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Characterization and performance evaluation of lithium-ion battery separators


Lithium-ion batteries (LIBs) with liquid electrolytes and microporous polyolefin separator membranes are ubiquitous. Though not necessarily an active component in a cell, the separator plays a key role in ion transport and influences rate performance, cell life and safety. As our understanding of separator properties and the interactions between the separator and the electrolyte deepens, it becomes evident that there are opportunities for improving separators to help meet the greater demands that new applications place on LIB technology. Here, we review the impact of the separator structure and chemistry on LIB performance, assess characterization techniques relevant for understanding structure–performance relationships in separator membranes, and provide an outlook on next-generation separator technology. Insights from this Review indicate that LIB performance can be improved by taking into account the interplay of the separator with its surroundings and indicate that, in the future, separators will be designed to play a more active role in LIB operation. Current and emerging characterization techniques will play an important role in guiding this evolution in separator technology.

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  1. 1.

    Palacín, M. R. & De Guibert, A. Why do batteries fail? Science 351, 1253292 (2016).

  2. 2.

    Arora, P. & Zhang, Z. Battery separators. Chem. Rev. 104, 4419–4462 (2004).

  3. 3.

    Lee, H., Yanilmaz, M., Toprakci, O., Fu, K. & Zhang, X. A review of recent developments in membrane separators for rechargeable lithium-ion batteries. Energy Environ. Sci. 7, 3857–3886 (2014). A review describing lithium-ion battery separator types, manufacturing routes and separator performance.

  4. 4.

    Deimede, V. & Elmasides, C. Separators for lithium-ion batteries: a review on the production processes and recent developments. Energy Technol. 3, 453–468 (2015).

  5. 5.

    Zhang, H., Zhou, M.-Y., Lin, C.-E. & Zhu, B.-K. Progress in polymeric separators for lithium ion batteries. RSC Adv. 5, 89848–89860 (2015).

  6. 6.

    Nunes-Pereira, J., Costa, C. M. & Lanceros-Méndez, S. Polymer composites and blends for battery separators: state of the art, challenges and future trends. J. Power Sources 281, 378–398 (2015).

  7. 7.

    Pintauro, P. N. Perspectives on membranes and separators for electrochemical energy conversion and storage devices. Polym. Rev. 55, 201–207 (2015).

  8. 8.

    Chandrasekaran, R. Quantification of contributions to the cell overpotential during galvanostatic discharge of a lithium-ion cell. J. Power Sources 262, 501–513 (2014).

  9. 9.

    Müller, S. et al. Quantifying inhomogeneity of lithium ion battery electrodes and its influence on electrochemical performance. J. Electrochem. Soc. 165, A339–A344 (2018).

  10. 10.

    Bandhauer, T. M., Garimella, S. & Fuller, T. F. A critical review of thermal issues in lithium-ion batteries. J. Electrochem. Soc. 158, R1–R25 (2011).

  11. 11.

    Liu, Q. Q., Petibon, R., Du, C. Y. & Dahn, J. R. Effects of electrolyte additives and solvents on unwanted lithium plating in lithium-ion cells. J. Electrochem. Soc. 164, A1173–A1183 (2017).

  12. 12.

    Valøen, L. O. & Reimers, J. N. Transport properties of LiPF6-based Li-ion battery electrolytes. J. Electrochem. Soc. 152, A882–A891 (2005).

  13. 13.

    Erickson, E. M. et al. Review-development of advanced rechargeable batteries: a continuous challenge in the choice of suitable electrolyte solutions. J. Electrochem. Soc. 162, A2424–A2438 (2015).

  14. 14.

    Doyle, M., Fuller, T. F. & Newman, J. The importance of the lithium ion transference number in lithium/polymer cells. Electrochim. Acta 39, 2073–2081 (1994).

  15. 15.

    Zugmann, S. et al. Measurement of transference numbers for lithium ion electrolytes via four different methods, a comparative study. Electrochim. Acta 56, 3926–3933 (2011).

  16. 16.

    Gores, H. J. et al. in Handbook of Battery Materials (eds Daniel, C. & Besenhard, J. O.) 525–626 (Wiley-VCH Verlag, Weinheim, 2011).

  17. 17.

    Djian, D., Alloin, F., Martinet, S., Lignier, H. & Sanchez, J. Y. Lithium-ion batteries with high charge rate capacity: influence of the porous separator. J. Power Sources 172, 416–421 (2007).

  18. 18.

    Harris, S. J. & Lu, P. Effects of inhomogeneities — nanoscale to mesoscale — on the durability of Li-ion batteries. J. Phys. Chem. C 117, 6481–6492 (2013).

  19. 19.

    Ramadass, P., Haran, B., White, R. & Popov, B. N. Capacity fade of Sony 18650 cells cycled at elevated temperatures: Part II. Capacity fade analysis. J. Power Sources 112, 614–620 (2002).

  20. 20.

    Lagadec, M. F., Ebner, M., Zahn, R. & Wood, V. Communication — Technique for visualization and quantification of lithium-ion battery separator microstructure. J. Electrochem. Soc. 163, A992–A994 (2016).

  21. 21.

    Cannarella, J. et al. Mechanical properties of a battery separator under compression and tension. J. Electrochem. Soc. 161, F3117–F3122 (2014). Compression experiments and simulations of separators; systematic analysis of strain rate-dependent mechanical properties of dry and immersed separators.

  22. 22.

    Cannarella, J. & Arnold, C. B. The effects of defects on localized plating in lithium-ion batteries. J. Electrochem. Soc. 162, A1365–A1373 (2015).

  23. 23.

    Wood, D. L., Li, J. & Daniel, C. Prospects for reducing the processing cost of lithium ion batteries. J. Power Sources 275, 234–242 (2015).

  24. 24.

    l’Abee, R., DaRosa, F., Armstrong, M. J., Hantel, M. M. & Mourzagh, D. High temperature stable Li-ion battery separators based on polyetherimides with improved electrolyte compatibility. J. Power Sources 345, 202–211 (2017).

  25. 25.

    Gor, G. Y., Cannarella, J., Leng, C. Z., Vishnyakov, A. & Arnold, C. B. Swelling and softening of lithium-ion battery separators in electrolyte solvents. J. Power Sources 294, 167–172 (2015).

  26. 26.

    Xu, J., Wang, L., Guan, J. & Yin, S. Coupled effect of strain rate and solvent on dynamic mechanical behaviors of separators in lithium ion batteries. Mater. Des. 95, 319–328 (2016).

  27. 27.

    Cannarella, J. & Arnold, C. B. Stress evolution and capacity fade in constrained lithium-ion pouch cells. J. Power Sources 245, 745–751 (2014).

  28. 28.

    Barai, A. et al. The effect of external compressive loads on the cycle lifetime of lithium-ion pouch cells. J. Energy Storage 13, 211–219 (2017).

  29. 29.

    Xu, J. et al. Deformation and failure characteristics of four types of lithium-ion battery separators. J. Power Sources 196, 137–145 (2016).

  30. 30.

    Peabody, C. & Arnold, C. B. The role of mechanically induced separator creep in lithium-ion battery capacity fade. J. Power Sources 196, 8147–8153 (2011).

  31. 31.

    Orendorff, C. J. The role of separators in lithium ion cell safety. Electrochem. Soc. Interface 21, 61–65 (2012).

  32. 32.

    Chandrasekaran, R. Quantification of bottlenecks to fast charging of lithium-ion-insertion cells for electric vehicles. J. Power Sources 271, 622–632 (2014).

  33. 33.

    Bach, T. C. et al. Nonlinear aging of cylindrical lithium-ion cells linked to heterogeneous compression. J. Energy Storage 5, 212–223 (2016).

  34. 34.

    Ecker, M., Shafiei Sabet, P. & Sauer, D. U. Influence of operational condition on lithium plating for commercial lithium-ion batteries — electrochemical experiments and post-mortem-analysis. Appl. Energy 206, 934–946 (2017).

  35. 35.

    Zhang, X., Zhu, J. & Sahraei, E. Degradation of battery separators under charge–discharge cycles. RSC Adv. 7, 56099–56107 (2017).

  36. 36.

    Whitaker, S. Flow in porous media I: a theoretical derivation of Darcy’s law. Transp. Porous Media 1, 3–25 (1986).

  37. 37.

    Torquato, S. Random Heterogeneous Materials (Springer Science+Business Media, New York, 2002).

  38. 38.

    Gor, G. Y., Cannarella, J., Prevost, J. H. & Arnold, C. B. A model for the behavior of battery separators in compression at different strain/charge rates. J. Electrochem. Soc. 161, F3065–F3071 (2014).

  39. 39.

    Finegan, D. P. et al. Characterising the structural properties of polymer separators for lithium-ion batteries in 3D using phase contrast X-ray microscopy. J. Power Sources 333, 184–192 (2016).

  40. 40.

    Lagadec, M. F., Zahn, R., Müller, S. & Wood, V. Topological and network analysis of lithium ion battery components: the importance of pore space connectivity for cell operation. Energy Environ. Sci. 11, 3194–3200 (2018). Transport simulations for different separator pore structures demonstrate the importance of non-traditional network parameters for describing separator performance.

  41. 41.

    Müllner, T., Unger, K. K. & Tallarek, U. Characterization of microscopic disorder in reconstructed porous materials and assessment of mass transport-relevant structural descriptors. New J. Chem. 40, 3993–4015 (2016).

  42. 42.

    Gering, K. L. Prediction of electrolyte conductivity: results from a generalized molecular model based on ion solvation and a chemical physics framework. Electrochim. Acta 225, 175–189 (2017).

  43. 43.

    Saito, Y., Morimura, W., Kuratani, R. & Nishikawa, S. Factors controlling the ionic mobility of lithium electrolyte solutions in separator membranes. J. Phys. Chem. C 120, 3619–3624 (2016). NMR measurements of diffusion coefficients of ions and solvent molecules in separator pores; discussion of how ion diffusion and electrolyte properties are influenced by separator geometry and surface interactions.

  44. 44.

    Saito, Y., Morimura, W., Kuse, S., Kuratani, R. & Nishikawa, S. Influence of the morphological characteristics of separator membranes on ionic mobility in lithium secondary batteries. J. Phys. Chem. C 121, 2512–2520 (2017).

  45. 45.

    Zahn, R., Lagadec, M. F., Hess, M. & Wood, V. Improving ionic conductivity and lithium-ion transference number in lithium-ion battery separators. ACS Appl. Mater. Interfaces 8, 32637–32642 (2016).

  46. 46.

    Lagadec, M. F., Zahn, R. & Wood, V. Designing polyolefin separators to minimize the impact of local compressive stresses on lithium ion battery performance. J. Electrochem. Soc. 165, A1829–A1836 (2018).

  47. 47.

    Bierenbaum, H. S., Isaacson, R. B., Druin, M. L. & Plovan, S. G. Microporous polymeric films. Ind. Eng. Chem. Prod. Res. Dev. 13, 2–9 (1974).

  48. 48.

    Sarada, T., Sawyer, L. C. & Ostler, M. I. Three dimensional structure of Celgard microporous membranes. J. Memb. Sci. 15, 97–113 (1983). Visualization of the three-dimensional microstructure of polypropylene separators using electron microscopy.

  49. 49.

    Lagadec, M. F., Ebner, M. & Wood, V. Microstructure of Targray PE16A Lithium-Ion Battery Separator (ETH Zurich, 2016);

  50. 50.

    Lagadec, M. F. & Wood, V. Microstructure of Celgard PP1615 Lithium-Ion Battery Separator (ETH Zurich, 2018);

  51. 51.

    Ferguson, J. C., Panerai, F., Borner, A. & Mansour, N. N. PuMA: the porous microstructure analysis software. SoftwareX 7, 81–87 (2018).

  52. 52.

    Cooper, S. J., Bertei, A., Shearing, P. R., Kilner, J. A. & Brandon, N. P. TauFactor: an open-source application for calculating tortuosity factors from tomographic data. SoftwareX 5, 203–210 (2016).

  53. 53.

    Hantel, M. M., Armstrong, M. J., DaRosa, F. & l’Abee, R. Characterization of tortuosity in polyetherimide membranes based on Gurley and electrochemical impedance spectroscopy. J. Electrochem. Soc. 164, A334–A339 (2017).

  54. 54.

    Abraham, K. M. & Alamgir, M. Polymer electrolytes reinforced by Celgard membranes. J. Electrochem. Soc. 142, 683–687 (1995).

  55. 55.

    Martinez-Cisneros, C., Antonelli, C., Levenfeld, B., Varez, A. & Sanchez, J. Y. Evaluation of polyolefin-based macroporous separators for high temperature Li-ion batteries. Electrochim. Acta 216, 68–78 (2016).

  56. 56.

    Song, J. Y., Wang, Y. Y. & Wan, C. C. Conductivity study of porous plasticized polymer electrolytes based on poly(vinylidene fluoride): a comparison with polypropylene separators. J. Electrochem. Soc. 147, 3219–3225 (2000).

  57. 57.

    Tung, K. L. et al. Recent advances in the characterization of membrane morphology. Curr. Opin. Chem. Eng. 4, 121–127 (2014).

  58. 58.

    Dahbi, M. et al. Interfacial properties of LiTFSI and LiPF6-based electrolytes in binary and ternary mixtures of alkylcarbonates on graphite electrodes and Celgard separator. Ind. Eng. Chem. Res. 51, 5240–5245 (2012).

  59. 59.

    Cheng, Q., He, W., Zhang, X., Li, M. & Song, X. Recent advances in composite membranes modified with inorganic nanoparticles for high-performance lithium ion batteries. RSC Adv. 6, 10250–10265 (2016).

  60. 60.

    Huang, C., Lin, C. C., Tsai, C. Y. & Juang, R. S. Tailoring surface properties of polymeric separators for lithium-ion batteries by cyclonic atmospheric-pressure plasma. Plasma Process. Polym. 10, 407–415 (2013).

  61. 61.

    Li, B. et al. Facile and nonradiation pretreated membrane as a high conductive separator for Li-ion batteries. ACS Appl. Mater. Interfaces 7, 20184–20189 (2015).

  62. 62.

    Xu, W. et al. Layer-by-layer deposition of organic-inorganic hybrid multilayer on microporous polyethylene separator to enhance the electrochemical performance of lithium-ion battery. ACS Appl. Mater. Interfaces 7, 20678–20686 (2015).

  63. 63.

    Stephan, A. M. Review on gel polymer electrolytes for lithium batteries. Eur. Polym. J. 42, 21–42 (2006).

  64. 64.

    Landesfeind, J., Hattendorff, J., Ehrl, A., Wall, W. A. & Gasteiger, H. A. Tortuosity determination of battery electrodes and separators by impedance spectroscopy. J. Electrochem. Soc. 163, A1373–A1387 (2016).

  65. 65.

    Huang, X. Separator technologies for lithium-ion batteries. J. Solid State Electrochem. 15, 649–662 (2011).

  66. 66.

    Thorat, I. V. et al. Quantifying tortuosity in porous Li-ion battery materials. J. Power Sources 188, 592–600 (2009).

  67. 67.

    Ehrl, A., Landesfeind, J., Wall, W. A. & Gasteiger, H. A. Determination of transport parameters in liquid binary electrolytes: I. Diffusion coefficient. J. Electrochem. Soc. 164, A826–A836 (2017).

  68. 68.

    Devaux, D. et al. Conductivity of carbonate- and perfluoropolyether-based electrolytes in porous separators. J. Power Sources 323, 158–165 (2016).

  69. 69.

    Zahn, R., Lagadec, M. F. & Wood, V. Transport in lithium ion batteries: reconciling impedance and structural analysis. ACS Energy Lett. 2, 2452–2453 (2017).

  70. 70.

    Plaimer, M. et al. Evaluating the trade-off between mechanical and electrochemical performance of separators for lithium-ion batteries: methodology and application. J. Power Sources 306, 702–710 (2016).

  71. 71.

    Xiao, X., Wu, W. & Huang, X. A multi-scale approach for the stress analysis of polymeric separators in a lithium-ion battery. J. Power Sources 195, 7649–7660 (2010).

  72. 72.

    Shi, D., Xiao, X., Huang, X. & Kia, H. Modeling stresses in the separator of a pouch lithium-ion cell. J. Power Sources 196, 8129–8139 (2011).

  73. 73.

    Cannarella, J. & Arnold, C. B. The effects of defects on localized plating in lithium-ion batteries. J. Electrochem. Soc. 162, A1365–A1373 (2015).

  74. 74.

    Pan, Y. & Zhong, Z. Modeling the ion transport restriction in mechanically strained separator membranes. J. Electrochem. Soc. 161, A583–A586 (2014).

  75. 75.

    Sheidaei, A., Xiao, X., Huang, X. & Hitt, J. Mechanical behavior of a battery separator in electrolyte solutions. J. Power Sources 196, 8728–8734 (2011).

  76. 76.

    Yan, S., Xiao, X., Huang, X., Li, X. & Qi, Y. Unveiling the environment-dependent mechanical properties of porous polypropylene separators. Polymer 55, 6282–6292 (2014).

  77. 77.

    Forgez, C., Vinh Do, D., Friedrich, G., Morcrette, M. & Delacourt, C. Thermal modeling of a cylindrical LiFePO4/graphite lithium-ion battery. J. Power Sources 195, 2961–2968 (2010).

  78. 78.

    Love, C. T. Perspective on the mechanical interaction between lithium dendrites and polymer separators at low temperature. J. Electrochem. Energy Convers. Storage 13, 031004 (2016). Analysis of the temperature- and shape-dependent mechanical interactions between lithium dendrites and separators.

  79. 79.

    Development of an Advanced Microporous Separator for Lithium Ion Batteries Used in Vehicle Applications (United States Advanced Battery Consortium, 2018).

  80. 80.

    Xu, H., Zhu, M., Marcicki, J. & Yang, X. G. Mechanical modeling of battery separator based on microstructure image analysis and stochastic characterization. J. Power Sources 345, 137–145 (2017).

  81. 81.

    Dai, J. et al. A rational design of separator with substantially enhanced thermal features for lithium-ion batteries by the polydopamine–ceramic composite modification of polyolefin membranes. Energy Environ. Sci. 9, 3252–3261 (2016).

  82. 82.

    Jana, A., Ely, D. R. & García, R. E. Dendrite–separator interactions in lithium-based batteries. J. Power Sources 275, 912–921 (2015).

  83. 83.

    Liu, X. M., Fang, A., Haataja, M. P. & Arnold, C. B. Size dependence of transport non-uniformities on localized plating in lithium-ion batteries. J. Electrochem. Soc. 165, 1147–1155 (2018). Experimental and theoretical analysis of how structural separator inhomogeneities affect ion transport.

  84. 84.

    Sun, F. et al. Morphological evolution of electrochemically plated/stripped lithium microstructures investigated by synchrotron X-ray phase contrast tomography. ACS Nano 10, 7990–7997 (2016).

  85. 85.

    Kerman, K., Luntz, A., Viswanathan, V., Chiang, Y.-M. & Chen, Z. Practical challenges hindering the development of solid state Li ion batteries. J. Electrochem. Soc. 164, A1731–A1744 (2017).

  86. 86.

    Xu, C., Ahmad, Z., Aryanfar, A., Viswanathan, V. & Greer, J. R. Enhanced strength and temperature dependence of mechanical properties of Li at small scales and its implications for Li metal anodes. Proc. Natl Acad. Sci. USA 114, 57–61 (2017).

  87. 87.

    Hallinan, D. T. & Balsara, N. P. Polymer electrolytes. Annu. Rev. Mater. Res. 43, 503–525 (2013).

  88. 88.

    Feng, X. et al. Thermal runaway mechanism of lithium ion battery for electric vehicles: a review. Energy Storage Mater. 10, 246–267 (2018).

  89. 89.

    Etacheri, V., Marom, R., Elazari, R., Salitra, G. & Aurbach, D. Challenges in the development of advanced Li-ion batteries: a review. Energy Environ. Sci. 4, 3243–3262 (2011).

  90. 90.

    Nitta, N., Wu, F., Lee, J. T. & Yushin, G. Li-ion battery materials: present and future. Mater. Today 18, 252–264 (2015).

  91. 91.

    Hassoun, J. & Scrosati, B. Advances in anode and electrolyte materials for the progress of lithium-ion and beyond lithium-ion batteries. J. Electrochem. Soc. 162, A2582–A2588 (2015).

  92. 92.

    Bauer, I., Thieme, S., Brückner, J., Althues, H. & Kaskel, S. Reduced polysulfide shuttle in lithium-sulfur batteries using Nafion-based separators. J. Power Sources 251, 417–422 (2014).

  93. 93.

    Zhu, W. et al. Improving the electrochemical performance of polypropylene separator through instantaneous photo-induced functionalization. J. Electrochem. Soc. 165, A1909–A1914 (2018).

  94. 94.

    Ryou, M. H. et al. Excellent cycle life of lithium-metal anodes in lithium-ion batteries with mussel-inspired polydopamine-coated separators. Adv. Energy Mater. 2, 645–650 (2012).

  95. 95.

    Sun, Y. Lithium ion conducting membranes for lithium-air batteries. Nano Energy 2, 801–816 (2013).

  96. 96.

    Kirchhöfer, M., Von Zamory, J., Paillard, E. & Passerini, S. Separators for Li-ion and Li-metal battery including ionic liquid based electrolytes based on the TFSI- and FSI- anions. Int. J. Mol. Sci. 15, 14868–14890 (2014).

  97. 97.

    Bruce, P. G. & Vincent, C. A. Steady state current flow in solid binary electrolyte cells. J. Electroanal. Chem. 225, 1–17 (1987).

  98. 98.

    Wood, V. X-ray tomography for battery research and development. Nat. Rev. Mater. 3, 293–295 (2018).

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The authors gratefully acknowledge support from an ETH research grant (0-20978-14) and the European Research Council (project 680070).

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The authors declare no competing interests.

Correspondence to Vanessa Wood.

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    Characterization and performance evaluation of lithium ion battery separators

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Further reading

Fig. 1: Separators in LIBs.
Fig. 2: Links between properties and performance.
Fig. 3: Separator structure and degradation.