The unusual delamination phenomenon of three kinds of lithium‐ion battery separators

Abstract

An unusual delamination phenomenon on three kinds of lithium‐ion battery separators was investigated in this study, which is closely associated with the compression resistance of the separator. The delamination trends of three kinds of polymer separators were analyzed systematically. Scanning electron microscopy, two‐dimensional wide‐angle X‐ray diffraction, compression and delamination tests show that a separator prepared by the dry process with uniaxial stretching delaminate hardest due to abundant connection or support structure along the thickness direction. However, the multilayer structure stacked along the thickness direction can be seen clearly for separators experiencing biaxial stretching, both for the dry process and wet process. In particular, a separator prepared by the wet process has the poorest connection or support structure along the thickness direction, leading to the strongest delamination trend and the worst compression resistance. Based on this, we control the delamination trend of the separator by adjusting the condensed structure of the precursor film. Besides, the delamination test can quantify the delamination trend of different kinds of separators accurately and further supplement the evaluation criteria of lithium‐ion battery separators, which can help us to better understand and design a separator with optimal microporous structure. © 2020 Society of Industrial Chemistry

Facile Preparation of a Trilayer Separator with a Shutdown Function Based on the Compounding of β-Crystal Polypropylene and Hydrogenated Petroleum Resin

“…In addition, the cross-sectional morphologies of the five separators are also shown in Figure f–j. Five separators display a typical multilayer structure stacked along the thickness direction due to the biaxial stretching of the β-crystal …”

“…Five separators display a typical multilayer structure stacked along the thickness direction due to the biaxial stretching of the β-crystal. 26 The porosity of five separators is shown in Figure 2a. The porosity of PP-0 is about 40%, which is the normal level for separators that are dry-processed with biaxial stretching.…”

“…Presently, three representative production processes have been commercialized: the wet process, dry process with uniaxial stretching, and dry process with biaxial stretching, 26,27 wherein the dry process with biaxial stretching has the most efficient manufacturing process and the lowest cost compared to the dry process with uniaxial stretching, in which the cast film must be annealed offline for a long time, and the wet process, which includes a solvent extraction step. 1,8,28 In the dry process with biaxial stretching, the cast film with high-content β-crystal (β-iPP) is prepared by adding a β-nucleating agent.…”

“…Presently, three representative production processes have been commercialized: the wet process, dry process with uniaxial stretching, and dry process with biaxial stretching, , wherein the dry process with biaxial stretching has the most efficient manufacturing process and the lowest cost compared to the dry process with uniaxial stretching, in which the cast film must be annealed offline for a long time, and the wet process, which includes a solvent extraction step. ,, In the dry process with biaxial stretching, the cast film with high-content β-crystal (β-iPP) is prepared by adding a β-nucleating agent. Then, this cast film is biaxially stretched, which includes longitudinal stretching in the mechanical direction (MD) to create pores and transverse stretching along the transverse direction (TD) to expand pores. − The pore-forming mechanism is that the β-iPP lamellae arrange loosely and can be separated directly to create pores during stretching.…”