Lithium-ion batteries:a new safety issue for ships?

Lithium-ion batteries:a new safety issue for ships?
http://ship.h5mag.com/ship_jul18/lithium-ion_batteries_a_new_safety_issu...

More and more ships are turning hybrid or fully electric and increasingly rely on lithium batteries as a power source. The technology has proven itself reliable and powerful, but safety concerns, such as thermal runaway, still linger. Elliot Gardner investigates

There has been a rise

in recent years in the number of hybrid and full-electric vessels in the maritime industry. Last year, China launched the world’s first all-electric cargo ship from Guangzhou, proving that electric power is not only feasible on the most demanding of vessels, but practical too. Estimates suggest that almost all commercial vessels will soon house some form of electric storage system as part of their power systems, and lithium-ion batteries are becoming one of the most popular choices for ship operators.

However, fears still linger around the potential dangers posed by lithium-ion battery systems in the logistics and transport industries. In 2010, for example, the UPS Airlines Flight 6 crash, which killed two people, was attributed to a cargo pallet containing lithium-ion batteries that auto-ignited aboard the aircraft.

To help address these concerns, classification society DNV GL in March announced the launch of a joint development project (JDP) to explore the use of lithium-ion batteries in the shipping industry.

Explaining the rationale behind the new endeavour, DNV GL senior engineer Benjamin Gully said: “Rules have been put in place that cover a lot of the dangers of lithium-ion batteries, but there's a real opportunity for the industry to benefit both in terms of the total level of safety as well as the efficiency of the approval process, by increasing the level of knowledge in the industry through technical data and answering hard to answer questions.”

Lithium-ion batteries on ships: the risks

Thermal runaway remains the most substantial risk related to the use of lithium-ion batteries. If a battery cell is damaged or subjected to intense heat, it suffers an exothermic reaction, causing more and more heat to be generated. If there are multiple battery cells housed together, this reaction can propagate to other cells, causing yet more heat, and increasing the likelihood of more cells failing. The end result is a reaction that’s near impossible to stop, and one that keeps getting worse.

While significant research has been conducted to eliminate this problem, runaway is still very much a reality. “Although there has been significant progress with lithium-ion batteries, it is still possible they can go through a thermal runaway and catch fire,” comments Skeleton Technologies space product development engineer Olivier Chabilan.

The risk is especially prevalent in maritime settings because of the sheer size of the batteries needed to run ships, compared to those used in cars or aircraft. “The only other systems that use batteries in such a large size can reduce the risk substantially by putting the batteries in a field somewhere next to a tower where nobody else is,” says Gully. “For maritime though, the likelihood of people being very close to the batteries is quite high.”

Lithium-ion battery failure also has the potential to release explosive gases, especially when water is involved. The water can react with the lithium to produce highly flammable hydrogen gas, and because ship-based battery systems are often in enclosed spaces, the risk of explosion is significantly heightened.

According to Chabilan, merely the environment ships travel though is enough to cause danger. “The close vicinity of water and ambient humidity are some of the challenges that are unique to the management of lithium-ion batteries on ships, together with the saline environment and occurring vibrations… Just like planes, ships travel through barren, desolate environments, hostile to human life, meaning that any issue on board can develop very quickly into catastrophic proportion, even when all possible precautions are taken.”

Weighing up the dangers

While on the face of it these potential dangers seem catastrophic, as with anything they can be almost entirely countered with appropriately designed systems and proper management of risk factors. “The risks are very tangible and realistic,” explains Gully, “but the solutions are really easily accessible.”

“In general, quantifying the risks is an important thing to do, and it’s something we’ll definitely be doing as part of the Maritime Battery Safety JDP, but my feeling is that the risks are realistically much lower than with diesel systems. I think the number of events you get is much lower, and we are already engineering systems to take care of the risks. If we ensure that everybody is taking the same measures to engineer systems to the same standards, then the consequences of any events will be significantly lower.”

The work of classification and standardisation societies like DNV GL helps to ensure systems are brought up to scratch and held to a higher standard. After all, it is within lithium-ion battery system manufacturers’ best interests to create a product that can be sold as broadly as possible.

And, of course, the risks have to be weighed up against the actual benefits that lithium-ion systems bring to the maritime sector. Batteries allow a much more economical and ecological approach to powering vessels; removing the need to constantly generate power means less strain is placed on the ship’s systems.

“The benefits are, without a doubt, huge," says Gully. “There are a number of vessels that, depending on the application, could benefit from batteries, even without them being an all-electric vessel. A battery just helps the power system work better. It becomes more optimised and operates more efficiently. And if the power system is designed with the battery power in mind, the benefits can be almost doubled.”