Cost-Benefit Comparison: Electric Bike Battery Chemistry NCA (Tesla) vs. NMC (BMW)

[Mike leroy]

Which eBike battery chemistry is better for Century rides in the Cascade Mountains, NCA or NMC? More importantly, how to improvise a "battery fuel gauge" to measure the runtime performance of the two battery chemistries. The formal term is state-of-charge.

A Smart Battery System is one approach. I am willing to accept the Cycle Analyst v3 as a make-shift "battery fuel gauge". The intelligence comes from the rider, but may be the best general solution for eBikes today. Maxim Integrated touts a combined voltage and charge approach that is claimed superior to either method alone; it is implemented in their ModelGauge m3 series of chips, such as MAX17050,[4][5] which is used in the Nexus 6 and Nexus 9Android devices, for example.[6]

A first order approximation of 17 Amp-hour battery might be able to complete the 100 mile Mount Shasta ride. A Google Sheet with Amp-hour consumption cases for Shasta.

If one battery is inadequate, then a 90 minute recharge at the lunch break location, i.e., 69 mile mark.

(Link Removed - No Longer Exists)​

The basic chemical differences are manganese (NMC) vs. aluminum (NCA). Tesla uses NCA. Nissan Leaf, Chevy Volt and BMW i3 use NMC.

An article from Battery University provides background information about an eBike "battery fuel gauge":

"Most batteries for medical, military and computing devices are “smart.” This means that some level of communication occurs between the battery, the equipment and the user. The definitions of “smart” vary among manufacturers and regulatory authorities and the most basic smart battery may contain nothing more than a chip that sets the charger to the correct charge algorithm.

In the eyes of the Smart Battery System (SBS) forum, these batteries cannot be called smart. The SBS forum states that a smart battery must provide state-of-charge (SoC) indications. Benchmarq was the first company to offer fuel-gauge technology in 1990 and today, many manufacturers offer integrated circuit (IC) chips in single-wire and two-wire systems, also known as System Management Bus (Intel/Duracell SMBus)."

Ion batteries require a battery management system to prevent operation outside each cell's safe operating area (max-charge, min-charge, safe temperature range) and to balance cells to eliminate state of charge mismatches. This significantly improves battery efficiency and increases capacity. As the number of cells and load currents increase, the potential for mismatch increases. The two kinds of mismatch are state-of-charge (SOC) and capacity/energy ("C/E"). Though SOC is more common, each problem limits pack charge capacity (mA·h) to that of the weakest cell.

Charts will be uploaded today as time permits.

 

[Mike leroy]

Li-ion Battery Chemistries From Battery Univ:

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"Most Li-manganese batteries “partner” with Lithium Nickel Manganese Cobalt Oxide (NMC) to improve the specific energy and prolong the life span. This combination brings out some of the best in each system and the so-called LMO (NMC) is chosen for most electric vehicles, such as the Nissan Leaf, Chevy Volt and BMW i3. The LMO part of the battery, which is about 30% on the Chevy Volt, provides high current boost on acceleration, the NMC part gives the long driving range.

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2 or NMC)
Leading battery manufacturers focus on a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can be tailored for high specific energy or high specific power, but not both. For example, NMC in an 18650 cell for moderate load condition has a capacity of about 2,800mAh and can deliver 4–5A; NMC in the same cell optimized for specific power has a capacity of only about 2,000mWh but delivers a continuous discharge current of 20A. A silicon-based anode will go to 4,000mAh but at reduced loading and shorter cycle life.

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 poor stability; manganese has the benefit of forming a spinel structure to achieve low internal resistance but offers a low specific energy. Combining the metals enhances each other strengths.

NMC is the battery of choice for power tools, e-bikes and other electric powertrains. The cathode combination of typically 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. Other combinations, such as NCM, CMN, CNM, MNC and MCN are also being offered in which the metal content of the cathode deviates from the 1/3-1/3-1/3 formula. Manufacturers keep the exact ratio a well-guarded secret. Figure 7 demonstrates the characteristics of the NMC.

The relationship between energy and power of a battery can best be represented in a Ragone plot. This plot places energy in Wh on the horizontal x-axis and power in W on the vertical y-axis. The diagonal lines across the field disclose the time the battery cells can deliver energy at various loading conditions. The derived power curve provides a clear demarcation line of what level of power a battery can deliver. The Ragone plot is logarithmic to display performance profiles of very high and low values.

The Sanyo UR18650F [4] has the highest specific energy and can power a laptop or e-bike for many hours at a moderate load. The Sanyo UR18650W [3], in comparison, has a lower specific energy but can supply a current of 20A. The A123 [1] has the lowest specific energy but offers the highest power capability by delivering 30A of continuous current.

For best results, battery manufacturers take the Ragone snapshot on new cells, a condition that is only valid for a short time. When calculating power and energy thresholds, design engineers must include battery fade that will develop as part of cycling and aging. A battery operated systems should still provide full function with a battery that has faded to 70 or 80 percent. A further consideration is temperature as a battery loses power when cold. The Ragone plot does not include these discrepancies.

It should be noted that loading a battery to its full power capability increases stress and shortens life. When a high current draw is needed continuously, the battery pack should be made larger. Tesla does this with their Model S cars by doubling and tripling the battery. An analogy is a heavy truck fitted with a large diesel engine that provides long and durable service as opposed to installing a souped-up engine of sports car with similar horsepower."

 

[Mike leroy]

Battery properties, compared on a scale from 1 to 5, are listed in a Google Spreadsheet:

1. specific energy or capacity
2. specific power or the ability to deliver high current
3. safety or the chances of venting with flame if abused
4. performance at hot and cold temperatures
5. life span reflecting cycle life and longevity

I need to pick the most relevant battery. Some batteries are 2800mA, while others closer to 4000mA. Sanyo UR18650 3000mA.

Unknown origin.

The first step is to make the association with battery properties (I.e., features) with six general benefits any non-technical consumer can relate to.

Specific Power - the amount of current the battery can provide
Specific Energy - Specific energy is synonymous with battery capacity and runtime. Defines the battery capacity in weight (Wh/kg); energy density or volumetric energy density is given in size (Wh/l).

 

[Mike leroy]

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