TW201438996A - Method for producing microparticles, method for producing positive electrode active material for lithium ion secondary cell, positive electrode active material, lithium ion secondary cell using same, and source emulsion for producing microparticles - Google Patents

Abstract

Provided is a method for producing microparticles, the method being characterized in being provided with: a step for spraying a source emulsion as droplets, the source emulsion being a water-in-oil emulsion obtained so that silicon-containing microparticles and a source solution containing source metal ions other than those of lithium and silicon in addition to lithium ions are dispersed in a flammable liquid; and a step for forming microparticles by combusting the flammable liquid in the droplets. The source emulsion may contain a surfactant. The surfactant may be a nonionic surfactant having an HLB of 3-6.

Description

Method for producing microparticles, method for producing cathode active material for lithium ion secondary battery, cathode active material, lithium ion secondary battery using the same, and raw material emulsion for fine particle production Technical field

The invention relates to a liquid material which is sprayed from a nozzle, A method and a manufacturing apparatus for producing fine particles by a spray combustion method in which a fine particle is burned in a flame. In particular, the present invention relates to the production of a positive electrode active material for a lithium ion secondary battery of a tannic acid type such as lithium iron silicate.

Background technique

In recent years, small and lightweight lithium ion secondary batteries have been widely used as power sources for mobile electronic devices such as mobile phones, notebook computers, digital cameras, and video cameras. Moreover, under the popularity of electric vehicles, lithium-ion batteries with high functionality and low cost are also required. Now, the positive electrode active material of a lithium ion secondary battery generally uses lithium cobaltate (LiCoO ₂ ). However, lithium cobalt oxide is a problem in which cobalt having a large resource and high toxicity and high toxicity is contained, and heating to a high temperature releases oxygen and may cause fire and has a low safety. On the other hand, the new positive electrode active material which is superior in thermal and chemical stability to lithium cobalt oxide and which can be obtained from a rich raw material system has lithium iron phosphate (LiFePO ₄ ) and lithium iron citrate having an olivine structure. (Li ₂ FeSiO ₄ ) and the like have attracted attention. However, these materials are originally low in conductivity, and the Li ion diffusion rate inside the crystal is slow, so it is processed into fine particles having a primary particle diameter of several tens to 100 nm.

The method for producing the above-mentioned nano-sized fine particles has been proposed to introduce a raw material solution prepared by dissolving a plurality of organometallic compounds containing a halogenated alkane and lithium or iron in a combustible organic solvent, such as lithium iron citrate. In the burner, the nozzle is sprayed from a nozzle attached to the tip end of the burner to be burned to form cerium oxide and the core particles of the metal oxide of each of the above metals, and the cerium oxide is formed by the agglomeration of the core particles. A technique of composite fine particles composed of a plurality of metal oxides (refer to, for example, Patent Document 1).

However, the active material of the bismuth hydride-based lithium ion battery produced by the method disclosed in the above patent document has a small particle size and good battery characteristics, but the raw material needs to use lithium and other metal materials which are soluble in an organic solvent. Raw materials are very expensive, so it is difficult to reduce the manufacturing cost of the active materials required.

Advanced technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2012-195134

Summary of invention

A method of spraying a raw material solution prepared by dissolving a plurality of organometallic compounds of lithium or iron in a flammable organic solvent and burning the same from a nozzle attached to the tip end of the burner, although the raw material has good combustion property. , but the particles can be made, but the raw materials are expensive, so there is a cost increase. question. Further, when a raw material solution prepared by dissolving a metal salt or the like in an aqueous solvent is used, the cost is low, but the flammability at the time of spraying is poor compared to when a plurality of organometallic compounds are dissolved in a flammable organic solvent. And the mixing of larger particles will occur.

In view of the above circumstances, it is an object of the present invention to provide a method for producing fine particles of a lithium ion secondary battery active material which can be produced by a spray combustion method and having a small particle size and a good property at a low cost. A lithium ion secondary battery of the method and a raw material emulsion thereof.

To achieve the foregoing objects, the present invention has the following features.

(1) The present invention is a method for producing fine particles, which comprises the steps of: preparing a raw material emulsion which is a water-in-oil emulsion and dispersing a raw material solution in the form of droplets in a flammable liquid, the raw material The solution contains at least a cerium-containing fine particle and a lithium source, and a raw material metal source other than cerium and lithium; a step of spraying the raw material emulsion into a droplet form; and a step of burning the flammable liquid in the liquid droplet to form fine particles.

(2) The method for producing fine particles as disclosed in (1), characterized in that lithium is Li, lanthanum is Si, and further selected from the group consisting of Fe, Mn, Ti, Cr, V, Ni, Co, Cu, and Zn. One or two or more metal elements of the group consisting of Al, Ge, Zr, Mo, and W are M, and are selected from the group consisting of Ti, Cr, V, Zr, Mo, W, P, and B. When at least one metal element in the constituent group is X, the composition of the fine particles is expressed by the formula as Li _y MSi _1-z X _z O ₄ , 1 ≦ y ≦ 2, and 0 ≦ z < 0.4.

(3) The method for producing a microparticle according to (1), characterized in that the aforementioned raw material The emulsion contains a surfactant.

(4) The method for producing fine particles disclosed in (3), characterized in that the surfactant is a nonionic surfactant having a HLB of 3 to 6.

(5) The method for producing fine particles disclosed in (1), characterized in that the droplets of the raw material solution dispersed in the flammable liquid have an average particle diameter of 0.5 to 10 μm.

(6) The method for producing fine particles disclosed in (1), characterized in that the droplets of the raw material emulsion sprayed have an average particle diameter of 5 to 500 μm.

(7) The method for producing a fine particle according to (1), characterized in that the ruthenium-containing fine particles are fine particles containing ruthenium dioxide or lithium niobate.

(8) The method for producing a fine particle according to (1), wherein the raw material solution contains lithium and a nitrate, a hydroxide, a hydrochloride, a sulfate, or an acetate selected from a raw material metal other than lithium and cesium. One or more kinds of raw materials in the group consisting of carbonates.

(9) The method for producing fine particles disclosed in (1), characterized in that the flammable liquid contains one or more types of oily fuels.

(10) The present invention is a method for producing a positive electrode active material for a lithium ion secondary battery, characterized in that the fine particles produced by the method for producing fine particles according to any one of (1) to (9) are selected from After mixing one or more carbon sources of a group consisting of organic polymer materials, saccharides, polyvalent alcohols, and carbonaceous materials, the mixture is fired in an inert gas atmosphere to form a tannic acid having an olivine structure. Transition metal lithium compound.

(11) The present invention is a positive electrode active material for a lithium ion secondary battery of a citrate type, which is produced by the production method disclosed in (10).

(12) The present invention is a lithium ion secondary battery produced by using the positive electrode active material disclosed in (11).

(13) The present invention relates to a water-in-oil type raw material emulsion for producing fine particles, in which a liquid droplet containing at least a raw material solution containing cerium fine particles and a lithium source and a raw material metal source other than cerium and lithium is dispersed in the flammable liquid.

According to the present invention, a positive electrode active material for a lithium ion secondary battery of a citrate type having a small particle size and excellent properties can be provided by a spray combustion method, and a method which can be produced at a low cost. A lithium ion secondary battery and a raw material emulsion and fine particle production apparatus for producing fine particles using the above materials and methods can be provided.

11‧‧‧Microparticle manufacturing equipment

13‧‧‧ Raw emulsion

15‧‧‧ spray nozzle

17‧‧‧ spray gas

19‧‧‧Material flow

21‧‧‧ droplets

23‧‧‧Combustion source

25‧‧‧flame

27‧‧‧Microparticles

31‧‧‧Combustible liquid

33‧‧‧ raw material solution

35‧‧‧Interactive surfactant

37‧‧‧ containing fine particles

41‧‧‧Processing room

43‧‧‧Microparticle recovery unit

45‧‧‧Exhaust gas

51‧‧‧nuclear particles

53‧‧‧Original particles

61‧‧‧Microparticle manufacturing equipment

63‧‧‧Season

Fig. 1 shows the structure of the fine particle production apparatus 11 of the first embodiment.

Figure 2 shows the construction of the raw material emulsion 13.

Figure 3 shows the construction of droplets 21 in feed stream 19.

4 shows the configuration of the microparticle manufacturing apparatus 11 and the microparticle recovery apparatus 43.

Figure 5 illustrates the formation of microparticles by a spray combustion method.

Fig. 6 shows the structure of a fine particle producing apparatus 61 of another example of the first embodiment.

Figure 7 is an optical micrograph of the raw material emulsion of Example 1.

Fig. 8 is a graph showing the results of X-ray diffraction measurement of the positive electrode active material of Example 1.

Fig. 9 is a scanning electron micrograph of the positive electrode active material of Example 1.

Fig. 10 shows the charge and discharge characteristics of the positive electrode active material of Example 1 and Comparative Example (solid line: Example 1, broken line: comparative example).

Form for implementing the invention

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

(First embodiment)

(Microparticle manufacturing device)

Fig. 1 is a schematic view showing the fine particle production apparatus 11 of the first embodiment. The microparticle production apparatus 11 includes a spray nozzle 15 that feeds the raw material emulsion 13 and the spray gas 17 to discharge the raw material stream 19 containing the liquid droplets 21 of the raw material emulsion 13, and a combustion source 23 that can burn the raw material stream 19. The combustion source 23 is connected to the spray nozzle 15, and the raw material stream 19 and the spray gas 17 can be burned to form the flame 25.

(raw emulsion)

Since the positive electrode active material for a bismuth hydride-based lithium ion secondary battery is produced by the fine particle production apparatus 11, the raw material emulsion 13 contains at least a lithium source, a ruthenium source, and a raw material metal source other than lithium and ruthenium. The raw material emulsion 13 contains a raw material metal source other than a lithium source, a cerium source, and the like, so that the obtained fine particles 27 contain an oxide of lithium, an oxide of cerium, and an oxide of a metal other than lithium and cerium, and The oxide or the like is crystallized, and the fine particles are crystallized to form a lithium transition metal niobate having an olivine structure. For example, using iron as a raw material metal other than lithium or lanthanum, and preparing a raw material emulsion 13 according to a ratio of stoichiometric components of each element according to Li:Fe:Si=2:1:1, an olivine structure can be obtained. Lithium iron citrate (Li ₂ FeSiO ₄ ).

Here, the composition of the microparticles obtained by the present invention is such that lithium is Li, yttrium is Si, and further selected from Fe, Mn, Ti, Cr, V, Ni, Co, Cu, Zn, Al, Ge. One or two or more metal elements of the group consisting of Zr, Mo, and W are M, and are selected from the group consisting of Ti, Cr, V, Zr, Mo, W, P, and B. When at least one of the metal elements is X, the composition of the fine particles may be expressed by Li _y MSi _1-z X _z O ₄ , 1 ≦ y ≦ 2, and 0 ≦ z < 0.4. In particular, when P and P other than the transition element are contained in X, if it is P, phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), ammonium phosphate ((NH) may be used as the raw material used. ₄ ) ₃ PO ₄ ), and if B, a boric acid (H ₃ BO ₃ ), ammonium pentaborate (NH ₄ B ₅ O ₈ ), a hydrate thereof, or the like can be used.

As shown in FIG. 2, the raw material emulsion 13 is a water-in-oil emulsion, and a raw material solution 33 containing at least cerium-containing fine particles 37 and lithium ions and lithium and lanthanum is dispersed in the flammable liquid 31 as droplets. Metal ions other than the raw materials.

(flammable liquid)

The flammable liquid 31 is not particularly limited as long as it is a flammable liquid, but preferably contains a singly selected from the group consisting of kerosene, kerosene, light oil, gasoline, turpentine, heavy oil, hexane, octane, decane, dodecane, and One or more fuels in the group consisting of toluene, toluene, and dimethyl ether. In terms of price and handling, it is preferred to use kerosene and light oil, and a mixture of kerosene and light oil can be used.

(containing strontium particles)

The cerium-containing fine particles 37 which have been dispersed in the raw material solution 33 are not particularly limited as long as they contain cerium-containing fine particles, but are preferably fine particles containing cerium oxide (SiO ₂ ) or lithium niobate (Li ₂ SiO ₃ ). This is because the ruthenium-containing fine particles 37 do not contain other metal elements which should not be contained in the positive electrode active material.

The smaller the particle diameter of the cerium-containing fine particles 37, the smaller the particle size of the obtained fine particles, and the smaller the particle diameter of the obtained positive electrode active material, the more suitable it is. The average particle diameter of the primary particles of the cerium-containing fine particles 37 is preferably 50 nm or less, more preferably 20 nm or less. The average particle diameter of the cerium-containing fine particles 37 can be determined by observation by an electron microscope or dynamic light scattering method.

Further, since the surface of the cerium-containing fine particles 37 is hydrophilic, it is dispersed in the raw material solution 33 instead of the flammable liquid 31. Depending on the type of bismuth-containing microparticles, it is possible to form a Pickering emulsion in which the emulsion can be stabilized for a long period of time.

(raw material metal)

In the raw material solution 33, in addition to the ruthenium-containing fine particles and the lithium source, a raw material metal source other than lithium and ruthenium is contained, but the other lithium contained in the raw material solution 33 and the raw material metal other than ruthenium may be used singly or in combination of iron. Fe), manganese (Mn), titanium (Ti), chromium (Cr), vanadium (V), nickel (Ni), cobalt (Co), copper (Cu), zinc (Zn), aluminum (Al), antimony ( Ge), zirconium (Zr), molybdenum (Mo), tungsten (W), and the like. In addition to lithium, the raw material solution 33 preferably contains a group selected from the group consisting of nitrates, hydroxides, hydrochlorides, sulfates, acetates, carbonates, citrates, and the like of a raw material metal other than lithium and cesium. One or more kinds of raw materials. For example, lithium source, lithium chloride, lithium carbonate or the like can be used as the lithium source. When iron is used as a raw material metal other than lithium or ruthenium, iron nitrate, ferrous chloride, ferric chloride or the like can be used as the iron source.

(surfactant)

Further, the raw material emulsion 13 is a water-in-oil type emulsion in which the raw material solution 33 is dispersed as droplets in the flammable liquid 31. To maintain this state for stability, a surfactant 35 should be added. The surfactant 35 allows the hydrophilic group to abut against the raw material solution 33, and causes the oleophilic group to lean against the flammable liquid 31 to stably disperse the raw material solution 33 in the flammable liquid 31. When the surfactant is not used, an emulsifier (combiner 63) is placed in front of the nozzle as in the microparticle production apparatus 61 of the example shown in FIG. 6, and the raw material emulsion 13 is supplied to the spray nozzle 15 after the ejection. The droplets 21 are formed by spraying while maintaining the water-in-oil emulsion. In this manner, the raw material solution 33 containing metal ions other than lithium-containing fine particles and lithium ions and containing raw materials other than lithium and cerium can be formed into a milky state in the flammable liquid 31, and can be produced without using the surfactant 35. In the flammable liquid 31, the raw material emulsion 13 of the water-in-oil emulsion of the raw material solution 33 is dispersed as droplets. Then, the raw material emulsion 13 is sprayed into droplets to burn the flammable liquid 31 in the droplets, and the fine particles 27 are formed.

As the surfactant 35, a nonionic surfactant having an HLB (hydrophilic-lipophilic balance) of 3 to 6 is preferably used. HLB means a hydrophilic lipophilic balance. By using a surfactant with a HLB of 3 to 6 low HLB, it is possible to form a water-in-oil type (W/O type, Water in oil type) in which the lipophilic group is on the outer side and the hydrophilic group is inside and the water particles are contained inside. Emulsion. Here, if the HLB is less than 3, the hydrophilicity is weak, and it is difficult to form a W/O type emulsion. If the HLB exceeds 6, the W/O emulsion will be unstable and easily form an O/W type emulsion, so Be applicable. Therefore, the preferred range of HLB is 3-6 as described above.

Moreover, since the cationic and anionic surfactants contain more metal components than carbon and hydrogen in the surfactant, the above metal components may be mixed. It is preferable to use a nonionic surfactant as the surfactant 35 because it becomes an impurity in the obtained fine particles or affects the device. As the surfactant 35, a fatty acid ester type nonionic surfactant such as sorbitol monooleate (trade name: Kao RHEODOL SP-O10V) can be used.

The raw material emulsion 13 is preferably a water-in-oil type emulsion. In the case of a water-in-oil emulsion, the droplet size of the raw material solution 33 in the raw material emulsion 13 will be smaller than that of the sprayed aqueous solution, so that fine particles having a small particle size can be obtained. That is, the raw material solution 33 is directly sprayed by the spray nozzle 15, and it is also difficult to obtain droplets having a particle diameter of several μm, but fine droplets of the raw material solution having a particle diameter of several μm can be formed in the emulsion. Since the droplets of the raw material solution 33 are fine, the heat transfer to the raw material solution 33 is faster, and fine particles having a smaller particle diameter can be produced.

Further, since the raw material emulsion 13 is a water-in-oil type emulsion, the flammable liquid on the surface of the droplet is relatively easy to burn. Moreover, the raw material solution is dispersed in the oil as a smaller droplet, so that particles having a smaller particle size can be obtained. Further, by controlling the ratio of the oil phase and the water phase, the droplets of the raw material solution can be heated to be split into fine droplets of the flammable liquid, so that the combustion of the raw material emulsion can be promoted.

Further, in the case of an oil-in-water type (O/W type, Oil in water type) emulsion, the surface of the droplet which is in contact with the flame is in an aqueous phase, so that it is not easily burned. Further, since the raw material solution is not dispersed in the form of droplets, coarse particles may be formed upon heating.

When the raw material solution 33 is dispersed in the flammable liquid 31, the particle size and the like are not particularly limited, but the average particle diameter of the droplets of the raw material solution 33 in the raw material emulsion 13 is preferably 0.5 to 10 μm. If the average particle diameter is the above-described degree, heat during combustion is more easily conducted to the inside of the liquid droplets of the raw material solution 33, and it is easy to generate fine particles. The particle size of the droplets of the raw material solution 33 can be made by the surfactant The concentration and type, the emulsification method at the time of preparation of the emulsion, the number of revolutions of the homogenizer, and the like are adjusted.

The droplet size of the raw material solution 33 in the raw material emulsion 13 can be known by observing the particle diameter of the droplets of the raw material solution by an optical microscope.

Further, the mass ratio of the raw material solution 33 to the flammable liquid 31 in the raw material emulsion 13 is preferably from 10:90 to 85:15. Furthermore, the mass ratio of the two is 40:60~80:20, and even 40:60~75:25 is better.

Further, in order to improve the combustibility of the raw material emulsion 13, an oxidizing liquid such as hydrogen peroxide may be added to the raw material emulsion 13.

(spray nozzle)

The spray nozzle 15 is a two-fluid spray nozzle, and the supplied raw material emulsion 13 can be dropletized and ejected as a raw material stream 19. The raw material emulsion 13 and the spray gas 17 are supplied to the spray nozzle 15, and the raw material emulsion 13 is crushed into fine droplets 21 by a high-speed gas stream of the spray gas 17.

As the spray gas 17, a mixed gas of nitrogen, argon, oxygen, air or the like can be used. In particular, in order to facilitate the combustion of the raw material stream 19, it is preferred to use oxygen as the spray gas 17. Further, in order to improve the flammability of the raw material stream 19, a premixed gas of a combustible gas and a combustion-supporting gas may be used as the spray gas 17.

(droplet)

The raw material stream 19 contains droplets 21 of the raw material emulsion 13. As shown in FIG. 3, the droplets 21 are slightly dispersed in the flammable liquid 31 as a raw material solution 33 containing fine particles of cerium and lithium ions and metal ions other than lithium and cerium.

The droplets 21 of the raw material emulsion 13 in the sprayed raw material stream 19 preferably have an average particle diameter of 5 to 500 μm, more preferably 10 to 50 μm. This is because When the raw material emulsion 13 is sprayed, the droplets 21 are easily burned.

The particle size of the droplets 21 of the raw material emulsion 13 in the sprayed raw material stream 19 can be obtained by evaluating the sprayed droplets 21 using a phase Doppler laser particle analyzer. The phase Doppler laser particle analyzer can determine the particle diameter of the droplet 21 in a non-contact manner by using the phase difference of the Doppler frequency obtained when the droplet 21 passes through the intersection of the two beams of laser light.

As shown in Fig. 1, the combustion source 23, also referred to as a pilot burner, allows the feedstock stream 19 ejected from the spray nozzle 15 to be combusted. The combustion source 23 is provided at the front of the spray nozzle 15, and is particularly provided near the tip end of the spray nozzle 15. The burned feed stream 19 will form a flame 25. The droplets 21 contained in the raw material stream 19 are exposed to a high temperature by the flame 25, and are oxidized and aggregated to form fine particles 27.

4 shows the configuration of the fine particle recovery device 43 of the microparticle manufacturing apparatus 11. The main part of the microparticle production apparatus 11 is disposed in the processing chamber 41, and is connected to the processing chamber 41 to be provided with the fine particle recovery device 43.

(Method of Producing Fine Particles in Microparticle Production Apparatus According to First Embodiment)

Hereinafter, a method of producing fine particles using the fine particle production apparatus 11 of the first embodiment will be described with reference to Fig. 1 .

First, the raw material emulsion 13 is supplied to the spray nozzle 15. The spray nozzle 15 is a two-fluid spray nozzle to which the spray gas 17 is supplied, and the raw material emulsion 13 can be dropletized to eject the raw material stream 19.

Next, the feed stream 19 will be burned by the combustion source 23 and form a flame 25. The droplets 21 of the raw material emulsion 13 form fine particles 27 in the flame 25.

Then, as shown in Fig. 4, the fine particles 27 formed in the flame 25 in the fine particle manufacturing apparatus 11 pass through the processing chamber 41 provided with the fine particle manufacturing apparatus 11, and are recovered by the fine particle recovery means 43 such as a bag filter or a cyclone. .

Figure 5 illustrates the formation of microparticles by a spray combustion method. The raw material emulsion 13 is sprayed from the spray nozzle 15 to form a spray (feed material stream 19) having droplets 21 having a particle diameter of several μm to several hundreds μm, and the liquid droplets 21 are heated in the flame 25 to generate fine particles 27. The flammable liquid 31 of the liquid droplets 21 is burned in the flame 25, and the solvent of the raw material solution 33 is evaporated, and the cerium-containing fine particles 37 are used as crystal nucleus, and lithium, cesium, lithium, and cerium are contained in the raw material emulsion. The raw material metal is oxidized by a combustion reaction to form core particles 51 (crystal nucleation). Further, in the flame 25, the core particles 51 are coalesced and aggregated to form the original particles 53 (oxidation, agglomeration) having a particle diameter of about several to 100 nm. The fine particles 27 such as the core particles 51 and the primary particles 53 generated in the processing chamber 41 are collected by the fine particle recovery device 43. The gas stream containing the fine particles 27 is discharged as the exhaust gas 45 after the fine particles 27 are recovered by the fine particle recovery device 43.

(Effects of the first embodiment)

In the fine particle production apparatus 11 of the first embodiment, the water-in-oil type raw material emulsion 13 is used, and the combustible liquid 31 is exposed on the surface of the liquid droplet 21, so that the flame 25 can be easily burned by the combustion source 23. Further, since the raw material emulsion 13 contains the raw material solution 33 in the form of fine droplets, coarse particles are not formed. Further, unlike the case of using an aqueous solvent, it can be rapidly heated to the inside of the liquid droplet 21, so that the fine fine particles 27 can be uniformly formed from the liquid droplets 21 without being mixed into the coarse particles.

Further, in the raw material emulsion 13, in addition to the low-cost water-soluble lithium source, In addition, metal sources of raw materials other than lithium and tantalum can be used, so that the cost of raw materials can be suppressed. In particular, even when a surfactant is used, the raw material cost can be more suppressed than when a lithium source which is soluble in a flammable liquid and a raw material metal source which is soluble in a flammable liquid are used.

(burner)

Further, in the fine particle production apparatus 11 and the fine particle production apparatus 61 of the first embodiment, a ring-shaped burner for forming a flame to be supplied into the raw material stream 19 may be provided. The annular burner is provided with a plurality of flame ports in an annular portion of the gas introduction pipe to which the flammable gas and the combustion-supporting gas have been supplied. Second, the feed stream 19 can be supplied to the flame formed by the annular burner. If a flame to be supplied to the raw material stream 19 can be formed, the burner is not limited to the annular burner, and a single burner such as a flame outlet can be used. The flammable gas is not particularly limited, and carbon hydrogen, hydrogen, or the like can be used. Further, although the combustion-supporting gas is not particularly limited, air, oxygen, or the like can be used.

(spray control gas ejection unit)

Further, in the fine particle production apparatus 11 and the fine particle production apparatus 61 of the first embodiment, a nozzle cover which is provided around the spray nozzle 15 and which can spray a spray control gas from the tip end may be provided. The nozzle cover is a cover of a multi-layer tube construction. The function of the nozzle cover is to protect the tip end of the spray nozzle 15 from the radiant heat of the burner to avoid clogging of the spray nozzle 15, and to flow the spray control gas from the tip end of the nozzle cover to form a gas flow covering the sprayed material stream 19, and to control The directivity and flow rate of the feed stream 19. The spray control gas may use a mixed gas of nitrogen, argon, oxygen, air or the like. As described above, by controlling the directivity and flow rate of the feed stream 19, the feed stream 19 fed to the flame 25 can be increased. The fine particles 27 are efficiently produced in proportion and the residence time of the raw materials in the flame 25 is controlled to control the particle diameter.

(Method for producing positive electrode active material)

The positive electrode active material of the nonaqueous electrolyte secondary battery can be obtained by crystallization treatment of the fine particles of the precursor of the active material for the lithium ion secondary battery obtained by the spray combustion method. In particular, after mixing the precursor particles with the carbon source, it is preferably calcined in an atmosphere of a passive gas filling. For example, in the case of lithium iron ruthenate, the iron component is mainly present in the precursor particle in the form of a trivalent state, but when it is calcined in an appropriate reducing environment, the iron component can be changed to a divalent value, and as a result, Then, a crystal of lithium iron citrate which functions as an active material for a lithium ion secondary battery having an olivine structure can be obtained.

As the inert gas, nitrogen gas, argon gas, helium gas, helium gas, carbon dioxide gas or the like can be used. Further, in order to improve the conductivity of the product, heat treatment may be performed in a hydrocarbon gas filling environment. As the carbon source for improving the conductivity of the product after the heat treatment, an organic polymer material such as polyvinyl alcohol, polyvinylpyrrolidone or carboxymethyl cellulose, a sugar such as glucose or sucrose, glycerin or ethylene glycol can be used. Carbonaceous materials such as polyvalent alcohols, carbon black, and graphite powder. However, if it is a substance which can generate a reducing carbon source by heat processing, it is not limited to the above.

It is preferred to carry out the crystallization of the precursor particles and the coating or carrying treatment by carbon in the same baking step. The heat-treated condition is a combination of a temperature of 300 to 900 ° C and a treatment time of 0.5 to 10 hours, and a desired fired product of crystallinity and particle diameter can be suitably obtained. Excessive heat loading due to high temperature and prolonged heat treatment may result in the formation of coarse single crystals and should be avoided. It is preferred to use heat treatment conditions capable of suppressing the size of the crystallites as much as possible under the heating conditions to which the desired crystalline or microcrystalline positive electrode active material can be obtained. The temperature of the heat treatment is preferably about 400 to 800 °C.

Further, after the obtained positive electrode active material is agglomerated in the firing step, it may be treated by a mortar, a ball mill or other grinding method to form a powder.

Example

Hereinafter, the present invention will be specifically described by way of examples.

<Example 1>

Lithium nitrate (LiNO ₃ ) and iron nitrate nonahydrate (Fe(NO ₃ ) ₃ .9H ₂ O) were dissolved in pure water, and then cerium oxide microparticles (AEROSIL 300 (produced by Japan AEROSIL) with an average primary particle diameter of 7 nm) were added. And the raw material solution is prepared. Further, varnish is prepared as a flammable liquid. Then, using Kao RHEODOL SP-O10V (sorbitol monooleate, HLB value of 4.3) as a surfactant, and according to the ratio of the raw material solution: flammable liquid: surfactant ratio of 65:33.5:1.5 The mixture was placed in a homogenizer equipped with a metal stirring blade, and stirred at 10,000 rpm for 10 minutes to prepare a water-in-oil type raw material emulsion. Further, in the lithium source, the iron source, and the rhodium source, Li, Fe, and Si in the raw material emulsion are 2:1:1 of the stoichiometric ratio of Li ₂ FeSiO ₄ . Further, the concentration in the raw material emulsion was set such that Li ₂ FeSiO ₄ produced by 1 kg of the raw material emulsion was 0.5 mol.

Fig. 7 is a photograph of the raw material emulsion of Example 1 observed by an optical microscope. The droplets of the raw material solution in the raw material emulsion were observed, and the particle diameter (droplet diameter) was about 1.5 μm.

The microparticle manufacturing apparatus 11 shown in Fig. 1 has been used in the above-mentioned original The emulsion is made into fine particles. First, the raw material emulsion is sprayed from the two-fluid spray nozzle (spray nozzle 15). The gas used for the spray is oxygen. The sprayed raw material spray (feedstream 19) is combusted by combustion source 23 to form flame 25. As a result, the fine particles 27 have been produced. The generated microparticles are recovered by the bag filter.

To 5wt% aqueous solution of polyvinyl alcohol by dry weight ratio of 10: The fine particles obtained in 8 hours at 650 ℃ baking the fine particles and a dispersion of polyvinyl alcohol, and after evaporation, under N ₂ gas atmosphere, for. During the calcination, carbonization of the polyvinyl alcohol and reduction of the transition metal occur, and formation and crystallization of lithium iron citrate occur. The obtained agglomerates are subjected to a grinding treatment to obtain a positive electrode active material.

Fig. 8 shows the results of X-ray diffraction measurement of the positive electrode active material after carbon coating. The black dots on the horizontal axis of Fig. 8 represent the occurrence of the peaks caused by the olivine-type lithium iron silicate (Li ₂ FeSiO ₄ ). In Example 1, it is known that a crystal of olivine-type lithium iron citrate (Li ₂ FeSiO ₄ ) can be obtained.

Fig. 9 shows the results of observing the positive electrode active material after the carbon coating with a scanning electron microscope. Microparticles having a particle diameter of about 50 to 200 nm have been observed. Further, the specific surface area of the positive electrode active material was measured by the BET method, and as a result, it was 16.2 m ² /g.

(Evaluation of battery characteristics)

The conductive active agent (carbon black) was mixed with 10% by weight of the positive electrode active material prepared in Example 1, and the mixed powder and the polyvinylidene fluoride (PVdF) of the binder were mixed at a ratio of dry weight to 90:10. After the N-methyl-2-pyrrolidone (NMP) solution, it was mixed with a self-rotating revolution mixer to prepare an anode slurry.

The anode slurry was applied to a 20 μm thick aluminum foil current collector at a coating amount of 50 g/m ² and dried at 120 ° C for 30 minutes. Then, it was subjected to rolling processing by a roll press, and die-cut into a disk shape having a diameter of 16 mm to prepare a positive electrode.

After the positive electrode is vacuum dried at 80 ° C for 8 hours, the metal is used for the negative electrode in the argon replacement working chamber with a dew point of -60 ° C or less, and the volume ratio of the electrolyte is 1:1. A solution obtained by dissolving a concentration of 1 M of LiPF6 in a mixed solvent of ethyl carbonate and diethyl carbonate, and using a 20 μm thick polyene microporous membrane for the partition to make a diameter of 20 mm. × 2016 type button battery with a thickness of 1.6mm.

Next, the test for evaluating the electrode characteristics of the positive electrode active material in the above-described button type lithium secondary battery was evaluated as follows.

At a test temperature of 25 ° C and a current rate of 0.1 C, the battery was charged to 4.5 V (for Li/Li ⁺ ) by the CC-CV method, and then the charging was stopped after the current rate dropped to 0.01 C. Thereafter, the discharge was carried out to 1.5 V by the CC method at the ratio of 0.1 C (the same as described above), and the initial discharge capacity was measured.

Fig. 10 is a graph showing a charge and discharge curve of a positive electrode active material prepared by dissolving a raw material active material of Example 1 and a raw material solution obtained by dissolving an organic metal compound in a flammable organic solvent as a comparative example. (a) is the charging curve and (b) is the discharge curve. The initial discharge capacity of the positive electrode active material of Example 1 shown by the solid line was 101 mAh/g. On the other hand, a raw material solution (lithium naphthenate, iron 2-ethylhexanoate, octamethylcyclotetramethylene) obtained by dissolving an organometallic compound in a flammable organic solvent as a comparative example shown by a broken line is used. The initial discharge capacity of the positive electrode active material prepared by using oxyalkylene or 2-ethylhexanoic acid was 100 mAh/g. As described above, the active material obtained by the present invention can attain the same battery characteristics as those of the active material prepared by dissolving the organic metal compound in a flammable organic solvent.

The cost of the raw materials of the examples using the water-in-oil emulsion can be greatly reduced to 1/3 to 1/10 as compared with the case of using the raw materials soluble in the solvent.

For example, the metal raw material soluble in the solvent is reacted with a fatty acid and a caustic alkali, and then an aqueous solution of the metal salt is added to perform metathesis, or the fatty acid and the metal compound are heat-treated at a high temperature, and the like is directly reacted. The raw material cost is increased due to the large scale of the manufacturing equipment or the long reaction time. Further, since a metal compound such as a metal salt is reacted with other substances, the cost is remarkably higher than that of the metal salt.

On the other hand, the cost of using the raw material of the water-in-oil type emulsion of the present invention is lower than that of a material which is soluble in a solvent because a relatively low-priced raw material such as a metal salt can be used.

As described above, by firing fine particles obtained by spraying a water-in-oil type raw material emulsion prepared by using a low-cost water-soluble raw material, lithium iron citrate having a small particle diameter and good battery characteristics can be obtained. . Further, when used, a positive electrode active material for a lithium ion secondary battery and a secondary battery using the same can be produced.

The preferred embodiments of the present invention have been described above with reference to the drawings, but the present invention is not limited by the above description. Those skilled in the art can devise various modifications and alterations within the scope of the technical idea disclosed in the present invention, and the scope of the invention is also understood to be included in the technical scope of the present invention.

11‧‧‧Microparticle manufacturing equipment

13‧‧‧ Raw emulsion

15‧‧‧ spray nozzle

17‧‧‧ spray gas

19‧‧‧Material flow

21‧‧‧ droplets

23‧‧‧Combustion source

25‧‧‧flame

27‧‧‧Microparticles

Claims (13)

A method for producing fine particles, comprising the steps of: preparing a raw material emulsion, wherein the raw material emulsion is a water-in-oil emulsion, and a raw material solution is dispersed in a liquid in a flammable liquid, the raw material solution containing at least cerium-containing fine particles and a lithium source and a raw material metal source other than cerium and lithium; a step of spraying the raw material emulsion into droplets; and a step of burning the flammable liquid in the liquid droplets to form fine particles. The method for producing fine particles according to claim 1, wherein lithium is Li, yttrium is Si, and further selected from the group consisting of Fe, Mn, Ti, Cr, V, Ni, Co, Cu, Zn, Al, Ge, Zr, One or two or more metal elements in the group of Mo and W are M, and are at least one selected from the group consisting of Ti, Cr, V, Zr, Mo, W, P, and B. When the metal element is X, the composition of the aforementioned fine particles is expressed by the formula as Li _y MSi _1-z X _z O ₄ , 1≦y≦2, 0≦z<0.4). The method for producing a fine particle according to claim 1, wherein the raw material emulsion contains a surfactant. The method for producing fine particles according to claim 3, wherein the surfactant is a nonionic surfactant having a HLB of 3 to 6. The method for producing fine particles according to claim 1, wherein the droplets of the raw material solution dispersed in the flammable liquid have an average particle diameter of 0.5 to 10 μm. The method for producing fine particles according to claim 1, wherein the droplets of the raw material emulsion sprayed have an average particle diameter of 5 to 500 μm. The method for producing fine particles according to claim 1, wherein the ruthenium-containing fine particles are fine particles containing ruthenium dioxide or lithium niobate. The method for producing fine particles according to claim 1, wherein the raw material solution contains lithium and a group selected from the group consisting of nitrates, hydroxides, hydrochlorides, sulfates, acetates, and carbonates of a raw material metal other than lithium and cesium. One or more kinds of raw materials in the group. The method for producing fine particles according to claim 1, wherein the flammable liquid contains one or more kinds of oily fuels. A method for producing a positive electrode active material for a lithium ion secondary battery, characterized in that the fine particles produced by the method for producing fine particles according to any one of claims 1 to 9 are selected from the group consisting of organic polymer materials After mixing one or more kinds of carbon sources in a group consisting of a saccharide, a polyvalent alcohol, and a carbonaceous material, the mixture is fired in an inert gas atmosphere to form a lithium transition metal halide having an olivine structure. Compound. A positive electrode active material for a lithium ion secondary battery of a citrate type, which is produced by the production method of claim 10. A lithium ion secondary battery produced by using the positive electrode active material of claim 11. A water-in-oil type raw material emulsion for producing fine particles, wherein a droplet of a raw material solution containing at least a fine particle containing cerium fine particles and a lithium source and a raw material other than cerium and lithium is dispersed in the flammable liquid.