Enoix, a company that produces all silicon negative electrode lithium batteries, has suddenly caught people's attention in recent days, as it announced on February 22 that it has reached an agreement with a shell company to go public through a backdoor listing, known as the Special Purpose Acquisition Company in the US stock market. This shell company is called Rodgers Silicon Valley Acquisition Corp. Its US stock code is RSVA, and the $230 million it holds will be exchanged for Enoix shares through this merger. The merger process is expected to be completed in the second quarter of 2021, at which time Enoix will receive a total of $405 million in financing for subsequent stages of development, and the company's valuation will reach $1.1 billion.



On the day of announcing its backdoor listing on February 22nd, RSVA's stock price surged rapidly from the previous day's closing price of $15.75, reaching a peak of $28.5, almost doubling. RSVA's market value reached a peak of $820 million, which is 3.5 times its holdings of $230 million in assets, indicating that some investors believe that the $230 million exchanged for Enoix shares will be worth $820 million. However, as emotions cooled down, RSVA's stock price began to decline continuously. As of the close on February 25th, the stock price has fallen to $16.56 and the total market value has also shrunk to $476 million. Why is Enoix's IPO not as popular as QuantumScape (which saw a 10 fold increase in market value after going public) at the end of last year? We can try to explore its technical aspects.





Enoix was founded in 2007, with a team of founders from IBM's department that produces hard disk read and write probes. They have transplanted the technology for manufacturing read and write probes into battery production and used lithography technology to meticulously design batteries. This technology roadmap is very different from other companies that produce silicon negative electrode materials. Other companies mainly focus on silicon particles, while Enoix focuses on engineering design and manufacturing processes. Enoix believes that the current battery packaging technology has a low space utilization rate, with actual energy storage materials accounting for less than 60% of the total volume. However, the battery design they use allows energy storage materials to account for more than 75% of the total volume of the battery. Placing more energy storage materials in the same sized battery is equivalent to improving the energy storage density of the battery.






The following diagram is a cross-sectional view of a traditional lithium battery. The packaging process involves making a single-layer battery into a long strip, which includes layers of positive and negative conductive metal foil, positive and negative electrodes, and separators stacked together. They are then rolled around the middle axis like toilet paper, and finally packaged with a metal or other material shell. The metal foil used in this design is relatively thick because it needs to withstand a certain amount of impact force during the production process and cannot break. In addition, the diaphragm is generally wider than the positive and negative electrode materials and metal foil to avoid accidental short circuit contact between the positive and negative electrode materials. The above design considerations will increase non energy storage space.






Enoix borrowed the production process of chips and solar panels, using a 1mm thick silicon wafer to make the battery. The following image is a top view of a silicon wafer. Enoix etches grooves with long stripes on the silicon wafer using photolithography, then electroplates conductive layers of positive and negative electrodes in the grooves, and fills them with positive electrode materials and separators respectively, resulting in a repeated battery structure from left to right. This battery structure makes full use of space, so it can increase the proportion of energy storage material space to over 75%.






Let's explore the detailed battery manufacturing process using the following diagram. Firstly, etch the silicon wafer until only the black part in the image remains - thick vertical stripes and thin vertical stripes. Wrap a layer of positive electrode conductive foil (blue part in the picture) with electroplating on the thin vertical stripes, which is much thicker than the metal foil of traditional lithium batteries (1 micron vs. 10 microns). The thick vertical stripes are all silicon negative electrodes, and a layer of negative electrode conductive foil is wrapped on the silicon negative electrode by electroplating (the purple red part in the picture). Next, apply ceramic particles on both sides of the thick vertical stripes and form a ceramic diaphragm through high-temperature sintering (yellow part in the picture). Finally, fill the positive electrode material between the thick and thin vertical stripes, and the structure of the battery is completed.





Although the thickness of such battery cells is only one millimeter, Enoix can achieve the required battery thickness by stacking them together. The batteries between different layers are connected to the positive electrode using a special connection process, and all negative electrode conductive foils are connected to the negative electrode of the battery. The production process of battery cells can adopt the assembly line production method shown in the following figure, which can achieve large-scale mass production.






Let's talk about its all silicon negative electrode again. In the above manufacturing process, we mentioned that the remaining black thick stripes after photolithography are all silicon negative electrodes. And Evonix has mentioned in many places that their all silicon negative electrode is designed with gaps inside the electrode to meet the volume expansion of silicon materials after absorbing lithium ions, without expanding and squeezing the battery outside the electrode. Evonix has not introduced how they create gaps in all silicon negative electrodes, but we have noticed some designs that can be achieved through photolithography by researching the patents applied by the company. Therefore, we speculate that Enoix can also add etching to the all silicon negative electrode during photolithography of silicon wafers, thereby creating different forms of voids inside the negative electrode, reserved for volume expansion during charging.





Finally, let's discuss Enoix's business model. Among Enoix's investors are semiconductor giants such as Intel, Qualcomm, and Cypress Semiconductors, but there are no companies related to automobiles or power batteries. Based on our analysis of its battery production process above, its scale production cost is bound to be much higher compared to traditional lithium batteries. The company's development plan released by Enoix itself also focuses on small electronic devices, wearable devices, which require high energy density and are less sensitive to battery costs for mass consumer electronics products. The energy density of Enoix finished batteries can reach 340 Wh/kg or 900 Wh/L, and have also passed 500 deep cycle tests, meeting the requirements of consumer electronics. Their first large-scale production line is under construction in California and is expected to start production in 2021. Due to the relatively small size of the consumer electronics battery market compared to the electric vehicle market, Enoix also plans to enter the power battery field within two to three years. In a research and development project funded by the US Department of Energy in 2020, they reached a partnership with Mitsubishi Motors of Japan to explore the feasibility of using this unique battery design for power batteries. In summary, Enoix's battery technology and business model determine that its target market is not as broad as that of power battery companies, which explains why the popularity of this company's IPO is far less than that of Quantum Scape.





**The article is for communication purposes only and cannot provide investment references. The author does not hold any company stocks mentioned in the article at the time of publication. Because the official account can't open the message function, if you have any questions or suggestions, please send a message to the official account, and we will reply as soon as possible, thank you! Scan the following QR code to follow ZH Energy Storage official account.





Reference:

1. QuantumScape official website https://www.quantumscape.com/

two Howto Build a Safer, More Energy-Dense Lithium-ion Battery。 https://spectrum.ieee.org/semiconductors/design/how-to-build-a-safer-more-energydense-lithiumion-battery

three Three-dimensionalbatteries and methods of manufacturing the same， US patent application number 10256500.



Related articles:

Quantum Scape's Lithium Metal Solid State Battery Rush at the Bottom of Technology

Why is Group14 Silicon Carbon Composite Materials Company, which has only been established for 4 years, so much attention?

Amperes, the first company to implement all silicon negative electrode lithium batteries?

Sila Nano, which is developing silicon negative electrode materials, has received a financing of $590 million!

The energy storage density of silicon is 10 times that of existing lithium battery negative electrode materials, why not replace it?



Author Introduction:

Dr. Xie Wei, Bachelor and Master of Materials Science from Tsinghua University, and Ph.D. in Chemical Engineering from the University of Texas (Austin) in the United States. Mainly engaged in the development of energy storage batteries, has held important positions in multinational corporations and startups, led multiple research and development projects funded by the US Department of Energy, and won the 2013 US Annual 100 Best Research and Development Technology Award. Published 17 papers in top journals in materials science and energy storage, served as a reviewer for 5 international journals, and has applied for 17 international invention patents.



Introduction to ZH Energy Storage Company:

Shenzhen ZH Energy Storage Technology Co., Ltd. is committed to the research and development, promotion, and application of energy storage technology, aiming to help achieve China's goal of "carbon neutrality" through the application of electrochemical energy storage technology. In the early stages of development, the company focused on providing technical support and consulting services to the Chinese energy storage market by leveraging its accumulated industry experience and outstanding research and development capabilities in the field of energy storage. At the same time, the company focuses on conducting research and analysis on the Chinese energy storage market, and developing or introducing the most advanced and effective energy storage technologies for the Chinese market.

Company's technical research and development direction: water-based energy storage batteries, lithium-ion battery materials, fuel cells, ion exchange membranes, coatings and adhesives, membrane separation technology.

Domestic business: technical cooperation, academic exchange, technical lectures on company technology research and development, research and development consulting, and guidance on paper writing.