Making Li-ion batteries safer

What makes them invaluable is their energy density - two to ten times more than other battery technologies.

However, Lithium-ion’s efficiency comes at a price. It’s the only mainstream battery chemistry that uses a flammable substance as an electrolyte, so while it’s more efficient than battery technologies with water-based electrolytes, such as nickel-cadmium and nickel-metal hydride, it also presents a greater fire risk. If overcharged or overheated, Li-ion cells tend to degrade with disastrous consequences.

While packaging and quality of the batteries themselves often are the key to preventing such consequences, designing multi-cell battery packs involves additional considerations. The fact is that no two cells, even from the same manufacturing batch, are identical in terms of state of charge (SOC), self-discharge rates, impedance, capacity and temperature characteristics. And that poses a challenge; when cells are placed in series and a battery charger monitors the voltage of the entire string, some cells can be overcharged.

To address this issue, engineers can implement cell balancing, which equalises the voltages and State-Of-Charge (SOC) among the cells, when they are at full charge. Balancing can be either voltage-based or SOC-based. It’s a non-trivial task that - aims both to increase the life of a battery pack and to enhance battery safety.

As battery-powered applications proliferate, designing for safe, efficient operation through cell balancing has assumed paramount importance.

Download the Texas Instruments whitepaper below. It examines the tradeoffs between various approaches.