Encapsulation of nano-Si into MOF glass to enhance lithium-ion battery anode performances

Although metal-organic framework (MOF) glasses have exhibited high potential to be applied as anode materials for lithium-ion batteries (LIBs), their electrochemical performances still need to be greatly improved to match the rapid development of green energy technologies. Silicon is a promising candidate for the next generation of LIB anode but suffers from vast volume fluctuations upon lithiation/delithiation. Here, we present a strategy to in situ grow a kind of MOF, namely, cobalt-ZIF-62 (Co(imidazole)_1.75(benzimidazole)_0.25) on the surface of Si nano particles, and then to transform the thus-derived material into Si@ZIF-glass composite (SiZGC) through melt-quenching. The robust hierarchical structure of the SiZGC based anode exhibits the specific capacity of ∼650 mA h g^-1, which is about three times that of pure ZIF glass and about six times that of pristine ZIF crystal at 1 A g^-1 after 500 cycles. The origin of this huge enhancement is revealed by performing structural analyses. The ZIF glass phase can not only contribute to lithium storage, but also buffer the volume changes and prevent the aggregation of Si nano particles during lithiation/delithiation processes.