Building oxygen-vacancy in Co3O4−x nanocrystal towards ultrahigh pseudocapacitance

The development of high capacity, superior rate capability and long lifespan anodes for lithium-ion batteries (LIBs) is an ongoing challenge for meeting the ever-increasing demand of high energy density and fast charging property. In this work, we report Co3O4−x nanocrystals with abundant oxygen-vacancy and pores as the anode for LIBs. Taking profit of the introduced oxygen-vacancy, pores and nanostructure, the Co3O4−x shows an increased electronic conductivity, shortened Li+ ions diffusion pathway, and enables ultrahigh pseudo-capacitive behavior, thereby providing a remarkable rate capability and an ultrahigh capacity beyond the redox chemistry. On the basis of this understanding, the Co3O4−x anode delivers high capacity (1616 mAh g−1 at 0.1 C, 1 C = 1000 mA g−1), excellent cycling stability and can operate well at rates of 0.1–20 C (842 mAh g−1 at 20 C), which is significantly improved comparable to that of common Co3O4. Furthermore, applications of ex-situ XRD, FTIR, Raman and XPS tests demonstrate the reversible Li+ ions storage mechanism in such well-designed Co3O4−x. Our study highlights the great feasibility and validity of oxygen-vacancy and nanostructure for improving the Li+ ions storage performance.