High voltage positive active material and method for preparing the same

Abstract

Disclosed herein is a high voltage cathode active material and a method for preparing the same. The cathode active material includes particles of a spinel-type compound having a composition represented by Formula (1) and a carbon-based material present on surfaces of the particles of the spinel-type compound:
Li.sub.1+aM.sub.xMn.sub.2xO.sub.4zA.sub.z(1) where 0.1a0.1, 0.3x0.8 and 0z0.1.

Claims

1. A cathode active material comprising: particles of a spinel-type compound having a composition represented by Formula (2); wherein the particles of the spinel-type compound has a material present on surfaces of the particles of the spinel-type compound, wherein the material consists of particles consisting of a carbon-based material:
Li.sub.1+aNi.sub.bM.sub.cMn.sub.2(b+c)O.sub.4zA.sub.z(2) where M is at least one selected from the group consisting of Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and period II transition metals, A is a monoanion or dianion, and 0.1a0.1, 0.3b0.6, 0c0.2, and 0z0.1, wherein the carbon-based material is physically and/or chemically bonded to the surfaces of the particles of the spinel-type compound of Formula (2), wherein an average particle diameter (D50) of the carbon-based material is equal to or greater than 2 nm and equal to or less than 500 nm, and the cathode active material is prepared by mixing the spinel-type compound of Formula (2) and a carbon precursor to form a resulting mixture, wherein the carbon precursor and the spinel-type compound are mixed using dry mixing, wherein the carbon precursor is petroleum-based pitch; and thermally treating the resulting mixture at a temperature of 400 to 800 C. under an inert atmosphere or an oxygen deficient atmosphere with an oxygen concentration of 35% by volume or less.

2. The cathode active material according to claim 1, wherein the carbon-based material covers equal to or greater than 20% and equal to or less than 100% of the entire surface of the spinel-type compound of Formula (2).

3. The cathode active material according to claim 2, wherein the carbon-based material covers equal to or greater than 50% and equal to or less than 80% of the entire surface of the spinel-type compound of Formula (2).

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

5. A battery pack comprising the lithium secondary battery according to claim 4.

6. An electric vehicle comprising the battery pack according to claim 5.

7. A method for preparing the cathode active material of claim 1, the method comprising: (1) mixing a spinel-type compound having a composition represented by Formula (2) and a carbon precursor, wherein the carbon precursor and the spinel-type compound are mixed using dry mixing, wherein the carbon precursor is petroleum-based pitch; (2) thermally treating the resulting mixture under an inert atmosphere or an oxygen deficient atmosphere with an oxygen concentration of 35% by volume or less:
Li.sub.1+aNi.sub.bMcMn.sub.2(b+c)O.sub.4zA.sub.z(2) where M is at least one selected from the group consisting of Ti, Co, Al, Cu, Fe, Mg, B, Cr, Zr, Zn and period II transition metals, A is a monoanion or dianion, and 0.1a0.1, 0.3b0.6, 0c0.2, and 0z0.1, (3) resulting in the cathode active material of claim 1.

8. The method according to claim 7, wherein the thermal treatment is performed at a temperature of 400 to 800 C.

9. The method according to claim 7, wherein the carbon precursor comprises at least one selected from the group consisting of petroleum-based pitch, tar, phenolic resin, furan resin and carbohydrate.

10. The method according to claim 7, wherein the inert atmosphere is a nitrogen (N.sub.2) or argon (Ar) atmosphere.

Description

BEST MODE

(1) The present invention will now be further described through examples. However, it should be noted that the following examples are given only to exemplify the present invention and the scope of the invention is not limited thereto.

EXAMPLE 1

(2) LiNi.sub.0.5Mn.sub.1.5O.sub.4 and petroleum-based pitch were introduced in a weight ratio of 100:5 into a conical agitator and were then mixed at 400 rpm for 1 hour. Thereafter, the mixture was thermally treated for 20 hours at a temperature of 500 C. under a nitrogen atmosphere, thereby preparing LiNi.sub.0.5Mm.sub.1.5O.sub.4 surface-modified with a carbon-based material.

(3) LiNi.sub.0.5Mn.sub.1.5O.sub.4 surface-modified with a carbon-based material, a conductive material and a binder were weighed in a ratio of 97:2.5:2.5 and then added to NMP, followed by mixing, to form a cathode mix. The cathode mix was applied to an aluminum foil with a thickness of 20 m, followed by rolling and drying, to form a cathode for lithium secondary batteries.

(4) A 2016 coin battery was then fabricated using the formed cathode for lithium secondary batteries, a lithium metal film as a counter electrode (i.e., an anode), a polyethylene membrane (Celgard, thickness: 20 m) as a separator, and a liquid electrolyte including 1M LiPF.sub.6 dissolved in a solvent in which ethylene carbonate, dimethylene carbonate and diethyl carbonate were mixed in a ratio of 1:2:1.

Comparative Example 1

(5) A coin battery was fabricated in the same manner as in Example 1, except that LiNi.sub.0.5Mm.sub.1.5O.sub.4, which was not surface-modified with a carbon-based material, was used as a cathode active material.

Experimental Example 1

(6) Initial Charge/Discharge Characteristics

(7) Coin batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged once at a current of 0.1 C within a voltage range of 3.5 to 4.9 V and charge/discharge characteristics were estimated. Estimation results are shown in Table 1 below.

(8) TABLE-US-00001 TABLE 1 Initial Charge Initial Charge Initial Charge/ Capacity Capacity Discharge Efficiency (mAh/g) (mAh/g) (%) Ex. 1 147.9 141.5 95.7 Comp. Ex. 1 147.3 138.6 94.1

Experimental Example 2

(9) Rapid Charging Characteristics

(10) Coin batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged at a current of 0.1 C and were then charged at a current of 5.0 C, and rapid charging characteristics were estimated. Estimation results are shown in Table 2 below.

(11) TABLE-US-00002 TABLE 2 0.1 C Charge 5 C Charge Rapid charging Capacity Capacity Efficiency (mAh/g) (mAh/g) 0.1 C/5.0 C (%) Ex. 1 147.9 135.8 91.8 Comp. Ex. 1 147.3 125.6 85.3

Experimental Example 3

(12) Service Life Characteristics

(13) Coin batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged 100 times at a current of 1.0 C and service life characteristics were estimated. Estimation results are shown in Table 3 below.

(14) TABLE-US-00003 TABLE 3 Service life Characteristics 100.sup.th/1.sup.st Discharge Capacity (%) Ex. 1 95.9 Comp. Ex. 1 91.8

Experimental Example 4

(15) Eluted Manganese Amount Measurement

(16) Coin batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged once at a current of 0.1 C within a voltage range of 3.5 to 4.9 V and were charged at a current of 0.1 C to 4.9 V. The batteries were then disassembled. A cathode obtained from each of the disassembled batteries was dipped in a container containing 15 mL of an electrolyte and was stored in an 80 C. constant temperature bath for 2 weeks. Then, the content of manganese eluted into the electrolyte was analyzed using an ICP (PerkinElmer, Model 7100).

(17) TABLE-US-00004 TABLE 4 Amount of Eluted Manganese (ppm) Ex. 1 76 Comp. Ex. 1 280

Experimental Example 5

(18) High Temperature Storage Characteristics Estimation

(19) Coin batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged once at a current of 0.1 C within a voltage range of 3.5 to 4.9 V and were charged at a current of 0.1 C to 4.9 V. The batteries were then stored in a 60 C. constant temperature bath for 1 week and the amount of self-discharge and the capacity recovery rate of each of the batteries were measured. When a battery is stored in a fully charged state at high temperature, decomposition of electrolyte on the surface of a cathode active material is accelerated, increasing self-discharge. This causes destruction of the structure of the cathode active material. This experiment was devised to observe this phenomenon.

(20) TABLE-US-00005 TABLE 5 Amount of Self- Capacity Recovery Discharge Rate (%) (%) Ex. 1 24 88 Comp. Ex. 1 62 45

INDUSTRIAL APPLICABILITY

(21) According to the present invention, all or part of the surface of particles of a spinel-type compound of the above Formula 1 are coated with a carbon-based material. This inhibits elution of manganese and electrolyte side reaction at a high voltage, thereby enabling provision of improved high-voltage lithium secondary batteries.