Electric Aviation
Electrification has expanded into the airline sector, which is the result of the attempted reduction of carbon footprint of the aviation industry, but it does open some interesting points for consideration. Currently, the aviation industry accounts for 2~3% of the total global carbon emissions – a small figure but considering other industries are working towards greener energy sources, this figure is expected to jump to ~27% by 2050. This means that the aviation industry will be placed under larger and larger pressure to become less carbon intensive, i.e. electrification must occur.
We must distinguish that the niche electric aviation aims at replacing is not long-haul, intercontinental flight, but it aims to replace short travel of under 250 miles. This comes from the innate nature of battery systems where the mass of the stored energy source is kept within the vehicle system even after conversion into thrust. By contrast, the current jet fuel system merely combusts away the jet fuel, leading to a lighter, more efficient aircraft throughout the flight. In addition, the poorer energy density of battery systems compared to jet fuel (~7% even when factoring in the efficiency of electric power trains), means that it’s too heavy to adopt purely electrified aviation for long-haul travel.
Having limited our discussion to short travel, the benefits of electrification of aviation are the following (based on my limited understanding & brief search) :
Lower operations cost (similar advantages found in EVs can be assumed),
Quieter operations (thereby opening new routes),
And increase mechanical reliability (again, similar advantages to EVs).
These benefits, along with greener operation, are reasons why electrification of aviation is gaining momentum (and capital investment). However, the benefits above are predicated based on one simple component reaching the performance and safety level required – the battery.
Cheaper battery systems are imperative, but this will follow as the aviation industry is a follower to the EV industry thereby enabling it to tap into the already existing design/process/SCM schemes. However, there is always the risk of having to compete with EV industry for valuable metals critical for battery manufacturing. A hunch of mine is that slightly more expensive battery systems will be tolerated as a burning battery in the middle of the sky is a greater safety hazard compared to a land-based EV – that is, more leniency in terms of battery design and material selection should be allowed to ensure that extra safety margin.
Fast charging is also critical as the airplanes are usually on the move and operated 24/7 by simply switching out the crew for the next flight. This means that, i) the aircraft should potentially be of a higher voltage system compared to EVs to improve efficiency and reduce required current, ii) adequate and extensive charging infrastructure must be built, and iii) the charging time must be such that it does not sacrifice operation time significantly compared to jet fuel system. Another thought of mine is that solar panels will be an effective addition as that higher travel elevation largely removes the cloudiness parameter from the equation and that the establishment of battery swapping stations may be an option to maximize operation time at smaller airports without the required charging infrastructure.
Overpotential over life is another factor that needs to be considered from material design. Unlike the EV where the driver behavior consists of short 2~30sec bursts of discharge, the electric aircraft essentially consists of constant or near-constant discharge throughout the entirety of the flight. This opens the door to overpotential buildup, which causes ‘sagging’ of voltage profiles thereby requiring more current for the same power output and runs the risk of reaching the voltage profile knee point even when enough SOC remains. Therefore, either the implemented battery system exhibits enough energy to ensure low equivalent C-rates to limit overpotential buildup OR to implement battery materials with good rate capability behavior to limit overpotential buildup (cathodes with higher Co content, high surface area anodes like hard carbons, etc.)
Safety from potential ISC is more related to process features of battery manufacturing, which can be overcome with slowing down production, increasing number of check points, and implementing safer design parameters. Further discussion is warranted but… this is a touchy subject and will be discussed hopefully in another post in the future but in a limited scope. However, selection of less energy dense materials like LFP can be a solution especially when considering the better thermal propagation characteristics of LFPs (not to mention the price benefits it brings).
BMS accuracy takes on an increased importance as, again, the ramification of safety event mid-flight is significantly higher than mid-driving. Now this can be achieved by having greater number of sensors for each battery to monitor the battery SOC and constructing precise prediction models based on large amount of data accumulated throughout the development phases. On the other hand, material selection can facilitate this by ensuring accurate SOC tracking based on voltage reading. This, unfortunately, is extremely difficult to pull off in the case of LFPs owing to its flat voltage profile.
Many of the lessons learned in the EV industry can be implemented in the electrification of aircrafts but it poses unique problems that must be accounted for. This may potentially mean that the batteries implemented in aircrafts be tailor made rather than using off-the-shelf EV batteries. However, the overall direction is the same as EVs – cheaper & safer systems, faster charging, and better battery management. Electrification of aircrafts are at a prototype stage, but what’s for certain is that it will expand and make the short distance travel niche its own.
