Study On Zinc-Cobalt Co-Doped Nickel Sulfide Cathodes Applied To Flexible Quasi-Solid-State Zinc-Nickel Battery

With the increasing demand for portable and wearable electronic devices promoting the development of electrochemical energy storage devices towards lightness,bendability and strong endurance,the design and fabrication of flexible cathode materials has become the key and difficulty for aqueous rechargeable zinc-based batteries.Nickel sulfide（Ni₃S₂）is of great interest in energy storage due to its high theoretical capacity(472 m Ah g^-1),low cost and simple fabrication method.In order to improve the electrochemical active sites of Ni₃S₂ and enhance the cycling stability of the battery,this paper used well-conducting nickel foam（NF）as a substrate,synthesizes zinc and cobalt co-doped nickel sulfide electrodes by a two-step hydrothermal method,and designs and prepares flexible quasi-solid-state Zn-Ni batteries.The main research results are as follows:（1）Oxide precursors were grown in situ on NF substrates by hydrothermal method,and the precursors were further sulfurized to obtain single-metal doped Zn-Ni₃S₂/NF and Co-Ni₃S₂/NF flexible electrodes.The experiments confirmed that the electrochemical performance of the metal-doped Ni₃S₂ electrode was improved,which was better than that of the precursor oxide electrode.This is mainly because the ability of sulfur to bind electrons is weaker than that of oxygen,and the chemical bond is longer,which is conducive to the transport of electrons.Using dimethylacrylamide gel as the quasi-solid electrolyte,the electrodes were assembled into flexible quasi-solid-state batteries for performance testing.The Zn-Ni₃S₂/NF//Zn battery has a capacity of 0.81 m Ahcm^-2 at a current density of 16 m A cm^-2;the Co-Ni₃S₂/NF//Zn battery has a capacity retention rate of 83.3%after 1500 cycles at a current density of 20 m A cm^-2.（2）On the basis of single doping,the effect of bimetallic doping nickel sulfide on battery performance was explored,and Zn Co-Ni₃S₂ electrodes were fabricated.The Zn Co-Ni₃S₂/NF electrode combines the high capacity of Zn-Ni₃S₂/NF and the stability of Co-Ni₃S₂/NF.The assembled flexible battery has a capacity of up to 2.3m Ah cm^-2 at a discharge current density of 12 m A cm^-2,the capacity retention rate is82%after 2000 cycles at a current density of 20 m A cm^-2.In addition,the flexible battery work normally under the condition of bending and puncturing.The performance of bimetallic doped nickel sulfide is far superior to that of single metal doped nickel sulfide,which is mainly attributed to the synergistic effect of bimetallic doping,which brings more active sites to the electrochemical reaction.This indicates that multi-metal doping is expected to be an effective strategy for Ni₃S₂ modification and has great potential to improve the performance of Zn-Ni batteries.