Xiaomi: After 800 charge cycles with HyperCharge, battery capacity remains 80 percent – tablets and phones – News

Lithium-ion batteries that can be quickly charged and discharged have been around for a long time and are not new in themselves.

Take, for example, the former A123 cells that can be used, among other things, for Li-ion starter batteries, where they can be >20C without any problem and can charge and discharge currents of thousands of amperes with a lunchbox-sized battery, with no problem and a lifespan of up to many years. You can also see this in newer cars with on-board 48V and a relatively small (500Wh) lithium-ion battery that should be able to recover braking energy effectively, for example, charging and discharging it at 20°C or more.

This often includes lithium iron phosphate or sometimes NMC technology, so other Li-ion variants than what we usually see in phones, with “large electrodes”. Read: a relatively large surface. This comes at the expense of capacity, there is a certain trade-off. By using the optimized high C cells (including electrodes and surface optimization) and thermal management of the cells you can also design systems for eg 20°C so that the cell temperature does not exceed 20° above ambient and a very long life can be guaranteed. For this reason, in addition to enhanced cells, hybrids and EVs usually also have thermal management (liquid cooling/heating).

The life of the Li-ion cell is a factor in which temperature also plays a very important role, in addition to the quality of the electrolyte. If the internal resistance of the cell is relatively high, you will have a lot of thermal development when charging quickly and this is at the cost of its life span. For this reason, the following generally applies: the higher the charging speed, the shorter the life span.

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So far, phones have been optimized for a large capacity for every size and weight, not for very high C values. With 200W charging technology for such a small battery, I often wonder how much this is at the expense of capacity. Here we are talking about a 4000mAh battery, which I suspect is much larger and heavier than the 4000mAh which can be charged at a maximum of 20W for example.

Assume that the “overload” of the 200W charging capacity is 50% magnitude. Then you can also choose a 6000mAh battery with “only” 20W charging instead of the 4000mAh you can charge with 200W. Personally, I would prefer it to have 50% more capacity than Ultra Fast Charging. I have no idea if this 50% estimate is correct in this case, the number is probably a lot smaller and the optimization lies elsewhere.

Additionally, you want to charge as efficiently as possible, because all the heat generated by the DC/DC charging electronics also heats up the battery. Assuming the cell voltage is 4 volts, at 200 watts there will be 50 amps (!). The heat generated is mainly determined by two factors:
1) Electronics charging
2) Heating the cell to its internal resistance.

For the first: if that’s 98% efficiency, that’s pretty good! But it still means 4W loss dissipation (2% * 200W). If the internal resistance of the cell is very good, it will be a comparable value, suppose that this is also a loss of 4 W at a load of 200 W. Then you burn 8 watts in the phone if you charge it with 200 watts. You should not have contact resistance, for example, a dirty conductor, because you will immediately catch fire.

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And if you are not actively cold, you will quickly get a temperature rise of 30-40 degrees delta T, even with a large phone and many aluminum elements. I think this is going very wrong in a tropical area with an ambient temperature of 40 degrees, you get a 70 to 80 degree phone and then I don’t think you get 50 charge cycles to 80%. Apart from the fact that you can’t grab your phone at that time :-(. So it seems to me that under these conditions the charging speed drops to 20W or 30W.

In other words, I think it’s a good test, and it may also be true under 100% perfect conditions and 5° ambient conditions, but under normal conditions you only have a great deal of overhead from this fast charging ability, and it’s better to have You have more capacity. And keep the charging electronics (and connectors, etc.) in control.

[Reactie gewijzigd door Timewa op 11 juni 2021 22:31]

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