All-solid-state lithium metal batteries (ASSLMBs) featuring sulfide solid electrolytes (SEs) are recognized as the most promising next-generation energy storage technology because of their exceptional safety and much-improved energy density. However, lithium dendrite growth in sulfide SEs and their poor air stability have posed significant obstacles to the advancement of sulfide-based ASSLMBs. Here, a thin layer (approximately 5 nm) of g-C₃N₄ is coated on the surface of a sulfide SE (Li₆PS₅Cl), which not only lowers the electronic conductivity of Li₆PS₅Cl but also achieves remarkable interface stability by facilitating the in situ formation of ion-conductive Li₃N at the Li/Li₆PS₅Cl interface. Additionally, the g-C₃N₄ coating on the surface can substantially reduce the formation of H₂S when Li₆PS₅Cl is exposed to humid air. As a result, Li–Li symmetrical cells using g-C₃N₄-coated Li₆PS₅Cl stably cycle for 1000 h with a current density of 0.2 mA cm⁻². ASSLMBs paired with LiNbO₃-coated LiNi_0.6Mn_0.2Co_0.2O₂ exhibit a capacity of 132.8 mAh g⁻¹ at 0.1 C and a high-capacity retention of 99.1% after 200 cycles. Furthermore, g-C₃N₄-coated Li₆PS₅Cl effectively mitigates the self-discharge behavior observed in ASSLMBs. This surface-coating approach for sulfide solid electrolytes opens the door to the practical implementation of sulfide-based ASSLMBs.

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.