KR102152369B1 - a fabricating method of metal oxide coated cathode material, metal oxide coated cathode material fabricated thereby, an electrode for lithium secondary battery and a lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a method of manufacturing a positive electrode active material coated with a metal oxide, a positive electrode active material coated with a metal oxide prepared thereby, an electrode for a lithium secondary battery including the same, and a lithium secondary battery. The present invention is a step of mixing a solvent, a metal alkoxide, and a coupling agent (mixing step) (S1), introducing a positive electrode active material into the mixed solution (injection step) (S2), and separating the positive electrode active material from the mixed solution (separation Step) (S3) and heat treatment of the separated positive electrode active material to obtain a positive electrode active material coated with a metal oxide (heat treatment step) (S4). According to the present invention, by coating a metal oxide on the surface of a three-component or more positive electrode active material or an olivine-based positive electrode active material using a sol-gel method, the dispersibility of the positive electrode active material is improved, and surface side reactions such as decomposition of the electrolyte on the surface of the positive electrode active material are prevented. Suppression and extend the life of the battery.

Description

Method of manufacturing a cathode active material coated with a metal oxide, a cathode active material coated with a metal oxide produced thereby, an electrode for a lithium secondary battery including the same, and a lithium secondary battery (a fabricating method of metal oxide coated cathode material, metal oxide coated cathode material) fabricated thereby, an electrode for lithium secondary battery and a lithium secondary battery including the same}

The present invention relates to a method of manufacturing a positive electrode active material coated with a metal oxide, a positive electrode active material coated with a metal oxide prepared thereby, an electrode for a lithium secondary battery including the same, and a lithium secondary battery. More specifically, a method for producing a positive electrode active material coating a metal oxide on the surface of a three-component or more positive electrode active material or an olivine positive electrode active material using a sol-gel method, and a positive electrode coated with a metal oxide prepared thereby It relates to an active material, an electrode for a lithium secondary battery including the same, and a lithium secondary battery.

Lithium secondary batteries are high-performance lithium secondary batteries used as energy sources for mobile information and communication devices such as mobile phones, PDAs (Personal Digital Assistants), MP3 players, camcorders, notebook computers, etc., electric motors, and hybrid electric vehicles (HEV). It can be widely applied as a secondary battery for high-power large-sized transportation equipment, etc.

Lithium ion secondary batteries are generally composed of a positive electrode and a negative electrode capable of intercalating and deintercalating lithium ions, a separator preventing physical contact between the positive electrode and the negative electrode, and an organic or polymer electrolyte that transfers lithium ions. Lithium ion secondary batteries generate electric energy through electrochemical oxidation and reduction reactions when lithium ions are inserted/desorbed from the positive electrode and the negative electrode.

A lithium-containing composite oxide, preferably a lithium-transition metal oxide, is used as the positive electrode active material, and a lithium metal, a lithium alloy, carbon (crystalline or amorphous), or a carbon composite is used as the negative electrode active material. In addition, the electrolyte serves as a medium for ion conduction, and a non-aqueous solvent may be used, and the non-aqueous solvent is composed of a lithium salt and other additives.

In general, when manufacturing an electrode, a slurry obtained by mixing an active material, a binder, and a conductive agent is applied to a current collector. It is not easy to uniformly disperse the active material in the slurry. If the active material is not uniformly dispersed, the slurry itself cannot have a uniform composition. In addition, a side reaction with the electrolyte occurs on the surface of the positive electrode active material, and hydrofluoric acid (HF) generated by decomposing the electrolyte affects the electrode, causing a problem of shortening the life of the secondary battery.

Korean Registered Patent Publication No. 10-0515029

The present invention is a method for producing a positive electrode active material coating a metal oxide on the surface of a three-component or more positive electrode active material or an olivine positive electrode active material using a sol-gel method, a positive electrode active material coated with a metal oxide prepared thereby, a lithium secondary comprising the same It is intended to provide a battery electrode and a lithium secondary battery.

In the first embodiment of the present invention, a step of mixing a solvent, a metal alkoxide, and a coupling agent (mixing step), adding a positive electrode active material to the mixed solution (injecting step), and separating the positive electrode active material from the mixed solution (separating step ), and heat treatment of the separated positive electrode active material to obtain a positive electrode active material coated with a metal oxide (heat treatment step), and may be a method of manufacturing a positive electrode active material coated with a metal oxide.

The cathode active material is not particularly limited, but Li _{1 +a} Ni _b Co _c Mn _d M _e O ₂ (-1<a<1, b+c+d+e=1, b>0, c> 0, d>0, e≥O, and M is at least one metal selected from transition metals) or at least one selected from the group consisting of an olivine-based positive electrode active material may be used.

As the solvent, isopropyl alcohol, N-methyl-2-pyrrolidone, γ-butylactone, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone (1,3 -dimetyl-2-imidazolidinone) and at least one selected from the group consisting of cyclohexane may be used.

The metal alkoxides include Si(OR) ₄ , Sn(OR) ₄ , Al(OR) ₄ , Zr(OR) ₄ , Ce(OR) ₄ , Ti(OR) _4, Zn(OR) ₂ , Mg(OR) ) ₂ , Ni(OR) ₂ and cobalt amino alkoxide (R is an alkyl group having 1 to 10 carbon atoms), and at least one selected from the group consisting of, more specifically, MTMS (methyltrimethoxysilane) Can be used.

As the coupling agent, at least one selected from the group consisting of glycidoxypropyltrimethoxysilane (GPTMS) and methyl triethoxysilane (MTES) may be used, preferably silica colloid You can use

The metal oxide may include at least one oxide selected from the group consisting of SiO ₂ , Al ₂ O ₃ , ZnO, ZnO ₂ , ZrO ₂ , MgO, NiO, CoO, Co ₃ O ₄ and TiO ₂ .

The second embodiment of the present invention may be a positive electrode active material manufactured according to the first embodiment.

The third embodiment of the present invention may be an electrode for a lithium secondary battery including the positive electrode active material of the second embodiment.

The fourth embodiment of the present invention may be a lithium secondary battery including the electrode of the third embodiment.

According to the present invention, the dispersibility of the positive electrode active material is improved by coating a metal oxide on the surface of a positive electrode active material of three or more components or an olivine positive electrode active material using a sol-gel method, and by suppressing side reactions on the surface of the positive electrode active material, the lithium secondary battery Life can be extended.

In addition, superior reversible capacity can be obtained compared to the uncoated positive electrode active material, and the capacity can be maintained even in the evaluation of long-life characteristics, so that the positive electrode active material according to the present invention has high performance It can be used for lithium secondary batteries.

1 is a flow chart illustrating a process of manufacturing a positive electrode active material coated with a metal oxide according to a first embodiment of the present invention.
2 is a schematic diagram showing particles of a positive electrode active material coated with a metal oxide according to the first embodiment of the present invention.
3 is a scanning electron microscope photograph of a cathode active material prepared according to Comparative Examples and Example 1 (A: Comparative Example, B: Example 1).

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided in order to more completely describe the present invention to those with average knowledge in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer explanation, and elements indicated by the same reference numerals in the drawings are the same elements.

The present invention is characterized in that the surface of the positive electrode active material is coated by a sol-gel method. In the sol-gel coating method, a metal organic compound or salt such as alkoxide is hydrolyzed to prepare a sol in which colloid particles are dispersed, and a dehydration-condensation reaction of the sol is prepared. ), and coating the object to be coated with this gel. Examples of the sol may include silica sol (SiO ₂ -sol), titania sol (TiO ₂ -sol), alumina sol (Al ₂ O ₃ -sol), and zirconia sol (ZrO ₂ -sol).

1 is a flowchart illustrating a process of manufacturing a positive electrode active material coated with a metal oxide according to a first embodiment of the present invention.

Referring to Figure 1, the first embodiment of the present invention is a step of mixing a solvent, a metal alkoxide, and a coupling agent (mixing step) (S1), injecting a positive electrode active material into the mixed solution (injection step) (S2), Metal oxide-coated, including the step of separating the positive electrode active material from the mixed solution (separation step) (S3), and the step of heat-treating the separated positive electrode active material to obtain a metal oxide-coated positive electrode active material (heat treatment step) (S4). It may be a method of manufacturing a cathode active material.

First, a mixed solution may be prepared by mixing a solvent, a metal alkoxide, and a coupling agent (mixing step) (S1). At this time, agitation may be performed so that the metal alkoxide and the coupling agent are uniformly mixed. As a result, an organic-inorganic hybrid coating solution in a sol state in which the metal is uniformly dispersed in a solvent may be formed.

There is no specific limitation as long as the solvent can dissolve the metal alkoxide and the coupling agent except for water. Specifically, as a polar solvent, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, and isobutyl acetate; Ketone solvents such as acetone, methyl ethyl ketone, isobutyl ketone, and cyclohexanone; And alcohol-based solvents such as ethanol, propanol, and butanol, and benzene, toluene, ethylbenzene, and the like can be used as non-polar solvents. Preferably isopropyl alcohol, N-methyl-2-pyrrolidone, γ-butylactone, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone (1,3- dimetyl-2-imidazolidinone) and at least one selected from the group consisting of cyclohexane may be used as the solvent.

Metal alkoxide or metal alcoholate is a form in which a metal atom is bonded with one or more alkyl groups by an oxygen atom, and can be expressed by the general formula of M(OR)x, and the hydroxyl group H of the alcohol ROH is A substituted derivative or a derivative in which the hydroxyl group H of the metal hydroxide M(OH)x is substituted with the alkyl group R may be used. The physical properties of metal alkoxides vary depending on the position on the periodic table of the metal element and the alkyl group bonded to it. Most metal alkoxides are strongly bonded by the force between molecules, which can be affected by the shape and size of the alkyl group.

Metal alkoxides include Si(OR) ₄ , Sn(OR) ₄ , Al(OR) ₄ , Zr(OR) ₄ , Ce(OR) ₄ , Ti(OR) _4, Zn(OR) ₂ , Mg(OR) ₂ , Ni(OR) ₂ and one or more selected from the group consisting of cobalt amino alkoxide may be used (R is an alkyl group having 1 to 10 carbon atoms), and in particular, one or two or more alkoxysilanes May be used by mixing, and by mixing two or more alkoxysilanes, the sol-gel reaction rate and the content of silica particles generated from the sol-gel method can be controlled. As the alkoxysilane, it is preferable to use TEOS (tetraethylorthosilicate) or MTMS (methyltrimethoxysilane), or a combination thereof, but is not limited thereto. The metal alkoxide can be appropriately selected in consideration of the metal oxide coating layer to be finally formed. When using Si(OR) ₄ as a metal alkoxide, SiO ₂ Metal oxide can be coated, and if Al(OR) ₄ is used as a metal alkoxide, Al ₂ O ₃ Metal oxide can be coated, and when Zr(OR) ₄ is used as a metal alkoxide, ZrO ₂ metal oxide can be coated, and when Ti(OR) ₄ is used as a metal alkoxide, TiO ₂ metal oxide is coated. Can be.

As the coupling agent, any one that can improve the dispersibility of the sol and improve the adhesion of the coating layer can be used. Specifically, glycidoxypropyltrimethoxysilane (GPTMS) or methyltriethoxysilane (methyl triethoxysilane (MTES)) may be used, these may be used in combination, and silica colloid may be preferably used.

Next, the positive electrode active material may be added to the mixed solution (injection step) (S2).

In order to coat the positive electrode active material, a positive electrode active material may be added to the coating solution in a sol state. There is no particular limitation on the object to be coated, but in this embodiment, the cathode active material is coated by a sol-gel method, and the cathode active material is Li _1+a Ni _b Co _c Mn _d M _e O ₂ (-1 <a<1, b+c+d+e=1, b>0, c>0, d>0, e≥O, and M is at least one metal selected from transition metals) or an olivine-based cathode active material It can be used, and they can also be used in combination.

Through this process, a coating layer may be formed on the surface of the positive electrode active material. The coating layer here is not a metal oxide, and the metal existing in the metal alkoxide forms a network structure through an organic material. The properties of the coating layer may vary depending on the temperature, pH, and time of the mixed solution.

Next, it is possible to separate the positive electrode active material from the mixed solution (separation step) (S3). There is no particular limitation on the method of separating the coated cathode active material from the solvent, but a vacuum filtration method is preferred.

Next, the separated positive electrode active material is heat treated to obtain a positive electrode active material coated with a metal oxide (heat treatment step) (S4). The material coated on the positive electrode active material by heat treatment is converted into a metal oxide, for example, SiO ₂ , Al ₂ O ₃ , ZnO, ZnO ₂ , ZrO ₂ , MgO, NiO, CoO, Co ₃ O ₄ or TiO ₂ Oxides can be formed. When two or more metal alkoxides are used, a composite metal oxide may be formed.

It is preferable that the metal oxide is formed so as to completely surround the positive electrode active material, but even if there is a portion not covered with the metal oxide, it is preferable because the reaction area of the side reaction can be reduced.

The heat treatment temperature may be 80 ℃ ~ 200 ℃. When the heat treatment temperature is lower than 80° C., aggregation between particles may occur, and when it is higher than 200° C., lithium intercalation efficiency may be deteriorated.

2 is a schematic diagram showing particles of a positive electrode active material coated with a metal oxide.

Referring to FIG. 2, the second embodiment of the present invention may be a positive electrode active material manufactured according to the first embodiment, which may have a core-shell structure coated with a metal oxide.

The core 10 is not particularly limited, but Li _{1 +a} Ni _b Co _c Mn _d M _e O ₂ (-1<a<1, b+c+d+e=1, b>0, c >0, d>0, e≥O, and M is at least one metal selected from transition metals) or at least one selected from the group consisting of an olivine-based positive electrode active material.

The shell 20 is SiO ₂ , Al ₂ O ₃ , ZnO, ZnO ₂ , ZrO ₂ , MgO, NiO, CoO, Co ₃ O ₄ And TiO ₂ It may include at least one type of metal oxide selected from the group consisting of.

The third embodiment of the present invention may be an electrode including the positive electrode active material of the second embodiment. The electrode of this embodiment can be produced by coating a slurry in which a positive electrode active material coated with a metal oxide, a conductive agent for imparting conductivity, a binder for binding the positive electrode active material and the conductive agent, and the like are mixed on the current collector. As the conductive agent and the binder, generally known ones can be used.

A lithium secondary battery may be manufactured using the electrode of the third embodiment, that is, a positive electrode active material coated with a metal oxide. For example, a positive electrode active material coated with a metal oxide is added to an organic solvent such as N-methyl-2-pyrrolidone together with a binder such as polyvinylidone and a conductive agent such as acetylene black and carbon black to prepare a positive electrode active material slurry. It can be manufactured first. When preparing a slurry, it is common to add a non-proton solvent to adjust the viscosity. The slurry composition is coated on a current collector such as aluminum foil, dried to prepare a positive electrode, and a negative electrode is prepared using carbon or lithium metal as a negative electrode. A separator is interposed between the positive electrode and the negative electrode, and then a certain tension is applied. A lithium secondary battery can be manufactured by winding it up, inserting it into a pouch, which is an exterior material of a battery, injecting an electrolyte, and sealing it.

Hereinafter, the present invention will be described in more detail through examples and comparative examples.

Example One

A commercially available isopropyl alcohol diluted solution (50%, Aldrich), a commercially available MTMS (methyltrimethoxysilane, Aldrich), and a commercially available colloidal silica suspension (30%, Aldrich) were prepared, and the weight of isopropyl alcohol, MTMS, and silica was 100 g, respectively, After weighing and mixing to 4g and 4g, the mixture was stirred for 1 hour. In order to control the aggregation rate during stirring, a certain amount of HNO ₃ (2wt%) was added to adjust the solution to pH 8 and stirred for 24 hours while maintaining at 30°C to prepare a coating solution in a sol state.

Cathode active material in the coating solution _{LiNi 1/3 Co 1/3} Mn 1/3 O 2 was added to the input (SFC), and subjected to heat treatment at 110 ℃ using an oven silica is coated on the surface of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder was prepared.

800g, 100g, and 100g, respectively, were mixed so that the weight ratio of the positive electrode active material, the conductive agent, and the binder was 8:1:1, and stirred to prepare a slurry. The prepared LiNi _{1 /3} Co _{1 /3} Mn _{1 /3} O ₂ was used as the cathode active material, carbon black was used as the conductive agent, and PVdF (Polyvinylidene fluoride) was used as the binder. PVdF (Polyvinylidene fluoride) was mixed with NMP (N-Methyl-2-pyrrolidone) and used.

The slurry was coated on an aluminum foil with a thickness of 4 to 20 μm using a doctor blade method, dried at 110 °C for 20 minutes, and pressed with a roll press to prepare an electrode. Assembled. When manufacturing the coin cell, a 1M (mol/L) solution of lithium hexafluorophosphate salt (LiPF ₆ ) was used as the electrolyte.

Example 2

An electrode and a coin cell were manufactured in the same manner as in Example 1, except that the coating solution was prepared as follows.

Commercially available (3-Glycidyloxypropyl)trimethoxysilane (98%, aldrich) and commercially available 3- (Trimethoxysilyl) propyl methacrylate (98%, aldrich) were mixed in a weight ratio of 10:1 to make 100 g, and then stirred for 1 hour. To adjust the aggregation rate during stirring, a certain amount of acetic acid (aldrich, 99.5%) was added to adjust the pH to 6, maintained at 30° C., and stirred for 24 hours to prepare a coating solution.

Comparative example

An electrode in the same manner as in Example 1, except that an electrode was manufactured using LiNi _{1 /3} Co _{1 /3} Mn _{1 /3} O ₂ (Samsung Fine Chemicals) not coated with silica as a positive electrode active material. And a coin cell was produced.

evaluation

In order to check whether the positive electrode active material was coated with silica, the positive electrode active material prepared according to Example 1 and Comparative Example was observed with a scanning electron microscope (SEM, Scanning Electron Microscopy, Jeol's JSM-7400F), and the results are shown in Fig. It is shown in 3 (A: Comparative Example, B: Example 1). Referring to FIG. 3, in the case of Example 1, a silica layer was coated on the surface of the positive electrode active material, so that the surface was confirmed to be smooth.

In addition, to examine the degree of dispersion of the positive electrode active material, a certain cross-sectional area of 10 cm x 10 cm is collected among the prepared electrodes, and a uniform surface is visually checked. If there is agglomeration on the electrode surface, The number was counted and the results were observed. The number of agglomerations occurred for 3 samples was counted and the average was calculated. The results are shown in Table 1.

Number of aggregates Average aggregate count Comparative example 10 15 13 13 Example 1 2 0 One One

Referring to Table 1, in the case of Example 1, agglomeration hardly occurred, but in the case of the comparative example, it can be seen that a large number of agglomeration occurred. From this, it can be seen that in the case of the present invention, the dispersibility of the positive electrode active material is improved.

In addition, in order to examine whether the life of the battery has improved, the coin cell produced above was repeatedly charged and discharged at 10C at room temperature, and the cycle to become 80% of the initial capacity was measured, and the results are shown in Table 2. Shown in.

Number of cycles Average number of cycles Comparative example 30 times 25 times 27 times 27.3 times Example 1 33 times 37 times Issue 35 35 times

Referring to Table 2, it was confirmed that the battery life of Example 1 was improved compared to that of Comparative Example.

The terms used in the present invention are for describing specific embodiments and are not intended to limit the present invention. Singular expressions should be viewed as including plural meanings, unless the context is clear. Terms such as "include" or "have" mean, but are not intended to exclude, features, numbers, steps, actions, components, or combinations thereof described in the specification. It is not intended to be limited by the embodiments and the accompanying drawings, but is intended to be limited by the appended claims. Therefore, various types of substitutions, modifications and changes will be possible by those of ordinary skill in the art within the scope not departing from the technical spirit of the present invention described in the claims, and this also belongs to the scope of the present invention. something to do.

10: cathode active material
20: metal oxide

Claims (11)

Mixing a solvent, a metal alkoxide, and a coupling agent (mixing step);
Injecting a positive electrode active material into the mixed solution (injection step);
Separating the positive electrode active material from the mixed solution (separating step); And
As a method for producing a positive electrode active material coated with a metal oxide comprising the step of heat-treating the separated positive electrode active material to obtain a positive electrode active material coated with a metal oxide (heat treatment step),
As the metal alkoxide, Si(OR) ₄ , Sn(OR) ₄ , Al(OR) ₃ , Zr(OR) ₄ , Ce(OR) ₄ , Ti(OR) _4, Zn(OR) ₂ , Mg(OR) ) ₂ , Ni(OR) ₂ and at least one selected from the group consisting of cobalt aminoalkoxide is used,
The method of manufacturing a positive electrode active material using a silica colloid as the coupling agent in the mixing step. The method of claim 1,
The cathode active material is Li _{1 +a} Ni _b Co _c Mn _d M _e O ₂ (-1<a<1, b+c+d+e=1, b>0, c>0, d>0, e ≥O, and M is at least one metal selected from transition metals) and an olivine-based cathode active material. A method for producing a cathode active material coated with a metal oxide using at least one selected from the group consisting of. The method of claim 1,
As the solvent, isopropyl alcohol, N-methyl-2-pyrrolidone, γ-butylactone, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone (1,3 -dimetyl-2-imidazolidinone) and a method of producing a positive electrode active material coated with a metal oxide using at least one selected from the group consisting of cyclohexane. delete The method of claim 1,
A method for producing a positive electrode active material coated with a metal oxide using MTMS (methyltrimethoxysilane) as the metal alkoxide. delete delete The method of claim 1,
The metal oxide is a metal oxide including at least one oxide selected from the group consisting of SiO ₂ , Al ₂ O ₃ , ZnO, ZnO ₂ , ZrO ₂ , MgO, NiO, CoO, Co ₃ O ₄ and TiO ₂ Method of manufacturing a coated positive electrode active material. A positive electrode active material coated with a metal oxide prepared according to any one of claims 1 to 3, 5 and 8. An electrode for a lithium secondary battery comprising the positive electrode active material of claim 9. A lithium secondary battery comprising the electrode of claim 10.

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