No abstract

NASICON-type of solid-state electrolyte, Na3Zr2Si2PO12 (NZSP), is one of the potential solid-state electrolytes for all-solid-state Na battery and Na–air battery. However, in solid-state synthesis, high sintering temperature above 1200 °C and long duration are required, which led to loss of volatile materials and formation of impurities at the grain boundaries. This hampers the total ionic conductivity of NZSP to be in the range of 10–4 S cm–1. Herein, we have reduced both the sintering temperature and time of the NZSP electrolyte by sintering the NZSP powders with different amounts of Na2SiO3 additive, which provides the liquid phase for the sintering process. The addition of 5 wt % Na2SiO3 has shown the highest total ionic conductivity of 1.45 mS cm–1 at room temperature. A systematic study of the effect of Na2SiO3 on the microstructure and electrical properties of the NZSP electrolyte is conducted by the structural study with the help of morphological and chemical observations using X-ray diffraction (XRD), scanning electron microscopy, and using focused ion-beam-time of flight-secondary ion mass spectroscopy. The XRD results revealed that cations from Na2SiO3 diffused into the bulk change the stoichiometry of NZSP, leading to an enlarged bottleneck area and hence lowering activation energy in the bulk, which contributes to the increment of the bulk ion conductivity, as indicated by the electrochemical impedance spectroscopy result. In addition, higher density and better microstructure contribute to improved grain boundary conductivity. More importantly, this study has achieved a highly ionic conductive NZSP only by facile addition of Na2SiO3 into the NZSP powder prior to the sintering stage.

The advent of 3D printing brought about the possibilities of microlattice metamaterials as advanced materials with the potentials to surpass the functionalities of traditional materials. Sound absorbing materials which are also tough and lightweight are of particular importance as practical engineering materials. There are however a lack of attempts on the study of metamaterials multifunctional for both purposes. Herein, we present four types of face‐centered cubic based plate and truss microlattices as novel metamaterials with simultaneous excellent sound and mechanical energy absorption performance. High sound absorption coefficients nearing 1 and high specific energy absorption of 50.3 J g−1 have been measured. Sound absorption mechanisms of microlattices are proposed to be based on a “cascading resonant cells theory”, an extension of the Helmholtz resonance principle that we have conceptualized herein. Characteristics of absorption coefficients are found to be essentially geometry limited by the pore and cavity morphologies. The excellent mechanical properties in turn derive from both the approximate membrane stress state of the plate architecture and the excellent ductility and strength of the base material. Overall, this work presents a new concept on the specific structural design and materials selection for architectured metamaterials with dual sound and mechanical energy absorption capabilities.