Lithium Battery Performance and Quality Tests
After a series complex and precise manufacturing process. Lithium battery will meet their final difficulty–Quality and Performance Tests. Here is the detailed introduction about battery manufacturing process.
Lithium battery is a product that requires high quality and high safety. Consumers often do not know the performance of the battery when using it, which leads to the work efficiency of the battery often not reaching the ideal goal when using it. Sometimes even blind use can cause battery explosions, and life safety will also be damaged. Therefore, it is essential to understand the performance of the battery.
The performance tests of lithium batteries include voltage, internal resistance, capacity, internal voltage, self-discharge rate, cycle life, sealing performance, safety performance, storage performance, appearance, etc. Performance test is up to 230 items. As well as overcharge, over discharge, weld-ability, corrosion resistance, etc.
The following is detailed introduction about some mainly tests.
CONTENT
1.Self-discharge test
The self-discharge test of lithium cell is:
Generally, 24 hours of self-discharge is used to quickly test its charge retention ability.
Step 1: Discharge the cell to 3.0V with the discharge rate at 0.2C and then charge to 4.2V with charging rate at 1C and constant current and constant voltage. The experiment requires that the cut-off current is 10mA.
Step 2: Shelve cell for 15 minutes
Step 3: Discharged the cell until the voltage drop to 3.0V with the discharge rate at 1C.
Step 4: Measure its discharge capacity as C1
Step 5: In constant current and voltage, charge the cell battery to 4.2V with the charge rate at 1C. Set the cut-off current is 100mA.
Step 6 : Shelve cell for 24 hours
Step 7：Measure its capacity as C2
If “ (C2/C1)*100% ” ≥ 99%, this cell passes this test.
2.Internal Resistance Measurement
We define the battery internal resistance as the resistance of current flowing through the inside of the battery when the battery is working. It is generally divided into AC internal resistance and DC internal resistance.
Due to the small internal resistance of rechargeable batteries, when measuring the DC internal resistance, the electrode is easily polarized and the internal resistance of polarization is generated. Therefore, its true value cannot be measured; and measuring its AC internal resistance can eliminate the influence of polarization internal resistance and obtain the true internal value.
The AC internal resistance test method:
Experiment characteristics: the battery is equivalent to an active resistor,
Step 1: Give battery a constant current of 1000HZ and 50mA
Step 2: Measure a series of voltage data
Step 3: “R=U/I”
Then the resistance is bingo.
3.IEC Standard Cycle Life Test:
IEC stipulates that the standard cycle life test of lithium batteries is:
Step 1: Discharge the cell to 3.0V with the discharge rate at 0.2C and then charge to 4.2V with charging rate at 1C and constant current and constant voltage. The experiment requires that the cut-off current is 20mA.
Step 2: Shelve cell for 1 hours at least
Step 3: Discharge the cell to 3.0V with the discharge rate at 0.2C
Step 4: Measure its capacity as C1
Step 5: Redo above steps for at least 500 times
If “(C500/C1)*100%”≥ 60%, this cell pass this test
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4.Internal pressure test：
The internal voltage test of lithium battery is: (UL standard)
The simulated battery is at an altitude of 15240m above sea level (low pressure 11.6kPa) to check whether the battery leaks or bulges.
Specific steps: Charge the battery 1C with constant current and constant voltage to 4.2V, with a cut-off current of 10mA, and then store it in a low-voltage box with a pressure of 11.6kPa and a temperature of (20±3℃) for 6 hours. The battery will not explode, catch fire, crack, or leak.
5.Drop Test
From its name, we know this test aims to imitate battery falling. In order to avoid battery easily damaged, this test is essential.
Step 1: Fully charge the battery pack
Step 2: Fall the battery at a height of 1M on the hard rubber sheet from different directions
Step 3: Redo above steps for 2-3 times
If the electrical performance of the battery pack is normal and the outer packaging is not damaged, this battery pack passes the test
6.Vibration test
The experimental method of lithium battery vibration is:
Discharge the battery to 3.0V with the discharge rate at 0.2C and then charge to 4.2V with charging rate at 1C and constant current and constant voltage. The experiment requires that the cut-off current is 10mA. After 24 hours of shelving, it will be vibrated in following conditions:
1.Amplitude 0.8mm；
2.Make the battery vibrate between 10HZ-55HZ, increasing or decreasing at a vibration rate of 1HZ per minute；
3.After vibration, the battery voltage change should be between ±0.02V, and the internal resistance change should be within 5m.
The lithium battery pack needs to be vibrated continuously and randomly for 21 hours under environmental conditions from -30℃ to 60℃, which can be equivalent to simulating hundreds of thousands of kilometers of driving fatigue.
The shaker is used to simulate the bumpy road conditions that the battery pack will encounter in actual use.
The environmental box is used to provide different temperature environments.
The charging and discharging motor is used to provide the actual working conditions of charging and discharging.
These three parts form a vibration test system with temperature and load, which truly simulates the situation when the real car is in use.
Purpose: Avoid the vibration of the battery caused by bumpy roads, which can cause poor fixation of battery products that are not of good quality. Loose parts and cracked housings can cause the battery to fail safely. For this reason, national standards require vibration testing of power batteries.
7.Fire Test
Under high-temperature oil and gas pyrotechnics, metal materials such as Lead and Zinc have already melted. However, the battery pack has to carry out this challenge of “survival” at such high temperatures.
In this extreme and dangerous test, the industry’s national standard is that the external fire burns for 130 seconds, and the battery does not catch fire or explode.
But in DNK, everything has the highest requirements.
National standards require that there is no fire or explosion after external combustion, while DNK challenges that the battery can still work normally after 130 seconds of external combustion. The national standard external combustion time requirement is 130 seconds. In DNK, after continuous combustion for 1 hour, the battery is still not in danger of explosion. Under such circumstances, even Aluminum with a melting point of 660℃ melts into a liquid early.
Purpose:Through such a rigorous fire test, even in the event of a fire or vehicle burning, there will be no danger of battery explosion, and secondary injuries will be avoided.
8.The high temperature and humidity test of lithium batteries is:
Step1: In current and constant voltage, charge the battery to 4.2V with the 1C charge rate. Set the cut-off current at 10mA.
Step 2: Place the battery in the box for 48 hours. Keep the temperature during 38-42℃ and keep the relative humidity during 90%-95%.
Step 3: Take out the battery.
Step 4: Shelve the battery for 2 hours, under the room temperature condition(20±5℃)
Step 5: Observe that there should be no abnormalities in the appearance of the battery.
Step 6: Discharge battery to 2.75V at 1C discharge rate
Step 7: Charge the battery at 1C charge rate.
Step 8: Measure the battery capacity witch should not be not less than 85% of the initial capacity.
Step 9: Redo the test no more than 3 times.
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9.Hit Test
Step 1: Fully charged the battery
Step 2: Place a 15.8mm diameter hard rod horizontally on the battery
Step 3: Use a 20-pound heavy object to fall from a height of 610mm and hit the hard rod.
If the battery do not explode, do not catch fire and do not leak liquid, it passes this test.
10.Acupuncture Test
The danger caused by a short circuit of the battery is great. Once a short circuit occurs, the battery will be discharged through the short circuit point. The release of a large amount of energy through the short circuit point in a short period of time will cause the temperature to rise rapidly, and in severe cases it will even cause the battery to catch fire and explode.
According to safety requirements, Needle Requirement:
- High-temperature resistant steel needle
- Diameter: 6-10mm
- Cone angle: 45-60° at the tip of the needle
- Smooth surface, no rust, oxide layer and oil stains
Step 1: Find out the position that can trigger thermal runaway by needle
Step 2: Pierce the single cell
Step 3: Keep the needle inside the cell for about 1 hour
Step 4: Pull out the needle and then observe for 1 hour
If the pierced cell do not catch fire and not explode, the cell is qualified.
In short, the main reason for battery thermal runaway is that the needle destroys the internal structure of the battery which causes short-circuits between positive and negative electrode plates inside the battery.
At this time, the energy will be quickly released through the short-circuit point in a short period of time, resulting in a rapid increase in temperature in a short period of time.
The SEI film and anode electrode material in the battery begin to decompose and release heat. Then the diaphragm decomposes and melts.
Finally, the cathode electrode and the electrolyte will decompose. The temperature continues to rise, causing thermal runaway.
If you are interested in Battery Thermal Runaway, here is the detailed introduction about lithium battery thermal runaway.
Lithium Battery Design Design Ebook Download(2M, 20 pages, PDF)
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