Test of metal
3DOM’s new Li-metal battery technology has been developed to offer greater energy density without sacrificing safety or cycle life, writes Stevie Knight
”There’s a whole group of vessels that haven’t pursued full electrification because they couldn’t achieve their objectives on battery power alone,” says Ben Gully, chief technology officer at LAVLE, producer of the Proteus energy storage system that utilises batteries produced by parent company 3DOM.
Similarly, he adds, there’s another set “that has even fallen outside the case for hybridisation”. However, much of this is about to change.
While they’re arguably the most flexible of green technologies and the ‘marriage broker’ between alternative energy sources, batteries have limitations. Of these, “the really big one is energy density”, says Gully. He explains: “As we continue to push traditional Li-ion batteries to higher and higher energy densities, the industry has been forced to make substantial sacrifices on both safety and cycle life.”
So, a change in approach may be necessary. So far, the focus has often been on creating a solid-state electrolyte.
However, Gully says, while developers have been messing about with the cathode for the past couple of decades, swapping the anode chemistry to lithium metal has an even more significant impact, doubling capacity “with production-ready cells at 420Wh/kg cycling in the lab now”.
Why hasn’t it been done before? The periodic table offers just a few outstanding candidates, the best being lithium – but in its metal form. The problem with this is that, while it increases the anode’s ability to hold the charged particles, it has a deplorable habit: it grows metal dendrites the way a wet cave grows stalactites. These are spiky enough to pierce through the separator and electrolyte, and the resulting short circuit can too easily result in thermal runaway, prompting toxic gas release, fire or explosion.
To counter this, LAVLE is utilising cell manufacturer 3DOM’s separator – a film with a homogeneous, three-dimensional pore structure. Recent experiments have shown how an uneven ionic current precipitates dendrites, so this separator removes the lumps in the flow of ions between the electrodes, which largely stops these dendrites from forming, and completely prevents them from penetrating through the separator.
It should be noted that this repositions the cart behind the horse, as one of the drivers for solid-state batteries was the possibility of sealing the tiny, molecular-level gaps in which dendrites could start to grow.
Interestingly, this separator can be applied to the interface and enable the use of novel non-flammable liquid electrolytes or solid-state chemistries, “opening up a pathway for us to pursue both kinds of battery”, says Gully. Since LAVLE has the battery management know-how, it can deploy either or both the liquid lithium metal developments and solid-state innovations, depending on what the market or applications demand.
Some like it hot
But it promises more than double the energy density. Instead of the typical Li-ion battery’s demand for operating temperatures inside a narrow 20-30°C band, these cells “actually love the heat” says Gully. “In fact, most competing solutions are only able to operate at highly elevated temperatures, up to 200°C on the test bench,” he adds.
One of the major achievements of LAVLE and 3DOM is cells that can provide the desired performance at room temperature. So, while these Li-metal chemistries can work well at ambient temperatures, they also won’t degrade even at well over 50°C. As a result, a lot of the problems (and ancillary systems) that currently centre on cooling can be shelved.
“This will be particularly relevant for smaller vessels, which are often the most space- and weight-constrained”, says Gully, allowing workboats with smaller hull volumes, such as cats, to electrify. For others, it will mean getting a full day’s duty out of the energy storage, rather than being limited by the need to return for a top-up charge.
So, according to Gully, this new Li-metal technology meets the requirement for higher energy “while also providing for the key factors of safety and cycle life”.
He continues: “Most of all, a much broader range of vessels can now be considered for fully electric operation.” Among the potential beneficiaries are boats that inevitably come with weight control issues. For instance, bar a couple of notable exceptions, most pilot and patrol craft have not been regarded as suitable for battery installations, especially given that energy efficiency drops away steeply the faster you travel. Alongside these are vessels with routes that demand enough onboard power to make headway against a running tide. It will take careful design, but the LAVLE/3DOM solution stands to flip these marginal decisions.
It will also give zero-emission boats elbow room to get creative. Photovoltaics, fuel cells and other energy sources are rising in efficiency, but they still require energy storage to make them genuinely viable. In short, Gully concludes, this Li-metal innovation is the catalyst needed to “open up usage and power system arrangements that we are only now able to start envisioning”. SBI