In Operando Visualization of Cation Disorder Unravels Voltage Decay in Ni‐Rich Cathodes,Small Methods

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In Operando Visualization of Cation Disorder Unravels Voltage Decay in Ni‐Rich Cathodes
Small Methods ( IF 10.7 ) Pub Date : 2020-09-29 , DOI: 10.1002/smtd.202000730
Ang Gao _{1,

2} , Xinyan Li _{1,

2} , Fanqi Meng _{1,

2} , Shengnan Guo ₁ , Xia Lu ₃ , Dong Su ₁ , Xuefeng Wang ₁ , Qinghua Zhang _{1,

4} , Lin Gu _{1,

2,

5}

Affiliation

Despite the high energy density of Ni‐rich layered‐oxide electrodes, their real‐world implementation in batteries is hindered by the substantial voltage decay on cycling, which mainly originates from bulk and surface structural degradation. Here, in operando observation of cation disorder, a major origin of structural degradation, reveals the voltage decay mechanism in Ni‐rich cathode. Viewed along [1 1–0] and [110] orientations by scanning transmission electron microscopy, it is demonstrated that transition metal (TM) migration gives rise to the drastic fluctuation of interlamellar spacing and NiO bond length, but almost exerts no influence on atom site in ab plane. Density functional theory calculations reveal that the fluctuation of the NiO bond length triggers voltage decay via lifting the energy level of the antibonding (3dz²‐2p)* orbits. Broadening bands by a shorter NiO bond increase the voltage slope of battery, which will reduce the accessible Li capacity within the stable voltage range of the electrolyte. Furthermore, a collaborative path of TM migration triggered by oxygen vacancy is verified to account for the TM migration. The finding provides insights into new chemistry to be explored for developing high‐capacity layered electrodes that evade voltage decay.

中文翻译：

阳离子紊乱的操作可视化揭示了富镍阴极中的电压衰减

尽管富镍层状氧化物电极具有高能量密度，但它们在电池中的实际应用受到循环电压大幅衰减的阻碍，这主要源于本体和表面结构退化。在这里，在对阳离子无序（结构退化的主要来源）的操作观察中，揭示了富镍正极的电压衰减机制。通过扫描透射电子显微镜沿 [1 1-0] 和 [110] 方向观察，证明过渡金属（TM）迁移引起层间距和 Ni  O 键长的剧烈波动，但几乎没有影响在 ab 平面的原子位点上。密度泛函理论计算表明，Ni O 键长通过提升反键 (3dz ² ‐2p)* 轨道的能级来触发电压衰减。更短的 Ni  O 键使能带变宽会增加电池的电压斜率，这将降低电解质稳定电压范围内的锂容量。此外，验证了由氧空位触发的 TM 迁移的协同路径以解释 TM 迁移。这一发现提供了对新化学的见解，以开发避免电压衰减的高容量分层电极。

更新日期：2020-09-29

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