Alessandro Bismuto

We revealed two types of corrosion of calcium metal in 0.3 m Ca(TFSI)₂/DMAc electrolytes: native passivation between Ca metal and DMAc solvent during initial aging and electrochemical corrosion between Ca metal and TFSI⁻ anion upon charging/discharging afterwards. Bearing those failure mechanisms in mind, we proposed additive strategy to simultaneously mitigate both corrosion types through in situ alloying and competitive Ca²⁺-I⁻ interactions.

Abstract

Calcium metal batteries (CMBs) are promising for large-scale energy storage due to calcium‘s abundance and high theoretical capacity, but hindered by poor compatibility between electrolyte and calcium metal. Here, we unveil two corrosion types of calcium in calcium bis(trifluoromethanesulfonimide)/dimethylacetamide [Ca(TFSI)₂/DMAc] electrolytes: native passivation from solvent reduction during aging and electrochemical corrosion from anion decomposition. The native passivation layer aggravates the electrochemical corrosion by the decomposition of TFSI⁻ to the large grain Ca²⁺-insulator CaF₂, leading to the calcium metal failure. We introduce a bifunctional SnI₂ electrolyte additive to simultaneously mitigate both corrosions. Sn²⁺ facilitate the spontaneous galvanic replacement reaction to form the Ca-Sn alloy, inhibiting native passivation, while I⁻ replace TFSI⁻ to participate in the Ca²⁺ primary solvation shell and prevent the electrochemical TFSI⁻ decomposition. By taking advantage of those features above, over 500 h of stable cycling with a reduced overpotential of 0.33 V at 0.1 mA cm⁻² and 0.1 mAh cm⁻² was achieved, outperforming state-of-the-art Ca(TFSI)₂-based electrolytes. Our work provides a fundamental understanding of corrosion at calcium metal surface and will guide suitable electrolyte design for anti-corrosion in metal batteries.

Nature Chemistry, Published online: 24 April 2023; doi:10.1038/s41557-023-01191-4

Creating Kekulé diradicaloids: That cyclic(alkyl)(amino)(carbene)—CAAC—donates one electron during the formation of a transient radical-cation was evidenced by electron paramagnetic resonance (EPR) spectroscopy. The disclosed property of CAAC as a one-electron reductant was utilized for the synthesis of acyclic(amino)(aryl)carbene-based Chichibabin hydrocarbons, a new class of Kekulé diradicaloids. More information can be found in the Research Article by P. Ghosh, H. Braunschweig, C. B. Yildiz, C. Schulzke, A. Jana, and co-workers (DOI: 10.1002/chem.202104567).

The redox chemistry of the newly synthesized homoleptic iron arsenic prismane cluster [{Cp*Fe}₃(μ₃,η^4:4:4-As₆)] (A) is investigated. While oxidation leads to an extended distortion of the prismane geometry by cleavage of one of the As−As bonds, reduction leads to a symmetrization of the cluster.

Abstract

The redox chemistry of the homoleptic iron prismane cluster [{Cp*Fe}₃(μ₃,η^4:4:4-As₆)] (A, Cp*=C₅Me₅) is investigated both electrochemically and synthetically. While its first oxidation leads to the diamagnetic species [{Cp*Fe}₃(μ₃,η^4:4:4-As₆)][X] ([1][TEF], [1][FAl], [TEF]⁻=[Al{OC(CF₃)₃}₄]⁻, [FAl]⁻=[FAl{O(1-C₆F₅)C₆F₁₀}₃]⁻), the second oxidation yields the paramagnetic [{Cp*Fe}₃(μ₃,η^4:4:4-As₆)][TEF]₂ ([2][TEF]₂ ). The reduction of A leads to the monoanionic compound [K@[2.2.2]-cryptand][{Cp*Fe}₃(μ₃,η^4:4:4-As₆)] ([K@crypt][3]), while a second reduction could only be traced spectroscopically. All compounds were comprehensively characterized, revealing the structural changes accompanying the described redox processes. All findings are supported by spectroscopic as well as computational studies.

Nature Chemistry, Published online: 27 October 2021; doi:10.1038/s41557-021-00832-w