TECHNICAL FIELD

The present disclosure relates to a binder composition for an electrochemical device, a slurry composition for an electrochemical device functional layer, a slurry composition for an electrochemical device adhesive layer, and a composite membrane.

BACKGROUND

Lithium ion secondary batteries and other non-aqueous batteries, electric double-layer capacitors, and lithium ion capacitors are examples of electrochemical devices that are conventionally used in a wide variety of applications.

Non-aqueous secondary batteries (hereinafter, also referred to simply as “secondary batteries”) such as lithium ion secondary batteries have characteristics such as compact size, light weight, high energy-density, and the ability to be repeatedly charged and discharged. A non-aqueous secondary battery generally includes battery components such as electrodes (positive and negative electrodes) and a separator that isolates the positive electrode and the negative electrode from one another and prevents short circuiting between the positive and negative electrodes.

A battery component of a secondary battery may be a component that includes a functional layer containing a binder and optionally containing particles compounded in order to cause the battery component to display a desired function (hereinafter, referred to as “functional particles”).

Specifically, there are cases in which a separator of a secondary battery is a separator that includes, on a separator substrate, an adhesive layer that contains a binder or a porous membrane layer that contains a binder and non-conductive particles serving as functional particles. Moreover, there are cases in which an electrode of a secondary battery is an electrode that includes an electrode mixed material layer containing a binder and electrode active material particles serving as functional particles on a current collector or an electrode that includes an adhesive layer or a porous membrane layer such as described above on an electrode substrate including an electrode mixed material layer on a current collector.

Attempts have been made to improve binder compositions containing binders with the aim of further enhancing secondary battery performance. In one example, Patent Literature (PTL) 1 proposes a technique for improving adhesiveness of an electrode mixed material layer to a current collector by using a specific binder composition.

CITATION LIST

Patent Literature

PTL 1: JP 2016-009544 A

SUMMARY

Technical Problem

However, with the conventional technique described above, it is difficult to ensure that an electrode mixed material layer has sufficient adhesiveness (peel strength), and it has not been possible to cause a secondary battery to display excellent rate characteristics and cycle characteristics. Therefore, there is room for improvement over the conventional technique in terms of providing a functional layer, such as an electrode mixed material layer, with excellent adhesiveness (peel strength) and improving rate characteristics and cycle characteristics of a secondary battery.

Accordingly, an objective of the present disclosure is to provide a binder composition for an electrochemical device that has excellent binding capacity and is capable of forming a functional layer (electrode mixed material layer, porous membrane layer, or adhesive layer) or a composite membrane that can improve rate characteristics and cycle characteristics of an electrochemical device (for example, a secondary battery).

Another objective of the present disclosure is to provide a slurry composition for an electrochemical device functional layer capable of forming a functional layer (electrode mixed material layer, porous membrane layer, or adhesive layer) or a composite membrane that has excellent adhesiveness (peel strength and process adhesiveness) and that can improve rate characteristics and cycle characteristics of an electrochemical device (for example, a secondary battery).

Yet another objective of the present disclosure is to provide a composite membrane that has excellent adhesiveness (peel strength) and that can improve rate characteristics and cycle characteristics of an electrochemical device (for example, a secondary battery).

Solution to Problem

The inventors conducted diligent investigation with the aim of solving the problems set forth above. The inventors discovered that by using a binder composition containing a specific binder and a specific organonitrogen compound to form a functional layer (electrode mixed material layer, porous membrane layer, or adhesive layer) or a composite membrane, adhesiveness (peel strength and process adhesiveness) of the obtained functional layer (electrode mixed material layer, porous membrane layer, or adhesive layer) or composite membrane can be increased while also causing an electrochemical device (for example, a secondary battery) including the functional layer (electrode mixed material layer, porous membrane layer, or adhesive layer) or composite membrane to display excellent rate characteristics and cycle characteristics, and in this manner completed the present disclosure.

Specifically, the present disclosure aims to advantageously solve the problems set forth above by disclosing a binder composition for an electrochemical device comprising a binder and an organonitrogen compound, wherein the binder is a polymer including at least one functional group selected from the group consisting of a carboxyl group (carboxy group), a hydroxyl group, a cyano group (nitrile group), an amino group, an epoxy group, an oxazoline group, an isocyanate group, and a sulfo group, and the organonitrogen compound includes at least one functional group selected from the group consisting of an azo group, a hydrazino group, a hydrazo group, and a nitroso group, has a 5% mass loss temperature of 140° C. or higher, and has a molecular weight of not less than 80 and not more than 1,000. A binder composition that contains a specific binder and a specific organonitrogen compound as set forth above has excellent binding capacity and can, therefore, be used to obtain a functional layer having excellent adhesiveness (peel strength). Moreover, by using a device component (battery component) that includes this functional layer, it is possible to cause an electrochemical device (for example, a secondary battery) to display excellent rate characteristics and cycle characteristics.

In the presently disclosed binder composition for an electrochemical device, it is preferable that the binder includes a carboxyl group (carboxy group), and that carboxyl group (carboxy group) content in the binder is not less than 0.01 mmol and not more than 15 mmol per 1 g of the binder. When the binder includes a carboxyl group (carboxy group) and when the carboxyl group (carboxy group) content in the binder is not less than 0.01 mmol and not more than 15 mmol per 1 g of the binder, binding capacity of the binder composition can be further increased, and adhesiveness (peel strength) of a functional layer and cycle characteristics of an electrochemical device (for example, a secondary battery) can be further improved.

In the presently disclosed binder composition for an electrochemical device, it is preferable that the binder includes a cyano group (nitrile group), and that cyano group (nitrile group) content in the binder is not less than 1.0 mmol and not more than 40 mmol per 1 g of the binder. When the binder includes a cyano group (nitrile group) and when the cyano group (nitrile group) content in the binder is not less than 1.0 mmol and not more than 40 mmol per 1 g of the binder, binding capacity of the binder composition can be further increased, and adhesiveness (peel strength) of a functional layer and rate characteristics of an electrochemical device (for example, a secondary battery) can be further improved.

In the presently disclosed binder composition for an electrochemical device, the organonitrogen compound preferably further includes an amide group. When the organonitrogen compound further includes an amide group, binding capacity of the binder composition can be further increased, and adhesiveness (peel strength) of a functional layer can be further improved.

In the presently disclosed binder composition for an electrochemical device, content of the organonitrogen compound is preferably not less than 0.5 mass % and not more than 85 mass % relative to the binder. When the content of the organonitrogen compound is not less than 0.5 mass % and not more than 85 mass % relative to the binder, binding capacity of the binder composition can be further increased, and adhesiveness (peel strength) of a functional layer and rate characteristics of an electrochemical device (for example, a secondary battery) can be further improved.

Moreover, the present disclosure aims to advantageously solve the problems set forth above by disclosing a slurry composition for an electrochemical device functional layer comprising any one of the binder compositions for an electrochemical device set forth above. When the slurry composition for an electrochemical device functional layer set forth above is used to form a functional layer, adhesiveness (peel strength) of the functional layer can be increased. Moreover, by using a device component (battery component) that includes this functional layer, an electrochemical device (for example, a secondary battery) can be caused to display excellent rate characteristics and cycle characteristics.

The presently disclosed slurry composition for an electrochemical device functional layer can further comprise an electrode active material. When the slurry composition set forth above also contains an electrode active material, the slurry composition can be used to form an electrode mixed material layer that has excellent adhesiveness and can cause a secondary battery to display excellent rate characteristics and cycle characteristics.

Also, the presently disclosed slurry composition for an electrochemical device functional layer can further comprise non-conductive particles.

Furthermore, the present disclosure aims to advantageously solve the problems set forth above by disclosing a slurry composition for an electrochemical device adhesive layer comprising any one of the binder compositions for an electrochemical device set forth above, and not comprising an electrode active material and non-conductive particles. By forming an adhesive layer from the slurry composition for an electrochemical device adhesive layer set forth above, adhesiveness (peel strength and process adhesiveness) of the adhesive layer can be increased. Moreover, by using a device component (battery component) that includes this adhesive layer, an electrochemical device (for example, a secondary battery) can be caused to display excellent rate characteristics and cycle characteristics.

Also, a slurry composition for a porous membrane comprises any one of the binder compositions for an electrochemical device set forth above. By forming a porous membrane from the slurry composition for a porous membrane set forth above, adhesiveness (peel strength) of the porous membrane can be increased. Moreover, by using a device component (battery component) that includes this porous membrane, an electrochemical device (for example, a secondary battery) can be caused to display excellent rate characteristics and cycle characteristics.

Moreover, the present disclosure aims to advantageously solve the problems set forth above by disclosing a composite membrane obtained through a slurry composition for a porous membrane layer or a slurry composition for an adhesive layer corresponding to the slurry composition for an electrochemical device functional layer set forth above being stacked on a separator substrate or introduced into a separator substrate. When the slurry composition for a porous membrane layer or slurry composition for an adhesive layer corresponding to the slurry composition for an electrochemical device functional layer set forth above is stacked on a separator substrate or introduced into a separator substrate, a composite membrane can be reliably formed.

Note that in the present specification, a functional layer that contains a binder and electrode active material particles is referred to as an “electrode mixed material layer”, a functional layer that contains a binder and non-conductive particles is referred to as a “porous membrane layer”, and a functional layer that contains a binder but contains neither electrode active material particles nor non-conductive particles is referred to as an “adhesive layer”. Moreover, a membrane obtained by forming a porous membrane layer or adhesive layer on a separator substrate or in a separator substrate through application or the like of a slurry composition for a porous membrane layer or a slurry composition for an adhesive layer with respect to the separator substrate is referred to as a “composite membrane”.

Advantageous Effect

According to the present disclosure, it is possible to provide a binder composition for an electrochemical device that has excellent binding capacity and is capable of forming a functional layer (electrode mixed material layer, porous membrane layer, or adhesive layer) or a composite membrane that can improve rate characteristics and cycle characteristics of an electrochemical device (for example, a secondary battery).

Moreover, according to the present disclosure, it is possible to provide a slurry composition for an electrochemical device functional layer capable of forming a functional layer (electrode mixed material layer, porous membrane layer, or adhesive layer) or a composite membrane that has excellent adhesiveness (peel strength and process adhesiveness) and that can improve rate characteristics and cycle characteristics of an electrochemical device (for example, a secondary battery).

Furthermore, according to the present disclosure, it is possible to provide a composite membrane that has excellent adhesiveness (peel strength) and that can improve rate characteristics and cycle characteristics of an electrochemical device (for example, a secondary battery).

