JP2019117768A - All-solid secondary battery - Google Patents

Abstract

To provide an all-solid secondary battery in which the occurrence of a short circuit is suppressed.SOLUTION: Provided is an all-solid secondary battery comprising: a positive electrode layer; a negative electrode layer; a solid electrolyte layer disposed between the positive and negative electrode layers; and a buffer layer disposed between the positive electrode layer and the solid electrolyte layer. In the all-solid secondary battery, the buffer layer contains a kind of metal other than Li and a kind of semimetal, and one or more selected from a group consisting of oxides and sulfides thereof; and the buffer layer has a thickness of 1.0 nm or more and 1000 nm or less. Thus, an all-solid secondary battery in which the occurrence of a short circuit is suppressed is provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an all solid secondary battery.

  In recent years, all solid secondary batteries have attracted attention. The all solid secondary battery has a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer disposed between these active material layers. In the all solid secondary battery, a medium for conducting lithium ions is a solid electrolyte.

  The all-solid-state secondary battery using such a solid electrolyte is largely different from the conventional lithium ion battery using an electrolytic solution in that all the constituents are solid materials. And since all the interfaces of an electrode active material and a solid electrolyte turn into a solid-solid interface, these interface resistance is large.

  Patent Document 1 discloses that phosphorus is interposed between the positive electrode active material layer and the solid electrolyte layer for the purpose of facilitating the movement of lithium ions between the positive electrode active material layer and the solid electrolyte layer and reducing the interface resistance. It has been proposed to arrange an interfacial modification layer containing lithium oxide.

JP 2017-126437 A

  By the way, in the all solid secondary battery, the interface between the layers becomes a solid / solid interface, so the distribution of the migration path of lithium ions becomes uneven, and as a result, current tends to be concentrated locally at the time of charge and discharge. In such a case, there is a problem that a short circuit is likely to occur in the all solid secondary battery. Patent Document 1 does not disclose the prevention of such a short circuit.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved all solid secondary battery in which the occurrence of a short circuit is suppressed. .

According to an aspect of the present invention, in order to solve the above problems,
A positive electrode layer,
A negative electrode layer,
A solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer;
A buffer layer disposed between the positive electrode layer and the solid electrolyte layer,
The buffer layer contains one or more selected from the group consisting of single metals and single metals other than Li, and oxides and sulfides of these metals;
An all solid secondary battery is provided, wherein the thickness of the buffer layer is 1.0 nm or more and 1000 nm or less.

  According to this aspect, the buffer layer fills the gaps between the solid electrolyte particles and the positive electrode active material particles constituting the solid electrolyte layer and the positive electrode active material layer in the vicinity of the interface between the solid electrolyte layer and the buffer layer of the positive electrode active material layer. As a result, the contact of the solid electrolyte particles and the positive electrode active material particles can be made more reliable. For this reason, the movement path of lithium ions is uniformly distributed in the all solid secondary battery at the time of charge and discharge, and it is possible to prevent the movement of lithium ions locally. As a result, a short circuit at the time of charge and discharge of the all solid secondary battery 1 is prevented.

Here, the Young's modulus of the single metal and the single semimetal may be 10 GPa or more and 400 GPa or less.
According to this aspect, it is possible to more effectively suppress the short circuit of the all solid secondary battery.

In addition, the single metal and the single metal mentioned above are Mg, Al, Ca, Ti, Cr, Fe, Zn, Ga, Se, Sr, Y, Zr, Mo, In, Sn, Ag, Sb, Ba and Bi. It may be one or more selected from the group consisting of
According to this aspect, it is possible to more effectively suppress the short circuit of the all solid secondary battery.

The single metal may be a base metal.
According to this aspect, it is possible to more effectively suppress the short circuit of the all solid secondary battery.

Further, the single metal may include Zn.
According to this aspect, it is possible to more effectively suppress the short circuit of the all solid secondary battery.

The solid electrolyte layer may also contain a solid electrolyte containing sulfur and one or more elements selected from the group consisting of silicon, phosphorus and boron.
According to this aspect, the lithium conductivity of the solid electrolyte layer is improved, and the battery characteristics of the all-solid secondary battery are improved.

  As described above, according to the present invention, it is possible to suppress the short circuit of the all solid secondary battery.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows schematic structure of the all-solid-state secondary battery which concerns on embodiment of this invention.

  The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. In the present specification and the drawings, components having substantially the same functional configuration will be assigned the same reference numerals and redundant description will be omitted. Further, each component in the drawing is appropriately enlarged or reduced for ease of explanation, and the size and ratio of each component in the drawing are different from actual ones.

<1. Configuration of all solid secondary battery>
First, based on FIG. 1, the structure of the all-solid-state secondary battery 1 which concerns on this embodiment is demonstrated. FIG. 1 is a cross-sectional view showing a schematic configuration of the all-solid secondary battery according to the present embodiment.

As shown in FIGS. 1 and 2, the all solid secondary battery 1 includes a positive electrode layer 10, a negative electrode layer 20, a solid electrolyte layer 30, and a buffer layer 40 as shown in FIG. 1.
(Positive layer)
The positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. Examples of the positive electrode current collector 11 include indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc Plates or foils made of Zn), aluminum (Al), germanium (Ge), lithium (Li) or alloys of these may be mentioned. The positive electrode current collector 11 may be omitted. The positive electrode current collector 11 is connected to the wiring through a terminal (not shown) when the all solid secondary battery 1 is used.

  The positive electrode active material layer 12 usually contains a positive electrode active material and a solid electrolyte. The solid electrolyte contained in the positive electrode active material layer 12 may or may not be the same as the solid electrolyte contained in the solid electrolyte layer 30. The details of the solid electrolyte will be described in detail in the section of the solid electrolyte layer 30.

  The positive electrode active material may be any positive electrode active material capable of reversibly absorbing and desorbing lithium ions.

  For example, the positive electrode active material is lithium cobaltate (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminumate (hereinafter referred to as NCA) , Lithium cobalt salts such as lithium lithium cobaltate (hereinafter referred to as NCM), lithium manganate (Lithium manganate), lithium iron phosphate (lithium iron phosphate), nickel sulfide, copper sulfide, sulfur, iron oxide, or vanadium oxide (Vanadium oxide) etc. can be used. Each of these positive electrode active materials may be used alone, or two or more may be used in combination.

  Further, the positive electrode active material is preferably formed by including the lithium salt of a transition metal oxide having a layered rock salt type structure among the lithium salts described above. Here, "layered" represents a thin sheet-like shape. The term "rock salt type structure" refers to a sodium chloride type structure which is a kind of crystal structure, and more specifically, face-centered cubic lattices formed by each of cations and anions are unit cells of one another. It represents a structure that is arranged offset by 1/2 of the weir.

The lithium salt of a transition metal oxide 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) ( where 0 < Lithium salts of ternary transition metal oxides such as x <1, 0 <y <1, 0 <z <1, and x + y + z = 1) can be mentioned.

  When the positive electrode active material contains a lithium salt of a ternary transition metal oxide having a layered rock salt type structure described above, the energy density and thermal stability of the all-solid secondary battery 1 can be improved.

The positive electrode active material may be covered by a covering layer. Here, the covering layer of the present embodiment may be any layer as long as it is known as a covering layer of the positive electrode active material of the all solid secondary battery. Examples of the coating layer, for _example, Li ₂ O-ZrO 2 or the like.

  In addition, when the positive electrode active material is formed of a lithium salt of a ternary transition metal oxide such as NCA or NCM, and includes nickel (Ni) as the positive electrode active material, the capacity density of all solid secondary battery 1 To reduce metal elution from the positive electrode active material in a charged state. Thereby, the all-solid-state secondary battery 1 which concerns on this embodiment can improve the long-term reliability in a charge condition, and a cycle (cycle) characteristic.

  Here, as a shape of a positive electrode active material, particle shapes, such as a spherical shape and an elliptical spherical shape, can be mentioned, for example. Further, the particle size of the positive electrode active material is not particularly limited, as long as it can be applied to the positive electrode active material of the conventional all solid secondary battery. The content of the positive electrode active material in the positive electrode active material layer 12 is not particularly limited, as long as it is a range applicable to the positive electrode layer of the conventional all solid secondary battery.

  In addition to the above-described positive electrode active material and solid electrolyte, the positive electrode active material layer 12 appropriately contains, for example, additives such as a conductive aid, a binder, a filler, a dispersant, and an ion conductive aid. It may be blended.

  As a conductive support agent which can be mix | blended with the positive electrode active material layer 12, graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder etc. can be mentioned, for example. Moreover, as a binder which can be added to the positive electrode active material layer 12, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene (polyethylene) Etc. can be mentioned. Furthermore, as a filler, a dispersing agent, an ion conductive support agent etc. which can be mix | blended with the positive electrode layer 10, the well-known material generally used for the electrode of a lithium ion secondary battery can be used.

(Anode layer)
The negative electrode layer 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. Examples of the negative electrode current collector 21 include indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc Plates or foils made of Zn), aluminum (Al), germanium (Ge), lithium (Li) or alloys of these may be mentioned. The negative electrode current collector 21 may be omitted.

  The negative electrode active material layer 22 can be, for example, a layer containing a negative electrode active material, a solid electrolyte, and a conductive additive.

  The negative electrode active material has a charge / discharge potential lower than that of the positive electrode active material contained in the positive electrode active material layer 12 and is made of an active material capable of alloying with lithium or capable of reversible absorption and release of lithium. Be done.

  For example, as the negative electrode active material, a metal active material, a carbon (carbon) active material, or the like can be used. As the metal active material, for example, metals such as lithium (Li), indium (In), aluminum (Al), tin (Sn), and silicon (Si), alloys of these, and the like can be used. Also, as the carbon active material, for example, artificial graphite, graphite carbon fiber, resin-calcined carbon, pyrolytic vapor-grown carbon, coke (coke), mesocarbon microbeads (MCMB), furfuryl alcohol resin-calcined Carbon, polyacene, pitch-based carbon fiber, vapor grown carbon fiber, natural graphite, non-graphitizable carbon and the like can be used. Note that these negative electrode active materials may be used alone or in combination of two or more.

  The same conductive aid as the conductive aid in the positive electrode active material layer 12 can be used as the conductive aid. For the solid electrolyte, the same compound as the solid electrolyte contained in the positive electrode active material layer 12 can be used. Therefore, the description of these components is omitted here.

In addition to the above-described negative electrode active material, solid electrolyte, and conductive additive, the negative electrode active material layer 22 is appropriately blended with additives such as a binder, a filler, a dispersant, and an ion conductive agent, for example. It may be As the additive to be added to the negative electrode active material layer 22, the same one as the additive to be added to the positive electrode active material layer 12 described above can be used.
In addition, the negative electrode layer 20 demonstrated above is connected to wiring through the terminal which is not shown in figure at the time of use of the all-solid-state secondary battery 1. FIG.

(Solid electrolyte layer)
The solid electrolyte layer 30 is formed between the positive electrode layer 10 and the negative electrode layer 20, and includes a solid electrolyte.

The solid electrolyte is made of, for example, a sulfide-based solid electrolyte material. As 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 a halogen element such as 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} is any positive number, Z is Ge, and 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} is a positive number, M is P, Si, Ge B, Al, either Ga or In), and the like. Here, the sulfide-based solid electrolyte material is produced by treating a starting material (for example, Li ₂ S, P ₂ S ₅ or the like) by a melt-quenching method, a mechanical milling method, or the like. Further, heat treatment may be further performed after these treatments. The solid electrolyte may be amorphous or crystalline, or may be in a mixed state.

In addition, it is preferable to use, as the solid electrolyte, a material containing sulfur and one or more elements selected from the group consisting of silicon, phosphorus and boron among the above-mentioned sulfide solid electrolyte materials. Thereby, the lithium conductivity of the solid electrolyte layer is improved, and the battery characteristics of the all-solid secondary battery 1 are improved. In particular, it is preferable to use a solid electrolyte containing at least sulfur (S), phosphorus (P) and lithium (Li) as constituent elements, and it is more preferable to use one containing Li ₂ S-P ₂ S ₅ in particular. .

Here, in the case of using a material containing Li ₂ S—P ₂ S ₅ as a sulfide-based solid electrolyte material forming a solid electrolyte, the mixing molar ratio of Li ₂ S and P ₂ S ₅ is, for example, Li ₂ S It may be selected in the range of P ₂ S ₅ = 50: 50 to 90:10. The solid electrolyte layer 30 may further contain a binder. Examples of the binder contained in the solid electrolyte layer 30 include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. The binder in the solid electrolyte layer 30 may be the same as or different from the binder in the positive electrode active material layer 12.

(Buffer layer)
The buffer layer 40 is disposed between the positive electrode active material layer 12 of the positive electrode layer 10 and the solid electrolyte layer 30. And the buffer layer 40 contains 1 or more types selected from the group which consists of single metals and single semimetals other than Li, these oxides, and sulfides. Thereby, the short circuit at the time of charge and discharge of the all-solid-state secondary battery 1 is prevented.

  More specifically, when the constituent components of the buffer layer 40 are a single metal or a single semimetal, they are oxidized by initial charge and discharge to form oxides or sulfides. And (semi) metal oxides and sulfides are micro-electrical resistors having relatively high electrical resistivity.

  Next, the buffer layer 40 is disposed between the positive electrode active material layer 12 and the solid electrolyte layer 30, but is generally pressed by a press when manufacturing the all-solid secondary battery 1. Therefore, the buffer layer 40 is a gap between the solid electrolyte particles and the positive electrode active material particles constituting the solid electrolyte layer 30 and the positive electrode active material layer 12 in the vicinity of the interface between the solid electrolyte layer 30 and the buffer layer 40 of the positive electrode active material layer 12. As a result, the solid electrolyte particles and the positive electrode active material particles can be more reliably in contact with each other. The contact of the solid electrolyte particles and the positive electrode active material particles due to the buffer layer 40 occurs relatively uniformly in the planar direction of the buffer layer 40 of the all solid secondary battery 1. For this reason, the movement path of lithium ions is uniformly distributed in the all solid secondary battery 1 at the time of charge and discharge, and it is possible to prevent the movement of lithium ions locally.

  Furthermore, as described above, the (semi) metal oxides and sulfides constituting the buffer layer 40 have relatively high electric resistivity, and the gaps in the vicinity of the surfaces of the solid electrolyte layer 30 and the positive electrode active material layer 12 have micro electric resistance. It is filled with a buffer layer 40 as an object. This prevents unintended shorting. Furthermore, since the gap is filled with such a buffer layer 40, undesired side reactions and the like in the vicinity of the interface between the solid electrolyte layer 30 and the positive electrode active material layer 12 are prevented. A short circuit at the time of charge and discharge of the all-solid-state secondary battery 1 is prevented by the above-mentioned effects acting synergistically.

  The Young's modulus of the single metal or the single semimetal constituting the buffer layer 40 is not particularly limited, but is, for example, 10 GPa or more and 400 GPa or less, preferably 100 GPa or more and 200 GPa or less. When the Young's modulus of the single metal or the single semimetal constituting the buffer layer 40 is within the above-described range, the buffer layer 40 appropriately expands when pressed as described above, and the buffer of the solid electrolyte layer 30 or the positive electrode active material layer 12 In the vicinity of the interface with the layer 40, the gaps between the solid electrolyte particles constituting the solid electrolyte layer 30 and the positive electrode active material layer 12 and the positive electrode active material particles can be appropriately filled. If the Young's modulus is less than the lower limit value, depending on the type of single metal or single metalloid, it may be excessively stretched when pressed, and interface resistance may be increased instead. On the other hand, when the above-mentioned Young's modulus exceeds the above-mentioned upper limit, depending on press conditions, a single metal or a single semimetal may not fully extend, and the effect which fills up the above-mentioned gap may not fully be acquired.

  The component which comprises the buffer layer 40 should just be single (semi) metals other than Li, these oxides, and sulfides as mentioned above. For example, such components include Mg, Al, Ca, Ti, Cr, Fe, Zn, Ga, Se, Sr, Y, Zr, Mo, In, Sn, Ag, Sb, Ba and Bi, and these. Oxides and sulfides of These components have the Young's modulus in the above-described range, so that the effects of the buffer layer 40 are sufficiently exhibited.

  Furthermore, the single metal is preferably a base metal. When the simplex metal is a base metal, it is easily oxidized to form an oxide or a sulfide. Therefore, the function of the buffer layer 40 is more reliably exhibited.

  The buffer layer 40 is preferably made of Zn or Bi or an oxide or sulfide of these, and is preferably made of an oxide or sulfide of Zn or Zn. These components have, in particular, a moderately large Young's modulus (Zn: 108 GPa, Bi: 32 GPa) and an appropriate size of electrical resistance (insulation). Therefore, the short circuit of the all solid secondary battery 1 is further suppressed.

  The buffer layer 40 is mainly composed of the simple (semi) metals mentioned above and their oxides and sulfides. Specifically, the content of single (semi) metals and their oxides and sulfides in the buffer layer 40 is, for example, 90% by mass or more, preferably 95% by mass or more. Buffer layer 40 may contain other substances resulting from the charge / discharge reaction of all solid secondary battery 1. Particularly preferably, the buffer layer 40 consists essentially of the above-mentioned simple (semi) metals and their oxides and sulfides.

  The thickness of the buffer layer 40 is 1.0 nm or more and 1000 nm or less. If the thickness of the buffer layer 40 is less than the above lower limit value, the function of the buffer layer 40 is not sufficiently exhibited, and the short-circuit suppression effect can not be obtained. On the other hand, when the thickness of the buffer layer 40 exceeds the above upper limit, the interface resistance by the buffer layer 40 is large, and the thickness of the buffer layer 40 which makes it difficult to suppress short circuit is preferably 50 nm to 500 nm. .

  In the all-solid secondary battery 1 described above, the buffer layer 40 prevents local concentration of current during charge and discharge, and a gap at the interface between the positive electrode active material layer 12 and the solid electrolyte layer 30. Is filled. Therefore, the all solid secondary battery 1 is prevented from being short circuited during charging and discharging.

<2. Method of manufacturing all solid secondary battery>
Then, an example of the manufacturing method of the all-solid-state secondary battery which concerns on this embodiment is demonstrated. In the all solid secondary battery 1 according to the present embodiment, after manufacturing the positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30, respectively, the positive electrode active material layer 12 on the positive electrode active material layer 12 or the positive electrode active of the solid electrolyte layer 30 is It can be manufactured by forming the buffer layer 40 on the surface on the material side and laminating the above-mentioned layers. The positive electrode layer 10, the negative electrode layer 20, and the solid electrolyte layer 30 can be produced by a known method.

(Positive electrode preparation process)
The positive electrode active material can be produced by a known method. Subsequently, the prepared positive electrode active material, a solid electrolyte prepared by a method described later, and various additives are mixed and added to a nonpolar solvent to form a slurry or a paste. Furthermore, the positive electrode layer 10 can be obtained by applying the obtained slurry or paste onto the positive electrode current collector 11, drying and rolling. The positive electrode layer 10 may be produced by compacting a mixture of the positive electrode active material and various additives in a pellet form without using the positive electrode current collector 11. In addition, in order to raise the density ratio of the positive electrode active material layer 12, a press process, such as a roll press, can also be performed as needed.

(Step of preparing negative electrode layer)
The negative electrode layer 20 can be produced by the same method as the positive electrode layer. Specifically, first, a negative electrode active material, a solid electrolyte, a conductive auxiliary agent, and various additives are mixed and added to a solvent such as water or an organic solvent to form a slurry or a paste. Furthermore, the negative electrode layer 20 can be obtained by applying the obtained slurry or paste to a current collector, drying it, and rolling it. A metal foil or a metal foil that forms an alloy with Li may be used as the negative electrode layer 20.

(Solid electrolyte layer preparation process)
The solid electrolyte layer 30 can be made of a solid electrolyte formed of a sulfide-based solid electrolyte material.

  First, the starting material is treated by a melt-quenching method or a mechanical milling method.

For example, in the case of using a melt quenching method, predetermined amounts of starting materials (eg, Li ₂ S, P ₂ S ₅ etc.) are mixed, pelletized, reacted in vacuum at a predetermined reaction temperature, and then quenched. Thus, 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. Furthermore, the quenching temperature of the reaction product is usually 10 ° C. or less, preferably 0 ° C. or less, and the quenching rate is usually about 1 ° C./sec to 10000 ° C./sec, preferably 1 ° C./sec. It is about ° C / sec.

In addition, when using mechanical milling, a sulfide-based solid electrolyte material can be produced by allowing a starting material (for example, Li ₂ S, P ₂ S ₅ or the like) to be stirred and reacted using a ball mill or the like. . Although the stirring speed and the stirring time in the mechanical milling method are not particularly limited, the faster the stirring speed, the faster the formation speed of the sulfide-based solid electrolyte material can be, and the longer the stirring time, the sulfide-based solid electrolyte material Conversion rate of raw materials can be increased.

  Thereafter, 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. When the solid electrolyte has a glass transition temperature, it may be changed from amorphous to crystalline by heat treatment.

  Subsequently, the solid electrolyte obtained by the above method is formed into a film, for example, by using a known film forming method such as an aerosol deposition method, a cold spray method, or a sputtering method. The solid electrolyte layer 30 can be manufactured. The solid electrolyte layer 30 may be produced by pressurizing the solid electrolyte particles alone. In addition, the solid electrolyte layer 30 may be produced by mixing a solid electrolyte, a solvent, and a binder, applying, drying, and pressurizing the solid electrolyte layer 30. In order to increase the density ratio of the solid electrolyte layer 30, a pressing process such as a roll press can also be performed as necessary.

(Buffer layer formation process)
Next, the buffer layer 40 is formed on the surface of the positive electrode active material layer 12 of the positive electrode layer 10 or the surface of the solid electrolyte layer 30 on the positive electrode active material side. The formation method of the buffer layer 40 is not particularly limited, physical vapor deposition such as vacuum evaporation, sputtering, ion plating, etc., chemical vapor deposition such as plasma CVD, wet coating such as spin coating, screen printing, etc. Can be used as appropriate. Among the above, it is simple to form a simple (semi) metal using physical vapor deposition such as vacuum deposition, and is preferable also from the viewpoint of controlling the thickness of the buffer layer 40.

(Lamination process)
Next, the positive electrode active material layer 12 (that is, the positive electrode layer 10), the solid electrolyte layer 30, and the negative electrode active material layer 22 (that is, the negative electrode layer 20) are stacked to fabricate an electrode stack. At this time, lamination is performed so that the buffer layer 40 is disposed between the positive electrode active material layer 12 and the solid electrolyte layer 30. Then, the electrode stack is pressed. The all solid secondary battery 1 is manufactured by the above steps. The specific pressing method for performing the pressing is not particularly limited, and may be a pressing method used for producing the conventional all solid secondary battery 1. For example, pressing may be performed by a roll press or the like.

  Hereinafter, the present invention will be described in more detail by way of examples. The examples are merely examples and do not limit the present invention.

[1. Production of all solid secondary battery]
Example 1
(Preparation of positive electrode structure)
LiNi _0.8 Co _0.15 Al _0.05 O ₂ (NCA) ternary powder as a positive electrode active material, and Li ₂ S—P ₂ S ₅ (80: 20 mol%) as a sulfide-based solid electrolyte The amorphous powder and the vapor grown carbon fiber powder as the positive electrode layer conductive substance (conductive auxiliary agent) were weighed at a mass% ratio of 60: 35: 5 and mixed using a rotation and revolution mixer.

  Subsequently, a dehydrated xylene solution in which styrene butadiene rubber (SBR) as a binder is dissolved is added to this mixed powder so that SBR becomes 5.0% by mass with respect to the total mass of the mixed powder, and the primary A mixture was prepared. Furthermore, a secondary mixed solution was prepared by adding an appropriate amount of dehydrated xylene for viscosity adjustment to the primary mixed solution. Furthermore, in order to improve the dispersibility of the mixed powder, a zirconia ball with a diameter of 5 mm is added to the secondary mixed solution so that the space, the mixed powder, and the zirconia ball occupy 1/3 of the total volume of the kneading vessel. It was thrown in. The tertiary mixed solution generated in this manner was introduced into a rotation and revolution mixer, and stirred for 3 minutes at 3000 rpm to prepare a positive electrode active material layer coating solution.

  Next, an aluminum foil current collector with a thickness of 20 μm is prepared as a positive electrode current collector, and the positive electrode current collector is placed on a desktop screen printing machine, and the metal mask has a hole diameter of 2.0 cm × 2.0 cm and a thickness of 150 μm. The positive electrode active material layer coating liquid was coated on the sheet using Thereafter, the sheet coated with the positive electrode active material layer coating liquid was dried on a hot plate at 60 ° C. for 30 minutes, and then vacuum dried at 80 ° C. for 12 hours. Thus, a positive electrode active material layer was formed on the positive electrode current collector. The total thickness of the positive electrode current collector and the positive electrode active material layer after drying was about 165 μm.

(Preparation of negative electrode structure)
Graphite powder (as vacuum dried at 80 ° C. for 24 hours) as a negative electrode active material and polyvinylidene fluoride (PVdF) as a binder were weighed at a mass% ratio of 95.0: 5.0. Then, these materials and an appropriate amount of N-methyl-2-pyrrolidone (NMP) are charged into a rotation and revolution mixer, stirred at 3000 rpm for 3 minutes, and defoamed for 1 minute to coat the negative electrode active material layer The solution was prepared.

  Next, a 20 μm thick nickel foil current collector is prepared as a negative electrode current collector, and using a metal mask having a pore size of 2.2 cm × 2.2 cm and a thickness of 250 μm, the negative electrode active material layer coating liquid is It was coated on the body. The sheet coated with the negative electrode layer coating liquid was housed in a dryer heated to 80 ° C. and dried for 15 minutes. Furthermore, the dried sheet was vacuum dried at 80 ° C. for 24 hours. Thus, a negative electrode structure was produced. The thickness of the negative electrode structure was about 140 μm.

(Preparation of solid electrolyte layer)
Dehydrated xylene solution in which SBR is dissolved in Li ₂ S-P ₂ S ₅ (80: 20 mol%) amorphous powder as a sulfide-based solid electrolyte, 2.0 mass based on the total mass of the mixed powder % To obtain a primary mixture. Furthermore, a secondary mixed solution was prepared by adding an appropriate amount of dehydrated xylene for viscosity adjustment to the primary mixed solution. Furthermore, in order to improve the dispersibility of the mixed powder, a zirconia ball with a diameter of 5 mm is added to the tertiary mixture so that the space, the mixed powder, and the zirconia ball occupy 1/3 of the total volume of the kneading vessel. It was thrown in. The tertiary mixed solution thus obtained was introduced into a rotation and revolution mixer, and stirred for 3 minutes at 3000 rpm to prepare a solid electrolyte layer coating solution.

  Polyethylene terephthalate (Polyethylene terephthalate: PET) was placed on a desktop screen printing machine, and a solid electrolyte layer coating liquid was coated on a PET sheet using a metal mask with a hole diameter of 2.5 cm × 2.5 cm and a thickness of 300 μm. . Thereafter, the resultant was dried on a hot plate at 40 ° C. for 10 minutes and then vacuum dried at 40 ° C. for 12 hours to form a solid electrolyte layer. The total thickness of the solid electrolyte layer after drying was around 180 μm.

(Preparation of buffer layer)
A 100 nm thick zinc layer as a buffer layer was formed on the positive electrode layer of the positive electrode structure obtained as described above by a vacuum evaporation method to obtain a positive electrode / buffer layer structure.

(Preparation of all solid secondary battery)
The positive electrode / buffer layer structure, the solid electrolyte layer and the negative electrode structure were punched out with a Thomson blade. The solid electrolyte layer on PET is stacked on the positive electrode / buffer layer structure so that the side of the buffer layer of the positive electrode / buffer layer structure is in contact, and bonded by a dry lamination method using a roll press with a roll gap of 150 μm. Thus, an assembly of the positive electrode / buffer layer structure and the solid electrolyte layer was formed.

  The solid electrolyte layer side of the assembly of the positive electrode / buffer layer structure and the solid electrolyte layer and the side surface of the negative electrode active material layer of the negative electrode structure are stacked, and pressure molding is performed at a pressure of 10 tons using a uniaxial press. Then, a single cell of the all solid secondary battery was manufactured.

(Encapsulation of all solid secondary battery)
The produced unit cell was put into an aluminum laminate film attached with a terminal, evacuated to 100 Pa with a vacuum machine, and heat sealed to pack.

Example 2
An all solid secondary battery according to Example 2 was manufactured in the same manner as Example 1, except that the thickness of the zinc layer formed by vacuum evaporation was 1,000 nm (1 μm).

Example 3
An all solid secondary battery according to Example 3 was manufactured in the same manner as Example 1 except that the thickness of the zinc layer formed by vacuum evaporation was 1.0 nm.

Example 4
An all solid secondary battery according to Example 4 was manufactured in the same manner as Example 1, except that the formation of the zinc layer as the buffer layer was performed not on the positive electrode active material but on the solid electrolyte layer. Specifically, a zinc layer was formed on the surface of the solid electrolyte layer by vacuum evaporation to form a solid electrolyte layer / buffer layer structure. Next, the buffer layer side of the solid electrolyte layer / buffer layer structure and the positive electrode active material layer side of the positive electrode structure are overlapped and bonded by a roll press to produce an all solid secondary battery according to Example 4. did.

Example 5
An all solid secondary battery according to Example 5 in the same manner as Example 1, except that vacuum evaporation was performed using bismuth (Bi) instead of zinc, and a bismuth layer was formed instead of the zinc layer as a buffer layer. Manufactured.

Example 6
An all solid secondary battery according to Example 6 in the same manner as Example 4, except that vacuum evaporation was performed using bismuth (Bi) instead of zinc, and a bismuth layer was formed instead of the zinc layer as a buffer layer. Manufactured.

Comparative Example 1
An all solid secondary battery according to Comparative Example 1 was manufactured in the same manner as Example 1 except that the buffer layer was not formed.

Comparative Example 2
An all solid secondary battery according to Comparative Example 2 was manufactured in the same manner as Example 1, except that the thickness of the zinc layer formed by vacuum deposition was 2,000 nm (2 μm).

Comparative Example 3
An all solid secondary battery according to Comparative Example 3 was manufactured in the same manner as Example 1, except that the thickness of the zinc layer formed by vacuum evaporation was 0.5 nm.

Comparative Example 4
Comparative Example 4 is the same as Example 1 except that no buffer layer is formed between the positive electrode active material layer and the solid electrolyte layer, and a buffer layer is formed between the negative electrode active material layer and the solid electrolyte layer. An all solid secondary battery according to Specifically, a zinc layer having a thickness of 100 nm was formed on the negative electrode active material layer surface of the negative electrode structure by vacuum evaporation to form a negative electrode / buffer layer structure. Next, the negative electrode / buffer layer structure and the positive electrode structure are stacked so that the buffer layer side surface of the negative electrode / buffer layer structure and the positive electrode active material layer side surface of the positive electrode structure are in contact, and pressure molding is performed with a uniaxial press. Did.

Comparative Example 5
No buffer layer is formed between the positive electrode active material layer and the solid electrolyte layer, but a buffer layer is formed between the negative electrode active material layer and the solid electrolyte layer, and the buffer layer is not the zinc layer but the bismuth layer In the same manner as in Example 1, an all solid secondary battery according to Comparative Example 5 was manufactured. Specifically, a bismuth layer having a thickness of 100 nm was formed on the surface of the negative electrode active material layer of the negative electrode structure by vacuum evaporation to form a negative electrode / buffer layer structure. Next, the negative electrode / buffer layer structure and the positive electrode structure are stacked so that the buffer layer side surface of the negative electrode / buffer layer structure and the positive electrode active material layer side surface of the positive electrode structure are in contact, and pressure molding is performed with a uniaxial press. Did.

[2. Evaluation]
(Short circuit test during charging)
The capacity (Ah) of the all-solid-state secondary battery (single cell) according to each example and comparative example was measured by TOSCAT-3100 charge / discharge evaluation apparatus manufactured by Toyo System. In the measurement of the initial capacity, charging was performed at 0.1 C at a C rate, and discharging was performed at 0.01 C. Then, it charged at an arbitrary rate (0.1 C, 0.33 C, 0.5 C) and discharged at 0.1 C. Here, the C rate means the ratio of the current value to the cell capacity.

  If a short circuit occurs during charging, the voltage may drop during charging, or the discharge capacity may decrease because charging can not be completed completely. Therefore, the occurrence of such a condition during charging was determined to be the occurrence of a short circuit, and the evaluation of the presence or absence of a short circuit was performed at all the rates for all solid secondary batteries (single cells) according to Examples and Comparative Examples. . The results are shown in Table 1.

(Evaluation of elemental state of buffer layer)
The all-solid secondary batteries according to Examples 1 to 4 after the short circuit test at the time of charge were disassembled, and the positive electrode / buffer layer structure was taken out. An X-ray photoelectron spectroscopy (XPS) measurement was performed from the buffer layer side of the positive electrode / buffer layer structure using an X-ray photoelectron spectrometer (ESCA5800 manufactured by ULVAC-PHI, Inc.). In any of Examples 1 to 4, a peak having a binding energy of about 1022 eV was observed, and it was found that zinc was present in a divalent manner. Furthermore, when the Auger measurement was performed, it was confirmed that a peak centered on about 497 eV in binding energy was observed, and the metal zinc in the buffer layer was changed to zinc oxide or zinc sulfide.

The configuration of the all solid secondary battery according to each example and comparative example and the result of the short circuit test at the time of charge are shown in Table 1.

  As is clear from Table 1, in the all-solid-state secondary batteries according to Examples 1 to 6, the short circuit during charging was suitably prevented, and the short circuit was prevented even at a high rate.

  On the other hand, in all solid secondary batteries according to Comparative Examples 1 to 5, a short circuit occurred even at a relatively low rate. In particular, in Comparative Examples 4 and 5, it was found that the short circuit can not be prevented even if the buffer layer is formed between the negative electrode active material layer and the solid electrolyte layer.

  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 obvious that those skilled in the art to which the present invention belongs can conceive of various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also fall within the technical scope of the present invention.

1 all solid secondary battery 10 positive electrode layer 11 positive electrode current collector 12 positive electrode active material layer 20 negative electrode layer 21 negative electrode current collector 22 negative electrode active material layer 30 solid electrolyte layer 40 buffer layer

Claims (6)

A positive electrode layer,
A negative electrode layer,
A solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer;
A buffer layer disposed between the positive electrode layer and the solid electrolyte layer,
The buffer layer contains one or more selected from the group consisting of a single metal and a single metalloid other than Li, and oxides and sulfides thereof.
The all-solid-state secondary battery whose thickness of the said buffer layer is 1.0 nm or more and 1000 nm or less.   The all-solid-state secondary battery according to claim 1, wherein Young's modulus of the single metal and the single semimetal is 10 GPa or more and 400 GPa or less.   The single metal and the single metal include Mg, Al, Ca, Ti, Cr, Fe, Zn, Ga, Se, Sr, Y, Zr, Mo, In, Sn, Ag, Sb, Ba and Bi. The all-solid-state secondary battery of Claim 1 or 2 which is 1 or more types selected from a group.   The all-solid-state secondary battery according to any one of claims 1 to 3, wherein the single metal is a base metal.   The all-solid-state secondary battery according to any one of claims 1 to 4, wherein the single metal includes Zn. The all solid according to any one of claims 1 to 5, wherein the solid electrolyte layer comprises a solid electrolyte containing sulfur and one or more elements selected from the group consisting of silicon, phosphorus and boron. Secondary battery.

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