KR20200086111A - Method of manufacturing cathode active material coated titanium dioxide - Google Patents

Abstract

The present invention relates to a method for manufacturing a positive electrode active material coated with titanium dioxide which comprises the following steps: (a) manufacturing a titanium precursor solution containing a titanium precursor, a solvent and a chelating agent; (b) coating the titanium precursor solution on the positive electrode active material, followed by drying the same; and (c) heat treating the dried positive electrode active material to manufacture the positive electrode active material coated with titanium dioxide. The method for manufacturing the positive electrode active material coated with titanium dioxide of the present invention is coated with thermally stable titanium dioxide (TiO_2), thereby having excellent thermal stability, and having an effect of improving charge/discharge capacity.

Description

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

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

With the rapid development of the electronics, telecommunications, and computer industries, and as camcorders, mobile phones, and notebook PCs continue to develop remarkably, the demand for lithium secondary batteries is increasing day by day as a power source for driving these portable telecommunication devices. In particular, as an eco-friendly power source, research and development are actively underway in Japan, Europe and the United States, as well as domestically, in relation to applications such as electric vehicles, uninterruptible power supplies, power tools, and satellites. Moreover, as the commercialization of lithium secondary batteries has recently expanded, the capacity of lithium secondary batteries has increased and safety issues have emerged.

Meanwhile, lithium cobalt oxide (LiCoO ₂ ) has been mainly used as a cathode material for lithium secondary batteries, but lithium nickel oxide (Li(Ni-Co-Al)O ₂ ) and lithium composite metal oxides are currently used as other layered anode materials. (Li(Ni-Co-Mn)O ₂ ), etc. are also used, and in addition, low-cost, high-stability spinel-type lithium manganese oxide (LiMn ₂ O ₄ ) and olivine-type lithium iron phosphate compound (LiFePO ₄ ) are also attracting attention.

However, a lithium secondary battery using lithium cobalt oxide, lithium nickel oxide, lithium composite metal oxide, or the like has excellent basic battery characteristics, but safety, particularly thermal safety, overcharge characteristics, etc. are not sufficient. To improve this, various safety devices such as a shut-down function of the separator, an additive of an electrolyte solution, and a safety circuit such as a protection circuit or a PTC have been introduced, but these devices also do not have high chargeability of the anode material. It is designed under circumstances. For this reason, if the chargeability of the positive electrode material is increased to meet the demand for high capacity, the operation of various safety devices tends to be insufficient, and there is a problem that safety is deteriorated.

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

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

The all-solid lithium secondary battery is a battery applied by pressing ceramic-based all-solid-state electrolyte particles containing no organic solvent at all, and the positive and negative electrodes located on both sides of the electrolyte layer according to the application of the solid electrolyte. In the pores (pores) existing in the existing lithium ion battery electrode, instead of a liquid electrolyte, an ion conductor solid electrolyte and an electron conductor are formed in a uniformly complex electrode structure, causing 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°C or higher, it is required to improve the thermal stability and initial capacity of the positive electrode material.

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

According to an aspect of the invention, (a) preparing a titanium precursor solution comprising a titanium precursor, a solvent and a chelating agent; (b) coating the titanium precursor solution on a positive electrode active material and drying it; And (c) heat-treating the dried positive electrode active material to produce a titanium dioxide-coated positive electrode active material; providing a method for producing a titanium dioxide-coated positive electrode active material.

The step (b) (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 positive electrode active material.

The titanium precursor solution may have a concentration of titanium precursor of 0.1 to 15 wt%.

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

The titanium precursor solution may have a titanium precursor concentration of 1 to 5 wt%.

The titanium precursor is titanium butoxide, titanium isopropoxide, titanium chloride, titanium tetraisopropoxide and tetra-n-butyl orotitanate (Tetra -n-butyl orthotitanate).

The solvent may include 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 one or more selected from the group consisting of acetylacetone and ethyl acetoacetate.

The positive electrode 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 -Nickel-manganese oxide, lithium-manganese oxide and may include one or more selected from the group consisting of lithium-nickel-based oxide.

The positive electrode active material may include lithium-nickel-cobalt-manganese oxide (NCM) represented by Chemical 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 .} It may include one or more selected from the group consisting of ₁ O ₂ .

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

According to another aspect of the 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 represented by the following formula (2) (LLZO); bookbinder; And a conductive material; mixing and rolling to produce an anode; 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 may include 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 with respect to 100 parts by weight of the titanium dioxide-coated positive electrode active material. Can.

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

The binder is polyethylene oxide (polyethyleneoxide), nitrile butadiene rubber (NBR, nitrile butadiene rubber), polyethylene glycol (polyethyleneglycol), polyacrylonitrile (polyacrylonitrile), polyvinyl chloride (polyvinylchloride), polymethyl methacrylate (polymethylmethacrylate), Contains at least one selected from the group consisting of polypropylene oxide, 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 fibers, carbon nanotubes, and graphene.

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

The production method of the titanium dioxide-coated positive electrode active material of the present invention has the effect of excellent thermal stability and improved charge/discharge capacity by coating the positive electrode active material with thermally stable titanium dioxide (TiO ₂ ).

1 is a flow chart of a method for manufacturing a titanium dioxide-coated positive electrode active material 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 the cathode active materials according to Examples 1 to 4 and Comparative Example 1 and the TiO ₂ powder (TiO ₂ -600° C.) heat-treated at 600°C.
4 is an XRD Rietveld analysis result of the positive electrode active material according to Examples 1 to 4 and Comparative Example 1.
5 is a SEM image of the positive electrode active material according to Examples 1 to 4 and Comparative Example 1.
6 is a charging and discharging characteristic curve of the all-solid-state lithium secondary battery according to Device Examples 1 to 4 and Device Comparative Example 1.
7 is a charging and discharging cycle characteristic curve of the all-solid-state lithium secondary battery according to Device Examples 1 to 4 and Device Comparative Example 1.
8 is a charge-discharge characteristic curve of the all-solid-state lithium secondary battery according to Device Examples 2 and 5 and Device Comparative Example 1.
9 is a charging and discharging cycle characteristic curve of the all-solid-state lithium secondary battery according to Device Examples 2 and 5 and Device Comparative Example 1.

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

However, the following description is not intended to limit the present invention to specific embodiments, and when it is determined that a detailed description of known technologies related to the present invention may obscure the subject matter of the present invention, the detailed description 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 this application, terms such as “include” or “have” are intended to indicate that a feature, number, step, operation, component, or combination thereof described in the specification exists, or that one or more other features or It should be understood that the existence or addition possibilities of numbers, steps, actions, elements, or combinations thereof are not excluded in advance.

1 is a flow chart of a method for manufacturing a titanium dioxide-coated positive electrode active material of the present invention.

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

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

The concentration of 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 orotitanate (Tetra -n-butyl orthotitanate) may include one or more selected from the group consisting of, preferably, titanium butoxide (Titanium butoxide).

The solvent may include 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, sulfate, chloride or mixture thereof containing Ti metal with water. At this time, a chelating agent such as acetylacetone may be added together to prevent rapid growth of TiO ₂ .

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

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

The step (b) (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 positive electrode active material.

The positive electrode 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 -Nickel-manganese oxide, lithium-manganese oxide and may include one or more selected from the group consisting of lithium-nickel-based oxide.

The positive electrode active material may include lithium-nickel-cobalt-manganese oxide (NCM) represented by Chemical 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 .} It may include one or more selected from the group consisting of ₁ O ₂ .

Finally, the dried Cathode active material A titanium dioxide coated positive electrode active material is prepared by heat treatment (step c).

In step (c), the heat treatment of the dried positive electrode active material 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 a lithium secondary battery, when TiO ₂ is coated on the surface of the positive electrode active material, it inhibits the reaction with the electrolyte. , It is possible to improve cycle characteristics and high rate characteristics by smoothly moving lithium ions and electrons.

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

First, a titanium dioxide-coated positive electrode 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; The anode was prepared by mixing and rolling (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 may include 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 with respect to 100 parts by weight of the titanium dioxide-coated positive electrode active material. Can.

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

The binder is polyethylene oxide (polyethyleneoxide), nitrile butadiene rubber (NBR, nitrile butadiene rubber), polyethylene glycol (polyethyleneglycol), polyacrylonitrile (polyacrylonitrile), polyvinyl chloride (polyvinylchloride), polymethyl methacrylate (polymethylmethacrylate), Contains at least one selected from the group consisting of polypropylene oxide, polydimethylsiloxane, polyvinylidenefluoride, polyvinylidenecarbonate and polyvinyl pyrrolidinone It may be, preferably it may include a polyethylene oxide (polyethyleneoxide).

The conductive material may include at least one selected from the group consisting of carbon black, acetylene black, ketjen black, carbon fibers, carbon nanotubes, and graphene.

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

The method of manufacturing the all-solid lithium secondary battery of the present invention includes (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 comprising a second lithium lanthanum zirconium oxide (LLZO) and a second binder; (c) laminating the anode and the solid electrolyte layer to produce a laminate; And (d) disposing a negative electrode on the solid electrolyte layer of the laminate, wherein the first and second lithium lanthanum zirconium oxides (LLZO) may be represented by the following Chemical Formula 2.

[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 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 (molar ratio of the starting material La:Zr:Al in distilled water to be 3:2:0.25) Al(NO ₃ ) ₃ ·9H ₂ O) was dissolved to prepare a starting material solution having a starting material concentration of 1 mol.

The starting material solution, 0.6 mol of ammonia water as a complexing agent, and an aqueous sodium hydroxide solution were added in an appropriate amount so that the pH was adjusted to 11 and the reaction temperature was 25°C, the reaction time was 4 hr, and the stirring speed of the stirring rod was 1,300 rpm. Coprecipitation yielded a precursor slurry in the form of a liquid slurry.

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

Preparation Example 2: Preparation of solid electrolyte layer

The 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 made so 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 for 5 minutes at 2,000 rpm using a Sinky mixer to prepare a mixture.

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

Example 1: A cathode active material coated with titanium dioxide (1wt%-600°C)

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

Example 2: A positive electrode active material coated with titanium dioxide (3wt%-600°C)

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

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

In Example 1, the NCM424 powder coated with TiO ₂ 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 positive electrode active material (3wt%-525℃)

TiO ₂ was coated in the same manner as in Example 1, except that the precursor solution in Example 1 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 comprising a titanium dioxide coated positive electrode active material (1wt%-600 ℃)

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 would be 55:5:30:10. That is, based on 100 parts by weight of the positive electrode active material prepared according to Example 1, 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 were mixed to prepare a mixture.

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 using a pestle bowl for 30 minutes to prepare a mixed powder. The mixed powder was transferred to a container dedicated to a Sinky mixer, and then the PEO binder was mixed in the weight ratio, mounted on the mixer, and mixed three times for 5 minutes at 2,000 rpm once to prepare a mixture. Next, acetonitrile (acetonitrile, ACN) was mixed with the mixture to adjust the appropriate viscosity, and a zircon ball was added, followed by mixing 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 an anode.

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

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

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

A positive electrode was prepared 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 comprising a titanium dioxide coated positive electrode active material (7wt%-600 ℃)

A positive electrode was prepared 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 comprising a titanium dioxide coated positive electrode active material (3wt%-525 ℃)

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

Comparative Example 1: Uncoated positive electrode active material

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

Comparative Example 2: Uncoated anode

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

Device Example 1: Preparation of 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 respectively punched to a size of Ø14 and Ø16 and then laminated. Next, a laminate was prepared by pressing at 0.3 MPa for 0.5 minute while heating to about 60°C.

An anode containing lithium metal was placed on the laminate, and an all-solid lithium secondary battery was manufactured with a coin cell of 2032 standard.

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

An all-solid-state lithium secondary battery was manufactured in the same manner as in Device Example 1, except that instead of using the cathode prepared according to Example 6 in Device Example 1, the anode prepared according to Example 7 was used.

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

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

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

An all-solid-state lithium secondary battery was manufactured in the same manner as in Device Example 1, except that instead of using the cathode prepared according to Example 6 in Device Example 1, the anode prepared according to Example 9 was used.

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

An all-solid-state lithium secondary battery was manufactured in the same manner as in Device Example 1, except that instead of using the cathode prepared according to Example 6 in Device Example 1, the anode prepared according to Example 10 was used.

Device comparison example 1: Preparation of all-solid lithium secondary battery

An all-solid-state lithium secondary battery was manufactured in the same manner as in Device Example 1, except that instead of using the anode prepared according to Example 1 in Device Example 1, the anode prepared according to Comparative Example 2 was used.

[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, in all temperature conditions, a clear peak was observed near the main peaks of 25°, 37°, and 48° on the Anatase phase, and it was found that the intensity of the peak increased as the heat treatment temperature increased. However, peaks of the Rutile phase were observed from 550℃ or higher, and at 600℃, the peaks were slightly more pronounced near the main peaks of the Rutile phases 27˚, 36˚, and 54˚. The two crystal structures shown in TiO ₂ powder according to the heat treatment temperature show incomplete phase transition, which was found to occur between 525 °C and 550 °C. The TiO ₂ powder on the Rutile has a higher surface cast free energy than the surface cast free energy on the Anatase, and when crystals are formed, Anatase is generated first and Rutile is generated. The mixing of the two phases can also be generated by Rutile phase formation of Anatase particles or encapsulation of Rutile phase on Anatase particles. Through XRD analysis, it was confirmed that the reference codes of ICSD 98-009-6946, ICSD 98-003-6413 and XRD peaks of Anatase phase and Rutile phase of TiO ₂ coincide, and the ratio of Rutile phase at 550 ℃ is 1.45%, 600 ℃ At 14.2%, it was found that the proportion of rutile phase increased rapidly as the heat treatment temperature increased.

Test Example 2: XRD analysis of the positive electrode active material coated with titanium dioxide

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

Referring to FIG. 3, the positive electrode active materials according to Examples 1 to 4 and Comparative Example 1 were observed with distinct peaks around 18° and 45°, which are the main peaks of NCM424, and the TiO ₂ peak was hardly observed and the coating content It can be seen that the peak decreases as this increases.

In addition, referring to the results of the Rietveld analysis of FIG. 4, a lattice constant having a Hexagonal structure has the same a and b values, and different c values. Looking at the lattice constant, the 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%), the a, b and c values slightly decreased. (a). And when the coating content is increased to 3wt% or more, the crystal size decreases, and in particular, in Example 4 (7.0 wt%), it is rapidly reduced. In addition, the lattice volume of Comparative Example 1 (NCM424) and Examples 1 to 3 showed an almost constant appearance, but increased rapidly in Example 4 (7.0 wt%). It is considered that LiTiO ₂ of Cubic structure was detected at about 3.5% in XRD when the coating concentration was 7.0 wt%, and it was determined that Li was eluted from the positive electrode active material and reacted with TiO ₂ on the surface (b).

In addition, the intensity ratio shows the ratio of the main peaks of the NCM-based active materials (104) and (003), and when this value is lower than 1.2, it indicates that it is structurally unstable. When comparing the ratio, as the coating concentration increased, the intensity ratio tended to decrease, and 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 a comparative example. 1 (NCM424) showed a similar value to the positive electrode active material (c). Therefore, when the coating content is 1.0, 3.0 wt%, it is expected to be structurally stable and exhibit good properties during charging and discharging.

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

5 is a SEM image of the positive electrode active material according to Examples 1 to 4 and Comparative Example 1.

Referring to FIG. 5, uncoated NCM424 (Comparative Example 1) is a material composed of secondary particles having a particle size of 5 to 10 μm by agglomeration of primary particles having a particle size of 0.1 to 0.5 μm. As the coating content increased, nanoparticles were formed on the surface of the positive electrode active material to observe the phenomenon that the surface of the positive electrode active material became rough. Particularly, in the case of the positive electrode active material according to Example 4 (7.0 wt%) in which LiTiO ₂ was detected in XRD analysis, particles estimated to be nano-sized LiTiO ₂ were observed on the surface of the particle when the magnification was 5000 times. Since this titanium dioxide and exceeds 5wt% by generating a different substance other than TiO ₂ during coating in order to coat the TiO ₂ on the surface is determined to be preferable to coating below 5 wt%.

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

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

Referring to FIG. 6, in the charge/discharge range, all of the all-solid-state lithium secondary batteries according to Device Examples 1 to 4 and Device Comparative Example 1 had a discharge capacity compared to a charge capacity of about 98%, and all-solid lithium according to Device Example 3 The charge capacity of the secondary battery was about 158 mAh/g, and the discharge capacity was 136 mAh/g, showing excellent characteristics, and the initial charge capacity and discharge capacity of the all-solid lithium secondary battery according to the device example 2 were the device example 3 Showed similar characteristics. In addition, the initial charge capacity of the all-solid-state 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-state lithium secondary battery according to the device example 4 showed a characteristic that the charging voltage is lowered and the discharge voltage is increased compared to other batteries. In particular, the device example 4 having a coating content of 7.0 wt% showed a characteristic that the charging voltage was lowered and the discharge voltage was increased compared to other samples. From this, a new LiTiO ₂ layer is created It is thought that the resistance increases during charging and discharging electrochemically, and the charge and discharge capacity decreases due to a decrease in the lithium content of NCM.

Also, referring to FIG. 7, as a graph comparing discharge capacities according to charge/discharge cycles, the capacity retention rate of Device Comparative Example 1 in the 50th cycle is 88.2%, Device Example 1 is 86.4%, Device Example 2 is 87.3%, Device Example 3 showed a capacity retention rate of 84.6% and Device Example 4 87.9%. The cycle characteristics of the device examples 2 and 4 showed similar characteristics. This showed 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 the device example 3 was high, but the capacity reduction width increased at the beginning of the cycle due to overcoating. Through this, 3.0 wt% is considered to be the optimal TiO ₂ coating composition, and the all-solid-state lithium _secondary battery according to Device Example 4 is formed with a separate LiTiO ₂ on the surface of the NCM active material, as mentioned above, although the coating amount increases. Reaction characteristics different from TiO ₂ are formed, and although the initial capacity is low, it is thought that it shows excellent cycle characteristics by increasing thermal stability and acting as an ion conductor.

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 charging and discharging characteristic curve of the all-solid-state lithium secondary battery according to the device examples 2, 5 and the device comparison example 1, and FIG. 9 is the all-solid-state lithium secondary battery according to the device examples 2, 5 and the device comparison example 1 It is a characteristic curve of charge/discharge cycles. The charging and discharging experiments were conducted in the section of 3.0 to 4.1 V, and both charging and discharging were measured at 0.1C-0.1C (CC-CV) for 50 cycles each.

8 and 9, 3 wt% coating of TiO ₂ at 600° C. heat treatment condition in which all solid lithium secondary battery and Rutile phase according to Device Example 5 partially coated TiO ₂ at 525° C. heat treatment condition showing only the Anatase phase was coated. Charge and discharge and cycle characteristics of the all-solid-state lithium secondary battery according to one device example 2 were compared. As a result, the initial discharge amount of the device comparative example 1 was 123.4 mAh/g, and the device example 2 was 133.1 mAh/g, whereas the device example 5 was found to have a significantly reduced initial capacity to about 111.1 mAh/g. However, the capacity retention rate due to the charge/discharge cycle characteristics was found to be somewhat better in the battery of the device examples 1 and 5 containing the TiO ₂ coated positive electrode active material than the battery of the device comparative example 1.

The scope of the present invention is indicated by the following claims rather than the above detailed description, and it should be interpreted that all changes or modified forms derived from the meaning and scope of the claims and equivalent concepts thereof are included in the scope of the present invention. do.

Claims (19)

(A) preparing a titanium precursor solution containing a titanium precursor, a solvent and a chelating agent;
(b) coating the titanium precursor solution on a positive electrode active material and drying it; And
(c) preparing a positive electrode active material coated with titanium dioxide by heat-treating the dried positive electrode active material;
Method for producing a titanium dioxide-coated positive electrode active material containing. According to claim 1,
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 positive electrode active material; Method for producing a titanium dioxide-coated positive electrode active material comprising a. According to claim 1,
Method for producing a titanium dioxide-coated positive electrode active material, characterized in that the concentration of the titanium precursor in the titanium precursor solution is 0.1 to 15wt%. According to claim 3,
Method for producing a titanium dioxide-coated positive electrode active material, characterized in that the concentration of the titanium precursor in the titanium precursor solution is 0.5 to 10wt%. According to claim 4,
Method of manufacturing a titanium dioxide-coated positive electrode active material, characterized in that the concentration of the titanium precursor in the titanium precursor solution is 1 to 5wt%. According to claim 1,
The titanium precursor is titanium butoxide, titanium isopropoxide, titanium chloride, titanium tetraisopropoxide and tetra-nbutyl orotitanate (Tetra- n-butyl orthotitanate) method for producing a titanium dioxide-coated positive electrode active material comprising at least one selected from the group consisting of. According to claim 1,
The solvent comprises one or more 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. According to claim 1,
The chelating agent is a method for producing a titanium dioxide-coated positive electrode active material comprising at least one selected from the group consisting of acetylacetone (Acetylacetone) and ethyl acetoacetate (Ethylacetoacetate). According to claim 1,
The positive electrode 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 -A method for producing a titanium dioxide-coated positive electrode active material comprising at least one member selected from the group consisting of nickel-manganese oxide, lithium-manganese oxide and lithium-nickel oxide. The method of claim 9,
Method for producing a titanium dioxide-coated positive electrode active material, characterized in that the positive electrode active material comprises a lithium-nickel-cobalt-manganese oxide (NCM) represented by the following Chemical Formula 1.
[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 9,
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 .} Method of manufacturing a titanium dioxide-coated positive electrode active material comprising at least one selected from the group consisting of ₁ O ₂ . According to claim 1,
Method for producing a titanium dioxide-coated positive electrode active material, characterized in that the heat treatment of the dried positive electrode active material in step (c) is performed at a temperature of 400 to 900 ℃. (A) preparing a titanium dioxide-coated positive electrode active material; And
(b) the titanium dioxide-coated positive electrode active material; Lithium lanthanum zirconium oxide represented by the following formula (2) (LLZO); bookbinder; And a conductive material; mixing and rolling to produce an anode; To
Method for manufacturing a positive electrode comprising:
[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 with respect to 100 parts by weight of the titanium dioxide-coated positive electrode active material Method of manufacturing a positive electrode, characterized in that. The method of claim 13,
The lithium lanthanum zirconium oxide (LLZO) method of manufacturing a positive electrode, characterized in that it comprises a single phase cubic structure. The method of claim 13,
The binder is polyethylene oxide (polyethyleneoxide), nitrile butadiene rubber (NBR, nitrile butadiene rubber), polyethylene glycol (polyethyleneglycol), polyacrylonitrile (polyacrylonitrile), polyvinyl chloride (polyvinylchloride), polymethyl methacrylate (polymethylmethacrylate), Contains at least one selected from the group consisting of polypropylene oxide, polydimethylsiloxane, polyvinylidenefluoride, polyvinylidenecarbonate and polyvinyl pyrrolidinone Method of manufacturing a positive electrode, characterized in that. The method of claim 13,
The conductive material is carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, and a method for producing a positive electrode, characterized in that it comprises at least one member selected from the group consisting of graphene. (a) preparing a positive electrode comprising a positive electrode active material prepared according to claim 1, a first lithium lanthanum zirconium oxide (LLZO), a first binder, and a conductive material;
(b) preparing a solid electrolyte layer comprising a second lithium lanthanum zirconium oxide (LLZO) and a second binder;
(c) laminating the anode and the solid electrolyte layer to produce a laminate; And
(d) disposing a negative electrode on the solid electrolyte layer of the laminate; includes,
The first and second lithium lanthanum zirconium oxide (LLZO) is represented by the following formula (2), a method for manufacturing an all-solid lithium secondary 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 method of claim 18,
Method for manufacturing an all-solid lithium secondary battery, characterized in that the negative electrode contains a lithium metal.

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