Factors affecting fast charging of lithium batteries -Lithium - Ion Battery Equipment
Each lithium battery has an optimal charging current value under different state parameters and environmental parameters. Then, from the perspective of battery structure, what are the factors that affect this optimal charging value?
The microscopic process of charging
Lithium batteries are referred to as "rocking chair" batteries, in which charged ions move between positive and negative electrodes to transfer charges to power external circuits or charge from an external power source. During the specific charging process, the external voltage is applied to the two poles of the battery, and the lithium ions are deintercalated from the positive electrode material and enter the electrolyte. At the same time, excess electrons pass through the positive electrode current collector and move to the negative electrode through the external circuit; lithium ions are in the electrolyte. It moves from the positive electrode to the negative electrode and passes through the separator to the negative electrode; the SEI film on the surface of the negative electrode is embedded in the graphite layered structure of the negative electrode and combines with electrons.（Lithium - Ion Battery Equipment）
The structure of the battery, both electrochemical and physical, that affects charge transfer throughout ionic and electronic operation will have an impact on fast charging performance.
Fast charging, requirements for each part of the battery
For batteries, if you want to improve power performance, you must work hard in all aspects of the battery as a whole, including positive electrodes, negative electrodes, electrolytes, diaphragms, and structural design.
positive electrode
In fact, almost all kinds of cathode materials can be used to make fast-charging batteries. The important properties to ensure include conductivity (reduce internal resistance), diffusion (guarantee reaction kinetics), life (do not explain), safety (do not explain) , Appropriate processing performance (the specific surface area should not be too large to reduce side reactions and serve safety).
Of course, the problems to be solved for each specific material may be different, but our common cathode materials can meet these requirements through a series of optimizations, but different materials are also different:
A. Lithium iron phosphate may focus more on solving the problems of electrical conductivity and low temperature. Carbon coating, moderate nano-ization (note that it is moderate, definitely not the simple logic of finer is better), and the formation of ionic conductors on the surface of particles are the most typical strategies.
B. The electrical conductivity of the ternary material itself is relatively good, but its reactivity is too high, so the ternary material is rarely nano-sized (nano-chemical is not an antidote for the improvement of material performance, especially in the field of batteries. There are sometimes many anti-uses), and more attention is paid to safety and inhibition of side reactions (and electrolytes), after all, one of the key points of the current ternary materials is safety, and the recent frequent battery safety accidents are also related to this. put forward higher requirements.
C. Lithium manganate is more important about life. At present, there are many lithium manganate series fast-charging batteries on the market.
negative electrode
When a lithium battery is charged, lithium migrates to the negative electrode. The high potential brought by the high current of fast charging will cause the negative electrode potential to be more negative. At this time, the pressure of the negative electrode to quickly accept lithium will increase, and the tendency to generate lithium dendrites will increase. Therefore, the negative electrode must not only meet the lithium diffusion requirements during fast charging Therefore, the actual important technical difficulty of fast charging cells is the intercalation of lithium ions in the negative electrode.
At present, the dominant negative electrode material in the market is still graphite (accounting for about 90% of the market share). There is no other fundamental reason - cheap, and the comprehensive processing performance and energy density of graphite are relatively good, and the shortcomings are relatively few. . Of course, the graphite negative electrode also has problems. Its surface is relatively sensitive to the electrolyte, and the intercalation reaction of lithium has a strong directionality. Therefore, it is important to perform graphite surface treatment to improve its structural stability and promote the diffusion of lithium ions on the substrate. direction.
The microscopic process of charging
Lithium batteries are referred to as "rocking chair" batteries, in which charged ions move between positive and negative electrodes to transfer charges to power external circuits or charge from an external power source. During the specific charging process, the external voltage is applied to the two poles of the battery, and the lithium ions are deintercalated from the positive electrode material and enter the electrolyte. At the same time, excess electrons pass through the positive electrode current collector and move to the negative electrode through the external circuit; lithium ions are in the electrolyte. It moves from the positive electrode to the negative electrode and passes through the separator to the negative electrode; the SEI film on the surface of the negative electrode is embedded in the graphite layered structure of the negative electrode and combines with electrons.（Lithium - Ion Battery Equipment）
The structure of the battery, both electrochemical and physical, that affects charge transfer throughout ionic and electronic operation will have an impact on fast charging performance.
Fast charging, requirements for each part of the battery
For batteries, if you want to improve power performance, you must work hard in all aspects of the battery as a whole, including positive electrodes, negative electrodes, electrolytes, diaphragms, and structural design.
positive electrode
In fact, almost all kinds of cathode materials can be used to make fast-charging batteries. The important properties to ensure include conductivity (reduce internal resistance), diffusion (guarantee reaction kinetics), life (do not explain), safety (do not explain) , Appropriate processing performance (the specific surface area should not be too large to reduce side reactions and serve safety).
Of course, the problems to be solved for each specific material may be different, but our common cathode materials can meet these requirements through a series of optimizations, but different materials are also different:
A. Lithium iron phosphate may focus more on solving the problems of electrical conductivity and low temperature. Carbon coating, moderate nano-ization (note that it is moderate, definitely not the simple logic of finer is better), and the formation of ionic conductors on the surface of particles are the most typical strategies.
B. The electrical conductivity of the ternary material itself is relatively good, but its reactivity is too high, so the ternary material is rarely nano-sized (nano-chemical is not an antidote for the improvement of material performance, especially in the field of batteries. There are sometimes many anti-uses), and more attention is paid to safety and inhibition of side reactions (and electrolytes), after all, one of the key points of the current ternary materials is safety, and the recent frequent battery safety accidents are also related to this. put forward higher requirements.
C. Lithium manganate is more important about life. At present, there are many lithium manganate series fast-charging batteries on the market.
negative electrode
When a lithium battery is charged, lithium migrates to the negative electrode. The high potential brought by the high current of fast charging will cause the negative electrode potential to be more negative. At this time, the pressure of the negative electrode to quickly accept lithium will increase, and the tendency to generate lithium dendrites will increase. Therefore, the negative electrode must not only meet the lithium diffusion requirements during fast charging Therefore, the actual important technical difficulty of fast charging cells is the intercalation of lithium ions in the negative electrode.
At present, the dominant negative electrode material in the market is still graphite (accounting for about 90% of the market share). There is no other fundamental reason - cheap, and the comprehensive processing performance and energy density of graphite are relatively good, and the shortcomings are relatively few. . Of course, the graphite negative electrode also has problems. Its surface is relatively sensitive to the electrolyte, and the intercalation reaction of lithium has a strong directionality. Therefore, it is important to perform graphite surface treatment to improve its structural stability and promote the diffusion of lithium ions on the substrate. direction.
