JP2016072029A - Positive electrode material for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode material for lithium secondary battery, by which a lithium secondary battery can be obtained which shows stable battery performance due to an olivine type lithium manganese iron phosphate of which the surface is coated with carbon hardly absorbing moisture.SOLUTION: A positive electrode material for lithium secondary battery is obtained by: mixing an olivine type lithium manganese iron phosphate compound and graphite in the proportion of (olivine type lithium manganese iron phosphate compound: graphite) 99:1-91:9 on a mass basis; and baking the resultant mixture at 460-790°C in a reducing atmosphere or inactive atmosphere. In the case that the material is left adsorbing moisture under the condition of a temperature of 20°C and a relative humidity of 50% until reaching its equilibrium, then the temperature of the material is raised to 250°C and further, the material is kept at the temperature for 20 minutes, and a moisture adsorption amount measured as an amount of moisture volatilized during a period of time from the time of the achievement of equilibrium to the time when the 20 minutes has elapsed is 2100 ppm or less.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode material for a lithium secondary battery capable of obtaining a lithium secondary battery having stable battery performance.

Secondary batteries used for portable electronic devices, hybrid cars, electric cars, and the like have been developed. In particular, lithium ion secondary batteries are widely known. Under these circumstances, lithium transition metal phosphate compounds such as Li (Fe, Mn) PO ₄ having an olivine type structure are not greatly affected by resource restrictions and can exhibit high safety. Therefore, it is an optimum positive electrode material for obtaining a high-output and large-capacity lithium ion secondary battery. However, these compounds have the property that it is difficult to sufficiently increase the conductivity due to the crystal structure, and there is room for improvement in the diffusibility of lithium ions. Has been made.

  For example, in Patent Document 1, an attempt is made to improve the performance of the obtained battery by making primary crystal particles ultrafine particles and shortening the lithium ion diffusion distance in the olivine-type positive electrode active material. In Patent Document 2, a conductive carbonaceous material is uniformly deposited on the particle surface of the positive electrode active material, and a regular electric field distribution is obtained on the particle surface to increase the output of the battery.

  On the other hand, in Patent Document 3, when a lithium iron phosphate-based composite oxide composite coated with carbon is used as a positive electrode active material, the discharge capacity after 10 cycles is affected by the water content of the positive electrode active material. It is described that the discharge capacity can be improved if the water content is reduced, and under such a concept, after the firing treatment of the raw material mixture containing the carbonaceous material, by performing pulverization treatment and classification treatment in a dry atmosphere, A technique for reducing the water content of the positive electrode active material to a certain value or less is disclosed.

  Furthermore, Patent Document 4 considers that an active material obtained by using primary particles having an increased specific surface area may be sensitive to deterioration by moist air if the surface is coated with carbon. In addition, a technique is disclosed in which a predetermined raw material is subjected to a synthesis reaction in a dry atmosphere to maintain a humidity level below a certain level during manufacture, storage, and use of a positive electrode material.

JP 2010-251302 A JP 2001-15111 A JP 2003-292309 A Special table 2010-508234 gazette

  Since the techniques described in Patent Documents 3 to 4 are intended to perform a drying process for reducing the water content of the positive electrode active material until the battery is processed, the process until the battery is obtained. Therefore, there is a demand for a technique that can effectively prevent deterioration in performance of electronic characteristics by simpler means.

  Accordingly, an object of the present invention is to provide a lithium secondary battery that has a property that the olivine-type lithium iron manganese phosphate itself, which is coated with carbon, hardly adsorbs moisture, and exhibits stable battery performance. It is providing the positive electrode material for secondary batteries.

  Therefore, the present inventors have made various studies, and using a olivine-type lithium iron manganese phosphate compound and graphite at a specific mass ratio, while being a positive electrode material obtained by performing treatment under specific conditions, It has been found that a lithium secondary battery capable of exhibiting excellent battery characteristics can be obtained because it has the property of hardly adsorbing moisture, and the present invention has been completed.

That is, in the present invention, after mixing an olivine type lithium manganese iron phosphate compound and graphite at a mass ratio (olivine type lithium manganese iron phosphate compound: graphite) 99: 1 to 91: 9, a reducing atmosphere or an inert atmosphere. When the water is adsorbed until it reaches equilibrium at a temperature of 20 ° C. and a relative humidity of 50%, after being heated to 250 ° C. and held for 20 minutes. The present invention provides a positive electrode material for a lithium secondary battery in which the amount of adsorbed water measured as the amount of water volatilized up to 2100 ppm or less.

  Since the positive electrode material for a lithium secondary battery of the present invention hardly adsorbs moisture, the amount of adsorbed moisture can be effectively reduced by a simple process without requiring strong drying conditions as a production environment. In the secondary battery, it is possible to stably exhibit excellent battery characteristics even under various usage environments.

The SEM image of the positive electrode material (composite particle) obtained in Example 1 is shown. The SEM image of the positive electrode material (composite particle) obtained in Example 3 is shown. The SEM image of the positive electrode material (composite particle) obtained by the comparative example 3 is shown.

Hereinafter, the present invention will be described in detail.
The positive electrode material for a lithium secondary battery of the present invention is prepared by mixing an olivine type lithium manganese iron phosphate compound and graphite in a mass ratio (olivine type lithium manganese iron phosphate compound: graphite) 99: 1 to 91: 9, It is obtained by firing at 460 to 790 ° C. in a reducing atmosphere or an inert atmosphere.

Specific examples of the olivine-type lithium iron manganese phosphate compound used in the present invention include, for example, the following formula (A):
LiFe _a Mn _b M _c PO ₄ (A)
(In the formula, M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. A, b and c are 0 <a <0.5, 0 .5 <b <1, and 0 ≦ c ≦ 0.2, and 2a + 2b + (valence of M) × c = 2.
It is represented by

The olivine-type lithium iron manganese phosphate represented by the above formula (A) contains at least manganese (Mn) and iron (Fe) which are transition metals. In the formula (A), M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and is preferably Mg or Zr. a is 0 <a <0.5, and preferably 0.1 ≦ a ≦ 0.3. b is 0.5 <b <1, and preferably 0.7 ≦ b ≦ 0.9. c satisfies 0 ≦ c ≦ 0.2, and preferably 0 ≦ c ≦ 0.1. These a, b and c are numbers satisfying 2a + 2b + (M valence) × c = 2. Specific examples of the olivine-type lithium iron manganese phosphate represented by the above formula (A) include LiMn _0.8 Fe _0.2 PO ₄ , LiMn _0.75 Fe _0.15 Mg _0.1 PO ₄ , LiMn _0.75 Fe _0.19 Zr _0.03 PO _{4 and the} like. Among them, LiMn _0.8 Fe _0.2 PO ₄ is preferable. An iron manganese manganese lithium compound is a primary particle obtained by mixing a lithium compound, a phosphoric acid compound, an iron compound and a manganese compound and performing a hydrothermal reaction.

  Examples of the lithium compound that can be used include lithium oxide and lithium hydroxide. Specific examples include lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, lithium oxide, lithium oxalate, and lithium acetate. These may be used alone or in combination of two or more. Among these, lithium hydroxide is preferable from the viewpoint of improving battery characteristics.

  Examples of phosphoric acid compounds that can be used include phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. These may be used alone or in combination of two or more. Among these, phosphoric acid is preferable from the viewpoint of improving battery characteristics.

  Examples of iron compounds that can be used include iron acetate, iron nitrate, and iron sulfate. These may be used alone or in combination of two or more. Among these, iron sulfate is preferable from the viewpoint of improving battery characteristics.

  Examples of manganese compounds that can be used include manganese acetate, manganese nitrate, and manganese sulfate. These may be used alone or in combination of two or more. Among these, manganese sulfate is preferable from the viewpoint of improving battery characteristics.

  The use molar ratio of these manganese compound and iron compound (manganese compound: iron compound) is preferably 99: 1 to 51:49, more preferably 95: 5 to 70:30, and still more preferably 90:10. ~ 75: 25.

Furthermore, you may use metal (M) compounds other than a manganese compound and an iron compound as needed. M in the metal (M) compound is Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and is synonymous with M in formula (A) described later. . As such metal (M) compounds, halides, sulfates, organic acid salts, hydrates thereof, and the like can be used. These may be used alone or in combination of two or more. Especially, it is preferable to use the metal (M) compound whose M is Mg or Zr from a viewpoint of improving a battery characteristic.
When these metal (M) compounds are used, the total amount of iron compound, manganese compound, and metal (M) compound is preferably 0.99 to 1.01 mol, more preferably 1 mol of lithium compound. Is 0.995 to 1.005 mol.

  As a method of obtaining primary particles of lithium iron manganese phosphate compound by mixing these lithium compound, phosphate compound, iron compound and manganese compound, and further, if necessary, hydrothermal reaction to obtain primary particles of iron manganese phosphate compound, for example, Journal of Power Source 196 ′ (2011), p6498-6501) can be used.

Specifically, for example, after first mixing a lithium compound, a phosphoric acid compound, and water, an iron compound and a manganese compound, and, if necessary, a metal (M) compound are added and further mixed to obtain an aqueous dispersion. Prepare. Next, the obtained aqueous dispersion is subjected to a hydrothermal reaction. The hydrothermal reaction should just be 100 degreeC or more, 130-250 degreeC is preferable and 140-230 degreeC is more preferable. The hydrothermal reaction is preferably performed in a pressure vessel. When the reaction is performed at 130 to 200 ° C, the pressure at this time is 0.3 to 1.5 MPa, and the pressure when the reaction is performed at 140 to 180 ° C is 0. 4 to 1.0 MPa. The hydrothermal reaction time is preferably 10 minutes to 3 hours, more preferably 10 minutes to 1 hour.
Thereafter, the lithium iron manganese phosphate compound can be isolated as primary particles by washing, filtering and drying. As the drying means, freeze drying or vacuum drying is used.

The BET specific surface area of the obtained olivine-type manganese iron phosphate lithium compound is preferably 5 to 40 m ² / g, more preferably 5 to ²⁰ m ² / g, from the viewpoint of effectively reducing the amount of adsorbed water. . When the BET specific surface area of the olivine type lithium manganese iron phosphate compound is less than 5 m ² / g, primary particles of the olivine type lithium manganese iron phosphate compound may become too large, and the battery characteristics may be deteriorated. On the other hand, if the BET specific surface area exceeds 40 m ² / g, the amount of moisture adsorbed may increase and affect battery characteristics.

The graphite mixed with the olivine-type manganese iron phosphate lithium compound is present as carbon that covers the surface of the olivine-type manganese iron phosphate lithium compound by firing it later. The BET specific surface area of such graphite is preferably 1 to 750 m ² / g, more preferably 3 to 500 m ² / g, from the viewpoint of effectively reducing the amount of adsorbed moisture.

  The olivine type lithium manganese iron phosphate compound and graphite are mixed at a mass ratio (olivine type lithium iron manganese phosphate compound: graphite) 99: 1 to 91: 9, preferably 98: 2 to 93: 7. . Thereby, carbon derived from graphite can effectively reduce the amount of adsorbed moisture of the obtained positive electrode material for a titanium secondary battery while efficiently and uniformly covering the surface of the olivine-type lithium iron manganese phosphate compound. .

  The olivine-type lithium iron manganese phosphate compound and graphite are mixed and then fired at 500 to 750 ° C. in a reducing atmosphere or an inert atmosphere. Thereby, the positive electrode material for lithium secondary batteries which carbonizes graphite and carries | supports the carbon concerning the surface of an olivine type lithium manganese iron phosphate compound uniformly and firmly can be obtained. A calcination temperature is 460-790 degreeC, Preferably it is 480-770 degreeC, More preferably, it is 500-750 degreeC. The firing time is preferably 10 minutes to 3 hours, more preferably 0.5 to 1.5 hours.

  The positive electrode material for a lithium secondary battery of the present invention is mixed in a sealed container having an impeller that rotates at a peripheral speed of 25 to 40 m / s after mixing the olivine-type manganese iron phosphate lithium compound and graphite as described above. Further, it is preferable to obtain by performing a mixing treatment while further applying a compressive force and a shearing force, and then firing in a reducing atmosphere or an inert atmosphere. In this way, by performing the mixing process between the mixing process and the baking process, the iron manganese manganese phosphate compound and the graphite are uniformly dispersed, and while the graphite is deformed or spread, it is firmly aggregated. Thus, the positive electrode material for a lithium secondary battery that can effectively reduce the BET specific surface area and can effectively suppress the adsorption of moisture can be formed as particles.

It is preferable that the mixing process while applying the compressive force and the shearing force is performed for 5 to 90 minutes in an airtight container having an impeller rotating at a peripheral speed of 25 to 40 m / s. The peripheral speed of the impeller is preferably 27 to 40 m / s from the viewpoint of effectively reducing the amount of adsorbed moisture by reducing the BET specific surface area of the obtained positive electrode material. In addition, the peripheral speed of an impeller means the speed of the outermost edge part of a rotary stirring blade (impeller), and can be represented by following formula (I).
Impeller peripheral speed (m / s) =
Impeller radius (m) × 2 × π × rotational speed (rpm) ÷ 60 (I)
From the viewpoint of effectively reducing the BET specific surface area of the obtained positive electrode material, the time for performing the mixing treatment while applying compressive force and shearing force depends on the peripheral speed of the impeller so that it becomes longer as the peripheral speed of the impeller is slower. Although it may vary, it is preferably 10 to 60 minutes.

The impeller peripheral speed and / or treatment time in the treatment of mixing while applying compressive force and shear force needs to be adjusted as appropriate according to the amounts of lithium iron manganese phosphate compound and graphite introduced into the container. Then, by operating the container, it becomes possible to perform a process of mixing the impeller and the inner wall of the mixture while applying a compressive force and a shearing force to the mixture. In this case, it is possible to form composite particles that are positive electrode materials for lithium secondary batteries in which graphite is densely and uniformly dispersed and the amount of adsorbed moisture can be effectively reduced.
For example, when the above mixing process is performed for 5 to 90 minutes in an airtight container equipped with an impeller rotating at a peripheral speed of 25 to 40 m / s, the total amount of lithium iron manganese phosphate compound and graphite charged in the container is effective. It is preferably 0.1 to 0.7 g, more preferably 0.15, per 1 cm ^{3 of} the container (a container corresponding to a portion capable of accommodating a lithium iron manganese phosphate compound and graphite among the sealed containers including the impeller). ~ 0.4g.

  From the viewpoint of enhancing the uniformity of the obtained positive electrode material for a lithium secondary battery, and from the viewpoint of improving the efficiency of the mixing treatment in the closed container equipped with the impeller, the iron manganese manganese phosphate compound and graphite are introduced into the closed container. These may be mixed in advance before charging.

Examples of the apparatus provided with a closed container capable of performing the mixing process while applying the compressive force and the shearing force include a high-speed shearing mill, a blade-type kneader, and the like. The nobilta (manufactured by Hosokawa Micron) can be suitably used. By using such an apparatus, it is possible to easily carry out a mixing process while applying a predetermined compressive force and shearing force, and the positive electrode material for a lithium secondary battery of the present invention can be obtained only by performing such a process. Can do.
As the processing conditions for the mixing, the processing temperature is preferably 5 to 80 ° C, more preferably 10 to 50 ° C. The treatment atmosphere is not particularly limited, but is preferably an inert gas atmosphere or a reducing gas atmosphere.

The positive electrode material for a lithium secondary battery according to the present invention volatilizes from the time when moisture is adsorbed until equilibrium is reached at a temperature of 20 ° C. and a relative humidity of 50% until the temperature is raised to 250 ° C. and held for 20 minutes. The amount of adsorbed water measured as the amount of water to be absorbed is 2100 ppm or less.
That is, in the present invention, the amount of adsorbed moisture of the positive electrode material for a lithium secondary battery and the time when water is adsorbed until equilibrium is reached at a temperature of 20 ° C. and a relative humidity of 50%, the temperature is raised to 250 ° C. for 20 minutes. The amount of water volatilized by the time it is held is regarded as the same amount, and the measured value of the volatilized water amount is taken as the adsorbed water amount of the positive electrode material for lithium secondary batteries. Thus, since the positive electrode material for lithium secondary batteries of the present invention hardly adsorbs moisture, the amount of adsorbed moisture can be effectively reduced without requiring strong drying conditions as a production environment, and the resulting lithium In the secondary battery, excellent battery characteristics can be stably exhibited even under various usage environments. The amount of adsorbed moisture is preferably 2075 ppm or less in the positive electrode material for a lithium secondary battery of the present invention.
The amount of water volatilized from the time when moisture is adsorbed until reaching equilibrium at a temperature of 20 ° C. and a relative humidity of 50% to when the temperature is raised to 250 ° C. and held for 20 minutes is, for example, the Karl Fischer moisture meter Can be measured.

The BET specific surface area of the positive electrode material for a lithium secondary battery of the present invention is preferably 5 to 21 m ² / g, more preferably 7 to ²⁰ m ² / g, from the viewpoint of effectively reducing the amount of adsorbed moisture. It is.

  The lithium secondary battery to which the positive electrode for a lithium secondary battery including the positive electrode material for a lithium secondary battery of the present invention can be applied is not particularly limited as long as the positive electrode, the negative electrode, the electrolytic solution, and the separator are essential components.

  Here, as long as lithium ions can be occluded at the time of charging and released at the time of discharging, the material structure is not particularly limited, and a known material structure can be used. For example, a carbon material such as lithium metal, graphite, or amorphous carbon. It is preferable to use an electrode formed of an intercalating material capable of electrochemically inserting and extracting lithium, particularly a carbon material.

  The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent that is usually used for an electrolyte solution of a lithium ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones An oxolane compound or the like can be used.

The type of the supporting salt is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₂ and LiN (SO ₃ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and organic salt derivatives It is preferable that it is at least 1 type of these.

  The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film may be used.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
The BET specific surface area and the amount of adsorbed water were measured according to the following method.
<< Measurement of BET specific surface area >>
The BET specific surface area was measured by a nitrogen adsorption method using a BET specific surface area measuring apparatus (Flow Soap II 2300, manufactured by Shimadzu Corporation).

<< Measurement of moisture content of positive electrode material (composite particles) adsorbed >>
The obtained positive electrode material (composite particles) is allowed to stand in an environment at a temperature of 20 ° C. and a relative humidity of 50% for 1 day to adsorb moisture until it reaches equilibrium. The amount of water volatilized up to this time was measured with a Karl Fischer moisture meter (MKC-610, manufactured by Kyoto Electronics Industry Co., Ltd.) and determined as the amount of adsorbed moisture in the positive electrode material.

[Production Example 1: Production of Compound A]
To 1.27 kg of LiOH.H ₂ O and 1.15 kg of H ₃ PO _4, 3000 cm ³ of ultrapure water was added and mixed (the pH at this time was about 10). To this aqueous dispersion, 0.56 kg of FeSO ₄ .7H ₂ O and 1.93 kg of MnSO ₄ .5H ₂ O were added and mixed. The obtained mixed solution was put into an autoclave and subjected to a hydrothermal reaction at 170 ° C. for 1 hour. The reaction solution was filtered and then lyophilized. Lyophilization (about 12 hours) gave Compound A (LiMn _0.8 Fe _0.2 PO ₄ , BET specific surface area 22 m ² / g, average particle size 82 nm).

[Production Example 2: Production of Compound B]
In the same manner as in Production Example 1, except that 0.42 kg of FeSO ₄ · 7H ₂ O and 1.70 kg of MnSO ₄ · 5H ₂ O were used in the aqueous dispersion of Production Example 1, 0.24 kg of MgSO ₄ · 7H ₂ O was used. Compound B (LiMn _0.75 Fe _0.15 Mg _0.1 PO ₄ , BET specific surface area 21 m ² / g, average particle size 88 nm) was obtained.

[Production Example 3: Production of Compound C]
Production Example 1 except that 0.53 kg of FeSO ₄ .7H ₂ O and 1.70 kg of MnSO ₄ .5H ₂ O were used in the aqueous dispersion of Production Example 1 and 0.11 kg of Zr (SO ₄ ) ₂ .4H ₂ O was used. In the same manner as in Example 1, Compound C (LiMn _0.75 Fe _0.19 Zr _0.03 PO ₄ , BET specific surface area 22 m ² / g, average particle diameter 78 nm) was obtained.

[Example 1]
97.0 g of compound A obtained in Production Example 1 and 3.0 g of graphite (high purity graphite powder, manufactured by Nippon Graphite Co., Ltd., BET specific surface area 5 m ^{2 /} g) were mixed in advance to obtain a mixture. The obtained mixture was put into a fine particle composite apparatus Nobilta (NOB-130, manufactured by Hosokawa Micron Corporation, power 5.5 kw), the processing temperature was 25 to 35 ° C., the impeller peripheral speed was 39 m / s, and the processing time was 30 minutes. As a result, composite preliminary particles were obtained.
Next, using an electric furnace purged with nitrogen gas, the obtained composite preliminary particles were fired at a temperature of 500 ° C. for 1 hour to obtain a positive electrode material.
The SEM image of the obtained positive electrode material is shown in FIG. 1, and each measurement result is shown in Table 1.

[Example 2]
A positive electrode material was obtained in the same manner as in Example 1 except that graphite pulverized material (high purity graphite powder, high BET product, manufactured by Nippon Graphite Co., Ltd., BET specific surface area 230 m ² / g) was used.
Table 1 shows the measurement results.

[Example 3]
A positive electrode material was obtained in the same manner as in Example 1 except that the obtained composite preliminary particles were fired at a temperature of 750 ° C. for 1 hour.
The SEM image of the obtained positive electrode material is shown in FIG. 2, and each measurement result is shown in Table 1.

[Example 4]
A positive electrode material was obtained in the same manner as in Example 1 except that 95.0 g of Compound A obtained in Production Example 1 and 5.0 g of graphite were used.
Table 1 shows the measurement results.

[Example 5]
A positive electrode material was obtained in the same manner as in Example 1 except that 93.0 g of Compound A obtained in Production Example 1 and 7.0 g of graphite were used.
Table 1 shows the measurement results.

[Example 6]
A positive electrode material was prepared in the same manner as in Example 1, except that 98.0 g of Compound A obtained in Production Example 1 and 2.0 g of graphite were obtained, and the resulting composite preliminary particles were calcined at a temperature of 750 ° C. for 1 hour. Obtained.
Table 1 shows the measurement results.

[Example 7]
A positive electrode material was prepared in the same manner as in Example 1, except that 98.0 g of Compound A obtained in Production Example 1 and 2.0 g of graphite were obtained, and the resulting composite preliminary particles were calcined at a temperature of 750 ° C. for 1 hour. Obtained.
Table 1 shows the measurement results.

[Example 8]
97.0 g of compound B obtained in Production Example 2 and 3.0 g of graphite (high purity graphite powder, manufactured by Nippon Graphite Co., Ltd., BET specific surface area of 5 m ^{2 /} g) were mixed in advance to obtain a mixture. The obtained mixture was put into a fine particle composite apparatus Nobilta (NOB-130, manufactured by Hosokawa Micron Corporation, power 5.5 kw), the processing temperature was 25 to 35 ° C., the impeller peripheral speed was 39 m / s, and the processing time was 30 minutes. As a result, composite preliminary particles were obtained.
Next, using an electric furnace purged with nitrogen gas, the obtained composite preliminary particles were fired at a temperature of 500 ° C. for 1 hour to obtain a positive electrode material.
Table 1 shows the measurement results.

[Example 9]
97.0 g of the compound C obtained in Production Example 3 and 3.0 g of graphite (high purity graphite powder, manufactured by Nippon Graphite Co., Ltd., BET specific surface area 5 m ^{2 /} g) were mixed in advance to obtain a mixture. The obtained mixture was put into a fine particle composite apparatus Nobilta (NOB-130, manufactured by Hosokawa Micron Corporation, power 5.5 kw), the processing temperature was 25 to 35 ° C., the impeller peripheral speed was 39 m / s, and the processing time was 30 minutes. As a result, composite preliminary particles were obtained.
Next, using an electric furnace purged with nitrogen gas, the obtained composite preliminary particles were fired at a temperature of 500 ° C. for 1 hour to obtain a positive electrode material.
Table 1 shows the measurement results.

[Comparative Example 1]
A positive electrode material was obtained in the same manner as in Example 1 except that ketjen black (EC300J, manufactured by Lion Corporation, BET specific surface area 800 m ² / g) was used instead of graphite.
Table 2 shows the measurement results.

[Comparative Example 2]
A positive electrode material was obtained in the same manner as in Example 1 except that high-performance ketjen black (EC600JD, manufactured by Lion Corporation, BET specific surface area 1300 m ² / g) was used instead of graphite.
Table 2 shows the measurement results.

[Comparative Example 3]
A positive electrode material was obtained in the same manner as in Example 1 except that the obtained composite preliminary particles were not fired.
The SEM image of the obtained positive electrode material is shown in FIG. 3, and each measurement result is shown in Table 2.

[Comparative Example 4]
A positive electrode material was obtained in the same manner as in Example 1 except that the obtained composite preliminary particles were fired at 300 ° C.
Table 2 shows the measurement results.

[Comparative Example 5]
A positive electrode material was obtained in the same manner as in Example 1 except that the obtained composite preliminary particles were fired at 800 ° C.
Table 2 shows the measurement results.

[Comparative Example 6]
A positive electrode material was obtained in the same manner as in Example 1 except that 90.0 g of compound A obtained in Production Example 1 and 10.0 g of graphite were used.
Table 2 shows the measurement results.

[Comparative Example 6]
A positive electrode material was obtained in the same manner as in Example 1 except that 90.0 g of compound A obtained in Production Example 1 and 10.0 g of graphite were used.
Table 2 shows the measurement results.

[Comparative Example 7]
A positive electrode material was obtained in the same manner as in Example 1 except that the peripheral speed of the Nobilta impeller was 9 m / s.
Table 2 shows the measurement results.

[Comparative Example 8]
A positive electrode material was obtained in the same manner as in Example 1 except that the treatment time of Nobilta was 3 minutes.
Table 2 shows the measurement results.

[Comparative Example 9]
95.0 g of compound A obtained in Production Example 1, glucose (5.0 g in terms of carbon), 28 mL of ethanol, and 2 mL of water were pulverized and mixed in a ball mill for 1 hour under an argon hydrogen atmosphere (hydrogen concentration: 3%) And calcining at 700 ° C. for 1 hour to obtain a positive electrode material.
Table 2 shows the measurement results.

<Evaluation of charge / discharge characteristics>
Using the positive electrode materials obtained in Examples 1 to 9 and Comparative Examples 1 to 9, positive electrodes of lithium ion secondary batteries were produced. Specifically, the obtained positive electrode material, ketjen black, and polyvinylidene fluoride were mixed at a mixing ratio of 75:15:10, and N-methyl-2-pyrrolidone was added to this and kneaded sufficiently. A slurry was prepared. The positive electrode slurry was applied to a current collector made of an aluminum foil having a thickness of 20 μm using a coating machine, and vacuum dried at 80 ° C. for 12 hours. Thereafter, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.
Next, a coin-type lithium ion secondary battery was constructed using the positive electrode. A lithium foil punched to φ15 mm was used for the negative electrode. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 1 was used. As the separator, a known one such as a polymer porous film such as polypropylene was used. These battery components were assembled and housed in a conventional manner in an atmosphere with a dew point of −50 ° C. or lower to produce a coin-type lithium secondary battery (CR-2032).

Using the manufactured lithium secondary battery, the initial discharge capacity of 0.1 C (17 mAh / g) and the discharge capacity after 10 cycles in a 30 ° C. temperature environment with a discharge capacity measuring device (HJ-1001SD8, manufactured by Hokuto Denko) Was measured.
The results are shown in Tables 1-2.

  From the above results, it can be seen that the positive electrode material of the example can surely reduce the amount of adsorbed moisture as compared with the positive electrode material of the comparative example, and can also exhibit excellent performance in the obtained battery.

Claims (5)

  After mixing an olivine type lithium manganese iron phosphate compound and graphite at a mass ratio (olivine type lithium manganese iron phosphate compound: graphite) 99: 1 to 91: 9, 460 to 790 ° C. in a reducing atmosphere or an inert atmosphere. The amount of water volatilized from when water is adsorbed until it reaches equilibrium at a temperature of 20 ° C. and a relative humidity of 50% until it is heated to a temperature of 250 ° C. and held for 20 minutes. As a positive electrode material for a lithium secondary battery, the adsorbed water content measured as is 2100 ppm or less.   After mixing the olivine-type lithium iron manganese phosphate compound and graphite, in a sealed container equipped with an impeller rotating at a peripheral speed of 25 to 40 m / s, mixing is performed while further applying compressive force and shearing force. The positive electrode material for a lithium secondary battery according to claim 1, obtained by performing for -60 minutes and then firing in a reducing atmosphere or an inert atmosphere. The olivine-type lithium manganese iron phosphate compound has the following formula (A):
LiFe _a Mn _b M _c PO ₄ (A)
(In the formula, M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd. A, b and c are 0 <a <0.5, 0 .5 <b <1, and 0 ≦ c ≦ 0.2, and 2a + 2b + (valence of M) × c = 2.
The positive electrode material for lithium secondary batteries of Claim 1 or 2 represented by these.   The lithium secondary battery according to any one of claims 1 to 3, wherein the olivine-type lithium manganese iron phosphate compound is obtained by subjecting a lithium compound, a phosphate compound, an iron compound, and a manganese compound to a hydrothermal reaction. Positive electrode material.   The positive electrode for lithium secondary batteries containing the positive electrode material for lithium secondary batteries of any one of Claims 1-4.