In this work, a novel free-standing CuCo 2 S 4 nanosheet cathode (CuCo 2 S 4 @Ni) with high catalytic activity is fabricated for aprotic lithium−oxygen (Li−O 2 ) 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 CuCo 2 S 4 , 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 welldesigned 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−O 2 cell based on CuCo 2 S 4 @Ni cathode is fabricated and can work under different bending and twisting conditions. This free-standing electrode provides a new strategy for developing Li−O 2 batteries with excellent performance and flexible wearable devices.

Catalysts with high performance are urgently needed in order to accelerate the reaction kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in lithium–oxygen (Li–O2) batteries. Herein, utilizing thermodynamically metastable Ti atoms on the Ti3C2Tx MXene nanosheet surface as the nucleation site, oxygen vacancy-rich TiO2 nanoparticles were in situ fabricated on Ti3C2Tx nanosheets (V-TiO2/Ti3C2Tx) and used as the oxygen electrode of Li–O2 batteries. Oxygen vacancy (Vo) can boost the migration rate of electrons and Li+ as well as act as the active sites for catalyzing the ORR and OER. Based on the above merits, V-TiO2/Ti3C2Tx-based Li–O2 battery shows improved performance including the ultralow overpotential of 0.21 V, high specific capacity of 11 487 mA h g–1 at a current density of 100 mA g–1, and excellent round-trip efficiency (93%). This work proposes an effective strategy for researching high-performance oxygen electrodes for Li–O2 batteries via introducing Vo-rich oxides on two-dimensional MXene.

Developing bifunctional electrocatalysts is the primary challenge to improve the reaction efficiency of zinc-air batteries. Lattice-strain engineering constructs high-efficiency oxygen redox catalysts by tuning the physicochemical properties of nanomaterials. However, the randomness and complexity of lattice mismatch make it difficult to effectively identify the structure-activity relationship between the strain and catalyst. Herein, a strategy of Ru triggered partial coordination environment mutation of ZnIn 2 S 4 (R 0.1 ZIS) to regulate the d-band center of catalytic sites is provided, which dramatically activates intrinsic activity and accelerates electron transfer. Density functional theory calculations and system characterizations reveal that local lattice strain causes anti-bonding orbital to occupy more electrons and narrower bandwidth, reduce the migration energy barrier of * OH deprotonation and optimize the adsorption/desorption process of oxygen-containing intermediates, thus demonstrating extraordinary catalytic performance in oxygen reduction reaction and oxygen evolution reaction. Expectedly, the R 0.1 ZIS-based cell delivers the open circuit potential of 1.587 V almost identical to the theoretical voltage, and an ultralow voltage gap of 0.71 V after undergoing 262 h operation. This work offers a promising avenue for building lattice-strain engineering to realize robust bifunctional electrocatalysts.