where to buy high current 26650 imr or 32650 batteries?

Hey moviles,

I wanted to throw this out there incase you have not thought of it. Have you ever thought of getting some Emoli cells out of a Milwaukee 28v battery pack? You can score 7 raw cells out of that pack. I did this about 2 years ago. I reach for my Emoli when I have a mod with over a 10A draw. If I remember correctly here are the specs.

Lithium Ion Cells.
Encased in a stainless steel can.
mAh (actually mAh) 3.7 volt cells, charge voltage of 4.2 volts.
Continuous discharge rate of 20A and burst of 60A.

Of the 7 cells I have lost 3 of my cells over the years. Two of them I lost from over discharging, so beware not to take them lower than 3.0 volts. I have no idea how the third one died. And for what it is worth I cut apart a DeWALT battery pack to get 10 A123 cells of which not one has died to date. I know that A123 cells are LiFePO4 cells and only 3.3 volt (not what you wanted) but I wanted to say they have proven to be extremely robust.

P.S. You can charge the Emoli on a standard Lithium charger.

Happy Mods!

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There are many sizes of cylindrical lithium-ion (Li-ion) cells, and the number of sizes continues to grow. Some are optimized for use in simple devices such as toys and flashlights; others are mainly found powering portable electronics and electric vehicles. This FAQ begins by reviewing the broad landscape of cylindrical Li-ions, including protected and non-protected cells for various applications. It then digs more deeply into a comparison of today&#;s two most common formats, the and . It closes looking into the future, including larger formats and improvements in cell and pack construction techniques leading to the development of premium-performance energy storage systems.

Battery protection elements

Various cylindrical Li-ion batteries are offered in protected and unprotected packaging. Most electronic equipment, electric vehicles, and other commercial applications favor unprotected batteries due to their higher capacity ratings and lower prices; in these applications, the battery protection is built into the system, not the battery.

Consumer batteries are offered in both protected and unprotected styles. Protected batteries are safer to use in simple devices such as flashlights and toys (Figure 1). Common battery protection elements protect against excessive currents and overheating high internal pressures, and overvoltage conditions and include:

• Positive temperature coefficient (PTC) thermistor to protect against overheating and indirectly over current. PTCs automatically reset when the fault is removed.
• Current interrupt device (CID) is built-in to most &#;s and other large formats. It is a pressure valve placed beside the PTC to disable the cell if the internal pressure becomes too high.
• Tab/lead meltdown (fusible link) can be included to break the circuit under overvoltage conditions.
• The printed circuit board (PCB) provides over discharge, over charge, and over current protection. Some protection PCBs are resettable and reset automatically or when the cell is placed in a charger.

Common sizes of cylindrical Li-ions include:

• &#; is smaller but similar in size to a primary AA battery. Capacities are typically under 1,000 mAh.
• &#; is close in size to a primary CR123A battery, but the rechargeable is normally a little longer. The has a nominal voltage of 3.6/3.7V, while the CR123A has a nominal voltage of 3.0V. Typical capacities of cells range from 700 to 800 mAh.
• &#; are longer and wider in diameter compared with an AA battery. While the measures 18mm in diameter and 65mm long, there can be minor dimensional variations between manufacturers. batteries are generally 3.6/3.7 volts and have capacity ratings from 2,300 to 3,600 mAh.
• &#; were designed to be a larger and higher capacity replacement for batteries. Like the , the has a nominal voltage of 3.6/3.7V. The was designed to replace the in EV battery packs. The capacity of these batteries ranges from about 4,000 to 5,000 mAh.
• &#; were originally designed for high-rate applications such as flashlights. They are available from a more limited number of manufacturers than the smaller formats and can have capacities as high as 10,000 mAh.

Cylindrical cell construction comparison

Cylindrical cells are produced using wound electrodes. That has the advantage of faster production compared with various stacked and pouch formats. Cells such as the and are wound jelly roll formats that have the shape of an Archimedean spiral. The periodic distance between the windings is the jelly roll is dascs, and is a key parameter determining the performance of the cells. In these cells, dascs, is the sum of the thicknesses of the cathode and anode (both double side coated), and twice the thickness of the separator (Figure 2). Cell resistance and heating characteristics are directly related to dascs. Higher dascs values result in higher maximum temperatures during full discharge.

As a result of the greater quantity of active materials, cells have an increased capacity of over 0.9Ah, and cells have an increased capacity of about 1.35Ah compared with cells. Increasing cell size results in a better ratio of energy-storing versus non-energy storage materials. Using even larger formats such as the , , and formats is expected to result in a capacity gain per high-energy cell of 1.8 Ah, 3.1 Ah, and 5.8 Ah, respectively, compared to the (Figure 3).

Some of the similarities and differences between the and include:

1. Charge and discharge voltages curves coincide up to about 0.5C for both formats. The stronger heating and lower resistance of cells than the results in higher polarization in the and deviations between the voltage curves for the two formats at higher C rates.
2. The has about 50% greater capacity and energy density than the for discharge rates up to about 3.75C.
3. Specific energy and energy density increases for the are lower and range from about 2% to 6%, depending on the internal cell construction.
4. Capacity fade as a function of cycles is similar and linear for both formats at a rate of 1C and an ambient temperature of 25 °C.

Pack level considerations

As designers move from cells to larger or even cells, pack costs are expected to shrink due to needing fewer cells to store a given amount of energy. For example, moving up from cells to cells means that one-third fewer cells will be needed to obtain the same total energy storage (Figure 4).

Fewer cells mean that the battery management system (BMS) for a pack consisting of cells will need to monitor one-third fewer cells, reducing complexity and cost. The percentage of space in the voids between the cells will be about the same for a pack of and a pack of cells. As a result, the amount of cooling liquid in the voids will be similar, and the total pack volume per Wh will also be similar. Of course, a pack using cells will be at least 5mm higher compared with the equivalent energy storage using s, so simple retrofitting will not usually be possible.

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Beyond the to the

According to Tesla, the still under development cell promises further increases in performance, including 5X the Whrs and 6X the Watts, to deliver 16% more driving range than cells. The is not just a larger cell; it includes a new &#;tabless&#; electrode design.

As cylindrical cells get larger and larger in diameter, the heat dissipation at the core becomes worse. The new &#;tabless&#; design transfers heat axially through the aluminum and copper current collectors to the bottom of the cell, enabling efficient bottom-side cooling of a battery pack and ensuring more even temperature profiles inside individual cells (Figure 5). Improved thermal management is expected to support faster charging and discharging.

for power tools

Like the proposed cells, the packs of cells designed for power tools use improved packaging to deliver increased performance. For example, a standard 18V battery using cells can produce up to 800 W of power output. The newer packs based on cells can produce up to 1,440 W, an 80% increase. As noted above, the inherently has about 50% greater capacity and energy density than the for discharge rates up to about 3.75C, so where does the added performance come from?

It&#;s the packaging. The packs use welded cell connectors, copper endplates, and power rails to reduce the resistance in the packaging. In addition, improved thermal management transfers about 20% more heat out of the cells. The net result is that runtime gains up to 100% compared with packs and delivers 80% more power.

The combination of cells and the improved packaging technology results in premium performance battery packs that enable new applications beyond portable power tools. Electric power equipment for landscaping and lawn care, battery-powered construction equipment, and high-capacity battery-powered portable inverters are coming onto the market using these premium battery packs. And the higher added value of the premium packs supports the addition to more features such as smart packs that include built-in microprocessors and Bluetooth communications that can be used to enable password control of the packs, enhancing security, users can set notifications, and remotely check battery status.

Summary

There&#;s an expansive and growing selection of cylindrical Li-ion cells that designers can use for specific applications. Each of the many options delivers performance tradeoffs, and some are available in protected and unprotected models giving designers an even wider selection. In the future, larger cell formats are expected to supplant today&#;s and to deliver higher performance. Improvements in cell and battery pack construction are contributing to the development of premium performance energy storage systems.

References

vs. Li-ion cells &#; A direct comparison of electrochemical, thermal, and geometrical properties, Journal of Power Sources
Energy Density of Cylindrical Li-Ion Cells: A Comparison of Commercial to the Cells, Journal of the Electrochemical Society
Safety Limitations Associated with Commercial Lithium-ion Cells, NASA
Tesla Battery Day, Enpower
What is the Difference Between &#;Protected&#; and &#;Unprotected&#; Batteries?, Fenix

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