Multiscale and Multimodal Characterization of Electrochemical and Mechanical Properties on Energy Materials Surfaces and Interfaces

Abstract

Atomic Force Microscopy (AFM) is a powerful tool to study various properties of the materials. AFM applications are wide and are still growing in many fields. In this work, AFM will be used for battery and nanoparticles multi characterization.The Li-ion battery due to its high energy density and operating voltage has been extensively used in various electronic devices, energy grids, and in the automotive industry. However, mechanical improvements, such as the increase in the amount of the active material have already reached their limits, so for further development, it is necessary to study the chemical reactions, the aging mechanism, and the properties and structures of the battery materials at multiscale. In this work, a novel LiNi0.6Mn0.2Co0.2O2 (NCM622) cathode and natural graphite anode have been investigated as a testing battery system. The local electrochemical functionalities and their relationship with surface morphology have been examined by observing the concentration and distribution of Li-ion pathways for different cycle states (state of charge (SOC)) as well as for several cycles using Electrochemical Strain Microscopy (ESM). In addition, the conductive AFM (c-AFM) analysis was also made to explore the conduction paths, and the elastic modulus, was measured to observe the mechanical properties change. In addition, solid electrolyte interface (SEI) parameters were also investigated along with the mechanical properties. Moreover, using electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM), dynamic behavior, resistance, and structural heterogeneities were also characterized. The experimental results of the integrated multiscale analysis demonstrate the substantial variations of properties at different SOC and cycles, as well as establish the relationship between the electrical, mechanical and morphological surface properties and lithium-ion distributions/redistribution. A study on the relationship between the lithium-ion distribution and the structure of the electrode materials will provide a further understanding of property changes at different SOC and the electrochemical degradation mechanisms of lithium-ion rechargeable batteries at the nanoscale.Copper metal has become of growing interest these days due to its excellent electrical properties, abundant resources, and inexpensiveness compared to noble metals. Moreover, the copper nanoparticles (Cu NPs) have received even more attention due to prominent potential applications in catalysis and nano-electronic devices field as a result of high surface area and unique properties. However, the copper surface is prone to undesirable oxidation processes, which have not been effectively prevented yet. In this work, the novel material (electride with Cu NPs) proposed by Sung Wng Kim's Group from Sungkyunkwan University was characterized using Kelvin Probe Force Microscopy (KPFM) mode in AFM. It was observed that Cu NPs had lower work function than bulk copper, indicating the negative charge state, which helped to hinder the oxidation of Cu NPs at the ambient conditions. Two different electrides (Gd2C and Ca2N) with Cu NPs were tested and the similar phenomenon was detected, implying the universal mechanism for electrons transfer from electride to Cu NPs. Thus, this study predicts the emerging applications of non-oxidized Cu NPs in the nano-electronic devices and catalysis field.