可充电锂氧气（Li-O₂）电池以其巨大的理论比能量、环境友好性和低成本被认为是满足电动汽车需求的最有前途的下一代电池系统之一，但其ORR/OER动力学缓慢和绝缘性的不溶放电产物Li₂O₂导致电池出现过电位增大，能量效率降低，循环寿命受限等问题，大大限制了Li-O₂电池的实际应用。近年来研究结果表明，通过合理的正极催化剂设计能够加速电化学反应动力学，提高充放电效率。此外，正极催化剂还可以诱导Li₂O₂在空气电极表面的生长路径和形态演变，从而提升Li-O₂电池性能。本论文针对当前Li-O₂电池的关键问题，以钴氧化物为基础，设计合成具有高催化活性中心的空心结构催化剂，探索催化剂与充放电机制的内在联系。主要研究内容包括：

     1. 通过调控合成过程，将Co₃O₄中的Co²⁺和Co³⁺位点替换为催化惰性的Zn²⁺和Al³⁺，形成仅含有Co³⁺_Oh的ZnCo₂O₄，和含有Co²⁺_Td的CoAl₂O₄，从而研究Co的不同几何构型和氧化态对Li-O₂电池性能的影响。电池性能测试结果显示，ZnCo₂O₄催化的Li-O₂电池比CoAl₂O₄具有更长的循环寿命，且能够催化生成更小尺寸的Li₂O₂，从而促进放电产物的可逆分解。因此，Co₃O₄中的Co³⁺_Oh位点相对于Co²⁺_Td具有更好的电催化活性。理论计算表明，Co³⁺_Oh位点可以通过调节对中间产物LiO₂的吸附能，从而影响放电产物形貌，加速电池反应动力学，最终提高了Li-O₂电池性能。

      2. 通过调控钴氧化物的结晶过程，成功地调控了Li-O₂电池反应机理。研究表明，低结晶度钴氧化物ZIF-67-260对LiO₂有较强的亲和力，可以促进电极表面形成膜状LiO₂并抑制其进一步向Li₂O₂转化。ZIF-67-260催化的Li-O₂电池通过非晶态膜状LiO₂的可逆生成和分解，显著降低了充电反应过电位，提高了电池循环稳定性（97圈）。相比之下，高结晶度的ZIF-67-320更倾向于通过溶液介导机制形成聚集型放电产物，并最终导致电池过电位增大，能量效率降低。理论计算结果与实验结果相一致。

      3. 通过双溶剂法将贵金属Ru引入ZIF-67骨架结构中以提高钴氧化物的催化活性。透射电子显微镜（TEM）和X射线光电子能谱（XPS）测试结果表明，合成的Ru@ZIF-67-280中的RuO₂纳米粒子均匀分散在钴氧化物基体中，没有出现团聚现象。超细的RuO₂纳米粒子作为高催化活性中心，丰富了催化剂的反应活性位点，同时引起Co₃O₄晶格畸变，大大提高了Li-O₂电池性能。与没有进行贵金属调节活性位点的ZIF-67-280相比，Ru@ZIF-67-280具有更优的循环稳定性（272圈）和更高的能量效率。

Rechargeable Li-O₂ batteries are considered as one of the most promising battery systems for electric vehicle, due to their huge theoretical specific energy, environmental friendliness and low cost. But the slow ORR/OER kinetics and the insulating insoluble discharge product Li₂O₂ lead to the increase of overpotential, the decrease of energy efficiency and poor cycle life, which greatly limits the practical application of Li-O₂ batteries. In recent years, researches have shown that rational cathode catalyst design can accelerate the electrochemical reaction kinetics, improve charge-discharge efficiency. In addition, the cathode catalyst can also induce the growth path and morphological evolution of Li₂O₂, thereby enhancing the performance of Li-O₂ batteries. Herein, aiming at the key problems of Li-O₂ batteries, hollow structure catalysts with high catalytic activity centers was designed based on cobalt oxide, and explore the intrinsic connection between the catalysts and the charge-discharge reaction mechanism at the same time. The main researches are as followed:

1. In this chapter, the Co²⁺ and Co³⁺ sites in Co₃O₄ are replaced by inert Zn²⁺ and Al³⁺ to form ZnCo₂O₄ with only Co³⁺_Oh, while CoAl₂O₄ with only Co²⁺_Td, thus to study the effect of different geometrical configuration and oxidation state of cobalt cations on the performance of Li-O₂ batteries. The battery performance tests show that the Li-O₂ batteries catalyzed by ZnCo₂O₄ have a longer cycle life than CoAl₂O₄, which can catalyze the formation of smaller-sized Li₂O₂, thereby promoting the reversible decomposition of discharge products. Therefore, the Co³⁺_Oh sites in Co₃O₄ have better electrocatalytic activity relative to Co²⁺_Td. Theoretical calculations show that the Co³⁺_Oh sites can affect the morphology of the discharge products by adjusting the adsorption energy of the intermediate product LiO₂, accelerate the reaction kinetics, and ultimately improve the performance of Li-O₂ batteries.

2. In this chapter, the reaction mechanism of Li-O₂ batteries is successfully adjusted by regulating the crystallization process of cobalt oxide. Experimental results show that the lower crystallinity cobalt oxide hollow sphere ZIF-67-260 has a stronger affinity for LiO₂, which can promote the formation of film-like LiO₂ on the electrode surface and inhibit the further conversion to Li₂O₂. The batteries catalyzed by ZIF-67-260 operate based on the generation and decomposition of amorphous film-like LiO₂, which significantly reduce the charge overpotential and improve the cycle life (around 100 cycles). In contrast, ZIF-67-320 with high crystallinity is more likely to go through the solution-mediated mechanism and induce the aggregation of discharge product, resulting in the sluggish kinetics and limited performance. The theoretical calculation results are consistent with the experimental results.

3. In this chapter, the noble metal Ru is introduced into the ZIF-67 framework by a double solvents approach to enhance the catalytic activity of cobalt oxides. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) tests show that the RuO₂ nanoparticles are uniformly dispersed in the cobalt oxide matrix without agglomeration on the outer surface of Ru@ZIF-67-280. The ultra-fine RuO₂ nanoparticles act as highly catalytically active centers, enriching the reactive sites of the catalyst, and causing Co₃O₄ lattice distortion at the same time, which greatly improves the performance of Li-O₂ batteries. Compared with ZIF-67-280, Ru@ZIF-67-280 exhibits superior cycling stability (272 cycles) and betterer energy efficiency.