WO2024075771A1 - Solid-state battery, and solid-state battery manufacturing method - Google Patents

Abstract

The present invention makes it possible to stably obtain a solid-state battery having excellent cycle characteristics.　A solid-state battery (1) includes: a positive electrode layer (10); a negative electrode layer (20) opposite to the positive electrode layer; and an electrolytic layer (30) provided therebetween. For example, the solid-state battery (1) has an impedance of 100000 Ω or more, which is measured by an AC impedance method before performing charging/discharging and which is estimated from a circular arc approximated in a frequency range from 0.3 Hz to 0.1 Hz on a complex number plane. The solid-state battery (1) exhibiting said impedance has excellent long-term cycle characteristics while having favorable initial characteristics without occurrence of short-circuiting. The solid-state battery (1) which has a good quality and has, in addition to initial characteristics, excellent cycle characteristics can be stably obtained before performing charging/discharging or before shipment.

Description

Solid-state battery and method for manufacturing the same

The present invention relates to a solid-state battery and a method for manufacturing a solid-state battery.

A solid-state battery is known that includes a positive electrode layer that contains a solid electrolyte and a positive electrode active material, a negative electrode layer that faces the positive electrode layer and contains a solid electrolyte and a negative electrode active material, and an electrolyte layer that contains a solid electrolyte and is provided between them.

With regard to such solid-state batteries, for example, a technology is known that sets the difference between the resistivity associated with ion movement and the resistivity associated with electron movement to 0 kΩ·cm or more and 100 kΩ·cm or less, suppressing local reactions within the electrode layer and improving charge/discharge efficiency (Patent Document 1).

Also, a technology is known in which a laminate of a positive electrode, a negative electrode, and an electrolyte layer, in which a phosphate compound is contained in either the positive electrode active material, the negative electrode active material, or the solid electrolyte, is energized (charged) in the presence of an appropriate amount of moisture to reduce the interface impedance and improve the charge/discharge characteristics (Patent Document 2).

Also, a known inspection technique is to apply an AC signal between the electrodes of a secondary battery before the first charge to measure the impedance, and determine whether or not there is a short circuit between the electrodes based on the difference between the impedance measurement results of a normal battery and a short-circuited battery displayed on a complex plane (Patent Document 3).

International Publication No. 2014/002858 JP 2008-243560 A JP 2009-289757 A

In a solid-state battery including a positive electrode layer containing a solid electrolyte and a positive electrode active material, a negative electrode layer facing the positive electrode layer containing a solid electrolyte and a negative electrode active material, and an electrolyte layer containing a solid electrolyte provided between them, the characteristics may vary among multiple individual batteries due to the configuration and manufacturing process. For example, there may be variations in cycle characteristics, which are an indicator of whether a certain level of performance can be obtained with repeated charging and discharging. In this case, it is possible that some solid-state batteries do not exhibit good cycle characteristics. With conventional technology, for example, while it is possible to distinguish between good and bad products in terms of initial characteristics before charging and discharging or before shipping, it is difficult to sufficiently distinguish between good and bad products in terms of cycle characteristics, which are long-term characteristics, and there are cases where solid-state batteries with excellent cycle characteristics cannot be obtained stably.

In one aspect, the present invention aims to stably obtain a solid-state battery with excellent cycle characteristics.

In one embodiment, a solid-state battery is provided that includes a positive electrode layer, a negative electrode layer facing the positive electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer, and has an impedance of 100,000 Ω or more as measured by an AC impedance method before charging and discharging and estimated from an arc approximated in the frequency range of 0.3 Hz to 0.1 Hz on a complex plane.

In one embodiment, a solid-state battery is provided that includes a positive electrode layer, a negative electrode layer facing the positive electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer, and that has an impedance on a complex plane that is measured by an AC impedance method before charging and discharging, with a real part of 140 Ω or less and an imaginary part of -400 Ω or less at 1 Hz.

In one embodiment, a solid-state battery is provided that includes a positive electrode layer, a negative electrode layer facing the positive electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer, and that has an impedance on a complex plane that is measured by an AC impedance method before charging and discharging, with a real part of 68 Ω or less and an imaginary part of -56 Ω or less at 10 Hz.

In another aspect, a method for manufacturing each of the above solid-state batteries is provided.

In one aspect, it becomes possible to stably obtain a solid-state battery having excellent cycle characteristics.
The objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

1A to 1C are diagrams illustrating an example of a method for manufacturing a solid-state battery. FIG. 1 is a diagram showing an example of a Cole-Cole plot obtained by impedance measurement. FIG. 13 is a diagram showing an example of measurement results of charge/discharge characteristics. FIG. 13 is a diagram showing an example of the relationship between the capacity maintenance rate and the moisture content and impedance. FIG. 1 is a plot of the real part Z′ and the imaginary part Z″ of impedance at 1 Hz. FIG. 1 is a plot of the real part Z′ and the imaginary part Z″ of impedance at 10 Hz.

One type of battery known is a solid-state battery that includes a battery element that includes a positive electrode layer that includes a positive electrode active material and a solid electrolyte, etc., a negative electrode layer that faces the positive electrode layer and includes a negative electrode active material and a solid electrolyte, etc., and a layer of solid electrolyte provided between the positive electrode layer and the negative electrode layer. Because solid-state batteries do not use flammable organic electrolytes like lithium-ion secondary batteries, they have the advantages of being safer by reducing the risks of leakage, combustion, explosion, and generation of toxic gases, being easy to handle in the atmosphere, and being able to maintain performance even under low and high temperature conditions.

For example, Li ₂ CoP ₂ O ₇ is used as the positive electrode active material of the solid-state battery. For example, Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ (0<x<1), which is a type of NASICON (Na Super Ionic Conductor) type oxide solid electrolyte, can be used as the solid electrolyte of the solid-state battery. For example, Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ can be used as the solid electrolyte of the solid-state battery. In the following, Li ₂ CoP ₂ O ₇ is referred to as "LCPO" and Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ (0<x<1) is referred to as "LAGP".

Here, in the manufacture of the battery elements of a solid-state battery, sintering is carried out to sinter the internal materials such as LAGP, but in the case of a battery element including a positive electrode layer using LCPO, the sintering temperature is limited to a relatively low temperature range, for example 600°C to 650°C, in order to bring it into a good crystalline state. As a result of sintering at such a relatively low temperature, voids and cracks may occur inside the battery element. Although voids and cracks affect the battery characteristics of a solid-state battery including a battery element, they are difficult to confirm by visual inspection, and it is difficult to distinguish good solid-state batteries that exhibit certain battery characteristics by visual inspection.

One method for evaluating the battery characteristics of solid-state batteries is to use the AC impedance method to measure the impedance at a specified frequency for solid-state batteries before they are charged/discharged or shipped. Based on the measured value, the presence or absence of short circuits in solid-state batteries before they are charged/discharged or shipped can be determined, i.e., good and bad solid-state batteries can be distinguished or pre-shipment inspections can be performed.

However, even solid-state batteries that are deemed good by this method may tend to experience deterioration in characteristics as the number of repeated charge/discharge cycles increases. In other words, solid-state batteries that are deemed good in terms of initial characteristics may include some that are deemed defective in terms of long-term cycle characteristics. It is desirable to be able to stably obtain solid-state batteries that have excellent long-term cycle characteristics in addition to initial characteristics such as the presence or absence of short circuits before charging/discharging or before shipping.

In view of the above, a method for stably obtaining a solid-state battery having excellent cycle characteristics will be described below.
[Solid-state battery]
First, examples of materials used to form the positive electrode layer and the negative electrode layer of the solid-state battery, as well as the electrolyte layer provided therebetween, will be described.

(LCPO powder)
First, powders of Li raw material, Co raw material, and P raw material are prepared in amounts based on the composition of LCPO. For example, _Li2NO3 is used as the Li raw material powder. For example, Co( _NO3 ) ₂ or Co( _NO3 ) _2.6H2O is used as the Co raw material powder. For example, _NH4H2PO4 is used as _{the P} raw material powder. These _raw material powders are _weighed and prepared so as to have the composition of LCPO obtained by firing described later.

The prepared Li, Co and P raw materials are mixed with citric acid and pure water in a container such as a beaker, and the container is heated using a hot plate or the like to evaporate the water. The mixture obtained by evaporation of the water is crushed using an agate mortar or the like, and the crushed mixture is fired at a temperature of 600°C to 700°C for 2 to 6 hours. The fired body obtained by firing is crushed using an agate mortar or the like to obtain a powder with a specified average particle size (e.g., 7 μm), and the crushed product is further crushed using a ball mill or the like. This results in LCPO powder adjusted to a specified average particle size (e.g., 1 μm).

For example, by such a method, LCPO powder is prepared for use as a positive electrode active material in a positive electrode layer of a solid-state battery.
The Li raw material of LCPO may be another Li compound such as Li ₂ CO ₃ , and the Co raw material may be another Co compound such as CoCO _3. In addition, in addition to the above-mentioned wet process in which the Li raw material, the Co raw material, and the P raw material are mixed in liquid together with citric acid, other methods may be used to form LCPO, such as a wet process in which the Li raw material, the Co raw material, and the P raw material are mixed while adding pure water to them without using citric acid, or a dry process in which citric acid and pure water are not used.

(LAGP powder)
LAGP can be formed using a solid-phase method. First, powders of Li ₂ CO ₃ , Al ₂ O ₃ , GeO ₂ and NH ₄ H ₂ PO ₄ , which are raw materials for LAGP, are weighed and prepared so as to have a predetermined composition ratio. These raw material powders are mixed using a magnetic mortar, a ball mill, etc., and the mixture obtained by mixing is pre-fired at a temperature of 300° C. to 400° C. for 3 to 5 hours. The powder obtained by pre-fire is melted by heat treatment at a temperature of 1200° C. to 1400° C. for 1 to 2 hours. The material obtained by melting is quenched and vitrified. As a result, amorphous LAGP powder is obtained. The amorphous LAGP powder thus obtained may also be fired under conditions of, for example, 600° C. to 900° C. As a result, crystalline LAGP powder is obtained. The obtained LAGP powder is pulverized and adjusted to a desired particle size.

For example, this method prepares LAGP powder for use in the electrolyte layer, positive electrode layer, and negative electrode layer of a solid-state battery. Either amorphous LAGP powder or crystalline LAGP powder may be used for the electrolyte layer, positive electrode layer, and negative electrode layer of a solid-state battery. Both amorphous LAGP powder and crystalline LAGP powder may be used for the electrolyte layer, positive electrode layer, and negative electrode layer of a solid-state battery.

(Electrolyte Layer Material)
As an example, the LAGP powder obtained by the above method (either or both of amorphous and crystalline LAGP powder) is mixed with a binder, a solvent, etc., and coated on a carrier such as a polyethylene terephthalate (PET) film by a doctor blade method, etc., to form a green sheet for an electrolyte layer. In the following, the polyethylene terephthalate film is referred to as a "PET film."

For example, LAGP powder is used as a ceramic powder, and a certain amount of binder is added to the ceramic powder, and a certain amount of anhydrous alcohol is added as a solvent to obtain a mixture, which is then mixed in a ball mill or the like to form a paste-like electrolyte layer material. The paste-like electrolyte layer material thus formed is degassed in a vacuum, and then coated once or multiple times on a PET film by a doctor blade method to form a sheet-like electrolyte layer material corresponding to the electrolyte layer. For example, one sheet-like electrolyte layer material thus formed can be used as an electrolyte layer green sheet. Furthermore, in order to adjust to the desired thickness, multiple sheets of the electrolyte layer material thus formed can be stacked and pressed together to form an electrolyte layer green sheet. The electrolyte layer green sheet containing one or multiple stacked sheet-like electrolyte layer materials may be cut to a predetermined planar size. For example, the electrolyte layer green sheet thus formed is used to form the electrolyte layer of a solid-state battery.

In another example, the LAGP powder obtained by the above method, a binder, a solvent, etc. are mixed to form an electrolyte layer paste, which is a paste-like electrolyte layer material. For example, the electrolyte layer paste formed in this way is used to form the electrolyte layer of a solid-state battery by screen printing.

(Positive electrode layer material)
As an example, the LAGP powder (either or both of amorphous and crystalline LAGP powder) obtained by the above method, a conductive assistant, a positive electrode active material, a binder, a solvent, a plasticizer, etc. are mixed and coated on a carrier such as a PET film by a doctor blade method to form a green sheet for a positive electrode layer. LCPO is used as the positive electrode active material. For example, a carbon material such as carbon nanofiber, carbon black, graphite, graphene, or carbon nanotube, or a conductive material such as iron silicide is used as the conductive assistant.

For example, a mixture of LAGP powder and a positive electrode active material in a mass ratio of 50:50 is used as a ceramic powder, and a certain amount of binder and anhydrous alcohol as a solvent are added to the ceramic powder to obtain a mixture, which is then mixed in a ball mill or the like to form a paste-like positive electrode layer material. The formed paste-like positive electrode layer material is degassed in a vacuum, and then coated once on a PET film by a doctor blade method, or multiple times to adjust to the desired thickness and amount of positive electrode active material, to form a sheet-like positive electrode layer material corresponding to the positive electrode layer. For example, one sheet-like positive electrode layer material thus formed can be used as a positive electrode layer green sheet. Furthermore, in order to adjust to the desired thickness and amount of positive electrode active material, multiple sheets of the formed sheet-like positive electrode layer material can be stacked and pressed to form a positive electrode layer green sheet. The positive electrode layer green sheet containing one or multiple stacked sheet-like positive electrode layer materials may be cut to a predetermined planar size. For example, the positive electrode layer green sheet formed in this manner is used to form the positive electrode layer of a solid-state battery.

In another example, the LAGP powder obtained by the above method, a conductive additive, a positive electrode active material, a binder, a dispersant, a plasticizer, a non-aqueous solvent, etc. are mixed together to form a positive electrode layer paste, which is a paste-like positive electrode layer material. For example, the positive electrode layer paste formed in this manner is used to form the positive electrode layer of a solid-state battery by screen printing.

(Negative electrode layer material)
As an example, the LAGP powder (either or both of amorphous and crystalline LAGP powder) obtained by the above method, a conductive assistant, a negative electrode active material, a binder, a solvent, a plasticizer, etc. are mixed and coated on a carrier such as a PET film by a doctor blade method to form a green sheet for a negative electrode layer. TiO ₂ , Nb ₂ O ₅ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₄ Ti ₅ O ₁₂ , etc. are used as the negative electrode active material. For example, carbon materials such as carbon nanofibers, carbon black, graphite, graphene, or carbon nanotubes, and conductive materials such as iron silicide are used as the conductive assistant.

For example, a mixture of LAGP powder and anode active material in a mass ratio of 50:50 is used as a ceramic powder, and a certain amount of binder and anhydrous alcohol as a solvent are added to the ceramic powder to obtain a mixture, which is then mixed in a ball mill or the like to form a paste-like anode layer material. The paste-like anode layer material thus formed is degassed in a vacuum, and then coated once on a PET film by a doctor blade method, or multiple times to adjust to the desired thickness and amount of anode active material, to form a sheet-like anode layer material corresponding to the anode layer. For example, one sheet-like anode layer material thus formed can be used as a green sheet for the anode layer. Furthermore, in order to adjust to the desired thickness and amount of anode active material, multiple sheets of the sheet-like anode layer material thus formed can be stacked and pressed together to form a green sheet for the anode layer. The green sheet for the anode layer containing one or multiple stacked sheets of anode layer material may be cut to a predetermined planar size. For example, the negative electrode layer green sheet formed in this manner is used to form the negative electrode layer of a solid-state battery.

In another example, the LAGP powder obtained by the above method, a conductive assistant, an anode active material, a binder, a dispersant, a plasticizer, a non-aqueous solvent, etc. are mixed together to form a paste for the anode layer, which is a paste-like anode layer material. For example, the paste for the anode layer formed in this way is used to form the anode layer of a solid-state battery by screen printing.

Next, a method for manufacturing a solid-state battery using the above-mentioned materials will be described.
1A and 1B are diagrams for explaining an example of a method for manufacturing a solid-state battery. Fig. 1A is a schematic cross-sectional view of a main part of an example of a laminate formation step. Fig. 1B is a schematic cross-sectional view of a main part of an example of a terminal formation step.

For example, a laminate 1a as shown in FIG. 1(A) is formed. The laminate 1a is an example of a battery element of a solid-state battery. The laminate 1a shown in FIG. 1(A) includes a positive electrode layer 10, an opposing negative electrode layer 20, and an electrolyte layer 30 provided therebetween. The positive electrode layer 10 and the negative electrode layer 20 are covered by an electrolyte layer 30 made of the same or different electrolyte material as the electrolyte layer 30 provided between the positive electrode layer 10 and the negative electrode layer 20, for example, so that a portion of each of them is exposed at both ends of the laminate 1a, as shown in FIG. 1(A).

The positive electrode layer 10 of the laminate 1a is formed using a positive electrode layer green sheet or a positive electrode layer paste prepared using the above method. The negative electrode layer 20 of the laminate 1a is formed using a negative electrode layer green sheet or a negative electrode layer paste prepared using the above method. The electrolyte layer 30 of the laminate 1a is formed using an electrolyte layer green sheet or an electrolyte layer paste prepared using the above method. These materials are laminated or screen printed in a predetermined order and arrangement, and pressed together, and further cut to separate into individual laminates 1a (battery elements) as necessary, to form the laminate 1a as shown in FIG. 1(A).

The obtained laminate 1a is degreased. For example, it is heated in an air atmosphere at a temperature of about 300°C to 600°C to remove the binder remaining in the laminate 1a by thermal decomposition, i.e., degreasing is performed. The heating temperature in the degreasing process can be set based on the thermal decomposition temperature of the binder contained in the positive electrode layer green sheet or positive electrode layer paste, the electrolyte layer green sheet or electrolyte layer paste, and the negative electrode layer green sheet or negative electrode layer paste used to form the laminate 1a.

The degreased laminate 1a is sintered in a non-oxidizing atmosphere such as nitrogen, for example, at a temperature higher than that for degreasing. This sintering sinters the LAGP and other substances contained in the degreased laminate 1a. The sintering temperature for the laminate 1a is set to a predetermined temperature range, for example, 600°C to 650°C, in order to ensure that the positive electrode layer 10 obtained by sintering is in a good crystalline state.

After the laminate 1a is fired, as shown in FIG. 1B, terminals having a laminated structure of an electrode 60, a Ni layer 70, and a Sn layer 80 are formed on both ends of the laminate 1a. For example, a conductive paste containing glass frit is applied to both ends of the laminate 1a, and baked by heating to form the electrodes 60. The electrodes 60 are formed so as to be connected to the positive electrode layer 10 exposed on one end side of the laminate 1a and the negative electrode layer 20 exposed on the other end side. On the surface of the formed electrode 60, for example, a Ni layer 70 is formed by plating, and further, a Sn layer 80 is formed on the surface of the Ni layer by plating. As a result, a solid-state battery 1 as shown in FIG. 1B is obtained, which is provided with terminals for mounting on other components such as a circuit board.

When the solid-state battery 1 is charged, lithium ions are conducted from the positive electrode layer 10 through the electrolyte layer 30 to the negative electrode layer 20 and are absorbed, and when the solid-state battery 1 is discharged, lithium ions are conducted from the negative electrode layer 20 through the electrolyte layer 30 to the positive electrode layer 10 and are absorbed. In the solid-state battery 1, charging and discharging operations are realized by this type of lithium ion conduction.

The configuration of the solid-state battery is not limited to that of the solid-state battery 1 described above.
For example, a configuration may be adopted in which a current collector is provided on each of the surfaces of the positive electrode layer 10 and the negative electrode layer 20 (the upper surface of the positive electrode layer 10 and the lower surface of the negative electrode layer 20 in FIG. 1(B)) that are disposed with the electrolyte layer 30 interposed therebetween, and the current collectors are exposed at both ends of the laminate (battery element) and connected to the electrodes 60 or the like.

In addition, while FIG. 1(B) above illustrates a solid-state battery 1 having one positive electrode layer 10 and one negative electrode layer 20 with an electrolyte layer 30 between them, a stacked solid-state battery can also be obtained by stacking multiple positive electrode layers 10 and multiple negative electrode layers 20 alternately with an electrolyte layer 30 between them.

Also, in the portion that will become the outer surface of the laminate (battery element) that includes at least one each of the positive electrode layer 10 and the negative electrode layer 20 and the electrolyte layer 30 between them, instead of the electrolyte layer 30, or in addition to the outside of the electrolyte layer 30, a coating layer using a material such as glass or ceramics that is harder than the electrolyte layer 30 may be formed. In this case, a paste is prepared by mixing a material such as glass with a binder, etc., and a laminated structure is formed so that the portion that will become the outer surface of the laminate is made of this paste, and the structure is degreased and fired (cut before that if necessary).

[Characteristic evaluation of solid-state batteries]
Next, as an example, a description will be given of the evaluation of the characteristics of the above-described solid-state battery 1. Here, as the evaluation of the characteristics of the solid-state battery 1, a moisture amount measurement, an impedance measurement, and a cycle measurement of the discharge capacity were carried out.

(Moisture content measurement)
The moisture content was measured by the Karl Fischer method. A coulometric titration moisture measuring device was used for the moisture content measurement by the Karl Fischer method. The measurement conditions were as follows: the sample was heated at 120° C., and the amount of moisture released [%] was measured using nitrogen as a carrier gas. The measurement time was 5 minutes.

(Impedance measurement)
The impedance measurement was performed by an AC impedance method. A frequency response analyzer and a potentiostat were used for the impedance measurement by the AC impedance method. The measurement conditions were a temperature of 25°C, an AC voltage of 5 mV, and a frequency range of 1 MHz to 0.1 Hz (also referred to as "1 MHz-0.1 Hz"). For a sample of the solid-state battery 1 before charging/discharging or before shipping, the frequency was set to 1 kHz and the impedance [Ω] was measured as a normal initial evaluation. Furthermore, for a sample of the solid-state battery 1 before charging/discharging or before shipping, the frequency was set to a frequency range of 1 MHz to 0.1 Hz and the impedance [Ω] was estimated from an arc approximated in the frequency range of 0.3 Hz to 0.1 Hz (also referred to as "0.3 Hz-0.1 Hz") on the complex plane in the Cole-Cole plot (also referred to as "Nyquist plot") obtained by the measurement.

The Cole-Cole plot of the solid-state battery 1 obtained by measurement using the AC impedance method can be approximated by a semicircle or an arc. The diameter of the semicircle or arc varies depending on the impedance of the solid-state battery 1 and the presence or absence of a short circuit. For example, a solid-state battery 1 with low impedance or a short-circuited solid-state battery 1 will have a small diameter semicircle or arc. The diameter of the semicircle or arc is a value that reflects the internal components and impedance of the solid-state battery 1. By setting an equivalent circuit including a resistor R, a capacitor C, etc. that corresponds to the internal components of the solid-state battery 1 or that expresses the functions of the internal components, and performing equivalent circuit fitting on the arc that is approximated in the frequency range of 0.3 Hz to 0.1 Hz on the complex plane in the Cole-Cole plot obtained by measurement, the values of the resistor R and capacitor C of the equivalent circuit that corresponds to the internal components of the solid-state battery 1 or that expresses the functions of the internal components, and the impedance value of the solid-state battery 1 can be obtained.

Note that, in the "frequency range of 0.3 Hz to 0.1 Hz", "0.3 Hz" and "0.1 Hz" are set as follows. "0.3 Hz" is set to a frequency that is 0.3 Hz when rounded off to the first decimal place, i.e., any frequency in the range of 0.25 Hz to 0.34 Hz. "0.1 Hz" is set to a frequency that is 0.1 Hz when rounded off to the first decimal place, i.e., any frequency in the range of 0.05 Hz to 0.14 Hz. The same applies to "0.1 Hz" in the "frequency range of 1 MHz to 0.1 Hz". Here, the frequency that is 0.3 Hz when rounded off to the first decimal place is also referred to as "0.3 Hz", and the frequency that is 0.1 Hz when rounded off to the first decimal place is also referred to as "0.1 Hz".

(Discharge capacity)
The solid-state battery 1 was repeatedly charged and discharged for multiple cycles. The solid-state battery 1 was charged and discharged at a constant current with a current value of 25 μA/cm ² , a charging upper limit voltage of 3.6 V, and a discharging lower limit voltage of 0 V, and was charged and discharged for 40 cycles at 20° C. From the results of the multiple repeated charge and discharge cycles, the ratio of the discharge capacity [μAh] after charging in the 40th cycle to the discharge capacity [μAh] after charging in the 1st cycle was calculated as the capacity retention rate [%].

(Discussion)
The moisture content [%] obtained for eight solid-state battery 1 samples (samples No. 1-8), the impedance ("1 kHz impedance") [Ω] under a frequency condition of 1 kHz, which is a value for a normal initial evaluation, the impedance ("0.31 Hz-0.12 Hz impedance") [Ω] estimated from an arc approximated in the frequency range of 0.31 Hz to 0.12 Hz (also referred to as "0.31 Hz-0.12 Hz") on a complex plane, and the discharge capacity [μAh] and capacity retention rate [%] after each charge in the 1st and 40th cycles in repeated charge and discharge are shown in Table 1. The frequency range of 0.31 Hz to 0.12 Hz is an example of the above-mentioned "frequency range of 0.3 Hz to 0.1 Hz".

FIG. 2 shows an example of a Cole-Cole plot obtained by impedance measurement. In FIG. 2, the horizontal axis represents the real part Z' [Ωcm ² ] of the complex impedance, and the vertical axis represents the imaginary part Z" [Ωcm ² ] of the complex impedance. FIG. 2 shows an example of a Cole-Cole plot obtained by measurement in the frequency range from 1 MHz to 0.1 Hz. FIG. 2 shows an example of a Cole-Cole plot of a sample of solid-state battery 1 (sample No. 1-8) and a sample of a short-circuit battery.

Note that the solid-state battery 1 samples No. 1-8 are samples of solid-state battery 1 that are not short-circuited at least before charging/discharging or before shipping. In FIG. 2, when the Cole-Cole plot obtained by measurement is approximated by an arc, the Cole-Cole plot of the solid-state battery 1 samples No. 1-8 that are not short-circuited is approximated by an arc with a larger diameter than the Cole-Cole plot of the short-circuit battery sample No. 9. The impedance estimated from the approximated arc is larger for the solid-state battery 1 samples that are not short-circuited (larger arc diameter) than for the short-circuit battery sample (smaller arc diameter).

The impedance [Ω] estimated from the arc approximated in the frequency range of 0.31 Hz to 0.12 Hz on the complex plane in the Cole-Cole plot obtained for solid-state battery 1 (sample No. 1-8) and short-circuit battery (sample No. 9) (approximate frequency range 0.31 Hz-0.12 Hz (frequency range specified)) and the impedance [Ω] estimated from the arc approximated in the frequency range of 1 MHz to 0.1 Hz on the complex plane (approximate frequency range 1 MHz-0.1 Hz (frequency range not specified)) are shown in Table 2.

In addition, an example of the measurement results of the charge and discharge characteristics is shown in Figure 3. Figure 3 (A) shows the measurement results of the charge and discharge characteristics of the solid battery 1 of sample No. 1 (water content 0.0000%, capacity retention rate 92.4%) as an example. Figure 3 (B) shows the measurement results of the charge and discharge characteristics of the solid battery 1 of sample No. 2 (water content 0.0160%, capacity retention rate 86.9%) as an example. As shown in Figures 3 (A) and 3 (B), in the solid battery 1, the discharge capacity tends to decrease with an increase in the number of repeated charge and discharge cycles. In addition, an example of the relationship between the capacity retention rate and the water content and impedance is shown in Figure 4. In Figure 4, the horizontal axis represents the capacity retention rate [%] of the discharge capacity at a cell voltage of 1V, and the vertical axis represents the water content [%] (left) and impedance [Ω] (right).

First, from Table 1, for solid-state battery 1 sample No. 1-8, no correlation was found between the discharge capacity at the 1st cycle, the discharge capacity at the 40th cycle, and the capacity retention rate of the discharge capacity at the 40th cycle relative to the discharge capacity at the 1st cycle. Furthermore, from Table 1, no correlation was found between the results of impedance measurement at a frequency of 1 kHz, which is the usual initial evaluation of solid-state battery 1, and the results of the capacity retention rate of the discharge capacity at the 40th cycle relative to the discharge capacity at the 1st cycle.

Therefore, the relationship between the impedance estimated from the Cole-Cole plot as shown in FIG. 2 and the capacity retention rate was examined.
For the solid-state battery 1 of sample No. 1-8 before charging/discharging or before shipment, a Cole-Cole plot as shown in FIG. 2 is obtained by measuring in the frequency range from 1 MHz to 0.1 Hz. Using such a Cole-Cole plot, the impedance of the solid-state battery 1 of sample No. 1-8 before charging/discharging or before shipment, which is estimated from an arc approximated in the frequency range from 1 MHz to 0.1 Hz without specifying the frequency range, shows a value as shown in Table 2 ("Approximate frequency range 1 MHz-0.1 Hz (no frequency range specified)"), and all of the values are higher than the impedance of a short-circuited battery. Using only this result, the solid-state battery 1 of sample No. 1-8 before charging/discharging or before shipment is classified as a non-defective product without an initial short circuit.

However, as shown in Table 1, some of the solid-state batteries 1 of Sample No. 1-8 have cycle characteristics that are not necessarily sufficient, such as a capacity retention ratio of the discharge capacity at the 40th cycle to the discharge capacity at the 1st cycle being less than 90%. Therefore, while it is possible to distinguish products with good initial characteristics using only the impedance estimated from an arc approximated in the frequency range from 1 MHz to 0.1 Hz without specifying the frequency range using a Cole-Cole plot, it may not be possible to accurately distinguish products with good initial characteristics as well as good cycle characteristics, which are long-term characteristics.

On the other hand, the impedance of the solid-state battery 1 of sample No. 1-8 before charging/discharging or before shipping, which is estimated from an arc approximated by a frequency range of 0.31 Hz to 0.12 Hz using a Cole-Cole plot obtained by measurement in the frequency range of 1 MHz to 0.1 Hz as shown in Figure 2, with the frequency range specified, shows values as shown in Table 1 ("0.31 Hz-0.12 Hz impedance") and Table 2 ("approximate frequency range 0.31 Hz-0.12 Hz (frequency range specified)"). As shown in Figure 4, roughly speaking, there is a tendency that the capacity retention rate of the discharge capacity at the 40th cycle relative to the discharge capacity at the 1st cycle increases with an increase in impedance. However, more strictly, as shown in Tables 1 and 2, the impedance of sample No. 1-8, which is estimated by specifying the approximate frequency range to be 0.31 Hz to 0.12 Hz, is less than 100,000 Ω (100 kΩ). In solid-state batteries 1, 2-6 and 8, it is difficult to say that there is a clear correlation between the impedance and the capacity retention rate.

For example, in sample No. 2-4, where the impedance estimated by specifying the approximate frequency range from 0.31 Hz to 0.12 Hz is less than 100,000 Ω and the capacity retention rate is below 90%, there is no clear correlation between the impedance and the capacity retention rate. In samples No. 5, 6, and 8, where the impedance estimated by specifying the approximate frequency range from 0.31 Hz to 0.12 Hz is less than 100,000 Ω and the capacity retention rate is above 90%, there is no clear correlation. For example, as in samples No. 5 and 6, there are cases where the impedance is relatively significantly different even if the capacity retention rate is about the same. In addition, as in samples No. 5 and 8, there are cases where the relationship between the magnitude of the capacity retention rate and the magnitude of the impedance is reversed. Thus, for a solid-state battery 1 in which the impedance estimated by specifying the approximate frequency range as a frequency range from 0.31 Hz to 0.12 Hz is less than 100,000 Ω, it is difficult to say that a clear correlation can be stably obtained between the impedance and the capacity retention rate, and it may not be possible to stably distinguish solid-state batteries 1 that can achieve a high capacity retention rate based on the impedance with high accuracy.

In contrast, in the solid-state batteries 1 of samples 1 and 7, in which the impedance estimated by specifying the approximate frequency range to be 0.31 Hz to 0.12 Hz is 100,000 Ω (100 kΩ) or more, a high capacity retention rate of 90% or more can be stably obtained as shown in Tables 1 and 2. Therefore, if the solid-state batteries 1 before charging/discharging or before shipping are discriminated from those having an impedance estimated to be 100,000 Ω or more by specifying the approximate frequency range to be 0.31 Hz to 0.12 Hz, it can be said that it is possible to stably discriminate solid-state batteries 1 having good initial characteristics as well as good cycle characteristics, which are long-term characteristics. It is considered that samples such as sample No. 6, which have an impedance estimated to be less than 100,000 Ω and close to 100,000 Ω by specifying the approximate frequency range to be 0.31 Hz to 0.12 Hz, are on the border or near the border with samples such as sample No. 1 and 7, which have a high capacity retention rate of 90% or more stably obtained. From this, it can be considered that by specifying the approximate frequency range to be between 0.31 Hz and 0.12 Hz and discriminating solid-state batteries 1 with an estimated impedance of 100,000 Ω or more, it is possible to stably discriminate solid-state batteries 1 that are good not only in terms of initial characteristics but also in terms of cycle characteristics, which are long-term characteristics.

Furthermore, as for the moisture content of the solid-state battery 1, as shown in FIG. 4, it is difficult to say that there is a clear correlation between the moisture content of the solid-state battery 1 and the capacity retention rate, but since the moisture content of the solid-state battery 1 may affect the initial characteristics and long-term characteristics, it is preferable that the moisture content is low. The moisture content of the solid-state battery 1 is preferably less than 0.0100%, and more preferably less than 0.0010%. Furthermore, in order to achieve cycle characteristics, which are excellent long-term characteristics, it is desirable that the moisture content of the solid-state battery 1 is less than 0.0000%, as in the solid-state batteries 1 of Samples No. 1 and 7 above.

From Table 1, samples No. 2 and 8, which have a moisture content of more than 0.0100%, may not be able to achieve a high capacity retention rate of 90% or more. Samples No. 3-6, which have a moisture content of 0.0100% or less but have an impedance estimated by specifying the approximate frequency range to be between 0.31 Hz and 0.12 Hz and giving an estimated impedance of less than 100,000 Ω, may also not be able to achieve a high capacity retention rate of 90% or more. Samples No. 1 and 7 (moisture content 0.0000%), which have a moisture content of less than 0.0100% and have an estimated impedance of 100,000 Ω or more when the approximate frequency range is specified to be between 0.31 Hz and 0.12 Hz, can stably achieve a high capacity retention rate of 90% or more. Samples No. 2 and 3, which have a moisture content of 0.0100% and have an estimated impedance of less than 100,000 Ω when the approximate frequency range is specified to be between 0.31 Hz and 0.12 Hz, can stably achieve a high capacity retention rate of 90% or more. It is believed that samples such as No. 6 are at or near the border with samples such as No. 1 and No. 7, which stably provide a high capacity retention rate of 90% or more. From this, it can be believed that by discriminating solid-state batteries 1 with a moisture content of less than 0.0100% and an impedance of 100,000Ω or more estimated by specifying the approximate frequency range from 0.31 Hz to 0.12 Hz, it is possible to stably discriminate solid-state batteries 1 that are good not only in terms of initial characteristics but also in terms of cycle characteristics, which are long-term characteristics.

As described above, the solid-state battery 1 before charging/discharging or before shipping is measured in the frequency range of 1 MHz to 0.1 Hz by the AC impedance method, and the impedance is estimated from an arc approximated in the frequency range of 0.3 Hz to 0.1 Hz on the complex plane of the Cole-Cole plot obtained by the measurement. Then, a solid-state battery 1 with an estimated impedance of 100,000 Ω (100 kΩ) or more is discriminated as a good product. A solid-state battery 1 with an impedance of 100,000 Ω or more has good initial characteristics without short circuits, and the capacity retention rate of the discharge capacity after charging at the 40th cycle relative to the discharge capacity after charging at the 1st cycle in repeated charging/discharging is stably high at 90% or more, and can be said to be a solid-state battery 1 with excellent cycle characteristics, which are long-term characteristics. Such a solid-state battery 1 is discriminated as a good product. According to the above method, it is possible to accurately and stably discriminate a good solid-state battery 1 that has excellent cycle characteristics, which are long-term characteristics, in addition to the initial characteristics, before charging/discharging or before shipping.

Furthermore, by making the moisture content of the solid-state battery 1 before charging/discharging or before shipping less than 0.0100%, preferably less than 0.0010%, and more preferably less than 0.0000%, it becomes possible to more accurately and stably distinguish good solid-state batteries 1 that have excellent initial characteristics as well as cycle characteristics, which are long-term characteristics.

The above explanation shows an example (referred to as the first embodiment) in which a solid-state battery 1 before charging/discharging or before shipping is measured in the frequency range of 1 MHz to 0.1 Hz by the AC impedance method, the impedance is estimated from an approximated arc in the frequency range of 0.3 Hz to 0.1 Hz on the complex plane of the Cole-Cole plot obtained by the measurement, and a good product is discriminated based on the estimated impedance. Note that, according to the discrimination criterion described in the first embodiment, that is, the impedance estimated from an approximated arc in the frequency range of 0.3 Hz to 0.1 Hz on the complex plane of the Cole-Cole plot is 100,000 Ω or more, among the above-mentioned samples No. 1-9, solid-state batteries 1 such as samples No. 1 and 7 are discriminated as good products.

In addition, the impedance at a specific frequency may be extracted from the Cole-Cole plot as shown in FIG. 2, and a good solid-state battery 1 may be discriminated based on the extracted impedance. For example, a solid-state battery 1 having a moisture content of less than 0.0100% and a capacity retention ratio of the discharge capacity after charging at the 40th cycle to the discharge capacity after charging at the 1st cycle in repeated charging and discharging is 90% or more is discriminated as a good-quality battery. That is, among the above samples No. 1-9, solid-state batteries 1 such as samples No. 1 and 5-7 are discriminated as good-quality batteries. An example (referred to as a second embodiment) of discriminating solid-state batteries 1 such as samples No. 1 and 5-7 as good-quality batteries based on the impedance at a specific frequency extracted from the Cole-Cole plot is described below.

Table 3 shows the results of extracting impedance at frequencies of 1 Hz and 10 Hz from the Cole-Cole plot in Figure 2 above.

Table 3 shows the real part Z' and imaginary part Z" of the impedance at 1 Hz, and the real part Z' and imaginary part Z" of the impedance at 10 Hz. In Table 3, among the above samples 1-9, samples 1 and 5-7 that have a moisture content of less than 0.0100% and have a capacity retention ratio of the discharge capacity after the 40th charge cycle to the discharge capacity after the 1st charge cycle in repeated charge and discharge are deemed to be good products, while the other samples 2-4, 8, and 9 are deemed to be defective products. In this second example, in addition to samples 1 and 7, samples 5 and 6 are also deemed to be good products.

Figure 5 is a plot of the relationship between the real part Z' and the imaginary part Z" of the impedance at 1 Hz. Figure 6 is a plot of the relationship between the real part Z' and the imaginary part Z" of the impedance at 10 Hz. In Figures 5 and 6, the horizontal axis represents the real part Z' [Ω] of the impedance, and the vertical axis represents the imaginary part Z" [Ω] of the impedance.

The real part Z' and imaginary part Z" of the impedance at 1 Hz for sample No. 1-9 as shown in Table 3 have a relationship as shown in the plot in Figure 5. The real part Z' and imaginary part Z" of the impedance at 10 Hz for sample No. 1-9 as shown in Table 3 have a relationship as shown in the plot in Figure 6. Here, from Table 3 and Figure 5, sample No. 1 and 5-7 that are considered to be good products in this second embodiment have a real part Z' of the impedance at 1 Hz of 140 Ω or less and an imaginary part Z" of -400 Ω or less. Also, from Table 3 and Figure 6, sample No. 1 and 5-7 that are considered to be good products in this second embodiment have a real part Z' of the impedance at 10 Hz of 68 Ω or less and an imaginary part Z" of -56 Ω or less.

From these findings, it can be said that a solid-state battery 1 before charging/discharging or before shipping is measured in the frequency range of 1 MHz to 0.1 Hz by the AC impedance method, and the solid-state battery 1 with the real part Z' at 1 Hz being 140 Ω or less and the imaginary part Z" being -400 Ω or less in the impedance on the complex plane of the Cole-Cole plot obtained by the measurement can be discriminated as a good product. Also, it can be said that a solid-state battery 1 before charging/discharging or before shipping is measured in the frequency range of 1 MHz to 0.1 Hz by the AC impedance method, and the solid-state battery 1 with the real part Z' at 10 Hz being 68 Ω or less and the imaginary part Z" being -56 Ω or less in the impedance on the complex plane of the Cole-Cole plot obtained by the measurement can be discriminated as a good product. In other words, such ranges of the real part Z' and imaginary part Z" of the impedance at 1 Hz and the real part Z' and imaginary part Z" of the impedance at 10 Hz can be set as discrimination criteria for discriminating between good solid-state batteries 1.

As in this second embodiment, a solid-state battery 1 having a specified characteristic, for example a solid-state battery 1 having a low water content and a high capacity retention rate such as samples No. 1 and 5-7, can be discriminated as a good product based on the range of the real part Z' and imaginary part Z" of the impedance at a specified frequency. Even with the discrimination criteria as in this second embodiment, it is possible to accurately and stably discriminate a good solid-state battery 1 having excellent cycle characteristics, which are long-term characteristics, in addition to the initial characteristics, before charging/discharging or before shipping.

The above is merely illustrative. Moreover, numerous variations and modifications are possible for those skilled in the art, and the present invention is not limited to the exact configurations and applications shown and described above, and all corresponding modifications and equivalents are deemed to be within the scope of the present invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS LIST 1 Solid-state battery 1a Laminate 10 Positive electrode layer 20 Negative electrode layer 30 Electrolyte layer 60 Electrode 70 Ni layer 80 Sn layer

Claims (15)

1. A positive electrode layer;
   a negative electrode layer facing the positive electrode layer;
   an electrolyte layer provided between the positive electrode layer and the negative electrode layer;
   Including,
   A solid-state battery having an impedance of 100,000 Ω or more as measured by an AC impedance method before charging and discharging and estimated from an approximated arc in a frequency range from 0.3 Hz to 0.1 Hz on a complex plane.
2. The solid-state battery according to claim 1, wherein the moisture content is less than 0.0100%.
3. The positive electrode layer is
   Li1 _{+ xAlxGe2 -x} ( _PO4 ) ₃ (0<x<1),
   _{Li2CoP2O7 , ​}
   The solid-state battery of claim 1 , comprising:
4. The solid-state battery according to claim 1, in which the capacity retention rate of the discharge capacity after the 40th charge cycle relative to the discharge capacity after the 1st charge cycle during repeated charge and discharge is 90% or more.
5. A positive electrode layer;
   a negative electrode layer facing the positive electrode layer;
   an electrolyte layer provided between the positive electrode layer and the negative electrode layer;
   Including,
   A solid-state battery having an impedance on a complex plane measured by an AC impedance method before charging and discharging, in which the real part at 1 Hz is 140Ω or less and the imaginary part is −400Ω or less.
6. The solid-state battery according to claim 5, wherein the moisture content is less than 0.0100%.
7. The positive electrode layer is
   Li1 _{+ xAlxGe2 -x} ( _PO4 ) ₃ (0<x<1),
   _{Li2CoP2O7 , ​}
   The solid-state battery of claim 5 .
8. The solid-state battery according to claim 5, in which the capacity retention rate of the discharge capacity after the 40th charge cycle relative to the discharge capacity after the 1st charge cycle during repeated charge and discharge is 90% or more.
9. A positive electrode layer;
   a negative electrode layer facing the positive electrode layer;
   an electrolyte layer provided between the positive electrode layer and the negative electrode layer;
   Including,
   A solid-state battery having an impedance on a complex plane measured by an AC impedance method before charging and discharging, in which the real part at 10 Hz is 68 Ω or less and the imaginary part is −56 Ω or less.
10. The solid-state battery according to claim 9, wherein the moisture content is less than 0.0100%.
11. The positive electrode layer is
    Li1 _{+ xAlxGe2 -x} ( _PO4 ) ₃ (0<x<1),
    _{Li2CoP2O7 , ​}
    The solid-state battery of claim 9 , comprising:
12. The solid-state battery according to claim 9, in which the capacity retention rate of the discharge capacity after the 40th charge cycle relative to the discharge capacity after the 1st charge cycle during repeated charge and discharge is 90% or more.
13. preparing a solid-state battery including a positive electrode layer, a negative electrode layer facing the positive electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer;
    discriminating, from among the prepared solid-state batteries, those having an impedance of 100,000Ω or more, which is measured by an AC impedance method before charging and discharging and is estimated from an arc approximated in a frequency range of 0.3 Hz to 0.1 Hz on a complex plane;
    A method for manufacturing a solid-state battery, comprising:
14. preparing a solid-state battery including a positive electrode layer, a negative electrode layer facing the positive electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer;
    discriminating the solid-state batteries from among the prepared solid-state batteries, the solid-state batteries having impedances on a complex plane measured by an AC impedance method before charging and discharging, the real part at 1 Hz being 140Ω or less and the imaginary part being −400Ω or less;
    A method for manufacturing a solid-state battery, comprising:
15. preparing a solid-state battery including a positive electrode layer, a negative electrode layer facing the positive electrode layer, and an electrolyte layer provided between the positive electrode layer and the negative electrode layer;
    discriminating the solid-state batteries from among the prepared solid-state batteries, the solid-state batteries having impedances on a complex plane measured by an AC impedance method before charging and discharging, the real part at 10 Hz being 68 Ω or less and the imaginary part being −56 Ω or less;
    A method for manufacturing a solid-state battery, comprising:

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