Evmenenko Guennadi, Fister Timothy T, Castro Fernando C, Chen Xinqi, Lee Byeongdu, Buchholz D Bruce, Dravid Vinayak P, Fenter Paul, Bedzyk Michael J
Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
Phys Chem Chem Phys. 2019 Apr 24;21(17):8897-8905. doi: 10.1039/c9cp01527b.
Observations of the initial lithiation of NiO electrodes demonstrate how to seed conversion reactions using interfaces in a thin film Ni/NiO bilayer architecture. Operando X-ray reflectivity (XRR) reveals that structural changes in a NiO film begin at potentials near the theoretical reduction potential (1.8-2.0 V) with detectable lithiation of both the buried Ni/NiO interface and the outer NiO surface that occur prior to the reaction of the NiO film. This initial conversion reaction is most pronounced in ultrathin NiO films (∼20 Å) with only small changes to the NiO film surface for thicker films (∼67 Å). The limited reactivity of thicker NiO films probed using operando grazing incidence small-angle X-ray scattering (GISAXS) shows the growth of nanoparticles at the electrode/electrolyte interface during initial lithium ion insertion, with a 16-20 Å average radius. Ex situ X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and scanning transmission electron microscopy/electron energy loss spectroscopy (STEM/EELS) confirm our conclusions about the morphological changes accompanying initial stage of lithiation in these conversion reaction electrodes. The present study reveals the interconnected challenges of solid-solid transitions, overpotentials, interfacial nucleation and kinetics, and transition metal dissolution in conversion-type electrodes that are critical for their use as electrodes in lithium-ion batteries.
对NiO电极初始锂化过程的观察表明了如何利用薄膜Ni/NiO双层结构中的界面引发转化反应。原位X射线反射率（XRR）显示，NiO薄膜的结构变化始于接近理论还原电位（1.8 - 2.0 V）的电位，在NiO薄膜发生反应之前，埋入的Ni/NiO界面和外部NiO表面都出现了可检测到的锂化现象。这种初始转化反应在超薄NiO薄膜（约20 Å）中最为明显，而对于较厚的薄膜（约67 Å），NiO薄膜表面只有微小变化。使用原位掠入射小角X射线散射（GISAXS）探测较厚NiO薄膜的有限反应活性，结果表明在初始锂离子插入过程中，电极/电解质界面处纳米颗粒的生长，其平均半径为16 - 20 Å。非原位X射线光电子能谱（XPS）、飞行时间二次离子质谱（ToF-SIMS）以及扫描透射电子显微镜/电子能量损失谱（STEM/EELS）证实了我们关于这些转化反应电极锂化初始阶段伴随的形态变化的结论。本研究揭示了固-固转变、过电位、界面成核与动力学以及过渡金属溶解等相互关联的挑战，这些对于转化型电极在锂离子电池中用作电极至关重要。
