Enhanced Cycling Stability of O3-Type Na[Ni0.5Mn0.5]O2 Cathode through Sn Addition for Sodium-Ion Batteries

Despite their high discharge capacity, O3-type layered cathodes for sodium-ion batteries (SIBs) suffer from rapid capacity fading caused by detrimental phase transitions. A series of O3-type layered Na[Ni0.5Mn0.5]O2 (NM) cathodes with different amounts of Sn were synthesized in this study by using uniformly Sn-coated precursors prepared by a wet method to address this problem. The introduction of Sn proportionally modified the morphologies of the Sn-NM cathodes to have higher tap densities. The cycling stability of the NM cathode with 1 mol % Sn was improved, maintaining 84.9% of its initial capacity after 100 cycles and ∼15% higher than that of the bare NM cathode. The improvement in cycling stability is attributed to the introduced Sn, which mitigates structural distortions caused by monoclinic phase transitions and suppresses abrupt contraction during the detrimental P3′-to-O3′ phase transition in the highly charged state. In addition, the precipitated Sn nanoparticles on the cathode surface protect the internal primary particles from parasitic attacks by the infiltrated electrolyte. The proposed strategy provides an effective method to improve the cycling stability of O3-type layered cathodes for SIBs by modifying their morphology and inhibiting deleterious electrolyte attacks.