Optimization Of Electrolyte Interface Properties Of Nickel-cobalt Compounds And Study Of Alkaline Electrochemical Energy Storage Mechanis

With the rapid development of mobile electronic devices,high-performance electrical energy storage devices urgently needed.Among current energy storage devices,alkaline aqueous energy storage devices have received intensive research attention owing to non-flammable nature and high ionic conductivity of aqueous electrolytes.Hybrid supercapacitors（HSCs）combine the high-energy density of battery-type electrodes and high-power density of capacitor-type electrodes together,which have the potential to achieve both high-energy and high-power performance.Meanwhile,nickel-zinc（Ni-Zn）batteries have the advantages of high specific power,high specific energy,and high voltage,making them very promising for commercial applications.However,limited electronic conductivity and redox reversibility of nickel-based compound cathodes limit the overall device performance of HSCs and Ni-Zn batteries,and therefore high-performance cathode materials are still urgently needed.A large number of transition metal elements have rich chemical valence,and a variety of transition metal compounds can be synthesized.The introduction of nickel-based compounds can significantly improve the performance of electrode materials.Here,advanced Ni-Co bimetal compounds are developed as cathode materials for high-performance HSCs and Ni-Zn applications,and the components and morphology of these Ni-Co bimetal compounds are optimized their performance.The main contents are as follows:（1）A precursor transformation method was developed for the preparation of Ni Co-P/PO_x heterostructure with a hollow and sea-urchin-like structure.The hollow structure of the precursor was formed by a anion exchange reaction between pregenerated hydroxide particles with CO₃^2–,and the subsequent anisotropic growth of Ni_xCo_1–x（CO₃）_0.5OH nanowires results in the formation of a sea-urchin-like structure.Then,the precursor was transformed to Ni Co-P/PO_x heterostructure while maintaining the hollow sea-urchin-like structure by a phosphatation reaction,where a great deal of highly crystalline phosphide nanoparticles are dispersed in an amorphous phosphate matrix.The unique hierarchical structure of Ni Co-P/PO_x combines the advantages of hollow and three-dimensional sea-urchin-like structures,which can improve the utilization of active materials for energy storage.By tuning the Ni to Co ratios,the performance of Ni Co-P/PO_x heterostructure was maximized,and the Ni₂Co-P/PO_x electrode exhibits the best performance with a Ni to Co ratio of 2:1.It exhibits a high specific capacity of 180.7 m A h g^–1 at 1 A g^–1.The HSC assembled based on Ni₂Co-P/PO_x has a maximum specific energy of 48.6 W h kg^–1 at a specific power of 0.78 k W kg^–1 and a capacity retention of 79%after 10,000 cycles(5 A g^–1).Ni₂Co-P/PO_x//Zn also demonstrates high specific energy(308.0 W h kg^–1 at 828.4 W kg^–1)and stable cycling performance（76.0%capacity retention after 1000 cycles）.（2）Oleylamine and oleic acid were used as organic solvents to fabricate Ni Co-S nanoparticles in a straightforward thermal injection approach.The size of the nanoparticles was regulated by controlling the volume of oleylamine.The effect between particel sizes and electrochemical energy storage performance of Ni Co-S is studied.The Ni Co-S synthesized using 15 m L of oleylamine exhibits the best performance in terms of specific capacity,rate performance,and cycling stability.The small nanoparticle size shorten the diffusion distance for electrolyte ions,making the Ni Co-S active materials as a high-performance electrode materials.Additionally,the performance of the electrode material is examined by tuning Ni and Co contents.Ni Co-S has a specific capacity of 163.3 m A h g^–1 at 1 A g^–1,and the capacity retention rate is 80%after 2000 cycles.Ni Co-S//RGO has a specific capacity of 61.1 m A h g^–1 at 1 A g^–1 and a specific energy of 44.4 W h kg^–1(at 0.73k W kg^–1).Ni Co-S//Zn has a specific capacity of 143.2 m A h g^–1 at 1 A g^–1 and a maximum specific energy of 236.9 W h kg^–1 at 1.7 k W kg^–1.（3）Ni-Co selenide/graphene composites with small size Ni-Co selenide particles were synthesized,which exhibited excellent energy storage performance.Ni-Co selenide particles have metallic conductivity,and relatively small size can reduce ion diffusion distance.Large surface area of graphene reduces the diffusion distance of electrolyte,resulting in faster reaction kinetics and enhanced cycling stability.Energy storage performance can be significantly enhanced by the composite structure.The effect of the selenization degree and nickel-cobalt contents are used to tune the energy storage performance.The Ni-Co selenide/graphene composite exhibits excellent performance in terms of specific capacity and cycling stability when the selenidation ratio of selenide powder to precursor is 5,and a Ni to Co ratio is 1:1.It exhibits a high specific capacity of134.9 m A h g^–1 at 1 A g^–1.Ni_0.5Co_0.5–Se/RGO–5//RGO achieved a high specific energy of39.4 W h kg^–1(at 780 W kg^–1),and a capacity retention of 79%after 10000 cycles(at 3 A g^–1).The specific capacity of Ni_0.5Co_0.5–Se/RGO–5//Zn was 146.9 m A h g^–1 at 1 A g^–1,achieving a high specific energy of 154.3 W h kg^–1(at 500 W kg^–1)and a capacity retention of 62%(at 5 A g^–1)after 2000 cycles.