Safety Testing Standards for Power Li-ion Battery – Part 2

1.5 Nail Penetration

The nail penetration test evaluates the safety of the battery by penetrating the steel needle through the sample at a certain speed. The steel needle passes through the battery, damaging the integrity of the electrode and diaphragm, resulting in a short circuit in the battery and continuous heat generation. The severity level of nail penetration test is relatively high, and only three of the standards introduced in this article include this test. According to the difference of the test samples, the test parameters (needle depth, steel needle diameter, needle speed, etc.) of the needle test are quite different. SAEJ2464 200 and GB/T31485-2015 both require the steel needle to remain in the sample for 1h after penetrating the sample, but FreedomCAR does not specify.


1.6 Rollover

The rollover test simulates the rollover and overturn that the vehicle may encounter in an accident, which is also called rotation in some standards (UL2580-2013, SAEJ2929 2013). SAEJ2929 2013 does not separately specify the rollover test item, which is included in the extrusion test item, and the rollover test is required after the extrusion test.


The overturn test of the above five standards can be roughly divided into three categories: SAE J2464 2009, FreedomCAR, and GB/T 31467.3-2015 all require that the sample be rotated at a rate of 360 °/min (6 °/s) for one cycle, and then in 90 ° step increments, each position shall be maintained for 60 min and rotated for one cycle. The difference is that SAEJ2464 2009 and FreedomCAR do not specify the rotation axis, and GB/T31467.3-2015 specifies that the sample needs to rotate in two directions of the x-axis and the v-axis. SAE J2929 2013 requires the sample to rotate 90 ° within 1~3 min, and then keep it for 5 min, and rotate for one cycle. UL 2580 2013 requires the sample to rotate at a speed of 90/15s for one cycle, and it needs to rotate in two or three directions. In particular, it is pointed out that the test is not carried out for liquid-rich lead-acid batteries.


1.7 Drop

The drop test simulates the situation that the power battery accidentally slips from the vehicle or falls from a high place. The test requires the sample to fall freely to the ground from the specified height in a certain direction.


Except FreedomCAR, which requires falling on the cylindrical surface of the cylindrical steel bar, other standards require falling on the concrete ground or hard surface. As for the drop height, SAE J2464 2009, GB/T31485-2015 and GB/T 31467.3-2015 specify a fixed drop height ranging from 1 to 2 m. SAE J2929 2013 and UL 2580 2013 specify that the drop height should be at least 1 m from the most likely drop height. FreedomCAR requires that the drop height should not exceed 10 m. The specific height should be determined according to the reliable abuse conditions during the manufacture, assembly and normal use of the battery. UL2580 2013 stipulates that the sample should be dropped at least once. When it is dropped only once, it cannot be dropped horizontally. The sample should be tilted 10 ° to make the edge contact with the ground; When the number of falls is more than one, there should be at least one non-horizontal fall. The number of falls is not specified in other standards.


2.Environmental Safety


2.1 Thermal Shock Cycle

Thermal shock cycling test has different names in different standards, such as temperature cycling (IEC 62660-2 (3), GB/T 31485-2015), temperature shock (GB/T 31467.3-2015), thermal shock (SAE J2929 2013), thermal cycling (UL 2580 2013). The purpose of this test is to verify the ability of power battery to resist sudden and rapid changes in ambient temperature. It is the most widely used test item. All standards and specifications in this paper include this item. This test requires that the sample be rapidly converted between two extreme temperatures and kept for a certain time, and be cycled for 5 times or more times. It should be noted that the relevant thermal control device or cooling device should be closed before the test. Except IEC 62660-2:2010, which requires a minimum temperature of – 20 ℃ for the test when the sample is working, other standards and specifications require a minimum temperature of – 40 ℃, while the requirements for the maximum temperature are different, ranging from+60 ℃ to+85 ℃.


The temperature conversion time indirectly specifies the temperature change rate. The temperature conversion time of IEC 62660-2 (3) and GB/T 31485-2015 is longer, which is more than 2 h, while the time specified in other standards is less than 30min. The number of cycles is mostly 5 or 30. Generally speaking, there are many cycles with long temperature conversion time, except for GB/T 31485-2015. It should be noted that SAE J2929 2013 refers to UN38.3 and SAE J2464 2009, which stipulate that the parameters of both standards can be selected. UL 2580 2013 quoted the non-working part of SAEJ2464 2009 and IEC 62660-2:2010 samples, and selected the quoted standards according to the sample type.


2.2 Thermal Stability

Thermal stability test is also known as high temperature endurance (IEC 62660-2 (3)) test, heating (UL2580 2013, GB/T 31485-2015) test, which is used to evaluate the stability of battery under high temperature.


There are 6 items in the standard specifications described in this article that include thermal runaway test, which can be divided into 2 categories according to the test process.


The first category is IEC6260-2:2010, IEC 62660-3:2016, UL 2580 2013, GB/T 31485-2015, in which UL2580 2013 directly refers to IEC 62660-2:2010. This category of standards requires that the temperature be directly heated to the specified temperature at the rate of 5 ℃/min, and the heating shall be stopped after 30 min or 120 min;


The second type is SAE J2464 2009 and FreedomCAR, which require heating in steps of 5 ℃ and holding at each temperature for a certain time until the specified temperature is reached or the sample has a serious accident, and then starting from the last temperature step, heating in steps of 2 ℃ and holding at each temperature for at least 1h until the sample has thermal runaway, so as to determine the thermal runaway temperature. The first type of thermal runaway test focuses more on evaluating the stability of the battery under high temperature, while the second type of test focuses more on estimating the thermal runaway temperature of the battery.


2.3 Fire

The fire test evaluates the safety performance of the battery in case of fire by exposing the battery sample to fire or by simulation. The names of these tests are different. In this paper, external fire exposure (GB/T 31467.3-2015), exposure to fire (Iso 12405-3:2014), high temperature hazard (SAE J2464 2009), exposure to simulated vehicle fire (SAE J2929 2013), external fire exposure (UL2580 2013), internal fire exposure (UL 2580 2013) Tests such as projectile (UL2580 2013), fire resistance (ECER100-02 2013) and simulated fuel fire (Freedom CAR) are all classified into one category, which is collectively referred to as fire test.


The test process of ISO 12405-3:2014, ECE R100-02 2013 and GB/T31467.3-2015 is similar. Put the fuel into a flat plate container, ignite and preheat it for 60s, and then put the flat plate under the sample to expose it directly under the flame for 70s. Then cover the flat plate and hold it for 60s to end the test. The test process of SAE J2464 2009 and FreedomCAR is similar. Instead of using an open flame for the test, the sample is put into a cylindrical metal copper, heated to 890 ℃ within 90 seconds, maintained for 10 minutes, or other conditions prevent the test from continuing. SAE J2929 2013 does not specify the test process, but the responsible organization specifies the details, and provides SAE J2464, ECE R34, SAE J2579, KoreanMUSS 18-3, FMVSS 304 and other standards for reference. UL2580 2013  has three fire test items.


For the external combustion test, the sample is heated to 590 ℃ by open flame, and then kept for 20 minutes. The internal combustion test verifies the impact on the whole battery stack after the thermal runaway of the single battery. It can promote the thermal runaway of the single battery in the central position within 10 minutes by heating, acupuncture and other means. Observe the condition of the battery stack. This test is only applicable to lithium ion batteries. The combustion ejection quoted UL 1642-2012, so that the sample was directly exposed to the open fire until it caught fire or exploded.

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