Sodium/Lithium Storage Properties And Synchrotron Radiation Spectroscopy Of Prussian Blue Derivative Anode Materials

Nowadays,energy shortages,rising carbon emissions and serious environmental problems occur frequently,because of the heavy global dependence on fossil fuels.Therefore,it is crucial to develop green and sustainable energy storage technologies.Metal-ion batteries,as new generation of batteries,have received extensive attention.Among them,lithium-ion batteries（LIBs）are efficient energy storage devices,and have been widely used in mobile phones,computers,electric vehicles,etc.LIBs are also promising for further large-scale power grids.On the other hand,due to the scarcity of lithium reserves,sodium-ion batteries（SIBs）have been applied commercially as an effective alternative.Anode material is one of the most important components that directly affect the electrochemical performance of LIBs and SIBs.Prussian blues（PBs）and their analogues（PBAs）are promising precursor and template materials benefiting from rich composition,open three-dimensional framework structure,facile preparation method and low cost.Various metal compounds derived from PBs and PBAs have diverse compositions and unique nanostructures,which can be great choices of excellent anode materials for LIBs and SIBs.This paper focuses on the microstructure design,fine material characterization and synchrotron radiation spectroscopy of Prussian blue derivative anode materials to study their sodium and lithium storage mechanisms,providing experimental basis and technical reference for the subsequent development of high-performance LIBs and SIBs.The main research contents and achievements are as follows:1.Mainly through a simple co-precipitation method and a solid-state reaction,a nanoscale hollow cubic iron-cobalt bimetallic sulfide coated with a nitrogen-doped carbon matrix derived from PBA was designed for an anode material for SIB.Although many metal sulfides have been applied as anodes for SIBs,very few iron-cobalt bimetallic active sulfides have been reported so far.As expected,this iron-cobalt bimetallic sulfide nanobox anode exhibits excellent outstanding high specific capacity,good rate performance and long cycle stability,both compared with the previously reported mono cobalt or iron sulfides,and compared with the few reported iron-cobalt bimetallic sulfides.In addition,ex situ X-ray diffraction（XRD）and ex situ synchrotronradiation-based X-ray absorption fine spectroscopy（XAFS）were carried out to explore the redox process of iron and cobalt during the charge and discharge process and the synergy between the two metals.This unique nitrogen-doped carbon-coated hollow cubic nanobox structure provides an effective reference for nanostructure design methods of other Prussian blue derivatives and other metal sulfide composites,also provides a basis synthesis and mechanism reference for the development of highperformance SIBs sulfide anodes.2.Through a simple two-step synthesis method of co-precipitation and hightemperature annealing,an ultra-small Co₃O₄ nanoparticle derived from PBA were prepared,with a particle size of about 15 nm.This ultrasmall Co₃O₄ nanostructure can minimize the structural damage due to volume expansion and provide more active sites for Li+storage.Owing to the enhanced active surface/interface and optimized charge transport properties,such ultrasmall Co₃O₄ nanoparticle exhibits an excellent reversible capacity of 1637.3 mAh g^-1 at 0.1 A g^-1 after one cycle.In addition,it exhibits an glorious cycling stability at 10 A g^-1,with a specific capacity retention of about 511.2 mAh g^-1 after 2000 cycles.The superiority and stability of such ultrasmall nanoparticles at high current densities demonstrate the promising practical application of fastcharging LIBs.Furthermore,with the help of ex situ XRD,Raman and XAFS characterization technologies,the good reversibility of Co₃O₄ nanoparticles during the charge and discharge process,and the promotion of the possible Co-Li alloy,are proved.This nanostructure design and appropriate particle size adjustment scheme can provide an experimental basis for the application of Co₃O₄ and more transition metal oxides in fast-charging LIBs.3.Using a simple two-step plan of hydrothermal and high-temperature annealing,a carbon doping-induced Prussian blue derivative Fe₂O₃ hollow cubic box was synthesized and used as the anode for LIBs.Carbon-doped Fe-PBs cubic precursors were obtained in one facile way by adding sucrose during the hydrothermal synthesis.Under the induction of carbon doping,the Fe-PBs-derived Fe₂O₃ exhibits a hollow cubic box structure after annealing.Specifically,the LIBs with the induced hollow Fe₂O₃ anode shows outstanding capacity(1108.7 mAh g^-1 after one cycle)and longterm cycle stability(2000 cycles at 1 A g^-1).Soft X-ray absorption spectroscopy（s-XAS）and other characterization results demonstrate that sucrose-derived carbon induces the coordination changes of carbon atom in Fe₂O₃,thereby affecting the lithium storage mechanism.In adidition,the reversible evolution of the SEI film on the electrode during charge and discharge was analyzed by in situ Fourier transform infrared spectroscopy（FTIR）.Such sucrose-derived carbon-induced Prussian blue derivatives provide promising candidates for LIBs and could stimulate further development of highperformance LIBs.