Oxygen-Defect-Rich B‑ZnCo₂O_4‑x Nanocatalyst for Efficient Conversion Kinetics of Lithium–Sulfur Batteries

High specific capacity and long cycle life are the key to high-performance lithium–sulfur (Li–S) batteries, but they are hard to achieve simultaneously due to the notorious polysulfide shuttle effect. Transition metal oxide nanocatalysts are expected to help address the above issue, but their low conductivity and cumbersome synthesis process limit their application. Here, we propose a defect engineering strategy to induce electron rearrangement by heteroatom doping. Boron-doped spinel-type oxide (B-ZnCo₂O_4‑x) is synthesized by a two-step hydrothermal method for separator modification. The boron-produced oxygen vacancy (O_V) increases unsaturated sites by changing the electron cloud density, and therefore, the B-ZnCo₂O_4‑x nanocatalyst can reduce the reaction energy barrier and accelerate the nucleation and activation rate of Li₂S. Meanwhile, the unique pore defects effectively increase the Li⁺ flux and ensure battery performance at a high rate and high sulfur loading. The battery equipped with a B-ZnCo₂O_4‑x-modified separator delivered an initial specific capacity of 1108 mAh g^–1 at 0.2 C and a capacity retention rate of 80.4% at 0.5 C after 200 cycles. In particular, at a high sulfur loading of 10.0 mg cm^–2, the battery yielded a first-cycle capacity of 1321.9 mAh g^–1. This work demonstrates that boron-doping-enabled defect engineering is an effective strategy to improve the catalytic activity of transition metal oxides for application in Li–S batteries.