Help Ensure the Integrity and Safety of EV Battery Systems

Revision 3 of UNECE Regulation No. 100 (R100) imposes a number of new and updated requirements on manufacturers of rechargeable electrical energy storage systems (REESS) designed for use in motor vehicles manufactured, sold, or operated in the European Union and other countries.

R100 now includes a new overcurrent test and adjusted requirements on the system-on-chip (SOC) level, as well as new requirements relating to thermal propagation. All of these are intended to ensure the integrity and safe operation of such systems under anticipated operating conditions, as well as to provide a higher level of safety for vehicle drivers and passengers.

Although these updated requirements will increase the compliance burden for battery manufacturers, they will also ease the acceptance and use of battery packs with type approval, thereby broadening the market for manufacturers. In this article, we’ll provide a summary of the requirements and the benefits likely to accrue to battery manufacturers.

World Forum for the Harmonization of Vehicles

The creation of global standards for motor vehicles, including electric vehicles and REESS, falls under the purview of the World Forum for the Harmonization of Vehicles. Originally formed in 1952, the Forum is today a permanent working party (WP 29) operating under the auspices of the Transport Division of the United Nations Economic Commission for Europe (UNECE). The primary objective of the Forum is to establish globally harmonized regulations for motor vehicles in order to remove barriers to international trade, promote road safety, and protect the environment.

The work of the Forum has its legal basis in the so-called 1958 Agreement, formally known as the “Agreement concerning the adoption of uniform technical prescriptions for wheeled vehicles, equipment and parts which can be fitted and/or be used on wheeled vehicles and the conditions for reciprocal recognition of approvals granted on the basis of these prescriptions.” Under the terms of the Agreement, signatory countries agree to a mutual recognition of type approvals. This means that they comply with a common set of technical specifications and requirements in connection with motor vehicles produced within their respective countries and allow for the importation, sale, and use of motor vehicles from other countries that meet these specifications.

Initially, the agreement was only open to ECE member countries. But, in 1995, the agreement was revised to allow the participation of non-ECE members. At present, 64 countries worldwide are signatories to the 1958 Agreement, but two major vehicle markets, the U.S. and China, have not signed the agreement.

Specific technical requirements for motor vehicles are documented in approximately 130 separate UN Regulations (formerly known as “UNECE Regulations” or “ECE Regulations”). Individual regulations address topics as diverse as vehicle components like lighting and instrumentation, and operational characteristics including crashworthiness and environmental compatibility.

To demonstrate compliance with UN Regulations, manufacturers must submit vehicle products and components to an authorized third party (“Technical Service”) for type approval evaluation. Reports of these evaluations are then submitted by the Technical Service to the type-approval authority in the signatory country, which then issues the actual type approval certificates and authorizes manufacturers to apply the E-mark to their products. Type approvals issued in one signatory country are deemed legally equivalent to those issued in other signatory countries. Accordingly, vehicles and components that have received type approval in one signatory country must be accepted for importation, sale or use in all other signatory countries.

As the U.S. is not a signatory to the Forum’s 1958 Agreement and does not recognize UN Regulation-type approvals, manufacturers seeking to sell motor vehicles in the U.S. must meet that country’s Federal Motor Vehicle Safety Standards (FMVSSs) that address the design, construction, performance, and durability of motor vehicles and motor vehicle components. However, unlike type approval requirements in Forum signatory countries, compliance with U.S. motor vehicle safety standards is demonstrated by a manufacturer’s self-certification, and independent verification is not required prior to vehicle sale, importation, or use.

The CCC Mark (China Compulsory Certificate) is a mandatory requirement for both domestically manufactured products and products imported into China. Automotive products that require the CCC Mark include many whole, completed, or incomplete vehicles that fall in the L, M, and N categories, as well as motorcycles in the O category and vehicle parts (e.g., seat belts, tires, safety glass products, and headlamps). The CCC certification procedure involves the testing of the product itself, as well as a factory inspection and the creation of documentation.

UNECE Regulation No. 100

UNECE Regulation No. 100 is officially titled “Uniform provisions concerning the approval of vehicles with regard to specific requirements for the electric power train.” Also referred to as R100, the Regulation addresses the safety requirements specific to the electric power train of road vehicles, as well as those high-voltage components and systems that are “galvanically connected” to the high-voltage bus of the electric power train.

R100 was originally published in 1996 under the terms of the Forum’s 1958 Agreement. Revision 1 of the Regulation was issued in March 2011 to ensure that the Regulation kept pace with new automotive technologies, with minor amendments issued in 2012 and 2013. However, since its inception, applications for type approval under R100 have been limited exclusively to entire motor vehicle assemblies. Evaluations of the safety and performance of vehicle components, such as drive trains and battery packs, were conducted as part of a total vehicle assessment, and limited in scope and depth.

Because R100 type approvals covered an entire vehicle, vehicle manufacturers seeking type approval were subject to a complex and time-consuming testing and evaluation process. More problematic, the “whole vehicle” approach to type approval meant that vehicle manufacturers were unable to change individual systems or components or to substitute components from one sub-manufacturer with those from another since any changes to the originally approved design would require a new type approval application for the complete high voltage electrical powertrain.

The publication of the second revision of R100 in 2013 introduced significant changes in the overall type approval process applicable to REESS, including electric vehicle batteries, and became mandatory in July 2016. For the first time, the Regulation provided a separate approval path for REESS and rechargeable battery packs, along with an expanded set of specific tests exclusively applicable to these systems.

Revision 3 came into force in June 2021 and is thus applicable to type approval. The transition period between Revision 2 and 3 is currently in effect, with the application of Revision 3 being obligatory from September 2023 for new type approvals and from September 2025 for all type approvals. Annex 9 of Revision 3 defines the specific test standards for type approval of traction batteries for all types of electric vehicles (EVs), including hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs).

Safety Requirements

R100 contains two parts. Part I covers safety requirements of a vehicle for the electric power train, such as protections against electrical shock. This includes protection against electrical shock, requirements applicable to the REESS, and preventing unintended vehicle movement. Protection against electrical shock includes protection against direct contact, protection against indirect contact, and requirements on insulation resistance.

Additional requirements regarding protection against water effects have been introduced in Revision 3. The Revision states that the vehicle shall maintain isolation resistance after exposure to water. The vehicle needs to comply with requirements regarding an insolation resistance warning system. Otherwise, compliance of isolation resistance of the electrical design of the vehicle after water exposure or protection against water effects must be proven. Requirements applicable to the REESS include accumulation of gas, warning in the event of failure, warning in the event of low energy content, and compliance with Part II of this Regulation.

Part II covers requirements of the REESS with regards to its safety. This includes proof of design and the requirements for component testing before installation in the vehicle. Revision 3 introduces a new mandatory battery test procedure addressing overcurrent protection, which increases the number of mandatory tests from nine to ten. All mandatory test procedures are described in Annex 9 of this Regulation (9A Vibration Test, 9B Thermal shock and cycling, 9C Mechanical shock, 9D Mechanical integrity, 9E Fire resistance, 9F External short circuit protection, 9G Overcharge protection, 9H Over‑discharge protection, 9I Over-temperature protection and 9J Over-current protection).

Additional requirements regarding low-temperature protection, warning in the event of operational failure, and warning in the case of thermal event and thermal propagation have also been introduced in Revision 3.

REESS

The essential requirements regarding the REESS in Revision 3 of R100 can be found in Section 6 of the Regulation. Annex 9 provides detailed information on the specific testing procedures applicable to the REESS identified in Section 6 of the Regulation. As specified in this Annex, R100-required assessments for the REESS include the following tests:

• Vibration—The vibration test is intended to verify the safety performance of the REESS under vibration conditions similar to those likely to be experienced during normal vehicle operations. The REESS under test is subject to a vibration having a sinusoidal waveform with a logarithmic sweep between 7 Hz and 50 Hz and back to 7 Hz in the span of 15 minutes. This sweep is repeated 12 times for a total test period of three hours. At the completion of the vibration testing, the REESS is subject to a standard discharge followed by a standard charge and then observed for one hour. New requirements in Revision 3 include a fully charged battery before the start of testing and the added acceptance criteria “no venting.”
• Thermal Shock and Cycling—The thermal shock and cycling test is intended to verify the resistance of the REESS to sudden changes in temperature likely to be experienced during its life. The REESS is first stored for at least six hours at a test temperature of 60°C, followed by six hours of storage at -40°C. The maximum time interval between test temperature extremes shall be 30 minutes. This cycle is repeated five times, followed by a storage period at ambient temperatures for 24 hours. At the completion of the thermal shock and cycling test, the REESS is subject to a standard discharge followed by a standard charge and then observed for one hour. New requirements in Revision 3 are a fully charged battery before the start of testing and the added acceptance criterion of “no venting.”
• Mechanical Shock—The purpose of the mechanical test is to verify the safety performance of the REESS under inertial loads that may occur in vehicle crash conditions. The REESS is accelerated or decelerated at speeds specified in the tables accompanying the Regulation, and the actual gravitational force is compared with the values specified in the tables. Upon the completion of the mechanical shock test, the REESS is observed for one hour. A new requirement in Revision 3 is a fully charged battery before the start of testing.
• Mechanical Integrity—The mechanical integrity test is intended to verify the safety performance of the REESS under the kinds of contact loads that might be experienced in vehicle crash conditions. The REESS is crushed between a resistance plate and a crush plate with a force of at least 100 kN with an onset time of less than three minutes and a hold time of between 100 milliseconds and 10 seconds. At the completion of the mechanical integrity test, the REESS is observed for one hour. A new requirement in Revision 3 is a fully charged battery before the start of testing.
• Fire Resistance—The purpose of the fire resistance test is to verify the resistance of the REESS to exposure from a fire originating outside of a vehicle in order to provide a driver and passengers with sufficient escape time. The REESS is subject to both direct and indirect exposure to a flame that has been produced by burning commercial fuel or LPG gas. At the completion of the fire resistance test, the REESS is observed for a period of three hours, or until it has cooled to ambient temperature, whichever is less. Revision 3 introduces the LPG burner test for the first time. It is now possible to choose between the test methods with gasoline or LPG as a fire source. The new LPG method requires additional measurement of the flame temperature and does not include an indirect exposure period to the flames. Instead, the direct exposure time is increased to two minutes.
• External Short Circuit Protection—The external short circuit protection test is intended to verify the performance of the short circuit protection system that limits the consequences associated with short circuits. The REESS is subject to an intentional short circuit by connecting the positive and negative terminals, using a connection with resistance of not more than 5 mΩ. The short circuit condition is continued until the function of the short circuit protection can be confirmed or for at least one hour after the temperature measured on the REESS casing has stabilized. At the completion of the external short circuit protection test, the REESS is subject to a standard discharge followed by a standard charge, if not inhibited, and then observed for one hour. New requirements in Revision 3 are a fully charged battery before the start of testing and the added acceptance criterion of “no venting.”
• Overcharge Protection—The purpose of the overcharge protection test is to verify the performance of the overcharge protection system. When conducting the overcharge protection test, the REESS is charged until it automatically interrupts or limits the charging or until it is charged to twice its rated capacity. At the completion of the overcharge protection test, the REESS is subject to a standard discharge followed by a standard charge, if not inhibited, and then observed for one hour. The new requirement in Revision 3 is the added acceptance criterion of “no venting.”
• Over-Discharge Protection—The over-discharge protection test is intended to verify the performance of the over-discharge protection system. During the over-discharge protection test, the REESS is discharged until it interrupts or limits the discharge or when it is discharged to 25% of its nominal voltage level. At the completion of the over-discharge protection test, the REESS is subject to a standard discharge followed by a standard charge, if not inhibited, and then observed for one hour. The new requirement in Revision 3 is the added acceptance criterion of “no venting.”
• Over-Temperature Protection—The purpose of the over-temperature protection test is to verify the resistance of the REESS against internal overheating during operation, even when the REESS’s cooling function fails. When conducting the over-temperature protection test, the REESS is first repeatedly charged and discharged with a steady current so as to increase the temperature of cells as rapidly as possible. The REESS is then placed in a convection oven or climatic chamber, and the temperature of the oven or chamber is gradually increased to a pre-determined level. The test is concluded when the REESS inhibits and/or limits the charge and or discharge to prevent the temperature increase or when the temperature is stabilized. The new requirement in Revision 3 is the added acceptance criterion of “no venting.”
• Over Current Protection—This is an entirely new test procedure introduced by Revision 3. Its purpose is to verify the performance of the overcurrent protection system during external charging of REESS. During the test, the battery is charged with the maximum charging current, with the charging current increased over five seconds from the highest normal charge current to the overcurrent level. Charging is then continued at this overcurrent level. Charging is terminated when the overcurrent protection of the battery terminates the charging current, or the battery temperature is stabilized over two hours. Immediately after the termination of charging, the REESS is subject to a standard discharge followed by a standard charge, if not inhibited, and then observed for one hour.

It is important to note that testing values that differ from those presented in Annex 9 of the Regulation may be applied in coordination with the Technical Service, depending on the requirements or preferences of the manufacturer of an REESS or the vehicle.

Revision 3 of R100 also includes a new requirement regarding thermal propagation. This refers to the sequential occurrence of thermal runaway within a REESS, triggered by thermal runaway of a cell in that REESS. This means that either 1) vehicle occupants shall not be exposed to any hazardous environment caused by thermal propagation triggered by an internal REESS, or 2) the vehicle system is required to provide a signal to activate the advance warning system five minutes prior to the presence of a hazardous situation inside the vehicle to provide sufficient time for passengers to escape. Furthermore, the REESS or vehicle system shall have functions or characteristics in the cell or REESS that are intended to protect vehicle occupants.

While this requirement doesn’t come with a mandatory test, real-case scenarios have shown that proving compliance without additional practical testing is very difficult. Consent between technical services, manufacturers, and official authorities to conduct additional thermal propagation testing will ensure compliance with this important new requirement.

Conclusion

Revision 3 of R100 introduces some important new and modified requirements for manufacturers of REESS and rechargeable batteries for electric vehicles. It also maintains the type approval scheme introduced by Revision 2, a change that is likely to continue increasing competition in the REESS marketplace.