JP4608946B2 - Lithium composite oxide material and use thereof - Google Patents

Description

  The present invention relates to a lithium composite oxide material and a method for producing the same. The present invention also relates to a lithium ion secondary battery constructed using such a material.

A material mainly composed of an oxide having lithium and one or more transition metals as constituent metal elements (lithium composite oxide material) is useful as a positive electrode active material of a lithium battery. An example of such a material is one in which the oxide is a composite oxide of lithium, nickel, cobalt, and aluminum. Patent document 1 is mentioned as an example of the prior art document regarding such a positive electrode active material.
JP 2003-331841 A

Such a lithium composite oxide material can be manufactured (synthesized) by the following method, for example. That is, depending on the composition of the target lithium composite oxide, a raw material mixture containing a metal compound corresponding to the metal component constituting the oxide in a predetermined molar ratio is prepared. And it is the method of baking the mixture at high temperature (typically 750 degreeC or more).
By the way, the lithium composite oxide material is often prepared in a particulate form because it is easily used for various applications (for example, a positive electrode active material of a battery). When the material is used as a positive electrode active material or the like of a secondary battery, the structure of the surface portion of such particles (for example, the degree of crystallinity) can greatly affect the performance of the battery. However, the lithium composite oxide material obtained through high-temperature firing as described above tends to have low crystallinity on the surface portion of the particles.

  Therefore, an object of the present invention is to provide a lithium composite oxide material having good crystallinity on the surface portion of particles. Another object of the present invention is to provide a method for producing such materials. Yet another object is to provide a lithium ion secondary battery constructed using such materials. Another related object is to provide a method for easily and appropriately grasping the structure (degree of crystallinity, etc.) of particles mainly composed of lithium composite oxide. Moreover, it is providing the method of improving the crystallinity of the surface part of such particle | grains.

  The present inventor relates to a material mainly composed of a composite oxide having lithium, nickel, cobalt and aluminum as constituent metal elements, and three specific regions (range of Raman shift) in Raman spectrum measurement of particles constituting the material. It has been found that the degree of crystallinity can be properly grasped by paying attention to. And it discovered that the lithium composite oxide material (primary calcination material) baked at high temperature had low crystallinity of the surface part compared with the inside of the particle | grains which comprise this material. Furthermore, the method of improving the crystallinity of the surface part was discovered.

According to the present invention, there is provided a lithium composite oxide material mainly comprising a composite oxide having lithium, nickel, cobalt, and aluminum as constituent metal elements. The particles constituting the material are the first Raman whose Raman spectrum of the surface portion of the particles appears in the region of 560 ± 5 cm ⁻¹ in the Raman spectrum measurement by visible light excitation (for example, excitation light having a wavelength of 514.5 nm). A band, a second Raman band appearing in a region of 545 ± 5 cm ⁻¹ , and a third Raman band appearing in a region of 465 ± 5 cm ⁻¹ . Here, the expression of the Raman band in the region means that at least the peak position (Raman shift) of the Raman band belongs to the range of the region.
The first, second and third Raman bands are related to the crystallinity of the composite oxide. Therefore, the fact that these Raman bands are observed in the Raman spectrum of the surface portion of the particle indicates that the disorder of the crystal structure in the surface portion is small (that is, the crystallinity is high). A lithium composite oxide material containing such particles as a constituent element can be useful as an electrode active material or the like.

In one preferred embodiment of the material disclosed herein, the first Raman band appearing in a region of 560 ± 5 cm ⁻¹ in a Raman spectrum measurement by visible light excitation, and 545 ± 5 cm ^{− A} second Raman band appearing in a region of ¹ and a third Raman band appearing in a region of 465 ± 5 cm ⁻¹ . That is, the first and second Raman bands appearing in the region of 560 ± 5 cm ⁻¹ , the second Raman band appearing in the region of 545 ± 5 cm ⁻¹ , and 465 ± And a third Raman band appearing in a region of 5 cm ⁻¹ . Typically, each of the first, second, and third Raman bands appearing in each of the above-described regions appears at substantially the same position (wave number) in the surface portion and the internal Raman spectrum.
Particles exhibiting such a Raman spectrum have good crystallinity both on the surface and inside of the particles. Therefore, the homogeneity between the crystal structure inside the particle and the crystal structure of the surface portion is good. A lithium composite oxide material containing such particles as a constituent element can be useful as an electrode active material or the like.

  In a preferred embodiment, the intensity of the Raman band in the Raman spectrum of the surface portion is 30 to about the intensity of at least one of the first, second and third Raman bands in the internal Raman spectrum. It is in the range of 110% (more preferably 50 to 100%). Such particles have particularly good homogeneity between the crystal structure inside the particles and the crystal structure of the surface portion.

In the lithium composite oxide material provided by the present invention, the average particle diameter of the particles constituting the material is preferably in the range of about 3 to 100 μm. A lithium composite oxide material having an average particle size in the above range is suitable for applications such as battery electrode active materials (for example, positive electrode active materials of lithium ion secondary batteries).
In addition, the particle | grains which comprise the lithium composite oxide material disclosed here WHEREIN: In one preferable form of this material, primary particles (particles of the minimum unit) aggregate (aggregate) to form secondary particles. In such a case, unless otherwise specified, the secondary particles are referred to as “particles constituting a lithium composite oxide material”. Further, for lithium composite oxide materials in a form mainly composed of independent (non-aggregated) primary particles, the primary particles are referred to as “particles constituting the lithium composite oxide material”.

The present invention also provides a method for producing a lithium composite oxide material mainly comprising a composite oxide having lithium, nickel, cobalt and aluminum as constituent metal elements. The method includes a step of preparing a primary fired product mainly composed of a composite oxide having lithium, nickel, cobalt and aluminum as constituent metal elements. Further, the method includes a step of bringing the fired product into contact with a lithium solution. In the step of contacting with the lithium solution, the Raman spectrum of the surface portion of the particles constituting the primary fired product is a first Raman band appearing in the region of 560 ± 5 cm ⁻¹ in the Raman spectrum measurement by visible light excitation, and 545 ±. The second Raman band appearing in the region of 5 cm ⁻¹ and the third Raman band appearing in the region of 465 ± 5 cm ⁻¹ are performed.
According to this manufacturing method, the crystallinity of the surface portion of the particles constituting the fired product can be improved by bringing the primary fired product into contact with the lithium solution. Thereby, it can be set as the particle | grains provided with the surface part which shows the Raman spectrum which has a 1st, 2nd, and 3rd Raman band in the area | region mentioned above, respectively. Therefore, the material manufactured by such a method can have good crystallinity of the surface portion of the particles constituting the material. This manufacturing method is suitable as a method for manufacturing any of the lithium composite oxide materials described above.

As the primary fired product, for example, a product obtained by firing a raw material mixture containing lithium ions, nickel ions, cobalt ions and aluminum ions can be used. The firing temperature of the raw material mixture is usually suitably in the temperature range exceeding about 700 ° C., preferably in the temperature range of about 720 ° C. or higher, and preferably in the temperature range of about 740 ° C. or higher. Further preferred.
In one preferred embodiment of the invention disclosed herein, the raw material mixture includes a hydroxide formed by adding an alkali to a solution containing lithium ions, nickel ions, cobalt ions, and aluminum ions as a main component. Raw material hydroxide. The lithium-containing composite oxide material obtained from such a raw material hydroxide can be useful as an electrode active material. For example, a battery with better battery performance can be constructed by using such a lithium-containing composite oxide material as a positive electrode active material.
As a solution for obtaining the raw material hydroxide, a solution (typically an aqueous solution) containing lithium nitrate, nickel nitrate, cobalt nitrate and aluminum nitrate can be suitably used. In addition, it is particularly preferable to use NH ₄ OH as the alkali added to the solution. The lithium-containing composite oxide material obtained using the raw material hydroxide (raw material mixture) thus obtained can be particularly useful as an electrode active material or the like.

  The manufacturing method disclosed herein can further include a step of heating the primary fired product to a temperature range lower than the firing temperature of the primary fired product after contacting the lithium solution. Thereby, at least one of the stability, sustainability, and certainty of the effect (typically the effect of improving the crystallinity) caused by contacting the lithium solution can be further increased. Moreover, by performing the said heating process at the temperature lower than the calcination temperature range of a primary baked material, it is suppressed that the crystallinity of a particle | grain surface part falls in this heating process.

  According to the present invention, there is further provided a battery including any one of the above-described materials or a material manufactured by any of the above-described methods as a component. A typical example of such a battery is a lithium battery (typically a lithium ion secondary battery) including such a material as an electrode active material (typically a positive electrode active material). Any of the lithium-containing composite oxide materials disclosed herein has good crystallinity at the surface of the particle, and therefore, lithium ions can be easily inserted and / or desorbed from the particle surface. Therefore, batteries constructed using such materials can exhibit good battery performance (eg, low temperature output).

  Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that technical matters other than the contents particularly mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the technical contents disclosed in the present specification and the common general technical knowledge in the field.

The lithium composite oxide material provided by the present invention is mainly composed of a composite oxide having lithium (Li), nickel (Ni), cobalt (Co), and aluminum (Al) as constituent metal elements. A preferred example of such a composite oxide is a composite oxide having a structure in which Co and Al are substituted (solid solution) in a part of Ni sites in lithium nickelate (LiNiO ₂ ) (hereinafter, such composite oxide is referred to as a composite oxide). (It may be expressed as “LiNi (Co, Al) O ₂ ”). Such a complex oxide typically has a layered rock salt type crystal structure. Suitable composite oxide as the main component of the complex oxide material according to the present invention, for example, an oxide represented by the composition formula _{LiNi x Co y Al z O 2} . Here, x is a number satisfying 0 <x <1, preferably in the range of 0.1 <x <0.9, and more preferably in the range of 0.6 <x <0.9. . Further, y is a number satisfying 0 <y <1, and preferably in a range of 0.1 <y <0.9. z is a number satisfying 0 <z <1, and preferably in the range of 0.01 <z <0.2. There is a relationship of x + y + z = 1 between these x, y and z.

  The lithium-containing composite oxide may contain other constituent metal elements in addition to Li, Ni, Co, and Al. For example, manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), tungsten (W ), Copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), and cerium (Ce). It may contain metal elements. The content (molar ratio) of these metal elements is preferably in a range smaller than the content of any metal element of Li, Ni, Co, and Al. For example, it is preferably in the range of 0.1 mol or less (more preferably 0.05 mol or less) with respect to 1 mol of lithium.

  The lithium-containing composite oxide material disclosed herein (hereinafter sometimes simply referred to as “composite oxide material”) is provided as having a particulate (powder) form as a preferred embodiment. The Although not particularly limited, it is usually preferable that the average particle diameter of the particles (typically secondary particles) is in the range of about 3 to 100 μm. A more preferable range is about 3 to 50 μm, and a further preferable range is about 5 to 30 μm. The shape of the particles constituting the composite oxide material is typically almost spherical. In a preferred embodiment of the material disclosed herein, the main component of the material is secondary particles formed by agglomerating primary particles mainly composed of the composite oxide. The average particle diameter of the primary particles (smallest unit particles) constituting the secondary particles may be, for example, about 0.1 to 2 μm (preferably 0.2 to 1 μm).

The “surface portion” (surface layer portion) of the particles constituting the composite oxide material refers to the surface of the particles (typically secondary particles) and the vicinity thereof. For example, a portion from the surface of the particle to a depth of about 30% or less (preferably about 20% or less) with respect to the radius of the particle can be a “surface portion”. For example, for particles having an average particle diameter (diameter) of about 5 μm or more, a portion from the particle surface to a depth of about 2 μm (preferably up to about 1 μm) can be defined as a “surface portion”.
On the other hand, the “inside” of the particle refers to a portion inside the surface portion. For example, a portion where the distance from the center of the particle is smaller than about 70% (preferably about 50%) of the radius of the particle can be defined as “inside”. For example, for particles having an average particle diameter of about 5 μm or more, a portion on the inner side of about 1 μm (preferably about 2 μm) from the particle surface can be defined as “inside”.

The complex oxide material disclosed herein has a specific Raman spectrum in the surface portion of particles (secondary particles) constituting the material in the Raman spectrum measurement by visible light excitation (for example, excitation light having a wavelength of 514.5 nm). This is characterized by the appearance of a Raman band in each region (range of Raman shift). The specific areas are 560 ± 5 cm ⁻¹ area (especially 560 ± 2 cm ⁻¹ area), 545 ± 5 cm ⁻¹ area (especially 545 ± 2 cm ⁻¹ area), and 465 ± 5 cm ⁻¹ area. (Especially the region of 465 ± 2 cm ⁻¹ ). In this specification, the Raman bands respectively appearing in the above regions are referred to as first, second and third Raman bands in order from the largest wave number (Raman shift). These names are for convenience and are not intended to limit the relative intensity of each Raman band.

  As a method for measuring the Raman spectrum, a conventionally known method or the like can be employed without any particular limitation. For example, the Raman spectrum can be obtained using a commercially available Raman spectroscopic analyzer. The measurement range (beam diameter) for obtaining the Raman spectrum is preferably about 2 μm or less, and more preferably about 1 μm or less. Thus, it is preferable to employ a method (apparatus) that can realize a relatively narrow measurement range. The Raman spectrum inside the particles can also be measured in the same manner as the surface portion of the particles. For example, the cross section of the particle is exposed, and the Raman spectrum can be measured at an arbitrary position such as the outer peripheral portion (surface portion) and the central portion (inside) in the cross section.

  In one preferable embodiment of the composite oxide material disclosed herein, any of the Raman spectra obtained from the surface portion and the inside of the particles constituting the material is visually observed in each of the above-described regions (or Having a distinctly distinct Raman band (at least by analyzing the Raman spectrum). In this case, the intensity of the Raman band appearing in each region is compared between the Raman spectrum of the surface portion and the internal Raman spectrum, and at least one of the Raman bands of the surface portion (preferably two, more preferably three). The intensity of the Raman band (peak height) in the range of about 10 to 120% (more preferably about 30 to 110%, more preferably about 50 to 100%) with respect to the intensity of the internal Raman band. It is preferable that it exists in.

  Such a composite oxide material can be preferably manufactured by bringing a lithium solution into contact with a primary fired product mainly composed of an oxide containing Li, Ni, Co, and Al. The method for obtaining the primary fired product is not particularly limited. For example, a conventionally known method such as a solid phase method or a coprecipitation method can be appropriately selected. Typically, a primary fired product can be obtained by firing a raw material mixture containing Li, Ni, Co, and Al. For example, according to the composition of the composite oxide material to be manufactured, the raw material mixture is prepared by mixing a compound powder (raw material powder) containing a constituent metal element of the composite oxide that is the main component of the material at a predetermined ratio. Can be a thing. The raw material powder includes an oxide containing a metal element constituting the composite oxide, or a compound that can be converted into an oxide by heating (a hydroxide, carbonate, nitrate, sulfate, phosphate, Acetates, oxalates, halides, oxyhalides, and the like) may be used. This raw material powder may contain a compound (a composite metal oxide, a composite metal carbonate, or the like) containing two or more of the metal elements constituting the composite oxide.

  In a preferred embodiment, the raw material mixture is a hydroxide containing at least one metal element among Li, Ni, Co, and Al (a single hydroxide or a mixture of two or more hydroxides). May be the main constituent. A preferred example of such a hydroxide is mainly a hydroxide precipitated by adding alkali to a solution containing Li ions, Ni ions, Co ions and Al ions (typically a solution showing acidity). It is a raw material hydroxide as a constituent component. The anion (counter ion) contained in the solution is one or more selected from the group consisting of nitrate ion, carbonate ion, sulfate ion, halide ion (for example, chloride ion), hydroxide ion and the like. obtain. For example, a solution in which the anion is mainly nitrate ions and / or hydroxide ions is preferable. Such a solution can be suitably prepared, for example, by dissolving a predetermined amount of lithium nitrate, nickel nitrate, cobalt nitrate and aluminum nitrate in water.

As the alkali to be added to the solution, one or two or more selected from ammonia water (NH ₄ OH), alkali metal hydroxide (eg, lithium hydroxide), alkaline earth metal hydroxide, and the like are used. be able to. Of these, it is particularly preferable to use ammonia water. Moreover, you may use together ammonia water and other alkalis (lithium hydroxide etc.). It is particularly preferable to use ammonia water alone because it is easy to control the operation and / or characteristics of the resulting precipitate. For example, 0.8 equivalent or more (for example, 0.8 to 1.5 equivalent, preferably 1 to 1.5 equivalent) with respect to the total amount of Li ion, Ni ion, Co ion and Al ion contained in the solution Aqueous ammonia containing NH ₄ OH may be added.
A precipitate (mainly hydroxide) generated thereby can be used as a raw material hydroxide. This precipitate may be one in which one or more of Li, Ni, Co, and Al are co-precipitated. If necessary, a material obtained by mixing the precipitate with another material (for example, a compound containing one or more of Li, Ni, Co, and Al) may be used as the raw material hydroxide.

By firing such a raw material mixture, a primary fired product mainly composed of a composite oxide (LiNi (Co, Al) O ₂ ) having Li, Ni, Co and Al as constituent metal elements can be obtained. The firing conditions at this time are not particularly limited as long as the primary firing products can be synthesized (manufactured) from the raw material mixture. For example, as the firing atmosphere, an oxidizing atmosphere, an inert gas atmosphere, or the like can be selected as appropriate. Usually, firing in an oxidizing atmosphere (for example, in the air) is preferable. Although it depends on the composition of the raw material mixture and the like, it is usually appropriate to fire at a temperature exceeding 700 ° C. (eg, 700 to 1000 ° C.). From the viewpoint of improving the properties of the finally obtained composite oxide material, it is preferable to fire at a temperature of about 720 ° C. or higher (eg, 720 to 900 ° C.), and about 740 ° C. or higher (eg, 740 ° C. to 850 ° C.). It is more preferable to bake at a temperature of ° C. A particularly preferable firing temperature is about 750 ° C. or higher (for example, 750 to 800 ° C.). According to the primary fired product fired at such a temperature, the finally obtained composite oxide material has better characteristics as a battery electrode active material and the like (for example, battery capacity, internal resistance, normal temperature and / or low temperature output, One or more of the cycle characteristics, durability, etc.).

Here, of the metal elements contained in the raw material mixture, Li is more likely to evaporate than other metal elements when exposed to high temperatures. In particular, Li on the surface of the particles is easily lost due to transpiration. For this reason, when manufacturing a primary baked product, baking may proceed in a state where a part (or all) of Li that should be on the surface portion of the particles is lost. This can be a factor of lowering the crystallinity of the surface portion of the particles constituting the fired product (disturbing the crystal structure of the surface portion) in the primary fired product obtained by the firing. This phenomenon tends to become more prominent when the firing temperature at the time of synthesizing the primary fired product is increased. The low crystallinity of the surface portion of the particles constituting the primary fired product can be grasped by, for example, the absence of a Raman band in any of the above-described regions in the Raman spectrum of the surface portion.
The present inventor has found that the crystallinity of the surface portion can be improved (disturbance of the crystal structure can be reduced) by replenishing the surface portion of the particles constituting the primary fired product with Li. As a method of replenishing the surface portion of the particles with Li, a method of treating the primary fired product with a Li solution (typically, contacting with the Li solution) is simple and preferable.

  As the Li solution used for the Li solution treatment, a solution in which a Li compound is dissolved in an appropriate solvent can be used. The solvent is preferably an aqueous solvent or alcohol. Here, the aqueous solvent refers to water or a mixed solvent mainly composed of water. Examples of the organic solvent that constitutes the mixed solvent with water include organic solvents that can be uniformly mixed with water, such as lower alcohols (eg, alcohols having 1 to 3 carbon atoms) such as methanol, ethanol, and ethylene glycol, and acetone. One type or two or more types can be selected. A preferred example of the Li solution used for the Li solution treatment is a Li solution in which a lithium salt is dissolved in a solvent substantially consisting of water. The lithium salt may be one or more selected from lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium bromide, lithium chloride and the like. An example of a particularly preferred Li solution is an aqueous solution of lithium hydroxide (LiOH). Moreover, you may use Li solution which contains lithium alkoxide in alcohol. For example, a Li solution containing a Li alkoxide of an alcohol in a lower alcohol (for example, an alcohol having 1 to 6 carbon atoms) such as ethanol, propanol, or butanol can be used. A preferred example is a propanol solution of Li propoxide.

  Although not particularly limited, it is appropriate that the Li concentration of the Li solution used for the treatment is usually in the range of about 0.01 to 0.5 mol / liter (L). A preferable range of the Li concentration is, for example, about 0.02 to 0.15 mol / L, and a more preferable range is, for example, about 0.03 to 0.08 mol / L. Further, an aqueous lithium hydroxide solution containing about 0.01 to 0.3% by mass (more preferably 0.015 to 0.1% by mass) of lithium hydroxide, about 0.01 to 0.3% by mass (more A propanol solution or the like containing preferably 0.015 to 0.1% by mass of Li alkoxide (for example, propoxide) can be preferably used.

A preferred example of the method for bringing the primary fired product into contact with the Li solution is a method of impregnating the fired product with the Li solution. From the viewpoint of facilitating uniform and rapid processing, it is preferable to disperse the fired product (typically in particulate form) in the Li solution. The time for performing the Li solution treatment (time for contacting with the Li solution) is not particularly limited. An appropriate treatment time can be set in consideration of the progress of the Li solution treatment, the productivity of the composite oxide material, and the like. Usually, the treatment time is preferably about 3 to 30 minutes. Moreover, the temperature of the Li solution to be used is not particularly limited. Usually, for example, a Li solution of about 5 to 50 ° C. (more preferably about 10 to 40 ° C.) can be preferably used.
By performing such a Li solution treatment, the crystallinity of the surface portion of the particles constituting the primary fired product can be increased. Typically, a Raman band can appear in each of the predetermined regions in the Raman spectrum of the surface portion.

  The target lithium composite oxide material can be obtained, for example, by separating the fired product from the Li solution and drying it. This drying may be performed at room temperature, or may be performed under heating as necessary. For example, drying time can be shortened by heating to about 60-180 degreeC temperature range. Further, the fired product after the Li treatment may be further heated to a high temperature. However, the heating temperature range at this time is preferably a temperature range lower than the firing temperature range of the primary fired product. For example, the temperature range is preferably about 50 ° C. or more lower than the firing temperature range of the primary fired product, and more preferably about 100 ° C. or more. The heating temperature range is preferably about 700 ° C. or less, more preferably about 600 ° C. or less, and further preferably about 550 ° C. or less. When Li solution treatment is performed using a Li solution containing Li alkoxide and / or organic Li salt (such as lithium acetate), the fired product after the Li solution treatment is 300 ° C. or higher (more preferably 400 ° C. or higher). It is preferable to remove the organic component by heating to the temperature range. For example, the fired product can be refired in a temperature range of about 400 to 600 ° C.

  The manufacturing method disclosed herein can further include a step of measuring a Raman spectrum of the surface portion of the particle. For example, the quality of the obtained composite oxide material (the degree of crystallinity of the particle surface portion) can be measured by measuring the spectrum of the surface portion after the Li solution treatment (after that when performing the heating step). Can be confirmed. As a result, it is possible to provide a complex oxide material with stable quality (with little variation).

In addition, the Li solution treatment as described above improves the crystallinity (particularly the crystallinity of the surface portion) of particles mainly composed of a composite oxide having Li, Ni, Co and Al as constituent metal elements, as another aspect. It can be seen as a method. This method is, for example, a particle mainly composed of a composite oxide having Li, Ni, Co, and Al as constituent metal elements, and in the Raman spectrum of the surface layer portion of the particle (processed particle), It can be preferably applied to particles that do not show a Raman band in the region. Such particles may be particles constituting a commercially available composite oxide material mainly composed of LiNi (Co, Al) O ₂ . By performing the lithium solution treatment, the crystallinity of the surface portion of such particles to be treated can be increased. For example, in the Raman spectrum of the surface portion of the particle, the surface portion has a Raman band that can be identified with the naked eye in a region of 560 ± 5 cm ^−1, a region of 545 ± 5 cm ⁻¹ , and a region of 465 ± 5 cm ^−1. It is possible to improve the crystallinity (modify the surface portion).

  The lithium battery disclosed here (typically, a lithium ion secondary battery) includes any of the complex oxide materials described above as an electrode active material. In a preferred embodiment of such a battery, the battery is constructed using a positive electrode having the composite oxide material (positive electrode active material). For example, any of the complex oxide materials described above can be used as a positive electrode in a form in which the composite oxide material is attached to a positive electrode current collector together with a conductive material, a binder (binder), and the like as necessary. As the positive electrode current collector, a rod-like body, a plate-like body, a foil-like body or the like mainly composed of a conductive metal such as Al, Ni, or Ti can be used. Alternatively, carbon paper or the like may be used as the positive electrode current collector. As the conductive material, a carbon material such as carbon black (acetylene black or the like), a conductive metal powder such as Ni powder, or the like can be used. As the binder (binder), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), styrene butadiene block copolymer (SBR), Carboxymethyl cellulose (CMC) or the like can be used.

A positive electrode having a configuration in which a positive electrode active material is attached to the surface of a positive electrode current collector can be suitably produced, for example, in the following manner. That is, the positive electrode active material is mixed with an appropriate solvent together with a conductive material, a binder, a thickener and the like used as necessary to prepare a liquid positive electrode composition. This composition is attached to the positive electrode current collector. For example, the said composition is apply | coated to the single side | surface or both surfaces of a sheet-like positive electrode electrical power collector (Al foil etc.).
As a solvent used for the preparation of the positive electrode composition, both an aqueous solvent (for example, water) and a non-aqueous solvent (for example, N-methylpyrrolidone) can be used. When an aqueous solvent is used, the positive electrode composition can contain a lithium source that dissolves in the aqueous solvent and supplies Li ions in addition to the positive electrode active material and the like. As the lithium source, for example, one or two or more selected from lithium salts such as lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium bromide, and lithium chloride can be used. An example of a particularly preferred lithium source is lithium hydroxide.

  As the negative electrode, a negative electrode current collector having a negative electrode active material attached thereto can be used. As the negative electrode current collector, a rod-like body, a plate-like body, a foil-like body or the like mainly composed of copper (Cu), Al, Ni, Ti or the like can be used. Alternatively, carbon paper or the like may be used as the negative electrode current collector. As the negative electrode active material, a carbon material having an amorphous structure and / or a graphite structure can be used. Examples of such a carbon material include natural graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, soft carbon, and the like. Such a negative electrode active material can be made into a negative electrode in a form in which the negative electrode active material is attached to a negative electrode current collector together with a binder or the like as necessary. As the binder, the same as the positive electrode can be used.

  In a preferred aspect of the lithium secondary battery disclosed herein, the secondary battery includes a positive electrode having a structure in which a mixture containing a positive electrode active material is attached to one side or both sides of a sheet-like positive electrode current collector. In addition, a negative electrode having a structure in which a mixture containing a negative electrode active material is attached to one side or both sides of a sheet-like negative electrode current collector is provided. The present invention can be preferably applied to a lithium secondary battery or the like having a laminated electrode body or a wound electrode body having a structure in which such a positive electrode and a negative electrode are laminated via a separator. As the separator, for example, a porous film made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) can be used. Moreover, you may use the woven fabric or nonwoven fabric which consists of a polypropylene, a polyethylene terephthalate (PET), methylcellulose (MC) etc.

Solvents constituting the electrolyte include propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, dimethyl carbonate One or two or more selected from diethyl carbonate (DEC), ethyl methyl carbonate, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, and the like can be used. Further, as supporting salts to be contained in the electrolytic solution, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ One or two or more lithium compounds selected from the above can be used. Of these, LiPF ₆ is particularly preferred.

  Hereinafter, experimental examples relating to the present invention will be described. However, the present invention is not intended to be limited to the specific examples.

<Experimental example 1>
A composite oxide material (sample 1) mainly composed of LiNi (Co, Al) O ₂ was produced by the following method.
That is, predetermined amounts of lithium nitrate, nickel nitrate, cobalt nitrate, and aluminum nitrate were weighed in such a ratio that the molar ratio of each metal was Li: Ni: Co: Al = 10: 8: 1.5: 0.5. These nitrates were dissolved in water to prepare a solution (aqueous solution) containing Li ions, Ni ions, Co ions, and Al ions. In this solution, an amount of NH corresponding to approximately 1.2 times the amount of nitrate ions contained in the solution (that is, approximately 1.2 equivalents relative to the total amount of Li ions, Ni ions, Co ions, and Al ions). Aqueous ammonia containing ₄ OH was added. The resulting precipitate was collected by suction filtration, dried at 120 ° C. for about 180 minutes, and then fired at 750 ° C. for about 180 hours. As a result, a primary fired product mainly composed of LiNi (Co, Al) O ₂ was obtained. This primary fired product was mainly composed of secondary particles in which primary particles were aggregated. The average particle diameter of the secondary particles was about 10 μm.

The obtained primary fired product was brought into contact with a lithium solution. That is, the particulate primary fired product was charged and dispersed in an aqueous lithium solution containing 0.05% by mass of LiOH, and left for 10 minutes with stirring. Thereafter, the fired product was collected by suction filtration, dried at 120 ° C. for about 180 minutes, and then heated at 500 ° C. for about 180 hours. In this way, a lithium composite oxide material (sample 1) mainly composed of LiNi (Co, Al) O ₂ was obtained.

<Experimental example 2>
A composite oxide material (sample 2) mainly composed of LiNi (Co, Al) O ₂ was obtained in the same manner as in Example 1 except that the treatment of bringing the primary fired product into contact with the lithium aqueous solution was not performed.

<Experimental example 3>
For the sample 1 obtained in Experimental Example 1 and the sample 2 obtained in Experimental Example 2, the surface portion and the internal Raman spectrum were measured, respectively. As a measuring apparatus, a dispersion Raman spectroscopic analyzer (model name “RAMANOR T64000”) manufactured by Jobin Yvon was used. The measurement conditions were excitation light: 514.5 nm (argon ion laser) and laser beam diameter: 1 μm. The measurement sample was produced as follows. That is, the particles constituting Sample 1 and Sample 2 were dispersed in a resin composition mainly composed of an acrylic resin, and the resin composition was cured to fix the particles. The resin (cured product) was polished to expose the cross section of the particles. And about the cross section, the Raman spectrum of the part (surface part) inscribed in the particle | grain surface and the center part (inside) of particle | grains was measured.

  The obtained Raman spectra are shown in FIG. 1 (Sample 1) and FIG. 2 (Sample 2). In each figure, the spectrum shown at the top is obtained from the surface portion of the particle, and the spectrum shown at the bottom is obtained from the inside of the particle. In addition, the vertical axis of the figure indicates the intensity of the spectrum, and the surface spectrum and the internal spectrum are displayed with their positions shifted vertically to make the figure easier to see.

As shown in FIGS. 1 and 2, in the Raman spectrum of the interior of the particle, (with Li solution treatment) Sample 1 and in any of the sample 2 (without Li solution process), approximately 560 cm ^-1, about 545cm ^-1 And three Raman bands appeared at a position of about 465 cm ⁻¹ . This indicates that both the sample 1 and the sample 2 have good crystallinity of LiNi (Co, Al) O ₂ inside the particles.
On the other hand, in the Raman spectrum of the surface portion of the particle, three Raman bands appeared in Sample 1 at almost the same position as the inside of the particle (see FIG. 1). This indicates that the difference in crystal structure between the surface portion and the inside of the particle constituting the sample 1 is small (that is, there is little disorder in the crystal structure of the particle surface portion). On the other hand, in sample 2, no Raman band was observed at the above position in the Raman spectrum of the surface portion of the particle (see FIG. 2). This indicates that the crystallinity of the surface portion of the particle is low.
Thus, from the comparison of the Raman spectrum of the surface portion of the particle, the sample 1 obtained by performing the treatment for replenishing Li to the surface portion of the particle constituting the primary fired product (Li solution treatment) is subjected to the treatment. It can be seen that the crystallinity of the surface portion of the particles is clearly better than that of the sample 2 which was not present.

<Experimental example 4>
Using the sample 1 and the sample 2 obtained in the above experimental example as the positive electrode active material, lithium ion secondary batteries were respectively produced.
That is, Sample 1 or Sample 2 as a positive electrode active material and acetylene black as a conductive material are mixed with ion-exchanged water together with polytetrafluoroethylene (PTFE) and carboxymethyl cellulose (CMC) to obtain a paste-like positive electrode A composition was prepared. The approximate mass ratio of each material (other than water) contained in this composition is 85% by mass for the positive electrode active material, 10% by mass for acetylene black, 2% by mass for PTFE, and 3% by mass for CMC. This positive electrode composition was applied (attached) to both surfaces of an Al foil serving as a positive electrode current collector to prepare a sheet-like positive electrode (positive electrode sheet) having a positive electrode active material-containing layer on both surfaces of the positive electrode current collector. .

  Moreover, graphite as a negative electrode active material was mixed with ion-exchanged water together with CMC and a styrene butadiene block copolymer (SBR) to prepare a paste-like negative electrode composition. The approximate mass ratio of each material (other than water) contained in this composition is 98% by mass for the negative electrode active material (graphite), 1% by mass for CMC, and 1% by mass for SBR. This negative electrode composition was applied (attached) to both sides of a copper foil as a negative electrode current collector to prepare a sheet-like negative electrode (negative electrode sheet) having a negative electrode active material-containing layer on both sides of the negative electrode current collector. .

A porous polyethylene sheet having a thickness of about 25 μm was used as the separator. The positive electrode sheet and the negative electrode sheet were stacked so as to face each other through this separator sheet, and this was wound in the longitudinal direction to produce a wound electrode body. A lithium ion secondary battery was constructed using the obtained electrode body and non-aqueous electrolyte. As the electrolytic solution, a 3: 7 (volume ratio) mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) containing LiPF ₆ as a supporting salt at a concentration of about 1 mol / liter was used. Thus, a battery (battery 1) using the composite oxide material of sample 1 as the positive electrode active material and a battery (battery 2) using the composite oxide material of sample 2 as the positive electrode active material were produced.

<Experimental example 5>
The battery performance of the battery 1 and the battery 2 produced by the above experimental example was evaluated.
That is, at an environmental temperature of 60 ° C., the battery was charged to 4.1 V at a constant current of 2 C and then discharged to 3.0 V at the same current density. This cycle (charging to 4.1 V with a constant current of 2 C and discharging to 3.0 V) was repeated 100 times.
After the above cycle was performed, constant current charging at a current density of 1/5 C was performed at room temperature with an upper limit voltage of 4.1 V, and the state of charge (SOC) of the battery was adjusted to 40%. The battery charged to 40% SOC was set in a -30 ° C. thermostat, and the charge / discharge for 10 seconds was repeated with the lower limit voltage set to 3.0V. From the current-voltage straight line at this time, the value of the low temperature output (W) at −30 ° C. was calculated.
As a result, the battery 1 using the sample 1 (with Li solution treatment) as the positive electrode active material has an improved low-temperature output value by about 10% compared to the battery 1 using the sample 2 (without Li solution treatment). It was.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

The contents disclosed in this specification include the following.
(1) An electrode active material mainly composed of a composite oxide having Li, Ni, Co and Al as constituent metal elements. The active material has a Raman spectrum of at least 560 in the Raman spectrum measurement by visible light excitation (for example, excitation light having a wavelength of 514.5 nm) at least on the surface portion (preferably the surface portion and inside) of the particles constituting the active material. It has a first Raman bands appearing in the region of ± ^{5 cm -1,} a second Raman bands appearing in the region of 545 ± ^{5 cm -1,} and a third Raman bands appearing in the region of 465 ± ^{5 cm -1.}
An electrode active material having such characteristics is useful as, for example, a component of a battery (typically a lithium battery). A battery constructed using such an electrode active material can exhibit good battery characteristics. In particular, it is suitable as a positive electrode active material for a lithium ion secondary battery.

(2) A method for grasping the crystallinity of a material mainly composed of a composite oxide having Li, Ni, Co and Al as constituent metal elements. In the Raman spectrum measurement by visible light excitation, the crystallinity is measured using the presence and / or intensity of a Raman band (peak) in each region of 560 ± 5 cm ⁻¹ , 545 ± 5 cm ⁻¹ and 465 ± 5 cm ⁻¹ as an index. It is characterized by grasping. In these regions, when no identifiable Raman band is observed, the crystallinity is low, and when an identifiable Raman band is observed, the higher the intensity (for example, the peak height), the higher the crystallinity. As a result, the degree of crystallinity of the material can be grasped. In addition, knowledge about the crystal structure of the material can be obtained. If the material is primarily in particulate form, the method can be performed on the outer surface of the particles (typically secondary particles). Thereby, the degree of crystallinity of the outer surface can be grasped. Moreover, you may implement the said method with respect to the cross section of particle | grains. In this case, the degree of crystallinity of each part (surface part, center part, etc.) of the particle can be grasped according to the measurement location.
The technique for grasping the degree of crystallinity in this way can be applied to any of the above-described methods for producing a composite oxide material. For example, as described in (3) below, the method (2) can be carried out as one step of the production method.

(3) In the method for producing any lithium composite oxide material described above, after the step of bringing the primary fired product into contact with the Li solution, the step of performing the crystallinity grasping method of (2) above on the fired product Is further provided. In the production method including the heating step after being brought into contact with the Li solution, the method (2) may be performed at any timing before and after the heating step. In a preferred embodiment of such a production method, the method (2) is performed so that the crystallinity of at least the surface portion of the particles constituting the fired product can be grasped. Thereby, the grade of the effect (effect which improves the crystallinity of a surface part) by having contacted the primary baked material with Li solution can be grasped | ascertained efficiently. Further, the crystallinity inside the particles may be grasped.
According to this manufacturing method, it is possible to provide a lithium-containing oxide material having a more stable quality (small variation). Further, by using the composite oxide material thus manufactured as a positive electrode active material, a lithium battery with more stable battery performance (small variation in quality) can be constructed. For example, a high-performance lithium battery can be manufactured (provided) stably.

FIG. 4 is a characteristic diagram showing the Raman spectrum of the surface part and the inside of the particles constituting the sample 1. FIG. 6 is a characteristic diagram showing the Raman spectrum of the surface portion and the inside of the particles constituting Sample 2.

Claims (10)

A lithium composite oxide material mainly comprising a composite oxide having lithium, nickel, cobalt and aluminum as constituent metal elements,
The Raman spectrum of the surface portion of the particles constituting the material is a first Raman band appearing in the region of 560 ± 5 cm ⁻¹ and the second appearing in the region of 545 ± 5 cm ^{−1 in} the Raman spectrum measurement by visible light excitation. A lithium composite oxide material having a Raman band and a third Raman band appearing in a region of 465 ± 5 cm ⁻¹ . A first Raman band appearing in a region of 560 ± 5 cm ^−1, a second Raman band appearing in a region of 545 ± 5 cm ^{−1 in} a Raman spectrum measurement by visible light excitation, and a 465 The material according to claim 1, having a third Raman band appearing in the region of ± 5 cm ⁻¹ .   The intensity of the Raman band in the Raman spectrum of the surface portion is in the range of 30 to 110% with respect to the intensity of at least one of the first, second and third Raman bands in the internal Raman spectrum. The material according to claim 2.   The material according to any one of claims 1 to 3, wherein an average particle diameter of the particles is in a range of 3 to 100 µm. A method for producing a lithium composite oxide material mainly comprising a composite oxide having lithium, nickel, cobalt and aluminum as constituent metal elements,
Preparing a primary fired product mainly composed of a composite oxide having lithium, nickel, cobalt and aluminum as constituent metal elements;
The first Raman band appearing in the region of 560 ± 5 cm ⁻¹ and the first appearing in the region of 545 ± 5 cm ^{−1 in} the Raman spectrum measurement by visible light excitation in the Raman spectrum of the particles constituting the primary fired product. Bringing the fired product into contact with a lithium solution so as to show a second Raman band and a third Raman band appearing in a region of 465 ± 5 cm ⁻¹ ;
A method for producing a lithium composite oxide material comprising:   The primary calcined product is obtained by calcining a raw material hydroxide whose main constituent is a hydroxide precipitated by adding an alkali to a solution containing lithium ions, nickel ions, cobalt ions and aluminum ions. The method of claim 5, wherein   The method according to claim 6, wherein the solution is an aqueous solution containing lithium nitrate, nickel nitrate, cobalt nitrate, and aluminum nitrate. The method of claim 6, wherein the alkali is NH ₄ OH.   The method according to any one of claims 5 to 8, wherein after the primary fired product is brought into contact with the lithium solution, the primary fired product is heated to a temperature range lower than a firing temperature range of the primary fired product.   A lithium ion secondary battery comprising the material according to claim 1 as a positive electrode active material.

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