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The solid-state Li–O2 battery is considered an ideal candidate for high-performance energy storage because of its high safety, due to use of non-flammable and non-volatile electrolytes, and high specific energy, as it uses Li metal and O2 gas as active materials. We present an original solid-state Li–O2 cell composed of a Li metal anode, a flexible polymer interlayer, a perovskite-structured Al-doped Li–La–Ti–O (A-LLTO) solid electrolyte, and an integrated cathode in which a porous A-LLTO solid electrolyte frame was covered with a carbon layer and CoO nanoparticles as the catalyst for the cyclic oxygen evolution and reduction reactions. The designed solid-state cell operated safely in pure O2 atmosphere at temperatures from 25 °C to 100 °C and delivered the first discharge capacity from 796 mA h gC+CoO−1 to 4035 mA h gC+CoO−1, respectively, at a current density of 0.05 mA cm−2. Notably, at 50 °C, the cell was maintained for 132 cycles under a limited capacity mode of 500 mA h gC+CoO−1 at a high current density of 0.3 mA cm−2, demonstrating the first step of success towards realizing Li batteries with high energy and cyclability, as well as safety.

Lithium (Li) metal can be degraded by factors such as irregular Li stripping, Li dendritic growth, and the growth of a solid electrolyte interphase (SEI) layer, finally leading to the performance deterioration of Li–air batteries. In particular, the operation of the Li–air battery in ambient air remains a considerable challenge due to the possible occurrence of parasitic reactions on Li metal with moisture and other contaminants diffusing from the outside air. In this work, a protected Li electrode (PLE) composed of Li metal covered with a bilayer lithium phosphorous oxynitride (LiPON)/aluminium substituted lithium lanthanum titanate (A-LLTO) solid electrolyte was suggested. The mechanism for the degradation of Li electrodes with and without the LiPON/A-LLTO protection layer was compared using the Li symmetric cell and Li–air cell by investigating the electrochemical performance of cells and the growth of Li dendrites. The Li symmetric cell employing the LiPON/A-LLTO exhibited superior cyclability to the cell without the solid electrolyte due to the effective suppression of Li dendritic growth. Further, the aprotic Li–air cell employing the PLE showed outstanding electrochemical performance when operated in pure oxygen and even in an air atmosphere: a long life span of 128 cycles in oxygen atmosphere and 20 cycles in air atmosphere under the limited capacity mode of 1000 mA h g−1. The obtained excellent performance of the Li–air cell employing the PLE is attributed to the effective suppression of the Li dendrite growth and electrolyte decomposition with the presence of LiPON/A-LLTO. In addition, dense LiPON/A-LLTO completely protected the Li metal electrode from the penetration of oxygen, moisture, and other contaminants which can degrade the Li metal electrode.

Germanium oxide (GeO2), which possesses great potential as a high-capacity anode material for lithium ion batteries, has suffered from its poor capacity retention and rate capability due to significant volume changes during lithiation and delithiation. In this study, we introduce a simple synthetic route for producing nanosized GeO2 anchored on a nitrogen-doped carbon matrix (GeO2/N–C) via the sol–gel method followed by a calcination process in an inert argon atmosphere. The GeO2/N–C showed superior electrochemical performance over pure GeO2; almost 91.8% capacity retention of 905 mA h g−1 was shown after 200 cycles at the rate of C/2. Interestingly, even at a high rate of 20C, a specific capacity of 412 mA h g−1 was retained. This unique anode performance of GeO2/N–C is derived from the effective combination of nano-size GeO2 and its uniform distribution in a nitrogen-doped carbon matrix. Herein, the nitrogen doped-carbon matrix not only strengthens the structure but also promotes the lithium diffusion in the GeO2/C–N material. Further, the adaptability of GeO2/N–C as an anode in a full cell configuration in combination with the LiCoO2 cathode was demonstrated by exhibiting high specific capacity and good cyclability.

Herein, we report the catalytic activities of porous nano-crystalline oxides with surface active sites synthesized by a wet chemical route. Zr doped ceria (ZDC) has been tested as active oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts in air electrodes for Li–O2 batteries. A ZDC-based air electrode exhibits a higher discharge capacity than that of a bare carbon-based air electrode. ZDC loaded in carbon air electrodes delivers a discharge capacity of 8435 mA h g−1. The higher discharge voltages of Li–O2 cells with ZDC, instead of bare carbon, could have originated from the higher oxygen reduction activity of ZDC. These oxides show a lower potential for Li2O2 oxidation than pure carbon. A significant increase in the kinetics for Li2O2 oxidation indicates the influence of the ZDC catalyst on the oxygen evolution reaction. The ORR and OER properties of the catalyst are explained in terms of the high fraction of active defect sites on its surface.