Water–Salt Oligomers Enable Supersoluble Electrolytes for High‐Performance Aqueous Batteries. Issue 13 (26th February 2021)

• Record Type: Journal Article
• Authors: Cai, Shengying; Chu, Xingyuan; Liu, Chang; Lai, Haiwen; Chen, Hao; Jiang, Yanqiu; Guo, Fan; Xu, Zhikang; Wang, Chunsheng; Gao, Chao
• Is Part Of: Advanced materials. Volume 33:Issue 13(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-02-26
• Subjects: aqueous rechargeable batteries -- supersoluble electrolytes -- water–salt oligomers -- zinc–halogen chemistry; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adma.202007470
• Languages: English
• ISSNs: 0935-9648

Abstract

Abstract: Aqueous rechargeable batteries are highly safe, low‐cost, and environmentally friendly, but restricted by low energy density. One of the most efficient solutions is to improve the concentration of the aqueous electrolytes. However, each salt is limited by its physical solubility, generally below 21–32 mol kg −1 (m). Here, a ZnCl2 /ZnBr2 /Zn(OAc)2 aqueous electrolyte with a record super‐solubility up to 75 m is reported, which breaks through the physical solubility limit. This is attributed to the formation of acetate‐capped water–salt oligomers bridged by Br − /Cl − ‐H and Br − /Cl − /O‐Zn 2+ interactions. Mass spectrometry indicates that acetate anions containing nonpolarized protons prohibit the overgrowth and precipitation of ionic oligomers. The polymer‐like glass transition temperature of such inorganic electrolytes is found at ≈− 70 to − 60 ° C, without the observation of peaks for salt‐crystallization and water‐freezing from 40 to − 80 ° C. This supersoluble electrolyte enables high‐performance aqueous dual‐ion batteries that exhibit a reversible capacity of 605.7 mAh g −1, corresponding to an energy density of 908.5 Wh kg −1, with a coulombic efficiency of 98.07%. In situ X‐ray diffraction and Raman technologies reveal that such high ionic concentrations of the supersoluble electrolyte enable a stage‐1 intercalation of bromine into macroscopically assembled graphene cathode. Abstract : Water–salt oligomers break through the physical solubility limits of aqueous electrolytes, enabling high‐capacity rechargeable batteries based on zinc–halogen chemistry. The polymer‐like characters of such electrolytes are confirmed by relatively large molecular‐ion peaks and low glass‐transition temperatures. In situ electrochemical technologies reveal a stage‐1 intercalation of bromine into the graphene cathode during charging, accounting for the high capacity of the assembled batteries.