阅读说明：本技术 锂离子电容器用正极 (Positive electrode for lithium ion capacitor ) 是由 杉原良介 渡边桂一 于 2018-04-27 设计创作，主要内容包括：需要能够提高锂离子电容器的电池特性(特别是速率特性)的锂离子电容器的正极。本发明的锂离子电容器用正极的特征在于,在正极活性物质中含有选自Li<Sub>2</Sub>TiO<Sub>3</Sub>、Li<Sub>4</Sub>Ti<Sub>5</Sub>O<Sub>12</Sub>、Na<Sub>2</Sub>TiO<Sub>3</Sub>、K<Sub>2</Sub>Ti<Sub>2</Sub>O<Sub>5</Sub>中的一种以上的钛酸盐。(A positive electrode of a lithium ion capacitor capable of improving battery characteristics (particularly rate characteristics) of the lithium ion capacitor is required. The positive electrode for a lithium ion capacitor of the present invention is characterized in that the positive electrode active material contains Li 2 TiO 3 、Li 4 Ti 5 O 12 、Na 2 TiO 3 、K 2 Ti 2 O 5 Titanate of more than one kind of (1).)

1. A positive electrode for a lithium ion capacitor, characterized in that a positive electrode active material contains Li₂TiO₃、Li₄Ti₅O₁₂、Na₂TiO₃、K₂Ti₂O₅Titanate of more than one kind of (1).

2. The positive electrode for a lithium ion capacitor according to claim 1, wherein the titanate is contained in an amount of 0.5 to 50 wt% based on the positive electrode active material.

Technical Field

The present invention relates to a lithium ion capacitor in a power storage device, and more particularly to a positive electrode in a material constituting the lithium ion capacitor. More specifically, the present invention relates to a positive electrode for a lithium ion capacitor, which contains Li₂TiO₃、Li₄Ti₅O₁₂、Na₂TiO₃、K₂Ti₂O₅Thereby, the capacitor characteristics (particularly rate characteristics) can be improved even though it has no conductivity by itself.

Background

In recent years, development of a lithium ion capacitor having both high output and long life characteristics of an electric double layer capacitor and high energy characteristics of a lithium ion battery has been advanced, and various applications have been proposed (patent documents 1 to 3).

Here, the electric double layer capacitor is a power storage device that performs charge and discharge by utilizing a phenomenon in which an ion component in an electrolyte solution is adsorbed/desorbed at an electrode interface, and thus, it is naturally possible to be a fast charge and discharge type power storage device in structure, but since the lithium ion capacitor also uses elements of the lithium ion battery (specifically, charge and discharge by utilizing an oxidation-reduction reaction), the fast charge and discharge performance is inferior to that of the electric double layer capacitor, and a countermeasure against the fast charge and discharge performance (particularly, rate characteristic) is required as in the lithium ion battery.

In addition, as a conventional measure against the rapid charge and discharge characteristics (particularly, rate characteristics) of a lithium ion capacitor, a general measure is to reduce the particle size of the material of the negative electrode or to increase the specific surface area.

Disclosure of Invention

Problems to be solved by the invention

As a result of intensive studies by the inventors of the present application, the following findings were obtained: by including a specific titanate in the positive electrode of the lithium ion capacitor, the rate characteristics of the lithium ion capacitor can be improved.

Conventionally, it is common technical knowledge that when an additive that does not have conductivity and does not contribute to storage is added to a positive electrode of a lithium ion capacitor, the capacitor characteristics are rather deteriorated, and this knowledge has thus subverted the conventional technical knowledge.

That is, since the lithium ion capacitor has a structure in which anions in the electrolyte are adsorbed on the positive electrode, it is theoretically preferable to use a material having a large specific surface area and high conductivity for the positive electrode in order to improve the capacitor characteristics, but since the capacity of the activated carbon used for the positive electrode is originally smaller than that of the battery active material, the capacity is further reduced when an additive that does not contribute to the storage is added to the positive electrode in this state. In addition, when acetylene black or the like is added for the purpose of imparting conductivity, although the rate property is improved in this case, the specific surface area is decreased, and as a result, the capacity is decreased.

Under the circumstances, the conventional technical common knowledge is that the activated carbon has low conductivity and acetylene black as a conductive aid has to be added even if the capacity is lowered. In the present invention, a specific titanate is used, and although this titanate is not conductive, the rate characteristics can be improved, and therefore, the conventional technical common knowledge is reversed.

Patent documents 4 to 6 propose applications featuring the use of a lithium compound in an electric storage device, but the applications are merely inventions for capturing protons generated in an electric storage device, and the technical idea is different from the present invention in which titanate is used as a material of a positive electrode for the purpose of improving the rate characteristics of a lithium ion capacitor.

Means for solving the problems

In order to achieve the above object, a positive electrode for a lithium ion capacitor according to the present invention is characterized in that a positive electrode active material contains Li selected from Li₂TiO₃、Li₄Ti₅O₁₂、Na₂TiO₃、K₂Ti₂O₅Titanate of more than one kind of (1).

The positive electrode for a lithium ion capacitor is characterized by containing 0.5-50 wt% of titanate relative to a positive electrode active material.

(basic structure)

The positive electrode for a lithium ion capacitor of the present invention contains Li as a positive electrode active material₂TiO₃、Li₄Ti₅O₁₂、Na₂TiO₃、K₂Ti₂O₅One or more specific titanates as a basic structure. As described above, the present invention can improve the rate characteristics of a lithium ion capacitor by including an additive (specific titanate) that does not have conductivity and does not contribute to electric storage in the positive electrode of the lithium ion capacitor, which is preferable for a conventional lithium ion capacitor. In addition, although the titanate itself has no conductivity, the rate characteristics can be improved.

Although the mechanism for improving the rapid charge/discharge performance of the titanate itself, which does not have conductivity, is not clear, it is considered that the addition of the titanate may improve the ion mobility at the interface between the positive electrode and the electrolyte solution and in the positive electrode.

(lithium titanate)

The lithium titanate used for the positive electrode of the lithium ion capacitor of the present invention needs to have Li₂TiO₃Or Li₄Ti₅O₁₂The lithium titanate having the composition of (1) as a main component.

Here, since lithium titanate is generally produced (synthesized) by mixing and firing a Li source and a Ti source as raw materials, not only Li is synthesized₂TiO₃、Li₄Ti₅O₁₂Also, ramsdellite type (LiTi) can be synthesized₂O₄: type 124, Li₂Ti₃O₇Type 237), lithium titanate.

Therefore, the term "as a main component" in the present invention means that even when lithium titanate having various structures is contained as described above, Li is contained₂TiO₃Or Li₄Ti₅O₁₂The lithium titanate having the composition of (1) as a main component. In particular, with Li₂TiO₃Or Li₄Ti₅O₁₂The content of the lithium titanate having the composition of (3) is preferably 70% or more, more preferably 90% or more, and still more preferably 95% or more.

(sodium titanate)

The sodium titanate used in the positive electrode for a lithium ion capacitor of the present invention should be Na₂TiO₃As the main component.

Further, sodium titanate is synthesized in various structures in the same manner as lithium titanate, and therefore has the meaning of having Na even when sodium titanate having various structures is contained₂TiO₃The sodium titanate having the composition of (1) as a main component. In particular, having Na₂TiO₃The content of sodium titanate having the composition of (3) is preferably 70% or more, more preferably 90% or more, and still more preferably 95% or more.

(Potassium titanate)

The potassium titanate used for the positive electrode for the lithium ion capacitor of the present invention should be K₂Ti₂O₅As the main component.

Further, potassium titanate is synthesized in various structures in the same manner as lithium titanate, and therefore has a meaning of having K even when it contains potassium titanate in various structures₂Ti₂O₅The potassium titanate having the composition of (1) as a main component. In particular, having K₂Ti₂O₅The content of potassium titanate having the composition (2) is preferably 70% or more, more preferably 90% or more, and still more preferably 95% or more.

(content)

These titanates have an effect of improving the rate characteristics, i.e., the rapid charge and discharge performance of the lithium ion capacitor, as the content thereof is increased.

On the other hand, these titanates have an effect of improving the rapid charge and discharge performance and an effect of suppressing gas generation, but the gas generation suppressing effect is present in an optimum range of the content, and when excessive addition is performed, the amount of gas generation is rather increased. Specifically, when 60 wt% of titanate was contained in the positive electrode active material, 0.16ml of gas was generated, and the same amount of gas as that generated when the titanate was not contained (0.15ml) was generated.

Therefore, the upper limit of the content of these titanates is preferably set to less than 60 wt% in order to achieve both the improvement of rate characteristics and the suppression of gas generation, and the specific numerical range of the content of titanates is preferably set to 0.5 to 50 wt%, more preferably 1 to 30 wt%, and still more preferably 10 to 20 wt% with respect to the positive electrode active material of the lithium ion capacitor.

Since titanate is not an active material, it is expected that the capacity of a lithium ion capacitor generally decreases when titanate is added to a positive electrode.

However, although the reason is not clear, Li is used for lithium titanate₂TiO₃In the case of (2), as described later, no decrease in capacitance was observed. Therefore, Li is preferably used among the titanates from the viewpoint of the effect of improving the rapid charge/discharge performance (rate characteristics), the effect of suppressing gas generation, and the ability to suppress a decrease in capacitance₂TiO₃。

Effects of the invention

According to the positive electrode for a lithium ion capacitor of the present invention, the positive electrode for a lithium ion capacitor contains Li₂TiO₃、Li₄Ti₅O₁₂、Na₂TiO₃、K₂Ti₂O₅Thereby, the battery characteristics (particularly rate characteristics) of the lithium ion capacitor can be improved, although it does not have conductivity by itself.

In addition, in the lithium ion capacitor, Li is used as a negative electrode active material₄Ti₅O₁₂When the titanate is contained in the positive electrode, the battery characteristics (particularly rate characteristics) can be improved.

Furthermore, in addition to using Li having a large specific surface area₄Ti₅O₁₂In the case of the negative electrode combination of (3), a lithium ion capacitor exhibiting more excellent battery characteristics can be obtained. In this case, the specific surface area of the negative electrode active material is preferably 10m²A value of at least/g, more preferably 20m²More than g, most preferably 50m²More than g.

According to the positive electrode for a lithium ion capacitor of the present invention, the above-described effects can be further improved by setting the content of titanate to a specific range.

Drawings

FIG. 1 shows that Li is used as an anode active material₄Ti₅O₁₂The lithium ion capacitors (the lithium ion capacitors of examples 1 to 11 and comparative examples 1, 3, and 4) thus produced are schematically illustrated in their structures.

Fig. 2 is a schematic diagram showing the structure of a lithium ion capacitor (lithium ion capacitors of examples 12 to 13 and comparative example 2) in which graphite is used as a negative electrode active material.

Detailed Description