KR19990034749A - Lithium-ion secondary battery employing a lithium composite oxide, a method of manufacturing the same, and a positive electrode using the same - Google Patents

Abstract

The aqueous solution of cobalt salt and nickel salt is added to the aqueous solution of ammonia as a complex and an alkaline solution as a pH regulator and co-precipitated for a predetermined time to form a nickel-cobalt composite hydroxide in which the aggregates of acicular primary particles form spherical secondary particles. Lithium prepared by the method comprising the steps of adding lithium hydroxide to the composite hydroxide, the first heat treatment at 280-420 ℃, and the second heat treatment at 650-700 ℃ the result obtained by the first heat treatment The composite oxide (LiNi _(1-xy) Co _x M _y O ₂ (M = Al, Ca, Mg and B is at least one metal atom selected from x, 0.1 is 0.3 to 0.3, y is 0 to 0.1)) The aggregate of a rectangular primary particle forms a spherical secondary particle, and the tap density is high. When the lithium composite oxide is used as a positive electrode active material, a high capacity lithium ion secondary battery can be obtained.

Description

Lithium-ion secondary battery employing a lithium composite oxide, a method of manufacturing the same, and a positive electrode using the same as an active material

The present invention relates to a lithium secondary battery, and relates to a lithium composite oxide having a spherical particle shape, a method for manufacturing the same, and a lithium ion secondary battery employing a positive electrode using the lithium composite oxide as an active material.

With the rapid progress in miniaturization, weight reduction, and wirelessization of electronic devices, particularly camcorders, cellular phones, and notebook computers, there is an increasing demand for secondary batteries having small size, light weight, and high energy density as driving power for these electronic devices. In this respect, in particular, lithium secondary batteries have attracted attention.

Lithium metal is the lightest metal on the planet, so it has the largest electric capacity per unit mass and its electronegativity, which can be used as a negative electrode material of a battery. However, lithium in the metal state may be passivated by the reaction with the organic solvent to grow dendritic and cause short circuits in the battery, which may cause serious problems in the safety of the battery. Accordingly, carbon has been developed as an anode material capable of replacing lithium metal, having an electrode potential most similar to that of lithium metal, having a layered structure, and capable of reversible intercalation / deintercalation of lithium ions.

The electrode reaction of a lithium secondary battery composed of a carbon anode, a metal oxide anode, and a liquid electrolyte is as follows.

During charging, lithium ions in the positive electrode are removed and lithium ions in the electrolyte are inserted into the carbon layered structure so that the concentration of lithium ions in the electrolyte is kept constant. During discharge, the lithium ions are inserted / reinserted in the opposite direction of charging. This is going on. This battery is called a rocking-chair cell in that lithium ions reciprocate between two electrodes due to charging and discharging. Also, this battery is also called a lithium ion battery because lithium metal is not involved and lithium exists in an ionic state. .

In the lithium ion secondary battery as described above, lithium metal oxide is used as the positive electrode material, and in particular, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO _2, and the like are known. Co-based lithium oxide is already commercialized and widely used, but has the disadvantage of high cobalt price and harmfulness. Nickel-based lithium oxide is inexpensive, low in metal hazards and high in capacity, but has a disadvantage in that powder synthesis is not easy and life characteristics are not good. In order to solve this problem, lithium composite oxides represented by LiMM'O _x (wherein M and M 'are Co, Mn, Ni, V, Fe, W, etc.) are developed. That is, by replacing a portion of Ni in LiNiO ₂ with another metal, the synthesis can be made easier and lifespan characteristics can be improved. The improvement of these properties is known to depend greatly on the crystal structure or particle shape of the finally formed lithium oxide. For example, in the case where the particle shape of the positive electrode active material of the particles is irregular and fine (about 5 μm in average particle size), it is advantageous to insert / de-insert lithium ions, so that a battery having a high capacity can be obtained, and the tab is close to a spherical shape. Since it is advantageous to increase the tap density, it is possible to increase the relative weight ratio of the positive electrode active material in manufacturing a battery.

In Japanese Patent Application Laid-Open No. 7-37576, platelet single crystal particles (primary particles) of nickel hydroxide precipitated by neutralization reaction of an aqueous nickel salt solution and an aqueous alkali solution are aggregated into spherical or ellipsoidal forms to form secondary particles. A method of preparing nickel-based lithium oxide is disclosed by heat treating a secondary particle of nickel hydroxide, a lithium compound, and optionally a magnesium compound in an oxygen atmosphere. In the nickel-based lithium oxide produced by this method, a plurality of plate-shaped primary particles forming a layered structure by stacking a plurality of flakes form a secondary particle, and the secondary particles are spherical or ellipsoidal, about 2 to 20. It has an average particle diameter of 탆. That is, a method of forming secondary particles through an assembly process of collecting primary particles having a layered structure is used. However, since the primary particles are aggregated to form secondary particles by using the granulation method, it is difficult to refine the particle size of the finally obtained active material and careful attention is also required to optimize the conditions of the granulation process.

In Japanese Patent Application Laid-Open No. 8-339806, an alkali solution is added to a mixed solution of cobalt salt and nickel salt to coprecipitate cobalt hydroxide and nickel hydroxide to obtain a composite hydroxide, and then single crystal particles of the composite hydroxide are spherical or ellipsoidal. The secondary particles are collected to form a secondary compound, and then a lithium compound is added to the composite hydroxide and subjected to heat treatment, whereby the layered structure part is exposed to the outside of the spherical or elliptical secondary particles (LiNi ₍₁ -Ni). _x) M _x O ₂ (M = Co or Al, x = 0.05 to 0.3) is disclosed. In this method, the spherical secondary particles are formed at the time of obtaining a composite hydroxide of Ni and Co, and the particle shape is almost maintained even after heat treatment by addition of a lithium compound. According to this method, however, the capacity characteristics are improved when the heat treatment temperature is about 750 ° C., but the maintenance of the particle form becomes difficult when the temperature is increased. In addition, since the layered structure part is exposed to the outside of the secondary particles, the tap density is not so high. In general, the tap density is higher as the surface state of the particles are flat, the higher the tap density can increase the relative charge amount of the active material in the production of the positive electrode, which is advantageous to increase the capacity of the battery. In the case of the conventional lithium composite oxide prepared according to the conventional method, the tap density was usually 2.4-2.7 g / cm ³ level.

An object of the present invention is to provide a spherical lithium composite oxide having a high tap density.

Another object of the present invention is to provide a method for simply preparing the spherical lithium composite oxide.

Another object of the present invention is to provide a lithium ion secondary battery employing a positive electrode having the spherical lithium composite oxide as an active material.

Figures 1a, 1b, 1c and 1d is a composite oxide and its particle surface obtained after the first heat treatment (Fig. 1a and 1b) and the secondary heat treatment (Fig. 1c and 1d) in the production of a lithium composite oxide according to an embodiment of the present invention A scanning electron microscope (SEM) photograph showing the state.

2A and 2B are graphs showing charge and discharge test results of a battery employing a lithium composite oxide prepared according to an embodiment of the present invention as a positive electrode.

3A, 3B, 3C, and 3D illustrate composite oxides and particle surfaces obtained after primary heat treatment (FIGS. 3A and 3B) and secondary heat treatment (FIGS. 3C and 3D) in the preparation of a lithium composite oxide according to one embodiment of the present invention. A scanning electron microscope (SEM) photograph showing the state.

4A and 4B are graphs showing charge and discharge test results of a battery employing a lithium composite oxide prepared according to another embodiment of the present invention as a positive electrode.

In the present invention, in order to attain the object, which is an aggregate of primary particles of the square forms a secondary particle of a spherical shape, the lithium composite oxide, characterized in that the tap density of 2.4-3.2g / cm ³ _{(LiNi (1- xy)} Co _x M _y O ₂ (M = Al, Ca, Mg, and at least one metal atom selected from B, x is 0.1 to 0.3, y is 0 to 0.1) is provided.

The primary particles are triangular to pentagonal, preferably rectangular, with an average particle size of 0.2-0.5 μm and an average particle size of secondary particles of 5 to 20 μm.

Another object of the present invention, a) adding ammonia water as a complex and an alkaline solution as a pH adjuster to a mixed aqueous solution of cobalt salt and nickel salts and co-precipitated for 6-10 hours to extract the nickel-cobalt composite hydroxide, b) the complex Adding a lithium hydroxide to the hydroxide and performing a first heat treatment at 280-420 ° C., c) a lithium composite oxide comprising a second heat treatment at 650-700 ° C. (LiNi _{(1- x)} Co _x 0 ₂ (x is 0.1 to 0.3)).

In step a), before adding the complexing agent and the pH adjusting agent to the mixed aqueous solution of nickel salt and cobalt salt, a third metal salt containing at least one metal atom selected from Al, Ca, Mg and B is added to the total metal salt (nickel Salt, cobalt salt and third metal salt) in an amount of 0.1 mole ratio or less.

Both the primary heat treatment and the secondary heat treatment are performed in a dry air atmosphere.

Still another object of the present invention is to provide a lithium ion secondary battery comprising a positive electrode, a carbon-based negative electrode, and a non-aqueous electrolytic solution containing lithium oxide as an active material, wherein the lithium oxide of the positive electrode is formed of spherical secondary particles. Lithium composite oxide (LiNi _(1-x) Co _x M _y O ₂ (M = Al, Ca, Mg and B) at least one metal constituting the secondary particles and having a tap density of 2.4-3.2 g / cm ³ Atom, x is 0.1 to 0.3, y is 0 to 0.1)) is achieved by a lithium ion secondary battery.

Hereinafter, the principle of the present invention will be described through a more detailed description of the method for producing a lithium composite oxide of the present invention.

First, ammonia water and an alkaline solution are added to a mixed aqueous solution containing a cobalt salt and a nickel salt, optionally, a third metal salt selected from aluminum, calcium, magnesium or boron. Here, the aqueous ammonia serves to control the shape of the complex hydroxide formed as a complex, and the alkaline solution serves to maintain a pH suitable for coprecipitation in the mixed aqueous solution as a pH adjusting agent. The preferred pH range is 10.5 to 11.5 to maintain basicity. Extraction of the coprecipitation product after a predetermined time after the coprecipitation forms a composite hydroxide of spherical nickel-cobalt, and optionally a nickel-cobalt-third metal, in which needle-like fine particles are aggregated. At this time, the shape of the particles can be adjusted according to the coprecipitation reaction time and pH. In the present invention, the co-precipitate was extracted at the time point where the secondary particles form a sphere while continuously monitoring the particle shape of the co-precipitate. In the present invention, the coprecipitation time was 6-10 hours. When the coprecipitation time is less than 6 hours, the surface state of the finally obtained lithium composite oxide particles is not flat, and it is difficult to obtain a tap density in a desired range, and the coprecipitation time is 10 hours. In the above case, primary particles constituting the finally obtained lithium composite oxide particles are fused, which is advantageous for improving the tap density, but decreases the insertion / deinsertion efficiency of lithium ions.

Lithium hydroxide is partially added to the surface of the nickel-cobalt composite oxide or the nickel-cobalt-third metal composite oxide by adding lithium hydroxide to the spherical composite hydroxide in which the needle-shaped fine particles are aggregated, and performing primary heat treatment at 280-420 ° C. After forming an intermediate product in a dissolved state, and slowly cooled to room temperature, and then subjected to a second heat treatment at 650-700 ° C. and then cooled to room temperature. The first heat treatment and the second heat treatment are carried out for 4-7 hours and 10-20 hours, respectively, in which the form of the particles can be preferably maintained.

That is, in the present invention, it is very important that the aggregate of needle-shaped primary particles grows into spherical secondary particles after extraction for a predetermined time after co-precipitating the nickel-cobalt composite hydroxide. In the present invention, a needle, preferably an aggregate of needle-like fine particles having a length of about 1 μm or less and a width of about 0.1 μm or less, forms a composite hydroxide of spherical particles, and then uses this as a starting material. A lithium composite oxide with a unique structure is produced. Therefore, the present invention is characterized in that the particle form of the final product is obtained in a desired form by adjusting the particle form of the starting compound, and ammonia water is used to control the particle form of the starting compound. In the reaction mechanism of coprecipitation, by using ammonia water as a complexing agent and controlling only the coprecipitation reaction time, it is possible to easily control the particle form of the composite hydroxide as a starting compound.

Since the method for producing the positive electrode using the lithium composite oxide prepared as an active material is not particularly limited, a method commonly used may be applied as it is. In addition, in manufacturing a lithium ion secondary battery using the positive electrode thus prepared, a conventional method may be used as it is.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

<Example 1>

In the reactor, nitrates of nickel, cobalt, and magnesium were mixed at a molar ratio of 0.79: 0.19: 0.02 to form a solution having a molar concentration of 2.5M of all metals, to which ammonia water was added in an amount of 1 mol and 6M NaOH was added thereto. And co-precipitated using a pH of about 11. After 6 hours, the spherical nickel-cobalt composite hydroxide was separated. LiOH is mixed on the surface of the nickel-cobalt composite oxide by mixing the composite hydroxide and LiOH.H ₂ O at a ratio of 1: 1 and then heating it to 400 ° C. at a heating rate of 2 ° C. per minute in a dry air atmosphere. Intermediate products that were present in partially dissolved state were obtained and then maintained at this temperature for 6 hours and then cooled slowly to obtain SEM images (see FIGS. 1A and 1B). Subsequently, the oxide formed by the heat treatment was heated to about 700 ° C. at a temperature increase rate of about 1 ° C. per minute, and then subjected to secondary heat treatment (sintering) under a dry air atmosphere at this temperature for about 16 hours, followed by a cooling rate of about 1 ° C. per minute. Scanning electron micrographs were taken by cooling to room temperature (see FIGS. 1C and 1D).

Figure 1a is a SEM image of the nickel-cobalt oxide obtained after the first heat treatment with the coprecipitation reaction time of 6 hours, showing that LiOH is almost decomposed by the heat treatment and adhered or dissolved on the surface of the nickel-cobalt oxide. 1B is an SEM photograph showing the surface state of the particles shown in FIG. 1A.

FIG. 1C is a SEM photograph of a lithium composite oxide finally obtained after secondary heat treatment (sintering), and FIG. 1D is a SEM photograph showing the surface state of the particles shown in FIG. 1C. The average particle size of the powder particles after sintering is similar to the average particle size of the starting material, but the fine primary particles are changed from needle bed to square, and the square particles slightly protrude out of the secondary particles.

The tap density of the lithium composite oxide powder obtained by cooling after the secondary heat treatment was about 2.4 g / cm ³ .

Subsequently, a coin battery for a test was made according to a conventional method using the powder, followed by charging and discharging experiments at 0.2C. The result is shown as a graph of FIGS. 2A and 2B. From the graphs of FIGS. 2A and 2B, the initial capacity was 160 mAh / g, and it can be seen that the initial capacity was almost maintained even after 30 charge / discharge cycles.

<Example 2>

A lithium composite oxide was prepared in the same manner as described in Example 1, except that the coprecipitation reaction time was 10 hours.

FIG. 3A is a SEM photograph of a nickel-cobalt oxide obtained after the first heat treatment with a coprecipitation reaction time of 10 hours, similarly to FIG. 1A, in which LiOH is almost decomposed and adhered or dissolved on the surface of the nickel-cobalt oxide. 3b is a SEM photograph showing the surface state of the particles shown in FIG. 3a. Comparing FIG. 3A and FIG. 1A and FIG. 3B and 1B, when the coprecipitation time was set to 10 hours, it turns out that the surface state of particle | grains becomes more dense and flat.

FIG. 3C is a SEM photograph of a lithium composite oxide finally obtained after secondary heat treatment (sintering). FIG. 3D is a SEM photograph showing the surface state of the particles shown in FIG. 3C. 3C and 1C and 3D and 1D show that even if the coprecipitation time is changed, the size of the secondary particles of the lithium composite oxide finally obtained is not significantly affected, but the particles obtained when the surface state is set to 10 hours It can be seen that it is much flatter.

The tap density of the lithium composite oxide powder obtained by cooling after the secondary heat treatment was about 3.2 g / cm ³ .

<Example 3>

Only nickel salt and cobalt salt were used in a molar ratio of 0.8: 0.2, and in the first heat treatment, the mixture was heated to 350 ° C. at a temperature rising rate of 5 ° C. per minute for 8 hours, and then cooled to room temperature at a cooling rate of 3 ° C. per minute, 2 Lithium composite oxide in the same manner as described in Example 1 except that the heat treatment was heated at a temperature increase rate of 3 ℃ per minute and reacted at 700 ℃ for 16 hours and then cooled to room temperature at a cooling rate of 2 ℃ per minute After preparing a coin battery was prepared. A charge and discharge experiment was conducted using this battery. After charging and discharging twice at 0.2C and then performing 20 times charging and discharging at 0.5C, the results are shown as graphs of FIGS. 4A and 4B. It can be seen from FIGS. 4A and 4B that there is almost no decrease in capacity even when charging and discharging at 0.5C.

In the case of using the lithium composite oxide prepared in the above example as the positive electrode active material, the particle shape of the active material as a whole may increase the filling rate per unit volume, and the spherical particles themselves are aggregates of rectangular fine particles. It is advantageous for the insertion / deinsertion of ions. In addition, since the surface state of the final particle is easily controlled by controlling the coprecipitation reaction time within an appropriate range in the manufacturing process of the lithium composite oxide, the manufacturing process is simple.

The lithium composite oxide according to the present invention can increase the battery capacity when used as a positive electrode active material of a lithium ion secondary battery because it is easy to insert / de-insertion of lithium ions and has a high tap density, and can be manufactured by a simple method.

Claims (12)

Lithium composite oxide (LiNi _(1-xy) Co _x M _y O _{2 )} , characterized in that the aggregate of minute rectangular primary particles is composed of spherical secondary particles and has a tap density of 2.4-2.7 g / cm ³ . (M = Al, Ca, Mg, and at least one metal atom selected from B, x is from 0.1 to 0.3, y is from 0 to 0.05). The lithium composite oxide of claim 1, wherein the primary particles have a rectangular shape and the average size of the particles is 0.2-0.5 μm. The lithium composite oxide of claim 1, wherein an average particle diameter of the secondary particles is 5 to 20 μm. a) extracting the nickel-cobalt composite hydroxide by coprecipitation for 6-10 hours by adding an aqueous ammonia solution as a complex and an alkaline solution as a pH adjusting agent to a mixed aqueous solution of cobalt salt and nickel salt, b) primary heat treatment at 280-420 ° C. by adding lithium hydroxide to the composite hydroxide, and c) a lithium composite oxide comprising a second heat treatment of the resultant obtained by the first heat treatment at 650-700 ° C. ((LiNi _(1-x) Co _x O ₂ (x is 0.1 to 0.3)) Manufacturing method. 5. The method according to claim 4, wherein the salt of at least one metal selected from Al, Ca, Mg, and B is added to the total metal salt before adding the complexing agent and the pH adjusting agent to the mixed solution of nickel salt and cobalt salt in step a). It adds in the following ratios. The method of claim 4 or 5, wherein the lithium composite oxide (LiNi _(1-xy) Co _x M _y O ₂ (M = Al, Ca, Mg and B is at least one metal atom selected from B, x is from 0.1 to 0.3, y is 0 to 0.1)), characterized in that the aggregate of minute rectangular primary particles is composed of spherical secondary particles. 7. The method of claim 6, wherein the tap density of the lithium composite oxide is 2.4-3.2 g / cm ³ . The method of claim 4 or 5, wherein the primary heat treatment is performed in a dry air atmosphere. The method of claim 4 or 5, wherein the secondary heat treatment is performed in a dry air atmosphere. In a lithium ion secondary battery comprising a positive electrode having a lithium oxide as an active material, a carbon-based negative electrode, and a non-aqueous electrolyte, the lithium oxide of the positive electrode is composed of spherical secondary particles in a collection of minute rectangular primary particles. Lithium composite oxide with a tap density of 2.4-3.2 g / cm ³ (LiNi _(1-xy) Co _x M _y O ₂ (M = Al, Ca, Mg and B is at least one metal atom selected from, and x is 0.1 To 0.3, and y is 0 to 0.1)). The lithium composite oxide of claim 10, wherein the primary particles have a rectangular shape and have an average size of 0.2-0.5 μm. The lithium composite oxide of claim 9, wherein the secondary particles have an average particle diameter of 5 to 20 μm.