JP6952467B2 - Positive active material for all-solid-state secondary batteries, positive-positive active material layer for all-solid-state secondary batteries, and all-solid-state secondary batteries - Google Patents

Description

The present invention relates to a positive electrode active material for an all-solid secondary battery, a positive active material layer for an all-solid secondary battery, and an all-solid-state secondary battery.

In recent years, an all-solid-state secondary battery using a solid electrolyte having lithium ion conductivity has attracted attention. As the solid electrolyte of such an all-solid secondary battery, for example, a sulfide-based solid electrolyte having high lithium ion conductivity has been proposed.

However, the sulfide-based solid electrolyte may react with the positive electrode active material particles during charging and generate a resistance component at the interface with the positive electrode active material particles. In such a case, the resistance at the interface between the positive electrode active material particles and the solid electrolyte increases, and the conductivity of lithium ions decreases, so that the output of the all-solid secondary battery decreases. It should be noted that such a reaction at the interface between the positive electrode active material and the solid electrolyte is particularly large when the load on the all-solid-state secondary battery is large (for example, when the all-solid-state secondary battery is charged to a higher voltage, or all. It tends to have high resistance when discharging a solid-state secondary battery with a large current.

As an invention for solving the above problems, an invention in which the surface of positive electrode active material particles is covered with a coating layer has been proposed. For example, _{an invention in which positive electrode active material particles are coated with Li 2} O-P ₂ O _5- Nb ₂ O _5- B ₂ O _3- GeO ₂ system glass (Patent Document 1), positive electrode active material particles are an amorphous carbon film. (Patent Document 2), an invention in which positive electrode active material particles are coated with a solid electrolyte (Patent Document 3), and an invention in which positive electrode active material particles are coated with an oxide-based material containing lithium zirconium oxide (Patent Document 4). ), An invention in which the positive electrode active material particles are coated with an inorganic material containing a tungsten element (Patent Document 5), and an invention in which the positive electrode active material particles are coated with a Li ion conductive oxide having a BO-Si structure (Patent Document 6). ), The invention in which the positive electrode active material particles are coated with glass containing at least one of V and P or Te (Patent Document 7). in covering, the covering layer _PO ⁴ _3-, ^{SiO 4} _4-, invention to a material having a _GeO ^{4 4-and} _BO ^{3 3-} at least one polyanion structure (Patent Document 8), a positive electrode active material particles _{An invention of coating Li 4} SiO _{4- Li 3} BO ₃ and LiNbO ₃ which are Li ion conductive oxides (Patent Document 9), an invention of coating positive electrode active material particles with Li ₃ BO ₃ (Patent Document 10), a positive electrode An invention in which active material particles are coated with a lithium ion conductive oxide (Li and Ti-containing system) (Patent Document 11), an element in which the coating layer for coating positive positive material particles is highly reactive with sulfide-based solid electrolyte particles. An invention containing (Al, Co, Mn, Mg) (Patent Document 12), and an invention in which positive electrode active material particles are coated with an oxide having a 4-coordination structure containing Group 13 elements (Al, B, Ga) (Patent Document 13). ) Etc. have already been reported.

In the inventions disclosed in Patent Documents 1 to 13, the coating layer has a one-layer structure. Patent Documents 14 to 15 disclose a coating layer having a two-layer structure. Specifically, Patent Document 14 discloses an invention in which the first lithium ion conductor is a coating layer on the lower layer side and the second lithium ion conductor is a coating layer on the upper layer side. The lithium ion conductivity of the first lithium ion conductor is 1 × 10 ^-7 S / cm or more, and the second lithium ion conductor is at least one of B, Si, P, Ti, Zr, Al and W. It is composed of a Li-containing compound having a polyanion structure having. Patent Document 15 discloses an invention in which the coating layer on the lower layer side (the side closer to the positive electrode active material particles) is composed of amorphous carbon, and the coating layer on the upper layer side is composed of a lithium-containing oxide.

Japanese Unexamined Patent Publication No. 2016-81822 Japanese Unexamined Patent Publication No. 2015-88383 Japanese Unexamined Patent Publication No. 2015-201372 Japanese Unexamined Patent Publication No. 2014-116149 International Publication No. 2012/1005048 International Publication No. 2012/157119 International Publication No. 2014/0133837 Patent No. 5455766 Patent No. 5578280 Japanese Unexamined Patent Publication No. 2012-89406 International Publication No. 2007/004590 Japanese Unexamined Patent Publication No. 2016-024907 Patent No. 5551880 Japanese Unexamined Patent Publication No. 2016-103411 Patent No. 5737415

However, in the inventions disclosed in Patent Documents 1 to 14, the characteristics of the all-solid-state secondary battery could not be sufficiently enhanced. Therefore, it is presumed that these inventions cannot sufficiently suppress the reaction at the interface between the sulfide-based solid electrolyte and the positive electrode active material. Further, although the invention disclosed in Patent Document 15 contributes to the improvement of solid-state battery characteristics, the blast method, the aerosol deposition method, and the cold spray method (aerosol deposition method) are used when coating the amorphous carbon film. Since it is necessary to use a time-consuming film forming method such as a cold spray method, a sputtering method, a CVD method, and a thermal spraying method, there is a problem that the productivity is not sufficient.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to further improve the characteristics of the all-solid-state secondary battery and to improve the productivity, which is new and improved. It is an object of the present invention to provide a positive electrode active material for an all-solid-state secondary battery, a positive-side active material layer for an all-solid-state secondary battery, and an all-solid-state secondary battery.

In order to solve the above problems, according to a certain viewpoint of the present invention, the positive electrode active material particles, the first coating layer that coats the surface of the positive electrode active material particles, and the first coating layer that covers the surface of the first coating layer. The first coating layer comprises two coating layers, and the first coating layer contains any one or more selected from the group consisting of the first lithium-containing oxide and the lithium-containing phosphor oxide, and the first lithium-containing oxidation. The substance contains at least one selected from the group consisting of zirconium element, niobium element, titanium element, and aluminum element, and the lithium-containing phosphor oxide is any one selected from zirconium element and titanium element. Including the above, the second coating layer contains a second lithium-containing oxide containing any one selected from the group consisting of germanium element, niobium element, and gallium element, and includes the first coating layer and the first coating layer. Provided is a positive electrode active material for an all-solid secondary battery, which is characterized in that the composition of the coating layer 2 is different from that of the coating layer.

According to the above viewpoint of the present invention, the positive electrode active material particles are coated with the first coating layer and the second coating layer. The first coating layer and the second coating layer have a specific composition. This makes it possible to suppress the reaction that occurs at the interface between the positive electrode active material particles and the solid electrolyte. Further, the first coating layer and the second coating layer can be easily produced because they can be produced by applying the alkoxide constituting these coating layers to the surface of the positive electrode active material particles and firing them. Therefore, the productivity is also good.

Here, the first lithium-containing oxide may be any one or more selected from the group consisting of lithium zirconium oxide, lithium niobium oxide, lithium titanium oxide, and lithium aluminum oxide.

From this point of view, the reaction occurring at the interface between the positive electrode active material particles and the solid electrolyte can be further suppressed.

Further, the lithium zirconium oxide may have a composition represented by aLi ₂ O-ZrO ₂ (0.1 ≦ a ≦ 2.0).

From this point of view, the reaction occurring at the interface between the positive electrode active material particles and the solid electrolyte can be further suppressed.

Further, the lithium-containing phosphor oxide may be any one or more selected from the group consisting of lithium zirconium phosphorus oxide and lithium titanium phosphorus oxide.

From this point of view, the reaction occurring at the interface between the positive electrode active material particles and the solid electrolyte can be further suppressed.

Further, the second lithium-containing oxide may be any one or more selected from the group consisting of lithium germanium oxide, lithium niobium oxide, and lithium gallium oxide.

From this point of view, the reaction occurring at the interface between the positive electrode active material particles and the solid electrolyte can be further suppressed.

Further, the average secondary particle size of the positive electrode active material particles may be 10 μm or less.

From this point of view, the characteristics of the all-solid-state secondary battery can be further improved.

Further, the positive electrode active material particles may be a lithium salt of a transition metal oxide having a layered rock salt type structure.

From this point of view, the characteristics of the all-solid-state secondary battery can be further improved.

Also, the positive electrode active material particles _may be LiNi _x Co y _Al z _{O 2} or LiNi _x Co _y Mn _z O lithium salt ternary transition metal oxides represented by _2.

From this point of view, the characteristics of the all-solid-state secondary battery can be further improved.

According to another aspect of the present invention, there is provided a positive electrode active material layer for an all-solid-state secondary battery, which comprises the above-mentioned positive electrode active material for an all-solid-state secondary battery.

From this viewpoint, a positive electrode active material layer in which the reaction occurring at the interface between the positive electrode active material particles and the solid electrolyte is suppressed is provided.

According to another aspect of the present invention, there is provided an all-solid-state secondary battery, which comprises the above-mentioned positive electrode active material layer for an all-solid-state secondary battery.

From this viewpoint, an all-solid-state secondary battery in which the reaction occurring at the interface between the positive electrode active material particles and the solid electrolyte is suppressed is provided.

Here, a sulfide-based solid electrolyte may be contained.

From this viewpoint, the reaction occurring at the interface between the positive electrode active material particles and the sulfide-based solid electrolyte can be suppressed.

As described above, according to the present invention, the positive electrode active material particles are coated with the first coating layer and the second coating layer. The first coating layer and the second coating layer have a specific composition. This makes it possible to suppress the reaction that occurs at the interface between the positive electrode active material particles and the solid electrolyte. Further, the first coating layer and the second coating layer can be easily produced because they can be produced by applying the alkoxide constituting these coating layers to the surface of the positive electrode active material particles and firing them. Therefore, the productivity is also good.

It is sectional drawing which shows typically the layer structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the structure of the positive electrode particle which concerns on the same embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

<1. Overview of all-solid-state rechargeable batteries ＞
The all-solid-state secondary battery according to the embodiment of the present invention is a secondary battery using a solid electrolyte as an electrolyte. Further, the all-solid-state secondary battery according to the present embodiment is a so-called all-solid-state lithium ion secondary battery in which lithium ions move between the positive electrode and the negative electrode.

Here, since the positive electrode active material and the electrolyte are solid in the all-solid secondary battery using the solid electrolyte, the electrolyte is introduced into the positive electrode active material as compared with the lithium ion secondary battery using the organic solvent as the electrolyte. Is hard to penetrate. Therefore, in the all-solid-state secondary battery, the area of the interface between the positive electrode active material and the electrolyte tends to be small, and it is necessary to sufficiently secure the movement path of lithium ions and electrons between the positive electrode active material and the solid electrolyte. ..

Therefore, for example, a technique has been proposed in which the area of the interface between the positive electrode active material and the solid electrolyte is increased by forming the positive electrode layer as a mixed layer of the positive electrode active material and the solid electrolyte.

However, when a sulfide-based solid electrolyte is used, repeated charging and discharging may cause a reaction at the interface between the positive electrode active material and the solid electrolyte to generate a resistance component. When such a resistance component is generated, the interfacial resistance between the positive electrode active material and the solid electrolyte increases. It should be noted that such a reaction at the interface between the positive electrode active material and the solid electrolyte is particularly large when the load on the all-solid-state secondary battery is large (for example, when the all-solid-state secondary battery is charged to a higher voltage, or all. It tends to have high resistance when discharging a solid-state secondary battery with a large current.

Therefore, in an all-solid secondary battery using a sulfide-based solid electrolyte, it has been required to suppress the formation of a resistance component at the interface between the positive electrode active material and the solid electrolyte.

The present inventor has a reaction in which the positive electrode active material deteriorates (for example, the valence of the transition metal element contained in the positive electrode active material fluctuates) and a reaction in which the solid electrolyte deteriorates at the interface between the positive electrode active material and the solid electrolyte. I speculated that there is a possibility that Therefore, the present inventor has studied coating the positive electrode active material particles with a coating layer for suppressing the deterioration of the positive electrode active material and a coating layer for suppressing the reaction in which the solid electrolyte deteriorates. I came up with an all-solid-state secondary battery related to the form.

In the all-solid-state secondary battery 1 according to the present embodiment, the surface of the positive electrode active material particles 101 is coated with the first coating layer 102, and the surface of the first coating layer 102 is coated with the second coating layer 103. Here, as shown in Examples described later, if the stacking order of the first coating layer 102 and the second coating layer 103 is changed, the characteristics of the all-solid-state secondary battery 1 are deteriorated. From this, it is presumed that the first coating layer 102 mainly suppresses the deterioration of the positive electrode active material particles 101, and the second coating layer 103 mainly suppresses the deterioration of the solid electrolyte 300. Further, the first coating layer 102 and the second coating layer 103 suppress the direct contact between the positive electrode active material particles 101 and the solid electrolyte 300. Therefore, it is possible to suppress the formation of a resistance component at the interface between the positive electrode active material particles 101 and the solid electrolyte 300. Further, the first coating layer 102 and the second coating layer 103 are made of a material having lithium ion conductivity. Therefore, the first coating layer 102 and the second coating layer 103 can secure a movement path of lithium ions between the positive electrode active material particles 101 and the solid electrolyte 300, and the battery of the all-solid-state secondary battery 1 can be secured. The characteristics can be improved.

<2. Configuration of all-solid-state secondary battery>
Next, the configuration of the all-solid-state secondary battery according to the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view schematically showing the layer structure of the all-solid-state secondary battery 1 according to the present embodiment. Further, FIG. 2 is a cross-sectional view schematically showing the configuration of the positive electrode active material 100 of the all-solid-state secondary battery 1 according to the present embodiment.

As shown in FIG. 1, the all-solid-state secondary battery 1 has a structure in which a positive electrode layer 10, a negative electrode layer 20, and a solid electrolyte layer 30 located between the positive electrode layer 10 and the negative electrode layer 20 are laminated.

(Positive electrode layer)
The positive electrode layer 10 contains a positive electrode active material 100 and a solid electrolyte 300. Further, the positive electrode layer 10 may further contain a conductive auxiliary agent in order to supplement the electron conductivity. The solid electrolyte 300 will be described later in the solid electrolyte layer 30.

Here, as shown in FIG. 2, the positive electrode active material 100 further covers the positive electrode active material particles 101, the first coating layer 102 that covers the surface of the positive electrode active material particles 101, and the first coating layer 102. A second coating layer 103 is provided.

(Positive electrode active material particles)
The positive electrode active material particles 101 are formed of a positive electrode active material that has a higher charge / discharge potential than the negative electrode active material contained in the negative electrode particles 200, which will be described later, and can reversibly occlude and release lithium ions.

For example, the positive electrode active material particles 101 include lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA), and lithium nickel cobalt manganate (hereinafter referred to as NCA). It can be formed by using lithium salts such as NCM), lithium manganate, lithium iron oxide, nickel sulfide, copper sulfide, sulfur, iron oxide, vanadium oxide and the like. These positive electrode active materials may be used alone or in combination of two or more.

Further, the positive electrode active material particles 101 are preferably formed by containing the lithium salt of the transition oxide having a layered rock salt type structure among the above-mentioned lithium salts. Here, "layered" represents a thin sheet-like shape. The "rock salt type structure" represents a sodium chloride type structure which is one of the crystal structures. Specifically, the face-centered cubic lattice formed by each of the cations and anions is a unit cell of each other. Represents a structure that is offset by 1/2 of the ridge.

The lithium salt of a transition oxides having such a layered rock-salt structure, for _{example, LiNi x Co y Al z O} 2 (NCA), or _{LiNi x Co y Mn z O 2} (NCM) ( however, 0 <x Examples thereof include lithium salts of ternary transition oxides such as <1, 0 <y <1, 0 <z <1, and x + y + z = 1).

When the positive electrode active material particles 101 contain the lithium salt of the ternary transition oxide having the above-mentioned layered rock salt type structure, the energy density and thermal stability of the all-solid-state secondary battery 1 can be improved. ..

Here, in the positive electrode active material 100 according to the present embodiment, the reaction between the positive electrode active material particles 101 and the solid electrolyte 300 is suppressed by the first coating layer 102 and the second coating layer 103, so that the all-solid secondary is secondary. The battery characteristics of the battery 1 can be further improved.

Further, when the positive electrode active material particles 101 are formed of a lithium salt of a ternary transition oxide such as NCA or NCM and contain nickel (Ni) as the positive electrode active material, the capacity of the all-solid-state secondary battery 1 The density can be increased and metal elution from the positive electrode active material in the charged state can be reduced. Thereby, the all-solid-state secondary battery 1 according to the present embodiment can improve the long-term reliability and the cycle characteristics in the charged state.

Here, examples of the shape of the positive electrode active material particles 101 include particle shapes such as a true spherical shape and an elliptical spherical shape. The average secondary particle size of the positive electrode active material particles 101 is, for example, preferably 20 μm or less, and more preferably 10 μm or less. The lower limit of the average secondary particle size is not particularly limited, but may be, for example, 0.1 μm or more. The "average particle secondary diameter" represents the number average diameter (D50) in the particle size distribution of the particles obtained by the scattering method or the like, and can be measured by a particle size distribution meter or the like.

The content of the positive electrode active material particles 101 in the positive electrode layer 10 is, for example, preferably 10% by mass or more and 99% by mass or less, and more preferably 20% by mass or more and 90% by mass or less.

(First coating layer)
The first coating layer 102 coats the surface of the positive electrode active material particles 101. In particular, in the present embodiment, by forming the first coating layer 102 with the materials listed below, the reaction occurring at the interface between the positive electrode active material particles 101 and the solid electrolyte 300 is suppressed. In particular, it is presumed that the reaction in which the positive electrode active material particles 101 deteriorate is suppressed. Further, the first coating layer 102 has lithium ion conductivity.

The first coating layer 102 contains any one or more selected from the group consisting of the first lithium-containing oxide and the lithium-containing phosphorus oxide. Here, the first lithium-containing oxide contains at least one selected from the group consisting of zirconium element, niobium element, titanium element, and aluminum element, and the lithium-containing phosphor oxide contains zirconium element and titanium. Includes any one or more selected from the elements.

Examples of the first lithium-containing oxide include lithium zirconium oxide (Li-Zr-O), lithium niobium oxide (Li-Nb-O), lithium titanium oxide (Li-Ti-O), and lithium. Examples thereof include aluminum oxide (Li—Al—O). The first lithium-containing oxide may be composed of any one or more of these.

Here, the lithium zirconium oxide has a composition represented by, for example, aLi ₂ O-ZrO ₂ (0.1 ≦ a ≦ 2.0). aLi ₂ O-ZrO ₂ (hereinafter, also referred to as LZO) is a composite oxide of _{Li 2} O and ZrO _2. Since LZO is chemically stable, _{by forming the first coating layer 102 with such aLi 2} O-ZrO ₂ , the reaction between the positive electrode active material particles 101 and the solid electrolyte 300 is further increased. It can be suppressed. The range of a is preferably 0.1 ≦ a ≦ 2.0. By setting a in the above range, it is possible to further improve the battery characteristics of the all-solid-state secondary battery 1. Therefore, the first coating layer 102 is preferably composed of LZO.

Here, when the first coating layer 102 is composed of LZO, the molar ratio of LZO to the positive electrode active material particles 101 (that is, the coating amount of LZO) is preferably 0.1 mol% or more and 2.0 mol% or less. .. When the coating amount of LZO is in the above range, the discharge capacity and the load characteristics can be further improved. On the other hand, when the coating amount of LZO is less than 0.1 mol%, the effect of suppressing the reaction between the positive electrode active material particles 101 and the solid electrolyte 300 may not be sufficient, which is not preferable. Further, when the coating amount of LZO exceeds 2.0 mol%, the lithium ion conductivity between the positive electrode active material particles 101 and the solid electrolyte 300 may decrease, which is not preferable.

Examples of the lithium-containing phosphor oxide include lithium zirconium phosphor oxide (Li-Zr-PO ₄ ) and lithium titanium phosphor oxide (Li-Ti-PO ₄ ). The lithium-containing phosphor oxide may be composed of any one or more of these.

The thickness of the first coating layer 102 is preferably 1 nm or more and 50 nm or less, and more preferably 5 nm or more and 30 nm or less. When the thickness of the first coating layer 102 is included in the above range, the characteristics of the all-solid-state secondary battery 1 can be improved without lowering the conductivity of lithium ions. On the other hand, when the thickness of the first coating layer 102 is less than 1 nm, the reaction between the positive electrode active material particles 101 and the solid electrolyte 300 may not be sufficiently suppressed. Further, when the thickness of the first coating layer 102 exceeds 50 nm, the lithium ion conductivity between the positive electrode active material particles 101 and the solid electrolyte 300 may decrease.

The thickness of the first coating layer 102 described above can be measured using, for example, a cross-sectional image obtained by a transmission electron microscope (TEM) or the like. The same applies to the thickness of the second coating layer 103.

(Second coating layer)
The second coating layer 103 covers the surface of the first coating layer 102. In particular, in the present embodiment, by forming the second coating layer 103 with the materials listed below, the reaction occurring at the interface between the positive electrode active material particles 101 and the solid electrolyte 300 is suppressed. In particular, it is presumed that the reaction in which the solid electrolyte 300 deteriorates is suppressed. Further, the second coating layer 103 has lithium ion conductivity.

The second coating layer 103 contains a second lithium-containing oxide containing any one selected from the group consisting of germanium element, niobium element, and gallium element.

Examples of the second lithium-containing oxide include lithium germanium oxide (Li-Ge-O), lithium niobium oxide (Li-Nb-O), and lithium gallium oxide (Li-Ga-O). Can be mentioned. The second lithium-containing oxide may be composed of any one or more of these.

Here, the compositions of the first coating layer 102 and the second coating layer 103 are different from each other. As a result, the characteristics of the all-solid-state secondary battery 1 are further improved.

The total thickness of the first coating layer 102 and the second coating layer 103 is preferably 1 nm or more and 500 nm or less, and more preferably 15 nm or more and 70 nm or less. When the total thickness of the first coating layer 102 and the second coating layer 103 is included in the above range, the reaction between the positive electrode active material particles 101 and the solid electrolyte 300 is further carried out without lowering the conductivity of lithium ions. It can be suppressed. On the other hand, when the total thickness of the first coating layer 102 and the second coating layer 103 is less than 1 nm, the effect of suppressing the reaction between the positive electrode active material particles 101 and the solid electrolyte 300 may not be sufficient. Not preferred. Further, when the total thickness of the first coating layer 102 and the second coating layer 103 exceeds 500 nm, the lithium ion conductivity between the positive electrode active material particles 101 and the solid electrolyte 300 may decrease. Not preferred.

In the above, the first coating layer 102 and the second coating layer 103 may cover at least a part of the positive electrode active material particles 101. That is, the entire surface of the positive electrode active material particles 101 may be coated with the first coating layer 102 and the second coating layer 103, and a part of the surface of the positive electrode active material particles 101 is the first coating layer. It may be coated with 102 and a second coating layer 103.

Further, in addition to the above-mentioned positive electrode active material 100 and solid electrolyte 300, additives such as a conductive agent, a binder, a filler, a dispersant, and an ionic conductive agent are appropriately blended in the positive electrode layer 10. May be.

Examples of the conductive agent that can be blended in the positive electrode layer 10 include graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, and the like. Examples of the binder that can be blended in the positive electrode layer 10 include polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and the like. Further, as the filler, dispersant, ion conductive agent and the like that can be blended in the positive electrode layer 10, known materials generally used for electrodes of lithium ion secondary batteries can be used.

(Negative electrode layer)
As shown in FIG. 1, the negative electrode layer 20 includes negative electrode particles 200 and a solid electrolyte 300. The solid electrolyte 300 will be described later in the solid electrolyte layer 30.

The negative electrode particles 200 are negative electrode active material materials having a lower charge / discharge potential than the positive electrode active material contained in the positive electrode active material particles 101 and capable of alloying with lithium or reversibly storing and releasing lithium. It is composed.

For example, as the negative electrode active material, a metal active material, a carbon active material, or the like can be mentioned. Examples of the metal active material include metals such as lithium (Li), indium (In), aluminum (Al), tin (Sn), and silicon (Si), alloys thereof, and the like. Examples of the carbon active material include artificial graphite, graphite carbon fiber, resin calcined carbon, thermally decomposed vapor-grown carbon, coke, mesocarbon microbeads (MCMB), and furfuryl alcohol resin calcined. Examples thereof include carbon, polyacene, pitch-based carbon fibers, vapor-grown carbon fibers, natural graphite, and non-graphitizable carbon. These negative electrode active materials may be used alone or in combination of two or more.

Further, in addition to the above-mentioned negative electrode particles 200 and the solid electrolyte 300, the negative electrode layer 20 may appropriately contain additives such as a conductive agent, a binder, a filler, a dispersant, and an ionic conductive agent. ..

As the additive to be blended in the negative electrode layer 20, the same additives as those blended in the positive electrode layer 10 described above can be used.

(Solid electrolyte layer)
The solid electrolyte layer 30 is formed between the positive electrode layer 10 and the negative electrode layer 20 and contains the solid electrolyte 300.

The solid electrolyte 300 is composed of a sulfide-based solid electrolyte material. The sulfide-based solid electrolyte material, for _{example, Li 2 S-P 2 S} 5, Li 2 S-P 2 S 5 -LiX (X is halogen, e.g. _{I, Cl), 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, Li2 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 (m, n are positive numbers, Z is either Ge, Zn or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS _{2 -Li 3} PO ₄ , Li ₂ S-SiS _{2-Li p} MO _q (p, q are positive numbers, M is any of P, Si, Ge, B, Al, Ga or In) and the like can be mentioned. Here, in the sulfide-based solid electrolyte material, the starting material (for example, Li ₂ S, P ₂ S _5, etc.) of the sulfide-based solid electrolyte material is treated by a melt quenching method, a mechanical milling method, or the like. Made in. Further, after these treatments, further firing may be performed.

Further, in the solid electrolyte 300, of the above sulfide solid electrolyte material, sulfur (S) as at least an element, it is preferable to use a material containing phosphorus (P) and lithium (Li), in particular Li 2 _S-P it is more preferable to use those containing ₂ S _5.

_{Here, when a material containing Li 2} SP ₂ S ₅ is used as the sulfide solid electrolyte material forming the solid electrolyte 300, _{the mixed molar ratio of Li 2} S and P ₂ S ₅ is, for example, Li ₂ S. : P ₂ S ₅ = 50:50 to 90:10 is selected.

Further, as the shape of the solid electrolyte 300, for example, a particle shape such as a true spherical shape or an elliptical spherical shape can be mentioned. The particle size of the solid electrolyte 300 is not particularly limited, but the average secondary particle size of the solid electrolyte 300 is preferably 0.01 μm or more and 30 μm or less, and more preferably 0.1 μm or more and 20 μm or less. .. As described above, the average secondary particle diameter represents the number average diameter (D50) in the particle size distribution of the particles obtained by the scattering method or the like.

The configuration of the all-solid-state secondary battery 1 according to the present embodiment has been described in detail above.

<2. Lithium-ion secondary battery manufacturing method>
Subsequently, a method for manufacturing the all-solid-state secondary battery 1 according to the present embodiment will be described. The all-solid-state secondary battery 1 according to the present embodiment can be manufactured by manufacturing the positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30, respectively, and then laminating each of the above layers.

(Preparation of positive electrode layer)
First, the positive electrode active material 100 is produced by forming the first coating layer 102 and the second coating layer 103 in order on the surface of the positive electrode active material particles 101.

The positive electrode active material particles 101 can be produced by a known method. For example, when NCA is used as the positive electrode active material particles 101, first, Ni (OH) ₂ powder, Co (OH) ₂ powder, and Al ₂ O ₃ · H ₂ O powder so as to have the same composition ratio as the generated NCA. and LiOH · _{H 2} O powder were mixed and pulverized by a ball mill (ball mill) and the like. Next, the mixed and crushed raw material powder is mixed with a predetermined dispersant, binder and the like to adjust the viscosity and the like, and then molded on a sheet. Further, the positive electrode active material particles 101 can be produced by firing the sheet-shaped molded body at a predetermined temperature and pulverizing the fired molded body with a sieve or the like. Here, the particle size of the positive electrode active material particles 101 can be adjusted by changing the fineness of the sieve used for crushing the molded product.

Subsequently, the first coating layer 102 and the second coating layer 103 are sequentially formed on the surface of the positive electrode active material particles 101 produced above. The first coating layer 102 is formed on the surface of the positive electrode active material particles 101 by, for example, the following method. That is, the solution is prepared by stirring and mixing the metal element alkoxide (alkoxide) constituting the first coating layer 102 in a solvent such as alcohol. Then, the prepared solution is sprayed on the surface of the positive electrode active material particles 101 and dried. The spraying can be performed by, for example, a rolling fluidized bed granulation / coating machine FD-MP-01E manufactured by Paulec Co., Ltd. Then, the positive electrode active material particles 101 that have been sprayed and dried with the solution are fired. By the above steps, the first coating layer 102 is formed on the surface of the positive electrode active material particles 101. The second coating layer 103 is formed on the first coating layer 102 in the same manner as the first coating layer 102. The first coating layer 102 and the second coating layer 103 may be produced by a method other than the method described above.

By the above method, the positive electrode active material 100 sequentially coated with the first coating layer 102 and the second coating layer 103 can be produced.

Subsequently, the prepared positive electrode active material 100, the solid electrolyte 300 prepared by the method described later, and various additives are mixed and added to a solvent such as water or an organic solvent to form a slurry or paste. To form. Further, the positive electrode layer 10 can be obtained by applying the obtained slurry or paste to a current collector, drying it, and then rolling it.

(Preparation of negative electrode layer)
The negative electrode layer 20 can be produced in the same manner as the positive electrode layer. Specifically, the negative electrode particles 200, the solid electrolyte 300 produced by the method described later, and various additives are mixed and added to a solvent such as water or an organic solvent to form a slurry or paste. Further, the negative electrode layer 20 can be obtained by applying the obtained slurry or paste to a current collector, drying it, and then rolling it. The negative electrode particles 200 can be produced by a known method using a negative electrode active material.

Here, examples of the current collector used in the positive electrode layer 10 and the negative electrode layer 20 include indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), and the like. A plate-like body or a foil-like body made of cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li) or an alloy thereof can be used. Even if the positive electrode layer 10 or the negative electrode layer 20 is formed by compacting and molding a mixture of the positive electrode active material 100 or the negative electrode particles 200 and various additives into a pellet shape without using a current collector. good.

(Preparation of solid electrolyte layer)
The solid electrolyte layer 30 can be made of a solid electrolyte 300 formed of a sulfide-based solid electrolyte material.

First, the starting raw material is processed by a melt quenching method or a mechanical milling method.

For example, when the melt quenching method is used, starting materials (for example, Li ₂ S, P ₂ S _5, etc.) are mixed in a predetermined amount, and the pellets are reacted in a vacuum at a predetermined reaction temperature and then quenched. By doing so, a sulfide-based solid electrolyte material can be produced. The reaction temperature of the mixture of Li ₂ S and P ₂ S ₅ is preferably 400 ° C. to 1000 ° C., more preferably 800 ° C. to 900 ° C. The reaction time is preferably 0.1 hour to 12 hours, more preferably 1 hour to 12 hours. Further, the quenching temperature of the reaction product is usually 10 ° C. or lower, preferably 0 ° C. or lower, and the quenching rate is usually about 1 ° C./sec to 10000 ° C./sec, preferably 1 ° C./sec to 1000 ° C. It is about ° C./sec.

When the mechanical milling method is used, a sulfide-based solid electrolyte material can be produced by stirring and reacting the starting raw materials (for example, Li ₂ S, P ₂ S _{5, etc.) using a ball mill or the like.} .. The stirring speed and stirring time in the mechanical milling method are not particularly limited, but the faster the stirring speed, the faster the production rate of the sulfide-based solid electrolyte material, and the longer the stirring time, the more the sulfide-based solid electrolyte material. The conversion rate of the raw material of the above can be increased.

Then, the mixed raw material obtained by the melt quenching method or the mechanical milling method is heat-treated at a predetermined temperature and then pulverized to produce a particulate solid electrolyte 300.

Subsequently, the solid electrolyte 300 obtained by the above method is subjected to, for example, a blast method, an aerosol deposition method, a cold spray method, a sputtering method, a CVD method, a thermal spraying method, or the like. The solid electrolyte layer 30 can be produced by forming a film using a known film forming method. The solid electrolyte layer 30 may be produced by pressurizing the solid electrolyte 300 alone. Further, the solid electrolyte layer 30 may be formed by mixing the solid electrolyte 300 with a solvent, a binder or a support and pressurizing the solid electrolyte layer 30. Here, the binder or the support is added for the purpose of reinforcing the strength of the solid electrolyte layer 30 and preventing a short circuit of the solid electrolyte 300.

(Manufacturing of lithium-ion secondary batteries)
Further, the positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30 produced by the above method are laminated and pressurized so as to sandwich the solid electrolyte layer 30 between the positive electrode layer 10 and the negative electrode layer 20. The all-solid secondary battery 1 according to the embodiment can be manufactured.

(Example 1)
(Preparation of positive electrode active material)
_{LiNi 0.8} Co _0.1 Mn _0.1 O ₂ (NCM) was prepared as the positive electrode active material particles 101. The average secondary particle size of the positive electrode active material particles 101 was measured by the scattering method and found to be 7 μm. Then, a surface coating treatment was performed using a mixed solution of lithium methoxide, zirconium propoxide, and ethanol. Specifically, the mixed solution of the above NCM was adjusted so that the coating amount _{of Li 2} O-ZrO _{2 (LZO) with respect to the NCM was 0.5 mol%.} Then, the surface of the positive electrode active material particles 101 was coated with the mixed solution using a rolling fluidized bed granulator / coating machine FD-MP-01E manufactured by Paulec Co., Ltd. Specifically, the conditions are that the mass of the positive electrode active material particles 101 is 500 g, the supply air temperature is 90 ° C., the supply air volume is 0.23 m3 / h, the rotor rotation speed is 400 rpm, the admise air volume is 50 NL / min, and the spray speed is about 5 g / min. The above mixed solution was sprayed on the surface of the positive electrode active material particles 101. Then, the positive electrode active material particles 101 coated with the mixed solution were dried. The coating particles obtained by the above surface coating treatment were fired at 350 ° C. for 1 hour in an air atmosphere to form a first coating layer 102 made of LZO on the surface of the positive electrode active material particles 101.

Then, a mixed solution of lithium methoxyde and germanium propoxide and ethanol was prepared. Specifically, the coverage of _{Li 2 O-GeO 2 (LGeO} ) for NCM was adjusted mixed solution to a 0.5 mol%. Then, a second coating layer 103 made of LGeO was formed on the first coating layer 102 by the same treatment as described above. Through the above steps, a positive electrode active material 100 in which the first coating layer 102 and the second coating layer 103 are coated on the positive electrode active material particles 101, that is, a double layer layer coated positive electrode active material is obtained. Next, when some positive electrode active materials were observed using a cross-sectional image or the like with a transmission electron microscope, the thickness of the first coating layer 102 was in the range of 5 to 30 μm, and the first coating was found to be in the range of 5 to 30 μm. The total thickness of the layer 102 and the second coating layer 103 was in the range of 15 to 70 μm.

(Manufacturing of all-solid-state secondary battery)
_{First, the reagents Li 2} S, P ₂ S ₅ , and Li Cl, which are the starting materials of the sulfide-based electrolyte material, were weighed so as to have the target composition of Li ₆ PS _{5 Cl.} Then, a mechanical milling treatment was performed in which these reagents were mixed in a planetary ball for 20 hours. The mechanical milling treatment was performed at a rotation speed of 380 rpm, at room temperature, and in an argon atmosphere.

_{A powder sample having a Li 6} PS ₅ Cl composition obtained by the above mechanical milling treatment was pressed (pressure 400 MPa / cm ² ) to obtain pellets having a diameter of 13 mm and a thickness of about 0.8 mm. The obtained pellets were covered with gold leaf and further placed in a carbon crucible to prepare a sample for heat treatment. The obtained heat treatment sample was vacuum-sealed in a quartz glass tube. Then, the heat treatment sample was placed in an electric furnace, and the temperature inside the electric furnace was raised from room temperature to 550 ° C. at 1.0 ° C./min. Then, the heat treatment sample was heat-treated at 550 ° C. for 6 hours. Then, the heat treatment sample was cooled to room temperature at 1.0 ° C./min. The recovered sample after heat treatment was crushed in an agate mortar. The crushed sample was diffracted by X-ray crystal, and it was confirmed that the target Argyrodite crystal was produced. Then, the sample after this heat treatment was used as the solid electrolyte 300.

Then, the positive electrode active material 100, the solid electrolyte 300, and the carbon nanofiber (CNF) which is a conductive agent prepared above were mixed at a mass ratio of 83:15: 3 to prepare a positive electrode mixture. A metal Li foil (thickness 30 μm) was used as the negative electrode. The positive electrode mixture (10 mg), solid electrolyte 300 (150 mg), and metal Li negative electrode were laminated in this order and ^{pressurized at a pressure of 3 ton / cm 2} to obtain a test cell.

(Load characteristic evaluation)
The obtained test cell was charged at 25 ° C. with a constant current of 0.05 C to an upper limit voltage of 4.0 V, and then discharged to a discharge end voltage of 2.5 V with a constant current of 0.05 C. Then, the capacity at the time of discharge was measured, and this was used as the initial discharge capacity. Then, the test cell was discharged at 0.05C, 0.5C, and 1C, respectively, and the rate characteristics were measured. Then, the ratio of the 1C discharge capacity to the initial discharge capacity was used as an index of the load characteristics. It can be said that the higher this value is, the smaller the internal resistance of the battery is and the better the load characteristics are.

(Cycle life test)
The obtained test cell was charged at 25 ° C. with a constant current of 0.05 C to an upper limit voltage of 4.0 V, and a charge / discharge cycle of 0.5 C discharge to a discharge end voltage of 2.5 V was repeated for 50 cycles. Then, the ratio of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was defined as the retention rate of the discharge capacity. The retention rate of the discharge capacity is a parameter indicating the cycle characteristics, and the larger this value is, the better the cycle characteristics are. The results are summarized in Table 1. The unit of "initial discharge capacity" shown in Tables 1 to 4 is "mAh / g".

(Example 2)
(Preparation of positive electrode active material)
The NCM used in Example 1 was prepared as the positive electrode active material particles 101. Then, the first coating layer 102 made of LZO was formed on the surface of the positive electrode active material particles 101 by the same treatment as in Example 1.

Then, a mixed solution of lithium methoxydo and niobium ethanolide and ethanol was prepared. Specifically, the mixed solution was adjusted so that the coating amount _{of Li 2} O-Nb ₂ O _{5 (LNbO) with respect to NCM was 0.5 mol%.} Then, the second coating layer 103 made of LNbO was formed on the first coating layer 102 by the same treatment as in Example 1. Next, when some positive electrode active materials were observed using a cross-sectional image or the like with a transmission electron microscope, the thickness of the first coating layer 102 was in the range of 5 to 30 μm, and the first coating was found to be in the range of 5 to 30 μm. The total thickness of the layer 102 and the second coating layer 103 was in the range of 15 to 70 μm. Then, a test cell was prepared by the same treatment as in Example 1, and the load characteristics and cycle life were evaluated. The results are summarized in Table 1.

(Comparative Example 1)
The same treatment as in Example 1 was performed except that the second coating layer 103 was not formed. That is, in Comparative Example 1, only the coating layer made of LZO was formed on the surface of the positive electrode active material particles 101. The results are summarized in Table 1.

(Comparative Example 2)
The same treatment as in Example 1 was performed except that the first coating layer 102 was not formed. That is, in Comparative Example 2, only the coating layer made of LGeO was formed on the surface of the positive electrode active material particles 101. The results are summarized in Table 1.

(Comparative Example 3)
The NCM used in Example 1 was prepared as the positive electrode active material particles 101. Then, the first coating layer 102 made of LGeO was formed on the surface of the positive electrode active material particles 101 by the same treatment as in Example 1. Then, a second coating layer 103 made of LZO was formed on the first coating layer 102 by the same treatment as in Example 1. Then, a test cell was prepared by the same treatment as in Example 1, and the load characteristics and cycle life were evaluated. The results are summarized in Table 1.

(Comparative Example 4)
The NCM used in Example 1 was prepared as the positive electrode active material particles 101. Then, the first coating layer 102 made of LNbO was formed on the surface of the positive electrode active material particles 101 by the same treatment as in Example 2. Then, a mixed solution of lithium methoxyde and titanium isopropoxide and ethanol was prepared. Specifically, the mixed solution was adjusted so that the coating amount _{of Li 2} Ti ₂ O _{5 (LTO) with respect to NCM was 0.5 mol%.} Then, the second coating layer 103 made of LTO was formed on the first coating layer 102 by the same treatment as in Example 1. Then, a test cell was prepared by the same treatment as in Example 1, and the load characteristics were evaluated. The results are summarized in Table 1. In Comparative Example 4, the cycle life was not evaluated because the rate characteristics were poor.

(Comparative Example 5)
The NCM used in Example 1 was prepared as the positive electrode active material particles 101. Then, a mixed solution of lithium methoxyde, zirconium propoxide, and germanium propoxide and ethanol was prepared. Specifically, the mixed solution was adjusted so that the coating amount _{of Li 2} O-ZrO _2- GeO _{2 (LZGeO) with respect to NCM was 0.5 mol%.} Then, by the same treatment as in Example 1, only the coating layer made of LZGeO was formed on the first coating layer 102. Then, a test cell was prepared by the same treatment as in Example 1, and the load characteristics were evaluated. The results are summarized in Table 1. In Comparative Example 5, the cycle life was not evaluated because the rate characteristics were poor.

(evaluation)
In Examples 1 and 2, all of the initial discharge capacity, the rate characteristic, and the cycle characteristic were good. On the other hand, in Comparative Examples 1 to 5, any of the initial discharge capacity, the rate characteristic, and the cycle characteristic was low. In particular, the structure of Comparative Example 3 is one in which the stacking order of the first coating layer 102 and the second coating layer 103 is changed, but the initial discharge capacity is lower than that of the examples. In Comparative Example 4, the stacking order of the first coating layer 102 and the second coating layer 103 was changed, but not only the initial discharge capacity but also the rate characteristics were lower than those of the examples. In Comparative Example 5, the constituent elements of the first coating layer 102 and the constituent elements of the second coating layer 103 were combined into one layer, but the initial discharge capacity was also low.

(Example 3)
The test cell prepared in the same manner as in Example 1 was charged at 25 ° C. with a constant current of 0.05 C to an upper limit voltage of 4.1 V, and then discharged to a discharge end voltage of 2.5 V with a constant current of 0.05 C. Then, the capacity at the time of discharge was measured, and this was used as the initial discharge capacity. Then, the test cell was discharged at 0.05C, 0.5C, and 1C, respectively, and the rate characteristics were measured. Then, the ratio of the 1C discharge capacity to the initial discharge capacity was used as an index of the load characteristics. Further, as a cycle life test, the obtained test cell is charged at 25 ° C. with a constant current of 0.05 C to an upper limit voltage of 4.1 V, and then charged / discharged to discharge 0.5 C to a discharge end voltage of 2.5 V. The cycle was repeated 50 cycles. Then, the ratio of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was defined as the retention rate of the discharge capacity. That is, in Example 3, the same processing as in Example 1 was performed except that the charging voltage of the test cell was 4.1 V. The results are summarized in Table 2.

(Example 4)
The test cell prepared in the same manner as in Example 2 was evaluated in the same manner as in Example 3. The results are summarized in Table 2.

(Comparative Example 6)
The test cell prepared in the same manner as in Comparative Example 1 was evaluated in the same manner as in Example 3. The results are summarized in Table 2.

(Comparative Example 7)
The test cell prepared in the same manner as in Comparative Example 2 was evaluated in the same manner as in Example 3. The results are summarized in Table 2.

(Comparative Example 8)
The test cell prepared in the same manner as in Comparative Example 3 was evaluated in the same manner as in Example 3. The results are summarized in Table 2.

(Comparative Example 9)
The test cell prepared in the same manner as in Comparative Example 4 was evaluated in the same manner as in Example 3. The results are summarized in Table 2. In Comparative Example 9, the cycle life was not evaluated because the rate characteristics were poor.

(Comparative Example 10)
The test cell prepared in the same manner as in Comparative Example 5 was evaluated in the same manner as in Example 3. The results are summarized in Table 2. In Comparative Example 10, the cycle life was not evaluated because the rate characteristics were poor.

(evaluation)
Similar results were obtained even when the voltage was increased to 4.1V.

(Example 6)
The test cell prepared in the same manner as in Example 1 was charged at 25 ° C. with a constant current of 0.05 C to an upper limit voltage of 4.2 V, and then discharged to a discharge end voltage of 2.5 V with a constant current of 0.05 C. Then, the capacity at the time of discharge was measured, and this was used as the initial discharge capacity. Then, the test cell was discharged at 0.05C, 0.5C, and 1C, respectively, and the rate characteristics were measured. Then, the ratio of the 1C discharge capacity to the initial discharge capacity was used as an index of the load characteristics. Further, as a cycle life test, the obtained test cell is charged at 25 ° C. with a constant current of 0.05 C to an upper limit voltage of 4.2 V, and charged / discharged to discharge 0.5 C to a discharge end voltage of 2.5 V. The cycle was repeated 50 cycles. Then, the ratio of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was defined as the retention rate of the discharge capacity. That is, in Example 6, the same processing as in Example 1 was performed except that the charging voltage of the test cell was set to 4.2 V. The results are summarized in Table 3.

(Example 7)
The test cell prepared in the same manner as in Example 2 was evaluated in the same manner as in Example 6. The results are summarized in Table 3.

(Comparative Example 11)
The test cell prepared in the same manner as in Comparative Example 1 was evaluated in the same manner as in Example 6. The results are summarized in Table 3.

(Comparative Example 12)
The test cell prepared in the same manner as in Comparative Example 2 was evaluated in the same manner as in Example 6. The results are summarized in Table 3.

(Comparative Example 13)
The test cell prepared in the same manner as in Comparative Example 3 was evaluated in the same manner as in Example 6. The results are summarized in Table 3.

(Comparative Example 14)
The test cell prepared in the same manner as in Comparative Example 4 was evaluated in the same manner as in Example 6. The results are summarized in Table 3. In Comparative Example 14, the cycle life was not evaluated because the rate characteristics were poor.

(Comparative Example 15)
The test cell prepared in the same manner as in Comparative Example 5 was evaluated in the same manner as in Example 6. The results are summarized in Table 3. In Comparative Example 15, the cycle life was not evaluated because the rate characteristics were poor.

(evaluation)
Similar results were obtained even when the voltage was increased to 4.2V.

(Example 8)
_{LiNi 0.8} Co _0.15 Al _0.05 O ₂ (NCA) was prepared as the positive electrode active material particles 101. The average secondary particle size of the positive electrode active material particles 101 was measured by the scattering method and found to be 7 μm. Then, a surface coating treatment was performed using a mixed solution of lithium methoxydo and zirconium propoxide and ethanol. Specifically, the mixed solution of the above NCA was adjusted so that the coating amount _{of Li 2} O-ZrO _{2 (LZO) with respect to NCA was 0.5 mol%.} Then, the surface of the positive electrode active material particles 101 was coated with the mixed solution using a rolling fluidized bed granulator / coating machine FD-MP-01E manufactured by Paulec Co., Ltd. Specifically, the conditions are that the mass of the positive electrode active material particles 101 is 500 g, the supply air temperature is 90 ° C., the supply air volume is 0.23 m ³ / h, the rotor rotation speed is 400 rpm, the admise air volume is 50 NL / min, and the spray speed is about 5 g / min. Below, the mixed solution was sprayed onto the surface of the positive electrode active material particles 101. Then, the positive electrode active material particles 101 coated with the mixed solution were dried. The coating particles obtained by the above surface treatment were fired at 350 ° C. for 1 hour in an air atmosphere to form a first coating layer 102 made of LZO on the surface of the positive electrode active material particles 101.

Then, a mixed solution of lithium methoxyde and germanium propoxide and ethanol was prepared. Specifically, the coverage of _Li 2 _O-GeO 2 for NCA (LGeO) was adjusted mixed solution to a 0.5 mol%. Then, a second coating layer 103 made of LGeO was formed on the first coating layer 102 by the same treatment as described above. Through the above steps, a positive electrode active material 100 in which the first coating layer 102 and the second coating layer 103 are coated on the positive electrode active material particles 101, that is, a double-coated positive electrode active material was obtained. Next, when some positive electrode active materials were observed using a cross-sectional image or the like with a transmission electron microscope, the thickness of the first coating layer 102 was in the range of 5 to 30 μm, and the first coating was found to be in the range of 5 to 30 μm. The total thickness of the layer 102 and the second coating layer 103 was in the range of 15 to 70 μm.

(Manufacturing of all-solid-state secondary battery)
_{First, the reagents Li 2} S and P ₂ S ₅ , which are the starting materials of the sulfide-based electrolyte material, were weighed so as to have the target composition of Li ₃ PS _4. Then, a mechanical milling treatment was performed in which these reagents were mixed in a planetary ball for 20 hours. The mechanical milling treatment was performed at a rotation speed of 380 rpm, at room temperature, and in an argon atmosphere.

The sample obtained by the above mechanical milling treatment was pulverized with an agate mortar. The crushed sample was diffracted by X-ray crystallography, and it was confirmed that _{Li 2} S and P ₂ S _{5 used as starting materials did not remain.} Then, the sample after pulverization was used as the solid electrolyte 300.

Then, the positive electrode active material 100, the solid electrolyte 300, and the carbon nanofiber (CNF) which is a conductive agent prepared above were mixed at a mass ratio of 60:35: 5 to prepare a positive electrode mixture. Further, a negative electrode mixture was prepared by mixing graphite, a solid electrolyte 300, and VGCF, which is a conductive agent, at a mass ratio of 60:35: 5. The positive electrode mixture (15 mg), the solid electrolyte (100 mg), and the negative electrode mixture (15 mg) were laminated in this order and ^{pressurized at a pressure of 3 ton / cm 2} to obtain a test cell.

(Load characteristic evaluation)
The obtained test cell was charged at 25 ° C. with a constant current of 0.05 C to an upper limit voltage of 4.0 V, and then discharged to a discharge end voltage of 2.5 V with a constant current of 0.05 C. Then, the capacity at the time of discharge was measured, and this was used as the initial discharge capacity. Then, the test cell was discharged at 0.05C, 0.5C, and 1C, respectively, and the rate characteristics were measured. Then, the ratio of the 1C discharge capacity to the initial discharge capacity was used as an index of the load characteristics.

(Cycle life test)
The obtained test cell was charged at 25 ° C. with a constant current of 0.05 C to an upper limit voltage of 4.0 V, and a charge / discharge cycle of 0.5 C discharge to a discharge end voltage of 2.5 V was repeated for 50 cycles. Then, the ratio of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was defined as the retention rate of the discharge capacity. The results are summarized in Table 4.

(Comparative Example 16)
The NCA used in Example 8 was prepared as the positive electrode active material particles 101. Then, the first coating layer 102 made of LGeO was formed on the surface of the positive electrode active material particles 101 by the same treatment as in Example 8. Then, a second coating layer 103 made of LZO was formed on the first coating layer 102 by the same treatment as in Example 8. Then, a test cell was prepared by the same treatment as in Example 8, and the load characteristics and cycle life were evaluated. The results are summarized in Table 4.

(Comparative Example 17)
The same treatment as in Example 8 was performed except that the second coating layer 103 was not formed. That is, in Comparative Example 17, only the coating layer made of LZO was formed on the surface of the positive electrode active material particles 101. The results are summarized in Table 4.

(Comparative Example 18)
The NCA used in Example 8 was prepared as the positive electrode active material particles 101. Then, by performing the same treatment as in Example 2 except that the first coating layer 102 was not formed, only the coating layer made of LNbO was formed on the surface of the positive electrode active material particles 101. Then, a test cell was prepared by the same treatment as in Example 8, and the load characteristics and cycle life were evaluated. The results are summarized in Table 4.

(Comparative Example 19)
The same treatment as in Example 8 was carried out except that the first coating layer 102 was not formed. That is, in Comparative Example 19, only the coating layer made of LGeO was formed on the surface of the positive electrode active material particles 101. The results are summarized in Table 4.

(evaluation)
Similar results were obtained when the positive electrode active material particles 101 were changed to NCA.

As described above, according to the present embodiment, the positive electrode active material particles 101 are coated with the first coating layer 102 and the second coating layer 103, and the first coating layer 102 and the second coating layer 103 are Contains certain elements. Therefore, the characteristics of the all-solid-state secondary battery can be further improved. Further, since each coating layer is produced by applying alkoxide, which is a constituent element of these coating layers, to the positive electrode active material particles 101 and firing them, it can be easily produced. Therefore, the productivity is also good.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

1 All-solid secondary battery 10 Positive electrode layer 20 Negative electrode layer 30 Solid electrolyte layer 100 Positive electrode active material 101 Positive electrode active material particles 102 First coating layer 103 Second coating layer 200 Negative electrode particles 300 Solid electrolyte

Claims (11)

Positive electrode active material particles and
A first coating layer that coats the surface of the positive electrode active material particles, and
A second coating layer that covers the surface of the first coating layer is provided.
The first coating layer contains any one or more selected from the group consisting of a first lithium-containing oxide and a lithium-containing phosphorus oxide.
The first lithium-containing oxide contains any one or more selected from the group consisting of zirconium element, niobium element and titanium element.
The lithium-containing phosphor oxide contains any one or more selected from zirconium element and titanium element.
The second coating layer contains a second lithium-containing oxide containing any one selected from the group consisting of germanium element, niobium element, and gallium element.
A positive electrode active material for an all-solid-state secondary battery, characterized in that the compositions of the first coating layer and the second coating layer are different from each other. The whole according to claim 1, wherein the first lithium-containing oxide is at least one selected from the group consisting of lithium zirconium oxide, lithium niobium oxide, and lithium titanium oxide. Positive electrode active material for solid secondary batteries. The positive electrode active material for an all-solid-state secondary battery according to claim 2, wherein the lithium zirconium oxide has a composition represented by aLi2O-ZrO2 (0.1 ≦ a ≦ 2.0). The lithium-containing phosphor oxide is any one or more selected from the group consisting of lithium zirconium phosphor oxide and lithium titanium phosphor oxide, according to any one of claims 1 to 3. The positive electrode active material for all-solid-state secondary batteries described. Claims 1 to 4 are characterized in that the second lithium-containing oxide is at least one selected from the group consisting of lithium germanium oxide, lithium niobium oxide, and lithium gallium oxide. The positive electrode active material for an all-solid-state secondary battery according to any one of the above items. The positive electrode active material for an all-solid-state secondary battery according to any one of claims 1 to 5, wherein the average secondary particle size of the positive electrode active material particles is 10 μm or less. The positive electrode active material for an all-solid-state secondary battery according to any one of claims 1 to 6, wherein the positive electrode active material particles are a lithium salt of a transition metal oxide having a layered rock salt type structure. .. The positive electrode active material for an all-solid-state secondary battery according to claim 7, wherein the positive electrode active material particles are lithium salts of a ternary transition metal oxide represented by LiNixCoyAlzO2 or LiNixCoyMnzO2. The positive electrode active material layer for an all-solid-state secondary battery, which comprises the positive electrode active material for an all-solid-state secondary battery according to any one of claims 1 to 8. An all-solid-state secondary battery comprising the positive electrode active material layer for an all-solid-state secondary battery according to claim 9. The all-solid-state secondary battery according to claim 10, further comprising a sulfide-based solid electrolyte.

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