LiPo Inrush current damage - Page 1
Forum section: electronics / projects

author: yanir
author_rank: Regular Contributor
timestamp: November 21, 2015, 05:45:20 pm
content: Hi, Im looking for information on the effects of transient large inrush currents on lithium ion battery cells. It's fairly common knowledge that exceeding Max C rate on a battery pack or cell is bad due to accelerated plating on the anode. My question is, if there is essentially a short on the battery measured in micro seconds (10-25) does it follow that I've added to this affect? How much can be expected (is there a way to calculate this)?.I've found that when connecting lipo battery packs to a capacitive load results in an arc, ringing at high voltages, and massive inrush current. In the RC world no one really seems to mind. There are arc arrestors which is essentially a series resistor. This may be ok for an hobby RC quadcopter or plane, but I don't like adding loss to any system.I've done a lot of googling, and couldn't find anything specific to the affects of inrush current on lipo battery cycle lifetime. I do plan on doing some experiments on the effects, but I'm wondering if anyone out there know the answer. Thanks.

author: retrolefty
author_rank: Super Contributor
timestamp: November 21, 2015, 05:52:13 pm
content: Quote from: yanir on November 21, 2015, 05:45:20 pmI think most people in the R/C world just deal with the two battery current ratings of max charge rate and max discharge rate. If your circuit doesn't exceed either max specs for the battery in operation then what's to worry about other then maybe max cell temp which wouldn't amount to much for short load induced transients?

author: yanir
author_rank: Regular Contributor
timestamp: November 21, 2015, 06:03:21 pm
content: Quote from: retrolefty on November 21, 2015, 05:52:13 pmthese transients are very high, in simulation about 1.6KA, and it doesn't take much capacitance to do that. After many cycles I'm concerned that cycle life/capacity will be reduced. Say for instance that we add to the of ESR of the battery per inrush event due to anode plating. This would effectively reduce the capacity of a pack over 500 cycles (at 1C discharge). Would it be by 1% or 10%, etc?

author: Siwastaja
author_rank: Super Contributor
timestamp: November 21, 2015, 06:10:32 pm
content: Exceeding maximum rating is mainly problematic only on charging (lithium plating on negative electrode). On the discharge side, it is more about thermal performance; the ions can't go to "the wrong place" like they can do with too much charging current. I wouldn't be too worried. If your cables and connectors are fine (they are not getting welded), then the amount of energy is fairly small anyway. This is the case if you have just standard electrolytic caps, and not many kilograms of them.Never parallel two batteries or ultracaps at different voltages, however, as there is too much energy involved.Charging is order of magnitude worse, so I'd prefer not to do direct connection to a live voltage supply outputting considerably higher voltage than the cell terminal voltage, even if it is a proper CC-CV supply, if it has limited reaction time or a lot of output capacitance.I have never heard of any kind of plating on positive electrode, but please correct me if I'm wrong. I have gaps in my knowledge, too.How do you "simulate" the resistance of the circuit at the time of connection? It will be much more than the wire resistance only; most of the loss happens at the barely touching connector.

author: yanir
author_rank: Regular Contributor
timestamp: November 21, 2015, 06:16:50 pm
content: Quote from: Siwastaja on November 21, 2015, 06:10:32 pmFrom Battery University:http://batteryuniversity.com/learn/article/bu_808b_what_causes_li_ion_to_dieLithium-plating on the surface of the anode caused by high charging rates. (The elevated capacity loss at higher C-rates in Figure 4 might be caused by this.)It's been my understanding that faster C rate discharge increases internal impedance. The exact chemical mechanism I'm not sure of, but I read in some papers that it's due to anode plating. I'll see if I can find them again.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 21, 2015, 06:29:42 pm
content: Quote from: yanir on November 21, 2015, 06:16:50 pmYes yes, this is basics, but anode (negative electrode) plating can only happen duringcharge, not discharge. Inrush current when connecting to an empty capacitor bank should be mostlydischarge, even though there might be some ringing effects from stray inductance, which could of course matter in extreme cases.You may want to elaborate a bit on your actual scenario, it would help.QuoteNever heard of this. Would be interested. Continous fast discharge may increase DCR solely by temperature effects like calendar aging, but I don't think this would be a significant contribution, so if you're right, there is probably something else going on. Extreme peaks could cause localized hotspotting?

author: yanir
author_rank: Regular Contributor
timestamp: November 21, 2015, 08:47:43 pm
content: Quote from: Siwastaja on November 21, 2015, 06:29:42 pmFound a paper that explains the relationship of capacity fade and battery discharge:http://www.che.sc.edu/Faculty/Popov/drbnp/website/Publications_PDFs/Web38.PDFCapacity fade study of lithium-ion batteries cycled at high discharge ratesAbstractCapacity fade of Sony US 18650 Li-ion batteries cycled using different discharge rates was studied at ambient temperature. The capacitylosses were estimated after 300 cycles at 2C and 3C discharge rates and were found to be 13.2 and 16.9% of the initial capacity, respectively.At 1C discharge rate the capacity lost was only 9.5%. The cell cycled at high discharge rate (3C) showed the largest internal resistance increaseof 27.7% relative to the resistance of the fresh cells. The rate capability losses were proportional with the increase of discharge rates. Half-cellstudy and material and charge balances were used to quantify the capacity fade due to the losses of primary active material (Liþ), thesecondary active material (LiCoO2/C)) and rate capability losses. It was found that carbon with 10.6% capacity loss after 300 cyclesdominates the capacityHaven't read the whole paper, but this seems to make the point.The scenario is when connecting a 4S battery to a board with with ~100uF - 800uF (2 separate boards) of capacitance I see ringing that can go past 40V (due to the parasitic inductance in the leads and traces), and in sim the inrush current is quite high, exceeding the max C rate of the pack (by many times). I am concerned about the ringing's effect on the battery itself and also the inrush current on the battery and caps. I will measure the actual inrush current soon, but the results I'm seeing in sim are causing me concern.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 22, 2015, 08:51:08 am
content: Yes, to be pedantic you really should use a precharge circuit for any large capacitor bank. It can be as simple as connecting the pack through a power resistor for a second, then quickly connecting the pack directly. Or you can use relays (or expensive DC contactors, depending on ratings) to do the same, but you need some control logic to prevent the actual load running through the precharge resistor.