Understanding the UK’s most advanced aerospace battery facility
August 2, 2024
The first tethered hover of Vertical Aerospace’s second-generation VX4 aircraft, achieved last week, marked the coming together of a myriad of engineering endeavours and technological feats. Powering this achievement was Vertical’s proprietary battery pack, developed at the eVTOL developer’s Vertical Energy Centre in Bristol. During Farnborough 2024, Aerospace Global News asked Vertical’s chief technology officer Michael Cervenka: just what makes this facility the “UK’s most advanced aerospace battery facility?”
Two years is a long time in this industry
Vertical Aerospace has come an “enormous way in terms of technology development and maturation as a company, and actually the whole industry has in two years,” mused Cervenka, contemplating the company’s journey since the 2022 Farnborough International Airshow. During this period, alongside completing its first round of flight testing, Vertical also opened its 15,000 sq ft, multi-million-pound state-of-the-art battery facility in March 2023, where it is integrating its proprietary battery technology with strategic supplier Molicel’s lithium-ion cell expertise.
However, with 95% of cell suppliers automotive-focused, “nobody yet has got a certified battery system that meets the power needs, the energy needs and safety needs for [this] kind of [eVTOL] product,” explained Cervenka. So, how is Vertical approaching the challenge; acknowledging – in Cervenka’s words – that there’s “no silver bullet” to solve a complex set of regulatory and performance challenges overnight?
“Really rapid iteration”
Describing the strengths of the Vertical Energy Centre, “it’s that sort of agility that has the mindset of: How do you ultimately get something you can do at scale, but in an environment where you can do that really rapid iteration?” explained Cervenka, citing the on-site expertise of the Bristol-based battery centre as vital to performing “that pioneering iteration much, much more quickly than a normal company”.
Head of powertrain Limhi Somerville concurs, having previously stated: We can build something one day, we can have it manufactured the next day, and we can be testing it later that week – that just wouldn’t be possible if we didn’t have it all in one facility”, adding that Vertical “can do in a day what would have taken weeks before”.
Vertical has four levels of battery iteration: from the first stage (where items are tested alongside off-the-shelf components) to the third and fourth iterations, requiring aerospace controls and bonded stores. For this, Cervenka cites “having all of the manufacturing and testing capabilities that [Vertical needs] next to the engineers in one place” as key.
Testing, testing
Reaffirming the “lots and lots of innovation in iterations” as key to a successful product – one that is safe, robust, compliant with all relevant standards (“but not so overengineered that we don’t have a commercially viable product”) – Cervenka also elaborated on the extensive testing being carried out at the Vertical Energy Centre.
The battery system itself is broken into eight sub-packs, with Vertical having carried out over 1,185 hours of sub-pack testing to date, alongside tens of thousands of hours at a module level and millions at a cellular level. Vertical has conducted thorough thermal runaway testing, crash testing, vibration testing, shock testing, abuse testing, hardware and software verification testing – “all of which gives [it] the foundational elements to say this battery is safe and it’s going to perform”.
Cervenka also highlighted how the August 2023 crash of test aircraft one (during the final flight of its test campaign) provided an unexpected opportunity to learn more from the ensuing hard landing, with elements such as the fuselage and batteries remaining intact. “From an engineering point of view, it was gold,” he added.
Incremental power improvements
Vertical is targeting an entry into service with a battery system able to deliver peak power of 1.4MW, with Somerville confirming that although the VX4 “can enter into service with what we have here,” Vertical is nevertheless predominately focusing on a facility that “allows [it] to scale up very quickly”.
Cervenka elaborated that Vertical’s battery performance has risen 20% in the last few years; a lot of it coming from the Molicel P45 cell itself, with further incremental improvements resulting from reduced weight in the battery system (via use of composite cases and fixings). As Vertical moves towards certification standard, a little more weight will be lost, with the company now eyeing “a slightly different shape of the battery packs to optimise them for packaging”.
However, although Cervenka explained that the rate of lithium-ion cell performance improvement has mostly plateaued (with most automotive applications offering minimal gains of 3%-4% a year), Molicel sees “huge opportunities for really significant improvements over the next few years” far above the incremental improvements elsewhere. “They have a whole series of technology steps over the next few years that will give us really big improvements in performance and empower them to scale.”
Into service
And the improvements are set to continue after the VX4 has entered service. With the aircraft in “high utilisation,” the batteries will require charging more often, necessitating replacing them for new units up to twice a year – enabling Vertical to offer a re-certified, higher-performance product during scheduled swap-outs. “This is a key part of us owning the battery system with better Mocicell cells,” Cervenka pointed out. “The aircraft will get better throughout its life and we’ll see really rapid progress in terms of the capabilities”. Vertical is currently targeting an entry into service date of 2026 – so watch this space: after all, “two years is a massively long time in this world!”
