JP2010114206A - Negative electrode film for lithium-ion capacitor, and electrode film-forming coating material composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode film for lithium-ion capacitor, which is suitably used for a capacitor with high output density by increased energy density per unit volume and reduction of internal resistance, the capacitor responding to power use for an automobile, a crane or the like; and to provide an electrode film-forming coating material composition. <P>SOLUTION: The negative electrode film for lithium-ion capacitor is obtained by applying, onto a metal foil, an electrode film-forming coating material composition containing graphite, a conductive aid and a binder in an aqueous medium containing a dispersant, and by heating and drying the coating material composition to coat the metal foil. The conductive aid is composed of at least any one of Ketjen black, acetylene black and graphite. The particle size distribution of component particles in the negative electrode film is composed of D<SB>10</SB>particle size of 0.3 μm or more, D<SB>50</SB>particle size of 0.5-15 μm, and D<SB>90</SB>particle size of 30 μm or less. The specific surface area of the negative electrode film ranges from 7 to 75 m<SP>2</SP>/g, and the surface roughness of the negative electrode film ranges from 0.1 to 1.5 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a coating composition for forming a negative electrode film and an electrode film of a lithium ion capacitor suitable for a capacitor having a high output density by reducing a high energy density and internal resistance per unit volume, such as for automobiles and cranes. .

  Electric Double Layer Capacitor (EDLC) has a large capacity, high output and maintenance-free features. Regeneration of self-luminous road fences, instantaneous voltage drop compensation devices, smoothing power supplies for solar cells, cranes, etc. It has been used for power supplies and idling stop power supplies for automobiles, and further expansion is expected in the future. Lithium-Ion Capacitor (LIC), which uses lithium ion intercalation reaction for the negative electrode, can make the energy density about 4 times higher than that of EDLC. Development as a power source is expected.

For example, in Patent Document 1, with respect to energy density and output density, at the same time as characteristics at room temperature, characteristics at low temperature, in particular, to provide an improved power storage device in which capacitance does not decrease. A negative electrode active material particle having a 50% volume cumulative diameter (D ₅₀ ) of 0.1 to 2.0 μm is formed, and the total mesopore volume of the negative electrode active material particle is 0.005 to 1.0 cm ³ / g. A lithium ion capacitor having a negative electrode made of a carbon material or a polyacene-based material having a specific surface area of 0.01 to 1000 m ² / g is disclosed.

Patent Document 2 also discloses a core carbon particle, a surface of the carbon particle, and a carbon particle surface for the purpose of providing a negative electrode active material for an electricity storage device that is further improved in low temperature characteristics, energy density, and high output. / Or consisting of a carbon composite with fibrous carbon having a graphene structure formed inside, and mesopores having a total mesopore volume of 0.005 to 1.0 cm ³ / g and a pore diameter of 100 to 400 mm are all mesopores A negative electrode material that occupies 25% or more of the volume, and the carbon composite has a specific surface area of 0.01 to 2000 m ² / g, and the carbon particles are graphitizable carbon, non-graphitizable carbon, graphite And a negative electrode active material made of at least one of polyacene-based materials.

Patent Document 3 discloses that a negative electrode active material has an average lattice spacing of d ₀₀₂ of 0.00 for the purpose of providing a negative electrode material capable of obtaining high energy density, high output density, and high durability in a lithium ion capacitor. 335-0.337 nm of graphite is used, and the negative electrode active material has a difference (D ₉₀ -D ₁₀ ) ≦ 7.0 μm between 90% volume cumulative diameter (D ₉₀ ) and 10% volume cumulative diameter (D ₁₀ ). Graphite and a lithium ion capacitor having a 50% volume cumulative diameter (D ₅₀ ) of D ₅₀ ≦ 4.0 μm are disclosed.

JP 2006-303330 A JP 2008-66053 A JP 2008-103596 A

  However, for power applications such as automobiles and cranes, high energy density per unit volume and high output density capacitors by reducing internal resistance are required. Further expansion of lithium ion capacitor applications further reduces internal resistance. And cost reduction is an important issue.

  Graphite has a structure in which hexagonal network surfaces made of carbon atoms are stacked, and regularly has lithium ion storage sites in the stacked layers. When used as a negative electrode material for a lithium ion battery, a battery having a high capacity and a small voltage drop can be designed and widely used in consumer applications such as for PCs and mobile phones. However, graphite having a higher capacity and higher crystallinity is more easily oriented in the film, so that it is necessary to improve applications that require output. In addition, it has been proposed to use fine particles as a negative electrode coating for lithium ion capacitors. However, the investigation of the optimization of the coating structure and the reduction of the resistance value is insufficient, the internal resistance is high, and the capacitance varies. There was a problem.

  As a paint for forming a negative electrode of a lithium ion secondary battery using graphite, although there is a type of organic solvent-based slurry in which the binder is polyvinylidene fluoride powder and the medium is N-methylpyrrolidone, it is examined from the lithium ion secondary battery In the shallow lithium ion capacitor, the present inventors consider that the negative electrode forming paint is hardly studied.

  Furthermore, in a lithium ion capacitor, since it is necessary to pre-dope lithium ions in the negative electrode, the design of the negative electrode material is different in direction from the design method of the negative electrode material for lithium ion batteries. Specifically, reduction of internal resistance and improvement of capacity are given top priority, and the allowable range of irreversible capacity is increased. For this reason, when designing a negative electrode for a lithium ion capacitor, an unprecedented design such as a high specific surface area, a small particle size, and an optimized coating film structure is required.

  In order to popularize lithium ion capacitors, it is necessary to obtain an electrode coating that achieves an increase in the capacitance of the capacitor and a reduction in internal resistance. Accordingly, an object of the present invention is to optimize the particle size of the constituent particles in the negative electrode coating, particularly the particle size of graphite, which is the main constituent material of the coating, to optimize the coating conditions of the coating composition for forming the electrode coating, and to obtain the coating It is an object to provide a coating composition for forming a negative electrode film and an electrode film of a lithium ion capacitor suitable for a high power density capacitor by reducing a high energy density per unit volume and internal resistance by optimizing the film structure of .

In order to solve the above-mentioned problems, the present invention applied an electrode film-forming coating composition containing graphite, a conductive additive and a binder onto a metal foil by a coating method in an aqueous medium containing a dispersant. And a negative electrode film of a lithium ion capacitor formed into a film at a heating temperature of 60 to 180 ° C.
The conductive auxiliary agent comprises at least one of ketjen black, acetylene black and graphite,
The particle size distribution of the constituent particles in the negative electrode _{coating, D 10} particle size of 0.3μm or _{more, D} range ₅₀ particle size of 0.5 to 15 _m, and a _{D 90} particle size is 30μm or less,
The specific surface area of the negative electrode film is in the range of 7 to 75 m ² / g,
The negative electrode film of the lithium ion capacitor is characterized in that the surface roughness of the negative electrode film is in the range of 0.1 to 1.5 μm.
Here, the “constituent particles in the negative electrode coating” refer to particles containing graphite and a conductive additive, which are the granular compounding materials mainly constituting the negative electrode coating, and by refining the particles constituting the negative electrode coating, The diffusion resistance of lithium ions is reduced, which contributes to reduction of internal resistance, that is, improvement of output. Also, the coatability of the electrocoat forming paste (coating composition) affects the smoothness and density of the coating, which is an important requirement for forming a negative electrode coating with excellent coating smoothness.

In order to solve the above-mentioned problems, the present invention applies an electrode film-forming coating composition containing graphite and a binder to an aqueous medium containing a dispersant on a metal foil, followed by drying by heating. A negative electrode film of a lithium ion capacitor formed into a film,
The particle size distribution of the constituent particles in the negative electrode _{coating, D 10} particle size of 0.3μm or _{more, D 50} ranging particle size of 0.5 to 15 _m, and a _{D 90} particle size is 30μm or less,
The specific surface area of the negative electrode coating is in the range of 7 to ²⁰ m ² / g,
The negative electrode film of the lithium ion capacitor is characterized in that the surface roughness of the negative electrode film is in the range of 0.1 to 1.5 μm.

  In order to solve the above-mentioned problem, the present invention provides the negative electrode film having a Raman spectrum spectrum in which the R value is in the range of 0.4 to 1.3 and the half-width W value of the D band is in the range of 17 to 40. It is preferable to use the negative electrode film of the lithium ion capacitor. It is important that the specific structure of the negative electrode film constituting particles is not deteriorated by the fine particles of the graphite particles.

  Moreover, in order to solve the said subject, it is preferable to set this invention as the negative electrode film of the said lithium ion capacitor whose sheet resistance value of the film thickness of the said negative electrode film is 40 ohms or less. In order to reduce internal resistance, it is important to reduce electrical resistance.

Moreover, in order to solve the said subject, it is preferable to set this invention as the negative electrode film of the said lithium ion capacitor whose coating film density of the said negative electrode film is 0.8-1.2 g / cm < ³ > range. In order to improve the capacity of the lithium ion capacitor, it is necessary to increase the coating density. By adopting the above-described configuration, the lithium ion capacitor having an excellent capacity and output is obtained.

In order to solve the above-mentioned problems, the present invention provides a coating composition for forming an electrode film comprising graphite, a conductive aid and a binder in an aqueous medium containing a dispersant,
The conductive auxiliary agent is composed of any of ketjen black, acetylene black and graphite,
The particle size distribution is such that the D ₁₀ particle diameter is 0.3 μm or more, the D ₅₀ particle diameter is in the range of 0.5 to 15 μm, the D ₉₀ particle diameter is 30 μm or less, and the R value of the Raman spectrum is 0.25 to 0.25. A range of 0.7,
The graphite having a half-width W value of D band in the range of 17 to 30;
Lithium obtained by adding the conductive auxiliary agent having an R value in the Raman spectrum of 0.2 to 1.65 and a half-width W value of D band in the range of 17 to 95 A coating composition for forming an electrode film of an ion capacitor is provided.

In order to solve the above-mentioned problems, the present invention provides a coating composition for forming an electrode film comprising graphite and a binder in an aqueous medium containing a dispersant,
The particle size distribution is such that the D ₁₀ particle diameter is 0.3 μm or more, the D ₅₀ particle diameter is in the range of 0.5 to 15 μm, the D ₉₀ particle diameter is 30 μm or less, and the R value of the Raman spectrum is 0.25 to 0.25. A range of 0.7,
A coating composition for forming an electrode film of a lithium ion capacitor, wherein the graphite having a half-width W value of D band in the range of 17 to 30 is added.

  By configuring the negative electrode film of the lithium ion capacitor of the present invention as described above, it is possible to improve the capacity, output and cost of the lithium ion capacitor. In addition, since it is important to optimize the particle size and structure of the active material constituting the negative electrode film by making the fine particles of graphite, an optimum and stable quality negative electrode film can be obtained by defining the structure of the graphite. It is done. A high-quality negative electrode film for a lithium ion capacitor can be obtained by an optimal blend of a conductive additive, a water-soluble dispersant, and an aqueous binder, which are other blending materials. Furthermore, since the negative electrode film-forming paste according to the present invention is an aqueous medium product, the working environment is improved, and the production cost can be reduced.

The first feature of the invention mainly in the negative electrode coating lithium-ion capacitor composed of graphite and conductive auxiliary agent, the particle size distribution of the constituent particles of the negative electrode in the coating is D ₁₀ particle size of 0.3μm or more, D _{When the 50} particle diameter is in the range of 0.5 to 15 μm, the D ₉₀ particle diameter is 30 μm or less, the specific surface area of the negative electrode film is in the range of 7 to 75 m ² / g, and the surface roughness of the negative electrode film is 0.1 to 1 The range is 5 μm. The particle size distribution in the negative electrode film is determined by a method of observing a film cross section with a scanning electron microscope (SEM). In addition, it is possible to specify the particle size distribution by laser diffraction particle size distribution measurement using the negative electrode film forming paste in advance as a sample object, and the particle size distribution specified by such measurement is also the particle size distribution of the constituent particles of the present invention. Included as

The 10% volume cumulative diameter D ₁₀ particle diameter, that is, the value closer to the lower limit of the particle diameter of the constituent particles is 0.3 μm or more, preferably 0.4 μm or more. D The ₁₀ particle size of less than 0.3 [mu] m, lowers the crystallinity of graphite is not preferable because the capacity is greatly reduced. In other words, the volume-based particle amount of less than 0.3 μm is preferably less than 10% in the negative electrode coating.

The so-called average particle diameter D ₅₀ particle diameter (50% volume cumulative diameter) is in the range of 0.5 to 15 μm, preferably in the range of 1 to 7 μm, particularly preferably in the range of 1.5 to 5 μm. When the D ₅₀ particle diameter is less than 0.5 μm, the number of fine particles increases, so that the contact resistance between the particles increases and the electric resistance value of the negative electrode coating increases, which is not preferable. On the other hand, if the average particle diameter of the negative electrode coating-constituting particles exceeds 15 μm, the particle diameter is too large, so that the diffusion resistance of lithium ions in the pores is increased and it is difficult to obtain an electrode having a target internal resistance.

The D ₉₀ particle diameter (90% volume cumulative diameter), that is, the value closer to the upper limit of the particle diameter of the constituent particles is less than 30 μm, preferably 20 μm or less, particularly preferably 10 μm or less. When the D ₉₀ particle diameter is 30 μm or more, coating defects such as stripe unevenness are liable to occur in coating with a film thickness of 60 μm or less, which is not preferable because the yield during coating is reduced.

Next, the specific surface area of the negative electrode film is in the range of 7 to 75 m ² / g, preferably in the range of 7 to 50 m ² / g, particularly preferably in the range of 8 to 25 m ² / g. The specific surface area of the coating film is important for optimizing the capacity and output (internal resistance). When the specific surface area is 7 to 75 m ² / g, both the capacity and the internal resistance are excellent. When the specific surface area of the coating exceeds 75 m ² / g, the structure of the graphite particles as the main constituent material may be deteriorated and the capacity may be reduced. The electrical resistance value of the coating and the density of the coating tend to decrease as the specific surface area increases. From this tendency, the specific surface area of the negative electrode film is preferably in the range of 7 to 75 m ² / g.

  Further, the specific surface area of the coating has a correlation with the specific surface area of the graphite particles of the main constituent material. On the other hand, there is no correlation between the particle size of the graphite particles and the specific surface area of the graphite particles. The reason for this is as follows. When the graphite particles are pulverized by a dry pulverizer using beads as a medium, the particles are aggregated at the same time as the particles are pulverized, making it difficult to obtain particles having a particle diameter of about 1 μm or less. By proceeding with the dry pulverization treatment, particles having a large specific surface area composed of aggregates of primary particles become particles, but the particles prepared by such a method have a large particle diameter and become graphite having a large specific surface area. Of course, such graphite particles can also be used in the present invention.

  The surface roughness of the negative electrode film is in the range of 0.1 to 1.5 μm, particularly preferably in the range of 0.2 to 0.6 μm. The surface roughness of the coating affects the uniformity of coating, the density of the resulting coating, and the hardness of the coating. When the surface roughness of the film is 1.5 μm or more, the density of the film becomes small, resulting in a decrease in capacity. On the other hand, when the surface roughness is 0.1 μm or less, the graphite particles become finer, the inherent structure collapses, and the capacity decreases. In addition, since the fine graphite particles are filled in the coating, the hardness of the coating becomes too high, which may cause a problem during slitting or winding in the electrode processing step.

The paste particle size _{D 10} particle size of 0.3μm or more from the _{above, the D 50} particle size is 0.5 to 15 _{m, D 90} particle size prescribed in 30μm or less, coating performance improved, film properties improve, the electrode This is important for improving the characteristics. Further, in optimizing the capacity and output (internal resistance) as a negative electrode film of a lithium ion capacitor using graphite, the particle size distribution of the negative electrode film constituting particles, the specific surface area and the surface roughness of the negative electrode film are important.

  In order to reduce the high capacity and internal resistance of lithium ion capacitors, it is necessary that the structure is not deteriorated due to the fine particles of graphite, and that the conductive assistant is optimally dispersed. It is important that the R value of the spectral spectrum is in the range of 0.4 to 1.3, and the half width W value of the D band is in the range of 17 to 40. The coating is composed of graphite, conductive aid, and dispersant and binder, but the inventors have determined that the Raman spectral characteristics of the coating vary depending on the blending amount of graphite and conductive aid in the coating and the dispersion state of these particles. As a result, it was measured by the Raman spectroscopic characteristics of the coating how the conductive assistant was dispersed around the graphite particles, and the optimum coating composition state was quantified.

  That is, the R value of the Raman spectrum as a film becomes 0.4 or less when the R value of the graphite used is too small or the amount of the conductive assistant is too small. When the R value of graphite is too small, the number of sites where lithium ions intercalant decreases, leading to an increase in internal resistance. Moreover, when there are too few amounts of conductive support agents, the sheet resistance of a coating film rises and an internal resistance increases. On the other hand, when the R value of the Raman spectrum as the film is 1.3 or more, the film structure is deteriorated due to the refinement of graphite and the edge sites are increased, resulting in an increase in irreversible capacity and a decrease in capacity. That is, the R value of the Raman spectrum of the film has a correlation with the internal resistance and capacity of the film, and is important and preferable in the range of 0.4 to 1.3.

  On the other hand, when the half width W value of the D band is 17 or less, it is considered that the graphite surface has good crystallinity and there are many regular layers. However, it is estimated that the resistance during lithium ion discharge increases, and the internal resistance is Get higher. On the other hand, when the half width W value of the D band is 40 or more, since the amorphous state is advanced due to the refinement of the graphite, the inherent structure of the graphite is deteriorated and the capacity is reduced. Further, when the amount of the conductive assistant is increased, the half-value width W value of the D band becomes 40 or more, but the compounding amount of graphite is reduced and the capacity is reduced.

  The sheet resistance value when the film thickness of the negative electrode film is 40 μm is 80Ω or less, preferably 10 to 60Ω, more preferably 15Ω to 40Ω. In order to reduce the internal resistance of the negative electrode coating, it is necessary to reduce the electrical resistance. It has been found that by optimizing the crystal structure of graphite and optimizing the compounding amount of the conductive aid, the sheet resistance value becomes about 10Ω. Although the sheet resistance can be reduced to 10Ω or less by increasing the crystallinity of graphite, increasing the particle size, and further increasing the blending amount of the conductive additive, it causes an increase in internal resistance and a decrease in capacity. Further, the sheet resistance value increases due to the refinement of graphite and the increase in specific surface area. However, when the resistance value is 80Ω or more, the electrical resistance becomes too high and the effect of reducing the internal resistance is not recognized.

Furthermore, the coating density needs to be high in order to improve the capacity, the coating film forming paste according to the present invention is applied, and the density of the coating film after drying is in the range of 0.8 to 1.2 cm ³ / g. Is required, preferably in the range of 0.95 to 1.2 cm ³ / g. As described above, the characteristic values of the negative electrode coating have been described, but individual factors for achieving these are attributable to the material used. That mainly _{D 10} particle size of constituent particles consisting of graphite 0.3μm or _more, the range _{D 50} particle size of 0.5 to 15 _{m, D 90} particle size of less 30 [mu] m. This point is the same as the characteristic value of the negative electrode film.

The R value in the Raman spectrum of the graphite particles is in the range of 0.25 to 0.7, and the W value is in the range of 17 to 30. This requirement stipulates the structure of the active material, and the R value and W value are increased by making the particles fine. However, in this range, there is no decrease in capacity and no problem is recognized. Particularly preferably, the graphite has a D ₁₀ particle diameter of 0.3 μm or more, a D ₅₀ particle diameter of 1 to 8 μm, a D ₉₀ particle diameter of 15 μm or less, and an R value in a Raman spectrum of 0.25 to 0.6. , W value is in the range of 18-28.

Further, any one of ketjen black, acetylene black, and graphite having an R value of the Raman spectrum of 0.2 to 1.6 and a half-width W value of the D band of 17 to 95 as the conductive assistant is used. It is preferable to use it. Ketjen black can be said to be a hollow carbon black having a structure with an R value of 1.5 to 1.6 and a W value of around 68 and having advanced graphitization. Acetylene black has a structure with an R value of 1.0 to 1.1 and a W value of around 90. Further, graphite used as a conductive aid is preferable because it has a D ₅₀ particle size of about 4 μm and good crystallinity, and an R value of about 0.25 and a W value of about 18 exhibit high conductivity.

  Although it is important to keep the blending amount of the conductive auxiliary agent to a minimum and to have a low resistance value, in order to make the addition amount the minimum, the bulk density is low and the particulate material is effective. Ketjen black with the lowest bulk density is effective with the minimum amount. Although acetylene black has a higher bulk density than Ketjen black, it has good compatibility with other compounding materials, and a high-density coating can be obtained. A negative electrode film containing ketjen black and acetylene black as a conductive auxiliary agent can reduce the contact resistance between graphite active material particles, and the electrical resistance is reduced. In addition, scaly graphite having good crystallinity is effective as a conductive aid because of its low bulk density and good conductivity.

  Further, it is also effective that the dispersant is a sodium salt or ammonium salt of carboxymethyl cellulose, and the binder is an emulsion of either a styrene butadiene elastomer or an acrylic elastomer. Representative examples of carboxymethylcellulose include carboxymethylcellulose sodium salt, carboxymethylcellulose ammonium salt, and carboxymethylcellulose calcium salt. In the present invention, sodium salt or ammonium salt of carboxymethyl cellulose is used. In particular, when sodium salt of carboxymethyl cellulose is used, the dispersion stability of graphite and conductive aid is good, and even if the paste (coating composition) is partially dried, it has good re-solubility in water and coating. A paint with no undissolved material can be produced by the previous stirring.

  Binders include (meth) acrylic acid ester (co) polymers, acrylic elastomers such as styrene / (meth) acrylic acid ester copolymers, styrene butadiene elastomers such as styrene / butadiene copolymers, and acrylonitrile / butadiene copolymers. Combined, polybutadiene, etc. can be used. Each binder can be used alone or in combination of two or more. By adjusting these, the coating density after coating and coating can be improved and the film structure can be optimized, and the capacity can be improved and the internal resistance can be reduced. Further, by reducing the size of the graphite particles, defects such as coating unevenness during coating can be improved, which can contribute to an increase in yield. A water-based paste is excellent in working environment and safety during paste production and coating, and a coating with low resistance and good adhesion can be obtained by optimizing the conductive aid, dispersant, and binder.

Moreover, as a viscosity structure of paste (coating composition), it is preferable that the viscosity value of 30 rpm by a B-type viscometer at 25 ° C. is 600 to 2400 mPa · s, and the viscosity value at 60 rpm is 500 to 2300 mPa · s. When a negative electrode film is formed by a coating method, the film thickness is generally set to about 20 μm to 80 μm. As a coating machine, there are a die coater, a blade coater, a comma coater, a lip coater, a reverse roll coater, and the like. Recently, a die coater used for forming an electrode for a lithium ion battery has been used. The die coater can form a film with a uniform film thickness, and can also apply a pattern of circuit elements. In order to carry out uniform coating with few coating film defects such as streak unevenness using a die coater, in particular, the D ₉₀ particle diameter should be reduced, and coarse particles and foreign substances should adhere to the die edge and manifold, It is also necessary to prevent clogging. In this respect, as defined in the first aspect of the present invention, it is necessary to adjust the D ₉₀ particle diameter of the coating to 30 μm or less. By setting the viscosity at the rotor 30 rpm to 600 to 2500 mPa · s and the viscosity at 60 rpm to 500 to 2300 mPa · s, uniform coating with a die coater becomes possible.

Examples of the present invention will be described below, but the present invention is not limited to these examples.
(Adjustment of paint and sample)
Graphite particles having different particle diameters, specific surface areas, and structures, and ketjen black, acetylene black, or graphite were blended in an aqueous solution in which carboxymethyl cellulose (CMC) was dissolved in pure water and dispersed with a ball mill for 3 hours. . Thereafter, a predetermined amount of acrylic emulsion or SBR emulsion was blended and stirred for 30 minutes. Tables 1 and 2 show the formulations used for the study.

(Viscosity evaluation of paint)
The viscosity of the prepared paint was measured at 30 rpm and 60 rpm using a BL type viscometer. The measurement temperature was 25 ° C. The viscosity was measured using a stirrer having a propeller-type stirring blade and stirring for 30 minutes under a stirring condition of 1000 prm.

(Particle size distribution of paint)
It measured using the laser diffraction type particle size distribution analyzer. The refractive index was 2.00-0.1i.

(Preparation of coating)
The prepared paint was applied onto a 19 μm thick copper foil using a blade coater with a gap of 100 μm. Thereafter, it was dried with hot air at 100 ° C. for 30 minutes, and then dried with a vacuum dryer at 75 ° C. for 30 minutes to produce an electrode film having a thickness of 40 μm.

(Specific surface area of coating and active material)
The specific surface area and pore structure of graphite particles and conductive auxiliary particles used as the electrode coating and paste material thus prepared were measured by BET method by nitrogen adsorption using ASAP2010 manufactured by Micromeritics.

(Surface roughness of coating)
The center line average roughness of the produced electrode coating was measured using a surface roughness profile measuring machine. In the measurement, the stylus diameter was 2 μm, the measurement speed was 0.3 mm / s, the measurement length was 4 mm, and the cut-off value was 0.8 mm.

(Raman spectral characteristics of coatings and active materials)
As analysis method of the surface structure of the manufactured electrode coating and a carbon material, the area of the peak of the Raman spectroscopy by (NRS-2100 of Renishow Ltd.), G-band (1580 cm ^-1 vicinity) and D-band (1360 cm around ^-1) The R value (I ₁₃₆₀ / I ₁₅₈₀ ), which is the ratio, was determined. An argon (Ar) laser beam having a wavelength of 514 nm was used for the measurement. In measuring the area, it was assumed that the shape of the curve of the two peaks near the G band and the D band approximated to the Lorentz function, rewritten by fitting to this, and the R value was obtained from the area ratio.
For the Raman spectral characteristics of the active material, an appropriate amount of the active material to be used was collected on a slide glass, and the R value was measured by the above method.

(Evaluation of coating density)
The dried electrode was punched out to a size of φ13 mm, and the electrode weight was measured. The density of the coating was calculated by subtracting the weight of the underlying copper foil.

(Sheet resistance value of coating)
The sheet resistance value of the produced electrode film was measured by a four-end needle method.

(Capacity and internal resistance evaluation)
A positive electrode active material paste using phenol-based alkali activated carbon as an active material was applied and formed into a film on a 40 μm aluminum foil using a blade coater to prepare a positive electrode having a film thickness of 100 μm and φ20 mm.
Next, a negative electrode active material paste using graphite as an active material was applied to a 19 μm thick copper foil with a blade coater to form a negative electrode having a film thickness of 50 μm and φ20 mm.
The film formation of the positive and negative electrodes is as follows.
The paste coating film was dried at 100 ° C. for 30 minutes with hot air and then under reduced pressure at 120 ° C. for 12 hours. Then, it moved in the glove box of argon atmosphere, and lithium ion dope to the negative electrode by graphite was performed. First, lithium metal was stacked on a φ20 mm graphite electrode via a separator to prepare a monopolar cell. The electrolyte is a hexafluoride solute in a solvent consisting of ethylene carbonate (EC) / dimethyl carbonate (DMC) / propylene carbonate (PC) (where the volume ratio is EC: DMC: PC = 30: 30: 40). A solution in which lithium phosphate (LiPF ₆ ) was dissolved at a molar concentration of 1.2 mol / liter (M / l) was used. Charging to the negative electrode was stopped when the charge capacity reached 350 mAh / g, and a half-charged negative electrode was created. Thereafter, a positive electrode made of activated carbon was opposed to the half-charged negative electrode via a separator to prepare a test cell.
The capacitance (F) until the charging voltage decreased from 3.8 V to 2.2 V was determined at a measurement temperature of 25 ° C. and a discharge current of 20 mA. Further, the capacity [mAh / g] at a discharge current of 20 mA was determined. Furthermore, the internal resistance (Ω) was determined from the initial voltage drop when the discharge current was 20 mA.

The example is an example in which an electrode film forming paste containing graphite, a conductive additive and a binder in an aqueous medium containing a dispersant is used. In order to improve the capacity and reduce the internal resistance, it is important to combine a suitable graphite structure with a conductive additive. An Example shows the result of having examined the physical property of graphite, changing the specific surface area 12-150 m < ² > / g, R value 0.25-0.70 of Raman spectroscopic analysis, and W value 17-30.

Comparative Example 1 is an example using non-graphitizable carbon as an active material. Non-graphitizable carbon has low internal resistance and relatively high capacity, and is used as a negative electrode for lithium ion capacitors. However, for further capacity improvement and cost reduction, it is important to use graphite in the negative electrode, and studies were conducted to reduce internal resistance using graphite. Comparative Examples 1 and 3 and Example 1 4 of constituent particles in the coating D ₁₀ particle size is a particle size distribution, D ₅₀ particle size and D ₉₀ to change the particle size, also the specific surface area and surface roughness of the film The result of examining optimization is shown.
Here, the particle diameter and the specific surface area do not necessarily have a correlation, and graphite having a large particle diameter by granulating or agglomerating fine particles can also be used.

In Comparative Example 2, the D ₅₀ particle size of the coating-constituting particles is 8.2 μm and is within the scope of the invention, but the coating specific surface area is as small as 5 m ² / g and is outside the scope of the invention. Further, the R value of Raman spectroscopic analysis of the coating film is 0.38, and the W value is 17.5, both of which are small and out of the scope of the invention. That is, the crystallinity of graphite is good, the graphite has a few edge surfaces, and the internal resistance is as high as 6.3Ω. Comparative Example 3 is an example in which the D ₅₀ particle size is as large as 18 μm, which is outside the scope of the invention. In the coating property with a film thickness of 60 μm, the coating unevenness is large, and there is a problem in terms of coating quality and productivity. is there. Moreover, the smoothness (coating surface roughness) of the coating is 2.1 μm, and there is a problem in reliability in terms of the uniformity of the coating.

Examples 1 to 4 are examples in which the D ₅₀ particle size of the coating is 1 to 15 μm and the specific surface area is 7 to 75 m 2 / g, but the coatability is good, and the smoothness of the coating (coating surface roughness) is The thickness is 0.1 to 1.4 μm, and a uniform film can be formed. In addition, both the capacitance and internal resistance are good.

Example 1 is an example in which the D ₁₀ particle diameter is 0.3 μm, the D ₅₀ particle diameter is 1.0 μm, the D ₉₀ particle diameter is 2.1 μm, and the specific surface area of the coating is 17 m ² / g. Since it is uniformly dispersed, the coating film surface roughness is 0.1 μm, a smooth coating film can be formed, and a thin film electrode can be formed. Since the fine particle formation is progressing, the coating density tends to decrease at 0.81 g / cc. Therefore, the capacity tends to decrease at 22 mAh, but the internal resistance is low.

In Example 2, the specific surface area of the coating is 7 m ² / cc, which is the lower limit. However, since the crystallinity of graphite is good, the capacity is as high as 25 mAh / g, but the internal resistance is high, and the upper limit of the present invention is high. It is.

Example 3 is an example in which the specific surface area of the coating is 75 m ² / g, but the internal resistance is low and good. However, there is deterioration of the crystal structure of graphite, and although the target capacity is cleared, a decrease in capacity can be confirmed.

Example 4 is an example in which the D ₅₀ particle size of the coating is 15 μm and the specific surface area is 47 μm. Although D ₅₀ particle in the aggregation of particles is larger, the specific surface area of the film is large internal resistance was good in capacity both. Even at a film thickness of 60 μm, the smoothness of the coating film was 1.4 μm, there was no coating unevenness, and no problem was observed.

It has been shown in Examples 1 to 4, as a dispersing agent CMC-Na, may be used CMC-NH _3, as a binder emulsion SBR elastomer or an acrylic elastomer can be used.

These results, the particle size distribution of the constituent particles of the negative electrode in the _{coating, D 10} particle size of 0.3μm or _{more, D 50} range of particle size _{0.8～15Myuemu,} at _{D 90} particle size is 30μm or less, the negative electrode It was confirmed that it was important that the specific surface area of the film was in the range of 7 to 75 m ² / g and the surface roughness of the negative electrode film was in the range of 0.1 to 1.5 μm.

Table 2 shows an example in which optimization of the coating structure was examined using graphite as an active material and acetylene black, ketjen black and graphite as a conductive additive, and a comparative example using a material outside the scope of the invention. Show.
Comparative Example 4 is an example in which the constituent particles in the negative electrode coating were further refined. By increasing the particle size of graphite as an active material until the D ₅₀ particle size became 0.7 μm, the coating density was reduced to 0.79 g / cc, and the capacity was 21 mAh / g or less.

Comparative Example 5 uses Ketjen Black as a conductive additive and shows a high viscosity example. It was confirmed that the paste with a viscosity of 30 rpm of 2550 mPa · s and a viscosity of 60 rpm of 2400 mPa · s had a reduced spread of the paint and it was difficult to form a uniform film of 60 μm.
Moreover, since there were many compounding quantities of ketjen black with a low bulk density, the coating-film density fell and it confirmed that a capacity | capacitance fell. The R and W values of the Raman spectroscopic analysis of the coating increase with increasing ketjen black. The coating film of this example has an R value of 1.4 and a W value of 41. However, in order to optimize the coating film structure, it is necessary to set the R value and the W value within a range of numerical values smaller than this value. It was confirmed that there is.

  Example 5 is an example in which acetylene black and ketjen black are used as conductive assistants to reduce the sheet resistance value. Although the coating film density was reduced to 0.82, the sheet resistance could be reduced to 20Ω, and good results were obtained for the capacity, capacitance, and internal resistance.

  Further, Example 6 is an example in which graphite having a large specific surface area is used as an active material in the same manner as in Example 3. However, Example 6 is an example in which reduction of the electric resistance value was examined using a graphite auxiliary having good crystallinity. Although the internal resistance was higher than that of Example 3, the capacity was increased and good results were shown.

Example 7 is an example in which a film was formed using graphite as an active material without using a conductive additive. Since the specific surface area of the film was suppressed to 20 m ² / g, the sheet resistance of the film was 80Ω, the internal resistance was 5Ω, and the capacity was good.

Comparative Example 6 is an example in which the specific surface area of the coating is 85 m ² / g. The internal resistance is good at 3.5Ω, but the capacity is reduced to 20 mAh / g, and the crystal structure of graphite is progressing.

As described above, the negative electrode for a lithium ion capacitor should have a coating film structure defined by specific surface area and Raman spectroscopic characteristics, and a negative electrode coating excellent in capacity and internal resistance can be obtained by defining the structure of the material used. Was confirmed.

Claims (7)

A negative electrode film for a lithium ion capacitor in which a coating composition for forming an electrode film comprising graphite, a conductive additive and a binder is applied onto a metal foil in an aqueous medium containing a dispersant, and is heated and dried to form a film. Because
The conductive auxiliary agent comprises at least one of ketjen black, acetylene black and graphite,
The particle size distribution of the constituent particles in the negative electrode _{coating, D 10} particle size of 0.3μm or _{more, D 50} ranging particle size of 0.5 to 15 _m, and a _{D 90} particle size is 30μm or less,
The specific surface area of the negative electrode film is in the range of 7 to 75 m ² / g,
A negative electrode film for a lithium ion capacitor, wherein the negative electrode film has a surface roughness in the range of 0.1 to 1.5 μm. A coating composition for forming an electrode film comprising graphite and a binder in an aqueous medium containing a dispersant is applied on a metal foil, and is a negative electrode film for a lithium ion capacitor that is formed by heating and drying,
The particle size distribution of the constituent particles in the negative electrode _{coating, D 10} particle size of 0.3μm or _{more, D 50} ranging particle size of 0.5 to 15 _m, and a _{D 90} particle size is 30μm or less,
The specific surface area of the negative electrode coating is in the range of 7 to ²⁰ m ² / g,
A negative electrode film for a lithium ion capacitor, wherein the negative electrode film has a surface roughness in the range of 0.1 to 1.5 μm.   3. The lithium ion capacitor according to claim 1, wherein an R value of a Raman spectrum of the negative electrode film is in a range of 0.4 to 1.3, and a full width at half maximum W of a D band is in a range of 17 to 40. 4. Negative electrode coating.   The negative electrode film for a lithium ion capacitor according to any one of claims 1 to 3, wherein the negative electrode film has a sheet resistance value of 80? The coating film density of the negative electrode film is in the range of 0.8 to 1.2 g / cm ³ , The negative electrode film of the lithium ion capacitor according to claim 1. In an aqueous medium containing a dispersant, a coating composition for forming an electrode film comprising graphite, a conductive aid and a binder,
The conductive auxiliary agent comprises at least one of ketjen black, acetylene black and graphite,
The particle size distribution is such that the D ₁₀ particle diameter is 0.3 μm or more, the D ₅₀ particle diameter is in the range of 0.5 to 15 μm, the D ₉₀ particle diameter is 30 μm or less, and the R value of the Raman spectrum is 0.25 to 0.25. A range of 0.7,
The graphite having a half-width W value of D band in the range of 17 to 30;
Lithium obtained by adding the conductive assistant having an R value of Raman spectrum of 0.2 to 1.65 and a half-width W value of D band of 17 to 95 A coating composition for forming an electrode film of an ion capacitor. An electrode film-forming coating composition comprising graphite and a binder in an aqueous medium containing a dispersant,
The particle size distribution is such that the D ₁₀ particle diameter is 0.3 μm or more, the D ₅₀ particle diameter is in the range of 0.5 to 15 μm, the D ₉₀ particle diameter is 30 μm or less, and the R value of the Raman spectrum is 0.25 to 0.25. A range of 0.7,
A coating composition for forming an electrode film of a lithium ion capacitor, wherein the graphite having a half-width W value of D band in the range of 17 to 30 is added.