Coupled Effect of Low Temperature and Electrolyte Immersion on the Tensile Properties of Separators in Lithium-Ion Batteries

Abstract

The performance degradation at low temperatures and frequent safety accidents have aggravated security risks and inhibited the long-term service of lithium-ion batteries (LIBs). As a key component of LIBs, the separator has a great impact on the performance and safety of the battery. In this study, tensile tests of two commercial polyolefin separators (Celgard 2325 and Celgard PE) are performed under low-temperature and immersion conditions. Four representative temperature points and dimethyl carbonate [(DMC), the common solvent in electrolytes] are selected to investigate the coupling effect on the mechanical properties of the separators. The results show that both the separators have anisotropy, but the performance of Celgard 2325 varies more significantly than that of Celgard PE along different directions. Additionally, it is found that with a decrease in the temperature, the tensile strength of the two separators increases, while the elongation decreases. Electrolyte immersion induces a softening tendency in Celgard 2325. Due to the special effect of the residual electrolyte on polyethylene fibers, Celgard PE shows the opposite result. Furthermore, the effect of low temperature is revealed by the analysis of the crystallinity and molecular structure, which can be obtained by X-ray diffraction and Raman spectroscopy, respectively. In addition, the contact angle is measured to describe the wettability variation related to low temperature. The present work provides a theoretical basis and experimental data for the application and development of separators.

Environmental Stress-Induced Fracture Behavior of Polypropylene Battery Separators: Insights into Creep Behavior and Mechanical Stability

“…A larger discrepancy in solubility parameters leads to a diminished effect of surface disturbance and solvent-induced swelling on the separator. 39 The presence of surface energy leads to a tendency for interface separation between the solvent and the separator. Moreover, introducing solvents with lower solubility parameters suppresses yielding behavior, as shown in the magnified area of the strain from 0 to 20% in Figure 4b.…”

“…This increase is attributed to the pore elastic effect within the porous structure. The compression by solvents prompts internal material flow to occupy pores, enhancing both strength and modulus. ,− …”

“…Figure c,d reveals that as the difference in solubility parameter between the solvent and PP increases, there is a decrease in both the elastic modulus and the strain-hardening modulus of the stress–strain curves, accompanied by an increase in yield strain and stress. A larger discrepancy in solubility parameters leads to a diminished effect of surface disturbance and solvent-induced swelling on the separator . The presence of surface energy leads to a tendency for interface separation between the solvent and the separator.…”

Opportunities and Challenges of Calendering Sulfide‐Based Separators for Solid‐State Batteries

“…In the future, one challenge will be to achieve high tensile strength such as described for polyolefin-based separators for good process handling. [52,53] In the next step, different roller circumferential speeds and roll temperatures were investigated in terms of nail penetration tests and tensile strength, and the results are presented in Figure 8a) and b), respectively. The line load was kept constant at 300 N mm À 1 .…”