WO2019059036A1

WO2019059036A1 - Fibrous carbon material and method for producing same

Info

Publication number: WO2019059036A1
Application number: PCT/JP2018/033565
Authority: WO
Inventors: 章史八尾; 啓之大森; 聖唯鈴木
Original assignee: セントラル硝子株式会社
Priority date: 2017-09-19
Filing date: 2018-09-11
Publication date: 2019-03-28
Also published as: JP2019053954A

Abstract

This fibrous carbon material is a surface-modified fibrous carbon material used as a conductive aid for an electrode of a non-aqueous electrolyte secondary battery, and is characterized in that the ratio of fluorine atoms to carbon atoms, i.e., the F/C ratio, is at least 0.001 and less than 0.025, and the ratio of oxygen atoms to carbon atoms, i.e., the O/C ratio, is at least 0.05 and less than 0.2 as measured by XPS analysis. Since the element ratios of fluorine and oxygen on the surface of the fibrous carbon material are controlled within the appropriate ranges by a surface modification treatment, the cycle characteristics of a non-aqueous electrolyte secondary battery can be improved compared to the case in which an untreated fibrous carbon material is used.

Description

Fibrous carbon material and method for producing the same

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

For the positive electrode and the negative electrode of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, a composite oxide of metal 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 adopting a lithium ion secondary battery is increasing. One of the important characteristics of the non-aqueous electrolyte secondary battery for automobiles is an output characteristic indicating the magnitude of the amount of current allowed to flow per unit time, and a cycle characteristic capable of maintaining the discharge capacity even when charging and discharging are repeated.

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. Therefore, the conductive aid forming the conductive network in the electrode is uniform throughout the electrode material and There is a technique to reduce the electrode resistance by dispersing it in high concentration. Since carbon black has a structure in which primary particles called a structure are linked in a chain-like manner, it is necessary to use a dispersing agent in order to prevent aggregation and breakage of the structure 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 which is a conductive additive by using a nitrogen-based surfactant as a dispersant. Further, Patent Document 2 discloses a method of stably dispersing a positive electrode active material, a binder, and a carbon material which is a conductive support agent by using a triazine derivative or the like as a dispersant.

In addition, Patent Document 3 discloses an active material (A), a conductive aid (B), and a binder as a method of producing an electrode slurry for a lithium ion battery in which the dispersibility of the conductive aid is improved without using a dispersant. Disclosed is a method for producing a slurry (G) comprising the step of removing (F) from the mixture of (C) and a solvent (D) in a supercritical fluid or subcritical fluid (F).

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

Further, in Patent Document 11, in a non-aqueous electrolyte secondary battery using a fluorinated carbon as a positive electrode, a material obtained by fluorinating a fibrous carbon material, a carbon nanotube, a carbon nanofiber, and a gas phase are used. An electrode is described that includes a fibrous conductive agent, such as grown carbon fiber, and a binder. Furthermore, 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 positive electrode active material particles, and as the conductive material, It is said that carbon black, carbon fiber, graphite and the like are used.

Further, according to Patent Document 13, preferably, a mixture of a carbon-based conductive material such as carbon black or carbon fiber hydrophilically treated with fluorine gas diluted with oxygen and an electrode active material in the presence of a fluorine resin is used as the fluorine resin Disclosed is a method for producing a lithium battery with high output and high energy density by using an electrode material composited by firing at a temperature above the melting temperature and below the temperature at which the electrode active material does not thermally decompose.

JP, 2011-14457, A JP, 2013-73724, A JP, 2016-9564, A Japanese Patent Application Laid-Open No. 9-27344 JP, 2006-86116, A JP 2007-42620 A JP 2004-103435 A JP, 2008-16456, A JP, 2004-273433, A JP 2005-340152 A JP, 2008-112652, A WO 2014/181778 JP 2015-228290 A

It is known that carbon black and fibrous carbon materials used as conductive aids have poor dispersibility in pastes. Therefore, dispersants such as surfactants are used together with the paste. However, according to Patent Document 3, the surfactant described in Patent Document 1 has a problem that when it uses lithium cobaltate used as a general positive electrode active material, decomposition occurs at the time of battery reaction, and therefore the cycle characteristics are inferior. It is pointed out that there is. In addition, it is pointed out that the compound described in Patent Document 2 is insufficient in dispersibility and is not excellent in oxidation stability, so that problems remain in cycle characteristics. Also, the dispersant is an impurity for the battery.

Patent Documents 4, 6, 7, 11, 13 and the like disclose that a fibrous carbon material is used as a conductive aid, and the fibrous carbon material can provide a conductive network having a higher dimension than carbon black. However, fibrous carbon materials are very prone to aggregation and are difficult to uniformly disperse in the electrode.

Therefore, the present invention is to improve the dispersibility in the paste by performing a surface modification treatment on the fibrous carbon material, and to improve the cycle characteristics of the non-aqueous electrolyte secondary battery as compared with the case of no treatment. It is an object of the present invention to provide a method for producing a fibrous carbon material for a conductive additive of an electrode of a non-aqueous electrolyte secondary battery, and a fibrous carbon material obtained by the method.

As a result of various studies made by the present inventors to achieve the above object, in order to obtain a fibrous carbon material suitable as a conductive support agent for electrodes of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, It has been found that it is necessary to control the elemental ratio of fluorine and oxygen to carbon on the surface of the surface-modified fibrous carbon material in an appropriate range. After the surface modification treatment with fluorine at a specific temperature (hereinafter referred to as "fluorination treatment") using a processing gas with the fluorine concentration set in a specific range and the balance as an inert gas, post-treatment to contact with gaseous water This element ratio can be controlled by carrying out, and the use of the electrode using the 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, wherein 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 an oxygen atom to carbon atom ratio, that is, an O / C ratio of 0.05 or more and less than 0.2. Provide carbon material.

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

According to the present invention, by performing a surface modification treatment on a fibrous carbon material, it is possible to improve the cycle characteristics of the non-aqueous electrolyte secondary battery as compared with the case of no treatment, and the conductivity of the electrode of the non-aqueous electrolyte secondary battery It is possible to provide a method for producing a fibrous carbon material for auxiliary agents, and a fibrous carbon material obtained by the method.

Hereinafter, embodiments of the present invention will be described below. Note that the scope of the present invention is not limited to these descriptions, and can be appropriately changed and implemented without departing from the spirit of the present invention other than the following examples.

First, the fibrous carbon material of the present invention and the method for producing the same will be described. The fibrous carbon material of the present invention is a surface-modified fibrous carbon material, and is produced by performing a fluorine treatment step on the fibrous carbon material and further performing a post treatment step.

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 Is preferably 50, and 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 by the number. As such fibrous carbon materials, vapor grown carbon fibers, carbon nanotubes, carbon nanofibers and the like can be mentioned. For example, vapor grown carbon fiber commercially available from Showa Denko KK as VGCF (registered trademark) can be used as a fibrous carbon material. In addition, the fibrous carbon material before performing the fluorine treatment may be called 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 the water adsorbed to the untreated fibrous carbon material by heating or vacuum degassing before performing the fluorine treatment. This is because if water remains, it reacts with fluorine to generate hydrogen fluoride, which may adversely affect the production apparatus and the like.

In the fluorination method of the present invention, fibrous carbon material is usually charged into a cylindrical container. Here, by flowing a processing gas adjusted so that the fluorine concentration is in a predetermined range, fluorination, ie, a fluorine atom is chemically bonded to the surface of the fibrous carbon material to form a C—F bond. The container material can be safely processed if it is a metal material, but from the viewpoint of corrosion resistance, a stainless steel material such as SUS304 or SUS316 or nickel is desirable from the viewpoint of corrosion resistance.

The processing gas in fluorine processing consists of fluorine gas and an inert gas. The concentration of fluorine gas in the processing gas is 0.01 to 5% by volume, preferably 0.05 to 4% by volume. When the fluorine gas concentration is in this range, it is possible to obtain a fibrous carbon material in which the F / C ratio and the O / C ratio after post-treatment are in the desired ranges, which is good without increasing the internal resistance value. A non-aqueous electrolyte secondary battery having cycle characteristics is obtained. It is preferable that neither fluorine nor a gas other than the inert gas, for example, oxygen, be 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 O / C ratio after post-treatment to a desired O / C ratio, and the reaction with the fibrous carbon material rapidly progresses, There is a possibility of dust explosion depending on the situation.

If the treatment temperature is higher than 50 ° C, explosion may occur due to the progress of fluorination more than expected, or if the temperature is lower than 10 ° C, equipment and energy for cooling may be needed to create a cooling state. Since the cost is an issue, processing at around room temperature is desirable. However, when heat is generated when the fibrous carbon material contacts fluorine, the device may be cooled using cooling water or the like to control the reaction.

With regard to the treatment time, a sufficient time is required for the fibrous carbon material and the fluorine to uniformly contact, and it is desirable to secure 10 minutes or more, and more desirably 30 minutes or more. If it is too long, the performance as a conductive additive is not affected, but the production efficiency is lowered, so it is desirable to be within 2 hours. Further, after the fluorine treatment, in order to remove as much as possible the fluorine physically adsorbed to the fibrous carbon material, that is, the fluorine which does not contribute to the surface modification, it is preferable to deaerate under a vacuum state.

The processing pressure is not particularly limited, but from the viewpoint of safety, it is preferably 700 Torr (93.3 kPa) or less, and more preferably 500 Torr (66.7 kPa) or less. Further, in order to obtain a sufficient reaction rate, the pressure is preferably 10 Torr (1.3 kPa) or more, and more preferably 50 Torr (6.7 kPa) or more. The preferable flow rate of the processing gas may vary depending on the size and the structure of the reaction apparatus, and 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, an atmosphere containing a predetermined humidity, or water vapor. Post-treatment steps can be carried out at 10-30 ° C., but can be treated at ambient or ambient temperature without heating. In the case of exposure to 30 to 80% of the atmosphere in relative humidity, treatment may be performed for 2 hours to 48 hours, and in the case of exposure to water vapor having a relative humidity of 100%, 30 minutes to 2 hours. You can do the processing.

On the surface of the fibrous carbon material, C—F groups and the like are generated by fluorine treatment. In the post-treatment step, the C—F group on the surface is converted to a C—OF group, a C—OH group, or a COOH group by the action of H ₂ O to modify the surface. The presence or absence of a C-OF group, a C-OH group, or a COOH group on the surface can be confirmed by XPS or the like. The surface-modified fibrous carbon material is considered to improve the dispersibility in the paste for electrode production as compared with that before the modification. It is estimated that this conversion is completed about one hour after the end of the post-treatment process. However, in some of the C—F groups in the fibrous carbon material, F is strongly bonded to C due to the difference in the bonding state of the carbon atom to which the fluorine atom is bonded to other carbon atoms, and so on. Remains without reacting with ₂ O. In addition, it is preferable to vacuum degas and remove HF generated simultaneously at the same time.

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

If the F / C ratio and O / C ratio of the fibrous carbon material after treatment after the post-treatment step are high and there are too many fluorine atoms or oxygen atoms on the surface of the fibrous carbon material, the internal resistance of the battery will increase and the battery Cycle characteristics deteriorate. Although the cause is not clear, the present inventors speculate as follows. For example, it is conceivable that the contact resistance between the fibrous carbon material and the fibrous carbon material becomes high in the network formed by the fibrous carbon material, with fluorine atoms and oxygen atoms on the surface of the fibrous carbon material becoming impurities. . In addition, when there are too many fluorine atoms or oxygen atoms, excessive fluorination reaction destroys the fused benzene ring of the fibrous carbon material, and as a result, the movement of π electrons on the fibrous carbon material is inhibited, and fibrous carbon It is conceivable that the conductivity of the material itself is degraded.

Next, a non-aqueous electrolyte secondary battery using the treated fibrous carbon material of the present invention will be described. An electrolyte for a non-aqueous electrolyte secondary battery, an alkali metal ion including lithium ion and sodium ion, or an anode material capable of reversibly inserting and desorbing an alkaline earth metal ion; lithium ion and sodium ion An electrochemical device using a positive electrode material in which an alkali metal ion or an alkaline earth metal ion can be reversibly inserted and detached is referred to as a non-aqueous electrolyte secondary battery.

The non-aqueous electrolyte secondary battery of the present invention is characterized by using the fibrous carbon material after the treatment of the present invention, and other components used in general non-aqueous electrolyte secondary batteries are used. Be That is, it comprises a positive electrode and a negative electrode capable of absorbing and releasing lithium ions and the like, a current collector made of metal foil, a separator, a container, and the like.

The negative electrode is not particularly limited, but materials in which alkali metal ions such as lithium ion and sodium ion, or alkaline earth metal ions can be reversibly inserted and released are used, and the positive electrode is not particularly limited. However, materials in which alkali metal ions such as lithium ion and sodium ion, or alkaline earth metal ions can be reversibly inserted and released are used.

When the treated fibrous carbon material of the present invention is used as a conductive additive for the negative electrode, the negative electrode active material capable of absorbing and desorbing lithium ions and the like, a binder, a treated fibrous carbon material and a dispersion medium are mixed. After slurrying, it is applied to a metal foil which is a current collector, dried and pressurized to form a negative electrode layer. In addition, you may use together not only fibrous carbon material but particulate carbon materials, such as carbon black, as a conductive support agent. As various materials capable of absorbing and desorbing lithium ions and the like, for example, when the cation is lithium, lithium metal as an anode material, alloys and intermetallic compounds of lithium and other metals, artificial graphite and natural materials Graphite, carbon materials such as 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 absorbing and desorbing lithium ions and the like, a binder, a treated fibrous carbon material and a dispersion medium are mixed. After slurrying, the slurry 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, as well as the after-processing fibrous carbon material of this invention as a conductive support agent. In addition, before slurrying, the positive electrode active material, the post-treatment fibrous carbon material, the conductive additive and the like may be dry-mixed in a ball mill or the like. In the case of a lithium ion secondary battery, as an active material, for example, lithium-containing transition metal complex oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Co of lithium-containing transition metal complex oxides thereof, A mixture of a plurality of transition metals such as Mn and Ni, a part of the transition metal of the lithium-containing transition metal complex oxide substituted with a metal other than the other transition metals, LiFePO ₄ called olivine, LiCoPO ₄ And phosphoric acid compounds of transition metals such as LiMnPO ₄ , oxides such as TiO ₂ , V ₂ O ₅ and MoO ₃ , and sulfides such as TiS ₂ and FeS. Alternatively, conductive polymers such as polyacetylene, polyparaphenylene, polyaniline and polypyrrole, activated carbon, polymers generating radicals, carbon materials and the like are used.

The amount of the conductive aid contained in the electrode layer of the positive electrode layer or the negative electrode layer, that is, the amount of the conductive aid in the solid component in the slurry is preferably 0.1 to 20% by mass, 0.5 It is more preferable to include ~ 10% by mass, and further preferable to include 1 to 8% by mass.

As a binder used for the positive electrode or the negative electrode material, polytetrafluoroethylene, polyvinylidene fluoride, SBR resin or the like is used. In addition, as a dispersion medium of 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 will be given below together with comparative examples, but the present invention is not limited to the following examples.

Example 1-1
<Preparation of fibrous carbon material after fluorine treatment and post treatment (hereinafter referred to as “after treatment”)
A gas-grown carbon fiber (VGCF (registered trademark)-H, manufactured by Showa Denko KK) with a fiber diameter of 150 nm is used as an untreated fibrous carbon material, enclosed in a 5 L container made of SUS 304, and the inside is evacuated. The water adsorbed to the fibrous carbon material was removed. Here, 200 Torr (26.7 kPa) of fluorine diluted to 0.05% by volume with nitrogen was enclosed, and then flowed for 30 minutes at a total flow rate of 0.5 SLM. The above reaction was performed at room temperature (25 ° C.). After the end of circulation, the inside of the container was sufficiently replaced with nitrogen. Thereafter, the inside of the container was again depressurized to a vacuum state and degassed overnight to remove as much as possible of the fluorine adsorbed to the fibrous carbon material. Subsequently, the inside of the container was repressurized to the atmospheric pressure and exposed to the atmosphere (air temperature 25 ° C., relative humidity 45 to 50%) for 24 hours. The fibrous carbon material after processing 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 with a beam diameter of 100 μm.

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

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

<Fabrication of non-aqueous electrolyte secondary battery>
A non-aqueous solvent was impregnated into an aluminum laminate outer packaging cell (capacity: 30 mAh) including the test NCM positive electrode, the test graphite negative electrode, and the cellulose separator, to obtain a non-aqueous 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 non-aqueous solvents is 2: 1: 3. Lithium hexafluorophosphate (hereinafter referred to as “LiPF ₆ ”) was dissolved as a solute in the solvent at a concentration of 1.0 mol / L using a mixed solvent of 4: 4 to prepare an electrolytic solution. In addition, said preparation was performed, maintaining a liquid temperature at 25 degreeC.

<Battery evaluation>
The following evaluation was implemented about each of the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example.

<Evaluation 1: Measurement of internal resistance of battery>
First, conditioning was performed under the following conditions at an ambient temperature of 25 ° C. using the manufactured cell. That is, as the initial charge and discharge, constant current constant voltage charging is performed at a charge upper limit voltage 4.3 V, 0.1 C rate (3 mA), and discharge is performed at a 0.2 C rate (6 mA) constant current up to the discharge termination voltage 3.0 V Thereafter, charge / discharge cycle of charging at constant current / constant voltage with 0.2C rate (6mA) with charge upper limit voltage of 4.3V and discharging at constant current with 0.2C rate (6mA) to final discharge voltage of 3.0V three times I repeated it. The internal resistance of the battery was then measured. Table 1 describes the measurement results of the internal resistance in each of the examples and the comparative examples. 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, charge at constant current constant voltage at 3C rate (90mA) with charge upper limit voltage 4.3V at environmental temperature of 55 ° C and then discharge at 3C rate (90mA) constant current to discharge final voltage 3.0V This charge and discharge was repeated 100 cycles. The ratio of the discharge capacity at the 100th cycle to the initial (first cycle) discharge capacity was taken as the cycle capacity retention rate to evaluate the high temperature cycle characteristics of the cell. 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 ratio after 100 cycles of Comparative Example 1 is 100.

Embodiment 1-2
In the preparation of the fibrous carbon material after treatment, the same test as in Example 1-1 was conducted, except that the concentration of diluted fluorine used was 2% by volume, and the contact time with fluorine was 10 minutes.

Embodiment 1-3
The same test as in Example 1-1 was conducted except that the concentration of diluted fluorine used was 0.5 vol% when producing the fibrous carbon material after treatment.

Embodiment 1-4
The same test as in Example 1-1 was conducted except that the concentration of diluted fluorine used was changed to 2% by volume when producing a fibrous carbon material after treatment.

[Example 1-5]
The same test as in Example 1-1 was conducted except that the concentration of diluted fluorine used was 4 vol% when producing the fibrous carbon material after treatment.

[Example 1-6]
The same test as in Example 1-1 was conducted except that the pressure at the time of contacting with diluted fluorine was 50 Torr (6.7 kPa) when producing the fibrous carbon material after treatment.

[Example 1-7]
The same test as in Example 1-1 was conducted except that the pressure at the time of contact with diluted fluorine was set to 500 Torr (66.7 kPa) when producing the fibrous carbon material after treatment.

[Example 1-8]
The same as Example 1-4, except that the concentration of diluted fluorine used was 4% by volume and the pressure at the time of contact with diluted fluorine was 500 Torr (66.7 kPa) in the preparation of the fibrous carbon material after treatment. The test was done.

[Example 1-9]
The same as Example 1-1 except that carbon nanotubes with an average fiber diameter of 11 nm (AMC (registered trademark), Ube Industries, Ltd.) were used as the untreated fibrous carbon material when producing the fibrous carbon material after treatment Test was conducted.

[Example 1-10]
The same test as in Example 1-9 was conducted, except that the treatment time at the time of contact with diluted fluorine was 90 minutes, in the preparation of the fibrous carbon material after treatment.

Example 1-11
In the preparation of the fibrous carbon material after treatment, a test similar to that in Example 1-1 was conducted, except that the treatment temperature was 40 ° C. and the treatment time was 10 minutes.

Example 1-12
After the treatment, when preparing the fibrous carbon material, the treatment temperature is 40 ° C, the treatment time is 10 minutes, and water vapor at normal temperature (nitrogen gas with 100% relative humidity) is supplied for 1 hour in the post-treatment step. The same test as in Example 1-1 was conducted except for the above.

Comparative Example 1-1
The same test as in Example 1-1 was conducted, except that a fluorine-free nitrogen gas was circulated instead of the fluorine treatment step.

Comparative Example 1-2
The same test as in Example 1-1 was conducted, except that the concentration of diluted fluorine used was 0.005% by volume, at the time of preparation of the fibrous carbon material after treatment.

Comparative Example 1-3
In the preparation of the fibrous carbon material after treatment, the same test as in Example 1-1 was conducted, except that the concentration of diluted fluorine used was 7% by volume.

Comparative Example 1-4
The same test as in Example 1-1 was conducted, except that in the preparation of the fibrous carbon material after treatment, the concentration of fluorine was 4 vol%, the concentration of oxygen was 10 vol%, and the gas diluted with nitrogen was circulated. .

Comparative Example 1-5
The same test as in Example 1-1 was conducted except that the treatment temperature at the time of contact with diluted fluorine was set to 80 ° C. when producing a fibrous carbon material after treatment.

Comparative Example 1-6
The same test as in Example 1-1 was conducted except that oxygen gas was supplied in the post-treatment step when producing the fibrous carbon material after treatment.

Comparative Example 1-7
In the preparation of the fibrous carbon material after treatment, a test similar to that in Example 1-1 was conducted, except that nitrogen gas was supplied in the post-treatment step.

[Comparative Example 1-8]
In the preparation of the fibrous carbon material after treatment, the carbon nanotubes used in Example 1-9 were used as the untreated fibrous carbon material, and in the fluorine treatment step, an example was carried out except that nitrogen gas not containing fluorine was circulated. The same test as 1-1 was conducted.

The results of Examples 1-1 to 1-12 and Comparative Examples 1-1 to 1-8 are summarized in Table 1.

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 in the range of 0.05 to 5% by volume of fluorine concentration is brought into contact with the fibrous carbon material, By performing a post-treatment step of bringing a gas into contact with water, the ratio of fluorine atoms to carbon atoms, that is, the F / C ratio measured by XPS analysis is 0.001 or more and less than 0.025, and oxygen atoms It can be seen that it is possible to obtain a treated fibrous carbon material characterized in that the ratio to carbon atoms, that is, the O / C ratio is 0.1 or more and less than 0.2. Moreover, the non-aqueous electrolyte secondary battery manufactured using the processed fibrous carbon material in these ranges has a fluorine concentration outside the above range or is treated with diluted fluorine containing oxygen gas. It can be seen that the internal resistance value is lower than the material, and a high discharge capacity retention rate is maintained. According to XPS analysis, at least one functional group of C-OF group, C-OH group, or COOH group is present on the surface of the fibrous carbon material of Examples 1-1 to 1-12 after treatment. I found out.

On the other hand, according to the result of Comparative Example 1-2, at a fluorine concentration of 0.005% by volume, the surface modification hardly progresses, and the F / C ratio and the O / C value hardly change, and the inside No change was observed in the resistance value and the cycle characteristics. Further, according to the results of Comparative Example 1-3, at a fluorine concentration of 7 vol%, although the F / C ratio and the O / C value increased greatly, the internal resistance value increased and the cycle characteristics deteriorated. It is considered that this is because the fluorine concentration is too high, the surface roughness of the fibrous carbon material is remarkable, and the charge transport is inhibited.

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 fibrous carbon material after treatment is increased, the internal resistance value is increased, and the cycle characteristics are improved. It has fallen. This is considered to be an increase in internal resistance due to the change in the cross-linked structure of the fibrous carbon material by the fluorine treatment with fluorine and oxygen, and the conduction path between carbon and carbon being inhibited.

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

In Comparative Example 1-6, the oxygen gas was exposed in the post-treatment step after the fluorine treatment, but it has a high F / C ratio equal to that of Comparative Example 1-7, and the CF group is a COF group etc. An increase in the O / C ratio was observed, which appeared to have been changed, or the terminal substituent which had been in an unstable bonding state was oxidized. In Comparative Example 1-6, the internal resistance value was high, and the cycle characteristics decreased.

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

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

<Fabrication of positive electrode>
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM) powder as the positive electrode active material and acetylene black (hereinafter “AB”) as the conductive additive are dry mixed for 30 minutes using a ball mill, A polyvinylidene fluoride (hereinafter referred to as "PVDF"), which is a bonding material, was uniformly dispersed in NMP dissolved in advance, mixed, and NMP for viscosity adjustment was further added to prepare an NCM mixture paste. This paste is applied onto an aluminum foil (current collector), dried at 100 ° C. for 1 h, pressurized with a roller at 4 kN / m ² , and processed into a predetermined size. Obtained. The solid content ratio in the positive electrode was NCM: AB: PVDF = 85: 5: 10 (mass ratio).

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

The preparation of the non-aqueous 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]
The same tests as in Example 2-1 were conducted using the treated fibrous carbon materials obtained in Examples 1-2 to 1-12 and Comparative Examples 1-1 to 1-8.

The results of Examples 2-1 to 2-12 and Comparative Examples 2-1 to 2-8 are summarized in Table 2.

Similar to Examples 1-1 to 1-12, the internal resistance value is lowered in Examples 2-1 to 1-12 as compared with Comparative Examples 2-1 to 2-8, and the discharge capacity is high. It can be seen that the maintenance rate is maintained.

Claims

A fibrous carbon material used as a conductive aid for an electrode of a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and an electrolyte,
The ratio of fluorine atom to carbon atom, that is, the ratio of F / C is 0.001 or more and less than 0.025, and the ratio of oxygen atom to carbon atom, that is, the O / C ratio determined by XPS analysis Fibrous carbon material which is 0.05 or more and less than 0.2.
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 is present 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 an aspect ratio (average fiber length / average fiber diameter) of the fibrous carbon material is 10 or more.
The fibrous 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 collector, which is a metal foil,
An electrode layer formed on the current collector, 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 comprising:
A positive electrode, a negative electrode, and an electrolyte;
The nonaqueous electrolyte secondary battery which is an electrode for nonaqueous electrolyte secondary batteries of any one or both of the said positive electrode and the said negative electrode according to claim 7.
A method of producing a fibrous carbon material according to claim 1, wherein
A fluorine treatment step of bringing a fibrous carbon material into contact with a treatment gas comprising fluorine gas and an inert gas at 10 ° C. to 50 ° C., wherein the concentration of 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 of 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 an atmosphere of 30 to 80% in relative humidity for 2 hours or more and 48 hours or less. 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 for 30 minutes or more and within 2 hours.
The fiber according to any one of claims 9 to 11, comprising a step of performing a degassing step by placing the fibrous carbon material under a reduced pressure environment after the fluorine treatment step and before the post treatment step. Method of carbon-like carbon material.
The method for producing a fibrous carbon material according to any one of claims 9 to 12, further comprising the step of performing a degassing step by placing the fibrous carbon material in a reduced pressure environment after the post-treatment step.
A process of dispersing the fibrous carbon material according to claim 1 and the electrode active material in a dispersion medium to form a paste;
Applying the paste to a current collector and drying it;
A method for producing an electrode for a non-aqueous electrolyte secondary battery, comprising:
The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 14, further comprising a binder and a viscosity modifier in the paste.