Science and technology
Out of the laboratory, solid-state battery mass production technology meets a major breakthrough!
Among the many candidates for next-generation power batteries, solid-state batteries are the most promising. All solid-state batteries not only have relatively high technology maturity, but also have won the support of a group of top international scholars such as Goodenough and Cui Wei. Many lithium-ion battery companies at home and abroad have also made all-solid-state battery technology an important next-generation technology reserve. The two most significant advantages of all solid state batteries are as follows:
High energy density
The current lithium-ion battery uses graphite material as the negative electrode. The theoretical specific capacity of graphite is only 372 mAh/g, which is far from meeting the demand of high-energy lithium-ion battery. The theoretical specific capacity of metal Li negative electrode can reach 3860 mAh/g. An ideal high-energy battery negative electrode material, but Li metal negative electrode will form Li dendrites during repeated charge and discharge, resulting in low coulombic efficiency and increased risk of short circuit, while solid electrolyte has high shear modulus. It can better inhibit the growth of Li dendrites, so we can use metal Li as the negative electrode in solid-state batteries. Related studies have shown that even at lower areal density, replacing the traditional graphite with metal Li can still make the energy density of the battery. Increase by more than 35%. If we use NCM811 material as the positive electrode, the energy density of the battery can reach 500Wh/kg or more. Even the energy density of LFP as the positive electrode can be increased to more than 300Wh/kg. This is unmatched by traditional liquid electrolyte lithium-ion batteries.
2. High security
Safety is another thorny issue facing liquid electrolyte lithium-ion batteries, and the emergence of solid electrolytes has greatly improved the safety of lithium-ion batteries. Studies have shown that Li/LFP batteries using liquid electrolytes begin to self-exotherm at around 90 °C, causing thermal runaway of the battery at around 178 °C, while the self-heating temperature of Li/LFP cells using solid electrolytes increased to 247 °C. Above, and no thermal runaway occurred throughout the process. Conventional liquid electrolyte lithium ion batteries are often caused by large-area internal short circuit caused by heat shrinkage and melting of the diaphragm, which leads to thermal runaway. In the case of inorganic solid electrolytes, the thermal stability is significantly higher than that of polymer-based separator materials. Therefore, the risk of short-circuiting of the positive and negative electrodes caused by high temperature is almost zero, so that the risk of thermal runaway of the lithium ion battery using the solid electrolyte is greatly reduced. At the same time, even if the battery is out of control, the combustible composition of the solid electrolyte is much lower than that of the traditional carbonate electrolyte, which can significantly reduce the severity of thermal runaway of the lithium ion battery, and has significant safety for the power battery. Improvement.
Solid electrolytes can be divided into three main categories:
1) an oxide electrolyte such as a common LLZO-based electrolyte;
2) a sulfide electrolyte such as a Li2S-P2S5 electrolyte;
3) An organic polymer electrolyte such as a common PEO-based polymer electrolyte or the like.
These types of solid electrolytes have their own advantages and disadvantages. In general, polymer electrolytes have excellent processing properties and can form good interface contact with electrode materials. However, such electrolytes have a low electrical conductivity at room temperature, so lithium ion batteries using polymer electrolytes are difficult to work at temperatures below 60 °C. Further, a solid polymer electrolyte typified by a PEO-based electrolyte is easily oxidatively decomposed on the positive electrode side of a high potential, resulting in deterioration of battery performance. The sulfide solid electrolyte has a very high electrical conductivity at room temperature, is close to the liquid electrolyte, and has good processing properties, but is unstable in the atmosphere and easily produces highly toxic H2S gas with the water therein. Therefore, the entire process needs to be protected under an inert atmosphere. Carrying on, the production cost is high. The oxide electrolyte has high conductivity and good stability in air, but its interface with the electrode material needs to be optimized, and the oxide electrolyte is brittle and the processing performance is poor.
Solid-state batteries are the most promising next-generation power battery candidates, and countries have invested a lot of money in related technology research. As the first powerhouse of lithium-ion batteries, Japan also announced the development of a new generation of high-efficiency "all solid-state battery" core technologies in 2018, including 23 automotive, battery and materials companies including Toyota, Honda and Nissan, and 15 academic institutions. The plan is to fully master all solid-state battery technology by 2022. Japan's all-solid-state technology route is mainly based on sulfides. Toyota, the leader in this field, launched a sulfide solid-state battery as early as 2010. The prototype energy density introduced in 2014 reached 400Wh/kg. Learn about Toyota's plan to industrialize sulfide solid-state batteries by 2020.
Domestically, research on all-solid-state lithium-ion batteries has focused on key raw materials and battery preparation technologies for solid-state batteries, such as Tsinghua University, Institute of Physics of the Chinese Academy of Sciences, Shanghai Institute of Ceramics, and Qingdao Energy Research Institute. Process research and development, the major power battery manufacturers also regard solid-state battery technology as an important technical reserve for the next generation. Battery companies including Ningde Times and BYD are all in the process of deploying related technologies. However, according to the technical roadmap of each company, it is basically necessary to wait until 2025 before launching related technology products.
However, although solid-state batteries have advantages that are currently unmatched by lithium-ion batteries, the development of all-solid-state batteries is still a road full of thorns, and there are still a lot of problems to overcome:
1. Bad interface contact
In an all-solid-state battery, the transition metal oxide particles are still the main positive electrode material. When the electrode is formed, a large number of complex pores are formed in the electrode, and the conventional liquid electrolyte can penetrate into the pores, thereby ensuring that all the active materials are Can participate in the electrochemical reaction. However, the solid electrolyte does not have fluidity, so it is difficult to ensure sufficient contact between the active material particles and the solid electrolyte, and the volume change of the active material during charging and discharging of the battery further destroys the contact interface between the solid electrolyte and the active material particles, resulting in solid electrolyte. The large contact resistance with the active material affects the performance of the solid state lithium ion battery.
2. Lithium dendrite growth
Yes, you are not mistaken, there is still a problem of lithium dendrites in solid-state batteries. Generally, we believe that the good mechanical strength of solid electrolytes can effectively inhibit the growth of Li dendrites, but studies have shown that Li dendrites can still follow Li7La3Zr2O12 (LLZO). The grain boundary of Li2S-P2S5 solid electrolytes grows rapidly, and internal short circuits often occur in dozens of cycles, which seriously affects the service life of all-solid lithium-ion batteries.
3. Interface stability issues
The problem of interface stability is mainly reflected in two aspects: on the one hand, some traditional organic polymer electrolytes, such as PEO, will oxidize and decompose on the positive side of high voltage, resulting in increased contact resistance and deterioration of battery performance; The oxide solid electrolyte and the sulfide solid electrolyte may undergo reductive decomposition on the negative electrode side, resulting in a decrease in the performance of the solid state battery.
4. High cost
High cost is also one of the urgent problems that all solid-state lithium-ion batteries need to solve. Take the common garnet structure of LLZO electrolyte as an example, its current price is as high as 2000$/kg, which is much higher than the traditional carbonate electrolyte. Second, the cost of the production process accounts for 75% of the current cost of solid-state batteries. According to the calculation, the production process cost will be as high as 750-2500$/kWh in small batch production (10000/year). Even if the production scale is expanded to 100 million/year, the production process cost is still as high as 75-240$/kWh. It accounts for more than 50% of battery cost, which is much higher than the current lithium-ion battery process cost.
The three technical routes for solid-state lithium batteries have been around for a long time. In the early days of solid-state battery technology, due to the relatively low conductivity of solid electrolyte materials, most of the research and development focused on improving the conductivity of solid electrolytes. Therefore, sulfide electrolytes and oxide solid electrolytes with high ionic conductivity attracted a wide range. attention. However, with the continuous advancement of technology, it has been found that conductivity is not the main factor restricting the development of solid-state batteries. Interface problems and mass production processes have gradually become the next difficult point for solid-state batteries to overcome. Sulfide and oxide electrolytes have poor machinability, interface contact problems and mass production process problems have been delayed, and polymer electrolytes have the best of the three technical routes due to their excellent processing characteristics and good interface contact. A kind of hope.
Polymer-based solid-state lithium-ion batteries have made great progress in academic research, but their industrialization process is still relatively slow, and there is no clear commercialization schedule. In stark contrast to the slow pace of other manufacturers, the top domestic power battery manufacturer Wanxiang 1-2 released a heavy news on June 24, announcing its acquisition with Ionic Materials, an advanced materials company, in the development of all-solid-state batteries. A milestone in progress. The company has developed a high-energy-density, high-safety solid-state lithium-ion battery product by combining Ionic Materials' advanced conductive polymer material technology with A123's ternary/graphite material technology. This achievement has made the mass production of large-size all-solid-state lithium-ion batteries a reality, and has pushed electric vehicles toward safer and lighter targets.
Why does Wanxiang One Two Three lead the introduction of polymer solid-state lithium-ion battery products ahead of other power battery manufacturers? This is related to solving the oxidation resistance of the polymer electrolyte in the high potential cathode material. We know that traditional PEO-based polymer electrolytes have relatively high temperature ionic conductivity, but their ability to resist oxidation is poor due to the presence of CO bonds in their main chain, making it difficult to apply in electrochemical systems with voltages above 4V. This is undoubtedly unacceptable for the pursuit of high energy density power batteries. In response to this problem, Wanxiang Yi 2 and Ionic Materials jointly strengthened the problem of oxidative decomposition of polymer electrolytes at high potentials by means of surface coating modification and polymer electrolyte modification, which significantly improved the problem. The rate and cycle performance of high voltage system polymer batteries (shown below) make it possible to use NCM811 materials in polymer based solid state lithium ion batteries.
"Safety" is the bottom line that Wanxiang one or two has always adhered to in the development and production of power batteries. This standard is no exception in the development of all-solid-state lithium-ion batteries. Compared with the traditional liquid electrolyte lithium ion battery, the solid lithium ion battery has not been used with flammable and volatile carbonate electrolyte, so the safety has been greatly improved, and the 10Ah solid battery has passed the harsh In the acupuncture experiment, the maximum temperature of the battery during the acupuncture process is only 39 °C, and no fire or explosion occurs at all, which is of great significance for improving the safety of the electric vehicle.
The cost issue is an insurmountable obstacle to the application of all-solid-state lithium-ion batteries. Research shows that the cost of the production process of the all-solid-state battery manufacturing process accounts for more than 75%, making the cost of all-solid-state batteries high. Wanxiang One Two Three broke the limitation of the existing solid-state battery production process, and innovatively utilized the traditional lithium-ion battery production equipment to achieve mass production of all solid-state batteries, greatly reducing production costs, and smoothing the application of all-solid-state batteries. An obstacle.
Wanxiang 1-2's success in solid-state batteries stems from its precise route positioning. When other manufacturers are still between the three technical routes, Wanxiang is keenly aware of the application of polymer electrolyte systems on solid-state batteries. Great potential, and quickly established a comprehensive strategic partnership with Ionic Materials, a leading company in the polymer electrolytes field, combining the advantages of each other in polymer electrolytes with the advantages of universal ternary/graphite material systems. A breakthrough in mass production technology for solid-state batteries. “The cooperation between Wanxiang and Ionic Materials is a very creative and successful cooperation. This cooperation has finally produced the technologically advanced products we are proud of. We are honored to be the pioneers of the industry to launch this product first” Jim Paye, chief technology officer of Wanxiang Yi 2, said. Mike Zimmerman, CEO of Ionic Materials, agrees that “a series of synergies between our two companies is a necessary condition for success in the growing battery arena. We look forward to the future, we are commercializing this technology. Continued success in the application process."
Wanxiang is a world-class designer and manufacturer of power battery systems. For a long time, Wanxiang insisted on the “black” bottom line of “safety”. The 48V light-mixing system manufactured by the company has won the market with its excellent performance and excellent safety performance. Widely recognized, Wanxiang firmly holds the throne of the world's largest 48V system manufacturer. The all-solid-state lithium-ion battery introduced this time is another milestone in the improvement of the safety of lithium-ion batteries, and it also demonstrates the determination and perseverance of Wanxiang's unswerving bottom line. Bao Jianfeng has been grinding out, plum blossoms have come from bitter cold, and Wanxiang has long adhered to technology-driven development. Its products cover high-power light-mixing systems, transportation high-energy density solutions, and energy storage systems. It is a global lithium-ion battery. And a global leader in system design and manufacturing.