JP2019053954A - Fibrous carbon material and method for manufacturing the same - Google Patents

Abstract

To provide: a method for manufacturing fibrous carbon material for a conductive assistant of an electrode of a nonaqueous electrolyte secondary battery, which can enhance the cycle characteristics of a nonaqueous electrolyte secondary battery by performing a surface modification treatment on fibrous carbon material in comparison to the cycle characteristics achieved without performing such a surface modification treatment; and fibrous carbon material obtained by the method.SOLUTION: A fibrous carbon material to be used as a conductive assistant of a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode and an electrolyte, of which the ratio of fluorine atoms to carbon atoms, namely F/C ratio is no less than 0.001 and less than 0.025, and the ratio of oxygen atoms to the carbon atoms, namely O/C ratio is no less than 0.05 and less than 0.2, where those are measured by XPS analysis.SELECTED DRAWING: None

Description

  The present invention relates to a fibrous carbon material used as a conductive additive for an electrode of a nonaqueous electrolyte secondary battery represented by a lithium ion secondary battery, a method for producing the same, and a nonaqueous electrolyte secondary battery including the fibrous carbon material. The present invention relates to an electrode, a manufacturing method thereof, and a nonaqueous electrolyte secondary battery including the electrode.

  For the positive electrode and negative electrode of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, a metal composite oxide is mainly used for the positive electrode as an active material, and a carbon-based material such as graphite is mainly used for the negative electrode. A paste type electrode is used in which a paste containing carbon black or graphite fine powder as a conductive additive and a binder is applied to a metal foil as a current collector to form an electrode layer on the current collector. .

  In recent years, the number of electric vehicles that employ lithium ion secondary batteries has increased. One of the important characteristics of non-aqueous electrolyte secondary batteries for automobiles is output characteristics indicating the amount of current that can flow per unit time, and cycle characteristics that can maintain discharge capacity even after repeated charge and discharge.

  In order to improve the output characteristics of the non-aqueous electrolyte secondary battery, it is important to reduce the internal resistance of the battery as much as possible. For this reason, the conductive auxiliary agent that forms the conductive network in the electrode is uniformly distributed throughout the electrode material. There is a technique for reducing electrode resistance by dispersing it at a high concentration. Since carbon black has a structure in which primary particles called a structure are connected in a chain form, it is necessary to use a dispersing agent in order to prevent the structure from agglomerating and cutting and to appropriately disperse it in the electrode material. Patent Document 1 discloses a method of uniformly dispersing a positive electrode active material and a carbon material that is a conductive additive by using a nitrogen-based surfactant as a dispersant. Patent Document 2 discloses a method of stably dispersing a positive electrode active material, a binder, and a carbon material as a conductive auxiliary agent by using a triazine derivative or the like as a dispersant.

  Patent Document 3 discloses an active material (A), a conductive assistant (B), and a binder as a method for producing an electrode slurry for a lithium ion battery in which the dispersibility of the conductive assistant is improved without using a dispersant. The manufacturing method of the slurry (G) including the process of removing (F) from what mixed (C) and the solvent (D) in the supercritical fluid or the subcritical fluid (F) is disclosed.

  Further, it is known that when a fibrous carbon material is used as a conductive aid for the positive electrode or the negative electrode, the change in the electrode structure can be suppressed with charge / discharge, and the cycle characteristics are improved. For example, Patent Document 4 and Patent Document 5 disclose non-aqueous electrolyte secondary batteries that include a fibrous carbon material as a conductive additive in the positive electrode, and Patent Document 6, Patent Document 7, and Patent Document 8 disclose a negative electrode. Discloses a lithium secondary battery containing carbon fiber as a conductive additive. Patent Documents 9 and 10 disclose a method for producing an electrode containing carbon nanotubes as a conductive agent in the positive electrode or the negative electrode.

  Patent Document 11 discloses a non-aqueous electrolyte secondary battery using carbon fluoride as a positive electrode, a material obtained by fluorinating a fibrous carbon material, a carbon nanotube, a carbon nanofiber, and a gas phase. An electrode including a fibrous conductive agent such as grown carbon fiber and a binder is described. Further, Patent Document 12 discloses a lithium ion secondary battery using a positive electrode material having a particulate or fibrous fluorine-containing carbon material on the surface of the positive electrode active material particles. Carbon black, carbon fiber, graphite, etc. are used.

  According to Patent Document 13, a mixture of a carbon-based conductive material such as carbon black or carbon fiber and an electrode active material, which is preferably hydrophilized with a fluorine gas diluted with oxygen, is mixed with the fluororesin in the presence of the fluororesin. A method for producing a high output and high energy density lithium battery by using a composite electrode material by firing at a temperature not lower than the melting temperature and not higher than the temperature at which the electrode active material is not thermally decomposed is disclosed.

JP 2011-14457 A JP 2013-73724 A JP-A-2006-9564 JP-A-9-27344 JP 2006-86116 A JP 2007-42620 A JP 2004-103435 A JP 2008-16456 A JP 2004-273433 A JP-A-2005-340152 JP 2008-111262 A WO2014 / 181778 Japanese Patent Laying-Open No. 2015-228290

  It is known that carbon black and fibrous carbon materials used as conductive aids have poor dispersibility in pastes. Therefore, a dispersant is used. However, according to Patent Document 3, the surfactant described in Patent Document 1 has a problem that when lithium cobaltate used as a general positive electrode active material is used, decomposition occurs during battery reaction, resulting in poor cycle characteristics. It has been pointed out that there is. In addition, it has been pointed out that the compound described in Patent Document 2 also has a problem in cycle characteristics because the dispersibility is insufficient and the oxidation stability is not always excellent. Further, the dispersant becomes an impurity for the battery.

  Patent Documents 4, 6, 7, 11, 13 and the like describe that a fibrous carbon material is used as a conductive additive, and that the fibrous carbon material can provide a higher-dimensional conductive network than carbon black. However, the fibrous carbon material is very easy to aggregate and difficult to uniformly disperse in the electrode. Therefore, the present invention improves the dispersibility in the paste by performing a surface modification treatment on the fibrous carbon material, and improves the cycle characteristics of the nonaqueous electrolyte secondary battery as compared with the case of no treatment. An object of the present invention is to provide a method for producing a fibrous carbon material for use as a conductive additive for an electrode of a nonaqueous electrolyte secondary battery, and a fibrous carbon material obtained by the method.

  As a result of various studies to achieve the above object, the present inventors have found that a fibrous carbon material suitable as a conductive aid for an electrode for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery can be obtained by using fluorine. It was found that the elemental ratio of fluorine and oxygen to carbon on the surface of the fibrous carbon material subjected to surface modification treatment must be controlled within an appropriate range. After a surface modification treatment with fluorine at a specific temperature (hereinafter referred to as “fluorine treatment”) using a treatment gas in which the fluorine concentration is set to a specific range and the balance is an inert gas, a post-treatment that makes contact with gaseous water By doing this, it is possible to control this element ratio, and using an electrode using a fibrous carbon material after fluorine treatment can lower the internal resistance of the battery and improve the cycle characteristics of the battery. I found it.

  That is, the present invention is a fibrous carbon material used as a conductive aid for a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and an electrolyte, the ratio of fluorine atoms to carbon atoms measured by XPS analysis, A fibrous form having an F / C ratio of 0.001 or more and less than 0.025 and a ratio of oxygen atoms to carbon atoms, that is, an O / C ratio of 0.05 or more and less than 0.2. Provide carbon materials.

The present invention also provides a fluorine treatment step in which the fibrous carbon material is brought into contact with a treatment gas comprising a fluorine gas and an inert gas at 10 ° C. to 50 ° C., wherein the concentration of the fluorine gas in the treatment gas is 0.01 to 5% by volume,
A post-treatment step of bringing the fibrous carbon material after fluorine treatment into contact with gaseous water;
A method for producing a fibrous carbon material is also provided.

  According to the present invention, by conducting a surface modification treatment on the fibrous carbon material, the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved as compared with the case of non-treatment. The manufacturing method of the fibrous carbon material for adjuvants, and the fibrous carbon material obtained by the method can be provided.

  Hereinafter, embodiments of the present invention will be described. It should be noted that the scope of the present invention is not limited by these descriptions, and can be changed and implemented as appropriate without departing from the spirit of the present invention other than the following examples.

  In the present invention, a fluorine treatment process is performed on the fibrous carbon material, and a post-treatment process is further performed. The average fiber diameter of the fibrous carbon material used in the present invention is preferably 1 nm or more and 1 μm or less, more preferably 10 nm or more and 500 nm or less, and the aspect ratio (average fiber length / average fiber diameter) is 10 or more. Preferably, it is 50 or more, more preferably 100 or more. The average fiber diameter and the average fiber length can be calculated by observing a plurality of fibrous carbon materials in the field of view with a transmission electron microscope or a scanning electron microscope, and arithmetically averaging the numbers. Examples of such a fibrous carbon material include vapor grown carbon fiber, carbon nanotube, and carbon nanofiber. For example, vapor grown carbon fiber commercially available as VGCF (registered trademark) from Showa Denko KK can be used as the fibrous carbon material. In addition, the fibrous carbon material before performing the fluorine treatment may be referred to as an untreated fibrous carbon material, and the fibrous carbon material after the fluorine treatment and the post-treatment is treated with the fibrous carbon material or the surface-modified fibrous carbon. Sometimes called material.

  First, in the present invention, it is preferable to remove moisture adsorbed on the untreated fibrous carbon material by heating or vacuum degassing before performing the fluorine treatment. This is because if moisture remains, it reacts with fluorine to generate hydrogen fluoride, which may adversely affect the production apparatus and the like.

  In the fluorine treatment method of the present invention, the fibrous carbon material is usually charged into a cylindrical container. Here, a treatment gas adjusted so that the fluorine concentration falls within a predetermined range is circulated, whereby fluorine atoms are chemically bonded to the surface of the fibrous carbon material to form C—F bonds. The container material can be safely processed as long as it is a metal material. However, from the viewpoint of corrosion resistance, stainless steel materials such as SUS304 and SUS316 and nickel are desirable for continuous processing.

  The treatment gas in the fluorine treatment is composed of fluorine gas and inert gas. The concentration of the fluorine gas in the processing gas is 0.01 to 5% by volume, and preferably 0.05 to 4% by volume. When the fluorine gas concentration is within this range, a fibrous carbon material having a desired F / C ratio and O / C ratio after the post-treatment can be obtained, and the internal resistance value is increased without increasing. A non-aqueous electrolyte secondary battery having cycle characteristics can be obtained. It is preferable that a gas other than fluorine and an inert gas, such as oxygen, is not mixed in the processing gas, and even if mixed, the concentration of the mixed gas is preferably 1% by volume or less. For example, when oxygen is mixed in the processing gas, it becomes difficult to control the post-treatment O / C ratio to a desired O / C ratio, and the reaction with the fibrous carbon material proceeds rapidly. There is a possibility of dust explosion.

  When the processing temperature is higher than 50 ° C, there is a risk of explosion due to the progress of fluorination more than expected, and when the processing temperature is lower than 10 ° C, cooling equipment and energy are required to create a cooling state. Since the cost is a problem, it is desirable to perform the treatment at around room temperature. However, in the case where heat is generated at the time of contact between the fibrous carbon material and fluorine, the apparatus may be cooled using cooling water or the like for controlling the reaction.

  Regarding the treatment time, a sufficient time is required for the fibrous carbon material and fluorine to uniformly contact, and it is desirable to ensure 10 minutes or more, and more desirably 30 minutes or more. If it is too long, there is no effect on the performance as a conductive additive, but the production efficiency is lowered, so that it is preferably within 2 hours. In addition, after the fluorine treatment, it is preferable to deaerate in a vacuum state in order to remove as much as possible the fluorine physically adsorbed on the fibrous carbon material, that is, fluorine not contributing to the surface modification.

  The processing pressure is not particularly limited, but is preferably 700 Torr (93.3 kPa) or less, more preferably 500 Torr (66.7 kPa) or less from the viewpoint of safety. In order to obtain a sufficient reaction rate, it is preferably 10 Torr (1.3 kPa) or more, and more preferably 50 Torr (6.7 kPa) or more. Since the preferable flow rate of the processing gas varies depending on the size and structure of the reaction apparatus, it may be appropriately adjusted.

  After the fluorine treatment, the post-treatment step is performed by exposing the fibrous carbon material to gaseous water, for example, air containing a predetermined humidity or water vapor. The post-treatment step can be performed at 10 to 30 ° C., but can be performed at ambient temperature or normal temperature without heating. In addition, when exposed to the atmosphere of 30 to 80% relative humidity, the treatment may be performed for 2 hours or more and 48 hours or less, and when exposed to water vapor of 100% relative humidity, 30 minutes or more and 2 hours or less. What is necessary is just to process.

A C—F group or the like is generated on the surface of the fibrous carbon material by fluorine treatment. In the post-treatment process, the C—F group on the surface is converted into a C—OF group, a C—OH group, a COOH group, or the like by the action of H ₂ O, and the surface is modified. The presence or absence of C-OF groups, C-OH groups, or COOH groups on the surface can be confirmed by XPS or the like. It is considered that the fibrous carbon material having a modified surface has improved dispersibility in the paste for electrode preparation as compared with that before the modification. This conversion is estimated to be completed in about one hour after the end of the post-processing step. However, some of the C—F groups in the fibrous carbon material are such that F is firmly bonded to C due to the difference in bonding status between the carbon atom to which the fluorine atom is bonded and other carbon atoms, etc. It remains without reacting with ₂ O. In addition, it is preferable to remove HF produced | generated simultaneously by vacuum deaeration after that.

  At this time, the ratio of fluorine atoms to carbon atoms, that is, the F / C ratio, measured by XPS (X-ray photoelectron spectroscopy) analysis of the surface of the post-treatment fibrous carbon material after the post-treatment step is 0.001 or more and 0.025. It is less than 0.015 and 0.022 or less. The ratio of oxygen atoms to carbon atoms, that is, the O / C ratio is 0.05 or more and less than 0.2, and preferably 0.10 or more and less than 0.19. If the F / C ratio and the O / C ratio are within the above ranges, the dispersibility in the paste for electrode production is improved while suppressing an increase in resistance derived from fluorine and carbon, and a fibrous carbon material Makes it easier to form a network.

  When the F / C ratio and O / C ratio of the post-treatment fibrous carbon material after the post-treatment process are high and the surface of the fibrous carbon material has too many fluorine atoms or oxygen atoms, the internal resistance of the battery increases, and the battery The cycle characteristics of the deteriorated. Although the cause is not clear, the present inventors presume as follows. For example, fluorine atoms and oxygen atoms on the surface of the fibrous carbon material become impurities, and in the network formed by the fibrous carbon material, the contact resistance between the fibrous carbon material and the fibrous carbon material may be increased. . If there are too many fluorine atoms or oxygen atoms, the condensed benzene ring of the fibrous carbon material is destroyed by an excessive fluorination reaction. As a result, the movement of π electrons on the fibrous carbon material is inhibited, and the fibrous carbon material It is conceivable that the conductivity of the material itself deteriorates.

  Next, a non-aqueous electrolyte secondary battery using the treated fibrous carbon material of the present invention will be described. Non-aqueous electrolyte secondary battery electrolyte solution, negative electrode material capable of reversibly inserting and removing alkali metal ions such as lithium ions and sodium ions, or alkaline earth metal ions, lithium ions and sodium ions An electrochemical device using a positive electrode material into which alkali metal ions or alkaline earth metal ions can be reversibly inserted and removed is called a non-aqueous electrolyte secondary battery.

  The nonaqueous electrolyte secondary battery of the present invention is characterized by using the post-treatment fibrous carbon material of the present invention, and the other components used are those used in general nonaqueous electrolyte secondary batteries. It is done. That is, it comprises a positive electrode and a negative electrode capable of inserting and extracting lithium ions, a current collector made of metal foil, a separator, a container, and the like.

  The negative electrode is not particularly limited, but a material capable of reversibly inserting and desorbing alkali metal ions such as lithium ions and sodium ions or alkaline earth metal ions is used, and the positive electrode is not particularly limited. However, materials in which alkali metal ions such as lithium ions and sodium ions or alkaline earth metal ions can be reversibly inserted and removed are used.

  When the treated fibrous carbon material of the present invention is used as a negative electrode conductive additive, a negative electrode active material capable of occluding and releasing lithium ions, a binder, a treated fibrous carbon material, and a dispersion medium are mixed. Then, after forming a slurry, it is applied to a metal foil as a current collector, dried and pressed to form a negative electrode layer. In addition, not only fibrous carbon materials but also particulate carbon materials such as carbon black may be used in combination as the conductive assistant. Examples of various materials capable of inserting and extracting lithium ions include, for example, when the cation is lithium, lithium metal as an anode material, alloys and intermetallic compounds of lithium with other metals, artificial graphite and natural materials. Carbon materials such as graphite and activated carbon, metal oxides, metal nitrides and the like are used.

When the treated fibrous carbon material of the present invention is used as a conductive additive for the positive electrode, a positive electrode active material capable of occluding and releasing lithium ions, a binder, a treated fibrous carbon material and a dispersion medium are mixed. Then, after forming a slurry, it is applied to a metal foil as a current collector, dried and pressurized to form a positive electrode layer. In addition, you may use together particulate carbon materials, such as carbon black, not only the post-process fibrous carbon material of this invention as a conductive support agent. Further, before the slurrying, the positive electrode active material, the post-treatment fibrous carbon material, the conductive auxiliary agent and the like may be dry-mixed with a ball mill or the like. In the case of a lithium ion secondary battery, as the active material, for example, lithium-containing transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Co of these lithium-containing transition metal composite oxides, A mixture of a plurality of transition metals such as Mn and Ni, a transition metal of the lithium-containing transition metal composite oxide partially substituted with a metal other than the transition metal, LiFePO ₄ and LiCoPO ₄ called olivine , Transition metal phosphate compounds such as LiMnPO ₄ , oxides such as TiO ₂ , V ₂ O ₅ and MoO ₃ , sulfides such as TiS ₂ and FeS, and the like are used. Alternatively, conductive polymers such as polyacetylene, polyparaphenylene, polyaniline, and polypyrrole, activated carbon, polymers that generate radicals, carbon materials, and the like are used.

  The amount of the conductive additive contained in the electrode layer of the positive electrode layer or the negative electrode layer, that is, the amount of the conductive additive in the solid component in the slurry is preferably 0.1 to 20% by mass, It is more preferable to contain 10 mass%, and it is more preferable to contain 1-8 mass%.

  As a binder used for the positive electrode or the negative electrode material, polytetrafluoroethylene, polyvinylidene fluoride, SBR resin, or the like is used. Further, as a dispersion medium for the slurry, an organic solvent such as N-methyl-2-pyrrolidone (hereinafter “NMP”), an aqueous solvent such as water, or the like is used.

  Examples of the present invention are listed below together with comparative examples, but the present invention is not limited to the following examples.

[Example 1-1]
<Production of fibrous carbon material after fluorine treatment and after treatment (hereinafter referred to as "after treatment")>
As an untreated fibrous carbon material, vapor-grown carbon fiber with a fiber diameter of 150 nm (VGCF (registered trademark) -H, manufactured by Showa Denko KK) is enclosed in a 5 L SUS304 container, and the inside is evacuated. The water adsorbed on the fibrous carbon material was removed. Here, 200 Torr (26.7 kPa) of fluorine diluted to 0.05% by volume with nitrogen was sealed, and then allowed to flow at a total flow rate of 0.5 SLM for 30 minutes. In addition, said reaction was performed at room temperature (25 degreeC). After the end of distribution, the inside of the container was sufficiently replaced with nitrogen. Thereafter, the inside of the container was again depressurized to a vacuum state and deaerated overnight to remove as much as possible the fluorine adsorbed on the fibrous carbon material. Subsequently, the inside of the container was restored to atmospheric pressure and exposed to the atmosphere (temperature 25 ° C., relative humidity 45-50%) for 24 hours. The treated fibrous carbon material obtained by these operations is XPS (“PHI VersaProbe II”, manufactured by ULVAC-PHI, X-ray source: Al, X-ray: AlKα ray (1486.6 eV), output: 23.8 W. The surface composition was measured at a beam diameter of 100 μm).

<Preparation of positive electrode>
As the positive electrode active material, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM) powder and the treated fibrous carbon material produced in Example 1-1 were dry mixed using a ball mill for 30 minutes, The binder, polyvinylidene fluoride (hereinafter referred to as “PVDF”), was dispersed in NMP previously dissolved and mixed, and NMP for viscosity adjustment was further added to prepare an NCM mixture paste. This paste is applied on an aluminum foil (current collector), dried at 100 ° C. for 1 h, pressurized with a roller at 4 kN / m ² , and then a test NMC positive electrode processed to a predetermined size is obtained. It was. The solid content ratio in the positive electrode was NCM: fibrous carbon material after treatment: PVDF = 85: 5: 10 (mass ratio).

<Preparation of graphite negative electrode>
As a negative electrode active material, graphite powder was uniformly dispersed in NMP in which PVDF as a binder was previously dissolved, mixed at 2000 rpm for 20 minutes using a kneader, and further NMP for viscosity adjustment was added. An agent paste was prepared. This paste was applied onto a copper foil (current collector), dried at 50 ° C. for 1 hour, pressurized with a roller at 4 kN / m ² , and then a test graphite negative electrode processed into a predetermined size was obtained. It was. The solid content ratio in the negative electrode was graphite powder: PVDF = 90: 10 (mass ratio).

<Preparation of nonaqueous electrolyte secondary battery>
An aluminum laminate outer cell (capacity 30 mAh) comprising the above test NCM positive electrode, test graphite negative electrode, and cellulose separator was impregnated with a nonaqueous solvent to obtain a nonaqueous electrolyte secondary battery. The volume ratio of ethylene carbonate (hereinafter “EC”), propylene carbonate (hereinafter “PC”), dimethyl carbonate (hereinafter “DMC”), and ethyl methyl carbonate (hereinafter “EMC”) as the non-aqueous solvent is 2: 1: 3. : 4 was used, and lithium hexafluorophosphate (hereinafter referred to as “LiPF ₆ ”) was dissolved as a solute in the solvent to a concentration of 1.0 mol / L to prepare an electrolytic solution. In addition, said preparation was performed maintaining a liquid temperature at 25 degreeC.

<Battery evaluation>
<Evaluation 1: Measurement of battery internal resistance>
The following evaluation was implemented about each of the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example.
First, conditioning was performed using the fabricated cell at an environmental temperature of 25 ° C. under the following conditions. That is, as the first charge / discharge, the battery is charged at a constant current and constant voltage at a charging upper limit voltage of 4.3 V and a 0.1 C rate (3 mA), and discharged at a 0.2 C rate (6 mA) constant current up to a discharge end voltage of 3.0 V. Thereafter, charging / discharging cycle is performed three times by charging at a constant current / constant voltage at a charging upper limit voltage of 4.3V and a 0.2C rate (6 mA) and discharging at a constant current of 0.2C (6 mA) to a discharge end voltage of 3.0V. Repeated. Thereafter, the internal resistance of the battery was measured. Table 1 shows the measurement results of the internal resistance in each example and comparative example. In addition, the numerical value of the internal resistance described in Table 1 is a relative value when the internal resistance of Comparative Example 1 is 100.

<Evaluation 2: Measurement of high-temperature cycle characteristics>
After performing the above conditioning, after charging at a constant current and constant voltage at an upper limit voltage of 4.3 V and a 3 C rate (90 mA) at an environmental temperature of 55 ° C., the battery is discharged at a constant current of 3 C (90 mA) to a discharge end voltage of 3.0 V. This charging / discharging was repeated 100 cycles. The ratio of the discharge capacity at the 100th cycle to the initial (first cycle) discharge capacity was defined as the cycle capacity retention rate, and the high temperature cycle characteristics of the cell were evaluated. In addition, the numerical value of the cycle characteristic after 100 cycles described in Table 1 is a relative value when the discharge capacity retention rate after 100 cycles of Comparative Example 1 is 100.

[Example 1-2]
In the production of the fibrous carbon material after the treatment, the same test as in Example 1-1 was performed except that the concentration of diluted fluorine used was 2% by volume and the contact time with fluorine was 10 minutes.
[Example 1-3]
In the production of the fibrous carbon material after the treatment, the same test as in Example 1-1 was performed except that the concentration of the diluted fluorine used was changed to 0.5% by volume.
[Example 1-4]
The same test as in Example 1-1 was performed except that the concentration of diluted fluorine used was changed to 2% by volume in the production of the fibrous carbon material after the treatment.
[Example 1-5]
In the production of the fibrous carbon material after the treatment, the same test as in Example 1-1 was performed except that the concentration of the diluted fluorine used was changed to 4% by volume.

[Example 1-6]
In the production of the fibrous carbon material after the treatment, the same test as in Example 1-1 was performed, except that the pressure when contacting with diluted fluorine was 50 Torr (6.7 kPa).
[Example 1-7]
In the production of the fibrous carbon material after the treatment, the same test as in Example 1-1 was performed, except that the pressure when contacting with diluted fluorine was 500 Torr (66.7 kPa).
[Example 1-8]
In producing the fibrous carbon material after the treatment, the concentration of the diluted fluorine used was 4% by volume, and the pressure at the time of contacting with the diluted fluorine was 500 Torr (66.7 kPa). A test was conducted.

[Example 1-9]
The same as Example 1-1, except that carbon nanotubes having an average fiber diameter of 11 nm (AMC (registered trademark), manufactured by Ube Industries Co., Ltd.) were used as the untreated fibrous carbon material in the production of the treated fibrous carbon material. The test was conducted.
[Example 1-10]
The same test as in Example 1-9 was performed except that the treatment time for bringing into contact with diluted fluorine was 90 minutes in the production of the fibrous carbon material after treatment.
[Example 1-11]
In the production of the fibrous carbon material after the treatment, the same test as in Example 1-1 was performed except that the treatment temperature was 40 ° C. and the treatment time was 10 minutes.
[Example 1-12]
When producing the fibrous carbon material after treatment, the treatment temperature is set to 40 ° C., the treatment time is set to 10 minutes, and water vapor at normal temperature (nitrogen gas with a relative humidity of 100%) is supplied for 1 hour as gaseous water in the post-treatment process. A test similar to that of Example 1-1 was performed except that.

[Comparative Example 1-1]
Instead of the fluorine treatment step, the same test as in Example 1-1 was performed except that nitrogen gas not containing fluorine was circulated.
[Comparative Example 1-2]
In the production of the fibrous carbon material after the treatment, the same test as in Example 1-1 was performed except that the concentration of the diluted fluorine used was 0.005% by volume.
[Comparative Example 1-3]
In producing the fibrous carbon material after the treatment, the same test as in Example 1-1 was performed except that the concentration of diluted fluorine used was changed to 7% by volume.
[Comparative Example 1-4]
In producing the fibrous carbon material after the treatment, the same test as in Example 1-1 was performed except that the fluorine concentration was 4% by volume, the oxygen concentration was 10% by volume, and the gas diluted with nitrogen was circulated. .

[Comparative Example 1-5]
In producing the fibrous carbon material after treatment, the same test as in Example 1-1 was performed except that the treatment temperature at the time of contacting with diluted fluorine was 80 ° C.
[Comparative Example 1-6]
In producing the post-treatment fibrous carbon material, the same test as in Example 1-1 was performed except that oxygen gas was supplied in the post-treatment process.
[Comparative Example 1-7]
In producing the fibrous carbon material after treatment, the same test as in Example 1-1 was performed except that nitrogen gas was supplied in the post-treatment process.
[Comparative Example 1-8]
In producing the post-treatment fibrous carbon material, the carbon nanotube used in Example 1-9 was used as the untreated fibrous carbon material, and in the fluorine treatment step, nitrogen gas not containing fluorine was circulated. The same test as 1-1 was performed.

  From the results of Examples 1-1 to 1-12 and the results of Comparative Examples 1-1 to 1-8, the diluted fluorine gas having a fluorine concentration in the range of 0.05 to 5% by volume is brought into contact with the fibrous carbon material, By performing a post-treatment step in contact with gaseous water, the ratio of fluorine atoms to carbon atoms, as measured by XPS analysis, that is, the F / C ratio is 0.001 or more and less than 0.025, and oxygen atoms It can be seen that a post-treatment fibrous carbon material can be obtained which is characterized in that the ratio to carbon atoms, that is, the O / C ratio is 0.1 or more and less than 0.2. In addition, the non-aqueous electrolyte secondary battery produced using the treated fibrous carbon material in these ranges is a fibrous carbon whose fluorine concentration is outside the above range or which has been treated with diluted fluorine containing oxygen gas. It can be seen that the internal resistance value is lower than that of the material, and a high discharge capacity retention rate is maintained. In addition, by XPS analysis, at least one functional group of a C—OF group, a C—OH group, or a COOH group exists on the surface of the treated fibrous carbon material of Examples 1-1 to 1-12. I found out.

  On the other hand, from the result of Comparative Example 1-2, at the fluorine concentration of 0.005% by volume, the surface modification hardly progressed, and the F / C ratio and the O / C value hardly changed. There was no change in resistance and cycle characteristics. Further, from the result of Comparative Example 1-3, when the fluorine concentration was 7% by volume, the F / C ratio and the O / C value increased significantly, but the internal resistance value increased and the cycle characteristics deteriorated. This is presumably because the fluorine concentration was too high and the surface of the fibrous carbon material was so rough that it inhibited charge transport.

  In Comparative Example 1-4, since the fibrous carbon material was treated with a gas obtained by diluting fluorine and oxygen with nitrogen, the O / C value of the treated fibrous carbon material was increased, the internal resistance value was increased, and the cycle characteristics were increased. Declined. This is presumably because the cross-linking structure of the fibrous carbon material was changed by the fluorine treatment with fluorine and oxygen, and the conductive path between carbon and carbon was hindered, so that the internal resistance value was increased.

  In Comparative Example 1-5, since the treatment temperature was 80 ° C., the fluorine treatment proceeded strongly, and the F / C ratio of the treated fibrous carbon material was greatly increased. It was considered that the surface of the fibrous carbon material was roughened during the fluorine treatment, the internal resistance value increased, and the cycle characteristics deteriorated.

  In Comparative Example 1-6, it was exposed with oxygen gas in the post-treatment step after the fluorine treatment, but it had a high F / C ratio equivalent to that of Comparative Example 1-7, and the CF group was changed to a COF group or the like. There was an increase in the O / C ratio, which seems to have changed or the terminal substituents that were in an unstable bond state were oxidized. In Comparative Example 1-6, the internal resistance value was high, and the cycle characteristics deteriorated.

  In Comparative Example 1-7, since the fibrous carbon material was subjected to a post-treatment process with an inert gas after the fluorine treatment, a large amount of fluorine components remained in the treated fibrous carbon material, and the fibrous carbon material before treatment Since the O / C ratio hardly increased as compared with the above, it was considered that no COH group or COOH group was generated, and the internal resistance value was high and the cycle characteristics were low.

[Example 2-1]
The post-treatment fibrous carbon material obtained in Example 1-1 was used as a conductive additive for the negative electrode as follows.

<Preparation of positive electrode>
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM) powder as a positive electrode active material and acetylene black (hereinafter referred to as “AB”) as a conductive auxiliary agent were dry-mixed for 30 minutes using a ball mill. An NCM mixture paste was prepared by uniformly dispersing and mixing the polyvinylidene fluoride (hereinafter referred to as “PVDF”), which is a dressing material, in NMP in which the material was previously dissolved, mixing, and adding NMP for viscosity adjustment. This paste is applied on an aluminum foil (current collector), dried at 100 ° C. for 1 h, pressurized with a roller at 4 kN / m ² , and then processed into a predetermined size for a test NMC positive electrode. Obtained. The solid content ratio in the positive electrode was NCM: AB: PVDF = 85: 5: 10 (mass ratio).

<Preparation of graphite negative electrode>
A graphite powder as a negative electrode active material and a post-treatment fibrous carbon material produced in Example 1-1 as a conductive auxiliary agent are dispersed in NMP in which PVDF as a binder is previously dissolved, and a kneader is used. Were mixed for 20 minutes at 2000 rpm, and NMP for viscosity adjustment was further added to prepare a graphite mixture paste. This paste was applied on a copper foil (current collector), dried at 50 ° C. for 12 hours, pressurized with a roller at 4 kN / m ² , and then a test graphite negative electrode processed into a predetermined size was obtained. It was. The solid content ratio in the negative electrode was graphite powder: post-treatment fibrous carbon material: PVDF = 85: 5: 10 (mass ratio).

The production of the nonaqueous electrolyte secondary battery and the battery evaluation were performed in the same manner as in Example 1-1.

[Examples 2-2 to 2-12, Comparative Examples 2-1 to 2-8]
Using the post-treatment fibrous carbon materials obtained in Examples 1-2 to 1-12 and Comparative Examples 1-1 to 1-8, tests similar to those in Example 2-1 were performed.
Similar to Example 1, it can be seen that Example 2 also has a lower internal resistance value than that of Comparative Example 2, and maintains a high discharge capacity retention rate.

Claims (15)

A fibrous carbon material used as a conductive aid for an electrode of a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and an electrolyte,
The ratio of fluorine atoms to carbon atoms, that is, the F / C ratio is 0.001 or more and less than 0.025, and the ratio of oxygen atoms to carbon atoms, that is, the O / C ratio, is measured by XPS analysis. A fibrous carbon material that is 0.05 or more and less than 0.2.   2. The fibrous form according to claim 1, wherein at least one functional group selected from the group consisting of a C—OF group, a C—OH group, and a COOH group exists on the surface of the fibrous carbon material. Carbon material.   The fibrous carbon according to claim 1 or 2, wherein the F / C ratio is 0.015 or more and less than 0.022, and the O / C ratio is 0.10 or more and less than 0.19. material.   The fibrous carbon material according to any one of claims 1 to 3, wherein an average fiber diameter of the fibrous carbon material is 1 nm or more and 1 µm or less.   The fibrous carbon material according to any one of claims 1 to 4, wherein the fibrous carbon material has an aspect ratio (average fiber length / average fiber diameter) of 10 or more.   The fibrous carbon material according to any one of claims 1 to 5, wherein the fibrous carbon material is at least one selected from the group consisting of vapor-grown carbon fibers, carbon nanotubes, and carbon nanofibers. Carbon material. A current collector made of metal foil;
An electrode layer formed on the current collector and comprising the fibrous carbon material according to any one of claims 1 to 6 and an electrode active material,
An electrode for a non-aqueous electrolyte secondary battery. Having a positive electrode, a negative electrode, and an electrolyte;
The nonaqueous electrolyte secondary battery in which any one or both of the said positive electrode and the said negative electrode are the electrodes for nonaqueous electrolyte secondary batteries of Claim 7. It is a manufacturing method of the fibrous carbon material of Claim 1,
A fluorine treatment step in which the fibrous carbon material is brought into contact with a treatment gas comprising a fluorine gas and an inert gas at 10 ° C. to 50 ° C., wherein the concentration of the fluorine gas in the treatment gas is 0.01 to 5 volumes; %
A post-treatment step of bringing the fibrous carbon material after fluorine treatment into contact with gaseous water;
A method for producing a fibrous carbon material, comprising:   10. The fibrous carbon material according to claim 9, wherein in the post-treatment step, the fibrous carbon material after fluorine treatment is exposed to the atmosphere of 30 to 80% in relative humidity within 2 hours to 48 hours. Production method.   The method for producing a fibrous carbon material according to claim 9, wherein in the post-treatment step, the fibrous carbon material after the fluorine treatment is exposed to water vapor within 30 minutes to 2 hours.   The fiber according to any one of claims 9 to 11, comprising a step of performing a deaeration step by placing the fibrous carbon material in a reduced pressure environment after the fluorine treatment step and before the post-treatment step. For producing a carbonaceous material.   The manufacturing method of the fibrous carbon material of any one of Claims 9-12 including the process of performing a deaeration process by putting a fibrous carbon material in a pressure-reduced environment after the said post-processing process. A step of creating a paste by dispersing the fibrous carbon material according to claim 1 and an electrode active material in a dispersion medium;
Applying the paste to a current collector and drying;
The manufacturing method of the electrode for nonaqueous electrolyte secondary batteries containing. The method for producing a nonaqueous electrolyte secondary battery electrode according to claim 14, further comprising a binder and a viscosity modifier in the paste.