Battery separator, battery equipped with separator, and method and system for forming the same.

Abstract

A microporous sheet product suitable for use as a battery separator and a method for forming the same. According to one embodiment, the method includes forming an extrusion mixture of one or more thermoplastic polymers and a fluid having a high vapor pressure. The mixture is then extruded through a die head, cooled, and shaped in a first vapor zone above the upper limit of the elasticity (UL) to form a solid sheet material. The sheet material then undergoes a two-step process in a second vapor zone below the lower limit of the elasticity (UL), where the first step involves a first stretching / fluid vaporization at a higher temperature and the second step involves a second stretching / fluid vaporization at a lower temperature. The resulting sheet is then annealed to remove the remainder of the fluid, forming a sheet product having a thickness characterized by a structure of smaller and larger micropore layers across its thickness.

Claims

1. A method for manufacturing a microporous sheet product, (a) A step of melt-extruding an extrusion mixture to form a cast sheet, wherein the extrusion mixture comprises at least one thermoplastic polymer and a compatibilizer, the at least one thermoplastic polymer comprises at least one polyolefin, and the compatibilizer comprises a first organic fluid, (b) A step of cooling the cast sheet in a first gas zone, wherein the first gas zone comprises a first organic vapor, the first organic vapor comprises a first organic fluid in vapor form, and the first organic vapor is present in at least a portion of the first gas zone at a concentration exceeding UEL, (c) A step of performing at least some stretching of the cast sheet cooled in a second gas zone, wherein the second gas zone comprises a second organic vapor, the second organic vapor comprises the first organic fluid in vapor form, and the second organic vapor is present in the second gas zone at a concentration below LEL or above UEL. A method that includes this.

2. The method according to claim 1, wherein the first organic vapor is present in the first gas zone at a volume concentration of at least 3%.

3. The method according to claim 1, wherein a portion of the first organic vapor condenses on a cast roll, forming a skin layer of fluid condensate thereon, and the cooling step includes cooling the cast sheet on the skin layer of condensate on the cast roll.

4. The method according to claim 1, wherein the concentration exceeding the UEL is achieved by the outflow of ambient oxygen from the enclosure defining the first gas zone.

5. The method according to claim 1, wherein the melt extrusion step includes increasing the energy input of the extruder by at least 0.15 kWh / kg by increasing the rpm of the extruder screw and / or by adding a kneading block.

6. The method according to claim 1, wherein the first organic vapor is present throughout the entire first gas zone at a concentration exceeding the UEL.

7. The method according to claim 1, wherein the first organic vapor is present at a concentration exceeding UEL only in a portion of the first gas zone.

8. The method according to claim 1, wherein the first gas zone is defined by an enclosure and the cooling step is provided by at least one chilled roll, and the first organic vapor is present at a concentration exceeding UEL, starting at or near the inlet of the enclosure and extending to the vicinity of the chilled roll.

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