Area Oversizing of Lithium Metal Electrodes in Solid‐State Batteries: Relevance for Overvoltage and thus Performance?. Issue 10 (9th April 2021) - Stolz, Lukas
Abstract: Systematic and systemic research and development of solid electrolytes for lithium batteries requires a reliable and reproducible benchmark cell system. Therefore, factors relevant for performance, such as temperature, voltage operation range, or specific current, should be defined and reported. However, performance can also be sensitive to apparently inconspicuous and overlooked factors, such as area oversizing of the lithium electrode and the solid electrolyte membrane (relative to the cathode area). In this study, area oversizing is found to diminish polarization and improves the performance in LiNi0.6 Mn0.2 Co0.2 O2 (NMC622)||Li cells, with a more pronounced effect under kinetically harsh conditions (e. g., low temperature and/or high current density). For validity reasons, the polarization behavior is also investigated in Li||Li symmetric cells. Given the mathematical conformity of the characteristic overvoltage behavior with the Sand's equation, the beneficial effect is attributed to lower depletion of Li ions at the electrode/electrolyte interface. In this regard, the highest possible effect of area oversizing on the performance is discussed, that is when the accompanied decrease in current density and overvoltage overcomes the Sand's threshold limit. This scenario entirely prevents the capacity decay attributable to Li + depletion and is in line with the mathematically predicted values. Abstract : Large and in charge : Oversizing the area of Li and electrolyte membranes should not be disregarded for systematic development of Li metal batteries, as it can have a significant impact on the performance, particularly under kinetically harsher conditions, when the relation between the performance and current density becomes sensitive, such as at low temperatures and/or higher rates.