JP-7857206-B2 - Coating liquid for electrode layer formation

Inventors

• 早川 敬之
• 松島 良介
• 佐久間 聡
• 阿部 寛史

Assignees

• 三菱鉛筆株式会社

Dates

Publication Date

20260512

Application Date

20221031

Claims (4)

1. A carbon nanotube dispersion coating solution comprising at least carbon nanotubes, oxidized cellulose nanofibers, an active material, a binder, and water, A coating liquid for forming an electrode layer, characterized in that the oxidized cellulose nanofiber has a peak height ratio (C=O/C-O) of 0.70 or less between the peak height of the C-O originating peak (around 1062 cm⁻¹ ) and the peak height of the C=O originating peak (around 1610 cm⁻¹ ) in the infrared spectroscopic spectrum, or a peak height ratio (C=O/O-H) of 1.35 or less between the peak height of the O-H originating peak (around 3340 cm⁻¹) and the peak height of the C=O originating peak (around 1610 cm⁻¹ ).
2. The coating solution according to claim 1, wherein 85% or more of the oxidized cellulose nanofibers have a fiber length of 50 to 250 nm.
3. The coating liquid according to claim 1 or 2, wherein the binder is synthetic rubber.
4. An electrode composition comprising the coating liquid described in claim 1.

Description

This invention relates to a coating liquid for forming electrode layers, which is a raw material for manufacturing electrodes of lithium-ion batteries and the like. With the spread of electric vehicles and the miniaturization, weight reduction, and increased performance of portable devices such as mobile phones and notebook computers, there is a growing demand for rechargeable batteries with high energy density and higher capacity. Against this backdrop, lithium-ion rechargeable batteries, which use non-aqueous electrolytes due to their high energy density and high voltage characteristics, are increasingly being used in many devices. Studies have been conducted to explore how using carbon nanotube dispersions as negative and positive electrode materials in lithium-ion secondary batteries can improve conductivity, reduce electrode resistance, and efficiently form conductive networks with small amounts of material. Recently, carbon nanotube dispersions using cellulose nanofibers as dispersants have also become known. For example, Patent Document 1 discloses a carbon nanotube dispersion containing carbon nanotubes, cellulose nanofibers, and a dispersion medium, for the purpose of providing a carbon nanotube dispersion that suppresses aggregation of carbon nanotubes and exhibits high dispersion stability. The cellulose nanofibers are fine cellulose fibers with a maximum fiber diameter of 1000 nm or less and a number-average fiber diameter of 2 nm to 150 nm, wherein some of the hydroxyl groups are replaced with at least one functional group selected from the group consisting of carboxyl groups and aldehyde groups, and the fine cellulose fibers have a cellulose type I crystal structure. Patent Document 2 discloses a nanomaterial composition that can improve the surface hardness of a molded article, characterized by comprising a dispersion medium and cellulose nanofibers and carbon nanotubes dispersed in the dispersion medium. Furthermore, Patent Document 3 discloses a dispersion stabilizer for electrode coating liquids for energy storage devices that provides excellent dispersion stability of electrode active materials and conductive materials, enabling the production of uniform electrodes even when using a dispersion device with weak shear force. The dispersion stabilizer contains cellulose fibers satisfying the following conditions: (a) a number average width of the shorter side is 2 to 200 nm; (b) an aspect ratio of 7.5 to 250; and (c) having type I cellulose crystals with a crystallinity of 70% to 95%. The document also discloses a dispersion liquid for electrode coatings that further provides (d) an anionic functional group, and (e) the anionic functional group is a carboxyl group, with a content of 1.2 to 2.5 mmol/g. Furthermore, Patent Document 4 discloses an electrode binder composition that provides electrodes exhibiting high durability even when using active materials with large volume changes, electrodes for energy storage devices made using the same, and energy storage devices equipped with such electrodes. The composition comprises (A) at least one or more polymer components selected from the group consisting of fluorine-based polymers, butadiene-based polymers, and thermoplastic elastomers; (B) a fibrous nanocarbon material with an average fiber diameter of 0.5 nm to 20 nm and a fiber length of 0.5 μm to 1 mm; (C) a cellulose material; (D) nanocellulose fibers; and (E) water, characterized in that the mass ratio of (A) to (B) is (A)/(B) = 60/40 to 98/2. Patent Document 5 discloses a dispersion containing a dispersion medium, metal-containing oxidized cellulose nanofibers containing metals other than sodium in the form of salts, and single-walled nanotubes. While carboxylated cellulose nanofibers obtained by TEMPO oxidation are described as the oxidized cellulose nanofibers, their properties are not described. TEMPO oxidation of cellulose nanofibers is usually carried out as completely as possible. Furthermore, Non-Patent Document 1, "FY2017 Performance Evaluation Project for Cellulose Nanofiber-Utilizing Products (FY2017 Ministry of the Environment Commissioned Project) (Identification of Issues for the Practical Application of Lithium-Ion Batteries for Idling Stop Vehicles Using Cellulose Nanofibers) Results Report, March 16, 2018: Daiichi Kogyo Seiyaku Co., Ltd.", describes how applying cellulose nanofibers to the manufacture of lithium-ion battery electrodes makes it possible to create an aqueous cathode coating solution and significantly improves battery degradation associated with charging and discharging. It also mentions improved discharge capacity retention during cycles. However, carbon nanotube dispersions, such as those described in Patent Documents 1-5 and Non-Patent Document 1, still have challenges, including a decrease in dispersibility over time and difficulty in achieving a high level of both stability and conductivity. In particular, when mixing with cellulose nanofibers, the dispe