Ion transport restriction in mechanically strained separator membranes

• Published in: Journal of power sources Vol. 226; pp. 149 - 155
• Main Authors: Cannarella, John, Arnold, Craig B.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.03.2013; Elsevier
• Subjects: Applied sciences; Capacity fade; Charge transfer; Compressing; Deformation; Direct energy conversion and energy accumulation; Electric cells; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Exact sciences and technology; Impedance; Lithium batteries; Lithium-ion battery; Mechanical stress; Membranes; Power fade; Separator; Separators; Tortuosity; Lithium-ion battery; Power fade; Capacity fade; Mechanical stress; Tortuosity; Separator; Compression; Alkaline storage battery; Ion transport; Secondary cell; Porous material; Lithium battery; Compressive stress; Porosity; State of charge; Impedance; Charge transfer; Power law; Alkaline cell; Mechanical deformation
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2012.10.093

We use AC impedance methods to investigate the effect of mechanical deformation on ion transport in commercial separator membranes and lithium-ion cells as a whole. A Bruggeman type power law relationship is found to provide an accurate correlation between porosity and tortuosity of deformed separators, which allows the impedance of a separator membrane to be predicted as a function of deformation. By using mechanical compression to vary the porosity of the separator membranes during impedance measurements it is possible to determine both the α and γ parameters from the modified Bruggeman relation for individual separator membranes. From impedance testing of compressed pouch cells it is found that separator deformation accounts for the majority of the transport restrictions arising from compressive stress in a lithium-ion cell. Finally, a charge state dependent increase in the impedance associated with charge transfer is observed with increasing cell compression. ► We model and measure the resistance increase associated with separator deformation. ► We show a Bruggeman relation can model tortuosity changes in deformed separators. ► We measure the α and γ Bruggeman parameters for monolayer separator membranes. ► We measure in situ the impedance changes in a pouch cell under applied compression.