High‐Performance Sodium Metal Anodes Enabled by a Bifunctional Potassium Salt

• Published in: Angewandte Chemie International Edition 2018-07, Vol.57 (29), p.9069-9072
• Main Authors: Shi, Qiuwei, Zhong, Yiren, Wu, Min, Wang, Hongzhi, Wang, Hailiang
• Format: Article
• Language: English
• Subjects: Anions; Anodes; Batteries; bifunctional additives; Cations; Chemical reactions; Dendritic structure; Electrodes; Electrolytes; Electrostatic shielding; Flux density; Lithium; Metals; Organic chemistry; Oxynitrides; Potassium; Potassium salts; Rechargeable batteries; Sodium; sodium metal anodes; solid electrode interface; Solid electrolytes
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201803049

Developing Na metal anodes that can be deeply cycled with high efficiency for a long time is a prerequisite for rechargeable Na metal batteries to be practically useful despite their notable advantages in theoretical energy density and potential low cost. Their high chemical reactivity with the electrolyte and tendency for dendrite formation are two major issues limiting the reversibility of Na metal electrodes. In this work, we introduce for the first time potassium bis(trifluoromethylsulfonyl)imide (KTFSI) as a bifunctional electrolyte additive to stabilize Na metal electrodes, in which the TFSI− anions decompose into lithium nitride and oxynitrides to render a desirable solid electrolyte interphase layer while the K+ cations preferentially adsorb onto Na protrusions and provide electrostatic shielding to suppress dendritic deposition. Through the cooperation of the cations and anions, we have realized Na metal electrodes that can be deeply cycled at a capacity of 10 mAh cm−2 for hundreds of hours. Working together: Through the cooperation of the cations and anions of a bifunctional electrolyte additive, potassium bis(trifluoromethylsulfonyl)imide, Na metal electrodes that can be deeply cycled at a capacity of 10 mAh cm−2 for hundreds of hours have been realized.