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Amprius’ silicon nanowire Li-ion batteries power Airbus Zephyr S HAPS solar aircraft

Amprius, Inc., a manufacturer and developer of high energy and high capacity lithium-ion batteries, announced that the company is supplying advanced lithium-ion cells to the Airbus Defence and Space Zephyr Program. Using Amprius’ cells, which contain a 100% silicon anode, the Zephyr S flew more than 25 days, setting a new endurance and altitude record for stratospheric flight.

The Zephyr platform is a new class of unmanned air vehicle that operates as a high-altitude pseudo-satellite (HAPS) enabling affordable, persistent, local satellite-like services. Combining solar power and lithium ion batteries, the Zephyr aircraft holds world records for endurance as well as altitude, flying at 70,000 feet or higher.

This stratospheric platform can fly for months at a time and combines the persistence of a satellite with the flexibility of an unmanned aerial vehicle (UAV). The platform is expected to be used in a wide range of emerging applications, including maritime surveillance and services, border patrol missions, communications, forest fire detection and navigation.

Our collaboration with Amprius in the application of their silicon nanowire based lithium ion cells to the Zephyr has been important to the success of the HAPS program. The high specific energy of Amprius batteries enable the Zephyr to fly uninterrupted in the stratosphere which would not be possible with lower performance batteries. This will further extend the capability and utility of the Zephyr platform for our customers.

—Sophie Thomas, Airbus HAPS Program Director

Based on its proprietary silicon nanowire technology, Amprius has demonstrated breakthrough performance in energy density and cycle life. Silicon anodes have much higher specific capacity compared to graphite anodes which are used in conventional lithium ion batteries. However, in particle or film structures silicon is not stable and lasts only a few recharge cycles. Amprius’ silicon nanowire structures overcome this instability and thereby enable hundreds of cycles with specific energies of over 435 Wh/kg and energy densities in excess of 1200 Wh/liter.

The silicon nanowire structure includes a metallically conductive nanowire core, metallurgically connected to the current collector. This connection is essential in creating and maintaining a stable electrical connection and mechanical structure at the electrode level, according to an Amprius presentation at the Power Sources Conference earlier this year. Each silicon wire is directly connected and does not need to rely on particle-to-particle contacts for conductivity; the silicon material remains in electrical contact over the entire cycle life of the cell.

The fast loss of electrical connectivity and changes in mechanical structure that plague the majority of other silicon technologies are virtually non-existent in the rooted silicon nanowire anodes. Moreover, this significant stability is achieved in a structure that is virtually 100% silicon, without any binder or conductive additive to dilute its active material content.

—Constantin Ionel Stefan, Amprius

The nanowire material structure also enables a relatively high 94% first coulombic efficiency in half cells and 90% coulombic efficiency in full cells with LCO cathode.


With the same cathode and separator components, the silicon nanowire anode technology significantly increases energy density and specific energy (solid circles are demonstrated products). Source: Amprius.

Amprius maintains an R&D lab and corporate headquarters in Sunnyvale, California; an R&D lab and state-of-the-art pilot production line in Nanjing, China; and a manufacturing facility in Wuxi, China. Amprius is financed by leading venture capital and private equity investors including Trident Capital, VantagePoint Capital Partners, Google Executive Chairman Eric Schmidt, IPV Capital, Kleiner Perkins Caufield & Byers, SAIF Partners, Chinergy Capital, Wuxi IDG and DADI Capital.



Good news for future much lower cost satellites for improved communication +++ services.

Lower altitude lower cost communication/navigation satellites could replace many current ground portable phone stations and supply services for future ADVs. A new network could also service the shipping industry with lower cost communication and surveillance services. .


Higher energy density could make that eVTOL possible.


90% coulombic efficiency doesn't sound very high.

Best current li-ion is 98%+.

Of course, if energy density and specific energy is very high, this will still have a market.


90 % coulombic efficiency = 10 % of the electrons supplied used by parasitic reactions...
Difficult to imagine such a battery able to perform hundreds of cyclces with specific energy higher than 435 Wh/kg.
May be it was the energy efficiency instead ?


25 days in the HAPS application would be just 25 or 26 cycles. I wonder if the batteries were the limiting factor.

Joe Yang

Great batteries and materials science.

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