EV solid state battery - development status and future prospect
What is a solid state battery
Lithium batteries are mainly composed of cathode materials, anode materials, electrolytes, and separators. There are two forms of electrolytes: liquid and solid. Lithium-ion batteries are currently mainly using liquid organic solvent electrolytes.
At present, the comprehensive performance of liquid lithium batteries, whether it is lithium iron phosphate batteries or ternary lithium batteries, has almost reached its limit under the support of various technologies, and it is becoming more and more difficult to make new breakthroughs in technology.
Under the requirements of higher safety and energy density, solid state battery was introduced. Solid state batteries use solid state electrolytes with high ion conductivity and stability to replace flammable and explosive organic electrolytes.
At the same time, in terms of cathode and anode materials, solid state batteries can continue to use the liquid lithium battery material system, and there is more room for upgrading. Compared with traditional liquid lithium batteries, solid state batteries have the advantages of high energy density, high safety, and long life.
According to the difference in the content of liquid electrolyte in the battery, solid state batteries can be divided into three types: all-solid-state, quasi-solid-state, and semi-solid-state. Among them, the all-solid state battery does not contain any liquid electrolyte, the mass percentage of the liquid electrolyte of the quasi-solid battery is less than 5%, and the mass percentage of the liquid electrolyte of the semi-solid battery is less than 10%.
Types of ev solid state battery
At the current stage, the ev solid state battery industry has not yet reached a consensus on the technical route of solid state batteries. According to the different electrolytes, the mainstream solid state batteries on the market can be divided into three technical paths – polymers, oxides and sulfides.
Three major solid state battery technology paths and characteristics:
| Solid electrolyte type | Ionic conductivity | Advantages | Disadvantages | Research direction |
|---|---|---|---|---|
| Polymer solid electrolyte | Room temperature: 10-7~10-5S/cm; 65-78℃: 10-4S/cm | Good flexibility, easy large-scale preparation, low film shear modulus, no reaction with lithium metal | Low ionic conductivity, low oxidation voltage (<4V) | Blend, copolymerize or crosslink PEO with other materials to form an organic-inorganic hybrid system to improve performance |
| Oxide solid electrolyte | 10-6~10-3S/cm | High chemical and electrochemical stability, good mechanical properties, high electrochemical oxidation potential | Poor interface contact | Improve electrical conductivity: replace elements or dope with the same kind of heterovalent elements |
| Sulfide solid electrolyte | 10-7~10-2S/cm | High electrical conductivity (comparable to liquid electrolyte), good mechanical properties, low grain boundary impedance | Easy to oxidize, moisture sensitive | Improve electrolyte stability, reduce production costs, element doping to play a synergistic effect of each element |
- Polymer
Polymer is the first to promote commercial application among the three technical routes, but it has not formed a trend. The advantage of polymer is that it is easy to process, compatible with the existing production equipment and process of liquid electrolyte, has good mechanical properties and is relatively soft. But its shortcomings are also fatal.
Solid state lithium polymer battery needs to be charged and discharged normally at a high temperature of 60℃, and the polymer itself has poor chemical stability, which cannot be applied to high voltage battery cathode materials (such as lithium cobaltate, high-nickel ternary, etc.). In addition, the thermal safety of polymers is not strong, and fire or even combustion may occur at high temperatures.
Europe is the first region to promote the industrialization of polymer solid state batteries, but currently, Europe is gradually turning to investment. Famous European automakers have invested in global battery companies for many times. Volkswagen, BMW, Mercedes-Benz, etc. have all invested in corresponding start-up companies to strive for the competitiveness in the next generation of all-solid state batteries.
- Sulfide
Japan and South Korea are committed to the sulfide route. Sulfide has the highest conductivity among the three material systems, and has a wide electrochemical stability window (above 5V). However, the thermodynamic stability of sulfides is very poor, and how to maintain high stability is a big problem. In addition, sulfides still cannot avoid the generation of lithium dendrites.
At the production level, because sulfide easily reacts with water and oxygen in the air to produce highly toxic hydrogen sulfide gas, the preparation process of sulfide solid-state batteries is relatively complicated. In general, sulfide has the greatest potential among all solid state batteries, and many power battery leading companies (Toyota, Honda, LG, etc.) choose it as the main technology path.
- Oxide
At the current stage, China is focusing on the oxide route. Oxide has good conductivity and stability, thermal stability up to 1000℃, and good mechanical stability and electrochemical stability. However, compared with sulfides, the conductivity of oxides is still low, which makes the performance of oxide solid-state batteries encounter a series of problems such as limited capacity and rate performance.
In addition, the hard characteristics of oxides lead to all-solid-state batteries made of oxides will be batteries with very high porosity, and these pores cannot conduct lithium.
Therefore, the oxide solid-state battery currently developed in China is actually in the direction of solid-liquid mixing, with both the solid electrolyte layer of the oxide and the infiltration of the electrolyte, which can fill the pores and allow it to have a complete lithium-conducting channel.
A number of solid-state battery companies in China (Beijing Welion, Jiangsu Qingtao, Ningbo Ganfeng, and Taiwan Huineng) have chosen the solid-liquid mixing technology route based on oxide materials.
Development status of ev solid state battery
China’s semi-solid-state batteries have reached the industry-leading level, and all-solid-state batteries still need to break through. Since the technical and process problems of all-solid-state batteries have not been completely resolved, Chinese battery companies generally choose the gradual development route of “from liquid to semi-solid to all-solid”.
Chinese car companies are actively cooperating with solid-state battery companies, such as NIO cooperating with Welion New Energy, BAIC, SAIC, and GAC investing in Qingtao Energy, etc. The entry of car companies provides battery companies with multiple guarantees in terms of capital, technology, and customers, and accelerates the commercialization of semi-solid batteries.
At present, the semi-solid battery technology of many Chinese battery companies has reached the international leading level.
Japan carried out the planning and layout of all-solid-state batteries earlier, and is currently in a leading position in technology globally. From a global perspective, Japan, South Korea and other places have strong power battery innovation and development capabilities.
From 2000 to the end of March 2022, in terms of the number of patents related to all-solid-state batteries in the world, South Korea’s Samsung Electronics ranks fourth in the world, and the remaining top 5 are Japanese auto companies, of which Toyota Motor (Toyota Motor) ranks first, with 1331 known patents, which is three times the number of second-ranked patents.
Toyota has been researching ev solid state battery since the 1990s, and has a wide range of application patents, from the structure of the battery itself to materials and manufacturing processes. From 2016 to 2020, the number of Toyota patents has increased by about 40%, and Japan has become the country with the most ev solid state battery technology patents.
The industrialization prospect of semi-solid batteries is promising. Compared with liquid batteries, the material system of semi-solid batteries has changed less, and separators and liquid electrolytes are still used. By reducing the content of liquid electrolyte inside the battery, the specific energy and safety of the battery can be improved to a certain extent.
Most of its preparation methods follow the traditional lithium-ion battery technology and equipment technology. Relying on China’s mature industrial chain and high willingness to use new technologies, China’s ev solid state battery industrialization process is relatively fast.
Mass production of all-solid-state batteries is difficult to achieve in the short term. On the one hand, there are still technical difficulties to be overcome in all-solid-state batteries. For example, the ionic conductivity of solid-state electrolytes is much lower than that of liquid electrolytes, which leads to a significant increase in battery internal resistance, poor battery cycle performance, and poor rate performance.
On the other hand, the high cost severely restricts the commercialization of all-solid-state batteries. In addition, the all-solid-state battery industry does not yet have the basic conditions for large-scale production:
- All-solid-state battery-related equipment and key raw materials have not yet formed a scale;
- A standard system for all-solid-state batteries has not yet been established globally;
- The world’s first-class electric vehicle companies have not carried out the test and verification of the matching of all-solid-state batteries and complete vehicles.
EV solid state battery industry prospects
The huge market potential of ev solid state battery
Solid-state batteries have incomparable advantages over liquid batteries in terms of energy density and safety. The breakthrough of solid-state battery technology and the improvement of product maturity not only meet the market’s demand for high performance, safety and sustainability, but also make the capital market’s confidence in the industry continue to increase.
Under the optimism of the industry and the multi-party layout, the solid-state battery industry is expected to achieve rapid development. Relevant agencies predict the future market of solid-state batteries, and 2023 is expected to become the first year of semi-solid-state batteries, and it is expected to initially form a scale by 2026.
According to public information, many new energy car companies around the world have announced that they will start loading semi-solid batteries in small batches in 2023. Global leading car companies such as BMW, Mercedes-Benz, Volkswagen and Toyota all plan to launch electric vehicles equipped with solid-state batteries around 2025.
Automakers such as Deepal, immotors, GAC Aion, and Hiphi generally plan to install semi-solid batteries in vehicles by 2025. With the technological development of semi-solid batteries and the growing demand for electric vehicles, the market penetration rate of semi-solid batteries is expected to be close to 5% in 2026.
New industrial opportunities brought by ev solid state battery
The development of ev solid state battery may have a certain impact on the existing industrial chain and the entire industrial system, but it also brings new opportunities and development space for related industries.
- Detection and evaluation: Due to the different characteristics of ev solid state battery, new detection methods and equipment need to be developed to evaluate the performance, safety and stability of batteries.
- Production equipment: The production process of ev solid state battery is different from that of traditional liquid batteries, so it is necessary to develop and improve relevant production equipment.
- Production efficiency: During the production process of ev solid state battery, compared with liquid batteries, there are differences in temperature, pressure, etc. , which may have an impact on production efficiency and energy consumption.
- Evolution of the industrial system: The traditional battery manufacturing industry needs transformation and adjustment to adapt to the development trend of ev solid state battery. At the same time, the application of ev solid state battery will drive the development of related industrial chains, such as material suppliers, equipment manufacturers, system integrators, etc., to form a new industrial ecosystem.
The impact of solid state battery technology on the EV industry
At the current stage, mid-to-low-end automakers are more inclined to use traditional liquid batteries. On the one hand, the cost of solid-state batteries is still high, which limits their application in the mid-to-low-end car market.
Mid- and low-end cars usually focus on cost-effectiveness and price competitiveness, so for these automakers, the adoption of solid-state battery technology may increase product costs, thereby affecting market competitiveness. On the other hand, solid-state battery technology is relatively new compared to traditional liquid batteries, and its technical reliability and stability have yet to be verified.
Mid- and low-end automakers are more inclined to adopt proven and relatively mature technologies to reduce technical risks. High-end automakers will adopt solid-state battery technology more quickly. Compared with low-end and mid-end cars, consumers in the high-end car market pay more attention to technological innovation and technological content.
Solid state battery technology has the advantages of high energy density, safety and fast charging, which is more in line with the high-performance demand of the high-end automotive market. It should be noted that with the continuous development of solid-state battery technology and further reduction in cost, it is also expected to be promoted in the low-end and mid-end car market.
With the maturity of technology and the expansion of commercial scale, solid-state battery technology is expected to have a profound impact on the entire automotive industry in the future.
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