Sada Krishnakanth, Kmiec Steven, Manthiram Arumugam
Materials Science and Engineering Program and Texas Materials Institute, The University of Texas at Austin, Austin, Texas, 78712, USA.
Angew Chem Int Ed Engl. 2024 Jun 17;63(25):e202403865. doi: 10.1002/anie.202403865. Epub 2024 May 15.
The O-type layered nickel oxides suffer from undesired cooperative Jahn-Teller distortion stemming from Ni ions and undergo multiple biphasic structural transformations during the insertion/extraction of large Na ions, posing a significant challenge to stabilize the structural integrity. We present here a systematic investigation of the impact of substituting 5 % divalent (Mg) or trivalent (Al or Co) ions for Ni to alleviate Naion ordering and perturb the Jahn-Teller effect to enhance structural stability. We gauge a fundamental understanding of the Mg-O and Na-O or Mg-O-Na bonding interactions, noting that the ionicity of the Mg-O bond deshields the electronic cloud of oxygen from Na ions. Furthermore, calculations of the Van Vleck distortion modes reveal a relaxation of NiO octahedra from Jahn-Teller distortion and a reduced electron density at the interlayer with Mg substitution. Long-range (operando X-ray diffraction) and short-range (magic angle spinning nuclear magnetic resonance) structural analyses provide insights into reduced ordering, allowing a stable continuous solid solution. Overall, Mg-substitution results in a high-capacity retention of ~96 % even after 100 cycles, showcasing the potential of this strategy for overcoming the structural instabilities and enhancing the performance of sodium-ion batteries.
O型层状镍氧化物存在源自镍离子的不良协同 Jahn-Teller 畸变，并且在大尺寸钠离子嵌入/脱出过程中会经历多次双相结构转变，这对稳定结构完整性构成了重大挑战。我们在此展示了一项系统性研究，即通过用5%的二价（Mg）或三价（Al 或 Co）离子替代 Ni，以减轻钠离子有序化并扰乱 Jahn-Teller 效应，从而增强结构稳定性。我们深入了解了Mg-O与Na-O或Mg-O-Na的键合相互作用，注意到Mg-O键的离子性使氧的电子云免受钠离子的影响。此外，对范弗莱克畸变模式的计算表明，NiO八面体从Jahn-Teller畸变中弛豫，并且在Mg替代的层间电子密度降低。远程（原位X射线衍射）和短程（魔角旋转核磁共振）结构分析为减少有序化提供了见解，从而实现稳定的连续固溶体。总体而言，即使在100次循环后，Mg替代仍能保持约96%的高容量，展示了该策略在克服结构不稳定性和提高钠离子电池性能方面的潜力。
