Why is CR2025 battery technology so popular around the world?

　　"Automotive News": Are CR2025 battery the same thing as the all-solid-state lithium batteries we heard about? What is an CR2025 battery? How to understand these conceptual differences?

　　Ouyang Minggao: CR2025 battery, each of these words cannot be omitted or changed. "All-solid-state" is different from "solid-state". "Lithium battery" and "lithium-ion battery" are not the same concept. The so-called "CR2025 battery" is a lithium battery in which the electrode and electrolyte materials used are solid within the operating temperature range and do not contain any liquid components, so our full name is "all-solid-state electrolyte lithium battery". According to whether they can be repeatedly charged and discharged, they can be further divided into all-solid-state lithium primary batteries and all-solid-state lithium secondary batteries. Primary batteries are actually already useful. All-solid-state lithium secondary batteries are further divided into all-solid-state lithium-ion batteries and lithium metal batteries. These two concepts need to be distinguished. The so-called all-solid-state lithium metal batteries use lithium metal as the negative electrode. The negative electrodes of most power batteries currently in use are Carbon, silicon carbon or lithium titanate.

　　The concept of all-solid-state lithium batteries appeared earlier than lithium-ion batteries. Lithium-ion batteries only have a history of about 25 years. They were invented by the Japanese and have only been used in cars for more than 10 years. They are very young but making rapid progress. The all-solid-state lithium batteries referred to in the early days were all-solid-state metal lithium batteries with metallic lithium as the negative electrode. This was the previous concept.

　　"Automotive News": What is the specific difference between solid-state lithium-ion batteries and all-solid-state lithium batteries?

　　Ouyang Minggao: CR2025 battery are not necessarily all solid-state electrolytes, but also a little liquid. They are a mixture of liquid and solid. The difference lies in the mixing ratio. A true solid-state lithium-ion battery has a solid electrolyte, but there is a small amount of liquid electrolyte in the cell; the so-called semi-solid state means that half of the battery is solid electrolyte and half is liquid electrolyte, or half of the cell is solid and half is liquid. , so there are also quasi-solid lithium batteries, which are mainly solid and a small amount of liquid.

　　"Automotive News": What are the characteristics and advantages of all-solid-state lithium batteries? Why does it attract the attention and investment in research and development of the global power battery industry?

　　Ouyang Minggao: The main factor is that it can solve the two key problems currently plaguing the development of power batteries, namely poor safety and low energy density. All-solid-state lithium batteries have several potential technical advantages. First, they are highly safe. Due to the use of highly thermally stable solid electrolytes instead of flammable conventional organic solvent electrolytes, battery combustion problems can be effectively solved. Second, the energy density is high. Due to the ultra-high capacity of metallic lithium, the energy density of solid-state metallic lithium batteries can be greatly improved compared with conventional liquid lithium-ion batteries based on the same positive electrode. It should be noted that since the density and usage of solid electrolytes are higher than those of liquid electrolytes, the advantages of all-solid-state lithium batteries are not obvious when the positive and negative electrode materials are the same. Third, the range of positive electrode material selection is wide, because all-solid-state lithium batteries can directly use metallic lithium as the negative electrode, and there is no requirement that the positive electrode structure must contain lithium. Some high-capacity lithium-poor materials can also be used as positive electrodes; in addition, inorganic solid electrolytes The wide voltage window also provides the possibility for the application of high-voltage cathode materials. Fourth, the system has a high specific energy. Since the electrolyte has no fluidity, it can be easily connected in series to form high-voltage monomers, which is beneficial to improving the efficiency and energy density of the battery system.

　　True all-solid-state metal lithium battery technology has not yet matured

　　"Automotive News": Judging from the advantages you introduced, all-solid-state lithium batteries can solve many shortcomings of current power battery products. But why has it not been widely used in the market? What are the main problems? How would you rate the overall development level of this type of technology?

　　Ouyang Minggao: Its first problem is that the ionic conductivity of the solid electrolyte material is low. There are currently three types of solid electrolytes, one is a polymer, one is an oxide, and one is a sulfide. There are now batteries with polymer electrolytes, which are installed on some vehicles in France. The problem is that they need to be heated to 60 degrees before the ionic conductivity rises and the battery can work normally. At present, oxide electrolytes are generally much lower than liquid electrolytes. Only some indicators of sulfide solid electrolytes are close to liquid electrolytes. For example, Toyota uses sulfide solid electrolytes, so the main breakthrough in solid electrolytes is in sulfide solid electrolytes.

　　The second problem is the poor contact and stability of the solid/solid interface. It is very easy for liquids to combine with solids, just penetrate them. But solid-to-solid contact and stability are its big problems. Although the lithium ion conductivity of sulfide electrolytes has been improved, there are still problems with interface contact and stability.

　　The third problem is the rechargeability of metallic lithium. In solid electrolytes, lithium surfaces also suffer from powdering and dendrite growth problems. Its cyclicity and even safety still need to be studied. Of course, there is another problem, that is, the manufacturing cost is high.

　　Based on the above problems, especially the solid-state interface contact, stability and rechargeability of metallic lithium, the true all-solid-state metallic lithium battery technology is still immature and there are still technical uncertainties. At present, solid-state lithium-ion batteries and solid-state polymer lithium batteries are mainly showing or having breakthroughs, performance advantages and industrialization prospects.

　　"Automotive News": What is the current progress of research on solid-state lithium batteries at home and abroad? Are there any companies or technological breakthroughs worthy of attention?

　　Ouyang Minggao: Now solid-state lithium batteries continue to heat up, and the United States, Europe, Japan, South Korea, and China are all investing in it. The mentality of each country is different. For example, the United States is dominated by small companies and entrepreneurial companies. There are two companies in the United States worth paying attention to, both of which are start-ups. One is S-akit3. Its newly developed battery is expected to enable electric vehicles to have a driving range of 500 kilometers. It is still in its infancy. There is also a Solid-State. The United States is primarily based on disruptive technologies. Japan is focusing on large-capacity solid-state lithium batteries with inorganic solid electrolytes, the most famous of which is Toyota, whose products will be commercialized in 2022. Toyota is not making an all-solid-state lithium metal battery, but a solid-state lithium-ion battery. The negative electrode is graphite, using a sulfide electrolyte, and a high-voltage positive electrode. The single battery capacity is 15 ampere hours and the voltage is more than ten volts. I think this is reliable. So in Japan, there is no subversion. It is still based on lithium-ion batteries. The positive and negative electrodes can still use some previous materials or technologies. South Korea focuses on the research and development of large-capacity solid-state lithium batteries with inorganic solid electrolytes, and also uses graphite-based anodes instead of metallic lithium anodes, similar to Japan. The situation in China, Japan and South Korea is similar because we already have a huge lithium-ion battery industry chain and we don’t want to tear it down and start over.

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