KR100353620B1 - Modified lithium nickel oxide compounds for positive electrodes of the secondary batteries - Google Patents

Abstract

The present invention relates to a lithium nickel-based oxide composition for a cathode electrode of a lithium ion secondary battery, and a method for manufacturing the same. More particularly, a lithium nickel cobalt oxide composition and a method for manufacturing the same have improved elemental substitution at high speed and efficiency. will be.

Lithium nickel-based oxide for the positive electrode of the lithium secondary battery of the present invention is substituted with iron and cobalt instead of nickel (LiNi _1-xy Fe _x Co _y O _2, x, y is the atomic fraction of the elements of the oxide composition, respectively 0.05≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3), the lithium ion secondary battery prepared by using the oxide as an active material can not only reduce the manufacturing cost by replacing expensive lithium cobalt-based oxide that is commercially available, The performance and energy density of the lithium secondary battery can be improved.

Description

Modified lithium nickel oxide compounds for positive electrodes of the secondary batteries}

The present invention relates to a lithium nickel-based oxide composition for a cathode electrode of a lithium ion secondary battery and a method for manufacturing the same, and more particularly, to a lithium nickel cobalt oxide composition and a method for manufacturing the same having improved high-speed discharge efficiency and electrode life by element substitution. will be.

Currently, the demand for reusable secondary batteries is rapidly increasing due to the development of portable home appliances, and among these secondary batteries, lithium ion secondary batteries are most frequently studied and commercialized due to high energy density and discharge voltage.

Requirements for the lithium ion secondary battery positive electrode are as follows.

(1) have a high discharge capacity,

(2) The use voltage must be high to obtain high energy density,

(3) It should have excellent electrode life for long time use.

(4) In order to increase the energy density per volume, the thickness of the active material in the electrode plate needs to be increased during battery manufacturing, which requires a high speed discharge efficiency.

The first commercially available cathode material of a lithium ion secondary battery is a lithium cobalt oxide-based material. Lithium cobalt oxides have excellent electrode life and high fast discharge efficiency, but the material has the disadvantage of being very expensive and having a relatively small discharge capacity. Efforts have been made to replace lithium nickel oxide, which has a high discharge capacity and a relatively low cost, with a new anode material. However, the lithium nickel oxide has a high discharge capacity, but has a disadvantage of poor electrode life and high speed discharge efficiency. It was also difficult to manufacture. In particular, lithium nickel oxide has a disadvantage in that its discharge capacity is drastically decreased due to cationic mixing phenomenon in which the positions of lithium ions and transition metal nickel change as charging and discharging proceeds.

In order to improve the problem of the lithium nickel oxide has been studied by many researchers, in particular to try to solve this problem by replacing the hetero-transition metal instead of nickel. Otsuku [A. Ueda and T. Ohzuku, J. Electrochem. Soc , Vol. 141, NO. 8 (1994) 2010-2014), which significantly improved cationic mixing by substituting cobalt for nickel. Delmas [C. Delmas et al ., Journal of Power Sources, 43-44 (1993) 595-602, etc., also greatly improved electrode life by substituting cobalt for nickel. Yoshio [M. Yoshio et al ., Journal of Power Sources , 74 (1998) 4 6-53, et al ., Improved electrode life and high-speed discharge efficiency by substituting manganese for lithium nickel oxide. However, the above methods have partially improved in terms of cationic mixing, electrode life, and high-speed discharge efficiency, but none of them met all of them. Also, the above methods greatly reduced the discharge capacity to meet the requirements of lithium ion secondary batteries. It was insufficient to meet.

After examining the problems of the prior arts, the present inventors found that electrode life and high-speed discharge efficiency are improved without large capacity change by substituting cobalt and iron for lithium lithium oxide, which is a promising material for lithium secondary batteries, instead of cobalt and iron. Came out.

Therefore, the object of the present invention is to replace the cobalt and iron in the lithium nickel-based oxide, the manufacturing cost is low, and the performance-to-price ratio can be increased, and the high capacity, high performance lithium secondary which improves the high-speed discharge efficiency and electrode life without large capacity reduction The present invention provides a battery positive electrode material and a method of manufacturing the same.

Figure 1 (a) is an electron microscope (SEM) photograph of the powder filtered using a 500 mesh and 325 mesh sieve pulverized iron-substituted lithium nickel cobalt oxide.

Figure 1 (b) is an electron micrograph (SEM) of the powder passed through a 500 mesh sieve pulverized lithium nickel cobalt oxide substituted.

2 is a graph showing the results of X-ray diffraction analysis according to the iron substitution of lithium nickel cobalt oxide.

3 is a discharge capacity curve according to iron substitution of lithium nickel cobalt oxide.

4 is a graph showing the high-speed discharge efficiency according to the iron replacement of lithium nickel cobalt oxide.

5 is a graph showing the current density dependency of lithium-nickel cobalt oxide substituted with iron.

6 is a graph showing a change in discharge capacity according to the number of charge and discharge cycles of iron-substituted lithium nickel cobalt oxide.

The lithium ion secondary battery of the present invention is composed of a cathode and a liquid electrolyte composed of an active material in which carbon and lithium nickel-based oxides are partially substituted with iron and cobalt instead of nickel. The carbon cathode and the liquid electrolyte are not particularly limited and known ones may be used as they are.

Hereinafter, the present invention will be described in detail with respect to a lithium nickel-based active material for a positive electrode of a lithium secondary battery.

The lithium nickel-based oxide composition for the positive electrode of the lithium secondary battery of the present invention is represented by the following general formula (I).

LiNi _1-xy Fe _x Co _y O ₂ (I)

In the above formula,

x and y are the atomic fractions of the oxide composition elements, respectively.

0.05 ≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3

Is a value satisfying

If the fraction of Fe exceeds 0.1, the capacity decreases, which is not preferable. If the fraction of Co exceeds 0.3, the electrode life is improved, but the width of the capacity decreases is not preferable.

The lithium nickel oxide composition of the present invention is prepared using a solid phase reaction method, and includes the following steps.

(1) uniformly mixing the weighed starting material,

(2) pelletizing the powder prepared by pulverizing the mixed powder to an appropriate size, and first heat treating the pellet under a predetermined temperature;

(3) re-pulverizing the pellets obtained in the step (2), and repeating the process of (2), followed by a second heat treatment,

In order to manufacture a positive electrode using the active material obtained by the above process, the process of screening the active material powder having a predetermined size by regrinding the pellet obtained in the step (3);

After dissolving the binder in an organic solvent, the selected active material powder and the conductive material are well mixed in the solution and dried to prepare a lithium ion secondary battery positive electrode.

If more detailed step by step the manufacturing process as follows.

As starting materials used in the present invention, lithium, nickel, iron, cobalt carbonates, hydroxides, nitrates and pure oxides can be used.

Weighed starting materials are prepared by uniform mixing by stirring for at least 12 hours using a stirrer in a ball mill or distilled water. The ball mill is mixed using distilled water and nickel balls, and the mixed powder is heated to evaporate distilled water and then pulverized well.

The powder prepared by the above process is pressed into a pellet shape and subjected to a first heat treatment process in an oxygen atmosphere. At this time, the heat treatment temperature is preferably 650 to 850 占 폚, and heat treatment is performed for 6 to 48 hours. If the heat treatment temperature or time is less than the above range, it is difficult to expect sufficient crystallization, and if it exceeds the above range, the oxide itself may be decomposed, which is not preferable. After the primary heat treatment, the pellets are pulverized and mixed well to prepare pellets again.

The pellets prepared by the first heat treatment by the electrical process are subjected to the second heat treatment again under an oxygen atmosphere. Secondary heat treatment is also preferably performed at 650 to 850 ° C for 6 to 48 hours. The pellet after the second heat treatment selects only the active material powder of a predetermined size using a sieve after regrinding.

The positive electrode first melts the binder in an organic solvent, and then mixes and mixes the active material and the conductive material in the solution well, and then the mixed solution is coated on aluminum foil, dried in a vacuum oven at about 140 degrees Celsius, and then pressed using a press. Manufacture.

Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited to these Examples.

Example 1 Fabrication of Oxide and Anode Electrode

As starting materials, nitrates of lithium, nickel, iron, and cobalt were respectively weighed in a reaction tank in a molar ratio of 1: 0.78: 0.02: 0.2, and prepared by mixing uniformly by stirring in a ball mill or distilled water for 12 hours using a stirrer. . Next, the powder prepared by the above process was pressed into pellets and subjected to a first heat treatment in an oxygen atmosphere. At this time, the heat treatment temperature was set to 650 ℃ for 12 hours, and after the primary heat treatment, the pellet was regrind and mixed well to prepare a pellet again.

The pellets prepared by the first heat treatment by the above-described process were subjected to the second heat treatment again under an oxygen atmosphere. Secondary heat treatment was also performed at 800 ° C. for 12 hours. After the second heat treatment, the pellets mainly obtained powders between 26 and 45 micrometers (μm) using 500 mesh and 325 mesh sieves after regrinding, and very small powders were attached to the powders. In addition, only the very finely sized active material powder of several micrometers (μm) or less was selected using a 500 mesh body. 1 (a) is an electron micrograph (SEM) of a powder obtained by pulverizing iron-substituted lithium nickel cobalt oxide and filtered using a 500 mesh and a 325 mesh sieve. It can be seen that it consists of a very small powder attached to the powder, Figure 1 (b) is an electron microscope (SEM) picture of the powder passed through a 500 mesh sieve of lithium nickel cobalt oxide substituted with iron, several micrometers It can be confirmed that each mainly consists of a powder of (μm).

In the positive electrode, first, a polyvinylidene binder is dissolved in an N-methylpyrrolidinone solvent, the active material and the conductive material are mixed well in the solution, and then the mixed solution is coated on an aluminum foil. It was prepared by drying in a vacuum oven at 140 degrees Celsius using a press.

Using the positive electrode and the lithium metal foil prepared above, a coin-shaped test half cell made of stainless steel was manufactured to perform a charge / discharge test. At this time, the charging and discharging speed was performed using various current densities between 18 mA / g and 360 mA / g.

<Example 2>

A half cell was manufactured under the same conditions as in Example 1, except that nitrates of lithium, nickel, iron, and cobalt were each used as a starting material in a molar ratio of 1: 0.75: 0.05: 0.2.

<Example 3>

A half cell was prepared under the same conditions as in Example 1, except that nitrates of lithium, nickel, iron, and cobalt were each used as a starting material in a molar ratio of 1: 0.73: 0.07: 0.2.

<Example 4>

A half cell was manufactured under the same conditions as in Example 1, except that nitrates of lithium, nickel, iron, and cobalt were each used as a starting material in a molar ratio of 1: 0.7: 0.1: 0.2.

<Test Example 1> X-ray diffraction analysis according to iron substitution of lithium nickel cobalt oxide

FIG. 2 shows the results of X-ray diffraction analysis according to the molar ratio change by changing the iron substitution amount of lithium nickel cobalt oxide to a molar ratio of 0, 0.05, 0.07, and 0.1. As can be seen from the results, it was confirmed that the layered structure was very well developed in all compositions, and no other second phase or impurities were formed.

Test Example 2 Measurement of Discharge Capacity According to Iron Substitution of Lithium Nickel Cobalt Oxide

FIG. 3 is a curve showing a result of measuring a discharge capacity of an iron substitution amount of lithium nickel cobalt oxide prepared in Example as 0, 0.02, 0.05, 0.07, 0.1. It was found that even when iron was substituted, there was no sudden decrease in discharge capacity, but rather, the capacity was increased until iron was replaced by 0.05.

<Test Example 3> High-speed discharge efficiency measurement according to the iron replacement of lithium nickel cobalt oxide

Figure 4 shows the results of the high-speed discharge efficiency was measured for the object produced by the iron substitution amount of lithium nickel cobalt oxide prepared according to the embodiment 0, 0.02, 0.03, 0.05, 0.07, 0.1. The fast discharge efficiency increased until iron was replaced by 0.05, but decreased more than that. The white bars represent the high-speed discharge efficiency of the powder filtered using 500 mesh and 325 mesh bodies and the gray bars represent the high-speed discharge efficiency of the powder passed through the 500 mesh sieve. As the size of the powder becomes smaller, it was confirmed that the high speed discharge efficiency increased.

Test Example 4 Current Density Dependency Measurement

FIG. 5 shows the current density dependency of lithium nickel cobalt oxide having an iron substitution value of 0.05 prepared according to the embodiment and lithium nickel cobalt oxide without iron. According to the experimental results, it can be seen that the current density dependency of the lithium-nickel cobalt oxide substituted with iron of the present invention is excellent.

<Test Example 5> Change of discharge capacity according to the number of charge and discharge cycles

6 shows the change in discharge capacity according to the number of charge and discharge cycles of lithium nickel cobalt oxide having iron substitution amounts of 0.05 and 0.1 and conventional lithium nickel cobalt oxide not substituted with iron. It can be seen that the electrode life of the lithium-nickel cobalt oxide substituted with iron of the present invention is increased.

The present invention relates to the development of cathode materials for high-performance, high-capacity lithium secondary batteries. In particular, the present invention can reduce manufacturing costs by replacing expensive lithium cobalt-based oxides that are commercially available, and can also reduce the performance and energy density of conventional lithium secondary batteries. Can improve. Therefore, the proportion of lithium secondary batteries in the secondary battery market used in home appliances such as mobile phones, camcorders, and notebook computers can be further increased, and high-capacity and high-performance secondary batteries can accelerate the development of electric vehicles, which are the main performance factors.

Claims (6)

Lithium nickel-based oxide composition for a positive electrode of a lithium ion secondary battery represented by the following general formula (I). LiNi _1-xy Fe _x Co _y O ₂ (Ⅰ) In the above formula, x and y are values satisfying 0.05 ≦ x ≦ 0.1 and 0.05 ≦ y ≦ 0.3 as the atomic fraction of the oxide composition elements, respectively. The lithium nickel-based oxide composition for a cathode electrode of a lithium ion secondary battery according to claim 1, wherein the powder of the active material oxide has a size of 45 µm or less. In the method for producing a lithium nickel oxide composition for the positive electrode of a lithium ion secondary battery, Uniformly mixing the weighed starting material, Pulverizing the prepared powder by pulverizing the mixed powder to an appropriate size, and subjecting the pellets to primary heat treatment for 6 to 48 hours at 650 to 850 ° C. in an oxygen atmosphere, Re-pulverizing the pellets obtained by the first heat treatment step to pelletize the powder, and then the pellets are subjected to a second heat treatment for 6 to 48 hours at 650 ~ 850 ℃ in an oxygen atmosphere, Re-pulverizing the pellets obtained in the second heat treatment step to select the active material powder having a predetermined size to produce an oxidation composition for the positive electrode of a lithium ion secondary battery. The method of claim 3, wherein the starting material is lithium, nickel, iron, cobalt carbonate-based, hydroxide-based, nitrate-based, the pure oxide of the oxide composition for the cathode electrode of a lithium ion secondary battery characterized in that used Way. The method of claim 3, wherein the average particle size of the active material powder obtained after the second heat treatment is 45 µm or less. A lithium ion secondary battery comprising a cathode electrode comprising the lithium nickel oxide composition of claim 1 as an active material.