KR102012414B1 - All solid lithium secondary battery including composite interfacial layer and method for manufacturing the same - Google Patents

Abstract

The present invention relates to an all-solid-state lithium secondary battery, which comprises: a negative electrode comprising lithium metal; a composite interface layer formed on the negative electrode and comprising graphite, first lithium lanthanum zirconium oxide (LLZO), and a first binder; a solid electrolyte layer formed on the composite interface layer; and a positive electrode formed on the solid electrolyte layer. The all-solid-state lithium secondary battery and a method for manufacturing the same of the present invention have an effect of enhancing charge/discharge characteristics and cycle characteristics by controlling an interface between the negative electrode and the solid electrolyte by introducing the composite interface layer between the negative electrode and the solid electrolyte layer.

Description

All solid lithium secondary battery including a composite interface layer and a method of manufacturing the same {ALL SOLID LITHIUM SECONDARY BATTERY INCLUDING COMPOSITE INTERFACIAL LAYER AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to an all-solid-state lithium secondary battery including a composite interface layer, and a method for manufacturing the same, and more particularly, to include a composite interface layer having improved cycle characteristics by introducing a composite interface layer between a negative electrode and a solid electrolyte layer. It relates to an all-solid lithium secondary battery and a method of manufacturing the same.

Lithium secondary batteries have high electrochemical capacity, high operating potential, and excellent charge / discharge cycle characteristics. Therefore, they are in demand for portable information terminals, portable electronic devices, small household power storage devices, motorcycles, electric vehicles, and hybrid electric vehicles. It is increasing. The proliferation of such applications is required to improve the safety and performance of lithium secondary batteries.

Conventional lithium secondary batteries ignite easily when exposed to moisture in the air by using a liquid electrolyte has always raised safety issues. This safety issue is becoming more and more an issue as electric vehicles become visible.

Accordingly, recently, all-solid-state secondary batteries using solid electrolytes made of inorganic materials, which are non-combustible materials, have been actively researched for the purpose of improving safety. All-solid-state secondary batteries are attracting attention as next-generation secondary batteries in terms of safety, high energy density, high output, long life, simplification of manufacturing process, battery size / compact size and low cost.

The core technology of the all-solid-state secondary battery is to develop a solid electrolyte showing high ion conductivity. Solid electrolytes for all-solid-state secondary batteries known to date include sulfide solid electrolytes and oxide solid electrolytes. Oxide solid electrolytes show lower ionic conductivity than sulfide solid electrolytes, but have recently attracted attention due to their excellent stability.

In addition, in the case of a battery in which a solid electrolyte is applied to a battery in which an organic electrolyte is applied, interface control is advantageous, and thus lithium metal may be used as a negative electrode, thereby enabling high capacity and high voltage of the battery. In particular, when the graphite-based electrode is used as the negative electrode of the all-solid lithium battery, since the irreversibility is greatly increased in one cycle, there is a problem in that the cycle characteristics decrease rapidly, and it is known that it is more advantageous to use lithium metal as the negative electrode.

However, when the interface is formed by direct contact between the solid electrolyte and the lithium metal, there is a problem that the cycle characteristics gradually decrease.

An object of the present invention is to solve the above problems, by introducing a composite interface layer between the negative electrode and the solid electrolyte layer, by controlling the interface between the negative electrode and the solid electrolyte to provide a composite interface layer having excellent charge and discharge characteristics and cycle characteristics It is to provide an all-solid lithium secondary battery comprising and a method of manufacturing the same.

According to one aspect of the invention,

A negative electrode comprising lithium metal; A composite interface layer formed on the cathode and including graphite, first lithium lanthanum zirconium oxide (LLZO), and a first binder; A solid electrolyte layer formed on the composite interface layer; An anode formed on the solid electrolyte layer; There is provided an all-solid lithium secondary battery comprising a.

The composite interface layer may have a thickness of 1 to 50 μm.

The thickness of the composite interface layer may be 10 to 30 ㎛.

The composite interface layer may include 400 to 800 parts by weight of the first lithium lanthanum zirconium oxide (LLZO) and 100 to 500 parts by weight of the first binder based on 100 parts by weight of the graphite.

The composite interface layer may further include 5 to 50 parts by weight of the first lithium salt based on 100 parts by weight of the first binder.

The content of the graphite in the composite interface layer may be 10 to 300 parts by weight based on 100 parts by weight of the first binder.

Preferably, the content of the graphite in the composite interface layer may be 50 to 150 parts by weight based on 100 parts by weight of the first binder.

The solid electrolyte layer includes a second lithium lanthanum zirconium oxide (LLZO), a second binder, and a second lithium salt, and the anode includes a cathode active material, a third lithium lanthanum zirconium oxide (LLZO), a third binder, and a conductive material. It may include.

The all-solid-state lithium secondary battery, the negative electrode containing a lithium metal; A composite interface layer formed on the cathode and including graphite, first lithium lanthanum zirconium oxide (LLZO), a first binder, and a first lithium salt; A solid electrolyte layer formed on the composite interface layer and including a second lithium lanthanum zirconium oxide (LLZO), a second binder, and a second lithium salt; And a cathode formed on the solid electrolyte layer and including a cathode active material, a third lithium lanthanum zirconium oxide (LLZO), a third binder, and a conductive material.

The first lithium lanthanum zirconium oxide (LLZO), the second lithium lanthanum zirconium oxide (LLZO) and the third lithium lanthanum zirconium oxide (LLZO) are each independently aluminum-doped lithium lanthanum zirconium oxide (LLZO). Can be.

[Formula 1]

Li _x La _y Zr _z Al _w O ₁₂ (5≤x≤9, 2≤y≤4, 1≤z≤3, 0 <w≤1)

The first lithium lanthanum zirconium oxide (LLZO), the second lithium lanthanum zirconium oxide (LLZO), and the third lithium lanthanum zirconium oxide (LLZO) may have at least one structure selected from a cubic structure and a tetragonal structure. It may include.

The first lithium lanthanum zirconium oxide (LLZO), the second lithium lanthanum zirconium oxide (LLZO), and the third lithium lanthanum zirconium oxide (LLZO) may have a single phase cubic structure.

The first binder, the second binder and the third binder are each independently polyethylene oxide, polyethyleneglycol, polyacrylonitrile, polyvinylchloride, polymethylmethacrylate. ), Polypropyleneoxide, polydimethylsiloxane, polyvinylidenefluoride, polyvinylidenecarbonate, and polyvinylpyrrolidinone. Can be.

The first binder, the second binder, and the third binder may each independently include polyethylene oxide.

The first lithium salt and the second lithium salt are each independently lithium perchlorate (LiClO ₄ ), lithium triflate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ) And lithium trifluoromethanesulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ).

The cathode active material may be a three-component lithium metal oxide (NMC) of Ni-Co-Mn represented by Chemical Formula 2 below.

[Formula 2]

LiNi _p Co _q Mn _r O ₂ (0 <p <0.9, 0 <q <0.5, 0 <r <0.5, p + q + r = 1)

The conductive material may include at least one selected from carbon black, acetylene black, and ketjen black.

According to another aspect of the invention,

(a) forming a negative electrode comprising lithium metal; (b) forming a composite interface layer including graphite, first lithium lanthanum zirconium oxide (LLZO), a first binder, and a first lithium salt on the cathode; (c) forming a solid electrolyte layer including a second lithium lanthanum zirconium oxide (LLZO), a second binder, and a second lithium salt on the composite interface layer; And (d) forming an anode including a cathode active material, a third lithium lanthanum zirconium oxide (LLZO), a third binder, and a conductive material on the solid electrolyte layer; Provided is a method of manufacturing an all-solid-state lithium secondary battery comprising a.

The all-solid-state lithium secondary battery of the present invention and a method for manufacturing the same have an effect of improving charge and discharge characteristics and cycle characteristics by controlling an interface between the negative electrode and the solid electrolyte by introducing a composite interface layer between the negative electrode and the solid electrolyte layer.

1 is a structure of an all-solid-state lithium secondary battery according to the present invention.
2 is a graph showing charge and discharge characteristics of Comparative Examples 1 and 2. FIG.
3 is a graph showing cycle characteristics of Comparative Examples 1 and 2. FIG.
4 is a graph showing one-time charge and discharge characteristics of Examples 2-1 to 2-3 and Comparative Example 1. FIG.
5 is a graph showing the cycle characteristics of Examples 2-1 to 2-3, Comparative Example 1.
6 is a graph showing one-time charge and discharge characteristics of Example 2-2 and Comparative Example 2. FIG.
7 is a graph showing the cycle characteristics of Example 2-2 and Comparative Example 2.
8 is a graph of overvoltage characteristics of a symmetric cell to which a compound interface layer is not applied.
FIG. 9 is a graph of overvoltage characteristics of a symmetric cell to which a composite interface layer according to Example 1-1 is applied.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

However, the following descriptions are not intended to limit the present invention to specific embodiments, and detailed descriptions of well-known techniques related to the present invention will be omitted when it is determined that the present invention may obscure the gist of the present invention. .

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "having" are intended to indicate that there is a feature, number, step, operation, component, or combination thereof described in the specification, and one or more other features or It should be understood that it does not exclude in advance the possibility of the presence or addition of numbers, steps, operations, components, or combinations thereof.

1 is a structure of an all-solid-state lithium secondary battery according to the present invention. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

Hereinafter, the all-solid-state lithium secondary battery of the present invention will be described in detail with reference to FIG. 1.

The all-solid-state lithium secondary battery of the present invention is a negative electrode containing a lithium metal; A composite interface layer formed on the cathode and including graphite, first lithium lanthanum zirconium oxide (LLZO), and a first binder; A solid electrolyte layer formed on the composite interface layer; An anode formed on the solid electrolyte layer; It may include.

The composite interface layer may have a thickness of 1 to 50 μm.

The thickness of the composite interface layer may be 10 to 30 ㎛.

The composite interface layer may include 400 to 800 parts by weight of the first lithium lanthanum zirconium oxide (LLZO) and 100 to 500 parts by weight of the first binder based on 100 parts by weight of the graphite.

The composite interface layer may further include 5 to 50 parts by weight of the first lithium salt based on 100 parts by weight of the first binder.

The content of the graphite in the composite interface layer may be 10 to 300 parts by weight based on 100 parts by weight of the first binder.

Preferably, the content of the graphite in the composite interface layer may be 50 to 150 parts by weight based on 100 parts by weight of the first binder.

The solid electrolyte layer includes a second lithium lanthanum zirconium oxide (LLZO), a second binder, and a second lithium salt, and the anode includes a cathode active material, a third lithium lanthanum zirconium oxide (LLZO), a third binder, and a conductive material. It may include.

The all-solid-state lithium secondary battery, the negative electrode containing a lithium metal; A composite interface layer formed on the cathode and including graphite, first lithium lanthanum zirconium oxide (LLZO), a first binder, and a first lithium salt; A solid electrolyte layer formed on the composite interface layer and including a second lithium lanthanum zirconium oxide (LLZO), a second binder, and a second lithium salt; And a cathode formed on the solid electrolyte layer and including a cathode active material, a third lithium lanthanum zirconium oxide (LLZO), a third binder, and a conductive material. It may include.

The first lithium lanthanum zirconium oxide (LLZO), the second lithium lanthanum zirconium oxide (LLZO) and the third lithium lanthanum zirconium oxide (LLZO) are each independently aluminum-doped lithium lanthanum zirconium oxide (LLZO). Can be.

[Formula 1]

Li _x La _y Zr _z Al _w O ₁₂ (5≤x≤9, 2≤y≤4, 1≤z≤3, 0 <w≤1)

The first lithium lanthanum zirconium oxide (LLZO), the second lithium lanthanum zirconium oxide (LLZO), and the third lithium lanthanum zirconium oxide (LLZO) may have at least one structure selected from a cubic structure and a tetragonal structure. It may include.

The first lithium lanthanum zirconium oxide (LLZO), the second lithium lanthanum zirconium oxide (LLZO), and the third lithium lanthanum zirconium oxide (LLZO) may have a single phase cubic structure.

The first binder, the second binder and the third binder are each independently polyethylene oxide, polyethyleneglycol, polyacrylonitrile, polyvinylchloride, polymethylmethacrylate. ), Polypropyleneoxide, polydimethylsiloxane, polyvinylidenefluoride, polyvinylidenecarbonate, and polyvinylpyrrolidinone. Can be.

The first binder, the second binder, and the third binder may each independently include polyethylene oxide.

The first lithium salt and the second lithium salt are each independently lithium perchlorate (LiClO ₄ ), lithium triflate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ) And lithium trifluoromethanesulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ).

The cathode active material may be a three-component lithium metal oxide (NMC) of Ni-Co-Mn represented by Chemical Formula 2 below.

[Formula 2]

LiNi _p Co _q Mn _r O ₂ (0 <p <0.9, 0 <q <0.5, 0 <r <0.5, p + q + r = 1)

The conductive material may include at least one selected from carbon black, acetylene black, and ketjen black.

Hereinafter, the manufacturing method of the all-solid-state lithium secondary battery of the present invention will be described in detail.

Method of manufacturing an all-solid lithium secondary battery of the present invention comprises the steps of (a) forming a negative electrode containing a lithium metal; (b) forming a composite interface layer including graphite, first lithium lanthanum zirconium oxide (LLZO), a first binder, and a first lithium salt on the cathode; (c) forming a solid electrolyte layer including a second lithium lanthanum zirconium oxide (LLZO), a second binder, and a second lithium salt on the composite interface layer; And (d) forming an anode including a cathode active material, a third lithium lanthanum zirconium oxide (LLZO), a third binder, and a conductive material on the solid electrolyte layer; It may include.

EXAMPLE

Hereinafter, a preferred embodiment of the present invention will be described. However, this is for illustrative purposes and the scope of the present invention is not limited thereby.

Production Example  1: aluminum Doped  Preparation of Lithium Lanthanum Zirconium Oxide (Al-LLZO)

Lanthanum nitrate (La (NO ₃ ) ₃ · 6H ₂ O) and zirconium nitrate (ZrO (NO ₃ ) ₂ · 2H ₂ O) so that the molar ratio of La: Zr: Al, starting material, in distilled water is 3: 2: 0.25. And aluminum nitrate (Al (NO ₃ ) ₃ .9H ₂ O) to prepare an aqueous starting material solution having a concentration of 1 mol of starting material.

The starting solution of the Kuet Taylor vortex reactor was added with an appropriate amount of the starting material solution, 0.6 mol of ammonia water, and an aqueous sodium hydroxide solution as a complexing agent to obtain a mixed solution having a pH of 11, and a reaction temperature of 25 ° C., a reaction time of 4 hr, The stirring speed of the stirring rod was coprecipitated at 1,300 rpm to discharge the precursor slurry in the form of a liquid slurry to the discharge part. In the coprecipitation reaction of the Kuet Taylor vortex reactor, the Taylor number was set to 640 or more.

The precursor slurry was washed with purified water and then dried overnight. The dried precursor was ground in a ball mill, then excess LiOH.H ₂ O was added and mixed in a ball mill to prepare a mixture. The LiOH.H ₂ O content of the mixture was added in an excessive amount of 3 wt% to 103 parts by weight based on 100 parts by weight of Li in the solid electrolyte in which the content of Li in LiOH.H ₂ O was produced. The mixture was calcined at 900 ° C. for 2 hours and then ground to produce lithium lanthanum zirconium oxide (Al-LLZO) doped with aluminum.

Preparation Example 2 Preparation of Positive Electrode

100 parts by weight of the positive electrode active material NMC (lithium nickel cobalt manganese oxide), 9.1 parts by weight of lithium-lanthanum zirconium oxide (Al-LLZO) doped with aluminum prepared according to Preparation Example 1, 18.2 parts by weight of a conductive material Super-P, and a binder 54.5 parts by weight of PEO was mixed to prepare a mixture of NMC (lithium nickel cobalt manganese oxide), aluminum lanthanum zirconium oxide (Al-LLZO), Super-P, and PEO.

At this time, the PEO binder is a mixed solution containing PEO (polyethylene oxide, molecular weight 600,000, melting temperature: 65 ℃), ACN (Acetonitrile) and LiClO ₄ , the PEO binder is designed to have an ion conductivity, and The content ratio of LiClO ₄ was set to [EO]: [Li] = 15: 1.

Specifically, NMC, lithium lanthanum zirconium oxide (Al-LLZO) doped with aluminum and Super-p were weighed in the above weight ratio, and then mixed for 30 minutes using a mortar and pestle to prepare a mixed powder. The mixed powder was transferred to a dedicated container for Thinky mixer, mixed with PEO binder by the weight ratio, and mounted on a mixer to mix 3 times at 2,000 rpm for 5 minutes once to prepare a mixture. Next, ACN (Acetonitrile) was mixed with the mixture to adjust to an appropriate viscosity, and zircon balls were added and mixed at 2,000 rpm for 5 minutes to prepare a slurry. The slurry was cast on aluminum foil and dried in vacuo to prepare a positive electrode.

Preparation Example 3 Preparation of Solid Electrolyte Layer

42.9 parts by weight of polyethylene oxide (PEO) was weighed based on 100 parts by weight of aluminum-doped lithium lanthanum zirconium oxide (Al-LLZO) prepared according to Preparation Example 1, and 5 minutes at 2,000 rpm using a Thinky mixer. Stirring to prepare a mixture of aluminum lanthanum zirconium oxide (Al-LLZO) and PEO doped with aluminum.

In this case, the PEO solid electrolyte binder is a mixed solution containing PEO (polyethylene oxide, molecular weight 200,000, melting temperature: 65 ℃), ACN (Acetonitrile) and LiClO ₄ , the PEO solid electrolyte binder is designed to have an ion conductivity The content ratio of PEO and LiClO ₄ was set to [EO]: [Li] = 15: 1.

ACN was mixed into the mixture and stirred with a syncy mixer to adjust to an appropriate viscosity. Next, 2 mm zircon balls were added and stirred for 5 minutes at 2,000 rpm with a syncy mixer to prepare a slurry. The slurry was cast on a polyethylene terephthalate (PET) film, dried at room temperature, and adjusted to a thickness of 150 μm to prepare a solid electrolyte layer.

Example 1 Preparation of Composite Interface Layer

Example 1-1: Compound Interface Layer

600 parts by weight of aluminum-doped lithium lanthanum zirconium oxide (Al-LLZO) and 300 parts by weight of PEO binder based on 100 parts by weight of the graphite were mixed with graphite and aluminum doped lithium lanthanum zirconium oxide (Al-LLZO). And a mixture of PEO.

In this case, the PEO binder is a mixed solution containing polyethylene oxide (PEO), acetonitrile (ACN) and LiClO ₄ , the PEO binder is designed to have ionic conductivity, and ACN 284 parts by weight and LiClO ₄ compared to 100 parts by weight of PEO. Prepared by 16 parts by weight, LiClO ₄ and ACN was first stirred at room temperature for about 5 minutes, and then PEO was added to prepare at room temperature for 24 hours.

Specifically, first, the graphite in the dry state and lithium lanthanum zirconium oxide (Al-LLZO) doped with aluminum of Preparation Example 1 are mixed with a stirrer or mortar for about 10 minutes, and then the PEO binder solution is added to the silky mixer. (Thinky mixer) while stirring three times at about 2,000 rpm three times, after adjusting the slurry viscosity suitable for casting with ACN, the casting was carried out to prepare a composite interface layer at about 10 to 30 ㎛.

Example 1-2 Composite Interface Layer

Based on 100 parts by weight of the graphite in Example 1-1, instead of mixing 600 parts by weight of lithium lanthanum zirconium oxide (Al-LLZO) doped with aluminum of the Preparation Example 1 and 300 parts by weight of PEO binder based on 100 parts by weight of the graphite By using the same method as in Example 1-1, except that 133 parts by weight of lithium-lanthanum zirconium oxide (Al-LLZO) doped with aluminum and 100 parts by weight of the PEO binder were mixed.

Example 1-3 Composite Layer

Based on 100 parts by weight of the graphite in Example 1-1, instead of mixing 600 parts by weight of lithium lanthanum zirconium oxide (Al-LLZO) doped with aluminum of the Preparation Example 1 and 300 parts by weight of PEO binder based on 100 parts by weight of the graphite By using the same method as in Example 1-1, except that 17 parts by weight of lithium lanthanum zirconium oxide (Al-LLZO) doped with aluminum and 50 parts by weight of a PEO binder were mixed.

Example 2: Preparation of All Solid Lithium Secondary Battery

Example 2-1: All-Solid Lithium Secondary Battery

Anode prepared according to Preparation Example 2 / Solid electrolyte layer prepared according to Preparation Example 3 / Composite interface layer prepared according to Example 1-1 / Cathode applying 0.05 t (50 μm) of lithium metal to a coin of 2032 standard An all-solid lithium secondary battery was produced as a cell.

Example 2-2: All-Solid Lithium Secondary Battery

An all-solid-state lithium secondary battery in the same manner as in Example 2-1 except for using the compound interface layer prepared according to Example 1-2 instead of using the compound interface layer prepared according to Example 1-1. Paper was prepared.

Example 2-3: All-Solid Lithium Secondary Battery

An all-solid-state lithium secondary battery in the same manner as in Example 2-1 except for using the compound interface layer prepared according to Example 1-3 instead of using the compound interface layer prepared according to Example 1-1. Paper was prepared.

Comparative Example 1: All-Solid Lithium Secondary Battery

Instead of using the composite interface layer prepared according to Example 1-1, except that the composite interface layer prepared according to Example 1-1 was not used, all solid lithium was prepared in the same manner as in Example 2-1. A secondary battery was manufactured.

Comparative Example 2: All-Solid Lithium Secondary Battery

An all-solid lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except for using the negative electrode having 0.2 t lithium metal instead of the negative electrode having 0.05 t lithium metal.

[Test Example]

Test Example 1: Charging and Discharging Characteristics and Cycle Characteristics According to Lithium Metal Thickness

2 and 3 are graphs showing charge and discharge characteristics and cycle characteristics of Comparative Examples 1 and 2. FIG. Measurement conditions were measured in the 3.0 ~ 4.1V section with 0.1C charge-discharge current.

According to FIGS. 2 and 3, the initial capacity of Comparative Example 1 in which the thickness of the lithium metal (cathode) is 0.05t is slightly superior to that of Comparative Example 2 in which the thickness of the lithium metal (cathode) is 0.2t. It was found that the rate of dose reduction with repetition was further increased.

Therefore, in order to improve this, a compound interface layer was applied between the lithium metal and the solid electrolyte layer of 0.05t.

Test Example 2: Charge and Discharge Characteristics and Cycle Characteristics According to Graphite Content

4 and 5 are graphs showing the charge-discharge one-time characteristics and the cycle characteristics of Examples 2-2 and 2-3 and Comparative Example 1; Measurement conditions were measured in the 3.0 ~ 4.1V section with 0.1C charge-discharge current.

According to FIG. 4, the initial capacities of the all-solid-state lithium secondary batteries manufactured according to Examples 2-2 and 2-3 were increased compared to the all-solid lithium secondary batteries prepared according to Comparative Example 1.

However, according to FIG. 5, it can be seen that the cycle characteristics of the all-solid-state lithium secondary battery prepared according to Example 2-3 decreased compared to the all-solid-state lithium secondary batteries prepared according to Examples 2-1 and 2-2. there was. This can be presumed to reduce the cycle characteristics due to excessive application of graphite.

Therefore, it was found that the graphite composition of the all-solid-state lithium secondary battery prepared in Example 2-2 was most suitable.

Test Example 3: Charge and Discharge Characteristics and Cycle Characteristics by Application of Composite Interface Layer

6 and 7 are graphs showing one-time charge and discharge characteristics and cycle characteristics of Example 2-2 and Comparative Example 2. FIG. Measurement conditions were measured in the 3.0 ~ 4.1V section with 0.1C charge-discharge current.

6 and 7, the initial capacity of the all-solid-state lithium secondary battery (composite interface layer applied) prepared according to Example 2-2 compared to the all-solid-state lithium secondary battery (not applied composite interface layer) prepared according to Comparative Example 2 And it was confirmed that the effect of the cycle characteristics are all improved.

Therefore, when lithium metal is used as the negative electrode, dead cell (dendrite) is generated and cycle characteristics are reduced. By applying the composite interface layer, it was confirmed that the cycle characteristics were improved.

Test Example 4: Overvoltage Characteristics by Application of Composite Interface Layer

8 and 9 are graphs of overvoltage characteristics of symmetric cells according to the application of a compound interface layer. A symmetric cell was fabricated for a lithium metal (cathode) of 0.05t, and charged and discharged at a current density of 0.1 mA / cm ² for 1 hour at 70 ° C. for a total of 65 hours.

Referring to FIG. 8, in the case of a symmetric cell in which lithium metal is applied to both surfaces of the solid electrolyte layer, the width of the potential through the lithium strip is about ± 0.05V.

9, the width of the potential through the symmetric cell lithium strip to which the composite interface layer and the lithium metal according to Example 1-1 were applied to both surfaces of the solid electrolyte layer was about ± 0.04V.

Therefore, it can be seen that the overvoltage is reduced when the composite interface layer is applied.

The scope of the present invention is shown by the following claims rather than the above description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

Claims (18)

A negative electrode comprising lithium metal;
A composite interface layer formed on the cathode and including graphite, first lithium lanthanum zirconium oxide (LLZO), and a first binder;
A solid electrolyte layer formed on the composite interface layer; And
An anode formed on the solid electrolyte layer; Including,
And the composite interface layer includes 400 to 800 parts by weight of the first lithium lanthanum zirconium oxide (LLZO) and 100 to 500 parts by weight of the first binder, based on 100 parts by weight of the graphite. The method of claim 1,
The thickness of the composite interface layer is an all-solid lithium secondary battery, characterized in that 1 to 50 ㎛. The method of claim 1,
The thickness of the composite interface layer is an all-solid lithium secondary battery, characterized in that 10 to 30 ㎛. delete The method of claim 1,
And the composite interface layer further comprises 5 to 50 parts by weight of the first lithium salt based on 100 parts by weight of the first binder. The method of claim 1,
The content of the graphite in the composite interface layer is an all-solid lithium secondary battery, characterized in that 10 to 300 parts by weight based on 100 parts by weight of the first binder. The method of claim 6,
The content of the graphite in the composite interface layer is an all-solid lithium secondary battery, characterized in that 50 to 150 parts by weight based on 100 parts by weight of the first binder. The method of claim 1,
The solid electrolyte layer includes a second lithium lanthanum zirconium oxide (LLZO), a second binder, and a second lithium salt,
And the cathode comprises a cathode active material, a third lithium lanthanum zirconium oxide (LLZO), a third binder, and a conductive material. The method of claim 1, wherein the all-solid-state lithium secondary battery,
A negative electrode comprising lithium metal;
A composite interface layer formed on the cathode and including graphite, first lithium lanthanum zirconium oxide (LLZO), a first binder, and a first lithium salt;
A solid electrolyte layer formed on the composite interface layer and including a second lithium lanthanum zirconium oxide (LLZO), a second binder, and a second lithium salt; And
A positive electrode formed on the solid electrolyte layer and including a positive electrode active material, a third lithium lanthanum zirconium oxide (LLZO), a third binder, and a conductive material; All-solid-state lithium secondary battery comprising a. The method of claim 9,
The first lithium lanthanum zirconium oxide (LLZO), the second lithium lanthanum zirconium oxide (LLZO) and the third lithium lanthanum zirconium oxide (LLZO) are each independently aluminum-doped lithium lanthanum zirconium oxide (LLZO). Phosphorus all-solid lithium secondary battery.
[Formula 1]
Li _x La _y Zr _z Al _w O ₁₂ (5≤x≤9, 2≤y≤4, 1≤z≤3, 0 <w≤1) The method of claim 9,
The first lithium lanthanum zirconium oxide (LLZO), the second lithium lanthanum zirconium oxide (LLZO), and the third lithium lanthanum zirconium oxide (LLZO) may have at least one structure selected from a cubic structure and a tetragonal structure. All-solid-state lithium secondary battery comprising a. The method of claim 11,
The first lithium lanthanum zirconium oxide (LLZO), the second lithium lanthanum zirconium oxide (LLZO) and the third lithium lanthanum zirconium oxide (LLZO) all solid lithium secondary battery, characterized in that the cubic structure. The method of claim 9,
The first binder, the second binder and the third binder are each independently polyethylene oxide, polyethyleneglycol, polyacrylonitrile, polyvinylchloride, polymethylmethacrylate. ), Polypropylene oxide, polydimethylsiloxane, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene carbonate, and at least one selected from polyvinyl pyrrolidinone. All-solid-state lithium secondary battery, characterized in that. The method of claim 13,
And the first binder, the second binder, and the third binder each independently include polyethylene oxide. The method of claim 9,
The first lithium salt and the second lithium salt are each independently lithium perchlorate (LiClO ₄ ), lithium triflate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LipF ₆ ), lithium tetrafluoroborate (LiBF ₄ ) And lithium trifluoromethanesulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ) All-solid lithium secondary battery comprising at least one selected from. The method of claim 8,
The cathode active material is an all-solid lithium secondary battery, characterized in that the three-component lithium metal oxide (NMC) of Ni-Co-Mn represented by the formula (2).
[Formula 2]
LiNi _p Co _q Mn _r O ₂ (0 <p <0.9, 0 <q <0.5, 0 <r <0.5, p + q + r = 1) The method of claim 8,
And the conductive material comprises at least one selected from carbon black, acetylene black, and ketjen black. (a) forming a negative electrode comprising lithium metal;
(b) forming a composite interface layer including graphite, first lithium lanthanum zirconium oxide (LLZO), a first binder, and a first lithium salt on the cathode;
(c) forming a solid electrolyte layer including a second lithium lanthanum zirconium oxide (LLZO), a second binder, and a second lithium salt on the composite interface layer; And
(d) forming an anode including a cathode active material, a third lithium lanthanum zirconium oxide (LLZO), a third binder, and a conductive material on the solid electrolyte layer;
And the composite interface layer comprises 400 to 800 parts by weight of the first lithium lanthanum zirconium oxide (LLZO) and 100 to 500 parts by weight of the first binder with respect to 100 parts by weight of the graphite.

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