IBEX 2024: Solid State Marine’s solid state lithium batteries

In a first for IBEX, this year’s show featured a startup pavilion for early-stage companies to display at the show in a cost effective manner. I spent some time checking out the exhibitors in the pavilion and was very pleased to come across Solid State Marine’s booth. It is exciting to see solid state lithium batteries packaged and ready to be sold to the boating public. Solid State Marine is, to my knowledge, the first company offering solid state lithium batteries to the marine electrical market.

You may be wondering what makes a battery solid state. After all, typically when we talk about solid-state in technology we mean a device with no moving parts and nearly all batteries qualify based on that definition. In batteries, solid-state is a reference to the electrolyte, not indicating no moving parts. Quite literally, the electrolyte is in a solid state, not liquid or gel as is the case for other lithium (and most lead acid) chemistries.

A recent Getting Technical column I wrote for Trade Only focused on emerging battery technologies and discussed solid state batteries in greater depth. The promise of solid-state cells and batteries is higher power density, reduced or no flammability, better performance in extreme temperatures, and potentially longer lifespans. The two cells shown above each feature the same energy capacity but as you can see, the solid state cell on the left weights one pound while the LiFePO4 cell on the right weights just over five pounds. For further comparison, a 300 amp hour Solid State Marine battery weights 40 pounds while the Epoch Dual Purpose 300 ah, 12-volt battery weighs 82.

Solid State Marine (SSM) offers batteries in 12, 24, 36, and 48 volt nominal voltages. In 12-volt they offer 90, 210, 300, and 750 amp hour batteries. The 90 amp hour battery sells for $1,000 while the 750 amp hour battery is just shy of $6,000. Impressively, that 750 amp hour battery weighs just 100 pounds. Compared to LiFePO4 batteries, there is a price premium. However, the premium isn’t huge, especially in light of the maturity of the technology.

Even the smallest capacity 12-volt battery can both start engines with a 650 cold cranking amp (CCA) rating. All three larger batteries are rated for 1,500 CCA. Additionally, the 90 amp hour battery sustains continuous discharge loads of up to 150 amps and peak currents of up to 300 amps. Again, the three larger batteries all sustain 250 amps continuously and 500 amp peak discharge.

Solid-state is quite new technology and comes with several unknowns as well as some implementation challenges. One of the biggest challenges, especially at 12-volts, is the higher voltage of solid-state as compared to LiFePO4. LiFePO4 cells have a nominal voltage of roughly 3.2 volts and rest when fully charged at about 3.4 volts per cell. That means a fully charged 4-cell, LiFePO4 battery rests at about 13.6 volts. Additionally, the maximum charging voltage recommended for nearly all LiFePO4 batteries is 14.6 volts. That voltage range works well with equipment designed for 12-volt nominal electrical systems.

Solid state cells typically have higher nominal and resting voltages, though they can vary depending on the exact implementation of the technology. For example, Solid State Marine’s cells appear to be nominal 3.6 volts. Further, they call for charging at 4.2 volts per cell. That means a 4-cell battery will have a nominal voltage of 14.4 and charges at 16.8 volts. That is high enough to cause concern about components designed for 12-volt nominal power systems. The first thing I checked was the power rating of Fusion Apollo RA-770 stereo head unit. A quick check of the manual shows a 16 volt maximum rating. I imagine you may be able to address this by reducing peak charging votlage, but there are questions to be answered about the impact on the battery of not being charged to recommended voltage.

Fortunately, the high voltage problem really only exists for 12-volt nominal replacements. At 24, 36, and 48 volts, SSM controls the voltage by removing one or more cells. For example, the 24 volt replacements have a charge voltage rating of 29.4 volts. I find it easiest to compare those voltages by comparing to what they’d be at 12-volt nominal. In this case, that would 14.7 volts and a perfectly safe peak voltage.

I am hopeful I will be getting a test battery soon and begin to put this exciting new technology through its paces. I’m also looking forward to a little bit of destructive testing. You may have seen a video I posted of EPT stabbing a solid state cell from last year’s METSTRADE. I’m hoping to be able to further explore the safety of this technology. If it is able to deliver the increased power density, wider temperature, greater cycle life, and better safety, I’m excited. So, watch this space and let’s see what develops.