When our customers approach us about battery reliability, the most pressing question is always, “How do we prevent catastrophic battery failures?” While the rate of field failures is statistically low at only 1 to 10 ppm, the impact of battery failures has often been severe in recent years. Higher energy densities, and the use of lithium ion batteries closer to the human body are to blame for the severity of impact.
It seems like a month does not go by, without hearing news reports about battery explosions in e-cigs, headphones, smartphones or other electronic gadgets. Granted that stories about explosions are considered newsworthy, but has the statistical rate of battery failures actually gone up in the last few years? Has the impact of battery failures increased and if so, why? And, I am of course talking about Lithium ion batteries, the go-to battery chemistry in rechargeable electronic devices owing to their high energy density. I am certain you do not want to be carrying around a brick for a smartphone.
In recent years the practice of buying spare e-cigarette batteries online has started to increase, with some users scouting for higher amp-hour/power batteries in order to get a better vaping experience. This is particularly true for mechanical mod e-cigs, which are highly customizable and do not use protection circuitry. The battery protection circuit is what keeps a lithium-ion battery within its operating window, and prevents it from overheating, overcharge and other potentially dangerous situations.
My cousin recently came to me with a battery problem. He got a drone for Christmas, and he had not opened it for a while. "Last Christmas, right?", I asked. Apparently, it was the Christmas before (i.e a year and a half of being in a box). "Uh-oh," I say. I almost knew what was coming. The drone obviously did not work, and I got to see a picture of a very bloated Lithium Ion pouch cell. Your Lithium-Ion battery does need some attention from you every few months in the form of a periodic recharge, or you will end up with a cell that looks like the image below. (My colleagues have brought me plenty of gadgets with the plastic case popped open from a bloated battery)
In my conversations with product engineers and designers, I often come across people who feel confident that their lithium-ion batteries are safe because they passed standards-based safety tests. If that is indeed the case, then why did major global companies experience thermal events even after having passed compliance tests? And that brings up a bigger question – are standards-based tests such as UL safety tests sufficient to guarantee lithium-ion battery safety?
The race to improve the performance and reliability of batteries is on, from electric vehicles to advances in wearables and mobile devices. In the pursuit of performance and the desire to outpace competitors, manufacturers may be tempted to overlook potential shortfalls. Most notably, Samsung made news when the company halted production of its Galaxy Note 7 and eventually scrapped the entire product after devices caught fire.
In part 1 of this 3-part blog series, we discussed the most important metrics for battery selection. One thing to remember about battery selection is that it is essentially about managing tradeoffs. You trade off some battery metrics in order to gain in others – for example in order to gain power density, you may have to trade off energy density.
In part 1 of this 3-part blog series, we discussed the most important metrics for battery selection. One thing to remember about battery selection is that it is essentially about managing tradeoffs. You trade off one feature in order to gain in another – for example in order to gain power density, you may have to reduce energy density.
Samsung finally released details early this week on the root cause of the Galaxy Note 7 fires and explosions that started to show up in August 2016. You can find details on the story here, but the gist of the matter is – failures and explosions started to show up with batteries from Manufacturer A, soon after the phone started to sell. Samsung provided replacement phones with batteries from Manufacturer B, but the failures and explosions continued (if you are in the battery world you would use the phrase “spontaneous disassembly”). The company had to halt production and eventually scrap the entire product.
The one thing to remember about battery selection is that there is no such thing as a perfect battery that works for every application. Selecting the right battery for your application is about identifying the most important battery metrics and trading these off against others. For instance, if you need a lot of power for your application, cell internal resistance needs to be minimized, and this is often done by increasing electrode surface area. But this also increases inactive components such as current collectors and conductive aid, so energy density is traded off to gain power.
