Chen Shaojie, director of solid-state battery research and development of Honeycomb Energy Technology Co., Ltd., attended the forum and delivered a keynote speech-"Challenges and Thinking of All-solid-state Lithium Battery Technology Research and Development".
The following is a record of the speech:
Good morning, experts and teachers! I am honored to have this opportunity to share with you, because I worked in the Chinese Academy of Sciences for a long time before, and later joined the hive, so I will report to you in combination with the work experience of these two work units.
First, the background is introduced.
Solid state batteries have several main advantages:
1, solid electrolyte replaces flammable and explosive electrolyte, so it is relatively safe.
2. The illiquidity of the solid electrolyte can boost the battery in series, which can reduce the packaging cost of the battery on the one hand and improve the volume energy density on the other.
3. Because it is relatively safe, the cooling system can be omitted or used less at the package level, further improving the space utilization rate. It is also considered that the cathode material with higher voltage can be matched, which makes the lithium metal cathode possible.
Because of these advantages, it has carried out extensive technical research at home and abroad. As far as all-solid-state technology is concerned, the most representative enterprises are Toyota and Samsung.
Judging from the trend of patent application, in fact, since the 1970s, Europe and America have taken the lead in applying for polymer electrolytes. Since 2000, inorganic solid electrolyte materials have been widely used, mainly in Japan.
China didn't apply for inorganic solid electrolyte on a large scale until 20 10, and it also showed explosive growth in recent years, which shows the heat of technology.
The industry also has high enthusiasm and concern for this technology. Some very famous companies and great companies, including Toyota, Volkswagen, Ford, BMW, Mercedes-Benz and so on. , has invested in and laid out this technology. Toyota plans to showcase this concept car with all-solid-state batteries at this month's Tokyo Olympic Games.
Looking back, there are many kinds of solid electrolytes, and there are three kinds of industrialization attempts: sulfide, oxide and polymer.
As far as room temperature conductivity is concerned, sulfide is higher, followed by oxide and polymer is the lowest.
Polymer electrolyte all-solid-state battery.
The most typical polymer is PEO. It is generally believed that oxygen atoms and lithium ions are complexed, dissociated and complexly conductive. PEO has a high crystallinity, so its free-moving volume at room temperature is relatively small, and its conductivity is usually low, which is only 6 times that of 10.
The common modification method is to add inorganic fillers, including fast ionic conductors that conduct ions and inert fillers that do not conduct ions.
By introducing inorganic dielectric, two benefits can be formed:
(1) Using Lewis acid-base theory can improve the migration number of lithium ions.
(2) Cross-linking centers are formed, which reduces the cleanliness of PEO and improves the electrical conductivity and mechanical properties.
A lot of research has been done in this field before, and overall, the conductivity can reach minus four 10.
In addition to inorganic compounding, it can also be modified through the design level of molecular structure, and thermally cured or photocured through cross-linking, grafting and polymerization. Unfortunately, at present, the conductivity still does not exceed minus 3 of 10, especially at room temperature.
We have done a job in the verification of lithium battery of polymer all-solid prototype. Small monomer * * * is directly coated on the surface of lithium ferrous phosphate pole piece, and the integrated structure of positive electrode and electrolyte is constructed through light or thermal curing, so as to reduce the interface impedance.
Unfortunately, the conductivity of electrolyte is relatively low, and the flexible battery can only have better battery performance below 60 degrees. Further, the internal series structure was verified and realized by using the illiquidity of the polymer. It is indeed possible to realize internal boosting in one package and one battery cell package.
In terms of industrialization, weak lightning technology is involved, including 3000 taxis, and its recent application in Mercedes-Benz and Mercedes-Benz electric buses. The production methods they adopt are mainly extrusion and volume-to-volume mass production.
The whole battery cell uses lithium ferrous phosphate as the positive electrode, PEO as the electrolyte and lithium metal as the negative electrode. The whole battery module does not need a cooling system, and the whole battery cell can only work at 60-80 degrees. In fact, at this temperature, the polymer is in a molten state, so it lacks certain mechanical strength. Recently, it was recalled because of some insulation short circuit events.
Generally speaking, the advantages of polymers are flexible molecular structure design and large imagination space. In addition, the process is relatively simple and has good compatibility and stability.
The challenge is that the transmission performance of lithium ion is not high enough, especially the narrow window, and there are still some problems in the basic understanding of lithium ion transmission mechanism, dynamics and macroscopic properties.
All-solid state battery with oxide electrolyte system.
There are many experts here. Please correct me if I am wrong. The main types of oxides are perovskite, NASICON and garnet.
The typical representative of perovskite type is LLTO, which usually has high ionic conductivity, but its disadvantage is that it is unstable in contact with lithium metal and can reduce tetravalent titanium to trivalent titanium.
The typical representatives of Naxi Kang are LATP and LAGP. Usually, the conductivity is only minus 4 times of 10, but it has good stability, wide electrochemical window and light specific gravity. Its shortcomings are also obvious, such as low conductivity, weak and inflexible ceramic electrolyte and unstable lithium.
LLZO is a typical garnet type, with high conductivity, up to minus 3 times of 10, and wide electrochemical window. However, the synthesis price is relatively high, and the specific gravity is relatively large, and the flakes are brittle, and there will be some side reactions in the air.
Honeycomb energy has accumulated oxides, including powder and ceramic chips, and made corresponding research. In the verification of oxide all-solid-state lithium battery, LAGP ceramic sheet is used as electrolyte separator, lithium ferrous phosphate is used as positive electrode, metallic lithium is used as negative electrode, and PEO is used for protection.
The whole battery has a very good cycle at the working temperature of 60 degrees, but it is a great technical challenge to make the ceramic sheet thin and reduce the specific gravity.
In terms of industrialization, many researches on oxides are mainly in Japan and South Korea, mainly because they have some applications of all-solid-state batteries in micro devices, including sensors and computer chips.
Of course, TDL also uses organic and inorganic composite methods to manufacture flexible battery, and can also manufacture flexible battery with 2 ampere-hours and 4 ampere-hours, but the battery needs to work in a relatively high temperature environment.
The picture on the right shows Quantum Scape technology, which was very popular some time ago. The technical core is to make the ceramic sheet thin and basically flexible, and the single battery shows very good battery performance.
I think it is still difficult to make the battery bigger, so oxide stability is a very good advantage as a whole. The challenges are low room temperature conductivity, high particle ratio, poor film formation, and some of them are sensitive to air, so the stacking technology is difficult.
All-solid state battery with sulfide electrolyte system.
Sulfide electrolyte has sulfur-lithium system, which is usually divided into ternary system and binary system.
1, ternary.
In addition to lithium sulfide and phosphorus pentasulfide, a third component, usually germanium sulfide, silicon sulfide, tin sulfide and aluminum sulfide, can be introduced to construct a three-dimensional ion channel with high conductivity.
However, materials such as germanium sulfide and silicon sulfide are very expensive, each gram costs 400 yuan to 500 yuan, and many companies have stopped production because of storage problems, so personally, it may be a great challenge to control the cost of these materials if they want to be industrialized.
2. Binary.
As the name implies, the binary system uses two raw materials: lithium sulfide and phosphorus pentasulfide. Lithium sulfide accounts for more than 70% or even 90% of the cost of sulfide electrolyte. We can think about how to reduce the amount of lithium sulfide to further control the cost.
3. Silver germanium sulfide ore.
The most typical example is the lithium sulfur hexaphosphate used in the public reports of Samsung and Hitachi shipbuilding.
As far as preparation methods are concerned, there are usually ball milling method, melt extraction method, liquid phase method and recent gas phase method. I think these are all good progress, which can further reduce the cost from the process of mass production.
Finally, I would like to mention the optimization of the synthesis of lithium sulfide. In fact, because the whole industrial chain has not been formed, people have not paid much attention to the synthesis scheme of phosphorus sulfide. In fact, there are many synthetic schemes of lithium sulfide.
From the perspective of reducing the cost of electrolyte materials, on the one hand, the synthesis scheme of raw material lithium sulfide can be optimized, and the scale can be realized, which can be completely below 9000 yuan per kilogram. Combined with the optimization of electrolyte composition design, the cost can be completely reduced to less than 5,000 yuan per kilogram, and further reduced to less than 654.38+0 million per ton by using scale effect. This is the idea of cost control.
Of course, there is stability. We all say that sulfides are unstable. In the actual production process, we have to face the stability of the solvent, including the stability of the drying chamber.
Our previous work shows that it can be improved to some extent by selecting nonpolar solvents and doping elements.
As for the stability of lithium, binary system is more stable than ternary system because it is a reversible reaction. In addition, through material modification, such as aluminum iodide doping 3 14 system, the stability can also be significantly improved, and at the same time, through interface modification, including the protection of lithium metal. , can be modified accordingly.
In terms of industrialization, solid power is widely reported, which adopts the traditional preparation method of lithium battery. According to them, they reduced all the equipment and sites for injection, molding and exhaust, and the calculated cost could be reduced by 34%.
Because solid-state batteries are relatively safe, there is no need for a cooling system at the battery level, which can be reduced by 9% accordingly. The whole battery cell adopts NMC ternary high nickel series, the negative electrode is high silicon negative electrode and lithium metal, and the electrolyte is sulfide.
They plan that this year's roadmap is 340 WHr/kg and 720 WHr/L, and the mass production plan is in 2026. I believe that lithium metal will be later than 2026.
The biggest advantage of sulfide is its high conductivity at room temperature and soft quality. The challenge is poor stability, which is really difficult, and the engineering technology is very difficult.
Another point that is often overlooked is that all-solid-state batteries really need external restraint pressure during their operation. At present, our domestic research in this field is relatively blank, while Japan has proposed solutions from different dimensions of battery, module and PACK for our reference.
Next, I want to report to you on the progress of all-solid-state cellular energy. First, we have developed an electrolyte material, which can maintain 96% conductivity within two hours in the drying room, and has formed a capacity of100g.
Furthermore, we also made a positive electrode and developed a positive electrode plate of 4 mAh per square centimeter. When charged and discharged at 0. 1C at room temperature, the first effect can reach 96.3% and the clone number can reach 220. This rate of 0. 1C can be completely close to the current liquid level.
In terms of cycle, we chose the ratio of1/3 c. From this cycle, we can have a better cycle at present, but we really need to focus on the next step in terms of magnification.
At the same time, we also want to make the pole piece thicker and make it an electrode with a thickness of 5 mAh per square centimeter. Unfortunately, the first effect has decreased and the specific capacity has been lost. This is the next difficult problem to be solved.
As for the electrolyte membrane, we also use wet coating, and the thickness can reach 20-30 microns at room temperature, which is basically close to the data reported by Samsung. Honeycomb Energy has accumulated in material technology, components, devices and testing, and applied for 54 patents.
At present, AH-class all-solid-state lithium battery is being developed. The anode is made of ternary high nickel material, the cathode is mainly made of silicon-based alloy material, and the electrolyte and electrolyte membrane are independently developed by us. The energy density can reach 320 WHr/kg, and the safety is fully guaranteed. It also passed acupuncture and some demonstrations of cutting and burning.
Fourth, summary and prospect.
Oxides, polymers and sulfides all have their own advantages and disadvantages. We believe that the innovation and breakthrough of the key material solid electrolyte is the key to accelerate the application of all-solid-state technology. We are also glad to see the emergence of new materials such as halides, which gives us more choices.
In addition to materials, it is also necessary to solve the problems at the processing level, mainly including four aspects:
(1) Improved control of materials and interfaces.
(2) Solve the challenges and costs of treatment.
(3) Exceeding the performance of advanced lithium-ion batteries.
(4) Keep the best stacking pressure of the solid-state battery pack without affecting the cost and energy density.
We believe that all-solid-state batteries for 3C consumer products, special batteries and other applications will be realized in a short time. In fact, they have been realized in Japan's aerospace field. It may take more time for all-solid-state batteries to meet the performance, cost and manufacturability of electric vehicles.
As an enterprise that aims to advance through innovation and build a great company, Honeycomb Energy is willing to continue to pay attention to the development of this technology. Thank you!