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Integrating energy storage technologies with clean carbon dioxide (CO2) recycling is considered to be a promising solution to alleviate global warming caused by CO2 emission and meet the ever-increasing demand for electrical energy supplies. Recently, a rechargeable aprotic lithium-CO2 (Li-CO2) electrochemical system has been proposed as a new strategy for both energy storage and CO2 capture. However, the study of such a system remains preliminary, and its development still faces huge challenges such as low energy efficiency and electrolyte decomposition caused by a large charge overpotential, which are primarily attributed to the sluggish kinetics of the CO2 activation reaction in Li-CO2 batteries. Therefore, the reasonable design and fabrication of catalysts with excellent catalytic activity and high stability remain a formidable challenge to develop practical Li-CO2 batteries. In this review, based on the introduction of the structure and fundamental electrochemistry of Li-CO2 batteries, we provide an up-to-date and comprehensive review on state-of-the-art design strategies toward highly active catalytic materials and cathode structures for Li-CO2 batteries, inspiring research interests and concerns to this emerging energy storage system and promoting its practical application for future advances in this field.

Electrocatalysis for the oxygen evolution reaction (OER) plays an irreplaceable role in numerous green and efficient energy conversion or storage techniques such as water electrolysis, fuel cells, and metal-air batteries. High-performance catalysts are always needed despite the sluggish kinetics of the four electron-transfer OER process. In this paper, for the first time, by employing a simple new strategy of "confined Fe overdoping", the OER activity of Ni3S2 in alkaline solution is significantly boosted, showing an overpotential of 350 mV at 10 mA cm-2, which is even lower than that of the benchmark IrO2. The designed catalyst (Meso C-NiFeS) is composed of mesoporous highly graphited N-doped carbon and nanodomain/defect/strain-rich NiFeS nanoparticles. The mesoporous carbon support facilitates mass/electron transfer, while confined Fe overdoping leads to smaller and defect/strain-rich nanodomains. DFT calculations prove that Fe doping could induce compressing strains, which is beneficial for the OER process, modify electronic states of Ni3S2, and act as active sites at the same time. This overdoping strategy can trigger a synergic effect combining size decrease, electronic structure modification, and defect/strain engineering. Moreover, this simple strategy is easy to implant to other catalysts.

The design and development of high-efficient electrocatalysts plays a decisive role in improving the stability of lithium-oxygen (Li-O 2 ) batteries. Here, two-dimensional (2D) MoS 2 nanosheets anchored on hollow carbon spheres (MoS 2 /HCS) composites is designed and reported as promising cathode catalysts for Li-O 2 batteries. The MoS 2 /HCS-based Li-O 2 battery shows superior electrochemical performance, in terms of high capacity (4010 mA h g -1 ) and enhanced cycling performance (104 cycles). X-ray photoelectron spectroscopy (XPS) results reveal that the formation of Li 2 CO 3 and other side products can be effectively alleviated when MoS 2 /HCS electrode is used as the cathode. On the basis of experimental studies, it is found that the synergistic effects, which originated from the superior catalytic property of MoS 2 nanosheets and the good electrical conductivity of HCS with high surface area, is the main reason for performance improvement. The synergistic effects induced by the dispersed MoS 2 nanosheets anchored on nanostructured HCS cathodes provide a promising strategy for developing catalysts of O 2 electrode for Li-O 2 batteries with excellent performance.

High-performance flexible lithium-oxygen (Li-O2) batteries with excellent safety and stability are urgently required due to the rapid development of flexible and wearable devices. Herein, based on an integrated solid-state design by taking advantage of component-interaction between poly(vinylidene fluoride-co-hexafluoropropylene) and nanofumed silica in polymer matrix, a stable quasi-solid-state electrolyte (PS-QSE) for the Li-O2 battery is proposed. The as-assembled Li-O2 battery containing the PS-QSE exhibits effectively improved anodic reversibility (over 200 cycles, 850 h) and cycling stability of the battery (89 cycles, nearly 900 h). The improvement is attributed to the stability of the PS-QSE (including electrochemical, chemical, and mechanical stability), as well as the effective protection of lithium anode from aggressive soluble intermediates generated in cathode. Furthermore, it is demonstrated that the interaction among the components plays a pivotal role in modulating the Li-ion conducting mechanism in the as-prepared PS-QSE. Moreover, the pouch-type PS-QSE based Li-O2 battery also shows wonderful flexibility, tolerating various deformations thanks to its integrated solid-state design. Furthermore, holes can be punched through the Li-O2 battery, and it can even be cut into any desired shape, demonstrating exceptional safety. Thus, this type of battery has the potential to meet the demands of tailorability and comformability in flexible and wearable electronics.

The interfacial interaction between catalysts and substrates has been considered as a pivotal factor determining the activities in different applications. However, interfacial interaction-dependent catalytic activities are currently neglected in understanding oxygen involved reaction in Li-O2 battery, seriously restricting the development of high performance Li-O2 battery. Herein, Ru@hierarchically porous carbon (Ru@HPC) with well-defined interfaces are fabricated and employed as cathode in Li-O2 battery. Notably, Ru@HPC based Li-O2 battery demonstrate better performance than that based on cathode formed by simply mixing Ru nanoparticles with hierarchically porous carbon (Ru/HPC). The Ru@HPC improved performance with a large specific capacity of ~7100 mA h g−1, high round-trip efficiency of 71%, high rate capability, and excellent cyclic stability of over 125 cycles (over 40 days). Density functional theory calculations indicated that the interfacial interaction between Ru nanoparticles and carbon substrate in Ru@HPC, which triggers electron transfer from ruthenium to carbon and thus optimizes the surface adsorption energy of the reactants and intermediate, facilitates the performance improvement of Li-O2 battery. Our study for the first time reveals that the interfacial interaction between catalyst and substrate is a critical factor determining the Li-O2 battery performance and offers a promising design strategy of catalyst for Li-O2 batteries.

The aprotic lithium-oxygen (Li-O 2 ) battery has excited huge interest due to it having the highest theoretical energy density among the different types of rechargeable battery. The facile achievement of a practical Li-O 2 battery has been proven unrealistic, however. The most significant barrier to progress is the limited understanding of the reaction processes occurring in the battery, especially during the charging process on the positive electrode. Thus, understanding the charging mechanism is of crucial importance to enhance the Li-O 2 battery performance and lifetime. Here, recent progress in understanding the electrochemistry and chemistry related to charging in Li-O 2 batteries is reviewed along with the strategies to address the issues that exist in the charging process at the present stage. The properties of Li 2 O 2 and the mechanisms of Li 2 O 2 oxidation to O 2 on charge are discussed comprehensively, as are the accompanied parasitic chemistries, which are considered as the underlying issues hindering the reversibility of Li-O 2 batteries. Based on the detailed discussion of the charging mechanism, innovative strategies for addressing the issues for the charging process are discussed in detail. This review has profound implications for both a better understanding of charging chemistry and the development of reliable rechargeable Li-O 2 batteries in the future.

In this work, a novel free-standing CuCo2S4 nanosheet cathode (CuCo2S4@Ni) with high catalytic activity is fabricated for aprotic lithium–oxygen (Li–O2) battery. This deliberately designed oxygen electrode is found to yield lower overpotential (0.82 V), improved specific capacity (9673 mA h g–1 at 100 mA g–1), and enhanced cycle life (164 cycles) as compared to the traditional carbonaceous electrode. The improved performance can be ascribed to the superb spinel structure of CuCo2S4, in which both Cu and Co exhibit more abundant redox properties, improving oxygen reduction reaction and oxygen evolution reaction kinetics effectively and boosting the electrochemical reactions. Furthermore, the well-designed architecture also plays a critical role in the improved performance. Encouraged by the excellent catalytic activity of this free-standing cathode, large-scale pouch-type Li–O2 cell based on CuCo2S4@Ni cathode is fabricated and can work under different bending and twisting conditions. This free-standing electrode provides a new strategy for developing Li–O2 batteries with excellent performance and flexible wearable devices.