion during plating and volume contraction during stripping, which induces the breakage of the solid electrolyte interphase” (SEI) layer and exposes fresh Na to the liquid electrolyte

  • In-depth X-ray photoelectron spectroscopy (XPS) analysis revealed a uniform SEI composed of inorganic sodium fluoride (NaF) and sodium oxide (Na2O) on the surface of the Na anode

  • Since Na metal anodes undergo unwanted side reactions with liquid electrolytes, it is crucial to assess whether solid electrolytes (SEs) can replace them in practical applications

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Summary

Challenges of Na Metal Anodes

To effectively use Na anodes in practical rechargeable battery systems, several challenges need to be overcome, the greatest of which are Coulombic efficiency and cyclability.[4,20,21] High Coulombic efficiency during cycling can minimize the amount of the required active Na in the battery system, reduce the materials cost, and increase the energy density of the entire system. Na anodes undergo severe volume expansion during plating and volume contraction during stripping, which induces the breakage of the SEI layer and exposes fresh Na to the liquid electrolyte. This effect accelerates further side reactions that deplete the limited Na metal and electrolyte in the. Guoxiu Wang is the director of the Centre for Clean Energy Technology and a distinguished professor at University of Technology Sydney (UTS), Australia He is an expert in materials chemistry, electrochemistry, energy storage and conversion, and battery technologies. The repeated plating/stripping of Na-ion/Na leads to accumulation of “dead” Na, formation of more SEI, increased porosity of the Na anode, and the depletion of electrolyte, inducing poor cycling stability

Liquid Electrolyte Engineering
Ether-Based Electrolytes
Electrolyte Additives
Nanostructured Hosts for Na Metal
Solid-State Electrolyte Engineering
Preventing “Cross-Talk” and Dendrite Growth
Optimizing Properties of Solid Electrolytes
Outlook and Future Perspectives
Findings
Conflict of Interest

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