JP2016060934A - Porous aluminum sintered compact, production method thereof, and production method of electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the output or energy density of each of various power storage devices such as electric double-layer capacitors and lithium ion secondary batteries.SOLUTION: A porous aluminum sintered compact has a skeleton formed by sintering aluminum powder and voids and the total void ratio of 80-90 vol.%. When the diameter D(μm) and specific surface area S(cm/g) of each of the voids are measured by a mercury penetration method and a distribution of the measured diameters D(μm) is shown by a log differential void specific surface area distribution, the porous aluminum sintered compact has the void diameter Dp of 20-150 μm, when the log differential void specific surface area dS/d(LogD) shows a peak, and W/H of 5.0-50.0 when the height of the peak is defined as H and the half-value width of the peak is defined as W. A production method of the porous aluminum sintered compact and another production method of an electrode by using the porous aluminum sintered compact as a current collector are also provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a porous aluminum sintered body that can be used as a current collector of an electrode of an electric storage device such as an electric double layer capacitor or a lithium ion secondary battery, and a method for producing the same. And it is related with the manufacturing method of the electrode which used the said porous aluminum sintered compact for the electrical power collector.

  Conventionally, metal foil has been used as a current collector for electrodes of various power storage devices. For the metal foil, a material having high corrosion resistance such as copper, nickel, and various stainless steels is used. For example, in the case of an electric double layer capacitor or a lithium ion secondary battery, an aluminum foil having high chemical stability with respect to the electrolytic solution is used for the current collector of the positive electrode.

The manufacturing procedure of the electrode using the metal foil as a current collector is generally as follows. First, a mixture containing an active material is uniformly coated on the surface of the metal foil to an appropriate thickness. The active material is a material responsible for the transfer of electrons and ions. For example, in the case of a lithium ion secondary battery, the active material on the positive electrode side includes a lithium transition metal oxide such as lithium cobaltate (LiCoO ₂ ). A carbon material such as graphite is used for the active material on the negative electrode side. The mixture is a slurry obtained by adding appropriate amounts of a conductive material and a binder to the active material and further adjusting the viscosity with a solvent. The conductive material is a substance that is added to the active material to enhance conductivity, and for example, a powder of carbon or the like is used. For the binder, for example, a resin such as vinylidene fluoride is used. Next, after the metal foil coated with the mixture is dried, the adhesion between the active material and the conductive material in the mixture and between the metal foil (current collector) and the active material or the conductive material is increased. In addition, the electrode is manufactured by compressing it with a press or the like.

  In recent years, it has been proposed to use a porous body for the current collector of an electrode instead of the metal foil (Patent Documents 1 and 2). A large number of pores are formed inside the porous body, and the skeleton holds the voids. Among the voids, the voids, which are large voids formed by surrounding the wall of the skeleton, communicate with each other, so that the porous body has an open cell structure. When such a porous body is used as a current collector, the skeleton plays a role as a current collector, while the mixture containing an active material is filled in the pores. Therefore, the electrode using a porous body as a current collector has an increased amount of active material retained and can also prevent the active material from dropping compared to a conventional electrode using a metal foil as a current collector. It is effective for increasing the output and energy density of power storage devices.

  As a method for producing an aluminum porous body used for such a current collector, the void-forming particles are removed from a molded body of aluminum powder in which void-forming particles are dispersed, and then sintered. “Space holder method” (Patent Document 3) and “Slurry foaming method” in which a porous molded body is made by foaming a slurry of aluminum powder to which a sintering aid such as titanium is added (Patent) Document 4) has been proposed.

Japanese Patent Laid-Open No. 08-339941 JP 2011-249254 A JP 2009-256788 A JP 2010-255089 A

  It is effective to use the porous body of Patent Documents 1 to 4 as a current collector for an electrode of an electricity storage device. However, even with electrodes using these porous bodies, the output and energy density of the electricity storage device may be reduced.

  An object of the present invention is to provide an aluminum porous body that is advantageous for improving the output and energy density of the power storage device when used as a current collector for electrodes of various power storage devices, a method for producing the same, and the aluminum porous body. It is providing the manufacturing method of the electrode used for the electrical power collector.

  The present inventor has studied an aluminum porous body that is advantageous for improving the output and energy density of an electricity storage device when used as a current collector for an electrode of the electricity storage device. As a result, the aluminum porous body was made into a sintered body of aluminum powder, and the internal structure capable of filling the mixture (active material) in an optimal distribution state was further found for the porous sintered body. The present invention has been reached.

That is, the present invention is a porous aluminum sintered body having a skeleton and voids obtained by sintering aluminum powder, and having an overall porosity of 80 to 90% by volume,
When the void diameter D (μm) and the specific surface area S (cm ² / g) were measured by mercury porosimetry, and the distribution of the void diameter D (μm) was expressed by Log differential void specific surface area distribution, Log differential void specific surface area dS / d (LogD) has a peak diameter Dp of 20 to 150 μm and a ratio of the peak height H to the half width W of the peak at W / The porous aluminum sintered body is characterized in that H is 5.0 to 50.0.

And this invention is a manufacturing method of the porous aluminum sintered compact which has the frame | skeleton and space | gap which aluminum powder sintered, and the whole porosity is 80-90 volume%,
An aluminum powder having an average particle size of 50 μm or less, and particles for forming the voids, the average particle size being larger than the average particle size of the aluminum powder and 500 μm or less, the void-forming particles, Mixing an aluminum powder and a binder for binding the void-forming particles to obtain a mixture;
Molding the mixture to obtain a molded body in which the void-forming particles are dispersed between the aluminum powders;
Removing the void-forming particles from the molded body to obtain a green body before sintering;
Degreasing and sintering the green body;
It is a manufacturing method of the porous aluminum sintered compact characterized by including this.

  And this invention fills the space | gap of the said porous aluminum sintered compact of this invention with the mixture containing an active material, and compresses the porous aluminum sintered compact after filling the said mixture. It is the manufacturing method of the electrode which makes it.

  ADVANTAGE OF THE INVENTION According to this invention, the output and energy density of various electrical storage devices can be improved.

2 is a scanning electron microscope (SEM) photograph showing an example of the surface of a porous aluminum sintered body of Invention Example 1. It is a SEM photograph which shows an example of the surface of the porous aluminum sintered compact of the example 2 of this invention. It is a SEM photograph which shows an example of the surface of the porous aluminum sintered compact of the example 3 of this invention. It is a SEM photograph which shows an example of the surface of the porous aluminum sintered compact of the example 4 of this invention. 6 is an SEM photograph showing an example of the surface of a porous aluminum sintered body of Comparative Example 11. 6 is an SEM photograph showing an example of the surface of a porous aluminum sintered body of Comparative Example 12. 3 is an optical micrograph showing an example of a cross section of a porous aluminum sintered body of Invention Example 2. 6 is an optical micrograph showing an example of a cross section of a porous aluminum sintered body of Comparative Example 12. In the porous aluminum sintered body of the present invention, the ratio of the diameter Dp of the void where the Log differential void surface area dS / d (LogD) exhibits a peak, the peak height H at the Dp, and the half-value width W of the peak It is a graph showing the relationship with a certain W / H. It is an example of Log differential void | hole specific surface area distribution calculated | required by implementing the mercury intrusion method to the porous aluminum sintered compact of the example 2 of this invention. It is an example of the Log differential void | hole specific surface area distribution calculated | required by implementing the mercury intrusion method to the porous aluminum sintered compact of the comparative example 12. It is a SEM photograph which shows an example of the cross section of the positive electrode using the porous aluminum sintered compact of the example 2 of this invention. It is a SEM photograph which shows an example of the cross section of the positive electrode using the porous aluminum sintered compact of the example 3 of this invention. 10 is a SEM photograph showing an example of a cross section of a positive electrode using the porous aluminum sintered body of Comparative Example 12. It is a figure which shows the charging / discharging cycle characteristic of the positive electrode of the lithium ion secondary battery which used the porous aluminum sintered compact of this invention examples 1-4 and the comparative examples 11 and 12 for the electrical power collector.

  The feature of the present invention is that the porous aluminum sintered body has an internal structure that can be filled with a mixture (active material) in an optimal distribution state when it is used as a current collector of an electrode. Specifically, it is easy to uniformly fill the inside of the porous material with the active material, and further, the distance between the filled active material and the skeleton of the porous material for collecting current is easily maintained. Below, each component of this invention is demonstrated.

(1) About the porous aluminum sintered body of the present invention (1-1) The porous body of the present invention is made of aluminum.
The porous body of the present invention can be used as a current collector for electrodes of various power storage devices. And especially when using as an electrical power collector of the positive electrode of an electrical double layer capacitor or a lithium ion secondary battery, since it is necessary to ensure the chemical stability with respect to electrolyte solution, the material of the porous sintered compact is made into aluminum. Moreover, in the case of an electric double layer capacitor, it contributes to the weight reduction of a capacitor module by using for an electrical power collector of a negative electrode.

(1-2) The porous body of the present invention is a porous aluminum sintered body having a skeleton and voids obtained by sintering aluminum powder.
Usually, the porous body has a “pore” inside because it is porous, and has a “frame” for holding the void. Since the porous body of the present invention is a sintered body of aluminum powder, in addition to the “void” surrounded by the wall surface of the skeleton, the voids in the voids are the aluminum powder in the skeleton. Also included are “micropores” consisting of the gaps. That is, when the skeleton is an aggregate of many aluminum powders, there are pores having a size smaller than the pores, which are gaps between individual aluminum powders. The pores larger than the pores are at least partially in communication with each other, and the active material (that is, the mixture) is exclusively filled in the pores. The small pores in the skeleton that are not filled with the active material are crushed by the compression process and hardly affect the characteristics of the electricity storage device. By using such a porous body as a current collector, the amount of active material filled in the voids can be increased, and the active material can be prevented from falling off. It is effective for conversion.

(1-3) The porous body of the present invention is a porous aluminum sintered body having an overall porosity of 80 to 90% by volume.
And, it is used as a current collector for electrodes of various power storage devices, and the present invention assumes that the gap is filled with an active material (exactly, the pores surrounded exclusively by the wall surface of the skeleton). In the porous body, it is important to adjust the porosity of the entire porous body. That is, as the porosity of the porous body is higher, the amount of active material that can be filled in the porous body is increased, and the volume energy density of the electrode is increased. However, if the porosity becomes too high, the skeleton becomes thin and the strength of the porous body becomes low. When the porous body after being filled with the mixture (that is, the active material) is compressed, It becomes easy to cut. In addition, the surface area of the skeleton that collects current is reduced with respect to the amount of the mixture, and the internal resistance of the entire electrode increases or the electrical resistance of the skeleton (current collector) itself increases. Therefore, the porosity of the porous body of the present invention is 80 to 90% by volume as a whole. Preferably it is 85 volume% or less.

(1-4) In the porous body of the present invention, the diameter D (μm) of the voids and the specific surface area S (cm ² / g) are measured by mercury porosimetry, and the distribution of the diameter D (μm) of the voids is determined. When expressed by the Log differential void specific surface area distribution, the void diameter Dp at which the Log differential void specific surface area dS / d (LogD) has a peak is 20 to 150 μm.
In an electrode using a porous body, when the distance between the skeleton of the porous body serving as a current collector and the active material is reduced, the internal resistance is reduced, and the output and energy density of the electricity storage device can be improved. In order to reduce the distance, it is effective to select pores filled with the active material among the voids of the porous body and adjust the size of the pores to be small. However, in the case of the porous body of the present invention which is a sintered body of aluminum powder, the inside thereof contains many pores smaller than these pores in addition to the pores.

Therefore, in the present invention, the mercury intrusion method is used as a method for selectively extracting the vacancies from the various types of voids and confirming their sizes. The mercury intrusion method uses the high surface tension of mercury to apply pressure to allow mercury to enter the gap, and the distribution of voids (void diameter, volume or (Surface area) can be obtained hypothetically. And it is a method suitable for calculating | requiring the distribution condition when the magnitude | size of a space | gap covers a wide range like the relationship of the said void | hole and pore which concerns on this invention. The result of measuring the diameter and surface area of each void by this mercury intrusion method is the void distribution of “Log differential void specific surface area distribution” of the specific surface area S (cm ² / g) with respect to the void diameter D (μm). It is possible to confirm a tendency of the size of the gap over a wide range.

  FIG. 10 is a Log differential void specific surface area distribution obtained by performing a mercury intrusion method on an example of the porous aluminum sintered body of the present invention (Invention Example 2 of Examples described later). Specifically, a Log differential void specific surface area (vertical axis) obtained by dividing the differential void specific surface area dS by the logarithmic difference value d (logD) of the void diameter is obtained, and this is calculated as the average diameter (horizontal) of the voids in each section. (Axis) is plotted. FIG. 10 shows a peak with a large Log differential void specific surface area at a void diameter position near 55 μm. Note that the void corresponding to the diameter of the void smaller than the vicinity of 20 μm where the peak has been lowered is the “pore” formed by the gap of the aluminum powder. A pore is a randomly formed void. Therefore, there is no clear peak of the Log differential void specific surface area in the corresponding void diameter region.

And the space | gap corresponding to the diameter of the space | gap near 55 micrometers is a "hole" enclosed by the wall surface of frame | skeleton only. The pores are voids that are artificially adjusted in size so as to provide an effect related to the loading of the active material. Therefore, a clear peak of the Log differential void specific surface area can be confirmed at the position of the void diameter near 55 μm corresponding thereto. And by making this Dp 150 μm or less, the size of the holes can be effectively reduced. As a result, the distance between the mixture (active material) filled in the holes and the skeleton for collecting current can be effectively reduced, and the output and energy density of the electricity storage device can be improved. Preferably, the Dp is 120 μm or less. More preferably, it is 70 μm or less.
If the Dp is too small, it becomes difficult to uniformly fill the vacancies with the active material, and the output and energy density of the electricity storage device are reduced. Therefore, the Dp is set to 20 μm or more. Preferably, it is 50 μm or more.

(1-5) In the porous body of the present invention, in the Log differential void specific surface area distribution, W / H which is a ratio of the peak height H to the half width W of the peak in Dp is 5.0 to 50.0.
In the mercury intrusion method, as the pressure applied to the mercury is increased, mercury enters the smaller gaps in order from the larger gaps. Therefore, the Dp obtained by the mercury intrusion method represents the above-mentioned “hole diameter”, while the “window” diameter (communication) connecting the holes communicating with each other is communicated. It can also be said that the degree of In addition, W / H, which is the ratio between the peak height H of the Log differential void specific surface area of FIG. 10 and the half-value width W of the peak in Dp, represents the spread of the “diameter of the communication port”. I can say that. As the W / H value increases, the diameter distribution of the communication ports connected to one hole expands and the number of communication ports increases (visually, the outline of the holes is unclear). It becomes the structure of the space | gap which is easy to fill a mixture. Therefore, the W / H is 5.0 or more.

  In the holes that are not sufficiently filled with the mixture, the communication of the active material between the adjacent holes through the communication port is poor. Such an active material is firmly surrounded by the wall surface of the skeleton by the previous compression process, and the connection with the active material in the adjacent pores becomes very poor, or is completely blocked by the wall surface and isolated. Resulting in. If the connection between the active materials is poor in the electrode in use, free movement of ions to the active material is inhibited, and for example, in the case of a lithium ion secondary battery, lithium ions are difficult to move to the negative electrode side. The active material does not function well. And when an active material is completely isolated, an ion movement will be completely lost and an active material will stop functioning. As a result, the discharge capacity per unit mass of active material is reduced.

  On the other hand, if the value of W / H becomes too large, a communication port having an excessively large diameter with respect to the hole diameter is generated, and the filled mixture cannot be held in the hole, for example, during drying. Will fall out. On the other hand, a communication port having an excessively small diameter is also generated, and filling the mixture itself becomes difficult at this communication port. As a result, it becomes difficult to uniformly fill the mixture inside the porous body. Therefore, the W / H is 50.0 or less.

(2) About the manufacturing method of the porous aluminum sintered compact of this invention In the manufacturing method of the porous aluminum sintered compact of this invention mentioned above, from the molded object of the aluminum powder in which the particle | grains for space | gap formation were disperse | distributed, A “space holder method” is employed in which the void-forming particles are removed and sintered. That is,
Mixing aluminum powder, void-forming particles for forming voids, and a binder for binding the aluminum powder and the void-forming particles to obtain a mixture;
Molding the mixture to obtain a molded body in which the void-forming particles are dispersed between the aluminum powders;
Removing the void-forming particles from the molded body to obtain a green body before sintering;
Degreasing and sintering the green body;
It is a manufacturing method of the porous aluminum sintered compact containing this.
And the porous aluminum sintered compact of this invention can be manufactured by employ | adopting the following conditions for said space holder method.

(2-1) The aluminum powder has an average particle size of 50 μm or less.
The aluminum powder forms a skeleton of a porous aluminum sintered body. By the way, in the space holder method, the diameter of the void-forming particles is calculated based on the degree of shrinkage during sintering and the like, and a void having a target size (specifically, a skeleton) Use the size of the hole that can be obtained. At this time, if the particle size of the aluminum powder is too large, a gap between the void-forming particles and the aluminum powder surrounded along the surface becomes large, and the size of the voids is controlled by the particle size of the void-forming particles. Becomes difficult. As a result, since the hole diameter and the communication port are increased, Dp is increased, and since the spread of the aperture distribution is increased, W / H is excessively increased. And as above-mentioned, when Dp becomes large, internal resistance will increase and W / H will become large too much, and uniform filling of the mixture in a porous body will become difficult. Furthermore, as the particle size of the aluminum powder increases, the surface area of the skeleton decreases and the current collection efficiency from the active material decreases. Therefore, in the method for producing a porous aluminum sintered body of the present invention having a void distribution of Dp of 20 to 150 μm and W / H of 5.0 to 50.0, the average particle size of the aluminum powder is 50 μm. The following is preferable. In addition, about a minimum, it can be set as 10 micrometers or more in consideration of the ease of handling of powder, for example.

(2-2) The void-forming particles have an average particle size larger than the average particle size of the aluminum powder. And the said average particle diameter shall be 500 micrometers or less.
When the average particle diameter of the void forming particles is smaller than that of the aluminum powder, it is possible to enlarge the pores formed by the gaps of the aluminum powder in the skeleton. However, it does not lead to the formation of pores surrounded by the wall of the skeleton, the size of which corresponds to the voids with Dp of 20 μm or more. Therefore, in the method for producing a porous aluminum sintered body of the present invention, the void-forming particles have an average particle size larger than the average particle size of the aluminum powder. On the other hand, if the average particle size of the void-forming particles is excessively large, the pores are increased and it is difficult to obtain the Dp value of 150 μm or less. Therefore, in the method for producing a porous aluminum sintered body of the present invention, the void-forming particles have an average particle size of 500 μm or less.

(2-3) The void-forming particles are preferably paraffin wax particles.
Since the paraffin wax particles are moderately soft, the contact frequency and the contact area between adjacent void-forming particles can be increased by the pressure at which the mixture is formed. As a result, the green body after removing the void-forming particles can increase the communication frequency between the pores and the diameter of the communication port, and the values of Dp and W / H of the porous aluminum sintered body of the present invention can be increased. It is effective to satisfy.

(2-4) It is preferable to remove the void-forming particles from the molded body with a solvent.
The green body before sintering is generally heated to a sintering temperature and sintered following heating for degreasing. In the case of the method for producing a porous aluminum sintered body of the present invention, the mixing ratio of the void-forming particles contained in the molded body is large. Therefore, if heat degreasing is performed as it is, the void-forming particles in the molded body may be dissolved in large quantities at the time of temperature rise for the heat degreasing, or a decomposition gas may be generated, and the molded body may collapse. Therefore, it is preferable that the void-forming particles in the molded body are selectively dissolved and removed with a solvent before heating and degreasing.

(2-5) In the step of degreasing and sintering the green body, at least one step is preferably performed in a vacuum or an inert gas atmosphere. Moreover, it is preferable to attach a reducing agent in a sintering furnace at the time of sintering.
Significant surface oxidation of the aluminum powder forming the green body can be a factor in poor sintering. Therefore, in the step of degreasing and sintering the green body, it is preferable that at least one step is performed in a vacuum or an inert gas atmosphere. More preferably, both the degreasing and sintering steps are performed in a vacuum or an inert gas atmosphere. And it is preferable to mix reducing gas in sintering atmosphere at the time of sintering. For example, by attaching a reducing agent such as magnesium or calcium in the sintering furnace, these reducing agents are sublimated in the sintering atmosphere and subjected to a reduction reaction with the oxide film on the surface of the aluminum powder, thereby exposing the metal base of aluminum to the surface. It is effective to make it.

(3) About the manufacturing method of the electrode of this invention The manufacturing method of the electrode of this invention uses the porous aluminum sintered compact of this invention for a collector. That is, this is a method for producing an electrode in which the porous aluminum sintered body of the present invention is filled with a mixture containing an active material in the pores of the porous aluminum sintered body and the porous aluminum sintered body is compressed after the mixture is filled. .
When the porous aluminum sintered body of the present invention is filled with the mixture, vacuum impregnation, rubbing with a spatula or the like can be used. After filling the mixture, a drying step may be provided according to the conventional method. The porous aluminum sintered body after being filled with the mixture is subjected to compression processing in order to increase the adhesion between the active material in the mixture, the conductive material, and the skeleton surface. At this time, for example, compression molding using a press or a roll can be used for the compression processing. As a result, the mixture (active material) filled in the porous body is three-dimensionally uniformly and firmly held, and a high-performance electrode can be manufactured.

The porous aluminum sintered bodies of Invention Examples 1 to 4 and Comparative Examples 11 and 12 were prepared according to the procedure for producing the porous aluminum sintered body shown in Table 1. Each of the shapes is a sheet having a thickness of about 1 mm.
The porous aluminum sintered bodies of Invention Examples 1 to 4 and Comparative Example 11 were produced by the space holder method. First, aluminum powder having an average particle size shown in Table 1 and paraffin wax particles as void forming particles are mixed at a volume ratio shown in Table 1, and then 3 mass% polyvinyl alcohol aqueous solution as a binder is added thereto and kneaded. A mixture was prepared. Next, the mixture was press-molded with a mold and dried to prepare a sheet-like molded body. Next, the molded body was immersed in normal paraffin heated to 80 ° C., and the paraffin wax particles in the molded body were dissolved and extracted to obtain a porous green body. The green body was degreased by holding it in an argon atmosphere at 500 ° C. for 2 hours, and then magnesium was attached to the tray on which the degreased green body was placed and covered with a molybdenum lid, and 585 to 595 ° C. The porous aluminum sintered body was manufactured by holding for 1 hour in a vacuum and sintering.

The porous aluminum sintered body of Comparative Example 12 was produced by a slurry foaming method. Titanium hydride (TiH ₂ ) as a sintering aid was mixed with aluminum powder having an average particle diameter (11 μm) shown in Table 1 to obtain a raw material powder. To this raw material powder, methylcellulose as a binder, a plasticizer, a surfactant, and pure water were added and kneaded to obtain a molding slurry. And after extending this slurry to a sheet form, it was made to foam and dried, and the sheet-like porous molded object was produced. The porous molded body was degreased by holding it in an argon atmosphere at 500 ° C. for 2 hours, and then sintered by holding it in an argon atmosphere at 650 ° C. for 1 hour to obtain a porous aluminum sintered body. Manufactured.

1 to 6 are SEM photographs of the surfaces of the porous aluminum sintered bodies of Invention Examples 1 to 4 and Comparative Examples 11 and 12, respectively, in order. 7 and 8 are optical micrographs of cross sections of the porous aluminum sintered bodies of Invention Example 2 and Comparative Example 12 in this order. 7 and 8, the sample is obtained by polishing a porous aluminum sintered body embedded in a resin. And the part shown with the light color is a skeleton, and the part shown with the dark color is a space | gap.
Inventions 1-4 and Comparative Example 11 are manufactured by the space holder method. The pores surrounded by the wall of the skeleton communicate with each other. Further, the skeleton includes pores having a size smaller than the pores, which are gaps between aluminum powders. And the diameter of the communicating port connected to one hole is various, and there are many communicating ports, As a result, the outline of a hole is unclear. And, such a mode of pores is also achieved on the outer surface (FIGS. 1 to 5) of the porous body, and the pores with unclear outlines are directed to the outside as openings with unclear outlines. Open.
Comparative Example 12 was manufactured by a slurry foaming method. Compared to Examples 1 and 2 of the present invention, there is no significant difference in the size of the holes surrounded by the wall surfaces of the skeleton. However, the communication port connected to one hole is a circular shape having a relatively uniform diameter and the number thereof is small, and the outline of the hole is clear as compared with the example of the present invention. Then, on the outer surface of the porous body (FIG. 6), the pores with clear outlines are opened “independently” toward the outside as circular openings with clear outlines.

Next, the porous aluminum sintered bodies of Invention Examples 1 to 4 and Comparative Examples 11 and 12 were subjected to measurement of void distribution by mercury porosimetry, and Log differential void specific surface area distribution of each porous aluminum sintered body. Asked. As the measuring device, a pore distribution measuring device “Autopore 9520 type” manufactured by Micromeritics Co., Ltd. handled by Shimadzu Corporation was used. The measurement conditions were a mercury contact angle of 130.0 degrees and a mercury surface tension of 485.0 dynes / cm. About 0.2 g of a porous aluminum sintered body was used as a sample. Table 2 shows the diameter Dp of the void at which the Log differential void specific surface area dS / d (LogD) exhibits a peak, and the ratio of the peak height H to the half width W of the peak at the Dp. (A graph showing the relationship between Dp and W / H in Table 2 is shown in FIG. 9). Table 2 also shows the porosity of each porous aluminum sintered body.
FIG. 10 shows the Log differential void specific surface area distribution of Example 2 of the present invention, and FIG. 11 shows the Log differential void specific surface area distribution of Comparative Example 12. For example, when Invention Example 2 and Comparative Example 12 are compared, there is no significant difference in the value of Dp. However, the W / H of Comparative Example 12 is small, about half that of Example 2 of the present invention. This result reflects the state of FIGS. 6 and 8 in the porous aluminum sintered body of Comparative Example 12.

A positive electrode of a lithium ion secondary battery was produced using the porous aluminum sintered bodies of Invention Examples 1 to 4 and Comparative Examples 11 and 12 that had been evaluated as described above as current collectors. First, a material having a width of 10 mm × length of 25 mm is cut out from a porous aluminum sintered body having a thickness of about 1 mm, and a portion having a length of 10 mm from the end (a porous portion impregnated with the mixture) is left and pressed. Then, the holes were crushed to obtain a current collector. In addition, the part which pressed and crushed the void | hole becomes a terminal for wiring in the test cell produced later. Next, the 10 mm × 10 mm porous part of the current collector is immersed in a container containing a mixture and sealed in a desiccator, and the inside of the desiccator is decompressed with a vacuum pump, and the porous part is combined. The agent was impregnated. The mixture is mixed with LiN _1/3 Mn _1/3 Co _1/3 O ₂ active material, carbon-based conductive material and vinylidene fluoride binder, and the viscosity is adjusted with normal methylpyrrolidone. Then, a slurry was used.

  And after drying the electrical power collector after impregnating a mixture, the mixture which protruded from the porous part was removed. Due to the evaporation of the normal methylpyrrolidone, the mixture contracted due to the volatilization of the normal methyl pyrrolidone, resulting in a gap in the porous. Further, the mixture was slid into one side of the porous part with a spatula and dried. The mixture was rubbed and dried to remove the mixture that protruded again from the porous portion. Then, the porous portion that had been filled with the mixture was subjected to compression processing by a hand press, and this was used as a positive electrode. 12 to 14 are SEM photographs of cross sections of the positive electrodes according to Invention Examples 2 and 3 and Comparative Example 12, respectively. 12-14, the sample is what the cut surface of the said positive electrode was grind | polished by ion milling (The arc-shaped site | parts visible on the both lower ends of FIG. 12, 13 are unpolished parts). The upper side of the figure is the outer surface of the positive electrode (porous body). The portion shown in light color is a mixture (active material), and the portion shown in dark color is a current collector (skeleton). The black spots found in the mixture are carbon-based conductive materials, not voids.

  In order to evaluate the characteristics as a positive electrode of a lithium ion secondary battery by sandwiching the positive electrode with a lithium plate for a negative electrode and a reference electrode through a separator made of porous polyethylene soaked with electrolyte and having a thickness of 30 μm. A test cell was prepared. And charging / discharging was repeated with respect to this test cell at the rate of 0.1C, the discharge capacity (mAh / g) of the positive electrode per 1g of active material was measured, and the charge / discharge cycle characteristic of each positive electrode was evaluated. The results are shown in FIG.

  From FIG. 15, the positive electrodes according to Invention Examples 1 to 4 showed a high discharge capacity of 100 mAh / g or more up to 15 cycles. Among them, Examples 1 to 3 of the present invention having a small Dp (hole diameter) have a short internal resistance and a discharge capacity compared to Example 4 of the present invention because the distance between the surface of the skeleton for collecting current and the active material is short. Is expensive. And compared with Example 3 of the present invention, the discharge capacity of Examples 1 and 2 of the present invention having a large Dp (hole diameter) is high because the Dp is reasonably large. As shown in FIGS. This is because the mixture could be uniformly filled into the pores from the inner surface to the outer surface of the material.

  On the other hand, the positive electrode according to Comparative Example 11 had a non-uniform distribution of the mixture because the W / H indicating the degree of communication between the holes of the current collector was too large. And Dp (hole diameter) is relatively large, and the distance between the surface of the skeleton that collects current and the active material is long. Moreover, since the surface area of the skeleton is small, the internal resistance is high, and it is considered that a low discharge capacity of 80 to 60 mAh / g was exhibited. In Comparative Example 11, the discharge capacity could not be recovered, and the measurement was stopped in 12 cycles.

In Comparative Example 12, Dp (hole diameter) is a value close to Inventive Examples 1 and 2. However, W / H, which indicates the degree of communication between the holes, was small, indicating a low discharge capacity of 100 mAh / g or less, which was about 70% of the discharge capacity of Example 2 of the present invention. This is presumably because the mixture was not sufficiently filled into the pores due to the state of the void distribution shown in FIGS. In FIG. 14 showing the cross section of the electrode, the ratio of the wall surface of the skeleton is large with respect to the amount of the active material, and the active material is surrounded by the wall surface of the skeleton, and the cooperation with the active material in the adjacent holes is poor. An area is seen. Further, on the outer surface of the electrode, the mixture into the porous body was caused by the fact that the opening having a clear outline was “independently” opened on the outer surface of the porous body (FIG. 6). Since it was difficult to fill in, a thin mixture layer was formed. It is considered that these prevent the smooth movement of lithium ions.

Claims (3)

A porous aluminum sintered body having a skeleton and voids obtained by sintering aluminum powder and having an overall porosity of 80 to 90% by volume,
When the void diameter D (μm) and the specific surface area S (cm ² / g) were measured by mercury porosimetry, and the distribution of the void diameter D (μm) was expressed by Log differential void specific surface area distribution, Log differential void specific surface area dS / d (LogD) has a peak diameter Dp of 20 to 150 μm and a ratio of the peak height H to the half width W of the peak at W / A porous aluminum sintered body, wherein H is 5.0 to 50.0. A method for producing a porous aluminum sintered body having a skeleton and voids obtained by sintering aluminum powder and having a total porosity of 80 to 90% by volume,
An aluminum powder having an average particle size of 50 μm or less, and particles for forming the voids, the average particle size being larger than the average particle size of the aluminum powder and 500 μm or less, the void-forming particles, Mixing an aluminum powder and a binder for binding the void-forming particles to obtain a mixture;
Molding the mixture to obtain a molded body in which the void-forming particles are dispersed between the aluminum powders;
Removing the void-forming particles from the molded body to obtain a green body before sintering;
Degreasing and sintering the green body;
The manufacturing method of the porous aluminum sintered compact characterized by including this. An electrode comprising: a porous aluminum sintered body according to claim 1 filled with a mixture containing an active material in a void; and the porous aluminum sintered body after being filled with the mixture being compressed. Production method.