Facile multi-step tactics to harvest copper-doped O3-type layered NaNi1/ 3Fe1/3Mn1/3O2 and mitigate capacity decay

Abstract

<p>O3-type layered metal oxide cathode manifests conspicuous virtues of high specific capacity and low preparation cost, which has promising commercial prospects. When exposed to moisture or air condition, the cathode usually suffers from irreversible phase transition, surface corrosion, gas generation and other defects. Herein, Cu-doped NaNi_1/3Fe_1/3Mn_1/3O₂ is prepared by multi-step tactics. The experimental results show that NaCu_0.004Ni_0.329Fe_1/3Mn_1/3O₂ exhibits a high discharge capacity of 140 mAh <em>g</em>⁻¹ at 100 mA <em>g</em>⁻¹, and retains 90 % capacity retention over100 cycles at 100 mA <em>g</em>⁻¹. Galvanostatic intermittent titration technique (GITT) results reveal that the Na⁺ diffusion coefficient is well enhanced by Cu-doping. Cu-doping enlarges the interlayer spacing and facilitates Na⁺ diffusion, and Cu²⁺ has partially changed Mn³⁺ into Mn⁴⁺, thereby augmenting Na-storage capability and capacity retention. These findings provide ideas for trace doping of layered oxides as cathode and represent a further step in the development of sodium ion batteries.<br></p>