I. Technical Principles
Lithium-ion batteries are classified into two types: liquid lithium-ion batteries (LIB) and polymer lithium-ion batteries (PLB). They use lithium-containing compounds as the positive electrode, such as binary or ternary materials like lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), or lithium iron phosphate (LiFePO4); the negative electrode uses lithium-carbon intercalation compounds, such as graphite, soft carbon, hard carbon, and lithium titanate; and the electrolyte is composed of lithium salts dissolved in organic carbonates. During charging, lithium atoms transform into lithium ions and migrate through the electrolyte to the carbon electrode, where they combine with external electrons and are stored as lithium atoms. The entire process is reversible during discharge.
Compared to other traditional batteries, lithium-ion batteries have advantages such as high specific energy, high rated voltage, strong high-current discharge capability, high power handling capacity, and low self-discharge rate. Their specific energy (200Wh/kg) is about five times that of lead-acid batteries, with a single-cell operating voltage of 3.7V or 3.2V, a cycle life of 3000-5000 cycles in shallow charge-discharge mode, and an energy storage efficiency exceeding 90%. However, lithium-ion batteries have poor overcharge/discharge resistance, complex assembly and protection circuits, and relatively high costs compared to traditional batteries like lead-acid batteries. These factors limit the application of lithium-ion batteries in large-scale power and energy storage battery fields. With the development of new energy vehicles, renewable energy, and distributed power station technologies, the application of lithium-ion batteries in new energy vehicles, renewable energy grid integration, and small-scale distributed power stations is receiving increasing attention.
II. Key Technologies
Electrode materials are a crucial technology for lithium-ion batteries, closely related to battery cost and performance. Lithium-cobalt oxide batteries have been abandoned for high-power, high-capacity applications due to their expensive materials and poor safety. Lithium-manganese oxide batteries offer advantages in low cost and high performance, with higher safety than lithium-cobalt oxide batteries, making them a popular alternative technology for electric vehicle batteries. Lithium iron phosphate batteries possess a relatively stable oxidation state, good safety performance, good high-temperature performance, and advantages such as being non-toxic, pollution-free, having widely available raw materials, and being inexpensive, making them one of the most popular electric vehicle battery technologies and a promising candidate for energy storage systems. Key technologies for lithium-ion batteries used in large-scale energy storage also include overall battery system design, battery system integration and assembly, and battery pack testing.
III. Current Application Status
The concept of lithium-ion batteries was proposed in the 1960s when Bell Labs developed a carbon anode that could replace lithium metal electrodes, making the idea a reality. Since Sony successfully commercialized lithium-ion batteries in 1991, they have been widely used in the electronics industry. In recent years, with the development of materials and battery technology, the application of lithium-ion batteries in electric vehicles, energy storage batteries, and other fields has received increasing attention. Currently, Japanese companies such as Sony, Sanyo (now merged with Panasonic), Nissan AESC, and South Korean companies such as Samsung SDI and LG Chem are all vigorously developing lithium manganese oxide batteries. In 2008, the American company A123 pioneered the development of a 2MW lithium-ion energy storage battery, and Altair Nanotechnologies has established a 1MW/250kWh trailer-mounted lithium-ion battery energy storage system. Currently, approximately 18MW of lithium-ion battery energy storage systems are connected to the grid globally for engineering demonstrations or grid services. Chinese companies, represented by BYD, Lishen, and BAK, have actively invested in the research and development and production of lithium-ion batteries and have made good progress. During the Shanghai World Expo, the State Grid Corporation of China built and connected a 100kW lithium-ion battery demonstration system to the grid. The Zhangbei National Wind Power Monitoring and R&D Center, led by the State Grid Electric Power Research Institute and invested in by the National Development and Reform Commission, plans to use 18MW of lithium-ion battery energy storage for testing its application in wind farm power generation and grid connection. China Southern Power Grid has already built a 4MW lithium-ion battery energy storage demonstration power station, whose primary function is peak shaving and valley filling.
IV. Development Trends
In lithium-ion battery research, a key focus is on improving the performance of the battery's electrodes and electrolytes by controlling the size, composition, structure, and morphology of particles. In electrode material research, a crucial aspect is combining this with carbon coating technology to reduce electrochemically active materials to submicron or smaller sizes to achieve core-shell electrodes. Other emerging technologies, including lithium-ion batteries with nanoalloy negative electrodes, silicon-based lithium-ion batteries, lithium-ion batteries using organic electrode materials, and lithium-air batteries, are also gradually appearing.
