challenges of high quality and high performance cell...

KIT – The Research University in the Helmholtz Association

wbk Institute of Production Science

www.wbk.kit.edu

Challenges of high Quality and high Performance Cell Stacking

Prof. Dr.-Ing. Jürgen Fleischer

Mainz, 2017/01/31

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© wbk Institute of Production ScienceProf. Dr.-Ing. J. Fleischer, Prof. Dr.-Ing. G. Lanza, Prof. Dr.-Ing. habil. V. Schulze

Process Chain for the Li-Ion Cell Production

Introduction

Mixing and Coating Calendering Stacking Contacting Diverters Filling and Sealing Formation

High processing speed to ensure economic efficiency

High accuracy to fulfill cell performance, lifetime and

safety requirements

Optimization of handling processes to reduce

unproductive idle times

Prevention of mechanical stresses to the sensitive

electrodes and separator

Objectives related to Stacking

Source: KIT

Especially stacking processes have long cycle-times

and are therefore cost drivers [1]

Today´s stacking processes are often sequential

and inefficient [2]

Handling of thin layers (electrode and separator)

is a highly challenging task [3]

Know-how about stacking processes is pre-dominantly

located in the Asian region [4]

Engineering Challenges related to Stacking

[1] Schröder, R.; Aydemir, M.; Glodde, A.; Seliger, G. (2016): Design and Verificationof an Innovative Handling System for Electrodesin Manufacturing Lithium-ion Battery Cells. In: ProcediaCIRP 50, S. 641–646.

[2] Glodde, A.; Aydemir, M.; Schröder, R.; Seliger, G. (2016): Produktivitätsgesteigerte Zellverbundherstellung*. Kontinuierliche Verfahrensführung zur Herstellung von z-gefalteten Lithium-Ionen-Batteriezellen. In: wt-online, S. 583–587.

[3] Kampker, A.; Kampker, Achim (2014): Elektromobilproduktion. Berlin: Springer Vieweg.[4] Schmitt, J.; Raatz, A.; Dietrich, F.; Dröder, K.; Hesselbach, J. (2014): Processand performance optimization by selective assembly of battery electrodes. In: CIRP Annals- Manufacturing Technology 63 (1), S. 9–12.

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Round Winding

State of the Art

Process (continuous)

Short processing times

No alignment of individual sheets

Continuous process allows single acceleration and

deceleration sequence

Suitable for high production volumes

Long-term production experience

Advantages

Mechanical stress due to small bending radii in the

cell’s center

Unsuitable for processing thick electrodes (bending

radii)

Disadvantages

Double-sided coated electrodes

and separator as input materials

Electrodes wound up together

with separator around mandrel

Round cell after

winding

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Prismatic Winding

State of the Art

Process (continuous)

Mechanical stress due to small bending radii on

compound sides

Mechanical stress due to compression

Unsuitable for processing thick electrodes (bending

radii)

Disadvantages

Short processing times

No alignment of individual sheets

Continuous process allows single acceleration and

deceleration sequence

Suitable for high volume production

Advantages

Electrodes wound up together

with separator around flat mandrel

After winding mandrel is extracted,

“Jelly Roll” is compressed Double-sided coated electrodes


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Single Sheet Stacking

State of the Art

Process (discontinuous)

Long processing times, e.g. through the need for vision

systems and robots for stack formation

Alignment of individual sheets necessary

Cutting burrs propose risk for separator penetration

Particle contamination by laser or die-cutting requires

subsequent cleaning

Disadvantages

No mechanical stress due to bending radii

Suitable for the processing of thick electrodes

High volumetric energy density

Advantages

Electrodes separated via laser or die-cutting,

separator cut via laser or cutting-blade

Single sheets stacked

alternating



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Z-Folding (discontinuous)

State of the Art

Process (discontinuous)

Long processing times, e.g. through the need for vision

systems and robots for stack formation

Alignment of individual sheets necessary

Similar disadvantages with respect to contamination

and cutting burrs as for Single Sheet Stacking

Disadvantages

No mechanical stress due to bending radii

Suitable for the processing of thick electrodes

High volumetric energy density

Improved cell-performance due to larger surface area

(better cooling)

Advantages

Electrodes separated via

laser or die-cuttingSingle electrode sheets are

folded into continuous separator



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Challenges

Cell Stacking

Reduction of the cycle time is needed

Minimization of individual steps

Increase of process speed

High process stability (Cp, Cpk)

Process Performance

High accuracy is needed

High cutting edge quality is required

To prevent contamination sub-sequent cleaning is most

likely needed

No cross-contamination between the anode and

cathode

No deformation or damage to electrodes and separator

Process Quality

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Addressing Challenges with current Technology

Cell Stacking

Process-

Performance

Process-

Quality

Cell cycle time [s]: ~ 120 [1] *

Cell cycle time [s]: ~ 81-83 [1] *

Cell cycle time [s]: ~ 30-36 [1] *

* Reference 50 Ah Pouch-Cell; ** Refers to the condition of the electrode

Small loose particles **(e.g. from separation process)

[1] Schröder, R.; Aydemir, M.; Glodde, A.; Seliger, G. (2016): Design and Verification of an Innovative Handling System for Electrodesin Manufacturing Lithium-ion Battery Cells. In: Procedia CIRP 50, S. 641–646.

[5] Schilling, A.; Schmitt, J.; Dietrich, F.; Dröder, K. (2016): Analyzing Bending Stresses on Lithium-Ion Battery Cathodesinduced by the Assembly Process. In: Energy Technol. 4 (12), S. 1502–1508.

Large loose particles ** (e.g. through delamination [10])

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Requirements

High cutting edge quality

with respect to electrodes

and separator

High positioning

accuracy

High production speed

(

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Cut & Place - Machine Assembly


Cutting tool with integrated handling system

Fixation of the electrode’s orientation while cutting

Direct placement of the fixed electrode onto the

cell-stack

Approach Single Sheet Stacking Cutting die with integrated Gripper

Defined electrode position

The electrode’s position is defined by the

cutting die, thus no subsequent detection

through vision systems is needed

The electrode’s orientation is kept through

the integrated handling system, wherefore

no subsequent positioning is necessary

Very high accuracy due to only one degree of

freedom and direct placement on the cell stack

Main Advantages

Source: KIT

Guide barsDie cutter cylinder

Vacuum ejector

Electrode web

Vacuum gripper

Die cutting punch

Tool aperture

Source: PCO [8]

Source: Festo [9]

[7] Baumeister, M.; Fleischer, J. (2014): Integrated cut and place module for high productive manufacturing of lithium-ion cells. In: CIRP Annals - Manufacturing Technology 63 (1), S. 5-8.

[8] https://w ww.pco.de/sensitive-cameras/pcopixelf ly-usb/

[9] https://w ww.festo.com.cn/rep/de_de/assets/EXPT_9747mk_1_710px.jpg

Source: Baumeister [7]

Source: KIT

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Cut & Place - Video


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Cut & Place - Meeting Target System Requirements


Repeatability during positioning

Source: Baumeister [2]

[7] Baumeister, M.; Fleischer, J. (2014): Integrated cut and place module for high productive manufacturing of lithium-ion cells. In: CIRP Annals - Manufacturing Technology 63 (1), S. 5-8.

Requirements

High cutting edge quality with

respect to electrodes

and separator

High positioning

accuracy

The tool’s cutting gap measures

merely 3 µm, resulting in a high

cutting edge quality and no

observed particle accumulations

[2]

Deviation between gripper and

ideal position ≤ 8 µm for

electrode depositing [2]

High production speed

(

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Cut & Place - Conclusion


Only one degree of freedom

Very high stacking-accuracy

Reduced risk for lithium-plating

High cutting edge quality

No subsequent cleaning

No particle accumulation

Contamination largely eliminated

Cross contamination between modules was not further

examined

No deformation /damages to electrodes has been

observed

Mechanical cutting

minimal heat input

Process Quality

High stacking speeds realizable

(not verified yet)

Fast and reliable separation of electrodes

No subsequent orientation

Unproductive idle times reduced

To make a statement about the adaptability and

scalability of the proposed concept further

assessments are necessary

Process Performance

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Unsolved Challenges in Single Sheet Stacking

Outlook

Single Sheet Stacking is still comparatively slow

The space between modules (electrodes

and separator) leaves room for minimization

The ball-screw-drive is limiting the

demonstrator’s operational speed

Handling and cutting the separator is

difficult due to its limpness

The cell stack needs to be build up sheet-

per-sheet (sequentially)

Statistical coverage for the Cut & Place approach

needs to be performed

Relationships between process parameters have

not been sufficiently investigated yet

High speed stacking

Reduction of the space between modules

Using a faster type of drive between

modules, e.g. linear motor

High process stability

Handling new emerging materials

Electrodes of various thicknesses

Very thin separators

Cost reduction

Modularization

Flexibility

Present Vision

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Helix - Approach

New Approaches

Continuous cell assembly for flat Lithium-Ion batteries

4 continuous material lines

2 x separator coil

1 x anode coil: intermitted double-sided coated

1 x cathode coil: intermitted single-sided coated

Zigzag folding in the intermittent gap

Approach aims at using advantages from continuous and

discontinuous manufacturing processes

Approach Continuous Material Feed

1

2

3

Source: KIT

No tight bending radii

No contamination through particles

Higher energy density compared to Z-folding

Main Advantages

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Helix - Meeting Target System Requirements

New Approaches

Requirements

No mechanical damage to

electrodes and separator

No cross-contamination

between electrodes

Material is folded in the intermittent gap,

wherefore a damage to the electrode’s

coating can be avoided

Anode is surrounded by the separator

during processing, wherefore no anode

material can contaminate the cathode

No foreign particles

between layers

High material

utilization

Reduced risk for foreign particles between

layers due to the absence of cutting

processes

No cutting waste since the cell stack is

created by folding the electrodes and

separator

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Summary

Current technologies for battery manufacturing have been introduced

Main challenges with respect to quality and process performance were outlined

Based on these challenges, a Target System was defined to address current challenges

Two new approaches, which have been developed at the wbk – Institute for Production Science, were introduced and

their impact on current challenges with respect to quantity and performance was explained

Lastly, unsolved challenges which need to be addressed in future research were discussed

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Thank you for listening!

Prof. Dr.-Ing. Jürgen Fleischer

Kaiserstr. 12, 76131 Karlsruhe

Tel.: +49 721 608 44009

[email protected]

www.wbk.kit.edu

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