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Rechargeable lithium ion batteries have ruled the consumer electronics market for the past 20 years and have great significance in the growing number of electric vehicles and stationary energy storage applications. However, in addition to concerns about electrochemical performance, the limited availability of lithium is gradually becoming an important issue for further continued use and development of lithium ion batteries. Therefore, a significant shift in attention has been taking place towards new types of rechargeable batteries such as sodium-based systems that have low cost. Another important aspect of sodium battery is its potential compatibility with the all-solid-state design where solid electrolyte is used to replace liquid one, leading to simple battery design, long life span, and excellent safety. The key to the success of all-solid-state battery design is the challenge of finding solid electrolytes possessing acceptable high ionic conductivities at room temperature. Herein, we report a novel sodium superionic conductor with NASICON structure, Na3.1Zr1.95Mg0.05Si2PO12 that shows high room-temperature ionic conductivity of 3.5 × 10−3 S cm−1. We also report successful fabrication of a room-temperature solid-state Na-S cell using this conductor.

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Solid electrolytes potentially provide safety, Li dendrites blocking, and electrochemical stability in Li-metal batteries. Large efforts have been devoted to disperse ceramic nanoparticles in a poly­(ethylene oxide) (PEO) matrix to improve the ions transport. However, it is challengeable to create efficient framework for ions transport with nanoparticles. Here we report for the first time garnet nanosheets to provide interconnected Li-ions transport pathway in a PEO matrix. The garnet nanosheet fillers would not only facilitate ions transport but also enhance ionic conductivity in comparison with their nanoparticle counterparts. A composite solid polymer electrolyte containing 15 wt % garnet nanosheets exhibits a practically useful conductivity of 3.6 × 10–4 S cm–1 at room temperature. Besides, the composite electrolyte can robustly isolate Li dendrites in a symmetric lithium metal-composite electrolyte battery during reversible Li dissolution/deposition at a relatively low temperature of 40 °C. The symmetric cell with composite electrolyte shows flat voltage and low interfacial resistance over a galvanostatic cycling of 200 h at a current density of 0.1 mA cm–2. A solid-state Li/LiFePO4 battery with the composite polymer electrolyte exhibits a capacity of 98.1 mAh g–1 and a capacity retention of 97.5% after 30 cycles at a temperature of 40 °C. This finding provides a strategy to explore superionic conductors.

The development of solid electrolytes with superior electrical and electrochemical performances for the room-temperature operation of sodium (Na)-based batteries is at the infant stage and still remains a challenge.

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electric vehicles because of their high energy density and long cycle life, etc. However, traditional LIBs are composed of organic liquid electrolytes in which there exists latent danger of fire and even explosion. [1] Thanks to the remarkable mechanical strength and inflammable nature of solid-state electrolytes, solid-state batteries (SSBs) are expected to address the critical safety issues of the traditional LIBs. [2] Simultaneously, the solid-state electrolytes are capable to resist the growth of lithium dendrites enabling possible use of lithium-metal anodes to replace graphite thus markedly improving the energy density.With the discovery of sodium super ion conductor (NASICON) in 1976 by Goodenough et al., [3] numerous research has been focused on oxide ceramic electrolytes (OCEs), including several crystal structures like NASICON-type, perovskite-type, LISICON-type (lithium superionic conductor), and garnet-type, etc. [4] The OCEs have been shown to be very promising for the development of SSBs given their advantages of high ionic conductivity (10 −4 -10 −3 S cm −1 at 25 °C), wide electrochemical High room-temperature ionic conductivities, large Li + -ion transference numbers, and good compatibility with both Li-metal anodes and high-voltage cathodes of the solid electrolytes are the essential requirements for practical solid-state lithium-metal batteries. Herein, a unique "superconcentrated ionogel-in-ceramic" (SIC) electrolyte prepared by an in situ thermally initiated radical polymerization is reported. Solid-state static 7 Li NMR and molecular dynamics simulation reveal the roles of ceramic in Li + local environments and transport in the SIC electrolyte. The SIC electrolyte not only exhibits an ultrahigh ionic conductivity of 1.33 × 10 −3 S cm −1 at 25 °C, but also a Li + -ion transference number as high as 0.89, together with a low electronic conductivity of 3.14 × 10 −10 S cm −1 and a wide electrochemical stability window of 5.5 V versus Li/Li + . Applications of the SIC electrolyte in Li||LiNi 0.5 Co 0.2 Mn 0.3 O 2 and Li||LiFePO 4 batteries further demonstrate the high rate and long cycle life. This study, therefore, provides a promising hybrid electrolyte for safe and high-energy lithium-metal batteries.