The development path for high energy density includes: high-voltage cathode materials and high-capacity cathode and anode materials. High-voltage cathode materials generally refer to cathode materials used in batteries with a voltage higher than 4.2V. High-voltage materials are available for lithium cobalt oxide, lithium manganese oxide, and ternary cathodes.
High-voltage lithium cobalt oxide batteries are already commercially mature and widely used in high-end digital products, offering higher energy density than ordinary ternary batteries. Currently, high-voltage lithium cobalt oxide batteries typically operate at 4.35V, but 4.4V and 4.5V high-voltage lithium cobalt oxide batteries may see large-scale application in the next 3-5 years.
Ternary high-voltage cathode materials have limited applications and are primarily in the research stage. However, ternary high-voltage cathode materials may be the breakthrough point for achieving an energy density of 300Wh/kg in the future.
Currently, the specific capacity of ternary NCM811 materials has exceeded 180 mAh/g. High voltage can be achieved through coating or doping, and its specific capacity will be further improved (high-voltage materials are equivalent to activating lithium that is inactive at low voltage, making greater use of the material). However, there are still many technical problems to be solved in the high-voltage application of ternary materials, and the stability of the material itself has not yet been resolved.
The charging potential of lithium manganese oxide cathode material can reach 4.7V, and its crystal structure is very stable.
Currently, lithium manganese oxide batteries have an energy density of 150Wh/kg, higher than that of lithium iron phosphate batteries. Lithium manganese oxide has a stable crystal structure and good thermal stability, making its batteries very safe. Among them, the lithium manganese oxide-lithium titanate system battery shows excellent application prospects in the fast-charging field.
Lithium iron phosphate (LFP) has already reached near its theoretical capacity, making it difficult to activate more lithium ions through high voltage, resulting in very limited effectiveness. However, lithium iron manganese (vanadium) phosphate (LFP) and lithium iron silicate (LFS) have higher energy densities and are popular research areas for many research institutions and companies. Lithium iron silicate molecules contain two lithium ions, and their theoretical specific capacity is as high as 332 mAh/g.
High-voltage cathode materials require high-voltage electrolytes to ensure the proper functioning of the entire battery system. To ensure stable operation of the electrolyte under high-voltage conditions, it is essential to improve the solvent's oxidation resistance while simultaneously preventing direct contact between the cathode and the electrolyte. Methods to improve the electrolyte's oxidation resistance include using fluorinated solvents; however, these solvents are too expensive for large-scale application.
Other novel antioxidant solvents, such as ionic liquids, possess excellent ionic conductivity and antioxidant capabilities, making them excellent solvents for lithium batteries. However, their high price currently hinders large-scale adoption. Methods to prevent direct contact between electrolytes include cathode material coating and cathode film-forming additives. Extensive research has been conducted on cathode material coating and additives, demonstrating significant effectiveness and representing important future approaches to improving antioxidant properties.
The large-scale development and application of ternary materials started relatively late, and there is still significant room for improvement in energy density. Currently, mainstream material manufacturers have achieved levels of 180 mAh/g, while the theoretical capacity of high-nickel ternary materials can reach 270 mAh/g, indicating substantial room for further improvement. High-capacity ternary materials currently suffer from water sensitivity, low initial efficiency, and poor cycle life. These problems may be resolved with advancements in process technology, making lithium-rich cathodes a hot research topic for many research institutions and companies.
On the other hand, silicon-based anode materials can significantly improve the specific capacity of the anode. Graphite has traditionally been the primary anode material, and graphite anode technology is very mature, with actual capacities very close to theoretical capacities. To improve the specific capacity of the anode, other materials must be used.
Metal anodes such as silicon and tin are very suitable choices. Sony in Japan was one of the first to use tin composite anodes to improve battery energy density and has already launched high-capacity 18650 products to the market. In recent years, silicon composite anodes have gained attention, among which silicon-carbon composite anodes and silicon suboxide-graphite composite anodes are relatively mature technologies, and Japanese and Korean companies have already applied them to high-capacity products.
Currently, domestic material manufacturers and cell manufacturers are gradually launching high-capacity silicon-based anode products. Silicon has a theoretical specific capacity of 4200 mAh/g, but its volume expansion effect is very large, so it is often combined with graphite to reduce the impact of expansion. Lithium metal anodes have a higher specific capacity than silicon anodes, but the dendrite problem remains unresolved, posing a high safety risk. Furthermore, lithium metal readily reacts with the electrolyte, reducing its cycle life. Currently, lithium metal anode batteries are still difficult to commercialize on a large scale.
