摘要
硫化物Li_(3)PS_(4)是重要的含硫快离子导体,锂离子电导率高,机械性能优异,化学兼容性好,属于全固态电池中一类重要的固态电解质.Li_(3)PS_(4)具有多种晶体结构(玻璃态、α相、β相、γ相),而晶体结构对于材料离子电导率有决定性的影响,因此探究不同Li_(3)PS_(4)晶体结构的合成条件及其转变过程对固态电解质的应用有重要意义.本文通过原位变温Raman和室温X射线衍射(XRD)分析发现,通过球磨法所得glass-Li_(3)PS_(4)在首次升温过程中(240℃)优先转变为亚稳态的β-Li_(3)PS_(4),此时冷却到室温能保持β相结构,并具有较高的离子电导率(0.65 mS cm^(-1)).当烧结温度继续升高(>480℃),β相会转变为离子电导率更高但热力学不稳定的α-Li_(3)PS_(4),在后续的降温过程中,α相会直接转变为热力学更稳定但离子电导率差的γ-Li_(3)PS_(4).此外,γ-Li_(3)PS_(4)和β-Li_(3)PS_(4)具有一定的结构记忆效应,即使经历二次低温烧结后(240℃)也能维持其固有的结构.以上结果表明,首次烧结温度对于Li_(3)PS_(4)材料的结构和离子电导率具有重要的影响,合理控制烧结温度能够成功制备出具有更高离子电导率的β-Li_(3)PS_(4)固态电解质.此外,所制备的β-Li_(3)PS_(4)固态电解质对锂表现出相对优异的界面性能.
Traditional lithium-ion batteries have a low energy density and pose safety risks due to the use of graphite-based anode materials and combustible organic liquid electrolytes.Advanced next-generation battery devices are urgently needed to store more energy and be used more safely in emerging and existing technologies such as electric vehicles and distributed energy storage.All-solid-state batteries made up of high-voltage cathodes and lithium metal anodes are promising candidates for achieving high safety and competitive energy power density.The nonflammable solid electrolytes (SEs) are key components that separate cathode and anode,migrate lithium ions,and support the cell framework.Among different types of SEs,thiophosphates Li_(3)PS_(4),as a thio-LISICON (lithium superionic conductor),have attracted considerable interest of researchers as inorganic SEs due to their superior room-temperature ionic conductivities,desirable mechanical properties,and compliant chemical compatibility.According to the arrangement mode of PS;tetrahedron,Li_(3)PS_(4)possesses different polymorph structures (glass-,α-,β-,andγ-Li_(3)PS_(4)),which play a critical role in ionic conductivity because of the strong dependence on ionic conductivity and crystalline phases.Under heat treatment conditions,polymorphs can transform into each other.Thus,investigating the synthesis conditions and phase transitions between different crystal structures is of great significance for the application of SEs.Ball-milling combined with a heat-sintering process is used to create different-structured Li_(3)PS_(4).In situ variable temperature Raman and room-temperature X-ray diffraction are used to delineate the transitions between different phases,focusing on investigating the transition conditions among different crystal structures and the relationship between the structures and ionic conductivity.Glass-Li_(3)PS_(4)can be easily obtained by ball-milling Li_(2)S and P_(2)S_(5)powders and preferentially transformed into the metastableβ-phase when the sintering temperature is raised to 240℃,which can retain the β-Li_(3)PS_(4)structure and show high ionic conductivity (0.65mS cm^(-1)) after cooling to room temperature.Once at a higher sintering temperature (>480℃),theβ-phase will then transform into the super-higher ionic conductivity but thermodynamically unstableα-phase.More interesting,theα-phase would directly transform into a thermodynamically stableγ-phase without the appearance ofβ-phase during the subsequent cooling process,while theγ-phase is not a favorable structure for Li-ions migration due to its low ionic conductivity (0.004m S cm^(-1)).Furthermore,we discuss some potential strategies for lowering the phase transition temperature to obtainα-Li_(3)PS_(4)superconductors at room temperature (e.g.,generation of pinning effect from element doping to restrict the movement and rearrangement of PS;tetrahedron,use of the high surface-area framework to stabilize the hightemperature structure,and the quenching process).Moreover,γ-phase and β-phase Li_(3)PS_(4)show a certain fabric memory effect,which enables them to retain their inherent structure even after resintering at 240℃.The results reveal that the thermodynamically metastable β-Li_(3)PS_(4)can be easily obtained at room temperature by precisely controlling the sintering temperature;there is no need for an assisted route such as forming nanoporous using solvent-assisted route or substituting cationic to obtain“β-like”phase.Finally,the Li-Li symmetric batteries assembled from different structural Li_(3)PS_(4)phases show that the β-Li_(3)PS_(4)provides better interfacial stability,which may meet the demands of SEs in solid-state batteries.
作者
梁嘉宁
许晓伟
曾诚
王书豪
梁昊樾
李会巧
Jianing Liang;Xiaowei Xu;Cheng Zeng;Shuhao Wang;Haoyue Liang;Huiqiao Li(State Key Laboratory of Materials Processing and Die&Mould Technology,School of Materials Science and Engineering,Huazhong University of Science and Technology,Wuhan 430074,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2022年第11期1190-1200,共11页
Chinese Science Bulletin
基金
国家自然科学基金(52072138,51772115)
国家重点研发计划(2018YFE0206900)
湖北省自然科学基金创新群体项目(2019CFA002)资助。
