17:30 A Li ion battery degrades slower if it is charged and discharged over narrower range . For example, two cycles between 20% and 70% is better than one cycle between 0% and 100%, although the cumulative Ah is the same. This is because during cycling, the volume of the anode material changes with stage of charge as much as 13%. The repeated volume change tears up the SEI (solid-electrolyte-interface) and fragmentation of the particles. Both are causes of battery degradation
@Ansforce Жыл бұрын
So do you mean two cycles between 20% and 50% is better than one cycle between 20%and 80%, right?
@onchang6020 Жыл бұрын
Right. Although that was not what I said word-for-word, I agree that two cycles between 20% and 50% is better than one cycle between 20%and 80%. In both cases, the cumulative Ah passed are the same, since 2*(50-20) = 80 - 20. In my last comment, I said Two cycles between 20% and 70% is better than one cycle between 0% and 100%. Again, in both cases, the cumulative Ah passed are the same, since 2*(70-20)=100 - 0. You and I were stating the same principle, we just used different numerical examples. The degradation of Li ion batteries is somewhat complex. The degradation mechanisms for positive, negative electrode are different, and their dependence on temperature, voltage, current and time are also different. It highly depends on some design and manufacturing issues, particularly the cathode/anode ration, and the electrolyte additives.
@Ansforce Жыл бұрын
@@onchang6020 Thanks for your information. Do we work in the barrery company or university? Is it in Taiwan?
@onchang6020 Жыл бұрын
Yes. In the last 37 years, I have spent 35 years in battery related industry and 2 years in the semiconductor industry, all in the US. I currently work for a company that develops software for battery management system.
Unlike graphite, lithium titanate does not have the problem of lithium plating because of the following reason. When neatly fully lithiated, the potential of graphite is about +60mV. That of Lithium titanate is about +1200mV vs. lithium metal. For a lithium ion arriving at the negative electrode surface, it is energetically more favorable to intercalate into graphite or lithium titanate than to plate out as lithium metal. However, the preference is a lot stronger in lithium titanate (1200 mV) then in graphite (60 mV). This is the first reason why lithium dendrite does not form on lithium titanate electrode. The second reason is that, because of the higher potential of lithium titanate, the electrolyte is not reduced at the surface of negative electrode to form SEI (solid-electrolyte interface), which causes the loss of electrolyte solvent and lithium ion. Therefore, lithium titanate can be used as Namo powder with high surface area. The large surface area reduces the current density, also reduces the chance of lithium plating.
8:46 The lithium salt in the electrolyte of almost all NMC lithium ion batteries is LiPF6. The others are no longer used today. LiBF4 and LiCF3SO3 solubility are too low. LiClO4 is a strong oxidizing agent and is quite dangerous. LiAsF6 contains arsenic. The oxide of arsenic As2O3 砒霜 is toxic. The main mechanism of lithium ion mass transport through the electrolyte, liquid or solid, is NOT diffusion, it is migration. Diffusion is driven by concentration gradient. Migration is driven by potential gradient (or electric field). In Diffusion, anion and cation move in the same direction. In migration, the anion and cation move in opposite directions initially, then the anion stops moving, the cation continue to move. This is because during charge, the cation Li+ is generated from the positive electrode, and inserts into the negative electrode, whereas the anion does not participate in the electrochemical reaction at all.
@Ansforce Жыл бұрын
Thanks for your command. I should use migration not diffusion. It is different. How do I translate migration into Chinese?
@onchang6020 Жыл бұрын
I actually do not know for sure. In the context of ionic movement in electrolytes, migration means the same as "electrophoresis" 電泳. Google translates "electrophoretic migration" into 電泳遷移. I think it is OK.
@Ansforce Жыл бұрын
But electrophoresis should be in liquid right? Probably 遷移 is better for migration in solid electrolyte.