Preparation And Electrochemical Performance Of Cathode Materials For Aqueous Rechargeable Nickel-Zinc Batteries

Energy shortage and environmental pollution have been recognized as the two most challenging problems in the 21^stt century with the rapid development of the economy,which cause the exploitation of renewable clean energy becoming an inevitable trend in the future.Accordingly,the quest for new energy conversion and storage devices with high performance are critical to utilize the renewable energy efficiently.With compelling superiority of safe,environmental friendly,low-cost,abundant resources and high theoretical capacity,aqueous nickel-zinc?Ni//Zn?batteries have attracted the widespread attention of researchers in recent years.Nevertheless,Ni//Zn batteries still have a series of problems,such as the low capacity and inferior cycling stability caused by the poor electrochemical reversibility and conductivity of nickel-based cathode materials,as well as the uncontrollable dendrite formation in Zn anode,which restrict the further development and popularization of Ni//Zn batteries in practical applications to some extent.In this paper,nickel trisulfide?Ni₃S₂?and nickel molybdate?NiMoO₄?were explored as the research objects.Aiming at the low capacity and inferior cycling stability of nickel-based cathode materials in Ni//Zn batteries,we used the structural control and electrolyte modification to boost their electrochemical performance and explored the structure-function relationship systematically.The specific research works were carried out as followed:1.The self-supporting three-dimensional?3D?Ni₃S₂ nanosheeets were uniformly synthesized on the conductive nickel foam substrate by a simple hydrothermal method and further coated with a layer of PANI,forming a Ni₃S₂@PANI core-shell nanosheet material.Benefiting from the improved conductivity and protection of PANI layer,the Ni₃S₂@PANI core-shell electrode showed impressive electrochemical performance and durability.By comparison with the untreated Ni₃S₂,the Ni₃S₂@PANI electrode exhibited a high capacity of 247.6 mAh g^-11 at 11.4 A g^-1,and an excellent cyclic stability with no obvious capacity fading after 10000 cycles.A typical Ni//Zn battery was demonstrated with the Ni₃S₂@PANI electrode as the cathode,a commercial Zn plate as the anode and a solution made of 6 mol L^-11 KOH and 0.2 mol L^-11 Zn?CH₃COO?₂ as the electrolyte?denoted as Ni₃S₂@PANI//Zn?,which reveals superior capacity(242.8 mAh g^-11 at the current density of 5.1 A g^-1)and ultra-stable cyclability?no capacity fading after 5000 cycles?.Furthermore,the Ni₃S₂@PANI//Zn battery yielded an excellent energy density of 386.7 Wh kg^-11 while a maximum power density of 38.8 kW kg^-1.2.A two-step synthesis method was developed to synthesize the 3D NiMoO₄nanowires/Ni-carbon?NiMoO₄-NC?composite on nickel foam substrate,which effectively improves the electron and ion transport rates of NiMoO₄.The as-prepared NiMoO₄-NC electrode displayed a higher specific capacity of 221.0 mAh g^-11 at 3.4 A g^-1than the pristine NiMoO₄ nanowires directly grown on Ni foam?NiMoO₄-NF?.Subsequently,an electrolyte additive was proposed to inhibit the dissolution of the cathode material,thereby greatly boosting the cycling stability of the NiMoO₄-NC electrode from 48.6%to 88.6%capacity retention after 3000 cycles.The as-fabricated NiMoO₄-NC//Zn battery with NiMoO₄-NC cathode and Zn plate anode presented remarkable capacity(232.2 mAh g^-11 at 3.4 A g^-1)and great cycling durability?85.9%capacity retention after 3000 cycles?,yielding an admirable energy density of 407.8 Wh kg^-11 at 3.4 A g^-1,together with a remarkable power density of 18.1 kW kg^-11 at 10.7 A g^-1.