JP2017084764A - Carbon material for secondary battery negative electrode, active material for secondary battery negative electrode, secondary battery negative electrode and manufacturing method for second battery negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a carbon material, which is able to improve the carbonization yield of a carbon material for a secondary battery negative electrode and the battery characteristic of a secondary battery.SOLUTION: A manufacturing method for a carbon material for a secondary battery is provided. In a mixing step, resin compositions containing at least aromatic condensed polymer whose phenol molecules separate by its being heated to a first temperature higher than 25°C and an organic soluble medium decomposing material having a fusion point or softening point that differs from the fusion point or softening point of the aromatic condensed polymer by 100[K] or less in temperature are mixed at a second temperature higher than the fusion point or softening point of the aromatic condensed polymer and the fusion point or softening point of the organic soluble medium decomposing material, and thereby a resin mixture is obtained. In a calcination step, the resin mixture is heated to a temperature higher than the first temperature, the aromatic condensed polymer is subjected to solvolysis by use of the organic soluble medium decomposing material and then thermally hardened and carbonized.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing a carbon material for a secondary battery negative electrode, and an active material for a secondary battery negative electrode including the production method, a secondary battery negative electrode, and a method for producing each secondary battery.

  In recent years, the use of secondary batteries has been studied in various technical fields ranging from small electrical products such as mobile phones to large machine products such as automobiles. As the secondary battery, various types such as a non-aqueous electrolyte secondary battery using an organic electrolyte as an electrolyte or a solid battery using a solid electrolyte have been studied. In both types of secondary batteries, chemical species (for example, lithium ions) that serve as charge carriers for the secondary battery move between the positive electrode active material layer and the negative electrode active material layer to charge and discharge. Is repeated.

  In such secondary batteries, the electrode active material layer provided on the negative electrode generally contains a carbon material as an electrode active material. The electrode active material layer absorbs chemical species such as lithium ions between carbon material layers having a layer structure, and discharges the chemical species stored from the interlayer, thereby charging and discharging in a secondary battery. Is possible.

  The carbon material can be manufactured from various materials. Although graphite is generally used, attempts have been made to produce phenol resin, coal or petroleum pitch as a starting material.

  In Patent Literature 1, petroleum pitch powder is mixed with polyamic acid which is a starting material of polyimide at room temperature, heated to remove the polyamic acid solvent, imidized and fired to produce a carbon material for a negative electrode. It is described to do. In addition, Patent Document 1 describes that a resin mixed with coal pitch powder is heated and solidified to produce a novolac-type phenol resin which is a thermoplastic resin. Patent Document 1 describes that a carbon material is produced by adding a powder of petroleum pitch or coal pitch to a thermosetting resin such as furfuryl alcohol resin or polyparaphenylene terephthalamide. In this Patent Document 1, the pitch addition amount is set so that the original characteristics of the carbon component from the aromatic condensation polymer are not impaired, and a part of the components of petroleum pitch and coal pitch does not melt. It is described that it is preferable to reduce the amount.

  Patent Document 2 describes a method for producing a carbon material in which pitch and resin are melt-mixed at or above the softening point of the pitch and above the melting point of the resin, and then carbonized. According to this manufacturing method, the pitch becomes a matrix and a carbon network structure is formed at a relatively low temperature by carbonization. In the example of Patent Document 2, a novolac type phenolic resin (product number: PR311), which is a thermoplastic resin, and coal-based pitch are mixed with powder, melt-kneaded and then fired to produce a carbon material. Have been described.

Japanese Patent Laid-Open No. 9-298063 JP 2007-91557 A

  Due to the widespread use of secondary batteries in recent years, there has been a demand for efficient production of carbon materials and further improvement of battery characteristics. From this point of view, the production methods of Patent Documents 1 and 2 still have room for improvement. .

  This invention is made | formed in view of the above subjects, and provides the manufacturing method of the carbon material which can improve the carbonization yield of the carbon material for secondary battery negative electrodes, and the battery characteristic of a secondary battery. Is. Moreover, this invention provides the manufacturing method of the active material for secondary battery negative electrodes, a secondary battery negative electrode, and a secondary battery including the manufacturing method of this carbon material for secondary battery negative electrodes.

  The method for producing a carbon material for a secondary battery negative electrode (hereinafter also simply referred to as “carbon material”) according to the present invention comprises an aromatic condensation polymer in which phenol molecules are separated by heating to a first temperature higher than 25 ° C. And a resin composition containing at least the organic solvolysis material having a melting point or softening point of which the temperature difference from the melting point or softening point of the aromatic condensation polymer is 100 [K] or less, A mixing step of mixing at a second temperature higher than the melting point or softening point of the organic solvolysis material and lower than the first temperature to obtain a resin mixture; A baking step in which the resin mixture is heated to a temperature higher than the first temperature, the aromatic condensation polymer is solvated and decomposed with the organic solvolysis material, and then thermoset and carbonized; Including the.

  The method for producing a secondary battery negative electrode active material (hereinafter, also simply referred to as “negative electrode active material”) of the present invention includes the method for producing a secondary battery negative electrode carbon material of the present invention.

  The method for producing a secondary battery negative electrode (hereinafter also simply referred to as “negative electrode”) of the present invention includes the method for producing a secondary battery negative electrode active material of the present invention.

  The manufacturing method of the secondary battery of this invention includes the manufacturing method of the secondary battery negative electrode of this invention.

  According to the method for producing a carbon material according to the present invention, a carbon material can be obtained by solvolysis of an aromatic condensation polymer with an organic solvolysis material, followed by thermosetting and carbonization. For this reason, carbonization is performed after thermosetting in a state where the growth of the liquid crystal state of the aromatic condensation polymer is promoted by a solvolysis reaction (solvolysis), so that the carbonization yield is improved and chemical species such as lithium ions are improved. It becomes a carbon material with excellent occlusion and release. Thereby, the secondary battery using the carbon material manufactured by this invention as an active material for negative electrodes is excellent in battery characteristics, such as charge capacity and discharge capacity.

It is a schematic diagram which shows an example of a lithium ion secondary battery provided with the negative electrode manufactured using the carbon material concerning embodiment of this invention. It is a graph which shows the relationship between the pitch ratio concerning Example 1 to 3, Reference Example 1, and Comparative Examples 1 and 2, and the carbonization yield. (A) is a temperature-programmed desorption spectrum of the resol type phenol resin of Comparative Example 1. (B) is a temperature-programmed desorption spectrum of the resin mixture of Example 1. (C) is a temperature programmed desorption spectrum of the organic solvolysis material (pitch) of Comparative Example 2. (A) is a temperature-programmed desorption spectrum of the novolak type phenol resin of Comparative Example 3. (B) is a temperature programmed desorption spectrum of the resin mixture of Reference Example 2. (A) is a temperature-programmed desorption spectrum of pyrene in the organic solvolysis material (pitch) of Comparative Example 2. (B) is a temperature programmed desorption spectrum of pyrene in the resin mixture of Reference Example 2. (C) is a temperature programmed desorption spectrum of pyrene in the resin mixture of Example 1.

Hereinafter, a carbon material for a secondary battery according to an embodiment of the present invention and a manufacturing method thereof (hereinafter, may be referred to as the present manufacturing method) will be described.
This manufacturing method includes a mixing step and a firing step.
In the mixing step, a resin composition containing at least an aromatic condensation polymer and an organic solvolysis material is mixed at a second temperature to obtain a resin mixture. An aromatic condensation polymer is a material from which phenol molecules are separated by heating to a first temperature higher than 25 ° C. (normal temperature). The organic solvolysis material has a melting point or softening point where the temperature difference from the melting point or softening point of the aromatic condensation polymer is 100 [K] or less. The second temperature is a temperature higher than the melting point or softening point of the aromatic condensation polymer and the melting point or softening point of the organic solvolysis material and lower than the first temperature.
In the firing step, the above-mentioned resin mixture is heated to a temperature higher than the first temperature, and the aromatic condensation polymer is solvated and decomposed with an organic solvolysis material, followed by thermosetting and carbonization.

  Next, this embodiment will be described in detail.

(Aromatic condensation polymer)
A thermosetting resin can be used as the aromatic condensation polymer. The thermosetting resin here is a self-condensing thermosetting resin having a self-reactive functional group that self-condenses by heating, and a curing agent-added thermosetting resin that can be thermoset by adding a curing agent. Resin. The aromatic condensation polymer used for the carbon material of the present embodiment is a resin material that is thermally cured by heating, and is further carbonized by decomposition and recombination of a part of the thermoset by heating to a high temperature. . Upon such decomposition and recombination, the phenol molecules separate from the thermoset. The first temperature described above is the carbonization start temperature of the aromatic condensation polymer and is higher than the thermosetting temperature. The aromatic condensation polymer may be liquid or solid at room temperature.

  As an example of such a self-condensation type thermosetting resin, a resol type phenol resin (melting point: about 80 ° C.) or a benzoxazine resin can be preferably used. As the resol type phenol resin, a solid resol type phenol resin synthesized by reacting phenols with formaldehyde in the presence of an alkali catalyst can be preferably used. In addition, as an example of a curing agent-added thermosetting resin, a novolac-type phenol resin that is thermally cured by the addition of a curing agent such as hexamethylenetetramine can be preferably used.

The weight average molecular weight of the aromatic condensation polymer is preferably 5 × 10 ³ or more, more preferably 1 × 10 ⁴ or more, and further preferably 2 × 10 ⁴ or more. The upper limit of the weight average molecular weight is not particularly limited, but can be 1 × 10 ⁵ or less. By setting it as said range, the compatibility of an aromatic condensation polymer and organic solvolysis material becomes favorable, and a polycyclic aromatic is formed suitably in a mixing process. Thereby, the carbonization yield of the carbon material obtained through a baking process improves. The weight average molecular weight of the aromatic condensation polymer can be determined by gel permeation chromatography (GPC) soluble in tetrahydrofuran (THF).

  The aromatic condensation polymer is preferably a phenolic hydroxyl group-containing resin having a hydroxyl group equivalent of 300 g / eq or less. The hydroxyl group equivalent of the aromatic condensation polymer is more preferably 200 g / eq or less, further preferably 150 g / eq or less, and particularly preferably 120 g / eq or less. Examples of such resins include novolak-type phenol resins, resol-type phenol resins, and modified phenolic hydroxyl group-containing resins in which an arbitrary modifier is bonded between phenols and phenols. It is not limited. Here, the hydroxyl equivalent means the molecular weight for one hydroxyl group in the phenolic hydroxyl group-containing resin. The hydroxyl equivalent can be measured in accordance with the neutralization titration method defined in JIS K 0070 (1992).

  In addition, examples of the aromatic condensation polymer include epoxy resins such as bisphenol type epoxy resin or novolak type epoxy resin; cyanate resin; phenol furfural resin; aromatic polyether ketone; aromatic polyester resin. The aromatic condensation polymer may be a modified product obtained by modifying the above-described resin with various components.

  The curing temperature of the thermosetting resin is preferably 100 ° C. or higher, and more preferably 125 ° C. or higher. By setting it as this hardening temperature, it copolymerizes favorably with the pitch mentioned later, a crystal structure develops, and a carbonization yield improves.

(Organic solvolysis material)
The organic solvolysis material is an auxiliary agent that causes a solvolysis reaction in the aromatic condensation polymer in the baking step to perform solvolysis (solvolysis). By such solvolysis, the growth of the aromatic ring crystal state in the aromatic condensation polymer is promoted, and the occlusion and release of chemical species are improved in the carbon material after firing. In the firing step described later, the temperature difference between the melting point or softening point of the organic solvolysis material and the melting point or softening point of the aromatic condensation polymer is 100 [K] or less, preferably 20 [K] or less. Solvent decomposition is satisfactorily generated and formation of an aromatic ring crystal structure is promoted. Thereby, the carbonization yield of the carbon material manufactured through a baking process improves.

  Pitch can be used as the organic solvolysis material. As the pitch, it is possible to use coal-based pitch obtained by liquefying coal or distilling off low-boiling components of coal tar, petroleum-based pitch by-produced during ethylene production, or those obtained by crosslinking these pitches. Pitch is a solid or highly viscous viscoelastic body at room temperature (25 ° C), has a melting point or softening point higher than normal temperature, and fluidity is generated or increased by heating above this melting point or softening point. It becomes liquid.

  The melting point or softening point of the pitch is preferably 200 ° C. or lower, and more preferably 100 ° C. or lower. Thereby, the second temperature set higher than the melting point or softening point of the pitch can be set sufficiently lower than the first temperature, which is the decomposition temperature of the aromatic condensation polymer. Therefore, when the aromatic condensation polymer and the organic solvolysis material (pitch) are mixed at the second temperature, the aromatic condensation polymer is sufficiently suppressed from being decomposed and recombined.

The organic solvolysis material may contain metal impurities. However, it is preferable that the metal impurities have a low concentration. Specifically, in the organic solvolysis material used in the present embodiment, the amount of iron (Fe) impurities detected by energy dispersive X-ray microanalysis (EDX) is preferably 50 ppm or less, and 20 ppm or less. It is more preferable that The organic solvolysis material preferably has an amount of zinc (Zn) impurities detected by EDX of 20 ppm or less, and more preferably 5 ppm or less.
By setting the amount of metal impurities in the above range, it is possible to prevent metal impurities from depositing on the negative electrode and destroying the protective coating (SEI: Solid Electrolyte Interphase). For this reason, in the secondary battery which uses the carbon material of this embodiment as a negative electrode, deterioration of battery capacity is suppressed.

(Resin composition)
The resin composition used in this production method is a mixture containing at least an aromatic condensation polymer and an organic solvolysis material. The resin composition preferably contains an organic solvolysis material at a mass ratio of 30% or more and 60% or less with respect to the aromatic condensation polymer, as will be described in detail in Examples described later.

  In addition to this, a curing agent may be added to the resin composition depending on the type of the aromatic condensation polymer. As the curing agent, for example, when the aromatic condensation polymer is a novolac type phenol resin, hexamethylenetetramine, polyacetal, or the like can be preferably used. Further, when the aromatic condensation polymer is a self-condensation type thermosetting resin such as a resol type phenol resin or a benzoxazine resin, a curing agent may optionally be added as a thermosetting aid. When the aromatic condensation polymer is a resol type phenol resin, hexamethylene tetramine can be used as a heat curing aid, and when it is a benzoxazine resin, hexamethylene tetramine or polyacetal can be used as a heat curing aid.

  Examples of other additives blended in the resin composition include organic acids, inorganic acids, nitrogen-containing compounds, oxygen-containing compounds, aromatic compounds, and non-ferrous metal atoms. These additives can be used alone or in combination of two or more depending on the type and properties of the resin used.

In the mixing step in the present production method, the aromatic condensation polymer and the organic solvolysis material are made liquid by bringing the above resin composition to the second temperature and melt-mixed with each other. The starting temperature of the mixing step is not particularly limited, and may be higher or lower than the melting point or softening point of the aromatic condensation polymer. When the aromatic condensation polymer is solid at room temperature, the starting temperature of the mixing step can be lower than the melting point or softening point of the aromatic condensation polymer, for example, normal temperature (25 ° C.). In the mixing step, the aromatic condensation polymer and the organic solvolysis material may be melted in liquid form and mixed with each other by heating from the start temperature to the second temperature. Such melt mixing can be performed with a kneader equipped with a heating device.
When a liquid aromatic condensation polymer is heated to a predetermined high temperature or higher, it generally gels and loses fluidity. The second temperature may be a temperature at which the aromatic condensation polymer and the organic solvolysis material gel. As a result, the copolymerization of the aromatic condensation polymer and the organic solvolysis material is promoted in the firing step, and a crystalline carbonized structure develops. For this reason, the carbonization yield of the carbon material is improved. The time for heating at the second temperature in the mixing step is not particularly limited, but may be 1 minute or more and 60 minutes or less, preferably 10 minutes or more.

  At the second temperature, the aromatic condensation polymer may initiate thermosetting. However, at the second temperature, solvolysis of the aromatic condensation polymer does not substantially occur. That is, the second temperature may be higher than the melting point or softening point of the aromatic condensation polymer and may be equal to or higher than the thermal curing (starting) temperature of the aromatic condensation polymer. On the other hand, the second temperature is lower than the first temperature, which is the carbonization start temperature of the aromatic condensation polymer, and lower than the carbonization start temperature of the organic solvolysis material.

The second temperature should be 10 [K] or more higher than the highest temperature (MP _MAX ) of the melting point or softening point of the aromatic condensation polymer or the melting point or softening point of the organic solvolysis material. preferable. The second temperature is preferably lower than the temperature of +200 [K] from the highest temperature (MP _MAX ). The second temperature can be, for example, 150 ° C. or higher and 200 ° C. or lower. The second temperature is preferably lower than the first temperature, which is the decomposition temperature at which the phenol monomer is separated from the aromatic condensation polymer, at a temperature range of 100 [K] or more, and 200 [K]. It is more preferable that the temperature range is low.

  When the aromatic condensation polymer is a resol type phenol resin or a benzoxazine resin, the first temperature (carbonization start temperature) varies depending on the weight average molecular weight, but is about 400 ° C. or higher and 450 ° C. or lower.

(Resin mixture)
The resin mixture is a resin material obtained by melt-mixing the resin composition at the second temperature, and is a firing precursor that is subjected to a firing process. The resin mixture may be a resin material obtained by thermosetting an aromatic condensation polymer.

In the present manufacturing method, the firing process may be performed in a plurality of stages of heating processes each including a temperature raising process. Hereinafter, the aspect in which a baking process contains a 1st baking process and a 2nd baking process is demonstrated.
In the first firing step, the resin mixture is fired at a third temperature higher than the first temperature (carbonization start temperature) to solvolytically decompose the aromatic condensation polymer, followed by primary carbonization to obtain a carbon material precursor. It is a process of obtaining a body.
The second baking step is a step of pulverizing the carbon material precursor and baking it at a fourth temperature higher than the third temperature to cause secondary carbonization.

  Since the first firing step and the second firing step include a pulverization step between the two steps, they are independent of each other as a step. A cooling step may be included after the first firing step and before or after the grinding step.

  The first firing step is performed at a third temperature higher than the first temperature (for example, 400 ° C. to 450 ° C.). The third temperature is the maximum temperature of the first firing step, and can be a temperature exceeding 450 ° C., preferably 500 ° C. or higher. The third temperature can be 600 ° C. or lower. In the first firing step, the aromatic condensation polymer is solvated and decomposed with the organic solvolysis material by heating to a third temperature higher than the first temperature, which is the carbonization start temperature of the aromatic condensation polymer. .

  In the first firing step, the temperature may be increased from room temperature to a temperature increase rate in the range of 1 ° C./hour to 200 ° C./hour. Here, it is good to make the temperature increase rate in a 1st baking process slower than the temperature increase rate in a 2nd baking process. Thereby, when it heats from normal temperature to a 3rd temperature in a 1st baking process, it will straddle over the 1st temperature from which an aromatic condensation polymer decomposes | disassembles and recombines and a phenol molecule isolate | separates. For this reason, it is suppressed that the decomposition reaction of the aromatic condensation polymer suddenly occurs.

  Here, according to the study of the present inventors, the generation profile of the phenol gas generated from the resin mixture in the first baking step is lower than the generation profile of the phenol gas when the aromatic condensation polymer is baked alone. It became clear to shift to. This is because the aromatic condensation polymer and the organic solvolysis material are melt-mixed in the mixing step in the present production method, and further heated to a temperature higher than the first temperature in the first firing step. We think that aromatic condensation polymer and organic solvolysis material co-carbonize in one firing process, and aromatic condensation polymer is easily decomposed at low temperature by monomeric phenol molecule. It is done. And, since the co-carbonization phenomenon of the aromatic condensation polymer and the organic solvolysis material occurs, the carbonization yield of the carbon material compared with the case where the aromatic condensation polymer is baked alone, as will be described later. It was revealed that the charge / discharge capacity of the secondary battery was improved.

Therefore, the aromatic condensation polymer used in this production method preferably has a phenol gas generation profile shifted to a low temperature side in the first firing step. In order to specify the occurrence of such a co-carbonization phenomenon, the resin mixture may be analyzed by a temperature programmed desorption method instead of actually performing the first firing step. That is, with respect to the amount of phenol gas detected at the peak temperature at which phenol molecules are separated from the aromatic condensation polymer, the temperature is 50 [K], preferably 100 [K] lower than the peak temperature (hereinafter, It is preferable that phenol gas is detected significantly even at a temperature of interest).
As a more specific condition, when the resol type phenol resin is heated, the peak temperature at which the phenol molecules are separated is about 480 ° C. Therefore, in the case of using a resol type phenol resin for the aromatic condensation polymer, the amount of phenol gas generated at a temperature of about 380 ° C. to 430 ° C. (target temperature) is less than the phenol gas generated at 480 ° C. If it is confirmed by the temperature programmed desorption method that it is a significant amount, the resin of this embodiment obtained by melt-mixing an aromatic condensation polymer (resol type phenol resin) and an organic solvolysis material in a mixing step It can be said that the resin mixture is well co-carbonized when the mixture is actually subjected to the first firing step.

  The amount of phenol gas generated at the temperature of interest is preferably 40% or more and 1000% or less, and more preferably 50% or more, with respect to the amount of phenol gas generated at the peak temperature. Further, when analyzing the resin mixture by the temperature programmed desorption method, various combinations of the low temperature side temperature corresponding to the temperature of interest and the high temperature side temperature corresponding to the peak temperature can be set. The high temperature side temperature does not necessarily coincide with the peak temperature in the aromatic condensation polymer, and may be in the vicinity thereof. As specific conditions, if the first temperature at which the phenol molecules are separated from the aromatic condensation polymer and the third temperature, which is the highest temperature in the first firing step, are higher than 500 ° C., the first firing Regarding the resin mixture used in the process, the amount of phenol detected at 400 ° C. (low temperature side temperature) by the temperature programmed desorption method is also detected at 500 ° C. (high temperature side temperature) by the temperature programmed desorption method. It is preferable that it is 40% or more and 1000% or less with respect to the amount of phenol.

  Temperature-programmed desorption (TPD) can be performed using a commercially available temperature-programmed desorption gas analyzer.

Comparative Example 1 of aromatic condensation polymer (resole type phenol resin) alone, resin obtained by melt-mixing aromatic condensation polymer (resol type phenol resin) and organic solvolysis material (pitch) at a mass ratio of 2: 1 The present inventor conducted analysis by the temperature programmed desorption method for a total of 3 samples of Example 1 as a mixture and Comparative Example 2 of the organic solvolysis material (pitch) alone. The temperature programmed desorption method was performed using TPD Type R Photo manufactured by Rigaku Corporation as a temperature programmed desorption gas analyzer. The sample amount was common at 70 mg, and helium gas was supplied as a carrier gas at a flow rate of 300 ml / min. In addition, each sample of Comparative Example 1, Example 1 and Comparative Example 2 was heated and melted and mixed for 15 minutes in a vat heated to 150 ° C. or higher and 200 ° C. or lower, and then cooled to room temperature. .
In the temperature programmed desorption method, the sample was heated from room temperature to 600 ° C. at a rate of temperature increase of 5 ° C./min to 10 ° C./min, and a molecule having a predetermined molecular weight was captured to create a spectrum (see below). 3 (a) to FIG. 3 (c)).

As a result, in the case of Comparative Example 1 in which a resol type phenol resin was heated alone as an aromatic condensation polymer, peaks of phenol spectra were generated at about 150 ° C. and about 480 ° C. (see FIG. 3A). It is considered that the peak at about 150 ° C. was generated by volatilization of unreacted phenol contained in the thermoset green body. On the other hand, the peak at about 480 ° C. is considered to be a peak temperature at which a large amount of phenol gas is generated when the thermoset green body starts to be carbonized and the thermoset decomposes and recombines. The spectral intensity indicating the amount of phenol was about 4.8 × 10 ⁻¹⁰ [A]. The intensity of the phenol spectrum at 400 ° C. was about 1.0 × 10 ⁻¹⁰ [A], and the intensity of the phenol spectrum at 500 ° C. was about 4.4 × 10 ⁻¹⁰ [A].
Therefore, in Comparative Example 1, the amount of phenol detected at 400 ° C. (low temperature side temperature) by the temperature programmed desorption method is the same as the amount of phenol detected at 500 ° C. (high temperature side temperature) by the temperature programmed desorption method. It was about 23%. In addition, the ratio of the detected amount of phenol here is the ionic current intensity at the corresponding temperature in the spectrum obtained by the temperature programmed desorption method performed under the above-described analysis conditions (temperature rising rate is 5 ° C./min). It is the thing which calculated | required ratio.

In addition, a phenol spectrum peak was generated at about 150 ° C. and about 480 ° C. (peak temperature) in the resin mixture of Example 1 in which a resol type phenol resin and pitch were melt-mixed (see FIG. 3B). However, in Example 1, the intensity of the phenol spectrum at the peak at about 480 ° C. increased to about 7.3 × 10 ⁻¹⁰ [A]. In Example 1, the intensity of the phenol spectrum at 400 ° C. is about 3.9 × 10 ⁻¹⁰ [A], and the intensity of the phenol spectrum at 500 ° C. is about 6.9 × 10 ⁻¹⁰ [A]. there were.
Therefore, in Example 1, the amount of phenol detected at 400 ° C. (low temperature side temperature) by the temperature programmed desorption method is the same as the amount of phenol detected at 500 ° C. (high temperature side temperature) by the temperature programmed desorption method. On the other hand, it was about 57%.

On the other hand, in the case of Comparative Example 2 where the pitch was heated alone as the organic solvolysis material, the only peak of the phenol spectrum was generated at about 220 ° C., and its intensity was about 1.5 × 10 ⁻¹⁰ [A]. (See FIG. 3 (c)).

  From the above results, in the case of Example 1, in the vicinity of 400 ° C., that is, in the vicinity of the target temperature, the resol type phenolic resin in the green body is co-carbonized with the pitch, which is lower than the peak temperature of 480 ° C. It was found that carbonization started at temperature, the green body was decomposed, and phenol gas (a monomer of an aromatic condensation polymer) began to be generated.

Returning to the present manufacturing method, the pulverization step performed in the firing step will be described.
Although the grinding | pulverization method in a grinding | pulverization process is not specifically limited, For example, arbitrary grinding | pulverization apparatuses can be used. Examples of the pulverizer include an impact-type pulverizer such as a ball mill device, a vibrating ball mill device, a rod mill device or a bead mill device, or an airflow pulverizer such as a cyclone mill device, a jet mill device or a dry airflow pulverizer. In the pulverization step, the carbon material precursor may be classified using a sieve or the like in addition to these pulverization apparatuses. Or you may perform a grinding | pulverization process using the grinder which has a classification function.

The average particle size of the carbon material precursor after the pulverization step is such that the particle size D ₅₀ at 50% accumulation in the volume-based cumulative distribution is preferably 1 μm or more and 50 μm or less, and more preferably 2 μm or more and 30 μm or less. .

A 2nd baking process is a process of baking and carbonizing the carbon material precursor which is the hardened | cured material produced | generated at the 1st baking process. In the second firing step, the carbon material precursor is fired at a fourth temperature that is higher than the maximum temperature (third temperature) of the first firing step. In the second firing step, the temperature is increased from room temperature at a temperature increase rate in the range of 1 ° C./hour to 500 ° C./hour. It is preferable that the temperature increase rate in the second baking step is larger than the temperature increase rate in the first baking step.
The fourth temperature can be 800 ° C. or higher and 3000 ° C. or lower. The heating at the fourth temperature can be carried out by maintaining for 0.1 hour or more and 50 hours or less, preferably 0.5 hour or more and 10 hours or less. The atmosphere at the time of the second firing step is not particularly limited. For example, in addition to an inert gas atmosphere containing an inert gas such as nitrogen or helium gas, a mixed gas atmosphere in which a small amount of oxygen is mixed with the inert gas, hydrogen, or the like It is possible to employ a reducing gas atmosphere mainly containing the reducing gas.

The carbon material of the present embodiment obtained by performing the second firing step is generally called hard carbon or non-graphitizable carbon, and has a (002) plane obtained by an X-ray diffraction method using CuKα rays as a radiation source. The average interplanar distance d ₀₀₂ is 0.340 nm or more, preferably 0.375 nm or more.

  Hereinafter, the negative electrode active material of the present invention including the carbon material of the present invention, the secondary battery negative electrode of the present invention including the negative electrode active material layer including the negative electrode active material, and the present invention including the secondary battery negative electrode. The secondary battery will be described.

  The active material for secondary battery negative electrodes of this embodiment contains the carbon material (carbon material) for secondary battery negative electrodes mentioned above. Therefore, the manufacturing method of the active material for secondary battery negative electrodes includes the manufacturing method of the said carbon material. By containing the carbon material described above, the negative electrode active material of the present embodiment has a high carbonization yield and excellent charge / discharge characteristics of the secondary battery. The negative electrode active material refers to a material capable of occluding and releasing chemical species that serve as charge carriers in the secondary battery negative electrode. Examples of the chemical species include lithium ions or sodium ions in an alkali metal ion secondary battery. The negative electrode active material may be substantially composed of only the carbon material of the present embodiment, but may further include a material different from the carbon material. Examples of such materials include materials generally known as negative electrode materials such as silicon, silicon monoxide, and other graphite materials.

  Further, the secondary battery negative electrode of the present embodiment has at least the surface of the secondary battery negative electrode active material layer including the secondary battery negative electrode active material of the present embodiment described above and the secondary battery negative electrode active material layer. And a negative electrode current collector disposed in the portion. In addition, the secondary battery of the present embodiment is configured to include the above-described secondary battery negative electrode, an electrolytic layer, and a secondary battery positive electrode. Therefore, the method for producing a secondary battery negative electrode includes a method for producing a secondary battery negative electrode active material, and the method for producing a secondary battery includes a method for producing a secondary battery negative electrode.

  Examples of the secondary battery include, but are not limited to, an alkali metal secondary battery such as a lithium ion secondary battery or a sodium ion secondary battery. The secondary battery includes various types using different electrolytes such as a non-aqueous electrolyte secondary battery and a solid secondary battery. In the following description, a lithium ion secondary battery will be described as an example of a secondary battery.

  Below, an example of the lithium ion secondary battery containing the carbon material of this embodiment is demonstrated using FIG. FIG. 1 is a schematic view showing an example of a lithium ion secondary battery 100 including the carbon material of the present embodiment. The lithium ion secondary battery 100 includes a negative electrode 10, a positive electrode 20, a separator 30, and an electrolytic layer 40.

  As shown in FIG. 1, the negative electrode 10 includes a negative electrode active material layer 12 and a negative electrode current collector 14. The negative electrode active material layer 12 is laminated and disposed on at least part of the surface of the negative electrode current collector 14. The negative electrode active material layer 12 contains the carbon material described above. The negative electrode current collector 14 is not particularly limited, and a current collector that can be used for the negative electrode can be appropriately selected and used. For example, a copper foil or a nickel foil can be used.

The negative electrode 10 can be manufactured as follows, for example.
A known organic polymer binder and an appropriate amount of a viscosity adjusting solvent or water are added to the negative electrode active material and kneaded to prepare a negative electrode slurry. The obtained slurry can be formed into a sheet shape, a pellet shape, or the like by compression molding, roll molding, or the like, and the negative electrode active material layer 12 can be obtained. The negative electrode 10 can be obtained by laminating the negative electrode active material layer 12 and the negative electrode current collector 14 thus obtained. Moreover, the negative electrode 10 can also be manufactured by apply | coating the obtained negative electrode slurry to the negative electrode collector 14, and drying.

The electrolytic layer 40 fills between the positive electrode 20 and the negative electrode 10, and is a layer in which lithium ions move by charge / discharge. The electrolytic layer 40 can be configured by filling a known electrolyte. As the electrolyte, for example, a nonaqueous electrolytic solution in which a lithium salt serving as an electrolyte is dissolved in a nonaqueous solvent is used. As the electrolyte, a known substance can be used. For example, a lithium metal salt such as LiClO ₄ or LiPF ₆ can be used.

  In the case of a secondary battery other than the non-aqueous electrolyte secondary battery, the electrolytic layer 40 has a gel polymer electrolyte containing a polymer material such as polyethylene oxide or polyacrylonitrile, or a solid such as zirconia. The aspect which has electrolyte is mentioned.

  The separator 30 is not particularly limited, and can be a member that is permeable to chemical species such as lithium ions, and a known separator can be used. For example, a porous film, a nonwoven fabric, or the like configured using polyethylene or polypropylene is used. Can be mentioned.

As illustrated in FIG. 1, the positive electrode 20 includes a positive electrode active material layer 22 and a positive electrode current collector 24.
The positive electrode active material layer 22 can be formed of a known positive electrode active material. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), and ternary Li (Ni _1/3 Mn _1/3). A composite oxide such as Co _1/3 ) O ₂ ; a conductive polymer such as polyaniline and polypyrrole; and the like can be used.
The positive electrode active material contains an organic polymer binder and a conductive material in the same manner as the negative electrode active material described above. The blending amounts of the organic polymer binder and the conductive material in the positive electrode active material are not particularly limited, and may be the same as the negative electrode active material or may be blended in an amount different from the negative electrode active material.

  As the positive electrode current collector 24, a known positive electrode current collector can be used. For example, an aluminum foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, or the like can be used.

  Although the lithium ion secondary battery 100 has been described above as an example, the carbon material of the present embodiment can also be used for a secondary battery using alkali ions other than lithium ions as chemical species such as sodium ions.

  Examples of the present invention and comparative examples will be described below. However, the present invention is not limited to the following examples and comparative examples. In Examples, “part” indicates “part by mass”, and “%” indicates “% by mass”.

  The carbon mixture is produced by subjecting the resin mixture of Example 1 described above to the thermal desorption method analysis results to the first and second firing steps, and further using such a carbon material, a half-cell lithium ion secondary A battery was prepared and charge / discharge characteristics were evaluated. This will be described in detail below.

<Creation of carbon material>
100 parts of phenol, 55 parts of paraformaldehyde, and 1 part of zinc acetate are placed in a three-necked flask equipped with a stirrer and a condenser, reacted at 100 ° C. for 3 hours, dehydrated, and then subjected to reaction conditions at 100 ° C. for 2 hours. Was then aged to obtain 90 parts of a solid resol type phenolic resin. On the other hand, as an organic solvolysis material (pitch), coal-based pitch powder obtained by distilling off low-boiling components from coal tar was prepared. The pitch softening point temperature was 74 ° C. or higher and 80 ° C. or lower, toluene insoluble content (TI) was 10% or higher, and quinoline insoluble content (QI) was 0.3% or lower.

Next, Examples 1 to 3, Reference Example 1, and Comparative Example 1 were prepared by changing the blending ratio of the organic solvolysis material (pitch) and the aromatic condensation polymer (resole type phenol resin) as follows. And 2 were prepared.
That is, the blending ratio with the pitch: resol type phenol resin was 1: 2 in Example 1, 1: 5 in Example 2, 1: 1 in Example 3, 2: 1 in Reference Example 1, and Comparative Example 1 It was set to 0: 1 and 1: 0 in Comparative Example 2. That is, the pitch ratio defined as (pitch ratio) = mass of pitch / (mass of pitch + mass of resol type phenol resin) is 0 in Comparative Example 1, 0.33 in Example 1, and 0 in Example 2. .17, 0.5 in Example 3, 0.67 in Reference Example 1, and 1 in Comparative Example 2.
Further, Reference Example 2 in which the blending ratio of the organic solvolysis material (pitch) and the aromatic condensation polymer (novolak type phenol resin) was 1: 2, and Comparative Example 3 in which the blending ratio was 0: 1 were used. Got ready. That is, the pitch ratio defined as (pitch ratio) = mass of pitch / (mass of pitch + mass of novolac type phenol resin) was 0.33 in Reference Example 2 and 0 in Comparative Example 3.
For Examples 1 to 3 and Reference Example 1, the total mass of the resol type phenolic resin and the pitch, in Comparative Example 1, the mass of the resol type phenolic resin, in Comparative Example 2, the mass of the pitch, , The total mass of the novolac type phenolic resin and the pitch, and in Comparative Example 3, the mass of the novolac type phenolic resin was measured as the carbon mass of the starting material.

  In the mixing step, Examples 1 to 3 and Reference Example 1 were mixed for 15 minutes until gelation in a vat heated to 180 ° C., and Reference Example 2 was mixed for 20 minutes in a vat heated to 200 ° C. And mixed with a spatula. Thus, for Reference Example 2, the novolac type phenol resin and pitch were melt-mixed, and for Examples 1 to 3 and Reference Example 1, the resol-type phenol resin and pitch were melt-mixed.

  In the first firing step, heating is performed from room temperature to 550 ° C. at a heating rate of 100 ° C./hour in a nitrogen atmosphere using a vacuum-replacement electric furnace and held at 550 ° C. for 1.5 hours. did. Thereby, the resin of each example was thermoset to obtain a carbon material precursor. Regarding Examples 1 to 3 and Reference Example 1, a resol type phenol resin was subjected to solvent decomposition with pitch and then primary carbonized to obtain a carbon material precursor. Regarding Reference Example 2, a novolac type phenolic resin was solvated and decomposed with pitch and then primary carbonized to obtain a carbon material precursor. The mass of the obtained carbon material precursor was measured, the ratio with the carbon mass of the starting material was calculated, and the carbonization yield by the primary firing step was determined.

In the second firing step, a pulverization step was first performed. In the pulverization step, the carbon material precursor, which is the thermoset of each example, was naturally allowed to cool to room temperature (about 22 ° C.), and then centrifugal pulverization (coarse pulverization) and ball mill pulverization (fine pulverization) were performed. In the pulverization step, the carbon material precursor was pulverized to an average particle diameter (particle diameter D ₅₀ ) of about 15 μm for the pitch-only comparative example 2, and the carbon material precursor was average particle diameter (particle diameter D) for the other examples. ₅₀ ) Grind to 10 μm or more and 10.5 μm or less.

Next, it heated from normal temperature to 1200 degreeC by the temperature increase rate of 300 degreeC / hour in nitrogen atmosphere, and hold | maintained at 1200 degreeC for 2 hours. Thereby, the resin of each example was secondarily carbonized.
Thereafter, the particles were sized using a 105-mesh sieve to obtain a carbon material according to each example. The mass of the obtained carbon material was measured, the ratio with the mass of the carbon material precursor after the primary firing was calculated, and the carbonization yield by the secondary firing step was determined.

FIG. 2 is a graph showing the relationship between the pitch ratio and the carbonization yield according to Examples 1 to 3, Reference Example 1 and Comparative Examples 1 and 2 when the blending ratio of the resol type phenol resin and the pitch is changed. It is. Specifically, the pitch ratios in Examples 1 to 3, Reference Example 1, and Comparative Examples 1 and 2 are plotted on the horizontal axis, and the total carbonization yield through the primary and secondary firing steps is plotted on the vertical axis. . The one-dot chain line shown in the figure is a line segment connecting the results of Comparative Example 1 and Comparative Example 2. This dashed-dotted line has shown the arithmetic mean of the carbonization yield at the time of baking a resol type phenol resin and a pitch separately. The carbonization yield in Comparative Example 1 (pitch ratio = 0) is 57.5%, and the carbonization yield in Comparative Example 2 (pitch ratio = 1) is 45.9%. For example, the pitch ratio = 0. The arithmetic average of the carbonization yield at 5 is 51.7% = (57.5% + 45.9%) / 2.
On the other hand, since the total carbonization yield of the carbon material in Example 3 was 54.2%, it was 104.9 [%] = 54.2 / 51.7 × 100 from the calculated value of the arithmetic mean. The carbonization yield is improved by [%]. In this specification, the ratio of the total carbonization yield actually measured with respect to the arithmetic mean value of the carbonization yield computed from the result of the comparative example 1 and the comparative example 2 is called a co-carbonization effect. When this co-carbonization effect exceeds 100%, it can be said that the improvement effect of the carbonization yield exceeding the state which baked the resol type phenol resin and pitch separately is recognized.

  Table 1 below summarizes the pitch ratio, the measured value of the total carbonization yield, the calculated value of the arithmetic mean, and the co-carbonization effect for Examples 1 to 3 and Reference Example 1. From the results shown in FIG. 2 and Table 1, from the viewpoint of carbonization yield of the carbon material, a co-carbonization effect is recognized over a range where the pitch ratio exceeds 0% and is 60% or less. As in Examples 1 to 3, a co-carbonization effect of about 105% or more was observed in the range of 15% to 60%. In addition, regarding the total carbonization yield of the carbon material of Reference Example 2 in which the novolac-type phenol resin and pitch were co-carbonized, no significant effect as in Examples 1 to 3 was observed.

<TPD analysis>
With respect to the carbon materials of Examples, Comparative Examples, and Reference Examples, the raw material resin or resin mixture was analyzed by a temperature programmed desorption method (TPD). 3 (a) to 3 (c) show the resol type phenol resin of Comparative Example 1, the resin mixture of Example 1, and the organic solvolysis material (pitch) of Comparative Example 2 by the temperature programmed desorption method, respectively. It is the temperature-programmed desorption spectrum analyzed. 4 (a) and 4 (b) are temperature programmed desorption spectra of the novolac phenol resin of Comparative Example 3 and the resin mixture of Reference Example 2. FIG. 5A to 5C are temperature-programmed desorption spectra of the organic solvolysis material (pitch) of Comparative Example 2, the resin mixture of Reference Example 2, and the resin mixture of Example 1. FIG. 3 to 5, the horizontal axis represents temperature [° C.], and the vertical axis represents ion current intensity [A] of a quadrupole mass spectrometer (QMS).

  TPD was performed as follows. That is, TPD Type R Photo manufactured by Rigaku Corporation was used as a temperature-programmed desorption gas analyzer. The ionization method is an electron impact ionization method. The sample amount of the resin or resin mixture used as the raw material for the carbon material was 70 mg in common, and helium gas was supplied as a carrier gas at a flow rate of 300 ml / min. Then, the resin or resin mixture was heated from 30 ° C. to 600 ° C. at a rate of temperature increase of 10 ° C./min, and a spectrum having a predetermined molecular weight was captured.

  However, the attribution of peaks observed in each temperature programmed desorption spectrum was as follows. That is, the peak of mass m divided by charge z (m / z) = 78 is benzene, m / z = 94 peak is phenol, m / z = 108 peak is cresol, m / z = 178 peak Is an anthracene, and the peak at m / z = 202 is the spectrum of pyrene.

As shown in FIG. 3 (a), in Comparative Example 1 prepared by using a resole-type phenol resin alone without blending pitch, two peaks of the phenol spectrum were generated at about 150 ° C and about 480 ° C.
As shown in FIG. 3B, in the resin mixture of Example 1 in which a resol type phenolic resin and pitch were melt-mixed, the same tendency as in Comparative Example 1 was observed with respect to the phenol spectrum. And the peak of pyrene occurred in two places in total, one place at 100 to 200 ° C. and one place at 300 to 500 ° C.
As shown in FIG.3 (c), in the comparative example 2 produced only with the pitch, the peak of the phenol and the pyrene generate | occur | produced at about 230 degreeC.

As shown in FIG. 4 (a), in Comparative Example 3 prepared with novolac-type phenol resin alone without blending pitch, a sharp first peak of the phenol spectrum was generated at about 360 ° C., and at about 450 ° C. A second peak duller than the first peak occurred.
As shown in FIG. 4B, in the resin mixture of Reference Example 2 in which pitch and novolac type phenol resin were mixed, a sharp peak of the phenol spectrum was generated at about 340 ° C., and pyrene was observed at 100 ° C. or more and 400 ° C. or less. Peak occurred.

The following tendencies were observed for the temperature programmed desorption spectrum of pyrene. That is, as shown in FIG. 5 (a), in Comparative Example 2 prepared with only the pitch, one sharp peak was generated at about 230 ° C. As shown in FIG. 5B, a broad peak was generated from about 190 ° C. to about 270 ° C. in Reference Example 2, which is a co-carbonized material of novolac type phenol resin with a pitch ratio of 33%. Then, as shown in FIG. 5 (c), in the resin mixture of Example 1, which is a co-carbonized material of a resol type phenol resin with a pitch ratio of 33%, a sharp first peak occurs at about 170 ° C. In addition, a sharp second peak was generated at about 380 ° C. Between the first peak temperature and the second peak temperature, there was a temperature (about 250 ° C.) at which the ionic current intensity reached the base level.
In other words, the temperature-programmed desorption spectrum of the pyrene component applied to the resin mixture of Example 1 independently has a first peak at a temperature below 300 ° C. and a second peak at a temperature of 300 ° C. or higher. ing. Here, having the first and second peaks independently means that there exists a temperature at which the ion current intensity becomes the base level between the temperature of the first peak and the temperature of the second peak. .
That is, a single curve having a sharp peak is generated in the spectrum of pitch alone (Comparative Example 2), whereas it is broad in the spectrum of the resin mixture of Reference Example 2 which is a co-carbonized material of novolac type phenol resin and pitch. One curve with a sharp peak was generated. The broad peak means that there are a plurality of local peaks, and there is no temperature at which the ion current intensity becomes the base level between the temperatures of the peaks. In the spectrum of the resin mixture of Example 1, which is a co-carbonized material of resol type phenolic resin and pitch, it was found that two curves each having a sharp peak were generated. In Example 1, it is found that the curves exist independently on the low temperature side and the high temperature side across 300 ° C. (that is, the temperature at which the ionic current intensity becomes the base level is interposed between the curves). It was.

  Therefore, in the temperature-programmed desorption spectrum of pyrene shown in FIGS. 5A to 5C, intensity integral values were calculated for the low temperature side, the high temperature side, and the entire temperature range with 300 ° C. as the boundary. That is, the integrated intensity value at 30 ° C. or more and less than 300 ° C., the integrated intensity value at 300 ° C. or more and less than 600 ° C., and the integrated intensity value in the entire temperature range of 30 ° C. or more and less than 600 ° C. were calculated. The integrated intensity value is a value obtained by integrating the ionic current intensity [A] over each temperature range, and corresponds to the amount of the pyrene component desorbed by heating from the resin or the resin mixture in each temperature range. The results are shown in Table 2.

  Next, in each example of Comparative Example 2, Reference Example 2 and Example 1, the ratio of the integrated intensity value of pyrene at less than 300 ° C. and the integrated intensity value of pyrene at 300 ° C. or higher was calculated. The results are shown in Table 3. As shown in Table 3, it was found that 92% of the total amount of the pyrene component desorbed at a temperature was desorbed at less than 300 ° C. in the resin of Comparative Example 2 prepared by pitch alone. In addition, in the resin mixture of Reference Example 2 which is a co-carbonized material of novolac-type phenolic resin and pitch, it was found that 81% of the total amount of pyrene component desorbed at a temperature was desorbed at less than 300 ° C. On the other hand, in the resin mixture of Example 1 which is a co-carbonized material of a resol type phenolic resin and pitch, 19% of the total amount of pyrene components desorbed at a temperature is desorbed at less than 300 ° C., and 81% is 300%. It was found that it desorbed at a temperature higher than ℃.

  That is, the total amount of pyrene detected at 300 ° C. or more and less than 600 ° C. is higher than the total amount of pyrene detected at 30 ° C. or more and less than 300 ° C. in the temperature programmed desorption method. There were more. More specifically, the total amount of pyrene detected at 300 ° C. or more and less than 600 ° C. is more than twice the total amount of pyrene detected at 30 ° C. or more and less than 300 ° C. by the temperature programmed desorption method , Preferably 3 times or more, and in Example 1 exceeded 4 times. The total carbonization yield of the carbon material produced by applying the primary and secondary firing steps to the resin mixture of Example 1 exceeded the arithmetic average as shown in Table 1 above.

  Although the cause of this phenomenon is not always clear, when a carbon material is obtained from the resin mixture of Example 1 obtained by co-carbonizing a resol type phenol resin and pitch, in the first firing step, a self-reactive thermosetting resin is used. It can be considered that this is caused by confining a pitch component inside the resol-type phenolic resin that is gelled and then thermally cured. For this reason, it is considered that the pitch component is suppressed from volatilizing from the carbon material precursor in the subsequent second firing step, and as a result, the total carbonization yield is improved. On the other hand, when a carbon material is obtained from the resin mixture of Comparative Example 2 which is pitch alone or Reference Example 2 obtained by co-carbonizing novolac type phenolic resin and pitch, the crosslinking reaction of the thermosetting resin does not occur as in Example 1. The carbon material precursor after the first firing step does not confine the pitch component significantly, and therefore the pitch component easily volatilizes in the second firing step, and it is considered that the improvement of the total carbonization yield was not seen. It is done.

  According to the above method, whether or not the resin mixture is capable of improving the total carbonization yield of the carbon material by paying attention to the temperature-programmed desorption spectrum mainly relating to the pyrene component volatilized from the pitch is determined as a firing step. It can be determined before.

<Creation of half-cell lithium-ion secondary battery>
Using the negative electrode (working electrode), counter electrode and electrolyte solution containing the carbon material obtained in each example, a half cell was prepared as follows.

(Creation of negative electrode)
In order to evaluate the battery characteristics of the carbon material of each example obtained as described above, a negative electrode was prepared as follows.
First, 100 parts of the carbon material of each example is blended in a ratio of 3 parts of styrene / butadiene rubber as a binder, 1.5 parts of carboxymethyl cellulose as a thickener, and 2 parts of acetylene black as a conductive material, and pure water is added. An appropriate amount was added and diluted to obtain a slurry-like negative electrode mixture.
The obtained slurry-like mixture for negative electrode was applied to a copper foil (current collector) having a thickness of 10 μm by the same amount, preliminarily dried at 60 ° C. for 2 hours, and then vacuum dried at 120 ° C. for 15 hours. Next, a disk-shaped lithium ion secondary having a diameter of 13 mm and an electrode active material layer (a portion excluding the current collector) having a thickness of 50 μm is punched out into a predetermined shape by being pressed into a thickness of 60 μm by a roll press. A negative electrode for a battery was prepared. The shape of the half cell was a 2032 type coin cell shape.

(Create counter electrode)
A lithium metal having a diameter of 12 mm and a thickness of 1 mm was prepared as a counter electrode.

(Preparation of electrolyte)
An electrolytic solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 mol / liter in a mixed solution (volume ratio 3: 7) of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). .

(Charge / discharge conditions)
The charging / discharging conditions of the half cell were as follows. Charging of a half cell means moving lithium ions from a counter electrode made of metallic lithium to a negative electrode (working electrode) containing a carbon material by applying a voltage. On the other hand, half-cell discharge means that lithium ions move from a negative electrode (working electrode) containing a carbon material to a counter electrode composed of metallic lithium.

Charging / discharging conditions: Constant current charging is performed at a measurement temperature of 25 ° C., a current density during charging of 25 mA / g, and when the potential reaches 0 mV, constant voltage charging is performed while maintaining 0 mV. The amount of electricity charged to 2.5 mA / g was taken as the charge capacity. The amount of electricity charged during constant current charging was defined as a constant current charging capacity.
Next, constant current discharge was performed at a current density of 25 mA / g during discharge, and the amount of electricity when the potential reached 2.5 V was defined as the discharge capacity.
A total of two cycles of charging / discharging under the above conditions were performed.

  Table 4 below summarizes the charge / discharge capacity and charge / discharge efficiency of the first cycle and the constant current charge capacity of the second cycle for each of the Examples, Reference Examples, and Comparative Examples. The charge / discharge efficiency (efficiency) was calculated using the following mathematical formula (1).

[Equation 1]
Charge / Discharge Efficiency (%) = Discharge Capacity (mAh / g) / Charge Capacity (mAh / g) × 100 (1)

As shown in Table 4, the charge capacity and discharge capacity of the first cycle and the constant current charge capacity of the second cycle of the half-cell secondary batteries using the carbon materials of Examples 1 to 3 are higher than those of Comparative Examples 1 and 2. It became a thing. Here, the constant current charge capacity in the second cycle is an important characteristic value because it is a charge capacity at a constant current close to the actual use situation in the second cycle in which the battery characteristics are stable. A higher value was obtained as compared with Example 2. As a result, from the viewpoint of the charge / discharge capacity of the secondary battery, Examples 1 to 3, particularly Examples 1 and 3, gave good results. In other words, from the viewpoint of the charge / discharge capacity of the secondary battery, an improvement effect is recognized over a range where the pitch ratio exceeds 0% and is 60% or less, and the pitch ratio is particularly 30% or more and 60% or less. In Examples 1 and 3 which are the above, good improvement effects were observed.
From the above, it can be said that the resin composition used in the mixing step of the present production method preferably contains the organic solvolysis material in a mass ratio of 30% to 60% with respect to the aromatic condensation polymer.

The above embodiment includes the following technical idea.
(1) The temperature difference between the aromatic condensation polymer from which phenol molecules are separated by heating to a first temperature higher than 25 ° C. and the melting point or softening point of the aromatic condensation polymer is 100 [K] or less. And an organic solvolysis material having at least a melting point or a softening point, the melting point or the softening point of the aromatic condensation polymer, and the melting point or the softening point of the organic solvolysis material. A mixing step of obtaining a resin mixture by mixing at a second temperature that is higher than the first temperature and lower than the first temperature; and heating the resin mixture to a temperature higher than the first temperature to obtain the aromatic condensation polymer. A method for producing a carbon material for a negative electrode of a secondary battery, comprising: a calcination decomposition with the organic solvolysis material, followed by heat curing and carbonization.
(2) In the firing step, the resin mixture is fired at a third temperature higher than the first temperature, whereby the aromatic condensation polymer is primaryly carbonized after being solvated and decomposed to obtain a carbon material precursor. (1) including a first firing step of obtaining a body, and a second firing step of pulverizing the carbon material precursor and firing the carbon material precursor at a fourth temperature higher than the third temperature to perform secondary carbonization. The manufacturing method of the carbon material for secondary battery negative electrodes as described in).
(3) The third temperature is higher than 500 ° C., and the resin mixture subjected to the first baking step has a phenol amount detected at 400 ° C. by a temperature programmed desorption method. 40% or more and 1000% or less with respect to the amount of phenol detected at 500 degreeC by the temperature-programmed desorption method, The manufacturing method of the carbon material for secondary battery negative electrodes as described in said (2) characterized by the above-mentioned.
(4) Any one of (1) to (3) above, wherein the resin composition contains the organic solvolysis material in a mass ratio of 30% to 60% with respect to the aromatic condensation polymer. The manufacturing method of the carbon material for secondary battery negative electrodes of description.
(5) The carbon material for a secondary battery negative electrode according to any one of (1) to (4), wherein the aromatic condensation polymer is a thermosetting resin and the organic solvolysis material is a pitch. Manufacturing method.
(6) The manufacturing method of the carbon material for secondary battery negative electrodes as described in said (5) whose said melting | fusing point or the said softening point of the said pitch is 200 degrees C or less.
(7) The manufacturing method of the carbon material for secondary battery negative electrodes as described in said (5) or (6) whose curing temperature of the said thermosetting resin is 100 degreeC or more.
(8) The method for producing a carbon material for a secondary battery negative electrode according to any one of (5) to (7), wherein the thermosetting resin is a resol type phenol resin or a benzoxazine resin.
(9) The organic solvolysis material is any one of (1) to (8), wherein the amount of iron (Fe) impurities detected by energy dispersive X-ray microanalysis (EDX) is 50 ppm or less. The manufacturing method of the carbon material for secondary battery negative electrodes of description.
(10) The organic solvolysis material according to any one of (1) to (9), wherein the amount of zinc (Zn) impurities detected by energy dispersive X-ray microanalysis (EDX) is 20 ppm or less. The manufacturing method of the carbon material for secondary battery negative electrodes of description.
(11) A method for producing an active material for a secondary battery negative electrode, comprising the method for producing a carbon material for a secondary battery negative electrode according to any one of (1) to (10) above.
(12) A method for producing a secondary battery negative electrode, including the method for producing an active material for a secondary battery negative electrode according to (11) above.
(13) A method for producing a secondary battery, including the method for producing a secondary battery negative electrode described in (12) above.

DESCRIPTION OF SYMBOLS 10 Negative electrode 12 Active material layer 14 for negative electrodes Negative electrode collector 20 Positive electrode 22 Positive electrode active material layer 24 Positive electrode collector 30 Separator 40 Electrolytic layer 100 Lithium ion secondary battery

Claims (15)

A melting point where the temperature difference between the aromatic condensation polymer from which phenol molecules are separated by heating to a first temperature higher than 25 ° C. and the melting point or softening point of the aromatic condensation polymer is 100 [K] or less. Or an organic solvolysis material having a softening point, and a resin composition containing at least the melting point or the softening point of the aromatic condensation polymer and a temperature higher than the melting point or the softening point of the organic solvolysis material. And a mixing step of obtaining a resin mixture by mixing at a second temperature lower than the first temperature;
A secondary battery comprising: a baking step in which the resin mixture is heated to a temperature higher than the first temperature, and the aromatic condensation polymer is solvated and decomposed with the organic solvolysis material, followed by thermosetting and carbonization. Manufacturing method of carbon material for negative electrode. The firing step is
A first firing step of calcining the resin mixture at a third temperature higher than the first temperature to first carbonize the aromatic condensation polymer and then carbonize the aromatic condensation polymer to obtain a carbon material precursor; ,
The carbon material precursor is pulverized, and then calcined at a fourth temperature higher than the third temperature to be second carbonized, and a secondary firing step charcoal for secondary battery negative electrode according to claim 1. Material manufacturing method. The third temperature is higher than 500 ° C., and
The amount of phenol detected at 400 ° C. by the temperature programmed desorption method is less than the amount of phenol detected at 500 ° C. by the temperature programmed desorption method. It is 40% or more and 1000% or less, The manufacturing method of the carbon material for secondary battery negative electrodes of Claim 2 characterized by the above-mentioned.   The spectrum of the temperature programmed desorption method of the pyrene component applied to the resin mixture independently has a first peak at a temperature of less than 300 ° C and a second peak at a temperature of 300 ° C or higher. 3. A method for producing a carbon material for a secondary battery negative electrode according to 3.   In the resin mixture, the total amount of pyrene detected at 300 ° C. or more and less than 600 ° C. is larger than the total amount of pyrene detected at 30 ° C. or more and less than 300 ° C. by the temperature programmed desorption method. The manufacturing method of the carbon material for secondary battery negative electrodes of Claim 4 characterized by these.   6. The secondary battery according to claim 1, wherein the resin composition contains the organic solvolysis material in a mass ratio of 30% to 60% with respect to the aromatic condensation polymer. Manufacturing method of carbon material for negative electrode.   The method for producing a carbon material for a secondary battery negative electrode according to any one of claims 1 to 6, wherein the aromatic condensation polymer is a thermosetting resin, and the organic solvolysis material is a pitch.   The method for producing a carbon material for a secondary battery negative electrode according to claim 7, wherein the melting point or the softening point of the pitch is 200 ° C. or less.   The method for producing a carbon material for a secondary battery negative electrode according to claim 7 or 8, wherein a curing temperature of the thermosetting resin is 100 ° C or higher.   The method for producing a carbon material for a secondary battery negative electrode according to any one of claims 7 to 9, wherein the thermosetting resin is a resol type phenol resin or a benzoxazine resin.   The secondary battery according to any one of claims 1 to 10, wherein the organic solvolysis material has an iron (Fe) impurity amount of 50 ppm or less detected by energy dispersive X-ray microanalysis (EDX). Manufacturing method of carbon material for negative electrode.   The secondary battery according to any one of claims 1 to 11, wherein the organic solvolysis material has an amount of zinc (Zn) impurities detected by energy dispersive X-ray microanalysis (EDX) of 20 ppm or less. Manufacturing method of carbon material for negative electrode.   The manufacturing method of the active material for secondary battery negative electrodes including the manufacturing method of the carbon material for secondary battery negative electrodes as described in any one of Claims 1-12.   The manufacturing method of a secondary battery negative electrode including the manufacturing method of the active material for secondary battery negative electrodes of Claim 13.   The manufacturing method of a secondary battery including the manufacturing method of the secondary battery negative electrode described in Claim 14.

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