Battery safety degradation determination method and information processing device

Abstract

To identify alkaline ion rechargeable batteries with reduced safety more quickly and easily. [Solution] A method for determining the reduced safety of an alkaline-ion secondary battery, which is a secondary battery that can be charged and discharged by the movement of alkaline ions, characterized in that a distinctive indicator exhibited by a battery that has been previously judged to have reduced safety is stored in advance as a judgment criterion, and when the alkaline-ion secondary battery to be judged satisfies the judgment criterion, it is determined that the safety of the battery has reduced.

Description

[Technical Field]

[0001] This invention relates to a method for determining whether the safety of a battery has deteriorated, and to an information processing device. [Background technology]

[0002] In recent years, secondary batteries that charge and discharge by the movement of alkaline ions such as lithium ions and sodium ions (hereinafter also referred to as "alkaline ion secondary batteries") have been adopted in a wide range of products, including mobile devices such as smartphones and tablet terminals, electric vehicles, and stationary power storage devices.

[0003] For example, there are plans to reuse alkaline ion secondary batteries, which were primarily used in electric vehicles, as stationary energy storage systems. Energy storage systems generally require a longer operating life and higher reliability compared to electric vehicles. Therefore, when reusing alkaline ion secondary batteries, it is necessary to non-destructively identify batteries with reduced safety and remove them from the energy storage system.

[0004] As a method for identifying batteries with reduced safety, for example, Patent Document 1 discloses a method for detecting the safety status of a lithium-ion secondary battery, characterized by calculating the absolute value of the derivative of the discharge curve excluding the voltage drop of the lithium-ion secondary battery, determining a first battery voltage when the degree of increase in the absolute value of the derivative is greater than a threshold, determining a second battery voltage corresponding to the first battery voltage at which the oxidation heat generated inside the lithium-ion secondary battery during overcharging begins to increase, and detecting the safety status of the lithium-ion secondary battery based on the determined second battery voltage.

[0005] Furthermore, Patent Document 2 discloses a safety device for a lithium-ion battery module that includes a health monitoring component configured to detect degradation and transmit an output signal based on changes in the shape or dimensions of battery cells within the lithium-ion battery module. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-138351 [Patent Document 2] Japanese Patent Publication No. 2019-165001 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The method disclosed in Patent Document 1 considers the heat-generating point, where the inside of a lithium-ion secondary battery changes from an endothermic state to an exothermic state when overcharged within the voltage range of actual operation, as a safety point on which the lithium-ion secondary battery's degradation depends. Furthermore, the device disclosed in Patent Document 2 detects degradation based on changes in the shape or dimensions of the battery cells within the lithium-ion battery module. In other words, in both methods, by the time these events are observed, the safety of the lithium-ion secondary battery has already deteriorated, and it can be said that it is at a stage where its use in an energy storage system must be stopped. In addition, the method disclosed in Patent Document 2 requires the installation of numerous sensors such as thermocouples and strain gauges within the battery module.

[0008] This invention has been made in view of the above-mentioned problems, and aims to identify alkaline ion secondary batteries with reduced safety more quickly and easily. [Means for solving the problem]

[0009] According to one embodiment of the present invention, a method for determining the reduced safety of an alkaline-ion secondary battery is provided, characterized in that, for an alkaline-ion secondary battery which is a secondary battery capable of being charged and discharged by the movement of alkaline ions, a characteristic indicator exhibited by a battery that has been previously determined to have reduced safety is stored in advance as a determination criterion, and when the alkaline-ion secondary battery to be judged satisfies the determination criterion, it is determined that the safety of the battery has reduced.

[0010] According to the method described above, alkaline ion secondary batteries with reduced safety can be identified more quickly and easily than with conventional methods.

[0011] Preferably, the criterion is a criterion relating to the voltage of the alkaline-ion secondary battery during charging. In one embodiment, the criterion is that the battery capacity from the point in time when a predetermined voltage is exceeded until the end of charging is greater than or equal to a predetermined threshold relative to the reversible capacity of the alkaline-ion secondary battery. The threshold is, for example, 5%. Alternatively or additionally, the criterion is that the battery capacity from the point in time when the differential value of the voltage change with respect to the capacity is exceeded until the end of charging is greater than or equal to a predetermined threshold relative to the reversible capacity of the alkaline-ion secondary battery. The threshold is, for example, 14%.

[0012] According to this method, the safety of an alkaline ion secondary battery can be determined by measuring its voltage and capacity, making it simpler than conventional methods.

[0013] Preferably, the judgment criterion is a criterion relating to a value obtained by measuring the AC impedance of an alkaline ion secondary battery. In one embodiment, the judgment criterion is that the diffusion time obtained by measuring the AC impedance is greater than or equal to a predetermined threshold.

[0014] According to this method, the safety of an alkaline ion secondary battery can be determined by performing a well-known AC impedance measurement on the battery being evaluated, making it simpler than conventional methods.

[0015] Preferably, the alkaline ion secondary battery is a battery that uses carbon as the negative electrode. Also preferably, the alkaline ion secondary battery is a battery that uses lithium iron phosphate as the positive electrode.

[0016] According to another embodiment of the present invention, for an alkali ion secondary battery that can be charged and discharged by the movement of alkali ions, there is a storage unit that stores in advance, as a determination criterion, characteristic indicators presented by a battery that has been previously determined to have reduced safety, and a determination unit that determines that the safety of the alkali ion secondary battery to be determined has decreased when the battery satisfies the determination criterion. An information processing apparatus including the same is provided.

Effects of the Invention

[0017] According to the present invention, it is possible to more quickly and easily identify an alkali ion secondary battery with reduced safety.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram showing a functional block configuration of an information processing apparatus according to an embodiment of the present invention. [Figure 2] It is a diagram showing a hardware configuration of an information processing apparatus according to an embodiment of the present invention. [Figure 3] (a) shows the transition of the capacity and battery voltage during charging and discharging of an alkali ion secondary battery that has been previously determined to have reduced safety, and (b) shows the transition of the capacity and battery voltage during charging and discharging of an alkali ion secondary battery that has been previously determined to be safe. [Figure 4] (a) and (b) are diagrams plotting the relationship between SOH and ΔSOC for a group of alkali ion secondary batteries that have been previously determined to have reduced safety and a group of alkali ion secondary batteries that have been previously determined to be safe. [Figure 5] It is a Nyquist diagram showing the results of performing AC impedance measurement on an alkali ion secondary battery that has been previously determined to have reduced safety and an alkali ion secondary battery that has been previously determined to be safe. [Figure 6](a) is a plot of the relationship between SOH and diffusion resistance Rdif for a group of alkaline ion secondary batteries that were judged to have reduced safety in advance, and for a group of alkaline ion secondary batteries that were judged to have safe safety in advance, and (b) is a plot of the relationship between SOH and diffusion time Tdif. [Modes for carrying out the invention]

[0019] One embodiment of the present invention will be described below with reference to the diagram.

[0020] Figure 1 is a diagram showing the functional block configuration of an information processing device according to one embodiment of the present invention. Figure 2 shows the hardware configuration of an information processing device according to one embodiment of the present invention.

[0021] The information processing device 2 is a device that has a function to determine whether or not the safety of an alkaline-ion secondary battery has deteriorated (hereinafter referred to as the "safety deterioration determination function"). Examples of alkaline-ion secondary batteries include lithium-ion batteries and sodium-ion batteries.

[0022] Information processing device 2 is implemented by a program processing device (computer), such as a server or a personal computer (PC). Information processing device 2 determines whether the safety of the alkaline ion secondary battery to be evaluated has deteriorated by performing data processing according to the installed program.

[0023] As shown in Figure 1, the information processing device 2 includes a voltage / capacitance measurement unit 20, an AC impedance measurement unit 22, a determination unit 24, an output unit 26, and a storage unit 30 as functional blocks for realizing the safety degradation determination function. Each of these functional blocks is realized through the cooperation of the hardware resources constituting the information processing device 2 shown in Figure 2 with the software installed on the information processing device 2 (various programs including the program related to the safety degradation determination function), as will be described later. The hardware configuration of the information processing device 2 will be described below.

[0024] As shown in Figure 2, the information processing device 2 includes, for example, a computing device 102, a storage device 104, an I / F (Interface) device 110, and a bus 112 as hardware resources.

[0025] The arithmetic unit 102 is composed of processors such as a CPU (Central Processing Unit) and a DSP (Digital Signal Processor). The storage device 104 has a storage area for storing a program 106 that causes the arithmetic unit 102 to perform various data processing operations and data 108 used in the data processing by the arithmetic unit 102, and is composed of, for example, ROM (Read Only Memory), RAM (Random Access Memory), HDD, and flash memory.

[0026] The program 106 stored in the storage device 104 includes a program for implementing the basic functions of the information processing device 2, as well as a program for the information processing device 2 to implement the safety degradation determination function. Furthermore, by installing the program 106 in an existing storage device 104, the safety degradation determination method for alkaline ion secondary batteries according to this embodiment can be implemented. In this case, it is not necessary to reconfigure the hardware configuration of the storage device 104 in order to execute the safety degradation determination method for alkaline ion secondary batteries.

[0027] The data 108 stored in the storage device 104 includes, for example, various parameters used for data processing by the arithmetic unit 102, as well as measurement results and judgment results, which will be described later.

[0028] Furthermore, program 106 and data 108 may be distributed via a network, or they may be written to a computer-readable storage medium such as a CD-ROM or memory card and distributed therein.

[0029] The I / F device 110 is a device that transmits and receives data to and from the outside, and consists of, for example, a communication control circuit, input / output ports, and an antenna for wired or wireless communication. The information processing device 2 can also control the charging and discharging of the alkaline-ion secondary battery using an external charging circuit via the I / F device 110, acquire the voltage and charge status of the alkaline-ion secondary battery, and operate external FFT analyzers, AC impedance analyzers, etc.

[0030] Bus 112 interconnects the arithmetic unit 102, the storage device 104, and the I / F device 110, enabling the transmission and reception of data between these devices.

[0031] The information processing device 2 implements each functional block of the information processing device 2 shown in Figure 1 by having the arithmetic unit 102 perform calculations according to the program 106 stored in the storage device 104 and by controlling the storage device 104, the I / F device 110, and the bus 112.

[0032] Although not shown in the diagram, the information processing device 2 may, if necessary, include an input device for detecting input of information from an external source, and an output device for outputting information obtained through data processing by the arithmetic unit 102.

[0033] The information processing device 2 may be configured as a dedicated device for determining the deterioration of the safety of an alkaline-ion secondary battery, or it may be a device incorporated into a product that utilizes an alkaline-ion secondary battery, such as a stationary power storage device.

[0034] The following describes in detail each functional block of the information processing device 2.

[0035] The voltage / capacity measurement unit 20 is a functional unit for acquiring measurement results of the voltage and capacity of the alkaline-ion secondary battery to be evaluated during charging and discharging. The voltage / capacity measurement unit 20 works in cooperation with, for example, a device that controls the charging and discharging of the alkaline-ion secondary battery to be evaluated, to acquire the voltage and capacity of the battery during charging and discharging.

[0036] The AC impedance measurement unit 22 is a functional unit for obtaining the results of AC impedance measurements for the alkaline ion secondary battery to be evaluated.

[0037] The determination unit 24 determines that the safety of the battery being measured is compromised if the measurement results obtained by the voltage / capacity measurement unit 20 and / or the measurement results obtained by the AC impedance measurement unit 22 meet the determination criteria stored in the memory unit 30, and determines that the battery is safe if the criteria are not met.

[0038] The output unit 26 outputs the result of the determination made by the determination unit 24.

[0039] The memory unit 30 pre-stores characteristic indicators exhibited by alkaline ion secondary batteries that have been previously determined to have reduced safety, as criteria for determining safety. Examples of the criteria will be described below with reference to Figures 3 to 6.

[0040] Example 1 Figure 3(a) shows the changes in capacity (C) and battery voltage during charging (D) and discharging (D) of alkaline ion secondary batteries that were judged to have reduced safety, while Figure 3(b) shows the changes in capacity (C) and battery voltage (D) during charging (C) and discharging (D) of alkaline ion secondary batteries that were judged to be safe. Furthermore, the safety of each battery was determined individually by disassembling and analyzing each secondary battery and based on the presence or absence of battery swelling, abnormal heat generation, non-uniform deposition of alkali metals in the negative electrode, etc.

[0041] As can be seen from Figure 3, in batteries judged to be safe, the voltage rise at the end of charging (in this case, after the voltage reaches 3.4V) is rapid (see the shaded area in Figure 3(b)), whereas in batteries judged to be less safe, the voltage rise at the end of charging (after the voltage reaches 3.4V) is gradual (see the shaded area in Figure 3(a)). The inventors of this application considered that if a gradual voltage rise at the end of charging could be detected, it would be possible to detect batteries with reduced safety.

[0042] The first indicator for detecting the voltage rise at the end of charging is the ratio of the increase in capacity from the point where the voltage is nearly constant during charging to the end of charging, to the reversible capacity of the battery. In the example in Figure 3(a), the increase in capacity from when the voltage exceeds 3.4V to the end of charging is 15Ah, so the ratio ΔSOC to the reversible capacity of 170Ah is ΔSOC = 15 / 170 = 8.8%. In the example in Figure 3(b), the increase in capacity from when the voltage exceeds 3.4V to the end of charging is 1Ah, so the ratio ΔSOC to the reversible capacity of 170Ah is ΔSOC = 1 / 170 = 0.6%. It is thought that by calculating ΔSOC for each group of alkaline-ion secondary batteries, one group is possible to distinguish between those judged to have reduced safety and those judged to be safe.

[0043] A second indicator for detecting the voltage rise at the end of charging is the ratio of the increase in capacity from the point when the differential value of the voltage change with respect to capacity, dV / dQ, exceeds a predetermined value until the end of charging, to the battery's reversible capacity. In the example in Figure 3, dV / dQ > 1mV / Ah was defined as the point at which the voltage transitioned from being nearly constant to increasing during charging. It is thought that the two groups can be distinguished by calculating ΔSOC for each group of alkaline-ion secondary batteries, one group that was previously judged to have reduced safety and the other that was previously judged to be safe.

[0044] In the example above, the voltage remains almost constant at 3.4V during charging. However, this is merely one example of an alkaline-ion secondary battery that uses lithium iron phosphate as the positive electrode and carbon as the negative electrode (LFP / Gr battery). This voltage is determined appropriately through experiments, simulations, etc., depending on the constituent materials and capacity of the alkaline-ion secondary battery.

[0045] Furthermore, a similar trend is observed during the discharge of alkaline ion rechargeable batteries as during charging. Specifically, batteries deemed safe exhibit a rapid voltage drop at the end of discharge (in this case, after the voltage reaches 3.1V) (see "D" in Figure 3(b)), while batteries deemed unsafe exhibit a gradual voltage drop at the end of discharge (after the voltage reaches 3.1V) (see "D" in Figure 3(a)). However, the difference between the two is not as pronounced as during charging.

[0046] Figure 4(a) plots the relationship between SOH (State of Health, capacity retention rate) and ΔSOC in the region where the voltage exceeds 3.4V during charging for two groups of alkaline-ion secondary batteries: one group that was judged to have reduced safety and another that was judged to be safe. The circles in the figure represent data for the battery group that was judged to have reduced safety, while the other marks represent data for the battery group that was judged to be safe.

[0047] As can be seen from the figure, all batteries judged to have reduced safety had a ΔSOC of 5% or higher. Therefore, a ΔSOC of ≥ 5% can be used as a criterion for determining reduced safety. Furthermore, a simple decrease in SOH does not necessarily correlate with a decrease in battery safety, highlighting the importance of using ΔSOC as an indicator.

[0048] Figure 4(b) plots the relationship between SOH and ΔSOC in the region where dV / dQ exceeds a predetermined threshold (in this case, 1mV / Ah) during charging, for a group of alkaline-ion secondary batteries that were judged to have reduced safety and a group of alkaline-ion secondary batteries that were judged to be safe. The marks in the figure are the same as in Figure 4(a).

[0049] As can be seen from the figure, all batteries judged to have reduced safety had a ΔSOC of 14% or higher. Therefore, ΔSOC ≥ 14% can be used as a criterion for determining reduced safety. Furthermore, a simple decrease in SOH does not necessarily correlate with a decrease in battery safety, highlighting the importance of using ΔSOC as an indicator.

[0050] Example 2 Figure 5 is a Nyquist diagram showing the results of AC impedance measurements performed on an alkaline-ion secondary battery that was previously judged to have reduced safety (labeled "A" in Figure 5) and an alkaline-ion secondary battery that was previously judged to be safe (labeled "B" in Figure 5). The horizontal axis represents the real part of the impedance, and the vertical axis represents the imaginary part of the impedance. Since AC impedance measurement is a measurement method well known to those skilled in the field of batteries, a detailed explanation is omitted. Furthermore, the safety of each battery was determined individually by disassembling and analyzing each secondary battery and based on the presence or absence of battery swelling, abnormal heat generation, non-uniform deposition of alkali metals in the negative electrode, etc.

[0051] As shown in Fig. 5, the battery "A" with reduced safety and the safe battery "B" show clearly different trends in the Nyquist plot. That is, in the battery with reduced safety, in the straight-line part with a positive slope, the interval between plots is longer than that of the safe battery. This means that in the battery with reduced safety, the diffusion resistance R dif is larger and the diffusion time T dif tends to be longer than that of the safe battery.

[0052] Fig. 6(a) is a graph in which AC impedance measurements were respectively performed on a group of alkaline ion secondary batteries pre-judged to have reduced safety and a group of alkaline ion secondary batteries pre-judged to be safe, and the relationship between SOH and diffusion resistance R dif was plotted. The circles in the figure are the data of the battery group pre-judged to have reduced safety, and the other marks are the data of the battery group pre-judged to be safe.

[0053] As can be seen from the figure, in the batteries pre-judged to have reduced safety, the diffusion resistance R dif was 1.6×10 -4 Ω or more in all cases. Therefore, R dif ≥1.6×10 -4 Ω can be used as a criterion for judging reduced safety. Also, a mere decrease in SOH does not necessarily correlate with a decrease in battery safety, and the importance of using R dif as an index can be understood.

[0054] Fig. 6(b) is a graph in which AC impedance measurements were respectively performed on a group of alkaline ion secondary batteries pre-judged to have reduced safety and a group of alkaline ion secondary batteries pre-judged to be safe, and the relationship between SOH and diffusion time T dif was plotted. The marks in the figure are the same as those in Fig. 6(a).

[0055] As can be seen from the figure, in the batteries pre-judged to have reduced safety, the diffusion time Tdif The duration was 5 seconds or longer. Therefore, T dif A threshold of ≥5 seconds can be used as a criterion for determining a decrease in safety. Furthermore, a simple decrease in SOH does not necessarily correlate with a decrease in battery safety. dif This highlights the importance of using this as an indicator.

[0056] As described above, according to the present invention, it becomes possible to identify alkaline ion secondary batteries with reduced safety status earlier and more easily than in the past, using a non-destructive method.

[0057] The present invention is effective in situations such as the following: 1. When reusing alkaline-ion secondary batteries that were primarily used in electric vehicles and mobile devices as stationary energy storage systems, it is possible to identify and remove batteries with reduced safety from among the many alkaline-ion secondary batteries before incorporating them into the energy storage system. This makes it possible to operate the energy storage system more stably and for a longer period of time. 2. When operating a stationary energy storage system that reuses alkaline ion secondary batteries that were primarily used in electric vehicles and mobile devices, it is possible to identify batteries with reduced safety from among the batteries incorporated into the system. In this case, it is possible to remove the batteries with reduced safety and reconstruct the energy storage system, or, for batteries that are judged to have reduced safety, it is possible to take preventive measures such as easing the charging speed to extend the battery life or operating the batteries in a relatively good charging environment.

[0058] Since secondary batteries typically used in electric vehicles are thought to contain a relatively large number of batteries with reduced safety, this invention is particularly effective when reusing batteries from electric vehicle applications for energy storage applications.

[0059] As described in the above examples, ΔSOC≧5%, ΔSOC≧14%, R dif ≥ 1.6 × 10 -4 Ω, Tdif The threshold of ≥5 sec is merely one example for alkaline ion secondary batteries that use lithium iron phosphate as the positive electrode and carbon as the negative electrode (LFP / Gr battery). These thresholds should be set appropriately according to the characteristics of the battery being evaluated. In other words, for multiple batteries with the same characteristics, the characteristic values ​​of batteries with reduced safety and batteries that are safe are plotted, and the threshold is set to a value that clearly distinguishes between the two.

[0060] The method according to the present invention may be implemented in a control device that manages the charge state and voltage of an alkaline ion secondary battery, which is typically installed in alkaline ion secondary batteries used in mobile devices, electric vehicles, and stationary power storage devices. In this case, the program for implementing the above method may be pre-installed in such a control device, or it may be installed later in a control device for a battery that is already on the market. [Explanation of Symbols]

[0061] 2... Information processing unit, 20... Voltage / capacitance measuring unit, 22... AC impedance measuring unit, 24... Judgment unit, 102... Calculation unit, 104... Memory device, 110... I / F device.

Claims

1. Regarding alkaline-ion rechargeable batteries, which are rechargeable batteries that can be charged and discharged by the movement of alkaline ions, characteristic indicators exhibited by batteries that have been previously judged to have reduced safety are stored in advance as criteria for judgment. A method for determining a decrease in battery safety, characterized in that, when the alkaline ion secondary battery to be judged meets the aforementioned judgment criteria, it is determined that the safety of the battery has deteriorated.

2. The method for determining a decrease in safety according to claim 1, characterized in that the judgment criterion is a criterion relating to the voltage of an alkaline ion secondary battery during charging.

3. The safety degradation determination method according to claim 2, wherein the determination criterion is that the battery capacity from the point in time when a predetermined voltage is exceeded during charging of an alkaline ion secondary battery until the end of charging is equal to or greater than a predetermined threshold relative to the battery's reversible capacity.

4. The method for determining a decrease in safety according to claim 3, wherein the threshold is 5% of the battery's reversible capacity.

5. The safety degradation determination method according to claim 2, wherein the determination criterion is that the battery capacity from the point in time when the differential value of the voltage change with respect to the capacity exceeds a predetermined value during charging of an alkaline ion secondary battery until the end of charging is equal to or greater than a predetermined threshold relative to the reversible capacity of the battery.

6. The method for determining a decrease in safety according to claim 5, wherein the threshold is 14% of the battery's reversible capacity.

7. The method for determining a decrease in safety according to claim 1, characterized in that the judgment criterion is a criterion relating to a value obtained by measuring the AC impedance to an alkaline ion secondary battery.

8. The method for determining a decrease in safety according to claim 7, wherein the determination criterion is that the diffusion time obtained by the AC impedance measurement is greater than or equal to a predetermined threshold.

9. The method according to any one of claims 1 to 8, characterized in that the alkaline ion secondary battery is a battery using carbon as the negative electrode.

10. The method according to any one of claims 1 to 8, characterized in that the alkaline ion secondary battery is a battery using lithium iron phosphate as the positive electrode.

11. Regarding alkaline ion rechargeable batteries, which are rechargeable batteries that can be charged and discharged by the movement of alkaline ions, a memory unit is provided in advance that stores characteristic indicators exhibited by batteries that have been judged to have reduced safety as judgment criteria. A determination unit determines that the safety of an alkaline ion secondary battery subject to evaluation has deteriorated when the aforementioned determination criteria are met, An information processing device equipped with the following features.

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