DE112016004121T5 - Lithium-ion capacitor and carbon material for a positive electrode active material - Google Patents

Abstract

A lithium ion capacitor having a high capacity and a low internal resistance is realized. A carbon material according to the present invention is used as a positive electrode active material of a lithium ion capacitor. The carbon material has a pore volume of 1.0 to 1.5 ml / g for pores having a diameter of 1.7 nm or more; a pore volume less than or equal to 0.1 ml / g for pores having a diameter of 1.0 nm or less; and a total content of functional groups of 0.3 to 0.6 mmol / g.

Description

TERRITORY

The present invention relates to a lithium ion capacitor and a carbon material for a positive electrode positive electrode active material.

BACKGROUND

In recent years, a lithium ion capacitor has attracted attention as an electric double layer capacitor. Like in the Japanese Patent Application KOKAI Publication No. 2010-192853 As is described, a lithium-ion capacitor essentially comprises a positive electrode of active carbon and a negative electrode of a material from which lithium ions can be taken up and from which lithium ions can be released. A separator is disposed between the positive and negative electrodes. The stack also includes a nonaqueous electrolyte containing a lithium salt.

In the lithium-ion capacitor, the negative electrode may contain lithium ion received or may be doped with lithium ion. This keeps the potential of the negative electrode smaller than in a conventional electric double layer capacitor. Therefore, the lithium ion capacitor can achieve a large working voltage range as compared with the conventional electric double layer capacitor. In addition, the lithium ion capacitor can achieve a high capacity as compared with the conventional electric double layer capacitor.

SUMMARY

Generally, the lithium-ion capacitor requires a trade-off between capacitance and internal resistance. That is, a high-capacity lithium-ion capacitor generally has a high internal resistance.

An object of the present invention is to realize a lithium ion capacitor having a high capacitance and a low internal resistance.

According to a first aspect of the present invention, there is provided a carbon material for a positive electrode active material of a lithium ion capacitor, the carbon material having: a pore volume of 1.0 to 1.5 ml / g for pores having a diameter of 1, 7 nm or more; a pore volume less than or equal to 0.1 ml / g for pores having a diameter of 1.0 nm or less; and a total content of functional groups of 0.3 to 0.6 mmol / g.

• einer positiven Elektrode, die einen Positivelektroden-Stromsammler der positiven Elektrode und eine erste polarisierenden Elektrode, die auf dem Positivelektroden-Stromsammler der positiven Elektrode aufgebracht ist,
• wobei die erste polarisierende Elektrode das Kohlenstoffmaterial gemäß dem ersten Aspekt als Positivelektroden-Aktivmaterial enthält;
• einer negativen Elektrode mit einem Negativelektroden-Stromsammler und einer zweiten polarisierenden Elektrode, die auf dem Negativelektroden-Negativelektroden-Stromsammler angeordnet ist, wobei die zweite polarisierende Elektrode Negativelektroden-Aktivmaterial enthält, das Lithium-Ionen aufnehmen kann und abgeben kann und wobei die negative Elektrode ist so angeordnet, dass die zweite polarisierende Elektrode der ersten polarisierenden Elektrode gegenüberliegt;
• einem Separator, der zwischen der positiven Elektrode und der negativen Elektrode angeordnet ist; und
• einem nichtwässrigen Elektrolyt, der ein Lithiumsalz enthält und zwischen dem Stromsammler der positiven Elektrode und dem Negativelektroden-Stromsammler angeordnet ist.

According to a second aspect of the present invention, there is provided a lithium ion capacitor comprising:

• a positive electrode comprising a positive electrode positive electrode current collector and a first polarizing electrode mounted on the positive electrode positive electrode current collector;
• wherein the first polarizing electrode contains the carbon material according to the first aspect as the positive electrode active material;
• a negative electrode having a negative electrode current collector and a second polarizing electrode disposed on the negative electrode negative electrode current collector, the second polarizing electrode containing negative electrode active material capable of accepting and discharging lithium ions and being the negative electrode disposed so that the second polarizing electrode faces the first polarizing electrode;
• a separator disposed between the positive electrode and the negative electrode; and
• a nonaqueous electrolyte containing a lithium salt and disposed between the positive electrode current collector and the negative electrode current collector.

list of figures

• 1 Fig. 10 is a sectional view schematically showing a part of the lithium-ion capacitor according to the embodiment of the present invention.
• 2 Fig. 10 is a graph showing an example of pore distribution of the carbon material.
• 3 Fig. 12 is a graph showing an example of a relationship between the internal resistance and the pore volume for pores having diameters of 1.7 nm or more.
• 4 Fig. 10 is a graph showing an example of the relationship between the total content of functional groups and the capacity.
• 5 Fig. 10 is a graph showing an example of the relationship between the total pore volume and the internal resistance.

DETAILED DESCRIPTION

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

Before describing a lithium ion capacitor according to the embodiment of the present invention, a method for obtaining a pore distribution and a total content of functional groups will be explained.

The pore distribution is obtained by a BJH method (Barrett-Joyner-Halenda) used in "J. At the. Chem. Soc. (1951), 73, pp. 373-380 "And the like is described. Specifically, in a nitrogen gas atmosphere at 77.4 K (boiling temperature of nitrogen), the content (cm ³ / g) of nitrogen gas adsorbed by a carbon material is measured at each pressure P while the pressure P (mmHg) of the nitrogen gas is gradually increased. Assuming that dividing the pressure P (mmHg) by the saturated vapor pressure Po (mmHg) of the nitrogen gas gives the relative pressure P / P ₀ , the content of adsorbed nitrogen gas for each relative pressure P / P _{0 is} recorded to be an adsorption isotherm to obtain. After that, a pore distribution is obtained by the BJH method using this adsorption isotherm. The "pore volume" (to be explained later) is a value obtained from this pore distribution.

The total content of functional groups is obtained by a tritration method called the Bohem method (for the Bohem method, see, for example, "Fundamentals and applications of activated carbon" by The Carbon Society of Japan, published by Kondansha Ltd.). In particular, a sodium ethoxide solution is prepared at 0.1 mol / l. Subsequently, 20 ml of this solution and 2 g of a carbon material are placed in a flask. This dispersion liquid is centrifuged for three minutes at 2,000 rpm. This dispersion liquid is then stirred by means of ultrasound for 20 minutes. After that, the dispersion liquid is filtered and 5 ml of the filtrate are titrated with a hydrochloric acid solution. Based on the result of the titration, the necessary amount of a hydrochloric acid per unit mass of carbon material is obtained. The "total content of functional groups" is the amount of substance and corresponds to the total content of a phenolic hydroxyl group, a carboxyl group, a carboxyl group of the lactone type and a quinone group.

1 Fig. 10 is a sectional view schematically showing a part of the lithium-ion capacitor according to the embodiment of the present invention.

A lithium-ion capacitor 1 according to the embodiment of the present invention comprises a container (not shown). The container comprises, for example, a container base body with a hollow structure in which an opening is formed and a lid for closing the opening of the container base body. In one example, one part of the container plays the role of a positive electrode as an external terminal, and another part of the container plays the role of a negative electrode as an external terminal.

This container contains a positive electrode 2 , a negative electrode 3 , a separator 4 , a nonaqueous electrolyte 5 and the same.

The positive electrode 2 includes a positive electrode current collector 21 and a first polarizing electrode 22 ,

The positive electrode current collector 21 is for example a metal foil. The metal foil is made, for example, from an alloy or a single metal, for example aluminum.

The first polarizing electrode 22 covers at least one major surface of the positive electrode current collector 21 , The polarizing electrode 22 may only one main surface of the positive electrode current collector 21 or both major surfaces of the positive electrode current collector 21 cover. For example, the polarizing electrode covers 22 both major surfaces of the positive electrode current collector 21 ,

The polarizing electrode 22 includes a powdery and / or fibrous carbon material as a positive electrode active material 22a , The positive electrode active material 22a is a specific activated carbon. The positive electrode active material 22a will be described later in detail.

The polarizing electrode 22 may also contain other materials than the positive electrode active material 22a For example, a binder and a conductive agent include. As binder, so a material, the particles of the positive electrode active material 22a can bind to each other and in the nonaqueous electrolyte 5 insoluble, for example, a fluororesin such as polyvinylidene fluoride, polytetrafluoroethylene and polyvinyl fluoride, an alkali metal salt of carboxymethyl cellulose, an ammonium salt of carboxymethyl cellulose or an organic polymer such as polyimide resin, polyamide resin, polyacrylic acid and sodium polyacrylate can be used. For the Leitmittel can z. As a conductive powder can be used, which is made of a carbonaceous material such as acetylene black.

The mass ratio of positive electrode active material 22a to polarizing electrode 22 For example, it falls within the range of 70 to 90 percent by mass and is typically 80 percent by mass. When the mass ratio is reduced, it becomes difficult to achieve a high capacity. On the other hand, when the mass ratio is increased, it becomes difficult to achieve a low internal resistance or the mechanical strength of the polarizing electrode 22 may be lower.

The negative electrode 3 includes a negative electrode current collector 31 and a second polarizing electrode 32 ,

The negative electrode current collector 31 is for example a metal foil or a metal plate. The metal foil or metal plate is made of, for example, an alloy or a single metal such as copper.

The second polarizing electrode 32 covers at least one major surface of the negative electrode current collector 31 , The polarizing electrode 32 can only the main surface of the current collector of the negative electrode 31 or both major surfaces of the negative electrode current collector 31 cover. As an example, the polarizing electrode covers 32 both major surfaces of the negative electrode current collector 31 ,

The polarizing electrode 32 includes a powdery and / or fibrous negative electrode active material 32a , The negative electrode active material 32a is a material in which lithium ions can be taken up and from which lithium ions can be released, for example a carbon material such as amorphous carbon. Lithium ions are incorporated in the negative electrode active material 32a endowed or taken up in it.

The polarizing electrode 32 may be other materials than the negative electrode active material 32a include, for example, a binder and conductive agent. As the binder and the conductive agent, those for the polarizing electrode, respectively 22 described examples of binders and conductive agents are used.

The mass ratio of negative electrode active material 32a to polarizing electrode 22 For example, it falls within the range of 80 to 95 percent by mass and is typically 90 percent by mass. When the mass ratio is reduced, it becomes difficult to achieve a high capacity. On the other hand, when the mass ratio is increased, it becomes difficult to achieve a low internal resistance or the mechanical strength of the polarizing electrode 32 may be lower.

The separator 4 is a non-conductive layer through which the non-aqueous electrolyte permeates. The separator 4 is, for example, a paper, a woven fabric, a nonwoven fabric, a porous layer or a porous one Sheet. The separator 4 For example, it is made of glass, a synthetic resin such as polyethylene or polypropylene, or a natural polymer compound such as cellulose.

The positive electrode 2 and the negative electrode 3 are arranged so that the polarizing electrodes 22 and 32 lie opposite each other. The separator 4 is between the positive electrode 2 and the negative electrode 3 arranged. In one example, the positive electrode 2 and the negative electrode 3 received in the container in a state in which they are wound, so that the separator 4 is arranged in between. The positive electrode current collector 21 and the negative electrode current collector 31 are each connected as external terminals electrically connected to the positive electrode and the negative electrode.

The nonaqueous electrolyte 5 is between the positive electrode current collector 21 and the negative electrode current collector 31 inserted. The polarizing electrodes 22 and 32 are with the nonaqueous electrolyte 5 soaked.

The non-aqueous electrolyte is, for example, a liquid electrolyte, ie, an electrolyte solution. The nonaqueous electrolyte 5 may be a solid electrolyte.

The nonaqueous electrolyte 5 For example, it is obtained by dissolving a compound that can generate lithium ions in a proton-free organic solvent. An example of the compound is a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ). Examples of the proton-free organic solvent are propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, acetonitrile, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, or a derivative or mixtures thereof.

The positive electrode active material 22a will be described in detail next.

In order to reduce the internal resistance of the polarizing electrode with respect to the positive electrode of the lithium-ion capacitor, adsorption and release of electrolyte ions to and from the pores of the positive electrode active material are important. Conventionally, the movement of the electrolyte ions is accelerated by increasing the specific surface area or the pore volume of the positive electrode active material.

The inventors have found the following fact as a result of intensive study. This is that a pore having a pore diameter of 1.0 nm or less significantly affects the movement of the electrolyte ions. When a pore has a pore diameter of 1.7 nm or more, the size of the pore diameter hardly affects the movement of the electrolyte ions. The reason for this is assumed to be that the pore diameter is sufficiently larger than the size of the dissolved electrolyte ions. Therefore, it is advantageous to reduce the pore volume for pores having diameters of 1.0 nm or less and to increase the pore volume for pores having diameters of 1.7 nm or more. However, if the pore volume is excessively increased for pores having diameters of 1.7 nm or more, the capacity of the lithium ion capacitor per unit volume becomes small.

In this embodiment, the content of functional groups of the carbon material having the above pore distribution is adjusted to improve the ability of the carbon material to adsorb the electrolyte ions. However, because the functional group is bonded to the peripheral surface of the carbon crystallites, it is impossible to arbitrarily increase the content of functional groups. An excess content of functional groups reduces the size of the effective pore diameter. This means that an excess content of functional groups impairs the movement of the ions, which increases the internal resistance. In order to avoid this situation, an upper limit for the content of functional groups is set in this embodiment.

The as positive electrode active material 22a in the lithium-ion capacitor 1 used carbon material has a pore volume of 1.0 to 1.5 ml / g for pores with diameters of 1.7 nm or more. As described above, pores having pore diameters of 1.7 nm or more do not significantly affect the movement of the electrolyte ions. Therefore, by increasing the pore volume for pores having diameters of 1.7 nm or more, it is possible to reduce a resistance caused by the movement of the electrolyte ions. However, if the volume is excessively increased, the internal resistance hardly increases along with an increase in volume and the capacity decreases. The pore volume for pores having diameters of 1.7 nm or more is preferably 1.12 to 1.43 ml / g.

Furthermore, the carbon material has a pore volume equal to or less than 0.1 ml / g for pores having diameters of 1.0 nm or less. Pores with pore diameters of 1.0 nm or less contribute slightly to the adsorption of ions. That is, even if the pore volume is increased for pores having diameters of 1.0 nm or less, the capacity hardly increases. Pores with pore diameters of 1.0 nm or less affect the movement of the electrolyte ions. Therefore, when the pore volume is increased for pores having diameters of 1.0 nm or less, the internal resistance increases. Therefore, the volume is preferably small.

The carbon material has a total content of functional groups of 0.3 to 0.6 mmol / g. The functional group of the carbon material plays a role in improving the ion adsorption performance of the carbon material. Therefore, the total content of functional groups is preferably large. However, if the total content of functional groups is excessively increased, initial deterioration may be caused by disintegration of the functional group. In this case, the functional group may additionally affect the movement of the electrolyte ions. The total content of functional groups of the carbon material is preferably 0.33 to 0.56 mmol / g.

The carbon material has a total pore volume of, for example, 1.3 to 2.0 ml / g, preferably 1.5 to 2.0 ml / g. When the total pore volume is equal to or larger than 1.5 ml / g, the movement of the electrolyte ions is accelerated, whereby the internal resistance is reduced. However, if the total pore volume is excessively increased, the bulk density of the carbon material decreases, resulting in a small capacity of the lithium-ion capacitor 1 results.

In addition, the carbon material has a specific surface area obtained by using a BET adsorption isotherm (Brunauer-Emmet plate), for example, 2100 to 2500 m ² / g. As the specific surface area increases, the movement of the electrolyte ions is accelerated. However, if the specific surface is excessively increased, the bulk density of the carbon material decreases, resulting in a small capacity of the lithium-ion capacitor 1 results.

The carbon material has an average pore size of, for example, 2.6 to 3.3 nm, preferably 2.7 to 3.2 nm. If the average pore diameter is sufficiently large, the movement of the electrolytes ions is accelerated, whereby the internal resistance is reduced. However, if the average pore diameter is excessively increased, the capacity of the lithium ion capacitor 1 becomes small. It should be noted that the average pore diameter is a value (4 x V / SSA) obtained by multiplying a value by the factor 4 the value obtained by dividing the total pore volume V by a BET specific surface area SSA.

This carbon material preferably has a peak value of pore diameter of 1.7 nm or more. The peak value of the pore diameter indicates the pore diameter obtained when a derivative ΔV / ΔD of the total pore volume V to a pore diameter D has the maximum value in the pore distribution obtained by the method described above. When the maximum value of the pore diameter is sufficiently large, the movement of the electrolyte ions is accelerated, whereby the internal resistance is reduced. There is no upper limit to the maximum value of the pore diameter. However, if the maximum value of the pore diameter is excessively increased, the capacity of the lithium-ion capacitor becomes 1 small. Accordingly, the maximum value of the pore diameter is preferably equal to or less than 2 nm.

A carbon material that acts as a positive electrode active material 22a can be prepared, for example, by the following method.

First, a carbon material having the specified pore distribution is prepared. For example, a coconut shell activated carbon, which could also be called coconut shell carbide or coconut shell carbon material, is subjected to water vapor activation. The activation atmosphere, that is, the water vapor, for example, contains 2 to 5 vol. Sauersoff. This makes it possible to obtain a carbon material having a pore distribution satisfying the above-described conditions.

Next, this carbon material is treated with a chemical solution. An example of the chemical solution is an aqueous salt solution such as nitric acid aqueous solution or sulfuric acid aqueous solution.

In this method, for example, the pore volume for pores having diameters of 1.7 nm or more changes according to the oxygen concentration in the atmosphere in the activation process. In particular, when the steam activation is performed in an oxygen-free atmosphere, the pore volume becomes small for pores having diameters of 1.7 nm or more. Conversely, when the oxygen concentration in the atmosphere is increased, the pore volume becomes large for pores having diameters of 1.7 nm or more. By setting the oxygen concentration between 2 to 5% by volume, a carbon material is obtained whose pore distribution satisfies the conditions described above.

In addition, the pore volume for pores having diameters of 1.0 nm or less changes according to, for example, the temperature in the activation process. In particular, when the temperature is lowered, the pore volume becomes small for pores having diameters of 1.0 nm or less. Conversely, when the temperature is raised, the pore volume becomes large for pores having diameters of 1.0 nm or less.

The total content of functional groups of this carbon material varies according to, for example, the concentration of an acid used in processing with the chemical solution. More specifically, as the concentration of the acid is increased, the total content of functional groups becomes high. Conversely, as the concentration of the acid is reduced, the total content of functional groups becomes small. The concentration of the acid is, for example, 0.005 to 2 mol / l. It should be noted that the total content of functional groups can be lowered by performing a reduction treatment, for example, heating in an inert atmosphere.

The total pore volume changes, for example, according to the time in the activation process. In particular, when the time is shortened, the entire pore volume becomes small. Conversely, if the time is prolonged, the total pore volume becomes large.

EXAMPLES

Hereinafter, examples of the invention will be described.

<Preparation of sample S1>

A coconut shell activated carbon or coconut shell carbide was subjected to steam activation. More specifically, at the time of steam activation, the carbide was subjected to heating in a rotary kiln at 800 ° C for two hours. As an activation atmosphere, an atmosphere obtained by introducing 3% by volume of oxygen into the water vapor was used. Next, the carbon material was treated with 0.1 mol / L of a nitric acid aqueous solution and the functional group was transferred to the carbon material. After that, the carbon material was ground, whereby a powder having an average particle size of 5 μm was obtained. This powder is hereinafter referred to as "Sample S1".

<Preparation of Sample S2>

A powder of carbon material was obtained by the same method as that described for Sample S1, except that the concentration of the nitric acid aqueous solution was 0.5 mol / l. This powder is hereinafter referred to as "Sample S2".

<Preparation of sample S3>

A powder of carbon material was obtained by the same method as that described for Sample S1, except that the concentration of the nitric acid aqueous solution was 2 mol / l. This powder is hereinafter referred to as "sample S3".

<Preparation of Sample S4>

A powder of carbon material was obtained by the same method as that described for Sample S1, except that the heating time in steam activation 4 Hours was. This powder is hereinafter referred to as "sample S4".

<Preparation of Sample S5>

A powder of carbon material was obtained by the same method as that described for Sample S1, except that the concentration of the nitric acid aqueous solution was 3 mol / L. This powder is hereinafter referred to as "sample S5".

<Preparation of Sample S6>

A powder of carbon material was obtained by the same method as that described for Sample S1, except that the treatment with aqueous nitric acid solution was omitted. This powder is hereinafter referred to as "Sample S6".

<Preparation of Sample S7>

An equivalent weight carbon was subjected to alkali activation using 4 equivalent weights of potassium hydroxide. Specifically, the 4 equivalent weights of potassium hydroxide were added to an equivalent weight of powdered coal. After sufficiently mixing the mixture, the mixture was subjected to activation processing in a nitrogen atmosphere at 800 ° C for 8 hours. After that, the mixture was purified to remove potassium. Subsequently, the carbon material was ground, whereby a powder having an average particle size of 5 μm was obtained. This powder is hereinafter referred to as "Sample S7".

<Preparation of Sample S8>

A coconut shell activated carbon was subjected to steam activation. To be precise, the carbide was subjected to heating in a rotary kiln at 950 ° C for 4 hours. As an activation atmosphere, water vapor was used. The oxygen concentration of the water vapor is equal to or less than 1 vol.%. Next, the carbon material was ground, whereby a powder having an average particle size of 5 μm was obtained. This powder is hereinafter referred to as "sample S8".

<Preparation of Sample S9>

A coconut shell activated carbon was subjected to steam activation. To be specific, the steam activation was carried out by the same method as described for Sample S1, except that the heating time 6 Hours. Next, the carbon material was ground, whereby a powder having an average particle size of 5 μm was obtained. This powder is hereinafter referred to as "Sample S9".

<Preparation of Sample S10>

A powder of carbon material was obtained by the same method as described for Sample S1, except that the heating time for steam activation was 1 hour. This powder is hereinafter referred to as "Sample S10".

<Evaluation 1>

The specific surface area and pore distribution were measured for each of Samples S1 to S9. The measurement was carried out by the BJH method using a NOVA-3000 manufactured by Quantachrome. The results are shown in Table 1 below and in 2 summarized. [Table 1] example Capacity (F / ml) Internal resistance (Ω cm ² ) Pore volume (ml / g) Total content of functional groups (mmol / g) Specific surface area (m ² / g) Total pore volume (ml / g) Average pore diameter (nm) Maximum value of the pore diameter (nm) 1.7 nm or more 1.0 nm or less S1 73.2 6.1 1.12 0.03 0.33 2185 1.51 2.73 1.74 S2 73.8 5.9 1.12 0.03 0.37 2185 1.51 2.73 1.74 S3 73.4 5.8 1.12 0.03 0.56 2185 1.51 2.73 1.74 S4 70.9 6.1 1.43 0.06 0.38 2350 1.81 3.1 1.98 S5 70.3 8.2 1.12 0.03 0.71 2185 1.51 2.73 1.74 S6 68.3 6 1.12 0.03 0.18 2185 1.51 2.73 1.74 S7 60.8 9.3 1.01 0.16 0.31 3300 1.79 2.17 1.61 S8 71.3 7.8 0.54 0.1 0.35 2050 1.04 2.07 1.62 S9 63.7 6.2 1.52 0.06 0.32 2650 2.02 3.27 2.05 S10 64.9 7.2 1.07 0.05 0.36 2209 1.47 2.66 1.74

2 Fig. 12 is a graph showing an example of the pore distribution of the carbon material.

In 2 the abscissa represents the pore diameter and the ordinate represents the derivative ΔV / ΔD of the total pore volume V according to the pore diameter D. It should be noted that in 2 the derivative ΔV / ΔD is indicated as "ΔV / ΔlogD" because a logarithmic coordinate for the abscissa is used.

In 2 a curve C1 represents data obtained for the sample S1. A curve C2 represents data obtained for the sample S8.

As is clear from the comparison between the curves C1 and C2, the sample S1 has a large pore volume compared to the sample S8 for pores having diameters of 1.7 nm or more.

<Evaluation 2>

The sample S1 as the positive electrode material, the conductive agent and the binder were mixed in a mass ratio of 81.8: 9.1: 9.1. Cabot made carbon black VALCAN XC-72 was used as the conductive agent and polyvinylidene fluoride was used as the binder. A coating film of this mixture was formed by a coating method and pressed by a press roll machine. After that, the pressed coating film was punched into a disc shape having an area of 2 cm ² and then dried in a vacuum at 120 ° C for 12 hours.

This disk was used as a working electrode to assemble a three-pole button cell. A lithium foil was used as a counter electrode and as a reference electrode. As a non-aqueous electrolyte solution, a solution obtained by dissolving lithium hexafluorophosphate in a mixed liquid of ethylene carbonate and diethyl carbonate was used. The concentration of lithium hexafluorophosphate was 1 mol / l.

Additional 3-prong button cells were prepared by the same method except that Samples S2 through S9 were used instead of Sample S1.

Each of the three-pole button cells was charged to a voltage of 3 to 4.25 V with a constant current of 2 mA / cm ² and held at this voltage for five minutes. Thereafter, each of the three-pole button cells with a constant current of 2 mA / cm ^{2 was} discharged and the capacity and the Internal resistance per unit volume of the three-pole button cell was determined. The results are shown in Table 1 and in the above 3 and 4 summarized.

3 Fig. 12 is a graph showing an example of the relationship between the internal resistance and the pore volume for pores having a diameter of 1.7 nm or more. In 3 The abscissa represents the pore volume for pores having a diameter of 1.7 nm or more per unit mass of the positive electrode active material and the ordinate represents the internal resistance of the working electrode of the three-pole button cell. In the in 3 The graphs shown for the samples S2, S4, S8, S9 and S10, whose total contents of functional groups are nearly equal to each other, are plotted to determine the influence of the pore volume on pores having diameters of 1.7 nm or more on the internal resistance of the working electrode make clear.

4 Fig. 10 is a graph showing an example of the relationship between the total content of functional groups and the capacity. In 4 The abscissa represents the total content of functional groups per unit mass of the positive electrode active material, and the ordinate represents the capacity of the working electrode. In the in 4 The graphs shown in FIG. 1 show the data obtained for samples S1 to S3, S5 and S6, whose pore distributions are almost equal to each other in order to understand the influence of the total content of functional groups on the capacity.

5 Fig. 10 is a graph showing an example of the relationship between the total pore volume and the internal resistance. In 5 the abscissa represents the pore volume per unit mass of the positive electrode active material and the ordinate represents the internal resistance of the working electrode of the three-pole button cell. In the in 5 In the graphs shown, the data obtained for samples S2, S4, S8 and S10 whose total contents of functional groups are nearly equal to each other are plotted to make clear the influence of the entire pore volume on the internal resistance of the working electrode.

In the 3 The data shown indicate that if the pore volume for pores with diameters of 1.7 nm or more is about 1 to 1.5 ml / g, a low internal resistance can be achieved. In the 4 The data shown indicate that when the total content of functional groups is about 0.3 to 0.6 mmol / g, a large capacity can be achieved. In the 5 The data shown indicate that if the total pore volume is equal to or greater than 1.5 ml / g, a lower internal resistance can be achieved. When the data for sample S7 is compared with the data for samples S1 to S4 in Table 1, it turns out that when the pore volume for pores having diameters of 1.0 nm or less exceeds about 0.1 ml / g, the Internal resistance becomes large and the capacity becomes small.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2010192853 [0002]

Cited non-patent literature

• "J. At the. Chem. Soc. (1951), 73, pp. 373-380 [0010]

Claims (3)

A carbon material for a positive electrode active material of a lithium ion capacitor, wherein the carbon material comprises: a pore volume of 1.0 to 1.5 ml / g for pores having a diameter of 1.7 nm or more; a pore volume less than or equal to 0.1 ml / g for pores having a diameter of 1.0 nm or less; and a total content of functional groups of 0.3 to 0.6 mmol / g. Carbon material after Claim 1 wherein the carbon material has a total pore volume of 1.5 ml / g or more. A lithium ion capacitor comprising: a positive electrode having a positive electrode current collector and a first polarizing electrode mounted on the positive electrode current collector, the first polarizing electrode detecting the carbon material Claim 1 or 2 as positive electrode active material; a negative electrode having a negative electrode current collector and a second polarizing electrode mounted on the negative electrode current collector, the second polarizing electrode containing negative electrode active material capable of receiving and discharging lithium ions, and the negative electrode being arranged in that the second polarizing electrode faces the first polarizing electrode; a separator disposed between the positive electrode and the negative electrode; a nonaqueous electrolyte containing a lithium salt and disposed between the positive electrode current collector and the negative electrode current collector.

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