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Electron passivation in CaF2 on calcium metal anodes
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2022-11-26 , DOI: 10.1039/d2cp02274e
Kevin Batzinger 1 , Manuel Smeu 1
Affiliation  

Current electrolytes in calcium-ion batteries suffer from a lack of stability and degradation caused by reduction from the anode. The solid-electrolyte interphase (SEI) that forms on the anodes during operation stems the flow of electrons from the anode to the electrolyte. CaF2 is a common inorganic compound found in the SEI, and is derived from electrolyte salts such as Ca(PF6)2. CaF2 can exist in crystalline, polycrystalline, and amorphous phases in the SEI, and as recent work has shown, different phases of the same compound can have vastly different electronic conductivities. Using the non-equilibrium Green's function technique with density functional theory (NEGF-DFT), we find that amorphous phase systems enhance electron tunneling in thin CaF2 films by 1–2 orders of magnitude when compared to crystalline and polycrystalline CaF2 systems. Transport through several amorphous structures was considered showing that, despite their random structures, their conductance properties are similar. Through analysis of the decay constant β and the low-bias conductance of each system, we show that crystalline and polycrystalline CaF2 offer greater protection of the electrolyte than amorphous CaF2.

中文翻译:

钙金属阳极上 CaF2 的电子钝化

目前钙离子电池中的电解质缺乏稳定性,并且由于阳极还原而退化。运行期间在阳极上形成的固体电解质界面 (SEI) 阻止电子从阳极流向电解质。CaF 2是SEI中常见的无机化合物,衍生自Ca(PF 6 ) 2等电解质盐。CaF 2在 SEI 中可以以结晶、多晶和非晶相存在,并且正如最近的研究表明的那样,同一化合物的不同相可能具有截然不同的电子电导率。将非平衡格林函数技术与密度泛函理论 (NEGF-DFT) 结合使用,我们发现与结晶和多晶 CaF 2系统相比,非晶相系统将薄 CaF 2薄膜中的电子隧穿增强了 1-2 个数量级。通过几种非晶结构的传输被认为表明,尽管它们的结构是随机的,但它们的电导特性是相似的。通过分析每个系统的衰减常数β和低偏压电导,我们表明晶体和多晶 CaF 2提供比无定形 CaF 2更大的电解质保护。
更新日期:2022-11-30
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