28/12/2020
Discussion about the comparatively popular solid-state batteries recently
Recently, QuantumScape, a solid-state battery company that has received investment from German Volkswagen and SAIC Motor Corporation and other auto companies, said that its lithium metal batteries will soon be applied to cars and trucks, attracting the attention of the industry and capital circles. And Quantum Scape went on the market in November this year.
Bailing Research invited senior experts in solid-state batteries to make an in-depth analysis on this topic.
1. Why develop solid-state batteries
The cruising range is the core reason that restricts the development of electric vehicles. The improvement of the cruising range mainly depends on increasing the energy density of the battery. The energy density of the lithium ion battery is mainly determined by the material system of the positive and negative electrodes. Under the limitation of the existing positive and negative material system, The ultimate energy density of lithium-ion battery packs is difficult to meet the requirements.
If you want to increase the energy density, you need to replace the positive and negative materials, such as using lithium metal for the negative electrode, but the lithium metal negative electrode has high requirements for the battery, so there is a solid state battery.
# In fact, the metal anode battery is earlier than the graphite anode battery
In the early days, lithium batteries consisted of lithium metal anode + solid electrolyte materials, and lithium metal batteries were once commercialized by Moli. However, lithium metal will form "dendrites" and grow up quickly during the charging and discharging process of the battery, piercing the diaphragm and causing an internal short circuit, causing a rapid accumulation of heat inside the battery and a rapid rise in temperature, which will eventually cause the battery to catch fire and explode. At that time, when seeking to solve the problem of lithium dendrites, it was discovered that graphite could alleviate the problem of lithium dendrites. Lithium-ion batteries were introduced to the market by Japan's Sony due to the discovery of graphite negative electrodes.
# Episode End #
Graphite anode is suitable for scenarios with low energy density. If energy density is desired, it is necessary to face the lithium metal anode again to solve the problem of inhibiting lithium dendrites. Solid electrolytes are promising to improve battery safety. This is the reason why solid-state batteries are concerned.
2. The actual situation of current mainstream solid-state batteries
In the current mainstream liquid electrolyte batteries, the liquid electrolyte accounts for 15% to 25% of the mass fraction of the entire battery. Now commonly referred to as solid-state batteries, such as domestic Beijing Weilan, Jiangsu Qingtao, Ningbo Fengli, Taiwan Huineng and other products, are actually solid-liquid hybrid batteries with electrolyte content ranging from 1% to 10%. The strictly defined all-solid-state battery does not have any electrolyte, which means that the mass fraction of the electrolyte is 0, and the solid electrolyte is used as the conductor medium in this battery.
3. Advantages and disadvantages of solid-state batteries
3.1 Advantages
1) High safety: The solid electrolyte has a much higher ignition point than the liquid electrolyte, is not flammable, and will not flow or leak.
2) Improve energy density: The solid form can inhibit the growth of lithium dendrites and can make lithium metal negative electrodes possible. The energy density of the lithium metal negative electrode battery can be increased by more than 35%. If the high nickel ternary NCM811 is used as the positive electrode, the battery energy density can reach more than 500Wh/kg. Using lithium iron phosphate as the positive electrode, the battery energy density can also reach more than 300Wh/kg .
3) Reduce active materials and increase energy density: Lithium-ion batteries have both sides in the same current collector, one is the positive electrode and the other is the negative electrode. Therefore, its internal must be connected in parallel, and external series and parallel equipment is required, so some of it is inactive Ingredients. However, solid-state batteries can be directly connected in series within the battery using bipolar technology; no inactive components or cooling systems are required. Because solid-state batteries remove inactive components, the energy density of solid-state batteries can be increased a lot, increasing the space by 40%.
4) Make flexibility possible: the solid electrolyte is not afraid of leakage or damage, and the battery can achieve a stretching range of more than 300%. This kind of bendable battery can be used for wearable and large deformation places.
3.2 Disadvantages
1) The interface impedance increases, resulting in large volume changes: The positive and negative electrodes of solid-state batteries have no electrolyte, and fast lithium conduction is achieved through surface-to-surface contact, which will increase the interface impedance, making energy consumption internal and unable to achieve fast charging. In addition, the volume of the positive electrode and negative electrode changes during charging and discharging, reaching more than 10%. Based on this, there is a big problem in the solid-solid interface contact during the battery cycle. This has also led to increased difficulty in mass production of solid-state batteries, and they cannot be industrialized as quickly as lithium-ion batteries.
2) High cost: Since the industry is still in its infancy, the cost of solid-state battery materials is relatively high. For example, the typical solid electrolyte material for oxides-lithium lanthanum zirconium oxide (LLZTO), currently sells for US$200/kg, and if it is sulfide , More advanced lithium silicon phosphorous sulfur materials or lithium phosphorous sulfur materials, the price is more than 100,000 US dollars / kg, the cost is very high.
4. The main technical routes and classifications of solid-state batteries (correction: the hydride in the picture is actually an oxide)
At present, all solid-state lithium batteries are mainly divided into 4 different technical routes:
1) The thin film is all solid: the positive, negative, and solid electrolytes are all very thin (thickness is in the order of microns), which can be achieved by chemical v***r deposition (CVD) or physical v***r deposition (PVD). This technical route has small battery capacity and energy Lower density (because of lower overall capacity). However, it has good cyclability and adapts to high voltage. It typically represents thin-film solid electrolyte materials such as LiPON, which are mainly used in high-precision industries such as electronic devices. It may also be used in scenarios with high safety performance requirements, but not suitable for electric vehicles , Drones, aerospace equipment and other scenarios.
2) The polymer is all solid: the material system is mainly polyethylene oxide (PEO) system. The main advantage is that it is easy to process, can prepare large-capacity batteries, is mechanically soft, and has similar properties to the currently used electrolyte (essentially organic solvent). Therefore, the production line is close to the polymer solid-state battery production line, so it is the easiest to use existing equipment to achieve mass production of solid-state batteries. Main disadvantages: 1) Ionic conductivity is the lowest, it must be heated to 60 or 85 ℃ above, the ionic conductivity will increase, close to 10-3 S/cm, 2) easy to short circuit (because the polymer is relatively soft, so lithium dendrites are easy It penetrates the solid electrolyte and causes a short circuit); 3) Energy density is limited. Because the polymer is organic, the electrochemical stability is not good, and it has good compatibility with lithium iron phosphate, but it is not compatible with ternary, resulting in the energy density cannot be improved. .
3) Oxide in all solid state: the conductivity is higher than that of polymer, the ion conductivity of oxide can reach 10-4~10-5 S/cm, and it can reach the level of 10-3 S/cm by doping, so it can be It can conduct lithium at low temperature and can withstand high voltage, which is significantly more stable than polymer under high voltage. Typical representatives are lithium lanthanum zirconium oxide, LAGP, LATP and other oxide materials. The main disadvantages are: 1) The mechanical properties of the oxide are hard, and if it is used to make the electrolyte sheet, it is easier to brittle; 2) The solid-solid contact is not very good, making it difficult to prepare large-capacity batteries. But as far as China is concerned, the oxide system is the most popular. For example, domestic brands such as Weilan mostly use oxides as battery materials.
4) The sulfide is all solid: the sulfide itself has the highest ionic conductivity and good contact, so its overall ionic conductivity performance is very good. It is the most likely technical route for all-solid-state batteries in the future. However, the product price is very high and the air stability is poor. Sulfide in the air, especially after contact with water, directly produces H2S. H2S is not only toxic, but also has a bad smell. This is the biggest problem in use and limits its wide application.
5. Major solid-state battery companies at home and abroad are progressing towards industrialization
According to industry chain research, solid-state batteries will be gradually commercialized in 2025 and become the main technical route for power batteries in 2030. In this context, major countries in the world are vigorously deploying in this field:
1) Europe and America
Mainly include Cymbet, Quantum Scape, SolidPower, Polyplus, 24M, Sakti3 and other companies:
Cymbet: A thin-film solid-state battery company in the United States, making thin-film solid-state batteries;
24M: Founded by Professor Jiang Yeming of MIT (founder of A123), he is currently working on a semi-solid concept, making both positive and negative electrodes thick.
Sakti3 in cooperation with Dyson, UK. It used to be more brilliant, and now it has closed down, but it was once more brilliant.
Quantum Scape: A recently popular company that has been listed on the US stock market and has received investment from automakers such as Volkswagen, Mainland Germany and the domestic SAIC Group;
US stock SEEO company received investment from German Bosch
German BMW is making solid-state batteries.
2) China
At present, there are many solid-state batteries in China, such as Qingtao, Weilan, Ganfeng Lithium, and Wuxi Haite. And CATL and other leading battery companies are vigorously developing solid-state batteries, but have not announced on a large scale. In addition, SAIC and Guoxuan Hi-Tech are doing it.
3) South Korea
There are three main companies in South Korea, Hyundai, LG Chem, and Samsung. Samsung released more than 1,000 cycles of sulfide all-solid-state batteries on Nature Energy in March 2020, which is also the best sulfide all-solid-state battery in public data.
4) Japan
There are a lot of companies in Japan that have invested in solid-state batteries, and they are now basically jointly developed. Toyota, Panasonic, Hitachi, and NGK all work together to make sulfide all-solid-state batteries.
6. Application prospects of solid-state batteries
Hitachi of Japan started to make sulfide all-solid-state batteries in 2017, and supply them to aerospace vehicles in 2019. So in the near term, solid-state batteries may be used in military industry, high-precision equipment, and some slightly niche markets. By 2025 and 2030, the target is the market for new energy vehicle power batteries. When energy density and safety are further improved in the future, it will be applied to transportation industries such as electric ships and electric aircrafts. If the cost drops to a certain level, it will also enter the consumer electronics market such as mobile phones and computers. In addition, technical fields such as aerospace national security and large-scale energy storage will gradually be covered as energy density increases and costs decrease.
