KR101937926B1 - Manufacturing method of a positive electrode active material for rechargable lithium battery, positive electrode active material for rechargable lithium battery manufacture using the same, and rechargable lithium battery including the same - Google Patents

Abstract

According to an embodiment of the present invention, there is provided a method for preparing a cathode active material for a lithium secondary battery, comprising: preparing two or more metal salt aqueous solutions each containing Ni, Co, and Mn in different ratios; Mixing the at least two aqueous metal salt solutions to prepare an active material precursor; And adding a lithium source material to the active material precursor to produce a lithium composite oxide.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode active material for a lithium secondary battery manufactured using the same, and a lithium secondary battery comprising the same. BACKGROUND ART THE SAME, AND RECHARGABLE LITHIUM BATTERY INCLUDING THE SAME}

The present invention relates to a method for producing a cathode active material for a lithium secondary battery, a cathode active material for a lithium secondary battery manufactured using the same, and a lithium secondary battery comprising the cathode active material.

The lithium secondary battery is manufactured as a high-performance small-sized battery, and is used not only as an energy storage source for mobile information communication devices including smart phones, notebook computers, and computers, but recently, Vehicle, hybrid electric vehicle, and the like.

The positive electrode active material, which is one of the constituent elements of such a lithium secondary battery, has a structure capable of releasing / inserting lithium ions in general. Among them, the cathode active material having a high manganese content shows high stability and low capacity. However, in order to realize the above-mentioned high-power type large-sized battery, it is necessary to develop a cathode active material having excellent capacity and stability.

On the other hand, the higher the nickel content of the positive electrode active material, the higher the capacity thereof. However, it is pointed out that the stability is low as compared with the cathode active material having a high manganese content, and the electrochemical capacity is lowered due to repeated charge and discharge, so that the life characteristic is poor.

Specifically, the chemical change for the positive electrode active material containing nickel, then the oxidation number of nickel ions with lithium ions desorbed from the Ni ²⁺ is changed into Ni ^{+ 4, 4 +} Ni is unstable, so as lithium (NiO) oxide .

Since oxygen is generated during such a chemical change, the stability is evaluated to be low, and the lithium oxide is stable and can not exhibit its electrochemical capacity. In addition, since such a phenomenon is intensified at a higher temperature than a normal temperature, there is a problem that the stability at a high temperature and the life characteristics are further deteriorated.

In this regard, various researches have been made to improve the lifetime characteristics while ensuring a high capacity of the lithium secondary battery, but a fundamental solution to the above-mentioned problems has not yet been proposed.

The present invention provides a method for producing a positive electrode active material for a lithium secondary battery having improved electrochemical characteristics, a positive electrode active material for a lithium secondary battery manufactured using the same, and a lithium secondary battery comprising the same.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the precise form disclosed. It can be understood.

According to an embodiment of the present invention, there is provided a method of preparing a cathode active material for a lithium secondary battery, comprising: preparing two or more metal salt aqueous solutions in which Ni, Co, and Mn are mixed at different ratios; Mixing the at least two aqueous metal salt solutions to prepare an active material precursor; And adding a lithium source material to the active material precursor to produce a lithium composite oxide.

The active material precursor may include at least two regions having different contents of Ni, Co, and Mn from the center portion to the surface portion.

The lithium source material may include lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), and combinations thereof.

The molar ratio of the lithium source material to the active material precursor may range from 0.95: 1 to 1.2: 1.

The step of preparing the lithium composite oxide may include mixing and firing the active material precursor and the lithium source material.

In the firing step, the metal included in the active material precursor may be diffused.

The firing step may be performed at a temperature ranging from 650 to 950 占 폚.

The calcining step may be performed for 5 to 20 hours.

The lithium composite oxide may be a layered compound.

And a cathode active material for a lithium secondary battery manufactured by the above-described manufacturing method.

anode; cathode; And an electrolyte positioned between the positive electrode and the negative electrode, and may include the above-mentioned positive electrode active material.

According to the present invention, the initial capacity, lifetime characteristics, and residual lithium value including the cathode active material for a lithium secondary battery can be improved.

1 is an EDS cross-sectional image according to Example 1. Fig.
2 is an EDS cross-sectional image according to the second embodiment.
3 is an EDS cross-sectional image according to Embodiment 3. Fig.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, the well-known functions or constructions will not be described in order to clarify the present invention.

In order to clearly illustrate the present disclosure, portions that are not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification. In addition, since the sizes and thicknesses of the individual components shown in the drawings are arbitrarily shown for convenience of description, the present invention is not necessarily limited thereto.

A method of preparing a cathode active material for a lithium secondary battery according to an embodiment of the present invention includes preparing two or more metal salt aqueous solutions in which Ni, Co, and Mn are mixed in different ratios, mixing the two or more metal salt aqueous solutions, Producing; And adding a lithium source material to the active material precursor to produce a lithium composite oxide.

In preparing the metal salt aqueous solution, a solution containing a compound including Ni, Co, and Mn as a metal salt is prepared. The aqueous metal salt solution according to one embodiment may include two or more aqueous metal salt solutions in which Ni, Co, and Mn are mixed in different ratios.

Specifically, NiSO ₄ · 6H ₂ O is used as a raw material of nickel, CoSO ₄ · 7H ₂ O is used as a raw material of cobalt, and MnSO ₄ · H ₂ O is used as a raw material of manganese. Two or more different aqueous metal salt solutions were prepared.

An active material precursor including Ni, Co, and Mn can be prepared by injecting two or more aqueous metal salt solutions, a chelating agent, and a basic aqueous solution prepared through the steps described above into a reactor.

Specifically, a solution in which NaOH and NH ₄ OH are mixed at a molar ratio of 1 to 3: 1 is prepared, and then the solution is reacted with a metal salt solution having a content of Ni, Co, and Mn of 2 or more. Whereby an active precursor comprising Ni, Co, and Mn can be formed.

The active material precursor prepared according to an embodiment of the present invention may include at least two regions having different concentrations of Ni, Co and Mn from the central portion to the surface portion. In other words, the active material precursor may be represented by Ni _x Co _y Mn _z (OH) ₂ and may include two or more regions having different x, y, and z values.

The active material precursor thus prepared is mixed with a lithium source material (LiOH, Li ₂ CO _{3 ,} or a combination thereof).

The mixture of the active material precursor and the lithium source material may further include a doping raw material. The doping source material may be a compound containing at least one element selected from Zr, Ti, Mg, Al, Ni, Mn, Zn, Fe, Cr, Mo and W or a mixture of the above compounds.

The active material precursor and the lithium raw material may be mixed in a molar ratio of 0.95: 1 to 1.2: 1. The mixed active material precursor and the lithium raw material can be calcined in an atmosphere or an oxygen atmosphere for 5 to 20 hours at a temperature range of 650 to 950 캜 to form a lithium composite oxide.

According to the above-described firing step, diffusion of the metal can occur between two or more regions containing the active material precursor and having different compositions. An active material precursor having two or more regions represented by Ni _x Co _y Mn _z (OH) ₂ and having different x, y and z values according to diffusion can be formed of a lithium complex oxide having a uniform composition.

The finally obtained lithium composite oxide may be represented by the following Formula 1, and the cathode active material for a lithium secondary battery according to an embodiment of the present invention may include the lithium composite oxide.

Li _x Ni _a Co _b Mn _c M _{d d} O ₂

In the formula 1, M1 is Zr, Ti, Mg, Al, Ni, Mn, Zn, Fe, Cr, Mo, or W; 0.90 = x = 1.07, 0.7 = <c = 0.3, 0 = d <0.01, and a + b + c + d = 1.

In general, lithium carbonate (Li ₂ CO ₃ ) and lithium hydroxide (LiOH) lithium inevitably exist in the surface of the lithium composite oxide containing Ni, Co, and Mn inevitably, .

A battery in which a lithium composite oxide in which residual lithium is present on the surface is applied to a positive electrode as a positive electrode active material causes generation of gas by residual lithium during charging and discharging. Of specifically residual LiOH lithium may react with the CO ₂ that is caused by air in the CO ₂ or carbonate-based electrolyte solution decomposed to form Li ₂ CO _3. Li ₂ CO ₃ can also react with HF to generate CO ₂ gas. Such gas generation causes problems such as a decrease in the initial capacity of the battery and a decrease in initial charge / discharge efficiency. However, the cathode active material produced by the production method according to an embodiment of the present invention can reduce residual lithium.

The cathode active material prepared according to one embodiment of the present invention can be usefully used for the anode of a lithium secondary battery. The lithium secondary battery includes a cathode and an electrolyte including an anode active material together with a cathode.

The positive electrode is prepared by preparing a positive electrode active material composition by mixing a positive electrode active material according to an embodiment of the present invention, a conductive material, a binder and a solvent, and then directly coating and drying on the aluminum current collector. Or by casting the positive electrode active material composition on a separate support, then peeling the support from the support, and laminating the resulting film on an aluminum current collector.

The conductive material may be carbon black, graphite, metal powder, and the binder may include vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene And mixtures thereof. Further, N-methylpyrrolidone, acetone, tetrahydrofuran, decane and the like are used as the solvent. At this time, the content of the cathode active material, the conductive material, the binder and the solvent is used at a level normally used in a lithium secondary battery.

The negative electrode is prepared by mixing an anode active material, a binder and a solvent in the same manner as in the case of the anode. The anode active material composition is directly coated on the copper current collector or cast on a separate support, and the anode active material film, Laminated. 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. For example, lithium metal, lithium alloy, coke, artificial graphite, natural graphite, organic polymeric compound combustion material, . The conductive material, the binder and the solvent are used in the same manner as in the case of the above-mentioned anode.

The separator may be polyethylene, polypropylene, polyvinylidene fluoride or a multilayer film of two or more thereof. The separator may be a polyethylene / polypropylene double-layer separator, It is needless to say that a mixed multilayer film such as a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator and the like can be used.

As the electrolyte to be charged into the lithium secondary battery, a non-aqueous electrolyte or a known solid electrolyte may be used, and a lithium salt dissolved therein may be used.

The solvent of the non-aqueous electrolyte is not particularly limited, but cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and 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? -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 and the like can be used. These may be used singly or in combination. Particularly, a mixed solvent of cyclic carbonate and chain carbonate can be preferably used.

As the electrolyte, a gelated 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.

Wherein the lithium salt is selected from the group consisting of 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 , LiCl, and LiI.

Hereinafter, the embodiment will be described in detail. The following examples are illustrative of the present invention only and are not intended to limit the scope of the present invention.

First, aqueous solutions of metal salts of 1 mol / L to 3 mol / L are prepared using NiSO ₄ , CoSO ₄ and MnSO ₄ . At least two aqueous metal salt solutions having different ratios of NiSO ₄ , CoSO ₄ and MnSO ₄ are prepared. NH ₄ OH and NaOH were mixed at a molar ratio of 0.2 to 2: 2. Thereafter, two or more aqueous metal salt solutions having different concentrations, NH ₄ OH and NaOH were slowly stirred to prepare an active material precursor solution. Thereafter, the obtained active material precursor solution was removed from moisture and dried in an oven at 110 ° C. for 12 hours or more to obtain an active material precursor. The obtained precursor of the active material may be represented by Ni _x Co _y Mn _z (OH) ₂ and may include two or more regions having different values of x, y and z.

The active material precursors according to Examples 1, 2, and 3 thus prepared were as shown in Figs. 1, 2, and 3, respectively. It was confirmed that each of Example 1, Example 2, and Example 3 can have the compositions described in Tables 1, 2, and 3 according to the positions shown in Figs. That is, it has been confirmed that the active material precursor according to an embodiment of the present invention includes at least two regions having different contents of Ni, Co, and Mn.

Example 1 Mn (at%) Co (at%) Ni (at%) One 17.21 11.79 71 2 17.05 11.69 71.26 3 16.88 11.91 71.21 4 16.85 11.81 71.34 5 16.26 11.49 72.25 6 16.37 11.82 71.80 7 17.37 12.67 69.97 8 17.90 12.76 69.34 9 16.36 12.54 71.10 10 16.28 12.69 71.04

Example 2 Mn Co Ni One 11.25 8.49 80.26 2 12.24 9.78 77.98 3 13.28 9.97 76.75 4 13.61 9.69 76.70 5 14.09 9.80 76.12 6 14.72 9.64 75.64 7 13.55 9.92 76.53 8 10.91 9.45 79.64 9 10.43 9.28 80.29 10 6.36 8.52 85.13

Example 3 Mn Co Ni One 9.03 6.10 85.87 2 10.99 6.85 83.17 3 11.97 7.67 81.36 4 13.48 7.23 81.29 5 14.24 7.54 80.22 6 8.98 6.69 85.33 7 5.24 6.41 89.35 8 4.58 5.77 90.65 9 4.08 5.78 91.15 10 3.97 5.30 91.73

Then, the active material precursor according to Examples 1 to 3 was mixed with 0.95 to 1.1 mol of LiOH and fired at a temperature of 650 to 950 ° C to obtain a lithium composite oxide, and the resulting cathode active material was subjected to electrochemical evaluation Respectively.

Aqueous metal salt solution 1 Aqueous metal salt solution 2 Aqueous metal salt solution 3 Average composition Comparative Example 1 _{Ni 0 .7 Co 0 .125 Mn 0} .175 - - _{Ni 0 .7 Co 0 .125 Mn 0} .175 Example 1 _{Ni 0 .9 Co 0 .05 Mn 0} .05 _{Ni 0 .5 Co 0 .2 Mn 0} .3 - _{Ni 0 .7 Co 0 .125 Mn 0} .175 Comparative Example 2 _{Ni 0 .8 Co 0 .07 Mn 0} .13 _{Ni 0 .8 Co 0 .07 Mn 0} .13 Example 2 _{Ni 0 .95 Co 0 .02 Mn 0} .03 _{Ni 0 .8 Co 0 .08 Mn 0} .12 _{Ni 0 .55 Co 0 .17 Mn 0} .28 _{Ni 0 .8 Co 0 .07 Mn 0} .13 Comparative Example 3 _{Ni 0 .85 Co 0 .06 Mn 0} .09 _{Ni 0 .85 Co 0 .06 Mn 0} .09 Example 3 _{Ni 0 .95 Co 0 .02 Mn 0} .03 _{Ni 0 .9 Co 0 .03 Mn 0} .07 _{Ni 0 .65 Co 0 .13 Mn 0} .22 _{Ni 0 .85 Co 0 .06 Mn 0} .09

Coin cells were prepared for Comparative Examples 1 to 3 and Examples 1 to 3 shown in Table 4, and electrochemical characteristics were evaluated. The coin cell was fabricated using CR-2032, and the initial capacity was measured through the first 0.1C charge / discharge. Residual lithium was obtained by immersing the obtained cathode active material in ultrapure water and stirring for 5 minutes, separating the cathode active material from water and measuring LiOH / Li ₂ CO ₃ dissolved in the water. The cycle life evaluation was carried out by charging / discharging 50 times at a current of 0.5 C at 25 캜. The results are shown in Table 5 below.

Average composition Initial capacity (0.1 C) Residual lithium (LiOH / Li ₂ CO ₃₎ Life characteristics Comparative Example 1 _{Ni 0 .7 Co 0 .125 Mn 0} .175 190.1 mAh / g 9,521 / 4,982 95.8 Example 1 _{Ni 0 .7 Co 0 .125 Mn 0} .175 192.5 mAh / g 8,124 / 4,012 97.1 Comparative Example 2 _{Ni 0 .8 Co 0 .07 Mn 0} .13 201.5 mAh / g 12,021 / 6,872 92.6 Example 2 _{Ni 0 .8 Co 0 .07 Mn 0} .13 203.6 mAh / g 9,756 / 5,125 95.3 Comparative Example 3 _{Ni 0 .85 Co 0 .06 Mn 0} .09 207.4 mAh / g 13,125 / 7,532 90.2 Example 3 _{Ni 0 .85 Co 0 .06 Mn 0} .09 209.7 mAh / g 11,354 / 5,865 94.3

The results are shown in Table 5. As can be seen from Table 5, Examples 1, 2 and 3 including the cathode active material obtained by using the active material precursor according to the Examples have improved initial capacities, compared with Comparative Examples 1, 2 and 3 having the same average composition, It was confirmed that the residual lithium amount was reduced and the lifetime characteristics were improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It is obvious to those who have. Accordingly, it should be understood that such modifications or alterations should not be understood individually from the technical spirit and viewpoint of the present invention, and that modified embodiments fall within the scope of the claims of the present invention.

Claims (11)

Preparing two or more metal salt aqueous solutions in which Ni, Co, and Mn are mixed at different ratios;
Mixing the at least two aqueous metal salt solutions to prepare an active material precursor; And
And adding a lithium source material to the active material precursor to produce a lithium composite oxide,
The difference in content of Mn between the central portion and the surface portion of the active material precursor is 6 at% or less, the difference in content of Ni is 6 at% or less,
Wherein the active material precursor includes at least two regions having different contents of Ni, Co, and Mn from the center portion to the surface portion,
Wherein the content of Ni is at least three regions different from each other from the center portion to the surface portion, and the Ni content is high in order of the center portion> the surface portion> the middle portion. delete The method of claim 1,
Wherein the lithium source material comprises lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), and combinations thereof. The method of claim 1,
Wherein the molar ratio of the lithium source material to the active material precursor is 0.95: 1 to 1.2: 1. The method of claim 1,
Wherein the step of preparing the lithium composite oxide comprises mixing and firing the active material precursor and the lithium source material, and firing the lithium composite material. The method of claim 5,
Wherein the metal contained in the active material precursor is diffused in the firing step. The method of claim 5,
Wherein the calcining step is performed in a temperature range of 650 to 950 캜. The method of claim 5,
Wherein the calcining step is performed for 5 to 20 hours. The method of claim 1,
Wherein the lithium composite oxide is a layered compound. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 9. anode; cathode; And an electrolyte positioned between the anode and the cathode,
The lithium secondary battery of claim 10, wherein the positive electrode comprises the positive electrode active material.

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