Method of manufacturing secondary battery and secondary battery using the same

Abstract

Disclosed are a method of manufacturing a secondary battery having an electrode assembly sealed therein including: (a) sealing a battery case after introducing an electrode assembly having a structure, in which a separator is interposed between a positive electrode and a negative electrode, and an electrolyte thereinto; and (b) removing gases generated at an abnormal operation state of a battery or high temperature from an internal battery environment by pressing both sides of the battery case having the electrode assembly embedded therein in the sealing (a) to increase internal pressure of the battery case in the sealing, wherein the electrode assembly includes a spinel-structure lithium nickel manganese composite oxide as a positive electrode active material and a lithium metal oxide as a negative electrode active material.

Claims

1. A method of manufacturing a secondary battery having an electrode assembly sealed therein, the method comprising: sealing a battery case composed of a rectangular or cylindrical metal can after introducing an electrode assembly having a structure, in which a separator is interposed between a positive electrode and a negative electrode, and an electrolyte thereinto; and removing gases generated at an abnormal operation state of a battery or high temperature from an internal battery environment by pressing both sides of the battery case having the electrode assembly embedded therein in the sealing to increase internal pressure of the battery, wherein the electrode assembly comprises a spinel-structure lithium nickel manganese composite oxide represented by Formula 1 below as a positive electrode active material and a lithium metal oxide represented by Formula 2 below as a negative electrode active material:
LixM.sub.yMn.sub.2yO.sub.4zA.sub.z(1) wherein 0.9x1.2, 0<y<2, and 0z<0.2, M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi; A is at least one monovalent or divalent anion;
Li.sub.aM.sub.bO.sub.4cA.sub.c(2) wherein M is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr; 0.1a4 and 0.2b4, wherein a and b are determined according to oxidation number of M; 0c<0.2, wherein c is determined according to oxidation number of A; and A is at least one monovalent or divalent anion, wherein, in the removing, the pressing of the battery case is performed by pressing the both sides of the battery case using a compression plate.

2. The method according to claim 1, wherein pressure applied in the removing is 2 atm to 10 atm.

3. The method according to claim 1, wherein the pressure applied in the removing is 3 atm to 8 atm.

4. The method according to claim 1, wherein the battery case can be used under a pressure of 10 atm.

5. The method according to claim 1, wherein the gases are consumed by being reduced at a negative electrode through applied pressure.

6. The method according to claim 1, wherein the oxide of Formula 1 is represented by Formula 3 below:
Li.sub.xNi.sub.yMn.sub.2yO.sub.4(3) wherein 0.9x1.2 and 0.4y0.5.

7. The method according to claim 1, wherein the oxide of Formula 1 is LiNi.sub.0.5Mn.sub.1.5O.sub.4 or LiNi.sub.0.4Mn.sub.1.6O.sub.4.

8. The method according to claim 1, wherein the oxide of Formula 2 is represented by Formula 4 below:
Li.sub.aTi.sub.bO.sub.4(4) wherein 0.5a3 and 1b2.5.

9. The method according to claim 1, wherein the oxide of Formula 2 is Li.sub.1.33Ti.sub.1.67O.sub.4 or LiTi.sub.2O.sub.4.

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 drawing, in which:

(2) FIG. 1 is a graph illustrating cycle characteristics of a secondary battery according to Example 1 in Experimental Example 1 of the present invention;

(3) FIG. 2 is a graph illustrating cycle characteristics of a secondary battery according to Comparative Example 1 in Experimental Example 1 of the present invention;

(4) FIG. 3 is a photograph illustrating separators of a secondary battery according to Example 1 in Experimental Example 2 of the present invention; and

(5) FIG. 4 is a photograph illustrating separators of a secondary battery according to Comparative Example 1 in Experimental Example 2 of the present invention

MODE FOR INVENTION

(6) 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

(7) (a) A positive electrode mixture was prepared by adding 90 wt % of LiNi.sub.0.5Mn.sub.0.5O.sub.4 as a positive electrode active material), 5 wt % of Super-P as a conductive material), and 5 wt % of PVdF as a binder to NMP. Subsequently, the resultant mixture was coated, dried, and pressed over an aluminum collector in a loading amount of 1.2 mAh/cm.sup.2, thereby completing preparation of a positive electrode for a secondary battery. 83 wt % of Li.sub.1.33Ti.sub.1.67O.sub.4 as a negative electrode active material, 5 wt % of Super-P as a conductive material, and 12 wt % of PVdF as a binder were added to NMP, thereby completing preparation of a negative electrode mixture. Subsequently, the resultant mixture was coated, dried, and pressed over an aluminum collector in a loading amount of 1.1 mAh/cm.sup.2, thereby completing preparation of a negative electrode. So as to prepare an electrolyte for a secondary battery, 1 M LiPF.sub.6 was added to a solvent of ethylene carbonate (EC):dimethyl carbonate (DMC):ethyl methyl carbonate (EMC)=3:4:3. A porous separator manufactured using polypropylene was interposed between the positive electrode and the negative electrode, thereby completing manufacture of an electrode assembly. Subsequently, the electrolyte for the secondary battery was injected into the battery case and then sealed. As a result, a lithium secondary battery was manufactured.

(8) (b) In the sealing (a), both sides of the battery case having the electrode assembly embedded therein were pressed under a pressure of 3 atm and, thus, internal pressure of the battery case was increased.

Comparative Example 1

(9) A lithium secondary battery was manufactured in the same manner as in Example 1, except that, in the removing (b), both sides of a battery case were not pressed.

Experimental Example 1

(10) The lithium secondary batteries manufactured according to Example 1 and Comparative Example 1 were charged at 0.5 C and discharged at 0.5 C, and then rate characteristics thereof were measured. Results are illustrated in FIGS. 1 and 2 below, respectively.

(11) It can be confirmed that, as illustrated in FIG. 1 below, gas generation in the battery according to Example 1 externally pressed during manufacture of the secondary battery was inhibited or the generated gases were consumed and, as such, cycle characteristics of the battery are constant. However, it can be confirmed that, as illustrated in FIG. 2 below, large amounts of gases exist inside the case of the secondary battery, which was not externally pressed, according to Comparative Example 1 and, as such, cycle characteristics are not constant. This is because the internal pressure of the secondary battery case becomes high when external pressure is applied thereto and, as such, side reaction such as gas generation is decreased. This is also because generated gases are dissolved in the electrolyte under high pressure and, as such, non-uniform reaction due to undissolved gaseous bubbles is decreased.

Experimental Example 2

(12) The lithium secondary batteries manufactured according to Example 1 and Comparative Example 1 were charged at 0.5 C and discharged at 0.5 C. Subsequently, the batteries were decomposed and photographs of separators were taken. The photographs are illustrated in FIGS. 3 and 4 below, respectively.

(13) According to FIG. 3 below, it can be confirmed that amounts of gases inside the battery, which was externally pressed, according to Example 1 and non-uniform reaction thereof were decreased and, as such, separators are uniform. On the other hand, it can be confirmed that, according to FIG. 4 below, non-uniform reaction occurred due to large amounts of gases existing inside the battery, which was not externally pressed, according to Comparative Example 1 and, as such, separators are not uniform.

(14) 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

(15) As described above, since a method of manufacturing a secondary battery according to the present invention includes pressing both sides of a battery case having an electrode assembly embedded therein so as to increase internal pressure of the battery case, generation of carbon dioxide during charge and discharge of the battery may be inhibited and, at the same time, previously generated gases may be consumed by being reduced at a negative electrode.

(16) Therefore, side reactions occurring due to large amounts of gases existing inside the battery may be decreased. Accordingly, excellent stability may be exhibited and rate characteristics may also be improved.