Argonne National Laboratory has developed a way to make commercially viable lithium-ion (Li-ion) batteries for plug-in hybrid electric vehicles (PHEVs) and electric vehicles that are safer, will last longer, and cost less than current Li-ion batteries. Argonne researchers, Drs. Khalil Amine and Zonghai Chen, accomplished this goal by making only a small change to the Li-ion chemistry. The scientists are testing a new molecule based on boron and fluorine as an additive in the electrolyte of Li-ion batteries. By adding a small amount of this substance to battery cells, they found they can keep individual cells in the battery from reaching unsafe voltage levels. The new molecule picks up electrons and keeps the cell charge from increasing if the cell reaches an unsafe voltage level.
Reliance on rechargeable lithium batteries is growing because they offer the greatest chance for breakthroughs. The development of hybrid electric vehicles (HEVs) and PHEVs can be increased by removing barriers related to calendar and operating life, safety, and cost. The performance limitations arise largely because of uncontrolled reactions that occur at high and low potentials at the electrolyte/electrode interface, leading to high cell impedance, reduced energy and power output, and a limited cycle life (less than two years). Argonne’s invention is a charge transfer mechanism for Li-ion battery overcharge protection. When the battery is overcharged, the redox shuttle is oxidized by losing an electron to the positive electrode. The radical cation formed is then diffused back to the negative electrode, causing the cation to obtain an electron and be reduced. The net reaction is to shuttle electrons from the positive electrode to the negative electrode without causing chemical damage to the battery (Figure 1).
Applications and Industries
- Hybrid electric vehicles
- Plug-in hybrid electric vehicles
- Prevents overcharge and improves safety
- Balances cell in a battery pack
- Reduces cost
- Increases reliability
- Saves $100–200 per battery pack, thanks to the change in chemistry. Savings result from lower battery manufacturing and maintenance costs, as well as from an extension of battery life.
- Provides 500+ overcharge cycles compared to others that work for only a few cycles