Improving the Cycling Stability of Aqueous Zinc-Ion Batteries by Preintercalation of Polyaniline in Hydrated Vanadium Oxide

Supramolecular channels via crown ether functionalized polyaniline for proton-self-doped cathode in aqueous zinc-ion battery

Polyaniline (PANI) has been widely used as a cathode in aqueous zinc-ion batteries (AZIBs) because of its attractive conductivity and energy storage capability. However, the extensive application of PANI is limited by spontaneous deprotonation and slow diffusion kinetics. Herein, an 18-crown-6-functionalised PANI pseudorotaxane (18C6@PANI) cathode is successfully developed through a facile template-directed polymerisation reaction. The 18C6@PANI cathode exhibits a high specific capacity of 256 mAh g-1 at 0.2 A/g, excellent rate performance of 134 mAh g-1 at 6 A/g and outstanding cycle stability at a high current density of 3 A/g over 10,000 cycles. Experimental and theoretical analyses demonstrate the formation of the -N-Zn-O- structure. The abundant supramolecular channels in pseudorotaxane, induced by crown ether functional groups, are beneficial for achieving superior cyclability and rate capability. These encouraging results highlight the potential for designing more efficient PANI-based cathodes for high-performance AZIBs.

Vanadium Oxide Cathode Coinserted by Ni2+ and NH4+ for High-Performance Aqueous Zinc-Ion Batteries

Vanadium-based oxides have garnered significant attention as cathode materials for aqueous zinc-ion batteries (AZIBs) because of their high theoretical capacity and low cost. However, the limited reaction kinetics and poor long-term cycle stability hinder their widespread application. In this paper, we propose a novel approach by coinserting Ni2+ and NH4+ ions into V2O5·3H2O, i.e., NNVO. Structural characterization shows that the coinsertion of Ni2+ and NH4+ not only extends the interlayer spacing of V2O5·3H2O but also significantly promotes the transport kinetics of Zn2+ because of the synergistic "pillar" effect of Ni2+ and NH4+, as well as the increased oxygen vacancies that effectively lower the energy barrier for Zn2+ insertion. As a result, the AZIBs with an NNVO electrode exhibit a high capacity of 398.1 mAh g-1 (at 1.0 A g-1) and good cycle stability with 89.1% capacity retention even after 2000 cycles at 5.0 A g-1. At the same time, a highly competitive energy density of 262.9 Wh kg-1 is delivered at 382.9 W kg-1. Considering the simple scheme and the resultant high performance, this study may provide a positive attempt to develop high-performance AZIBs.

Enhancing organic cathodes of aqueous zinc-ion batteries via utilizing steric hindrance and electron cloud equalization

Polyaniline (PANI), with merits of high electronic conductivity and capacity, is a promising material for zinc (Zn)-ion batteries. However, its redox window in Zn batteries is often limited, mainly due to the oxidative degradation at high potentials-in which imine groups can be attacked by water molecules. Here, we introduce phytic acid, a kind of supermolecule acid radical ion, as a dopant and electrolyte additive. Various in/ex situ analyses and theoretical calculations prove that the steric hindrance effect can prevent electroactive sites from the attack by water molecules. Meanwhile, the redox reaction can be stabilized by an even distribution of electron cloud due to the conjugated structure of phenazine groups. Accordingly, the assembled Zn-PANI battery can allow stable and long-term charge-discharge reactions to occur at a potential as high as 2.0 V with a discharged plateau of 1.5 V, and it also shows high rate performance and stable long cycle life (75% capacity retention after 1000 cycles at 10 A g-1).