KR102308458B1 - Positive active material surface-modified with metal sulfide and lithium all state solid battery including the same - Google Patents

Abstract

The present application relates to a positive electrode active material whose surface is modified with a single metal or a double metal sulfide, and a lithium all-solid-state battery including the same.

Description

A cathode active material surface-modified with a metal sulfide and a lithium all-solid-state battery comprising the same

The present application relates to a positive electrode active material whose surface is modified with a single metal or a double metal sulfide, and a lithium all-solid-state battery including the same.

A lithium all-solid-state battery is a battery that can directly convert chemical energy into electrical energy by using a sulfide-based or oxide-based solid electrolyte and oxidizing or reducing lithium ions through an all-solid material. In particular, due to advantages such as eco-friendliness, safety, and high energy density capacity storage, the low energy density, high cost, and toxicity problems that are the limitations of currently commercially available lithium secondary batteries can be solved, so the demand as a sustainable secondary battery is increasing. .

However, in the all-solid-state battery, irreversibility due to interfacial side reactions between the sulfide- or oxide-based solid electrolyte and the positive electrode during the charge/discharge reaction and the non-uniform distribution and capacity of electrode charges due to interfacial resistance and space-charge layer formation There are problems such as degradation. In addition, the low ionic conductivity of the all-solid material itself hinders the commercialization of the lithium all-solid-state battery, which is a next-generation battery.

In order to solve the problems, positive electrode active materials using lithium metal sulfide and the like have been developed. However, this positive electrode active material is a new positive electrode active material, and while the charge/discharge performance is significantly increased compared to the oxide-based positive active material in terms of capacity, the capacity maintenance rate during the charging and discharging process is very low compared to the existing oxide-based positive electrode active material or negative electrode active material. have.

In addition, the same oxide-based positive electrode active material was surface-treated with lithium metal oxide and applied to an all-solid-state battery to improve charge/discharge performance, but the disadvantages were not improved enough to achieve commercialization.

According to an embodiment of the present application, it is intended to increase the reversibility and charge/discharge performance of a lithium all-solid-state battery by surface-treating a cathode active material with a metal sulfide.

One aspect of the present application is a cathode active material having metal sulfide nanoparticles attached to the surface, wherein the metal sulfide is _{a single metal sulfide represented by M a} S _b (provided that 0.1≤a≤10 and 0.1≤b≤10). -metal sulfide); or M1 _x M2 _y S _z (provided that 0.1≤x≤10, 0.1≤y≤10, and 0.1≤z≤10), which is a positive electrode active material that is a bi-metal sulfide.

Another aspect of the present application is the above-described positive active material; sulfide-based solid electrolyte material; and a composite material including a conductive material.

Another aspect of the present application is a composite layer comprising the above-described composite material; an all-solid electrolyte material layer; and a lithium all-solid-state battery including a counter electrode layer.

According to an embodiment of the present application, it is possible to provide a positive electrode active material surface-modified with a metal sulfide.

According to an embodiment of the present application, it is possible to provide a positive electrode active material surface-modified with a small amount of metal sulfide by increasing the surface area by surface treatment with nano-sized particles compared to the micro-unit-sized metal oxide.

According to an embodiment of the present application, the interfacial resistance or resistance to side reactions occurring between the sulfide-based solid electrolyte is improved, the performance degradation problem is reduced, and the surplus lithium ions of the sulfide to be surface-treated are captured or lost from side reactions. Due to the effect of inhibiting lithium ions, the irreversibility of the all-solid-state battery can be improved.

1 is a graph showing the results of X-ray diffraction analysis of a material for surface modification for a positive electrode active material according to an embodiment of the present application.
FIG. 2 is a graph showing the results of X-ray diffraction analysis for a material obtained by modifying a single metal sulfide and a double metal sulfide for surface modification into a positive electrode active material and a comparative example according to an embodiment of the present application.
3 is an image taken using a field emission scanning electron microscope (FE-SEM) of the positive electrode active material and the comparative example according to an embodiment of the present application.
4 is an image taken using a field emission transmission electron microscope (FE-TEM) of the cathode active material according to an embodiment of the present application.
5 is a graph showing the results of the initial charge/discharge analysis of the positive electrode active material in which the surface is modified with cobalt sulfide, which is a single metal sulfide, according to an embodiment of the present application and a comparative example.
6 is a graph showing the initial charge/discharge analysis results of the positive electrode active material and the comparative example in which the surface is modified with nickel cobalt sulfide, which is a double metal sulfide, according to an embodiment of the present application.
7 is a graph showing the analysis results of the 20 times charge/discharge capacity of the positive electrode active material surface-modified with a single metal sulfide and a double metal sulfide according to an embodiment of the present application and a comparative example and a graph showing the cycle capacity retention rate. .
8 is an analysis result of rate characteristic capacity by varying the current density from 7.5 mA/g to 300 mA/g of the positive electrode active material surface-modified with single metal sulfide and double metal sulfide according to an embodiment of the present application and Comparative Example; It is a graph showing (C-rate performance).
9 is an X-ray photoelectron spectroscopy analysis result to analyze the side reaction between the positive electrode active material and the sulfide-based solid electrolyte by disassembling the coin cell after the charge/discharge performance analysis for the coin cell and the comparative example according to an embodiment of the present application. is a graph
10 is a transmission electron microscope and electron energy to visually analyze the side reaction and surface between the positive electrode active material and the sulfide-based solid electrolyte by disassembling the coin cell after rough discharge performance analysis in the coin cell and the comparative example according to an embodiment of the present application; It is a graph showing the analysis result of loss spectroscopy.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that the features, components, etc. described in the specification are present, and one or more other features or components may not be present or may be added. Doesn't mean there isn't.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

In the present application, the term “nano” may mean a size of nanometers (nm), for example, may mean a size of 1 to 1,000 nm, but is not limited thereto. In addition, in the present specification, the term "nanoparticle" may mean particles having an average particle diameter of nanometers (nm), for example, may mean particles having an average particle diameter of 1 to 1,000 nm, It is not limited.

The lithium all-solid-state battery according to the present invention can increase the lifespan of the lithium all-solid-state battery during charging by supplying a sufficient amount of electrolyte to the cathode and the anode, as shown in Schemes 1 and 2 below.

[Scheme 1]

LiCoO ₂ → Li _{1 - x} CoO ₂ ⁺ + xLi ⁺ + 2e ^-

[Scheme 2]

xLi ⁺ + In + 2e ^- → LiIn

[Scheme 3]

2LiCoO ₂ + Li ₇ P ₂ S ₈ I → Li ₂ S + 2CoO ₂ + Li ₇ P ₂ S ₇ I

2CoO ₂ + Li ₇ P ₂ S ₇ I → 2CoO ₂ -S + Li ₇ P ₂ S ₅ I

[Scheme 4]

Li ₇ P ₂ S ₈ I → Li ₂ S + Li ₅ P ₂ S ₇ I

Li ₅ P ₂ S ₇ I → Li ₂ S + Li ₃ P ₂ S ₆ I

Li ₃ P ₂ S ₆ I → Li ₂ S + LiPS ₂ S ₅ I ?

Hereinafter, the positive electrode active material, the composite material, and the lithium all-solid-state battery of the present application will be described in more detail.

The cathode active material of the present application is a cathode active material in which metal sulfide nanoparticles are attached (coated) to the surface, wherein the metal sulfide is _{a single metal sulfide represented by M a} S _b (provided that 0.1≤a≤10 and 0.1≤b≤10). (single-metal sulfide); or a _{bi-metal sulfide represented by M1 x} M2 _y S _z (provided that 0.1≤x≤10, 0.1≤y≤10, and 0.1≤z≤10).

As described above, by modifying the positive electrode active material with sulfide, the interfacial resistance or resistance to side reactions occurring between sulfide-based solid electrolytes is improved, the performance degradation problem is reduced, It is possible to improve the irreversibility of the all-solid-state battery due to the effect of suppressing lithium ions that are lost or lost from side reactions.

Here, the cathode active material may be a lithium compound. The lithium compound is not particularly limited, but LiCoO ₂ , LiFePO ₄ , LiMn ₂ O ₄ , Li[Ni _x Co _y Al _z ]O ₂ (0.1≤x,y,z≤1) and Li[Ni _x Co _y Mn _z ]O ₂ (0.1≤x,y,z≤1) may include one selected from the group consisting of.

Here, the metal sulfide is preferably included in an amount of 0.01 to 5.0 parts by weight, based on 100 parts by weight of the positive electrode active material.

The degree of performance improvement varies depending on the content of the metal sulfide used for surface modification, and if the content is excessive or small, the performance may be reduced conversely. In the present application, by treating 0.1 parts by weight to 0.5 parts by weight of the metal sulfide relative to 100 parts by weight of the positive electrode active material, it is possible to induce a reduction in side reaction prevention interfacial resistance and an improvement in electrochemical performance. The positive electrode active material is excellent in the effect of significantly improving the performance of the battery by improving the flammability of the positive electrode active material by controlling the metal sulfide content of the metal sulfide within the above range.

The cathode active material used as a raw material for the metal sulfide according to the present invention includes a reforming method using a solvent and a dry coating method without using a solvent. In addition, in order to modify the surface of the cathode active material using the metal sulfide raw material, sound wave energy or vibration energy using a sintering process or gravitational acceleration is required, and the sintering temperature is smoothly in the range of 100°C to 700°C. It can be used for surface modification and the gravitational acceleration used for dry reforming can be variously allowed from 2G to 100G.

As described above, a single metal sulfide may be used, or a double metal sulfide may be used.

The single metal sulfide is one selected from the group consisting of Li, Ni, Co, Mn, Cu, Zn, Fe, Cr, V, Ti, Zr, Nb, Mo, Ag, Al, Ga, Ge, Sn, Bi and Pb. species of metals.

In particular, the surface of the positive electrode active material may be modified by a wet surface treatment method using the single metal sulfide (solution coating method). Detailed surface modification methods are described in Experimental Examples.

In addition, the double metal sulfide is from the group consisting of Li, Ni, Co, Mn, Cu, Zn, Fe, Cr, V, Ti, Zr, Nb, Mo, Ag, Al, Ga, Ge, Sn, Bi and Pb. It may include two selected metals.

The surface of the cathode active material may be modified by a resonant acoustic coating method using the double metal sulfide. Detailed surface modification methods are described in Experimental Examples.

When the dry surface treatment method is performed, the gravitational acceleration condition of the dry mixer is 0 G to 60 G, and the execution time may be 60 minutes or less.

Another embodiment of the present application, the composite material (composite) is the above-described positive electrode active material; sulfide-based solid electrolyte material; and a conductive material.

The composite material may include the positive active material described above; sulfide-based solid electrolyte material; and an anode active material.

The composite material may include 50 to 90 parts by weight of a cathode active material, 10 to 40 parts by weight of a sulfide-based solid electrolyte material, and 1 to 10 parts by weight of a conductive material.

The anode active material may include artificial graphite, natural carbon Li ₄ Ti ₅ O ₁₂ , Sn, Li, and Si or a Si-C-based alloy.

A lithium all-solid-state battery according to another embodiment of the present application includes a composite layer including the composite material described above; an all-solid electrolyte material layer; and a counter electrode layer. The specific structure of the lithium all-solid-state battery is not particularly limited, and any structure applicable in the art is applicable as long as the above-described components are included. In addition, in addition to the above-described components, any additional components applicable in the present technical field are applicable to the lithium all-solid-state battery of the present application.

In particular, the all-solid electrolyte material layer may include a sulfide-based solid electrolyte or an oxide-based solid electrolyte. The positive electrode active material of the present application may provide a similar effect to not only the sulfide-based solid electrolyte but also the oxide-based solid electrolyte.

Hereinafter, the present application will be described in more detail through experimental examples.

[ Experimental example ]

Example One

High nickel-based LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ Commercial grade LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ powder (6 micrometer, 2.0 g), cobalt chloride monohydrate (CoCl ₂ ^. H ₂ O, Aldrich) and sodium diethyldithiocarbamate trihydrate (Sodiom diethyldithiocarbamate, 2NaS ₂ CN(C ₂ H ₅ ) .3H ₂ was used ₂ O, Aldrich).

Cobalt chloride monohydrate ^{_{(CoCl 2. H 2 O,}} Aldrich) and a stoichiometric with 2-fold excess of sodium diethyl di-thio-carbamate trihydrate _{(Sodiom diethyldithiocarbamate, 2NaS 2 CN (} C 2 H 5) 2. 3H 2 O, Aldrich) was dissolved in 100 ml tertiary distilled water for 10 minutes. Only when each is completely dissolved at room temperature, an aqueous solution of sodium diethyldithiocarbamaate trihydrate is slowly added to an aqueous solution of cobalt chloride monohydrate, and Bis(diethyldithiocarbamato)cobalt(Bis(diethyldithiocarbamato)cobalt( II)) complexes were formed. This complex was filtered as a precipitate, washed with 1L of tertiary distilled water, and then dried in an oven at 80°C for 12 hours.

The dried vice (diethyldithiocarbameto) cobalt complex was _{coated in dichloromethane (CH 2} Cl ₂ ) LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ Dissolve at 0.025% based on the weight of the powder, and commercial grade LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ powder (6 micrometer, 2.0 g) was dissolved in dichloromethane put in another beaker and stirred at 400 rpm or more for 10 minutes each. After stirring for 10 minutes, an aqueous solution of vice (diethyldithiocarbameto) cobalt dichloromethane _{was slowly added to an aqueous solution of dichloromethane containing LiNi 0.6} Co _0.2 Mn _0.2 O ₂ powder, and 50° C. to 80° C. until a residue remained. was heated to a temperature of After the solvent is evaporated and the remaining residue is heated at 80° C. for 2 hours in a vacuum oven, heated at a temperature increase rate of 5° C. per minute in a tube-type electric furnace in a nitrogen flow atmosphere for 2 hours to decompose the cobalt complex to 0.025% by weight _{LiNi 0} with monocobalt sulfide modified on the surface _{. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ powder was produced. Example 1 having a cupric oxide content of 0.025% of monocobalt sulfide was prepared. Copper nitrate monohydrate was added using ethanol as a solvent. After that, the mixture is stirred on a heating stirrer, and in order to apply the modified positive electrode active material to an all-solid-state battery, positive electrode active material: sulfide-based solid electrolyte (Li ₇ P ₂ S ₈ I): conductive material Super-P = 70: 28 : Mix using a mortar at a weight ratio of 2. After that, after pelletizing at 300 bar with a hydraulic press, the pellets were crushed and mixed, and this process was repeated a total of three times to complete the electrode active material composition. To construct an all-solid-state battery, a sulfide-based solid electrolyte Li ₇ P ₂ S ₈ I was placed in a 16 pi cylindrical steel mold/molder and pressed at 300 bar for 3 minutes. An indium foil (Nilaco) was used as a negative electrode or a current collector, and a positive electrode active material: a sulfide-based solid electrolyte (Li ₇ P ₂ S ₈ I): a conductive material Super-P = 70: 28: 2 weight ratio as a positive electrode of the positive electrode composition and indium foil were used as the current collector, and a 0.5 mm spacer was used for the negative electrode side to manufacture a coin cell for an all-solid-state battery, and a 1.0 mm spacer and a spring were used for the positive electrode side. A 2032 type coin cell was manufactured.

Example 2

Example 2 was prepared in the same manner as in Example 1, except that 0.05% of monocobalt sulfide based on the weight of the cathode active material was used.

Example 3.

Example 3 was prepared in the same manner as in Example 1, except that monocobalt sulfide in an amount of 0.075% based on the weight of the cathode active material was used.

Example 4

NiCo ₂ S _{4 Using a} double metal sulfide (nickel cobalt sulfide), the surface is modified high nickel-based LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ To prepare a positive electrode active material, NiCo ₂ S ₄ double metal sulfide nanoparticles (NiCo ₂ S ₄ nanoparticles) was synthesized alone.

Nickel nitrate hexahydrate ^{_{(Ni (NO 3) 2.}} 6H 2 O, Aldrich) and nickel nitrate hexahydrate ^{_{(2Co (NO 3) 2.}} 6H 2 O, Aldrich) of ethanol amine were dissolved in (ethanolamine, 20ml, Aldrich) , thiourea (thiourea, 4CH ₄ N ₂ S, Aldrich) was dissolved by stirring for 10 minutes by adding 3 equivalents of distilled water using 3 equivalents. After stirring for 10 minutes each, the thiourea aqueous solution was slowly added to the ethanolamine aqueous solution of nickel nitrate-cobalt hexahydrate, and then stirred for another 10 minutes to form a precipitate.

Then, the entire mixture was transferred to a 100 ml Teflon-lined autoclave, sealed and calcined at 200 °C for 14 hours at a temperature increase rate of 5 °C/min. After cooling naturally, the autoclave was opened to take a solution, and nickel cobalt sulfide nanoparticles were recovered by centrifugation.

After that, 0.01 g of recovered nickel cobalt sulfide (0.1% by weight) and _{10 g of LiNi 0.6} Co _0.2 Mn _0.2 O ₂ as a positive electrode active material were put in a zirconia container filled with 80% of the volume and sealed in a resonant-acoustic mixer ( Using LabRAM II, Resodyn Inc.), the nickel cobalt sulfide nanoparticles were modified on the surface of LiNi _{0 by mixing at 60 G under the acceleration of gravity for 20 minutes. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ got In addition, using this, a coin cell for an all-solid-state battery was manufactured in the same manner as in Example 1.

Example 5

Example 5 was prepared in the same manner as in Example 4, except that 0.3% of nickel cobalt sulfide based on the weight of the positive electrode active material was used.

Example 6

Example 6 was prepared in the same manner as in Example 4, except that 0.5% of nickel cobalt sulfide based on the weight of the positive electrode active material was used.

comparative example

_{LiNi 0} without surface modification (coating) _{. 6} Co _{0 . 2} Mn _{0 . 2} O _{2 Through the} same process as in Example 1, except for using the powder, a comparative example was prepared.

Experimental example One

_{LiNi 0} , treated with a single metal sulfide prepared in Examples 1 to 3 _{. 6} Co _{0 . 2} Mn _{0 . 2} O _{2 LiNi 0} , which was calcined at 400 ° C. for 2 hours, and treated with the double metal sulfide prepared in Examples 4 to 6 _{. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ was synthesized by reforming at a high energy gravitational acceleration of 60 G for 20 minutes, so LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . To determine whether 2} O ₂ was oxidized to sulfided or side reactions occurred, X-ray diffraction (XRD) was analyzed for each.

Here, the X-ray diffraction was measured using D/MAX 2500-V/PC (CuKa radiation, 40 kV, 100 mA) of Rigaku (Japan), and a 1.5406 Å wavelength was scanned at a rate of 0.02°/sec. X-ray diffraction patterns were obtained in the range of 2θ to 10-90°.

First, to find out whether single-metal sulfide (M _a S _b (0.1≤a,b≤10)) or double-metal sulfide was synthesized, each material was diffracted and furthermore, single-metal sulfide (single-metal sulfide) _{LiNi 0} surface-modified with metal sulfide, M _a S _b (0.1≤a,b≤10)) or double metal sulfide _{. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ X-ray diffraction (XRD) of the positive electrode active material was analyzed, and the results are shown in FIGS. 1 and 2 , respectively.

As shown in FIGS. 1 and 2 , it was confirmed whether single cobalt sulfide and nickel cobalt sulfide were synthesized through an x-ray diffraction pattern. As a result of comparison with the references, it was confirmed that each crystal structure was consistent with the references. In addition, it was confirmed that the surface-modified positive electrode active material with respect to the diffraction patterns of Comparative Examples and Examples 1 to 6 maintains the existing structure without noticeable lattice change. At the same time, the surface-modified sulfide pattern was not detectable compared to the positive electrode active material because it was small.

_{In addition, LiNi 0 surface-modified with a} single-metal sulfide (single-metal sulfide, M a S _b (0.1≤a,b≤10)) or a double-metal sulfide, respectively _{. 6} Co _{0 . 2} Mn _{0 . 2} O _{2 For} the surface analysis of the positive electrode active material, the positive electrode active material prepared in Comparative Examples and Examples 1 to 6 and the commercially obtained Comparative Example LiNi _0.6 Co _0.2 Mn _0.2 O ₂ powder of a field emission scanning electron microscope (FE-SEM, JEOL Co., Ltd., JSM-7610F) was taken to obtain an image, based on the electron microscope image for Example 5 - using electron dispersive spectroscopy (electron dispersive spectroscopy), the image was obtained and , Examples 2 and 5 were photographed using a field emission transmission electron microscope (FE-TEM, JEOL, JEL-2100F) to obtain images, and are shown in FIGS. 3 to 4 , respectively.

As shown in FIG. 3 , the cathode active materials prepared in Examples 1 to 3 each had an average particle size of about 1 to 6 μm LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ was found to be particles, and cobalt sulfide on the surface of the particles was LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ Modified on the particle surface, in particular, from Example 3 excess cobalt sulfide LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . 2} O ₂ was identified on the surface. _{In addition, LiNi 0} treated with bimetallic sulfide nanoparticles _{. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ can be confirmed in Examples 4 to 6, it was confirmed that the double metal sulfide is coated in an increasing amount relative to the weight. For the comparative example, LiNi _{0 . 6} Co _{0 . 2} Mn _{0 . The 2} O ₂ powder had an average particle size of about 1 to 6 μm, and was the same as in Examples, but it was confirmed that the particle surface was smooth and clean. In addition, through Example 5, it was quantitatively confirmed that the major elements of the three-component positive electrode active material including element O were detected with strong intensity and a small amount of sulfide was detected.

4, the lattice length and thickness of the modified material of the cobalt sulfide or nickel cobalt sulfide modified in the positive electrode active material through FE-TEM analysis in Examples 2 and 5, which are the most optimal conditions in Experimental Example 2 below, were measured. Confirmed.

Experimental example 2.

In order to evaluate the degree of improvement in the reversibility of the positive electrode active material according to the present invention, the following experiment was performed.

Working electrodes were prepared from the compositions prepared in Examples 1 to 6 and Comparative Examples, respectively. Voltage potential curves were measured using galvanostatic charge-discharge at a current density of 7.5 mA/g (double metal sulfide and single metal sulfide) or 15 mA/g at 3.68 V to 2.38 V while charging and discharging the all-solid-state battery cell. . The measured results are shown in FIGS. 5 and 6 . In addition, the discharge capacity was recorded up to 20 times by measuring the charge/discharge performance at a current density of 15 mA/g in the same voltage range of the cell for 20 times. Additionally, for Examples 1 to 6 and Comparative Examples, the current density was increased to 7.5 mA/g to 300 mA/g by varying the current density to measure the decrease in the discharge capacity, and the results are shown in FIG. 7 .

As shown in FIGS. 5 and 6 , it can be seen that some of the positive electrode active materials according to the present invention have excellent reversibility for an all-solid-state battery.

Specifically, in the case of an all-solid-state battery cell including an electrode manufactured using the positive electrode active material prepared in Examples 1 to 6, the discharge capacity in the first charge/discharge process was 114.6, 118.4, when the current density was 7.5 mA/g. , 99.4, 125.97, 128.7, and 98.9 mAh/g, and at a current density of 15 mA/g, 94.5, 96.4, 94.4, 115.9, 118.0, and 84.7 mAh/g. In addition, among the positive active materials of Examples 1 to 3, wherein the positive electrode active materials are single metal sulfide-modified positive electrode active materials, only Example 2 exhibited superior discharge performance compared to Comparative Examples, and during 20 charge/discharge cycles, a decrease in discharge capacity was observed. When viewed, the cycle performance performed in Example 2 was superior to the cycle performance of the comparative example, but caused a problem that was much lower than the cycle performance of Example 5. In addition, the positive electrode active material coated with single metal sulfide showed a continuous decrease in capacity. When looking at the range of change in the discharge capacity, it can be seen that the capacity retention rate of the positive electrode active material prepared in Example 2 is significantly lowered compared to that of Example 5 even after charging and discharging 10 times. The battery cell of Comparative Example containing a commercially obtained cathode active material had an initial discharge capacity of 86.0 mAh/g at 15 mA/g and 121.82 mAh/g at 7.5 mA/g, and was charged and discharged 10 times. After that, it can be seen that the capacity retention rate is significantly lowered and the charging/discharging process is not performed properly. In addition, the discharge capacity up to 10 times of charging and discharging was 119.7 mAh/g, which was not significantly different from the initial capacity. This means that reversibility is increased by suppressing side reactions of metal sulfides introduced into the positive electrode active material according to the present invention and reducing interfacial resistance. From these results, it can be seen that the positive electrode active material according to the present invention has excellent reversibility, thereby improving battery life.

In addition, when the charge/discharge cycle is 5 times, the maximum capacity of the first electrode according to a constant current in relation to the positive electrode active material coated with the double metal sulfide may be 120 to 130. _{This is pure LiNi 0} used in the preparation of the positive electrode active material _{. 6} Co _{0 . 2} Mn _{0 .} It was found that the performance was improved compared to that measured using ₂ O _{2 .}

Referring to FIG. 7 , in the case of a coin cell to which a cathode active material coated with cobalt sulfide, which is a single metal sulfide, is applied, as compared to the all-solid-state battery cell of Comparative Example, which rapidly decreases as the number of charge/discharge increases, Examples 1 to 3 are rapidly It can be said that the problem of capacity decrease has been alleviated.

In addition, in Example 2, it was confirmed that it had a discharge capacity of 53.2 mA/g from the first discharge capacity larger than that of the cell of the comparative example until 20 times of charging and discharging, and exhibiting a capacity retention rate of 50% until 20 times of charging and discharging.

On the other hand, compared to the positive electrode active material coated with double metal sulfide, it shows a continuous decrease in capacity, which means that even if single metal sulfide is modified on the surface of the positive electrode, chronic interfacial resistance reduction or side reactions at the electrode cannot be suppressed. On the other hand, in the case of Examples 5 and 6, it was found that the capacity retention rate or discharge capacity was significantly improved compared to Comparative Examples and Examples 1 to 3, and in Examples 5 and 6, the capacity increased from the second discharge capacity compared to the initial discharge capacity. It can be seen that it draws a decreasing parabolic shape, which indicates that the bimetal sulfide not only reduces the interfacial resistance or suppresses side reactions, but also the ability of lithium ions to store or hold the remaining lithium in a confined coin cell. could have guessed. It was confirmed that Example 5 proceeded without a decrease in the high dose even up to 14 cycles, and then rapidly decreased. This, of course, provides room for improvement in the future, and, nevertheless, showed an excellent capacity retention rate in 20 cycles compared to Comparative Example or Example 2.

Experimental example 3

Rate characteristics were analyzed based on Comparative Examples and Examples 1 to 3 and Examples 4 to 6 showing a continuous decrease in capacity, and the results are shown in FIG. 8 .

As shown in FIG. 8, each of the all-solid-state battery cells proceeded for 3 cycles at a current density of 0.05C (7.5mA/g) to 0.1, 0.2, 0.5, and 1 to 2C (300 mA/g), and practically As a result, it was confirmed that only Example 6 exhibited similar values to the initial discharge capacity during charging and discharging at a current density of 0.05 C-rate again after such rate characteristic analysis.

Experimental example 4

After 20 charging/discharging performance analysis for Examples 2 and 5, which are optimal conditions along with Comparative Examples, the inside of the coin cell was opened to perform x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) to electron energy loss spectroscopy (EELS) ) to confirm the degree of side reaction generated from the discharge of each battery cell.

The results are shown in FIGS. 9 and 10 . In FIG. 9 , in the case of Comparative Example, it was found that the area of S 2p 3/2 to 1/2 peak of the sulfide-based solid electrolyte decreased, and the area of -OS- peak generated as a side reaction between the positive electrode active material and the solid electrolyte increased significantly. . On the other hand, in Example 2 coated with a single metal sulfide, the area of -OS- peak was found to have a relaxed level compared to the comparative example, so it was confirmed that the side reaction was somewhat suppressed, and in Example 6 in which the double metal sulfide was modified It was confirmed that the area of -OS- peak, which is a side reaction, was greatly reduced.

Transmission electron microscopy (TEM) to electron energy loss spectroscopy (EELS) were performed only for Comparative Example and Example 5 based on the results of the above-described experimental examples to visually analyze whether a side reaction between the interface between the positive electrode active material and the solid electrolyte was cross- Sectional line mapping was analyzed through EELS to analyze how the side reactions occurring at the interface were alleviated compared to the comparative example. The results are shown in FIG. 10 .

As shown in FIG. 10, it was found that the side reaction was greatly reduced due to the surface modification of the double metal sulfide at the actual interface, and by confirming that a large amount of lithium was detected in the all-solid material, almost no decomposition of the all-solid material occurred and the original shape was obtained. was confirmed to be maintained.

Specifically, it was found that the side reaction was greatly reduced due to the surface modification of the double metal sulfide at the actual interface, and by confirming that a large amount of lithium was detected in the all-solid material, it was confirmed that the decomposition of the all-solid material hardly occurred and the original shape was maintained. . In addition, it was confirmed through line mapping whether sulfur and phosphorus penetrated into the cathode active material around the interface and caused a side reaction. In the comparative example, it can be seen that sulfur and phosphorus, which should not be seen, are continuously detected from the inside, resulting in fluorescence of the positive electrode active material due to direct contact. On the other hand, in the case of Example 5 modified with a double metal sulfide, lithium was largely detected from both sides during line mapping of the positive electrode active material, and sulfur started to be detected from the coating layer of nickel cobalt sulfide, and also started to be weakly detected. And it was confirmed that sulfur and phosphorus were hardly detected in the positive electrode active material layer. Also, looking at the height of the interface between the positive electrode active material and the solid electrolyte, it can be seen that the interface of Comparative Example forms a fairly deep corrugation, whereas the interface of Example 6 was protected by nickel cobalt sulfide, and the corrugation was hardly visible. Accordingly, it was confirmed that the electrochemical performance of the cathode active material coated with the metal sulfide was superior.

Although the above has been described with reference to the preferred embodiments of the present application, those skilled in the art will make various modifications and changes to the present application within the scope without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand that you can.

Claims (14)

As a positive electrode active material having metal sulfide nanoparticles attached to the surface,
The metal sulfide is included in an amount of 0.01 parts by weight to 0.5 parts by weight, based on 100 parts by weight of the positive electrode active material,
The metal sulfide
In the case of _a single-metal sulfide represented by M a S _b (provided that 0.1≤a≤10 and 0.1≤b≤10), the single-metal sulfide is Ni, Co, Mn, Cu, Zn, Fe, Cr, V, Zr, Nb, Ag, Al, Ga, Ge, Sn, Bi, and containing one kind of metal selected from the group consisting of Pb, the positive electrode active material is a wet surface treatment method (solution) using the single metal sulfide It is a positive electrode active material whose surface is modified by coating method),
The cathode active material is a solution in which a single metal sulfide is dissolved in a solvent dichloromethane (CH ₂ Cl ₂ ) and a solution in which a cathode active material is dissolved in a solvent dichloromethane (CH ₂ Cl ₂ ) After heating to a temperature of 50° C. to 80° C. After evaporation of the solvent, the remaining residue is heated in a vacuum oven at 80° C. for 2 hours, and then heated for 2 hours at a temperature increase rate of 5° C. per minute in a tube-type electric furnace in a nitrogen flow atmosphere to decompose single metal sulfides to decompose single metal sulfides. A positive electrode active material modified on this surface. The method of claim 1,
The positive electrode active material is a lithium compound. 3. The method of claim 2,
The lithium compound is LiCoO ₂ , LiFePO ₄ , LiMn ₂ O ₄ , Li[Ni _x Co _y Al _z ]O ₂ (0.1≤x,y,z≤1) and Li[Ni _x Co _y Mn _z ]O ₂ ( A cathode active material comprising one selected from the group consisting of 0.1≤x, y, z≤1). delete delete delete delete delete As a positive electrode active material having metal sulfide nanoparticles attached to the surface,
The metal sulfide is included in an amount of 0.01 parts by weight to 0.5 parts by weight, based on 100 parts by weight of the positive electrode active material,
The metal sulfide
In the case of a bi-metal sulfide expressed by M1xM2ySz (provided that 0.1≤x≤10, 0.1≤y≤10, and 0.1≤z≤10), the bi-metal sulfide is Ni, Co, Mn, Cu, Zn , Fe, Cr, V, Zr, Nb, Ag, Al, Ga, Ge, Sn, Bi and containing two kinds of metals selected from the group consisting of Pb, the positive electrode active material is a dry surface treatment using the double metal sulfide It is a positive electrode active material whose surface is modified by a resonant acoustic coating method,
When the dry surface treatment method is performed, the gravitational acceleration condition of the dry mixer is 0 G to 60 G, and the execution time is 60 minutes or less. The cathode active material of claim 1 or 9;
sulfide-based solid electrolyte material; and
A composite material including an anode active material. 11. The method of claim 10,
The composite material further includes a conductive material, wherein the composite material comprises 50 to 90 parts by weight of a cathode active material, 10 to 40 parts by weight of a sulfide-based solid electrolyte material, and 1 to 10 parts by weight of a conductive material. 11. The method of claim 10,
The negative active material is artificial graphite (artificial carbon), natural graphite (natural carbon), Li ₄ Ti ₅ O ₁₂ , Sn, Li, and a composite material comprising a Si or Si-C alloy-based material. A composite layer comprising the composite of claim 10; an all-solid electrolyte material layer; And a lithium all-solid-state battery comprising a counter electrode layer. 14. The method of claim 13,
The all-solid-state electrolyte material layer includes a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

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