WO2015045254A1 - Lithium-titanium compound oxide - Google Patents

Lithium-titanium compound oxide Download PDF

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WO2015045254A1
WO2015045254A1 PCT/JP2014/004118 JP2014004118W WO2015045254A1 WO 2015045254 A1 WO2015045254 A1 WO 2015045254A1 JP 2014004118 W JP2014004118 W JP 2014004118W WO 2015045254 A1 WO2015045254 A1 WO 2015045254A1
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lithium
composite oxide
titanium composite
negative electrode
active material
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PCT/JP2014/004118
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French (fr)
Japanese (ja)
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なつみ 後藤
白根　隆行
長谷川　正樹
智輝 辻
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三洋電機株式会社
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/003—Titanates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G45/00—Compounds of manganese
    • C01G45/12—Manganates manganites or permanganates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G45/00—Compounds of manganese
    • C01G45/12—Manganates manganites or permanganates
    • C01G45/1221—Manganates or manganites with a manganese oxidation state of Mn(III), Mn(IV) or mixtures thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/30—Three-dimensional structures
    • C01P2002/32—Three-dimensional structures spinel-type (AB2O4)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/74—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by peak-intensities or a ratio thereof only
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/77—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by unit-cell parameters, atom positions or structure diagrams
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a lithium titanium composite oxide, and more particularly to a lithium titanium composite oxide as a negative electrode active material for a lithium ion secondary battery.
  • Li 4 Ti 5 O 12 As a negative electrode active material used for a lithium ion secondary battery, a lithium titanium composite oxide has attracted attention.
  • the lithium titanium composite oxide represented by the composition formula Li 4 Ti 5 O 12 has a flat charge / discharge potential for occluding and releasing lithium ions in the vicinity of about 1.5 V on the basis of lithium metal. When applied as a negative electrode active material, metal lithium is unlikely to precipitate. Further, Li 4 Ti 5 O 12 is a negative electrode active material having excellent cycle characteristics because it hardly undergoes volume expansion and contraction due to insertion and extraction of lithium ions.
  • Li 4 Ti 5 O 12 has low electron conductivity because titanium (Ti) is tetravalent. Therefore, manganese (Mn) is added for the purpose of imparting electron conductivity to the particles of Li 4 Ti 5 O 12 .
  • Patent Document 1 describes that a part of Ti in a crystal of Li 4 Ti 5 O 12 is substituted with an element such as Mn to change the electron density of Ti to improve electron conductivity. .
  • Patent Document 1 by substituting a part of Ti element of Li 4 Ti 5 O 12 with Mn element, the electron conductivity is improved and the discharge rate characteristics are improved. Irreversible capacity increases.
  • An object of the present invention is to provide a lithium titanium composite oxide capable of reducing the irreversible capacity.
  • Lithium-titanium composite oxide according to the present invention has a spinel crystal structure formula is represented by Li 4 + x M y Ti 5 -xy O 12 + ⁇ , wherein, -0.2 ⁇ x ⁇ 0.2, 0 ⁇ y ⁇ 0.3, ⁇ 0.1 ⁇ ⁇ ⁇ 0.1, M includes at least Mn, and the average valence of Mn is 2 or more and less than 4 And
  • the lithium titanium composite oxide as the negative electrode active material for a lithium ion secondary battery according to the present invention can reduce the irreversible capacity.
  • FIG. 6 is a graph showing (022) peak intensity when the (111) peak intensity in the XRD spectrum is set to 100 for the lithium titanium composite oxides of Examples 1 and 2 and Comparative Example 1. It is a figure which shows an initial stage charge / discharge curve about the coin-type battery for evaluation of Example 1. FIG. It is a figure which shows an initial stage charge / discharge curve about the coin-type battery for evaluation of Example 2. FIG. It is a figure which shows an initial stage charge / discharge curve about the coin-type battery for evaluation of the comparative example 1.
  • the lithium titanium composite oxide of the embodiment of the present invention is used as a negative electrode active material for a lithium ion secondary battery.
  • the lithium ion secondary battery has, for example, a configuration in which an electrode body in which a positive electrode and a negative electrode are stacked via a separator and a nonaqueous electrolyte are accommodated in an exterior body.
  • each component of the lithium titanium composite oxide and the lithium ion secondary battery will be described in detail.
  • Lithium-titanium composite oxide is represented by the general formula is represented by Li 4 + x M y Ti 5 -xy O 12 + ⁇ , wherein, -0.2 ⁇ x ⁇ 0.2,0 ⁇ y ⁇ 0.3, ⁇ 0.1 ⁇ ⁇ ⁇ 0.1, M includes at least Mn and has a spinel crystal structure.
  • Li 4 Ti 5 O 12 has a spinel crystal structure belonging to the space group Fd-3m, and the electronic state of titanium (Ti) located at the six-coordinate 16d site is d 0 , It is an insulator.
  • Ti titanium-titanium composite oxide
  • the electron density of Ti can be changed and the electron conductivity can be improved.
  • X is preferably in the range of ⁇ 0.2 ⁇ x ⁇ 0.2.
  • the amount of Li may be more or less than the desired composition amount in the process of synthesizing the lithium titanium composite oxide, but if it is within the above range, good battery performance can be obtained.
  • M includes at least Mn, but may further include an element other than Mn.
  • M may contain Fe, Mg, Nb, or Zn for the purpose of improving electronic conductivity.
  • M may contain B, V, Sr or the like for the purpose of increasing the particle size of the lithium titanium composite oxide.
  • M includes at least Mn, but may further include at least one element of Fe, Mg, Nb, Zn, B, V, and Sr.
  • Y is preferably in the range of 0 ⁇ y ⁇ 0.3. If even a small part of Ti is replaced by Mn, the lithium titanium composite oxide exhibits excellent electronic conductivity, and therefore y should be larger than zero. On the other hand, when y increases, the discharge capacity tends to decrease in the lithium ion secondary battery using the lithium titanium composite oxide of the present embodiment as the negative electrode active material. Since the reduction of the discharge capacity is remarkable, it is not preferable.
  • the average valence was taken as the average of these valences.
  • an index of the average valence of Mn a method in which no change in valence occurs in the process of analyzing the average valence was adopted.
  • the lattice constant calculated from the (022) peak intensity when the (111) peak intensity in the diffraction pattern measured by the method is 100 and the diffraction pattern measured by the X-ray diffraction (XRD) method was used.
  • X-ray absorption fine structure analysis if an X-ray absorption spectrum is measured with sufficient accuracy in the energy region near the absorption edge of the element of interest, attenuation occurs in the energy region of several tens of eV from the absorption edge. Large structural vibrations are observed. This is called an X-ray absorption near edge structure (XANES), which mainly contains information on the electronic state and three-dimensional structure of the element of interest.
  • the element of interest is Mn, and the average valence of Mn is evaluated from the position of the Mn—K absorption edge.
  • the energy (absorbance) after normalization of the peak derived from the Mn—K shell in the XANES spectrum was 0.5.
  • the standardization method was the intensity (absorbance) at an energy 100 eV higher than the energy at the inflection point of the peak derived from the Mn—K shell. If the position of the Mn—K absorption edge of the lithium titanium composite oxide is higher than 6547.0 eV, the average valence of Mn is considered to be 4 or more, which is not preferable.
  • the position of the Mn—K absorption edge of the lithium titanium composite oxide is preferably 6543.0 eV or more and 6547.0 eV or more. When the position of the Mn—K absorption edge is in the above range, the average valence of Mn is preferably 2 or more and less than 4 valence.
  • X-ray diffraction (XRD) measurement contains information on atoms arranged at predetermined lattice points in a certain crystal structure.
  • the average valence of Mn was evaluated from the value of the (022) peak intensity when the (111) peak intensity of the spinel structure in the diffraction pattern was 100. This is synonymous with the percentage (%) of the (022) / (111) peak intensity ratio.
  • the (111) peak intensity of the lithium titanium composite oxide is 100
  • the (022) peak intensity is less than 1.5
  • the average valence of Mn present at the lattice point derived from the (022) peak intensity Is not preferred because it is tetravalent or higher.
  • the (022) peak intensity when the (111) peak intensity of the lithium titanium composite oxide is 100 is preferably 1.5 or more.
  • the (022) peak intensity is in the above range, which is preferable because the average valence of Mn is not less than 2 and less than 4.
  • the lattice constant calculated from the diffraction pattern is such that the ionic radius of Mn increases as the valence of Mn substituted at the Ti site decreases from tetravalent to trivalent or divalent, so that the value of the lattice constant increases. Conceivable.
  • a lattice constant of less than 0.8360 is not preferable because the average valence of Mn is 4 or more. Therefore, the lattice constant is preferably 0.8360 nm or more and 0.8380 nm or less.
  • the average valence of Mn is preferably 2 or more and less than 4 valence.
  • a Li compound selected from the group consisting of LiO 2 , Li 2 CO 3 , LiOH and the like can be used as a Li raw material.
  • Mn raw material an Mn compound having an average valence of Mn selected from the group consisting of MnCO 3 , MnO, Mn 2 O 3 and the like having a valence of 2 to less than 4 can be used.
  • the lithium-titanium composite oxide as the negative electrode active material is a mixture of the Li raw material and an Mn raw material having an average valence of 2 or more and less than 4 at a predetermined ratio, and is fired in an inert gas atmosphere such as nitrogen or argon. It is obtained by doing.
  • the negative electrode includes the lithium titanium composite oxide obtained above in the negative electrode active material, and includes a negative electrode current collector such as a metal foil and a negative electrode active material layer formed on the negative electrode current collector.
  • the negative electrode current collector a metal foil that hardly forms an alloy with lithium in the potential range of the negative electrode or a film in which a metal that hardly forms an alloy with lithium in the potential range of the negative electrode is disposed on the surface layer is used.
  • a metal that hardly forms an alloy with lithium in the potential range of the negative electrode it is common to use copper that is easy to process at low cost and has good electronic conductivity.
  • the negative electrode active material of the present invention has a high potential range. Therefore, it is preferable to use aluminum.
  • a negative electrode current collector using aluminum is more preferable than copper because it has a fusing property during abnormal heat generation.
  • the negative electrode active material layer includes a negative electrode active material that is the lithium titanium composite oxide, a conductive agent, a binder, and the like, mixed with water or an appropriate solvent, and applied onto the negative electrode current collector. It is a layer obtained by drying and rolling.
  • the negative electrode active material may include a negative electrode active material generally used in a lithium ion secondary battery capable of occluding and releasing Li in some cases. .
  • the conductive agent is used to increase the electronic conductivity of the negative electrode active material layer.
  • a conductive carbon material, metal powder, organic material, or the like is used.
  • acetylene black, ketjen black, and graphite are used as the carbon material
  • aluminum is used as the metal powder
  • a phenylene derivative is used as the organic material.
  • acetylene black is preferably used.
  • These conductive agents may be used alone or in combination of two or more.
  • the binder is used to maintain a good contact state between the negative electrode active materials and between the negative electrode active material and the conductive agent, and to enhance the binding property of the negative electrode active material and the like to the negative electrode current collector surface.
  • a fluorine polymer, a rubber polymer, or the like can be used as the binder.
  • PVdF polyvinylidene fluoride
  • the binder may be used in combination with a thickener such as carboxymethylcellulose (CMC).
  • Such a positive electrode includes, for example, a positive electrode current collector such as a metal foil and a positive electrode active material layer formed on the positive electrode current collector.
  • a positive electrode current collector a metal foil that is stable in the potential range of the positive electrode or a film in which a metal that is stable in the potential range of the positive electrode is arranged on the surface layer is used.
  • the metal stable in the potential range of the positive electrode it is preferable to use aluminum (Al).
  • the positive electrode active material layer includes a conductive agent, a binder and the like in addition to the positive electrode active material, and these are mixed with an appropriate solvent, applied onto the positive electrode current collector, dried and rolled. It is.
  • a transition metal oxide containing lithium (Li) or a transition metal oxide in which a part of the transition metal element contained in the transition metal oxide is substituted with a different element can be used.
  • the transition metal element includes at least one selected from the group consisting of scandium (Sc), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), and the like.
  • Various transition metal elements can be used.
  • As the different element at least one different element selected from the group consisting of magnesium (Mg), aluminum (Al), lead (Pb), antimony (Sb), boron (B) and the like can be used.
  • positive electrode active materials include LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiMnO 2 , LiNi 1-y Co y O 2 ( Examples include 0 ⁇ y ⁇ 1), LiNi 1-yz Co y Mnz O 2 (0 ⁇ y + z ⁇ 1), LiFePO 4 and the like. Only one type of positive electrode active material may be used alone, or two or more types may be used in combination.
  • the conductive agent and the binder those similar to those used in the negative electrode can be used without particular limitation.
  • the conductive agent a conductive carbon material, metal powder, organic material, or the like is used.
  • the binder a fluorine-based polymer, a rubber-based polymer, or the like can be used.
  • the non-aqueous electrolyte includes a non-aqueous solvent, an electrolyte salt that dissolves in the non-aqueous solvent, and an additive.
  • the non-aqueous electrolyte is not limited to a non-aqueous electrolyte that is a liquid electrolyte, and may be a solid electrolyte.
  • cyclic carbonate As the non-aqueous solvent, cyclic carbonate, chain carbonate, nitriles, amides and the like can be used.
  • cyclic carbonate a cyclic carbonate, a cyclic carboxylic acid ester, a cyclic ether, or the like can be used.
  • chain carbonate a chain ester, a chain ether, or the like can be used. More specifically, cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), cyclic carboxylic acid esters such as ⁇ -butyrolactone (GBL), and chain esters such as ethyl methyl carbonate (EMC) and dimethyl carbonate ( DMC) or the like can be used.
  • PC propylene carbonate
  • EC ethylene carbonate
  • GBL ⁇ -butyrolactone
  • EMC ethyl methyl carbonate
  • DMC dimethyl carbonate
  • a mixture of EC as a cyclic carbonate which is a high dielectric constant solvent and EMC as a chain carbonate which is a low viscosity solvent it is preferable to use a mixture of EC as a cyclic carbonate which is a high dielectric constant solvent and EMC as a chain carbonate which is a low viscosity solvent.
  • the halogen substituted body which substituted the hydrogen atom of the said non-aqueous solvent with halogen atoms, such as a fluorine atom, can be used.
  • a lithium salt can be used as the electrolyte salt.
  • the lithium salt LiPF 6 , LiBF 4 , LiClO 4 or the like generally used as a supporting salt in a conventional lithium ion secondary battery can be used. These lithium salts may be used alone or in combination of two or more.
  • the additive is considered to have a function of suppressing the reaction between the non-aqueous electrolyte and the positive electrode or the negative electrode by decomposing at the interface with the positive electrode or the negative electrode and forming an ion-permeable film on the surface of the positive electrode or the negative electrode.
  • the positive electrode or negative electrode surface is an interface between the nonaqueous electrolyte and the positive electrode or negative electrode active material, that is, the surface of the positive electrode or negative electrode active material layer and the surface of the positive electrode or negative electrode active material.
  • the additive include vinylene carbonate (VC), ethylene sulfite (ES), ⁇ -butyrolactone (GBL), cyclohexylbenzene (CHB), and the like.
  • the additive may be used alone or in combination of two or more.
  • the ratio of the additive in the nonaqueous electrolyte is preferably an amount that can sufficiently form a film derived from the additive, and is preferably 0.01% by mass or more and 5% by mass or less with respect to the total amount of the nonaqueous electrolyte.
  • a porous film having ion permeability and insulating properties disposed between the positive electrode and the negative electrode is used.
  • the porous film include a microporous thin film, a woven fabric, and a non-woven fabric.
  • polyolefin is preferable, and more specifically, polyethylene, polypropylene, and the like are preferable.
  • lithium-titanium composite oxides as negative electrode active materials for lithium ion secondary batteries used in Examples 1 and 2 and Comparative Example 1, and an evaluation coin-type lithium ion secondary battery including the same were prepared.
  • a method for synthesizing a negative electrode active material for a lithium ion secondary battery and a specific method for producing an evaluation coin-type lithium ion secondary battery including a negative electrode active material for a lithium ion secondary battery are as follows.
  • Example 1 [Synthesis of negative electrode active material]
  • the lithium-titanium composite oxide comprises Li 2 CO 3 as a Li raw material and MnCO 3 as a Mn raw material having an average valence of 2 or more and less than 4 valences.
  • Li / Ti / Mn 4.0000: 4.825 : It mixed so that it might become a composition ratio of 0.175, and it obtained by baking in argon atmosphere.
  • the obtained lithium titanium composite oxide was pulverized into a negative electrode active material.
  • the lithium titanium composite oxide as the negative electrode active material obtained above, acetylene black as the conductive agent, and polyvinylidene fluoride as the binder are prepared so as to have a weight ratio of 100: 15: 5.
  • NMP N-methyl-2-pyrrolidone
  • the trade name “Awatori Nertaro” manufactured by Shinky Corporation was used.
  • This slurry was applied onto an aluminum negative electrode current collector having a thickness of 15 ⁇ m and dried in an electric furnace maintained at 100 ° C. to form a negative electrode active material layer. After drying, it was rolled using a roller and punched to produce a pellet-shaped electrode.
  • a nonaqueous electrolyte is obtained by dissolving 1.0 mol / L of LiPF 6 as an electrolyte salt in a nonaqueous solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) are mixed at a volume ratio of 1: 3. A water electrolyte was used.
  • EC ethylene carbonate
  • EMC ethylmethyl carbonate
  • An evaluation coin-type lithium ion secondary battery (hereinafter referred to as an evaluation coin-type battery) was prepared by the following procedure using the negative electrode and non-aqueous electrolyte prepared as described above.
  • a lithium metal foil as a counter electrode is pressure-bonded to the inside of the bottom of a coin-type battery outer casing made of steel and made of a lid and a bottom, and a separator, negative electrode, and steel circular Arranged in the order of the counter plate and the disc spring.
  • As the separator two PE microporous membranes manufactured by Asahi Kasei E-Materials Co., Ltd. were used in an overlapping manner. Thereafter, the lid was covered and the battery outer package was caulked and sealed to obtain an evaluation coin-type battery.
  • Comparative Example 1 In the synthesis of the negative electrode active material, a lithium titanium composite oxide and a coin cell battery for evaluation of Comparative Example 1 were produced in the same manner as in Example 1 except that the firing atmosphere was changed from argon to air.
  • FIG. 1 is a diagram showing a XANES spectrum.
  • the vertical axis is normalized intensity (absorbance), and the horizontal axis is energy (unit: eV).
  • the peak observed around 6545 eV was taken as the peak derived from the Mn—K shell, and the energy at which the normalized intensity (absorbance) was 0.5 was taken as the position of the Mn—K absorption edge.
  • the peak observed around 6550 eV was taken as the peak derived from the Mn—K shell, and the energy at which the normalized intensity (absorbance) was 0.5 was taken as the position of the Mn—K absorption edge.
  • Table 1 shows the measurement results of the positions of the Mn—K absorption edges of Example 1 and Comparative Example 1.
  • FIG. 2 is a diagram showing the (022) peak intensity when the (111) peak intensity is set to 100 from the diffraction pattern obtained by XRD measurement.
  • the vertical axis is the (022) peak intensity when the (111) peak intensity is 100
  • the horizontal axis is the diffraction angle 2 ⁇ (unit: degree) when using the Cu—K ⁇ ray.
  • Table 1 shows the values of the (022) peak intensity shown in FIG.
  • Example 1 From Table 1, in Example 1, the position of the Mn—K absorption edge is 6543.4 eV and is in the range of 6543.0 eV or more and 6547.0 eV or less, and the (111) peak intensity is 100 (022) The peak intensity is 2.31 and 1.5 or more, and the lattice constant is 0.8368 nm and 0.8360 nm or more and 0.8380 nm or less. From this, it was confirmed that the average valence of Mn of the lithium titanium composite oxide of Example 1 is not less than 2 and less than 4. Also in Example 2, as in Example 1, the (022) peak intensity was 2.35 when the (111) peak intensity was 100, which was 1.5 or more, and the lattice constant was 0.8368 nm. From 0.8360 nm to 0.8380 nm, it was confirmed that the average valence of Mn of the lithium titanium composite oxide was not less than 2 and less than 4.
  • Comparative Example 1 the position of the Mn—K absorption edge is 6647.7 eV, which is larger than 6547.0 eV, and the (022) peak intensity when the (111) peak intensity is 100 is 1.48 and less than 1.5, and the lattice constant is 0.8356 nm and less than 0.8360 nm. From this, it was confirmed that the average valence of Mn of the lithium titanium composite oxide of Comparative Example 1 is 4 or more.
  • the discharge refers to discharge in a battery in which the negative electrode active materials of Examples 1 and 2 and Comparative Example 1 are combined with a commonly used positive electrode exemplified by LiCoO 2 or the like.
  • the above coin-type battery for evaluation has a negative electrode as a working electrode and a metallic lithium (Li) as a counter electrode, it should be charged originally, but in a battery in which a commonly used positive electrode and negative electrode are combined.
  • the reverse charge / discharge direction is expressed in accordance with the charge / discharge behavior of the negative electrode. That is, charging means flowing a current so as to decrease the potential of the negative electrode serving as the working electrode, and discharging means flowing current so as to increase the potential of the negative electrode serving as the working electrode.
  • an electrochemical measurement system manufactured by Solartron was used. First, the battery was charged at a constant current of 0.05 C until the battery voltage reached 1 V, and the initial charge capacity (mAh) was measured. Thereafter, the battery was discharged at a constant current of 0.05 C until the battery voltage reached 3 V, and the initial discharge capacity (mAh) was measured.
  • the initial charge capacity and the initial discharge capacity determined above are respectively divided by the mass (g) of the lithium-titanium composite oxide that is the negative electrode active material contained in the negative electrode, and the obtained values are respectively charged capacity densities (units). : MAh / g) and discharge capacity density (unit: mAh / g).
  • Irreversible capacity ratio (%) (charge capacity density ⁇ discharge capacity density) / charge capacity density ⁇ 100
  • Table 2 shows the results of charge capacity density, discharge capacity density, and irreversible capacity ratio for Examples 1 and 2 and Comparative Example 1.
  • FIG. 3 shows the initial charge / discharge curve for Example 1. In FIG. 4, the initial stage charge / discharge curve about Example 2 was shown.
  • FIG. 5 shows an initial charge / discharge curve for Comparative Example 1. 3 to 5, the vertical axis represents the battery voltage (unit: V), and the horizontal axis represents the capacity density (unit: mAh / g).
  • Examples 1 and 2 use a Mn raw material having an average valence of Mn of 2 or more and less than 4 as a Mn material of a lithium titanium composite oxide that is a negative electrode active material.
  • the average valence of Mn of the lithium-titanium composite oxide was maintained in the range of 2 to less than 4 as in the Mn average valence of the Mn raw material. Conceivable.
  • the lithium-titanium composite oxide as a negative electrode active material for lithium ion secondary batteries the general formula is represented by Li 4 + x M y Ti 5 -xy O 12 + ⁇ , wherein, -0 2 ⁇ x ⁇ 0.2, 0 ⁇ y ⁇ 0.3, ⁇ 0.1 ⁇ ⁇ ⁇ 0.1, M includes at least Mn, and the average valence of Mn is not less than 2 and less than 4 Preferably it is.
  • the lithium titanium composite oxide according to the present invention is used as a negative electrode active material for a lithium ion secondary battery, the irreversible capacity ratio can be reduced.

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Abstract

A lithium-titanium compound oxide having a spinel crystal structure, and represented by the general formula Li4+xMyTi5-x-yO12+α. In the formula, -0.2≤x≤0.2, 0<y≤0.3, -0.1≤α≤0.1, M contains at least Mn, and the average valence of Mn is at least 2 and less than 4.

Description

リチウムチタン複合酸化物Lithium titanium composite oxide
　本発明は、リチウムチタン複合酸化物、特にリチウムイオン二次電池用負極活物質材料としてのリチウムチタン複合酸化物に関する。 The present invention relates to a lithium titanium composite oxide, and more particularly to a lithium titanium composite oxide as a negative electrode active material for a lithium ion secondary battery.
　リチウムイオン二次電池に用いられる負極活物質材料としてリチウムチタン複合酸化物が注目されている。組成式Ｌｉ4Ｔｉ5Ｏ12で表されるリチウムチタン複合酸化物は、リチウム金属基準で約１．５Ｖ付近にリチウムイオンを吸蔵放出する平坦な充放電電位をもつため、リチウムイオン二次電池の負極活物質材料として適用した場合、金属リチウムの析出が起こりにくい。また、Ｌｉ4Ｔｉ5Ｏ12は、リチウムイオンの吸蔵放出に伴う体積の膨張収縮がほとんど起こらないとされることから、サイクル特性に優れる負極活物質材料である。 As a negative electrode active material used for a lithium ion secondary battery, a lithium titanium composite oxide has attracted attention. The lithium titanium composite oxide represented by the composition formula Li 4 Ti 5 O 12 has a flat charge / discharge potential for occluding and releasing lithium ions in the vicinity of about 1.5 V on the basis of lithium metal. When applied as a negative electrode active material, metal lithium is unlikely to precipitate. Further, Li 4 Ti 5 O 12 is a negative electrode active material having excellent cycle characteristics because it hardly undergoes volume expansion and contraction due to insertion and extraction of lithium ions.
　しかしながら、Ｌｉ4Ｔｉ5Ｏ12は、チタン（Ｔｉ）が４価で存在するため電子伝導性が低い。そこで、Ｌｉ4Ｔｉ5Ｏ12の粒子に電子伝導性を付与する目的でマンガン（Ｍｎ）が添加される。例えば、特許文献１には、Ｌｉ4Ｔｉ5Ｏ12の結晶中のＴｉの一部をＭｎ等の元素で置換し、Ｔｉの電子密度を変化させ電子伝導性を向上させることが記載されている。 However, Li 4 Ti 5 O 12 has low electron conductivity because titanium (Ti) is tetravalent. Therefore, manganese (Mn) is added for the purpose of imparting electron conductivity to the particles of Li 4 Ti 5 O 12 . For example, Patent Document 1 describes that a part of Ti in a crystal of Li 4 Ti 5 O 12 is substituted with an element such as Mn to change the electron density of Ti to improve electron conductivity. .
特開２０１３－１２４９６号公報JP 2013-12896 A
　特許文献１に開示される技術では、Ｌｉ4Ｔｉ5Ｏ12のＴｉ元素の一部をＭｎ元素で置換することで、電子伝導性が向上し放電レート特性は向上するが、Ｍｎ置換量に応じて不可逆容量が増大する。 In the technique disclosed in Patent Document 1, by substituting a part of Ti element of Li 4 Ti 5 O 12 with Mn element, the electron conductivity is improved and the discharge rate characteristics are improved. Irreversible capacity increases.
　本発明の目的は、不可逆容量を低減できるリチウムチタン複合酸化物を提供することである。 An object of the present invention is to provide a lithium titanium composite oxide capable of reducing the irreversible capacity.
　本発明に係るリチウムチタン複合酸化物は、スピネル型の結晶構造を有し、一般式がＬｉ4+xＭyＴｉ5-x-yＯ12+αで表され、式中、－０．２≦ｘ≦０．２、０＜ｙ≦０．３、－０．１≦α≦０．１であり、Ｍは少なくともＭｎを含み、Ｍｎの平均価数が２価以上４価未満であることを特徴とする。 Lithium-titanium composite oxide according to the present invention has a spinel crystal structure formula is represented by Li 4 + x M y Ti 5 -xy O 12 + α, wherein, -0.2 ≦ x ≦ 0.2, 0 <y ≦ 0.3, −0.1 ≦ α ≦ 0.1, M includes at least Mn, and the average valence of Mn is 2 or more and less than 4 And
　本発明に係るリチウムイオン二次電池用負極活物質材料としてのリチウムチタン複合酸化物は、不可逆容量を低減できる。 The lithium titanium composite oxide as the negative electrode active material for a lithium ion secondary battery according to the present invention can reduce the irreversible capacity.
実施例１と比較例１のリチウムチタン複合酸化物について、規格化後のＸＡＮＥＳスペクトルを示す図である。It is a figure which shows the XANES spectrum after normalization about the lithium titanium complex oxide of Example 1 and Comparative Example 1. 実施例１～２と比較例１のリチウムチタン複合酸化物について、ＸＲＤスペクトルにおける（１１１）ピーク強度を１００としたときの（０２２）ピーク強度を示す図である。FIG. 6 is a graph showing (022) peak intensity when the (111) peak intensity in the XRD spectrum is set to 100 for the lithium titanium composite oxides of Examples 1 and 2 and Comparative Example 1. 実施例１の評価用コイン型電池について、初期充放電カーブを示す図である。It is a figure which shows an initial stage charge / discharge curve about the coin-type battery for evaluation of Example 1. FIG. 実施例２の評価用コイン型電池について、初期充放電カーブを示す図である。It is a figure which shows an initial stage charge / discharge curve about the coin-type battery for evaluation of Example 2. FIG. 比較例１の評価用コイン型電池について、初期充放電カーブを示す図である。It is a figure which shows an initial stage charge / discharge curve about the coin-type battery for evaluation of the comparative example 1. FIG.
　以下、本発明に係る実施の形態につき、詳細に説明する。なお、以下に示す実施形態は、本発明の技術思想を具体化するための一例であって、本発明はこの実施形態に限定されない。本発明の実施形態のリチウムチタン複合酸化物は、リチウムイオン二次電池用負極活物質材料として用いられる。当該リチウムイオン二次電池は、例えば、正極及び負極がセパレータを介して積層された電極体と、非水電解質とが外装体に収容された構成を有する。以下に、リチウムチタン複合酸化物と、リチウムイオン二次電池の各構成部材について詳述する。 Hereinafter, embodiments according to the present invention will be described in detail. In addition, embodiment shown below is an example for actualizing the technical idea of this invention, and this invention is not limited to this embodiment. The lithium titanium composite oxide of the embodiment of the present invention is used as a negative electrode active material for a lithium ion secondary battery. The lithium ion secondary battery has, for example, a configuration in which an electrode body in which a positive electrode and a negative electrode are stacked via a separator and a nonaqueous electrolyte are accommodated in an exterior body. Hereinafter, each component of the lithium titanium composite oxide and the lithium ion secondary battery will be described in detail.
　〔リチウムチタン複合酸化物〕
　リチウムチタン複合酸化物は、一般式がＬｉ4+xＭyＴｉ5-x-yＯ12+αで表され、式中、－０．２≦ｘ≦０．２、０＜ｙ≦０．３、－０．１≦α≦０．１であり、Ｍは少なくともＭｎを含み、スピネル型の結晶構造を有する。ここで、Ｌｉ4Ｔｉ5Ｏ12は、空間群Ｆｄ－３ｍに属するスピネル型の結晶構造を有し、６配位１６ｄサイトに位置するチタン（Ｔｉ）の電子状態がｄ0であり、白色の絶縁体である。しかしながら、ＴｉをＭｎで置換し、上記一般式で表されるリチウムチタン複合酸化物とすることでＴｉの電子密度を変化させ電子伝導性を向上させることができる。 [Lithium titanium composite oxide]
Lithium-titanium composite oxide is represented by the general formula is represented by Li 4 + x M y Ti 5 -xy O 12 + α, wherein, -0.2 ≦ x ≦ 0.2,0 <y ≦ 0.3, −0.1 ≦ α ≦ 0.1, M includes at least Mn and has a spinel crystal structure. Here, Li 4 Ti 5 O 12 has a spinel crystal structure belonging to the space group Fd-3m, and the electronic state of titanium (Ti) located at the six-coordinate 16d site is d 0 , It is an insulator. However, by substituting Ti with Mn to obtain a lithium titanium composite oxide represented by the above general formula, the electron density of Ti can be changed and the electron conductivity can be improved.
　ｘは、－０．２≦ｘ≦０．２の範囲であることが好ましい。Ｌｉ量は、リチウムチタン複合酸化物の合成の過程で所望の組成量より過不足が生じることがあるが、上記範囲内であれば、良好な電池性能が得られる。 X is preferably in the range of −0.2 ≦ x ≦ 0.2. The amount of Li may be more or less than the desired composition amount in the process of synthesizing the lithium titanium composite oxide, but if it is within the above range, good battery performance can be obtained.
　Ｍは、少なくともＭｎを含むがＭｎ以外の元素をさらに含んでいてもよい。例えば、電子伝導性向上の目的で、Ｍは、Ｆｅ、Ｍｇ、Ｎｂ、またはＺｎを含んでいてもよい。また、リチウムチタン複合酸化物を大粒径化させる目的で、Ｍは、Ｂ、Ｖ、またはＳｒ等を含んでいてもよい。このように、Ｍは、少なくともＭｎを含むが、Ｆｅ、Ｍｇ、Ｎｂ、Ｚｎ、Ｂ、Ｖ、及びＳｒのうち少なくとも１種の元素をさらに含んでいてもよい。 M includes at least Mn, but may further include an element other than Mn. For example, M may contain Fe, Mg, Nb, or Zn for the purpose of improving electronic conductivity. Further, M may contain B, V, Sr or the like for the purpose of increasing the particle size of the lithium titanium composite oxide. Thus, M includes at least Mn, but may further include at least one element of Fe, Mg, Nb, Zn, B, V, and Sr.
　ｙは、０＜ｙ≦０．３の範囲であることが好ましい。Ｔｉのごく一部でもＭｎで置換されれば、リチウムチタン複合酸化物は優れた電子伝導性を発揮することからｙは０より大きければよい。一方、ｙが増大すると、本実施形態のリチウムチタン複合酸化物を負極活物質材料として用いたリチウムイオン二次電池において放電容量が減少する傾向にあり、上記上限値０．３より大きい場合には、放電容量の減少が顕著なため好ましくない。 Y is preferably in the range of 0 <y ≦ 0.3. If even a small part of Ti is replaced by Mn, the lithium titanium composite oxide exhibits excellent electronic conductivity, and therefore y should be larger than zero. On the other hand, when y increases, the discharge capacity tends to decrease in the lithium ion secondary battery using the lithium titanium composite oxide of the present embodiment as the negative electrode active material. Since the reduction of the discharge capacity is remarkable, it is not preferable.
　このように、Ｔｉの一部をＭｎに置換すると、Ｍｎの置換量ｙに応じて、電子伝導性が向上し放電レート特性は向上する。しかしながら、Ｍｎが還元されることにより初期充電時の不可逆容量が増大する。 Thus, when a part of Ti is substituted with Mn, the electron conductivity is improved and the discharge rate characteristic is improved according to the substitution amount y of Mn. However, the reduction of Mn increases the irreversible capacity during initial charging.
　そこで、Ｔｉの一部をＭｎに置換させるために、リチウムチタン複合酸化物を合成する際、４価の平均価数を有するＭｎ原料ではなく、２価以上４価未満の平均価数を有するＭｎ原料を用い不活性ガス雰囲気下で焼成することで、置換されたＭｎの平均価数が２価以上４価未満となると考えられる。本発明者は、このようにして得られたリチウムチタン複合酸化物はＭｎが予め還元された状態で存在するため、電子伝導性を向上させつつ初期充電時の不可逆容量を低減させることができると考案した。 Therefore, when synthesizing a lithium-titanium composite oxide in order to substitute a part of Ti with Mn, not Mn raw material having an average valence of tetravalent but Mn having an average valence of not less than 2 but less than 4 It is considered that the average valence of the substituted Mn becomes 2 or more and less than 4 by firing in an inert gas atmosphere using raw materials. The present inventor found that the lithium-titanium composite oxide obtained in this way exists in a state where Mn has been reduced in advance, so that the irreversible capacity during initial charging can be reduced while improving the electronic conductivity. Devised.
　Ｍｎの価数は、リチウムチタン複合酸化物内において複数の状態を取りうると考えられることから、これら価数の平均として平均価数とした。Ｍｎの平均価数の指標としては、平均価数を分析する過程で価数変化が生じない方法を採用した。このような指標として、Ｘ線吸収微細構造解析（ＸＡＦＳ）法で測定したＸ線吸収スペクトルから求められるＸ線吸収端近傍構造（ＸＡＮＥＳ）スペクトルにおけるＭｎ－Ｋ吸収端の位置、Ｘ線回折（ＸＲＤ）法で測定した回折パターンにおける（１１１）ピーク強度を１００としたときの（０２２）ピーク強度、及びＸ線回折（ＸＲＤ）法で測定した回折パターンから算出される格子定数を用いた。 Since the valence of Mn is considered to be able to take a plurality of states in the lithium titanium composite oxide, the average valence was taken as the average of these valences. As an index of the average valence of Mn, a method in which no change in valence occurs in the process of analyzing the average valence was adopted. As such an index, the position of the Mn—K absorption edge in the X-ray absorption near edge structure (XANES) spectrum obtained from the X-ray absorption spectrum measured by the X-ray absorption fine structure analysis (XAFS) method, the X-ray diffraction (XRD) The lattice constant calculated from the (022) peak intensity when the (111) peak intensity in the diffraction pattern measured by the method is 100 and the diffraction pattern measured by the X-ray diffraction (XRD) method was used.
　Ｘ線吸収微細構造解析（ＸＡＦＳ）の測定においては、注目元素の吸収端付近のエネルギー領域で、充分な精度でＸ線吸収スペクトルを測定すると、吸収端から数十ｅＶのエネルギー領域において減衰を伴う大きな構造性振動が観測される。これをＸ線吸収端近傍構造（ＸＡＮＥＳ：Ｘ－ｒａｙ　ａｂｓｏｒｐｔｉｏｎ　ｎｅａｒ　ｅｄｇｅ　ｓｔｒｕｃｔｕｒｅ）と呼び、主に注目元素の電子状態や立体構造に関した情報を含有している。本発明では、注目元素をＭｎとし、Ｍｎ－Ｋ吸収端の位置からＭｎの平均価数の評価を行った。 In X-ray absorption fine structure analysis (XAFS) measurement, if an X-ray absorption spectrum is measured with sufficient accuracy in the energy region near the absorption edge of the element of interest, attenuation occurs in the energy region of several tens of eV from the absorption edge. Large structural vibrations are observed. This is called an X-ray absorption near edge structure (XANES), which mainly contains information on the electronic state and three-dimensional structure of the element of interest. In the present invention, the element of interest is Mn, and the average valence of Mn is evaluated from the position of the Mn—K absorption edge.
　Ｍｎ－Ｋ吸収端の位置の定義としては、ＸＡＮＥＳスペクトルにおけるＭｎ－Ｋ殻に由来するピークの規格化後の強度（吸光度）が０．５となるエネルギーとした。規格化の方法は、Ｍｎ－Ｋ殻に由来するピークの変曲点のエネルギーよりも１００ｅＶ高いエネルギーにおける強度（吸光度）をとした。リチウムチタン複合酸化物のＭｎ－Ｋ吸収端の位置が６５４７.０ｅＶより高エネルギー側にあるとＭｎの平均価数が４価以上であると考えられるため好ましくない。リチウムチタン複合酸化物のＭｎ－Ｋ吸収端の位置は、６５４３．０ｅＶ以上６５４７．０ｅＶ以上であることが好ましい。Ｍｎ－Ｋ吸収端の位置が上記範囲にあると、Ｍｎの平均価数が２価以上４価未満であるため好適である。 As the definition of the position of the Mn—K absorption edge, the energy (absorbance) after normalization of the peak derived from the Mn—K shell in the XANES spectrum was 0.5. The standardization method was the intensity (absorbance) at an energy 100 eV higher than the energy at the inflection point of the peak derived from the Mn—K shell. If the position of the Mn—K absorption edge of the lithium titanium composite oxide is higher than 6547.0 eV, the average valence of Mn is considered to be 4 or more, which is not preferable. The position of the Mn—K absorption edge of the lithium titanium composite oxide is preferably 6543.0 eV or more and 6547.0 eV or more. When the position of the Mn—K absorption edge is in the above range, the average valence of Mn is preferably 2 or more and less than 4 valence.
　Ｘ線回折（ＸＲＤ）測定においては、ある結晶構造において所定の格子点に配置される原子の情報を含有している。本発明では、回折パターンにおけるスピネル構造の（１１１）ピーク強度を１００としたときの（０２２）ピーク強度の値からＭｎの平均価数の評価を行った。これは、（０２２）／（１１１）ピーク強度比の百分率（％）と同義である。リチウムチタン複合酸化物の（１１１）ピーク強度を１００としたときの（０２２）ピーク強度は、１．５未満であると、（０２２）ピーク強度に由来する格子点に存在するＭｎの平均価数が４価以上であるため好ましくない。よって、リチウムチタン複合酸化物の（１１１）ピーク強度を１００としたときの（０２２）ピーク強度は、１．５以上であることが好ましい。（１１１）ピーク強度を１００としたときの（０２２）ピーク強度が上記範囲にあると、Ｍｎの平均価数が２価以上４価未満であるため好適である。 X-ray diffraction (XRD) measurement contains information on atoms arranged at predetermined lattice points in a certain crystal structure. In the present invention, the average valence of Mn was evaluated from the value of the (022) peak intensity when the (111) peak intensity of the spinel structure in the diffraction pattern was 100. This is synonymous with the percentage (%) of the (022) / (111) peak intensity ratio. When the (111) peak intensity of the lithium titanium composite oxide is 100, the (022) peak intensity is less than 1.5, and the average valence of Mn present at the lattice point derived from the (022) peak intensity Is not preferred because it is tetravalent or higher. Therefore, the (022) peak intensity when the (111) peak intensity of the lithium titanium composite oxide is 100 is preferably 1.5 or more. When the (111) peak intensity is 100, the (022) peak intensity is in the above range, which is preferable because the average valence of Mn is not less than 2 and less than 4.
　また、回折パターンから算出した格子定数は、Ｔｉサイトに置換されるＭｎの価数が４価から３価、２価と小さくなるにつれてＭｎのイオン半径が大きくなるため、格子定数の値は大きくなると考えられる。格子定数は、０．８３６０未満であるとＭｎの平均価数が４価以上であるため好ましくない。よって、格子定数は、０．８３６０ｎｍ以上０．８３８０ｎｍ以下であることが好ましい。格子定数が上記範囲にあるとＭｎの平均価数が２価以上４価未満であるため好適である。 In addition, the lattice constant calculated from the diffraction pattern is such that the ionic radius of Mn increases as the valence of Mn substituted at the Ti site decreases from tetravalent to trivalent or divalent, so that the value of the lattice constant increases. Conceivable. A lattice constant of less than 0.8360 is not preferable because the average valence of Mn is 4 or more. Therefore, the lattice constant is preferably 0.8360 nm or more and 0.8380 nm or less. When the lattice constant is in the above range, the average valence of Mn is preferably 2 or more and less than 4 valence.
　このようなリチウムチタン複合酸化物の合成には、Ｌｉ原料としてＬｉＯ2、Ｌｉ2ＣＯ3、及びＬｉＯＨ等からなる群より選ばれるＬｉ化合物を用いることができる。また、Ｍｎ原料としては、ＭｎＣＯ3、ＭｎＯ、及びＭｎ2Ｏ3等からなる群より選ばれるＭｎの平均価数が２価以上４価未満のＭｎ化合物を用いることができる。負極活物質としてのリチウムチタン複合酸化物は、上記Ｌｉ原料と平均価数が２価以上４価未満のＭｎ原料とを所定の割合で混合し、窒素またはアルゴンなどの不活性ガス雰囲気下で焼成することによって得られる。 For the synthesis of such a lithium-titanium composite oxide, a Li compound selected from the group consisting of LiO 2 , Li 2 CO 3 , LiOH and the like can be used as a Li raw material. As the Mn raw material, an Mn compound having an average valence of Mn selected from the group consisting of MnCO 3 , MnO, Mn 2 O 3 and the like having a valence of 2 to less than 4 can be used. The lithium-titanium composite oxide as the negative electrode active material is a mixture of the Li raw material and an Mn raw material having an average valence of 2 or more and less than 4 at a predetermined ratio, and is fired in an inert gas atmosphere such as nitrogen or argon. It is obtained by doing.
　〔負極〕
　負極は、負極活物質に上記で得られたリチウムチタン複合酸化物を含み、金属箔等の負極集電体と、負極集電体上に形成された負極活物質層とで構成される。 [Negative electrode]
The negative electrode includes the lithium titanium composite oxide obtained above in the negative electrode active material, and includes a negative electrode current collector such as a metal foil and a negative electrode active material layer formed on the negative electrode current collector.
　負極集電体には、負極の電位範囲でリチウムと合金をほとんど作らない金属の箔、または負極の電位範囲でリチウムと合金をほとんど作らない金属を表層に配置したフィルム等が用いられる。負極の電位範囲でリチウムと合金をほとんど作らない金属としては、低コストで加工がしやすく電子伝導性の良い銅を用いることが一般的であるが、本発明の負極活物質は電位範囲が高いため、アルミニウムを用いることが好適である。アルミニウムを用いた負極集電体は、異常発熱時などに溶断性を有するため、銅よりも好適である。 As the negative electrode current collector, a metal foil that hardly forms an alloy with lithium in the potential range of the negative electrode or a film in which a metal that hardly forms an alloy with lithium in the potential range of the negative electrode is disposed on the surface layer is used. As a metal that hardly forms an alloy with lithium in the potential range of the negative electrode, it is common to use copper that is easy to process at low cost and has good electronic conductivity. However, the negative electrode active material of the present invention has a high potential range. Therefore, it is preferable to use aluminum. A negative electrode current collector using aluminum is more preferable than copper because it has a fusing property during abnormal heat generation.
　負極活物質層は、上記リチウムチタン複合酸化物である負極活物質、導電剤、及び結着剤等を含み、これらを水あるいは適当な溶媒で混合し、負極集電体上に塗布した後、乾燥及び圧延することにより得られる層である。なお、負極活物質には、上記リチウムチタン複合酸化物のほかに、場合によっては、Ｌｉを吸蔵放出することのできる一般的にリチウムイオン二次電池で用いられる負極活物質を含んでいてもよい。 The negative electrode active material layer includes a negative electrode active material that is the lithium titanium composite oxide, a conductive agent, a binder, and the like, mixed with water or an appropriate solvent, and applied onto the negative electrode current collector. It is a layer obtained by drying and rolling. In addition to the lithium titanium composite oxide, the negative electrode active material may include a negative electrode active material generally used in a lithium ion secondary battery capable of occluding and releasing Li in some cases. .
　導電剤は、負極活物質層の電子伝導性を高めるために用いられる。導電剤には、導電性を有する炭素材料、金属粉末、有機材料等が用いられる。具体的には、炭素材料としてアセチレンブラック、ケッチェンブラック、及び黒鉛等、金属粉末としてアルミニウム等、及び有機材料としてフェニレン誘導体等が挙げられる。中でも、アセチレンブラックを用いることが好適である。これら導電剤は、単独で用いてもよく、２種類以上を組み合わせて用いてもよい。 The conductive agent is used to increase the electronic conductivity of the negative electrode active material layer. As the conductive agent, a conductive carbon material, metal powder, organic material, or the like is used. Specifically, acetylene black, ketjen black, and graphite are used as the carbon material, aluminum is used as the metal powder, and a phenylene derivative is used as the organic material. Among these, acetylene black is preferably used. These conductive agents may be used alone or in combination of two or more.
　結着剤は、負極活物質同士及び負極活物質と導電剤との間の良好な接触状態を維持し、かつ負極集電体表面に対する負極活物質等の結着性を高めるために用いられる。結着剤としては、フッ素系高分子、ゴム系高分子等を用いることができる。中でも、フッ素系高分子であるポリフッ化ビニリデン（ＰＶｄＦ）を用いることが好適である。結着剤は、カルボキシメチルセルロース（ＣＭＣ）等の増粘剤と併用されてもよい。 The binder is used to maintain a good contact state between the negative electrode active materials and between the negative electrode active material and the conductive agent, and to enhance the binding property of the negative electrode active material and the like to the negative electrode current collector surface. As the binder, a fluorine polymer, a rubber polymer, or the like can be used. Among these, it is preferable to use polyvinylidene fluoride (PVdF) which is a fluorine-based polymer. The binder may be used in combination with a thickener such as carboxymethylcellulose (CMC).
　〔正極〕
　正極は、リチウムイオン二次電池の正極として用いられているものを特に限定なく用いることができる。このような正極としては、例えば、金属箔等の正極集電体と、正極集電体上に形成された正極活物質層とで構成される。正極集電体には、正極の電位範囲で安定な金属の箔、または正極の電位範囲で安定な金属を表層に配置したフィルム等が用いられる。正極の電位範囲で安定な金属としては、アルミニウム（Ａｌ）を用いることが好適である。正極活物質層は、正極活物質の他に、導電剤、結着剤等を含み、これらを適当な溶媒で混合し、正極集電体上に塗布した後、乾燥及び圧延して得られる層である。 [Positive electrode]
What is used as a positive electrode of a lithium ion secondary battery can be used for a positive electrode without limitation. Such a positive electrode includes, for example, a positive electrode current collector such as a metal foil and a positive electrode active material layer formed on the positive electrode current collector. As the positive electrode current collector, a metal foil that is stable in the potential range of the positive electrode or a film in which a metal that is stable in the potential range of the positive electrode is arranged on the surface layer is used. As the metal stable in the potential range of the positive electrode, it is preferable to use aluminum (Al). The positive electrode active material layer includes a conductive agent, a binder and the like in addition to the positive electrode active material, and these are mixed with an appropriate solvent, applied onto the positive electrode current collector, dried and rolled. It is.
　正極活物質には、リチウム（Ｌｉ）を含む遷移金属酸化物、あるいは上記遷移金属酸化物に含まれる遷移金属元素の一部が異種元素によって置換された遷移金属酸化物等を用いることができる。遷移金属元素には、スカンジウム（Ｓｃ）、マンガン（Ｍｎ）、鉄（Ｆｅ）、コバルト（Ｃｏ）、ニッケル（Ｎｉ）、銅（Ｃｕ）、及びイットリウム（Ｙ）等からなる群から選ばれる少なくとも１種の遷移金属元素を用いることができる。異種元素としては、マグネシウム（Ｍｇ）、アルミニウム（Ａｌ）、鉛（Ｐｂ）、アンチモン（Ｓｂ）及びホウ素（Ｂ）等からなる群から選ばれる少なくとも１種の異種元素を用いることができる。 As the positive electrode active material, a transition metal oxide containing lithium (Li) or a transition metal oxide in which a part of the transition metal element contained in the transition metal oxide is substituted with a different element can be used. The transition metal element includes at least one selected from the group consisting of scandium (Sc), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), and the like. Various transition metal elements can be used. As the different element, at least one different element selected from the group consisting of magnesium (Mg), aluminum (Al), lead (Pb), antimony (Sb), boron (B) and the like can be used.
　このような一般的に用いられている正極活物質の具体例には、リチウム含有遷移金属酸化物として、ＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎ2Ｏ4、ＬｉＭｎＯ2、ＬｉＮｉ1-yＣｏyＯ2（０＜ｙ＜１）、ＬｉＮｉ1-y-zＣｏyＭｎzＯ2（０＜ｙ＋ｚ＜１）、ＬｉＦｅＰＯ4等が挙げられる。正極活物質は、１種のみを単独で用いてもよく、２種以上を組み合わせて用いてもよい。 Specific examples of such commonly used positive electrode active materials include LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiMnO 2 , LiNi 1-y Co y O 2 ( Examples include 0 <y <1), LiNi 1-yz Co y Mnz O 2 (0 <y + z <1), LiFePO 4 and the like. Only one type of positive electrode active material may be used alone, or two or more types may be used in combination.
　導電剤及び結着剤には、負極で用いられているものと同様のものを特に限定になく用いることができる。導電剤には、導電性を有する炭素材料、金属粉末、有機材料等が用いられる。また、結着剤は、フッ素系高分子、ゴム系高分子等を用いることができる。 As the conductive agent and the binder, those similar to those used in the negative electrode can be used without particular limitation. As the conductive agent, a conductive carbon material, metal powder, organic material, or the like is used. As the binder, a fluorine-based polymer, a rubber-based polymer, or the like can be used.
　〔非水電解質〕
　非水電解質は、非水溶媒、非水溶媒に溶解する電解質塩及び添加剤を含む。非水電解質は、液体電解質である非水電解液に限定されず、固体電解質であってもよい。 [Non-aqueous electrolyte]
The non-aqueous electrolyte includes a non-aqueous solvent, an electrolyte salt that dissolves in the non-aqueous solvent, and an additive. The non-aqueous electrolyte is not limited to a non-aqueous electrolyte that is a liquid electrolyte, and may be a solid electrolyte.
　非水溶媒には、環状カーボネート、鎖状カーボネート、ニトリル類、アミド類などを用いることができる。環状カーボネートとしては、環状炭酸エステル、環状カルボン酸エステル、環状エーテル等を用いることができる。鎖状カーボネートとしては、鎖状エステル、鎖状エーテル等を用いることができる。より具体的には、環状炭酸エステルとしてプロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）等、環状カルボン酸エステルとしてγ－ブチロラクトン（ＧＢＬ）等、鎖状エステルとしてエチルメチルカーボネート（ＥＭＣ）、ジメチルカーボネート（ＤＭＣ）等を用いることができる。中でも、高誘電率溶媒である環状炭酸エステルとしてＥＣと、低粘度溶媒である鎖状炭酸エステルとしてＥＭＣを混合して用いることが好適である。また、上記非水溶媒の水素原子をフッ素原子などのハロゲン原子で置換したハロゲン置換体を用いることができる。 As the non-aqueous solvent, cyclic carbonate, chain carbonate, nitriles, amides and the like can be used. As the cyclic carbonate, a cyclic carbonate, a cyclic carboxylic acid ester, a cyclic ether, or the like can be used. As the chain carbonate, a chain ester, a chain ether, or the like can be used. More specifically, cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), cyclic carboxylic acid esters such as γ-butyrolactone (GBL), and chain esters such as ethyl methyl carbonate (EMC) and dimethyl carbonate ( DMC) or the like can be used. Among them, it is preferable to use a mixture of EC as a cyclic carbonate which is a high dielectric constant solvent and EMC as a chain carbonate which is a low viscosity solvent. Moreover, the halogen substituted body which substituted the hydrogen atom of the said non-aqueous solvent with halogen atoms, such as a fluorine atom, can be used.
　電解質塩には、リチウム塩を用いることができる。リチウム塩には、従来のリチウムイオン二次電池において支持塩として一般に使用されているＬｉＰＦ6、ＬｉＢＦ4、ＬｉＣｌＯ4等を用いることができる。これらのリチウム塩は、１種で使用してもよく、また２種類以上組み合わせて使用してもよい。 As the electrolyte salt, a lithium salt can be used. As the lithium salt, LiPF 6 , LiBF 4 , LiClO 4 or the like generally used as a supporting salt in a conventional lithium ion secondary battery can be used. These lithium salts may be used alone or in combination of two or more.
　添加剤は、正極あるいは負極との界面で分解し、正極あるいは負極表面にイオン透過性の被膜を形成することで、非水電解液と正極あるいは負極との反応を抑制する機能を有すると考えられる。なお、ここでいう正極あるいは負極表面とは、非水電解液と正極あるいは負極活物質との界面であり、つまり正極あるいは負極活物質層の表面及び正極あるいは負極活物質の表面を意味する。添加剤としては、例えば、ビニレンカーボネート（ＶＣ）、エチレンサルファイト（ＥＳ）、γ―ブチロラクトン（ＧＢＬ）、及びシクロヘキシルベンゼン（ＣＨＢ）等が挙げられる。 The additive is considered to have a function of suppressing the reaction between the non-aqueous electrolyte and the positive electrode or the negative electrode by decomposing at the interface with the positive electrode or the negative electrode and forming an ion-permeable film on the surface of the positive electrode or the negative electrode. . Here, the positive electrode or negative electrode surface is an interface between the nonaqueous electrolyte and the positive electrode or negative electrode active material, that is, the surface of the positive electrode or negative electrode active material layer and the surface of the positive electrode or negative electrode active material. Examples of the additive include vinylene carbonate (VC), ethylene sulfite (ES), γ-butyrolactone (GBL), cyclohexylbenzene (CHB), and the like.
　添加剤は、１種のみを単独で用いてもよく、２種以上を組み合わせて用いてもよい。非水電解質に占める添加剤の割合は、添加剤由来の被膜を十分に形成できる量であることが好ましく、非水電解質の総量に対して０．０１質量％以上５質量％以下が好ましい。 The additive may be used alone or in combination of two or more. The ratio of the additive in the nonaqueous electrolyte is preferably an amount that can sufficiently form a film derived from the additive, and is preferably 0.01% by mass or more and 5% by mass or less with respect to the total amount of the nonaqueous electrolyte.
　〔セパレータ〕
　セパレータには、正極と負極との間に配置されるイオン透過性及び絶縁性を有する多孔性フィルムが用いられる。多孔性フィルムとしては、微多孔薄膜、織布、不織布等が挙げられる。微多孔薄膜セパレータに用いられる材料としては、ポリオレフィンが好ましく、より具体的にはポリエチレン、ポリプロピレン等が好適である。 [Separator]
As the separator, a porous film having ion permeability and insulating properties disposed between the positive electrode and the negative electrode is used. Examples of the porous film include a microporous thin film, a woven fabric, and a non-woven fabric. As a material used for the microporous thin film separator, polyolefin is preferable, and more specifically, polyethylene, polypropylene, and the like are preferable.
　以下、実施例および比較例を挙げ、本発明をより具体的に詳細に説明するが、本発明は、以下の実施例に限定されるものではない。以下では、実施例１～２及び比較例１に用いるリチウムイオン二次電池用負極活物質としてのリチウムチタン複合酸化物、及びそれを具備する評価用コイン型リチウムイオン二次電池を作製した。リチウムイオン二次電池用負極活物質の合成方法、及びリチウムイオン二次電池用負極活物質を具備する評価用コイン型リチウムイオン二次電池の具体的な作製方法は以下の通りである。 Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following, lithium-titanium composite oxides as negative electrode active materials for lithium ion secondary batteries used in Examples 1 and 2 and Comparative Example 1, and an evaluation coin-type lithium ion secondary battery including the same were prepared. A method for synthesizing a negative electrode active material for a lithium ion secondary battery and a specific method for producing an evaluation coin-type lithium ion secondary battery including a negative electrode active material for a lithium ion secondary battery are as follows.
　（実施例１）
　［負極活物質の合成］
　リチウムチタン複合酸化物は、Ｌｉ原料としてのＬｉ2ＣＯ3と、平均価数が２価以上４価未満であるＭｎ原料としてのＭｎＣＯ3とをＬｉ／Ｔｉ／Ｍｎ＝４．０００：４．８２５：０．１７５の組成比となるように混合し、アルゴン雰囲気下で焼成することによって得た。得られたリチウムチタン複合酸化物は、乳鉢粉砕を行い負極活物質とした。 Example 1
[Synthesis of negative electrode active material]
The lithium-titanium composite oxide comprises Li 2 CO 3 as a Li raw material and MnCO 3 as a Mn raw material having an average valence of 2 or more and less than 4 valences. Li / Ti / Mn = 4.0000: 4.825 : It mixed so that it might become a composition ratio of 0.175, and it obtained by baking in argon atmosphere. The obtained lithium titanium composite oxide was pulverized into a negative electrode active material.
　［負極の作製］
　次に、上記で得られた負極活物質としてのリチウムチタン複合酸化物と、導電剤としてのアセチレンブラックと、結着剤としてのポリフッ化ビニリデンとを重量比で１００：１５:５となるよう用意し、これとＮ－メチル－２－ピロリドン（ＮＭＰ）溶液と練合してスラリーを調製した。練合にはシンキー社製の商品名「あわとり練太郎」を用いた。このスラリーを厚さ１５μｍのアルミニウム製の負極集電体上に塗布し、１００℃に保持した電気炉内で乾燥させ負極活物質層を形成した。乾燥後、ローラーを用いて圧延し、打ち抜いてペレット状の電極を作製した。 [Production of negative electrode]
Next, the lithium titanium composite oxide as the negative electrode active material obtained above, acetylene black as the conductive agent, and polyvinylidene fluoride as the binder are prepared so as to have a weight ratio of 100: 15: 5. This was kneaded with an N-methyl-2-pyrrolidone (NMP) solution to prepare a slurry. For the kneading, the trade name “Awatori Nertaro” manufactured by Shinky Corporation was used. This slurry was applied onto an aluminum negative electrode current collector having a thickness of 15 μm and dried in an electric furnace maintained at 100 ° C. to form a negative electrode active material layer. After drying, it was rolled using a roller and punched to produce a pellet-shaped electrode.
　［対極の作製］
　負極活物質としてのリチウムチタン複合酸化物の特性を調べるために、上記正極ではなく金属リチウム（Ｌｉ）を対極として用いた。一般に、リチウムイオン二次電池では、前述したように正極活物質にＬｉＣｏＯ2等のリチウム含有遷移金属複合酸化物を用いる。しかしながら、ここでは、正極活物質に依存しない、負極活物質そのものの特性を調べるために、電極に一般に用いられる正極活物質ではなく、リチウム金属箔を打ち抜いて対極として用いた。このような方法は、活物質の評価をするのによく用いられる。 [Production of counter electrode]
In order to investigate the characteristics of the lithium-titanium composite oxide as the negative electrode active material, metal lithium (Li) was used as a counter electrode instead of the positive electrode. In general, in a lithium ion secondary battery, a lithium-containing transition metal composite oxide such as LiCoO 2 is used as a positive electrode active material as described above. However, here, in order to investigate the characteristics of the negative electrode active material itself, which does not depend on the positive electrode active material, a lithium metal foil was punched out and used as a counter electrode instead of a positive electrode active material generally used for electrodes. Such a method is often used to evaluate an active material.
　［非水電解質の作製］
　エチレンカーボネート（ＥＣ）とエチルメチルカーボネート（ＥＭＣ）とを体積比１：３で混合させた非水溶媒に、電解質塩としてのＬｉＰＦ6を１．０ｍｏｌ／Ｌ溶解させ液状の非水電解質である非水電解液とした。 [Production of non-aqueous electrolyte]
A nonaqueous electrolyte is obtained by dissolving 1.0 mol / L of LiPF 6 as an electrolyte salt in a nonaqueous solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) are mixed at a volume ratio of 1: 3. A water electrolyte was used.
　［評価用コイン型リチウムイオン二次電池の作製］
　前述のようにして作製した負極、非水電解液を用いて、評価用コイン型リチウムイオン二次電池（以下、評価用コイン型電池とする）を以下の手順で作製した。スチール製で蓋部と底部からなるコイン型の電池外装体の底部の内側に対極となるリチウム金属箔を圧着し、その上に非水電解液を含浸させたセパレータ、負極、スチール製の円形のあて板、皿バネの順で配置し収容した。セパレータには、旭化成イーマテリアルズ社製のＰＥ微多孔膜を２枚重ねて用いた。その後、蓋部をかぶせ電池外装体をかしめて密閉し、評価用コイン型電池を得た。 [Production of coin-type lithium-ion secondary battery for evaluation]
An evaluation coin-type lithium ion secondary battery (hereinafter referred to as an evaluation coin-type battery) was prepared by the following procedure using the negative electrode and non-aqueous electrolyte prepared as described above. A lithium metal foil as a counter electrode is pressure-bonded to the inside of the bottom of a coin-type battery outer casing made of steel and made of a lid and a bottom, and a separator, negative electrode, and steel circular Arranged in the order of the counter plate and the disc spring. As the separator, two PE microporous membranes manufactured by Asahi Kasei E-Materials Co., Ltd. were used in an overlapping manner. Thereafter, the lid was covered and the battery outer package was caulked and sealed to obtain an evaluation coin-type battery.
　(実施例２)
　負極活物質の合成において、組成比をＬｉ／Ｔｉ／Ｍｎ＝４．０００：４．８２５：０．１７５からＬｉ／Ｔｉ／Ｍｎ＝３．８８３：４．９４２：０．１７５に変更したこと以外は、実施例１と同様にして実施例２のリチウムチタン複合酸化物及び評価用コイン型電池を作製した。 (Example 2)
In the synthesis of the negative electrode active material, except that the composition ratio was changed from Li / Ti / Mn = 4.0000: 4.825: 0.175 to Li / Ti / Mn = 3.883: 4.942: 0.175. Produced the lithium titanium composite oxide and evaluation coin-type battery of Example 2 in the same manner as in Example 1.
　(比較例１)
　負極活物質の合成において、焼成雰囲気をアルゴンから空気に変更したこと以外は、実施例１と同様にして比較例１のリチウムチタン複合酸化物及び評価用コイン型電池を作製した。 (Comparative Example 1)
In the synthesis of the negative electrode active material, a lithium titanium composite oxide and a coin cell battery for evaluation of Comparative Example 1 were produced in the same manner as in Example 1 except that the firing atmosphere was changed from argon to air.
　［Ｍｎ－Ｋ吸収端の位置の確認］
　負極活物質の合成で得られた実施例１及び比較例１のチウムチタン複合酸化物中について、Ｍｎの平均価数を確認するため、ＸＡＦＳ測定を行い、Ｘ線吸収スペクトルから求められるＭｎ－Ｋ吸収端のＸＡＮＥＳスペクトルからＭｎの平均価数を求めた。ＸＡＦＳ測定は、放射光施設ＳＰｒｉｎｇ－８のビームスラインＢＬ１６Ｂ２にて行った。測定は、分光結晶としてＳｉ（１１１）チャンネルカットモノクロメータを用い、Ｍｎ－Ｋ殻付近のＸ線エネルギー範囲を走査し、蛍光法により行った。測定結果を図１に示す。 [Confirmation of position of Mn-K absorption edge]
In order to confirm the average valence of Mn in the titanium-titanium composite oxide of Example 1 and Comparative Example 1 obtained by synthesis of the negative electrode active material, XAFS measurement was performed and Mn—K absorption obtained from the X-ray absorption spectrum The average valence of Mn was determined from the XANES spectrum at the end. XAFS measurement was performed at the beam line BL16B2 of the synchrotron radiation facility SPring-8. The measurement was performed by a fluorescence method using an Si (111) channel cut monochromator as a spectral crystal, scanning the X-ray energy range near the Mn—K shell. The measurement results are shown in FIG.
　図１は、ＸＡＮＥＳスペクトルを示す図である。図１において、縦軸は規格化された強度（吸光度）であり、横軸はエネルギ（単位：ｅＶ）である。実施例１は、６５４５ｅＶ付近に観測されるピークをＭｎ－Ｋ殻由来のピークとして、その規格化後の強度（吸光度）が０．５となるエネルギーをＭｎ－Ｋ吸収端の位置とした。比較例１は、６５５０ｅＶ付近に観測されるピークをＭｎ－Ｋ殻由来のピークとして、その規格化後の強度（吸光度）が０．５となるエネルギーをＭｎ－Ｋ吸収端の位置とした。実施例１及び比較例１のＭｎ－Ｋ吸収端の位置の測定結果を表１に示す。 FIG. 1 is a diagram showing a XANES spectrum. In FIG. 1, the vertical axis is normalized intensity (absorbance), and the horizontal axis is energy (unit: eV). In Example 1, the peak observed around 6545 eV was taken as the peak derived from the Mn—K shell, and the energy at which the normalized intensity (absorbance) was 0.5 was taken as the position of the Mn—K absorption edge. In Comparative Example 1, the peak observed around 6550 eV was taken as the peak derived from the Mn—K shell, and the energy at which the normalized intensity (absorbance) was 0.5 was taken as the position of the Mn—K absorption edge. Table 1 shows the measurement results of the positions of the Mn—K absorption edges of Example 1 and Comparative Example 1.
　［ピーク強度比の確認］
　負極活物質の合成で得られた実施例１～２及び比較例１のリチウムチタン複合酸化物について、Ｍｎの平均価数を確認するため、ＸＲＤ測定を行った。回折パターンから（１１１）ピーク強度を１００としたときの（０２２）ピーク強度を算出し、Ｍｎの平均価数を求めた。ＸＲＤ測定には、スペクトリス社製のＸＲＤ測定装置（商品名：「Ｘ‘ｐｅｒｔ　ＰＲＯ」）を用いた。測定結果を図２に示す。 [Confirmation of peak intensity ratio]
For the lithium titanium composite oxides of Examples 1 and 2 and Comparative Example 1 obtained by synthesis of the negative electrode active material, XRD measurement was performed to confirm the average valence of Mn. The (022) peak intensity when the (111) peak intensity was set to 100 was calculated from the diffraction pattern, and the average valence of Mn was determined. For XRD measurement, an XRD measurement apparatus (trade name: “X'pert PRO”) manufactured by Spectris was used. The measurement results are shown in FIG.
　図２は、ＸＲＤ測定によって得られた回折パターンから（１１１）ピーク強度を１００としたときの（０２２）ピーク強度を示す図である。図２において、縦軸は（１１１）ピーク強度を１００としたときの（０２２）ピーク強度であり、横軸はＣｕ－Ｋα線を用いたときの回折角２θ（単位：ｄｅｇｒｅｅ）である。図２に示される（０２２）ピーク強度の値を表１に示す。 FIG. 2 is a diagram showing the (022) peak intensity when the (111) peak intensity is set to 100 from the diffraction pattern obtained by XRD measurement. In FIG. 2, the vertical axis is the (022) peak intensity when the (111) peak intensity is 100, and the horizontal axis is the diffraction angle 2θ (unit: degree) when using the Cu—Kα ray. Table 1 shows the values of the (022) peak intensity shown in FIG.
　［格子定数の確認］
　負極活物質の合成で得られた実施例１～２及び比較例１のリチウムチタン複合酸化物について、Ｍｎの平均価数を確認するため、ＸＲＤ測定を行い、回折パターンから格子定数を算出し、Ｍｎの平均価数を求めた。ＸＲＤ測定には、スペクトリス社製のＸＲＤ測定装置（商品名：「Ｘ‘ｐｅｒｔ　ＰＲＯ」）を用いた。測定結果を表１に示す。 [Confirmation of lattice constant]
For the lithium titanium composite oxides of Examples 1 and 2 and Comparative Example 1 obtained by synthesis of the negative electrode active material, XRD measurement was performed to confirm the average valence of Mn, and the lattice constant was calculated from the diffraction pattern. The average valence of Mn was determined. For XRD measurement, an XRD measurement apparatus (trade name: “X'pert PRO”) manufactured by Spectris was used. The measurement results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１より、実施例１は、Ｍｎ－Ｋ吸収端の位置が６５４３．４ｅＶであって６５４３．０ｅＶ以上６５４７．０ｅＶ以下の範囲にあり、（１１１）ピーク強度を１００としたときの（０２２）ピーク強度が２．３１であって１．５以上であり、格子定数が０．８３６８ｎｍであって０．８３６０ｎｍ以上０．８３８０ｎｍ以下である。このことから、実施例１のリチウムチタン複合酸化物のＭｎの平均価数は、２価以上４価未満であることが確認された。実施例２についても実施例１と同様に、（１１１）ピーク強度を１００としたときの（０２２）ピーク強度が２．３５であって１．５以上であり、格子定数が０．８３６８ｎｍであって０．８３６０ｎｍ以上０．８３８０ｎｍ以下であることから、リチウムチタン複合酸化物のＭｎの平均価数が２価以上４価未満であることが確認された。 From Table 1, in Example 1, the position of the Mn—K absorption edge is 6543.4 eV and is in the range of 6543.0 eV or more and 6547.0 eV or less, and the (111) peak intensity is 100 (022) The peak intensity is 2.31 and 1.5 or more, and the lattice constant is 0.8368 nm and 0.8360 nm or more and 0.8380 nm or less. From this, it was confirmed that the average valence of Mn of the lithium titanium composite oxide of Example 1 is not less than 2 and less than 4. Also in Example 2, as in Example 1, the (022) peak intensity was 2.35 when the (111) peak intensity was 100, which was 1.5 or more, and the lattice constant was 0.8368 nm. From 0.8360 nm to 0.8380 nm, it was confirmed that the average valence of Mn of the lithium titanium composite oxide was not less than 2 and less than 4.
　これに対して、比較例１は、Ｍｎ－Ｋ吸収端の位置が６６４７．７ｅＶであって６５４７．０ｅＶより大きい値であり、（１１１）ピーク強度を１００としたときの（０２２）ピーク強度が１．４８であって１．５未満であり、格子定数が０．８３５６ｎｍであって０．８３６０ｎｍ未満である。このことから、比較例１のリチウムチタン複合酸化物のＭｎの平均価数は、４価以上であると確認された。 On the other hand, in Comparative Example 1, the position of the Mn—K absorption edge is 6647.7 eV, which is larger than 6547.0 eV, and the (022) peak intensity when the (111) peak intensity is 100 is 1.48 and less than 1.5, and the lattice constant is 0.8356 nm and less than 0.8360 nm. From this, it was confirmed that the average valence of Mn of the lithium titanium composite oxide of Comparative Example 1 is 4 or more.
　［不可逆容量率の評価］
　実施例１～２及び比較例１の評価用コイン型電池について、不可逆容量率を確認する目的で初期充放電容量の評価を行った。ここでの放電とは、実施例１～２及び比較例１の負極活物質とＬｉＣｏＯ2等で例示される一般に用いられる正極とを組み合わせた電池における放電のことをいう。ここでは、上記評価用コイン型電池は負極を作用極とし金属リチウム（Ｌｉ）を対極としていることから、本来ならば、充電というべきであるが、一般に用いられる正極と負極とを組み合わせた電池における負極の充放電挙動に合わせて、逆の充放電方向の表現をしている。つまり、充電とは作用極となる負極の電位を降下させるように電流を流すことであり、放電とは作用極となる負極の電位を上昇させるように電流を流すことである。 [Evaluation of irreversible capacity ratio]
For the evaluation coin-type batteries of Examples 1 and 2 and Comparative Example 1, the initial charge / discharge capacity was evaluated for the purpose of confirming the irreversible capacity rate. The discharge here refers to discharge in a battery in which the negative electrode active materials of Examples 1 and 2 and Comparative Example 1 are combined with a commonly used positive electrode exemplified by LiCoO 2 or the like. Here, since the above coin-type battery for evaluation has a negative electrode as a working electrode and a metallic lithium (Li) as a counter electrode, it should be charged originally, but in a battery in which a commonly used positive electrode and negative electrode are combined. The reverse charge / discharge direction is expressed in accordance with the charge / discharge behavior of the negative electrode. That is, charging means flowing a current so as to decrease the potential of the negative electrode serving as the working electrode, and discharging means flowing current so as to increase the potential of the negative electrode serving as the working electrode.
　不可逆容量率の評価には、ソーラトロン社製の電気化学測定システムを用いた。まず、電池電圧が１Ｖに達するまで０．０５Ｃの定電流で充電を行い初期充電容量（ｍＡｈ）を測定した。その後、０．０５Ｃの定電流で電池電圧が３Ｖに達するまで放電を行い、初期放電容量（ｍＡｈ）を測定した。上記で求めた初期充電容量と初期放電容量とを、それぞれ負極中に含まれる負極活物質であるリチウムチタン複合酸化物の質量（ｇ）で除し、得られた値をそれぞれ充電容量密度（単位：ｍＡｈ／ｇ）、放電容量密度（単位：ｍＡｈ／ｇ）とした。充電容量密度から放電容量密度を差し引いた値が不可逆容量であり、不可逆容量をもとに下記の式にて算出した値を不可逆容量率とした。
　不可逆容量率（％）＝（充電容量密度－放電容量密度）／充電容量密度×１００ For evaluation of the irreversible capacity ratio, an electrochemical measurement system manufactured by Solartron was used. First, the battery was charged at a constant current of 0.05 C until the battery voltage reached 1 V, and the initial charge capacity (mAh) was measured. Thereafter, the battery was discharged at a constant current of 0.05 C until the battery voltage reached 3 V, and the initial discharge capacity (mAh) was measured. The initial charge capacity and the initial discharge capacity determined above are respectively divided by the mass (g) of the lithium-titanium composite oxide that is the negative electrode active material contained in the negative electrode, and the obtained values are respectively charged capacity densities (units). : MAh / g) and discharge capacity density (unit: mAh / g). The value obtained by subtracting the discharge capacity density from the charge capacity density is the irreversible capacity, and the value calculated by the following formula based on the irreversible capacity is defined as the irreversible capacity ratio.
Irreversible capacity ratio (%) = (charge capacity density−discharge capacity density) / charge capacity density × 100
　表２に、実施例１～２及び比較例１について、充電容量密度、放電容量密度、及び不可逆容量率の結果を示す。また図３には、実施例1についての初期充放電カーブを示した。図４には、実施例２についての初期充放電カーブを示した。図５には、比較例１についての初期充放電カーブを示した。図３～５において、縦軸は電池電圧（単位：Ｖ）であり、横軸は容量密度（単位：ｍＡｈ／ｇ）である。 Table 2 shows the results of charge capacity density, discharge capacity density, and irreversible capacity ratio for Examples 1 and 2 and Comparative Example 1. FIG. 3 shows the initial charge / discharge curve for Example 1. In FIG. 4, the initial stage charge / discharge curve about Example 2 was shown. FIG. 5 shows an initial charge / discharge curve for Comparative Example 1. 3 to 5, the vertical axis represents the battery voltage (unit: V), and the horizontal axis represents the capacity density (unit: mAh / g).
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表２及び図３～５より、実施例１～２と比較例１とを比較した場合、実施例１～２において不可逆容量率は低減する結果となった。これは、実施例１～２は、負極活物質であるリチウムチタン複合酸化物のＭｎ原料として、Ｍｎが２価以上４価未満の平均価数を有するＭｎ原料を用い、且つリチウムチタン複合酸化物の合成時の焼成段階において不活性ガス雰囲気下で行ったため、リチウムチタン複合酸化物のＭｎの平均価数が、Ｍｎ原料のＭｎ平均価数と同様に２価以上４価未満を維持したものと考えられる。これに対して、比較例１は、空気雰囲気下で焼成を行ったため焼成中にＭｎが酸化され、このようなリチウムチタン複合酸化物を用いた場合に、初期充電時にＭｎが還元され不可逆容量が増大したものと考えられる。 From Table 2 and FIGS. 3 to 5, when Examples 1 and 2 were compared with Comparative Example 1, the irreversible capacity ratio was reduced in Examples 1 and 2. This is because Examples 1 and 2 use a Mn raw material having an average valence of Mn of 2 or more and less than 4 as a Mn material of a lithium titanium composite oxide that is a negative electrode active material. The average valence of Mn of the lithium-titanium composite oxide was maintained in the range of 2 to less than 4 as in the Mn average valence of the Mn raw material. Conceivable. On the other hand, in Comparative Example 1, since firing was performed in an air atmosphere, Mn was oxidized during firing, and when such a lithium-titanium composite oxide was used, Mn was reduced during initial charging, resulting in an irreversible capacity. This is thought to have increased.
　上記のことから、リチウムイオン二次電池用負極活物質材料としてのリチウムチタン複合酸化物は、一般式がＬｉ4+xＭyＴｉ5-x-yＯ12+αで表され、式中、－０．２≦ｘ≦０．２、０＜ｙ≦０．３、－０．１≦α≦０．１であり、Ｍは少なくともＭｎを含み、Ｍｎの平均価数が２価以上４価未満であることが好適である。本発明によるリチウムチタン複合酸化物は、リチウムイオン二次電池用負極活物質材料として用いた場合に不可逆容量率を低減できる。 From the above, the lithium-titanium composite oxide as a negative electrode active material for lithium ion secondary batteries, the general formula is represented by Li 4 + x M y Ti 5 -xy O 12 + α, wherein, -0 2 ≦ x ≦ 0.2, 0 <y ≦ 0.3, −0.1 ≦ α ≦ 0.1, M includes at least Mn, and the average valence of Mn is not less than 2 and less than 4 Preferably it is. When the lithium titanium composite oxide according to the present invention is used as a negative electrode active material for a lithium ion secondary battery, the irreversible capacity ratio can be reduced.

Claims (5)

  1. 　スピネル型の結晶構造を有し、一般式がＬｉ4+xＭyＴｉ5-x-yＯ12+αで表され、式中、－０．２≦ｘ≦０．２、０＜ｙ≦０．３、－０．１≦α≦０．１であり、Ｍは少なくともＭｎを含み、Ｍｎの平均価数が２価以上４価未満であることを特徴とするリチウムチタン複合酸化物。 Has a spinel crystal structure, the general formula is represented by Li 4 + x M y Ti 5 -xy O 12 + α, wherein, -0.2 ≦ x ≦ 0.2,0 <y ≦ 0. 3. A lithium-titanium composite oxide, wherein −0.1 ≦ α ≦ 0.1, M includes at least Mn, and the average valence of Mn is not less than 2 and less than 4.
  2. 　請求項１に記載のリチウムチタン複合酸化物において、
    　前記Ｍは、Ｆｅ、Ｍｇ、Ｎｂ、Ｚｎ、Ｂ、Ｖ、及びＳｒのうち少なくとも１種をさらに含むことを特徴とするリチウムチタン複合酸化物。     In the lithium titanium composite oxide according to claim 1,
    Said M further contains at least 1 sort (s) among Fe, Mg, Nb, Zn, B, V, and Sr, The lithium titanium complex oxide characterized by the above-mentioned.
  3. 　請求項１または２に記載のリチウムチタン複合酸化物において、
    　Ｘ線吸収微細構造解析（ＸＡＦＳ）法で測定したＸ線吸収スペクトルから求められるＸ線吸収端近傍構造（ＸＡＮＥＳ）スペクトルにおけるＭｎ－Ｋ吸収端の位置が６５４３．０ｅＶ以上６５４７．０ｅＶ以下の範囲にあることを特徴とするリチウムチタン複合酸化物。     In the lithium titanium composite oxide according to claim 1 or 2,
    The position of the Mn—K absorption edge in the X-ray absorption near edge structure (XANES) spectrum obtained from the X-ray absorption spectrum measured by the X-ray absorption fine structure analysis (XAFS) method is in the range of 6543.0 eV or more and 6547.0 eV or less. A lithium-titanium composite oxide characterized by being.
  4. 　請求項１または２に記載のリチウムチタン複合酸化物において、
    　Ｘ線回折（ＸＲＤ）法で測定した回折パターンにおける（１１１）ピーク強度を１００としたとき、（０２２）ピーク強度が１．５以上となることを特徴とするリチウムチタン複合酸化物。     In the lithium titanium composite oxide according to claim 1 or 2,
    A lithium-titanium composite oxide, wherein (022) peak intensity is 1.5 or more, where (111) peak intensity in a diffraction pattern measured by X-ray diffraction (XRD) method is 100.
  5. 　請求項１または２に記載のリチウムチタン複合酸化物において、
    　Ｘ線回折（ＸＲＤ）法で測定した回折パターンから算出した格子定数が０．８３６０ｎｍ以上０．８３８０ｎｍ以下であることを特徴とするリチウムチタン複合酸化物。     In the lithium titanium composite oxide according to claim 1 or 2,
    A lithium titanium composite oxide having a lattice constant calculated from a diffraction pattern measured by an X-ray diffraction (XRD) method of 0.8360 nm or more and 0.8380 nm or less.
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