Amprius Technologies: Independent Test Lab Verified Amprius’ 500 Wh/kg Battery Cell

It stores twice the energy of a comparable, commercially available lithium-ion cell.

Amprius 500 Wh/kg battery cell
Mar 28, 2023 at 8:55am ET

By: Mark Kane

Amprius Technologies announced that the performance of its latest lithium-ion battery cells was independently verified by Mobile Power Solutions, confirming unprecedented energy density.

According to the company, its lithium-ion cells, based on the Silicon Anode Platform, offer roughly two times higher energy density than state-of-the-art,= commercially available lithium-ion cells, which means a two times longer run time (or alternatively, half the weight/size, assuming the capacity is the same).

The Mobile Power Solutions’ report (available here) indicates that the Amprius’ 6.6 Ah battery cells, with a nominal voltage of 3.45 V, have an energy density of more than 500 watt-hours per kilogram (Wh/kg) and more than 1,300 watt-hours per liter (Wh/l). That’s a step above 450 Wh/kg reported in February 2022.

That’s a fantastic result, achieved at a temperature of 77 degrees Fahrenheit (25 degrees Celsius).

  • cell nominal capacity: 6.604 Ah
  • cell nominal voltage: 3.45 V
  • cell nominal energy: 22.8 Wh
  • gravimetric energy density: >504 Wh/kg
  • volumetric energy density: >1321 Wh/l
  • test conditions: 77 °F (25°C) and C/10 charge/discharge current (aside C/100 charging at the top, above 4.37 V)

The charging and discharging current during the test was C/10 (10-hour charging and 10-hour discharging cycle), which is relatively slow for EV applications. At C/10 current, a 100-kilowatt-hour (kWh) battery would deliver just 10 kilowatts (kW) of power.

We don’t know whether there was any limitation in the charging/discharging power due to the silicon-rich anode, but this is an important thing for electric cars (specifically, the cycle life at higher currents).

Amprius’ general info says that its batteries can recharge in as low as six minutes to 80 percent state-of-charge (SOC) (it was verified in 2021 for 370 Wh/kg cells). On the other hand, the same info says that the cycle life varies from 200 to 1,200. Usually, the lower numbers were correlated with higher energy density, higher charging/discharging current, and non-optimum temperatures.

In the worst case scenario – 200 cycles, a 100 kWh battery would be worth some 20,000 kWh of energy until its capacity will decrease to 80 percent of the initial value. That would be just 80,000 miles (128,700 km), assuming energy consumption of 250 Wh/mi (155 Wh/km).


Anyway, Amprius targets the aviation industry first and the electric vehicle segment “eventually.” The company does not say anything about the price, which might be another factor as to why aviation is the starting point (they prioritize energy density above longevity and price).

“Amprius’ next-generation cells are well positioned to power products in the fast-growing aviation and, eventually, electric vehicles markets, estimated to be collectively over $100 billion in battery demand by 2025.”

The prototypes of the record-breaking battery cells will be shipped to select customers in 2023.

AALTO HAPS, the Airbus subsidiary developing the 100% solar-electric High Altitude Platform Station for connectivity and earth observation applications, was mentioned in the press release, which indicates that it will be one of the lucky select customers.

Jon Bornstein, President of Amprius Lab said:

“These cells provide a run time of 200% compared to state-of-the-art graphite cells, while being lighter and smaller than other batteries with the same energy content. This latest validation continues Amprius’ track record of producing the world’s most powerful battery cells and sets an industry benchmark for next-generation battery technology that will ultimately revolutionize how high we fly, how far we travel and how long we can use our devices.”

Earlier this year, Amprius announced that it signed a letter of intent for an approximately 774,000 square foot facility in Brighton, Colorado to build its first battery plant – initially 0.5 gigawatt-hours (GWh) per year, with a target for 5 GWh/year later. Technically, the factory might be expanded up to 10 GWh/year the press release says.

Read the press release: