Eberhard Meissner
Bio
Eberhard Meissner has been conducting research on batteries since 1985. With VARTA Batterie AG and later with Johnson Controls Power Solutions, he managed for 27 years various development teams in the fields of lead–acid batteries and lithium-ion batteries. Retired in 2019, he continues working on batteries, especially in analysis of micro-scale mechanisms behind the macro-scale effects witnessed in battery behaviour. Eberhard has been presenting at ELBC since 1990 and is author and co-author of numerous publications. In 2014, he was awarded the 2014 Gaston Planté Medal for his contribution to the development of lead–acid battery science and technology.
The negative electrode is not only the site of the NAM charge/discharge (main) reaction, but also of two independent side reactions: hydrogen evolution (H2↑) and oxygen reduction (O2↓). The three internal electro-chemical charge-transfer currents sum up to negative electrode’s external electrical current iel = icharge-discharge + iH2↑ + iO2↓ measured at the battery terminal. As electrons required for cathodic side reactions may be provided at any time by anodic NAM discharge, the external electrical current does not control the rates of internal reactions. Species involved in main reactions and in hydrogen evolution are abundant in the electrolyte; therefore, their kinetics depend mainly (in different manners) on local potential, acid concentration and temperature. However, oxygen is usually sparse at NAM surface;the rate of oxygen reduction is mainly controlled by actual local concentration of oxygen dissolved in the electrolyte. Therefore, hydrogen evolution and the presence of hydrogen formed already during previous operation, stored either as gas in micro-bubbles or dissolved in electrolyte – may impede oxygen access to the NAM surface according Henry’s Law. This may influence oxygen reduction rate: sudden “H2↑ bursts” may even “wash out” O2↓ from electrolyte and gas bubbles. Less access of oxygen to NAM and lower oxygen reduction (O2↓) reaction may increase loss of water from the cell. As local potential, acid concentration and oxygen concentration may vary over all the NAM sites of an electrode, complex distributions of charge-transfer reaction currents may be generated over both electrode plane and electrode thickness. The presentation will address consequences from these considerations for battery operation and long-term behaviour, especially in dynamic duties, for both flooded and valve-regulated lead batteries.
