The layered transition metal oxides are an essential class of cathode materials in sodium-ion batteries. However, the capacity decay mechanisms of many materials at a wide voltage window are still ambiguous. Therefore, research on the intrinsic structure of materials at the electronic or atomic level is of great significance to unlock the potential of more materials. In this study, a new family of layered NaNi_0.45Mn_0.3Ti_0.2M_0.05O₂ (M=Nb/Mo/Cr) has been demonstrated to combine high specific capacity (NaNi_0.45Mn_0.3Ti_0.2Cr_0.05O₂, 12 mA g ⁻¹, 185.7 mAh g ⁻¹, 2-4.2 V) with preferable Na⁺ insertion/extraction activity (1920 mA g ⁻¹, 111.2 mAh g ⁻¹). The participation of Ni²⁺/Ni³⁺ and Cr³⁺/Cr⁴⁺/Cr⁶⁺ in the redox reaction upon cycling significantly contributes to the superior specific capacity, and the diffusion kinetics calculation indicates that the substitution of Cr for Ni can create a more suitable path with a low energy barrier for Na⁺ movement, which is particularly crucial for the rate performance. Besides, the unfavourable cycling stability is affected by the distortion of the crystal structure, suggesting that the Jahn-Teller effect of Mn³⁺/Ni³⁺ and the second-order Jahn-Teller effect of Nb⁵⁺/Mo⁶⁺ (d⁰ transition metal) together with Cr⁶⁺ migration caused by disproportionation of Cr⁴⁺ have inescapable responsibilities. Additionally, the reversible phase transition between the O3 and P3 phases upon Na⁺ insertion/extraction at a wide voltage window is identified by in situ XRD measurements and verified to be the key factor of the high coulombic efficiency for NMTCr. An in-depth understanding of NMTNb and NMTMo can provide new insights for material design and exploitation. The composition-structure-property relationships behind the electrochemical performance can be comprehended profoundly by coupling the experimental verification with density functional theory calculations.

层状过渡金属氧化物是钠离子电池中必不可少的阴极材料。但是，许多材料在宽电压窗口下的容量衰减机制仍然不清楚。因此，研究电子或原子级材料的本征结构对于释放更多材料的潜力具有重要意义。在这项研究中，分层纳尼的一个新的家庭_0.45的Mn _0.3的Ti _0.2中号_0.05 ö ₂（M = NB /钼/ Cr）的已被证明比容量高结合（纳尼_0.45的Mn _0.3的Ti _0.2的Cr _0.05 Ò ₂，12毫安克^-1，185.7毫安克^-1，2-4.2 V）与优选的Na ⁺插入/提取活性（1920毫安克^-1，111.2毫安克^-1）。Ni ²⁺ / Ni ³⁺和Cr ³⁺ / Cr ⁴⁺ / Cr ⁶⁺在循环时参与氧化还原反应显着促进了优异的比容量，并且扩散动力学计算表明用Cr代替Ni可以为Na ⁺创建低能量势垒的更合适路径运动，这对于速率表现尤为重要。此外，不良的循环稳定性受晶体结构变形的影响，表明Mn ³⁺ / Ni ³⁺的Jahn-Teller效应和Nb ⁵⁺ / Mo ⁶⁺的二阶Jahn-Teller效应（d ⁰过渡金属）与Cr ⁴⁺歧化引起的Cr ⁶⁺迁移具有不可回避的责任。此外，Na ⁺时O3和P3相之间的可逆相变通过原位XRD测量可确定在宽电压窗口内的插入/提取，并被证实是NMTCr高库仑效率的关键因素。对NMTNb和NMTMo的深入了解可以为材料设计和开发提供新的见识。通过将实验验证与密度泛函理论计算相结合，可以深刻理解电化学性能背后的组成-结构-性质关系。