On the Health of Lithium-Ion Batteries | tb.lx Knowledge Pills
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Electric vehicles seem to be one of the answers to reaching the carbon neutrality goals proposed by the European Union by 2050. But going electrical brings challenges, and many variables need to be considered. Our first knowledge pill tackles one of the topics the tech world is facing: the issues related to the aging process of Lithium-ion batteries used not only in electric vehicles but also in everyday appliances.
Why do batteries age?
Lithium-ion batteries come in many shapes and forms, but they all share the same aging issue. We refer to the gradual but inevitable total power storage capacity degradation as aging. This capacity degradation has two leading causes: the passage of time and the charge/discharge cycles. Lithium is a highly reactive chemical element with a single electron in its outermost layer, readily ionizing. Battery technology uses this electrochemical potential to store and release electric power to feed our appliances and vehicles. The storage process relies on reversible reactions occurring within the battery, with Lithium ions traveling between the anode (the negative terminal) and cathode (the positive terminal), reacting with other battery components reversibly. Unfortunately, due to Lithium’s very high chemical activity, some of the Lithium will also irreversibly react with other unwanted battery components, thereby becoming unavailable for power storage. These uncontrollable reactions will slowly deplete the amount of free Lithium in the battery, thereby decreasing the total amount of power the battery can store. This degradation process is irreversible and unstoppable. As users, our only option is to try and reduce the speed at which this process occurs.
Measuring battery aging
Imagine that your combustion engine car has a fuel tank that shrinks over time and that you can only fill up a limited number of times. In essence, this is how Lithium-ion batteries behave, as their full-charge capacity diminishes over time and have a limited number of total charges. To measure the battery health, we must know what these quantities are: the total charge capacity and the number of full recharges. We calculate the first quantity as the percentual decrease of the total charge capacity compared to the design full charge capacity. Generally, batteries become unusable below 80% degradation (70% under some circumstances). Below this value, some batteries present a heightened risk of generating thermal events (catching fire). Fortunately, batteries fitted in modern devices provide a means to estimate this value. Your smartphone likely provides this facility, and you can easily find applications to install on your laptop that serve the same purpose. Usually, these applications also estimate our second measurement, the equivalent number of complete cycles. This estimate reflects that, more often than not, users only partially discharge and recharge their batteries, so there is a need to calculate the equivalent degradation impact of a partial charge. And partial charges are a good thing!
Prolonging battery life
Although battery aging is unavoidable and irreversible, we can still do something about it. There are a few rules to promote better battery life and delay senescence.
- When not in use, ensure the battery has around 50% power. This ensures that the Lithium ions are evenly distributed between the anode and cathode, lowering the potential for Lithium shenanigans.
- Avoid using and recharging the battery under high temperatures. Basic knowledge of chemistry tells you that one speeds up reactions through heat, so we might favor those irreversible Lithium reactions that deplete the battery’s total capacity.
- One should favor short discharge and recharge cycles (say 20% to 80%) because the most detrimental aging effects occur when the battery is either discharged or fully charged. The middle ground is easier on the aging process.
- Choose slower charges over fast charges.
Summary
Lithium-ion batteries will inexorably age by slowly losing their ability to hold an electric charge. This phenomenon derives from the high chemical reactivity of Lithium when it irreversibly combines with other battery components. Although inevitable and unstoppable, this aging process can be slowed down by adopting well-known best practices.
This article was written by João Paulo Figueira, Data Scientist at tb.lx, based in Lisbon, Portugal. 🚛🌿.
