Cycling Aging of Lithium-ion Batteries-Introduction and Temperature

In this day and age, the uses of lithium-ion batteries are rapidly increasing in different areas, and this has necessitated the understanding of their aging behavior. Battery aging is associated either with calendar aging or cycle aging. Calendar aging refers to the aging of the battery while it is stored on the shelf and not in any use, whereas Cycle aging refers to aging in the process of charge/discharge of the battery, i.e., its usage. The former depends particularly on temperature and the state of charge (SOC), and the latter has the additional factors of the current rate and charge or discharge cut-off voltages.

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 Cycle aging has not been exhausted much in comparison to calendar aging, but a point of amalgamation is that a higher current rate accelerates the aging of a battery. Considering the cause of Lithium-ion batteries aging from a chemical point of view, changes in the interface of electrode/ electrolyte in the negative electrode is the chief cause. A solid electrolyte interface is responsible for both capacity fade and resistance increase.  This paper is going to eye cycling aging of lithium-ion batteries in relation to the current and temperature factor and crown it by giving the required operational temperature.

Effect of Current on Cycle Aging of Lithium-ion Batteries

There are few studies that have been conducted in regards to the effect of current on lithium-ion batteries. The result of tests that have been conducted indicates that, even if the room temperature is controlled, for high current rates, the battery's temperature proportionally increases, which makes it hard to determine whether the aging is as a result of temperature or current. However, in a few studies, battery aging has been considered a function of charge and discharge rate. Below are the effects of current on the cycle aging of batteries;

1.Lower currents result in low cell temperatures, and a slow charging battery is in good condition near the end of its charge, thus moderate aging.

2.High currents have a great effect on aging. In comparison to the discharging currents, high current age the battery at a faster rate. Temperature and current rate are almost inseparable since the battery temperature is dependent on the current rate. Aging due to high voltage can explain the variance in aging during the charging and discharge by taking into account the internal voltage of the battery higher than the applied one during discharge and low during charge.

3.Long-lasting charging periods, even with only low current rates, promote lithium plating. Lithium plating is a reaction that forms metallic lithium on the negative instead of intercalating into it. This accumulation may lead to dendrite growth, which may result in an internal short circuit.

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How does temperature affect lithium-ion batteries?

Temperature and heat generation is a key aspect when considering the performance, safety, and aging of lithium-ion batteries. The temperatures under which lithium batteries operate must be controlled, knowing that their safety and health depend on temperature failure to which catastrophic situations such as fires may result. The temperature will also affect how LiB will perform over time, either prolong or reduce its life span. Either way, a high temperature or a low temperature is not good for the batteries health, and this is shown as follows;

1.An increase in temperature affects the chemical reaction inside the battery. An increase in temperature produces a corresponding catalytic action in the chemical reactions.  Lithium-ion batteries have a high performance and increased storage at higher temperatures. The side effect of this increased performance is the degradation of the lifecycle of the battery over time. The lifecycle can be greatly diminished due to prolonged exposure to high temperatures. High temperatures lead to an additional and accelerated SEI formation, and hence, capacity loss.

2.Exposure of Lithium batteries to cold also has a big impact on battery performance and safety. The internal resistance of the battery increases with the drop in temperature and will require more effort for the battery to charge, thus lowering the capacity. 

Understanding and controlling temperature and aging in operating batteries is thus a multi-scale problem that spans the micro/nanoscale within single material layers to huge, interconnected LIB packs. To summarize, cycle aging reduces with temperature when comparing usage-dependent and usage-independent battery aging.

Operating Temperature Range of LiB Battery

When charging lithium-ion Batteries, the temperatures should be placed at approximately 18-21°C. Charging a cold battery should be shunned since the cells will be damaged, especially during the cold winter seasons. Allow the battery first to warm up to room temperatures in order to charge at room temperature and under optimum conditions. Never place your battery exposed on a hot sunny day since at 60°C, the LiB losses capacity and abilities, thus damaging the battery.

On the other hand, lithium batteries should be used at temperatures that range from 10 to 55 °C. The battery's internal temperature that is conducive to charging ranges from 5 to 45 °C. A sensor is placed on the battery to ensure the charging does not exceed the required range.

Batteries that are not in use should be stored in cool and not in the cold. In the unused status, batteries also lose their energy. The loss varies by approximately 3% to 5% each month in Lithium-ion Batteries.

Conclusion

In conclusion, many factors influence the aging process, including SoC levels, charging/discharging cut-off voltages, temperature, and current flow. Due to losses inside the battery, the current rate has a direct impact on the battery temperature. High charging/discharging currents, in particular, result in a significant increase in battery temperature.

However, for the effective use of LIBs in these market sectors, high energy, high power, and quick charging rates are necessary; this is generally coupled with huge quantities of heat being created and non-uniform current distribution. As response rates and diffusivity are temperature sensitive, this leads to safety issues, reduced performance, and long-term durability issues. Thermal management systems are used to regulate the temperature of the battery within an ideal range, with the goal of achieving uniform temperature distribution. Aside from reversible heat, generated heat is an indicator of lost work during the charging and discharging process.