JP7069727B2 - Negative electrode layer - Google Patents

Description

The present disclosure relates to a negative electrode layer used in an all-solid-state battery.

An all-solid-state battery is a battery having a solid electrolyte layer between a positive electrode layer and a negative electrode layer. For example, Patent Document 1 describes a negative electrode active material that expands 5 cm ³ to 15 cm ³ with a charge of 1 Fd, a positive electrode active material that contracts 5 cm ³ to 15 cm ³ with a charge of 1 Fd, and a lithium ion secondary battery containing a solid electrolyte. It has been disclosed. This technique aims to provide a lithium ion secondary battery having excellent cycle characteristics and high capacity by optimizing the balance between the expansion of the negative electrode and the contraction of the positive electrode.

Patent Document 2 describes a secondary particle containing an active material having a volume expansion coefficient of 5% or more, a conductive auxiliary agent, and a first binder, and a second binder having an elastic modulus different from that of the first binder. A battery electrode containing a binder and having a porosity of 18% to 70% is disclosed. The purpose of this technique is to provide a battery electrode capable of suppressing deformation and cracking of the electrode and improving the cycle characteristics of the secondary battery even if the active material expands or contracts. There is. Further, Patent Document 3 describes silicon secondary particles that can be used as a negative electrode of a lithium ion secondary battery, in which silicon fine particles having a particle size of 50 nm to 100 nm are used as nuclei, and amorphous graphite carbon is provided around the nuclei. Disclosed are secondary silicon particles, which are formed by agglomerating coated silicon fine particles on which a shell is formed. An object of this technique is to provide silicon secondary particles having high conductivity and suppressed volume change during charge and discharge.

Japanese Unexamined Patent Publication No. 2014-0297991 Japanese Unexamined Patent Publication No. 2009-224239 Japanese Unexamined Patent Publication No. 2012-254899

The all-solid-state battery has a problem that the cycle characteristics are deteriorated due to the volume change of the negative electrode active material during charging and discharging. The present disclosure has been made in view of the above circumstances, and provides a negative electrode layer used in an all-solid-state battery capable of suppressing a decrease in cycle characteristics due to a volume change of a negative electrode active material during charging / discharging.

In order to achieve the above object, in the present disclosure, the negative electrode layer used in an all-solid-state battery has a negative electrode active material and a sulfide solid electrolyte, and the negative electrode active material contains a Si element or a Sn element. Provided is a composite particle having a plurality of particles and a binder and having a void ratio of 15% or less, and providing a negative electrode layer.

According to the present disclosure, the negative electrode active material is a composite particle having a plurality of particles containing Si element or Sn element and a binder, and the void ratio of the negative electrode layer is 15% or less, so that the negative electrode during charging and discharging is performed. It is possible to provide a negative electrode layer used for an all-solid-state battery, which can suppress a decrease in cycle characteristics due to a change in the volume of an active material.

When the negative electrode layer of the present disclosure is used in an all-solid-state battery, it has an effect that deterioration of cycle characteristics due to a volume change of the negative electrode active material during charging / discharging can be suppressed.

It is an image obtained by observing the composite particle in the present disclosure with a scanning electron microscope. It is an image obtained by observing the composite particle in the present disclosure with a scanning electron microscope.

Hereinafter, the negative electrode layer of the present disclosure will be described in detail.

The negative electrode layer of the present disclosure is a member used for an all-solid-state battery and has a negative electrode active material and a sulfide solid electrolyte, and the negative electrode active material has a plurality of particles containing Si element or Sn element and a binder. It is a composite particle and is a member having a void ratio of 15% or less.

According to the present disclosure, the negative electrode active material is a composite particle having a plurality of particles containing Si element or Sn element and a binder, and the void ratio of the negative electrode layer is 15% or less, so that the negative electrode during charging and discharging is performed. It is possible to provide a negative electrode layer used for an all-solid-state battery, which can suppress a decrease in cycle characteristics due to a change in the volume of an active material. The following can be inferred as the specific reason.

First, when a negative electrode active material containing a Si element or a Sn element is used, there is a problem that the volume of the negative electrode active material tends to expand and contract during charging and discharging. For example, during charging, the negative electrode active material may expand due to expansion, which may cause cracks in the negative electrode active material itself. In this case, the negative electrode active material is atomized and isolated, and the path of the ion path and the electron path with the surroundings. May run out. Further, at the time of discharge, the negative electrode active material shrinks, so that a gap is generated at the interface between the negative electrode active material and the solid electrolyte, and there is a possibility that the path of the ion path or the electron path is cut off. As described above, if the interface between the negative electrode active material and the solid electrolyte cannot be maintained and the path of the ion path or the electron path cannot be maintained, there is a problem that charging / discharging cannot be performed and the capacity retention rate is lowered.

On the other hand, according to the present disclosure, a composite particle having a plurality of particles containing Si element or Sn element and a binder is used as a negative electrode active material, and the void ratio of the negative electrode layer is set to 15% or less to reduce the negative electrode. The interface between the active material and the solid electrolyte can be maintained, and the path of the ion path and the electron path can be maintained. Therefore, it is presumed that the above-mentioned problems can be solved, the decrease in the capacity retention rate can be suppressed, and as a result, the decrease in the cycle characteristics can be suppressed.

Further, in the present disclosure, composite particles can be generated by using a plurality of particles having a relatively small particle diameter. As described above, by using the composite particle having a plurality of particles having a relatively small particle diameter as the negative electrode active material, the reactivity of the negative electrode active material can be enhanced, and a high-capacity all-solid-state battery can be obtained. It is presumed to be. Further, in the present disclosure, since the composite particles have a binder, the composite particles are suppressed from being destroyed in the mixing step when the negative electrode layer is produced, and the space of a plurality of particles is maintained to expand the negative electrode active material. It is presumed that the contraction can be alleviated.

The negative electrode layer of the present disclosure is used for an all-solid-state battery. Further, the negative electrode layer has a negative electrode active material and a sulfide solid electrolyte.

(1) Negative electrode active material The negative electrode active material of the present disclosure is a composite particle having a plurality of particles containing Si element or Sn element and a binder.

The plurality of particles containing the Si element or the Sn element may contain only one of the Si element and the Sn element, or may contain both the Si element and the Sn element. Further, the particles may contain, for example, Fe element, Co element, Ni element, Ti element, Cr element, B element, P element and the like in addition to the Si element and the Sn element. Such particles may be a simple substance of Si element or Sn element, or may be an alloy containing Si element or Sn element. Examples of the alloy include alloys such as iron, cobalt, nickel, titanium and chromium.

The particles may be primary particles or may be aggregates of nano-sized primary particles. The particles are usually fine particles, and the particle diameter thereof is, for example, 30 nm or more, 50 nm or more, or 100 nm or more. On the other hand, the particle size of the particles is, for example, 9 μm or less, may be 7 μm or less, or may be 3 μm or less. The particle diameter of the particles can be determined by using, for example, a laser diffraction type particle distribution measuring device.

Examples of the particle shape of the particles include a true spherical shape and an elliptical spherical shape.

The negative electrode active material is a composite particle having a plurality of particles containing a Si element or a Sn element and a binder. As shown in FIG. 1, for example, the composite particle has a structure in which a plurality of particles are aggregated. Note that FIG. 1 is an image obtained by observing the composite particles with a scanning electron microscope. Further, the composite particle has a binder in a plurality of particles and does not contain a sulfide solid electrolyte. The number of particles contained in the composite particles is, for example, 3 or more, 20 or more, or 100 or more. The number of particles contained in the composite particles can be measured, for example, from an image obtained by observing with an electron microscope. The plurality of particles constituting the composite particle may be only the particles containing the Si element or the Sn element, or may have particles other than the particles containing the Si element or the Sn element. The ratio of the particles containing the Si element or the Sn element to all the particles constituting the composite particle is, for example, 80% or more, 90% or more, or 100%.

The composite particle has the above-mentioned plurality of particles and a binder, and can be regarded as a secondary particle in which the above-mentioned plurality of particles are aggregated. The particle size of the composite particle is, for example, 1 μm or more, may be 2 μm or more, or may be 3 μm or more. On the other hand, the particle size of the composite particle is, for example, 15 μm or less, may be 7 μm or less, or may be 3 μm or less. The particle size of the composite particle can be determined by using, for example, a laser diffraction type particle distribution measuring device.

Examples of the binder contained in the composite particles include a binder generally used for the negative electrode layer. For example, polyimide, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylic acid salt, polyacrylic acid ester, amine-modified butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVDF). ), Polytetrafluoroethylene (PTFE) and the like. Only one type of binder may be used, or a plurality of types may be mixed and used.

The content of the binder contained in the composite particles is not particularly limited as long as the desired composite particles can be produced by using a plurality of particles. The ratio of the binder to the total of the particles and the binder is, for example, 10 wt% or less, and may be 5 wt% or less. On the other hand, the ratio of the binder to the total of the particles and the binder is, for example, 0.5 wt% or more.

Composite particles can be obtained by aggregating a plurality of particles. The method for producing the composite particles is not particularly limited, and examples thereof include wet generation and dry generation. The generation of composite particles by wet treatment can be performed, for example, by spray-drying or rolling a mixed solution in which a plurality of particles and a binder are mixed. On the other hand, the generation of composite particles by the dry method can be performed, for example, by compressing a plurality of particles or applying a physical impact. An example of a specific method for producing composite particles will be shown in Examples described later.

The negative electrode layer has a negative electrode active material. The negative electrode active material contained in the negative electrode layer may be only one type or two or more types. When the negative electrode active material of the negative electrode layer is two or more kinds, the negative electrode active material of the negative electrode layer may have other negative electrode active materials other than the above-mentioned negative electrode active material. Examples of other negative electrode active materials include general negative electrode active materials, for example, metal active materials such as In and Al, and mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Such as carbon active material and the like.

The content of the negative electrode active material contained in the negative electrode layer is preferably higher from the viewpoint of capacity. The content of the negative electrode active material contained in the negative electrode layer is, for example, 60 wt% or more, preferably 70 wt% or more. On the other hand, the content of the negative electrode active material contained in the negative electrode layer is, for example, 99 wt% or less, and may be 95 wt% or less.

(2) Sulfide solid electrolyte Examples of the sulfide solid electrolyte include Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -Li I, Li ₂ SP ₂ S ₅ -Li ₂ O, and Li. ₂ SP ₂ S ₅ -Li ₂ O-LiI, 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 S-P ₂ S ₅ -Z _{m Sn} (However , M, 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, In) and the like. The above description of "Li ₂ SP _{2 S 5" means a sulfide solid electrolyte using a raw material composition containing Li 2 S and P 2 S 5 , and} the same applies to other descriptions. ..

When the sulfide solid electrolyte is a Li ₂ SP ₂ S ₅ system, the ratio of Li ₂ S and P ₂ S ₅ is the molar ratio of Li ₂ S: P ₂ S ₅ = 50: 50 to 100: 0. It may be within the range of Li ₂ S: P ₂ S ₅ = 75:25.

The sulfide solid electrolyte may be crystalline, amorphous, or glass-ceramic (crystallized glass).

Examples of the shape of the sulfide solid electrolyte include a particle shape. The average particle size (D ₅₀ ) of the sulfide solid electrolyte is, for example, 0.01 μm or more. On the other hand, the average particle size (D ₅₀ ) of the sulfide solid electrolyte is, for example, 40 μm or less, and may be 20 μm or less. The Li ion conductivity of the sulfide solid electrolyte at 25 ° C. is, for example, 1 × 10 ^-5 S / cm or more, preferably 1 × 10 ^-4 S / cm or more, and preferably 1 × 10 ^-3 S / cm. It is particularly preferable that it is / cm or more.

The negative electrode layer has a sulfide solid electrolyte. The sulfide solid electrolyte contained in the negative electrode layer may be of only one type or may be of two or more types.

The content of the sulfide solid electrolyte contained in the negative electrode layer is, for example, 1 wt% or more, and may be 10 wt% or more. On the other hand, the content of the sulfide solid electrolyte contained in the negative electrode layer is, for example, 90 wt% or less, and may be 80 wt% or less.

(3) Negative electrode layer The negative electrode layer is a member used for an all-solid-state battery. Further, the negative electrode layer has the above-mentioned negative electrode active material and the sulfide solid electrolyte. Further, the negative electrode layer has a porosity of 15% or less.

The porosity of the negative electrode layer may be 15% or less. The porosity of the negative electrode layer is, for example, 10% or less, preferably 7% or less, particularly preferably 5% or less, and particularly preferably 3% or less. Further, the porosity of the negative electrode layer is usually larger than 0%. When the porosity of the negative electrode layer has the above upper limit, the interface between the negative electrode active material and the solid electrolyte can be maintained, and the path of the ion path and the electron path can be maintained. As a result, it is possible to suppress a decrease in the capacity retention rate and, as a result, a decrease in cycle characteristics. The porosity of the negative electrode layer can be adjusted by pressing the negative electrode layer.

The above-mentioned "porosity" is the ratio of the volume of voids in the negative electrode layer to the entire negative electrode layer. For the porosity of the negative electrode layer, the porosity is A, and the total volume obtained by dividing the weight of each material contained in the negative electrode mixture (all the materials constituting the negative electrode layer) by the true density of each material is x. It is a value calculated by A (%) = (1-x / y) × 100, where y is the volume obtained from the actual dimensions of the negative electrode layer.

The negative electrode layer may have a conductive material in addition to the negative electrode active material and the sulfide solid electrolyte described above. Since the negative electrode layer has a conductive material, the electron conductivity is improved. In particular, as shown in FIG. 2, it is preferable that the composite particles contain a conductive material. Note that FIG. 2 is an image obtained by observing composite particles containing carbon fiber (VGCF) as a conductive material with a scanning electron microscope. By contacting a plurality of particle conductive materials constituting the composite particle, the path of the electron path can be maintained and the electron conductivity can be effectively improved. The conductive material may be arranged between the two composite particles. The conductive material is preferably a material having desired electron conductivity. Specific examples of the conductive material include carbon materials such as acetylene black, ketjen black and carbon fiber (VGCF), nickel, aluminum, SUS and the like. Further, the negative electrode layer does not have to have a conductive material. The content of the conductive material contained in the negative electrode layer is, for example, 1 wt% or more, and may be 5 wt% or more. On the other hand, the content of the conductive material contained in the negative electrode layer is, for example, 30 wt% or less, 25 wt% or less, or 20 wt% or less.

The thickness of the negative electrode layer varies greatly depending on the configuration of the all-solid-state battery, but can be, for example, 0.1 μm or more and 1000 μm or less.

(4) All-solid-state battery The negative electrode layer of the present disclosure is used for an all-solid-state battery. The all-solid-state battery usually has the following configuration. That is, it has a configuration including a positive electrode layer having a positive electrode active material, the above-mentioned negative electrode layer, and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer. Further, for example, even if a positive electrode collector that collects electricity in the positive electrode layer, a negative electrode current collector that collects electricity in the negative electrode layer, and a battery case that houses the above-mentioned members constituting the all-solid-state battery are provided. good. The members other than the negative electrode layer constituting the all-solid-state battery can be the same as the members used in a general all-solid-state battery, and thus the description thereof is omitted here.

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

The present disclosure will be described in more detail with reference to Examples below.

[Example 1]
<Generation of composite particles (secondary particle formation)>
Silicon particles (manufactured by High Purity Chemical Co., Ltd., primary particle diameter 5 μm) were prepared as active materials. The silicon particles (primary particles) and a solution (binder) containing polyamic acid, which is a precursor of polyimide made by Ube Corporation, have a primary particle: binder solid content = 97: 3 ratio (wt%). As described above, the mixture was dispersed in water to obtain a slurry. This slurry was sprayed into a spray dryer under the condition of a temperature of 150 ° C. and dried. As a result, composite particles (secondary particles) having a particle size (average particle size) of 7 μm were generated. Next, the produced composite particles were treated under an inert atmosphere at a temperature of 350 ° C. for 2 hours to imidize the polyamic acid into polyimide.

<Manufacturing of all-solid-state battery>
An all-solid-state battery was manufactured as follows.

(Preparation of positive electrode layer)
Butyl butyrate (dispersion medium), butyl butyrate solution (5 wt%) in which polyvinylidene fluoride (binder) is dissolved, and LiNi _1/3 Co _1/3 Mn _1/3 O coated with lithium niobate (protective coating). ₂ (Positive active material), Li ₂ SP ₂ S ₅ system glass ceramic (solid electrolyte), and VGCF (conducting material) are added to a polypropylene container, and an ultrasonic disperser (SMT Co., Ltd.) The product was stirred for 30 seconds using the product name UH-50). Then, the polypropylene container was shaken with a shaker (manufactured by Shibata Chemical Co., Ltd., product name TTM-1) for 3 minutes, and further stirred with an ultrasonic disperser for 30 seconds to prepare a paste for a positive electrode layer. Next, the obtained positive electrode layer paste is applied to an aluminum foil (positive electrode current collector) by a doctor blade method using an applicator, and then dried on a hot plate heated to 100 ° C. for 30 minutes. As a result, a positive electrode layer was produced.

(Preparation of negative electrode layer)
Butyl butyrate (dispersion medium), butyl butyrate solution (5 wt%) in which polyvinylidene fluoride (binder) is dissolved, the above-mentioned composite particles (negative electrode active material), and Li ₂ SP ₂ S ₅ system glass ceramic ( The solid electrolyte) and VGCF (conducting material) were added to the polypropylene container and stirred for 30 seconds using an ultrasonic disperser (manufactured by SMT Co., Ltd., product name UH-50). Then, the polypropylene container was shaken with a shaker (manufactured by Shibata Scientific Technology Co., Ltd., product name TTM-1) for 30 minutes to prepare a paste for the negative electrode layer. Next, the obtained negative electrode layer paste is applied to a copper foil (negative electrode current collector) by a doctor blade method using an applicator, and then dried on a hot plate heated to 100 ° C. for 30 minutes. As a result, a negative electrode layer was produced.

(Preparation of solid electrolyte layer)
A heptane (dispersion medium), a heptane solution (5 wt%) in which polyvinylidene fluoride (binder) is dissolved, and a Li ₂ SP ₂ S ₅ glass ceramic (solid electrolyte) containing lithium iodide are mixed with polypropylene. In addition to the manufacturing container, the mixture was stirred for 30 seconds using an ultrasonic disperser (manufactured by SMT Co., Ltd., product name UH-50). Then, the polypropylene container was shaken with a shaker (manufactured by Shibata Scientific Technology Co., Ltd., product name TTM-1) for 30 minutes to prepare a paste for a solid electrolyte layer. Next, the obtained solid electrolyte layer paste was applied to an aluminum foil (base) by a doctor blade method using an applicator, and then dried on a hot plate heated to 100 ° C. for 30 minutes. A solid electrolyte layer was prepared.

(Laminating / pressing process)
The solid electrolyte layer was laminated on the positive electrode layer so that the obtained solid electrolyte layer was in contact with the positive electrode layer, pressed at 1 ton / cm ² , and the aluminum foil (substrate) was peeled off from the solid electrolyte layer to form a solid electrolyte layer. A laminate with the positive electrode layer was prepared. Then, the obtained negative electrode layer was superposed on the solid electrolyte layer side of this laminated body and pressed so that the porosity of the negative electrode layer was 5% to complete the all-solid-state battery. The obtained all-solid-state battery cell was restrained with a restraining pressure of 2 Nm using a restraining jig, and placed in a desiccator for evaluation.

[Example 2]
An all-solid-state battery was produced in the same manner as in Example 1 except that the negative electrode layer was pressed so as to have a porosity of 7% in the laminating / pressing step.

[Example 3]
An all-solid-state battery was produced in the same manner as in Example 1 except that the negative electrode layer was pressed so as to have a porosity of 15% in the laminating / pressing step.

[Example 4]
An all-solid-state battery was produced in the same manner as in Example 1 except that a mixed dispersion of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) was used as a binder in the production of composite particles.

[Comparative Example 1]
An all-solid-state battery was produced in the same manner as in Example 1 except that silicon particles (primary particles not converted into secondary particles) were used as the negative electrode active material.

[Comparative Example 2]
An all-solid-state battery was produced in the same manner as in Example 1 except that the negative electrode layer was pressed so as to have a porosity of 18% in the laminating / pressing step.

[Comparative Example 3]
An all-solid-state battery was produced in the same manner as in Example 1 except that the negative electrode layer was pressed so as to have a porosity of 25% in the laminating / pressing step.

[evaluation]
(Measurement of capacity retention rate (%))
For the all-solid-state batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 3, constant current-constant voltage charging (termination current 1 / 100C) up to 4.55V at a 10-hour rate (1 / 10C) as initial charging. ), And the constant current-constant voltage discharge as the initial discharge was discharged to 2.50V. After that, constant current-constant voltage charging (final current 1 / 100C) was performed up to 4.35V, and constant current-constant voltage discharge was performed to discharge to 3.00V, and the discharge capacity of the all-solid-state battery before the durability test was measured. .. Then, as a durability test, a cycle of charging to 4.17 V at a 0.5 hour rate (2C) and then discharging to 3.17 V was repeated 300 times under the condition of 60 ° C. After the endurance test, constant current-constant voltage charging (termination current 1 / 100C) is performed up to 4.35V, and constant current-constant voltage discharge is performed to discharge to 3.00V to reduce the discharge capacity of the all-solid-state battery after the endurance test. It was measured. After that, (discharge capacity after the durability test) / (discharge capacity before the durability test) was calculated to calculate the capacity retention rate of the all-solid-state battery. The results are shown in Table 1.

(Measurement of SOC 20% resistance (Ω))
After the durability test described above, the all-solid-state battery was adjusted to SOC (State of Charge) 20%, discharged at a constant current (7C) for 5 seconds, and the resistance was determined from the decrease in current and voltage. The results are shown in Table 1.

As shown in Table 1, from the results of Example 1 and Comparative Example 1, it was found that the decrease in the capacity retention rate can be suppressed by using the composite particles as the negative electrode active material. Further, from the results of Examples 1 to 4 and Comparative Examples 2 and 3, by setting the porosity of the negative electrode layer to 15% or less, the decrease in the capacity retention rate is suppressed, and the resistance of SOC 20% becomes low resistance. It was found that excellent battery performance can be obtained.

Claims (1)

A negative electrode layer used in all-solid-state batteries.
It has a negative electrode active material and a sulfide solid electrolyte,
The negative electrode active material is a composite particle having a plurality of particles containing a Si element or a Sn element and a binder.
Porosity is 15% or less ,
A negative electrode layer having a primary particle diameter of 100 nm or more and 9 μm or less .

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