【作者】 王波；

【导师】 赵海雷；

【作者基本信息】 北京科技大学 ， 材料科学与工程， 2025， 博士

【摘要】 高镍层状氧化物因其高放电比容量、高工作电压和适中成本的优势,成为动力电池正极材料之一。然而,高度碱性、高度反应活性的表面化学性质、表面结构不稳定,以及晶界应力引起的颗粒开裂等问题,导致其循环稳定性和热稳定性差。本论文基于锂反应包覆策略,消除碱残留,构建“锂导电包覆/表面掺杂”复合表面结构,改善锂离子扩散动力学;设计放射状二次颗粒微结构并构建强金属-氧键,改善材料的循环稳定性和热稳定性;通过原位掺铌,调控前驱体的化学组成和微结构均匀性。主要研究成果如下:（1）基于锂反应包覆策略,设计并制备了具有“LiNbO₃包覆/Nb-掺杂”表面结构的LiNi_0.6Co_0.2Mn_0.2O₂（NCM622）正极材料。利用草酸铌铵与表面锂残留反应,生成LiNbO₃表面包覆层。借助高温热处理,使部分包覆元素固溶进晶格形成表面掺杂层。反应包覆降低了锂残留含量,Nb掺杂增强了表面结构稳定性,LiNbO₃表面包覆改善了电极反应动力学,使改性后的材料表现出优异的倍率性能、循环稳定性和热稳定性。（2）设计并制备了 Hf掺杂的 LiNi.895Co0.08Al0.02Hf0.005O2（NCA90-Hf0.5）正极材料。Hf掺杂可稳定晶格氧,增强表面结构稳定性,同时细化一次晶粒,并使它们发育成短棒状沿径向密实排布,降低颗粒孔隙率,消散晶界应力,提高正极颗粒的力学性能,显著改善了循环稳定性和热稳定性。在2.7-4.3 V,1 C下,100次循环后的容量保持率从82.0%提高至95.3%,而热失控温度从236℃提高到245℃,放热量降低了 26.3%。（3）采用 Hf-B 共掺杂协同改性高镍 LiNi0.888Co0.079Al0.02Hf0.003B0.01O2（NCA90-Hf0.3&B1）。Hf增强了晶体结构稳定性,B增加了一次晶粒的长/径比,并构建了放射状二次颗粒微结构。在2.7-4.3 V,1C下,NCA90-Hf0.3&B1在1 00和200次循环后的容量保持率分别是96.5%和89.5%,而NCA90仅为82.0%和 62.0%。（4）前驱体原位掺 Nb,实现对高镍 LiNi0.6Co0.025Mn0.015O2（NCM96）正极晶体结构和微观结构的协同调控,增强颗粒机械稳定性。Nb拉长了一次晶粒,降低了颗粒内部孔隙率,增强了晶界结合,提高了颗粒对电解液渗透的抵御作用。同时,Nb掺杂还提高了对晶格氧的稳定作用。与非原位掺杂相比（烧结实现的颗粒表面梯度掺杂）,原位掺杂能够更加显著地改善高镍NCM96正极的长循环稳定性。更多还原

【Abstract】 Due to their high discharge capacity,high operating voltage,and moderate costs,Ni-rich layered oxides are considered as one of the cathode materials for power batteries for electric vehicles.However,there are several intrinsic issues that limit their practical deployment,including highly alkaline and reactive surface chemistry,structural instability at a highly-delithiated state,and cracks of secondary particles caused by the grain boundary stress accumulation on lithiation/delithiation.These problems cause serious deterioration of the long-term cyclic stability and thermal stability of the cathodes.In this thesis,utilizing the lithium-reactive coating strategy,the lithium residuals on particle surface were eliminated and meanwhile a hybrid surface structure of LiNbO₃-coated/Nb-doped was constructed on the particle surface of Ni-rich oxides to improve the diffusion kinetics of lithium ions and stabilize the layered structure of the materials.Crystal structure with a strong metal-oxygen bonding,and a dense crystalline texture with the primary grains radially arranged in the secondary particles were designed to improve the cyclic and thermal stability of the Ni-rich cathode materials.Synergistic modification through the chemical doping and micromorphology optimization was successfully conducted.The Ni-rich hydroxide precursors were doped in-situ with niobium through coprecipitation,which enabled micromorphology of both.the precursor and the prepared cathode materials to be engineered,yielding uniformly modified products.The main research results of the thesis are as follows:（1）Based on the reactive coating strategy.ammonium niobium oxalate was employed to react with lithium residuals to form a LiNbO₃ coating layer on the surface of LiNi_0.6Co_0.2Mn_0.2O₂（NCM622）particles.During the heat treatment,some of Nb ions diffused into the lattice,forming a Nb-doped layer near the particle surface.As a results.the surface lithium residual was eliminated and the surface structural stability was enhanced.The lithium-ion conductive LiNbO₃ coating accelerated the electrode reaction kinetics.These merits enabled the modified NCM622 cathode to have excellent rate performance,good cyclic stability,and enhanced thermal stability.（2）Hf-doped LiNi0.90Co0.08Al0.02O2（NCA90）was designed and synthesized.Hfdoping can stabilize the lattice oxygen and enhance the surface structural stability of NCA90.Meanwhile,Hf-doping allowed refining the primary particles and developed them into short rod-shaped,with radial densely-arranged distribution inside of the NCA90 secondary particles.This particle structure with reduced porosity can dissipate grain boundary stresses,increase the mechanical toughness of the NCA90 particles,and thus significantly enhance the cycling stability.In 2.74.3 V,the capacity retention of the NCA90 electrode modified with only 0.5 mol%Hf was as high as 95.3%after 100 cycles,while that for the pristine materials is only 82.0%.Hf-doping also enhanced the thermal stability of NCA90.The onset temperature of the exothermic reaction was increased after the modification from 236℃ to 245℃,while the heat release was reduced by 26.3%.（3）Hf-B co-doping strategy was proposed to modify LiNi0.888Co0.079Al0.02Hf0.003B0.01O2（NCA90-Hf0.3&B1）.The Hf doping refined the primary particle size,while B doping increased aspect（length/width）ratio,and rendered particles to arrange densely along a radial direction in the secondary particles.In voltage of 2.7-4.3 V after 100 cycles,the capacity retention rate of NCA90-Hf0.3&B1 is 96.5%and 89.5%,respectively,while NCA90 is only 82.0%and 62.0%.（4）By in-situ Nb doping in the precursor,the synergistic regulation of the crystal structure and microstructure of Ni-rich LiNi0.96Co0.025Mn0.015O2（NCM96）cathode particles is achieved,enhancing the stability of the particle structure..Nb-doping decreased the primary grain size,reduced the particle porosity,improved the grainboundary combination,and enhanced the resistance of particle to electrolyte penetration.Besides,Nb-doping can stabilize the lattice oxygen and so increase the structural integrity of NCM96 cathode.Compared with ex-situ doping（gradient surface doping achieved through sintering）,the in-situ doping can significantly improve the long-term cycling stability of the NCM96 cathodes.更多还原