Porosity tailoring of the Zn-MOF-5 derived carbon materials and its effects on the performance as a cathode for lithium-air batteries

Abstract

Metal-organic framework(MOF)-derived carbon material is a promising material for lithium-air battery cathode, but its pores are small (<5 nm) and narrow distribution, making it difficult to be applied as a charge-discharge active site. Herein, we introduce two types of pore-tailored Zn-MOF-5-derived carbon materials and investigate the effects of the porosity characteristics on the performance of a lithium-air battery: 1) Zn-MOF-5 carbonized at 1000 °C, where the pores are generated by the Zn metal evaporation.; and 2) Zn-MOF-5 carbonized at temperatures below the evaporation temperature of Zn, followed by etching out process of generated ZnO by hydrofluoric acid(HF). The ZnOs undergo a morphological change from nanoparticles to nanorods due to the reaction with gaseous Zn. Carbon materials obtained by etching the ZnOs with various shapes and sizes result in wider pore distribution and larger size pores compared to samples carbonized at 1000 °C. The initial discharge capacity of etched carbon with large pores and a wide pore distribution shows up to 5 times higher capacity than carbonized material (cycled at a current density of 0.2 mA cm −2 ). Furthermore, the detailed microscopic studies show that the porosity and morphology of the carbon materials derived from Zn-MOF-5 affect the performance of lithium-air battery. - Two types of pore-tailored Zn-MOF-5-derived carbon materials were synthesized by carbonization and etching process for lithium-air battery. - Carbon materials obtained by etching zinc oxides with various shapes and sizes result in wider pore distribution and larger size pores compared to samples carbonized at 1000 °C. - The initial discharge capacity of the Zn-MOF-5-derived carbon materials can be improved by tailoring the porosity.