WO2017033480A1 - All-solid-state lithium secondary battery and secondary battery system provided with said secondary battery - Google Patents

Abstract

The purpose of the present invention is to provide a bulk-type all-solid-state lithium secondary battery which is able to be used in a higher temperature environment in comparison to conventional nonaqueous electrolyte lithium secondary batteries, while achieving a good balance between charge/discharge characteristics and cycle characteristics at high levels. An all-solid-state lithium secondary battery according to the present invention is characterized in that: a positive electrode and a negative electrode are laminated, with a solid electrolyte layer being interposed therebetween; the positive electrode contains positive electrode active material particles, a first ion conducting layer and a second ion conducting layer; the positive electrode active material particles are in the form of secondary particles, in each of which primary particles aggregate; the first ion conducting layer is a substance that transmits lithium ions between the positive electrode active material particles and the second ion conducting layer, and covers the secondary particles, while filling up the gaps among the primary particles which constitute the secondary particles; the second ion conducting layer is a substance that transmits lithium ions between the first ion conducting layer and the solid electrolyte layer, and additionally covers the secondary particles that are covered by the first ion conducting layer; and the first ion conducting layer, the second ion conducting layer and the solid electrolyte layer are formed from substances that are different from each other.

Description

All-solid lithium secondary battery and secondary battery system including the secondary battery

The present invention relates to a lithium ion secondary battery, and more particularly to an all-solid lithium secondary battery using a solid electrolyte as an electrolyte that propagates lithium ions, and a secondary battery system including the secondary battery.

Since lithium ion secondary batteries have a higher energy density than other secondary batteries, they are advantageous for reducing the size and weight of secondary batteries and increasing their capacity and output. For this reason, lithium-ion secondary batteries are used for power sources for automobiles such as small electric devices (for example, portable personal computers and mobile phones) and large electric devices (for example, HEV (hybrid vehicles) and EVs (electric vehicles)). Power supply and power storage power source).

In recent years, from the viewpoint of expanding the availability of lithium ion secondary batteries for large electrical equipment, installation in a high temperature environment such as in an engine room or outdoors has been studied, and lithium ion secondary batteries having a heat resistance of at least 80 ° C. or more are being studied. Secondary batteries are in demand. However, the conventional lithium ion secondary battery using a non-aqueous electrolyte is generally said to have a heat resistance temperature of about 60 ° C., and the solvent constituting the non-aqueous electrolyte is flammable. Therefore, there is a weak point from the viewpoint of heat resistance and fire resistance.

In contrast, all-solid lithium secondary batteries using solid electrolytes instead of non-aqueous electrolytes are currently being actively researched. All solid-state lithium secondary batteries use conventional lithium ions that use non-aqueous electrolytes because the solid electrolytes used (eg, solid polymer electrolytes and inorganic electrolytes) have a heat-resistant temperature exceeding 100 ° C and are not flammable. There is an advantage that it can be used in a higher temperature environment than a secondary battery. It is also said that the all solid lithium secondary battery can increase the energy density as compared with the conventional non-aqueous electrolyte lithium secondary battery.

On the other hand, in an all-solid lithium secondary battery, the solid electrolyte as a lithium ion conduction path does not have fluidity. Therefore, in order to increase the output of the secondary battery, the solid electrolyte itself needs to have high ionic conductivity. In addition, it is necessary to construct a good conduction path for lithium ions between the solid electrolyte and the electrode active material (to reduce the obstacle of ion conduction as much as possible). However, it is known that solid electrolytes with high ion conductivity are prone to oxidative degradation if they are repeatedly charged and discharged in direct contact with an electrode active material (especially a positive electrode active material). From the viewpoint of (for example, improving cycle characteristics), a device for preventing deterioration of the solid electrolyte is necessary.

For example, Patent Document 1 (Republished WO2006 / 018921) discloses a polymer lithium secondary battery in which an organic electrolyte is interposed between a positive electrode material and a negative electrode material, and the surface of the positive electrode active material particles constituting the positive electrode is A polymer lithium secondary, characterized in that at least a part thereof is coated with a deposit having ion conductivity and electron conductivity that is not easily oxidized even when oxygen is supplied from the positive electrode active material. A battery is disclosed. Further, the deposit is composed of fine particles of an inorganic solid electrolyte having ion conductivity and fine particles of a conductive material having electronic conductivity, and the fine particles of the inorganic solid electrolyte include phosphate, silicic acid containing lithium. It is disclosed that it consists of any one of salts, borates, sulfates, aluminates and the like, or a mixture thereof.

Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-059409) discloses an all solid state battery in which a polymer solid electrolyte is interposed between a positive electrode material and a negative electrode material, and the surface of positive electrode active material particles constituting the positive electrode. An all solid state battery characterized in that an inorganic oxide containing lithium is adhered to at least a part or the entire surface of the battery without being easily oxidized even when oxygen is supplied from the positive electrode active material. Is disclosed. Furthermore, it is disclosed that the inorganic oxide is composed only of a metal element and oxygen, and LiAlO ₂ is preferable.

The all-solid lithium secondary battery described in Patent Documents 1 and 2 (republished WO2006 / 018921 and JP2007-059409) improves cycle characteristics by suppressing oxidative decomposition of the polymer solid electrolyte under high voltage In addition, it is said that high energy density can be achieved.

Republished WO2006 / 018921 JP 2007-059409 A

According to Patent Documents 1 and 2 (republished WO2006 / 018921 and JP2007-059409), the surface of the positive electrode active material particles only needs to be at least partially coated with inorganic solid electrolyte particles having ion conductivity. It is said that. This is because the inorganic solid electrolyte particles serve as a gateway for lithium ions to escape to the polymer solid electrolyte (organic electrolyte) and prevent the positive electrode active material and the polymer solid electrolyte from coming into direct contact. This is because the oxidative decomposition of the polymer solid electrolyte can be suppressed. Further, since the surface portion of the positive electrode active material particles not covered with the inorganic solid electrolyte particles does not serve as a gateway for lithium ions to escape to the polymer solid electrolyte, the positive electrode active material particles / polymer solid electrolyte interface of this portion Even if a by-product is deposited on the battery, it does not cause a significant decrease in battery performance.

However, the fact that the inorganic solid electrolyte particles serving as the lithium ion gateway are attached to only a part of the surface of the positive electrode active material particles means that the lithium ion conduction paths are small and narrow, and the positive electrode active material particles It is thought that the effective ionic conduction resistance between the solid electrolyte and the polymer solid electrolyte is increased. In addition, since the adhesion between particles is considered to be close to point contact in principle, even if the entire surface of the positive electrode active material particles is covered with inorganic solid electrolyte particles, the effective contact area is not so large. It is done. As a result, the secondary batteries described in Patent Documents 1 and 2 (republished WO2006 / 018921 and Japanese Patent Application Laid-Open No. 2007-059409) are likely to be restricted in charge / discharge characteristics (for example, charge / discharge rate). It is.

On the other hand, when assuming a secondary battery for a large electric device, replacement in a relatively short period of time such as a secondary battery for a small electronic device is not allowed from an economical viewpoint. In other words, in a secondary battery for a large electric device, extending its life (for example, improving cycle characteristics) is one of the most promising issues.

Although all solid lithium secondary batteries can be broadly classified into bulk types and thin film types, a bulk type that can increase the absolute amount of the electrode active material is advantageous from the viewpoint of battery capacity. That is, when a large-capacity secondary battery for large-sized electrical equipment is assumed, a bulk-type all-solid lithium secondary battery is a target. In other words, since the battery capacity can be afforded with a bulk type configuration, there is less restriction due to the size of the electric device (the amount of power consumption), and the device can be widely applied.

Accordingly, an object of the present invention is to provide a bulk type all-solid lithium secondary battery that can be used in a higher temperature environment than a conventional non-aqueous electrolyte lithium secondary battery and has a high balance between charge / discharge characteristics and cycle characteristics. An object of the present invention is to provide a battery and a secondary battery system including the all-solid lithium secondary battery.

(I) One aspect of the present invention is an all-solid lithium secondary battery in which a positive electrode and a negative electrode are stacked via a solid electrolyte layer,
The positive electrode includes positive electrode active material particles, a first ion conductive layer, and a second ion conductive layer,
The positive electrode active material particles form secondary particles in which a plurality of primary particles are aggregated,
The first ion conductive layer is a material that mediates lithium ions between the positive electrode active material particles and the second ion conductive layer, and covers the secondary particles and constitutes the secondary particles. It fills the gaps between the particles,
The second ion conductive layer is a substance that conducts lithium ions between the first ion conductive layer and the solid electrolyte layer, and the secondary particles coated with the first ion conductive layer are laminated and coated. And
An all-solid lithium secondary battery is provided, wherein the first ion conductive layer, the second ion conductive layer, and the solid electrolyte layer are made of different materials.

In the all solid lithium secondary battery (I) according to the present invention, the present invention can be improved or changed as follows.
(I) The conductivity of the first ion conductive layer is 1 × 10 ⁻⁶ S / cm or more and 1 × 10 ⁻³ S / cm or less, and the conductivity of the second ion conductive layer is 1 × 10 ⁻⁵ S / cm or more and 1 × 10 ⁻² S / cm or less, and the conductivity of the solid electrolyte layer is 1 × 10 ⁻⁴ S / cm or more.
(Ii) The first ion conductive layer is made of an oxide electrolyte containing lithium, and the second ion conductive layer is made of an ion conductive polymer containing lithium salt or a ceramic electrolyte containing lithium.
(Iii) When the total of the positive electrode active material particles, the first ion conductive layer, and the second ion conductive layer is 100 parts by mass, the positive electrode active material particles are included in an amount of 60 parts by mass to 90 parts by mass. It is.
(Iv) When the total of the positive electrode active material particles, the first ion conductive layer, and the second ion conductive layer is 100 parts by mass, the first ion conductive layer is 5 parts by mass or more and 30 parts by mass or less. included.
(V) The conductivity of the solid electrolyte layer is higher than the conductivity of the second ion conductive layer.
(Vi) The positive electrode further includes a conductive material.

(II) Another aspect of the present invention provides a secondary battery system including the all-solid lithium secondary battery according to the above invention.

According to the present invention, it is a bulk-type all-solid lithium secondary battery that can be easily increased in capacity, can be used in a higher temperature environment than a conventional non-aqueous electrolyte lithium secondary battery, and has charge and discharge characteristics. It is possible to provide an all-solid lithium secondary battery in which the cycle characteristics are balanced at a high level. In addition, by using the all solid lithium secondary battery, it is possible to provide a secondary battery system that can be used in a higher temperature environment than a conventional non-aqueous electrolyte lithium secondary battery.

It is the cross-sectional schematic diagram which shows the basic structure of the single cell in the all-solid-state lithium secondary battery which concerns on this invention, and the expanded cross-sectional schematic diagram of a positive electrode. It is a cross-sectional schematic diagram which shows an example of the all-solid-state lithium secondary battery which concerns on this invention. It is a schematic diagram which shows the structural example of the secondary battery system which concerns on this invention.

(Basic idea of the present invention)
As described above, in an all-solid lithium secondary battery, the solid electrolyte layer needs to have high ionic conductivity, and a good conduction path for lithium ions is established between the solid electrolyte layer and the electrode active material particles. There is a need to. In addition, it is known that a solid electrolyte layer having high ion conductivity is likely to be oxidized and deteriorated when repeated charging and discharging in direct contact with electrode active material particles (particularly positive electrode active material particles). A device to prevent deterioration is necessary.

Regarding the suppression of deterioration of the solid electrolyte layer, an oxidation-resistant ion conductive material is formed on the surface of the electrode active material particles as taught in Patent Documents 1 and 2 (Republished WO2006 / 018921 and JP2007-059409). Doing is considered one of the effective solutions. However, all-solid lithium secondary batteries taught in Patent Documents 1 and 2 (republished WO2006 / 018921 and JP2007-059409) are considered to have room for further improvement in charge / discharge characteristics and cycle characteristics. It was.

Therefore, the present inventors conducted a detailed investigation and examination on factors affecting the charge / discharge characteristics and cycle characteristics of the bulk type all-solid lithium secondary battery. As a result of the investigation and examination, the electrode active material particles are likely to form secondary particles in which a plurality of fine primary particles are aggregated, and voids remain between the primary particles in the secondary particles. understood. From this, the primary particles on the outermost circumference constituting the secondary particles directly contribute to the charge and discharge of the secondary battery, but the primary particles inside the secondary particles (in contact with the oxidation-resistant ion conductive material). No primary particles) have a small contribution to the charge / discharge of the secondary battery, and thus it is considered that the charge / discharge characteristics are restricted.

Also, when the secondary particles are crushed due to repeated charging / discharging of the secondary battery, the primary particles on which the oxidation-resistant ion conductive material is not formed are exposed on the surface. When the newly exposed primary particles come into contact with the solid electrolyte, it is considered that it causes oxidation deterioration of the solid electrolyte layer (thereby causing deterioration of cycle characteristics).

The present inventors have conducted intensive research to overcome the above problems. As a result, by covering the secondary particles of the electrode active material with the first ion conductive layer and filling the gaps between the primary particles constituting the secondary particles, all the primary particles can be used for charging and discharging of the secondary battery. It was found that it can be directly contributed. In addition, secondary particles coated with the first ion conductive layer are covered with a second ion conductive layer made of a material different from the first ion conductive layer, thereby suppressing secondary particle crushing due to repeated charge and discharge. I found a possibility. The present invention has been completed based on this finding.

Hereinafter, embodiments according to the present invention will be described more specifically with reference to the drawings. However, the present invention is not limited to the embodiments described here, and can be appropriately combined and improved without departing from the technical idea of the invention. In the drawings, the same reference numerals are given to the same members / parts, and duplicate descriptions are omitted.

[Basic structure of a single cell of an all-solid lithium secondary battery]
FIG. 1 is a schematic cross-sectional view showing a basic structure of a single cell in an all-solid lithium secondary battery according to the present invention and an enlarged schematic cross-sectional view of a positive electrode. As shown in FIG. 1, a single cell 100 of an all solid lithium secondary battery according to the present invention has a positive electrode 110 and a negative electrode 130 stacked with a solid electrolyte layer 120 interposed therebetween. The positive electrode 110 includes a positive electrode current collector 111 and a positive electrode mixture layer 112, and the negative electrode 130 includes a negative electrode current collector 131 and a negative electrode mixture layer 132.

各 More specific explanation will be given for each component.

(Positive electrode current collector)
The positive electrode current collector 111 is not particularly limited as long as it is a low-resistance conductor having heat resistance that can withstand heat treatment when forming an ion conductive layer / solid electrolyte layer described later. The same thing as the positive electrode electrical power collector in a secondary battery can be used. For example, metal foil (thickness of 10 μm or more and 100 μm or less), perforated metal foil (thickness of 10 μm or more and 100 μm or less, pore diameter of 0.1 mm or more and 10 mm or less), expanded metal, foamed metal plate, glassy carbon plate and the like can be mentioned. Moreover, as a metal seed | species, aluminum, stainless steel, titanium, a noble metal (for example, gold, silver, platinum) etc. can be used.

(Positive electrode mixture layer)
The positive electrode mixture layer 112 includes positive electrode active material particles (primary particles 113 and secondary particles 114), a first ion conductive layer 115, and a second ion conductive layer 116. In addition, for the purpose of improving the conductivity of the positive electrode mixture layer 112, it is preferable to add a conductive material (not shown) so as to adhere to the secondary particles 114 of the positive electrode active material.

As shown in FIG. 1, the positive electrode active material particles used in the single cell 100 of the all-solid lithium secondary battery of the present invention form secondary particles 114 in which a plurality of primary particles 113 are aggregated. The first ion conductive layer 115 covers the secondary particles 114 and fills the gaps between the primary particles 113 constituting the secondary particles 114, and between the positive electrode active material particles and the second ion conductive layer 116. Mediates lithium ions. The second ion conductive layer 116 is formed by laminating and covering the secondary particles 114 covered with the first ion conductive layer 115, and mediates lithium ions between the first ion conductive layer 115 and the solid electrolyte layer 120. In the present invention, the first ion conductive layer 115, the second ion conductive layer 116, and the solid electrolyte layer 120 are preferably made of different materials.

(Positive electrode active material)
There is no particular limitation on the material of the positive electrode active material particles, and a positive electrode active material used in a conventional lithium ion secondary battery can be used. For example, a lithium composite oxide containing a transition metal is preferable, and specific examples include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , Li ₂ Mn. ₃ MO ₈ (M = Fe, Co, Ni, Cu, Zn), Li _1-x M _x Mn ₂ O ₄ (M = Mg, B, Al, Fe, Co, Ni, Cr, Zn, Ca, x = 0.01-0.1), LiMn _2-x M _x O ₂ (M = Co, Ni, Fe, Cr, Zn, Ta, x = 0.01-0.2), LiCo _1-x M _x O ₂ (M = Ni, Fe, Mn, x = 0.01 to 0.2), LiNi _1-x M _x O ₂ (M = Mn, Fe, Co, Al, Ga, Ca, Mg, x = 0.01 to 0.2), LiNi _1-xy Mn _x Co _y O ₂ (x = 0.1 to 0.8, y = 0.1 to 0.8, x + y = 0.1 to 0.9), LiFeO ₂ , LiFePO ₄ , LiMnPO _{4 and the} like.

The particle diameter of the positive electrode active material particles (secondary particles 114) is defined to be equal to or less than the thickness of the positive electrode mixture layer 112. When there are coarse particles in the positive electrode active material powder having a particle size equal to or larger than the thickness of the positive electrode mixture layer 112 to be formed, the coarse particles are removed in advance by sieving classification, wind classification, etc. Particles having a thickness equal to or smaller than that of the positive electrode mixture layer 112 are selected. The particle size of the positive electrode active material particles is the average particle size of the secondary particles 114, and can be measured using a known particle size distribution measuring apparatus using a laser scattering method.

(Conductive material)
The conductive material was made from conductive fibers (for example, vapor-grown carbon, carbon nanotubes, pitch (byproducts such as petroleum, coal, coal tar, etc.) and carbonized at high temperature, and acrylic fibers. Carbon fiber etc.) are preferably used. The conductive material may be a material having a lower electrical resistivity than the positive electrode active material and not oxidatively dissolved at the charge / discharge potential of the positive electrode (usually 2.5 to 4.5 V). Examples include corrosion resistant metals (such as titanium and gold), carbides (such as SiC and WC), and nitrides (such as Si ₃ N ₄ and BN). A carbon material having a high specific surface area (for example, carbon black or activated carbon) can also be used.

(First ion conduction layer)
As described above, the first ion conductive layer 115 covers the secondary particles 114 and fills the gaps between the primary particles 113 constituting the secondary particles 114, so that the positive electrode active material particles and the second ion conductive layers are filled. It is a substance that mediates lithium ions with 116. The first ion conductive layer 115 is required not to undergo oxidative degradation at the charge / discharge potential of the positive electrode, and is chemically inert to the positive electrode active material (primary particles 113) (for example, the positive electrode active material). It does not chemically react with the substance).

The conductivity of the first ion conductive layer 115 is applicable to the present invention as long as it is in the range of 1 × 10 ⁻⁶ to 1 × 10 ⁻³ S / cm, and the charge / discharge potential of the positive electrode is higher than the high conductivity. Priority is given not to oxidative degradation. For example, even if the conductivity of the first ion transmission layer 115 is a relatively low value in the range of 1 to 10 ⁻⁶ to 1 × 10 ⁻⁵ S / cm, it is better to select a material with excellent oxidation resistance. Effective for extending the life of secondary batteries.

As the first ion conductive layer 115, an oxide electrolyte containing lithium can be preferably used. Specific examples are perovskite type La _0.51 Li _0.34 TiO _2.94 , NASICON type Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , garnet type Li ₇ La ₃ Zr ₂ O ₁₂ , amorphous type Li _2.9 PO _3.3 N _0.4 or Li _3.6 Si _0.6 P _0.4 O ₄ , glass type 50Li ₄ SiO ₄ -50Li ₃ BO ₃ , Li _1.07 Al _0.69 Ti _1.46 (PO ₄ ) ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ , Li ₃ BO ₃ , LiVO ₃ etc. are mentioned.

As shown in FIG. 1, in the present invention, since all the primary particles 113 of the positive electrode active material are in contact with the first ion conductive layer 115, the movement / exit of lithium ions is facilitated, and all the primary particles 113 are in contact with each other. The particles 113 can directly contribute to charge / discharge of the secondary battery. As a result, the charge / discharge characteristics of the secondary battery can be improved.

The first ion conductive layer 115 is preferably the minimum amount necessary to coat the positive electrode active material particles (primary particles 113 and secondary particles 114) (do not coat the positive electrode active material particles excessively). . By not covering the positive electrode active material particles excessively with the first ion conductive layer 115, the stress caused by the volume change of the positive electrode active material particles due to charge / discharge (lithium ion occlusion / release) It can be easily absorbed, and an effect of suppressing crushing of the secondary particles 114 can be expected. In addition, by suppressing the crushing of the secondary particles 114, it is possible to suppress the direct contact between the primary particles 113 and the second ion conductive layer 116 and to prevent the secondary ion conductive layer 116 from being oxidized and deteriorated. Can also be expected.

(Second ion conduction layer)
The second ion conductive layer 116 is formed by laminating and covering the secondary particles 114 coated with the first ion conductive layer 115, and a substance that mediates lithium ions between the first ion conductive layer 115 and the solid electrolyte layer 120. It is. Further, the second ion conductive layer 116 is made of a material different from that of the first ion conductive layer 115, and it is desired to contribute to the improvement of the surface flatness of the positive electrode mixture layer 112.

The conductivity of the second ion conductive layer 116 is applicable in the range of 1 × 10 ⁻⁵ to 1 × 10 ⁻² S / cm. It is more preferable to select a material having a conductivity of 1 × 10 ⁻⁴ S / cm or more, and it is further preferable to select a material having a higher conductivity than that of the first ion conductive layer 115.

As the second ion conductive layer 116, for example, an ion conductive polymer having an average molecular weight of 5,000 to 500,000 is preferable. Specific examples include polyethylene glycol (PEG), polyethylene oxide (PEO), polyaniline (PAn), and polyvinylidene fluoride. (PVDF). It is preferable to add a lithium salt (for example, LiBF ₄ , lithium trifluoromethanesulfonimide (LiTFSI)) to these ion conductive polymers.

As the second ion conductive layer 116, a ceramic electrolyte containing lithium with an electrolyte different from that of the first ion conductive layer 115 can be preferably used. Specific examples include Li ₃ BO ₃ , Li ₇ La ₃ Zr ₂ O. ₁₂ , Li ₇ P ₃ S ₁₁ , Li _3.25 P _0.95 S ₄ , Li ₁₀ GeP ₂ S ₁₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , 30Li ₂ S-26B ₂ S ₃ -44LiI, 63Li ₂ S-36SiS _2- 1Li ₃ PO ₄ , 57Li ₂ S-38SiS ₂ -5Li ₄ SiO ₄ , 70Li ₂ S-30P ₂ S ₅ , 50Li ₂ S-50GeS _{2 and the} like.

The significance of stacking the secondary particles 114 with the second ion conductive layer 116 made of a material different from that of the first ion conductive layer 115 is as follows.

When the first ion conductive layer 115 and the second ion conductive layer 116 are formed of the same material, the interface between the first ion conductive layer 115 and the second ion conductive layer 116 is the same kind of interface. In this state, if a crack occurs due to a change in the volume of the electrode active material associated with charge / discharge (lithium ion occlusion / release), the crack progresses (as a result, the secondary particles 114 are crushed). ) Can hardly be expected.

On the other hand, when the secondary particles 114 are laminated and coated with the second ion conductive layer 116 made of a different material from the first ion conductive layer 115, a different interface is formed between the first ion conductive layer 115 and the second ion conductive layer 116. Therefore, the effect of suppressing the progress of cracks and suppressing the crushing of the secondary particles 114 can be expected. Further, even if the secondary particles 114 are crushed, the secondary particles 114 and the solid electrolyte 120 are prevented from coming into direct contact with each other (suppressing oxidative deterioration of the solid electrolyte 120). Can also be expected. As a result, the cycle characteristics of the secondary battery can be improved.

Further, since the secondary particles 114 covered with the first ion conductive layer 115 are basically still in the form of particles, if the positive electrode mixture layer 112 is formed without the second ion conductive layer 116 being laminated, the positive electrode mixture layer Irregularities caused by the secondary particles 114 are likely to remain on the surface of 112. In that case, since the solid electrolyte layer 120 does not have fluidity, it is difficult to ensure a sufficient contact area between the positive electrode mixture layer 112 and the solid electrolyte layer 120, which is a cause of a decrease in charge / discharge characteristics of the secondary battery. It is easy to become. Furthermore, when the secondary battery is charged and discharged in a high temperature environment with insufficient contact between the positive electrode mixture layer 112 and the solid electrolyte layer 120, electric field concentration occurs at the contact point between the positive electrode mixture layer 112 and the solid electrolyte layer 120. As a result, deterioration of the solid electrolyte layer 120 may be induced.

In other words, in order to secure a sufficient contact area between the solid electrolyte layer 120 and the positive electrode mixture layer 112 and suppress deterioration of the solid electrolyte layer 120, it is desirable that the surface of the positive electrode mixture layer 112 has high flatness. . Therefore, in the present invention, the secondary particles 114 coated with the first ion conductive layer 115 are laminated and coated with the second ion conductive layer 116, thereby embedding irregularities caused by the secondary particles 114, and the positive electrode mixture layer The surface flatness of 112 is improved. Thereby, it is considered that the secondary operation and effect that the contact area between the positive electrode mixture layer 112 and the solid electrolyte layer 120 can be sufficiently secured and the deterioration of the solid electrolyte layer 120 can be suppressed are exhibited.

(Solid electrolyte layer)
As long as the solid electrolyte layer 120 has high ionic conductivity (relatively higher ionic conductivity than the first ionic conductive layer 115 and the second ionic conductive layer 116), the solid electrolyte layer 120 is a solid of a conventional all-solid lithium secondary battery. An electrolyte can be used. For example, a ceramic electrolyte containing lithium with an electrolyte different from the second ion conductive layer 116 (for example, Li ₁₀ GeP ₂ S ₁₂ , Li ₇ P ₃ S ₁₃ , 70Li ₂ S-30P ₂ S ₅ , La _0.1 Li _0.34 TiO _2.94 , Li _1.1 Al _0.7 Ti _1.5 (PO ₄ ) ₃ etc.) can be preferably used. In addition, an ion conductive polymer (for example, PEG, PEO, PAn, PVDF) having an average molecular weight of 5000 or more and 20000 or less obtained by adding a lithium salt (for example, LiBF ₄ or LiTFSI) with an electrolyte different from that of the second ion conductive layer 116 is preferably used. be able to.

The conductivity of the solid electrolyte layer 120 is applicable as long as it is 1 × 10 ⁻⁴ S / cm or more, and a material having a higher conductivity than that of the second ion conductive layer 116 is selected. In particular, it is preferable to select a material of 1 × 10 ⁻³ S / cm or more.

The thickness of the solid electrolyte layer 120 is preferably 5 μm or more and 200 μm or less. When the thickness of the solid electrolyte layer 120 is less than 5 μm, the mechanical strength of the solid electrolyte layer 120 is insufficient and the positive electrode 110 and the negative electrode 130 are easily short-circuited. On the other hand, when the thickness of the solid electrolyte layer 120 exceeds 200 μm, the electric resistance of the solid electrolyte layer 120 becomes too large and the capacity of the secondary battery decreases. The thickness of the solid electrolyte layer 120 is more preferably 10 μm or more and 100 μm or less, and further preferably 20 μm or more and 50 μm or less.

(Negative electrode current collector)
Similarly to the positive electrode current collector 111, the negative electrode current collector 131 is not particularly limited as long as it is a low-resistance conductor having heat resistance that can withstand heat treatment when forming the ion conductive layer / solid electrolyte layer. The same thing as the negative electrode electrical power collector in the nonaqueous electrolyte lithium secondary battery of this can be used. For example, metal foil (thickness of 10 μm or more and 100 μm or less), perforated metal foil (thickness of 10 μm or more and 100 μm or less, pore diameter of 0.1 mm or more and 10 mm or less), expanded metal, foamed metal plate, glassy carbon plate and the like can be mentioned. Moreover, as a metal seed | species, copper, stainless steel, titanium, a noble metal (for example, gold | metal | money, silver, platinum) etc. can be used.

(Negative electrode mixture layer)
The negative electrode mixture layer 132 includes at least a negative electrode active material, and further includes a third ion conductive layer as necessary. Further, for the purpose of improving the conductivity of the negative electrode mixture layer 132, a conductive material may be further added to and mixed with the negative electrode active material. As the conductive material to be added to and mixed with the negative electrode mixture layer 132, the same material as that of the positive electrode mixture layer 112 can be used.

(Negative electrode active material)
There is no particular limitation on the material of the negative electrode active material, and a negative electrode active material used in a conventional lithium ion secondary battery can be used. Specifically, carbon-based materials (eg, graphite, graphitizable carbon material, amorphous carbon material), conductive polymer materials (eg, polyacene, polyparaphenylene, polyaniline, polyacetylene), lithium composite oxide ( For example, lithium titanate: Li ₄ Ti ₅ O ₁₂ ), metal lithium, or a metal alloyed with lithium (eg, aluminum, silicon, tin) can be used.

(Third ion conduction layer)
When the negative electrode active material is particulate, it is preferable to use a third ion conductive layer. The third ion conductive layer covers the negative electrode active material particles and fills the gaps between the particles, and is a material that mediates lithium ions between the negative electrode active material and the solid electrolyte layer 120. The third ion conductive layer is required not to undergo reductive degradation at the charge / discharge potential of the negative electrode. For example, polyethylene oxide (PEO) holding an electrolyte such as lithium borohydride (LiBH ₄ ), lithium bistrifluoromethanesulfonylimide (LiTFSI), or lithium phosphate oxynitride (LiPON) can be preferably used.

In addition, when the negative electrode active material is not in a particulate form (for example, in the case of a foil form or a plate form), the third ion conductive layer may not be used. In the case where the negative electrode active material is formed of a low resistance conductor equivalent to the negative electrode current collector 131 in a foil shape or a plate shape, the negative electrode active material may also serve as the negative electrode current collector 131.

(Single cell manufacturing method)
Next, a method for manufacturing the single cell 100 of the all-solid lithium secondary battery will be briefly described.

The positive electrode 110 is manufactured by applying and heating and drying a positive electrode mixture slurry on one or both surfaces of the positive electrode current collector 111, followed by compression molding using a press or the like, and cutting into a predetermined size. . Similarly, the negative electrode 130 is obtained by applying a negative electrode mixture slurry to one or both surfaces of the negative electrode current collector 131 and heating and drying, and then compressing and molding the negative electrode slurry using a press machine or the like. Produced.

There is no particular limitation on the application method of the positive electrode mixture slurry and the negative electrode mixture slurry, and conventional methods (for example, a doctor blade method, a dipping method, a spray method) can be used. Moreover, it is also possible to laminate | stack a several mixture layer on a collector by performing from application | coating to heat drying in multiple times.

The positive electrode mixture slurry and the negative electrode mixture slurry are prepared by coating each electrode active material with a predetermined ion conductive layer and then mixing a conductive material, a binder, a solvent, and the like as necessary.

There is no particular limitation on the method of forming and filling the first ion conductive layer 115 on the surface of the secondary particles 114 of the positive electrode active material and the gaps between the primary particles 113 inside, as a result of such a configuration. Good. For example, a solution and a secondary solution of a salt of a metal element constituting the first ion conductive layer 115 (for example, in the case of perovskite type La _0.51 Li _0.34 TiO _2.94 , carbonates or hydroxides of La, Li, Ti) After thoroughly mixing the particles 114, a heat treatment (at a temperature of 300 ° C. or more and 1000 ° C. or less in the atmosphere or nitrogen or argon atmosphere in which the oxygen concentration is controlled) is performed to form the first ion conductive layer 115 in a desired manner. Can be formed and filled to form.

Next, the positive electrode mixture layer 112 is formed while the secondary particles 114 covered with the first ion conductive layer 115 are further laminated and covered with the second ion conductive layer 116. There is no particular limitation on the method of laminating and coating with the second ion conductive layer 116, and it is sufficient that such a configuration is obtained as a result.

For example, when a ceramic electrolyte is used as the second ion conductive layer 116, the same method as that for the first ion conductive layer 115 can be used. Thereafter, a conductive material, a binder, a solvent, and the like are mixed with the secondary particles 114 that are laminated and coated with the first ion conductive layer 115 and the second ion conductive layer 116 to produce a positive electrode mixture slurry. A desired positive electrode mixture layer 112 can be formed by applying and heating and drying a positive electrode mixture slurry.

As another method, a ceramic electrolyte powder to be the second ion conductive layer 116 is separately prepared and mixed with the secondary particles 114 coated with the first ion conductive layer 115 together with a conductive material, a binder, a solvent, and the like. A positive electrode mixture slurry is prepared. In this case, after applying the positive electrode mixture slurry and heating and drying, heat treatment (in the atmosphere or in an atmosphere of nitrogen or argon with a controlled oxygen concentration, a temperature of 300 ° C. or higher and 1000 ° C. or lower) is applied to the second ion. The positive electrode mixture layer 112 can be formed while forming the conductive layer 116 in a desired form.

On the other hand, when an ion conductive polymer to which a lithium salt is added is used as the second ion conductive layer 116, first, the lithium salt, the ion conductive polymer, an appropriate solvent (for example, a nonaqueous solvent), and the first ion conductive layer. The secondary particles 114 coated with 115 are mixed well. Thereafter, a conductive material and a binder are further mixed to produce a positive electrode mixture slurry.

In this case, the positive electrode mixture layer 112 can be formed while the second ion conductive layer 116 is formed in a desired form by applying and heating and drying the positive electrode mixture slurry. Further, the second ion conductive layer 116 can be filled in the gap between the secondary particles 114.

The mixing ratio of the positive electrode active material (secondary particle 114) and the ion conductive layer (first ion conductive layer 115, second ion conductive layer 116) is the secondary particle 114 when the total of both is 100 parts by mass. Is preferably 60 parts by mass or more and 90 parts by mass or less, and the ion conductive layer is preferably the remainder (that is, 10 parts by mass or more and 40 parts by mass or less). When the mixing ratio of the secondary particles 114 is less than 60 parts by mass, the positive electrode active material is insufficient and the energy density of the secondary battery is lowered. On the other hand, when the mixing ratio of the secondary particles 114 exceeds 90 parts by mass, the maximum current value that can be charged / discharged due to the lack of the ion conductive layer is reduced, and the cycle characteristics are deteriorated.

The mixing ratio of the first ion conductive layer 115 is preferably 5 parts by mass or more and 30 parts by mass or less. When the mixing ratio of the first ion conductive layer 115 is less than 5 parts by mass, the gap between the primary particles 113 inside the secondary particles 114 cannot be sufficiently filled. On the other hand, when the mixing ratio of the first ion conductive layer 115 exceeds 30 parts by mass, the second ion conductive layer 116 is insufficient and the secondary ion 114 cannot be sufficiently laminated and covered with the second ion conductive layer 116.

As described above, when the negative electrode active material is in the form of particles, it is preferable to coat the negative electrode active material particles with the third ion conductive layer. There is no particular limitation on the method of forming the third ion conductive layer on the surface of the negative electrode active material particles, and it is sufficient that such a form is obtained as a result.

For example, the electrolyte constituting the third ion conductive layer, the ion conductive polymer, a suitable solvent (for example, a non-aqueous solvent), and negative electrode active material particles are mixed well. Thereafter, a conductive material and a binder are further mixed to prepare a negative electrode mixture slurry. The third ion conductive layer can be formed in a desired form by applying and heating and drying the negative electrode mixture slurry. Further, the gap between the negative electrode active material particles can be filled with the third ion conductive layer.

The mixing ratio of the negative electrode active material particles and the third ion conductive layer is 70 parts by mass or more and 95 parts by mass or less of the negative electrode active material particles when the total of both is 100 parts by mass, and the remaining third ion conductive layer (That is, 5 parts by mass or more and 30 parts by mass or less). When the mixing ratio of the negative electrode active material particles is less than 70 parts by mass, the energy density of the secondary battery decreases. On the other hand, when the mixing ratio of the negative electrode active material particles exceeds 95 parts by mass, the maximum current value that can be charged / discharged due to the shortage of the third ion conductive layer is lowered and the cycle characteristics are also lowered.

As described above, when the negative electrode active material is not particulate (for example, foil or plate), the third ion conductive layer may not be used. In the case where the negative electrode active material is formed of a low resistance conductor equivalent to the negative electrode current collector 131 in a foil shape or a plate shape, the negative electrode active material may also serve as the negative electrode current collector 131.

When the conductive material is mixed with the electrode mixture slurry (positive electrode mixture slurry, negative electrode mixture slurry), the mixing ratio of the conductive material is, when the total of the electrode active material particles and the ion conductive layer is 100 parts by mass, 3 parts by mass or more and 10 parts by mass or less are preferable. When the mixing ratio of the conductive material is less than 3 parts by mass, the effect of mixing the conductive material (improvement of conductivity of the electrode mixture layer) is hardly obtained. When the mixing ratio of the conductive material exceeds 10 parts by mass, the effect of mixing the conductive material is saturated, and the relative ratio of the electrode active material in the electrode mixture layer is decreased. The energy density of the battery decreases.

The formation method of the solid electrolyte layer 120 is not particularly limited, and a conventional method can be used. For example, when a ceramic electrolyte is used as the solid electrolyte layer 120, the ceramic electrolyte is synthesized and pulverized to prepare a powder of the ceramic electrolyte, and then mixed with a binder, a solvent, etc. to produce a solid electrolyte slurry. A desired solid electrolyte layer 120 can be formed by applying and drying the solid electrolyte slurry.

Further, when an ion conductive polymer to which a lithium salt is added is used as the solid electrolyte layer 120, a desired solid electrolyte layer 120 can be formed in the same manner as the formation method in the second ion conductive layer 116.

[Overall configuration of all-solid lithium secondary battery]
The overall configuration of the all-solid lithium secondary battery will be described. FIG. 2 is a schematic cross-sectional view showing an example of an all-solid lithium secondary battery according to the present invention. In the all-solid lithium secondary battery 200 shown in FIG. 2, strip-shaped single cells 100 are stacked via a solid electrolyte layer 120 to form an electrode group 210. Since the solid electrolyte layer 120 does not have fluidity, the solid electrolyte layer 120 can also serve as a separator that prevents a short circuit between the positive electrode 110 and the negative electrode 130 in the all-solid lithium secondary battery. In other words, the all-solid lithium secondary battery 200 does not require a separate separator as used in the conventional non-aqueous electrolyte lithium secondary battery.

Note that the structure of the electrode group 210 is not limited to a stack of strip-shaped single cells 100, but is a structure in which long single cells 100 are wound (for example, a columnar shape or a flat columnar shape). There may be.

The electrode group 210 is accommodated in a battery container 220 having at least an inner surface electrically insulated so that the accommodated electrode group 210 is not in electrical contact with the battery container 220. As the shape of the battery container 220, a shape (for example, a rectangular tube shape, a cylindrical shape, or a flat and long cylindrical shape) that matches the shape of the electrode group 210 is usually selected. The material of the battery case 220 is selected from materials having mechanical strength and corrosion resistance (for example, aluminum, stainless steel, nickel-plated steel, aluminum laminate film, engineering plastic).

In order to suppress oxidative deterioration of the electrolyte in the electrode group 210, the battery container 220 is sealed with a lid 221 so that oxygen in the atmosphere does not enter the battery. There is no particular limitation on the attachment of the lid 221 to the battery case 220, and a conventional method (for example, welding, caulking, adhesion) can be employed.

The positive electrode 110 is connected to the positive electrode external terminal 213 via the positive electrode lead 211, and the negative electrode 130 is connected to the negative electrode external terminal 214 via the negative electrode lead 212. The external terminals 213 and 214 are electrically insulated from the battery container 220 and the lid 221 by an electrical insulating seal 222 so as not to be short-circuited via the battery container 220 and the lid 221. The leads 211 and 212 can take any shape (for example, a wire shape, a foil shape, or a plate shape), and a structure and material that can reduce electrical loss and ensure chemical stability are selected. The electrical insulating seal 222 is selected from materials (for example, a fluororesin, a thermosetting resin, and a glass hermetic seal) that are excellent in electrical insulation and airtightness.

Current blocking mechanism using a positive temperature coefficient resistance element in the middle of the positive electrode lead 211 or the negative electrode lead 212, or in the connection part between the positive electrode lead 211 and the positive electrode external terminal 213, or in the connection part between the negative electrode lead 212 and the negative electrode external terminal 214 (Not shown) is preferably provided. When the current interruption mechanism is provided, when the temperature inside the battery becomes high, charging / discharging of the all-solid lithium secondary battery 200 can be stopped to protect the battery.

With the above configuration, an all-solid lithium secondary battery that can be charged and discharged at a high voltage of 3 V or higher can be provided.

[Secondary battery system]
A configuration of a secondary battery system including an all solid lithium secondary battery will be described. The secondary battery system according to the present invention is defined as a system having at least two or more all-solid lithium secondary batteries connected in series or in parallel and having a charge / discharge control mechanism. FIG. 3 is a schematic diagram showing a configuration example of the secondary battery system according to the present invention.

In the secondary battery system 300 shown in FIG. 3, two all-solid lithium secondary batteries 200A and 200B are connected in series. The negative external terminal 215 of the all-solid lithium secondary battery 200A arranged on the right side of FIG. 3 is connected to the negative input terminal of the charge / discharge control mechanism 320 by the power cable 311. The negative external terminal 215 of the all solid lithium secondary battery 200B arranged on the left side of the drawing is connected to the positive external terminal 214 of the all solid lithium secondary battery 200A by the power cable 312. Further, the positive external terminal 214 of the all-solid lithium secondary battery 200B is connected to the positive input terminal of the charge / discharge control mechanism 320 by the power cable 313. With such a wiring configuration, the two all-solid lithium secondary batteries 200A and 200B can be charged or discharged while being controlled by the charge / discharge control mechanism 320.

The charge / discharge control mechanism 320 exchanges power with the external device 330 via the power cables 314 and 315. The external device 330 includes various electric devices such as an external power source and a regenerative motor for supplying power to the charge / discharge control mechanism 320 in addition to an external load. Moreover, an inverter and a converter can be provided according to the kind of alternating current and direct current which an external apparatus respond | corresponds.

The power generator 340 is connected to the charge / discharge control mechanism 320 via power cables 316 and 317. As the power generation device 340, a power generation device that generates renewable energy (for example, a wind power generation device, a geothermal power generation device, or a solar cell) or a normal power generation device (for example, a fuel cell, a gas turbine generator, or the like) can be used. .

When the power generation device 340 is generating power, the charging / discharging control mechanism 320 shifts to the charging mode, supplies power to the external device 330, and charges surplus power to the all-solid lithium secondary batteries 200A and 200B. When the power generation amount of the power generator 340 is less than the required power of the external device 330, the charge / discharge control mechanism 320 shifts to the discharge mode so that power is supplied from the all-solid lithium secondary batteries 200A, 200B.

The charge / discharge control mechanism 320 preferably stores a program so that such charge / discharge mode transition is automatically performed. The charge / discharge control mechanism 320 preferably stores a program so as to control the charge / discharge range of the all-solid lithium secondary batteries 200A, 200B to a range of 10% to 90%. Thereby, durability of the secondary battery system 300 can be improved.

The secondary battery system 300 according to the present invention includes, for example, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric construction machine, a transporting device, a construction machine, a care device, a light vehicle, an electric tool, a robot, and a home use. It can be used as a power source for power storage systems, remote island power storage systems, space stations, and the like.

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

[Production and evaluation of all-solid lithium secondary battery]
Examples 1 to 7 and Comparative Example 1 were made such that the combinations of the positive electrode active material, the first ion conductive layer, the second ion conductive layer, the solid electrolyte layer, and the negative electrode active material were as shown in Table 1 described later. The electrode groups (1) to (3) were prepared, an all-solid lithium secondary battery was assembled, and the battery characteristics of the produced all-solid lithium secondary battery were evaluated.

In Examples 1 to 7 according to the present invention, the ion conductive layer formed on the positive electrode active material particles has a two-layer structure, and the mixing ratio of the positive electrode active material particles, the first ion conductive layer, and the second ion conductive layer is set to “ 60 parts by mass: 10 parts by mass: 30 parts by mass ”. On the other hand, in Comparative Examples 1 to 3 that deviate from the definition of the present invention, the ion conductive layer formed on the positive electrode active material particles has a single layer structure, and the mixing ratio of the positive electrode active material and the ion conductive layer is set to “60 parts by mass: 40 "Mass parts".

(Preparation of all-solid lithium secondary battery)
(1) Production of positive electrodes of Examples 1 to 7 As positive electrode active material particles, LiCoO ₂ (average particle size of secondary particles 5 μm), LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (secondary particles of An average particle diameter of 5 μm) and LiFePO ₄ (average particle diameter of secondary particles of 7 μm) were used. LiFePO ₄ was prepared by supporting a carbon layer on the surface of secondary particles.

Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , La _0.51 Li _0.34 TiO _2.94 , Li _2.9 PO _3.3 N _0.4 , 50Li ₄ SiO ₄ -50Li ₃ BO ₃ , and LiVO ₃ were used as the first ion conductive layer. . The conductivity (unit: S / cm) at 25 ° C. of each first ion conductive layer is also shown in Table 1.

As the second ion conductive layer, polyethylene oxide (PEO) to which lithium trifluoromethanesulfonimide (LiTFSI) was added and Li ₇ La ₃ Zr ₂ O ₁₂ were used. The conductivity (unit: S / cm) at 25 ° C. of each second ion conductive layer is also shown in Table 1.

Formation and filling of the first ion conductive layer on the positive electrode active material particles are carried out by thoroughly mixing the phosphate solution of the metal element constituting the first ion conductive layer and the positive electrode active material particles, followed by heat treatment (in air, 650 C.).

For samples using PEO to which LiTFSI was added as the second ion conductive layer (Examples 1 to 3), a solution in which LiTFSI and PEO (average molecular weight 20000) were dissolved using propanol as a solvent was prepared. The positive electrode mixture slurries of Examples 1 to 3 were prepared by thoroughly mixing with the positive electrode active material particles having the layer formed therein.

Next, the positive electrode mixture slurries of Examples 1 to 3 were applied to both sides of the positive electrode current collector (gold foil with a thickness of 20 μm) using the doctor blade method, and dried by heating (in the atmosphere, 150 ° C.). A positive electrode mixture layer was formed. Thereafter, it was compression-molded by a roll press and cut into a predetermined size to produce positive electrodes of Examples 1 to 3.

On the other hand, in the samples using Li ₇ La ₃ Zr ₂ O ₁₂ as the second ion conductive layer (Examples 4 to 7), the positive electrode active material particles on which the first ion conductive layer was formed and Li ₇ La ₃ Zr ₂ O After thoroughly mixing with ₁₂ powders (average particle size 300 nm), ethyl cellulose (binder) and butyl carbitol acetate (solvent) were further added and mixed to prepare positive electrode mixture slurries of Examples 4-7.

Next, the positive electrode mixture slurries of Examples 4 to 7 were applied to both surfaces of the positive electrode current collector (gold foil with a thickness of 20 μm) using the doctor blade method, and after heat drying (in the atmosphere, 150 ° C.) Then, heat treatment (in an argon atmosphere, 700 ° C.) was performed to form a positive electrode mixture layer. Thereafter, the positive electrodes of Examples 4 to 7 were produced by cutting into a predetermined size.

(2) Production of Positive Electrodes of Comparative Examples 1 to 3 As the positive electrode active materials of Comparative Examples 1 to 3, the same LiCoO ₂ (average particle diameter of secondary particles 5 μm) as in Example 4 was used.

The ion conduction layer of Comparative Example 1 was only Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ used as the first ion conduction layer in Example 4. In the same manner as in Example 4, the ion conductive layer was formed on the positive electrode active material particles after thoroughly mixing the phosphate solution of the metal element constituting the ion conductive layer and the positive electrode active material particles, followed by heat treatment (in air , 650 ° C.). Thereafter, ethyl cellulose (binder) and butyl carbitol acetate (solvent) were added to and mixed with the positive electrode active material particles on which the ion conductive layer was formed to prepare the positive electrode mixture slurry of Comparative Example 1.

Next, the positive electrode mixture slurry of Comparative Example 1 was applied to both surfaces of the positive electrode current collector (gold foil with a thickness of 20 μm) using the doctor blade method in the same manner as in Example 1, and dried by heating (in the atmosphere, 150 ° C) to form a positive electrode mixture layer. Then, it compression-molded with the roll press machine, cut | disconnected to the predetermined magnitude | size, and produced the positive electrode of the comparative example 1. The positive electrode of Comparative Example 1 can be said to be an example in which the second ion conductive layer is absent from the positive electrode of Example 4.

The ion conductive layer of Comparative Example 2 was only Li ₇ La ₃ Zr ₂ O ₁₂ used as the second ion conductive layer in Example 4. Li ₇ La ₃ Zr ₂ O ₁₂ powder (average particle size 300 nm) and positive electrode active material particles were mixed well, then ethyl cellulose (binder) and butyl carbitol acetate (solvent) were further added and mixed. Two positive electrode mixture slurries were prepared.

The ion conductive layer of Comparative Example 3 includes the ion conductive layer material (Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ ) of Comparative Example 1 and the ion conductive layer material (Li ₇ La ₃ Zr ₂ O ₁₂ ) of Comparative Example 2. A mixture of was used. Here, Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ was prepared as a powder having an average particle diameter of 300 nm by preparing a bulk of the substance using a sol-gel method and pulverizing the obtained bulk. The mixing ratio of the positive electrode active material particles, the Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ powder, and the Li ₇ La ₃ Zr ₂ O ₁₂ powder is “60 parts by mass: 10 parts by mass: 30 parts by mass”, and they are often used. After mixing, ethyl cellulose (binder) and butyl carbitol acetate (solvent) were further added and mixed to prepare the positive electrode mixture slurry of Comparative Example 3.

Next, the positive electrode mixture slurries of Comparative Examples 2 to 3 were applied to both surfaces of the positive electrode current collector (gold foil with a thickness of 20 μm) using the doctor blade method, as in Examples 4 to 7, and dried by heating. After heat treatment (in air, 150 ° C.), heat treatment (in argon atmosphere, 700 ° C.) was performed to form a positive electrode mixture layer. Thereafter, the positive electrodes of Comparative Examples 2 to 3 were produced by cutting into a predetermined size. The positive electrode of Comparative Example 2 can be said to be an example in which the first ion conductive layer is absent from the positive electrode of Example 4. Further, the positive electrode of Comparative Example 3 can be said to be an example in which the first ion conductive layer and the second ion conductive layer are not in a laminated structure with respect to the positive electrode of Example 4.

(3) Production of negative electrode Using lithium metal foil (thickness 0.3 mm) as a negative electrode active material and a negative electrode current collector, cut to a predetermined size to produce a negative electrode for an all-solid lithium secondary battery did.

(4) Production of electrode group Li _1.1 Al _0.7 Ti _1.5 (PO ₄ ) ₃ was used as the solid electrolyte layer. First, a predetermined amount of Li ₃ PO ₄ , AlPO ₄ , and TiPO ₄ as raw materials are mixed, melted at a high temperature of 1000 to 1500 ° C., and then rapidly cooled to obtain glassy Li _1.1 Al _0.7 Ti _1.5 (PO ₄ ) ₃ bulk was obtained. Next, the bulk was pulverized to prepare Li _1.1 Al _0.7 Ti _1.5 (PO ₄ ) ₃ powder (average particle size 300 nm). Thereafter, ethyl cellulose (binder) and butyl carbitol acetate (solvent) were added and mixed to prepare a solid electrolyte slurry.

The solid electrolyte slurry was applied to both surfaces of the positive electrode and the negative electrode prepared in advance using a doctor blade method, and the solvent was evaporated to form a solid electrolyte layer. Next, the positive electrode and the negative electrode are alternately laminated through the solid electrolyte layer, and the laminate is dried by heating (in the atmosphere, 150 ° C.) and then compression-molded by a press machine. The electrode groups of Examples 1 to 3 were produced. The whole was heated to 100 ° C. during compression molding, and each electrode and the solid electrolyte layer were brought into close contact with each other. The electrical conductivity (unit: S / cm) at 25 ° C. of the solid electrolyte layer is also shown in Table 1.

(4) Assembly of all-solid lithium secondary battery All-solid lithium secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 (see FIG. 2) were assembled using the above electrode group. The produced all solid lithium secondary battery was designed to have an outer dimension of 100 mm × 70 mm × 20 mm and a rated capacity of 5 Ah.

(Test evaluation)
(A) Low-speed charge / discharge test (0.5C rate initial capacity evaluation)
About the all-solid-state lithium secondary battery prepared above, the following low-speed charge / discharge tests were implemented and initial capacity was evaluated.

For secondary batteries using LiCoO ₂ or LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as the positive electrode active material (Examples 1, 2, 4, 5, 7 and Comparative Examples 1 to 3) First, the secondary battery was placed in an environment of 120 ° C. to stabilize the temperature. Next, the battery was charged at a constant current (2.5 A) corresponding to a 2-hour rate (0.5 C rate) until the battery voltage reached 4.2 V from the open circuit state. After the battery voltage reached 4.2 V, 4.2 V was maintained until the current value was equivalent to 100 hours. Thereafter, charging was stopped and a 30-minute rest period was provided. Next, constant current discharge corresponding to a 2-hour rate (0.5 C rate) was started, and the battery was discharged until the battery voltage reached 3.0 V. Thereafter, the discharge was stopped and a 30 minute rest period was provided. The process so far is referred to as initial aging. The discharge capacity obtained after repeating this initial aging three times was used as the 0.5 C rate initial capacity of the secondary battery.

For secondary batteries using LiFePO ₄ as the secondary battery positive electrode active material (Examples 3 and 6), the same as above except that the charge / discharge voltage of the initial aging was in the range of 4.0 to 2.0 V. The initial capacity of 0.5C rate was measured.

The charge / discharge time rate (C rate) means a current value for charging / discharging the design capacity of the secondary battery in a predetermined time. For example, the 1 hour rate (1C rate) is a current value for charging and discharging the design capacity of the secondary battery in 1 hour. Specifically, when the design capacity of the battery is C (unit: Ah), the current value of the 2-hour rate (0.5 C rate) is C / 2 (unit: A).

Example 5 Each of the secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 was manufactured, and the above test was performed in the same manner to calculate the average value of 0.5C rate initial capacity. For the rated capacity, an initial capacity of 0.5C rate of 95% or more was evaluated as “pass”, and an initial capacity of 0.5C rate of less than 95% was evaluated as “fail”. The results are shown in Table 2 described later.

(B) High-speed charge / discharge test (1C rate initial capacity evaluation)
After performing the above-mentioned low-speed charge / discharge test, a sufficient rest time was set. Thereafter, each secondary battery was placed in an environment of 85 ° C. to stabilize the temperature. Next, the initial charge capacity of the 1C rate was measured under the condition that the charge / discharge voltage conditions were the same as in the low-speed charge / discharge test, and the charge / discharge time rate (C rate) was 1 hour rate (1C rate).

The average value of 5 pieces was calculated as above. The 1C rate initial capacity of 90% or more with respect to the rated capacity was evaluated as “pass”, and the 0.5C rate initial capacity of less than 90% was evaluated as “fail”. The results are shown in Table 2.

(C) Cycle test (cycle characteristic evaluation)
After performing the above high-speed charge / discharge test, sufficient rest time was set. Thereafter, each secondary battery was placed in an environment of 120 ° C. to stabilize the temperature. Next, the 0.5 C rate capacity after 20 cycles of charge and discharge were measured under the same conditions as in the previous low-speed charge and discharge test.

The average value of 5 pieces was calculated as above. A 0.5C rate capacity within -5% with respect to the initial capacity of 0.5C rate was evaluated as "pass", and a 0.5C rate capacity with more than -5% was evaluated as "fail". The results are shown in Table 2.

As shown in Tables 1 and 2, Comparative Examples 1 to 3 that are out of the scope of the present invention failed in all test evaluations of 0.5C rate initial capacity, 1C rate initial capacity, and 0.5C rate capacity after 20 cycles. Met. When viewed individually, in Comparative Example 1 having no second ion conductive layer, there is a high possibility that the contact between the positive electrode mixture layer and the solid electrolyte layer is insufficient, and charging in a high-temperature environment. It is thought that the deterioration of the solid electrolyte layer was induced by the discharge. As a result, it was considered that the 1C rate initial capacity and the 0.5C rate capacity after 20 cycles were significantly reduced.

In Comparative Example 2 having no first ion conductive layer, the initial capacity of the 0.5C rate is greatly reduced because the gap between the primary particles constituting the positive electrode active material secondary particles is not filled with the ion conductive layer. It was considered. In addition, since the second ion conductive layer is in direct contact with the positive electrode active material particles, it is considered that the second ion conductive layer, which has lower oxidation resistance than the first ion conductive layer, was oxidized and deteriorated due to charge / discharge in a high temperature environment. It was.

In Comparative Example 3 in which the first ion conductive layer and the second ion conductive layer do not have a laminated structure, the second ion conductive layer is in direct contact with the positive electrode active material particles and constitutes the positive electrode active material secondary particles. Since the gap between the particles was not filled with the ion conductive layer, it was considered that the result was as if the weak points of Comparative Examples 1 and 2 were combined.

In contrast to Comparative Examples 1 to 3, the secondary batteries of Examples 1 to 7 passed all the test evaluations of 0.5C rate initial capacity, 1C rate initial capacity, and 0.5C rate capacity after 20 cycles. That is, the secondary battery according to the present invention can be used in a higher temperature environment than the conventional non-aqueous electrolyte lithium secondary battery, and is a bulk-type all solid that balances charge and discharge characteristics and cycle characteristics at a high level. It was proved to be a lithium secondary battery.

The above-described embodiments and examples are described for the purpose of helping understanding of the present invention, and the present invention is not limited to the specific configurations described. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. That is, according to the present invention, a part of the configurations of the embodiments and examples of the present specification can be deleted, replaced with other configurations, and added with other configurations.

100 ... single cell, 110 ... positive electrode, 111 ... positive electrode current collector, 112 ... positive electrode mixture layer, 113 ... primary particles, 114 ... secondary particles, 115 ... first ion conductive layer, 116 ... second ion conductive layer, 120 ... Solid electrolyte layer, 130 ... Negative electrode, 131 ... Negative electrode current collector, 132 ... Negative electrode mixture layer, 200, 200A, 200B ... All solid lithium secondary battery, 210 ... Electrode group, 211 ... Positive electrode lead, 212 ... Negative electrode Lead, 213 ... Positive electrode external terminal, 214 ... Negative electrode external terminal, 220 ... Battery container, 221 ... Lid, 222 ... Electrical insulation seal, 300 ... Secondary battery system, 311, 312, 313, 314, 315, 316, 317 ... Power cable, 320 ... charge / discharge control mechanism, 330 ... external device, 340 ... power generation device.

Claims (8)

1. An all-solid lithium secondary battery in which a positive electrode and a negative electrode are laminated via a solid electrolyte layer,
   The positive electrode includes positive electrode active material particles, a first ion conductive layer, and a second ion conductive layer,
   The positive electrode active material particles form secondary particles in which a plurality of primary particles are aggregated,
   The first ion conductive layer is a material that mediates lithium ions between the positive electrode active material particles and the second ion conductive layer, and covers the secondary particles and constitutes the secondary particles. It fills the gaps between the particles,
   The second ion conductive layer is a substance that conducts lithium ions between the first ion conductive layer and the solid electrolyte layer, and the secondary particles coated with the first ion conductive layer are laminated and coated. And
   The all-solid lithium secondary battery, wherein the first ion conductive layer, the second ion conductive layer, and the solid electrolyte layer are made of different materials.
2. In the all-solid-state lithium secondary battery of Claim 1,
   The conductivity of the first ion conductive layer is 1 × 10 ⁻⁶ S / cm or more and 1 × 10 ⁻³ S / cm or less,
   The conductivity of the second ion conductive layer is 1 × 10 ⁻⁵ S / cm or more and 1 × 10 ⁻² S / cm or less,
   An all-solid lithium secondary battery, wherein the solid electrolyte layer has an electrical conductivity of 1 × 10 ⁻⁴ S / cm or more.
3. In the all-solid-state lithium secondary battery of Claim 1 or Claim 2,
   The first ion conductive layer is made of an oxide electrolyte containing lithium,
   The all-solid lithium secondary battery, wherein the second ion conductive layer is made of an ion conductive polymer containing a lithium salt or a ceramic electrolyte containing lithium.
4. In the all-solid-state lithium secondary battery in any one of Claims 1 thru | or 3,
   When the total of the positive electrode active material particles, the first ion conductive layer, and the second ion conductive layer is 100 parts by mass, the positive electrode active material particles are included in an amount of 60 parts by mass to 90 parts by mass. An all-solid lithium secondary battery.
5. In the all-solid-state lithium secondary battery of Claim 4,
   The all-solid lithium secondary battery, wherein the first ion conductive layer is included in an amount of 5 parts by mass or more and 30 parts by mass or less.
6. In the all-solid-state lithium secondary battery in any one of Claims 1 thru | or 5,
   The all-solid lithium secondary battery, wherein the solid electrolyte layer has a conductivity higher than that of the second ion conductive layer.
7. The all solid lithium secondary battery according to any one of claims 1 to 6,
   The all-solid lithium secondary battery, wherein the positive electrode further includes a conductive material.
8. A secondary battery system comprising the all solid lithium secondary battery according to any one of claims 1 to 7.

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