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In hunting for safe and cost‐effective materials for post‐Li‐ion energy storage, the design and synthesis of high‐performance solid electrolytes (SEs) for all‐solid‐state batteries are bottlenecks. Many issues associated with chemical stability during processing and storage and use of the SEs in ambient conditions need to be addressed. Now, the effect of water as well as oxyhdryl group (.OH) on NaBi3O4Cl2 are investigated by evaluating ionic conductivity. The presence of water and.OH results in an increase in ionic conductivity of NaBi3O4Cl2 owing to diffusion of H2O into NaBi3O4Cl2, partially forming binding.OH through oxygen vacancy repairing. Ab initio calculations reveal that the electrons significantly accumulate around.OH and induce a more negative charge center, which can promote Na+ hopping. This finding is fundamental for understanding the essential role of H2O in halide‐based SEs and provides possible roles in designing water‐insensitive SEs through control of defects. [ABSTRACT FROM AUTHOR]

Owing to several advantages of metallic sodium (Na), such as a relatively high theoretical capacity, low redox potential, wide availability, and low cost, Na metal batteries are being extensively studied, which are expected to play a major role in the fields of electric vehicles and grid-scale energy storage. Although considerable efforts have been devoted to utilizing MXene-based materials for suppressing Na dendrites, achieving a stable cycling of Na metal anodes remains extremely challenging due to, for example, the low Coulombic efficiency (CE) caused by the severe side reactions. Herein, a g-C 3 N 4 layer was attached in situ on the Ti 3 C 2 MXene surface, inducing a surface state reconstruction and thus forming a stable hetero-interphase with excellent sodiophilicity between the MXene and g-C 3 N 4 to inhibit side reactions and guide uniform Na ion flux. The 3D construction can not only lower the local current density to facilitate uniform Na plating/stripping but also mitigate volume change to stabilize the electrolyte/electrode interphase. Thus, the 3D Ti 3 C 2 MXene@g-C 3 N 4 nanocomposite enables much enhanced average CEs (99.9% at 1 mA h cm -2 , 0.5 mA cm -2 ) in asymmetric half cells, long-term stability (up to 700 h) for symmetric cells, and stable cycling (up to 800 cycles at 2 C), together with outstanding rate capability (up to 20 C), of full cells. The present study demonstrates an approach in developing practically high performance for Na metal anodes.

NASICON-type of solid-state electrolyte, Na 3 Zr 2 Si 2 PO 12 (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 Na 2 SiO 3 additive, which provides the liquid phase for the sintering process. The addition of 5 wt % Na 2 SiO 3 has shown the highest total ionic conductivity of 1.45 mS cm -1 at room temperature. A systematic study of the effect of Na 2 SiO 3 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 Na 2 SiO 3 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 Na 2 SiO 3 into the NZSP powder prior to the sintering stage.