Study On Properties Of Cathode Materials For Non-Aqueous Al-Air Battery

The reserve of electrical energy is one of the important measures for us to face the energy shortage.Today,lithium-ion batteries have been widely used in various electronic industries.However,with the rapid development of remote electric vehicles,lithium-ion batteries can no longer meet their needs.Therefore,metal-air batteries with high specific energy density,low cost,and environment-friendly have come into focus.The theoretical energy density(8100 Wh kg^-1)of the aluminum-air batteries is only lower than that of the lithium-air batteries(11700 Wh kg^-1),and the aluminum element is the highest metal element in the earth’s crust,which is not only inexpensive but also non-polluting,so it has become a hot research topic.For aluminum-air batteries,the research on aqueous systems is relatively mature,but the self-discharge corrosion of water-based aluminum-air batteries is severe and Al³⁺cannot be electrodeposited in aqueous solutions,the non-aqueous electrolyte is the key to solve this problem.Therefore,combining all aspects,aluminum chloride/1-ethyl-3-methylimidazolium chloride（AlCl₃/[EMIm]Cl）was selected as the electrolyte for aluminum-air batteries.In this paper,the electrochemical performances of aluminum-air batteries for carbon microspheres（CMs）,boron-doped carbon microspheres（B-CMs）and graphene（rGO）as cathode catalysts were investigated to explore the best cathode catalysts.The CMs are synthesized by a simple reflux-calcination method,they are spherical structures with many small pores on the surface and has a large specific surface area.When pure CMs were used as cathode materials,the initial discharge capacity reached 835 mAh g^-11 at a current density of 25 mA g^-1.And it can stably circulate 35 times at the capacity cut-off of 200 mAh g^-1with a current density of 50mA g^-1.From the XPS elemental analysis,the most likely discharge product was Al₂O₃.Boron-doped carbon microspheres（B-CMs）were prepared by soaking carbon microsphere precursors in a saturated solution of boric acid and then calcining them.After tests,it was found that the composite material obtained when the mass ratio of carbon spheres and boric acid saturated solution was 1:20 was the best.It not only had a significant catalytic effect on oxygen reduction but also had a good catalytic effect on oxygen evolution reaction.It is a bifunctional catalyst that is very suitable for the cathode material of metal-air batteries.XRD,Raman,SEM and other tests show that B atoms have been successfully loaded on the carbon spheres and boron is mainly present in the form of boron carbide.B atom doping makes the surface of the carbon spheres defective to obtain a larger specific surface area.When B-CMs were used as the cathode material,the initial discharge capacity of the aluminum air battery was as high as 4800 mAh g^-11 at a current density of 25 mA g^-1,which was 5.8 times that of pure CMs,the discharge platform is high,between 1.0-1.8 V.Graphene has made significant contributions to improving the specific capacity and rate performance of lithium-air batteries due to its excellent electrochemical performance.When the rGO sample is used as a cathode catalyst,compared with the CMs,the voltage difference of the aluminum-air battery is small,the discharge platform is high,and the cycle life is long,which is a good dual-function catalyst.