The comparative structural, Mössbauer, and electrochemical studies of the Na_xMn_2/3Fe_1/3O₂ and Na_xMn_1/2Fe_1/2O₂ systems show that the change in the Mn/Fe ratio has a significant influence on the overlap between the Mn^3+/4+ and Fe^3+/4+ redox couples. The P2-type structure is maintained in the 0.3 < x < 0.8 domain. For the highest intercalation amount, structural distortions occur due to the Jahn–Teller effect of the Mn³⁺ ions. The macroscopic distortion results from a competition between the opposite effects of Mn³⁺ and Fe³⁺: the isotropic character of Fe³⁺ tends to prevent the macroscopic distortion. For the lower sodium amounts, the instability of the interstitial trigonal prismatic space leads to the formation, by slab gliding, of a very disordered structure. Even if this structural transition is reversible, a strong capacity fading is observed if the cell is charged above 4 V verus Na/Na⁺.

中文翻译：

---

Mn / Fe比对作为钠离子电池正极材料的P2-Na _x Mn ₁ - _y Fe _y O ₂相的电化学和结构性能的影响

Na _x Mn _2/3 Fe _1/3 O ₂和Na _x Mn _1/2 Fe _1/2 O ₂体系的比较结构，Mössbauer和电化学研究表明，Mn / Fe比的变化具有显着性对Mn ^{3 + / 4 +}和Fe ^{3 + / 4 +}氧化还原对之间重叠的影响。P2型结构保持在0.3 < x <0.8域中。对于最高的插入量，由于Mn ³⁺离子的Jahn–Teller效应而发生结构变形。Mn ³⁺的相反作用之间的竞争导致宏观畸变和Fe ³⁺：Fe的各向同性字符³⁺倾向于防止宏观失真。对于较低的钠含量，间隙三角形棱柱空间的不稳定性导致通过平板滑动形成非常无序的结构。即使这种结构转变是可逆的，但如果电池的充电电压高于4 V对Na / Na ^+，也会观察到强烈的容量衰减。