Design and synthesis of hollow NiCo2O4 nanoboxes as anodes for lithium-ion and sodium-ion batteries.

Hollow porous NiCo2O4-nanoboxes (NCO-NBs) were synthesized with zeolitic imidazolate framework-67 (ZIF-67) nanocrystals as the template followed by a subsequent annealing treatment. The structure and morphology of the NCO-NBs were characterized using X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. When tested as potential anode materials for lithium-ion batteries, these porous NCO-NBs with a well-defined hollow structure manifested enhanced performance of Li storage. The discharge capacity of the NCO-NBs remained 1080 mA h g(-1) after 150 cycles at a current rate of 500 mA g(-1) and 884 mA h g(-1) could be obtained at a current density of 2000 mA g(-1) after 200 cycles. Even when cycled at a high density of 8000 mA g(-1), a comparable capacity of 630 mA h g(-1) could be achieved. Meanwhile, the Na storage behavior of NCO-NBs as anode materials of sodium ion batteries (SIBs) was initially investigated and they exhibited a high initial discharge capacity of 826 mA h g(-1), and a moderate capacity retention of 328 mA h g(-1) was retained after 30 cycles. The improved electrochemical performance for NCO-NBs could be attributed to the hierarchical hollow structure and the desirable composition, which provide enough space to alleviate volume expansion during the Li(+)/Na(+) insertion/extraction process and facilitate rapid transport of ions and electrons.