Bimetallic zeolite imidazolate framework for enhanced lithium storage boosted by the redox participation of nitrogen atoms

In this work, a bimetallic zeolitic imidazolate framework (ZIF) CoZn-ZIF was synthesized via a facile solvothermal approach and applied in lithium-ion batteries. The as-prepared CoZn-ZIF shows a high reversible capacity of 605.8 mA h g⁻¹ at a current density of 100 mA g⁻¹, far beyond the performance of the corresponding monometallic Co-ZIF- 67 and Zn-ZIF-8. Ex-situ synchrotron soft X-ray absorption spectroscopy, X-ray diffraction, and electron paramagnetic resonance techniques were employed to explore the Li-storage mechanism. The superior performance of CoZn-ZIF over Co- ZIF-67 and Zn-ZIF-8 could be mainly attributed to lithiation and delithiation of nitrogen atoms, accompanied by the breakage and recoordination of metal nitrogen bond. Morever, a few metal nitrogen bonds without recoordination will lead to the amorphization of CoZn-ZIF and the formation of few nitrogen radicals.