24Apr 2015

Ok, ok, I should not be joking about the name. Safety is a serious matter. But let’s talk honestly today about dishonesty.

 

Ultrafire is a China-based vendor of 18650 lithium-ion cells.  One can buy their 18650 cells from eBay, Amazon and lots of other web-based stores. I was intrigued last week when I saw on eBay Ultrafire 18650 cells advertised with a charge capacity of 5,000 mAh. Wow, 5Ah! Is this real? The most I had seen ever were 3,400 mAh from Panasonic (what’s inside the Tesla) and 4,000 mAh was the next promised land. But 5,000 mAh? I really wanted one.

 

You gotta love e-commerce. Within less than 48 hours, I was the proud owner of 4 Ultrafire 18650 cells each labeled 5,000 mAh — exactly as shown in the photograph above. Now to put things in perspective, an 18650 cell has a volume of about 17 cc. These cells are rated at a maximum voltage of 4.2 V and an average voltage of 3.7 V. A quick calculation reveals that they would have an energy density in excess of 1,000 Wh/l. Now, that’s either serious lying or some serious innovation. Let’s find out.

My team was generous enough with their time to run a capacity test on these Ultrafire cells, and compare them relative to the Panasonic 3.4 Ah cells. For you tech geeks wanting the specifics, the Panasonic cells were charged and discharged at 1.7 A (0.5 C rate) whereas the Ultrafire cells had a  much smaller charge/discharge current of 500 mA.  The cells were all charged from a minimum of 3.0 V up to a maximum of 4.2 V with a termination current of C/20, then discharged back to 3.0 V. Temperature was maintained at 25 ºC. What did we measure?

The graph shows the standard discharge curves for both Ultrafire and Panasonic cells. Panasonic provides a capacity of 3,000 mAh vs. the advertised 3,400 mAh. In actuality, one would probably get very very close to 3,400 mAh had we gone down to 2.7 V and charged at a much slower rate of 0.2 C (instead of 0.5 C). The Panasonic cell is made with an NCA cathode which provides additional energy down to 2.7 V. So Panasonic seems quite honest with their capacity claim.

But Ultrafire is not even close…shame on you, Ultrafire! The advertised 5,000 mAh has a charge capacity of barely above 1,000 mAh. I have known that crooks are everywhere attempting everything under the sun, but for some naive reason, I had thought that lithium-ion batteries might be, just might be immune to this degree of cheating. But making a claim that is 5X reality, well, I’d better reset my expectations.

The lesson du jour: if you see Ultrafire cells, run, and run fast!