Recently, sulfide-based solid-state electrolytes (SSEs) have attracted much attention owing to their high ionic conductivity and feasible mechanical features. The environmental stability of sulfide-based SSEs is one of the critical aspects due to the possible decomposition, and ionic conductivity change will affect the fabrication and electrochemical performance of the batteries. Thus, important efforts have been made to reveal and improve their environmental stability, and a timely summary of the progress is urgently needed. In this review, we first clarify the definition of environmental stability and its significance in the context of practical use. After indicating the degradation mechanisms of sulfide-based SSEs, we summarize several effective strategies to improve their stability and also highlight the related theoretical studies. The stability of organic solvents of sulfide SSEs is also summarized and discussed, which may help reliable sulfide SSEs in the battery system. The main target of this review is to gain insights and provide useful guidance to further improve the environmental stability of sulfide SSEs, which will finally promote the commercialization of sulfide-based all-solid-state batteries.

In this study, dual-metal atomic pairs of manganese (Mn)-iron (Fe) binuclear sites (BNSs) with two conjoint MnN₄ and FeN₄ moieties (MnFeN₈) anchored onto a graphite-like structure (GLS) (Mn-Fe BNSs/GLS) were constructed. The binuclear MnFeN₈ structure was verified experimentally and theoretically. Magnetic measurements and Gaussian calculations reveal that this unique Mn-Fe BNSs exhibit strong short-range electronic interaction between Mn and Fe sites, which decouples two paired d electrons in Fe sites, thereby transforming Fe sites from an intermediate to a high spin state. The optimal electronic configuration of Fe sites and their binuclear structure facilitate an oxygen reduction reaction (ORR) thermodynamically and dynamically, respectively, endowing Mn-Fe BNSs with improved ORR performance.

Lithium-rich layered oxides (LLOs) are promising candidate cathode materials for safe and inexpensive high-energy-density Li-ion batteries. However, oxygen dimers are formed from the cathode material through oxygen redox activity, which can result in morphological changes and structural transitions that cause performance deterioration and safety concerns. Herein, a flake-like LLO is prepared and aberration-corrected scanning transmission electron microscopy (STEM), in situ high-temperature X-ray diffraction (HT-XRD), and soft X-ray absorption spectrum (sXAS) are used to explore its crystal facet degradation behavior in terms of both thermal and electrochemical processes. Void-induced degradation behavior of LLO in different facet reveals significant anisotropy at high voltage. Particle degradation originates from side facets, such as the (010) facet, while the close (003) facet is stable. These results are further understood through ab initio molecular dynamics calculations, which show that oxygen atoms are lost from the {010} facets. Therefore, the facet degradation process is that oxygen molecular formed in the interlayer and accumulated in the ab plane during heating, which result in crevice-voids in the ab plane facets. The study reveals important aspects of the mechanism responsible for oxygen -anionic activity-based degradation of LLO cathode materials used in lithium-ion batteries. In particular, this study provides insight that enables precise and efficient measures to be taken to improve the thermal and electrochemical stability of an LLO.

Conventional lithium-ion batteries (LIBs) with liquid electrolytes are challenged by their big safety concerns, particularly used in electric vehicles. All-solid-state batteries using solid-state electrolytes have been proposed to significantly improve safety yet are impeded by poor interfacial solid–solid contact and fast interface degradation. As a compromising strategy, in situ solidification has been proposed in recent years to fabricate quasi-solid-state batteries, which have great advantages in constructing intimate interfaces and cost-effective mass manufacturing. In this work, quasi-solid-state pouch cells with high loading electrodes (≥3 mAh cm⁻²) were fabricated via in situ solidification of poly(ethylene glycol)diacrylate-based polymer electrolytes (PEGDA-PEs). Both single-layer and multilayer quasi-solid-state pouch cells (2.0 Ah) have demonstrated stable electrochemical performance over 500 cycles. The superb electrochemical stability is closely related to the formation of robust and compatible interphase, which successfully inhibits interfacial side reactions and prevents interfacial structural degradation. This work demonstrates that in situ solidification is a facile and cost-effective approach to fabricate quasi-solid-state pouch cells with both excellent electrochemical performance and safety.

Carbonaceous materials have long been considered promising anode materials for Na-ion batteries. However, the electrochemical performance of conventional carbon anodes is generally poor because the sodium ion storage solely relies on the disordered region of the carbon materials in a carbonate-based electrolyte. The solvent co-intercalation mechanism for Na ions has been recently reported in natural graphite anodes for Na-ion batteries with ether-based electrolytes, but their capacities are still unsatisfactory. We show here for the first time that by combining regular Na ion storage in the disordered carbon layer and solvent co-intercalation mechanism in the graphitized layer of a commercial N330 carbon black as an anode material for Na-ion batteries in ether-based electrolyte, the reversible capacity could be fully realized and doubled in magnitude. This unique sodium intercalation process resulted in a significantly improved electrochemical performance for the N330 electrode with an initial reversible capacity of 234 mAh·g^–1 at 50 mA·g^–1 and a superior rate capability of 105 mAh·g^–1 at 3, 200 mA·g^–1. When cycled at 3, 200 mA·g^–1 over 2, 000 cycles, the electrode still exhibited a highly reversible capacity of 72 mAh·g^–1 with a negligible capacity loss per cycle (0.0167%). Additionally, surface-sensitive C K-edge X-ray absorption spectroscopy, with the assistance of electrochemical and physicochemical characterizations, helped in identifying the controlled formation and evolution of a thin and robust solid electrolyte interphase film. This film not only reduced the resistance for sodium ion diffusion, but also maintained the structural stability of the electrode for extended cycle reversibility. The superior electrochemical performance of N330 carbon black strongly demonstrated the potential of applying ether-based electrolytes for a wide range of carbon anodes apart from natural graphite.