为了应对日益紧迫的能源和环境问题，走可持续发展道路，新能源已逐渐成为全球最大新增电能来源。锂离子电池作为绿色、高效的能量转换和存储装置是新能源推广应用(如新能源汽车)的核心技术之一。但正极材料的性能正限制着锂离子电池性能的进一步提升。高镍三元材料以其高比能量的特性正逐步应用到电动汽车领域，而其安全性、倍率性能以及循环稳定性等仍需要进一步改善。本论文对高镍三元材料的合成和改性进行了系统的研究，通过双导电包覆层包覆，Zr⁴⁺全方位修饰以及锂位掺杂提高高镍三元材料的电化学性能。最后还以LiCoO₂型废旧锂离子电池为参考，开展了锂离子电池的资源化回收研究。主要取得了以下成果： (1)研究了Li₃PO₄和PPy双导电包覆层对高镍三元材料电化学性能的影响。 (NH₄)₂HPO₄与材料表面残留锂反应生成Li₃PO₄点状包覆层，从而降低材料表面残留锂，抑制电解液中HF的产生，同时提高材料离子导电性。通过化学氧化聚合法合成PPy进行二次包覆，连续的PPy包覆层能够弥补Li₃PO₄包覆缺陷，抑制活性材料与电解液的副反应，降低颗粒内部裂纹的生成，同时提高材料电子导电性。双导电包覆层包覆材料具有良好的循环性能和倍率性能，2.8～4.5 V电压范围内，1 C充放电，200周循环后，本体和双导电包覆层包覆材料容量保持率分别为65.8％和86.5％，10 C倍率放电比容量从125.7 mAh／g上升到159.7 mAh／g。 (2)采用Zr⁴ ⁺全面改善高镍三元材料结构稳定性和电化学性能。在前躯体合成过程中，将Zr⁴ ⁺掺杂到Ni₀.₈Co₀.₁Mn₀.₁(OH)₂前躯体表层，在混锂煅烧过程中，通过离子迁移实现Zr⁴ ⁺梯度掺杂，同时在材料表面形成高离子导电性Li₂ZrO₃包覆层。Zr⁴ ⁺不仅占据材料过渡金属位，还占据锂位，位于过渡金属层的Zr⁴ ⁺通过强的Zr-O结合能稳定材料晶体结构，位于锂层的Zr⁴ ⁺作为“支撑离子”抑制锂层在循环过程中坍塌，同时降低材料阳离子混排。通过浓度梯度掺杂降低掺杂量，抑制锂位掺杂的“阻塞效应”，从而改善材料循环稳定性和倍率性能。2.8～4.5 V电压范围内，1 C充放电，材料200周容量保持率从69.9％上升到83.2％；10 C倍率放电比容量从131.6 mAh／g上升到164.7 mAh／g。 (3)探究不同离子半径碱金属离子锂位掺杂对高镍三元材料结构和电化学性能的影响。在混锂过程中加入掺杂元素碳酸盐，高温煅烧后得到碱金属离子掺杂的高镍三元材料。锂位掺杂元素的离子半径严重影响材料的结构稳定性和电化学性能。碱金属离子锂位掺杂能够增大锂层间距，降低阳离子混排，并作为锂层“支撑离子”稳定材料结构，提高材料电化学性能；当锂位掺杂离子半径过大时(K⁺、Rb⁺)，其“阻塞效应”大于“支撑效应”，阻碍Li⁺扩散，同时，过大的离子半径，尤其是Rb⁺，将会导致材料发生晶格畸变，改变材料结构，影响材料电化学性能。在2.8～4.3 V电压范围，1 C倍率下，本体、Na⁺掺杂、K⁺掺杂和Rb⁺掺杂样品200周容量保持率分别为93.2％、97.2％、88.7％和92.9％，10 C倍率放电比容量为140、154.5、135.6和136.3 mAh／g。 (4)设计了一种无酸的回收过程回收18650型锂离子电池，并通过与Li₂CO₃热处理再生LiCoO₂正极材料，总回收率达到95.78％。回收过程具有良好的容错率，再生LiCoO₂结晶性良好，具有均匀的粒径分布和适中的pH值，失效正极材料中所含Co₃O₄在热处理后基本消失。再生材料具有良好的电化学性能，3～4.3 V电压范围内， 0.1 C充放电，首周放电比容量为150.3 mAh／g，100周容量保持率为93.2％。再生正极材料中含有少量杂质元素A1和Cu，当A1元素含量少于0.4％，Cu元素含量少于0.6％时，不会降低材料的电化学性能。该回收工艺及技术为高镍三元废旧锂离子电池资源化回收提供了参考。 关键词：锂离子电池；高镍三元材料；层状；包覆；掺杂；再生

To deal with the increasingly urgent energy and environmental problems and take the road of sustainable development, new energy has gradually become the world's largest source of newly increased electrical energy. As a green and efficient energy conversion and storage device, lithium-ion battery is the key to the application of new energy, such as new energy vehicles. However, the performance of the cathode material is limiting the performance of lithium-ion batteries. Ni-rich cathode materials are being gradually applied to the electric vehicle field due to high energy density. However, its safety performance, rate performance and cycle stability need to be further improved. In this paper, we systematically studied the synthesis and modification of Ni-rich cathode materials. The electrochemical properties of Ni-rich cathode materials were improved through dual-conductive layers coating, comprehensive modification with Zr⁴⁺ and Li-sites doping. Finally, the recycling research of spent lithium ion battery is carried out based on spent LiCoO₂ type lithium ion batteries as a reference. The main achievements are as follows: (1)We demonstrate the effect of dual-conductive layers composed of Li₃PO₄and PPy for layered Ni-rich cathode material. (NH₄)₂HPO₄ transformed to Li₃PO₄ after reacting with surface lithium residuals, and formed an inhomogeneous coating layer which would remarkably reduce the surface lithium residuals, improve the ionic conductivity of the cathode materials and reduce the generation of HF in eletrolyte. The PPy coating layer was synthesized by chemical oxidative polymerization. The PPy layer could form a uniform film which can make up for the Li₃PO₄ coating defects, enhance the electronic conductivity, reduce the generation of internal cracks and inhibit the side reactions between the cathode materials and electrolyte. The electrochemical test showed that the modified cathodes exhibited much improved cycling stability and rate capability. The capacity retention of the modified cathode material was 86.5% while the bare sample was 65.8% at 1 C and 2.8 ～ 4.5 V after 200 cycles, and the bare and modified sample performed 125.7 mAh/g and 159.7mAh/g at 10 C, respectively. (2)We applied Zr⁴⁺ in the outer layer of Ni₀.₈Co₀.₁Mn₀.₁(OH)₂ through co-precipitation method. The distribution of the Zr⁴⁺ in the final cathode materials showed a gradient distribution due to ion migration during thermal treatment. And a Li₂ZrO₃ coating layer was formed on the surface as a fast ion conductive layer. The doped Zr⁴⁺ could not only occupy TM slabs but also Li slabs. The doped Zr⁴⁺ in the TM slabs could stabilize the crystal structure due to strong Zr-O bonding energy, and the doped Zr⁴⁺ in the Li slabs could act as pillar ions to improve the structural stability and reduce cation mixing. The gradient-doping could take advantage of the “pillar effect” while restrain the “blocking effect” of the pillar ions, thus improving cycling and rate performance of the Ni-rich cathode materials. The capacity retention of the modified sample reached 83.2% compare to 69.9% for bare sample after 200 cycles at 1 C (200 mA/g) between 2.8 to 4.5 V, and the discharge capacity was up to 164.7 mAh/g at 10 C compare to 131.6 mAh/g for bare sample. (3)The influence of Li sites doping with different ion radii on the structure and electrochemical properties for Ni-rich cathode materials was investigated. The Li sites doped Ni-rich cathode materials were obtained through calcining alkali carbonate with Li₂ZrO₃ and Ni-rich precursor. The ionic radii of the doped elements had a serious effect on the structural stability and electrochemical properties for the cathode materials. Alkali ions doped in the Li sites could enlarge Li layer spacing, decrease cation mixing and stabilize the crystal structure as “pillar ions” to improve the electrochemical properties. However, while the too large alkali ions (K⁺, Rb⁺) doped in the Li sites, the "blocking effect" is greater than "pillar effect" which will block the Li⁺ diffusion channel, inhibit Li⁺ diffusion. At the same time, the excessive ionic radii, especially the Rb⁺ would cause cell distortion, leading to structure change, thus affecting electrochemical properties. The capacity retention of the bare, Na⁺ doped, K⁺ doped and Rb⁺ doped samples after 200 cycles at 1 C and 2.8 ～ 4.3 V was 93.2%, 97.2%, 88.7% and 92.9%, respectively. The discharge capacity at 10 C and 2.8 ～ 4.3 V for the bare, Na⁺ doped, K⁺ doped and Rb⁺ doped samples was 140, 154.5, 135.6 and 136.3 mAh/g, respectively. (4)An acid-free recycling process was proposed and used to recycle spent 18650-type LiCoO₂ batteries, and the recycled cathode materials have been renovated by thermal treatment with LiCoO₂. The total recovery weight ratio reached 95.78%. The renovation process had high fault tolerance for renovating the spent cathode materials. The renovated cathode materials possessed an ordered and crystalline layer structure, uniform particle size distribution and moderate pH value. The Co₃O₄ in the pristine cathode materials decreased during the renovation process. The renovated cathode materials had good electrochemical properties. The initial discharge capacity of the renovated cathode materials was 150.3 mAh/g and delivered a discharge capacity of 140.1 mAh/g after 100 cycles with a capacity retention of 93.2%. There were some impurities in the renovated cathode materials such as A1 and Cu elements. When the ratio of A1 element was less than 0.4% and Cu element was less than 0.6%, they would not reduce the electrochemical properties of the renovated cathode materials. The recycling process provides a reference for the recycling of the spent Ni-rich type lithium ion batteries. Key Words: Lithium ion battery; Ni-rich material; layered; coating; doping; renovate