Extending battery lifespan and capacity through self-healing materials

One of the greatest challenges in the fight against climate change is energy storage. Fossil fuel essentially stores itself, with its energy locked inside its own chemical bonds. But how do you store more sustainable, but otherwise ephemeral, forms of energy, like the power of the wind and sun?

For Eric Detsi, associate professor in materials science and engineering, the answer is batteries, with the caveat that batteries powerful enough to meet the future's energy demands-the International Energy Agency projects that worldwide battery capacity will need to sextuple by 2030-do not yet exist.

In most batteries used today, from the disposable alkaline batteries in household appliances like alarm clocks to the rechargeable lithium-ion batteries in hybrid and electric vehicles, the electrodes between which ions flow are typically made of solid materials like metal oxides or graphite. But, as Detsi points out, each cycle of charging and discharging the battery damages the material, because the electrodes expand and contract, sometimes by as much as 300%, which is one of the reasons why even rechargeable batteries gradually lose capacity and eventually fail.

"There is a need for materials that can store a large amount of lithium, sodium and magnesium for use in high-performance batteries," says Detsi. "The problem is that the more lithium, sodium or magnesium a battery material can store, the more it expands and shrinks during charging and discharging, resulting in huge volume change."

Detsi's group has been studying batteries made primarily of sodium and magnesium, which are cheaper and less ethically fraught since sodium and magnesium are plentiful in the earth's crust. More importantly, sodium and magnesium resources are abundant in the U.S.

The group is using these metals to develop electrodes that shift between liquid and solid states to avoid damage during charge cycles while still being easy to manufacture. "When the material is in the solid phase, it will start degrading due to the huge volume changes occurring during charge storage," says Detsi. "However, when the material transforms from solid to liquid, it 'heals' itself by recovering from volume-change-induced degradation."

Read more at Penn Engineering Today.