NXP Semiconductors, Texas Instruments, Analog Devices, Infineon Technologies and others are digging in for a battle to build better battery management chips at the heart of hybrid and electric cars. They are rolling out more advanced chips that can squeeze every drop of energy from the battery cells in electric cars and protect them from harm or losing charge capacity prematurely.
As the automobile industry confronts the looming electric vehicle (EV) era, many of the world's top car manufacturers are trying to design batteries that are safer, charge faster and have more energy than the lithium-ion batteries currently in use. Every EV is packed with as many battery cells as possible to increase the capacity of the modules and packs housing them, which often weigh thousands of pounds and come in various sizes and configurations.
Every cell in the battery pack must be wired to a battery management IC that is used to watch over the voltage, current and temperature of all of the battery cells crammed in a module to keep them from expending precious energy. The capacity of lithium-ion battery cells diminishes over time and usage so every cell in the system needs to be managed and regulated to keep it within a safe charge level and boost performance.
According to industry insiders, improvements in these battery monitors can extend the driving range of an EV by around 5% to 10% in a single leap. Now some of the largest players in the semiconductor industry are wrestling to win more of the fast-growing market for battery management chips.
Every EV today has several major building blocks. The onboard charger, or OBC, is used to convert AC current to the DC current required to recharge the battery pack. The traction inverter is used to convert DC from the battery pack into AC to propel the main electric motor driving the EV, playing the same role as a traditional engine management system (EMS).
The dc-dc converter inside the EV pulls power from the battery and steps down the voltage to supply loads to electronics such as headlights, power windows, seat controls and side mirrors.
The battery management system, or BMS, acts as the brains of the battery pack in the car by carefully managing the output, charge and discharge of the battery during its lifetime. The system also accurately monitors each independent battery cell and the pack housing them to ensure that they are operating safely. The BMS also directly impacts the electric car's range, not only on its current drive, but also over the lifespan of its internal battery.
The system also has safeguards to protect the battery from permanent damage. It balances out the levels of charge in the battery to increase the range per charge as well.
The current generation of lithium ion (Li-ion) batteries in cars now are feats of engineering. These batteries, which powered the global revolution in consumer electronics, pack lots of energy into a small package, have slow self-discharge rates and handle high voltages. But despite its overall advantages, the lithium-ion formulations currently in use are a huge cost. The battery pack is by far the single most expensive component in electric vehicles.
Battery costs have long been the major challenge to making electric cars affordable for the masses. A battery currently accounts for 25% to 40% of the EV's cost, analysts estimate.
While the Li-ion battery is the most expensive component in electric cars, it is also among the most fragile. They can become a safety hazard because they sport flammable substances, and if they are damaged or incorrectly charged or drained, they can overheat uncontrollably in a "thermal runaway" that can result in smoke, fires or even explosions. Sudden surges in voltage or temperature and short-circuits can also have harsh consequences.
To prolong the battery's life and protect it from damage, the BMS needs to continuously assess the state of charge (SOC) and state of health (SOH) of the cells and the modules and packs housing them.
The SOC is a measure of the remaining charge in the battery compared to its total charging capacity, ranging from 0% (completely empty) to 100% (fully charged). An alternate form of the same measurement is depth of discharge (DoD), which ranges from 100% to 0%. The state of charge informs the driver how long the electric vehicle can last on its remaining charge.
Overcharging or undercharging can also devastate the battery cells. The battery can become stressed, leading to premature charge termination and a reduction in the battery’s useful life.
The SOH represents the remaining lifespan of the battery by comparing its current status to its factory specifications. In general, lithium-ion batteries roll out of a production plant at 100% before losing storage capacity over time due to the stress of continuous charging and discharging. Once the battery capacity become insufficient for EVs, they need to be replaced.
But because repairing or replacing the battery packs can cost many thousands of dollars, auto manufacturers are trying to prolong the battery's total capacity for as long as possible.