Suppressing the P2-O2 phase transition and Na+/vacancy ordering in Na0.67Ni0.33Mn0.67O2 by a delicate multicomponent modulation strategy

Abstract

P2-type Na_0.67Ni_0.33Mn_0.67O₂ is a promising cathode for sodium-ion batteries with features of high specific capacity and air resistance, whereas its cycling stability and rate performance are dissatisfactory suffering from the disastrous P2-O2 phase transition and Na⁺/vacancy ordering during sodium-ion de/intercalation, which makes it an obstruction for future practical applications. Herein, a delicate multicomponent modulation strategy is proposed to tackle these two issues simultaneously, in which Li⁺ and Ti⁴⁺ are introduced to replace the Ni²⁺ and Mn⁴⁺, respectively, whereas the Na⁺ content is also designed according to the principle of charge balance. Consequently, the designed cathode (Na_0.72Ni_0.28Li_0.05Mn_0.57Ti_0.10O₂) can deliver an enchanting cycling stability of 80% at 1 C after 200 cycles along with a considerable rate performance of 82.7 mAh g⁻¹ at 5 C. In situ X-ray diffraction measurement demonstrates the destructive P2-O2 phase transition is suppressed and converted into a P2-Z phase transition with superior reversibility as well as smooth charge/discharge curves with better Na⁺/vacancy disordering. In addition, the full cell matched with hard carbon anode delivers an excellent energy density of 263.4 Wh kg⁻¹ at 37.3 W kg⁻¹, exhibiting great practicality. Our work presents a mean to rationally design the component of layered oxide cathode and achieve fabulous performance for sodium ion batteries.