Design And Synthesis Of Novel Chalcogenides-based Sodium Solid Electrolytes

Rechargeable secondary batteries have been widely used in mobile devices such as mobile phones and computers due to their high energy density,long cycle life and high operating voltage.However,the current secondary batteries based on organic electrolytes have the potential safety hazard of electrolytes leakage and fire.Therefore,the development of high-safety batteries is essential.In recent years,all-solid-state sodium batteries with advantages of low cost and high safety have attracted significant interests.To build such batteries,the development of sodium solid electrolytes(SSEs)with good performance is a key requirement,and thus receives tremendous research attentions.Among various investigated solid electrolytes,including Beta-alumina,NASICON,chalcogenides,complex hydride and antiperovskite,chalcogenides with decent room temperature conductivity and superior formability experience a great upsurge in research.Extensive researches on chalcogenide-based SSEs have been conducted since 2012,when Na₃PS₄is reported and adopted in the all-solid-state battery by Tatsumisago and his coworkers.After that,most of sodium SEs are investigated mainly based on group 15elements(e.g.Na₃PS₄,Na₃Sb S₄).Therefore,expanding the system of sulfide-based sodium solid electrolytes,deepening the understanding on structure and property relationship is of great significance to promote the further development of sulfide-based sodium solid electrolytes.The group 14 element Snis chemically stable and environmentally friendly.Herein,a series of sodium superionic conductors are explored starting from Na₄SnS₄and by following strategies of cation substitution and anion doping.And the effects of the relevant strategies are investigated by structural analysis,This work not only demonstrates a promising method to explore new ionic conductors,but also enriches the family of the group 14 element Snbased superionic conductors.The specific research content is as follows:1.To extend the horizon,we demonstrate a development route from group 14element based sodium chalcogenide.Na₄Sn_0.67Si_0.33S₄ with a distinctly new structure with space group I4₁/acd and 3D diffusion pathway realize by silicon substitution in Na₄SnS₄,which shows 2 orders of magnitude conductivity improvement than that of the mother compound Na₄SnS₄.And the Na₄Sn_0.67Si_0.33S₄can be taken as a high tolerance structural template for extensive chemical manipulation.Based on the structural template,aliovalent substitution of P for[Sn_0.67Si_0.33]lead to a wide range of solid solutions of Na₄–_x[Sn_0.67Si_0.33]₁–_xP_xS₄(0?x<0.6)with developing enhanced sodium conductivity.Increasing of vacancy population and weak Na-S interaction induced from P substitution are main reasons for the improvement of ionic conductivity.The highest ionic conductivity reaches 1.6×10^–3S cm^–1 with x=0.25.In addition,air stability is demonstrated.2.Strategy of Sb-substitution is carried out on the template structure Na₄Sn_0.67Si_0.33S₄.A series of quinary sulfide-based sodium fast ionic conductors formulated as Na₄–_x[Sn_0.67Si_0.33]₁–_xSb_xS₄.Among them,the highest ambient ionic conductivity(1.75×10^-4S cm^-1)is achieved when x=0.2.The new fast ionic conductor Na_3.8[Sn_0.67Si_0.33]_0.8Sb_0.2S₄is isostructural to its structure template Na₄Sn_0.67Si_0.33S₄and thus crystallizes in the space group of I4₁/acd.It is shown that the incorporation of Sb improves the ionic conductivity.It is mainly due to the enlarged crystal lattice.Furthermore,using Na_3.8[Sn_0.67Si_0.33]_0.8Sb_0.2S₄ as solid electrolytes,room temperature all-solid-state sodium battery of Na₃Sn|Se_0.05S_0.95-p PAN is realized,which proves the novel fast ionic conductor a potential candidate to apply in sodium solid state battery.3.The strategy of halogen doping is successfully demonstrated on the Na-Sn-Si-P-S system,improved ionic conductivities and reduced activation energies are achieved.Using Na_3.67[Sn_0.67Si_0.33]_0.67P_0.33S₄,a novel SSE with high structural tolerance,as the pristine structure,the halogen-doped samples formulated as Na_3.57[Sn_0.67Si_0.33]_0.67P_0.33S_3.9X_0.1(X=Cl,Br,I)are synthesized.Therein,Na_3.57[Sn_0.67Si_0.33]_0.67P_0.33S_3.9I_0.1,the I-doped sample hold the highest ambient ionic conductivity of 1.08×10^-3S cm^-1and lowest activaition energy of 0.24 e V.Effects of halogen doping are investigated by structure analysis.Furthermore,with Na_3.57[Sn_0.67Si_0.33]_0.67P_0.33S_3.9I_0.1as solid electrolytes,the assembled all-solid-state sodium battery shows decent cyclic stability at 30 ^oC.This work systematically manifests the effect of halogen doping in SSEs,providing a versatile method to develop novel sodium solid electrolytes.In this work,a template structure with high structural tolerance based on Na₄SnS₄was explored.On account of the structural tolerance,a series systematical strategy of cation substitution and anion doping were applied to develop new SSEs.It is of guiding significance to electrolytes materials design and beneficial for developing all-solid-state sodium batteries.