“Chemistry matters,” he says. “Lithium ion is a huge catch-all term for about 10 to 15 subchemistries. And they all have different characteristics.”
When evaluating lithium ion batteries, it’s important to consider whether they’re susceptible to thermal runaway, how quickly they can be charged or discharged (the c-rate), their efficiency in charging and discharging, and their energy density, he says.
Thermal Runaway Poses Hazards in Some Chemistries
Thermal runaway can pose safety hazards. Thermal runaway occurs when heat is generated at rates faster than the battery can manage. This can lead to battery cell failures and fires. However, failures affect only about one in 40 million cells.
Among the leading battery types, lithium nickel cobalt aluminum oxide (NCA) batteries, which appear in Tesla and Panasonic products, for example, are subject to thermal runaway. So are lithium nickel manganese cobalt oxide batteries (NMC), says Kennedy. The company he works with, Blue Planet Energy, utilizes premium lithium ion ferrous phosphate, (LFP), which isn’t susceptible to thermal runaway, a major advantage for the company.
How Quickly Can Batteries Charge and Discharge?
Another important consideration when choosing batteries is how quickly they can be charged or discharged, which is called the c-rate. The NCA batteries possess a high c-rate. Tesla’s electric car chargers–superchargers–are a good example. “You can pull up to a supercharger and cram in a rate two to three times the overall capacity of your battery in a short period of time. For example, that might be 200 kW of supercharging into a 80 KWh battery” Kennedy says.
Watt/hours in vs Watt/hours out Defines Efficiency
A third consideration is efficiency. “If you put 100 watt/hours into a battery, how much can you take back out?” he says. LFP batteries are 99% efficient, NCA batteries are 95% efficient and lead acid batteries are 65% efficient. For LFP this yields 99 watt/hours available, NCA, 95 watt/hours, and lead acid a trailing 65 watt/hours.
Yet another issue is energy density, which affects the size of the battery. Denser batteries can store more energy in a smaller space.
“The energy density is about how big the battery is per unit of energy stored. NCA chemistries are more than twice as dense as some other chemistries. Energy density is a huge consideration in electric vehicle (EV) applications. In stationary (home or business) applications, not as much.” Kennedy says.
The NCA batteries are more than twice as dense as LFP batteries, which means Tesla’s Powerwall is smaller than a Blue Planet unit that provides the same amount of energy. “You can hang a Powerwall in your garage, while Blue Planet’s battery system is the size of a refrigerator,” he says.
Is There a Battery Winner?
While Kennedy uses the Blue Planet Energy system, he’s quick to say that he’s a huge fan of Tesla.
“Tesla is crushing it because the company is aligning EV production with stationary energy storage. They continue to drive the price down,” he says.
Overall, he prefers the Blue Planet Energy chemistry.
“I think Blue Planet wins for two reasons. It has the longest cycle life of any of these batteries, with a 21-year cycle life. It’s also chemically stable, there are no issues around thermal runaway and fire safety and containment. That’s the clear advantage.”
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