JP2008037682A - Method for treating active carbon, treated active carbon, and storage battery using the treated active carbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for modifying active carbon so that the decomposition of an electrolyte is suppressed on a pore wall, active carbon obtained by such a treatment, and a storage battery which utilizes the active carbon and in which reduction of power output and capacity is suppressed over a long period of time. <P>SOLUTION: The present invention is embodied in a method for modifying a pore wall of active carbon. This treatment method comprises the steps of: (step S2) bringing active carbon into contact with an amine compound, a carboxyl group being adsorbed to the surface of the active carbon containing a pore wall; (step S3) immersing the active carbon which is brought into contact with the amine compound in an acid having a high viscosity; and (step S4) immersing the active carbon taken out of the acid in a treatment liquid having a low viscosity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for treating activated carbon, a treated activated carbon, and a power storage device using the treated activated carbon.

In a power storage device such as a lithium secondary battery, when the electrode surface area is large, the electric double layer effect can be obtained in a wide range, so that a large current can be secured.
Activated carbon is suitable for increasing the surface area of the electrode because of its large specific surface area per unit weight. For example, the lithium secondary battery disclosed in Patent Document 1 includes activated carbon in the positive electrode. The lithium secondary battery of Patent Document 1 has a large initial output and initial charge / discharge capacity.

JP 2002-260634 A

Producing a lithium secondary battery containing activated carbon in the positive electrode can increase the output and capacity immediately after the start of use of the lithium secondary battery, but the output and capacity become more noticeable as the usage time elapses. It will drop to.
The inventors' research has revealed that the reason why the output and capacity are reduced is due to the pores of the activated carbon. Activated carbon has many pores. The organic electrolyte also enters the pores of the activated carbon. The organic electrolyte that has entered the pores is difficult to circulate and continues to contact the pore walls. Molecules constituting the organic electrolytic solution are likely to be decomposed when kept in contact with the activated carbon for a long time. Furthermore, when an electrical action accompanying charging / discharging of the battery is applied to the activated carbon, an electric field is generated in the pores of the activated carbon. The organic electrolyte remaining on the pore walls is decomposed by the action of the electric field.
A lithium secondary battery is a sealed battery. Since the lithium secondary battery generates gas when the organic electrolyte is decomposed, the internal pressure of the lithium secondary battery increases. As a result, the battery output and the battery capacity are reduced.
In the above, the case of a lithium secondary battery including activated carbon in the positive electrode has been described. However, in a power storage device including activated carbon in the electrode, a phenomenon in which the electrolytic solution is likely to be decomposed at the pore walls generally occurs.

The present invention provides a treatment method for modifying the pore walls so that the decomposition of the electrolytic solution is suppressed in the pores of the activated carbon.
The present invention also provides activated carbon that has been modified so as to suppress decomposition of the electrolyte in the pores.
In addition, the present invention provides a power storage device that uses activated carbon that has been modified so that decomposition of the electrolytic solution at the pore walls is suppressed, and in which a decrease in output and capacity is suppressed over a long period of time.

The present invention is embodied in a method for modifying the pore walls of activated carbon.
This treatment method comprises a step of contacting activated carbon having a carboxyl group adsorbed on the surface including pore walls with an amine compound, a step of immersing activated carbon contacted with the amine compound in a highly viscous acid, A step of immersing the activated carbon extracted from the substrate in a low-viscosity processing solution.
Said high viscosity means viscosity so high that it cannot penetrate into the pores of activated carbon. On the other hand, low viscosity refers to a viscosity that is so low that it can enter the pores of the activated carbon.

In the present specification, “activated carbon in which carboxyl groups are adsorbed on the surface including pore walls” refers to those in which carboxyl groups are adsorbed on the outer peripheral surface of the activated carbon and the surfaces of the pore walls. For example, activated carbon in which carboxyl groups are adsorbed during the production process, such as activation treatment, is also included in “activated carbon in which carboxyl groups are adsorbed on the surface including pore walls”.
The “amine compound” in the present specification is not particularly limited as long as it is a compound that can be aminated by binding to a carboxyl group. For example, in addition to general primary to quaternary amines, diamines, hydroxylamines, and amino alcohols are also included.
The “highly viscous acid” in the present specification refers to an acidic liquid having such a high viscosity that it cannot enter the pores of the activated carbon (the opening diameter is often about 100 nm).
The “treatment liquid” in this specification refers to a liquid containing a component that acts on an amino group to generate an insulating material. As an example of the treatment liquid, a liquid containing a polymerized fatty acid can be given. When such a treatment liquid is used, an amino group and a polymerized fatty acid act to produce a polyamide resin. As another example of the treatment liquid, a treatment liquid containing a cation such as a metal ion and an anion such as a halide ion, concentrated sulfate ion, phosphate ion, or carbonate ion can be given. When such a treatment liquid is used, the cation and anion salts are selectively deposited on the activated carbon having an amino group.

In the treatment method of the present invention, the carboxyl group on the surface of the activated carbon (the surface including the pore walls) is aminated in the step of bringing activated carbon into contact with the amine compound. The amines adsorb on the surface including the pore walls of the activated carbon. As used herein, “amines” refers to those having a weak alkaline property represented by a general formula of —COORNH ₂ , —CONHRNH ₂ , —CONHR, and —CONRR ′. When amines are adsorbed on the activated carbon surface, the surface of the activated carbon is biased to weak alkalinity.
Next, the activated carbon having amines adsorbed on the surface is immersed in a highly viscous acid. The amines in contact with the acid are neutralized. Activated carbon has a porous structure. Highly viscous acids cannot penetrate into the pores. The amines on the outer peripheral surface of the activated carbon are neutralized by the acid, but the amines on the pore walls of the activated carbon are not neutralized by the acid. As a result, activated carbon having amines adsorbed on the pore walls and neutralized on the outer peripheral surface is obtained.
Next, the activated carbon is pulled up from the highly viscous acid, and the activated carbon is immersed in the treatment liquid. The treatment liquid is a low-viscosity liquid that can enter the pores of the activated carbon, and the components in the treatment liquid and amines on the pore walls act to produce an insulating material. This insulating substance is firmly adsorbed on the innermost hole wall.
According to the present processing method, it is possible to obtain activated carbon in which a film made of an insulating material is formed on the pore wall surface, and the activated carbon is exposed without the insulating material attached to the outer peripheral surface. The insulating material only needs to be formed so as to cover the pore walls, and the state of the coating is not limited. For example, the film may be formed so that insulating substances generated in a scale shape overlap. In addition, the state where the insulating substance is deposited on the surface of the film-like insulating substance and the pores are partially filled is also included in the state where the film is formed on the pore wall surface.
The activated carbon treated by this method has low activity on the pore walls because the insulating material is attached to the pore walls. Further, since the insulating material film is provided on the pore wall surface, it is difficult to generate an electric field in the pore. It is possible to remarkably suppress the decomposition of the electrolyte solution entering the pores.

In the treatment method of the present invention, the viscosity of the highly viscous acid is preferably 0.020 Pa / sec or more and 0.95 Pa / sec or less, and the viscosity of the low viscosity treatment liquid is preferably 0.0015 Pa / sec or less.
An acid having a viscosity of 0.020 Pa / sec or more is difficult to enter into the pores of activated carbon having an opening diameter of about 100 nm. When the viscosity of the acid is 0.95 Pa / sec or more, the activated carbon becomes difficult to disperse and the processing efficiency is deteriorated. The viscosity of the highly viscous acid is preferably 0.020 Pa / sec or more and 0.95 Pa / sec or less. As one specific example, concentrated sulfuric acid having a viscosity of 0.027 Pa / sec in an environment with a temperature of 0 ° C. can be used.
A liquid having a viscosity of 0.0015 Pa / sec or less can enter the pores of activated carbon having an opening diameter of about 100 nm. If the viscosity of the treatment liquid is 0.0015 Pa / sec or less, the treatment liquid can be brought into contact with the pore walls of the activated carbon to perform surface treatment of the pore walls.

In a preferred treatment method of the present invention, a treatment liquid containing ions containing a metal element is used.
“Ions containing metal elements” include cations of simple metals (eg, Na ⁺ , Ca ²⁺ , Fe ²⁺ , Zn ²⁺ , Zr ⁴⁺ , Ti ⁴⁺ ) and complex ions containing metal elements ( For example, TiO ₃ ²⁻ , AlO ₂ ⁻ ) are included.
When ions containing a metal-containing element are contained in the treatment liquid, an insulating material film made of a metal compound can be formed on the pore walls of the activated carbon.

  The metal element preferably contains one or more metal elements selected from titanium, zirconium, and zinc. When the activated carbon treated by this treatment method is used for an electrode of a lithium secondary battery, titanium, zirconium, and zinc do not inhibit the electrode reaction related to charge / discharge. The activated carbon obtained by the treatment method of the present invention is suitable for an electrode of a lithium secondary battery.

  It is preferable that phosphate ion is contained in the treatment liquid. When phosphate ions are contained in the treatment liquid, insulating metal phosphate can be deposited on the pore walls of the activated carbon.

  In the treatment method of the present invention, the treatment liquid contains fluorine ions, and the pH is preferably 2 or more and 6 or less. When such a treatment liquid is used, the reactivity of the treatment liquid is kept constant.

The invention can also be embodied in activated carbon with modified pore walls. The activated carbon of the present invention is characterized in that the activated carbon is exposed on the outer peripheral surface of the activated carbon and has a film made of an insulating material on the pore wall surface.
“The activated carbon is exposed on the outer peripheral surface of the activated carbon” means that the insulating material is not substantially attached to the region of the outer peripheral surface of the activated carbon. “Having a coating made of an insulating material on the pore wall surface” means that a coating of an insulating material is formed on substantially the entire pore wall. Therefore, activated carbon having a region where a coating of an insulating material is not formed in a small region of the pore wall is included in the activated carbon having a coating made of an insulating material on the pore wall surface. Similarly, activated carbon in which an insulating material adheres to a small area of the outer peripheral surface is also included in the activated carbon with the outer peripheral surface exposed.
When the activated carbon of the present invention is employed in an electrode used in a state where the organic electrolyte is soaked, the electrolyte is hardly decomposed. Moreover, even if an electrical action is applied to the activated carbon, an electric field is hardly generated in the pores. When the activated carbon of the present invention is used, decomposition of the organic electrolyte solution entering the pores is suppressed.

The insulating substance forming a film on the pore wall surface of the activated carbon is preferably an inorganic metal compound. Inorganic metal compounds have poor reactivity with organic solvents.
The inorganic metal compound may be an oxide. An oxide is one of inorganic metal compounds whose properties are stable even when exposed to an organic solvent.
The inorganic metal compound may be a phosphate. Phosphate is one of inorganic metal compounds that have stable properties even when exposed to organic solvents.

  The metal compound preferably contains one or more metals selected from titanium, zirconium, and zinc. Titanium, zirconium, and zinc are difficult to be substances that inhibit the electrode reaction of a lithium secondary battery. Activated carbon in which an insulating substance made of a compound of titanium, zirconium, or zinc forms a film on the pore wall surface is suitable for an electrode material of a lithium secondary battery.

The present invention also provides a novel power storage device. In the power storage device provided by the present invention, the electrolytic solution is an organic electrolytic solution, and the electrode material includes any one of the activated carbons described above.
As described above, when the organic electrolyte is left in the pores of the untreated activated carbon or when an electrical action is applied to the activated carbon, the organic electrolyte entering the pores is decomposed. A phenomenon occurs. Adoption of the activated carbon of the present invention as an electrode material suppresses decomposition of the organic electrolyte.

First, the main features of the embodiments described below are listed.
(Characteristic 1) The electrode material of the lithium secondary battery contains activated carbon with modified pore walls.
(Characteristic 2) A film of an insulating material is formed on the pore walls of the activated carbon after the treatment. This insulating material contains zinc phosphate (Zn ₃ (PO ₃ ) ₂ ).
(Characteristic 3) A film of an insulating material is formed on the pore walls of the activated carbon after the treatment. This insulating substance contains zirconium oxide (ZrO ₂ ).
(Feature 4) A coating of an insulating material is formed on the pore walls of the activated carbon after the treatment. This insulating film contains titanium oxide (TiO ₂ ) and zirconium oxide (ZrO ₂ ).
(Characteristic 5) It is prepared so that the concentration of metal ions in the treatment liquid is 5 ppm or more and 5000 ppm or less.
(Characteristic 6) The fluorine ion concentration in the treatment liquid is adjusted to be 0.1 ppm or more and 100 ppm or less.
(Feature 7) The amine that derivatizes the carboxyl group on the surface of the activated carbon is diethylamine.
(Feature 8) The highly viscous acid used for neutralization of amines on the surface of activated carbon is concentrated sulfuric acid.
(Characteristic 9) Activated carbon is activated carbon used for the process of removing impurities in the plating bath.

<First Example: Treatment 1 of activated carbon>
In this example, zinc phosphate was adhered to the pore walls of the activated carbon to form an insulating material region on the pore walls.
First, the shape of the activated carbon before processing will be described with reference to FIGS. FIG. 1 is a schematic diagram showing activated carbon 1 before treatment. FIG. 2 is a cross-sectional view of the activated carbon 1.
As shown in FIGS. 1 and 2, the activated carbon 1 is a porous material having a large number of pores 14. The pores 14 are formed from the outer peripheral surface 12 toward the inside.

FIG. 3 is a flowchart showing a procedure according to the activated carbon treatment method of the present embodiment. The processing procedure of the present embodiment will be described with reference to FIG.
In this process, first, activated carbon 1 having carboxyl groups adsorbed on the pore walls and the outer peripheral surface was prepared (step S1 in FIG. 3). As shown in the partial cross-sectional view of FIG. 4, carboxyl groups are adsorbed on the outer peripheral surface 12 and the walls of the pores 14 of the activated carbon 1. The carboxyl group (—COOH) of the activated carbon 1 is adsorbed during the activation process.

Next, an aqueous solution containing 10 w% of a diamine represented by the general formula NH ₂ —R—NH ₂ is prepared. R in the above general formula is an alkyl group. In this example, ethylenediamine was used as the diamine. The liquid property of the diamine solution is weakly alkaline. Activated carbon 1 was immersed in the diamine solution (step S2 in FIG. 3).
The activated carbon 2 obtained by being immersed in a diamine solution is shown in FIG. FIG. 6 is a partial cross-sectional view of the activated carbon 2. When activated carbon 1 is immersed in a diamine solution, -COOH on the surface and one amino group of diamine are dehydrated to form an amide bond. The surface of the activated carbon 2 is covered with a region 16 of —CO—NH—R—NH ₂ .

Next, the activated carbon 2 was immersed in concentrated sulfuric acid (step S3 in FIG. 3). Since concentrated sulfuric acid was used in an environment at 0 ° C., the viscosity of concentrated sulfuric acid was 0.027 Pa / sec.
FIG. 8 shows a sectional view schematically showing the structure of the activated carbon 3 obtained by immersing in concentrated sulfuric acid, and FIG. 7 shows a partial sectional view thereof. Since concentrated sulfuric acid is highly viscous, it cannot penetrate into the pores 14 of the activated carbon 2. -CO-NH-R-NH ₂ in the outer peripheral surface 12 of the activated carbon 2 is reacted with concentrated sulfuric acid, to produce a -CO-NH-R-NH- HSO 3. In the activated carbon 3 obtained by the treatment in step S3, a —CO—NH—R—NH—HSO ₃ region 18 is formed on the outer peripheral surface. Since this —CO—NH—R—NH—HSO ₃ region 18 has low activity, the reactivity of the outer peripheral surface 12 of the activated carbon 3 becomes low.
On the other hand, since concentrated sulfuric acid cannot enter the pores 14, —CO—NH—R—NH _{2 on} the pore wall does not react with concentrated sulfuric acid. Therefore, the pore wall of the activated carbon 3 is maintained in a state in which the —CO—NH—R—NH ₂ region 17 is formed.

Next, the activated carbon 3 obtained in step S3 was immersed in the treatment liquid (step S4 in FIG. 3). In this example, the treatment liquid has a zinc ion concentration of (Zn) of 1300 ppm, a phosphate ion (PO ₄ ³⁻ ) concentration of 12500 ppm, and a fluorine ion (F ⁻ ) concentration of 200 ppm. The prepared one was used.
The treatment liquid was prepared so that the viscosity was 0.0006 to 0.0013 Pa / sec at room temperature. By maintaining the viscosity of the treatment liquid in the above range, the treatment liquid can enter the pores 14 of the activated carbon 3.
The treatment liquid was prepared so that the pH was 2-6.

When the activated carbon 3 is immersed in the treatment liquid, the treatment liquid enters the pores 14 of the activated carbon 3. Since the liquid of the treatment liquid is weakly acidic, —CO—NH—R—NH _{2 on} the wall surface 17 of the pore 14 is coordinated with H ⁺ to N, and —CO—NH—R—NH ₃ ⁺ region 19 (This step is illustrated in FIG. 9). The —CO—NH—R—NH ₃ ⁺ region 19 is in a positively charged state. Therefore, PO ₃ ³⁻ contained in the treatment liquid is attracted to the pore wall having a positive charge. Then, PO ₃ ³⁻ and Zn ²⁺ attracted to the pore wall react to generate Zn ₃ (PO ₃ ) ₂ . As a result, Zn ₃ (PO ₃ ) ₂ is selectively deposited in the pore wall region where CO—NH—R—NH ₃ ⁺ is formed. At this stage, a Zn ₃ (PO ₃ ) ₂ region 20 is formed on the pore wall of the pore 14 (this stage is illustrated in FIG. 10). Zn ₃ (PO ₃ ) ₂ is an insulating material. By forming the Zn ₃ (PO ₃ ) ₂ region 20 on the pore wall of the pore 14, the activity in the pore 14 of the activated carbon 4 becomes low.
As described above, activated carbon 4 having low pore activity was obtained.

<Second Example: Treatment 2 of activated carbon>
In this embodiment, zirconium oxide (ZrO ₂ ) is attached to the pore walls of the pores of the activated carbon to form a film of an insulating material. The processing procedure of this embodiment is the same as that of the first embodiment except that the components of the processing liquid are different. The processing procedure of the present embodiment is similar to the procedure up to the step of obtaining the activated carbon 3 by immersing the activated carbon of the first embodiment in concentrated sulfuric acid, and therefore redundant description and drawings are omitted.

  First, a method for preparing the treatment liquid of this example will be described. As the treatment liquid of this example, first, an aqueous solution having a zirconium concentration of 200 ppm was prepared using a zirconium oxynitrate solution and nitric acid. Hydrofluoric acid (HF) was injected into this aqueous solution to prepare a fluorine ion concentration of 50 ppm. Further, sodium hydroxide (NaOH) was added to prepare a treatment solution. The treatment solution was adjusted to a pH of about 3 by adding NaOH.

Then, the activated carbon 3 is immersed in the treatment liquid. The treatment liquid enters the pores 14 of the activated carbon 3. Since the treatment liquid is weakly acidic, -CO-NH-R-NH _{2 on} the wall surface 18 of the pore 14 is coordinated with H ⁺ to become -CO-NH-OR-NH ₃ ⁺ . Zr ions contained in the treatment liquid are oxidized to form ZrO ₂ and are selectively deposited in a region where CO—NH—R—NH ₃ ⁺ is formed. A ZrO ₂ region 21 is formed on the pore wall of the pore 14 (this step is illustrated in FIG. 11). The ZrO ₂ region 21 is a region where an insulating film is formed. As the ZrO ₂ region 21 is formed, the activated carbon 5 has low activity in the pores 14.
As described above, activated carbon 5 having low pore activity was obtained.

<Third embodiment: treatment 3 of activated carbon>
In this embodiment, zirconium oxide (ZrO ₂ ) and titanium oxide (TiO ₂ ) are attached to the pore walls of the pores of the activated carbon to form an insulating material region. The processing procedure of this embodiment is the same as that of the first embodiment except that the components of the processing liquid are different. The processing procedure of the present embodiment is similar to the procedure up to the step of obtaining the activated carbon 3 by immersing the activated carbon of the first embodiment in concentrated sulfuric acid, and therefore redundant description and drawings are omitted.

  First, a method for preparing the treatment liquid of this example will be described. The treatment liquid of this example was first prepared using a hexafluorozirconic acid (IV) aqueous solution, a concentrated titanium sulfate (IV) aqueous solution, concentrated calcium sulfate and nitric acid, with a zirconium concentration of 1000 ppm, a titanium concentration of 2000 ppm, and a calcium concentration of An aqueous solution with 5 ppm and nitrate radical of 1000 ppm was prepared. Using potassium hydroxide (KOH) and hydrofluoric acid (HF) in this aqueous solution, the treatment solution was adjusted so that the pH was approximately 5. HF was injected so that the fluorine ion concentration was 2250 ppm.

Then, the activated carbon 3 is immersed in the treatment liquid. When the activated carbon 3 is immersed in the treatment liquid, the treatment liquid enters the pores 14 of the activated carbon 3. Since the liquid of the treatment liquid is weakly acidic, H ⁺ coordinates to -CO-NH-R-NH ₃ ⁺ in -CO-NH-R-NH _{2 on} the wall surface 18 of the pore 14. Zr ions contained in the treatment liquid are oxidized to form ZrO ₂ , and Ti ions are oxidized to form TiO ₂ . ZrO ₂ and TiO ₂ ions are selectively deposited in the region where CO—NH—R—NH ₃ ⁺ is formed. A ZrO ₂ + TiO ₂ region 22 composed of ZrO ₂ and TiO ₂ is formed on the wall surface of the pore (this step is illustrated in FIG. 12). The activated carbon 6 in which the ZrO ₂ + TiO ₂ region 22 is formed on the pore wall of the pore 14 has low activity in the pore 14.
As described above, activated carbon 6 having low pore activity was obtained.

<Fourth Example: Production of Lithium Secondary Battery>
A lithium secondary battery (1) including the activated carbon 4 obtained in the first example as a positive electrode was produced.
First, the manufacturing procedure of the positive electrode plate will be described.
First, the activated carbon 4 obtained in the first embodiment, a positive electrode active material, carbon black as a conductive material, and a fluororesin (tetrafluoroethylene) as a binder are mixed with water to form a positive electrode active material paste. Was prepared. Lithium nickel cobalt composite oxide was used as the positive electrode active material. The positive electrode active material paste obtained above was continuously applied to both sides of the aluminum current collector foil and dried. In this way, a positive electrode sheet was produced. This positive electrode sheet was cut into a long shape, and a positive electrode plate of a lithium secondary battery (1) was produced. A positive electrode lead was welded to the end of the positive electrode plate.

Next, the manufacturing procedure of the negative electrode plate will be described.
A graphite active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed with water to prepare a negative electrode active material paste. The negative electrode active material paste obtained above was applied to both sides of the copper current collector foil and dried. In this way, a negative electrode sheet was produced. This negative electrode sheet was cut into a long shape, and a negative electrode plate of the lithium secondary battery (1) was produced. A negative electrode lead was welded to the end of the negative electrode plate.

Next, the positive electrode plate and the negative electrode plate are overlapped and wound with the separator interposed therebetween. A porous sheet made of microporous polyethylene was used as the separator. A laminated electrode body was produced by winding a laminated sheet composed of a positive electrode plate, a separator and a negative electrode plate. The electrode body was accommodated in the battery case so that the negative electrode lead and the positive electrode lead were drawn out of the battery case. Next, the electrolytic solution was injected into the battery container under reduced pressure. As the electrolytic solution, a general electrolytic solution used in a conventional lithium secondary battery can be used. Here, an electrolytic solution in which 1 mol / L LiPF ₆ was dissolved in a 70:30 (mass ratio) mixed solvent of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) was used. Thus, the lithium secondary battery (1) provided with the activated carbon 4 was manufactured.

<Comparative example: Production of comparative lithium secondary battery>
In this comparative example, a lithium secondary battery (2) having activated carbon 1 before the treatment for forming an insulating film in the pores on the positive electrode was produced. This comparative example is the same as the manufacturing procedure of the lithium secondary battery (1) manufactured in the fourth example except that the activated carbon provided for the positive electrode is activated carbon 1. In this comparative example, the description about manufacture of a lithium secondary battery (2) is abbreviate | omitted.

<Experimental example: Storage test of lithium secondary battery>
In this experimental example, a storage experiment was performed using the lithium secondary battery (1) manufactured in Example 4 and the lithium secondary battery (2) manufactured in Comparative Example. The procedure of the preservation experiment is as follows.
First, initial outputs of the lithium secondary battery (1) and the lithium secondary battery (2) were measured. As for the output, a low temperature output under a low temperature condition of −10 ° C. and a normal temperature output under a normal temperature condition of 25 ° C. were measured.
Subsequently, the lithium secondary battery (1) and the lithium secondary battery (2) were put into a 60 degreeC thermostat, and were hold | maintained for 100 hours.
Thereafter, the lithium secondary battery (1) and the lithium secondary battery (2) were taken out of the thermostatic chamber, and the low temperature output and the normal temperature output were measured. The results of the storage experiment are shown in Table 1.

As shown in Table 1, the discharge capacity before the storage test was assured for the lithium secondary batteries (1) and (2). Moreover, the output before a preservation | save test ensured the equivalent output in both lithium secondary batteries (1) and (2). Regardless of the treatment of the activated carbon of the first embodiment, it was found that the lithium secondary battery provided with activated carbon at the positive electrode can obtain the same initial output and initial discharge capacity.
The rate of change in discharge capacity after the storage test was 96.33% for the lithium secondary battery (1) and 95.57% for the lithium secondary battery (2). It was found that the rate of change in discharge capacity was slightly improved in the lithium secondary battery (1) subjected to the treatment of the first example.
The low-temperature output change rates after the storage test were 70.59% for the lithium secondary battery (1) and 63.64% for the lithium secondary battery (2). The low-temperature output change rate was found to be about 7% better for the lithium secondary battery (1) than the lithium secondary battery (2). The room temperature output change rate after the storage test was 67.09% for the lithium secondary battery (1) and 63.75% for the lithium secondary battery (2). The room temperature output change rate was found to be about 3% better for the lithium secondary battery (1) than the lithium secondary battery (2).

  From the results of this experimental example, it was found that the lithium secondary battery provided with the activated carbon having the insulating film formed on the pore walls of the pores on the positive electrode has excellent storage characteristics. In the lithium secondary battery (2), even if the organic electrolyte enters the pores of the activated carbon, the organic electrolyte is difficult to decompose at the pore walls. Gas from decomposition of the organic electrolyte is unlikely to be generated at the pore walls of the activated carbon. When the battery internal pressure increases, the internal resistance of the lithium secondary battery increases. In the lithium secondary battery (1), since the generation of gas due to the decomposition of the organic electrolyte is suppressed, the battery internal pressure of the lithium secondary battery (1) is unlikely to increase. As a result, in the lithium secondary battery (1), it is considered that the increase in internal resistance is suppressed and the output after the storage test is also maintained.

On the other hand, the lithium secondary battery (2) as a comparative example has no insulating film formed on the pore walls of the pores. For this reason, an organic electrolyte solution is easy to decompose | disassemble in the pore wall part of activated carbon during a storage test. As a result of this experimental example, the lithium secondary battery (2) showed a decrease in low-temperature output and normal-temperature output after the storage test. This is probably because the organic electrolyte that entered the pores of the activated carbon decomposed during the storage test and the internal pressure of the battery increased. As for the lithium secondary battery (2), it is considered that the internal resistance of the battery increased as a result of the increase of the battery internal pressure, and the output after the storage test decreased.
From the results of this experimental example, it was found that when the activated carbon 4 obtained by the treatment of the first example was provided in the positive electrode material, the output decrease after the storage test was suppressed.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  For example, although the lithium secondary battery was shown in the said Example, you may use the activated carbon of this invention for the impurity removal of the bath liquid for plating.

  Regardless of the method of electroplating or electroless plating, if impurities are mixed in the bath solution of the plating bath, gas is generated during the plating process or the plating film thickness becomes uneven. For this reason, the bath liquid is subjected to purification treatment to remove impurities. Organic impurities and inorganic impurities are mixed in the bath liquid before the purification treatment. Organic impurities are removed by activated carbon treatment. This purification method is a method utilizing the property that activated carbon adsorbs organic substances. Inorganic impurities are decomposed by weak electrolytic treatment. A metal having a lower potential than the metal of the plating material is removed by weak electrolysis.

  When conventional activated carbon (activated carbon in which a film made of an insulating material is not formed on the pore walls) is used for the activated carbon treatment, the activated carbon treatment and the weak electrolytic treatment cannot be performed in synchronization. Activated carbon also incorporates organic impurities into the pore walls. When a weak electrolysis treatment is performed, an electrical effect is added to the activated carbon. When an electric action is applied to the activated carbon in a state where organic impurities are taken into the pores, an electric field is generated on the pore walls, and a phenomenon occurs in which the organic impurities are dissolved again into the bath liquid from the pores.

  When the activated carbon to which the treatment of the present invention is applied is used for the activated carbon treatment, the activated carbon treatment and the weak electrolysis treatment can be performed in synchronization. The activated carbon according to the present invention (activated carbon in which a coating made of an insulating material is not formed on the pore walls) does not generate an electric field on the pore walls even when a weak electrolytic treatment is performed. Even if an electric action is applied to the activated carbon in a state where the organic impurities are taken into the pores, the phenomenon that the organic impurities are decomposed and dissolved again in the bath liquid does not occur. Since the activated carbon treatment and the weak electric field treatment can be performed in synchronization, the purification treatment of the bath liquid can be completed in a short time.

The activated carbon to which the treatment of the present invention has been applied can be immersed in a bath solution for electrolytic plating during the plating treatment.
Electrolytic plating is performed by immersing an anode made of a metal of a plating material and a cathode made of a material of an object in a plating bath and flowing a direct current between both electrodes. The bath solution for electrolytic plating contains additives such as brighteners, stress reducers, pit inhibitors, and organic complexing agents. When an electrolytic current is passed through the plating process, the additive is reduced at the cathode and oxidized at the anode. As a result, the additive decomposes. Activated carbon is added to remove the additive degradation products from the bath liquor. When conventional activated carbon is used, if an electrolytic current for plating is applied while the activated carbon is in the bath solution, the decomposition product that has entered the pores of the activated carbon is further decomposed and gasified, or decomposed and then the bath solution again. The phenomenon of melting inside occurs. When conventional activated carbon was used, it was necessary to interrupt the plating process.

  In the activated carbon according to the present invention, a film made of an insulating material is formed on the pore walls. The activated carbon according to the present invention is immersed in a bath solution, and no electric field is generated on the pore walls even when an electrolytic current is applied to the bath solution. Even if an electrical action is applied to the activated carbon in a state where the decomposition product of the additive is taken into the pores, the decomposition product is difficult to decompose. When the activated carbon according to the present invention is immersed in an electroplating bath solution, plating can be performed while removing decomposition products. Since the contamination of the bath liquid by the decomposition products is suppressed, the quality of the plating process is not easily lowered even if the number of plating processes is increased.

  The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

It is the top view which showed typically the activated carbon before a process. It is sectional drawing which showed typically the cross-sectional structure of the activated carbon before a process. It is a flowchart which shows the process sequence of 1st Example. It is a fragmentary sectional view which shows the surface structure of the activated carbon before a process. It is sectional drawing of the activated carbon in which amines were formed. It is a fragmentary sectional view which shows the surface structure of the activated carbon in which amines were formed. It is a fragmentary sectional view showing the surface structure of activated carbon after concentrated sulfuric acid treatment. It is sectional drawing which shows the activated carbon after a concentrated sulfuric acid process. It is a fragmentary sectional view which shows the state which hydrogen ion coordinated to amines. It is sectional drawing which shows the cross-section of the activated carbon processed by 1st Example. It is sectional drawing which shows the cross-section of the activated carbon processed by 2nd Example. It is sectional drawing which shows the cross-section of the activated carbon processed by 3rd Example.

Explanation of symbols

1, 2, 3, 4, 5: activated carbon 12: outer peripheral surface 14: pores 16, 17: —CO—NH—R—NH ₂ region 18: —CO—NH—R—NH—HSO ₃ region 19: — CO-NH-R-NH ₃ ⁺ region 20: Zn ₃ (PO ₄ ) ₂ region 21: ZrO ₂ region 22: ZrO ₂ + TiO ₂ region

Claims (12)

A method of modifying the pore walls of activated carbon,
Contacting activated carbon having carboxyl groups adsorbed on the surface including the pore walls with an amine compound;
Immersing the activated carbon in contact with the amine compound in a highly viscous acid that cannot enter the pores;
A step of immersing the activated carbon extracted from the acid in a low-viscosity treatment liquid that can enter the pores;
A method for treating activated carbon. The acid has a viscosity of 0.020 Pa / sec or more and 0.95 Pa / sec or less,
The processing method according to claim 1, wherein the viscosity of the processing liquid is 0.0015 Pa / sec or less.   The processing method according to claim 1, wherein the processing liquid contains an ion containing a metal element.   The processing method according to claim 3, wherein the metal element is one or more metal elements selected from titanium, zirconium, and zinc.   The processing method according to claim 3 or 4, wherein the processing liquid contains phosphate ions.   The processing method according to claim 3, wherein the processing liquid contains fluorine ions and has a pH of 2 or more and 6 or less. An activated carbon having an outer peripheral surface and pores opened on the outer peripheral surface;
On the outer peripheral surface, the activated carbon is exposed,
An activated carbon having a coating made of an insulating material on the pore wall surface.   The activated carbon according to claim 7, wherein the insulating substance is an inorganic metal compound.   The activated carbon according to claim 8, wherein the inorganic metal compound is an oxide.   The activated carbon according to claim 8, wherein the inorganic metal compound is a phosphate.   The activated carbon according to claim 8, wherein the inorganic metal compound contains one or more metals selected from titanium, zirconium, and zinc. The electrolyte is an organic electrolyte,
An electrode material includes the activated carbon according to any one of claims 7 to 11, and a power storage device.

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