Solvothermal Synthesis of a Novel Calcium Metal-Organic Framework: High Temperature and Electrochemical Behaviour

The rapid growth in the field of metal-organic frameworks (MOFs) over recent years has highlighted their high potential in a variety of applications. For biological and environmental applications MOFs with low toxicity are vitally important to avoid any harmful effects. For this reason, Ca-based MOFs are highly desirable owing to their low cost and high biocompatibility. Useful Ca MOFs are still rare owing to the ionic character and large size of the Ca2+ ion tending to produce dense phases. Presented here is a novel Ca-based MOF containing 2,3-dihyrdoxyterephthalate (2,3-dhtp) linkers Ca(2,3-dhtp)(H2O) (SIMOF-4). The material undergoes a phase transformation on heating, which can be followed by variable temperature powder X-ray diffraction. The structure of the high temperature form was obtained using single-crystal X-ray diffraction. The electrochemical properties of SIMOF-4 were also investigated for use in a Na ion battery.

Why Is Tetrahydrofuran a Good Solvent for Calcium Batteries? Insights From Ab Initio Molecular Dynamics Simulations

Calcium batteries are rapidly emerging as a potential, future energy storage technology; however, their advancement relies heavily on understanding of the liquid electrolyte component in terms of stability and interactions with a calcium metal anode. Tetrahydrofuran, a cyclic ether, is an experimentally common and promising solvent for the preparation of stable and efficient calcium electrolytes. However, insights into the reasons why are lacking, which could unveil key principles to electrolyte design. In this report, we provide a theoretical study employing ab initio molecular dynamics (AIMD) simulations of the interactions of Ca metal with the cyclic ether tetrahydrofuran (THF). The results show that the electrochemical breakdown and decomposition of THF at the Ca surface is highly orientation- and surface-site dependent, thereby significantly reducing the likelihood of its instability in a randomly organized bulk solvent. Likewise, in bulk electrolytes, its likelihood for breakdown is further diminished, in preference for coordination Ca2+ to form solvated structure. Hence, the finding that molecules require such strict conditions for their decomposition is an important selection and design principle for any solvent to prepare suitable calcium electrolytes. These findings are critical to the advancement of the calcium batteries.

Why Is Tetrahydrofuran a Good Solvent for Calcium Batteries? Insights From Ab Initio Molecular Dynamics Simulations

Calcium batteries are rapidly emerging as a potential, future energy storage technology; however, their advancement relies heavily on understanding of the liquid electrolyte component in terms of stability and interactions with a calcium metal anode. Tetrahydrofuran, a cyclic ether, is an experimentally common and promising solvent for the preparation of stable and efficient calcium electrolytes. However, insights into the reasons why are lacking, which could unveil key principles to electrolyte design. In this report, we provide a theoretical study employing ab initio molecular dynamics (AIMD) simulations of the interactions of Ca metal with the cyclic ether tetrahydrofuran (THF). The results show that the electrochemical breakdown and decomposition of THF at the Ca surface is highly orientation- and surface-site dependent, thereby significantly reducing the likelihood of its instability in a randomly organized bulk solvent. Likewise, in bulk electrolytes, its likelihood for breakdown is further diminished, in preference for coordination Ca2+ to form solvated structure. Hence, the finding that molecules require such strict conditions for their decomposition is an important selection and design principle for any solvent to prepare suitable calcium electrolytes. These findings are critical to the advancement of the calcium batteries.

High Performance Voltage Tailorable Room-temperature Ca-metal Batteries

Calcium metal battery as one of the promising alternatives beyond Li-metal technology is challenged by the lack of suitable cathodes with considerable energy performance, and stable Ca anode of long-term stability and lower polorization potentials for Ca-plating/stripping. Here, by recycling cellulose waste paper of wide sources in our daily life, we develop feasible cathodes for Ca-metal batteries of good high-voltage and wide-window-voltage adaptability (0.005-4.9 V vs. Ca/Ca2+), except for considerable energy performance (~517.5 Wh kg-1 at 0.1 A g-1). Meanwhile, through tailorable Ca-plating/stripping potentials (∆V= ~0.65 V) induced by electrolyte modification, proof-of-concept Ca-metal batteries not only delivered enhanced storage capability (101 mAh g-1 vs. 51 mAh g-1 at 0.1 A g-1 in the window voltage of 2.0-4.7 V ) and cycling stability (~77% capacity retention for 100 cycles), but also simutaneously held high output average working voltage of ~3.2V.