On May 3rd, BMW and Ford Motor Company announced a joint investment of $130 million in solid-state lithium-ion battery company SolidPower, betting on future electric vehicle solid-state battery technology, thereby bringing the startup Solid Power to the forefront.

BMW claims its goal is to achieve mass production of electric vehicles by 2030, while Ford recently announced in its financial report that it will invest $22 billion in the development and production of electric vehicle products by 2025. The California Quantum Scape solid-state lithium battery company, which went public at the end of last year, is a startup invested by Volkswagen, which has invested over $200 million in this company. Last month, General Motors announced an investment of $139 million in SolidEnergy Systems, a solid-state lithium-ion battery company in the Boston area, and also announced a total investment of $27 billion in the research and production of electric vehicles by 2025. At this point, it seems that these large European and American car manufacturers have already placed bets on solid-state lithium battery companies. We will gradually analyze the technical characteristics of these solid-state lithium battery companies for you.

Solid Power was founded in Colorado, USA in 2011. But in the initial years of its establishment, it was unknown and there was not even any public financing news. It was not until 2017 that the company received its earliest angel round investment of $3.5 million, and then received two A-round financing totaling $48 million in 2018 and 2020. Then suddenly announced this month that it had received a Series B financing of $130 million, becoming a star company in the solid-state lithium battery industry. According to news reports, Solid Power now has the ability to produce 20Ah multi-layer battery blocks, and with the latest Series B financing, the company will strive to achieve 100Ah battery block production by 2022, providing validation products for BMW and Ford's electric vehicle battery testing.

Due to the lack of mention of its technical features in previous news reports on Solid Power, we conducted a search on the patents applied by the company and found three key technology patents. The first patent focuses on the assembly method of the company's solid-state lithium battery, which is similar to conventional lithium metal solid-state batteries in overall battery design. However, the few small technical details mentioned in it may be some of the company's innovations. For example, in terms of adhesive materials, they mentioned self healing polymer materials. These materials form a protective film on the surface of electrode materials, and if they are punctured by crystal branches, they have the ability to self heal and recover into a film, thereby protecting the electrode material from reacting with other active ingredients for consumption. In terms of solid-state electrolytes, they mentioned the addition of halogen elements to help form a stable and high ionic conductivity interface layer between lithium metal and positive electrode active materials, in order to improve the overall performance of the battery.

The second key patent focuses on solid-state electrolyte materials. At present, the LGPS solid electrolyte containing lithium germanium phosphorus silicon elements is the best electrolyte for lithium metal batteries. Its lithium ion conductivity at room temperature can reach 12mS/cm, which is more than 10 times that of commonly used ceramic electrolytes. However, a drawback of this material is that its electrochemical stability window is very small, only stable between 2.1V and 2.4V relative to the Li/Li+reaction. Beyond this operating window, the material generates products with extremely low ionic conductivity, greatly reducing the operational performance of the battery. In this patent, SolidPower proposed a solid-state electrolyte LiBS based on lithium boron sulfur elements. According to theoretical calculations, the thermodynamic stability window of the solid-state electrolyte is between 1.6V and 2.2V relative to the Li/Li+reaction, which is twice as large as the LGPS electrolyte. Between 1.0~1.6V and 2.2~3.8V, although the electrolyte is thermodynamically unstable, it can still maintain a certain degree of stability in kinetics, thus greatly improving the operating window and performance of solid-state batteries. Meanwhile, the lithium ion conductivity of the electrolyte may be more than twice that of the LGPS electrolyte. On the other hand, due to the low cost of the elements used in this electrolyte, the cost of each component is $20/kg for lithium, $5/kg for boron, and $1/kg for sulfur. Therefore, the electrolyte cost can be as low as $0.05 per square meter for a thickness of 10 microns, which will greatly reduce the total cost of solid-state batteries.

Although theory is beautiful, reality is still quite challenging. Solid Power presents actual test data in this patent, which shows that the ion conductivity of the LiBS electrolyte system is still far below the theoretical value. Based on this, it is speculated that Solid Power will vigorously strengthen the performance research of solid electrolytes in subsequent work, achieving a high level of theoretical performance.

The third key patent of Solid Power is about adhesive materials, focusing on materials based on lithium polysulfide. The patent claims that this type of material can solve the problem of incompatibility between conventional adhesive materials and solvents or other active materials during the preparation process, greatly improving the stability of finished batteries and reducing the cost of the preparation process. Since the patent does not involve too many technical parameters, we will not go into too much detail.

In summary, Solid Power's focus seems to be on solid electrolyte and adhesive materials, and they hope to improve the performance of solid-state batteries by improving these two components. It seems that they have not done much interpretation of the possible problems in lithium metal negative electrodes. If some issues related to lithium metal negative electrodes are not properly resolved, the long-term cycling stability of the battery will be greatly reduced. Therefore, we look forward to seeing more cycling stability data of SolidPower batteries in the future, which will help us understand the technological development level of their solid-state batteries.

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Reference:

1. US Patent Application No. US20210126281, Solidelectrolyte material and solid-state battery made therewith

2. International patent application number WO2019051305, Ceramicmaterial with high lithium ion conductivity and high electrochemical stabilityfor use as solid-state electrolyte and electrode additive

3. US Patent Application No. US20180083303, Binderand slurry compositions and solid state batteries made therewith



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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 and academic exchange between liquid flow batteries and high-energy density lithium-ion batteries, technical lectures on the company's technology research and development direction, research and development consulting, and guidance on paper writing.