KR20210103874A - Cathode Active Material for Lithium Secondary Battery and Method for Manufacturing The Same - Google Patents

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, comprising a compound represented by chemical formula 1, and a method for manufacturing the cathode active material the for lithium secondary battery, comprising the steps of: mixing a lithium-containing compound, an iron-containing compound, and a tantalum-containing compound in a solvent; drying the mixture to obtain a powder; and calcining the powder to obtain the compound represented by the chemical formula (1): Li_(1+x)Fe_yTa_zO_2. In the chemical formula 1, 0 < x <= 0.5, 0 < y <= 1, and 0 < z <= 0.5 and, only, x+y+z=1. According to the present invention, it is possible to provide a high-performance lithium secondary battery by having a higher ion capacity.

Description

Cathode Active Material for Lithium Secondary Battery and Method for Manufacturing The Same

The present invention relates to a cathode active material for a lithium secondary battery and a method for manufacturing the same.

_{Conventional lithium secondary batteries have a LiNi a} Co _b Mn _c O ₂ (a+b+c=1) layered structure (layered structure: R3-m or C2/m) made of nickel, cobalt, and manganese. The material having the above was used as a positive electrode material (positive electrode active material). However, with the recent development of electric vehicles and large-capacity energy storage systems, the development of anode materials having a new composition with higher performance is required.

Among them, a cathode material having an excess lithium rock salt structure (space group: Fm-3m) has been recently studied, and a material that has the advantages of high energy expression from excess lithium and structural stability from the rock salt structure. There is a lot of research going on to find out.

In the present invention, a rock salt structure material composed of a transition metal having a composition not previously used such as excess lithium, iron, and tantalum was synthesized, and it is intended to be applied as a positive electrode active material of a lithium secondary battery.

An object of the present invention is to provide a positive electrode active material for a lithium secondary battery having a rock salt structure having a composition not used as an existing positive electrode active material such as excess lithium, iron, and tantalum for a high-performance lithium secondary battery having a higher ion capacity.

The present invention provides a positive electrode active material for a lithium secondary battery comprising a compound represented by the following formula (1).

[Formula 1]

Li _1+x Fe _y Ta _z O ₂

In Formula 1, 0<x≤0.5, 0<y≤1, 0<z≤0.5, provided that x+y+z=1.

In addition, the present invention comprises the steps of mixing a lithium-containing compound, an iron-containing compound and a tantalum-containing compound in a solvent; drying the mixture to obtain a powder; and calcining the powder to obtain a compound represented by the formula (1).

_{Unlike LiNi a} Co _b Mn _c O ₂ (a+b+c=1), which is used as a positive electrode active material for a lithium secondary battery, the positive active material for a lithium secondary battery of the present invention contains an excess of lithium and thus has a higher ion capacity By having a high-performance lithium secondary battery can be provided, and structural stability according to the rock salt structure can also be secured as compared to the positive electrode active material having a layered structure.

1 is a view showing the XRD analysis result of the positive electrode active material according to Experimental Example 1 of the present invention.
2 is a view showing an electron micrograph of the positive active material according to Experimental Example 2 of the present invention.
3 is a diagram illustrating a voltage-capacity graph of a secondary battery using a positive active material according to Experimental Example 3 of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention provides a cathode active material for a lithium secondary battery.

The positive active material for a lithium secondary battery may include a compound represented by Formula 1 below.

[Formula 1]

Li _1+x Fe _y Ta _z O ₂

In Formula 1, 0<x≤0.5, 0<y≤1, 0<z≤0.5, provided that x+y+z=1.

When the compound of Formula 1 does not satisfy the above composition, it is structurally impossible to synthesize itself, and impurities may be generated.

Specifically, the compound represented by Formula 1 may have a rock salt structure (layered structure: Fm-3m). The rock salt structure refers to a face-centered cubic system such as sodium chloride. In sodium chloride, chlorine ions form a cubic dense structure, and sodium ions smaller than chlorine ions fill the gaps between chloride ions. At this time, each ion is It means an arrangement that forms an octahedron shape adjacent to a type of ion.

In addition, the compound represented by Formula 1 is different from the conventionally mainly used materials such as lithium iron phosphate (LiFePO ₄ ^{) of divalent iron (Fe 2+} ), etc. Although it contains trivalent iron (Fe ³⁺ ), the combination with tantalum Therefore, the electrochemical performance of the lithium secondary battery can be improved.

The compound represented by Formula 1 includes tantalum (Ta) having a high oxidation number (+5) in the composition, thereby increasing the lithium content in the composition, and the compound is formed in an excess lithium composition, thereby providing a high-performance lithium secondary battery make it possible In addition, since the electronegativity is lower than that of niobium (Nb) having the same oxidation number as tantalum, the oxidation/reduction reaction of lattice oxygen can be facilitated.

As described above, as the compound represented by Chemical Formula 1 of the present invention has a rock salt structure, it has superior structural stability compared to the positive electrode active material having a layered structure. Specifically, in the layered structure, a layer made of only lithium and a layer made of only a transition metal exist independently. However, a layer made of only lithium may have a problem in that the structure collapses due to an empty layer when lithium escapes during the charging process. have. On the other hand, in the case of a rock salt structure like the compound represented by Chemical Formula 1 of the present invention, since lithium and the transition metal are uniformly mixed and arranged, a structural change in which a specific layer collapses does not occur.

In Formula 1, it may be 0.1≤x≤0.3, or 0.4≤y≤0.7, or 0.1≤z≤0.3. Alternatively, in Formula 1, 0.1≤x≤0.3, 0.4≤y≤0.7, 0.1≤z≤0.3, with the proviso that x+y+z=1. When the compound represented by Formula 1 satisfying the above composition is used as a cathode active material of a lithium secondary battery, the electrochemical performance (high capacity and/or high energy density, etc.) of the lithium secondary battery through high energy expression due to excess lithium ) can be improved.

The compound represented by Formula 1 may further include a carbon-based coating. Specifically, the compound represented by Formula 1 may further include a carbon-based coating formed by coating the compound with a carbon-based material.

The carbon-based coating is graphite, expanded graphite, carbon black, carbon nanotube, citric acid, acetic acid, polyvinylalcohol. , sucrose, and glucose (glucose) may include at least one carbon-based material selected from.

In the case of carbon-based coating of the compound represented by Formula 1 as described above, when the compound is used as a cathode active material, electrical conductivity can be improved, thereby improving the performance of a lithium secondary battery.

The present invention also provides a method of manufacturing a cathode active material for a lithium secondary battery.

The manufacturing method of the positive electrode active material for a lithium secondary battery may include mixing a lithium-containing compound, an iron-containing compound, and a tantalum-containing compound in a solvent; drying the mixture to obtain a powder; and calcining the powder to obtain a compound represented by the following formula (1).

[Formula 1]

Li _1+x Fe _y Ta _z O ₂

In Formula 1, 0<x≤0.5, 0<y≤1, 0<z≤0.5, provided that x+y+z=1.

The lithium-containing compound may include at least one selected from _{Li 2} CO ₃ , Li ₂ O, LiOH, Li ₂ O _{2 , and LiCl.}

The iron-containing compound may include at least one selected from _{Fe 2} O ₃ , FeO, and Fe ₃ O _{4 .}

The tantalum-containing compound is tantalum pentoxide (Ta ₂ O ₅ ), tantalum pentachloride (TaCl ₅ ), tantalum methoxide (Ta(OCH ₃ ) ₅ ), tantalum ethoxide (tantalu ethoxide, Ta(OC ₂ H) ₅ ) ₅ ), tantalum butoxide (Ta(OCH ₂ CH ₂ CH ₂ CH ₃ ) ₅ ), and lithium tantalate (LiTaO ₃ ) may include at least one selected from the group consisting of.

The solvent may include at least one selected from ethanol, butanol, and acetone.

In the step of mixing the lithium-containing compound, the iron-containing compound, and the tantalum-containing compound, the lithium-containing compound and iron-containing compound may contain 30 to 60 parts by weight of iron and 10 to 25 parts by weight of tantalum based on 100 parts by weight of lithium in the mixture. and mixing the compound and the tantalum containing compound.

The drying may be performed at room temperature (20 to 25° C.).

The firing may be performed at 900 to 1200° C. for 10 to 30 hours. Specifically, it may be carried out at 900 to 1000° C. for 15 to 25 hours.

After the firing, the method may further include mixing the compound represented by Formula 1 and a carbon-based material to form a carbon-based coating. When the carbon-based coating is formed as described above, the performance of the lithium secondary battery may be improved by improving electrical conductivity. The compound represented by Formula 1 and the carbon-based material may be mixed in a weight ratio of 7:1 to 10:1, specifically, may be mixed in a weight ratio of 8:1 to 9.5:1. When the mixed weight ratio of the compound represented by Formula 1 and the carbon-based material satisfies the above range, the electrochemical performance of a lithium secondary battery using the compound as a positive active material may be improved.

The carbon-based material includes graphite, expanded graphite, carbon black, carbon nanotube, citric acid, acetic acid, and polyvinylalcohol. , sucrose (sucrose), and may include at least one selected from glucose (glucose).

The compound represented by Formula 1 may have a layered structure (Fm-3m).

The present invention also provides a lithium secondary battery.

The lithium secondary battery may include a positive electrode; cathode; and an electrolyte; wherein the positive electrode may include a positive electrode active material for a lithium secondary battery including the compound represented by Chemical Formula 1 described above.

The positive electrode is, for example, a positive electrode active material composition (slurry) including the positive electrode active material, a conductive material, a binder, etc. is molded into a certain shape, or the positive electrode active material composition is manufactured by a method in which the composition is applied to a current collector such as an aluminum foil can be

Specifically, a cathode active material composition in which the cathode active material, a conductive material, a binder, and a solvent are mixed may be prepared. The positive electrode active material composition is directly coated on a metal current collector to manufacture a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a positive electrode plate.

As the conductive material, carbon black, graphite fine particles, etc. may be used, but it is not limited thereto, and any conductive material that can be used as a conductive material in the art may be used. For example, graphite, such as natural graphite and artificial graphite; Conductive materials such as carbon black, acetylene black, and Ketjen black may be used.

The binder includes vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber-based polymer, etc. may be used, but is not limited thereto, and any binder that can be used as a binder in the art may be used.

The solvent may be N-methyl-2-pyrrolidone (NMP), acetone, or water, but is not limited thereto and any solvent that can be used in the art may be used.

The content of the positive active material, the conductive material, the binder, and the solvent may be included at a level commonly used in a lithium secondary battery. At least one of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium secondary battery.

Next, the negative electrode, for example, a negative active material composition comprising a negative active material, a conductive material, a binder, etc. is molded into a predetermined shape, or the negative electrode active material composition is applied to a current collector such as aluminum foil can be manufactured by a method have.

The negative active material composition is prepared by mixing the negative active material, the conductive material, the binder and the solvent. The negative active material composition is directly coated and dried on a metal current collector to manufacture a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a negative electrode plate.

The negative active material is not particularly limited to those generally used in the art, but more specifically, lithium metal, a metal alloyable with lithium, a transition metal oxide, a transition metal sulfide, and a material capable of doping and dedoping lithium. , a material capable of reversibly intercalating and deintercalating lithium ions, a conductive polymer, and the like may be used.

In the negative active material composition, the conductive material, the binder, and the solvent may be the same as those of the positive active material composition. Meanwhile, it is also possible to form pores in the electrode plate by further adding a plasticizer to the positive active material composition and/or the negative active material composition.

The content of the negative active material, the conductive material, the binder, and the solvent may also be at a level commonly used in a lithium secondary battery.

At least one of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium secondary battery.

The electrolyte may be composed of an electrolyte and a lithium salt. As the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyl lactone, 1,2-dimethoxy ethane, tetra hydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo An aprotic organic solvent such as a nate derivative, a tetrahydrofuran derivative, an ether, methyl pyropionate, or ethyl propionate may be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymerization agent containing an ionic dissociation group, etc. may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, etc. of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS _{2 and the like may be used.}

The lithium salt is a material readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenyl lithium borate, and imide can

In addition, for the purpose of improving charge/discharge characteristics, flame retardancy, etc. in the electrolyte, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart incombustibility, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene) carbonate), propene sultone (PRS), and vinyl carbonate (VC) may be further included.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. Next, the present invention will be described in more detail through specific examples.

Example 1 - Li _1.15 Fe _0.7 Ta _0.15 O ₂ synthesis

1) Li ₂ CO ₃ , Fe ₂ O ₃ , and Ta ₂ O ₅ are mixed evenly through a ball mill using ethanol as a solvent in a ratio of Li : Fe : Ta = 1.1845 : 0.7 : 0.15.

2) After mixing, the precursor was dried at room temperature and the powder was recovered.

3) After calcining at 950° C. for 20 hours, the powder was recovered.

Example 2 - Li _1.2 Fe _0.6 Ta _0.2 O ₂ synthesis

In the same manner as in Example 1, except that in Example 1, Li: Fe: Ta = 1.1845: 0.7: 0.15, instead of Li: Fe: Ta = 1.236: 0.6: 0.2, was mixed. A cathode active material was synthesized.

Example 3 - Li _1.25 Fe _0.5 Ta _0.25 O ₂ synthesis

In Example 1, in the same manner as in Example 1, except that Li:Fe:ta=1.2875:0.5:0.25 was mixed instead of the ratio of Li:Fe:Ta=1.1845:0.7:0.15. A cathode active material was synthesized.

Example 4 - Carbon coated Li _1.15 Fe _0.7 Ta _0.15 O ₂ synthesis

1) The powder recovered in Example 1: graphite = 9: 1 was mixed.

2) The weight ratio of the ball to the powder for the ball mill process was 20: 1, and the container was sealed in an argon gas atmosphere.

3) After ball mill dry coating was performed at 500 rpm for 10 hours or more, the powder was recovered to obtain a carbon-coated cathode active material.

Example 5 - Anode Preparation

1) The positive electrode active material of Example 1: Super-P: PVDF = 80: 10: an electrode was prepared in a ratio of 10.

2) NMP (N-methyl-2-pyrrilidone) was added to prepare a slurry, and then applied on the Al current collector.

3) The current collector coated with the slurry was dried at a high temperature.

4) 120℃ before secondary battery assembly After drying in a vacuum oven for 10 hours or more, moisture in the electrode was removed.

Experimental Example 1 - X-ray diffraction analysis

X-ray diffraction (XRD) was performed to analyze the crystal structure of the positive active materials of Examples 1 to 3, and the results are shown in FIG. 1 . All of the compositions of Examples 1 to 3 were confirmed to have a rock salt structure of space group Fm-3m.

Afterwards, XRD analysis of the positive active material of Example 4, which was coated with dry carbon through a ball mill process, was performed, and it was confirmed that the rock salt structure was still maintained.

Experimental Example 2 - Electron Microscopy Analysis

The positive active material of Examples 1 to 3 and the particle shape and particle size of Example 4 coated with carbon through a ball mill process were confirmed through an electron microscope (Field-Emission Scanning Electron Microscopy, FE-SEM), and the results are shown in Fig. 2 is shown.

Experimental Example 3 - Electrochemical Performance

Lithium metal as a negative electrode and a reference electrode is an electrolyte in _{which ethyl carbonate (Ethyl Carbonate) and dimethyl carbonate (Dimethyl Carbonate) in which 1.0M of LiPF 6} is dissolved are mixed in a ratio of 1:1 (volume ratio), and the positive electrode active material of Example 4 was used as an anode, and performance evaluation was performed at 60°C with a 2032 type coincell. In the case of the positive electrode, an electrode was manufactured in the manner described in Example 4. The operating voltage was charged/discharged in the range of 1.5 ~ 4.8 V and 1.35 ~ 4.8 V compared to lithium metal, and the current density was 10mA·g ^-1 , 29mA·g ^-1 . ^{When charging/discharging with a current density of 10 mA g -1} within the range of 1.5 to 4.8 V, the first discharge capacity is about 215 mA g ^-1 and 10 mA·g -1 within the range of 1.35 to 4.8 V When ^{charging/discharging was performed with a current density of g -1} , the first discharge capacity showed a capacity of about 237 mA·g ^-1 . ^{When charging/discharging was performed with a current density of 29 mA·g -1} within the range of 1.5 to 4.8 V, the first discharge capacity was about 198.5 mA·g ^-1 . A voltage-capacity graph is shown in FIG. 3 .

Claims (20)

A positive active material for a lithium secondary battery comprising a compound represented by the following formula (1):
[Formula 1]
Li _1+x Fe _y Ta _z O ₂
In Formula 1, 0<x≤0.5, 0<y≤1, 0<z≤0.5, provided that x+y+z=1. The method according to claim 1,
The compound represented by Formula 1 has a rock salt structure (Layered structure: Fm-3m), a cathode active material for a lithium secondary battery. The method according to claim 1,
0.1≤x≤0.3 in Formula 1, the positive electrode active material for a lithium secondary battery. The method according to claim 1,
In Chemical Formula 1, 0.4≤y≤0.7, the positive active material for a lithium secondary battery. The method according to claim 1,
In Formula 1, 0.1≤z≤0.3, the positive active material for a lithium secondary battery. The method according to claim 1,
A cathode active material for a lithium secondary battery, further comprising a carbon-based coating covering the compound represented by the formula (1). 7. The method of claim 6,
The carbon-based coating is graphite, expanded graphite, carbon black, carbon nanotube, citric acid, acetic acid, polyvinylalcohol. , sucrose, and glucose A cathode active material for a lithium secondary battery comprising at least one carbon-based material selected from among. mixing a lithium-containing compound, an iron-containing compound, and a tantalum-containing compound in a solvent;
drying the mixture to obtain a powder; and
calcining the powder to obtain a compound represented by the following formula (1);
A method for producing a positive active material for a lithium secondary battery, comprising:
[Formula 1]
Li _1+x Fe _y Ta _z O ₂
In Formula 1, 0<x≤0.5, 0<y≤1, 0<z≤0.5, provided that x+y+z=1. 9. The method of claim 8,
The lithium-containing compound includes _{at least one selected from Li 2} CO ₃ , Li ₂ O, LiOH, Li ₂ O _2, and LiCl, a method of manufacturing a cathode active material for a lithium secondary battery. 9. The method of claim 8,
The iron-containing compound is Fe ₂ O ₃ , FeO, and Fe ₃ O _{4 The} method for producing a cathode active material for a lithium secondary battery comprising at least one selected from the group consisting of. 9. The method of claim 8,
The tantalum-containing compound is tantalum pentoxide (Ta ₂ O ₅ ), tantalum pentachloride (TaCl ₅ ), tantalum methoxide (Ta(OCH ₃ ) ₅ ), tantalum ethoxide (tantalu ethoxide, Ta(OC ₂ H) ₅ ) ₅ ), tantalum butoxide (tantalum butoxide, Ta(OCH ₂ CH ₂ CH ₂ CH ₃ ) ₅ ), and lithium tantalate (lithium tantalite, LiTaO ₃ ) Lithium secondary comprising at least one selected from A method of manufacturing a positive active material for a battery. 9. The method of claim 8,
Wherein the solvent comprises at least one selected from ethanol, butanol, and acetone. 9. The method of claim 8,
The lithium-containing compound, the iron-containing compound, and the tantalum-containing compound are mixed so as to have a content of 30 to 60 parts by weight of iron and 10 to 25 parts by weight of tantalum based on 100 parts by weight of lithium in the mixture, manufacturing a cathode active material for a lithium secondary battery Way. 9. The method of claim 8,
The drying step is performed at room temperature, the method of manufacturing a cathode active material for a lithium secondary battery. 9. The method of claim 8,
The calcining step is performed at 900 to 1200° C. for 10 to 30 hours, a method of manufacturing a cathode active material for a lithium secondary battery. 9. The method of claim 8,
After the firing, the method of manufacturing a positive electrode active material for a lithium secondary battery further comprising the step of forming a carbon-based coating by mixing the compound represented by Formula 1 and a carbon-based material. 17. The method of claim 16,
The compound represented by Formula 1 and the carbon-based material are mixed in a weight ratio of 7: 1 to 10: 1, a method for producing a cathode active material for a lithium secondary battery. 17. The method of claim 16,
The carbon-based material includes graphite, expanded graphite, carbon black, carbon nanotube, citric acid, acetic acid, and polyvinylalcohol. , sucrose (sucrose), and glucose (glucose) will include at least one selected from, a method of manufacturing a cathode active material for a lithium secondary battery. 9. The method of claim 8,
The compound represented by Formula 1 has a rock salt structure (Layered structure: Fm-3m), the method of manufacturing a cathode active material for a lithium secondary battery. anode;
cathode; and
Electrolyte; contains,
The positive electrode comprising the positive electrode active material according to any one of claims 1 to 7, a lithium secondary battery.

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