Fast Ionic Conductivity in the Most Lithium-Rich Phosphidosilicate Li14SiP6

Solid electrolytes with superionic conductivity are required as a main component for all-solid-state batteries. Here we present a novel solid electrolyte with three-dimensional conducting pathways based on “lithium-rich” phosphidosilicates with ionic conductivity of σ > 10–3 S cm–1 at room temperature and activation energy of 30–32 kJ mol–1 expanding the recently introduced family of lithium phosphidotetrelates. Aiming toward higher lithium ion conductivities, systematic investigations of lithium phosphidosilicates gave access to the so far lithium-richest compound within this class of materials. The crystalline material (space group Fm3m), which shows reversible thermal phase transitions, can be readily obtained by ball mill synthesis from the elements followed by moderate thermal treatment of the mixture. Lithium diffusion pathways via both tetrahedral and octahedral voids are analyzed by temperature-dependent powder neutron diffraction measurements in combination with maximum entropy method and DFT calculations. Moreover, the lithium ion mobility structurally indicated by a disordered Li/Si occupancy in the tetrahedral voids plus partially filled octahedral voids is studied by temperature-dependent impedance and 7Li NMR spectroscopy.具有超离子导电性的固体电解质是全固态电池的核心组成部分。本工作报道了一种基于“富锂磷硅化物”的新型固体电解质，其具备三维导电通路，室温下离子电导率σ＞10^-3 S·cm^-1，活化能为30~32 kJ·mol^-1，拓展了近期报道的锂基磷代碳族化合物家族。为获得更高的锂离子电导率，研究人员对锂基磷硅化物开展了系统研究，得到了该类材料中迄今锂含量最高的化合物。该结晶材料的空间群为Fm3m，表现出可逆热相变，可通过以单质为原料的球磨合成法制备，随后对混合物进行适度热处理即可轻松制得。研究人员结合变温粉末中子衍射测试、最大熵法（Maximum Entropy Method）与密度泛函理论（DFT）计算，分析了锂离子通过四面体空隙与八面体空隙的扩散通路。此外，研究人员通过变温阻抗谱与锂-7核磁共振（7Li NMR）光谱，对由四面体空隙中Li/Si无序占位与部分占据的八面体空隙所表征的锂离子迁移特性展开了研究。