Degradation of battery separators under charge–discharge cycles

Abstract

Researchers have reported on the electrochemical aging of lithium-ion batteries. The mechanisms of battery capacity loss, such as consumption of electrolytes and fading of electrodes, commonly seen as fracture of coatings, have been studied intensively. The widely used polymeric separators sandwiched between cathode and anode, which do not directly contribute to the electrochemical properties of the cell, are usually taken as chemically, thermally and structurally stable materials. In this paper, the degradation of a dry processed trilayer separator due to charge-discharge cycles is investigated. It has been found that the separators that underwent higher cycles failed at lower lateral punch force and smaller deformation. Live cell tests also indicate that the deformation and force intensity at the onset of short circuit decreased for a cell after 1200 cycles compared to those for a non-cycled cell, when under lateral indentation. Different characterization methods were used to understand this charge-discharge induced mechanical aging. SEM through-thickness views of the separators show no significant pore size change, but reaction products accumulated in pores of the separator middle layer. FTIR (Fourier Transform Infrared) examination of the surfaces of those separators shows there was no apparent chemical bond change on the surface of the separator during charging and discharging process.

Elliptical lithium‐ion batteries: Transverse and axial loadings under wet/dry conditions

“…This is consistent with previous studies of dry processed polymeric separators by Zhang et al 25,26 For the axial compression loading case, no significant difference was observed between location of first peak and onset of short circuit between dry and wet cells. In the case of the hemispherical punch indentation, no difference was observed in the fracture patterns between wet and dry cells, both having cracks in the direction parallel to the MD.…”

“…A recent review on the modeling of lithium-ion cells revealed 1 that previous studies have focused mostly on two common form factors, pouch 2-7 and cylindrical [7][8][9][10][11][12][13][14][15][16][17][18][19] cells and their components. [20][21][22][23][24][25][26] A third type of batteries commonly used in various applications such as electric vehicles is the prismatic cell. The main difference between prismatic and cylindrical cells is the arrangement of electrode-separator layers.…”

Topological and network analysis of lithium ion battery components: the importance of pore space connectivity for cell operation

“…36 By leveraging known trends in how a structure of a given topology shrinks under thermal stress, 37 deforms in response to compressive or tensile stresses, 38,39 or maintains connectivity despite closing of branches or nodes, 36 it will be possible to predict a separator's response to many of the dynamic processes experienced during cell manufacturing and operation. 40 Connectivity density can be calculated via a Minkowski functional and is important when describing homogenisation of ion concentration gradients across microstructures. Similarly, other morphological and topological parameters are helpful when assessing surface interactions and effects.…”

A Nacre‐Inspired Separator Coating for Impact‐Tolerant Lithium Batteries

“…Under the stress of external shock, the microporous polyolefin separator can easily deform, accompanied with the change of inside porous network, including the pore closure, leading to the inhomogeneous Li + ion flux in the battery . The nonuniform Li + ion flux can then create high local current density to trigger lithium dendrite growth on the electrode, resulting in short circuit and even explosion of lithium batteries …”

“…[11] The nonuniform Li + ion flux can then create high local current density to trigger lithium dendrite growth on the electrode, resulting in short circuit and even explosion of lithium batteries. [12][13][14][15] Currently, ceramic nanoparticle coat ings are widely used to protect micro porous polyolefin separators because of their good electrolyte wettability and high thermal stability. [16,17] However, these ceramic nanoparticle coatings cannot provide enough protec tion for the microporous polyolefin separators against external impacts because of the limited mechanical energy dissipation capabilities.…”