Kitz Paul G, Lacey Matthew J, Novák Petr, Berg Erik J
Electrochemistry Laboratory , Paul Scherrer Institut , CH-5232 Villigen PSI , Switzerland.
Department of Chemistry-Ångström Laboratory , Uppsala University , Box 538, SE-751 21 Uppsala , Sweden.
Anal Chem. 2019 Feb 5;91(3):2296-2303. doi: 10.1021/acs.analchem.8b04924. Epub 2019 Jan 9.
An operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) with simultaneous in situ electrochemical impedance spectroscopy (EIS) has been developed and applied to study the solid electrolyte interphase (SEI) formation on copper current collectors in Li ion batteries. The findings are backed by EIS simulations and complementary analytical techniques, such as online electrochemical mass spectrometry (OEMS) and X-ray photoelectron spectroscopy (XPS). The evolution of mass and the mechanical properties of the SEI are directly correlated to the electrode impedance. Electrolyte reduction at the anode carbon active material initiates dissolution, diffusion, and deposition of reaction side products throughout the cell and increases electrolyte viscosity and the ohmic cell resistance as a result. On Cu the reduction of CuO and HF occurs at >1.5 V and forms an initial LiF-rich interphase while electrolyte solvent reduction at <0.8 V vs Li/Li adds a second, less rigid layer on top. Both the shear storage modulus and viscosity of the SEI generally increase upon cycling but-along with the SEI Li diffusion coefficient-also respond reversibly to electrode potential, likely as a result of Li/EC interfacial concentration changes. Combined EIS-EQCM-D provides unique prospects for further studies of the highly dynamic structure-function relationships of electrode interphases in Li ion batteries.
已开发出一种带有耗散监测的原位电化学石英晶体微天平（EQCM-D），并结合原位电化学阻抗谱（EIS），用于研究锂离子电池中铜集流体上固体电解质界面（SEI）的形成。这些发现得到了EIS模拟以及在线电化学质谱（OEMS）和X射线光电子能谱（XPS）等补充分析技术的支持。SEI的质量演变和机械性能与电极阻抗直接相关。阳极碳活性材料处的电解质还原引发了整个电池中反应副产物的溶解、扩散和沉积，结果增加了电解质粘度和电池欧姆电阻。在铜上，CuO和HF的还原在>1.5V时发生，形成富含LiF的初始界面，而相对于Li/Li在<0.8V时电解质溶剂的还原则在顶部添加了第二个刚性较小的层。SEI的剪切储能模量和粘度通常在循环时增加，但与SEI的Li扩散系数一起，也会对电极电位产生可逆响应，这可能是由于Li/EC界面浓度变化所致。EIS-EQCM-D联用为进一步研究锂离子电池中电极界面高度动态的结构-功能关系提供了独特的前景。
