TECHNICAL FIELD

The present disclosure relates to a separator and an electrochemical device including the same. Particularly, the present disclosure relates to a separator having improved adhesion with an electrode and an electrochemical device including the same.

The present application claims priority to Korean Patent Application No. 10-2016-0071214 filed on Jun. 8, 2016 in the Republic of Korea, the disclosures of which are incorporated herein by reference.

BACKGROUND ART

Recently, energy storage technology has been given an increasing attention. Efforts into research and development for electrochemical devices have been actualized more and more, as 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. In this context, electrochemical devices have been most spotlighted. Among such electrochemical devices, development of rechargeable secondary batteries has been focused. More recently, active studies have been conducted about designing a novel electrode and battery in order to improve the capacity density and specific energy in developing such batteries.

Among the commercially available secondary batteries, lithium secondary batteries developed in the early 1990's have been spotlighted, since they have a higher driving voltage and significantly higher energy density as compared to conventional batteries, such as Ni-MH, Ni—Cd and sulfuric acid-lead batteries using an aqueous electrolyte. However, such lithium ion batteries have a problem of ignition and explosion caused by the use of an organic electrolyte and a disadvantage of a difficulty in manufacture.

Recent lithium ion polymer batteries improve such a problem and disadvantage of lithium ion batteries and are expected as one of the next-generation batteries. However, such lithium ion polymer batteries still have a relatively low capacity as compared to lithium ion batteries and particularly show an insufficient discharge capacity at low temperature. Thus, there is an imminent need for improving this.

Although such electrochemical devices have been produced from many production companies, safety characteristics thereof show different signs. Evaluation and securement of safety of such electrochemical devices are very important. The most important consideration is that electrochemical devices should not damage users upon their malfunction. For this purpose, safety standards strictly control ignition and smoke emission in electrochemical devices. With regard to safety characteristics of electrochemical devices, there is great concern about explosion when an electrochemical device is overheated to cause thermal runaway or perforation of a separator. Particularly, a polyolefin-based porous substrate used conventionally as a separator for an electrochemical device shows a severe heat shrinking behavior at a temperature of 100° C. or higher due to its material property and a characteristic during its manufacturing process, including orientation, thereby causing a short-circuit between a cathode and an anode.

To solve the above-mentioned safety problems of an electrochemical device, there has been suggested a separator having a porous organic-inorganic coating layer formed by applying a mixture of an excessive amount of inorganic particles and a binder onto at least one surface of a porous substrate having a plurality of pores.

DISCLOSURE

Technical Problem

The present disclosure is designed to solve the problems of the related art, and therefore the present disclosure is directed to providing a separator which has excellent dispersibility of inorganic particles and a binder, and thus shows improved adhesive property with an electrode.

The present disclosure is also directed to providing an electrochemical device including the separator.

Technical Solution

In one aspect of the present disclosure, there is provided the separators according to the following embodiments.

According to a first embodiment, there is provided a separator including:

a porous substrate having a plurality of pores; and

a pair of porous coating layers formed on at least one surface of the porous substrate, and including a plurality of inorganic particles and a binder disposed partially or totally on the surface of the inorganic particles to connect and fix the inorganic particles with each other,

wherein the binder is used in an amount of 5-40 wt % based on the total weight of the porous coating layer,

the inorganic particles include boehmite particles,

the binder includes a fluorine-based binder and a rubber-based binder, and the fluorine-based binder and the rubber-based binder are used at a weight ratio of 80:20-99.9:0.1.

According to a second embodiment, there is provided the separator of the first embodiment, wherein the fluorine-based binder is any one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polytetrafluoroethylene and polychlorotrifluoroethylene, or a mixture of at least two of them.

According to a third embodiment, there is provided the separator of the first embodiment or the second embodiment, wherein the rubber-based binder is any one selected from the group consisting of nitrile-butadiene rubber, hydrated nitrile-butadiene rubber, styrene-butadiene rubber, hydrated styrene-butadiene rubber and silicone rubber, or a mixture of at least two of them.

According to a fourth embodiment, there is provided the separator of any one of the first embodiment to the third embodiment, wherein the inorganic particles further include non-boehmite particles other than boehmite particles.

According to a fifth embodiment, there is provided the separator of the fourth embodiment, wherein the non-boehmite particles and boehmite particles are used at a weight ratio of 1:99-99:1.

According to a sixth embodiment, there is provided the separator of the fourth embodiment or the fifth embodiment, wherein the non-boehmite particles include inorganic particles having a dielectric constant of 5 or more, inorganic particles capable of transporting lithium ions or a mixture thereof.

According to a seventh embodiment, there is provided the separator of the sixth embodiment, wherein the inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3(PZT), Pb1-xLaxZr1-yTiO3(PLZT), PB(Mg3Nb2/3)O3—PbTiO3(PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC or a mixture thereof.

According to an eighth embodiment, there is provided the separator of the sixth embodiment, wherein the inorganic particles capable of transporting lithium ions include lithium phosphate (Li3PO4), lithium titanium phosphate (LixTiy(PO4)3, 0<x<2, 0<y<3), lithium aluminum titanium phosphate (LixAlyTiz(PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP)xOy-based glass (0<x<4, 0<y<13), lithium lanthanum titanate (LixLayTiO3, 0<x<2, 0<y<3), lithium germanium thiophosphate (LixGeyPzSw, 0<x<4, 0<y<1, 0<z<1, 0<w<5), lithium nitride (LixNy, 0<x<4, 0<y<2), SiS2-based glass (LixSiySz, 0<x<3, 0<y<2, 0<z<4), P2S5-based glass (LixPySz, 0<x<3, 0<y<3, 0<z<7) or a mixture thereof.

According to a ninth embodiment, there is provided the separator of any one of the first embodiment to the eighth embodiment, wherein the porous substrate is a polyolefin-based porous substrate.

According to a tenth embodiment, there is provided the separator of the ninth embodiment, wherein the polyolefin-based porous substrate includes any one polymer selected from the group consisting of polyethylene, polypropylene, polybutylene and polypentene, or a combination thereof.

According to an eleventh embodiment, there is provided the separator of any one of the first embodiment to the tenth embodiment, wherein the porous substrate has a thickness of 5-50 μm, a pore size of 0.01-50 μm and a porosity of 10-95%.

In another aspect of the present disclosure, there is also provided the electrochemical devices according to the following embodiments.

According to a twelfth embodiment, there is provided an electrochemical device including a cathode, an anode and a separator interposed between the cathode and the anode, wherein the separator is the separator as defined in any one of the first embodiment to the eleventh embodiment.

According to a thirteenth embodiment, there is provided an electrochemical device of the twelfth embodiment, which is a lithium secondary battery.

Advantageous Effects

According to an embodiment of the present disclosure, a fluorine-based binder is used in combination with a rubber-based binder so that the dispersion stability of a slurry for forming a porous coating layer may be improved significantly. Thus, the dispersion and arrangement of the inorganic particles and binder in the porous coating layer become homogeneous, resulting in a significant increase in binding force between the inorganic particles and the binder and adhesion between an electrode and a separator. As a result, it is possible to improve the life characteristics of a battery.

Further, since boehmite particles having relatively low density are used, it is possible to assist weight lightening of a separator and electrochemical device. It is also possible to control a rapid increase in internal temperature of an electrochemical device caused by abnormal operation by virtue of excellent heat-absorbing property of boehmite particles.

