Agent for dispersing electrically conductive carbon material, and dispersion of electrically conductive carbon material

Abstract

Provided is an agent for dispersing an electrically conductive carbon material, in which the agent consists of a polymer which has an oxazoline group in a side chain and which is obtained by using an oxazoline group-containing monomer such as that represented by formula (1) for example, and in which the agent exhibits excellent dispersion of an electrically conductive carbon material and produces a thin film that exhibits excellent adhesion to a current collection substrate when formed into a thin film together with the electrically conductive carbon material.

(In the formula, X denotes a polymerizable carbon-carbon double bond-containing group, and R¹-R⁴ each independently denote a hydrogen atom, a halogen atom, an alkyl group optionally having a branched structure having 1-5 carbon atoms, an aryl group having 6-20 carbon atoms, or an aralkyl group having 7-20 carbon atoms.)

Description

TECHNICAL FIELD[0001]This invention relates to an agent for dispersing an electrically conductive carbon material, and to a dispersion of an electrically conductive carbon material. More specifically, the invention relates to a conductive carbon material-dispersing agent consisting of a polymer having pendant oxazoline rings, and to a conductive carbon material dispersion which contains this dispersing agent, an electrically conductive carbon material and a solvent and which is suitable for use as a conductive thin film-forming composition.BACKGROUND ART[0002]With the need for smaller size, lower weight and higher functionality in portable electronic devices such as smart phones, digital cameras and handheld game consoles, active progress has been made recently in the development of high-performance batteries and demand for secondary batteries, which can be repeatedly used by charging, is growing rapidly.[0003]Lithium ion secondary batteries in particular, because of their high ener...

AI Technical Summary

Benefits of technology

[0029]The inventive agent for dispersing an electrically conductive carbon material not only has an excellent ability to disperse electrically conductive carbon materials such as carbon nanotubes, carbon black and graphene, it also has a high adhesion to metal current-conducting substrates used in electrodes for energy storage devices such as lithium ion secondary batteries and electrical double-layer capacitors.

[0030]Conductive carbon material dispersions prepared using the electrically conductive carbon material-dispersing agent of the invention are suitable as conductive thin-film-forming compositions for forming a conductive bonding layer that bonds together the current-collecting substrate and active material which make up the electrode of an energy storage device.

[0031]That is, by using the electrically conductive carbon material dispersion of the invention, an electrically conductive thin-film having excellent adhesion to the current-collecting substrate can be formed without using another adhesive polymer, thus enabling the formation of a conductive thin-film which contains a high concentration of carbon nanotubes and has excellent adhesion to the current-collecting substrate. This means that the electrical resistance of the conductive bonding layer can be lowered, making it possible, particularly in applications such as electrical vehicle applications where a large current is instantaneously required, to draw off current without causing a voltage drop. At the same time, this enables the production of secondary batteries having a long cycle life.

[0032]The conductive carbon material dispersion of the invention, because it readily forms a thin-film merely by being coated onto a substrate and the resulting thin-film exhibits a high electrical conductivity, is suitable for the production of conductive thin-films. Moreover, in addition to giving, as noted above, a thin-film having excellent adhesion to the substrate, it is able to reproducibly and efficiently form a large-surface area thin-film by a wet method, making it highly suitable for use in not only energy storage device applications, but also in a broad range of applications as various types of semiconductor materials and electrically conductive materials.

[0033]FIG. 1 is a graph showing the impedance measurement results for electrical double-layer capacitors fabricated in Examples 5-1 and 5-2 and Comparative Example 5-1.

[0034]The invention is described more fully below.

Problems solved by technology

However, the bonding strength of the above binders to the current collector is less than adequate.

During production operations such as electrode plate cutting steps and winding steps, some of the active material and conductive material separates from the current collector and falls off, causing micro-shorting and variability in the battery capacity.

In addition, with long-term use, due to swelling of the binder on account of the electrolyte solution or to changes in the volume of the electrode mixture associated with volume changes resulting from lithium intercalation and deintercalation by the active material, the contact resistance between the electrode mixture and the current collector increases or some of the active material or conductive material separates from the current collector and falls off, leading to a deterioration in the battery capacity and leading also to problems from the standpoint of safety.

As a result, the separation or peeling of such electrode mixtures from the current collector is a problem in urgent need of a solution.

However, a drawback of dispersing agents capable of dispersing CNTs to a high concentration is that they have a low adhesion to the current collectors used in secondary batteries.

A problem in such cases is that the CNT concentration within the conductive binder layer decreases, as a result of which the conductivity of the layer declines.

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