JP2021093343A - Cathode active material and battery - Google Patents

Abstract

To provide a cathode active material having small volume change due to charge and discharge.SOLUTION: In the present disclosure, the above problems can be solved by providing a cathode active material comprising primary particles having an Si phase, an MSi phase (M is a transition metal element) that is a silicide phase, and a first void.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a negative electrode active material and a battery.

In recent years, batteries have been actively developed. For example, the automobile industry is developing batteries for use in electric vehicles or hybrid vehicles. Further, Si particles are known as an active material used in a battery.

For example, Patent Document 1 discloses porous silicon particles having voids as a negative electrode active material. Patent Document 2 discloses particles in which a Si phase is dispersed in a silicide phase as a negative electrode active material. Patent Document 3 discloses composite particles containing particles composed of a Si phase and particles composed of a silicide phase as a negative electrode active material.

Japanese Unexamined Patent Publication No. 2013-203626 JP 2015-095301 Japanese Unexamined Patent Publication No. 2013-235682

Si particles have a large theoretical capacity and are effective for increasing the energy density of batteries. On the other hand, Si particles have a large volume change during charging and discharging.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a negative electrode active material having a small volume change due to charging / discharging.

In order to solve the above problems, in the present disclosure, a negative electrode active material containing primary particles having a Si phase, an MSi phase (M is a transition metal element) which is a silicide phase, and a first void is used. provide.

According to the present disclosure, since the primary particles have a Si phase, an MSi phase which is a silicide phase, and a first void, it can be used as a negative electrode active material having a small volume change due to charging and discharging.

In the above disclosure, the ratio of the transition metal element to the total of the Si element and the transition metal element contained in the primary particles may be 2 mol% or more and less than 50 mol%.

In the above disclosure, the ratio of the first void may be 3% or more.

In the above disclosure, the transition metal element may be at least one of W, Mo, Cr, V, Nb, Fe, Ti, Zr, Hf and Os.

In the above disclosure, the transition metal element may be at least one of Cr, Ti, Zr, Hf and Os.

In the above disclosure, the negative electrode active material may be secondary particles in which a plurality of the primary particles are aggregated and have a second void.

Further, in the present disclosure, the battery has 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, and is the negative electrode active material. Provided is a battery in which the material layer contains the above-mentioned negative electrode active material.

According to the present disclosure, since the negative electrode active material layer contains the above-mentioned negative electrode active material, it is possible to obtain a battery in which an increase in the restraining pressure due to charging / discharging is suppressed.

Further, in the above disclosure, the negative electrode active material layer contains the negative electrode active material, the thickness of the negative electrode active material layer in the stacking direction is α (μm), and the average particle size of the secondary particles is β (μm). ), The battery may have β / α of 0.02 or more and 0.5 or less.

According to the present disclosure, since the thickness of the negative electrode active material layer in the stacking direction and the average particle size of the secondary particles have a predetermined relationship, the battery is such that the increase in the restraining pressure due to charging and discharging is further suppressed. Can be done.

In the present disclosure, it is possible to obtain a negative electrode active material having a small volume change due to charging / discharging.

It is the schematic sectional drawing which shows an example of the battery in this disclosure. 6 is a cross-sectional SEM image of the negative electrode active material (primary particles) obtained in Example 4. 6 is a cross-sectional SEM image of the negative electrode active material (primary particles) obtained in Comparative Example 4. It is a graph which shows the mechanical strength obtained by the phase-field method.

Hereinafter, the negative electrode active material and the battery in the present disclosure will be described in detail.

A. Negative electrode active material The negative electrode active material in the present disclosure includes primary particles having a Si phase, an MSi phase (M is a transition metal element) which is a silicide phase, and a first void.

According to the present disclosure, since the primary particles have a Si phase, an MSi phase which is a silicide phase, and a first void, it can be used as a negative electrode active material having a small volume change due to charging and discharging.

Batteries are required to have high energy density. Therefore, it is being studied to use a Si material having excellent capacitance characteristics as an active material. However, when a Si material having a diamond-shaped crystal structure is used especially for an all-solid-state battery, cracks may occur inside the electrode during repeated charging and discharging, which may shorten the battery life. In addition, since a large amount of stress is applied to the restraint parts of the battery in the charged state, it becomes necessary to adopt a restraint structure having high rigidity, and the restraint jig may become large. As a result, the energy density of the entire battery may decrease. Therefore, various studies have been made on suppressing the expansion of the Si material by charging and discharging.

For example, Patent Document 1 discloses Si particles having voids inside, and Patent Document 3 discloses composite particles having voids between primary particles. However, these voids may be crushed by the press pressure at the time of electrode fabrication, and there is room for improvement in suppressing the expansion of Si particles. Further, Patent Document 2 discloses particles in which the Si phase is dispersed in the silicide phase, but there is a possibility that cracks may occur at the interface between the VDD phase and the Si phase during charging, and the expansion suppression of the Si particles is improved. There is room.

On the other hand, in the negative electrode active material in the present disclosure, the primary particles have a Si phase, an MSi phase which is a silicide phase, and a first void. As a result, even if a press is applied during the production of the electrode, the silicide phase acts as a pillar and the first void can be maintained. As a result, the expansion of Si particles can be suppressed. Also, in general, when the primary particles have voids (first voids), the resistance tends to increase. However, since the silicide phase has electron conductivity, it is possible to suppress an increase in resistance even if it has a first void.

1. 1. Primary Particle The primary particle in the present disclosure has a Si phase, an MSi phase which is a silicide phase, and a first void.

(1) Si phase The primary particles in the present disclosure have a Si phase. The Si phase is a simple phase of Si.

The area ratio (%) of the Si phase in the primary particles may be, for example, 30% or more, 40% or more, or 50% or more. On the other hand, the area ratio of the Si phase is, for example, 90% or less, 80% or less, or 70% or less. The area of the Si phase may be smaller, the same, or larger than the area ratio of the MSi phase described later, but from the viewpoint of capacitance, it is preferable that the area ratio of the Si phase is large.

The area ratio of the Si phase can be determined by, for example, SEM (scanning electron microscope) observation. The cross section of the negative electrode active material is observed by SEM to obtain a photograph of the particles. The area is determined by distinguishing the Si phase from the obtained photograph using image analysis software. Then, the area ratio (%) is calculated from the following formula. The number of samples is preferably large, for example, 20 or more, 30 or more, 50 or more, or 100 or more.
Area ratio (%) = 100 x (Si phase area) / (primary particle area)

(2) MSi phase The primary particles in the present disclosure have an MSi phase. The MSi phase is a silicide phase, and M is a transition metal element described later. Further, the ratio of M (transition metal element) and Si (Si element) in the MSi phase is not particularly limited as long as it is a ratio capable of forming VDD.

The transition metal element M in the MSi phase is preferably at least one of W, Mo, Cr, V, Nb, Fe, Ti, Zr, Hf and Os. Further, among these elements, at least one of Cr, Ti, Zr, Hf and Os is particularly preferable. The transition metal element M in the MSi phase may be only one kind of the above elements or two or more kinds.

The ratio of the transition metal element M is, for example, 2 mol% or more, 5 mol% or more, or 10 mol% or more with respect to the total of the Si element and the transition metal element M contained in the primary particles. It may be 20 mol% or more. On the other hand, the ratio of the transition metal element M is, for example, less than 50 mol%, 40 mol% or less, or 30 mol% or less. The "Si element contained in the primary particles" includes both the Si element in the Si phase and the Si element in the MSi phase. The proportion of transition metal element M can be confirmed, for example, by high frequency inductively coupled plasma (ICP) emission spectroscopic analysis.

The area ratio (%) of the MSi phase in the primary particles is, for example, 5% or more, 10% or more, or 20% or more. On the other hand, the area ratio of the MSi phase is, for example, 60% or less, 50% or less, or 40% or less. The area ratio of the MSi phase can be obtained from the following formula in the same manner as the area ratio of the Si phase.
Area ratio (%) = 100 x (MSi phase area) / (primary particle area)

(3) First void The primary particles in the present disclosure have a first void. The ratio of the first voids (first porosity) is, for example, 3% or more, 5% or more, 10% or more, or 20% or more. On the other hand, the ratio of the first void may be, for example, 60% or less, 50% or less, 40% or less, or 30% or less. The ratio of the first voids can be calculated from the following formula in the same manner as the area ratio of the Si phase described above.
First porosity (%) = 100 x (first void area) / (primary particle area)

The area of the first void in the above formula may be, for example, 1 nm ² or more, 5 nm ² or more, 10 nm ² or more, ^{or 100 nm 2} or more. On the other hand, the area of the first void portion in the above formula is, for example, 500 nm ² or less, and ^{may be 300 nm 2} or less. The area of the first void portion can be calculated using, for example, image analysis software as described above.

Further, it is preferable that the negative electrode active material in the present disclosure maintains the above-mentioned first porosity also in the electrode and the battery. This is because expansion can be suppressed also in the electrodes and the battery.

The position of the first void in the primary particle is not particularly limited, and may be near the surface of the primary particle or near the center of the primary particle.

(4) Primary Particle The composition of the primary particle in the present disclosure is not particularly limited as long as it has the above-mentioned elements, phases and first voids.

Each of the above phases of the primary particles may exist as one continuous phase or as a plurality of discontinuous phases, but the latter is preferable. This is because the local expansion of the negative electrode active material can be suppressed. Further, when each of the Si phase, the MSi phase and the first void exists as a plurality of discontinuous phases, the cross section of the primary particle is, for example, a mottled pattern, that is, the Si phase, the MSi phase, and the first void. It can be observed as a pattern in which voids are dispersed. Further, in the relationship between the Si phase and the MSi phase, the cross section of the primary particle may be observed as a sea-island structure in which the Si phase is the sea and the silicide phase (MSi phase) is the island. In the case of the sea-island structure, the number of MSi phases (islands) in the primary particles may be 10 or more, 50 or more, or 100 or more. On the other hand, the number of islands is, for example, 500 or less. The area of the island may be, for example, 1 nm ² or more, 5 nm ² or more, 10 nm ² or more, ^{or 100 nm 2} or more. On the other hand, the area of the island is, for example, 500 nm ² or less, and ^{may be 300 nm 2} or less. The area of the first void portion can be calculated using, for example, image analysis software as described above.

Further, the primary particles may have only the Si phase, the MSi phase and the first voids described above, or may have other phases. Examples of the other phase include the Li phase. The ratio (area ratio) of the other phases in the primary particles is, for example, 5% or less, 3% or less, and may be 1% or less.

The average primary particle size of the negative electrode active material is, for example, 50 nm or more, 100 nm or more, or 150 nm or more. On the other hand, the average primary particle size of the negative electrode active material is, for example, 3000 nm or less, may be 1500 nm or less, or may be 1000 nm or less. The average primary particle size of the negative electrode active material can be determined by, for example, observation by SEM. The number of samples is preferably large, for example, 20 or more, 50 or more, or 100 or more. The average primary particle size of the negative electrode active material can be appropriately adjusted by, for example, appropriately changing the production conditions of the negative electrode active material or performing a classification treatment.

2. Secondary particles Further, the negative electrode active material in the present disclosure may be secondary particles in which a plurality of the above primary particles are aggregated and have a second void. This is because when the negative electrode active material is the secondary particles, the voids (first voids) of the primary particles and the secondary voids of the secondary particles can further suppress the expansion of the negative electrode active material layer and the battery. The second void means a void inside the secondary particle observed when the cross-sectional view of the secondary particle is obtained, excluding the void (first void) of the primary particle.

The ratio of the second porosity (second porosity) is, for example, 3% or more, 5% or more, 10% or more, or 20% or more. On the other hand, the second porosity is, for example, 60% or less, 50% or less, 40% or less, or 30% or less. The second porosity can be calculated from the following formula in the same manner as the porosity of the primary particles (first porosity).
Second porosity (%) = 100 x (second void area) / (secondary particle area)

Further, in relation to the thickness (α) of the negative electrode active material layer described later in the stacking direction, the average particle size (β) of the secondary particles is preferably a value in which β / α satisfies a predetermined range. β / α is, for example, 0.02 or more, may be 0.1 or more, or may be 0.2 or more. On the other hand, β / α is, for example, 0.5 or less, may be 0.4 or less, or may be 0.3 or less. The specific range of the average particle size of the secondary particles will be described later.

3. 3. Negative electrode active material The negative electrode active material in the present disclosure includes the above-mentioned primary particles. The negative electrode active material may be the above-mentioned primary particles or may be secondary particles in which the above-mentioned primary particles are aggregated. Further, it may have a tertiary particle structure having a plurality of domains of secondary particles.

Examples of the shape of the negative electrode active material in the present disclosure include particles. The average secondary particle size (β) of the negative electrode active material in the present disclosure is, for example, 1 μm or more, 2 μm or more, 5 μm or more, or 7 μm or more. On the other hand, the average secondary particle size of the negative electrode active material is, for example, 60 μm or less, may be 40 μm or less, but is particularly preferably 20 μm or less. The measurement and adjustment of the average secondary particle size are the same as those of the above primary particles.

The negative electrode active material in the present disclosure is usually used for a battery. The battery will be described in detail in "B. Battery" described later.

The method for producing the negative electrode active material in the present disclosure is not particularly limited, but for example, a preparatory step for preparing a precursor containing a Si element, a transition metal element and a Li element, and the above-mentioned extraction of the Li element from the precursor. Examples thereof include a method having a Li extraction step for obtaining a negative negative active material.

The preparation step is a step of preparing a precursor containing a Si element, a transition metal element, and a Li element. Precursors may be purchased or prepared by themselves. In the case of self-preparation, for example, a method of mixing a Si element source and a transition metal element source to prepare a Si alloy, and adding a Li element source to the Si alloy and mixing them can be mentioned. The amounts of the Si element and the transition metal element contained in the precursor are not particularly limited as long as the negative electrode active material in the present disclosure is obtained, and can be appropriately adjusted. Further, the amount of Li element is not particularly limited. The transition metal element is the transition metal element M described above.

The Li extraction step is a step of forming a first void by extracting the Li element from the precursor to obtain the above-mentioned negative electrode active material. Examples of the method for extracting Li include a method in which a Li extraction solvent such as ethanol and acetic acid is reacted with a precursor for a predetermined time.

By the above steps, a negative electrode active material which is a primary particle can be produced. Further, the void ratio in the primary particles is adjusted by, for example, changing the amount of Li element in the precursor in the preparation step, the type of Li extraction solvent in the Li extraction step, and the reaction time between the Li extraction solvent and the precursor. be able to. For example, the porosity can be increased by increasing the amount of Li element in the precursor.

Further, in the present disclosure, a method for producing a negative electrode active material, which is a secondary particle in which a plurality of the above primary particles are aggregated and has a second void, is a method of producing water, a surfactant, a template material, and the like. A preparatory step of preparing a micelle solution containing a polymerization initiator, a polymerization reaction step of adding the above-mentioned primary particles to the above-mentioned micelle solution to carry out a polymerization reaction, and a heat treatment step of heat-treating the micelle solution after the above-mentioned polymerization reaction. And, a method for producing a negative electrode active material having the above can be provided. In such a method, a negative electrode active material having a second void inside the secondary particles can be produced. Further, the negative electrode active material which is the secondary particles can also be produced, for example, by adding a solvent such as butyl butyrate to the powder material containing the primary particles and the binder described above and granulating the particles. ..

B. Battery FIG. 1 is a schematic cross-sectional view showing an example of a battery in the present disclosure. The battery 10 shown in FIG. 1 has 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 positive electrode active material layer 1. It has a positive electrode current collector 4 for collecting current, a negative electrode current collector 5 for collecting current in the negative electrode active material layer 2, and a battery case 6 for accommodating these members. In the present disclosure, the negative electrode active material layer 2 contains the above-mentioned negative electrode active material.

According to the present disclosure, by containing the above-mentioned negative electrode active material in the negative electrode active material layer, it is possible to obtain a battery capable of suppressing an increase in the restraining pressure due to charging and discharging.

1. 1. Negative electrode active material layer The negative electrode active material layer is a layer containing at least the above-mentioned negative electrode active material. Since the negative electrode active material is the same as the content described in "A. Negative electrode active material" above, the description here is omitted.

The negative electrode active material layer may contain only the above-mentioned negative electrode active material as the negative electrode active material, or may contain another negative electrode active material. In the latter case, the proportion of the above-mentioned negative electrode active material in all the 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, 30% by weight or more, or 40% by weight or more. On the other hand, the proportion of the negative electrode active material may be, for example, 80% by weight or less, 70% by weight or less, or 60% by weight or less.

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

Examples of the conductive material include carbon materials and metal particles. Specific examples of the carbon material include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), carbon fibers, carbon nanotubes (CNT), carbon nanofibers (CNF), and vapor-grown carbon fibers. Examples thereof include fibrous carbon materials such as (VGCF). Examples of the metal particles include Ni, Cu, Fe, and SUS. The proportion of the conductive material 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 material is, for example, 30% by weight or less, and may be 20% by weight or less.

Examples of the binder include rubber-based binders such as butadiene rubber, hydride butadiene rubber, styrene butadiene rubber (SBR), hydride styrene butadiene rubber, nitrile butadiene rubber, hydride nitrile butadiene rubber, and ethylene propylene rubber, and polyvinylidene fluoride (polyvinylidene fluoride). PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), fluoride-based binders such as polytetrafluoroethylene and fluororubber, polyolefin-based thermoplastic resins such as polyethylene, polypropylene and polystyrene, polyimides and polyamides. Examples thereof include imide-based resins such as imide, amide-based resins such as polyamide, acrylic resins such as polymethyl acrylate and polyethyl acrylate, and methacrylic resins such as polymethyl methacrylate and polyethyl methacrylate. The proportion 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. When the negative electrode active material contains the above-mentioned secondary particles in the negative electrode active material layer, the thickness (α) of the negative electrode active material layer is preferably a value in which the above-mentioned β / α satisfies a predetermined numerical range. ..

2. Positive electrode active material layer The positive electrode active material layer is a layer containing at least a positive electrode active material. Further, the positive electrode active material layer may further contain at least one of a solid electrolyte, a conductive material and a binder, if necessary.

Examples of the positive electrode active material include an oxide active material. Examples of the oxide active material used in the lithium ion battery include LiCoO ₂ , LiMnO ₂ , Li ₂ Nimn ₃ O ₈ , LiVO ₂ , LiCrO ₂ , LiFePO ₄ , LiCoPO ₄ , LiNiO ₂ , and LiNi _1/3 Co _{1 /.} Examples thereof include oxide active materials such as _{3 Mn 1/3} O _2. Further, a coat layer containing a Li ion conductive oxide such as _{LiNbO 3} may be formed on the surface of these active materials.

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

The types and proportions of the solid electrolyte, the conductive material and the binder used in the positive electrode active material layer are the same as those described in "1. Negative electrode active material layer" above, and thus the description thereof is omitted here. ..

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

3. 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 constituting the electrolyte layer may be a liquid electrolyte (electrolyte solution) or a solid electrolyte, but the latter is preferable.

Typical examples of the solid electrolyte 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.

Examples of the sulfide solid electrolyte having lithium ion conductivity include Li element and 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 can be mentioned. Further, the sulfide solid electrolyte may further contain at least one of an O element and a halogen element. Examples of the halogen element include F element, Cl element, Br element, and I element.

The sulfide solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-P 2 S 5 -LiI, Li 2 S-P 2 S 5 -GeS 2, Li 2 S-P 2 S 5 - Li ₂ O, Li ₂ S-P ₂ S _{5 -Li 2} O-LiI, Li ₂ S-P ₂ S ₅ -LiI-LiBr, Li ₂ S-SiS ₂ , Li ₂ S-SiS _2- LiI, Li ₂ 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 SB 2} S ₃ , Li ₂ SP ₂ S _{5- Z m} S _n (where m and n are positive numbers. Z is any of Ge, Zn, 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 and In. Is it?).

Further, the oxide solid electrolyte having lithium ion conductivity is, for example, at least one of Li element and Y element (Y is Nb, B, Al, Si, P, Ti, Zr, Mo, W and 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 electrolytes; Perobskite-type solid electrolytes such as (Li, La) TiO ₃ , (Li, La) NbO ₃ , (Li, Sr) (Ta, Zr) O _3, etc .; Li (Al, Ti) (PO ₄ ) ₃ , Li (Al, Ga) (PO ₄ ) ₃ pear-con type solid electrolyte; Li-PO _{-based solid electrolyte such as Li 3 PO 4} , LIPON (a compound in which a part of O of _{Li 3} PO _{4 is replaced with N)} Examples thereof include Li-BO solid electrolytes such as compounds in which a part of O of _{Li 3} BO ₃ and Li _{3 BO 3 is replaced with C.}

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

4. Other Configuration The battery in the present disclosure has at least the above-mentioned negative electrode active material layer, positive electrode active material layer and electrolyte layer. Further, it usually has a positive electrode current collector that collects electricity from the positive electrode active material layer and a negative electrode current collector that collects electricity from the negative electrode active material layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium and carbon. On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel and carbon.

Further, the battery in the present disclosure may further have a restraining jig for applying a restraining pressure to the positive electrode active material layer, the electrolyte layer and the negative electrode active material layer along the thickness direction. As the restraint jig, a known jig can be used. The restraining pressure is, for example, 0.1 MPa or more, may be 1 MPa or more, or may be 5 MPa or more. On the other hand, the restraining pressure is, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

5. Battery The battery in the present disclosure is preferably a lithium ion battery. Further, the battery in the present disclosure may be a liquid-based battery or an all-solid-state battery, but the latter is preferable. This is because the effect of suppressing an increase in the restraining pressure due to charging / discharging in the present disclosure can be further enjoyed.

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

Further, the battery in the present disclosure may be a single battery or a laminated battery. The laminated battery may be a monopolar type laminated battery (parallel connection type laminated battery) or a bipolar type laminated battery (series connection type laminated battery). Examples of the shape of the battery include a coin type, a laminated type, a cylindrical type and a square type.

The present disclosure is not limited to the above embodiment. The above embodiment is an example, and any object having substantially the same structure as the technical idea described in the claims of the present disclosure and exhibiting the same effect and effect is the present invention. Included in the technical scope of the disclosure.

[Example 1]
(Synthesis of negative electrode active material (primary particles))
(1) Preparation of Silicide An ingot was prepared by mixing 2 mm to 5 mm lumpy Si (manufactured by High Purity Chemical Co., Ltd.) and 2 mm to 5 mm lumpy transition metal (Cr) by argon arc dissolution. The ratio of Si element and Cr element was set to X = 2 in (100-X) Si- (X) M in Table 1 below. This ingot was crushed with a tungsten mortar and further crushed with a ball mill to prepare a Si alloy powder (SiO).

(2) Preparation of Porous Silicide (Negative Electrode Active Material) Metal Li (manufactured by Honjo Metal) was added so as to be 0.60 g with respect to the weight of Si contained in the prepared Si alloy powder of 0.65 g. Then, it was mixed in an agate mortar under an Ar atmosphere to obtain a LiSi precursor. To 1.0 g of the obtained LiSi precursor, 250 ml of ethanol (manufactured by Nacalai Tesque) at 0 ° C. was added, and the mixture was reacted in a glass reactor under an Ar atmosphere for 120 minutes. Then, the liquid and the solid reaction product A were separated by suction filtration, and the solid reaction product A was recovered. To 0.5 g of the recovered solid reaction product A, 50 ml of acetic acid (manufactured by Nacalai Tesque) was added, and the mixture was reacted in a glass reactor under an air atmosphere for 60 minutes. Then, the liquid and the solid reaction product B were separated by suction filtration, and the solid reaction product B was recovered. The solid reaction product B was vacuum dried at 100 ° C. for 2 hours to prepare porous silicide (negative electrode active material).

(Manufacturing of evaluation battery)
_{0.75Li 2} S-0.25P ₂ S ₅ 0.7 g as a solid electrolyte, 0.6 g of the negative electrode active material whose average particle size (average primary particle size) was adjusted to 3 μm, and VGCF as a conductive material were 0. 06 g and 0.24 g of a butyl butyrate solution containing 5% by weight of a PVDF resin as a binder were added to a polypropylene container. This container was ultrasonically treated in an ultrasonic disperser for 30 seconds and then shaken for 30 minutes using a shaker to obtain a negative electrode mixture. The obtained negative electrode mixture was applied onto a current collector (copper foil) by a blade method using an applicator, and air-dried for 60 minutes. The negative electrode precursor thus obtained was dried on a hot plate adjusted to 100 ° C. for 30 minutes to prepare a negative electrode.

_{0.75Li 2} S-0.25P ₂ S ₅ 0.3 g as a solid electrolyte _{, LiNi 1/3} Co _1/3 Mn _1/3 O _{2 2} g as a positive electrode active material, and 0.03 g of VGCF as a conductive material. , 0.3 g of a butyl butyrate solution containing 5% by weight of a PVDF resin as a binder was added to a polypropylene container. This container was ultrasonically treated in an ultrasonic disperser for 30 seconds and then shaken for 30 minutes using a shaker to obtain a positive electrode mixture. The obtained positive electrode mixture was applied onto a current collector (aluminum foil) by a blade method using an applicator, and air-dried for 60 minutes. The positive electrode precursor thus obtained was dried on a hot plate adjusted to 100 ° C. for 30 minutes to prepare a positive electrode.

_{0.75Li 2} S-0.25P ₂ S ₅ 0.4 g having an average particle size of 2 μm as a solid electrolyte and 0.05 g of a heptane solution containing 5% by weight of ABR resin as a binder were placed in a polypropylene container. Added. This container was sonicated in an ultrasonic disperser for 30 seconds and then shaken for 30 minutes using a shaker to obtain a paste. The obtained paste was applied onto a substrate (aluminum foil) by a blade method using an applicator, and dried on a hot plate adjusted to 100 ° C. for 30 minutes to prepare a solid electrolyte layer.

The negative electrode, the solid electrolyte layer, and the positive electrode obtained as described above were laminated so as to be in contact with each other in this order. A pressure of 200 MPa was applied to this laminate at 130 ° C. for 3 minutes to prepare an evaluation battery (all-solid-state battery).

[Examples 2 to 6]
The amount of Cr was changed so that the ratio of the transition metal element in the negative electrode active material became the value shown in Table 1. Further, the amount of Li in the above "(2) Preparation of porous silicide (negative electrode active material)" was adjusted to be the value of the first porosity in Table 1. Except for these, an evaluation battery was produced in the same manner as in Example 1.

[Comparative Example 1]
An evaluation battery was produced in the same manner as in Example 1 except that Si particles were used as the negative electrode active material.

[Comparative Example 2]
An evaluation battery was produced in the same manner as in Example 1 except that "(1) Fabrication of silicide" was not performed in Example 1 and only "(2) Preparation of porous silicide (negative electrode active material)" was performed. did.

[Comparative Example 3]
An evaluation battery was produced in the same manner as in Example 1 except that "(2) Preparation of porous silicide (negative electrode active material)" was not performed in Example 1 and only "(1) Preparation of silicide" was performed. did.

[Comparative Example 4]
A negative electrode active material was prepared according to the method of Patent Document 2 (Japanese Unexamined Patent Publication No. 2015-095301). An evaluation battery was produced in the same manner as in Example 1 except that this negative electrode active material was used. The transition metal element contained in the silicide phase was the same as in Example 1.

[Comparative Examples 5 and 6]
The amount of Cr was changed so that the ratio of the transition metal element in the negative electrode active material was 50 mol%. Further, the amount of Li in the above "(2) Preparation of porous silicide (negative electrode active material)" was adjusted to be the value of the first porosity in Table 1. Except for these, an evaluation battery was produced in the same manner as in Example 1.

[Evaluation 1]
(First porosity)
Cross-sectional SEM images of the negative electrode active materials (negative electrode active materials before the production of the evaluation battery) produced in Examples 1 to 6 and Comparative Examples 1 to 6 were acquired. Based on the acquired SEM image, the first porosity was calculated from the following formula. Each porosity is shown in Table 1. Further, the primary particle images of Example 4 and Comparative Example 4 are shown in FIGS. 2 and 3.
First porosity (%) = 100 x (first void area) / (primary particle area)

As shown in FIG. 2, it was confirmed that the negative electrode active material (Example 4) in the present disclosure has a Si phase, an MSi phase, and a first void inside the primary particles. Further, as shown in FIG. 2, the Si phase, the MSi phase, and the first voids each existed as a plurality of discontinuous phases, and the cross section of the negative electrode active material was mottled. On the other hand, as shown in FIG. 3, in Comparative Example 4, the first void was not confirmed at all.

(Amount of increase in restraint pressure)
Each of the evaluation batteries produced in Examples 1 to 6 and Comparative Examples 1 to 6 was restrained at a predetermined pressure, and was energized at a constant current to a predetermined voltage at 0.1 C for initial charging. In the initial charge, the confining pressure of the battery was monitored, and the confining pressure in the charged state was measured. The amount of increase in the restraint pressure was relatively evaluated with the value of Comparative Example 1 as 1.00. The results are shown in Table 1.

(resistance)
The resistance at 25 ° C. and 60% SOC (State of Charge) was determined for each of the evaluation batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 6. Specifically, after charging to a voltage of 3.7 V at 0.245 mA, the battery was discharged at 7.35 mA for 5 seconds, and the internal resistance was calculated from the change in voltage. The resistance was relatively evaluated with the value of Comparative Example 1 as 1.00. The results are shown in Table 1.

As shown in Table 1, in Comparative Example 2 in which the MSi phase (0045 phase) did not exist and the first void was provided, the increase in the restraining pressure was not suppressed and the resistance was high. It is considered that this is because the first void was crushed in the pressing process at the time of electrode production because the silicide phase did not exist. Further, in Comparative Example 3 and Comparative Example 4 which have a Si phase and a silicide phase and do not have a first void, cracks occur at the interface between the VDD phase and the Si phase during charging, and an increase in the restraining pressure is suppressed. could not.

On the other hand, in the evaluation batteries (Examples 1 to 6) using the negative electrode active material (primary particles) in the present disclosure, the increase in the restraining pressure was remarkably suppressed. It is considered that this is because the silicide phase acted as a pillar and the first void could be maintained. Further, as can be seen from Comparative Example 2, the normal resistance tends to increase when the first void is provided. However, since the silicide phase has electron conductivity, the evaluation batteries in Examples 1 to 6 could suppress the increase in resistance. Further, in Comparative Examples 5 and 6 in which the ratio of the transition metal element was 50 mol%, only the silicide phase was formed and the Si phase was not formed.

From the above, it was confirmed that since the negative electrode active material (primary particles) in the present disclosure has a small volume change due to charging and discharging, an increase in the restraining pressure can be suppressed in a battery using the negative electrode active material (primary particles).

[Example 7]
(Synthesis of negative electrode active material (secondary particles))
A solution of water, a surfactant (hexadecyltrimethylammonium bromide), a template material (styrene), and a polymerization initiator (2,2'-azobis (2,4-dimethylvaleronitrile)) is heated. The micelle solution was prepared. Then, the primary particles (first porosity 60%) prepared in Example 4 and an organic solvent (octane) were added to the micelle solution and reacted for 3 hours (polymerization reaction). The polymerization reaction was terminated by cooling. Then, by performing a heat treatment at 500 ° C., secondary particles in which the primary particles were aggregated were produced. The average particle size of the secondary particles was appropriately adjusted so that the ratio (β / α) of the average particle size of the secondary particles to the thickness of the negative electrode active material layer in the stacking direction was the value shown in Table 2. .. Further, the secondary particles produced by such a method have voids (second voids) inside.

(Battery production)
Using the secondary particles as the negative electrode active material, the ratio (β / α) of the average particle diameter (β) of the secondary particles to the thickness (α) in the stacking direction of the negative electrode active material layer is the value in Table 2. The average particle size of the secondary particles and the thickness of the negative electrode active material layer were adjusted so as to be. An evaluation battery was produced in the same manner as in Example 1 except for the above.

[Examples 8 to 11]
The average particle size of the secondary particle size and the thickness of the negative electrode active material layer were adjusted so that β / α had the values shown in Table 2. Except for the above, an evaluation battery was produced in the same manner as in Example 7.

[Evaluation 2]
(Amount of increase in restraint pressure)
The amount of increase in the restraining pressure of each evaluation battery produced in Examples 7 to 11 was measured by the same method as in Evaluation 1. The amount of increase in the restraint pressure was relatively evaluated with the value of Example 7 as 1.00. The results are shown in Table 2.

(resistance)
The resistance of each evaluation battery produced in Examples 7 to 11 was calculated by the same method as in Evaluation 1. The resistance was relatively evaluated with the value of Example 7 as 1.00. The results are shown in Table 2.

As shown in Table 2, the larger the β / α, the smaller the amount of increase in the restraint pressure. It is considered that this is because the average particle size of the secondary particles is relatively large, so that the voids between the secondary particles in the negative electrode active material layer are increased and the expansion of the negative electrode active material can be absorbed. On the other hand, when β / α became too large, the battery resistance increased sharply. It is considered that this is because the voids between the secondary particles become relatively large and the Li ion conductivity between the secondary particles decreases. From the above, it is considered that β / α is preferably 0.02 or more and 0.5 or less in the battery in consideration of the effect of suppressing the amount of increase in the restraining pressure and the increase in resistance.

(Mechanical strength of silicide)
The mechanical strengths of Si and various silicides were calculated from simulations by the Phase-Field method. The result is shown in FIG. The silides circled in the figure are those which are phase-separated and do not react with Li. If the mechanical strength is higher than that of silicon (Si), it is considered that the silicide can sufficiently play a role as a pillar in the primary particles. Further, it is considered that the silicide that undergoes phase separation and does not react with Li can easily maintain the structure as a pillar.

1 ... Positive electrode active material layer 2 ... Electrolyte layer 3 ... Negative electrode active material layer 4 ... Positive electrode current collector 5 ... Negative electrode current collector 6 ... Battery case 10 ... Battery

Claims (8)

A negative electrode active material containing primary particles having a Si phase, an MSi phase (M is a transition metal element) which is a silicide phase, and a first void. The negative electrode active material according to claim 1, wherein the ratio of the transition metal element to the total of the Si element and the transition metal element contained in the primary particles is 2 mol% or more and less than 50 mol%. The negative electrode active material according to claim 1 or 2, wherein the ratio of the first voids in the primary particles is 3% or more. The negative electrode activity according to any one of claims 1 to 3, wherein the transition metal element is at least one of W, Mo, Cr, V, Nb, Fe, Ti, Zr, Hf and Os. material. The negative electrode active material according to claim 4, wherein the transition metal element is at least one of Cr, Ti, Zr, Hf and Os. The negative electrode active material according to any one of claims 1 to 5, wherein the negative electrode active material is a secondary particle in which a plurality of the primary particles are aggregated and has a second void. 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 in which the negative electrode active material layer contains the negative electrode active material according to any one of claims 1 to 6. The negative electrode active material layer contains the negative electrode active material according to claim 6.
When the thickness of the negative electrode active material layer in the stacking direction is α (μm) and the average particle size of the secondary particles is β (μm), β / α is 0.02 or more and 0.5 or less. , The battery according to claim 7.

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