JP3718072B2 - Secondary battery electrode material and method for producing coated body using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention has good coatability using scaly natural graphite particles as a raw material.Secondary battery electrode materialIt is about. AlsoSecondary battery electrode materialThe present invention relates to a method for producing a coated body using the above.
[0002]
[Prior art]
  Natural graphite is usually crushed or medium-crushed ore, then subjected to physical or chemical scouring to increase purity and further pulverized to the desired particle size.
[0003]
  Regarding the pulverization of natural graphite to the target particle size, “25. Latest powder and particle process technology assembly (Process), published by Industrial Technology Center Co., Ltd., March 15, 1974, first edition, first print”, “25. Page 275 of the “Graphite” chapter states that “the one with the friction pulverization type tends to flatten the particles and the fluid energy type pulverization increases the friction between the particles. In the impact friction type pulverization, the pulverization proceeds well, but if it becomes a fine powder of 1 μm or less, it tends to adhere and forms an aggregate, and the bulk specific gravity and the like are lowered. In FIG. 25.3 on pages 274 to 275, a photograph of the change in the shape of the particles due to pulverization is published.
[0004]
  JP-A-8-213020 and JP-A-8-298117 relating to the application of the present applicant have disclosed disclosure of scaly natural graphite by jet milling. In the examples, Hosokawa Micron micron jet and Alpine Grinding is performed using a counter jet mill. According to these publications, scaly natural graphite is crushed in a state of being crushed and crushed by a normal grinding method such as a ball mill, whereas by jet milling, scaly natural graphite is sharply crushed. There is an explanation that it is refused.
[0005]
  The scaly natural graphite can be used as an electrode material for a secondary battery, particularly as a negative electrode material for a lithium secondary battery. When flaky natural graphite is used for this purpose, flaky natural graphite is often mixed with a solvent and a binder to form a slurry, which is applied to an object. In this case, since the scaly natural graphite literally has a scaly (plate-like) shape, the fluidity when mixed with the solvent and the binder is poor, and a large amount of solvent is required to obtain a predetermined viscosity. Thus, a coating layer having a predetermined thickness may not be formed. Therefore, in order to improve fluidity, conventionally, a method of pulverizing until the particle size becomes several μm, a method of ensuring fluidity by adding various surfactants, a method of stirring vigorously for a long time, etc. have been taken. It was.
[0006]
[Problems to be solved by the invention]
  In the above-mentioned “Latest Particle Process Technology Assembly (Process)”, there is a rounded shape with rounded corners that can be obtained by fluid energy type pulverization. This means that the corners of the graphite particles can be taken, and it does not mean that the graphite particles are made like a sphere.
[0007]
  The description of the above-mentioned JP-A-8-213020 and JP-A-8-298117 is also intended to pulverize flaky natural graphite without losing its flaky shape within the category of pulverization.
[0008]
  And when scaly natural graphite is used as an electrode material for a secondary battery, the method of finely pulverizing natural graphite to ensure fluidity is actually not easy to make it 5 μm or less because graphite is slippery. If the size is larger than that, the effect of improving the fluidity is small. Depending on the application, it may be restricted to make the particle size too small, but such a case cannot be dealt with. Although the addition of the surfactant is effective in improving the fluidity, it is often difficult to balance the selection of the surfactant and the amount of the surfactant, and constantly maintain the optimum state. Moreover, since addition of a surfactant is restricted depending on the use, it is unsuitable for such use. The method of improving fluidity by vigorous stirring for a long time is time consuming and labor intensive, so it cannot be avoided from being industrially disadvantageous, and the necessary fluidity cannot be obtained even by vigorous stirring for a long time. There are many.
[0009]
  As described above, it is known to pulverize scaly natural graphite particles, but it is still possible to obtain spherical particles by modifying the raw scaly natural graphite particles so as to approximate a spherical shape. It is believed that it is unknown.
[0010]
  The present applicant has found a modified flaky natural graphite particle obtained by spheroidizing flaky natural graphite particles to a circularity of 0.86 or more and a method for producing the same, and has already filed a patent application as Japanese Patent Application No. 10-68532. Based on the application, foreign applications are also filed.
[0011]
  However, when the spheroidized scale-like natural graphite modified particles are mixed with a binder and a medium (solvent) to be slurried and applied to an object such as copper foil, the viscosity decreases immediately after application, and dripping or repelling occurs. (Repellency) may occur. Therefore, when the viscosity of the slurry is increased to avoid such trouble, the smoothness of the application tends to be impaired because the slurry is a dilatant fluid. It was also found that when the slurry was applied to a copper foil, dried and pressed to be used as a negative electrode for a secondary battery, there was a problem that the discharge capacity at a large discharge current value was limited.
[0012]
  Under such circumstances, the present invention can remarkably improve the applicability of the slurry to an object in a system using particles obtained by spheroidizing flaky natural graphite. When producing a negative electrode, it is possible to increase the discharge capacity at a large discharge current value.Secondary battery electrode materialProviding andSecondary battery electrode materialAn object of the present invention is to provide a method for producing a coated body using the above.
[0013]
[Means for Solving the Problems]
  Of the present inventionSecondary battery electrode materialIs
  Spherical particles (A) having a roundness of 0.86 or more, modified from flaky natural graphite particles so as to approximate a sphere, and non- or low-sphericalized particles of flaky natural graphite particles having a circularity of less than 0.86 (B)It is an electrode material for secondary batteriesabout,
  The spheroidized particles (A) have (1) a circularity of 0.86 or more, and (2) a microscopic observation of the fracture surface, the graphite section has a cabbage-like appearance in various directions. And (3) the peak intensity ratio Ih of the 002 plane (the plane parallel to the graphite layer) and the 110 plane (the plane perpendicular to the graphite layer) by the X-ray diffraction method, which is an index of randomness of orientation₁₁₀/ Ih₀₀₂Satisfying all the requirements of ≥0.0050,
and,
  The blending ratio of the spheroidized particles (A) to the non-spheroidized particles (B) is 99.9: 0.1 to 55:45 by weight ratio,
It is characterized by.
[0014]
  The manufacturing method of the coated body of the present invention is as described above.Secondary battery electrode materialIs applied to the object (O) in a slurry state.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
  The present invention will be described in detail below.
[0016]
<Sphericalized particles (A)>
  The spheroidized particles (A) are particles having a roundness of 0.86 or more obtained by modifying the scaly natural graphite particles so as to approach a sphere.
[0017]
  This spheroidized particle (A) is
  (1) In addition to a circularity of 0.86 or more,
  (2) In the microscopic observation of the fracture surface, the graphite section has a cabbage-like appearance in various directions, and
  (3) Peak intensity ratio Ih of 002 plane (plane parallel to the graphite layer) and 110 plane (plane perpendicular to the graphite layer) by X-ray diffraction method, which is an index of randomness of orientation₁₁₀/ Ih₀₀₂Is required to satisfy all the requirements of 0.0050 or more. (1) Circularity, (3) Peak intensity ratio Ih₁₁₀/ Ih₀₀₂This measuring method will be described and defined in the section of the examples described later.
[0018]
  Regarding the circularity of (1), the spheroidized particles (A) have a circularity of 0.86 or more, preferably 0.88 or more. Incidentally, the roundness of the scaly natural graphite particles available on the market is, for example, about 0.84. Since the circularity is an index when the particles are projected on a two-dimensional plane, the raw scaly natural graphite particles and the spheroidized particles (A) in the present invention seem to be numerically close, As the degree of circularity increases, the spheroidization is actually progressing more than expected from the numerical value.
[0019]
  The appearance of the fracture surface in (2) is related to the orientation index in (3) below, but the characteristics of the spheroidized particles (A) are represented from the top of the appearance. As for the scaly natural graphite particles at the raw material stage, it is confirmed by microscopic observation that the graphite sections are layered only in almost the same direction, but in the case of spheroidized particles (A), there are various graphite sections. It has a cabbage-like appearance. From this appearance, it can be seen that the spheroidized particles (A) have a layered structure of scaly natural graphite, but the structure has been modified into a chimera.
[0020]
  With respect to the orientation index of (3), the spheroidized particles (A) have a 002 plane (plane parallel to the graphite layer) and 110 plane (perpendicular to the graphite layer) by X-ray diffraction (reflection method), which is an index of orientation randomness. Peak intensity ratio Ih₁₁₀/ Ih₀₀₂However, it is 0.0050 or more, preferably 0.0080 or more, more preferably 0.0100 or more. Incidentally, the peak intensity ratio Ih of scaly natural graphite particles available on the market₁₁₀/ Ih₀₀₂Is about 0.0015 to 0.0018 or around, and is significantly smaller than that of the spheroidized particles (A), and the randomness of the orientation is extremely small.
[0021]
<Method for producing spheroidized particles (A)>
  The spheroidized particles (A) satisfying all the requirements (1), (2) and (3) described above can be preferably produced industrially by the method described below.
[0022]
  That is, the spheroidized particles (A) are charged with scaly natural graphite particles from the feeder (12) into the tank (11) using a tank (11) having a collision area and a flow area where jet air currents collide with each other. In addition, by blowing a jet stream from the opposed nozzle (13) provided on the lower side of the tank (11), the particles collide with each other in the lower collision area in the tank (11), and the upper part in the tank (11). In the flow zone on the side, particles are circulated and flowed, while fine powder below the classification limit is discharged out of the tank by the classifier (14) provided at the top of the tank (11), and the above operation is performed in batches. Can be manufactured.
[0023]
  As the graphite particles as the raw material, scaly natural graphite particles with high crystallinity are used. Since this scaly natural graphite is usually available in a purity of more than 85% to 99%, if necessary, the purity can be further increased by an appropriate means.
[0024]
  Particle size of scaly natural graphite charged as a raw materialIsSecondary battery electrode materialConsidering the use asThe average particle size is often about 1 to 100 μm, particularly about 5 to 60 μm.
[0025]
  As an apparatus for modifying the scaly natural graphite particles as a raw material, a tank (11) having a collision area where a jet stream collides and a flow area is used. As this tank (11), for example, a fluidized bed type counter jet mill on the market can be used, or it can be improved for the purpose of the present invention.
[0026]
  From the feeder (12) of the tank (1), scaly natural graphite particles are charged into the tank (11). The feeder (12) is preferably installed as a hopper type at an appropriate location in the tank (11). In this case, the feeder (12) can be used as an outlet for the modified particles. The feeder (12) can also be provided at the bottom of the tank (11) as a screw type. The amount of scale-like natural graphite particles charged into the tank (11) is determined in consideration of the effective space of the tank (11), but not so strict. However, when the charged amount is extremely small, the particles are not smoothly flowed. When the charged amount is extremely large, the particles are excessively crushed, making it difficult to obtain modified particles having the desired properties.
[0027]
  A counter nozzle (13) is provided on the lower side of the tank (11) through the tank wall, and a jet stream is blown from the counter nozzle (13), so that an air current is generated in the lower collision area of the tank (11). Collide the particles inside. The counter nozzle (13) is preferably provided in a plurality, particularly three. The speed of the jet stream blown from the opposed nozzle (13), the amount of blown gas, the tank pressure, etc. are set so that smooth collision and flow can be achieved, and the desired degree of spheroidization can be achieved by setting the operation time appropriately. As illustrated.
[0028]
  Particles collide with each other in the lower collision area in the tank (11), but circulating particles flow in the upper flow area in the tank (11). In a steady state, the particles generally blow up at the center of the tank (11) and fall down along the wall of the tank (11).
[0029]
  A classifier (14) is provided in the upper part of the tank (11) to discharge fine powder below the classification limit to the outside of the tank. As the classifier (14), a high-speed rotating classifier is usually used. The discharge amount at this time varies depending on the particle size of the scaly natural graphite particles used as a raw material.
[0030]
  It is important to perform the above operations in batch. If the operation is continuously performed as in ordinary jet mill grinding, the raw material particles are continuously supplied, and the ground particles are continuously taken out from the upper part of the tank, the desired spheroidized particles (A) are obtained. Can't get.
[0031]
  By performing the above operations while adjusting the conditions, modification by particle aggregation, adhesion, pressure bonding, growth, etc. due to collision, grinding to remove corners, etc., resulting in changes in particle size distribution, orientation The spheroidized particles (A) satisfying the conditions (1), (2) and (3) described above can be obtained.
[0032]
  The preferred particle size of the spheroidized particles (A) is 5 to 50 μm, in particular 10 to 30 μm, in terms of average particle size. It is not practical to make the particle size extremely small, and when the particle size is extremely large, the viscosity of the slurry is too low.
[0033]
<Non to low spheroidized particles (B)>
  The non-sphericalized particles (B) are particles whose scaly natural graphite particles have a circularity of less than 0.86, usually 0.85 or less. Such particles are obtained by performing insufficient modification when obtaining the scaly natural graphite particles used as a raw material for the production of the above-mentioned spheroidized particles (A) or the spheroidized particles (A). Particles are used.
[0034]
  The preferred particle size of these non-spheroidized particles (B) is 1 to 50 μm, especially 2 to 25 μm in average particle size. It is not practical to make the particle size extremely small, and when the particle size is extremely large, the viscosity of the slurry is too low.
[0035]
<Secondary battery electrode material>
  Of the present inventionSecondary battery electrode materialConsists of the above-mentioned spheroidized particles (A) and non-spheroidized particles (B), and the blending ratio is set to 99.9: 0.1 to 55:45 by weight ratio. A preferred range is 99.5: 0.5 to 55:45, a particularly preferred range is 99: 1 to 60:40, and a more preferred range is 95: 5 to 70:30. When the blending ratio of non-or low spheroidized particles (B) is extremely small, the effect of improving the coatability when made into a slurry is insufficient, while when too large, the viscosity tends to be too high and the coatability tends to be impaired.
[0036]
  thisSecondary battery electrode materialAn important aspect is that the slurry is in the form of a slurry composed of the spheroidized particles (A), the non-sphericalized particles (B), the binder (C) and the medium (D).
[0037]
  Here, as the binder (C), when the medium (D) is water, carboxymethylcellulose, methylcellulose, ethylcellulose, alginic acid, gelatin, casein, albumin, gum arabic, gum tragacanth, etc. Synthetic water-soluble polymers such as alcohol, polyvinyl ether, polyvinyl pyrrolidone, polyethylene oxide and sodium polyacrylate, and water-dispersible polymers such as polyester and polyurethane are used. When the medium (D) is an organic solvent (for example, N-methylpyrrolidone), an organic solvent-soluble polymer (for example, polyvinylidene fluoride) is used as the binder (C).
[0038]
  Of the present inventionThe electrode material of the secondary battery isIt can be suitably used as an electrode material for non-aqueous secondary batteries, particularly as a negative electrode material for lithium secondary batteries.it can.
[0039]
  MnO as a positive electrode material in lithium secondary batteries₂, LiCoO₂, LiNiO₂, LiNi_1-yCo_yO₂, LiMnO₂, LiMn₂O_Four , LiFeO₂As an electrolytic solution, an organic solvent such as ethylene carbonate, or a low boiling point of the organic solvent and dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxymethane, ethoxymethoxyethane, etc. LiPF₆ , LiBF_Four , LiClO_Four, LiCF_ThreeSO_ThreeA solution in which an electrolyte solution solute such as is dissolved is used.
[0040]
  In the case of a lithium secondary battery, the charge / discharge reaction is as follows (the reaction from the left side to the right side is a charge reaction, the reaction from the right piece to the left side is a discharge reaction), and lithium ions travel between the positive and negative electrodes: To do.
      6C + LiCoO₂ = C₆Li + CoO₂
[0041]
<Manufacturing method of coated body>
  aboveSecondary battery electrode materialCan be applied to the object (O) in a slurry state. There is no limitation on the type of object (O), but it is used as an electrode material for secondary batteries, especially as a negative electrode material for lithium secondary batteries.In relation,The object (O) is often a conductor, particularly a copper foil.
[0042]
<Action>
  In the present invention, the spherical particles (A) having a specific circularity (0.86 or more), a fractured surface appearance and an orientation index, which are modified so as to approximate a spherical shape, are used. Since (A) is used in a mixture with non-spheroidized particles (B) whose scaly natural graphite particles have a circularity of less than 0.86 at a specific range of weight ratio, the mixture is used as a slurry. When the slurry is applied to the object (O) in a state, the slurry changes to a Newtonian fluid, and when the shear rate (coating speed) is low, the yield value is increased and the viscosity becomes high. Even if it raises, a viscosity does not change, therefore the applicability | paintability with respect to a target object can be improved significantly, and the target application body can be manufactured smoothly.
[0043]
  The coated body thus obtained(In other words, secondary battery electrodes)Since the spheroidized particles (A) are used as the main material, the performance is excellent, and for example, the discharge capacity at a large discharge current value can be increased.
[0044]
【Example】
  The following examples further illustrate the invention.
[0045]
                            [Preparation of spherical particles (A)]
<manufacturing device>
  FIG. 1 is a schematic view of an apparatus for producing spheroidized particles (A). This test equipment consists of a cylindrical tank (11) (the dimensions are shown in Fig. 1), and three counter nozzles (13) (nozzle inner diameter 6.3mm) are centered on the lower side of the tank (11). (Only one of them is shown in FIG. 1), and a high-speed rotary classifier as an example of a classifier (14) is arranged at the top of the tank (11). is there. The feeder (12) is provided on the side wall of the tank (11), and a blowing nozzle (15) is provided at the bottom of the tank (11).
[0046]
<Reforming operation>
  Chinese scaly natural graphite (particle size: passing 100 mesh 90% or more) was pulverized with a counter-type jet mill until the average particle size became 20 μm and used as raw material particles (B-1). Similarly, it was pulverized until the average particle size was 30 μm and used as raw material particles (B-2), and pulverized until the average particle size was 5 μm and used as raw material particles (B-3). Of these, 20 μm and 30 μm of raw material particles (B-1) and (B-2) are charged in a predetermined amount from the feeder (12) to the tank (11), and each of the three opposed nozzles (13). After blowing the air from the air and modifying the particles over a predetermined time, air is sent from the blowing nozzle (15) and the modified particles in the tank (11) are taken out from the feeder (12) to make the desired spheroid Particles (A) were obtained. At this time, the reforming operation conditions were changed, and from the raw material particles (B-1), spherical particles (A-1) having an average particle diameter of 17 μm and spherical particles (A-2) having an average particle diameter of 10 μm were obtained. As a result, spherical particles (A-3) having an average particle diameter of 25 μm and spherical particles (A-4) having an average particle diameter of 20 μm were obtained from the raw material particles (B-2). As will be described later, the raw material particles (B-3) were evaluated for Comparative Example 1 and Examples 1-2, and the spheroidized particles (A-4) were evaluated for Reference Example 1 and Examples 1-2, respectively. Using.
[0047]
<Break view of spheroidized particles (A) and appearance of raw material particles>
  Fig. 2 is a fracture view of the spheroidized particles (modified particles) (A) (when the spheroidized particles (A-4) obtained above are fixed with epoxy resin, frozen and solidified with liquid nitrogen, and then broken. 2 is a photocopy of a photomicrograph at a magnification of 5000 times showing a fractured surface). As shown in FIG. 2, the spheroidized particles (A) have a cabbage-like appearance in which the graphite slices face in various directions and include a layered structure of scaly natural graphite. It can be seen that the shape has been modified. Although not shown, spheroidized particles (A-1), (A-2), and (A-3) have the same structure.
[0048]
  On the other hand, FIG. 3 is an external view of a scaly natural graphite particle used as a raw material (a copy of a micrograph of the raw material particle (B-1) at a magnification of 2000). From FIG. 3, it can be seen that, in the raw scaly natural graphite particles, the graphite sections are layered only in substantially the same direction. Although not shown, the raw material particles (B-2) and (B-3) have the same structure.
[0049]
<Circularity of spherical particles (A)>
  The roundness of the scaly natural graphite particles used as the spheroidized particles (A) and the raw material particles (B) obtained above was photographed, and the particles having a diameter of 5 μm or more were photographed.
    Circularity = (perimeter of equivalent circle) / (perimeter of particle projection image)
As a result, the circularity of the raw material particles (B) was 0.84 regardless of the particle size, whereas the circularity of the spheroidized particles (A) was increased to 0.88 to 0.91. Here, the equivalent circle is a circle having the same projected area as the captured particle image. The peripheral length of the particle projection image is the length of the contour line obtained by connecting the edge points of the binarized particle image. FIG. 4 is an explanatory diagram showing how to determine the circularity of particles, where the circumference of the black circle is the circumference of the equivalent circle, and the circumference of the polygon formed by the white broken line is the circumference of the particle projection image. is there.
[0050]
<Orientation of spheroidized particles (A)>
  Peak intensity ratio Ih of 002 plane (plane parallel to the graphite layer) and 110 plane (plane perpendicular to the graphite layer) by X-ray diffraction method, which is an index of randomness of orientation₁₁₀/ Ih₀₀₂In a preliminary test, since it was found that the influence on the scanning speed and the rotational speed was small, the measurement was performed under the following conditions.
[0051]
  ・ Device: “RINT2000” manufactured by Rigaku Corporation
  ・ Cell: Inner diameter 2.4cm, Height 0.315cm
  -Filling the cell with the sample: Weigh 2 g of the powder, put it in a mold with a radius of 1.2 cm, and press it with a load of 500 kg until the thickness reaches 0.315 cm.
  ・ Sample density: 2.0g / [(1.2)²cm²× π × 0.315cm] = 1.40g / cm^Three (Same as electrode density in battery test)
  ・ Measurement angle: 3-90 °
  ・ Scanning speed: 9 ° / min
  ・ Rotation speed: 60rpm
  -Data processing: integral intensity calculation, 9 smoothing points, automatic background removal. From the peak areas of the 002 plane peak (26.5 °) and the 110 plane peak (77.5 °), the following formula was used.
    Peak intensity ratio Ih₁₁₀/ Ih₀₀₂= (Net Int (002) surface) / (net Int (110) surface)
[0052]
  As a result, the peak intensity ratio of the scaly natural graphite particles used as the raw material particles (B) was 0.0015, 0.0018, and 0.0018, whereas the peak intensity ratio of the spheroidized particles (A) was notably 0.0072 to 0.0150. It was found that the numerical value was large and the randomness of the alignment was progressing.
[0053]
<Summary of conditions and results>
  The conditions and results are summarized in Table 1 below. As mentioned earlier, (A-1) and (A-2) of the spheroidized particles (A) were reformed using (B-1) of the raw material particles (B). Among the spheroidized particles (A), (A-3) and (A-4) are those obtained by performing a reforming operation using (B-2) of the raw material particles (B). The bulk density is obtained by putting 30 to 50 g of particles in a 100 cc graduated cylinder, lightly hitting the cylinder wall, and measuring the volume.
[0054]
[Table 1]
  
                  Raw material particles (B) Spheroidized particles (A)
   B-1 B-2 B-3 A-1 A-2 A-3 A-4
  Raw material charge (kg)---1 3 1 8
  Air pressure (kg / cm²)---1 1 1 1
  Air volume (m^Three/ min)---2.2 2.2 2.2 2.2
  Operation time (min) - - - Five 50 15 30
  Average particle size (μm) 20 30 5 17 10 25 20
  Circularity (-) 0.84 0.84 0.84 0.88 0.90 0.91 0.91
  Bulk density (g / cc) 0.3 0.5 0.2 0.6 0.8 0.7 0.8
  Peak intensity ratio 0.0015 0.0018 0.0018 0.0087 0.0150 0.0072 0.0110
[0055]
                      [Examples 1-2, Reference Example 1, Comparative Example 1]
Example 1
  Of the above spheroidized particles (A), particles (A-4) having an average particle diameter of 20 μm and non-low to low spheroidized particles (B) as an example of flaky natural graphite particles having an average particle diameter of 5 μm (B-3) ) And a 90:10 mixture by weight to a 1% strength by weight aqueous solution of CMC (carboxymethylcellulose Na salt) so that the solid content is 45% by weight, and the mixture is stirred and mixed at 3000 rpm for 60 minutes. It was made into a slurry, applied onto a copper foil as an example of the object (O), and dried using a doctor blade. The viscosity η in the range where the shear rate is 5 / s to 50 / s is approximately 0.40 × 10^ThreeThe cp was constant and showed a trend of Newtonian fluid, and the slurry coating property was smooth.
[0056]
Example 2
  Of the above spheroidized particles (A), particles (A-4) having an average particle diameter of 20 μm and non-low to low spheroidized particles (B) as an example of flaky natural graphite particles having an average particle diameter of 5 μm (B-3) ) And a mixture of 80:20 by weight with an aqueous solution of CMC having a concentration of 1% by weight so that the solid content is 45% by weight. It applied using the doctor blade on the copper foil as an example, and dried. The viscosity η in the range where the shear rate is 5 / s to 50 / s is about 0.33 × 10^ThreeThe cp was constant and showed a trend of Newtonian fluid, and the slurry coating property was smooth.
[0057]
Reference example 1
  Of the above spheroidized particles (A), only particles (A-4) having an average particle diameter of 20 μm are added to a 1% by weight aqueous solution of CMC so that the solid content is 45% by weight, and stirred and mixed at 3000 rpm. Then, it was made into a slurry, applied onto a copper foil as an example of the object (O) using a doctor blade, and dried. The viscosity η in the range where the shear rate is 5 / s to 50 / s is 0.35 × 10 5 as the shear rate increases.^Threecp → 0.67 × 10^ThreeThe cp increased and showed a dilatant fluid tendency. At this time, the copper foil tended to repel the slurry, and the coating property was not smooth.
[0058]
Comparative Example 1
  Only the scaly natural graphite particles (B-3) having an average particle diameter of 5 μm as an example of non-sphericalized particles (B) are added to an aqueous solution containing 1% by weight of CMC so that the solid content becomes 35% by weight. The mixture was added to a slurry by stirring and mixing at 3000 rpm, applied onto a copper foil as an example of the object (O) using a doctor blade, and dried. The viscosity η in the range where the shear rate is 5 / s to 50 / s is 0.4 × 10 as the shear rate increases.^Threecp → 0.1 × 10^ThreeAlthough it decreased with cp, the coating property of the slurry at this time was smooth. However, this is because the concentration was kept at 35% by weight, and when the concentration was higher than that, the viscosity increased rapidly and smooth coating became difficult. For example, when the solid content was 45% by weight, the viscosity became so high that coating could not be performed.
[0059]
                            [Battery test, charge / discharge performance]
  In Examples 1-2, Reference Example 1 and Comparative Example 1, after applying the slurry to the copper foil and drying, pressing was performed so that the thickness of the coating film was 70 μm, and the particle density was adjusted to 1.4 g / cc. A test electrode was prepared. A bipolar electrode was obtained by bonding lithium foil to a stainless steel plate as a counter electrode. Assembly is performed in a dry box adjusted to a moisture value of 20 ppm or less, and the electrolyte is 1M-LiPF.₆/ (EC + DEC (1: 1)), that is, LiPF in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1₆Was dissolved at a rate of 1M.
[0060]
  The charge / discharge test has a discharge current of 0.05C (0.2mA / cm²), 1.0C (3.7mA / cm²), 2.0C (8.0mA / cm²). Charging is 0.1mA / cm for both²I went there. The results of the charge / discharge performance test are shown in Table 2 below. In Table 2, discharge capacity ratio (%) measures the discharge capacity (mAh / g) at each discharge current,
     100 × (1.0C or 2.0C discharge capacity) / (0.05C discharge capacity)
Is obtained by
[0061]
  From Table 2, it can be seen that in Examples 1 and 2, the decrease in discharge capacity at a large discharge current value 2C is small, that is, it is suitable for a negative electrode material for a high load, high capacity battery.
[0062]
[Table 2]
  
            Weight ratio  Initial efficiencyDischarge capacity ratio (%)
   (A): (B) (%) 1C 2C
  Reference Example 1 100: 0 92.9 97.4 57.7
  Comparative Example 1 0: 100 84.0 91.7 38.5
  Example 1 90: 10 92.7 95.5 63.8
  Example 2 80: 20 91.3 95.9 61.7
    note. (A) uses (A-4) and (B) uses (B-3).
[0063]
【The invention's effect】
  As described in the section of action, according to the present invention, in a system using particles obtained by spheroidizing flaky natural graphite, the applicability of the slurry to an object can be remarkably improved. Thus, when the negative electrode of the secondary battery is produced, the discharge capacity at a large discharge current value can be increased.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an apparatus for producing spheroidized particles (A).
[Fig. 2] Fig. 2 is a fracture view of spheroidized particles (modified particles) (A) (spheroidized particles (A-4) fixed with epoxy resin, frozen and solidified with liquid nitrogen, then broken when broken 2 is a photocopy of a photomicrograph at a magnification of 5000 times showing a cross section.
FIG. 3 is an external view of a scaly natural graphite particle used as a raw material (a copy of a micrograph of the raw material particle (B-1) at a magnification of 2000).
FIG. 4 is an explanatory diagram showing how to determine the circularity of particles.
[Explanation of symbols]
  (11) ... tank,
  (12)… Feeder,
  (13) ... Opposite nozzle,
  (14) Classifier,
  (15)… Blow-up nozzle

Claims (3)

Spherical particles (A) having a roundness of 0.86 or more, modified from flaky natural graphite particles so as to approximate a sphere, and non- or low-sphericalized particles of flaky natural graphite particles having a circularity of less than 0.86 (B) an electrode material for a secondary battery comprising :
The spheroidized particles (A) have (1) a circularity of 0.86 or more, and (2) a microscopic observation of the fracture surface, the graphite section has a cabbage-like appearance in various directions. And (3) the peak intensity ratio Ih ₁₁₀ / Ih _{002 of the 002} plane (plane parallel to the graphite layer) and the 110 plane (plane perpendicular to the graphite layer) by X-ray diffraction, which is an index of randomness of orientation Satisfying all the requirements of ≥0.0050,
and,
The blending ratio of the spheroidized particles (A) to the non-spheroidized particles (B) is 99.9: 0.1 to 55:45 by weight ratio,
An electrode material for a secondary battery . 2. The electrode material for a secondary battery according to claim 1, wherein the composition is in the form of a slurry comprising spheroidized particles (A), non-spheroidized particles (B), a binder (C) and a medium (D). A method for producing an applied body, wherein the electrode material of the secondary battery according to claim 1 or 2 is applied to an object (O) in a slurry state.

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