For lithium ion, including cycle life and shelving life, cycle life refers to the cycle times of battery charge and discharge under certain conditions (such as a certain voltage range, charge and discharge rate, and ambient temperature), when the discharge specific discharge capacity reaches a specified value (such as 80% of the initial value). The ving life is to tested its storage performance at high temperatures. In refers to the circuit in the open circuit state, a certain temperature (80℃), humidity conditions after a certain time of battery performance, mainly measure the capacity retention rate and capacity recovery rate, detect its gas rise, etc.
Why is the cycle life reduced?
Lithium-ion batteries work through the migration of ions between positive and negative electrodes. In theory, in this mechanism, lithium-ion batteries can work forever. However, with the extension of time, the battery performance decreases due to the increase of temperature and the aging.
What are the aging factors?
The discharge depth of lithium battery refers to the ratio of the discharge amount of lithium battery to the total stored power (nominal capacity). The smaller the number, the lower the discharge. For example, the discharge depth is 80%, which means the discharge to the remaining 20% of the capacity. The effect of discharge depth on the battery is: the deeper the discharge depth, the more easily the battery life is shortened; the other aspect is the performance on the discharge curve, the deeper the discharge goes, the less stable the voltage and current.
The higher the battery temperature and overcharge, the battery life will decrease. As shown in the figure, it will also burden lithium-ion batteries under heating or high charging voltage. 30℃ is a high temperature for most lithium-ion batteries, and the voltage above 4.10V / battery is high voltage. Exposing fully charged batteries to high temperatures for a longer time puts more pressure on lithium ions than increasing the number of battery cycles.
Most lithium ions are charged to 4.20V, and the battery cycle life doubles when the charging cut-off voltage is reduced by 0.1V. For example, when the lithium-ion battery is charged to 4.2V, it can usually cycle 300-500 cycles; if the charging cut-off voltage is set to 4.10V for 600-1000 cycles; for 1200-2000 cycles; for 2400-4000 cycles for 3.90V.
However, a lower charging voltage tends to reduce the battery capacity. Usually, for every 70 mV reduction in the charging cut-off voltage, the total capacity of the battery will be reduced by 10%, and when the cut-off voltage is increased again, 100% of the capacity will be obtained.
For the cycle life, the optimal charging voltage for lithium-ion batteries is 3.92V. Battery experts believe that this critical value eliminates all voltage-related adverse effects and, when below that value, may have other adverse effects on the battery. Table 4 summarizes the battery capacity status at different charging levels, and all values are valuations.
In addition to these factors, there are also charging rates, and there are some factors that we can hardly control. For example, lithium batteries, just in the initial stage of use, undergo the formation of a solid electrolyte phase interface membrane (SEI film).
So try to use the lithium battery and charge the battery at room temperature; choose a relatively low power level, keep the actual power around it, and avoid always full charge.