Electrochemical Behaviors of LixMO (x=0.79, 0.30, 0.08; M=Ni/Co/Mn) Recycled from Spent Li-ion Batteries as Cathodic Catalyst for Lithium-Oxygen Battery

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 LixMO (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 LixMO 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 LixMO materials (0.79 -> 0.30 -> 0.08). The dependence of the electrochemical behaviors on the lithium content and lattice structure of the LixMO catalysts was also investigated systematically. Compared to that of Li0.79MO and Li0.08MO, lithium-oxygen batteries with Li0.30MO 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 Li0.30MO 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 LixMO catalysts. The superior catalytic activity of Li0.30MO 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.