Investigation of the Reaction Mechanism of Cu(II)O Conversion Material As High Capacity Anode Material for Lithium-Ion Batterie

Abstract

Introduction - CuO as a transition metal oxide has been used as Li-CuO primary battery for more than 30 years and the discharge reaction mechanism has been investigated ever since1. However, debates still exist as regarding to whether intermediate composites would be formed during the electrochemical discharge. Nowadays, CuO has become a powerful electrode candidate in the lithium-ion battery field because of its high theoretical capacity and nontoxic nature2. As the anode material for lithium-ion batteries, traditional graphitic carbon such as mesocarbon microbeads (MCMB) and natural graphite are under challenge of CuO due to their limited specific capacities, which cannot satisfy the demand for future energy storage, especially for electric vehicle application3. Experimental - With a commercial available CuO as raw material, a high capacity retaining CuO anode electrode has been fabricated with modifying/varying electrode preparation parameters. Among them, particle size and binder usage, as well as tableting pressure have proved to have great influence on the electrochemical performance of the cell. When matched with a commercial NMC cathode, the corresponding full pouch bag cell shows a specific capacity of 655.8mAh/g (capacity calculated based on CuO, Figure 1) within the voltage range of 0.7-4.0 V at room temperature. To understand the beneficial effect of the preparation method, the reaction mechanism of the modified CuO electrode is investigated. With the help of different characterization methods such as in-situ X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), electrochemical characterization (Cyclic Volatammerty, CCCV), a detailed picture can be obtained. In-situ XRD reveals phase changes at different voltages. Hence, the reaction between CuO and Li can be distinguished. Besides, the corresponding TEM images and X-ray Photoelectron Spectroscopy (XPS) analysis at different voltages allow to determine the thickness change of the electrolyte decomposition layer, which covers the active material and has been speculated to contribute to the capacity of the cell as well4. Furthermore, the catalytic activity of divided metallic copper is well known in organic chemistry when dealing with hydrogenation of olefin or carboxyl compounds5. To better understand the catalytic mechanism between metallic copper and the commonly used organic electrolytes, storage tests have been conducted to investigate if the electrolyte decomposition will be facilitated in LP30 electrolyte (EC:DMC 3:7, 1M LiPF6) with the appearance of pure copper particles. In addition, electrolytes are collected after charging the cells to different voltages to investigate whether a specific copper oxide which forms at that voltage has a particular effect on the electrolyte degradation. All the aged electrolytes are studied by means of Ion Chromatography (IC) and Gas chromatography–Mass Spectrometry (GC-MS). Acknowledgment – The authors would like to thank the German Research Foundation (DFG) for funding this work within the joint Priority Program 1473 “Materials with New Design for Improved Lithium Ion Batteries – WeNDeLIB”.