Will Batteries Always Swell at High Temperatures? — High-Temperature Test Standards Introduction
Introduction
When it comes to the performance of lithium-ion batteries, high temperature is definitely one of the unavoidable topics. The reasons are simple: lithium-ion batteries generate heat during charging and discharging; they are often stored or even used in high-temperature environments; and our planet is continuously getting warmer…
In the field of lithium-ion batteries, what are the common high-temperature test standards? What are the mechanisms of performance degradation under high temperatures? How can the high-temperature performance of batteries be improved? These are exactly the topics this article series aims to share with you.
To begin our discussion on high temperature, the iRay Energy editor would first like to introduce the wide variety of high-temperature test standards. In summary, current high-temperature test standards can be divided into three major categories: high-temperature storage where battery performance does not significantly decline, thermal shock where performance is essentially lost, and cycling under high-temperature conditions. Under each category, many specific test standards have been derived.
During the storage and transportation of lithium-ion batteries, the following scenarios are inevitable: use in tropical or scorching summer regions, long-term sea transportation, or being exposed to direct sunlight in a car recorder. The commonality among these environments is that lithium-ion batteries remain in a high-temperature environment for hours or even weeks, and they must still function normally after such storage.
To verify the reliability of batteries under these conditions, high-temperature storage tests were introduced. Below are some common high-temperature storage conditions:
| Temperature | Time | Description | |
|---|---|---|---|
|
60℃ |
7 days |
General standard |
|
|
60℃ |
30 days |
Special requirement for drone batteries, sea-shipped batteries, etc. |
|
|
85℃ |
4 h |
General standard |
|
|
80℃ |
48h |
Special requirement for car recorder batteries, etc. |
|
After high-temperature storage, capacity and voltage decrease, while thickness and internal resistance increase. To evaluate cell performance after high-temperature storage, the following parameters are usually assessed:
| Parameter | Description & General Requirements | |
|---|---|---|
|
Capacity Recovery Ratio |
Key parameter, generally required at 90–95% |
|
|
Remaining Capacity Ratio |
Secondary parameter, usually 5–10% lower than recovery capacity |
|
|
Hot-Measured Swelling Rate |
Key parameter, generally required ≤10% |
|
|
Cold-Measured Swelling Rate |
Secondary parameter |
|
|
Voltage Drop Ratio |
Secondary parameter |
|
|
Internal Resistance Growth Ratio |
Secondary parameter |
Among these, the capacity recovery ratio determines the fundamental performance of the battery after storage (how much usable energy remains), making it one of the most critical concerns for customers. Another equally important parameter is the hot-measured swelling rate at the end of storage. If swelling is too severe, the battery may push open the device’s battery cover, rendering the device completely unusable.
Therefore, after various high-temperature storage conditions, the most important requirements are that the battery remains functional, and the key indicators are the capacity recovery ratio and the swelling rate during high-temperature storage.
During use, batteries may be exposed to extreme conditions such as surrounding fires or abnormal overheating of the device. Under such harsh circumstances, it is already difficult enough for the battery to remain functional; it is considered fortunate if the battery simply does not ignite or explode.
To simulate these extreme heating conditions, thermal shock tests were introduced. The most common test is the national standard of 130℃ for 30 minutes. Other certifications include 130℃ for 10 minutes and 150℃ for 10 minutes. Since such high temperatures exceed the decomposition temperature of some battery components and the boiling point of certain electrolyte solvents, batteries inevitably swell significantly or even drop to zero voltage after thermal shock.
Thus, the typical requirements for thermal shock tests are simply no fire and no explosion. In addition, since 130–160℃ is the melting threshold of separators, setting the temperature either much higher or lower would greatly reduce the relevance of the test. Below is a chart showing the characteristics of lithium-ion batteries across different temperature ranges:
Characteristic diagram of lithium-ion batteries in different temperature ranges
For power batteries, drone batteries, and those designed for long-term operation in hot regions, good high-temperature storage performance alone is not enough—they must also withstand cycling under high-temperature conditions.
The most common high-temperature cycling tests are performed at 45–55℃. There is no universal standard for cycle count, but it is typically 30–80% of the cycle count at room temperature. In the booming power battery market, the importance of high-temperature cycling is sometimes considered even greater than that of room-temperature cycling.
Summary
These are the three most common high-temperature tests:
After high-temperature storage, the battery must continue functioning, with the main criteria being capacity recovery ratio and hot-measured swelling rate.
After thermal shock, the battery will almost certainly lose its charge/discharge capability, so the only requirement is no fire and no explosion.
During high-temperature cycling, battery lifespan is significantly shortened, and cells designed for special working conditions must be evaluated at 45–55℃.
Conclusion
At this point, some readers may say: “The title tricked me again—the editor still hasn’t said whether batteries will always swell at high temperatures!”
Don’t worry—the meal must be eaten one bite at a time. In the following articles of this series, we will dive into the mechanisms behind battery changes at high temperatures and how to improve high-temperature performance.
