Stanford University researchers have developed rechargeable batteries that can store up to six times more charge than ones that are currently commercially available.
Rechargeable batteries are everywhere. In rechargeable batteries, electrons travel from one side to another, and recharging reverts the chemistry back to its original state to await another use. Sodium-chlorine or lithium-chlorine based rechargeable batteries show promise in terms of charging rates and energy density. However, chlorine is too reactive and there is a challenge to convert it back to a chloride with high efficiency.
Researchers from Stanford University have developed faster rechargeable batteries by improving existing battery technologies using thionyl chloride. This chemical is one of the main ingredients of lithium-thionyl chloride batteries.
Researchers in one of their experiments found that the conversion of one chemical to another had somehow stabilized, resulting in some rechargeability. “I didn’t think it was possible,” Stanford chemistry Professor Hongjie Dai said. “It took us about at least a year to really realize what was going on.”
The team studied the reversible chemistries and tried ways to make this process more efficient with many different materials for the battery’s positive electrode. They achieved a breakthrough when they formed the electrode using an advanced porous carbon material. According to the researchers, the carbon material has a nanosphere structure filled with many ultra-tiny pores. In practice, these hollow spheres act like a sponge, sopping up copious amounts of otherwise touchy chlorine molecules and storing them for later conversion to salt inside the micropores.
“The chlorine molecule is being trapped and protected in the tiny pores of the carbon nanospheres when the battery is charged,” doctoral candidate Guanzhou Zhu explained. “Then, when the battery needs to be drained or discharged, we can discharge the battery and convert chlorine to make NaCl—table salt—and repeat this process over many cycles. We can cycle up to 200 times currently and there’s still room for improvement.”
Researchers have achieved 1,200 milliamp hours per gram of positive electrode material, while the capacity of commercial lithium-ion batteries today is up to 200 milliamp hours per gram.
The research appeared in the journal Nature.