Amprius Launches Silicon-Anode Battery For eVTOL

With its energy-dense batteries already flying in solar-power stratospheric uncrewed aircraft built by Airbus and BAE Systems, Amprius has unveiled a high-power version of its silicon-anode lithium-ion cell for drones and electric-vertical-takeoff-and-landing (eVTOL) vehicles.

The battery cell has a power density of 400 Wh/kg at a C/5 discharge rate typical of electric vehicles. This compares with 250 Wh/kg for a commercial graphite-anode lithium-ion battery, Amprius says.

But the battery is designed to also provide high power and can go as high as a 10C discharge rate without exceeding the temperature limit, the company says, noting conventional cells are limited to around 4C. The new high-power, high-energy cell can also be charged at high rate, reaching an 80% charge in 6 min. or fewer.

High power is required for eVTOL vehicles for short durations during takeoff and landing. The new cell has a power density of 3,500 watts per kilogram at a 1C discharge rate, rising to 4,400 watts per kilogram if the battery is 100% discharged at 10C. At 10C and a typical 30% depth of discharge, power density is about 2,800 watts per kilogram. This compares with around 500 watts per kilogram for a conventional cell, Amprius says.

“The discharge rate requirements for eVTOL depend on the aircraft design. Our high discharge rate capability allows us to support a higher payload without running out of power. It demonstrates that our cell can sustain very high rates of discharge while still maintaining high energy levels,” Amprius says.

Lilium is using silicon-anode cells from Ionblox for the batteries in its Lilium Jet ducted-fan eVTOL. According to independent testing data released by the companies, these cells have an energy density of 327.5 Wh/kg and a power density of more than 3,000 watts per kilogram using a 12C rate for 30-sec. bursts.

In March, Amprius introduced a 500 Wh/kg silicon-anode battery cell designed for high-altitude platform systems that fly for long durations at low power. The battery has flown on Airbus’ Zephyr and BAE’s Phasa-35 stratospheric aircraft.

“The cells use the same anode architecture and similar cathode chemistry, but they have different designs. The 500 Wh/kg cell is an ultrahigh-energy design for ultralong duration, low-power discharge,” the company says.

The cycle life for silicon-anode cells can be shorter than for conventional graphite-anode batteries. “Initial testing suggests that the new ultrahigh-power, high-energy cell will surpass a few hundred cycles under standard conditions,” Amprius says.

Fremont, California-based Amprius expects to have samples of the high-power, high-energy cell available for testing by customers by year’s end, with the commercialization of the new battery scheduled for early 2024.