Recently, SilLion, a battery startup based in Colorado, USA, gained attention due to its relationship with Tesla. As early as two years ago, there were rumors that Tesla had acquired this company when its research and operation work entered a secret mode, but there was no confirmation. A few days ago, it was discovered that the name of the patent ownership agency that this company originally owned had changed to Tesla, confirming everyone's speculation that the company had already been acquired by Tesla and had been undergoing ownership changes for over two years.



Why is this company favored by Tesla? The main reason is that it is a startup enterprise that produces silicon carbon negative electrode materials. Tesla announced at last year's Battery Day that Tesla's batteries have started adding a small amount of silicon negative electrode material to improve their energy density. However, the addition ratio should not exceed 10% of the negative electrode material, mainly due to the difficulty in solving the volume expansion problem of silicon during charging and discharging. We have also published an article introducing this question: "The energy storage density of silicon is 10 times that of existing lithium battery negative electrode materials, why not replace it?".



The most important patent application of SilLion is about how to add a high proportion of silicon negative electrode material to batteries. The basic principle is to add polyacrylonitrile (PAN: Polyacrylonitrile) to the negative electrode slurry containing nano silicon particles, allowing PAN to form a 3-5 nanometer thick protective layer on the surface of the silicon particles. Due to its good ductility and conductivity, PAN can stretch and not break with the expansion of silicon particles, maintaining a stable protective effect. At the same time, good conductivity does not significantly increase the internal resistance of the battery.



The test data of the soft pack battery using this technology is shown in the following figure. Under the condition of C/2 discharge rate, the capacity retention rate is still 72% after 1264 cycles. This data is already very effective for soft pack batteries with high silicon content.







In this patent, data on the content of two types of silicon in negative electrode materials are cited: 30% and 60%. By comparison, 30% of the data is relatively good, indicating that the PAN protective layer can play a good role within this silicon content. However, when the silicon content reaches 60%, the battery performance significantly decreases, indicating that PAN coating still cannot solve the technical problem of higher silicon content.



Based on this speculation, Tesla will focus on increasing silicon content in the improvement of battery negative electrode materials in the future. We predict that the silicon content in Tesla's next-generation battery negative electrode materials will be in the range of 15% -25%. This content range can increase the energy density of the negative electrode material by 50% -100%, and the overall energy density of the battery by 20% -40%, which will be a significant improvement in the performance of existing products.



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Reference:

one https://electrek-co.cdn.ampproject.org/c/s/electrek.co/2021/11/05/tesla-confirms-acquisition-siilion-battery-startup-new-patent/amp/

two Large-formatbattery anodes comprising silicon particles。 US Patent Application No. 20190267617A1



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