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Lithium Batteries: Cylindrical Versus Prismatic

Anton Beck
Written by Anton Beck
Posted on August 6, 2019 at 8:27 AM

By and large, lithium batteries bring a wide range of different benefits to the table that are difficult - if not impossible - to replicate in any other way. Also commonly referred to as lithium-metal batteries (due to the fact that they use lithium as an anode), they're typically capable of offering a very high-charge density (read: longer lifespan) than other alternatives that are on the market today.

For that reason alone, lithium batteries have a wide range of applications in our daily lives, especially for those critical in nature that we tend not to spend too much time thinking about. Specialized types of lithium batteries are used in pacemakers and other implanted medical devices, for example, because they can often last 15 years (or longer) under the right circumstances. They've even started to replace traditional alkaline batteries in many everyday devices like clocks, digital cameras, watches, portable data assistants, and more, all thanks to that longer lifespan that minimizes the need to replace the battery over time.

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But, regardless of the specific application you're looking at, when it comes time to actually select a lithium battery for your own uses, you will have two major options available to you. Cylindrical and prismatic lithium batteries are very common in today's modern, tech-driven world, and each brings with them their own unique sets of advantages and best practices that are certainly worth exploring.

What Are Cylindrical Lithium Batteries?

Cylindrical lithium batteries, as the name suggests, feature electrodes that are encased in a cylindrical cell that is wound very tightly within a specially designed metal casing. This unique makeup helps to minimize the chances that the electrode material inside will break up, even under the heaviest of use conditions.

Cylindrical Lithium Batteries

Example of cylindrical lithium batteries.

Issues like mechanical vibrations, thermal cycling from charging and discharging, and the mechanical expansion of current conductors are all things that can affect a battery's lifespan. Therefore, the design of these cylindrical units is intended to help mitigate risk from these and other factors as much as possible.

On the inside of a cylindrical battery, a series of cells are combined and operate in parallel to one another. This is done to help increase both the voltage and the overall capacity of the battery pack.

For these reasons, cylindrical batteries are usually the kind that are found in the aforementioned medical device systems. Smaller, more specially designed cylindrical cells are also commonly found in portable devices like laptop computers. Notably, Tesla also made headlines recently by selecting cylindrical lithium batteries to power its fleet of popular electric cars.

What Are Prismatic Lithium Batteries?

A prismatic lithium battery, on the other hand, features a cell that has been encased in either aluminum or steel, mainly for the purposes of increased stability. This, in turn, creates several key advantages right out of the gate. Because of this unique construction and makeup, prismatic lithium batteries tend to be very thin, very light and offer an effective use of space.

prismatic lithium batteriesExample of prismatic lithium batteries.

Because the rectangular shape of your average prismatic Li battery offers far better layering than other options, they typically give engineers a higher level of flexibility when designing products that will one day feature prismatic batteries as power sources. Because of that, it should come as no surprise that prismatic batteries are typically found in smartphones, tablets, and similar types of electronic devices where mobility is a major priority.

Due to these properties, modern day prismatic batteries are also commonly used in larger critical applications like energy storage systems and in electric powertrains.

Cylindrical Versus Prismatic Batteries: Breaking Things Down

There's a reason why cylindrical lithium batteries are the most commonly available (and used) type today. When compared to their prismatic counterparts, they can typically be produced much faster and with a lower cost-per-KWh (kilowatt hour) at the same time. The design itself better supports the types of automation processes that are commonplace in factories and in other manufacturing environments across the country, for example, which only aid in creating a better sense of product consistency and keeping those ultimate costs as low as possible.

One of the major reasons why prismatic cells have increased in popularity over the last few years, however, has to do with their large capacity. That, coupled with their naturally prismatic shape, make it very easy to connect four different cells together to help create something like a 12-volt battery pack.

The prismatic design does come with its own challenges, however, particularly as they relate to what happens if something goes wrong. If one cell in a prismatic battery goes bad for any reason, for example, the entire battery pack that it is a part of is essentially compromised. Because the cells in a cylindrical battery are combined in a series and in parallel, these are the types of problems that designers and other engineers don't really have to worry about.

Because of the design of cylindrical Li batteries, they also tend to radiate heat (and thus control their own temperature) more easily than their prismatic counterparts. Because of the way that prismatic cells are all placed together, this certainly works to increase the capacity, but it also leaves room for a higher probability of design inconsistency and short circuiting. The larger size of the prismatic cell may also be attractive in certain situations, but it also minimizes the chances that such a battery could be used in a heavily automated environment. That larger cell size also creates perhaps the biggest disadvantage for prismatic batteries: the increased capacity makes it far more difficult for the battery management system to properly regulate heat and prevent the battery itself from overcharging.

As previously stated, the thin form factor of a prismatic battery leads to increased flexibility for product designers - this does, however, create a few disadvantages of its own. It is that very same design that ultimately makes prismatic batteries somewhat difficult and expensive to properly design and manufacturer, which are costs that are almost certainly passed along to consumers. That flexibility has also created a limited number of "standardized" cell sizes, which only adds to difficulty in that regard. This also contributes to a higher than average KWh price as well.

It's important to note, however, that the topic of costs is also one that comes with a few important caveats. Experts agree that because prismatic cells can often be larger than their cylindrical counterparts and will thus cost more initially, they offer more opportunity for cost reduction in the long-term. Based on that, you may want to think about the cost factor in the following way: is it more important to save money now by going cylindrical, or can you depend on your ability to innovate and potentially save a larger amount of money over time? The answer to that question, of course, is one that only you can answer based on whatever it is you're trying to do.

Maybe the biggest advantage of cylindrical batteries in most situations is that they are very safe. If the internal pressure of a cylindrical lithium battery grows too high, most of the cells are designed to rupture - thus mitigating safety risks from situations like a fire or an explosion.

In The End

None of this is to say that cylindrical lithium batteries are inherently "better" than their prismatic counterparts, or vice versa. As is often the case with these types of situations, there is no "one-size-fits-all" approach to battery selection. Much of your decision will ultimately come down to the eventual application and the amount of risks and potential disadvantages that you're willing to accept as a result. There will be some situations where a prismatic battery absolutely makes the most sense. There will be situations where cylindrical batteries seem like the logical choice.

More often than not, choosing the right type of lithium battery to meet your needs will come down to three factors:

  1. The amount of money you're willing to pay, the effectiveness of the battery you're trying to unlock, and the safety considerations given the application.
  2. If space isn't necessarily at a premium and you need to find a cost-effective way to guarantee both performance and longevity, cylindrical batteries offer what you need.
  3. If cost isn't a factor and you need as much power as possible in an already small space, prismatic is likely the direction you'll want to head in.

Only by trying to learn as much about these options as possible will you be able to make the best decision given your needs in the moment. Ultimately, your ability to do that successfully is all that matters.

Topics: Battery Packs

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