All-solid-state lithium batteries (ASSLBs) have the potential to revolutionize battery systems for electric vehicles due to their benefits in safety, energy density, packaging, and operable temperature range. As the key component in ASSLBs, inorganic lithium-ion-based solid-state electrolytes (SSEs) have attracted great interest, and advances in SSEs are vital to deliver the promise of ASSLBs. Herein, a survey of emerging SSEs is presented, and ion-transport mechanisms are briefly discussed. Techniques for increasing the ionic conductivity of SSEs, including substitution and mechanical strain treatment, are highlighted. Recent advances in various classes of SSEs enabled by different preparation methods are described. Then, the issues of chemical stabilities, electrochemical compatibility, and the interfaces between electrodes and SSEs are focused on. A variety of research addressing these issues is outlined accordingly. Given their importance for next-generation battery systems and transportation style, a perspective on the current challenges and opportunities is provided, and suggestions for future research directions for SSEs and ASSLBs are suggested.

Development of the next-generation, high-energy-density, low-cost batteries will likely be fueled by sodium (Na) metal batteries because of their high capacity and the abundance of Na. However, their practical application is significantly plagued by the hyper-reactivity of Na metal, unstable solid electrolyte interphase (SEI), and dendritic Na growth, leading to continuous electrolyte decomposition, low Coulombic efficiency, large impedance, and safety concerns. Herein, we add a small amount of SnCl2 additive in a common carbonate electrolyte so that the spontaneous reaction between SnCl2 and Na metal enables in situ formation of a Na–Sn alloy layer and a compact NaCl-rich SEI. Benefitting from this design, rapid interfacial ion transfer is realized and direct exposure of Na metal to the electrolyte is prohibited, which jointly achieve a nondendritic deposition morphology and a markedly reduced voltage hysteresis in a Na/Na symmetric cell for over 500 h. The Na/SnCl2-added electrolyte/Na3V2(PO4)3 full cell exhibits high capacity retention over cycling and excellent rate capability (101 mAh/g at 10 C). This work can provide an easily scalable and cost-effective approach for developing high-performance Na-metal batteries.

Most Li+/Na+-conducting solid electrolytes are unstable in moisture, and the formed hydroxides and carbonates on their surfaces result in the increase of the interfacial resistance between solid electrolytes and alkali metal anodes. In this study, heat treatment was used to remove the byproduct coating on the surface of Na3Zr2Si2PO12 (NZSP) that also leads to the generation of Na-ion deficient surface simultaneously. This surface chemistry approach was used to reduce the interfacial resistance and suppress Na-dendrite growth during Na plating. A combination of the metallic Na wetting test, density functional theory, and electrochemical measurement was employed to investigate the origins of ultralow interfacial resistance and mechanism between the Na-ion deficient surface and the metallic Na anode. The analysis demonstrates that the Na-ion-deficient surface effectively improves the contact between NZSP and the metallic Na anode. Moreover, an ultrathin passivating layer involving Na2O was formed between NZSP with metallic Na that protected the NZSP electrolyte from the reduction by metallic Na. This study not only motivates the need for further understanding of the surface chemistry of NZSP but also provides guidelines for the future design of the Na-ion solid–electrolyte interface.

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Room-temperature solid-state sodium batteries (SSBs) are viewed as one of the most promising candidates for next-generation energy storage devices because of their cost-effectiveness, safety performance, and high energy density. Na + ion superionic conductor (NASICON) type solid electrolyte (SE) shows great perspective due to its high ionic conductivity at room temperature. However, the high interfacial resistance between Na metal anode and NASICON SE is still thwarting the stable operation of SSBs. In this work, we successfully reduce the Na|NASICON interfacial resistance from 1658 to 101 Ω•cm 2 by lowering surface tension of Na metal via compositing Na metal with amorphous SiO 2 . Enabled by the enhanced interface contact, the solidstate Na-SiO 2 |NASICON|Na-SiO 2 symmetric cell can endure current density up to 500 μA/cm 2 and stably cycle for more than 135 h, while Na|NASICON|Na symmetric cell shorts in less than 10 h under 100 μA/cm 2 . This Letter provides an effective route to form close contact between Na metal anode and NASICON SE and fuels studies concerning Na|NASICON interface in the future.

Elemental doping represents a prominent strategy to improve interfacial chemistry in battery materials. Manipulating the dopant spatial distribution and understanding the dynamic evolution of the dopants at the atomic scale can inform better design of the doping chemistry for batteries. In this work, we create a targeted hierarchical distribution of Ti 4+ , a popular doping element for oxide cathode materials, in LiNi 0.8 Mn 0.1 Co 0.1 O 2 primary particles. We apply multiscale synchrotron/electron spectroscopy and imaging techniques as well as theoretical calculations to investigate the dynamic evolution of the doping chemical environment. The Ti 4+ dopant is fully incorporated into the TMO 6 octahedral coordination and is targeted to be enriched at the surface. Ti 4+ in the TMO 6 octahedral coordination increases the TM−O bond length and reduces the covalency between (Ni, Mn, Co) and O. The excellent reversibility of Ti 4+ chemical environment gives rise to superior oxygen reversibility at the cathode−electrolyte interphase and in the bulk particles, leading to improved stability in capacity, energy, and voltage. Our work directly probes the chemical environment of doping elements and helps rationalize the doping strategy for high-voltage layered cathodes.

The logo of 110th Anniversary of Tongji University is represented using the crystal structure of garnet inorganic solid‐state electrolyte as units. In article number https://doi.org/10.1002/adma.201705702, Wei Luo, Yunhui Huang, and co‐workers summarize the recent progress on lithium‐based inorganic solid‐state electrolytes. The challenges and the corresponding advanced strategies for developing all‐solid‐state lithium batteries are highlighted. Image credit: Jiaqi Dai, University of Maryland.

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