JP5487719B2 - Manufacturing method of all-solid lithium secondary battery, and all-solid lithium secondary battery obtained by the manufacturing method - Google Patents

Description

  The present invention relates to a method for producing an all solid lithium secondary battery, and an all solid lithium secondary battery obtained by the production method.

  The secondary battery can convert the decrease in chemical energy associated with the chemical reaction into electrical energy and perform discharge. In addition, the secondary battery converts electrical energy into chemical energy by flowing current in the opposite direction to that during discharge. A battery that can be stored (charged). Among secondary batteries, lithium secondary batteries are widely used as power sources for notebook personal computers, mobile phones, and the like because of their high energy density.

In the lithium secondary battery, when graphite (expressed as C ₆ ) is used as the negative electrode active material, the reaction of the formula (1) proceeds at the negative electrode during discharge.
C ₆ Li → C ₆ + Li ⁺ + e ⁻ (1)
The electrons generated by the equation (1) reach the positive electrode after working with an external load via an external circuit. Then, lithium ions (Li ⁺ ) generated in the formula (1) move from the negative electrode side to the positive electrode side by electroosmosis in the electrolyte sandwiched between the negative electrode and the positive electrode.

Further, when lithium cobaltate (Li _0.4 CoO ₂ ) is used as the positive electrode active material, the reaction of the formula (2) proceeds at the positive electrode during discharge.
Li _0.4 CoO ₂ + 0.6 Li ⁺ + 0.6e ⁻ → LiCoO ₂ (2)
At the time of charging, the reverse reactions of the above formulas (1) and (2) proceed in the negative electrode and the positive electrode, respectively, and in the negative electrode, graphite (C ₆ Li) into which lithium has entered by graphite intercalation is present in the positive electrode. Since lithium cobaltate (Li _0.4 CoO ₂ ) is regenerated, re-discharge is possible.

  Generally, in an electrode of a lithium secondary battery, an electrolyte is mixed and used in order to increase the mobility of lithium ions. In the case of an all-solid lithium secondary battery in which a solid electrolyte is mixed with an electrode, the electrolyte and the active battery are compared with a lithium secondary battery in which an electrolyte containing a liquid or an electrolyte is mixed. It was difficult to maintain the ion conduction path at the interface with the substance. In other words, when a solid electrolyte is used, even if the bonding interface between the solid electrolyte and the electrode active material is initially in good electrochemical contact, the ions are expanded due to expansion / contraction caused by ions entering and exiting the active material. There is a problem that the transmission path is broken and it is difficult to maintain the cycle performance.

  Techniques for solving such problems associated with the use of solid electrolytes have been developed so far. In Patent Document 1, in a stacked solid secondary battery in which a solid electrolyte made of an inorganic oxide is interposed between a positive electrode and a negative electrode, at least one of the electrodes has a volume in a discharge end state with respect to a charge end state. There is disclosed a technique of a stacked solid secondary battery characterized in that an active material made of an inorganic oxide sintered body having a change rate of 1.5% or less is used.

JP 2000-331684 A

The technique disclosed in Patent Document 1 limits the active material that can be used only to an active material having a volume change rate within a certain range. Therefore, even if the technique disclosed in Patent Document 1 is used, it is not always possible to select an optimal active material for the required battery performance.
The present invention has been accomplished in view of the above circumstances, and provides an all-solid lithium secondary battery manufacturing method that suppresses delamination between layers, and an all-solid lithium secondary battery obtained by the manufacturing method. Objective.

The first method for manufacturing an all-solid lithium secondary battery of the present invention, containing the positive electrode current collector, and, LiCoO ₂ or _{Li (1 + x) Mn (} 2-x) O 4 a (0 ≦ x <0.1) A positive electrode body having a positive electrode active material layer, a negative electrode current collector, a negative electrode body having a negative electrode active material layer containing at least a negative electrode active material, and Li _0.5 sandwiched between the positive electrode body and the negative electrode body A method for producing an all solid lithium secondary battery having La _0.5 TiO ₃ or Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ with a sintering step, wherein the Li _{0. When} preparing ₅ La _0.5 TiO ₃ or Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ , and using the Li _0.5 La _0.5 TiO ₃ as a support using the positive electrode containing LiCoO _2, wherein the _{Li 1.5 l 0.5 Ge 1.5 (PO 4)} 3 when to the support using a positive electrode containing _{Li (1 + x) Mn (} 2-x) O 4 (0 ≦ x <0.1), The residual stress at the interface between the support and the positive electrode active material layer of the positive electrode body is relaxed in a temperature region below the sintering temperature, compared to when sintering without applying stress in a direction perpendicular to the surface direction, and When the all-solid lithium secondary battery is charged, the residual stress at the interface between the support and the positive electrode active material layer is 0 when the charge depth X is 1 or more in the range of 0 <X <100. %, A sintering step of integrating with the support by sintering while applying a stress in a direction perpendicular to the surface direction of the positive electrode active material layer .

In the method for producing an all solid lithium secondary battery having such a configuration, in the temperature region below the sintering temperature, the residual stress at the interface between the support and the positive electrode active material layer is set to a certain range or less. Peeling between the support and the positive electrode active material layer can be suppressed. In addition, the method for manufacturing an all-solid lithium secondary battery having such a configuration is a method of remaining at the interface between the support and the positive electrode active material layer in a charged state that is expected to be most frequently used in actual use. The stress can be designed to be 0%, and it is possible to suppress delamination between the support and the positive electrode active material layer due to expansion and contraction caused by ions entering and leaving the active material during charging. .

The second method for manufacturing an all-solid lithium secondary battery of the present invention, the electrode current collector, and containing LiCoO ₂ or _{Li (1 + x) Mn (} 2-x) O 4 (0 ≦ x <0.1) An electrode body having a positive electrode active material layer on one surface of the electrode current collector and a negative electrode active material layer containing at least a negative electrode active material on the other surface of the electrode current collector, Sintering of an all-solid lithium secondary battery having Li _0.5 La _0.5 TiO ₃ or Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ sandwiched between two electrode bodies a manufacturing method involving the step, the step of preparing said _Li 0.5 _La 0.5 TiO ₃ or _{Li 1.5 Al 0.5 Ge 1.5 (PO} 4) 3, as well as the _{Li 0.5} containing LiCoO ₂ is when the la _0.5 TiO ₃ and the support The active material layer was used by relatively and the support, said _{Li 1.5 Al 0.5 Ge 1.5 (PO} 4) 3 when to support _{Li (1 + x) Mn (} 2-x) The positive electrode active material layer containing O ₄ (0 ≦ x <0.1) is used relative to the support, and the support is more than the case of sintering without applying stress in the direction perpendicular to the plane direction. When the residual stress at the interface between the body and the positive electrode active material layer of the electrode body is relaxed in a temperature region below the sintering temperature and the all-solid lithium secondary battery is charged, the charging depth X is 0 <X < Stress is applied in a direction perpendicular to the surface direction of the positive electrode active material layer so that the residual stress at the interface between the support and the positive electrode active material layer is 0% at a value of 1 or 2 in the range of 100. include sintering process, it is integrated with the support by sintering while applying And features.

  The all solid lithium secondary battery of the present invention is obtained by the above production method.

  According to the present invention, in the temperature region below the heating temperature, the residual stress at the interface between the support and the electrode active material layer is set to a certain range or less, whereby the support and the electrode active material layer Peeling between layers can be suppressed.

It is a figure which shows an example of the all-solid-state lithium secondary battery of this invention, Comprising: It is the figure which showed typically the cross section cut | disconnected in the lamination direction. It is the graph which showed the simulation result of the all-solid-state lithium secondary battery using the laminated body of Example 1 and 2 and Comparative Example 1 and 2.

  The method for producing an all solid lithium secondary battery according to the present invention includes an electrode current collector, an electrode body having an electrode active material layer containing at least an electrode active material, and lithium ion conduction sandwiched between the two electrode bodies. An all-solid lithium secondary battery having a conductive solid electrolyte, which is a manufacturing method involving a heating step, the step of preparing the electrode current collector or the lithium ion conductive solid electrolyte, and the electrode current collector The residual stress at the interface between the support and the electrode active material layer of the electrode body is higher than that when the substrate or the lithium ion conductive solid electrolyte is used as a support and heating is performed without applying a stress in the plane direction. And applying stress in a surface direction to at least one of the support and the electrode active material layer so as to relax in a temperature region below the heating temperature, thereby integrating the support and the electrode active material layer. Heating step of, characterized in that it comprises a.

As one aspect of the method for producing an all solid lithium secondary battery of the present invention, a positive electrode current collector, a positive electrode body having a positive electrode active material layer containing at least a positive electrode active material, a negative electrode current collector, and at least Method of manufacturing an all-solid lithium secondary battery having a negative electrode body having a negative electrode active material layer containing a negative electrode active material, and the lithium ion conductive solid electrolyte sandwiched between the positive electrode body and the negative electrode body, accompanied by a heating step And the structure of including the process of preparing the electrode collector of the electrode body of either the said positive electrode body or the said negative electrode body, or the said lithium ion conductive solid electrolyte can be taken.
Moreover, as one aspect of the method for producing an all solid lithium secondary battery of the present invention, the electrode current collector and a positive electrode active material layer containing at least a positive electrode active material are provided on one surface of the electrode current collector. In addition, the electrode body having a negative electrode active material layer containing at least a negative electrode active material on the other surface of the electrode current collector, and a lithium ion conductive solid electrolyte sandwiched between the two electrode bodies The all-solid-state lithium secondary battery having the following structure can be used.
That is, by carrying out the manufacturing method according to the present invention, an all-solid lithium secondary battery having an electrode current collector composed of two types of a positive electrode current collector and a negative electrode current collector, and a positive electrode current collector and a negative electrode current collector. Any battery of an all-solid-state lithium secondary battery having a bipolar electrode including an electrode current collector integrated with an electric body can be manufactured.
Hereinafter, unless otherwise specified, the specification mainly describes a method for producing an all-solid lithium secondary battery having an electrode current collector composed of two types of a positive electrode current collector and a negative electrode current collector.

The “all-solid lithium secondary battery” in the present invention refers to a lithium secondary battery in which each element is all solid. Therefore, for example, a lithium secondary battery using a liquid electrolyte as an electrolyte is not included in the present invention.
In the present invention, the “solid electrolyte” refers to an organic electrolyte. In this case, the organic electrolyte includes not only a polymer electrolyte but also a gel electrolyte.

As described above, normally, in an active material used in an all-solid lithium secondary battery, expansion / contraction occurs due to charge / discharge reaction of the battery, that is, insertion or release reaction of lithium ions into / from the active material. . On the other hand, the solid electrolyte used in the battery does not change in volume due to the insertion or withdrawal reaction of lithium ions. Accordingly, stress is concentrated at the interface between the electrode active material layer and the solid electrolyte during the charge / discharge reaction, and distortion occurs. If charging / discharging is repeated in such a strained state, cracks occur at the interface between the electrode active material layer and the solid electrolyte, the lithium ion transmission path is interrupted, and the overall battery performance is degraded. Arise.
The present invention is an all-solid lithium secondary battery that suppresses delamination during continuous use by predicting and designing the residual stress at the interface between the electrode active material layer and other layers at the time of battery completion in the heating process. It aims at providing the manufacturing method of.

The method for producing an all solid lithium secondary battery of the present invention includes a step of preparing a support capable of forming an electrode active material layer in advance, and a heating step of integrating the electrode active material layer and the support. .
The “support” in the present invention refers to any of a positive electrode current collector, a negative electrode current collector, and a lithium ion conductive solid electrolyte. That is, as a support capable of forming a positive electrode active material layer, either a positive electrode current collector or a lithium ion conductive solid electrolyte can be selected, and a support capable of forming a negative electrode active material layer As for, either a negative electrode electrical power collector or a lithium ion conductive solid electrolyte can be selected.
Details of materials and the like that can be used for the positive electrode current collector, the negative electrode current collector, and the lithium ion conductive solid electrolyte will be described later.

  More specifically, the heating step in the production method according to the present invention has either one of the electrode current collector or the lithium ion conductive solid electrolyte as a support, and is heated without applying a stress in the plane direction. By applying a stress in the plane direction to at least one of the support and the electrode active material layer so that the residual stress at the interface between the support and the electrode active material layer is relaxed in a temperature region below the heating temperature, Is a step of integrating the electrode active material layer with the electrode active material layer.

Especially when the support and the electrode active material layer have different coefficients of thermal expansion, even if the support and the electrode active material layer are integrated without applying stress in the surface direction during the heating process, After cooling, a residual stress is generated at the interface between the support and the electrode active material layer. Thus, the support and the electrode are so relaxed that the residual stress at the interface between the support and the electrode active material layer is relaxed in the temperature region below the heating temperature, rather than the residual stress when heated without applying a stress in the plane direction. One of the main features of the present invention is to apply a stress in a plane direction to at least one of the active material layers to integrate the support and the electrode active material layer.
In this heating step, if necessary, the support and the electrode active material layer may be integrated in a state where stress is applied in a direction substantially perpendicular to the interface between the support and the electrode active material layer. Good.

As a residual stress test method / measurement method, the lattice constant around the interface between the support and the electrode active material layer is measured by XRD (X-ray diffractometry) and compared with the original lattice constant. it can.
Specifically, the lattice constant around the interface between the support and the electrode active material layer and each lattice constant of the support and the electrode active material layer before bonding are obtained, and the lattice constant before bonding is determined from the lattice constant after bonding. The residual stress can be obtained by removing each of the above.

FIG. 1 is a diagram showing an example of an all-solid lithium secondary battery of the present invention, and is a diagram schematically showing a cross section cut in the stacking direction. The all solid lithium secondary battery of the present invention is not necessarily limited to this example.
The all solid lithium secondary battery 100 includes a positive electrode body 16 containing a positive electrode active material layer 12 and a positive electrode current collector 14, a negative electrode body 17 containing a negative electrode active material layer 13 and a negative electrode current collector 15, and the positive electrode body. 16 and the lithium ion conductive solid electrolyte 11 sandwiched between the negative electrode body 17.
Hereinafter, the positive electrode body and the negative electrode body, the lithium ion conductive solid electrolyte, and other components (separator etc.), which are components of the all solid lithium secondary battery of the present invention, will be described separately.

1. Positive electrode body and negative electrode body The positive electrode body used in the present invention has a positive electrode current collector and a positive electrode active material layer containing at least a positive electrode active material.
The negative electrode body used in the present invention has a negative electrode current collector and a negative electrode active material layer containing at least a negative electrode active material.

Specific examples of the positive electrode active material used in the present invention include LiCoO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNiPO ₄ , LiMnPO ₄ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoMnO _4. , Li ₂ NiMn ₃ O ₈ , Li ₃ Fe ₂ (PO ₄ ) _3, Li ₃ V ₂ (PO ₄ ) _{3 and the} like. Among these, in the present invention, LiCoO ₂ is preferably used as the positive electrode active material.

  The thickness of the positive electrode active material layer used in the present invention varies depending on the intended use of the all-solid lithium secondary battery or the like, but is preferably in the range of 10 μm to 250 μm, preferably 20 μm to 200 μm. It is particularly preferably within the range, and most preferably within the range of 30 μm to 150 μm.

  The average particle diameter of the positive electrode active material is, for example, preferably in the range of 1 μm to 50 μm, more preferably in the range of 1 μm to 20 μm, and particularly preferably in the range of 3 μm to 5 μm. If the average particle size of the positive electrode active material is too small, the handleability may be deteriorated. If the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. Because. The average particle diameter of the positive electrode active material can be determined by measuring and averaging the particle diameter of the active material carrier observed with, for example, a scanning electron microscope (SEM).

The positive electrode active material layer may contain a conductive material, a binder, and the like as necessary.
The conductive material included in the positive electrode active material layer used in the present invention is not particularly limited as long as the conductivity of the positive electrode active material layer can be improved. For example, carbon black such as acetylene black and ketjen black Etc. Moreover, although content of the electrically conductive material in a positive electrode active material layer changes with kinds of electrically conductive material, it is in the range of 1 mass%-10 mass% normally.

  Examples of the binder included in the positive electrode active material layer used in the present invention include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Further, the content of the binder in the positive electrode active material layer may be an amount that can fix the positive electrode active material or the like, and is preferably smaller. The content of the binder is usually in the range of 1% by mass to 10% by mass.

  The positive electrode current collector used in the present invention has a function of collecting the positive electrode active material layer. Examples of the material for the positive electrode current collector include aluminum, SUS, nickel, iron, and titanium. Of these, aluminum and SUS are preferable. Moreover, as a shape of a positive electrode electrical power collector, foil shape, plate shape, mesh shape etc. can be mentioned, for example, Foil shape is preferable.

As the positive electrode electrolyte included in the positive electrode body used in the present invention, it is preferable to use a solid electrolyte. Specifically, a solid oxide electrolyte, a solid sulfide electrolyte, or the like can be used as the solid electrolyte.
Specifically, as the solid oxide electrolyte, LiPON (lithium phosphate oxynitride), Li _1.3 Al _0.3 Ti _0.7 (PO ₄ ) ₃ , La _0.51 Li _0.34 TiO _{0 .74} , Li ₃ PO ₄ , Li ₂ SiO ₂ , Li ₂ SiO ₄ , Li _0.5 La _0.5 TiO ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ etc. be able to.
Specific examples of the solid sulfide electrolyte include Li ₂ S—P ₂ S ₅ , Li ₂ S—SiS ₂ , Li _3.25 P _0.25 Ge _0.76 S _{4, and the} like.
As the positive electrode electrolyte included in the positive electrode body used in the present invention, a polymer electrolyte, a gel electrolyte, and the like described later can be used.

The method for producing a positive electrode used in the present invention includes (a) a method of forming a positive electrode active material layer on a positive electrode current collector as a support, and (b) a lithium ion conductive solid electrolyte described later. As a support, a positive electrode active material layer is formed thereon, and a positive electrode current collector is joined onto the positive electrode active material layer.
A case where the method (a) is selected will be described. First, a positive electrode current collector to be a support is prepared, a positive electrode layer containing a positive electrode active material and a positive electrode electrolyte is formed thereon, and the positive electrode current collector is heated by applying stress to the surface direction of the positive electrode active material layer. The electric body and the positive electrode layer are integrated. The method for applying the stress is not particularly limited, and examples thereof include a method by pressurization by uniaxial pressing in the z-axis direction (stacking direction).
Next, a case where the method (b) is selected will be described. First, a lithium ion conductive solid electrolyte to be a support is prepared, a positive electrode layer containing a positive electrode active material and a positive electrode electrolyte is formed thereon, and heat is applied while applying stress to the surface direction of the positive electrode active material layer. The positive electrode current collector and the positive electrode layer are integrated. The method for applying the stress is not particularly limited, and the method described above can be used. Then, a positive electrode body is completed by joining a positive electrode current collector to the surface of the integrated laminate on the positive electrode active material layer side.
After forming the positive electrode active material layer, the positive electrode active material layer may be pressed in order to improve the electrode density.

In the method for producing an all solid lithium secondary battery of the present invention, when the all solid lithium secondary battery obtained by the production method is charged, the charging depth X is a value of 1 or 2 or more in the range of 0 <X <100. In the heating step, the electrode active material layer may be integrated with the support by heating while applying a stress in the surface direction so that the residual stress at the interface between the support and the electrode active material layer is 0%. preferable. By adopting such a configuration, the residual stress at the interface between the support and the electrode active material layer is designed to be 0% in a charged state that is expected to be most frequently used in actual use. It is possible to suppress peeling between the support and the electrode active material layer due to expansion and contraction caused by ions entering and leaving the active material during charging.
For example, when an electrode active material layer having a higher coefficient of thermal expansion than that of the support is used, the electrode active material layer is oriented in the plane direction after cooling even when integrated without applying stress during the heating process. Residual stress that shrinks works. Therefore, the support-electrode active material layer laminate in which such residual stress is applied has the effect of counteracting the stress generated as the active material expands due to charge and discharge when used in a battery. Have
Further, for example, when an electrode active material layer having a lower thermal expansion coefficient than that of the support is used, even when integrated without applying stress during the heating step, the electrode active material is oriented in the plane direction after cooling. Residual stress that expands the layer works. Therefore, when the support-electrode active material layer laminate in which such residual stress is applied is used in a battery, it is effective to counteract the stress generated as the active material contracts due to charge / discharge. Have

A normal hybrid vehicle battery is repeatedly discharged (that is, traveled) and charged (that is, regenerated) at an intermediate charging depth. Therefore, an ordinary hybrid vehicle battery is preferably designed so that the depth of charge is 40 to 80%, most preferably the depth of charge is 60% and the residual stress is minimized.
On the other hand, the plug-in hybrid vehicle battery can maintain a high charging state with a charging depth of 80 to 100% during plug-in charging, but has a smaller battery capacity than a normal hybrid vehicle battery. For this reason, even if the discharge is the main, the discharge and the charge are actually repeated at the end of the running state. Accordingly, the battery for plug-in hybrid vehicles is preferably designed so that the residual stress is minimized when the charging depth is 80% or less, most preferably the charging depth is 20% or less.

In the all-solid-state method for producing a lithium secondary battery of the present _invention, Li and _{(1 + x) Mn (2} -x) O 4 ( spinel manganese) it can be used as the positive electrode active material.
Spinel manganese, which is widely used as a positive electrode material for lithium ion secondary batteries, is separated into two phases once exposed to high temperature at a composition ratio of x ≦ 0.25, and even if cooled to room temperature again. It is known that it does not return to a single phase.
However, as a result of investigating the physical properties of spinel manganese in the high temperature range, the composition ratio of 0.1 ≦ x ≦ 0.2 is a single phase at room temperature, but Li _{(1 + y)} Mn _{(2-y in the} high temperature range. ₎ It was found that the linear expansion coefficient is not constant because it is separated into two phases of O ₄ and Li ₂ MnO ₃ . Similar examination results are also pointed out in, for example, the 2008 Battery Discussion Session 1B18.
Therefore, in the present invention, when Li _{(1 + x)} Mn _(2-x) O ₄ (0 ≦ x ≦ 0.1) is used as the positive electrode active material, the temperature during the heat treatment is not particularly limited. it can. On the other hand, in the present invention, when Li _{(1 + x)} Mn _(2-x) O ₄ (0.1 ≦ x ≦ 0.2) is used as the positive electrode active material, heat treatment is performed at a temperature of 450 ° C. or lower. Moreover, peeling between the layers of the lithium ion conductive solid electrolyte and the positive electrode active material layer can be suppressed.

  The negative electrode active material used for the negative electrode active material layer is not particularly limited as long as it can occlude / release lithium ions. For example, metal lithium, lithium alloy, metal oxide, metal sulfide, Examples thereof include metal nitrides and carbon materials such as graphite. The negative electrode active material may be in the form of a powder or a thin film.

The negative electrode active material layer may contain a conductive material, a binder, and the like as necessary.
What was mentioned above can be used for the binder and the said electrically conductive material which can be used in a negative electrode active material layer. Moreover, it is preferable to select suitably the usage-amount of a binder and a electrically conductive material according to the use etc. of an all-solid-state lithium secondary battery. Further, the film thickness of the negative electrode active material layer is not particularly limited, but for example, it is preferably in the range of 10 μm to 100 μm, and more preferably in the range of 10 μm to 50 μm.
As the negative electrode electrolyte included in the negative electrode body used in the present invention, a solid electrolyte is preferably used. Specifically, as the solid electrolyte, the above-described solid oxide electrolyte, solid sulfide electrolyte, or the like can be used. As the negative electrode electrolyte included in the negative electrode body used in the present invention, a polymer electrolyte, a gel electrolyte, and the like described later can be used.

As the material and shape of the negative electrode current collector, the same materials and shapes as those of the positive electrode current collector described above can be employed.
As a manufacturing method of the negative electrode body used in the present invention, a method similar to the above-described manufacturing method of the positive electrode body can be employed.

2. Lithium ion conductive solid electrolyte The lithium ion conductive solid electrolyte used in the present invention performs lithium ion exchange between the positive electrode active material and the negative electrode active material described above. Specific examples of the solid electrolyte include polymer electrolytes and gel electrolytes, and the above-described solid oxide electrolytes and solid sulfide electrolytes.

The polymer electrolyte contains a lithium salt and a polymer. The lithium salt is not particularly limited as long as it is a lithium salt used in a general lithium secondary battery. For example, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , Examples thereof include LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) _3, and LiClO ₄ . The polymer is not particularly limited as long as it forms a complex with a lithium salt, and examples thereof include polyethylene oxide.

The gel electrolyte contains a lithium salt, a polymer, and a nonaqueous solvent.
The lithium salt described above can be used as the lithium salt.
The non-aqueous solvent is not particularly limited as long as it can dissolve the lithium salt. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1 , 2-diethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone and the like. These nonaqueous solvents may be used alone or in combination of two or more. Moreover, room temperature molten salt can also be used as a non-aqueous electrolyte.
The polymer is not particularly limited as long as it can be gelled, and examples thereof include polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride (PVDF), polyurethane, polyacrylate, and cellulose. Can be mentioned.

3. Other component As another component, a separator can be used for the all-solid-state lithium secondary battery of this invention. The separator is disposed between the positive electrode current collector and the negative electrode current collector described above, and usually has a function of preventing the contact between the positive electrode active material layer and the negative electrode active material layer and holding the solid electrolyte. Have. Furthermore, as for the separator, examples of the material of the separator include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Among these, polyethylene and polypropylene are preferable. The separator may have a single layer structure or a multilayer structure. Examples of the separator having a multilayer structure include a separator having a two-layer structure of PE / PP and a separator having a three-layer structure of PP / PE / PP. Furthermore, in the present invention, the separator may be a nonwoven fabric such as a resin nonwoven fabric or a glass fiber nonwoven fabric. Moreover, the film thickness of the said separator is not specifically limited, It is the same as that of the separator used for a general all solid lithium secondary battery.
Moreover, the battery case which accommodates the all-solid-state lithium secondary battery of this invention can also be used as another component. The shape of the battery case is not particularly limited as long as it can accommodate the positive electrode body, the negative electrode body, the solid electrolyte, and the like described above. Specifically, a cylindrical shape, a square shape, a coin shape, a laminate shape, and the like. Etc.

  The all solid lithium secondary battery according to the present invention can be manufactured by a method similar to the method of manufacturing a general lithium secondary battery. Specifically, in an inert atmosphere, first, the positive electrode body, the negative electrode body and the separator are housed in a battery case, then a solid electrolyte is added to the battery case, and finally the battery case is sealed. Can do.

1. Examination in the case of using LiCoO ₂ as the positive electrode active material In the following examples, Li _0.5 La _0.5 TiO ₃ which is a kind of lithium ion conductive solid electrolyte is used as a support, and a kind of positive electrode active material is used. A simulation method and results of an all-solid lithium secondary battery using a laminate in which a certain LiCoO ₂ is integrated with the support under the following conditions are shown.
In the simulation, LiCoO _{2 has} a thermal expansion coefficient of 40 × 10 ⁻⁶ K ⁻¹ , Li _0.5 La _0.5 TiO _{3 has} a thermal expansion coefficient of 5 × 10 ⁻⁶ K ⁻¹ , and lithium ion insertion / extraction. The calculation was performed assuming that the thermal expansion coefficient of LiCoO ₂ associated with is 2.6% (when the charging depth is 0 to 100%).
The stress applied to leave the stress at the interface is a compressive stress. This simulation is a simulation that assumes the use of a known technology for pressureless shrinkage firing of ceramics (that is, technology for applying pressure to prevent shrinkage in the surface direction).

[Example 1]
Li _0.5 La _0.5 TiO ₃ (support) and LiCoO ₂ (positive electrode active material layer) are heated and integrated under a temperature condition of 700 ° C., and the support and the positive electrode active material layer are A laminate of Example 1 was obtained in which 2.5% of stress remained at the interface.

[Example 2]
Li _0.5 La _0.5 TiO ₃ (support) and LiCoO ₂ (positive electrode active material layer) are uniaxially pressurized and heated to integrate them while controlling the amount of shrinkage in the plane direction, A laminate of Example 2 was obtained in which 1.3% of the stress was left at the interface between the support and the positive electrode active material layer.

[Comparative Example 1]
Li _0.5 La _0.5 TiO ₃ (support) and LiCoO ₂ (positive electrode active material layer) are heated and integrated under a temperature condition of 800 ° C., and the support and the positive electrode active material layer are The laminated body of the comparative example 1 which left 3.2% of stress in the interface was obtained.

[Comparative Example 2]
Li _0.5 La _0.5 TiO ₃ (support) and LiCoO ₂ (positive electrode active material layer) are uniaxially pressurized and heated to integrate them while controlling the amount of shrinkage in the plane direction, A laminate of Comparative Example 2 was obtained in which no stress remained at the interface between the support and the positive electrode active material layer.

FIG. 2 is a graph showing simulation results of all-solid lithium secondary batteries using the laminates of Examples 1 and 2 and Comparative Examples 1 and 2. The vertical axis shows the residual stress (%) at the interface between Li _0.5 La _0.5 TiO ₃ (support) and LiCoO ₂ (positive electrode active material layer), and the horizontal axis shows the charging depth (%) of the battery. ing.
The laminated body of Comparative Example 2 is assembled in a state where the residual stress at 0% charge / discharge depth is 0%. Therefore, as can be seen from FIG. 2, the laminate of Comparative Example 2 has a residual stress of 2.6% at the time of 100% charge / discharge and 0.5% to at the time of 20% to 100% charge / discharge. It has a wide range of stress of 2.6%.
Moreover, the laminated body of the comparative example 1 is assembled in the state whose residual stress at the time of 0% of charge / discharge depth is 3.2%. Therefore, as can be seen from FIG. 2, the laminate of Comparative Example 1 has a residual stress of 0.6% at the time of 100% charge / discharge, and from 0.6% to at the time of 20% to 100% charge / discharge. It has a wide range of stress of 2.7%.
In both the laminates of Comparative Examples 1 and 2, the charge depth X at which the residual stress becomes 0% does not exist in the range of 0 <X <100. Therefore, in the range of the charging depth that can be normally used, the interface between the support and the positive electrode active material layer is always distorted, and as a result, there is a possibility that peeling occurs at the interface due to continuous use.

On the other hand, the laminate of Example 1 is assembled with a residual stress of 2.5% at a charge / discharge depth of 0%. Therefore, as can be seen from FIG. 2, the laminate of Example 1 has a residual stress of 0.1% during 100% charge / discharge, and 0% -2. It has a stress in a narrower range than that of the laminates of Comparative Examples 1 and 2 of 0%.
The laminated body of Example 2 is assembled in a state where the residual stress at a charge / discharge depth of 0% is 1.3%. Therefore, as can be seen from FIG. 2, the laminate of Example 2 has a residual stress of 1.3% at the time of 100% charge / discharge, and 0% to 1.0 at the time of 20% to 100% charge / discharge. It has a stress in a narrower range of 3% than the laminates of Comparative Examples 1 and 2.
The laminate of Example 2 has a residual stress of 0% when the charge depth is 50%. Further, in the laminated body of Example 1, the residual stress becomes 0% when the charging depth is 96%.
As described above, the all-solid lithium secondary battery using the laminates of Examples 1 and 2 has a residual stress at the interface between the support and the electrode active material layer at a predetermined temperature, that is, at the temperature during charge and discharge. By being within 2.0%, peeling between the support and the electrode active material layer can be suppressed. Moreover, the all-solid lithium secondary battery using the laminates of Examples 1 and 2 is in a charged state that is expected to be most frequently used in actual use, that is, in the case of the laminate of Example 1. The residual stress at the interface between the support and the electrode active material layer can be designed to be 0% at a charging depth of 96% and in the case of the laminated body of Example 2 at a charging depth of 50%. It is possible to suppress delamination between the support and the electrode active material layer due to expansion and contraction accompanying the entry and exit of ions into the active material.

The laminate shown in Example 1 can be actually manufactured by the following procedure. The powder of Li _0.5 La _0.5 TiO _{3 used} as the raw material of the support is mixed with Li ₂ CO ₃ , La ₂ O ₃ and TiO ₂ in a stoichiometric ratio of 0.5: 0.5: 1. What was calcined in the air at 800 ° C. for 4 hours and further at 1300 ° C. for 6 hours is prepared. Commercially available LiCoO ₂ powder as a raw material for the positive electrode active material can be used. Li _0.5 La _0.5 TiO ₃ and LiCoO ₂ can also be produced by a solid phase method or a sol-gel method.
First, a green compact of Li _0.5 La _0.5 TiO ₃ having a diameter of 13 mm and a thickness of 1 mm is produced by uniaxial pressing at 50 kg / cm ³ using a cylindrical die. The green compact is heat-treated at a temperature of 1350 ° C. for 6 hours to produce a pellet of Li _0.5 La _0.5 TiO _{3 in} a pellet state.

Next, a green compact of LiCO ₂ having a diameter of 10 mm and a thickness of 1 mm is produced on a pellet of Li _0.5 La _0.5 TiO _{3 in} a pellet state. Thereafter, the laminated body of the sintered body and the green compact is subjected to a heat treatment for 10 hours under a temperature condition of 700 ° C., whereby Li _0.5 La _0.5 TiO ₃ and LiCO ₂ are laminated. A body-shaped sintered body can be produced.

Moreover, the laminated body shown in the said Example 2 can be actually produced with the following procedures.
The steps up to the step of producing a compact of LiCO ₂ on the sintered body of Li _0.5 La _0.5 TiO _{3 in} the pellet state are the same as those of the laminate of Example 1. Then, while applying a compressive stress to the interface between Li _0.5 La _0.5 TiO ₃ and LiCO ₂ with respect to the laminate of the sintered body and the green compact, the temperature is 700 ° C. for 10 hours. By performing heat treatment, an integrated sintered body in which Li _0.5 La _0.5 TiO ₃ and LiCO ₂ are laminated can be produced. The stress required to accurately apply 1.3% residual stress to the interface between Li _0.5 La _0.5 TiO ₃ and LiCO ₂ is a variable of the compressive stress applied to the interface and the rate of temperature rise. Can be calculated by performing a simulation in advance.

The laminated body shown in Comparative Example 1 is the same as the laminated body of the sintered body of Li _0.5 La _0.5 TiO ₃ and the green compact of LiCO ₂ described in the description of the production of the laminated body of Example 1. On the other hand, it can be obtained by performing a heat treatment at 800 ° C. for 10 hours.
The laminated body shown in Comparative Example 2 is the same as the laminated body of the sintered body of Li _0.5 La _0.5 TiO ₃ and the green compact of LiCO ₂ described in the description of the production of the laminated body of Example 2. On the other hand, in the direction parallel to the interface between Li _0.5 La _0.5 TiO ₃ and LiCO ₂ , stress is applied for 10 hours under the temperature condition of 700 ° C. while applying a stress different from that in the production of the laminate of Example 2. It can be obtained by heat treatment.

2. Examination when Li _{(1 + x)} Mn _(2-x) O ₄ is used as the positive electrode active material In the following examples, Li _1.5 Al _0.5 Ge _1. which is a kind of lithium ion conductive solid electrolyte _{. 5} (PO ₄ ) ₃ was used as a support, and a laminate in which Li _{(1 + x)} Mn _(2-x) O ₄ which is a kind of positive electrode active material was integrated with the support under the following conditions was used. A simulation method and results of an all-solid lithium secondary battery are shown.
In the simulation, the calculation was performed by setting the thermal expansion coefficient of Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ to 13 × 10 ⁻⁶ K ⁻¹ .

[Example 3]
Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (support), Li _{(1 + x)} Mn _(2-x) O ₄ (0 ≦ x <0.1) (positive electrode active material layer), Were integrated by heating under a temperature condition of 400 ° C. In the simulation, the calculation was performed by setting the thermal expansion coefficient of Li _{(1 + x)} Mn _(2-x) O ₄ (0 ≦ x <0.1) to 13 × 10 ⁻⁶ K ⁻¹ .

[Example 4]
Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (support) and Li _{(1 + x)} Mn _(2-x) O ₄ (0.1 ≦ x <0.2) (positive electrode active material layer) And were integrated under heating at 400 ° C. In the simulation, the calculation was performed by setting the thermal expansion coefficient of Li _{(1 + x)} Mn _(2-x) O ₄ (0.1 ≦ x <0.2) to 13 × 10 ⁻⁶ K ⁻¹ .

[Comparative Example 3]
Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (support) and Li _{(1 + x)} Mn _(2-x) O ₄ (0.1 ≦ x <0.2) (positive electrode active material layer) And were integrated under heating at a temperature of 600 ° C. In the simulation, the thermal expansion coefficient of Li _1.1 Mn _1.9 O ₄ of 500 ° C. or higher is 24 × 10 ⁻⁶ K ⁻¹ , and the thermal expansion coefficient of Li _1.2 Mn _1.8 O ₄ of 500 ° C. or higher. The calculation was performed with a coefficient of 34 × 10 ⁻⁶ K ⁻¹ .

The laminated body of Comparative Example 3 has a thermal expansion coefficient of Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ as a support and Li _{(1 + x)} Mn ₍ positive electrode active material) during heating. _{2-x) Since} there is a significant difference between the thermal expansion coefficients of O ₄ (0.1 ≦ x <0.2), the layers between the support and the electrode active material layer are integrated when integrated by heating. It is difficult to prevent peeling. The difference in thermal expansion coefficient between the support and the positive electrode active material is that the positive electrode active material is separated into two phases of Li _{(1 + y)} Mn _(2-y) O ₄ and Li ₂ MnO ₃ under the temperature condition of 600 ° C. This is what happens.
On the other hand, the laminates of Examples 3 and 4 were, at the time of heating, Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ as a support and Li _{(1 + x)} Mn ₍ positive electrode active material _{). Since 2-x)} O ₄ has the same coefficient of thermal expansion, peeling between the support and the electrode active material layer can be suppressed when integrating by heating.

DESCRIPTION OF SYMBOLS 11 ... Solid electrolyte 12 ... Positive electrode active material layer 13 ... Negative electrode active material layer 14 ... Positive electrode collector 15 ... Negative electrode collector 16 ... Positive electrode body 17 ... Negative electrode body 100 ... All solid lithium secondary battery

Claims (3)

A positive electrode current collector, and a positive electrode body having a positive electrode active material layer containing LiCoO ₂ or Li _{(1 + x)} Mn _(2-x) O ₄ (0 ≦ x <0.1) ;
A negative electrode current collector, and a negative electrode body having a negative electrode active material layer containing at least a negative electrode active material;
An all solid lithium secondary battery having Li _0.5 La _0.5 TiO ₃ or Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ sandwiched between the positive electrode body and the negative electrode body, A manufacturing method involving a sintering process,
Preparing the Li _0.5 La _0.5 TiO ₃ or Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ;
When the Li _0.5 La _0.5 TiO ₃ is used as a support, a positive electrode containing LiCoO ₂ is used, and the Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ is used as a support. When using a positive electrode body containing Li _{(1 + x)} Mn _(2-x) O ₄ (0 ≦ x <0.1) and sintering without applying stress in a direction perpendicular to the plane direction Than when the residual stress at the interface between the support and the positive electrode active material layer of the positive electrode body is relaxed in a temperature region lower than the sintering temperature and the all solid lithium secondary battery is charged, Is perpendicular to the surface direction of the positive electrode active material layer so that the residual stress at the interface between the support and the positive electrode active material layer is 0% at a value of 1 or 2 in the range of 0 <X <100. It is integrated with the support by sintering while applying stress in any direction. Sintering process,
A method for producing an all-solid-state lithium secondary battery, comprising: An electrode current collector and a positive electrode active material layer containing LiCoO ₂ or Li _{(1 + x)} Mn _(2-x) O ₄ (0 ≦ x <0.1) on one surface of the electrode current collector, And the electrode body which has the negative electrode active material layer containing a negative electrode active material at least on the other surface of the electrode current collector,
Sintering of an all-solid lithium secondary battery having Li _0.5 La _0.5 TiO ₃ or Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ sandwiched between two electrode bodies A manufacturing method involving a process ,
Preparing the Li _0.5 La _0.5 TiO ₃ or Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ ;
When the Li _0.5 La _0.5 TiO ₃ is used as a support, a positive electrode active material layer containing LiCoO ₂ is used relative to the support, and the Li _1.5 Al _0.5 Ge _{1. When 5} (PO ₄ ) ₃ is used as a support, a positive electrode active material layer containing Li _{(1 + x)} Mn _(2-x) O ₄ (0 ≦ x <0.1) is used relative to the support. However, the residual stress at the interface between the support and the positive electrode active material layer of the electrode body is relaxed in a temperature region below the sintering temperature, compared to when sintering without applying stress in a direction perpendicular to the surface direction. When the all-solid lithium secondary battery is charged, the residual stress at the interface between the support and the positive electrode active material layer when the charge depth X is 1 or 2 or more in the range of 0 <X <100. Perpendicular to the surface direction of the positive electrode active material layer so that the Sintering step of integrating with the support by sintering while stress applied in the direction,
A method for producing an all-solid-state lithium secondary battery, comprising: An all-solid lithium secondary battery obtained by the production method according to claim 1 or 2 .

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