KR20190013424A - Lithium secondary battery - Google Patents

Abstract

Provided is a lithium secondary battery, comprising: first and second current collectors; an anode and a cathode provided between the first and second current collectors; and a hybrid solid electrolyte provided between the anode and the cathode and comprising a mixture of an organic electrolyte and an inorganic electrolyte. The organic electrolyte comprises ethylene carbonate (CE), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or a mixture thereof. The inorganic electrolyte comprises lithium lanthanum zirconium oxide (LLZO), lithium silicon titanium phosphate (LSTP), lithium aluminum titanium phosphate (LATP), or a mixture thereof.

Description

LITHIUM SECONDARY BATTERY [0002]

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery including a solid electrolyte.

Lithium ion secondary batteries are currently used as a key power source for portable electronic communication devices such as mobile phones and notebook computers. Electric storage and energy storage system, which have high storage capacity, excellent charge / discharge characteristics and high processability compared to other energy storage such as a capacitor, a fuel cell, ESS) have attracted great attention as next generation energy storage devices.

The lithium secondary battery includes a positive electrode, a negative electrode, and an electrolyte that provides a pathway for lithium ions between the positive electrode and the negative electrode, and a separator. The lithium secondary battery includes an anode, a cathode, To generate electrical energy. Lithium secondary battery Lithium metal having a high energy density is used as a negative electrode, and a liquid solvent is used as an electrolyte. In the present lithium secondary battery, the organic liquid electrolyte is used as a driving element for high performance and high energy storage devices.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithium secondary battery having high stability.

SUMMARY OF THE INVENTION The present invention provides a lithium secondary battery having improved electrical characteristics.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a lithium secondary battery including: a positive electrode and a negative electrode provided between first and second current collectors, a first current collector and a second current collector, And a hybrid solid electrolyte provided between the negative electrode and composed of a mixture of an organic electrolyte and an inorganic electrolyte. The organic electrolyte may include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or mixtures thereof. The inorganic electrolyte may include lithium lanthanum zirconium oxide (LLZO), lithium silicon titanium phosphate (LSTP), lithium aluminum titanium phosphate (LATP), or a mixture thereof.

The hybrid solid electrolyte of the lithium secondary battery according to the embodiments of the present invention may have a low open circuit voltage. That is, the hybrid solid electrolyte is capable of smoothly separating / inserting lithium ions at the electrode, and has high battery capacity and excellent electrical cycle characteristics. Hybrid solid electrolytes can have high electronic conductivity. Hybrid solid electrolytes can have high lithium ion conductivity.

1 is an exploded perspective view illustrating a lithium secondary battery according to an embodiment of the present invention.
2 is a cross-sectional view illustrating a lithium secondary battery according to embodiments of the present invention.
3 is a graph for explaining the initial discharge capacity and cycle characteristics of Experimental Example 1. FIG.
4 is a graph for explaining the initial capacity of Experimental Example 2. Fig.
5 is a graph for explaining the initial capacity of Experimental Example 3;
6 is a graph for explaining the interfacial resistance characteristics of Experimental Example 4;

In order to fully understand the structure and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It will be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or essential characteristics thereof. Those of ordinary skill in the art will understand that the concepts of the present invention may be practiced in any suitable environment.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. As used herein, the terms 'comprises' and / or 'comprising' mean that the stated element, step, operation and / or element does not imply the presence of one or more other elements, steps, operations and / Or additions.

When a film (or layer) is referred to herein as being on another film (or layer) or substrate it may be formed directly on another film (or layer) or substrate, or a third film Or layer) may be interposed.

 Although the terms first, second, third, etc. have been used in various embodiments herein to describe various regions, films (or layers), etc., it is to be understood that these regions, do. These terms are merely used to distinguish any given region or film (or layer) from another region or film (or layer). Thus, the membrane referred to as the first membrane in one embodiment may be referred to as the second membrane in another embodiment. Each embodiment described and exemplified herein also includes its complementary embodiment. Like numbers refer to like elements throughout the specification.

The terms used in the embodiments of the present invention may be construed as commonly known to those skilled in the art unless otherwise defined.

Hereinafter, a lithium secondary battery according to the concept of the present invention will be described with reference to the drawings.

1 is an exploded perspective view illustrating a lithium secondary battery according to an embodiment of the present invention. 2 is a cross-sectional view illustrating a lithium secondary battery according to embodiments of the present invention.

1 and 2, a lithium secondary battery includes a first current collector 110, a second current collector 120, a first electrode 210, a second electrode 220, and a hybrid solid electrolyte 300. .

The first current collector 110 and the second current collector 120 may be spaced apart from each other. The first current collector 110 and the second current collector 120 may include a metal. For example, the first current collector 110 may include aluminum (Al), and the second current collector 120 may include copper (Cu). The first current collector 110 may have no or little voltage decomposition reaction due to contact with the first electrode 210, which will be described later. The second current collector 120 may have little or no voltage decomposition reaction due to contact with the second electrode 220, which will be described later. The first current collector 110 and the second current collector 120 may have pads 112 and 122 extending to one side. The first current collector 110 and the second current collector 120 may be electrically connected to the outside through the pads 112 and 122. At least one of the pad 112 of the first current collector 110 and the pad 122 of the second current collector 120 may be partially surrounded by the insulating layer 130. The insulating layer 130 may prevent the pads 112 and 122 from being brought into intensive contact with the hybrid solid electrolyte 300 described later. The insulating layer 130 may not be provided if necessary.

The first electrode 210 and the second electrode 220 may be provided between the first current collector 110 and the second current collector 120. The first electrode 210 and the second electrode 220 may be spaced apart from each other. The first electrode 210 may be in contact with the first current collector 110 and the second electrode 220 may be in contact with the second current collector 120.

The first electrode 210 may be a positive electrode. The first electrode 210 may be composed of a cathode active material, a conductive material, and a binder. For example, the cathode active material may be selected from the group consisting of lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₄ ), olivine (LiFePO ₄ ), natural graphite, mixture or a solid solution thereof. The conductive material may be at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon fiber, carbon nanotube (CNT), linear carbon, carbon black, acetylene black black) or ketjen black. The binder may comprise a fluoropolymer such as polyvinylidene fluoride (PVdF).

The second electrode 220 may be a negative electrode. The second electrode 220 may be composed of a negative electrode active material, a conductive agent, and a binder. For example, the negative electrode active material may be a carbon-based material (for example, graphite, hard carbon or soft carbon), a non-carbon material (for example, tin (Sn) Si), lithium titanium oxide (Li _x TiO ₂ ) or spinel lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ )), or a lithium metal or silicon / graphite composite. The conductive material may be at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon fiber, carbon nanotube (CNT), linear carbon, carbon black, acetylene black black) or ketjen black. The binder may comprise a fluoropolymer such as polyvinylidene fluoride (PVdF).

According to embodiments, the first electrode 210 and the second electrode 220 may further contain a solid electrolyte. For example, the solid electrolyte may include an oxynitride-based electrolyte, a phosphate-based electrolyte, an oxide-based electrolyte, or a sulfide-based electrolyte. The oxynitride-based electrolyte may include lithium phosphorus oxynitride (LiPON). The phosphate-based electrolyte may include lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), or lithium silicon titanium phosphate (LSTP). The oxide-based electrolyte may include lithium garnet metal oxide (LLZO) or perovskite metal oxide lithium garnet (LLTO). The solid electrolyte may not be provided to the first electrode 210 and the second electrode 220 as needed.

The hybrid solid electrolyte 300 may be provided between the first electrode 210 and the second electrode 220. The thickness of the hybrid solid electrolyte 300 may be 1 um to 50 um. The hybrid solid electrolyte 300 may provide a path through which lithium (Li) ions migrate between the first electrode 210 and the second electrode 220. The hybrid solid electrolyte 300 may be composed of an organic electrolyte and an inorganic electrolyte. The organic electrolyte may include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or mixtures thereof. The inorganic electrolyte may include lithium lanthanum zirconium oxide (LLZO), lithium silicon titanium phosphate (LSTP), lithium aluminum titanium phosphate (LATP), or a mixture thereof. The weight of the inorganic electrolyte may be 5% to 25% of the organic electrolyte. The hybrid solid electrolyte 300 may have less change in voltage due to the movement of lithium (Li) ions due to charging and discharging.

The hybrid solid electrolyte 300 may have a low open circuit voltage. For example, the open circuit voltage of the hybrid solid electrolyte 300 may be between 1 mV and 20 mV. The hybrid solid electrolyte 300 may have a small difference between the actual driving voltage and the external monitoring voltage during charge / discharge due to the low open circuit voltage. That is, in the hybrid solid electrolyte 300, lithium ions can be easily removed / inserted from the first electrode 210 and the second electrode 220, and the battery capacity and the electrical cycle characteristics can be excellent. For example, the hybrid solid electrolyte 300 may have a high electronic conductivity. The hybrid solid electrolyte 300 may have a high lithium ion conductivity.

The lithium secondary battery can be formed through the following process.

The first slurry may be formed by mixing the cathode active material, the conductive material, and the binder. The cathode active material, the conductive material, and the binder may be the same as or similar to those described with reference to FIG. The first electrode 210 may be formed by applying the first slurry by a Dr. blade method.

The second slurry may be formed by mixing the negative electrode active material, the conductive material, and the binder. The negative electrode active material, the conductive material, and the binder may be the same as or similar to those described with reference to FIG. The second electrode 220 may be formed by applying the second slurry by a Dr. blade method.

A third slurry can be formed by stirring the organic electrolyte and the inorganic electrolyte in the gel electrolyte. The organic electrolyte and the inorganic electrolyte may be the same as or similar to those described with reference to FIG. The gel electrolyte may be an electrolyte containing hydroxypropyl cellulose or polyvinylidene fluoride (PVdF). The organic electrolyte may be a liquid electrolyte. The weight of the organic electrolyte may be 1 to 5 times the weight of the gel electrolyte. The inorganic electrolyte may be a solid electrolyte. The weight of the inorganic electrolyte may be 0.25 times to 1 time the weight of the gel electrolyte. Thereafter, the hybrid solid electrolyte 300 may be formed by applying the third slurry. Application of the third slurry can be carried out by a casting method, a screen printing method, or a transfer method. The hybrid solid electrolyte 300 may be formed to a thickness of 1 [mu] m to 50 [mu] m. According to embodiments, the third slurry may further comprise a binder or an electrolyte.

The first electrode 210 and the second electrode 220 may be provided between the first current collector 110 and the second current collector 120. A hybrid solid electrolyte 300 is provided between the first electrode 210 and the second electrode 220 so that a lithium secondary battery can be manufactured.

The lithium secondary battery according to embodiments of the present invention can exhibit optimal electrical characteristics depending on the constituent components and shape of the hybrid solid electrolyte.

The electrical characteristics of the hybrid solid electrolyte according to the thickness were simulated. Here, the hybrid solid electrolyte is composed of a gel electrolyte of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), an organic liquid electrolyte in which ethylene carbonate (EC), propylene carbonate (PC) and ethyl methyl carbonate (EMC) Lithium-silicon-titanium phosphate (LSTP) inorganic solid electrolyte. The weight of the inorganic solid electrolyte was 50% of the weight of the gel electrolyte, and the weight of the organic liquid electrolyte was 400% of the weight of the gel electrolyte.

Film type The thickness (um) Open circuit voltage (mV) PVdF-HFP + EC / PC / EMC + LSTP 0 200 to 240 PVdF-HFP + EC / PC / EMC + LSTP 25 1 to 20

Table 1 is a table for explaining electrical characteristics according to the thickness of the hybrid solid electrolyte. According to Table 1, when the thickness of the hybrid solid electrolyte was about 300 mu m, the hybrid solid electrolyte exhibited an open circuit voltage of 200 mV to 240 mV. When the thickness of the hybrid solid electrolyte was about 20 mu m, the hybrid solid electrolyte exhibited an open circuit voltage of 1 mV to 20 mV. The thinner the hybrid solid electrolyte, the lower the open circuit voltage and the better the electrical properties.

The electrical properties of the hybrid solid electrolyte were simulated according to the content of the inorganic solid electrolyte. Here, the hybrid solid electrolyte is composed of a gel electrolyte of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), an organic liquid electrolyte in which ethylene carbonate (EC), propylene carbonate (PC) and ethyl methyl carbonate (EMC) Lithium-silicon-titanium phosphate (LSTP) inorganic solid electrolyte. The weight of the organic liquid electrolyte was 400% of the gel electrolyte, and the thickness of the hybrid solid electrolyte was 20um.

Film type Solid electrolyte content (%) Open circuit voltage (mV) PVdF-HFP + EC / PC / EMC 0 60 to 80 PVdF-HFP + EC / PC / EMC + LSTP 25 1 to 20 PVdF-HFP + EC / PC / EMC + LSTP 50 1 to 20 PVdF-HFP + EC / PC / EMC + LSTP 75 1 to 20 PVdF-HFP + EC / PC / EMC + LSTP 100 1 to 20

Table 2 is a table for explaining the electrical characteristics according to the content of the inorganic solid electrolyte. According to Table 2, when the content of the inorganic solid electrolyte was formed to 25%, 50%, 75%, and 100% of the gel electrolyte, the hybrid solid electrolyte exhibited an open circuit voltage of 1 mV to 20 mV . When the content of the inorganic solid electrolyte was formed to 0% of the gel electrolyte, the hybrid solid electrolyte showed an open circuit voltage of 60 mV to 80 mV. As the inorganic solid electrolyte is added to the organic solid electrolyte in the hybrid solid electrolyte, the open circuit voltage is lowered and the electrical characteristics are improved.

(Example)

Lithium cobalt oxide (LiCoO ₂ ) as a cathode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 92: 4: 4 to form a first slurry. A first electrode was prepared by applying a first slurry using the Dr. blade method. The first electrode was fabricated with a width of 2 cm, a length of 2 cm, and a thickness of 162 um.

Natural graphite as a negative electrode active material, carbon black as a conductive material and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 93: 6: 1 to form a second slurry. A second electrode was prepared by applying a second slurry using the Dr. blade method. The second electrode was fabricated with a width of 2.2 cm, a length of 2.2 cm and a thickness of 145 um.

Hydroxypropyl cellulose and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) were stirred to form a gel electrolyte. Ethylene carbonate (EC), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed at a weight ratio of 1.5: 1: 1.5 to form an organic liquid electrolyte. The liquid electrolyte, the inorganic solid electrolyte of lithium silicon titanium phosphate (LSTP), N-methyl-2-pyrrolidone (NMP) and acetone were mixed in the gel electrolyte to prepare a hybrid solid electrolyte. At this time, the liquid electrolyte was mixed at a weight of four times the weight of the gel electrolyte, and the solid electrolyte was mixed at a weight of 0.5 relative to the weight of the gel electrolyte. The hybrid solid electrolyte was fabricated with 2.2 m width, 2.2 cm width and 30 m thickness.

Aluminum (Al) was used for the first current collector, and copper (Cu) was used for the second current collector.

A lithium secondary battery was fabricated using the first current collector, the second current collector, the first electrode, the second electrode, and the hybrid solid electrolyte thus prepared. The open circuit voltage between the first electrode and the second electrode of the lithium secondary battery was measured at 7 mV.

(Experimental Example 1)

A cell test of the lithium secondary battery fabricated according to the embodiment was performed. 3 is a graph for explaining the initial discharge capacity and cycle characteristics of Experimental Example 1. FIG. As shown in FIG. 3, it can be seen that the lithium secondary battery exhibits a high initial discharge capacity of 18 mAh (122 mAh / g). As a result of measuring the 15 cycle average discharge efficiency, it can be seen that the lithium secondary battery exhibits a high capacity retention rate of 99.72%.

(Experimental Example 2)

Lithium secondary batteries were fabricated in the same manner as in Examples, except that the contents of the organic liquid electrolyte were 1 and 0.5 times. 4 is a graph for explaining the initial capacity of Experimental Example 2. Fig. As shown in FIG. 4, when the content of the organic liquid electrolyte is low, the initial capacity is increased. That is, according to the present invention, by adjusting the content of each component of the hybrid solid electrolyte, an optimum initial capacity can be realized.

(Experimental Example 3)

Lithium secondary batteries were fabricated in the same manner as in Example, except that the inorganic solid electrolyte had weights of 0.25, 0.5, 0.75, and 100 by weight of the gel electrolyte. 5 is a graph for explaining the initial capacity of Experimental Example 3; As shown in FIG. 5, regardless of the content of the inorganic solid electrolyte, the hybrid solid electrolyte exhibits a high initial discharge capacity of 122 mAh / g.

(Experimental Example 4)

The interfacial resistance characteristics of the hybrid solid electrolyte and the polyethylene (PE) separator of the examples were compared and analyzed. The thickness of the polyethylene (PE) separator was 30 mu m, which was the same as that of the hybrid solid electrolyte. 6 is a graph for explaining the interfacial resistance characteristics of Experimental Example 4; As shown in FIG. 6, it can be confirmed that the interface resistance of the hybrid solid electrolyte is lower than that of the polyethylene (PE) separator. That is, the hybrid solid electrolyte according to the present invention can improve the electronic conductivity.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

110: The 1st Collection 120: The 2nd Collection
210: first electrode 220: second electrode
300: Hybrid solid electrolyte

Claims (1)

A first collector and a second collector;
A positive electrode and a negative electrode provided between the first current collector and the second current collector; And
And a hybrid solid electrolyte provided between the positive electrode and the negative electrode, the hybrid solid electrolyte comprising a mixture of an organic electrolyte and an inorganic electrolyte,
Wherein the organic electrolyte comprises ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC)
Wherein the inorganic electrolyte comprises lithium lanthanum zirconium oxide (LLZO), lithium silicon titanium phosphate (LSTP), lithium aluminum titanium phosphate (LATP), or a mixture thereof.

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