TECHNICAL FIELD
The present application claims priority to Korean Patent Application No. 10-2020-
0135019 filed on October 19, 2020 in the Republic of Korea.
10 The present disclosure relates to a separator for a lithium secondary battery and a
lithium secondary battery including the same.
BACKGROUND ART
Recently, energy storage technology has been given an increasing attention. As
15 the application of energy storage technology has been extended to energy for cellular
phones, camcorders and notebook PC and even to energy for electric vehicles, there has
been an increasing need for providing batteries used as power sources for such electronic
devices with high energy density. Lithium secondary batteries are those satisfying such a
need best. Therefore, active studies have been conducted about such lithium secondary
20 batteries.
In general, such a lithium secondary battery includes a positive electrode including
a positive electrode active material, a negative electrode including a negative electrode
active material, a non-aqueous electrolyte containing a lithium salt and an organic solvent,
3
and a separator interposed between the positive electrode and the negative electrode so that
both electrodes may be insulated electrically from each other.
Herein, when the separator and electrodes are laminated in order to manufacture a
lithium secondary battery, the separator may be compressed locally by heat and pressure.
5 In addition, the separator may be compressed locally due to volumetric swelling caused by
repetition of charge/discharge cycles. Then, lithium dendrite may be formed at such a
locally compressed portion, resulting in an internal short-circuit.
Particularly, use of metal oxide for a negative electrode, instead of graphite, has
been increased recently in order to increase the energy density of a lithium secondary
10 battery. Such a metal oxide has high hardness so that the problems caused by the
compression of a separator may become severe.
In addition, in the case of a separator including a polyolefin-based porous substrate
and a porous coating layer formed on at least one surface of the porous substrate and
including inorganic particles and a binder polymer used currently as a separator, the porous
15 polymer substrate may be compressed locally due to the inorganic particles. When the
porous coating layer itself is compressed by heat and pressure, some problems, including
an increase in resistance caused by blocking of the pores in the porous coating layer, may
occur.

WHAT IS CLAIMED IS:
1. A separator for a lithium secondary battery, comprising:
a porous polymer substrate; and
5 a porous coating layer disposed on at least one surface of the porous polymer
substrate, and comprising inorganic particles having a Mohs hardness of 3.5-8.5 and a
binder polymer,
wherein the binder polymer comprises a first binder polymer having a storage
modulus at 70°C of 500 Mpa or more.
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2. The separator for a lithium secondary battery according to claim 1, wherein
the inorganic particle comprises TiO2, SiO2, or two or more of them.
3. The separator for a lithium secondary battery according to claim 1, wherein
15 the first binder polymer comprises polyvinylidene fluoride-co-hexafluoropropylene
containing hexafluoropropylene (HFP) monomers at 1-3 wt%, poly(acrylic acid)-copoly(vinyl alcohol), or two or more of them.
4. The separator for a lithium secondary battery according to claim 1, wherein
20 the binder polymer further comprises a second binder polymer having a storage modulus at
70°C of 50 Mpa or less.
5. The separator for a lithium secondary battery according to claim 4, wherein
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the weight ratio of the first binder polymer to the second binder polymer is 0.8:1-1.2:1.
6. The separator for a lithium secondary battery according to claim 4, wherein
the second binder polymer comprises polyvinylidene fluoride-co-trichloroethylene,
5 polyvinylidene fluoride-co-chlorotrifluoroethylene, polymethyl methacrylate,
polyacrylonitrile, polyvinyl pyrro1idone, polyvinyl acetate, polyvinyl alcohol,
polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate
butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinylalchol,
cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile10 styrene-butadiene copolymer, polyimide, or two or more of them.
7. The separator for a lithium secondary battery according to claim 1, which
shows a decrease in thickness of 7% or less under a condition of lamination of electrodes
with the separator.