JP2018163764A - Electrode material for lithium ion secondary battery, electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an electrode material which enables the improvement in an input characteristic of a lithium ion secondary battery; an electrode including the electrode material; and a lithium ion secondary battery having the electrode.SOLUTION: An electrode material for a lithium ion secondary battery according to the present invention comprises core particles of a substance represented by the general formula, LiFeMnMPO(where 0.05≤x≤1.0 and 0≤y≤0.14, provided that M is at least one kind element selected from Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge and rare earth elements), and a carbonaceous coating which covers the surface of each core particle. As to the electrode material, the ratio (I/I) of a D band peak intensity and a G band peak intensity in Raman spectra obtained by Raman spectroscopic measurement is 1.10 or more and 1.55 or less, and the ratio (DBP/NMP) of a DBP oil absorption and a NMP oil absorption is 1.3 or less. An electrode for a lithium ion secondary battery according to the invention comprises the electrode material for a lithium ion secondary battery according to the invention. A lithium ion secondary battery according to the invention comprises a positive electrode, a negative electrode and a nonaqueous electrolyte, which has, as the positive electrode, the electrode for a lithium ion secondary battery according to the invention.SELECTED DRAWING: None

Description

  The present invention relates to an electrode material for a lithium ion secondary battery, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  In recent years, with the rapid development of clean energy technology, it is necessary to create an environment that is friendly to the earth, such as oil removal, zero emission, and the spread of power-saving products. In particular, recently, a large-capacity storage battery that supplies electric energy to electric vehicles, a large-capacity storage battery that supplies electric energy in the event of an emergency or disaster, portable information devices, and portable information It is a secondary battery that supplies electric energy to a terminal or the like. As the secondary battery, for example, a lead storage battery, an alkaline storage battery, a lithium ion battery, and the like are known. In particular, a lithium ion battery can be reduced in size, weight, and capacity, and has excellent characteristics such as high output and high energy density. For this reason, it has been commercialized as a high-output power source for electric tools and other electric tools, and the development of materials for next-generation lithium ion secondary batteries has become active all over the world.

  Recently, HEMS (Home Energy Management System) has been spotlighted as a collaboration between a large-capacity storage battery that supplies electric energy and a house. HEMS is a system that intelligently consumes energy by managing information related to household electricity and control systems such as smart home appliances, electric vehicles, and solar power generation to manage automatic control, optimization of power supply and demand, etc. is there.

LiCoO ₂ and LiMnO ₂ are common as electrode active materials used for the positive electrodes of lithium ion batteries that are currently in practical use. However, Co is unevenly distributed on the earth and is a scarce resource. Therefore, when used in large quantities, there are problems in that the product cost increases and stable supply becomes difficult. Therefore, as a positive electrode active material replacing LiCoO ₂ , spinel-based LiMn ₂ O ₄ , ternary LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , lithium ferrate (LiFeO ₂ ), lithium iron phosphate Research and development of positive electrode active materials such as (LiFePO ₄ ) has been actively promoted. Among these electrode materials, LiFePO ₄ having an olivine structure has attracted attention as an electrode material that has no problem in terms of resources and cost as well as safety. This olivine-based electrode material typified by LiFePO ₄ contains phosphorus as a constituent element and is strongly covalently bonded to oxygen. Therefore, the olivine-based electrode material is superior in safety because there is no risk of releasing oxygen at a high temperature compared to electrode materials such as LiCoO ₂ and there is no risk of ignition due to oxidative decomposition of the electrolyte. It is.

However, LiFePO ₄ having such advantages also has a problem of low electron conductivity. This low electronic conductivity is considered to be the slow diffusion of lithium ions inside the active material derived from the structure and the low electronic conductivity. Therefore, as a method for improving the electron conductivity of the electrode active material, a method for uniformly depositing a conductive carbonaceous material obtained by pyrolyzing an organic substance on the surface of the electrode active material has been proposed (for example, Patent Documents). 1).

Furthermore, it is known that the degree of development of the graphite structure of the carbonaceous film covering the surface of the electrode active material can be evaluated by the peak intensity ratio (I _D / I _G ) of the G band and D band of the Raman spectrum (patent) Reference 2). Then, by 0.9 or less the value of I D _/ I _G, able to develop a graphite structure of the carbonaceous film, thereby further can improve the electron conductivity of the electrode active material, a positive electrode The internal resistance can be reduced.

JP 2001-015111 A International Publication No. 2016/178280 Pamphlet

However, even if the peak intensity ratio (I _D / I _G ) of the D band and G band is lowered and the graphite structure of the carbonaceous film covering the surface of the electrode active material is developed, the lithium ion secondary battery In some cases, the input characteristics are not good, and on the contrary, it becomes worse.
Then, an object of this invention is to provide the electrode material which can improve the input characteristic of a lithium ion secondary battery, the electrode containing the electrode material, and the lithium ion secondary battery which has the electrode.

The inventors of the present invention have intensively studied to solve the above problems. As a result, when the inventors develop the graphite structure of the carbonaceous film that covers the surface of the electrode active material, the electron conductivity of the electrode active material is improved, but the ionic conductivity of the electrode active material is decreased. I found. The inventors of the present invention have a peak intensity ratio (I _D / I _G ) between the D band and the G band within a predetermined range, and a ratio between the DBP oil absorption amount and the NMP oil absorption amount (DBP / NMP) is a predetermined value. The inventors have found that the input characteristics of a lithium ion secondary battery can be improved by using the following electrode materials, and have completed the present invention. That is, the present invention is as follows.

[1] General formula LiFe _x Mn _{1- xy My} PO ₄ (0.05 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.14, where M is Mg, Ca, Co, Sr, Ba , Ti, Zn, B, Al, Ga, In, Si, Ge, and a rare earth element), and a carbonaceous film covering the surface of the center particle, The peak intensity ratio (I _D / I _G ) of the D band and G band of the Raman spectrum obtained by spectroscopic measurement is 1.10 to 1.55, and the ratio of DBP oil absorption and NMP oil absorption (DBP / NMP) ) Is a lithium ion secondary battery electrode material having a value of 1.3 or less.
[2] The lithium ion concentration according to the above [1], wherein the peak intensity ratio (I _D / I _G ) of the D band and G band of the Raman spectrum obtained by Raman spectroscopy is 1.25 or more and 1.45 or less. Secondary battery electrode material.
[3] The electrode material for a lithium ion secondary battery according to the above [1] or [2], wherein the ratio of DBP oil absorption and NMP oil absorption (DBP / NMP) is 1.20 or more and 1.24 or less.
[4] An electrode for a lithium ion secondary battery comprising the electrode material for a lithium ion secondary battery according to any one of [1] to [3].
[5] A lithium ion secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode has the electrode for a lithium ion secondary battery according to the above [4].

  ADVANTAGE OF THE INVENTION According to this invention, the electrode material which can improve the input characteristic of a lithium ion secondary battery, the electrode containing the electrode material, and the lithium ion secondary battery which has the electrode can be provided.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[Electrode materials for lithium ion secondary batteries]
The electrode material for a lithium ion secondary battery of the present embodiment (hereinafter simply referred to as an electrode material) has a general formula of LiFe _x Mn _{1- xy My} PO ₄ (0.05 ≦ x ≦ 1.0, 0 ≦ y). ≦ 0.14, where M is represented by at least one selected from Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements) The peak intensity ratio (I _D / I _G ) of the Raman spectrum obtained by Raman spectroscopy includes a center particle and a carbonaceous film that covers the surface of the center particle, and is 1.10 or more and 1 The ratio of DBP oil absorption and NMP oil absorption (DBP / NMP) is 1.3 or less. Thereby, the input characteristic of a lithium ion secondary battery can be improved.

(Center particle)
The central particles used in the electrode material of the present embodiment have a general formula of LiFe _x Mn _{1- xy My} PO ₄ (0.05 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.14, where M Is a central particle represented by at least one selected from Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements. The rare earth elements are 15 elements of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, which are lanthanum series. Further, the central particles used in the electrode material of the present embodiment may be one kind of central particles represented by the general formula LiFe _x Mn _{1- xy My} PO ₄ or a combination of two or more kinds. Or a central particle.

The specific surface area of the center particles used for the electrode material of the present embodiment is preferably 5 m ² / g or more and 30 m ² / g or less, more preferably 9 m ² / g or more and 25 m ² / g or less.
When the specific surface area of the center particles is 5 m ² / g or more, the time required for the movement of lithium ions and electrons in the center particles can be shortened, and the output characteristics of the lithium ion secondary battery can be improved. When the specific surface area of the center particles is 30 m ² / g or less, an increase in the weight of the carbonaceous film accompanying an increase in the specific surface area of the center particles can be suppressed, and the charge / discharge capacity can be increased. The specific surface area of the center particle is a specific surface area measured by the BET method.

(Carbonaceous film)
The carbonaceous film used for the electrode material of the present embodiment covers the surface of the center particle and improves the electron conductivity of the electrode material. The coverage of the carbonaceous film is preferably 60% or more, and more preferably 80% or more and 95% or less.
When the coverage of the carbonaceous film is 60% or more, the coating effect of the carbonaceous film can be sufficiently obtained.
The coverage of the carbonaceous film can be measured using a transmission electron microscope (TEM), an energy dispersive X-ray spectrometer (EDX), or the like.

The film thickness of the carbonaceous film is preferably 1.0 nm or more and 10.0 nm or less, and the average film thickness of the carbonaceous film is preferably 2.0 nm or more and 7.0 nm or less.
It can suppress that the sum total of the movement resistance of the electron in a carbonaceous film becomes it that the average film thickness of a carbonaceous film is 2.0 nm or more. Thereby, the raise of the internal resistance of a lithium ion secondary battery can be suppressed, and the voltage fall in a high-speed charge / discharge rate can be prevented. Further, when the average film thickness of the carbonaceous film is 7.0 nm or less, the formation of steric hindrance that hinders lithium ions from diffusing in the carbonaceous film can be suppressed. Becomes lower. As a result, an increase in the internal resistance of the battery is suppressed, and a voltage drop at a high speed charge / discharge rate can be prevented.
Moreover, when the film thickness of the carbonaceous film is 1.0 nm or more, it becomes easy to make the average film thickness of the carbonaceous film 2.0 nm or more, and when the film thickness is 10.0 nm or less, the average film It becomes easy to make the thickness 7.0 nm or less.
The film thickness of the carbonaceous film can be measured using a transmission electron microscope.

The “internal resistance” referred to here is mainly the sum of the charge transfer resistance and the lithium ion transfer resistance, and the charge transfer resistance is proportional to the thickness of the carbonaceous film, the density of the carbonaceous film, and the crystallinity. The lithium ion migration resistance is inversely proportional to the film thickness of the carbonaceous film, the density of the carbonaceous film, and the crystallinity.
As an evaluation method of the internal resistance, for example, a current pause method or the like is used. In this current pause method, the internal resistance is the wiring resistance, contact resistance, charge transfer resistance, lithium ion transfer resistance, lithium reaction resistance at the positive and negative electrodes, interelectrode resistance determined by the distance between the positive and negative electrodes, lithium ion solvation, desolvation It is measured as the sum of the resistance related to the sum and the SEI (Solid Electrolyte Interface) movement resistance of lithium ions.

The density of the carbonaceous film calculated from the carbon content of the carbonaceous film, the average film thickness of the carbonaceous film, the coverage of the carbonaceous film, and the specific surface area of the electrode material is 0.3 g / cm ³ or more and 1.5 g / cm. It is preferably ³ or less, and more preferably 0.4 g / cm ³ or more and 1.0 g / cm ³ or less.
Here, the reason why the density of the carbonaceous film is limited to the above range is that if the density of the carbonaceous film calculated by the carbon content of the carbonaceous film is 0.3 g / cm ³ or more, the carbonaceous film is This is because sufficient electronic conductivity is exhibited. On the other hand, if the density of the carbonaceous film is 1.5 g / cm ³ or less, since the graphite microcrystal having a layered structure is small in the carbonaceous film, when lithium ions diffuse in the carbonaceous film. No steric hindrance due to graphite microcrystals. Thereby, lithium ion movement resistance does not become high. As a result, the internal resistance of the lithium ion secondary battery does not increase, and the voltage drop at the high-speed charge / discharge rate of the lithium ion secondary battery does not occur.

( _ID / _IG )
The peak intensity ratio (I _D / I _G ) of the D band and G band of the Raman spectrum obtained by the Raman spectroscopic measurement of the electrode material of this embodiment is 1.10 or more and 1.55 or less, preferably 1. 25 or more and 1.45 or less.
When the peak intensity ratio (I _D / I _G ) between the D band and the G band is less than 1.10, the ion conductivity of the electrode material is deteriorated, and the input characteristics of the lithium ion secondary battery may be deteriorated. Further, when the peak intensity ratio (I _D / I _G ) of the D band and the G band is larger than 1.55, the electron conductivity of the electrode material is deteriorated, and the input characteristics of the lithium ion secondary battery may be deteriorated. is there.
The G band is a peak appearing in the vicinity of 1590 cm ^{−1 of} the Raman spectrum, and is a peak attributed to the graphite structure of the carbonaceous film. On the other hand, the D band is a peak that appears in the vicinity of 1350 cm ^{−1 of} the Raman spectrum and is a peak due to a defect in the carbonaceous film.

(DBP / NMP)
The ratio of DBP oil absorption and NMP oil absorption (DBP / NMP) is 1.3 or less, preferably 1.20 or more and 1.24 or less.
If the ratio of DBP oil absorption amount and NMP oil absorption amount (DBP / NMP) is larger than 1.3, the ion conductivity of the electrode material may be deteriorated, and the input characteristics of the lithium ion secondary battery may be deteriorated.
The NMP oil absorption is an electrode in accordance with JIS K 5101-13-1 “Purified linseed oil method” except that N-methyl-2-pyrrolidinone (NMP) is used instead of linseed oil. This is the value measured for the material. In addition, the DBP oil absorption was measured for electrode materials in accordance with JIS K 5101-13-1 “Purified Soiled Oil Method” except that dibutyl phthalate (DBP) was used instead of oil. Value.

The value of the peak intensity ratio (I _D / I _G ) of the D band and G band of the Raman spectrum obtained by the Raman spectroscopic measurement of the electrode material is mainly attributed to the crystal state of the carbonaceous film. On the other hand, the ratio of DBP oil absorption and NMP oil absorption (DBP / NMP) is mainly attributed to the shape of the carbonaceous film. The combination of the crystalline state of the carbonaceous film suitable for improving the input characteristics of the lithium ion secondary battery and the shape of the carbonaceous film suitable for improving the input characteristics of the lithium ion secondary battery, that is, the electrode The peak intensity ratio (I _D / I _G ) of the D band and G band of the Raman spectrum obtained by Raman spectroscopic measurement of the material is 1.10 or more and 1.55 or less, and the DBP oil absorption amount and the NMP oil absorption amount are By setting the ratio (DBP / NMP) to 1.3 or less, the input characteristics of the lithium ion secondary battery can be further improved.

(Carbon content)
The carbon amount of the electrode material of the present embodiment, that is, the carbon amount of carbon forming the carbonaceous film is preferably 0.3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the center particle. More preferably, it is 6 parts by mass or more and 3 parts by mass or less.
When the carbon amount of the electrode material is 0.3 parts by mass or more, the discharge capacity at the high-speed charge / discharge rate of the lithium ion secondary battery is increased, and sufficient charge / discharge rate performance can be realized. On the other hand, when the carbon content is 10 parts by mass or less, the battery capacity of the lithium ion secondary battery per unit mass of the electrode material can be increased.

(Specific surface area)
The specific surface area of the electrode material of the present embodiment is preferably 5 m ² / g or more and 30 m ² / g or less, more preferably 9 m ² / g or more and 25 m ² / g or less.
When the specific surface area of the electrode material is 5 m ² / g or more, coarsening of the electrode material can be suppressed and the diffusion rate of lithium ions can be increased. Thereby, the battery characteristic of a lithium ion secondary battery can be improved. On the other hand, since the electrode density can be increased when the specific surface area of the electrode material is 30 m ² / g or less, the energy density of the lithium ion secondary battery can be increased. The specific surface area of the electrode material is a specific surface area measured by the BET method.

(Average particle size of primary particles)
The average particle diameter of the primary particles of the electrode material of the present embodiment is preferably 0.01 μm or more and 5 μm or less, more preferably 0.02 μm or more and 2 μm or less.
When the average primary particle diameter of the electrode material is 0.01 μm or more, an increase in carbon mass due to an increase in the specific surface area of the electrode material can be suppressed, thereby reducing the charge / discharge capacity of the lithium ion secondary battery. Can be suppressed. On the other hand, when the average primary particle diameter of the electrode material is 5 μm or less, the movement time of lithium ions or the movement time of electrons moving through the electrode material can be shortened. Thereby, the deterioration of the output characteristic resulting from the increase in the internal resistance of the lithium ion secondary battery can be suppressed.

  Here, the average particle diameter is a volume average particle diameter. The average particle size of the primary particles is selected by randomly selecting 100 primary particles, and measuring the particle size (major axis) of each primary particle with a scanning electron microscope (SEM). It can be obtained as a value.

(Average particle size of secondary particles)
The average particle diameter of the secondary particles formed by aggregating a plurality of primary particles of the electrode material of the present embodiment is preferably 0.5 μm or more and 20 μm or less, more preferably 0.7 μm or more and 10 μm or less.
When the average particle diameter of the secondary particles of the electrode material is 0.5 μm or more, the electrode material, the conductive additive, the binder resin (binder), and the solvent are mixed to prepare an electrode material paste for a lithium ion secondary battery. When preparing, it can suppress that a conductive support agent and a binder are needed in large quantities. Thereby, the battery capacity of the lithium ion secondary battery per unit mass in the electrode material layer of the positive electrode of the lithium ion secondary battery can be increased. On the other hand, when the average particle diameter of the secondary particles of the electrode material is 20 μm or less, the dispersibility and uniformity of the conductive additive and the binder in the electrode material layer of the positive electrode of the lithium ion secondary battery can be increased. it can. As a result, the discharge capacity in high-speed charge / discharge of the lithium ion secondary battery is increased.

  Here, the average particle diameter is a volume average particle diameter. The average particle diameter of the secondary particles of the electrode material can be measured using a laser diffraction scattering type particle size distribution measuring device or the like. Alternatively, 100 secondary particles may be selected at random, and the major axis and minor axis of each secondary particle may be measured with a scanning electron microscope (SEM) to obtain the average value. .

[Method for producing electrode material]
The electrode material of this embodiment can be manufactured, for example, by the following electrode material manufacturing method. The manufacturing method of the electrode material of the present embodiment has the general formula LiFe _x Mn _{1- xy My} PO ₄ (0.05 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.14, where M is Mg , Ca, Co, Sr, Ba, Ti, Zn, B, at least one selected from the group consisting of Al, Ga, In, Si, Ge, and rare earth elements), a carbon film precursor, water A step (A) of producing a slurry containing a slurry, a step (B) of drying the slurry to produce a dried product of the slurry, and a step of firing the dried product in a non-oxidizing atmosphere of 500 ° C. or higher and 1000 ° C. or lower. (C) is included.

(Process (A))
In the step (A), the general formula LiFe _x Mn _{1- xy My} PO ₄ (0.05 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.14, where M is Mg, Ca, Co, A slurry containing central particles represented by Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements), a carbon film precursor, and water. Make it.

The central particles used in the method for producing an electrode material have the general formula LiFe _x Mn _{1- xy My} PO ₄ (0.05 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.14, where M is Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and a rare earth element).
For example, LiFe _x Mn _{1- xy My} PO ₄ is a slurry-like mixture obtained by mixing a Li source, a divalent iron salt, a phosphoric acid compound, and water using a pressure-resistant airtight container. Obtained by thermal synthesis. The Li source is selected from the group consisting of lithium salts such as lithium acetate (LiCH ₃ COO) and lithium chloride (LiCl), and lithium hydroxide (LiOH). Examples of the divalent iron salt include iron (II) chloride (FeCl ₂ ), iron (II) acetate (Fe (CH ₃ COO) ₂ ), and iron (II) sulfate (FeSO ₄ ). Examples of the phosphoric acid compound include phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and diammonium hydrogen phosphate ((NH ₄ ) 2 HPO ₄ ).

  The compounding amount of the carbon film precursor when converted to carbon element with respect to 100 parts by mass of the central particles is 1.0 part by mass or more and 5.0 parts by mass or less, preferably 2.5 parts by mass or more and 10 parts by mass or less. It is. When the compounding amount of the carbon film precursor when converted to carbon element with respect to 100 parts by mass of the center particle is 1.0 part by mass or more and 5.0 parts by mass or less, the carbon amount of the electrode material is about 0.8. It can be set to be not less than 2.5% by mass.

  Examples of the organic compound used as the carbonaceous film precursor include polyvinyl alcohol (PVA), polyvinyl pyrrolidone, cellulose, starch, gelatin, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polystyrene sulfonic acid, polyacrylamide, and polyvinyl acetate. Glucose, fructose, galactose, mannose, maltose, sucrose, lactose, glycogen, pectin, alginic acid, glucomannan, chitin, hyaluronic acid, chondroitin, agarose, polyether, dihydric alcohol, trihydric alcohol, phenol resin, etc. . These may be used alone or in combination of two or more. Among these carbonaceous film precursors, a particularly preferred carbonaceous film precursor is a mixture of polyvinyl alcohol (PVA), sucrose and a phenol resin.

The compounding ratio of the organic compound with respect to the center particle is preferably 0.8 part by mass or more and 2.5 parts by mass or less with respect to 100 parts by mass of the center particle when the total amount of the organic compound is converted into the carbon amount.
Here, when the compounding ratio in terms of carbon amount of the organic compound is 0.8 parts by mass or more, when a secondary battery is formed, the discharge capacity at the high-speed charge / discharge rate is increased, and sufficient charge / discharge rate performance is realized. It becomes possible to do. When the compounding ratio in terms of carbon amount of the organic compound is 2.5 parts by mass or less, the average film thickness of the carbonaceous film can be 3.0 nm or less.

These center particles and the organic compound are dissolved or dispersed in water to prepare a uniform slurry. In this dissolution or dispersion, a dispersant may be added.
The method for dissolving or dispersing the center particles and the organic compound in water is not particularly limited as long as the center particles are dispersed and the organic compound is dissolved or dispersed. Examples of the apparatus for dissolving or dispersing the organic compound include a medium stirring type dispersion apparatus that stirs medium particles at high speed, such as a planetary ball mill, a vibration ball mill, a bead mill, a paint shaker, and an attritor. The organic compound is preferably a saccharide whose structure contains a large amount of oxygen. Monosaccharides and disaccharides are more preferable. When there is much oxygen, the part which will be cleaved during baking will increase and it will be easy to form the pore in a carbon layer.

  In this dissolution or dispersion, it is preferable to disperse the central particles as primary particles, and then stir to add and dissolve the organic compound. In this way, the surface of the primary particle of the central particle is coated with the organic compound, and as a result, the carbon derived from the organic compound is uniformly interposed between the primary particles of the central particle.

(Process (B))
In the step (B), the slurry is dried to produce a dried product of the slurry. For example, this slurry is sprayed in a high-temperature atmosphere, for example, air of 70 ° C. or higher and 250 ° C. or lower and dried.

(Process (C))
In the step (C), the dried product is fired at a firing temperature in the range of 500 ° C. to 1000 ° C., preferably 600 ° C. to 900 ° C. The firing time is, for example, not less than 0.1 hour and not more than 40 hours.
If the firing temperature is less than 500 ° C., the decomposition and reaction of the organic compound contained in the dried product obtained by drying the slurry does not proceed sufficiently, and the organic compound may not be sufficiently carbonized. As a result, a decomposition product of a high-resistance organic compound may be generated in the obtained electrode material. When the firing temperature is higher than 1000 ° C., Li in the center particles may evaporate and a composition shift may occur in the center particles. When the composition shift occurs, the grain growth of the center particle is promoted, and as a result, the discharge capacity at the high-speed charge / discharge rate is reduced, and it may be difficult to realize sufficient charge / discharge rate performance.

As this non-oxidizing atmosphere, an inert atmosphere such as nitrogen (N ₂ ) and argon (Ar) is preferable, and when it is desired to suppress oxidation more, a reducing gas such as hydrogen (H ₂ ) is contained in a volume of about several volume%. A reducing atmosphere is preferred.

In this firing process, it is possible to control the pore size distribution of the obtained electrode material by appropriately adjusting the conditions for firing the dried slurry, for example, the heating rate, maximum holding temperature, holding time, etc. It is.
As described above, the surface of the primary particles of the central particles is coated with the carbon generated by the thermal decomposition of the organic compound in the dried product, and thus the electrode composed of secondary particles in which carbon is interposed between the primary particles of the central particles. A material is obtained.

[Electrode for lithium ion secondary battery]
The electrode for a lithium ion secondary battery of the present embodiment (hereinafter simply referred to as an electrode) includes the electrode material of the present embodiment.
In order to produce the electrode of this embodiment, for example, the electrode material of this embodiment, a binder composed of a binder resin, and a solvent are mixed to prepare an electrode-forming paint or an electrode-forming paste. At this time, a conductive aid such as carbon black may be further added as necessary.
As the binder, that is, the binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, and the like are preferably used.
Although the compounding quantity of binder resin with respect to said electrode material is not specifically limited, For example, binder resin is 1 mass part or more and 30 mass parts or less with respect to 100 mass parts of electrode materials, Preferably they are 3 mass parts or more and 20 mass parts or less. To do.

  Examples of the solvent used for the electrode-forming paint or electrode-forming paste include water; methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol and diacetone alcohol. Alcohols; ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, esters such as γ-butyrolactone; diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol mono Ethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethyl Ethers such as glycol monoethyl ether; Ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone, and cyclohexanone; Amides such as dimethylformamide, N, N-dimethylacetoacetamide, and N-methylpyrrolidone And glycols such as ethylene glycol, diethylene glycol, and propylene glycol. These may be used alone or in combination of two or more.

Next, the electrode-forming paint or electrode-forming paste is applied to one surface of the metal foil, and then dried, and the metal on which the coating film containing the electrode material and the binder is formed on one surface Get a foil.
Next, this coating film is pressure-bonded and dried to produce a current collector (electrode) having an electrode material layer on one surface of the metal foil.
Thus, an electrode capable of improving the electronic conductivity can be produced without impairing the lithium ion conductivity of the present embodiment.

[Lithium ion secondary battery]
The lithium ion secondary battery of this embodiment has the electrode of this embodiment as a positive electrode.
This lithium ion secondary battery can increase both the electronic conductivity and the ionic conductivity of the positive electrode by using the electrode of the present embodiment as the positive electrode. As a result, a lithium ion secondary battery having improved input characteristics can be provided.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the following Example.

The electrode materials of Examples 1 to 6 and Comparative Examples 1 to 10 were produced as follows.
"Example 1"
Li ₃ PO ₄ as the Li source, P source, and FeSO ₄ aqueous solution as the Fe source were mixed at a molar ratio of Li: Fe: P = 3: 1: 1 to prepare a 1000 L raw material slurry. I put it in. Thereafter, a heating reaction was performed at 195 ° C. for 2.5 hours. After this reaction, the reaction product was cooled to room temperature to obtain a precipitated cake product. The precipitate was sufficiently washed with distilled water several times to obtain a cake-like active material.

  Next, 53.9 kg (in terms of solid content) of this active material, 123.9 g of an aqueous polyvinyl alcohol solution adjusted in advance to a solid content of 20%, 19.8 g of sucrose powder, 45. Using 2 g and zirconia balls having a diameter of 1 mm as medium particles, a dispersion treatment was performed for 2 hours in a bead mill to prepare a uniform slurry.

  Next, this slurry was sprayed into an air atmosphere at 160 ° C. and dried to obtain an active material granule coated with an organic substance having an average particle size of 7 μm.

  A graphite sintered body having an average length of 10 mm in the longitudinal direction is added to the granulated body as a heat conduction auxiliary substance so as to be 5% by volume with respect to 100% by volume of the obtained granulated body. A raw material for firing was obtained. 2.5 kg of this raw material for firing was spread on a graphite sheath having a volume of 10 L, fired for 1.5 hours in a non-oxidizing gas atmosphere at 720 ° C., and then kept at 40 ° C. for 30 minutes to obtain a fired product. . The fired product was passed through a sieve having a diameter of 75 μm, and the graphite sintered body was removed to obtain the electrode material of Example 1.

"Example 2"
An electrode material of Example 2 was obtained in the same manner as in Example 1 except that the addition amount of sucrose powder was 39.7 g and the addition amount of the phenol resin solution was 30.1 g.

"Example 3"
An electrode material of Example 3 was obtained in the same manner as in Example 1 except that the addition amount of sucrose powder was 59.7 g and the addition amount of the phenol resin solution was 15.0 g.

"Comparative Example 1"
An electrode material of Comparative Example 1 was obtained in the same manner as in Example 1 except that the sucrose powder was not added and the addition amount of the phenol resin solution was 60.4 g.

"Comparative Example 2"
The electrode material of Comparative Example 2 was obtained in the same manner as in Example 1 except that the amount of sucrose powder added was 79.7 g and no phenol resin solution was added.

“Comparative Example 3”
The electrode material of Comparative Example 3 was obtained in the same manner as Example 1 except that the addition amount of polyvinyl alcohol aqueous solution adjusted to 20% solid content in advance was 40.9 g and the addition amount of sucrose powder was 99.8 g. It was.

“Comparative Example 4”
An electrode material of Comparative Example 4 was obtained in the same manner as in Example 1 except that the addition amount of sucrose powder was 39.7 g and the addition amount of the phenol resin solution was 30.1 g.

“Comparative Example 5”
An electrode material of Comparative Example 5 was obtained in the same manner as in Example 1 except that the addition amount of sucrose powder was 59.7 g and the addition amount of the phenol resin solution was 15.0 g.

Example 4
Li ₃ PO ₄ as the Li source, P source, FeSO ₄ aqueous solution as the Fe source, MnSO ₄ aqueous solution as the Mn source, MgSO ₄ aqueous solution as the Mg source, CoSO ₄ aqueous solution as the Co source, and Ca (OH) ₂ aqueous solution as the Ca source These are mixed in a molar ratio of Li: Fe: Mn: Mg: Co: Ca: P = 3: 0.2448: 0.70: 0.05: 0.0002: 0.005: 1 A 1000 L raw material slurry was prepared and placed in a pressure vessel. Thereafter, a heating reaction was performed at 145 ° C. for 2.5 hours. After this reaction, the reaction product was cooled to room temperature to obtain a precipitated cake product. The precipitate was sufficiently washed with distilled water several times to obtain a cake-like active material.

  Then, 55.9 kg (in terms of solid content) of this active material, 185.9 g of a polyvinyl alcohol aqueous solution, 29.7 g of sucrose powder, and a phenol resin solution 67. Using 8 g and zirconia balls having a diameter of 1 mm as medium particles, dispersion treatment was performed for 2 hours in a bead mill to prepare a uniform slurry.

  Next, this slurry was sprayed into an air atmosphere at 150 ° C. and dried to obtain an active material granule coated with an organic substance having an average particle size of 9 μm.

  A graphite sintered body having an average length of 10 mm in the longitudinal direction is added to the granulated body as a heat conduction auxiliary substance so as to be 5% by volume with respect to 100% by volume of the obtained granulated body. A raw material for firing was obtained. 2.5 kg of this raw material for firing was spread on a graphite sheath having a volume of 10 L, fired for 2.5 hours in a non-oxidizing gas atmosphere at 720 ° C., and then kept at 40 ° C. for 30 minutes to obtain a fired product. . This fired product was passed through a sieve having a diameter of 75 μm, and the graphite sintered body was removed to obtain an electrode material of Example 4.

"Example 5"
An electrode material of Example 5 was obtained in the same manner as in Example 4 except that the addition amount of sucrose powder was 59.58 g and the addition amount of the phenol resin solution was 45.11 g.

"Example 6"
An electrode material of Example 6 was obtained in the same manner as in Example 4 except that the addition amount of sucrose powder was 89.51 g and the addition amount of the phenol resin solution was 22.51 g.

“Comparative Example 6”
An electrode material of Comparative Example 6 was obtained in the same manner as in Example 4 except that the sucrose powder was not added and the addition amount of the phenol resin solution was 90.54 g.

“Comparative Example 7”
The electrode material of Comparative Example 7 was obtained in the same manner as in Example 4 except that the amount of sucrose powder added was 119.55 g and no phenol resin solution was added.

“Comparative Example 8”
The electrode material of Comparative Example 8 was obtained in the same manner as in Example 4 except that the addition amount of the polyvinyl alcohol aqueous solution adjusted to 20% solid content in advance was 61.4 g and the addition amount of sucrose powder was 149.69 g. It was.

"Comparative Example 9"
An electrode material of Comparative Example 4 was obtained in the same manner as in Example 4 except that the addition amount of sucrose powder was 59.58 g and the addition amount of the phenol resin solution was 45.11 g.

"Comparative Example 10"
An electrode material of Comparative Example 10 was obtained in the same manner as in Example 4 except that the addition amount of sucrose powder was 89.51 g and the addition amount of the phenol resin solution was 22.51 g.

  The addition amounts of the polyvinyl alcohol aqueous solution, sucrose powder and phenol resin solution used in the preparation of the electrode materials of Examples 1 to 3 and Comparative Examples 1 to 5, and the electrode materials of Examples 1 to 3 and Comparative Examples 1 to 5 Table 1 shows the respective firing temperatures when these are manufactured.

  Addition amounts of polyvinyl alcohol aqueous solution, sucrose powder, and phenol resin solution used in the production of the electrode materials of Examples 4 to 6 and Comparative Examples 6 to 10, and the electrode materials of Examples 4 to 6 and Comparative Examples 6 to 10 Table 2 shows the respective firing temperatures when these are manufactured.

(Evaluation of electrode material)
The following evaluation was performed about the electrode material of Examples 1-6 and Comparative Examples 1-10.

(1) Carbon content The carbon content of the electrode materials of Examples 1 to 6 and Comparative Examples 1 to 10 was measured using a carbon analyzer (manufactured by Horiba, Ltd., model number: EMIA-220V).

(2) Specific surface area Using the specific surface area meter (BELSORP-mini, manufactured by Nippon Bell Co., Ltd.), the electrode materials of Examples 1-6 and Comparative Examples 1-10 by the BET method by nitrogen (N ₂ ) adsorption. The specific surface area was measured.

(3) Bulk density The bulk densities of the electrode materials of Examples 1 to 6 and Comparative Examples 1 to 10 were measured according to JIS R 1628: 1997 “Method for measuring bulk density of fine ceramic powder”.

(4) Raman spectroscopy measurement Raman spectra of the electrode materials of Examples 1 to 6 and Comparative Examples 1 to 10 were measured using a Raman spectrometer (LabRab HR evolution UV-VIS-NIR, manufactured by Horiba, Ltd.). .
The Raman spectrum obtained by this measurement was subjected to fitting processing by convolution of a Gaussian function and a Lorentz function (analysis software: LabSpec6, function name: GaussLor () (manufactured by Horiba, Ltd.)), and the obtained D band The peak intensity ratio (I _D / I _G ) between the D band and the G band was calculated from the peak intensity (I _D ) and the peak intensity (I _G ) of the G band.

(5) NMP oil absorption amount Implemented in accordance with JIS K 5101-13-1 “Purified linseed oil method” except that N-methyl-2-pyrrolidinone (NMP) was used in place of oil. NMP oil absorption of the electrode materials of Examples 1 to 6 and Comparative Examples 1 to 10 was measured.

(6) DBP oil absorption amount Except for using dibutyl phthalate (DBP) instead of linseed oil, Examples 1-6 according to JIS K 5101-13-1 “Purified linseed oil method” And the DBP oil absorption of the electrode material of Comparative Examples 1-10 was measured.

(7) 5C constant current charge capacity About the 5C constant current charge capacity, it evaluated using the lithium ion secondary battery produced using the electrode material of Examples 1-6 and Comparative Examples 1-10.

(Production of lithium ion battery)
The electrode materials of Examples 1 to 6 and Comparative Examples 1 to 10, polyvinylidene fluoride (PVdF) as a binder, and acetylene black (AB) as a conductive auxiliary agent have a mass ratio of 90: 5: 5. Then, N-methyl-2-pyrrolidinone (NMP) as a solvent was added to impart fluidity to prepare a slurry.
Next, this slurry was applied onto an aluminum (Al) foil having a thickness of 15 μm and dried. Then, it pressurized with the pressure of 600 kgf / cm < ² >, and produced the positive electrode of the lithium ion secondary battery which has an electrode area of 2 square centimeters and an electrode density of 1.6 g / cc.

The positive electrode and lithium metal as a negative electrode were disposed, and a separator made of porous polypropylene having a thickness of 25 μm was disposed between the positive electrode and the negative electrode to obtain a battery member. This battery member was placed in a coin cell container having a diameter of 2 cm and a thickness of 3.2 mm.
On the other hand, ethylene carbonate and diethyl carbonate were mixed at 1: 1 (mass ratio), and a 1M LiPF ₆ solution was added to prepare an electrolyte solution having lithium ion conductivity.
Next, 0.4 ml of the electrolyte solution was injected into the coin cell container, so that the battery member was immersed in the electrolyte solution, thereby producing a lithium ion secondary battery.

(Charge capacity)
Using a battery charge / discharge device (Hokuto Denko Co., Ltd., model number: SM8), the positive electrode voltage for lithium ion secondary batteries produced using the electrode materials of Examples 1 to 3 and Comparative Examples 1 to 5 In the lithium ion secondary batteries manufactured using the electrode materials of Examples 4 to 6 and Comparative Examples 6 to 10 until the voltage becomes 4.2 V with respect to the Li equilibrium voltage, the positive electrode voltage becomes the Li equilibrium voltage. On the other hand, constant current charging was performed until the voltage reached 4.3 V, and the capacity at that time was evaluated.

  The evaluation results of the electrode materials of Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 3, and the evaluation results of the electrode materials of Examples 4 to 6 and Comparative Examples 6 to 10 are shown in Table 4.

By comparing Examples 1 to 6 and Comparative Examples 1 to 10, the peak intensity ratio (I _D / I _G ) of the D band and G band of the Raman spectrum obtained by Raman spectroscopy was 1.10 or more and 1 It was found that when an electrode material having a DBP oil absorption amount and an NMP oil absorption amount (DBP / NMP) of 1.3 or less was used, the input characteristics of the lithium ion secondary battery were improved.

Claims (5)

General formula LiFe _x Mn _{1- xy My} PO ₄ (0.05 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.14, where M is Mg, Ca, Co, Sr, Ba, Ti, Center particles represented by at least one selected from Zn, B, Al, Ga, In, Si, Ge and rare earth elements;
A carbonaceous coating covering the surface of the central particle,
The peak intensity ratio (I _D / I _G ) of the D band and G band of the Raman spectrum obtained by Raman spectroscopy is 1.10 or more and 1.55 or less,
An electrode material for a lithium ion secondary battery having a ratio of DBP oil absorption and NMP oil absorption (DBP / NMP) of 1.3 or less. 2. The electrode for a lithium ion secondary battery according to claim 1, wherein a peak intensity ratio (I _D / I _G ) of the D band and G band of the Raman spectrum obtained by Raman spectroscopy is 1.25 or more and 1.45 or less. material.   3. The electrode material for a lithium ion secondary battery according to claim 1, wherein a ratio (DBP / NMP) of the DBP oil absorption amount and the NMP oil absorption amount is 1.20 or more and 1.24 or less.   The electrode for lithium ion secondary batteries containing the electrode material for lithium ion secondary batteries of any one of Claims 1-3. A lithium ion secondary battery having a positive electrode, a negative electrode and a non-aqueous electrolyte,
The lithium ion secondary battery in which the said positive electrode has the electrode for lithium ion secondary batteries of Claim 4.