With an energy density of 245 watt hours per kilogram, a solid state marine battery from Italy’s Sealance enables electric boats and ships to pack more electricity storage into less onboard weight and space.

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A solid state battery uses a solid material as the electrolyte – the material that allows electric charge to flow from one electrode to another. Most electrolytes now are either liquid or gel. Solid state promises important advantages over those in three aspects: energy density, recharging speed and safety.

Lighter, faster, safer

Literally some of the best minds on the planet are working on ways to make huge leaps in all three areas, but that is easier said than done. So, the chemistry is advancing bit by bit, and the Sealence battery is a big step, not least because it is beyond the laboratory stage and is actually being commercially produced and can power vessels now.

Gravimetric energy density – the amount of electricity that can be stored in the weight – is more important for electric boats than for land vehicles because A: a boat needs to float and B: there is much more resistance to overcome with the hull of a boat moving through water than with a car on wheels moving through air.

The energy density of the Sealence battery is impressive because it measures the density of the entire battery pack. A quick lesson: when we talk about a battery in a toy or flashlight we are actually talking about a single battery cell.

Energy density measured for entire battery pack

A single cell doesn’t have much voltage, so with boats (and EVs), those battery cells are linked and fastened together to increase the voltage. First they are connected to make modules, then the modules are connected to make a battery pack.

 

When you read or hear the words ‘energy density’, it is often referring to how many watt hours of electricity can be stored in a kilogram of individual, unlinked cells. But if you take into account all of the wires and compounds and protective casing that go into a battery pack to make it usable, the energy density goes down because the overall weight went up.

As you can see from the photo, Sealence took its entire battery pack and put it on a scale, with it weighing in at just under 306 kg. That battery pack holds 75 kiloWatt-hours of electricity, so the energy density of the working pack is 245 kWh/kg.

Sealence was actually founded by Italian entrepreneur William Gobbo in 2017 to develop the DeepSpeed electric hydrojet boat motor, which is now available in two models: 230 kW (313 hp) and 600 kW (815 hp).

Like many electric boat motor manufacturers, Gobbo and his team discovered that the real challenge with electric marine propulsion is not in the motors, but in the batteries.

Davide Lusigagne

At the same time Gobbo was starting Sealence, a young Professor of Engineering at the University of Parma, Davide Lusignani, was creating a cluster of professors, researchers and engineers focused on electric mobility. It was called the eDriveLab and first concentrated on EVs and the auto manufacturers like Ferrari in Italy’s ‘Motor Valley’. The lab’s growing list of patents came to the attention of Gobbo.

In early 2020 Sealence and eDriveLab started working together on a range extender for large boats and later that year joined forces under the Sealence corporate umbrella.

Their initial marine battery, the SafeLi, focussed on safety, as the name suggests. It incorporated the next generation of an eDriveLAB cooling system where the individual cells are immersed in a liquid that maintains optimum temperature and also prevents fire spreading if one cell ignites from physical damage.

Solid state marine battery stores 66% more energy

At the same time that they were developing the SafeLi, the Sealence team was also working on a solid state battery with its advantages in charging speed, safety, and energy density. To give you an idea of the energy density advantage, the 240 Wh/kg that Sealence’s solid state battery can store is 66% more than SafeLi technology.

There are many companies working on solid state batteries in the EV world, but it was only a few days ago, on May 20, that BMW announced it had completed its first on-road tests using all-solid-state battery cells. Congratulations to Sealence for being ready to go now with a solid state marine battery that has been specifically designed and constructed for use on the water.

The increased energy density will make a big difference in range, especially for larger boats and commercial vessels. A work boat can be out on the water earning money 66% longer. An electric ferry can service a route that is 66% longer or make 66% more trips without recharging. If more batteries are needed to extend range, they can do it using 1/3 less weight.

As Gobbo told Gian Basilio Nieddu of the Italian new energy website Vaielletrico “This is the real future of zero-emissions boating. By greatly reducing weight and space, all the necessary batteries can be loaded onto ships, thus allowing for long autonomy. For some projects our solution is the only possible technological choice. We have signed orders of several million euros and have a commercial pipeline of tens of millions.”

Sealence

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