JP2017220318A - Composite active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite active material capable of reducing reaction resistance when being used mainly in a lithium battery.SOLUTION: A composite active material 10 includes: an oxide active material 1; an oxide solid electrolyte layer 2 coating the surface of the oxide active material 1; and a sulfide solid electrolyte layer 3 coating the surface of the oxide solid electrolyte layer 2. The composite active material includes a spherical carbon particle 4 in the sulfide solid electrolyte layer 3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a composite active material that can reduce reaction resistance by being used mainly in lithium batteries.

  A lithium ion secondary battery has the characteristics that it has a higher energy density than other secondary batteries and can operate at a high voltage. For this reason, it is used as a secondary battery that can be easily reduced in size and weight in information equipment such as a mobile phone, and in recent years, there is an increasing demand for large motive power such as for electric vehicles and hybrid vehicles.

  Since the electrolyte widely used in the conventional lithium battery is a flammable organic solvent, it is necessary to mount a system for ensuring safety, such as a safety device that suppresses a temperature rise at the time of a short circuit. On the other hand, a solid battery in which the liquid electrolyte is changed to a solid electrolyte does not use a flammable organic solvent in the battery, and thus the system can be simplified. Therefore, development of solid state batteries is underway.

In the field of such a solid battery, attention is paid to the active material and the electrolyte material, and there is an attempt to improve battery performance by covering the surface of the active material with an electrolyte layer. For example, Patent Document 1 discloses using, as an active material for a lithium ion battery, a composite active material in which a surface of an oxide active material coated with an oxide solid electrolyte is further coated with a sulfide solid electrolyte. .
Patent Document 2 discloses that a coating layer made of an ion conductive oxide is formed on the surface of an active material and has carbon particles penetrating the coating layer.

JP, 2014-154407, A JP, 2014-011028, A

  In order to reduce the reaction resistance of the battery, it is important that ions and electrons can move smoothly on the active material surface. When an oxide-based solid electrolyte layer and a sulfide-based solid electrolyte layer are provided on the surface of the active material as in Patent Document 1, since the solid electrolyte has low electron conductivity, the electron path is easily blocked, and reaction resistance Becomes larger.

  This invention is made | formed in view of the said subject, and it aims at providing the composite active material which can reduce reaction resistance by being mainly used for a lithium battery.

In order to solve the above problems, in the present invention, an oxide active material, an oxide solid electrolyte layer covering the surface of the oxide active material, and a sulfide solid electrolyte covering the surface of the oxide solid electrolyte layer A composite active material having a layer, wherein the sulfide solid electrolyte layer has spherical carbon particles.

  According to the present invention, since it has spherical carbon particles in the sulfide solid electrolyte layer, it has good electronic conductivity, and therefore, it can be a composite active material with low reaction resistance. In addition, according to the present invention, since the carbon particles are spherical, it is easy to maintain the crystallinity of the carbon particles, and the electron conductivity can be improved.

  The composite active material of the present invention has an effect that the reaction resistance can be reduced mainly by being used in a lithium battery.

It is a schematic diagram which shows an example of the composite active material of this invention. It is a result of the resistance measurement value of the battery for evaluation obtained in Examples 1-7 and Comparative Examples 1-4.

  Hereinafter, the composite active material which is an embodiment of the present invention will be described in detail.

A. Composite active material The composite active material of the present invention comprises an oxide active material, an oxide solid electrolyte layer covering the surface of the oxide active material, and a sulfide solid electrolyte layer covering the surface of the oxide solid electrolyte layer. And having a spherical carbon particle in the sulfide solid electrolyte layer.

  FIG. 1 is a schematic view showing an example of the composite active material of the present invention. 1 includes an oxide active material 1, an oxide solid electrolyte layer 2 formed on the surface of the oxide active material 1, and a sulfide formed on the surface of the oxide solid electrolyte layer 2. A solid electrolyte layer 3 and spherical carbon particles 4 contained in the sulfide solid electrolyte layer 3.

  According to the present invention, since the sulfide solid electrolyte layer has spherical carbon particles, a composite active material having good electronic conductivity can be obtained. As a result, a battery with low reaction resistance can be provided, and battery output can be improved.

Further, the present inventors have examined that the ionic conductivity of the oxide solid electrolyte is extremely small compared with the electronic conductivity of the carbon particles. Therefore, in order to reduce the reaction resistance, the oxide solid electrolyte and the oxide solid electrolyte are oxidized. It was necessary to improve the contact of the active material, while the contact between the carbon particles and the oxide active material did not greatly contribute to the reaction resistance. That is, in the composite active material of the present invention, since carbon particles are contained in the sulfide solid electrolyte layer, the electrons of the composite active material are prevented without interfering with the contact (ion conduction) between the oxide solid electrolyte and the oxide active material. The conductivity can be improved.

  Below, the composite active material which is embodiment of this invention is demonstrated for every structure.

1. Oxide active material The active material in the present invention is preferably an oxide active material. This is because a high-capacity active material can be obtained. In addition, the oxide active material and the sulfide solid electrolyte easily react, and both react to form a high resistance layer. On the other hand, by providing an oxide solid electrolyte layer on the surface of the oxide active material, there is an advantage that both reactions can be suppressed.

The type of the oxide active material is not particularly limited, but is preferably selected as appropriate according to the type of battery. For example, the layered rock salt-type oxide _{(LiCoO 2, LiNiO 2, Li} 1 + x Ni 1-y-z Mn y Co z O 2, LiVO 2, LiCrO 2 , etc. (However, x, y are positive numbers)), spinel Heteroelement _- substituted Li having a composition represented by a compound (LiMn ₂ O ₄ , Li _{1 + x} Mn _2−xy M _y O ₄ (M is one or more selected from Al, Mg, Co, Fe, Ni, Zn)) -Mn spinel, Li ₂ NiMn ₃ O ₈ etc.), lithium titanate (Li _x TiO _y etc.), lithium metal phosphate (LiMPO ₄ (M is one or more selected from Mn, Co, Fe, Ni)), NASICON type active material (Li ₃ V ₂ P ₃ O ₁₂ etc.), transition metal oxide vanadium oxide (V ₂ O ₅ ), molybdenum oxide (MoO ₃ ), lithium silicon oxide ( Li _x Si _y O _z), oxides such as Li ₄ Ti _{5 O 12} is used.

Although the shape of an oxide active material is not specifically limited, For example, it is preferable that it is a particulate form. Examples of the shape of the particles include a true sphere and an elliptic sphere. The average particle size of the active material is preferably in the range of 500 nm to 100 μm, for example, and more preferably in the range of 1 μm to 20 μm.

2. Oxide solid electrolyte layer The oxide solid electrolyte layer in the present invention is formed on the surface of the oxide active material, and is composed of an oxide solid electrolyte. By providing the oxide solid electrolyte layer on the surface of the oxide active material, the reaction between the oxide active material and the sulfide solid electrolyte can be suppressed.

The oxide solid electrolyte contains oxygen element (O), has ionic conductivity, and is chemically active to the oxide active material to the extent that it can cover all or part of the surface of the oxide active material. If it has affinity, it will not specifically limit. For example, an oxide containing a Group 1 or Group 2 element and a Group 3 to Group 6 or Group 13 to Group 15 element is preferable. Among these, a Li-containing oxide containing lithium as a Group 1 element is more preferable. Specifically, LiNbO ₃ , Li ₃ BO ₃ , LiBO ₂ , Li ₂ CO ₃ , LiAlO ₂ , Li ₄ SiO ₄ , Li ₂ SiO ₃ , Li ₃ PO ₄ , Li ₂ SO ₄ , Li ₂ TiO ₃ , Li Examples include ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₂ O ₅ , Li ₂ ZrO ₃ , Li ₂ MoO _4, and Li ₂ WO _4. Among them, LiNbO ₃ is more preferable.

Further, the oxide solid electrolyte may be a Li-containing oxide composite compound. As such a composite compound, any combination of the above-described Li-containing oxides can be employed. For example, Li ₃ PO ₄ —Li ₄ SiO ₄ , Li ₃ BO ₃ —Li ₄ SiO ₄ , Li ₃ PO ₄ -Li ₄ GeO _4, and the like can be given. Other examples include Li ₂ O—B ₂ O ₃ —P ₂ O ₅ , Li ₂ O—SiO ₂ , Li ₂ O—B ₂ O ₃ , Li ₂ O—B ₂ O ₃ —ZnO, etc. amorphous _oxide, and the like _{LiI-Al 2 O 3, Li} 5 La 3 Ta 2 O 12, Li 7 La 3 Zr 2 O 12, Li 6 BaLa 2 Ta 2 O 12 crystalline oxide such as such as it can.

  The average thickness of the oxide solid electrolyte layer is usually less than 100 nm. Especially, it is preferable that it is 30 nm or less, and it is more preferable that it is 20 nm or less. This is because if the average thickness is too large, an increase in electronic resistance due to the oxide solid electrolyte layer may not be sufficiently suppressed. On the other hand, the average thickness is, for example, preferably 0.1 nm or more, and more preferably 1 nm or more. This is because if the average thickness is too small, the reaction between the oxide active material and the sulfide solid electrolyte may not be sufficiently suppressed. In addition, the said average thickness can be calculated | required from the image analysis by a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

  Moreover, the average coverage of the oxide solid electrolyte layer with respect to the oxide active material is, for example, preferably 50% or more, and more preferably 80% or more. The oxide solid electrolyte layer may cover the entire surface of the oxide active material. The average coverage of the oxide solid electrolyte layer can be measured using, for example, a transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), or the like.

3. Sulfide solid electrolyte layer The sulfide solid electrolyte layer in the present invention is formed on the surface of the oxide solid electrolyte layer, and is composed of a sulfide solid electrolyte. By providing the sulfide solid electrolyte layer on the surface of the oxide solid electrolyte layer, the ionic resistance can be reduced.

The sulfide solid electrolyte contains elemental sulfur (S), has ionic conductivity, and has sufficient chemical properties with the oxide solid electrolyte to the extent that it can cover all or part of the surface of the oxide solid electrolyte layer. There is no particular limitation as long as it has good affinity. For _{example, Li 2 S-P 2 S} 5, Li 2 S-P 2 S 5 -LiI, Li 2 S-P 2 S 5 -LiI-LiBr, 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 ( where m and n are positive numbers. Z is any one of Ge, Zn, and Ga.), Li ₂ S—GeS ₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS ₂ —Li _x. MO _y (provided that, x, y is a positive number .M is, P, Si, Ge, B , a , Ga, either an In.) And the like. Among _them, it is preferably one containing a _{Li 2 S-P 2 S 5} , those containing _{Li 2 S-P 2 S 5} -LiI-LiBr is particularly preferred.

  The average thickness of the sulfide solid electrolyte layer is usually less than 100 nm. Especially, it is preferable that it is 30 nm or less, and it is more preferable that it is 20 nm or less. This is because if the average thickness is too large, an increase in electronic resistance due to the sulfide solid electrolyte layer may not be sufficiently suppressed. On the other hand, the average thickness is, for example, preferably 1 nm or more, and more preferably 5 nm or more. This is because if the average thickness is too small, the ion path is interrupted and the increase in ion resistance may not be sufficiently suppressed. In addition, the said average thickness can be calculated | required from the image analysis by a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

  Moreover, the average coverage of the sulfide solid electrolyte layer with respect to the oxide solid electrolyte layer is, for example, preferably 50% or more, and more preferably 80% or more. The sulfide solid electrolyte layer may cover the entire surface of the oxide solid electrolyte layer. The average coverage of the sulfide solid electrolyte layer can be measured using, for example, a transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), or the like.

4). Carbon particle The carbon particle in this invention is contained in the said sulfide solid electrolyte layer. By containing the carbon particles in the sulfide solid electrolyte layer, a good electron path can be formed. The carbon particles may be exposed from the sulfide solid electrolyte layer. Moreover, it is preferable that carbon particles are not contained in the oxide solid electrolyte layer. This is because the ionic conductivity between the oxide active material and the oxide solid electrolyte can be improved.

  The type of carbon particles is not particularly limited, and examples thereof include crystalline carbon (carbon capable of defining substantially all atomic positions), microcrystalline carbon, amorphous carbon, and the like. Microcrystalline carbon or amorphous carbon is preferred. Examples of the carbon particles corresponding to microcrystalline carbon or amorphous carbon include carbon black, activated carbon, hard carbon, soft carbon, and mesoporous carbon. Among these, carbon black is preferable. Furthermore, ketjen black and acetylene black are preferable among carbon blacks. Of these, acetylene black is more preferable. This is because the ratio of the carbon component is high and the electron conductivity is also high.

  For example, the shape of the carbon particles is preferably spherical, and examples thereof include a true sphere and an elliptic sphere. This is because the crystallinity can be easily maintained and the electron conductivity can be improved. The term “spherical” in the present invention means a shape including a shape close to a so-called sphere, such as an ellipsoid, or a shape having irregularities on the surface inevitably generated when producing spherical particles.

The average particle diameter of the carbon particles is, for example, preferably in the range of 1 nm to 150 nm, and more preferably in the range of 1 nm to 50 nm. This is because if the average particle size is too large, the increase in ionic resistance may not be sufficiently suppressed. Further, when the weight ratio is the same, the number of carbon particles is reduced, and an electron path cannot be formed efficiently. The average particle diameter can be obtained from image analysis using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The number of samples is preferably 100 or more.

The ratio of the carbon particles to the composite active material varies greatly depending on the size of the carbon particles, but the ratio of the carbon particles is preferably greater than 0 and 5 wt% or less with respect to 100 wt% of the composite active material, It is more preferably 0.1 wt% or more and 1.0 wt% or less, and further preferably 0.1 wt% or more and 0.5 wt% or less. This is because if the proportion of carbon particles is too large, an increase in ionic resistance may not be sufficiently suppressed.

5). Others When a battery electrode is produced using the composite active material according to the embodiment of the present invention, a binder (acrylic binder, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc., as necessary) ), A conductive material (acetylene black, ketjen black, carbon fiber, carbon nanotube, etc.), a dispersion medium (butyl butyrate, dibutyl ether, heptane, etc.) and the like. As the electrode substrate, SUS, Cu, Ni, Al, Fe, Pt or the like can be used.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The present invention is not limited to the examples.

[Example 1]
(Manufacture of composite active materials)
A coated active material in which LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (oxide active material, average particle size: 6.0 μm) was coated with LiNbO ₃ (oxide solid electrolyte) was prepared. Next, 40 g of the coated active material, 4.75 g of 10LiI-15LiBr-75 (75Li ₂ S-25P ₂ S ₅ ) particles (sulfide solid electrolyte, average particle size: 0.5 μm), acetylene black (carbon particles, spherical, (Average particle size: 24 nm) 0.05 g is put into a compression shredding force breaking device and treated for 12.5 minutes at a spacing of 1 mm between the rotor rotor blades and the wall, a pressure of 100 Pa, and a rotor rotational speed of 18.5 m / s. A composite active material was produced. The ratio of carbon particles at this time was 0.10 wt%.

[Example 2]
In Example 1, a composite active material was produced in the same manner as in Example 1 except that the ratio of the spherical carbon particles in the composite active material was changed to 0.15 wt%.

[Example 3]
In Example 1, a composite active material was produced in the same manner as in Example 1 except that the ratio of the spherical carbon particles in the composite active material was changed to 0.25 wt%.

[Example 4]
In Example 1, a composite active material was produced in the same manner as in Example 1 except that the ratio of the spherical carbon particles in the composite active material was changed to 0.50 wt%.

[Example 5]
In Example 1, a composite active material was produced in the same manner as in Example 1 except that the average particle diameter of the spherical carbon particles in the composite active material was changed to 24 nm and the ratio of the carbon particles was changed to 0.125 wt%.

[Example 6]
In Example 5, a composite active material was produced in the same manner as in Example 5 except that the ratio of the spherical carbon particles in the composite active material was changed to 0.25 wt%.

[Example 7]
In Example 5, a composite active material was produced in the same manner as in Example 5 except that the ratio of the spherical carbon particles in the composite active material was changed to 0.50 wt%.

[Comparative Example 1]
In Example 1, a composite active material was produced in the same manner as in Example 1 except that the proportion of carbon particles in the composite active material was changed to 0%.

[Comparative Example 2]
In Example 3, a composite active material was produced in the same manner as in Example 3 except that the shape of the carbon particles in the composite active material was changed to a fibrous form (Showa Denko: VGCF-H).

[Comparative Example 3]
In Comparative Example 2, a composite active material was produced in the same manner as in Comparative Example 2, except that the ratio of the fibrous carbon particles in the composite active material was changed to 0.50 wt%.

[Comparative Example 4]
In Comparative Example 2, a composite active material was produced in the same manner as in Example 1 except that the ratio of the fibrous carbon particles in the composite active material was changed to 0.75 wt%.

(Production of evaluation battery)
Composite active material: sulfide solid electrolyte _{(10LiI-15LiBr-75 (75Li} 2 S-25P 2 S 5)): conductive material (VGCF-H): binder (PVdF) = 94.8: 3.3: It mixed so that it might become 1.3: 0.6 (weight ratio). The obtained mixture was put into heptane to obtain a positive electrode slurry. Next, the positive electrode slurry was dispersed with an ultrasonic homogenizer, coated on an aluminum foil, dried, and punched out at 1 cm ² . This obtained the positive electrode.

Next, negative electrode active material (natural graphite): sulfide solid electrolyte (10LiI-15LiBr-75 (75Li ₂ S-25P ₂ S ₅ ): binder (PVdF) = 64.1: 34.7: 1.2 The resulting mixture was put into heptane to obtain a negative electrode slurry, and then the negative electrode slurry was dispersed with an ultrasonic homogenizer and coated on a copper foil, It was dried and punched out at 1 cm ² , thereby obtaining a negative electrode.

Next, 61 mg of a sulfide solid electrolyte was used as a separator layer, and a positive electrode and a negative electrode were arranged on both sides thereof, and pressed at 6.0 ton / cm ² for 1 minute. The obtained power generation element was restrained by a stainless steel bar at a restraint pressure of 15 MPa to produce an evaluation battery. At this time, the thicknesses of the positive electrode, the separator, and the negative electrode were 39 μm, 300 μm, and 55 μm, respectively.

(Resistance measurement)
Evaluation of composite active materials obtained in Examples 1 to 7 and Comparative Examples 1 to 4 The reaction resistance in the battery was adjusted to an OCV potential of 3.66 V, then measured by an AC impedance method with a voltage amplitude of 10 mV, and a resistance of 1000 Hz A value obtained by subtracting a resistance value of 0.5 MHz from the value was measured as a reaction resistance. Table 1 shows the shape of the carbon particles contained in the composite active materials obtained in Examples 1 to 7 and Comparative Examples 1 to 4, the average particle diameter of the carbon particles, the ratio of the carbon particles, and the reaction resistance of the evaluation battery. . In addition, the particle diameter of fibrous carbon refers to the diameter of a cylindrical circular part.

FIG. 2 is a graph showing the relationship between the ratio of carbon particles in the composite active materials obtained in Examples 1 to 7 and Comparative Examples 1 to 4 and the reaction resistance of an evaluation battery using the composite active material. . As shown in FIG. 2, Examples 1 to 7 were confirmed to have lower reaction resistance than Comparative Examples 1 to 4.

DESCRIPTION OF SYMBOLS 1 ... Oxide active material 2 ... Oxide solid electrolyte layer 3 ... Sulfide solid electrolyte layer 4 ... Carbon particle 10 ... Composite active material

Claims (1)

An oxide active material,
An oxide solid electrolyte layer covering the surface of the oxide active material;
A sulfide solid electrolyte layer covering a surface of the oxide solid electrolyte layer;
A composite active material having
The sulfide solid electrolyte layer has spherical carbon particles.

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