ISO 6469-1:2019/Amd 1:2022
(Amendment)Electrically propelled road vehicles — Safety specifications — Part 1: Rechargeable energy storage system (RESS) — Amendment 1: Safety management of thermal propagation
Electrically propelled road vehicles — Safety specifications — Part 1: Rechargeable energy storage system (RESS) — Amendment 1: Safety management of thermal propagation
Véhicules routiers électriques — Spécifications de sécurité — Partie 1: Système de stockage d'énergie rechargeable (RESS) — Amendement 1: Management de la sécurité de la propagation thermique
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 6469-1
Third edition
2019-04
AMENDMENT 1
2022-11
Electrically propelled road vehicles —
Safety specifications —
Part 1:
Rechargeable energy storage system
(RESS)
AMENDMENT 1: Safety management of
thermal propagation
Véhicules routiers électriques — Spécifications de sécurité —
Partie 1: Système de stockage d'énergie rechargeable (RESS)
AMENDEMENT 1: Management de la sécurité de la propagation
thermique
Reference number
ISO 6469-1:2019/Amd.1:2022(E)
ISO 6469-1:2019/Amd.1:2022(E)
© ISO 2022
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ii
ISO 6469-1:2019/Amd.1:2022(E)
Foreword
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electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
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on the ISO list of patent declarations received (see www.iso.org/patents).
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 37,
Electrically propelled vehicles.
A list of all parts in the ISO 6469 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iii
ISO 6469-1:2019/Amd.1:2022(E)
Electrically propelled road vehicles — Safety
specifications —
Part 1:
Rechargeable energy storage system (RESS)
AMENDMENT 1: Safety management of thermal propagation
Introduction
Insert a new clause “Introduction” as follows:
With the rapid development of the electric vehicle industry, its core component, the rechargeable
energy storage system (RESS), has increasingly attracted attention, especially the safety
requirements of RESS have raised a large interest within the public. This document specifies the
general safety requirements for the RESS of electrically propelled road vehicles.
This document also focuses on the safety performance of the lithium-ion battery. One central safety
issue for lithium-ion battery systems is the potential for propagation of a thermal runaway event
due to a cell thermal failure. For this purpose, this document provides methods for testing thermal
runaway risk mitigation to support the development of vehicle and system safety concepts.
The document primarily provides a tool kit for vehicle and RESS manufacturers to evaluate their
product safety in terms of thermal propagation. It should enable RESS and/or vehicle manufacturers
to get a deeper knowledge of the system behaviour in case of an internal failure of a single cell.
Combined tests on cell and system level based on this document will provide comparable results
about the RESS safety.
Since it does not contain neither pass or fail criteria for thermal propagation, it is not foreseen to be
used for homologation purposes.
Scope
Add the following paragraph after the first paragraph.
Specifically, for lithium-ion based RESS, this document specifies demonstration methods for
thermal runaway risk mitigation in case of a cell failure leading to an internal short circuit,
including the collection of associated data. It also specifies a selection of different test methods for
thermal propagation. The selected tests can be carried out at vehicle level or for RESS and RESS
subsystem if appropriate.
Terms and definitions
Add the following additional terminological entries in Clause 3:
3.31
functional unit
entity of hardware or software, or both, capable of accomplishing a specified purpose
[SOURCE: ISO/IEC 2382:2015, 2121310, modified — Notes to entry were removed.]
ISO 6469-1:2019/Amd.1:2022(E)
3.32
internal short circuit
isolation failure inside a cell
Note 1 to entry: Formation of internal short circuits in a single cell may have different causes. The severity of
the internal short circuit depends on the nature of the short and what parts of the cell that are involved. Some
examples of potential causes of internal short circuit to consider are listed below:
— manufacturing defect involving foreign object debris (i.e. particles deposited on the electrode surfaces
during cell manufacturing);
— manufacturing defect due to misalignment of electrode active material and separator;
— separator pinholes and creasing;
— separator shrinkage;
— electronically conductive burrs;
— current collector insulation flaws;
— lithium metal deposition at charging due to intercalation limitations;
— copper corrosion and formation of copper dendrites during cell operation;
— mechanical deformation of the cell, e.g. denting of the cell packaging during manufacture or deformation of
the electrode coil or stack resulting from cycling.
3.33
operational design domain
specific operating domain(s) in which the RESS (3.22) is designed to operate, including but not limited
to voltage/SOC (3.26) range, current range, temperature range, environmental conditions, and other
domain constraints
3.34
safety case for thermal propagation of the RESS
argument that the safety requirements for the RESS (3.22) are complete and satisfied by evidence
compiled from the work product of the safety activities during development
Note 1 to entry: Safety case for thermal propagation (3.37) of the RESS means in this document that a logical
and hierarchical set of work products that describe risks in terms of hazards presented by the RESS in case
of an internal short circuit (3.32) and the subsequent thermal energy release within the RESS, and which sets
expectations and guidance for future performance, if hazards are controlled successfully.
3.35
target cell
cell in which thermal runaway (3.38) is initiated
3.36
thermal event
condition (event which occurs) when the temperature within RESS (3.22) rises significantly or is higher
than the maximum operating temperature (3.17) as defined by the supplier (3.27) or customer (3.6)
Note 1 to entry: Depending on the situation (e.g. amount of heat generation compared to heat dissipation) a
thermal event may or may not lead to a thermal runaway (3.38).
3.37
thermal propagation
transfer of thermal energy generated from thermal runaway (3.38) of a single cell to adjacent cells, which
results in the thermal runaway of other cells in a RESS (3.22) or any assembly of RESS components
ISO 6469-1:2019/Amd.1:2022(E)
3.38
thermal runaway
heat generation caused by uncontrolled exothermic reactions inside the cell
Clause 5
Add a new subclause after 5.6 as follows:
5.7 Thermal propagation requirements
5.7.1 General
Thermal propagation requirements apply only to a lithium-ion RESS or RESS subsystem used for the
propulsion of electric vehicles. Internal short circuit is a condition that can cause thermal runaway in
a cell with subsequent thermal propagation in a RESS or RESS subsystem and which is not considered
in other standards. Internal short circuit can be caused by contamination through the manufacturing
process, by several events during operation and by aging (see 3.32).
The variety of lithium-ion technologies and the different cell construction types do not allow the
definition of one single test method that covers all conditions in a safe, comparable, and reproducible
way. This document provides three approaches to evaluate safety performance against thermal
propagation for a RESS or RESS subsystem.
5.7.2 Safety performance of RESS
Safety performance of a RESS or RESS sub-system shall be considered by one of the following
approaches:
1) demonstrating system robustness against a thermal failure of one cell to limit or withstand
propagation effects by choosing test methods as specified in 6.7;
2) employing appropriate detection systems to identify early markers indicating a latent fault in a cell
and demonstrate risk mitigation by the system safety approach detailed in Clause 7.
Clause 6
Add the following subclauses after 6.6 as follows:
6.7 Thermal propagation test
6.7.1 General
This subclause provides test methods to demonstrate the behaviour of a RESS or RESS subsystem in
case of internal short circuit or thermal runaway caused by failure of a single cell. It also provides the
test methods to generate measurement data which can be used to evaluate the safety performance of
a RESS or RESS subsystem. The test method should be selected according to the intended test purpose
and the possibilities for implementing the trigger method. Installation of a second trigger source may
be performed by the test agency but is not required. A guidance for method selection based on cell type
and test cases is given in Table 9.
ISO 6469-1:2019/Amd.1:2022(E)
Table 9 — Guidance for method selection
Trigger Applicable cell Application at Application at Application at Remarks
method type (limita- RESS subsys- RESS level vehicle level
tions provided tem level
in relevant
clauses)
Internal Any cell type Yes Yes Yes Cell manufacture is the only
heater one to be able to introduce the
internal heater inside the cell
before electrolyte filling.
Localized Any cell type Yes Yes Yes Heating element parameter
rapid exter- may vary depending on differ-
nal heating ent battery chemistries or cell
type choices
Nail pene- Any cell type Yes Yes Yes This trigger method cannot
tration be applied to any position in a
RESS or RESS subsystem. Can
only be applied to the cells
located in the outer perimeter
of the pack.
NOTE 1 All trigger methods have intrinsic limitations and are state-of-the-art. Additional trigger methods can
be developed as appropriate.
NOTE 2 These test methods are developed for lithium-ion RESS and vehicles using such RESS but are also
applicable to other battery chemistries and future electric vehicle energy storage technologies and lithium-
ion technology for other applications/industries. Using these methods outside of existing lithium-ion battery
chemistries or manufacturing methods for electric vehicles, requires further validation to determine the
suitability of the method is necessary.
If not otherwise specified, the tests described apply to the RESS or RESS subsystem referred to as
device under test (DUT) in the following text. All methods utilize the initiation of thermal runaway in a
target cell.
6.7.2 Target cell selection
For target cell selection, the number of adjacent cells, cell packaging, and the distance between cells
in proximity to the potential target cell shall be considered. Installation of a trigger for the chosen
target cell shall not impede the functionality of the original cell or RESS design and its safety features,
such as venting, cooling, battery management system, gas permeability, spacing between cells or other
components and thermal barriers.
In the field, a single cell thermal runaway may occur in any cell location within the RESS. For externally
applied triggers, force may be required to maintain the method in proximity to the target cell and this
may dictate the choice of the target cell. Target cell selection should follow a worst-case scenario in
terms of thermal propagation.
Examples of conditions to consider are:
— thermal couplings to other cells and to RESS cooling mechanisms;
— thermal insulation around cells;
— geometrical aspect of electrical configuration, e.g. series or parallel connections;
— venting paths inside the RESS;
— configuration of battery management sensors and sampling rate.
ISO 6469-1:2019/Amd.1:2022(E)
Determination of the worst-case scenario may require preliminary tests, calculations or analysis,
considering RESS or RESS subsystem design, cell capacity/chemistry/designs, or cooling system.
The selection of a single cell within the DUT depends on the chosen trigger method and the RESS design
and shall be agreed between the customer and supplier.
If the intended application scenario is deemed not to have been covered by the tests, then repeating
the test procedure with cells in different locations that represent the likely thermal environments and
relationships within the RESS may be considered.
NOTE Placing the chosen trigger between battery cells using the existing RESS construction is sufficient but
placing the trigger on an edge cell requires additional support structure and forces to maintain adequate contact
between the target cell and trigger.
6.7.3 Test conditions
The test is conducted in either a suitable indoor or an outdoor environment. In case of outdoor testing
there shall be no precipitation for the duration of the test. Immediately prior to the test commencing,
wind speed shall be measured at a location which is no more than 5 m from the DUT and the average
wind speed over 10 min shall be less than 28 km/h. It shall be ensured that the results are not affected
by gusts of wind. Gusts shall not exceed 36 km/h when measured over a period of 20 s. Test set up
should consider the impact of features such as shielding screens or walls which may create excessive
funnelling affects during test execution.
The test should be carried out under the conditions as described in 6.1 with the following exceptions:
— charge the DUT to maximum permissible SOC from the battery management system, or a specific
value of SOC as agreed between the customer and supplier;
— maintain the RESS temperature between 18 °C to maximum permissible operating temperature;
— maintain a humidity between 10 % and 90 %;
— maintain the atmospheric pressure between 86 kPa – 106 kPa.
For test procedure on vehicle or RESS level, necessary function of the thermal management, battery
management and any other battery control systems, shall be operational during the test. For guidance
for thermal cooling power estimation see Annex E.
In addition to those presented previously in this subclause, the following conditions should be met for
this method:
— to ensure that the DUT is tested at the appropriate SOC according to this subclause, preconditioning
of the DUT should be performed as follows
— discharge the DUT at a constant current of 0,2 It A, down to the specified final voltage
— charge the DUT to test SOC according to the method specified by the manufacturer.
NOTE 1 Charging and discharging currents for the tests are based on the value of the rated capacity (Cn Ah).
These currents are expressed as a multiple of It A, where: It A = Cn Ah/1 h (see IEC 61434).
NOTE 2 The RESS which cannot be discharged at a constant current of 0,2 It A can be discharged at the current
specified by manufacturer.
6.7.4 Evidence criteria of thermal runaway occurrence in target cell
6.7.4.1 Evidence criteria of thermal runaway occurrence in the target cell and other cells
ISO 6469-1:2019/Amd.1:2022(E)
For battery cells with an energy density of less than 130 Wh/kg, evidence of occurrence for thermal
runaway during propagation test is provided if one of the following sets of criteria is met and last more
than 3 s:
— temperature rise dT/dt >1 K/s and temperature exceeding the thermal runaway onset temperature
determined by the cell manufacturer;
or
— temperature exceeding the thermal runaway onset temperature determined by the cell manufacturer
with a rapid and distinct voltage drop;
or
— temperature exceeding the thermal runaway onset temperature determined by the cell manufacturer
with venting gas or smoke release at least one post disassembly analysis criteria in 6.7.4.2;
or
— temperature rise dT/dt > 1 K/s and venting gas or smoke release and rapid and distinct voltage
drop.
For battery cells with an energy density equal to or greater than 130 Wh/kg, evidence of occurrence for
thermal runaway during propagation test is provided if one of the following sets of criteria is met and
last more than 0,5 s:
— temperature rise dT/dt >15 K/s and temperature exceeding the thermal runaway onset temperature
determined by the cell manufacturer;
or
— temperature exceeding the thermal runaway onset temperature determined by the cell manufacturer
with a rapid and distinct voltage drop;
or
— temperature exceeding the thermal runaway onset temperature determined by the cell manufacturer
with venting gas or smoke and at least one post disassembly analysis criteria in 6.7.4.2;
or
— temperature rise dT/dt > 15 K/s with venting gas or smoke release and a rapid and distinct voltage
drop.
NOTE The energy density of a cell is calculated according to IEC 62660-1:2018, 7.6.3.1.
Rapidly changing technologies will require adjustment of the above given parameters, because the
parameter 130 Wh/kg to distinguish large or small energy densities of cells has been determined from
existing data.
6.7.4.2 Post-test disassembly analysis observations
The following indicators can be considered as supportive evidence of occurrence for thermal runaway:
— occurrence of ejected solid material;
— failure of the BMS or signal faults (if the BMS is still active). Logged faults in the BMS shall be
analysed. Thermal runaway indicators shall be specified and documented if required.
ISO 6469-1:2019/Amd.1:2022(E)
The following indicators are post-analysis criteria as evidence of whether a thermal runaway has
occurred in the target cell and whether this has resulted in thermal propagation in the RESS or RESS
subsystem:
— mass loss greater than its electrolyte mass of the initiated cell;
— RESS or cell rupture;
— RESS deformation;
— material formation indicating high temperatures (e.g. molten and re-solidified aluminium or
copper);
— specific reaction products such as e.g. metallic nickel or cobalt, lithium-aluminium oxide;
— current collector foil absence (partial or total);
— thermal decomposition of polymer materials, e.g. separator, isolation material.
6.7.5 Data recording and measurement
6.7.5.1 General advice
Unless otherwise specified in the test methods, the information, documents and data as listed in 6.7.5
shall be provided. Measurement accuracy mentioned in this document shall apply.
6.7.5.2 Recorded data and measurements
The following information shall be recorded during the test, during the observation period and shall be
presented in the test report.
All data measurement systems shall be referenced to the same starting time and shall be recorded for
an observation period of at least 1 h.
At the RESS and RESS subsystem level the following information shall be recorded:
— identification of test method, chosen trigger method and description of test setup used;
— test conditions (e.g. ambient temperature, SOC, other pre-conditioning parameters);
— battery management system live-data, if available (e.g. single cell voltages, temperatures, isolation
faults, other warnings) recorded at a rate that matches the systems’ maximum output rate;
— temperature of the target cell [°C];
— temperature of one adjacent cell (if possible);
— independent measurement of DUT voltage as a function of time and if possible, include the BMS pack
voltage for comparison;
— voltage of the target cell (if possible);
— video and audio recording including indication of a time stamp of any observable system state
change during test (such as defined in 6.7.5.3);
— condition of DUT at the end of test supported by photographs (before and after test) or video;
— temperature of vented gas [°C] exiting the RESS;
— attach thermocouples, not only on the initiation module, but also on the surfaces of adjacent modules,
if possible, to observe thermal propagation between modules;
ISO 6469-1:2019/Amd.1:2022(E)
— additional temperature measurement with distributed sensors at the battery surface and at the
venting port (if applicable);
— at the end of the test measure the isolation resistance on RESS or RESS subsystem level.
At the vehicle level, the information recorded shall be the same as the RESS level in addition to:
— warning indications or alarms to vehicle occupants.
The following data may be provided as additional information:
— infrared temperature video,
— weight loss of target cell,
— multi-gas measurement inside the vehicle for relevant flammable and toxic gases e.g. CO, H , CH and
2 4
VOCs levels by agreement between customer and supplier. In that case, the measurement method
and result shall be reported.
NOTE It is possible to stop the test before the observation period at any time for the safety of personnel and
test facilities.
6.7.5.3 Test events and outcome description
During the test, observation of at least the occurrences of the following events should be noted:
— deformation,
— venting,
— leakage,
— smoking,
— rupture,
— fire,
— explosion.
Table 10 can be used for guidance to report the test outcome.
Table 10 — Possible test outcomes
Sce- Description Effect
nario
0 Target cell was not triggered to thermal runaway
by the chosen trigger.
1 Target cell thermal runaway was successfully There is no thermal event of target cell. System controls
initiated by chosen trigger method. and mitigations have stabilized the cell.
2 Target cell thermal runaway was successfully Thermal runaway occurs in target cell, but there is no
initiated by chosen trigger method. propagation to adjacent cells.
3 Target cell thermal runaway was successfully Target cell is destroyed by thermal runaway. Propaga-
initiated by chosen trigger method. Propagation tion occurs in adjacent cells but does not spread beyond
is observed. cell-block or module.
4 Target cell thermal runaway was successfully Target cell is destroyed by thermal runaway. Propagation
initiated by chosen trigger method. Propagation occurs in adjacent cells, cell-blocks or modules but is
is observed. arrested so that no full pack thermal propagation occurs.
ISO 6469-1:2019/Amd.1:2022(E)
TTabablele 1 100 ((ccoonnttiinnueuedd))
Sce- Description Effect
nario
5 Target cell thermal runaway was successfully Target cell is destroyed by thermal runaway. Propagation
initiated by chosen trigger method. Propagation occurs in adjacent cells, cell-blocks or modules but is not
is observed. arrested so that full pack thermal propagation occurs.
6.7.6 Triggering of the DUT through an internal heater
6.7.6.1 Introduction and method specification
This test method relies on an internal, localized short circuit inside the cell created by a local heater.
The purpose of this test is to create a thermal runaway through the creation of a hole in the separator
of the triggered cell. The hole comes from the local melting of the separator induced by the local heater.
6.7.6.2 Test description
6.7.6.2.1 Trigger method description
The heater is a resistor made of a tungsten flat spiral (Figure 5). The coil is wrapped in one layer of
separator with similar melting temperature as the cell separator.
The important parameters of the resistor heater are
— thickness of heating filament: see Figure 5,
— resistance: (200 ± 5) mΩ,
— heating power: from 50 watts to 200 watts between 10 s and 120 s to the cell,
— the entire heating area shall be located on the separator.
The resistance, power and duration shall be adjusted according to the electrochemistry and the size of
the cell.
NOTE Energy is only released in the tungsten portion of the device since the external leads do not generate
significant heat and, therefore, this additional energy does not influence the outcome of the test.
Dimensions in millimetres
NOTE The wire diameter is usually 0,1 mm to 0,3 mm.
Figure 5 — Example of an internal heater flat spiral of tungsten
6.7.6.2.2 DUT preparation
ISO 6469-1:2019/Amd.1:2022(E)
The heater is inserted in the connected electrode stack or jelly roll before cell sealing with the following
steps. These steps are adapted for cylindrical and prismatic cells. A similar internal heater can be used
for pouch cells with an adapted sealing principle.
Step 1: Two holes are drilled into the cover to allow the electrical feedthrough of the heater from inside
the cell to the outside (Figure 6).
Figure 6 — Example of specific holes in cover for heater connection
Step 2: Unroll the separators and the electrodes to insert the heater.
Step 3: Locate the heater on the last wrap of electrode (Figure 8). The heater should be placed between
the outermost negative and positive electrodes for the cell, if possible (see Figures 7, 8 and 9). The
location should be determined between the customer and supplier.
Avoid unrolling a larger part of the jelly roll, since this can lead to damage of the jelly roll. Use an outer
stack in case of stacked layers.
Key
1 positive electrode
2 separator
3 negative electrode
a
180 mm from end of positive electrode and 15 mm from end of negative electrode, tolerance ±5 mm.
Figure 7 — Example of heater location inside the cylindrical cell
ISO 6469-1:2019/Amd.1:2022(E)
Key
1 positive electrode
2 separator
3 negative electrode
a
180 mm from end of positive electrode and 15 mm from end of negative electrode, tolerance ±5 mm.
Figure 8 — Example of heater location inside the prismatic cell
Figure 9 — Example of heater located on the last lap of negative electrode
Step 4: Wind the jelly roll with the heater (see Figure 10).
Figure 10 — Example of jelly roll equipped with heater
ISO 6469-1:2019/Amd.1:2022(E)
Step 5: Insulate the heater supply wires from the other parts of the cell. They are directed through
the specific holes in the cover (see Figure 11). Assemble the lithium-ion cell according to standard
manufacturing processes (e.g. electrolyte filling, cover welding).
All wires used in the RESS or RESS subsystem shall be electrically isolated. Furthermore, it should be
ensured that no electrolyte or gases can leak out through the space between the wire strand and the
wire insulator.
Selection of resin is critical as the strength of seal shall be greater than any installed vent of the cell.
Furthermore, it should be ensured that no electrolyte or gases can leak out through the space between
the wire strand and the wire insulator.
After cell cover welding, obtain the final sealing of the cell by adding a resin at the interface of the
heater supply wires terminals and the cover. Perform the formation of the prepared cell in a designated
chamber for that particular purpose. Ensure the sealing of the hole in the cell by using a resin (e.g.
epoxy glue). After it is completely dry, carry out a helium test to check the sealing before filling the cell
with electrolyte (see Figure 12).
NOTE 1 When the helium test is successful, cells are ready to be filled and formed.
a) picture
b) illustration
Key
1 resin for sealing of the heater supply
2 supply wires of the heater
Figure 11 — Example of finished cell with heater
ISO 6469-1:2019/Amd.1:2022(E)
Figure 12 — Example of cell before filling with electrolyte
Assemble the prepared cell inside the RESS or RESS subsystem according to the standard configuration.
If the modified cell is integrated into a RESS subsystem, without connecting wires (temperature sensor
and internal power supply), some module modification may be necessary. Create a hole with sufficient
diameter on the RESS or RESS subsystem case for all wires, thermocouple, voltage sensor, and so on. Fill
in the hole of an initiation module with heat-resistant resin to prevent the inflow of oxygen or flame to
escape from the hole during the test.
Connect the heater terminals by a dedicated connection box to the power supply.
Re-assemble and seal the DUT. Connect all wires of the heater, thermocouples and voltage sensors to
the outside of the RESS or RESS subsystem though a hole in the RESS casing and seal the holes with
heat-resistant resin (see Figure 13).
a) internal view
ISO 6469-1:2019/Amd.1:2022(E)
b) external view
Figure 13 — Example of RESS sub system with target cell
NOTE 2 In Figure 13 b), the circle indicates where the wires of the heater of the thermo-couplers are connected
to the RESS.
6.7.6.2.3 Test procedure
The test procedure consists of the following steps:
— checking and connecting the heater;
— checking heater resistance;
— applying the heater current profile specified in Table 11 and Figure 14 until thermal runaway;
— discontinue the heating sequence when thermal runaway has been confirmed according to the
criteria in 6.7.4;
— continue the measurements until the cell temperature decreases to 60 °C.
NOTE Stepwise heating avoids breaking the heating wire.
ISO 6469-1:2019/Amd.1:2022(E)
Key
X time [s]
Y current [A]
Figure 14 — Current profile for heater
Table 11 — Current profile for heater
Time [s] Current [A]
0 0
0 5
5 5
5 10
10 10
10 15
15 15
15 18
20 18
20 23
25 23
205 35
295 35
295 40
360 40
6.7.6.2.4 Data collection and recording specific to the method
Annex D provides an example for reporting and presenting test results.
ISO 6469-1:2019/Amd.1:2022(E)
In addition to those presented in 6.7.5, the following data should be collected for this method:
— heater power supply current [A];
— heater power supply voltage [V].
6.7.7 Triggering of the DUT through localized rapid external heating
6.7.7.1 Introduction and method specification
The DUT is a RESS, a RESS subsystem or a vehicle.
This test is performed by applying heat to the external surface of one target lithium-ion battery cell
within the RESS via an external heater until thermal runaway is achieved with minimal increase in
temperature of the adjacent lithium-ion battery cell(s) prior to thermal runaway within the target cell.
The increase of temperature of adjacent cell(s), prior to thermal runaway in the target cell, shall remain
below the maximum operating or storage temperature (whichever is higher) for the RESS. The native
cooling strategy (if installed), battery control unit (BCU) and any other battery control systems, which
are necessary for the test, shall be operational during the test. The heater selection, installation and
operation shall be performed with minimal invasiveness to the original un-modified RESS and RESS
subsystem operation. The test may be conducted at a vehicle level whereby the response of the vehicle
level detection and/or safety system (warning symbols, alarms), tenability of the vehicle and effect on
surrounding environment could be evaluated.
The method has the following two limitations.
1) The target cell shall have a sufficiently exposed surface area to mount the heating element on its
surface. As such, some cell positions within a RESS may not be suitable for potential target cells.
Significant modification of the RESS to accommodate surface mounting of the element for a given
cell position may alter the RESS functionality or its native safety system and may lead to an
inaccurate result.
2) If the heating element is inserted between two cells, then thermal runaway may be initiated in
two cells simultaneously unless sufficient thermal insulation or barriers are added that does not
impede natural RESS functionality.
6.7.7.2 Test description
6.7.7.2.1 Trigger method description
The trigger method applies a high-powered heat pulse, locally, to the external surface of the target
lithium-ion cell. The successful implementation of the method requires the application of sufficient
power to the chosen heating element to achieve, at a minimum, the set temperature, but it shall also
not apply so much power that there is a premature heating element failure nor a side wall failure of the
target cell prior to thermal runaway.
This method has been demonstrated to provide high reproducibility and high repeatability for initiating
single cell thermal runaway within the RESS system and sub-systems. The heating device should be a
resistive heating element, or other suitable heating device/technology capable of delivering the target
parameters. Target parameters for the heating element are listed in Table 12. Table 12 was developed
using pouch, prismatic and cylindrical cells designed for application in electrically propelled vehicles
using high energy lithium-ion battery chemistries. Different battery chemistries or cell type choices
(especially large prismatic cells) require variations to the target parameters.
Since thermal runaway conditions will be different for each cell type/chemistry/cell construction, etc.,
the test method shall be tailored based on those cell properties, such as capacity, format and chemistry.
ISO 6469-1:2019/Amd.1:2022(E)
These adjustments may be established through single-cell/small group of cells characterization testing
(see 6.7.7.3.1) using the chosen heating device. External heating methods that do not meet the listed
criteria may have significant deficiencies (adjacent cell heat up, significant RESS or RESS subsystem
modifications, activating RESS level safety mechanisms to prevent thermal excursions/runaway).
Table 12 — Heating element selection guide – Target Parameters
Parame- Value Reasoning
ter
Heating Ni-chrome with an isolating barrier Achieve high temperatures and prevent element failures
element or another suitable resistive heating
Isolating material may include alumina, ceramic, or fiber-
material material
glass.
Thick- <5 Minimize introduction of foreign objects, some RESS
ness designs may require a thinner heating element.
[mm]
Area As small as possible, but no larger than Concentrate heat to the smallest feasible area on the cell
20 % of the surface area of the targeted surface.
face of the target cell
Heating ≥15 Similar to heating rates observed within thermal
Rate runaway conditions to minimize adjacent cell or RESS
a
[°C/s] preheating.
Maxi- 100 °C > chosen heater setpoint temper- Heater shall maintain integrity at the chosen operating
mum ature temperature and take into account temperature devia-
heater tions from heater element to thermocouple upon applica-
b
tempera- tion of high power.
ture [°C]
Control Thermostatic closed loop Avoids undesirable test results, such as heating element
method burnout, elevated heating element temperature, battery
c
for heat- cell sidewall ruptures due to high element temperature.
er
a
Ideally the heating rate is measured directly by a thermocouple on the chosen heater.
b
This temperature may need adjustment for other chemistries and potentially other cell construction techniques (cell
sidewall ruptures).
c
Using a low voltage power source for the heating element will require higher currents (thicker wires), while a higher
voltage source will require more resistant isolating material and higher levels of user safety while implementing the test.
6.7.7.2.2 DUT preparation
The DUT may be the full RESS, the RESS subsystem or the in-vehicle RESS with minimum modifications
to the original un-modified DUT. Defined cooling/safety strategy and the battery management system
used within the RESS and RESS subsystem shall be fully operational. The coolant flow could be null
or active depending on the BMS. Any manipulation of RESS components, such as thermal barriers,
cooling plates/channels, electrical connections, and cell to cell spacing shall be kept at a minimum
and be reported. As the localized rapid heating method is externally activated, some minimal level of
modification may be tolerated, but the original sealing capability of the RESS shall not be compromised
through the introduction of the heating element.
For minimum modifications, all cell connecting busbars, tab welding, safety relevant components, BMS
software should be maintained and un-compromised within the DUT according to their delivery stage.
The installation of the chosen heating element should only modify the RESS by permitting electrical
and thermocouple connections to the heating element. These connections shall provide greater seal
integrity than the other connectors in the RESS.
Any leakage in the pack shall be through the pre-existing seals rather than through the connections for
the chosen heating element or sense wiring.
ISO 6469-1:2019/Amd.1:2022(E)
Instrumentation of the RESS or RESS subsystem shall also be kept at a minimum.
The chosen heating element shall be set to avoid contact to any RESS assembly surface except for
the target cell. Intimate thermal contact between the heating element and the target cell surface is
important for the successful application of this method. Thermal contact between the heating element
and target cell may be improved through various methods [avoiding air gaps, addition of a heat transfer
paste and applying pressure (which should be maintained throughout the test)].
A sample of potential heater application methods are shown in Figure 15 and the applied method is
dependent on the RESS or RESS subsystem design. In many cases, there is insufficient clearance to
adequately thermally insulate the cells adjacent to the target cell, moreover the addition of insulation
may have more disadvantages (additional foreign material may interfere with the RESS designed
clearances and thermal management) than advantages (more realistic single-cell thermal runaway
initiation). Maintain a contact pressure for the heating element on the target cell during the test to
ensure contact and optimal heat transfer, see also Figure 15.
a) RESS with large spacings between cells
b) centre cell fixed spacing (e.g. prismatic cells)
c) centre cell compressed modules (e.g. pouch cells)
ISO 6469-1:2019/Amd.1:2022(E)
d) edge cell
Key
1 target cell
2 adjacent cell
3 battery enclosure wall
4 heating element
5 heat transfer paste
6 ceramic paper
7 wire or high-temperature tape
Figure 15 — Methods to apply pressure on the heating element to maintain heating element
contact to target cell throughout the test
For selection of key 3 in Figure 15:
a) heating element may trigger two thermal runaway events simultaneously (or nearly simultaneous)
and should only be selected if other options are not feasible; and
b) a thermal insulator on the adjacent cell could be used as long as it does not influence the native
thermal management system of the RESS.
For implementation in vehicle level tests, the vehicle should be agnostic to the insertion of this trigger
method into the RESS, any pass required through the vehicle body should be minimized.
NOTE 1 Nickel plated brass IP68 cable glands provides suitable sealing in most applications.
NOTE 2 Using a heat transfer paste having a thermal conductivity of >2 W/(mK) with an operating temperature
>500 °C, while applying pressure of approximately 20 kPa usually provides good results.
6.7.7.2.3 Test methodology
The heating methodology shall follow the following temperature/time profile:
ISO 6469-1:2019/Amd.1:2022(E)
Key
1 phase 1 ramp
2 phase 2 soak
3 power off
NOTE This is a sample profile for the localized rapid external heating test methodology. The thermal
runaway of the target cell occurs during the ramp or soak phase in the actual test.
Figure 16 — Heating methodology profile for the localized rapid external heating test
A temperature controller (i.e. thermostat) should be utilized to track the temperature/time profile
as shown in Figure 16 via closed loop control. This approach necessitates the inclusion of a heating
element temperature sensor, ideally located on the heating element. Temperature feedback minimizes
undesirable test results such as element burnout and cell sidewall failures.
Parameters to use with this test methodology for typical lithium-ion battery cells for electric vehicles
are shown in Table 13 as a guideline. The customer and supplier shall agree on specific values. Heating
element setpoint temperature is dependent on cell chemistry, and manufacturing design and shall be
above the critical temperature which is necessary to initiate thermal runaway reactions. The heating
rate and soak times are dependent on the thermal conductivity of chosen cell and its design/chemistry.
Measures shall be taken to ensure a maximum heat transfer effectiveness into the cell, such that there
is a minimum time and minimum total energy input into the system to achieve a single cell thermal
runaway. The maximum time allowed for the first thermal runaway event shall be agreed between the
manufacturer and the test lab (see soak time in Table 13). The effect of the heat generated by the heating
element on the adjacent cells or chosen RESS architecture shall be minimized and shall be lower than
the maximum operating temperature of the RESS or RESS subsystem.
NOTE It is anticipated that RESS designs using a cell with a thicker cell wall will require a longer soak time
than those RESS designs using cells with a pouch bag design.
ISO 6469-1:2019/Amd.1:2022(E)
Table 13 — Typical heater parameters for implementation of localized rapid external heating
methodology
a
Parameter Pouch cell Cylindrical Prismatic Remarks
18650/ 21700
Heating rate 15 to 50 15 to 25 10 to 25 These values are based
...
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