Polymer Chain‐Guided Ion Transport in Aqueous Electrolytes of Zn‐Ion Batteries

Abstract

As a promising candidate for next‐generation energy storage devices, Zn metal battery excels with their good safety, high specific capacity, and economic attractiveness. However, it still suffers from a narrow electrochemical window, notorious dendrite formation, and sluggish Zn ion transfer. Aqueous electrolyte engineering has been regarded as an effective way to improve these. It is shown that by adding sodium polystyrene sulfonate (PSS) polymers into a dilute 1 m Zn(OTf)2 aqueous electrolyte, compact water shells with stronger hydrogen bonding and more ordered structures are formed around the polymer chains. As a result, a fast transport channel to the zinc ions is provided. The PSS chains also protect the zinc electrode from directly contacting the water molecules and thus suppress water decomposition. With these merits, a Zn//Cu cell demonstrates a high coulombic efficiency of ≈99% after 1500 h cycling. Meanwhile, a record‐high cumulative Zn plating capacity of 10 000 mA h cm−2 is obtained using a Zn||Zn cell. In addition, the Zn//C@V2O5 full cell achieves almost 100% capacity retention after 1000 cycles. This work provides a new strategy for designing advanced electrolyte systems excelling in ion transport kinetics.

Dual-Salt Mixed Electrolyte for High Performance Aqueous Aluminum Batteries

“…This may be due to the occurrence of Al 3+ embedding and ejection. 33,38 Further ex-situ XPS studies were carried out, and the Al 2p peak showed the same results as XRD, becoming less Al during charging and more Al during discharging (Figure 4d). During the discharging process the Al ions start to insert into the cathode again and the peaks start to move in the opposite direction again, and the spacing of the (022) crystal plane is propped up again.…”

“…A ex-situ XRD was done on the cathode (Figure b), and the movement of the peak can be seen when magnified (Figure c).There is a regular movement; that is, the peak red-shifts when charging and blue-shifts when discharging. This may be due to the occurrence of Al 3+ embedding and ejection. , Further ex-situ XPS studies were carried out, and the Al 2p peak showed the same results as XRD, becoming less Al during charging and more Al during discharging (Figure d). During the discharging process the Al ions start to insert into the cathode again and the peaks start to move in the opposite direction again, and the spacing of the (022) crystal plane is propped up again .…”

“…During charging, Mn 2+ is gradually oxidized into Mn 3+ and Mn 4+ , but it does not completely transform; there is still some Mn 2+ there. 33 During discharging, the Mn 4+ /Mn 3+ reaction and the Mn 3+ /Mn 2+ reaction occur successively, with the Mn 2+ content gradually increasing until finally the difference between points G and A is not very large. The charge and discharge process corresponds to the long charge and discharge platform of the previous cycle curve.…”

“…At the high current density of 500 mA g –1 , it has a clear advantage over batteries that add several other concentrations of LiOTF. This is due to the formation of an Al x MnO 2 structure at the cathode during the charging processa structure that better maintains the structural stability of the electrode and allows for a smoother embedding and detachment of Al ions. , After that, the battery was then cycled with different concentrations of electrolyte, and the battery with 0.5 M LiOTF added to the dual-salt electrolyte had a better cycling performance (Figure d). At other concentrations electrolytes do not have a full cycle life due to corrosion of the anode during cycling.…”

“…At point A it has become Al x MnO 2 , so there is some Mn 3+ and Mn 4+ present, but most of it is still in the form of Mn 2+ . During charging, Mn 2+ is gradually oxidized into Mn 3+ and Mn 4+ , but it does not completely transform; there is still some Mn 2+ there . During discharging, the Mn 4+ /Mn 3+ reaction and the Mn 3+ /Mn 2+ reaction occur successively, with the Mn 2+ content gradually increasing until finally the difference between points G and A is not very large.…”