In situ synthesis of layered nickel organophosphonates for efficient aqueous nickel-zinc battery cathodes

Aqueous nickel-zinc (Ni-Zn) batteries have received increasing research interests because of their reliable safety and economical-friendliness. However, the retarded ionic diffusion, low capacity and limited stability of traditional Ni-based cathodes greatly impedes the practical application of Ni-Zn batteries. Herein, two metal organophosphonate materials of Ni methylphosphonate (Ni-MPA) and Ni phenylphosphonate (Ni-PPA) directly grown on Ni foam are constructed successfully through one step solvothermal technique. These two self-supported Ni organophosphonates featured hybrid two-dimensional (2D) structures consisting of alternating inorganic and organic layers, where the inorganic layers are formed by six-coordinated Ni2+ bridged by oxygen atoms and capped by organophosphonate groups, availing to provide rich open redox reaction sites, rapid ion diffusion and structural flexibility. The research results reveal that the organic groups in phosphonic acid ligands have important influence on their electrochemical properties. Consequently, the Ni-MPA electrode exhibits a higher specific capacity of 2.27 mAh/cm2 compared to that of the Ni-PPA electrode (1.1 mAh/cm2) at 3.0 mA/cm2; however, it demonstrates a more rapid transformation rate into Ni(OH)2 in an alkaline solution. Furthermore, the constructed Ni-MPA//Zn battery can deliver an impressive areal energy density of 2.95 mWh/cm2, good rate performance as well as a long-term cycling stability.

Enhancing Energy Conversion Efficiency and Durability of Alkaline Nickel-Zinc Batteries with Air-Breathing Cathode

Despite their high output voltage and safety advantages, rechargeable alkaline nickel-zinc batteries face significant challenges associated with the cathodic side reaction of oxygen evolution, which results in low energy efficiency (EE) and poor stability. Herein, we propose to leverage the side oxygen evolution reaction (OER) in nickel-zinc batteries by coupling electrocatalysts for oxygen reduction reactions (ORR) in the cathode, thus constructing an air breathing cathode. Such a novel battery (Ni-ZnAB), designed in a pouch-type cell with a lean electrolyte, exhibits an outstanding EE of 85% and a long cycle life of 100 cycles at 2 mA cm-2, which are significantly superior to those of traditional Ni-Zn batteries (54%, 50 cycles). Compared to Ni-Zn, the enhanced EE of Ni-ZnAB is attributed to the contribution from ORR, while the improved cycling stability is because the stability of the anode, cathode and electrolyte are also enhanced in Ni-ZnAB. Furthermore, an ultrahigh stability of 500 cycles with an average EE of 84% at 2 mA cm-2 was achieved using a mold cell with rich electrolyte, demonstrating the strong application potential of Ni-ZnAB.

One-Pot Synthesis of NiSe(2) with Layered Structure for Nickel-Zinc Battery

Transition metal organic framework materials and their selenides are considered to be one of the most promising cathode materials for nickel-zinc (denoted as Ni-Zn) batteries due to their low cost, environmental friendliness, and controllable microstructure. Yet, their low capacity and poor cycling performance severely restricts their further development. Herein, we developed a simple one-pot hydrothermal process to directly synthesize NiSe₂ (denotes as NiSe₂-X based on the molar amount of SeO₂ added) stacked layered sheets. Benefiting from the peculiar architectures, the fabricated NiSe₂-1//Zn battery based on NiSe₂ and the Zn plate exhibits a high specific capacity of 231.6 mAh g^-1 at 1 A g^-1, and excellent rate performance (162.8 mAh g^-1 at 10 A g^-1). In addition, the NiSe₂//Zn battery also presents a satisfactory cycle life at the high current density of 8 A g^-1 (almost no decay compared to the initial specific capacity after 1000 cycles). Additionally, the battery device also exhibits a satisfactory energy density of 343.2 Wh kg^-1 and a peak power density of 11.7 kW kg^-1. This work provides a simple attempt to design a high-performance layered cathode material for aqueous Ni-Zn batteries.

Aluminum-doping-based method for the improvement of the cycle life of cobalt-nickel hydroxides for nickel-zinc batteries

The unsatisfactory cycle life of nickel-based cathodes hinders the widespread commercial usage of nickel-zinc (Ni-Zn) batteries. The most frequently used methods to improve the cycle life of Ni-based cathodes are usually complicated and/or involve using organic solvents and high energy consumption. A facile process based on the hydrolysis-induced exchange of the cobalt-based metal-organic framework (Co-MOF) was developed to prepare aluminum (Al)-doped cobalt-nickel double hydroxides (Al-CoNiDH) on a carbon cloth (CC). The entire synthesis process is highly efficient, energy-saving, and has a low negative impact on the environment. Compared to undoped cobalt-nickel double hydroxide (Al-CoNiDH-0%), the as-prepared Al-CoNiDH as the electrode material displays a remarkably improved cycling stability because the Al-doping successfully depresses the transition in the crystal phase and microstructure during the long cycling. Benefiting from the improved performance of the optimal Al-CoNiDH electrode (Al-CoNiDH-5% electrode), the as-constructed aqueous Ni-Zn battery with Al-CoNiDH-5% as the cathode (Al-CoNiDH-5%//Zn) displays more than 14% improvement in the cycle life relative to the Al-CoNiDH-0%//Zn battery. Moreover, this Al-CoNiDH-5%//Zn battery achieves a high specific capacity (264 mAh g^-1), good rate capability (72.4% retention at a 30-fold higher current), high electrochemical energy conversion efficiency, superior fast-charging ability, and strong capability of reversible switching between fast charging and slow charging. Furthermore, the as-assembled quasi-solid-state Al-CoNiDH-5%//Zn battery exhibits a decent electrochemical performance and satisfactory flexibility.

A Flexible Quasi-Solid-State Nickel-Zinc Battery with High Energy and Power Densities Based on 3D Electrode Design

A flexible quasi-solid-state Ni-Zn battery is developed by using tiny ZnO nanoparticles and porous ultrathin NiO nanoflakes conformally deposited on hierar chical carbon-cloth-carbon-fiber (CC-CF) as the anode (CC-CF@ZnO) and cathode (CC-CF@NiO), respectively. The device is able to deliver high performance (absence of Zn dendrite), superior to previous reports on aqueous Ni-Zn batteries and other flexible electrochemical energy-storage devices.