JP2019121557A - Negative electrode layer - Google Patents

Abstract

To provide a negative electrode layer to be used for an all-solid battery, which can suppress the worsening of a cycle characteristic owing to the volume change of a negative electrode active substance during charge and discharge.SOLUTION: A negative electrode layer comprises a negative electrode active substance and a sulfide solid electrolyte. The negative electrode active substance comprises composite particles having a plurality of particles containing Si or Sn element and a binder. The negative electrode layer has a porosity of 15% or less.SELECTED DRAWING: Figure 1

Description

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

The all solid battery is a battery having a solid electrolyte layer between the positive electrode layer and the negative electrode layer. For example, Patent Document 1, a negative electrode active material to ^{5cm 3 ~15cm} 3 inflated at charging 1FD, the positive electrode active material ^{5cm 3 ~15cm} 3 contraction in charge 1FD, a lithium ion secondary battery including a solid electrolyte It is disclosed. This technique aims to provide a lithium ion secondary battery excellent in cycle characteristics and having a high capacity by optimizing the balance between the expansion of the negative electrode and the contraction of the positive electrode.

  In Patent Document 2, a second particle having a volume expansion coefficient of 5% or more, a conductive auxiliary agent, and a first binder, and a second particle having a second elastic coefficient different from that of the first binder is used. A battery electrode containing a binder and having a porosity of 18% to 70% is disclosed. This technique is intended to provide a battery electrode which can suppress the occurrence of deformation and cracks in the electrode and improve the cycle characteristics of the secondary battery even if expansion and contraction of the active material occur. There is. Further, Patent Document 3 is a silicon secondary particle that can be used for the negative electrode of a lithium ion secondary battery, wherein silicon fine particles having a particle diameter of 50 nm to 100 nm are used as a core, and carbon of amorphous graphite around the core. Disclosed is a silicon secondary particle in which a shell-formed coated silicon fine particle is aggregated. This technique is intended to provide silicon secondary particles that have high conductivity and in which volume change during charge and discharge is suppressed.

JP, 2014-029791, A JP, 2009-224239, A JP 2012-254899 A

  The all-solid-state battery has a problem that the cycle characteristics are degraded due to the volume change of the negative electrode active material during charge and discharge. The present disclosure has been made in view of the above-described circumstances, and provides a negative electrode layer used for an all-solid-state battery that can suppress a decrease in cycle characteristics due to a volume change of the negative electrode active material during charge and discharge.

  In order to achieve the above object, in the present disclosure, the present disclosure is a negative electrode layer used for an all solid battery, which has a negative electrode active material and a sulfide solid electrolyte, and the negative electrode active material contains Si element or Sn element. Provided is a composite particle having a plurality of particles and a binder, and having a porosity 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 porosity of the negative electrode layer is 15% or less. The negative electrode layer used for the all-solid-state battery which can suppress the fall of the cycling characteristics by the volume change of an active material can be provided.

  The negative electrode layer of the present disclosure exhibits an effect of being able to suppress a decrease in cycle characteristics due to a volume change of the negative electrode active material during charge and discharge by being used for an all solid battery.

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 battery, and includes a negative electrode active material and a sulfide solid electrolyte, and the negative electrode active material includes a plurality of particles containing Si element or Sn element and a binder. It is a composite particle, and is a member having a porosity 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 porosity of the negative electrode layer is 15% or less. The negative electrode layer used for the all-solid-state battery which can suppress the fall of the cycling characteristics by the volume change of an active material can be provided. The following can be inferred for specific reasons.

  First, when the negative electrode active material containing Si element or Sn element is used, there is a problem that the volume of the negative electrode active material is easily expanded and shrunk during charge and discharge. For example, at the time of charging, the negative electrode active material may expand to cause a crack in the negative electrode active material itself. In this case, the negative electrode active material is atomized and becomes isolated, and a path of ion and electron paths with the surroundings. There is a risk of In addition, during 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, which may break the path of the ion path or the electron path. As described above, when it is not possible to maintain the interface between the negative electrode active material and the solid electrolyte and the path of the ion path and the electron path, charge and discharge can not be performed, and the capacity retention rate is reduced.

  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 porosity of the negative electrode layer is 15% or less. 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 problems as described above can be solved, the decrease in capacity retention rate can be suppressed, and as a result, the decrease in cycle characteristics can be suppressed.

  Also, the present disclosure can produce composite particles using a plurality of relatively small particle sizes. Thus, by using the composite particles having a plurality of relatively small particle sizes as the negative electrode active material, the reactivity of the negative electrode active material can be enhanced, and a high capacity all solid battery can be obtained. It is guessed that. Furthermore, according to the present disclosure, since the composite particles have a binder, the composite particles are prevented from being broken in the mixing step of producing the negative electrode layer, and the spaces of the plurality of particles are maintained to expand the negative electrode active material. It is speculated that contraction can be alleviated.

  The negative electrode layer of the present disclosure is used for an all solid state battery. In addition, 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 a Si element or a Sn element and a binder.

  The plurality of particles containing Si element or Sn element may contain only one of Si element and Sn element, or may contain both Si element and Sn element. In addition to the Si element and the Sn element, the particles may contain, for example, an Fe element, a Co element, a Ni element, a Ti element, a Cr element, a B element, and a P element. Such particles may be a single element of Si element or Sn element, or may be an alloy containing Si element or Sn element. As said alloy, alloys, such as iron, cobalt, nickel, titanium, and chromium, are mentioned, for example.

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

  As a particle shape of the said particle | grain, a true spherical shape, an elliptical spherical shape, etc. are mentioned, for example.

  The negative electrode active material is a composite particle having a plurality of particles containing Si element or Sn element and a binder. The composite particles have, for example, a structure in which a plurality of particles are aggregated as shown in FIG. FIG. 1 is an image obtained by observing composite particles with a scanning electron microscope. In addition, the composite particles have a binder in a plurality of particles and are in a state not containing a sulfide solid electrolyte. The number of particles contained in the composite particles is, for example, 3 or more, and may be 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 observation with an electron microscope. The plurality of particles constituting the composite particles may be only particles containing Si element or Sn element, or may have particles other than particles containing Si element or Sn element. Among all the particles constituting the composite particles, the ratio of particles containing Si element or Sn element is, for example, 80% or more, and may be 90% or more, or may be 100%.

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

  As a binder which a composite particle has, the binder generally used for a negative electrode layer is mentioned. For example, polyimide, styrene butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid, polyacrylate, polyacrylate, amine-modified butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVDF) And polytetrafluoroethylene (PTFE). The binder may be used alone or in combination of two or more.

  The content of the binder contained in the composite particles is not particularly limited as long as a desired composite particle can be produced 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 of producing the composite particles is not particularly limited, and examples thereof include wet production and dry production. The wet-type composite particles can be produced, 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, dry production of composite particles can be performed, for example, by compressing a plurality of particles and applying physical impact. In addition, an example of the specific production | generation method of composite particle is shown to the Example mentioned later.

  The negative electrode layer has a negative electrode active material. The negative electrode active material of the negative electrode layer may be only one type, or two or more types. Moreover, when the negative electrode active material which a negative electrode layer has is 2 or more types, the negative electrode active material which a negative electrode layer has may have other negative electrode active materials other than the negative electrode active material mentioned above. Examples of other negative electrode active materials include common negative electrode active materials, for example, metal active materials such as In and Al, and meso carbon micro beads (MCMB), highly oriented graphite (HOPG), hard carbon, soft carbon And other carbon active materials.

  The content of the negative electrode active material contained in the negative electrode layer is preferably larger in terms of capacity. The content of the negative electrode active material contained in the negative electrode layer is, for example, 60 wt% or more, and 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 As a 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 -Li ₂ O, Li _{2 S-P 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 S-B ₂ S ₃ , Li ₂ S-P ₂ S ₅ -Z _m S _n (wherein , M and n are positive numbers, and Z is any 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, y are positive numbers, M is P, Si, Ge, B, Al, Ga, or In.) And the like. Incidentally, the above description _"Li 2 _S-P 2 _{S 5"} means a sulfide solid electrolyte obtained by using a raw material composition containing Li ₂ S and _P 2 _{S 5,} the same applies to the other according .

When the sulfide solid electrolyte is a Li ₂ S-P ₂ S ₅ system, the ratio of Li ₂ S and P ₂ S ₅ is, in molar ratio, Li ₂ S: P ₂ S ₅ = 50: 50 to 100: 0 It is preferable that Li ₂ S: P ₂ S ₅ = 75: 25.

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

Examples of the shape of the sulfide solid electrolyte include particle shapes. 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 diameter (D ₅₀ ) of the sulfide solid electrolyte is, for example, 40 μm or less, and may be 20 μm or less. Further, 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 1 × 10 ⁻³ S It is particularly preferable to be at least / cm.

  The negative electrode layer has a sulfide solid electrolyte. The sulfide solid electrolyte contained in the negative electrode layer may be only one type, or 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 battery. In addition, the negative electrode layer has the negative electrode active material and the sulfide solid electrolyte described above. Furthermore, the porosity of the negative electrode layer is 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, and more preferably 5% or less, and particularly preferably 3% or less. In addition, the porosity of the negative electrode layer is usually larger than 0%. When the porosity of the negative electrode layer has the above-described upper limit, the interface between the negative electrode active material and the solid electrolyte can be maintained, and the ion path and the path of the electron path can be maintained. As a result, it is possible to suppress the decrease in capacity retention rate and, as a result, to suppress the 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 the void in the negative electrode layer to the whole of the 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 composite (all materials constituting the negative electrode layer) by the true density of each material is x. When the volume obtained from the actual dimension of the negative electrode layer is y, it is a value calculated by A (%) = (1-x / y) × 100.

  The negative electrode layer may have a conductive material in addition to the negative electrode active material and the sulfide solid electrolyte described above. When 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. FIG. 2 is an image obtained by observing a composite particle containing carbon fiber (VGCF) as a conductive material with a scanning electron microscope. By contacting the plurality of particle conductive materials constituting the composite particles, it is possible to maintain the path of the electron path and to effectively improve the electron conductivity. The conductive material may be disposed 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, carbon fiber (VGCF), nickel, aluminum, SUS, and the like. In addition, the negative electrode layer may not 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, and may be 25 wt% or less, or may be 20 wt% or less.

  The thickness of the negative electrode layer largely varies depending on the configuration of the all-solid-state battery, but can be, for example, 0.1 μm to 1000 μm.

(4) All-Solid-State Battery The negative electrode layer of the present disclosure is used for an all-solid-state battery. An all solid state battery usually has the following configuration. That is, it has the structure provided with the positive electrode layer which has a positive electrode active material, the negative electrode layer mentioned above, and the solid electrolyte layer formed between the positive electrode layer and the negative electrode layer. Also, for example, even if a positive electrode current collector for collecting current in the positive electrode layer, a negative electrode current collector for collecting current in the negative electrode layer, and a battery case housing the above-described members constituting the all-solid battery Good. In addition, about members other than the negative electrode layer which comprises an all-solid-state battery, since it can be made to be the same as the member used for a general all-solid-state battery, description here is abbreviate | omitted.

  The present disclosure is not limited to the above embodiment. The above-described embodiment is an exemplification, which has substantially the same configuration as the technical idea described in the claims of the present disclosure, and exhibits the same operation and effect as the present invention. It is included in the technical scope of the disclosure.

  Hereinafter, the present disclosure will be described more specifically by showing examples.

Example 1
<Formation of composite particles (secondary particle formation)>
Silicon particles (manufactured by Kojundo Kagaku Co., Ltd., primary particle diameter: 5 μm) were prepared as active materials. The above-mentioned silicon particles (primary particles) and a solution (binder) containing polyamic acid, which is a precursor of polyimide manufactured by Ube Industries, Ltd., become a ratio (wt%) of primary particles: binder solid content = 97: 3. The mixture was dispersed in water to obtain a slurry. The slurry was sprayed into a spray dryer at a temperature of 150 ° C. to dry it. Thereby, composite particles (secondary particles) having a particle diameter (average particle diameter) of 7 μm were produced. Next, the produced composite particles were treated at a temperature of 350 ° C. for 2 hours in an inert atmosphere to carry out imidization from polyamic acid to polyimide.

<Fabrication of all solid state battery>
An all solid state battery was produced as follows.

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

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

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

(Lamination and pressing process)
The solid electrolyte layer is laminated on the positive electrode layer so that the obtained solid electrolyte layer is in contact with the positive electrode layer, and pressed at 1 ton / cm ² to peel off the aluminum foil (substrate) from the solid electrolyte layer to obtain a solid electrolyte layer A laminate with the positive electrode layer was produced. Thereafter, the obtained negative electrode layer was stacked on the solid electrolyte layer side of this laminate, and pressed so that the porosity of the negative electrode layer was 5%, thereby completing the all-solid battery. The obtained all-solid-state battery cells were restrained under a restraint pressure of 2 N · m using a restraint 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 pressing was performed so that the porosity of the negative electrode layer was 7% in the stacking and pressing steps.

[Example 3]
An all-solid-state battery was produced in the same manner as in Example 1 except that in the laminating and pressing steps, pressing was performed so that the porosity of the negative electrode layer was 15%.

Example 4
An all solid battery was produced in the same manner as in Example 1 except that a mixed dispersion of carboxymethylcellulose (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 pressing was performed so that the porosity of the negative electrode layer was 18% in the laminating and pressing steps.

Comparative Example 3
An all-solid-state battery was produced in the same manner as in Example 1 except that pressing was performed so that the porosity of the negative electrode layer was 25% in the laminating and pressing steps.

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

(Measurement of resistance (Ω) of SOC 20%)
After the endurance test described above, the all solid state battery was adjusted to SOC (State of Charge) 20%, discharged at constant current (7 C) 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 use of the composite particles as the negative electrode active material can suppress the decrease in the capacity retention rate. 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 capacity retention rate is suppressed, and the resistance of SOC 20% becomes low. It was found that excellent battery performance was obtained.

Claims (1)

A negative electrode layer used for an all solid state battery,
Having 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 Si element or Sn element and a binder,
Negative electrode layer whose porosity is 15% or less.