Abstract
To create both greener and high-power metal-ion batteries, it is of prime importance to invent an unprecedented electrode material that will be able to store a colossal amount of charge carriers by a redox mechanism. Employing periodic DFT calculations, we modeled a new metal-organic framework, which displays energy density exceeding that of conventional inorganic and organic electrodes, such as Li- and Na-rich oxides and anthraquinones. The designed MOF has a rhombohedral unit cell in which an Ni(II) node is coordinated by 2,5-dicyano-p-benzoquinone linkers in such a way that all components participate in the redox reaction upon lithiation, sodiation and magnesiation. The spatial and electronic changes occurring in the MOF after the interaction with Li, Na and Mg are discussed on the basis of calculated electrode potentials versus Li0/Li+, Na0/Na+ and Mg0/Mg2+, respectively. In addition, the specific capacities and energy densities are calculated and used as a measure for the electrode applicability of the designed material. Although the highest capacity and energy density are predicted for Li storage, the greater structural robustness toward Na and Mg uptake suggests a higher cycling stability in addition to lower cost. The theoretical results indicate that the MOF is a promising choice for a green electrode material (with <10% heavy metal content) and is well worth experimental testing.
Highlights
Matching the high-power and large-scale energy storage with environmental constraints entails to consider replacement of the current lithium-ion batteries (LIBs) with technologies, in which more abundant, cheaper and safer elements are used [1,2,3,4]
Given that sodium and magnesium have higher redox potentials versus SHE than lithium (−2.71 V for Na0/Na+ and −2.37 V for Mg0/Mg2+ compared to −3.04 V for Li0/Li+ [9]), the enhancement of the energy density of SIBs and MIBs can only be achieved through the advancement of a new class of electrode materials that have the unique property of colossal specific capacity—a phenomenon not feasible for conventional electrodes based on transition metal oxides and phosphates
Coordination of Ni(II) with CN-groups from 2,5-dicyano-p-quinone ligands leads to the formation of a rhombohedral Metal-organic frameworks (MOFs), the charge neutralization being achieved by Cl counterions
Summary
Matching the high-power and large-scale energy storage with environmental constraints entails to consider replacement of the current lithium-ion batteries (LIBs) with technologies, in which more abundant, cheaper and safer elements are used [1,2,3,4]. Given that sodium and magnesium have higher redox potentials versus SHE than lithium (−2.71 V for Na0/Na+ and −2.37 V for Mg0/Mg2+ compared to −3.04 V for Li0/Li+ [9]), the enhancement of the energy density of SIBs and MIBs can only be achieved through the advancement of a new class of electrode materials that have the unique property of colossal specific capacity (i.e., able to exchange a huge amount of Na+ or Mg2+ ions)—a phenomenon not feasible for conventional electrodes based on transition metal oxides and phosphates This particularity follows from the ability of the electrode material to provide simultaneously flexible structural sites for storage and diffusion of large amounts of Na+ or Mg2+ ions, as well as to compensate through high redox activity the charges of all transportable metal ions. The participation of the organic ligands in the redox reaction is less dependent on the radius and charge of alkali or alkaline earth ions than in the case of inorganic electrodes
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