鋰氧氣電池之釕貴金屬催化反應機制

Abstract

近年來鋰氧氣電池之研究受到高度重視，因其具極高之能量密度，被視為新世代電動車能源。然而目前於實際應用上仍然存在許多挑戰，例如：過電位高、循環穩定性差、低充電速率，此些問題均與鋰氧氣電池放電產物Li2O2之差勁導電性、導離子性相關。目前研究中，普遍使用貴金屬釕Ru進行催化，並與多壁奈米碳管形成陰極複合材料(Ru/CNT)，使用Ru/CNT陰極具大表面積、高放電容量與較低過電位之特點。然而我們對於釕金屬之催化機制了解甚少，且相較於傳統鋰離子電池仍然存在過高之過電位與低循環性能。本研究藉由濺鍍技術控制局部性分布之釕金屬催化劑，探討貴金屬Ru之充電反應催化機制，並使用奈米X光繞射儀觀測Li2O2之分解與Ru之局部性分布關係。本研究顯示液態電池系統中Li2O2為均相分解，固態電池系統中Li2O2為異相分解，與Ru接觸之Li2O2先行被分解，表示電解液(TEGDME)參與Ru之催化作用，Ru催化效果與電解液之分解相關，其分解之可溶性副產物充當電子受體Acceptor或Redox Mediator (RM)，幫助絕緣之Li2O2傳導電子，藉此有效降低充電過電位，但同時也縮短電池之循環壽命。In recent years, research on lithium-oxygen battery has been highly valued, because of their extremely high energy density, it is regarded as the energy source of the new generation of electric vehicles. However, practical applications still face many challenges, such as high overpotential, poor cycle stability, and low charging rate. These problems are all related to the poor conductivity and ion conductivity of Li2O2, the discharge product of lithium-oxygen batteries. In the current research, the noble metal ruthenium Ru is commonly used for catalysis, and the cathode composite material (Ru/CNT) is formed with multi-walled carbon nanotubes. The Ru/CNT cathode has the characteristics of a large surface area, high discharge capacity, and low overpotential. However, we know little about the catalytic mechanism of ruthenium metal, and compared with traditional lithium-ion batteries, there are still too high overpotential and low cycle performance.In this study, the locally distributed ruthenium metal catalyst was controlled by sputtering technology. The catalytic mechanism of the charging reaction of noble metal Ru was investigated. The relationship between the decomposition of Li2O2 and the local distribution of Ru was observed using a nanometer X-ray diffractometer. This study shows that Li2O2 decomposes in a homogeneous process in a liquid battery system, and Li2O2 decomposes in a heterogeneous process in a solid-state battery system. The Li2O2 in contact with Ru is decomposed first, which means that the electrolyte (TEGDME) participates in the catalysis of Ru. The catalytic effect of Ru is related to the decomposition of the electrolyte. The soluble by-products of its decomposition act as electron acceptors or Redox Mediators (RM), helping the insulating Li2O2 conduct electrons, thereby effectively reducing the charging overpotential and shortening the battery's cycle life.