We usually think batteries wear out because we repeatedly charge and use them.
But batteries spend most of their lives doing nothing, and new research suggests that this quiet time can cause surprisingly large losses in some next-generation battery technologies.
Researchers at the UCLA Samueli School of Engineering have investigated what happens to metal-based batteries while they sit unused.
Two studies, published in Joule and Nature Communications, reveal why some batteries lose capacity during storage and offer possible ways to slow the damage.
This process is known as “calendar aging”—the gradual deterioration of a battery over time even when it is not being charged or discharged.
According to the researchers, batteries can spend more than 70% of their lifetime at rest, yet most battery research has focused on what happens during repeated charging and use.
That could be an important oversight.
Scientists are exploring metals such as zinc, sodium and magnesium as possible alternatives to today’s lithium-ion batteries. Researchers usually evaluate these technologies partly by measuring their cycling efficiency, or how well a battery retains and recovers energy through repeated charge-and-discharge cycles.
But a battery that performs well during cycling may still deteriorate significantly while sitting unused.
In the Joule study, researchers compared batteries using lithium, sodium, aluminum and magnesium metal anodes. All showed high cycling efficiency, but their performance during storage was very different.
After sitting unused for two weeks, the lithium, sodium and aluminum batteries had lost roughly 10% to 20% of their capacity. Over months or years, such losses could seriously reduce a battery’s useful life.
Magnesium performed dramatically better, losing less than 0.5%.
The researchers found that magnesium naturally develops a protective layer on its surface while resting. This layer greatly reduces corrosion. When the battery starts charging again, the protective layer can reversibly dissolve, giving magnesium an unusually adaptable defense against idle-time damage.
The second study focused on zinc batteries and identified another possible solution.
Researchers examined the electrolyte, the substance that carries electrically charged particles between a battery’s electrodes. They discovered that water molecules surrounding dissolved zinc ions were especially reactive and played a major role in corroding the zinc.
With a conventional electrolyte, a zinc battery could lose more than one-third of its capacity after sitting unused for only 24 hours.
The researchers redesigned the electrolyte by making it extremely dilute and adding carefully selected ingredients. With the new formulation, capacity loss dropped to less than 1.5% after 24 hours. The battery could also continue operating stably through thousands of charging cycles.
Although the zinc research is still at the proof-of-concept stage, the researchers believe similar strategies could work with other metal-based batteries.
The findings suggest that future batteries should be designed not only to survive thousands of charging cycles but also to remain healthy during the long periods when nothing is happening.
If these ideas can be successfully scaled up, they could eventually help create longer-lasting batteries for electric vehicles, electronics and renewable-energy storage systems.
