CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/KR2018/002790 filed on Mar. 8, 2018, which claims priority from Korean Patent Application Nos. 10-2017-0030759, filed on Mar. 10, 2017, and 10-2018-0027369, filed on Mar. 8, 2018, all of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a separator used in a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to a separator for a lithium secondary battery, in which a lithium metal layer is formed on one side of a porous substrate, and a lithium secondary battery including the same.

BACKGROUND ART

Demand for secondary batteries as an energy source has been significantly increased as technology development and demand with respect to mobile devices have increased, and, among these secondary batteries, lithium secondary batteries having high energy density, high operating potential, long cycle life, and low self-discharging rate have been commercialized and widely used.

Also, recently, in line with growing concerns about environmental issues, a significant amount of research into electric vehicles (EVs) and hybrid electric vehicles (HEVs), which may replace vehicles using fossil fuels, such as gasoline vehicle and diesel vehicle, one of major causes of air pollution, has been conducted. Nickel-metal hydride (Ni-MH) secondary batteries have mainly been used as power sources of the electric vehicles (EVs) and hybrid electric vehicles (HEVs), but research into the use of lithium secondary batteries having high energy density, high discharge voltage, and output stability has been actively conducted, and some of the research has been commercialized.

A lithium secondary battery consists of a structure in which an electrode assembly having a porous separator disposed between a positive electrode and a negative electrode, in which electrode collectors are respectively coated with active materials, is impregnated in a non-aqueous electrolyte including a lithium salt.

The lithium secondary battery is charged/discharged only by a lithium source of the positive electrode active material of the positive electrode and life characteristics are degraded when the reversible lithium source is insufficient. A technique for recycling the battery with degraded life characteristics by supplementing the lithium source through a method of injecting an additional electrolyte solution has been known, but it is inconvenient in that a process of making a passage for the further injection to the already completed cell and closing the passage again is necessary.

Thus, a lithium secondary battery, which includes a separate lithium electrode capable of separately supplementing lithium during the degradation of the battery, has been proposed. For example, Korean Patent Application Laid-open Publication No. 2005-0116795 discloses a secondary battery including an additional lithium electrode in addition to a positive electrode and a negative electrode. The document discloses the secondary battery in the form in which the additional lithium electrode is stacked and separated by a separator and at least one of the positive electrode and the negative electrode, and discloses a method in which a current collector of each electrode is exposed to the outside of the secondary battery through a terminal so that a lithium electrode terminal and at least one of the positive electrode terminal or the negative electrode terminal are connected to supply lithium ions to the positive electrode or the negative electrode during the degradation of the battery.

In terms of the fact that the process of making a passage for the further injection to the already completed cell and closing the passage again is not necessary, the method has an advantage of eliminating the inconvenience, but, since the separate lithium electrode is stacked with the positive electrode and the negative electrode to configure a cell, the method is disadvantageous in that an overall thickness of the cell is increased.

Japanese Patent Application Laid-open Publication No. 2002-324585 discloses a secondary battery which includes a third electrode further including a lithium metal in addition to a positive electrode and a negative electrode, but the third electrode is disposed away from an electrode assembly including the positive electrode and the negative electrode.

The method is advantageous in that the process of making a passage for the further injection to the already completed cell and closing the passage again is not necessary and the lithium metal does not increase the overall thickness of the cell, but, since the lithium metal is disposed on a side at a predetermined distance from the electrodes requiring supplement of lithium, the method is disadvantageous in that the supplement of lithium ions is not uniformly performed on the overall electrode.

Thus, there is a need to develop a lithium secondary battery in which a lithium source may be more effectively supplemented to an electrode while there is no inconvenience due to the formation of the separate passage for the supplement of lithium and a thickness or capacity of the battery is not affected.

DISCLOSURE OF THE INVENTION

Technical Problem

An aspect of the present invention provides a separator for a lithium secondary battery which includes a lithium metal layer capable of providing a lithium source to a secondary battery with degraded life characteristics.

Another aspect of the present invention provides a lithium secondary battery including the separator for a lithium secondary battery.

Technical Solution

According to an aspect of the present invention, there is provided a separator for a lithium secondary battery including a porous substrate; and a lithium metal layer formed on one side of the porous substrate,

wherein the lithium metal layer is formed along an outer circumferential surface of the porous substrate and has a window frame shape with an empty interior.

According to another aspect of the present invention, there is provided a method of preparing a separator for a lithium secondary battery which includes:

forming an electrode active material layer by coating a porous substrate with an electrode active material slurry including an electrode active material and a binder.

According to another aspect of the present invention, there is provided a lithium secondary battery including:

a positive electrode; a negative electrode; and a separator disposed between the positive electrode and the negative electrode,

wherein the separator includes a porous substrate; and a lithium metal layer formed on one side of the porous substrate, and the lithium metal layer is formed along an outer circumferential surface of the porous substrate and has a window frame shape with an empty interior,

wherein the lithium metal layer surrounds edges of the positive electrode at a position spaced apart from the positive electrode.

Advantageous Effects

A separator for a lithium secondary battery according to the present invention includes a porous substrate including a lithium metal layer on one side thereof, wherein the lithium metal layer is formed on an outer circumferential surface of the porous substrate and is a window frame-shaped planar layer with an empty interior, and thus, when a lithium secondary battery, in which a positive electrode is disposed in the window frame-shaped interior formed by the lithium metal layer, is configured, the lithium metal layer may effectively supplement lithium ions to the positive electrode during the degradation of the lithium secondary battery.

