Preparation Of Carbon-based Bimetallic Selenides And Their Research On Sodium/Potassium Ion Batteries

Sodium-ion batteries（SIBs）and potassium-ion batteries（PIBs）,as promising replacements for lithium-ion batteries（LIBs）,are prospective to be new energy storage technologies utilized in large-scale energy storage on account of the rich sodium and potassium resources,low cost and high energy density.Nevertheless,their practical applications are severely limited by factors such as fast capacity decay,sluggish charge storage dynamics,and low reversibility.Hence,searching anode materials which can give full play to the excellent characteristics for SIBs and PIBs has become the most critical issue to date.Among a variety of novel anode materials,prussian blue analogues（PBAs）and derivatives have the advantages of three-dimensional micro/nano-structure,controllable size and adjustable chemical composition,which has great application prospect.In this thesis,the composition control and micro-structure design are carried out using different PBAs as precursors,and three kinds of composites consisting of transition metal selenides and carbon materials are successfully constructed and prepared via solution precipitation method and gas phase selenization reaction.Their electrochemical performance as anode materials for SIBs and PIBs and the mechanism of enhanced sodium/potassium storage performance are systematically studied.The main research contents are as follows:Firstly,we developed a facile salt-template strategy combined with one-step carbonization and selenization process for constructing the carbon-coated Ni-Fe-Se nanocubes embedded in porous nitrogen-doped graphene sheets（Ni-Fe-Se@p NGS）,in which the core-shell Ni-Fe-Se nanocubes homogeneously distributed and embedded in the 2D porous N-doped graphene sheets with spherical cavity through sodium chloride（Na Cl）and silica（Si O₂）nanospheres as dual templates.Benefiting from the unique and novel structural advantages of Ni-Fe-Se@p NGS composite,Ni-Fe-Se@p NGS electrode for SIBs can provide high sodium storage capacity(419.8 m Ah g^-1at 0.1 A g^-1after 100 cycles),excellent rate capability,and good cyclic stability,even at a high current density(263.2 m Ah g^-1at 1.0 A g^-1after 1000cycles).In addition,it also exhibits outstanding cycle life(188.5 m A h g^-1after 100 cycles at0.1 A g^-1)and rate performance for PIBs.Secondly,dual-carbon confined Mn Se/Fe Se₂nanocubes（DCC-Mn Se/Fe Se₂）are prepared through a simple liquid phase reaction at room temperature to coat with polydopamine（PDA）,combined with gas phase selenization process using Mn-Fe PBA as precursors.The results demonstrate that DCC-Mn Se/Fe Se₂composites with dual-carbon protection can effectively alleviate the structural collapse of electrode material caused by volume change during the cycling process,and improve the conductivity of the whole material.Compared with the control groups without dual-carbon protection,the cycle stability and rate performance of DCC-Mn Se/Fe Se₂electrodes are distinctly improved.In the sodium ion batteries,the specific capacity of DCC-Mn Se/Fe Se₂electrode is 407.6 m Ah g^-1after 100 cycles at 0.1 A g^-1.Even at1.0 A g^-1,the specific capacity of 208.0 m Ah g^-1after 1000 cycles can be obtained.Moreover,it also exhibits excellent potassium storage performance,and maintains a specific capacity of150.7 m Ah g^-1after 100 cycles at 0.1 A g^-1.Thirdly,using Ni-Co PBA as precursors and one-dimensional carbon nanotubes（CNTs）as conductive bridges,Ni-Co-Se nanocubes derived from Ni-Co PBA interconnected with CNTs are successfully constructed by a simple precipitation strategy combined with subsequent heat-treatment selenization process（Ni-Co-Se-CNT）.The Ni-Co-Se-CNT composites with high conductive network structure are composed of interlaced carbon nanotubes adhered or embedded in Ni-Co-Se nanocubes,and the surface of each Ni-Co-Se nanocubes is uniformly coated with a thin nitrogen-doped amorphous carbon layer.Owing to the unique three-dimensional interconnection structure,Ni-Co-Se-CNT anode exhibits significantly enhanced sodium/potassium storage properties.As the anode material for SIBs,the specific capacity of Ni-Co-Se-CNT electrode is 305.4 m Ah g^-1after 300 cycles at 0.1 A g^-1.Even at1.0 A g^-1,it still provides a specific capacity of 193.6 m Ah g^-1after 500 cycles.Besides,it also exhibits outstanding cycle life and rate performance for PIBs,and maintains a specific capacity of 134.1 m Ah g^-1after 100 cycles at 0.1 A g^-1.