Synergistic engineering on surface chemistry and morphology in Ti₃C₂T_x MXene towards high rate and durable LiO₂...

The lithium‑oxygen battery (LOB) has emerged as an appropriate candidate for next-generation power supply system, owing to the ultrahigh theoretical energy density (3480 Wh kg^-1) and relatively low cost. However, some intrinsic challenges, including high redox overpotentials, limited rate capability, and poor cyclic life, continue to hinder the practical deployment of lithium‑ oxygen batteries. The fundamental limitations originate from sluggish oxygen reduction/evolution reaction (ORR/OER) kinetics and parasitic side reactions, which can be effectively mitigated by employing efficient cathode electrocatalysts. In this contribution, we report a rational engineering strategy for modulating the electronic and physical structure of MXene, as an advanced bifunctional ORR/OER catalyst in LOBs. The conventional layered skeleton of MXenes were reconstructed into hollow spheres and entangled wires. This structural transformation substantially increased the surface area, exposing more interlayer sites for rapid charge transfer over ORR/OER reactions, thereby enhancing the specific capacity and cycling stability even under high rate. Concurrently, the F dominated surface of MXene from traditional chemical etching, was changed into the oxygen-related groups as the primary moieties, where MXene spheres exhibited a higher proportion of oxygen terminations, and MXene belts featured greater hydroxyl group density. The optimized surface groups can decrease the ORR/OER reaction barriers, resulting in the boosted catalytic capability and reaction reversibility of modified MXenes, demonstrated through the experimental and theoretical validations. Collectively, the LOBs with the cathode catalysts of MXene spheres and belts can exert an ultrahigh full discharge capacity of 22,997 and 17,434 mAh g^-1, respectively. The overpotentials of LOBs with MXene spheres and belts cathodes were as low as 0.58 and 0.76 V, at 500 mA g^-1 and 500 mAh g^-1. Noteworthy, the according LOBs employing MXene spheres can separately deliver the long lifespan of 134, 118, and 126 cycles, even in the harsh conditions of 1000, 2000 and 3000 mA g^-1 under a cutoff capacity of 1000 mAh g^-1. This work can inspire further exploration into multidimensional optimization strategies for MXene-based electrocatalysts, paving the way for high rate and long life LOBs.