JP2013252995A - Lithium manganese complex oxide and carbon composite thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium manganese-based positive electrode material which is a positive electrode material capable of being used in place of a LiCoO-based positive electrode material, and exhibiting excellent charge and discharge characteristics, and which can be manufactured by an easy manufacturing method by using elements being inexpensive and little restricted in terms of natural resources.SOLUTION: A novel lithium manganese complex oxide can be obtained which consists of only a crystal phase of a cubic rock-salt type structure by mixing and crushing a raw material by a mechanical milling method, the raw material including lithium oxide and manganese oxide, and which exhibits excellent charge and discharge characteristics. A composite more increased in a discharge capacity can be obtained by filling a mixture of the complex oxide and a carbon material in a conductive vessel, and by sintering the mixture under a non-oxidizing atmosphere, while being pressurized, and by energizing a DC pulse current.

Description

  The present invention relates to a lithium manganese composite oxide, a composite of the composite oxide and carbon, and a production method thereof.

  With the development of various devices and systems in recent years, there is an increasing demand for higher performance of storage batteries as a power source. In particular, lithium ion secondary batteries are widely used as secondary batteries that power electronic devices such as portable communication devices and laptop computers, and are also expected to be used as motor drive batteries for automobiles from the viewpoint of reducing environmental impact. Has been. For this reason, the demand for lithium ion secondary batteries is expected to increase further in the future, and the development of high energy density lithium ion secondary batteries corresponding to higher performance of these devices is demanded.

In the current lithium ion secondary battery, lithium cobalt oxide (LiCoO ₂ ) is mainly used as the positive electrode material, but because it contains a large amount of cobalt, which is a rare metal, the material cost of the lithium ion secondary battery is reduced. It has become one of the factors that raise it. In the future, it is considered difficult to respond to the increase in demand accompanying the expansion of applications for in-vehicle use, etc. and the increase in size of batteries, using only a positive electrode material made of LiCoO ₂ .

Lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), etc. have been researched and developed as cathode materials that can be substituted for LiCoO ₂ as materials that are cheaper and less resource-constrained. Some have been put to practical use as alternative materials. However, LiNiO ₂ has the problem of reducing battery safety during charging, while LiMn ₂ O ₄ has trivalent manganese eluting into the electrolyte during high-temperature (about 60 ° C) charging and discharging, which is the battery performance. However, there is not much progress in substitution for these materials.

On the other hand, among lithium manganese oxides, a positive electrode material called Li ₂ MnO ₃ has also been proposed, and since it has a high capacity, research and development has been actively conducted in recent years. Lithium manganese oxides containing iron (iron-containing Li ₂ MnO ₃ and titanium-containing Li ₂ MnO ₃ ) exhibit high capacity, especially when they have a specific chemical composition and transition metal ion distribution, excellent at high current density at room temperature It has been reported that it exhibits excellent discharge characteristics at low temperatures (see Patent Documents 1-6 below).

In addition, lithium titanium oxide (iron-containing Li ₂ TiO ₃ and iron- and nickel-containing Li ₂ TiO ₃ ) having a cubic rock salt type crystal structure, which has been conventionally difficult to utilize as a positive electrode material for lithium secondary batteries, It has also been reported that it can be used as a positive electrode material for lithium ion secondary batteries (Patent Documents 7 to 8 below).

As described above, various reports have been made on lithium manganese-based positive electrode materials that can be substituted for LiCoO ₂ -based positive electrode materials. However, in order to further improve the charge / discharge characteristics and reduce the cost of materials, Further optimization of the chemical composition and manufacturing conditions of the positive electrode material including control is desired.

  In addition, conventional lithium manganese oxide is often produced by a multi-stage complicated process centering on coprecipitation-hydrothermal-firing method, and the production cost is reduced even if the raw material cost is kept low. There is a concern of raising costs. For this reason, from the viewpoint of a practical production process, it is required to produce a positive electrode material having excellent performance by simplifying the production method.

JP 2002-68748 A JP 2002-121026 A JP 2005-154256 A JP 2008-63211 A JP 2009-179501 A JP 2009-274940 A JP2003-48717 JP2003-306322A

The present invention has been made in view of the current state of the prior art described above, and its main purpose is a positive electrode material having excellent charge / discharge characteristics that can replace the LiCoO ₂ -based positive electrode material, and is inexpensive and resource-intensive. It is an object of the present invention to provide a lithium manganese based positive electrode material that can be manufactured by a simple manufacturing method using an element with few restrictions.

  The present inventor has intensively studied to achieve the above-described object. As a result, according to the method of producing a composite oxide by the mechanical milling method using lithium oxide and manganese oxide as raw materials, lithium manganese consisting only of the crystal phase of cubic rock salt type crystal structure is achieved by a simple treatment method in one step. It has been found that composite oxides can be produced. The composite oxide obtained by this method is superior to lithium manganese oxide containing a monoclinic layered rock salt structure or titanium-containing lithium manganese oxide consisting only of a cubic rock salt crystal structure. It has charge / discharge characteristics, and in particular, it has been found that the average discharge voltage is high and the discharge capacity is increased. Furthermore, according to the method of filling the lithium manganese composite oxide together with the carbon material in a conductive container and conducting a heating reaction by applying a direct current pulse current under pressure in a non-oxidizing atmosphere, the lithium manganese composite oxide It was found that a composite in which a product and a carbon material are firmly bonded can be obtained, and that the obtained composite becomes a material having a higher discharge capacity when used as a positive electrode material for a lithium ion secondary battery.

  The present invention has been completed as a result of further research based on these findings.

That is, the present invention provides the following lithium manganese composite oxide, a composite of the composite oxide and a carbon material, a production method thereof, a positive electrode material for a lithium ion secondary battery, and a lithium ion secondary battery. is there.
Item 1. A lithium manganese composite oxide represented by a composition formula Li _{1 + x} Mn _1-x O ₂ (-1/3 <x <1/3) and consisting only of a crystal phase of a cubic rock salt structure.
Item 2. The lithium manganese composite oxide according to item 1 and a carbon material joined to each other,
(1) The amount of the carbon material is 0.01 to 30% by weight based on the total amount of the lithium manganese composite oxide and the carbon material,
(2) The tap density of the composite is 30% or more larger than the tap density of the mixture of the lithium manganese composite oxide and carbon material used as a raw material,
(3) Put 0.5 g of the complex and 50 mL of water in a 100 mL beaker, and rotate the rotor with a length of 3 cm and a central cross-sectional diameter of 5 mm at 200 rpm for 5 minutes. Having a bond strength defined by the fact that the bond with the material does not delaminate,
A lithium manganese composite oxide-carbon composite characterized by the above.
Item 3. Item 3. The composite according to Item 2, wherein the carbon material is acetylene black, ketjen black, or vapor grown carbon fiber.
Item 4. Item 2. The method for producing a lithium manganese composite oxide according to Item 1, wherein lithium oxide and manganese oxide are used as raw materials, and the raw materials are mixed and pulverized by a mechanical milling method.
Item 5. The mixture of the lithium manganese composite oxide and the carbon material according to the above item 1 is filled in a container having conductivity, and a DC pulse current is applied in a non-oxidizing atmosphere while the mixture is pressurized. Item 4. The method for producing a lithium manganese composite oxide-carbon composite according to Item 2 or 3, wherein the lithium manganese composite oxide is carbonized.
Item 6. A positive electrode material for a lithium ion secondary battery comprising the lithium manganese composite oxide according to Item 1.
Item 7. Item 4. A positive electrode material for a lithium secondary battery, comprising the lithium manganese composite oxide-carbon composite according to item 2 or 3.
Item 8. 8. A lithium ion secondary battery comprising the positive electrode material according to item 6 or 7 as a constituent element.

  The present invention will be described in detail below.

Lithium-manganese composite oxide and method for producing the same The lithium-manganese composite oxide of the present invention is represented by the composition formula Li _{1 + x} Mn _1-x O ₂ (-1/3 <x <1/3). It is a complex oxide consisting only of the crystal phase of a cubic rock salt structure. The composite oxide consisting only of the crystal phase of the cubic rock salt structure represented by the above composition formula is a novel oxide that has not been known so far, and is excellent when used as a positive electrode material for a lithium ion secondary battery. It is a material having charge / discharge performance.

  The lithium manganese composite oxide of the present invention can be obtained by using lithium oxide and manganese oxide as raw materials and sufficiently pulverizing and mixing the raw materials by a mechanical milling method. Lithium oxide and manganese oxide used as raw materials may be mixed so that the molar ratio of Li and Mn is the same as the molar ratio of Li and Mn in the target composite oxide.

  The mechanical milling method is a method of grinding and mixing raw materials while applying mechanical energy. According to this method, the raw materials are included in the raw materials by applying mechanical impact and friction to the raw materials and mixing them. Each oxide particle can be vigorously brought into contact and refined to change physical properties, morphology, and the like.

  As the mechanical milling device, for example, a ball mill, a vibration mill, a turbo mill, a disk mill or the like can be used, and among these, a vibration mill is preferable. The material of the pot and the vibrator is not particularly limited. For example, a pot made of zirconia, agate, stainless steel, or the like can be used. The particle size of the vibrator is not particularly limited, but for example, a vibrator having a diameter of 10 to 60 mm can be used.

  Various conditions for mechanical milling may be set so that a desired composite oxide can be obtained. For example, when a composite is produced by a vibration mill, a raw material mixture and a grinding vibrator are added to the pot, and mechanical milling processing may be performed at a predetermined rotation speed and time. As an example of the processing conditions, the rotation speed is preferably in the range of 100 rpm to 1000 rpm, and more preferably in the range of 200 rpm to 600 rpm. In addition, the treatment time when performing the vibration mill is preferably in the range of, for example, 1 hour to 100 hours, and more preferably in the range of 2 hours to 10 hours. Mechanical milling is usually performed at a temperature near room temperature.

  The atmosphere when performing mechanical milling is not particularly limited, but it is preferable to use an inert gas atmosphere such as helium, argon, or nitrogen in order to suppress the reaction between moisture and carbon dioxide gas in the atmosphere and the raw material. .

の立方晶岩塩型構造の結晶相のみからなるものであり、従来知られていない新規な酸化物である。 According to the method described above, lithium oxide and manganese oxide used as raw materials are ground and mixed by mechanical milling, and react with each other to form a composition formula Li _{1 + x} Mn _1-x O ₂ (-1/3 < A lithium manganese composite oxide represented by x <1/3) is formed. The lithium manganese composite oxide represented by the above composition formula obtained by this method is a space group.

This is a novel oxide that has not been known so far.

  The composite oxide has a higher average discharge voltage and a higher discharge capacity than lithium manganese oxide having a monoclinic layered rock salt structure or titanium-containing lithium manganese oxide having only a cubic rock salt crystal structure. High and charge / discharge efficiency is also good.

Lithium manganese composite oxide-carbon composite and method for producing the same In the present invention, a lithium manganese composite oxide consisting only of a crystal phase of a cubic rock salt structure obtained by the above-described method is used as a composite with a carbon material. Therefore, the conductivity can be improved, and a positive electrode material having more excellent charge / discharge performance, in particular, high discharge capacity can be obtained.

The composite of lithium manganese composite oxide and carbon material has a cubic rock salt structure represented by the above composition formula Li _{1 + x} Mn _1-x O ₂ (-1/3 <x <1/3). Lithium manganese composite oxide consisting only of crystalline phase and raw material consisting of carbon material are mixed well, then filled into a conductive container, and heated and reacted by applying DC pulse current in a non-oxidizing atmosphere. It can be obtained by the method.

  The particle size of the lithium manganese composite oxide used as a raw material by this method is not particularly limited, but it is usually preferable to use a powdery material having an average particle size of about 1 to 50 μm. In the present specification, the average particle size is a particle size at which the cumulative frequency distribution is 50% in the particle size distribution measurement by a dry laser diffraction / scattering method.

  The carbon material is not particularly limited. For example, a powder obtained by thermally decomposing acetylene at a high temperature, a powder obtained by a so-called explosion method, such as a known acetylene black powder, ketjen black, vapor grown carbon fiber (VGCF), etc. Can be used.

  The average particle size of the carbon material is also not particularly limited, but it is usually preferable to use a powdery or needle-like material of about 0.005 to 10 μm, preferably about 0.01 to 1 μm.

  In order to produce a composite of lithium manganese composite oxide and carbon material, first, the lithium manganese composite oxide and carbon material used as raw materials are mixed well, then filled into a container having electron conductivity, and non-oxidized In a neutral atmosphere, the raw material mixture is baked by an electric current sintering method in which a direct-current pulse current is applied, which is called a discharge plasma sintering method, a pulse electric current sintering method, a plasma activated sintering method, etc. in a state where the mixture is pressurized. Tie. Thereby, the target lithium manganese composite oxide-carbon composite can be obtained.

  Specifically, by filling a container having electron conductivity with a mixture of a composite oxide and a carbon material as raw materials, and applying a pulsed ON-OFF direct current while applying pressure in a non-oxidizing atmosphere, Electric current sintering can be performed.

The electric current sintering is performed in a non-oxidizing atmosphere, for example, in an inert gas atmosphere such as Ar or N ₂ or in a reducing atmosphere such as H ₂ . Further, a reduced pressure state in which the oxygen concentration is sufficiently low, for example, a reduced pressure state in which the oxygen partial pressure is about 20 Pa or less may be used.

  When a container that can ensure a sufficiently sealed state is used as a container having electron conductivity, the inside of the container may be a non-oxidizing atmosphere. Further, the container having electron conductivity may not be completely sealed. When an incompletely sealed container is used, the container is accommodated in the reaction chamber, and the reaction chamber is filled with an inert gas atmosphere. A non-oxidizing atmosphere such as a reducing atmosphere may be used. Thereby, the reaction between the lithium manganese composite oxide and the carbon powder can be performed in a non-oxidizing atmosphere. In this case, for example, the inside of the reaction chamber is preferably an inert gas atmosphere or a reducing gas atmosphere of about 0.1 MPa or more.

  The mixing ratio of the lithium manganese composite oxide and the carbon material may be about 0.001 to 30% by weight, particularly preferably about 0.01 to 20% by weight, based on the total amount of both. When the amount of the carbon powder is less than 0.001% by weight, the improvement of the electronic conductivity of the lithium manganese composite oxide is insufficient, and the effect of forming the composite may not be sufficiently obtained. On the other hand, at 30% by weight or more, when used as a positive electrode active material, the weight energy density and volume energy density of the battery decrease as the weight ratio and volume ratio of the composite oxide in the formed composite decrease. Therefore, it is not preferable.

  The container having electron conductivity is not particularly limited as long as it has electron conductivity. Carbon, iron, iron oxide, copper, aluminum, tungsten carbide, carbon and / or iron oxide mixed with silicon nitride. What is formed from etc. can be used conveniently.

  By applying a direct current pulse current in a state in which the mixed powder of the composite oxide and the carbon material is filled in such an electron conductive container, a discharge phenomenon that occurs in the particle gap of the filled mixed powder is used to discharge. Particle oxide purification activation by plasma, discharge shock pressure, etc., electric field diffusion effect caused by electric field, thermal diffusion effect by Joule heat, plastic deformation pressure by pressurization, etc. act as driving force for particle bonding, Joined via a carbon material.

  As an apparatus for carrying out current sintering, there is a particular limitation as long as it is possible to heat, cool, pressurize, etc. a mixed powder of lithium manganese composite oxide and carbon powder and to apply a current necessary for discharge. Not. For example, a commercially available electric current sintering apparatus (discharge plasma sintering apparatus) can be used. Such an electric current sintering apparatus and its principle are disclosed in, for example, Japanese Patent Laid-Open No. 10-251070.

  A specific example of the method for producing a lithium manganese composite oxide-carbon composite of the present invention will be described below with reference to FIG. 1 showing a schematic diagram of an electric current sintering apparatus.

  The electric sintering apparatus 1 includes a die (electron conductive container) 3 on which a sample 2 is loaded and a pair of upper and lower punches 4 and 5. The punches 4 and 5 are supported by punch electrodes 6 and 7, respectively, and a pulse current is supplied through the punch electrodes 6 and 7 while applying pressure to the sample 2 loaded in the die 3 as necessary. Can do. The material of the die 3 is not limited, and examples thereof include a carbon material such as graphite.

  In the apparatus shown in FIG. 1, the energization part including the above-described container 3 having electron conductivity, energization punches 4 and 5, and punch electrodes 6 and 7 is accommodated in a water-cooled vacuum chamber 8. It can be adjusted to a predetermined atmosphere by the control mechanism 15. Therefore, the atmosphere control mechanism 15 may be used to adjust the inside of the chamber to a non-oxidizing atmosphere.

  The control device 12 drives and controls the pressurization mechanism 13, the pulse power source 11, the atmosphere control mechanism 15, the water cooling mechanisms 16 and 10, and the temperature measurement device 17. The control device 12 is configured to drive the pressurizing mechanism 13 so that the punch electrodes 6 and 7 pressurize the raw material mixture at a predetermined pressure.

  The condition for the energization process may be a condition for forming a high-density composite that satisfies the conditions described below.

The temperature (heating temperature) of the die (electron conductive container) 3 at the time of specific energization treatment can be appropriately selected according to the types of lithium manganese composite oxide and carbon material, the particle size thereof, etc. What is necessary is just about 200-700 degreeC, and what is necessary is just about 300-600 degreeC. If the heating temperature is less than 200 ° C., bonding with the carbon material may be insufficient. On the other hand, when the heating temperature exceeds 700 ° C., Li _{1 + x} Mn _1-x O ₂ having a cubic rock salt structure is reduced and decomposed to form orthorhombic LiMnO ₂ as an impurity, which is not preferable. Accordingly, a heating temperature of about 300 to 600 ° C. is suitable.

  For example, a pulsed ON-OFF direct current having a pulse width of about 2 to 3 milliseconds and a period of about 3 Hz to 300 Hz can be used as the pulse current applied for heating. Although the specific current value varies depending on the type and size of the electron conductive container, the specific current value may be determined so as to be in the temperature range described above. For example, when a graphite mold with an inner diameter of 15 mm is used, about 200 to 1000 A is preferable, and when a mold with an inner diameter of 100 mm is used, about 1000 to 8000 A is preferable. During processing, the current value may be controlled so that a predetermined temperature can be managed by increasing or decreasing the current value while monitoring the mold material temperature.

  The electric current sintering is preferably performed in a state where a raw material powder made of a lithium manganese composite oxide and a carbon material is pressurized. As a specific method, for example, the raw material powder filled in the electron conductive container 3 may be pressurized through the punch electrodes 6 and 7. The pressure at the time of pressurizing the raw material powder is, for example, about 5 to 60 MPa, preferably about 10 to 50 MPa. When the pressure is less than 5 MPa, the bonding between the lithium manganese composite oxide and the carbon material becomes insufficient, and when the pressure exceeds 60 MPa, decomposition of the lithium manganese composite oxide is promoted, which is not preferable. Usually, a pressure of about 10 to 50 MPa is suitable.

  The sintering time by electric current sintering varies depending on the amount of raw materials used, the sintering temperature, etc., and thus cannot be specified in general, but it is usually sufficient to heat until reaching the heating temperature range described above, and the temperature range described above. If it reaches | attains, you may cool immediately, or you may hold | maintain in this temperature range, for example to about 2 hours.

  After conducting the electric current sintering treatment at a predetermined temperature by the method described above, the electron conductive container is cooled, the formed composite is taken out from the container, and lightly pulverized with a mortar or the like as necessary. The lithium manganese composite oxide-carbon composite to be recovered can be recovered. When a large amount of current sintering treatment is performed, a large mold material is used, and the above process may be scaled up.

  The composite of lithium manganese composite oxide and carbon of the present invention is a lithium manganese composite oxide that is strongly bonded and densified through a carbon material that is a conductive material. It is not in a state where the composite oxide and the carbon powder are mixed, but in a state where the carbon is adhered to a part or the whole of the surface of the composite oxide, it is in a strongly bonded state, and the density is greatly increased compared to the raw material mixture. ing. Specifically, the tap density of the composite is 30% or more larger than the tap density of the mixture of the lithium manganese composite oxide powder and the carbon material used as the raw material. The upper limit of the tap density increase is not particularly limited, but it varies depending on the temperature, pressure, etc. during pressure electric current sintering, but usually increases to about 80% compared to the tap density of the raw material mixture. It becomes.

  The tap density in this specification is about 0.5g after pulverizing the sample in a glove box with an argon gas atmosphere with a dew point of -70 ° C or less for 10 minutes or more, and throwing it into a 10 mL capacity cylinder. Then, after tapping 100 times, the density was measured.

  At this time, the composite was joined by placing 0.5 g of the composite and 50 ml of water in a 100 ml beaker, stirring the rotor with a length of 3 cm and a central cross-sectional diameter of 5 mm at 200 rpm for 5 minutes. Is also defined by the fact that the carbon material does not separate. In this respect, it is clearly distinguished from a mixture of the composite oxide and carbon powder.

Applications of lithium manganese composite oxide-carbon composite The lithium manganese composite oxide-carbon composite obtained by the above-described method is a close junction between the lithium manganese composite oxide having the above-described excellent charge / discharge characteristics and the carbon material. As a result, the density is high and the electron conductivity is improved. Therefore, by using the composite as a positive electrode material for a lithium ion secondary battery, a lithium ion secondary battery having a high average discharge voltage, a high discharge capacity, and a good charge / discharge efficiency can be obtained.

A lithium ion secondary battery using the composite as a positive electrode active material can be produced by a known method. That is, except that the composite obtained by the method of the present invention is used as a positive electrode active material, a known metal lithium, a carbon-based material (activated carbon, graphite) or the like is used as a negative electrode material, and a known electrolyte is used as an electrolyte solution. Using a solution obtained by dissolving lithium perchlorate, lithium salt such as LiPF _{6 in} a solvent such as ethylene carbonate or dimethyl carbonate, and using other known battery components, a lithium ion secondary according to a conventional method What is necessary is just to assemble a battery.

  The lithium manganese composite oxide of the present invention is a novel material consisting only of a crystal phase having a cubic rock salt type crystal structure, and is a substance having excellent charge / discharge performance as a positive electrode material for a lithium ion secondary battery. It is a substance with a high average discharge voltage and a large discharge capacity. According to the production method of the present invention, a novel complex oxide having such excellent performance can be obtained by a simple method of one step by a relatively simple method called a mechanical milling method.

  In addition, a composite obtained by conducting current sintering of the lithium manganese composite oxide and the carbon material is a material with improved conductivity, and can be effectively used as a positive electrode material having a higher discharge capacity.

  For this reason, both the lithium manganese composite oxide of the present invention and the composite of the composite oxide and the carbon material are highly useful substances as the positive electrode active material of the lithium ion secondary battery.

  Further, according to the production method of the present invention, a complex oxide and a complex having such excellent performance can be produced relatively easily.

Schematic of an example of an electric current sintering apparatus. 2 is an X-ray diffraction pattern of samples obtained in Example 1 and Example 2. FIG. It is a graph which shows the charging / discharging characteristic of the lithium ion secondary battery which uses the sample obtained in Example 1 and Example 2 as a positive electrode active material. 6 is an X-ray diffraction pattern of samples obtained in Example 3 and Example 4. FIG. It is a graph which shows the charging / discharging characteristic of the lithium ion secondary battery which uses the sample obtained in Example 3 and Example 4 as a positive electrode active material. 2 is an X-ray diffraction pattern of a sample obtained in Comparative Example 1. FIG. It is a graph which shows the charge / discharge characteristic of the lithium ion secondary battery which uses the sample obtained by the comparative example 1 as a positive electrode active material. 6 is an X-ray diffraction pattern of a sample obtained in Comparative Example 2. FIG. It is a graph which shows the charging / discharging characteristic of the lithium ion secondary battery which uses the sample obtained by the comparative example 2 as a positive electrode active material.

1 Electric current sintering equipment 2 Sample 3 Die (conductive container)
4, 5 Punch 6, 7 Punch electrode 8 Water-cooled vacuum chamber 9 Cooling water channel 10, 16 Water cooling mechanism 11 Power source for sintering 12 Controller 13 Pressurizing mechanism 14 Position measuring mechanism 15 Atmosphere controlling mechanism 17 Temperature measuring apparatus

  The present invention will be specifically described below with reference to examples and comparative examples.

Example 1
Commercially available Li ₂ O and MnO ₂ were weighed at a molar ratio of 1: 1 (atomic ratio Li / Mn = 2), and placed in a zirconia pot under an argon gas atmosphere. ) And processed for 2 hours by a mechanical milling method.

のみで解析できることが判った。また解析から得られたMn/(Li+Mn)比は、約0.337(4)であり、ほぼ初期の目的組成であるLi₂MnO₃の組成で表されるものであった。 The X-ray diffraction pattern of the obtained sample is shown in FIG. As is clear from Fig. 2, it consists only of peaks attributed to Li ₂ MnO _3, and from X-ray Rietveld analysis, this sample is a cubic rock salt crystalline phase.

It turned out that it can analyze only by. Further, the Mn / (Li + Mn) ratio obtained from the analysis was about 0.337 (4), which was expressed by the composition of Li ₂ MnO ₃ which is the initial target composition.

  FIG. 3 shows a charge / discharge curve when this sample is used as a positive electrode active material and a charge / discharge test is performed under the following conditions.

Charge / discharge test conditions <br/> Positive electrode: Active material 10mg + AB5mg + PTFE0.5mg mixed and crimped on Al mesh.
Negative electrode: metallic lithium.
Electrolyte: LiPF ₆ dissolved in EC + DMC solvent.
Test temperature: 30 ° C.
Current density (per active material): 23mA / g
Potential range: 1.5-4.8V
As a result of the above discharge test, the discharge capacity was about 210 mAh / g, the average discharge voltage was about 3.0 V, and the value of titanium-containing Li ₂ MnO ₃ consisting only of the cubic rock salt structure described in Comparative Example 1 (described later) Discharge capacity of about 120 mAh / g, average discharge voltage of about 2.2 V), and the value of Li ₂ MnO ₃ containing the monoclinic layered rock salt structure described in Comparative Example 2 (discharge capacity of about 100 mAh / g, average discharge voltage of about 1.9 Excellent discharge characteristics compared to V).

Example 2
Li ₂ MnO ₃ (average particle size of about 7 μm) prepared in Example 1 was mixed with acetylene black (AB) (average primary particle size of about 0.04 μm) so that the weight ratio was Li ₂ MnO ₃ : AB = 98: 2. This was placed in a zirconia pot and mixed with a planetary ball mill at 200 rpm for 30 minutes. This was filled in a graphite container having an inner diameter of 15 mm and set in the chamber of an electric sintering machine SPS-3.20MK-IV (manufactured by Fuji Radio Engineering Co., Ltd.), and then the pressure in the chamber was reduced to about 20 Pa.

  Thereafter, the inside of the chamber was filled with argon gas to atmospheric pressure, and the raw material powder filled in the graphite container was pressurized at about 30 MPa. Further, a DC pulse current of about 400 A (pulse width 2.5 milliseconds, period 30 Hz) was applied to the graphite jig, and the vicinity of the sample was heated at about 10 ° C./min. After the temperature reached 400 ° C., the temperature was maintained at that temperature for 5 minutes, the applied current and pressurization were stopped, and the graphite container was allowed to cool naturally.

  After cooling to near room temperature, a sample was taken out from the graphite container and pulverized in a mortar under an argon gas atmosphere to obtain a lithium manganese composite oxide / acetylene black composite.

のみで解析でき、Mn/(Li+Mn)比は約0.346(2)であり、通電焼結処理前とほぼ同程度であることから、分解等を起こさずに、Li₂MnO₃-C複合体を作製することが出来たことが確認できた。 FIG. 2 shows an XRD pattern of the obtained sample. As shown in FIG. 2, it consisted only of peaks attributed to Li ₂ MnO ₃ and carbon, and no impurity phase was observed. From X-ray Rietveld analysis, Li ₂ MnO ₃ is a cubic rock salt type crystal phase

Only can be analyzed, Mn / (Li + Mn) ratio is about 0.346 (2), since the previous current sintering process is almost the same, without causing decomposition, Li ₂ MnO ₃ -C complex It was confirmed that the body could be produced.

After pulverizing the resulting composite in a glove box with an argon gas atmosphere with a dew point of about -90 ° C, about 0.5 g is collected, put into a 10 mL capacity cylinder, tapped 100 times, and then the density is measured. did. As a result, the tap density was 1.4 g / cm ³ , an increase of more than 40% compared to the value before current sintering (approximately 0.9 g / cm ³ ), and Li ₂ MnO ₃ and acetylene black were firmly bonded. I was able to confirm. Furthermore, 0.5 g of the sample after the energization treatment was taken out into the atmosphere, placed in a 100 mL beaker with 50 mL of water, and a rotor with a length of 3 cm and a central cross-sectional diameter of 5 mm was stirred 200 minutes per minute and left standing for 5 minutes. All of the sample powder settled, and no suspended matter such as carbon powder was observed. From this, it was confirmed that Li ₂ MnO ₃ was firmly bonded to acetylene black in the composite obtained by the above method.

FIG. 3 shows a charge / discharge curve when the charge / discharge test was conducted in the same manner as in Example 1 using the obtained Li ₂ MnO ₃ —C composite as the positive electrode active material. The discharge capacity is about 280 mAh / g, the average discharge voltage is about 2.7 V, and the value of titanium-containing Li ₂ MnO ₃ consisting only of the cubic rock salt structure described in Comparative Example 1 described later (discharge capacity is about 120 mAh / g, Discharge superior to that of Li ₂ MnO ₃ (discharge capacity of about 100 mAh / g, average discharge voltage of about 1.9 V) including the monoclinic layered rock-salt structure described in Comparative Example 2 The characteristics are shown. Moreover, it has confirmed that the discharge capacity became large compared with the case where the lithium manganese composite obtained in Example 1 was used as a positive electrode active material.

のみで解析できることが分かった。また解析から得られるMn/(Li+Mn)比は約0.324(2)であり、ほぼ初期の目的組成であるLi₂MnO₃の組成で表されるものであった。 Example 3
Commercially available Li ₂ O and MnO ₂ were weighed in a molar ratio of 1.2: 1 (atomic ratio Li / Mn = 2.4) and placed in a zirconia pot under an argon gas atmosphere in the same manner as in Example 1 to perform mechanical milling. For 2 hours. The resulting X-ray diffraction pattern of the sample, as shown in FIG. 4, which consist of only the peak attributed to Li ₂ MnO _3, be Li ₂ MnO ₃ single phase by one-stage process is obtained It could be confirmed. From X-ray Rietveld analysis, this sample is a cubic rock salt type crystal phase

It turned out that it can analyze only by. Further, the Mn / (Li + Mn) ratio obtained from the analysis was about 0.324 (2), which was expressed by the composition of Li ₂ MnO ₃ which is the initial target composition.

FIG. 5 shows a charge / discharge curve when a charge / discharge test was performed under the same conditions as in Example 1 using this sample as the positive electrode active material. The discharge capacity is about 200 mAh / g and the average discharge voltage is about 3.0 V. The value of titanium-containing Li ₂ MnO ₃ consisting only of the cubic rock salt structure described in Comparative Example 1 described later (discharge capacity about 120 mAh / g, Discharge superior to that of Li ₂ MnO ₃ (discharge capacity of about 100 mAh / g, average discharge voltage of about 1.9 V) including the monoclinic layered rock-salt structure described in Comparative Example 2 The characteristics are shown.

Example 4
The Li ₂ MnO ₃ (average particle size of about 7 μm) prepared in Example 3 was acetylene black (AB) (average primary particle size of about 0.04 μm) in a weight ratio of Li ₂ MnO ₃ : AB = 98: 2. The mixture was mixed and subjected to current sintering treatment at 400 ° C. for 5 minutes in the same manner as in Example 2.

のみで解析でき、Mn/(Li+Mn)比は約0.345(2)であり、通電焼結処理前とほぼ同程度であった。また、実施例２と同じ方法で測定したタップ密度は約1.4g/cm³であり、通電処理前の値（約0.9g/cm³）に比べ40％以上増大しており、Li₂MnO₃とABが強固に接合していることが確認できた。更に、通電処理後の試料0.5ｇを水50ｍＬとともに100ｍＬビーカーに入れ、長さ３ｃｍ、中心部断面直径5ｍｍの回転子を毎分200回転させて5分間攪拌し静置したところ、試料粉は全て沈殿し、炭素粉等の浮遊物は確認されなかった。このことから、上記した通電焼結処理により、Li₂MnO₃がアセチレンブラックと強固に接合していることが確認できた。以上により、上記方法により、分解等を起こさずに、Li₂MnO₃-C複合体を作製することが出来た。 The XRD pattern of the obtained sample is as shown in FIG. 4 and consists only of peaks attributed to Li ₂ MnO ₃ and carbon, and no impurity phase was observed. From X-ray Rietveld analysis, Li ₂ MnO ₃ is a cubic rock salt type crystal phase

The Mn / (Li + Mn) ratio was about 0.345 (2), almost the same as that before the electric current sintering treatment. Further, the tap density measured by the same method as in Example 2 is about 1.4 g / cm ^3, which is an increase of 40% or more compared to the value before the energization treatment (about 0.9 g / cm ³ ), and Li ₂ MnO ₃ It was confirmed that AB and AB were firmly joined. Furthermore, 0.5 g of the sample after the energization treatment was placed in a 100 mL beaker with 50 mL of water, and a rotor with a length of 3 cm and a central cross-sectional diameter of 5 mm was stirred at 200 rpm for 5 minutes. Precipitation occurred and no suspended matter such as carbon powder was observed. From this, it was confirmed that Li ₂ MnO ₃ was firmly bonded to acetylene black by the above-described electric sintering treatment. As described above, a Li ₂ MnO ₃ —C composite could be produced by the above method without causing decomposition or the like.

FIG. 5 shows a charge / discharge curve when a charge / discharge test was performed under the same conditions as in Example 1 using the obtained Li ₂ MnO ₃ —C composite as a positive electrode active material. The discharge capacity is about 200 mAh / g, the average discharge voltage is about 3.0 V, and the value of titanium-containing Li ₂ MnO ₃ consisting only of the cubic rock salt structure described in Comparative Example 1 described later (discharge capacity of about 120 mAh / g, Discharge superior to that of Li ₂ MnO ₃ (discharge capacity of about 100 mAh / g, average discharge voltage of about 1.9 V) including the monoclinic layered rock-salt structure described in Comparative Example 2 The characteristics are shown.

のみで解析でき、その格子定数はa = 4.1087(5)Åであり、実施例１のLi₂MnO₃試料（a = 4.0712(5)Å）より増大していた。また解析から得られる(Mn+Ti)/(Li+Mn+Ti)比は、約0.312(3)であり、当初の目的であるTi含有Li₂MnO₃が作製できたことが確認できた。 Comparative Example 1
Commercially available Li ₂ O, MnO ₂ , and TiO ₂ were weighed at a molar ratio of 1: 0.5: 0.5, and placed in a zirconia pot under an argon gas atmosphere in the same manner as in Example 1, and then 2 by mechanical milling. Time processed. The X-ray diffraction pattern of the obtained sample is as shown in FIG. 6 and consists of only a peak attributed to Li _{1 + x} (Mn _1-y Ti _y ) _1-x O ₂ . It was confirmed that a Li _{1 + x} (Mn _1-y Ti _y ) _1-x O ₂ single phase was obtained. From X-ray Rietveld analysis, this sample is a cubic rock salt type crystal phase

The lattice constant was a = 4.1087 (5) Å, which was larger than the Li ₂ MnO ₃ sample of Example 1 (a = 4.0712 (5) Å). Further, the (Mn + Ti) / (Li + Mn + Ti) ratio obtained from the analysis was about 0.312 (3), and it was confirmed that the Ti-containing Li ₂ MnO _{3 which} was the original purpose could be produced.

FIG. 7 shows a charge / discharge curve when this Ti-containing Li ₂ MnO ₃ sample was used as the positive electrode active material and a charge / discharge test was performed under the same conditions as in Example 1. The discharge capacity was about 120 mAh / g and the average discharge voltage was about 2.2 V, which was lower than the values measured in Examples 1 and 2.

と立方晶岩塩型構造の結晶相

に由来するピークが認められ、X線リートベルト解析から、両者の比率は約70:30であった。
このLi₂MnO₃を正極活物質として、実施例１と同一条件で充放電試験した時の充放電曲線を図９示す。放電容量は約100mAh/g、平均放電電圧は約1.9Vであり、実施例１及び２で得られた値に比べて低い値であった。 Comparative Example 2
LiOH and MnO ₂ were weighed at a molar ratio of 1: 2, mixed, and then heat-treated in an ordinary electric furnace at 700 ° C. for 3 hours. The obtained sample has a monoclinic layered rock salt type crystal phase as shown in FIG.

And the crystal phase of cubic rock salt structure

From the X-ray Rietveld analysis, the ratio between the two was about 70:30.
FIG. 9 shows a charge / discharge curve when a charge / discharge test is performed under the same conditions as in Example 1 using this Li ₂ MnO ₃ as the positive electrode active material. The discharge capacity was about 100 mAh / g and the average discharge voltage was about 1.9 V, which was lower than the values obtained in Examples 1 and 2.

Comparative Example 3
Li ₂ MnO ₃ produced in Example 1 was mixed with acetylene black (AB) so that Li ₂ MnO ₃ : AB = 98: 2 by weight ratio. About this mixed powder, the tap density measured in the same manner as in Example 2 was about 0.9 g / cm ³ , which was lower than the value of the composite prepared in Example 2 (about 1.4 g / cm ³ ). In addition, 0.5 g of this mixed powder was put in a 100 mL beaker with 50 mL of water, and a rotor with a length of 3 cm and a central cross-sectional diameter of 5 mm was rotated 200 times per minute and stirred for 5 minutes. However, fine powder floating in water was confirmed, and floating carbon powder was confirmed on the water surface. This indicates that Li ₂ MnO ₃ and AB cannot be joined firmly by mixing alone.

Claims (8)

A lithium manganese composite oxide represented by a composition formula Li _{1 + x} Mn _1-x O ₂ (-1/3 <x <1/3) and consisting only of a crystal phase of a cubic rock salt structure. A lithium-manganese composite oxide according to claim 1 and a carbon material joined together,
(1) The amount of the carbon material is 0.01 to 30% by weight based on the total amount of the lithium manganese composite oxide and the carbon material,
(2) The tap density of the composite is 30% or more larger than the tap density of the mixture of the lithium manganese composite oxide and carbon material used as a raw material,
(3) Put 0.5 g of the complex and 50 mL of water in a 100 mL beaker, and rotate the rotor with a length of 3 cm and a central cross-sectional diameter of 5 mm at 200 rpm for 5 minutes. Having a bond strength defined by the fact that the bond with the material does not peel,
A lithium manganese composite oxide-carbon composite characterized by the above. The composite according to claim 2, wherein the carbon material is acetylene black, ketjen black or vapor grown carbon fiber. 2. The method for producing a lithium manganese composite oxide according to claim 1, wherein lithium oxide and manganese oxide are used as raw materials, and the raw materials are mixed and pulverized by a mechanical milling method. The mixture of the lithium manganese composite oxide and the carbon material according to claim 1 is filled in a container having conductivity, and a DC pulse current is applied in a non-oxidizing atmosphere while the mixture is pressurized. The method for producing a lithium manganese composite oxide-carbon composite according to claim 2, wherein the lithium manganese composite oxide is carbonized. A positive electrode material for a lithium ion secondary battery comprising the lithium manganese composite oxide according to claim 1. A positive electrode material for a lithium secondary battery comprising the lithium manganese composite oxide-carbon composite according to claim 2. The lithium ion secondary battery which uses the positive electrode material of Claim 6 or 7 as a component.

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