Solid-state battery and method for manufacturing the same

Abstract

To provide a manufacturing method of a solid-state battery, capable of confirming the presence / absence of a short circuit in the solid-state battery before delivery, and quickly preventing an effluence of a defection item.SOLUTION: A manufacturing method of a solid-state battery, includes: a battery preparation step of preparing the solid-state battery having a positive electrode layer, a negative electrode layer, and a sulfide solid electrolyte layer arranged between the positive electrode layer and the negative electrode layer; and an over discharge step of over-discharging the solid-state battery.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to solid-state batteries and methods for manufacturing solid-state batteries. [Background technology]

[0002] In recent years, secondary batteries such as lithium-ion secondary batteries have been suitably used as portable power sources for personal computers, mobile terminals, etc., and as power sources for driving vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs).

[0003] In the manufacture of solid-state batteries, it is necessary to check for short circuits before shipping, reject defective products that cause short circuits, and prevent them from being released into the market. In particular, in solid-state batteries that have a sulfide solid electrolyte layer, sulfides (e.g., CuS) formed by the reaction between metal components mixed in the sulfide solid electrolyte layer and sulfur components contained in the sulfide solid electrolyte layer can cause short circuits. For example, in Patent Document 1, the presence or absence of a short circuit in a battery is confirmed by aging the battery before the first charge, that is, by subjecting the battery to a long-term heat treatment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-191183 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional manufacturing methods for solid-state batteries, as shown in Patent Document 1, defective products that may short-circuit after a long heating process are distinguished, making it difficult to quickly identify whether a solid-state battery has a short circuit or not before shipping and to quickly prevent the outflow of defective products. In view of the above circumstances, the present invention aims to provide a solid-state battery and a method for manufacturing the solid-state battery that can check for the presence or absence of a short circuit in the solid-state battery before shipping and quickly prevent the release of defective products. [Means for solving the problem]

[0006] <1> a battery preparation step of preparing a solid-state battery having a positive electrode layer, a negative electrode layer, and a sulfide solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; an overdischarge step of overdischarging the solid-state battery; A method for manufacturing a solid-state battery comprising: <2> The overdischarge step is a step of overdischarging the solid-state battery by applying a voltage of less than −0.5 V. <1> or <2> A method for manufacturing the solid state battery according to claim 1. <3> the overdischarge step involves overdischarging the solid-state battery at a temperature in the range of 25°C to 150°C; <1> or <2> A method for manufacturing the solid state battery according to claim 1. <4> the overdischarge step involves overdischarging the solid-state battery at a temperature in the range of 60°C to 85°C, <3> A method for manufacturing the solid state battery according to claim 1. <5> The aforementioned <1> ~ <4> 10. A solid-state battery manufactured by the method for manufacturing a solid-state battery according to any one of claims 1 to 9. [Effects of the Invention]

[0007] According to the present disclosure, a solid-state battery and a method for manufacturing the solid-state battery are provided that can check for the presence or absence of a short circuit in the solid-state battery before shipping and quickly prevent the release of defective products. DETAILED DESCRIPTION OF THE INVENTION

[0008] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the present disclosure, in the numerical ranges described in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0009] Hereinafter, an embodiment of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention.

[0010] <Solid-state battery manufacturing method> The method for manufacturing a solid-state battery according to the present disclosure includes a battery preparation step of preparing a solid-state battery having a positive electrode layer, a negative electrode layer, and a sulfide solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and an overdischarge step of overdischarging the solid-state battery.

[0011] Overdischarge refers to applying a voltage between the electrodes before charging, causing electrons to flow from the negative electrode to the positive electrode, thereby generating a current.

[0012] According to the manufacturing method of the solid-state battery of the present disclosure, sulfides produced by the reaction of metal components (e.g., metallic copper contained in the negative electrode) mixed in the sulfide solid electrolyte layer with sulfur components contained in the sulfide solid electrolyte layer are electron conductors, and the sulfides are accelerated from the negative electrode side to the positive electrode side by overdischarge. This makes it possible to check for short circuits caused by metal foreign matter mixed in the sulfide solid electrolyte layer of the solid-state battery before shipping, and quickly prevent the release of defective solid-state batteries.

[0013] Furthermore, the manufacturing method for a solid-state battery according to the present disclosure reduces degradation of the solid-state battery that occurs during the process of checking for the presence or absence of a short circuit in the solid-state battery. Conventional manufacturing methods for solid-state batteries involve an aging process, in which the solid-state battery is placed in a high-temperature environment for a long period of time (for example, at 80°C for approximately 30 days), in order to check for the presence or absence of a short circuit in the solid-state battery. However, during this process, materials contained in the solid-state battery may be degraded by heat, resulting in a decrease in battery performance (more specifically, an increase in resistance value). In this regard, the manufacturing method for a solid-state battery according to the present disclosure involves an overdischarge process, which allows for the presence or absence of a short circuit in the solid-state battery to be quickly checked, thereby reducing degradation of the solid-state battery.

[0014] In a solid-state battery according to the present disclosure manufactured through an overdischarge process, the concentration of metallic foreign matter mixed into the sulfide solid electrolyte layer is diffused in the direction opposite to the direction in which the overdischarge voltage is applied (i.e., from the negative electrode side toward the positive electrode side). On the other hand, in a solid-state battery manufactured without an overdischarge process, the metallic foreign matter mixed into the sulfide solid electrolyte layer tends to diffuse three-dimensionally in a concentric pattern. Therefore, by analyzing the concentration gradient of metallic foreign matter around the region where the metallic foreign matter is likely to be mixed from a cross section of the solid-state battery, it can be confirmed that the battery was manufactured through an overdischarge process.

[0015] Hereinafter, each step of the method for manufacturing a solid-state battery according to the present disclosure will be described in detail.

[0016] [Battery preparation process] In the battery preparation step, a solid-state battery is prepared, which includes a positive electrode layer, a negative electrode layer, and a sulfide solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The positive electrode layer includes, for example, a layer containing a positive electrode active material and a current collector foil. The negative electrode layer includes, for example, a negative electrode active material layer and a current collector foil. Any known solid-state battery can be used as long as it includes a positive electrode layer, a negative electrode layer, and a sulfide solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. Specific materials for the positive electrode layer, the negative electrode layer, and the sulfide solid electrolyte layer include those similar to those listed in JP 2020-191183 A.

[0017] [Overdischarge process] In the overdischarge step, the solid-state battery is overdischarged.

[0018] The overdischarge step may involve, for example, overdischarging the solid-state battery at a temperature range of 25°C or higher, overdischarging the solid-state battery at a temperature range of 30°C or higher, or overdischarging the solid-state battery at a temperature range of 50°C or higher. In the overdischarge step, from the viewpoint of more efficiently promoting the movement of short-circuit components (e.g., sulfides) generated in the sulfide solid electrolyte layer from the negative electrode side to the positive electrode side and more quickly detecting a short circuit, the solid battery is preferably overdischarged at a temperature in the range of 25°C or higher and 150°C or lower, more preferably at a temperature in the range of 60°C or higher and 85°C or lower, and even more preferably at a temperature in the range of 70°C or higher and 85°C or lower. In terms of reducing battery degradation, the overdischarge step preferably overdischarges the solid-state battery at a temperature of 250° C. or less, more preferably at a temperature of 200° C. or less, and even more preferably at a temperature of 150° C. or less. If the battery exterior is a laminate, the solid-state battery may be overdischarged at a temperature of 100° C. or less.

[0019] In one embodiment, the overdischarge step may be, for example, a mode in which the solid-state battery is placed in a thermostatic chamber and overdischarged while being heated.

[0020] The means for overdischarging the solid-state battery is not particularly limited, and may be natural discharge, or the solid-state battery may be electrically connected to a discharge device for discharging. From the viewpoint of more efficiently promoting the movement of short-circuit components (e.g., sulfides) generated in the sulfide solid electrolyte layer from the negative electrode side to the positive electrode side and more quickly confirming a short circuit, it is preferable to discharge the solid-state battery by electrically connecting it to a discharge device.

[0021] From the viewpoint of more efficiently promoting the movement of short-circuit components (e.g., sulfides) generated in the sulfide solid electrolyte layer from the negative electrode side to the positive electrode side and more quickly detecting a short circuit, the overdischarge step is preferably a step of overdischarging the solid battery by applying a voltage of less than −0.5 V, more preferably a step of overdischarging the solid battery by applying a voltage of −7.0 V or more and −1.0 V or less, and even more preferably a step of overdischarging the solid battery by applying a voltage of −6.5 V or more and −1.5 V or less.

[0022] In one embodiment, the overdischarge step is preferably a step of overdischarging the solid-state battery by applying a voltage while heating, from the viewpoint of more efficiently promoting the movement of short-circuit components (e.g., sulfides) generated in the sulfide solid electrolyte layer from the negative electrode side to the positive electrode side and more quickly confirming a short circuit, and more preferably a step of overdischarging the solid-state battery by applying a voltage of −1.5 V or less at a temperature in the range of 60° C. or more and 85° C. or less.

[0023] [Other steps] The method for manufacturing a solid-state battery according to the present disclosure may further include other steps in addition to the battery preparation step and the overdischarge step, as necessary. 1) a removal step of removing solid-state batteries that have short circuits after the over-discharge step; 2) an aging process in which the solid-state battery is aged after the over-discharge process; 3) an initial charging step of initially charging the solid-state battery after the battery preparation step (preferably after the overdischarge step); 4) a discharging step of discharging the solid-state battery after the battery preparation step (preferably after the initial charging step); 5) A stacking process of stacking solid-state batteries after the battery preparation process; 6) a cutting step of cutting the solid-state battery after the battery preparation step; The above steps 3) to 6) are desirable steps for shipping a solid-state battery that has been confirmed to be free of short circuits caused by short-circuit components (e.g., sulfides) that occur in the sulfide solid electrolyte layer.

[0024] In one embodiment, the method for producing a solid state battery according to the present disclosure may further include, after the overdischarge step, a pre-charge step and a discharge step.

[0025] <Solid battery> The solid-state battery according to the present disclosure is manufactured by the method for manufacturing a solid-state battery according to the present disclosure. According to the present disclosure, as described above, the presence or absence of short circuits in solid-state batteries is checked during the manufacturing stage before shipping, and the release of defective products with short circuits is quickly prevented, thereby obtaining solid-state batteries that do not have short circuits due to metallic foreign matter mixed into the sulfide solid electrolyte layer. [Example]

[0026] Example 1 1. Preparation of paste for positive electrode layer Positive electrode active material LiNi with surface treatment of LiNbO3 0.8 (CoAl) 0.2 O2, conductive carbon, solid electrolyte, binder resin, and solvent were mixed using an ultrasonic homogenizer (UH-50 manufactured by SMT Corporation) to prepare a paste for the positive electrode layer.

[0027] 2. Preparation of paste for negative electrode layer Li4Ti5O 12 The conductive carbon, binder resin, and solvent were mixed for 30 minutes using an ultrasonic homogenizer (UH-50 manufactured by SMT Corporation), and then the solid electrolyte was further added and mixed for 30 minutes using an ultrasonic homogenizer (UH-50 manufactured by SMT Corporation) to prepare a paste for the negative electrode layer.

[0028] 3. Preparation of sulfide solid electrolyte layer paste A solution containing 5% by mass of a solvent and a binder resin was mixed with a sulfide solid electrolyte, a LiI-LiBr-Li2-P2S5-based glass ceramic with an average particle size of 2.5 μm, in a polypropylene container using an ultrasonic homogenizer (UH-50 manufactured by SMT Co., Ltd.). Next, the mixture was shaken for 30 seconds using a shaker to obtain a paste for the sulfide solid electrolyte layer.

[0029] 4. Preparation of sheets for each layer The paste for the positive electrode layer was applied onto an aluminum foil by a blade method using an applicator, and then dried for 30 minutes in a hot press at 100°C to obtain a sheet for the positive electrode layer. The paste for the sulfide solid electrolyte layer was applied to the surface of an aluminum foil by a blade method using an applicator, and then dried for 30 minutes on a hot press at 100°C to obtain a sheet for the sulfide solid electrolyte layer. The paste for the negative electrode layer was applied to the surface of the copper foil by a blade method using an applicator, and dried on a hot press at 100° C. for 30 minutes to obtain a sheet for the negative electrode layer.

[0030] 5. Fabrication of Lithium-ion Secondary Batteries The above-mentioned negative electrode layer sheet and sulfide solid electrolyte layer sheet were stacked in this order and pressed. The aluminum foil of the sulfide solid electrolyte layer sheet was peeled off, transferring the sulfide solid electrolyte layer to the surface of the negative electrode layer that did not have the copper foil, obtaining a sulfide solid electrolyte layer / negative electrode (negative electrode layer / aluminum foil) laminate. Next, the positive electrode layer sheet was stacked on the sulfide solid electrolyte layer side of the laminate so that the surface of the positive electrode layer sheet that did not have the aluminum foil was in contact with the surface of the positive electrode layer sheet that did not have the aluminum foil. This was roll-pressed at 165°C and 5 ton / cm to obtain a laminate having a positive electrode (aluminum foil / positive electrode layer), a sulfide solid electrolyte layer, and a negative electrode in this order. This laminate was then laminated and sealed, and restrained at 5 MPa to prepare a lithium-ion secondary battery, which is a solid-state battery. This solid-state battery is a lithium-ion secondary battery with a configuration that is prone to pseudo-short circuits by using copper foil as the negative electrode current collector foil.

[0031] 6. The lithium-ion secondary battery prepared in step 5 above was placed in a thermostatic chamber at the temperature shown in Table 1, and the battery was connected to a charge / discharge device. Then, the battery was set to 0.1C equivalent, and after the cell voltage reached -0.1V, constant voltage discharge was started at the voltage shown in Table 1. The constant voltage discharge was terminated when the cell voltage rose and reached 0V, which was considered to be a short circuit. The time to reach short circuit is shown in Table 1. As described above, a short circuit was observed in the solid-state battery, and it was confirmed that the battery was defective.

[0032] <Examples 2 and 3> 1 to 5. A lithium ion secondary battery, which is a solid-state battery, was prepared in the same manner as in Example 1. 6. The specifications were the same as in Example 1, except that the temperature in the thermostatic chamber and the overdischarge voltage were set to the specifications shown in Table 1. A short circuit was observed in the defective solid-state battery, and it was confirmed to be a defective product. The time to reach a short circuit is shown in Table 1.

[0033] <Comparative Example 1> 1 to 5. A lithium ion secondary battery, which is a solid-state battery, was prepared in the same manner as in Example 1. 6. Instead of the overdischarge step, an aging treatment was performed in which the battery was left standing in a thermostatic chamber at 80°C, as described in JP 2020-191183 A. The time to short circuit is shown in Table 1. For convenience, the aging temperature (marked with an asterisk) is listed in the [Overdischarge Temperature] section in Table 1, but the overdischarge step was not performed in Comparative Example 1.

[0034] [Table 1]

[0035] As described above, it was found that the manufacturing method in the example can check for the presence or absence of a short circuit in a solid-state battery before shipping in a shorter time than the manufacturing method in the comparative example, and can quickly prevent the outflow of defective products.

[0036] Example 4 1 to 3. A paste for a positive electrode layer, a paste for a negative electrode layer, and a paste for a sulfide solid electrolyte layer were obtained by the same method as in Example 1. 4. Preparation of sheets for each layer A positive electrode layer sheet and a sulfide solid electrolyte layer sheet were obtained by the same method as in Example 1. In addition, a negative electrode layer sheet was obtained by the same method as in Example 1, except that aluminum foil was used instead of copper foil. 5. A lithium ion secondary battery, which is a solid-state battery, was obtained in the same manner as in Example 1. 6. The lithium-ion secondary battery prepared in step 5 above was placed in a thermostatic chamber at the temperature shown in Table 2 and connected to a charge / discharge device. The battery was then discharged at a constant current equivalent to 0.1 C until it reached -1.8 V, after which it was discharged at a constant voltage of -1.8 V. The overdischarge test was terminated after 10 hours. The battery was then charged at a constant current equivalent to 0.3 C until it reached a voltage equivalent to 40% charge, at which point it was charged at a constant voltage. Charging was terminated when the current reached 0.01 C. The battery was then discharged at a constant current equivalent to 46 C, and the resistance value was calculated by dividing the difference between the voltage before charge and the voltage after 0.1 seconds of discharge by the current equivalent to 46 C. Table 2 shows the obtained resistance values ​​relative to the resistance value of the solid-state battery before the overdischarge process ("Initial" in the [Relative Resistance] section in Table 2). The relative resistance value after the overdischarge process was divided by the relative resistance value before the overdischarge process to calculate the resistance increase rate. The values ​​of the time to short circuit, the resistance value, and the resistance increase rate are shown in Table 2. In the table, since no short circuit was observed in the solid-state battery of Example 4 even after the overdischarge step was carried out for 10 hours, the "time to short circuit (indicated by * in Table 2)" refers to the "measurement end time." As described above, it was found that the solid state battery produced in Example 4 could be checked in a short time before shipping to ensure that there was no short circuit in the solid state battery.

[0037] <Comparative Example 2> 1 to 5. A lithium ion secondary battery, which is a solid-state battery, was obtained by the same method as that described in Example 4. 6. Instead of the overdischarge step, an aging process was performed in which the battery was placed in a constant temperature bath at 80°C, as described in JP 2020-191183 A. The battery was then charged at a constant current equivalent to 0.3 C, and after reaching a voltage equivalent to a 40% charge depth, it was charged at a constant voltage, and charging was terminated when the current reached 0.01 C. The battery was then discharged at a constant current equivalent to 46 C, and the resistance value was calculated by dividing the difference between the voltage before charge and the voltage after 0.1 seconds of discharge by the current equivalent to 46 C. The resistance values ​​obtained before and after the aging treatment are shown in Table 2 as relative values ​​to the initial resistance value of the solid state battery before the overdischarge step in Example 4. The resistance increase rate was calculated by dividing the relative resistance value after the aging treatment by the relative resistance value before the aging treatment. The short circuit arrival time, resistance value, and resistance increase rate are shown in Table 2. For convenience, the aging temperature (indicated by * in Table 2) is listed under the item [Overdischarge temperature] in Table 2, but the overdischarge step was not carried out in Comparative Example 2.

[0038] In Table 2, "initial" in the item [relative resistance value] refers to the resistance value of the solid-state battery before the aging process or the overdischarge process. In Table 2, "at the end" in the item [Relative resistance value] refers to the resistance value of the solid-state battery when the aging process or the overdischarge process is completed. In Table 2, each resistance value is a relative resistance value with the initial resistance value in Example 4 as the reference.

[0039] [Table 2]

[0040] As described above, it was found that the manufacturing method in the examples requires less time to check for the presence or absence of a short circuit in the solid-state battery than the manufacturing method in the comparative examples, and therefore reduces the increase in the resistance value of the solid-state battery, that is, reduces the deterioration of the solid-state battery.

Claims

1. a battery preparation step of preparing a solid-state battery having a positive electrode layer, a negative electrode layer, and a sulfide solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; an overdischarge step of overdischarging the solid-state battery; Including, the negative electrode layer contains lithium titanate as a negative electrode active material, The overdischarge step involves overdischarging to a range of less than −0.5 V and greater than or equal to −1.8 V. How solid-state batteries are manufactured.

2. 2. The method for producing a solid-state battery according to claim 1, wherein the overdischarge step is a step of overdischarging the solid-state battery by applying a voltage of less than −0.5 V.

3. The method for manufacturing a solid-state battery according to claim 1 , wherein the overdischarge step overdischarges the solid-state battery at a temperature in the range of 25° C. to 150° C.

4. The method for manufacturing a solid-state battery according to claim 3 , wherein the overdischarge step overdischarges the solid-state battery at a temperature in the range of 60° C. to 85° C.

5. a battery preparation step of preparing a solid-state battery having a positive electrode layer, a negative electrode layer, and a sulfide solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; an overdischarge step of overdischarging the solid-state battery; Including, the overdischarge step is a step of overdischarging the solid-state battery by applying a voltage of less than −0.5 V; The overdischarge step involves overdischarging the solid-state battery at a temperature in the range of 60°C to 85°C. How solid-state batteries are manufactured.

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