Lithium polymer battery electrolyte leakage

1. Lithium polymer battery leakage concept

When the aluminum plastic packaging shell of a lithium polymer battery is broken, has poor sealing, or is corroded and cracked, the 

electrolyte inside it will leak out, and at the same time, outside air will enter the battery body, causing the battery to bulge. Leakage is 

defined by the customer as non-compliance. Condition type.

2. Introduction to battery leakage detection methods and solutions

In order to prevent the problem of liquid leakage in lithium polymer batteries, engineering technology on the one hand improves the 

packaging method and improves the sealing performance of the package. On the other hand, it improves the method of testing for liquid 

leakage. Generally, there are the following methods for testing whether the battery is leaking:

(1) Appearance inspection, through 100% manual inspection, observe whether there is electrolyte leakage and battery appearance 

deformation, etc. This method is a traditional method and is easy to operate in reality, but it relies on the detection ability of personnel 

and its anti-fool performance is poor. This is the original detection method.

(2) Vacuum detection, using the vacuum method, takes advantage of the air-blowing characteristics of the leaking battery to evacuate 

the entire battery, forming a large pressure difference inside and outside the leaking battery. The electrolyte may be flowed out of the 

battery along with internal gas production. Then conduct a visual inspection and pick out those that do not conform. The detection rate 

of this method is low, but it is also a commonly used method because of its better operability.

(3) Leak material detection. Once the battery leaks, the electrolyte inside it will flow out of the battery. If the electrolyte can be sensitively 

detected, it can be judged whether the battery is leaking. The limitation of this method is that it has no form. Testing institutions are 

particularly sensitive to electrolytes and have fewer applications. They generally use chemical reagents such as pH test paper and litmus 

test solution. If the method problem of detecting electrolyte can be solved, it will be a promising detection method.

At the beginning of the design of the detection plan, we developed according to the third method, and focused on the development of 

instruments that can detect electrolytes. Through market research, we learned that VOC detectors can be very sensitive to organic matter, 

and electrolytes The main components are also organic, so there are significant opportunities for improved applications.

3. Introduction to VOC detector

Based on the above situation, VOC detector (Volatile Organie Compounds) is an instrument that uses a set of photo ionization sensors 

PID (photo ionization detector) to detect organic volatile components. It is used for trace VOC volatilization detection and is mainly used 

in environmental testing and indoor testing. Environment, safety supervision, factory exhaust emissions and other industries. The working 

process and principle is: the gas in the environment to be detected is sucked into the photoionizer through the built-in air pump for ionization, 

ionizing the organic gas, collecting the ionization voltage, and converting it into a digital display. The size of the value reflects the organic 

matter in the environment. The molar content of gas, the general units are PPb, PPm. Gongcai.com recommends two PID photoionization 

sensors for detecting VOC gases, PID-AH and PID-A1; PID-A1 is a large-range sensor with a detection range of 100ppb~6000ppm, while 

PID-AH is a sensor with a small range and sensitivity. High-end products have a detection range of VOC gases from 1ppb to 50ppm.

4. Path analysis of scheme design principles

(1) Experimental test of sensitivity of VOC detector to organic volatile gases

The experiment was conducted in 5 groups. The test objects were ordinary environment, pole piece workshop, electrolyte atmosphere, next 

to qualified batteries, and next to leaking batteries. The values displayed by the tester were: 0-10PPb, 500--I 000PPb, Above 5000PPm, 

0-20PPb, 50-200PPb. It can be seen from the above simple experiment that the VOC detector is very sensitive to organic gases in the 

environment, and it is also sensitive to the polymer electrolyte. Different environments can cause obvious changes in the VOC detector's 

readings. This shows that it is possible to use a VOC detector to detect leakage.

(2) Battery test experiment

a. A normal battery has good sealing, and its internal electrolyte will not appear outside the battery. A small amount of organic volatile 

components will cause a small change in the VOC detector's display or not cause a change in the display during experimental testing, and 

the test value will be small. It shows that there is no large amount of organic volatile matter, the battery is not damaged, and the battery is 

judged to be OK.

b. Leaking battery, the seal fails, and the electrolyte inside it can escape from the leakage point to the outside of the battery in some way. 

The electrolyte decomposes to produce volatility or its small molecular components escape. During experimental testing, it is detected by 

VOC It is detected by the instrument, causing a large change in the display. A large test value indicates that there is a large amount of 

organic volatile matter. The battery may leak or there is electrolyte on the surface, and the battery is judged to be NG.

5. Optimize experimental plan design

(1) Optimization of detection parameters

a. Design a 2-factor experiment of single detection number (6-24) and vacuum time (10-15s) to evaluate the impact of the normal number 

of batteries and vacuum holding time on the detection system.

b. Design a fixed vacuuming time of 15 seconds. When detecting 6, 12, 18 or 24 normal batteries at a time, dynamically detect the change 

process of the VOC detector and read the readings of the VOC detector at the 10th and 15th seconds. , analyze the difference.

c. The vacuuming time is fixed at 15 seconds, and the number of normal batteries in a single test is 24. The numerical changes of the VOC 

detector during the vacuum test are dynamically detected, and the favorable reading time is analyzed.

Through the analysis of experimental results and data, it was found that as the number of normal batteries in a single test increases, the 

vacuum holding time increases and the test values increase; for the readings of different test numbers in each group, the difference between 

the 10th and 15th seconds is Basically consistent, that is, the numerical change rate is the same; during each set of tests, the VOC test value 

first increased and then decreased with the increase of time, reaching the MAX value at about 5s, so the favorable reading time is in the 

range of 5-10s. Inside.

Through the above analysis and improvement, it is finally determined that the parameters for VOC inspection of leaking batteries are test 

temperature 20C, vacuum degree -90KPa, vacuum time 15s, pumping detection time 10s, using flowing compressed gas, and the test 

quantity is 8Pcs for small batteries and 8Pcs for large batteries. The battery is 30 PCS, and a special strictly sealed test device is used to 

collect volatile components, and the test environment is stable.

(2) Detection method verification

For verification measurements using the aforementioned optimized conditions, it can be found from the analysis of experimental data that 

the test values of normal batteries are less than the upper limit of the test, and their values are normally distributed; the test values of leaking 

batteries are all greater than the upper limit. values, and their values are scattered and irregular; the test values of large-type batteries are 

much larger than the test values of small-type batteries. The above data can quantitatively reflect the difference between normal batteries 

and leaking batteries, and can determine whether the battery is leaking.

6 Conclusion

Through research on lithium polymer ion battery leakage detection methods, we have realized new applications. The VOC detector is an 

effective detection method for lithium polymer battery leakage.