Origins of Dendrite Formation in Sodium–Oxygen Batteries and Possible Countermeasures

Abstract

One limiting phenomenon for the cycle life of metal–oxygen batteries is the growth of dendrites during metal plating (cell charging). For the relatively new sodium–oxygen cell, this subject has been scarcely investigated, until now. Therefore, dendrite formation is systematically investigated herein, with the aim of gaining a more detailed understanding of the underlying mechanisms and relevant control parameters. Electrochemical impedance spectroscopy, cycling experiments, and optical characterization techniques are applied in situ and ex situ; sodium dendrite growth is directly visualized, for the first time, by means of a tubular glass cell. The growth of instable surface morphologies is discussed from a theoretical perspective to comprehend the experimentally observed dendrite growth. Furthermore, countermeasures against issues with dendrites are discussed, with the aim of increasing the cycle life of sodium–oxygen batteries.

Design Strategies to Enable the Efficient Use of Sodium Metal Anodes in High‐Energy Batteries

“…Furthermore, the lack of flexibility does not allow the SEI to constrain the volume expansion during Na plating, and therefore, cracks can form easily in the SEI. The enhanced Na‐ion flux in cracks accelerates nonuniform Na plating as the energy barrier of Na‐ion diffusion in those areas becomes lower . Consequently, Na dendrites grow abundantly from the cracks upon further Na plating.…”

A Sodium Polysulfide Battery with Liquid/Solid Electrolyte: Improving Sulfur Utilization Using P2S5 as Additive and Tetramethylurea as Catholyte Solvent

“…The choice of NaOTf/2G as electrolyte solution is motivated because of its good stability and low interface resistance compared with other electrolyte solutions . Despite these advantages, it is of note that dendrite formation remains an issue, see Figure S2, Supporting Information.…”

Incorporating Diamondoids as Electrolyte Additive in the Sodium Metal Anode to Mitigate Dendrite Growth

“…Dendrites may either melt (“soft‐shorts”), or heat up but remain intact (“hard‐shorts”) . Both scenarios can lead to local overheating of the organic electrolyte up to its ignition temperature . To mitigate or suppress the growth of dendrites, a variety of strategies have been proposed in the past: 1) Specific cycling protocols (e.g., shallow cycling, pulsed charging) that only utilize a small amount of active material or allow for a higher ion concentration near the surface of the anode that is plated; 2) modification of the electrode (e.g., using intercalation electrodes, 3 D‐structured electrodes, liquid electrodes); 3) mechanical suppression (e.g., solid electrolytes, polymer‐membrane) and 4) modification of the electrolyte (e.g., NaF, InF 3 , fluoroethylene carbonate (FEC), nanodiamond particles) …”

“…The aim of most electrolyte modifications is to form a more stable solid electrolyte interphase (SEI) that alters the metal plating processes and slows or avoids dendrite growth. However, the formed SEI might still crack owing to its inhomogeneous mechanical and physical properties, resulting in accelerated growth of dendrites owing to a channeled flux of metal ions into these cracks . As an alternative, Gogotsi's group recently proposed nanodiamond particles as an electrolyte additive to mitigate dendrite growth in lithium‐metal‐based batteries .…”