Nb掺杂改性LiNiO2正极材料的制备及电化学性能研究

Preparation and Electrochemical Performance of Niobium-Doped Modified LiNiO2 Cathode Materials

摘要:

高镍层状氧化物LiNiO₂具有高理论比容量和相对低廉价格，被认为是下一代锂离子动力电池的正极材料之一。当LiNiO₂正极材料应用于锂离子电池时，其循环稳定性无法满足要求，需经改性后才能得以应用。采用固相法合成了Nb掺杂的层状LiNi_1-xNb_xO₂（x=0.005、0.01、0.015）正极材料，利用X射线衍射、扫描电子显微镜和X射线能谱等测试手段，分析了Nb掺杂量（摩尔百分比）对其晶体结构、微观形貌及元素分布的影响，并通过恒电流间歇滴定和交流阻抗测试研究了其电化学性能。结果表明，随着Nb元素掺杂量的提高，LiNi_1-xNb_xO₂材料的晶格晶面间距逐渐扩大，一次颗粒尺寸逐渐减小。在LiNiO₂材料中引入Nb⁵⁺离子，提高了LiNi_1-xNb_xO₂材料的锂离子扩散系数，并通过稳定晶体结构，抑制了Nb掺杂材料在充放电过程中的相变，有利于其电化学性能的提升。当Nb掺杂量为1%时，LiNi_1-xNb_xO₂材料表现出较好的倍率性能，在10 C大电流密度下的放电比容量高达134.1 mAh?g^-1；随着Nb掺杂量的增加，LiNi_1-xNb_xO₂材料循环稳定性同步提升，当Nb掺杂量为1.5%时，LiNi_1-xNb_xO₂材料经150次循环后的容量保持率为73.3%，远高于未掺杂LiNiO₂样品的36.2%。表明，Nb掺杂可改善LiNiO₂正极材料的晶体结构和电化学性能，为其在下一代锂离子动力电池的应用提供了理论依据。

Abstract:

The layered nickel-rich oxide LiNiO₂，characterized by its high theoretical specific capacity and relatively low cost，is considered one of the next-generation cathode materials for lithium-ion batteries. However，its cycling stability fails to meet requirements when applied in lithium-ion batteries，necessitating modification before practical use. Layered LiNi_1-xNb_xO₂（x=0.005，0.01，0.015）cathode materials doped with Nb were synthesized via solid-state reaction. The effects of niobium doping level（in mole percentage）on the crystal structure，microstructure，and elemental distribution were investigated using techniques such as X-ray diffraction， scanning electron microscopy， and energy-dispersive X-ray spectroscopy. Additionally，electrochemical tests were conducted to evaluate their electrochemical performance. The results indicate that with an increase in the Nb doping level，the interplanar spacing of the LiNi_1-xNb_xO₂ material lattice gradually enlarges，while the primary particle size decreases. Introducing Nb⁵⁺ ions into the LiNiO₂ material enhances the lithium ion diffusion coefficient of LiNi_1-xNb_xO₂ and stabilizes the crystal structure，suppressing phase transitions during charge-discharge processes，thereby improving electrochemical performance. When the Nb doping level is 1%，LiNi_1-xNb_xO₂ exhibits excellent rate capability，with a discharge specific capacity of 134.1 mAh?g^-1 at a high current density of 10 C. Moreover，the cycling stability of LiNi_1-xNb_xO₂ improves with increasing Nb doping level. For instance，when the Nb doping level is 1.5%，the capacity retention of LiNi_1-xNb_xO₂ after 150 cycles is 73.3%，which is significantly higher than that of the undoped LiNiO₂ sample at 36.2%. This study demonstrates that Nb doping can improve crystal structure and electrochemical properties of the LiNiO₂ cathode material， providing a theoretical basis for its application.