锂-氧气电池因其超高的理论比容量而受到科研界的广泛关注, 但其存在较为严重的充放电极化和较差的循环稳定性等问题, 从而极大地限制其商业化进程. 因此设计出有效的正极催化剂是解决锂-氧气电池面临的这些棘手问题的必要手段. 通过对不同充电状态的废旧锂电池正极进行回收制得三种不同锂含量的多元金属氧化物Li_xMO (x=0.79, 0.30, 0.08; M=Ni/Co/Mn), 并分别用作锂-氧气电池正极催化剂. 系统研究了Li_xMO材料中锂含量及晶体结构对其电化学性能的影响. 电化学测试结果表明, 与Li_0.79MO和Li_0.08MO催化剂相比, 基于Li_0.30MO为正极催化剂的锂-氧气电池在电流密度100 mA•g^–1和限定容量800 mAh•g^–1的条件下具有较高的放电比容量(14655.9 mAh•g^–1)、较低的充电电压(3.83 V)和较高的能量转换效率(72.2%). 而且该电池体系在充放电循环140圈后充电终止电压仍低于4.3 V. 最终认为制得的Li_0.30MO材料具有优异的催化性能归因于其稳定的层状-岩盐相复合结构以及结构中富含的氧化镍相和氧空位之间的协同作用. 这些优点能够促进放电产物的可逆形成与分解, 从而提高锂-氧气电池循环性能.

Lithium-oxygen battery has been studied as a hot spot because of its high theoretical specific capacity. But its severe discharge/charge polarization and poor cycle stability greatly hinder its large-scale applications at current stage. The rational design of cathodic catalysts for the oxygen reduction/evolution reaction (ORR/OER) is thus essential to reduce overpotential and extend cycling stability. Three kinds of multi-metal oxides Li_xMO (x=0.79, 0.30, 0.08; M=Ni/Co/Mn) with different lithium contents, which were recycled from the cathodes of spent lithium-ion batteries in different charging states, were explored as cathodic catalysts for lithium-oxygen batteries, respectively. The lithium content and phase structure of these multi-metal oxides Li_xMO were determined by inductive coupled plasma emission spectrometer (ICP) and X-ray diffraction (XRD). Phase transformation from layer to NiO-like rock-salt was observed upon continuous deintercalation of Li⁺ in Li_xMO materials (0.79→0.30→0.08). The dependence of the electrochemical behaviors on the lithium content and lattice structure of the Li_xMO catalysts was also investigated systematically. Compared to that of Li_0.79MO and Li_0.08MO, lithium-oxygen batteries with Li_0.30MO catalyst have delivered a higher specific capacity of 14655.9 mAh•g^–1, a lower charge potential of 3.83 V, and a higher round-trip efficiency of 72.2% under the limited capacity of 800 mAh•g^–1 and current density of 100 mA•g^–1. Moreover, the charge terminal voltage of Li_0.30MO catalyst is stable lower than 4.3 V even after 140 cycles. Furthermore, the ex-situ scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) techniques were used to elucidate the reaction mechanisms with different Li_xMO catalysts. The superior catalytic activity of Li_0.30MO cathode can be mainly attributed to the synergistic effect between its layered/NiO-like rock-salt complex structure and oxygen vacancy formed, which can promote the reversible formation and decomposition of discharge product and improve the cycling stability of lithium-oxygen battery. Hence, the result corroborates that recycling of spent cathodes from lithium-ion batteries can serve as novel strategy to design large-scale and effective catalysts for lithium-oxygen battery.