Enabling high energy dense batteries through silicon nanowire anodes 

Ionel Stefan – CTO Amprius

0:00:00   today I'll talk about the
0:00:05   extreme performance off little mind cells enabled by the silicon unaware and Empress is now a 12
0:00:13   year old company, and Empress Technology says the U. S branch focused on Silicon Nano around
0:00:19   products. The first cell product with silicon, Anwar Arnold, was released in 2018, and current
0:00:29   performance succeeds 1200 water per liter and 450 watt hours per kilogram. This is all possible due
0:00:36   to many related technologies that enable the silicon on our platform, including 100% silicon on our
0:00:44   structure, sell electro chemistry and sell designs. The reason why we're discussing silicon today is
0:00:53   it's very high storage capacity for lithium, in fact, the highest among all materials. The main
0:00:59   difference versus graphite that makes test capacity possible is the storage mechanism graphite
0:01:06   stores leading between layers in a so called inter curation reaction resulting in a maximum ratio
0:01:13   off about 1 to 6 off lithium to carbon atoms. There are no carbon carbon bonds broken into his
0:01:21   reaction, and the structure suffers minimal changes, which makes the reaction very reversible.
0:01:29   Leading reacts with silicon by very different mechanism breaking silicon silicon bonds informing
0:01:38   inter metallic or ali faces with a maximum ratio 15 to 4 at room temperature. This allowing or
0:01:47   conversion reaction called, is a much more difficult reaction to reverse toe the initial structure
0:01:54   after the litigation because all silicon silicon bones need to be reformed, and that is one of the
0:02:02   difficulties in making silicon a replacement for graphite. However, research is pushing in that
0:02:09   direction because the storage capacity is about 10 times higher than that of graphite has shown here
0:02:16   for the silicon nanowires. Ronald, these are half cell data for silicon and graphite. Down to 10
0:02:23   million gold, very close toe litem plating. The pure silicon structure proves that almost
0:02:32   theoretical capacity could be achieved. And then the first efficiency, which is a gap here, um, can
0:02:40   be as high as that for graphite at 94%. Okay, the advantage brought in by silicon and it can be
0:02:49   easily seen in this model comparison Ah, model that was already proven in riel sell products. First,
0:02:57   the model replaces the graphite shown in orange with silicon in a state of the art graphite cell. Um,
0:03:06   with 300 watt hours per kilogram and 730 water per liter performance levels. Even this direct
0:03:16   replacement already increases the specific energy toe, 400 watt hours per kilogram and the energy
0:03:22   density toe 1080 water per liter. Moreover, in the silicon sell, the cattle now becomes the thicker
0:03:31   electrode, Um, and because the thickness in the in the graph itself was not the limiting thickness,
0:03:40   higher loadings are possible. So in silicon cells, with higher loading results in cells that are
0:03:49   slightly thinner and slightly heavier. Um, due to the increased proportion off the cattle in the
0:03:57   cell and ah specific energy of 450 watt hours per kilogram and 1320 what are her? Later? This
0:04:07   configuration was already validated temperatures and results in practical and capacity off about
0:04:13   22,000 million power program and 1500 million power per cubic centimeter. Overall, the model for
0:04:22   small cell indicates a 33% improvement by direct replacement and 50% improvement with high electoral
0:04:30   loading and no other cell component changes off course. We cannot discuss silicon without talking
0:04:37   about the route off all difficulties with US material. The volume change during litigation. A
0:04:43   typical value for graphite is about 10% change in volume during litigation, while the silicon
0:04:48   capacity is almost 10 times as high. The volume changes almost 30 times higher for silicon and
0:04:54   graphite. That makes it very difficult for the mechanical stability of the material. For example,
0:05:01   films off silicon crack buckle or can wrinkle or even break the supporting foil particles also crack
0:05:09   and disconnect from from the conductive network becoming inactive. The swelling properties off
0:05:15   silicon are responsible for the three main failure mechanism of the silicon anad. The material
0:05:21   polarization and electrode collapse mentioned earlier are effects um, at the material and electoral
0:05:28   level due to the repeated cycles on falling expansion and contraction. A third mechanism involves
0:05:34   reactions of the materials surface, which, due to its growth over time, leads to S C. I A population
0:05:42   impedance growth and electrolyte consumption. The resolution to material electro swelling is, ah,
0:05:49   structure that limits material swelling through material porosity and electro swelling by wire
0:05:54   density, which is the distance between the wires. The third failure mechanism I see a growth is
0:06:01   mitigated by a final coating that creates a smooth, low surface area for interactions with the
0:06:07   electrolyte. The manufacturing off such structure includes three steps on unaware growth Step bulk
0:06:16   Silicon Deposition Step uh, which takes, uh, care off most of the silicon amount and the final dance
0:06:25   coating step. The three D structure ensures not only enough porosity for the material, but also
0:06:31   enough the position surface for high loading off silicon. This is very important for reducing the
0:06:38   cycling capacity of material, the rial structure off Deano, the Second and Iran. It looks similar to
0:06:45   the target somewhat like a microscopic double sided carpet. This structure is mechanically robust,
0:06:52   has very good electric conductivity and connectivity and the high porosity, which makes it ideal for
0:06:58   high power applications.
0:07:02   The scalability of the manufacturing was demonstrated by integrating the three main manufacturing
0:07:07   processes into a roll to roll pilot line adapting technologies from solar industry. The pilot lines,
0:07:14   single piece off equipment replaces all graphite and not related equipment and processes powder
0:07:20   mixing slurry, preparation, coating, drawing and culinary. The end product off the pilot line is a
0:07:28   role are not ready for cell assembly. Empress has recently installed a second pilot line to
0:07:34   accommodate the initial demand for Silicon Nano. Our cells um together having a capacity off almost
0:07:41   half a megawatt hour. As I mentioned earlier, the Silicon Anwar Arnold has intrinsically high power
0:07:49   capability. This Rigoni plot shows that three power energy platforms that were developed by matching
0:07:57   silicon unaware Ronald toe different capital structures with high loading cattle. The specific
0:08:04   energy reaches 450 water per kilogram but has relatively narrow power range. This platform is used
0:08:12   in application that need operation times of many hours and optimize. Highlighting structure resulted
0:08:18   in cells with specific energy off 400 what are per kilogram and specific power off 1000. What per
0:08:26   kilogram when match with high power cattle. The seller results resulted still have high specific
0:08:34   energy off over 350 watt hours per kilogram and can support 3000. What per kilogram specific power
0:08:42   continuously. The limits are usually visible in a cell body temperature shown next to each data
0:08:49   point we recommend, usually below 60 degree at the end of discharge.
0:08:57   Let's talk about some other sell properties. The cycle life is probably the most important and
0:09:03   directly impacted by the mechanism discussed before. However, the silicon nanowires structures
0:09:08   mitigates this failure mechanism and can enable cycle like the satisfied the requirements for
0:09:14   multiple applications. For example, silicon lithium cobalt oxide cells with a specific energy off
0:09:21   over 400 watt hours per kilogram can cycle over 200 cycles as at full depth of discharge. Other
0:09:28   cells off chemistry match for power applications can cycle over 700 cycles. In general, the cycle
0:09:36   life is affected by the same factors in as graphite and can be improved by the same methods as, uh,
0:09:42   those used in graphics cells.
0:09:46   The silicon unaware Arnold has another advantage over graphite, the higher and potential. This means
0:09:53   that the risk of leading plating and then transformation is significantly reduced even at full
0:09:58   charge, which allows the cells to operate at lower temperature as low as the electrolyte supports it,
0:10:05   um, and enable both fast charging at low temperature and charging below zero degrees Celsius. For
0:10:14   example, a silicon NMC cell chemistry developed for evey applications has higher than 70% energy
0:10:22   retention at minus 20 degrees C. Um, which exists the D. O. E and use ABC goals for 2025. In a NASA
0:10:31   project, emperors developed a new electoral formulation that was liquid at minus 50 degree and was
0:10:38   able to cycle at that temperature. Both charge and this year retaining about 70% off the room
0:10:45   Temperature capacity at silver five rate
0:10:51   silicon materials as are seen as the solution for highly charging because theano thicknesses uh much
0:10:58   with this compared to graphite, as I mentioned earlier, um, pure silicon electoral also have higher
0:11:05   potential in low risk off plating. Lithium does. It's not a surprise that without any specific cell
0:11:13   design changes, silicon NMC cells can be charged more than 80% in 15 minutes, exceeding current TV
0:11:20   targets. Moreover, high charge rates don't seem to negatively impact the cycle of us for graphic
0:11:26   cells. Now I want toe mention a few examples of products and applications. This is the table off
0:11:35   cells that we currently produce basically metrics off the power energy chemistries and three form
0:11:41   factors. 50 by 55 millimeter, a double length, 50 by 105 millimeter and the 54 by 65 millimeter
0:11:51   footprint to sell. These are pouch cells and each form factor can have different thicknesses from
0:11:57   three millimeter toe 10 millimeter, accommodating a range of capacities from as low as a million per
0:12:03   hour ranges toe 15 per hour. The last form factor, uh, could be used as a direct replacement for 18
0:12:13   6 50 cells because, uh, three pouch cells can fit in the space. A local allocated toe 3 86 50 cells,
0:12:22   resulting in a 50% increase in energy density at battery level or more, depending on the power
0:12:29   capability off the 18 6 50 cell
0:12:34   on application that is in development with Invent This power and sponsored by are mystified by Assad
0:12:41   is the conform. A warble battery Theis application uses the high energy Silicon Nano our platform,
0:12:48   Um, and the new version, developed in 2020 was certified and demonstrated in the field has an energy
0:12:59   content that doubles the previous version in the same footprint and wait. This year, we are working
0:13:06   on a version that will be safe to nail in bullet penetration with the same energy content. Another
0:13:13   application or applications because the field is expanding at a very high rate is the electric drone
0:13:20   market, both for military and commercial applications. For example, the power and energy platform
0:13:27   enable a new recording endurance for quad copters, demonstrated by a military contractor with
0:13:32   Emperor ourselves. The power energy platform is particularly suitable for electrical, vertical
0:13:39   takeoff and landing applications because it has the power capability for takeoff and landing and the
0:13:45   energy for long endurance cruising with over 400 water per kilogram and supporting continuous three
0:13:52   she operation in the drone profile shown here, the cruise face has been doubled with the Silicon
0:13:59   Nano ourselves toe 120 minutes for from an initial number off about 60 minutes. Um, the battery in
0:14:10   the picture is a 725 watt hour with slightly over 2 kg weight, which means, UH, 320 watt hours per
0:14:21   kilogram at the battery level, including the case, including the connections. The higher platform,
0:14:29   the higher power platform, was developed for extending the range and payload capabilities off small
0:14:35   drones that typically fly for 15 to 20 minutes. Silicon unaware cells usually enable a doubling off
0:14:41   the endurance or an increasing payload. The cells that supporters performance can be discharged at
0:14:47   up to 60 continuously, we thought, exceeding the maximum temperature off 60 degrees Celsius and
0:14:55   support shorter duration pulses off upto 10 c. We're still having a specific energy off over 350.
0:15:03   What are per kilogram
0:15:06   in general, as shown in the summary slides, feedback and results from our customers indicate the
0:15:12   silicon cells enable a step change in performance, typically doubling lifetime mission time, talk
0:15:18   time or range, depending on application.
0:15:23   Looking forward, we plan to release products with a specific energy off 500 water per kilogram in
0:15:29   2021 the C the technology scaling to 600 or even 700 water per program in the future, depending on
0:15:38   the advancement off cattle materials as well. We are continuously improving the other performance
0:15:43   metrics in particular cycle, life and calendar life and based on some recent results, expect to
0:15:50   double the current numbers this year. In parallel, we are scaling up the manufacturing equipment and
0:15:56   expect toe have the first manufacturing line in 2022 ramping up towards gay about our capacity by
0:16:03   the middle of the decade.
0:16:06   In summary, the Silicon Nano. Our technologies will address and enable markets in the order or
0:16:13   manufacturing volume and price sensitivity, starting with the relatively exotic stratospheric solar
0:16:19   electric grounds or pseudo satellites that cannot fly literally. We taught batteries with a specific
0:16:25   energy off a least 400 watt hours per kilogram. Next smaller markets that required performance, such
0:16:32   as military and wearable applications, followed by drones and urban and mobility applications. We
0:16:38   are actively developing cells and working with the manufacturers and expect that this market will
0:16:43   benefit from the performance discussed here when manufacturing reaches corresponding target levels.
0:16:51   I want to thank the organizer for inviting this talk and organizing a symposium on this topic and
0:16:58   two people listening for their interest. I also want to acknowledge the support over the years from
0:17:04   from any government agency and especially from C five ice are who has recently found in multiple
0:17:09   development projects, with silicon unaware out, Thank you.