Method of storing all-solid-state battery

Abstract

To provide a method of storing an all-solid-state battery, capable of suppressing an increase in an internal resistance after a storage period.SOLUTION: The present invention provides a method for storing an all-solid-battery, in which a battery comprises: lithium nickel cobalt aluminum oxide as a positive electrode active material; sulfide as a solid electrolyte; and lithium titanate as a negative electrode active material, and the method comprises a step of holding a voltage of the battery at a hold voltage between 0.8 volts or more and 1.0 volts or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for storing all-solid-state batteries.

Background Art

[0002] All-solid-state batteries may be stored for a long time, similar to electrolyte-based lithium-ion secondary batteries.

[0003] Patent Document 1 discloses a method for storing a lithium-ion secondary battery in an attempt to maintain battery characteristics during long-term storage. The method includes a step of holding the lithium-ion secondary battery at a storage temperature that suppresses the reaction between the electrode body and the electrolyte, and a step of performing charging so as to keep the state of charge (SOC) of the battery during storage at 0% or more and 40% or less.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Regarding all-solid-state batteries, there is room for improvement in suppressing the increase in internal resistance after the storage period.

[0006] An object of the present disclosure is to provide a method for storing all-solid-state batteries that can suppress the increase in internal resistance after the storage period.

Means for Solving the Problems

[0007] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> A method for storing an all-solid-state battery, The battery has lithium nickel cobalt aluminum oxide as a positive electrode active material, The battery has a sulfide as a solid electrolyte, and The battery has lithium titanate as a negative electrode active material, The method includes holding the voltage of the battery at a holding voltage of 0.8 volts or more and 1.0 volts or less. Method for storing an all-solid-state battery.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a method for storing an all-solid-state battery that can suppress an increase in internal resistance after a storage period.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present disclosure will be described in detail. The present disclosure is not limited only to the following embodiments, and can be variously modified and implemented within the scope of the gist of the disclosure.

[0010] 《Method for Storing an All-Solid-State Battery》 The method for storing an all-solid-state battery according to the present disclosure is The battery has lithium nickel cobalt aluminum oxide as a positive electrode active material, The battery has a sulfide as a solid electrolyte, and The battery has lithium titanate as a negative electrode active material, The method includes holding the voltage of the battery at a holding voltage of 0.8 volts or more and 1.0 volts or less.

[0011] The object of the method of the present disclosure, that is, the object to be stored, is the above all-solid-state battery. The method of the present disclosure continues for at least a part of the storage period of the all-solid-state battery. By the method of the present disclosure, an increase in internal resistance after the storage period can be suppressed, that is, an increase in the internal resistance increase rate {(internal resistance value of the all-solid-state battery after the storage period / internal resistance value of the all-solid-state battery before the storage period) × 100} after the storage period can be suppressed. As a result, the life of the battery can be extended.

[0012] In the present disclosure, the "storage period" at the above-mentioned holding voltage is, for example, 1 week or more, 3 weeks or more, 1 month or more, 40 days or more, 3 months or more, 6 months or more, or 1 year or more, and also, for example, 5 years or less, 3 years or less, 1 year or less, 10 months or less, or half a year or less. However, it is not limited to the above examples and may be a period according to the purpose of storage in the present disclosure. Here, the purpose of "storage" in the present disclosure includes not only the state where all-solid-state batteries continue to be located at specific coordinates but also the state involving coordinate movement of the batteries, for example, the transport state of the batteries.

[0013] Note that the storage temperature is, for example, 0°C or higher, 10°C or higher, or 20°C or higher, and also, for example, 80°C or lower, 70°C or lower, or 60°C or lower. However, it is not limited to the above examples.

[0014] The all-solid-state battery to which the method of the present disclosure is applied is having lithium nickel cobalt aluminum oxide as a positive electrode active material, having a sulfide as a solid electrolyte, and having lithium titanate as a negative electrode active material.

[0015] Typical lithium-ion batteries are liable to have their battery characteristics significantly deteriorated by storage. Conventionally, regarding lithium-ion batteries, there has been an understanding that when the voltage of such a battery becomes low, for example, when the battery voltage drops below 2.7 V, it enters an over-discharged state and the battery performance significantly deteriorates.

[0016] In contrast, the present inventors have found that by holding the voltage of the above-mentioned specific all-solid-state battery at a low holding voltage of 0.8 V or more and 1.0 V or less, it is possible to suppress an increase in internal resistance after the storage period for such all-solid-state batteries. Here, the holding voltage may be a fixed value or a variable value.

[0017] The method of the present disclosure may include the following first step: Discharging the all-solid-state battery until the voltage of the all-solid-state battery reaches the holding voltage.

[0018] By including the first step in the method of the present disclosure, the voltage of an all-solid-state battery having a voltage exceeding the holding voltage can be actively reduced, and the voltage of the battery can be quickly reached to the holding voltage.

[0019] The first step may be performed on an all-solid-state battery having a voltage exceeding 1.0 volt, or may be performed on an all-solid-state battery that already has a voltage of 1.0 volt or less but has a voltage exceeding the intended holding voltage.

[0020] The discharge in the first step may be CC discharge. "CC discharge" in the present disclosure means discharge while maintaining a constant current value (Constant Current discharge).

[0021] Further, the method of the present disclosure may include the following second step: After the first step, stopping the discharge of the battery.

[0022] By including the second step in the method of the present disclosure, after the voltage reaches the holding voltage, active discharge of the all-solid-state battery can be avoided.

[0023] On the other hand, when the all-solid-state battery self-discharges during storage, even if active discharge is not performed, the voltage of the battery gradually decreases over time and may become lower than the intended holding voltage.

[0024] Therefore, the method of the present disclosure may include the following third step: Charging the all-solid-state battery until the voltage of the all-solid-state battery reaches the holding voltage.

[0025] By including the third step in the method of the present disclosure, the voltage of an all-solid-state battery having a voltage less than the intended holding voltage is increased, thereby reliably preventing a situation where the voltage of the battery becomes less than 0.8 volts.

[0026] The charging in the third step may be CV charging. "CV charging" in the present disclosure means charging while maintaining a constant voltage value (Constant Voltage charging; constant voltage charging).

[0027] In addition, the third step may be intermittently performed with the first step. By including the first step and the third step intermittently in the method of the present disclosure, it becomes easier to make the voltage of the battery coincide with the holding voltage over the storage period.

[0028] Regarding the all-solid-state battery to which the method of the present disclosure is applied, its specific configuration will be further described below.

[0029] The all-solid-state battery has a positive electrode current collector, a positive electrode active material layer, a solid electrolyte, a negative electrode current collector, and a negative electrode active material layer in this order. Among these, for the positive electrode active material and the negative electrode active material, the above description can be referred to.

[0030] Examples of sulfides as the solid electrolyte include, for example, Li2S-SiS2, LiX-Li2S-SiS2, LiX-Li2S-P2S5, LiX-Li2S-P2S5, LiX-Li2S-Li2O-P2S5, Li2S-P2S5, etc. However, sulfides as the solid electrolyte are not limited to the above examples.

[0031] Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, carbon, etc. The positive electrode current collector may be, for example, in the form of a foil, a mesh, or a porous shape.

[0032] The positive electrode active material layer contains a positive electrode active material. For the positive electrode active material, the above description can be referred to. In addition, the battery may have a compound other than lithium titanate as the positive electrode active material. Examples of the compound include known oxides applicable as the positive electrode active material of the all-solid-state battery.

[0033] The positive electrode active material layer may contain a positive electrode active material, for example, 50% by mass or more, or 70% by mass or more, and 99% by mass or less, or 95% by mass or less. The positive electrode active material layer may optionally contain a conductive assistant and a binder, and may have a certain thickness. For the conductive assistant, the binder, and the thickness, reference may be made to the above description regarding the negative electrode active material layer.

[0034] Examples of the material of the negative electrode current collector include SUS, aluminum, copper, nickel, carbon, etc. The negative electrode current collector may be, for example, in the form of a foil, a mesh, or a porous material.

[0035] The negative electrode active material layer contains a negative electrode active material. For the negative electrode active material, reference may be made to the above description. Note that the battery may have a compound other than lithium nickel cobalt aluminum oxide as the negative electrode active material. Examples of the compound include known compounds applicable as the negative electrode active material of an all-solid-state battery.

[0036] The negative electrode active material layer may contain a negative electrode active material, for example, 50% by mass or more, or 70% by mass or more, and 99% by mass or less, or 95% by mass or less. The negative electrode active material layer may optionally contain a conductive assistant and a binder. The conductive assistant may be, for example, a carbon material or a metal material, etc., and as the binder, a known material that is chemically and electrically stable may be used. The negative electrode active material layer may have a certain thickness. The thickness of the negative electrode active material layer may be, for example, 0.1 μm or more and 1 mm or less.

[0037] The all-solid-state battery may include a battery case for housing each layer of the battery, and may also include terminals connectable to a current collector, etc. Further, the battery may include a restraining member for restraining each layer along the stacking direction. For these, those similar to the conventional ones may be used.

[0038] Examples of the shape of the all-solid-state battery to which the method of the present disclosure is applied include a coin type, a laminate type, a cylindrical type, and a rectangular type, etc.

[0039] The method of the present disclosure is executed by a computer including a memory and a processor. The memory has, for example, RAM or ROM, and temporarily or permanently stores various data used in arithmetic processing executed by the processor and various data generated during the arithmetic processing. Here, the memory stores a voltage value within a range of 0.8 volts or more and 1.0 volt or less as a "holding voltage".

[0040] All-solid-state batteries to which the method of the present disclosure is applied the above computer, a power source for charging the battery, and a sensor for acquiring information on the battery, may together constitute a storage system for executing the method of the present disclosure. At least a part of the storage system may be physically mounted on a predetermined structure. Such a structure is, for example, a vehicle. Hereinafter, various controls in the storage system for executing the method of the present disclosure will be described.

[0041] The all-solid-state battery starts discharging based on an instruction from the computer and stops discharging based on an instruction from the computer. The power source starts power supply to the all-solid-state battery based on an instruction from the computer and stops power supply to the all-solid-state battery based on an instruction from the computer. The sensor is a voltage sensor and detects voltage information of the all-solid-state battery. The voltage information is transmitted to the computer as an electrical signal.

[0042] Here, the computer sequentially acquires the voltage of the all-solid-state battery. When it detects that the voltage of the battery exceeds the holding voltage, it drives the battery to discharge, and when it detects that the voltage of the battery is less than the holding voltage, it drives the power source to charge. When the computer detects that the voltage of the battery has reached the holding voltage, it may stop driving both the battery and the power source to stop charging and discharging.

[0043] Note that the computer is not limited to the mode in which all its functional units are physically configured in the above structure. At least some of the functional units in the computer may be virtually arranged in an external server.

[0044] By the above control by the computer, the voltage of the all-solid-state battery is maintained at a holding voltage of 0.8 volts or more and 1.0 volts or less over the storage period. Thereby, the battery is stored at a voltage of 0.8 volts or more and 1.0 volts or less.

[0045] The method of the present disclosure has been described above. However, the present disclosure is not limited to only the above-described embodiments, and can be variously modified and implemented within the scope of the gist of the disclosure.

[0046] In one aspect, the memory may store a voltage value of a predetermined value located at 0.8 volts or more and 1.0 volts or less as a "threshold voltage". In this case, when the computer obtains a voltage below the threshold voltage, the computer may control a predetermined warning device to issue a predetermined warning to the user.

[0047] Examples of the warning device include an alarm and a screen, etc., and examples of the warning include an alarm sound and a warning screen, etc. Since it is easy to avoid unnecessary warnings, the threshold voltage is preferably less than the holding voltage.

Example

[0048] 《Example 1》 Lithium nickel cobalt aluminum oxide was used as the positive electrode active material, sulfide was used as the solid electrolyte, and lithium titanate was used as the negative electrode active material, and an all-solid-state battery was produced by a conventional method.

[0049] The produced battery was stored in an environment of 60°C for 42 days. Here, the target value of the voltage to be maintained during storage was set to 0.8 volts (V).

[0050] 《Evaluation》 〈Internal resistance increase rate〉 For all-solid-state batteries, the internal resistance values were measured before and after the storage period. Using the measured values, the internal resistance increase rate after the storage period {(internal resistance value of the all-solid-state battery after the storage period / internal resistance value of the all-solid-state battery before the storage period) × 100} was calculated.

[0051] 《Examples 2 and Comparative Examples 1 to 3》 All-solid-state batteries were stored and evaluated in the same manner as in Example 1, except that the number of storage days and the target value of the voltage to be maintained during storage were changed as shown in Table 1.

[0052] 《Results》 The internal resistance increase rates (%) after the storage period for each example are shown in Table 1.

[0053]

Table 1

[0054] As shown in Table 1, in the cases of Example 1 and Example 2, an increase in internal resistance after the storage period could be suppressed as compared with the cases of Comparative Examples 1 to 3. From the results shown in Table 1, it is inferred that any voltage value selected from the range of 0.8 volts or more and 1.0 volt or less functions suitably as the holding voltage.

[0055] Also, in the cases of Example 1 and Example 2, since an increase in internal resistance after the storage period could be suppressed even at a severe temperature of 60°C, according to the method of the present disclosure, it is inferred that at a milder temperature (for example, room temperature around 25°C), an increase in internal resistance can be suitably suppressed over a further long period.

Industrial Applicability

[0056] The method of the present disclosure can be applied to all-solid-state batteries that require long-term storage, such as long-term storage in warehouses and long-term transportation on ships. By using the method of the present disclosure, an increase in internal resistance after the storage period can be suppressed. As a result, the battery used after the storage period can fully exhibit its characteristics. The method of the present disclosure can be suitably used in the field of all-solid-state batteries and the field of structures capable of mounting all-solid-state batteries.

Claims

【Claim 1】 A method for storing an all-solid-state battery, wherein the battery has lithium nickel cobalt aluminate as a positive electrode active material, wherein the battery has a sulfide as a solid electrolyte, and wherein the battery has lithium titanate as a negative electrode active material, the method including holding the voltage of the battery at a holding voltage of 0.8 volts or more and 1.0 volts or less, a method for storing an all-solid-state battery.

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