JP2023167178A - Electrode material and all-solid-state battery using the same - Google Patents

Abstract

To provide an electrode material using titanium oxide that does not require a step of coating titanium oxide with a solid electrolyte or its precursor and can suppress side reactions even when sintering is performed at a temperature higher than 600°C.SOLUTION: In an electrode material containing titanium oxide particles including titanium oxide particles having an anatase crystal structure, the average primary particle diameter is 300nm to 1500nm as determined by measuring the directional diameter with an electron microscope, and the abundance ratio of particles with a primary particle diameter of less than 300 nm is less than 12%.SELECTED DRAWING: None

Description

The present invention relates to an electrode material and an all-solid-state battery using the same.

In recent years, against the backdrop of growing interest in environmental issues, energy sources have been switching from oil and coal to electricity in various industrial fields. The use of power storage devices such as batteries and capacitors is expanding in a variety of fields, including the following. Currently, secondary batteries using nonaqueous electrolytes, such as lithium ion secondary batteries, are widely used as power storage devices. As secondary batteries using non-aqueous electrolytes, batteries using various materials for electrodes have been proposed, and for example, batteries using titanium oxide as a negative electrode are known (see Patent Document 1). Note that titanium oxide, which is a type of titanium oxide, is widely used for purposes other than electrode active materials of batteries, and is also used, for example, to adjust the refractive index of resin films (see Patent Document 2). Batteries using such non-aqueous electrolytes run the risk of ignition or explosion due to the use of flammable organic solvents in the electrolyte, and the electrolyte freezes in extremely low temperatures, causing the battery to no longer function. There are drawbacks. For this reason, all-solid-state batteries using solid electrolytes have attracted attention in recent years, and research and development are being actively conducted.

Among the solid electrolytes used in all-solid-state batteries, solid electrolytes made of inorganic materials are broadly classified into oxide-based ones and sulfide-based ones. Among these, oxide-based solid electrolytes are generally hard materials and have high grain boundary resistance, so sufficient performance cannot be obtained simply by mixing them with electrode active material powder. For this reason, sintering is performed to bond the electrode active material and the solid electrolyte, but during sintering, undesirable reactions that cause a decrease in battery performance may occur at the interface. For example, in an all-solid-state battery that uses titanium oxide as a negative electrode active material and a phosphoric oxide solid electrolyte, a side reaction phase is formed due to sintering, and the negative electrode operating potential becomes high. To address this problem, a method has been proposed in which the surface of titanium oxide is coated with a solid electrolyte to enable sintering at low temperatures and to suppress the formation of side reaction phases (see Patent Documents 3 and 4). In addition, for the purpose of suppressing the interfacial reaction between Li ₂ CoP ₂ O ₇ , which is a positive electrode active material, and a solid electrolyte, there are methods of coating Li ₂ CoP ₂ O ₇ with Li ₄ P ₂ O ₇ (see Patent Document 5) and , at least one selected from the group consisting of lithium phosphate, lithium niobate, and lithium silicate is used as a solid electrolyte in order to suppress the interfacial reaction between Li ₄ Ti ₅ O ₁₂ , which is a negative electrode active material, and the solid electrolyte. A method (see Patent Document 6) has been proposed. Furthermore, a method has been proposed in which the electrode active material is covered with a solid electrolyte film to suppress oxidation of the positive electrode active material during sintering and to improve battery stability (see Patent Documents 7 and 8).

JP2017-168265A Japanese Patent Application Publication No. 2011-136871 JP 2019-050083 Publication JP 2019-179669 Publication Japanese Patent Application Publication No. 2020-113376 Japanese Patent Application Publication No. 2018-125286 Japanese Patent Application Publication No. 2018-120724 Japanese Patent Application Publication No. 2013-125750

Among various techniques for suppressing defects during sintering to bond the electrode active material and solid electrolyte, Patent Documents 3 and 4 using titanium oxide as the electrode active material include coating titanium oxide with a solid electrolyte. However, it is stated that it was confirmed that no side reactions occur by setting the sintering temperature to 600°C, but from the viewpoint of improving the density of the all-solid-state battery, it is desirable to sinter at a higher temperature. Furthermore, since the techniques of Patent Documents 3 and 4 require a step of coating titanium oxide with a solid electrolyte or its precursor, there is room for improvement from the viewpoint of reducing the number of steps.

The present invention was made in view of the above-mentioned current situation, and does not require a step of coating titanium oxide with a solid electrolyte or its precursor, and suppresses side reactions even when sintering is performed at a temperature higher than 600°C. The purpose of the present invention is to provide an electrode material using titanium oxide that can

The present inventor has developed an electrode using titanium oxide that does not require the step of coating titanium oxide with a solid electrolyte or its precursor and can suppress side reactions even when sintered at a temperature higher than 600°C. After various studies on the material, we found that it contains titanium oxide particles with an anatase crystal structure, has an average primary particle diameter of 300 nm to 1500 nm according to a prescribed measurement method, and the abundance ratio of particles with a primary particle diameter of less than 300 nm is less than 12%. We have discovered that when titanium oxide particles are used as an electrode material, side reactions can be suppressed even when sintering is performed at a temperature higher than 600 ° C. without a step of coating with a solid electrolyte or its precursor, The present invention has now been completed.

The present invention includes the following electrode materials.
[1] An electrode material containing titanium oxide particles, the titanium oxide particles containing titanium oxide particles having an anatase crystal structure, and having an average primary particle diameter of 300 nm as determined by measuring the diameter in a direction with an electron microscope. ~1500 nm, and the abundance ratio of particles with a primary particle diameter of less than 300 nm is less than 12%.
[2] The electrode material has a peak height I _R of a diffraction peak of rutile-type titanium oxide (plane index 110) and a peak height I _A of a diffraction peak (plane index 101) of anatase-type titanium oxide in XRD measurement. , (I _R ×1.32/(I _A +I _R ×1.32))×100 is less than 50.0, the electrode material according to [1].
[3] The electrode material according to [1] or [2], wherein the electrode material is used for an all-solid-state battery.
[4] An all-solid-state battery comprising the electrode material according to any one of [1] to [3] above.

The electrode material of the present invention does not require the step of coating titanium oxide with a solid electrolyte or its precursor, and can suppress side reactions even when sintered at a temperature higher than 600°C, so it is completely solid. It can be suitably used as an electrode material for batteries.

A diagram showing the relationship between voltage and capacity from the start of charging of a battery including an electrode prepared using TiO ₂ particles 1 and 2 of Examples 1 and 2 and comparison TiO ₂ particles 1 and 2 of Comparative Examples 1 and 2. It is.

Preferred embodiments of the present invention will be specifically described below, but the present invention is not limited to the following description, and can be applied with appropriate modifications within the scope of the gist of the present invention. Note that combinations of two or more of the individual preferred embodiments of the present invention described below also correspond to preferred embodiments of the present invention.

1. Electrode material The titanium oxide particles contained in the electrode material of the present invention include titanium oxide particles having an anatase crystal structure, and have an average primary particle diameter of 300 nm to 1500 nm as determined by measuring the diameter in a direction using an electron microscope. The abundance ratio of particles having a primary particle diameter of less than 300 nm is less than 12%.
Here, the term "primary particles" refers to the smallest particles constituting the powder. Particles in which two or more primary particles are aggregated are called "agglomerated particles" and are distinguished from primary particles.
Since the titanium oxide particles have an average primary particle size of 300 nm or more and the abundance ratio of particles with a primary particle size of less than 300 nm is less than 12%, the surface area of the titanium oxide particles becomes small and contact with the solid electrolyte is reduced. By reducing the area, side reactions with the solid electrolyte can be sufficiently suppressed.
In addition, by having the average primary particle diameter of 1500 nm or less, sufficient insertion sites for ions such as Li ⁺ can be secured during the electrode reaction, and ions such as Li ⁺ can reach the inside of the titanium oxide particles sufficiently. Since the titanium oxide particles can diffuse into the interior and contribute to charging and discharging, sufficient charging and discharging capacity can be ensured.
The average primary particle diameter is preferably 300 to 1,300 nm, more preferably 300 to 1,100 nm, still more preferably 600 to 1,100 nm, and particularly preferably 800 to 1,100 nm.

The primary particle diameter is measured using a scanning electron microscope (SEM, for example, but not limited to, JSM-7000F, manufactured by JEOL Ltd.) at a 10,000x field of view. The particle diameter (nm) defined by the distance between parallel lines is measured. The directional diameter is measured for about 150 to 1000 primary particles in a SEM photograph, and the average value of the cumulative distribution is taken as the average primary particle diameter. For aggregated particles, the particles are divided into primary particles and the directional diameter is measured.

In the titanium oxide particles contained in the electrode material of the present invention, the abundance ratio of particles having a primary particle diameter of less than 300 nm is less than 12%. Thereby, even when sintering is performed at a temperature higher than 600° C., side reactions with the solid electrolyte can be sufficiently suppressed.
The abundance ratio of particles having a primary particle diameter of less than 300 nm is measured by the method described in the Examples below.
The abundance ratio of particles having a primary particle diameter of less than 300 nm is preferably less than 11%, more preferably less than 10%.

The above-mentioned _electrode material has _{an I} It is preferable that the value (rutilation rate) represented by ×1.32/(I _A +I _R ×1.32) ×100 is less than 50.0.
The peak height I _A of the diffraction peak (plane index 101) of the anatase-type titanium oxide powder is detected as a value 1.32 times larger than the peak height I _R of the diffraction peak (plane index 110) of the rutile-type titanium oxide powder. Therefore, in the above calculation formula, it is multiplied by a coefficient of 1.32.
If the content of rutile titanium oxide is low, such as the value (rutile rate) expressed by I _R × 1.32 / (I _A + I _R × 1.32) × 100, is less than 50.0. , an all-solid-state battery made using an electrode material containing titanium oxide has better charge-discharge characteristics.
The rutilation rate is more preferably 40 or less, still more preferably 20 or less, even more preferably 10 or less, particularly preferably 5.0 or less.
The value of the rutilation rate can be measured by the method described in the Examples below.

The BET specific surface area of the titanium oxide particles is not particularly limited, but is preferably 0.8 to 7.0 m ² /g. More preferably, it is 1.0 to 5.0 m ² /g, and still more preferably 1.3 to 4.5 m ² /g.
The above BET specific surface area can be measured by the method described in the Examples below.

The titanium oxide particles may contain components other than titanium oxide.
The other components mentioned above are not particularly limited, but include phosphoric acid, dihydrogen phosphate, hydrogen phosphate, phosphate, phosphoric anhydride, metaphosphoric acid, hexametaphosphate, tripolyphosphate, pyrophosphate phosphoric acid, Examples include phosphorus compounds such as diphosphorus pentoxide, compounds containing alkali metal elements and alkaline earth metal elements, metal oxides containing Al, Si, Fe, Zr, and Nb, and compounds containing their sulfates, S, and Cl. It will be done.

The content of the other components in the titanium oxide particles is not particularly limited, but is preferably from 0 to 10 parts by weight based on 100 parts by weight of the titanium oxide particles. More preferably, it is 0 to 5.0 parts by mass.

The content of phosphorus in the titanium oxide particles is not particularly limited, but is preferably 0 to 8.0 parts by mass in terms of P ₂ O ₅ based on 100 parts by mass of the titanium oxide particles. More preferably, it is 0 to 5.0 parts by mass.

The content of the alkali metal salt in the titanium oxide particles is not particularly limited, but it is preferably 0 to 8.0 parts by mass in terms of alkali metal oxide based on 100 parts by mass of the titanium oxide particles. More preferably, it is 0 to 5.0 parts by mass.

2. Method for producing titanium oxide particles included in electrode material The method for producing titanium oxide particles included in the electrode material of the present invention is not particularly limited, but includes a step of mixing titanium hydroxide with an alkali metal salt and/or a phosphorus compound. It is preferable to manufacture by performing (a) and a step (b) of firing the mixture obtained in the mixing step (a).

The titanium hydroxide used in the above step (a) is generally a compound represented by the composition formula: H ₂ TiO ₃ or H ₄ TiO ₄ . It is sometimes called "metatanic acid" or simply "titanic acid" and is a well-known compound represented by chemical formulas such as TiO(OH) ₂ and Ti(OH) ₄ .

When an alkali metal salt is used in step (a) above, the alkali metal salt is considered to act as a flux when firing titanium oxide and promote the growth of primary particles.
Specifically, the above alkali metal salts include lithium hydroxide, lithium chloride, lithium sulfate, lithium hydrogen sulfate, lithium nitrate, lithium carbonate, lithium hydrogen carbonate, lithium formate, lithium acetate, lithium thiosulfate, lithium citrate, and oxalic acid. Lithium salts such as lithium, lithium glutamate, lithium ascorbate, lithium phosphate, lithium oxide; sodium hydroxide, sodium chloride, sodium sulfate, sodium hydrogen sulfate, sodium nitrate, sodium carbonate, sodium hydrogen carbonate, sodium formate, sodium acetate, Sodium salts such as sodium thiosulfate, sodium citrate, sodium oxalate, sodium glutamate, sodium ascorbate, sodium phosphate; potassium hydroxide, potassium chloride, potassium sulfate, potassium hydrogen sulfate, potassium nitrate, potassium carbonate, potassium hydrogen carbonate, Examples include potassium salts such as potassium acetate, potassium citrate, potassium oxalate, and potassium phosphate; and cesium salts such as cesium hydroxide, cesium chloride, cesium sulfate, cesium nitrate, cesium carbonate, and cesium phosphate.
Among these, sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, cesium sulfate, chlorides such as lithium chloride, sodium chloride, potassium chloride, cesium chloride, lithium phosphate, sodium phosphate, potassium phosphate, phosphoric acid Phosphates such as cesium are preferred.

In the above step (a), when an alkali metal salt is used, the amount of the alkali metal salt added is 100 parts by mass of titanium hydroxide as TiO ₂ as an alkali metal oxide, that is, as a mass converted to an alkali metal oxide. The total amount is preferably 1.0 to 11.0 parts by mass. The amount added is preferably 1.0 to 5.0 parts by weight, and even more preferably 1.0 to 3.0 parts by weight.

In the above step (a), the phosphorus compounds that can be used include the above-mentioned phosphorus compounds.

The amount of the phosphorus compound added in step (a) is preferably 0 to 10.0 parts by mass as P ₂ O ₅ per 100 parts by mass of titanium hydroxide as TiO ₂ . More preferably, it is 0 to 5.0 parts by mass, and even more preferably 0 to 3.0 parts by mass.
When the alkali metal salt is a phosphate, the alkali metal phosphate is also a phosphorus compound.

Step (a) may be performed without a solvent or in the presence of a solvent. Usable solvents include, but are not particularly limited to, water such as pure water and ion-exchanged water, and water-soluble organic solvents such as alcohols such as methanol, ethanol, n-propanol, and i-propanol, ethylene glycol, diethylene glycol, and glycerin. Examples include polyhydric alcohols such as N-methylpyrrolidone, pyrrolidone solvents such as N-methylpyrrolidone, and ketone solvents such as acetone. Among these, water is preferred because the salt has high solubility, and water slurries of titanium hydroxide are available on the market and are inexpensive.

The mixing method in step (a) is not particularly limited, and for example, dry or wet mixing may be performed using a known mixer such as a rotary blade, a rotary tank, a mixer, or a ball mill.

In the above step (a), various additives may be further added as necessary. Examples of the additive include, but are not limited to, ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), acidic ammonium sulfate ((NH ₄ )HSO ₄ ), and the like. By adding these components, it is expected that grain growth will proceed evenly and that the particle size distribution of the obtained titanium oxide will be more uniform.

After the above step (a), a drying step of drying the mixture obtained in step (a) may be performed. When performing the drying step, the drying temperature is not particularly limited as long as the titanium oxide is sufficiently dried, but it is preferably 80 to 200°C. The temperature is more preferably 90 to 150°C, and even more preferably 100 to 120°C.

The firing temperature in the above step (b) is 750 to 1200°C. The lower limit of the firing temperature is preferably 800°C, more preferably 850°C. Moreover, the upper limit is preferably 1100°C, more preferably 1000°C.

In the method for producing titanium oxide particles described above, the fired powder may be crushed if necessary. The method of crushing is not particularly limited, and includes automatic mortar crushing, hammer mill crushing, fluid energy mill crushing, bead mill crushing by repulping into a medium, and the like.

3. Electrode for all-solid-state batteries The electrode material of the present invention can sufficiently suppress side reactions with solid electrolytes and has excellent charge-discharge characteristics, so it is suitably used in all-solid-state batteries.
The present invention also provides an electrode for an all-solid-state battery constructed using the electrode material of the present invention.
The all-solid battery electrode of the present invention is constructed using the electrode material of the present invention, but preferably further contains a solid electrolyte. If it contains a solid electrolyte, lithium ions will efficiently diffuse into the electrode active material in an all-solid-state battery, and the transfer will be performed smoothly.
When the electrode for an all-solid-state battery of the present invention includes a solid electrolyte, the content of the solid electrolyte is preferably 1 to 70% by mass based on the titanium oxide contained in the electrode. More preferably, it is 1 to 60% by mass, and even more preferably 1 to 50% by mass.

The all-solid-state battery electrode of the present invention may further contain components other than the solid electrolyte. Other components include conductive aids such as carbon black, carbon nanofibers, and acetylene black.

When the electrode for an all-solid-state battery of the present invention contains a conductive additive, the content of the conductive additive is preferably 1 to 60% by mass based on the titanium oxide contained in the electrode. More preferably, it is 1 to 40% by mass, and even more preferably 1 to 30% by mass.

The all-solid-state battery electrode of the present invention may contain components other than the electrode material of the present invention, solid electrolyte, and conductive aid. Other components include binders and the like.
As the binder, one or more of polytetrafluoroethylene, polyvinylidene fluoride, acrylic polymer, etc. can be used.

In the all-solid-state battery electrode of the present invention, the proportion of other components other than the electrode material of the present invention, solid electrolyte, and conductive aid should be 50% by mass or less with respect to 100% by mass of the all-solid-state battery electrode. is preferred. More preferably, it is 35% by mass or less, and still more preferably 30% by mass or less. The mass of the all-solid-state battery electrode means the mass of components excluding volatile components in the electrode material composition described below.

4. Method for producing an electrode for an all-solid-state battery The method for producing an electrode for an all-solid-state battery of the present invention is not particularly limited. A method including a step of forming a film made of the composition on a solid electrolyte, a step of firing a solid electrolyte having a film made of the electrode material composition, and sintering the electrode and the solid electrolyte to form a composite is used. be able to.

In the above method, it is preferable that the electrode material composition containing the electrode material of the present invention and a binder further contains a solid electrolyte. When a solid electrolyte is included, the ratio of the solid electrolyte to titanium oxide contained in the electrode material composition is preferably the same as in the case where the all-solid battery electrode of the present invention contains a solid electrolyte.

In the above method, it is preferable that the electrode material composition containing the electrode material of the present invention and a binder further contains a conductive additive. When a conductive additive is included, the ratio of the conductive additive to titanium oxide contained in the electrode material composition is the same as in the case where the all-solid-state battery electrode of the present invention contains a conductive additive. It is preferable.

In the above method, the binder contained in the electrode material composition containing the electrode material and binder of the present invention is not particularly limited as long as it functions as a binder, and the same binder as described above can be used.

In the above method, the ratio of the binder contained in the electrode material composition containing the electrode material of the present invention and a binder is preferably 0 to 60% by mass based on 100% by mass of the electrode material composition. More preferably, it is 0 to 40% by mass, and still more preferably 0 to 30% by mass.

In the above method, the electrode material composition containing the electrode material of the present invention and a binder may contain components other than the electrode material of the present invention, the binder, the solid electrolyte, and the conductive aid. Other components include solvents and the like.

The above solvents include water, alcohols such as methanol, ethanol, and terpineol; ether solvents such as dimethyl ether and diethyl ether; ketone solvents such as acetone and diethyl ketone; and ester solvents such as butyl acetate and ethyl acetate. , benzene, toluene, and other aromatic solvents, one or more of them can be used.

The content of other components such as the solvent is preferably 50% by mass or less based on 100% by mass of the electrode material composition. More preferably, it is 40% by mass or less, and still more preferably 30% by mass or less.

In the step of forming a film made of an electrode material composition on a solid electrolyte in the above method, the method of forming a film made of an electrode material composition on a solid electrolyte is not particularly limited. For example, a method of coating and drying can be used.

In the above method, the sintering temperature in the step of sintering the solid electrolyte having a membrane made of the electrode material composition to composite the electrode and the solid electrolyte is particularly limited as long as the electrode and the solid electrolyte are sufficiently composited. However, it is preferably 500 to 800°C. The temperature is more preferably 550 to 700°C, even more preferably 600 to 650°C.
Further, the firing time is not particularly limited as long as the electrode and solid electrolyte are sufficiently composited, but it is preferably 1 to 24 hours. More preferably, the time is 2 to 12 hours, and even more preferably 4 to 8 hours.
Further, from the viewpoint of preventing combustion of carbon, which is a conductive additive, it is preferable that the firing is performed in an atmosphere of an inert gas such as helium, nitrogen, or argon, or under vacuum.

The above method includes a step of preparing an electrode material composition containing the electrode material of the present invention and a binder, a step of forming a film made of the obtained electrode material composition on a solid electrolyte, and a step of forming the electrode material composition from the electrode material composition. The method may include steps other than the step of firing the solid electrolyte having the film to sinter the electrode and the solid electrolyte to form a composite. Other steps include a step of subjecting the solid electrolyte having a film made of the electrode material composition to pressure pressing or cold isostatic pressure treatment before firing.

The solid electrolyte used in the present invention is not particularly limited as long as it is an oxide-based one, and includes Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ , Li _7+x La ₃ Zr _2-y A _y O ₁₂ (A is represents one or more elements selected from the group consisting of Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, and Ge), Li ₅ La ₃ Nb ₂ O ₁₂ , Li _x La _(1-x)/3 One or more of NbO ₃ , Li ₃ PO ₄ and Li ₄ SiO ₄ and solid solutions thereof, Li ₂ SiO ₃ , Li ₆ SiO ₅ and the like can be used. Among these, Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ (hereinafter also referred to as LAGP) is preferred.
When LAGP is used as a solid electrolyte, the following formula (1) is obtained when sintering with titanium oxide.
TiO ₂ + Li _1+x Al _x Ge _2-x (PO ₄ ) ₃
→ Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ + GeO ₂ (1)
A side reaction of Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ (hereinafter also referred to as LATP) and GeO ₂ is formed. Causes electrical potential. In contrast, by using the electrode material of the present invention, the formation of such side reaction phases can be effectively suppressed, and the charging and discharging reactions using titanium oxide as the electrode active material can proceed sufficiently, thereby increasing the operating potential. The occurrence of high potential can be suppressed. It is considered that when LAGP is used as the solid electrolyte in this way, the effect of using the electrode material of the present invention is more fully exhibited.

5. All-solid-state battery The present invention is also an all-solid-state battery characterized by comprising the electrode material (electrode for an all-solid-state battery) of the present invention. As mentioned above, by using the electrode material of the present invention, the formation of a side reaction phase when sintering with a solid electrolyte is suppressed, effectively suppressing the increase in the operating potential of the electrode, and improving the charge/discharge characteristics. An excellent all-solid-state battery (all-solid-state secondary battery) can be obtained.

In the all-solid-state battery of the present invention, the electrode constructed using the electrode material of the present invention may be used as a positive electrode or a negative electrode, but is preferably used as a negative electrode. When used as a negative electrode, various lithium compounds and other various metal compounds capable of intercalating and deintercalating lithium can be used as positive electrode active materials.
When the all-solid battery electrode of the present invention is used as a negative electrode, the positive electrode active materials include Li _x FePO ₄ , Li _x Fe _1-y Mny PO ₄ , _{Li x CoPO 4} (0<x≦1, and 0 ≦y≦1) Lithium phosphate having an olivine structure; lithium manganese composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium manganese cobalt composite oxide, lithium manganese nickel Composite compounds, composite oxides of lithium and other metals such as spinel-type lithium manganese nickel composite oxides, lithium nickel cobalt manganese composite oxides, etc. can be used.

A positive electrode constructed using the above positive electrode active material may contain other components other than the positive electrode active material. Other components include conductive aids such as carbon black, carbon nanofibers, and acetylene black; binders such as polytetrafluoroethylene, polyvinylidene fluoride, and acrylic polymers.

The positive electrode may be produced by forming a film made of a positive electrode material composition containing a positive electrode active material on a current collector.

In the present invention, the current collector used for producing the electrode may be any material that can be used as a current collector, such as magnesium, titanium, zinc, nickel, manganese, iron, copper, aluminum, Gold etc. can be used.

Specific examples are given below to explain the present invention in detail, but the present invention is not limited only to these examples. Unless otherwise specified, "%" and "wt%" mean "% by weight (% by mass)". The method for measuring each physical property is as follows.

<Rutilation rate>
The rutilation rate is calculated by dividing the peak intensity I _R of the diffraction peak of rutile titanium oxide (plane index 110) and the peak intensity I _A of the diffraction peak (plane index 101) of anatase titanium oxide in the XRD spectrum by I _R ×1 It is a value expressed by .32/(I _A + I _R ×1.32) ×100. Note that the XRD measurement was carried out using a parallel beam method using RINT-TTRIII manufactured by Rigaku. Further, the X-ray output was set to 50 kV, 300 mA, and step mode (step width: 0.01°). In the analysis, background processing was performed using integrated powder X-ray analysis software PDXL2 manufactured by Rigaku Co., Ltd., and peak intensities I _A and I _R were calculated.

<Primary particle diameter>
(For comparisons other than TiO ₂ particles 1)
The primary particle diameter is defined as the diameter in a fixed direction (distance between two parallel lines in a fixed direction sandwiching the particle) in a 10,000x field of view in a photograph taken using a scanning electron microscope (JSM-7000F, manufactured by JEOL Ltd.). The diameter (μm) of 150 primary particles in the SEM photograph was measured, and the average value of the cumulative distribution was determined. Regarding aggregated particles, the particles were divided into primary particles and the directional diameter was measured.
(Comparative case of TiO ₂ particles 1)
The primary particle diameter is the particle diameter defined by the diameter in a fixed direction (the distance between two parallel lines in a fixed direction that sandwich the particle) in a 1000x field of view in a photograph taken using a scanning electron microscope (JSM-7000F, manufactured by JEOL Ltd.). (μm), the directional diameter of 150 primary particles in the SEM photograph was measured, and the average value of the cumulative distribution was determined. Regarding aggregated particles, the particles were divided into primary particles and the directional diameter was measured.

<How to calculate abundance ratio>
The sum of the primary particle diameters of all the particles whose directional diameters were measured using an electron microscope using the method described above is determined, and the ratio of the cumulative value of the primary particle diameter of particles whose primary particle diameter is less than 300 nm to the total sum is determined as the abundance ratio A, 300 nm. The ratio of the cumulative value of the primary particle diameter of particles with a diameter of 3000 nm or more and less than 3000 nm was defined as the abundance ratio B, and the ratio of the cumulative value of the primary particle diameter of the particles with a diameter of 3000 nm or more was defined as the abundance ratio C.

<BET specific surface area, BET conversion diameter>
Using a fully automatic specific surface area measuring device (Macsorb, manufactured by Microtrac), the BET specific surface area was measured by adsorption/desorption measurement after degassing at 200°C for 30 minutes and preheating at 200°C for 5 minutes. .

<Side reaction rate evaluation>
(1) 8 g each of titanium oxide particles and solid electrolyte (glass-LAGP) were weighed out and mixed for 3 hours using a stirrer mortar.
(2) The powder mixed in (1) was fired at 650°C, 700°C, or 750°C (temperature increase rate: 300°C/h).
(3) XRD measurement was performed on the fired powder.
The spectrum obtained by the XRD measurement was subjected to BG treatment, and the side reaction rate between titanium oxide and LAGP was calculated based on the following equation (2) from the XRD chart after the BG treatment.
Side reaction rate = I _LATP / I _LAGP (2)
I _LATP : Strongest peak intensity of LATP at 29.6±0.5° I _LAGP : Strongest peak intensity of LAGP at 30.5±0.5°

<Preparation Example 1: (Preparation of glass-LAGP)>
25 g of crystal particles of Li _1.3 Al _0.3 Ge _1.7 (PO ₄ ) ₃ were melted at 1200° C. for 1 hour and then rapidly cooled. After pulverizing in a planetary ball mill at 200 rpm for 2 hours, it was passed through a 150 μm sieve to collect glass-LAGP.

<Example 1>
Weigh out 100g of titanium hydroxide slurry (manufactured by Sakai Chemical Industry Co., Ltd., ST-C) as _TiO2 (100 parts by mass as _TiO2 ), place it in a porcelain evaporation dish with an outer diameter of 150mm and a capacity of 400ml, and add 80g/l of sulfuric acid. 125 ml of potassium aqueous solution (10.0 parts by mass as K ₂ SO ₄ ) was added, stirred for 30 minutes, and evaporated to dryness at 100°C. The obtained powder was passed through a sieve with an opening of 300 μm, and then left and fired at 900° C. for 4 hours. The fired powder was crushed in an alumina mortar for 15 minutes. 90 g of crushed powder was repulped in 880 mL of 0.1 M hydrochloric acid, stirred for 30 minutes, passed through a sieve with an opening of 40 μm, the repulp liquid under the sieve was transferred to a Buchner funnel and filtered, and washed with 2 liters of pure water. It was evaporated to dryness at 100°C. The obtained powder 1 was passed through a 150 μm sieve to obtain TiO ₂ particles 1.

<Example 2>
Weigh out 100 g of titanium hydroxide slurry (ST-C, manufactured by Sakai Chemical Industries, Ltd.) as TiO ₂ (100 parts by mass as TiO ₂ ), place it in a porcelain evaporating dish with an outer diameter of 150 mm and a capacity of 400 ml, and add 95% triphosphate. A suspension of 5.44 g of lithium (2.0 parts by mass as Li ₂ O, 3.17 parts by mass as P ₂ O ₅ ) in 10 mL of pure water was added, stirred for 30 minutes, and evaporated to dryness at 100 °C. hardened. The obtained powder was passed through a sieve with an opening of 300 μm, and then left and fired at 870° C. for 4 hours. The fired powder was crushed in an alumina mortar for 15 minutes. 90 g of crushed powder was repulped in 880 mL of 0.1 M hydrochloric acid, stirred for 30 minutes, passed through a sieve with an opening of 40 μm, the repulp liquid under the sieve was transferred to a Buchner funnel and filtered, and washed with 2 liters of pure water. It was evaporated to dryness at 100°C. The obtained powder was passed through a 150 μm sieve to obtain TiO ₂ particles 2.

<Comparative example 1>
To 1200 mL of pure water, 600 mL of titanyl sulfate concentrate and 360 g of NaCl were added and mixed. The mixed solution was heated and stirred at 90° C. and refluxed for 3 hours. The obtained slurry was filtered and washed with water to obtain solid content. The solid content was again repulped into pure water, and an ammonia aqueous solution was added until the pH of the slurry became about 8-9. Washing was performed again with pure water, and the solid content was dried to obtain metatitanic acid aggregates.
The obtained metatitanic acid aggregates were dispersed in pure water, 3.0 wt% of 85% phosphoric acid was added and mixed as _P2O5 to _TiO2 in the metatitanic acid aggregates, and the mixture was _stirred at 100°C. Evaporated to dryness. The obtained powder was calcined at 900° C. for 4 hours, washed with 0.1 M HCl, and dried to obtain comparative TiO ₂ particles 1.

<Comparative example 2>
TiO ₂ (Sakai Chemical Industry Co., Ltd. product: SA-120) was used as comparative TiO ₂ particles 2.

<Example 3>
24.75 g of TiO ₂ particles 2 obtained in Example 2 and 0.2475 g of Comparative TiO ₂ particles 2 obtained in Comparative Example 2 were added to 200 mL of pure water, stirred with a stirrer for 30 minutes, and heated at 100 ° C. After drying, it was passed through a 150 μm sieve to obtain TiO ₂ particles 3.

<Comparative example 3>
23.75 g of TiO ₂ particles 2 obtained in Example 2 and 1.1875 g of Comparative TiO ₂ particles 2 obtained in Comparative Example 2 were added to 200 mL of pure water, stirred with a stirrer for 30 minutes, and heated at 100 ° C. After drying, it was passed through a 150 μm sieve to obtain comparative TiO ₂ particles 3.

<Comparative example 4>
22.5 g of TiO ₂ particles 2 obtained in Example 2 and 2.250 g of Comparative TiO ₂ particles 2 obtained in Comparative Example 2 were added to 200 mL of pure water, stirred with a stirrer for 30 minutes, and heated at 100 ° C. After drying, it was passed through a 150 μm sieve to obtain comparative TiO ₂ particles 4.

The above physical properties were evaluated for the titanium oxide particles of Examples 1 to 3 or Comparative Examples 1 to 4, and the results are shown in Table 1. In the particle size distribution, the proportion of particles whose primary particle diameter (length) is greater than 0 nm and less than 300 nm is defined as the abundance ratio A, and the proportion of particles whose primary particle diameter (length) is 300 nm or more and less than 3000 nm is defined as the abundance ratio B. The proportion of particles having a particle diameter (length) of 3000 nm or more was defined as the abundance ratio C.

For TiO ₂ particles 1 to 3 of Examples 1 to 3 and comparative TiO ₂ particles 2 to 4 of Comparative Examples 2 to 4, the side reaction rate with LAGP at firing temperatures of 650° C., 700° C., and 750° C. was measured.
The results are shown in Table 2.

<Preparation of electrode>
Add TiO ₂ particles 1 of Example 1, acetylene black, and polytetrafluoroethylene (PTFE) in a weight ratio of 80:10:10 to an agate mortar, and mix well for 1 hour while dropping acetone. A paste was made. The prepared paste was pasted on a nickel mesh and dried at 150° C. under vacuum to prepare electrode 1.
Using TiO ₂ particles 2 of Example 2 and comparison TiO ₂ particles 1 and 2 of Comparative Examples 1 and 2, electrode 2, comparative electrode 1, and comparative electrode 2 were produced in the same manner as in Example 1 above.

<Electrode performance evaluation>
On the negative electrode body, a copper foil, the electrode 1 produced using the TiO ₂ particles 1 of Example 1, a separator, a metal Li foil, and a copper foil were stacked in this order, and finally the positive electrode body was placed on top and screwed. A battery for electrode performance evaluation was constructed using 1 mol/L LiPF ₆ EC:DEC (1:1 v/v%) as the electrolyte. Electrode performance was evaluated using the following method.
Electrode performance was similarly evaluated for electrode 2 and comparative electrodes 1 and 2 using the TiO ₂ particles of Example 2 and comparison TiO ₂ particles 1 and 2 of Comparative Examples 1 and 2. The results are shown in Table 3 and Figure 1.
The charge/discharge test was performed at a current density of 0.05 C for 3 cycles after being left at an open circuit voltage for 12 hours.
Note that, as shown in the following formulas (3) and (4), the insertion reaction of lithium into titanium oxide was defined as charging, and the desorption reaction of lithium was defined as discharging.
"charging"
TiO ₂ (A) + Li ⁺ +e ⁻ →LiTiO ₂ (3)
《Discharge》
LiTiO ₂ →TiO ₂ (A) + Li ⁺ +e ^- (4)
Regarding each condition, charging was CC charging and the 1.2V termination was 1.6V, the 3rd cycle was 1.0V termination, and the discharging was CC discharge and 3.0V termination. Using the charging curve of the third cycle, the electrode performance shown in Table 3 was analyzed.

From the results in Table 2, in Examples 1 to 3, in which the abundance ratio of particles with a primary particle size of less than 300 nm was less than 12%, the side reaction with the solid electrolyte was sufficiently suppressed even when the firing temperature was 700°C or 750°C. It has become clear that it is possible to suppress the
Moreover, from the results in Table 3, it became clear that Examples 1 and 2, in which the average primary particle diameter was 1500 nm or less, also had excellent charge-discharge characteristics.

<Evaluation of the amount of side reactions when a mixture of TiO ₂ and LAGP is fired at 650°C (charge/discharge test)>
The glass-LAGP prepared in Preparation Example 1 and the TiO ₂ particles 1 of Example 1 were added at a weight ratio of 1:1 and mixed for 3 hours. The powder was then baked at 650°C for 4 hours (heating rate 300°C/h). did.
The above baked powder, acetylene black, and polytetrafluoroethylene (PTFE) were added to an agate mortar at a weight ratio of 80:10:10, and mixed thoroughly for 1 hour while dropping acetone to prepare a paste. The prepared paste was attached to a nickel mesh and dried at 150° C. under vacuum to produce an electrode 1A (650° C.).
Further, using the TiO ₂ particles 2 of Example 2 and the comparative TiO ₂ particles 2 of Comparative Example 2, electrode 2A and comparative electrode 2A were produced in the same manner as the electrode 1A.

Electrode performance evaluation was performed in the same manner as in Example 1, except that electrodes 1A, 2A, and 2A were used instead of electrodes 1, 2, and comparison electrode 2.
For batteries each equipped with electrode 1A, electrode 2A, and comparison electrode 2A, the voltage (V) from the start of charging and the charging capacity Q (mAh/g) are plotted (plot A), and the absolute value of dV/dQ ( |dV/dQ|) and charging capacity Q were plotted (plot B).
In plot B, the region from the start of battery charging to the end of charging can be divided into the following three regions.
(1) Region 1: From the start of charging to the point where |dV/dQ|=0.0025 around 1.6V, region 1 is caused by the original electrode reaction using TiO ₂ as an active material and the side reaction between TiO 2 and LAGP. This is also the region where the charging reaction due to generated LATP also progresses.
(2) Region 2: Range of |dV/dQ|≦0.0025 after region 1 Region 2 is a region where charging reaction by LATP does not proceed, but reversible charging reaction originating from anatase type TiO ₂ proceeds. be.
(3) Region 3: This is the region after region 2 where the charging reaction of each component has sufficiently progressed until the end of charging.
The charging capacity in each of these regions is measured, and the degree of side reaction in the titanium oxide electrode is evaluated from the value (called the C value) of (charging capacity in region 1)/(charging capacity in region 1 + region 2) do.
The results are shown in Table 4.

From the results in Table 4, it can be confirmed that Examples 1 and 2 have lower C values than Comparative Example 2, and side reactions can be sufficiently suppressed.
Although Comparative Example 2 has excellent charge/discharge capacity from the results in Table 3, it is confirmed from the results in Tables 2 and 4 that the side reaction with LAGP progresses significantly, and the potential of the electrode is likely to increase. I can say that.

From the above, in titanium oxide particles having an anatase crystal structure, by setting the average primary particle size within a predetermined range and keeping the abundance ratio of particles with a primary particle size of less than 300 nm below a predetermined ratio, it is possible to It has become clear that even when sintering is performed at high temperatures, side reactions can be suppressed and sufficient charge/discharge capacity can be ensured.

Claims (4)

An electrode material containing titanium oxide particles,
The titanium oxide particles include titanium oxide particles having an anatase crystal structure, and have an average primary particle diameter of 300 nm to 1500 nm as determined by measuring the diameter in a direction using an electron microscope, and particles with a primary particle diameter of less than 300 nm. An electrode material having an abundance ratio of less than 12%. The _{electrode material} has (I The electrode material according to claim 1, wherein the value of _R x 1.32/(I _A + I _R x 1.32)) x 100 is less than 50.0. The electrode material according to claim 1 or 2, wherein the electrode material is used for an all-solid-state battery. An all-solid-state battery comprising the electrode material according to claim 1 or 2.

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