LITHIUM COMPOUND, NICKEL-BASED CATHODE ACTIVE MATERIAL, METHOD FOR PREPARING LITHIUM OXIDE, METHOD FOR PREPARING NICKEL-BASED CATHODE ACTIVE MATERIAL, AND SECONDARY BATTERY USING SAME

Abstract

The present invention relates to a lithium compound, a nickel-based cathode active material, a method for preparing lithium oxide, a method for preparing a nickel-based cathode active material, and a secondary battery using same. The lithium compound includes primary particles of Li.sub.2O having an average particle diameter (D50) of less than or equal to 5 μm; and secondary particles composed of the primary particles.

Claims

1. A lithium compound, comprising Li.sub.2O primary particles having an average particle diameter (D50) of less than or equal to 5 μm; and secondary particles composed of the primary particles.

2. The lithium compound of claim 1, wherein the secondary particle has a spherical shape.

3. The lithium compound of claim 1, wherein the average particle diameter (D50) of the secondary particles is 10 to 100 μm.

4. The lithium compound of claim 3, wherein the average particle diameter (D50) of the secondary particles is 10 to 30 μm.

5. A nickel-based cathode active material derived from a lithium compound including primary Li.sub.2O particles having an average particle diameter (D50) of less than or equal to 5 μm and secondary particles composed of the primary particles; and a nickel raw material.

6. The nickel-based cathode active material of claim 5, wherein the cathode active material is Li.sub.2NiO.sub.2, and Dmin is greater than or equal to 5 μm.

7. The nickel-based cathode active material of claim 6, wherein the cathode active material comprises a residual lithium compound of less than or equal to 2.5 wt % based on 100 wt % of the total weight.

8. A method for preparing lithium oxide, comprising reacting hydrogen peroxide (H.sub.2O.sub.2) and lithium hydroxide (LiOH) to obtain over-lithiated oxide (Li.sub.2O.sub.2); and heat-treating the over-lithiated oxide to obtain lithium oxide (Li.sub.2O), wherein in the reacting of the hydrogen peroxide (H.sub.2O.sub.2) and lithium hydroxide (LiOH) to obtain a over-lithiated oxide (Li.sub.2O.sub.2), a mole ratio (Li/H.sub.2O.sub.2) of lithium of lithium hydroxide to hydrogen peroxide is 1.9 to 2.4.

9. The method of claim 8, wherein in the reacting of the hydrogen peroxide (H.sub.2O.sub.2) and lithium hydroxide (LiOH) to obtain a over-lithiated oxide (Li.sub.2O.sub.2), the reaction temperature is 40 to 60° C.

10. The method of claim 8, wherein in the reacting of hydrogen peroxide (H.sub.2O.sub.2) and lithium hydroxide (LiOH) to obtain over-lithiated oxide (Li.sub.2O.sub.2), the reaction of hydrogen peroxide (H.sub.2O.sub.2) and lithium hydroxide (LiOH) is accompanied by stirring at 500 rpm or more.

11. The method of claim 8, wherein the heat-treating of the over-lithiated oxide to obtain lithium oxide (Li.sub.2O) is performed at 400 to 600° C. in an inert atmosphere.

12. A method for preparing a nickel-based cathode active material, comprising reacting hydrogen peroxide (H.sub.2O.sub.2) and lithium hydroxide (LiOH) to obtain over-lithiated oxide (Li.sub.2O.sub.2); heat-treating the over-lithiated oxide to obtain lithium oxide (Li.sub.2O); and firing the lithium oxide and nickel raw material to obtain a nickel-based cathode active material; wherein in the reacting of the hydrogen peroxide (H.sub.2O.sub.2) and lithium hydroxide (LiOH) to obtain a over-lithiated oxide (Li.sub.2O.sub.2), a mole ratio (Li/H.sub.2O.sub.2) of lithium of lithium hydroxide to hydrogen peroxide is 1.9 to 2.4.

13. (canceled)

Description

DESCRIPTION OF THE DRAWINGS

[0054] FIG. 1 is a schematic flowchart of a method for preparing lithium oxide according to an embodiment of the present invention.

[0055] FIG. 2 is a SEM photograph of the particle shape according to the result of Experiment 2.

[0056] FIG. 3 is a SEM photograph of particle according to Experiment 3.

[0057] FIG. 4 is a schematic view of a co-precipitation reactor used in an embodiment of the present invention.

[0058] FIG. 5 is an SEM photograph of the particles according to Experiment 4.

[0059] FIG. 6 is a schematic view of a furnace designed for Li.sub.2O preparation.

[0060] FIG. 7 is a SEM photograph after mixing the raw materials in Experiment 6, and FIG. 8 is a SEM photograph of LNO synthesized after sintering.

[0061] FIG. 9 is a charge/discharge curve of the coin cell manufactured in Experiment 6.

[0062] FIG. 10 is a SEM photograph of commercially available Li.sub.2O (left) and a SEM photograph of Li.sub.2O according to the present example.

MODE FOR INVENTION

[0063] Hereinafter, embodiments of the present invention are described in detail. However, these embodiments are exemplary, the present invention is not limited thereto and the present invention is defined by the scope of claims.

[0064] 1. Li/H.sub.2O.sub.2 Ratio, Temperature Experiment

[0065] Experiment Method

[0066] After introducing LH powder and H.sub.2O.sub.2, a stirring reaction was started, wherein the reaction time was 60 minutes.

[0067] The resultant was filtered with a vacuum-filtering device to recover the Li.sub.2O.sub.2 powder. The recovered powder was dried in a 130° C. vacuum oven for 3 hours. The powder was quantitatively analyzed in a Rietveld refinement method after the XRD measurement. (HighScore Plus Program made by Malvern Panalytical Ltd. was used)

[0068] Li.sub.2O.sub.2 acquisition yield=(Li.sub.2O.sub.2 acquisition amount)/(Li.sub.2O.sub.2 acquisition amount when the injected Li raw material is 100% converted), wherein a temperature is a predetermined temperature, and a measured temperature may be 2 to 3° C. lower than that.

[0069] Table 1 shows results with respect to purity of the synthesized Li.sub.2O.sub.2 powders.

TABLE-US-00001 TABLE 1 Li.sub.2O.sub.2 purity [wt %] Li/H.sub.2O.sub.2 LiOH—H.sub.2O H.sub.2O.sub.2 (34.5%) Temperature (° C.) [mol/mol] [g] [g] 25 40 50 60 70 80 1.4 70 117 65.3 98.6 98.4 93.3 90.5 98.3 1.6 80 117 61.5 99 97 95.6 91.7 98.7 1.7 85 117 68.2 96.8 97.4 97.7 95.1 97 1.8 90 117 78.7 96.4 95.9 98 91.9 97.2 1.9 95 117 90.8 98.4 96.3 98.3 93.2 96.9 2.2 110 117 97.4 97.4 96.1 97.2 89.1 90.9 2.4 120 117 97.1 96.4 95.4 96.5 84.3 94.7 2.6 130 117 97.3 94.3 94.4 95.1 89.2 93.4 2.8 140 117 59.1 84.6 80.2 94.4 83.5 77.7 3.0 150 117 72.2 61.6 61.2 87.9 67.3 65.9

[0070] Table 2 shows weights of the synthesized dry powders. The weights of the synthesized dry powders need to be compared with Li.sub.2O.sub.2 acquisition amounts when theoretically 100% converted. Since the obtained powders are not 100% Li.sub.2O.sub.2, simply a heavy weight is not good.

TABLE-US-00002 TABLE 2 Weight of Synthesized Li.sub.2O.sub.2 Theoretical H.sub.2O.sub.2 [g], dry powder Li.sub.2O.sub.2 Li/H.sub.2O.sub.2 LiOH—H.sub.2O (34.5%) Temperature (° C.) amount [mol/mol] [g] [g] 25 40 50 60 70 80 [g] 1.4 70 117 30.816 25.43 27.6 25.66 27.84 24.71 38.3 1.6 80 117 29.896 29.62 31.53 29.63 31.4 29.3 43.7 1.7 85 117 33.776 31.49 34.14 31.24 34.44 34.9 46.5 1.8 90 117 35.597 33.77 35.53 34.84 38.09 36.39 49.2 1.9 95 117 33.804 34.56 38.69 37.59 40.47 38.43 51.9 2.2 110 117 40.18 43.44 46.44 45.25 47.98 46.99 60.1 2.4 120 117 44.42 47.28 48.98 48.77 50.73 50.34 65.6 2.6 130 117 45.53 50.16 52.7 51.73 53.31 50.99 71.1 2.8 140 117 61.53 53.22 54.83 53.15 55.61 59.46 76.5 3.0 150 117 57.88 56.73 61.4 60.19 59.22 57.32 82.0

[0071] The results of Tables 1 and 2 may be used to calculate the Li.sub.2O.sub.2 acquisition yields, and the results are shown in Table 3. Specifically, the results of Table 3 were obtained by multiplying the results of Table 1 with the results of Table 2 and dividing the products by theoretical Li.sub.2O.sub.2 amounts.

TABLE-US-00003 TABLE 3 H.sub.2O.sub.2 Li.sub.2O.sub.2 acquisition yield [%] Li/H.sub.2O.sub.2 LiOH—H.sub.2O (34.5%) Temperature (° C.) [mol/mol] [g] [g] 25 40 50 60 70 80 1.4 70 117 52.6 65.5 71.0 62.6 65.8 63.5 1.6 80 117 42.0 67.1 69.9 64.8 65.8 66.1 1.7 85 117 49.6 65.6 71.6 65.7 70.5 72.9 1.8 90 117 56.9 66.2 69.3 69.4 71.1 71.9 1.9 95 117 59.1 65.5 71.7 71.1 72.6 71.7 2.2 110 117 65.1 70.4 74.2 73.1 71.1 71.0 2.4 120 117 65.7 69.5 71.2 71.7 65.2 72.7 2.6 130 117 62.3 66.6 70.0 69.2 66.9 67.0 2.8 140 117 47.5 58.8 57.5 65.6 60.7 60.4 3.0 150 117 51.0 42.6 45.8 64.5 48.6 46.1

[0072] At a low temperature, since LH was precipitated and not converted into Li.sub.2O.sub.2, Li.sub.2O.sub.2 purity was decreased. At a high temperature, H.sub.2O.sub.2 was decomposed, decreasing the Li.sub.2O.sub.2 purity.

[0073] When a Li/H.sub.2O.sub.2 ratio was low, a Li.sub.2O.sub.2 production yield was expected to decrease due to its high dissolution loss in H.sub.2O.sub.2. When the Li/H.sub.2O.sub.2 ratio was high, LH was precipitated, decreasing the Li.sub.2O.sub.2 purity.

[0074] An optimal ratio obtained therefrom is shown in Table 4.

TABLE-US-00004 TABLE 4 Parameter Temperature range Li/H.sub.2O.sub.2 mole ratio Optimal synthesis range 40° C. to 60° C. 1.9 to 2.4

2. Reaction Time Experiment

[0075] Li.sub.2O.sub.2 was precipitated at 60° C. by controlling reaction time within various ranges as shown in Table 5 below. A specific method was the same as in Experiment 1.

TABLE-US-00005 TABLE 5 XRD analysis (wt %) Particle size observation Reaction time Li.sub.2O.sub.2 D50 [um] 10 min. 98.6 90 30 min. 97.5 90 60 min. 98.3 100 90 min. 99.1 90 “+60 min. waiting” 97.7 105

[0076] FIG. 2 is a SEM photograph showing a particle shape according to the result of Experiment 2.

[0077] At the 60° C., a reaction was completed within a short time of 10 minutes. After waiting for 60 minutes, the purity decreased. As the waiting time increased, the Li.sub.2O.sub.2 purity decreased. The reason is that LiOH increased according to decomposition of hydrogen peroxide. There was almost no difference in particle size and shape.

[0078] Table 6 shows the results of Experiment 2.

TABLE-US-00006 TABLE 6 Parameter Reaction time Temperature Optimal synthesis range 10 minutes to 90 minutes Irrelevant

3. Reactor Rpm Influence Experiment

[0079] A shape change according to rpm of a reactor was examined. Li.sub.2O.sub.2 with purity of 98% or higher was synthesized regardless of rpm. FIG. 3 is a SEM photograph showing particles of Experiment 3.

[0080] There was no shape change at greater than or equal to 500 rpm. The particles had a nonuniform size at 150 rpm.

[0081] When rpm was controlled to be greater than or equal to 500, desired effects were expected to be obtained.

4. Synthesis Experiment Using Co-Precipitation Reactor

[0082] FIG. 4 is a schematic view of a co-precipitation reactor used in an embodiment of the present invention.

[0083] Specifically, a co-precipitation reactor used for synthesizing a secondary battery cathode precursor was used to synthesize Li.sub.2O.sub.2. The reactor and an impeller had shapes shown in FIG. 4.

[0084] In order to shorten the reaction time, a method of injecting the hydrogen peroxide solution was changed.

[0085] A quantitative injection was basically used, but in order to shorten the reaction time, the hydrogen peroxide solution was added manually and then added with a quantitative pump, followed by reacting them.

[0086] The results are shown in Table 7.

TABLE-US-00007 TABLE 7 D = 80 cm, H2O2 injection LiOH—H.sub.2O H.sub.2O.sub.2 T = 10 cm method and Li.sub.2O.sub.2 Li.sub.2O Li.sub.2O.sub.2 (98.5%) (34.5%) T. Vel. reaction time D50 D50 purity rpm [kg] [kg] [m/sec] min [um] [um] [wt %] Remarks 150 3 3.4 0.785 Quantitative 50 35 98.6 a injection (15 min) + 60 min reaction 500 3 3.4 2.618 Quantitative 30 21 97.5 b injection (15 min) + 60 min reaction 750 3 3.4 3.927 Quantitative 20 14 98.3 c injection (15 min) + 60 min reaction 750 5.2 6 3.927 Quantitative 25 17.5 98.4 d injection (40 min) + 60 min reaction 750 5.2 6 3.927 Quantitative 20 14 98.3 e injection after putting 2 kg (15 min) + 60 min reaction

[0087] FIG. 5 is an SEM photograph snowing the particles according to Experiment 4.

[0088] As a result of using the co-precipitation reactor, sphericity of particles was increased.

[0089] In addition, the higher rpm, the smaller D50 of secondary particles. (Comparison of a, b, and c)

[0090] When H.sub.2O.sub.2 was quantitatively slowly added, the particles became larger. (Comparison of d with e)

[0091] A reaction rate and rpm may be adjusted to control a particle size.

5. Preparation of Lithium Oxide

[0092] Li.sub.2O.sub.2 synthesized in Experiment 4 was converted into Li.sub.2O through a heat treatment at 420° C. for 3 hours under a nitrogen atmosphere. Converted components are shown in Table 8.

TABLE-US-00008 TABLE 8 D = 80 cm, H.sub.2O.sub.2 injection LiOH—H.sub.2O H.sub.2O.sub.2 T = 10 cm method and Li.sub.2O.sub.2 Li.sub.2O.sub.2 Li.sub.2O Li.sub.2O (98.5%) (34.5%) T. Vel. reaction time D50 purity D50 purity rpm [kg] [kg] [m/sec] min [um] [wt %] [um] [wt %] Remarks 150 3 3.4 0.785 Quantitative 50 98.6 35 97.9% a injection (15 min) + 60 min reaction 500 3 3.4 2.618 Quantitative 30 97.5 21 96.2% b injection (15 min) + 60 min reaction 750 3 3.4 3.927 Quantitative 20 98.3 14 97.4% c injection (15 min) + 60 min reaction 750 5.2 6 3.927 Quantitative 25 98.4 17.5 97.6% d injection (40 min) + 60 min reaction 750 5.2 6 3.927 Quantitative 20 98.3 14 97.4% e injection after putting 2 kg (15 min) + 60 min reaction

[0093] The results show that particle size and shape were affected by Li.sub.2O.sub.2.

[0094] Additionally, a furnace as shown in FIG. 6 was manufactured and used for the heat treatment.

[0095] 10 g of Li.sub.2O.sub.2 was charged inside, and after removing the internal air with a vacuum pump for 30 minutes, the heat treatment was started while flowing N.sub.2. When the heat treatment was completed, powder was discharged and cooled down under a nitrogen atmosphere to be recovered.

[0096] During the heat treatment, a flow rate of the nitrogen varied from 1 L to 5 L per minute, but there was no difference depending on the flow rate.

[0097] Table 9 shows the heat treatment results.

TABLE-US-00009 TABLE 9 Temp Time Li.sub.2O.sub.2 Li.sub.2O LiOH LiOH—H.sub.2O Li.sub.2CO.sub.3 (° C.) (min.) [wt %] [wt %] [wt %] [wt %] [wt %] 350 30 97.3 2.2 0 0.5 0 350 60 93.8 6.1 0 0.2 0 350 90 84.6 15.1 0 0.3 0 350 120 79.6 20 0 0.4 0 400 30 31.9 67.4 0 0.5 0.2 400 60 0.1 99.4 0 0.3 0.2 400 90 0.2 99 0 0.5 0.3 400 120 0 99.7 0 0.3 0 450 30 0 99.6 0 0.4 0 450 60 0 99.6 0 0.4 0 450 90 0 99.7 0 0.3 0 450 120 0 99.8 0 0.2 0 500 30 0 99.6 0 0.4 0 500 60 0 99.7 0 0.3 0 500 90 0 99.8 0 0.2 0 500 120 0 99.8 0 0.2 0 600 30 0 99.5 0 0 0.5 600 60 0 99.6 0 0.4 0 600 90 0 99.2 0 0.8 0

[0098] As shown in Table 9, Li.sub.2O.sub.2 was completely converted into Li.sub.2O, when heat-treated at 400° C. or higher for 60 minutes or more.

6. LNO Synthesis and Cell Data Analysis

[0099] 20 g of NiO and 8.85 g of Li.sub.2O were mixed for 5 minutes with a small mixer. Herein, the used Li.sub.2O was a sample c of Table 8.

[0100] The mixed powder was exposed to 700° C. for 12 hours in a nitrogen atmosphere furnace to synthesize Li.sub.2NiO.sub.2. The synthesized powder was 28.86 g.

[0101] FIG. 7 is a SEM photograph after the mixing, and FIG. 8 is a SEM photograph of synthesized LNO after the sintering.

[0102] The synthesized Li.sub.2NiO.sub.2 was used to manufacture a CR2032 coin cell, and electrochemical characteristics thereof were evaluated. An electrode was manufactured by coating an active material layer to be 50 to 80 μm thick on a 14 mm-thick aluminum thin plate.

[0103] Electrode slurry was prepared by mixing Li.sub.2NiO.sub.2: denka black (D.B.): PvdF=85:10:5 wt % and then, coated, vacuum-dried, and pressed to form a coating layer having a final thickness of 40 to 60 μm. An electrolyte solution was an organic solution prepared by using a mixed solvent of EC:EMC=1:2 and dissolving LiPF.sub.6 salt at a concentration of 1 M.

[0104] The manufactured coin cell was charged and discharged at a 0.1 C-rate, in a CCCV mode under a 1% condition within a range of 4.25 V to 3.0 V. Charge and discharge curves of three coin cells are shown in FIG. 9 and Table 10.

TABLE-US-00010 TABLE 10 CR2032 coin cell Charge Discharge Irreversible Reversible Characteristic capacity capacity capacity efficiency evaluation result [mAh/g] [mAh/g] [mAh/g] [%] 1 391.72 131.07 260.65 33.46 2 391.12 132.33 258.79 33.83 3 386.81 129.59 257.22 33.51 average 389.88 130.99 258.88 33.6

[0105] FIG. 10 is a SEM photograph (left) showing commercially available Li.sub.2O and a SEM photograph showing Li.sub.2O according to the present example.

[0106] The particles according to the examples were clearly distinguished as secondary particles.

[0107] Tables 11, 12, and 13 are evaluation data of LNO's resultants obtained by firing two Li.sub.2O particles of FIG. 10 as described above.

[0108] LNO's according to the examples exhibited improved characteristics in all aspects.

TABLE-US-00011 TABLE 11 Dmin D50 Dmax Particle size analysis result [um] [um] [um] Comparative material 4.47 13.23 39.23 Developed product 5.12 17.33 77.33 Incremental 0.65 4.1 0.65 (developed product-comparative material) Increase rate 14.50% 31.00% 97.10% (incremental/comparative material)

TABLE-US-00012 TABLE 12 LNO NiO Li.sub.2O XRD phase analysis result (%) (%) (wt %) Sum Comparative material 90.90% 7.60% 1.50%  100% Developed product 94.50% 4.90% 0.60%  100% Incremental 3.60% −2.70% −0.90% 0.00% (developed product- comparative material) Increase rate 3.90% −35.80% −57.00% 0.00% (incremental/comparative material)

TABLE-US-00013 TABLE 13 Residual lithium analysis LiOH [wt %] Li.sub.2CO.sub.3 [wt %] Comparative material 4.19 0.36 Developed product 1.75 0.47 Incremental −2.44 0.11 (developed product-comparative material) Increase rate −58.20% 30.60% (incremental/comparative material)

[0109] Table 14 shows the evaluation results of coin cells using LNO's obtained after the firing two Li.sub.2O's of FIG. 10 as described above.

[0110] The cell data of the examples were significantly improved.

TABLE-US-00014 TABLE 14 CR2032 coin cell Charge Discharge Irreversible Reversible Characteristic capacity capacity capacity efficiency evaluation result [mAh/g] [mAh/g] [mAh/g] [%] Developed product 414.4 144.5 269.9 34.90% Comparative material 403.6 139.5 264.1 34.60% Incremental 10.8 5 5.8 0.30% (developed product- comparative material) Increase rate 2.70% 3.60% 2.20% 0.90% (incremental/ comparative material)

[0111] The present invention may be embodied in many different forms, and should not be construed as being limited to the disclosed embodiments. In addition, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the technical spirit and essential features of the present invention. Therefore, the aforementioned embodiments should be understood to be exemplary but not limiting the present invention in any way.