TECHNICAL FIELD

The present disclosure relates to a separator d an electrochemical device including the same. More particularly, the present disclosure relates to a separator having improved metal ion adsorption capability and an electrochemical device including the same.

The present application claims priority to Korean Patent Application No. 10-2016-0154378 filed on Nov. 18, 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 polymer onto at least one surface of a porous substrate having a plurality of pores.

However, for example, when a secondary battery is overcharged, an excessive amount of transition metal ions are dissolved out of a cathode and are inserted to an anode, and thus highly reactive transition metal is deposited on the anode surface and the cathode becomes thermally unstable. In addition, rapid exothermal reaction may occur due to the decomposition of an organic solvent used as an electrolyte. Therefore, the problems related with the safety of a battery, such as overheating, ignition and explosion, are not solved completely.

Therefore, there is still a need for a battery having novel constitutional elements capable of removing such excessive metal ions causing the safety-related problems.

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 capable of adsorbing an excessive amount of transition metal ions from a cathode.

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

Technical Solution

To solve the above-mentioned problems, the separators according to the following embodiments are provided in one aspect of the present disclosure.

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

a porous substrate having a plurality of pores; and

a first porous coating layer and a second porous coating layer formed on one surface and the other surface of the porous substrate, respectively, wherein each of the first porous coating layer and the second porous coating layer independently include a plurality of inorganic particles, a binder polymer disposed on a part or the whole of the surface of the inorganic particles so that the inorganic particles are connected and fixed with each other, and an anionic surfactant,

wherein the inorganic particles include boehmite particles and non-boehmite particles, and

the boehmite particles and the binder polymer are present at a weight ratio of 1:1-1:5.

According to a second embodiment, there is provided the separator of the first embodiment, wherein the anionic surfactant is at least one selected from the group consisting of a C6-C20 alkylbenzene sulfonate salt, C6-C20 alkyl sulfonate salt, C6-C20 monoalkyl sulfate salt, C6-C20 alkylpolyglycol ether sulfate salt, C6-C20 mono- and di-alkyl sulfosuccinate salts, C6-C20 α-olefin sulfonate salt, and a C6-C20 sulfonated fatty acid salt.

According to a third embodiment, there is provided the separator of the first or the second embodiment, wherein the anionic surfactant is present in each of the first porous coating layer and the second porous coating layer independently in an amount of 0.1-20 wt % based on the weight of each of the first porous coating layer and the second porous coating layer, respectively.

According to a fourth embodiment, there is provided the separator of the third embodiment, wherein the weight ratio of the non-boehmite particles to boehmite particles in each of the first porous coating layer and the second porous coating layer is independently 1:99-99:1.

According to a fifth embodiment, there is provided the separator of any one the first to the fourth embodiments, wherein the binder polymer is used for each of the first porous coating layer and the second porous coating layer independently in an amount of 5-40 wt % based on the weight of each of the first porous coating layer and the second porous coating layer.

According to a fifth embodiment, there is provided the separator of any one the first to the fourth embodiments, wherein the binder polymer is present in each of the first porous coating layer and the second porous coating layer independently in an amount of 5-40 wt % based on the weight of each of the first porous coating layer and the second porous coating layer, respectively.

According to a seventh embodiment, there is provided the separator of any one of the first to the sixth embodiments, wherein the non-boehmite particles are inorganic particles having a dielectric constant of 5 or more, inorganic particles capable of transporting lithium ions or a combination thereof.

According to an eighth embodiment, there is provided the separator of any one of the first to the seventh embodiments, wherein the average particle diameter of the boehmite particles is 0.01-0.9 times of that of the non-boehmite particles.

According to a ninth embodiment, there is provided the separator of any one of the first to the eighth embodiments, wherein the average particle diameter of the non-boehmite particles is 0.5-3 μm.

According to a tenth embodiment, there is provided the separator of any one of the first to the ninth embodiments, wherein the average particle diameter of the boehmite particles is 0.05-0.4 μm.

According to an eleventh embodiment, there is provided the separator of any one of the first to the tenth embodiments, wherein the porous substrate is a polyolefin-based porous substrate.

According to a twelfth embodiment, there is provided the separator of any one of the first to the eleventh embodiments, wherein the binder polymer includes any one selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan and carboxyl methyl cellulose, or a combination of two or more of them.

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

According to a thirteenth 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 same as defined in any one of the first embodiments to the twelfth embodiments.

According to a fourteenth embodiment, there is provided an electrochemical device, which is a lithium secondary battery.

Advantageous Effects

According to an embodiment of the present disclosure, an anionic surfactant is incorporated to a porous coating layer. Thus, transition metals, such as Mn, Ni, Co and Fe, dissolved out of a cathode upon overcharging are adsorbed, thereby preventing degradation of an anode caused by deposition of such transition metals on the anode. In addition, it is possible to reduce side reactions in a battery, such as reaction between a transition metal and an electrolyte, and thus to improve the cycle life and high-temperature storage capability of the battery.

Additionally, boehmite particles having relatively low density are used to assist weight lightening of a separator and an electrochemical device. Further, it is 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 the boehmite particles.

