High voltage positive active material and lithium secondary battery comprising the same

Abstract

Disclosed are a cathode active material for high voltage and a lithium secondary battery including the same. More particularly, a cathode active material including spinel-type compound particles having a composition represented by Formula 1 below;
Li.sub.1+aM.sub.xMn.sub.2−xO.sub.4−zA.sub.z  (1) where a, x and z are defined in a specification of the present invention, and metal oxides or metal hydroxides present on surfaces of the spinel-type compound particles, and a lithium secondary battery including the same.

Claims

1. A cathode active material comprising spinel-type compound particles having a composition represented by Formula 1:
Li.sub.1+aM.sub.xMn.sub.2−xO.sub.4−zA.sub.z  (1) wherein M is at least one selected form the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, and Zn; A is a monovalent anion or divalent anion; and −0.1≦a≦0.1, 0.3≦x≦0.8, and 0≦z≦0.1; and wherein the spinel-type compound particles have a surface layer of metal oxides or metal hydroxides, the metal oxides or the metal hydroxides are oxides or hydroxides of at least one metal selected from the group consisting of Al, Mg, Ni, Co, Ti, Cr, Mo, Bi, Zn, Zr, Ru and W, and wherein the metal oxides or the metal hydroxides adhere to surfaces of spinel-type compound particles in a particle form and wherein the metal oxides or the metal hydroxides cover from about 50% to about 80% of an overall surface of a spinel-type compound represented by Formula 1.

2. The cathode active material according to claim 1, wherein the spinel-type compound is a compound represented by Formula 2 below:
Li.sub.1+a Ni.sub.bM.sub.cMn.sub.2−(b+c)O.sub.4+zA.sub.z  (2) wherein M is at least one selected from the group consisting of Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, and Zn; A is a monovalent anion or divalent anion; and −0.1≦a≦0.1, 0.3≦b≦0.6, 0≦c≦0.2, and 0≦z≦0.1.

3. The cathode active material according to claim 1, wherein A independently is at least one selected from the group consisting of a halogen such as F, Cl, Br, I and the like, S, and N.

4. A cathode active material comprising spinel-type compound particles having a composition represented by Formula 1:
Li.sub.1+aM.sub.xMn.sub.2 −xO.sub.4−zA.sub.z  (1) wherein M is at least one selected form the group consisting of Ni, Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and Period II transition metals; A is a monovalent anion or divalent anion; and −0.1≦a≦0.1, 0.3≦x≦0.8, and 0≦z≦0.1; and wherein a metal oxide film or a metal hydroxide film is formed on the surfaces of spinel-type compound particles, the metal oxides or the metal hydroxides are oxides or hydroxides of at least one metal selected from the group consisting of Al, Mg, Ni, Co, Ti, Cr, Mo, Bi, Zn, Zr, Ru and W, wherein the metal oxide film or the metal hydroxide film is formed on entire surfaces of the spinel-type compound particles to form a core-shell structure.

5. The cathode active material according to claim 1, wherein the metal oxide or the metal hydroxide physically and/or chemically combines with a surface of the spinel-type compound.

6. The cathode active material according to claim 1, wherein an average diameter (D50) of the metal oxides or the metal hydroxide particles is 20 nm to 1000 nm.

7. The cathode active material according to claim 4, wherein the metal oxide or the metal hydroxide film has a thickness of 50 nm to 500 nm.

8. The cathode active material according to claim 1, wherein the cathode active material is prepared by wet-mixing and drying a spinel-type compound having a composition represented by Formula 1 and a metal oxide precursor or a metal hydroxide precursor.

9. The cathode active material according to claim 1, wherein the cathode active material is prepared by dry-mixing and heat-treating a spinel-type compound having a composition represented by Formula 1 and a metal oxide precursor or a metal hydroxide precursor.

10. A lithium secondary battery comprising the cathode active material according to claim 1.

11. The lithium secondary battery according to claim 10, wherein initial charge and discharge efficiency measured after charging and discharging once at a current of 0.1 C in a voltage range of 3.5 to 4.9 V is 95% or more.

12. The lithium secondary battery according to claim 10, wherein high speed charge efficiency measured by charging at a current of 5.0 C after charging and discharging at a current of 0.1 C is 86% or more.

13. The lithium secondary battery according to claim 12, wherein the high speed charge efficiency is 90% or more.

14. The lithium secondary battery according to claim 10, wherein lifespan characteristics measured by charging and discharging one hundred times at a current of 1.0 C are 92% or more.

15. The lithium secondary battery according to claim 10, wherein, after decomposing a battery by charging to 4.9 V at a current of 0.1 C after charging and discharging once at a current of 0.1 C in a voltage range of 3.5 to 4.9 V, and then soaking a cathode obtained from the decomposed battery in a container containing 15 ml of a liquid electrolyte comprising 1 M LiPF.sub.6 dissolved in a solvent in which ethylene carbonate, dimethyl carbonate and diethyl carbonate were mixed in a ratio of 1:2:1 and storing in a 80° C. constant-temperature bath for two weeks, an amount of manganese eluted in an electrolyte measured with an inductively coupled plasma optical emission spectrometer is 60 ppm or more and less than 280 ppm.

16. The lithium secondary battery according to claim 15, wherein the amount of manganese is 80 ppm or more and less than 250 ppm.

17. The lithium secondary battery according to claim 16, wherein the amount of manganese is 90 ppm or more and less than 200 ppm.

18. A battery pack comprising the lithium secondary battery according to claim 7.

19. An electric vehicle comprising the battery pack according to claim 18 as a power source.

Description

MODE FOR INVENTION

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

EXAMPLE 1

(2) After mixing LiNi.sub.0.5Mn.sub.1.5O.sub.4 as a cathode material with 0.2 wt % of 70 nm magnesium oxide, a resulting mixture was inserted into an agitator (Noblita™ available from HOSOKAWA MICRON) and then was mixed for one hour at a rate of 1000 rpm. Subsequently, a resulting mixture was heat-treated for five hours at 400 in the atmosphere state to prepare LiNi.sub.0.5Mm.sub.1.5O.sub.4 surface-modified with a magnesium oxide.

(3) The surface-modified LiNi.sub.0.5Mn.sub.1.5O.sub.4: a conductive material:a binder of 95:2.5:2.5 were weighed and then mixed in NMP to prepare a cathode mixture, which was then coated on aluminum foil having a thickness of 20 μm. The coated cathode mixture was pressed and then dried, resulting in a cathode.

(4) The cathode for lithium secondary batteries, a lithium metal film as an opposite electrode (i.e., anode), a polyethylene film (Celgard, thickness: 20 μm) as a separator, a liquid electrolyte including 1 M LiPF.sub.6 dissolved in a solvent in which ethylene carbonate, dimethyl carbonate and diethyl carbonate were mixed in a ratio of 1:2:1 were used to manufacture a 2016 coin cell.

EXAMPLE 2

(5) A 2016 coin cell was manufactured in the same manner as in Example 1, except that 50 nm aluminum oxide was used instead of the magnesium oxide of Example 1.

EXAMPLE 3

(6) A 2016 coin cell was manufactured in the same manner as in Example 1, except that an aluminum hydroxide of 120 nm was used instead of the magnesium oxide of Example 1.

COMPARATIVE EXAMPLE 1

(7) A 2016 coin cell was manufactured using LiNi.sub.0.5Mn.sub.1.5O.sub.4, in which the surface modification process according to Example 1 was not carried out, as a cathode material.

COMPARATIVE EXAMPLE 2

(8) A 2016 coin cell was manufactured in the same manner as in Example 1, except that 2 μm magnesium oxide of was used instead of the magnesium oxide of Example 1.

EXPERIMENTAL EXAMPLE 1

(9) Initial Charge and Discharge Characteristics

(10) Charge and discharge characteristics of the coin cell manufactured according to each of Examples 1 to 3,and Comparative Examples 1 and 2 were measured by charging and discharging once at a current of 0.1 C in a voltage range of 3.5 to 4.9 V. Results are summarized in Table 1 below.

(11) TABLE-US-00001 TABLE 1 Initial charge Initial discharge efficiency capacity Initial charge and (mAh/g) (mAh/g) discharge efficiency (%) Example 1 147.6 142.1 96.3 Example 2 148.2 142.0 95.8 Example 3 147.9 141.1 95.4 Comparative 147.3 138.6 94.1 Example 1 Comparative 142.5 129.4 90.8 Example 2

EXPERIMENTAL EXAMPLE 2

(12) High Speed Charge Characteristics

(13) The coin cell manufactured according to each of Examples 1 to 3,and Comparative Examples 1 and 2 was charged and discharged at a current of 0.1 C, and then was charged at a current of 5.0 C to measure high speed charge characteristics. Results are summarized in Table 2 below.

(14) TABLE-US-00002 TABLE 2 Charge capacity Charge capacity High speed at 0.1 C at 5 C charge efficiency (mAh/g) (mAh/g) 5.0 C/0.1 C (%) Example 1 147.6 132.1 89.5 Example 2 148.2 134.0 90.4 Example 3 147.9 134.6 91.0 Comparative 147.3 125.6 85.3 Example 1 Comparative 142.5 115.0 80.7 Example 2

EXPERIMENTAL EXAMPLE 3

(15) Lifespan Characteristics

(16) The coin cell manufactured according to each of Examples 1 to 3, and Comparative Examples 1 and 2 was charged and discharged one hundred times at a current of 1.0 C 100 to measure lifespan characteristics. Results are summarized in Table 3 below.

(17) TABLE-US-00003 TABLE 3 Lifespan characteristics 100.sup.th/1.sup.st discharge capacity (%) Example 1 98.4 Example 2 96.7 Example 3 94.2 Comparative 91.8 Example 1 Comparative 84.5 Example 2

EXPERIMENTAL EXAMPLE 4

(18) Measurement of Amount of Eluted Manganese

(19) The coin cell manufactured according to each of Examples 1 to 3,and Comparative Examples 1 and 2 was charged and discharged once at a current of 0.1 C in a voltage range of 3.5 to 4.9 V, and then was charged to 4.9 V at a current of 0.1 C to decompose the coin cell. A cathode obtained from the decomposed coin cell was soaked in a container containing 15 mL of electrolyte and then was stored for two weeks in an 80 constant-temperature bath. Subsequently, the amount of manganese eluted in an electrolyte was measured using an ICP (model No. 7100 available from PerkinElmer).

(20) TABLE-US-00004 TABLE 4 Measurement of amount of eluted manganese (ppm) Example 1 137 Example 2 164 Example 3 91 Comparative Example 1 280 Comparative Example 2 59

(21) 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.

INDUSTRIAL APPLICABILITY

(22) The present invention provides a lithium secondary battery for high voltage by partially or entirely adhering metal oxide particles or metal hydroxide particles to surfaces of spinel-type compound particles of Formula 1,or by forming a metal oxide film or a metal hydroxide film on the surfaces of the spinel-type compound particles of Formula 1,so as to suppress side reaction of an electrolyte and elution of manganese at a high voltage.