Professor Gerd Ceder, co-leader of the MIT battery IRG, and MRSEC-supported graduate student ByoungWoo Kang wanted to dispel the myth that batteries have low power rates.
Basing their theory on a 2004 paper with Anton Van der Ven and Dane Morgan in which extremely high lithium ion speed was predicted in LiFePO4, Ceder and Kang realized that they needed to change the surface structure of the lithium iron phosphate battery material (LiFePO4) in order to prove this high power rate experimentally.
When a lithium (Li) battery is discharged, Li ions move from the anode, through the electrolyte, into the active cathode material.Â’ While the theory shows that once Li arrives at the surface of the particles, Li diffusion to the inside can be lighting fast, obstacles exist for the Li to get there fast enough. Kang and Ceder speculated that absorption on the surface and movement of Li to the proper entry surfaces was limiting the discharge rate. By using computer calculations of the material, they created a modified composition of LiFePO4 and processing scheme that leaves a glassy, fast ion conductor on the surface, thereby leading the lithium ions rapidly to the proper "tunnels" for more efficient movement.
The researchers have demonstrated small batteries that can deliver their full energy in 10 seconds to 1 minute. Such high rate materials can be valuable in everything from rapidly charging cell phones to high-powered hybrid and plug-in hybrid vehicles.
While LiFePO4 may not be the best material for cell phones and laptops due to its lower energy density than current materials, Ceder and Kang think that there may be other materials out there with very high rate capability and currently have just such a large computational search underway. Ceder believes the work could make it into the marketplace within two to three years.
