Charging a lithium-ion battery may seem straightforward, but it involves a complex interplay of electrical, thermal and chemical dynamics that must be carefully managed. Well controlled charging helps to ensure performance, safety and longevity.
This article will give an insight how achieving lithium-ion batteries charging in a way that is time efficient, safe and leads to limited battery degradation.
Why Voltage, Temperature and Current do matter
When charging a lithium-ion battery, the basic is to keep the Voltage within safe limits. Overvoltage can lead to degradation or even safety hazard, while charging with a too low voltage may result in an incompletely charged battery.
Temperature is another critical factor. Batteries must be charged within a wide thermal window. Exceeding the temperature boundaries may cause accelerated wear and in extreme cases a thermal runaway. These temperature boundaries require an electronic control system (BMS) that can dynamically adjust the charging parameters real-time.
The lithium ion battery lifespan is significantly influenced by the charging process itself. High charging currents, desirable for fast charging, can accelerate aging by inducing a higher risk of battery degrading, leading to increasing internal resistance. In turn, the increased resistance leads to elevated temperatures during charging. These higher temperatures on their own can also contribute to an increase in chemical degradation, reducing the battery life as well. So fast charging is bad for the battery cycle life. Cleantron is balancing fast charging with minimal wear which can only be achieved with a deep understanding of the mechanisms behind degradation, enabling positive trade-offs from these mechanisms.
Fast Charging: What Happens Inside the Battery and how to prevent battery degradation
To understand these mechanisms better, it is helpful to examine what happens inside a battery when being charged at a high rate. When charging an EV, it is noticeable how the initial charging phase is typically relatively rapid. The reason for this is that when the Cell is still far from achieving its maximum voltage, the high current charge has minimal penalty as the potential of the electrode is not yet too high.
However, as the battery gets closer to being full the battery charging rated typically goes down. This slowdown is necessary to prevent the electrode potential from reaching a critical level. A critical high potential promotes side reactions that degrade the Cell.
These degradation effects are further worsened by ion collisions. This process is comparable to a parking lot: when it’s empty, finding a spot is relatively easy, and can be done at a high speed. However, when the parking lot is getting full, it becomes harder and harder to find a spot, and if you drive too quickly the risk of having a crash into another car increases. Lithium-ions experience something similar while charging resulting in damage and therefore to battery degradation.
The standard response to prevent battery degradation is to decrease the speed at the end of charging, typically with a fixed profile. However the more smart battery management of Cleantron controls this dynamically, especially when taking the temperature boundaries into account.
How Temperature Affects Lithium-Ion Battery Charging and Safety
The temperature plays a drastic role in charging. It is preferable for a battery to not be too cold nor too hot at the start of charging. A temperature around 25°C is generally considered ideal. While in many applications it is possible to equip the battery pack with a suitable thermal management system to cool or heat the battery to this temperature. There are various ways to do this, such as air cooling, cooling via a cooling plate with a coolant or refrigerant and finally immersion cooling. All with varying degrees of complexity and increasing degrees of effectiveness. Cleantron is working on a novel implementation of immersion cooling that also enhances safety, more on which in a later article.
However, it is not always a possibility to include an active cooling system. One example for this are the swappable packs such as the P4X and CLP, where portability and swappable is a core feature that would be impacted by including a cooling system. On these packs we thus need to react to the temperature inside the pack to ensure optimal performance, rather than control it to stay in the optimal performance range.
If the battery is hot, it may overheat (and the battery management stops the charging process) or if it does not reach this critical level, it undergo chemical degradation, especially when high charging currents are applied for a longer time. On the other hand, charging at low temperatures increases the risk of lithium plating, which is also worsened by high charging currents.
Cleantron’s Adaptive Charging Algorithms
It becomes clear that more than just voltage and charging time need to be carefully monitored. For this reason, Cleantron provides its customers with in-house developed adaptive charging algorithms.
This algorithm can be finetuned based on the customers wishes, such as (extreme) fast charging. As a standard, the Cleantron Battery Modules P4P, P4X and CLP are equipped with an all-purpose version of the algorithm. This standard takes into account the Current temperature of the battery and sets the ideal Charging Current and the end of Charge Voltage based on this measurement.
Besides this, the algorithm also takes into account the actual State of Charge level of the battery, as well as the State of Health, ensuring that the charging is always optimal at any point in the battery’s life. As a result, Cleantron battery packs help extend their own lifespan, reducing carbon footprint, and deliver greater long-term value.
Why Cleantron for Electric Vehicles Batteries?
Cleantron is an European leader in advanced lithium-ion batteries. We provide made in The Netherlands advanced batteries for light electric vehicles and other market sectors, like agricultural and industrial applications and solutions. Our products are built on captive BMS technology and the commitment to a long-term reliability. Whether you’re developing LEVs or micro cars, our battery technology gives you the flexibility and reliability to scale successfully.
We provide a full range of modular batteries, including low voltage and high voltage solutions.
Alongside our standard batteries, Cleantron’s core business is to develop tailored battery modules for OEM customers.
Contact us to see how Cleantron can help power your next product.
FAQ
What is the charging current for a lithium-ion battery?
There is no single Charging Current for a lithium-ion battery, as this depends on:
- Which chemistry is inside the battery
- The capacity of the battery
- The type of battery cell (power type vs energy type)
- Pack-level constraints (Electronics and Thermal)
How to increase lithium-ion battery life?
Don’t keep the battery charging if it has already reached 100% and avoid deep discharges.
If a deep discharge (DUV) occurs the battery is normally beyond repair, so should not be used (“repaired” as some call it). Circumventing the BMS electronic safety measures and charging a battery after a deep-discharge results in a clear risk of fire due to Li plating. Particularly if the charging after the deep-discharge is performed too fast.
When storing a battery for long, make sure to charge it to avoid over-discharge. It is better not to charge it at 100%: if kept in storage at high SOC, the battery might degrade faster, particularly if stored in a very warm environment (> 40°C). In general, it is best to store the battery in a non humid environment (10 – 20°C) with 50% < SOC < 80%.
What are common mistakes to avoid, when charging a li-ion battery?
- Never revert polarity when connecting a battery, it’s very dangerous. Most chargers have a safety function implemented to prevent that.
- Never charge above the supplier’s specified limits to avoid dangerous situations.
- Do not keep the charger connected for a long time once a battery is full. A battery will age faster if forced constantly at 100% SOC, particularly if it’s NMC Li-ion battery (which goes to higher voltages).
- If the battery has to be stored for several months, it is a good practice to charge it before, however not all the way to full. If left in storage for too long, it might end up deep-discharging. Even if it’s not connected to anything, its BMS will keep tapping a very small Current to keep functional, which over the months will drain the battery gradually.
