MATERIAL AND PROCESS DEVELOPMENT FOR LITHIUM ......EMBATT1.0: water based processes for thick...
1
www.ikts.fraunhofer.de © Fraunhofer IKTS MATERIAL AND PROCESS DEVELOPMENT FOR LITHIUM BIPOLAR BATTERIES Kristian Nikolowski*, Mareike Wolter, Marco Fritsch, Stefan Börner, Beate Capraro Fraunhofer-Institut für Keramische Technologien und Systeme IKTS, Dresden, Germany INTRODUCTION Conventional monopolar lithium batteries are limited in energy density due to the high share of inactive components and limited volume utilization on cell as well as on system level. The EMBATT bipolar battery concept (fig. 1) reduces the amount of inactive components and leads to improved integration properties for automotive applications. Main challenges which have been identified concern: Technological solutions for electrode and system manufacturing Material innovations for active material, electrolyte and current collector Fraunhofer IKTS is addressing these topics in the projects EMBATT1.0 (manufacturing technology) and EMBATT2.0 (material innovations) as summarized in table 1. Table 1: Comparison of the generations of the EMBATT bipolar battery EMBATT1.0 EMBATT2.0 Materials Commercial LFP and LTO Liquid electrolyte Al-current collector High voltage system LTO/LNMO with optimized particle morphology Polymer electrolyte Polymer current collector Energy density on battery system level > 200 Wh/l > 450 Wh/l Contact: Dr.-Ing. Kristian Nikolowski | Fraunhofer Institute for Ceramic Technologies and Systems IKTS | System Integration and Technology Transfer | Mobile Energy Storage Systems | Winterbergstrasse 28, 01277 Dresden, Germany | Phone +49 351 2553-7267 | [email protected] WATER BASED ELECTRODES Slurry development Water based slurry recipes have been developed for LTO and LFP. Then, electrodes were manufactured on pilot scale coating equipment. Plot 1 shows the results of LTO limited coin cells. Increasing electrode thickness The slurry recipes and coating parameters were optimized with the goal of increasing electrode thickness. Plots 2 and 3 show the area specific capacity and the normalized capacity, respectively. An NMP based electrode is added for comparison. Figure 1: Schematic representation of the EMBATT concept. Plot 1: Cycling test for 5 coin cells, LTO/LFP, 1C/1C, 25 °C Figure 2: Al2O3 layer coated on LFP based cathode. SEPARATOR COATING Replacement of additional separators With the aim of omitting a conventional separator, which has to be placed in the cell during the manufacturing process, a technology was developed to apply a separator directly on the electrode. In figure 2, an Al2O3 based separator was coated directly on the LFP cathode. By optimizing the coating process, thicknesses of approx. 30 µm could be achieved. In EMBATT2.0, a solid polymeric electrolyte will be applied simultaneously. ACKNOWLEDGEMENT 1 This work is supported by funds from Europäische Fonds für regionale Entwicklung (EFRE) and the Freistaat Sachsen in frame of the "ePadFab" project. ACKNOWLEDGEMENT 2 The project is conducted together with our partners thyssenkrupp System Engineering GmbH and IAV GmbH. Plot 2: Rate capability for water based LTO electrodes Plot 3: Norm. capacity for water based LTO electrodes BIPOLAR CELLS AND STACKS Test cells Dedicated bipolar test cells have been developed. They consist of electrodes coated on an Aluminum current collector. One side is coated with LFP and the other one with LTO. The electrode are is 5 x 5 cm 2 . An insulator is used to electrically separate the adjacent current collectors and for mechanical stability. Electrolyte filling and assembly Two capillaries are inserted between the electrodes (Fig. 3). Different filling strategies have been evaluated inside an Ar-filled glovebox. Electrochemical characterization First, the performance of the electrodes in the bipolar test setup (Fig. 3) have been verified by comparing with the performance in coin cells (Plot 4). Then, bipolar stacks consisting of 4 single cells have been manufactured. In plot 5 the stack voltage as well as the sing cell voltages are shown. Plot 5: Bipolar stack voltage and single cell voltages CONCLUSIONS AND OUTLOOK Several technological solutions for the manufacturing of large bipolar batteries have been developed in EMBATT1.0: water based processes for thick electrodes, bipolar electrodes, separators coated on the electrodes and electrolyte filling strategies. In the recently started project EMBATT2.0 material innovations such as dedicated active materials, polymeric electrolytes and polymer based current collectors will increase energy densities up to 450 Wh/l on system level. Plot 4: Comparison of coin cell and bipolar single cell Figure 3: Components of the bipolar stack. Cathode (left) with separator, electrolyte filling capillary and insulator and Anode (right). To form a bipolar test battery several of the shown components are stacked and the single cells are filled with electrolyte. 0 50 100 40 60 80 100 120 140 160 180 Spec. Capacity / mAh/g Cycle number 0,996 0,998 1,000 1,002 1,004 CE LTO vs. LFP; A/K=0,77 20 µm Al LFP Al 2 O 3 0 1 2 3 4 5 6 7 8 9 10 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 Area specific capacity / mAh/cm 2 C-Rate Water based: 31 µm 59 µm 79 µm 102 µm NMP based: 43 µm 0 1 2 3 4 5 6 7 8 9 10 0,0 0,2 0,4 0,6 0,8 1,0 Water based: 31 µm 59 µm 79 µm 102 µm NMP based: 43 µm Normalized capacity C-Rate 1 2 3 4 5 6 7 8 9 0% 50% 100% 50% 0% 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 Bipolar stack, 4 cells Bipolar stack, cell 1 Bipolar stack, cell 2 Bipolar stack, cell 3 Bipolar stack, cell 4 state of charge (normalized) U / V (bipolar stack) U / V (single cells) 0% 50% 100% 50% 0% 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 Coincell Bipolar, single cell state of charge U / V Insulator LFP / cathode LTO / anode Separator Capillary
Transcript of MATERIAL AND PROCESS DEVELOPMENT FOR LITHIUM ......EMBATT1.0: water based processes for thick...
www.ikts.fraunhofer.de © Fraunhofer IKTS
MATERIAL AND PROCESS DEVELOPMENT FOR LITHIUM BIPOLAR BATTERIES
Kristian Nikolowski*, Mareike Wolter, Marco Fritsch, Stefan Börner, Beate Capraro
Fraunhofer-Institut für Keramische Technologien und Systeme IKTS, Dresden, Germany
INTRODUCTION Conventional monopolar lithium batteries are limited in energy density due to the high share of inactive components and limited volume utilization on cell as well as on system level. The EMBATT bipolar battery concept (fig. 1) reduces the amount of inactive components and leads to improved integration properties for automotive applications. Main challenges which have been identified concern: Technological solutions for electrode and system manufacturing Material innovations for active material, electrolyte and current collector Fraunhofer IKTS is addressing these topics in the projects EMBATT1.0 (manufacturing technology) and EMBATT2.0 (material innovations) as summarized in table 1.
Table 1: Comparison of the generations of the EMBATT bipolar battery
EMBATT1.0 EMBATT2.0
Materials Commercial LFP and LTO Liquid electrolyte Al-current collector
High voltage system LTO/LNMO with optimized particle morphology Polymer electrolyte Polymer current collector
Energy density on battery system level
> 200 Wh/l > 450 Wh/l
Contact: Dr.-Ing. Kristian Nikolowski | Fraunhofer Institute for Ceramic Technologies and Systems IKTS | System Integration and Technology Transfer | Mobile Energy Storage Systems | Winterbergstrasse 28, 01277 Dresden, Germany | Phone +49 351 2553-7267 | [email protected]
WATER BASED ELECTRODES Slurry development Water based slurry recipes have been developed for LTO and LFP. Then, electrodes were manufactured on pilot scale coating equipment. Plot 1 shows the results of LTO limited coin cells. Increasing electrode thickness The slurry recipes and coating parameters were optimized with the goal of increasing electrode thickness. Plots 2 and 3 show the area specific capacity and the normalized capacity, respectively. An NMP based electrode is added for comparison.
Figure 1: Schematic representation of the EMBATT concept.
Plot 1: Cycling test for 5 coin cells, LTO/LFP, 1C/1C, 25 °C
Figure 2: Al2O3 layer coated on LFP based cathode.
SEPARATOR COATING Replacement of additional separators With the aim of omitting a conventional separator, which has to be placed in the cell during the manufacturing process, a technology was developed to apply a separator directly on the electrode. In figure 2, an Al2O3 based separator was coated directly on the LFP cathode. By optimizing the coating process, thicknesses of approx. 30 µm could be achieved. In EMBATT2.0, a solid polymeric electrolyte will be applied simultaneously.
ACKNOWLEDGEMENT 1 This work is supported by funds from Europäische Fonds für regionale Entwicklung (EFRE) and the Freistaat Sachsen in frame of the "ePadFab" project.
ACKNOWLEDGEMENT 2 The project is conducted together with our partners thyssenkrupp System Engineering GmbH and IAV GmbH.
Plot 2: Rate capability for water based LTO electrodes
Plot 3: Norm. capacity for water based LTO electrodes
BIPOLAR CELLS AND STACKS Test cells Dedicated bipolar test cells have been developed. They consist of electrodes coated on an Aluminum current collector. One side is coated with LFP and the other one with LTO. The electrode are is 5 x 5 cm2. An insulator is used to electrically separate the adjacent current collectors and for mechanical stability. Electrolyte filling and assembly Two capillaries are inserted between the electrodes (Fig. 3). Different filling strategies have been evaluated inside an Ar-filled glovebox. Electrochemical characterization First, the performance of the electrodes in the bipolar test setup (Fig. 3) have been verified by comparing with the performance in coin cells (Plot 4). Then, bipolar stacks consisting of 4 single cells have been manufactured. In plot 5 the stack voltage as well as the sing cell voltages are shown.
Plot 5: Bipolar stack voltage and single cell voltages
CONCLUSIONS AND OUTLOOK Several technological solutions for the manufacturing of large bipolar batteries have been developed in EMBATT1.0: water based processes for thick electrodes, bipolar electrodes, separators coated on the electrodes and electrolyte filling strategies. In the recently started project EMBATT2.0 material innovations such as dedicated active materials, polymeric electrolytes and polymer based current collectors will increase energy densities up to 450 Wh/l on system level.
Plot 4: Comparison of coin cell and bipolar single cell
Figure 3: Components of the bipolar stack. Cathode (left) with separator, electrolyte filling capillary and insulator and Anode (right). To form a bipolar test battery several of the shown components are stacked and the single cells are filled with electrolyte.
0 50 10040
60
80
100
120
140
160
180
Spec
. Cap
acity
/ m
Ah/
g
Cycle number
0,996
0,998
1,000
1,002
1,004
CE
LTO vs. LFP; A/K=0,77
20 µm
Al
LFP
Al2O3
0 1 2 3 4 5 6 7 8 9 10
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
Are
a sp
ecifi
c ca
pacit
y / m
Ah/
cm2
C-Rate
Water based: 31 µm 59 µm 79 µm 102 µm
NMP based: 43 µm
0 1 2 3 4 5 6 7 8 9 10
0,0
0,2
0,4
0,6
0,8
1,0
Water based: 31 µm 59 µm 79 µm 102 µm
NMP based: 43 µm
Nor
mal
ized
cap
acity
C-Rate
1
2
3
4
5
6
7
8
9
0% 50% 100% 50% 0%
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
2,4
2,6
Bipolar stack, 4 cells Bipolar stack, cell 1 Bipolar stack, cell 2 Bipolar stack, cell 3 Bipolar stack, cell 4
state of charge (normalized)
U /
V (b
ipol
ar s
tack
)
U /
V (s
ingl
e ce
lls)
0% 50% 100% 50% 0%
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
2,4
2,6
Coincell Bipolar, single cell
state of charge
U /
V
InsulatorLFP / cathode
LTO / anodeSeparatorCapillary
