Absorptive Glass Mat

Compression-recovery model of Absorptive Glass Mat (AGM) separator

Guided by X-ray micro-computed tomography analysis

A b s t r a c t   Absorptive glass mat (AGM) separators play a key role in enhancing the cycle life of the valve regulated lead acid (VRLA) batteries by maintaining the elastic characteristics under a defined level of compression force with the plates of the electrodes. Inevitably, there are inherent challenges to maintain the required level of compression characteristics of AGM separators during the charge and discharge of the battery. Herein, we report a three-dimensional (3D) analytical model for predicting the compression-recovery behavior of AGM separators by formulating a direct relationship with the constituent fiber and structural parameters. The analytical model of compression-recovery behavior of AGM separators has successfully included the fiber slippage criterion and internal friction losses. The presented work uses, for the first time, 3D data of fiber orientation from X-ray micro-computed tomography, for predicting the compression-recovery behavior of AGM separators. A comparison has been made between the theoretical and experimental results of compression-recovery behavior of AGM samples with defined fiber orientation characteristics. In general, the theory agreed reasonably well with the experimental results of AGM samples in both dry and wet states. Through theoretical modeling, fiber volume fraction was established as one of the key structural parameters that modulates the compression hysteresis of an AGM separator.   I n t r o d u c t i o n:   Valve regulated lead acid (VRLA) batteries, a common variant of traditional lead-acid batteries, have evolved as a major constituent serving the worldwide battery market share. Technological advances in terms of requirement of powerful and reliable power sources pose an enormous challenge for VRLA batteries to compete with the emerging dominance of lithium ion and nickel based batteries [1e3]. Some of these challenges can be realized by deconstructing the design aspects of key attributes of VRLA batteries. Absorptive glass mat (AGM) used as a separator plays a key role for the successful functioning of VRLA batteries throughout the lifetime [4]. One of themajor functions of the AGM separator is to enhance the life cycle of the VRLA battery by maintaining the elastic characteristics under defined level of compression forces with the plates of the electrodes when it is soaked in an electrolyte solution [5]. This is a challenging task for an AGM separator as it shrinks in the thickness direction due to the fact that the constituent glass fibers have a greater affinity to each other in the wet state that inevitably results in a loss of compression force [6e9]. Further, there is a reduction in the thickness of an AGM separator after the load is being removed (also known as recovery) due to the losses in internal friction and the viscoelastic effects of glass fibers [8,10]. Consequently, these effects result in the loss of the contact between the separator and the electrode plates.  

By,

P.V. Kameswara Rao,

Alumni,

Government Institute of Textile Technology.

  (For further information, Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour)