What are the methods for measuring the “slightly less” amount of electrolyte injection for lithium batteries? The performance of lithium ion batteries is closely related to the electrolyte, and the amount of electrolyte has a greater impact on the battery’s electrochemical and safety performance. A proper electrolyte injection volume is not only beneficial to increase energy density and reduce costs, but also plays an important role in improving the cycle life of lithium batteries.

What are the methods to detect the “slightly less” electrolyte injection volume of lithium batteries?

Since the electrolyte will continue to undergo oxidation and reduction reactions on the positive and negative electrodes during the operation of the lithium battery, too little injection volume is detrimental to the cycle life of the lithium ion battery. At the same time, if the amount of electrolyte is too small, it will also cause some Active materials cannot be infiltrated, which is not conducive to the development of lithium battery capacity. However, too much injection volume will also cause problems such as a decrease in the energy density of lithium ion batteries and an increase in cost. Therefore, how to determine the appropriate injection volume is important for the performance and performance of lithium batteries. The balance between costs is particularly important.

“Slightly less, less, and less severely” the electrolyte injection volume of lithium batteries is a general statement, and there is no strict requirement. Even if the electrolyte is slightly less, the lithium battery is already a defective product. Cells with a little less electrolyte are not easy to be found. At this time, the capacity and internal resistance of the cells are normal. There are three methods to detect that the lithium battery has a little less electrolyte. .

1. Remove the battery

Disassembly is a destructive test and only one cell can be tested at a time. Although the problem can be determined intuitively and accurately, the actual use of this method to screen cells is basically unnecessary.

2. Weighing

The accuracy of this method is low, because the pole piece, aluminum plastic film, etc. will also have weight differences; since the electrolyte of the lithium battery is “slightly less”, then the actual retention of each battery cell will not vary greatly. , So the weight difference of other materials is likely to be greater than the difference in electrolyte weight.

Of course, you can accurately and timely know the problem cell by measuring the amount of liquid or the amount of liquid retained by each cell during liquid injection, but instead of weighing the full cell, it is better to increase the accuracy and Optimize the process to treat the symptoms and the root cause.

3. Test

This is the focus of the question. What kind of test method can be used to screen out cells with “slightly less” electrolyte, which is equivalent to what kind of abnormalities will occur in cells with “slightly less” electrolyte. At present, only two methods are known to measure cells with normal capacity and internal resistance, but with slightly less electrolyte. These two methods are: cycle, rate discharge platform.

What effect does the electrolyte injection volume have on the performance of lithium batteries?

①The influence of electrolyte volume on lithium battery capacity

The capacity of lithium batteries increases as the electrolyte content increases. The best capacity for lithium batteries is that the separator will soak. It can be seen that the amount of electrolyte is insufficient, the positive electrode plate is not fully wetted, and the separator is not wetted, resulting in large internal resistance and low capacity. The increase in electrolyte is conducive to making full use of the capacity of the active material. This shows that the capacity of a lithium battery has a great relationship with the amount of electrolyte. The capacity of lithium batteries increases with the amount of electrolyte, but eventually tends to be constant.

②The influence of electrolyte volume on the cycle performance of lithium battery

The electrolyte is less, the conductivity is low, and the internal resistance increases faster after cycling. Accelerating the decomposition or volatilization of the partial electrolyte of the lithium battery is the rate at which the cycle performance of the battery decreases. Too much electrolyte will lead to side reactions and increase in gas production, resulting in a decrease in cycle performance. Moreover, too much electrolyte is wasted. It can be seen that the amount of electrolyte has a significant impact on the cycle performance of the lithium battery. Too little or too much electrolyte is not conducive to the cycle performance of the battery.

③The influence of electrolyte volume on the safety performance of lithium batteries

One of the reasons for the explosion of lithium batteries is that the injection volume cannot meet the process requirements. When the amount of electrolyte is too small, the internal resistance of the battery is large and the heat generation is large. An increase in temperature will cause the electrolyte to quickly decompose to produce gas, and the separator will melt, which will cause the lithium battery to swell and short-circuit and explode. When the amount of electrolyte is too much, the amount of gas generated during charging and discharging is large, the internal pressure of the battery is large, and the case is broken, causing electrolyte leakage. When the electrolyte temperature is high, it will catch fire when it encounters air.

Electrolyte is used as a medium for lithium ion migration and charge transfer. In order to ensure the full application of active materials, each void area of ​​the battery core is required to be filled with electrolyte. Therefore, the internal space volume of the battery can also be used to roughly determine the battery’s demand for electrolyte. quantity. It can be seen that the amount of lithium battery electrolyte has a significant impact on the cycle performance of the battery. Too much or too little electrolyte is not conducive to the cycle performance of the lithium battery.