JP2023138351A - Lithium ion secondary battery safety state detection method, device, system, power storage device, power supply device, drive device, power control device, power balance adjustment device, and program - Google Patents

Abstract

To provide a lithium ion secondary battery safety state detection method that can detect signs of an unsafe state of a lithium ion secondary battery.SOLUTION: A lithium ion secondary battery safety state detection method includes calculating an absolute value of a differential coefficient of a discharge curve excluding the voltage drop of lithium ion secondary battery, determining a first battery voltage when the degree of increase in the absolute value of the differential coefficient is greater than a threshold, determining a second battery voltage at which oxidation heat generated inside the lithium ion secondary battery starts to increase when the lithium ion secondary battery is overcharged, corresponding to the first battery voltage, and detecting the safety state of the lithium ion secondary battery on the basis of the determined second battery voltage.SELECTED DRAWING: Figure 18

Description

The present invention relates to a method, device, system, power storage device, power supply device, drive device, power control device, power balance adjustment device, and program for detecting a safe state of a lithium ion secondary battery.

In recent years, demand for lithium ion secondary batteries has been increasing as power sources for mobile devices, hybrid vehicles, electric vehicles, power storage, etc. Since lithium ion secondary batteries are storage batteries with high energy density per weight, concerns about the safety of the battery when the battery is overcharged have become a constant issue.

To address such problems, there has been a conventional technique for detecting the safety state of lithium ion secondary batteries. For example, Patent Document 1 discloses a technique for cooling a secondary battery that has abnormally generated heat when a sensor that detects an abnormal temperature change in a lithium ion secondary battery detects an abnormal temperature change in the secondary battery.

However, in conventional systems for detecting the safe state of lithium-ion secondary batteries, the unsafe state of the lithium-ion secondary battery is determined only after the lithium-ion secondary battery has transitioned to the unsafe state or immediately before the transition. I can't.

An object of the present invention is to provide a method for detecting a safe state of a lithium ion secondary battery that can detect signs of an unsafe state of the lithium ion secondary battery.

One aspect of the present invention is a method for detecting the safety state of a lithium ion secondary battery, comprising: calculating the absolute value of a differential coefficient of a discharge curve excluding a voltage corresponding to a voltage drop of the lithium ion secondary battery; A first battery voltage is determined when the degree of increase in the absolute value of the differential coefficient is larger than a threshold value, and, corresponding to the first battery voltage, the voltage inside the lithium ion secondary battery is determined when the lithium ion secondary battery is overcharged. The second battery voltage at which the generated oxidation heat starts to increase is determined, and the safe state of the lithium ion secondary battery is detected based on the determined second battery voltage.

According to one aspect of the present invention, a sign of an unsafe state of a lithium ion secondary battery can be detected.

The relationship between the amount of electricity charged or the amount of electricity discharged and the voltage of a lithium ion battery cell (when the electrolyte does not contain a methacrylic acid compound) is shown. The relationship between the amount of charged electricity or the amount of discharged electricity and voltage of a lithium ion battery cell (when the electrolyte contains a methacrylic acid compound) is shown. The relationship between the capacity of a secondary battery (when the positive electrode capacity decreases) and the positive and negative electrode potentials is shown. The relationship between the capacity of a secondary battery (when the negative electrode capacity decreases) and the positive and negative electrode potentials is shown. The relationship between the capacity of a secondary battery (when the state of charge between the positive and negative electrodes is different) and the positive and negative electrode potentials is shown. This shows the relationship between the capacity and voltage of a lithium ion battery. This shows temperature changes during charging and discharging of a lithium ion battery. It shows temperature changes during charging and discharging (4.8V) of a lithium ion battery. The relationship between the charging voltage and the irreversible amount of electricity of a lithium ion battery is shown. The relationship between capacity and voltage of a degraded lithium ion battery is shown. This figure shows the relationship between the amount of electricity stored in a deteriorated lithium-ion battery and the voltage at which it starts to generate heat during charging. Charging and discharging curves of lithium-ion batteries whose storage capacity varies depending on deterioration are shown. The relationship between the voltage that increases the slope of the discharge curve and the voltage that causes heat generation is shown. This figure shows a charge/discharge curve in an environment where the internal resistance of a lithium ion battery changes. The relationship between battery temperature, state of charge, and internal resistance in a lithium ion battery is shown. This shows changes in the current flowing through a lithium-ion battery. This shows the change in internal resistance of a lithium-ion battery. 3 is a flowchart for implementing a method for detecting the safety state of a lithium ion secondary battery. 1 is an example of a safety state detection system according to an embodiment of the present invention. 1 is an example of a power storage device according to an embodiment of the present invention. 1 is an example of a use of a lithium ion secondary battery according to an embodiment of the present invention. 1 is an example of a use of a lithium ion secondary battery according to an embodiment of the present invention. 1 is an example of a use of a lithium ion secondary battery according to an embodiment of the present invention. 1 is an example of a use of a lithium ion secondary battery according to an embodiment of the present invention. 1 is an example of a hardware configuration of a safety state detection device according to an embodiment of the present invention. 1 is an example of a functional configuration of a safety state detection device according to an embodiment of the present invention.

Embodiments of the present invention will be described below. FIG. 18 is a flowchart for implementing a method for detecting the safety state of a lithium ion secondary battery.

The safety state detection method for a lithium ion secondary battery (hereinafter sometimes referred to as a safety state detection method or detection method) according to the present embodiment is a method for detecting the safety state of a lithium ion secondary battery.

The inventor discovered that when a lithium-ion secondary battery in actual operation is overcharged, the point at which the battery internally changes from an endothermic state to a heat-generating state depends on the deterioration of the lithium-ion secondary battery. We have discovered a method to predict the unsafe state of lithium-ion secondary batteries from points.

Specifically, in a lithium-ion battery cell that does not contain a methacrylic acid compound in its electrolyte, after the charge amount exceeds 170% during overcharging, the battery surface temperature increases and gas is generated inside the battery, causing the battery to become airtight. As a result of the destruction, no discharge can occur (Figure 1).

On the other hand, lithium ion battery cells containing a methacrylic acid compound in the electrolyte do not show any voltage increase during overcharging and do not generate gas. Even after overcharging by 250%, it can be discharged and a sufficient discharge capacity can be obtained (Figure 2).

Lithium ion battery cells that contain a methacrylic acid compound in the electrolyte have a faster timing than those that do not contain a methacrylic acid compound, specifically because the battery surface temperature increases from around 130% charge during overcharging. It is understood that an oxidation reaction is occurring inside the battery even if no gas is generated.

However, even if the battery voltage is the same, the chargeable and dischargeable capacity of a lithium-ion secondary battery decreases as the number of battery cycles increases, and the state of charge between the positive and negative electrodes may shift due to side reactions or self-discharge within the battery. (Figures 3 to 5).

Therefore, based on the relationship between the charge/discharge capacity and battery voltage of a lithium ion secondary battery, we verified whether it was possible to detect heat generation points in the overcharge region within the operating voltage range (Figure 6).

Generally, it is known that in a lithium ion secondary battery, when the stoichiometric composition of Li decreases due to charging, the crystalline state of Li _1-x MO ₂ cannot be maintained and O is released. Therefore, in the overcharge region, oxygen is released due to oxidation (heat generation) at the positive electrode due to the oxidation of the positive electrode active material Li _1-x MО ₂ or the oxidation of the electrolyte (LiPF ₆ or carbonate solvent), and the released oxygen This is thought to cause the negative electrode to oxidize (generate heat).

In addition, in a lithium ion secondary battery, heat is generated by oxidation of the positive and negative electrodes, heat is absorbed by reduction, and the battery temperature increases or decreases by the sum of these factors. Note that in this embodiment, a lithium ion secondary battery was used that absorbs heat during charging and generates heat during discharging (FIG. 7).

In this embodiment, when the target lithium ion secondary battery was charged and discharged at 4.8V, when the voltage exceeded 4.64V during charging (heat absorption), the battery temperature started to increase and the charging reaction of the active material occurred. It was confirmed that there was an oxidation other than the oxidation caused by (Fig. 8).

Furthermore, from the following formula (1), the relationship between the charging voltage and the irreversible amount of electricity of the target lithium ion battery is shown (FIG. 9).
(Amount of charged electricity - Amount of discharged electricity)/Amount of discharged electricity x 100...(1)

In the above formula (1), (charged electricity amount - discharged electricity amount) depends on the number of moles of reactions (side reactions) that occur other than the charging reaction, and the discharged electricity amount is the mole of the stored charging reaction. Depends on the number. FIG. 9 shows that, as indicated by the arrow, another reaction other than the charging reaction is included, and this part is considered to be involved in the increase in battery temperature.

It was also confirmed that the voltage at which the absolute value of the voltage slope begins to change significantly at the end of discharge varies depending on battery deterioration (FIG. 10). Note that in FIG. 10, Type A is an unused cell. Type B is a cell after deterioration due to charging and discharging at 40° C. and 4.2V to 1.0V. Type C is a cell after deterioration due to charging and discharging at 60° C. and 4.2V to 1.0V.

It was also found that there is a correlation between the amount of electricity stored in a deteriorated battery and the voltage at which it starts to generate heat during charging (Figure 11). From this correlation, whether the correlation remains even if the stress that causes battery deterioration (for example, repeated charging and discharging) changes, or whether the electrode potential cannot be estimated because the voltage changes due to deterioration, or whether the measured value within the range of use We verified whether safety points could be detected.

In this embodiment, a safety point is detected from the charge/discharge curve of a lithium ion battery whose storage capacity differs due to deterioration (FIG. 12). Specifically, the unsafe state at the time of overcharging is predicted from the discharge curve by using the correlation between the battery storage amount, the point at which the first derivative of the discharge curve increases, and the point at which the overcharge temperature increases (FIG. 13).

Furthermore, in this embodiment, a charge/discharge curve was created in an environment where the internal resistance of the lithium ion battery changes (FIG. 14). The measured battery voltage of the lithium ion secondary battery is obtained from the following equation (2).
[Battery voltage (measured)] = [electrode potential difference (excluding voltage drop)] ±iR... (2)
(However, +i indicates charging, -i indicates discharging)

Here, the voltage drop is the voltage of the lithium ion secondary battery when a current i is passed through the lithium ion secondary battery with internal resistance R, from the high voltage part (+ terminal) to the low voltage part (- terminal ) When a current is caused to flow in the external circuit in the forward direction (discharging), the voltage drops by iR from the equilibrium potential of the electrochemical device. When current flows in the opposite direction from the - terminal to the + terminal in the external circuit (when charging), an overvoltage occurs by iR.

Moreover, FIG. 15 shows the relationship among battery temperature, state of charge, and internal resistance in a lithium ion battery. FIG. 16 shows changes in the current flowing through the lithium ion battery. FIG. 17 shows the change in internal resistance of the lithium ion battery obtained from FIGS. 15 and 16. It can be seen from FIG. 17 that the internal resistance of the lithium ion secondary battery does not change easily over time, and becomes approximately constant as the electric capacity of the lithium ion secondary battery increases.

The present invention was obtained from such findings.

FIG. 18 is a flowchart for implementing a method for detecting a safe state of a lithium ion secondary battery (hereinafter referred to as a safe state detecting method) according to this embodiment. In the safe state detection method of this embodiment, first, the absolute value of the differential coefficient (discharge voltage differential coefficient) of the discharge curve excluding the voltage drop of the lithium ion secondary battery is calculated (FIG. 18, step S1). .

The lithium ion secondary battery used in the safe state detection method of this embodiment includes a serially assembled battery of one cell or two or more cells. The lithium ion secondary battery of this embodiment has a flowing current that changes with elapsed time, and may be a used lithium ion secondary battery. Here, "used" means something that has been substantially used at least once and can be reused.

A lithium ion secondary battery is a type of nonaqueous electrolyte battery that uses an ionically conductive electrolyte solution (for example, an electrolyte solution in which a lithium salt or the like is dissolved) in an aprotic organic solvent as an electrolyte solution.

In this embodiment, the type of lithium ion secondary battery is not limited, but preferably, the positive electrode active material used in the positive electrode contains a lithium transition metal oxide containing manganese, and the negative electrode is made of a carbon material. A lithium-ion secondary battery is used. In this lithium ion secondary battery, lithium ions are deintercalated and occluded at the positive electrode, and lithium ions are intercalated and deintercalated at the negative electrode, thereby performing charging and discharging.

In lithium ion secondary batteries, a carbon material capable of intercalating and deintercalating lithium ions is used as a negative electrode active material, and a lithium-containing metal oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ is used as a positive electrode active material. used.

In this embodiment, the positive electrode active material of the lithium ion secondary battery is not particularly limited, but Li _x MO ₂ (where M is a transition metal, and when the lithium ion secondary battery is charged to 3.8V, x<0 .5).

In this specification, the voltage corresponding to the voltage drop is obtained by subtracting the product of the current flowing through the lithium ion secondary battery and the internal resistance of the lithium ion secondary battery from the voltage of the lithium ion secondary battery.

In the discharge curve, when the amount of electricity stored in the lithium ion secondary battery is X (Ah), the voltage for the voltage drop is when the absolute value of the current flowing through the lithium ion secondary battery satisfies the condition of X (A) or more. Preferably, the discharge curve is updated (where X is a positive real number).

The absolute value of the differential coefficient of the discharge curve indicates the slope of voltage change during discharge.

In addition, in the safe state detection method of this embodiment, the conditions for implementing the safe state detection method or the obtained results are displayed on a screen (not shown) before calculating the absolute value of the discharge voltage differential coefficient. It's okay. Further, the absolute value of the obtained discharge voltage differential coefficient may be recorded in a memory (not shown) in an input/output manner.

In the safe state detection method of this embodiment, next, the first detection is performed when the absolute value of the differential coefficient starts to increase rapidly (that is, the degree of increase in the absolute value of the discharge voltage differential coefficient is greater than the threshold value). Find the battery voltage. Specifically, it is determined whether the degree of increase in the absolute value of the discharge voltage differential coefficient calculated in step S1 is greater than a threshold value (FIG. 18, step S2).

In addition, if it is determined that the degree of increase in the absolute value of the discharge voltage differential coefficient is greater than the threshold value, the absolute value of the differential coefficient begins to increase rapidly (in other words, the degree of increase in the absolute value of the discharge voltage derivative (bigger than the threshold value), the first battery voltage is determined. Specifically, the differential coefficient increase voltage V _dcp during discharging is determined as the first battery voltage (FIG. 18, step S3). The differential coefficient increase voltage V _dcp during discharge corresponds to the point at which the first-order differential coefficient of the discharge curve increases.

Note that the absolute value of the differential coefficient that has started to increase rapidly is preferably 1.5 times or more, more preferably 1.8 times or more, and even more preferably is 2.0 times or more.

For example, if the time taken for a lithium-ion secondary battery to start discharging from full charge until it becomes empty is set as 100, then the nth and n+1th discharge voltage differentials are obtained when the time is sampled at time intervals divided by 100. Comparing the absolute values of the coefficients, the absolute value of the n+1th discharge voltage differential coefficient is 1.5 times (preferably 1.8 times, more preferably 2.0 times) the absolute value of the nth discharge voltage differential coefficient. double), it is determined that there has been a sudden decrease.

In other words, the degree of increase in the absolute value of the discharge voltage differential coefficient is calculated from the absolute value of the discharge voltage differential coefficient calculated one step before the absolute value of the discharge voltage differential coefficient calculated in step 1S1. It is the degree of increase in the absolute value of the voltage differential coefficient. The threshold value for the degree of increase in the absolute value of the discharge voltage differential coefficient is preferably 1.5 times, more preferably 1.8 times, and even more preferably 2.0 times.

Further, if it is determined in step S2 that the discharge voltage differential coefficient is less than or equal to the threshold value, the process returns to step S1.

Next, in correspondence to the first battery voltage determined in step S3, a second battery voltage is determined at which the oxidation heat generated inside the lithium ion secondary battery starts to increase when the lithium ion secondary battery is overcharged. Specifically, an unsafe sign point V _USP is calculated as the second battery voltage (FIG. 18, step S3). The unsafe sign point V _USP corresponds to the above-mentioned overcharge temperature increase point (heat generation point in the overcharge region).

The second battery voltage (unsafe sign point V _USP ) can be estimated, for example, by substituting the first battery voltage (differential coefficient increase voltage at discharge V _dcp ) into the model equation shown in equation (3) below. It will be done.
V _USP = -0.2310V _dcp +5.1957...(3)

The approximate formula representing V _USP varies depending on the type and design of the lithium-ion battery, and for a particular lithium-ion battery, it is calculated by calculating the voltage at which heat absorption changes to heat generation during overcharging of cells with different deterioration and the slope of the voltage at the end of discharge. It is defined by looking at the voltage at which the absolute value begins to change significantly.

Next, the safe state of the lithium ion secondary battery is detected based on the second battery voltage (unsafe sign point V _USP ) obtained in step S4. Specifically, the safety level of the lithium ion secondary battery is calculated, and the safety level of the lithium ion secondary battery is ranked into A, B, and C (FIG. 18, step S5).

The threshold for ranking is, for example, the condition that rank A is "currently safe" [V _USP > β _A (β _A = 4.60V)], and the condition that rank B is "might become unsafe in the near future". [V _USP > β _B (β _B = 4.57V)], rank C is the condition that "there is a high possibility that an unsafe event will occur, it is necessary to stop using it and replace the battery" [V _USP > β _C (β _C =4.55V)] and determine the rank (FIG. 18, step S6).

If the rank is determined to be A in step S6, the process returns to step S1 and the absolute value of the discharge voltage differential coefficient is calculated. If the rank determination is B, the process proceeds to step S7, where it is determined that the lithium ion secondary battery is at the "unsafe sign level," and the process further returns to step S1, where the absolute value of the discharge voltage differential coefficient is calculated. If the rank is determined to be B, the process proceeds to step S8, where it is determined that the lithium ion secondary battery is at the "unusable level," and the implementation of the safe state detection method is ended.

In addition, in the safe state detection method of this embodiment, the absolute value of the obtained discharge voltage differential coefficient, the first battery voltage (differential coefficient increase voltage V _dcp during discharge), and the second battery voltage (unsafe sign point V _USP ), ranking thresholds, and safety level determination results may be displayed on a screen (not shown).

In addition, the absolute value of the obtained discharge voltage differential coefficient, the first battery voltage (differential coefficient increase voltage during discharge V _dcp ), the second battery voltage (unsafe sign point V _USP ), the threshold for ranking, and the safety level The determination result may be recorded in a memory (not shown) in an input/output manner.

Furthermore, the amount of power that can be stored in the lithium ion secondary battery can be predicted based on the first battery voltage. Specifically, it is determined that the higher the first battery voltage (discharging differential coefficient increase voltage V _dcp ), the higher the discharge capacity of the lithium ion secondary battery.

The safe state detection method of this embodiment is controlled by a computer having, for example, a CPU (Central Processing Unit), a storage device, and an input interface for receiving signals from external devices such as a keyboard. Good too.

In the safe state detection method of the present embodiment, as described above, when the absolute value of the differential coefficient of the discharge curve excluding the voltage corresponding to the voltage drop of the lithium ion secondary battery starts to increase rapidly, Find the voltage. Furthermore, a second battery voltage, corresponding to this first battery voltage, at which oxidation heat generated inside the lithium ion secondary battery when overcharged starts to increase is determined. Then, the safe state of the lithium ion secondary battery is detected based on the determined second battery voltage.

As a result, the heat generation point where the inside of the battery changes from an endothermic state to a heat generating state when the lithium ion secondary battery is overcharged within the voltage range in actual operation can be regarded as a safety point where the lithium ion secondary battery is dependent on deterioration. I can do it. Therefore, according to the present embodiment, it is possible to detect a sign of an unsafe state of the lithium ion secondary battery during actual operation, so it is possible to predict the time to replace the lithium ion secondary battery, etc.

In the safe state detection method of this embodiment, as described above, the absolute value of the differential coefficient that has started to increase rapidly is 1.5 times or more of the absolute value of the differential coefficient immediately before it started to increase rapidly. , it is possible to accurately identify the point of heat generation when a lithium-ion secondary battery is overcharged. Therefore, according to the present embodiment, signs of an unsafe state of the lithium ion secondary battery can be detected with high accuracy.

In the safe state detection method of this embodiment, as described above, the voltage for the voltage drop is changed from the voltage of the lithium ion secondary battery to the current flowing to the lithium ion secondary battery and the internal resistance of the lithium ion secondary battery. The product is subtracted. This makes it possible to accurately determine the point of heat generation during overcharging, even when a lithium-ion secondary battery is in actual use. Therefore, signs of an unsafe state of the lithium ion secondary battery can be detected with high accuracy.

In the safe state detection method of this embodiment, as described above, when the amount of electricity stored in the lithium ion secondary battery is X (Ah), the voltage for the voltage drop is the absolute value of the current flowing through the lithium ion secondary battery. When satisfies the condition that is greater than or equal to X(A), the discharge curve is updated (X is a positive real number). Thereby, the discharge curve, which is the basis of the heat generation point, can be changed depending on conditions such as the number of cells, discharge capacity, and state of deterioration of the lithium ion secondary battery.

As described above, in the safe state detection method of the present embodiment, by predicting the amount of power that can be stored in the lithium ion secondary battery based on the first battery voltage, the failure of the lithium ion secondary battery during actual operation is achieved. It is possible to grasp the current battery performance as well as the signs of the safety state.

In the safe state detection method of this embodiment, as described above, the positive electrode active material of the lithium ion secondary battery is Li _x MO ₂ (where M is a transition metal, and the lithium ion secondary battery is charged to 3.8V). (sometimes x<0.5). As a result, the discharge curve that is the basis of the heat generation point becomes clear (because the discharge curve is less likely to have multiple stages), so that the absolute value of the differential coefficient of the discharge curve can be accurately calculated.

As described above, in the safe state detection method of this embodiment, even if the lithium ion secondary battery is a used lithium ion secondary battery, a sign of an unsafe state can be detected at the start of actual operation. It becomes possible to recycle lithium-ion secondary batteries. From this perspective, the present embodiment can contribute to building a decarbonized or recycling-oriented society and achieving carbon neutrality and Sustainable Development Goals (SDGs).

The safe state detection method of this embodiment can be used for various power sources by utilizing the above-mentioned effects. That is, the safe state detection method of this embodiment can detect the safe state of the lithium ion secondary battery that constitutes the power source. Therefore, it is possible to detect a sign of an unsafe state of the lithium ion secondary battery that constitutes the power supply during actual operation, so it is possible to predict when to replace the lithium ion secondary battery in the power supply.

Further, the power source including the lithium ion secondary battery in the safe state detection method of this embodiment can be used for various purposes. Applications of the power source include, for example, drive devices, lifting devices, power control devices, and the like.

Examples of the drive device include, but are not limited to, vehicles such as hybrid cars and electric cars; elevating devices such as elevator devices, and the like.

In the case of a vehicle, for example, a power source including a lithium ion secondary battery in the safety state detection method of this embodiment is installed in a hybrid electric vehicle driven by an internal combustion engine and a motor. The onboard power source can function as a power source for starting the engine, restarting the engine after idling, supplying power during acceleration, and regenerating power by braking in the hybrid electric vehicle.

Note that the hybrid electric vehicle is an example of a drive device in which a power source including a lithium ion secondary battery is used in the safety state detection method of the present embodiment.

Further, in the case of an elevator device, for example, a power source including a lithium ion secondary battery in the safety state detection method of the present embodiment is mounted on the elevator device. The installed power source can be installed in an elevator system as a power source for alleviating power fluctuations when energy consumption and energy generation are switched due to vertical movement and onboard weight.

Note that the elevator device is another example of a drive device in which a power source including a lithium ion secondary battery is used in the safety state detection method of the present embodiment.

In the present embodiment, even when a lithium ion secondary battery in actual operation constitutes a power source used in a drive device, a sign of an unsafe state of the lithium ion secondary battery can be detected. Therefore, it is possible to predict when to replace the lithium ion secondary battery in the power source.

In the case of a power control device, for example, a power source including a lithium ion secondary battery in the safe state detection method of this embodiment is installed in a power balance adjustment device or the like. The installed power supply can be used as a power source in a power balance adjustment device to alleviate fluctuations in grid power, or as a power source to alleviate fluctuations in power generation and power consumption from renewable energy such as solar power generation and wind power generation. It can work.

Note that the power balance adjustment device is an example of a power control device used in a power source including a lithium ion secondary battery in the safe state detection method of the present embodiment. In this embodiment, even when a lithium ion secondary battery in actual operation constitutes a power source used in a power balance adjustment device, a sign of an unsafe state of the lithium ion secondary battery can be detected. Therefore, it is possible to predict when to replace the lithium ion secondary battery in the power source.

Hereinafter, a description will be given of the safety state detection device 13, the safety state detection system 1, and the power storage device 20 that can execute the above-described method for detecting the safety state of a lithium ion secondary battery.

[Safety state detection device, safety state detection system]
FIG. 19 is an example of a safety state detection system 1 according to an embodiment of the present invention. The safety state detection system 1 includes a lithium ion secondary battery 11, a voltage measuring device 12, a computer (safety state detection device) 13, a secondary battery control device (switch) 14, and a display device 15. I can do it. Each will be explained below.

The lithium ion secondary battery 11 is a detection target (that is, a lithium ion secondary battery whose safety state is to be detected).

Voltage measuring device 12 measures the voltage of lithium ion secondary battery 11 .

The computer (safety state detection device) 13 executes the above-described method for detecting the safety state of a lithium ion secondary battery. The computer (safety state detection device) 13 may be composed of one or more computers. Note that the computer (safety state detection device) 13 may be implemented as an integrated circuit.

The secondary battery control device (switch) 14 is a device (switch) that controls the lithium ion secondary battery 11.

The display device 15 is a device that displays the safety status of the lithium ion secondary battery 11 and the like. Note that the computer (safety state detection device) 13 may have the function of the display device 15.

[Power storage device]
FIG. 20 is an example of a power storage device 20 according to an embodiment of the present invention. Power storage device (also called a battery pack) 20 can include a lithium ion secondary battery 21 and a protection circuit 22. Each will be explained below.

The lithium ion secondary battery 21 is a detection target (that is, a lithium ion secondary battery whose safety state is to be detected).

The protection circuit 22 is a circuit installed in the lithium ion secondary battery 21, and executes the above-described method for detecting the safe state of the lithium ion secondary battery.

Hereinafter, an example will be described in which the lithium ion secondary battery, which is the object of the above-mentioned safety state detection, is used as a power supply device.

FIG. 21 is an example of an application of the lithium ion secondary battery according to an embodiment of the present invention. For example, a drive device (eg, a vehicle such as a hybrid vehicle or an electric vehicle, a train, an elevator, etc.) 31 includes a power storage device 20 that executes the above-described method for detecting the safety state of a lithium ion secondary battery.

FIG. 22 is an example of an application of the lithium ion secondary battery according to an embodiment of the present invention. As shown in FIG. 22, drive device 31 and power storage device 20 may be implemented as separate devices.

FIG. 23 is an example of an application of the lithium ion secondary battery according to an embodiment of the present invention. For example, a power control device (for example, a controller that controls an elevator) 32 controls a drive device 31 that includes a power storage device 20 that executes the above-described method for detecting a safe state of a lithium ion secondary battery.

FIG. 24 is an example of an application of the lithium ion secondary battery according to an embodiment of the present invention. For example, the power balance adjustment device 33 uses the power storage device 20 that executes the above-described method for detecting the safety state of a lithium ion secondary battery as a power source for alleviating fluctuations in grid power, or as a power source for solar power generation, wind power generation, etc. It can be used as a power source to alleviate fluctuations in power generation and power consumption using renewable energy.

[Hardware configuration]
FIG. 25 is an example of the hardware configuration of the safety state detection device 13 according to an embodiment of the present invention.

As shown in FIG. 25, the safety state detection device 13 is constructed by a computer, and includes a CPU 101, ROM 102, RAM 103, HD 104, HDD (Hard Disk Drive) controller 105 , a display 106, an external device connection I/F (Interface) 107, a network I/F 108, a data bus 109, a keyboard 110, a pointing device 111, a DVD-RW (Digital Versatile Disk Rewritable) drive 113, and a media I/F 115. There is.

Among these, the CPU 101 controls the operation of the entire safety state detection device 13. The ROM 102 stores programs used to drive the CPU 101, such as IPL. RAM 103 is used as a work area for CPU 101. The HD 104 stores various data such as programs. The HDD controller 105 controls reading and writing of various data to the HD 104 under the control of the CPU 101. The display 106 displays various information such as a cursor, menu, window, characters, or images. The external device connection I/F 107 is an interface for connecting various external devices. The external device in this case is, for example, a USB (Universal Serial Bus) memory, a printer, or the like. Network I/F 108 is an interface for data communication using a communication network. The bus line 109 is an address bus, a data bus, etc. for electrically connecting each component such as the CPU 101 shown in FIG. 25.

Further, the keyboard 110 is a type of input means that includes a plurality of keys for inputting characters, numerical values, various instructions, and the like. The pointing device 111 is a type of input means for selecting and executing various instructions, selecting a processing target, moving a cursor, and the like. The DVD-RW drive 113 controls reading and writing of various data to and from the DVD-RW 112, which is an example of a removable recording medium. Note that it is not limited to DVD-RW, but may be DVD-R or the like. The media I/F 115 controls reading or writing (storage) of data to a recording medium 114 such as a flash memory.

[Functional configuration]
FIG. 26 is an example of a functional configuration of the safety state detection device 13 according to an embodiment of the present invention. The safety state detection device 13 can include a first battery voltage calculation section 1001, a second battery voltage calculation section 1002, and a determination section 1003. Further, the safe state detection device 13 can function as a first battery voltage calculation unit 1001, a second battery voltage calculation unit 1002, and a determination unit 1003 by executing a program. Each will be explained below.

The first battery voltage calculation unit 1001 calculates a first battery voltage (differential coefficient increase voltage V _dcp during discharging).

Specifically, the first battery voltage calculation unit 1001 calculates the absolute value of the differential coefficient (discharge voltage differential coefficient) of the discharge curve excluding the voltage corresponding to the voltage drop of the lithium ion secondary battery (note that the above-mentioned (The voltage for the voltage drop is the voltage of the lithium ion secondary battery minus the product of the current flowing through the lithium ion secondary battery and the internal resistance of the lithium ion secondary battery.) The first battery voltage calculation unit 1001 determines whether the degree of increase in the absolute value of the calculated discharge voltage differential coefficient is greater than a threshold value. When it is determined that the degree of increase in the absolute value of the discharge voltage differential coefficient is greater than the threshold value, the first battery voltage calculation unit 1001 determines that when the absolute value of the discharge voltage differential coefficient starts to increase rapidly (that is, When it is determined that the degree of increase in the absolute value of the discharge voltage differential coefficient is larger than the threshold value, the first battery voltage (discharge differential coefficient increase voltage V _dcp ) is determined. Note that the discharge differential coefficient increasing voltage V _dcp corresponds to the point at which the first-order differential coefficient increases in the above-mentioned discharge curve.

The second battery voltage calculation unit 1002 calculates the second battery voltage (unsafe sign point V _USP ).

Specifically, the second battery voltage calculation unit 1002 calculates the second battery voltage by substituting the first battery voltage (discharging differential coefficient increasing voltage V _dcp ) into the model equation shown in equation (3) below, for example. The battery voltage (unsafe sign point V _USP ) can be calculated. Note that the unsafe sign point V _USP corresponds to the above-mentioned overcharge temperature increase point (heat generation point in the overcharge area).
V _USP = -0.2310V _dcp +5.1957...(3)

As mentioned above, the approximate formula expressing V _USP varies depending on the type and design of the lithium-ion battery (not limited to the above formula (3)), and for a particular lithium-ion battery, It is defined by examining the voltage at which heat absorption changes to heat generation during charging and the voltage at which the absolute value of the voltage slope begins to change significantly at the end of discharge.

The determination unit 1003 determines the safe state of the lithium ion secondary battery based on the second battery voltage (unsafe sign point V _USP ).

For example, the determination unit 1003 calculates the safety level of the lithium ion secondary battery, and ranks the safety level of the lithium ion secondary battery into A, B, and C. The threshold for ranking is, for example, the condition that rank A is "currently safe" [V _USP > β _A (β _A = 4.60V)], and the condition that rank B is "might become unsafe in the near future". [V _USP > β _B (β _B = 4.57V)], rank C is the condition that "there is a high possibility that an unsafe event will occur, it is necessary to stop using it and replace the battery" [V _USP > β _C (β _C =4.55V)] and determine the rank. The determination unit 1003 may display the determination result or may store it in memory.

Each function of the embodiments described above can be realized by one or more processing circuits. Here, the term "processing circuit" as used herein refers to a processor programmed to execute each function by software, such as a processor implemented by an electronic circuit, or a processor designed to execute each function explained above. This includes devices such as ASICs (Application Specific Integrated Circuits), DSPs (digital signal processors), FPGAs (field programmable gate arrays), and conventional circuit modules.

Although the embodiments of the present invention have been described above, the present invention is not limited to specific embodiments, and various modifications and changes can be made within the scope of the invention described in the claims. .

1 Safety state detection system 11 Lithium ion secondary battery 12 Voltage measuring device 13 Computer (safety state detection device)
14 Secondary battery control equipment (switch)
15 Display device 20 Power storage device 21 Lithium ion secondary battery 22 Protection circuit 31 Drive device 32 Power control device 33 Power balance adjustment device 101 CPU
102 ROM
103 RAM
104 HD
105 HDD controller 106 Display 107 External device connection I/F
108 Network I/F
109 Bus 110 Keyboard 111 Pointing device 112 DVD-RW
113 DVD-RW drive 114 Recording media 115 Media I/F
1001 First battery voltage calculation unit 1002 Second battery voltage calculation unit 1003 Judgment unit

JP2020-47606A

Claims (15)

A method for detecting the safety state of a lithium ion secondary battery, the method comprising:
Calculating the absolute value of the differential coefficient of the discharge curve excluding the voltage corresponding to 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 differential coefficient is greater than a threshold value,
Determining a second battery voltage at which oxidation heat generated inside the lithium ion secondary battery starts to increase when the lithium ion secondary battery is overcharged, corresponding to the first battery voltage;
A method for detecting a safety state of a lithium ion secondary battery, comprising detecting a safety state of the lithium ion secondary battery based on the determined second battery voltage. The degree of increase is the degree of increase from the absolute value of the differential coefficient calculated one time before the absolute value of the calculated differential coefficient to the absolute value of the calculated differential coefficient,
The method for detecting a safe state of a lithium ion secondary battery according to claim 1, wherein the threshold value is 1.5 times. 2. The voltage corresponding to the voltage drop is the voltage of the lithium ion secondary battery minus the product of the current flowing through the lithium ion secondary battery and the internal resistance of the lithium ion secondary battery. A method for detecting a safe state of a lithium ion secondary battery described in . When the amount of electricity stored in the lithium ion secondary battery is X (Ah), the voltage corresponding to the voltage drop is such that when the absolute value of the current flowing through the lithium ion secondary battery satisfies the condition that 4. The method for detecting a safe state of a lithium ion secondary battery according to claim 3, wherein the discharge curve is updated (where X is a positive real number). 5. The method for detecting a safe state of a lithium ion secondary battery according to claim 4, wherein the storable amount of electricity of the lithium ion secondary battery is predicted based on the first battery voltage. The positive electrode active material of the lithium ion secondary battery contains Li _x MO ₂ (where M is a transition metal, and x<0.5 when the lithium ion secondary battery is charged to 3.8V). The method for detecting the safety state of a lithium ion secondary battery according to claim 5. Calculating the absolute value of the differential coefficient of the discharge curve excluding the voltage corresponding to the voltage drop of the lithium ion secondary battery, and determining the first battery voltage when the degree of increase in the absolute value of the differential coefficient is greater than a threshold value. , a first battery voltage calculation unit,
a second battery voltage calculation unit that determines a second battery voltage at which oxidation heat generated inside the lithium ion secondary battery starts to increase when the lithium ion secondary battery is overcharged, in accordance with the first battery voltage;
A safety state detection device comprising: a determination unit that detects a safety state of the lithium ion secondary battery based on the determined second battery voltage. A safety state detection system including a lithium ion secondary battery and a safety state detection device,
Calculate the absolute value of the differential coefficient of the discharge curve excluding the voltage corresponding to the voltage drop of the lithium ion secondary battery, and calculate the first battery voltage when the degree of increase in the absolute value of the differential coefficient is greater than a threshold value. a first battery voltage calculation unit that calculates the voltage;
a second battery voltage calculation unit that determines a second battery voltage at which oxidation heat generated inside the lithium ion secondary battery starts to increase when the lithium ion secondary battery is overcharged, in accordance with the first battery voltage;
A safety state detection system comprising: a determination unit that detects a safety state of the lithium ion secondary battery based on the determined second battery voltage. A power storage device including a lithium ion secondary battery and a protection circuit,
The protection circuit is
Calculate the absolute value of the differential coefficient of the discharge curve excluding the voltage corresponding to the voltage drop of the lithium ion secondary battery, and calculate the first battery voltage when the degree of increase in the absolute value of the differential coefficient is greater than a threshold value. seek,
Determining a second battery voltage at which oxidation heat generated inside the lithium ion secondary battery starts to increase when the lithium ion secondary battery is overcharged, corresponding to the first battery voltage;
A power storage device, wherein a safety state of the lithium ion secondary battery is detected based on the determined second battery voltage. The power storage device according to claim 9, wherein the lithium ion secondary battery is a used lithium ion secondary battery. The power supply device using a lithium ion secondary battery as a power source according to any one of claims 7 to 10, wherein a result according to the rank determination of the safety state of the lithium ion secondary battery is presented on a display device. A drive device using the power supply device according to claim 11. A power control device using the power supply device according to claim 11. A power balance adjustment device using the power supply device according to claim 11. The safety state detection device calculates the absolute value of the differential coefficient of the discharge curve excluding the voltage corresponding to the voltage drop of the lithium ion secondary battery, and detects the first one when the degree of increase in the absolute value of the differential coefficient is larger than the threshold value. a first battery voltage calculation unit that calculates the battery voltage of
a second battery voltage calculation unit that determines a second battery voltage at which oxidation heat generated inside the lithium ion secondary battery starts to increase when the lithium ion secondary battery is overcharged, in accordance with the first battery voltage;
A program, characterized in that the program functions as a determination unit that detects a safety state of the lithium ion secondary battery based on the determined second battery voltage.

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