The concepts of 'calendar life' and 'capacity loss' during lithium-ion battery storage are critical metrics that define the reliability and economic viability of these energy storage solutions. The calendar life of a lithium-ion battery refers to the total time a battery can retain a usable capacity while in storage without being cycled. Capacity loss, on the other hand, is the reduction in the amount of energy a battery can store or deliver after a certain period, often due to chemical changes within the battery during storage or use.
The ENPOLITE plots shown below compare several hundred battery cells in a single bubble plot derived from a raw dataset. The lifetime plot is a visual representation of how storage conditions affect the lifespan of various li-ion cells. The plot is a useful tool, offering insights into the optimal storage conditions for different types of cells.
The first thing to note is the legend. The 'Bubble size' corresponds to the number of days per loss of 1 Wh/kg, serving as a relative measure of the cell's lifespan. Larger bubbles indicate a longer lifespan before the cell loses a significant amount of its storable energy. The 'Reference' buble size is set at 100 days per loss of 1 Wh/kg (at the bottom-right side).
The graph encapsulates data from a total of 307 cells, each tested at multiple specific storage energies (denoted along the x-axis) and at various storage temperatures (along the y-axis).
The mauve-colored bubbles stand out, denoting the exceptional performance of the NMC cells, specifically the NMC11 type. These cells demonstrated remarkable lifespan, particularly at a storage temperature of 20 °C, outperforming others by maintaining their capacity even after 580 days of storage at a high energy level. The robustness of these cells is attributed to their single-crystal NMC532 cathode particles and specialized electrolyte additives.
Some cells exhibited over 100% capacity retention over time. This seemingly paradoxical result is shown by the bubbles with maximum area & transparent coloration, indicating a remarkable lifetime that defies the typical degradation expectation.
The dataset covers specific storage energies ranging from an inert 0 Wh/kg to a substantial 225 Wh/kg. This extensive range is demonstrated by the dark-red bubbles, which represent data from tests that explored the full potential of specific storage energies at both 25 and 50 °C.
The influence of storage temperature on cell lifetime is significantly evident. Higher temperatures correlate with a shorter lifespan across the datasets, reinforcing the importance of temperature management in battery storage.
Comments