Finite phosphorene derived partial reduction of metal organic framework nanofoams for enhanced lithium storage capability

As a new class of crystalline porous materials, metal organic frameworks (MOFs) are promising in lithium-ion batteries (LIBs). However, the electrical conductivity and stability of conventional MOFs cannot meet the demand by next-generation high-rate LIBs. Herein, a partially-reduced MOF nanofoam (NiCo-MOF(P) NF) is synthesized by adding a small amount of phosphorene during the sol-gel self-assembly process. Since the amount of surface metallic species is increased, the carrier concentration and electrical conductivity are improved. Moreover, the structural stability is enhanced by phosphorus-oxygen and phosphorus-metal bonds generated during partial reduction. Although the phosphorus concentration is quite low (<2 wt%), the NiCo-MOF(P) NFs exhibit three times higher reversible lithium storage capacity (1230.3 mA h g⁻¹ at 0.2 A g⁻¹) compared to the stock NiCo-MOF after 250 cycles. At a higher current density (2.0 A g⁻¹), the NiCo-MOF(P) NFs maintain the high capability (550 mA h g⁻¹) after 700 cycles. These results demonstrate that the novel process of phosphorene-induced mild reduction improves the lithium storage capability of mixed-valence MOFs. The surface functionalization strategy and unique in situ molecular interactions have large potential in the development of advanced functional materials.