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Li–CO2/O2 batteries, a promising energy storage technology, not only provide ultrahigh discharge capacity but also capture CO2 and turn it into renewable energy. Their electrochemical reaction pathways' ambiguity, however, creates a hurdle for their practical application. This study used copper selenide (CuSe) nanosheets as the air cathode medium in an environmental transmission electron microscope to in situ study Li–CO2/O2 (mix CO2 as well as O2 at a volume ratio of 1:1) and Li–O2 batteries as well as Li–CO2 batteries. Primary discharge reactions take place successively in the Li–CO2/O2–CuSe nanobattery: (I) 4Li+ + O2 + 4e− → 2Li2O; (II) Li2O + CO2 → Li2CO3. The charge reaction proceeded via (III) 2Li2CO3 → 4Li+ + 2CO2 + O2 + 4e−. However, Li–O2 and Li–CO2 nanobatteries showed poor cycling stability, suggesting the difficulty in the direct decomposition of the discharge product. The fluctuations of the Li–CO2/O2 battery's electrochemistry were also shown to depend heavily on O2. The CuSe‐based Li–CO2/O2 battery showed exceptional electrochemical performance. The Li–CO2/O2 battery offered a discharge capacity apex of 15,492 mAh g−1 and stable cycling 60 times at 100 mA g−1. Our research offers crucial insight into the electrochemical behavior of Li–CO2/O2, Li–O2, and Li–CO2 nanobatteries, which may help the creation of high‐performance Li–CO2/O2 batteries for energy storage applications. [ABSTRACT FROM AUTHOR]

Layered transition metal dichalcogenides have great potential as anodes of sodium‐ion batteries (SIBs) due to their high theoretical specific capacity. However, the restacking severely limits their accessible sites, leading to undesirable specific capacity, cycle stability, and working temperature range. Herein, a hierarchical 2D VS2/Ti3C2Tx MXene hybrid is designed via a simple liquid‐mixing method, where VS2 is confined in the conductive Ti3C2Tx matrix with chemical connections built between them. The in situ transmission electron microscopy analyses reveal that the hybrid depends on a very fast and reversible intercalation/de‐intercalation process between VS2 and NaxVS2 (where x = 1) to store sodium. Theoretical calculations disclose that the Ti3C2Tx matrix remarkably enhances the charge transfer and alleviates the volume expansion of VS2 especially after Na+ is inserted. Consequently, such a rational design exhibits an intercalation pseudocapacitance‐dominant mechanism, with excellent specific capacity (522 mAh g−1 at 0.2 A g−1), rate capability (342 mAh g−1 at 10 A g−1), cycle life (116% after 3000 cycles), and also all‐climate workability (with high specific capacity and long‐term cycle stability even at 70 and −40 °C). This study may open up a new vision to design fast‐charging, long‐cycle, and all‐climate SIBs anodes based on the intercalation pseudocapacitance. [ABSTRACT FROM AUTHOR]

Lithium-oxygen (Li-O2) batteries have been considered as an ideal solution to solving the global energy crisis. Silver (Ag) or Ag-based catalyst have been extensively studied due to their high catalytic activities in Li-O2 batteries. However, it remains a challenge to track the catalytic mechanism during the charge/discharge process. Here, a nanoscale processing method was used to assemble a Li-O2 nanobattery in an aberration-corrected environmental transmission electron microscope (ETEM), where a single Ag nanowire (NW) was used as catalyst for O2 electrode. A visualization of the lithium ion insertion process during the electrochemical reactions were achieved in this nanobattery. Numerous Ag nanoparticles (NPs) were observed on the surface of the Ag NW, which were covered by the discharge product Li2O2. By simultaneously studying the evolution of the interface and the phase transformation, it can be concluded that those Ag NPs wrapped around Ag NW acted as catalyst during the subsequent charge/discharge reaction. Based on those studies, Ag NPs decorated on porous carbon were synthesized, and it can simultaneously improve the cycling stability (100 cycles) and the maximum specific capacity (17,371 mAh·g−1 at a current density of 100 mA·g−1) in a coin cell Li-O2 battery. This study suggests that nanoscale Ag may be a promising catalyst for Li-O2 battery. [ABSTRACT FROM AUTHOR]

Metals fluorides (MFs) are potential conversion cathodes to replace commercial intercalation cathodes. However, the application of MFs is impeded by their poor electronic/ionic conductivity and severe decomposition of electrolyte. Here, a composite cathode of FeF2 and polymer‐derived carbon (FeF2@PDC) with excellent cycling performance is reported. The composite cathode is composed of nanorod‐shaped FeF2 embedded in PDC matrix with excellent mechanical strength and electronic/ionic conductivity. The FeF2@PDC enables a reversible capacity of 500 mAh g–1 with a record long cycle lifetime of 1900 cycles. Remarkably, the FeF2@PDC can be cycled at a record rate of 60 C with a reversible capacity of 107 mAh g–1 after 500 cycles. Advanced electron microscopy reveals that the in situ formation of stable Fe3O4 layers on the surface of FeF2 prevents the electrolyte decomposition and leaching of iron (Fe), thus enhancing the cyclability. The results provide a new understanding to FeF2 electrochemistry, and a strategy to radically improve the electrochemical performance of FeF2 cathode for lithium‐ion battery applications. [ABSTRACT FROM AUTHOR]