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Battery pack construction must take into account a variety of parameters including: the voltage and runtime requirements, the loading conditions, and the size and weight limitations. In order to better meet the pack requirements, the design of the battery pack must utilize the space provided effectively. Thus, the selection of the type of cell to be used within the pack will decide its overall packing capability. With higher packing capability, a greater number of cells will fit into the battery pack, extending vehicle range, especially if the cell has high energy densities. A Ragone plot is a plot used for comparing the energy density of various energy-storing devices. On such a chart the values of specific energy (in W·h/kg) are plotted versus specific power (in W/kg). Both axes are logarithmic, which allows comparing performance of very different devices. Ragone plots can reveal information about gravimetric energy density, but do not convey details about volumetric energy density. A Ragone chart depicting the range of specific energy and power levels achievable by current generation battery cell technology. Note that the specific energy and power of the final assembled battery pack will be lower than that of the constitutive cells Thermal runaway occurs when  a Li-ion cell gets so hot that it starts to generate its own heat. This happens because the separator – the polymer film that separates the anode and cathode – melts around 80 degrees C. This can cause an internal short, allowing current to run unabated within the battery. This uncontrolled current leads to further heating. As the cell gets hotter the electrolyte starts to evaporate at 100 C, leading to a high pressure inside the cell, further increasing the temperature. At a critical temperature, the cathode begins to shed oxygen, making the cell combustible due to rapid reaction between the oxygen and electrolyte. For an LCO cathode, oxygen breaks away from the cobalt at 150 C. For an LFP cathode, the oxygen-phosphorus bond is not broken until 350 C. This is the primary argument for the safety of LFP cells. It is actually hard to get to 350 C inside the cell because the rate of heat transfer out of the cell increases with cell temperature. Of course, Li-ion cells have a number of safeguards in place to prevent any increase in temperature, and the onset of thermal runaway.  The first line of defense is the Battery Management  System, which prevents overcharging, overdischarging, and external shorting. All of these things could cause an internal short or a rise in cell temperature.  Cells are also equipped with a “polyswitch” that prevents excessively high currents out of the cell. Lithium-ion has significantly higher cycle life than lead acid in deep discharge applications. The disparity is further increased as ambient temperatures increase. The cycle life of each chemistry can be increased by limiting the depth of discharge (DoD), discharge rate, and temperature, but lead acid is generally much more sensitive to each of these factors . The reason we plot Discharge Capacity (instead of Discharge Time) is that Lithium has a higher and more stable terminal voltage than AGM, so plotting the curves with Discharge Capacity in mind gives a more accurate comparison of the chemistries, showing that Lithium increases useable energy at higher loads due to higher and more stable terminal voltages.