Oxygen Vacancy Engineering Induced by Binary Metal Ions Pre-Intercalation to Realize Stable Na⁺ Storage at High...

Oxygen vacancy (Vo) engineering is an important lattice modification strategy to achieve the balance between Na⁺ storage number and lattice stability of layered oxide cathodes. However, the as-reported Vo regulation strategies usually present poor modulation accuracy, which would be detrimental to achieve better balance. Herein, the binary metal ions pre-intercalation strategy is developed, where the differentiated coordination capabilities between interlayer metal ions and oxygen atoms are cleverly employed to realize the fine regulation of Vo content. Further, taking new layered HNaV₆O₁₆·4H₂O sodium-ion battery cathode as an example, the fine regulation of the relative Vo content is achieved by utilizing the coordination number difference of CoO₄ and NiO₅ polyhedron constituted by pre-intercalating Co²⁺ and Ni²⁺. Thus, the excellent balance between specific capacity and cycling stability is realized by enhancing Na⁺ storage at high voltage, where a capacity of 93.3 mAh g^-1 and retention rate of 76% after 200 cycles at 990 mA g^-1 are obtained. It is also revealed that Vo can be used as a descriptor for capacity contribution and Na⁺ diffusion coefficient at high voltage, which describe an approximative volcano curve and are more sensitive to the Vo content in the neighborhood of 2.0.