JP2016017018A - Method for producing non-graphitizable carbon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a hardly graphitized carbon material by completing an infusibilizing treatment efficiently in a manufacturing method of the hardly graphitized carbon material which is a negative electrode material for lithium ion secondary battery.SOLUTION: There is provided a manufacturing method of a hardly graphitized carbon material having a crosslinking treatment process for applying a crosslinking treatment to a raw material of the hardly graphitized carbon material to obtain a crosslinking treatment article, an infusibilizing treatment process for applying an infusibilizing treatment on a carbon material to obtain an infusibilizing treatment article, a process for burning the infusibilizing treatment article to obtain the hardly graphitized carbon material, where the carbon material is the crosslinking treatment article satisfying all of conditions of (a) or (c) or a crosslinking treatment article having adjusted particle size distribution of the crosslinking treatment article obtained in the crosslinking treatment process satisfying all of (a) or (c) in the infusibilizing treatment process. In particle size distribution measured by a laser diffraction method by using water as a dispersant, (a) frequency of particles having particle diameter of 8 to 16 μm of 50 to 75%, (b) frequency of particles having particle diameter of 1 to 2 μm (B) of 15 to 20%, (c) a relationship of frequency of particles having particle diameter of 1 to 2 μm (B)/frequency of particles having particle diameter of 8 to 16 μm (A)=0.25 to 0.35 is satisfied.SELECTED DRAWING: None

Description

  The present invention relates to an infusibilization treatment method for producing a non-graphitizable carbon material, a negative electrode material for a lithium ion secondary battery, and a lithium ion secondary battery.

Due to the recent increase in awareness of global environmental protection issues, attention has been drawn to hybrid vehicles and electric vehicles that can reduce the amount of fossil fuel used and CO ₂ emissions.

  As a negative electrode material for an in-vehicle battery of a hybrid vehicle or an electric vehicle, a non-graphitizable carbon material having both high input / output characteristics and cycle characteristics has attracted attention. Especially for hybrid vehicle batteries, non-graphitizable carbon materials are suitable because they require high input / output characteristics and life characteristics that can be repeatedly charged and discharged for a long time by repeatedly starting the vehicle and charging regenerative energy. Yes.

  As a non-graphitizable carbon material as a negative electrode material for a lithium ion secondary battery, a material using petroleum pitch or coal pitch as a raw material has been reported. Further, for example, Patent Documents 1 and 2 disclose manufacturing methods using these non-graphitizable carbon materials as raw materials.

  However, under the conditions disclosed in Patent Documents 1 and 2, it was not possible to efficiently obtain a non-graphitizable carbon material having favorable characteristics. The reason is that it is necessary to perform an infusibilization treatment when obtaining a non-graphitizable carbon material from pitch as a raw material, but the provisions regarding the infusibilization treatment conditions described in Patent Documents 1 and 2 are insufficient. This is because of this.

  Various studies have been made on the infusibilization conditions of the graphitizable carbon material other than the non-graphitizable carbon material (for example, Patent Document 3). However, under the infusibilization treatment conditions specified in Patent Document 3, infusibilization of the non-graphitizable carbon material cannot be realized efficiently.

JP, 2013-144633, A JP-A-8-115723 JP 2003-331834 A

  The present invention has been made in view of the above points, and by providing provisions for the conditions of infusibilization treatment in the production of a non-graphitizable carbon material to be a negative electrode material for a lithium ion secondary battery, the efficiency is improved. The object is to complete the infusibilization treatment well and produce a non-graphitizable carbon material.

As a result of intensive studies to achieve the above object, the present inventors have found that the particle size distribution of the carbon material to be infusibilized in the infusibilization step essential in the method for producing a non-graphitizable carbon material is: It was found that if all the following conditions (a) to (c) were satisfied, the infusibilization process could be completed without fusing while improving the processing efficiency, and the present invention was completed.
In the particle size distribution measured by laser diffraction / scattering method using water as dispersion medium:
(A) The frequency (A) of particles having a particle diameter of 8 to 16 μm is 50 to 75% (b) The frequency (B) of particles having a particle diameter of 1 to 2 μm is 15 to 20% (c ) The frequency of particles having a particle diameter of 1 to 2 μm (B) / the frequency of particles having a particle diameter of 8 to 16 μm (A) = 0.25 to 0.35 is established.

That is, this invention is the following (1)-(12).
(1) A cross-linking process for obtaining a cross-linked product by subjecting the raw material of the non-graphitizable carbon material to a cross-linking process, an infusibilizing process for obtaining an infusible product by subjecting the carbon material to an infusible process, and infusibilization And baking the treated product to obtain a non-graphitizable carbon material,
In the infusibilization treatment step, a cross-linking treatment product in which the carbon material satisfies all the conditions (a) to (c) or a cross-linking treatment product obtained in the cross-linking treatment step so as to satisfy all the conditions (a) to (c). A method for producing a non-graphitizable carbon material, which is a cross-linked product having an adjusted particle size distribution.
In the particle size distribution measured by laser diffraction / scattering method using water as dispersion medium:
(A) The frequency (A) of particles having a particle diameter of 8 to 16 μm is 50 to 75% (b) The frequency (B) of particles having a particle diameter of 1 to 2 μm is 15 to 20% (c ) The frequency of particles having a particle diameter of 1 to 2 μm (B) / the frequency of particles having a particle diameter of 8 to 16 μm (A) = 0.25 to 0.35 is established (2) The particle size distribution was adjusted The production method according to (1) above, wherein the crosslinked product is one in which the particle size distribution is adjusted by pulverizing the crosslinked product obtained in the crosslinking treatment step.
(3) The particle size distribution is adjusted by classifying and mixing the cross-linked product obtained by adjusting the particle size distribution in the cross-linking process or the product obtained by pulverizing the cross-linked product obtained in the cross-linking process. The production method according to (1), wherein
(4) A non-graphitizable carbon material produced by the production method according to any one of (1) to (3) above.
(5) A negative electrode material for a lithium ion secondary battery comprising a non-graphitizable carbon material produced by the production method according to any one of (1) to (3) above.
(6) A lithium ion secondary battery using the non-graphitizable carbon material produced by the production method according to any one of (1) to (3) as a negative electrode material.
(7) An infusibilizing method for producing a non-graphitizable carbon material, wherein the particle size distribution of the carbon material to be infusibilized satisfies the conditions (a) to (c).
In the particle size distribution measured by laser diffraction / scattering method using water as dispersion medium:
(A) The frequency (A) of particles having a particle diameter of 8 to 16 μm is 50 to 75% (b) The frequency (B) of particles having a particle diameter of 1 to 2 μm is 15 to 20% (c ) The frequency of particles having a particle diameter of 1 to 2 μm (B) / the frequency of particles having a particle diameter of 8 to 16 μm (A) = 0.25 to 0.35 is established (8) In the above (7) An infusibilized product obtained by the infusible treatment method described.
(9) The manufacturing method according to (1) above, wherein in the infusibilization treatment step, the carbon material is a cross-linked product satisfying all the conditions (a) to (c).
(10) The production method according to the above (1), which is a cross-linked product in which the particle size distribution is adjusted so that the carbon material satisfies all the conditions (a) to (c) in the infusibilization treatment step.
(11) The production method according to (10), wherein the particle size distribution is adjusted by pulverizing the crosslinked product obtained in the crosslinking treatment step.
(12) The particle size distribution is adjusted by classifying and mixing the crosslinked product obtained in the crosslinking treatment step or the crosslinked treatment product obtained by pulverizing the crosslinked treatment product obtained in the crosslinking treatment step. Manufacturing method.

According to the present invention, a non-graphitizable carbon material can be produced by efficiently completing the infusibilization treatment in an infusible process that is unavoidable in the process of producing a non-graphitizable carbon material.
Further, when the non-graphitizable carbon material produced by the production method of the present invention is used as a negative electrode material for a lithium ion secondary battery, the first charge / discharge capacity can be increased.

It is sectional drawing which shows the coin-type secondary battery for evaluation.

[Method for producing non-graphitizable carbon material]
A conventional method for producing a general non-graphitizable carbon material (for example, a method for producing a non-graphitizable carbon material described in JP2013-144633A) crosslinks the raw material of the non-graphitizable carbon material. A cross-linking step for obtaining a cross-linked product by performing a treatment, a pulverizing step for adjusting the particle size by pulverizing the obtained cross-linked product (for example, setting the average particle size after pulverization to 1 to 50 μm), and adjusting the particle size An infusibilization step for obtaining an infusible treated product by subjecting the cross-linked product to an infusible treatment, and a firing step for obtaining a non-graphitizable carbon material by calcining the obtained infusible treated product.

The characteristic point of the method for producing the non-graphitizable carbon material of the present invention compared with the conventional general non-graphitizable carbon material is that the particle size distribution of the carbon material subjected to the infusibilization treatment in the infusibilization process Is that the following conditions (a) to (c) are satisfied.
In the particle size distribution measured by laser diffraction / scattering method using water as dispersion medium:
(A) The frequency (A) of particles having a particle diameter of 8 to 16 μm is 50 to 75% (b) The frequency (B) of particles having a particle diameter of 1 to 2 μm is 15 to 20% (c ) The frequency of particles having a particle diameter of 1 to 2 μm (B) / the frequency of particles having a particle diameter of 8 to 16 μm (A) = 0.25 to 0.35 is established.

That is, the method for producing a non-graphitizable carbon material of the present invention (hereinafter also simply referred to as “the production method of the present invention”) is a cross-linking process in which a raw material of the non-graphitizable carbon material is subjected to a crosslinking treatment to obtain a crosslinked product The infusibilization process comprising: a treatment step; an infusibilization treatment step for obtaining an infusible treatment product by subjecting the carbon material to an infusibilization treatment; and a step for obtaining a non-graphitizable carbon material by firing the infusibilization treatment product. In the treatment step, the carbon material satisfies all the conditions (a) to (c), or the crosslinked product obtained in the crosslinking treatment step so as to satisfy all the conditions (a) to (c). A method for producing a non-graphitizable carbon material, which is a cross-linked product in which the particle size distribution of the processed product is adjusted.
Hereinafter, the production method of the present invention will be described in detail.

<Crosslinking treatment>
First, a raw material of the non-graphitizable carbon material (hereinafter also simply referred to as “raw material”) is subjected to a crosslinking treatment to obtain a crosslinked product.

  Here, it does not specifically limit as a raw material used for the manufacturing method of this invention, A conventionally well-known thing can be used. Examples thereof include pitches such as coal-based pitches and petroleum-based pitches; resins such as phenol resins and furan resins; mixtures of pitches and resins; Among these, pitches such as coal pitch and petroleum pitch are preferable from the viewpoint of economy and the like.

  Examples of a method for subjecting the above-mentioned raw material to a crosslinking treatment include, for example, a method using an air blowing reaction; a dry method using an oxidizing gas (air, oxygen, ozone, etc.); nitric acid, sulfuric acid, hypochlorous acid, or two of these. And a wet method using an aqueous solution of the above mixture. Among these, the method by an air blowing reaction is preferable.

  The air blowing reaction is a reaction that raises the softening point by heating the raw material and blowing an oxidizing gas (for example, air, oxygen, ozone, or a mixed gas of two or more thereof). According to the air blowing reaction, for example, a crosslinked product (for example, air blown pitch) having a high softening point of 200 ° C. or higher can be obtained.

  Note that the air blowing reaction is a reaction in a liquid phase state, and it is known that oxygen atoms are hardly taken into the carbon material as compared with a crosslinking treatment in a solid phase state. According to Japanese Patent Application Laid-Open No. 9-153359, in the air blowing reaction, a reaction mainly consisting of oxidative dehydration proceeds, polymerization proceeds by biphenyl type cross-linking, and this is achieved by infusibilization treatment and firing. It is said that a non-graphitizable carbon material having a three-dimensional structure without orientation in which the cross-linked portion is dominant and having a large number of voids in which lithium is occluded remains is obtained.

  The conditions for the air blowing reaction are not particularly limited, but if the temperature is too high, a mesophase is generated, and if it is low, the reaction rate is slow, so 280 to 420 ° C is preferable, and 320 to 380 ° C is more preferable. Moreover, as blowing amount of oxidizing gas, 0.5-15 L / min per 1000g of pitches as compressed air is preferable, and 1.0-10 L / min is more preferable. The reaction pressure may be normal pressure, reduced pressure, or increased pressure.

  The softening point of the cross-linked product such as air bronze pitch obtained by the cross-linking treatment is preferably 200 to 400 ° C., more preferably 250 to 350 ° C., from the easiness of the infusible treatment described later.

The crosslinked product obtained in the crosslinking treatment step is subjected to a particle size adjustment treatment (described later), and the particle size distribution is adjusted so that the particle size distribution satisfies all of (a) to (c).
However, when the particle size distribution of the cross-linked product obtained in the cross-linking process satisfies all the above conditions (a) to (c), a particle size adjusting process (described later) is performed to adjust the particle size distribution. Instead, infusibilization processing (described later) may be performed.

<Granularity adjustment processing>
The crosslinked product obtained in the crosslinking treatment step is subjected to a particle size adjustment treatment (described later) to adjust the particle size distribution so that the particle size distribution satisfies all of (a) to (c).
The particle size distribution may be adjusted by pulverizing the crosslinked product so that the particle size distribution of the crushed crosslinked product satisfies all the above conditions (a) to (c). With or without classification, the particles may be classified and mixed so that the particle size distribution of the mixed crosslinked product satisfies all the conditions (a) to (c).
The methods of pulverization, classification and mixing are not particularly limited, and conventionally known methods can be used.

<Infusibilization treatment>
Next, the particle size distribution of the cross-linked product obtained in the cross-linking treatment step, which satisfies all the above conditions (a) to (c), or the cross-linked product obtained in the cross-linking treatment step is described in the above (a) to (c). An infusibilized treatment is performed on the cross-linked product adjusted to satisfy all of the above conditions to obtain an infusible treated product. The infusibilization treatment is performed on a cross-linked product such as air blow pitch, and is a kind of cross-linking treatment (oxidation treatment) performed in a solid phase state. As a result, oxygen is taken into the structure of the cross-linked product, and the cross-linking proceeds to make it difficult to melt even at high temperatures.

  The amount of oxygen in the infusibilized product obtained by the infusible treatment is preferably 3 to 20% by mass, and more preferably 5 to 15% by mass because it prevents fusion during the firing treatment.

  As an infusible treatment method, a dry method using an oxidizing gas is performed. The oxidizing gas is not particularly limited as long as it contains an oxidizing substance such as oxygen and ozone. The oxidizing gas may be diluted with an inert gas (for example, nitrogen, helium, etc.). . Although content of the oxidizing substance in oxidizing gas is not specifically limited, Preferably it is 1-100 volume%, More preferably, it exists in the range of 5-80 volume%. If it is within this range, the crosslinking treatment (oxidation treatment) is sufficiently performed without excess or deficiency.

  The blowing amount of the oxidizing gas is not particularly limited, but is preferably 1.0 to 20 L / min, more preferably 2.0 to 10 L / min as compressed air per 1000 g. The reaction pressure may be normal pressure, reduced pressure, or increased pressure.

  It is necessary to select the maximum processing temperature for the infusibilization treatment below the softening point of the crosslinked product. Moreover, 50-200 degreeC / hour is preferable and the temperature increase rate in the case of performing by a batch type from a viewpoint which prevents a fusion | melting more, and 75-175 degreeC / hour is more preferable.

In the present invention, in the dry-type infusibilization treatment, the particle size distribution of the carbon material to be infusibilized needs to satisfy all of the following conditions.
In the particle size distribution measured by laser diffraction / scattering method using water as dispersion medium:
(A) The frequency (A) of particles having a particle diameter of 8 to 16 μm is 50 to 75% (b) The frequency (B) of particles having a particle diameter of 1 to 2 μm is 15 to 20% (c ) The frequency of particles having a particle diameter of 1 to 2 μm (B) / the frequency of particles having a particle diameter of 8 to 16 μm (A) = 0.25 to 0.35 is established.

  In order for the particle size distribution of the carbon material to be infusible to satisfy all of the above conditions, the above-described particle size adjustment processing is performed.

  The measurement method of the particle size distribution is preferably a measurement method that satisfies the requirements of the international standard ISO 13320: 2009 for the particle size analysis method by the laser diffraction / scattering method using water as a dispersion medium. More specifically, it is more preferable to use a laser diffraction / scattering particle size distribution analyzer LMS-2000e (manufactured by Seishin Enterprise Co., Ltd.) and deionized water as a dispersion medium, and measure according to the provisions of international standard ISO 13320: 2009. .

The reason for this provision will be described below.
A cross-linked product (for example, air bron pitch) during the infusibilization treatment generates a large amount of heat during the temperature rising process and is likely to be fused. This is because the bonding between the cross-linked product and oxygen proceeds at an accelerated rate. In the case of vigorous fusion, the interior of the cross-linked product cannot be in contact with oxygen, and as a result, oxygen uptake is hindered and the amount of oxygen in the infusibilized product is reduced.

  The presence or absence of this fusion is greatly affected by the particle size distribution of the carbon material (for example, air bron pitch) to be infusibilized. When the particle size distribution is biased toward the larger particle size, such as when the carbon material to be infusibilized consists only of coarse powder, the contact area with the atmosphere per volume is reduced and heat is not easily dissipated into the atmosphere. Therefore, it becomes easy to store heat, so that fusion is likely to occur. On the other hand, when the carbon material to be infusibilized is composed of only fine powder, when the particle size distribution is biased toward the smaller particle size, the oxidation reaction tends to proceed excessively because the contact area with the atmosphere increases. Similarly, fusion is likely to occur.

  Therefore, as a result of repeated investigations, the inventors realized a particle size distribution containing coarse powder and fine powder at a suitable ratio in two ridges, thereby promoting excessive heat oxidation while promoting heat dissipation to the atmosphere and pitch oxidation reaction. It was found that it is possible to suppress fusion and prevent fusion. By realizing this particle size distribution, it is possible to avoid the above-described problems that may occur when the carbon material to be infusible is made of only fine powder or only of coarse powder. Moreover, at the same time, since the particle size distribution is likely to be densely packed as compared with the case of one mountain, the load applied from the upper part to realize the same filling thickness can be reduced. There is an advantage in that heat radiation to the atmosphere is properly maintained without being crimped, heat is hardly stored, and fusion can be prevented.

  That is, the frequency (A) of particles having a particle diameter of 8 to 16 μm is 75% or less, the frequency (B) of particles having a particle diameter of 1 to 2 μm is 15% or more, and B / A ≧ 0.25. The particle size is not too rough, the contact area with the atmosphere per volume is increased, and heat is easily dissipated into the atmosphere, so that it is difficult to store heat and fusion is less likely to occur. Therefore, the amount of oxygen tends to increase. On the other hand, the frequency (A) of particles having a particle diameter of 8 to 16 μm is 50% or more, the frequency (B) of particles having a particle diameter of 1 to 2 μm is 15% or more, and B / A ≦ 0.35. The particle size is not too fine, the contact area with the atmosphere is reduced, the oxidation reaction proceeds appropriately, and fusion is less likely to occur. Therefore, the amount of oxygen tends to increase.

  The prescribed particle size distribution need not be pulverized at one time, and there is no problem even if it is realized by mixing samples that have been sorted under a plurality of conditions in advance.

<Baking treatment>
A non-graphitizable carbon material is obtained by firing the infusibilized product obtained by the infusible treatment in an atmosphere of an inert gas such as reduced pressure or nitrogen. At this time, the heating rate is preferably 50 to 150 ° C./hour, more preferably 80 to 120 ° C./hour. Moreover, 900-1300 degreeC is preferable and the maximum holding temperature (baking temperature) has more preferable 1000-1200 degreeC.

[Non-graphitizable carbon material]
The non-graphitizable carbon material obtained by the above production method of the present invention (hereinafter sometimes referred to as “the non-graphitizable carbon material of the present invention”) can be preferably used as a negative electrode material for a lithium ion secondary battery. .

  In addition, the particle size distribution d50 value of the non-graphitizable carbon material of the present invention is usually 1 to 100 μm. Among these, when the particle size becomes coarser than the particle size specified at the time of infusibilization, it does not reach the fusion at the time of infusibilization, but it is due to the effect that some adhesion appears or adhesion occurs at the time of firing. Moreover, when it becomes fine, it is a time which grind | pulverizes again after infusibilization.

The specific surface area of the non-graphitizable carbon material is not particularly limited, from the viewpoint of the initial charge and discharge efficiency and safety of the lithium ion secondary battery, preferably 15 m 2 / ^g or less, 8m 2 / ^g or less is more preferable. The specific surface area is measured by nitrogen gas adsorption BET method. In order to realize such powder characteristics, the infusibilized product may be pulverized after the infusible treatment and before the firing treatment.

[Lithium ion secondary battery]
Next, a lithium ion secondary battery (hereinafter also referred to as “the lithium ion secondary battery of the present invention”) used as a negative electrode material using the non-graphitizable carbon material of the present invention will be described.

In general, a lithium ion secondary battery includes a negative electrode, a positive electrode, and a nonaqueous electrolyte as main battery components. The positive and negative electrodes are each composed of a lithium ion carrier, and lithium ions are input and output between layers. In essence, this is a battery mechanism in which lithium ions are doped into the negative electrode during charging and are dedoped from the negative electrode during discharging.
The lithium ion secondary battery of the present invention is not particularly limited except that the non-graphitizable carbon material of the present invention is used as the negative electrode material, and other battery components are general lithium ion secondary battery elements. Follow.

<Negative electrode>
The method for producing the negative electrode from the non-graphitizable carbon material of the present invention is not particularly limited, and can be performed according to a normal molding method. At the time of producing the negative electrode, a negative electrode mixture obtained by adding a binder to the non-graphitizable carbon material of the present invention can be used. As the binder, those having chemical stability and electrochemical stability with respect to the electrolyte are preferably used. Usually, the binder is preferably used in an amount of about 1 to 20% by mass in the total amount of the negative electrode mixture. Specific examples of the binder include polyvinylidene fluoride, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR). Moreover, you may add carbon materials other than the non-graphitizable carbon material of this invention, and a graphite material as an active material. Furthermore, for example, carbon black, carbon fiber, or the like may be added as a conductive agent.

  The particle size of the non-graphitizable carbon material of the present invention is adjusted by classification, etc., and mixed with a binder to prepare a negative electrode mixture, and this negative electrode mixture is usually applied to one or both sides of a current collector. To form a negative electrode mixture layer. At this time, a normal solvent can be used. The shape of the current collector used for the negative electrode is not particularly limited, and examples thereof include a foil shape; and a net shape such as a mesh and an expanded metal. Examples of the current collector include copper, stainless steel, and nickel.

<Positive electrode>
As a material for the positive electrode (positive electrode active material), it is preferable to select a material that can be doped / dedoped with a sufficient amount of lithium ions. Examples of such positive electrode active materials include transition metal oxides, transition metal chalcogenides, vanadium oxides and lithium-containing compounds thereof, and a general formula M _x Mo ₆ S _8-y (wherein x is 0 ≦ x ≦ 4, y is a numerical value in the range of 0 ≦ y ≦ 1, and M represents a metal such as a transition metal), a chevrel phase compound represented by lithium iron phosphate, activated carbon, activated carbon fiber, and the like. May be used alone or in combination of two or more. For example, a carbonate such as lithium carbonate can be added to the positive electrode.

The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. Specifically, the lithium-containing transition metal oxide is LiM (1) _1-p M (2) _p O ₂ (wherein p is a numerical value in the range of 0 ≦ p ≦ 1, M (1), M (2) is composed of at least one transition metal element), or LiM (1) _2-q M (2) _q O ₄ (wherein q is a numerical value in the range of 0 ≦ q ≦ 1, M (1 ), M (2) is composed of at least one transition metal element). Here, examples of the transition metal element represented by M include Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, and the like. Co, Fe, Mn, Ti, Cr, V Al is preferred.
Such lithium-containing transition metal oxides are, for example, Li, transition metal oxides or salts as starting materials, these starting materials are mixed according to the composition, and fired in a temperature range of 600 to 1000 ° C. in an oxygen atmosphere. Can be obtained. Note that the starting materials are not limited to oxides or salts, and can be synthesized from hydroxides or the like.

  As a method of forming a positive electrode using such a positive electrode material, for example, a positive electrode mixture layer is formed by applying a positive electrode mixture composed of a positive electrode material, a binder and a conductive agent to both surfaces of a current collector. As the binder, those exemplified for the negative electrode can be used. As the conductive agent, for example, a carbon material, graphite, carbon black, or VGCF can be used. The shape of the current collector is not particularly limited, and the same shape as the negative electrode is used.

  In forming the above-described negative electrode and positive electrode, various conventionally known additives such as a conductive agent and a binder can be appropriately used.

<Electrolytes>
As the electrolyte, a normal nonaqueous electrolyte containing a lithium salt such as LiPF ₆ or LiBF ₄ as the electrolyte salt is used.
The non-aqueous electrolyte may be a liquid non-aqueous electrolyte or a polymer electrolyte such as a solid electrolyte or a gel electrolyte.

  In the case of a liquid nonaqueous electrolyte solution, an aprotic organic solvent such as ethylene carbonate, propylene carbonate, dimethyl carbonate or the like can be used as the nonaqueous solvent.

In the case of a polymer electrolyte, a matrix polymer gelled with a plasticizer (non-aqueous electrolyte) is included. Examples of the matrix polymer include ether-based polymers such as polyethylene oxide and cross-linked products thereof, fluorine-based polymers such as polymethacrylate-based, polyacrylate-based, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene copolymer. Can be used alone or as a mixture, and among them, a fluorine-based polymer is preferable from the viewpoint of redox stability and the like.
As the electrolyte salt and non-aqueous solvent constituting the plasticizer (non-aqueous electrolyte solution) contained in the polymer electrolyte, those described above can be used.

In the lithium ion secondary battery of the present invention, a separator can be used. For example, a negative electrode containing the non-graphitizable carbon material of the present invention, a gel electrolyte, and a positive electrode are used in this order using a gel electrolyte. It is also possible to configure by stacking and housing in the battery outer packaging material.
The structure of the lithium ion secondary battery of the present invention is arbitrary, and is not particularly limited with respect to its shape and form. For example, it may be a stacked type, a wound type, a cylindrical type, a square type, or a coin type Can be selected arbitrarily.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.

[Example 1]
<Manufacture of non-graphitizable carbon materials>
(Crosslinking treatment)
The pitch as a raw material was subjected to a crosslinking treatment to produce a crosslinked product having a softening point shown in the column of “softening point (° C.)” of “Crosslinked product” in Table 1.
(Crushing process)
The manufactured crosslinked product was pulverized, and the particle size distribution of the crosslinked product was adjusted as shown in the column “Particle size distribution of crosslinked product” in Table 1.
(Infusibilization process)
In the cross-linked product with the adjusted particle size distribution, the maximum processing temperature, the heating rate of 150 ° C./hour, the filling thickness of 35 mm, in the air shown in the column “Maximum processing temperature (° C.)” of “Infusibilization processing” in Table 1 Infusible treatment was performed by dry method. The oxygen content of the infusibilized product is shown in the column of “Oxygen content (mass%)” of “Infusible product” in Table 1. This value is a value measured using an elemental analyzer.
(Baking process)
The infusibilized product was fired. The firing treatment was performed by raising the temperature to 1150 ° C. at a rate of 100 ° C./hour in a nitrogen atmosphere and holding at 1150 ° C. for 3 hours.

<Fusion during infusibilization>
Of the particle size distribution, the frequency (A) of particles having a particle diameter of 8 to 16 μm, the frequency (B) of particles having a particle diameter of 1 to 2 μm, and the ratio of B to A (B / A) are defined. Regarding Examples 1 to 6 included in the range, no fusion occurred during the infusibilization treatment, and the oxygen content was as high as 5% by mass or more.
On the other hand, in Comparative Examples 1 and 2 in which the frequency of particles having a particle diameter of 8 to 16 μm is outside the specified range, and in Comparative Examples 3 and 4 in which the frequency of particles having a particle diameter of 1 to 2 μm is outside the specified range, Due to the fact that the amount of coarse powder is large, heat is easily stored, or because the amount of fine powder is relatively large, the reaction with oxygen is likely to proceed excessively. Remains in value. Further, while the frequency (A) of particles having a particle diameter of 8 to 16 μm and the frequency (B) of particles having a particle diameter of 1 to 2 μm are within the specified range, the ratio value of the former to the latter (B / A ) Is out of the specified range, even in Comparative Examples 5 and 6, the oxygen amount is low due to the occurrence of fusion.
The present inventors consider that the cause of this fusion occurs as a cause of the fusion occurring in Comparative Examples 2 to 4, but because the ease of filling the powder is not good, the same 35 mm thickness is prepared. It is thought that the generated heat was not dissipated into the atmosphere because the infusibilization treatment was performed with the pitch being pressure-bonded as a result.

[Example 2]
<Manufacture and evaluation of lithium ion secondary batteries>
Using the non-graphitizable carbon material produced in Example 1 (hereinafter also referred to as “carbon powder”) as the negative electrode material, a button-type secondary battery was produced in the following manner, and the battery was evaluated.

(Preparation of negative electrode mixture paste)
The obtained carbon powder was mixed at a ratio of carbon powder: polyvinylidene fluoride = 95: 5, NMP (1 methyl 2 pyrrolidone) was used as a solvent, and a planetary mixer was used for mixing and stirring to prepare a negative electrode mixture paste. Obtained.

(Production of electrodes)
The obtained negative electrode mixture paste was applied onto a 15 μm thick copper foil, and after the solvent was volatilized at 100 ° C. with a blow dryer, it was punched into a circular shape with a diameter of 15.5 mm, and a hand press machine was used. After pressurizing a pressure of 250 MPa over 20 seconds, it was vacuum-dried at a temperature of 100 ° C. for 8 hours to obtain a negative electrode.

(Production of evaluation battery)
Next, a coin-type secondary battery for evaluation (also simply referred to as “evaluation battery”) shown in FIG. 1 was produced using the produced working electrode (negative electrode). FIG. 1 is a cross-sectional view showing a coin-type secondary battery for evaluation.
First, a lithium metal foil was pressed against a nickel net and punched out into a circular shape with a diameter of 15.5 mm, thereby producing a disc-shaped counter electrode 4 made of lithium foil in close contact with the current collector 7a made of nickel net.
Next, the separator 5 impregnated with the electrolyte solution is laminated between the working electrode (negative electrode) 2 in close contact with the current collector 7b and the counter electrode 4 in close contact with the current collector 7a, and then the working electrode 2 is stacked. Is accommodated in the exterior cup 1 and the counter electrode 4 is accommodated in the exterior can 3. An evaluation battery was produced by sealing.
In the manufactured evaluation battery, the peripheral part of the exterior cup 1 and the exterior can 3 is caulked through the insulating gasket 6 to form a sealed structure. Inside the sealed structure, as shown in FIG. 1, in order from the inner surface of the outer can 3 to the inner surface of the outer cup 1, a current collector 7a, a counter electrode 4, a separator 5, a working electrode (negative electrode) 2, and The current collector 7b is laminated.

(Charge / discharge test)
About the produced evaluation battery, the following charging / discharging tests were done at 25 degreeC. In this test, the process of doping lithium ions into the carbon powder was referred to as “charging”, and the process of dedoping from the carbon powder was referred to as “discharge”.
First, constant current charging was performed until the circuit voltage reached 0 mV at a current value of 0.9 mA, switching to constant voltage charging was performed when the circuit voltage reached 0 mV, and charging was continued until the current value reached 20 μA. . The charge capacity (mAh / g) (first charge capacity) was determined from the energization amount during that time. Then, it rested for 120 minutes. Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5 V, and the discharge capacity (mAh / g) (first discharge capacity) was determined from the amount of current applied during this period. The results are shown in the column of “First discharge capacity (mAh / g)” in Table 1.

  The first discharge capacity of the obtained material has a high value of 380 mAh / g or more in Examples 1 to 6. In any case, the oxygen content of the infusibilized product is 5.0% by mass or more. On the other hand, in Comparative Examples 1 to 6 in which fusion occurred at the time of infusibilization, the discharge capacity remained below 360 mAh / g at the maximum, and the fusion that occurred at the time of infusibilization adversely affects the battery characteristics.

DESCRIPTION OF SYMBOLS 1 Exterior cup 2 Working electrode 3 Exterior can 4 Counter electrode 5 Separator 6 Insulating gasket 7a Current collector 7b Current collector

Claims (8)

A crosslinking treatment step for obtaining a crosslinked product by subjecting the raw material of the non-graphitizable carbon material to a crosslinking treatment;
An infusibilization treatment step for obtaining an infusible treatment product by subjecting the carbon material to an infusibilization treatment;
Firing the infusibilized product to obtain a non-graphitizable carbon material,
In the infusibilization treatment step, the carbon material is obtained in the crosslinking treatment step so that the carbonized material satisfies all of the following conditions (a) to (c) or satisfies the following conditions (a) to (c). A method for producing a non-graphitizable carbon material, which is a cross-linked product in which the particle size distribution of the obtained cross-linked product is adjusted.
In the particle size distribution measured by laser diffraction / scattering method using water as dispersion medium:
(A) The frequency (A) of particles having a particle diameter of 8 to 16 μm is 50 to 75% (b) The frequency (B) of particles having a particle diameter of 1 to 2 μm is 15 to 20% (c ) The frequency of particles having a particle diameter of 1 to 2 μm (B) / the frequency of particles having a particle diameter of 8 to 16 μm (A) = 0.25 to 0.35 is established.   The manufacturing method according to claim 1, wherein the cross-linked product having the adjusted particle size distribution is obtained by adjusting the particle size distribution by pulverizing the cross-linked product obtained in the cross-linking process.   The particle size distribution is obtained by classifying and mixing the cross-linked product obtained by adjusting the particle size distribution in the cross-linked product obtained in the cross-linking process or the cross-linked product obtained by pulverizing the cross-linked product obtained in the cross-linking process. The manufacturing method of Claim 1 which is what adjusted.   A non-graphitizable carbon material produced by the production method according to claim 1.   The negative electrode material for lithium ion secondary batteries containing the non-graphitizable carbon material manufactured by the manufacturing method of any one of Claims 1-3.   The lithium ion secondary battery which uses the non-graphitizable carbon material manufactured by the manufacturing method of any one of Claims 1-3 as a negative electrode material. An infusibilizing method for producing a non-graphitizable carbon material, wherein the particle size distribution of the carbon material to be infusibilized satisfies the following conditions (a) to (c).
In the particle size distribution measured by laser diffraction / scattering method using water as dispersion medium:
(A) The frequency (A) of particles having a particle diameter of 8 to 16 μm is 50 to 75% (b) The frequency (B) of particles having a particle diameter of 1 to 2 μm is 15 to 20% (c ) The frequency of particles having a particle diameter of 1 to 2 μm (B) / the frequency of particles having a particle diameter of 8 to 16 μm (A) = 0.25 to 0.35 is established.   An infusibilized product obtained by the infusible treatment method according to claim 7.