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Amprius is a Fremont, California-based developer and manufacturer of high energy density lithium-ion battery materials and batteries. The company's silicon nanowire anode and silicon-graphite anode deliver anode capacity up to 3200 mAh/g and battery energy density up to 510 Wh/Kg. These batteries were first brought on market and sold in 2013. Amprius's silicon technology was originally developed at Stanford University.
Amprius says part of their technology platform includes a battery ecosystem, including cell design, product development, quality and abuse testing, anode manufacturing, high capacity cathode development, prelithiation, high voltage electrolyte formulation, and battery packaging. They are also working towards better manufacturing technologies for silicon anodes. And they are working towards ne cathode materials to increase the energy density of their batteries.
Amprius's silicon nanowire technology was developed to solve problems with silicon in batteries. Their technique is to store lithium in silicon nanowires, nanowires about one-thousandth the thickness of a sheet of paper. These nanowires still swell when they take-up lithium but the nanotechnology keeps the silicon from fracturing.
The silicon nanowires are better able to withstand the swelling and shrinking of charging, which fractures traditional silicon-based anodes, because at a smaller, nano, scale they have a higher percentage of their atoms at their surface relative to the number in their interior. More surface atoms means they can move more easily in response to stresses and strain. They paired this with a carbon shell through which lithium ions could readily pass for the silicon nanoparticles. These shells gave the silicon atoms ample room to swell and shrink while protecting them. Amprius said the coating allowed the anodes to retain 74% of their capacity after 1000 cycles of charging and discharging.
Cross Section Image of Amprius Technologies' Silicon Nanowire Anode
Their resulting technology includes 100% silicon nanowire anodes, silicon-graphite composite anodes, lithium-rich cathodes, and high voltage electrolytes tailored for silicon.
Amprius says the benefits of using nanowires include:
- toleration of volume expansion
- micro and macro porosity that accommodates swell
- improved solid-electrolyte-interphase and cycle life
- reduced anode thickness compared to graphite electrode thickness.
- silicon is connected directly to the substrate with no binders and nothing to block the flow of electricity
Amprius says the applications of their batteries have included:
- energy cells for high altitude pseudo satellites
- cells for conformal-wearable battery packs
- power cells for quadcopters
- power cells for electric vertical take off and landing vehicles
- smart phone batteries
- power cells for electric vehicles
In 2016, Amprius introduced equipment for high volume manufacturing of their silicon nanowire anodes. The equipment uses inline, continuous, and roll-to-roll production methods to produce the silicon nanowires.
Filed February 2, 2018, the patent includes nanostructures for lithium ion battery electrodes and methods of fabrication. In some embodiments, a nanostructure template coated with silicon coating is provided. The silicon coating may include a non-conformal, more porous layer and a conformal, denser layer on the non-conformal, more porous layer.
Filed November 25, 2015, the patent includes electrode layers for use in rechargeable batteries and related fabrication techniques. The electrode layers have interconnected hollow nanostructures that contain high capacity electrochemically active materials. In certain embodiments, a fabrication technique involves forming a nanoscale coating around multiple template structures and partially removing and/or shrinking structures to form hollow cavities.
Filed September 18, 2015, the patent includes electrochemically active electrode materials, electrodes using such materials, and methods of manufacturing such electrodes. Electrochemically active electrode materials may include a high surface area template containing a metal silicide and a layer of high capacity active material deposited over the template.
Filed July 2, 2012, the patent includes template electrode materials and structures for lithium ion cells. According to various embodiments, an electrode can include a nanostructured template, an electrochemically active material layer coating the template, and a first intermediate layer between the nanostructured template and electrochemically active layer.
Filed March 22, 2012, the patent includes a lithium ion battery electrode with silicon nanowires used for insertion of lithium ions and including a conductivity enhancement. And it had the nanowires growth-rooted to the conductive substrate.
In 2018, Amprius's silicon nanowire batteries were selected for use in Airbus's Zephyr program. The Zephyr program is manufacturing the Zephyr S high-altitude pseudo-satellite (HAPS) which is solar-powered and unmanned. The Zephyr S was able to fly for more than 25 days and set a record for stratospheric flight at the time.
Following from the Zephyr program's early success, Airbus Defence and Space partnered with Amprius. Part of the partnership included financing towards the development of new batteries based on silicon nanowire anode technology and the development of higher volume production capacity of silicon nanowire energy cells.
