A lithium-ion battery is a secondary battery that uses a lithium-containing compound as the positive electrode. During charging and discharging, lithium ions are extracted and inserted back and forth between the positive and negative electrodes to achieve charging and discharging. The internal components of a lithium-ion battery mainly consist of a positive electrode, a negative electrode, an electrolyte, and a separator.
Lithium-ion batteries primarily function by the movement of lithium ions between the positive and negative electrodes. During charging and discharging, Li+ ions repeatedly insert and extract between the two electrodes: during charging, Li+ ions extract from the positive electrode, pass through the electrolyte, and insert into the negative electrode, leaving the negative electrode in a lithium-rich state; the reverse occurs during discharging.
Lithium-ion batteries have many significant characteristics, and their advantages are mainly manifested in the following ways:
1. High voltage: The working voltage of a single cell is as high as 3.7-3.8V (3.2V for lithium iron phosphate, which is 3 times that of Ni-Cd and Ni-MH batteries).
2. High specific energy: The actual specific energy that can be achieved is about 555Wh/kg, which means that the material can achieve a specific capacity of more than 150mAh/g (3-4 times that of Ni-Cd, 2-3 times that of Ni-MH, which is close to about 88% of its theoretical value).
3. Long cycle life: Batteries typically last for over 500 cycles, even exceeding 1000 cycles, with lithium iron phosphate batteries reaching 8000 cycles. For appliances with low-current discharge, a longer battery life significantly enhances their competitiveness.
4. Excellent safety performance: Pollution-free and without memory effect. As the predecessor of Li-ion batteries, lithium batteries were limited in their application areas because metallic lithium easily forms dendrites and causes short circuits. Li-ion batteries do not contain elements such as cadmium, lead, and mercury that pollute the environment. A major drawback of some processes (such as sintered Ni-Cd batteries) is the "memory effect," which severely restricts the use of batteries, but Li-ion batteries do not have this problem at all.
5. Low self-discharge: The self-discharge rate of fully charged Li-ion after one month of storage at room temperature is about 2%, which is much lower than that of Ni-Cd (25-30%) and Ni-MH (30-35%).
6. Fast charging: 1C charging for 30 minutes can reach more than 80% of the nominal capacity, while phosphorus iron batteries can reach 90% of the nominal capacity in 10 minutes.
7. Operating temperature: The operating temperature is -25~45°C. With improvements in the electrolyte and positive electrode, it is expected to be extended to -40~70°C.
Lithium-ion batteries also have some shortcomings, mainly in the following aspects:
1. Aging: Unlike other rechargeable batteries, the capacity of lithium-ion batteries declines slowly, depending on the number of uses and temperature. This degradation can be represented by a decrease in capacity or an increase in internal resistance. Because it is temperature-dependent, it is more noticeable in electronic products with high operating currents. Replacing graphite with lithium titanate appears to extend battery life.
2. Recycling rate: Approximately 1% of new products need to be recycled for various reasons.
3. Not tolerant of overcharging: When overcharged, excessively embedded lithium ions will be permanently fixed in the crystal lattice and cannot be released, which can lead to a short battery life.
4. Not tolerant of over-discharge: During over-discharge, too many lithium ions are de-intercalated or de-intercalated in the electrode, which can lead to lattice collapse and thus shorten the lifespan.
In recent years, the application range of lithium-ion batteries has become increasingly wide. Lithium batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Currently, lithium batteries are gradually expanding into fields such as electric bicycles and electric cars.
