JP2019087590A - Pre-doping agent for lithium ion capacitor, positive electrode for lithium ion capacitor using pre-doping agent for lithium ion capacitor and lithium ion capacitor, manufacturing method for lithium ion capacitor, and pre-doping method for lithium ion capacitor - Google Patents

Abstract

To provide a pre-doping agent for lithium ion capacitor, capable of generating a lithium ion required for pre-doping by only normal charge operation (aging) without using a conventional metallic lithium foil.SOLUTION: The pre-doping agent for lithium ion capacitor according to the present invention includes a chemical compound expressed by LiTiO(1.5≤a≤4.5, 2.7≤b≤4.8) as its major component.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pre-doping agent used for a lithium ion capacitor (in particular, a lithium ion capacitor using graphite as a negative electrode active material). Specifically, by using lithium titanate having a specific composition as a main component, the lithium ion necessary for pre-doping is generated only by ordinary charging operation (aging) without using a conventional metal lithium foil. The present invention relates to a pre-doping agent capable of The present invention also relates to a pre-doping agent capable of reducing the volume (miniaturization, thinning) of a lithium ion capacitor.
Further, the present invention relates to a positive electrode for lithium ion capacitor, a lithium ion capacitor, a method for manufacturing a lithium ion capacitor, and a method for pre-doping a lithium ion capacitor using this pre-doping agent.

Lithium ion capacitors are characterized by having a high energy density compared to electric double layer capacitors, and have been put into practical use rapidly in recent years. One of the lithium ion capacitors is a graphite lithium ion capacitor using graphite as a negative electrode active material.
Such a graphite-based lithium ion capacitor has the advantage of being able to increase the voltage and energy density as compared to other lithium ion capacitors, while the graphite used for the negative electrode active material generates a potential difference with the positive electrode in the initial stage There is no lithium ion to
Therefore, the graphite-based lithium ion capacitor needs a treatment (operation) called pre-doping in which lithium ions are previously doped into graphite at the time of manufacture.

And as methods of this pre-doping, the following methods (1) to (3) are known at present.
(1) After bonding metal lithium foil as a lithium supply source to all the negative electrodes, a plurality of positive electrodes and negative electrodes are laminated to form an electrode, and then an electrolytic solution is injected and left to stand, thereby leaving lithium ions from metal lithium. A method of releasing (eluting) and doping lithium ion into the negative electrode active material (FIG. 4).

  (2) A metal lithium foil is disposed on the upper part of the electrode formed by laminating a plurality of positive electrodes and negative electrodes, and then the electrolytic solution is injected and left to allow lithium ions from metal lithium to be from above to below the electrode (negative electrode). A method called a so-called vertical pre-doping method (FIG. 5) in which the negative electrode active material of each negative electrode is released (eluted) and doped with lithium ions.

  (3) Using a metal foil with holes in the current collector and arranging a metal lithium foil at a fixed interval in an electrode in which a plurality of positive and negative electrodes are laminated, the electrolyte is poured and left to stand. The so-called horizontal pre-doping method (FIGS. 6 and 7) in which lithium ions are released (eluted) from lithium and doped into the negative electrode active material of each negative electrode through the holes of the metal foil.

However, the conventional pre-doping methods shown in (1) to (3) have the following problems.
First, since the method (1) requires a period of several days to several tens days until pre-doping is completed, there is a problem that it is not practical. Also, since the metallic lithium foil is as thin as about 30 μm, the volume of the lithium ion capacitor, which is the final product, will increase if the metallic lithium foils for the multiple negative electrodes are laminated. There is a problem that the volume energy density is lowered. Furthermore, when the pre-doping process is completed, most of the metal lithium foil becomes lithium ions and is eluted, so there is also a problem that a waste product is generated in the final product lithium ion capacitor.

  Next, the method (2) releases (elutes) lithium ions downward from above the electrode (negative electrode) to perform pre-doping, so the upper part of the negative electrode located in the vicinity of the metallic lithium foil is effective. Pre-doping will be performed, but if lithium ions do not sufficiently extend below the electrode (negative electrode), sufficient pre-doping will not be performed on the lower portion of the negative electrode which is separated from the metallic lithium foil, There is a problem that the pre-doping process can not be performed.

  Next, although the method (3) has the advantage of enabling uniform pre-doping compared to the method (2), it is necessary to arrange the perforated metal foil and the metal lithium foil at regular intervals. As a result, the volume of the lithium ion capacitor is increased, and as a result, the volume energy density is lowered. In addition, since it is necessary to allow lithium ions to pass all the way through, the accuracy of the holes formed in the metal foil is required, and as a result, there is a problem that the production of the metal foil is costly.

  Furthermore, since all of the above pre-doping methods (1) to (3) use metal lithium with no water capacity, equipment such as a dry room is required in producing a lithium ion capacitor, and the equipment becomes extensive. There is a problem. In addition, there is also a problem that the pre-doping process is terminated halfway and metal lithium remains in the lithium ion capacitor.

Therefore, in recent years, a pre-doping method not using metal lithium foil has been proposed (Patent Documents 1 and 2).
Specifically, in Patent Document 1, a lithium metal composite oxide having a specific composition is used as a pre-doping agent, and the pre-doping agent is mixed with a positive electrode active material and applied with a voltage for initial charge (aging). A technique for performing pre-doping is disclosed (refer to [claim 1], [claim 8], and [claim 11] to [claim 13] of Patent Document 1).
Patent Document 2 discloses a technique in which an organic sulfur compound having a specific composition is used as a pre-doping agent, and the pre-doping agent is mixed with an electrolytic solution or a positive electrode active material and pre-doping is performed by applying (aging) a voltage for initial charge. Are disclosed (see [claim 1], [claim 5], [claim 7], [claim 11] and [claim 12] of Patent Document 2). Moreover, the pre-doping agent described in Patent Document 2 describes that the M component (lithium or sodium) is released (eluted) as a metal ion, and then becomes an oxide to form a protective film on the positive electrode. (See [0024] and [0032] of Patent Document 2).

JP, 2016-12620, A JP, 2014-199723, A

  However, in the pre-doping agent of Patent Document 1, the voltage of the initial charge must be increased to 4.5 V (see [claim 11] and [claim 12] of Patent Document 1). There is a problem that the deterioration of the lithium ion capacitor is accelerated since the oxidative decomposition of the electrolyte starts when the voltage becomes 4.3 V or more.

  Moreover, although the pre-doping agent of Patent Document 2 can protect the positive electrode after the M component release (elution), the protective film becomes an element that increases the resistance when viewed from the entire lithium ion capacitor. There is a problem of

As a result of intensive studies conducted by the inventors of the present invention, it is found that operation with a normal charging voltage is carried out without using a conventional metallic lithium foil by mixing lithium titanate having a specific composition with the positive electrode active material. It has been found that lithium ions necessary for pre-doping can be generated only by (aging), and pre-doping can be performed.
In addition, it has been found that, by using such lithium titanate as a pre-doping agent, it is possible to reduce the volume (miniaturization, thin film formation) of a lithium ion capacitor.
Furthermore, it came to obtain the knowledge that the water removal in a lithium ion capacitor can be performed simultaneously with a pre-doping process.

The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a pre-doping agent used for a lithium ion capacitor (in particular, a lithium ion capacitor using graphite as a negative electrode active material). .
Another object of the present invention is to provide a lithium ion capacitor positive electrode and a lithium ion capacitor using this pre-doping agent, a method of manufacturing a lithium ion capacitor, and a method of pre-doping a lithium ion capacitor.

In order to achieve the above object, the pre-doping agent for a lithium ion capacitor according to claim 1 of the present invention comprises Li _a TiO _b (1.5 ≦ a ≦ 4.5, 2.7 ≦ b ≦ 4.8) It is characterized in that the compound represented is a main component.

The pre-doping agent for a lithium ion capacitor according to claim 2 of the present invention is a compound represented by Li _c TiO _d (1.5 ≦ c ≦ 2.3, 2.7 ≦ d ≦ 3.5) or Li _e TiO It is characterized in that at least one of the compounds represented by _f (3.5 ≦ e ≦ 4.5, 3.7 ≦ f ≦ 4.8) is a main component.

  The pre-doping agent for a lithium ion capacitor according to claim 3 of the present invention is characterized in that a part of Li is substituted by one or more elements selected from an alkali metal or an alkaline earth metal or hydrogen.

  The pre-doping agent for a lithium ion capacitor according to claim 4 of the present invention is characterized in that the alkali metal or the alkaline earth metal is any one of Na, K, Mg, Ca, Sr, and Ba.

  The positive electrode for a lithium ion capacitor according to claim 5 of the present invention is characterized in that the pre-doping agent for a lithium ion capacitor of the present invention is contained in a positive electrode active material.

  In the positive electrode for lithium ion capacitors according to claim 6 of the present invention, the content of the pre-doping agent for lithium ion capacitors is 1 to 60% by mass with respect to the total mass of the positive electrode active material and the pre-doping agent for lithium ion capacitors It is characterized by

  A lithium ion capacitor according to claim 7 of the present invention is characterized by comprising the pre-doping agent for a lithium ion capacitor according to the present invention, a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator, and an electrolytic solution. I assume.

  The lithium ion capacitor according to claim 8 of the present invention is characterized in that the negative electrode active material is at least one of a carbon-based material or a silicon-based material capable of storing lithium ions.

  The method for producing a lithium ion capacitor according to claim 9 of the present invention comprises a positive electrode using activated carbon as a positive electrode active material, a separator, a negative electrode using graphite as a negative electrode active material, and the pre-doping agent for lithium ion capacitor of the present invention It is characterized in that lithium ion is doped from the pre-doping agent for lithium ion capacitor to the negative electrode active material by providing an electrolyte and performing initial charging.

  The lithium ion capacitor pre-doping method according to claim 10 of the present invention comprises a positive electrode using activated carbon as a positive electrode active material, a separator, a negative electrode using graphite as a negative electrode active material, and the pre-doping agent for lithium ion capacitor of the present invention A method of pre-doping a lithium ion capacitor comprising an electrolytic solution, characterized in that lithium ion is doped from the pre-doping agent for lithium ion capacitor to the negative electrode active material by initial charging.

  The lithium ion capacitor pre-doping method according to claim 11 of the present invention is characterized in that the voltage in the first charge is 1.2 to 3.8 V.

  According to the pre-doping agent for lithium ion capacitors of the present invention, since lithium titanate having a specific composition is used as a main component, lithium ions necessary for pre-doping can be generated by ordinary charging operation (aging). Pre-doping can be performed without using a metallic lithium foil such as

Also, as shown in the following chemical reaction formula, a proton acts as a driving force by which lithium ions are released (eluted) from the lithium titanate, but in the case where water is present in the lithium ion capacitor, By consuming protons derived from moisture by the reaction, it is possible to remove moisture in the lithium ion capacitor simultaneously with the pre-doping process.
^{_{Li a TiO b + aH + →}} aLi + + H a TiO b
Li _c TiO _d + cH ⁺ → cLi ⁺ + H _c TiO _{d
^{Li e TiO f + eH + →}} eLi + + H e TiO f
Li _4-x M _x TiO ₄ + (4-x) H ⁺ → (4-x) Li ⁺ + H _4-x M _x TiO ₄
Li _2-y M _y TiO ₃ + (2-y) H ⁺ → (2-y) Li ⁺ + H _2-y M _y TiO ₃
In addition, the proton for releasing (eluting) lithium ion is not restricted to what originates in water. For example, compounds having a carboxyl group, compounds having an amino group, aromatic compounds and the like can be mentioned.

  Furthermore, among the negative electrode active materials used for the lithium ion capacitor, there is a material that causes a phenomenon that a part of lithium ions occluded at the time of initial charge is not released at the time of discharge, that is, a material having irreversible capacity. If a lithium ion capacitor is added to the positive electrode, the irreversible capacity can be compensated by the lithium ions supplied from the pre-doping agent even when such a negative electrode active material is used.

According to the positive electrode for lithium ion capacitor of the present invention and the lithium ion capacitor, since the pre-doping agent for lithium ion capacitor of the present invention is used, it is not necessary to use metal lithium foil or metal foil with holes. The volumetric energy density of the ion capacitor can be improved. In addition, the volume reduction (miniaturization, film thinning) of the lithium ion capacitor can be performed. Moreover, the problem of film formation to a positive electrode like patent document 2 can also be prevented.
Furthermore, since it is not necessary to use a metal lithium foil or a metal foil with holes, the manufacturing process of the lithium ion capacitor can be simplified, and the manufacturing cost can be reduced.

  According to the pre-doping agent for a lithium ion capacitor in accordance with the third and fourth aspects of the present invention, using various compositions derived from the basic structure (composition) by substituting a part of Li with a specific element Can.

  According to the positive electrode for a lithium ion capacitor according to claim 6 of the present invention, the content of the pre-doping agent for a lithium ion capacitor is in a specific range with respect to the total mass of the positive electrode active material and the pre-doping agent for a lithium ion capacitor Sufficient lithium ions can be supplied to the negative electrode active material.

  According to the lithium ion capacitor according to claim 8 of the present invention, since the carbon-based material and / or the silicon-based material capable of storing lithium ions is used as the negative electrode active material, lithium released (eluted) from the pre-doping agent Ions can be stored to increase the voltage of the lithium ion capacitor.

  According to the method of manufacturing a lithium ion capacitor according to the present invention, since the pre-doping agent for a lithium ion capacitor of the present invention is used, pre-doping can be performed only by performing a normal charging operation (aging). In addition, equipment such as a dry room, which is required in the manufacture of a lithium ion capacitor using a conventional metal lithium foil, becomes unnecessary, and the equipment can be simplified. Further, film formation on the positive electrode as in Patent Document 2 can be prevented, and an increase in the resistance of the entire lithium ion capacitor can be prevented.

  According to the method for pre-doping a lithium ion capacitor according to the present invention, pre-doping can be performed only by performing a normal charging operation (aging). Further, by setting the voltage at the time of pre-doping to a voltage in a specific range, it is possible to perform pre-doping without deteriorating the electrolytic solution.

The cross-sectional schematic diagram which compared the lithium ion capacitor using the pre-doping agent of this invention, and the lithium ion capacitor using the former pre-doping agent (FIG. 1 (a) is a cross-sectional schematic drawing of the lithium ion capacitor using the pre-doping agent of this invention Fig. 1 (b) is a cross-sectional schematic view of a lithium ion capacitor using a conventional pre-doping agent. It is a cross-sectional schematic diagram which shows one Embodiment of the lithium ion capacitor using the pre-doping agent of this invention. X-ray diffraction chart of the pre-doping agent of Example 1 and Example 2 (FIG. 3 (a) is an X-ray diffraction chart of the pre-doping agent of Example 1, and FIG. 3 (b) is an X-ray diffraction of the pre-doped agent of Example 2 Chart). It is a cross-sectional schematic diagram which shows the most basic conventional lithium ion capacitor which uses metal lithium foil. It is a cross-sectional schematic diagram which shows the lithium ion capacitor using the conventional pre dope method (vertical pre dope method). It is a cross-sectional schematic diagram which shows the lithium ion capacitor using the conventional pre-doping method (horizontal pre-doping method, the metal lithium foil which opened the hole). It is a cross-sectional schematic diagram which shows the lithium ion capacitor using the conventional pre dope method (When the number of lamination | stacking of an electrode is large by the horizontal pre dope method, the metal lithium foil which opened the hole is used).

(Basic structure)
The pre-doping agent of the present invention is mainly composed of a compound represented by the composition formula (basic structure) represented by Li _a TiO _b (1.5 ≦ a ≦ 4.5, 2.7 ≦ b ≦ 4.8) It is characterized by Thus, according to the present invention, by using lithium titanate having a specific composition as a pre-doping agent, lithium ion necessary for pre-doping only by ordinary charging operation (aging) without using a conventional metal lithium foil. Can be generated. Moreover, volume reduction (miniaturization, thin film formation) of a lithium ion capacitor can be performed by using as such a pre-doping agent.

And among the lithium titanates having the above composition formula, a compound represented by Li _c TiO _d (1.5 ≦ c ≦ 2.3, 2.7 ≦ d ≦ 3.5) (so-called 213-type titanium) Lithium acid, or a compound represented by Li _e TiO _f (3.5 ≦ e ≦ 4.5, 3.7 ≦ f ≦ 4.8) (so-called 414-type lithium titanate) as a main component It is preferable that Specifically, in the X-ray diffraction peak, lithium titanate of type 414 has a strongest peak (= peak of relative intensity 100%) in the region of 2θ = 43.7 ± 0.3 °, and is typically other The peak is in the region of 2θ = 33.1 ± 0.3 °. In addition, lithium titanate type 213 has a strongest peak (= peak having a relative intensity of 100%) in a region of 2θ = 18.5 ± 0.3 °, and a typical other peak is 20.7 ± 1.0. In the region of ° Therefore, the pre-doping agent of the present invention is mainly composed of a compound having a peak at any of 2θ = 18.5 ± 0.3 ° and 43.7 ± 0.3 ° in these regions. preferable.

The pre-doping agent of the present invention is, as shown in the above composition formula, only the basic composition (Li ₄ TiO ₄ ) of lithium titanate of 414 type and the basic composition (Li ₂ TiO ₃ ) of lithium titanate of 213 type. However, even if the composition ratio of lithium and oxygen is slightly increased or decreased from the composition ratio of the above basic composition, the technical effect of the present invention is exhibited. Specifically, taking the example to be described later as an example, in addition to lithium titanate having a basic composition of 414 type (Example 1) and lithium titanate having a basic composition of 213 type (Example 2), the above basic composition The lithium titanate (Examples 32 to 35) and the like, which slightly increase and decrease from the composition ratio of the above, also exhibit the technical effects of the present invention.

Further, among these, compounds having a compound represented by Li _e TiO _f (3.5 ≦ e ≦ 4.5, 3.7 ≦ f ≦ 4.8) (so-called 414-type lithium titanate) as a main component Is preferred. This is because the higher the molar ratio of Li, the higher the pre-doping effect.

In the present invention, "having as the main component" means that a Li compound or a Ti compound other than the compound represented by the composition of Li / Ti (molar ratio) may be present. As such Li compounds and Ti compounds, for example, LiOH, Li ₂ CO ₃ , TiO _{2 and the} like present on the surface can be mentioned.
Moreover, although Li / Ti (molar ratio) in the present invention is in the range of 1.5 to 4.5, it may be possible to have a compound having a composition different from the compound represented by the above composition formula. It is also the meaning of
Specifically, the content (purity) of the compound having the composition represented by the above basic structure is 65% or more, more preferably 78% or more, and most preferably 86% or more. Regarding the content (purity), the intensities of the X-ray diffraction peaks of the 414 type or 213 type lithium titanate and the impurities such as Li ₄ Ti ₅ O ₁₂ , TiO ₂ and Li ₂ CO _{3 described above.} It will be calculated from the ratio. When the content of impurities is small (when the content is several percent or less) or when the impurity is an amorphous impurity phase, in addition to the X-ray diffraction peak ratio, Raman spectroscopy or photoelectron spectroscopy is performed. Calculated from the intensity ratio of the peak of the type 414 or 213 lithium titanate and the peak of the impurity. In addition, about the pre-doping agent of the Example mentioned later, since it produces paying attention so that an impurity does not exist, a content rate (purity) will be about 100% (99 to 99.5% correctly). ing.

Since the pre-doping agent of the present invention is contained and used in the positive electrode active material of a lithium ion capacitor as described later, when the particle diameter of the pre-doping agent is large, the smoothness of the produced positive electrode is deteriorated, and micro shorts and lithium There is a problem of causing deterioration of the ion capacitor.
Therefore, the particle diameter of the pre-doping agent of the present invention is essentially smaller than the film thickness of the positive electrode, and specifically, it is preferably 100 to 1 μm, more preferably 30 to 1 μm, and 10 Most preferably, it is -2.5 μm.

In addition, when the powder resistance of the pre-doping agent is high, there is a problem that the resistance of the lithium ion capacitor becomes high and the rapid charge and discharge performance is deteriorated.
Therefore, the powder resistance of the pre-doping agent of the present invention is preferably less than 1.0 × 10 ⁷ Ω · cm.
The powder resistance can also be reduced to less than 1.0 × 10 ⁷ Ω · cm by coating and / or mixing the carbonaceous material with the pre-doping agent of the present invention.

(Alkali metal, alkaline earth metal, hydrogen)
The pre-doping agent of the present invention can also replace part of Li with another element. And as an element used for such substitution, one or more elements chosen from an alkali metal, an alkaline earth metal, and hydrogen can be mentioned. Specifically, in the case of lithium titanate of type 414, mention is made of a compound represented by Li _4-x M _x TiO ₄ (M is an alkali metal or alkaline earth metal or hydrogen, 0 <x <4). In the case of lithium titanate of type 213, a compound represented by Li _{2 -yM y} TiO ₃ (M is an alkali metal or alkaline earth metal or hydrogen, 0 <y <2) can be mentioned.
From the viewpoint of safety and cost, Na, K, Mg, Ca, Sr, and Ba are preferably used as the alkali metal and the alkaline earth metal.

(Positive electrode for lithium ion capacitor, lithium ion capacitor, pre-doping method)
The technical effect of the pre-doping agent of the present invention can be exhibited by containing it in the positive electrode active material of the lithium ion capacitor, particularly by containing it in the positive electrode active material of the lithium ion capacitor using graphite as the negative electrode active material. .
Specifically, the positive electrode 3 having the positive electrode active material 2 containing the pre-doping agent 1 of the present invention, the negative electrode 5 having the negative electrode active material 4 (especially graphite), the separator 6 and the terminal 7 are shown in FIG. The lithium ion capacitor is manufactured by stacking and housing in the housing 8 as shown in Fig. 7) and injecting the electrolyte solution 9 into the housing 8, and then lithium ion ion is performed by initial charge (pre-doping process). The capacitor is ready for use.
On the other hand, as shown in FIG. 1 (b) and FIGS. 4 to 7, the conventional lithium ion capacitor has a metal lithium foil 10, a metal foil (copper foil) 11 with a hole, and a metal foil with a hole (Aluminum foil) 12 is required. That is, after melting by pre-doping, the metal lithium foil 10 has a space corresponding to that, and as a result, the volume energy density of the conventional lithium ion capacitor decreases. Also, for the metal foil (copper foil) 11 with holes and the metal foil (aluminum foil) 12 with holes, the process of making holes is complicated, making the manufacturing process complicated and complicated, and the manufacturing cost Too high.
Therefore, since the pre-doping agent of the present invention does not use metal lithium foil or metal foil with holes as in the prior art, it is possible to improve the volume energy density of the lithium ion capacitor and reduce the lithium ion capacitor. Packaging (miniaturization, thinning) can be performed.
In addition, about the form which contains the pre-doping agent of this invention in the positive electrode active material of a lithium ion capacitor, the form mixed with a positive electrode active material, the form supported on the surface of a positive electrode active material, a positive electrode active material, a conductive support agent etc. Various forms, such as a form which applies the pre-doping agent of the present invention on the surface of the electrode concerned after it mixes and makes shape of an electrode (positive electrode), can be adopted.

In addition, when the pre-doping agent of the present invention is contained in the positive electrode active material and subjected to initial charging (aging), lithium titanate which is the pre-doping agent of the present invention is as shown below with protons caused by water etc. in lithium ion capacitors. Will cause a positive reaction.
^{_{Li a TiO b + aH + →}} aLi + + H a TiO b
Li _c TiO _d + cH ⁺ → cLi ⁺ + H _c TiO _{d
^{Li e TiO f + eH + →}} eLi + + H e TiO f
Li _4-x M _x TiO ₄ + (4-x) H ⁺ → (4-x) Li ⁺ + H _4-x M _x TiO ₄
Li _2-y M _y TiO ₃ + (2-y) H ⁺ → (2-y) Li ⁺ + H _2-y M _y TiO ₃
Then, lithium ions (Li ⁺ ) generated by the reaction move in the capacitor, and finally remain in the negative electrode active material such as graphite, whereby the doping is completed. In addition, since the reaction shown above occurs, water removal in the lithium ion capacitor can be performed simultaneously with the pre-doping process.
The proton for generating lithium ion (Li ⁺ ) is not limited to one derived from water. For example, compounds having a carboxyl group, compounds having an amino group, aromatic compounds and the like can be mentioned. More specific examples include stearic acid, benzoic acid, methyl benzoate, succinic acid, succinimide, amino acid, vinylene carbonate, dialkyl pyrocarbonate and the like, but the characteristics of carboxyl group, amino group and aromatic compound If it has, it is not limited to these.

Also, for the pre-doping agent of the present invention, the voltage applied in the pre-doping can be a conventional voltage referred to as aging. Specifically, for the pre-doping agent of the present invention, the above reaction is caused even when the voltage is as low as 1.2 V to 3.8 V as in the normal charging operation (lithium ion (Li ⁺ ) Can be generated and pre-doping can be performed.
Therefore, the pre-doping agent of the present invention can perform pre-doping simultaneously with the initial charge. Further, unlike the conventional pre-doping agent (pre-doping agent of Patent Document 1), since it is not necessary to apply a high voltage (4.5 V), it is possible to perform pre-doping without deteriorating the electrolytic solution such as oxidative decomposition of the electrolytic solution. become.

  The content of the pre-doping agent of the present invention is not particularly limited, but it is preferably 1 to 60 mass% with respect to the total mass of the positive electrode active material and the pre-doping agent, and among them, 5 to 46 It is more preferable to set it as mass%, and it is further more preferable to set it as 10-30 mass% also in it.

  When the pre-doping agent of the present invention is used in a lithium ion capacitor (included in the positive electrode active material of a lithium ion capacitor), at least one of a carbonaceous material and a silicon material capable of storing lithium ions in the negative electrode active material. It is preferable to use Examples of such carbon-based or silicon-based materials include graphite, soft carbon, hard carbon, acetylene black, ketjen black, carbon nanotubes, graphene, silicon, silicon monoxide and the like.

(Method of producing pre-doping agent)
The method for producing a pre-doping agent of the present invention is a method of preparing a compound represented by a composition formula (basic structure) represented by Li _a TiO _b (1.5 ≦ a ≦ 4.5, 2.7 ≦ b ≦ 4.8) with high purity And from the point of being easily obtained, it is preferable to manufacture by firing once with the temperature at firing being in the range of 550 to 950 ° C., among which the temperature at firing is in the range of 750 to 900 ° C. It is preferable to manufacture by baking for 1 to 3 hours (one baking) as 800-850 degreeC most preferably.

(Method of manufacturing lithium ion capacitor)
The method for producing a lithium ion capacitor according to the present invention comprises a positive electrode using activated carbon as a positive electrode active material, a separator, a negative electrode using graphite as a negative electrode active material, a pre-doping agent according to the present invention, and an electrolyte. To prepare a negative electrode active material from the pre-doping agent of the present invention by doping lithium ions.

  Next, the present invention will be described in detail based on Examples, Comparative Examples, Preparation Examples, and Comparative Preparation Examples. The present invention is not limited to the following examples.

Example 1 Synthesis of Li ₄ TiO ₄
First, titanyl sulfate (made by Taika TM crystal) was dissolved in water to prepare a 300 g / L aqueous solution.
Next, ortho-titanic acid was precipitated by neutralizing the prepared aqueous solution to pH 7.5 with aqueous ammonia at a concentration of 28 mass%.
Next, the prepared orthotitanic acid is filtered and washed, and then made into a slurry using water, and lithium carbonate (manufactured by FMC) is made to have a Li / Ti (molar ratio) of 4.0 / 1.0. The mixture was adjusted to and mixed to make a mixture.
Next, a powder was produced by drying the produced mixed liquid using a spray drier.
Finally, 825 ° C. The powder was produced in the atmosphere, Puridopu agent of Example 1 by calcining for 2 hours (the composition _formula: Li ₄ TiO 4) were produced.

Example 2 Synthesis of Li ₂ TiO ₃
A pre-doping agent (composition formula: Li ₂ TiO ₃ ) of Example 2 was produced in the same manner as Example 1 except that Li / Ti (molar ratio) was adjusted to be 2.0 / 1.0.

(Example 3: Synthesis of Li ₂ TiO ₃ low temperature calcined product)
A pre-doping agent (composition formula: Li ₂ TiO ₃ , low-temperature fired product of Example 2) of Example ₃ was produced in the same manner as Example 2 except that the baking temperature was 550 ° C.

Example 4 Synthesis of Li _3.8 Na _0.2 TiO ₄
First, titanyl sulfate (made by Taika TM crystal) was dissolved in water to prepare a 300 g / L aqueous solution.
Next, ortho-titanic acid was precipitated by neutralizing the prepared aqueous solution to pH 7.5 with aqueous ammonia at a concentration of 28 mass%.
Next, the prepared orthotitanic acid is filtered and washed, and then made into a slurry using water, to which lithium carbonate (manufactured by FMC) and sodium carbonate (manufactured by Sigma Aldrich) are Li / Na / Ti (molar ratio) A mixture was prepared by mixing and adjusting to 3.8 / 0.2 / 1.0.
Next, a powder was produced by drying the produced mixed liquid using a spray drier.
Finally, the pre-doping agent (Li _3.8 Na _0.2 TiO ₄ ) of Example 4 was produced by baking the produced powder in air at 825 ° C. for 2 hours.

Example 5 Synthesis of Li _3.8 K _0.2 TiO ₄
A pre-doping agent (Li _3.8 K _0.2 TiO ₄ ) of Example 5 was produced in the same manner as in Example 4 except that potassium carbonate (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 6: Synthesis of Li _3.8 H _0.2 TiO ₄
Example 6 is obtained by immersing 410 g of the pre-doping agent (Li ₄ TiO ₄ ) of Example 1 in 142.9 ml of 0.1 mol / L HCl aqueous solution and holding for 12 hours with stirring, followed by filtration, washing and drying. Pre-doping agent (Li _3.8 H _0.2 TiO ₄ ) was prepared.

Example 7 Synthesis of Li _3.8 Mg _0.2 TiO ₄
A pre-doping agent (Li _3.8 Mg _0.2 TiO ₄ ) of Example 7 was produced in the same manner as in Example 4 except that magnesium carbonate (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 8 Synthesis of Li _3.8 Ca _0.2 TiO ₄
A pre-doping agent (Li _3.8 Ca _0.2 TiO ₄ ) of Example 8 was produced in the same manner as in Example 4 except that calcium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 9 Synthesis of Li _3.8 Sr _0.2 TiO ₄
A pre-doping agent (Li _3.8 Sr _0.2 TiO ₄ ) of Example 9 was produced in the same manner as in Example 4 except that strontium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 10 Synthesis of Li _3.8 Ba _0.2 TiO ₄
A pre-doping agent (Li _3.8 Ba _0.2 TiO ₄ ) of Example 10 was produced in the same manner as in Example 4 except that barium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 11 Synthesis of Li _1.6 Na _2.4 TiO ₄
A pre-doping agent (Li _1.6 Na ₂ ) of Example 11 was prepared in the same manner as Example 4, except that Li / Na / Ti (molar ratio) was adjusted to be 1.6 / 2.4 / 1.0. _.4 TiO ₄ ) was prepared.

Example 12 Synthesis of Li _1.6 K _2.4 TiO ₄
A pre-doping agent (Li _1.6 K _2.4 TiO ₄ ) of Example 12 was produced in the same manner as in Example 11 except that potassium carbonate (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 13 Synthesis of Li _1.6 H _2.4 TiO ₄
Example 13 is obtained by immersing 410 g of the pre-doping agent (Li ₄ TiO ₄ ) of Example 1 in 1.71 L of 0.1 mol / L HCl aqueous solution and holding for 12 hours with stirring, followed by filtration, washing and drying. Pre-doping agent (Li _1.6 H _2.4 TiO ₄ ) was prepared.

(Synthesis of _{Li 1.6 Mg} 2.4 TiO ₄ Example ₁₄₎
A pre-doping agent (Li _1.6 Mg _2.4 TiO ₄ ) of Example 14 was produced in the same manner as in Example 11 except that magnesium carbonate (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

(Synthesis of _{Li 1.6 Ca} 2.4 TiO ₄ Example ₁₅₎
A pre-doping agent (Li _1.6 Ca _2.4 TiO ₄ ) of Example 15 was produced in the same manner as in Example 11 except that calcium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 16 Synthesis of Li _1.6 Sr _2.4 TiO ₄
A pre-doping agent (Li _1.6 Sr _2.4 TiO ₄ ) of Example 16 was produced in the same manner as in Example 11 except that strontium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 17 Synthesis of Li _1.6 Ba _2.4 TiO ₄
A pre-doping agent (Li _1.6 Ba _2.4 TiO ₄ ) of Example 17 was produced in the same manner as in Example 11 except that barium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 18 Synthesis of Li _1.9 Na _0.1 TiO ₃
A pre-doping agent (Li _1.9 Na _{0 of} Example 18) was prepared in the same manner as in Example 4 except that Li / Na / Ti (molar ratio) was adjusted to 1.9 / 0.1 / 1.0. _.1 TiO ₃ ) was prepared.

Example 19 Synthesis of Li _1.9 K _0.1 TiO ₃
A pre-doping agent (Li _1.9 K _0.1 TiO ₃ ) of Example 19 was produced in the same manner as in Example 18 except that potassium carbonate (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

(Synthesis of _{Li 1.9} H 0.1 TiO ₃ Example ₂₀₎
Example 20 is obtained by immersing 310 g of the pre-doping agent (Li ₂ TiO ₃ ) of Example 2 in 90.9 ml of 0.1 mol / L HCl aqueous solution and holding with stirring for 12 hours, followed by filtration, washing and drying. Pre-doping agent (Li _1.9 H _0.1 TiO ₃ ) was prepared.

(Synthesis of _{Li 1.9 Mg} 0.1 TiO ₃ Example ₂₁₎
A pre-doping agent (Li _1.9 Mg _0.1 TiO ₃ ) of Example 21 was produced in the same manner as in Example 18 except that magnesium carbonate (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

(Synthesis of _{Li 1.9 Ca} 0.1 TiO ₃ Example ₂₂₎
A pre-doping agent (Li _1.9 Ca _0.1 TiO ₃ ) of Example 22 was produced in the same manner as in Example 18 except that calcium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 23 Synthesis of Li _1.9 Sr _0.1 TiO ₃
A pre-doping agent (Li _1.9 Sr _0.1 TiO ₃ ) of Example 23 was produced in the same manner as in Example 18 except that strontium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

(Synthesis of _{Li 1.9 Ba} 0.1 TiO ₃ Example ₂₄₎
A pre-doping agent (Li _1.9 Ba _0.1 TiO ₃ ) of Example 24 was produced in the same manner as in Example 18 except that barium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 25 Synthesis of Li _1.2 Na _0.8 TiO ₃
A pre-doping agent (Li _1.2 Na ₀ ) of Example 25 was prepared in the same manner as Example 4, except that Li / Na / Ti (molar ratio) was adjusted to 1.2 / 0.8 / 1.0. _.8 TiO ₃ ) was prepared.

Example 26 Synthesis of Li _1.2 K _0.8 TiO ₃
A pre-doping agent (Li _1.2 K _0.8 TiO ₃ ) of Example 26 was produced in the same manner as in Example 25 except that potassium carbonate (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 27 Synthesis of Li _1.2 H _0.8 TiO ₃
Example 27 is obtained by immersing 310 g of the pre-doping agent (Li ₂ TiO ₃ ) of Example 2 in 727.3 ml of 0.1 mol / L HCl aqueous solution and holding with stirring for 12 hours, followed by filtration, washing and drying. Pre-doping agent (Li _1.2 H _0.8 TiO ₃ ) was prepared.

(Example 28: Synthesis of Li _1.2 Mg _0.8 TiO ₃ )
A pre-doping agent (Li _1.2 Mg _0.8 TiO ₃ ) of Example 28 was produced in the same manner as in Example 25 except that magnesium carbonate (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

(Synthesis of _{Li 1.2 Ca} 0.8 TiO ₃ Example ₂₉₎
A pre-doping agent (Li _1.2 Ca _0.8 TiO ₃ ) of Example 29 was produced in the same manner as in Example 25 except that calcium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

(Example 30: Synthesis of Li _1.2 Sr _0.8 TiO ₃ )
A pre-doping agent (Li _1.2 Sr _0.8 TiO ₃ ) of Example 30 was produced in the same manner as in Example 25 except that strontium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 31 Synthesis of Li _1.2 Ba _0.8 TiO ₃
A pre-doping agent (Li _1.2 Ba _0.8 TiO ₃ ) of Example 31 was produced in the same manner as in Example 25 except that barium hydroxide (manufactured by Sigma Aldrich) was used instead of sodium carbonate.

Example 32 Synthesis of Li _4.5 TiO _4.8
A pre-doping agent (Li _4.5 TiO _4.8 ) of Example 32 was produced in the same manner as in Example 1 except that Li / Ti (molar ratio) was adjusted to 4.5 / 1.0. .

Example 33 Synthesis of Li _3.5 TiO _3.7
A pre-doping agent (Li _3.5 TiO _3.7 ) of Example 33 was produced in the same manner as in Example 1 except that Li / Ti (molar ratio) was adjusted to 3.5 / 1.0. .

(Example 34: Synthesis of Li _2.3 TiO _3.5 )
A pre-doping agent (Li _2.3 TiO _3.5 ) of Example 34 was produced in the same manner as in Example 1 except that Li / Ti (molar ratio) was adjusted to 2.3 / 1.0. .

(Example 35: Synthesis of Li _1.5 TiO _2.7 )
A pre-doping agent (Li _1.5 TiO _2.7 ) of Example 35 was produced in the same manner as in Example 1 except that Li / Ti (molar ratio) was adjusted to 1.5 / 1.0. .

Comparative Example 1: Synthesis of LiTi ₂ O ₄
First, titanyl sulfate (made by Taika TM crystal) was dissolved in water to prepare a 300 g / L aqueous solution.
Next, ortho-titanic acid was precipitated by neutralizing the prepared aqueous solution to pH 7.5 with aqueous ammonia at a concentration of 28 mass%.
Next, the prepared orthotitanic acid is filtered and washed, and then made into a slurry using water, and lithium carbonate (manufactured by FMC) is made to have a Li / Ti (molar ratio) of 0.5 / 1.0. The mixture was adjusted to and mixed to make a mixture.
Next, a powder was produced by drying the produced mixed liquid using a spray drier.
Finally, the pre-doping agent (composition formula: LiTi ₂ O ₄ ) of Comparative Example 1 was produced by baking the produced powder in a reducing atmosphere (10% hydrogen, 90% nitrogen) for 2 hours at 950 ° C.

Comparative Example 2: Synthesis of Li ₄ Ti ₅ O ₁₂
Comparative Example 2 in the same manner as Comparative Example 1 except that Li / Ti (molar ratio) was adjusted to be 0.8 / 1.0, and the produced powder was fired in the air at 750 ° C. for 2 hours. Pre-doping agent (Li ₄ Ti ₅ O ₁₂ ) was prepared.

Comparative Example 3: Synthesis of H ₄ TiO ₄
Comparative Example 2 was obtained by immersing 10 g of the pre-doping agent (Li ₄ TiO ₄ ) of Example 1 in 2.86 L of a 0.1 mol / L aqueous HCl solution and holding for 12 hours with stirring, followed by filtration, washing and drying. Pre-doping agent (H ₄ TiO ₄ ) was prepared.

Comparative Example 4 Synthesis of H ₂ TiO ₃
Comparative Example 3 is obtained by immersing 10 g of the pre-doping agent (Li ₂ TiO ₃ ) of Example 2 in 1.82 L of 0.1 mol / L HCl aqueous solution and holding for 12 hours with stirring, followed by filtration, washing and drying. Pre-doping agent (H ₂ TiO ₃ ) was prepared.

Comparative Example 5 Synthesis of Li ₆ MnO ₄
First, manganese sulfate (manufactured by Hayashi Pure Chemical Industries, Ltd.) was dissolved in water to prepare a 300 g / L aqueous solution.
Next, manganese hydroxide was deposited by neutralizing the prepared aqueous solution to pH 7.5 with ammonia water at a concentration of 28 mass%.
Next, the prepared manganese hydroxide is filtered and washed, and then made into a slurry using water, and lithium carbonate (manufactured by FMC) is made to have a Li / Mn (molar ratio) of 6.0 / 1.0. The mixture was adjusted to and mixed to make a mixture.
Next, a powder was produced by drying the produced mixed liquid using a spray drier.
Finally, 875 ° C. The powder was produced in the atmosphere, Puridopu agent of Comparative Example 5 by calcining for 2 hours (the composition _formula: Li 6 MnO ₄₎ was prepared.

Comparative Example 6: Synthesis of Li ₅ AlO ₄
First, weigh aluminum hydroxide (manufactured by Sigma Aldrich) and lithium hydroxide (manufactured by FMC) so that Li / Al (molar ratio) becomes 5.0 / 1.0, and add to water and mix. Thus, a mixture was prepared.
Next, a powder was produced by drying the produced mixed liquid using a spray drier.
Finally, the pre-doping agent (composition formula: Li ₅ AlO ₄ ) of Comparative Example 6 was produced by baking the produced powder in the air at 925 ° C. for 2 hours.

(Measurement of specific surface area)
Next, the specific surface area of the pre-doping agent of each example and each comparative example was measured using a nitrogen adsorption measuring device (manufactured by Mountech Co., Ltd.). The results are shown in Table 1 below.
As a result, in all of the examples other than Example 3 (low-temperature baked product), lithium titanate was small in specific surface area, and it was confirmed that there was no problem in functional expression as a pre-doping agent. Moreover, also about the pre-doping agent of Example 3, the specific surface area was 30 m < ² > / g, and it has confirmed that it was a level which is not trouble as a pre-doping agent.

(Measurement of particle size)
Next, the particle diameter of the pre-doping agent of each of the examples and the comparative examples was measured using a laser diffraction scattering measurement apparatus (manufactured by Nikkiso Co., Ltd.). At this time, water was used as a dispersion medium, and dispersion was performed for 30 seconds with ultrasonic waves, and used as a measurement sample. The results are shown in Table 1 below.
As a result, in Examples 1 to 35, the particle sizes were all 10 μm or less, which was a level that did not adversely affect the smoothness of the electrode. On the other hand, in Comparative Example 6, since the particle diameter was larger than 100 μm, the smoothness of the electrode was deteriorated, and the characteristics of the lithium ion capacitor were also adversely affected.

(Measurement of powder resistance)
Next, after compressing the pre-doping agent of each Example and each comparative example by force of 10 kN, the powder resistance was measured using the powder resistance measuring system (made by Mitsubishi Chemical Analytech Co., Ltd.). The results are shown in Table 1 below.
As a result, in all of Examples 1 to 35, the powder resistance was less than 1.0 × 10 ⁷ Ω · cm, which was a level that did not adversely affect the characteristics of the lithium ion capacitor. On the other hand, in all of Comparative Examples 1 to 6, the powder resistance exceeds 1.0 × 10 ⁷ Ω · cm, which is a level that adversely affects the characteristics of the lithium ion capacitor.

(X-ray diffraction analysis)
X-ray diffraction analysis was performed on the pre-doping agents of Example 1 and Example 2. The results are shown in FIG.
As a result, it was confirmed that there is a peak (indicated by ★ in FIG. 3) due to lithium titanate for any pre-doping agent. Specifically, for the pre-doping agent of Example 1, the strongest peak (= peak with 100% relative intensity) attributed to lithium titanate of type 414 is in the region of 2θ = 43.7 ± 0.3 °, It was confirmed that a typical other peak is in the region of 33.1 ± 0.3 °. In the pre-doping agent of Example 2, the strongest peak (= 100% relative intensity peak) attributed to lithium titanate of type 213 is in the region of 2θ = 18.5 ± 0.3 °, and the other peaks are 20.7. It could be confirmed that it was in the range of ± 1.0 °.

(Preparation of lithium ion capacitor and pre-doping process)
Next, a lithium ion capacitor was produced using the pre-doping agent of the produced example and comparative example, and pre-doping was performed.

(Preparation Example 1)

(Production of positive electrode)
First, using activated carbon (YP-50F made by Kuraray) as a positive electrode active material, the pre-doping agent (Li ₄ TiO ₄ ) of Example 1 as a pre-doping agent, and acetylene black (Denka black manufactured by Denki Kagaku Kogyo Co., Ltd.) The resultant was added to a polyvinylidene fluoride solution (KF Co., Ltd. KF polymer # 7208) as a binder, and was kneaded using a planetary mixer.
The content of the pre-doping agent at this time was adjusted to 5% with respect to the total mass of the positive electrode active material and the pre-doping agent, as shown by the following calculation formula.
Pre-doping agent content (%) = mass of pre-doping agent 剤 (mass of positive electrode active material + mass of pre-doping agent) × 100
Furthermore, the mass ratio of (positive electrode active material + pre-doping agent) / conductive auxiliary agent / binder was adjusted to be 77/9/14. That is, the mass ratio of the positive electrode active material / pre-doping agent / conductive auxiliary agent / binder was adjusted to be 73/4/9/14.
Next, N-methyl-2-pyrrolidone (manufactured by Kishida Chemical Co., Ltd.) was added to the prepared kneaded product as a dispersion medium, and the viscosity was adjusted to prepare a paint for positive electrode.
Finally, the prepared positive electrode paint is coated on both sides on the etched aluminum foil (JCC-20CB, manufactured by Nippon Capacitor Industry Co., Ltd.) which is a current collector, dried at 130 ° C. for 5 minutes, and cut into a size of 3 cm × 4 cm to obtain a positive electrode. Was produced.

(Fabrication of negative electrode)
First, graphite (CGB-20 manufactured by Nippon Graphite Industry Co., Ltd.) is used as a negative electrode active material, and acetylene black (Denka black manufactured by Denki Kagaku Kogyo Co., Ltd.) is used as a conductive support agent. It added to the 1 mass% aqueous solution of -1496B, and knead | mixed using the planetary mixer.
Next, a paint for a negative electrode was produced by adding styrene butadiene rubber (manufactured by JSR) as a binder to the produced kneaded product. The mass ratio of the negative electrode active material / conductive auxiliary agent / thickener / binder was 95/1/3.
Finally, the prepared paint for negative electrode is applied on both sides to a copper foil (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) as a collector, dried at 100 ° C. for 5 minutes, and cut out into a size of 3.3 cm × 4.3 cm. The negative electrode was produced by this method.

(Fabrication of lithium ion capacitor)
The positive electrode, the negative electrode, and the separator (made by Nippon High Paper Industry Co., Ltd.) manufactured above were laminated as shown in FIG. 2 and then stored in an aluminum laminate case.
Next, 1 M LiPF ₆ in EC / DEC = 1/2 (manufactured by Kishida Chemical Co., Ltd.), which is an electrolytic solution, was injected, and vacuum sealing was performed to fabricate a lithium ion capacitor of Preparation Example 1.
The electrical capacity of the positive electrode of the lithium ion capacitor of Preparation Example 1 is 16.4 mAh, the electrical capacity of the negative electrode is 163.5 mAh, the electrical capacity is 16.4 mAh, and the capacity ratio of the positive and negative electrodes (negative electrode / positive electrode) is 10. there were.

(Pre-doping process)
Next, using the charge and discharge measurement device (manufactured by Hokuto Denko), the prepared lithium ion capacitor of Preparation Example 1 is subjected to 3 at a charge rate of 1 C (current density of 1.37 mA / cm ² ) under an environment of 25 ° C. After charging to 8 V, pre-doping was performed by holding for 3 hours.

(Preparation Examples 2 to 48)
In the preparation of the positive electrode, preparation examples 2 to 2 are carried out in the same manner as in Preparation Example 1 except that the mass ratio of the positive electrode active material / pre-doping agent / conductive assistant / binder and the content of the pre-doping agent are as shown in Table 2. 48 lithium ion capacitors were prepared and pre-doped. The lithium ion capacitor of Preparation Example 43 was prepared by charging the pre-doping treatment to 1.2 V at a charging rate of 1 C, and holding it for 3 hours.
(Production Example 49)
In preparation of the positive electrode, the mass ratio of the positive electrode active material / pre-doping agent / conductive auxiliary agent / binder and the content of the pre-doping agent are as shown in Table 2 and the electric capacity of the negative electrode is 81.8 mAh. In the same manner as in Production Example 1, a lithium ion capacitor of Production Example 49 was produced and pre-doping treatment was performed. The capacity ratio of the positive and negative electrodes (negative electrode / positive electrode) was 5.

(Comparative Production Example 1)
A lithium ion of Comparative Preparation Example 1 was prepared in the same manner as in Preparation Example 1 except that the pre-doping agent was not used and the mass ratio of the positive electrode active material / conductive auxiliary agent / binder was 77/9/14. A capacitor was produced, and the same operation as in the pre-doping process of Production Example 1 was performed.

(Comparative Production Example 2)
(Production of positive electrode)
The mass ratio of the positive electrode active material / conductive auxiliary agent / binder was set to 77/9/14 without using pre-doping agent, and Preparation Example 1 and Example 1 were used except that aluminum expanded metal (made by Hohsen Co., Ltd.) was used as a current collector. The positive electrode was produced similarly.

(Fabrication of negative electrode)
A negative electrode was produced in the same manner as in Production Example 1 except that copper expanded metal (manufactured by Hosen Co., Ltd.) was used as a current collector.

(Fabrication of lithium ion capacitor)
Lithium ion of Comparative Preparation Example 2 in the same manner as in Preparation Example 1 except that the prepared positive electrode, negative electrode, separator (made by Nippon High Paper Industry Co., Ltd.), and one metal lithium foil of 0.032 g are laminated as shown in FIG. A capacitor was made.

(Pre-doping process)
Next, the lithium ion capacitor of Comparative Preparation Example 2 produced was left standing for 1 day in an environment of 25 ° C. to perform pre-doping treatment by the vertical pre-doping method.

(Comparative Production Example 3)
In the pre-doping process, a lithium ion capacitor was produced in the same manner as in Comparative Production Example 2 except that the cells were allowed to stand for 10 days, and pre-doping was performed.

(Comparative Preparation Example 4)
In the pre-doping process, a lithium ion capacitor was produced in the same manner as in Comparative Production Example 2 except that the cells were allowed to stand for 20 days, and pre-doping was performed.

(Comparative Preparation Example 5)
A lithium ion capacitor of Comparative Preparation Example 5 was produced in the same manner as Comparative Production Example 2 except that two pieces of 0.016 g of metal lithium foil were laminated and laminated as shown in FIG.

(Comparative Preparation Example 6)
A lithium ion capacitor of Comparative Preparation Example 6 was produced in the same manner as Comparative Production Example 3 except that two pieces of 0.016 g of metal lithium foil were laminated and laminated as shown in FIG.

(Comparative Production Example 7)
A lithium ion capacitor of Comparative Preparation Example 7 was produced in the same manner as Comparative Production Example 4 except that two pieces of 0.016 g of metal lithium foil were laminated and laminated as shown in FIG.

(Comparative Production Examples 8 to 14)
Comparative preparation is performed in the same manner as in Preparation Example 1 except that the predoping agent used in the preparation of the positive electrode, the mass ratio of the positive electrode active material / predoping agent / conductive auxiliary agent / binder, and the predoping agent content are as shown in Table 2. The lithium ion capacitors of Examples 8-14 were prepared and pre-doped.
The lithium ion capacitors of Comparative Production Examples 12 and 14 were charged to 4.5 V at a charge rate of 1 C, and then held for 1 hour to perform pre-doping treatment.

(Evaluation of lithium ion capacitor)
Next, the following items were evaluated about the lithium ion capacitor of each preparation example and each comparative preparation example.

(Calculation of charge depth (theoretical value))
The charge depth (theoretical value) of each of the manufactured lithium ion capacitors was calculated by the following calculation formula. Here, the charge depth is a value indicating what percentage of the capacity of the negative electrode can be charged by Li ⁺ released from the pre-doping agent.
Charge depth (%) = Li content (mol) of pre-doping agent ÷ Li storage amount (mol) of negative electrode active material × 100

(Measurement of cell voltage and resistance)
The voltage and DC resistance after pre-doping of each of the manufactured lithium ion capacitors were measured using a resistance meter (manufactured by Nichiki Denki).

(Evaluation of capacitor characteristics (discharge capacity and capacity maintenance rate))
The capacitor characteristics (discharge capacity and capacity retention rate) were evaluated for each of the manufactured lithium ion capacitors.
Specifically, charge / discharge was performed in the range of 2.2 to 3.8 V under an environment of 25 ° C. using a charge / discharge measurement device (manufactured by Hokuto Denko). The charge and discharge rate is 1C and 100C, the initial charge capacity is evaluated by performing the charge and discharge test at the charge and discharge rate 1C, and the charge and discharge test at the charge and discharge rate 100C is performed. The evaluation of The current density at a charge / discharge rate of 1 C was 1.37 mA / cm ² , and the current density at a charge / discharge rate of 100 C was 137 mA / cm ² .
Furthermore, the capacity retention rate was calculated from the discharge capacities of 1 C and 100 C by the following formula.
Capacity retention rate (%) = 100 C discharge capacity (mAh) / 1 C discharge capacity (mAh) x 100

(Evaluation of water removal effect)
In the lithium ion capacitor, when there is a large amount of water in the capacitor, a large amount of gas is generated to increase the volume of the cell (lithium ion capacitor). Therefore, the water removal effect of the pre-doping agent of the present invention was evaluated by measuring the cell volume before and after the pre-doping treatment.
Specifically, based on the Archimedes principle, the volume of the cell before and after the pre-doping treatment was measured from the mass when the cell was immersed in pure water, and the volume was evaluated by calculating from the following equation.
Cell volume change ΔV (ml) = Cell volume after pre-doping (ml)-Cell volume before pre-doping (ml)

  The results for each preparation example and comparative preparation example are shown in Table 3.

As a result, it was confirmed that the following lithium ion capacitor can be obtained by containing the pre-doping agent of the present invention (Example) in the positive electrode.
(1) The depth of charge can be increased simply by performing the normal charging operation (aging) without using metal lithium foil as in the prior art, and furthermore, the discharge capacity as designed can be expressed. it can. Furthermore, since the cell resistance does not increase, it is possible to obtain a lithium ion capacitor having a practical capacity maintenance rate. Specifically, the battery exhibits a charge depth of 10% or more and a discharge capacity of 16.4 mAh, and further has a charge capacity (rapid chargeability) at 100 C that is better than a lithium ion capacitor using a conventional metal lithium foil, Since the rate characteristics can be realized while maintaining the charge capacity (initial charge capacity) at 1 C in a practical range, it is possible to obtain a lithium ion capacitor having a practical capacity maintenance rate.
In addition, water can be removed from the lithium ion capacitor.
(2) The depth of charge of the lithium ion capacitors of Preparation Examples 15 to 42 using Examples 4 to 31 in which a part of Li was substituted by an alkali metal, an alkaline earth metal, hydrogen or the like as the pre-doping agent A lithium ion capacitor can be obtained which expresses a discharge capacity of 16.4 mAh and has a capacity retention rate of 42 to 55%.
(3) The lithium ion capacitor of Preparation Example 43 exhibits a charge depth of 10% or more, a discharge capacity of 16.4 mAh, and a high capacity of 86% even if the cell voltage at the time of pre-doping treatment is 1.2 V A lithium ion capacitor having a retention rate can be obtained.
(4) The depth of charge of the lithium ion capacitors of Preparation Examples 44 to 47 using the ones in which the lithium ratio was increased or decreased from the basic composition of Li ₄ TiO ₄ and Li ₂ TiO ₃ as the pre-doping agent (Examples 32-35) A lithium ion capacitor can be obtained which exhibits a discharge capacity of 16.4 mAh and a capacity retention rate of 67 to 76%.
(5) A lithium ion capacitor having a capacity retention ratio of 76% is obtained also for the lithium ion capacitor of Preparation Example 48 using Li ₄ TiO ₄ and Li ₂ TiO ₃ in combination (Example 48) as pre-doping agents. be able to.
(6) With regard to the lithium ion capacitor of Preparation Example 49, by setting the positive / negative electrode capacitance ratio to 5, the charge depth can be made 62% even when the pre-doping agent content is 12%, A lithium ion capacitor having a capacity retention rate of 57% can be obtained.

On the other hand, the following results were obtained for the pre-doping agent of the comparative example and the lithium ion capacitor of the comparative preparation example.
(1) In the lithium ion capacitor of Comparative Preparation Example 1 which does not use a pre-doping agent, since the pre-doping treatment can not be performed from the beginning, the discharge capacity is extremely low (1 C: 5.1 mAh, 100 C: 2.3 mAh).
(2) In the lithium ion capacitors of Comparative Preparation Examples 2 to 7 using metal lithium foil as in the prior art, predoping is insufficient only by standing still for one day, and it is impossible to evaluate the battery characteristics itself. The Further, in the type using one metal lithium foil (comparative preparation examples 2 to 4), it takes 20 days or more to complete the pre-doping treatment, and the type using two metal lithium foils (comparative preparation examples 5 to 7) In the above, it took 10 days or more to complete the pre-doping process. Furthermore, in the lithium ion capacitors of Comparative Preparation Examples 2 to 7, even if the pre-doping treatment is completed (Comparative Preparation Examples 4, 6, and 7), the cell resistance after pre-doping is high and gas generation is large, The migration distance of Li ions is long, and the capacity retention rate is low (7 to 16%).
That is, in the lithium ion capacitor of the comparative preparation example, the volume of the cell is larger by the thickness of the metal lithium foil than the lithium ion capacitor of the preparation example. On the other hand, since the capacity retention ratio of the lithium ion capacitor of the comparative preparation example is lower than that of the lithium ion capacitor of the preparation example as described above, the volume energy density of the conventional lithium ion capacitor (lithium ion capacitor of the comparison preparation example) It could be confirmed that the
(3) In the lithium ion capacitors of Comparative Preparation Examples 8 and 9 using LiTi ₂ O ₄ or Li ₄ Ti ₅ O ₁₂ (Comparative Examples 1 and 2), in which the ratio of Li in 1 mol is low as the pre-doping agent, pre-doping If the content of the agent is not as high as 47% and 56%, the same effect as the pre-doping agent of the present invention can not be exhibited.
(4) In the lithium ion capacitors of Comparative preparation examples 10 and 11 using H ₄ TiO ₄ and H ₂ TiO ₃ (comparative examples 3 and 4) containing no Li as a pre-doping agent, the discharge capacity can not be increased because pre-doping can not be performed. It is low, and the capacity retention rate is also low.
(5) In the lithium ion capacitors of Comparative Production Examples 12 to 14 using Li ₆ MnO ₄ (Comparative Example 5) or Li ₅ AlO ₄ (Comparative Example 6) which is not lithium titanate as the pre-doping agent, pre-doping treatment is performed In order to achieve this, the cell voltage must be set to a high voltage (4.5 V) (Comparative Preparations 12 and 14), and at that time, the electrolytic solution was decomposed. Then, in the lithium ion capacitors of Comparative Production Examples 12 and 14, the cell resistance increased, and the capacity retention rate decreased.
In addition, in the case of setting the voltage at the time of pre-doping to 3.8 V which is the same as the pre-doping agent of the present invention (comparative preparation example 13), decomposition of the electrolytic solution could be suppressed, but less lithium ions are generated from the pre-doping agent As a result, the pre-doping treatment becomes insufficient, resulting in a decrease in initial discharge capacity and capacity retention rate. Furthermore, in Comparative Preparation Example 14, since the particle diameter of the pre-doping agent (Comparative Example 6) was larger than 100 μm, irregularities were generated on the surface of the positive electrode.

From the above, the pre-doping agent for a lithium ion capacitor of the present invention having a specific composition can be pre-doped only by a normal charging operation (aging) by using it in a lithium ion capacitor (especially by containing it in a positive electrode). It turned out that the necessary lithium ions can be generated and pre-doping can be performed without using a conventional metal lithium foil.
Further, since the lithium ion capacitor of the present invention uses the pre-doping agent for lithium ion capacitors of the present invention, it is not necessary to use a metal lithium foil, and as a result, the volume energy density of the lithium ion capacitor can be improved. I understand. Therefore, it was found that the volume reduction (miniaturization, film thinning) of the lithium ion capacitor can be performed.
Furthermore, it was found that water removal in the lithium ion capacitor can be performed simultaneously with the pre-doping treatment.

  The pre-doping agent of the present invention can be used in a lithium ion capacitor.

Reference Signs List 1 pre-doping agent 2 positive electrode active material 3 positive electrode 4 negative electrode active material 5 negative electrode 6 separator 7 terminal 8 housing 9 electrolyte 10 metal lithium foil 11 metal foil with a hole (copper foil)
12 metal foil with holes (aluminum foil)
C lithium ion capacitor

Claims (11)

1. A pre-doping agent for a lithium ion capacitor comprising a compound represented by Li _a TiO _b (1.5 ≦ a ≦ 4.5, 2.7 ≦ b ≦ 4.8) as a main component.
A compound represented by Li _c TiO _d (1.5 ≦ c ≦ 2.3, 2.7 ≦ d ≦ 3.5) or Li _e TiO _f (3.5 ≦ e ≦ 4.5, 3.7 ≦ 2. The pre-doping agent for a lithium ion capacitor according to claim 1, wherein at least one of the compounds represented by f ≦ 4.8) is a main component.
Part of Li is
The pre-doping agent for a lithium ion capacitor according to claim 1 or 2, which is substituted by one or more elements selected from an alkali metal or an alkaline earth metal or hydrogen.
The alkali metal or alkaline earth metal is
The pre-doping agent for a lithium ion capacitor according to claim 3, which is any one of Na, K, Mg, Ca, Sr and Ba.
A positive electrode for a lithium ion capacitor comprising the pre-doping agent for a lithium ion capacitor according to any one of claims 1 to 4 in a positive electrode active material.
The content of the pre-doping agent for the lithium ion capacitor is
The positive electrode for a lithium ion capacitor according to claim 5, wherein the amount is 1 to 60% by mass with respect to the total mass of the positive electrode active material and the pre-doping agent for a lithium ion capacitor.
A lithium ion capacitor pre-doping agent according to any one of claims 1 to 4, a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, a separator, and an electrolytic solution. Lithium ion capacitor.
The lithium ion capacitor according to claim 7, wherein the negative electrode active material is at least one of a carbon-based material or a silicon-based material capable of storing lithium ions.
A positive ion using activated carbon as a positive electrode active material, a separator, a negative electrode using graphite as a negative electrode active material, the pre-doping agent for lithium ion capacitors according to any one of claims 1 to 4, and an electrolytic solution A method of manufacturing a lithium ion capacitor, comprising: lithium ion is doped to the negative electrode active material from the pre-doping agent for lithium ion capacitor by performing initial charging.
A positive ion using activated carbon as a positive electrode active material, a separator, a negative electrode using graphite as a negative electrode active material, the pre-doping agent for lithium ion capacitors according to any one of claims 1 to 4, and an electrolytic solution What is claimed is: 1. A lithium ion capacitor pre-doping method comprising: lithium ion is doped from the pre-doping agent for lithium ion capacitor to the negative electrode active material by initial charging.
11. The method of pre-doping a lithium ion capacitor according to claim 10, wherein the voltage at the initial charge is 1.2 to 3.8V.