2.3.4. Battery

The automotive and aviation industries are currently dominated by lithium-ion batteries; therefore, to establish the configuration of the battery, we considered six important factors: the Specific Energy, Specific Power, Cost, Life Span, Safety and Performance. Lithium cobalt oxide (*LiCoO*2)—LCO; lithium nickel manganese cobalt oxide (*LiNiMnCoO*2)— NMC; and lithium iron phosphate (*LiFePO*4)—LFP batteries are the three most promising concepts for future batteries [52].

Figure 3 shows a comparison between the main variables investigated for the selection of the battery. Figure 3a presents a comparison between the specific power and the specific energy of the three selected battery types. Those figures, in combination with the requirements for the aircraft powertrain, are used to decide on the battery chemistry. High power needs to be achieved, and high specific energy use is attenuated since the batteries will be used mainly at takeoff and not during the flight. For this reason, a LFP battery that meets those characteristics was chosen.

Figure 3a indicates specific powers up to 2000 W/kg with 140 Wh/kg for LFP batteries. Figure 3b represents a radar chart that relates the aforementioned variables where LFP batteries stand out with respect to their life span, safety and specific power. LFP batteries have an ideal cycle life of 1000–2000 with a charge rate between 1 and C and discharge rate of between 1 and C and 3C. This means that the battery can provide between one and three times its capacity in energy output per hour [53]. However, it is important to note that the discharge rate of LFP batteries is generally higher than the charge rate; however, they maintain better performance during their life cycle compared to the other batteries mentioned [54].

**Figure 3.** (**a**) Specific power vs. specific energy of Li-ion batteries distinguished by cell chemistry [55]. (**b**) Radar chart of LFP, LCO and NMC battery comparison [56].

#### 2.3.5. Superconducting Motors and Power Electronics

As mentioned in Section 2.3.2, the hydrogen is used to cool the powertrain components. This enables the use of superconducting materials for the motors, inverters and cables. The efficiencies and masses for the cables and inverters were estimated using the values from Hartmann et al. [47]. The superconducting motor mass can be estimated with the equation of Lukaczyk et al. [42], while the efficiency was estimated at 98% [47]. Power densities for high-temperature superconducting (HTS) motors producing 1 MW above 13 kW/kg are feasible according to Yoon et al. [57] with their market readiness expected in the early 2030s [58]. The total power of the aircraft is expected above the reference aircraft's power at about 4000 kW. The selected power density for the motor is 15 kW/kg, resulting in a slightly heavier motor than the estimation equation according to Komiya et al. [41] would predict.
