Ternary lithium battery classification
Ternary lithium batteries, that is, lithium batteries that use nickel cobalt manganese oxide (NCM) or nickel cobalt aluminum oxide (NCA) as the positive electrode material, have various classification methods according to different classification standards.
Introduction to Lithium-ion Batteries (LIB)
Lithium-ion batteries are mainly composed of four parts: positive electrode materials, negative electrode materials, separators, and electrolytes. The positive electrode materials must participate in chemical reactions and also provide Li+ as a lithium ion source; the negative electrode materials are also an important component of the battery, generally carbon, lithium titanate, and silicon-based alloy materials; the main function of the separator is to prevent the positive and negative electrode materials from directly contacting each other and causing a short circuit, and it is generally a porous membrane material such as polyethylene or polypropylene; the role of the electrolyte is to provide a channel for the transmission of lithium ions and promote the reversible reaction of the electrode. It is mainly composed of electrolyte lithium salts, non-aqueous organic solvents, and necessary additives.
Figure 1. Applications of lithium-ion batteries
Lithium cobalt oxide is the first commercialized cathode material for lithium-ion batteries. Its theoretical gram capacity after complete delithiation is 274 mAh/g, its true density is as high as 5.1 g/cm 3 , and its actual compacted density can reach 4.2 g/cm 3. It has an extremely high volume energy density (the advantage is prominent under high voltage) and is still the most widely used cathode material for consumer batteries.In fact, lithium cobalt oxide has three crystal structures, namely high-temperature phase HT- LiCo O 2 , low-temperature phase LT - LiCo O 2 , and rock salt phase LiCo O 2. Among them, the synthesis temperature of low-temperature phase lithium cobalt oxide is relatively low, and the crystal structure characteristics are between the layered structure and the spinel structure. The Li layer contains about 25% Co atoms, and the Co layer contains about 25% Li atoms. The bulk density is low and the electrochemical performance is poor. It is rarely used as a commercial positive electrode material. The structure of rock salt phase lithium cobalt oxide is highly disordered, and Li and Co are randomly arranged inside the crystal without obvious rules.
32.What is the IEC standard cycle life test?
IEC stipulates that the standard cycle life test for NiMH batteries is:
After the battery is discharged at 0.2C to 1.0V/piece
01) Charge at 0.1C for 16 hours, then discharge at 0.2C for 2 hours and 30 minutes (one cycle)
02) Charge at 0.25C for 3 hours and 10 minutes, discharge at 0.25C for 2 hours and 20 minutes (2-48 cycles)
03) Charge at 0.25C for 3 hours and 10 minutes, discharge at 0.25C to 1.0V (49th cycle)
04) Charge at 0.1C for 16 hours, leave for 1 hour, and discharge at 0.2C to 1.0V (50th cycle). For NiMH batteries, repeat 1-4 for a total of 400 cycles, and the 0.2C discharge time should be greater than 3 hours; for NiCd batteries, repeat 1-4 for a total of 500 cycles, and the 0.2C discharge time should be greater than 3 hours.
I. Some important concepts
Lithium iron phosphate battery (LFP) and ternary lithium battery (NCM/NCA) are two mainstream lithium-ion battery technologies. The following are their main differences:
Lithium-ion battery overview
Lithium-ion battery is a secondary battery. Its working principle is: during the charge and discharge process, lithium ions are in a state of movement from positive electrode → negative electrode → positive electrode. During the charge and discharge process, lithium ions are intercalated and deintercalated back and forth between the two electrodes. That is, during charging, lithium ions are deintercalated from the positive electrode and intercalated into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state. The opposite is true during discharge.
Lithium-ion batteries are complex systems consisting of positive electrode materials, negative electrode materials, electrolytes, separators, conductive agents, binders and packaging materials. Due to their high operating voltage, high specific energy density, long cycle life and wide operating temperature range, lithium-ion batteries have been widely used in new energy vehicles, energy storage and consumer electronics.
1. Electrolyte
It is an important component of lithium batteries. It conducts lithium ions inside the battery and has an important impact on the performance and life of the battery. Lithium battery electrolyte is usually composed of organic solvents, electrolytes and additives.
Organic solvent is the main component of electrolyte, which is usually a flammable, explosive and toxic liquid, such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc. These organic solvents can dissolve electrolytes to form ion conductors, and can also provide a certain electrochemical stability.
Electrolyte is an ion conductor in the electrolyte, which is usually a lithium salt, such as LiPF6, LiBF4, LiClO4, etc. These lithium salts can dissociate into lithium ions and negative ions in the electrolyte, thereby realizing the conduction of lithium ions.
Additives are some chemical substances added to improve the performance of the electrolyte, such as conductive agents, film formers, corrosion inhibitors, etc. These additives can improve the conductivity, stability and corrosion resistance of the electrolyte, thereby improving the performance and life of the battery.
The performance of lithium battery electrolyte has an important impact on the performance and life of the battery. Therefore, factors such as electrochemical performance, stability, safety and cost need to be considered when designing and preparing the electrolyte. At the same time, the preparation and use of the electrolyte also need to strictly comply with relevant safety regulations and operating procedures to ensure the safety and reliability
The formation process is an indispensable step in the manufacturing of lithium-ion batteries, as it directly affects the battery’s performan...
