First Self-Healing, High Capacity Battery Electrode Created

A team of international researchers has created a self-healing battery electrode that can be used to improve the longevity and performance of lithium batteries. The improved batteries can be incorporated in next generation electric cars, cell phones and other devices.

Lithium ion batteries are the popular rechargeable batteries that are used in cell phones, laptops and iPods. The energy density of this lithium ion is high and it is a low maintenance battery. They can go through hundreds of charge and discharge cycles. Despite these advantages, the lithium ion batteries are not completely flawless.

One of the major concerns is 'aging'. The silicon in the lithium batteries has the capacity to hold the electrons for a longer period. But at the same time this silicon material expands three times its normal size during the charging process and when electrons are released it again shrinks. This swelling and shrinking process leads to cracks in the brittle silicon material, which finally falls apart due to the wear and tear. After a year there is deterioration in the capacity, irrespective of its usage. The battery can last maximum for two years.  

But researchers at the Stanford University have overcome this drawback and have invented a battery that might never wear out.

The secret to it is the stretchy polymer coating for the electrodes that is based on a research used to make electronic skin coatings for robots, prosthetic limbs and sensors. This stretchy polymer binds the electrodes together and heals the tiny cracks that develop during the battery operation. Tiny nanoparticles of carbon were added in the stretchy polymer to aid in electricity conduction.

"Self-healing is very important for the survival and long lifetimes of animals and plants," said Chao Wang, a postdoctoral researcher at Stanford and one of the two principal authors of the paper. "We want to incorporate this feature into lithium ion batteries so they will have a long lifetime as well."

The researchers created the self-healing coating by weakening some of the chemical bonds present within the polymer due to which the material falls apart easily after which the broken ends automatically bind together due to chemical attractions.

"We found that silicon electrodes lasted 10 times longer when coated with the self-healing polymer, which repaired any cracks within just a few hours," said Zhenan Bao, a professor of chemical engineering at Stanford.

For over 100 charge and discharge cycles the electrode functioned well without losing the energy storage capacity. Though a cell phone has 50 cycles and an electric vehicle 3,000 cycles, this new creation shows that the capacity of storing energy is in the practical range.

The researchers strongly believe that this self-healing polymer could work for other electrode materials too.

The findings have been documented in Nature Chemistry.