Electrode active material and lithium secondary battery comprising the same

Abstract

Disclosed are an electrode active material for lithium secondary batteries, comprising at least one selected from compounds represented by the following formula 1, and a lithium secondary battery comprising the same.
Li.sub.xMo.sub.4−yM.sub.yO.sub.6−zA.sub.z  (1) wherein 0≦x≦2, 0≦y≦0.5, 0≦z≦0.5, M is a metal or transition metal cation having an oxidation number of +2 to +4, and A is a negative monovalent or negative bivalent anion.

Claims

1. A cathode active material for secondary batteries comprising at least one selected from compounds having a function of being capable of deintercalation and intercalation of lithium ions, represented by the following formula 1:
Li.sub.xMo.sub.4−yM.sub.yO.sub.6−zA.sub.z  (1) wherein 0<x≦2; 0<y≦0.5; 0≦z≦0.5; M is at least one selected from the group consisting of W, Nb, V, Al, Mg, Ti, Co, Ni and Mn; and A is at least one selected from the group consisting of halogen, S and N.

2. The cathode active material according to claim 1, wherein x satisfies 0<x≦1.

3. A cathode in which the cathode active material according to claim 1 is applied to a current collector.

4. A lithium secondary battery comprising the cathode according to claim 3.

5. The lithium secondary battery according to claim 4, the lithium secondary battery comprises an anode comprising carbon, metal composite oxides, a lithium metal, lithium alloys, silicon-based alloys, tin-based alloys, metal oxides, conductive polymers, or Li—Co—Ni based materials, wherein the anode comprising carbon is non-graphitized carbon and graphitized carbon, wherein the metal composite oxides is Li.sub.xFe.sub.2O.sub.3 (0≦x≦1), Li.sub.xWO.sub.2 (0≦x≦1) or Sn.sub.xMe.sub.1−xMe′.sub.yO.sub.z (Me: Mn, Fe, Pb, Ge; Me′: Al, B, P, Si, Group I, II and III elements of the Periodic Table, halogen atoms; 0<x≦1; 1≦y≦3; and 1≦z≦8), wherein the metal oxides is at least one selected from the group consisting of SnO, SnO.sub.2, PbO, PbO.sub.2, Pb.sub.2O.sub.3, Pb.sub.3O.sub.4, Sb.sub.2O.sub.3, Sb.sub.2O.sub.4, Sb.sub.2O.sub.5, GeO, GeO.sub.2, Bi.sub.2O.sub.3, Bi.sub.2O.sub.4, and Bi.sub.2O.sub.5, or wherein the conductive polymers is polyacetylene.

6. The lithium secondary battery according to claim 5, wherein the anode comprises the carbon that is non-graphitized carbon and graphitized carbon.

7. The lithium secondary battery according to claim 5, wherein the anode comprises the metal composite oxides that is Li.sub.xFe.sub.2O.sub.3 (0≦x≦1), Li.sub.xWO.sub.2 (0≦x≦1) or Sn.sub.xMe.sub.1−xMe′.sub.yO.sub.z (Me: Mn, Fe, Pb, Ge; Me′: Al, B, P, Si, Group I, II and III elements of the Periodic Table, halogen atoms; 0<x≦1; 1≦y≦3; and 1≦z≦8).

8. The lithium secondary battery according to claim 5, wherein the anode comprises the metal oxides that is at least one selected from the group consisting of SnO, SnO.sub.2, PbO, PbO.sub.2, Pb.sub.2O.sub.3, Pb.sub.3O.sub.4, Sb.sub.2O.sub.3, Sb.sub.2O.sub.4, Sb.sub.2O.sub.5, GeO, GeO.sub.2, Bi.sub.2O.sub.3, Bi.sub.2O.sub.4, and Bi.sub.2O.sub.5.

9. The lithium secondary battery according to claim 5, wherein the anode comprises the conductive polymers that is polyacetylene.

10. A battery module comprising the lithium secondary battery according to claim 4 as a unit battery.

11. A power storage device comprising the battery module according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a schematic view illustrating a LiMo.sub.4O.sub.6 crystal structure;

(3) FIG. 2 is a graph showing results of Experimental Example 2;

(4) FIG. 3 is a graph showing results of Experimental Example 3;

(5) FIG. 4 is a graph showing results of Experimental Example 4; and

(6) FIG. 5 is a graph showing results of Experimental Example 5.

BEST MODE

(7) 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

(8) In, MoO.sub.3 and Mo satisfying a stoichiometric ratio were sealed under vacuum in a silica tube. This tube was heated in a furnace at a temperature of 895° C. for 4 days to perform synthesis, the resulting product and lithium iodide (LiI) were sealed under vacuum in the silica tube and were then reacted at a temperature of 460° C. for 12 hours to prepare lithium molybdenum oxide.

(9) The lithium molybdenum oxide as a cathode active material, KS 6 as a conductive material and KF 1100 as a binder were mixed at a ratio (weight ratio) of 8:1:1, the mixture was stirred together with NMP as a solvent, and the resulting mixture was coated on an aluminum foil as a metal current collector. The resulting product was dried at 120° C. in a vacuum oven for 2 hours or longer to fabricate a cathode.

(10) A coin-type battery was fabricated using the cathode, an anode as a Li metal, a porous polypropylene separator, and a solution of 1M LiPF.sub.6 salt in a solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed at a volume ratio of 1:1, as an electrolyte.

Comparative Example 1

(11) A lithium secondary battery was fabricated in the same manner as in Example 1, except that a cathode active material was prepared using LiCoO.sub.2 instead of lithium molybdenum oxide.

Experimental Example 1

(12) The lithium secondary batteries fabricated in Example 1 and Comparative Example 1 were charged and discharged at 2.0 to 4.2V and at the same time, lifespan thereof were measured. The results are shown in Table 1 below.

(13) TABLE-US-00001 TABLE 1 Cathode active Theoretical Actual Mean material capacity capacity voltage Ex. 1 Li.sub.1+xMo.sub.4O.sub.6  56 mAh/g  55 mAh/g 3.4 V (0 ≦ x ≦ 1) Comp. Ex. 1 LiCoO.sub.2 273 mAh/g 150 mAh/g 3.8 V

(14) As can be seen from Table 1 above, the compound according to the present invention exhibited an actual capacity comparable to theoretical capacity, in spite of having a smaller capacity than LiCoO.sub.2, and a high mean voltage of 3.4 V, when used for a cathode active material.

Experimental Example 2

(15) The lithium molybdenum oxide prepared in Example 1 was subjected to X-ray diffraction (XRD).

(16) XRD data was obtained at room temperature using a Bragg-Brentano diffractometer (Bruker-AXS D4 Endeavor) equipped with a Cu X-ray tube and Lynxeye detector under conditions of an angle increase by 0.025° and an angle range of 10°≦2θ≦70°. The X-ray diffraction data was subjected to Rietveld refinement using a TOPAS program and the results are shown in FIG. 2.

(17) Preparation of the lithium molybdenum oxide could be seen from characteristic peaks of FIG. 2.

Experimental Example 3

(18) The lithium molybdenum oxide obtained in Example 1 was reacted with LiI at 460° C. for 12 hours and the reaction was continuously repeated. At this time, a content of Li in the synthesized substance was measured using ICP-AES (Perkin-Elmer). As a result, Li was substituted at a ratio of 1.72 or less, with respect to Mo. It could be seen from calculation chemistry that a Li—O distance was 2.0 Å which is a reliable level, when a substitution amount of Li was thermodynamically calculated to 2, with respect to Mo. FIG. 3 schematically shows this crystal structure.

Experimental Example 4

(19) For the coin batteries fabricated in Example 1, electric properties of the cathode active material were evaluated using an electrochemical analyzer (VSP, Bio-Logic Science Instruments). The coin batteries were tested at 0 to 4.0V and at a scanning rate of 0.5 mV/s using cyclic voltammetry (CV). The results are shown in FIG. 4.

(20) As can be seen from FIG. 4, Li ions are reversibly intercalated and deintercalated to lithium molybdenum oxide according to the present invention.

Experimental Example 5

(21) For the coin batteries fabricated in Example 1, electric properties of the cathode active material were evaluated using an electrochemical analyzer (VSP, Bio-Logic Science Instruments). The coin batteries were tested in a charge-discharge mode at 2.0 to 4.2V. The results are shown in FIG. 5.

(22) As can be seen from FIG. 5, the secondary battery using the lithium molybdenum oxide according to the present invention as a cathode active material had a capacity of about 55 mAh/g, corresponding to 98% of the theoretical capacity and a mean voltage of 3.4V. Also, an SOC state can be easily observed through OCV because the charge and discharge graph has linearity.

INDUSTRIAL APPLICABILITY

(23) As apparent from the afore-going, lithium secondary batteries using the electrode active material according to the present invention undergo neither structural variation of oxide even during repeated charge and discharge nor structural collapse during over-charge, thus securing safety and being advantageously useful for power sources of electric vehicles or large-capacity power storage devices.

(24) 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.