INR-21700-P45B cylindrical rechargeable battery cell

The Molicel INR-21700-P45B is a cylindrical 21700 lithium-ion rechargeable cell, a low-impedance power cell designed for applications that draw high current from a compact cell. Molicel lists drones and eVTOLs among its target uses, together with motorcycle racing and high-performance electric vehicles, so the cell is a building block for battery packs in aircraft propulsion.

The cell is intended to be assembled into packs by battery manufacturers or integrators. Its low internal impedance reduces heat generation at high discharge current and limits voltage sag under the short, heavy loads seen at take-off, climb and hover in electric vertical lift aircraft.

The main figures are a nominal voltage of 3.6 V and a typical capacity of 4.5 Ah, equal to 16.2 Wh of stored energy per cell. The specific energy is 242 Wh/kg (gravimetric) and the volumetric energy density is 643 Wh/L. The discharge current is 45 A, equivalent to 10 C on a 4.5 Ah cell, which matters for a pack sized on peak power rather than energy. The standard charge current is 4.5 A, and the maximum charge rate is 3 C for faster turnaround between flights. Dividing pack power by these current ratings gives the number of parallel cells required.

Mechanically, the cell has a maximum diameter of 21.6 mm and a maximum height of 70.2 mm, with a maximum weight of 69 g. Designers must leave room for these maximum dimensions, for cell holders or welded nickel strips and for the spacing needed for thermal management. External connections, protection circuitry, cooling and the battery management system are defined by the pack design, as the product is supplied as a cell and not as a pack.

For documentation the maker's product page lists test reports and certificates for UL, UN and IEC, together with a safety data sheet and a datasheet, which are released on request through a form. Pack builders should obtain these documents for transport and safety qualification of their own battery assemblies.

Typical applications are battery packs for eVTOL aircraft, multirotor and other electric drones, and other high-power electric platforms such as racing motorcycles and sports cars.