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The demand for high-energy sustainable rechargeable batteries has motivated the development of lithium-oxygen (Li-O 2 ) batteries. However, the inherent safety issues of liquid electrolytes and the sluggish reaction kinetics of existing cathodes remain fundamental challenges. Herein, we demonstrate a promising photo-assisted solid-state Li-O 2 battery based on metal-organic framework-derived mixed ionic/electronic conductors, which simultaneously serve as the solid-state electrolytes (SSEs) and the cathode. The mixed conductors could effectively harvest ultraviolet-visible light to generate numerous photoelectrons and holes, which is favorable to participate in the electrochemical reaction, contributing to greatly improved reaction kinetics. According to the study on conduction behavior, we discover that the mixed conductors as SSEs possess outstanding Li + conductivity (1.52 × 10 -4 S cm -1 at 25 °C) and superior chemical/electrochemical stability (especially toward H 2 O, O 2 - , etc.). Application of mixed ionic electronic conductors in photo-assisted solid-state Li-O 2 batteries further reveals that a high energy efficiency (94.2%) and a long life (320 cycles) can be achieved with a simultaneous design of SSEs and cathodes. The achievements present the widespread universality in accelerating the development of safe and high-performance solid-state batteries.

The design of highly efficient electrocatalysts is a promising strategy to improve the electrochemical kinetics of Li-CO 2 batteries. However, electrocatalysts usually aim to reduce the energetic barrier for the corresponding electrochemical reactions; little attention has been given to modulating the kinetics that directly determine the local concentration of reaction molecules surrounding catalysts. Herein, we present a systematic study on the role of Li + reunion on the improvement of reaction kinetics in Li-CO 2 batteries with a Cu cone cathode. Specifically, this local, geometry-driven tip effect can enrich the local electron concentration to facilitate Li + ions diffusion from the bulk electrolyte to the surface of catalyst, leading to boosted catalytic performance. Further studies demonstrate that Cu(II/I) as a solid redox mediator dominates the reversible bulk redox reactions in a Cu cone cathode, which acts as an electron-hole transfer agent and permits the efficient reduction and oxidation of solid Li 2 CO 3 , contributing to an accessible theoretical discharge voltage, low charge potential below 3.2 V, impressive rate capability, and a long cycling stability (333 days) for Li-CO 2 batteries. The exploitation of the sharp-tip enhancement effect and dynamic creation of catalytic active sites is expected to become routine practice in future mechanistic studies for metal-air batteries.

At present, photoassisted Li-air batteries are considered to be an effective approach to overcome the sluggish reaction kinetics of the Li-air batteries. And, the organic liquid electrolyte is generally adopted by the current conventional photoassisted Li-air batteries. However, the superior catalytic activity of photoassisted cathode would in turn fasten the degradation of the organic liquid electrolyte, leading to limited battery cycling life. Herein, we tame the above limitation of the traditional liquid electrolyte system for Li-CO 2 batteries by constructing a photoassisted all-solid-state Li-CO 2 battery with an integrated bilayer Au@TiO 2 /Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP)/LAGP (ATLL) framework, which can essentially improve battery stability. Taking advantage of photoelectric and photothermal effects, the Au@TiO 2 /LAGP layer enables the acceleration of the slow kinetics of the carbon dioxide reduction reaction and evolution reaction processes. The LAGP layer could resolve the problem of liquid electrolyte decomposition under illumination. The integrated double-layer LAGP framework endows the direct transportation of heat and Li + in the entire system. The photoassisted all-solid-state Li-CO 2 battery achieves an ultralow polarization of 0.25 V with illumination, as well as a high round-trip efficiency of 92.4%. Even at an extremely low temperature of -73 °C, the battery can still deliver a small polarization of 0.6 V by converting solar energy into heat to achieve self-heating. This study is not limited to the Li-air batteries but can also be applied to other battery systems, constituting a significant step toward the practical application of all-solid-state photoassisted Li-air batteries.

Metal halide perovskite quantum dots, with high light-absorption coefficients and tunable electronic properties, have been widely studied as optoelectronic materials, but their applications in photocatalysis are hindered by their insufficient stability because of the oxidation and agglomeration under light, heat, and atmospheric conditions. To address this challenge, herein, we encapsulated CsPbBr 3 nanocrystals into a stable iron-based metal-organic framework (MOF) with mesoporous cages (∼5.5 and 4.2 nm) via a sequential deposition route to obtain a perovskite-MOF composite material, CsPbBr 3 @PCN-333(Fe), in which CsPbBr 3 nanocrystals were stabilized from aggregation or leaching by the confinement effect of MOF cages. The monodispersed CsPbBr 3 nanocrystals (4-5 nm) within the MOF lattice were directly observed by transmission electron microscopy and corresponding mapping analysis and further confirmed by powder X-ray diffraction, infrared spectroscopy, and N 2 adsorption characterizations. Density functional theory calculations further suggested a significant interfacial charge transfer from CsPbBr 3 quantum dots to PCN-333(Fe), which is ideal for photocatalysis. The CsPbBr 3 @PCN-333(Fe) composite exhibited excellent and stable oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activities in aprotic systems. Furthermore, CsPbBr 3 @PCN-333(Fe) composite worked as the synergistic photocathode in the photoassisted Li-O 2 battery, where CsPbBr 3 and PCN-333(Fe) acted as optical antennas and ORR/OER catalytic sites, respectively. The CsPbBr 3 @PCN-333(Fe) photocathode showed lower overpotential and better cycling stability compared to CsPbBr 3 nanocrystals or PCN-333(Fe), highlighting the synergy between CsPbBr 3 and PCN-333(Fe) in the composite.

A number of inherent and thorny obstacles still stand in the way of the practical application of Li-O 2 batteries, which require development of an advanced lithium anode and O 2 cathode. Herein, the strategy of a symmetrical Li-O 2 battery is presented. Specifically, Cu nanoneedle arrays with a nanoengineered Au coating are grown directly on a Cu foam substrate (Au/Cu@FCu), which can act as both the anode backbone and the cathode in a Li-O 2 battery. The excellent conductivity, high porosity, large specific surface, and superior lithiophilicity as well as high catalytic activity of the Au/Cu@FCu electrodes can simultaneously regulate the deposition behavior of the lithium metal in the anode and catalyze the formation/decomposition of Li 2 O 2 in the cathode. As a result, the Li uniformly deposited on the Au/Cu@FCu anode without Li dendrites, showing a high Coulombic efficiency over 96% and a long and stable cycle lifetime over 970 h. At the same time, the Au/Cu@FCu cathode demonstrates extremely low overpotentials (0.64 V) and a much higher specific capacity of 27 270 mAh g -1 compared to the Li-O 2 batteries with a carbon-free cathode reported to date. Moreover, the "ebb and flow" phenomenon of the anode and cathode morphology is also observed in the Li-O 2 battery.