The Next Best Ebike Battery for 2013?

April 20, 2013
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There is a recently introduced battery chemistry that we will likely be seeing a lot of soon. Lithium-Nickel-Manganese-Cobalt-Oxide, or LiNiMnCoO2/NMC. Since Asian battery manufacturers have been working on a wide variety of alternative chemistries, a manufacturer standards group has chosen the  abbreviation NMC for this chemistry (although one wholesaler stubbornly calls it NCM).

Nissan, Imara, Microvast, and Zero E-motorcycles are now using NMC after extensive testing. Let’s take a quick run down memory lane to show how battery chemistry has evolved in just a few short decades. The following is not the order of their invention, just what my foggy memory recalls as seeing them used in E-bike battery packs.

SLA-Sealed Lead Acid. Deep-cycle electric wheelchair batteries. Nobody pedals a wheelchair, so their bulk and weight were not an issue, but their low price keeps them as the battery of choice for wheelchairs and mobility scooters for the elderly. For a bicycle, the industry was on a constant lookout for something better.

 

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Sealed Lead Acid (SLA) remains the most affordable entry-level battery option. However, their life-cycle is so short, it is more cost-effective to pay twice as much to get a lithium-based battery that will last 6-times longer.

 

NiCd-Nickel Cadmium. This chemistry was half the size per a given power compared to SLA. But it has a low C-rate (Current producing capability) so anyone who made a pack out of them was restricted to low amps. There were no large packs for sale. E-bikers had to purchase rechargeable flashlight batteries and solder together a pack of a higher voltage, for which an off-the-shelf charger could be found to charge it up. Because of the low price of SLA chargers, 36V and 48V NiCd systems were common. When the price of nickel went up and the price of Lithium came down, NiCd died a quick death. Not even cordless drills use these anymore.

NiMH-Nickel Metal Hydride. This was the battery of choice for military application and the first-gen Prius hybrid car. Very reliable and stable, with a long cycle life. It has a high nickel content, so its expensive now (but the nickel can be re-cycled). With a low C-rate, you need a very big battery to draw high peak amps. Perhaps not a problem on a car with its huge battery pack, but on a bicycle, the smaller pack restricts the user to low amp-draw performance.

LiFePO4-Lithium Iron Phosphate. This was the first lithium chemistry that really took off for use in cordless drills and laptop computers. Mass production brought the prices down, and E-bikers began buying cordless drill packs and gutting them for the cylindrical cells, so they could be re-configured from the stock 18V up to 48V (or more). The common low C-rate was around 1C, so builders began making packs for high voltage to get better performance without stressing the pack by trying to pull high amps. LiFePO4 requires a sophisticated Battery-Management-System (BMS) to stay healthy.

The higher C-rate of 3C for the newer LiFePO4 (from A123) keeps these popular so you don’t need a huge pack to get fairly adequate amps. To get a continuous 24A, you’d only need a 8-Ah battery. Fairly affordable, and small enough to fit in a bike frame.

An 18V cordless drill pack opened up to reveal 5 of the 18650 cells using LiFePO4. The Duracell battery is an AA for comparing the sizes.

A common 18V cordless drill pack opened up to reveal five of the 18650 cells using LiMn. The Duracell battery is an AA-size for comparison.

LiMn/LiMnO2-Lithium Manganese Oxide. Adding manganese to the cathode made this chemistry more stable and less sensitive to individual cell balancing issues. If you were using LiFePO4, and one cell began losing its amp-hour capacity, the rest of the pack would get dragged down to the weakest cells level. Demanding high amps with one weak cell in the pack would cause the entire pack to wear out much earlier than it should have.  With LiMn, the packs just seems to stay in balance, with all the individual cells aging equally.

Its low C-rate of 1C means you need a large pack if you want higher amps. Justin at ebikes.ca was an early adopter of LiMn for his E-bikes because his customers wanted a trouble-free product that wasn’t fussy and lasted a long time. Makita cordless tools use LiMn, as do many laptop computers. Last year Zero E-motorcycles were using LiMnO2, but this year they moved up to NMC (found listed below). [edit: Due to customer desires and safety concerns, LiMn has been improved and now in 2014, there are high current LiMn]

LiPo-Lithium Polymer, also called LiCo-Lithium Cobalt (“polymer” just means the electrolyte is a gel, but if you are shopping for LiCo, the catalog will often call it LiPo)

You may have read recently about the “Bad Girl” of battery chemistries. Its rediculously high C-rate of 20C minimum (you can actually find them with a higher C-rate than this!) means that this is the battery of choice for Electric racers. A proper charging system is expensive, but the batteries themselves were surprisingly cheap when sourced directly from China. What’s the bad part? On rare occasions, they might…CATCH ON FIRE!? 

The high C-rate is not the only reason LiPo is adored by the high performance crowd, the addition of Cobalt to the cathode meant that more power would fit in a smaller package. This was driven by the boom in Radio-Controlled (RC) models in the late 1990’s (RC airplanes, cars, helicopters, etc). When that market suddenly expanded, an Australian enthusiast started a company to supply RC parts from factories in China. Hobby King.com was born. Last year, due to popular demand, HK has opened warehouses in The USA and in Germany (edit: even more countries have HK warehouses now).

Mike Cisler adjusts one of his planes at a Ypsilanti RC meet. Pic by Daniel Brenner

Mike Cisler adjusts one of his planes at a Ypsilanti RC meet. Pic by Daniel Brenner

RC motors and RC batteries used what E-bikers considered to be fairly lower voltages (14V-22V), which RC enthusiasts needed in order to keep the batteries small in the compact RC planes. The number of E-bikes outside of China is low compared to the the number of global RC products. People who would never ride a bicycle under any circumstances might have several expensive RC models. Since RC components were designed to use lower voltages, the users tweaked their systems to draw more amps for better performance. RC buyers didn’t care about the occasional fire (a rare event), they wanted higher-amp batteries.

The RC roots of LiPo are why they are most frequently sold in flat square foil packets with no protective covers. Hard-case cylindrical cells take up too much volume inside  an RC model (airspace between the round cylinders), and RC builders are free to add as much (or as little) protective housing as they want to the flat foil-packs.

This is also why the common and affordable RC smart-chargers are powered by a separate DC power supply. Many RC enthusiasts spend a day at a park, and while flying an RC plane, they have several other battery packs that are charging from their cars 12V system.

6S LiPo pack with the cover removed, showing the flat foil-packs

6S  / 22V LiPo pack with the cover removed, showing the six flat foil-packs

As a side-note, the Boeing 777 Dreamliner battery fire was using LiCo. They wanted a battery that was as light as possible, and as compact as possible. I am not an engineer, but I agree with the statement made by “Tesla” electric car maker Elon Musk, when he said that there was NOT adequate heat insulation between each cell. Better individual cell insulation would prevent a bad cell that was getting hot from heating up the surrounding cells. That is what led to a domino effect. The Tesla cars have a cell cooling system, and the on-board computer can detect and cut-off any cell-group that is getting hot.

So…a year ago, you could have the safe but low C-rate LiMn/LiFePO4…or, the sexy but dangerous LiPo/LiCo 20C+ batteries.

NMC/LiNiMnCoO2/Li-NMC-O2-Lithium Nickel Manganese Cobalt Oxide

Battery manufacturers are continuing to research for developments in dozens of battery chemistries, and a couple of years ago, a big improvement to LiPo/LiCo chemistries began to be produced. A high-Cobalt cathode (LiCo) provides very good power density, but how can we make it more stable and reliable? Here’s a quote from batteryuniversity.com

The secret of NMC lies in combining nickel and manganese. An analogy of this is table salt, in which the main ingredients of sodium and chloride are toxic on their own but mixing them serves as seasoning salt and food preserver. Nickel is known for its high specific energy but low stability; manganese has the benefit of forming a spinel structure to achieve very low internal resistance but offers a low specific energy.

Combining the metals brings out the best in each. NMC is the battery of choice for power tools and powertrains for vehicles. The cathode combination of one-third nickel, one-third manganese and one-third cobalt offers a unique blend that also lowers raw material cost due to reduced cobalt content

Some of the NMC sellers are advertising their chemistry as 5C, but real-world use by E-bike builders has them calling NMC a solid reliable 3C chemistry, which can provide a continuous 30A from an affordable and compact 10-Ah battery (temporary peak amp-draws can be higher, as it is with any of these chemistries). This may sound only as good as the most recent LiFePO4, but NMC is smaller, and is not as fussy about keeping the individual cells balanced.

A recent quote from ES member SamTexas on claimed max C-rates: “…I have in front of me Samsung’s own Nickel (Manganese) 18650 cells….I have tested these cells at 3C continuous and they do deliver full capacity at that rate. Push it to 5C and they become hot and capacity is greatly reduced…

You can actually buy an E-bike NMC pack right now, but it remains to be seen which retailer will prove to be the most reliable. An NMC pack will be about 25% smaller and lighter than an equivalent LiFePO4/LiMnO2 pack. The extensive testing done by Zero, Tesla, and Nissan gives us a great deal of confidence in the safe and effective use of NMC over the next year…

Something that’s worthy of note, is that “AllCell” is using a block of graphite/wax composite Phase-Change-Material (PCM) using a patented formula. If a single cell suddenly starts running hot, the heat is instantly spread out across the PCM block, which would prevent a thermal runaway event. According to a recent press-release:

“…The wax is micro-encapsulated within the graphite matrix. When the wax melts, there’s enough surface tension between the wax and a graphite matrix that it doesn’t leak out. You could heat the material up to 300° C (570F), and it will become soft enough for a thumbprint, but it will remain solid…”

Allcell PCM block, which holds 18650-format cells.

AllCell PCM block, which holds 18650-format cells.

 

NMC battery suppliers we’ve found so far:

cell_man

ampedbikes.com

AllCell.com

Chicago Electric Bikes

Battery Space

Hi-Power Cycles

Its Electric

BMS Battery

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Whats Next?…It’s NCA!

If you are excited about this improvement in battery chemistry, (NCM being 25% smaller/lighter that the fussy LiFePO4, and 300% better C-rate than the reliable and non-fussy LiMnO2) you may also be asking the question…What chemistry is next?

Well, we here at electricbike.com are glad you asked! As of this month (Feb 2013), nobody is selling completed packs with the new NCA chemistry to the public, but the cylindrical cell that will be up to bat next is…

NCA…LiNiCoAl / Lithium Nickel Cobalt Aluminum (sometimes called NCR) The battery chemistry research industry is still driven by the HUGE global sales of laptop computers, cellphones, and cordless tools. Mass production has made the 18650 format the best cost per volume cell. The 18650 number means that it is 18mm in diameter, 65mm long, and the zero means it is a cylinder instead of a flat foil packet. (the 18650 is roughly the size of an adult male thumb) [edit: in 2014, Tesla electric cars are now using Panasonic NCA batteries]

Panasonic and Samsung are the only manufacturers I know of that are producing this chemistry (several other manufacturers buy these and re-label them as their own). Since you would have to buy the bare cells in order to solder together your own pack, I wouldn’t have mentioned these just yet, but…EBAY-seller supowerbattery111 is selling these, and…he will also professionally spot-weld the cells into groups for a small fee, which reduces your pack-building efforts down to about 1/10th of what it would be otherwise. His main business seems to be refurbishing cordless tool battery packs that have worn out.

Spot-welded tabs on 18650 cells. This is a 1S/4P group.

Spot-welded tabs on 18650 cells. This is a 1S/4P group.

However you decide to configure the series and parallel groups, and whether you want a triangle shape (to fit in the bike frame) or a simple rectangle, that is completely up to you.

Be aware the NCA chemistry can be had in a low-amp and high amp version. By having a single 3100-mAh cell inside the cylinder, the internal volume is maximized (good for laptops and cordless drills by providing the absolute longest run-time). But…by putting a couple of cell-divisions inside that same cylinder with a parallel connection, the internal volume is reduced to 2900-mAh, but the amp producing ability is doubled, with the NCA chemistry being advertised as capable of 10A per cell, which is roughly a C-rate of a continuous 3C.

A cell that provides close to a “real world” 2.8-Ah per 18650 cell is pretty impressive, and the 3C current-producing capability is perfect for E-bikes (a 15-Ah pack can provide a continuous 45A, and our favorite power level of 30A can be provided by a very small 10-Ah pack). If you know of anyone who builds a pack out of these, please contact us, as we are very keen to discover whatever strengths or weaknesses they may have. If you are shopping to buy these, make certain you get these specific part numbers, because similar part numbers will only have half the C-rate.

Panasonic, NCR 18650 PD, 2900 mAh

Samsung, INR 18650 29E, 2900 mAh

 

 

 

MACmisc 002

 

If you liked this story, stay up to date by checking out our January 2014 article on “High current batteries that are NOT LiPo

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Written by Ron/Spinningmagnets, Feb 2013

 

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego. Hydraulic mechanic in the 1980's/Los Angeles. Heavy equipment operator in the 1990's/traveled to various locations. Dump truck driver in the 2000's/SW Utah. Currently a water plant operator since 2010/NW Kansas


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