Investigation Of Energy Storage Performances And First-principles Calculation Of Transition Metal Phosphides/phosphates

With the rapid development of clean energy sources such as solar energy,wind energy and tidal energy,how to effectively store these intermittent energies for continuous use has become an important challenge for the efficient use of energy.Therefore,it is significance for realizing wide coverage of clean and renewable energy to develop efficient energy storage systems.In recent years,rechargeable aqueous zinc-based batteries（AZBs）have shown obvious potential in the application of large-scale energy storage systems due to their high theoretical capacity,low cost,high operation safety and environmental friendliness.However,due to the relatively low energy density and poor cyclic stability of AZBs cathode materials in aqueous solution,the application in the field of high specific energy is restricted.Therefore,improving the comprehensive electrochemical properties of AZBs cathode materials has become a focus in the field of energy storage.Among them,the transition metal phosphides/phosphate with metal characteristics is recognized as a promising electrode material because of its high specific capacitance and good electrical conductivity.In this regard,we have successfully synthesized nickel-cobalt-based phosphides/phosphate electrode materials with specific morphology,high conductivity and long cycle stability through First-principle calculation prediction and experimental design,and applied them to AZBs with high-voltage system.The main study results are as follows:（1）Hierarchical crystalline Ni-Co phosphide coated with amorphous phosphate nanoarrays（C-Ni Co P@A-Ni Co PO₄）self-supporting on the Ni foam was designed and constructed by one-step hydrothermal method and electrochemical deposition method.In this unique core-shell structure,the hexagonal phosphide with high conductivity offers ultra-fast electronic transmission and amorphous phosphate with high stability and open-framework can provide more favorable ions diffusivity and stable protective barrier.The morphology,lattice structure,elemental valence state,OH^-adsorption energy and electron transfer capacity of the electrode materials were analyzed by means of characterization)and First-principles calculation.As results,the C-Ni Co P@A-Ni Co PO₄ electrode exhibits higher specific capacity of 350.6 m Ah g^-1,and excellent cyclic stability with 92.6%retention after 10000 cycles.Moreover,the C-Ni Co P@A-Ni Co PO₄ is coupled with Zn anode to assemble aqueous pouch battery that delivers ultra-high energy density(626.33Wh kg^-1 at 1.72 k W kg^-1)with extraordinary rate performance(452.05 Wh kg^-1 at 33.56k W kg^-1).Meanwhile,the corresponding quasi-solid flexible battery with polyacrylamide hydrogel electrolyte exhibits favorable durability under frequent mechanical strains,which indicates the great promise of crystalline/amorphous hierarchical electrodes in field of energy storage.（2）An in situ interfacial modification strategy is presented to constructed high-performance cathode（N-NCP@PO_x）with ultrathin amorphous phosphate interfacial coating for alkaline zinc batteries.The in situ amorphous phosphate layers are beneficial to the adsorption and deprotonation of OH^-confirmed by First-principles calculations,and are superior interfacial layers to protect the active species from passivation.This elaborate design enables the active species and structures synergistic effect endowing the electrode of N-NCP@PO_x with remarkable energy storage capability and electrochemical stability.As results,the full cell of N-NCP@PO_x//Zn alkaline zinc batteries deliver outstanding specific capacity(358.3 m Ah g^-1 at 1 A g^-1),rate performance(132.2 m Ah g^-1 at 20 A g^-1)and cyclic stability(94%retention after 6000 cycles at 10 A g^-1).This study will stimulate further development of transition metal phosphides with amorphous interface layers as high performance cathode for energy storage devices.（3）A hierarchical phosphide hetero-structure（Ni Co P@Ni₂P）as cathode material for AZBs is constructed by the one-step phosphorization strategy.Reasonable heterogeneous interface design can reshape the interface properties of electrode devices by introducing the desired active sites.The charge redistribution at the heterogeneous interface of Ni Co P@Ni₂P cathode is demonstrated via experiment and theoretical calculation.Thanks to the elaborate hetero-interface,the Ni Co P@Ni₂P electrode enjoying the favorable ion adsorption energy and fast interfacial diffusion kinetics exhibits a high specific capacity(358.3 m Ah g^-1 at 1 A g^-1)and outstanding rate capability(224.4 m Ah g^-1 at 20 A g^-1).The as-assembled AZBs coupled with Zn anode present a high energy density of 596.3Wh kg^-1 at the power density of 1.7 k W kg^-1,and retains 429.5 Wh kg^-1 even at a very high power density of 24.3 k W kg^-1.Specifically,this full cell can work well at a low temperature of-30℃,with an ultra-high specific capacity of 307.9 m Ah g^-1 at 1 A g^-1 and outstanding stability of 85%retention after 2000 cycles at 10 A g^-1.This heterogeneous interface engineering strategy provides a new idea for the practical application of AZBs.