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Lithium‐oxygen batteries (LOBs) are promising next‐generation rechargeable battery candidates due to theoretical energy densities that exceed those of conventional lithium‐ion batteries. Although LOB with high cell level energy density has been demonstrated under lean electrolyte and high areal capacity conditions, their cycle life is still poor, and the cell degradation mechanism remains unclear. In the present study, by use of a three‐electrode electrochemical setup and in situ MS analytical techniques, it is revealed that the reaction efficiency of the negative lithium electrode largely decreases due to chemical crossover from the positive oxygen electrode side, such as H2O and CO2. Based on this mechanistic understanding, a LOB with an ultra‐lightweight flexible ceramic‐based solid‐state separator with 6 µm thickness that effectively protects the lithium electrode against chemical crossover without diminishing the energy density of LOBs is fabricated. Notably, a 400 Wh kg−1 class LOB exhibits a stable discharge/charged process for >20 cycles. The strategy demonstrated in this study sheds light on the direction for the practical implementation of LOBs with high energy densities and long cycle lives. [ABSTRACT FROM AUTHOR]

Lithium-oxygen (Li–O 2 ) batteries with ionic liquid-based electrolytes have attracted much attention because of their superior battery performance and high safety. However, the practical energy capacities achieved to date are markedly lower than those of Li-ion batteries. A dominant factor that limits the energy capacities of Li–O 2 batteries is the insulating characteristics and insolubility of lithium peroxide (Li 2 O 2 ), which gradually accumulates on the positive electrode as a discharge product. Herein, we report that ammonium ions function as a promoter for the solution-route formation of Li 2 O 2 , which results in a significant improvement of the energy capacity of Li–O 2 cells. Scanning electron microscopy analyses revealed that the structure of Li 2 O 2 changed from spherical particles to toroidal particles with an increase in the ammonium ions concentration. Ionic additives that have been reported to function as promoters the solution-route formation of Li 2 O 2 in ether-based electrolyte systems do not exhibit a promoting effect in ionic liquid-based electrolytes. [ABSTRACT FROM AUTHOR]

There is growing demand for practical implementation of lithium–oxygen batteries (LOBs) due to their superior potential for achieving higher energy density than that of conventional lithium‐ion batteries. Although recent studies demonstrate the stable operation of 500 Wh kg−1‐class LOBs, their cycle life remains fancy. For further improving the cycle performance of LOBs, the complicated chemical degradation mechanism in LOBs must be elucidated. In particular, the quantitative contribution of each cell component to degradation phenomenon in LOBs under lean‐electrolyte and high‐areal‐capacity conditions should be clarified. In the present study, the mass balance of the positive‐electrode reaction in a LOB under lean‐electrolyte and high‐areal‐capacity conditions is quantitatively evaluated. The results reveal carbon electrode decomposition to be the critical factor that prevents the prolonged cycling of the LOB. Notably, the carbon electrode decomposition occur during charging at voltages higher than 3.8 V through the electrochemical decomposition of solid‐state side products. The findings of this study highlight the significance of improving the stability of the carbon electrode and/or forming Li2O2, which can decompose at voltages lower than 3.8 V, to realize high‐energy‐density LOBs with long cycle life. [ABSTRACT FROM AUTHOR]

Although lithium–oxygen batteries have attracted attention due to their extremely high energy densities, rational design, and critical evaluation of high‐energy‐density cathode for practical Li–O2 batteries is still urgently needed. Herein, the multiscale, angstrom‐to‐millimeter, precisely controllable synthesis of binder‐free cathodes with minimally stacked graphene free from edge sites is demonstrated. The proposed Li–O2 battery, based on a hierarchically porous cathode with a practical mass loading of >4.0 mg cm−2, simultaneously exhibits an unprecedented specific areal (>30.0 mAh cm−2), mass (>6300 mAh g−1), and volumetric (>480 mAh cm−3) capacities. The battery displays the optimal energy density of 793 Wh kg−1 critically normalized to the total mass of all active materials including electrolytes and even discharge products Li2O2. Comprehensive in situ characterizations demonstrate a unique discharge mechanism in hierarchical pores which contributes to competitive battery performance. Superior rate performance in a current density range of 0.1 to 0.8 mA cm−2 and long‐cycle stability (>260 cycles) at a current density of 0.4 mA cm−2, outperforming state‐of‐the‐art carbon cathodes. This study yields insight into next‐generation carbon cathodes, not only for use in practical Li–O2 batteries, but also in other metal–gas batteries with high energy densities. [ABSTRACT FROM AUTHOR]

Lithium metal anode is regarded as the ultimate negative electrode material due to its high theoretical capacity and low electrochemical potential. However, the significantly high reactivity of Li metal limits the practical application of Li metal batteries. To improve the stability of the interface between Li metal and an electrolyte, a facile and scalable blade coating method was used to cover the commercial polyethylene membrane separator with an inorganic/organic composite solid electrolyte layer containing lithium-ion-conducting ceramic fillers. The coated separator suppressed the interfacial resistance between the Li metal and the electrolyte and consequently prolonged the cycling stability of deposition/dissolution processes in Li/Li symmetric cells. Furthermore, the effect of the coating layer on the discharge/charge cycling performance of lithium-oxygen batteries was investigated. [ABSTRACT FROM AUTHOR]

In the article "Hierarchically Porous and Minimally Stacked Graphene Cathodes for High-Performance Lithium-Oxygen Batteries," Wei Yu, Hirotomo Nishihara, and their colleagues present a design for a carbon cathode using a free-standing graphene mesosponge sheet (GMS-sheet) for Li-O2 batteries. The GMS-sheet has a hierarchical porous structure that allows for a large loading of Li2O2 toroids, resulting in a high areal capacity (>30.0 mAh cm−2) and long cycle stability (>260 cycles) at a current density of 0.4 mAh cm−2. This research contributes to the development of high-performance lithium-oxygen batteries. [Extracted from the article]