IEC 62933-4-2:2025

IEC 62933-4-2 ®
Edition 1.0 2025-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electric energy storage (EES) systems –
Part 4-2: Guidance on environmental issues – Assessment of the environmental
impact of battery failure in an electrochemical based storage system

Systèmes de stockage de l’énergie électrique (EES) –
Partie 4-2: Recommandations relatives aux problèmes environnementaux –
Évaluation de l’impact environnemental d’une défaillance de batterie dans un
système de stockage d’énergie électrochimique
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IEC 62933-4-2 ®
Edition 1.0 2025-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electric energy storage (EES) systems –

Part 4-2: Guidance on environmental issues – Assessment of the environmental

impact of battery failure in an electrochemical based storage system

Systèmes de stockage de l’énergie électrique (EES) –

Partie 4-2: Recommandations relatives aux problèmes environnementaux –

Évaluation de l’impact environnemental d’une défaillance de batterie dans un

système de stockage d’énergie électrochimique

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 13.020.30, 27.010 ISBN 978-2-8327-0147-8

– 2 – IEC 62933-4-2:2025 © IEC 2025
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references. 6
3 Terms, definitions and abbreviated terms . 6
3.1 Terms and definitions . 6
3.2 Abbreviated terms . 8
4 General . 8
5 Failure of the electrochemical accumulation system in a BESS resulting in
environmental issues . 8
5.1 General . 8
5.2 View of the subsystem structure in a BESS and the battery-related failure
site . 9
5.3 Classification of BESS types . 9
5.4 Failure of batteries in the electrochemical accumulation subsystem of a
BESS . 10
6 Guidelines for assessing the environmental impact of a failure of the battery of the
electrochemical accumulation subsystem of the BESS . 11
6.1 General . 11
6.2 Root causes of battery and flow battery failures resulting in impact on the
environment . 11
6.2.1 General . 11
6.2.2 Root causes resulting in battery and flow battery failures . 12
6.2.3 Environmental impacts upon disassembly and disposal of a failed
battery . 14
6.3 Reporting the assessment . 14
Annex A (informative) Summary of typical properties of commercially available
electrochemical energy storage systems for BESS installations . 16
Annex B (informative) Potential environmental impacts related to the type of battery
in the BESS . 22
B.1 General . 22
B.2 Cells with non-aqueous electrolyte – C-A type . 22
B.3 Cells with aqueous electrolyte – C-B type . 22
B.4 Cells with solid electrolyte and operating at temperatures above 250 °C –C-
C type . 23
B.5 Cells with aqueous but recirculating electrolyte or flow cells – C-D type . 23
B.6 Cells with any other electrochemical couple, electrolyte and energy storage
concept or combinations thereof – C-Z type . 23
B.7 Environmental impacts upon disassembly and disposal of a failed battery . 23
Annex C (informative) Selected BESS application scenarios . 24
Annex D (informative) Description of batteries used in BESS . 25
D.1 General . 25
D.2 Cells with non-aqueous electrolyte – C-A type . 25
D.3 Cells with aqueous electrolyte – C-B type . 26
D.4 Cells with solid electrolyte operating at temperatures above 250 °C –
C-C type . 26
D.5 Cells with aqueous but recirculating electrolyte or flow cells – C-D type . 27
D.6 Cells with any other electrochemical couple, electrolyte and energy storage
concept or combinations thereof – C-Z type . 27

Bibliography . 28

Figure 1 – Example of a BESS structure . 9
Figure 2 – Failure sites in the electrochemical accumulation subsystem within the
scope of this document (highlighted in grey) . 10
Figure 3 – Proximate root causes leading to a battery or flow battery failure in the
BESS with associated environmental impacts . 12
Figure C.1 – BESS application scenarios. 24

Table 1 – Classification of BESS types . 10
Table 2 – Excerpt of a possible assessment report describing failures of a specific
battery and the resulting environmental impacts . 15
Table A.1 – Summary list of typical properties of commercially available
electrochemical energy storage systems in BESS installations – Part 1 . 17

– 4 – IEC 62933-4-2:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL ENERGY STORAGE (EES) SYSTEMS –

Part 4-2: Guidance on environmental issues –
Assessment of the environmental impact of battery
failure in an electrochemical based storage system

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
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shall not be held responsible for identifying any or all such patent rights.
IEC 62933-4-2 has been prepared by IEC technical committee 120: Electrical Energy Storage
(EES) Systems. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
120/387/FDIS 120/403/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
A list of all parts in the IEC 62933 series, published under the general title Electrical energy
storage (EES) systems, can be found on the IEC website.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
– 6 – IEC 62933-4-2:2025 © IEC 2025
ELECTRICAL ENERGY STORAGE (EES) SYSTEMS –

Part 4-2: Guidance on environmental issues –
Assessment of the environmental impact of battery
failure in an electrochemical based storage system

1 Scope
This part of IEC 62933 defines the requirements for evaluating and reporting the negative
impact on the environment caused by the failure of a cell, flow cell, battery or flow battery in
the accumulation subsystem of a battery energy storage system (BESS).
The batteries within this scope used in a BESS are classified according to the type of their
electrolyte. These electrolyte types are aqueous, non-aqueous or solid.
The environmental impacts directly caused by the failure of other components of the BESS are
not within the scope of this document.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1.1
cell
basic functional unit, consisting of an assembly of electrodes, electrolyte, container, terminals
and usually separators, that is a source of electric energy obtained by direct conversion of
chemical energy
[SOURCE: IEC 60050-482:2004, 482-01-01, modified – the Note has been deleted.]
3.1.2
flow cell
secondary cell characterized by the spatial separation of the electrodes and the movement of
the energy storage fluids
[SOURCE: IEC 62932-1:2020, 3.1.14, modified – the Note has been deleted.]

3.1.3
flow battery
two or more flow cells electrically connected including all components for use in an
electrochemical energy storage system
3.1.4
battery
one or more cells fitted with devices necessary for use, for example case, terminals, marking
and protective devices
[SOURCE: IEC 60050-482:2004, 482-01-04]
3.1.5
battery system
assembly of batteries or flow batteries installed on racks or in cabinets with associated
electrical, electromechanical, environmental control components and ready to operate
3.1.6
battery management system
BMS
electronic system associated with a battery which has functions to control current in case of
overcharge, overcurrent, overdischarge and overheating and which monitors and/or manages
the battery's state, calculates secondary data, reports that data and/or controls its environment
to influence the battery's safety, performance and/or service life
[SOURCE: IEC 62619:2022, 3.12, modified – the Notes have been deleted.]
3.1.7
failure
loss of ability of the cell, flow cell, battery or flow battery to perform as required
Note 1 to entry: This failure results in a fault of the accumulation subsystem and by derivation, of the BESS.
[SOURCE IEC 60050-192:2015, 192-03-01, modified – replaced "item" with "the cell, flow cell,
battery or flow battery", notes have been deleted and added new Note 1.]
3.1.8
failure cause
set of circumstances that leads to failure
Note 1 to entry: A failure cause can originate during specification, design, manufacture, transportation, installation,
operation or maintenance of an item
[SOURCE: IEC 60050-192:2015, 192-03-11]
3.1.9
environment
natural and man-made surroundings in which an EES system is installed, operates and
interacts, including buildings and facilities, air, water, land, natural resources, flora, fauna
(including human inhabitants) of those surroundings
[SOURCE: IEC 60050-904:2014, 904-01-01, modified – expansion of the scope to include man-
made surroundings, dynamic interactions, and specific EES system contexts.]
3.1.10
system integrator
entity that specializes in planning, coordinating, building, implementing and testing of systems

– 8 – IEC 62933-4-2:2025 © IEC 2025
3.1.11
manufacturer
entity that produces the specified item and owns the manufacturing process by which it was
created
3.2 Abbreviated terms
BESS battery energy storage system
BMS battery management system
EES electrical energy storage
HVAC heating, ventilation and air conditioning
LFP lithium iron phosphate
LTO lithium titanium oxide
MSDS material safety data sheet
NCA nickel cobalt aluminium oxide
NMC nickel manganese cobalt oxide
PCS power conversion system
POC point of connection
SDS safety data sheet
SOC state of charge
SOH state of health
VRLA valve regulated lead acid
4 General
The environmental impact of a battery failure depends on the battery type, design and structures.
This document provides guidance and requirements on how to identify the potential impacts on
the environment when the battery of an electrochemical energy accumulation system fails.
The operation, under conditions licensed by the local authorities, of the BESS including its
batteries and flow batteries, is considered to occur without any negative environmental impact.
5 Failure of the electrochemical accumulation system in a BESS resulting in
environmental issues
5.1 General
A failure is defined in this document as a loss of ability of the cell, flow cell, battery or flow
battery in the electrochemical accumulation subsystem to perform as required. This failure
results in a fault of the accumulation subsystem and, by derivation, can result also in a failure
of the BESS with possibly environmental issues.
For the present document, those failure-inducing causes are considered if the subsequent
failure(s) of the cell, flow cell, battery or flow battery in the electrochemical accumulation
subsystem negatively impact(s) the environment surrounding the BESS.

The failure causes to be considered in this document are the result of:
1) electrochemical accumulation subsystem internal causes such as a fault developing due to
weakness of materials or of an assembly or divergent chemical or electrochemical reactions;
or
2) electrochemical accumulation subsystem external causes such as a fault developing due to
a failure of ancillary equipment, unfavourable environmental conditions or loss of essential
parameters, data and functions needed for safe operation.
Failures of other subsystems of the BESS are not assessed within this document for their direct
negative impact on the environment.
5.2 View of the subsystem structure in a BESS and the battery-related failure site
The typical subsystems architecture of a BESS is shown in Figure 1 with the location of the
battery highlighted
NOTE The location of the electrochemical accumulation subsystem and its battery are highlighted in the dark grey
box.
Figure 1 – Example of a BESS structure
5.3 Classification of BESS types
The BESS types are categorized in Table 1, according to IEC 62933-5-2, into five types based
on the specific features of the installed electrochemical storage system, i.e. the installed battery
type and its electrolyte.
– 10 – IEC 62933-4-2:2025 © IEC 2025
Table 1 – Classification of BESS types
BESS type designation Distinguishing design features
Cell with non-aqueous electrolyte
C-A
(e.g., Li-ion)
Cell with aqueous electrolyte
C-B
(e.g., Pb acid, NiMH)
Cell with solid electrolyte and operating above 250 °C or defined as HT (high
temperature) cell
C-C
(e.g., NaS, NaNiCl)
Cell with aqueous but recirculating electrolyte or defined as flow cell
C-D
(e.g., V5+/V2+)
Cell with any other electrochemical couple, electrolyte and energy storage concept
or combinations thereof
C-Z
(e.g., Li metal with solid electrolyte, electrochemical double layer capacitors)

The classification of the battery types used in a BESS and listed in Table 1 is subject to
evolutions as advances in battery technology bring changes in electrolytes and cell designs.
The attributes of a BESS type designation, based on the installed battery and reported in the
environmental impact assessment document, are only informative in nature. They do not
release the system integrator and battery manufacturer carrying out the environmental impact
assessment of a battery failure according to this document, from considering all features of the
battery or flow battery of the BESS at hand.
5.4 Failure of batteries in the electrochemical accumulation subsystem of a BESS
The failure sites in the electrochemical accumulation subsystem in this document are
highlighted in Figure 2.
Figure 2 – Failure sites in the electrochemical accumulation subsystem
within the scope of this document (highlighted in grey)

6 Guidelines for assessing the environmental impact of a failure of the battery
of the electrochemical accumulation subsystem of the BESS
6.1 General
Batteries and flow batteries are equipment containing reactive metals and chemicals and are
also sources of uninterruptable flows of electrical energy. These components and effects can
be released into the environment in an uncontrolled fashion when the battery or flow battery in
the accumulation subsystem fails.
The system integrator of the BESS, therefore, carries out, in collaboration with the
electrochemical accumulation subsystem, a systematic assessment of when and how wear-out,
ageing, deterioration, damage, non-compliance, environmental factors, flawed operation(s) or
outright failure(s) of a constituent of the BESS result in failures of the electrochemical
accumulation subsystem with a subsequent impact on the environment.
To ensure a structured assessment of the failures, an overview of the cell designs is presented
in Annex D. This is followed in Annex B by an overview of the environmental impacts resulting,
upon a failure, from the battery and flow battery materials, their reactions and associated
disruptive electric effects.
In 6.2 a structured set of root causes of such failures is presented. These root causes reflect
the multiple origins of a failure of the battery or flow battery in a BESS and are applicable to
the designs C-A to C-Z, respectively.
6.2 Root causes of battery and flow battery failures resulting in impact on the
environment
6.2.1 General
Internal and external causes that can result in a failure of the cell, flow cell, battery or flow
battery and possibly have an impact on the environment, are reviewed and enumerated below.
Potential failures are systematically listed below, which are further the result of root causes
depicted in Figure 3.
• Performance degradation
– inability to deliver rated energy (cause 1)
– inability to accept rated energy (cause 2)
• System degradation
– failed structural integrity (cause 3)
– failed system integrity (cause 4)
• Subsystems degradation
– failed accessory components (cause 5)
– failed control subsystem (cause 8)
– failed auxiliary subsystem (cause 9)
• Unexpected inputs from the POC/interface
– failed environmental controls (cause 6)
– failed electric integrity (cause 7)
• Unexpected external environment impacts to the system
– environmental impacts (cause 10)

– 12 – IEC 62933-4-2:2025 © IEC 2025
A schematic view of key proximate (immediate) root causes leading to failures is shown in
Figure 3.
Figure 3 – Proximate root causes leading to a battery or flow battery failure
in the BESS with associated environmental impacts
6.2.2 Root causes resulting in battery and flow battery failures
6.2.2.1 General
The assessment of the failures and their environmental impacts shall be carried out on the
battery and its layout by the system integrator in collaboration with the battery or flow battery
manufacturer. Local regulations can apply and can designate any other entity to perform the
assessment.
This assessment shall be made available, in an appropriate format and detail, to the interested
parties such as the BESS operator, licensing authorities, environmental protection agencies or
other relevant entities for follow-up actions as needed. Local regulations can apply.
The assessment activity starts from the relevant proximate, i.e. close-by root cause(s), and
details their resulting impacts on the cells, flow cell, battery and flow battery.
These impacts can lead to their failure resulting in a fault of the BESS.

The failure causes of the cell, flow cell, battery, or flow battery are evaluated with due diligence
for their potential impact on the environment, as relevant.
Due diligence is defined as the degree of care that is to be reasonably expected or that is legally
required for the task.
This evaluation is done in a detailed and exhaustive description and quantification of the
impacts and damage patterns so that concrete mitigation actions can be planned and
undertaken by the addressee.
The planning of failure prevention measures or environmental impact mitigation activities is not
within the scope of this document, but its logical consequences are worth considering.
To guide this assessment, key proximate root causes of these failures are listed below.
6.2.2.2 Performance degradation
• [Cause 1]: Cell, flow cell, battery, or flow battery deterioration that results in an inability to
deliver the rated energy at the rated BESS operating conditions, for example, inactivation
or decomposition of active mass, increased internal resistance, obstruction in energy
storage fluid circuits.
• [Cause 2]: Cell, flow cell, battery, or flow battery deterioration that results in an inability to
accept the rated energy at the rated BESS operating conditions, for example, increased
internal resistance, formation of barrier layers, fractures in the solid electrolyte ceramic.
6.2.2.3 System degradation
• [Cause 3]: Failure of the structural integrity:
[Cause 3a]: failure of the structural integrity of the cell or battery for example, cell case-to-
cover weld failures, breach of liquid or gas barriers, corroded current collectors;
[Cause 3b]: Failure of the structural integrity of the flow cell and flow battery, for example,
rupture of electrolyte circuits, collapse of flow cell assembly, loss of fluid level controls,
electrolyte tank head space disruptive gas venting.
• [Cause 4]: Failure of the system integrity of the battery system, for example, collapse of
racks or cabinets, decreased dielectric strength of assemblies, lack of preventive
maintenance and repair, accidental liquid, vapor or gas venting.
6.2.2.4 Subsystem degradation
• [Cause 5]: Failure of the accessory components of the battery system, for example, BMS,
safety valves, gas monitors, pumps, level indicators, heaters.
6.2.2.5 Control system degradation
• [Cause 6]: Failure of the environmental controls of the battery or flow battery for example,
loss of heating, ventilation and air conditioning (HVAC) functions, impeded air exchange,
loss of heating or cooling fluids.
• [Cause 7]: Failure of the electrical integrity of the battery or flow battery, for example,
damaged cabling, degraded control signals, non-reacting or blown fuses, breakdown of the
electrical insulation.
• [Cause 8]: Failure of the control and energy management system of the battery or flow
battery, for example, loss of SOC status information, loss of data communication to and
from the battery, loss of battery management data files.
• [Cause 9]: Failure of the auxiliary systems of the battery or flow battery for example,
breached access control, inoperative fire protection systems, remote site surveillance.

– 14 – IEC 62933-4-2:2025 © IEC 2025
6.2.2.6 Environmental conditions degradation
• [Cause 10]: Environmental impacts on the battery or flow battery, for example, excessive
wind loads, flooding of the BESS site, lightning strikes, ground movements, biological
phenomena.
6.2.3 Environmental impacts upon disassembly and disposal of a failed battery
The disposal and disassembly of failed batteries or flow batteries of the BESS requires
particular attention so as not to increase the likelihood that new or additional environmental
damages occur.
All batteries contain hazardous materials that require special consideration when a failed
battery or flow battery is dismantled and its components are readied for disposal or recycling.
Whereas batteries with cells of the C-B type have well established processes for safe
dismantling, disposal and recycling operations, more recent cell designs such as, for example,
the C-A type, currently lack such robust and proven methodologies.
It is therefore recommended that BESS operators keep abreast of the necessary methodologies
governing battery dismantling, disposal and make them part of the on-site operating instructions.
Local regulations can apply.
MSDSs and SDSs can provide pertinent guidance for such activities.
6.3 Reporting the assessment
Depending on the present or targeted location of the BESS, the assessment report is adjusted
according to the local regulation(s) applicable in this matter.
An example of the assessment report is shown below in Table 2.
If the format, layout and data granularity required by the addressee of the assessment are not
available, the assessment report shall provide:
1) the description of the battery or flow battery and type designation (C-A to C-Z);
2) the rated battery capacity expressed in ampere-hours and associated discharge duration in
hours, i.e. watt hours of energy content;
3) the total weight of the installed cells of the battery or the total volume of electrolyte of the
flow battery;
4) the name and address of the cell or flow battery manufacturer or supplier;
5) the address of the site where the BESS is to be or is installed;
6) the listing of individual proximate root causes in accordance with 6.2.1 as relevant, and
resulting in the failure of the cell, battery, flow cell or flow battery at hand;
7) the description of the impact of the root cause on the cell, battery, flow cell or flow battery
at hand and causing its failure;
8) the description of the identified negative impact on the environment caused by the failure of
the cell, battery, flow cell or flow battery at hand;
9) any quantitative values, as available, of the damage levels useful for a subsequent
environmental impact-mitigation planning;
10) any relevant MSDSs and SDSs relevant for the concerned battery system;
11) date, name and address of the assessment entity.

Table 2 – Excerpt of a possible assessment report describing failures
of a specific battery and the resulting environmental impacts
Failure and environmental impact description
Impact on
Identified negative
Proximate cell-battery Quantitative levels of resulting
Causes environmental
root cause Flow cell damages (as available)
impact
Flow battery
Cell case weld Leakage of Ground short arcing Release of 110 mg HF equivalent
failure electrolyte Fire mass per damaged cell
Danger of IDLH of HF: 30 ppm
3a
electrocution when
Combustion value:
DC voltage > 30V
-1
16 MJ.kg cell weight
Loss of BMS Exothermic event Fire Release of 110 mg HF equivalent
functionality developing in the Toxic electrolyte mass per damaged cell
cell string within pyrolysis vapours IDLH of HF: 30 ppm
48 h Fire extinguishing
Cell combustion value:
water contamination
-1
16 MJ.kg cell weight
with referenced
Water soluble solids:
substances
LiPF 12 g/cell
NaP0 4 g/cell
LiPO 55 g/cell
LiOH 2 g/cell
A thorough assessment of the environmental impact caused by the failure of the battery system
can result in documents containing sensitive information. The concerned information shall be
properly designated by the assessor and handled accordingly by the addressee as agreed.

– 16 – IEC 62933-4-2:2025 © IEC 2025
Annex A
(informative)
Summary of typical properties of commercially available electrochemical
energy storage systems for BESS installations
The data presented in Table A.1 give an informative overview of key typical properties of
mainstream batteries used in BESS installations. Other electrochemical systems or design
variants exist that might be, less frequently, also used or planned in such installations.
The values presented are intended to give the planners and users of such systems a
summarized and comparable view of aspects and features that can be relevant when they are
reviewing the assessment of the environmental impacts of a failure of the electrochemical
storage system, i.e. the battery or flow battery of the BESS.
These data are not intended to replace the relevant values the system integrator and battery
manufacturer of the actual battery system will use for the actual battery in the concerned BESS
installation.
The data presented are subjected to changes as battery technology and referred standards
evolve.
Table A.1 – Summary list of typical properties of commercially available electrochemical energy
storage systems in BESS installations – Part 1
Sodium nickel
Property Lead-acid Lithium-ion Nickel metal hydride Redox flow Sodium sulphur
chloride
Type designation C-B C-A C-B C-D C-C C-C
Li Ni Co Mn O
1-A x y 2 2
+Li C
A 6
⇋
2 NiOOH + H M
+ 2+ +
LiNi Co Mn O
Pb+PbO +2H SO VO + V + 2H
2Na+xS 2NaCl+Ni
x y z 2
2 2 4 2
(M=LaCeTiNi)
+C
Electrochemical active 6
⇋ ⇋
⇋ ⇋
species and reaction ⇋
or
2+ 3+ Na S 2Na+NiCl
2PbSO +2H O
VO + V H O 2 x 2
4 2
2Ni(OH) +M 2
+
Li +FePO +LiC
4 6
⇋
+
LiFePO +C +Li
4 6
Secondary
2H O → 2H +O 2H O → 2H +O 2H O → 2H +O
electrochemical None None None
2 2 2 2 2 2 2 2 2
reaction
Cylindrical cells
Spirally wound
Prismatic cells
Cell design for BESS Cylindrical cells Prismatic bipolar flow
Prismatic cells
Cylindrical cells Prismatic cells
application Spirally wound cell stacks
VRLA design
Stacked or wound
plates
LiMn O 3,8 V
2 4
LiNi Co Mn O
x y z 2
Nominal single cell
2,0 V 1,2 V 1,00 V to 1,55 V 2,075 V 2,6 V
voltage
3,7 V
LiFePO 3,2 V
Typical BESS cell Energy storage fluid
100 Ah to 1 500 Ah 3 Ah to 100 Ah 2 Ah to 12 Ah ≈ 725 Ah ≈ 38 Ah
capacity volume dependent
Typical cell operating
25 °C to 40 °C 25 °C to 35 °C 25 °C to 40 °C 10 °C to 50 °C 300 °C to 360 °C 265 °C to 330 °C
temperature in a BESS
– 18 – IEC 62933-4-2:2025 © IEC 2025

Sodium nickel
Property Lead-acid Lithium-ion Nickel metal hydride Redox flow Sodium sulphur
chloride
Type designation C-B C-A C-B C-D C-C C-C
Ethylene carbonate
(EC)
Dimethyl carbonate KOH
β-Al O – solid
Vanadium chlorides 2 3
(DMC) 28 %
H SO
O – solid
2 4 β-Al
2 3
and sulfates in H O
40 %
w/w
Electrolyte and other
Na – molten
w/w
ancillary components H SO 25 % w/w
2 4 NaAlCl – molten
in H O
Diethyl
in H O Sulfur – molten
carbonate (DEC)
LiOH
HCl 10 % w/w
(catholyte)
NaOH
LiClO
LiPF
NMC/NCA
-1
≈ 14 g.Ah to
≈ 25 g to
Weight per Ah at 5 h
-1 -1 -1 -1 -1
rate of bare BESS
≈ 82 g.Ah ≈ 16 g.Ah ≈ 20 g.Ah ≈ 7,3 g.Ah ≈ 18 g.Ah
40 g energy fluid per
type single cell
Ah
LFP
-1
≈ 30 g.Ah
-1
≈ 3 g.Ah
Electrolyte quantity
-1 -1 -1 -1 -1
≈ 15 g.Ah ≈ 2 g.Ah to ≈ 5 g.Ah n.a. ≈ 0,76 g.Ah ≈ 3,2 g.Ah
per Ah and cell
-1
≈ 5 g.Ah
Liquid absorbed Liquid absorbed Liquid absorbed
Electrolyte status Liquid Solid Solid
Immobilized Immobilized Immobilized
Na metal
H H
Flammable content Organic Electrolyte Carbon-plastic matrix Na metal
2 2
free elemental sulfur
Carbon felt
Al Ni
Current collector Graphite felt
Pb and Pb alloy Al and Cu Ni-plated steel
material
Carbon felt Carbon felt
Carbon-plastic
composites
Ion exchange Integrated in solid Integrated in solid
Separator AGM glass mat PE – PP PP – Polyamide
membrane electrolyte electrolyte

Sodium nickel
Property Lead-acid Lithium-ion Nickel metal hydride Redox flow Sodium sulphur
chloride
Type designation C-B C-A C-B C-D C-C C-C
None
Gas emission in
H H
None None None
2 H when excessive 2
operation 2
internal pressure
Yes – Scored burst
Overpressure safety
disc
Yes – resealable Yes – resealable Yes – resealable None None
valve
Pouch excluded
< 200 hPa pouch
Internal operating
< 200 hPa < 600 hPa < 2 000 hPa None None
< 30 000 hPa
pressure
cylindrical
State-of-charge SoC
I-V-time-ΣAh V-time V-time Reference cell ΣAh-voltage ΣAh-OCV
detection method
Charge method CC-CV CC-CV CC-CV CC-CV CP CC-CV
Yes
Yes
Yes
Yes Yes
Yes
Sensitivity toward
Li plating
Fracture of
Cell overheating H emission
H emission
overcharge and 2
β-Al O electrolyte when OCF > 1,5 cell
O emission 2 3
Thermal runaway
consequences 2 CO emission
Thermal runaway
2 overheating
barrier
Thermal runaway
Electrolyte fire
Yes
Yes
Yes
Yes Yes
H emission
Yes Internal shorts
2 Fracture of
Sensitivity toward
Irreversible cell β-Al O electrolyte Irreversible cell
overdischarge
2 3
Internal shorts Thermal runaway
Excessive internal
degradation degradation
barrier
pressure
Fire
Single cell or flow cell Ni-plated steel, Al,
ABS, PP, PVC, PSU Ni-plated steel PE, PP, PVC, EPDM Al Ni-plated steel
container material Pouch film
Crimp seal
Glue seal
EPDM gasket
Case-to-cover seal TiG weld Crimp seal TiG weld Laser weld
PE/PP weld
Hot-plate seal
Laser weld
Cell container and
Pouch film only
cover burning HB(x) to V-0 n.a n.a. n.a. n.a.
HB(x) to V-0
classification
...