WO2015001632A1 - Cathode material for lithium ion secondary battery, cathode for lithium ion secondary battery, lithium ion secondary battery, and method for producing each of same - Google Patents

Abstract

Provided is a cathode material that is for a lithium ion secondary battery and that has superior energy density and electron conductivity. The cathode material for a lithium ion secondary battery comprises a composite particle (20) of: a first particle (30), which is a cathode active material represented by general formula Li_xMn_aM1_bO₂ (where in the formula, M1 is at least one element selected from the group consisting of Ni, Cu, Zn, Co, Fe, Cr, V, Ti, Mg, Al, Sn, Mo, Nb, V, Zr, Ta, Ru, and W, 1.0 < x ≤ 1.4, 0 < a < 1.0, 0 < b < 1.0, and a+b ≤ 1.0); and a second particle (40, 50) having an electrical conductivity of at least 1.0×10^-5 S/m.

Description

Positive electrode material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, lithium ion secondary battery and manufacturing method thereof

The present invention relates to a positive electrode material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a method for producing them.

At present, secondary batteries are used in natural energy power generation, ships, railways, electric vehicles, etc., which are being widely used as a technology with reduced environmental load.
In natural energy power generation that uses a secondary battery as a storage system for generated electricity, a large-capacity storage capable of responding to fluctuations in the amount of power generation can be realized at low cost, and ships equipped with a secondary battery as a driving power supply In railways, electric vehicles, etc., it is required to increase the range by one charge.
Then, development of a lithium ion secondary battery in which Li ⁺ is in charge of electrical conduction has been promoted as a secondary battery meeting such a demand. Lithium ion secondary batteries have characteristics of superior energy density compared to nickel hydrogen batteries and lead storage batteries, but in order to realize higher capacity, a positive electrode for lithium ion secondary batteries is configured New positive electrode active materials are being developed.

Li ₂ MnO ₃ -LiMO ₂ solid solution positive electrode active material (hereinafter referred to as manganese-based solid solution positive electrode active material) is one of the positive electrode active materials for lithium ion secondary batteries expected to have high capacity. Since manganese-based solid solution positive electrode active materials have low raw material costs and high safety, improvements are being made to improve practicability.
Heretofore, there has been known a technique for improving the electrical characteristics of a positive electrode by using manganese-based solid solution positive electrode active material particles in combination with other particles.

For example, Patent Documents 1 and 2 disclose Li _a Mn _b M _c O _Z (M is _a technology for providing a non-aqueous electrolyte battery excellent in storage capacity and cycle performance under high temperature and high temperature. And at least one element selected from the group consisting of Ni, Co, Al and F, wherein a, b, c and Z are 0 ≦ a ≦ 2.5, 0 <b ≦ 1, 0 ≦ c ≦ 1, 2 The positive electrode containing the lithium manganese containing oxide represented by <= Z <= 3 and the Fe containing phosphorus compound of an olivine structure is disclosed.

Further, Patent Document 3 discloses a composition formula (1) as a technology for providing a positive electrode active material for an electric device which can exhibit excellent initial charge / discharge efficiency while maintaining a high reversible capacity by maintaining a high reversible capacity. ) in _{Li 1.5 [Ni a Co b Mn} c [Li] d] O 3 ( formula (1), Li is lithium, Ni is nickel, Co is cobalt, Mn is manganese, O represents oxygen, a, b, c and d are the first active consisting of the transition metal oxide represented by 0 <d <0.5, a + b + c + d = 1.5, 1.0 <a + b + c <1.5. Substance and the composition formula (2) LiM _{a '} Mn _2-a' O ₄ (in the formula (2), Li is lithium, M is at least one metal element having a valence of 2 to 4, Mn is manganese, O is Represents oxygen, and a ′ satisfies the relation of 0 ≦ a ′ <2.0)), and has a crystal structure And a second active material composed of a spinel type transition metal oxide belonging to the space group Fd-3m, and the content ratio of the first active material to the second 3) The relationship represented by 100: 0 <M _A : M _B <0: 100 (in the formula (3), M _A represents the mass of the first active material, and M _B represents the mass of the second active material) A positive electrode active material for an electric device is disclosed, which is characterized in that

JP, 2012-033507, A Unexamined-Japanese-Patent No. 2010-225486 International Publication No. 2013/005737

However, the positive electrodes disclosed in Patent Document 1 and Patent Document 2 are produced by simply mixing primary particles of a lithium manganese-containing oxide and an Fe-containing phosphorus compound having an olivine structure. In addition, the positive electrode disclosed in Patent Document 3 is manufactured by simply mixing the powder of the first active material and the powder of the second active material corresponding to primary particles.
As described above, in the positive electrode in which the primary particles of the manganese-based solid solution positive electrode active material and the primary particles of other particles used in combination are simply mixed, the conductive path between the particles of the primary particles is not appropriately formed. Even if the total amount of active materials is unchanged, there is a problem that the energy density is reduced.
Therefore, an object of the present invention is to provide a positive electrode material for a lithium ion secondary battery excellent in energy density and electron conductivity.

In order to solve the above problems, the positive electrode material for a lithium ion secondary battery according to the present invention has a general formula Li _x Mn _a M 1 _b O _{2 ± c} (wherein, M 1 represents Ni, Cu, Zn, Co, Fe, At least one element selected from the group consisting of Cr, V, Ti, Mg, Al, Sn, Mo, Nb, V, Zr, Ta, Ru and W, 1.0 <x ≦ 1.4, A first particle represented by 0 <a <1.0, 0 <b <1.0, a + b ≦ 1.0, 0 ≦ c ≦ 0.2), and the electric conductivity is 1.0 × It is characterized in that it comprises a composite particle of a second particle of 10 ^-5 S / m or more.

ADVANTAGE OF THE INVENTION According to this invention, the positive electrode material for lithium ion secondary batteries excellent in energy density and electronic conductivity can be provided.

It is a cross-sectional schematic diagram which shows an example of the lithium ion secondary battery which concerns on this embodiment. It is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example. It is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example. It is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example. It is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example. It is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example. It is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example. It is a cross-sectional schematic diagram which shows one form of the positive electrode active material particle contained in the positive electrode material which concerns on a comparative example.

Hereinafter, a positive electrode material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a method of manufacturing the same according to an embodiment of the present invention will be described in detail.

The positive electrode material according to the present embodiment is formed by combining a first particle, which is a primary particle of a manganese-based solid solution positive electrode active material, and a second particle, which is a primary particle of a compound that contributes to improvement of electron conductivity. The present invention relates to a positive electrode material comprising secondary particles (composite particles) to be granulated.

The first particle according to the present embodiment is a positive electrode active material represented by _a general formula Li _x Mn _a M1 _b O ₂ and contains at least Mn and M1 as a transition metal element.
The first particles, and _Li 2 MnO ₃ also having layered rock-salt structure as LiCoO _2, a solid solution of LiM1O _2, rewritten and _{Li [Li 1/3 Mn 2/3] O} 2 -LiM1O 2 As such, the main Li is disposed between the layers of the layered structure, and a part of the excess Li is based on the regularly arranged structure in the metal layer formed by Mn and M1.
The manganese-based solid solution positive electrode active material having such a structure is capable of ionizing and desorbing not only Li arranged in the layer but also Li arranged in the metal layer, and therefore 200 mAh / g It becomes a positive electrode material which shows the comparatively high discharge capacity which exceeds.
However, since the electron conductivity is not necessarily excellent, its improvement is desired. Therefore, in the positive electrode material according to the present embodiment, the first particles and the second particles excellent in electron conductivity described later are complexed to form secondary particles, thereby improving the electron conductivity of the particles. I am trying to In the present specification, the value of the electrical conductivity is used as a scale for evaluating the superiority or inferiority of the electron conductivity. The electrical conductivity of a general manganese-based solid solution positive electrode active material is said to be 1.0 × 10 ⁻⁶ S / m or less.

In the above general formula, the composition ratio x of Li is more than 1.0 and not more than 1.4.
By setting the composition ratio of Li to a value exceeding 1.0, the crystal structure of the positive electrode active material becomes relatively stable, and the discharge capacity normally required can be secured.
In addition, by setting the composition ratio of Li to 1.4 or less, the internal resistance and the decrease in electrochemical activity can be suppressed, and the discharge capacity normally required can be secured. When the composition ratio of Li exceeds 1.4, a voltage of about 5.0 V (vs. Li ⁺ / Li) or more is required to ionize and desorb Li from the positive electrode active material during charging, so There is a possibility that the battery may be oxidatively decomposed to reduce the battery life.

In the above general formula, M1 is an electrochemically active element responsible for the redox reaction. Specifically, at least one element selected from transition metals such as Ni, Cu, Co, Fe, Cr, V, Ti, Mo, Nb, Zr, Ta, Ru, W, etc., or Zn, Mg, Al And at least one element selected from the group consisting of Sn.
M1 can be suitably selected from these elements according to the desired characteristic given to a battery. For example, from the viewpoint of raw material cost, the ratio of expensive metals such as Co, Cr, Mo, Zr, Ta, Ru, W is low, and the ratio of relatively inexpensive metals such as Ni, Fe, Ti is high. preferable. From the viewpoint of weight energy density, it is preferable that the ratio of elements having a relatively small atomic weight, such as Ni, Fe, V, Ti, Mg, and Al, be high. Further, from the viewpoint of the discharge voltage, Ni and Fe are preferable, and Ni having a larger change in valence is preferable.

In the above general formula, the composition ratio a of Mn is more than 0 and less than 1.0, the composition ratio b of M1 is more than 0 and less than 1.0, and the composition ratio of Mn and the composition ratio of M1 b is a value satisfying the relationship of a + b ≦ 1.0.
That is, as long as the first particles according to the present embodiment contain both Mn and M1, the composition ratio of these can be set to an appropriate ratio. By satisfying such a relationship, the crystal structure of the positive electrode active material is relatively stably maintained.

However, the first particles according to the present embodiment are not limited to those having a composition that strictly satisfies the relationship of these values. For example, as long as the layered structure of the solid solution is substantially formed, the composition may have a non-stoichiometric ratio, and some elements may be irregularly coordinated.

The second particle according to the present embodiment is a particle having electron conductivity superior to that of the first particle, and is a particle showing a value of at least 1.0 × 10 ⁻⁵ S / m or more. In addition, electrical conductivity is a value in the case where the particle is pressurized and the density is 2.2 g / cm ³ at room temperature.
Therefore, the composite particle formed by the first particle and the second particle has an improved electron conductivity as compared with the case of the first particle alone. In addition, since the second particles usually have extremely small particle diameters, it is difficult to measure the electrical conductivity by the second particles alone. Therefore, the electrical conductivity of the second particle is estimated from the electrical conductivity of the composite particle and the first particle, as necessary.

The second particles according to this embodiment are mainly particles formed of a positive electrode active material.
As a positive electrode active material for forming the second particles, a positive electrode active capable of inserting and extracting lithium ions at 2.0 V (vs. Li ⁺ / Li) or more and 5.0 V or less (vs. Li ⁺ / Li) Any substance can be selected from positive electrode active materials used for general lithium ion secondary battery positive electrodes, but oxides having a stable crystal structure in a high voltage region of about 5.0 V are preferable. _{Specifically, LiMnO 2, LiCoO 2, LiNiO} 2, or layered cathode active material represented by LiM3O ₂ such _{LiCrO 2, LiV 2 O 4,} LiMn 2 O 4, LiNi 0.5 Mn 1.5 O 4 And spinel-structured positive electrode active materials represented by LiM ₄ O ₄ such as LiCoMnO ₄ . In the above notation, M3 and M4 are Ni, Cu, Zn, Co, Fe, Mn, Cr, V, Ti, Mg, Al, Sn, Mo, Nb, V, Zr, Ta, Ru and At least one element selected from the group consisting of W is shown.
Further, in the general formula _{Li y M2 d X e O f} ( wherein, M2 is, Ni, Cu, Zn, Co , Fe, Mn, Cr, V, Ti, Mg, Al, Sn, Mo, Nb, V, Zr At least one element selected from the group consisting of Ta, Ru and W, X is a typical element which forms an anion by binding to oxygen (O), and the composition ratio y of Li is 0 or more and 2 Hereinafter, the positive electrode active material represented by the composition ratio d of M2 is 1 or more and 2 or less, the composition ratio e of X is 1 or more and 2 or less, and the composition ratio f of O is 3 or more and 7 or less. Specific examples of such a positive electrode active material include olivine-structured positive electrode active materials such as LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , and LiMnPO ₄ , and polyanion-based positive electrode active materials such as Li ₂ MnSiO ₄ .
The second particle according to the present embodiment may be formed by combining one type selected from among the plurality of types of positive electrode active materials described above with the first particle, but a combination of two or more types may be combined with the first particle. It may be complexed.

In addition, the second particle according to the present embodiment is a particle in which the electric conductivity at a density of 2.2 g / cm ³ exhibits a value of at least 1.0 × 10 ⁻⁵ S / m or more. The particles may be made only of particles, but the conductive material for improving the electric conductivity of the second particles may be attached to the particle surface or coated on the particle surface. In particular, among the positive electrode active materials forming the second particles, LiFePO ₄ or the like having an olivine structure does not have good electron conductivity, so it is preferable to coat the conductive material to form the second particles.

As the conductive material, at least one of a metal oxide and a carbon material can be used.
As the metal oxide, a compound which has dispersibility and lithium ion conductivity and is chemically stable is preferable. Specifically, SnO ₂ , TiO ₂ , SiO ₂ , V ₂ O ₃ , V ₂ O ₅ , WO ₃ , NiO, CuO, ZrO ₂ , TiO ₂ -P ₂ O _{5 and the} like can be mentioned. The TiO ₂ -P ₂ O ₅ may be doped with SnO ₂ , CuO, NiO, FeO or the like.
In the positive electrode active material forming the second particles, crystals are released when lithium ions are released in the range of 2.0 V (vs. Li ⁺ / Li) to 5.0 V (vs. Li ⁺ / Li) or less With respect to a positive electrode active material whose structure becomes unstable, in particular, a positive electrode active material in which the covalent bond between metal atom and oxygen atom is weak such as LiNiO ₂ etc., Al ₂ O ₃ , MgO, ZnO, TiO ₂ , ZrO ₂ , MoO it is preferable to coat _2, V ₂ O ₅ or the like of the metal oxide as the withstand voltage process.

As a carbon material, the carbon material utilized as a conductive support agent in a general lithium ion secondary battery can be used. Specific examples thereof include carbon particles such as natural graphite and carbon black, and carbon fibers such as carbon nanotubes and carbon nanohorns. Among carbon materials having a graphene structure, the surface spacing of the Miller index (002) surface corresponding to the graphene surface is preferably 0.38 nm or less. By this, the electron conductivity of the composite particle can be stably improved.

The second particle according to the present embodiment preferably contains an olivine-structured positive electrode active material in that the discharge voltage is high, the particle diameter can be appropriately controlled, and the electron conductivity is excellent. In particular, it is preferable to include an active material in which LiFePO ₄ , LiMnPO ₄ or its transition metal site is substituted with at least one element selected from the group consisting of Co, V, Mo, Ti, Al, Mg and Fe. Among these, an olivine structure positive electrode active material represented by a general formula LiMn _z Fe _1-z PO ₄ (in the formula, z is more than 0 and not more than 1) is preferable.

It is preferable that the particle sizes of the first particles and the second particles that constitute the composite particles according to the present embodiment be controlled.
The particle diameter of the first particles forming the composite particles is 50 nm or more and 800 nm or less, preferably 60 nm or more and 800 nm or less.
The particle diameter of the second particles forming the composite particles is 5 nm or more and 400 nm or less, preferably 10 nm or more and 200 nm or less, and more preferably 20 nm or more and 200 nm or less.
When the first particle and the second particle satisfy such a particle diameter relationship, it is possible to improve the electron conductivity in the composite particle without impairing the energy density.
In the present specification, the particle diameter is a particle observed on a scanning electron microscope (SEM) or a transmission electron microscope (TEM) on the outline of the particle image. It is defined as the distance of the largest of the distances between any two points present.

The BET specific surface area of the first particles forming the composite particles is 0.6 m ² / g or more and 15.0 m ² / g or less, preferably 0.8 m ² / g or more and 10.0 m ² / g or less, more preferably 1 .0m ² / g or more 8.0m ² / g or less.
Further, BET specific surface area of the second particles forming the composite particles, 3.0 m ² / g or more 80.0m ² / g or less, preferably 4.0 m ² / g or more 70.0m ² / g or less, more preferably Is 2.0 m ² / g or more and 60.0 m ² / g or less.
Since the 1st particle and the 2nd particle have a specific surface area of such a range, the fall of the tap density is suppressed and, therefore, the volumetric energy density of the manufactured battery can be maintained.
The BET specific surface area indicates the particle surface area per unit weight derived by the BET theory. For example, by using nitrogen as an adsorption gas, it is calculated from the adsorption amount at the equilibrium pressure and the adsorption isotherm at 77 K. be able to.

The average particle size of the second particles forming the composite particles is 1/2 or less, preferably 1/3 or less, more preferably 1/4 or less of the average particle size of the first particles forming the composite particles.
When the average particle size of the second particles is equal to or less than 1/2 of the average particle size of the first particles, the weight energy density and the volume energy density will be good.
The average particle diameter is defined as a median diameter (D ₅₀ ) based on the number of particles observed by observing several tens of fields of view using a scanning electron microscope or a transmission electron microscope.

The composite particles according to the present embodiment form secondary particles formed by combining the first particles and the second particles described above. A collection of the composite particles is used as a positive electrode material included in a positive electrode for a lithium ion secondary battery.
The composite particle according to the present embodiment may be a composite of the first particle and the second particle, and the above-described conductive material.
The electric conductivity of the composite particle thus made into a positive electrode material is 1.0 × 10 ⁻⁵ S / m or more. By using such composite particles, it is possible to compensate for the electron conductivity of the manganese-based solid solution positive electrode active material expected to have a high capacity. In addition, electrical conductivity is a value in the case where the powder of the composite particles is pressurized at a room temperature to make the density 2.2 g / cm ³ .

The particle size of the composite particles is 30 μm or less, preferably 0.5 μm or more and 30 μm or less.
If the particle size is 30 μm or less, granulation as composite particles is relatively easy.

In the composite particles, the first particles and the second particles are preferably uniformly dispersed. When these are uniformly dispersed, the conductive network inside the composite particle is properly constructed.
Therefore, in the composite particle used as the positive electrode material, at least a portion of the second particle is dispersed in a region where the distance from the center of the composite particle is a half or less of the radius of the composite particle. Is preferred. The center and the radius of the composite particle are the center and the radius of the area equivalent circle set in the electron microscope image.
In addition, it is preferable that the first particle contained in the composite particle has at least one second particle between the particle and the other first particle closest to the first particle. Preferably, the particles and the second particles are sintered. Such a configuration forms conductive paths between particles of the first particle.

The volume ratio V1 / V2 of the volume V1 of the first particle to the volume V2 of the second particle in any region of the composite particles is preferably more than 1.5, more preferably more than 2.0, More preferably, the value is more than 0, and more preferably, more than 4.0. The content of the first particles in the composite particles is preferably 30% by volume to 99% by volume, and the content of the second particles is preferably 1% by volume to 70% by volume .
When the first particle and the second particle satisfy such a volume relationship, the weight energy density and the volume energy density will be good.
The volume of each particle is a value calculated from the particle diameter described above assuming that the particle is spherical. The volume ratio can be calculated by counting the number of particles contained in a field of view of several μm square for composite particles of a predetermined thickness using a transmission electron microscope and determining the total volume occupied by each particle. . The volume ratio is observed for several tens of fields using a transmission electron microscope, and the arithmetic mean is determined.

The method of manufacturing the positive electrode material according to the present embodiment mainly includes the steps of mixing the raw materials, the steps of preparing the first particles, the steps of mixing the primary particles, and the step of granulating the composite particles. It contains.

In the step of mixing the raw materials, the lithium-containing compound, the manganese-containing compound, and the compound containing the element of M1, which are the raw materials of the first particles, are mixed to obtain a raw material powder.
The mixing of the raw materials can be carried out by using a general precision grinder such as a ball mill, jet mill, sand mill or the like.
Moreover, as a raw material of 1st particle | grains which concern on this embodiment, the compound containing the element of a lithium containing compound, a manganese containing compound, and M1 is used in the ratio which achieves the element composition ratio of a desired positive electrode active material, respectively.

Examples of lithium-containing compounds include lithium carbonate (Li ₂ CO ₃ ), lithium chloride (LiCl), lithium sulfate (Li ₂ SO ₄ ), lithium nitrate (LiNO ₃ ), lithium acetate (CH ₃ CO ₂ Li), water Lithium oxide (LiOH) or the like can be used.
Since lithium may volatilize during firing, the composition ratio of lithium after firing tends to be lower than the composition ratio of charge. Therefore, as the amount of the lithium-containing compound, it is preferable to use, as a raw material, an amount of about 1.01% by mass or more and 1.05% by mass or less of the amount corresponding to the desired composition.

Examples of manganese-containing compounds include manganese carbonate (MnCO ₃ ), manganese sulfate (MnSO ₄ ), manganese nitrate (Mn (NO ₃ ) ₂ ), manganese acetate (Mn (CH ₃ COO) ₂ ), manganese oxide (MnO) And manganese hydroxide (Mn (OH) ₂ ) can be used.

Moreover, as a compound containing the element of M1, oxides, carbonates, sulfates, acetates, borates and the like can be used.

In the step of preparing the first particles, the mixed compound is calcined to granulate the first particles which are primary particles.
The firing atmosphere may be performed under any of an inert gas atmosphere such as nitrogen or Ar and an oxidizing gas atmosphere such as in the air depending on the particles to be granulated.
The firing temperature can be set to a suitable temperature of about 500 ° C. or more and 1000 ° C. or less.

In the step of mixing primary particles, mixing of the primary particles and the second particles of the prepared first particles is performed. A dispersion medium such as pure water is used for mixing to obtain a slurry in which primary particles are dispersed.
In this step, when the first particles and the second particles are granulated as composite particles, it is necessary to appropriately manage the aggregation state of the first particles and the second particles. Then, when mixing primary particles, a primary particle is made into the state couple | bonded by adding a binder.
Examples of the binder include acetyl cellulose, polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone and the like.
Moreover, in order to improve the dispersibility of the first particles and the second particles, a dispersant such as polyacrylate can be used in combination.
In addition, what is necessary is just to mix the 2nd particle | grains according to the conventional method according to the classification of the particle | grains to be used.

In the step of granulating the composite particles, the slurry in which the primary particles are mixed and dispersed is spray-dried using a spray dryer. Then, the mixed first particles and second particles are fired to granulate the composite particles.
The firing temperature in this step is preferably 400 ° C. or less. It is because there exists a possibility that the battery characteristic of the primary particle which forms composite particles or composite particles as a calcination temperature is high heat of a grade which greatly exceeds 400 ° C, for example.
Moreover, it is preferable to remove the binder added at the time of mixing of primary particles by the heating at the time of baking. Therefore, as the binder, it is preferable to select one that can be removed by heating at 400 ° C. or less.
Note that the firing may be performed under any of an inert gas atmosphere such as nitrogen or Ar and an oxidizing gas atmosphere such as in the air.

The composite particles thus granulated can be used as a positive electrode material for a lithium ion secondary battery having a function as a positive electrode active material.
The positive electrode for a lithium ion secondary battery according to the present embodiment includes the steps of preparing a positive electrode mixture slurry mainly using the positive electrode material, the conductive material, and the binder described above, and using the positive electrode mixture slurry as a positive electrode current collector. It manufactures by passing through the process of coating, and the process of shape | molding a positive electrode. The manufactured positive electrode comprises a positive electrode material, a conductive material and a binder.

As a conductive material, the conductive material used for the general positive electrode for lithium ion secondary batteries can be used.
Specific examples of the conductive material include natural graphite powder, carbon fiber, carbon black, metal powder, conductive polymer and the like. Specifically, carbon black includes acetylene black, furnace black, thermal black, channel black and the like, metal powders include aluminum, nickel, copper, silver and the like, and conductive polymers include polyphenylene and the like.

As a binder, the binder used for the general positive electrode for lithium ion secondary batteries can be used.
Specifically, for example, fluorine-based resins such as polyvinylidene fluoride (PVDF), polytetrafluorinated ethylene, and polyhexafluoropropylene, styrene-based resins such as styrene-butadiene rubber, and olefins such as polyethylene and polypropylene Examples thereof include resins, acrylic resins such as polyacrylic acid, polymethacrylic acid and polyacrylonitrile, and cellulose resins such as carboxymethyl cellulose and hydroxyethyl cellulose.

In the step of preparing the positive electrode mixture slurry, the positive electrode active material, the binder, and the conductive material are mixed to prepare a positive electrode mixture slurry.
As the mixing means, it is preferable to use a high-viscosity stirrer having a relatively high shear force, and specific examples include a planetary mixer, a disperser mixer, and a rotation / revolution mixer.

Examples of the solvent used for mixing include amides such as N-methylpyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, alcohols such as methanol, ethanol, propanol and isopropanol, ethylene glycol, Examples thereof include polyhydric alcohols such as diethylene glycol and glycerin, ethers, dimethyl sulfoxide, tetrahydrofuran, water and the like.

In the step of applying the positive electrode mixture slurry to the positive electrode current collector, the prepared positive electrode mixture slurry is applied to the positive electrode current collector and dried to form a positive electrode mixture layer.
For coating of the positive electrode mixture slurry, general coating means such as a die coater, a gravure coater, and a doctor blade can be used.
As the positive electrode current collector, an aluminum foil or the like having a thickness of about 10 μm to 30 μm is generally used, but may be in the form of expanded metal, punching metal or the like.

The positive electrode current collector on which the positive electrode mixture layer is formed is compression molded by applying a predetermined pressure by a roll press or the like, and then cut or punched into a desired shape to obtain a positive electrode for a lithium ion secondary battery. The thickness of the positive electrode mixture layer formed by compression is, for example, about 50 μm to 300 μm.
The positive electrode for a lithium ion secondary battery produced through the above steps is applied to a lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery, a separator, and an electrolytic solution.
According to such a positive electrode according to the present embodiment, it is possible to obtain a lithium ion secondary battery excellent in rate characteristics, reduced in internal resistance, and improved in output.

In the negative electrode for lithium ion secondary batteries, a negative electrode mixture containing a negative electrode active material and a binder is coated on a negative electrode current collector, as in the case of a negative electrode used for a general lithium ion secondary battery. The negative electrode mixture layer formed and the negative electrode current collector are provided.
The negative electrode active material is not particularly limited as long as it is a negative electrode active material used for a general lithium ion secondary battery negative electrode, and, for example, graphite, coke, pyrolytic carbon, carbon fiber, hard carbon, amorphous Carbon materials such as carbon, lithium metal oxides such as Si, Ti, and Sn represented by lithium titanate, and elements such as Si, Al, Sn, Sb, In, Ga, alkaline earth metals and lithium Alloy, lithium metal, or a composite of these can be used.
In addition, as a binder in a negative electrode, the thing similar to the binder used in the above-mentioned positive electrode can be used. Moreover, the electrically conductive material used in the above-mentioned positive electrode can also be used.

A negative electrode for a lithium ion secondary battery is prepared by using a negative electrode active material, a conductive material, and a binder as main raw materials through a step of preparing a negative electrode mixture slurry and a step of applying a negative electrode mixture slurry to a negative electrode current collector. Manufactured.
In the step of preparing the negative electrode mixture slurry, the negative electrode active material and the binder solution are mixed in a solvent such as N-methyl pyrrolidone or water to prepare a negative electrode mixture slurry.
In the case where the negative electrode contains a conductive material, a desired amount may be weighed and mixed with the negative electrode active material and the binder.

In the step of applying the negative electrode mixture slurry to the negative electrode current collector, the prepared negative electrode mixture slurry is applied to the negative electrode current collector and dried to form a negative electrode mixture layer.
As the negative electrode current collector, a copper foil or the like having a thickness of about 5 μm to 20 μm is generally used, but may be in the form of expanded metal, punching metal or the like. Further, nickel or the like can be used instead of copper.
The negative electrode current collector on which the negative electrode mixture layer is formed is compression molded by applying a predetermined pressure by a roll press or the like, and then cut or punched into a desired shape to obtain a negative electrode for a lithium ion secondary battery. The thickness of the negative electrode mixture layer formed by compression is, for example, about 20 μm or more and 70 μm or less.

FIG. 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery according to the present embodiment.
The lithium ion secondary battery 1 has a cylindrical shape.
The positive electrode 2 and the negative electrode 3 are stacked and arranged so as to sandwich the separator 4 and wound, and are housed in a metal battery can 5 made of stainless steel (SUS) or aluminum.

As the separator 4, a microporous film made of a polyolefin such as polyethylene or polypropylene, a resin such as polyamide or aramid, or a fibrous glass can be used. The separator 4 may be coated with an insulating inorganic compound layer such as alumina or glass in order to improve heat resistance or flame retardancy.

The positive electrode 2 is electrically connected to the sealing lid 8 through the positive electrode lead 6, and the negative electrode 3 is electrically connected to the battery can 5 through the negative electrode lead 7. The positive electrode lead 6 and the negative electrode 3, negative electrode Insulating plates 10 are respectively disposed between the leads 7 and the positive electrode 2 to prevent a short circuit.
Thus, after the electrolyte is injected in dry air or under an inert gas atmosphere, the battery can 5 accommodating the electrodes is sealed by the gasket 9 and sealed by the sealing lid 8.
The exterior of the battery is not limited to the form shown in FIG. 1, and may be square, button-shaped or the like. In addition, it may be a bag-like aluminum laminate sheet or the like lined with an insulating sheet such as polyethylene or polypropylene.

A non-aqueous electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent is used as the electrolytic solution.
Examples of lithium salts include lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), and the like. Or it can be used combining multiple types.
As the non-aqueous solvent, linear or cyclic carbonate solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, and fluorine solvents such as perfluoroalkyl ether can be used. These carbonates may be fluorine-substituted derivatives or the like.
In addition, in order to improve battery life, vinylene carbonate, phenylcyclohexane, 1,3-propanesultone, diphenyl disulfide, etc. are added to the electrolytic solution, and in order to improve flame retardancy, phosphoric acid ester etc. May be added.

The application of the lithium ion secondary battery according to the present embodiment is not particularly limited, and, for example, a storage system for a natural energy power generation system such as solar light or wind power, an elevator for recovering a part of kinetic energy Etc., can be used as a large power source exemplified as a power source for industrial equipment such as a power source for various business use or household use, a power source for railways, ships, power vehicles such as electric vehicles and hybrid electric vehicles, and the like.
Further, it can be used as a small power source exemplified for various portable devices, information devices, household electric devices, electric tools, and the like.

EXAMPLES The present invention will next be described in detail by way of examples, which should not be construed as limiting the technical scope of the present invention.

The positive electrode material according to the present embodiment was manufactured, and the form of the composite particle was observed.

First particles in which the element of M1 in the general formula of the manganese solid solution positive electrode active material is Ni were prepared by the following procedure.
First, lithium carbonate, manganese carbonate and nickel carbonate were added to a zirconia pot, acetone was added, and the mixture was pulverized and mixed without dissolution using a planetary ball mill. And the obtained slurry was dried and the raw material powder was obtained.
The raw material powder was calcined at 500 ° C. for 12 hours in the air to obtain a calcined body of lithium transition metal oxide.
Subsequently, the calcined body was added to a zirconia pot, acetone was added, and the mixture was pulverized and mixed without dissolution using a planetary ball mill.
The obtained slurry was dried and then fired in the air at 1000 ° C. for 12 hours to obtain first particles.
Elemental analysis of the obtained first particles revealed that the composition was 0.5Li ₂ MnO ₃ -0.5LiNi _0.625 Mn _0.375 O ₂ .

Next, a second particle was prepared by the following procedure.
First, iron (III) citrate hydrate (FeC ₆ H ₅ O ₇ · n H ₂ O) as an Fe source, and manganese acetate tetrahydrate (Mn (CH ₃ COO) _2. 4 H ₂ O) as an Mn source Each was weighed so that Fe and Mn would be 2: 8 and dissolved in pure water, to which was added citric acid monohydrate (C ₆ H ₈ O ₇ .H ₂ O) as a chelating agent.
The amount of chelating agent added was such that the total amount of citrate ions was 80 mol% with respect to the total amount of metal ions. In addition, a chelating agent is added in order to prevent the formation of a precipitate and to dissolve the metal ion uniformly.
Next, lithium dihydrogen phosphate and a lithium acetate aqueous solution were added to obtain a raw material solution in which these were dissolved. The concentration of the raw material solution was adjusted so that the total concentration of iron ions and manganese ions was 0.2 mol / L. In addition, the composition ratio of Li, Fe and Mn, and PO ₄ was adjusted to be 1.05: 1: 1 to make the lithium excessive. The reason why lithium is used in excess is to suppress the occurrence of cation mixing between Li and Fe or Mn, and to compensate for the defects caused by the volatilization of part of Li at the time of firing.
Excess lithium reacts with phosphoric acid to form lithium phosphate (Li ₃ PO ₄ ), and the phase formed by this lithium phosphate may increase the internal resistance of the battery, according to the present embodiment. Composite particles have the advantage that the effect of this is reduced, as the conducting network is properly constructed.

Next, the prepared raw material solution was spray-dried using a spray dryer to obtain a raw material powder in which each element was uniformly dispersed in a citric acid matrix.
And the obtained raw material powder was temporarily baked at 400 degreeC in air over 10 hours using the box-type electric furnace.
To the obtained calcined body, sucrose was added in an amount of 7% by mass with respect to the total mass of the calcined body. Sucrose is added as a carbon source to form a carbon material of a conductive material. The sucrose also acts as a particle size control agent for the second particles to be prepared.
Subsequently, after adding pure water as a dispersion medium to the calcined body to which sucrose was added, it was mixed using a ball mill for 2 hours.

Next, the obtained slurry was spray-dried using a spray dryer to obtain a calcined powder.
Then, the calcined powder was subjected to main firing at 700 ° C. for 10 hours in an Ar gas atmosphere using a tubular furnace, to obtain second particles which are olivine-structured positive electrode active materials.
Elemental analysis of the obtained second particles revealed that the composition was LiFe _0.2 Mn _0.8 PO ₄ .

Next, the first particle of the composition of 0.5Li ₂ MnO ₃ -0.5LiNi _0.625 Mn _0.375 O ₂ obtained, and the _second of the composition of LiFe _0.2 Mn _0.8 PO ₄ are obtained. Composite particles were granulated from the particles.
First, the first particles and the second particles were dispersed in pure water and mixed using a ball mill.
Subsequently, polyvinyl alcohol as a binder was added so as to be 1% by mass with respect to the total weight of the first particles and the second particles, and further mixing was performed.
Then, the obtained slurry was spray-dried using a spray dryer to obtain a composite particle precursor powder.
Subsequently, the composite particle precursor powder was fired at 400 ° C. for 5 hours in a nitrogen gas atmosphere using an electric furnace to obtain composite particles.

Next, the positive electrode for lithium ion secondary batteries was produced using the obtained composite particle.
The positive electrode active material, the conductive additive and the binder are uniformly mixed to prepare a positive electrode slurry, the positive electrode slurry is applied on a 20 μm thick aluminum current collector foil, dried at 120 ° C., and the electrode density is adjusted by a press. An electrode plate was obtained by compression molding to 2.2 g / cm ³ . Thereafter, the electrode plate was punched into a disk shape having a diameter of 15 mm and used as a positive electrode.

The cross section of the produced positive electrode was observed by a scanning type microscope, a transmission type microscope and energy dispersive X-ray analysis, and the form of the composite particle contained in the positive electrode mixture layer in the positive electrode was observed.

FIG. 2: is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example.
In the positive electrode mixture layer observed, the composite particles 20 in the form shown in the figure were contained in a dispersed state.
The composite particle 20 includes a first particle 30 and a second particle 40, and aggregation of primary particles of the plurality of first particles 30 and primary particles of the plurality of second particles 40 is performed. The composite particles 20 were formed by
The conductive material 50 was attached to the surface of the second particle 40 to cover the second particle 40.
In this form, the second particles 40 are uniformly dispersed so as to be interposed between the dispersed first particles 30.

According to such a configuration, the second particles 40, which are positive electrode active materials, form a conductive network connecting the particles of the first particles 30, and therefore, in the positive electrode mixture layer without impairing the energy density. It is believed that the effect of improving the electron conductivity can be obtained.

FIG. 3: is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example.
In the positive electrode mixture layer observed, the composite particles 20 in the form shown in FIG. 3 were contained in a dispersed state.
The conductive material 50 was attached to the surface of the second particle 40 to cover the second particle 40.
In this embodiment, the second particles 40 are dispersed so as to be interposed between the dispersed first particles 30 in a state of being partially aggregated among the plurality of second particles 40.

According to such a configuration, the second particles 40, which are positive electrode active materials, form a conductive network connecting the particles of the first particles 30, and therefore, in the positive electrode mixture layer without impairing the energy density. It is believed that the effect of improving the electron conductivity can be obtained. Moreover, it is assumed that the effect is effective in spite of the fact that the second particles 40 are partially aggregated.

In the observation of the morphology, at least a part of the second particle is dispersed in a region where the distance to the center of the composite particle is a half or less of the radius of the composite particle for many composite particles 20 The condition was recognized. In addition, the content of the first particles in the composite particles was in the range of 30% by volume or more and 99% by volume or less.

From the observation of the form of the composite particle by the scanning microscope, the transmission type microscope and the energy dispersive X-ray analysis described above, the form shown in FIGS. 4 to 7 can be adopted as the positive electrode material according to the present embodiment. Conceivable.

FIG. 4: is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example.
In the embodiment shown in FIG. 4, the first particles 30 are made of a manganese-based solid solution positive electrode active material, and the second particles 40 are made of a positive electrode active material and have a plate-like particle shape.
The conductive material 50 adheres to the surface of the second particle 40 and covers the second particle 40.
In this form, the second particles 40 are dispersed so as to be interposed between the plurality of dispersed first particles 30, and the conductive material 50 covering the second particles 40 is the first Good contact with the surface of the particles 30 to form a conductive path.

According to such a configuration, the second particle 40, which is a positive electrode active material, forms a conductive network connecting the plurality of particles of the first particle 30, so that the positive electrode mixture can be obtained without losing the energy density. It is considered that the effect of improving the electron conductivity in the layer can be obtained.

FIG. 5: is a cross-sectional schematic diagram which shows one form of the composite particle contained in the positive electrode material which concerns on an Example.
In the embodiment shown in FIG. 5, the first particles 30 are made of a manganese-based solid solution positive electrode active material, and the second particles 41 are made of a positive electrode active material excellent in electron conductivity.
In this form, the second particles 41 themselves are not dispersed so that the second particles 41 whose surfaces are not covered with the conductive material 50 intervene between the respective particles of the dispersed first particles 30, and the second particles 41 themselves , Form a conductive path between the particles of the first particle 30.

According to such a configuration, the second particles 41, which are positive electrode active materials, form a conductive network connecting the particles of the first particles 30, so that in the positive electrode mixture layer, the energy density is not impaired. It is believed that the effect of improving the electron conductivity can be obtained. Also, the effect on the energy density is advantageous because it does not include the conductive material 50.

FIG. 6 is a schematic cross-sectional view showing one form of composite particles contained in the positive electrode material according to the example.
In the embodiment shown in FIG. 6, the first particles 30 are made of a manganese-based solid solution positive electrode active material, and the second particles 40 are made of a positive electrode active material. The composite particle 20 includes the first particle 30, the second particle 40, and the conductive material particle 50A, and the primary particles of the plurality of first particles 30 and the primary particles of the plurality of second particles 40. The composite particles 20 are formed by aggregation of the particles and the plurality of conductive material particles 50A.
In addition, the conductive material 50 adheres to the surface of the second particle 40 and covers the second particle 40.
In this embodiment, the second particles 40 and the conductive material particles 50A are dispersed so as to be interposed between the dispersed first particles 30 and the conductive material covering the second particles 40. 50 and the dispersed conductive material particles 50A form a conductive path between the particles of the first particles 30.

According to such a configuration, the second particle 40 and the conductive material particle 50A form a conductive network connecting the particles of the first particle 30, so that the electron conductivity in the positive electrode mixture layer is improved. It is thought that an effect can be obtained. In addition, since a part of the conductive network connecting the particles of the first particle 30 is formed by the second particle 40 which is a positive electrode active material, it is presumed that the energy density is unlikely to be impaired.

FIG. 7 is a schematic cross-sectional view showing one form of composite particles contained in a positive electrode material according to an example.
The positive electrode mixture layer contains a large number of composite particles 20 in the form shown in the figure in a dispersed state.
In the embodiment shown in FIG. 7, the first particles 30 are made of a manganese-based solid solution positive electrode active material, and the second particles 40 are made of a positive electrode active material. The composite particle 20 includes a first particle 30, a second particle 40, and a fibrous conductive material 50B. The composite particle 20 includes primary particles of the plurality of first particles 30 and a plurality of second particles 40. Composite particles 20 are formed by the aggregation of primary particles.
In addition, the conductive material 50 adheres to the surface of the second particle 40 and covers the second particle 40.
In this embodiment, the second particles 40 and the fibrous conductive material 50B are dispersed so as to be interposed between the respective particles of the dispersed first particles 30, and the second particles 40 are coated. The material 50 and the dispersed fibrous conductive material 50 B form a conductive path between the particles of the first particles 30.

According to such a configuration, the second particle 40 and the fibrous conductive material 50B form a conductive network connecting the particles of the first particle 20, so the electron conductivity in the positive electrode mixture layer is improved. It is believed that the effect of In addition, since the second particle 40, which is a positive electrode active material, constitutes a part of the conductive network connecting the particles of the first particle 30, energy density is unlikely to be impaired, and the effect on the electron conductivity is The conductive material 50B is considered to be advantageous because a conductive network connecting the plurality of particles of the first particle 30 is formed.

FIG. 8 is a schematic cross-sectional view showing one form of positive electrode active material particles contained in a positive electrode material according to a comparative example.
Among positive electrodes of conventional lithium ion secondary batteries, there are positive electrodes in which other primary particles 40C are used in combination with positive electrode active material particles 30C which are primary particles.
In the dispersed state of particles in such a conventional positive electrode material (comparative example), a particle group in which positive electrode active material particles 30C are aggregated and a particle group in which other primary particles 40C are aggregated are usually aggregated. It is represented by the state as shown in FIG.
In such a form, there is a possibility that good electron conductivity may not be secured in positive electrode active material particles 30C and the like existing near the center of the region (inside the left broken line) where positive electrode active material particles 30C are aggregated. It is believed that the volume and weight energy density are diminished.

REFERENCE SIGNS LIST 1 lithium ion secondary battery 2 positive electrode for lithium ion secondary battery 3 negative electrode for lithium ion secondary battery 4 separator 5 battery can 6 positive electrode lead 7 negative electrode lead 8 sealing lid 9 gasket 10 insulating plate 20 composite particles 30 first particles 40 , 41 second particles 50, 50A, 50B conductive material (particles)

Claims (13)

1. General formula Li _x Mn _a M1 _b O ₂
   (Wherein, M 1 is at least selected from the group consisting of Ni, Cu, Zn, Co, Fe, Cr, V, Ti, Mg, Al, Sn, Mo, Nb, V, Zr, Ta, Ru and W It is one kind of element, and is a positive electrode active material represented by 1.0 <x ≦ 1.4, 0 <a <1.0, 0 <b <1.0, a + b ≦ 1.0). The first particle,
   A second particle having an electrical conductivity of 1.0 × 10 ⁻⁵ S / m or more,
   A positive electrode material for a lithium ion secondary battery, comprising: composite particles of
2. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein an average particle diameter of the first particles is 50 nm or more and 800 nm or less.
3. 2. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein an average particle size of the second particles is 5 nm or more and 400 nm or less.
4. In the composite particle,
   In a region where the distance to the center of the composite particle is a distance of 1/2 or less of the radius,
   The positive electrode material for a lithium ion secondary battery according to claim 1, wherein at least a part of the second particles is dispersed.
5. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein an average particle diameter of the composite particles is 0.5 μm or more and 30 μm or less.
6. The content of the said 1st particle | grains in the said composite particle is 30 volume% or more and 99 volume% or less, The positive electrode material for lithium ion secondary batteries of Claim 1 characterized by the above-mentioned.
7. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the second particle is a positive electrode active material capable of inserting and extracting lithium ions at 2.0 V or more and 5.0 V or less. .
8. The positive electrode material for a lithium ion secondary battery according to claim 7, wherein the second particles are coated with a carbon material.
9. The second particle is
   General formula Li _y M2 _d X _e O _f
   (Wherein, M 2 is selected from the group consisting of Ni, Cu, Zn, Co, Fe, Mn, Cr, V, Ti, Mg, Al, Sn, Mo, Nb, V, Zr, Ta, Ru and W X is a typical element which forms an anion by binding to oxygen (O), and 0 ≦ y ≦ 2, 1 ≦ d ≦ 2, 1 ≦ e ≦ 2, 3 ≦ f ≦ 7)
   The positive electrode active material for a lithium ion secondary battery according to claim 1, which is a positive electrode active material represented by
10. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the second particle is a positive electrode active material having an olivine structure.
11. It is a manufacturing method of the positive electrode material for lithium ion secondary batteries according to claim 1,
    Mixing the lithium-containing compound, the manganese-containing compound, and the compound containing the element of M1;
    Calcining the mixed compound to prepare the first particles;
    Mixing the prepared first particles and the second particles;
    Calcinating the mixed first particles and the second particles to granulate composite particles;
    A method for producing a positive electrode material for a lithium ion secondary battery, comprising:
12. A positive electrode for a lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 10.
13. A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 12.

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