Precursor for preparing lithium composite transition metal oxide and method for preparing the same

Abstract

Disclosed is a transition metal precursor used for preparation of lithium composite transition metal oxide, the transition metal precursor comprising a composite transition metal compound represented by the following Formula 1:
M(OH.sub.1x).sub.2yA.sub.y/n(1) wherein M comprises two or more selected from the group consisting of Ni, Co, Mn, Al, Cu, Fe, Mg, B, Cr and second period transition metals; A comprises one or more anions except OH.sub.1x; 0<x<0.5; 0.01y0.5; and n is an oxidation number of A. The transition metal precursor according to the present invention contains a specific anion. A lithium composite transition metal oxide prepared using the transition metal precursor comprises the anion homogeneously present on the surface and inside thereof, and a secondary battery based on the lithium composite transition metal oxide thus exerts superior power and lifespan characteristics, and high charge and discharge efficiency.

Claims

1. A lithium composite transition metal oxide using a transition metal precursor used for preparation of the lithium composite transition metal oxide, the transition metal precursor comprising a composite transition metal compound represented by the following Formula 2:
Ni.sub.bMn.sub.cCo.sub.1(b+c+d)M.sub.d(OH.sub.1x).sub.2yA.sub.y/n(2) wherein 0.3b0.9; 0.1c0.6; 0d0.1; b+c+d1; M comprises one, or two or more selected from the group consisting of Al, Mg, Cr, Ti, Cu, Fe and Zr; A is PO4; 0<x<0.5; 0.01y0.5; and n is an oxidation number of A.

2. The lithium composite transition metal oxide according to claim 1, wherein the anion A is present in an amount of 0.05 to 3% by weight, based on the total amount of the lithium composite transition metal oxide.

3. The lithium composite transition metal oxide according to claim 1, wherein the composite transition metal compound has a tap density of 1.5 to 2.5 g/cc.

4. The lithium composite transition metal oxide according to claim 1, wherein the composite transition metal compound is present in an amount of 30% by weight or more, based on the total amount of the transition metal precursor.

5. The lithium composite transition metal oxide according to claim 1, wherein the anion A is homogenously present on the surface and inside thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only to illustrate the present invention and should not be construed as limiting the scope and spirit of the present invention.

EXAMPLE 1

(2) 2 L of distilled water was added to a 3 L tank for a wet-type reactor and nitrogen gas was continuously injected into the tank at a rate of 1 L/min to remove dissolved oxygen. At this time, a temperature of distilled water in the tank was maintained at 45 to 50 C. using a temperature maintenance apparatus. In addition, distilled water present inside the tank was stirred at a rate of 1,000 to 1,200 rpm using an impeller connected to a motor mounted outside the tank.

(3) Nickel sulfate, cobalt sulfate, and manganese sulfate were mixed at a ratio (molar ratio) of 0.40:0.20:0.40 to prepare a transition metal aqueous solution having a concentration of 1.5M. Separately, a 3M sodium hydroxide aqueous solution containing 0.1 mol % of Na.sub.3PO.sub.4 was prepared. The transition metal aqueous solution was continuously pumped with a metering pump at 0.18 L/hr to the tank for wet-type reactors tank. The sodium hydroxide aqueous solution was variably pumped such that pH of distilled water present in the wet-type reactor tank was maintained at 11.0 to 11.5 using a control device connected in order to control pH of distilled water in the tank. At this time, an ammonia solution having a concentration of 30% was also continuously pumped to the reactor as an additive at a rate of 0.035 L to 0.04 L/hr. An average retention time of the solutions in the wet-type reactor tank was adjusted to about 5 to 6 hours by controlling flows of the sodium hydroxide aqueous solution and the ammonia solution. After the reaction in the tank reached a steady state, the resulting product was allowed to stand for a retention time to synthesize a density-high composite transition metal precursor.

(4) After the reaction reaches the steady state, a nickel-cobalt-manganese composite transition metal precursor prepared by continuously reacting transition metal ions of the transition metal aqueous solution, hydroxyl ions of sodium hydroxide and ammonia ions of the ammonia solution for 20 hours was continuously obtained through an overflow pipe mounted on the top of a side of the tank.

(5) The composite transition metal precursor thus obtained was washed several times with distilled water and dried in a 120 C. constant-temperature drier for 24 hours to obtain a nickel-cobalt-manganese composite transition metal precursor.

EXAMPLE 2

(6) A transition metal precursor was prepared in the same manner as in Example 1, except that a 3M aqueous sodium hydroxide solution containing 0.2 mol % of Na.sub.3PO.sub.4 was used.

EXAMPLE 3

(7) A transition metal precursor was prepared in the same manner as in Example 1, except that a 3M aqueous sodium hydroxide solution containing 0.5 mol % of Na.sub.3PO.sub.4 was used.

EXAMPLE 4

(8) A transition metal precursor was prepared in the same manner as in Example 1, except that 0.1 mol % of (NH.sub.4).sub.2HPO.sub.4 was used, instead of Na.sub.3PO.sub.4.

COMPARATIVE EXAMPLE 1

(9) A transition metal precursor was prepared in the same manner as in Example 1, except that a 3M aqueous sodium hydroxide solution containing no Na.sub.3PO.sub.4 was used.

EXPERIMENTAL EXAMPLE 1

Content Analysis of PO4 Ion

(10) 0.01 g of each transition metal precursor prepared in Examples 1 to 4 and Comparative Example 1 was accurately weighted and added to a 50 ml corning tube, and a small amount of acid was added dropwise thereto, followed by shaking. The mixed sample was dissolved into a clear state and a concentration of PO.sub.4 ions in the sample was measured by ion chromatography (model DX500 manufactured by Diones Corp.). Results are shown in the following Table 1.

(11) TABLE-US-00001 TABLE 1 Sample PO.sub.4 ion content (wt %) Ex. 1 0.19 Ex. 2 0.40 Ex. 3 1.05 Ex. 4 0.20 Comp. Ex. 1 0

(12) As can be seen from ion chromatography analysis results shown in Table 1, the content of PO.sub.4 ions in the precursor linearly increased as an amount of the precursor increased.

EXPERIMENTAL EXAMPLE 2

Measurement of Tap Density

(13) The transition metal precursors prepared in Examples 1 to 4 and Comparative Example 1 were tapped 1,000 or more times with a powder multi-tester (manufactured by Seishin Trading Co., Ltd.) and tap densities thereof were measured.

(14) TABLE-US-00002 TABLE 2 Sample PO.sub.4 ion content (wt %) Ex. 1 1.92 Ex. 2 2.04 Ex. 3 2.20 Ex. 4 1.95 Comp. Ex. 1 1.71

(15) As can be seen from ion chromatography analysis results of Table 2, the precursors containing PO.sub.4 of Examples had extremely high tap densities, as compared to the precursor of Comparative Example.

EXAMPLE 5 to 8

(16) Each of the nickel-cobalt-manganese composite transition metal precursors prepared in Examples 1 to 4 and Li.sub.2CO.sub.3 were mixed at a ratio (weight ratio) of 1:1, heated at a temperature increase rate of 5 C./min and then calcined at 950 C. for 10 hours to prepare a cathode active material powder of Li[Ni.sub.0.4Co.sub.0.2Mn.sub.0.4]O.sub.2.

(17) The cathode active material powder thus prepared, Denka as a conductive material and KF1100 as a binder were mixed at a weight ratio of 95:2.5:2.5 to prepare a slurry and the slurry was uniformly coated to an aluminum foil having a thickness of 20 m. The aluminum foil was dried at 130 C. to produce a cathode for lithium secondary batteries.

(18) A 2016 coin battery was produced using the cathode for lithium secondary batteries, the lithium metal foil as a counter electrode (anode), a polyethylene membrane as a separator (Celgard, thickness: 20 m) and a liquid electrolyte of 1M LiPF.sub.6 in a mixed solvent containing ethylene carbonate, dimethylene carbonate and diethyl carbonate at a ratio of 1:2:1.

COMPARATIVE EXAMPLE 2

(19) The nickel-cobalt-manganese composite transition metal precursor prepared in Comparative Example 1 was mixed with Li.sub.2CO.sub.3 at a ratio (weight ratio) of 1:1, heated at a temperature increase rate of 5 C./min and calcined at 950 C. for 10 hours to prepare Li[Ni.sub.0.4Co.sub.0.2Mn.sub.0.4]O.sub.2. The Li[Ni.sub.0.4Co.sub.0.2Mn.sub.0.4]O.sub.2 thus prepared was mixed with 1% by weight of Li.sub.3PO.sub.4 to prepare a cathode active material powder.

(20) The cathode active material powder was mixed with Denka as a conductive material and KF1100 as a binder at a weight ratio of 95:2.5:2.5 to prepare a slurry and the slurry was uniformly coated onto aluminum foil having a thickness of 20 m. The aluminum foil was dried at 130 C. to produce a cathode for lithium secondary batteries.

(21) A 2016 coin battery was produced using the cathode for lithium secondary batteries, the lithium metal foil as a counter electrode (anode), a polyethylene membrane as a separator (Celgard, thickness: 20 m) and a liquid electrolyte of 1M LiPF.sub.6 in a mixed solvent containing ethylene carbonate, dimethylene carbonate and diethyl carbonate at a ratio of 1:2:1.

COMPARATIVE EXAMPLE 3

(22) The nickel-cobalt-manganese composite transition metal precursor prepared in Comparative Example 1 was mixed with Li.sub.2CO.sub.3 in a ratio (weight ratio) of 1:1, heated at a temperature increase rate of 5 C./min and calcined at 950 C. for 10 hours to prepare Li[Ni.sub.0.4Co.sub.0.2Mn.sub.0.4]O.sub.2. The entire surface of Li[Ni.sub.0.4Co.sub.0.2Mn.sub.0.4]O.sub.2 thus prepared was coated with 1% by weight of Li.sub.3PO.sub.4 using mechanical fusion to prepare a cathode active material powder and a 2016 coin battery was then produced in the same manner as in Comparative Example 2.

COMPARATIVE EXAMPLE 4

(23) The nickel-cobalt-manganese composite transition metal precursor prepared in Comparative Example 1 was mixed with Li.sub.2CO.sub.3 at a ratio (weight ratio) of 1:1, heated at a temperature increase rate of 5 C./min and calcined at 950 C. for 10 hours to prepare Li[Ni.sub.0.4Co.sub.0.2Mn.sub.0.4]O.sub.2. Then, a 2016 coin battery was produced in the same manner as in Comparative Example 2.

EXPERIMENTAL EXAMPLE 3

(24) Regarding the coin batteries prepared in Examples 5 to 8 and Comparative Examples 2 to 4, electrical properties of cathode active materials at 3.0 to 4.25V were evaluated using an electrochemical analyzer (Toyo System, Toscat 3100U). The results are shown in the following Table 3.

(25) TABLE-US-00003 TABLE 3 Initial charge/discharge Initial charge/discharge Sample capacity (mAh/g) efficiency (%) Ex. 5 159.1 90.1 (Ex. 1) Ex. 6 161.2 91.2 (Ex. 2) Ex. 7 160.4 90.6 (Ex. 3) Ex. 8 159.3 90.3 (Ex. 4) Comp. 156.8 88.9 Ex. 2 Comp. 157.4 89.1 Ex. 3 Comp. 157.7 89.2 Ex. 4

(26) As can be seen from Table 3, batteries according to Examples produced using the precursors treated with PO.sub.4 exhibited improved charge/discharge efficiency and thus increased discharge capacity. The batteries of Comparative Examples exhibited low charge/discharge capacity and efficiency, as compared to batteries of Examples.

EXPERIMENTAL EXAMPLE 4

(27) The coin batteries produced in Examples 5 to 8 and Comparative Examples 2 to 4 were charged at 0.2 C and discharged at 0.2 C and 2 C, and rate characteristics thereof were evaluated.

(28) TABLE-US-00004 TABLE 4 Rate characteristics Sample 2 C/0.2 C (%) Ex. 5 Ex. 1) 90.4 Ex. 6 (Ex. 2) 91.5 Ex. 7 (Ex. 3) 90.3 Ex. 8 (Ex. 4) 90.1 Comp. Ex. 2 88.7 Comp. Ex. 3 89.1 Comp. Ex. 4 88.7

(29) As can be seen from Table 4, batteries according to Examples produced using the precursors treated with PO.sub.4 exhibited improved rate characteristics and, in particular, the battery according to Example 6 produced using the precursor treated with 0.2 mol % of PO.sub.4 exhibited optimal performance. The batteries of Comparative Examples using precursors not treated with PO.sub.4 exhibited bad 2 C rate characteristics, as compared to batteries of Examples.

(30) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.