No abstract

No abstract

Calendar aging of lithium metal batteries, in which cells' components degrade internally due to chemical reactions while no current is being applied, is a relatively unstudied field. In this work, a model to predict calendar aging of lithium metal cells is developed using two sets of readily obtainable data: solid electrolyte interphase (SEI) layer composition (measured via X‐ray photoelectron spectroscopy) and SEI stability (measured as a degradation rate using a simple constant current–constant voltage charging protocol). Electrolyte properties such as volume and salt concentration are varied in order to determine their effect on SEI stability and composition, with subsequent impacts to calendar aging. Lower salt concentrations produce a solvent‐based, more soluble SEI, while the highest concentration produces a salt‐based, less soluble SEI. Higher electrolyte volumes promote dissolution of the SEI and thus decrease its stability. The model predicts that lithium metal would be the limiting factor in calendar aging, depleting long before the electrolyte does. Additionally, the relative composition of the electrolyte during aging is modeled and found to eventually converge to the same value independent of initial salt concentration.

No abstract

Understanding the behavior of lithium-ion batteries exposed to thermal excursion is of great interest to plug-in hybrid electric vehicle (PHEV) applications, because vehicles often endure wide weather conditions in operation. Here we investigate a composite {LixMn2O4 + LixNi1/3Mn1/3Co1/3O2}-based commercial cell design to assess performance and degradation under thermal excursion from 25°C; through −20°C, −5°C, 10°C, 25°C, 40°C, and 60°C; to 25°C. In each isothermal regime, a reference performance test with charge and discharge cycles at C/25, C/5, C/2, 1C, and 2C is conducted to quantify cell capacity, rate capability, and other performance variations. The capacity fade caused by the thermal excursion is attributed to origins including loss of active material, degradation in reaction kinetics, and the ohmic resistance increases. Using electrochemical inference techniques, we found that thermal excursion in the range of −5°C to 40°C is benign to capacity fade. Exposure to −20°C and 60°C respectively leads to irreversible fade. The capacity fade at −20°C induced Li inventory loss and did not cause kinetic degradation, whereas the exposure at 60°C resulted in degradation in reaction kinetics. The evaluation protocols and results are helpful in assisting the study of path dependence of cell degradation in thermal aging.