Making a lithium ion battery separator

摘要

A porous polymer separator for use in a lithium ion battery is formed by a temperature-induced phase separation method. The porous polymer separator includes a polymer matrix having opposed major faces and a network of pore openings that extends between the major faces and permits intrusion of a lithium-ion conducting electrolyte solution. As part of the temperature-induced phase separation method, a single phase polymer solution that includes a polymer material dissolved in a miscible mixture of a real polymer solvent and a polymer non-solvent is prepared at an elevated temperature above room temperature. A film is then formed from the single phase polymer solution and cooled to phase-separate the polymer material into a solid polymer precipitate. Additional polymer non-solvent is then used to remove the real polymer solvent from the solid polymer precipitate followed by drying.

主权项

1. A method of making a porous polymer separator that, in a lithium ion battery, is sandwiched between a negative electrode and a positive electrode to provide an electrically insulative physical barrier that mechanically separates the two electrodes, the method comprising:
preparing a single phase polymer solution that includes a polymer material dissolved in a miscible mixture of a real polymer solvent and a polymer non-solvent, the single phase polymer solution having an elevated temperature above room temperature that facilitates solvation of the polymer material in the miscible mixture of the real polymer solvent and the polymer non-solvent, the polymer non-solvent being selected from the group consisting of water, a C1-C6 aliphatic alcohol, acetone, and mixtures thereof; forming a film from the single phase polymer solution that has a thickness of up to about 150 μm; cooling the film from the elevated temperature to phase-separate the polymer material into a solid polymer precipitate; exposing the solid polymer precipitate to additional polymer non-solvent to remove, by solvent exchange, the real polymer solvent from the solid polymer precipitate; and drying the solid polymer precipitate to remove the polymer non-solvent and any residual of the real polymer solvent from the solid polymer precipitate to form a polymer matrix having opposed major face surfaces and defining a network of pore openings that traverses the polymer matrix and fluidly connects the major face surfaces.