Reversible Oxygen Redox Chemistry in Aqueous Zinc‐Ion Batteries

Abstract

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising energy-storage devices owing to their low cost and high safety.H owever,t heir energy-storage mechanisms are complex and not well established. Recent energy-storage mechanisms of ZIBs usually depend on cationic redox processes.A nionic redox processes have not been observed owingt ot he limitations of cathodes and electrolytes.H erein, we describe highly reversible aqueous ZIBs based on layered VOPO 4 cathodes and awater-in-salt electrolyte.Suchbatteries displayr eversible oxygen redoxc hemistry in ah igh-voltage region. The oxygen redoxp rocess not only provides about 27 %a dditional capacity,b ut also increases the average operating voltage to around 1.56 V, thus increasing the energy density by approximately 36 %. Furthermore,t he oxygen redoxprocess promotes the reversible crystal-structure evolution of VOPO 4 during charge/discharge processes,t hus resulting in enhanced rate capability and cycling performance.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Recent Progress in the Electrolytes of Aqueous Zinc‐Ion Batteries

“…[16c] Such water-in-salt electrolyte not only displays nearly 100 %C oulombic efficiency withoutt he growth of dendrites during Zn plating/strippingp rocess, but also suppresses the consumption of water in the open atmosphere. In addition, the highly concentrated electrolytes of 21 m LiTFSI and 1 m Zn(CF 3 SO 3 ) 2 solution could also expand the electrochemically stable voltage windowst oa pproximately 2.60 Vi n comparison with the case of conventional ZnSO 4 electrolyte of 2.4 V. [26] Therefore, the assembled Zn/VOPO 4 battery could operate at the high voltage of about 2.1 V. In addition, owing to the existence of PO 4 3À polyanions, the VOPO 4 nanosheet displays ah ighera verage operating voltage ( % 1.56 V). Furthermore, since the electron density of the oxygen in V x O y polyhedra wasincreasedd ue to the introductionofP ÀOc ovalence, oxygen redoxi so bserved in Zn/VOPO 4 battery.T he oxygen redox chemistry can provide additional capacity of about 27 % at the high voltage region,l eadingt oa ni ncrease of the energy density.B esides, to broaden the electrochemically stable potential windowo fZ nCl 2 electrolytes, 30 m highly con-centrated ZnCl 2 electrolyte was developed.…”

Recent Progress on Zinc-Ion Rechargeable Batteries

“…To completely eliminate the formation of Zn dendrites, Wang et al developed a unique aqueous electrolyte at high concentrations composed of 1 M Zn(TFSI) 2 and 20 M LiTFSI, proved to achieve 100% Coulombic efficiency and no dendrite formation during Zn plating/stripping [121]. In addition, Chen and his co-workers developed Zn/VOPO 4 batteries using a water-in-salt electrolyte to realize reversible oxygen redox chemistry in a high voltage region [122]. Since Zn metal anodes show high corrosion current and low positive corrosion potential in 1 M Zn(Tr) 2 electrolyte, they applied highly concentrated 21 M LiTFSI/1 M Zn(Tr) 2 water-in-salt electrolyte in ZIBs, which can suppress the corrosion of zinc and also constrain the dissolution of VOPO 4 cathode due to the limited activity of water.…”

High‐Performance and Ultra‐Stable Aqueous Supercapacitors Based on a Green and Low‐Cost Water‐In‐Salt Electrolyte

“…Electrolytes, the source of the ions that conduct between two electrodes, play a very important role in determining the operating voltage and the overall performance of devices . Therefore, considerable efforts have been devoted to design and optimize reasonable electrolytes in recent years . Compared with aqueous electrolytes, ionic liquids and organic electrolytes usually exhibit wider electrochemical windows (>3.0 V), which notably have advantage of higher energy density .…”

“…[17][18][19] Therefore, considerable efforts have been devoted to design and optimize reasonable electrolytes in recent years. [20][21][22][23][24][25] Compared with aqueous electrolytes, ionic liquids and organic electrolytes usually exhibit wider electrochemical windows (> 3.0 V), which notably have advantage of higher energy density. [26] But the higher viscosity and lower conductivity (usually up to 20 mS cm À 1 ) of ionic liquids still render their further application for electrochemical capacitors (ECs).…”