Technical innovation of lithium battery fast charging -Lithium - Ion Battery Equipment
Each kind of lithium battery has an optimal charging current value under different state parameters and environmental parameters. From the perspective of battery structure, what are the factors that affect the optimal charging value.
Micro process of charging
Lithium battery is called "rocking chair type" battery. Charged ions move between the positive and negative electrodes to transfer charge, supply power to external circuits or charge from external power sources. During the specific charging process, the external voltage is loaded on the two poles of the battery, lithium ions are disembedded from the positive electrode material and enter the electrolyte, at the same time, excess electrons are generated to move to the negative electrode through the external circuit through the positive collector; Lithium ions move from the positive electrode to the negative electrode in the electrolyte, passing through the diaphragm to the negative electrode; The SEI film on the surface of the negative electrode is embedded into the graphite layer structure of the negative electrode and combines with the electrons.(Lithium - Ion Battery Equipment)
During the operation of ions and electrons, the battery structure that affects charge transfer, whether electrochemical or physical, will affect the fast charging performance.
Fast charging, requirements for all parts of the battery
For the battery, if you want to improve the power performance, you need to work hard in all aspects of the battery, mainly including the positive pole, negative pole, electrolyte, diaphragm and structure design.
positive electrode
In fact, almost all kinds of positive electrode materials can be used to manufacture fast charging batteries. The main properties to be guaranteed include conductivity (reduce internal resistance), diffusion (ensure reaction kinetics), life (no explanation is required), safety (no explanation is required), and proper processing performance (the specific surface area should not be too large, reduce side reactions, and serve safety).
Of course, the problems to be solved for each specific material may be different, but common cathode materials can meet these requirements through a series of optimization, but different materials also have differences:
A. Lithium iron phosphate may focus more on solving the problems of conductivity and low temperature. Carbon coating, moderate nanocrystallization (note that it is moderate, not the simple logic that the finer the better), and the formation of ionic conductor on the particle surface are the most typical strategies.
B. Ternary materials have good electrical conductivity, but their reactivity is too high, so there is little work on nano materials (nano materials are not a panacea for improving material performance, especially in the battery field, there are many reactions sometimes). More attention is paid to safety and inhibition of side reactions (with electrolyte). After all, safety is the lifeblood of ternary materials at present, The recent frequent battery safety accidents also put forward higher requirements in this regard.
C. Lithium manganate is more important for its service life. At present, there are many lithium manganate fast charging batteries on the market.
negative pole
When a lithium ion battery is charged, lithium migrates to the negative electrode. However, the high potential brought by the fast charging large current will lead to the negative electrode potential being more negative. At this time, the pressure on the negative electrode to quickly accept lithium will increase, and the tendency to generate lithium dendrites will increase. Therefore, during the fast charging, the negative electrode should not only meet the dynamic requirements of lithium diffusion, but also solve the security problems caused by the increased tendency to generate lithium dendrites. Therefore, the main technical difficulty of the fast charging core is actually the insertion of lithium ions in the negative electrode.
At present, the dominant anode material in the market is still graphite (accounting for about 90% of the market share). The fundamental reason is that it is cheap. Besides, the comprehensive processing performance and energy density of graphite are excellent, with relatively few shortcomings. Of course, there are problems with the graphite anode. Its surface is sensitive to the electrolyte, and the intercalation reaction of lithium has strong directivity. Therefore, the main direction to be worked on is to conduct graphite surface treatment, improve its structural stability, and promote the diffusion of lithium ions on the base.
Micro process of charging
Lithium battery is called "rocking chair type" battery. Charged ions move between the positive and negative electrodes to transfer charge, supply power to external circuits or charge from external power sources. During the specific charging process, the external voltage is loaded on the two poles of the battery, lithium ions are disembedded from the positive electrode material and enter the electrolyte, at the same time, excess electrons are generated to move to the negative electrode through the external circuit through the positive collector; Lithium ions move from the positive electrode to the negative electrode in the electrolyte, passing through the diaphragm to the negative electrode; The SEI film on the surface of the negative electrode is embedded into the graphite layer structure of the negative electrode and combines with the electrons.(Lithium - Ion Battery Equipment)
During the operation of ions and electrons, the battery structure that affects charge transfer, whether electrochemical or physical, will affect the fast charging performance.
Fast charging, requirements for all parts of the battery
For the battery, if you want to improve the power performance, you need to work hard in all aspects of the battery, mainly including the positive pole, negative pole, electrolyte, diaphragm and structure design.
positive electrode
In fact, almost all kinds of positive electrode materials can be used to manufacture fast charging batteries. The main properties to be guaranteed include conductivity (reduce internal resistance), diffusion (ensure reaction kinetics), life (no explanation is required), safety (no explanation is required), and proper processing performance (the specific surface area should not be too large, reduce side reactions, and serve safety).
Of course, the problems to be solved for each specific material may be different, but common cathode materials can meet these requirements through a series of optimization, but different materials also have differences:
A. Lithium iron phosphate may focus more on solving the problems of conductivity and low temperature. Carbon coating, moderate nanocrystallization (note that it is moderate, not the simple logic that the finer the better), and the formation of ionic conductor on the particle surface are the most typical strategies.
B. Ternary materials have good electrical conductivity, but their reactivity is too high, so there is little work on nano materials (nano materials are not a panacea for improving material performance, especially in the battery field, there are many reactions sometimes). More attention is paid to safety and inhibition of side reactions (with electrolyte). After all, safety is the lifeblood of ternary materials at present, The recent frequent battery safety accidents also put forward higher requirements in this regard.
C. Lithium manganate is more important for its service life. At present, there are many lithium manganate fast charging batteries on the market.
negative pole
When a lithium ion battery is charged, lithium migrates to the negative electrode. However, the high potential brought by the fast charging large current will lead to the negative electrode potential being more negative. At this time, the pressure on the negative electrode to quickly accept lithium will increase, and the tendency to generate lithium dendrites will increase. Therefore, during the fast charging, the negative electrode should not only meet the dynamic requirements of lithium diffusion, but also solve the security problems caused by the increased tendency to generate lithium dendrites. Therefore, the main technical difficulty of the fast charging core is actually the insertion of lithium ions in the negative electrode.
At present, the dominant anode material in the market is still graphite (accounting for about 90% of the market share). The fundamental reason is that it is cheap. Besides, the comprehensive processing performance and energy density of graphite are excellent, with relatively few shortcomings. Of course, there are problems with the graphite anode. Its surface is sensitive to the electrolyte, and the intercalation reaction of lithium has strong directivity. Therefore, the main direction to be worked on is to conduct graphite surface treatment, improve its structural stability, and promote the diffusion of lithium ions on the base.
