eVTOL developer Vertical Aerospace selected Molicel to provide battery cells for Vertical's VX4 eVTOL aircraft. (Photo: Vertical Aerospace)

Lithium-ion cell manufacturer Molicel was recently chosen by Vertical Aerospace to supply battery cells for the VX4 air taxi. Vertical is designing and manufacturing the VX4, its electric vertical take-off and landing (eVTOL) aircraft, with capacity for a single pilot and four passengers. The eVTOL developer is targeting entry into service in 2025 for the VX4. 

Vertical revealed its full-scale design of the VX4 in December 2021, and the company announced a merger with Broadstone Acquisition Corp. around the same time. Since then, Vertical’s ordinary shares have been listed on the New York Stock Exchange as EVTL. Conditional pre-orders for Vertical’s aircraft total 1,350, including customers such as American Airlines, Avolon, and Bristow.

Following the latest announcement from Vertical Aerospace, Molicel, or E-One Moli Energy Corp, will work in coordination with Vertical as a strategic partner to supply high-power cylindrical cells for the eVTOL aircraft. Vertical selected Molicel in part because of its high-power cylindrical cell format, which will help Vertical, in the process of certifying its aircraft, to demonstrate management of thermal runaway events.

“The cylindrical cell format has been selected by many OEMs, not only for eVTOLs but also automobiles, due to its CID top cap safety design which allows internal pressure to be released so as not to further accumulate heat inside,” a source from Molicel told Avionics International in an emailed statement. 

The company’s representative noted that the format offers the ability to release the pressure in a specific direction, enabling a high level of safety in the battery system. Additionally, the source wrote, “Its rigid body can protect a single cell to remain independent in a thermal runaway situation, which means the chances of propagation [are reduced] by the battery pack design.”

Based on the current agreement, Molicel’s team will support Vertical Aerospace throughout the certification process and during its eVTOL’s entry into service. 

The main advantage of Molicel’s battery cell, according to the company’s representative, is the low impedance—referring to both internal resistance and reactance. The low-impedance battery cell technology is well-suited for applications requiring a high rate of power discharge during the take-off and landing phases, as well as fast charging capabilities to increase ridership capacity. “Since the battery cell is designed for high power discharge and fast charge, the life cycle thus is much better compared to high impedance types of energy cells,” the source explained.

A joint working group was established between Vertical and Molicel that is focused on safety of the battery cell system for the VX4 as well as reliability and performance. Vertical’s eVTOL and the battery system from Molicel will be certified with both the UK’s Civil Aviation Authority (CAA) and the European Union’s Aviation Safety Agency (EASA).

Molicel operates a facility in Taipei with 1.6GWh in annual production capacity, and the company plans to open a second Gigafactory in Kaohsiung City, also in Taiwan, next year. According to the representative, annual capacity at this new facility is expected to reach 1.8GWh in 2024. The production process is designed to support Molicel’s customers with solutions for customization, and improved levels of accuracy are “key for keeping our latest low impedance cells INR21700-P45B suitable for high-quality mass production,” commented the company’s spokesperson. They added that this factory will have the highest production capacity for high-power cell manufacturing in the world.

According to the announcement from Vertical Aerospace, Molicel’s advanced manufacturing technology includes a unique approach to cell traceability that “will guarantee the consistency and quality required to meet aerospace standards.”

The founder and CEO of Vertical, Stephen Fitzpatrick, commented that safe, high-performance battery systems are necessary for electrifying aviation. “Molicel has a rich history of innovation and pushing the boundaries of what’s possible in energy storage. We see many similarities between ourselves and Molicel and we couldn’t think of a better partner to bring the VX4 to market,” Fitzpatrick stated in response to the formation of the new strategic partnership.

Molicel’s high-power lithium-ion cells offer Vertical Aerospace the ability to keep the aircraft’s weight low, and enable increased safety as well as improved charging capabilities, said Dr. Limhi Somerville, Head of Battery for Vertical, regarding the partnership with Molicel. “It has been a privilege to work alongside the excellent Molicel team in testing, evaluating and analysing their lithium-ion cells. Both here and in Taiwan,” Somerville remarked.

Avolon, an aircraft leasing company and one of several companies that has pre-ordered eVTOLs from Vertical Aerospace, placed an order for 500 VX4 aircraft last year. An announcement in March revealed that Air Greenland committed to purchasing or leasing multiple VX4 eVTOLs from Avolon to add to its fleet. Air Greenland and Avolon have also formed a working group to evaluate applications for eVTOL transportation in Greenland.

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