Building Safer Lithium-ion Batteries | RELiON

Lithium-ion battery technology has popped in and out of the news in recent years, mostly for safety concerns. But engineers who understand how lithium batteries work know that it’s among the best and safest commercial options for energy storage needs. So despite exploding cellphones, smoldering plane engines and hover boards that are too hot to ride, lithium-ion batteries remain the go-to energy storage technology worldwide and account for 83 percent of newly announced energy storage projects in 2016, according to a new report by Navigant Research.

Safety is a full-fledged design feature with lithium-ion batteries, and for good reason. As we’ve all seen, the chemistry and energy density that allows lithium-ion batteries to work so well also makes them flammable, so when the batteries malfunction they often make a spectacular and dangerous mess.

RELiON prides itself on offering lithium-ion batteries designed around safety and longevity. Although the lithium iron phosphate (LiFePO4) batteries we sell can’t currently be manufactured small enough for use in consumer electronics, the LiFePO4 technology is by far the safest chemistry available.

All RELiON batteries also come with either a Power Control Module (PCM) or Battery Management System (BMS) that have many extra safety features including; over-current, over-voltage, under-voltage, and over-temperature protection, and the cells come in an explosion-proof stainless steel casing.

But when it comes to smaller lithium batteries that power common consumer products, we admit the industry as a whole still has room to improve. And researchers know this, which means many groups around the world are finding new and inventive ways to beef up battery safety while improving battery efficiency.

Before we dive into three research projects that are improving battery safety, let’s refresh ourselves on how lithium battery malfunctions happen in the first place.

How can lithium batteries catch on fire or explode?

Lithium-ion batteries explode when the battery’s full charge is released instantly, or when the liquid chemicals mix with foreign contaminants and ignite. This typically happens in three ways: physical damage, overcharging, or electrolyte breakdown.

For example, if the internal separator or charging circuitry is damaged or malfunctions, then there are no safety barriers to keep the electrolytes from merging and causing an explosive chemical reaction, which then ruptures the battery packaging, combines the chemical slurry with oxygen, and instantly ignites all of the components.

There are a few other ways lithium batteries can explode or catch on fire, but thermal runaway scenarios like these are the most common. Common is a relative term, because lithium-ion batteries power most rechargeable products on the market, and it’s pretty rare for large-scale recalls or safety scares to happen.

Why LiFePO4 is Safe

As for the batteries RELiON uses, our lithium iron phosphate (LiFePO4) chemistry is inherently safe, so you don’t have to worry about a battery meltdown.

Here’s why.

LiFePO4 batteries have a chemical and mechanical structure that does not overheat to unsafe levels, unlike batteries made with a cobalt-oxide cathode or manganese-oxide cathode.

This is because the charged and uncharged states of LiFePO4 are physically similar and highly robust, which lets the ions remain stable during the oxygen flux that happens alongside charge cycles or possible malfunctions. Overall, the iron phosphate-oxide bond is stronger than the cobalt-oxide bond, so when the battery is overcharged or subject to physical damage then the phosphate-oxide bond remains structurally stable; whereas in other lithium chemistries the bonds begin breaking down and releasing excessive heat, which eventually leads to thermal runaway.

LiFePO4 works great for our customers' needs. But the chemistry doesn’t work as efficiently in batteries used in small electronics. The industry needs a different solution. And we might find it if the following three research projects pan out.

Self-healing lithium battery

Self-healing membranes have been all the rage for wearable technology, and now the research is being adapted for batteries. A self-healing lithium-ion battery has unique chemical structures that prevent lithium compounds from leaking out after the device has been damaged. Plus the batteries maintain their electrochemical functionality after healing. This should halt any messy explosions or fires upon the battery receiving physical damage and make batteries more resilient.

Although the self-healing battery concept still needs further research and refinement, a partnership between Samsung and researchers at Fudan University in Shanghai has produced among the most promising self-healing battery designs.

Their batteries are composed of carbon nanotubes that are loaded with lithium nanoparticles and fixed onto a self-healing polymer, according to an article in Chemistry World.

Within the self-healing polymer is a cellulose-based gel that acts as an electrolyte and separation membrane between the electrodes. This lets the battery self-repair if it’s damaged by simply pressing the two maimed sections together for a few seconds.

Solid-state Lithium-ion Battery

Lithium-ion batteries aren’t alone in the occasional safety snafu (without proper battery maintenance, lead-acid batteries can ignite too), but the results of a chemical breakdown in non-LiFePO4 batteries are often dramatic because the lithium slurry has highly combustible electrolytes. The simplest solution to this quandary is removing the liquid electrolyte from the equation. No flammable electrolytes, then no fire or explosions. And that’s exactly the approach some researchers are taking.

Several different research groups are experimenting with solid-state lithium batteries. By eliminating the liquid component and replacing it with a solid-state conductor, the resulting batteries could be more resilient and last longer. Plus the solid polymer opens the door to combining lithium batteries with thin-film fabrication to power miniaturized products and applications.

Progress in this innovation is slow-moving because most solids that also conduct ions don’t do so very effectively at room temperatures. Theoretically, chemists and engineers could create a solid electrolyte from any element, but the reality is that only a few options have shown promise. Of those, oxides and sulfides produce the best results.

Because of how volatile and toxic sulfides could be under the wrong circumstances, oxides are the preferred element to work with. And one particular oxide, a garnet-type compound known as cubic Li₇La₃Zr₂O₁₂ or c-LLZO, draws most of the attention because combines several useful qualities, according to an article in Chemical & Engineering News.

The c-LLZO is thermally and chemically stable. It doesn’t need a special processing environment, and it won’t emit any toxic byproducts like sulfur can. Plus the c-LLZO has a wider voltage range than common liquid electrolytes, which means the compound should be suitable for high-voltage batteries.

The downside so far from c-LLZO is the material only has a room temperature conductivity of 1-2 mS/cm, which is low compared to some electrolyte slurries but much greater than other oxides.

The Chemical & Engineering report says researchers are working to boost the conductivity value to make the product more market feasible.

Improved Charging Control Technology

When it comes to lithium-ion car batteries, safety is the most important feature — with an average distance-per charge being a close second. Tesla and Nissan are the two heavyweights in the electric car market, but Toyota says its researchers have solved the company’s safety concerns and they’re now moving forward with an all-electric Prius. The solution to their battery safety woes is improved control technology that accurately measures the temperature and operating condition of every cell in its new battery pack.

The control system can continuously measures how the battery cells are performing, and immediately acts on even slight signs of a potential short-circuit in individual cells. If the cells begin short circuiting or overheating, then the control system will either prevent the malfunction from spreading or shut down the entire battery.

Using this method makes the control system offer proactive protection instead of reactive protection, which can prevent any malfunctions from getting out of control.

These technologies are still a ways off from being market viable, and the entire RELiON Battery team is dedicated to providing our customers with the highest quality and safest lithium products currently available. Please get in touch with us to learn about how we can help your team achieve its energy needs safely and efficiently.