WO2023054235A1

WO2023054235A1 - All-solid-state battery

Info

Publication number: WO2023054235A1
Application number: PCT/JP2022/035615
Authority: WO
Inventors: 富沢祥江; 伊藤大悟; 横島克典
Original assignee: 太陽誘電株式会社
Priority date: 2021-09-29
Filing date: 2022-09-26
Publication date: 2023-04-06
Also published as: JP2023049768A

Abstract

This all-solid-state battery is characterized by comprising an oxide-based solid electrolyte layer, a positive electrode layer that is arranged on a first main surface of the oxide-based solid electrolyte layer, and a negative electrode layer that is arranged on a second main surface of the oxide-based solid electrolyte layer. This all-solid-state battery is also characterized in that: either one of the positive electrode layer and the negative electrode layer contains an active material which has higher electron conductivity in a charged state than in an uncharged state, while having a lower volume specific capacity than the active material of the other electrode layer, a higher active material volume ratio than the other electrode layer, and a lower volume ratio of a conductive assistant than the other electrode layer; and the ratio (T1/T2) of the average thickness T1 of the one electrode layer to the average thickness T2 of the other electrode layer is 0.75 to 1.3.　

Description

All-solid battery

The present invention relates to all-solid-state batteries.

In recent years, secondary batteries have been used in various fields. A secondary battery using an electrolytic solution has problems such as leakage of the electrolytic solution. Therefore, an all-solid-state battery is being developed that has a solid electrolyte and is composed of other elemental technologies that are also solid.

When a positive electrode active material and a negative electrode active material with different specific capacities are combined, in a general secondary battery, the maximum amount of active material is filled in the electrode layers of the positive and negative electrodes, and the thickness of the electrode layers is changed. It is common to balance the capacities of the positive and negative electrodes.

JP 2019-164484 A

For example, Patent Document 1 discloses an all-solid-state battery in which the filling rate of graphite, which is a negative electrode active material, is increased and combined with an NCA-based positive electrode active material. In this battery, since graphite has a higher volumetric capacity and a higher filling rate, the positive electrode layer must be made thicker in order to balance the capacity with the positive electrode. Since sulfide-based all-solid-state batteries can be fabricated by pressurization, it is possible to balance the capacity by such a thickness. In a solid-state battery, the combination of materials and the sintering temperature change drastically, and it becomes difficult to balance the capacity depending on the thickness.

As described in Non-Patent Document 1, if you try to balance the capacity by the thickness of the electrode layers of the positive and negative electrodes, problems such as interlayer separation and warping due to shrinkage mismatch between the positive and negative electrodes in the sintering process become problems.

When the thickness of the positive and negative electrode layers is the same, in order to increase the filling amount (volume ratio) of the electrode active material with the smaller volumetric capacity, a conductive agent or an ion conductive agent (solid electrolyte) is added to the electrode layer. It is necessary to reduce the filling amount (volume ratio) of , and the decrease in electronic conductivity and ionic conductivity becomes a problem.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an all-solid-state battery that can realize a good capacity balance while suppressing the shrinkage mismatch between the positive and negative electrodes in the sintering process. .

An all-solid-state battery according to the present invention includes an oxide-based solid electrolyte layer, a positive electrode layer provided on a first main surface of the oxide-based solid electrolyte layer, and a second main surface of the oxide-based solid electrolyte layer. one of the positive electrode layer and the negative electrode layer has higher electron conductivity during charging than when uncharged and more than the active material of the other electrode layer It contains an active material with a small volumetric capacity, has a higher volume ratio of the active material than the other electrode layer, has a lower volume ratio of the conductive aid than the other electrode layer, and has an average thickness T1 of the one electrode layer and and the ratio T1/T2 to the average thickness T2 of the other electrode layer is 0.75 or more and 1.3 or less.

In the all-solid-state battery, the one electrode layer may be the positive electrode layer, and the other electrode layer may be the negative electrode layer.

In the one electrode layer of the all-solid-state battery, the volume ratio of the solid electrolyte having ion conductivity is 30 Vol. % or more, 60 Vol. % or less.

In the all-solid-state battery, when the one electrode layer is the positive electrode layer, the active material that exhibits higher electron conductivity during charging than during uncharging is LiCoPO ₄ , Li ₂ CoP ₂ O ₇ or Li ₆ Co. ₅ (P ₂ O ₇ ) ₄ may be used.

In the one electrode layer of the all-solid-state battery, the volume ratio of the active material is 15 Vol. % or more, 55 Vol. % or less.

In the one electrode layer of the all-solid-state battery, the volume ratio of the conductive aid is 8 Vol. % or more, 24 Vol. % or less.

In the all-solid-state battery, when the one electrode layer is the negative electrode layer, the active material that exhibits higher electron conductivity during charging than during uncharging is Li _1.3 Al _0.3 Ti _1.7 ( _PO4 ) ₃ , _LiTi2 ( _PO4 ) ₃ , or _LiTiOPO4 .

According to the present invention, it is possible to provide an all-solid-state battery that can realize a good capacity balance while suppressing the shrinkage mismatch between the positive and negative electrodes in the sintering process.

1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery; FIG. 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery; FIG. 1 is a schematic cross-sectional view of a stacked all-solid-state battery; FIG. FIG. 3 is a schematic cross-sectional view of another stacked all-solid-state battery. It is a figure which illustrates the flow of the manufacturing method of an all-solid-state battery. (a) and (b) are figures which illustrate a lamination process.

Embodiments will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery 100 according to the first embodiment. As illustrated in FIG. 1 , the all-solid battery 100 has a structure in which a solid electrolyte layer 30 is sandwiched between a positive electrode layer 10 and a negative electrode layer 20 . For example, the positive electrode layer 10 is formed on the first main surface of the solid electrolyte layer 30 and the negative electrode layer 20 is formed on the second main surface of the solid electrolyte layer 30 .

The solid electrolyte layer 30 is mainly composed of a solid electrolyte having ionic conductivity. The solid electrolyte of the solid electrolyte layer 30 is, for example, an oxide-based solid electrolyte having lithium ion conductivity. The solid electrolyte is, for example, a phosphate-based solid electrolyte having a NASICON structure. A phosphate-based solid electrolyte having a NASICON structure has properties of high electrical conductivity and stability in the atmosphere. A phosphate-based solid electrolyte is, for example, a phosphate containing lithium. The phosphate is not particularly limited, but examples thereof include a composite lithium phosphate with Ti (eg, LiTi ₂ (PO ₄ ) ₃ ). Alternatively, Ti can be partially or wholly substituted with tetravalent transition metals such as Ge, Sn, Hf, and Zr. Moreover, in order to increase the Li content, it may be partially substituted with trivalent transition metals such as Al, Ga, In, Y and La. More specifically, for example, Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ , Li _1+x Al _x Zr _2-x (PO ₄ ) ₃ , Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ etc.

As illustrated in FIG. 2, the positive electrode layer 10 includes a positive electrode active material 12, a conductive aid 13, a solid electrolyte 14, and the like. The negative electrode layer 20 includes a negative electrode active material 22, a conductive aid 23, a solid electrolyte 24, and the like. By providing the positive electrode layer 10 with the positive electrode active material 12 and the negative electrode layer 20 with the negative electrode active material 22, the all-solid-state battery 100 can be used as a secondary battery. Electroconductivity is obtained in the positive electrode layer 10 and the negative electrode layer 20 by providing the positive electrode layer 10 with the conductive aid 13 and the negative electrode layer 20 with the conductive aid 23 . By providing the positive electrode layer 10 with the solid electrolyte 14 and the negative electrode layer 20 with the solid electrolyte 24 , ion conductivity is obtained in the positive electrode layer 10 and the negative electrode layer 20 . In FIG. 2, hatching of the solid electrolyte layer 30 is omitted. Further, hatching of the

solid electrolytes

14 and 24 is also omitted.

The positive electrode active material 12 is a positive electrode active material whose electron conductivity during charging is higher than that during uncharged (during empty charge). The positive electrode active material 12 is, for example, LiCoPO ₄ , Li ₂ CoP ₂ O ₇ or Li ₆ Co ₅ (P ₂ O ₇ ) ₄ or the like.

The negative electrode active material 22 is not particularly limited as long as it is an active material having a negative electrode action, and examples thereof include Nb ₂ O ₅ , V ₂ O ₅ and Ta ₂ O ₅ .

The

conductive aids

13 and 23 are not particularly limited as long as they are conductive materials, but are, for example, carbon materials. Alternatively, metal may be used as the

conductive aids

13 and 23 . Examples of metals for the

conductive aids

13 and 23 include Pd, Ni, Cu, Fe, and alloys containing these.

The

solid electrolytes

14 and 24 are not particularly limited as long as they are ion-conductive solid electrolytes. As the

solid electrolytes

14 and 24, for example, a solid electrolyte that is the main component of the solid electrolyte layer 30 can be used.

The negative electrode active material 22 is not particularly limited, but in the combination of the positive electrode active material 12 and the negative electrode active material 22, an active material having a smaller volumetric capacity than the negative electrode active material 22 is used as the positive electrode active material 12. Also, the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 is higher than the volume ratio of the negative electrode active material 22 in the negative electrode layer 20 . Also, the volume ratio of the conductive aid 13 in the positive electrode layer 10 is lower than the volume ratio of the conductive aid 23 in the negative electrode layer 20 .

According to this configuration, it is possible to realize a good capacity balance between the positive electrode layer 10 and the negative electrode layer 20 while minimizing the influence of the decrease in electronic conductivity. For example, when the positive electrode active material 12 has a smaller volumetric capacity than the negative electrode active material 22, in order to balance the capacities of the positive electrode layer 10 and the negative electrode layer 20 with the same electrode layer thickness, the filling of the positive electrode active material 12 It is desirable to increase the amount. However, if the amount of the conductive aid 13 is reduced, the electron conduction decreases and the resistance becomes high. Since the electron conduction in the positive electrode layer 10 can be sufficient in the charged state for operation, even if the difference between the thickness of the positive electrode layer 10 and the thickness of the negative electrode layer 20 is small, a good capacity balance can be realized. can.

Also, in the present embodiment, the ratio T1/T2 between the average thickness T1 of the positive electrode layer 10 and the average thickness T2 of the negative electrode layer 20 is set to 0.75 or more and 1.3 or less. Thus, by setting the ratio T1/T2 to 0.75 or more and 1.3 or less, the difference between the thickness of the positive electrode layer 10 and the thickness of the negative electrode layer 20 becomes small. Thereby, the shrinkage mismatch between the positive electrode layer 10 and the negative electrode layer 20 in the sintering process can be suppressed. As a result, warping in the all-solid-state battery 100 can be suppressed, and cracking can be suppressed.

As described above, the all-solid-state battery 100 according to the present embodiment can realize good capacity balance while suppressing the shrinkage mismatch between the positive and negative electrodes in the sintering process.

Note that the average thickness T1 of the positive electrode layer 10 and the average thickness T2 of the negative electrode layer 20 can be measured by averaging the thicknesses at 10 points through SEM observation of a cross section cut perpendicular to the stacking direction.

If the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 is too small, a sufficient capacity density may not be ensured. Therefore, it is preferable to set a lower limit to the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 . For example, in the positive electrode layer 10, the volume ratio of the positive electrode active material 12 is 15 Vol. % or more, and 17.5 Vol. % or more, and 20 Vol. % or more is more preferable.

If the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 is too large, there is a risk of an increase in internal resistance due to insufficient sintering and densification of the electrode and a decrease in electronic conductivity and ionic conductivity. Therefore, it is preferable to set an upper limit to the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 . For example, in the positive electrode layer 10, the volume ratio of the positive electrode active material 12 is 55 Vol. % or less, and 50 Vol. % or less, and 45 Vol. % or less.

If the volume ratio of the conductive aid 13 in the positive electrode layer 10 is too small, there is a risk of an increase in internal resistance due to a decrease in electronic conductivity. Therefore, in the positive electrode layer 10 , it is preferable to set a lower limit to the volume ratio of the conductive aid 13 . For example, in the positive electrode layer 10, the volume ratio of the conductive aid 13 is 8 Vol. % or more, and 9 Vol. % or more, and 10 Vol. % or more is more preferable.

If the volume ratio of the conductive additive 13 in the positive electrode layer 10 is too large, there is a risk of a decrease in capacity, insufficient sintering and densification of the electrode, and an increase in internal resistance due to a decrease in ionic conductivity. Therefore, it is preferable to set an upper limit to the volume ratio of the conductive additive 13 in the positive electrode layer 10 . For example, in the positive electrode layer 10, the volume ratio of the conductive aid 13 is 24 Vol. % or less, and 22 Vol. % or less, and 20 Vol. % or less.

If the volume ratio of the solid electrolyte 14 in the positive electrode layer 10 is too small, the ionic conductivity may decrease and the sintering and densification of the electrode may be insufficient. Therefore, it is preferable to set a lower limit to the volume ratio of the solid electrolyte 14 in the positive electrode layer 10 . For example, in the positive electrode layer 10, the volume ratio of the solid electrolyte 14 is 30 Vol. % or more, and 35 Vol. % or more, and 40 Vol. % or more is more preferable.

If the volume ratio of the solid electrolyte 14 in the positive electrode layer 10 is too large, there is a risk of an increase in internal resistance due to a decrease in capacity and electron conductivity. Therefore, it is preferable to set an upper limit to the volume ratio of the solid electrolyte 14 in the positive electrode layer 10 . For example, in the positive electrode layer 10, the volume ratio of the solid electrolyte 14 is 65 Vol. % or less, and 60 Vol. % or less, and 55 Vol. % or less.

If the volume ratio of the negative electrode active material 22 in the negative electrode layer 20 is too small, it may not be possible to secure a sufficient capacity density. Therefore, it is preferable to set a lower limit to the volume ratio of the negative electrode active material 22 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the negative electrode active material 22 is 10 Vol. % or more, and 12.5 Vol. % or more, and 15 Vol. % or more is more preferable.

In the negative electrode layer 20, if the volume ratio of the negative electrode active material 22 is too large, there is a risk of an increase in internal resistance due to insufficient sintering and densification of the electrode and a decrease in electronic conductivity and ionic conductivity. Therefore, it is preferable to set an upper limit for the volume ratio of the negative electrode active material 22 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the negative electrode active material 22 is 45 Vol. % or less, and 40 Vol. % or less, and 35 Vol. % or less.

If the volume ratio of the conductive aid 23 in the negative electrode layer 20 is too small, there is a risk of an increase in internal resistance due to a decrease in electronic conductivity. Therefore, it is preferable to set a lower limit to the volume ratio of the conductive additive 23 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the conductive aid 23 is 16 Vol. % or more, and 18 Vol. % or more, and 20 Vol. % or more is more preferable.

If the volume ratio of the conductive aid 23 in the negative electrode layer 20 is too large, there is a risk of a decrease in capacity, insufficient sintering and densification of the electrode, and an increase in internal resistance due to a decrease in ionic conductivity. Therefore, it is preferable to set an upper limit to the volume ratio of the conductive aid 23 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the conductive aid 23 is 50 Vol. % or less, and 45 Vol. % or less, and 40 Vol. % or less.

If the volume ratio of the solid electrolyte 24 in the negative electrode layer 20 is too small, the ionic conductivity may decrease and the sintering and densification of the electrode may be insufficient. Therefore, it is preferable to set a lower limit to the volume ratio of the solid electrolyte 24 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the solid electrolyte 24 is 30 Vol. % or more, and 35 Vol. % or more, and 40 Vol. % or more is more preferable.

If the volume ratio of the solid electrolyte 24 in the negative electrode layer 20 is too large, there is a risk of an increase in internal resistance due to a decrease in capacity and electron conductivity. Therefore, it is preferable to set an upper limit to the volume ratio of the solid electrolyte 24 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the solid electrolyte 24 is 65 Vol. % or less, and 60 Vol. % or less, and 55 Vol. % or less.

From the viewpoint of suppressing shrinkage mismatch between the positive electrode layer 10 and the negative electrode layer 20 in the sintering process, the ratio T1/T2 is 0.75 or more and 1.30 or less. It is preferably 0.80 or more and 1.25 or less.

By the way, with the spread of IoT devices and wearable devices, there are expectations for the adoption of all-solid-state batteries that are small and thin, yet have high capacity, high output, and an emphasis on safety. Furthermore, in backup applications, constant voltage (CV) charging and high rate discharge (pulse discharge) are required. Since the CV chargeable secondary battery does not require a current control IC, the number of parts and the volume occupied inside the device can be reduced, so there is an advantage that the size and cost can be reduced.

For example, a non-aqueous electrolyte secondary battery capable of high-current pulse discharge on the order of mA has been developed by etching the inner lid surface of the battery storage can to form an uneven structure to reduce the resistance. Alternatively, by providing a carbon layer on the current collector and bringing it into contact with the sintered electrode plate, the contact is maintained by the pressure of the caulking of the storage can, so that it can be operated repeatedly under the usage conditions for IoT devices such as CV charging and pulse charging/discharging. A coin-type lithium secondary battery has been developed in which the battery resistance does not easily increase even when the battery is heated.

These secondary batteries are designed to reduce the internal resistance as much as possible and prevent the resistance from increasing, making them suitable for high-rate discharge such as pulse discharge. On the other hand, in order to simplify charging, it is necessary to provide a limiting resistor in order to prevent a momentary large current from flowing during CV charging. It can be said that it is unsuitable for applications where simplification is particularly desired.

For example, if a low-resistance all-solid-state battery is used at any charge rate (SOC: State of Charge) to enable high-rate discharge, a large current will flow when CV charging is performed from a low SOC state, and the limiting resistance Without it, there are concerns about battery failure and effects on circuits. On the other hand, if the resistance of the battery is increased, the amount of current during charging can be suppressed, but it is not suitable for high-rate discharge. Therefore, there is a demand for an all-solid-state battery that has a high resistance when the SOC is low before charging and a low resistance when the SOC is high after charging.

In the all-solid-state battery 100 according to the present embodiment, the positive electrode active material 12 that exhibits higher electron conductivity when fully charged than when uncharged is used, and the volume ratio of the conductive aid 13 in the positive electrode layer 10 to the negative electrode layer 20 is Since it is lower than the volume ratio of the conductive aid 23, a large current at low SOC is suppressed, and stable CV charging becomes possible. On the other hand, since the electron conductivity of the positive electrode active material 12, which is rate-limiting during charging, increases at high SOC, high-rate discharge is possible.

(Second embodiment)
In the second embodiment, the negative electrode layer 20 includes a negative electrode active material 22 having a higher electron conductivity during charging than when uncharged and having a smaller volumetric capacity than the positive electrode active material 12 of the positive electrode layer 10. The volume ratio of the active material is higher than that of the positive electrode layer 10 and the volume ratio of the conductive aid is lower than that of the positive electrode layer 10 . Differences from the first embodiment will be described below.

The negative electrode active material 22 is a negative electrode active material whose electron conductivity during charging is higher than that during charging (during empty charging). The negative electrode active material 22 _is , for example, _{Li1.3Al0.3Ti1.7} ( _PO4 ) ₃ , _LiTi2 ( _PO4 ) ₃ , _LiTiOPO4 , or the like _.

The positive electrode active material 12 is not particularly limited as long as it is an active material having a positive electrode action, and examples thereof include LiFePO ₄ , LiMnPO ₄ and LiMn ₂ O ₄ .

The positive electrode active material 12 is not particularly limited, but in the combination of the positive electrode active material 12 and the negative electrode active material 22, an active material having a smaller volumetric capacity than the positive electrode active material 12 is used as the negative electrode active material 22. Also, the volume ratio of the negative electrode active material 22 in the negative electrode layer 20 is higher than the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 . Also, the volume ratio of the conductive aid 23 in the negative electrode layer 20 is lower than the volume ratio of the conductive aid 13 in the positive electrode layer 10 .

According to this configuration, it is possible to realize a good capacity balance between the positive electrode layer 10 and the negative electrode layer 20 while minimizing the influence of the decrease in electronic conductivity.

In the present embodiment, the average thickness of the negative electrode layer 20 is denoted as T1, and the average thickness of the positive electrode layer 10 is denoted as T2. In the present embodiment, by setting the ratio T1/T2 to 0.75 or more and 1.3 or less, the difference between the thickness of the positive electrode layer 10 and the thickness of the negative electrode layer 20 becomes small. Thereby, the shrinkage mismatch between the positive electrode layer 10 and the negative electrode layer 20 in the sintering process can be suppressed. As a result, warping in the all-solid-state battery 100 can be suppressed, and cracking can be suppressed.

From the above, in the present embodiment as well, it is possible to achieve a good capacity balance while suppressing the shrinkage mismatch between the positive and negative electrodes in the sintering process.

If the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 is too small, a sufficient capacity density may not be ensured. Therefore, it is preferable to set a lower limit to the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 . For example, in the positive electrode layer 10, the volume ratio of the positive electrode active material 12 is 10 Vol. % or more, and 12.5 Vol. % or more, and 15 Vol. % or more is more preferable.

If the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 is too large, there is a risk of an increase in internal resistance due to insufficient sintering and densification of the electrode and a decrease in electronic conductivity and ionic conductivity. Therefore, it is preferable to set an upper limit to the volume ratio of the positive electrode active material 12 in the positive electrode layer 10 . For example, in the positive electrode layer 10, the volume ratio of the positive electrode active material 12 is 45 Vol. % or less, and 40 Vol. % or less, and 35 Vol. % or less.

If the volume ratio of the conductive aid 13 in the positive electrode layer 10 is too small, there is a risk of an increase in internal resistance due to a decrease in electronic conductivity. Therefore, in the positive electrode layer 10 , it is preferable to set a lower limit to the volume ratio of the conductive aid 13 . For example, in the positive electrode layer 10, the volume ratio of the conductive aid 13 is 16 Vol. % or more, and 18 Vol. % or more, and 20 Vol. % or more is more preferable.

If the volume ratio of the conductive additive 13 in the positive electrode layer 10 is too large, there is a risk of a decrease in capacity, insufficient sintering and densification of the electrode, and an increase in internal resistance due to a decrease in ionic conductivity. Therefore, it is preferable to set an upper limit to the volume ratio of the conductive additive 13 in the positive electrode layer 10 . For example, in the positive electrode layer 10, the volume ratio of the conductive aid 13 is 50 Vol. % or less, and 45 Vol. % or less, and 40 Vol. % or less.

If the volume ratio of the negative electrode active material 22 in the negative electrode layer 20 is too small, it may not be possible to secure a sufficient capacity density. Therefore, it is preferable to set a lower limit to the volume ratio of the negative electrode active material 22 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the negative electrode active material 22 is 15 Vol. % or more, and 17.5 Vol. % or more, and 20 Vol. % or more is more preferable.

In the negative electrode layer 20, if the volume ratio of the negative electrode active material 22 is too large, there is a risk of an increase in internal resistance due to insufficient sintering and densification of the electrode and a decrease in electronic conductivity and ionic conductivity. Therefore, it is preferable to set an upper limit for the volume ratio of the negative electrode active material 22 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the negative electrode active material 22 is 55 Vol. % or less, and 50 Vol. % or less, and 45 Vol. % or less.

If the volume ratio of the conductive aid 23 in the negative electrode layer 20 is too small, there is a risk of an increase in internal resistance due to a decrease in electronic conductivity. Therefore, it is preferable to set a lower limit to the volume ratio of the conductive additive 23 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the conductive aid 23 is 8 Vol. % or more, and 9 Vol. % or more, and 10 Vol. % or more is more preferable.

If the volume ratio of the conductive aid 23 in the negative electrode layer 20 is too large, there is a risk of a decrease in capacity, insufficient sintering and densification of the electrode, and an increase in internal resistance due to a decrease in ionic conductivity. Therefore, it is preferable to set an upper limit to the volume ratio of the conductive aid 23 in the negative electrode layer 20 . For example, in the negative electrode layer 20, the volume ratio of the conductive aid 23 is 24 Vol. % or less, and 22 Vol. % or less, and 20 Vol. % or less.

Note that, in the present embodiment, the negative electrode active material 22 that exhibits higher electron conductivity in the fully charged state than in the uncharged state is used, and the volume ratio of the conductive support agent 23 in the negative electrode layer 20 is the same as that of the conductive support agent 13 in the positive electrode layer 10 . , the large current at low SOC is suppressed, and stable CV charging becomes possible. On the other hand, since the electron conductivity of the negative electrode active material 22, which is rate-limiting during charging, increases at high SOC, high-rate discharge is possible.

(Layered all-solid-state battery)
FIG. 3 is a schematic cross-sectional view of a stacked all-solid-state battery 100a in which a plurality of battery units are stacked. The all-solid-state battery 100a includes a laminated chip 60 having a substantially rectangular parallelepiped shape. In the laminated chip 60, the first external electrode 40a and the second external electrode 40b are provided so as to be in contact with two side surfaces of the four surfaces other than the top surface and the bottom surface of the stacking direction end. The two side surfaces may be two adjacent side surfaces or two side surfaces facing each other. In the present embodiment, the first external electrode 40a and the second external electrode 40b are provided so as to be in contact with two side surfaces (hereinafter referred to as two end surfaces) facing each other.

In the following description, those having the same composition range, the same thickness range, and the same particle size distribution range as the all-solid-state batteries 100 according to the first and second embodiments are denoted by the same reference numerals. detailed description is omitted.

In the all-solid-state battery 100a, a plurality of positive electrode layers 10 and a plurality of negative electrode layers 20 are alternately laminated with solid electrolyte layers 30 interposed therebetween. Edges of the plurality of positive electrode layers 10 are exposed on the first end surface of the laminated chip 60 and are not exposed on the second end surface. Edges of the plurality of negative electrode layers 20 are exposed on the second end surface of the laminated chip 60 and are not exposed on the first end surface. Thereby, the positive electrode layer 10 and the negative electrode layer 20 are alternately connected to the first external electrode 40a and the second external electrode 40b. The solid electrolyte layer 30 extends from the first external electrode 40a to the second external electrode 40b. Thus, the all-solid-state battery 100a has a structure in which a plurality of battery units are stacked.

A cover layer 50 is laminated on the upper surface of the laminated structure of the positive electrode layer 10, the solid electrolyte layer 30, and the negative electrode layer 20 (in the example of FIG. 3, the upper surface of the uppermost positive electrode layer 10). A cover layer 50 is also laminated on the lower surface of the laminated structure (in the example of FIG. 3, the lower surface of the lowermost positive electrode layer 10). The cover layer 50 is mainly composed of, for example, an inorganic material containing Al, _Zr , Ti, etc. (eg, _Al2O3 , _ZrO2 , TiO2 _, etc.). The cover layer 50 may contain the main component of the solid electrolyte layer 30 as a main component.

The positive electrode layer 10 and the negative electrode layer 20 may have collector layers. For example, as illustrated in FIG. 4 , the first current collector layer 11 may be provided within the positive electrode layer 10 . Also, a second current collector layer 21 may be provided in the negative electrode layer 20 . The first current collector layer 11 and the second current collector layer 21 are mainly composed of a conductive material. For example, metal, carbon, or the like can be used as the conductive material of the first current collector layer 11 and the second current collector layer 21 . By connecting the first collector layer 11 to the first external electrode 40a and connecting the second collector layer 21 to the second external electrode 40b, the current collection efficiency is improved.

Next, a method for manufacturing the all-solid-state battery 100a illustrated in FIG. 3 will be described. FIG. 5 is a diagram illustrating the flow of the method for manufacturing the all-solid-state battery 100a.

(Process for preparing raw material powder for solid electrolyte layer)
First, raw material powder for the solid electrolyte layer that constitutes the solid electrolyte layer 30 described above is prepared. For example, raw material powder of an oxide-based solid electrolyte can be produced by mixing raw materials, additives, and the like and using a solid-phase synthesis method or the like. By dry pulverizing the obtained raw material powder, it is possible to adjust to a desired average particle size. For example, a planetary ball mill using 5 mmφ ZrO ₂ balls is used to adjust the desired average particle size.

(Process for preparing raw material powder for cover layer)
First, raw material powder of ceramics that constitutes the cover layer 50 is prepared. For example, raw material powder for the cover layer can be produced by mixing raw materials, additives, and the like and using a solid-phase synthesis method or the like. By dry pulverizing the obtained raw material powder, it is possible to adjust to a desired average particle size. For example, a planetary ball mill using 5 mmφ ZrO ₂ balls is used to adjust the desired average particle size. When the solid electrolyte layer 30 and the cover layer 50 have the same composition, raw material powder for the solid electrolyte layer can be substituted.

(Electrode layer paste preparation step)
Next, internal electrode pastes for producing the above-described positive electrode layer 10 and negative electrode layer 20 are individually produced. For example, an internal electrode paste can be obtained by uniformly dispersing a conductive aid, an electrode active material, a solid electrolyte material, a sintering aid, a binder, a plasticizer, and the like in water or an organic solvent. As the solid electrolyte material, the solid electrolyte paste described above may be used. A carbon material or the like is used as the conductive aid. A metal may be used as the conductive aid. Examples of the metal of the conductive aid include Pd, Ni, Cu, Fe, and alloys containing these. Pd, Ni, Cu, Fe, alloys containing these, and various carbon materials may also be used.

Examples of sintering aids for internal electrode paste include Li—B—O compounds, Li—Si—O compounds, Li—C—O compounds, Li—S—O compounds, Li—P—O A glass component such as any one or more of the glass components such as base compounds is included.

(External electrode paste preparation process)
Next, an external electrode paste for producing the first external electrode 40a and the second external electrode 40b is prepared. For example, an external electrode paste can be obtained by uniformly dispersing a conductive material, a glass frit, a binder, a plasticizer, and the like in water or an organic solvent.

(Solid electrolyte green sheet manufacturing process)
A solid electrolyte slurry having a desired average particle size is prepared by uniformly dispersing the raw material powder for the solid electrolyte layer in an aqueous solvent or an organic solvent together with a binder, a dispersant, a plasticizer, etc., followed by wet pulverization. get At this time, a bead mill, a wet jet mill, various kneaders, a high-pressure homogenizer, or the like can be used, and it is preferable to use a bead mill from the viewpoint of being able to simultaneously adjust the particle size distribution and disperse. A binder is added to the obtained solid electrolyte slurry to obtain a solid electrolyte paste. By applying the obtained solid electrolyte paste, the solid electrolyte green sheet 51 can be produced. The coating method is not particularly limited, and a slot die method, a reverse coating method, a gravure coating method, a bar coating method, a doctor blade method, or the like can be used. The particle size distribution after wet pulverization can be measured, for example, using a laser diffraction measurement device using a laser diffraction scattering method.

(Lamination process)
As illustrated in FIG. 6A , an internal electrode paste 52 is printed on one surface of a solid electrolyte green sheet 51 . A reverse pattern 53 is printed on a region of the solid electrolyte green sheet 51 where the internal electrode paste 52 is not printed. As the reverse pattern 53, the same one as the solid electrolyte green sheet 51 can be used. A plurality of solid electrolyte green sheets 51 after printing are alternately shifted and laminated. As illustrated in FIG. 6B, the laminate is obtained by crimping the cover sheets 54 from above and below in the lamination direction. In this case, in the laminate, the internal electrode paste 52 for the positive electrode layer 10 is exposed on one end surface, and the internal electrode paste 52 for the negative electrode layer 20 is exposed on the other end surface. A laminate is obtained. The cover sheet 54 can be formed by coating the raw material powder for the cover layer in the same manner as in the solid electrolyte green sheet production process. The cover sheet 54 is formed thicker than the solid electrolyte green sheet 51 . The thickness may be increased during coating, or may be increased by stacking a plurality of coated sheets.

Next, the external electrode paste 55 is applied to each of the two end faces by a dipping method or the like and dried. Thereby, a molding for forming the all-solid-state battery 100a is obtained.

(Baking process)
Next, the obtained laminate is fired. The firing conditions are oxidizing atmosphere or non-oxidizing atmosphere, and the maximum temperature is preferably 400° C. to 1000° C., more preferably 500° C. to 900° C., without any particular limitation. A step of holding below the maximum temperature in an oxidizing atmosphere may be provided to sufficiently remove the binder until the maximum temperature is reached. In order to reduce process costs, it is desirable to bake at as low a temperature as possible. After firing, reoxidation treatment may be performed. Through the above steps, the all-solid-state battery 100a is produced.

It should be noted that current collector layers can be formed in the positive electrode layer 10 and the negative electrode layer 20 by sequentially laminating the internal electrode paste, the current collector paste containing a conductive material, and the internal electrode paste. can.

All-solid-state batteries were produced according to the embodiments, and their characteristics were investigated.

(Example 1)
LiCoPO ₄ (LCP: substantial volumetric capacity of 450 mAh/cm ³ ), whose electronic conductivity is improved by charging, is applied as the positive electrode active material, carbon powder (C) is applied as the conductive aid, and Li is used as the solid electrolyte. -Al-Ge-P-O based ionic conductor (LAGP) was applied, and an internal electrode paste for the positive electrode layer was prepared so that the volume ratio of LCP, C and LAGP was 35:15:50.

Nb ₂ O ₅ (volume specific capacity up to 1 V vs. Li/Li ⁺ 920 mAh/cm ³ ) was applied as the negative electrode active material, carbon powder (C) was used as the conductive aid, and Li—Al—Ge— was used as the solid electrolyte. A PO-based ionic conductor (LAGP) was applied, and the internal electrode paste for the negative electrode layer was prepared so that the volume ratio of Nb ₂ O ₅ , C and LAGP was 17.5:32.5:50. bottom.

A solid electrolyte green sheet with a thickness of 20 μm was produced by a tape casting method using a slurry composed of a solid electrolyte made of LAGP, an organic binder, a dispersant, a plasticizer, and an organic solvent.

On the first solid electrolyte green sheet, the internal electrode paste for the positive electrode layer was applied by screen printing. An internal electrode paste for a negative electrode layer was applied onto the second solid electrolyte green sheet by screen printing. The internal electrode paste for the positive electrode layer and the internal electrode paste for the negative electrode layer were made to have the same thickness. A plurality of first solid electrolyte green sheets and a plurality of second solid electrolyte green sheets were laminated such that the positive electrode layer and the negative electrode layer were alternately pulled out to the left and right to obtain a green chip of a laminated all-solid-state battery. . The green chip was sintered by degreasing and firing, and an external electrode paste was applied and cured to form an external electrode, thereby obtaining a stacked all-solid-state battery.

When the appearance of the stacked all-solid-state battery was observed, no warping or cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 1.20 mAh, and the capacity estimated from the total amount of the negative electrode active material was 1.23 mAh. However, when the battery characteristics were actually evaluated, the battery capacity was 1.15 mAh. there were.

(Comparative example 1)
LiFePO ₄ (LFP: volume specific capacity 610 mAh/cm ³ ) is used as the positive electrode active material, and the volume ratio of LFP, C, and LAGP is 26:24:50. An all-solid battery was fabricated in the same manner as in Example 1 except for the above.

When the appearance of the stacked all-solid-state battery was observed, no warping or cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 1.21 mAh, and the capacity estimated from the total amount of the negative electrode active material was 1.23 mAh. However, when the battery characteristics were actually evaluated, the battery capacity was 0.67 mAh. there were.

(Comparative example 2)
An internal electrode paste for the positive electrode layer was prepared so that the volume ratio of LCP, C and LAGP was 20:30:50. An all-solid-state battery was produced in the same manner as in Example 1, except that the size was increased 75 times.

When observing the appearance of the stacked all-solid-state battery, cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 1.20 mAh, and the capacity estimated from the total amount of the negative electrode active material was 1.23 mAh. , the capacity could not be measured.

(Comparative Example 3)
An all-solid battery was produced in the same manner as in Example 1, except that the internal electrode paste for the positive electrode layer was produced such that the volume ratio of LCP, C, and LAGP was 17.5:32.5:50.

When the appearance of the stacked all-solid-state battery was observed, no warping or cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 0.60 mAh, and the capacity estimated from the total amount of the negative electrode active material was 1.23 mAh. However, when the battery characteristics were actually evaluated, the battery capacity was 0.55 mAh. there were.

(Example 2)
An internal electrode paste for the positive electrode layer was prepared so that the volume ratio of LCP, C, and LAGP was 28:22:50, and the thickness of the positive electrode layer was 1.25 times the thickness of the negative electrode layer. An all-solid-state battery was produced in the same manner as in 1.

When observing the appearance of the stacked all-solid-state battery, a very slight warp was observed, but no cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 1.20 mAh, and the capacity estimated from the total amount of the negative electrode active material was 1.23 mAh. However, when the battery characteristics were actually evaluated, the battery capacity was 1.12 mAh. there were.

(Comparative Example 4)
An internal electrode paste for the positive electrode layer was prepared so that the volume ratio of LCP, C, and LAGP was 26:24:50, and the thickness of the positive electrode layer was 1.35 times the thickness of the negative electrode layer. An all-solid-state battery was produced in the same manner as in 1.

(Example 3)
An all-solid battery was produced in the same manner as in Example 1, except that the internal electrode paste for the negative electrode layer was produced such that the volume ratio of Nb ₂ O ₅ , C and LAGP was 25:25:50.

When the appearance of the stacked all-solid-state battery was observed, no warping or cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 1.20 mAh, and the capacity estimated from the total amount of the negative electrode active material was 1.71 mAh. However, when the battery characteristics were actually evaluated, the battery capacity was 1.18 mAh. there were.

(Comparative Example 5)
An internal electrode paste for the positive electrode layer was prepared so that the volume ratio of LCP, C, and LAGP was 30:25:45, and the volume ratio of Nb ₂ O ₅ , C, and LAGP was 25:25:50. An all-solid-state battery was produced in the same manner as in Example 1, except that the internal electrode paste for the negative electrode layer was produced such that

When the appearance of the stacked all-solid-state battery was observed, no warping or cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 1.03 mAh, and the capacity estimated from the total amount of the negative electrode active material was 1.71 mAh. However, when the battery characteristics were actually evaluated, the battery capacity was 0.99 mAh. there were.

(Comparative Example 6)
An internal electrode paste for the positive electrode layer was prepared so that the volume ratio of LCP, C, and LAGP was 30:25:45, and the volume ratio of Nb ₂ O ₅ , C, and LAGP was 35:15:50. An all-solid-state battery was produced in the same manner as in Example 1, except that the internal electrode paste for the negative electrode layer was produced such that

When the appearance of the stacked all-solid-state battery was observed, no warping or cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 1.03 mAh, and the capacity estimated from the total amount of the negative electrode active material was 2.39 mAh. However, when the battery characteristics were actually evaluated, the battery capacity was 0.92 mAh. there were.

The results of Examples 1-3 and Comparative Examples 1-6 are shown in Tables 1 and 2.

Examples 1-3 and Comparative Examples 1-6 were evaluated. If the actual capacity [mAh] was 1 mAh or more and neither warpage nor cracks occurred, it was judged to be good. If the actual capacity [mAh] was 1 mAh or more, and if warpage occurred but cracks did not occur, it was determined to be good "◯". If it was neither very good "⊚" nor good "◯", it was judged to be bad "x".

Examples 1 to 3 were judged to be very good or good. This is because the positive electrode layer contains an active material whose electronic conductivity is higher when charged than when uncharged and whose volumetric capacity is smaller than that of the active material of the negative electrode layer, and the active material volume ratio is higher than that of the negative electrode layer. This is probably because the volume ratio of the conductive aid was lower than that of the layer, and the ratio T1/T2 between the average thickness T1 of the positive electrode layer and the average thickness T2 of the negative electrode layer was 0.75 or more and 1.3 or less. .

On the other hand, Comparative Examples 1 to 6 were judged to be defective. In Comparative Example 1, it is presumed that LiFePO ₄ was used as the positive electrode active material, since the electron conductivity does not increase after charging. For Comparative Examples 2 and 4, it is estimated that T1/T2 exceeded 1.3. As for Comparative Example 3, it is presumed that the positive electrode layer and the negative electrode layer had the same volume ratio of the active material. As for Comparative Example 5, it is presumed that the positive electrode layer and the negative electrode layer had the same volume ratio of the conductive aid. As for Comparative Example 6, it is presumed that this is because the volume ratio of the active material in the negative electrode layer was higher than that in the positive electrode layer.

In addition, for Examples 1 to 3 and Comparative Examples 1 to 6, the inrush current [mA] when CV charging was performed from SOC = 0% and the rate (C) for a battery capacity of 1 mAh were measured. Further, for Examples 1 to 3 and Comparative Examples 1 to 6, a pulse discharge test was conducted in which SOC=100% and 20 mA/100 μsec were repeated 100 times at intervals of 1 sec, and the pulse voltage drop [V] was measured. These results are shown in Tables 1 and 2. Comparative Examples 2 and 4 could not be measured because cracks were generated. If the inrush current was 5C or less, the CV charging was determined to be good "O", and if it was not 5C or less, the CV charging was determined to be poor "x". In addition, when the pulse voltage drop was 0.16 V or less, the pulse discharge was determined to be good, and when it was not 0.16 V or less, the pulse discharge was determined to be defective (x).

In Examples 1 to 3, both CV charging and pulse discharging were judged to be good "◯". This is because the positive electrode active material used has a higher electron conductivity when fully charged than when uncharged, and the volume ratio of the conductive aid in the positive electrode layer was lower than the volume ratio of the conductive aid in the negative electrode layer. It is estimated to be.

(Example 4)
Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ (LATP: Volume specific capacity up to 1 V vs. Li/Li ⁺ 350 mAh/cm ³ ), which improves electronic conductivity by charging, is used as the negative electrode active material. is applied, carbon powder (C) is applied as a conductive agent, Li—Al—Ge—P—O-based ionic conductor (LAGP) is applied as a solid electrolyte, and the volume ratio of LATP, C and LAGP is An internal electrode paste for the negative electrode layer was prepared so as to have a ratio of 35:15:50. LiFePO ₄ (LFP: volume specific capacity 610 mAh/cm ³ ), whose electronic conductivity does not increase after charging, was applied as the positive electrode active material, and the positive electrode layer was adjusted so that the volume ratio of LFP, C, and LAGP was 20:25:55. An internal electrode paste was prepared for Other conditions were the same as in Example 1.

When the appearance of the stacked all-solid-state battery was observed, no warping or cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 1.22 mAh, and the capacity estimated from the total amount of the negative electrode active material was 1.23 mAh. However, when the battery characteristics were actually evaluated, the battery capacity was 1.04 mAh. there were.

(Comparative Example 7)
An internal electrode paste for the negative electrode layer was prepared so that the volume ratio of LATP, C and LAGP was 25: 25: 50, and the volume ratio of LFP, C and LAGP was 25: 25: 50. , an all-solid-state battery was fabricated in the same manner as in Example 4.

When the appearance of the stacked all-solid-state battery was observed, no warping or cracks were observed. The capacity estimated from the total amount of the positive electrode active material was 1.52 mAh, and the capacity estimated from the total amount of the negative electrode active material was 0.88 mAh. However, when the battery characteristics were actually evaluated, the battery capacity was 0.85 mAh. there were.

The results of Example 4 and Comparative Example 7 are shown in Tables 3 and 4.

Example 4 and Comparative Example 7 were evaluated. If the actual capacity [mAh] was 1 mAh or more and neither warpage nor cracks occurred, it was judged to be good. If the actual capacity [mAh] was 1 mAh or more, and if warpage occurred but cracks did not occur, it was determined to be good "◯". If it was neither very good "⊚" nor good "◯", it was judged to be bad "x".

In Example 4, it was judged to be very good or good. This is because the negative electrode layer contains an active material whose electronic conductivity is higher when charged than when uncharged and whose volumetric capacity is smaller than that of the active material of the positive electrode layer, and the volume ratio of the active material is higher than that of the positive electrode layer. This is probably because the volume ratio of the conductive aid was lower than that of the layer, and the ratio T1/T2 between the average thickness T1 of the negative electrode layer and the average thickness T2 of the positive electrode layer was 0.75 or more and 1.3 or less. .

On the other hand, Comparative Example 7 was determined to be defective. As for Comparative Example 7, it is presumed that the volume ratio of the active material in the positive electrode layer and the negative electrode layer was the same.

In addition, for Example 4 and Comparative Example 7, the inrush current [mA] when CV charging was performed from SOC = 0% and the rate (C) for a battery capacity of 1 mAh were measured. Further, for Example 4 and Comparative Example 7, a pulse discharge test was conducted in which SOC=100% and 20 mA/100 μsec were repeated 100 times at intervals of 1 sec, and the pulse voltage drop [V] was measured. These results are shown in Tables 3 and 4. If the inrush current was 5C or less, the CV charging was determined to be good "O", and if it was not 5C or less, the CV charging was determined to be poor "x". In addition, when the pulse voltage drop was 0.16 V or less, the pulse discharge was determined to be good, and when it was not 0.16 V or less, the pulse discharge was determined to be defective (x).

In Example 4, both CV charging and pulse discharging were judged to be good "◯". This is because the negative electrode active material used has a higher electron conductivity when fully charged than when uncharged, and the volume ratio of the conductive aid in the negative electrode layer was lower than the volume ratio of the conductive aid in the positive electrode layer. It is estimated to be.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention described in the scope of claims. Change is possible.

Claims

an oxide-based solid electrolyte layer;
a positive electrode layer provided on the first main surface of the oxide-based solid electrolyte layer;
a negative electrode layer provided on the second main surface of the oxide-based solid electrolyte layer,
Either one of the positive electrode layer and the negative electrode layer contains an active material having a higher electron conductivity during charging than when uncharged and having a smaller volumetric capacity than the active material of the other electrode layer, The volume ratio of the active material is higher than that of the other electrode layer, and the volume ratio of the conductive aid is lower than that of the other electrode layer,
An all-solid-state battery, wherein a ratio T1/T2 between the average thickness T1 of the one electrode layer and the average thickness T2 of the other electrode layer is 0.75 or more and 1.3 or less.
The one electrode layer is the positive electrode layer,
2. The all-solid-state battery according to claim 1, wherein the other electrode layer is the negative electrode layer.
In the one electrode layer, the volume ratio of the solid electrolyte having ion conductivity is 30 Vol. % or more, 65 Vol. % or less, the all-solid-state battery according to claim 1 or 2.
When the one electrode layer is the positive electrode layer, the active material that exhibits higher electron conductivity during charging than during uncharging is LiCoPO 4 , Li 2 CoP 2 O 7 or Li 6 Co 5 (P 2 O 7 ) . ) 4 , the all-solid-state battery according to any one of claims 1 to 3.
In the one electrode layer, the volume ratio of the active material is 15 Vol. % or more, 55 Vol. % or less, the all-solid-state battery according to any one of claims 1 to 4.
In the one electrode layer, the volume ratio of the conductive aid is 8 Vol. % or more, 24 Vol. % or less, the all-solid-state battery according to any one of claims 1 to 5.
When the one electrode layer is the negative electrode layer, the active material that exhibits higher electron conductivity during charging than during uncharging is Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 and LiTi. 2 (PO 4 ) 3 or LiTiOPO 4 , the all-solid-state battery according to claim 1.