Graphite, a robust host for reversible lithium storage, enabled the first commercially viable lithium-ion batteries. However, the thermal degradation pathway and the safety hazards of lithiated graphite remain elusive. Here, solid-electrolyte interphase (SEI) decomposition, lithium leaching, and gas release of the lithiated graphite anode during heating were examined by in situ synchrotron X-ray techniques and in situ mass spectroscopy. The source of flammable gas such as H2 was identified and quantitively analyzed. Also, the existence of highly reactive residual lithium on the graphite surface was identified at high temperatures. Our results emphasized the critical role of the SEI in anode thermal stability and uncovered the potential safety hazards of the flammable gases and leached lithium. The anode thermal degradation mechanism revealed in the present work will stimulate more efforts in the rational design of anodes to enable safe energy storage.

Lithium reactivity with electrolytes leads to their continuous consumption and dendrite growth, which constitute major obstacles to harnessing the tremendous energy of lithium-metal anode in a reversible manner. Considerable attention has been focused on inhibiting dendrite via interface and electrolyte engineering, while admitting electrolyte-lithium metal reactivity as a thermodynamic inevitability. Here, we report the effective suppression of such reactivity through a nano-porous separator. Calculation assisted by diversified characterizations reveals that the separator partially desolvates Li+ in confinement created by its uniform nanopores, and deactivates solvents for electrochemical reduction before Li0-deposition occurs. The consequence of such deactivation is realizing dendrite-free lithium-metal electrode, which even retaining its metallic lustre after long-term cycling in both Li-symmetric cell and high-voltage Li-metal battery with LiNi0.6Mn0.2Co0.2O2 as cathode. The discovery that a nano-structured separator alters both bulk and interfacial behaviors of electrolytes points us toward a new direction to harness lithium-metal as the most promising anode.

Oxygen redox at high-voltage has emerged as a transformative paradigm for high-energy battery cathodes by offering extra capacity beyond conventional transition-metal redox. However, it suffers from voltage hysteresis, voltage fade, and capacity drop upon cycling. Here, we show that, by eliminating the domain boundaries in the often-considered single-crystalline battery particles, layered oxide cathodes demonstrate exceptional capacity and voltage stability during high-voltage operation. Our combined experimental and theory studies for the first time reveal that the elimination of domain boundaries could enhance the reversible lattice oxygen redox while inhibiting the irreversible oxygen release, leading to significantly suppressed structural degradation and improved mechanical integrity during battery cycling and abuse heating. The robust oxygen redox enabled through domain boundary control provides practical opportunities towards high-energy, long-cycling, and safe batteries. MainHigh-energy batteries rely on high-capacity and high-voltage operation of the cathodes.Fundamentally, the capacity of a transition metal oxide-based cathode is determined by the amount of active Li, while the voltage is defined by the redox reactions affected by structural configurations 1 . This has led to two associated trends in recent cathode development: Li-excess compounds due to the large amount of Li (capacity) and oxygen redox (OR) at high-voltage 2-6 .However, intensive studies have shown that OR activities can trigger detrimental structural effects such as oxygen release, surface reactions, and phase transition, leading to severe voltage hysteresis, voltage fade, and poor capacity stability 3,5 . Despite extensive mechanistic understanding 3,5 and material optimization such as structural control [7][8][9] , chemical composition manipulation 10 , and cationic/anionic doping [11][12][13] , the fundamental origin of the OR instability remains under active debate, and the practical control of high-voltage operation involving OR remains a formidable challenge. The key relies on a strategy that enhances the reversible OR in the lattice, while suppressing or even eliminating other detrimental oxygen activities.Theoretical studies suggest that the surface could favour the migration of oxygen ions and promote the formation of oxygen vacancies due to the open atomic structure [14][15][16] . Therefore, surface-initiated irreversible oxygen loss and the associated structural transformation have long been considered as the root cause of the capacity decay and voltage fade of Li-excess layered cathodes when activating the OR process [16][17][18] . However, surface coatings to mitigate the oxygen loss have proven insufficient to achieve a fully reversible OR 5,18,19 .Grain boundaries (GBs), the surface that separates individual grains from each other, play a vital role in materials' properties. In layered oxide cathodes, the GBs have been predominantly referred to the boundaries between primary particles of polycrystalline cathodes, while ...

Lithium-sulfur batteries have theoretical specific energy higher than state-of-the-art lithium-ion batteries. However, from a practical perspective, these batteries exhibit poor cycle life and low energy content owing to the polysulfides shuttling during cycling. To tackle these issues, researchers proposed the use of redox-inactive protective layers between the sulfur-containing cathode and lithium metal anode. However, these interlayers provide additional weight to the cell, thus, decreasing the practical specific energy. Here, we report the development and testing of redox-active interlayers consisting of sulfur-impregnated polar ordered mesoporous silica. Differently from redox-inactive interlayers, these redox-active interlayers enable the electrochemical reactivation of the soluble polysulfides, protect the lithium metal electrode from detrimental reactions via silica-polysulfide polar-polar interactions and increase the cell capacity. Indeed, when tested in a non-aqueous Li-S coin cell configuration, the use of the interlayer enables an initial discharge capacity of about 8.5 mAh cm−2 (for a total sulfur mass loading of 10 mg cm−2) and a discharge capacity retention of about 64 % after 700 cycles at 335 mA g−1 and 25 °C.

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