Recently, the Institute of High-Technology Research and Development Lithium-Ion Research Institute (GGII) visited more than 50 companies and participated in many forum exchanges. It found that lithium batteries have made great breakthroughs in high-energy density technology.
The high energy density development route includes: high voltage cathode material, high gram capacity positive and negative materials. A high voltage positive electrode material generally refers to a positive electrode material having a battery voltage higher than 4.2V. Lithium cobaltate, lithium manganate, and ternary have high voltage materials.
Among them, the commercialization of high-voltage lithium cobalt oxide is very mature, and it is widely used in high-end digital products, and its energy density is higher than that of ordinary ternary batteries. At present, the voltage of high-voltage lithium cobalt oxide battery is usually 4.35V, and the 4.4V, 4.5V high-voltage lithium cobalt oxide battery in the next 3-5 years can be used on a large scale.
The ternary high voltage positive electrode material is rarely used and is basically in the research stage. However, the ternary high-voltage cathode material may be the breakthrough point for achieving 300Wh/kg energy density in the future.
At present, the gram capacity of ternary NCM811 material has exceeded 180 mAh/g, and high voltage can be achieved by coating or doping, and its gram capacity is further improved (high voltage material is equivalent to activation of lithium which is inactive at low voltage, and larger The use of materials). However, there are still many technical problems that have not been solved in the current high voltage of ternary materials, and the stability of the materials themselves has not been solved.
The lithium manganate cathode material has a charging potential of up to 4.7V and a very stable lattice structure.
At present, the lithium manganese oxide battery has an energy density of 150 Wh/kg, which is higher than the energy density of the lithium iron phosphate battery. Lithium manganate crystal has stable crystal structure and good thermal stability, and the safety of lithium manganate battery is very high. Among them, lithium manganate-lithium titanate battery has excellent application prospects in the field of fast charging.
Lithium iron phosphate is close to the theory due to its capacity, and it is difficult to activate more lithium by high voltage, and the effect is very limited. However, iron manganese (vanadium) phosphate and lithium iron silicate have higher energy density, which is a hot field in many research institutions and enterprises. The lithium iron silicate molecule contains two lithium ions, and its theoretical gram capacity is as high as 332 mAh/g.
The high voltage cathode material requires a high voltage electrolyte to work well throughout the battery system. In order for the electrolyte to operate stably in a high voltage environment, it is necessary to increase the oxidation resistance of the solvent while blocking the direct contact of the positive electrode with the electrolyte. The method for improving the oxidation resistance of the electrolyte includes a fluorinated solvent, and the price of the fluorinated solvent is too high, which is difficult to achieve in large-scale applications.
Other new antioxidant solvents such as ionic liquids have good ionic conductivity and oxidation resistance. They are excellent solvents for lithium batteries, but they are currently expensive and difficult to promote on a large scale. The method of blocking direct contact between the electrolyte and the electrolyte includes coating of the positive electrode material and positive electrode film forming additive. There are many researches on the coating and additives of cathode materials, and the effect is very obvious. It is an important means to improve oxidation resistance in the future.
The large-scale development and application of ternary materials is relatively late, and there is still much room for improvement in terms of energy density. At present, mainstream material manufacturers have been able to achieve 180mAh/g level, while the theoretical capacity of ternary high-nickel materials can reach 270mAh/g, and there is still much room for improvement. At present, high-capacity ternary materials are sensitive to water, low in efficiency, and poor in cycle. With the advancement of process technology, these problems can be solved, and the lithium-rich positive electrode is also a hot spot for many research institutions and enterprises.
On the other hand, the silicon-based anode material can greatly increase the gram capacity of the anode. The anode materials have been dominated by graphite, and the graphite anode technology is very mature. The actual capacity is very close to the theoretical capacity. To increase the negative gram capacity, other materials must be used.
Metal anodes such as silicon tin are very suitable choices. At the earliest Japanese sony, the use of tin composite anodes to increase the energy density of batteries has already introduced high-capacity 18650 products to the market. In recent years, silicon composite anodes have received much attention. Among them, silicon-carbon composite anodes and oxy-silica-graphite composite anodes are relatively mature, and Japanese and Korean companies have already applied them to high-capacity products.
At present, domestic material factories and battery manufacturers have gradually introduced silicon-based anode high-capacity products. The theoretical gram capacity of silicon is 4200 mAh/g, but the volume expansion effect is very large, so it is often combined with graphite to reduce the influence of expansion. The metal lithium negative electrode has a higher gram capacity than the silicon negative electrode, but its dendrite problem is not solved, and the safety risk is high. Moreover, metal lithium reacts easily with the electrolyte to lower its cycle life. At present, metal lithium anode batteries are difficult to be introduced to the market on a large scale.
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