Electrolyte Reactivity at Negative Electrodes
Parasitic reactions in negative electrodes are a major cause of lithium ion battery fade. In this thesis, studies regarding parasitic reactions at the negative electrode, especially on inactive materials, were explored using a newly developed type of symmetric cell, termed double half-cells (DHCs). DHCs are designed to provide a precise and accurate tool to measure the irreversible capacity that only requires the use of a standard charger. Quantitative electrolyte reactivities on Cu, Ni, 304 stainless steel (SS), Ti, Fe, Mo, and TiN, were obtained, through cycling graphite/inactive material blended electrodes in DHCs. Combining the results from electrolyte reactivity, initial irreversible capacity, and impedance growth, TiN and Ti were found to have the lowest cathodic electrolyte reactivity in both vinylene carbonate (VC)-free and VC-containing electrolyte, with a reactivity less than graphite. In contrast, the commonly used negative electrode inactive materials: Cu (for the current collector) and Ni (tabs) have high irreversible capacities, high electrolyte reaction rates (2-3.5 times graphite) and high impedance growth. These studies show that the current materials widely in use today at the negative electrode could be reducing the lifetime and rate capability of Li-ion batteries. The use of more inert materials, such as Ti or TiN, may result in an increase of Li-ion battery cycle life.