JP2018154545A - Nanoparticle aggregate, nanoparticle calcined product, and method of producing these - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a peculiarly shaped nanoparticle aggregate capable of producing by an easy method dispensing with surface modification by an organic substance, and a nanoparticle calcined product.SOLUTION: The nanoparticle calcined product comprises a plurality of ceramic nanoparticles or metal nanoparticles having an average particle diameter of 30 nm or less linearly and continuously supported on a carbon chain having an average fiber diameter of 50 nm or less derived from a cellulose nanofiber, or the nanoparticle calcined product comprises a plurality of ceramic nanoparticles or metal nanoparticles having an average particle diameter of 30 nm or less linearly and continuously arranged by being induced by a cellulose nanofiber having an average fiber diameter of 50 nm or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nanoparticle assembly and a nanoparticle fired product containing ceramic nanoparticles or metal nanoparticles and having a unique shape, and a method for producing them.

  Ceramic particles having a particle diameter of 1 to 100 nm (hereinafter referred to as “ceramic nanoparticles”) and metal nanoparticles (hereinafter referred to as “metal nanoparticles”) are ceramic particles or metals having a larger particle diameter. One of the features is that the specific surface area is larger than that of particles, and the quantum effect is manifested in optical, electrical, or magnetic properties. For example, when the specific surface area of ceramic particles increases, the proportion of atoms exposed on the particle surface also increases, and the efficiency of chemical reactions with external substances such as catalytic chemical reactions increases, so ceramic nanoparticles and metal nanoparticles ( Hereinafter, it is also referred to as “nanoparticle”.) Is known as a highly useful material in all fields.

More specifically, for example, titanium oxide (TiO ₂ ) has a higher refractive index than diamond, does not absorb visible light, and has excellent chemical stability. Widely used in paints as colorants and UV absorbers, but by making them nanoparticles, photocatalytic functions for sunscreen cosmetics and anatase type (self-cleaning only with sunlight, air purification, water quality As a useful material such as a paint having a purification, antibacterial / antifungal) and a catalyst carrier, it can be expected to be used in a wider range of fields.

Alumina (Al ₂ O ₃ ) has high chemical stability, mechanical strength, a small coefficient of thermal expansion, a large electrical insulation resistance, etc., and is therefore used as a ceramic, ceramic material, grinding / polishing material, etc. However, if this is made into nanoparticles, it can be further utilized as a useful material in various electronic parts and catalyst carriers. Furthermore, boehmite (AlOOH), which is a monohydrate of alumina, is also excellent in chemical stability and is used as a resin additive, etc., but by making it into nanoparticles, surface coating materials, enzymes It can be used for immobilization carriers, alcohol dehydration membranes, and the like. Further, cerium oxide (CeO ₂ ) used as an abrasive is also excellent in oxygen storage ability and ultraviolet shielding effect, and by using it as nanoparticles, it can be used as a useful catalyst.

  In order to effectively bring out the properties of such nanoparticles, it is important to control the crystallinity and surface properties of such nanoparticles, further control the particle size and homogenize the chemical composition. In addition, as a method for producing such nanoparticles, a method by a gas phase method such as a vapor phase chemical deposition (CVD) method, or a method by a liquid phase method such as a coprecipitation method, an alkoxide method, a sol-gel method, or a hydrothermal method is used. However, the realization of a production method capable of precisely controlling the size, shape, chemical composition and the like of particles more efficiently is also desired, and various studies have been made.

  For example, Patent Document 1 discloses organically modified metal oxide fine particles in which the surface of the metal oxide fine particles is modified with an organic substance, and describes that such particles can be produced by a supercritical hydrothermal method using a supercritical fluid. Yes. Patent Document 2 discloses a powder composed of oxide microcrystal particles in which 50% by mass or more of oxide microcrystal particles composed of a crystal plane whose outermost surface is constituted by an oxygen ion layer. It is also described that this can be obtained by the supercritical hydrothermal method as in Patent Document 1.

  On the other hand, organic solvent-based binders such as polyvinylidene fluoride (PVDF) and polyimide are frequently used as binders used when producing positive electrodes and negative electrodes such as lithium ion secondary batteries. Under these circumstances, water-based binders such as styrene butadiene rubber (SBR) and polyacrylic acid are being used from the viewpoint of environmental considerations and simplification of the electrode manufacturing process, as described in Patent Document 3. If cellulose nanofiber (CNF) is used, improvement of cycle characteristics in the secondary battery is expected.

JP 2005-193237 A JP 2007-217265 A International Publication No. 2013/042720

However, in the above-mentioned Patent Documents 1 and 2, the supercritical hydrothermal method used when producing nanoparticles is a special high-temperature and high-pressure method in which the temperature is 350 to 450 ° C. and the pressure is 16 to 50 MPa (160 to 500 bar). In addition, after the particles are collected, the surface of the particles is modified with an organic substance so as to avoid agglomeration and stabilize the dispersion as fine particles.
Further, as in Patent Document 3, when CNF is used as an electrode binder for a secondary battery, even if a surfactant is present, it is difficult to uniformly mix with a hydrophobic conductive aid. Therefore, the electrode mixture layer easily peels off from the current collector during the charge / discharge cycle of the secondary battery, and the cycle characteristics have not been sufficiently improved.

  Accordingly, an object of the present invention is to provide a nanoparticle aggregate and a fired nanoparticle having a specific shape that can be produced by a simple method without requiring surface modification with an organic substance.

  Therefore, the present inventors have made various studies, and by using cellulose nanofibers as a shaft or base material and presenting a shape in which a plurality of ceramic nanoparticles or metal nanoparticles are supported or arranged in succession, the usefulness of the present invention can be improved. It has been found that a high nanoparticle aggregate or nanoparticle fired product can be obtained, and the present invention has been completed.

  That is, the present invention provides a nanoparticle aggregate in which a plurality of ceramic nanoparticles or metal nanoparticles are linearly continuously supported on cellulose nanofibers having an average fiber diameter of 50 nm or less.

  Further, the present invention is a nanoparticle fired product in which a plurality of ceramic nanoparticles or metal nanoparticles are linearly continuously supported on a carbon chain derived from cellulose nanofibers having an average fiber diameter of 50 nm or less, or an average The present invention provides a nanoparticle fired product that is derived from cellulose nanofibers having a fiber diameter of 50 nm or less, and in which a plurality of ceramic nanoparticles or metal nanoparticles are linearly continuously arranged.

Furthermore, the present invention provides the following steps (I) to (II):
(I) a step of preparing a slurry containing a ceramic raw material compound or metal raw material compound containing at least one metal element, and cellulose nanofibers;
(II) The method for producing a nanoparticle aggregate, comprising the step of obtaining the nanoparticle aggregate by subjecting the obtained slurry to a hydrothermal reaction at a temperature of 100 ° C. or higher and a pressure of 0.3 to 0.9 MPa. Is to provide.

  According to the nanoparticle aggregate or the nanoparticle fired product of the present invention, the ceramic nanoparticles or the metal nanoparticles are formed by presenting a unique shape in which the ceramic nanoparticles or the metal nanoparticles are supported or induced on the cellulose nanofibers. Since nanoparticles do not easily aggregate, it is possible to easily produce a molded body such as a porous structure or a film using the nanoparticles. In addition, since the cellulose nanofibers can be easily removed from the molded body by firing in an oxygen atmosphere, a product composed only of ceramic nanoparticles or metal nanoparticles can be easily obtained. Furthermore, by firing in a reducing atmosphere, the cellulose nanofibers can be left as chain carbon in the molded body, and conductivity can be easily imparted to the resulting product.

  Moreover, according to the nanoparticle aggregate | assembly of this invention, the specific function which a nanoparticle has can be added to a cellulose nanofiber as needed. For example, by supporting ceramic nanoparticles or metal nanoparticles having conductivity on cellulose nanofibers, it is possible to impart high conductivity to the binder used in the production of an electrode constituting a secondary battery. An electrode can be produced without requiring an agent or a surfactant. Therefore, it is possible to increase the ratio of the active material in the electrode mixture layer while effectively enhancing the binding force between the electrode materials or between the electrode material and the current collector, and the separation of the peeling during the charge / discharge cycle can be increased. It is possible to realize a secondary battery that effectively suppresses generation and is excellent in energy density and cycle characteristics.

FIG. 1 (a) is a TEM photograph showing the nanoparticle aggregate of boehmite (AlOOH) obtained in Example 1, and FIG. 1 (b) is a TEM photograph showing the cellulose nanofibers used. 4 is a TEM photograph showing nanoparticles of boehmite (AlOOH) obtained in Comparative Example 1. FIG. 3A is a TEM photograph showing a nanoparticle aggregate supported on cellulose nanofibers for use as a binder for an electrode of a secondary battery, and FIG. 3A is a nanoparticle aggregate of lithium cobaltate obtained in Example 2; FIG. 3B is a nanoparticle aggregate of tin oxide obtained in Example 3, and FIG. 3C is a nanoparticle aggregate of zinc oxide obtained in Example 4. is there.

Hereinafter, the present invention will be described in detail.
The nanoparticle aggregate of the present invention (hereinafter also referred to as “nanoarray”) includes a plurality of ceramic nanoparticles or metal nanoparticles on cellulose nanofibers (hereinafter also referred to as “CNF”) having an average fiber diameter of 50 nm or less. Are supported continuously in a straight line. The nanoarray means a shape in which one nanoscale structure is arranged on the other nanoscale structure, and the nanoarray of the present invention is a CNF having an average fiber diameter of 50 nm or less, that is, one nanoscale. The scale structure has a skewer-like or corn-like shape in which a plurality of ceramic nanoparticles or metal nanoparticles, that is, the other nanoscale structure is supported linearly and continuously.
Here, the average particle diameter means an average value of measured values of the particle diameter (long axis length) of several tens of particles in observation with an electron microscope of SEM or TEM.

  As described above, the nanoarray of the present invention is such that ceramic nanoparticles or metal nanoparticles are supported linearly and continuously on CNF, so that it is not necessary to modify the surface of the nanoparticles for the purpose of suppressing aggregation. Since it maintains a dispersed state, it can be easily processed into a molded body using this. In addition, since the ceramic nanoparticles or the metal nanoparticles themselves have electrical conductivity, no additional conductive aid is required, and they are highly useful as binders for producing secondary battery electrodes.

  In the nanoarray of the present invention, the surface of the encapsulated CNF becomes a nucleation site for heterogeneous nucleation of ceramics or metal, and the ceramic nanoparticles or metal nanoparticles surround the ultrafine CNF or adhere to the thick CNF surface. In the same manner, the crystal growth is continued until the adjacent nanoparticle is in contact with the crystal growing, so that the nanoparticles are not firmly aggregated and are supported firmly and continuously on the CNF without being agglomerated unnecessarily. Thus, it is considered that a unique shape for skewers or corn is formed.

The cellulose nanofiber (CNF) constituting the nanoarray of the present invention is a skeletal component that occupies about 50% of all plant cell walls, and is obtained by defibrating the plant fibers constituting such cell walls to a nano size. It is a lightweight high-strength fiber that can be used and has good dispersibility in water.
In addition, since the cellulose molecular chain constituting the CNF has a periodic structure formed of carbon, it is carbonized to form a chain axis while forming a conductive path, effectively imparting conductivity to the nanoarray. You can also.

The average fiber diameter of CNF is 50 nm or less, preferably 20 nm or less, and more preferably 10 nm or less. Although there is no restriction | limiting in particular about a lower limit, Usually, it is 1 nm or more.
In addition, the average length of CNF is preferably 100 nm to 100 μm, more preferably 1 μm to 100 μm, and further preferably 5 μm to 100 μm, from the viewpoint of efficiently processing the molded body from the nanoarray.

  Furthermore, when the nanoparticle aggregate of the present invention is used as a binder for electrodes of a secondary battery, the average length of CNF is preferably 100 nm to 200 μm from the viewpoint of binding properties as a binder for electrodes of a secondary battery. More preferably, it is 1 micrometer-200 micrometers, More preferably, it is 10 micrometers-100 micrometers. In this case, the viscosity at 25 ° C. of the CNF slurry having a concentration of 5% by mass is preferably 30,000 to 200,000 mPa · s, more preferably 40000 to 150,000 mPa · s, and further preferably 45,000 to 120,000 mPa · s. .

  The ceramic nanoparticles or metal nanoparticles constituting the nanoarray of the present invention contain at least one kind of metal element and can form nano-sized particles and have conductivity. There is no particular limitation as long as it is present. Examples of metal elements constituting such ceramic nanoparticles or metal nanoparticles include Group VIII elements such as Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt; Cu, Ag, Au Group IB elements such as Zn, Cd and Hg; Group IIB elements such as Zn, Cd and Hg; Group IIIB elements such as B, Al, Ga, In and Tl; Group IVB such as Si, Ge, Sn and Pb Elements; Group VB elements such as As, Sb and Bi; Group VIB elements such as Te and Po; and Group IA to VIIA elements such as Li. Among them, Li, Co, Ag, Au, Zn, In, Pt, Rh, Pd, Ru, Fe, Ni, Cu, Cd, Hg, Al, Ga, Tl, Si, Ge, Sn, Pb, Ti, Zr , Mn, Eu, Y, Nb, Ce, Ba and the like are preferable. Among these, in order to use the nanoparticle aggregate of the present invention as a binder for an electrode of a secondary battery, such ceramic nanoparticles or metal nanoparticles are Li, Co, Ag, Au, Zn, In, Pt, Rh, Pd, And a metal element selected from Ru is more preferable.

Specific examples of such ceramic nanoparticles or metal nanoparticles include particles of the above-mentioned metal elements, such as simple substances, oxides or hydroxides, or composite oxides. For example, SiO ₂ , TiO ₂ , ZnO _{2. , SnO 2, Al 2 O 3} , MnO, MnO 2, NiO, Eu 2 O 3, Y 2 O 3, Nb 2 O 3, Nb 2 O 5, InO, ZnO, Fe 2 O 3, Fe 3 O 4, Co ₃ O ₄ , ZrO ₂ , CeO ₂ , VO ₂ , V ₂ O ₅ , AlOOH, Y ₃ Al ₅ O ₁₂ , BaTiO ₃ , In ₂ O ₃ —SnO ₂ , MgO—Al ₂ O ₃ —SiO ₂ , SiO _{2 -Al 2 O 3, SiO 2} -TiO 2, SiO 2 -ZrO 2, TiO 2 -ZrO 2, SiO 2 -Al 2 O 3 -ZrO 2 , and the like. Moreover, in order to use the nanoparticle aggregate of the present invention as a binder for an electrode of a secondary battery, LiCoO ₂ , SnO ₂ , ZnO, One or more selected from Au, Ag, In, Pt, Rh, Pd, and Ru are more preferable.

  Further, when there are a plurality of valences that can be taken by the metal elements constituting the ceramic nanoparticles or metal nanoparticles, oxygen is easily desorbed on the outermost surface of the nanoarray, and the activity of the crystal plane is further improved. Therefore, the ceramic nanoparticle or metal nanoparticle constituting the nanoarray of the present invention contains a transition metal capable of taking a plurality of valences. Is preferred. Especially, it is more preferable that such a transition metal is selected from the group consisting of Ce, Pr, Fe, Ni, Cu, V, and Co from the viewpoint of taking into consideration the influence on the human body.

  The ceramic nanoparticles or metal nanoparticles constituting the nanoarray of the present invention are composed of microcrystalline particles. Specifically, the average particle diameter of such nanoparticles is preferably 30 nm or less, more preferably 20 nm or less. Although there is no restriction | limiting in particular about a lower limit, Usually, it is 3 nm or more.

  Moreover, when using the nanoparticle aggregate | assembly of this invention as a binder for electrodes of a secondary battery, the average particle diameter of a nanoparticle becomes like this. Preferably it is 30 nm or less, More preferably, it is 25 nm or less. Although there is no restriction | limiting in particular about a lower limit, Usually, it is 0.1 nm or more.

  In addition, examples of the crystal habit of ceramic nanoparticles or metal nanoparticles include a plate shape, a needle shape, a hexahedron shape, and a column shape. Among these, hexahedral particles that are elongated in the axial length direction of CNF are preferable from the viewpoint of being firmly supported with CNF and securing a conductive path in the electrode.

  The nanoarray of the present invention is preferably an aggregate of ceramic nanoparticles or metal nanoparticles having a uniform particle diameter or shape, but is an aggregate of ceramic nanoparticles or metal nanoparticles having different particle diameters or shapes. Alternatively, it may be an aggregate of two or more kinds of ceramic nanoparticles or metal nanoparticles having different chemical compositions.

The fired nanoparticle of the present invention has a plurality of ceramic nanoparticles or metal nanoparticles supported linearly and continuously on a carbon chain derived from cellulose nanofibers having an average fiber diameter of 50 nm or less, or an average fiber diameter. Is induced by cellulose nanofibers of 50 nm or less, and a plurality of ceramic nanoparticles or metal nanoparticles are linearly continuously arranged. Here, the cellulose nanofiber and the ceramic nanoparticle or metal nanoparticle have the same meaning as described above.
These nanoparticle fired products are chain carbons in which cellulose nanofibers are carbonized by firing, and ceramic nanoparticles or metal nanoparticles are supported linearly and continuously on this, or by firing. Cellulose nanofibers are removed to leave ceramic nanoparticles or metal nanoparticles, and these nanoparticles are arrayed linearly and continuously as if guided by the removed cellulose nanofibers. Is. Each of them has a unique shape derived from the nanoarray, and like the nanoarray, can be processed into a useful molded body, and is expected to be used in various fields.

The nanoarray of the present invention comprises the following steps (I) to (II):
(I) a step of preparing a slurry containing a ceramic raw material compound or metal raw material compound containing at least one metal element, and cellulose nanofibers;
(II) The obtained slurry can be obtained by a production method including a step of obtaining a nanoparticle aggregate by subjecting the obtained slurry to a hydrothermal reaction at a temperature of 100 ° C. or more and a pressure of 0.3 to 0.9 MPa.
By using such a production method, the nanoarray of the present invention exhibiting a unique shape can be obtained without using a supercritical hydrothermal method requiring special conditions at high temperature and high pressure as described in Patent Documents 1 and 2 above. Can be obtained. Moreover, a highly useful nanoarray can be obtained as a binder which does not require a separate conductive auxiliary agent like the binder described in Patent Document 3 above.

Step (I) is a step of preparing a slurry containing a ceramic raw material compound or metal raw material compound containing at least one metal element, and cellulose nanofibers.
In the step (I), first, a slurry A is obtained by mixing a ceramic raw material compound or metal raw material compound containing at least one metal element, water, and cellulose nanofibers. The metal element contained in the ceramic raw material compound or the metal raw material compound has the same meaning as described above.
Specific examples of such ceramic raw material compounds or metal raw material compounds include metal compounds such as aluminum compounds, silicon compounds, titanium compounds, cerium compounds, zinc compounds, tin compounds, lithium compounds, and cobalt compounds. Of these, sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides, halides, and the like of the above metal elements can be preferably used.

When preparing the slurry A by mixing these ceramic raw material compound or metal raw material compound and cellulose nanofiber, water is used. The amount of water used is 10 to 300 with respect to 1 mol of the metal element of the ceramic raw material compound or the metal raw material compound in terms of the solubility or dispersibility of each raw material, the ease of stirring, the efficiency of the hydrothermal reaction, and the like. Mole is preferable, and 50 to 200 mol is more preferable.
Further, the content of cellulose nanofibers in the slurry A is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 8 parts in terms of carbon atoms with respect to 100 parts by mass of water in the slurry A. Part by mass.

  In step (I), an alkaline solution is then added to the slurry A to form a slurry B, and the metal component dissolved or dispersed in the slurry B is converted to a metal hydroxide by a neutralization reaction. In order to add the alkaline solution, it is preferable to add dropwise an amount sufficient to keep the pH of the slurry B at 10-14. As such an alkaline solution, for example, an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia or the like can be used, but sodium hydroxide, sodium carbonate or a mixed solution thereof is preferably used.

  The slurry B is preferably stirred to cause the neutralization reaction to proceed from the viewpoint of satisfactorily producing the metal hydroxide. The temperature of the slurry B during the neutralization reaction is preferably 5 ° C. or higher, more preferably 10 to 60 ° C. Further, the stirring time of the slurry B is preferably 5 minutes to 120 minutes, more preferably 30 to 60 minutes.

Step (II) is a step of obtaining the nanoparticle aggregate by subjecting the obtained slurry B to a hydrothermal reaction at a temperature of 100 ° C. or higher and a pressure of 0.3 to 0.9 MPa.
The temperature during the hydrothermal reaction may be 100 ° C. or higher, and preferably 130 to 180 ° C. The hydrothermal reaction is preferably carried out in a pressure vessel, and when the reaction is carried out at 130 to 180 ° C, the pressure at this time is preferably 0.3 to 0.9 MPa, and the reaction is carried out at 140 to 160 ° C. The pressure is preferably 0.3 to 0.6 MPa. The hydrothermal reaction time is preferably 0.5 to 24 hours, more preferably 0.5 to 15 hours.

The obtained hydration reaction product is a nanoarray composed of cellulose nanofibers and metal oxides, or cellulose nanofibers and metal oxides containing crystal water, or cellulose nanofibers and metals. After filtration, it is washed with water. It can be isolated by drying. When washing the nanoarray with water, it is preferable to use 5 to 100 parts by mass of water with respect to 1 part by mass of the nanoarray.
As the drying means, freeze drying or vacuum drying is used, and freeze drying is preferable.

In addition, when the nanoparticle assembly of the present invention is used as a binder for an electrode of a secondary battery, from the viewpoint of reducing aggregation of the nanoarray, a nanoarray having a desired concentration can be obtained by repulping the nanoarray after washing without drying. You may prepare the slurry to contain. The concentration of such a nanoarray is preferably 0.5 to 20% by mass, more preferably 1.0 to 15% by mass in the slurry from the viewpoint of handling during the preparation of the electrode slurry of the secondary battery, Preferably it is 1.5-12 mass%.
In addition, when using the nanoparticle aggregate of the present invention as a binder for an electrode of a secondary battery, from the viewpoint of enhancing the dispersibility of the cellulose nanofiber, the cellulose nanofiber slurry is hydrothermally treated in advance, and then the ceramic raw material compound or the metal raw material A nanoparticle aggregate may be obtained by adding a slurry of the compound and subjecting it to a hydrothermal reaction.

The method for producing a fired nanoparticle of the present invention may further include a step (III) of subjecting the nanoparticle aggregate obtained in the step (II) to firing in a reducing atmosphere. Thereby, the cellulose nanofabric contained in the nanoarray obtained by isolation in the step (II) can be carbonized, and a fired product with good conductivity can be obtained.
Here, from the viewpoint of preventing sintering of the nanoparticles, the firing temperature is preferably 200 to 800 ° C, more preferably 200 to 700 ° C. The firing time is preferably 5 minutes to 10 hours, and more preferably 5 minutes to 5 hours.

Moreover, the manufacturing method of the nanoparticle fired product of the present invention includes a step of subjecting the nanoparticle aggregate obtained in the step (II) to firing in an oxygen atmosphere instead of including the step (III) ( III) 'can also be provided. Thereby, the cellulose nanofibers contained in the nanoarray obtained by isolation in the step (II) can be removed, and a plurality of remaining ceramic nanoparticles or metal nanoparticles are guided to the removed cellulose nanofibers. As a result, it is possible to obtain a fired product that is arranged linearly and continuously.
The firing temperature and firing time in step (III) ′ are the same as in step (III).

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Example 1: Nanoarray made of boehmite (AlOOH)]
_{Al 2 (SO 4) 3 ·} 16H 2 O 3.15g, cellulose nanofibers 3.89 g (Daicel FineChem Co., KY100G, water content 90 wt%), and water 55mL were mixed for 60 minutes to prepare a slurry A1 . 12.0 g of 10 mass% NaOH aqueous solution was added to the obtained slurry A1 and mixed for 5 minutes to prepare slurry A2.
Slurry A2 was charged into an autoclave and subjected to a hydrothermal reaction at 140 ° C. for 1 hour. The resulting hydrothermal reaction product was allowed to cool, then filtered, washed with water, dried in hot air at 80 ° C. for about 4 hours, and a boehmite (AlOOH) nanoarray (BET specific surface area 250 m ² g ^{− 1} ) was obtained.

  A TEM observation image of the obtained boehmite (AlOOH) nanoarray is shown in FIG. 1 (a), and a TEM observation image of the used cellulose nanofiber (KY100G) is shown in FIG. 1 (b). The TEM used was JEM-ARM200F manufactured by JEOL Ltd.

[Comparative Example 1: Boehmite (AlOOH) nanoparticle aggregate]
A boehmite (AlOOH) nanoparticle aggregate (BET specific surface area 200 m ² g ⁻¹ ) was obtained in the same manner as in Example 1 except that cellulose nanofibers were not added.
TEM observation was performed in order to confirm the aggregation state of the nanoparticle aggregate of the obtained boehmite (AlOOH). The obtained TEM photograph is shown in FIG.

[Example 2: Aggregate of lithium cobaltate nanoparticles]
A slurry A1 was prepared by mixing 1.90 g of Co (OH) ₂ , 19.29 g of cellulose nanofiber (manufactured by Sugino Machine Co., Ltd., TMa-1202, water content 98 mass%), and 55 mL of water for 60 minutes. To the obtained slurry A1, 12.0 g of a 10% by mass concentration LiOH aqueous solution was added and mixed for 5 minutes to prepare a slurry A2. Slurry A2 was charged into an autoclave and subjected to a hydrothermal reaction at 140 ° C. for 1 hour. The resulting hydrothermal reaction product was allowed to cool, then filtered, washed with water, repulped with water, and a lithium cobaltate nanoarray (BET specific surface area of 160 m) for use as a binder for a secondary battery electrode. ² g ⁻¹ ) was obtained as a slurry (concentration 10% by mass).

[Example 3: Aggregation of tin oxide nanoparticles]
A slurry B1 was prepared by mixing 4.60 g of SnCl ₂ .2H ₂ O, 19.29 g of cellulose nanofiber (manufactured by Sugino Machine Co., Ltd., TMa-1202, water content 98 mass%), and 55 mL of water for 60 minutes. To the obtained slurry B1, 12.0 g of a 10% by mass NaOH aqueous solution was added and mixed for 5 minutes to prepare slurry B2. Slurry B2 was charged into an autoclave and subjected to a hydrothermal reaction at 140 ° C. for 1 hour. The resulting hydrothermal reaction product was allowed to cool, then filtered, washed with water, repulped with water, and a tin oxide nanoarray (BET specific surface area of 200 m ²⁾ for use as a binder for an electrode of a secondary battery. g- ¹ ) was obtained as a slurry (concentration: 10% by mass).

[Example 4: Aggregate of zinc oxide nanoparticles]
(CH ₃ COO) ₂ Zn 3.75 g, cellulose nanofiber 19.29 g (manufactured by Sugino Machine, TMa-1202, water content 98 mass%), and water 55 mL were mixed for 60 minutes to prepare slurry C1. To the obtained slurry C1, 12.0 g of a 10% by mass NaOH aqueous solution was added and mixed for 5 minutes to prepare slurry C2. Slurry C2 was charged into an autoclave and subjected to a hydrothermal reaction at 140 ° C. for 1 hour. The resulting hydrothermal reaction product is allowed to cool, then filtered, washed with water, repulped with water, and a zinc oxide nanoarray (BET specific surface area of 200 m ²⁾ for use as a binder for an electrode of a secondary battery. g- ¹ ) was obtained as a slurry (concentration: 10% by mass).

[Comparative Example 2: CNF binder]
A 1 wt.% Aqueous dispersion of a commercially available cellulose powder (Fibra-Cell BH-100, manufactured by Celite) was prepared, and defibrated 50 times at 200 MPa using Starburst (manufactured by Sugino Machine). A CNF binder for use as a binder for an electrode of a secondary battery was obtained.

[Comparative Example 2: SBR binder]
A commercially available SBR (styrene butadiene rubber) binder (manufactured by MTI Japan, EQ-Lib-SBR) was used as it was as a binder for an electrode of a secondary battery.

<Observation of particle shape>
The particle shape of the nanoarray obtained in Examples 2 to 4 for use as a binder for an electrode of a secondary battery was observed by TEM. The obtained TEM photograph is shown in FIG.

≪Evaluation of cycle characteristics in secondary batteries≫
The positive electrode of the lithium ion secondary battery was produced using the binder for electrodes of the secondary battery obtained in Examples 2-4 and Comparative Examples 2-3.
First, a positive electrode active material (LiMn _0.7 Fe _0.3 PO ₄ ) was produced in advance by the following method.

<Production of LiMn _0.7 Fe _0.3 PO ₄ >
1272 g of LiOH.H ₂ O and 4 L of water were mixed to obtain slurry X1. Next, 1153 g of 85% phosphoric acid aqueous solution was dropped at 35 mL / min while stirring the obtained slurry X1 at a temperature of 25 ° C. for 3 minutes, followed by CNF (Wma-1202, manufactured by Sugino Machine, (Fiber diameter 4-20 nm) 5892 g was added and stirred at a speed of 400 rpm for 12 hours to obtain a slurry Y1 containing Li ₃ PO ₄ .
The obtained slurry Y1 was purged with nitrogen so that the dissolved oxygen concentration of the slurry Y1 was 0.5 mg / L, and then 1688 g of MnSO ₄ · 5H ₂ O and 834 g of FeSO ₄ · 7H ₂ O were added to the total amount of the slurry Y1. Thus, slurry Z1 was obtained. The molar ratio of MnSO ₄ and FeSO ₄ added (manganese compound: iron compound) was 70:30.
Next, the obtained slurry Z1 was charged into an autoclave and subjected to a hydrothermal reaction at 170 ° C. for 1 hour. The pressure in the autoclave was 0.8 MPa. After the hydrothermal reaction, the produced crystal was filtered, and then washed with 12 parts by mass of water with respect to 1 part by mass of the crystal. The washed crystal was lyophilized at −50 ° C. for 12 hours to obtain Complex X2.
1000 g of the obtained composite X2 was collected, and 1 L of water was added thereto to obtain a slurry Y2. The obtained slurry Y2 was dispersed with an ultrasonic stirrer (T25, manufactured by IKA) for 1 minute to uniformly color the whole, and then spray-dried (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.). Then, it was subjected to spray drying to obtain a granulated body Z2.
The obtained granulated body Z2 was calcined at 700 ° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration: 3%), and lithium manganese iron phosphate (LiMn) on which 2.0% by mass of CNF-derived carbon was supported. _0.7 Fe _0.3 PO ₄ , amount of carbon = 2.0 mass%, average particle size: 100 nm).

<Manufacture of lithium ion secondary batteries>
Next, a coin-type lithium ion secondary battery was manufactured using the positive electrode active material (LiMn _0.7 Fe _0.3 PO ₄ ) obtained above and the binders obtained in Examples 2 to 4 and Comparative Examples 2 to 3. . Specifically, when using the binders of Examples 2 to 4, the positive electrode active material and the binder obtained above were mixed at a mixing ratio of 90:10 by mass ratio, and water was added to this and kneaded sufficiently. A positive electrode slurry was prepared. When using the binders of Comparative Examples 2 to 3, the positive electrode active material, acetylene black, binder, and sodium carboxymethylcellulose obtained above were mixed at a mass ratio of 90: 5: 2.5: 2.5. Water was added to and kneaded sufficiently to prepare a positive electrode slurry.
Next, the obtained positive electrode slurry was applied to a current collector made of an aluminum foil having a thickness of 20 μm using a coating machine, and vacuum-dried at 80 ° C. for 12 hours. Thereafter, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.
A lithium foil punched to φ15 mm was used for the negative electrode. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was used. As the separator, a known one such as a polymer porous film such as polypropylene was used. These battery components were assembled and accommodated in a conventional manner in an atmosphere having a dew point of −50 ° C. or lower to obtain a coin-type secondary battery (CR-2032).
The cycle characteristics were evaluated using the obtained secondary battery. Specifically, a constant current charge with a current density of 170 mA / g and a voltage of 4.5 V and a constant current discharge with a current density of 170 mA / g and a final voltage of 2.0 V, and a discharge at a current density of 170 mA / g (1.0 CA). The capacity was determined. Furthermore, a 100-cycle repeated test under the same charge / discharge conditions was performed, and the capacity retention rate (%) was determined by the following formula (I). All charge / discharge tests were performed at 30 ° C.
Capacity retention (%) = (discharge capacity after 100 cycles) / (discharge capacity after 1 cycle)
× 100 ... (I)
The results are shown in Table 1.

Claims (9)

  A nanoparticle aggregate in which a plurality of ceramic nanoparticles or metal nanoparticles are supported linearly and continuously on cellulose nanofibers having an average fiber diameter of 50 nm or less.   The nanoparticle aggregate according to claim 1, wherein the ceramic nanoparticles or metal nanoparticles have an average particle size of 30 nm or less.   The nanoparticle aggregate according to claim 1 or 2, which is a binder for an electrode of a secondary battery.   A fired nanoparticle product in which a plurality of ceramic nanoparticles or metal nanoparticles are supported linearly and continuously on a carbon chain derived from cellulose nanofibers having an average fiber diameter of 50 nm or less.   A nanoparticle fired product that is derived from cellulose nanofibers having an average fiber diameter of 50 nm or less and in which a plurality of ceramic nanoparticles or metal nanoparticles are linearly continuously arranged.   The nanoparticle fired product according to claim 4 or 5, wherein the average particle size of the ceramic nanoparticles or metal nanoparticles is 30 nm or less. Next steps (I) to (II):
(I) a step of preparing a slurry containing a ceramic raw material compound or metal raw material compound containing at least one metal element, and cellulose nanofibers;
(II) The obtained slurry is provided with the process of attaching | subjecting the obtained slurry to hydrothermal reaction with a temperature of 100 degreeC or more and a pressure of 0.3-0.9 MPa, and obtaining a nanoparticle aggregate | assembly. A method for producing a nanoparticle aggregate. Next steps (I) to (III):
(I) a step of preparing a slurry containing a ceramic raw material compound or metal raw material compound containing at least one metal element, and cellulose nanofibers;
(II) A step of subjecting the obtained slurry to a hydrothermal reaction at a temperature of 100 ° C. or higher and a pressure of 0.3 to 0.9 MPa to obtain a nanoparticle aggregate (III) Furthermore, the manufacturing method of the nanoparticle baked product of Claim 4 or 6 provided with the process attached | subjected to baking in a reducing atmosphere. Next steps (I) to (III) ′:
(I) a step of preparing a slurry containing a ceramic raw material compound or metal raw material compound containing at least one metal element, and cellulose nanofibers;
(II) A step of subjecting the obtained slurry to a hydrothermal reaction at a temperature of 100 ° C. or higher and a pressure of 0.3 to 0.9 MPa to obtain a nanoparticle aggregate. (III) ′ Obtained nanoparticle aggregate The manufacturing method of the nanoparticle baked product of Claim 5 or 6 further equipped with the process of attaching | subjecting to baking by oxygen atmosphere.