【Technical Field】
[1] This application claims the benefit of priority
to Korean Patent Application No. 2021-0083162 filed on
June 25, 2021, the disclosure of which is incorporated
herein by reference in its entirety.
[2] The present invention relates to a separator for
secondary batteries. More particularly, the present
invention relates to a separator for secondary batteries
configured such that porosity of each of a separator
substrate and an inorganic layer constituting the
separator is adjusted, whereby impregnability of the
separator is adjusted.
【Background Art】
[3] A lithium secondary battery may be manufactured
by receiving, in a battery case, an electrode assembly
configured such that a separator is interposed between a
positive electrode and a negative electrode, injecting an
electrolytic solution into the battery case, and
hermetically sealing the battery case.
[4] The separator, which blocks electrical connection
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between the positive electrode and the negative electrode
to secure insulation, may be configured to have a
structure in which a coating layer including an inorganic
material and a binder is formed on a polyolefin-based
substrate made of a porous material such that lithium
ions can move. The polyolefin-based material has low
resistance to heat. For this reason, the coating layer
may be added, whereby high-temperature safety and
mechanical characteristics of the separator may be
improved.
[5] The coating layer including the inorganic
material and the binder is configured to have a pore
structure such that a space, into which a liquid
electrolytic solution is introduced, is increased,
whereby impregnability with the electrolytic solution and
lithium ion conductivity are improved.
[6] In the lithium secondary battery, the
electrolytic solution is a movement path of lithium ions
and therefore improving impregnability of the separator
with the electrolytic solution to lower resistance of the
separator is very important.
[7] In particular, as the utilization field of the
lithium secondary battery expands to a device requiring
high voltage and high capacity, the size of a battery
cell tends to be increased. Therefore, there is a need
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to develop a separator having improved impregnability
with an electrolytic solution as a separator applicable
to a battery cell having an increasing volume.
[8] In connection therewith, Patent Document 1
relates to an inorganic oxide powder used to form an
inorganic oxide porous film having excellent heat
resistance, insulation, and film strength even in small
apparent weight and having porosity necessary to impart
sufficient ion permeability, wherein the inorganic oxide
powder is added to a surface of at least one of a
positive electrode, a negative electrode, and a separator.
[9] That is, in Patent Document 1, an inorganic oxide
powder having characteristics capable of improving ion
permeability is used, whereby physical properties of the
separator are improved.