High electron flow damages the internal chemistry of the cell. Usually, high C-rates can provide high currents to the load, but they also contribute to ageing of the cell. 5.2 Current factorĬ-rates determine how quickly a cell can be charged or discharged. Temperature also determines the capacity of the cell, as at low temperatures the electron mobility drops and at high temperatures it increases. If the operating temperature is 30☌, ageing of the cell accelerates and the lifespan decreases rapidly. Lithium-ion cells can achieve a long lifespan if they are operated within the temperature range of 10–30☌. Therefore, constant monitoring is required. Lithium-ion cells have high energy density, which means that they are volatile and can be dangerous to their surroundings in the case of thermal breakdown. 5 Need for monitoringĪs discussed earlier, temperature, current and voltage are parameters that determine whether the cell can perform efficiently or not. This is due to the CC–CV (constant current–constant voltage) charging algorithm of lithium-ion batteries. It can be noted that after 3.8 V in Table 3, the magnitude of the current drops significantly. This is due to the damage made to the internal structures of the cells because of charging and discharging, although it is bound to happen even if lower C-rates are used, but higher C-rates cause more damage and the overall capacity of a cell reduces rapidly, as is clearly visible in Fig. But if a cell is charged or discharged at higher C-rates, then this reduces the average number of cycles and, if the C-rates are lower, this reduces the average lifespan. The lifespan of a cell is determined using the average cycles for which it can function. The lifespan of a cell is defined as the number of times it can be charged completely and then completely discharged this is also termed as a single cycle. But lithium-ion cells possess high C-rates and this has made them the norm in high-power applications such as smartphones and electric vehicles.Įven though high C-rates reduce the time to charge and a huge amount of energy can also be extracted in a short period, this comes with the demerit of a reduction in the average lifespan of the cell. Since lead–acid batteries can only have lower C-rates, they are preferred in day-to-day applications such as home inverters and car batteries. Ĭ-rates are not limited to lithium-ion cells, but are also used with different chemistries such as nickel–cadmium or lead–acid. Usually, for applications in which huge power in a short span of time is required while charging or discharging, as smartphones or drones, batteries with high C-rates are preferred whereas if the application does not need huge power in a short span of time, lower C-rates are preferred. Meanwhile, negative temperatures correspond to <90% of usable capacity at –1☌, which drops down to 50% at –30☌ and the cell fails to perform due to sluggish electrochemistry, as is visible in Figs 3 and 4. This is due to the fact that the number of collisions taking place inside the cell increases and this significantly harms the internal chemistry, which is evident from Figs 3 and 4 in which high temperature levels have >100% of usable capacity, thereby reducing the average lifespan of the cell. But higher temperatures also bring a drawback to lithium-ion cells, as they also accelerate the rate of degradation of the cell. Īnother explanation for more capacity argues that the ions have more mobility and energy at higher temperatures, and hence more charges get extracted from the cell as compared to at lower temperatures. Where k represents the rate constant, T represents the temperature in Kelvin, A is the constant for each chemical reaction, E a is the activation energy and k B is the Boltzmann constant.
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