JP7259792B2 - Negative electrode active material, method for producing negative electrode active material, and battery - Google Patents

Description

The present disclosure relates to a negative electrode active material, a method for producing the negative electrode active material, and a battery.

Batteries have been actively developed in recent years. For example, in the automotive industry, the development of batteries used in electric vehicles or hybrid vehicles and active materials used in batteries is underway.

For example, a Si-based active material is known as a negative electrode active material used for a negative electrode layer of an all-solid-state battery. For example, Patent Literature 1 discloses an all-solid battery using composite particles of Si and carbon as a negative electrode active material. Patent Documents 2 and 3 disclose the use of porous silicon as a negative electrode active material.

JP 2017-054720 A JP 2013-008487 A JP 2013-203626 A

A negative electrode active material is required to have a small amount of expansion due to charging. The present disclosure has been made in view of the above circumstances, and a main object of the present disclosure is to provide a negative electrode active material with a small amount of swelling due to charging.

In order to solve the above problems, the present disclosure provides a negative electrode active material used in a battery, wherein the negative electrode active material is non-woven fabric particles containing Si fibers, and the average particle diameter of the negative electrode active material (D ₅₀ ) is 0.2 μm or more and 3.6 μm or less, and the negative electrode active material is amorphous.

According to the present disclosure, since the negative electrode active material is non-woven fabric particles containing Si fibers, the negative electrode active material can be made to have a small amount of expansion due to charging.

In the above disclosure, the peak position may be at 2θ=28.4°±0.5° and the Si-derived peak a may not be observed in the XRD measurement using CuKα rays.

In the above disclosure, in the XRD measurement using CuKα rays, the peak position is at 2θ=28.4°±0.5°, and a peak a derived from Si is observed, and the peak position is 2θ=24. A peak b that is at 0 ° to 32.0 ° and has a half width of 3 ° or more is observed. When the intensity of the peak a is Ia and the intensity of the peak b is Ib, the XRD intensity ratio (Ia/Ib) may be 3.80 or less.

In the above disclosure, the peak position may be at 2θ=20.8°±0.5° and the peak c derived from SiO ₂ may not be observed in the XRD measurement using CuKα rays.

In the disclosure above, the peak position is at 2θ=20° to 30°, and the peak d derived from lithium silicate may not be observed.

In the above disclosure, the Si fibers may have an average diameter of 8 nm or more and 70 nm or less.

In the above disclosure, the Si fibers may have an aspect ratio (average length/average diameter) of 1 or more and 50 or less.

Further, in the present disclosure, a dispersing step of adding a dispersion medium to a LiSi precursor containing Si element and Li element to obtain a LiSi precursor dispersion, and adding a Li extraction solvent to the LiSi precursor dispersion. and extracting the Li element from the LiSi precursor to obtain non-woven fabric-like particles containing Si fibers, wherein the dispersion medium has a dielectric constant of 3.08 or less. Provided is a method for producing a negative electrode active material.

According to the present disclosure, by performing the Li extraction step after the dispersion step, it is possible to produce a negative electrode active material that is non-woven fabric-like particles containing Si fibers.

In the above disclosure, the dispersion medium may be at least one of n-butyl ether, 1,3,5-trimethylbenzene and n-heptane.

In the above disclosure, the Li extraction solvent may be at least one of ethanol, 1-propanol, 1-butanol, 1-hexanol and acetic acid.

The above disclosure may include a washing step of washing the non-woven fabric particles with an acid after the Li extraction step.

Further, in the present disclosure, a battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer, wherein the negative electrode active material A battery is provided in which the layer contains the negative electrode active material described above.

According to the present disclosure, the negative electrode active material layer contains the negative electrode active material described above, so that the battery can reduce the binding pressure.

The negative electrode active material according to the present disclosure has the effect of having a small amount of expansion due to charging.

FIG. 2 is a flow chart showing an example of a method for producing a negative electrode active material in the present disclosure; 1 is a schematic cross-sectional view showing an example of a battery in the present disclosure; FIG. 4 shows the result of XRD measurement of the negative electrode active material in Example 1. FIG. 1 is a TEM image of negative electrode active materials in Examples 1 and 2 and Comparative Example 1. FIG. 4 is an SEM image of a negative electrode active material in Comparative Example 1. FIG. 2 shows the results of XRD measurement of negative electrode active materials in Examples 8 to 10. FIG.

The negative electrode active material, the method for producing the negative electrode active material, and the battery according to the present disclosure will be described in detail below.

A. Negative electrode active material The negative electrode active material in the present disclosure is a negative electrode active material used in a battery, the negative electrode active material is a non-woven fabric containing Si fibers, and the average particle diameter (D ₅₀ ) is 0.2 μm or more and 3.6 μm or less, and the negative electrode active material is amorphous.

According to the present disclosure, since the negative electrode active material is non-woven fabric particles containing Si fibers, the negative electrode active material can be made to have a small amount of expansion due to charging. For example, as in Patent Documents 1 to 3 above, it is known to use high-capacity Si particles as a negative electrode active material. However, when Si particles are used as the negative electrode active material, expansion due to charging increases. On the other hand, in Patent Document 1, expansion is suppressed by adjusting the particle size of the negative electrode active material and providing a predetermined gap in the negative electrode (negative electrode active material layer). Moreover, in Patent Documents 2 and 3, expansion is suppressed by making the negative electrode active material particles porous. However, there is room for further improvement in swelling reduction. On the other hand, as a result of extensive studies, the inventors of the present invention have found that a non-woven fabric-like negative electrode active material in which Si fibers are three-dimensionally entangled can be obtained by a predetermined method. The porous negative electrode active material particles described in Patent Documents 2 and 3 are considered to have a shape as shown in the microscope image of Comparative Example 1 described later, and the negative electrode active material having a shape such as that of the present disclosure has been conventionally unknown. Furthermore, the inventors have found that such a negative electrode active material can further reduce the amount of swelling during charging.

Also, the negative electrode active material in the present disclosure is amorphous. Amorphous, that is, low-crystalline silicon, is thought to have a longer Si—Si bond distance than crystalline silicon. It is thought that the expansion of time) can be further suppressed.

Furthermore, the negative electrode active material in the present disclosure has a predetermined average particle size ( _D50 ). When a negative electrode active material with a large average particle size is used for the negative electrode active material layer, ions are preferentially inserted into the negative electrode active material with a large particle size, and the negative electrode active material layer locally expands significantly. However, with an average particle size as disclosed in the present disclosure, it is believed that ions are uniformly inserted into the entire negative electrode active material, and the negative electrode active material layer uniformly expands. As a result, it is considered that expansion of the negative electrode active material layer as a whole can be suppressed.
The negative electrode active material in the present disclosure will be described in more detail below.

The negative electrode active material in the present disclosure is non-woven fabric particles containing Si fibers. In the present disclosure, the non-woven fabric means a mesh shape in which Si fibers are three-dimensionally entangled.

Si fibers in the present disclosure may have a predetermined average diameter. The average diameter is, for example, 8 nm or more, may be 10 nm or more, may be 15 nm or more, or may be 20 nm or more. On the other hand, the average diameter is, for example, 70 nm or less, may be 60 nm or less, may be 50 nm or less, may be 40 nm or less, or may be 30 nm or less. Also, the Si fibers in the present disclosure may have a predetermined average length. The average length is, for example, 50 nm or more and 400 nm or less. Here, the length of the Si fiber in the present disclosure is defined as the length from one connection point (point where a plurality of Si are connected) to the other connection point (point where a plurality of Si are connected). The average length and average diameter of Si fibers can be determined, for example, by observation with a scanning electron microscope (SEM). The number of samples is preferably large, for example 100 or more.

Also, the Si fibers in the present disclosure may have a predetermined aspect ratio (average length/average diameter). The aspect ratio (average length/average diameter) is, for example, 1 or more, may be 5 or more, may be 15 or more, or may be 20 or more. On the other hand, the aspect ratio (average length/average diameter) is, for example, 50 or less, may be 40 or less, or may be 30 or less.

The Si fiber in the present disclosure may be a simple substance of Si, or may be an alloy containing Si element as a main component. The proportion of Si element in the alloy is, for example, 50 at % or more, may be 70 at % or more, or may be 90 at % or more. Examples of metal elements other than Si elements in the alloy include Li elements.

The negative electrode active material in the present disclosure has a predetermined average particle size ( _D50 ). The average particle diameter (D ₅₀ ) is 0.2 μm or more, and may be, for example, 0.5 μm or more, 1.0 μm or more, or 1.5 μm or more. On the other hand, the average particle diameter (D ₅₀ ) is 3.6 μm or less, and may be, for example, 3.0 μm or less, 2.5 μm or less, or 2.0 μm or less. When the average particle diameter (D ₅₀ ) of the negative electrode active material is within the above range, when it is used in the negative electrode active material layer, ions are uniformly inserted into the entire negative electrode active material, and the negative electrode active material layer is uniformly expanded. By doing so, it is considered that the expansion of the entire negative electrode active material layer can be suppressed. The average particle size (D ₅₀ ) can be determined, for example, by observation with a scanning electron microscope (SEM). The number of samples is preferably large, for example 100 or more. A method for adjusting the average particle size (D ₅₀ ) will be described later in "B. Manufacturing method of negative electrode active material".

Also, the negative electrode active material in the present disclosure is amorphous. Here, in the present disclosure, the term “amorphous” means that a halo peak (a broad peak in the halo pattern) is confirmed in XRD measurement using CuKα rays. The halo peak preferably has a peak position at 2θ=24.0° to 32.0° in XRD measurement using CuKα rays. Similarly, the halo peak preferably has a peak position at 2θ=40.0° to 60.0°. Further, the half width of the halo peak is, for example, 3° or more, may be 5° or more, or may be 10° or more. In the present disclosure, in the XRD measurement using CuKα rays, a halo peak having a peak position at 2θ = 24.0 ° to 32.0 ° and a half width of 3 ° or more (peak b described later ) is preferably observed.

In addition, the negative electrode active material in the present disclosure has a peak position at 2θ = 28.4 ° ± 0.5 ° in XRD measurement using CuKα rays, and even if peak a derived from Si is not observed Well, it may be observed that the former means that the negative electrode active material is more amorphous than the latter. Peak a is a peak derived from the Si crystal phase (diamond-shaped Si crystal phase). Moreover, "the peak a is not observed" means that the intensity of the peak a is so small that it cannot be distinguished from the surrounding noise. This definition is the same for peaks other than peak a.

The peak position of peak a may be 2θ=28.4°±0.4° or 2θ=28.4°±0.2°. The half-value width of peak a is usually smaller than the half-value width of peak b, for example, 3° or less, may be 1° or less, or may be 0.5° or less.

In addition, the negative electrode active material in the present disclosure usually has a peak position at 2θ = 24.0 ° to 32.0 ° and a half width of 3 ° or more in XRD measurement using CuKα rays. is observed. Peak b is one of the halo peaks described above and is different from peak a. The half width of peak b may be, for example, 4° or more, 5° or more, or 10° or more. The peak intensity Ib of the peak b can be calculated by fitting the obtained diffraction pattern.

When peak a is observed and the intensity of peak a is Ia and the intensity of peak b is Ib, the XRD intensity ratio (Ia/Ib) may be within a predetermined range. The XRD intensity ratio (Ia/Ib) is, for example, 3.80 or less, may be 3.50 or less, may be 3.00 or less, or may be 2.50 or less. On the other hand, the XRD intensity ratio (Ia/Ib) is, for example, 0.95 or more, may be 0.99 or more, may be 1.50 or more, or may be 2.00 or more. A method for adjusting the XRD intensity ratio will be described later in "B. Manufacturing method of negative electrode active material". The term "peak intensity" refers to the height from the X-axis (2θ) in the diffraction chart.

In addition, the negative electrode active material in the present disclosure has a peak position at 2θ = 20.8 ° ± 0.5 ° in XRD measurement using CuKα rays, and no peak c derived from SiO ₂ is observed. may also be observed, but the former is preferred. This is because a negative electrode active material containing few impurities can be obtained. The peak position of peak c may be 2θ=20.8°±0.4° or 2θ=20.8°±0.2°. The half width of peak c is usually smaller than the half width of peak b, for example, 3° or less, may be 1° or less, or may be 0.5° or less.

When peak a and peak c are observed and the intensity of peak a is Ia and the intensity of peak c is Ic, the XRD intensity ratio (Ic/Ia) is preferably small. The XRD intensity ratio (Ic/Ia) is, for example, 1.1 or less, may be 1.05 or less, or may be 1.00 or less. On the other hand, when peak a is not observed and peak c is observed, the intensity at 2θ=28.4° is defined as Ia′. The XRD intensity ratio (Ic/Ia') preferably satisfies the same relationship as the XRD intensity ratio (Ic/Ia) described above.

In addition, the negative electrode active material in the present disclosure has a peak position at 2θ = 20 ° to 30 ° in XRD measurement using CuKα rays, and peak d derived from lithium silicate may not be observed. may be used, but the former is preferred. This is because a negative electrode active material containing few impurities can be obtained. Peak d is a peak derived from lithium silicate. At 2θ=20° to 30°, the positions at which peak d is obtained include, for example, 2θ=24.7±0.5° and 2θ=26.0±0.5°. Peak d may be observed as a single peak or as multiple peaks. Lithium _silicate is a compound _containing Li, Si and O, typically _Li6Si2O7 . The half width of peak d is usually smaller than the half width of peak b, for example, 3° or less, may be 1° or less, or may be 0.5° or less.

When peak a and peak d are observed and the intensity of peak a is Ia and the intensity of peak d is Id, the XRD intensity ratio (Id/Ia) is preferably small. The XRD intensity ratio (Id/Ia) is, for example, 0.8 or less, and may be 0.6 or less. When multiple peaks d are observed, the highest intensity among the multiple peaks d is Id. On the other hand, when peak a is not observed and peak d is observed, the intensity at 2θ=28.4° is Ia′. The XRD intensity ratio (Id/Ia') preferably satisfies the same relationship as the XRD intensity ratio (Id/Ia) described above.

Also, the negative electrode active material in the present disclosure may have a predetermined porosity. The porosity is, for example, 5% or more, may be 10% or more, or may be 20% or more. On the other hand, the porosity is, for example, 50% or less, may be 40% or less, or may be 30% or less. The porosity can be determined, for example, by observation with a scanning electron microscope (SEM). The number of samples is preferably large, for example 100 or more. The porosity can be an average value obtained from these samples.

Also, the negative electrode active material in the present disclosure is used in batteries. The battery will be described later in "C. Battery".

B. Method for Producing Negative Electrode Active Material FIG. 1 is a flow diagram showing an example of a method for producing a negative electrode active material according to the present disclosure. The method for producing a negative electrode active material according to the present disclosure includes a dispersing step of adding a dispersion medium to a LiSi precursor containing Si element and Li element to obtain a LiSi precursor dispersion, and and a Li extraction step of adding an extraction solvent to extract the Li element from the LiSi precursor to obtain non-woven fabric-like particles containing Si fibers. Further, in the present disclosure, the dielectric constant of the dispersion medium is 3.08 or less.

According to the method for producing a negative electrode active material according to the present disclosure, by performing the Li extraction step after the dispersing step, it is possible to produce a negative electrode active material that is non-woven fabric-like particles containing Si fibers. Because the dispersion medium used in the dispersion step has a predetermined dielectric constant, the reaction between the LiSi precursor and the Li extraction solvent can be suppressed, and the rate at which the Li element is extracted from the LiSi precursor can be suppressed. Conceivable. This is probably because the Li extraction solvent is quickly mixed with the dispersion medium at the time of addition by using a dispersion medium having a predetermined dielectric constant, and the concentration of the Li extraction solvent on the surface of the LiSi precursor decreases. As a result, it is presumed that the reaction between the LiSi precursor and the Li extraction solvent is suppressed. In addition, it is presumed that by suppressing the Li extraction reaction as described above, only the Li element is extracted from the LiSi precursor and the Si skeleton remains, thereby obtaining non-woven fabric-like particles. If the Li extraction reaction is not suppressed, the Si skeleton is also extracted at the same time as the Li element, and it is presumed that non-woven fabric-like particles cannot be obtained.

1. Dispersing Step The dispersing step in the present disclosure is a step of adding a dispersion medium to a LiSi precursor containing Si element and Li element to obtain a LiSi precursor dispersion.

The LiSi precursor is not particularly limited as long as it contains Si element and Li element, and may be purchased commercially or prepared by oneself. Examples of the method for preparing the LiSi precursor include a method of mixing a raw material containing Si element and a raw material containing Li element. Examples of the mixing method include a method of mixing Si particles and Li particles in an Ar atmosphere using an agate mortar, and a method of mixing Si particles and Li particles using a mechanical milling method.

The LiSi precursor preferably has a Si (diamond type) crystal phase. The crystal phase of Si has typical peaks at 2θ = 28.4°, 47.3°, 56.1°, 69.2°, and 76.4° in XRD measurement using CuKα rays. . These peak positions may vary within a range of ±0.5° or within a range of ±0.3°. The LiSi precursor may have a Si (diamond-type) crystal phase as a main phase. The “main phase” refers to a crystal phase to which the peak with the highest intensity belongs in the XRD chart.

Also, the composition of the LiSi precursor is not particularly limited. The LiSi precursor may contain only Li element and Si element, and may further contain other metal elements. The total ratio of Li element and Si element to all metal elements contained in the LiSi precursor is, for example, 50 mol % or more, may be 70 mol % or more, or may be 90 mol % or more. In the LiSi precursor, the ratio of Li element to the sum of Si element and Li element is, for example, 30 mol % or more, may be 50 mol % or more, or may be 80 mol % or more. On the other hand, the proportion of Li element is, for example, 95 mol % or less, and may be 90 mol % or less.

The dielectric constant of the dispersion medium in the present disclosure is 3.08 or less. A dispersion medium having a dielectric constant of 3.08 or less is generally classified as an aprotic dispersion medium. The dielectric constant is 3.08 or less, and may be, for example, 3.00 or less, or may be 2.50 or less. On the other hand, the dielectric constant is, for example, 1.50 or more, may be 1.70 or more, may be 1.90 or more, or may be 2.00 or more. If the dielectric constant is too much higher than 3.08, the dispersion medium itself may react with the LiSi precursor and aggregate, failing to disperse well. The dielectric constant can be measured, for example, by the method described in JIS C 2565 (cavity resonator method, etc.).

The dispersion medium may or may not have a benzene ring, but the latter is preferred. Examples of the dispersion medium include saturated hydrocarbons such as n-heptane, n-octane, n-decane, 2-ethylhexane and cyclohexane; unsaturated hydrocarbons such as hexene and heptene; and 1,3,5-trimethyl Aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, propylbenzene, cumene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene, n-butyl ether, n-hexyl ether, isoamyl ether, diphenyl ether , methylphenyl ether, and cyclopentyl methyl ether. Among these, n-butyl ether, 1,3,5-trimethylbenzene and n-heptane are preferred, and 1,3,5-trimethylbenzene is particularly preferred. The dielectric constant of n-butyl ether is 3.08, the dielectric constant of 1,3,5-trimethylbenzene is 2.279, and the dielectric constant of n-heptane is 1.94.

Moreover, it is preferable that the dispersion medium has a small water content. This is because moisture reacts with the LiSi precursor. The water content in the dispersion medium is, for example, 100 ppm or less, may be 50 ppm or less, may be 30 ppm or less, or may be 10 ppm or less.

The LiSi precursor dispersion can be obtained by adding a dispersion medium to the LiSi precursor and mixing them. A mixing method is not particularly limited.

The average particle size ( _D50 ) of the negative electrode active material of the present disclosure can be adjusted, for example, by changing the type of dispersion medium. The average particle size (D ₅₀ ) can also be adjusted by the combination of the type of dispersion medium and the Li extraction solvent described later. The average particle size ( _D50 ) can also be adjusted by changing the average particle size of the LiSi precursor itself.

Regarding the XRD intensity ratio of the negative electrode active material of the present disclosure, the main factor is the rate at which Li is extracted from the LiSi precursor (reactivity between the LiSi precursor and the Li extraction solvent), and the extraction of Li is slow. If there is, it is possible to obtain silicon with a low XRD intensity ratio and low crystallinity. Therefore, the XRD intensity ratio can be adjusted by, for example, the type of dispersion medium, the type of Li extraction solvent described later, and the combination of the dispersion medium and the Li extraction solvent.

2. Li Extraction Step The Li extraction step in the present disclosure is a step of adding a Li extraction solvent to the LiSi precursor dispersion to extract the Li element from the LiSi precursor to obtain the nonwoven fabric-like particles described above.

The Li extraction solvent is not particularly limited as long as it can extract the Li element from the LiSi precursor. Examples of Li extraction solvents include primary alcohols such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol, 2-propanol, 2-butanol, 2-pentanol, and 2-hexanol. Secondary alcohols such as, tertiary alcohols such as tert-butyl alcohol, phenols such as phenol, glycols such as 1,2-ethanediol and 1,3-butanediol, propylene glycol monomethyl ether, ethylene glycol monomethyl ether, etc. Examples include glycol ethers, pyranoses such as bD-glucopyranose, furanoses such as erythrofuranose, and polysaccharides such as glucoses and fructose. Examples of the Li extraction solvent include acid solutions such as acetic acid, formic acid, propionic acid, and oxalic acid. Among them, the Li extraction solvent is preferably at least one of ethanol, 1-propanol, 1-butanol, 1-hexanol and acetic acid. As the Li extraction solvent, only one kind of the above compounds may be used, or two or more kinds thereof may be used. Moreover, it is preferable that the Li extraction solvent has a small water content. The water content in the Li extraction solvent is, for example, 100 ppm or less, may be 50 ppm or less, may be 30 ppm or less, or may be 10 ppm or less. If the water content is too high, Si may be oxidized, degrading battery performance.

The Li extraction process may be performed in one stage or in two stages. For example, when the Li extraction step is one step, it can be a step of reacting the cooled LiSi precursor dispersion with any Li extraction solvent other than the acid solution. When the Li extraction step has two steps, the reaction solution obtained after the first step may be reacted with the acid solution. By performing the Li extraction step in two steps, the Li element can be more reliably extracted from the LiSi precursor.

3. Washing Step In the present disclosure, a washing step may be performed after the Li extraction step.

In the present disclosure, by performing the cleaning step, it is possible to suppress contamination of the negative electrode active material with impurities. In addition, since agglomeration is suppressed in a negative electrode active material containing few impurities, it is possible to manufacture a negative electrode active material with a smaller amount of swelling due to charging. In addition, the expansion of the battery using such a negative electrode active material and the increase in the confining pressure are further suppressed. The impurities are considered to be, for example, by-products of polymerization of Li and Si contained in the solution after extraction of Li, as described below.

A reaction solution in which Li and Si are dissolved in the form of ethoxylithium and tetraethoxysilane may adhere to the surface of the nonwoven fabric particles after the Li extraction step. Ethoxylithium and tetraethoxysilane have the property of forming glass by hydrolysis or dehydration condensation (sol-gel reaction) by reacting with moisture in the atmosphere. Therefore, lithium silicates such as Li ₆ Si ₂ O ₇ and SiO ₂ may remain as impurities on the surface of the negative electrode active material. Here, the sol-gel reaction is accelerated by a base catalyst. Therefore, by performing the washing step in the present disclosure, the reaction solution can be removed from the surface of the nonwoven fabric-like particles while suppressing the sol-gel reaction. As a result, impurities can be suppressed from remaining on the surface of the negative electrode active material, and aggregation of the negative electrode active material can be suppressed.

When the concentration of the LiSi precursor in the sum of the LiSi precursor dispersion liquid and the Li extraction solvent is high, the production efficiency increases, but the amount of impurities generated increases. Therefore, when the concentration of the LiSi precursor is 3.3 g/L or more, the washing process can improve the production efficiency and reduce the amount of impurities generated.

The washing step in the present disclosure is a step of washing the non-woven fabric particles with an acid after the Li extraction step. Usually, the washing process includes a recovery process of recovering the non-woven fabric particles from the solution after the Li extraction process, and a cleaning process of cleaning the recovered non-woven fabric particles with an acid. The recovery treatment is not particularly limited as long as it is a method capable of recovering the non-woven fabric particles, and for example, filtration of the reaction solution after the Li extraction step can be mentioned.

The washing treatment is a treatment for washing the nonwoven-like particles with an acid, and is not particularly limited as long as it is a method of contacting the nonwoven-like particles with an acid. Examples of such a method include a method of continuously filtering while adding an acid-containing solution to the non-woven fabric-like particles recovered by filtration. The time and number of times of washing treatment are not particularly limited.

The acid used for the washing treatment is not particularly limited, and the same acid as the Li extraction solvent can be mentioned. The acid used in the cleaning treatment is preferably the same as the acid used in the Li extraction step.

The negative electrode active material obtained in the above steps can be recovered by any method. For example, a method of separating a solid reactant (negative electrode active material) from the solution after the Li extraction step and the solution after the washing step, and drying the resulting negative electrode active material can be mentioned.

4. Negative Electrode Active Material The negative electrode active material obtained by the manufacturing method described above is the same as described in "A. Negative Electrode Active Material" above, so description thereof is omitted here.

C. Battery FIG. 2 is a schematic cross-sectional view showing an example of a battery in the present disclosure. A battery 10 shown in FIG. 2 includes a positive electrode active material layer 1, a negative electrode active material layer 2, an electrolyte layer 3 formed between the positive electrode active material layer 1 and the negative electrode active material layer 2, and a negative electrode current collector 5 for collecting current of the negative electrode active material layer 2 . These members may be housed in a general exterior body. In the present disclosure, the negative electrode active material layer 2 contains the negative electrode active material described above.

According to the present disclosure, the negative electrode active material layer contains the negative electrode active material described above, so that the battery can reduce the binding pressure.

1. Negative Electrode Active Material Layer The negative electrode active material layer is a layer containing at least the negative electrode active material described above. Since the content of the negative electrode active material is the same as that described in the above "A. Negative electrode active material", description thereof is omitted here.

The negative electrode active material layer may contain only the above-described negative electrode active material as the negative electrode active material, or may contain other negative electrode active materials. In the latter case, the ratio of the above-described negative electrode active material in all negative electrode active materials may be, for example, 50% by weight or more, 70% by weight or more, or 90% by weight or more. .

The ratio of the negative electrode active material in the negative electrode active material layer is, for example, 20% by weight or more, may be 30% by weight or more, or may be 40% by weight or more. On the other hand, the proportion of the negative electrode active material is, for example, 80% by weight or less, may be 70% by weight or less, or may be 60% by weight or less.

Moreover, the negative electrode active material layer may further contain at least one of an electrolyte, a conductive aid, and a binder, if necessary. The type of electrolyte will be described in detail in "3. Electrolyte layer" described later. The proportion of the electrolyte in the negative electrode active material layer is, for example, 1% by weight or more, may be 10% by weight or more, or may be 20% by weight or more. On the other hand, the proportion of the electrolyte in the negative electrode layer is, for example, 60% by weight or less, and may be 50% by weight or less.

Conductive aids include, for example, carbon materials and metal particles. Specific examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). is mentioned. Examples of metal particles include Ni, Cu, Fe, and SuS. The proportion of the conductive aid in the negative electrode active material layer is, for example, 1% by weight or more, and may be 5% by weight or more. On the other hand, the proportion of the conductive aid is, for example, 30% by weight or less, and may be 20% by weight or less.

Examples of binders include rubber binders such as butadiene rubber, hydrogenated butadiene rubber, styrene butadiene rubber (SBR), hydrogenated styrene butadiene rubber, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, ethylene propylene rubber, polyvinylidene fluoride ( PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene, fluoride-based binders such as fluororubber, polyolefin-based thermoplastic resins such as polyethylene, polypropylene, and polystyrene, polyimide, polyamide Examples include imide resins such as imide, amide resins such as polyamide, acrylic resins such as polymethyl acrylate and polyethyl acrylate, and methacrylic resins such as polymethyl methacrylate and polyethyl methacrylate. The ratio of the binder in the negative electrode active material layer is, for example, 1% by weight or more and 30% by weight or less.

The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

2. Positive Electrode Active Material Layer The positive electrode active material layer is a layer containing at least a positive electrode active material. Moreover, the positive electrode active material layer may further contain at least one of an electrolyte, a conductive aid, and a binder, if necessary.

Examples of positive electrode active materials include oxide active materials. Examples of oxide active materials used in lithium ion batteries include LiCoO ₂ , LiMnO ₂ , Li ₂ NiMn ₃ O ₈ , LiVO ₂ , LiCrO ₂ , LiFePO ₄ , LiCoPO ₄ , LiNiO ₂ , LiNi _1/3 Co _1/ Oxide active materials such as _{3Mn1 / 3O2} are included. Moreover, a coat layer containing a Li ion conductive oxide such as LiNbO ₃ may be formed on the surface of these active materials.

The proportion of the positive electrode active material in the positive electrode active material layer is, for example, 20% by weight or more, may be 30% by weight or more, or may be 40% by weight or more. On the other hand, the proportion of the positive electrode active material is, for example, 80% by weight or less, may be 70% by weight or less, or may be 60% by weight or less.

The types and proportions of the solid electrolyte, conductive aid, and binder used in the positive electrode active material layer can be the same as those described for the negative electrode active material layer, so descriptions thereof are omitted here. do.

The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

3. Electrolyte Layer The electrolyte layer is a layer formed between the positive electrode active material layer and the negative electrode active material layer. The electrolyte forming the electrolyte layer may be a liquid electrolyte (electrolytic solution) or a solid electrolyte, but the latter is preferred.

Solid electrolytes typically include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes; and organic polymer electrolytes such as polymer electrolytes.

Sulfide solid electrolytes having lithium ion conductivity include, for example, Li element, X element (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and a solid electrolyte containing an S element. Moreover, the sulfide solid electrolyte may further contain at least one of the O element and the halogen element. Halogen elements include, for example, F element, Cl element, Br element, and I element.

Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -GeS ₂ , Li ₂ SP ₂ S ₅ - _Li2O , _Li2SP2S5 - _{Li2O -} LiI, _Li2SP2S5 -LiI _- LiBr _{, Li2S} - _SiS2 , _Li2S - _{SiS2 -} LiI, _Li2 S—SiS ₂ —LiBr, Li ₂ S—SiS ₂ —LiCl, Li ₂ S—SiS ₂ —B ₂ S ₃ —LiI, Li ₂ S—SiS ₂ —P ₂ S ₅ —LiI, Li ₂ S—B ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m Sn (where m and n are positive numbers; Z is one of Ge, Zn, and Ga), Li ₂ S—GeS ₂ , Li ₂ S -SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (where x and y are positive numbers, M is any of P, Si, Ge, B, Al, Ga, In ).

Further, as the oxide solid electrolyte having lithium ion conductivity, for example, Li element, Y element (Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, S ), and a solid electrolyte containing an O element. Specific examples include garnet types such as Li ₇ La ₃ Zr ₂ O ₁₂ , Li _7-x La ₃ (Zr _2-x Nb _x )O ₁₂ (0≦x≦2), and Li ₅ La ₃ Nb ₂ O ₁₂ Solid electrolyte; Perovskite solid electrolyte such as (Li, La) TiO ₃ , (Li, La) NbO ₃ , (Li, Sr) (Ta, Zr) O ₃ ; Li(Al, Ti)(PO ₄ ) ₃ , Nasicon-type solid electrolyte of Li(Al, Ga)(PO ₄ ) ₃ ; Li—P—O-based solid electrolyte such as Li ₃ PO ₄ and LIPON (compound in which part of O in Li ₃ PO ₄ is replaced with N) Li—B—O-based solid electrolytes such as Li ₃ BO ₃ and compounds obtained by substituting a portion of O in Li ₃ BO ₃ with C;

Since the content of the binder is the same as that described in the above "1. Negative electrode active material layer", the description thereof is omitted here.

The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

4. Other Configurations A battery according to the present disclosure has at least the negative electrode active material layer, the positive electrode active material layer, and the electrolyte layer described above. Furthermore, it usually has a positive electrode current collector that collects current for the positive electrode active material layer and a negative electrode current collector that collects current for the negative electrode active material layer. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium and carbon. On the other hand, examples of materials for the negative electrode current collector include SUS, copper, nickel and carbon.

5. Battery The battery in the present disclosure is preferably a lithium ion battery. Also, the battery in the present disclosure may be a liquid battery or an all-solid battery, but the latter is preferred.

Also, the battery in the present disclosure may be a primary battery or a secondary battery, but is preferably a secondary battery. This is because it can be repeatedly charged and discharged, and is useful, for example, as an in-vehicle battery. The secondary battery also includes the use of a secondary battery as a primary battery (use for the purpose of initial charging only).

Also, the battery in the present disclosure may be a single cell or a laminated battery. The laminated battery may be a monopolar laminated battery (parallel connected laminated battery) or a bipolar laminated battery (series connected laminated battery). The shape of the battery includes, for example, coin type, laminate type, cylindrical type and rectangular type.

Note that the present disclosure is not limited to the above embodiments. The above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present disclosure and produces the same effect is the present invention. It is included in the technical scope of the disclosure.

[Example 1]
(Synthesis of negative electrode active material)
A LiSi precursor was obtained by mixing 0.65 g of Si particles (particle size: 5 μm, manufactured by Kojundo Chemical Co., Ltd.) and 0.60 g of Li metal (manufactured by Honjo Metal Co., Ltd.) in an agate mortar under an Ar atmosphere. In a glass reactor under an Ar atmosphere, 1.0 g of a LiSi precursor and 125 ml of a dispersion medium (1,3,5-trimethylbenzene, manufactured by Nacalai Tesque) are combined with an ultrasonic homogenizer (UH-50, manufactured by SMT). was mixed using The LiSi precursor dispersion obtained after mixing was cooled to 0° C., 125 ml of ethanol (manufactured by Nacalai Tesque) was added dropwise, and reaction was allowed for 120 minutes. After the reaction, 50 ml of acetic acid (manufactured by Nacalai Tesque) was added dropwise and reacted for 60 minutes. After the reaction, the liquid and the solid reactant (negative electrode active material) were separated by suction filtration. The resulting solid reactant was vacuum-dried at 120° C. for 2 hours to recover the negative electrode active material. The average particle size (D ₅₀ ) of the obtained negative electrode active material was 0.27 μm.

(Synthesis of solid electrolyte)
0.550 g of Li ₂ S (manufactured by Furuuchi Chemical), 0.887 g of P ₂ S ₅ (manufactured by Aldrich), 0.285 g of LiI (manufactured by Nippo Chemical), and 0.277 g of LiBr (manufactured by Kojundo Chemical) , and mixed in an agate mortar for 5 minutes. 4 g of n-heptane (dehydrated grade, manufactured by Kanto Kagaku) was added to the resulting mixture, and mechanical milling was performed using a planetary ball mill for 40 hours to obtain a solid electrolyte.

(Preparation of battery for evaluation)
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Nichia Corporation) was subjected to surface treatment using LiNbO ₃ to obtain a positive electrode active material. 1.5 g of this positive electrode active material, 0.023 g of a conductive agent (VGCF, manufactured by Showa Denko), 0.239 g of the solid electrolyte, 0.011 g of a binder (PVdF, manufactured by Kureha), and butyl butyrate (manufactured by Kishida Chemical) ) were mixed with 0.8 g using an ultrasonic homogenizer (UH-50, manufactured by SMT) to obtain a positive electrode mixture.

1.0 g of the negative electrode active material synthesized above, 0.04 g of a conductive agent (VGCF, manufactured by Showa Denko), 0.776 g of the solid electrolyte, 0.02 g of a binder (PVdF, manufactured by Kureha), and butyl butyrate (Kishida Kagaku) and 1.7 g were mixed using an ultrasonic homogenizer (UH-50, manufactured by SMT) to obtain a negative electrode mixture.

0.065 g of the above solid electrolyte was placed in a 1 cm ² ceramic mold and pressed at 1 ton/cm ² to prepare a separate layer (solid electrolyte layer). 0.018 g of the positive electrode mixture was added to one side of the mixture and pressed at 1 ton/cm ² to prepare a positive electrode active material layer. A negative electrode active material layer was produced by putting 0.0054 g of the above negative electrode mixture on the side opposite to the positive electrode active material layer and pressing at 4 ton/cm ² . Aluminum foil was used for the positive electrode current collector, and copper foil was used for the negative electrode current collector. Thus, an evaluation battery (all-solid battery) was produced.

[Examples 2 to 7]
A negative electrode active material was synthesized in the same manner as in Example 1, except that the dispersion medium and the Li extraction solvent were changed as shown in Table 1, and a battery for evaluation was produced. Also, the average particle size (D ₅₀ ) of each negative electrode active material obtained was measured. Table 2 shows the results.

[Comparative Example 1]
A negative electrode active material was synthesized in the same manner as in Example 1, except that ethanol cooled to 0° C. was used as the Li extraction solvent without using a dispersion medium in the synthesis of the negative electrode active material, and a battery for evaluation was produced. . Also, the average particle size (D ₅₀ ) of the obtained negative electrode active material was measured. Table 2 shows the results.

[Comparative Examples 2 to 4]
A negative electrode active material was synthesized and a battery for evaluation was produced in the same manner as in Comparative Example 1, except that the Li extracting solvent was changed as shown in Table 1. Also, the average particle size (D ₅₀ ) of each negative electrode active material obtained was measured. Table 2 shows the results.

[Evaluation 1]
(XRD measurement)
The negative electrode active materials obtained in Examples 1-7 and Comparative Examples 1-4 were subjected to X-ray diffraction (XRD) measurement using CuKα rays. The XRD data obtained in Example 1 are shown in FIGS. 3(a) and 3(b). FIG.3(b) is the graph which expanded a part of Fig.3 (a). As shown in FIG. 3(a), halo peaks were confirmed near 2θ=25° to 30° and near 2θ=50° to 60°. The former peak corresponds to peak b. Also, as shown in FIG. 3B, a very slight peak a was confirmed at the position of 2θ=28.4°. In addition, in FIG.3(b), the judgment of "the peak a was not confirmed" is also possible level. Moreover, in FIG. 3, the peak position of the peak a and the peak position of the peak b were substantially the same. From this data, the XRD intensity ratio (Ia/Ib) was found to be Ia/Ib=0.99, and Ia and Ib had almost the same intensity. XRD intensity ratios were obtained in the same manner for Examples 2 to 7 and Comparative Examples 1 to 4. Table 2 shows the results.

As shown in Table 2, it was confirmed that Examples 1 to 7 had a smaller XRD intensity ratio than Comparative Examples 1 to 4, and the negative electrode active material had a lower crystallinity and was more amorphous.

(Microscopic observation)
The shapes of the negative electrode active materials obtained in Examples 1 and 2 and Comparative Example 1 were observed using a transmission electron microscope (TEM). The results are shown in FIG. Also, the shape of the negative electrode active material obtained in Comparative Example 1 was observed using a scanning electron microscope (SEM). The results are shown in FIG.

As shown in FIG. 4, it was confirmed that the negative electrode active material of the example in which the LiSi precursor was dispersed in the dispersion medium and then Li was extracted was formed by three-dimensionally entangled Si fibers. rice field. On the other hand, the negative electrode active material of Comparative Example 1, in which Li was extracted without dispersing the LiSi precursor in the dispersion medium, had a completely different shape from that of the Example. This is because, as can be seen from the SEM image shown in FIG. 5, the negative electrode active material of Comparative Example 1 does not have a non-woven fabric shape, but simply has a porous particle shape. The reason why the fiber shape was not confirmed in Comparative Example 1 is presumed that not only the Li element but also the Si skeleton was extracted from the LiSi precursor at the same time because the Li extraction reaction was not suppressed.

(porosity, average diameter and aspect ratio)
Cross-sectional images of the negative electrode active materials obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were obtained using a scanning electron microscope (SEM) to measure the porosity. In the examples, the average diameter and aspect ratio of Si fibers were also calculated. Table 2 shows the results.

As shown in Table 2, Examples 1 to 4 had a higher porosity than Comparative Examples 1 to 4, but Examples 5 to 7 had a lower porosity than Comparative Example 1 (12% porosity). . In general, when the porosity is high, the amount of expansion (increase in confining pressure) tends to be small because expansion can be absorbed more. However, as will be described later, Examples 5 to 7, which have a smaller porosity than Comparative Example 1, had significantly smaller increases in confining pressure. Moreover, in the examples, the aspect ratio was 1 or more, and it was confirmed to be fibrous.

(Confining pressure increase)
The evaluation batteries obtained in Examples 1 to 7 and Comparative Examples 1 to 4 were CC/CV charged at 0.245 mA to 4.55 V, and then CC/CV discharged at 0.245 mA to 3.0 V. . At the first charge, the confining pressure of the battery was monitored and the confining pressure at 4.55V was measured. A relative evaluation was made with the confining pressure in Comparative Example 1 set to 1.00. Table 2 shows the results. As shown in Table 2, in Examples 1-7, the increase in confining pressure was significantly smaller than in Comparative Examples 1-4.

As described above, it was confirmed that the negative electrode active material having a small average particle size, low crystallinity, and a non-woven fabric shape can be obtained with the method for producing a negative electrode active material according to the present disclosure. It was also confirmed that when the negative electrode active material thus obtained is used in an all-solid-state battery, the amount of increase in the constraint pressure of the battery can be significantly suppressed.

[Example 8]
A negative electrode active material was synthesized in the same manner as in Example 1, and an evaluation battery was produced.

[Example 9]
As shown in Table 3, 12 g of LiSi precursor, 400 ml of 1,3,5-trimethylbenzene, 400 mL of ethanol, and 600 mL of acetic acid were used in synthesizing the negative electrode active material. A negative electrode active material was synthesized in the same manner as in Example 1 except for the above, and a battery for evaluation was produced. Moreover, when the average particle diameter ( _D50 ) of the obtained negative electrode active material was measured, it was 1.34 μm.

[Example 10]
As shown in Table 3, 12 g of LiSi precursor, 400 ml of 1,3,5-trimethylbenzene, 400 mL of ethanol, and 600 mL of acetic acid were used in synthesizing the negative electrode active material. After the reaction between the LiSi precursor dispersion and acetic acid, the liquid and solid reactants were separated by suction filtration using a filter. Then, suction filtration was continued while adding 100 mL of acetic acid to the solid reactant deposited on the filter, thereby washing the solid reactant with acetic acid. The washed solid reactant was vacuum-dried at 120° C. for 2 hours to synthesize a negative electrode active material. A battery for evaluation was produced in the same manner as in Example 1 except for the above. Moreover, when the average particle diameter ( _D50 ) of the obtained negative electrode active material was measured, it was 0.61 μm.

[Evaluation 2]
(XRD measurement)
In the same manner as in Evaluation 1, the negative electrode active materials obtained in Examples 8 to 10 were subjected to X-ray diffraction (XRD) measurement using CuKα rays. The XRD data obtained are shown in FIG. As shown in FIG. 6, in Example 9, peak c derived from SiO ₂ and peak d derived from lithium silicate were confirmed. On the other hand, in Examples 8 and 10, peak c derived from SiO ₂ and peak d derived from lithium silicate were not confirmed. In addition, in FIG. 6, peak c is marked with ●, and peak d is marked with ▴.

(Confining pressure increase)
Confining pressure was measured for the evaluation batteries obtained in Examples 8 to 10 in the same manner as in Evaluation 1. A relative evaluation was made with the confining pressure in Example 8 set to 1.00. Table 4 shows the results.

As shown in Table 4, in Example 9 in which the production scale of the negative electrode active material was increased and the washing step was not performed, the average particle size of the negative electrode active material and the amount of increase in the confining pressure were larger than in Example 8. rice field. On the other hand, in Example 10 in which the washing step was performed, the average particle size of the negative electrode active material was smaller than in Examples 8 and 9, and the amount of increase in confining pressure was further suppressed. This is believed to be due to the removal of impurities such as _SiO2 and lithium silicate by the cleaning process. As described above, it was confirmed that, by performing the washing step in the method for producing a negative electrode active material according to the present disclosure, aggregation of the negative electrode active material due to remaining impurities can be suppressed, and an increase in the confining pressure can be further suppressed.

DESCRIPTION OF SYMBOLS 1... Positive electrode active material layer 2... Negative electrode active material layer 3... Electrolyte layer 4... Positive electrode collector 5... Negative electrode collector 10... Battery

Claims (7)

A negative electrode active material used in a battery,
The negative electrode active material is a non-woven fabric containing Si fibers,
The average particle size (D ₅₀ ) of the negative electrode active material is 0.2 μm or more and 3.6 μm or less,
A negative electrode active material, wherein the negative electrode active material is amorphous. 2. The negative electrode active material according to claim 1, wherein, in XRD measurement using CuKα rays, the peak position is at 2θ=28.4°±0.5° and no peak a derived from Si is observed. a dispersing step of adding a dispersion medium to a LiSi precursor containing Si element and Li element to obtain a LiSi precursor dispersion;
a Li extraction step of adding a Li extraction solvent to the LiSi precursor dispersion to extract the Li element from the LiSi precursor to obtain non-woven fabric-like particles containing Si fibers;
A method for producing a negative electrode active material, wherein the dispersion medium has a dielectric constant of 3.08 or less. 4. The method for producing a negative electrode active material according to claim 3 , wherein the dispersion medium is at least one of n-butyl ether, 1,3,5-trimethylbenzene and n-heptane. 5. The method for producing a negative electrode active material according to claim 3 , wherein the Li extraction solvent is at least one of ethanol, 1-propanol, 1-butanol, 1-hexanol and acetic acid. 6. The method for producing a negative electrode active material according to any one of claims 3 to 5 , further comprising a washing step of washing the non-woven fabric particles with an acid after the Li extraction step. A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer,
A battery, wherein the negative electrode active material layer contains the negative electrode active material according to claim 1 .

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