KR102201326B1 - Method of manufacturing cathode active material coated titanium dioxide - Google Patents

Abstract

The present invention (a) preparing a titanium precursor solution containing a titanium precursor, a solvent and a chelating agent; (b) coating and drying the titanium precursor solution on a positive electrode active material; And (c) heat-treating the dried cathode active material to prepare a cathode active material coated with titanium dioxide. In the method of manufacturing a positive electrode active material coated with titanium dioxide of the present invention, by coating the positive electrode active material with thermally stable titanium dioxide (TiO ₂ ), thermal stability is excellent and charge/discharge capacity is improved.

Description

Manufacturing method of the cathode active material coated with titanium dioxide {METHOD OF MANUFACTURING CATHODE ACTIVE MATERIAL COATED TITANIUM DIOXIDE}

The present invention relates to a method of manufacturing a positive electrode active material coated with titanium dioxide, and by coating the positive electrode active material with thermally stable titanium dioxide (TiO ₂ ), a titanium dioxide-coated positive electrode active material having excellent thermal stability and improved charge/discharge capacity It relates to a manufacturing method.

With the rapid development of the electronics, telecommunications, and computer industries, as camcorders, mobile phones, notebook PCs, etc. continue to develop remarkably, demand for lithium secondary batteries as a power source capable of driving these portable electronic communication devices is increasing day by day. In particular, research and development are being actively conducted in Japan, Europe, and the United States, as well as in Korea, in connection with the application of electric vehicles, uninterruptible power supplies, power tools, and satellites as eco-friendly power sources. Moreover, as the commercialization of lithium secondary batteries is expanded in recent years, the problem of increasing the capacity and safety of lithium secondary batteries has been further raised.

On the other hand, lithium cobalt oxide (LiCoO ₂ ) was mainly used as a positive electrode material for lithium secondary batteries, but now lithium nickel oxide (Li (Ni-Co-Al) O ₂ ) and lithium composite metal oxide as other layered positive electrode materials. (Li(Ni-Co-Mn)O ₂ ) and the like are also used, and in addition, spinel-type lithium manganese oxide (LiMn ₂ O ₄ ) and olivine-type lithium iron phosphate compound (LiFePO ₄ ) with low cost stability are also attracting attention.

However, a lithium secondary battery using lithium cobalt oxide, lithium nickel oxide, lithium composite metal oxide, etc., has excellent basic battery characteristics, but safety, particularly thermal safety, overcharge characteristics, and the like are not sufficient. In order to improve this, various safety mechanisms such as a shut-down function of the separator, additives for electrolyte, and safety devices such as protection circuits and PTCs have been introduced, but these devices also have not very high chargeability of the anode material. It is designed under circumstances. For this reason, when the chargeability of the positive electrode material is increased in order to meet the demand for higher capacity, there is a problem that the operation of various safety mechanisms tends to be insufficient, and safety is deteriorated.

As such, various battery solutions are being developed to innovate the safety anxiety, the limit of the increase in energy density, and the high cost burden, which were pointed out as the limit of lithium secondary batteries in the current market. All solid lithium secondary batteries aiming for complete safety, 10 Metal-air batteries capable of increasing energy density by more than twice, next-generation sodium-based batteries suitable for storage of large-capacity energy, and magnesium batteries using abundant magnesium resources are currently attracting attention as representative next-generation batteries.

Among them, in the case of an all-solid lithium secondary battery, the greatest advantage is securing complete safety by using a solid electrolyte instead of a liquid electrolyte used in the existing lithium ion battery. The solid electrolyte is a key material for overcoming the limitations of use of existing liquid electrolytes due to the high capacity and high voltage of the lithium ion battery electrode and ensuring the safety of high-performance lithium ion batteries.

The all-solid lithium secondary battery is a battery applied by pressurizing ceramic-based all-solid-state electrolyte particles that do not contain any organic solvents, and according to the application of a solid electrolyte, the positive and negative electrodes located on both sides of the electrolyte layer are The electrode structure in which an ion conductor solid electrolyte and an electron conductor are uniformly combined instead of a liquid electrolyte in the pores (pores) existing in the existing lithium-ion battery electrode causes many problems in physical contact with the electrode.

In addition, since the all-solid lithium secondary battery is used at a high temperature of 60℃ or higher, thermal stability and initial capacity improvement of the positive electrode material is required.

An object of the present invention is to solve the above problems, by coating a positive electrode active material with thermally stable titanium dioxide (TiO ₂ ), to provide a method of manufacturing a titanium dioxide-coated positive electrode active material having excellent thermal stability and improved charge/discharge capacity. Have.

According to an aspect of the present invention, (a) preparing a titanium precursor solution comprising a titanium precursor, a solvent and a chelating agent; (b) coating and drying the titanium precursor solution on a positive electrode active material; And (c) heat-treating the dried cathode active material to prepare a cathode active material coated with titanium dioxide.

The step (b) is (b-1) preparing a mixture by mixing and stirring the titanium precursor solution and the positive electrode active material; (b-2) filtering the mixture; And (b-3) drying the filtered mixture to prepare a dried cathode active material.

The concentration of the titanium precursor in the titanium precursor solution may be 0.1 to 15 wt%.

The concentration of the titanium precursor in the titanium precursor solution may be 0.5 to 10 wt%.

The concentration of the titanium precursor in the titanium precursor solution may be 1 to 5 wt%.

The titanium precursor is titanium butoxide, titanium isopropoxide, titanium chloride, titanium tetraisopropoxide, and tetra-n-butyl orthotitanate (Tetra -n-butyl orthotitanate) may contain at least one selected from the group consisting of.

The solvent may contain at least one selected from the group consisting of ethanol, methanol, tetrahydrofuran, propanol, isopropanol, dichlorobenzene, methylene chloride, chlorobenzene, tert-butyl alcohol, distilled water, and nitric acid. have.

The chelating agent may include at least one selected from the group consisting of acetylacetone and ethyl acetoacetate.

The cathode active material is lithium-nickel-cobalt-manganese oxide (NCM), lithium-nickel-cobalt-aluminum oxide (NCA), lithium-nickel-cobalt oxide, lithium-cobalt oxide, lithium-iron oxide, lithium -It may include at least one selected from the group consisting of nickel-manganese-based oxide, lithium-manganese-based oxide, and lithium-nickel-based oxide.

The positive electrode active material may include lithium-nickel-cobalt-manganese oxide (NCM) represented by Formula 1 below.

[Formula 1]

Li _{1 + a} Ni _x Co _y Mn _z O ₂ (0≤a≤0.2, 0<x<1, 0<y<1, 0<z<1, x+y+z=1)

The lithium-nickel-cobalt-manganese oxide (NCM) is LiNi _{0 . 4} Co _{0 . 2} Mn _{0 . 4 O 2, LiNi 0.5 Co 0.2} Mn 0.3 O 2, LiNi 1/3 Co 1/3 Mn 1 / in ₃ O _2, LiNi _{0. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ and LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ It may include one or more selected from the group consisting of.

The heat treatment of the dried positive electrode active material in step (c) may be performed at a temperature of 400 to 900°C.

According to another aspect of the present invention, (a) preparing a titanium dioxide coated positive electrode active material; And (b) the titanium dioxide coated positive electrode active material. Lithium lanthanum zirconium oxide (LLZO) represented by the following Chemical Formula 2; bookbinder; And a conductive material; mixing and rolling to prepare a positive electrode; It provides a method of manufacturing a positive electrode comprising a.

[Formula 2]

Li _x Al _p Ga _q La _y Zr _z O ₁₂ (5≤x≤9, 0≤p≤4, 0≤q≤4, 2≤y≤4, 1≤z≤3)

The positive electrode includes 1 to 30 parts by weight of the lithium lanthanum zirconium oxide (LLZO), 40 to 80 parts by weight of the binder, and 5 to 30 parts by weight of the conductive material, based on 100 parts by weight of the titanium dioxide-coated positive electrode active material. I can.

The lithium lanthanum zirconium oxide (LLZO) may have a single-phase cubic structure.

The binder is polyethyleneoxide, nitrile butadiene rubber (NBR), polyethyleneglycol, polyacrylonitrile, polyvinylchloride, polymethylmethacrylate, Includes at least one selected from the group consisting of polypropyleneoxide, polydimethylsiloxane, polyvinylidenefluoride, polyvinylidenecarbonate, and polyvinyl pyrrolidinone. can do.

The conductive material may include at least one selected from the group consisting of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, and graphene.

According to another aspect of the present invention, (a) a positive electrode including a positive electrode active material, a first lithium lanthanum zirconium oxide (LLZO), a first binder, and a conductive material prepared according to the method of manufacturing the titanium dioxide-coated positive electrode active material. Manufacturing steps; (b) preparing a solid electrolyte layer including a second lithium lanthanum zirconium oxide (LLZO) and a second binder; (c) manufacturing a laminate by laminating the anode and the solid electrolyte layer; And (d) disposing a negative electrode on the solid electrolyte layer of the laminate; including, wherein the first and second lithium lanthanum zirconium oxide (LLZO) are represented by the following formula (2), an all-solid lithium secondary It provides a method of manufacturing a battery.

[Formula 2]

Li _x Al _p Ga _q La _y Zr _z O ₁₂ (5≤x≤9, 0≤p≤4, 0≤q≤4, 2≤y≤4, 1≤z≤3)

The negative electrode may include lithium metal.

In the method of manufacturing a positive electrode active material coated with titanium dioxide of the present invention, by coating the positive electrode active material with thermally stable titanium dioxide (TiO ₂ ), thermal stability is excellent and charge/discharge capacity is improved.

1 is a flowchart of a method of manufacturing a positive electrode active material coated with titanium dioxide of the present invention.
2 is an XRD analysis result of titanium dioxide (TiO ₂ ) powder heat-treated at 450, 500, 525, 550, 600, 700 and 800°C.
3 is an XRD analysis result of a positive electrode active material according to Examples 1 to 4 and Comparative Example 1 and TiO ₂ powder (TiO ₂ -600°C) heat-treated at 600°C.
4 is an XRD Rietvelt analysis result of positive electrode active materials according to Examples 1 to 4 and Comparative Example 1.
5 is an SEM image of a cathode active material according to Examples 1 to 4 and Comparative Example 1.
6 is a charge/discharge characteristic curve of an all-solid lithium secondary battery according to Device Examples 1 to 4 and Device Comparative Example 1. FIG.
7 is a charge/discharge cycle characteristic curve of an all-solid lithium secondary battery according to Device Examples 1 to 4 and Device Comparative Example 1. FIG.
8 is a charge/discharge characteristic curve of an all-solid lithium secondary battery according to Device Examples 2 and 5 and Device Comparative Example 1. FIG.
9 is a charge/discharge cycle characteristic curve of an all-solid lithium secondary battery according to Device Examples 2 and 5 and Device Comparative Example 1. FIG.

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

However, the following description is not intended to limit the present invention to a specific embodiment, and in describing the present invention, when it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted. .

The terms used herein are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, elements, or combinations thereof described in the specification, but one or more other features or It is to be understood that the possibility of the presence or addition of numbers, steps, actions, elements, or combinations thereof is not preliminarily excluded.

1 is a flowchart of a method of manufacturing a positive electrode active material coated with titanium dioxide of the present invention.

Hereinafter, a method of manufacturing a positive electrode active material coated with titanium dioxide according to the present invention will be described in detail with reference to FIG. 1.

First, a titanium precursor solution including a titanium precursor, a solvent and a chelating agent is prepared (step a).

The concentration of the titanium precursor in the titanium precursor solution may be 0.1 to 15 wt%, preferably 0.5 to 10 wt%, and more preferably 1 to 5 wt%.

The titanium precursor is titanium butoxide, titanium isopropoxide, titanium chloride, titanium tetraisopropoxide, and tetra-n-butyl orthotitanate (Tetra -n-butyl orthotitanate) may include at least one selected from the group consisting of, and preferably, may include titanium butoxide.

The solvent may contain at least one selected from the group consisting of ethanol, methanol, tetrahydrofuran, propanol, isopropanol, dichlorobenzene, methylene chloride, chlorobenzene, tert-butyl alcohol, distilled water, and nitric acid. have.

TiO ₂ can be obtained by hydrolyzing an alkoxide containing a Ti metal, a sulfate, a chloride, or a mixture thereof with water. In this case, in order to prevent the rapid growth of TiO ₂ , a chelating agent such as acetylacetone may be added together.

The chelating agent may include at least one selected from the group consisting of acetylacetone and ethyl acetoacetate.

Next, the titanium precursor solution Positive electrode active material Coat and dry (step b).

The step (b) is (b-1) preparing a mixture by mixing and stirring the titanium precursor solution and the positive electrode active material; (b-2) filtering the mixture; And (b-3) drying the filtered mixture to prepare a dried cathode active material.

The cathode active material is lithium-nickel-cobalt-manganese oxide (NCM), lithium-nickel-cobalt-aluminum oxide (NCA), lithium-nickel-cobalt oxide, lithium-cobalt oxide, lithium-iron oxide, lithium -It may include at least one selected from the group consisting of nickel-manganese-based oxide, lithium-manganese-based oxide, and lithium-nickel-based oxide.

The positive electrode active material may include lithium-nickel-cobalt-manganese oxide (NCM) represented by Formula 1 below.

[Formula 1]

Li _{1 + a} Ni _x Co _y Mn _z O ₂ (0≤a≤0.2, 0<x<1, 0<y<1, 0<z<1, x+y+z=1)

The lithium-nickel-cobalt-manganese oxide (NCM) is LiNi _{0 . 4} Co _{0 . 2} Mn _{0 . 4 O 2, LiNi 0.5 Co 0.2} Mn 0.3 O 2, LiNi 1/3 Co 1/3 Mn 1 / in ₃ O _2, LiNi _{0. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ and LiNi _{0 . 8} Co _{0 . 1} Mn _{0 . 1} O ₂ It may include one or more selected from the group consisting of.

Finally, the dried Cathode active material Heat treatment to prepare a positive electrode active material coated with titanium dioxide (step c).

The heat treatment of the dried positive electrode active material in step (c) may be performed at a temperature of 400 to 900°C, preferably 525 to 600°C.

Titanium dioxide has a band gap and can be used as a semiconductor, and is used in a wide range of fields such as catalysts and cosmetic materials for solar cells.In lithium secondary batteries, when TiO ₂ is coated on the surface of the positive electrode active material, it suppresses the reaction with the electrolyte. , By smoothing the movement of lithium ions and electrons, cycle characteristics and high rate characteristics can be improved.

Hereinafter, the method of manufacturing the positive electrode of the present invention will be described in detail.

First, a titanium dioxide coated cathode active material is prepared (step a).

Finally, the titanium dioxide coating Cathode active material ; Lithium lanthanum zirconium oxide represented by the following formula (2) ( LLZO ); bookbinder; And Conductive material; Mixing and rolling to prepare a positive electrode (step b).

[Formula 2]

Li _x Al _p Ga _q La _y Zr _z O ₁₂ (5≤x≤9, 0≤p≤4, 0≤q≤4, 2≤y≤4, 1≤z≤3)

The positive electrode includes 1 to 30 parts by weight of the lithium lanthanum zirconium oxide (LLZO), 40 to 80 parts by weight of the binder, and 5 to 30 parts by weight of the conductive material, based on 100 parts by weight of the titanium dioxide-coated positive electrode active material. I can.

The lithium lanthanum zirconium oxide (LLZO) may have a single-phase cubic structure.

The binder is polyethyleneoxide, nitrile butadiene rubber (NBR), polyethyleneglycol, polyacrylonitrile, polyvinylchloride, polymethylmethacrylate, Includes at least one selected from the group consisting of polypropyleneoxide, polydimethylsiloxane, polyvinylidenefluoride, polyvinylidenecarbonate, and polyvinyl pyrrolidinone. It can be, and preferably may include polyethylene oxide (polyethyleneoxide).

The conductive material may include at least one selected from the group consisting of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, and graphene.

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

The method of manufacturing an all-solid lithium secondary battery of the present invention comprises (a) a positive electrode active material prepared according to the method of manufacturing the titanium dioxide-coated positive electrode active material, a first lithium lanthanum zirconium oxide (LLZO), a first binder, and a conductive material. Manufacturing an anode; (b) preparing a solid electrolyte layer including a second lithium lanthanum zirconium oxide (LLZO) and a second binder; (c) manufacturing a laminate by laminating the anode and the solid electrolyte layer; And (d) disposing a negative electrode on the solid electrolyte layer of the laminate, wherein the first and second lithium lanthanum zirconium oxide (LLZO) may be represented by Formula 2 below.

[Formula 2]

Li _x Al _p Ga _q La _y Zr _z O ₁₂ (5≤x≤9, 0≤p≤4, 0≤q≤4, 2≤y≤4, 1≤z≤3)

The negative electrode may include lithium metal.

[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.

Manufacturing example 1: aluminum Doped Preparation of lithium lanthanum zirconium oxide (Aluminum doped lithium lanthanum zirconium oxide, Al-LLZO)

Lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), zirconium hydrochloride (ZrOCl ₂ ·8H ₂ O) and aluminum nitrate so that the molar ratio of the starting material La:Zr:Al to distilled water is 3:2:0.25 Al(NO ₃ ) ₃ ·9H ₂ O) was dissolved to prepare a starting material solution having 1 molar concentration of the starting material.

The starting material solution, 0.6 mol of aqueous ammonia, and an appropriate amount of sodium hydroxide aqueous solution were added as a complexing agent to obtain a mixed solution whose pH was adjusted to 11, and the reaction temperature was 25°C, the reaction time was 4 hours, and the stirring speed of the stirring rod was 1,300 rpm. By co-precipitation, a precursor slurry in the form of a liquid slurry was obtained.

After washing the precursor slurry with purified water, it was dried for 24 h. After pulverizing the dried precursor with a ball mill, excess LiOH·H ₂ O was added and mixed with a ball mill to prepare a mixture. The LiOH·H ₂ O content of the mixture was added in an excess of 3 wt% so that the content of Li in LiOH·H ₂ O was 103 parts by weight based on 100 parts by weight of Li in the solid electrolyte. The mixture was calcined at 900° C. for 2 hours and then pulverized to prepare aluminum-doped lithium lanthanum zirconium oxide (Al-LLZO).

Preparation Example 2: Preparation of solid electrolyte layer

A mixture was prepared so that the weight ratio of LLZO and the binder was 70:30. That is, a mixture was prepared by mixing 42.9 parts by weight of a polyethylene oxide (PEO) binder based on 100 parts by weight of LLZO prepared according to Preparation Example 1.

At this time, the PEO binder was such that the mixing ratio of polyethylene oxide (PEO, molecular weight 200,000) and LiClO ₄ was [EO]:[Li] = 15:1.

Specifically, first, the LLZO and PEO binders prepared according to Preparation Example 1 were weighed in the above weight ratio, and then stirred at 2,000 rpm for 5 minutes using a Thinky mixer to prepare a mixture.

Acetonitrile (ACN) was mixed with the mixture, and stirred with a Sinki mixer to adjust the viscosity to an appropriate viscosity. Next, a 2mm zircon ball was added and stirred for 5 minutes at 2,000 rpm with a Sinki mixer to prepare a slurry. The slurry was cast on a PET (polyethylene terephthalate) film and dried at room temperature to prepare a solid electrolyte layer.

Example 1: Titanium dioxide coated cathode active material (1wt%-600 ℃)

Titanium butoxide (Ti (OC ₄ H ₉ )) as a titanium source and acetylacetone (Acetylacetone) as a chelating agent were calculated in a weight ratio of 5:1 in 100 ml of ethanol, and stirred at room temperature for 24 hours to prepare a titanium precursor solution. At this time, the precursor solution was prepared in an amount of 1.0 wt% A positive electrode active material NCM424 was added to the precursor solution, stirred at room temperature for 4 hours, and filtered, and the powder obtained by filtering in an oven at a temperature of 60° C. After drying for 24 hours, it was heat-treated at 600° C. for 7 hours at a heating rate of 5° C. per minute in air to prepare TiO ₂ coated NCM424 powder.

Example 2: Titanium dioxide-coated cathode active material (3wt%-600 ℃)

In Example 1, a TiO ₂ coated NCM424 powder was prepared in the same manner as in Example 1, except that the precursor solution was prepared at 3.0 wt% instead of 1.0 wt%.

Example 3: A cathode active material coated with titanium dioxide (5wt%-600°C)

In Example 1, TiO ₂ coated NCM424 powder was prepared in the same manner as in Example 1, except that the precursor solution was prepared at 5.0 wt% instead of 1.0 wt%.

Example 4: A cathode active material coated with titanium dioxide (7wt%-600°C)

In Example 1, TiO ₂ coated NCM424 powder was prepared in the same manner as in Example 1, except that the precursor solution was prepared at 7.0 wt% instead of 1.0 wt%.

Example 5: Titanium dioxide-coated cathode active material (3wt%-525 ℃)

In Example 1, TiO ₂ was coated in the same manner as in Example 1, except that the precursor solution was prepared at 3.0 wt% instead of 1.0 wt%, and heat treated at 525° C. instead of heat treatment at 600° C. NCM424 powder was prepared.

Example 6: A positive electrode containing a positive electrode active material coated with titanium dioxide (1wt%-600°C)

A mixture was prepared so that the weight ratio of the positive electrode active material, solid electrolyte, binder, and conductive material prepared according to Example 1 was 55:5:30:10. That is, a mixture was prepared by mixing 9.1 parts by weight of LLZO prepared according to Preparation Example 1, 54.5 parts by weight of PEO binder, and 18.2 parts by weight of conductive material Super-P based on 100 parts by weight of the cathode active material prepared according to Example 1.

Specifically, first, the positive electrode active material prepared according to Example 1, LLZO and Super-p prepared according to Preparation Example 1 were weighed in the above weight ratio, and then mixed for 30 minutes using a mortar to prepare a mixed powder. The mixed powder was transferred to a container dedicated to a Thinky mixer, and then the PEO binder was mixed at the weight ratio, and mounted on a mixer to prepare a mixture by mixing three times for 5 minutes at 2,000 rpm. Next, acetonitrile (ACN) was mixed with the mixture to adjust the viscosity to an appropriate viscosity, and a zircon ball was added and mixed at 2,000 rpm for 5 minutes to prepare a slurry. The slurry was cast on an aluminum foil and dried in a vacuum oven at 60° C. for 24 hours to prepare a positive electrode.

Example 7: A positive electrode containing a positive electrode active material coated with titanium dioxide (3wt%-600°C)

In Example 6, a positive electrode was manufactured in the same manner as in Example 6, except that the positive electrode active material prepared according to Example 2 was used instead of using the positive electrode active material prepared according to Example 1.

Example 8: A cathode comprising a cathode active material coated with titanium dioxide (5wt%-600°C)

A positive electrode was manufactured in the same manner as in Example 6, except that the positive electrode active material prepared according to Example 3 was used instead of the positive electrode active material prepared according to Example 1 in Example 6.

Example 9: A positive electrode containing a positive electrode active material coated with titanium dioxide (7wt%-600°C)

A positive electrode was manufactured in the same manner as in Example 6, except that the positive electrode active material prepared according to Example 4 was used instead of the positive electrode active material prepared according to Example 1 in Example 6.

Example 10: A positive electrode containing a positive electrode active material coated with titanium dioxide (3wt%-525°C)

A positive electrode was manufactured in the same manner as in Example 6, except that the positive electrode active material prepared according to Example 5 was used instead of using the positive electrode active material prepared according to Example 1 in Example 6.

Comparative Example 1: Uncoated cathode active material

NCM 424 powder was used as a positive electrode active material.

Comparative Example 2: Uncoated anode

In Example 6, a positive electrode was manufactured in the same manner as in Example 6, except that the positive electrode active material NCM 424 powder according to Comparative Example 1 was used instead of using the positive electrode active material prepared according to Example 1.

Device Example 1: Preparation of an all-solid lithium secondary battery

The positive electrode prepared according to Example 6 and the solid electrolyte layer prepared according to Preparation Example 2 were punched into Ø14 and Ø16 sizes, respectively, and then laminated. Next, while heating to about 60° C., the laminate was prepared by pressing at 0.3 MPa for 0.5 minutes.

An all-solid lithium secondary battery was manufactured with a 2032 standard coin cell by placing a negative electrode including lithium metal on the laminate.

Device Example 2: Preparation of an all-solid lithium secondary battery

An all-solid lithium secondary battery was manufactured in the same manner as in Device Example 1, except for using the positive electrode prepared according to Example 7 instead of using the positive electrode prepared according to Example 6 in Device Example 1.

Device Example 3: Preparation of an all-solid lithium secondary battery

An all-solid lithium secondary battery was manufactured in the same manner as in Device Example 1, except that the positive electrode prepared according to Example 8 was used instead of the positive electrode prepared according to Example 6 in Device Example 1.

Device Example 4: Preparation of an all-solid lithium secondary battery

An all-solid lithium secondary battery was manufactured in the same manner as in Device Example 1, except for using the positive electrode prepared according to Example 9 instead of using the positive electrode prepared according to Example 6 in Device Example 1.

Device Example 5: Preparation of an all-solid lithium secondary battery

An all-solid lithium secondary battery was manufactured in the same manner as in Device Example 1, except for using the positive electrode prepared according to Example 10 instead of using the positive electrode prepared according to Example 6 in Device Example 1.

Device Comparative Example 1: Preparation of an all-solid lithium secondary battery

In Device Example 1, an all-solid lithium secondary battery was manufactured in the same manner as in Device Example 1, except that a positive electrode prepared according to Comparative Example 2 was used instead of using the positive electrode prepared according to Example 1.

[Test Example]

Test Example 1: Titanium dioxide (TiO) according to the heat treatment temperature ₂ ) XRD analysis of powder

2 is an XRD analysis result of titanium dioxide (TiO ₂ ) powder heat-treated at 450, 500, 525, 550, 600, 700 and 800°C.

Referring to FIG. 2, distinct peaks were observed around 25˚, 37˚, and 48˚, which are the main peaks of the Anatase phase under all temperature conditions, and it can be seen that the intensity of the peak increases as the heat treatment temperature increases. However, it was found that the peaks of the rutile phase were observed from the heat treatment temperature of 550 ℃ or higher, and the peaks appeared slightly more clearly around 27˚, 36˚, and 54˚, which are the main peaks of the rutile phase at 600 ℃. Two crystal structures appearing in the TiO ₂ powder according to the heat treatment temperature show an incomplete phase transition, which was found to occur between 525 ℃ and 550 ℃. The TiO ₂ powder on the Rutile has a higher surface cast free energy than the surface cast free energy on the Anatase. When crystals are formed, Anatase is first generated and then Rutile is generated. The mixing of the two phases may also be generated by forming a Rutile phase of Anatase particles or encapsulating a Rutile phase in Anatase particles. Through XRD analysis, it was confirmed that the XRD peaks coincide with the reference codes of ICSD 98-009-6946 and ICSD 98-003-6413, which are reference codes for the Anatase and Rutile phases of TiO ₂ , and the ratio of the Rutile phase at 550 ℃ was 1.45%, 600 ℃ It was found to be 14.2% in, and as the heat treatment temperature increased, the ratio of the rutile phase rapidly increased.

Test Example 2: XRD analysis of a cathode active material coated with titanium dioxide

3 is an XRD analysis result of a positive electrode active material according to Examples 1 to 4 and Comparative Example 1 and TiO ₂ powder (TiO ₂ -600°C) heat-treated at 600°C. 4 is an XRD Rietvelt analysis result of the positive electrode active material according to Examples 1 to 4 and Comparative Example 1.

3, in the positive electrode active materials according to Examples 1 to 4 and Comparative Example 1, distinct peaks were observed around 18° and 45°, which are the main peaks of NCM424, and the TiO ₂ peak was hardly observed, and the coating content It was found that the higher the increase, the lower the peak.

In addition, referring to the Rietvelt analysis result of FIG. 4, the lattice constants having a hexagonal structure have the same values of a and b, and different values of c. Looking at the lattice constants, a, b and c values tended to increase as the coating content increased to 1-3 wt%, but in the case of Example 3 (5.0 wt%), a, b and c values were slightly decreased. (a). In addition, when the coating content is increased to 3 wt% or more, the size of the crystal decreases, and in particular, it is rapidly decreased in Example 4 (7.0 wt%). In addition, the lattice volume was substantially constant in Comparative Example 1 (NCM424) and Examples 1 to 3, but increased rapidly in Example 4 (7.0 wt%). This is because about 3.5% of LiTiO ₂ having a Cubic structure was detected in XRD when the coating concentration was 7.0 wt%, and it was judged that Li was eluted from the positive electrode active material and reacted with TiO ₂ on the surface (b).

In addition, the intensity ratio represents the ratio of (104) and (003), which are the main peaks of the NCM-based active material, and when this value is lower than 1.2, it indicates structural instability. Comparing the ratio, as the coating concentration increased, the intensity ratio tended to decrease, the positive electrode active material of Example 1 (1.0 wt%) showed the highest value, and the positive electrode active material of Example 2 (3.0 wt%) was Comparative Example. It showed a value similar to that of the positive electrode active material of 1 (NCM424) (c). Therefore, when the coating content is 1.0 or 3.0 wt%, it is structurally stable and is expected to exhibit good properties during charge and discharge.

Test Example 3: SEM analysis of the positive electrode active material coated with titanium dioxide

5 is an SEM image of a cathode active material according to Examples 1 to 4 and Comparative Example 1.

Referring to FIG. 5, the non-coated NCM424 (Comparative Example 1) is a material composed of secondary particles having a particle diameter of 5 to 10 μm in which primary particles having a particle diameter of 0.1 to 0.5 μm are aggregated. As the coating content increased, nanoparticles were formed on the surface of the positive electrode active material and the surface of the positive electrode active material became rough. In particular, in the case of the cathode active material according to Example 4 (7.0wt%) in which LiTiO ₂ was detected in XRD analysis, particles estimated to be nano-sized LiTiO ₂ were observed on the surface of the particles when the magnification was 5000 times. Through this, when titanium dioxide is coated in excess of 5 wt%, a material other than TiO ₂ is generated. Therefore, in order to coat TiO ₂ on the surface, it is considered that coating at 5 wt% or less is preferable.

Test Example 4: Performance evaluation of an all-solid lithium secondary battery

6 is a charge/discharge characteristic curve of an all-solid lithium secondary battery according to Device Examples 1 to 4 and Device Comparative Example 1, and FIG. 7 is an all-solid lithium secondary battery according to Device Examples 1 to 4 and Device Comparative Example 1. It is a characteristic curve of a charge/discharge cycle. Charging and discharging experiments were conducted in the 3.0 ~ 4.1 V section, and both charging and discharging were measured at 0.1C-0.1C (CC-CV) for 50 cycles each.

6, in the charging/discharging range, all solid lithium secondary batteries according to Device Examples 1 to 4 and Device Comparative Example 1 had a discharge capacity of about 98% compared to the charging capacity, and all solid lithium according to Device Example 3 The charging capacity of the secondary battery was about 158 mAh/g and the discharge capacity was 136 mAh/g, showing excellent characteristics.The all-solid lithium secondary battery according to Device Example 2 also had an initial charge capacity and a discharge capacity of Device Example 3 And showed similar characteristics. In addition, the initial charging capacity of the all-solid lithium secondary battery according to Device Example 4 was 135 mAh/g and the discharge capacity was 119 mAh/g, showing the lowest characteristics. In particular, the all-solid lithium secondary battery according to Device Example 4 exhibited characteristics of lowering the charging voltage and increasing the discharging voltage compared to other batteries. In particular, Device Example 4 having a coating content of 7.0 wt% showed a characteristic of lowering the charging voltage and increasing the discharge voltage compared to other samples. From this, a new LiTiO ₂ layer is created It is believed that the resistance increases during charge and discharge electrochemically, and the charge/discharge capacity decreases due to the decrease in the lithium content of NCM.

In addition, referring to FIG. 7, as a graph comparing discharge capacities according to charge/discharge cycles, the capacity retention rate of Device Comparative Example 1 at the 50th cycle was 88.2%, Device Example 1 86.4%, Device Example 2 87.3%, and Device Example 3 showed a capacity retention rate of 84.6% and Device Example 4 of 87.9%. As for the cycle characteristics, Device Examples 2 and 4 showed similar characteristics. This shows that when the coating content was 5.0 wt%, the amount of TiO ₂ produced on the surface was large, and the initial discharge capacity of Device Example 3 was high, but the capacity reduction width increased at the beginning of the cycle due to excessive coating. Through this, it is considered that 3.0 wt% is the optimal TiO ₂ coating composition, and the all-solid lithium _secondary battery according to Device Example 4 has a separate LiTiO ₂ formed on the surface of the NCM active material as mentioned above, although the coating amount is increased. It has a reaction characteristic different from that of TiO ₂ , and the initial capacity is low, but it is thought that this increases thermal stability and acts as an ion conductor, showing excellent cycling characteristics.

Test example 5: different heat treatment temperatures TiO ₂ coating Cathode active material Applied All solid Lithium secondary battery Charge/discharge cycle characteristics

8 is a charge-discharge characteristic curve of an all-solid lithium secondary battery according to Device Examples 2 and 5 and Device Comparative Example 1, and FIG. 9 is a diagram of an all-solid lithium secondary battery according to Device Examples 2 and 5 and It is a characteristic curve of a charge/discharge cycle. Charging and discharging experiments were conducted in the 3.0 ~ 4.1 V section, and both charging and discharging were measured at 0.1C-0.1C (CC-CV) for 50 cycles each.

Referring to Figures 8 and 9, Anatase sangman appear 525 ℃ heat treatment conditions all-solid lithium secondary battery and Rutile different from 3wt% coated with TiO ₂ in a 600 ℃ heat treatment conditions, some may appear along the TiO ₂ to 3wt% coated device in Example 5 in The charge/discharge and cycle characteristics of an all-solid lithium secondary battery according to Example 2 were compared. As a result, it was found that the initial discharge capacity of Device Comparative Example 1 was 123.4 mAh/g, and Device Example 2 was 133.1 mAh/g, while the initial capacity of Device Example 5 was significantly reduced to about 111.1 mAh/g. However, it was found that the batteries of Device Examples 1 and 5 including the TiO ₂ coated positive electrode active material were somewhat superior to the battery of Device Comparative Example 1 in terms of capacity retention by charge/discharge cycle characteristics.

The scope of the present invention is indicated by the claims to be described later rather than the detailed description, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention. do.

Claims (19)

(a) preparing a titanium precursor solution comprising a titanium precursor, a solvent and a chelating agent;
(b) coating and drying the titanium precursor solution on a positive electrode active material; And
(c) heat treating the dried positive electrode active material to prepare a positive electrode active material coated with titanium dioxide; including,
The concentration of the titanium precursor in the titanium precursor solution is 1 to 5wt%,
The positive electrode active material includes a lithium-nickel-cobalt-manganese oxide (NCM) represented by the following Formula 1,
In step (c), the heat treatment of the dried positive electrode active material is performed at a temperature of 400 to 900° C., a method for producing a titanium dioxide-coated positive electrode active material.
[Formula 1]
Li _1+a Ni _x Co _y Mn _z O ₂ (0≤a≤0.2, 0<x<1, 0<y<1, 0<z<1, x+y+z=1) The method of claim 1,
Step (b)
(b-1) preparing a mixture by mixing and stirring the titanium precursor solution and a positive electrode active material;
(b-2) filtering the mixture; And
(b-3) drying the filtered mixture to prepare a dried positive electrode active material; a method of manufacturing a titanium dioxide-coated positive electrode active material comprising: delete delete delete The method of claim 1,
The titanium precursor is titanium butoxide, titanium isopropoxide, titanium chloride, titanium tetraisopropoxide, and tetra-nbutyl orthotitanate (Tetra- n-butyl orthotitanate), characterized in that it comprises at least one selected from the group consisting of titanium dioxide coated cathode active material. The method of claim 1,
The solvent contains at least one selected from the group consisting of ethanol, methanol, tetrahydrofuran, propanol, isopropanol, dichlorobenzene, methylene chloride, chlorobenzene, tert-butyl alcohol, distilled water and nitric acid. Method for producing a titanium dioxide-coated positive electrode active material, characterized in that. The method of claim 1,
The method for producing a titanium dioxide-coated positive electrode active material, wherein the chelating agent comprises at least one selected from the group consisting of acetylacetone and ethyl acetoacetate. delete delete The method of claim 1,
The lithium-nickel-cobalt-manganese oxide (NCM) is LiNi _0.4 Co _0.2 Mn _0.4 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ and LiNi _0.8 Co _0.1 Mn _0.1 O _{2 A} method for producing a titanium dioxide-coated positive electrode active material comprising at least one selected from the group consisting of. delete (1) preparing a titanium dioxide coated positive electrode active material; And
(2) the titanium dioxide coated positive electrode active material; Lithium lanthanum zirconium oxide (LLZO) represented by the following Chemical Formula 2; bookbinder; And a conductive material; mixing and rolling to prepare a positive electrode; Including,
Step (1) above
(a) preparing a titanium precursor solution comprising a titanium precursor, a solvent and a chelating agent;
(b) coating and drying the titanium precursor solution on a positive electrode active material; And
(c) heat treating the dried positive electrode active material to prepare a positive electrode active material coated with titanium dioxide; including,
The concentration of the titanium precursor in the titanium precursor solution is 1 to 5 wt%,
The positive electrode active material includes a lithium-nickel-cobalt-manganese oxide (NCM) represented by the following Formula 1,
The method of manufacturing a positive electrode, wherein the heat treatment of the dried positive electrode active material in step (c) is performed at a temperature of 400 to 900°C:
[Formula 1]
Li _1+a Ni _x Co _y Mn _z O ₂ (0≤a≤0.2, 0<x<1, 0<y<1, 0<z<1, x+y+z=1)
[Formula 2]
Li _x Al _p Ga _q La _y Zr _z O ₁₂ (5≤x≤9, 0≤p≤4, 0≤q≤4, 2≤y≤4, 1≤z≤3) The method of claim 13,
The positive electrode comprises 1 to 30 parts by weight of the lithium lanthanum zirconium oxide (LLZO), 40 to 80 parts by weight of the binder, and 5 to 30 parts by weight of the conductive material based on 100 parts by weight of the titanium dioxide-coated positive electrode active material. Method for producing a positive electrode, characterized in that. The method of claim 13,
The method of manufacturing a positive electrode, characterized in that the lithium lanthanum zirconium oxide (LLZO) has a single-phase cubic structure. The method of claim 13,
The binder is polyethyleneoxide, nitrile butadiene rubber (NBR), polyethyleneglycol, polyacrylonitrile, polyvinylchloride, polymethylmethacrylate, Includes at least one selected from the group consisting of polypropyleneoxide, polydimethylsiloxane, polyvinylidenefluoride, polyvinylidenecarbonate, and polyvinyl pyrrolidinone. Method of manufacturing a positive electrode, characterized in that. The method of claim 13,
The method of manufacturing a positive electrode, wherein the conductive material comprises at least one selected from the group consisting of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, and graphene. (a') preparing a positive electrode including a titanium dioxide-coated positive electrode active material, a first lithium lanthanum zirconium oxide (LLZO), a first binder, and a conductive material;
(b') preparing a solid electrolyte layer including a second lithium lanthanum zirconium oxide (LLZO) and a second binder;
(c') manufacturing a laminate by laminating the anode and the solid electrolyte layer; And
(d') disposing a negative electrode on the solid electrolyte layer of the laminate; Including,
The first and second lithium lanthanum zirconium oxides (LLZO) are represented by Formula 2 below,
The step (a')
(1) preparing a titanium dioxide coated positive electrode active material; And
(2) the titanium dioxide coated positive electrode active material; The first lithium lanthanum zirconium oxide (LLZO); The first binder; And mixing and rolling the conductive material to prepare a positive electrode; Including,
Step (1) above
(a) preparing a titanium precursor solution comprising a titanium precursor, a solvent and a chelating agent;
(b) coating and drying the titanium precursor solution on a positive electrode active material; And
(c) heat treating the dried positive electrode active material to prepare a positive electrode active material coated with titanium dioxide; including,
The concentration of the titanium precursor in the titanium precursor solution is 1 to 5wt%,
The positive electrode active material includes a lithium-nickel-cobalt-manganese oxide (NCM) represented by the following Formula 1,
The method of manufacturing an all-solid lithium secondary battery, wherein the heat treatment of the dried positive electrode active material in step (c) is performed at a temperature of 400 to 900°C:
[Formula 1]
Li _1+a Ni _x Co _y Mn _z O ₂ (0≤a≤0.2, 0<x<1, 0<y<1, 0<z<1, x+y+z=1)
[Formula 2]
Li _x Al _p Ga _q La _y Zr _z O ₁₂ (5≤x≤9, 0≤p≤4, 0≤q≤4, 2≤y≤4, 1≤z≤3) The method of claim 18,
The method for manufacturing an all-solid lithium secondary battery, characterized in that the negative electrode comprises a lithium metal.

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