KR100923442B1 - New cathode active material - Google Patents

Abstract

The present invention relates to a novel cathode active material that can be used in a lithium secondary battery and a method of manufacturing the same.

The cathode active material is a first step of preparing a coating solution in which the Al feed precursor is dispersed in a solvent; A second step of dissolving the Al feed precursor in a solvent by heating the coating solution of the previous step to 40 to 100 ° C; In the preparation of the first lithium composite oxide capable of intercalating / deintercalating lithium ions, a residual lithium supply precursor is formed by using an excess lithium supply precursor. Preparing a first lithium composite oxide remaining on or in the particle surface; A fourth step of swelling by adding a solvent to the first lithium composite oxide; A fifth step of adding the coating solution to the first lithium composite oxide swelled in the solvent and then stirring the coating solution; And a sixth step of forming a second lithium composite oxide in which a LiAlO ₂ -containing film is continuously formed on the first lithium composite oxide particles by heating the resultant material at 700 ° C. to 1000 ° C. in the previous step.

Description

New Cathode Active Material {NEW CATHODE ACTIVE MATERIAL}

The present invention relates to a novel positive electrode active material usable in a lithium secondary battery and a method of manufacturing the same.

Recently, with the trend toward miniaturization and light weight of portable electronic devices, the need for high performance and high capacity of batteries used as power sources for these devices is increasing.

A battery generates power by using a material capable of electrochemical reactions at a positive electrode and a negative electrode. A representative example of such a battery is a lithium secondary battery, which generates electrical energy by a change in chemical potential when lithium ions are intercalated / deintercalated at a positive electrode and a negative electrode.

The lithium secondary battery is manufactured by using a material capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and filling an organic electrolyte or a polymer electrolyte between the positive electrode and the negative electrode.

As a cathode active material of a lithium secondary battery, a lithium composite metal compound is used. Examples thereof include a composite of LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1- x} Co _x O ₂ (0 <x <1), and LiMnO ₂ . Metal oxides are being studied.

Among the cathode active materials, Mn-based cathode active materials such as LiMn ₂ O ₄ and LiMnO ₂ are easy to synthesize, are relatively inexpensive, have the best thermal stability compared to other active materials when overcharged, and have low environmental pollution and are attractive. Although it has a disadvantage, the capacity is small.

LiCoO ₂ exhibits good electron conductivity, high battery voltage, and excellent electrode characteristics, and is a representative cathode active material commercialized and marketed by Sony. However, it has the disadvantage of high price and low stability at high rate charge and discharge.

LiNiO ₂ is the least expensive of the above-mentioned positive electrode active material, and exhibits the highest discharge capacity of battery characteristics, but has difficulty in synthesis and has the disadvantage of being most structurally unstable during charge and discharge of the above-mentioned positive electrode active material.

In order to improve the electrochemical properties of the positive electrode active material of the lithium secondary battery, a lot of research through composition change, particle size control and surface treatment has been continuously conducted.

An object of the present invention is to provide a cathode active material for a lithium secondary battery with improved performance.

The present invention comprises a first step of preparing a coating solution in which the Al feed precursor is dispersed in a solvent; A second step of dissolving the Al feed precursor in a solvent by heating the coating solution of the previous step to 40 to 100 ° C; In the preparation of the first lithium composite oxide capable of intercalating / deintercalating lithium ions, a residual lithium supply precursor is formed by using an excess lithium supply precursor. Preparing a first lithium composite oxide remaining on or in the particle surface; A fourth step of swelling by adding a solvent to the first lithium composite oxide; A fifth step of adding the coating solution to the first lithium composite oxide swelled in the solvent and then stirring the coating solution; And a sixth step of forming a second lithium composite oxide in which a LiAlO ₂ -containing film is continuously formed on the first lithium composite oxide particles by heating the resultant material at 700 ° C. to 1000 ° C. in the previous step. Provided is a method for producing a cathode active material of oxide.

In addition, the present invention is the first lithium composite oxide core particles capable of intercalating / deintercalating lithium ions; And a coating layer in which LiAlO ₂ formed by reacting Al introduced and diffused into the inner surface of the core particles and the lithium supply precursor remaining in the first lithium composite oxide core particles are present in a continuous coating form. Provided is a cathode active material including a lithium composite oxide and a secondary battery using the same.

The positive electrode active material according to the present invention can improve the high voltage characteristic and the rate characteristic of the battery using the same.

Hereinafter, the present invention will be described in detail.

As used herein, the term "residual lithium supply precursor" refers to an excess of lithium supply precursor used in excess of stoichiometry when preparing first lithium composite oxide core particles capable of intercalating / deintercalating lithium ions. Non-limiting examples of feed precursors include lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH), lithium nitrate, lithium acetate, lithium oxide, lithium sulfate, lithium chloride, and the like, with lithium hydroxide being preferred. Do.

In the manufacturing method according to the present invention, Al in the Al supply precursor reacts with Li remaining on or near the surface of the first lithium composite oxide (eg, LiCoO ₂ ) capable of intercalating / deintercalating lithium ions. Most of which is present as LiAlO ₂ , and only some may be present as Al ₂ O ₃ (Example 1).

In addition, the positive electrode active material produced by the method according to the invention can be a LiAlO ₂ formed is coated with a continuous film shape nor be coated with a particulate, a thin coating layer containing a LiAlO ₂ (see Fig. 1c).

In the present specification, the coating in the form of a continuous coating is LiAlO ₂ Means no observation in particulate form.

The surface of the active material reacts with the electrolyte to cause deterioration of the active material. In the present invention, the Al-containing oxide is not a coating layer composed of a plurality of particles, but a continuous coating layer having no particle state can be suppressed to deteriorate the active material.

Preferred examples of Al feed precursors include Al-alkoxides (eg Al isopropoxide), but oxides containing aluminum (eg, alumina), hydroxides (eg, aluminum hydroxide), as long as they can react with Li, Oxyhydroxides, nitrates, chlorides, carbonates, acetates, oxalates, citrates, or mixtures thereof.

In the present invention, the solvent of the coating liquid and the solvent to swell the first lithium composite oxide to be coated are not limited as long as they can dissolve the Al feed precursor or swell the first lithium composite oxide, respectively. However, non-limiting examples thereof include alcohol (eg isopropyl alcohol, ethyl alcohol, methyl alcohol), water, benzene toluene, chloroform, carbon tetrachloride, Petroleum hydrocarbons or mixtures thereof. As the solvent, C ₁ to C ₆ lower alcohols are preferable.

On the other hand, it is preferable that the solvent which dissolves an Al supply precursor and the solvent which swells a 1st lithium composite oxide are the same.

The present invention is characterized in that the Al feed precursor in the solvent is used as a solution rather than a dispersion.

In the production method of the positive electrode active material according to the present invention, if the Al feed precursor is not completely dissolved in a solvent such as alcohol, the Al feed precursor is maintained in a dispersed state as fine particles and tends to be coated in the form of fine particles at the time of coating. If Al feed precursor is dispersed, uniform coating is not possible. Therefore, the present invention completely dissolves the Al supply precursor in a solvent such as alcohol to form a coating layer in the form of a film.

On the other hand, the present invention preferably further comprises the step of finely dispersing the Al feed precursor through high-speed stirring after the first step, in order to facilitate the dissolution of the coating solution in the second step.

Meanwhile, the present invention prevents the Al-supply precursor from depositing on the first lithium composite oxide by adding a solvent such as alcohol to the first lithium composite oxide to be coated. Due to this, it is possible to ensure the uniformity of the coating, it is possible to form the coating product in the form of a film rather than a particle form.

In addition, the present invention preferably further adds a step of removing the solvent by evaporation after the fifth step. This is because the calcination through heat treatment in the sixth step can be facilitated by evaporating the solvent. As a method of evaporating the solvent, there is a method of evaporating the solvent by supplying hot water after mixing coating, drying by hot air, drying by indirect heating method, and drying under reduced pressure.

On the other hand, the manufacturing method of the positive electrode active material according to the present invention is heat-treated at 700 ℃ or more, the shape deposited slightly varies depending on the firing temperature. Above 700 ° C, Al-alkoxides such as coated Al-Isopropoxide tend to react with Li and diffuse inside. The heat treatment time may be 12 hours to 18 hours.

On the other hand, the active material heat-treated as described above is good to disperse by passing the ultrasonic shift.

In the method for preparing a cathode active material according to the present invention, the first lithium composite oxide raw material may have a diameter of 6 to 20 μm before coating with LiAlO ₂ .

According to the present invention, the first lithium composite oxide capable of intercalating / deintercalating lithium ions may use any lithium-containing composite metal oxide as long as it can intercalate / deintercalate lithium ions. Non-limiting examples thereof include the compound of formula (1).

[Formula 1]

LiA _{1 -x- y} B _x C _y O ₂

Wherein 0 <x ≦ 0.3, 0 ≦ y ≦ 0.01, wherein A is an element selected from the group consisting of Ni, Co, and Mn, and B is Ni, Co, Mn, B, Mg, Ca, Sr , Ba, Ti, V, Cr, Fe, Cu and Al is an element selected from the group, C is Ni, Co, Mn, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Element selected from the group consisting of Cu and Al)

The lithium composite oxide is preferably a lithium cobalt composite oxide represented by the following formula (2).

[Formula 2]

Li _x Co _{1 - y} Me _y O _{2 -a}

(Me represents one or two or more metal elements selected from Ni, B, Mg, Ca, Sr, Ba, V, Cr, Fe, Cu, Al, Ti. _X is 1.0≤x≤1.1, y is 0 ≤ y ≤ 0.0, a is -0.1 ≤ a ≤ 0.1)

The lithium composite oxide of Formula 2 is LiCoO ₂ As well as complex oxides in which some of the cobalt atoms are replaced with other metal elements.

The material prepared through the above steps may be used as an electrode active material, preferably a positive electrode active material of a lithium secondary battery.

On the other hand, except for using the positive electrode active material prepared according to the present invention, it is possible to manufacture an electrode and / or a secondary battery by a conventional method.

The lithium secondary battery may include a positive electrode including a positive electrode active material; A negative electrode including a negative electrode active material; Electrolytes present between them; And optionally a separator, wherein the lithium composite metal oxide according to the present invention is used as the electrode active material, preferably the cathode active material.

An example of the lithium secondary battery of the present invention is as follows.

The positive electrode is prepared by mixing a positive electrode active material according to the present invention, a conductive material, a binder and a solvent to prepare a positive electrode active material composition, and then coating and drying the aluminum active material directly. Alternatively, the cathode active material composition may be cast on a separate support, and then the film obtained by peeling from the support may be manufactured by laminating on an aluminum current collector.

The conductive material is carbon black, acetylene black, graphite, metal powder, the binder is vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetra Fluoroethylene and mixtures thereof are possible. In addition, N-methylpyrrolidone, acetone, tetrahydrofuran, decane, etc. are used as a solvent. In this case, the contents of the positive electrode active material, the conductive material, the binder, and the solvent are used at levels commonly used in lithium secondary batteries.

The negative electrode is likewise mixed with a negative electrode active material, a binder and a solvent to prepare a negative electrode active material composition, which is directly coated on a copper current collector or cast on a separate support, and the negative electrode active material film peeled from the support is laminated to a copper current collector Manufacture. At this time, the negative electrode active material composition may further contain a conductive material if necessary.

As the negative electrode active material, a material capable of intercalating / deintercalating lithium is used, and for example, lithium metal, lithium alloy, coke, artificial graphite, natural graphite, organic polymer compound combustor, carbon fiber, or the like is used. . In addition, a conductive material, a binder, and a solvent are used similarly to the case of the positive electrode mentioned above.

As the electrolyte to be charged in the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt is usually used.

Although the solvent of the said non-aqueous electrolyte is not specifically limited, Cyclic carbonates, such as ethylene carbonate, a propylene carbonate, butylene carbonate, vinylene carbonate; Chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate; Esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and γ-butyrolactone; Ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane and 2-methyltetrahydrofuran; Nitriles such as acetonitrile; Amides, such as dimethylformamide, etc. can be used. These can be used individually or in combination of two or more. In particular, a mixed solvent of a cyclic carbonate and a linear carbonate can be preferably used.

As the electrolyte, a gel polymer electrolyte in which an electrolyte solution is impregnated with a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , One selected from the group consisting of LiCl and LiI is possible.

The separator may be used as long as it is commonly used in a lithium secondary battery. For example, polyethylene, polypropylene, polyvinylidene fluoride, or two or more multilayer films thereof may be used, a polyethylene / polypropylene two-layer separator, Of course, mixed multilayer membranes such as polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator, and the like may be used.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

Example 1

After dispersing Al-Isopropoxide finely in Al-Isopropoxide in isopropyl alcohol through high-speed stirring, it was heated to a temperature of 40 ° C. or higher to prepare a 6 wt% coating solution in which Al-Isopropoxide was completely dissolved in isopropyl alcohol. It was.

LiCoO ₂ in the manufacture using a large excess of Li ₂ CO ₃ or more stoichiometric unreacted Li ₂ CO ₃ is prepared for LiCoO ₂ that remains on the surface or inside the particles, and LiCoO ₂ was Wetting them with isopropyl alcohol. After putting the coating liquid in the LiCoO ₂ Wetting to the isopropyl alcohol in order to sufficiently disperse the LiCoO ₂ in the coating solution it was stirred for 1 hour. The alcohol was then removed by evaporation while stirring at 60 ° C. under vacuum. Heat treatment was performed at 700 ° C. for 8 hours while the alcohol was removed, and the heat-treated active material was dispersed by ultrasonic shift. As a result, an SEM image of the prepared cathode active material is shown in FIG. 1.

The prepared cathode active material has a particle size of 12 μm, and the coating layer of the prepared cathode active material is LiAlO ₂ through FIG. 1C. It was confirmed that the coating occurred in the form of a continuous film without coating with particles.

On the other hand, as a result of confirming neutralization titration with 0.1 N HCl, it was also confirmed that the residual Li ₂ CO ₃ was lowered from 0.072% by weight to 0.05% by weight. That is, as shown in Table 1 below, the content of residual Li ₂ CO ₃ (soluble) is lowered, and the coating layer may predict that Al-Isopropoxide reacts with the residual Li ₂ CO ₃ to form a coating layer.

TABLE 1

Residual Li ₂ CO ₃ Before coating 0.072 weight% After coating and firing 0.05 wt%

In addition, it was confirmed that the prepared cathode active material had a LiAlO ₂ coating layer in which only part of Al ₂ O ₃ was present on the surface of LiCoO ₂ . CoAlO ₂ was not detected in the coating layer. 2 is a peak showing the structure of a typical LiCoO ₂ as XRD of the prepared cathode active material, and it can be seen that other materials such as CoAlO ₂ are not mixed.

Inorganic element measurement with an inductively coupled plasma, the coating layer was found to be 500ppm Al compared to LiCoO ₂ .

Slurry was prepared by using the prepared positive electrode active material, binder, and carbon in a weight ratio of 95: 2.5: 2.5 for battery chemistry evaluation. Coating on an aluminum foil, vacuum drying for 2 hours and then press to prepare a plate. A coin battery was fabricated using the manufactured electrode plate as a positive electrode and a lithium metal as a negative electrode, and the life characteristics and the charge and discharge characteristics according to various rates at 4.3V were evaluated by the capacity change after the initial capacity and 10 cycles (see FIGS. 3 and 4). ). Compared with Comparative Example 1 (FIG. 5), it can be seen that the charging and discharging characteristics and the lifespan characteristics of the battery prepared by Example 1 are improved.

Comparative Example 1

A coin battery was fabricated in the same manner as in Example 1 except that the electrode was manufactured using LiCoO ₂ used in Example 1 as a cathode active material without forming a coating layer, and then, at various times of 4.3 V and the first charge and discharge cycle, Charge and discharge characteristics were evaluated according to the rate (see FIG. 5).

Example 2

A positive electrode active material and a coin cell were manufactured in the same manner as in Example 1 except that the heat treatment temperature was treated at 750 ° C. instead of 700 ° C., and the charge and discharge characteristics were evaluated at various rates at 4.3 V and the first charge and discharge cycle. It was. (See Figure 6)

Comparative Example 2

A positive electrode active material and a coin cell were manufactured in the same manner as in Example 1 except that the heat treatment temperature was treated at 600 ° C. instead of 700 ° C. to evaluate the charge and discharge characteristics according to various rates at 4.3 V and the first charge and discharge cycle. It was. (See Figure 7)

Examples 1, 2 and Comparative Example 2 were coated under the same conditions when manufacturing the positive electrode active material, but the heat treatment temperature was different after coating, and the battery performance after treatment at 700 ° C. and 750 ° C. was higher than that at 600 ° C. it was good. In particular, Example 1 baked at 700 ° C showed the best properties. However, Comparative Example 2 also showed better battery performance than Comparative Example 1 using the positive electrode active material which was not coated.

1a and b are SEM pictures of the positive electrode active material prepared in Example 1, Figure 1c is a TEM picture.

2 is XRD of the positive electrode active material prepared in Example 1. FIG.

3 is a charge and discharge graph according to various rates at 4.3V and the first charge and discharge cycle of the coin battery prepared in Example 1;

4 is a charge and discharge graph according to various rates at 4.3V after 10 cycles of the coin battery prepared in Example 1. FIG.

5 is a charge / discharge graph according to various rates in 4.3V and the first charge and discharge cycle of the coin battery prepared in Comparative Example 1.

FIG. 6 is a charge / discharge graph according to various rates at 4.3 V and the first charge and discharge cycle of the coin battery prepared in Example 2. FIG.

7 is a charge and discharge graph according to various rates in 4.3V and the first charge and discharge cycle of the coin battery prepared in Comparative Example 2.

Claims (9)

A first step of preparing a coating solution in which an Al feed precursor is dispersed in a solvent; A second step of dissolving the Al feed precursor in a solvent by heating the coating solution of the previous step to 40 to 100 ° C; In the preparation of the first lithium composite oxide capable of intercalating / deintercalating lithium ions, a residual lithium supply precursor is formed by using an excess lithium supply precursor. Preparing a first lithium composite oxide remaining on or in the particle surface; A fourth step of swelling by adding a solvent to the first lithium composite oxide; A fifth step of adding the coating solution of the second step to the first lithium composite oxide swelled in the solvent and then stirring; And A sixth step of forming a second lithium composite oxide in which a LiAlO ₂ -containing film is continuously formed on the first lithium composite oxide particles by heating the resultant material at the previous stage at 700 ° C. to 1000 ° C. Method for producing a positive electrode active material of a second lithium composite oxide, characterized in that it comprises a. The method of claim 1, wherein the Al feed precursor is Al-alkoxide. The method of claim 1, further comprising evaporating and removing the solvent after the fifth step. The method of claim 1, wherein the solvent for dissolving the Al feed precursor in the coating solution and the solvent for swelling the first lithium composite oxide are the same. The method of claim 1, wherein the first lithium composite oxide is a compound of Formula 1 below. [Formula 1] LiA _{1 -x- y} B _x C _y O ₂ Wherein 0 <x ≦ 0.3, 0 ≦ y ≦ 0.01, wherein A is an element selected from the group consisting of Ni, Co, and Mn, and B is Ni, Co, Mn, B, Mg, Ca, Sr , Ba, Ti, V, Cr, Fe, Cu and Al is an element selected from the group, C is Ni, Co, Mn, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Element selected from the group consisting of Cu and Al) The method of claim 1, wherein the first lithium composite oxide is a compound of Formula 2 below. [Formula 2] Li _x Co _{1 - y} Me _y O _{2 -a} (Me represents one or two or more metal elements selected from Ni, B, Mg, Ca, Sr, Ba, V, Cr, Fe, Cu, Al, Ti. _X is 1.0≤x≤1.1, y is 0 ≤ y ≤ 0.002, a is -0.1 ≤ a ≤ 0.1) First lithium composite oxide core particles capable of intercalating / deintercalating lithium ions; And a coating layer in which LiAlO ₂ formed by reacting Al introduced and diffused into the inner surface of the core particles and the lithium supply precursor remaining in the first lithium composite oxide core particles are present in a continuous coating form. A cathode active material containing a lithium composite oxide. The cathode active material according to claim 7, wherein the cathode active material is prepared by any one of claims 1 to 6. The secondary battery using the positive electrode containing the positive electrode active material of Claim 7.

Images