Lithiumstorage in a metal organic framework with diamondoid topology – a case study on metal formates

Abstract

In this manuscript, a systematic investigation on the electrochemical performance of as-synthesized metal organic framework (MOF) Zn₃(HCOO)₆ with diamondoid structure for the Li storage using conversion reaction at low potential is described. Nearly an invariable capacity of 560 mAh g⁻¹ (9.6 moles of Li) was obtained up to 60 cycles at 60 mA g⁻¹ within the voltage range 0.005–3.0 V. The regeneration of the MOF during the cycling and the improved cyclability are evidenced from the electrochemical results along with ex situ PXRD, FTIR and TEM studies. The electrochemical cycling suggests that metal formate frameworks react reversibly with Li through conversion reaction. The matrix involved during the cycling was lithium formate rather than the typical Li₂O and this is well supported by the ex situ FTIR results. The thermodynamic feasibility to transform the lithium formate to transition metal formate is more highly favored than from Li₂O and this is further confirmed by reacting lithium formate with respective transition metal nitrates. The reversible formation or regeneration of FOR1 MOF plays a vital role in attaining the superior Li storage performance. Ultimately, the observation of improved storage performance and good cycling stability of Co₃(HCOO)₆ and Zn_1.5Co_1.5(HCOO)₆, and the overall simple and eco-friendly synthesis method demonstrates that robust, thermally stable MOFs are a prospective class of electrode materials for Li ion batteries (LIBs).