KR100934612B1 - Cathode active material for nonaqueous electrolyte secondary battery, preparation method thereof, method for manufacturing nonaqueous electrolyte secondary battery, and positive electrode - Google Patents

Abstract

A cathode active material for a nonaqueous electrolyte secondary battery having a high charging efficiency and a high charging density that can be effectively improved by improving the load characteristics of the nonaqueous electrolyte secondary battery, and a manufacturing method thereof, the cathode active material comprising Li, D1 / D2 composed of composite oxide particles comprising at least one transition element selected from the group consisting of Co, Ni, Mn, and Fe, wherein the composite oxide particles have the longest diameter D1 and the shortest diameter D2 90% or more of spherical and / or ellipsoidal particles in the range of 1.0 to 2.0 are included.

Composite oxide, lithium compound, transition element, specific surface area, nonaqueous electrolyte, secondary battery, positive electrode active material, firing

Description

ANODE ACTIVE MATTER, PRODUCTION METHOD THEREFOR, NONAQUEOUS ELECTROLYTE SECONDARY BATTERY, AND PRODUCTION METHOD

The present invention provides a positive electrode active material for a nonaqueous electrolyte secondary battery that can effectively improve load characteristics and increase the capacity in a secondary battery using a nonaqueous electrolyte as an electrolyte, a method of manufacturing the same, and a nonaqueous electrolyte secondary using the positive electrode active material. A battery and the manufacturing method of the positive electrode for nonaqueous electrolyte secondary batteries.

In recent years, miniaturization, light weight, and high performance of portable electronic devices such as video cameras, portable CDs, cellular phones, PDAs, and notebook computers are being advanced. The power source of the portable electronic device requires a secondary battery having high capacity and high stability with excellent heavy load characteristics. Sealed lead-acid batteries and nickel-cadmium accumulators have been used as secondary batteries meeting these purposes. Lithium-ion secondary batteries are becoming practical as nickel-hydrogen storage batteries and non-aqueous electrolyte secondary batteries as batteries with higher energy density.

Lithium ion secondary batteries use carbon, such as carbon which can insert and remove lithium ions into a negative electrode active material, using a composite oxide of Li, a transition metal such as Co, Ni, and Mn as a positive electrode active material. It is a secondary battery using quality materials, and has a characteristic of having a large capacity and a high voltage as compared with nickel hydrogen storage batteries. However, in order to meet the recent demand for higher capacity and higher current, measures such as increasing the packing density of the positive electrode active material and increasing the weight of the positive electrode active material by reducing the amount of the conductive assistant mixed with the positive electrode active material are necessary. It became.

In order to meet these demands, various studies have been conducted. Among them, the cathode active material is spherical to increase the filling efficiency, and the filling efficiency is increased to increase the contact area between the active materials, thereby improving the conductivity and preparing the conductive material in the positive electrode. Attempts have been made to reduce and substantially increase the active weight.

For example, Japanese Patent Application Laid-Open No. 10-74516 discloses a technique in which a positive electrode active material is made into a hollow sphere to improve filling efficiency and increase a specific surface area, thereby increasing the contact area with the electrolyte solution to increase the responsiveness in heavy loads. Is disclosed. However, in this method, since the active material is hollow spherical, the improvement of the filling efficiency due to the spherical shape decreases the amount of active material that can be charged per unit volume, and high capacity cannot be expected.

Japanese Unexamined Patent Application Publication No. 11-273678 discloses a spherical positive electrode active material by mixing and calcining cobalt oxyhydroxide and a lithium compound using spherical or ellipsoidal cobalt oxyhydroxide as a cobalt source of a lithium cobalt positive electrode active material. Techniques for making are disclosed. Japanese Patent Laid-Open No. 11-288716 discloses a technique for producing a spherical positive electrode active material by mixing and firing a spherical or ellipsoidal nickel cobalt hydroxide and a lithium compound in which primary particles are radially aggregated.

However, in these methods, when the reaction for producing the positive electrode active material occurs, the decomposition reaction of the lithium compound and the decomposition reaction of the transition metal compound occur simultaneously. Since these decomposition reactions are accompanied by the production of gases such as steam and carbon dioxide gas, the produced active substance remains spherical but has a lot of voids, and the amount of active substance that can be charged per unit volume decreases. High doses cannot be expected.

(Initiation of invention)

SUMMARY OF THE INVENTION An object of the present invention is to provide a positive electrode active material for a nonaqueous electrolyte secondary battery having a high charging efficiency and a high packing density, which can effectively improve the load characteristics of the nonaqueous electrolyte secondary battery and to increase the capacity. .

Another object of the present invention is to provide a nonaqueous electrolyte secondary battery capable of obtaining excellent discharge capacity and a method for producing a positive electrode for the nonaqueous electrolyte secondary battery.

According to the present invention, a composite oxide particle comprising Li and at least one transition element selected from the group consisting of Co, Ni, Mn, and Fe, wherein the composite oxide particle has the longest diameter D1 and the shortest diameter A positive electrode active material for a non-aqueous electrolyte secondary battery containing 90% or more of spherical and / or ellipsoidal particles having D1 / D2 in the range of 1.0 to 2.0 when referred to as D2 is provided.

According to the present invention, step (A) of preparing a raw material mixture by mixing compound particles of at least one transition element selected from the group consisting of Co, Ni, Mn, and Fe and a raw material containing a lithium compound; Positive electrode active material for a nonaqueous electrolyte secondary battery comprising a step (B) of calcining at a temperature equal to or higher than the melting point of the lithium compound in the raw material mixture and a step (C) of firing at or above the decomposition temperature of the lithium compound in the raw material mixture The preparation of is provided.

Further, according to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material powder, a negative electrode, and an electrolytic solution, wherein the positive electrode active material powder comprises the positive electrode active material for a nonaqueous electrolyte secondary battery.

Furthermore, according to the present invention, as a method for producing a positive electrode for use in the nonaqueous electrolyte secondary battery, which is formed by molding a positive electrode active material containing composite oxide particles, the particle is mainly composed of particles having a particle diameter of 2 to 100 µm and an average particle diameter. It is 5-80 micrometers, and it contains Li and Co, Ni, Mn, and at least 1 sort (s) of transition elements selected from the group which consists of Fe, and when D1 / D2 is 1.0 when the longest diameter is D1 and the shortest diameter is D2, Step (a) of preparing at least two composite oxide particles having an average particle diameter of 10% or more from the composite oxide particles containing 90% or more of spherical and / or elliptic spherical particles in the range of -2.0, and the process ( Provided is a method for producing a positive electrode for a non-aqueous electrolyte secondary battery comprising the step (b) of mixing the composite oxide particles prepared in a) to obtain a positive electrode active material.

1 is a photograph of an SEM image at 1000 magnification of the positive electrode active material prepared in Example 1, and

2 is a SEM image of 5000 magnification of the positive electrode active material prepared in Example 1. FIG.

 (Preferred Embodiment of the Invention)

Hereinafter, the present invention will be described in more detail.

The positive electrode active material (hereinafter referred to as the positive electrode active material of the present invention) for a nonaqueous electrolyte secondary battery of the present invention contains Li and at least one transition element selected from the group consisting of Co, Ni, Mn and Fe. It consists of specific composite oxide particles.

Examples of the composite oxide include LiCo _X Ni ₁ such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ , LiCo _0.8 Ni _0.2 O ₂ , LiCo _0.5 Ni _0.5 O ₂ , LiCo _0.1 Ni _0.9 O _2, and the like. _And oxides represented by _-X O ₂ (0≤X≤1).

In addition to the above composition, the positive electrode active material of the present invention may contain at least one selected from the group consisting of alkali metals, alkaline earth metals, Ti, Zr, Hf, Y, Sc, rare earth metals, and the like. These metal elements have the effect of increasing the lattice spacing of the positive electrode active material of the present invention to increase its capacity, increase charge and discharge efficiency, improve the sinterability of the positive electrode active material, and increase the density.

The addition amount of these additional elements is preferably 1% by weight or less, and particularly preferably 0.5% by weight or less and 0.3% by weight or less. Even if it adds more than 1 weight%, density improvement cannot be expected, but since the capacity | capacitance of the positive electrode active material of this invention may fall, it is unpreferable.

The shape of the composite oxide particles as the positive electrode active material of the present invention is mainly spherical or ellipsoidal. Needles, spindles, plates, and irregular ones are not preferable because they cannot increase the charging efficiency, and even elliptic spheres have a large aspect ratio and are not preferable because the charging efficiency decreases when they are close to the spindle.

Accordingly, the composite oxide particles are spherical and / or ellipsoidal particles having a D1 / D2 (aspect ratio) of 1.0 to 2.0, preferably 1.0 to 1.5 when the longest diameter is D1 and the shortest diameter is D2. More than 90%.

The tap density of the positive electrode active material of the present invention is preferably higher. If the tap density is low, the filling efficiency of the positive electrode active material is deteriorated, so that many active materials cannot be filled in the volume of the limited electrode plate, and the capacity decreases. In the positive electrode active material of the present invention, the tap density is preferably at least 2.9 g / cm ³ , particularly preferably at least 3.0 g / cm ³ , more preferably at least 3.1 g / cm ³ . The upper limit of the tap density is not particularly limited, but is usually about 5.0 g / cm ³ .

The particle size distribution and average particle diameter of a particle play an important role in the improvement of the said tap density. If the particle size distribution is too wide or too narrow, the filling efficiency of the particles is deteriorated, and if the average particle diameter is too small, the surface energy of the particles is increased, which causes a decrease in the filling efficiency. If the average particle diameter is too large, it becomes difficult to uniformly apply the active substance onto the current collector when preparing the electrode.

Therefore, the particle diameter of the composite oxide particles constituting the positive electrode active material of the present invention is preferably in the range of 2 to 100 µm, particularly 10 to 100 µm, particularly 80% or more, more preferably 85% or more, Moreover, it is preferable that 90% or more exists in the said range. Moreover, it is preferable that an average particle diameter is 5-80 micrometers, especially 30-80 micrometers, and further 30-60 micrometers. If the average particle diameter is less than 5 µm or larger than 80 µm, even if the range of the particle diameter is in the above-described preferred range, the particle size distribution becomes too narrow and the filling efficiency is not preferable.

Here, the particle size of the composite oxide is a value measured with a laser diffraction particle size distribution meter (Micro Track HRA, manufactured by Honey Well), and the average particle diameter is a D50 value.

The specific surface area of the composite oxide is preferably 0.05 to 0.24 m ² / g, particularly preferably 0.1 to 0.2 m ² / g. When the specific surface area is less than 0.05m ² / g, the internal resistance of the positive electrode obtained becomes large, the high-rate discharge characteristic is not preferable because it decreases. On the other hand, exceeds 0.24m ² / g, the higher the reactivity as the electrolytic solution, obtained It is not preferable because the thermal stability of the anode is lowered.

In addition, when actually manufacturing a positive electrode using the composite oxide particle which comprises the positive electrode active material of this invention, in order to improve the filling efficiency of a positive electrode active material, the mixture of the at least 2 types of said composite oxide particle from which the said average particle diameter differs is prepared. It is preferable to use. At this time, it is preferable that the composite oxide particles to be mixed differ in average particle diameter by 10% or more.

The method for producing the positive electrode active material of the present invention is not particularly limited as long as the positive electrode active material of the present invention can be obtained. For example, it can obtain by the method of mixing the lithium compound used as a lithium source, and the compound of the transition element used as a transition metal source, setting a suitable condition, and baking. As a preferable method, the manufacturing method of this invention shown below is mentioned.

The manufacturing method of this invention performs the process (A) of first preparing the raw material mixture by mixing the compound particle of the transition element used as a specific transition metal source, and the raw material containing the lithium compound used as a lithium source.

The lithium compound serving as the lithium source preferably has a melting point of 800 ° C. or lower and a pyrolysis temperature of 1100 ° C. or lower, and examples thereof include inorganic salts such as lithium hydroxide, lithium chloride, lithium nitrate, lithium carbonate and lithium sulfate; Organic salts, such as lithium formate, lithium acetate, and a lithium oxalate, etc. are mentioned.

The compound particles of the transition element serving as the transition metal source are compound particles of at least one transition element selected from the group consisting of Co, Ni, Mn and Fe, and the pyrolysis temperature is preferably 1100 ° C. or lower, for example And hydroxides and carbonates. In view of the purpose of improving the tap density, oxide particles of transition metals which do not pyrolyze are preferable.

The particle shape of the transition metal source is preferably spherical and / or ellipsoidal spherical particles. As a method of obtaining such particles, for example, spherical particles may be spherical by granulation, liquid or slurry compounds may be spherical by spray drying or spray firing, spherical precipitation or the like. The method of directly obtaining the particle | grains of is mentioned. In the case of using spherical oxide particles, these spherical particles can be calcined and obtained. When the firing temperature at this time is low, the tap density is also lowered, and therefore, firing at a temperature of 500 ° C. or higher is preferable.                 

The spherical and / or elliptic spherical transition metal source preferably has a certain tap density at this stage. When the tap density in this step is low, the tap density of the obtained positive electrode active material also decreases. The tap density of such spherical and / or elliptic spherical transition metal sources is preferably 2.0 g / cm ³ or more, more preferably 2.2 g / cm ³ or more, and still more preferably 2.4 g / cm ³ or more. The upper limit of the tap density is not particularly limited, but is usually about 5.0 g / cm ³ .

In the production method of the present invention, in the raw material containing the lithium source and the transition metal source described above, if necessary, the above-described additive elements, that is, alkali metal, alkaline earth metal, Ti, Zr, Hf, Y, Sc and rare earth It may contain at least one metal compound selected from the group consisting of metals and the like. Mixing of these raw materials can be performed by a well-known method.

In the production method of the present invention, the firing of the raw material mixture prepared in step (A) is carried out in two steps of a specific calcination step and a specific calcination step in order to improve the tap density of the cathode active material of the present invention obtained.

A specific calcination process is a process (B) which calcinates at the temperature more than melting | fusing point of the lithium compound used for the raw material mixture in process (A). In this calcination step, the object is to impregnate the lithium compound in the compound particles of the transition element which is the raw material. Therefore, it is preferable that the upper limit of holding temperature is less than the decomposition temperature of a lithium compound, and also 300-950 degreeC, especially 500-800 degreeC is preferable. The holding time is preferably 10 to 300 minutes.

A specific baking process is a process (C) which bakes the compound of the transition element which passed through the calcination process, for example, the lithium compound impregnated above the decomposition temperature of the lithium compound used for the raw material mixture in process (A). In this firing step, a lithium compound is reacted with a compound of a transition element to produce a positive electrode active material of the present invention. Although the temperature at this time should just be the decomposition temperature of a lithium compound, when the decomposition temperature of a lithium compound is low, since it may require time for reaction with the compound particle of a transition element, Preferably it is 700-1100 degreeC, More preferably, it is 800-1100 degreeC. If the holding time is too short, the reaction will not be completed. If the holding time is too long, the solid phase reaction may proceed too much and the particles may adhere to each other. Preferably, the holding time is 10 to 1800 minutes, more preferably 10 to 900 minutes.

In the manufacturing method of this invention, although the positive electrode active material of this invention can be obtained by the said process, you may include another process as needed.

The nonaqueous electrolyte secondary battery of the present invention may include a positive electrode having a positive electrode active material powder, a negative electrode, and an electrolytic solution, and include the positive electrode active material of the present invention as the positive electrode active material, and another configuration, and other additional features. The configuration and the like can be appropriately selected from known ones.

In addition, in order to manufacture the positive electrode used for the said nonaqueous electrolyte secondary battery, it consists mainly of particle | grains of 2-100 micrometers of particle diameters, and has an average particle diameter of 5-80 micrometers, and is made of Li, Co, Ni, Mn, and Fe. 90% of spherical and / or ellipsoidal particles having at least one transition element selected from the group consisting of D1 / D2 in the range of 1.0 to 2.0 when the longest diameter is D1 and the shortest diameter is D2. A process of preparing a positive electrode active material by mixing the composite oxide particles prepared in the step (a) with the step (a) of preparing at least two composite oxide particles having an average particle diameter of 10% or more from the composite oxide particles including the above It can obtain by performing (b). The mixing ratio of at least two composite oxide particles having an average particle diameter of 10% or more is preferably in the range of 1: 9 to 9: 1 by weight ratio in the case of two types, for example.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a composite oxide of spherical and / or elliptic spherical particles, the aspect ratio of these particles is in the range of 1.0 to 2.0, and the tap density is 2.9 g / cm ³ or more. In the case of using the electrode, the electrode density can be about 3.4 to 3.7 g / cm ³ , and the discharge capacity and the load characteristics per volume in the nonaqueous electrolyte secondary battery can be effectively improved. Moreover, in the manufacturing method of this invention, such a positive electrode active material can be obtained easily. Furthermore, the nonaqueous electrolyte secondary battery of the present invention uses the positive electrode active material of the present invention, so that the discharge capacity and the load characteristics can be improved.

(Example)

Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to this.

Example 1

100 g of cobalt metal having a purity of 99.8% was dissolved in nitric acid, and then diluted with pure water to obtain 1650 ml. Subsequently, 820 ml of 4N sodium hydroxide solution was added and stirred, followed by filtration to obtain a hydroxide cake composed of spherical or ellipsoidal particles. The cake was baked at 850 ° C. for 4 hours to obtain cobalt oxide particles as 137 g of spherical or ellipsoidal particles. After uniformly mixing 137 g of the obtained cobalt oxide particles and 65 g of lithium carbonate, the obtained mixture was calcined at 700 ° C. for 240 minutes, and further calcined at 850 ° C. for 300 minutes to obtain spherical or ellipsoidal particles.

The obtained particles were irradiated with an ICP emission spectrophotometer, an X-ray diffractometer, an electron microscope, and a tapped denser device (manufactured by Seishin Corporation, XYT-2000). The particle size of the primary particles was 0.2 to 10 µm, It was found that the particle size was a composite particle having a particle size of 10 to 100 µm, an aspect ratio of 1 to 1.5, and particles of LiCoO ₂ having a shape having a tap density of 3.2 g / cm ³ or more. In addition, it was found that the specific surface area of the particles was 0.15 m ² / g.

In addition, the measurement of the tap density measured 10.0g of the obtained particle | grains in 20 ml cylinders, and measured it by tap height 2cm and tap collection time 200 times. The specific surface area was measured by 1 g of the obtained particles, degassed at 200 ° C. for 20 minutes, and then subjected to N ₂ adsorption BET method using the brand name “N0VA2000” manufactured by Canthachromes. The results are shown in Table 1.

In addition, the SEM photograph of 1000 magnification of the particle | grains as the obtained positive electrode active material is shown in FIG. 1, and the SEM photograph of 5000 magnification is shown in FIG.

Further, the obtained particles, acetylene black as a conductive aid, and PTFE as a binder were mixed in a weight ratio of 50:40:10 to prepare a positive electrode mixture to prepare a positive electrode made of a stainless steel sheet as a current collector. Moreover, the negative electrode of the lithium metal which used the stainless steel plate as an electrical power collector was produced. Furthermore, lithium perchlorate was dissolved at a rate of 1mo1 / L in a solution in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1, to prepare an electrolyte solution. The lithium ion secondary battery was produced using the obtained positive electrode, negative electrode, and electrolyte solution.

The initial discharge capacity of the obtained battery was measured with a charge upper limit voltage of 4.3 V and a discharge lower limit voltage of 3 V under conditions of a charge current density of 3 mA / cm ² . Further, the obtained particles, graphite as a conductive aid and PVDF as a binder were mixed in a weight ratio of 90: 5: 5, and applied to an Al current collector having a thickness of 20 µm by the doctor blade method, and the pressure was 3 t / cm ^2. It pressed and produced the electrode. The volume and weight of the obtained electrode were measured, the volume and weight of Al collector were subtracted, and electrode density was computed. The results are shown in Table 1.

Examples 2-5

The cake firing temperature of Example 1 was 500 ° C, 700 ° C, 800 ° C or 900 ° C, the plasticity time was 240 minutes, 480 minutes, 360 minutes or 640 minutes, and the main firing temperature was 800 ° C, 850 ° C, 900 ° C or 950 Example 1 was carried out for 600 minutes, 1200 minutes, 60 hours or 100 hours, respectively, except that lithium oxalate, 47 g of lithium nitrate, 35 g of lithium hydroxide, or 44 g of lithium sulfate were used instead of lithium carbonate. By the same operation, the particle size of the primary particle was 0.2-10 micrometers, the particle size of the secondary particle was 10-100 micrometers, the spherical or elliptic spherical particle of aspect ratio 1-1.5 was produced, and each measurement and evaluation were performed. . The results are shown in Table 1.

Examples 6-11

Instead of the hydroxides which are spherical or ellipsoidal particles, the molar ratio of nickel atoms and cobalt atoms is 8: 2, 5: 5, 1: 9 or 10: 0, and the coprecipitation hydroxides or the molar ratio of cobalt atoms and manganese atoms is 5: The particle size of the primary particles was 0.2 to 10 µm, and the particle size of the secondary particles was 10 by the same operation as in Example 1, except that a monovalent coprecipitation hydroxide and a coprecipitation hydroxide having a molar ratio of manganese atoms and nickel atoms of 1: 1 were used. It was composite particle which is -100 micrometers, the spherical or elliptic spherical particle with aspect ratio 1-1.5 was produced, and each measurement and evaluation were performed. The results are shown in Table 1.

Comparative Examples 1 and 2

A needle-like or amorphous composite oxide was produced and measured and evaluated in the same manner as in Example 1 except that a needle-like or amorphous hydroxide was used instead of the spherical or elliptic-shaped particles. The results are shown in Table 1.                 

Examples 12-14

The particles prepared in Example 1 were classified, divided into small particle groups having an average particle diameter of 10 µm and large particle groups having an average particle diameter of 70 µm, and each was 1: 1 (Example 12) and 3: 7 (Example) by weight ratio. 13) or 1: 9 (Example 14), to obtain a positive electrode active material, and to prepare an electrode in the same manner as in Example 1, each measurement and evaluation were performed. The results are shown in Table 2.

Claims (10)

Oxide of a transition element obtained by firing at 500 to 900 ° C. of compound particles of at least one transition element selected from the group consisting of Co, Ni, Mn, and Fe, wherein the particle shape is at least one selected from spherical and ellipsoidal (A) preparing a raw material mixture by mixing raw materials containing particles and a lithium compound; (B) calcining at a temperature equal to or higher than the melting point of the lithium compound in the raw material mixture; And A method for producing a positive electrode active material comprising the step (C) of firing at or above the decomposition temperature of a lithium compound in a raw material mixture, When the longest diameter is D1 and the shortest diameter is D2, the nonaqueous electrolyte secondary containing at least one particle selected from spherical and elliptic spheres in the range of 1.0 to 1.5, and having a tap density of 2.9 to 3.3 g / cm 3 Method for producing a positive electrode active material for batteries. 2. The process according to claim 1, wherein the temperature in the step (B) is 300 to 950 ° C, the holding time is 10 to 300 minutes, the temperature in the step (C) is 700 to 1100 ° C, and the holding time is 10 to 1800. Method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, characterized in that the powder. delete delete delete delete delete delete delete delete

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