Specific energy and energy density increases for the 21700 are lower and range from about 2% to 6%, depending on the internal cell construction.The 21700 has about 50% greater capacity and energy density than the 18650 for discharge rates up to about 3.75C.The stronger heating and lower resistance of 21700 cells than the 18650 results in higher polarization in the 18650 and deviations between the voltage curves for the two formats at higher C rates. Charge and discharge voltages curves coincide up to about 0.5C for both formats.Some of the similarities and differences between the 1860 include: Higher d ascs values result in higher maximum temperatures during full discharge.įigure 3: Additional windings in the formats 20700 to 30700 produce higher capacities and energy densities than the 18650. Cell resistance and heating characteristics are directly related to d ascs. In these cells, d ascs, is the sum of the thicknesses of the cathode and anode (both double side coated), and twice the thickness of the separator (Figure 2). The periodic distance between the windings is the jelly roll is d ascs, and is a key parameter determining the performance of the cells. Cells such as the 1860 are wound jelly roll formats that have the shape of an Archimedean spiral. That has the advantage of faster production compared with various stacked and pouch formats. They are available from a more limited number of manufacturers than the smaller formats and can have capacities as high as 10,000 mAh.Ĭylindrical cells are produced using wound electrodes. 26650 – were originally designed for high-rate applications such as flashlights.The capacity of these batteries ranges from about 4,000 to 5,000 mAh. The 21700 was designed to replace the 18650 in EV battery packs. Like the 18650, the 21700 has a nominal voltage of 3.6/3.7V. 21700 – were designed to be a larger and higher capacity replacement for 18650 batteries.18650 batteries are generally 3.6/3.7 volts and have capacity ratings from 2,300 to 3,600 mAh. While the 18650 measures 18mm in diameter and 65mm long, there can be minor dimensional variations between manufacturers. 18650 – are longer and wider in diameter compared with an AA battery.Typical capacities of 16340 cells range from 700 to 800 mAh. The 16340 has a nominal voltage of 3.6/3.7V, while the CR123A has a nominal voltage of 3.0V. 16340 – is close in size to a primary CR123A battery, but the rechargeable 16340 is normally a little longer.Capacities are typically under 1,000 mAh. 14500 – is smaller but similar in size to a primary AA battery.(Image: lygte-info)Ĭommon sizes of cylindrical Li-ions include: Some protection PCBs are resettable and reset automatically or when the cell is placed in a charger.įigure 1: Protected battery construction showing some basic protection devices. The printed circuit board (PCB) provides over discharge, over charge, and over current protection.Tab/lead meltdown (fusible link) can be included to break the circuit under overvoltage conditions.It is a pressure valve placed beside the PTC to disable the cell if the internal pressure becomes too high. ![]()
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