Na3Zr2Si2PO12 solid-state electrolyte with glass-like morphology for enhanced dendrite suppression

Rechargeable batteries based on solid-state electrolytes are of great interest and importance for the next-generation energy storage due to their high energy output and improved safety. For building the solid-state batteries, Na 3 Zr 2 Si 2 PO 12 (NZSP) represents a promising candidate as it features high chemical stability against air exposure and a high Na + conductivity. NZSP pellets were usually calcined at a high temperature, and the high volatility of Na and P elements easily led to the formation of impurity phase. In this work, the effects of calcination temperature and stoichiometry on the phase purity and ionic conductivity of the NZSP electrolyte were studied. At an elevated sintering temperature, the NZSP electrolyte showed a high ionic conductivity owing to decreased porosity, and the highest ionic conductivity at 30 °C was observed to be 2.75 × 10 –5 S·cm −1 with an activation energy of 0.41 eV. For the stoichiometry, the introduction of 5 mol% excessive P results in formation of more Na 3 PO 4 and glass-like phase at the grain boundary, which caused the blurred grain boundary and reduced grain barrier, and effectively suppressed Na dendrite growth, then accounted for improved cycling performance of a Na||Na symmetric cell. Our work provided insights on reasonable design and preparation of NZSP electrolyte towards practical realization of solid-state Na-metal batteries. Graphical abstract 摘要 基于固态电解质的可充电电池表现出高的能量密度和高安全性, 具有重要的研究意义。其中, Na 3 Zr 2 Si 2 PO 12 (NZSP)具有高离子电导率以及高的空气稳定性, 是一类很有前景的固态电解质。NZSP通常需要高温焙烧, 但是高的焙烧温度易导致Na, P等元素的挥发, 从而导致杂相的形成。在本工作中, 我们研究了焙烧温度以及化学计量比对NZSP相结构以及离子电导率的影响。随着焙烧温度升高, NZSP电解质孔隙率降低, 电导率升高, 30 °C时最高的离子电导率为2.75 × 10 –5 S·cm −1 , 活化能0.41 eV。同时, 当引入5 mol%过量的P时, 产生更多的Na 3 PO 4 , 并在晶界处形成玻璃态, 从而有效抑制钠枝晶, 提高Na||Na对称电池的循环稳定性。我们的工作为NZSP电解质的设计与制备提供了新见解。