The New Safety Standard for Lithium-Ion Cells and Batteries

Lithium-ion cells and batteries produced in or imported into China are now regulated in accordance with China’s Compulsory Certification (CCC) system. The China State Administration for Market Regulation (SAMR) announced CCC requirement for lithium-ion cells and batteries used in portable electronic equipment through Notice No. 10 issued in 2023.¹ Effective August 1, 2024, all regulated lithium-ion cells and batteries must be CCC-certified for compliance with the requirements set forth in GB 31241.

GB 31241, “Lithium-ion cells and batteries used in portable electronic equipment – Safety technical specification,” was originally issued in 2014 and more recently replaced by the 2022 version, GB 31241-2022.² GB 31241-2022 is not equivalent to any current international standard. However, relevant reference standards include, but are not limited to, IEC 62133-2:2017,³ UN 38.3 (7^th Revision),⁴ and UL 1642:2020.⁵

GB 31241-2022 imposes new and updated requirements on manufacturers of lithium-ion cells and batteries. This article provides a summary of the requirements in GB 31241-2022 and guidance on their application.

Scope

GB 31241-2022 specifies safety technical requirements for lithium-ion cells and batteries used in portable electronic equipment. Examples include:

• Portable office products: notebook computers, tablets, etc.;
• Mobile communications products: mobile phones, cordless telephones, walkie talkies, etc.;
• Portable audio/video products: portable televisions, portable audio/video players, cameras, video recorders, voice recorders, Bluetooth headsets, portable speakers, etc.; and
• Other portable products: electronic navigators, digital picture frames, game consoles, e-books, mobile power supplies, portable energy storage power supplies, portable projectors, wearable equipment, etc.

There may be additional requirements for cells and batteries used in portable electronic products in vehicles, ships, aircraft, etc., and for other devices used in the fields of medical, mining, and undersea operations. However, GB 31241-2022 is not applicable to lithium-ion cells and batteries used in electronic cigarettes.

Terms and Definitions

Terms and definitions specific to this standard and/or not commonly used in the other standards are listed in Table 1. Terms including “nominal voltage,” “nominal energy,” “reference test current,” “end-of-discharge voltage,” “lower limit charging temperature,” “lower limit discharging temperature,” and “allowable maximum surface temperature” are new to the 2022 edition of GB 31241. At the same time, the standard no longer defines or uses the terms “venting,” “rupture,” and “routine test.”

* GB 31241-2022 clause number

Table 1: GB 31241 terms and definitions

Type Tests

Demonstrating compliance with the requirements of GB 31241 includes conducting certain tests listed in Table 2 and Table 3. The general acceptance criteria for each test are that the sample being tested does not generate a fire, explode, or leak as a result of testing.

X: applicable, -: not applicable

Table 2: Type tests for cells and batteries

Table 3: Type tests for batteries with protection circuit (Note: “n” is the number of cells connected in series or blocks of cells connected in parallel in the battery)

Charging, Discharging, and Conditioning Procedures

Prior to testing, cells and batteries are subject to charging, discharging, and/or conditioning, as applicable. The manufacturer-specified charging procedure is preferred. An alternative charging procedure (which is new to this version) is to charge at 0.2 I_t A. When the terminal voltage reaches the limited charging voltage (U_cl), change to constant voltage charging until the charging current is less than or equal to 0.2 I_t A.

A cell or battery is discharged at a constant current of the recommendation discharging current (I_cr) down to the end of discharge voltage (U_de). This discharge procedure is new and replaces the manufacturer-specified procedure.

Cells and batteries are to be conditioned with two charge-discharge cycles. The interval between charge and discharge is 10 minutes. New to the 2022 version of GB 31241 is the introduction of an electrostatic discharge (ESD) test for batteries equipped with protection circuits. In such cases, the ESD test must be conducted after two charge-discharge cycles and being fully charged, using a ± 4 kV contact discharge and ± 8 kV air discharge.

Test Items

Table 2 lists required tests for cells and batteries. The same or similar tests found in 62133-2:2017 and in UN 38.3 (7^th Edition and 8^th Edition) are also included in the table for comparison.

For batteries incorporating a protection circuit, additional test items, as listed in Table 3, apply.

Sample Capacity Test

The sample is fully charged and is then left idle for 10 minutes. Then, the capacity is measured as the sample is being discharged.

Durability

This test applies only to user-replaceable batteries. The test is conducted by rubbing the marking for 15 seconds with a piece of cotton cloth soaked with water, then rubbing the marking for 15 seconds with a piece of cotton cloth soaked with 75% (alcohol by volume) medical use alcohol.

External Short Circuit

A test sample is deliberately short-circuited by connecting the positive and negative terminals 30 minutes after the surface temperature of the test sample reaching 57 °C ± 4 °C (for a cell) or room temperature (for a battery). The total external resistance shall be 80 mΩ ± 20 mΩ.

For cells, the test sample remains on test until the surface temperature declines by 20 % of the maximum temperature rise, or for a period of 24 hours, whichever is sooner. Batteries with the protection circuit removed remain on test for 24 hours, while batteries with a protection circuit remain on test until the protection circuit activates.

Overcharge

A fully discharged cell is charged at a constant current of the maximum charging current (I_cm) until reaching the voltage of U_cl + 0.4 (U_cl < 4.25), 4.65 (4.25 ≤ U_cl <4.35), or U_cl + 0.2 (U_cl ≥ 4.45), then followed by constant voltage charging. (Note that the charging current and voltage in the 2022 version of GB 31241 are different than those specified in the 2014 version.)

During testing, monitor the cell temperature change. Terminate testing after either:

1. The longer period of 7 hours or the charging time declared by the manufacturer, or
2. The cell’s temperature declines by 20 % of the maximum temperature.

When there is a difference between the results of a) and b), those generated during the longer of the two options takes precedence.

Forced Discharge

A fully discharged cell is subjected to a forced-discharge at 1 I_t A to the negative value of the upper limit charging voltage (-U_up). The total duration for the forced discharge testing is 90 minutes.

Low Pressure (Altitude Simulation)

Fully charged cells are placed in a vacuum chamber with an ambient temperature of 20 °C ± 5 °C. The internal pressure of the vacuum chamber is gradually reduced to a pressure equal to 11.6 kPa (simulating an altitude of 15,240 m), and then remains under test for 6 hours.

Temperature Cycling (Thermal Cycling, Thermal Rest)

The fully-charged cells are placed in a programmable test chamber at 20 °C ± 5 °C. The test chamber’s temperature is increased to 72 °C ± 2 °C and maintained at this temperature for 6 hours. Then the test chamber’s temperature is reduced to – 40 °C ± 2 °C and maintained at this temperature for 6 hours. The transition time between different temperatures does not exceed 30 minutes. After repeating this cycle 10 times, the cells are stored for a minimum of 6 hours at a room temperature of 20 °C ± 5 °C.

Vibration

A fully charged test sample is subject to a vibration having a sinusoidal waveform with a logarithmic sweep between 7 Hz and 200 Hz and back to 7 Hz traversed in a 15-minute time span. This cycle is repeated 12 times for a total of three hours for each mounting position of the test sample. Cylindrical and button test samples are vibrated in both their axial and longitudinal directions. Prismatic and pouch samples are vibrated in three mutually-perpendicular directions.

Acceleration Impact (Mechanic Shock, Shock)

The fully charged cells or batteries are secured on the impact table for semi-sinusoidal pulse impact test. Within the first 3 ms, the minimum average acceleration is 75 g_n, the peak acceleration is 150 g_n ± 25 g_n, and the pulse duration is 6 ms ± 1 ms. Each test cell or battery is subjected to three acceleration impact tests in each direction.

Free Fall

Each fully charged cell or battery is dropped from a height of 1.0 m onto a flat concrete floor, except for user-replaceable batteries, which are dropped from a height of 1.5 m. Both terminal sides of the cylindrical and button cells and batteries are dropped once. The cylindrical side is dropped twice. There are four drop tests in total. Each side of the prismatic and pouch cells and batteries are dropped once. There are six drop tests in total.

Crush

Each fully charged cell is crushed, perpendicular to the direction of the flat surfaces, between two flat surfaces. The force for the crushing is applied by a device exerting a force of 13.0 kN ± 0.78 kN at a speed of 0.1 mm/s. Once the maximum force has been applied, or an abrupt voltage drop of one-third of the original voltage has been obtained, the force is released.

A cylindrical cell is crushed with its longitudinal axis parallel to the flat surfaces of the crushing apparatus. A button cell is crushed with its upper and lower sides parallel to the flat surfaces of the crushing apparatus. For prismatic cells (hard shell), pouch cells with a length less than 25 mm, and other types of cells, perform the crush test only on the wide surface of the cell.

For pouch cells with a length not less than 25 mm, place a steel semi-cylinder with a diameter of 25 mm on the wide surface of the cell for crushing. The longitudinal axis of the semi-cylinder body passes through the geometric center of the wide surface and is perpendicular to the direction of the electrode tab. The length must be greater than the size of the crushed cell. Release the force once the crush force reaches the force listed in Table 10 of the standard. This test procedure is new to this version.

Heavy Object Impact

A fully charged cell is placed on the surface of the platform. A metal bar of 15.8 mm ± 0.2 mm in diameter is placed horizontally on the upper surface of the geometric center of the cell. A weight with a mass of 9.1 kg ± 0.1 kg falls freely from a height of 610 mm ± 25 mm on to the cell. Each cell is to be subjected to only one single impact. This test does not apply to pouch cells. This is the same test as the impact test found in Clause 14 of UL 1642 5^th Edition.

Thermal Abuse (Heating)

A fully charged cell is placed in a test chamber. The chamber’s temperature is raised at a rate of 5 °C/min ± 2 °C/min to a temperature of 130 °C ± 2 °C. The cell remains at this temperature for 30 min before the test is terminated.

Projectile (Combustion Jet)

A fully charged cell is placed on a steel wire screen of a test apparatus shown in Figure C.2 of the standard, which is equivalent to Figure 20.1 of UL 1642 5^th Edition. If the cell falls off the screen during test, a single metal wire can be used to secure the cell to the screen. A cell is heated and remains on the screen until it explodes, has completed burned out, or is heated for 30 minutes without explosion or catching fire.

Stress Relief (Case Stress at High Ambient Temperature)

The thermoplastic materials used in the molded or injection-molded enclosure or structure must not result in shrinkage or deformation that affects the safety of the cell when the internal stress generated by molding or injection molding is released. The fully charged battery is placed in an air circulating oven at a temperature of 70 °C ± 2 °C for 7 hours. The battery is then removed and allowed to return to room temperature.

High Temperature Use

Batteries shall be sufficiently safe when used under high temperature conditions. To ensure compliance with this requirement, a fully charged battery is placed in a high temperature test chamber with the temperature set to the maximum value of:

• The manufacturer-specified upper limit charging temperature and upper limit discharging temperature of the battery;
• The manufacturer-specified upper limit charging temperature and upper limit discharging temperature of the cell; or
• 80 °C.

After the surface temperature of the sample stabilizes, the battery remains under these test conditions for 7 hours.

Washing

This test applies to hand-held and pocket-sized portable electronic equipment containing lithium-ion batteries. The test apparatus for the washing test is shown in Figure C.3 of the standard. The washing solution has a pH value of 11.0 ± 0.1 (a NaOH solution with a mass fraction of 0.004 % can be used) and is maintained at a temperature of 45° C ± 2° C during the test.

The test is performed by the following steps: solution preparation, immersion, stirring, dehydration, and drying. If the sample can be charged and discharged following the washing, continue one discharge-charge cycle, and then end the test. If the sample cannot continue to charge and discharge, then end the test.

Overvoltage charging

A fully-charged battery is continuously charged at the constant current of the maximum charging current (I_cm) to the specified test voltage or the maximum bearable voltage (whichever is higher) and is then maintained at that voltage for constant-voltage charging. The specified test voltage is 6 V (when n =1) or (n × 6.0) V (when n ≥ 2), with n representing the number of cells connected in series or blocks of cells connected in parallel in the battery.

For batteries with the protection circuit removed, charge for 1 hour or (C/ I_cm) hour, whichever is longer. For battery with protection circuit retained, charge until the protection circuit activates.

Overcurrent Charging

A fully discharged battery is charged at a constant current of 1.5 times the overcurrent charging protection current (1.5 I_cp). For batteries with the protection circuit removed, charge to the upper limited charging voltage U_up. For batteries with the protection circuit retained, charge until the protection circuit activates.

Undervoltage Discharging

A fully charged battery is discharged at the constant current of the maximum discharging current (I_dm). For batteries with the protection circuit removed, discharge to (n x 0.15) V, with n representing the number of cells connected in series or blocks of cells connected in parallel in the battery. For batteries with the protection circuit retained, discharge until the protection circuit activates.

Overcurrent Discharging

A fully charged battery is discharged at the constant current of 1.5 times the overcurrent discharging protection current (1.5 I_dp). For batteries with the protection circuit removed, discharge to the end-of discharge voltage. For batteries with the protection circuit retained, discharge until the protection circuit activates.

Reverse Charging

A fully charged battery is reverse charged to the negative upper limited charging voltage (-U_up) at the recommendation charging current I_cr. For batteries with the protection circuit removed, charge for 90 minutes. For batteries with the protection circuit retained, discharge until the protection circuit activates.

Labeling Requirements

For lithium-ion cells and batteries, the following information, in Chinese, must appear on the product:

• Product name, model;
• Rated capacity, nominal energy, limited charging voltage, nominal voltage;
• Positive and negative polarities;
• Factory of manufacture; and
• Date of manufacture or batch number.

For CCC-regulated cells and batteries, the CCC mark shall be applied to the product. CCC mark requirements are stipulated in Attachment 2 of CNCA 2023 Notice No. 12.⁶

Warning Instructions

Warning instructions in Chinese shall be placed on the batteries or on the smallest package. For user-replaceable batteries that can be placed in an ingestion gauge, warning instructions in Chinese shall also be provided on their smallest package.

Conclusion

GB 31241-2022 introduces important new and updated requirements. Compliance with this standard is mandatory for cells and batteries used in portable electronic equipment.

Acknowledgment

The author wishes to express her sincere appreciation to Wayne Owens, Certification Manager at HYTORC, for his mentorship and support.

References

1. SAMR 2023 Notice No. 10, “Announcement of the State Administration for Market Regulation on the Implementation of Compulsory Product Certification Management for Lithium-Ion cells and Other Products.”
2. GB 31241-2022, “Lithium-ion cells and batteries used in portable electronic equipment – Safety technical specifications,” December 29, 2022.
3. IEC 62133-2:2017 Edition 1.0, “Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications – Part 2: Lithium system,” February 7, 2017.
4. UN 38.3, “Manual of Tests and Criteria,” Seventh revised edition, United Nations, 2019.
5. UL 1642, “Standard for Safety Lithium Batteries,” Sixth Edition, September 29, 2020.
6. CNCA 2023 Notice No. 12, “Announcement of the National Certification and Accreditation Administration on Improving the Management of Compulsory Product Certification Certificates and Marks,” August 10, 2023.