Phosphorus vacancies enriched Ni2P nanosheets as efficient electrocatalyst for high-performance Li–O2 batteries

Abstract

Compared with the lithium-ion batteries (LIBs), lithium-oxygen batteries (LOBs) demonstrate ultra-high theoretical energy density (≈3505 W h kg−1), which arouse tremendous research interest worldwide. However, the serious challenges facing LOBs are the sluggish oxygen redox kinetics during the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) process, resulting in poor specific capacity and inferior cyclability. Herein, we fabricate phosphorus vacancies enriched Ni2P nanosheets on carbon cloth (denoted as Vp-Ni2P@CC) via a simple NaBH4 reduction strategy as oxygen electrode for high-performance LOBs. Interestingly, the Vp-Ni2P@CC based LOBs exhibit outstanding performance including large specific capacity (10 796 mA h g−1@500 mA g−1) and excellent cyclability (235 cycles@500 mA g−1) compared with LOBs with the Ni2P@CC electrode. It is found that the abundant phosphorus vacancies in the Vp-Ni2P@CC not only act as active sites for oxygen electrode reactions but also enhance the mobility of electron/Li+, simultaneously promoting the improvement of ORR/OER kinetics. Moreover, the restrained electrons around Ni–P bonds are delocalized due to the presence of phosphorus vacancies, which narrow down the band gap in Vp-Ni2P@CC, eventually contributing to high electrical conductivity and excellent electrocatalytic activity. The study provides a new orientation for further developing oxygen electrode catalysts for LOBs.