Negative lithium deposition is an abnormal phenomenon that may occur in lithium batteries under specific conditions, posing a serious threat to the performance and safety of the battery. So, as ordinary users, how can we determine if the lithium battery we are using has experienced negative lithium deposition?
1 Understand the basic concept of lithium deposition on negative electrodes
Negative electrode lithium deposition, as the name suggests, refers to the process in which lithium ions fail to successfully embed into the negative electrode material during the charging of a lithium battery, but instead precipitate in the form of metallic lithium on the surface of the negative electrode. This phenomenon usually occurs under specific conditions such as low temperature, fast charging, and overcharging. The precipitated metallic lithium often exists in the form of dendritic crystals, known as lithium dendrites. The growth of lithium dendrites not only reduces the overall performance and shortens the cycle life of the battery, but may also puncture the separator, causing internal short circuits and even serious consequences such as fires or explosions.
2 Common signs of lithium deposition in negative electrodes
Although the internal structure and chemical reactions of lithium batteries are complex, we can preliminarily determine whether the negative electrode lithium deposition phenomenon has occurred through some external signs:
Battery capacity degradation:
The negative electrode lithium deposition will consume the movable lithium ions inside the battery, resulting in a gradual decrease in battery capacity. If you find that the battery's usage time is significantly shortened, or the battery runs out quickly after charging, this may be a signal of lithium deposition in the negative electrode.
Abnormal charging:
During the charging process, if the battery heats up, expands, or experiences abnormally prolonged charging time, it may also be a sign of lithium deposition from the negative electrode. Especially in low-temperature environments or when using high rate charging, these phenomena are more pronounced.
Unstable battery performance:
Negative lithium deposition can affect the performance stability of batteries. If you notice significant voltage fluctuations or abnormal discharge curves during battery use, it may be due to lithium deposition from the negative electrode.
3 Non destructive testing method for lithium deposition on negative electrodes
For ordinary users, it is obviously unrealistic to directly disassemble the battery to observe whether there is lithium metal precipitation on the negative electrode surface. Fortunately, researchers have developed various non-destructive methods for detecting lithium deposition in negative electrodes, which can evaluate the internal state of the battery without disassembling it. Here are some common non-destructive testing methods:
1. Abnormal heating during charging
Self inspection method: Charge the device with the original charger for 30 minutes at room temperature (20-25 ℃), and touch the device casing with your hand.
Danger signs: Local temperature exceeding 50 ℃ (feeling noticeably hot, unable to touch continuously for 3 seconds); The temperature does not decrease but increases during the later stage of charging (normal batteries should gradually cool down after 90% charge).
Principle: Lithium evolution will intensify side reactions, leading to an increase in internal resistance and more conversion of electrical energy into thermal energy.
2. Diving style degradation of battery life
Self inspection method: Record the usage time of the device from full charge to 20% power, and observe continuously for 3 times.
Warning signs: The battery life has been reduced by more than 30% (if the original video playback time was 6 hours, now it is less than 4 hours); Voltage drops sharply when the battery is low (such as when the battery level of a mobile phone drops from 15% to 1% instantly).
4 Professional testing methods (precise diagnosis)
1. Electrochemical testing method
Negative electrode potential measurement
By measuring the negative electrode potential through a three electrode system, if it is below 0V (vs. Li/Li ⁺), it indicates the occurrence of lithium deposition. This method is precise but requires laboratory testing.
Voltage relaxation method
After charging, let it stand for several hours and plot the voltage variation curve over time. Lithium precipitation can cause a "turning point" in the curve, as the reaction between lithium dendrites and electrolyte consumes lithium ions.
Electrochemical Impedance Spectroscopy (EIS)
Lithium deposition can alter the impedance characteristics of batteries. The charge transfer impedance decreases (due to the addition of lithium deposition branches), but the ohmic impedance may increase due to the thickening of the SEI film.
2. Physical characterization method
Disassemble and observe
Gray white metallic lithium deposits appear on the negative electrode surface, or the separator changes color and thickens locally.
Ultrasonic/X-ray testing
Observe the growth of lithium dendrites inside the battery through non-destructive imaging technology.
3. Long term monitoring method
Coulomb efficiency analysis
Lithium deposition can lead to a decrease in charging and discharging efficiency. By monitoring the Coulomb efficiency with a high-precision coulomb meter, if it continues to be low, it may indicate lithium deposition.
Dynamic discharge detection
During the discharge process, abnormal monitoring of the voltage platform may result in voltage fluctuations or platform shortening due to lithium deposition.
5 Preventive measures and suggestions
To avoid the phenomenon of negative electrode lithium deposition in lithium batteries, we can take the following preventive measures:
Avoid low-temperature charging:
Charging at low temperatures increases the risk of lithium deposition on the negative electrode. Therefore, whenever possible, it is advisable to avoid charging lithium batteries in low-temperature environments.
Reasonable use of fast charging function:
Although fast charging technology can greatly shorten charging time, excessively high charging rates may also lead to lithium deposition in the negative electrode. Therefore, when using the fast charging function, it is necessary to ensure that the battery is within the appropriate temperature range and avoid frequent use of fast charging.
Regular maintenance of batteries:
Regular maintenance and inspection of batteries, timely detection and handling of battery problems, can extend the service life of batteries and reduce the risk of negative electrode lithium deposition.