A gradient boracic polyanion-doping method is applied to Ni-rich LiNi_0.8Co_0.15Al_0.05O₂ (NCA) cathode material in this study to suppress the capacity/potential fade during charge-discharge cycling. Scanning electron microscope (SEM) results show that all samples present spherical morphology and the secondary particle size increases with increasing boron content. X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) results demonstrate that boracic polyanions are successfully introduced into the bulk material and more enriched in the outer layer. XPS analysis further reveals that the valence state of Ni³⁺ is partly reduced to Ni²⁺ at the surface due to the incorporation of boracic polyanions. From the electrochemical measurements, B0.015-NCA electrode exhibits excellent cycling performance, even at high potential and elevated temperature. Moreover, the SEM images illustrate the presence of cracks and a thick SEI layer on pristine particles after 100 cycles at high temperature, while the B0.015-NCA particles show an intact structure and thin SEI layer. Electrochemical impedance spectroscopy confirms that the boracic polyanion doping could hinder the impedance increase during cycling at elevated temperature. These results clearly indicate that the gradient boracic polyanion-doping contributes to the remarkable enhancement of structure stability and cycling performance of NCA.

在本研究中，梯度硼聚阴离子掺杂方法应用于富镍LiNi _0.8 Co _0.15 Al _0.05 O ₂（NCA）正极材料，以抑制充放电循环过程中的容量/电位衰减。扫描电子显微镜（SEM）结果表明，所有样品均呈现球形形态，并且次级颗粒尺寸随硼含量的增加而增加。X射线衍射（XRD），透射电子显微镜（TEM）和X射线光电子能谱（XPS）结果表明，硼酸聚阴离子已成功引入块状材料中，并在外层中更富集。XPS分析进一步揭示了Ni ³⁺的价态部分还原为Ni ²⁺由于掺入了硼酸聚阴离子而在表面上形成的。根据电化学测量，即使在高电势和高温下，B0.015-NCA电极也具有出色的循环性能。此外，SEM图像显示了在高温下100次循环后原始颗粒上存在裂纹和较厚的SEI层，而B0.015-NCA颗粒显示出完整的结构和较薄的SEI层。电化学阻抗谱证实，硼酸聚阴离子掺杂可能会在高温下循环过程中阻碍阻抗增加。这些结果清楚地表明，梯度硼原子聚阴离子掺杂有助于显着提高NCA的结构稳定性和循环性能。