KR102267160B1 - Cathod active material and manufacturing method of the same - Google Patents

Abstract

The present invention relates to a positive electrode active material and a method for manufacturing the same, and more particularly, _{to a positive electrode active material comprising LiAlO 2} on the surface of an Al compound and residual lithium by reacting the same, and to a method for manufacturing the same.

Description

Cathode active material and manufacturing method thereof

The present invention relates to a positive electrode active material and a method for manufacturing the same, and more particularly, _{to a positive electrode active material including LiAlO 2} produced by reacting an Al compound and residual lithium on a surface thereof, and a method for manufacturing the same.

A method for preparing a lithium composite oxide generally includes preparing a transition metal precursor, mixing the transition metal precursor and a lithium compound, and then calcining the mixture.

In this case, LiOH and/or Li ₂ CO ₃ are used as the lithium compound. In general, when the Ni content of the cathode active material is 65% or less, Li ₂ CO ₃ is used, and when the Ni content is 65% or more, it is preferable to use LiOH because it is a low-temperature reaction. However, since the Ni rich system having a Ni content of 65% or more is a low-temperature reaction, there is a problem in that the amount of residual lithium present in the form _{of LiOH, Li 2} CO _{3 on the surface of the positive electrode active material is high.} Such residual lithium, ie, unreacted LiOH and Li ₂ CO ₃ , reacts with an electrolyte and the like in the battery to generate gas and cause swelling, thereby causing a problem in which high-temperature stability is seriously deteriorated. In addition, unreacted LiOH may cause gelation due to high viscosity when mixing the slurry before manufacturing the electrode plate.

In order to remove such unreacted Li, a water washing process is generally introduced, but in this case, the surface of the cathode active material is damaged during washing, thereby causing another problem in that capacity and rate characteristics are lowered and resistance is increased when stored at a high temperature.

An object of the present invention is to provide a novel positive electrode active material capable of improving lifespan characteristics, high temperature storage characteristics, and particle strength while removing unreacted Li, and a method for manufacturing the same.

The present invention provides a positive electrode active material including _{LiAlO 2} on the surface in order to solve the above problems.

The positive electrode active material according to the present invention is characterized in that it contains _{LiAlO 2 , which exhibits a peak at 2θ of 45 to 46 in XRD.}

The positive electrode active material according to the present invention is characterized in that it is represented by the following formula (1).

[Formula 1] Li _1+a Ni _b M1 _c M2 _d O ₂

(In Formula 1, a = 0, 0.75 ≤ b ≤ 0.95, b + c + d = 1,

M1 is any one or more selected from the group consisting of Co, Cr, Mo, Ti and Zr,

M2 is any one or more selected from the group consisting of Mn, Al, Cr, Mo, Ti and Zr)

It is characterized in that the residual lithium of the positive electrode active material according to the present invention is 0.6 wt% or less.

The positive electrode active material according to the present invention is characterized in that the particle strength is 150 MPa or more.

The present invention also

A first step of preparing a cathode active material;

There is provided a method for producing a cathode active material according to the present invention, comprising a second step of heat-treating a compound containing Al and the cathode active material.

In the method for manufacturing a cathode active material according to the present invention, the compound containing Al is Al(OH) ₃ , Al ₂ O ₃ , Al(NO ₃ ) ₃ , Al ₂ (SO ₄ ) ₃ , AlCl ₃ , AlH ₃ , AlF ₃ and AlPO _{4 It} is characterized in that it is selected from the group consisting of.

The method for producing a cathode active material according to the present invention is

between the first step and the second step

Step 1-1 of preparing a water washing solution while maintaining a constant temperature;

a first 1-2 step of adding a cathode active material to the washing solution and stirring;

Steps 1-3 of drying the washed positive electrode active material; It is characterized in that it further comprises.

In the method for manufacturing a cathode active material according to the present invention, the washing solution is distilled water or an aqueous alkali solution.

In the manufacturing method of the positive electrode active material according to the present invention, in the drying step, it is characterized in that vacuum drying is performed at a drying temperature of 80 to 200 ° C. and a drying time of 5 to 20 hours.

The cathode active material according to the present invention is doped with aluminum so that residual lithium present on the surface reacts with aluminum to form LiAlO ₂ , thereby exhibiting the effect of not only reducing residual lithium but also increasing particle strength.

1 shows the results of measuring XRD of the active materials prepared in Examples and Comparative Examples of the present invention.
Figure 2 shows the results of measuring the particle strength of the active material prepared in Example and Comparative Example of the present invention.
3 and 4 show the results of measuring the amount of residual lithium in the active materials prepared in Examples and Comparative Examples of the present invention.
5 shows the results of measuring the lifespan characteristics of the batteries including the active materials prepared in Examples and Comparative Examples of the present invention.

Hereinafter, the present invention will be described in more detail by way of Examples. However, the present invention is not limited by the following examples.

<Example> Concentration gradient cathode active material coating

20 liters of distilled water and 840 g of ammonia as a chelating agent were put in a batch reactor (capacity 70L, output of rotation motor 80W or more), and the motor was stirred at 400 rpm while maintaining the temperature in the reactor at 50°C.

As a second step, 2.2 liters/hour of a 2.5M aqueous solution of the first precursor mixed with nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 9: 1: 0, and a 28% aqueous ammonia solution of 0.15 liters/hour was continuously introduced into the reactor. In addition, a 25% concentration of sodium hydroxide aqueous solution was supplied to adjust the pH so that the pH was maintained at 11. The impeller speed was adjusted to 400 rpm. 27 L of the prepared first precursor aqueous solution, ammonia, and sodium hydroxide solution were continuously introduced into the reactor.

Next, as a third step, nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 65:15:20 were mixed in an aqueous solution for forming a concentration gradient layer at a concentration of 2.5M, and in a separate stirrer in addition to the batch reactor. After fixing the volume of the first precursor aqueous solution having a concentration of 2.5M to 10L, in which nickel sulfate, cobalt sulfate, and manganese sulfate prepared in the second step were mixed at a molar ratio of 9: 1: 0, at a rate of 2.2 liters/hour A second precursor aqueous solution was prepared by stirring while being added, and was introduced into the batch reactor at the same time. It was introduced into a batch reactor while mixing the aqueous solution for forming the concentration gradient layer until the mole ratio of nickel sulfate, cobalt sulfate, and manganese sulfate in the second precursor aqueous solution became 4: 2:4, which is the concentration of the shell layer, An aqueous ammonia solution having a concentration of 28% was added at a rate of 0.08 L/hour, and the sodium hydroxide solution was maintained so that the pH was 11. At this time, the second precursor aqueous solution, ammonia, and sodium hydroxide solution were 17L.

Next, as a fourth step, a third aqueous precursor solution in which nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in a molar ratio of 4:2:4 was added in a batch reactor until it occupied a volume of 5 L, and the reaction was carried out. After this was completed, a spherical nickel-manganese-cobalt composite hydroxide precipitate was obtained from a batch reactor.

The precipitated composite metal hydroxide was filtered, washed with water, and dried in a hot air dryer at 110° C. for 12 hours. The inner core layer was (Ni _0.9 Co _0.1 )(OH) ₂ and the outer shell layer was (Ni _0.9 Co _0.1 )(OH) A precursor powder in the form of a metal complex oxide having a continuous concentration gradient from ₂ to (Ni _0.4 Co _0.2 Mn _0.4 )(OH) _{2 was obtained.}

The metal composite hydroxide and lithium hydroxide (LiOH) were mixed in a molar ratio of 1:1.02, heated at a temperature increase rate of 2 °C/min, and calcined at 790 °C for 20 hours to form an inner core layer of Li(Ni _0.9 Co _0.1 )O ₂ As the outer shell layer of the furnace, a cathode active material powder having a continuous concentration gradient from _{Li(Ni 0.9} Co _0.1 )O ₂ to Li(Ni _0.4 Co _0.2 Mn _0.4 )O _{2 was obtained.}

After dry or wet coating the cathode active material particles with an Al compound, heat treatment was performed at 720°C.

<Example> Synthesis of NCA particles

In order to prepare an NCA-based cathode active material, a NiCo(OH) ₂ precursor was first prepared by a co-precipitation reaction. After mixing the metal composite hydroxide and lithium hydroxide in a molar ratio of 1:1.02, the mixture was heated at a temperature increase rate of 2°C/min and calcined at 750°C for 20 hours to obtain a cathode active material powder.

After dry or wet coating of the cathode active material particles with an Al compound, heat treatment was performed at 720 °C.

<Experimental Example> Measurement of XRD characteristics

XRD of the active materials prepared in Example 2 and Comparative Example 6 were measured, and the results are shown in FIG. 1 .

In FIG. 1 , it can be seen that, in the case of the particles prepared in Example 2 of the present invention, a peak is observed at 45° to 46°, unlike Comparative Example.

<Experimental Example> Particle strength measurement

The particle strength of the active materials prepared in Example 10 and Comparative Example 6 was measured, and the results are shown in FIG. 2 .

It can be seen from FIG. 2 that in the case of the particles prepared in Example 2 of the present invention, the particle strength is improved by about 20% compared to the particles of Comparative Example.

<Experimental Example> Measurement of unreacted lithium

Measurement of unreacted lithium is measured by the amount of 0.1M HCl used until pH 4 is obtained by pH titration. First, 5 g of the positive electrode active material is put into 100 ml of DIW, stirred for 15 minutes, filtered, and after taking 50 ml of the filtered solution, 0.1 M HCl is added thereto to measure the HCl consumption according to the pH change to determine Q1 and Q2, , unreacted LiOH and Li ₂ CO ₃ were calculated according to the formula below.

M1 = 23.94 (LiOH Molecular weight)

M2 = 73.89 (Li2CO3 Molecular weight)

SPL Size = (Sample weight × Solution Weight) / Water Weight

LiOH(wt %) = [(Q1-Q2)×C×M1×100]/(SPL Size×1000)

Li ₂ CO ₃ (wt%)=[2×Q2×C×M2/2×100]/(SPL Size×1000)

_{The results of measuring the concentrations of unreacted LiOH and Li 2} CO ₃ in the NCA-based lithium composite oxides prepared in Examples and Comparative Examples by applying this method are shown in Tables 2 and 3 below.

In FIG. 3 , in Comparative Example 4, no washing or surface treatment was performed, so the residual lithium was measured to be high, and in Example 7, in which heat treatment was performed after coating an aluminum compound, the residual lithium was reduced compared to Comparative Example 4.

In addition, in Example 3, in which an aluminum compound was coated with a concentration gradient type NCM positive active material in FIG. 3 and then heat-treated, compared to Comparative Example 2 in which no post-treatment was performed, residual lithium was improved.

<Experimental example> Evaluation of charging and discharging characteristics

Each coin cell was prepared using the positive electrode active material prepared in Examples and Comparative Examples as the positive electrode and lithium metal as the negative electrode, and C/10 charging and C/10 discharging rates (1 C = 150 mA/g) The results of the charging/discharging experiment between 3 and 4.3 V are shown in FIG. 5 and Tables 2 and 4 above.

4 , it can be seen that in the case of the embodiment in which Al coating was performed after washing with water, the lifespan characteristics were excellent. In FIG. 4 , Comparative Example 3 and Comparative Example 5 are concentration gradient type NCM and NCA positive electrode active materials that have been washed with water, respectively. After washing with water, Example 5, which is a concentration gradient type NCM, and Example 8, which is an NCA, which were coated with aluminum, had improved lifespan characteristics.

<Experimental example> Impedance measurement results before and after high temperature storage

The impedance before and after high-temperature storage of Example 3, which is an NCM-based cathode active material having a continuous concentration gradient, was measured, and the results are shown in Table 2 and FIG. 5 .

In FIG. 5 , it can be seen that the impedance before and after storage of Example 3 in which the heat treatment was performed after the Al compound coating was reduced compared to Comparative Example 2 in which washing and surface treatment were not performed.

Claims (6)

A core layer, at least one of a transition metal has a concentration gradient having a continuous concentration gradient, and a shell layer,
Further comprising _{LiAlO 2} on the surface of the shell layer,
The content of residual lithium present in the form _{of LiOH and Li 2} CO ₃ on the surface of the cathode active material relative to the total content of the cathode active material is 0.0141 wt% or less,
The particle strength is more than 150 MPa,
Represented by the following formula (1),
Concentration gradient type positive electrode active material:
[Formula 1] Li _1+a Ni _b M1 _c M2 _d O ₂
(In Formula 1, a = 0, 0.75≤b≤0.95, b+c+d=1,
M1 is any one or more selected from the group consisting of Co, Cr, Mo, Ti and Zr,
M2 is any one or more selected from the group consisting of Mn, Al, Cr, Mo, Ti and Zr).
The method of claim 1,
_{including LiAlO 2} in which 2θ in XRD peaks at 45° to 46°,
Concentration gradient type positive electrode active material.
In the method for manufacturing the concentration gradient type positive electrode active material according to claim 1,
preparing a cathode active material by mixing and firing a precursor in the form of a metal complex hydroxide and a lithium compound;
adding the prepared positive electrode active material to a washing solution and washing with water;
drying the washed positive electrode active material; and
Including; mixing and stirring the compound containing Al and the dried positive electrode active material;
A method for manufacturing a concentration gradient type positive electrode active material.
4. The method of claim 3,
The compound containing Al is selected from the group consisting of Al(OH) ₃ , Al ₂ O ₃ , Al(NO ₃ ) ₃ , Al ₂ (SO ₄ ) ₃ , AlCl ₃ , AlH ₃ , AlF ₃ and AlPO _{4 ,} etc. felled,
A method for manufacturing a concentration gradient type positive electrode active material.
4. The method of claim 3,
The washing solution is distilled water or an aqueous alkali solution,
A method for manufacturing a concentration gradient type positive electrode active material.
4. The method of claim 3,
The step of drying the washed positive electrode active material is vacuum drying at a drying temperature of 80 ~ 200 ℃, drying time of 5 ~ 20 hours,
A method for manufacturing a concentration gradient type positive electrode active material.

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