Solid-liquid hybrid semi-solid battery may be the ultimate route for electric vehicles

The concept of solid-state batteries is everywhere, but in fact there are many hidden tricks.

Recently, the term "silicon anode solid-state battery" has become increasingly popular.

This was announced by a Mercedes-Benz engineer. Mercedes-Benz's EQG model will be equipped with silicon anode solid-state batteries. It is reported that its energy density will be as high as 800Wh/L (about 400 Wh/kg), far exceeding traditional power batteries . Considering that EQG will not be launched on the market until 2025, it can only be said that "it's a waste of time to hear it."

However, silicon anodes seem to be an ideal material to replace the current graphite anodes (i.e. negative electrodes) of lithium batteries , because there is no need to modify existing battery processes and manufacturing equipment. After solving the silicon expansion problem, the advantages of silicon anodes are being reflected. Although Mercedes-Benz's technology is still in the laboratory stage, the combination of silicon anodes and solid-state batteries has once again filled the industry with imagination.

South Korea's POSCO Holdings is also preparing to develop silicon anode materials. Recently, POSCO Holdings decided to invest in Taiwan's Prologium Technology to develop core materials for the next generation of batteries. The two parties will jointly develop cathode materials, silicon anode materials, solid electrolytes, etc., and establish a global supply system.

ProLogium, founded in 2006, developed solid-state batteries in 2012. ProLogium has also partnered with major automakers such as Mercedes-Benz to develop solid-state batteries for electric vehicles .

However, from the current perspective, the development of the "beautiful-looking" all-solid-state battery is still very far away. It will take at least 5 to 10 years to achieve large-scale mass production and application, and it is full of variables. Many professionals also predict that all-solid-state batteries will not be fully commercialized until 10 years later, or even longer. Even CATL and Honda predict that all-solid-state batteries may not be used in cars until around 2030.

This is very intriguing. Although the technology is so difficult, why do people rush to develop solid-state batteries? Moreover, under the news of mass production of "solid-state batteries", are there solid-liquid hybrid semi-solid batteries that are "secretly developed"?

01How difficult is it?

Let me first briefly explain the concept of all-solid-state batteries. There are quite a few twists and turns here.

Now, what we usually call all-solid-state batteries are relative to the current liquid electrolyte lithium batteries . That is, batteries that use solid positive and negative electrode materials and solid electrolytes. At present, there are three mainstream routes for solid electrolytes: polymer route, oxide route (mainly in Europe and the United States) and sulfide route (mainly in Japan).

However, there are different opinions on the specific classification. For example, last year, Guo Yongsheng, director of the Advanced Technology Department of CATL’s 21C Innovation Laboratory, said, “After the solid-state battery is truly manufactured, I will divide it into three generations according to the positive and negative electrodes.”

The first generation is to replace the traditional liquid electrolyte with a solid electrolyte, and the positive and negative electrodes remain exactly the same. The second generation changes the negative electrode, replacing graphite and silicon with metallic lithium to increase energy density, while the positive electrode remains unchanged. The third generation changes both the positive and negative electrodes, such as using metallic lithium for the negative electrode and replacing the positive electrode with a high-energy material that does not contain lithium.

If we look at it from this perspective, the first generation is more under development in the industry. The Whoop Strap 4.0 silicon anode solid-state battery developed by Mercedes-Benz in cooperation with its investment company Sila Nano at the beginning of the article actually replaces the negative electrode and overcomes the defects of the lithium metal negative electrode, which can be regarded as the second generation.

In fact, many professionals in the industry have little hope for all-solid-state batteries. For example, Xu Xiaoxiong, general manager of Zhejiang Fengli New Energy, believes that semi-solid-state batteries that are a mixture of solid and liquid may be the ultimate route for automotive power batteries.

There are also those who resolutely give up the solid-state battery route. "We have completely given up on solid-state batteries because they really cannot be put into practice." Henrik Fisker, the founder of the American electric car startup Fisker, said helplessly at the end of last year. This technology is "when you feel that you have completed 90% and almost reached the goal, then you realize that the remaining 10% is much more difficult than the previous 90%."

Another solid-state battery manufacturer, SES (Massachusetts Solid Energy), has also given up on all-solid-state batteries. According to SES founder Hu Qichao, before 2015, SES was mainly engaged in the research and development of solid-state lithium metal batteries. However, "many car companies and power battery companies gradually realized that this was a distant dream, so we stopped the research and development of solid-state lithium metal batteries in 2015 and turned to the research and development of hybrid lithium metal batteries."

The so-called "solid-state lithium metal battery" by Hu Qichao is actually a solid-state battery with metal lithium as the negative electrode. As for the first generation of solid-state lithium-ion batteries (graphite and silicon as negative electrodes), SES believes that "it has been commercialized, but the advantages are not obvious, and the energy density and production process are not significantly improved compared with lithium-ion batteries." This illustrates the current situation of the industry from another perspective.

According to market research firm SNE Research, the global demand for solid-state batteries is expected to approach 500GWh in 2030. Among them, the global market for solid-state batteries is expected to reach 6 billion yuan in 2025, and my country's market share is expected to reach 3 billion yuan, and 20 billion yuan in 2030. However, if we compare it with the current market size of power batteries, we will know that solid-state batteries are just a drop in the bucket.

The current commercialization process of solid-state batteries is polarized. On the one hand, there are news that major companies are continuously investing in the research and development of all-solid-state batteries. On the other hand, there are more companies like SES that have given up on the extremely difficult mass production of all-solid-state lithium metal batteries and have chosen the mass production route of solid-liquid hybrid semi-solid-state batteries.

In November 2021, SES announced that it had developed the Apollo? hybrid lithium metal battery with a capacity of up to 107Ah, a weight of only 0.982 Kg, and an energy density of 417 Wh/kg (935 Wh/L). In addition, SES is also building a super factory with a production capacity of 1GWh in Shanghai, which is scheduled to be completed in 2023.

For SES, its semi-solid-state battery shares about 60% of the materials, manufacturing processes and other industrial chains with the current mainstream liquid lithium-ion battery, and has obvious advantages in energy density, safety, and good cycle life. Although the production line needs to be modified, the investment cost can be recovered as soon as possible after mass production.

Even Mercedes-Benz is preparing for semi-solid batteries. In December 2021, media reported that Farasis Energy 's solid-liquid hybrid semi-solid battery (Sample A) had been delivered to Mercedes-Benz. The news said that "the first generation of Farasis Energy's semi-solid battery with an energy density of 330Wh/kg was sent to Germany, and the battery prototype will be tested soon."

02Semi-solid-state batteries are just right

In fact, no matter what kind of battery it is, the truth will only be known if it can be mass-produced and installed in vehicles. It seems that all-solid-state batteries are still in the "storytelling" stage, and it is estimated that it will take another ten to eight years.

Solid-liquid hybrid semi-solid batteries, which are skirting the line of "solid-state batteries", have appeared frequently since 2021, and good news about mass production has continued to come. Moreover, most companies are now taking advantage of the "solid-state battery" hotspot from a marketing perspective, resulting in the concept of solid-state batteries flying all over the place, but in fact many of them are secretly doing so.

From the 360Wh/kg semi-solid-state battery pack released by NIO at the beginning of the year, to the exposure of the solid-liquid hybrid battery parameters of Weilan New Energy and Guoxuan High-tech , as well as the solid-liquid hybrid lithium metal battery of SES, and the first generation of semi-solid-state batteries of Jiangxi Ganfeng Lithium Battery installed in Dongfeng E70, all indicate that the mass production of semi-solid-state batteries has been significantly accelerated.

The Dongfeng E70, which has delivered 50 online-hailing vehicles, uses Ganfeng Lithium's first-generation solid-liquid hybrid lithium battery with an energy density of about 260Wh/kg. Currently, Ganfeng Lithium has built and put into use a 0.3GWh hybrid solid-liquid lithium-ion battery production line, which has the capacity for mass production.

In addition, Ganfeng Lithium claims that the energy density of the second-generation semi-solid-state battery cells will reach 360Wh/kg, that the B-type development has been completed in the first quarter of 2021, and that the SOP stage will be completed in the first quarter of 2023. However, it was originally expected that the C-type development would be completed in the first quarter of 2022, but now it seems that there is no movement.