Chando Paul Alexis, Shellhamer Jacob Matthew, Wall Elizabeth, He Wenlin, Hosein Ian Dean
Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York 13244, United States.
ACS Appl Energy Mater. 2023 Mar 30;6(7):3924-3932. doi: 10.1021/acsaem.3c00098. eCollection 2023 Apr 10.
The use of calcium (Ca) metal anodes in batteries is currently challenged by the development of a suitable solid electrolyte interface (SEI) that enables effective Ca ion transport. Native calcium electrolytes produce a passivation layer on the surface of the calcium electrodes during cycling, causing a decrease in capacity during cycling and the need for large overpotentials. The use of a hybrid SEI is a strategy to mitigate the uncontrolled production of a passivation layer and reduce the overpotentials needed for the plating and stripping of calcium. Here, we report the development of a hybrid potassium (K)/Ca SEI layer investigated in symmetric Ca//Ca cell configurations. Using KPF salt in a ternary mixture of carbonate solvent (EC/EMC/DMC), Ca//Ca cells can be cycled up to 200 h at a capacity of 0.15 mAh/cm with a current density of 0.025 mA/cm. The symmetrical cells consistently cycle at overpotentials of 1.8 V. Ex-situ X-ray diffraction (XRD) of cycled electrodes reveals plating and stripping of both calcium and potassium. Energy dispersive X-ray (EDX) maps confirm the plating of calcium and potassium during galvanostatic cycling. Scanning electron microscopy (SEM) cross-sectional views of the calcium electrodes reveal a continuous SEI layer formed over the calcium metal. XRD analysis reveals the SEI layer consists of K-based inorganics along with the identification of permanent and transient phases. FTIR outlines the parallel plating of both calcium and potassium at both regions of redox activity. Raman spectroscopy of the electrolyte reveals compositional changes over the course of cycling that promote increased plating and stripping. The results indicate that potassium electrolytes are a possible route for tuning the SEI to enable reversible calcium electrochemical cycling.
目前，电池中钙（Ca）金属阳极的使用面临着开发一种合适的固体电解质界面（SEI）的挑战，该界面能够实现有效的钙离子传输。天然钙电解质在循环过程中会在钙电极表面形成钝化层，导致循环过程中容量下降，并需要较大的过电位。使用混合SEI是一种减轻钝化层无控制产生并降低钙电镀和剥离所需过电位的策略。在此，我们报告了在对称Ca//Ca电池配置中研究的混合钾（K）/钙SEI层的开发情况。在碳酸盐溶剂（EC/EMC/DMC）的三元混合物中使用KPF盐，Ca//Ca电池在电流密度为0.025 mA/cm²、容量为0.15 mAh/cm²的情况下可循环200小时。对称电池在1.8 V的过电位下持续循环。循环电极的非原位X射线衍射（XRD）显示了钙和钾的电镀和剥离。能量色散X射线（EDX）图谱证实了恒电流循环过程中钙和钾的电镀。钙电极的扫描电子显微镜（SEM）横截面视图显示在钙金属上形成了连续的SEI层。XRD分析表明SEI层由基于K的无机物组成，同时还识别出了永久相和瞬态相。傅里叶变换红外光谱（FTIR）概述了在氧化还原活性的两个区域钙和钾的平行电镀。电解质的拉曼光谱揭示了循环过程中的成分变化，这些变化促进了电镀和剥离的增加。结果表明，钾电解质是调整SEI以实现可逆钙电化学循环的一条可能途径。
