Optimize battery formation process, reduce cost and increase efficiency -Lithium - Ion Battery Equipment
Fast charging at C/2 rate, and then discharging at C/10 rate can not only solve the lithium dendrite problem caused by rapid formation, but also reduce the formation time and cost;
Traditional long-term slow formation will lead to greater impedance rise and lower capacity retention.
So far, most lithium-ion batteries still rely on intercalated graphite materials as the anode, and during the first charge of the battery, electrolyte decomposition occurs on the graphite anode to form a solid electrolyte interphase (SEI). The stable SEI layer can act as a protective layer to prevent the continuous decomposition of the electrolyte and solvent co-intercalation into the graphite layer. An imperfect SEI layer would expose the graphite to the electrolyte, eventually leading to the destruction of the graphite structure. Therefore, battery formation is essential for the emergence of a stable SEI layer and for prolonged battery life and good capacity retention.(Lithium - Ion Battery Equipment)
However, the formation process of the SEI layer usually takes several days or even longer, which will reduce the production efficiency of the battery and increase the time cost. Occupy 6% of the battery production cost. However, formation is an indispensable step in battery production, and the quality of formation has a great impact on battery performance. Therefore, how to achieve a balance between cost and performance is a question worth exploring.
Theoretically speaking, the longer the time required for formation, the higher the cost required, so how to shorten the time for formation is a key point. The cycle rate during the formation period in the current literature is between C/10-C/20. In production This time can be shortened, but still restricts the production speed. High-energy batteries are typically characterized by high electrode area loading (2 mAh/cm^2), and while thick electrodes are important to reduce overall battery cost, they present new challenges for shortening battery formation times. Recently, professors DavidL.WoodIII and RoseE.Ruther of the Oak Ridge National Laboratory in the United States took the LiNi0.8Mn0.1Co0.1O2 (NMC811)/graphite battery system as an example to evaluate the different formation methods of five soft-pack lithium batteries. Formation times varied between 10 and 86 hours. The results show that long-term formation does not necessarily improve the long-term cycle performance of the battery. On the contrary, the best time to form the cycling method is in the middle value, where the impedance rise is minimal, the capacity retention can be improved and the lithium dendrite problem is also prevented.
As the saying goes, you can’t eat hot tofu in a hurry. The shortest formation method (10 hours) will cause serious lithium dendrite problems, and the impedance will increase sharply. The result is the shortest cycle life and the lowest capacity retention. The formation method with a medium duration (26-30 hours) has the best cycle performance, the smallest impedance rise, the highest first-time Coulombic efficiency, and the thinnest SEI film formation. Surprisingly, the timing of further additions to the formation method did not lead to any improvement in battery performance. On the contrary, the traditional slow formation will lead to a greater rise in battery impedance and lower capacity retention.
According to the above results, the author believes that fast C/2 rate charging and then C/10 rate discharge can not only solve the problem of lithium dendrites caused by fast charging, but also shorten the time for formation. This may have both fish and bear's paws. a way of.
Comparing F_30 and F_10, F_30 is equivalent to forming twice in the same way as F_10 (C/2CCCVChargeto4.2VtillCurrent<C/20, C/2Dischargeto3.0V). Why is there such a big difference in performance between the two? The impedance of F_30 is smaller , the SEI is thinner (and the difference is very large. By means of XpS elemental analysis, the author measured the SEI thickness of F_30 and F_10 to be about 54nm and 87nm respectively)? Could it be that the SEI becomes thinner if the larger current is turned into one more time?
We did not find a direct explanation in the text. The author mentioned in the article that when a large current is formed, the lithium deposition process will occur, but the lithium is still active at this time, so it will still participate in the electrochemical reaction during the next small current cycle. Then, our guess is: during the second cycle of the F_30 battery at a C/2 current density, the first deposited lithium re-joined the reaction, making the SEI film thinner.
Traditional long-term slow formation will lead to greater impedance rise and lower capacity retention.
So far, most lithium-ion batteries still rely on intercalated graphite materials as the anode, and during the first charge of the battery, electrolyte decomposition occurs on the graphite anode to form a solid electrolyte interphase (SEI). The stable SEI layer can act as a protective layer to prevent the continuous decomposition of the electrolyte and solvent co-intercalation into the graphite layer. An imperfect SEI layer would expose the graphite to the electrolyte, eventually leading to the destruction of the graphite structure. Therefore, battery formation is essential for the emergence of a stable SEI layer and for prolonged battery life and good capacity retention.(Lithium - Ion Battery Equipment)
However, the formation process of the SEI layer usually takes several days or even longer, which will reduce the production efficiency of the battery and increase the time cost. Occupy 6% of the battery production cost. However, formation is an indispensable step in battery production, and the quality of formation has a great impact on battery performance. Therefore, how to achieve a balance between cost and performance is a question worth exploring.
Theoretically speaking, the longer the time required for formation, the higher the cost required, so how to shorten the time for formation is a key point. The cycle rate during the formation period in the current literature is between C/10-C/20. In production This time can be shortened, but still restricts the production speed. High-energy batteries are typically characterized by high electrode area loading (2 mAh/cm^2), and while thick electrodes are important to reduce overall battery cost, they present new challenges for shortening battery formation times. Recently, professors DavidL.WoodIII and RoseE.Ruther of the Oak Ridge National Laboratory in the United States took the LiNi0.8Mn0.1Co0.1O2 (NMC811)/graphite battery system as an example to evaluate the different formation methods of five soft-pack lithium batteries. Formation times varied between 10 and 86 hours. The results show that long-term formation does not necessarily improve the long-term cycle performance of the battery. On the contrary, the best time to form the cycling method is in the middle value, where the impedance rise is minimal, the capacity retention can be improved and the lithium dendrite problem is also prevented.
As the saying goes, you can’t eat hot tofu in a hurry. The shortest formation method (10 hours) will cause serious lithium dendrite problems, and the impedance will increase sharply. The result is the shortest cycle life and the lowest capacity retention. The formation method with a medium duration (26-30 hours) has the best cycle performance, the smallest impedance rise, the highest first-time Coulombic efficiency, and the thinnest SEI film formation. Surprisingly, the timing of further additions to the formation method did not lead to any improvement in battery performance. On the contrary, the traditional slow formation will lead to a greater rise in battery impedance and lower capacity retention.
According to the above results, the author believes that fast C/2 rate charging and then C/10 rate discharge can not only solve the problem of lithium dendrites caused by fast charging, but also shorten the time for formation. This may have both fish and bear's paws. a way of.
Comparing F_30 and F_10, F_30 is equivalent to forming twice in the same way as F_10 (C/2CCCVChargeto4.2VtillCurrent<C/20, C/2Dischargeto3.0V). Why is there such a big difference in performance between the two? The impedance of F_30 is smaller , the SEI is thinner (and the difference is very large. By means of XpS elemental analysis, the author measured the SEI thickness of F_30 and F_10 to be about 54nm and 87nm respectively)? Could it be that the SEI becomes thinner if the larger current is turned into one more time?
We did not find a direct explanation in the text. The author mentioned in the article that when a large current is formed, the lithium deposition process will occur, but the lithium is still active at this time, so it will still participate in the electrochemical reaction during the next small current cycle. Then, our guess is: during the second cycle of the F_30 battery at a C/2 current density, the first deposited lithium re-joined the reaction, making the SEI film thinner.
