For on-highway vehicles, electrification is now seen as the way to go, but the future for electrified off-highway ones such as construction dozers, mining trucks and so on is less clear. Contact online >>
For on-highway vehicles, electrification is now seen as the way to go, but the future for electrified off-highway ones such as construction dozers, mining trucks and so on is less clear.
Off-highway mobile machines are often larger than the biggest on-road trucks, and vary widely in their size, power, cost, environmental harshness, and weight. For example, there are 0.5 t mini-excavators and 400 t haul trucks, and if you include non-terrestrial vehicles, there are 500 t aircraft and 55,000 t container ships in need of electrification. They are also usually supplied in tens of units or even single ones, even to major industrial operators.
So there''s a contrast between off-highway and on-highway automotive applications: for the latter, the problem of scarce batteries has arguably been ''solved'', as OEMs building road EVs in batches of 100,000 or so at a time are now supplied by high-volume, low-diversity pack manufacturers. Conversely, solving the problem of off-highway packs poses the challenge of optimising a production line around low-volume, highly diverse batches, potentially just a few packs at a time.
That challenge is what battery manufacturer Xerotech aims to solve. Based in Claregalway, in Ireland, it was founded by CEO Dr Barry Flannery in 2015, and the company now supplies packs to many off-highway EV OEMs. Dr Flannery began engineering battery packs in the early 2010s, and invented a new form of active thermal management, which is patented as Xerotherm.
Xerotech’s batteries are built around Xerotherm, using a scalable and modular product architecture called Hibernium (a reference to Hibernia, Ireland’s name during Classical Latin times).
As Dr Flannery explains, “Off-highway vehicle operators are some of the biggest companies on Earth, but even they don’t need more than a few, say, well-drilling vehicles or asphalt-grating trucks. So engineering batteries for that market means hundreds of different pack sizes, which can’t benefit from high-volume production as automotive packs do.”
Within each Hibernium module, typically there are cylindrical cells and the Xerotherm system of sidewall cooling, which consists of liquid-inflatable ultra-thin plastic ducts. The cells and ducts are held within a structural, insulative and fire-retardant foam. The modules come in six sizes and can be stacked up to 24 in a pack, sitting side by side and directly connected to one another via busbars.
On the front of each pack sits Xerotech''s battery disconnect unit (BDU), which contains the BMS, contactors and related safety and control subsystems, along with connections from the BMS master unit to module-level slave BMS boards for lower-level monitoring and commands.
But given the need for hundreds of pack sizes and the consequent length of Xerotech’s product catalogue – at the time of writing, it covered 678 different packs, each with its own eight-page datasheet – citing the exact specs for every Hibernium pack is cumbersome.
To date, its largest with a published datasheet is a 290 kWh solution weighing 1429 kg and measuring 2392 x 1201 x 430 mm, with a nominal voltage output of 691 V (480 V minimum, 805 V peak). Its smallest is a 10.4 kWh pack weighing 104 kg and with dimensions of 561 x 511 x 430 mm, and designed for a 60-101 V output range (86 V nominal).
Xerotech also records and publishes huge amounts of data from in-house testing, including charge and discharge maps across 0-100% SoH and 0-100% SoC (graphed in increments of 5% at a time) and also across full temperature ranges as tested for regulatory compliance.
These are published for cell, module and pack-level characteristics. It is also making public its IP on its pack engineering and science, aiming for openness on par with IC engine manufacturers.
Why such technological transparency? One reason is to back up the claims made in its test data. But Xerotech also estimates that the wider EV battery industry''s guardedness about the contents and manufacturing of its packs results in timescales of 18 months on average for customers to receive initial units of a new pack, slowing electrification efforts. Transparency is therefore key to enabling Xerotech''s shorter lead times.
Xerotech is agnostic regarding battery cell chemistries, partly in response to the rapidly changing nature of cell components and formulations. As Dr Flannery explains, “Cells have four key ingredients: anode, cathode, separator and electrolyte. Change any of those and you change the battery’s characteristics. What many people know as lithium-ion cells is actually a broad family, designated mostly by cathode, and NMC is the most widely used.
“But more cathodes are coming out, like LFMP [lithium iron manganese phosphate] or NMCA [nickel manganese cobalt aluminium]. And across the other ingredients there are new things like silicon anodes, inorganic electrolytes and ceramic separators, which could all significantly change cell characteristics like voltages, amp-hours, and thermal behaviours.”
Xerotech therefore avoids sticking too closely to one cell chemistry or supplier. That said, the company exclusively uses 21700 (or 2170) cylindrical cells, which are 70 mm long, 21 mm in diameter, 70 g net weight and 5600 mAh maximum capacity.
“2170s are generally the most widely available cell for different chemistries," Dr Flannery says. "They have their limitations, in that some future components like solid-state electrolytes or ceramic separators might not always be machine-wound well enough for cylindrical formats.
“Prismatic and pouch cells also generally have a longer cycle life, because they can use more viscous electrolytes as you don’t have to inject them into a tightly packed can. But cylindrical cells have the best robustness against thermal runaways thanks to their metal cell walls – prismatic and pouches just can’t match that.”
NMC, LFP and NCA cylindrical cells are the most common in Hibernium modules for their technological maturity and commercial availability. Given LFP''s often-touted safety benefits for risk-averse heavy industry operators, it might be assumed that LFP is inherently the best of these for off-highway, but Dr Flannery cautions against this.
“We’ve carried out a lot of safety testing to understand all the cells’ behaviours across all temperatures, SoH and SoC bands, all vibration and harshness conditions, and so on, and our BMS reacts accordingly with our thermal and electrical controls to give an equivalent level of safety whether it’s a pack built on LFP cells or the highest energy density NCA cells," he says.
“Cells have different failure modes. For instance, you generally get less flame in a thermal runaway with LFP than other cathode chemistries, but a lot more gas, which can be even worse if you’re underground with significant hydrogen build-up. There, it could be better if the vented material’s burning so workers aren''t trapped underground with a gas build-up, or the ATEX-risk of a small hydrogen explosion.”
On examining the use case, Xerotech has found that heavy-duty off-highway work needs the maximum energy possible, owing to the sheer sizes of the vehicles and the heavy lifting required, making NMC chemistries optimal for most customers.
“Maybe that’s unique to us because of our thermal and safety technologies, but there’s a real lack of education in the industry as to what datasheet parameters mean in practice," Dr Flannery remarks. "Should we supply someone with an LFP pack with 6000-8000 cycles, or a 40% more energy-dense NMC pack and then manage it for a smaller depth of discharge [DoD] window to achieve the same cycle life?
“In our view, OEMs will want either an energy pack, a power pack or a long cycle-life pack. And with new automotive standards requiring that smoke from a battery pack cannot enter the passenger compartment within 15 minutes of a thermal runaway being detected – which might increase in future – we’ll pick and foster whatever future cell innovations make sense for each of those requirements, along with alternatives for supply chain resilience. We think that’s how most of the market sees it as well.”
Among upcoming cell technologies, Xerotech is looking with anticipation at inorganic electrolytes and sodium-ion chemistries. The former does not flame (and Xerotech has announced a partnership with Innolith for its inorganic electrolyte cells), while the latter stands to bring down pack prices. It also expects to work with 4680 cylindrical cells, pending wider commercial availability and sufficient in-house testing to characterise their performance and safety.
The Xerotherm system of ducts runs longitudinally between every other row of cells in the Hibernium modules. The ducts are made from ultra-thin plastic and inflate with water-glycol according to the BMS’ command signals to the coolant pump.
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