How to tell a Battery Short Circuit? A Brief Introduction
If a sudden drop in voltage occurs during the cycle, it indicates that lithium dendrites have pierced the battery’s interior, causing a short circuit that brings the positive and negative electrodes into direct contact, thereby reducing the potential difference.
Figure 1 Schematic Diagram of Hard Short Circuit and Soft Short Circuit in Symmetrical Batteries
It should be noted that the short-circuit process can be an irreversible hard short-circuit, after which the voltage signal exhibits a constant low value (close to 0 V). The specific value depends on the current applied during the cycle, as the battery at this point behaves as a resistor, with the voltage value being linearly proportional to the current value. Alternatively, the short-circuit process can be a soft short-circuit triggered by partial contact, which is reversible to some extent.
Figure 2 Schematic Diagram of Different States of a Symmetrical Battery
During a soft short circuit, after dendrites pierce the separator and contact the opposite electrode, the subsequent dissolution of that electrode or the detachment of the dendrite from the electrode can cause the positive and negative electrodes to lose contact. Both scenarios can manifest as the restoration of the short circuit. At this point, the voltage signal experiences a slight dip corresponding to the instantaneous contact between the positive and negative electrodes via the dendrite. Subsequently, the voltage gradually changes on a new plateau without a noticeable abrupt drop; it may even exhibit a certain degree of voltage recovery before stabilizing. As shown in Figure 2, from left to right, the states represent the normal condition, hard short circuit, and soft short circuit of a zinc symmetric cell.
Figure 3: Voltage Changes in Zinc Symmetrical Batteries at Different States
Based on the interpretation of the short-circuit data above, determining whether a lithium symmetric battery has short-circuited can be directly observed from the voltage response curve: if a significant voltage drop occurs within a single cycle, it can be identified as a short circuit. Based on the behavior following the drop, hard short circuits and soft short circuits can be distinguished: – In a hard short circuit, the voltage drop is irreversible, and the voltage stabilizes at a fixed value afterward, appearing as a straight line in the response signal. If the current is altered, the voltage response signal increases proportionally to a fixed value and remains linear (at this point, the battery functions as a constant-value resistor). In contrast, a soft short-circuit exhibits a smaller voltage drop. Following the drop, the voltage response curve can recover to normal during the charge-discharge process, and the voltage does not stabilize at a fixed value.
[Note] Other Methods for Determining Short Circuits
1. EIS can also assist in determining whether a battery has short-circuited. It is recommended to test impedance at a lower temperature to prevent excessive heat from causing dendrite dissolution and fracture, which could affect impedance measurements.
(1) In the case of a hard short circuit, the EIS will exhibit a distinct inductive signal in the high-frequency region, with a small intersection value (impedance real part) between the high-frequency region and the x-axis. The low-frequency region will display irregular noise points.
(2) Soft short circuits exhibit normal EIS, but the battery’s static resistance and charge transfer resistance are significantly reduced. Since activation phenomena are common during testing of symmetrical lithium batteries, and the active surface area increases due to lithium dendrite growth, the decrease in battery impedance may also result from these factors. Therefore, it is difficult to determine soft short circuits solely through EIS; it must be combined with the battery’s voltage response signal for clarification.
2. Common microscopic analyses, such as scanning electron microscopy (SEM), allow direct visualization of lithium dendrites. However, due to the random nature of the observed sites, they cannot conclusively determine whether dendrite growth occurs across the entire electrode within specific microdomains. Beyond these conventional electrochemical and material characterization methods, in situ optical microscopy also serves as a direct means to assess the effectiveness of modifications.
For more information, you can delve deeper into the following articles:
[1]Symmetric Cells as an Analytical Tool for Battery Research: Assembly, Operation, and Data Analysis Strategies
[2]Short Circuit of Symmetrical Li/Li Cell in Li Metal Anode Research
[3] Soft Shorts Hidden in Zinc Metal Anode Research
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