Method for manufacturing solid-state battery

Abstract

In this invention, a solid-state battery before initial charging is subjected to a first preliminary treatment step for energizing same at a current density of 0.005 mA / cm2 or more at a temperature of 20°C or higher. It is preferable to perform, on the solid-state battery, a second preliminary treatment step for discharging a current at a current density of 0.005 mA / cm2 or more at a temperature of 20°C or higher after the first preliminary treatment step and before the initial charging. It is also preferable that the energization time in the first preliminary treatment step is 10 minutes or more. It is also preferable to perform the first preliminary treatment step at a temperature of 100°C or lower.

Description

Solid-state battery manufacturing method

[0001] The present invention relates to a method for manufacturing a solid-state battery.

[0002] In recent years, CO ２ Secondary batteries have been attracting attention as an effort to prevent global warming by reducing CO2 emissions. Solid-state batteries, in particular, are expected to be put into practical use as they combine safety and high energy density. However, the charging and discharging of solid-state batteries can cause dendrites of the constituent elements of the electrode active material to grow. These dendrites can contribute to short circuits between the positive and negative electrodes. The formation of dendrites is due to a problem unique to solid-state batteries: insufficient adhesion between the solid electrolyte and the active material. Therefore, in solid-state batteries, it is necessary to improve the adhesion between the solid electrolyte and the active material.

[0003] For the purpose of increasing the adhesion between the solid electrolyte and the active material, for example, Patent Document 1 proposes producing a solid-state battery by pressurizing an electrode group including electrodes and a solid electrolyte layer located between the electrodes at a pressure of 400 MPa or more and 1500 MPa or less.

[0004] JP 2018-120710 A

[0005] However, the method described in Patent Document 1 requires pressurization under high pressure conditions to enhance adhesion between the electrode and the solid electrolyte layer, which requires the use of, for example, a large press. Therefore, the method described in Patent Document 1 poses a problem in the simple manufacture of solid-state batteries. Therefore, an object of the present invention is to provide a simple method for manufacturing solid-state batteries that are less likely to cause short circuits.

[0006] The present invention relates to a method for manufacturing a solid-state battery, comprising: applying a current of 0.005 mA / cm to a solid-state battery before initial charging at a temperature of 20°C or higher; ２ The above-mentioned problems have been solved by providing a method for manufacturing a solid-state battery, which includes a first preliminary treatment step in which current is passed at the above current density.

[0007] The present invention will be described below based on preferred embodiments. The present invention relates to a method for manufacturing a solid-state battery. In this specification, a solid-state battery refers to a battery having a solid electrolyte layer. A solid-state battery is a battery that does not contain any liquid or gel-like substance as an electrolyte, or a battery that contains, for example, 50% by mass or less, particularly 30% by mass or less, and particularly 10% by mass or less of a liquid or gel-like substance as an electrolyte. The solid-state battery obtained by this manufacturing method has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer. There are no particular limitations on the types of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer. Any materials can be used for the positive electrode layer, the negative electrode layer, and the solid electrolyte layer as long as the completed solid-state battery operates properly.

[0008] The solid-state battery may be a primary battery or a secondary battery. Examples of the solid-state battery include, but are not limited to, lithium ion batteries and sodium ion batteries. The materials of the positive electrode layer, negative electrode layer, and solid electrolyte layer constituting the solid-state battery are selected appropriately depending on the type of the solid-state battery. When the solid-state battery is, for example, a lithium ion battery, the following materials can be used as the positive electrode layer, negative electrode layer, and solid electrolyte layer.

[0009] Examples of positive electrode active materials constituting the positive electrode layer include lithium (Li) metal, lithium cobalt oxide, lithium manganate, lithium iron phosphate, Ni-Co-Mn ternary lithium composite oxide (NCM), and Ni-Co-Al ternary lithium composite oxide (NCA). Examples of negative electrode active materials constituting the negative electrode layer include carbon-based materials such as graphite, artificial graphite, natural graphite, and non-graphitizable carbon (hard carbon), silicon, lithium (Li) metal, and lithium titanate. Examples of solid electrolytes constituting the solid electrolyte layer include sulfide solid electrolytes and oxide solid electrolytes. When a sulfide solid electrolyte is used, the solid electrolyte may be crystalline or amorphous. It is preferable to use a sulfide solid electrolyte containing lithium (Li), sulfur (S), and M. The M element is preferably at least one of phosphorus (P), germanium (Ge), antimony (Sb), silicon (Si), tin (Sn), aluminum (Al), titanium (Ti), iron (Fe), nickel (Ni), cobalt (Co), and manganese (Mn). It is particularly preferred that the M element contains at least phosphorus (P), and more preferably, the M element is only P. The advantages of the present invention are particularly pronounced when the sulfide solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure in addition to the above-mentioned elements. Whether or not the sulfide solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure can be determined by analyzing the solid electrolyte particles using X-ray diffraction or X-ray total scattering.

[0010] The positive electrode layer is produced by, for example, applying a positive electrode mixture containing the above-mentioned positive electrode active material powder, conductive additive, and solid electrolyte powder to the surface of a positive electrode current collector. The positive electrode current collector can be made of, for example, a metal such as stainless steel, gold, platinum, zinc, nickel, tin, aluminum, molybdenum, niobium, tantalum, tungsten, or titanium, or an alloy thereof.

[0011] The negative electrode layer is produced, for example, by applying a negative electrode mixture containing the above-described negative electrode active material powder and solid electrolyte powder to the surface of a negative electrode current collector. Alternatively, a negative electrode in a solid-state battery can be produced that includes a negative electrode current collector and a negative electrode layer that is disposed on the negative electrode current collector and contains a solid electrolyte but does not contain a negative electrode active material. The use of such a negative electrode not only improves initial characteristics and charge rate, but also facilitates the production of a solid-state battery that can effectively prevent battery short-circuiting. The specific reasons are as follows: First, this negative electrode does not contain a negative electrode active material but contains solid electrolyte particles. By using such a negative electrode in a battery, lithium ions that migrate from the positive electrode during charging are precipitated as metallic lithium, and the metallic lithium functions as the negative electrode active material. In other words, this is a so-called in-situ deposition-type negative electrode. In this case, using solid electrolyte particles with a volume-cumulative particle size within a predetermined range can suppress the growth of metallic lithium crystals into a dendritic shape, compared to conventional in-situ deposition-type negative electrodes, thereby suppressing battery short-circuiting. From this viewpoint, the solid electrolyte contained in the in-situ deposition type negative electrode has a volume cumulative particle size distribution measured by a laser diffraction scattering particle size distribution measurement method at cumulative volumes of 10 volume %, 50 volume %, and 90 volume %, respectively, as determined by D １０ , D ５０ and D ９０ When this is done, (D ９０ -D １０ ) / D ５０ It is preferable that the value of is less than 10.0. ９０ -D １０ ) / D ５０ is an index of the sharpness of the particle size distribution of the particles, and the closer this value is to 0, the more uniform the particle size distribution of the particles. When the particle size distribution becomes uniform, uniform voids are formed between the solid electrolyte particles, and during charging, lithium ions that have migrated from the positive electrode are precipitated as metallic lithium in the voids, thereby suppressing dendritic precipitation.

[0012] The solid electrolyte layer can be produced, for example, by dropping a slurry containing the above-mentioned solid electrolyte powder, binder, and solvent onto a substrate and scraping it off with a doctor blade or the like; by contacting the substrate with the slurry and then cutting it with an air knife; or by forming a coating film by screen printing or the like and then heat-drying to remove the solvent. Alternatively, the solid electrolyte layer can be produced by compacting the solid electrolyte powder by pressing or the like and then processing it appropriately. Instead of the above methods, a solid electrolyte sheet in which the solid electrolyte is supported on a porous support may be used as the solid electrolyte layer. The porous support is preferably one that can impart self-supporting properties and appropriate flexibility to the solid electrolyte sheet. From this perspective, a fiber sheet such as various nonwoven fabrics can be used as the porous support.

[0013] After the positive electrode layer, negative electrode layer, and solid electrolyte layer are manufactured, the solid electrolyte layer is then disposed between the positive electrode layer and the negative electrode layer, and these three components are enclosed in a container. The first and second preliminary treatment steps and the initial charging step, which will be described below, are then performed. In the following description, to distinguish between the first and second preliminary treatment steps and the initial charging step, the flow of current in the first and second preliminary treatment steps is referred to as "energization," and the flow of current after the initial charging step is referred to as "charging." Furthermore, the object through which current is passed in the first and second preliminary treatment steps is referred to as a "pre-charged cell," and the object after charging the pre-charged cell is referred to as a "solid-state battery." In other words, a pre-charged cell is also a solid-state battery in a state before the initial charging. The three components may be subjected to a compression treatment before or after being housed in the container. In particular, it is preferable to perform the pressure treatment in one or two of the following steps (i) the first preliminary treatment step and (ii) the second preliminary treatment step, from the viewpoint of suppressing the occurrence of short circuits due to charge and discharge in the manufactured solid-state battery. The pressure here is, for example, preferably 300 MPa or more, more preferably 400 MPa or more, and even more preferably 500 MPa or more. On the other hand, the pressure is, for example, preferably 1000 MPa or less, more preferably 900 MPa or less, and even more preferably 800 MPa or less.

[0014] In this manufacturing method, a solid-state battery is manufactured as a finished product by subjecting an uncharged cell to (i) a first preliminary treatment step. In the first preliminary treatment step, the uncharged cell is subjected to a current of 0.005 mA / cm at a temperature of 20°C or higher. ２ A process of passing current at the above current density is performed.

[0015] In a solid-state battery manufactured through the first preliminary treatment step, it is believed that a good interface is formed on the surface of the solid electrolyte particles. The presence of this interface allows smooth exchange of lithium ions between the solid-state electrolyte particles and the active material particles. As a result, problems such as localized current concentration within the battery are less likely to occur. As a result, a solid-state battery manufactured by this method can suppress the occurrence of short circuits due to charging and discharging. Each step will be explained below using the example of manufacturing a lithium-ion battery as a solid-state battery.

[0016] (i) First Pretreatment Step In this step, a predetermined current density is applied to the uncharged cell. Specifically, for example, 0.005 mA / cm ２ More preferably, 0.025 mA / cm ２ More preferably, 0.045 mA / cm ２ By passing current at a current density equal to or greater than this value, a solid-state battery capable of suppressing the occurrence of short circuits due to charging and discharging can be easily obtained. The current density is, for example, 0.55 mA / cm ２ It is preferable that the current is 0.35 mA / cm or less. ２ More preferably, it is 0.15 mA / cm or less. ２It is more preferable that the current density is equal to or less than this value. Even when current is passed at a current density equal to or less than this value, a solid battery capable of suppressing the occurrence of short circuits due to charging and discharging can be easily obtained. In this process, current may be passed while maintaining a constant current density, or may be passed while changing the current density. When current is passed while changing the current density, it is preferable that the current density is set within the above-mentioned range. From the viewpoint of more easily obtaining a solid battery capable of suppressing the occurrence of short circuits due to charging and discharging, it is desirable to pass current while maintaining a constant current density. The area of ​​the electrode when calculating the current density refers to the area in a plan view of the electrode layer formed on the surface of the current collector. When the areas of the electrode layers of the positive electrode and the negative electrode are different, the current density is calculated based on the area of ​​the electrode layer with the smaller area.

[0017] The applied voltage in this step is adjusted so that the current density falls within the above range.

[0018] In this process, maintaining the ambient temperature during current application within a predetermined range is advantageous from the viewpoint of easily obtaining a solid-state battery capable of suppressing the occurrence of short circuits due to charging and discharging. Specifically, provided that the current density during current application is within the above-mentioned range, the ambient temperature during current application is preferably set to, for example, 20°C or higher, more preferably 35°C or higher, and even more preferably 55°C or higher. Furthermore, provided that the current application rate is within the above-mentioned range, the ambient temperature during current application is preferably set to, for example, 100°C or lower, more preferably 80°C or lower, and even more preferably 70°C or lower. In this process, current application may be performed while maintaining a constant ambient temperature, or may be performed while varying the temperature within a range of 20°C to 100°C. From the viewpoint of more easily obtaining a solid-state battery capable of suppressing the occurrence of short circuits due to charging and discharging, it is desirable to perform current application while maintaining a constant ambient temperature. Note that, depending on the type of battery being applied, heat may be generated by current application, causing the battery to exhibit a temperature different from the ambient temperature. However, the temperature during current application in this process refers to the ambient temperature at which the cell is placed before charging.

[0019] In this step, maintaining the current application time within a predetermined range is advantageous from the viewpoint of easily obtaining a solid-state battery capable of suppressing the occurrence of short circuits due to charging and discharging. Specifically, provided that the current density during current application is within the above-described range, the current application time is preferably set to, for example, 10 minutes or more, more preferably 30 minutes or more, and even more preferably 50 minutes or more. Furthermore, provided that the current density during current application is within the above-described range, the current application time is preferably set to, for example, 25 hours or less, more preferably 20 hours or less, and even more preferably 10 hours or less. In this step, current application may be performed continuously or intermittently, as long as it is possible to apply current to the cell before charging. From the viewpoint of more easily obtaining a solid-state battery capable of suppressing the occurrence of short circuits due to charging and discharging, continuous current application is desirable.

[0020] (ii) Second Pretreatment Step In this step, the pre-charged cell after the first pretreatment step is discharged at a predetermined current density. ２ More preferably, 0.025 mA / cm ２ More preferably, 0.045 mA / cm ２ Discharging is performed at a current density of 0.55 mA / cm or more. By discharging at a current density of 0.55 mA / cm or more, a solid-state battery capable of suppressing the occurrence of short circuits due to charging and discharging can be easily obtained. The current density is, for example, 0.55 mA / cm. ２ It is preferable that the current is 0.35 mA / cm or less. ２ More preferably, it is 0.15 mA / cm or less. ２ It is more preferable that the current density is set to 0.05 V or less. Even when discharging is performed at a current density equal to or less than this value, a solid battery capable of suppressing the occurrence of short circuits due to charging and discharging can be easily obtained. In this step, discharging may be performed while maintaining a constant current density, or while changing the current density. When discharging is performed while changing the current density, it is preferable that the current density is set within the above-mentioned range. From the viewpoint of more easily obtaining a solid battery capable of suppressing the occurrence of short circuits due to charging and discharging, it is desirable to perform discharging while maintaining a constant current density.

[0021] In this process, maintaining the ambient temperature during discharge within a predetermined range is advantageous from the viewpoint of easily obtaining a solid-state battery capable of suppressing the occurrence of short circuits due to charging and discharging. Specifically, provided that the current density during discharge is within the above-described range, the ambient temperature during discharge is preferably set to, for example, 20°C or higher, more preferably 35°C or higher, and even more preferably 55°C or higher. Furthermore, provided that the current density during discharge is within the above-described range, the ambient temperature during discharge is preferably set to, for example, 100°C or lower, more preferably 80°C or lower, and even more preferably 70°C or lower. In this process, discharge may be performed while maintaining a constant ambient temperature, or may be performed while varying the temperature within a range of 20°C to 100°C. From the viewpoint of more easily obtaining a solid-state battery capable of suppressing the occurrence of short circuits due to charging and discharging, it is desirable to perform discharge while maintaining a constant ambient temperature.

[0022] In this step, maintaining the discharge time within a predetermined range is advantageous from the viewpoint of easily obtaining a solid-state battery capable of suppressing the occurrence of short circuits due to charging and discharging. Specifically, provided that the current density during discharge is within the above-mentioned range, the discharge time is preferably set to, for example, 10 minutes or more, more preferably 30 minutes or more, and even more preferably 50 minutes or more. Furthermore, provided that the current density during discharge is within the above-mentioned range, the discharge time is preferably set to, for example, 12 hours or less, more preferably 10 hours or less, and even more preferably 8 hours or less.

[0023] In this manufacturing method, the number of times the first and second pretreatment steps are performed is not limited and can be any number of times. Provided that both the first and second pretreatment steps are performed, these pretreatment steps can be performed, for example, once or multiple times. When the first and second pretreatment steps are repeated multiple times, it is preferable to perform them at least once, more preferably twice or more, and even more preferably three times or more. Furthermore, provided that both the first and second pretreatment steps are performed, it is preferable to perform these pretreatment steps 100 times or less, more preferably 50 times or less, and even more preferably 10 times or less. When the first and second pretreatment steps are repeated multiple times, the conditions for the first pretreatment step may be the same or different for each iteration. Similarly, the conditions for the second pretreatment step may be the same or different for each iteration.

[0024] The above-described operations result in the production of the desired solid-state battery. In this solid-state battery, a favorable interface is formed on the surface of the solid electrolyte particles by the above-described operations, allowing smooth exchange of lithium ions between the solid electrolyte particles and the active material particles. As a result, problems such as localized current concentration within the battery are less likely to occur. As a result, the solid-state battery produced by this method can suppress the occurrence of short circuits due to charging and discharging. The solid-state battery of the present invention obtained by the above-described operations can be put to practical use by first charging it to a predetermined depth of charge (first charging step). There are no particular limitations on the conditions for the first charging; a constant-current, constant-voltage (CCCV) charging method commonly used in the art can be used.

[0025]

[0023] In relation to the above-described embodiment, the following method for manufacturing a solid-state battery is further disclosed: [1] A method for manufacturing a solid-state battery, comprising: applying a current of 0.005 mA / cm to a solid-state battery before initial charging at a temperature of 20°C or higher. ２ a first preliminary treatment step of passing current at a current density equal to or greater than the above.

[0026] [2] After the first preliminary treatment step and before the first charge, the solid-state battery is charged at a current of 0.005 mA / cm at a temperature of 20°C or higher. ２ [1] A method for manufacturing a solid battery according to [1], wherein a second preliminary treatment step is performed in which the battery is discharged at a current density of 100° C. or more. [3] A method for manufacturing a solid battery according to [1] or [2], wherein the current application time in the first preliminary treatment step is 10 minutes or more. [4] A method for manufacturing a solid battery according to any one of [1] to [3], wherein the first preliminary treatment step is performed at a temperature of 100° C. or less. [5] A method for manufacturing a solid battery according to any one of [1] to [4], wherein the solid battery is a lithium ion battery. [6] A method for manufacturing a solid battery according to any one of [1] to [5], wherein the solid battery contains a sulfide solid electrolyte.

[0027] [7] The method for manufacturing a solid-state battery according to [6], wherein the sulfide solid electrolyte contains a crystalline phase having an argyrodite-type crystal structure. [8] The method for manufacturing a solid-state battery according to any one of [1] to [7], wherein the negative electrode of the solid-state battery is made of lithium (Li) metal.

[0028] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0029] [Example 1] (1) Production of a cell before charging ５．４ P.S. ４．４ Cl ０．８ Br ０．８A sulfide containing a crystalline phase with an argyrodite-type crystal structure, represented by the formula (containing 11.4 atm% halogen elements), was used as the sulfide solid electrolyte. The lower opening of a cylindrical container (MACOR®, opening diameter 10.5 mm, height 18 mm) with open top and bottom was blocked with a lower electrode (made of SUS), 0.1 g of the sulfide solid electrolyte powder was placed on top of it, and the container was blocked with an upper electrode (made of SUS). A solid electrolyte layer was then formed by uniaxial pressing at 540 MPa. The upper electrode was temporarily removed, and a 100 μm-thick lithium metal foil was placed on top and blocked with the upper electrode. The cylindrical container was then inverted, the lower electrode was temporarily removed, and a 100 μm-thick lithium metal foil was placed on the solid electrolyte layer, which was then blocked again with the lower electrode. The upper and lower electrodes were then constrained at a pressure of 60 MPa. This resulted in the production of a cell in which an electrode made of lithium metal was disposed on each side of the solid electrolyte layer. The cell was fabricated in a glove box filled with thoroughly dried argon gas (dew point of −60° C. or less).

[0030] (2) First preliminary treatment step: The ambient temperature was set to 25°C, and the current was 0.1 mA / cm ２ The pre-charged cell was energized at a constant current density of 1000 kJ / s for the duration shown in Table 1.

[0031] (3) Second Pretreatment Step: The ambient temperature remains at 25°C, and the current is 0.1 mA / cm ２ The pre-charged cell was discharged at a constant current density of 1000 kJ / s for a discharge time as shown in Table 1. In this way, the desired lithium ion solid state secondary battery was obtained.

[0032] (4) Repetition of the first preliminary treatment step and the second preliminary treatment step The first preliminary treatment step and the second preliminary treatment step were repeated as shown in Table 1. The conditions for each of the first preliminary treatment step and the second preliminary treatment step were the same.

[0033] Examples 2 to 6 and Comparative Example 1 A lithium ion solid state secondary battery was obtained in the same manner as in Example 1, except that the conditions and repetition numbers of the first pre-treatment step and the second pre-treatment step were as shown in Table 1 below.

[0034] [Evaluation] The critical current density (CCD) of the lithium ion solid state secondary batteries obtained in the Examples and Comparative Examples was measured by the following method. A higher CCD value means that the occurrence of a short circuit is more suppressed. The results are shown in Table 1 below. For the measurement, a potentio / galvanostat SP-200 manufactured by Bio-Logic Science Instruments was used.

[0035] [CCD measurement] At the first charge / discharge (first cycle), the current was 0.5 mA / cm ２ The lithium ion solid state secondary battery was charged at a current density of 0.5 mA / cm. ２ The second cycle was discharged at 1.0 mA / cm ２ The lithium ion solid state secondary battery was charged at a current density of 0.5 mA / cm. The discharge conditions were the same as the current density in the immediately preceding charge. From the third cycle onwards, the current density was 0.5 mA / cm, as in the first and second cycles. ２ The lithium ion solid state secondary battery was charged by increasing the current density step by step. The discharge conditions were the same as in the first and second cycles, and the current density was the same as in the immediately preceding charge. In both cycles, the charge or discharge was performed at 1.0 mA / cm ２ The charge / discharge cycle was then started, and the next cycle was carried out. This operation was carried out until the lithium ion solid state secondary battery was short-circuited. To ensure that the amount of electricity in each cycle was the same, the charge / discharge time was gradually shortened as the number of cycles increased. The CCD at the time of short-circuiting is shown in Table 1.

[0036]

[0037] As is clear from the results shown in Table 1, the solid state batteries obtained in the examples were found to be more suppressed from short-circuiting even when charged at a higher current density than the solid state batteries obtained in the comparative examples.

[0038] According to the present invention, a method for manufacturing a solid-state battery capable of suppressing the occurrence of short circuits is provided.

Claims

1. A method for manufacturing a solid-state battery, comprising: applying a current of 0.005 mA / cm to a solid-state battery before the first charge at a temperature of 20°C or higher; ２ a first preliminary treatment step of passing current at a current density equal to or greater than the above.

2. After the first pretreatment step and before the first charge, the solid-state battery is charged at a temperature of 20°C or higher with a current of 0.005 mA / cm ２ The method for producing a solid state battery according to claim 1 , further comprising the step of performing a second preliminary treatment step of discharging at a current density equal to or greater than the above.

3. The method for producing a solid-state battery according to claim 1, wherein the current application time in the first preliminary treatment step is 10 minutes or more.

4. The method for producing a solid-state battery according to claim 1, wherein the first pre-treatment step is carried out at a temperature of 100°C or less.

5. The method for producing a solid-state battery according to claim 1, wherein the solid-state battery is a lithium-ion battery.

6. The method for producing a solid-state battery according to claim 1, wherein the solid-state battery comprises a sulfide solid electrolyte.

7. The method for producing a solid-state battery according to claim 6, wherein the sulfide solid electrolyte contains a crystalline phase having an argyrodite-type crystalline structure.

8. The method for producing a solid-state battery according to claim 1, wherein the negative electrode of the solid-state battery is made of lithium (Li) metal.

Images