JP6246109B2 - Lithium / cobalt-containing composite oxide and method for producing the same, electrode for non-aqueous secondary battery using the lithium / cobalt-containing composite oxide, and non-aqueous secondary battery using the same - Google Patents

Description

  The present invention relates to a lithium-cobalt-containing composite oxide having excellent high-voltage charging characteristics, a method for producing the same, a non-aqueous secondary battery electrode using the lithium-cobalt-containing composite oxide, and a non-aqueous secondary battery using the same. The present invention relates to a secondary battery.

  In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers, and the practical application of electric vehicles, secondary batteries and capacitors used as these power sources are required to have higher performance and higher stability. It has been. In particular, non-aqueous secondary batteries represented by lithium secondary batteries are attracting attention as batteries having high energy density, and various improvements are being promoted as suitable power sources for the above devices.

As the positive electrode active material of the non-aqueous secondary battery, lithium cobalt oxide (LiCoO ₂ ) is mainly used because it is easy to manufacture and easy to handle. Further, in order to further improve the characteristics of lithium cobaltate, some elements of lithium cobaltate are replaced with other elements.

  For example, Patent Document 1 proposes a lithium cobaltate-based positive electrode active material in which a part of lithium (Li) and a part of cobalt (Co) in lithium cobaltate are substituted with other same elements. Patent Document 2 proposes a lithium cobaltate-based positive electrode active material in which a part of Li in lithium cobaltate is substituted with magnesium (Mg) and a part of Co is substituted with another element. Further, in Patent Document 3, a lithium cobaltate-based positive electrode active material having substantially no local cubic spinel-like structural phase in which a part of Co in lithium cobaltate is substituted with nickel (Ni) and manganese (Mn). Substances have been proposed.

International Publication No. 2002/0554511 Japanese Patent Laid-Open No. 10-241691 Special table 2008-544468

  On the other hand, recently, in order to further increase the capacity of the non-aqueous secondary battery, an attempt has been made to increase the charging voltage of the positive electrode from the conventional 4.2 to 4.5 V to 4.6 V or more based on the lithium metal. This means that when combined with a negative electrode using graphite as a negative electrode active material, the charging voltage of the battery becomes about 4.5 V or more, thereby increasing the initial discharge capacity. . However, when a positive electrode using the above-described lithium cobaltate-based positive electrode active material is charged to 4.6 V or more on the basis of lithium metal, the crystal structure of the lithium cobaltate-based positive electrode active material becomes unstable, and charge / discharge cycle characteristics are deteriorated. It turned out that there was a problem. Moreover, the high voltage provided with the positive electrode using a lithium cobaltate type positive electrode active material from the concern about the safety | security to charge the positive electrode using a lithium cobaltate type positive electrode active material to 4.6V or more on a lithium metal basis The non-aqueous secondary battery of the specification has not been put into practical use yet.

  Furthermore, in order to stabilize the crystal structure of the lithium cobaltate-based positive electrode active material, attempts have been made to increase the amount of the differently substituted element added. Although the crystal structure of the positive electrode active material can be stabilized, there is also a problem that the capacity of the lithium cobaltate positive electrode active material is reduced and the advantage of high capacity by high voltage charging is offset.

  In view of the above problems, the present invention provides a lithium-cobalt-containing composite oxide that has a stable crystal structure even under high voltage and a method for producing the same, and uses the lithium-cobalt-containing composite oxide to increase the capacity. An electrode for a non-aqueous secondary battery and a non-aqueous secondary battery excellent in charge / discharge cycle characteristics even under a high voltage are provided.

The lithium-cobalt-containing composite oxide of the present invention has a layered crystal structure and is represented by the following general composition formula (1).
(Li _1-x Mg _x ) _{1 + m} (Co _1-y M ¹ _y ) _{1 + n} M ² _z O ₂ (1)
However, the general composition formula (1), M ¹ represents a single element or group of elements containing at least Mn, M ² is Na, Sr, at least one selected from the group consisting of Ba and F represents a single element or element group including elemental, 0.015 ≦ x ≦ 0.08, 0.015 ≦ y ≦ 0.08,0 ≦ z ≦ 0.05, - 0.02 ≦ m ≦ 0.02 And -0.02 ≦ n ≦ 0.02 .

The method for producing a lithium-cobalt-containing composite oxide of the present invention includes a step of firing a composite compound containing cobalt and M ¹ , a compound containing lithium, and a compound containing magnesium, The M ¹ represents a single element or element group containing at least Mn, the number of moles of magnesium contained in the compound containing magnesium, and the number of moles of M ¹ contained in the composite compound containing cobalt and M ^1. And the number of moles of lithium contained in the compound containing lithium and the number of moles of cobalt contained in the composite compound containing cobalt and M ¹ are approximately equal.

  Moreover, the electrode for non-aqueous secondary batteries of this invention is characterized by including the said lithium * cobalt containing complex oxide of this invention as an active material.

  Moreover, the non-aqueous secondary battery of this invention is characterized by including the electrode for non-aqueous secondary batteries of the said invention as a positive electrode.

  According to the present invention, it is possible to provide a non-aqueous secondary battery having a high capacity and excellent charge / discharge cycle characteristics even under a high voltage.

FIG. 1 is a schematic diagram of a HAADF-STEM image of lithium cobaltate in which a part of the Li site is substituted with Mg. 2 is a diagram showing a HAADF-STEM image of the lithium-cobalt-containing composite oxide of Example 1. FIG.

  Hereinafter, although embodiment of this invention is described, these are only examples of the embodiment of this invention, and this invention is not limited to these content.

(Embodiment 1)
First, the lithium-cobalt-containing composite oxide of the present invention will be described. The lithium-cobalt-containing composite oxide of the present invention has a layered crystal structure and is represented by the following general composition formula (1).
(Li _1-x Mg _x ) _{1 + m} (Co _1-y M ¹ _y ) _{1 + n} M ² _z O ₂ (1)

However, in the general composition formula (1), M ¹ represents a single element or a group of elements containing at least Mn, and M ² is at least one selected from the group consisting of Na, Sr, Ba and F. Represents a single element or group of elements including elements, 0.001 ≦ x ≦ 0.08, 0.001 ≦ y ≦ 0.08, 0 ≦ z ≦ 0.05, −0.05 ≦ m ≦ 0.05 And −0.05 ≦ n ≦ 0.05.

  The lithium-cobalt-containing composite oxide represented by the general composition formula (1) has a stable crystal structure even when exposed to a high voltage of 4.6 V or more on the basis of lithium metal, and is charged and discharged under a high voltage. Excellent cycle characteristics.

  In particular, Mg in the general composition formula (1) is preferably arranged at the Li site in the crystal lattice of the crystal structure of the lithium-cobalt-containing composite oxide. Thereby, the crystal structure of the lithium-cobalt-containing composite oxide can be further stabilized, and charge / discharge cycle characteristics under a high voltage can be further improved.

Mn in M ¹ in the general composition formula (1) is preferably arranged at the Co site in the crystal lattice of the crystal structure of the lithium-cobalt-containing composite oxide. Since Mg is present at the Li site and Mn is present at the Co site, a spinel phase can be stably present locally in the crystal structure of the lithium-cobalt-containing composite oxide. -It is estimated that the cobalt-containing composite oxide has the spinel structure phase locally in its crystal structure, so that the layered crystal structure of the lithium-cobalt-containing composite oxide can be further stabilized. It is considered that the charge / discharge cycle characteristics under voltage can be further improved.

M ¹ may contain an element other than Mn. In the case where M ¹ contains at least one element selected from the group consisting of Cr, Fe, Ni, Zr, Ti, Mo, V, Al, B, and Ge, the above lithium-cobalt-containing composite oxide It is possible to further stabilize the crystal structure. In particular, it is desirable to contain Ni. However, in order not to inhibit the action of Mn, the content is preferably 50 mol% or less of M ¹ as a whole, and more preferably 35 mol% or less. Further, for elements other than Mn, Cr, Fe, Ni, Zr, Ti, Mo, V, Al, B, and Ge, the content thereof is 20 mol% of the entire M ¹ so as not to inhibit the action of the above-mentioned substitution elements. The following is desirable.

It should be noted that elements other than Mn in M ¹ are not necessarily arranged at the Co site, and depending on the type and content of the element, they may be arranged at the Li site or segregated at the grain boundaries. Conceivable.

  In the general composition formula (1), the difference between x and y is preferably 0.02 or less, and more preferably x ≧ y. Thereby, Mg can be reliably arranged at the Li site and Mn can be arranged at the Co site.

  Further, the c-axis lattice constant in the layered crystal structure of the lithium-cobalt-containing composite oxide is preferably 1.405 to 1.408 nm, more preferably 1.406 nm or more. Within this range, the crystal structure of the lithium-cobalt-containing composite oxide can be further stabilized.

In the general composition formula (1), x representing the content of Mg and y representing the content of M ¹ are too large, because the contents of Li and Co are reduced, leading to a decrease in capacity. Each of them needs to be 0.08 or less, and in order to obtain the above effect of addition of Mg and M ¹ , it is necessary to make each 0.001 or more.

Further, M ² in the general composition formula (1) is not necessarily contained, but by containing Na and F, the average valence of other contained elements can be adjusted, By containing Sr and Ba, which are alkaline earth metals, the crystallinity of the lithium / cobalt-containing composite oxide is improved, and the active sites of the lithium / cobalt-containing composite oxide are reduced, thereby constituting a battery. In this case, irreversible reaction with the non-aqueous electrolyte can be suppressed.

The M ² may contain elements other than Na, Sr, Ba and F. However, in order not to inhibit the action of the elements Na, Sr, Ba and F, the content thereof is the entire M ² . It is desirable to make it 20 mol% or less.

The element contained in M ² may be uniformly distributed in the lithium / cobalt-containing composite oxide, or may be segregated on the particle surface of the lithium / cobalt-containing composite oxide.

Since z representing the content of M ^{2 in} the general composition formula (1) is too large, the content of other elements decreases, so it is necessary to set it to 0.05 or less.

The lithium-cobalt-containing composite oxide of the present invention is based on a composition represented by (Li _1-x Mg _x ) (Co _1-y M ¹ _y ) O ₂ , but the atomic ratio of Li and Mg And the total atomic ratio of Co and M ¹ may be slightly deviated from 1: 1. In the above general composition formula (1), −0.05 ≦ m ≦ 0. In the range of 05 and −0.05 ≦ n ≦ 0.05, an oxide capable of obtaining good characteristics can be obtained. However, in order to make the lithium-cobalt-containing composite oxide of the present invention more excellent characteristics, m is preferably a value close to 0, preferably −0.02 ≦ m, and m It is desirable that ≦ 0.02. On the other hand, regarding n, in order to make the lithium-cobalt-containing composite oxide of the present invention more excellent, n is preferably a value close to 0, and preferably −0.02 ≦ n. In addition, it is desirable that n ≦ 0.02.

Next, the manufacturing method of the lithium cobalt containing complex oxide of this invention is demonstrated. The method for producing a lithium-cobalt-containing composite oxide of the present invention includes a step of firing a composite compound containing Co and M ¹ , a compound containing Li, and a compound containing Mg. ¹ represents a single element or group of elements containing at least Mn, and the number of moles of Mg contained in the compound containing the above-Mg, and the number of moles of M ¹ contained in the composite compound containing the Co and M ¹ The number of moles of Li contained in the compound containing Li is approximately equal to the number of moles of Co contained in the composite compound containing Co and M ¹ .

In the production process of the lithium-cobalt-containing composite oxide, as a synthesis raw material, a composite compound containing Co and M ¹ , a compound containing Li, and a compound containing Mg are used. Mg is likely to be arranged at the Li site in the crystal lattice of the lithium-cobalt-containing composite oxide, and M ¹ is easily arranged at the Co site.

Here, in the composite compound containing Co and M ^1, the atomic ratio of Co and M ¹ is approximately 99.9: 0.1 to 92: may be the 8 range, further, lithium cobalt-containing complex In order to allow a fine spinel phase to exist more stably in the crystal structure of the oxide, the composition ratio of the composite compound is adjusted so that 0.01 ≦ y in the general composition formula (1). It is desirable that 0.015 ≦ y, and it is desirable to adjust the composition ratio of the composite compound so that y ≦ 0.05, and it is more desirable that y ≦ 0.035. .

  The ratio of the compound containing Li and the compound containing Mg may be adjusted so that the number of moles of Li and the number of moles of Mg are in the range of approximately 99.9: 0.1 to 92: 8. Furthermore, in order to allow a fine spinel structure phase to exist more stably in the crystal structure of the lithium-cobalt-containing composite oxide, in the above general composition formula (1), 0.01 ≦ x is satisfied. The composition ratio of the composite compound is preferably adjusted, more preferably 0.015 ≦ x, and the composition ratio of the composite compound is preferably adjusted so that x ≦ 0.05, and x ≦ 0. .035 is more desirable.

Also, a composite compound containing Co and M ^1, the proportion of the compound containing compound and Mg containing Li, may be adjusted according to the range of m and n in the general formula (1). Specifically, each synthetic raw material is in the range of −0.05 ≦ m ≦ 0.05 and −0.05 ≦ n ≦ 0.05, and the difference between x and y is 0.02 or less. It is particularly desirable to adjust the composition and ratio. That is, the number of moles of Mg contained in the compound containing Mg is substantially equal to the number of moles of M ¹ contained in the composite compound containing Co and M ¹ , and Li contained in the compound containing Li. A more stable lithium / cobalt-containing composite oxide is synthesized by setting the production conditions so that the number of moles of Co and the number of moles of Co contained in the composite compound containing Co and M ¹ are substantially equal. can do.

  In addition, a part or all of the compound containing Li and the compound containing Mg may be replaced with a composite compound containing Li and Mg, and in this case also, the atomic ratio of each element falls within a predetermined range. What is necessary is just to adjust the ratio of each synthetic raw material.

In addition, when M ² is further added to the lithium-cobalt-containing composite oxide of the present invention, (Li _1-x Mg _x ) _{1 is} obtained by adding a compound containing M ² and baking in the above step. A compound represented by _{+ m} (Co _1-y M ¹ _y ) _{1 + n} M ² _z O ₂ can be formed.

As each synthetic raw material used by the said manufacturing method, the hydroxide, oxide, carbonate, acetate, sulfate, nitrate etc. which contain each element can be used, for example. In addition, a composite compound containing Co and M ¹ is obtained by synthesizing in advance by a coprecipitation method or the like, or obtained by combining a compound containing Co and a compound containing M ¹ by firing or mechanochemical reaction. be able to.

  The firing conditions can be, for example, 800 to 1050 ° C. for 1 to 24 hours, but once heated to a temperature lower than the firing temperature (for example, 250 to 850 ° C.) and kept at that temperature, the preliminary firing condition is maintained. It is preferable to heat and then raise the temperature to the firing temperature to advance the reaction. Although there is no restriction | limiting in particular about the time of preheating, Usually, what is necessary is just to be about 0.5 to 30 hours. The atmosphere during firing may be an atmosphere containing oxygen (that is, in the air), a mixed atmosphere of an inert gas (argon, helium, nitrogen, etc.) and oxygen gas, an oxygen gas atmosphere, etc. The oxygen concentration (volume basis) is preferably 15% or more, and more preferably 18% or more.

  At the above firing temperature, the crystal phase of the spinel structure usually changes to a layered crystal structure, and a layered single phase lithium-cobalt-containing composite oxide is obtained. However, in the present invention, the composition range is limited. By properly arranging each element, a minute spinel phase can be stably present locally in the layered crystal structure of the lithium-cobalt-containing composite oxide, thereby enabling high voltage It is presumed that the layered crystal structure of the lithium-cobalt-containing composite oxide can exist stably even below.

  However, the method for producing the lithium-cobalt-containing composite oxide of the present invention is not limited to the above production method, and may be produced by other production methods.

  The composition analysis of the lithium-cobalt-containing composite oxide can be performed as follows using an ICP (Inductive Coupled Plasma) method. First, 0.2 g of a lithium-cobalt-containing composite oxide to be measured is collected and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the mixture was further diluted 25 times with pure water and an ICP analyzer “ICP-757” manufactured by JARRELASH was used. The composition is analyzed by a calibration curve method. The composition formula can be derived from the obtained results.

  The layered crystal structure and c-axis lattice constant of the lithium / cobalt-containing composite oxide can be confirmed by X-ray diffraction measurement. Furthermore, the confirmation of Mg of Li site and Mn of Co site in the crystal lattice in the crystal structure of the lithium-cobalt-containing composite oxide, and confirmation of the local spinel structure phase are performed by scanning with a spherical aberration correction device. By obtaining a high-angle scattering annular dark-field scanning transmission microscope (HAADF-STEM) image using a transmission electron microscope (Cs-STEM), it can be performed by directly observing the arrangement of atoms in the crystal lattice.

  Specifically, HAADF-STEM is a technique for displaying the intensity of electrons inelastically scattered at a high angle by thermal diffuse scattering due to lattice vibration as an image, and the intensity of the image is proportional to the square of the atomic number. Therefore, contrast reflecting the difference in atoms can be obtained, and information on the local structure and element type in the scanned image can be obtained.

That is, lithium cobaltate (LiCoO ₂ having a layered structure of α-NaFeO ₂ type of space group R3-m (where “-” represents the superscript of 3 and means “R3 bar m”). ), The Li constituting the Li site has a small atomic number, so the contrast is weak in the HAADF-STEM image and difficult to confirm. However, when the Li site is substituted with Mg having a larger atomic number, the contrast is higher than that of Li. Therefore, an image indicating the presence of Mg at the Li site is observed. On the other hand, since the atomic number of Mg is smaller than the atomic number of Co, the contrast is weaker than the image of Co constituting the Co site, and the element species constituting the Li site can be specified. In addition, when the Co site is substituted with an element such as Mn or Ni, it is difficult to confirm that Mn or Ni is located at the Co site because the atomic numbers of these elements are close. If an element such as Ni is not recognized, it can be estimated that the substitution element is located at the Co site.

  FIG. 1 shows a schematic diagram of a HAADF-STEM image of lithium cobaltate in which a part of the Li site is substituted with Mg. In FIG. 1, the image of Li atoms present at the Li site is not clearly distinguished from the background because of its weak contrast. On the other hand, the image of Mg atoms present at the Li site has a contrast that is almost intermediate between the Li atoms and the Co atoms, and it can be confirmed that Mg atoms are present at the Li site.

  The proportion of the spinel structure phase in the lithium-cobalt-containing composite oxide is preferably such that a diffraction peak derived from the spinel structure does not appear clearly by X-ray diffraction measurement. This is because the lithium-cobalt-containing composite oxide of the present invention basically has a layered structure, and it is desirable that the formed spinel structure phase be as small as possible.

(Embodiment 2)
Next, the electrode for nonaqueous secondary batteries of the present invention will be described. The electrode for a non-aqueous secondary battery of the present invention is characterized by including the lithium-cobalt-containing composite oxide of the present invention described in Embodiment 1 as an active material. The electrode for a non-aqueous secondary battery of the present invention includes a lithium-cobalt-containing composite oxide of the present invention as an active material, and thus has a high capacity and excellent charge / discharge cycle characteristics even under a high voltage.

  The electrode for a non-aqueous secondary battery of the present invention is usually used as a positive electrode of a non-aqueous secondary battery. For example, a positive electrode mixture containing the lithium-cobalt-containing composite oxide of the present invention, a binder, a conductive additive and the like. A structure having a layer on one side or both sides of a current collector can be used.

  As a conductive support agent used for the said positive mix layer, what is chemically stable should just be in a battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; aluminum Metal powder such as powder; Carbon dioxide; Zinc oxide; Conductive whisker made of potassium titanate and the like; Conductive metal oxide such as titanium oxide; Organic conductive material such as polyphenylene derivative; One species may be used alone, or two or more species may be used in combination. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable.

  As the binder used for the positive electrode mixture layer, any of a thermoplastic resin and a thermosetting resin can be used as long as it is chemically stable in the battery. For example, polyvinylidene fluoride (PVDF), polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), styrene-butadiene rubber (SBR), tetrafluoroethylene-hexafluoroethylene Copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), and the like can be used.

  As the current collector used for the positive electrode, the same one as used for the positive electrode of a conventionally known non-aqueous secondary battery can be used. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

  The positive electrode contains, for example, a positive electrode mixture in which the lithium / cobalt-containing composite oxide (positive electrode active material) of the present invention, a binder, and a conductive additive are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP). A paste or slurry can be prepared, applied to one or both sides of a current collector, dried, and then subjected to a calendaring process as necessary. The manufacturing method of a positive electrode is not necessarily restricted to the said method, It can also manufacture with another manufacturing method.

  As the composition of the positive electrode mixture layer, for example, the amount of the positive electrode active material is preferably 65 to 98% by mass, the amount of the binder is preferably 1 to 15% by mass, and the amount of the conductive auxiliary agent is It is preferable that it is 1-20 mass%.

(Embodiment 3)
Next, the nonaqueous secondary battery of the present invention will be described. The non-aqueous secondary battery of the present invention is characterized by comprising the non-aqueous secondary battery electrode of the present invention described in Embodiment 2 as a positive electrode, and further comprising a negative electrode, a non-aqueous electrolyte and a separator. Yes. Since the nonaqueous secondary battery of the present invention includes the electrode for nonaqueous secondary battery of the present invention, it has a high capacity and excellent charge / discharge cycle characteristics even under a high voltage.

  Hereinafter, components other than the positive electrode of the nonaqueous secondary battery of the present invention will be described.

[Negative electrode]
For the negative electrode, for example, a negative electrode active material, a binder, and a negative electrode mixture layer containing a conductive auxiliary agent as necessary are provided on one or both sides of the current collector, and the negative electrode active material is used alone. Thus, a negative electrode or a negative electrode active material that is laminated as a negative electrode layer on a current collector can be used.

The negative electrode active material is not particularly limited as long as it is a negative electrode active material used in conventionally known non-aqueous secondary batteries, that is, a material capable of occluding and releasing lithium ions. For example, carbon-based materials that can occlude and release lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers. One kind or a mixture of two or more kinds is used as the negative electrode active material. In addition, elements such as silicon (Si), tin (Sn), germanium (Ge), bismuth (Bi), antimony (Sb), indium (In) and alloys thereof, lithium such as lithium-containing nitride or lithium-containing oxide A compound that can be charged and discharged at a low voltage close to that of a metal, or a lithium metal or lithium / aluminum alloy can also be used as the negative electrode active material. Among them, the negative electrode active material is preferably a material represented by SiO _x containing silicon and oxygen as constituent elements, or a composite of SiO _x and a carbon material (SiO _x -C composite). These SiO _x -based materials have a high capacity, and a high-capacity battery can be provided by combining the SiO _x -based material with the same high-capacity lithium-cobalt-containing composite oxide of the present invention. Furthermore, the combined use of the SiO _x -C composite and a graphitic carbon material excellent in load characteristics and charge / discharge cycle characteristics is more preferable.

The SiO _x may contain a microcrystalline or amorphous phase of Si. In this case, the atomic ratio of Si and O is a ratio including Si microcrystalline or amorphous phase Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and this amorphous SiO ₂ is dispersed in the SiO ₂ matrix. It is only necessary that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5. For example, in the case of a structure in which Si is dispersed in an amorphous SiO ₂ matrix and the molar ratio of SiO ₂ to Si is 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

  Examples of the binder used in the negative electrode mixture layer include polysaccharides such as starch, polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, regenerated cellulose, and diacetyl cellulose, and modified products thereof; polyvinyl chloride. , Polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyamide and other thermoplastic resins and their modified products; polyimide; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene -Polymers having rubber-like elasticity such as butadiene rubber (SBR), butadiene rubber, polybutadiene, fluoro rubber, polyethylene oxide, and their modified products; May be used alone or two or more al.

  A conductive material may be further added to the negative electrode mixture layer as a conductive aid. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black (trade name), acetylene black, etc. Etc.), carbon fiber, metal powder (powder made of copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivative and the like can be used alone or in combination. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

  As the current collector used for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used. Usually, a copper foil is used. In the negative electrode current collector, when the thickness of the whole negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit of the thickness is 5 μm in order to ensure mechanical strength. It is desirable to be.

  The negative electrode is, for example, a negative electrode mixture-containing paste in which the above-described negative electrode active material and binder, and further, if necessary, a conductive additive dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water, A slurry is prepared, applied to one or both sides of a current collector, dried, and then subjected to a calendaring process as necessary. The manufacturing method of a negative electrode is not necessarily restricted to the said manufacturing method, It can also manufacture with another manufacturing method.

  In the negative electrode mixture layer, it is preferable that the amount of the negative electrode active material is 80 to 99% by mass and the amount of the binder is 1 to 20% by mass. In addition, when a conductive material is separately used as a conductive auxiliary agent, these conductive materials in the negative electrode mixture layer should be used in such a range that the amount of the negative electrode active material and the amount of the binder satisfy the above preferable values. Is preferred. The thickness of the negative electrode mixture layer can be, for example, 10 to 100 μm.

[Non-aqueous electrolyte]
As the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an organic solvent can be used.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form lithium ions and does not easily cause a side reaction such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (SO ₂ F) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 7), LiN (RfOSO ₂ ) ₂ [where Rf is fluoroalkyl Organolithium salts such as the group] and the like can be used.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane, Chain ethers such as diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; ethylene Sulfites such as glycol sulfite; and the like. These may be used in combination of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

[Separator]
The separator preferably has a property of blocking its pores (that is, a shutdown function) at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower). A separator used in a normal non-aqueous secondary battery or the like, for example, a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP) can be used. The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be. Furthermore, a separator using a heat-resistant resin such as polyamideimide or polyimide, or a separator provided with heat resistance by forming a porous layer using inorganic particles on the surface of the microporous film may be used.

[Battery configuration]
Examples of the form of the nonaqueous secondary battery of the present invention include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can, an aluminum can, or the like as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  The non-aqueous secondary battery of this invention can be used for the same use as the various uses to which the lithium secondary battery known conventionally is applied, for example.

[Battery voltage]
The non-aqueous secondary battery of the present invention can be used with the upper limit of the charging voltage of the positive electrode being 4.6 V or more on the basis of lithium metal, and the charging voltage of the battery comprising the positive electrode of the present invention and the conventional negative electrode Even if the upper limit is set to a high voltage of 4.5 V or more, the charge / discharge cycle characteristics can be maintained satisfactorily.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of lithium-cobalt-containing composite oxide>
Cobalt hydroxide [Co (OH) ₂ ] 2.960 g and manganese acetate tetrahydrate [(CH ₃ COO) ₂ Mn · 4H ₂ O] 0.150 g were pulverized and mixed, and then pressurized to pellets Was made. This pellet was put in an electric furnace and fired at 400 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a Co · Mn-containing oxide pellet.

Next, 1.293 g of lithium hydroxide monohydrate (LiOH.H ₂ O), 0.036 g of magnesium hydroxide [Mg (OH) ₂ ] and the above Co · Mn-containing oxide pellets were pulverized and mixed. And then pressurizing to produce pellets. This pellet was put in an electric furnace and fired at 950 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a lithium-cobalt-containing composite oxide of this example.

About the said lithium * cobalt containing complex oxide, the composition analysis was performed as follows using ICP method mentioned above. First, 0.2 g of the lithium / cobalt-containing composite oxide was sampled and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were added in order and dissolved by heating. After cooling, the mixture was further diluted 25 times with pure water and an ICP analyzer “ICP-757” manufactured by JARRELASH was used. The composition was analyzed by a calibration curve method. From the obtained results, the composition of the lithium-cobalt-containing composite oxide was derived and found to be a composition represented by Li _0.98 Mg _0.02 Co _0.98 Mn _0.02 O ₂ .

Next, when the X-ray diffraction measurement was performed on the lithium-cobalt-containing composite oxide, the lithium-cobalt-containing composite oxide had an α-NaFeO ₂ type layered structure of the space group R3-m. It was confirmed that it had. Further, the c-axis lattice constant determined from the position of the (003) plane diffraction peak was 1.4067 nm, and no diffraction peak derived from the spinel structure was confirmed.

  Subsequently, the HAADF-STEM image of the lithium / cobalt-containing composite oxide was observed using the Cs-STEM described above. The obtained image is shown in FIG. From FIG. 2, since a contrast portion having an intermediate intensity between the background contrast and the Co atom contrast of the Co site was confirmed at the Li site, the crystal of the crystal structure of the lithium-cobalt-containing composite oxide was observed. It was confirmed that Mg was present at the Li site in the lattice. On the other hand, since a portion having a stronger contrast than Mg atoms was not confirmed at the Li site, it was estimated that Mn, which is an element heavier than Mg, is present at the Co site. Further, it was confirmed by electron beam diffraction that a spinel phase was locally present in the crystal structure of the layered structure.

  In the lithium-cobalt-containing composite oxide, in the range observed by HAADF-STEM, it seems that Mn is arranged at the Li site and Mg is arranged at the Co site. Since the location was not clearly recognized, it is presumed that almost all added Mg was arranged at the Li site, and almost all added Mn was arranged at the Co site.

<Preparation of positive electrode>
62 parts by mass of the lithium-cobalt-containing composite oxide (positive electrode active material) prepared above, 3 parts by mass of PVDF as a binder, 34 parts by mass of N-methyl-2-pyrrolidone (NMP) as a solvent, and a conductive additive 2 parts by mass of acetylene black was mixed using a hybrid mixer to prepare a positive electrode mixture-containing paste.

Next, the positive electrode mixture-containing paste is applied to one surface of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and the coating amount of the positive electrode mixture layer formed after drying is 16 mg / cm ^2. Heat drying was performed, and then calendering was performed to produce a positive electrode. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

<Preparation of negative electrode and separator>
As the negative electrode, Li metal was used, and a lead was formed by welding a tab to the Li metal. As the separator, a polyethylene microporous membrane separator was prepared.

<Production of experimental battery>
The positive electrode and the negative electrode were stacked with the separator interposed therebetween to prepare an experimental half cell. Further, as a non-aqueous electrolyte, a solution was prepared by dissolving LiPF ₆ to a concentration of 1.0 mol / L in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 2. Next, the non-aqueous electrolyte solution was injected into the half cell to produce an experimental battery of this example.

(Example 2)
<Preparation of lithium-cobalt-containing composite oxide>
2.959 g of cobalt hydroxide [Co (OH) ₂ ], 0.009 g of nickel hydroxide [Ni (OH) ₂ ] and manganese acetate tetrahydrate [(CH ₃ COO) ₂ Mn · 4H ₂ O] 112 g was pulverized and mixed, and then pressed to produce pellets. This pellet was put in an electric furnace and fired at 400 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to prepare a Co · Ni · Mn-containing oxide pellet.

Next, 1.293 g of lithium hydroxide monohydrate (LiOH.H ₂ O), 0.036 g of magnesium hydroxide [Mg (OH) ₂ ] and the above Co.Ni.Mn-containing oxide pellets were pulverized. And then pressed to prepare pellets. This pellet was put in an electric furnace and fired at 950 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a lithium-cobalt-containing composite oxide of this example.

When the composition analysis of the lithium-cobalt-containing composite oxide was performed using the ICP method in the same manner as in Example 1, it was found that the composition was represented by Li _0.98 Mg _0.02 Co _0.98 Mn _0.015 Ni _0.005 O _2. did.

Next, X-ray diffraction measurement of the lithium-cobalt-containing composite oxide was performed in the same manner as in Example 1. As a result, the crystal structure of the lithium-cobalt-containing composite oxide was α-NaFeO in the space group R3-m. It was confirmed to have a _two- type layered structure. The c-axis lattice constant determined from the position of the (003) plane diffraction peak was 1.4062 nm, and no diffraction peak derived from the spinel structure was confirmed.

  In addition, the lithium-cobalt-containing composite oxide was confirmed to contain Mg at the Li site in the crystal lattice in the same manner as in Example 1, and further, locally in the crystal structure of the layered structure. It was confirmed that a spinel structure phase was present in For the same reason as in Example 1, in the lithium-cobalt-containing composite oxide, it is presumed that almost all added Mg is arranged at the Li site.

<Production of experimental battery>
An experimental battery was produced in the same manner as in Example 1 except that the lithium / cobalt-containing composite oxide was used.

(Comparative Example 1)
<Preparation of lithium-cobalt-containing composite oxide>
3.029 g of cobalt hydroxide [Co (OH) ₂ ] was pulverized and then pressurized to produce pellets. This pellet was put in an electric furnace and fired at 400 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to prepare a Co-containing oxide pellet.

Next, 1.322 g of lithium hydroxide monohydrate (LiOH.H ₂ O) and the above Co-containing oxide pellets were pulverized and mixed, and then pressurized to produce pellets. This pellet was put in an electric furnace and fired at 950 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a lithium / cobalt-containing composite oxide of this comparative example.

When the composition analysis of the lithium-cobalt-containing composite oxide was performed using the ICP method in the same manner as in Example 1, it was found that the composition was represented by LiCoO ₂ .

Next, when the X-ray diffraction measurement was performed on the lithium-cobalt-containing composite oxide, the lithium-cobalt-containing composite oxide had an α-NaFeO ₂ type layered structure of the space group R3-m. It was confirmed that it had. The c-axis lattice constant determined from the position of the diffraction peak on the (003) plane was 1.4044 nm. Moreover, the diffraction peak derived from a spinel structure was not confirmed. Considering the production conditions of the lithium-cobalt-containing composite oxide, it is considered that the lithium-cobalt-containing composite oxide has a single phase having a layered crystal structure.

<Production of experimental battery>
An experimental battery was produced in the same manner as in Example 1 except that the lithium / cobalt-containing composite oxide was used.

(Comparative Example 2)
<Preparation of lithium-cobalt-containing composite oxide>
2.978 g of cobalt hydroxide [Co (OH) ₂ ] was pulverized and then pressurized to produce pellets. This pellet was put in an electric furnace and fired at 400 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to prepare a Co-containing oxide pellet.

Next, 1.301 g of lithium hydroxide monohydrate (LiOH.H ₂ O), 0.072 g of magnesium hydroxide [Mg (OH) ₂ ] and the above Co-containing oxide pellets were pulverized and mixed, Thereafter, the mixture was pressurized to produce a pellet. This pellet was put in an electric furnace and fired at 950 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a lithium / cobalt-containing composite oxide of this comparative example.

The composition analysis of the lithium-cobalt-containing composite oxide was performed using the ICP method in the same manner as in Example 1. As a result, it was found that the composition was represented by Li _0.96 Mg _0.04 CoO ₂ .

Next, X-ray diffraction measurement of the lithium-cobalt-containing composite oxide was performed in the same manner as in Example 1. As a result, the crystal structure of the lithium-cobalt-containing composite oxide was α-NaFeO in the space group R3-m. It was confirmed to have a _two- type layered structure. Further, the c-axis lattice constant determined from the position of the diffraction peak on the (003) plane was 1.4068 nm.

  Further, the lithium-cobalt-containing composite oxide was confirmed to contain Mg at the Li site in the crystal lattice in the same manner as in Example 1, but the spinel structure was included in the crystal structure of the layered structure. The presence of a phase could not be confirmed.

<Production of experimental battery>
An experimental battery was produced in the same manner as in Example 1 except that the lithium / cobalt-containing composite oxide was used.

(Comparative Example 3)
<Preparation of lithium-cobalt-containing composite oxide>
3.029 g of cobalt hydroxide [Co (OH) ₂ ] was pulverized and then pressurized to produce pellets. This pellet was put in an electric furnace and fired at 400 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to prepare a Co-containing oxide pellet.

Next, 1.292 g of lithium hydroxide monohydrate (LiOH.H ₂ O), 0.036 g of magnesium hydroxide [Mg (OH) ₂ ] and the above Co-containing oxide pellets are pulverized and mixed, Thereafter, the mixture was pressurized to produce a pellet. This pellet was put in an electric furnace and fired at 950 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a lithium / cobalt-containing composite oxide of this comparative example.

The composition analysis of the lithium-cobalt-containing composite oxide was performed using the ICP method in the same manner as in Example 1. As a result, it was found that the composition was represented by Li _0.98 Mg _0.02 CoO ₂ .

Next, X-ray diffraction measurement of the lithium-cobalt-containing composite oxide was performed in the same manner as in Example 1. As a result, the crystal structure of the lithium-cobalt-containing composite oxide was α-NaFeO in the space group R3-m. It was confirmed to have a _two- type layered structure. The c-axis lattice constant determined from the position of the diffraction peak on the (003) plane was 1.4059 nm.

  Further, the lithium-cobalt-containing composite oxide was confirmed to contain Mg at the Li site in the crystal lattice in the same manner as in Example 1, but the spinel structure was included in the crystal structure of the layered structure. The presence of a phase could not be confirmed.

<Production of experimental battery>
An experimental battery was produced in the same manner as in Example 1 except that the lithium / cobalt-containing composite oxide was used.

(Comparative Example 4)
<Preparation of lithium-cobalt-containing composite oxide>
2.989 g of cobalt hydroxide [Co (OH) ₂ ] was pulverized and then pressurized to produce pellets. This pellet was put in an electric furnace and fired at 400 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to prepare a Co-containing oxide pellet.

Next, 1.332 g of lithium hydroxide monohydrate (LiOH.H ₂ O), 0.036 g of magnesium hydroxide [Mg (OH) ₂ ] and the above Co-containing oxide pellets were pulverized and mixed, Thereafter, the mixture was pressurized to produce a pellet. This pellet was put in an electric furnace and fired at 950 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a lithium / cobalt-containing composite oxide of this comparative example.

When the composition analysis of the lithium-cobalt-containing composite oxide was performed using the ICP method in the same manner as in Example 1, it was found that the composition was represented by Li _1.00 Co _0.98 Mg _0.02 O ₂ .

Next, X-ray diffraction measurement of the lithium-cobalt-containing composite oxide was performed in the same manner as in Example 1. As a result, the crystal structure of the lithium-cobalt-containing composite oxide was α-NaFeO in the space group R3-m. It was confirmed to have a _two- type layered structure. The c-axis lattice constant obtained from the position of the (003) plane diffraction peak was 1.4050 nm, and no diffraction peak derived from the spinel structure was confirmed.

<Production of experimental battery>
An experimental battery was produced in the same manner as in Example 1 except that the lithium / cobalt-containing composite oxide was used.

(Comparative Example 5)
<Preparation of lithium-cobalt-containing composite oxide>
Cobalt hydroxide [Co (OH) ₂ ] 2.962 g and chromium hydroxide hydrate [Cr (OH) ₃ · 1.68H ₂ O] 0.081 g are pulverized and mixed, and then pressed to form pellets. Produced. This pellet was put in an electric furnace and fired at 400 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to prepare a Co · Cr-containing oxide pellet.

Next, 1.294 g of lithium hydroxide monohydrate (LiOH.H ₂ O), 0.036 g of magnesium hydroxide [Mg (OH) ₂ ] and the above Co · Cr-containing oxide pellets were pulverized and mixed. And then pressurizing to produce pellets. This pellet was put in an electric furnace and fired at 950 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a lithium / cobalt-containing composite oxide of this comparative example.

The composition analysis of the lithium-cobalt-containing composite oxide was performed using the ICP method in the same manner as in Example 1. As a result, it was found that the composition was represented by Li _0.98 Mg _0.02 Co _0.98 Cr _0.02 O ₂ .

Next, X-ray diffraction measurement of the lithium-cobalt-containing composite oxide was performed in the same manner as in Example 1. As a result, the crystal structure of the lithium-cobalt-containing composite oxide was α-NaFeO in the space group R3-m. It was confirmed to have a _two- type layered structure. Further, the c-axis lattice constant determined from the position of the (003) plane diffraction peak was 1.4057 nm, and no diffraction peak derived from the spinel structure was confirmed.

<Production of experimental battery>
An experimental battery was produced in the same manner as in Example 1 except that the lithium / cobalt-containing composite oxide was used.

(Comparative Example 6)
<Preparation of lithium-cobalt-containing composite oxide>
Cobalt hydroxide [Co (OH) ₂ ] 2.959 g and iron carbonate dihydrate (FeC ₂ O ₄ .2H ₂ O) 0.110 g are pulverized and mixed, and then pressed to produce pellets. did. This pellet was put in an electric furnace and fired at 400 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to prepare a Co · Fe-containing oxide pellet.

Next, 1.293 g of lithium hydroxide monohydrate (LiOH.H ₂ O), 0.036 g of magnesium hydroxide [Mg (OH) ₂ ] and the above Co · Fe-containing oxide pellets were pulverized and mixed. And then pressurizing to produce pellets. This pellet was put in an electric furnace and fired at 950 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a lithium / cobalt-containing composite oxide of this comparative example.

When the composition analysis of the lithium-cobalt-containing composite oxide was performed using the ICP method in the same manner as in Example 1, it was found that the composition was represented by Li _0.98 Mg _0.02 Co _0.98 Fe _0.02 O ₂ .

Next, X-ray diffraction measurement of the lithium-cobalt-containing composite oxide was performed in the same manner as in Example 1. As a result, the crystal structure of the lithium-cobalt-containing composite oxide was α-NaFeO in the space group R3-m. It was confirmed to have a _two- type layered structure. Further, the c-axis lattice constant determined from the position of the (003) plane diffraction peak was 1.4067 nm, and no diffraction peak derived from the spinel structure was confirmed.

<Production of experimental battery>
An experimental battery was produced in the same manner as in Example 1 except that the lithium / cobalt-containing composite oxide was used.

(Comparative Example 7)
<Preparation of lithium-cobalt-containing composite oxide>
Cobalt hydroxide [Co (OH) ₂ ] 2.958 g and nickel hydroxide [Ni (OH) ₂ ] 0.057 g were pulverized and mixed, and then pressurized to produce pellets. This pellet was put in an electric furnace and fired at 400 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to prepare a Co · Ni-containing oxide pellet.

Next, 1.292 g of lithium hydroxide monohydrate (LiOH.H ₂ O), 0.036 g of magnesium hydroxide [Mg (OH) ₂ ] and the above Co · Ni-containing oxide pellets were pulverized and mixed. And then pressurizing to produce pellets. This pellet was put in an electric furnace and fired at 950 ° C. for 5 hours in an air flow of 4 L / min in an air atmosphere to produce a lithium / cobalt-containing composite oxide of this comparative example.

When the composition analysis of the lithium-cobalt-containing composite oxide was performed using the ICP method in the same manner as in Example 1, it was found that the composition was represented by Li _0.98 Mg _0.02 Co _0.98 Ni _0.02 O ₂ .

Next, X-ray diffraction measurement of the lithium-cobalt-containing composite oxide was performed in the same manner as in Example 1. As a result, the crystal structure of the lithium-cobalt-containing composite oxide was α-NaFeO in the space group R3-m. It was confirmed to have a _two- type layered structure. The c-axis lattice constant determined from the position of the (003) plane diffraction peak was 1.4059 nm, and no diffraction peak derived from the spinel structure was confirmed.

<Production of experimental battery>
An experimental battery was produced in the same manner as in Example 1 except that the lithium / cobalt-containing composite oxide was used.

  About the battery for experiment produced in Examples 1-2 and Comparative Examples 1-7, the first time discharge capacity and the charge / discharge cycle characteristic (capacity maintenance factor) were measured with the following method.

<First discharge capacity>
Each battery is charged at normal temperature (25 ° C.) at a constant current of 0.1 C until it reaches 4.6 V (that is, charged until the potential of the positive electrode reaches 4.6 V based on lithium metal), and then 4.6 V. After performing constant current-constant voltage charging until the current value reaches 0.01 C, the battery is discharged to 2.5 V with a constant current of 0.1 C, and the resulting discharge capacity (mAh) is The initial discharge capacity per unit mass (mAh / g) was obtained by dividing by the mass of the positive electrode active material used.

  Further, for the battery of Comparative Example 1, the initial discharge capacity at a normal charging voltage was also measured as follows. A constant current-constant voltage in which the battery of Comparative Example 1 that was not charged / discharged was charged at room temperature (25 ° C.) at a constant current of 0.1 C until reaching 4.45 V, and then charged at a constant voltage of 4.45 V. After charging until the current value reaches 0.01 C, discharge to 2.5 V with a constant current of 0.1 C, and the resulting discharge capacity (mAh) is divided by the mass of the positive electrode active material. The initial discharge capacity per mass (mAh / g) was obtained.

<Charge / discharge cycle characteristics>
Each battery after the initial charge / discharge is repeated 10 cycles under the same conditions as the above initial charge / discharge, and the value obtained by dividing the discharge capacity obtained at the 10th cycle by the discharge capacity obtained at the 1st cycle is expressed as a percentage. Expressed as the capacity retention rate (%).

  The results are shown in Table 1. In Table 1, the composition formula of the positive electrode active material used is also shown.

  From Table 1, it can be seen that the batteries of Examples 1 and 2 using the lithium-cobalt-containing composite oxide of the present invention have a high capacity and a high capacity retention rate under a high voltage. In particular, it can be seen that the capacity retention rate of the battery of Example 2 using Mn and Ni as additive elements replacing Co is very high.

On the other hand, in the battery of Comparative Example 1 using the lithium-cobalt-containing composite oxide containing no additive element, a high capacity retention rate can be secured at a charging voltage of 4.45V, but the charging voltage is reduced to 4.6V. Then, it can be seen that the capacity retention rate decreases. Moreover, in the composition of LiCoO ₂ , the capacity retention rate of the batteries of Comparative Example 2 and Comparative Example 3 in which only a part of Li was replaced with Mg was lower than that of the batteries of Example 1 and Example 2. It can be seen that in the battery of Comparative Example 2 in which the amount of substitution of Mg is large, the initial discharge capacity is also reduced. Furthermore, in the composition of LiCoO ₂ , it can be seen that the battery of Comparative Example 4 in which only a part of Co is replaced with Mg has low initial discharge capacity and capacity retention rate.

  In the batteries of Comparative Examples 5 to 7 in which a part of Li is replaced with Mg and a part of Co is replaced with an element other than Mn (Cr, Fe and Ni), the lithium / cobalt-containing composite oxide of the present invention is used. It can be seen that the effect of improving the capacity retention rate under a high voltage is lower than the battery using the battery.

  In addition, X-ray absorption fine structure measurement using synchrotron radiation is performed on lithium-cobalt-containing composite oxide, and EXAFS analysis is performed, so that local structure information such as atomic coordination number and bond distance can be obtained. Thus, based on this, the Co—O bond distance showing the maximum frequency in the lithium-cobalt-containing composite oxide was calculated as follows.

  First, the batteries of Example 1 and Comparative Example 1 were discharged to 2.5 V at a constant current of 0.05 C after the batteries were assembled (that is, discharged until the positive electrode potential was 2.5 V on the basis of lithium metal). Then, the positive electrode was taken out after discharge, and the X-ray absorption fine structure measurement was performed to determine the Co—O bond distance in the state before charging of the lithium-cobalt-containing composite oxide.

  Next, for the other batteries of Example 1 and Comparative Example 1, after the battery was assembled, it was charged at a constant current of 0.05 C until it reached 4.6 V (that is, the positive electrode potential was 4.6 V on the lithium metal basis). Until the current value reaches 0.005C, and after the charging, the positive electrode is taken out and X-ray absorption fine structure measurement is performed. Thus, the bond distance between Co—O in the state after the lithium-cobalt-containing composite oxide was charged was determined.

  Table 2 shows the calculated amount of change in Co—O bond distance before and after the charge [(bond distance after charge) − (bond distance before charge)].

  From the change in the Co-O bond distance before and after charging, the change in Co and O bond energy can be estimated. The decrease in the Co-O bond distance after charging is thought to mean an increase in the Co and O bond energy, and it is estimated that the crystal structure is stabilized and deoxygenation from lithium cobalt oxide by charging is suppressed. Is done.

Therefore, in the lithium-cobalt-containing composite oxide of Example 1 in which a decrease in the Co-O bond distance was observed after charging, a part of the Li site was replaced with Mg and a part of the Co site was replaced with Mn. Thus, it is considered that the α-NaFeO ₂ type layered structure of the space group R3-m is more stabilized than the LiCoO _{2 of} Comparative Example 1 and the charge / discharge cycle characteristics are improved.

Claims (12)

A lithium-cobalt-containing composite oxide having a layered crystal structure and represented by the following general composition formula (1):
(Li _1-x Mg _x ) _{1 + m} (Co _1-y M ¹ _y ) _{1 + n} M ² _z O ₂ (1)
However, the general composition formula (1), M ¹ represents a single element or group of elements containing at least Mn, M ² is Na, Sr, at least one selected from the group consisting of Ba and F represents a single element or element group including elemental, 0.015 ≦ x ≦ 0.08, 0.015 ≦ y ≦ 0.08,0 ≦ z ≦ 0.05, - 0.02 ≦ m ≦ 0.02 And -0.02 ≦ n ≦ 0.02 .   The lithium / cobalt-containing composite oxide according to claim 1, wherein Mg is contained in Li sites in the crystal lattice of the crystal structure.   3. The lithium-cobalt-containing composite oxide according to claim 1, wherein Mn is contained in a Co site in the crystal lattice of the crystal structure.   4. The lithium-cobalt-containing composite oxide according to claim 2, wherein the crystal structure has a local spinel phase.   The lithium-cobalt-containing composite oxide according to any one of claims 1 to 4, wherein, in the general composition formula (1), a difference between x and y is 0.02 or less. In the general composition formula (1), M ¹ further contains at least one element selected from the group consisting of Cr, Fe, Ni, Zr, Ti, Mo, V, Al, B, and Ge. The lithium-cobalt-containing composite oxide according to any one of 1 to 5. The lithium / cobalt-containing composite oxide according to claim 6, wherein M ¹ in the general composition formula (1) contains Ni.   The lithium-cobalt-containing composite oxide according to claim 1, wherein x ≦ 0.035 in the general composition formula (1).   The lithium-cobalt-containing composite oxide according to claim 1, wherein a c-axis lattice constant in the crystal structure is 1.405 to 1.408 nm. A method for producing a lithium-cobalt-containing composite oxide according to any one of claims 1 to 9,
Firing a composite compound containing cobalt and M ¹ , a compound containing lithium, and a compound containing magnesium,
In the step,
M ¹ represents a single element or element group containing at least Mn,
The number of moles of magnesium contained in the compound containing magnesium is substantially equal to the number of moles of M ¹ contained in the composite compound containing cobalt and M ¹ , and the mole of lithium contained in the compound containing lithium. And the number of moles of cobalt contained in the composite compound containing cobalt and M ¹ is substantially equal.   An electrode for a non-aqueous secondary battery comprising the lithium-cobalt-containing composite oxide according to claim 1 as an active material.   A nonaqueous secondary battery comprising the electrode for a nonaqueous secondary battery according to claim 11 as a positive electrode.