Heterogeneous Interface Design Of Transition Metal Phosphides(Selenides) And Performance Of Sodium/Potassium Storage

Sodium ion batteries（SIBs）and potassium ion batteries（PIBs）are potential rechargeable secondary ion batteries that share the energy storage pressure of lithium ion batteries（LIBs）due to their abundance,low cost and similar energy storage mechanism with LIBs.Anode materials for SIBs and PIBs have been widely studied as key factors affecting the performance of the whole battery system.Transition metal phosphorus（selenium）compounds with earth-abundance are deemed as hot topic of anode materials for SIBs and PIBs due to the high theoretical capacity endowed from the conversion reactions of multi-electrons.However,the large ionic radius of Na⁺and K⁺present great challenges in ion dynamics and structural stability during sodium/potassium storage.Based on the analysis of the optimization strategies of transition metal phosphorus（selenium）electrode materials at home and abroad.In order to improvre the the reaction kinetics and cycle life of sodium/potassium storage,the transition metal phosphorus（selenium）electrode materials were transformed into excellent anode materials through internal heterogeneous interface design at the atomic level in coordination with other external optimization strategies.Simultaneous,the influence of electron（phase）structure change on the performance and mechanism of sodium/potassium storage was confirmed by structureal characterization and theoretical calculation,which laid a foumdation for the design of advanced electrode materials in the future.Here,Ni P₂ nanoparticles encapsulated in multiple-shelled hollow N-doped carbon microspheres（Ni P₂@MHNC）as electrode was constructed using Ni-MOF as precursor.And three control samples,including Ni P₂,Ni P₂@C and Ni P₂@NC,were also designed.The effects on heterogeneous interfaces,N-doped and multi-shell hollow structure on the sodium/potassium storage performance of Ni P₂ electrode were investigated systematically based on these four electodes.By comparing the cycling performance and kinetics of sodium/potassium storage of different electrodes not only indicates that Ni P₂/C heterogrneous interface plays a decisive role in the improvement of sodium/potassium cycling perforamce and reaction kinetics,but also reveals that the N-doped and multi-shelled hollow structure also contribute significantly to the improvement of sodium/potassium storage performance.Ultimately,the sodium/potassium storage perforamce of Ni P₂@MHNC electrode was improved by the synergy of multiple factors(the capacity retention rate of 80%at 0.1A g^-1 after 300 cycles for SIBs,and the capacity retention rate of 82%at 0.1 A g^-1after 200 cycles).Based on the above facts that the heterogeneous interface design can effectively improve the performance of sodium/potassium storage for electrode.The strategy of constructing homojunction with lattice adaptation advantage,namely phase-junction,was proposed to realize self-optimization of electrode materials.There was no reports on the optimization of sodium/potassium storage performance by phase structure or phase interface for the anisotropic semiconductor 1T’phase Re Se₂ system,which not only limits the in-depth understanding of the phase interface regulation of this electrode system,but also hinders the development of more efficient sodium/potassium storage electrode using the phase structure regulation.Therefore,a novel phase-junction 1T/T’Re Se₂ electrode was constructed by using the phase engineering strategy of liquid ammonia lithium.The structural characterization and performance testing showed that:1)The interlaminer van der Waals forces of 1T’Re Se₂ were destroyed after the bulk samples were transformed into two-dimensinal nanasheets,resulting in a decrease in the diffusion resistance of sodium and potassium ions.2)The introduction of high conductive 1T phase and the construction of phase interface accelerated electron and ion transfer.3)The phase-junction 1T/T’Re Se₂ with conductive and reversibility advantages was reconstructed after cycling to ensure the cycling stability and rare performance of electrode.1T/T’Re Se₂ as anode of sodium ion battery displayed 237 and 123 m A h g^-1 at 5 and 20 A g^-1 after 1200 cycles,respectively.1T/T’Re Se₂ as anode material of potassium ion battery delivered capacity retention rate of 49%at 0.1 A g^-1 after 100 cycles.According to the undersanding that the phase-junction can effectively improve the sodium/potassium storage performance of Re Se₂ electrode,the phase structure regulation and phase-junction interface design of typical Co Se₂ electrode with multiphase structure were further carried out.Therefore,a series of electrodes Co Se₂-x:1 were prepared by chemical vapor deposition method by adjusting the mass ratio（x:1）of selenium powder and precursor ZIF-67.The results showed that the phase-junction cubic phase/orthogonal phase-Co Se₂-10:1（c/o-Co Se₂）shows obvious superiority in cycling stability and reaction kinetics of sodium/potassium storage.Furthermore,the phase-junction c/o-Co Se₂ electrode was compounded with Si C nanowire to form a“sugar-coated haws on a stick-like”c/o-Co Se₂@Si C electrode.Experimental and theoretical results indicaded that the electron coupling effect and charge redistribution at the phase-junction interface reinforced the stability of Co Se₂during sodium/potassium storage and accelerated the transfer of Na⁺/K⁺and electrons,and the Si C nanowire played a pivotal role in stabilizing the active materials,improving the cycle stability,and providing fast transport pathways for electrons.Benefiting from these merits,the c/o-Co Se₂@Si C electrode exhibited improved sodium storage capacity and cyclic stability(capacity retention of 82%at 1 A g^-1 after1000 cycles)and excellent potassium storage performance(capacity retention rate of of 90%at 1.0 A g^-1after 500 cycles).In addition,the sodium storage mechanism of insertion-conversion and reconstruction of phase-junction of c/o-Co Se₂@Si C electrode was revealed by operando Raman,operando X-ray diffraction（XRD）and high-resolution transmission electron microscopy（HRTEM）characterizations.