JP2016072187A - Lithium ion secondary battery and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for increasing a capacity of a lithium ion secondary battery.SOLUTION: In a lithium ion secondary battery, a positive electrode active material that a positive electrode includes belongs to a space group Fd3-m, and includes lithium, and a lithium-containing transition metal compound including a transition metal M (M represents Mo, or a combination of Mo and at least one element selected from a group consisting of Mn, Co, Ni, W, and V); the mole ratio of the lithium to the transition metal M is 2.7-3.3; and the ratio of the mass of the lithium-containing transition metal oxide to a total mass of all the positive electrode active materials included in the positive electrode 21 is 0.8 or larger. Particles of the positive electrode active material have an average particle diameter of less than 5 μm.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a lithium ion secondary battery and a manufacturing method thereof.

  The lithium ion secondary battery not only has a large capacity and a large energy density, but also can be easily reduced in size and weight. Lithium ion secondary batteries are widely used as power sources for portable small electronic devices, electric vehicles, and the like, and the demand is increasing year by year.

In the development of a lithium ion secondary battery, increasing its capacity is one important technical issue. As a positive electrode material, a lithium-containing transition metal compound represented by Li _x MeO ₂ (Me is at least one selected from the group consisting of Co, Ni, Mn, and Al) has been conventionally used. In order to increase the capacity of Li _x MeO ₂ , attempts have been made to increase the charging voltage or optimize the surface structure (Patent Documents 1 and 2). However, the capacity of Li _x MeO ₂ is reaching its peak.

JP 2006-185794 A JP 2007-66745 A

  In view of the above circumstances, an object of the present disclosure is to provide a technique for increasing the capacity of a lithium ion secondary battery.

  The present disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode active material included in the positive electrode belongs to the space group Fd3-m, lithium And a transition metal M (M is Mo or Mo and at least one selected from the group consisting of Mn, Co, Ni, W and V) The molar ratio of lithium to M is 2.7 to 3.3, and the ratio of the mass of the lithium-containing transition metal compound to the total mass of all the positive electrode active materials contained in the positive electrode is 0.8 or more, Provided is a lithium ion secondary battery in which the average particle size of positive electrode active material particles is less than 5 μm.

  According to the above technique, a lithium ion secondary battery having a large capacity can be provided.

Schematic sectional view of a lithium ion secondary battery according to an embodiment of the present disclosure X-ray diffraction pattern of Li ₆ Mo ₂ O ₇ X-ray diffraction pattern of Li ₆ Mo _1.5 W _0.5 O ₇ It shows the initial discharge curve of Li ₆ Mo ₂ O ₇ It shows the initial discharge curve of Li ₆ Mo _1.5 W _0.5 O ₇ X-ray diffraction pattern of Li ₆ MoMnO ₇ It shows the initial discharge curve of Li ₆ MoMnO ₇ Shows the initial discharge curve of Li ₆ Mo ₂ O ₇ which has not been micronized (Comparative Example 2)

  As a result of intensive studies, the present inventors have found that a lithium ion secondary battery having a large capacity can be provided by using a positive electrode active material in which a plurality of electrons are involved in the charge / discharge reaction.

  A lithium ion secondary battery according to one embodiment of the present disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The positive electrode active material included in the positive electrode is , Belonging to space group Fd3-m, containing lithium and transition metal M (M includes Mo or Mo and at least one selected from the group consisting of Mn, Co, Ni, W and V) The lithium-containing transition metal compound has a molar ratio of lithium to the transition metal M of 2.7 to 3.3, and the mass of the lithium-containing transition metal compound relative to the total mass of all positive electrode active materials contained in the positive electrode Of the positive electrode active material particles is less than 5 μm.

  When this lithium-containing transition metal compound is used as a positive electrode active material, a plurality of electrons are involved in the charge / discharge reaction. Therefore, a lithium ion secondary battery having a large capacity can be provided. Further, when the positive electrode active material particles are finely divided (<5 μm), the diffusibility of lithium is improved, and the characteristics of the battery are improved accordingly.

  The average particle diameter of the positive electrode active material particles may be 500 nm or less. When the positive electrode active material particles have an average particle size of 500 nm or less, the diffusibility of lithium is sufficiently improved, and the characteristics of the battery are improved accordingly.

  The average particle diameter of the positive electrode active material particles may be 50 nm or more. If the average particle diameter is 50 nm or more, the possibility of significantly reducing the productivity of the positive electrode active material particles is low.

Further, the lithium-containing transition metal compound may be Li _α M _β O _γ (2.7β ≦ α ≦ 3.3β, 1.8 ≦ β ≦ 2.2, 6.4 ≦ γ ≦ 7.6). Good.

When Li _α M _β O _γ (2.7β ≦ α ≦ 3.3β, 1.8 ≦ β ≦ 2.2, 6.4 ≦ γ ≦ 7.6) is used as the positive electrode active material, a plurality of charge / discharge reactions are performed. As a result, the lithium ion secondary battery having a large capacity can be provided.

Further, the lithium-containing transition metal compound may be Li ₆ M ₂ O ₇ .

When Li ₆ Mo ₂ O ₇ is used as the positive electrode active material, a plurality of electrons are involved in the charge / discharge reaction. Therefore, a lithium ion secondary battery having a large capacity can be provided.

Further, the lithium-containing transition metal compound is _{Li α Mo β-x Me x} O γ (0 ≦ x ≦ 1.5, Me is Mn, Co, Ni, W, and at least one selected from the group consisting of V May be included). Further, the cathode active material may be a _{Li 6 Mo 2-x Me x} O 7 (0 ≦ x ≦ 1.5). Even if the transition metal M is replaced with another element, a lithium ion secondary battery having a large capacity can be provided.

  Further, the positive electrode may contain at least one other positive electrode active material other than the above lithium-containing transition metal compound.

  The at least one other positive electrode active material may be a lithium-containing transition metal compound capable of reversibly inserting and extracting lithium.

Further, the lithium-containing transition metal compound as at least one other positive electrode active material is Li ₂ MeO ₃ , LiMeO ₂ , Li ₄ MeO ₅ , Li ₂ MeO ₄ and LiMe ₂ O ₄ (Me is Mo, Mn, It may be at least one selected from the group consisting of Co, Ni, Fe, W, Cr and V.

  These materials can be suitably used as a positive electrode active material for a battery.

  Moreover, the lithium-containing transition metal compound may maintain the space group Fd3-m even after undergoing a charge / discharge reaction. In the first discharge, lithium is occluded in the 8a site in addition to the 16c site and the 16d site. That is, a three-electron reaction occurs. Based on this three-electron reaction, the battery has a large capacity.

  The nonaqueous electrolyte may contain at least one fluorine solvent selected from the group consisting of fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. When these fluorine solvents are contained in the nonaqueous electrolyte, the oxidation resistance of the nonaqueous electrolyte is improved. As a result, the battery can be stably operated even when the battery is charged at a high voltage.

  In addition, a method for manufacturing a lithium ion secondary battery according to one embodiment of the present disclosure includes a step of preparing a positive electrode, a negative electrode, and a separator, and a positive electrode, a separator, and a negative electrode so that the separator is disposed between the positive electrode and the negative electrode. The positive electrode active material included in the positive electrode belongs to the space group Fd3-m. The positive electrode active material further contains lithium and a transition metal M (M is Mo, or Mo and at least one selected from the group consisting of Mn, Co, Ni, W and V). The molar ratio of lithium to the transition metal M is 2.7 to 3.3, and the ratio of the mass of the lithium-containing transition metal compound to the total mass of all the positive electrode active materials contained in the positive electrode is 0. A negative electrode having a positive electrode active material particle average particle diameter of less than 5 μm and having lithium involved in charge / discharge reaction in advance is prepared.

Li ₆ Mo ₂ O ₇ changes to Li ₂ Mo ₂ O ₇ in the first charging step performed after the battery is assembled. In the first discharge step, Li ₂ Mo ₂ O ₇ changes to Li ₈ Mo ₂ O ₇ . In the first discharge, lithium is occluded in the 8a site in addition to the 16c site and the 16d site. In order to cause such a reaction, a negative electrode having lithium that participates in the charge / discharge reaction in advance is prepared. Thereby, a lithium ion secondary battery having a large capacity can be provided. In addition, when the positive electrode active material particles are finely divided (<5 μm), the diffusibility of lithium is improved, and the characteristics of the battery are improved (capacity is increased).

  The average particle diameter of the positive electrode active material particles may be 500 nm or less. When the positive electrode active material particles have an average particle size of 500 nm or less, the diffusibility of lithium is sufficiently improved, and the characteristics of the battery are improved accordingly.

  The average particle diameter of the positive electrode active material particles may be 50 nm or more. If the average particle diameter is 50 nm or more, the possibility of significantly reducing the productivity of the positive electrode active material particles is low.

Further, the lithium-containing transition metal compound may be Li _α M _β O _γ (2.7β ≦ α ≦ 3.3β, 1.8 ≦ β ≦ 2.2, 6.4 ≦ γ ≦ 7.6). Good.

The lithium-containing transition metal compound may be Li ₆ M ₂ O ₇ .

Further, the lithium-containing transition metal compounds _{Li α Mo β-x Me x} O γ (0 ≦ x ≦ 1.5, Me is Mn, Co, Ni, W, and at least one selected from the group consisting of V May be included).

Further, the cathode active material may be _{Li 6 Mo 2-x Me x} O 7 (0 ≦ x ≦ 1.5).

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

  As shown in FIG. 1, the coin-type battery 10 of this embodiment includes a positive electrode 21, a negative electrode 22, and a separator 14. The separator 14 is disposed between the positive electrode 21 and the negative electrode 22. The positive electrode 21, the negative electrode 22, and the separator 14 are impregnated with a non-aqueous electrolyte (non-aqueous electrolyte). The battery 10 further includes a case 11, a sealing plate 15, and a gasket 18. An electrode group is formed by the positive electrode 21, the negative electrode 22, and the separator 14. The electrode group is housed in the case 11. The case 11 is closed by the gasket 18 and the sealing plate 15.

The positive electrode 21 includes a positive electrode current collector 12 and a positive electrode active material layer 13 disposed on the positive electrode current collector 12. The positive electrode current collector 12 is made of a metal material such as aluminum, stainless steel, or aluminum alloy, for example. It is also possible to omit the positive electrode current collector 12 and use the case 11 as a positive electrode current collector. The positive electrode active material layer 13 includes, for example, Li ₆ Mo ₂ O ₇ as a positive electrode active material. The positive electrode active material layer 13 may contain additives such as a conductive agent, an ion conduction auxiliary agent, and a binder as necessary.

  The positive electrode active material included in the positive electrode active material layer 13 belongs to the space group Fd3-m, contains lithium and a transition metal M, and has a molar ratio of lithium to the transition metal M of 2.7 to 3.3. It may contain substantially only a certain lithium-containing transition metal compound. The positive electrode active material layer 13 may contain at least one other positive electrode active material other than the lithium-containing transition metal compound as the positive electrode active material. In the former case, “only a lithium-containing transition metal compound belonging to space group Fd3-m, containing lithium and transition metal M, and having a molar ratio of lithium to transition metal M of 2.7 to 3.3” “Substantially includes” means that no active material other than the lithium-containing transition metal compound is intentionally added to the positive electrode active material layer 13. In other words, a lithium-containing transition that belongs to the space group Fd3-m, occupies the total amount of the positive electrode active material, contains lithium and the transition metal M, and has a molar ratio of lithium to the transition metal M of 2.7 to 3.3. It means that the mass ratio of the metal compound is larger than 0.98. In the latter case, it belongs to the space group Fd3-m occupying the total amount of the positive electrode active material, contains lithium and the transition metal M, and the molar ratio of lithium to the transition metal M is 2.7 to 3.3. It means that the mass ratio of the lithium-containing transition metal compound is larger than 0.80.

The positive electrode active material may be substantially only Li ₆ Mo ₂ O ₇ . Moreover, the positive electrode active material layer 13 may include at least one other positive electrode active material other than Li ₆ Mo ₂ O ₇ and Li ₆ Mo ₂ O _{7 as} the positive electrode active material. In the former case, “the positive electrode active material contained in the positive electrode is substantially only Li ₆ Mo ₂ O ₇ ” means that the active material other than Li ₆ Mo ₂ O ₇ is intentionally positive electrode active material layer 13. Means it has not been added. In other words, it the ratio of the mass of Li ₆ Mo ₂ O ₇ to the total mass of the one or more positive electrode active material and Li ₆ Mo ₂ O ₇ contained inevitably in the cathode 21 is greater than 0.98 Means. In the latter case, Li ₆ Mo ₂ O ₇ is the main component of the positive electrode active material. The subcomponent of the positive electrode active material is not particularly limited, and a substance that contributes to the charge / discharge reaction can be used as the subcomponent. For example, the ratio of the mass of Li ₆ Mo ₂ O ₇ to the total mass of all the positive electrode active materials included in the positive electrode active material layer 13 is 0.8 or more. The upper limit of the ratio of Li ₆ Mo ₂ O ₇ is not particularly limited. From the viewpoint of distinguishing between the former case and the latter case, the upper limit of the ratio of Li ₆ Mo ₂ O ₇ is, for example, 0.98. By increasing the content ratio of Li ₆ Mo ₂ O ₇ in the positive electrode active material layer 13, the capacity of the battery 10 can be sufficiently secured.

Other than lithium-containing transition metal compounds belonging to space group Fd3-m, containing lithium and transition metal M, and having a molar ratio of lithium to transition metal M of 2.7 to 3.3, or Li ₆ Mo ₂ Examples of positive electrode active materials other than O ₇ include lithium-containing transition metal compounds capable of reversibly inserting and desorbing lithium. Li ₂ MeO ₃ , LiMeO ₂ , Li ₄ MeO ₅ , Li ₂ MeO ₄ and LiMe ₂ O ₄ (Me is composed of Mo, Mn, Co, Ni, Fe, W, Cr and V as lithium-containing transition metal compounds) At least one selected from the group consisting of at least one selected from the group can be used. Examples of positive electrode active materials other than Li ₆ Mo ₂ O ₇ include LiMoO ₂ , Li ₂ MoO ₃ , Li ₄ MoO ₅ , Li ₂ MnO ₃ , LiMn ₂ O ₄ , Li (Ni, Co, Mn) O ₂ , Li ₅ FeO ₄ , Li ₆ MnO ₄ , Li ₆ CoO ₄ , Li _1.2 (Mn, Co, Ni) O ₂ , LiCrO ₂ and LiWO ₂ may be mentioned. These materials can be suitably used as the positive electrode active material of the battery 10.

In addition, as for Li ₅ FeO ₄ , Li ₆ MnO ₄ and Li ₆ CoO ₄ , their initial charge / discharge efficiency is low (the initial charge capacity is larger than the initial discharge capacity). Therefore, at least one selected from the group consisting of Li ₅ FeO ₄ , Li ₆ MnO ₄ and Li ₆ CoO ₄ and Li ₆ Mo ₂ O ₇ whose initial charge capacity is smaller than the initial discharge capacity at an optimal ratio. By mixing, the initial charge / discharge efficiency can be close to 100%.

Note that the lithium-containing transition metal compound belonging to the space group Fd3-m, containing lithium and the transition metal M, and having a molar ratio of lithium to the transition metal M of 2.7 to 3.3 is charged and discharged. Maintains the space group Fd3-m. Similarly, Li ₆ Mo ₂ O ₇ , which is a kind of this lithium-containing transition metal compound, maintains the space group Fd3-m even after undergoing a charge / discharge reaction. Specifically, Li ₆ Mo ₂ O ₇ is changed to Li ₂ Mo ₂ O ₇ in the first charging step performed after the battery 10 is assembled. In the first discharge step, Li ₂ Mo ₂ O ₇ changes to Li ₈ Mo ₂ O ₇ . In the first discharge, lithium is occluded in the 8a site in addition to the 16c site and the 16d site. That is, a three-electron reaction occurs. Based on this three-electron reaction, the battery 10 has a large capacity.

Lithium-containing transition metal compound belonging to space group Fd3-m, containing lithium and transition metal M, and having a molar ratio of lithium to transition metal M of 2.7 to 3.3, or Li ₆ Mo ₂ O ₇ The average particle diameter of the primary particles is, for example, less than 5 μm. In other words, the average particle diameter of the positive electrode active material particles is less than 5 μm. When the particles of the positive electrode active material have such an average particle diameter, it is possible to provide the battery 10 having excellent characteristics (particularly charge / discharge characteristics).

The size of the positive electrode active material particles affects the diffusibility of lithium (lithium ions) contained in the positive electrode active material. Specifically, the smaller the positive electrode active material particles are, the smaller the lithium travel distance during charging and discharging is. In other words, it is presumed that the lithium desorption reaction and insertion reaction proceed smoothly during charge and discharge. For example, lithium of Li ₆ Mo ₂ O ₇ is occluded at the 16c site and the 16d site. Half of the 16d site is occupied by molybdenum and lithium. Therefore, molybdenum inhibits lithium migration. When the particles are large (≧ 5 μm), the diffusion of lithium is significantly inhibited by molybdenum. As a result, it is presumed that a battery having excellent characteristics cannot be obtained. In other words, the capacity of the battery is reduced by increasing the polarization resistance. On the other hand, when the positive electrode active material particles are made fine (<5 μm), the diffusibility of lithium is improved, and the characteristics of the battery are improved (capacity is increased).

  The average particle diameter of the positive electrode active material particles is desirably 500 nm or less. When the positive electrode active material particles have an average particle size of 500 nm or less, the diffusibility of lithium can be sufficiently improved. In addition, the minimum of the average particle diameter of the particle | grains of a positive electrode active material is 50 nm, for example. If the average particle diameter is 50 nm or more, the possibility of significantly reducing the productivity of the positive electrode active material particles is low.

Moreover, when the average particle diameter is appropriately adjusted, side reactions between the positive electrode active material and the electrolyte can be suppressed. Furthermore, good rate characteristics are exhibited. The average particle diameter of the positive electrode active material particles can be calculated by the following method. First, the particles of the positive electrode active material are observed with an electron microscope (SEM). The square root of the area S of the positive electrode active material particles in the obtained image is defined as the particle size a of the positive electrode active material particles (a = S ^1/2 ). The particle diameter a of the 50 positive electrode active material particles is calculated. The average value of the calculated particle diameter a is defined as the average particle diameter of the primary particles of the positive electrode active material. As will be described later, since Li ₆ Mo ₂ O ₇ was obtained almost in a single phase at this time, the calculated (average) particle size is presumed to be the particle size of Li ₆ Mo ₂ O ₇ . Further, when the isolating Li ₆ Mo ₂ O ₇ from the final product obtained in the production process of the Li ₆ Mo ₂ O ₇ is difficult, and a inevitable impurities and Li ₆ Mo ₂ O ₇ The particles can be considered as Li ₆ Mo ₂ O ₇ particles.

In order to impart good electron conductivity to the particles of the positive electrode active material, the particles of the positive electrode active material (for example, Li ₆ Mo ₂ O ₇ ) may be combined with an appropriate conductive agent (for example, carbon). Good. Specifically, a part of the surface of Li ₆ Mo ₂ O ₇ particles may be coated with a conductive agent. For example, positive electrode active material particles and acetylene black particles can be combined. The average particle diameter of the acetylene black particles is as small as several nanometers to several tens of nanometers. Therefore, even if acetylene black (carbon) particles are deposited on the surfaces of the positive electrode active material particles, the acetylene black particles do not significantly change the average particle size of the positive electrode active material particles. That is, the average particle diameter of the positive electrode active material particles combined with carbon is approximately equal to the average particle diameter of the positive electrode active material particles not combined with carbon.

Li ₆ Mo ₂ O which is an example of a lithium-containing transition metal compound belonging to the space group Fd3-m, containing lithium and a transition metal M, and having a molar ratio of lithium to the transition metal M of 2.7 to 3.3 The particles of ₇ can be produced, for example, by the following method. First, lithium compound particles and molybdenum compound particles are mixed to obtain a raw material mixture. Examples of the lithium compound include lithium hydroxide, lithium carbonate, and lithium oxide. Examples of molybdenum compounds include various molybdenum oxides and ammonium molybdate. The step of mixing the lithium compound particles and the molybdenum compound particles may be performed by a dry method or a wet method. In the mixing step, a mixing device such as a ball mill can be used. Li ₆ Mo ₂ O ₇ is obtained by firing the obtained raw material mixture. The firing step is performed, for example, in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere. Moreover, a baking process is implemented on the temperature conditions of 500-900 degreeC, and the time conditions of 12 to 24 hours, for example. By optimizing the conditions of the mixing process, the conditions of the firing process, and the like, active material particles that substantially contain only Li ₆ Mo ₂ O ₇ can be obtained.

Instead of the Li ₆ Mo ₂ O _7, or together with Li ₆ Mo ₂ O _7, a compound in which a part of Mo contained in the Li ₆ Mo ₂ O ₇ is replaced by another metal element as the positive electrode active material May be used. Such a compound is represented by Li ₆ Mo _2−x Me _x O ₇ (0 <x <2, or 0.1 ≦ x ≦ 1.5). Me is at least one selected from the group consisting of Mn, Co, Ni, W and V. By replacing part of Mo contained in Li ₆ Mo ₂ O ₇ with another metal element, various characteristics such as cycle characteristics may be improved. Li ₆ Mo ₂ O ₇ corresponds to Li ₆ Mo _2−x Me _x O ₇ (x = 0). That is, x may be 0 or more.

  The negative electrode 22 includes a negative electrode current collector 16 and a negative electrode active material layer 17 disposed on the negative electrode current collector 16. The negative electrode current collector 16 is made of a metal material such as aluminum, stainless steel, or aluminum alloy, for example. It is also possible to omit the negative electrode current collector 16 and use the sealing plate 15 as the negative electrode current collector. The negative electrode active material layer 17 contains a negative electrode active material. The negative electrode active material layer 17 may contain additives such as a conductive agent, an ion conduction auxiliary agent, and a binder as necessary.

As the negative electrode active material, a metal material, a carbon material, an oxide, a nitride, a tin compound, a silicon compound, or the like can be used. The metal material may be a single metal or an alloy. Examples of the metal material include lithium metal and lithium alloy. Examples of the carbon material include natural graphite, coke, graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), a silicon compound, or a tin compound can be preferably used. Each of the silicon compound and the tin compound may be an alloy or a solid solution. Examples of the silicon compound include SiO _x (0.05 <x <1.95). A compound (alloy or solid solution) obtained by substituting a part of silicon in SiO _x with another element can also be used. The other element is at least selected from the group consisting of boron, magnesium, nickel, titanium, molybdenum, cobalt, calcium, chromium, copper, iron, manganese, niobium, tantalum, vanadium, tungsten, zinc, carbon, nitrogen and tin. One type. Examples of tin compounds include Ni ₂ Sn ₄ , Mg ₂ Sn, SnO _x (0 <x <2), SnO ₂ and SnSiO ₃ . One kind of tin compound selected from these may be used alone, or a combination of two or more kinds of tin compounds selected from these may be used.

  The shape of the negative electrode active material is not particularly limited, and a negative electrode active material having a known shape such as a particle shape or a fiber shape can be used.

In addition, when using the material which does not contain lithium as a negative electrode active material, it is desirable that the amount of lithium exceeding the irreversible capacity of the negative electrode 22 is filled in the negative electrode 22 (negative electrode active material layer 17) beforehand. That is, when manufacturing the battery 10, it is recommended to prepare a negative electrode 22 having in advance lithium involved in the charge / discharge reaction as the negative electrode 22. In the first charging step performed after the battery 10 is assembled, Li ₆ Mo ₂ O ₇ changes to Li ₂ Mo ₂ O ₇ . In the first discharge step, Li ₂ Mo ₂ O ₇ changes to Li ₈ Mo ₂ O ₇ . In the first discharge, lithium is occluded in the 8a site in addition to the 16c site and the 16d site. In order to cause such a reaction, a negative electrode 22 having lithium that is involved in the charge / discharge reaction in advance is prepared. Thereby, the battery 10 having a large capacity can be provided.

  The method for filling (occluding) lithium in the negative electrode active material layer 17 is not particularly limited. Specifically, (a) a method of depositing lithium on the negative electrode active material layer 17 by a vapor phase method such as a vacuum evaporation method, and (b) a lithium metal foil and the negative electrode active material layer 17 are brought into contact with each other and both are heated. There is a way. In any method, lithium can be diffused into the negative electrode active material layer 17 by heat. There is also a method of electrochemically occluding lithium in the negative electrode active material layer 17. Specifically, a battery is assembled using a negative electrode 22 that does not have lithium and a lithium metal foil (positive electrode), and the battery is charged so that lithium is occluded in the negative electrode 22.

  As a binder for the positive electrode 21 and the negative electrode 22, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, polyacrylic Acid ethyl ester, polyacrylic acid hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene Styrene butadiene rubber, carboxymethyl cellulose and the like can be used. Further, selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid and hexadiene. A copolymer of two or more materials may be used as a binder. Furthermore, you may use the mixture of 2 or more types of materials selected from the above-mentioned material as a binder.

  As the conductive agent for the positive electrode 21 and the negative electrode 22, graphite, carbon black, conductive fiber, graphite fluoride, metal powder, conductive whisker, conductive metal oxide, organic conductive material, or the like can be used. Examples of graphite include natural graphite and artificial graphite. Examples of carbon black include acetylene black, ketjen black (registered trademark), channel black, furnace black, lamp black and thermal black. An example of the metal powder is aluminum powder. Examples of conductive whiskers include zinc oxide whiskers and potassium titanate whiskers. An example of the conductive metal oxide is titanium oxide. Examples of the organic conductive material include phenylene derivatives.

  As the separator 14, a material having a large ion permeability and a sufficient mechanical strength can be used. Examples of such materials include microporous thin films, woven fabrics and non-woven fabrics. Specifically, the separator 14 is preferably made of a polyolefin such as polypropylene or polyethylene. The separator 14 made of polyolefin not only has excellent durability, but can also exhibit a shutdown function when heated excessively. The thickness of the separator 14 is in the range of 10 to 300 μm (or 10 to 40 μm), for example. The separator 14 may be a single layer film composed of one kind of material or a composite film (or multilayer film) composed of two or more kinds of materials. The porosity of the separator 14 is, for example, in the range of 30 to 70% (or 35 to 60%). “Porosity” means the ratio of the volume of the pores to the total volume of the separator 14 and is measured, for example, by a mercury intrusion method.

  The nonaqueous electrolytic solution includes a nonaqueous solvent and a lithium salt dissolved in the nonaqueous solvent. As the non-aqueous solvent, a cyclic carbonate solvent, a chain carbonate solvent, a cyclic ether solvent, a chain ether solvent, a cyclic ester solvent, a chain ester solvent, a fluorine solvent, and the like can be used. Examples of the cyclic carbonate solvent include ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of the chain carbonate solvent include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of cyclic ether solvents include tetrahydrofuran, 1,4-dioxane and 1,3-dioxolane. Examples of the chain ether solvent include 1,2-dimethoxyethane and 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a chain ester solvent is methyl acetate. Examples of the fluorine solvent include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. One nonaqueous solvent selected from these may be used alone, or a combination of two or more nonaqueous solvents selected from these may be used.

  It is desirable that the non-aqueous electrolyte electrolyte contains at least one fluorine solvent selected from the group consisting of fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. . When these fluorine solvents are contained in the nonaqueous electrolytic solution, the oxidation resistance of the nonaqueous electrolytic solution is improved. As a result, even when the battery 10 is charged with a high voltage, the battery 10 can be stably operated.

The lithium _{salt, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiSO 3 CF 3, LiN (SO 2 CF 3) 2, LiN (SO 2 C 2 F 5) 2, LiN (SO 2 CF 3) ( SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ or the like can be used. One lithium salt selected from these may be used alone, or a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 to 2 mol / liter.

  The present disclosure is not limited to a coin-type lithium ion secondary battery. The present disclosure can be applied to lithium ion secondary batteries having various shapes such as a cylindrical type, a square type, a sheet type, a button type, a flat type, and a laminated type.

Example 1
Lithium oxide particles (high purity chemical, Li ₂ O, purity 99.9%) and molybdenum oxide particles (high purity chemical, MoO ₂ , purity 99.9%) are wet-ground and mixed by a ball mill. As a result, a powdery raw material mixture was obtained. The obtained raw material mixture was fired at 800 ° C. in an argon stream to obtain active material particles. The obtained active material particles were subjected to powder X-ray diffraction measurement. The results are shown in FIG. The X-ray diffraction diagram of FIG. 2 shows that Li ₆ Mo ₂ O ₇ is obtained almost in a single phase. Since each peak is broad, it can be understood that the crystallinity is low. The composition of the active material particles was examined by analyzing the X-ray diffraction data by the Rietveld method. The active material particles contained Li ₆ Mo ₂ O ₇ , Li ₂ MoO ₃ and Li ₄ MoO ₅ . The ratio of the mass of Li ₆ Mo ₂ O _{7 to} the mass of the active material particles was 0.95. The ratio of the mass of Li ₂ MoO _{3 to} the mass of the active material particles was 0.03. The ratio of the mass of Li ₄ MoO _{5 to} the mass of the active material particles was 0.02. The active material particles and carbon (acetylene black) were dry-mixed by a ball mill to make the active material particles fine, and the active material particles and carbon were combined. The average particle size (average primary particle size) of the active material particles combined with carbon was about 200 nm. The molar ratio of Li to Mo (Li / Mo) was found to vary within a range of 2.7 to 3.3. However, all of these active material particles belonged to the space group Fd3-m, and the initial discharge capacity of the battery described later was equivalent to the case of Li / Mo = 3.

In addition, when the chemical formula is Li _α M _β O _γ , β has a variation of about 1.8 ≦ β ≦ 2.2. Similarly, a variation of about ± 0.6 is observed for the molar ratio of the oxygen amount. It is thought that the reason is that oxygen deficiency and oxygen excess exist, but even when the molar ratio of oxygen fluctuates, the active material particles belong to the space group Fd3-m, An initial discharge capacity equivalent to Li ₆ Mo ₂ O ₇ was obtained. From this, the active material is considered to be Li _α M _β O _γ (2.7β ≦ α ≦ 3.3β, 1.8 ≦ β ≦ 2.2, 6.4 ≦ γ ≦ 7.6). .

  Next, by mixing 70 parts by mass of active material particles, 20 parts by mass of a conductive agent, 10 parts by mass of polyvinylidene fluoride (PVDF), and an appropriate amount of 2-methylpyrrolidone (NMP), a positive electrode composite was obtained. An agent slurry was obtained. A positive electrode mixture slurry was applied to one side of a positive electrode current collector formed of an aluminum foil having a thickness of 20 μm. The positive electrode mixture slurry was dried and rolled to obtain a positive electrode plate having a thickness of 60 μm provided with a positive electrode active material layer. The obtained positive electrode plate was punched into a circular shape having a diameter of 12.5 mm to obtain a positive electrode.

  A negative electrode was obtained by punching a 300 μm-thick lithium metal foil into a circular shape having a diameter of 14.0 mm.

Fluoroethylene carbonate (FEC), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 1: 6 to obtain a nonaqueous solvent. LiPF ₆ was dissolved in this non-aqueous solvent at a concentration of 1.0 mol / liter to obtain a non-aqueous electrolyte.

  A separator (Cerguard Co., product number 2320, thickness 25 μm) was impregnated with a non-aqueous electrolyte, and a CR2032 standard coin-type battery was produced in a dry box whose dew point was controlled at −50 ° C. Celguard (registered trademark) 2320 is a three-layer separator formed of a polypropylene layer, a polyethylene layer, and a polypropylene layer.

(Example 2)
Lithium oxide particles (high purity chemical, Li ₂ O, purity 99.9%) and molybdenum oxide particles (high purity chemical, MoO ₂ , purity 99.9%) and tungsten oxide particles (high purity) Chemical Co., Ltd., WO ₃ , purity 99.9%) was wet pulverized and mixed with a ball mill to obtain a powdery raw material mixture. The obtained raw material mixture was fired at 800 ° C. in an argon stream to obtain active material particles. The obtained active material particles were subjected to powder X-ray diffraction measurement. The results are shown in FIG. The X-ray diffraction diagram of FIG. 3 shows that Li ₆ Mo _1.5 W _0.5 O ₇ is obtained almost in a single phase. Since each peak is broad, it can be understood that the crystallinity is low. The composition of the active material particles was examined by analyzing the X-ray diffraction data by the Rietveld method. The active material particles contained Li ₆ Mo _1.5 W _0.5 O ₇ , Li ₂ MoO ₃ and Li ₅ MoO ₄ . The ratio of the mass of Li ₆ Mo _1.5 W _0.5 O _{7 to} the mass of the active material particles was 0.95. The ratio of the mass of Li ₂ MoO _{3 to} the mass of the active material particles was 0.03. The ratio of the mass of Li ₅ MoO _{4 to} the mass of the active material particles was 0.02. The active material particles and carbon (acetylene black) were dry-mixed by a ball mill to make the active material particles fine, and the active material particles and carbon were combined. The average particle size (average primary particle size) of the active material particles combined with carbon was about 200 nm. Using these active material particles, a coin-type battery was produced in the same manner as in Example 1.

(Example 3)
Particles of lithium oxide (High Purity Chemical Co., Li ₂ O, purity 99.9%), molybdenum oxide particles (High Purity Chemical Co., MoO ₂ , purity 99.9%), and manganese source MnMoO ₄ The sintered body was wet pulverized and mixed by a ball mill to obtain a powdery raw material mixture. The obtained raw material mixture was fired at 800 ° C. in a nitrogen stream to obtain active material particles.

The sintered body of MnMoO ₄ is pulverized and mixed with MnO (manufactured by Koyo Chemical Co., Ltd., MnO, purity 99.9%) and MoO ₃ (manufactured by Koyo Chemical Co., Ltd., MoO ₃ , purity 99.9%) with a ball mill. Thereafter, it was obtained by baking at 450 ° C. in an air atmosphere.

  As a result of ICP composition analysis of the active material particles produced as described above, the Li / (Mn + Mo) ratio was 3.

Further, powder X-ray diffraction measurement of the obtained active material particles was performed and shown in FIG. As a result, compared to the case of the active material particles obtained in Example 1, the peak of the X-ray diffraction pattern was shifted as shown in FIG. 6, and thus Li ₆ MoMnO ₇ was obtained in a substantially single phase. I can understand that.

Further, the composition of the active material particles was examined by analyzing the X-ray diffraction data by the Rietveld method. The active material particles contained Li ₂ MeO ₃ , LiMeO ₂ , and Li ₄ MoO ₅ .

  The above active material particles and carbon (acetylene black) were dry-mixed by a ball mill to make the active material particles fine and to make the active material particles and carbon composite. The average particle size (average primary particle size) of the active material particles combined with carbon was about 200 nm. In this example, the active material particles were used to produce a coin-type battery by the same method as in Example 1.

(Comparative Example 1)
Lithium hydroxide particles and nickel / cobalt / aluminum composite hydroxide particles were synthesized by a known method and mixed by a ball mill to obtain a powdery raw material mixture. The obtained raw material mixture was fired at 800 ° C. in an air atmosphere to obtain lithium nickel composite oxide particles. The average secondary particle size of the lithium nickel composite oxide particles was 10 μm (the primary particle size was about 200 nm). A coin-type battery was produced in the same manner as in Example 1 using lithium nickel composite oxide particles. Note that the composite of lithium nickel composite oxide particles and carbon was not performed.

(Comparative Example 2)
Active material particles were obtained in the same manner as in Example 1, except that the active material particles were not atomized and the active material particles and carbon were not combined. The average particle size (average primary particle size) of the active material particles was 5 μm. Using the obtained active material particles, a coin-type battery was produced in the same manner as in Example 1.

(Battery evaluation)
4 shows the initial discharge curve of Li ₆ Mo ₂ O ₇ , FIG. 5 shows the initial discharge curve of Li ₆ Mo _1.5 W _0.5 O ₇ , and FIG. 7 shows the initial discharge curve of Li ₆ MoMnO ₇ .

Evaluation was performed as follows. The current density for the positive electrode was set to 0.005 mA / cm ² and the battery of Example 1 was charged until a voltage of 4.8 V was reached. Thereafter, the discharge end voltage was set to 1.0 V, and the battery of Example 1 was discharged at a current density of 0.005 mA / cm ² . The initial discharge capacity of the battery of Example 1 was 450 mAh / g as shown in FIG. The initial discharge capacity of the battery of Example 2 was measured by the same method. The initial discharge capacity of the battery of Example 2 was 450 mAh / g as shown in FIG.

  Further, the initial discharge capacity of the battery of Example 3 was measured by the same method as in Examples 1 and 2. As a result, as shown in FIG. 7, the initial discharge capacity of the battery of Example 3 was 450 mAh / g.

In Comparative Example 1, the current density for the positive electrode was set to 0.005 mA / cm ^2, and the battery of Comparative Example 1 was charged until a voltage of 4.5 V was reached. Thereafter, the discharge end voltage was set to 2.5 V, and the battery of Comparative Example 1 was discharged at a current density of 0.005 mA / cm ² . The initial discharge capacity of the battery of Comparative Example 1 was 210 mAh / g.

In Comparative Example 2, the current density for the positive electrode was set to 0.005 mA / cm ² and the battery of Comparative Example 2 was charged until a voltage of 4.8 V was reached. Thereafter, the discharge end voltage was set to 1.0 V, and the battery of Comparative Example 2 was discharged at a current density of 0.005 mA / cm ² . The initial discharge capacity of the battery of Comparative Example 2 was 100 mAh / g as shown in FIG.

  As described above, the batteries of Example 1, Example 2, and Example 3 had a large initial discharge capacity. This is presumed to be an effect obtained by a plurality of electrons participating in charging / discharging. The initial discharge capacities (450 mAh / g) of the batteries of Example 1, Example 2, and Example 3 correspond to a three-electron reaction. From this, at the time of the first charge, it is presumed that lithium was occluded in the 8a site that was a vacancy before the charge.

  Another reason why the batteries of Example 1, Example 2 and Example 3 had a large initial discharge capacity was that the average particle size of the active material particles used in these Examples was small. Presumed to be. In fact, even though the composition of the positive electrode active material particles of Comparative Example 2 was the same as the composition of the positive electrode active material particles of Example 1, the initial discharge capacity of the battery of Comparative Example 2 was It was much smaller than the initial discharge capacity of the battery. In Comparative Example 2, the active material particles and carbon were not combined. However, when producing the battery of Comparative Example 2, a sufficient amount of conductive agent (carbon) was added to the positive electrode. Therefore, the conductivity of the positive electrode of the battery of Comparative Example 2 is not significantly inferior to the conductivity of the positive electrode of the battery of Example 1. Therefore, it is considered that the main factor causing the difference in the initial discharge capacity is the difference in the average particle diameter of the active material particles, in other words, the difference in the diffusibility of lithium.

As a result of preparing a plurality of samples in both Example 2 and Example 3, the molar ratio of Li to M (Li / M) was found to vary within the same range as in Example 1. All of these active material particles belonged to the space group Fd3-m. Moreover, when variation occurred in β and γ similarly to Example 1, the active material particles belonged to the space group Fd3-m. That is, the positive electrode active material of this embodiment is Li _α M _β O _γ (2.7 ≦ α / β ≦ 3.3β, 1.8 ≦ β ≦ 2.2, 6.4 ≦ γ ≦ 7.6. ).

In addition, although Example 3 demonstrated the compound which substituted a part of Mo with Mn and W, the substituted element is not restricted to Mn and W. For example, a part of Mo may be substituted with at least one element of Co and Ni. In order to replace at least a part of Mo with Co, CoO or CoMoO ₄ may be used as a raw material. In order to replace at least a part of Mo with Ni, NiO or NiMoO ₄ may be used as a raw material. In order to replace at least part of Mo with V, VO ₂ may be used as a raw material.

In other words, the positive electrode active material belongs to the space group Fd3-m, and includes at least one selected from the group consisting of lithium and transition metal M (M is Mo or Mo and Mn, Co, Ni, W, V). And a lithium-containing transition metal compound having a molar ratio of lithium to the transition metal M of 2.7 to 3.3. Even when the positive electrode active material is represented by Li _α M _β O _γ (2.7β ≦ α ≦ 3.3β, 1.8 ≦ β ≦ 2.2, 6.4 ≦ γ ≦ 7.6), The kind of M is the same, and the positive electrode active material is Li _α Mo _β-x Me _x O _γ (0 <x <2, or 0.1 ≦ x ≦ 1.5. Me is Mn, Co, Ni, W, And at least one selected from the group consisting of V and V).

In Example 3, a sintered body of MnMoO ₄ was used as the manganese source, but transition metal oxides such as MnO, Mn ₂ O ₃ , and MnO ₂ may be appropriately used as the manganese source. Similarly, although WO ₃ is used as the tungsten oxide particles in Example 2, WO ₂ or the like may be used as the tungsten source. Moreover, Mo can be substituted with two or more types of metal elements other than Mo by including two or more types of transition metal oxides or composite transition metal oxides in the raw material mixture.

  In addition, by adjusting the amount of Mn, Co, Ni, W and V transition metal oxide or composite transition metal oxide in the raw material mixture, the substitution amount of Mn, Co, Ni, W and V for Mo is changed. Can be made.

  The lithium ion secondary battery of the present disclosure is useful as a power source for portable electronic devices such as mobile phones, PDAs, personal computers, digital cameras, and portable game machines. The lithium ion secondary battery of the present disclosure is also useful as a driving power source for vehicles such as electric vehicles and hybrid vehicles.

10 Battery 14 Separator 21 Positive electrode 22 Negative electrode

Claims (19)

A positive electrode;
A negative electrode,
A separator disposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte,
The positive electrode active material included in the positive electrode belongs to the space group Fd3-m, and is selected from the group consisting of lithium and transition metal M (M is Mo or Mo and Mn, Co, Ni, W, and V). A lithium-containing transition metal compound containing at least one of
A molar ratio of the lithium to the transition metal M is 2.7 or more and 3.3 or less;
The ratio of the mass of the lithium-containing transition metal compound to the total mass of all the positive electrode active materials contained in the positive electrode is 0.8 or more,
The lithium ion secondary battery in which the average particle diameter of the particles of the positive electrode active material is less than 5 μm.   The lithium ion secondary battery according to claim 1, wherein the average particle diameter of the positive electrode active material particles is 500 nm or less.   The lithium ion secondary battery according to claim 1, wherein the average particle diameter of the positive electrode active material particles is 50 nm or more. The lithium-containing transition metal compound is Li _α M _β O _γ (2.7β ≦ α ≦ 3.3β, 1.8 ≦ β ≦ 2.2, 6.4 ≦ γ ≦ 7.6). The lithium ion secondary battery of any one of -3. The lithium ion secondary battery according to claim 1, wherein the lithium-containing transition metal compound is Li ₆ M ₂ O ₇ . The lithium-containing transition metal compounds _{Li α Mo β-x Me x} O γ (0 ≦ x ≦ 1.5, Me include Mn, Co, Ni, W, and at least one member selected from the group consisting of V The lithium ion secondary battery according to claim 4, wherein The positive active _{material, Li 6 Mo 2-x Me} x O 7 (0 ≦ x ≦ 1.5) lithium ion secondary battery according to claim 6 is.   The lithium ion secondary battery according to claim 4, wherein the positive electrode includes at least one other positive electrode active material other than the lithium-containing transition metal compound.   The lithium ion secondary battery according to claim 7, wherein the at least one other positive electrode active material is a lithium-containing transition metal compound capable of reversibly inserting and extracting lithium. The lithium-containing transition metal compound, which is the at least one other positive electrode active material, may be Li ₂ MeO ₃ , LiMeO ₂ , Li ₄ MeO ₅ , Li ₂ MeO ₄ and LiMe ₂ O ₄ (Me is Mo, Mn, The lithium ion secondary battery according to claim 9, comprising at least one selected from the group consisting of Co, Ni, Fe, W, Cr, and V).   The lithium ion secondary battery according to any one of claims 1 to 3, wherein the lithium-containing transition metal compound maintains the space group Fd3-m even after undergoing a charge / discharge reaction.   The nonaqueous electrolyte contains at least one fluorine solvent selected from fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. The lithium ion secondary battery described in 1. Preparing a positive electrode, a negative electrode and a separator;
Combining the positive electrode, the separator, and the negative electrode so that the separator is disposed between the positive electrode and the negative electrode,
The positive electrode active material included in the positive electrode belongs to the space group Fd3-m, and is selected from the group consisting of lithium and transition metal M (M is Mo or Mo and Mn, Co, Ni, W and V). A lithium-containing transition metal compound containing at least one)
A molar ratio of the lithium to the transition metal M is 2.7 or more and 3.3 or less;
The ratio of the mass of the lithium-containing transition metal compound to the total mass of all the positive electrode active materials contained in the positive electrode is 0.8 or more,
An average particle diameter of the positive electrode active material particles is less than 5 μm;
The manufacturing method of a lithium ion secondary battery which prepares the negative electrode which has lithium beforehand as the said negative electrode.   The method for producing a lithium ion secondary battery according to claim 13, wherein the average particle diameter of the particles of the positive electrode active material is 500 nm or less.   The method for producing a lithium ion secondary battery according to claim 13 or 14, wherein the average particle diameter of the particles of the positive electrode active material is 50 nm or more. The lithium-containing transition metal compound is Li _α M _β O _γ (2.7β ≦ α ≦ 3.3β, 1.8 ≦ β ≦ 2.2, 6.4 ≦ γ ≦ 7.6). The manufacturing method of the lithium ion secondary battery of any one of -15. The lithium-containing transition metal compound is a Li ₆ M ₂ O _7, a manufacturing method of a lithium ion secondary battery according to any one of claims 13 to 15. The lithium-containing transition metal compounds _{Li α Mo β-x Me x} O γ (0 ≦ x ≦ 1.5, Me include Mn, Co, Ni, W, and at least one member selected from the group consisting of V The method for producing a lithium ion secondary battery according to claim 16, wherein The positive active _{material, Li 6 Mo 2-x Me} x O 7 (0 ≦ x ≦ 1.5) a method for producing a lithium ion secondary battery according to claim 17.

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