I very much doubt that any electric plane based on lithium-ion battery technology will be a commercial success.
I believe that the first such success will be based on Lithium-Sulfur battery technology and will start in 3-5 years time.
Recent research breakthroughs around monoclinic gamma-phase sulfur appear to ease the main stumbling block of Lithium-Sulfur battery development (generation of
polysulfides).
https://www.researchgate.net/publica...Li-S_batteries
And I believe that the distant future winner will be Lithium-air battery technology.
To put things in perspective, the raw specific energy of fossil fuels is as high as 12 kWh/kg.
But only a fraction of this energy can be used to propel an airplane because of the thermic engine efficiency limitation, the propeller efficiency limitation, the weight of the engine, fuel tanks and hoses,
If we aim at comparing apples to apples, we should consider the usable mechanical power applied to the propeller shaft divided by the total weight of the propulsive system including the fuel weight.
If I take a modern turboprop engine like the PT6A-140A, for instance on a Cessna C208B (the aircraft doesn't have to be aerodynamically efficient for the sake of this comparison ;-) ),
the engine has a max cruise ESHP of 911 hp or 680 kW for an EFSC of 0.566 lb/ESHP/hr.
So, a flight of 3 hours at max cruise settings will consume 0.566 * 911 * 3 lb = 1547 lb of Jet A1 or 702 kg of fuel producing 2040 kWh of mechanical energy.
If we assume a propulsive system weight of 385 lbs + 143 lbs + 15 lbs + 15 lbs + 1547 lbs = 2105 lbs or 955 kg.
(engine_with_std_equipment + propeller + empty_tanks + other + fuel)
The useful mechanical energy divided by the total weight is 2040 kWh / 955 kg = 2.14 kWh/kg
So, we are just at 18% of the theoritical specific energy of Jet A1 and the PT6A-140A is one of the most efficient propulsive system for small airplanes.
If we do a similar calculation with a propulsive system based on Lithium-ion batteries, we start with a theoritical specific energy of up to 0.295 kWh/kg (Tesla's 4680-type battery cell).
This is only 2.5 % of the theoritical specific energy of jet fuel.
But, as with a thermodynamic engine, what counts is the usable specific energy.
An efficient light-weight (and expensive) electrical engine of 680 kW weights about 100 kg and has an efficiency of 90%.
For a complete battery pack, with electronic controllers, I'll extend the best battery pack specific energy available in Tesla cars : 0.160 kWh/kg.
For 2040 kWh, the pack should weight (100/90) * (2040 kWh / 0.160 kWh/kg) = 14,170 kg (not sure it fits in the plane ;-) )
I'll use the same propeller as for the PT6A-140A at 143 lbs or 65 kg and I'll add 15 kg of cables.
The total propulsive system weight is 100 kg + 65 kg + 14170 kg + 15 kg = 14,350 kg
The useful mechanical energy divided by the total weight is 2040 kWh / 14350 kg = 0.142 kWh/kg
This is just slightly less (11%) than the battery pack specific energy.
We are now at 6.6 % of the useful mechanical specific energy of jet fuel.
The lame situation of electric energy compared with fossil fuel energy has improved by a factor 2.7 when leaving theoretical specific energy comparison for useful mechanical specific energy comparison.
The 6.6 % of electric compared to fossil fuel means that we can expect that, all other things being equal, we can expect that lithium-ion electric fuel brings a reduction of range and endurance that is only 6.6 % of fossil fuel range and endurance.
Let's evaluate the prospects of Lithium-sulfur batteries and Lithium-air batteries.
The theoritical specific energy of lithium-sulfur batteries is expected to be around 550 Wh/kg.
If we apply the same energy density decrease ratio as for Tesla battery packs, the battery pack specific energy should be around (0.160/0.295) * 0.55 kWh/kg = 0.30 kWh/kg
The weight of a 2040 kWh battery pack will be (100/90) * (2040 kWh / 0.30 kWh/kg) = 7560 kg (about half of a lithium-ion equivalent)
The weight of the propulsive system of my electric Cessna Caravan will become 100 kg + 65 kg + 7560 kg + 15 kg = 7740 kg
The useful mechanical energy divided by the total weight is 2040 kWh / 7740 kg = 0.264 kWh/kg.
We are now at 12.3 % of the useful mechanical specific energy of jet fuel and 12.3% of the fossil fuel range and endurance.
For lithium-air batteries, a prospective assessment is more difficult.
The theoritical energy density is somewhere between 5 and 11 kWh/kg, depending on the nature of the electrolyte and the nature of the catalysts present at the cathode.
The higher end of the range is very close to the theoritical energy density of fossil fuels; so this is promising.
But, actually, the cathode absorbs oxygen during the discharge and becomes heavier as Li is transformed in Li2O2. the weight increase of lithium is with a factor 3.29.
As the discharged weight of the battery is as important as the charged weight of it, this ratio impacts the potential energy density of the battery.
It is thus reduced to a range between 1.5 kWh/kg and 3.3 kWh/kg.
If we compute as above the useful mechanical specific energy, we have:
Battery pack specific energy : between 0.814 kWh/kg and 1.79 kWh/kg.
Weight of a 2040 kWh battery pack : between 2785 kg and 1265 kg.
Total propulsive system weight : between 2965 kg and 1445 kg.
The useful mechanical specific energy : between 0.688 kWh/kg and 1.41 kWh/kg.
Percentage of useful mechanical specific energy of jet fuel : between 32% and 66%, with an equivalent relative range and endurance reduction.
I believe that below 10% of the theoritical fossil fuel range and endurance, nothing is commercially viable.
The 12.3% of Lithium-sulfur is just above this threshold and could be viable for niche markets.
The 32% to 66% anticipated performance of lithium-air would make it viable on markets where it can compete with synthetic fuels, in a situation where fossil fuels are so expensive that synthetic fuels replace them for aviation.