JP2021068672A - Manufacturing method of positive electrode of sodium all-solid-state battery - Google Patents

Abstract

To provide a manufacturing method of a positive electrode of a sodium all-solid-state battery capable of suppressing the interfacial resistance between a positive electrode active material having a P2-type layered crystal structure and a solid electrolyte.SOLUTION: A manufacturing method of a positive electrode of a sodium all-solid-state battery includes a step of mixing a positive electrode active material having a P2-type layered crystal structure and a NASICON-type phosphoric acid compound, and then performing heat-treatment at 300°C or higher and 600°C or lower.SELECTED DRAWING: Figure 2

Description

The present invention relates to a sodium all-solid-state battery.

Lithium-ion secondary batteries are used as power sources for mobile devices and vehicles by taking advantage of their high capacity and light weight. Since the electrolytic solution used here may leak, it is being considered to use a solid electrolyte instead of the electrolytic solution.

However, there is concern that the price of lithium as a raw material will rise. Therefore, as an alternative material to lithium, a sodium ion all-solid-state battery using sodium, which has abundant resources, is attracting attention. Sodium ion all-solid-state batteries are required to have sodium ion conductivity.

Patent Document 1 discloses that in a sodium secondary battery, a positive electrode active material having a P2-type layered crystal structure and a solid electrolyte are used for the positive electrode thereof.

Special Table 2018-514908

However, a reaction occurs at the contact site between the positive electrode active material having a P2-type layered crystal structure and the solid electrolyte, and by-products are generated to increase the interfacial resistance, so that the battery output may be insufficient.

The present application has been made in view of the actual situation, and provides a method for producing a positive electrode of a sodium all-solid-state battery capable of suppressing the interfacial resistance between a positive electrode active material having a P2-type layered crystal structure and a solid electrolyte. Is the main purpose.

The present application is a method for producing a positive electrode of a sodium all-solid-state battery as one means for solving the above problems, in which a positive electrode active material having a P2-type layered crystal structure and a NASICON-type phosphoric acid compound are mixed. Disclosed is a method for producing a positive electrode, which comprises a step of performing heat treatment at 300 ° C. or higher and 600 ° C. or lower.

According to the method for producing a positive electrode of a sodium all-solid-state battery disclosed in the present application, it is possible to suppress the interfacial resistance between the positive electrode active material having a P2-type layered crystal structure and the solid electrolyte.

It is the schematic sectional drawing of the sodium ion all-solid-state battery provided with the positive electrode disclosed in this application. It is a figure which shows the result of an Example and a comparative example.

[Manufacturing positive electrodes for sodium all-solid-state batteries]
<Preparation of positive electrode active material>
Prepare the positive electrode active material. In the present disclosure, the positive electrode active material is a composite oxide containing Na having a P2-type layered crystal structure.
Here, the "composite oxide containing Na" includes, in addition to the Na atom, a transition metal element containing at least one selected from Mn, Ni, Co, Fe, and Cr, and an O atom. .. For example, Na _x MO ₂ (0 <x ≦ 1, M is at least one of Mn, Ni, Co, Fe, and Cr) can be mentioned.

It can be confirmed by X-ray diffraction (XRD) measurement or the like that the positive electrode active material has a P2-type layered crystal structure.

The positive electrode active material is a precursor by mixing an acidic mixture containing a transition metal element such as an Mn source, a Ni source, or a Co source with a basic mixture containing a Na source, heating and stirring the mixture, and then filtering the mixture. The precursor can be obtained by mixing it with a further Na source and heating it at 700 ° C. or higher and 1000 ° C. or lower, preferably 900 ° C. When the heating reaction becomes a temperature lower than 700 ° C., an O3 type crystal structure is formed.

The shape of the positive electrode active material is preferably in the form of particles from the viewpoint of good handleability. The average particle size (D50) of the particles of the positive electrode active material is not particularly limited, but can be 0.5 μm or more and 20 μm or less.
In the present application, the average particle size of particles is a value of a volume-based median diameter (D50) measured by laser diffraction / scattering type particle size distribution measurement unless otherwise specified. The median diameter (D50) is a diameter (volume average diameter) at which the cumulative volume of the particles is half (50%) of the total when the particles are arranged in order from the smallest particle size.

<Synthesis of complex active material>
A composite active material is obtained by mixing the prepared positive electrode active material with a NASICON-type phosphoric acid compound containing Na atom, Zr atom, Si atom, P atom, and O atom and heat-treating.
In the present disclosure, this heat treatment is performed at 300 ° C. or higher and 600 ° C. or lower.
By heat-treating at a temperature within this range, the interfacial resistance can be reduced when the obtained composite active material is used for the positive electrode, and an all-solid-state battery having a large output can be obtained. It is considered that this is because the heat treatment within the temperature range forms a film having an effect of suppressing the formation of by-products on the positive electrode active material. Then, it is presumed that this film suppresses the formation of by-products and suppresses the increase in interfacial resistance.

In the NASICON type compound, the MO ₆ octahedron (M is a transition metal and Na, Zr, Si in the present disclosure) and the XO ₄ tetrahedron (X is P in the present disclosure) share an apex 3 It is a three-dimensionally arranged structure. Specific examples of the NASICON-type phosphoric acid compound include Na ₃ Zr ₃ Si ₃ PO ₁₂ .

The NASICON-type phosphoric acid compound is preferably in the form of particles from the viewpoint of good handleability. The average particle size (D50) of the particles is not particularly limited, but can be 0.5 μm or more and 2 μm or less.
In this case, the above-mentioned positive electrode active material powder and NASICON-type phosphoric acid compound powder are mixed, vacuum-sealed, and heat-treated within the above-mentioned temperature range to synthesize a composite active material.

However, both the positive electrode active material and the NASICON-type phosphoric acid compound do not have to be in the form of particles, and a composite active material may be synthesized by mixing either of them as a liquid phase and heat-treating within the above temperature range. it can.

<Preparation of solid electrolyte>
The solid electrolyte is not particularly limited as long as it is a solid electrolyte having sodium ion conductivity, and various solid electrolytes can be applied.
For example, Na ₃ MX ₆ can be mentioned. Here, M is Yb, Y, In or La, and X is Cl, Br or I. More _{specifically, Na 3 YbC l6, Na 3} YbBr 6, Na 3 YbI 6, Na 3 YCl 6, Na 3 YBr 6, Na 3 YI 6, Na 3 InC l6, Na 3 InBr 6, Na 3 InI 6 , Na ₃ LaC _l6 , Na ₃ LaBr ₆ , Na ₃ LaI _{6 and the like} .
In addition, Na ₃ PS ₄ , Na ₃ SbS ₄ , Na ₅ YSi ₄ O ₁₂ , Na ₆ Al ₆ Si ₁₀ O ₃₂ , Na ₈₆ Al ₈₆ Si ₁₆ O ₃₈₄ , and NaCB ₉ H ₁₀ and Na CB ₁₁ H ₁₂ A mixture of the above can also be mentioned.

<Preparation of positive electrode active material layer>
As the positive electrode active material layer, the positive electrode active material layer is prepared from the synthesized composite active material, the solid electrolyte, and if necessary, a conductive material and a binder. The method for producing the positive electrode active material layer is not particularly limited, and the positive electrode active material layer can be produced by a dry method or a wet method. That is, a predetermined component is added to a solvent to form a slurry, which is applied to the surface of a base material (which may be a positive electrode current collector or a solid electrolyte layer described later) and then dried to obtain a predetermined value. A positive electrode active material layer having a thickness (for example, 0.1 μm or more and 1 mm or less) can be produced by a wet method. Alternatively, the positive electrode active material layer may be obtained by dry mixing the above components and press molding.

The volume ratio of the positive electrode active material (positive electrode active material having a P2-type crystal structure) in the positive electrode active material layer to the positive electrode active material layer is not particularly limited, but is preferably 45% by volume or more, preferably 60 volumes. % Or more is more preferable.

When a conductive material is used, the type thereof is not particularly limited, and any known conductive material for a sodium ion all-solid-state battery can be used. For example, a carbon material is preferable, and a carbon material having high crystallinity is particularly preferable. This is because if the crystallinity of the carbon material is high, it becomes difficult for sodium ions to be inserted into the carbon material, and the irreversible capacity due to the insertion of sodium ions can be reduced. As a result, a sodium ion all-solid-state battery having even better cycle characteristics can be obtained. The crystallinity of the carbon material can be defined, for example, by the interlayer distance d002 and the D / G ratio. The interlayer distance d002 refers to the surface spacing of the (002) plane in the carbon material, and specifically corresponds to the distance between graphene layers. The interlayer distance d002 can be obtained from a peak obtained by, for example, an X-ray diffraction (XRD) method using CuKα rays. The D / G ratio is the D-band derived from the defect structure near ^{1350 cm -1 with} respect to the peak intensity of the G-band derived from the graphite structure near ^{1590 cm -1} observed in Raman spectroscopy (wavelength 532 nm). The peak intensity of. In the present invention, for example, the upper limit of d002 is preferably 3.54 Å or less, more preferably 3.50 Å or less. The lower limit is usually 3.36 Å or higher. The upper limit of the D / G ratio is preferably 0.90 or less, more preferably 0.80 or less, still more preferably 0.50 or less, and particularly preferably 0.20 or less. The content of the conductive material in the positive electrode active material layer is not particularly limited.

When a binder is used, it is not particularly limited as long as it is chemically and electrically stable, but for example, it is a fluorine-based binder such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Examples include binders, rubber-based binders such as styrene-butadiene rubber (SBR), olefin-based binders such as polypropylene (PP) and polyethylene (PE), and cellulose-based binders such as carboxymethyl cellulose (CMC). Can be done. The content of the binder in the positive electrode is not particularly limited.

<Preparation of positive electrode>
A positive electrode current collector is laminated on the positive electrode active material layer to form a positive electrode. However, depending on the material contained in the positive electrode active material layer, the positive electrode current collector may be omitted. In this case, the positive electrode active material layer itself becomes the positive electrode by itself.
Examples of the material of the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium and carbon. Examples of the shape of the positive electrode current collector include a foil shape, a mesh shape, and a porous shape.

[Sodium ion all-solid-state battery]
The positive electrode manufactured as described above can be applied to the positive electrode of an all-solid-state battery. The positive electrode manufactured by the method for manufacturing a positive electrode of the present application can suppress the interfacial resistance between the positive electrode active material and the solid electrolyte to a low level, and as a result, the battery output can be increased.

FIG. 1 shows a schematic cross-sectional view of a sodium ion all-solid-state battery 100 provided with a positive electrode 20 (positive electrode active material layer 22 and positive electrode current collector 24) manufactured by the positive electrode manufacturing method of the present disclosure. The sodium ion all-solid-state battery 100 shown in FIG. 1 has a positive electrode active material layer 22, a negative electrode active material layer 32, a solid electrolyte layer 10 formed between the positive electrode active material layer 22 and the negative electrode active material layer 32, and a positive electrode active material. It has a positive electrode current collector 24 that collects electricity from the material layer 22, and a negative electrode current collector 34 that collects electricity from the negative electrode active material layer 32. As described above, the positive electrode active material layer 22 and the positive electrode current collector 24 form the positive electrode 20. Further, the negative electrode active material layer 32 and the negative electrode current collector 34 form the negative electrode 30.

<Solid electrolyte layer 10>
In the present embodiment, the solid electrolyte layer 10 can be composed of the same solid electrolyte as the solid electrolyte contained in the positive electrode. The thickness of the solid electrolyte layer is appropriately adjusted depending on the configuration of the battery, and is not particularly limited, and is usually 0.1 μm or more and 1 mm or less.

<Positive electrode 20>
The positive electrode 20 has a positive electrode active material layer 22 and a positive electrode current collector 23, and the positive electrode manufactured by the above-described positive electrode manufacturing method is applied.

<Negative electrode active material layer 32>
The negative electrode active material layer 32 contains a negative electrode active material. More specifically, in addition to the negative electrode active material, a solid electrolyte, a conductive material, and a binder may be optionally included. The solid electrolyte can be considered in the same manner as the solid electrolyte described in the method for producing a positive electrode.

(Negative electrode active material)
The negative electrode active material is not particularly limited, and any known negative electrode active material for a sodium ion all-solid-state battery can be adopted. For example, metal materials containing sodium such as sodium metals and sodium alloys; carbon materials such as graphite, hard carbon and carbon black; sodium-transition metal composite oxides such as sodium titanate; oxidation consisting of elements other than sodium such as SiOx. Things; etc. The negative electrode active material is preferably in the form of particles like the positive electrode active material.

(Conductive material and binder)
In the negative electrode active material layer 32, a conductive material or a binder material that can be used in the positive electrode active material layer 22 can be used. The conductive material and the binder are optional components, and their contents are not particularly limited.

The method for producing the negative electrode active material layer 32 is not particularly limited, and like the positive electrode active material layer 22, it can be produced by a dry method or a wet method.

(Negative electrode current collector 34)
The negative electrode active material layer 32 is usually provided with a negative electrode current collector 34. Examples of the material of the negative electrode current collector 34 include stainless steel, aluminum, nickel, copper and carbon. Examples of the shape of the negative electrode current collector 34 include a foil shape, a mesh shape, and a porous shape. The negative electrode 30 can be easily manufactured by laminating the negative electrode current collector 34 on the negative electrode active material layer 32 described above. However, depending on the material contained in the negative electrode active material layer 32, the negative electrode current collector 34 may be omitted. In this case, the negative electrode active material layer 32 itself becomes the negative electrode 30.

<Manufacturing of all-solid-state batteries>
The production of the all-solid-state battery is not particularly limited, and examples thereof include the following methods.
One method is to add the component to be the positive electrode active material layer obtained by the above production method to a solvent to form a slurry, apply the slurry to one surface of the solid electrolyte layer, and then dry the slurry. A component serving as a negative electrode may be added to a solvent to form a slurry, and the slurry may be applied to the other surface of the fixed electrolyte layer and then dried. After that, the positive electrode current collector layer and the negative electrode current collector layer are laminated.
As another method, after the solid electrolyte layer is prepared, the positive electrode active material layer prepared as described above is laminated on one surface of the molded body, and the negative electrode active material layer is laminated on the other surface to form a laminated body. Sintering may be performed by applying pressure to the body. After that, the positive electrode current collector layer and the negative electrode current collector layer are laminated.

<Other configurations>
As the battery case, a general battery case can be used, and the battery case is not particularly limited. For example, a stainless steel battery case can be mentioned. Further, as the shape of the sodium ion all-solid-state battery, for example, a coin type, a laminated type, a cylindrical type, a square type and the like can be mentioned.

Hereinafter, the method for producing the positive electrode of the present disclosure will be described with reference to Examples.

[Preparation of positive electrode active material]
<Preparation of the first solution (acidic mixture)>
Manganese nitrate tetrahydrate _{(Mn (NO 3) 2 ·} 4H 2 O, Sigma-Aldrich Japan) 5.02 g, nickel nitrate hexahydrate _{(Ni (NO 3) 2 ·} 6H 2 O, Nacalai Tesque, Inc.) 2 .40G, and cobalt nitrate hexahydrate _{(Co (NO 3) 2 ·} 6H 2 O, sigma-Aldrich Japan) was 3.60g was dissolved in pure water 33.0 g, the acid mixture is a first solution Obtained.
<Preparation of second solution (basic mixture)>
4.25 g of sodium carbonate (Na ₂ CO ₃ , Sigma-Aldrich Japan) is dissolved in 40.0 g of pure water, _{2 mL of aqueous ammonia (NH 4} OH, Kishida Chemical Co., Ltd.) is added, and the mixture is stirred to obtain a second solution. A basic mixed solution was obtained.
<Synthesis of precursors>
44.0 g of the first solution and 45.0 g of the second solution were co-precipitated and heated and stirred overnight. The synthesized precursor was washed by suction filtration and dried.
<Synthesis of positive electrode active material>
The obtained precursor and sodium carbonate (Na ₂ CO ₃ , Sigma Aldrich Japan) were mixed and reacted at 900 ° C. in an air atmosphere to obtain a P2-type layered crystal structure of Na _0.7 Mn _0.5 Ni _0. A positive electrode active material of ₂ Co _0.3 O _{2 was obtained.}

[Synthesis of complex active material]
_{The obtained positive electrode active material and powder of Na 3} Zr ₂ Si ₂ PO ₁₂ , which is a NASICON-type phosphoric acid compound, were mixed, vacuum-sealed and heat-treated at a predetermined temperature to obtain a composite active material. .. Here, the determined temperatures are 300 ° C. for Example 1, 400 ° C. for Example 2, 500 ° C. for Example 3, 600 ° C. for Example 4, 200 ° C. for Comparative Example 1, and 700 ° C. for Comparative Example 2. Is.
The crystal structures of all the examples were examined by an X-ray diffractometer (Ultima IV, Rigaku Co., Ltd.), and it was confirmed that all the positive electrode active materials had a P2-type layered crystal structure.

[Synthesis of solid electrolyte]
Sodium sulfide (Na ₂ S, Sigma-Aldrich Japan), antimony sulfide (Sb ₂ S ₃ Sigma-Aldrich Japan), sulfur (S, Alpha Aesar) in a mol ratio of 3: 2: 1 in an inert atmosphere. This was mixed after weighing. This mixture was mechanically milled and synthesized under an inert atmosphere to obtain a _{Na 3} SbS _{4 solid electrolyte.}

[Cathode preparation]
The synthesized composite active material, the synthesized solid electrolyte, and the conductive material (carbon in this example) were measured at a mass ratio of 50:45: 5, mixed in a mortar, and formed into a columnar shape having a diameter of φ11 and a thickness of 50 μm. A positive electrode active material layer was obtained.
A current collector made of columnar stainless steel was laminated on the obtained positive electrode active material layer to obtain a positive electrode.

[Preparation of negative electrode]
An oil-soaked sodium metal (Sigma-Aldrich Japan) was processed into a disk shape, and a current collector made of columnar stainless steel was laminated on this to form a negative electrode.

[Preparation of solid electrolyte layer]
The solid electrolyte layer was prepared from the solid electrolyte used for the positive electrode active material layer. Specifically, a columnar stainless steel is fitted under the annular (doughnut-shaped) evaluation cell, and a jig for protecting the columnar stainless steel is placed under the columnar stainless steel. Put the solid electrolyte in the ring (inside the hole) of the annular evaluation cell, cover the upper side with columnar stainless steel, put a jig to protect the columnar stainless steel on the top, and press with 6 tons. It was made by compacting.

[Making all-solid-state batteries]
A positive electrode was laminated on one of the solid electrolyte layers obtained as described above, and a negative electrode was laminated on the other to obtain an all-solid-state battery. This was enclosed in a glass desiccator.

[Evaluation]
The interfacial resistance was measured for each example. In this measurement, a voltage of ± 10 mV was applied to the all-solid-state battery of each example with respect to the open circuit voltage, and the interfacial resistance was measured in the range of 0.01 Hz or more and 1 MHz or less. The results are shown in Table 1 and FIG.

表１、図２からわかるように、複合活物質を作製する際の熱処理温度が界面抵抗に大きく影響していることがわかった。

As can be seen from Tables 1 and 2, it was found that the heat treatment temperature at the time of producing the composite active material has a great influence on the interfacial resistance.

100 Sodium ion all-solid-state battery 10 Solid electrolyte layer 22 Positive electrode active material layer 24 Positive electrode current collector 32 Negative electrode active material layer 34 Negative electrode current collector

Claims (1)

A method for manufacturing the positive electrode of a sodium all-solid-state battery.
A method for producing a positive electrode, which comprises a step of mixing a positive electrode active material having a P2-type layered crystal structure and a NASICON-type phosphoric acid compound, and then performing a heat treatment at 300 ° C. or higher and 600 ° C. or lower.

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