Why Lithium-Ion Batteries Are Not Used as 12V Batteries in Premium Cars

In the automotive world, lead-acid batteries have long been the standard for 12V power supplies. Despite advancements in technology, lithium-ion (Li-ion) batteries have not yet made the leap to replacing them in premium cars. This article explores the reasons behind this decision, focusing on the operational constraints of Li-ion batteries and the advantages of lead-acid batteries.

The Limitations of Lithium-Ion Batteries

Lithium-ion batteries, while offering several advantages such as longer life and lighter weight, face significant challenges when used in 12V automotive applications. One of the critical hurdles is their temperature limitations. Li-ion batteries are highly sensitive to both high and low temperatures. For instance, a popular Molicell 21700 battery is only rated for a narrow operational temperature range of 0–60°C. Beyond this range, the battery's performance declines dramatically, and in extreme cases, it can cause thermal runaway—an extremely dangerous condition that can lead to overheating and fire.

When a car is parked in the sun, even on a chilly day, the interior temperature can rise to levels that exceed the battery's safe operating range. Additionally, internal combustion (IC) engines warm up the battery during operation, but once the engine starts, the immediate current demand can overwhelm the Li-ion battery. This high initial demand can lead to damages such as charge separation membranes and is a significant risk of deteriorating battery performance and potentially causing a fire. This operational temperature constraint makes Li-ion batteries unsuitable for non-electric drivetrain vehicles in most non-urban environments.

Cost and Performance Disparities

While cost is often cited as a reason for the continued use of lead-acid batteries, it is more about the performance and safety trade-offs. Lithium-ion batteries, despite being more expensive, are not a practical solution for high-performance, high-demand automotive applications. For instance, demanding a current output of 400A from a Li-ion battery can lead to significant thermal stresses, shortening the battery's lifespan and increasing the risk of thermal runaway.

The chemistry of Li-ion batteries is optimized for multiple discharge cycles rather than sustained high current draws. This is in contrast to lead-acid batteries, which are designed to handle high output currents without degrading as quickly. Modern premium cars, such as those in Tesla's lineup, use Lithium-ion batteries to power the electric drivetrain but rely on lead-acid batteries for starting and ancillary systems due to their better performance in these high-demand, low-temperature scenarios.

Advantages of Lead-Acid Batteries

Lead-acid batteries, particularly advanced variations like Absorbed Glass Mat (AGM) batteries, offer a more robust and reliable solution for 12V automotive applications. These batteries are designed to handle high current demands and are better suited for starting engines, which require a burst of power. AGM batteries are a hybrid between starter and deep-cycle batteries, providing the best of both worlds.

Their chemical composition allows them to maintain a higher charge level, which is beneficial for quick starts and frequent stop-and-go driving. In contrast, Li-ion batteries perform best when they are allowed to cycle through multiple charge and discharge cycles, making them less ideal for starting vehicles. Lead-acid batteries also offer better durability and safety in extreme temperatures, which is a significant factor in automotive applications.

Conclusion

In summary, while lithium-ion batteries have advanced significantly in recent years, their operational limitations at extreme temperatures and their higher cost make them unsuitable for 12V automotive applications, especially in premium vehicles. Lead-acid batteries, particularly AGM types, continue to provide the performance and reliability necessary for starting engines and powering ancillary systems in cars.

References

[1] Molicell 21700 Battery Specifications: [2] Tesla Battery Management System: _gb/tesla-battery-management-system [3] Lithium-Ion Battery Chemistry: [4] Lead-Acid Battery Chemistry: