Electrolytes speed up development of zinc batteries

Abstract

Zinc (Zn) batteries have attracted great attention since Zn anode is cost-effective and safe, and also exhibit high capacity and low potential. Much effort has been made to achieve superior battery performance, i.e., structural design of cathodes, optimizing electrolytes, and modification of Zn anode [1–3]. Zn batteries can apply aqueous electrolytes and non-aqueous electrolytes. However, both of them also suffer from some obstacles in the practical applications. For examples, aqueous Zn batteries face the challenges in the structural stability of cathodes, Zn dendrite growth, and hydrogen evolution at the Zn anode. There are some challenges in rare cathodes, low-voltage of cathodes for organic Zn batteries. Recently, two papers published in Angewandte Chemie International Edition from Wang’s group [1] and Energy Environmental Science from Li’s group [4] reported the new development of electrolytes for improving the performance of Zn batteries. Wang’s group [1] designed a non-aqueous zinc-organic battery, which was composed of phenanthrenequinone macrocyclic trimer (PQ-MCT) cathode, Zn foil anode, and the electrolyte of a N,N-dimethylformamide (DMF) solution with Zn. As shown in Fig. 1a, the single Zn coordinates with four DMF molecules [5], while the polar acyl groups (N–C=O) have a stronger binding energy with Zn surface than Zn [6]. Benefiting from the peculiar Zn–DMF structure, the DMF molecules can interact with Zn foil and serve as an intermediate to help Zn homogeneous transport to the Zn surface and even deposition, avoiding undesired dendrite growth and hydrogen evolution reaction. Meanwhile, PQ-MCT cathode can store Zn through reversible coordination reaction of Zn and C=O groups. The ZnkPQ-MCT cell can be cycled 20,000 times at 1 A g with ignorable capacity damping. Furthermore, the wide liquefaction temperature range of DMF renders a low freezing point and high boiling point to the electrolyte so that the full battery can be operated from 70 to 150 C. The contribution of this work lies in providing the deep understanding of the interaction between non-aqueous solvent molecule and Zn. Equally importantly, the using of DMF broadens the operation-temperature window of Zn batteries. Besides, the innovative application of organic cathode enables the ultra-long life of the Zn full battery. In conclusion, this work proposed the new strategy to design the novel Zn batteries with ultra-long cycling life and wide working temperature range. Li’s group proposed a high zinc-ion conductivity and high reversibility hybrid electrolyte which was composed of water, ethylene glycol (EG) and zinc sulfate salt (ZnSO4) [4]. Combining experiments and theoretical calculations, EG has been proved to have a unique solvation interaction with Zn, which can effectively decrease the solvation interaction of Zn with H2O, as shown in Fig. 2a. Besides, Zn prefers to coordinate with EG rather than H2O, contributing to the fast exchange of EG around Zn and fast conduction of Zn in the added-EG electrolyte [7]. Meanwhile, the introduction of EG can decrease the electrostatic potential of the Zn–5H2O solvation state, weakening the electrostatic repulsion between Zn cations (Fig. 2b), which is beneficial to a fast Zn-ion C.-X. Xu, J.-J. Jiang* School of Physics and Electronics, Hunan University, Changsha 410082, China e-mail: [email protected]