{"title":"Urea Calcium Borohydrides as Ca2+ Solid-State Electrolytes","authors":"Mads B. Amdisen, Torben R. Jensen","doi":"10.1021/acs.chemmater.4c03098","DOIUrl":null,"url":null,"abstract":"Solid-state calcium batteries can potentially contribute to future renewable energy storage systems, however the discovery of electrolytes with sufficiently high Ca<sup>2+</sup> conductivity at ambient conditions is a challenge. Here we present mechanochemical synthesis and properties of five different urea calcium tetrahydridoborate compositions as well as three crystal structures, Ca(BH<sub>4</sub>)<sub>2</sub>·<i>x</i>CO(NH<sub>2</sub>)<sub>2</sub>, <i>x</i> = 2, 4, and 6. The orthorhombic structure of Ca(BH<sub>4</sub>)<sub>2</sub>·2CO(NH<sub>2</sub>)<sub>2</sub> consists of dinuclear molecular units, [Ca<sub>2</sub>(BH<sub>4</sub>)<sub>4</sub>(OC(NH<sub>2</sub>)<sub>2</sub>)<sub>4</sub>], with the two Ca<sup>2+</sup> ions bridged by three urea molecules. The low symmetry monoclinic structures of Ca(BH<sub>4</sub>)<sub>2</sub>·4CO(NH<sub>2</sub>)<sub>2</sub> and Ca(BH<sub>4</sub>)<sub>2</sub>·6CO(NH<sub>2</sub>)<sub>2</sub> consist of [Ca(BH<sub>4</sub>)<sub>2</sub>(OC(NH<sub>2</sub>)<sub>2</sub>)<sub>4</sub>] and [Ca(OC(NH<sub>2</sub>)<sub>2</sub>)<sub>6</sub>]<sup>2+</sup> octahedra with BH<sub>4</sub><sup>–</sup> counterions in the later, and all three structures are held together by dihydrogen bonds. The calcium ionic conductivity reaches a maximum of σ(Ca<sup>2+</sup>) = 2.46 × 10<sup>–7</sup> S cm<sup>–1</sup> for the composition Ca(BH<sub>4</sub>)<sub>2</sub>–3.30CO(NH<sub>2</sub>)<sub>2</sub> at RT, and of σ(Ca<sup>2+</sup>) = 1.23 × 10<sup>–4</sup> S cm<sup>–1</sup> for Ca(BH<sub>4</sub>)<sub>2</sub>–6.52CO(NH<sub>2</sub>)<sub>2</sub> at 70 °C. Activation energies in the range 0.5 < <i>E</i><sub>a</sub> < 2.4 eV depending on the urea content and heating or cooling during measurement of ionic conductivity and an ionic transport number of <i>T</i><sub>ion</sub> = 0.997 are also reported. The investigation of this series of compounds and their composites provides approaches for optimizing multiple physical phenomena that facilitate increased cationic conductivity.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":"44 1","pages":""},"PeriodicalIF":7.2000,"publicationDate":"2025-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Chemistry of Materials","FirstCategoryId":"88","ListUrlMain":"https://doi.org/10.1021/acs.chemmater.4c03098","RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
Abstract
Solid-state calcium batteries can potentially contribute to future renewable energy storage systems, however the discovery of electrolytes with sufficiently high Ca2+ conductivity at ambient conditions is a challenge. Here we present mechanochemical synthesis and properties of five different urea calcium tetrahydridoborate compositions as well as three crystal structures, Ca(BH4)2·xCO(NH2)2, x = 2, 4, and 6. The orthorhombic structure of Ca(BH4)2·2CO(NH2)2 consists of dinuclear molecular units, [Ca2(BH4)4(OC(NH2)2)4], with the two Ca2+ ions bridged by three urea molecules. The low symmetry monoclinic structures of Ca(BH4)2·4CO(NH2)2 and Ca(BH4)2·6CO(NH2)2 consist of [Ca(BH4)2(OC(NH2)2)4] and [Ca(OC(NH2)2)6]2+ octahedra with BH4– counterions in the later, and all three structures are held together by dihydrogen bonds. The calcium ionic conductivity reaches a maximum of σ(Ca2+) = 2.46 × 10–7 S cm–1 for the composition Ca(BH4)2–3.30CO(NH2)2 at RT, and of σ(Ca2+) = 1.23 × 10–4 S cm–1 for Ca(BH4)2–6.52CO(NH2)2 at 70 °C. Activation energies in the range 0.5 < Ea < 2.4 eV depending on the urea content and heating or cooling during measurement of ionic conductivity and an ionic transport number of Tion = 0.997 are also reported. The investigation of this series of compounds and their composites provides approaches for optimizing multiple physical phenomena that facilitate increased cationic conductivity.
期刊介绍：
The journal Chemistry of Materials focuses on publishing original research at the intersection of materials science and chemistry. The studies published in the journal involve chemistry as a prominent component and explore topics such as the design, synthesis, characterization, processing, understanding, and application of functional or potentially functional materials. The journal covers various areas of interest, including inorganic and organic solid-state chemistry, nanomaterials, biomaterials, thin films and polymers, and composite/hybrid materials. The journal particularly seeks papers that highlight the creation or development of innovative materials with novel optical, electrical, magnetic, catalytic, or mechanical properties. It is essential that manuscripts on these topics have a primary focus on the chemistry of materials and represent a significant advancement compared to prior research. Before external reviews are sought, submitted manuscripts undergo a review process by a minimum of two editors to ensure their appropriateness for the journal and the presence of sufficient evidence of a significant advance that will be of broad interest to the materials chemistry community.
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