Lithium ion battery using crosslinkable separator

A separator for an electricity storage device, comprising 5 to 40 weight % of a silane-modified polyolefin and 60 to 95 weight % of a polyolefin other than the silane-modified polyolefin, wherein the loss modulus change ratio (RΔE″) is 1.5 to 20, as defined by the following formula (3):

• RΔE″=E″S/E″j (3)
• where E″j is the loss modulus measured at 160° C. to 220° C. for the separator for an electricity storage device before crosslinking reaction of the silane-modified polyolefin, E″s is the loss modulus measured at 160° C. to 220° C. for the separator for an electricity storage device after crosslinking reaction of the silane-modified polyolefin, and the measuring conditions for the loss modulus E″ (E″j or E″S) are specified by the following (i) to (iv):
• (i) the dynamic viscoelasticity measurement is carried out under the following conditions:
• Measuring apparatus:
• RSA-G2 (TA Instruments)
• Sample thickness:
• from 5 μm to 50 μm
• Measuring temperature range:
• −50 to 225° C.
• Temperature-elevating rate:
• 10° C./min
• Measuring frequency:
• 1 Hz
• Transform mode:
• sine wave tension mode (linear tension)
• Initial static tensile load:
• 0.5 N
• Initial gap distance (at 25° C.):
• 25 mm
• Auto strain adjustment:
• Enabled (range:
• 0.05 to 25% amplitude, 0.02 to 5 N sine wave load);
• (ii) the static tensile load is the median value of the maximum stress and minimum stress for each periodic motion, and the sine wave load is the vibrational stress centered on the static tensile load;
• (iii) the sine wave tension mode is measurement of the vibrational stress while carrying out periodic motion at a fixed amplitude of 0.2%, wherein in sine wave tension mode, the vibrational stress is measured while varying the gap distance and static tensile load so that the difference between the static tensile load and the sine wave load is within 20%, and when the sine wave load is 0.02 N or lower, the vibrational stress is measured while amplifying the amplitude value so that the sine wave load is no greater than 5 N and the increase in the amplitude value is no greater than 25%;
• and
• (iv) the loss modulus E″ is calculated from the obtained sine wave load and amplitude value, and the following formulas:
• σ*=σ0·Exp[i(ωt+δ)],
• ε*=ε0·Exp(iωt),
• σ*=E*·ε*
• E*=E′+iE″
• where σ*:
• vibrational stress, ε*:
• strain, i:
• imaginary number unit, ω:
• angular frequency, t:
• time, δ:
• phase difference between vibrational stress and strain, E*:
• complex modulus, E″:
• storage modulus, E″:
• loss modulus,
• vibrational stress:
• sine wave load/initial cross-sectional area
• static tensile load:
• load at minimum point of vibrational stress for each period (minimum point of gap distance for each period), and
• sine wave load:
• difference between measured vibrational stress and static tensile load.

A separator for an electricity storage device, comprising 5 to 40 weight % of a silane-modified polyolefin and 60 to 95 weight % of a polyolefin other than the silane-modified polyolefin, wherein the mixed storage modulus ratio (RE′mix) is 1.5 to 20, as defined by the following formula (2):

• RE′mix=E′a/E′0 (2)
• {where E′a is the storage modulus measured at 160° C. to 220° C. for the separator for an electricity storage device, E′0 is the storage modulus measured at 160° C. to 220° C. for a separator for an electricity storage device not containing the silane-modified polyolefin, and the measuring conditions for the storage modulus E′ (E′a or E′0) are specified by the following (i) to (iv):
• (i) the dynamic viscoelasticity measurement is carried out under the following conditions:
• Measuring apparatus:
• RSA-G2 (TA Instruments)
• Sample thickness:
• from 5 μm to 50 μm
• Measuring temperature range:
• −50 to 225° C.
• Temperature-elevating rate:
• 10° C./min
• Measuring frequency:
• 1 Hz
• Transform mode:
• sine wave tension mode (linear tension)
• Initial static tensile load:
• 0.5 N
• Initial gap distance (at 25° C.):
• 25 mm
• Auto strain adjustment:
• Enabled (range:
• 0.05 to 25% amplitude, 0.02 to 5 N sine wave load);
• (ii) the static tensile load is the median value of the maximum stress and minimum stress for each periodic motion, and the sine wave load is the vibrational stress centered on the static tensile load;
• (iii) the sine wave tension mode is measurement of the vibrational stress while carrying out periodic motion at a fixed amplitude of 0.2%, wherein in sine wave tension mode, the vibrational stress is measured while varying the gap distance and static tensile load so that the difference between the static tensile load and the sine wave load is within 20%, and when the sine wave load is 0.02 N or lower, the vibrational stress is measured while amplifying the amplitude value so that the sine wave load is no greater than 5 N and the increase in the amplitude value is no greater than 25%;
• (iv) the storage modulus E′ is calculated from the relationship between the obtained sine wave load and amplitude value, and the following formulas:
• σ*=σ0·Exp[i(ωt+δ)],
• ε*=ε0·Exp(iωt),
• σ*=E*·ε*
• E*=E′+iE″
• where σ*:
• vibrational stress, ε*:
• strain, i:
• imaginary number unit, ω:
• angular frequency, t:
• time, δ:
• phase difference between vibrational stress and strain, E*:
• complex modulus, E′:
• storage modulus, E″:
• loss modulus,
• vibrational stress:
• sine wave load/initial cross-sectional area
• static tensile load:
• load at minimum point of vibrational stress for each period (minimum point of gap distance for each period), and
• sine wave load:
• difference between measured vibrational stress and static tensile load.

A separator for an electricity storage device, comprising 5 to 40 weight % of a silane-modified polyolefin and 60 to 95 weight % of a polyolefin other than the silane-modified polyolefin, wherein the mixed loss modulus ratio (RE″mix) is 1.5 to 20.0, as defined by the following formula (4):

• RE″mix=E″a/E″0 (4)
• where E″a is the loss modulus measured at 160° C. to 220° C. for the separator for an electricity storage device, E″0 is the loss modulus measured at 160° C. to 220° C. for a separator for an electricity storage device not containing the silane-modified polyolefin, and the measuring conditions for the loss modulus E″ (E″a or E″0) are specified by the following (i) to (iv):
• (i) the dynamic viscoelasticity measurement is carried out under the following conditions:
• Measuring apparatus:
• RSA-G2 (TA Instruments)
• Sample thickness:
• from 5 μm to 50 μm
• Measuring temperature range:
• −50 to 225° C.
• Temperature-elevating rate:
• 10° C./min
• Measuring frequency:
• 1 Hz
• Transform mode:
• sine wave tension mode (linear tension)
• Initial static tensile load:
• 0.5 N
• Initial gap distance (at 25° C.):
• 25 mm
• Auto strain adjustment:
• Enabled (range:
• 0.05 to 25% amplitude, 0.02 to 5 N sine wave load);
• (ii) the static tensile load is the median value of the maximum stress and minimum stress for each periodic motion, and the sine wave load is the vibrational stress centered on the static tensile load;
• (iii) the sine wave tension mode is measurement of the vibrational stress while carrying out periodic motion at a fixed amplitude of 0.2%, wherein in sine wave tension mode, the vibrational stress is measured while varying the gap distance and static tensile load so that the difference between the static tensile load and the sine wave load is within 20%, and when the sine wave load is 0.02 N or lower, the vibrational stress is measured while amplifying the amplitude value so that the sine wave load is no greater than 5 N and the increase in the amplitude value is no greater than 25%;
• (iv) the loss modulus E″ is calculated from the obtained sine wave load and amplitude value, and the following formulas:
• σ*=σ0·Exp[i(ωt+δ)],
• ε*=ε0·Exp(iωt),
• σ*=E*·ε*
• E*=E′+iE″
• where σ*:
• vibrational stress, ε*:
• strain, i:
• imaginary number unit, ω:
• angular frequency, t:
• time, δ:
• phase difference between vibrational stress and strain, E*:
• complex modulus, E″:
• storage modulus, E″:
• loss modulus,
• vibrational stress:
• sine wave load/initial cross-sectional area
• static tensile load:
• load at minimum point of vibrational stress for each period (minimum point of gap distance for each period), and
• sine wave load:
• difference between measured vibrational stress and static tensile load.