Lithium-ion batteries, known as the "ultimate energy source" and "green energy," have been increasingly widely used in people's production and daily lives since their introduction in the 1990s, ranging from button batteries in electronic products and lithium batteries in mobile phones and digital devices to power batteries in electric vehicles. Compared with other batteries, lithium-ion batteries have significant advantages in terms of size, weight, and performance.
Lithium batteries within a reasonable voltage and capacity range should be used.
The pursuit of excessively large capacity and ultra-high voltage is flawed. Firstly, everything progresses from simple to complex, from difficult to easy. For example, ensuring the safety of a lighter is relatively easy, but ensuring the safety of a car fuel tank is much more difficult; the possibility of car fires and explosions in crashes remains unresolved. The more energy accumulated within a limited volume, the harder it is to manage. Currently, Suzhou Xingheng can only guarantee the safety of battery combinations up to 48V 10Ah. Secondly, higher voltage and larger capacity increase the complexity and failure rate of protection and balancing circuits. Therefore, Suzhou Xingheng does not advocate or support battery combinations exceeding 48V 10Ah.
To check the safety testing and certification of lithium batteries
I. UL Certification
Today, most countries and regions in the world require products involving safety, hygiene, and environmental protection to obtain safety certification before entering the market. The UL mark has become one of the world's most renowned safety certification marks.
The testing standards are as follows:
1. Shell
The lithium battery casing should have sufficient strength and rigidity to withstand excessive pressure without causing a fire. User-replaceable lithium batteries should be strong enough not to injure people.
2. Electrolytes
User-replaceable batteries should not contain pressurized vapors or emit toxic vapors or liquids that could harm the eyes, or the battery casing should leak less than 5 ml of liquid when subjected to impact under normal laboratory conditions (temperature 23°C).
3. Use
Lithium batteries should be protected against abnormal charging currents during use. The tested battery should have an acceptable charging current Ic. Under abnormal conditions, protective measures should be implemented in the end product.
4. Leakage
The standard for mass loss due to leakage or spillage is that the maximum mass loss of a cell or battery shall not exceed 0.5% for 1g, 0.2% for 1-5g, and 0.1% for 5g.
5. Mechanical testing
(1) Compression: A hydraulic piston with a diameter of 32 mm is used to apply a pressure of 13 kN (17.2 MPa) to the two flat surfaces of the battery. The pressure is released after the maximum pressure is reached. The sample does not catch fire or explode.
(2) Impact test: A 15.8 mm diameter rod is placed in the center of the sample, and a 9.1 kg weight is dropped from a height of 610 mm onto the sample. The sample does not ignite or explode.
(3) Acceleration: The battery is placed on a fixed fixture and accelerated in three mutually perpendicular directions (acceleration requirements: the minimum average acceleration should reach 75g within the initial 3ms, and the peak acceleration should be between 125-175g). The test temperature is 20±5℃. The sample should not catch fire or explode, and the sample should not leak.
(4) Vibration: The battery is subjected to simple resonant vibration (along three mutually perpendicular directions), with the vibration frequency changing at a rate of 1Hz/min in the range of 10-55Hz, recovering within 90-100min, and the amplitude being 0.8mm. The sample should not ignite, explode, or leak.
(5) Thermal shock: The sample is heated in a natural convection or forced convection oven at a rate of 5±2℃/min to 150℃ and held for 10 min before stopping. The sample should not ignite or explode.
(6) Thermal cycling test: The battery is placed in the test chamber and subjected to the following cycles:
① Heat to 70±3℃ within 30 minutes and keep warm for 4 hours.
② Cool down to 20±3℃ within 30 minutes and keep warm for 2 hours.
③ Increase the temperature to 40±3℃ within 30 minutes and keep it warm for 4 hours.
④ Cool down to 20±3℃ within 30 minutes.
⑤ Repeat the above cycle 9 times.
⑥ After 10 cycles, the battery should be left to stand for 7 days for testing. The sample should not catch fire, explode, or leak.
(7) High-altitude simulation: The sample battery was stored for 6 hours at an absolute pressure of 11.6 kPa (1.68 psi) and a temperature of 20 ± 3 °C (68 ± 5 °F). The sample battery should not explode or catch fire, and there should be no punctures or leaks.
6. Charge and discharge test
(1) Charge-discharge cycle: The test temperature is 25°C. The cells are charged and discharged according to the manufacturer's requirements until the capacity reaches 25% of the initial nominal capacity or after 90 consecutive days of cycling. No safety events should occur in the sample.
(2) Short-circuit test: Short-circuit the positive and negative terminals of the battery with a copper wire with a resistance of less than 0.1Ω. Discharge the battery until it catches fire or explodes, or until the battery is completely discharged and the casing temperature drops back to room temperature (the test is conducted at room temperature of 60±2℃). The sample should not catch fire or explode, and the temperature of the casing or battery casing should not exceed 150℃.
(3) Abnormal charging test: After normal discharge, charge with a current three times the normal charging current. No fire or explosion.
(4) Forced discharge test: The battery cell is fully discharged at room temperature, connected in series with a certain number of new battery cells of the same model, and the resulting battery pack is subjected to a short circuit test. The sample should not catch fire or explode.
(5) Overcharge: The battery is charged at 3C, 10V constant current and constant voltage when it is fully charged. When the current reaches 100mA, it is switched to constant voltage charging for 48 hours.
7. Signage
Batteries should be labeled with the manufacturer's name, trademark or logo, and model designation. Batteries should also be labeled with a warning and a corresponding description.
II. ExtraEnergy Standard
Extra
Energy Certification is a non-profit organization headquartered in Tanna, Germany. Its main work is to gather neutral information on light electric vehicles worldwide and provide value-added services. Among these services, the safety testing of lithium batteries is very strict and rigorous, and is recognized by most European customers.
The testing standards are shown in the table below.
Test method pre-test state test method safety standard
1. Abnormal charging at room temperature, empty battery, original factory assembly. The protection and management circuits are removed. With the battery pack fully charged, it is overcharged at 10A to 1.5 times the nominal voltage.
It does not catch fire or explode; the battery casing temperature is less than 120℃ during the test; the experimental wooden table is not scorched; and the released gas is non-toxic.
2 Short circuit
At room temperature, fully charged with the original charger, and assembled at the original factory.
By removing the protection and management circuits, the positive and negative terminals of the battery pack are directly short-circuited when the battery pack is fully charged.
It does not catch fire or explode; the battery casing temperature is less than 120℃ during the test; the experimental wooden table is not scorched; and the released gas is non-toxic.
The battery pack is subjected to triple compression at room temperature, fully charged with the original charger, and assembled at the original factory. A 15cm diameter steel roller applies 10 tons of pressure to the battery pack.
It will not catch fire or explode; the gas, solid, and liquid released from the battery are non-toxic.
III. CE Certification
In recent years, the use of the CE marking has increased significantly in the markets of the European Economic Area (European Union, European Free Trade Association member states, excluding Switzerland). Products bearing the CE marking indicate that they meet the requirements of a series of European directives concerning safety, health, environmental protection, and consumer protection.
