Classification of ternary lithium batteries
Ternary lithium battery refers to a lithium battery using three transition metal oxides of nickel, cobalt and manganese as cathode materials. Because it combines the advantages of lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide, its performance is better than any single component cathode material above. The experimental analysis shows that three elements with different valence form a superlattice structure. There is an obvious synergistic effect between the three components, which makes the material more stable, and the discharge platform is as high as 3.6V. Therefore, it is considered to be one of the promising cathode materials. The ternary battery has excellent electrochemical characteristics such as high energy density, good safety and stability, supporting high rate discharge, and the cost advantage of moderate price. It has been widely used in the field of small and medium-sized lithium batteries such as consumer digital electronic products, industrial equipment and medical instruments, and shows strong development potential in the field of power lithium batteries.
According to different performances, ternary lithium batteries are classified as follows:
1. Ternary polymer lithium battery
The three-element polymer lithium battery refers to the lithium battery used for cathode materials, nickel cobalt lithium manganate (Li (NiCoMn) O2) three cathode material, and gel polymer electrolyte. As the transmission medium of ionic movement, electrolyte is usually composed of solvents and lithium salts. The electrolyte of lithium secondary battery mainly consists of liquid electrolyte, ionic liquid electrolyte, solid polymer electrolyte and gel polymer electrolyte. The electrolyte of two lithium batteries is mainly composed of liquid electrolyte, ionic liquid electrolyte, solid polymer electrolyte and gel polymer electrolyte. Gel polymer electrolytes consist of polymers, organic solvents and lithium salts, and are prepared by mixing organic electrolyte and solid polymer matrix. Because of its existence in the form of gelation, it has the advantage of solid electrolyte and liquid electrolyte. Because electrolyte is confined in polymer chain, it has high ionic conductivity (up to 10S/cm-3S/cm) in a wide temperature range. Its advantage is that the diaphragm has high mechanical strength and the film provides a large surface area. The thinner the film, the higher the energy density, because more active substances can be embedded in the battery. In addition, its electrochemical stability is also very good and resistant to high temperature. Most of the high-temperature batteries on the market use polymer electrolyte.
2. Ternary power lithium battery
The so-called power battery means that the battery supports high rate and high current discharge, high power density and more energy released per unit time. Rate discharge capacity refers to the capacity retention of the battery when the charge discharge rate increases. The rate of charge and discharge is expressed by XC. 1C means that the nominal capacity of the battery can be used up in 1 hour, while the rate of discharge at 2C can be used for 30 minutes.
The power / magnification performance of the battery is closely related to the design of the battery and is affected by many factors, such as electrolyte, diaphragm, type of active material, size of active particles and so on. Among these factors, the thickness of the electrode is the main factor affecting the high current discharge capacity. The rate discharge capacity can be greatly improved by thinning the electrode, because the thin electrode has smaller electron impedance and ion impedance. However, thinning the electrode will lead to less active substance mass in the electrode, so the battery capacity will be reduced. Therefore, the main technical challenge of ternary power lithium battery is to increase the high current discharge capacity without reducing the capacity.
At present, there are many researches on ternary power lithium battery. The most mature technology is Panasonic of Japan. 30C discharge can be realized in the experimental stage. Among them, the power 18650 ternary lithium battery that has successfully realized commercial mass production has a discharge rate of 12C and a capacity of 3300mah. Some domestic manufacturers have achieved high discharge rate, but the stability of the battery needs to be improved. Especially after using for a period of time, its cycle life and rate discharge capacity will be greatly reduced. It has been reported that the rate performance of lithium battery can be improved by particle coating and modification.
3. Ternary low temperature lithium battery
The temperature characteristic of the battery is an indicator of battery reliability, and the performance of the battery can also be evaluated by changing the ambient temperature. The low-temperature characteristics of lithium battery are mainly investigated from the low-temperature discharge characteristics and cycle life. The main purpose of low-temperature battery * is to maintain the fluidity of materials under low-temperature conditions, so that lithium ions can shuttle freely between the positive and negative electrodes to realize the charge and discharge of the battery. For example, using electrolyte with low melting point and reducing the particle size of active materials will enhance the low-temperature performance of the battery. This is because the channel of lithium ion is increased, which makes up for the defect of slow movement of lithium ion at low temperature to a certain extent.
At present, ternary lithium battery manufacturers can basically achieve a discharge temperature of - 20 ℃, with a discharge capacity of more than 50% and a cycle life of about 400 times, which can fully meet the needs of ordinary electric appliances and power consumption scenarios. However, in special products such as aerospace and special equipment, or in severe cold environments such as North and high mountains, lithium batteries must be able to reach lower discharge working temperatures to meet harsh service conditions.