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LITHIUM-ION BATTERY
CELL PRODUCTION
PROCESS
Dr. Sarah Michaelis
Battery Production, Division Manager
Sarah.Michaelis@vdma.org
VDMA
Authors
Ehsan Rahimzei
Battery Production, Project Manager
Ehsan.Rahimzei@vdma.org
PEM der RWTH Aachen
Any questions?
Contact us!
Frankfurt am Main, December 2018
Printed by PEM of RWTH Aachen and VDMA,
3rd Edition
ISBN: 978-3-947920-03-7
Dr.-Ing. Dipl.-Wirt.-Ing.
Heiner Hans Heimes
Chief Engineer
Head of E-Mobility Laboratory
H.Heimes@pem.rwth-aachen.de
Christoph Lienemann,
M. Sc. M. Sc.
Team Leader Battery Production
C.Lienemann@pem.rwth-aachen.de
Prof. Dr.-Ing. Achim Kampker
Christian Offermanns, M. Sc.
Battery Production
C.Offermanns@pem.rwth-
aachen.de
Marc Locke, M. Sc.
Battery Production
M.Locke@pem.rwth-aachen.de
The German Mechanical Engineering
Industry Association (VDMA) represents
more than 3200 companies in the
mechanical engineering sector, which is
dominated by SMEs. The battery
production department focuses on
battery production technology. Member
companies supply machines, plants,
machine components, tools and services
in the entire process chain of battery
production: From raw material
preparation, electrode production and
cell assembly to module and pack
production.
PEM of RWTH Aachen University has been
active for many years in the area of
lithium-ion battery production. The range
of activities covers automotive as well as
stationary applications. Many national and
international industry projects with
companies throughout the entire value
chain as well as leading positions in
notable research projects allow PEM to
offer a broad expertise.
PEM
Chair of Production Engineering of E-
Mobility Components
Campus Boulevard 30
52074 Aachen
www.pem.rwth-aachen.de
VDMA
Battery Production
Lyoner Straße 18
60528 Frankfurt am Main
www.vdma.org
●The production of the lithium-ion battery cell consists of three main process
steps: electrode manufacturing, cell assembly and cell finishing.
●Electrode production and cell finishing are largely independent of the cell
type, while within cell assembly a distinction must be made between pouch
cells, cylindrical cells and prismatic cells.
●Regardless of the cell type, the smallest unit of any lithium ion cell consists
of two electrodes and a separator, which separates the electrodes from
each other. The ion-conductive electrolyte fills the pores of the electrodes
and the remaining space inside the cell.
Operating Principle
of a lithium-ion battery cell
Electrode manufacturing Cell assembly Cell finishing
Technological Development
of a lithium-ion battery cell
*Following: Vuorilehto, K.; Materialien und Funktion, In Korthauer, R. (ed.): Handbuch Lithium-Ionen-Batterien, Springer, Berlin, 2013, S.22
●Recent technology developments will reduce the material and
manufacturing costs of lithium-ion battery cells and further enhance their
performance characteristics.
●Permutations
–NMC 811 (high nickel batteries)
–Silicon Graphite Anodes (Si/C)
●Carrier materials and electrolytes
–Metal meshes
–Solid electrolytes
●Fourth generation technology
–Large format cells
–Lithium metal anodes
Product innovation (excerpt)
●Electrode manufacturing
–Extrusion
–Laser drying
●Cell assembly
–Laser cutting
–Lamination of the separator
●Cell finishing
–Integrated product carrier
concepts
–Energy recovery
Process innovation (excerpt)
Structure
Cell
designs:
Cell design
Pouch
Prismatic
Cylindrical
Electric
load
graphite
structure
Current
collector
(aluminium)
Microporous
separator
Current collector
(copper)
Electrolyte
(liquid)
Anode Cathode
e-
e-
e-
e-
e.g. NMC structure
Lithium-ion
Lithium-ion
Production process
●With the help of a rotating tool at least two separated raw materials are combined to form a so-
called slurry.
●The production of slurry requires not only active materials but also conductive additives, solvents
and binders.
●A distinction is made between mixing (dry mixing) and dispersing (wet mixing). In addition, the
process can be performed under vacuum to avoid gas inclusions.
●The choice of the mixing and dispersing sequence must be adapted to the electrode design to be
produced.
Additional information
●The onward transport to the process step "coating" takes place through pipework or in sealed
storage tanks.
●Active materials, conductive additives, solvents and binders are purchased components for many
cell manufacturers.
Invest for machinery and equipment: € 18-34 million
(Mixing)
Mixing
Electrode manufacturing
Process parameters & requirements
•Homogeneity of the slurry
•Particle size
•Purity (amount of foreign objects)
•Viscosity
Quality features [excerpt]
•Mixing and dispersing sequence
•Filter materials and filter systems
•Shear forces
•Mixing temperature
Production costs* [excerpt]
Quality influences [excerpt]
Cell assembly Cell finishing
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
•α: 0°- 10°
•Mixing time: 30 min to 5 h
•Temperature: 20°C to 40°C
•Atmosphere: protective gas, vacuum, room
atmosphere (clean room)
•Different mixers for anode and cathode to
avoid cross-contamination
Intensive mixer with
mixing tool
Active material:
Graphite (90 wt.%) )
Conductive carbon black: Nano
microscopic carbon, e.g. Super P®
(5 wt.%)
Solvent: Deionized water
Binder: CMC (3 wt.%)
Additive: SBR (2 wt.%)
Anode formulation*
Active material: Li(NiMnCo)O2
(90 wt.%)
Carbon black: Nano microscopic
carbon, e.g. Super P® (5 wt.%)
Solvent: N-Methyl-2-Pyrrolidone
(NMP)
Binder: PVDF (5 wt.%)
Cathode formulation*
Step II: Dispersing (wet)
Add solvent, disperse
and homogenize
Step I: Mixing (dry)
Active material, additives if necessary
(e.g. carbon black) and binder are
mixed dry
Pump
α
Tank
ω1
ω2
•Various mixing technologies and mixing
tools: Intensive mixers, planetary mixers,
dispersers, etc.
•Continuous mixing: The active materials and
additives are mixed in a continuous process
(extruder). The slurry is then stored or
transported directly via pipelines to the
coating process.
Technology alternatives [excerpt]
•Dry film thickness on one side: 50 μm -
100 μm (anode), 40 µm - 80 µm (cathode)
•Coating speed:
35 m/min - 80 m/min
•Coating width: up to 1500 mm
•Coating accuracy dry (± 2 g/m²)
Production process
●The foil is coated with the slurry using an application tool (e.g. slot die, doctor blade,
anilox roller).
●The foil is coated either continuously or intermittently in the coating direction.
●Generally, the top and bottom sides of the foil are coated sequentially.
●The coated foil is continuously transferred to the dryer. After the first drying process, the foil
coated on one side is fed back to the coating system by a manual transport process.
●Afterwards, the second side is coated according to the process described.
Additional information
●Aluminium foil (rolled) and copper foil (rolled or electrolytically produced) are usually purchased
components for the cell manufacturer.
●The film thicknesses (anode - copper foil and cathode - aluminium foil) vary between 5 μm and 25
μm depending on the cell design.
Invest for machinery and equipment: 16-35 Mio. €
(Coating & Drying)
Coating
Electrode manufacturing
Process parameters & requirements
•Coating thickness accuracy (homogeneity in
and across the coating direction)
•Surface quality (blowholes, particles)
•Adhesion between coating and substrate
Quality features [excerpt]
•Quality monitoring (surface quality, layer
thickness)
•Application tool
•Precision of the slurry pump
•Various application tools (e.g. slot die,
comma bar, anilox roller)
•Simultaneous coating: The top and bottom
sides of the foil are coated simultaneously by
two opposite application tools.
•Dry coating: With dry coating, the active
material is applied to the carrier foil in
powder form without solvent.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Cell assembly Cell finishing
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
Max.Min.
Copper or aluminium roll
(here: copper roll for anode)
Application system
(here: slot die)
Foil coated on one side
Application role
Measurement of the wet
layer thickness
Intermittent coating
Top view
Storage
•Drying speed:
35 m/min - 80 m/min
•Length of dryer: up to 100 m
•Temperature profile in the dryer zones: 50°C
- 160°C
•Solvent recovery (hazardous substances);
thermal afterburning
•Suitable foil pre-tensioning is important to
avoid film tears
Production process
●After coating, the applied active material is dried in a continuous process.
●The solvent is removed from the material by heat supply.
●The highly flammable solvent contained in the cathode coating is recovered or used for thermal
recycling.
●The transport of the foil is realized either by roller systems or by floatation air streams. For a
simultaneous, double-sided coating, floatation dryer must be used.
●The dryer is divided into different temperature zones to realize an individual temperature profile.
This is normally realized by a chamber system.
●After passing through the dryer, the foil is cooled down to room temperature and, depending on
the type of system, rewound (conventional) or directly coated on the second side (tandem
coating).
Additional information
●The throughput speed during coating defines the length of the dryer section.
Invest for machinery and equipment: 16-35 Mio. €
(Coating & Drying)
Drying
Electrode manufacturing
Process parameters & requirements
•Adhesion between coating and substrate
•Residual humidity
•Surface finish (cracks, inclusions, etc.)
Quality features [excerpt]
•Determination of the process parameters
depending on the electrode design
•Choice of foil pretension
•Temperature profile
•Infrared drying: The conventional
convection dryers can be supplemented by
infrared heating and thus made more
efficient.
•Laser drying: By using a laser, the dryer
length can be shortened and energy costs
can be saved. This technology is still in the
development phase.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Cell assembly Cell finishing
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
80°C80°C
160°C160°C
Solvent vapors
Air nozzle
Cooling rolls
Exhaust
outlet
Air nozzle
Chamber 1 Chamber 2 Chamber 3 Chamber 4
•Maintaining a constant line pressure of up to
2,500 N/mm
•Calendering speed:
60 m/min - 100 m/min
•Porosity is reduced from 50% (after drying)
by calendering to 20% to 40% (defined by
the gap width).
•Preheating sections and roller temperature
control is possible
(approx. 50°C -250°C)
Production process
●During calendering, the copper or aluminium foil coated on both sides is compressed by a rotating
pair of rollers.
●The electrode foil is first statically discharged and cleaned by brushes or air flow.
●The material is compacted by the top and bottom rollers.
●The pair of rollers generates a precisely defined line pressure.
●After calendering, the electrode foil is cleaned and rolled up again (roll-to-roll process).
Additional information
●Line pressure defines the porosity of the coated material which influences the subsequent wetting
properties of the electrodes and the energy density of the cell.
●If the line pressure is set too high, a squeezing process occurs and leads to stress cracks.
●The cleanliness of the rollers is crucial for preventing foreign particles from penetrating the
substrate material.
Invest for machinery and equipment: € 5-10 million
(Calendering)
Calendering
Electrode manufacturing
Process parameters & requirements
•Defined porosity
•Surface texture
•Adhesion between coating and substrate
Quality features [excerpt]
•Line pressure
•Roller material and diameter
•Surface accuracy and concentricity of the
rollers
•Roller temperature
•Hot rollers: Depending on the system
concept the top and bottom rollers can be
heated. In this way, the ductility of the active
material can be brought to a defined value.
Usually water or oil is used as the heating
medium.
Technology alternatives [excerpt]
Quality influences [excerpt]
Cell assembly Cell finishing
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
Production costs* [excerpt]
Max.
Min.
Dried
electrode foil
Static discharge
Cleaning incl.
suction Top roller
Bottom roller
Cleaning incl.
suction
Thickness
measurement
•Cutting speed (mechanical):
80 m/min - 150 m/min
•Suction for the separated edge strips
•Cutting width tolerance: ±150 µm up to
±250 µm
•Burr-free cutting
Production process
●The calendered mother rolls are usually fed to the slitting station by a manual transport process.
●Slitting is a separation process in which a wide electrode coil (mother roll) is divided into several
smaller electrode coils (daughter rolls).
●Generally, rolling knives are used for this purpose.
●The individual daughter rolls are cleaned and rewound after the cutting process (roll-to-roll
process).
Additional information
●The electrode coils are cleaned by suction and/or brushes.
●The cut quality of the electrode edges and the cleanliness of the coils are considered as the main
quality criteria.
●The cutting width of the daughter rolls can vary depending on the cell design and lies between
60 mm and 300 mm in many applications.
Invest for machinery and equipment: € 3-8 million
(Slitting)
Slitting
Electrode manufacturing
Process parameters & requirements
•Edge geometry (cutting burr)
•Thermal (temperature-affected zone) and
mechanical stress
•Particle contamination during the cutting
process
Quality features [excerpt]
•Finishing of cutting blades
•Process parameters as a function of coating
thickness
•Extraction of dust / cutting waste
•Laser slitting: A laser can also be used for
the cutting process. This technology offers
greater flexibility. However, the risk of
damage to the active material or
contamination by dust increases when laser
slitting is used.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
cell assembly cell finishing
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
Copper foil
Cutline
Continuous coating
Prism. / Cylind.
Suction
Mother roll Daughter roll
Copper foil
Cutline
Intermittent coating
Pouch
Suction
Mother roll Daughter roll
•Working pressure: 0.07 mbar < p < 1000
mbar
•Drying time: 12 h - 30 h per batch
•Drying temperature: 60°C - 150°C
•Inert gas supply
Production process
●The coated daughter rolls are pushed onto a special goods carrier.
●The coils are then stored in a vacuum oven.
●The drying time is approx. 12 hto 30 h. During the drying process, residual moisture and solvents
are removed from the coils.
●The reduction of residual moisture is achieved by evaporation at low temperatures as a result of a
low total pressure.
●After vacuum drying has been completed, the coils are transferred directly to the dry room or dry
packed under vacuum.
Additional information
●The vacuum ovens are often used as air locks into the dry room (for daughter rolls).
●In addition, it is possible to operate the vacuum ovens with inert gas in order to prevent corrosion.
Invest for machinery and equipment: € 6-12 million
(vacuum drying)
Vacuum Drying
Electrode manufacturing
Process parameters & requirements
•Constant heat supply and stable vacuum
•Longer resting times only possible in the dry
room
•Inert gas supply against corrosion
•Continuous dryers: In contrast to the
chamber concept, there are also
continuous drying processes in which the
daughter rolls are transported through a
long drying facility in a wound or
unwound state.
•Infrared dryer: Both technologies can be
supplemented by infrared heating.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Cell assembly Cell finishing
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
Quality features [excerpt]
•Surface condition (cracks, etc.)
•Residual moisture content (no residual
moisture desired)
A
Vacuum technology
incl. vacuum pump
Daughter
rolls
Side view (section A)
A
•Separation time punching:
approx. 0.2 s/sheet
•Tolerance requirements: approx. ±200 µm
width and length tolerance for the sheets
•Punching tool: Very good cutting edge
quality (depending on wear resistance)
Production process
●Separation is necessary for the production of the pouch cell and describes the separation of
anode, cathode and separator sheets from the roll material (daughter rolls).
●The dried daughter rolls are unwound and fed to the separation tool.
●The cutting process is usually carried out with a shear cut (punching tool) in a continuous process.
●Depending on the system concept, the individual sheets (coated on both sides) are stored in a
magazine or transferred directly to the next process step.
Additional information
●The blank edge of the sheets are later used as the welding area for the cell tabs.
●The waste as well as the cutting dusts are extracted and transported away in the process.
Invest for machinery and equipment: € 5-10 million
(Separating pouch)
Separation
Cell assembly
Process parameters & requirements
•Cutting edge geometry (e.g. smearing of
the active material over the cutting edges)
•Thermal and mechanical stress during the
cutting process
Quality features [excerpt]
•Heat-affected zone and suction of
evaporated material during laser cutting
•Finishing of tools
•Cutting/punching speed
•Laser ablation: A guided laser beam allows
the active material to be ablated again at
defined points, thus exposing the carrier
foil. This technology offers a high flexibility
with regard to the positioning of the cell
tabs.
•Laser cutting: Instead of a conventional
punching tool, the electrodes can also be
cut out by a laser.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Cell finishingElectrode manufacturing
Separated cathode sheets
Separated anode sheets
Intermittent coating
Punching unit
Electrode stack
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
Production process
●During the stacking process the separated electrode sheets are stacked in a repeating cycle of
anode, separator, cathode, separator, etc.
●A wide variety of stacking technologies exist, which are usually patented by specific manufacturers.
●A classic variant of stacking is the so-called Z-folding.
●The anode and cathode sheets are inserted alternately from the left and right into the z-shaped
folded separator. The separator is used in the form of an endless tape and is cut off after the
stacking process.
●The cell stack is finally fixed with adhesive tape.
Additional information
●The exact positioning of the individual sheets is considered as the central quality criterion.
●The sheets are usually transported and positioned by vacuum grippers.
●Depending on the cell specification, a cell stack can consist of up to 120 individual layers.
Invest for machinery and equipment: € 18-27 million
(Stacking pouch)
Stacking
Cell assembly
Process parameters & requirements
•Lamination process: The individual electrode
and separator sheets are laminated onto
each other in a continuous process and are
then usually pressed together by a heat
press.
•Pocket Stacking: The cathode sheets are
placed in a separator pocket. Afterwards
cathode and anode sheets are stacked
alternately.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Cell finishingElectrode manufacturing
•Z-folding: Individual anode and cathode
sheets are placed laterally in the Z-folded
separator web
•Single-sheet stacking: Separator is available
as a sheet for stack formation
•Stacking accuracy: ± 200 µm - 300 µm
•Z-folding and single-sheet stacking : cycle
times of 1 s/sheet
Quality features [excerpt]
•Positioning accuracy of the anode and
cathode sheets
•Damage-free electrode surfaces and edges
•Avoidance of electrostatic charging
•Position detection and alignment of sheets
of different sizes with a vacuum gripper
•Mechanical pre-tensioning of the separator
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
Position
recognition
Input
Collector
Output
Separator
•Deep drawing: up to 6 mm
•Ultrasonic welding with approx. 15 kHz - 40
kHz
•Packaging material: aluminium composite
film (polyamide/aluminium/polypropylene)
•Rule of thumb: "1 mm sealing seam width
corresponds to approximately one year of
cell lifetime".
Invest for machinery and equipment: € 16-23 million
(Packaging pouch)
Packaging
Cell assembly
Process parameters & requirements
•Low contact resistance as well as low
mechanical and thermal stress during the
welding process
•Fatigue strength and tightness of the
sealing seams
Quality features [excerpt]
•Reduction of thermal stress during
contacting and sealing process
•Seal seam width
•Sealing temperature and pressure
•Book folding process: Instead of two
individual pouch foils, a foil with two deep
drawn cavities can also be used for
insertion into the packaging. After the stack
has been inserted, the foil is folded like a
book and then sealed.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Cell finishingElectrode manufacturing
Production process
●To package the pouch cell, the current collector foils (anode - copper and cathode - aluminium)
are first contacted with the cell tabs using an ultrasonic or laser welding process.
●The cell stack is then positioned in the pouch foil. For this purpose, the pouch foil is deep-drawn in
an earlier process step.
●The pouch cell is usually sealed gas-tight on three sides in an impulse or contact sealing process.
●One side of the cell (often the bottom of the cell) is not finally sealed in order to be able to fill the
cell with electrolyte in the next process step.
Additional information
●The packaging materials are generally to be regarded as purchased parts.
●The deep drawing of the pouch foil is carried out either directly in the production line or in a
separate process.
Welding of cell tabs
Deep-drawn foils
Insertion
sealing
Partial sealing of
the pouch
Deep drawing of
the pouch foil
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
•Geometry of the dosing needle
•Working pressure: approx. 0.01 mbar
•Consistent, continuous or cyclic filling to
ensure homogeneous electrolyte distribution
•Very dry environment necessary
•Gravimetric control of the electrolyte
quantity
Production process
●After the packaging process the electrolyte is filled in.
●During electrolyte filling, a distinction must be made between the sub-processes "filling" and
"wetting".
●The electrolyte is filled into the cell under vacuum (filling) with the help of a high-precision
dosing needle.
●By applying a pressure profile to the cell (supply of inert gas and/or generation of a vacuum in
alternating operation), the capillary effect in the cell is activated (wetting).
●Evacuation and partial filling are repeated several times depending on the manufacturer and
cell type.
●Finally, the pouch foil is sealed under vacuum.
Additional information
●The electrolyte (e.g. LiPF6) is usually a purchased component and sets high requirements on the
process environment (fire protection, extraction, etc.), due to its classification as a hazardous
substance.
Invest for machinery and equipment: € 6-12 million
(Electrolyte filling pouch)
Electrolyte Filling
Cell assembly
Process parameters & requirements
•Dosing and distribution accuracy of the
electrolyte in the cell
•No electrolyte residues in the sealing seam
•Tightness of the sealed cell
Quality features [excerpt]
•Dosing method (e.g. dosing pump)
•Geometry and closing mechanism of the
dosing needle
•Electrolyte transport system (piping, etc.)
•No alternatives in series production.
Technology alternatives [excerpt]
Quality influences [excerpt]
Cell finishingElectrode manufacturing
Production costs* [excerpt]
Dosing
needle
A A
Electrolyte filling Top view
(section A)
Pouch foil
Gas bag
Cell tab
Output
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
Production process
●Winding is required for the production of prismatic cells and cylindrical cells and takes place after
vacuum drying of the daughter rolls.
●The electrode foils and two separator foils are wound around a winding mandrel (prismatic cell) or
a centre pin (cylindrical cell). The foil sequence is similar to the stacking process.
●The wound product is called jelly roll.
●The positioning of the individual foils of the Jelly Roll is finally secured by an adhesive strip.
Additional information
●The exact positioning and alignment of the electrode foils and separator foils is regarded as the
central quality criterion.
●The process times for the winding process are significantly shorter than for the stacking process
described above.
Invest for machinery and equipment: € 15-35 million
(Winding)
Winding
Cell assembly
Process parameters & requirements
Quality influences [excerpt]
Cell finishingElectrode manufacturing
Production costs* [excerpt]
•Machine throughput: up to 30 cells/minute
(cylindrical cell)
•Integration of the tab welding process in the
winding machine for cylindrical cells
•Machine throughput up to 6 cells/minute
(prismatic cell)
Quality features [excerpt]
•Positioning accuracy of anode and cathode
foils
•Damage-free electrode surfaces and edges
•Winding speed
•Web tension
•Web edge control
•Avoidance of electrostatic charging
Technology alternatives [excerpt]
•No alternatives in series production.
output
Output
Flat winding
Input
Cathode Separator Anode
Cathode
Separator
Anode Separator adhesive
tape
Input
Cathode Separator Anode
output
Jelly roll
Adhesive
tape
Output
Cathode
Separator
Anode
Center pin
Winding
Collector
* Study by the PEM of RWTH Aachen University: 225,000,000 cylindrical cells/a, cell capacity: 4.8 Ah, 4 GWh/a
•Frequency of ultrasonic welding:
approx. 15 kHz - 40 kHz
•Flexible beam guidance and shaping during
laser welding of the lid of the prismatic cell
•Connection between anode and housing:
resistance welding
Connection between cathode and cell lid:
laser welding
Production process
●In contrast to the cell stack in the pouch cell, the jelly roll is inserted into a robust metal housing.
●In the prismatic cell, the edges of the jelly roll are compressed, fixed and ultrasonically welded to
the contact terminals attached to the lid of the battery.
●An insulation foil protects the jelly roll during insertion into the prismatic housing.
●The housing is usually sealed by a laser welding process.
●The first step in the cylindrical cell process is to insert a bottom insulator and the jelly roll into the
cylindrical housing.
●Subsequently, the current collector of the anode is usually welded to the bottom of the housing
and the current collector of the cathode is welded to the lid.
●Finally, an insulation ring is inserted between the jelly roll and the lid.
Additional information
●The cell housing and the insulation materials are generally to be regarded as purchased parts.
Invest for machinery and equipment: 10-20 million €
(Packaging prism. / cylindr.)
Packaging
Cell assembly
Process parameters & requirements
•Low contact resistance as well as low
mechanical and thermal stress during the
welding process
•Insulation against the metallic housing
Quality features [excerpt]
•Reduction of thermal stress during welding
processes
•Purity of the metallic housing
•Handling of the jelly roll
•No alternatives in series production.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Cell finishingElectrode manufacturing
Cell housing
Insulator foil
Jelly roll incl.
contact terminals
Input
Insulator
foil
Insertion into the housing Welding of the housing
Insertion into the housing Welding of the terminals
* Study by the PEM of RWTH Aachen University: 225,000,000 cylindrical cells/a, cell capacity: 4.8 Ah, 4 GWh/a
•Working pressure: approx. 0.01 mbar
•Consistent, continuous or cyclic filling to
ensure homogeneous electrolyte distribution
•Very dry environment necessary
•Gravimetric control of the electrolyte
quantity
Production process
●The electrolyte filling takes place after the jelly roll has been inserted into the housing.
●During electrolyte filling, a distinction must be made between the sub-processes "filling" and
"wetting".
●The electrolyte is filled into the cell under vacuum (filling) with the help of a high-precision
dosing needle.
●By applying a pressure profile to the cell (supply of inert gas and/or generation of a vacuum in
alternating operation), the capillary effect in the cell is activated (wetting).
●Evacuation and partial filling are repeated several times depending on the manufacturer and
cell type.
●Afterwards the cells are sealed (e.g. crimping, beading, welding).
Additional information
●The electrolyte (e.g. LiPF6) is usually a purchased component and sets high requirements on the
process environment (fire protection, extraction, etc.), due to its classification as a hazardous
substance.
Invest for machinery and equipment: 12-18 million €
(Electrolyte filling prism. / cylindr.)
Electrolyte Filling
Cell assembly
Process parameters & requirements
•Dosing and distribution accuracy of the
electrolyte in the cell
•Tightness of the sealed cell
•electrolyte quantity
Quality features [excerpt]
•Dosing method (e.g. dosing pump)
•Geometry and closing mechanism of the
dosing needle
•Electrolyte transport system
•No alternatives in series production.
Technology alternatives [excerpt]
Quality influences [excerpt]
Cell finishingElectrode manufacturing
Production costs* [excerpt]
Electrolyte filling Final sealing of the valve
Electrolyte filling Sealing
Dosing
needle
Valve Cell terminal
Beading
* Study by the PEM of RWTH Aachen University: 225,000,000 cylindrical cells/a, cell capacity: 4.8 Ah, 4 GWh/a
•Defined pressure
•Homogeneous distribution of pressure over
the entire cell surface
•Process times between 2 and 5 seconds per
cell
•Ensuring the ideal coverage of the individual
electrode sheets
Production process
●After electrolyte filling, an optional roll pressing process can take place for the pouch cell.
●The lithium-ion pouch cell is clamped in a special good carrier with the help of a gripper.
●A servo motor guides the cell through two rollers that apply a defined pressure.
●The rollers are cleaned in the meantime by cleaning rollers.
●Roll pressing ensures optimum distribution and absorption of the electrolyte under defined
pressure.
●This step serves as preparation for the subsequent formation because electrochemically inactive
areas are avoided by the pressurisation.
Additional information
●Roll pressing ensures that the maximum capacity of the cells is achieved and the rejection rate is
reduced.
Invest for machinery and equipment: € 4-8 million
(Roll pressing pouch)
Roll Pressing
Cell finishing
Process parameters & requirements
•Optimum formation of the SEI layer during
the subsequent formation process
•Electrolyte distribution within the cell
•Capacity of the cell after formation
Quality features [excerpt]
•Pressure distribution
•Roller geometry
•Process control (number of passes, etc.)
•Depending on the manufacturer, a
vibrating table is used for prismatic and
cylindrical cells to ensure optimum
electrolyte wetting.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Electrode manufacturing Cell assembly
Pressure unit
Roller
Pouch cell
Pressure
cylinder
Good carrier
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
•First charge: approx. 0.1 C - 0.5 C; State of
Charge (SOC) approx. 20 % - 80 %
•Successive increase in C-rates with each
charging and discharging cycle
•Duration of formation process: up to 24 h
•Low contact resistances at the spring-loaded
contact pins
Production process
●The formation describes the first charging and discharging processes of the battery cell.
●For formation, the cells are put in special good carriers in formation racks and contacted by
spring-loaded contact pins.
●The cells are then charged or discharged according to precisely defined current and voltage
curves.
●During formation, lithium ions are embedded in the crystal structure of the graphite on the anode
side. Here the Solid Electrolyte Interface (SEI) is formed, which creates a interface layer between
the electrolyte and the electrode.
Additional information
●The parameters during formation vary depending on the cell manufacturer and have a high
impact on cell performance. They depend on the cell concept and chemistry and represent the
core knowledge of a cell manufacturer.
●In some cases, pouch cells in particular are pressurised during formation by special good carriers.
Invest for machines and plants: 70-90 Mio. €
(Formation)
Formation
Cell finishing
Process parameters & requirements
•Formation of the SEI layer
•Stability of the SEI layer
•Internal resistance of the cell
Quality features [excerpt]
•Orientation of the cells
•Contact method
•Process temperature
•Pressurisation, especially of pouch cells
•There are different procedures for the
formation depending on the cell
manufacturer and cell chemistry.
Technology alternatives [excerpt]
Quality influences [excerpt]
Electrode manufacturing Cell assembly
Production costs* [excerpt]
Filled gas bag
Output
Top view product carrier
Good
carriers
Spring-
loaded
contact pins
Charging cycles with increasing
current intensity
current
time
I
II
III
*Example pouch cell
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
•Folding and gluing of sealing seams to
increase volumetric energy density
•Damage-free folding of the edges
•Seam widths of up to 1 cm
•Sealing against moisture and oxygen
Production process
●With many pouch cells (especially with larger cells) there is a strong evolution of gas during the
first charging process.
●Pressurised good carriers are pressing this gas out of the cell into a dead space (also called
a gas bag).
●During degassing, the gas bag is pierced in a vacuum chamber and the escaping gases are
sucked off. The cell is then finally sealed under vacuum.
●The gas bag is separated and disposed as hazardous waste.
●Final folding and, if necessary, gluing of the seal edges to reduce the external dimensions of the
pouch cell can be carried out as an option.
Additional information
●The extracted gases must be post-treated (e.g. RTO) before they are fed into the exhaust system,
depending on occupational health and safety and environmental protection regulations.
Invest for machinery and equipment: 10-15 million €.
(Degassing pouch)
Degassing
Cell finishing
Process parameters & requirements
•Residual gas inside the cell
•Damage-free cell handling (different
characteristics of the gas bubbles)
Quality features [excerpt]
•Pressing of the cells for degassing
•Sealing and folding technology
•Suction of gases under vacuum and in a dry
atmosphere
•Particularly in the case of smaller cells with
lower gas generation and depending on
the manufacturer, the gas bag is not
separated after degassing.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Electrode manufacturing Cell assembly
Separated gas bag
Sealed
seam
Folded and
sealed seam
Die
Workpiece support
Die
Folding step 2Folding step 1
Piercing the gas bag
Sealing
Vacuum chamber
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
•State of charge of the cell at the beginning
of aging: 80 % - 100 % SOC
•Aging time: up to 3 weeks
•Normal temperature approx. 22°C, high
temperature approx. 30°C -50°C
Production process
●Aging represents the final step in cell production and is used for quality assurance.
●During aging, cell characteristics and cell performance are monitored by regularly measuring the
open circuit voltage (OCV) of the cell over a period of up to three weeks.
●A distinction is made between high temperature (HT) and normal temperature (NT) aging. The
cells usually first undergo HT aging and then NT aging.
●The cells are stored in so-called aging shelves and/or towers.
●No significant change in the cell properties over the entire period of time means that the cell is
fully functional and can be delivered to the customer.
Additional information
●In contrast to formation, the pouch cells are no longer pressurised in this process step.
●The duration of the aging process depends strongly on the respective cell manufacturer and the
cell chemistry used.
Invest for machinery and equipment: € 5-15 million
(Aging)
Aging
Cell finishing
Process parameters & requirements
•Capacity
•Internal resistance
•Self-discharge rate
Quality features [excerpt]
•Orientation of cells
•Packing density of the cell good carriers
•Ambient temperature
•There are different procedures for the
sequence and duration of HT and NT aging
depending on the cell manufacturer and
cell chemistry.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Electrode manufacturing Cell assembly
High
temperature
aging
Normal temperature
aging
OCV
measurements
for quality
assurance
OCV
measurements
for quality
assurance
*Example pouch cell
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
Invest for machinery and equipment: € 5-8 million
(EOL testing)
EOL Testing
Cell finishing
quality characteristics
•Different test sequences and durations exist
depending on the cell manufacturer.
Technology alternatives [excerpt]
Production costs* [excerpt]
Quality influences [excerpt]
Electrode manufacturing Cell assembly
Production process
●Before the cells leave the factory, they are tested in an EOL test rig.
●The cells are removed from the good carriers in the aging racks and fed to the testing station.
Here they are discharged to the shipping state of charge (capacity measurement).
●Depending on the manufacturer, pulse tests, internal resistance measurements (DC), optical
inspections, OCV tests and leakage tests are carried out.
●After testing, many cell manufacturers sort the cells according to their performance data (grading).
●Once the tests have been completed passed successfully, the cells can be packed and shipped.
Additional information
●For transport, the cells are usually provided with a plastic cover and stacked in a cardboard box.
Process parameters & requirements
•State of charge of the cell for shipping:
5 % - 20 % SOC
•Permissible loss rate: < 5 mV per week
•Increased loss rate: > 5mV per week may
indicate e.g. cell-internal short circuits
Class IIIClass IIClass I
Grading (classification)
Testing Packaging
*Optional process
•Cell handling •Low self-discharge
•Low internal resistance
•Constant capacity
*Example pouch cell
* Study by the PEM of RWTH Aachen University: approx. 45,000,000 pouch cells/a, cell capacity: 25 Ah, 4 GWh/a
Production Environment
Dry room Clean room
Drying unit
Heat exchanger
Dried air
Filtration
system
Mixing
Coating
Drying
Calendering
Slitting
Vacuum
drying
Separation
Stacking /
Winding
Packaging
EL filling
Formation
Degassing
HT aging
NT aging
EOL testing
Clean room
class
Dry room
(dew point) Temperature Annotations
ISO 8 /
22 ±2 °C
The electrode
manufacturing takes
place under clean
room conditions,
since foreign particles
in the coating cannot
be removed in the
later process by
cleaning methods
(e.g. suction).
ISO 7
ISO 7
-
ISO 8
semi-dry
(5°C to -5°C)
Dry
(0°C to -30°C)
22 ±2 °C
min.
ISO 7
Dry
(-25°C to -35°C)
Dry
(-40°C to -50°C)
Extra dry
(-50°C to -70°C)
The cell assembly
must be carried out
under dry conditions,
as water inside the
cell leads to strong
quality losses (service
life) and to a safety
risk (formation of
hydrofluoric acid).
/ /
22 ±3 °C
30 °C to
50 °C
22 ±3 °C
Cell finishing takes
place in a normal
environment. Since
the cell is already
sealed and degassing
takes place in a
vacuum chamber,
there are fewer
requirements for the
particle environment
and humidity.
