Advanced batteries are the key supporting technologies for the development of my country's dual-carbon strategy and electric China strategy. They have very important applications in production, life, and national security. In these application fields, high-energy density batteries, high power density batteries, high safety , Long-life battery is a very critical advanced technology.
The governments of Europe, the United States, Japan and South Korea are now attaching great importance to the research and industrial layout of power batteries. In 2020, Europe supported the "2030 Battery Innovation Roadmap", the United States formulated the "National Development Blueprint for Lithium Batteries in the United States 2021-2030", and Japan formulated the third phase of the "Innovative Battery Development for Electric Vehicles" project, especially It supports the research and development project of all-solid-state batteries for electric vehicles led by Toyota. South Korea also released the "2030 Secondary Battery Industry Development Strategy". It can be said that governments of various countries attach great importance to the research and development layout and development of power battery forward-looking technologies. Industrial Distribution.
Lithium-ion batteries with liquid electrolytes, which are widely used today, are at risk of thermal runaway. According to the research results of the team of Ouyang Minggao and Feng Xuning of Tsinghua University, the solid electrolyte layer of liquid lithium-ion batteries begins to decompose at a lower temperature, and then triggers a series of thermal runaway behaviors, which leads to safety in various application scenarios. sexual accident.
All over the world, both basic scientific research teams and industrial teams believe that the solution of replacing easily flammable liquid electrolytes with non-flammable solid electrolytes to form all-solid-state batteries has high safety and theoretically Has high energy density and power density.
Solid-state batteries may have advantages in the following aspects: First, they can be charged to higher voltages, the positive electrode material is not easy to evolve oxygen, the negative electrode can contain metallic lithium, and it is not easy to have side reactions with lithium continuously, and it is not easy to thermal runaway, Not easy to flatulence, good high temperature stability, support inner string. These advantages make it possible for the cells of solid-state batteries to have intrinsically safe characteristics, which can increase the size of the cells, increase the energy density, improve the module integration efficiency, allow higher charge and discharge rates, and also allow high-temperature operation to support thermal insulation. and self-heating thermal management. After the cell is enlarged, it is also convenient to implant multiple sensors, and at the same time, it has a long cycle life and no diving phenomenon. In addition, because the solid electrolyte does not have continuous side reactions, the entire material system is not sensitive to impurities, and at the same time, it is more convenient to support the process of dry electrodes, which may simplify the formation and aging process in the later stage, and also support the pretreatment more conveniently. Lithiumization process, thereby improving production efficiency and significantly reducing the cost of batteries, which are the possible advantages and advantages of all-solid-state batteries.
However, there are still many technical challenges for different types of all-solid-state batteries, including four types of all-solid-state batteries. The main problem of polymer all-solid-state batteries is that they can only operate at high temperatures and are not resistant to oxidation. They can only be matched with lithium iron phosphate positive electrodes, so the energy density is low. Thin-film all-solid-state batteries, large-capacity cells are difficult to manufacture, and the manufacturing cost is relatively high. Sulfide all-solid-state batteries, with very high ionic conductivity, are also the focus of global attention. However, at present, sulfide materials are air-sensitive, expensive, and have poor solid-solid contact inside the positive and negative electrodes. Oxide all-solid-state (battery), the electrolyte ceramic sheet is easily brittle, the interface resistance is high, and the large-capacity cell is difficult to prepare. Therefore, despite the high attention and high-intensity research and development of all-solid-state batteries in the world, there are still many technical challenges, and various technologies are being continuously developed to improve the problems faced by all-solid-state batteries.
Solid-state batteries have become the focus of research around the world, including many Japanese teams, American start-ups, and teams in Canada, South Korea, and Europe. Various countries are developing sulfide all-solid-state, solid-state metal lithium batteries, and polymer solid-state batteries. . Chinese start-up companies have developed this technical route of mixed solid-liquid electrolytes by combining the advantages of easy mass production of liquid electrolytes and the safer features of solid-state batteries. The choice of this technical route is different from the sulfides in Japan and South Korea, and also different from the metal lithium anodes in the United States. It is easier to mass-produce and can significantly improve the safety of existing liquid electrolyte lithium-ion battery products. And the technology development of these startups has reached a stage close to mass production. Therefore, we say that although Japan, South Korea, Europe, and the United States are relatively early in the research and development and industrial layout of all-solid-state batteries, China is the first to achieve mass production of solid-state batteries because it has chosen the route of hybrid solid-liquid batteries.
In all-solid-state batteries and the core of solid-state batteries, it is necessary to solve a series of key problems of materials. For sulfide electrolytes, the most difficult and most important thing to solve is to reduce the cost of production and improve the stability of air. Wu Fan's team at the Institute of Physics of the Chinese Academy of Sciences and the Yangtze River Delta Physics Research Center has been working on the development of air-stable and water-stable sulfide electrolytes for the past three years, and has made very significant progress. Using this water-stable and air-stable sulfide electrolyte, an all-solid-state battery has been developed, which has better capacity performance of the positive electrode material, which lays a very critical foundation for the development of sulfide and all-solid-state batteries.
A very important point in all-solid-state batteries is to solve the mechanical characteristics, and it is hoped that the interface between the positive electrode and the negative electrode can maintain a very good interface contact during the charging and discharging process. Therefore, everyone proposes to develop a composite electrolyte. Cui Guanglei's team from Qingdao Institute of Energy, Chinese Academy of Sciences has developed an in-situ polymerized solid electrolyte composed of sulfide electrolyte and PEGMEA (polyethylene glycol methyl ether acrylate), which has relatively high ionic conductivity and relatively low interface resistance. To a considerable extent, the problem of poor contact of the interface during the cycle is solved, so a better cycle property is obtained and the internal resistance is reduced.
In addition to sulfide electrolytes, which are widely concerned around the world, Chinese R&D teams are also actively developing lower-cost, high-ionic conductivity, and more stable electrolytes. The Ma Cheng team of the University of Science and Technology of China is the first in the world to develop a low-cost halogen-based solid-state electrolyte of lithium zirconium chloride (Li2ZrCl6), which has very important application prospects. At the same time, Tang Weiping's team from the Space Power Institute developed an oxide electrolyte with the highest ionic conductivity at room temperature. This oxide electrolyte is very stable, stable in air, and stable to metal lithium. The element does not contain precious elements and does not contain rare elements, that is, lithium zirconium silicon phosphorus oxide (Li3Zr2Si2PO12). Such materials may provide important options for safer and higher performance all-solid-state batteries and hybrid solid-liquid batteries in the future.
Widely used oxide solid-state electrolytes include garnet-structured lithium lanthanum zirconium oxide (Li7La3Zr2O12). The Institute of Physics of the Chinese Academy of Sciences has studied the stability of this material in air and understood the reaction of proton exchange in air. At the same time, the team of Nan Cewen of Tsinghua University also deeply studied the behavior of lithium dendrites penetrating the oxide solid electrolyte when this material encounters the metal lithium anode. Yu Xiqian's team from the Institute of Physics, Chinese Academy of Sciences used neutron imaging technology to deeply study the deposition behavior of metallic lithium in an all-solid-state electrolyte system with a three-dimensional structural microstructure, and found that the three-dimensional pore structure can alleviate the volume expansion and inhibit lithium dendrites grow.
In addition, it is very important to develop solid-state batteries and all-solid-state batteries. It is hoped that the battery can be charged to a high voltage, but after charging to a high voltage, the positive electrode has a relatively strong oxidizing ability. How can such an oxidizing ability be reduced while allowing electron ions What about transport? After 2018, the Institute of Physics team has been working on developing solutions for coating cathodes with ultrathin solid electrolytes. At present, important progress has been made in high-voltage lithium cobalt oxide for consumer electronics and ternary materials for power, and it is proved that the solid electrolyte-coated cathode has high thermal stability and electrochemical stability, It is a very important solution for high-voltage cathode materials, which is also an original in China.
On the negative side, to further improve the energy density, many teams at home and abroad have proposed solutions for anode-free metal lithium batteries. The most important thing is to prevent lithium precipitation and control the deposition form of lithium without negative electrode metal lithium. The team of Suo Liumin of the Institute of Physics adopted a liquid metal ultra-thin coating, which significantly improved the deposition efficiency of lithium and prevented lithium dendrites from forming in The growth behavior of the negative electrode, the developed prototype cell also reached more than 400Wh/kg.
The core purpose of developing solid-state batteries is to improve safety, but are solid-state batteries absolutely safe? An article in Joule this year has aroused widespread attention and discussion in the industry. Even in the high specific energy lithium metal battery, even if it is an all-solid state, there is a thermal runaway behavior. In fact, this thermal runaway behavior has also been proved in a series of studies since 2020 by the Institute of Physics, Chinese Academy of Sciences. Not all oxidizing solid electrolytes are stable when encountering metallic lithium. Two materials such as LATP and LAGP will still cause thermal runaway at higher temperatures when encountering metallic lithium, while perovskite-structured lithium lanthanum titanium oxide (Li0.33La0.56TiO3), and garnet-structured lithium lanthanum zirconium oxide (Li7La3Zr2O12) have higher and more stable behaviors for lithium, which means that solid-state batteries may not necessarily have all material systems on the negative side of thermal runaway. On the positive electrode side, we found that filling the solid electrolyte into the positive electrode can significantly improve the safety of the positive electrode side through the oxygen exchange behavior. It is also proved from the mechanism that using a solid electrolyte solution on the positive electrode side can improve the battery safety. It is also a very important realization.
On the whole, so far, the inorganic solid electrolytes and raw materials of all-solid-state batteries have not been mass-produced, and a supply chain has not been formed. The polymer electrolytes cannot be directly matched with high-voltage cathode materials. Low temperature performance is relatively poor. In addition, in the design of existing all-solid-state battery cells, the effect of volume change during cycling has not been fully resolved, and a high external pressure is required during testing. In addition, there are no mature mass production equipment for electrodes and cells, and the power management system integration solutions and application solutions for cells are not mature. The understanding of the safety of all-solid-state batteries in the life cycle is not comprehensive, the testing and evaluation are not complete, and a standard system has not been formed. In addition, the current cost-effectiveness of all-solid-state batteries is not clear. Therefore, we say that the mass production and commercialization of all-solid-state batteries still needs time to further deepen the understanding, optimize materials, and improve the technology of battery design and production, so as to gradually move towards commercial application.
Since the development of all-solid-state batteries is very difficult, another idea is, how can we make good use of the advantages of solid-state batteries? We propose the development idea of developing a hybrid solid-liquid electrolyte battery that is easy to engineer. This idea was not originally proposed by us. There are many teams at home and abroad.
We concluded that there are many ways to introduce solid electrolytes into cells, including coating on the surface of materials, additions in separators and electrode pores, direct introduction of solid electrolyte separator layers in the middle, and chemical reactions and electrochemical reactions. There are five non-conflicting methods for converting a liquid electrolyte into a solid electrolyte. These are the accumulation of long-term research in the past. The Institute of Physics started the research and development of all-solid-state batteries in 1976 by Mr. Chen Liquan, and then switched to liquid electrolyte lithium-ion batteries in the middle. Mr. Huang Xuejie led the team and founded Suzhou Xingheng. At present, we continue to develop hybrid solid-liquid and all-solid-state batteries on the original basis. In particular, a relatively original in-situ solid-state solution is proposed, which is to partially or completely convert the liquid electrolyte into a solid-state electrolyte through chemical and electrochemical reactions. If all are converted into solid-state electrolytes, it is an all-solid-state battery, which is a new research path for manufacturing all-solid-state batteries. Through this solution, we can be compatible with various existing positive and negative electrode materials, and also compatible with most battery materials of lithium-ion batteries, which can solve the problem of maintaining good contact between solid electrolyte and positive and negative electrode materials during the cycle, and can comprehensively balance The battery is charged to the requirements of high voltage, safety, lithium dendrite precipitation and volume expansion control.
Based on such solutions, we have developed a series of various types of batteries, including 150Wh/kg intrinsically safe solid-liquid hybrid energy storage batteries for large-scale energy storage. The performance of the national standard, including higher thermal runaway temperature, higher limit overcharge, and passing short-circuit and acupuncture tests.
In addition, we have also developed a 270Wh/kg high specific energy hybrid solid-liquid battery for drones, which currently has significant advantages in both energy density and safety, and has also passed the national standard for safety testing. In addition, we have also developed a portable energy storage inverter based on this solution, which is significantly higher than the energy density of the current modules in the industry.
In addition, we have developed a 300Wh/kg mixed solid-liquid power battery. By comparing the liquid and mixed solid-liquid acupuncture, the high specific energy cell can completely pass the acupuncture test at full charge, and can also pass the 150-degree test. the hot box. In addition, on this basis, we tested its low temperature performance and rate characteristics, which can well meet the requirements of power batteries.
On this basis, Beijing Weilan New Energy has further developed a 360Wh/kg power battery with higher specific energy, which can also pass safety tests such as acupuncture, overcharge and extrusion to meet the requirements of electric vehicles. We will cooperate with NIO to start mass production and application on the ET7 model, a hybrid solid-liquid electrolyte battery based on in-situ solidification with a single charge of 1,000 kilometers, a battery pack of 150 kWh, and a single unit of 360Wh/kg.
In addition, we have further developed cells with higher specific energy, including a 400Wh/kg hybrid solid-liquid battery, and developed a comprehensive solution of innovative cells and modules that can pass the shooting test. Outsiders do this for the first time, especially mods. We participated in the National Future Energy Storage Challenge in 2020, and a series of indicators have reached the international top or leading level. These tests are the results of third-party tests conducted by the Fifth Electronic Institute.
Overall, we believe that future batteries will develop towards higher specific energies, while the entire cell evolves from liquid to safer hybrid solid-liquid and all-solid-state batteries. The major directions include: cells with higher specific energy based on high nickel and lithium-rich manganese-based cathodes, as well as nano-silicon carbon anodes and lithium-carbon composite anodes, which can meet the requirements of passenger cars with a cruising range of 1000km and electric aircraft. ; And cathode materials based on modified lithium manganate, lithium iron phosphate, nickel manganese spinel, matched with high-capacity anode materials, solutions for 600 km battery life of pure electric vehicles; and for lower-cost energy storage Solutions for applied sodium-ion batteries and solid-state lithium iron phosphate batteries. This is our view on the future development route of power batteries and energy storage batteries.
In order to achieve mass production of solid-state batteries, an industrial chain needs to be built. For high specific energy batteries, we need to further de-optimize and develop new cathode materials, anode materials, electrolyte materials, pre-lithiation materials, super binders, conductive additives, and a new generation of metal-deposited current collectors. The new front-end, middle-end and back-end processes, as well as the implementation of intelligent factories, combine extreme manufacturing and minimalist manufacturing to form the next-generation industry 4.0-level solid-state lithium-ion battery industry chain
