ABSTRACT
Electrochemically reversible redox couples that embrace more electron transfer at a higher potential are the eternal target for energy storage batteries. Here, we report a four-electron aqueous zinc-iodine battery by activating the highly reversible I2/I+ couple (1.83 V vs. Zn/Zn2+) in addition to the typical I-/I2 couple (1.29 V). This is achieved by intensive solvation of the aqueous electrolyte to yield ICl inter-halogens and to suspend its hydrolysis. Experimental characterization and modelling reveal that limited water activity and sufficient free chloride ions in the electrolyte are crucial for the four-electron process. The merits of the electrolyte also afford to stabilize Zn anode, leading to a reliable Zn-I2 aqueous battery of 6000 cycles. Owing to high operational voltage and capacity, energy density up to 750 Wh kg-1 based on iodine mass was achieved (15-20 wt% iodine in electrode). It pushes the Zn-I2 battery to a superior level among these available aqueous batteries.
ABSTRACT
The highly reversible zinc-bromine redox couple has been successfully applied in the zinc-bromine flow batteries; however, non-electroactive pump/pipe/reservoir parts and ion-selective membranes are essential to suppress the bromine diffusion. This work demonstrates a zinc-bromine static (non-flow) battery without these auxiliary parts and utilizing glass fiber separator, which overcomes the high self-discharge rate and low energy efficiency while the advantages of the zinc-bromine chemistry are well preserved. It is achieved by a multifunctional additive, tetrapropylammonium bromide (TPABr), which not only mitigates the bromine cross-diffusion by regulating the fluidic bromine to a condensed solid phase but also provides a favorable interface for zinc electrodeposition toward non-dendritic growth. The proposed zinc-bromine static battery demonstrates a high specific energy of 142 Wh kg-1 with a high energy efficiency up to 94%. By optimizing the porous electrode architecture, the battery shows an ultra-stable cycling life for over 11,000 cycles with controlled self-discharge rate.
