Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime

Transcription

1 AABC Europe Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime Mainz Prof. Dr.-Ing. Andreas Jossen, Bernhard Rieger Institute for Electrical Energy Storage Technology (EES) Karlstrasse 45, Munich, Technical University of Munich Tel.: Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 1

2 Overview Motivation Courses of micro-mechanic issues From crystal level to cell level Strain within electrodes Coupled model approach Influence on cell design Validation and lifetime influence Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 2

3 In cylindrical cells, swelling can shorten lifetime The core is more stressed than the outer area One reason why upscaling of cylindrical cells is limited Source: Presentation Prof. T. Takamura Carbon Material in Power Sources. June 2005, ZSW Ulm Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 3

4 Investigation of the non linear aging effect Inhomogeneous plating: Higher compression results un faster li-plating (a) Outer part of the negative electrode exposed to 6 fast cycles. (b) Inner part of the same electrode showing a stripe pattern. Plating is marked by an ellipsis and arrows. (a) Computed tomographic crosscut of a pristine cell. The positive (1) and negative (2) current collector tabs are visible. The positive current collector is marked by an ellipsis, resulting deformations to the jelly rolls are marked by arrows. The positive current collector deforms the jelly roll. T. C. Bach, S. F. Schuster, E. Fleder, J. Müller, M. J. Brand, H. Lorrmann, A. Jossen, G. Sextl, Nonlinear aging of cylindrical lithium-ion cells linked to heterogeneous compression, Journal of Energy Storage, Vol. 5 (2015) Pages Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 4

5 Investigation of the non linear aging effect Forced heterogeneous compression by a hose clamp Heterogeneous compression results in li- plating in the areas with higher pressure. Possible reason is the compression of the separator and its local change in diffusion path. A hose clamp is placed on a cell. (b) Plating is visible on the overlap of the current collector imprints and the clamp which are visualized by black and red rectangles respectively. Conclusion: Better understanding of volume change and pressure within cells, electrodes and particles is necessary. T. C. Bach, S. F. Schuster, E. Fleder, J. Müller, M. J. Brand, H. Lorrmann, A. Jossen, G. Sextl, Nonlinear aging of cylindrical lithium-ion cells linked to heterogeneous compression, Journal of Energy Storage, Vol. 5 (2015) Pages Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 5

6 First volume change measurements Our initial investigations: Dilatometry of anode and cathode, displacement and single side laser scanning. A commercial pouch cell was selected Dilatometry with EL-CELL device Two side displacement measurement was set up A single side laser scanner was installed. B. Rieger, S. Schlueter, S.V. Erhard, J. Schmalz, G. Reinhart, A. Jossen, Multi-scale investigation of thickness changes in a commercial pouch type lithium-ion battery, Journal of Energy Storage (2016) Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 6

7 Measurement of volume change on crystal level of LCO Left figure: Unit cell parameters during charging for the O3 I and O3 II phases. Right figure: Comparison of the lattice unit cell volume change and the height change of the electrode during charging B. Rieger, S. Schlueter, S. V. Erhard and A. Jossen, Journal of The Electrochemical Society, 163 (8) A1595-A1606 (2016) Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 7

8 First volume change measurement Results of graphite-anode Non linear volume change - 1/3 approx. linear - next 1/3 reduced slope - last 1/3 increasing - at the end fast increase fits to stages in graphite Total volume change approx. 7% (reversible) Volume increases with lithiation Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 8

9 First volume change measurement Anode and cathode contribution to the battery thickness change during discharge Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 9

10 Influence of electrode structure Are structures based on spherical particles representative for real structures? Real structure reconstructed structure B. Rieger, S. Schlueter, S. V. Erhard and A. Jossen, Strain Propagation in Lithium-Ion Batteries from the Crystal Structure to the Electrode Level, Journal of The Electrochemical Society, 163 (8) A1595-A1606 (2016) Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 10

11 Measurement of volume change Modeling setup used in this study. a) Representative spherical particle model (RSPM). b) Realistic microstructure model (adapted from SEM cross-sectional images of the electrode) Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 11

12 Simulation results with representative spherical particle model Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 12

13 Relationship between volume change and thickness change Thickness change as a function of volume change and active material fraction: Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 13

14 Taking the thermal expansion into account Total expansion: Determined thermal expansion coefficients α cell at various SoC. Thermal expansion α cell = 1.1 μm K for a 6.5 mm thick cell B. Rieger, S.V. Erhard, K. Rumpf, A. Jossen, A new method to model the thickness change of a commercial pouch cell during discharge, J. Electrochem. Soc. 163 (2016) A1566-A Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 14

15 Simulation results Overall expansion Thermal expansion Intercalation expansion Simulated and measured displacement curves for different discharge rates. a) Overall pouch cell displacement t cell. b) Thermal displacement t th. c) Intercalation displacement t int B. Rieger, S.V. Erhard, K. Rumpf, A. Jossen, A new method to model the thickness change of a commercial pouch cell during discharge, J. Electrochem. Soc. 163 (2016) A1566-A Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 15

16 Coupled 3D Cell Model B. Rieger, S.V. Erhard, S. Kosch, M. Venator, A. Rheinfeldpf, A. Jossen, Multi-Dimensional Modeling of the Influence of Cell Design on Temperature, Displacement and Stress Inhomogeneity in Large-Format Lithium-Ion Cells, J. Electrochem. Soc. 163 (2016) A3099-A Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 16

17 Comparing of 2 cell designs Temperature at the end cc of discharge B. Rieger, S.V. Erhard, S. Kosch, M. Venator, A. Rheinfeldpf, A. Jossen, Multi-Dimensional Modeling of the Influence of Cell Design on Temperature, Displacement and Stress Inhomogeneity in Large-Format Lithium-Ion Cells, J. Electrochem. Soc. 163 (2016) A3099-A Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 17

18 Measurement (2d) of volume change Two 2d laser scanner system: Two 1d laser plus movement of scanner Two laser scanners scan the cell from both sides (frontside and backside) Inside a temperature controlled chamber Post-processing method for highly reproducible local thickness measurement (repeatability of approx. 10 μm between 100 cycles and 2 μm for consecutive measurements) Rieger, B., Schuster, S. F., Erhard, S. V., Osswald, P. J., Rheinfeld, A., Willmann, C., & Jossen, A. (2016). Multi-directional laser scanning as innovative method to detect local cell damage during fast charging of lithium-ion cells. Journal of Energy Storage, 8, Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 18

19 Measurement (2d) of volume change Charging of a cell with 1C rate At different temperatures At 40 C volume change is homogeneous and it is as expected (about 160 um) At 25 C there is an additional volume increase in the area of the terminals At 17 C the effect is increased. The volume change increases with decreasing distance to the terminals The volume change reaches a peak about cc charge phase is switched to cv charge phase. The thickness is decreasing to the expected value within about 30 minutes. Temperature effects have ben calculated and are not the reason for the effect. We assume increased Li-plating caused by the current density inhomogeneities Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 19

20 1C charging at different temperature 40 C 25 C 17 C Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 20

21 Reversible and irreversible volume change Laser-Checkup is conducted every 100 cycles inside the laser test benchto detect reversible and irreversible thickness changes Displacement overshoot results in faster capacity fade at 1C 25 C Linear aging for homogeneous load cases during charging Bernhard Rieger, Simon V. Erhard, Peter Keil, Andreas Jossen, Multi-Directional 3D Laser Scanning of Lithium-Ion Cells to Detect Inhomogeneity during Cycling and Aging, International Meeting on Lithium Batteries (IMLB) Chicago, June 19-24, Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 21

22 Reversible and irreversible volume change during lifetime Reversible thickness change (top) and irreversible thickness change (bottom) for aging at 0.5C charging rate Irreversible thickness increase is highest in the first 100 cycles and is evenly distributed Bernhard Rieger, Simon V. Erhard, Peter Keil, Andreas Jossen, Multi-Directional 3D Laser Scanning of Lithium-Ion Cells to Detect Inhomogeneity during Cycling and Aging, International Meeting on Lithium Batteries (IMLB) Chicago, June 19-24, Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 22

23 Reversible and irreversible volume change during lifetime Reversible thickness change (top) and irreversible thickness change (bottom) for aging at 1C charging rate Large irreversible thickness increase when lithium plating takes place Bernhard Rieger, Simon V. Erhard, Peter Keil, Andreas Jossen, Multi-Directional 3D Laser Scanning of Lithium-Ion Cells to Detect Inhomogeneity during Cycling and Aging, International Meeting on Lithium Batteries (IMLB) Chicago, June 19-24, Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 23

24 Conclusions Volume change by intercalation on crystal level has an significant impact on: Forces in electrode and between electrode and current collector Thickness change of electrodes and cells, even inhomogeneous Volume is also increased by temperature and by Li-plating Inhomogeneous compression, as seen in cylindrical cells, result in inhomogeneous Li-plating inside the cell. Li-plating starts first in areas with higher compression Volume change can be represented by simplified Electrode models Inhomogeneous current distribution results in inhomogeneous SoC, followed by inhomogeneous volume change and mechanical stress. During charging, inhomogeneous charge currents result in inhomogeneous li-plating, including overshooting in thickness. First 3D coupled mechanical-chemical-thermal model shows good results Further model improvement necessary, taking Li-plating into account Volume Change from Materials to Cell Level and Its Influence on Battery Lifetime 24