Moisture-limited electrode active material, moisture-limited electrode and lithium secondary battery comprising the same

Abstract

Disclosed are an electrode active material containing moisture in an amount less than 2,000 ppm per 1 g of lithium metal oxide or moisture in an amount less than 7,000 ppm per 1 cm.sup.3 of the lithium metal oxide, and an electrode containing moisture in an amount less than 2,000 ppm per 1 cm.sup.3 of an electrode mix.

Claims

1. An electrode mix comprising: a binder; and an anode active material containing (a) moisture that is equal to or greater than 900 ppm and is lower than 2,000 ppm with respect to the anode active material and (b) a lithium titanium oxide that is represented by the following Formula Li.sub.aTi.sub.bO.sub.4, in which 0.5≤a≤3 and 1≤b≤2.5.

2. The electrode mix according to claim 1, wherein the moisture contained in the anode active material is equal to or greater than 900 ppm and is lower than 1,500 ppm.

3. The electrode mix according to claim 1, further comprising a conductive material.

4. The electrode mix according to claim 1, wherein the lithium titanium oxide is Li.sub.1.33Ti.sub.1.67O.sub.4 or LiTi.sub.2O.sub.4.

5. The electrode mix according to claim 1, wherein the lithium titanium oxide is provided as a secondary particle formed of agglomerated primary particles.

6. The electrode mix according to claim 5, wherein the secondary particle has a particle diameter of 200 nm to 30 μm.

7. An electrode mix comprising: a conductive material; and an anode active material containing (a) moisture that is equal to or greater than 900 ppm and is lower than 2,000 ppm with respect to the anode active material and (b) a lithium titanium oxide that is represented by the following Formula Li.sub.aTi.sub.bO.sub.4, in which 0.5≤a≤3 and 1≤b≤2.5.

8. The electrode mix according to claim 7, further comprising a binder.

9. An anode slurry prepared by mixing the electrode mix of claim 8 with a solvent.

10. An anode electrode prepared from the slurry of claim 9.

11. An anode slurry prepared by mixing the electrode mix of claim 3 with a solvent.

12. An anode electrode prepared from the slurry of claim 11.

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 curve showing charge and discharge of batteries of exemplary Examples 1 and 2 according to the present invention; and

(3) FIG. 2 is a curve showing lifespan of batteries of exemplary Examples 1 and 2 according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) 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

(5) A solid containing Li(Ni.sub.0.5Mn.sub.1.5)O.sub.4 (BASF Corporation), Super-P (Timcal Corporation) and PVdF (Solef Corporation 6020) at a weight ratio of 95:5:5 was mixed with NMP as a solvent to prepare a cathode slurry. The cathode slurry was coated onto an aluminum foil with a thickness of 20 μm to produce a cathode with a load of 1 mAh/cm.sup.2.

(6) A solid consisting of Li.sub.1.33Ti.sub.1.67O.sub.4 (Posco ESM Corporation T30) having a limited moisture content of 330 ppm/g, Super-P (Timcal Corporation) and PVdF (Solef Corporation 6020) at a weight ratio of 95:5:5 was mixed with a NMP as a solvent to produce an anode slurry. The anode slurry was coated onto an aluminum foil with a thickness of 20 μm to produce an anode with a load of 1 mAh/cm.sup.2.

(7) Moisture content can be controlled by drying Li.sub.1.33Ti.sub.1.67O.sub.4 (Posco ESM Corporation T30) under vacuum at 130° C. for five days. Moisture content may be measured at 400° C. using a coulmetric Karl Fisher method.

(8) A battery was produced using the cathode, the anode and an electrolyte containing a carbonate electrolyte consisting of EC:DMC:EMC at a ratio of 1:1:1, and 1M LiPF.sub.6 as a salt.

Example 2

(9) A battery was produced in the same manner as in Example 1, except that Li.sub.1.33Ti.sub.1.67O.sub.4 (Posco ESM Corporation T30) having a limited moisture content of 900 ppm/g obtained by drying at 55° C. for 5 days was used as an anode active material.

Example 3

(10) A solid containing Li.sub.1.33Ti.sub.1.67O.sub.4 (Posco ESM Corporation T30), Super-P (Timcal Corporation) and PVdF (Solef Corporation 6020) at a weight ratio of 83:12:5 was mixed with NMP as a solvent to prepare an electrode mix slurry. The electrode mix slurry was coated onto an aluminum foil with a thickness of 20 μm to produce an anode with a load of 1 mAh/cm.sup.2.

Example 4

(11) An electrode assembly including 27 cathode and anode pairs was produced using the cathode of Example 1, the electrode (anode) of Example 3, and a porous polyethylene membrane (Celgard, thickness: 20 μm).

Experimental Example 1

(12) In order to evaluate moisture content effects on battery capacity, batteries of Examples 1 and 2 were subjected to charge/discharge testing under 0.1 C charge and 0.1 C discharge conditions. Results are shown in FIG. 1. Example 1 (solid line) having a relatively low moisture content per unit weight inhibited negative reactions caused by moisture and exhibited an increase in capacity.

Experimental Example 2

(13) In order to evaluate effects of moisture content on battery capacity, batteries of Examples 1 and 2 were charged and discharged 100 times at 25° C. under 0.1 C charge and 0.1 C discharge conditions. Results are shown in FIG. 2. Example 1 (solid line) having a relatively low moisture content per unit weight inhibited negative reactions caused by moisture and exhibited an increase in capacity.

Experimental Example 3

(14) Moisture contents of an experimental group in which the electrode of Example 3 was immersed in 1,2-dimethoxy ethane (DME) and was dried under vacuum at 55° C. and 130° C. for 5 days, and of a control group in which the electrode was not immersed in 1,2-dimethoxy ethane (DME) and was dried under vacuum at 55° C. and 130° C. for 5 days were measured at 400° C. using a coulmetric Karl Fisher method. Results are shown in Table 1.

(15) TABLE-US-00001 TABLE 1 Drying temperature Control group Experimental group  55° C. 840 ppm/g 627 ppm/g 130° C. 332 ppm/g 312 ppm/g

Experimental Example 4

(16) Moisture contents of an experimental group in which the electrode of Example 4 was immersed in 1,2-dimethoxy ethane (DME) and was dried under vacuum at 55° C. for 5 days, and of a control group in which the electrode was not immersed in 1,2-dimethoxy ethane (DME) and was dried under vacuum at 55° C. for 5 days were measured at 400° C. using a coulmetric Karl Fisher method. Results are shown in Table 2. The moisture content was measured based upon the innermost electrode (electrode of Example 3).

(17) TABLE-US-00002 TABLE 2 Drying temperature: 55° C. Control group Experimental group Electrode of 980 ppm/g 822 ppm/g Example 3 Separator 158 ppm/g 132 ppm/g

(18) 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.