Not all lithium-ion batteries are created equal
There’s a common perception that the lithium-ion batteries that power electric vehicles are not characteristically different from those that power our cell phones and laptops. While much of the technology is the same, there’s a big difference between powering an iPhone and a Model S. Despite astronomical improvements in recent decades, lithium-ion batteries are still reaching their maximum potential in terms of capabilities. They can have very high performance, but are occasionally temperamental—they have therefore been dubbed the “divas” of the energy world. Like any new technology, lithium-ion batteries can be both wondrous and problematic. As anyone who frequently uses a laptop or cell phone can attest, temperature can have a very noticeable impact on performance. Low temperatures inhibit the battery’s ability to discharge enough power and hold a charge, while high temperatures will degrade the battery’s performance and durability over time. Since these problems exist even with small electronics, it’s no surprise that similar problems plaguing electric vehicles have proved challenging to overcome. Thermal regulation is the key to creating higher performing lithium batteries, and is of particular importance for electric vehicles due to their size and exposure to external temperatures. Thermal management is also a critical aspect of the safety of electric vehicles, since “thermal runaway” when batteries overheat can pose a fire hazard. Thankfully, the electric vehicle industry’s need for batteries that provide sufficient power while maintaining optimal safety standards has pushed thermal management technology to the next level. A collective effort between the private sector and innovations developed in the national labs has yielded some impressive developments. First, consider what needs to be achieved and why. Thermal management is required to keep battery cells within desired temperature ranges, minimizing cell-to-cell variations in temperature and preventing the battery from going above or below acceptable limits. This maximizes the useful energy from the cells and battery pack. Ideally, thermal management systems themselves use little energy for operation. The reason thermal management is not utilized in cell phones is that these systems increase complexity, add cost, and consume additional energy. But in the case of electric vehicle batteries, which are of greater size and need to provide more energy than personal electronics batteries, most manufacturers agree that the value of a thermal management system in increasing the battery’s life and performance outweighs the additional cost and complexity. Thermal management systems are generally divided into aptly named air cooled and liquid cooled systems, and a fierce debate exists over which system is superior. According to Matt Keyser, senior engineer with the National Renewable Energy Laboratory, there are advantages to both systems. Air cooling systems are generally less complicated and lower cost, while liquid cooled systems take up less space and enable more aggressive driving, allowing the battery to handle a larger “pulse” of power. However, liquid cooling systems also have a slight potential to cause the liquid to leak, and repair can be costlier than for an air cooled system. Air systems will generally result in less temperature uniformity between cells, and may not work as quickly as a liquid cooled system. While air cooled systems can theoretically moderate heat as well as a liquid cooled system, the fan power required to do so would draw significant power from the engine. Entire industries are trying to solve this problem. Startups such as AllCell Technologies and the former A123 Systems have accomplished breakthroughs in thermal management. However, electric vehicle owners don’t have to wait for technology—they can take matters into their own hands. Motorists living in hot climates are advised against completely charging or discharging the battery. Charging the battery to 80 percent rather than 100 percent, and not completely depleting the battery, will improve performance. Furthermore, risking the temptation to drive hard and fast will reduce strain on the battery on hot days.