All-solid-state battery and method for confirming the form of an all-solid-state battery

Abstract

To provide an all-solid battery that has high output performance of a cell.SOLUTION: There is provided an all-solid battery obtained by performing charge and discharge to a battery formed by press-molding a solid electrolyte layer and an electrode layer including active material and solid electrolyte material, and subsequently re-press-molding the battery. The re-press molding is press molding with a molding pressure at which a strain energy generated in the active material in association with the charge and discharge and the re-press molding becomes smaller than the crack extension energy of the active material. When the all-solid battery is re-charged and re-discharged after the re-press molding and further pressed after the re-charge and re-discharge, the difference in porosity in the electrode layer before and after the pressing is smaller than a theoretical value of the porosity in the electrode layer calculated from the difference between the maximum value and the minimum value of the volume change rate of the active material when the all-solid battery is re-charged and re-discharged.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an all-solid-state battery and a method for confirming the form of an all-solid-state battery.

Background Art

[0002] Conventionally, an all-solid-state battery having an electrode layer containing an active material and a solid electrolyte material is known. In this type of all-solid-state battery, the active material expands and contracts during charge and discharge, while the solid electrolyte material does not expand and contract, so it cannot follow the volume change. Therefore, when the active material contracts, the porosity in the electrode layer increases. As a result, the contact area between the active material and the solid electrolyte material decreases, and there is a risk that the output performance of the cell will deteriorate.

[0003] Patent Document 1 discloses a method for manufacturing an all-solid-state lithium secondary battery having an electrode layer containing an active material and a solid electrolyte material. In this method for manufacturing an all-solid-state lithium secondary battery, in order to suppress a decrease in the output performance of the cell, after forming the all-solid-state lithium secondary battery, the all-solid-state lithium secondary battery is charged and discharged, and then press-molded again to reduce the voids between the active material and the solid electrolyte material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when an all-solid-state battery is formed, charged and discharged, and then press-molded again, strain energy is generated in the active material due to the contraction caused by charge and discharge and the molding pressure during press-molding. In such a manufacturing method, cracks may occur in the active material due to the strain energy, and as a result, there is a risk that the output performance of the cell will rather deteriorate.

[0006] The present invention is made in view of the above problems, and an object thereof is to provide an all-solid-state battery having high output performance of a cell.

Means for Solving the Problems

[0007] According to one aspect of the present invention, there is provided an all-solid-state battery obtained by press-molding a solid electrolyte layer and an electrode layer containing an active material and a solid electrolyte material, performing charge and discharge, and then performing re-press molding. The re-press molding is performed at a molding pressure such that the strain energy generated in the active material accompanying charge and discharge and re-press molding is smaller than the crack propagation energy of the active material. In this all-solid-state battery, when re-charge and discharge are performed after re-press molding and further pressing is performed after the re-charge and discharge, the difference in porosity in the electrode layer before and after the pressing is smaller than the theoretical value of the porosity in the electrode layer calculated from the difference between the maximum value and the minimum value of the volume change rate of the active material when re-charged and discharged.

Effects of the Invention

[0008] According to the all-solid-state battery of the present invention, since the strain energy generated in the active material accompanying charge and discharge and re-press molding is re-press molded at a molding pressure smaller than the crack propagation energy of the active material, cracks or the like do not occur. Further, in the all-solid-state battery of the present invention, when re-charge and discharge are performed after re-press molding and further pressing is performed after the re-charge and discharge, the porosity in the electrode layer before and after the pressing does not change by more than the volume change rate of the active material. That is, there are few voids generated during the use of the all-solid-state battery, and the internal resistance of the electrode layer is small. Therefore, it is possible to provide an all-solid-state battery having high output performance of a cell.

Brief Description of the Drawings

[0009]

Figure 1

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like.

[0011] FIG. 1 is a schematic configuration diagram showing the main configuration of a all-solid-state battery system 100 for manufacturing an all-solid-state battery (secondary battery) 1 according to an embodiment of the present invention.

[0012] As shown in FIG. 1, the all-solid-state battery system 100 includes an all-solid-state battery (secondary battery) 1, a voltage sensor 2, a voltage-current adjuster 3, an external power source 4, a current sensor 5, a pressurizing mechanism 6, a control unit 7, and the like.

[0013] The all-solid-state battery 1 is, for example, an all-solid-state lithium-ion secondary battery. The all-solid-state battery 1 includes a positive electrode layer 12 containing a positive electrode active material, a negative electrode layer 13 containing a negative electrode active material, and a solid electrolyte layer 11 formed between the positive electrode layer 12 and the negative electrode layer 13 and containing a solid electrolyte material (see FIG. 3). In addition, the positive electrode layer 12 and the negative electrode layer 13 also contain a solid electrolyte material. In this embodiment, as an example, the case where the all-solid-state battery 1 is an all-solid-state lithium-ion secondary battery will be described, but the all-solid-state battery 1 is not necessarily limited to an all-solid-state lithium-ion secondary battery.

[0014] The voltage sensor 2 is, for example, a voltmeter, and measures the cell voltage (voltage between terminals) between the positive electrode layer 12 and the negative electrode layer 13 of the all-solid-state battery 1. The measured voltage value is transmitted to the control unit 7 as a signal. Note that the installation position of the voltage sensor 2 is not particularly limited as long as it can measure the cell voltage between the positive electrode layer 12 and the negative electrode layer 13 of the all-solid-state battery 1.

[0015] The voltage-current adjuster 3 adjusts the voltage and current during charging and discharging of the all-solid-state battery 1. During charging of the all-solid-state battery 1, the voltage-current adjuster 3 adjusts the voltage and current of the power supplied from the external power source 4 to the all-solid-state battery 1. During discharging of the all-solid-state battery 1, the power discharged from the all-solid-state battery 1 is discharged to the external power source 4. Note that the voltage-current adjuster 3 is controlled by the control unit 7.

[0016] The external power source 4 is connected to a commercial power source or another secondary battery etc. (not shown), and supplies power to the all-solid-state battery 1 via the voltage and current adjustment unit 3. The external power source 4 outputs direct current and supplies power to the all-solid-state battery 1 at the voltage value and current value required for charging the all-solid-state battery 1. Further, the external power source 4 is provided with a power regeneration function. When there is a discharge from the all-solid-state battery 1, it converts direct current into alternating current and regenerates it to the commercial power source via the voltage and current adjustment unit 3, or can store the direct current discharge power in another secondary battery etc. via the voltage and current adjustment unit 3. Note that the external power source 4 is controlled by the control unit 7.

[0017] The current sensor 5 is, for example, an ammeter, measures the current value of the power supplied from the voltage and current adjustment unit 3 to the all-solid-state battery 1 during charging of the all-solid-state battery 1, and measures the current value of the power supplied from the all-solid-state battery 1 to the voltage and current adjustment unit 3 during discharge. The measured current value is transmitted to the control unit 7 as a signal. Note that the installation position of the current sensor 5 is not particularly limited as long as it can measure the current during charge and discharge of the all-solid-state battery 1.

[0018] The pressurizing mechanism 6 presses the all-solid-state battery 1. The pressurizing mechanism 6 is composed of, for example, a pressure press, a pressure roller, etc., but is not limited to these devices as long as it is used when press-forming a general all-solid-state battery. Note that the operation of the pressurizing mechanism 6 is controlled by the control unit 7.

[0019] The control unit 7 is composed of a computer equipped with a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface), and performs integrated control of the all-solid-state battery system 100. The control unit 7 controls, for example, the charge and discharge amount of the all-solid-state battery 1, the forming pressure during press-forming of the pressurizing mechanism 6, etc. Further, the control unit 7 executes processing for controlling the all-solid-state battery system 100 by executing a specific program.

[0020] Figure 2 is a flowchart for explaining the manufacturing process of the all-solid-state battery 1 according to the present embodiment, and Figure 3 is a schematic diagram showing the manufacturing process of the all-solid-state battery 1 according to the present embodiment.

[0021] As shown in FIGS. 2 and 3, the all-solid-state battery 1 of the present embodiment includes an all-solid-state battery forming process (S101 to S104), a charge / discharge process (S105), and a reshaping process (S106) in the manufacturing process.

[0022] The all-solid-state battery forming process (S101 to S104) is a process of press-forming a solid electrolyte layer 11 and electrode layers (a positive electrode layer 12 and a negative electrode layer 13) to form the all-solid-state battery (battery) 1. The all-solid-state battery forming process includes a solid electrolyte layer lamination process (S101), a positive electrode layer lamination process (S102), a negative electrode layer lamination process (S103), and a current collector lamination process (S104).

[0023] In the solid electrolyte layer lamination process (S101), the solid electrolyte material is press-formed by a pressing mechanism 6 to form the solid electrolyte layer 11. The solid electrolyte layer 11 is a layer containing a solid electrolyte material as a main component and having ionic conductivity, and is interposed between the positive electrode layer 12 and the negative electrode layer 13 described later. As the solid electrolyte material, for example, a sulfide solid electrolyte material, an oxide solid electrolyte material, a polymer electrolyte material, etc. can be used, but not limited thereto, and any known material conventionally used as the solid electrolyte material may be used. Further, the solid electrolyte layer 11 may contain a binder or the like in addition to the solid electrolyte material.

[0024] In the positive electrode layer lamination process (S102), a positive electrode forming material is placed on the solid electrolyte layer 11 and press-formed by a pressing mechanism 6 to form a positive electrode active material layer 121. The positive electrode forming material contains a positive electrode active material and a solid electrolyte material. Thus, by forming the electrode layer using the positive electrode forming material in which the active material and the solid electrolyte material are mixed, the solid electrolyte material penetrates into the electrode layer. Thereby, the area of the interface between the active material and the solid electrolyte material increases, the ionic conductivity of the positive electrode active material layer 121 is improved, and the output performance of the cell is improved.

[0025] The positive electrode active material is, for example, LiCoO2 (hereinafter referred to as LCO), Li(Ni-Mn-Co)O2, and those in which some of these transition metals are substituted by other elements (hereinafter referred to as NMC composite oxides), lithium-nickel-cobalt-aluminum composite oxides (hereinafter referred to as NCA composite oxides), etc. are used. Also, two or more positive electrode active materials may be used in combination. However, the positive electrode active material is not limited to these, and any known one conventionally used as the positive electrode active material may be used. The shape of the positive electrode active material is, for example, particulate, thin film, etc. The positive electrode active material layer 121 may contain a binder, a conductive aid, etc. in addition to the positive electrode active material.

[0026] In the negative electrode layer lamination step (S103), a negative electrode forming material is placed on the surface of the solid electrolyte layer 11 opposite to the surface on which the positive electrode active material layer 121 is formed, and press-molded by the pressing mechanism 6 to form the negative electrode active material layer 131. The material for forming the negative electrode contains a negative electrode active material and a solid electrolyte material. By including the solid electrolyte material in the material for forming the negative electrode, the ionic conductivity of the negative electrode active material layer 131 is improved as in the case of the positive electrode active material layer 121, and the output performance of the cell is improved.

[0027] The negative electrode active material contains metallic lithium or a lithium-containing alloy. The lithium-containing alloy is, for example, an alloy of Li and at least one of In, Al, Si, and Sn. Also, two or more negative electrode active materials may be used in combination. Note that as long as it contains at least metallic lithium or a lithium-containing alloy, other negative electrode active materials may be used. The shape of the negative electrode active material is, for example, particulate, thin film, etc. The negative electrode active material layer 131 may contain a binder, a conductive aid, etc. in addition to the negative electrode active material.

[0028] In the current collector lamination step (S104), the positive electrode current collector 122 is pressure-bonded to the surface of the solid electrolyte layer 11 opposite to the surface on which the positive electrode active material layer 121 is formed by the pressing mechanism 6, and the negative electrode current collector 132 is pressure-bonded to the surface of the solid electrolyte layer 11 opposite to the surface on which the negative electrode active material layer 131 is formed. The positive electrode current collector 122 and the negative electrode current collector 132 collect current for the positive electrode and the negative electrode, respectively.

[0029] As the materials constituting the current collectors 122 and 132, for example, metal materials such as aluminum, nickel, stainless steel (SUS), and alloys thereof can be used, but the materials are not limited thereto, and any material having a function of collecting current may be used. Further, the positive electrode current collector 122 and the negative electrode current collector 132 may be made of the same material or may be made of different materials. In the current collector lamination step (S104), the current collectors 122 and 132 are pressure-bonded to the positive electrode active material layer 121 and the negative electrode active material layer 131, respectively, to form the positive electrode layer 12 and the negative electrode layer 13, and the all-solid-state battery 1 is formed.

[0030] Note that the solid electrolyte layer lamination step (S101), the positive electrode layer lamination step (S102), the negative electrode layer lamination step (S103), and the current collector lamination step (S104) in the all-solid-state battery formation process (S101 to S104) do not necessarily have to be performed according to the above procedures and methods. That is, any known procedures and methods may be used as long as the all-solid-state battery 1 can be formed. For example, the solid electrolyte layer 11, the positive electrode active material layer 121 and the positive electrode current collector 122, and the negative electrode active material layer 131 and the negative electrode current collector 132 may be separately formed and then press-molded. In this case, after forming the solid electrolyte layer 11, a positive electrode forming material is placed on the positive electrode current collector 122 and pressure-bonded to form the positive electrode layer 12 including the positive electrode active material layer 121 and the positive electrode current collector 122. Next, a negative electrode forming material is placed on the negative electrode current collector 132 and pressure-bonded to form the negative electrode layer 13 including the negative electrode active material layer 131 and the negative electrode current collector 132. Subsequently, the solid electrolyte layer 11 is sandwiched between the positive electrode layer 12 and the negative electrode layer 13 by press-molding to form the all-solid-state battery 1. Further, for example, after forming the solid electrolyte layer 11, a positive electrode forming material and the positive electrode current collector 122 are placed on the solid electrolyte layer 11 and press-molded to laminate the positive electrode layer 12. Then, a negative electrode forming material and the negative electrode current collector 132 may be placed on the surface of the solid electrolyte layer 11 opposite to the surface on which the positive electrode layer 12 is formed, and press-molded to laminate the negative electrode layer 13.

[0031] FIG. 4a is a schematic diagram showing the positive electrode layer 12 after the all-solid-state battery formation process (S101 to S104), and FIG. 4b is a schematic diagram showing the positive electrode layer 12 after charge and discharge of the all-solid-state battery 1.

[0032] As shown in FIG. 4a, after the all-solid-state battery formation process (S101 to S104), in the positive electrode layer 12, the positive electrode active material 123 and the solid electrolyte material 111 exist in a state of being substantially in close contact.

[0033] When the all-solid-state battery 1 is charged and discharged in this state, the volume of the positive electrode active material 123 expands or contracts according to the charge and discharge state. On the other hand, since the solid electrolyte material 111 does not expand and contract, when the positive electrode active material 123 expands or contracts due to charge and discharge, the solid electrolyte material 111 cannot follow the volume change of the positive electrode active material 123. Therefore, when the positive electrode active material 123 contracts due to charge and discharge, as shown in FIG. 4b, a gap 14 is formed between the positive electrode active material 123 and the solid electrolyte material 111, and the interface between the positive electrode active material 123 and the solid electrolyte material 111 peels off. Also, when the positive electrode active material 123 expands and then contracts after charge and discharge, the solid electrolyte material 111 moves or plastically deforms within the positive electrode layer 12 due to the pressure when the positive electrode active material 123 expands, so the gap 14 between the positive electrode active material 123 and the solid electrolyte material 111 becomes even larger. Thus, when the gap 14 between the positive electrode active material 123 and the solid electrolyte material 111 becomes large and the contact area between the positive electrode active material 123 and the solid electrolyte material 111 decreases, there is a risk that the output of the cell deteriorates. Therefore, as described below, a charge and discharge process (S105) of charging and discharging the all-solid-state battery 1 after the all-solid-state battery formation process (S101 to S104) and a re-forming process (S106) of re-press molding the all-solid-state battery 1 after charge and discharge are executed. After charge and discharge, by re-press molding the all-solid-state battery 1 again in a state where the positive electrode active material 123 has contracted in volume, it is possible to reduce the gap 14 and interface peeling between the positive electrode active material 123 and the solid electrolyte material 111 that occur when the volume contracts.

[0034] In the charge / discharge process (S105), the all-solid-state battery 1 formed in the all-solid-state battery formation process (S101 to S104) is charged and discharged. As the charging and discharging method, a known method used for charging and discharging an all-solid-state battery can be employed. During charging, power is supplied from the external power source 4 to the all-solid-state battery 1 via the voltage / current adjuster 3. Also, during discharging, power is discharged to the external power source 4 via the voltage / current adjuster 3. Note that the charge / discharge amount in the charge / discharge process (S105) will be described later.

[0035] When the positive electrode active material 123 contracts or expands and then contracts during the charge / discharge process (S105), as shown in FIG. 4b, a gap 14 is formed between the positive electrode active material 123 and the solid electrolyte material 111, and the interface between the positive electrode active material 123 and the solid electrolyte material 111 peels off.

[0036] After the charge / discharge process (S105), in the reshaping process (S106), the all-solid-state battery 1 is press-molded again.

[0037] FIG. 4c is a schematic diagram showing the positive electrode layer 12 after the all-solid-state battery 1 is press-molded again. As shown in FIG. 4c, due to the reshaping process (S106), the gap 14 and the interface peeling between the positive electrode active material 123 and the solid electrolyte material 111 that occurred in the charge / discharge process (S105) are reduced. That is, the density of the positive electrode layer 12 increases and the interface contact property becomes good, so the output degradation of the cell is suppressed and the cell performance is improved.

[0038] In this way, by performing the reshaping process (S106), the output degradation of the cell can be suppressed. However, since the expansion and contraction rates of the volume of the positive electrode active material 123 differ depending on the amount of charge and discharge in the charge and discharge process (S105), unless a more appropriate amount of charge and discharge is selected, the effect of suppressing the output degradation of the cell by re-press molding cannot be sufficiently obtained. For example, when the volume of the positive electrode active material 123 simply expands due to charge and discharge in the charge and discharge process (S105), the output degradation of the cell is not sufficiently suppressed even by re-press molding. In addition, since the positive electrode active material 123 has different expansion and contraction characteristics with respect to charge and discharge depending on its type, it is also necessary to select an appropriate amount of charge and discharge for each type of the positive electrode active material 123. On the other hand, when the all-solid-state battery 1 is formed and then the all-solid-state battery 1 is charged and discharged and re-press molded, strain energy U is generated in the positive electrode active material 123 due to the contraction caused by charge and discharge and the molding pressure P during re-press molding. When this strain energy U exceeds a predetermined value, cracks occur in the positive electrode active material 123. Therefore, if an arbitrary amount of charge and discharge is selected in the charge and discharge process (S105), the strain energy U of the positive electrode active material 123 increases, and cracks occur in the positive electrode active material 123 during re-press molding, and instead, the output of the cell may deteriorate. Therefore, when manufacturing the all-solid-state battery 1 of the present embodiment, in the reshaping process (S106), re-press molding is performed at a molding pressure P at which cracks do not occur in the positive electrode active material 123. Specifically, re-press molding is performed at a molding pressure P such that the strain energy U of the positive electrode active material 123 is smaller than the crack propagation energy G of the positive electrode active material 123.

[0039] Hereinafter, the amount of charge and discharge in the charge and discharge process (S105) and the molding pressure of the re-press molding in the reshaping process (S106) will be described.

[0040] FIG. 5 is a graph for explaining the volume change of the positive electrode active material 123 during charge and discharge. The horizontal axis in FIG. 5 represents the Li content in the positive electrode active material 123, indicating that the amount of Li decreases as it goes to the right and increases as it goes to the left. During charging, since lithium ions are released from the positive electrode, the greater the charge amount of the all-solid-state battery 1 is as it goes to the right of the graph. The vertical axis in FIG. 5 represents the volume expansion rate ΔV / V (%) based on the state where the Li content in the positive electrode active material 123 is the highest. Note that the range of the charge rate (SOC) of 0 to 100% of the all-solid-state battery 1 in the graph of FIG. 5 varies depending on each all-solid-state battery 1.

[0041] As shown in FIG. 5, depending on the type of the positive electrode active material 123, the characteristics with respect to charge and discharge are different. For example, when the positive electrode active material 123 is LCO, until the SOC increases to a certain extent during charging, LCO expands, and after exceeding the maximum value of the volume expansion rate, the volume shrinks during charging. Also, for example, when the positive electrode active material 123 is an NMC composite oxide (NMC-111, NMC-523, NMC-622, NMC-811, etc.) or an NCA composite oxide, the volume of the positive electrode active material 123 always shrinks during charging and always expands during discharge.

[0042] FIGS. 6a and 6b are graphs for explaining the effect of re-press molding. FIG. 6a is a graph showing the effect of re-press molding when the positive electrode active material 123 expands, and FIG. 6b is a graph showing the effect of re-press molding when the positive electrode active material 123 contracts. FIGS. 6a and 6b show the depth of discharge (DOD) with respect to the voltage of the all-solid-state battery 1. It can be said that the deeper the dischargeable depth (i.e., the larger the value of DOD), the lower the resistance and the better the performance of the battery. Note that the expansion of the positive electrode active material 123 refers to the case where the volume of the positive electrode active material 123 only expands due to charge and discharge in the charge and discharge process (S105). On the other hand, the contraction of the positive electrode active material 123 includes not only the case where the volume of the positive electrode active material 123 shrinks due to charge and discharge in the charge and discharge process (S105), but also the case where the volume of the positive electrode active material 123 shrinks after expanding.

[0043] As shown in Fig. 6a, when the positive electrode active material 123 merely expands due to charging and discharging, there is almost no change in the DOD relative to the voltage of the all-solid-state battery 1 even if the battery is press-molded again. On the other hand, as shown in Fig. 6b, when the positive electrode active material 123 shrinks during charging and discharging, the depth of the DOD increases due to the press-molding again. That is, the effect of suppressing the output deterioration of the cell by the press-molding again is significantly observed when the positive electrode active material 123 shrinks during charging and discharging.

[0044] 7a and 7b, and 8a and 8b are graphs for explaining the charge and discharge amount in the charge and discharge step (S105). As in FIG. 5, each graph shows that the charge amount of the all-solid-state battery 1 increases toward the right of the graph.

[0045] As described above, the effect of suppressing the deterioration of the cell output by the second press molding is prominent when the positive electrode active material 123 shrinks during charging and discharging. Therefore, in the charging and discharging step (S105), charging and discharging is preferably performed until the volume of the positive electrode active material 123 shrinks more than the state where the positive electrode active material 123 is most expanded when the SOC of the all-solid-state battery 1 is in the range of 0% to 100%. For example, when the positive electrode active material 123 is LCO, the volume of the positive electrode active material 123 is shrunk more than the state where the LCO is most expanded (ΔV / V0). LCOmax The charge / discharge amount of the all-solid-state battery 1 is adjusted so that the positive electrode active material 123 is in a region R1 in FIG. 7a, where the volume of the positive electrode active material 123 is smaller than that of the NMC composite oxide (ΔV / V0). NMCmax The charge / discharge amount of the all-solid-state battery 1 is adjusted so that the all-solid-state battery 1 is in a region R2 in FIG. 7b, which is a state in which the volume is in a contracted state compared to the region R1.

[0046] More preferably, in the charge / discharge step (S105), charge / discharge is performed until the positive electrode active material 123 is in a state where it has shrunk more than the average particle diameter (hereinafter referred to as the average particle diameter) of the positive electrode active material 123 when the SOC of the all-solid-state battery 1 is in the range of 0% to 100%. For example, when the positive electrode active material 123 is LCO, the average particle diameter (ΔV / V0) of the LCO LCOaveAdjust the charge and discharge amount of the all-solid-state battery 1 so that it becomes the region R3 in FIG. 8a in a state where the volume is more contracted. Further, for example, when the positive electrode active material 123 is an NMC composite oxide, the average particle size (ΔV / V0) of the NMC composite oxide NMCave Adjust the charge and discharge amount of the all-solid-state battery 1 so that it becomes the region R4 in FIG. 8b in a state where the volume is more contracted. As a result, when the reshaping step (S106) is executed, the density of the positive electrode layer 12 is further increased, the interfacial contact property is further improved, and the output deterioration of the cell can be more reliably suppressed. Note that the average particle size of each positive electrode active material 123 can be determined in advance as a fixed value by experiments or the like.

[0047] Next, the molding pressure of the second press molding in the reshaping step (S106) will be described.

[0048] As described above, in the present embodiment, in the reshaping step (S106), the second press molding (re-press molding) is performed at a molding pressure P at which cracks do not occur in the positive electrode active material 123. When the strain energy U of the positive electrode active material 123 generated by the shrinkage due to charge and discharge and the molding pressure P during press molding becomes equal to or greater than the crack propagation energy G of the positive electrode active material 123, cracks occur in the positive electrode active material 123. Therefore, press molding is performed at a molding pressure P such that the strain energy U of the positive electrode active material 123 is smaller than the crack propagation energy G of the positive electrode active material 123.

[0049] The strain energy U of the positive electrode active material 123 is given by the following formula (1). Note that E in formula (1) is the Young's modulus of the positive electrode active material 123. As shown in formula (1), the strain energy U of the positive electrode active material 123 is determined by the Young's modulus E [Pa] of the positive electrode active material 123 and the molding pressure P [Pa].

Equation

[0050] FIG. 9 is a graph showing the relationship between the Young's modulus E of the positive electrode active material 123 and the SOC of the all-solid-state battery 1. As shown in FIG. 9, the Young's modulus E of the positive electrode active material 123 changes depending on the magnitude of the SOC of the all-solid-state battery 1. In FIG. 9, a type of NMC composite oxide is used as the positive electrode active material 123. Although the graph of the Young's modulus E differs depending on the type of the positive electrode active material 123, regardless of which positive electrode active material is used, the Young's modulus E changes depending on the magnitude of the SOC of the all-solid-state battery 1. That is, the strain energy U of the positive electrode active material 123 is determined by the type of the positive electrode active material 123, the SOC of the all-solid-state battery 1, and the forming pressure P during press forming.

[0051] Next, the crack propagation energy G of the positive electrode active material 123 is given by the following formula (2). In formula (2), K IC is the fracture toughness value of the positive electrode active material 123. Also, v is the Poisson's ratio of the positive electrode active material 123, which is determined by the type of the positive electrode active material 123. As shown in formula (2), the crack propagation energy G of the positive electrode active material 123 is related to the Young's modulus E [Pa] of the positive electrode active material 123 and the fracture toughness value K IC [Pa·m 1 / 2 of the positive electrode active material 123.

Equation

[0052] FIG. 10 is a graph showing the relationship between the fracture toughness value K IC of the positive electrode active material 123 and the SOC of the all-solid-state battery 1. As shown in FIG. 10, the fracture toughness value K IC of the positive electrode active material 123 changes depending on the magnitude of the SOC of the all-solid-state battery 1. In FIG. 10, a type of NMC composite oxide is used as the positive electrode active material 123. Although the graph of the fracture toughness value K IC differs depending on the type of the positive electrode active material 123, regardless of which positive electrode active material is used, the fracture toughness value K IC changes depending on the magnitude of the SOC of the all-solid-state battery 1. That is, the fracture toughness value K IC of the positive electrode active material 123 is determined by the type of the positive electrode active material 123 and the SOC of the all-solid-state battery 1.

[0053] Next, when the strain energy U of the positive electrode active material 123 becomes equal to or greater than the crack propagation energy G of the positive electrode active material 123, cracks occur in the positive electrode active material 123. Therefore, the condition for preventing cracks from occurring in the positive electrode active material 123 is expressed by the following formula (3).

Equation

[0054] In formula (3), the Young's modulus E and the fracture toughness value K IC are determined by the type of the positive electrode active material 123 and the SOC of the all-solid-state battery 1 (that is, the charge and discharge amount in the charge and discharge process (S105)), as described above. Therefore, in the reshaping process (S106), the control unit 7 adjusts the forming pressure P by the pressing mechanism 6 so as to satisfy formula (3) based on the type of the positive electrode active material 123 and the charge and discharge amount in the charge and discharge process (S105). Thereby, it is possible to surely prevent cracks from occurring in the positive electrode active material 123 in the reshaping process (S106) even when charging and discharging are performed at an arbitrary charge and discharge amount in the charge and discharge process (S105).

[0055] FIG. 11 is a graph showing the relationship between the number of re-press forming times and the depth of discharge (DOD). That is, it is a graph showing the relationship between the number of repetitions and the DOD of the positive electrode layer 12 when the charge and discharge process (S105) and the reshaping process (S106) are repeated after the reshaping process (S106). In FIG. 11, as an example, the relationship between the number of re-press forming times and the DOD when the positive electrode layer 12 with a solid electrolyte ratio (SE ratio) of 35% is used is cited.

[0056] As shown in FIG. 11, when the positive electrode layer 12 with an SE ratio of 35% is used, within the range of up to 3 times of re-press forming, after the re-forming process (S106), the more the charge-discharge process (S105) and the re-forming process (S106) are repeated, the larger the DOD value becomes (the deeper the dischargeable depth becomes). That is, after the re-forming process (S106), the more the charge-discharge process (S105) and the re-forming process (S106) are repeated, the higher the density of the all-solid-state battery 1 becomes, the interfacial contact property becomes good, and the effect of suppressing the output deterioration of the cell becomes larger. However, the effect of suppressing the output deterioration of the cell by repeating the charge-discharge process (S105) and the re-forming process (S106) is the largest in the first repetition, and as the number of repetitions increases, the effect becomes smaller.

[0057] In this way, by repeatedly executing the charge-discharge process (S105) and the re-forming process (S106), it is possible to further suppress the output deterioration of the cell. Therefore, in the present embodiment, preferably, after the re-forming process (S106), the charge-discharge process (S105) and the re-forming process (S106) are repeated at least once again.

[0058] Note that the limit value (ideal resistance value) that can improve the cell performance by the charge-discharge process (S105) and the re-forming process (S106) varies depending on the type of material of the all-solid-state battery 1 and the ratio of each material, and the ideal resistance value of each all-solid-state battery 1 can be stored in the control unit 7 in advance by experiments or the like. Therefore, for example, after the re-forming process (S106), the resistance value of the all-solid-state battery 1 may be measured, and the charge-discharge process (S105) and the re-forming process (S106) may be repeated until the resistance value approaches the ideal resistance value.

[0059] Also, for example, the resistance value of the all-solid-state battery 1 may be measured before the charge-discharge process (S105) and after the re-forming process (S106), and the charge-discharge process (S105) and the re-forming process (S106) may be repeated until the reduction rate of the resistance value becomes equal to or less than a predetermined value.

[0060] FIG. 12 is a flowchart for explaining a method for confirming the form of the all-solid-state battery 1.

[0061] As shown in FIG. 12, the all-solid-state battery 1 of the present embodiment can confirm its form by a recharge and discharge process (S201), a pressing process (S203), a process of measuring the porosity before and after pressing (S202, S204), and a comparison between the measured value and the theoretical value of the porosity (S205).

[0062] In step S201 (recharge and discharge process), the all-solid-state battery 1 is charged and discharged (recharged and discharged). As the charging and discharging method, a known method used for charging and discharging an all-solid-state battery can be used. In the present embodiment, as in the charging and discharging process (S105) in the manufacturing process, during charging, power is supplied from the external power source 4 to the all-solid-state battery 1 via the voltage and current adjustment unit 3, and during discharging, power is discharged from the all-solid-state battery 1 to the external power source 4 via the voltage and current adjustment unit 3. Due to charging and discharging, the volume of the positive electrode active material 123 changes (expands and contracts).

[0063] In step S202 (first porosity measurement process), the porosity in the positive electrode layer 12 of the all-solid-state battery 1 is measured. The porosity is calculated, for example, by measuring the thickness from a cross-sectional view (two-dimensional structure) of the positive electrode layer 12. In this case, the thickness can be obtained using, for example, SEM, AFM, Raman, TOF-SIMS, AES, XAFS, an optical microscope, etc. Also, the porosity may be calculated by measuring the thickness from the three-dimensional structure of the positive electrode layer 12. In this case, the thickness can be obtained using, for example, X-ray CT or CT-XAFS. Further, both the porosity and the performance of the all-solid-state battery 1 may be measured, and the porosity may be estimated from the performance results. Note that the method for measuring the porosity is not limited to the above, and any known method may be used.

[0064] In step S203 (pressing process), the all-solid-state battery 1 is pressed by the pressing mechanism 6.

[0065] In step S204 (second porosity measurement process), the porosity in the positive electrode layer 12 of the all-solid-state battery 1 after the pressing process (S203) is measured. The method for measuring the porosity is the same as that in step S202.

[0066] In step S205, the porosity φ measured before the pressing process (S202) b and the porosity φ measured after pressing (S204) a are compared with the theoretical value φ of the porosity in the positive electrode layer 12 calculated from the volume change of the positive electrode active material 123 due to charge and discharge (recharge and discharge) in step S201. t Specifically, the theoretical value φ of the porosity t is calculated from the following formula (4) obtained by multiplying the difference between the maximum value (ΔV / V0) max and the minimum value (ΔV / V0) min of the volume change rate of the positive electrode active material 123 due to charge and discharge (recharge and discharge) by the ratio R ac of the positive electrode active material 123 in the positive electrode layer 12.

Equation

[0067] For example, assume that charge and discharge (recharge and discharge) are performed within the range of R1 in FIG. 13 showing the charge amount of the all-solid-state battery 1 and the volume change of the positive electrode active material 123 when the positive electrode active material 123 is LCO. In this case, the theoretical value φ of the porosity is the product of the difference (ΔV / V0) max between the maximum value (ΔV / V0) min and the minimum value (ΔV / V0) max -(ΔV / V0) min of the volume change rate of LCO in the positive electrode layer 12 multiplied by the ratio of LCO in the positive electrode layer 12. t This gives the theoretical value φ of the porosity.

[0068] In the all-solid-state battery 1 of this embodiment, since the charge / discharge step (S105) and the reshaping step (S106) are performed, the voids 14 in the positive electrode layer 12 are small, and the density of the solid electrolyte material 111 in the positive electrode layer 12 is high. Therefore, during charging and discharging, the solid electrolyte material 111 is prevented from moving in the positive electrode layer 12 or from being plastically deformed due to the expansion pressure of the positive electrode active material 123. Therefore, even if the positive electrode active material 123 expands and contracts due to the charge / discharge (recharge / discharge) in step S201, the increase in the voids 14 in the positive electrode layer 12 is prevented. In contrast, for example, in an all-solid-state battery in which the charge / discharge step (S105) and the reshaping step (S106) are not performed or are performed insufficiently, the density of the solid electrolyte material 111 in the positive electrode layer 12 is low. Therefore, when charging and discharging (recharging and discharging) is performed, the expansion pressure of the positive electrode active material 123 causes the solid electrolyte material 111 to move significantly within the positive electrode layer 12 or to undergo plastic deformation, thereby significantly increasing the voids 14 within the positive electrode layer 12.

[0069] As described above, in the all-solid-state battery 1 of this embodiment, an increase in the voids 14 in the positive electrode layer 12 is suppressed even by charge / discharge (recharge / discharge), so the difference in porosity φ b -φ a is the theoretical value φ of the porosity calculated from the volume change of the positive electrode active material 123 due to charging and discharging using the above-mentioned formula (4). t That is, the all-solid-state battery 1 of the present embodiment satisfies the following formula (5).

number

[0070] In contrast, in an all-solid-state battery that has not undergone the charge / discharge step (S105) and the remolding step (S106), when charge / discharge (recharge / discharge) is performed as described above, the voids 14 in the positive electrode layer 12 are significantly increased due to the movement and plastic deformation of the solid electrolyte material 111 caused by the expansion pressure of the positive electrode active material 123. For this reason, the difference in porosity φ before and after pressing (S202) b -φ a is the theoretical value of porosity φ t The value will be greater than or equal to this.

[0071] Thus, in the all-solid-state battery 1 of the present embodiment, when recharging and discharging are performed after re-press molding and further pressing is performed after the recharging and discharging, the porosity in the electrode layer before and after pressing does not change by more than the volume change rate of the active material. That is, there are few voids 14 generated during the use of the all-solid-state battery, and the internal resistance of the electrode layer is small.

[0072] In addition, also in the recharging and discharging in step S201, similar to the charging and discharging process (S105) during the manufacture of the all-solid-state battery 1, preferably, the charging and discharging are performed until the volume of the positive electrode active material 123 contracts more than the state in which the positive electrode active material 123 expands most in the range where the SOC of the all-solid-state battery 1 is 0 percent or more and 100 percent or less. As a result, since the volume change of the positive electrode active material 123 becomes large, the movement of the solid electrolyte material 111 due to the expansion pressure of the positive electrode active material 123 and the increase in the voids 14 in the positive electrode layer 12 due to plastic deformation are remarkably manifested. Therefore, it becomes easier to determine whether the difference φ b -φ a in the porosity before and after pressing (S202) is equal to or greater than the theoretical value φ t of the porosity.

[0073] More preferably, in the recharging and discharging in step S201, the charging and discharging are performed until the positive electrode active material 123 contracts from the state in which it expands most to the state in which it contracts most in the range where the SOC of the all-solid-state battery 1 is 0 percent or more and 100 percent or less. As a result, since the volume change of the positive electrode active material 123 becomes larger, the movement of the solid electrolyte material 111 due to the expansion pressure of the positive electrode active material 123 and the increase in the voids 14 in the positive electrode layer 12 due to plastic deformation are more remarkably manifested. Therefore, it becomes easier to determine whether the difference φ b -φ a in the porosity before and after pressing (S202) is equal to or greater than the theoretical value φ t of the porosity.

[0074] According to the all-solid-state battery 1 of the above-described embodiment, the following effects can be obtained.

[0075] The all-solid-state battery 1 is obtained by re-press molding a battery formed by press molding after charge and discharge. The re-press molding is performed at a molding pressure P such that the strain energy U generated in the positive electrode active material 123 due to charge and discharge and re-press molding is smaller than the crack propagation energy G of the positive electrode active material 123. Therefore, no cracks or the like occur in the all-solid-state battery 1. Further, when the all-solid-state battery 1 is recharged and discharged after the re-press molding and then further pressed after the re-charge and discharge, the difference φ b -φ a in the porosity within the positive electrode layer 12 is smaller than the theoretical value φ t of the porosity within the positive electrode layer 12 calculated from the difference between the maximum value and the minimum value of the volume change rate of the positive electrode active material 123 when recharged and discharged. That is, when the all-solid-state battery 1 is recharged and discharged after the re-press molding and then further pressed after the re-charge and discharge, the porosity within the positive electrode layer 12 before and after pressing does not change by more than the volume change rate of the active material. Therefore, since there are few voids 14 generated during the use of the all-solid-state battery 1 and the internal resistance of the positive electrode layer 12 is small, an all-solid-state battery with high cell output performance can be provided.

[0076] The all-solid-state battery 1 is recharged and discharged from the state where the positive electrode active material 123 is most expanded to the state where it is most contracted after the re-press molding. When further pressed after the re-charge and discharge, the difference φ b -φ a in the porosity within the positive electrode layer 12 is smaller than the theoretical value φ t of the porosity within the positive electrode layer. Thus, even when the all-solid-state battery 1 is recharged and discharged under conditions such that the volume change of the positive electrode active material 123 is the largest, the difference φ b -φ a in the porosity within the positive electrode layer 12 before and after pressing after the re-charge and discharge is smaller than the theoretical value φ t of the porosity within the positive electrode layer 12. That is, regardless of the magnitude of the charge and discharge amount of the all-solid-state battery 1, the generation of voids 14 during the use of the all-solid-state battery 1 is suppressed. Therefore, an all-solid-state battery with high cell output performance can be provided.

[0077] In addition, in this embodiment, the characteristics of the all-solid-state battery 1 of this embodiment were described by taking the positive electrode layer 12 as an example, but the same can be said for the negative electrode layer 13. However, when lithium metal is used as the negative electrode active material, the decrease in the contact area between the active material and the solid electrolyte material 111 due to charge and discharge does not occur as significantly as in the positive electrode layer 12.

[0078] Also, in this embodiment, both the positive electrode layer 12 and the negative electrode layer 13 are configured to include an active material and the solid electrolyte material 111, but it is not necessarily limited to this. If at least one of the positive electrode layer 12 and the negative electrode layer 13 includes an active material and the solid electrolyte material 111, the above-described effects can be obtained, and the other may not include the solid electrolyte material 111.

[0079] Although the embodiments of the present invention have been described above, the above embodiments merely show a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

Explanation of Reference Numerals

[0080] 1 All-solid-state battery 2 Voltage sensor 3 Voltage and current adjustment unit 4 External power source 5 Current sensor 6 Pressurizing mechanism 7 Control unit 11 Solid electrolyte layer 12 Positive electrode layer 13 Negative electrode layer 100 All-solid-state battery system 111 Solid electrolyte material 111 123 Positive electrode active material

Claims

1. A method for confirming the form of an all-solid-state battery, comprising: a charge-discharge step of charging and discharging the all-solid-state battery; a first porosity measurement step of calculating the porosity in the electrode layer of the all-solid-state battery from a cross-sectional view of the electrode layer of the all-solid-state battery measured by SEM after the charge-discharge step; a pressing step of pressing the all-solid-state battery after the first porosity measurement step; a second porosity measurement step of calculating the porosity in the electrode layer from a cross-sectional view of the electrode layer of the all-solid-state battery measured by SEM after the pressing step, wherein it is confirmed whether the difference between the porosity calculated in the first porosity measurement step and the porosity calculated in the second porosity measurement step is smaller than the theoretical value of the porosity in the electrode layer calculated by multiplying the difference between the maximum value and the minimum value of the volume change rate of the active material in the electrode layer when charged and discharged by the ratio of the active material in the electrode layer; A method for confirming the form of an all-solid-state battery.

2. The method for confirming the form of an all-solid-state battery according to Claim 1, wherein in the charge-discharge step, the all-solid-state battery is charged and discharged from the state in which the active material is most expanded to the state in which it is most contracted. A method for confirming the form of an all-solid-state battery.

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