WO2016157348A1

WO2016157348A1 - Bulk-type all-solid-state lithium secondary battery

Info

Publication number: WO2016157348A1
Application number: PCT/JP2015/059831
Authority: WO
Inventors: 恵理奈横山; 純川治
Original assignee: 株式会社日立製作所
Priority date: 2015-03-30
Filing date: 2015-03-30
Publication date: 2016-10-06

Abstract

The purpose of the present invention is to provide a bulk-type all-solid-state battery having high heat resistance and high capacity. In order to solve the above-described problem, a bulk-type all-solid-state lithium secondary battery according to the present invention is characterized by being provided with a positive electrode having a positive electrode mixture layer, a negative electrode having a negative electrode mixture layer, and a solid electrolyte layer arranged between the positive electrode and the negative electrode, and is also characterized in that: at least one of the positive electrode mixture layer and the negative electrode mixture layer contains a lithium salt and a soft viscous crystal containing a pyrrolidinium cation represented by formula (1); and the content of the lithium salt relative to the total amount of the soft viscous crystal and the lithium salt is 0.1-20 mol%.

Description

Bulk type all solid lithium secondary battery

The present invention relates to a bulk type all solid lithium secondary battery.

¡All solid-state secondary batteries using non-flammable or flame-retardant solid electrolytes can have high heat resistance, can reduce module costs necessary for cooling, and can have high energy density. All-solid-state batteries are roughly classified into two types: thin-film all-solid batteries obtained by thinning electrodes and solid electrolyte layers and laminating the thin films, and bulk-type all-solid batteries obtained by laminating fine particles. . Compared with a thin-film all-solid secondary battery, a bulk-type all-solid battery has a higher capacity.

However, in bulk type all-solid-state secondary batteries, since voids exist between the electrolyte or electrode active material particles, the resistance at the electrolyte-active material interface is high, and lithium ion conduction is obstructed.

Therefore, a method of filling the voids between the electrolyte or electrode active material particles with a lithium ion conductive material has been proposed. Patent Document 1 discloses a bulk type all solid lithium secondary battery using borate glass as a filler and Patent Document 2 using a gel electrolyte as a filler. Patent Document 3 describes an all-solid lithium secondary battery using a heat-resistant plastic crystal.

WO2014 / 050500 JP-A-11-7981 WO08 / 081811

The treatment temperature of borate glass disclosed in Patent Document 1 is as high as 600 ° C. or higher, and may react with other electrode constituent members. Moreover, since the gel electrolyte currently disclosed by patent document 2 consists of organic molecules, there exists a possibility of raise | generating a decomposition reaction at high temperature, and there exists a subject in chemical stability. Further, when a gel electrolyte is used as the filler, there is a problem that when the battery driving temperature becomes a high temperature of 100 ° C. or higher, the fluidity of the gel increases and the structural strength of the electrode decreases.

Since the plastic crystal disclosed in Patent Document 3 has a melting point of about 100 ° C., it is not suitable for use at a high temperature exceeding 100 ° C.

An object of the present invention is to provide a bulk type all solid state battery having high heat resistance and high capacity.

In order to solve the above problems, a bulk type all solid lithium secondary battery according to the present invention includes a positive electrode having a positive electrode mixture layer, a negative electrode having a negative electrode mixture layer, and a solid electrolyte disposed between the positive electrode and the negative electrode. And at least one of the positive electrode mixture layer and the negative electrode mixture layer includes a plastic crystal containing a pyrrolidinium cation represented by the formula (1) and a lithium salt, and the plastic crystal and the lithium salt The content of the lithium salt with respect to the total amount of is 0.1 to 20 mol%.

The present invention can provide a bulk type all solid state battery having high heat resistance and high capacity.

It is sectional drawing of the all-solid-state lithium secondary battery which concerns on one Embodiment of this invention. 1 is a schematic cross-sectional view of a positive electrode layer according to an embodiment of the present invention. It is a schematic cross section of the solid electrolyte layer concerning one embodiment of the present invention. 1 is a schematic cross-sectional view of a negative electrode layer according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

FIG. 1 is a cross-sectional view of an all solid state secondary battery according to an embodiment of the present invention. The all-solid-state secondary battery 100 includes a positive electrode current collector 10, a negative electrode current collector 20, a battery case 30, a positive electrode mixture layer 40, a solid electrolyte layer 50, and a negative electrode mixture layer 60. The positive electrode 70 includes the positive electrode current collector 10 and the positive electrode mixture layer 40. The negative electrode 80 includes a negative electrode current collector 20 and a negative electrode mixture layer 60.

<Positive electrode current collector 10>
The positive electrode current collector 10 is electrically connected to the positive electrode 40. For the positive electrode current collector 10, an aluminum foil having a thickness of 10 to 100 μm, an aluminum perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0 to 10 mm, an expanded metal, a foam metal plate, or the like is used. In addition to aluminum, materials such as stainless steel, titanium, and carbon coated aluminum are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

<Negative electrode current collector 20>
The negative electrode current collector 20 is electrically connected to the negative electrode 60. For the negative electrode current collector 20, a copper foil having a thickness of 10 to 100 μm, a copper perforated foil having a thickness of 10 to 100 μm and a pore diameter of 0 to 10 mm, an expanded metal, a foam metal plate, or the like is used. In addition to copper, materials such as stainless steel, titanium, nickel, or carbon-coated aluminum are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

<Battery case 30>
The battery case 30 accommodates the positive electrode current collector 10, the negative electrode current collector 20, the positive electrode mixture layer 40, the solid electrolyte layer 50, and the negative electrode mixture layer 60. The shape of the battery case 30 is a cylindrical shape, a flat oval shape, a flat oval shape, a square shape, or the like according to the shape of the electrode group composed of the positive electrode mixture layer 40, the solid electrolyte layer 50, and the negative electrode mixture layer 60. May be selected. The material of the battery case 30 is selected from materials that are corrosion resistant to the battery material, such as aluminum, stainless steel, and nickel-plated steel.

<Positive electrode mixture layer 40>
In FIG. 2, the schematic cross section of the positive electrode which concerns on one Embodiment of this invention is shown. The positive electrode mixture layer 40 includes a positive electrode active material 41, a solid electrolyte 42, a positive electrode conductive agent 43, and a binder 44.

In the present invention, as the solid electrolyte 42, a lithium ion conductive plastic crystal composed of a plastic crystal and a lithium salt is used. The plastic crystal is an intermediate phase between a solid state and a liquid state, and exhibits high ionic conductivity while maintaining the solid state. It is known that when an ionic salt such as a lithium salt is added to the plastic crystal, the ionic conductivity is further improved by several orders of magnitude (Non-Patent Document 1). Therefore, lithium ion conductivity can be improved by using a lithium ion conductive plastic crystal as a solid electrolyte in the electrode mixture layer.

The plastic crystal is composed of a pyrrolidinium cation and an anion that forms an ion pair with the pyrrolidinium cation. The pyrrolidinium cation is preferably a cation represented by the formula (1).

In the formula (1), R1 and R2 are linear or branched alkyl groups having 1 to 4 carbon atoms. R1 and R2 are preferably any of a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and an isobutyl group, which are easy to rotate the cation.

Since the pyrrolidinium cation has a high melting point, it is possible to increase the heat resistance of the battery. In the conventional liquid battery, the upper limit of the battery driving temperature is as low as about 60 to 80 ° C. due to material deterioration at high temperature and a decrease in safety. The upper limit of the battery driving temperature can be increased by using a plastic crystal having a melting point of 60 ° C. or higher instead of the electrolytic solution. As a result, battery applications such as excavators that use batteries in high-temperature environments and car engine rooms are expanded. By applying a plastic crystal having a melting point of 60 ° C. or higher in a plastic crystal state exhibiting high ionic conductivity at the battery driving temperature, the above-described effect is exhibited.

As the anion, known anions such as hexafluorophosphate, tetrafluoroborate, thiocyanate, bisfluorosulfonylamide, bistrifluoromethanesulfonylamide and the like can be combined. In general, the smaller the volume, the higher the melting point. Therefore, from the viewpoint of increasing the heat resistance of the battery, anions such as hexafluorophosphate, tetrafluoroborate, thiocyanate, and trifluoromethanesulfonylimide having a high melting point are more preferable.

More preferably, the plastic crystal is at least one of the following formulas (2) to (4). This is because the plastic crystals of the formulas (2) to (4) have high ionic conductivity.

As examples of the lithium salt added to the plastic crystal _is represented by _{_{_{LiPF 6, LiBF 4, LiClO 4}}} , LiCF 3 SO 3, LiCF 3 CO 2, LiBOB, LiAsF 6, LiSbF 6, or lithium trifluoromethanesulfonyl imide Examples include lithium imide salts. In the present invention, these salts can be used alone or in combination. If the present embodiment does not decompose on the positive electrode and the negative electrode, other lithium salts may be used.

The addition concentration of the lithium salt in the lithium ion conductive plastic crystal is 0.1 to 20 mol%. More preferably, it is 0.5 to 15 mol%, and further preferably 1 to 10 mol%. When the content of the lithium salt is 0.1 mol% or less, the lithium ion conductivity is low, and the battery output decreases. When the content of the lithium salt is 20 mol% or more, the melting point is remarkably lowered by addition of lithium, and the heat resistance of the battery is lowered. Here, the lithium salt concentration (mol%) is the amount (mol) of lithium salt relative to the total amount of the substance amount (mol) of the plastic crystal and the substance amount (mol) of the lithium salt added to the plastic crystal. is there.

The content of the lithium ion conductive plastic crystal in the positive electrode mixture is preferably 10 to 90% by weight. When the content of the lithium ion conductive plastic crystal is less than 10% by mass, the ion conduction path is reduced and the resistance is increased. On the other hand, when the content of the lithium ion conductive plastic crystal is larger than 90% by mass, the amount of the active material is decreased and the energy density of the battery is decreased. Further, an electron conduction path cannot be formed, and the resistance is increased. The content of the thion ion conductive plastic crystal is more preferably 20 to 50% by weight, still more preferably 30 to 40% by weight.

In addition to the lithium ion conductive plastic crystal, a substance known as a solid electrolyte may be mixed. The solid electrolyte is not particularly limited as long as it is a solid material that conducts lithium ions, but it is desirable to include a nonflammable inorganic solid electrolyte from the viewpoint of safety. Specifically, Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ , LiAlGe (PO ₄ ) ₃ , Li _3.4 V _0.6 Si _0.4 O ₄ , Li ₂ P ₂ O An oxide glass represented by ₆ or the like, a perovskite oxide represented by Li _0.34 La _0.51 TiO _2.94 or a garnet oxide represented by LiLaZrO 2 can be used. The oxide conductor may contain a lithium halide such as LiCl or LiI. A sulfide-based inorganic solid electrolyte can also be suitably used.

Examples of the positive electrode active material 41 include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2−x MxO ₂ (where M = Co, Ni , Fe, Cr, Zn, Ti, at least one selected from the group consisting of x = 0.01 to 0.2, Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, Cu, Zn Li _1-x A _x Mn ₂ O ₄ (however, A = Mg, B, Al, Fe, Co, Ni, Cr, Zn, Ca, at least one selected from the group consisting of Species, x = 0.01 to 0.1), LiNi _1-x M _x O ₂ (where M = at least one selected from the group consisting of Co, Fe, and Ga, x = 0.01 to 0.2) ), LiFe O ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-x M _x O ₂ (where M = Ni, Fe, Mn, at least one selected from the group consisting of x = 0.01 to 0.2), LiNi _1-x M _x O ₂ (M = Mn, Fe, Co, Al, Ga, Ca, Mg, at least one selected from the group consisting of x = 0.01 to 0.2), Fe (MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , LiMnPO _{4 and the} like can be used. One kind or two or more kinds of the above materials may be contained as the positive electrode active material. In the positive electrode active material, lithium ions are desorbed in the charging process, and lithium ions desorbed from the negative electrode active material in the negative electrode mixture layer 60 are inserted in the discharging process.

The particle diameter of the positive electrode active material 41 is normally defined so as to be equal to or less than the thickness of the positive electrode mixture layer 40. Specifically, the particle size of the positive electrode active material is preferably 10 to 100 μm. When the positive electrode active material powder has coarse particles having a size larger than the thickness of the mixture layer, the coarse particles are removed in advance by sieving classification or wind classification to produce particles having a thickness of the mixture layer or less. Is preferred.

Further, since the positive electrode active material 41 is generally oxide-based and has high electric resistance, it is preferable to mix a positive electrode conductive agent 43 made of carbon powder for supplementing electric conductivity into the positive electrode mixture layer. Since both the positive electrode active material and the positive electrode conductive agent are usually powders, a binder can be mixed with the powders, and the powders can be bonded together and simultaneously bonded to the positive electrode current collector 10.

Examples of the positive electrode conductive agent include acetylene black, carbon black, and carbon materials such as graphite or amorphous carbon. Examples of the positive electrode binder include styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF), polyimide, and a mixture thereof. Imide binders are thermally stable and are particularly suitable for battery driving at high temperatures. In addition, a binder having a reactive group that crosslinks by heating or ultraviolet irradiation is also preferably used. As the reactive group, a vinylene group, a hydroxyl group, an epoxy group, an allyl group, a carbonyl group, or a reactive group obtained by substituting a part of the reactive group with a different element is preferably used.

A positive electrode slurry in which a positive electrode active material, a solid electrolyte, a positive electrode conductive agent, a positive electrode binder, and a solvent are mixed is attached to the positive electrode current collector 10 by a doctor blade method, a dipping method, a spray method, screen printing, or the like. The coating type positive electrode can be produced by drying and pressure forming with a roll press. In addition, a plurality of positive electrode mixture layers 40 can be laminated on the positive electrode current collector 10 by performing a plurality of times from application to drying. Alternatively, the positive electrode active material layer, the positive electrode conductive material, the plastic crystal, and the lithium salt are stirred by a known technique and formed into a pellet shape by pressurization to form a positive electrode mixture layer. In the pellet electrode, a configuration in which a binder is added according to the structural strength of the pellet is also possible.

As the positive electrode active material, a pellet may be produced using an active material combined with lithium ion conductive plastic crystal. As a composite method, known techniques may be suitably used. Specifically, mortar mixing, mechanical milling, a method of adding an active material to a plastic crystal diluted with a solvent and drying, or sputtering to the active material surface Examples thereof include a method of coating a lithium ion conductive plastic crystal.

The porosity of the positive electrode mixture layer is preferably in the range of 0.01 to 20%. This is because if the porosity exceeds 20%, the lithium ion conductivity is remarkably inhibited and a high capacity cannot be obtained. The lower the porosity of the positive electrode mixture layer, the lower the resistance. However, 0.01% is practically sufficient. From the viewpoint of lithium ion diffusion, the porosity is more preferably 0.01 to 10%, and particularly preferably 0.01 to 1%. By using the lithium ion conductive plastic crystal according to the present invention as a solid electrolyte, the porosity of the positive electrode mixture layer can be reduced. The porosity can be measured with a mercury porosimeter.

<Solid electrolyte layer 50>
FIG. 3 shows a schematic cross-sectional view of a solid electrolyte layer according to an embodiment of the present invention. The solid electrolyte layer 50 includes

solid electrolytes

51 and 52 and a binder 53.

The solid electrolyte 51 is not particularly limited as long as it is a solid material that conducts lithium ions, but it is preferable that the solid electrolyte 51 includes a nonflammable inorganic solid electrolyte from the viewpoint of safety. Specifically, Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ , LiAlGe (PO ₄ ) ₃ , Li _3.4 V _0.6 Si _0.4 O ₄ , Li ₂ P ₂ O An oxide glass represented by ₆ or the like, a perovskite oxide represented by Li _0.34 La _0.51 TiO _2.94 or a garnet oxide represented by LiLaZrO 2 can be used. The oxide conductor may contain a lithium halide such as LiCl or LiI. A sulfide-based inorganic solid electrolyte can also be suitably used. These solid electrolytes can be used alone or in combination of two or more.

As the solid electrolyte, lithium ion conductive plastic crystal 52 may be used. The same lithium ion conductive plastic crystal as that used for the positive electrode mixture layer can be used. As long as sufficient mechanical strength is maintained, the solid electrolyte layer may be formed of the lithium ion conductive plastic crystal 52 alone without using the other solid electrolyte 51. Moreover, what added the binder 53 to the lithium ion conductive plastic crystal 52 is good also as a solid electrolyte layer. As the binder, known ones can be used. Specifically, styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF), polyimide, a mixture thereof, and the like can be used.

In order to prevent a short circuit between the positive and negative electrodes, a short circuit prevention layer can be provided inside the solid electrolyte layer. Even when the battery is heated above the melting point of the plastic crystal, the presence of the short-circuit blocking layer can suppress the direct contact between the positive and negative electrodes, thereby ensuring the safety of the battery. As a material for the short-circuit prevention layer, a polyolefin polymer sheet made of polyethylene, polypropylene, etc. having a thickness of 20 to 100 μm, a two-layer structure in which a polyolefin polymer and a fluorine polymer sheet typified by tetrafluoropolyethylene are welded. Polyamide fiber sheets, glass fiber sheets and the like can be used. A mixture of ceramics and a binder may be formed in a thin layer on the surface of the short-circuit prevention layer so that the short-circuit prevention layer does not shrink when the battery temperature increases. The short-circuit prevention layer can be freely selected according to the kind of the plastic crystal in order to facilitate the penetration of the plastic crystal into the short-circuit prevention layer.

<Negative electrode mixture layer 60>
FIG. 4 shows a schematic cross-sectional view of a negative electrode according to an embodiment of the present invention. The negative electrode mixture layer 60 includes a negative electrode active material 61, a solid electrolyte 62, a negative electrode conductive agent 63, and a binder 64.

In the present invention, as the solid electrolyte 62, a lithium ion conductive plastic crystal composed of a plastic crystal and a lithium salt is used.

The same lithium ion conductive plastic crystal as that used for the positive electrode mixture layer can be used.

The content of the lithium ion conductive plastic crystal in the negative electrode mixture is preferably 10 to 90% by weight, and more preferably 20 to 50% by weight, like the positive electrode mixture.

As the negative electrode active material 61, a carbon material capable of reversibly inserting and desorbing lithium ions, silicon-based materials Si, SiO, tin-based materials, lithium titanate with or without a substitution element, lithium vanadium composite oxide, lithium And a negative electrode active material 61 made of an alloy of, for example, tin, aluminum, antimony and the like. As a carbon material, natural graphite, composite carbonaceous material in which a film is formed on natural graphite by a dry CVD method or a wet spray method, a resin material such as epoxy or phenol, or a pitch material obtained from petroleum or coal is used as a raw material. Examples thereof include artificial graphite and non-graphitizable carbon material produced by firing. The negative electrode active material 61 may contain one or more of the above materials.

The particle diameter of the negative electrode active material 61 is normally defined so as to be equal to or less than the thickness of the negative electrode mixture layer 60. Specifically, the particle size is preferably 10 to 100 μm. If the negative electrode active material 61 powder has coarse particles having a size equal to or greater than the thickness of the mixture layer, the coarse particles are removed in advance by sieving or airflow classification, and particles having a thickness of the negative electrode mixture layer 60 or less are removed. It is preferable to produce it.

When the negative electrode mixture layer 60 includes the negative electrode conductive agent 63 and the negative electrode binder 64, examples of the negative electrode conductive agent include acetylene black, carbon black, and carbon materials such as graphite or amorphous carbon. Examples of the negative electrode binder include styrene-butadiene rubber, carboxymethyl cellulose, polyvinylidene fluoride (PVDF), polyimide, and a mixture thereof. In particular, the imide-based binder is thermally stable and is a particularly suitable binder when driving a battery at a high temperature. In addition, a binder having a reactive group that crosslinks by heating or ultraviolet irradiation is also preferably used. As the reactive group, a vinylene group, a hydroxyl group, an epoxy group, an allyl group, a carbonyl group, or a reactive group obtained by substituting a part of the reactive group with a different element is preferably used.

The method for producing the negative electrode is not particularly limited, but the negative electrode slurry obtained by mixing the negative electrode active material 61, the lithium ion conductive plastic crystal 62, the negative electrode conductive agent 63, the negative electrode binder 64, and an arbitrary solvent is mixed with a doctor blade method or a dipping method. Or after being attached to the negative electrode current collector 20 by a spray method, a screen printing method or the like, the solvent is dried, and pressure forming is performed by a roll press to produce a coated negative electrode, a negative electrode active material, a positive electrode conductive material, A method in which a lithium conductive plastic crystal and a lithium salt are stirred by a known technique and formed into a pellet shape by pressurization is used as a negative electrode mixture layer. In the pellet electrode, a configuration in which a binder is added according to the structural strength of the pellet is also possible.

As the negative electrode active material, a pellet may be produced using an active material combined with lithium ion conductive plastic crystal. As a composite method, known techniques may be suitably used. Specifically, mortar mixing, mechanical milling, a method of adding an active material to a plastic crystal diluted with a solvent and drying, or sputtering to the active material surface Examples thereof include a method of coating a lithium ion conductive plastic crystal.

Similarly to the positive electrode mixture layer, the porosity of the negative electrode mixture layer is preferably 0.01 to 20%.

<Electrode layer>
The form of the positive electrode mixture layer and the negative electrode mixture layer attached to the current collector foil can be appropriately selected depending on the use and shape of the battery. A mixture material layer may be present so as to cover the entire surface of the current collector foil, or portions (hereinafter referred to as blanks) where the material mixture layer does not exist may be left at the four corners of the current collector foil.

As a method of forming a solid electrolyte layer containing lithium conductive plastic crystals on the mixture layer adhered to the current collector foil, pelletized or sheeted lithium conductive plastic crystals are laminated on the current collector foil. And a method of applying a lithium conductive plastic crystal mixed with a solvent onto an electrode mixture and distilling off the solvent can be suitably used. In order to fill the electrode with the lithium conductive plastic crystal, a method such as heating, vacuum evacuation, or pressurization may be applied.

As the shape of the electrode, there are a rolled (pellet type) electrode and a coated electrode, but a coated electrode is preferable. The rolled electrode is obtained by rolling an electrode mixture to form a sheet-like mixture layer and sticking the sheet-like mixture layer on a current collector foil. On the other hand, a coated electrode is an electrode obtained by coating an electrode mixture on a current collector foil. By using a coated electrode, it is easy to increase the area of the electrode. As a result, it can be applied to large-sized storage batteries for in-vehicle use and industrial use. In addition, since the electrode can be thinned, the energy density can be improved.

<Battery>
The all-solid-state battery may be a bipolar type in which a plurality of single cells each having a positive electrode mixture layer, a solid electrolyte layer, and a negative electrode mixture layer are stacked. Specifically, the area of the solid electrolyte layer containing the lithium ion conductive plastic crystal in contact with the electrode mixture layer is smaller than the blank area of the current collector foil and larger than that of the electrode mixture layer. A liquid short circuit between cells can be suppressed, and a battery configuration with higher energy density can be achieved. In order to suppress a liquid short circuit accompanying deformation of the solid electrolyte layer due to heating or pressure, a sealing structure can be applied to the blank portion. The sealing structure and material are not particularly limited, but known sealing materials such as adhesive seals and packings using high heat resistant materials such as silicone rubber, fluoro rubber, polyether ether ketone, polytetrafluoroethylene, etc. can be applied.

It is also possible to form a planar bipolar cell by forming a plurality of single cells on an insulating substrate and forming a conductive network between the single cells. A method for forming a single cell on an insulating substrate is not particularly limited, and a known technique can be applied. As a method for forming a conductive network, in addition to screen printing and a method in which a solution in which an electronic conductive material is dispersed in a solvent is applied and then dried, a method of connecting single cells with a conductive metal foil or an electronic conductive tape Can be applied.

In order to suppress an increase in resistance due to peeling between the electrode and the solid electrolyte layer, a heating step may be included at the time of cell production. Also, a heating mechanism can be provided outside the battery, and the plastic crystal can be deformed by heating to improve the bondability between the electrode and the solid electrolyte layer. A known technique can be applied as the heating mechanism, and specific examples include a method of coating the outside of the battery with a linear / planar heating element. By providing the above heating mechanism, even when the interfacial bondability between the electrode layer / solid electrolyte layer is reduced when an active material that changes in volume during charge / discharge, such as graphite or silicon-based active material, is applied, the battery is disassembled. The interface can be repaired without doing so.

In order to suppress peeling of the electrode mixture layer and the solid electrolyte layer, a pressurizing mechanism can be introduced into the all solid state battery. As the pressing method, an optimum method can be selected depending on the battery shape. For example, in a laminate pack type battery, a fixing plate can be installed so as to sandwich the laminate pack in the electrode stacking direction, and the fixing plate can be fixed with screws or the like, or a pressurizing instrument such as a spring can be used.

Hereinafter, modes for carrying out the present invention will be described by way of specific examples.

<Preparation of lithium conductive plastic crystal>
The plastic crystal represented by formula (2) and lithium bis (fluorosulfonyl) imide (LiTFSI), which is a lithium salt, are mixed in a glove box in an argon atmosphere using a mortar, sealed in a heat-resistant container, and heated to a temperature higher than the melting point. did. The mixture was stirred in a liquid state and air-cooled, then opened in a glove box, and the mixture was pulverized in a mortar. The prepared mixture was used as a lithium ion conductive plastic crystal. The lithium salt concentration was 5 mol%.

<Preparation of positive electrode>
Lithium cobaltate LiCoO ₂ (hereinafter referred to as LCO), lithium conductive plastic crystal (hereinafter referred to as IPC), and acetylene black (hereinafter referred to as AB) are weighed at a ratio of 30:50:20 (wt%). And mixed uniformly using an agate mortar. 0.3 g of the mixture was weighed, and a positive electrode pellet of 15 mmΦ was prepared using a die. All the above operations were carried out in an argon atmosphere glove box.

<Preparation of solid electrolyte layer>
0.1 g of lithium conductive plastic crystal was weighed and pressed with a die to produce a 15 mmφ pellet. The above operation was performed in a glove box in an argon atmosphere.

<Preparation of negative electrode layer>
Lithium titanate LiTi ₄ O ₁₂ (hereinafter referred to as LTO), lithium conductive plastic crystal, and AB were weighed at a ratio of 30:50:20 (wt%) and mixed uniformly using an agate mortar. . 0.1 g of the mixture was weighed and pressed using a die to prepare a negative electrode pellet of 15 mmΦ. All the above operations were carried out in an argon atmosphere glove box.

<Production of evaluation cell>
In a glove box in an argon atmosphere, a positive electrode pellet, a solid electrolyte layer, and a negative electrode pellet were stacked inside a stainless steel bipolar cell, and the four corners were fixed and sealed. The cell was placed in a thermostatic bath and heated at a temperature 10 ° C. lower than the melting point for 1 hour.

<Evaluation of electrochemical characteristics>
The cell was installed in a thermostat set at 60 ° C., and charge / discharge was performed in the voltage range of 4.2 to 2.5 V at a charge / discharge rate of 0.01 C, and the initial discharge capacity was measured. The charge / discharge current was set to 0.01 C with respect to the LCO design capacity.

An evaluation cell was produced in the same manner as in Example 1 except that the plastic crystal was changed to the formula (3) and the lithium salt was changed to LiPF ₆ . The electrochemical characteristics were also tested in the same manner as in Example 1 except that the set temperature of the thermostatic bath was set to 200 ° C.

An evaluation cell was prepared in the same manner as in Example 2 except that the plastic crystal was changed to the formula (4) and the lithium salt was changed to LiBF _6, and the electrochemical characteristics were measured.

The experiment was performed in the same manner as in Example 1 except that the addition concentration of the lithium salt was 0.1 mol%.

The experiment was performed in the same manner as in Example 1 except that the addition concentration of lithium salt was 20 mol%.

For the positive electrode mixture layer, LCO, lithium conductive plastic crystal, and AB are in a ratio of 50: 5: 45 (wt%), and for the negative electrode mixture layer, LTO, lithium conductive plastic crystal, and AB are 50: 5: The experiment was performed in the same manner as in Example 1 except that the ratio was 45 (wt%).

For the positive electrode mixture layer, LCO, lithium conductive plastic crystal, and AB are in a ratio of 10:80:10 (wt%), and for the negative electrode mixture layer, LTO, lithium conductive plastic crystal, and AB are 10:80: The experiment was performed in the same manner as in Example 1 except that the ratio was 10 (wt%).

For the positive electrode mixture layer, LCO, lithium conductive plastic crystal, AB, and PVDF are in a ratio of 40: 40: 4: 6 (wt%), and for the negative electrode mixture layer, LTO, lithium conductive plastic crystal, AB, The experiment was performed in the same manner as in Example 1 except that PVDF was used at a ratio of 40: 40: 4: 6 (wt%) and a coated electrode was used. The coated electrode was obtained by applying a slurry of LCO or LTO, lithium conductive plastic crystal, AB, PVDF, and N-methylpyrrolidone on a copper foil and distilling off NMP in a constant temperature layer at 80 ° C. . Thereafter, uniaxial pressing was performed. When the porosity of the positive electrode mixture layer and the porosity of the negative electrode mixture layer of Example 8 were measured, they were 11% and 12%, respectively.

For the positive electrode mixture layer, LCO, lithium conductive plastic crystal, AB, and PVDF are in a ratio of 40: 40: 4: 6 (wt%), and for the negative electrode mixture layer, LTO, lithium conductive plastic crystal, AB, The experiment was performed in the same manner as in Example 1 except that PVDF was used at a ratio of 40: 40: 4: 6 (wt%) and a coated electrode was used. The coated electrode was obtained by applying a slurry of LCO or LTO, lithium conductive plastic crystal, AB, PVDF, and N-methylpyrrolidone on a copper foil and distilling off NMP in a constant temperature layer at 80 ° C. . When the porosity of the positive electrode mixture layer of Example 9 and the porosity of the negative electrode mixture layer were measured, they were 5% and 3%, respectively.

(Comparative Example 1)
The experiment was performed in the same manner as in Example 1 except that the addition concentration of the lithium salt was 0.05 mol%. Also in Comparative Example 1, the discharge capacity was measured in the same manner as in Example 1. However, in the evaluation cell according to Comparative Example 1, the resistance was high and charging / discharging was impossible.

From Examples 1, 4, 5 and Comparative Example 1, it was found that when the additive concentration of the lithium salt was less than 0.1%, the resistance was increased and charge / discharge could not be performed. Moreover, when Examples 1, 4, and 5 were compared, the discharge capacity was maximum in Example 1 in which the concentration of the lithium salt added was 5%. In Example 4 in which the added salt concentration of the lithium salt was 0.1%, the ionic conductivity of the plastic crystal itself was lower and the resistance was higher than in Example 1, so that the discharge capacity was considered to be low. . In Example 5 in which the added salt concentration of the lithium salt was 20%, the ion conductivity was sufficient, but the melting point was 50 ° C. or lower, and the heat resistance was lowered.

When comparing Examples 1, 6, and 7, the discharge capacity of Example 1 was maximized. In Example 6, since the content of the plastic crystal in the electrode mixture layer was small, the ion conduction path was decreased and the resistance was increased. As a result, the discharge capacity was considered to be decreased. In Example 7, since the content of the plastic crystal in the electrode mixture layer was large, it was considered that the discharge capacity was reduced as a result of insufficient electron conduction path and increased resistance.

From comparisons of Examples 1, 8, and 9, it was found that the discharge capacity was improved by using a coated electrode rather than a pellet type electrode. It is considered that by using the coated electrode, an ion conduction path and an electron conduction path are formed in the entire electrode, and the resistance is reduced. Further, in Example 9 in which the electrode was pressed, the discharge capacity was increased as a result of the decrease in the gap as compared with Example 8 in which the electrode was not pressed. This is considered to be because the resistance was lowered as a result of filling the voids with plastic crystals or conductive aid by pressing.

DESCRIPTION OF SYMBOLS 10 ... Positive electrode collector, 20 ... Negative electrode collector, 30 ... Battery case, 40 ... Positive electrode mixture layer, 41 ... Positive electrode active material, 42 ... Lithium ion conductive plastic crystal, 43 ... Positive electrode conductive material, 44 ... Positive electrode binder, 50 ... solid electrolyte layer, 51 ... solid electrolyte particles, 52 ... lithium ion conductive plastic crystal, 53 ... electrolyte binder, 60 ... negative electrode mixture layer, 61 ... negative electrode active material, 62 ... lithium ion conductive soft material Viscous crystal 63 ... Negative electrode conductive material 64 ... Negative electrode binder 70 ... Positive electrode 80 ... Negative electrode 100 ... All solid state secondary battery

Claims

A bulk type all solid lithium secondary battery comprising a positive electrode having a positive electrode mixture layer, a negative electrode having a negative electrode mixture layer, and a solid electrolyte layer disposed between the positive electrode and the negative electrode,
At least one of the positive electrode mixture layer and the negative electrode mixture layer includes a plastic crystal containing a pyrrolidinium cation represented by the formula (1), and a lithium salt.
A bulk type all-solid-state lithium secondary battery, wherein a content of the lithium salt with respect to a total amount of the plastic crystal and the lithium salt is 0.1 to 20 mol%.

(In Formula (1), R1 and R2 are linear or branched alkyl groups.)
The bulk type all solid lithium secondary battery according to claim 1,
The bulk type all solid lithium secondary battery, wherein R1 and R2 are any one of a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and an isobutyl group.
The bulk type all solid lithium secondary battery according to claim 1,
A bulk type all-solid-state lithium secondary battery comprising at least one of trifluoromethanesulfonylimide, hexafluorophosphate, and tetrafluoroborate as an anion that forms an ion pair with the pyrrolidinium cation.
The bulk type all solid lithium secondary battery according to claim 1,
The bulk type all solid lithium secondary battery, wherein the plastic crystal is at least one of the following formulas (2) to (4).
A bulk type all solid lithium secondary battery according to any one of claims 1 to 4,
A bulk type all solid lithium secondary battery, wherein the plastic crystal and the lithium salt are combined.
A bulk type all solid lithium secondary battery according to any one of claims 1 to 4,
A bulk type all-solid-state battery, wherein a total amount of the plastic crystal content and the lithium salt content in the positive electrode mixture layer is 10 to 90% by weight.
A bulk type all solid lithium secondary battery according to any one of claims 1 to 4,
A bulk type all-solid-state lithium secondary battery, wherein a porosity of at least one of the negative electrode mixture layer and the positive electrode mixture layer is 0.01 to 20%.
A bulk type all solid lithium secondary battery according to any one of claims 1 to 7,
The positive electrode is an electrode obtained by coating the positive electrode mixture layer on the surface of a current collector,
A bulk type all-solid lithium secondary battery, wherein the negative electrode is an electrode obtained by coating the negative electrode mixture layer on the surface of a current collector.
A bulk type all solid lithium secondary battery according to any one of claims 1 to 8,
The positive electrode comprises a positive electrode current collector foil, the area of the positive electrode current collector foil is larger than the area of the positive electrode mixture layer,
The bulk-type all solid lithium secondary battery, wherein the negative electrode includes a negative electrode current collector foil, and an area of the negative electrode current collector foil is larger than an area of the negative electrode mixture layer.
A bulk type all solid lithium secondary battery according to any one of claims 1 to 9,
The positive electrode mixture layer is electrically bonded to one surface of the current collector,
The bulk type all-solid-state lithium secondary battery, wherein the negative electrode mixture layer is electrically joined to the other surface of the current collector.
A battery system comprising: the bulk type all solid lithium secondary battery according to any one of claims 1 to 8; and a temperature control device.