Electric vertical take-off and landing (eVTOL) aircraft offer the potential of personalised aviation and flying taxis in urban areas. However, eVTOL applications need very high-power density battery packs able to deliver high peak power during take-off and landing and that can be charged quickly between flights. At these high charge/discharge rates, a significant amount of heat is generated within the pack that needs to be safely dissipated. Large differences in temperature are experienced in different parts of that battery pack, which causes different cells to degrade at different rates, which can reduce battery life.
|By the numbers|
|Battery thermal management system weight||<5% of cell mass|
|Charge rate||15 miles/min|
|Charge rate relative to leading EVs||X2|
Comparison of Qdot’s projected battery performance with current state-of-art.
Most commercial cells are designed for electric vehicles and are optimised to store the maximum amount of energy per cell (energy density), rather than for power density or ability to be thermally managed. The challenge in optimising battery pack power densities for eVTOL applications is not only in the development of a lightweight thermal management system, but also in designing cells for efficient heat removal.
Under a Faraday Institution Entrepreneurial Fellowship, the University of Oxford spin-out Qdot has applied its proven and patented heat transfer technology, originally developed for use in nuclear fusion tokamaks, to the problem of effective heat dissipation in battery packs. More effective heat management has enabled a step change in the recharge rate of Li-ion batteries while protecting battery life. The thermal management requirements of tokamaks are exacting – heat loads can be in excess of 10 MW per square metre with temperatures over 100 million Kelvin.
The Faraday Institution Entrepreneurial Fellowship has been invaluable to the growth of our business and technology development. The connections it facilitated into Imperial and AMTE have been crucial. The fact that the fellowship did not require matched funding made a big difference for us as an early-stage business and has allowed us to build up testing and modelling capabilities critical to our future success. These capabilities, along with our proof-of-concept work, have provided a strong foundation, which we have successfully exploited to gain additional grant funding from other sources to continue our technology development.”
Jack Nicholas, Founder, Qdot
There are two methods of cooling of lithium-ion batteries. With surface cooling, high cooling rates are possible but at the expense of high layer to layer temperature differences, and uneven degradation, which shortens battery life. Tab cooling allows very small temperature differences between layers. Each layer behaves in the same way, degrades at the same rate, extending the life of the whole battery, and making it safer and more efficient. Source.
Qdot has been collaborating with researchers at Imperial College London working on the Faraday Institution’s Multi-Scale Modeling project, and with AMTE Power, to redesign a pouch cell to use tab cooling (see figure above) and to design a highly effective cooling system to achieve faster rates of heat transfer and much smaller temperature differences across and between cells. In doing so they have increased the recharge rates from ~6 miles/min to over 15 miles/min at cell level for eVTOL applications. They can achieve this whilst keeping the temperature rise in the cell to no more than 5°C and without causing large temperature differences between different parts of the battery. Using their heat dissipation technology, recharge rates are twice as fast as those in leading electric vehicles on the market today. This is one of the first practical implementations of tab cooling for any application.
Qdot describes their technology for electric vehicle applications
During the Entrepreneurial Fellowship Qdot has moved into its own laboratory facilities, developed key contacts in the aerospace industry, and increased its workforce from 2 to 7 full time equivalents. Follow-on technology development funding has been successfully secured through the Harwell Cross-Cluster Proof-of-Concept Fund, Tokomak Energy, the UK Innovation & Science Seed Fund and Innovate UK Accelerator Programme, and the Innovate UK and Office for Low Emission Vehicles Catalysing Green Innovation – Securing the Future of ZEV funding competition. It plans to seek funding from venture capitalists or angel investors in 2021.
Through using Qdot’s technology, battery designers may be one stage closer to no longer having to make trade-offs between power density and energy density.
In the near term Qdot plans to demonstrate its charge rate gains at the battery module and then pack level before deploying it on a partner’s demonstration eVTOL aircraft. Its longer-term aim is to enable the market for electrified flight through the development of hybrid propulsion systems – integrating its battery technology with electric power generating systems using renewable fuels.
The non-passenger eVTOL battery pack market is expected to grow from £16.4 billion in 2020 to over £31.1 billion by 2025, at a CAGR of 13.8%. Qdot’s particular focus will be on heavyweight drone applications in agriculture, construction, and logistics. Longer term, the passenger/non-passenger eVTOL propulsion market is estimated to represent a market opportunity of £92 billion by 2035. The UK historically has a strong aviation sector, which ranges from global manufacturers to SMEs, and has been estimated to provide £22 billion annually to the UK’s GDP. The country is therefore in a strong position to capture a significant proportion of the future eVTOL market.
In the medium term the company also plans to target other sectors that demand high availability or high performance such as motorsport and heavy goods vehicles. If successfully commercialised at low volume, Qdot battery packs would be assembled at their premises and sold to a system integrator. For higher volume manufacture, the technology would be licensed to speciality vehicle manufacturers.
Our collaboration with Qdot has allowed AMTE Power to identify cell design parameters that, once optimised, will help the development of our cells. It has also allowed us to understand and apply how the cell cooling technology Qdot is developing can help improve the overall performance and longevity of AMTE Power cells, and in conjunction provide a better solution for the applications the technologies will go into.”
Will Owens, Technical Sales Lead.
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Success story published July 2021.