LG M50T Grade A high capacity 5000mAh 21700 cell's test

[thunderheart]

Original article: https://www.thunderheartreviews.com/2019/08/lg-m50t-grade-a-test.html

LG INR21700 M50T is a 5000mAh Li-ion cell of 21700 size (also known as 2170).
LG M50T was previously known as M50 (without T) and even in the tentative version of the datasheet the model name was M50. More than a year ago i tested it (Grade B) and compared with Samsung 48G but then i was using v2.5 of my battery holder. This time i've tested a Grade A cell with the latest v3.0 holder.

The battery was bought from my reliable supplier (Queen Battery) and tested with ZKETECH EBC-A20 and a self-made battery holder. It's a PC-connected battery tester supporting 4-wire measuring and discharging at up to 20A.

I've used version 3.0 of my battery holder based on 0.5mm thick pure copper terminals

I've followed all the prescriptions of the IEC61960-2003 standard concerning battery's capacity measurement. Before each discharging cycle each battery was charged at standard charge current mentioned in its datasheet to charge end voltage. Before each discharging or charging i've held a 1-1.5hrs pause. The environment temperature was 25±2°C. To be sure in results i've done each test minimum twice (usually 3-7 times).


LG INR21700 M50T

The marking on the heat shrink tube of the tested cell is LGGBM50T21700 R229H165A2

LG M50T has the following specs according to its datasheet:
Nominal energy: 18.2Wh
Minimum energy: 17.6Wh
Nominal voltage: 3.63V
Standard charge current: 1455mA (0.3C)
Max. charge current:
0<t<25°C: 1455mA (0.3C)
25≤t≤45°C: 3.395A (0.7C)
Charge end voltage: 4.2V
Charge cut-off current: 50mA (100mA used)
Max. continuous discharge current:
-20<t<10°C: 2425mA (0.5C)
10≤t≤25°C: 14.55A (3.0C) (added in new version of datasheet)
25<t≤55°C: 7275mA (1.5C)
Discharge cut-off voltage: 2.5V
AC impedance at 1KHz: ≤25mΩ
Max weight (w/o washer): 70g

Cycle life:
After 300 cycles using 1.6A (0.33C) charge with 243mA (0.05C) cut-off and 1.6A (0.33C) discharge with 2.85V cut-off the energy should be ~80% of the initial value. Cells should rest 10min after charge and 20min after discharge.

Pay attention to the 14.55A continuous discharge rate - it was added in the new version of datasheet. You could also notice that there is no capacity rating in mAh, only energy in Wh, but the C-rating used tells us that by 1C LG means 4850mAh and by dividing 17.6Wh minimum energy by 3.63V nominal voltage we get the same 4850mAh which we can consider as minimum capacity. Respectively, the nominal capacity should be 18.2Wh / 3.63V = 5Ah (5000mAh).


DC IR at 4850mA (1C) in fully charged condition was 25±0.7mΩ (measured using EB Tester Software's Resistance test feature).

Measured dimensions: 21.2mm (diameter) × 70.5mm (length).

Measured weight: 69.25g

LG M50T Grade A capacity test results:

At 0.2C M50T's capacity is 26mAh lower than 5000mAh (which is not declared directly). Whatever, 4974mAh is not a bad result. The curves look good at up to 10A but at 15A the sag goes too deep so i'd consider 10A as the maximum for this cell.


Verdict

So, no surprise this time... Nothing special to say about this guy. LG M50T can be marked as a good 4950mAh / 10A cell and many sellers list it as a 10A cell, not a 15A one.

Here is the video version of this review:


Check out my YouTube channel for batteries, chargers and other stuff reviews.
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[neptronix]

Happy to see you reviewing some higher class goods. :thumb:

My thoughts..
Best case scenario puts us at 261.5 whrs/kg - nothing we haven't seen in the 18650 world. Crazy sag and loss of energy density at 1C; it'd be ideal to run it at much lower than that; i'd pick this cell for an application where you're running 0.5C continuously on average.... for situations where you need a lot of range and not a lot of power.

 

[thunderheart]

Hi neptronix!

I'm more worried with its poor cycle life. Only 300 cycles down to 80% are guaranteed using quite low 0.33C charge/discharge. So even at 0.5C continuous discharge which you recommend it won't last long (theoretically). If the real life experience isn't better - it would be a disappointment.
For comparison, Samsung 50E's datasheet says: "Capacity ≥ 3,802mAh(80%) after 500 cycles at 2.45A/0.5C charge with 245mA/0.05C cut-off and 4.9A/1C discharge with 2.5V cut-off".

 

[neptronix]

Yeah you're right. The 50E seems to be the better cell for this kind of purpose. Maybe the LG is cheaper or somethin'?

 

[thunderheart]

Yeah, it should be $0.4-0.5 cheaper than 50E but is that economy worth the difference in cycle life? For those who build packs for sale - yes. They need numbers. The bigger is the capacity - the higher is the price tag. But for DIY battery makers cycle life plays an important role i think.

 

[john61ct]

Is that cycle life spec observed from your testing, or published claim from LG?

 

[thunderheart]

It's taken from the datasheet

 

[Pajda]

Good point about M50T cycle life. I was satisfied with cycle life of initial "B-grade" M50 production from LG (cells without any marking, with bottom vent) so I expected even more from A-grade. But in the meantime I got this M50T for testing and recently an "A-grade" M50 (with marking without T and without bottom vent). And the cycle life of both of them is disappointment. There is great capacity loss in the begining.

some data:

LG chem M50T: 82% of intial capacity after 500cycles (0.5C charge - 1C discharge, 100% DoD),
Samsung 50E: 90% of intial capacity after 500cycles (0.5C charge - 1C discharge, 100% DoD),

By my opinion Samsung 50E is now the only choice in 21700 HE cells category, the lower cost of M50T cannot compensate for significantly worse cycle life.

 

[thunderheart]

Thanks for sharing, Pajda! It's a very important info!

 

[docware]

Here is another point of view at this cell. I measured LG M50T cell capacity and DCIR across the whole SOC.
Cell´s production date January 2019. Charging 1,45 A to 4,2 V, 0,05 A cut-off, 60 min rest.
Ambient temperature 25 ± 1 °C.
Equipment : GW Instek GDM-8351, Maynuo M9712, ZKETECH EBC-X for charging, Omega HH520, 4-wire testing fixture BF-2A.



Measured capacity is at the bottom of LG specification range, that is for LG cells quite common :



DCIR was measured according INTERNATIONAL STANDARD IEC 61960-3:2017, paragraph 7.7.3
"Measurement of the internal DC resistance". Testing current 10s 0,2C/1s 1C.
Actual measurement was done in 3 consecutive current pulses at each SOC point.


Voltage drop measured at the cell :



Typical DCIR slightly bellow 50 % SOC :



DCIR is mostly cca 26 miliohm, at 100 % SOC is 27,5 miliohm. Massive DCIR increase at SOC low end is typical for all Li-ion cells.



During 5 A discharge the cell surface warming up was measured. Equipment : thermocouple K, wires diameter 0,127 mm (Omega) fixed to cell by Kapton 0,05 mm tape, thermometer Omega HH 520.




Regarding mentioned shift of this cell to worse cycle life, one have to ask : isn´t it impact of LG´s need of massive redirecting it´s resources of high quality materials, technology and suppliers more and more to automotive instead consumer electronics (latest for Tesla GF3 in China) ?

 

[flippy]

that heating is quite concerning for sealed packs. no way that would stay at reasonable temperatures once squeezed in a sealed box with a couple hundred of his brothers and sisters...