Microporous membrane, lithium ion secondary battery and method of producing the microporous membrane
AssigneeToray Industries, Inc.
InventorTakeshi Ishihara
Life of this patent
Estimating the term…
Abstract
A microporous membrane has average membrane thickness of 15 μm or less, and relative impedance A after a heat compression treatment under a pressure of 4.0 MPa at 80° C. for 10 minutes of 140% or less, the relative impedance A being obtained by the equation below: Relative impedance A=(impedance measured at 80° C. after the heat compression treatment)/(impedance measured at room temperature prior to the heat compression treatment)×100.
Claims17
-16. (canceled)
A microporous membrane, wherein average membrane thickness is 15 μm or less, and relative impedance A after a heat compression treatment under a pressure of 4.0 MPa at 80° C. for 10 minutes is 140% or less, said relative impedance A being obtained by the equation below:
- Relative impedance A=(impedance measured at 80° C. after said heat compression treatment)/(impedance measured at room temperature prior to said heat compression treatment)×100.
A microporous membrane, wherein average membrane thickness is 15 μm or less, and relative impedance B after a heat compression treatment under a pressure of 4.0 MPa at 80° C. for 10 minutes is 120% or less, said relative impedance B being obtained by the equation below:
- Relative impedance B=(impedance measured at room temperature (25° C.) after said heat compression treatment)/(impedance measured at room temperature prior to said heat compression treatment)×100.
A method of producing a polyolefin microporous membrane, comprising:
- (a) an extrusion step of melt blending and extruding a resin composition containing a polyolefin resin and a pore-forming material,
- (b) a sheet forming step of sheet forming the extrudate obtained in said step (a) into a sheet,
- (c) a first stretching step of stretching the sheet-shaped product obtained in said step (b) at least twice in at least different axial directions,
- (d) an extraction step of extracting the pore-forming material from the stretched sheet obtained in said step (c), and
- (e) a second stretching step of stretching the sheet obtained in said step (d) at least once in at least one axial direction,
- wherein at least one of (i) and (ii):
- and (iii) are satisfied:
- (i) said step (c) is a first stretching step of stretching the sheet-shaped product at least once in a sheet transport direction (MD direction) and at least once in a sheet width direction (TD direction),
- and the MD stretching magnification and the TD stretching magnification in said step (c) satisfy Equations (1-1) and (1-2):
- TD stretching magnification≥MD stretching magnification−α (1-1),
- α=2.0 (1-2),
- (ii) the stretching temperature (T1) of a first axial stretching performed first in said step (c) and the maximum stretching temperature (T2) of a second stretching performed after the first axial stretching satisfy Equations (2-1) and (2-2),
- T1−T2≥β (2-1),
- β=0 (2-2),
- (iii) the stretching temperature (D (T)) in said step (e) satisfies Equations (3-1) and (3-2):
- SDT-D(T)≤γ (3-1)
- γ=12 (3-2).
Dependencies are inferred from the claim text.